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A TEEAyiSE ON CHEMISf|Y 



MACMILLAN AND CO., Limite_ 

LONIX)N • nOMHAV • CAICUIJ'A 
MKLROUKNK • MAllKAS 

THE MACMILLAN COMPANY 

NEW YORK • BOSTON • CIIICACiO 
UA(.LA$ • SAN FRANCISCO 

THE MACMILLAN CO. OF CAN^VDA, Ltd. 


TORONTO 



f 

ON CHEMISTRY 


BY 


The IteoftT Honourable SIR H. R. ROSCOE, F.R.S. 


AND 

C. ^piIORLEMJiER, F.R.S. 


VOLUMK II 

THE METALS 

PART II 


ChyHkat alias Alchsmin ct Spagirlca, est ars corpora ^ mixlat vellromposita, 
vel aggregata eliam in ^rincipin sua resolvendi, flitj "^4? principiis in talia 
comb inandi. Sta h h, 1 7 * 2 . 3 . 


NEW EDITION COMPLEXLY REVISED BY 
B. MOUAT JONES AND OTHERS 


MACMILLAN AND CO., LIMITED 
ST. MARTIN’S STREET, .i;.OND6n 
1923 



Hi l>rii>tnl IH' 
Tliird Hidhnn, 


(JOPVItKiHT 


Firfl Kilithn priiih'/ ls78 
7<>; .Wo/ni h'ldtioH, ISSU; H> p/inUii, 1S.S7, ISM 
I.sit7; h'UHioti, 1'.IU7: Fi/lh VJVi 

sixth Fititioii, 


I’RINTBD IK OUBAT BRITAN 




THE EOft.OWING ,A11E THE OHIEE OONTPAOTrONS 
’ EMPrX)yED IN THIS VWHHME 


Abbreviated Titi.e 

tilirRXAL 

Ainer. Chem. J. . .■ 

. American (‘hcmical^lourniil. 

Amer. J. Sci. . • 

Analyst . . . ^ . 

American .Joffrnal of SPicnee. 

'Die ^\^alyst. 

Annalm 

. Justus Lichig’s Annalen der (.11011110. 

Ann. Physik 

Annalen <ler Physik. 

Ann. Chirn. Phys. J! 

. Anjialcs de ('himic et de Physitpio. 

Ann. Mines . . • . 

. Annalea dcs Miiu*s. % 

Arch, h^krhiifl. . 

. Archives Nccrlandnls«.‘H dcs Sciences exacted et 
naf undies. ^ 

Pharm. ^ 

Atti R. Accud. Lined . 

.• .-\rchlv der Pharinazio. ■> 

. .Atti (h'lla lleale .Accailemia ilci Lincoi. 

Per. • • ^ • 

. lk*richte der dent sclien cliymiscdicii (Jcscllsehaft. 

Riochem. Zeit. t 

. Jlioeheinische Z^itHch^ift. 

Brit. Assoe. Reports . 

. Hoporta of the Hritish Assoi'intion. 

Pull. AceM. roy. Pclg. . ^ 

. .Acoiltunie royale de Hidgiqiu? “Hullclin <le la 
• Clusse lies Sciiuices. ) 

Bull. (kol. So(\ Amer. 

. Ihiilctin of tin* ( *(‘ologici^l Society of.y\ruArica. 

Pull. Soc. chim. . * . 

^ bulletin do la ♦Societo cliiu ^ipie de Paris. 

Ch^n. ('entr. 

. (dicmtsches Centndhlatt .V 

Chem. News . 

. (diomioal News. 

Chem* Zeit. . 

. (^hemiker Zeitung. 

Cog^pt. rend. 

. Comptes nuidiiii hobdomadain's dcs Ser-^^Jhs do 
rAcailcmie des Scienct's. 

Gazz 

. Cazzetta chimica italianji. 

. ecological Magazine. 

Geol. Mag. < ^ . 

Jahrb, Min. . 

. Neucs flahrlnieh fiir Miiicmlogie, Ceologic und 


J.Amer^Chcm. Soc. 

phyA. 

•4 Iron Steel Inst. 

V, Phar^ . . 

J. Physical Vhcm. ® 

J. pr. QJm. 

J. Roy. Agric. Soc. 

J. Russ. Phyi. Chem, Soc. 
» 

J. Soe. Chem. Ind. 

Joum. Chem. Soc. 
f^ndw. Versuchs‘Stnt. 
Mem. Manch. Phil. Soc. 

•o 

Min. Mag. . 

Monatsh. 

PfiHgePs Arc%v . 

J. . . . 

Pha.^ag. . , . 


l*altu*ont< )iigic. 

Journal of tho Ajiioricaii Choniical Sticieiy. , 

Journal dc (’hitnu* physique. 

Journal of tbo Iron and SUniI Insli plo. 

Journal do Pharnuwjic. 

Journal of Physical (’hemistry. 

Journal fiir praktischo Cheinie. 

Jouinai of the Koyal Agricultural Soe.iety, 

Journal of (ho Physical and Chemical ♦Society of 
lluHsia. ' 

Journal of the Society of Chemical Industry. 

Journal of (ho Chemical Society. J 

Dio landwirtschaftlichen Versuchs-Stationon. . 

Memoirs oml Proceedings of the Manehcst-cr 
Literary and Philosophical Socacty. 

Mineralogical Magazine. 

Monatshefte ftir Chomio und verwandte Tlieilo 
andersr Wissenschaften. 

Archiv fdr die gesammto Physiologitf^ des 
Menschen und der Thiere. 

Pharmaocutical Journal. 

Philosophical Magazine. 



CONTRACTIONS EMPLO’ 


^bbrZviated Tm4p Joubnal 

Thil. Tmtu. , # . . Philosophical Transactions of xl|/^ Royal Society. 

Pofjg. Ann. . . .* Po^Mendorft’s Annalen der*Physik und der 

• ‘(^fiie. • 

Proe. Chm. S(A . * . . ri'ocoedings of the Chemical Society. # 

Proe. K. Akad*W(lfnAeh.^ Koninldijkc Akademio van WetenschAppen t(0 

• • A....*....!...... 


Atl^Uirdim 
J^or, Boy. So^ . 

Pfoc. Boy. Soc. Kdin. . 
Quart. J. (Heal. ^or. 
irav. chim. . 

1 

RiUungshcr. K. Aknd. Wiss. 
^Berlin 

Zmi. final, Clum^ . 

Zeif. anffpw. Chcm. 

Zeik nmrg. ('hem. •. 

Zeit, (Jhem. .% . 

, Ztil. Kkktrvchem. 

Zeit. Krtj«t. Min. 

Ze.it. yhyftiknl, (JJmg. . 

Zcit.^di^iol. ('hem. 


Amstonlam. Proceedings fEngUsh Vefhfbn]. 
^)cccding8 of ^be Royal l^cicty. 

Proceedings of the Royal Sooiet^f Edinburgh. 
Quarterly Journal o^the Gcologi^ffl Socie^. 
Hecueil des iravaux* chimiques d|^ fays-llas et 

* de la Belgique. • ^ 

SitzungslKTichte der ^koniglich preussischcn 

.^kadeinic der Wissenschaften zu !^rlin. 

• Zcitsehrift fiir analytischo Cheinie. 
tZeitschrift fiir ange*iyand|i Chomie. 

ZrutscAirift fiir anorganiaAie Chomie. 

Ziutschrift ^r Cheinie. 

Zeitscbrift inr Elektrochemi?. 

Zeitschrift fiir Krystallographie und Miner- 
alogie. * 

Zi'itsehrift fiir physikalisc^o (Cheinie, Stiichio. 

luetrio und VerwandtHchaftslehre. 
lloppe-il^leylei’s Zcitschrift fur nlivsiofocriRf^hp 
Chomie. 



CONTENTi? 



Thb Ibom Group . 
Iron 

Cobalt . 

Nickil 

^ The RuTOEKinM Group 
RUI^enium 
Rhodium . 
Palladium 

The Planum Group 
Osmium 
Iridium 
Platimdm 


. ' 1200 
. 1210 
. 1329 
. 1355 
. 1388 
. 1388 
. 1398 
. 1400 
. 4422 
. .:^23 
. 1438 

. 1450 



c 



• The Radioactive J^kments . 1490 

. Ph«i«mbna of ttAOIOAlwiTV 1IS02 

The J’i9>pucTS of IJadioactive Chanob . . .1611 

Radius p ........ . *1516 

Actiniua?, .• ,*1626 


Tik^idm 

Uranium 


1627 

1528 


Atowc Structure 


1532 


INDEX 



CHEMISTp 



THE Metals (continued) 


GROUP IV«. 


hb-gr^tp (a) 

Suh-grgup (b) 

Carbon. 

Silicon. * 

Titanium. 

Germanium. 

Zii^onium. 

Tin. 

(Cerium). 

Lead. 

Hafnium. 


Thorium? 



374 In this group there is no well-defined* division of the 
elements.composing it into two distinct sub-groups, such as is 
noticeable in the others of the first seven groups, and the differ- 
ences observable J)etween the membeft of tic odd ai^ji %ven 
series are only of minor hnportance. 

Ceriym probably belongs to this group, but as its chemistry^ i| 
so intimately connected with that of the othei^members of the 
group of rare earth metals it has been Sescribed among them. 
The first t^ members of this group, carbA and silicon, tave 
already been ^[escribed among the npn-metallic elements. Both 
exis^ in the amorphous and crystalline states, silicon melting, 
onjy at a very high temperature, whilst carbon has not yet 
b6en m^lb^, although it volatilises at the highest attainable 
temperatures, the remaining elements all "have metallic 
properties, and, with the exception of tin and lead, possess Jiigh 
n^ell^ points; in the compact state they undergo at most a 
surface oxidation in the air at the ordinary temperature, but 
strongly heated readily combine with oxygen, an<!P, except 
in the case of lead, the oxide formed in presence of an excess of 

S ygen is the dioxide. The dioxides of the members having 
e lower atomic weights, including those of diarbon £id silicon, 
belykve chiefl)r as acid-forming oxides, but they iTecome n^re 
basic as the atomic weight of the element increase. These 
correspond in each case with a serie^ of sal^ in which 
YOL.n.*(n.) ‘ S31 " B 



832 Tta TrrAlpUM GR0X7P * 

- — > -- rr ^ 

tTO eiem'ent is tetravalenti and* except in the caselof 4ead, this 
series includes the, most important compouadg/* Le^d in its 
most characteristic compounds is divalent, and, §s is so frequently 
the case with elements having a high atomic weight, it presents 
many resemtilances to the elements having the next lowest 
«f!d next ||ighest atomi# weights, \iz., thallium and bisifluth. 

A very characteristic ^eries of double salts \pth the alkali 
halides is fielded b^ the tetrahalogeif derivatives of most of 
these elements, the oouble fluorides, which hav?\h^ general* 
t^ormula being tthe most important. In the case of 

silicon, titanium, germanium, zirconium, ^nd tin, these com- 
ppunds are isomornhbus, but this appears not to be the case 
with the thorium compound. The corresponding salt of lead 
has not been prepared, but an acid salt, PbF 4 , 3 KF,HF, exists, 
which is isomorphous with the analogous tin salt, SnF^.SKJ'jHF. 

'Carbon is distinguished from all other elements by the pro- 
pefty possessed by its atoms of uniting together in opQji or 
closed chains, forming nuclei, which may contain as many Is 
sixty atoms, andrwhich, in combination with the. other elements, 
give rise to the immense number of carbon compounds. The 
same, property is observable to a much jm&ller extent in silicon, 
but ’not in the ofher members of the group. In addition to 
the typical elemCnts, carbon and silicon, only germanium, tin,' 
and lead, ie., the members of the “ odd ” series, yield organo- 
metallic derivatives. 


THE TITANIUM GROUP. 

c 

TITANIUM. Ti- 481 . At. No. 2 .*. 

375 The Rev. William Gregor^ in 1789 discovered a ppw raelbsil 
contained in tlio mineral menachanite or ilmenite, Sccurring in 
Cornwall. In 1795 Klaproth investigated the compeSition of 
the mineral rutile, and discovered in it a new metal to which 
he gave the name of titanium. In a subsequent investigation bf 
ilmenitej in 1797, he found that the metal which that min^l 
contained was titanium. Klaproth found that rutile consisted 
mainly of titanium dioxide, but he did not succeed in obtainii^ 
the oxide hi the pure state, this having been first accomplishes 

by^ose in 1 S 2 I. 

Titaniufti, though not an abundant element, is very widely 
» CreU. Ann., 1791 



^ TITiJWUM B83 

distributed^ It is not found in the • metallic state, butfgocc Jn 
as the dioxid€| JiPg, in three minerals, rutile, brookits, and anatase, 
which possess (jjfferent crystalline forms * in comMnation with 
ferrous and ferric oxides in titanic iron ore or ilmeuite, FeTiOj ; 
•and^witTi lime and oxide of iron in perqfskite,,(0a,Fe)TiO3, as 
well aS in titanite or sphene,paTiSi 05 , s^liorlomite, Ca^Ti,Fe)SiO^, 
and keilhaujje, CaYt(Ti,Al,Fe)Si 05 . Magnetic iron ore also 
frequently contains lAger or smaller quantities ‘of titanium 
^ which ftidl Its way into many blast-furnace slags and pig-irons. 
Titanium occurs in small quantity ^in several other minerals 
and traces have been found in trap and baAlt, in many amphibofo 
and micas, and in garnet; hence it jccur^ijj most fertile sgils^in 
quantities between 0*3 and 0*6 per cent.,^ in many clays, and 
likewise in certain mineral wal^rs. It has been found in human 
and ox flesh and bone,^ and occurs in the ashes of all plants ^ in 
quantities up to 0-27 per cent. and in many peats.4 Its presence 
has-been detected in certain meteorites, and it Jorms en^iiy- 
fortant constituent of the solar atmosphere. • • 

Preparation ^ Metallic TiYaniwm.— Metallic titanium is difiicull 
to obtain in the pure condition ; the usual methods for the reduc- 
tion of the oxide, such ^s heating with metallic sodium and mag- 
nesium, yield products which still contain considerable quantitieg 
of titanium monoxide^ and the product obta>^d by the action 
of sodium on halogen derivatives of titanium also usually contains 
small* quantities of the monoxide, formed by^the action of'tbe 
moisture present, and of the nitridi, obtained by the direct 
union of th% metal with nitrogen, which itfs almost impdssiblo 
completely to exclude. Owing to the extreme readiness with 
which titanium and nitrogen combine at high temperatures, and 
to*the metallic appearance of the nitride, this compound was 
ylistak^ by the earlier investigators for the metal iffielf, as was 
ftko the dbmpoflnd which it forms with carbon and nitrogen, 
aow kilbwii as titanium cya^jonitride. 

Moissan ^used carbon with an excess of titanium dToxide 
It a very high temperature in the electric furn^e. Three 
^tinct layers were found in the solidified product, the uppermost 
Consisting of titanium containing about 5 per cent, of carbon, 
be second of the nitride, and the third of titanium monoxide. 


* Qeilmann, J. Landw.f 1920, 68, 107. 

> BMkerTUl% J. Amer. Chem. 8oc., 1899, 21, 1099. 

» Wait, J. Attur, Chem. Soc., 1896, 18, 402; Lippmann, Ber., 1^07, 80,^37. 

* Geilmann, J. Landw., 1920, 68, 107. * 

J. Amer. Chem. 8oc., 1899, 21, 402. 



gS4 rate TTTANipM GIWDF ^ 

t#p layer was heated again with an excess fi titanium 
dioxide; the ^antity of carbon was reduced to£ jftr cent., and 
^the product w&n free from nitrogen and silicon.^ ^ 

Nilson and ^P^ttersson?* by acting on titanium tetracbloride 
with sodium tn^an aia-tight cylinder of mild steel at a red Jieat* 
|VtiI)ared mjtallic titaniui in yellow ^ales, which had frequently 
a bluish surface colour. These, however, still conjoined a con- 
siderable qufiftitity of oxygen, probably a^ the monoxide. A still 
less pure product is obtained by heating potassium tftSnc^uoride ^ 



Metallic titanium Las been prepared by Stabler and Bachran ^ 
*by heating the dichloride in a current of hydrogen to 1100°, when 
• the reaction: 2 TiCl 2 = TiCl^ + Ti takes place. A method of 
preparing titanium of 99*7 per cent, purity has been described 
by I^dflszus.®* The method consists in ^placing a mixturq of 
sodflim and titanium tetrachloride in a steel bomB filled witlf 
hydrogen or carbon dioxide and containing a nun))>er of polished 
steel balls. The bomb is closed by a powerful screw and sealed 
with njoltcn lead. The bomb being closq^l, 4he whole i8*rotated 
at 20(f for 20-40 Ijours to produce an intimate mixture. The 
reaction Ts started ly heating the bomb strongly lor a few minutes. 
When the reaction is complete the bomb is cooled from the top 
downwards. The^ product is titanium in the form of minute 
^ crystals which are highly ftactivc. 

Titanium is a brittle, grey metal, which is har^ enough to 
scratch steel and quartz. It has a density 4*87 and milts at 1795°. 

is stable in the air at the orSinary temperature, but burns bril- 
liantly in oxygen at 610°. Titanium combines with nitro^n 
with extreSie readiness, in this respect resembling bo|pn arfcj 
magnesium ; the Reaction commences at about 800*, andlhe nitride 
‘ is alsq formed together with the oxide when the metal IJhms in 
the air. 

Titanium combines with the halogens when heated to form thd 
tetrahalidbs ; with chlorine the action takes place at 350°, wi^ 
bromine at 360° and with iodine at 400°. It dissolves slowiy 
in dilute sulphuric acid and in concentrated, hydrochloric acid, 
with liberaAon of hydrogen and formation of violet salts. It is* 

* MoiBsan, Qcmpt. rend.^ 1805. 120i 200. * Zeit. phynkal. CA«m, 1887, 1, 25. 

> Wedekind, Annalen, 1013, 896. 149. « Ber., 1911, M, 2907. 

amory. Chem., 1917, 98, 123. 



TITANIUM OOBfPOUNDS 


830 

- . • /“ 

converlild Ihto titanic acid by nitrifc acid an^ aqua re^a and 

decomposesiteibn at 70(^-800°. Moissan ^ has distjjled the metal 
in the electric kmace by the use qf a current of great intensity, 
^the mejal condensing in small crystals! 

Metallic titanium in the form of its Alleys is tised in the steel 
industry. Steel to which n small quamity of titanium has befti 
added is improved in Jensile strengtl^ and is largelj^ \]^ed on the 
American j*jil ways and for bridge construction. 

TITANIUM COmVoHJNDS. 

Titanium and dOxYG*Ei». 

376 Titanium combines with oxygen to form a numoer 01 • 
oxides, the most important being : 

Titanium monoxide, TiO. 

Titanium sesquioxide, Ti203. 

Titanium dioxide, TiOg. 

Titanium peroxide, Ti03. 

Titapim Monpxide, TiO, is obtained in the form of black, 
prismatic crystals l^ heating the dioxide strongly in the ijlectric 
furnace,^ and is^lso formed, togethei^with jnagnesiun^ tiCanate, 
wl^en titanium dioxidh is heated with the r(^isite quantity of 
mag^jesium powder : ^ 

2Ti02 + Mg = TiO|l- MgTi03. 

The hydrqpde, Ti(OH)2, is formed as a l^ck precipitate when 
an alkali hydroxide is added to a solution of titanium dichloride. 
It is readily oxidised in air to hydrated titanium dioxide. 

•Titanium Sesquioxide^ TijOg, is obtained by strongly ignitiilg 
flitanium dioxide in a current of hydrogen and allowing the 
produCT ta cooNn the gas. The same oxide may also be obtained 
as a capper-coloured, lustrous, crystalline mass, together with the' 
trichloride* and oxychloride of titanium, by passing a nlixture 
of hydrogen and the vapour of titanium tetrachloride over 
white-hot titanium dioxide. It is not attacked bja nitric or 
hydrochloric acids, but sulphuric acid dissolves it with formation 
of a violet solution (Ebelmen). 

The hydraled sesquioxide is formed by digesting a solution of 
titanic aci^in hydrochloric acid with metallic copper at 20-40*^ ; 
the solution attains a violet-blue colour, and when «pourec^ into 

rend., 1906, 142 , 673. *MolMan, Cmptfrend., 1892, 115 , 1034. . 

• • \Mhikler, JJer., 1890, 28 , 2668. ' 


836.1 


Trils TITANIUM G]|OUP^ 

aqueofts ammoni^ yields ^ dark brown precipitayo£1;itanous 
►lydroxide (Fdchs). ^he hydroxide is formed afe^^hen a solu- 
ion of the tnqjiloride is precipitated by alkalis. • 

When titaniuB^ sesquio'kide is shaken with milk of limp in the^ 
presence of oxygen it is oxidised to the dioxide. More ojj:ygen 
is Ebsorbedr than is necelsary for this change, whilst hydrogen 
peroxide is formed in anjoimt correspojiding to ihe whole of 
the oxygen absorbed. Water must therefore take^jjart in the 
reaction, and the phenomenon is probably a case of autoJidation 
(»^e Vol. L, p, 253). .Jn Ihe same way, when the sesquioxide 
is oxidised by a solution of chromic acid in th§ presence of potass- 
iuui iodide, or by jj^tassium permanganate in the presence of 
^ tartaric acid*, titanic acid is formed^and at the saAe time oxidation 
of the potassium iodide or tartaric acid is brought about.^ 

' Titanium Dioxide, TiOj, is trimorphous, occurring as three 
difhirent niinefals, rutile, anatase, and brookite. Rutile* crys- 
tidli.sejfin tetragonal prisms, having a specific gravity of 4'18-4»25^ 
isomorphous with those of tin dioxide or cassiterite, and possess- 
ing an adamantine^ustre and a brown or reddish cdour. Anatase 
crystallises in a totally different form of the tetragonal system, 
has a ^ocific gravity of 3*82-3*95, and a 4)r(twn or black colour. 

• Brookite prystalliseg in flftt, rhombic prisms and has a specific 
gravity of , 

^piorphous titanium dioxide is obtained by the decomposition 
of aqueous titanium chloride by ammonia, the precipitate 
being washed, dried, and ignited; or it may be directly prepared 
from rutile or titanft iron ore. In order to prepAe the pure 
oxide from rutile, the finely;powdered mineral is ^used with 
three times its weight of potassium carbonate, the sblidifijd 
mass powdered and dissolved, in a platinum vessel, in dilul^ 
hydrofluoric acid^, potassium titanofluoride being thjMformed* 
and the ferric oxide left free from titanium, xte mass is then 
^eatec^with sufficient water to dissolve the whole of the titanium 
double salt, the liquid boiled, and filtered hot. On cooling, the^ 
mass of the*titanofluoride crystallises out, and this, after washing 
with cold* water, may be purified by recrystaUisation. Th% 
titanofluoride is then dissolved in hot water and the titanium 
precipitated by ammonia as titanic hydroxide containing am- 
monia, whicl on igifltion yields pure titanium dioxide (Wfihler). 
Pure^ titanic oxide may also be obtained from titaffio ore in a 
similar manlier, or b^ fusing it with potassium bisulphate, or by 
yjanohot and Ritoher, Btr,, 1906, 320, 488. 



TITANIDM OOMPOUNIS W? 

ti ♦ ^ I, 

igniting ft m a mixture of chlorine a|id hydrochloric aci^wbi^ 
ferric chlori^l^ volatilised (Friedel and Gu4rin] : , 

2FeTi03 4Ha f Clj, = 2FeCl^+ 2Ti03 +*2H,0. 

• • * » * 

Amorphous titanium dioxide is a white, tasfeless powder 

which when gently heated has a lemonfyellow colou^ and wlflBfi 
strongly ignited appears brown. It^s a specific gravity of 
, from 3*89 tp ^*95, and wnen very strongly heated this^rises to 4-25. 

When it is heated with microcosmic salt (Ebelmen) or with 
borax (G. Rose) for some time to a «rhi^ heat, fine crystals of 
rutile are obtained, srhich have a specific gravity of 4»26. CrystA- 
line titanium dioxide can also be obtained by passing the gages 
obtained by decomposing molten potassium titanoftuoride with 
hydrogen chloride through a hot platinum tube into which a 
current of moist ^ir and hydrogen is also passed. In this way 
Hautofeuille ^ has shown that by treatment at fi temperature 
jot* exceeding the boiling point of cadmium (778*), anataOe gs 
produced, tile crystals of which have a specific gravity of 3*7 to 
3*9 ; at a temperature of about 1,000'’, steel-blue coloured rhombic 
crystal^ of brookite are obtained, which have a spcjcific gravity 
of 4-1, and closely* resemble the natural crystals fromJMiask. 

^ At still higher temperatures again, rtltile iii produced^ sd that 
thi§ last is the only fotm which is stable at a^gh temperature, 
and ip an acid or moist atmosphere.^ 

At the temperature of the oxy-hydrogep flame titanium 
dioxide fuses, forming a thin liquid, wliich solidifies to a confused 
crystalline Aass. 

In its chemical properties titanium dioxide closely resembles 
tljp cori^sponding silicon dioxide, behaving as an acid anhydride. 
1^ is insoluble in water, hydrochloric acid, and dilute sulphuric 
bcid, Jithpugh it dissolves when digested for some time with 
hot conceritrated sulphuric acid. The amorphous oxide dissolves 
on fusion with alkalis or alkali carbonates, unless it has^ been 
strongly ignited, forming the titanates, and also dissolves slowly 
in fused potassium hydrogen sulphate, yielding a clearfnass which 
dissolves perfectly in warm water. When this solutioi! is boiled, 
the hydrated dioxide is precipitated. Titanium dioxide corre- 
sponds to the most important series of titanium salts in which 
the metal is tetravalent. 

Titanic Acid and the Titanates.— A& is the case with the %palo- 

1 Ann, Chim. Phy»., 1865, [ 4 ], 4 , 129. 

> Friedel and Qu^ria, Bull. Soc. ehim., 18^4, 22, m. 



gjg TITANIW'’GB00P^ 

gous /lidc acid, several jiydrsto of vftiying eolation w 
known. Th^e ippeara to be little doubt tljs^Ahe hydratet 
ortholitanic (feid, Ti{OH)4, and metatilmic ocid, fTiO(OH)„ esirt, 
but in additjdh ^others have l)een prepared containing quantities 
of water intermediate, between the amounts required lor thesg 
tvi|? formula?, and also v{th less tha:^ that required by the latter 
^)rmula. These may possibly be the hydrates corresponding 
to the compicx titanic ac^ds, but they fiave not been obtained 
of sufliciently definite tomposition to enable this to bS ascertained. 

Ortholitanic Acid, Ti(OH^4, is obtained by adding an alkali to 
aVcold hydrpchloric acid solution of a titanate, and* forms a 
voluminous white precipitate which is soluble in dilute hydro- 
chloric acidcand sul^iuric acid, and loses wateicon drjiing, form- 
' ing other hydrates. When hca'ted it is converted into the 
, anhydride, the reaction being accompanied by evolution of light. 
WJien allowed^^to remain under water it is gradually concerted 
intaiiL'Jtatitanic acid.^ 

Meiatitank Acid, TiO(OH)2, is obtained by boiliifg a solutiofi 
of orthotitanic aci^ in hydrochloric acid, or by the^ction of nitric 
acid of specific gravity 1*25 on titanium. It is insoluble in 
acids except concentrated sulphuric aci^J. tWhen heated it is 
converled into the anhydii’de without emission of light. 

The other hydj;at*es also are frequently «poken of as “ ortho 
or “ meta ” acids, according as they are soluble or insoluble in 
dihAc acids. 

By the dialysis of a hydfochloric acid solution of orthotitanic 
acid, Orahani obtaii4''d a solution of colloidal titance acid, and 
von dor Pfordten has also obtained the acid as a colourless jelly.* 


Potassium Titanate, KjTiOg, is formed as a yellow,vfibrou8 
rilass wlien the dioxide is fused with potassium carbonate. On 
^ boiling titaKiic acid with caustic potash and evaporatjFag the^ 
solution, colourless, readily soluble prisms of IC2Ti03‘,4H20 are 
^ deposited. When a hydrochloric a^id solution of titanic acid 
is precipitated with potassium carbonate, an amortihous pre- 
cipitate of, potassium trititanate, K2Ti307,2H20, is thrown^ 
down, and this in presence of hydrochloric acid is converted 
into a hexatitanate, KaTi30i3,2H20, The fused anhydrous 
normal salt, when treated with water in excess, also yields a 
trititanate, KjTijO^^iSHaO, as a fine crystalline powder. 

When sodium carbonate and titanium dioxide art fused the 


» Wagner, Ber„ 1888, 81. 960. 
tinnalen, 1887, 887, 213. 



, TiT4Nimf ^HPomlbs i. sso 

w‘ " ■ ‘ 

fiirea Mu 'i titanates,^ Na8Ti50j4, Jra2Ti307, ^nd Na^TiSj, are 
obtained ; o* tlfese, N£^Ti5024 crystallises^ in forms resembling 
augite and has a^refractive index greater than 1-74^ 

Ccdcium Titanate^ CaTiOg .—This ocburs in Jibe Urals, in the 
valley of Zermatt in Switzerland, and ^ Magnet«Cove, Arkansas, 
as the mineral perofskite, which contanis in additiog 1 to eV 
cent, of ferrous oxide, |is well as traces of manganese and mag- 
nesium, Jt^forms rhombic crystals having a metallic or ada- 
mantinS lustre, a yellow or iron-black colour, and a specific 
gravity of 4*0. The crystals can be ytificially obtained Ip' 
fusing a mixture of potassium carbonate and titatiium didxiae 
with a large excei^ of calcium carbonate.^ • . • • 

CalciuimfitanSsilicate, CaTi^iOg, is found as titanite or sphene 
in brown, green, or black monoclinic crystals, having an ada- 
mantine or resinfius lustre and a specific gravity of 3-4 to 3‘56, 
occunring imbedded in granite, gneiss, mica-schisf, and graniflar 
limestone. ^Titanite cgn be obtained artificialhj by *f using 
calcium chloride with titanium dioxide and silica. The mineral 
guarinite has 4he same composition as titanite, and is found 
in tetrjgonal crystals, having a specific gravity of 3*487, in 
small cavities in a gfeyish trachyte at Monte Somma. • 
Ilmenite^ or Titanic Iron OrCy FeTiftj. — This mineral^ the one 
in jvhich titanium wa* first discovered, occui?4olerably widely 
di8trij;)ut-ed, and crystallises in black, hexagonal crystals. Ppe 
of^ts most important localities is Kjageroe, in Norway. Fine 
crystals are also found in Warwick Co., New York, and^ vast 
deposits oc(^r at Bay St, Paul, in Cana(fti. It is frequently 
found in the finely-divided state as sand on the shores of the 
Mersey ^)pposite Liverpool, in New •Zealand, and elsewhere^ 
specific gravity ranges from 4*5 to 5, and its coryposition is 
« variaile^one. It was thought to be an isomorphous mixture 
ef the sesquioxides of titanium and iron, but is^now regarded as 
a derivative of titanium dioxide. Many ilmenites contain 
magnesia,** and the formula has sometimes been written as 
[Fe,Mg)0,Ti02. 

li Oeikiditey a rare mineral from Ceylon, is a ferro-magnesian 
bitanate containing a high proportion of magnesia.^ 

Titanium Trioxide, or Titanium Peroxide, TiOg, is obtained by 
dropping titanium chloride into dilute aicbhol anSi adding a 

• 

* Nigftli, Ztit anarg. Chem., 1916, 241. 

* Ftenfield and FoOtc, Amer, J. 8ci., 1897, [4], 4, 10$. 

and Jones, Miner^logieal Magazine, 1906, 14» 160. 






Trite TITANIUM OqOUP 


S40^( 

arge Excess of l^drogen peroxide to the solution. Afcimonia, 
mmoniura c^bonate^ or potash is then added, %bu after a time 
bright yellojur precipitate separates out. The*precipitate con- 
ists of a hydrat^ of titaflium trioxide, TiOajSHgO, which retains 
ater and safts^very pcigistently, and dissolves in hydrochloric* 
sifi with e^^lution of a litlle chlorine and formation of a yellowish- 
red solution.^ 

When titanium trioxidc is treated at 0°'with hydroggn peroxide 
and potash and alcofiol are then added, crystals of jjlftassium 
p^oxide hyperlitanate^ Kj04,Ti03,K202,10H20, separate out, 
whilst if aodrf is used in place of potash the compound formed has 
th« fomposition (Na2O2)4,TJi2O7)10Il2O. These substances are 
, stable at O'",* but lose oxygen at Quinary tempetatures.^ 


JlTANIUM AND THE. HaLOGKNS. 

3ff7 TriJluor-idej TiF3, is obtainea as insomoiB 

violet powder by jgniting potassium titanofluoride in a current 
of hydrogen and ‘treating the product with hot water. It is 
also formed when the potassium titanofluoride is reduced in 
aquei^fls solution by zinc and hydrochloric acid or sodium 
amalgan*. It co^ibines with ammonium fluoride, forming the 
double salts (NlT4)2TiF3 and (NH4)3TiFe. ‘ 

<BHanhm Telmporide, TiF4, is obtained by the action of 
fluorine on warift, finely-fowdered titanium, or of anhydiwus 
hydrofluoric acid oi^ titanium tetrachloride at 10a-120°, or on 
powdered titanium at a red heat,® and also by t|ie action of 
liquid anhydrous hydrofluoric acid on the tetrachloride.* It 
may also be prepared by heating barium titanofluoride *to a 
heat.® ^ Iti is a white solid at the ordinary temperature, boils 
at 284^ and lia;j the specific gravity 2-798 at,27-5% w^lst itS 
vapour destiny at 444'" corresponds with the formula TiF^. It is 
very hygroscopic and dissolves in water to a clear solution, which 
on evaporation deposits crystals of TiF4,2H20. With dry^ 
ammonia^ it forms the compound TiF4,2NHg, which sublimes 
without decomposition and is soluble in water. Titaniuift 
tetrafluoride is decomposed by hot sulphuric acid with formation 
of the dioxide. 

* ClaMen, /?fr. *1888, 81, 370. 

* Melikoff md Piasarjowsky, 5cr., 1898, 81, 678. 

» Kuff and Ipaen, Ber^ 1903, 86, 1777. 

* Ruff and RlAo, Her,, 1904, 87, 673. » Mmalsh,, 1904, 2^ 1907. 



AND THE HAl^OENS .jUl 

'Wlien*tiill|uum dioxide is dissolved in hydrofluoric ibid a 
► fljrrupy liquica obtained, which probafcjy cont^ns hydrogen 
titanofluoridej lijTiFg. The titanq/luorides are* isomorphous 
^ith the,silicofliiorides, zirconofluorides* and stailnifiuorides. 

Potassium Titanojluoride or Potassium Fluolitcmate, KgTiF^j. — 
This salt may be prepared by the action of potassiu^i hydrogen 
fluoride on a solution of |jtaniiim dioxicfe in excess of concentrated 
phydrofluorig ^acid. It crystallises in snjall, lustrous leaflets, 
which may be recrystallised without change from hydrofluoric 
acid.^ The hydrated salt, K2TiFg,HljO, >s prepared either ly* 
adding potash to aqueous hydrogen titanofluorid^ (Berzelius), 
or, according to Wohler, by fusing titanium dioxide in a plathiiun 
crucible with t>^ce its w^eight of potassium carBonate and 
dissolving the fused and pulverised mass in a platinum dish 
in the requisite * quantity of dilute hydrofluoric acid. The 
potasstum salt then crystallises out in shining Scales dosdly 
r|sembling tjiose of boric acid and belonging to tli^ monoclifiic 
system (Marignac); they may be dried between filter paper 
and recrystallisSd from boiling water. It loses? its water at 100 ° 
and mel^s without decomposition at a white heat. The anhy- 
drous salt may be oBtahied from the hydrated salt by recwstal- 
^lisation from concentrated hydrofluoric Icid (Marchetti). ,Wnen a 
warm solution of potassflim titanofluoride is treat<M with hydrogen 
peroxide, potassium tilanaperoxyftuoride, TiOgFj.^iKF, is formedt* 
Spdium Tiianojlimide, NagTiFg, ^ obtaiiied in a similar 
manner to the preceding salt in hexagonal prisms most proljably 
isomOrphous Vith sodium silicofluoride (Mafignac). A solution 
containing an excess of hydrofluoric acid deposits small, glistening, 
rhqjnbic crystals having the composition Na2TiF0,NanF2. * 
Jimmonium Titanofliiorite, (NH4)2TiFg. — This sal^ was ob- 
tained %y ^ Berzelius, in rhombohedra isomorphous with the 
corresp^ding tin compound, by neutralising hydrogen titano- 
fluoride with ammonia. Another salt of composition * 

^ • (NH4)2TiFe,NH4F 

separates in tetragonal crystals from a solution of the* preceding 

salt in an excess of ammonium fluoride. 

" Titanium Dichloride^ TiClj, was obtained by Friedel and 
pn^rin * by passing dry hydrogen at a dull red heat over titanium 
trichloride. This compound is a very hygro’scopic hght brown 

^ Marchetti, Zett. anorg. Chem., 1895, 10 , 66. » 

•^iccini, Zeit. anorg. Chem., 1896, 10 , 438. ^ 

• />%«., 1876, [j], 7, 24. Stithler and Baehran, 911, 44^2906. , 



S4Z tI® TITANIUM dflOUP^ 

pow(ftr, whick c%n be volaftlised in hydrogen at a i^eit withom 
fusion. It yUma likg tinder on exposure to aii* ^ng off fume* 
of titanium t^rachloride and leaving a residue okitanium dioxide, 
It hisses when Arown inlo water, evolving hydrogen an^ yielding 
a yellow liquids • • t 

•Tiianim TiClj.— When the vapour of titanium 

tetrachloride mixed withi hydrogen is passed through a red-hot 
tube, dark violet scales of the trichloride are deposited (Ebelmen).< 
It may also be obtained by heating titanium tetrachloride in a 
•^osed tube with mole^ulaF silver at 180 - 200 ® : 

Tia + Ag=--TiCl 3 + AgCl. 

• • 

If the iftixture thus obtained is heated rftore strongly, the 
reverse action takes place (Friedel and Guerin). Titanium 
trichloride has also been obtained by the eleCtrolytic reduction 
of a solutior? of titanium tetrachloride in dilute hydrochloric 
aciS, Violet crystals of the composition TilTlgjGHgO being deposited 
wlfen the resulting liquid is either evaporated in vacuo or 
saturated at 0 ® with dry hydrochloric acid.^ • 

Titanium trichloride is non-volatile, and on heating decom- 
posestinto the dichloride and tetrachloricfie. When heated in 
the iSr, Jthick vagQurs of*titanium tetrachloride are emitted and^ 
titanium dioxide is left behind. It rerfdily deliquesces oq, ex- 
ppgure to moist air and dissolves in water with evolution 0/ heat, 
yielding a redd isW violet sjjlution. 

Titanium trichloride is a powerful reducing agent. Thus when 
boil^ with aqueous sulphurous acid, sulphur ^parates out, 
whilst nitric acid and the nitrates are reduced by it to ammonia 
J[Knecht), and the salts of gold, silver, and mercury to tlfe me^ls. 
Standard solutions of titanium trichloride have been used^n 
volumetric analysis for the estimation of ferric iron and^lso f<fr 
the analysis of a'number of colouring matters.* 

Dqpble compounds of titanium trichloride with the blondes 
of rubidium and cscsium have been prepared,® having the com- 
positions TiCl3,2RbCl,HjO and TiCl3,2C8Cl,H20. 

Titan%ttm Tetrachloride ^ TiCl4.— Metallic titanium does n# 
combine with chlorine at the ordinary temperature, but when 
heated to 360 ® it burns in the gas with brilliancy, forming the 

^Polidori, Zet^. anorg Chem.t 1899, 19« 900; SUhler, Ber.t 1904, 87* 4405; 
Spei^ and Son, Oerman Patent, 154542. * 

' Knecht, Ber., 1903, 86* 166; Knecbt and Hibbert, I'btd., 1903, 88* 1549; 1905, 
88, 3318; 1907, 40, 381»; 1910, 48, 3455. 

’ SOhler, Bhl 1904, 87, 4405. 



M 

tetiaohloBdlL (WdHer), According Friedel jwttd ’ (J«6rin, 
titanium diol^^as converted in presence of chorine at a white 
heat into titanii^pa tetrachloride, oxygen Tbeing e^felved. The 
tetrachloride is readily obtained by passing drjj ^j^Sorine over a 
Seated nfixture of titanium dioxide and carbon, yttlst it is also 
formed*, together with carbpnic oxide land hydrog^ chloridb^ 
when chlorofojm or carbon tetrachloride vapour is passed over 
heated titanium dioxide* * 

* It may alsS be obtained by heating powdered ferrotitanium in 
a current of chlorine or by treating ferr^itanium with hydros* 
chloric acid to dissolve out most of the iron, and heating the dried 
residue of titanic oxide with carbon iiyi strea^i of chlorine.* Jt js 
a mobile, transparent, colourless liquid, having a spedfic gravity 
of 1-7604 at 0° (Pierre). It freezes * at — 23 °, and boils at 136 - 4 ° 
( 134 - 8 °, Emich), its vapour having the normal specific gravity 
of 6-8^ (Dumas). It possesses a penetrating acid odour, and 
emit§ dense white fumes on exposure to air. • • * # 

^Titanium fetrachloride is decomposed by an exc&s of water 
with formation^! titanic acid, which remaini^ dissolved in the 
aqueous hydrochloric acid simultaneously foriped. By careful 
addition* of water it# is .possible to replace the chlorine ^toms 
one by one by hydroxyl, yielding the compounds TiCl3(t)H), 
TriCl2(OH)2, and fiCl(OH)3, whilst an excess of %ater converts it 
into Ti(OH)4. ^ 

^tanium tetrachloride yields a lai^e number of crystalhne 
compounds with other chlorides analogous to those formed by 
stannic chloride.* When dry ammonia gas ii passed over titan- 
ium tetrachloride it is rapidly absorbed, and a very hygro- 
scopic powder, TiCl4,4NH3, is formed which when ignited yields, 
a fellow sublimate of TiCl4,3NH4Cl. Other compounds with 
ajamonit ® have been prepared of the formula TiCl4,’bNH3 and 
TiCl4,8NH3* thes’h are solid bodies which lose abimonia readily 
in air aild on extracting with liquid ammonia yield ammopium 
chloride an«l a dark yellow substance, titammide^ Ti(NH,)4. 

• Titanium tetrachloride dissolves in concentrated hydrochloric 
a^id to form a yellow solution containing chhro-tUdfkic acid, 

>Renz.^«r., 1996, 89» 249. 

• Vtgouroux And Arrivant, Bull. 8oc, chim.f 1907, [4], 1, 19. ^ 

* * Emich, MomUsh., 1904, 25. 907. ' 

*See R^nh{^*m, and Schtttte, Zeit. anorg. Chem., 1901, 251 !^9; Ruff and 
Ipaen,^., 1903,26, 1777. 

*SUhler, Jffer., 1905, 28. 2619. S#e also Roaenbeim and Schtttte, Zeit. 

wufg, CAem., 1901, 26, 239. 

® .1 0 



844 


THE TITANIUM CjpOUP^ 

and when this solution is treated with tjl theoretioa 
quantity of ammonium chloride yellow crystijij mi ammoniun 
chlorotitanale separa‘te. ^ 

Titanium dxydloride^TipJi^^f is obtained, together with the 
trichloride, fi^lysn a mixture of hydrogen and the vhpour o! 
titanium tetrachloride » passed Ojyer the ignited dioxiSe. It 
forms redSish-brown, t^nslucent crystals, whi^ burn when 
heated in the air with formation of the dioxide and the tetra- 
chloride (Friedel and Gu6rin). Other oxychloriJeS fdso have^ 
•been prepared « 

^ Titanium* Tribromide, TiBrgjGHgO, is obtained in unstable, 
deliquescent, violet-colourc^ crystals when a solution of titanium 
tetrabromide in hydrobromic acid is electrolyaed, and the liquid 
then saturated with hydrobromic acid gas.^ 

Titanium Telrahrmide, TiBr 4 , is obtained when hydrobromic 
acid is passed^ver the heated chloride ® as an amber-yellow Jiygro- 
%ccfpi%, finely crystalline mass which has a specific gravijjy of 
2-d[ melts af 39'*, and boils at 230^.* • • 

It is readily .hydrolysed by water, forming oxybromides, 
TiBraOH and 2TiBr(0n)3,2H20. It combines directly with 
ammqnia, forming the compound TiBr^jBlJHa. It dissolves in 
hydrt)bromic acid^to form a blood-red solution which contains 
hromolitanic aq/t, HgTiBr^. When treated witli ammonium® 
chloride, the ammonium salt of this acid, (NH 4 ) 2 TiBrg, 2 fl 20 , 
separates in dark^red crystals. 

Titanium I)i4odide, Tif„5 is prepared by heating the t5;ra- 
iodide in a current»of hydrogen and mercury vapour. It is a 
black compound which forms non-volatile, hygroscopic leaflets of 
density 4*3. It is decomposed by water and is soluble tn boiling 
hydrochloric acid to form a blue solution. • 

Titaniulh Tri-iodide, TilajCHgO.— Deliquescent, violeticrystais 
of this composition are formed by the electrolytic reduction of 
a solution of the tetra-iodide in hydriodic acid.® • 

Titanium Tetra-iodide, Til^, is produced when iodihe vapour is 
passed over heated titanium (Weber) ; also W’hen dry hydriodift 
acid is ftissed into titanium tetracliloride, which is gradually 

1 Kuwalewsky, Zeit. anorg. Ohem.t 1900, 26, 180. Rosenheim and Schiitto, 
ZeiU anorg, C'Aem., li)01, 26. 230, 

•SUhler, W, 190#, 87. 4406. 

• Thorpe. Joufn. Chm, Soc., 1885. 47, 126. 

• fbuppa. ^roc. Roy. jS’oc., 1867, 8. 42. 

• Defaoqt and Copaux, Bull, Soc. cAim.. 1908. [3], 899. 

• Stahler, JJcn, 1004, *87, 4406. 

• 



OTAI^ AND SULPjtUR $45 

heated v/p t^ts boiling point. small quantity of ffe^lodine 
giving a vioUb.tinge may be removed by three or* four distilla* 
tions in a strea^L of hydrogen (Hautefeni&e). A third process 
consists in passing the vapour of titaifiiim te^clloride mixed 
Vith hySrogen and iodine vapour thipugh a 4 iibo heated to 
redne^. Titanium tetra-iodidc forms* brittle ma^ having* 
reddish-browi^ colour a^d metallic lus^^-e. It melts at 150° to a 
ycUowish-browm liquid, which solidifies on cooling in fine octa- 
*hedral cfysTals. It distils without decomposition at a tempera- 
ture slightly above 360°, giving rise orjnge-coloured vapoury* 
The specific gravity of its vapour at 440° has the normal value 
of 18*054. It fumes strongly in the^ir and dissolves readily jin 
water. 


Titanium and SuLPiiUR. 

378 •Titanium combines with sulphur to form the sulpjiijes, 
TJiSj* TijSg, ^d TiS, corresponding to the oxides of*i!ie metal * 
Titanium Dmdpkide, TiSg, is obtained by passing a mixture 
of titanium te^achloride vapour and sulphuretted hydrogen 
througluan ignited tube, and forms large brass-yellow, lustrous 
scales, closely rCsenAliftg mosaic gold. It burns when igpited 
,in the air, yielding fitanium dioxide aiKfsulphtlii dioxide.* 
Titanium Sesqumdpliidc, TijSg, is formed by pSssing a mixture 
of moist sulphuretted hydrogen and carbon disulphide vapeur 
ovQf titanium dioxide heated to briglifc redne^,^ or by igniting 
the disulphide in a current of an indifferent gas;^ it forms a 
greenish-blact or grey powder. It is stalble towards dilute 
solutions^ of acids and alkalis, but forms green solutions of 
unknown composition in concentrated sulphuric and nitric acids.'" 

iTitanmm Monosulphide^ TiS, is prepared by heating either of 
the for^oiiig ccmipounds in a current of hydrogen and is a 
lustrous^ubstance resembling bismuth. 

Titanous ^ulphcUcy TiS 04 , is formed when metallic titanifim is 
evolved in sulphuric acid and the solution evaporated to dryness. 

Titanium SesquistdpJiate, Ti 2 (S 04 ) 3 , 8 H 20 , is obtained by 
dissolving the metal in dilute sulphuric acid. The violet solu- 
tion on concentration assumes a fine blue lustre and deposits 
Ipiall tufts of crystals (Glatzel).* By repeated evaporation in 
vacuo of a sdution of titanium trichloride with dilute sulphuric 

^ Thorpe, Journ. Chem. 80 c. ^ 1886, 47, 401. 

* von der Pfordten, Annalen, 1886, 834 290. 

* Compare Sj^hlor, Ber.y 1906, 38, 2619. 


846 


tHe titanium 0|0UP^ 

acid, ^lofet ciystels of thei composition STi2(SOJgM804,25H2O 
are obtained^ and the same compound is fomgdr ilso by the 
electrolysis of a solution of titanium tetrachloride in concen- 
trated sulphuria |Lcid. This substance forms a violet solution in 
water, and oB j^peated evaporation with concentrated sulphuricP 
arfd in absgnce of air, yields the anl^drous sesquisulphate as an 
insoluble, green, crystalline powder (Stabler). Ti^nium sesqui- 
sulphate is decomposed by heat into siilphur dioxide, sulphur 
trioxido, and titaniun! dioxide. It forms an alumVitlf caesium* 
^Iphate, CB2S04,Ti2(J^04)3|24H20, which crystallises in cubes, 
and a similar alum with rubidium sulphate,^ whilst a double 
sujphate, Ti2(804)3,jra2S04,|yi20, has also been prepared.® The 
^ violet acid -salt forms with rubidium and ammonium sulphates 
the compounds 3Ti2(S04)3,Rb2S04,24H20 and 
‘ 3X12(804)3, (NH4)2S04,18H20 (Stabler). 

Noanml Titanium DLwlphate, 11(804)2, 3H2O, is formed by 
tha oxidatian of the sesquisulphate with nitric acid, and on 
evaporation remains as a transparent, yellowish, deliquescent, 
amorphous mass. The sulphate forms double* salts, such as 
K2S0^,Ti(S04)2.3H20, Ti(S04)2,Ca804, etc.% 

Basic Titanium Sulphajf, (li0)804, is obtained as a hard white 
mass by-dissolving'diy titanic acid in bojling s'Vilphuric acid and# 
evaporating,^ whilst crystals of (Ti0)S04, 51120 are obtained by 
bbtling titanic acid with alcoholic sulphuric acid and evaporating.® 
Several other balic sulplmtcs have been prepared « by heating 
titanium dioxide sulphuric acid in sealed tub^ at different 
temperatures. 


Titanium and Nitrogen. 

379 Titaniunk is one of the elements which very readily com- 
bine with nitrogen, and two compounds of these two elements 
are l&iown. , 

Titaniupi MononilridCf TiN, is obtained by heating titanium 
dioxide very strongly in the electric furnace in presence of 
nitrogen. A better method ^ is to heat titanium dioxide in a 

' Piocini, Gnzx., 1895, 25, [2], 542; Zeit. anerg. Cfum., 1898, 17, 355. 

•Spenoe aBd Son, Uenuan Patont, 149002 (1904). 

• Weinland aiM Ktthl, ZeiL anorg, Chem., 1907, 64 , 253. 

* Mere, Clm., 1800, 99, 157. 

* Rosenheim and Schtttte, Zeit. anorg. CAem., 1901, 29, 239. 

• Blondel, full. Soe. ehim.^ 1899, [3], 21, 262. » Ruff, Ber., 1909. 42.1K)0. 



OITAItUH AND CARBON 


m 


porcelain* l 3 Lt for six hours at 1460 - 1600 ® in a streati of 
'ammonia.. I? is^a bronze-yellow mass \vhich a specific 
gravity of 5*18 und is hard enougl^ to scratch rqbies and cut 
^mond§.i * 

Tita^ixm Nitride, Ti3N4.— -When the |oflij>ound 'f'iC]4,4NH^i8 
heated a copper coloured Compound is obtained/^ ^hich wat 
regarded as th# elenient^ntil Wohler ,*«sho wed that it contained 
^trogen anjJ gave it the formula Ti3N4. Wohler also prepared a 
dark blue compound with a coppery sheen to which he gave the 
formula TiNj. It has been shown by Schi^ider ^ that the fornuy* 
substance contains oxygen and the latter does not* exist. The 
tetranitride has been prepared by Ri»fi and TJreidel ® as follows : 
The compound T!Br4,8NH3 is^vashed with liquid ahimonia to 
form an orange-coloured substance of the approximate composition 
2Ti(NH3)4,TiBr4,8BlH3. The compound is then treated with a solu- 
tion of*an equivalent amount of potassamide in liqflid ammonia, 
wjjien monopotassium titanium di-imide, Ti(NlI)NK»^and tilanic 
nitride are formed. The nitride has a brown colour and is decom- 
posed by water ifito ammonia, and by heat into TiN and nitrogen. 

TITANIUM AND Oa^^BON. 

38^0 Titanium Carbide, TiC, is prepared by fusing titanium 
dioxidg with an excess of carbon, or with calcium carbide in tj^ 
electric furnace, and is thus obtained as a massjiaving a crystal- 
line fracture, apd a specific gravity of 1 * 25 ; it is not attacked by 
hydrochloric ftcid, is only slowly dissolved Hy aqua regia, and 
does not decompose steam at TOO*^. In other respects it resembles 
metallic rttanium, but burns more readily in oxygen.® 

^eel-grey crystals of titanium carbide have been obtained 
f*om cAf^iron prepared from titaniferous ores.^ Titanium 
carbide is used for making arc lamp electrodes. * 

Titanium Vyanonitride. -Nihen iron ores containing titapium 
are reduced*in the blast-furnace small brilliant copper-coloured 
cubes, which are hard enough to scratch glass and aJTe almost 
infusible, are found in cavities both of the slag and of tffe metal. 

A mass containing as much as 80 lb. has been found in a single 

^ ‘ Moiasan, Compl. rend., 1895, 120* 290. 

* Liebig, Pogg. Ann., 1830, 21. 259. 

* Arvnakn, ISM, 73, 34. « Ztii. anorg. Chtm., 1895, 8, 81. 

* Raff and Troidel, Ber., 1912, 46. 1364. 

* goimn, Ctmpl. rend., 1895, 120. 290; 1897. 126. 839^ 



84 $ 


Ae titanium dROUlJi 


blastfurnace ii\ the Ha A. This substance wasJ^xafcined 1 
Wollaston irf 1822 ajjd believed by him to be nffeteflic titanium 
but Wohler, in 1849 Bho\^ed that it contaiied nitrogen ai 
cyanogen, and, gave t) it the formula Ti(CN)2,3Ti3N2. I 
likewise obtaiaed it ArMficially ^ by heating a mixture of ferri 
«Janide q{ potassium and titaniitm dioxide in a well-close 
crucible at a temperatu**e sufficient melt niqjcel. Titanim 
cyanonitricfe can also be prepared by heating t^, whiteness 
mixture of titanium Sioxide and charcoal in a tube of carbo 
•an a stream of dry^itr#gen (Deville and Wohler).^ A thir 
method of preparation is to fuse potassium cyanide in the vapou 
of iitanium tetratliloridc f(Wbhler). It has a specific gravit; 
of 5 * 28 , afld is attacked only bj a mixture of nitric and hydro 
fluoric acids. When ignited in a current of steam it is decomposec 
as follows : • 

^ fl^i(CN)2,3Ti3N2 + 201120 = 2nCN 4 + ONHa + lOHg. 

• • • • 

Chlorine also decomposes this substance at a red heat, titanium 
tetrachloride and a volatile sublimate consisting of. a compound 
of titaniiun tetrachloride and cyanogen chloride being formed. 

fused with potash animonia is giv^n off, potassium titanate 
being produced, 


JJkte^ion Ay) Estimation of Titanium. 

Titanium is distinguished from tin inasmuch as its oxides 
are not reduced tff the metallic state when heat?d on charcoal 
before the blowpipe. AVith microcosrnic salt titanium dioxide 
yields a colourless bead in the outer flame, but m*thc jjmer 
flame tin? bead is yellow' whilst hot and assumes a violet cojpur 
on cooling. According to Riley, the delicacj^ of tlys ftactioif is 
increased by melting metallic zinc in the microcosjaic bead 
heated on charcoal, a distinct coloration being then obtained 
when the zinc is burnt away, even with minute quantities of 
titaniu^*! When fused in the microcosrnic bead with addition 
of a small quantity of an iron salt in the reducing flame, a bright- 
red bead is obtained. Titanium compounds do not colour 
the ga8-fl|ime, but both the spark and the arc spectrum show |n 
enormous npmber of bright lines, chiefly in the blue and green, 
wkich have been carefully mapped by Thal4n and Withers. 

» Phil Trans ,, 1$23, 118, 17. * Annaltn , 1850, 78, 34 ; 7i 21 J. 

1867, 108, 



IZHtOONIUM 


849 


MetaWc Jbc placed in a hydrocbldtic acid solution of i^tanio 
acid evolv^ hydrogen and the liquid a^siunes j violet-blue 
colour; a dark idplet precipitate ig formed if tl^ solution be 
not too dilute, and this gradually tutns whj^ by oxidation, 
^he violet-blue solution when diluted witlpwateikassunies a rose- 
colour, and this reaction serves for the detection of smajj quantitfas 
of titanium. ^Sodium ^iosulphate wjien boiled with a nearly 
neutral solution of a titanate precipitates the whole of the titanic 
acid, and tnis reaction serves as a means of separating titanium 
from iron and the metals of the group. ^ 

In order to remove silica, when present, the mixture is evapora- 
ted with hydrofluoric acid, the siliopn bein^ expelled as silicon 
tetrafluoride. 

Titanium is always estimated gravimetrically in the form of 
titanium dioxide,* this being thrown down from its solutions in 
acids 4 )y ammonia, or by saturating with sulphut dioxide and- 
boiling. Titaniimi may also be estimated volumctricalfy*by’ 
reducing titfinium dioxide to titanium sesquioxide Sy meani of 
zinc in an acid lolution and subsequently oxidiffing with standard 


permanganate. 

Atomic Weight of ^ikinium . — The atomic weight of titg-mum 
was first determi^jed by Kose ^ in 1829*t)y deev^mposing Jitanium 
^tetrachloride with water, weighing the titanic acid formed and 
estimating the chlorine in the filtrate, the nmnber found bejijg 
47*72. A redetermination was made^n 1885»by Thorpe,^ who 
analysed pure titanium tetrachloride and tetrabromide, the 
amount of silver required for complete precipitation of the 
halogen, the amount of silver halide formed, and the quantity 


of titaniiUm dioxide yielded by each being ascertained; thq 
avfrage of the results of the six series of expcrimenjjp gave the 
number9I8*l, which is at present (1922) adopted. 


a:iRCONIUM. Zr- 90 - 6 . At. No. 40 . 

. 382 In 1789 Klaproth found a new earth in the min^al zircon, 
to which he gave the name of zirconia. He discovered in 1795 
that the same earth was contained in hyacinth, a mineral found 
in Ceylon, and he thus ascertained the truth of Werner’s previous 
lupposition that these two minerals were identical. Zircon and 
hyacinth posaeas the formula ZrSi 04 , and are more of less coloj^ed 
by ferric oxide. Zirconium is found in a few other rare minerals, 
^^fygg.Ann., 1829,18,1^. * Jwm. Ckem, Soc.t l^Ol «7, 108. 



850 


Ae titanium QROUIJi* 

and accurs in aflpreciable'quiintities in Norwegianlrailite, wit! 
thoria and s^eral of^the rare earths.^ • . ^ 

The metaf^ zirconium waj first obtained by# Berzelius in th< 
form of an iron<grey po\^der by beating potassium zirconofluorid( 
with potassima The i^etal can also be obtained, according tc 
itoost, by, passing the vapour of zisconium chloride, ZrCl 4 , over 
heated sodium. The ignited amorphou^ metallic j^wder thus ob- 
tained is so finely divided that it passes through the ijpres of filter 
paper, but it assumes* a metallic lustre under the burnisher. The 
^amorphous metal ma^^ alsa be prepared by heating zirconia with 
magnesium ‘powder,^ and thus prepared it has a velvet-black 
appearance like woid charcoal. 

Wedekiifd^ has obtained a n^tal containing 99*09 per cent, 
of zirconium. He heats an intimate mixture of ZrOg and 
calcium shavings in an evacuated iron vessel. ‘When the reaction 
is completed* the contents of the tube are treated successively 
witli\ater^^cetic acid, dilute hydrochloric acid, and water, all 
the operations being conducted in absence of air. ‘ The residual 
powder is then washed with acetone and dried m vacuo at 250- 
300^ ; finally, at a temperature of 800-1000°, the powder sinters, 
buj^ca not melt ; it exhibits a mirror-like brilliancy on polishing. 
Zirconium of 99'^ per (^nt. purity has bcei^ obtained by the 
action of sodium on potassium zirconofluofide by the same method^ 
%>^th at deacri bed for titanium ) . 

Crystallised zii^onium yas first obtained by heating potassium 
zirconofluoride with aluminium at the temperature of melting 
iron; it is, howevfr, best prepared by heating zfreonia in the 
electric furnace with an insufficient quantity of carbon for its 
.complete reduction, and is thus obtained as a metallic button 
containing some zirconia but free from carbon and nitrogen. It 
may also be obtained by heating the carbide with zirefnia in«a 
similar manner,® or by heating potassium zirconofluoride with 
magjiesium in the electric furnace.® * 

Crystallised zirconium forms broad, apparently* monoclinic, 

• Phipaon, Chem. Nch a, 1890, 73, 145. See also Marclen and Rich, Bur. Mim* 
BuB., 10>1. 186. 

'Phipaon, Compt, rend., 1865, 61, 745; Chem. News, 1906, 88, 119; Winkler, 
Ber., 1800, 23, 2664. 

*^n«a/c»(.10]3, 385, 149; compare also Weiss and Neumann; Ze//. anor^^ 
Chem., 1910, 66, 248. 

'Podtaus, Zeit. anorg. Chem., 1917, 88, 123. See also Mfitlen and Rich, 
J. Arf. Engt Chem., 1920, 18, 651. 

• Moissan, Compt. repd., 1893, 116, 1222 ; Troost, ibid., 1428. 

• Wedekind, «Zei7. Kkktrochem., 1904, 10, 331. ^ 



coMPOuifts 'm 

plat^, bis Specific gravity of 4*08 at 15^^ an^ is hard eifough 
bo scratch glm find rabies. It is ooly vejy slowlv oxidised in 
bhe air even at a white heat, but bun^ in the oxy>h]^arogen flame, 
and yields the tetrachloride when h^ted to^dull redness in 
chlorine or hydrogen chloride. It is dissolved by caustic 
potash with evolution of hydrogen. It is only slowjy attacked 
by acids, with the exertion of hydrofluoric, even on heating, 
but is rapi^jr oxidised by aqua regia. The amorphous metal 
readily tikes fire in the air on warming. 


ZIRCONIUM COyPOUlJDS. 

383 Zirconium Oxide or Zir<^iia^ ZrOg.— In order* to prepare 
this oxide zircon is ignited and then quenched in water. The 
powdered mineraf is mixed with three to four times its weight 
of acid potassium fluoride, and gently heated ih a platinum' 
v^el until all moisture has been driven off. The plaSnuift 
crucible is then placed in a Hessian one, and both are well covered 
and exposed foi^wo hours to the strongest heatt>f a wind furnace. 
The pofcelain-like mass thus obtained is boiled with water 
containing hydroflu(flic«acid, and the insoluble potassium «]Jico- 
^fluoride filtered off. On cooling the solfftion, crj^stals of pptassium 
zircynofluoride are deposited, and these are purjfted by recrystal- 
lisatiop. The pure salt is then heated with sulphuric acid uptil 
all^he hydrofluoric acid is driven of!;^the residue is dissolved in 
w'ater, and the zirconia precipitated in the cold by ammonia.* 

In order tfl avoid the use of hydrofluoric %cid, the very finely 
powdered zircon may be treated as follows. It is first fused 
with hydVogen pota.ssium sulphate and the fused mass repeatedly 
b^ed out with water containing sulphuric acid, wh^ a residue 
(Jf basiS lyrconium sulphate, dZrOjjSSOj, 1411^0, is obtained, 
which is next fused with caustic soda in a silver basin. This is 
then lixiviated with water, the residual zirconia, which coiM^ains 
soda, washed with hot water and dissolved in hot concentrated 
sulphuric acid, the solution filtered and precipitated with 
ammonia.* The precipitate thus obtained consists of zirconium 
hydroxide, which readily parts with its water on heating. When 
heated at 140-200° it has the composition Zr0|,H|0, and is 
tnown as zirconic acid. A hydrated oxide containing less water 
than this is (flitained by repeatedly boiling zirconium oxychlqpde 

MonaUh., 1889, 80, 793. * Homberger, Mnakn, 1876, ISl* 232. 

•#r«i*,.Ber.,1870,8,M. ‘ ** 



852 


T&E TITANIUM G>OUPJ 


with f^ater and drying the precipitate at 100° ; this bdkn called 
metazirconic*acid^ ^According to van BeinmeJei^^ however, 
these substa^es are probably not true hydroxides, but colloidal 
zirconia, containing water in the form of a hydrogel. The 
hydroxide is slightly soh|ble in water, and colours yellow turmeric 
paper bro\^i. When precipitated and washed in the cold, it is 
easily soluble in dilute acids ; if, howevej, it be prqcipitated from 
a hot solution, or washed with boiling water, it is soluble only in 
concentrated acids. \Vhen heated to incipient redness tt is con- 
certed into zirconia wjth avolution of heat. The oxide thus ob- 
tained has the specific gravity ® 5*489, and is only slightly soluble 
eyp»in hydroflUorie^acid, bijt dissolves on heating in a mixture of 
two parts of sulphuric acid and ope part of water. An hydroxide 
of the formula Zr 50^(011)7, which gives rise to a chloride, 
Zr50gCl4,22H20, and a sulpliate, Zr508(S()2)2*,a:H204, has been 
described by iiodd."* • 

* Zirconia can be obtained in the crystalline state in the form 
of tetragonal prisms isornorphous w'ith cassiterite and rutile 
and having a specific gravity of 5*71.^ For tiiis purpose, the 
amorphous oxide is fused with borax in a porcelain furnace, the 
fiis(j(l«'residue being boiled out with sulphurfc acid. 

Pure ^irconia melts at 3^)00'’, and the fused pr9duct has a specific 
gravity 5*89. tfhe linear coefficient of expansion is 0*0000()084,* 
nearly the same as that of fused quartz. 

Zirconia is employed ir^ tlie preparation of rods for the Nernst 
electric lamp. Crucibles, etc., can be made by mixing zirconia 
with 10 per cent, ^f magnesia. Crucibles made ’from zirconia 
mixed with 1-3 p(T cent, of yttria ® do not soften until 2400°. 
.Flatinum can be melted in such crucibles with the oxy-hydrogen 
flame. Qjiartz can also be melted without destroying the 
crucible,'^ 

Zirconia, like* the dioxides of the other metals of this group, 
acts ns an acid-forming oxide, and yields salts corresponding to 
the metasilicates and metatitanates. 

Sodium* Zirconate, Na2Zr03, obtained by fusing the oxide 
w'ith sodium carbonate, forms a crystalline mass which is de- 

^ Ruor, Zeit. anorg. Chetn., 1905, 43 , 282. 
anorg. Chem.t 1900, 49 . 126. 

* Venable and Belden, J. Anur. Ch^m. Soc., 1898, 90 , 273. 

* Joum. Chem. 8oc., 1917, lU, 396. 

•Nordcnskiold, Pogg. Ann.t 1861, 114 . 612. 

* Huff and ^uschko, ZeiL anorg. Chtm.^ 1916, 97 , 73. 

’ and Lehmann, Zeii, anora. Chem.. 1909. fIR. 17» 



^zmCX^nM COMPOUNDS 858 

composed by water with separation of zirconia. When <C^ted 
^ with an exceh of^odium carbonate to whitenessMie^salt Na^ZrO^ 
is produced. is again decomposed by Vater with formation 
of hexagonal tablets having the composition Na2ZrgDi7,12H20 = 
f^a20,8Zr02,12H20. I • * 

Zirconium Sesquioxide} prepared as a green pow(fer 

by the combustion of zirconium liydride. On ignitidh in air, it 
is converted into the diSxide. * 

* Zirc&mufh^eroxide, Zr205,9H20, is obtained as a white powder 
when hydrogen peroxide is added to a solution of zirconium 
sulphate. Under certain conditions a tyd Ated oxide^ ZrOa.DHj^iC 
is formed,® and this when treated with excess of hy^drogcn peroxide 
and an .alkali hydroxide is stated \o forin*the all^ali salts 'of 
perzirconic acid, ^ K^/jr 20 ij^. * 

Zirconium and Hydrogen . — When zirconia is heated with 
magngsium powder in a current of hydrogen th^ latter is ab-^ 
sorbed, the product containing zirconium hydride, ZrlTg, together 
^ith zirconia and perhaps a lower oxide.* The hydride is also 
formed when hydrogen acts on the metal at a red heat.® It burns 
in the air to form the sescpiioxide. 

Zircffkium Fluorine , is obtained by heating zirconia 
with acid ammonium fluoride. Th^ residual mass is^i^sily 
soluble in water contayiing hydrofluoric acid* und crystallises in 
glislening, triclinic tablets having the composition ZrF4,3H20. 

According to Chauvenet, the hydrate, ZrF4,3H20, is reaHy 
Zrt)F2,2IlF,2HaO, for on heating t9 MO'’ ^ater is lost and 
ZrOF2,2HF Jeft, whilst at higher temperatures the compound 
ZrOFg, is formtjd.® The anhydrous compound sublimes and forms 
small, highly refractive prisms with a density 4*433. It dissolves 
sightly in water, and when the solution is warmed, zirconiurft 
Jjydrojfde is precipitated. It combines with liquM ammonia 
to form 5ZrF2,2Nll3. • 

Zircifniura fluoride forms a series of double salts with other i 
fluorides \fhich are isomorphous with the corresponding *silico- 
fluorides, titanifluorides, and stannifluorides. , 

Potassium Zirconojluoride, KgZrFg, is obtained bf igniting 

^ Woisfl aad Neumann. Zcit. anorg. Cfietn., 1909, 65, 248. 

* Bailey, Joum. Chetn. Soc., 188ft, 49 , 481. 

* Pissarjewsky, J. Russ. Phya. Chem. Soc^ 1900, 82, 609. 

* Winkler, ^cr., 1891, 24, 888. , 

* Wedekind, Ann., 1913, 305, 149; Weiss and Neumann, Zeit. anorg. ^hem.f 

1910,65,248. * 




854 


THE TITANIUM 



zirco|^*with acid potassiuqi fluoride or by pouring a sdution of 
potassium fl^orifle into an excess of zirconium^fluG-iide solution. 
It crystallists in siftall, acute, rhombic prisms, and dissolves 
at 2° in 128, ftt 15® in 71, and at 100® in 4 parts of water. 

When zircaniufn hydroxide is dissolved in the smallest quantity^ 
o^^hydrofluoric acid andihe liquid b poured into a concentrated 
solution of neutral potassium fluoride, the salt K2ZrFg,KF is 
precipitated, and crystallises from boiliAg water m fine needles. 

If sodium fluoride <ind zirconium fluoride are inixed in any 
proportion, the salt Na2ZrFg,4NaF is produced. It forms small, 
itonoclinic crystals wifich dissolve in 258 parts of water at 18®, 
and at 100° in about 60 parts of water. 

IVmmoniym salts, corresponding to the salts of potassium, and 
other double fluorides/ are knowfl. 

Zircmium Chlmide, ZrC^', is obtained by passing chlorine gas 
jver a heated^mixture of zirconia and charcoal, by the action of 
jhloivie or hydrogen chloride on the heated metal, when it is 
ibtriined as a white, crystalline sublimate by heating the dioxide 
vith phosphorus ^pentachloride at 190° in a sealed tube, and 
lest of all by heating the dioxide in a stream of chlorine and 
arbon tetrachloride at 800°. It may be*.recrystalliesd from 
ydt^ichloric acid, but it Js doubtful whether it has ever been 
btaincd’in this* way free from the ojcychloride. Zirconium ^ 
chloride forms with ammonia the compounds 2 ZrCl4,8NH3 and 
/f0l4,3NH3. On addition of water to the chloride heat is evolved, 
and zirconium o.^’chlorid^, ZrOCl2, formed, which rcradins 
dissolved in the acic^ solution. The same compound is obtained 
by dissolving zirconium hydroxide in dilute hydrochloric 
acid, and on evaporation crystallises out in prismatia needles 
Belonging to the tetragonal system, and having the composition 
ZrOCla.SHgf).* These are readily soluble in water, l^ve a^ij 
astringent taste,, and when heated to 50° losi? wateV, forming 
tmore basic oxychlorides, whilst by treatment with concentrated 
hydrochloric acid crystals of Zr0Cl2,6H20 and Zi0Cl2,3H,0 
have been obtained.^ 

Zircomum Bromide, ZrBr^, is prepared in a similar way to the 
chloride, and forms a white, crystalline powder which is easily 

» See also Wells and Foote, Zeit. anarg. Chem., 1895, 16, 434; Amer. J. Set 
1897, 8, 461. « \ 

« Stabler and I^nk, Ber., 1905, 86, 2611. Compare Matthews, J. Amer. Chem 
Soc., (898, 80, 815. * 

• WeibuU, ier., 1887, 80. 1394. 

• Venable and pasket^e, J. Amer, Chem. Soc., 1898,20. 821, 




^ZIKCKgNIUM COMPOUI«)S 8W 

volatilise at the temperature of the gas lli|ne. In contact 
with moist aSv ^nwater it forms zirc^um oxybromide, ZrOBr,, 
which crystallise^ in needles, and may also be J)repared by 
evaporating a solution of the hydroxide in hydrobromic acid, 
Irhen ZrOBrgjSHjO separates out.^ AVi^ amra^it,® zirconium 
bromide gives the compounds i^r4,4Nll3 aiid ZrBr4,10NH3. *A 
number of oxyj)romides jf the s^e ty^s as the oxychlorides are 
known. 

* Zirconmm Iodide, is obtained by pdhsing hydrogen iodide 
over zirconium or the carbide at S b^ght^red heat. Accordinj^ 
to Dennis and Spencer,* it is a white, crystalline body which S 
insoluble in water and acids-; Sti\Jiler an(i DtJiik,* how%v§r, 
state that it dissolves in water^and acids, the aqueons solution 
depositing colourless crystals of the oxyiodide, ZrOlg^H^O. 

Zirconium Suljdiide . — AVhcn metallic zirconium and sulphur 
are heated together in a current of hydrogen they •ombine with < 
evolution of heat to form a cinnamon-brown powder, iWiich 
aAumea a metallic lustre under the burnisher. This is not Rt- 
tacked by most^f the dilute acids, but dissolvas slowly in aqua 
regia and readily in hydrofluoric acid. When fused with potash, 
zirconia Rnd potassium sulphide are formed. ^ 

Zirconium Sulphate, Zr(804)2, obtained by dissolving 
f»xide or hydroxi(fe in sulphuric acid, evaporating, and*heating 
nearfy to redness. It is a white mass which dissolves slowjy 
but conipletely in cold, and quickly in hot ^^ater. Hydrated 
crystals are obtained by concentrating a solution which contains 
free acid, and these swell up on heating, like alum. The*sal 
decomposes at a red heat, leaving a residue of pure zirconia 
The behaviour of zirconium sulphate in solution ^ is best repre 
sen^ by the formula (Zr0)S04,H2S04, whilst the crystallim 
hylrate(k salt is {Zr0)S04,H2S04,3H20, and not Zr(S04)2,4H20 
as was formerly ’thought. If its solution be ^turated with 
zirconiuii hydroxide a basic salt, Zr(S04)2,Zr02 or (ZrOjSQi, is 
formed, and this is obtained on evajioration as a hydrated mass. 
If tile normal salt be precipitated with alcohol an insoluble salt, 
Zr(S04)2,2Zr02, is thrown down. A large number of* similar 

^ Roflenheim and Frank, Ber., 1007, 40, 803. 

'Matihews, J. Amer. Chem. Soc., 1898, 20, 839; SUhJer and Hank, Ber., 
I^ts88.261i. 

• J. Amer. Ch^. Soc., 1896, 18, 673. 

« 1904, 87, 1137. 

* Roer, Zeit, anofg. Chm., 1904, 42, 187; Buer and Levin, Aid., 1905. 

46, 449 r Rownheim and Frank. IMW. an baq 




866 OftE TITANIUM GflOUP^ 

basid ' sulphates^ have been described by Chauverifet^ and 
Rodd.* • • , 

Zirconium mi Nitrogen. — The nitride, Zrg^^,, is obtained by 
heating zirconu|m chldride to redness in a current of dry 
ammonia,® Sn^ also bj^ heating zirconia and magnesium in ^ 
kfosely-covered crucible.^ It is brownish-green, crystalline 
powder which oxidises \^th incandesc^ce when^ gently heated 
in air (Wedekind). A nitride of the lormula Zr^Ng is formed 
when the compound ZrCl4,8NH3 is heated to redness in nitrogen*^ 
^Matthews). Bruere^nd,Chauvenet ^ are unable to obtain the 
compound ZrgNg, but always obtain Z3N4, on heating ammonia 
dgrwatives of firc^ium cljoride. 

Zirconvm Nitrate, Zr(N03)4, is obtained as a yellow, gummy 
mass by dissolving the hydroxide in nitric acid and evaporating 
at a moderate heat. If the solution be e\tiporated in vacuo 
^over caustic«8oda and phosphorus pentoxide, extremely ohygro- 
«co]^c crystals of Zr(N03)4,5Il20 separate out.® The existence 
o^normal zirconium nitrate has been questioned by Chauvene\i,’ 
who finds that •the concentration of a solution of this salt 
always leads to the loss of nitric acid and the separation of 
tlm basic salts, Zr0(N03)2,2H20, at orclin{»ry temperatures, and 
Zrv(N03)2,3‘51I|Q, at temperatures below 10°. A number of 
other basic nitrates also exist. ‘ 

^ ^Zirconium Boride, Zr3B4, has been prepared by heating in the 
electric furnace ^ mixture of zirconium and boron ; ® it forms a 
steel-grey mass, consisting of microscopic crystals, and has the 
specific gravity 3-7f 

Zirconium Carbides.— Zirconium combines with carbon to 
form two carbides having the composition ZrCg ‘and ZrC. 
The dicarhide is obtained by heating zirconia with an exce/f!i of 
carbon in the electric furnace and lias a metallic ajppearaVe 
and brilliant frticturc, and is not decomposed*by water even on 
heating. The monocarbide is prepared in a similar matmer, but 
the mixture of zirconia and carbon is placed in a*carbon tube 
closed atf one end, which is then heated in the electric furnace. 

V 

» Compt. rend., 1917, 164, 864, 046; 165, 25 ; 1918, 167, 24, 126. 

* Journ. Chm. Soc., 1917, 111, 396. 

* Mi(tthews, J. Amr. Chtm. Soc., 1898, 20, 840. 

* Wedekind, '2>eiV. anorg. Chem., 1005, 45, 385. 

» Cmpl rend., 1918, 167, 201. 

* lUsenheim and Frank, Ber., 1907, 40, 803. 

* ChauTcnet aj^d NiooUe, Compt. rend., 1918, 166, 781, 821. 

* Tack|r and Moody, Jmm. Chem. <Soc., J 902, 81, 14. 




DETBCTIOl|^ANpi!ESTIMATrON Of ZIRCONIUM M7 


It has a |rey colour and metallic lustre, and isjhard enou^ to 
(Scratch quartz. , ft is permanent in the aij and is* not decom- 
posed by water, but burns brilliantly^ in oxygen. ^ ^ 

Zirconium Silicide, ZrSij. — This com^oimd js obtained by 
Seating a mixture of potaasium zircxyiofluoride,* aluminium, 
sulphur, and sand, the whole being covered with g layer of 
magnesium poyder.® forms small ^eel-grey crystals having 
the specific gravity 4‘88 at 22 '’. 

SUicald^ of Zirconium . — Of the.se, zircon*or hyacinth, ZrSi 04 , 
is the most important. It occurs in cayst^line rocks, especially^ 
in granular limestone, schist, gneks, syenite, and gAnite. The 
jhief localities arc in alluvial sands in i^eylon, < 
the Urals, in the Isle of Harris, yi Greenland, 
n the gold districts of Australia, and in many 
)laccs in North AAcrica. Zircon crystallises 
n tetragonal prisms and pyramids (Fig. 182), 
living an adamantine lustre ; they are colour- 
ess in the pure state. Usually, however, 
zircon is coloured red or yellow by ferric 
oxide. The colourlcs.s and smoke-coloured 
varieties are termed* jargon. This variety 



Fig. 182. 


exhibits a peculiai;absorption spectrum*from ^ 
which Sorby concluded ‘that it contained a • 


new element; to this he gave the name of jargoniurn, but sub- 
seqijently he found that tliese lines weje causc^ by the presence 
of uranium oxide. An artificial jargon yielded a similar 
spectrum, though neither uranium nor ziifonium compounds 
do so.® 


• Dkiection and Estimation of Zirconium. 

•384 Tne jrcactiyns of the zirconium salts are ^very similar to 
those of^the metals contained in cerite and gadolinite. A re- 
action of zirconium by which it is distinguished from the cerium 
metals is the formation of a basic potassium zirconium sulphate, 
insoluble in water and hydrochloric acid. This salt is'jbtained 
by adding a hot solution of potassium sulphate to a concentrated 
solution of a zirconium salt. This reaction also serves to 
4 ^parate zirconium from titanium, tantalum, and cglumbium. 
Another method of separating zirconium from the yietals of the 

^ Holuan, Compl. rend., 1803, 116, 1222; 1896, 122, 601. 

* Honigsebmid, Compt. rend., 1006, 148, 224* 

* fhm. Newe, 1810, 21, 73. 





m 


Ae titanium dkomj 

ceriifln and iro^i groups is to boil the solution witft sodium 
thiosulphat^ when sjrconium alone is precipitated as the thiosul- 
phate; this jn washing and heating leaves a residue of zirconia. 

Titanic acid.^nd thdria'are also precipitated together wit^ 
the zirconia l)y# sodium Jhiosulphate. In order to separate these, 
ammoniiii^ oxalate is added to the hydrochloric acid solution, 
when the thoria .is throwii down. Ami^onium cjyrbonate is now 
added to the filtered liquid, when, in the presence gf Jihe oxalate^ 
only titanic acid is precipitated, the zirconia remaininj in solu- 
tion (Hermann). Zirconium can readily be separated from iron, 
fitanium, eite., by means of hydrogen peroxide; this precipitates 
it^quantitativety f#om solutions of the sulphate as the hydrated 
peroxide (Bailey). 

The spectrum of zirconium has oeen mapped by Tbalen, and 
contains characteristic lines in the red and blfle. 

Atomic W%i(jht of Zirconium.~~l\\Q first accurate dettfrmina- 
fcion'^f the atomic weight of zirconium wus that of Marignac,^ wjjo 
frdm the analysis of potassium zirconofluoride obtained the 
number 90-03. Hailey,^ from the weight of zirc^iia yielded by a 
known quantity of pure zirconium sulphate, found th^ number 
[KHli, whilst Venables,® who estimated th^ zirconia obtained by 
beating the oxychloride, ^rOClj, 31 IjO, found Jhe number 90-78.^ 
A more recent determination made by tlTe nephelometric m^hod 
^jm the ratio 4Ag : ZKI 4 gives the value 91-76.^ The ;itomic 
weight now (192‘4) adopted is 90-6. 

HAFNIUM. At. No. 72 . 

^ Thomsen in 1895 and Bury ® in 1921 suggested on* chemical 
grounds ^at the missing element immediately preceding 
talum in the periodic system should be a tetravalenl^ hdmologfte 
of zirconium. *Bohr has drawn the same conclusion from his 
theojy of atomic structure (p. 79). These views have now 
received considerable confirmation from the recently reported 
discoveir by Coster and Hevesy,® using the method of X-ray 
spectroswpy (p. 72), of a new element, of atomic number 72, 
in numerous zirconium minerals, in one of which it appears to 
be present to the extent of at least 1 per cent. “ It seems 

» Ann. Chim^Phyt., 1860. [3], 00, 267. 

•iProc. Bey. 5oc., 1890, 46, 74. • J. Amer. Chm. 8^., 1808, SO, 119. 

« VenablM and Bell, J. Amer. Chem. Soc., 1017, 30, 1598. 

• J. Amer. qhem. 8^., 1921, 48, 1602. 

• Nature, 1983, U8, 79. 



» THORIUM 


be very probable that ordinary zirconium contains at feast 
from OOl to 0*1 {>er cent, of the new element. E^cially the 
latter circumstanfe proves that th^ element 72 i» chemically 
homologous to zirconium. Experiments are in piogrjss to isolate 
tie new element and to determine its cliemical properties. For 
the new element we propoiie the name Hafnium (Hafnias = 
Copenhagen).”* 

^ The atomjc^weight of this element mayjbe expected to be in 
the neighbourhood of 178. 

This discovery throws doubt on th^ cWni of Urbain's rare|^ 
earth element, Coltiiim (p. 829), to the position ^ 2 , though 
Dauvillier^ has recently supported* this clfim by mean^ of 
Z-ray spectroscopy. 

THORIUM. Th=t 232*4. At. No. 90^ 

385 In the year 1815 Berzelius believed that ho had fourf® in, 
seteral Swedish minerals a new earth to which hd gave l^e 
name of thoria, ^jut on further examination the substance turned 
out to be basic phosphate of yttrium. On the other hand, in 
1828,2 h^discovered a, distinct earth in a mineral from the i^and 
of Lovon, in Norway, now termed thorie, and to this the n^e 
%f thoria was giveh, as it agreed in many of it^jropcrtihs with 
the Substance previously so named. Besides being found in 
thorite,* this substance was discovered in other rare minerals ; 
thu^y Wohler in pyrochlor, by BergmSn and others in orangite, 
and by Karlen in monazite, a phosphate of cerium and 
lanthanum which contains 4-18 per cent, of thoria. Another 
source of thoria is the mineral euxinite from Arendal, in which 
this# earth was discovered by Mosander and Chydenius, and 
it^has also been found in Norwegian granite.® More recently 
it has been MiscoTfered in a mineral called thorianite occurring 
in Ceylonj which contains 70-80 per cent, of thoria, along with 
11-15 per cent. (UOg + UO 3 ), 2-3 per cent, of lead, and varying 
amounts of metals of the cerium and ytterbium group and SiOj 
and CaO.* It also contains helium, and when heated to^edness 
evolves 9 c.c. of this gas per 1 gram,® 

» Compt. rend., I9i% 174, 1347. 

^ Pogg. Ann., 1829, 16, 385. 

• Phipson, Chersf. News, 1896, 78, 145. 

* Dunstan, Nature, 1904, 00, 510; Uunstaa and Blake, Proc. Pay. Bof., 
1905,JV, [A}, 253; Punttan and Jones, Proc. Roy. 8oc., .V906, 77, [A], 646. 



m 


THE TITANIUM ftROUjI 


!rtie following table gives the coinposition of somi of these 
minerals.^ 

Thorite<<rom » • Monazite from 

I^vtin.,. • Thorianito. Ilmcngebirge. 


SiO, 


^ ThO^ 

78-8G 

T'A 

28-60 

ThO. 

68-91 

UO2 

^•03 

ThO, 

17-95 

uo, 

1-G4 

.UO3 

9-0'^ 

] 

SnO, 

2-10 


3-46 

CeOj 

CcA 

26-00 

MiijOj 

2-43 ^ 

‘ LagOg 

y 1-02 

La ^3 

•23-40 

CuO 

2-C2 , 


J 

MnO 

1-86 

MgO ' 

‘ 0-3G 

PbO 

2-59 

CaO 

1-68 

K ,0 

0»15, 


0-10 



Na, 0 * 

0-11 

CaO 

M3 


101-49 

PbO 

0-82 

Jle 

0-39 



SnOj 

0-01 


trace 



AIjO, 

eO-OG 

Insol. 

"‘1 0-20 



*11,0 ^ 

9-GG 

IINO3 




99-5J: 


U‘J-75 




Thorium occurs also in otlior minerals containing the metals 
of tj^c cerium group, as gadolinite and.orthite. In on^ of these 
mtherals Bahr believxuWhc luid found another ni*w metal, to 
which lie gavglihc name wasium, hutjie afterwards convinced 
himself that this substance is identical with thorium.^ * 
Doubts have been put forward as to the individuality of 
thorium, and ifaskervilfe,^ from experiments on the fracflonal 
distillation of the«chloridc in a current of chloBine, concludes 
that it contains two other elements to which he gives the 
^ names berzelium and carolinium. The work of otljer investi- 
gators, however, does not confirm this result, but points t# the 
uniform nature of thorium.* \ 

At the present time thorium compounds ate prefared on the 
majufacturing scale, as they form the chief constituent of the 
mantles employed for the Welsbach incandescent gas-burner; 
they aro put on the market chiefly in the form of crude thorium 
nitrato*which contains also the nitrates of zirconium and the 
cerite earths. Thorite is the most convenient raw material, 
but is not found in sufficient quantity, and the crude material 
mostly dhiployed is the Brazilian or American monazite said, 

^ See Sohilfing, Zeii. nngtxo, CKtm,t 1902, 15> 921, whei* a risumi of the 
analyses d! orangite and thorite is given. * Annalen, 1864, 182, 227. 

* BaakervUle, J. dimer. Chem. Soc., 1901, 83, 761; 1904, 26, 922;,JJer., 
1905, 88, 14^. See also Branner, Proc. Chem.^oc.t IMl, 17, 6J. 

^ Meyer and Gumprey, Ber., 1905, 88, 817 ; Ebeiiiard, ibid., 826. 



•thorium 861 



vhich has been formed by disintegration of the«rock contauiing 
he mineral monaSite. $ ; 

Although the jftocess adopted for*the preparatic^ on a large 
Male of thorium nitrate for the incandescent mafitlg industry is 
Kept secret, the following is a general •utline. yThe powdered 
monazite sand either from ‘Brazil or Carolina is moderately 
heated with toncentrai^d sulphuric ticid in cast-iron pans. 
^Vhen the r^f^tion is finished the partially solidified product is 
dissolved^n cold water. It is important that at this stage the 
solution be kept strongly acid, other\fiso l^ie phosphates of thj^ 
metals will be deposited. The undissoivcd residue* of quartz, 
ferrotitanium, zircon, magnetic oxide f)f iron, c^c., is separated by 
decantation. The solution is imw fractionally neutralised with 
magnesia. Owing to thorium phosphate being the least soluble 
of the phosphates, *the first fraction consists mainly of this. 

The trude phosphate is dissolved in concentrated T^iydrochjpric 
acjjd, oxalic acid added, when the thorium is precipitated ^ 
oxalate, togetlicr with small quantities of cerium and ytterbium 
metals. The w'dl washed precipitate is then treated with warm 
sodium ^arbonate solution. The thorium goes into solution 
with traces of yttetbifim metals, but the cerium renuyfiB 
^dissolved as tie double carbonafe. By j/reatme^t with 
alkali hydroxide the hydroxide is precipitated, of the oxalate is 
reprccipitated by means of hydrochloric acid. In order to 
remove traces of impurities the oxalatc^r hydroKide is converted 
into sulphate with sulphuric acid and the sulphate purified by 
being severaf times recrystallised, the 5 ilt Th(S04)2,8H20 
crystallising out. In order to prepare the nitrate this salt is 
boiled with ammonia, by which means the hydroxide is produced. 
Tfijs is well washed, and dissolved in nitric acid. Tim solution 
is^vaporatqji to (^ryncss, and heated on the water-bath until on 
ignition it is found to contain 48 to 49 per cent, of ThOj, 
representing the nitrate with practically 4H20.^ • 

Metallic tWium is obtained by heating potassium thorium 
chloride with sodium in an iron cylinder. Thus prejjared, it 
forms microscopic hexagonal tablets, having the colour of nickel, 
and giving a silver-white streak. It has also been prepared 
b^ the action of sodium vapour on the vapour of certaja volatile 
organic compoimds of thorium such as the acetylacetonate.* 

^ Boehm, i^nemigcnt inanstrtCt 3S9, -Noe. 17- U); Bieaeldorff, ibid.t 

I906r». 411. • 

* Sieiuen8 ftid -Habke, Gefman Patent, 133959, 1900. See also Moitsan 
and fidnigsohmid. Ann. CKim, Phui.. 1906. rsi 8. 182. 



862 


THE TITANIUM GROUP* 


According to von Bolton, ^ thorium melts at 146(J°, whilst 
Wartenberg^ gives ilTOO® as the melting point. At ordinary < 
temperature* the specific Jieat is 0*02787. H has a specific 
gravity of lJ*0*(Nil8on), and 11*32, but after heating and rolling 
12*16 (v. BoltOh), and Hikes fire when heated in the air, burning 
with a bright flame ; it dissolves ^ith difficulty in hydrochloric 
acid, and is not attaclftd by aqueoiS alkalis, •but is readily 
soluble in aqua regia ^ * with nitric acid it first dissolves rapidly, 
but soon becomes passive. At 450° thorium combines with 
^ghlorine, bromine, iodine,* and sulphur, with incandescence; at 
650° it combines witli hydrogen and nitrogen respectively to 
for/h the hydride ftml nitride. Thorium is slightly more electro- 
IKisitive than magnesium, it forms alloys with copper, aluminium, 
zirconium, tungsten, and nickel. In the case of nickel an inter- 
metallic compound, ThjjNi, has been Isolated. ^Thorium possesses 
* iha 4 )ropcrt/ of radioactivity, and this will be discussecf in the 
clj^pter oi^this subject. 

.COMPOUNDS OF THORIUM. 

Thorium Dioxide or Thoria, ThOj, is obtained from thorite 
or ora*gite by, heating* the powdered mineral with a slighj 
excess of sulphuric acid and a little water; the dried mgss Is 
^wwdered, heated to remove excess of sulphuric acid, and the 
residue carefiilly^dissolvwl in six to seven parts of ice-cold ^%iter. 
The solution is filtered from silica, and heated to the boiling 
point with ammonia. The precipitated hydroxides*are washed by 
decantation, dissolved in hydrochloric acid and precipitated with 
oxalic acid, the precipitate well washed by decantation, and 
ignited. •The thoria thus obtained still contains ceria, ytkria, 
and a little manganese. To obtain pure thqria tfip productf is 
again dissolved in sulphuric acid, the excess of sulphuric acid 
remfoved by careful heating, the powdered salt dissolved in ice- 
cold water, and the temperature of the solution allowed to rise 
gradually to 20°. A hydrated sulphate of thorium then separ- 
ates out as an insoluble precipitate, the other metals remaining 
in solution, and by repeating the process several times the 
thorium sulphate may be obtained perfectly pure. It is tbjn 
precipitately by ammonia and the hydroxide thus obtained 
ij^ited.^, * 

» Zc»<. Elektroehem., 1008, 14. 809. * Ibid.» 1909, 16, 33f 

* NUson, Ber., 1882, 15, 2619, 2537; 1883, 1#, 153. 

« KxllM uid Nihoa, fier., IS67> 80> 1066. 



ODMPOtikDS OF THORn?M 


8(9 

Pure thAria is a snow-white powder, which be ofitaiffed 
in tetragonal crystals, isomorphous with tjiose of^cassiterite 
and rutile, by heating the amorphous powder w'itji borax in 
aj>orcelain furnace. They possess a specific gravi^ of 10*2, 
and dissolve in sulphuric acid only on ^ng-continued boiling. 
As already mentioned, thoria forms the chief constituent of 
the Welsbach ii^andescen^ mantles, the«other and smaller con- 
stituents coijpi|ting of more basic oxides, that of ceriun 
being usually employed (see p. 815). * 

Meta-thorium Oxide is obtained by ignitij^g the oxalate, anc 
its peculiar deportment with volatile acids explaim? the fac 
that Bahr believed this to be the o^de of a» n^v metal. 
was considered to be ThaO^, bu^ has been found to liave the 
empirical formula ThOg, and, according to Wyrouboff anr 
Verneiiil,^ is a pol)1nerised form of thorium dioxide. If it bt 
treated with hydrochloric acid or nitric acid no apparent actijj^ 
tak^ place, but if the excess of jKjid be eva])orated on the water- 
batn, a browmsh, semi-transparent residue is left, and this 
dissolves in watcMo form a translucent, opalescent li([uid which 
appears milk-white in reflected light, and yields a precipitate 
with acids. Tliis is dife k) the fact that the oxide forms saljj 
with these acids wijhout loss of water, 8hd these are soh^ble in 
^ter but not in the acids, and are therefore precipitated again 
by addition of the acids to the solution. If the solution bq 
treaty with ammonia and the precijgtate dijed at 100®, a 
compound having the composition Th 407 ( 0 H) is obtained and 
this is insoluble in acids.^ • 

Thorium Peroxide, ThjjOy. — This unstable compound is pro- 
duced wheft hydrogen peroxide is added to the sulphate or 
acet^, and then excess of ammonia added.® It forms a 
gelatinous precipitate which on keeping slowly gives up 
oxygen, being converted into TliOg.^ * 

Thoriunf Hydride, Thn 4 , is obtained by heating thorium to a 
dull red heat ih hydrogen.® It is not acted upon by water, but 
dissolves in hydrochloric acid with evolution of hydrogen. * When 
heated in air, it decomposes with the evolution of hydrogen. At 
390® it has a dissociation pressure of one atmosphere. 

rend., 1S98, 127. 863; Zeit. anory. Chem., 1901, 28, Ann. 
Ckim. Phya., 1905, [8], 6, 441. 8oe also Bteveus, anora. Chem., 1901, 
27. 41. ^ 

* Cleve, BuU. sJ. chim., 1874, 21, 115. 

* W^uboff and Vemeuil, Ann. Chim. Phy$., 1906, [8], 

* Piwar^wikL Zfi/. angew. C1^., 1902, 81, 359. 

* Ma^ignon and Bel^pine, Convpt. rend., 1901, 182, 36. 

VOL. n. ^TT-l 



^HE TITANIUM tfROUl? 


8fi4 

Jsy Salts 0/9 Thorium.— The salts of thorium are •colourless, 
and when joluble jpsseas a strongly astringeift taste. • 

Thorium ^Fluoride^ Thp4, is obtained by the addition of 
hydrofluoric acid or a fluoride to a solution of a thorium salt as 
a gelatinous precipitate which passes into a heavy white powder, 
ThF4,8Hj^O, which loses 4 molecules of water in a vacuum and 
produces ThF4,4H20. «At 110® in afcurrent ^ hydrogen the' 
hydrate, ThF4,2H20, is formed, whilst at 250® the^ whole of the 
hydrates yield the*basic fluoride, Th(0H)F3,Ii20. •The oxy- 
fluoride, ThOF2, is farmed when ThF4,4H20 is heated at 800° in 
a current (R hydrogen fluoride, or by igniting thorium silicofluoride 
Ui% current cR hydrogen, • The same powder is produced by the 
action of liydrofluoric acid on tj^oria. The anhydrous product is 
obtained by leading hydrogen fluoride over anhydrous thorium 
chloride or bromide heated to 350-400°.^ • 

^otassiuih Thorojluoride^ K2ThF4,4H20, is obtained by boiling 
the hydr<jxide with potassium fluoride and hydrofluoric acid^ in 
tlie form of a heavy, black powder. When a solution of the 
chloride is precipitated with acid potassium €uoride the com- 
pound K2ThF4,4ThF4,H20 is thrown down. Other double 
fluorides with potassium fluoride are Imotvn, but as they are all 
insolu]^le in water and Hydrofluoric acid, it i§ \mcertain whether 
they are defiitite compounds or mixtufts.2 • 

( Thorium Chloride, ThCl4. — This is obtained by heating the 
oxide mixed wiih carbqfi in a current of chlorine, by hea^ng a 
mixture of the dioxide and phosphorus pentachloride in an 
evacuated tube, by heating the dioxide at a red hCat in a current 
of carbon monoxide and chlorine, vapour of carbon tetrachloride, 
chlorine and sulphur monochloride, or phosgene. ’It has the 
specific , gravity 4*59, melts at 820° (Moissan and Martinfgn),® 
and sublimes in white, shining tablets, its vapour density being 
12*42, corresponding to the above formula. It deliquesces on 
exposure to the air, and its solution may be obtained by dissolving 
the hydroxide in hydrochloric acid. The anhydrous chloride 
combines readily with ammonia to form a series of compounds 
with 4, 6, 7, 12, and 18 molecides of ammonia. These compounds 
are all formed by the direct action of either gaseous or liquid 
ammonia on the anhydrous chloride and on keeping lose ammonia 
and form the compound ThCl4,4NH3. Tliis latter compouncf is 
stable up to 120°, at 250° it is converted into ihe tetra-amide, 

^ Chauvonet, Con^pt rend., 1908, 146, 489. 

* Roaenhe*im, Saniter, and Davidsohn, Zeit.gnorg. Chem., 1903, 81^424. 

» Cempti rend., 1905, 140, 1510. * 



COMPOU:!n)S OF THORnftf 


885 


*Th(NHj4,*and at a red heat into the di-imide,^ yh(NH)j. fhe 
jstrongly concentrated solution solidifies to a, fibrous^ crystalline 
mass which on heating emits hydrogen chloride^ It forms 
hydrates with 2 , 4 , 7 , 8 , and 9 molecules of water, whilst a number 
of oxy- and hydroxy-chlorides have beei| described.* It forms 
with the chlorides of the alkali metals easily soluble double salts, 
as KCI,2ThCl4.1^HjO. 

Thorium forms a bromide and an iodide which are similar in 
flteir behat^iour to the chloride. * 

Thoriutn SulphidCy ThSj.— The metaUbur|is in sulphur vapour 
with great brilliancy, forming a yellow powder which*exhibits a 
metallic lustre under the burnisher, ai|d has pr^btdbly the abavp 
composition (Berzelius). It hasjDcen prepared pure 1 ^ passing 
dried hydrogen sulphide over thorium sulphate at a low red 
heat. It is a yellow powder which inflames spontaneously in 
the aiib® When carbon disulphide va})our is passed o^c 
thorium dioxide heated to redness k yields the ox^sulphi^f 
ThT)S, as a light brown substance.^ • 

Thorium Solphitte, Th(S04)2, obtained by di 8 .s«lving the oxide 
in hot concentrated sulphuric acid, or by rubbing up powdered 
thorite or orangito to paste with sulphuric acid, and heatiijg 
the mixture to until all the exoiss of sulphuric acid is 
(friven off. The mass m then treated with cold water and 
boiIe(f; a crystalline precipitate remaias, and this may bg^ 
purified by repeated solution in cold waiter an^ reprecipitation 
by boiling. If the solution be alloivcd to evaporate at the 
ordinary temperature, transparent mono(?linic crystals of 
Th(S04)2,9H20 are deposited, whereas above 43 ° a hydrate 
with 4H2O4S formed. Other hydrates with 2 , 6 , and 8 molecules 
of ^ter are known.® Thorium sulphate forms double ^Its with 
the, sulphates of the alkali metals; Th(S04)2,2K2S04,2Il20 
crystallises in regular prisms, which arc easily sdluble in water 
but do nof dissolve in a solution of potassium sulphate. Thorium 
sulphate fornfe a number of basic sulphates, and combines with 
pyridine, quinoline, phenylhydrazine, and diethylamine^to form 
well crystallised derivatives. 

* Chaurenet, Compt. rend.f 1910, 151, 387; Ann. Chim. 1911, [8], 

28 ^ 275 . , 

^Hnaenhelm and Schilling, Ber., 1900, 88, 977; Rosenheim, Samter, and 
Davidsolin, Zeii. oti^org. Chem., 1903, 85, 424; Knisa, ibid., 1897, ^4r 301. • 

* Hauser, Zeil. anorg. Chem., 1907, 58, 74. Compare also DuhoOi, CompL 
rend.,J908, 140, 815. 

* Krttip, Zei^ anorg. Chem., 5894, 6, 49. 

' R^ozeboom, Zeil. pkyeikal. Chem., 1890, 5, 198. 



)66 


te® TITANItJM feoUP 


0 ■ 

Thorium und^ Nitrogen , — A nitride, Th3N4, is form^ ^ when 

metallic thjriiim isj heated in a current of rftrogen, and when# 
the carbide^ is heated in ^ammonia or the di-imide in either 
ammonia or nitrogen,^ whilst a nitride of the same composition 
is obtained Tjytfeducingithc dioxide with magnesium or aluminium 
in an atiT\opshere of nitrogen.® The latter compound, however, 
differs from the former in that it is noh decomposed by water. 

Thorium Nitrate, Th(N03)4,12H20, is 
tallising in large, deriquescent tablets. 

^ obtained crystallising with 611 jO and and many double 

salts with bthcr nitrates are known.® Complex compoimds with 
tyitipyrine, p)1-idine, quinqlinc, and diethylamine have also been 
prepared. •* , 

The phosphate is insoluble both in water and phosphoric acid. 

Thorium Borides, ThB4 and ThB^, liave'been prepared by 
k., heating thotiurn dioxide with amorphous boron in the#electric 
•furhiace.* 

^Thorium Carbide, ThCj, is prepared by heatiifg thoria w*th 
sugar charcoal in the electric furnace, and forms# crystalline mass 
which is only slightly affected by concentrated acids but readily 
dissolves in dilute acids and is decomposed by water with evolu- 
tion of a mixture of rnetlnane, ethylene, acetylene, and hydrogen.’^ 

Thorium Sijicule, ThSij, is obtained^liy heating a mixture eft 
the double fluoride of potassium and thorium, potassium silico- 
fluoride, and powdered ^uminiurn at 12(Kr, or by heating silicon 
with thoria in the electric furnace.” It forms tetragonal ^ates 
of specific gravity 7‘96. • 

Thorium Carbonates. — No normal metacarbonate, Th{C03)2, of 
thorium has been obtained, but the ortho-carbonate,^T\\CO^, is 
known. This compound is obtained by treating thofium 
hydroxide with carbon dioxide under a pressure of 30-40 atngo- 
spheres. At ordinary pressures a basic carbdhate, th(0H)|C03, 
is qbtained. When ammonium carbonate solution is*added to 
solutions of thorium salts precipitates of basic cArbonates are 

^ Mat^hon and DeU^piiie, Comfl, rend., 1901, 132, 30. 

* Ohauvonot, Ann. (/him. Phyn., 1011, [8j, 23, 420. 

* Kuhlsohfitter, Annalen, 1901,317, 158. Compare Matignon and Del4pine, 
Ann. Chim. Phyn., 1907, fSJ. 10, 130. 

* Fuhspc^etV. angew. Chem., 1897, 4, 115. 

* Meyer and Jacoby, Zeit. ancy. Chem., 1901, 27, 359. 

^ Binet dii dassonneix, Compt. rend., 1905, 141, 191. a 

’ Moi^aAn, Cempt. rend., 1890, 122, 573: see also Moissan and l^^tard, Ann. 
Chim. Phya., 1897, [H 12, 427. 

■ Honigaofafbid, Compt. rend., 1906, 142, 280.c 


a very soluble salt crys- 
Nitratesliav^also been 



867 


DBTBCfnON AND ^ESTIMATION OP* THORIUM 

obtained.* These dissolve in excess of alkali carbonates lind 
•yield solutions from which crystalline double carbofates of the 
type 3 Na 2 C 03 Th(C 03 ) 2 , 12 H 20 may, be separated. Tliorium 
q^rbonate forms a double carbonate with thallium q^rbonate of 
the formula Th(C 03 ) 2 , 3 Th 2 C 03 . 

DETiicmoN Ajft) Estimation* OF Thorium. 

388 The Compounds of this metal gite no characteristic 
blowpipe or flame reaction. The ^Ikalis and ammonium 
sulphide precipitate from its solutions the hydroxide insoluble 
in excess, and the carbonates give rise to ^ piecipitate qf a 
basic carbonate, which dissolves in an excess of the reagent. 
Ammonia produces no precipitate in this solution as it does in 
the corresponding -one containing zirconium. Another charac- 
teristic, property of thorium is its reaction with ptd^assium sul^ 
phate, and especially the fact that the thiosulphate is thrown dif^ 
frdln thorium* solutions on addition of potassium thfl>sulpha 1 fc, 
a reaction by whjph this metal may be .sei)arate(lJrom the metals 
of the cerium group. In order to separate it from titanium, 
columbiuhi, and tantaluQi, ammonium oxalate is added to the 
solution, when the thorium alone is piecipitated ; if, however. 
In excess of ammonium* oxalate be used the flyrium bxalate 
dissofves. Thorium can be separated from zirconium by throwing 
down both metals as oxalates by ammonium oxalate, and then 
addAg an excess of o.xalic acid, when the zirconium oxalate 
dissolves completely, leaving behind the oaalate of thorium. 
Thorium is estimated as the oxide, obtained by igniting the 
precipitated hydroxide. 

Atomic Weight of thorium was determined b^ several 
chemists without concordant results. Thus Berzelius^ found 
235*5, and Delafohtaine ^ 229*7 as the mean of several well- 
agreeing analyses of the sulphate. Cleve, by the same method, 
obtained thrf number 232*6, whilst analyses of the oxalate 
yielded him the number 232*2. On the other hand, Kriiss 
and Nilson, by analysing the carefully purified sulphate, Obtained 
as a mean of several consistent experiments,® the number 232*4 , 
which is now (1922) adopted. 

• • 

‘ Pogg, Ann., 1829, 16 , 385. * Arch, Sd, phys. not., 18 , 343. 

• Ber.f 1887, 2(C 1665. Compare Meyer and Cumporz, Per., ]905|88, 81f. 



IHE GffiRMANIUM GROUP. 


GERMANIHJM. Gc = 7 /s. At. N^. 32. 

389 This element* was discovered in 1886 by Winkler in the 
course of an investigation of a new silver mineral found at 
** Freiberg hi 1885, and termed argyroditc, OeS2,4Ag2S. The 
preliminary fiiv^tigation, led him to suppose that the new 
element would occupy the vacant place between antimony and 
bismuth in the periodic classification,^ but further examination 
showed that the new element was tetravftlent, and identical 
fc^jvith the ekasilicon predicted by Mendcl6ev. The close agreement 
« DetWeen the predicted properties of the element and its compounds 
rfhd those actually observed by Winkler, has' already been 
mentioned (p. 70). » 

Cermanium is an extremely rare element : argyroditc and 
janfieldite,- a mineral of similar composition from Bolivia, 
contain 6 7 per cent.tKif the metal, but these are both rare. 
Traces of gernianium have been found in several minerals, par- 
^ticularly in zinc blendes, the richest source of the element now 
known being retort resi(|ue8 from the smelting of zinc from certain 
localities. It is separated by a process depending on the volatility 
of the tetrachloride ; 100 grams of the impure zine oxide are dis- 
solved in 2(X) c.c. of concentrated hydrochloric acid. On distillation 
in the presence of chlorine,tor some other oxidising trgent which 
prevents^ arsenic from volatilising, the distillate which jJ^ses 
over between 121'^ and contains all the germanium.® • 
Metallic getmanium is best obtained by the ‘reduction of 
germanium dioxide with carbon at a full red heat. •The semi- 
crystalline regulus is washed with water to remo\^ carbon, and 
fused with a little borax. It is thus obtained as a greyish- 
white, ^ brittle, lustrous metal, which frequently crystallises in 
octahedra,* has a specific gravity of 5-469, melts about 960°, and 
is not markedly volatile at 1350°. It oxidises at a high tempera- 
ture, is ^insoluble in hydrochloric acid, but dissolves in a^ua 

J?er., J886, 19, 210. • Ponfield, Arner. J. Sci., 1893, [3], 46, 107. ' 

* Buchanan, J. Ind. Eng. Chem., 1917, 9, 661. See also Dennis and Papish, 

J. Atner. Ch^ 1921, 43, 2131. o 

* See Kolkmeijer, Proc. K, Akad. Weknsch. Amsterdam, 1922, 96, i26. 

868 



COBIPOUSjDS of QERMAltIUM 


regia, and is converted by nitric acid into tl^e dioidder/It 
•combines directly frith the halogens. 

COMPOUNDS OF GERMANIUhP. 

390 Germanium forms two oxides, gei^anium jlicftcide, GeOj, 
and germanium monoxide, GeO. 

Gerrmnium Ij^ioxide^ (JcOg, the most important of these, is 
obtained from argyrodite as follows: the powdered mineral, 
mixed witJh nitre and potassium carbonate, ts introduced in small 
quantities at a time into a red-hot Hcsijjan crucible. On cooling, 
two layers are obtained ; the upper one, which contains all thd' 
germanium, is powdered, extracted ^ with Wjjtei^ the solution 
treated with sulphuric acid, and evaporated to dryness.* The acid 
residue dissolves in cold water, but almost all the germanium is 
deposited as oxide \)n standing; the remainder is precipitated as 
sulphide and converted into oxide by heating wdth nitric aci^ 
To purify the crude oxide, it is dissolved in hydrofluoric acid, 
potassium fluoride added ; potassium fluogermanate* separates 
out, and is con^'crted into a soluble thio-salt«by fusion with 
potassium carbonate and sulphur, this being decomposed by 
sulphuric acid, and tlie germanium precipitated as sulphide with 
^sulphuretted hydrogen. The sulphidt, mixed with a litfie 
sulphuric acid and heated, yields a mixture 5 ^ Bolphide and 
oxide, W'hich is converted into the pure oxide by roasting and 
treating w'ith nitric acid. Thus prepare^, it forms a dense, while 
powder, somewhat soluble in water, 1 part of the dioxide dis- 
solving in 24>1 parts of water at 20’’'’, and ii»95*3 parts at 100°; 
the solution on evaporation deposits microscopic rhombic crystals, 
^ermaniufn dioxide has acid properties, but also dissolves in acids 
it readily reduced by carbon, sodium, and magnesium. 

No germanium hydroxide of definite composition^has been 
prepared, but a colloidal hydrate is obtained by decomposing 
an alkalitie solution of the dioxide with carbon dioxide. 

GennanouS Oxide, GeO, is obtained by heating the dioxide 
with a small quantity of magnesium, or by heating the hydroxide ; 
it forms a greyish-black powder. The corresponding Itydroxide 
Ge( 0 H) 2 , obtained as a yellow or yellowish-red precipitate 
by the action of alkalis on germanium dichloride or germanium 
clloroform, and is soluble in excess of the alkali. Hantzsch ^ 
has shown that when this excess is neutralised •with hydro- 
chloric acid, some germanous hydroxide remains in* solution. 

* ZtH. ytorg, Cketn., 1902, 30, 289? 




870 


#HE GERMANIUiI group 


F^m the conductivity of this solution and also of ttie alkaline 
solution, and from jneasurements of the rate tft which the alkaline 
solution saponifies ethyl acetate, he concludes that germanous 
hydroxide m aqueous solution is a weak monobasic acid of the 
same type*as^ formic %cid, and has the constitution HGeO’Oft, 
whilst in alkaline solution the salt IlGeO ONa is present. In 
aqueous solution part o^the hydroxid^is also prgsent in the form 
Ge(OH),. * 

(tcmanium Hydrftle, GeH 4 , is formed when the tdlrachloride 
is rediiciul with sodiym %malgam. The hydrogen evolved burns 
'•with a blufch-red flame which dejiosits a mirror on a cold porcelain 
surface. A -mirror may a )80 be obtained in the same way as in 
iJlarsh’s wseiiic test, and on heating in air is converted into the 
white dioxide. The liydrogen evolv’ed as above gives a black 
precipitate with silver nitratt;, and this on treatment with nitric 
^ci(l gives germanium dioxide.^ • 

• i^erwmuutn Tetmjluoride, GeF 4 , prepared^ in 

the auhytTrous state', but large crystals containing fliree molecules 
of water are obtained by concentrating a solution of the dioxide 
in hydrofluoric acid. It combines with hydrofluoric acid to 
Jhiogenuauiv acid, w'hich has not«b(Mi prepared pure ; its 
]K)ta.ssiv)n salt, K^GeF^,, prepared by adding potassium fluoride 
to a sofution 9 ft lie dioxide in hydrofliKtric acid, and forms hexa- 
j^onal crystals, isomorplious with those of ammonium silicofluoride 
which are sparingly soluble in cold, but readily in hot w'ater^ 

(temamam TetrachUmde, GeCl 4 , is obtained by the direct 
union of germaniui^ and chlorine, hut is best j)repifred by heating 
the metal or the sulphide with mercuric chloride; it is a thin, 
colourless liquid, which fumes in the air, has a specific gravity 
of 1*887 at 18\ and boils- at 8(r5‘ It is slowly decomposed, by 
water with formation of hydrated germanium dioxide. • 

Germanium GIdoroform, GellCl,. - When germanium is heated 
in a current of hydrogen chloride it becomes red hSt, and a 
distillate is obtained which, after exposure to the air, separates 
into two layers. The heavier of these consists of germanium 
chlorof(9l:m, which is a colourless, fuming liquid, boiling at 76°. 
The lighter layer is germamum oxychloride, GeOClg, which is 
also a colourless liquid, but is less mobile than germanium 

* Vwg«len,.Zfit. anorg. Chern,, 1902, 4», 326. See also Pan|th, Matthiea, and 
8cM.nidt-Hfbbel, Her., 1922,65, [fi], 775, 2616; Mailer and Smith, J. Amer, 
Chrm. Soc., 1922, 44.^ 1909; Schenck, /?fc. trai\ rhim., 1922, 41, 669. 

* Dennis aivl Hance, J. Amer, Chem, Soc.» 19g2, 44. 299. ' 


DETECTION and” ESTIMATION 0# GERMANIUM fU 

cUorofoAn, does not fume in the air, and boils conside^bh 
above 100'’. Gerfimnmn dichloride, BeClj, js also lyowi]^; it ii 
a colourless, funikig liquid. ^ ^ 

Germanium Dmilphide, GeS 2 . — This compound, which is th( 
most characteristic of the germanium derivatives, is preparec 
by the action of sulphuretted hydrogen on a solution of ger- 
manium dioxide, or bydhe addition of an excess of a mineral 
^acid to a solp^ion of an alkali thiogermanate, sulphuretted hydro- 
gen bein^ passed through the solution to complete the precipita- 
tion. It is a white powder, only wettad with difiiculty by water. 
It is appreciably soluble, 1 part dissolving in 221*9 jfarts of col5 
water; it also readily dissolves in ammoniiim Sulphide. ^The 
thiogermanates are obtained fusing germanium ^derivatives 
with an alkali carbonate and sulphur.^ 

Germanium Moriosulphidey (leS, is obtained by carefully heating 
the disulphide In a current of hydrogen, and fornft thin plj^^ 
having a greyish-black colour and an almost mot-^lic lustre.* 
ite reduction easily proceeds further, with formation of metallic 
germanium. \V<4ien dissohed in alkalis and itpredpitated by 
acid, it forms brown flakes soluble in hot concentrated hydro- 
chloric acid with evohiti#n of hydrogen sulphide.^ 

• Detection anp Estimation ok (lERAfy^iUM. ^ 

391 Germanium salts impart no colour to the Bunsen dany*^ 
but the spark spectrum exhibits a numb<j|* of bri^t lines, especiall)^ 
in tSe blue and violet regions, the following among othem having 
been measured : 602J, 5893, 5131, 1814, j71«, 4685, 4261, 4179. 
It is most readily recognised by the precipitation in strongly 
acid solution of a white 8uli)hide, which is readily soluble in* 
alljtlis or ammonium sulphide, and slightly soluble ^n water ; 
this compound is also the most suitable yet known for its gravi- 
metric estimation.* When an aqueous solution *of hydrofluoric 
acid cont!liining any germanium compound is saturated with solid 
potassium cBloride, a grey, gelatinous precipitate of potassium 
fluogermanate is formed. 

Atomic Weigh of Germanium . — By the analysis of pure ger- 
manium chloride, Winkler, in 1886, found the atomic weight to 
be 72*5. More recently, Muller, by conversion of potassium 
flflogermanate to potassium chloride, has obtained the number 
72-42.* 

1 J. pr. r^m., 1880, [2], 34, 182; 1887, 12], 36, 177. 

4 Ber„ 1888, 21, 131. « J. Amer. Chtm. 1921,^, 1085. 



Tife GERMANIUM GROUP 


TIN (Sta%inum). Sn=ii57. At. No. 50 . 

392 This metal was known in early times. It is very imcer- 
;ain whethA the word* ‘ bedil ” in the Old Testament, which ft 
translated by the Greek word Kacairepo^y and by the Latin 
iannuMy was originally# used to designate tin.^ It is bkewise 
loubtful whether the metal which the Phoenicians are said to 
lave brought from fhe Cassiterides, the exact locality of which 
wras unknown to He|od(^us, was really tin. Possibly the Greek 
rtrord is coflnected with the Arabic “ kasdir,” which signifies tin. 
[J is, however* certain that at the beginning of our era the word 
ivas used Ho specify tin, for ^ny states that cassiteron and 
plmibuyn candidum are the same, and he adds that it is more 
expensive than 'plumbum nigrum (lead) ; he moreover states that 
ij^rves fomoldering the latter metal, and that it is obtained from 
the Cassiterides in the Atlantic Ocean. That the Cassiterides 
r&lly were the British Islands appears more than probable, lor 
after CjBsar’s conquest tin was carried from the Cornish mines 
through Gaul, by way of Marseilles to Italy ; ^ and Diodorus 
^culus mentions that the inhabitants earry the tin to*a certain 
island called Iktis, lyin^on the coast of Britain. “ During low 
water the int«rmediato space is left dty, and they then^carry 
pyer abundance of tin to this place in their carts,” There can 
be little doubt t^at the Jktis of Diodorus is St. Michael’s Mount, 
in Mount’s Bay, in Cornwall ; for up to the present day a cause- 
way exists, floodeif at high water, but dry at lo\f water, across 
which the inhabitants are in the habit of carrying goods to and 
from the mainland. The names by which Pliny de^gnates tin 
and lead^eom, however, to show that he did not consider fl^ese 
as distinct metals, but rather as varieties of one metal, andthe 
adds, “ Sequithr naturro plumbi cujus duo genera, nigrum atque 
candidum.” The word stannuin, which at a later peridd became 
the general designation for tin, also occurs in Pliny’s works, 
though it appears certain that by this word he did not signify tin, 
but railier any mixture of metals which contains lead. In the 
works of the Latin Geber the most important properties of tin 
are mentioned, such as the peculiar crackling sound which the 
metal emits when bent, as well as the fact that it forms brittle 
aljoys. Tih was termed Hermes by the early Gieek alchemists, 

but about A.D. 600 it received the name of ^us or Jupiter, and 

« 

^ Q. Smith, The Cassikrides, fLondon, 1863. ^ 



TIN 


873 


0 ' ' 4 (>^ ^ 

to it the sign Tf was given ; owing to the above-mentioned property 
' of forming brittle alloys it was, howeverf sometpnes termed 
diabolus metalloruh. , 

^ Tin has been found in small quantities in Siberia, jauiana, and 
Bolivia in the native state, together wiMi metallic gold, though 
the metallic tin from the last-named locality may, according to 
Forbes, possibly have Iften an artificial product. It has also 
Jbeen found in#mall tablets in bisniuthite f join Mexico. 

The chief ore of tin is cassiterite, or tinstone, a more or les 
pure form of the dioxide, SnOg, Lesf frequently it is found a 
tin pyrites, Cu4SnS4,(Fe,Zn)2SnS4, and occasionally as silicate 
It also occurs in small quantity in certain epidotes, as well iL 
columbites, tantalites, and oilier similar minerals. Various 
mineral waters contain traces of tin, and this metal has also been 
detected in certain meteoric masses. 

393 The Metallurgy of Tin } — Almost all comm*ercial tij^i^ 
obtained frorp tinstone, which is found in veins traversing the 
older crystalline and schistose rocks, and also as stream tin in 
water-worn nodbles amongst the detritus of 1 ;he same rocks. 
Tin ore is not, however, very widely distributed, only occurring 
in large quantities in a feV localities. The oldest and best known 
itin mines from which tin has continuously beqp obtai^Bd, pro- 
bably from the time of* the Phmnicians up to i^e present, are 
those of Cornwall. The ore there occurs in the granite and in 
the#metamorphic schistose rock, and m found»especially rich in 
the killas, a mctamorphic clay slate, and in the line of junction 
of this with granite. It is found in vciiLs or lodes, in beds or 
flats, and in ramifications of small veins or “ stock-werke,’* and 
th^e tin veins usually run in Cornwall in an easterly or westerly* 
direction. The following minerals are frequently found together 
With tinstone : wolfram, apatite, topaz, mica, tourmaline, arsenical 
pyrites, |tc. 

Tin min^ exist, though on a much smaller scale than in 
Cornwall, in other parts of Europe, as in Saxony, Bohemia, 
Russia, Sweden, France, and in the Spanish province dj Galicia. 
Very large deposits of tin ores are, however, found in other 
quarters of the globe. The princijial producers of tin ore are, at 
^jie present time, the Malay Peninsula, Bolivia, Dutch 
Islands of Banca and Billiton, Australia and Tasmania, Yunnan 
in China, anfl Nigeria. All these produce more tin, ore than 

'49ee also Metallurgy of Tin. Heniy Louis. McGraW-HUl Company, 
1911 . • 



S7.4 


T&E GERMANIUM OBOCP 

, — ■ J 

Coniwall. Tin* has also been found in Mexico, South Africa, 
Japan, Siaip and Surma. * 

Tin ores uay be smelted in shaft furnaces dir in reverberatory 
•urnaces, bijt as the ores obtained are generally very poor, co%- 
;aining only from 1 to € per cent, of tin, preliminary operations 
)f dressing or concentration are always necessary, and as con- 
liderable losses are expefienced in thesi operatioas, much atten- 
;ion is being given to the direct treatment of tin-b^iin^ material, 
vnd many suggestions have been put forward. These, however, 
ire not in a sufficiently acK'anced state to be considered in detail. 

The process adopted in Cornwall for the reduction of the metal 
Si if simple one* f'he ore, after being stamped, is washed to free 
t as much*as possible from gangi*, and is then roasted in calcining 
furnaces for the purpose of driving off the sulphur and arsenic 
3ontaiiie{l in the arsenical and ordinary pyrites, if these be present. 
sjKic vapoRrs from these revolving calcining furnaces are led 
nto chanj[)ers in which the arsenious oxide condenses. Tie 
jonstruction of an Oxland and Hocking's revolving calciner 
iS shown in Fi/{. 183. This consists of a lorfj^ cylinder lined 
ivith firebrick and [)lac(;d in an inclined position. Thj fire (h) 
^placed at the lower end (a), whilst the upj>er end is in con- 
lection^with chambers iff which the arsenioug oxide condenses.^ 
The ore is dri«d on the top of these clihmbers, which are piade 
iron plate, and then brought by means of the hopper (h) into 
the cylinder, th^ roastej ore falling down into the space^(F). 
This then undergoes a second washing in order to remove the 
ferric oxide and otlftr oxidised materials, and if copf er or bismuth 
3e present, is treated with dilute sulphuric or hydrochloric acid 
for its removal. After these operations the roasted ofe is found 
DO contaiii from 60 to 70 per cent, of tin. It sometimes happens 
ohat the tin ore is mixed with more or less wolfram, (Pe,Mn)WG 4 , 
and as this mineral possesses a high specific gravity it cannot 
be removed from the tin ore by washing. In order to remove 
this impurity, the presence of which in the smelting operations 
would ^fove injurious to the quality of the tin obtained, the 
ore is passed through some form of magnetic separator which 
extracts the wolfram and allows the tinstone to pass on. The 
prepared tin ore, or fm, is then mixed with one-fifth part 
its weight of anthracite and the mixture sprinkled with some water 
in aider to prevent the finely divided ore from b^ng blown by 
the drau^t into t jie flues. The construction of the reverberatory 
furnace is shown in Figs. 184 and 185 : ^be charge is^introluced 




Fio. 183. 



Fia. 185. 

expiration of six hours the reduced metal is tapped and allo\|^ed 
to run fronj the lower part of the hearth through the hole (f) into 
ttfb ve»wl (o). The impure tin thus obtained iS then cast into 
moulds, and these are refined by the process of liquation, ^This 
is effected *by placing the ingots in another similar i;pverberatory 


TIN 


877 


furnace v^ich is gradually heated, so that the ^e, more easily 
» fusible tin first mflts and runs into a cast-inon vess^ (h) placed 
below, whilst the less fusible alloy o( tin with iron^nd arsenic 
remains on the hearth. A fire is placed under the vessel (ii) in 
order to keep the metal liquid, and thists then stirred up with 
a pole of green dense wood. The length of this operation depends 
upon the qjialitg of the m^l which it is di‘8ired to obtain, and may 
[ast from on^t^ several hours. The dross which separates during 
the process of refining, and the “ hard-head,” or residue which 
remains on the hearth, both of whicb contain large (jjiantities^ 
of tin, are afterwards worked up. In order to prepare grain /in, 
the tin is heated until the metal becomes brittfe ahd crystalline; 
it is then broken up by a hammer, or allowed to fhll from a 
considerable height. 

The slags formed during the smelting operations generally 
contain sufficient tin to be worth extraction. This thi may 
as^iwills of metal or in chemical combination. Thg metal^* 
portion is often separated by crushing and wa.Hhing, or by allowing 
the slag to standnn a molten condition for some hours, when the 
metallic tin settles to the bottom. Slags containing tin in the 
combine(f condition are re-smclted with dross and other residues 
and strong bases high temperatures fh shaft oj: reverb^eratory 
furnaces. * • 

394 Separation of Tin from Tin Scrap, dc . — Tin is separate^ 
fron^tin scrap and tin can waste by in^ans of ilry chlorine gas. 
The tin waste is washed in an alkaline bath to remove grease, 
rinsed in watA, then heated in a furnace to Remove solder, and 
then treated in iron cylinders with chlorine, the cylinders being 
kept cool.^ The tin chloride thus formed is put on the market, 
and*the steel scrap, which contains less than 0-1 percent, tin, 
is «hydraulic(^Uy pressed into briquettes, and smelted in open- 
hearth furnaces. 

The electrolytic process formerly used, in which sodium hydrate 
was the electrolyte, proved expensive, as it required highly paid 
labour, expensive electric current, and gave as a prodiljt a tin 
mud of inferior quality, which required further smelting treatment 
bo convert it into marketable tin. 

The total amount of tin produced in 1919 was about 113,893 
tons.* 

395 Properiks and Uses of Tin.—Tm is a whife, ^brigh*ly 

* 0»t. Zeit.f. Berg. u. Hutt-We^en, 1909 , > 671 103 . 

^ Mineral Jndu^ry, 1919 , 88 , 605 . 




87 ^ 


GERMANfOM GROUP 


lustrous metal,# whicll melts at 232° (Heycock and* Neville), 
boils under ^tmosplieric pressure at about 2?70° (Greenwood),^ • 
and has a ^(pecific gravity, at 13° of 7-293 (Matthiessen). Its 
specific heat^is 0-05363 at 0°, 0-05549 at 54°, and 0-05690 at 97*6° 
(Griffiths).* Its atomic^ieat is therefore 6-37 — 6*76. Its average 
compressibility between 100 and 500 megabars is 0-000,001,7 
(Richards and Btull).® it is harder tian lead, J)ut fjpfter than • 
gold. It exhibits a fibrous fracture, and when^l^nt emits 
peculiar crackling sound caused by the friction of the Jrystalline 
^particles. Tin can b<j easily rolled or hammered out to foil, and 
at a temperature of UKf it may be drawn into wire, which, how- 
eyrt-, pos8es8es*biit slight tenacity; at 20(r it becomes so brittle 
that it niffy be powdered. A ^mple of Ranca tin which was 
exposed at St. Petfusburg to a very low temperature during the 
winter of 1867 8 , fell to granular, crystalline pieces or to a coarse 
^Hii^der. This alteration is due to the fact that tin, like sulphur, 
*exjats in i^ore than one form, dependent upon the temperature, 
the stable form below 18 ' being the grey powder or “ grey tin.’’ 
At ordinary teiflperatures common white tin iff in a metastable 
condition, but the change to the stable grey tin takes place with, 
oiftreme slowness. The rate of change niay, however, be acceler- 
ated by lowering the toihperature, the maxinpim velocity bein^ 
reached at — This alteration w'as*known to Aristotle^ who 
#<peaks of tin as “ melting ” when kept at low temperatures.* 
Between 18 " ancUlur tl\# stable form of tin is tetragonal, wjiilst 
above this temiforature it is rhombic.’'* If zinc be brought into 
a solution of tin clfloride the nu^tal separates out 7n the form of 
fine crystalline dendrites, and this deposit, known as the tin-tree 
(Arbor Jovis), was first prepared by Ilsemann in 1786 . When 
tin is mtjted and then allowed partially to solidify, the li^yid 
portion being |)oured olf, needle-shaped prismatic^ or tabukr 
crystals of the metal remain behind. Another mode of obtaining 
crystalline tin is to decompose tin chloride by a wealc electric 
current, when the metal is deposited in tetragonal prisms and 
pyrami^l^. Fine crystals of tin can also be obtained when water 

» PrtK. Hoy, Soc„ 1900, 82, [^1. 390, 

■ Ibid,, 1913,88,1.1]. WO- 

* Hub, a»rn. /iwl., 78, 1907. , 

* Cuhen and van Kyk, Ze.it. jihysikaL Chern,, 1899, 30, fiOl ; Hasslinger, 
MmMUth., look, 29 , 787; Cohen, Ziit, phyaikal Chem., 190f>, 68, 625; 1909, 
88,214. * 

* Findlay, The Pfutfie Hide, p. 39 (Longmans); Cohen and Goldsohmidt^v^etl. 
oiiory. CAem.,\904, 60, 225; J&nccko, Zeii. jdiyHkal Chem., 1915, 90, 913. 



TIN 


containing* zinc dust in suspension is gradually adM to a solution 
tin chloride. * • ^ 

Metallic tin remdins bright in dry 05 moist air at tie ordinary 
^mperature, but when melted it gradually oxidises^ forming a 
grejdsh- white skin on the surface, which* consists of a mixture 
of tin and stannous oxide and is gradually oxidised to the dioxide. 
It is dissolved Jby dilute^ and more rapidly by concentrated 
l^ydroc^ric #qjd, with evolution of hydrogen and formation of 
stannous cliloride ; it dissolves also in aqua regia and in hoi 
concentrated sulphuric acid, and is eonwrted by somewhal 
diluted nitric acid into metastannic acid. It dissolves also ir 
aqueous solutions of the alkalis, with formation of salts •oi 
metastannic acid and evolution of hydrogen. 

Tin is used for a large nimibcr of purposes, for the prepara- 
tion of vessels for household and technical use, for the manufac- 
ture of tinfoil, for tinning copper and iron, and es{)ecially foM 
preparing the ^alloys of tin. Tinned copper vessels jji^ere em- 
ployed by the ancients, for we find them described by Pliny; 
and ^he same author also mentions as a well-knotvn fact that in 
the process of tinning, the weight of copper articles increases 
but slightly, and he add5 that the substance termed stannurw 
^ employed for thia purpose. ^ ^ , 

Copper- and brass-ware* can readily be tinned by dipping the 
vessel into the molten metal. In order to cover the interior of 
a vesifel with a coating of tin, it is heated and aome molten tin 
poured in, which is then well divided over the surface by rubbing 
with rags. In* order to prevent the oxidatidli of the metal, a 
small quantity of resin or sal-ammoniac is added. Agricola 
was the firsl to mention the process of tinning iron. It appears, 
however, that at that time it was only slightly employwi. The 
prdbess is usually supposed to have been discovered in Bohemia 
in 1620, coming into use in England and France about 100 
years later. In the modern process of preparing the common 
tin plate, an important industry in South Wales, mild steel plates, 
after being annealed, rolled and “ pickled ” in weak acid solutions, 
are dipped in a bath of molten tin. On the surface of this is a 
layer of zinc chloride which acts as a flux, and the plates have 
to fass through this before they reach the tin. In the b|th they 
pa^ under a partition and emerge through a layer of hot grease, 
which floats oH the surface of the tin and is separate frota 
the flux by the partition. The plates pass b^ween rollers to 
remove^he efceas of ^in, and are ^en polished. 

VOL. n. (ir.) B 



THE GERMANIUM GROUP 


m 


Alloys of Tin. 

396 Sev^l of these alleys are largely employed m the arts. 
Tin and lead may be mixed in any proportion, and the alloys 
are harder and toughe*, but more readily fusible than either of 
the two metals. For this reason they are employed as solders. 
The following table give§ the composition of somg of tjfe different 
lead and tin alloys : 

. Common Pewter. Solder. 

Fine. Common. , Coarse. 

Tin ^ . 4 2 1 1 

lead , . 1 1 12 

In practice, a certain amount of antimony is often used to 

replace some of the tin in these alloys.^ 

^Ilronze is the name given to any alloy consisting chiefly of 
cejjper and tin, although other elements are frequently added to 
impart particular properties. 

The alloys corresponding in composition to tfic formula) SnCug 
and SnCu^ are definite chemical compounds, and are, the only 
l^nes ot the series which remain homogeneous after melting, a 
certain»amounfcof liquation taking place in all the others. Thp 
hardness of ftieso alloys increases as the proportion of oopper 
•m increased from pure tin to 35 per cent, of copper ; from 35 per 
cent, to 73 per tent. of%;opper the alloys are extremely brittle, 
and beyond 73 pej cent, of copper, the hardness diminishes as 
the copper is increased. The effect of heat on some of the copper- 
tin alloys is remarkable, for whilst steel is hardened bjr quenching 
in water, these alloys are hardened by slow cooling and when 
quenchefl in water they lose their brittleness and become malleable. 

Gun’Tnetal usually contains 9 parts of copper to 1 of tin, and has 
a yellow colour. This alloy also serves for the preparation of 
bronze medals. . 

S'pecidum-mcial is composed of 1 part of tin to 2 parts of copper 
melteit together, mth, frequently, addition of a small quantity 
of arsenic. It possesses a steel-grey colour, is very brittle, and 
takes a very high polish. 

BdUmial possesses a varying composition. It gener^y 
consists of, from 4 to 6 parts of copper to 1 of tin. It has a 
ySllowidh-grey colour, and readily melts to fonfl a thin liquid. 
It has a finely cgranular structure, is hard, brittle, and^very 
^ See Bannister and Tabor, Joum, IiUt. Metah, 1900,46, 68.* 



Analyses of*Alloys of Tin. 





Gto GERMANIUM GROUP 


soWous. ThQ Chinese gongs and tom-toms are cast*at a very 
high temperature, ^nd then quickly brought Imder the hammer;, 
in consequence the alloy becomes very dense.# . 

The preceding table gives the composition of some of the alloys 
♦described tfbove. i 

Phosphor-bronze . — The addition of phosphorus to bronze im- 
parts to it a character of greater hardness, elasticity, ^and tough- 
ness. This material is obtained by melting co^er with tin 
phosphide, soraetimfes with a small addition of lead. Tt contains 
from 0-25 to 2*5 pe^ cei^t. of phosphorus, and from 5 to 15 per 
‘ cent, of tfn, and is largely used, especially that containing from 
7 to 8 per cent, of tin, for portions of machinery for which hard- 
ness and ‘toughness are important properties. The alloy con- 
taining more tin has been employed for bell-metal. Its valuable 
properties arc connected with the fact that copper forms a homo- 
geneous alloy with tin phosphide, the presence of phosphorus 
preventing the oxides from dissolving tfnd thus impairing the 
({ualities of the. metal. 

Tin Afnalgam.— Tin readily combines wkh mercury with 
lowering of temperature. The amalgam may be formed more 
quickly when mercury is poured into molten tin, and,*according 
to the quantitj^ of mcroury added, the amalgam is either liquid, 
or fornis a granular or crystalline tnass. When mercury is 
^ made the negative pohi in a solution of tin dichloridc, fine crystals 
of the amalgan^are obf^ined containing from 44 to 51 per cent, 
of tin (Joule). Tin amalgam was formerly largely used for silver- 
ing mirrors, but nf)w has almost entirely been superseded by the 
use of silver. 

It is not certain when tin amalgam was first employed for 
manufacturing mirrors, inasmuch as, during the middle age^,^the 
processes used in the preparation of mirrors were kept secret. 
It is, howevef, clear that before amalgam was usecf, a surface of 
metallic lead was employed for obtaining a mirror tfs early as 
the thirteenth century, when such mirrors were coAimon. These 
were cnrved, and were prepared, as Beckman described in his 
ffistorp of Inventions, from large glass globes, into the interior 
of which a mixture of resin, molten lead, and sulphide of antimony 
was introduced, the fluid mass being brought over the surface 
until it*was all covered with a thin film. The globe was then 
c^yt into pieces, and the mirrors thus obtained wer% often employed 
as ornaments. A guild of glassTmirror makers existed at Nurem- 
berg in tha year 1373 ; whether they piade mirrors accordhag to 


COMPOUNDS OP TIN 


the above process is doubtful, but they, as well As French work* 
• men, sold products of their art in the Venetian marl^t up to the 
year 1500. The^se of amalgam fgr coating miifcrs is first 
mentioned by Kunkel, who recommends for the purpose an 
amalgam of 2 parts of quicksilver, 1 part^)f marcasite (bismuth), 
J part of tin, and J part of lead. 


COMPOUNDS OF TfN. 

Tin and Oxygen. 

397 The fact that tin readily forms a calx wfls observed at*an 
early period. Pelletier was theffirst, in the year 1795, to show 
that tin combines in two proportions with oxygen, forming two 
series of salts. This investigation was continued by Proust, but 
for a long time considerable doubt existed as to the number 
the oxidation products of the metal. Berzelius in 1812 assumed* 
that there were three oxides, 8nO, SUgOg, and SnOg, on the 
grounds that wheti the metal is oxidised by nitric hcid the highest 
oxide tbps prepared possesses a totally different chemical 
character from that obtaTned by precipitation with alkalis from 
^ solution of the salts of tin. The sublequent investigations of 
Davy, Gay-Lussac, and Iferzelius himself have prdved that only 
the first and last of these oxides exist. A peroxide, Sn 03 , has* 
also Jjeen prepared. • • 

Tin Monoxide or Stannous Oxides SnO. — TJiis oxide may be 
prepared in a variety of ways. In the first ^ace, it is obtained 
as an olive-coloured powder when stannous oxalate is ignited 
out of contact with air. Secondly, it may be prepared by adding 
a solution of potassium carbonate to one of tin dichloride, when 
a ^hite precipitate having the composition Sn 20 ( 0 II )2 is thrown 
down. This readily absorbs oxygen from the air, but if it be 
washed in absence of air and dried in a stream of carbon dioxide, 
the monoxide remains behind as a black powder. Stannous 
oxide is also obtained when the pure dichloride is mixgd with 
sodium carbonate, the mass heated until it has become black, 
and then lixiviated. If the hydrated oxide be boiled with a 
dijpte solution of caustic potash, the anhydrous oxide ispbtained 
as a crystalline powder, the crystab consisting of combinations 
of the cube anff dodecahedron. It may also be obtainq^ in Ifie 
crystalline state by digesting a nearly saturated solution of the 
hydrated oxide in acetic a«id at a temperature of 56"^. * 


884 TM GERMANIUM GROUP 

According to^Hantzsch,^ the hydroxide, SnOgH^j'is fSecipitated 
when caustic soda is added to a solution of sHiannous chloride in* 
the absenci of air. It dissolves in excess o^ the reagent, and, 
like gerniiyious hydroxide, acts as a weak monobasic acid, the 
solution containing sodium stannite, H*SnO*ONa. ^ 

Stannous oxide readily takes fire when heated in the air, and 
dissolves in acids with •formation of Jtannous ^alts, ^to which it 
corresponds. These^ are, however, more readily pl^tained by the 
action of acids upon the metal, and possess an unpleasant metallic 
taste, redden litmusf owing to hydrolysis, readily absorb oxygen, 
ind serve as powerful reducing agents. 

• •Z’lw THoxiite (fr Stannic Oxide, SnOg, occurs in nature as tin- 
itone, or*cassiterite, crystallising in the tetragonal system (Fig. 
86), and possessing an adamantine lustre. The crystals are 
seldom colourless, being generally tinted 
brown or black from the presence of the 
oxides of manganese and iron. Stream-tin 
is found in w'ater-worn nodules, and Wood- 
tin in reniform, fibrous masses. When tin 
is heated nearly to its boiling point in the 
air, it burns with* a luminous, wliite flame, 
andMhe dioxide which JjS thus formed in a 
state of fine division was formerly known 
as jlom jovis. If fused in the presence of 
air,# the surface of the metal soon becomes - 
coverea witn a grey pellicle, which then passes into a grey 
powder known al Jlores stanni, consisting of* a mixture of 
finely-divided metal with the oxide ; the mixture, on continued 
ignition, is wholly converted into stannic oxide. The dioxide 
is also dbtained on treating tin with nitric acid, when a vRjlent 
oxidation occurs. The hydrated white powder^ thus formed 
yields the dioxide on washing and igniting. If a solution of 
stonnic chloride be precipitated with ammonia, a gelatinous 
precipitate is obtained which can be completely washed only 
with difficulty. If, however, it be heated with a concentrated 
solution of an alkali sulphate, a dense precipitate is thrown down, 
and this can be easily washed and yields the pure dioxide on 
ignitioi^. An amorphous, white or straw-coloured powder is then 
obtained, which is quite insoluble in water and possesses a specific 
^]»vity of 6-71. On heating it changes colour, becoming lemon- 
yellow and then brown, but it assumes its original tint on cooling. 

^ Zeit. anoTff. Chtm., 1902, 80, 289 ; see alo Bury and PYtingteD»Voi(m. 
Ohm. 8oe., 1922, ISl, 1998. 



_ 1 • * 1 



cTiAmiNii; AUiU 


885 


The djbxide may also be obtained by the electrolysis df a 
solution of potassium or sodium chloride) a ,tin plate being used 
IS anode, and one^f platiniim as cathode.^ 

By heating amorphous stannic oxide in a current of hydrogen 
(hldride it may be obtained in microscopic crystals wMch have the 
form of cassiterite and a specific gravity of 6*72 (Deville).* The 
formation of crystalline stannic oxide h%s been observed in fusing 
the dross ^j^llected on the hearth of a gim-metal furnace, the 
crystals being liard, brittle, four-sided prisnft.s Stannic oxide can 
be fused only at a very high temperature, according to Cusack * 
1127°. It is not volatile, nor is it atta5<e(l by concentrated^ 
acids, with the exception of sulphuric acid. 

Stannic Hydroxides . — Two ^aiinic hydroxides adre known, 
which have the same composition, lljSnO.,, but different chemical 
properties. Berzelius,® who discovered the second form, intro- 
duced the term “ isomerism ” to designate this hitherto unknown 
phenomenon. They are both weak acids, but react differenfly# 
with other acfds, and form different salts with alkalis, ffom which 
they can be precipitated unchang(‘d by the addition of acids : 
thcjy are distinguished by the names stannic and meiasiannic or 
a- and ^-stannic acids. , 

Berzelius showed that they are b(|Jh in the same stage of 
^oxidation. The difference is not due to their* ;^ater Content, 
for this is variable, depending on Iioav they are dried, and the 
difference between the two forms persists through the varyifig 
degfees of hydration. Two views have^een held as to the cause 
of the differemce. The older is that the /9-f%rm is a polymer of 
a-stannic acid : the method of preparation of the a-acid, and the 
compositicn of its salts, make it probable that the molecule con- 
mils only one atom of tin, and that it has the simple formula 
I]^n03 : the work of Fr^my ® and Engel ^ on the salts and oxy- 
chlorides denved from /3-stannic acid indicate tl»t its molecule 
contains five atoms of tin, and that it can be given the formula 
H2Sn50ii,4H20. On the other hand, Mecklenburg® has pro- 
duced evidence that the two forms are both colloidal hydrates, 
differing only in the size of their particles ; while no cleifl: line of 
demarcation can be drawn between the two forms, the a-acid 

• Loxenz, Zeit. anorg. Chem., 1806, 12, 436. 

• Compt. rend., 1861, 58, 161- • Abel, Joum. Chem. 8oc* 1868, 119. 

« Pntc. Royal Acad.tmi, i 399. » AnnaleA, iai7, [2J, 5, 149. 

« Ann. Chim. Phye., 1848, [3], 28, 385. • * 

’ Compt. rend., 1897, 121 766; 1897, 125, 464, 661, 709. 

• anon. Chem., 1909,^ 368; 1912, 71 207; 1914, 81 A21. See also 
CoUils and Wood, Joum. Chem. 8oe., 1922, 121, 441. 



iftE GERMANIUM GROUP 


co^lsists of the relatively small particles and the /^-acid of the larger 
ones. , • , 

Berzeliui^ Engel, and others have described a third form, 
parastannic add. This is not an isomer of the a- and y^-forms, 
since it ha% a differenii water content from either of the otheft 
when dried under similar conditions. It has the composition 
H2Sn50ji,2H20, and isrf)bviously related closeljjto metastannic 
acid, and has been regarded as an internal anhydride of it; 
according to Kleinschmidt,^ however, it is identical with it. 

Stannic acid or a-gtanijic acid is obtained as a white, hydrated 
''preci{)itat(? by the action of calcium carbonate or alkali on a 
solution of a skirmic salt, or by the action of an acid on a stannate. 
Its water‘content depends on Jiow it has been dried; rapidly 
dried by suction and pressure it has the composition Sn02,4H20 
or H2[Sn(()iI)g] ; dried slowly in the air at room temperature, 
i^has the composition Sn02,2H20 or 1148064 ; dried in a vacuum 
• over sulphuric acid it has the composition SnOgjHgO or H2Sn03, 
bfit it is doubtful if these are definite hydrates. Th*e final product 
on heating is anhydrous stannic oxide. The freshly precipitated 
hydroxide, while still moist, dissolves slightly in water, to which 
^t imparts an acid reaction, and is readily soluble in dilbte acids, 
forming stannic salts, a#id in alkalis to form stannates. It is 
partially transformed to the ; 9 -forra om drying or on standing ii{ 
^contact with water, especially on heating. 

The Stannates. ^Only pne orthostannate, cobalt orthostannate, 
6028064, has as yet been prepared. It has been obtained by 
Hedvall ^ by fusing cobalto\is and stannic oxides with potassium 
chloride and dissolving out the excess stannic oxide with hydro- 
chloric acid. • 

The s^nnates of the other metals, when formed by fuSipn, 
have the formula when formed from solution have 

the formula M\Sn63,3H26. Bellucci and Parravano ® argue that 
these are derivatives of hexahydroxy-stannic acid, H2[Sn(GH)g] ; 
the three molecules of water are water of constitution, not W'ater 
of crystallisation, since they are often not expelled by long heating 
at 100 °*. All the stannates examined, namely, those of sodium, 
potassium, lead, silver, calcium^ strontium, and barium, contain 
three molecules of water; the potassium salt is isomorphous with 
the potassium salts of hexahydroxy-plumbic acid, H2[Pb(GH)y, 
ai^ the far'more stable hexahydroxy-platinic acid> H2[Pt(OH) J ; 

1 MwaUK lOia, 38, 140. • Arhiv Kern. Min. Oeol., 1914, 5. No. 18, 1. 

• Zeit, anorg. Chem., 19(M^46, 142. * 



MmiUSIAJNiVlU AVW • 


887 


they are afialogous to the hexachlorostannates, Hj{SnClg], and tin 
intermediate acid, M 2 [Cl 3 Sn(OH)J, exists. , 

The alkali stannates alone are soluble in water, |hd can be 
obCainedims measurable crystals ; starmates of the other metals 
are obtained as insoluble precipitates by (fcuble deconlposition. 

Potassium Stannate, KgSnOg, is obtained by fusing the dioxide 
with potash, or by dissolving the hydrated oxide in potash-lye. 
The solution elds on evaporation over sulphuric acid colourless, 
glistening, fhonibic prisms of K 2 [Sn( 0 }r) 3 ], ^\1lich have an alkaline 
taste and are readily soluble in w'ater. * Metallic copper brought 
into contact with the solution becomes covered with a bright 
coating of tin. 

Sodium Stannate, J^aaSnOg, is^prepared on a large «cale and 
employed extensively in calico-printing under the name of 
'preparing salts. It is obtained either by fusing the finely pow- 
dered or levigated tinstone with caustic soda, dissolving the mass 
in water to remove any ore that may be unacted uj)on, ancl 
evaporating th*e solution; or by heating tin with caustic soefe 
and Chili saltpetie. On evaporating the solution, crystals of 
NagSnOg.SHgO, or Na 2 [Sn(OH)g], are obtained, which are more 
soluble ii? cold than in iiot water. A tolerably concentrated 
solution of the salt which contains no caustic soda deposits on 
cooling fine prisms of the composition NagSiiOgjlCfrlgO, an^ these 
effloresce on exposure to air. ^ 

Meiastannic Acid and the Metastannjtte^. — In his Reflections 
on ite Hypothesis of Alkali and Acidum} published in 1670, 
Boyle remarks that aqua-fortis eats up ortJestroys more tin 
than it dissolves. On the other hand, he elsewhere ^ mentions 
that a solution of tin in aqua-fortis readily becomes gelatinous. 
KuAel, who also studied the action of nitric acid on ^'n, men- 
tions in his Laboratorium Chymicum that tin can only be dissolved 
when it is adSed in small quantities to an acid, and that heat must 
be altogether avoided, because white calx of tin is thrown down 
when the acid is hot. The explanation of these different state- 
ments is to be found in the facts that when the metal is* treated 
with weak nitric acid it forms either stannous or stannic hitrate, 
iccording to the degree of concentration of the acid, and that the 
atter salt easily decomposes with separation of a gelatinous 
(t&nic acid, whilst, on the other hand, when tin is aeffed upon 
3y strong nitric acid it is violently attacked with (Solution ^f 

* Boyle, Op. 4 , 284. 

* ** ^periments and^nsiderations Conoeraing Cobun." 



888 fBE GdBMANTOM GROtTP 

h^at and fomiation of an insoluble white powder consisting 0/ 
a mixture of a- ^nd ^S-stannip acids; Klemschmidt, however^ 
maintain£^that it is >5-stannyl nitrate, Sn50j(NOg)j,4H2O, and 
that this is readily hydrofysed to ^-stannic acid by washing with 
water. Metastannic iicid is also prepared by the addition "of 
acids to metastannates, or by their hydrolysis in dilute solution, 
by the hydrolysis of /9-stannyl chlorideiby the spontaneous change 
of a -stannic acid, and by the slow spontaneous hySro^is of staimic 
salts and stannate^. Engel finds that it has the eomposition 
Sn02,2Ha0 or HaSjjOijjOHaO when it is dried in the air, and 
SnOajHgO or HaSngOjijiHaO when it is dried in a vacuum over 
sulphuric aci4 .According to van Bemmelen,^ however, it always 
contains •less water than the^a-forrn when the two forms are 
treated similarly, and no definite hydrate exists. The final 
product on heating is stannic oxide. 

The freshly precipitated hydroxide reddens litmus paper, and 
IS distinguished from a-stannic acid, inasmuch as it is altogether 
fhsoluble in nitric acid, and swells up but does'not dissolve in 
strong sulphuric acid, forming the easily hydrolysed compound 
/9-stannyl sulphate, Sn50j,S04*4ir20 (Kleinschmidt). Hydro- 
chloric acid produces a compound, m^ta- or yS-stann^l chloride, 
which is soluble in watig* but insoluble in hydrochloric acid, and 
which Tilngelfdiind to liave the formulaiSn50jCl2,4H20. Numerous 
similar hydrated oxychlorides have been described. 

Jldetastannati^ are produced by the action of alkalis on 
metastannic acid or on solutions of its chloride : the best Itnown 
s sodium metasUnnate, w'hich is slightly soluble in water but 
.nsoluble in excess of alkali. Frcmy and Kleinschmidt find it 
can be represented by the formula NagSu^Oj 1,4^20. Other 
metast^ates of greater complexity have been described. • ^ , 

It is doubtful if any of these derivatives of the stannic hydr- 
oxides, exce|^ the easily crystallisable stannic salts and the 
stannates, are real compounds; their composition depends to a 
large extent on the method of preparation, and they are all 
readily»hydrolysablc. Mecklenburg has shown that the reaction 
betweAi /^-stannic acid and phosphoric acid is a typical adsorption 
effect. The composition of the product varies with the con- 
centration of the phosphoric acid in the solution according to the 
usual 1^ that holds when true chemical combination does liot 
ogcur, but*an adsorbed layer is fonned on the sui^ace of any very 
finely fiivided substMuse. It is tbali tbe meta- 

' Ber., 1880, 18, I|66. 



STANNOUS ' OOWQPOUNDI# 


• , ^ I — 

stannates/metastannyl chlorides, and other cqpipounds wi{h 
Acids are adsorptibn phenomena. Solutions of metastannyl 
chloride are not trte solutions, but colloidal. ^ 

Parastannic acid was discovered bf Berzelius, who called it 
^-stannic acid; since then this name has«been applied to meta- 
stannic acid. It has been studied by Engel, and is formed when 
metastannic aci^ is heatei in water at J00°. Its reactions are 
almost identi^jJ with those of ^-stannic acid, but it contains two 
less molecifles of water in its composition : • 

Dried in air. Dried in n v.'w^uum. * Pota.4iani wit. OhlorUe. 
Metostannlc acid . H,Pn 40 ,„ 9 ir ,0 K,Snj0,„4IT,0 K,Sii,0„,4ir,(.) Sn»0,C|„4ir,C 

Parastannic acid . lT,Sn,0i„7llj,0 ir,i?ni0,„2ir,0 K,Sn,0,„2 y Sn»(),( :i„3g,(: 

Colloidal or Soluble Stannic AcH was obtained by Graham ^ by 
the dialysis of a mixture of tin tetrachloride and alkali, or of 
sodium stannate and hydrochloric acid, the gelatinous mass 
which is first formed gradually dissolving. The liquid is con- 
verted on heating into colloidal metastannic acid. Traces of 
hydrochloric acid or of a salt bring about gelatinisation in both 
solutions. * 

Tin Pesoxide, SnOg. — This oxide is known only in the hydrated 
condition, and is prepared by the addition of barium peroxide 
to a solution of stannous^ chloride confUining hydrochloijc acid. 
The barium chloride is removed by dialysis, anePthe colloidal 
solution is evaporated. A white mass having the formula* 
HgSu^Oy or 2Sn03,H20 remains behind.^ • 

When stannic hydroxide is heated with jiydrogen peroxide 
at 70 °, and the mixture is desiccated, a perstannic acidf 
HSn()4,2HjO, is obtained, and this on heating at 100° yields the 
aci(^ HjSngO^jSIIgO. Potassium and sodium stannates when 
siihilarly treated form salts corresponding to these acidtl?® 

When concentrated alkali stannate solutions arc electrolysed 
at low temperatures and with low current densities, perstannates 
are formed, owing to anodic oxidation.* 

Stannous Compounds. 

398 Tin Difiiioride or Stannous Fluoride^ SnFg, is obtained by 
di^lving the hydrated monoxide in hydrofluoric acid. On 
evaporation in alienee of air this compound is obtained in the 
fonn of email, mrbite, monoclinic tablets. 

* Trans., 1881, 161, 213. * Spring, BuU. 8oe. chim., 1889. [3], 1, 180. 

» Tnimtar, IJcr., 1906, 88, 1184. * Coppadoro, Cfazz., 1908, 88» U 489. 



fHE QEBMANIUM GROUP 


t * 

■ Tin Dichloride or Stannous Chloride, SnClg, is obtained on the 
large scale by dissolving tin in hydrocblorib acid. On evapor» 
ating thel^olution and cooling, crystals of* hydrated stannous 
chloride, SnCl2,2H20, known in commerce as Tin Salt, separate 
out in transparent, lubnoclinic prisms which melt in their water 
of crystallisation at 40°, and on cooling again yield a crystalline 
mass. They have a specific gravity Af 2*71, aijd dissolve at the 
ordinary temperature in 0*37 part of water. Whgn^ore strongly 
heated they partially decompose with evolution df hydrogen 
chloride, but when ^ried in a vacuum over sulphuric acid they 
' lose their water. The anhydrous salt, which may also be obtained 
b5' heating tin ia hydrogen chloride, or with the requisite amount 
of corrosive sublimate, is a Vansparent mass having a fatty 
lustre and conchoidal fracture. It fuses at 250° to form an oily 
liquid which boils at 006°. Its vapour at low temperatures has a 
density always less than that required by the formula Sn2Cl4, but 
' at a high temperature the value becomes constant, agreeing with 
SnClj,^ whilst the freezing point of urethane is lowered by dissolving 
stannous chloride in it by an amount corresponding to the formula 
SnClg.* The hydrated salt dissolves in a small quantity of water 
^with lowering of temperature, forming a clear liquid which, 
when diluted with muchi water, becomes turbid, a basic chloridj, 
2Sn(Oll)Cl,H2t), being precipitated; this again dissolves on the 
^ pddition of acids. The same precipitate is formed when the 
clear solution is^exposed to the action of the air : 

OSnCla 2H2O +02= 2SnCl4 d- 4Sn(0H)Cl. 

Stannous chloride is soluble in alcoliol and in ether.® It 
combines with ammonia to form compounds whfch vary in 
composition according to the temperature of reaction.^ 
cooled in a freezing mixture, a yellow compound^ SnClg/ihTHj, 
is formed, which blackens on exposure to light, and is decomposed 
by moisture into stannous oxide and ammonium chloride. At 
ordinary temperatures, a mixture of SnCl2,2NH3 and SnClgj^^^a 
result^* whilst at 100° SnCl2,NH3 only is formed. At 120“300°, 
the compound 3SnCl2,2NHg is formed as a brownish-red, crystalline 
mass, which is the most stable of the three compounds. 

Tin J^bromide or Stannous Bromide, SnBrg, is obtained wjen 

^ BUtz and V. Meyer, Btr., 1888, 21, 22. ^ 

> Castoro, Oazt., 1898, 28. u, 317. 

* de Jong, Ztii. anorg. Chm., 1902, 41, 696. 

* Sofianoponloa, Cmpt. rend.«1911, 1^ 865.^ 



STANNOUS COMPOUNDS* 891 

• ; ; ; 7 "] 

tin is heated in hydrogen bromide or distilled •mth mercurio 

•bromide. It forms* a light yellow, translucent mass fusing at 
216-6°, and is soluble in water. A solution of thisf^ompound 
is obtained by acting with hot aqueous hydrobromic acid upon 
metallic tin. • 

Tin Di'iodide or Stannous Iodide^ Snij, is best obtained by 
adding a sn^all excess of iodide of potassium to a warm concen- 
trated solutio|i gf stannous chloride. It crystallises in yellowish- 
red needles*which dissolve only sliglitly in water, though readily 
in warm solutions of the chlorides and iodides of the alkali 
metals, and also in dilute hydrochloric acid. It melts at 316° 
solidifying to a crystalline mass which liquefies «t^ higher tem- 
perature. When heated in absenoe of air it is obtained ii! the form 
of a red, crystalline mass, yielding a scarlet powder. On treat- 
ment with dry ammonia, a yellow compound having the formula 
Snl2,2NIl3 is formed.^ If a.saturated solution of stannous iodide 
in hydriodic acid be cooled to 0°, pale yellow needles of io^osiannic 
acid, nSnlg, arc deposited. These are very unstable and readily 
decompose, formidg stannous iodide.^ • 

The fluoride, chloride, bromide, and iodide combine with the 
corresponding halide compounds of the alkali metals and with 
tjiosc of the metalu of the alkaline earths to fo^m cryijtalline 
double salts. * • 

Tin Monosulphide or Stannous Sulphide, SnS, is obtained by, • 
heatigg together the metal and sulj)hui*. Tliin tin foil takes 
fire spontaneously when brought into sulphur vapour. When 
thus obtained, ^t is a lead-grey, tough, crystalline mass, which 
melts at a higher temperature than the metal. When a solu- 
tion of staniJous chloride is saturated with sulphuretted hydrogen, 
a brbwn hydrated precipitate is obtained, which ont drying 
beeftmes black. This is scarcely soluble in ammonium sulphide, 
but dissolves on the addition of sulphur, and is also soluble in 
the polysulphides of the alkali metals, the stannous sulphide 
being first converted by the sulphur into stannic sulphide, which 
then dissolves, fencing ammonium thiostannate. Wh^n the 
iried precipitate is added to fused stannous chloride and the 
melted mass treated on cooling with dilute hydrochloric acid, 
ita^ous sulphide is obtained in metallic, glistening, crj^stalline 
JcalU, having SL specific gravity of 4-973. The crystalline variety 
nay also be obtained by heating the amorphous sulphidq in tile 

^ Ephraim and Schmidt, Ber., 1909, 42, 3866. 

i Young. J. An^. Chem. 8oc., 1897, 19, 861. 


fsE OfeRMANIUM GROUP 


electric furna(?e.^ Amorphous tin sulphide dissolves readily 
in hot hyd jpchloric«cid, whilst the crystallised substance dissolves 
Jess readiJ}! , ^ 

Stannous Sulphate, 80864, is formed by dissolving the metal 
or the hydrated oxide^in dilute sulphuric acid. On evaporation 
in a vacuum, microscopic, granular crystals are obtained which 
are only a little more soluble in hot •than in eold water. The 
solution readily deposits a basic salt. ^ 0 

Stannous Nitrate, Sn(NOa)2.— This salt is obtained by the 
action of very dilutemitric acid on the metal, ammonium nitrate 
being simultaneously produced : 

’ iSn +^OHNOj = 4Sn(N03)2 + NH 4 NO 3 + 3IIjO. 

Stannic Compounds. 

399 Tin Hydride.— li an alloy of tin and magnesium, the com- 
position of wliich corresponds to the formula MgaSn, is dissolve'd 
i?i hydrochloric acid, the hydrogen evolved contains small amounts 
of a volatile hydride of tin. This is condensed by liquid air, and 
can be re-evaporated without decomposition. On passing 
jbhrough a heated tube, it is decomposed, with the forniation of a 
characteristic tin mirro%2 

Tin TeJrafiuoride or Stannic Fluoride, 8nF4, is obtained as 
,a hygroscopic, white, crystalline substance by the action of 
anhydrous hyd|;ofluoriq acid on stannic chloride.® It boils at 
705 ", subliming below this temperature, and has the specific 
gravity 4-78 at 19 *. An aqueous solution of the fluoride may be 
obtained by dissolving the hydrated dioxide in hydrofluoric 
acid; the solution coagulates on boiling, and dewmposes on 
evaport^/ion with evolution of hydrogen fluoride. Galqpus 
ammonia combines with tin tetrafluoride at 43 °, forming a white 
compound, StiF4,NIl3, which lo.ses very little ammonia even at 
400 °.* When the fluoride and ammonia are heated together 
in a sealed tube at 120 — > 130 °, SnF4,2NH3 is formed. Both these 
compounds are soluble in ammonia. 

Liquid hydrogen sulphide decomposes the fluoride in a sealed 
tube, thus : SnF4 + 2H2S - SnSj + 4 IIF. 

Chlorine compounds of phosphorus bring about an exchange 

• 

> Mourlot, Conipt. reruL, 1897, 124, 788. 

Paneth ind Rer., 1919, 52, [i^j, 2020. See also JPaneth and othew, 
Ber., 1922, 56, [B], 769, 776. 

• Ruff and Plato, Ber., 1904, 87, 673, 

« Wolter.UAem. ZaU, 1912, 86, 166. 



STANNIC COBIPOUNDS 893 



of chlorine and fluorine, and metals react violehtly with the 
fluoride, liberating tin. • 

It combines witJ other fluorides, iorming a ch^acteristic 
series of double salts, the stannifluorides^ which mostly crystallise 
well and are isomorphous with the correspdhding double fluorides 
of silicon, titanium, germanium, and zirconium.^ 
Potassiufn^tamifiuoTidefK^riY fe obtained by neutralis- 
ing hydrofluo%i(%acid with potassium stannate, or by treating 
stannic chloride with a cold solution of potassium fluoride. ^ 

It crystallises in thin, nacreous tablets*or ia rhombic pyramids 
which are much more soluble in hot than in cold water. When 
the solution contains an excess of hydrofluoric Hcid, the satt 
KgSnFg.HKFg is deposited in mDnoclinic prisms. * 

The stannifluorides of sodium, ammonium, calcium, and 
magnesium are also crystalline soluble salts. 

Tin Tetrachloride or Stannic Chloride^ SnCl 4 , was first men- 
tioned by Libavius in 1605, who obtained it by distilling tin or 
its amalgam with excess of corrosive sublimate. It was termeJ 
by him Spiritus ar^enti vivi subliniali, but afterwafds it received 
the mme^Spiritm fimans Lihavii. For its preparation, the 
process originally proposed by Libavius may be employed, or# 
chlorine may be passed over tin foil, i^-platc sjrap (p^ 877), • 
or fused tin placed in a retort Wlien the strcanf of chlorine 
is quick, and especially if the gas-delivery tube dips into the,, 
rnolteg metal, an evolution of light and heat is observed. It 
may also be prepared by passing chloroform vapour over the 
heated dioxide.^ * 

Tin tetrachloride is a colourless, thin, fuming liquid, which 
jolidifies at ~ 33'^, has a specific gravity of 2*234 at 15°, and boils 
it m 8*9°,^ forming a colourless vapour liaving the normakspecific 
jraidty of 9*1997 (Dumas). At the boiling point it dissolves 
hombic sulphur, yellow phosphorus, and iodine, and can be 
nixed in all proportions with bromine and carbon disulphide, 
^Vhen mixed with turpentine so much heat is evolved that the 
hydrocarbon takes fire. Its property of fuming in the air (Trends 
>n the fact that it absorbs atmospheric moisture. In 1770, 
)emachy observed that it solidified when brought into con- 
act^ with one-third of its weight of water to form a crystalline 
aass termed butter of tin. Several distinct hydrates soluble in 
• 

‘ BfarigDAO, Ann. des Mines, 1859, [5], 19, 221. 

• Sniioh, Monatsh., 1904, 25, 907. » Ren*, Ber., 1906. 89, 249. 

< Thoi|^, Jwm. Chem. 8oc., ifiSO, 87, 331. 



894 


♦he germanium group 


^ — — > 

water may bft produced, according to the quantity of water 
which is ^ded. Thus the compound SnCl'jSHgO is formed by 
exposing fee anhydrous qbloride to the actioh of moist air, or by 
the evaporation of its aqueous solution. This hydrate crystal- 
lises in monoclinic nftedles which melt at 80 °, and on cooling 
again solidify to a crystalline mass. A second hydrate, having 
the composition SnC1^5H20, is obtained by the addition of a 
sufficient quantity of water to the anhydrous cyoride, or by the 
gentle evaporation of the aqueous solution. It is deposited in 
opaque, acute, moiv)clirMC prisms, which melt at a low tempera- 
ture and again solidfy to a crystalline mass. Lastly, large trans- 
parent, monb\iinic crystals of the hydrate SnCl4,8H20 are 
deposited in the cold from a dilute solution. On boiling a dilute 
aqueous solution of tin tetrachloride, stannic hydroxide is formed ; 
in very dilute solutions this precipitate forms on standing. 

Tin tetrachloride is employed by dyers as a valuable mor- 
dant. pHibbel in Holland is said to have made the discovery 
lhat by help of this salt a permanent red dye can be obtained 
from cochineal. Dyers were formerly in tfhe habit of pre- 
paring this mordant, known by the old names of tin-composition, 
c. physic, or dyer’s spirits, by dissolving tin, together with sal- 
» ammoniac or^common'salt, in nitric acid, pr by dissolving tin 
in aqua regia, whence the solution \Vas formerly termed nitro- 
. muriate of tin. It is usual now for dyers to employ the 
crystalline pentahydrate, SnCl4,5H20, which is a comipercial 
product known as oxymuriate of tin. It is also largely employed 
for weighting silk. ’ 

Anhydrous stannic chloride combines with ammonia to form 
a solid mass having the composition SnCl4(NH3)4, which can 
be subfimed and is soluble in water without decomposftion.^ 
It can be obtained in crystals by evaporating the aqueous Solu- 
tion over sulphuric acid, but if it be allowed to stand for some 
days, or if the liquid be warmed, stannic hydroxide separates 
out in a gelatinous form. Tin tetrachloride combines also with 
many^bther chlorides to form crystalline compounds,* such as 
SnCl4,2SCl4. This is obtained by the action of chlorine on 
tin disulphide, and forms large, yellow crystals, which melt 
at a summer temperature, and decompose above 40 °, yrith 
evolution of chlorine. If dry nitrous fumes are led into a solution 
tl stannic chloride, the compound SnCl4,Ng03 is deposited as a 

» Peraoz, Ann. Chim. Phya., 1830, 44, 322. 

* U. Rose, Pogg. Ann., mt, 42, 517. 



STAKNIC COMPOUNDS 


895 


• 

I yeHow^ amorphous mass, and if this be sublimed* or if the dry 
\ vapours from aqua^egia be passed into the ehlorid^ the com- 
i pound SnCl4,2NOO is produced, which crystallises ta bright, 

^ shining octahedra. If a solution of stannic chloride in chloroform 
L be used, a w^hite precipitate of Sn0Cl2,3SifCl4,N205 is obtained, 

P and this on heating yields a white sublimate of SnCl4,4NOCl.' 

^ Stannic chloride ^Iso combines with phesphorus pentachloride 
to form the \i^ound SnCl4,PCl5, which sublimes in glistening, 
colourless cfystals, but when kept even in closed vessels falls to 
an amorphous powder. . It has a peculiar, extremely pungent 
smell, and fumes strongly in the air. The compound 8nCl4,POCl3 
forms crystals which melt at 58 ®, and can be (Jwftilled at 180 ^* 
without decomposition. This compound fumes strongly in the 
air, and is at once decomposed by contact with water.® 

Like the fluoride, stannic chloride readily yields a series of 
double salts known as the slannichlorulcs, which present a simi- 
larity to the platinichlorides, but are less stable than tlys latter 
salts.® The free acid, HjjSnClg, is obtained in thin plates con- 
taining GHjO by saturating the pentahydrate, Sn 0 l 4 , 51 l 2 O, with 
hydrochloric acid gas at 28 ° and cooling to 0°.^ 

Ammonium Stannichloruk, (NH4)2SnCl3, separates as a crystal- • 
line powder when solutions of tlic twur salts are niixed^ and 
crystallises from dilute solution in small, regular octehedra. It 
dissolves at the ordinary temperature in 3 parts of water. Its,* 
concentrated solution can be boiled without decomposition, but 
when diluted tin hydroxide separates out. It was formerly much 
used by cabco-J 5 rinters under the name of pBik salty from its 
power of acting as a mordant for madder-red colours, but its use 
has been almost entirely superseded by the crystalline penta- 
hydrffted stannic chloride. • 

Telrahromide or Stannic Bromidcy SnBr4. — Tin and 
bromine unite together with evolution of light and heat. The 
bromide is best prepared by adding bromine very slowly to strips 
of tin, the temperature being kept between 35 ° and 59 °.® It is 
a white, crystalline mass, which fumes strongly on expostire to 
air and is easily soluble in water. It melts at 33 ° and boils at 

^ Thomas, Compi. rend., 1890. 122 , 32. 

* D^lmann, Annalen, 1852, 83, 257. 

* von Biron, J, Rus4. Fhys. Chem, 8oc., 1004. 31 , 489; BcUucci ana Parra* 

vano, AUi R. Accad.J^incef, 1904, [4], 13 , ii, 307; von Biron, J. Russ. Phy»^ 
Chem. Sot., 1906, 37 , 963, 994, 1036. • 

* Enael, Compt. rend., 1886, 103, 213; Seubert, Ber., 1887, 20, 793. 

* liOiSai^ ZeiLanorg. Chem., 1395, 9 , 305. 

VOp. n. (II.) 


F 



ta GERMANIUM GROUP 


201^. The specific gravity of the liquid is 3*349 at 36®, and'its 
vapour depsity is 7*92.^ It is easily soluble ill cold water, forming 
a colourldjs liquid from which the hydroxidfi is deposited slowly 
at the ordinary temperature and quickly on boiling. It yields 
crystalline stannihrorMdes with the alkali bromides. 

Tin Telraiodide, Snl 4 .~When tin and iodine are heated 
together, combinationtcommences atf 50®, and^at a higher tem- 
perature heat and light are emitted. In ordeal# prepare this 
compound, tin filings are first moistened with carboii disulphide, 
and then iodine is gradually added. It crystallises in red octa- 
hedra, melting at 146° and having a specific gravity of 4*696. 
IPin tetraiodi^boils at 295°, but sublimes at as low a tempera- 
ture as 180° in yellowish-red^needles, very similar in form to 
those of ammonium chloride. It is soluble in carbon disulphide, 
absolute alcohol, ether, chloroform, or benzene; with water 
it forms hydriodic acid and stannic oxide. 

Jf anpnonia be led into a solution of tin tetraiodide in carbon 
bisulphide, and at the same time the solvent be allowed to 
evaporate, a*white substance, Snl 4 , 8 NH 3 , ift formed. This is 
also formed by passing ammonia over the tetraiodide.^ 

, Tin Disulphide or Stannic Sidpkide, SnSg. — This compound, 
crystallising in six-sided tablets or in gold-goloured, translucent 
scales having a specific gravity of 4*425, is used as a bronze 
^powder for the purpose of bronzing articles of gypsum, wood, 
etc,, and is known in commerce as mosaic gold. The discovery 
of this compound is usually ascribed to Kunkel. He does 
indeed speak of a^ubliination of sulphide of tin aifti sal-ammoniac, 
but expresses himself so vaguely that it is impossible to recognise 
this compound from his description. It was wdU known in 
the eighteenth century under the names of mosaic gold, Sutfum 
mosaicim, or musivum. It was then prepared as at« the 
present day 'by subliming a mixture of tin amalgam, sulphur, 
and ammonium chloride, and as it was supposed to contain 
mercury it was often employed as a mercurial medicine. Peter 
Woulfe in 1771 showed that it did not contain mercury, and 
described other methods for its production, according to which 
it is still prepared. Thus, for instance, it is obtained in the form 
of a fine pigment by heating 18 parts of tin amalgam, containing 
6 parte of mercury, with 6 parte of ammonium chloride and 
\ parte dt sulphur, when ammonium chloride, xaercuric chloride, 

* Camelley and O’Shea, Joum. Chtm. 5oc., 1878, 83, 66. 

** Ephraim and Schmidt, Ber., 190C, 48 , 3866. c • 



STANNIC GOIffOUNCS ' 8S7 


and stannous chloride sublime, and stannic su!J)hide remains 
behind in the forra*of golden-yellow scales. -It is likewise pre- 
pared by heating fin monosulphide lyith 8 parts of mercuric 
chloride, or subliming tin filings with ammonium chloride and 
sulphur, and according to several other receipts given by Woulfe.^ 
Pelletier believed mosaic gold to be a compound of sulphur with 
the highest oxidittion prcfluct of tin, afid Proust, who found 
that it coul5%l]f obtained by heating stannous chloride or tin 
monoxide with sulphur, supposed it to be a compound of tin, 
sulphur, and a small quantity of oxygem The exact com- 
position was ascertained by J. Davy and Berzelius in the year 
1812 . The formation of mosaic gold from tiff^sulphur, aiM 
ammonium chloride appears to •take place according to the 
following equations (dmclin) : 

(I.) Sn + 4NH4CI = (NH^ClVSnCl^ d- H2 + ^NH., 

(11.) 2(NH4Cl)2SnCl2+ S2 = 8082+ SNH/’H fNH^ClljSnCV 

• k 

When heated, a portion sublimes without decomposition, but the 
greater part is resolved into sulphur and monosulphide. It is 
not attacked by hydrocliloric or nitric acid, but readily dissolves 
in aqua regia, as well a^ in caustic potash, when potassium • 
stannate and potassium thiost annate are Ibrmcd. If sulph\iretted 
hydrogen be led into a solution of the tetrachlorlfle a yellow 
precipitate is obtained. This consists of a mixture of tin disul-* 
phide«and tin dioxide, and is readily soluble in the sulphides of 
the alkali metals, when the (hiosfarmates are^forrned. 

Thiosiamic Acid . — When dilute hydrochloric acid is added 
to a solution of thiostannate, a yellow precipitate is obtained, 
which on drying forms an almost black powder possessing a 
brdwn streak and wax-like lustre, and having the composition 
HjSlbSg. When heated in absence of air it yield§ the golden- 
yellow disulphide.2 

Potassium Thiostannate, KgSnSj, 31120 , is prepared by boiling 
a concentrated solution of potassium sulphide with the necessary 
quantities of sulphur and tin; it crystallises in colaurless 
prisms. By a similar process, the sodium saU, Na2SnS3,2H20, 
is obtained in yellow, vitreous, regular octahedra.® When 
Bodk^m sulphide is fused with tin monosulphide and sulphur, a 
black, crystalline mass is obtained, yielding a dark-coloured 
solution, which %)n concentration at a low temperaturei yields 

> Trans., 1771, 61, 114. * Kiihn, Annakn, 1852. 84, 110. 

• » Ditte, Cofhpt. rend., 1882, 66, 641. 


IhE GEBBIANTOM OROtJP 


colourless crystals resembling gypsum, and having the formula 
Na4SnS4,l?HjO. • * 

Ammoikum thiostannn#^ is formed by dissolving the sulphides 
in yellow ammonium sulphide, and may be precipitated by 
alcohol in unstable yellow tablets of the composition ^ 
(Nn4)aSnS3,3H20. 

When mosaic gold fused with todine in^bsej^ce of air, a 
crystalline mass of SnSj4 is obtained, and this $ai. be sublimed, 
or recrystallised from solution in carbon disulphide. It is decom- 
posed by water into stannic oxide, sulphur, and hydriodic acid. 

Stannic Oxysulphide, 803083, IIIL^O.—This compound is 
obtained by tfih^wing precipitated stannic sulphide to remain in 
contact Vith ammonia, filtering and acidifying the filtrate, or 
by digesting the sulphide with ammonium carbonate and acidi- 
fying the filtered solution. It is a wliite mass which is soluble 
in ammonia and gradually becomes yellow on keeping.- 

Stannic Sulphate, 80(804)2.— As already mentioned, tin 
dioxide dissolves in concentrated sulplmric acid, and from the 
solution two"* crystalline bodies may be obtained having the 
empirical formula) 8002,2113804 and 81102,113804, \vhich may 
• be regarded as the normal sulphate, 80(804)2,21120, and the 
basic ^ 8ulph{iJ;e, 811(8^4)2,81102,21120. Jloth of these are 
dccomposcch' by water with separatron of stannic o.xide. 

. On mixing solutions of staimic acid in Hul[)huric acid, and 
calcium sulphate in sulphuric acid, and concentrating, regularly 
formed, colourless cubes are obtained of 80(80^)2, Ca804, JlHgO ; 
similar salts are obtained with barium, strontium, and lead 
sulphates.® 

Stunnic Nitrate, Sn(N03)4, is obtained as a white powder 
by the^action of 70 per cent, nitric acid on tin, but mustf be 
quickly removed, as it is rapidly converted into the liydAted 
dioxide. It is a white substance which is stable in presence of 
concentrated nitric acid at 90 ®, but is immediately decomposed 
at lOO®.** It dissolves in water, but the solution is almost im- 
medit^fely decomposed with separation of hydrated stannic oxide. 

Potassium Ammono-stannate, K2[Sn(NH2)g], is produced by 
the action of potassamide on stannic iodide in liquid ammonia,® 

‘ Stat^k, Zeit. anorg. Chetn,, 1898, 17, 117. tf . 

* Schmidt, Ber., 1804, 27, 2739. See also Chem. Centr., 1907, i., 397. 

c* VVeinlahd and KtthI, Ber., 1900,39, 2951. See alsaZei#. anorg. Chem., 
1907, 64. 259. 

* Montoniartini, Gazz., 1892, 22, 384. 

* FiUgoAild, J. Amer. Chem. Soc., 1907, 2$, 1G93. 


STANNIC COMPOUNDS • 890 


a reaction entirely analogous to the production of stannates by 
the action of alkalis in aqueous solution: 

6KNHj + SnI, = Kj[Sn(NJI,),] + 4KI. » 

6KOH + Snli = lySn(OII)^ + tKI. 

If this is heated at 145°, it loses three molecules of ammonia, 
wliich is analogpus to the behaviour of potassium stannate 
trihydrate : N ^ 

KJSn(NH2)6j = KoSnCNHla + SNIL. 

K2[Sn(OH),] == KgSnOa + 

No more ammonia can be driven off by heifllTig for scvciHi 
houi-s at 316°. • 

Tin and Phosphorus . — ^Vhen finely-divided tin is heated in 
the vapour of phosphorus, a silver-white, very brittle nmss, 
having the composition SnP, is obtained. This has a specific 
gravity of 6*56, and dissolves readily in hydrochloric acyd, but is * 
not attacked by nitric acid. AVhen phosphorus is thrown on to 
the surface of mJlten tin, combination also takCs place. The 
coinpoun(J containing the largest quantity of phosphorus which 
can thus be obtained h^s a silver-white colour, is not ver}i 
brittle, and may be cut with a knife ; >t appears^ to possess the 
composition SnaPg (l^dletier).^ If spongy tin, obtained by 
precipitating a tin salt with zinc, be brought into contact with • 
suchta quantity of phosphorus that one atom of the latter be 
present to nine atoms of the metal, a phosphide having the 
composition Sn^P is obtained. The same compound is formed 
whenever any of the other phosphides containing more phos- 
phorus is heated. This is a coarse, crystalline mass, which has 
the appearance of cast zinc. It melts at 370°, and is tised for 
the preparation of phosphor-bronze. 

Stannic Pyrophosphate is obtained by the action* of phosphoric 
acid on stannic acid, and is insoluble in water and in nitric acid. 
This reaction is employed for the separation of phosphoric acid 
from other bodies. For this purpose a known quantity of 
tin foil is added to the nitric acid solution of the body under 
investigation, when the whole of the phosphoric acid remains 
behind with the metastannic acid. ^ 

^ See alHO Stead, /. Soc. Chem. 2nd., 1897, 16, 200, 309; and Jo^bow, Compt. 
rend., 1909, 148, %0. , 



900 


ms OERJIANIUM GROUP 


Detijction and Estimation i3f Tin. 

* f 

400 Wh%n a small quantity of a tin compound is held in 
the reducing flame on charcoal, a majleable bead of metal is 
obtained, which easily dissolves in hot hydrochloric acid. This 
solution gives with a small quanti^ of mercuric chloride a 
white precipitate whiclf becomes grey on boiling : ^ 

(I.) + 2HgCl2 - SnCl^ + HgA 

(11.) SnCl^ + HgA = SnCl^ + 2Hg. 

f 

one of metallic globules be fused in a borax bead 
slightly tinted with cupric oxide and heated in the reducing 
flame, the bead will become of a red tint, due to the formation 
of cuprous oxide. 

Stannous salts yield a brown precipitate of stannous sulphide 
t with sulphuretted hydrogen, which dissolves in ammonium 
wdphide* containing polysulphides; the solution, on addition 
of an acid, deposits stannic sulphide. Ammonia and caustic 
alkalis give a white precipitate of stannous hydroxide, which 
is solubhj in excess of the latter reagents. Stannoiih chloride 
*gives a blue coloration with ammonium molybdate, and in 
this \\'%y 1 jiSrt of tin as stannous chloride may be detected 
in 1,500,000 parts of solution.^ 

Stannic salts yield a yellow precipitate of stannic sulphide 
with sulphuretted hydrogen, readily soluble in ammonium 
sulphide, and alicalis precipitate stannic hydroxide, which 
dissolves in an excess of the precipitant. 

Zinc precipitates metallic tin from solutions of the»tin salts in 
the form of glistening scales, or in a spongy or arborescent mass. 
The tin salts do not impart any colour to the non'lumim)us 
gas-flame, but the spark spectrum of the chloride exhibits two 
characteristic lines having wave-lengths of 4526 and 5631 
(Lecoq de Boisbaudran). These same lines are seen together 
with others in the spark spectrum of the metal, the most brilliant 
of the*tin lines being as follows (Thalen) : 6452, 5798, 6631, 
5588, 5563, 4526. 

In the processes of qualitative analysis tin is obtained together 
with tlft)se metals which are precipitated by sulphurefted 
hjdrogen in an acid solution. To separate tin^rom these the 

* I.A>ng8tafT, N'eu'.y. 1899, 80. 282: J 

82. 220. 


DETEOnOK AND ESTIMATION 0F TIN 


90i 


well- washed precipitate is treated mth yello^iir ammohium 
sulphide, filtered, and the filtrate acidified with cold dilute 
hydrochloric acid. •The precipitate may contain, bei^lde stannic 
sulphide, the sulphides of arsenic and* antimony. After it has 
been well washed with water, it is digestec^with solid ammonium 
carbonate to dissolve the sulphide of arsenic. The residue is then 
dissolved in concentrated boiling hydrocWoric acid, the solution 
boiled with Metallic copper, and the liquid tested for stannous 
chloride with mercuric chloride (see also ixider Antimony). 

Tin may be estimated as the oxide. If the metal or one 
of its alloys be under examination, it is oxidised with pure, t 
tolerably strong nitric acid, and the well-v(|i8hed residue 
ignited. From solution it is precipitated with ammopia as tSe 
hydroxide, but if it be present m the form of stannous salt it 
must be first oxidised with chlorine or hydrochloric acid and 
potassium chlorate. The precipitate obtained by ammonia is 
then dissolved in the smallest quantity of hydrochloric acid and ^ 
heated with a concentrated solution of sodium sulphate, ^hen the 
hydroxide is again precipitated, and this is not gelatinous, and 
may therefore be easily washed (Lowcnthal). When tin sulphide 
is obtained in the separation of tin from the other metals, it can 
be gradually converted into stannic oxide by gentle roasting 
and subsequent ignition. • • ^ • 

Tin is frequently estimated by volumetric methods, the 
processes depending on the oxidation of stannous chloride to* 
stannic chloride by means of standard solutions of ferric chloride 
or iodine. • • 

The electrolytic method has been employed for estimating tin 
as the metel, the process being carried out in the presence of 
amMionium oxalate or some other organic salt.^ It may be 
deposited also from solutions in ammonium sulphide.* 

Atomic Weight of Tin . — The early determinations of the 
atomic weight of tin were made by oxidising the metal to the 
dioxide, but the numbers obtained varied considerably. Thus 
Berzelius* found the number 117*65, and Mulder an^ Vlaan- 
deren* 116*3, whilst a later determination by the last-named 
gave the higher value 118*16. Dumas* by the same method 
obtained the number 118*06. Bongartz and Classen ^ employed 
• • 

1 Engels, Ber., 1895, 28, 3182; UoUard, Compi. rend., 1897, 124, 1451; 
Fischer, Ber., 1902, 86, 2348; etc. * , • 

* Pogg. Ann., 1820, 8, 177. • J. pr. Chem., 1849, 40, 36. 

‘ %nn. Chem. Pharm., I860. 118, 20. » Btr., 1888, 21, 2900. 

• • 




902 


gHE GERMANIUM GROUP 


four different .methods, namely, the oxidation of pure tin mth 
nitric acid, and the electrolysis of potassium stannichloride, 
ammoniuri! stannichloride, and stannic bromide. The average 
of the most trustworthy experiments gave the number 119*0. 
Briscoe,^ by analysis/)! the tetrachloride, obtained the number 
118*7, which is now (1922) adopted.^ This number has been 
confirmed by Baxter ai^ Starkweathei,® by electrolysis of stannic 
chloride, and by Krepelka,^ by analysis of the Jetr^romide. 

LEAD, (plumbum) Pb = 207*20. At. No. 82. 

*' 401 The first mention of lead occurs in the well-known passage 

in the Book fMob, Chap. XTX, and it is mentioned also in the 
Book of Numbers, Chap. XXM, as a portion of the spoil taken 
from the Midianites. It is found under the name of 6 ph 6 ret, 
derived from the word Aphdr, signifying to have a grey appear- 
ance. In the oldest Creek translations of the Old Testament 
' the wor<J occurs, and this as well as the word fioXv^Bo^i 

undoubtedly refers to lead. It appears that no exact distinction 
was drawn beTwcon the metals lead and tin tturing the time of 
the Israelites, but we find that Bliny points out a distinction 
fbetween these two metals, inasmuch *as he gives the name of 
plumbum nigrum to lead, whilst tin is designated as plumbtmi 
candidnm ({)*872). Lead was known to the ancient Egyptians, 

, ^8 lead plates have been found in the Temple of Bameses III. 

It has already bc(?n stated that the seven metals known to 
the ancients were supposed to be in some way ^oimected with 
the seven heavenly bodies which were then known to belong to 
our solar system. Dull, heavy lead was apportioned to Saturn, 
and this metal is designated in the writings of the alcheijists 
by the sign L. 

Lead is seldom found in the free state in nature. Native lead 
does, however* occur in small quantities in certain lead ores, and 
in volcanic tufa. The oxides of lead are found in the form of rare 
minerals, the yellow oxide, PbO, and the red oxide or red lead, 
Pb 304 . The commonest ore of lead is galena or lead sulphide, 
PbS; this is very widely distributed, generally occurring to- 
gether with quartz, calc-spar, fluor-spar, and heavy-spar, in the 
older as^well as in the more recent strata, and in almost ewy 

' Journ, Chm. Soc., 1915, 107, 03. 

' Astoi^. 1922, 100, 813, has shown that there ar? eight isotopes of 

tin of atomic weights, 120, 118, 116, 124, 119, 117, 122, 121. 

» J. Amtr.Chem. Soc., 1920, 48, 905. * * Ibid., 925. 



LEAD 


§ 


903 


*part of the world. Thus in Cornwall it occurs in veins in the 
coarse argillaceous «chist, provincially termeij killas ; in Derby- 
shire, Cuihberland, •Northumberland, and Yorkshire, it is found 
in mountain limestone; in CardigansBire and Montgomeryshire 
it occurs in the Lower Silurian; and fht chief deposits in the 
United States likewise occur in the same formation. Again, 
at Sala in Sweden, it isifoiind in graiyilar limestone, and in 
Freiberg in^ *cliistose gneiss, older than the carboniferous 
system. Enormous quantities of galena,* closely associated 
with zinc blende, occur in the Broken Hill deposits of Australia, 
in Burma, Rhodesia, etc. Sulphide of lead also occurs in com- * 
bination with the sulphides of antimony ancWopper in the 
minerals zinckenite, PbSb2S4, and bournonite, CuPb8bS3. In 
addition to these ores, lead carbonate occurs as the mineral 
cerussite, PbCOg, found in some localities, as in the neighbour- 
hood of Aix-la-€hapelle and of Santander in Spain, in sufficient 
quantity to be worked. It is also found in the lead mines of • 
Cornwall and Devonshire, in Yorkshire, at Leacfliills in 
Scotland, and at^cven Churches in County Wi#klow. Other 
naturally occurring compounds of lead are the basic chloride, 
occurring •as the minerals* mat lockite, Pb2Cl20, and mendipite,^ 
Pb3Cl202, and the sulphate of lead or anglesite, PbSO^, found 
associated with galena and carbonate of leacf ^t Leadhills 
and in other localities. Again, W'e have a basic sulphate called^ ^ 
lanarkite, Pb0,PbS04; leadhillite, PbS04,3PbC03 ; phosgenite* 
PbCi2*PbC03; stolzite or lead tungstate, PbW04; wulfenite 
or lead molybdate, PbMo04 ; crocoisite or lead Miromatc, PbCr04 ; 
pyromorphite or lead phosphato-chloride, SPbgPgOgjPbClg; 
mimetesite <or lead chloro-arsenate, 3l^bgAs208,PbCi2 ; as w’ell 
as impounds of lead with the rarer elements, ^ich as 
selc^um, tellurium, selenic acid, vanadic acid, etc. 

By far the greater quantity of the total lead •brought into 
the markets of the world is derived from galena. 

402 Smelling of Lead.— Lead is an easily reducible metal 
requiring but simple processes for its prodtiction, anddt w^as 
pr^uced in England during the Roman occupation in a Variety 
of localities. Numerous pigs of Roman lead have been found 
bearing Latin inscriptions. Whether lead was reduced in 
En^and before this period appears doubtful; the renfains of 
rude furnaces ip which lead ore was smelted in times 
are, however, found in Derbyshire and elsewhere, and are 
termed boles by the inhabitants. In these furnaces* the heat 




*HK GERMiUniJM GROUP , 

was not urged by an artificial blast of air, but piles of stone were 
built on the westejn brow of some eminence»so as to employ the 
natural currents of air on mountainous places^ A mixture of ore 
and charcoal was introduced into the interior of these furnaces, 
the lead being run out at the bottom after the operation. 

The form of furnace next employed was the ore-hearth^ a small, 
rectangular blast-furnace blown by billows worked by means of 
a water wheel. ^ Modifications of this furnace are^ill in use in 
certain localities. * * 

About the middlj of the eighteenth century lead smelting in 
reverberatory furnaces appears to have been introduced into 
England froitijflintshire, where it was in use in the year 1698. 

Three distinct processes are employed for lead smelting. The 
first of these, known as the air reduction process (Percy), is 
employed when the ore consists mainly of galena, and is free 
from silica and the sulphides of other metals. The second, or 
carbon reduction process, is employed for less pure ores and 
consists in the roasting of the ore and the subsequent reduction 
of the lead o.wde by carbonaceous matter. The third process is 
known as the precipitation process, the reduction of the lead being 
effected by metallic iron; this is chiefly practised In France, 
(icrmany, Spain, and North America, where the ore contains 
other metat, such as copper, antimony, and arsenic. It is 
however, to be remembered that two or even three of the above 
processes are often worked in the same furnace with the same 
charge of ore. • 

In the air redu&ion process the galena is roasted in a reverber- 
atory furnace until a portion of the sulphide is converted into 
oxide and sulphate ; the temperature is then raised, when 
metallic lead is formed together with sulphur dioxide. • The 
following reactions are usually given as representing the inter- 
action of the tinaltered lead sulphide with the oxide and sulphate : 
2PbO 4-PbS = 3Pb + S02. 

PbSO^ + PbS = 2Pb + 2 SO 2 . 

In presence of an excess of sulphur dioxide, however, lead is 
partially reconverted into sulphide and sulphate : * 

2 Pb+ 2 S 0 a-PbS+PbS 04 . 

“Description of Lead-Smelting in the Koifh of 
4ngland^. •Transactions of the Natural History Society of Northumberland, 
and ^ewcas(h•on^Tync, vol. 2, part i.; also J. J. Brown, jun., “ Load 
Smelting in the Ore-Hearth,” Trans, Am. Inst. Jdin. Eng 1911 42 4Q2 

Z '’To!;?' iuL.i»ch. 




LEAD 


906 


The reverberatory furnaces used for the English process of 
lead smelting are of two kinds, the Flintshii^ furnace and the 
flowing furnace. The difference between these is tiat in the 
first the slag is raked out in pasty lumps, whereas in the flowing 
furnace the slag is tapped out in the moken state and termed 
run-slag. The reaction which takes place during the early stages 
of reduction is identical in both cases, but^ in the flowing furnace, 
metallic iroi!^s^added to assist in the reduction of sulphide of 
lead. 

Fig. 187 shows the construction of the Flintshire furnace. The 
usual charge of ore is 20 cwt. This is introduced by means of 
a hopper (T) in the arch of the furnace. Thiphearth of the 
furnace (B) is hollowed out as §hown in the figure to permit 



• Fio. 187. 


the lead to dow through a tapping hole into an iron pot placed 
in f»nt of the furnace. The charge is evenly spread c^ver the 
surface and gently heated, the ore being well rabbled at intervals, 
and the temperature carefully regulated by opening or closing 
the various doors, so as to maintain the mass as hot as is possible 
without causing it to clot together; a portion of the sulphide 
is oxidised to oxide and sulphate, and the mass thus prepared 
for the following stage of the operation. During this ^art of 
the process the summings from the lead run off from the previous 
operation, which consist chiefly of lead containing a little sulphide, 
arefUWed, and are quickly acted on by the lead oxide and Alphate 
with formation pf metallic lead, which is run off front the tap- 
hole and contains more silver than the subsequent portions of 
the lAetal. After about tyo hours the temperature i^ raised to 
a bright red*heat, the metal being formed in quantitv. whilst 



eo6 


fHE GEEMANIUM GROtJP 

~ - • 

from time to time, in addition to stirring the mass, a small 
quantity of lime i^ added to stiffen the unreduced portion. This 
part of the process extends over an hour, and then for three- 
quarters of an hour the* temperature is further raised and an 
additional small quantity of lime added, which besides lessening 
the fusibility of the mass also liberates any lead oxide which 
may have combined with the silica, ilnd allows it to be reduced 
by tlie lead sulphide. Finally, the furnace is r^iigfd for three- 
quarters of an hout to the highest attainable temperature and 
a sufficient quantify of lime added partially to solidify the 
slag, which is raked out, and the lead run off from the tap-hole 
m the usual aianner. 

The gmf slag obtained may contain as much as 40 per cent, of 
lead, and is further worked up in the slag-hearth, which is a 
small shaft furnace, or may be mixed in with the charge for the 
larger blast furnaces. 

Iteduclian of Lead in Blast Farnaces.—Thk is the method now 
most generally adopted, as it is suitable for any class of ore and 
the percenta^ of lead may be much lower than that necessary 
for the other methods, whilst the presence of silica to a certain 
.extent is not disadvantageous. For#ores such as those which 
occur in the Harx, where the galena is mixed with iron and 
copper pyriU'S, zinc blende, fahl-orc, bournonite, and zinckenitc, 
the blast furnace method gives the best results, and this is 
suitable also for the reduction of the oxides or carbonates of 
lead. The process for sulphide ores consists first in roasting 
to get rid of sulphur and then smelting the r(5asted ore with 
fluxes and reducing agents in the blast furnace. The roasting 
was formerly effected in heaps, in shaft furnaces or reverberatory 
furnacei, the latter being worked by hand or mechanically. 

Several new methods of roasting galena have been introduced, 
in which the*ore is mixed with lime, gypsum, oxide of iron or 
other material, damped and fed on to a small fire in a converter- 
shaped vessel, through which air is blown, ^ or fed on to some 
type of sintering machine such as is used in the various 
l)wighT:-Lloyd processes for down-draft roasting. The chief 
advantage of these processes lies in the fact that the product 
obtained is very suitable for blast-furnace treatment, but 

' Mineral Industry^ 1005, 14» 402; see also “ Lead-Smelting and Refhung„’* 
by W. B. Kigalls, published by the Engineering and Journal, 1900; • 

for “ Thb Theory of Blast Boasting of Galena,” see Bannister, Trans. Inst. 
Min. and Met., 1912, 21, 346. 

* Report «/ Seventh Intemat. Cong, App. diem., 1909, 111^.4, 20. * 



LEAD 


907 


besides this the cost is less, the losses of metal are less, and the 
production of fine material is greatly reduced. • 

The blast furnace mostly used for lea^ and silver-lead smelting 




Fia. 188. 


is rectangular in plan, about 44 inches wide and 1^4 inches 
long inside at tife tuyere level. Fig. 188 is a section of %uch a 
fumage, which comprises a crucible portion (A), a shaft (B), ex- 
bending from the crucible tb the feed-floor (C), and a stack from 




008 GERMANIUM GROUP 

the feed-floor upwards. The furnaces are water-jacketed about the 
lower portion or hosh of the shaft, these jackets being made of 
cast iron or of steel, aijd through them water circulates con- 
tinually. These jackets are shown at D, and through the side 
jackets the tuyeres (fi) pass into the furnace. The shaft above 
these jackets is lined with firebrick, although in the newer 
furnaces the water jadkets are carried to the top. 

An Arents syphon tap is often fitted to thetcnicible portion 
of these furnaces for continuously drawing oS the lead. When 
the ores contain oopper the roasting is not carried so far, a 
certain amount of sulphur being left in the ore to combine with 
the copper fofthe formation of a cupriferous matte, and in this 
case a certain amount of unaltered lead sulphide will always be 
present in the matte. The furnace charge consists of a mixture 
of roasted ore, carbonaceous fuel, generally coke or a mixture 
of coke and charcoal, old slags and fluxes. The fluxes most 
used ferruginous ores, often carrying silver or gold, which is 
collected partly in the lead and partly in the matte if this be 
also formed,'’ ferruginous slags containing aft excess of ferrous 
oxide, and sometimes lime or limestone. The slag should con- 
tain between 30 and 35 per cent, of fehous oxide, between 10 and 
30 pef cent, pf lime, and between 30 and 50 per cent, of silica. 
The lead present in the form of oxide is reduced partly by the 
carbon monoxide in the gases and partly by solid carbon ; that 
present as sulphide, by iron, generally formed by reduct on of 
the oxide of iron present in the charge. Any silicate present 
is reduced by the action of carbon in the presence of ferrous 
oxide or lime, and any lead sulphate present is reduced by 
reaction with sulphide, or is converted into sulphide by the action 
of carbon and this sulphide reduced by metallic iron. * 
Softening of Lead. — The lead produced in these processes is 
hard, owing* to the presence of small quantities of antimony, 
arsenic, copper, zinc, iron, tin, bismuth, and sulphur, and it is 
necessary to remove these in order to render the lead marketable. 
Silve^' is also generally present and is removed by special pro- 
cesses, which are described later, and which enable the silver to 
be recovered. It is also necessary to remove impurities before 
desilv^sation, as copper, antimony and arsenic interfere ^th 
the Pattinson process, and these, together with nickel and dbbalt, 
Interfere* with Parkes’s process. • - ^ 

For the purpose of removing the impurities, the lead is 
melted itt a reverberatory furnace at% low tempemture. Uopper 



LBAB 


forms an alloy with some of the lead which is less fusible than 
lead itself and this leparates out as a scum on the ipolten lead 
and may be removed ; all the other commonly occurring impurities 
except bismuth are more readily oxidised than lead and are 
oxidised in the furnace together with a portion of the lead, the 
mixed oxides forming a dross on the surface which is removed 
from time to tim^ Bismuth cannot be got rid of in this manner, 
but it is coiSieiitrated with the silver in the Pattinson process 
for desilverisation. The hearths of modern reverberatory 
furnaces for the softening of hard lead consist of wrought iron 
pans lined with two thicknesses of firebrick and are often water- 
jacketed at the sides to diminish the corrosive action of the 
oxides formed on the material composing the hearth. 

Condensation of Lead Fume . — During the smelting processes 
a large amoimt of lead fume is carried away in suspension in 
the waste gases from the furnaces, and many devices have been 
introduced for condensing and collecting these fuipes, for 
subsequent treatment. In many works the arrangement con- 
sists merely in hafing very long flues between the^furnaces and 
the chimney, the amount of condensation depending on the 
length of the flue. In o^her works more complete condensa- 
tion is effected by arrangements for lowering the jelocity^of the 
gases, by first passing thb exit gases through large chambers 
containing baffle plates, and then through iron flues cooled by, 
the (yr. Other methods for condensing the fume consist of 
using a water spray or causing the gases to pass through layers 
of water on their way to the chimney. “ Bag houses are largely 
used for the condensation of lead fume ; in the use of these, the 
cooled gases are forced through canvas or twill bags on their 
way Ho the chimney. Electrostatic methods of precipitating 
the fume have been introduced into some works. 

403 Desilverisation . — Ordinary lead obtained b;f any of the 
above-mentioned processes always contains silver, and a very 
considerable proportion of the silver which now comes into 
the market is obtained from argentiferous galena. Informer 
times the only process by which this silver could be extracted 
was cupellation, by which the whole of the lead is oxidised, 
whijst metallic silver remains behind. The oxide hy then 
to be again reduced to metallic lead. It is, however, generally 
admitted that the process o( cupellation cannot be ecohqjnically 
carried on in the case of lead which contains less than 150 oz. of 
silver to the Jx)n, and consequently, as very large quantities of 



910 


fHE GERJtANIUM GROUP 

— ”• 

lead are brought into the market containing smaller quantities 
than this.^a larga portion of this silver i^as lost until Hugh 
Lee Pattinson in the year 1833 obtained a patent for an improved 
method of separating silver from lead, which soon came into 
general use and by %vhich large quantities of silver are now 
extracted from lead. 

This method depenok upon the fifct that if lead containing 
a small quantity of silver be melted, and tjje belted mass 
allowed to cool, a point is reached at which pure lead begins 
to crystallise out. If the crystals of lead which are thus 
formed be then withdrawn from the remainder of the metal* 
and this procwis continued until the greater part of the lead 
has been separated, it is found that the liquid which remains 
contains most of the silver. In order to render this process 
economical the lead requires to be repeatedly crystallised in a 
scries of iron pots, the lead rich in silver gradually accumu- 
• lating towards one end of the series, whilst the desilverised or « 
market lead is obtained at the other end. 

The meltett lead is first thoroughly skimmed, then the fire is 
withdrawn and the lead allowed to cool, care being taken to 
.break of! and mix with the liquid mass any portion that may 
solidif;^ on the sides of the pot. When the temperature reaches 
a certain point small crystals of leadlicgin to form, and at this 
, point the whole mass of metal is continually stirred with an iron 
rod, whereby the crystals sink to the bottom of the pqf and 
accumulate in considerable quantity. A perforated ladle is now 
introduced by mfans of which the crystals are ‘removed. The 
operation is thus carried on in successive stages until two-thirds 
or even seven-eighths of the original lead is removed from the 
pot. Hy this means in an actual working 846 cwt. of original 
lead was separated into 36 cwt. of rich lead containing 16§ to 
170 oz. of 8il\'er per ton, and 810 cwt. of poor lead containing 
7 to 10 dwt, of silver per ton. The silver is then extracted from 
the rich lead by the process of cupellation (p 461). 

A modification of the Pattinson process, known as the Luce- 
Rozan process, is now frequently adopted in place of the original 
method. For this only two pots are necessary, viz., an upper or 
melting pot, and a lower or crystallising pot. The former holds 
about 7, and the latter about 21 tons. 

• The -^pfode of working the plant is as foUocsvs ^ : The crys- 
tallising pot may be supposed to contain 14 tons of lead 
^ Cookson, Trana. Newcastle C^em. Soc.t 1878.« 



011 


lead 

r • ' ’’ ' " 

U crystals from a prevkn^ operation, and the melting pot 7 tons of 
lead of similar silvef content, already melted^ a moderate lire 
is set away in the fire-grate of the crystallising poE, and the 
contents of the melting pot skimmed *of their dross; the hot 
lead from the latter is then run on the warm crystals in the 
crystaUising pot, and with the aid of the moderate lire already 
referred to, the whole coEftente of this pot (now 21 tons) are 
rapidly melteH ^d brought into a working condition, when the 
charge is carefully skimmed; the melting pot is at the same 
time charged with 7 tons of lead from a j)revious operation 
containing one-lialf the amount of silver in the lead then being 
worked up, as this will be the assjiy of the crystals resulting 
from the operation about to be performed in the crystallising 
pot. The fire under the latter is then drawn, and steam at fifty 
to fifty-five pounds pressure per square inch admitted and dis- 
tributed evenly by means of a baffle plate. To hasten the 
cooling and consequent crystallisation, thin streams of water 
are allowed to run on to the surface of the lead, the crystallisation 
being more perfect»than in the old Pattinson process. As soon 
as two- thirds of the lead has crystallised out, the rich liquid lead 
is tapped off, the crystals being retained in the pot by means of 
perforated plates. The liquid lead is run into moulds and awaits 
its turn for further treatment.'^ The proj)ortion of silver fn the 
crystals is thus reduced to one-half, whilst that in the liquid 
run off is doubled, and this process of recrystallising is repeated 
as in Pattinson’s process, until the crystals are sufficiently poor 
in silver not to 'require further treatment, anc^the rich lead is 
w'orked up until its silver content is of the standard fit for 
cupellation. ^ 

ThJi process has the advantage over that of Pattinson^hat a 
greab saving is effected in fuel and the cosji of labour, and also 
that, except in the case of very hard lead, no further softening 
process is necessary. The original outlay and expenses for 
repairs are, however, considerably greater. 

Another process for desilverising lead is known as Parkts’s or 
Karsten’s zinc process. Molten lead and zinc do not mix^in all 
proportions, lead being capable of taking only 1-6 per cent, of 
zinc, whilst zinc takes only 1*2 per cent, of lead, and Karsten, in 
1842, concluded from experiments which he made on the Subject 
that leml gives up all the silver which it contains if melted with 
zinc, but he did not apply this conclusion to practical metal- 
In thj year 18^ .Alexander Parkes, of Birmingham, 

vegi. n. (II.) 0 



f HE GERMANIUM GROUP 


• 

patented a process for extracting silver fijom lead bj the above- 
mentioned reactign. For a ton of lead dbntaining 14 oz. of 
silver, 22-1 lb. of zinc are needed and a proportionate amount 
if wore silver be present. The alloy of zinc and silver rises 
to the surface during cooling, and when it solidifies it is with- 
drawn by means of a perforated ladle. In order to remove 
the small quantity nof zinc whicll is dissolved in the lead, 
the mixture is heated to dull redness and stean^Mf)wn through, 
the zinc befing thereby oxidised, whilst the main portion of the 
lead remains behiqd in the marketable state. The zinc-silver 
alloy is first heated to a temperature slightly above the melting 
point of leadAo liquate as much of the latter as possible, and 
the residue is heated with carbon in a crucible retort, whereby 
the zinc is distilled off and collected, the residual rich silver- 
lead alloy being cupelled in the usual manner. 

Gold and copper, which sometimes occur in market lead, can 
be sepa^rated from it in the same way, inasTuuch as these metals 
alloy with zinc even more readily than does silver, and this pro- 
cess has be«i satisfactorily carried out in England by Baker. 

A similar method is employed in the Harz; the lead is there 
melted with 0*10 per cent, of zinc, and the alloy is obtained as 
a scum on the surface, having the composition : 

Zn di Ag 

89*40 5*78 4*52 0*243 

On a second addition an alloy having the following comp?)sition 
is obtained : ^ 

^’0 Zn Cu Ag 

^1'05 5*21 3*50 0*238 

Market lead almost always contains traces of antimony, 
copper, and iron, and occasionally of zinc, nickel, and bisrfiuth* 
whilst the silver which it contains varies from 1 part in 40,000 
to 1 part in 200,000, but since the introduction of the method 
of desilverising by zinc and purification by steam the purity 
of thf commercial lead has very much increased. 

Elect ro-refimvg of Zead.^— Various attempts have been made 
from time to time to refine lead by an electrolytic process, but 
until Betts invented his process in 1901, no great su^ss 
was attained. In this process, the electrolyte consists of lead 

^ Haiuniolsbcrg, Ber. Entu\ Chem. /nd., 9.35. 

• ^ defining hy EUcirolym, by A. G. Bett« (John WUey & Sons. 

liMiS). I* _ •' i * 



fluosilicate solution ; the anodes are cast of the crude lead and 
the cathodes of pure lead. In order to obtain solid ^leposits of 
ead, the use of addition agents to th§ electrolyte is necessary; 
and in the process gelatine is mostly used, in the proportion 
of 1 part of gelatine to 5, 000 parts of solution. The impurities 
remain in the anode slime, and pure lead is deposited at the 
cathode, as showj;! by the following tabled 

% Cu Bi As Sb Pb 

Crude lead 1-40 0-14 7-4 4*0 0‘64 87*14 

Pure lead 0-001 0-0022 0-0025 0-8017 

Anode slime 9-3 0-52 44-58 25-32 4-7 10-3 


The following tabic shows the ])roductioii of lead in 1919, by 
the chief lead-producing countries in metric tons : ^ 


Australasia . 

. . 82,732 tons 

Belgium . 

. . . 4,157 „ 

Canada 

. . . 19,500 „ 

France . . . 

• 

. . . 10,928 ^ 

Germany . 

. . . 50,700 „ 

India .... 

. . . 19,090 .. 

Italy . . . • . 

. . . 10,264 

Mexico . ^ . 

. . . 70,229 

Spain .... 

. . . 99,912 „• 

United Kingdom 

. . . 13,100 „ 

United States . 

. . . 385,082 „ 


404 Chemically pure lead is prepared accoifling to Stas ^ as 
follows :—A solution of acetate of lead is heated in a leaden 
vcsvsel in coiftact with thin sheet lead to a temperature of from 
40” t<f 50” in order to precipitate silver and copper. The titrate 
is then poured into pure, very dilute sulphuric acid, and the 
lead sulphate formed carefully washed with absolution of 
ammonium carbonate and ammom'a, and thus converted into 
lead carbonate. A portion of this is then converted into lead 
oxide by carefully heating in a platinum basin, whilst to the 
remaining portion pure dilute nitric acid is added in such 
quantity that a portion of the carbonate remains undissolved, 
rhe oxide of lead is then added to the boiling solution of the 
litrate in order to precipitate traces of iron, and the Altered 
olution poured into one of pure ammonium carbonaffe; The 

‘ Ifiperial Mineral Resources Bureau,’ Statistical Summary, 1921. 

• Bull. Acad^roy. Belg., IStW, 10 , 296. * 




qfe GERMANIUM GROUP 


precipitated lead carbonate is then reduced by means of 
potassium <;yanide* and the metal thus formed fused a second 
time with the cyanide, A\hen it assumes in the molten state a 
convex surface like mercury. 

Lead, purified by Stas’s method, has been distilled in a vacuum 
at about 1200'^ in quartz vessels 1w Lambert and Cullis^; 
before the admission of air it has a orilliant metallic lustre. 

Properl ies and Uses of Lead . — Cohen and other/ have shown 
that lead probably exists in two allotropic forms; this has been 
confirmed by Jiinccke, who finds a transition point at about 60° 
by the study of temperature-pressure curves.® 

* Lead can edSily be crystallised in the form of regular octa- 
hedra by melting, allowing the molten metal partially to solidify, 
and pouring off the portion which is still liquid. Similar crys- 
tals are obtained by the electrolytic decomposition of solutions 
of lead salts, using a strong current, but with weak currents plates 
belonging probably to the monoclinic system are formed. It 
is also deposited at the cathode by the electrolysis of dilute 
sulpliuric acid with lead electrodes, sometimes in the spongy 
form consisting of microscopic needles, and sometimes in 
plates.® Similar crystals to these separate out in bright, shining, 
arborescent f^rms, known as the lead tree, if a piece of zinc be 
hung up iA a solution of lead acetate. Lead has a specific 
gravity of 11-254, or, after it has been poured into water, of 
11-363. On hammering it cracks and becomes lighter, bii;b if it 
be pressed it attains a specific gravity of 11-388. Richards and 
Wadswortli found that lead, purified by recrystallisation of the 
acetate and tlie chloride, prepared by electrolysis and fused in 
pure charcoal vessels in an atmosphere of hydrogen, has a density 
of 11-367 at 20'\^ Its atomic heat is 3-06 at — 250°, 4-48 at 
— 236°, and ^5-70 at — 188° (Kamerlingh Onnes and Keesotn ®); 
at higher temperatures it increases more slowly and Dulong and 
Petit’s law is obeyed. Thus, at ~ 73° it is 6-13, at 0° 6-31, 
at 136° 6-61. Its average compressibility between 100 and 500 
megabars is 0-000,002,2 (Richards and Stull).® It is soft and 
tough, may be cut with a knife, and leaves a streak upon 

• Journ. Chem. Soc., 1915, 107, 210. 

• ZeiL pSynikal Chtm., 1916, 90 , 313. c • 

» Elbs and Rixon, Zeit. Kiektrochem., 1903, 9 , 206; Haber, Zeit. anorg. 
Chem., ^18'98, 16 , 438. See also Hughes, J. Phy/t 'cal Chetx., 1922, 96 , 316. 

• J. Amer. Chem. Soc., 1910, 86, 221. 

• VerAlag. K. Akad. WeteMchappen, 1914, 93, 792. 

• Pub. Cam, Inst., 1907, 70. * c 



LEAD AND OXYGEN 9W 

• 

paper. It can easily be rolled out to thin foil, but it cannot be 
drawn out into fitie wire. The presence pf antimony, zinc, 
bismuth, t^enic, and silver increases the brittleness of lead. 

> Lead belongs to the class of white metals, though it has a decidedly 
bluish-grey tint indicated by the ex]w*esSion lead-grey. A 
freshly cut surface possesses a bright lustre, which, however, 
soon becomes dull from tuperficial oxi^tion. By tlie electro- 
lysis of leadn nitrate Wohler obtained a deposit on the negative 
pole of crystallised leaflets of lead possessing a red colour like 
that of copper. These did not dissolve in dilute acids, whilst 
they w'ere soluble in hot nitric acid, and, on dissolving, the colour 
resembled that of copper to the last moment. Lead melts ^t 
327°, and boils under atmospheric pressure at about 1525° 
(Greenwood).^ Its vapour density has been measured at 1870° 
by von Wartenberg ; ^ its molecular weight has been measured 
by the depression of freezing-point method in mercury solution 
by Ramsay ^ : from both results it is found to be monatomic. * 
Lead has been obtained in the colloidal form by reducing 
a solution of the dichloride with hydrazine hydrate in the cold.® 
Metallic lead is largely employed in the arts for a great variety 
of purposes on account pf its softness and pliability, its low^ 
melting point, the difliculty with which it undergoes oxidation 
at ordinary temperature.^^ and the fact that it Vj^hstalids the 
action of water and of many acids better than most of the 
common metals. 

Tffe most important alloys of lead are those which it forms 
with tin, which have been described under th*t metal (p. 880), 


COMPOUNDS OF LEAD. 

Lead and Oxygen. 

405 Lead forms five compounds with oxygen :* 
Lead suboxide, Pb-^O, 

Lead monoxide, PbO, 

Lead sesquioxide, PbjOg, 

Red lead, Pb 304 , 

Lead dioxide, PbOg. 

* Ann. Chetn. Pharm. Supjd., 1803, 2, 135. 

* Proc. Roy. Soc., 1909, g2, [A], 1680. 

* iteit. anorg. Chetn.f 1908, W. 320. 

^ Zeit. physikal. Chetn.^ 1889, 3, 359. 

Catbier, Ztit. anorg. Chetn.f 1902, 31, 448, 




916 


SHE GERMANIUM GROUP 


The most important of these is the strongly basic monoxide, 
which corresponds^ to the chief series of salts, in which lead is 
divalent, ^he dioxide acts as a weak basic oxide towards 
strong acids, as an acidic oxide to strong bases, and also behaves 
in many respects as a peroxide. The sesquioxide and red lead 
are probably salts formed by the combination of the basic 
monoxide and the acidjc dioxide (p. ftl8). 

Lead Monoxide^ PbO. — This compound was^ known to the 
ancients, as it is formed when lead is heated in contact with the 
air, and is, therefore^ produced in various metallurgical processes. 
The different forms of this compound were, however, regarded as 
djfferent substiyices, giving rise to the names j)lumlm 7 n ustum, 
scoria pln7nbi, scoria arijenti^ galoia, fioXvjShaivaf \i$dpyvpo<i, etc. 
When lead is heated to its point of volatilisation in the air, it 
takes fire and burns with a white light, yielding this oxide, 
which formerly received the name of flowers of l(‘ad or flares 
plu7nhL Lead, when heated in the air, becomes covered with 
a grey film, and if the surface be continually renew^ed, becomes 
wholly convicted into lead-ash, a ycllowisl> grey, pulverulent 
mixture of metallic lead and yellow monoxide, which, if heated 
^in tile air for a longer time, is v^holly converted into the 
latter. This yellow oxide is termed 77mssicot, whilst the other 
form (fi lead fnonoxidc, termed hthange, is obtained at a tem- 
.perature at which the oxide fuses, solidifying to a scaly, shining 
mass sometimes yellowish, sometimes inclined to red. 

Crystallised oxide of lead also occurs in nature as a mmeral 
found near Ven> (Vuz (Nr)ggerath). The crystals may be 
artificially obtained by allowing litharge to cool slowly; it 
forms rhombic octahedra, which are sometimes also found as a 
depositjjin the lead furnaces (Mitscherlich), and red, tetragonal 
crystals may also be obtained ((leuther). Lead oxide possesses 
a colour varying from lemon-yellow to reddish-yellow, and on 
heating assumes a brownish-red tint. Its specific gravity at 4° 
is 9*30 (Joule and Playfair). It is reduced to the metallic state 
by carbonic oxide at 100^ by hydrogen at 310^ and by carbon ^ 
in an Atmosphere of nitrogen at 550°. Litharge is largely used 
in the arts, especially for the manufacture of flint glass, and 
as a glaze for earthenw’arc ; it is used also for the preparation 
of red lead, lead acetate, lead nitrate, white lead, lead planter, 
and drying oils. Commercial litharge contain!^ carbon dioxide 
and water absorbed from the air, but they may be removed by 
t » Doeltz and Graumonn, MMurgit, 1907. 4 . 420. ‘ 




917 


LEAD AND OXYGEN * 


ignition. Not infrequently it contains small quantities of iron 
oxide and copper ojfide, the latter easily remoyable bj ammonia. 

Bask Lead Hydroxide, Pb20(0II)2.~Thi8 substance is 
obtained as a white precipitate by the action of air and water 
free from carbonic acid upon the metal, o% is thrown down as a 
white precipitate on the addition of ammonia or a fixed alkali 
to a lead salt; ^lis, howe’er, dissolves in a large excess of the 
reagent and t^e solution contains a jdamhiie, H-PbO-OR, in 
which the normal hydroxide acts as a weak monobasic acid.^ 
The basic hydroxide is obtained in colourlesi^ tetragonal crystals 
by exposing a cold solution of lead monoxide in caustic potash 
to the air, the carbon dioxide in the latter conveiting the caustic 
potash into potassium carbonate. 

The compound Pb3()2(OH)2 is formed according to Payen as 
follows : — 100 parts of a solution of basic acetate of lead, 
J^atu rated at 1G°, are added to 50 volumes of 
cold water which has previously been well boiled: admixture 
of 20 parts of ammonia and 30 parts of boiled water is then 
added, and the scflution allowed to stand at 25-30°, when the 
above hydroxide separates out in glittering octahedra. 

At 130° lead hydroxide loses a portion, and at 145° the whole,, 
of its water, being then converted into lead oxide. The 
hydroxides of lead as \\^*11 as the oxide turn mw.stened red 
litmus paper blue, as they aie somewhat soluble in water. Thejr* 
act strong bases but also combine with certain basic oxides. 
Thus when lead oxide is fused with the alkalis, alkaline earths, 
and other metallic oxides, a glass is formed, aftd, in consequence 
of this, lead oxide attacks clay crucibles. It di.ssolves also in 
caiLstic potash and soda as well as in lime and baryta water, 
yielffing yellow liquids. The calcium compound is ^slightly 
soluble in water, and crystallises in white needles on cooling. 

Lead Suboxide, Pb20, is formed when lead oxafate is heated 
in an atmosphere free from oxygen to a temperature below 300° 
(Dulong) : 

2PbC204 = Pb^O + CO + 3CO2, 

01 when lead oxide is reduced by CO at 300°.* It is a black, 
irel;^ety powder of specific gravity 8*342 at 18° (Tanjpann),* 
vhich, when heated in absence of air, or treated with caustic 

t 

1 Hantzsch, Zeit. anorg. Chem., 1902, 90, 289. 

* Brislee, Joum. Chem. Soe., 1908, 93 , 154. 

• * Zeit. anorg.'jChein.f 1901, 97, 304. 




918 


♦he germanium group 


soda Of acids, is decomposed into the metal and the monoxide. 
When lea(J is melted in the air the surface becomes covered 
first with a grey film, which, according to Berzelius, /consists 
of the suboxide. The suboxide has by some been considered 
to be an intimate •mixture of finely-divided lead and the 
monoxide. Against this view, however, is to be placed the 
fact that mercury ddcs not dissol's^ metallip lead from this 
grey powder, whilst a solution of sugar, which jiea^ily dissolves 
lead monoxide, does not take up any from this substance. After 
heating, dilute acetic acid or a solution of sugar does dissolve 
out lead oxide, whilst metallic lead remains behind in the 
ftoherent state.* CV)ld 10 per cent, sodium hydroxide decomposes 
it, forming sodium plumbite and metallic lead. 

A whole seri(?s of monovalent lead salts has recently been 
described by Denham. ^ By the action of methyl iodide, bromide, 
and chloride on the suboxide, the corresponding subhalide, 
Pbl, Pyir, or PbCl was obtained. They are sparingly soluble. 
The subacetate, PbCyiyOg, and the subsulphate, Pb2S04, are 
produced by**thc action of acetic anhydride aftd methyl sulphate 
on the suboxide. 

Lexui Smjv m'ide, PbgOg, is formed ♦when a solution of sodium 
hypochlorite is carefully added to a cold caustic potash solution 
of lea^ oxi^c (Winkelblech), or when a solution of red lead in 
acetic acid is precipitated by very dilute ammonia. The action 
of potassium plumbite on potassium plumbate produces ^ pre- 
cipitate of hydrated lead sesquioxide of composition PbgOgjSHgO 
or Pb[Pb(Oil)4].* ^ reddish-yellow, amorphous powder 

whicli does not part with the whole of its water at 150°. It is 
decomposed by acids into the monoxide and dioJtide, and is, 
therefore, considered to be a compound of the§e two, Pb0,Fb02, 
and may bo termed lead metaplumbate. • 

Red Lead Or Minium, Pb304. — This compound was described 
by Pliny, under the name of minium, but it was at that time 
not sufficiently distinguished from cinnabar and the red sulphide 
of arsenic. Dioscorides, however, mentions that it can be pre- 
pared from white lead ; “ cerussa, si coquaiur rufesdl ” ; and 
Geber says : “ plumbum aduritur et fit minium'^ 

Red lead is usually prepared by carefully heating very finely- 
dividei pure massicot or ^hite lead. For this purpose the oidde 
is hea^^cd'for about twenty-four hours either on the flat hearth 

» Jonm, Chem. Soc., 1917, 111, 29; 1918, 118, 249; 1919, 118, 109. 

* BoU^iooi and Farravano, Zeit, anorg. Chem., 1906, 80, ji07. 



IMAD AND OXYGEN t 


019 


of a reverberatory furnace, or in barrel-shaped vessels open at 
both ends, the masi being frequently stirred .and the heat not 
^ allowed to rise above dull redness (about 400°). The 'brightness 
and beauty of the colour depend much on the care spent on 
the roasting, as these properties are influenced especially by the 
particular molecular condition of the material, and this is 
produced only at,a given fferapcrature. • 

Bed lead i5 % scarlet, crystalline, granular powder, which, on 
heating, first assumes a finer red colour and afterwards turns 
violet, and lastly black, but on cooling regains. its original tint. 
When more strongly heated, at about 470°,^ it loses oxygen and 
is converted into the monoxide. Its specific gravity varies froiu 
8*6 to 9*1. Commercial red lead frequently contains the yellow 
oxide, litharge, mixed with it, which may be extracted by 
repeatedly dige.sting with a solution of lead acetate. Red 
lead is largely used as a paint and also in the preparation of 
flint glass. For both these purposes it is necessary that it 
should be as free as possible from iron, and in this case it is not 
infrequently prepated from white lead. Red lead^s also adul- 
terated with oxide of iron, red bole, powdered heavy spar, 
and brick dust. These mibstanccs remain undissolvcd when ^ 
red lead is digested in warm dilute nitric acid to which a little 
sugar has been added, whilst the red lead is cJis^^ilved com- 
pletely. Boiling hydrochloric acid extracts sesquioxide of iron . 
from^the impure oxide with formation of lead chloride and 
liberation of chlorine. Like the sesquioxide, it is decomposed 
by acids into the monoxide or a corresponding salt, and the 
dioxide, and is therefore regarded as a compound of two molecules 
of the formbr and one of the latter, 2 Pb 0 ,Pb 02 , and may be 
termed le/id orlhophfnbale. • 

L^ad Dioxide^ Lead Peroxide^ or Pace-cohured Oxide of Lead^ 
PbOj. — This substance was discovered by Scheele, who observed 
that red lead is coloured brown when treated with chlorine 
water, whilst Priestley found that nitric acid produces the same 
reaction. The properties of the puce-coloured lead oxide were 
more exactly examined by Proust and Vauquelin. 

Lead dioxide may be prepared according to a variety of 
me^ods. The simplest plan is to act upon red lead with 
dilute nitric acid ; 

PbjO, + 4HNO, = PbO, + 2Pb(NO,), + 2HjO!‘ * 

• 1 Hilbauer, Ckm. Zeit., 1900, 88» 960, 960. 



■ittt:* /NWDif a \rnTM’ /IP/ITTP 



It is likewise obtained by the action of chlorine upon lead salts 
in the presence o^ alkalis (Wohler), or by tearing a hot solution 
of a pure ‘lead salt with a soluble hypochlorite (Bottger) : 


PbO ^ NaClO = PbOg + NaCl. 

It is also prepared by the electrolysis of a solution of sodium 
chloride, in which litlfarge is suspended.^ « 

It is obtained in the dry way by fusing 4 parts df lead monoxide, 

1 part of potassium chlorate, and 8 parts of nitre (Liebig and 
Wohler). Lead oxide is also converted into the dioxide by the 
iction of ozone as well as of hydrogen peroxide. It is deposited 
It the positive pole when a solution of a lead salt in nitric 
icid is decomposed electrolytically.^ 

This substance is found native in the form of plattnerite, 
vhich crystallises in black, hexagonal prisms having a specific 
gravity of 9-4. The artificial dioxide sometimes assumes the 
orm oi brownish-black, six-sided tablets, but generally consists • 
if a dark brown powder having a specific gravity of 8*9 to 9’2. 

Lead dioxide decomposes on heating intt) oxygen and the 
nonoxide. It loses oxygen when simply exposed to sunlight, 
ed lead being formed. It has a stit)ngly oxidising action, and 
vhen |ritura1^d with one-sixth of its weight of sulphur, it takes 
ire and biftns with a brilliant flame,* forming sulphide of lead.* 
Aqueous hyj)ophosphorous acid is at once oxidised with formation 
d lead phosphate. When exposed to sulphur dioxj^e at 
)rdinary temperatures it becomes red hot and is converted into 
lead sulphate, >vflilst nitrogen peroxide and even ammonia con- 
vert it into lead nitrate. A large number of organic acids and 
other carbon compounds when triturated with it likewise cause 
evolution of light and heat. AVlien treated with hydroAloric 
acid, chloride of lead and free chlorine are formed. • 

Lead dioxide is often employed as an oxidising agent, as, for 
instance, in the analysis of organic substances containing sulphur, 
in order to separate the sulphur dioxide from carbon dioxide. 
The ij^xture of nitrate and dioxide, termed oxidised red lead, 
obtained by treating red lead with nitric acid, is employed in 
the manufacture of lucifer matches. 

Lea^ dioxide is capable of acting as a weak basic opde, 

' FabrtJI:, Griejihetm-E'kliron, German Patent, 124512. 

• Wofman, Zeit. Elektroebetn., 1897, 3, 537 ; HoUard,^ Compt. rend., 1003, 

186, 220, and others. ^ 

* Vauquelin, Ann. Chim, Ph^e., 1807, 63, 221. , 



LEAD Am OXYGEN t 


921 


yielding the unstable tetravalent lead salts, and also as a 
peroxide and an ^cid-forming oxide, formiijg compounds to 
which the name flumhaies has been given. Orthophimhates 
having the composition M^4Pb04 and metaphmhaies, M'gPbOg, 
are known, ^ and the free meiaphmhic •add, PbO(()H)2 or 
HgPbOg, is deposited at the positive pole as a black, lustrous 
substance on the^electrolyfts of a slightlf alkaline solution of 
lead sodium tar^ate. 

The orthoplumbates of the alkaline earths are obtained by 
heating the carbonates or hydroxides with^lead monoxide in 
presence of air, the calciimi salt, Ca2pb04, crystallising with four 
molecules of water in almost colourless, microscopic, transparenU 
crystals. Those compounds evolve oxygen on strongly heating, 
and it has been proposed to utilise this method for obtaining 
oxygen from the atmosphere on the large scale; the calcium 
salt has also been used as an oxidising agent.- 
The hydrosol of hydrated lead i)eroxidc (plumbic acjd) has 
been ])repared by the dialysis of potassium plumbate.® 

Potassium Metaphmhate, KgPbOgjSIfgO, is obtained in crystals 
by fusing lead dioxide with excess of caustic potash in a silver 
crucible, dissolving in wat 4 ?r, and evaporating in a vacuum.^ ^ 
The solution gives with most metallic salts precipitates of the 
corresponding inetaplumbaiies. m * 

Calcium Melaplumbale, CaPb03,4H2(), is obtained by digest- , 
ing the orthoplumbate with sodium peroxide and water, and 
from this other metaplumbates have been obtained.^ 

As already mentioned, lead sesquioxide and*red lead may be 
regarded as the metaplumbate and orthoplumbate of lead, 
their constitution being represented by the formula) Pb^PbOg 
and !Pb2”Pb04. Lead metaplumbate has been prepared from 
the calcium salt and is identical with the sesquioxide.® 

When calcium meta- or ortho-plumbate is heated in dry air 
it 250 "^, calcium perplumbale, CaPbgOg, is formed.’ 

^ Compare Bollucci, Alti It. Acend. Lincei, 1905, [5], 14, i., 457. 

‘Kasaner, ^rcA. 1890,228, 109; 1894,232,375; 1895, 288, *^1. 

• Bellucci and Parra vano, Atli R. Accad. Lineci, 1900, [6], 15, ii., 642. 

* Ann. Chim. Phy«., 1^, [3], 12, 490. 

* Qrfitzner and Hohncl, Arch. Pharm.^ 1805, 238, 512. 

• Uphnel, Arch. Pharm., 1896, 233, 601. 

» Kaasner, Arch. Pharm., 1899, 287, 409; 1900, 288, 449. 



iTHE GERMANIUM GROUP 


Lead and Hydrogen and the ^Halogens. 

406 Lehd Hydride— The existence of a volatile hydride of 
lead was first suspected from the behaviour of one of its radio- 
active isotopes. Atlerapts to prepare this compoimd from ordi- 
nary (non-radioactive) lead, by the action of acids on its mag- 
nesium alloy, failed:^ but Paneth %nd Norring have succeeded 
in obtaining it by a combined electrolysis-s^ark . process. The 
electrode gases contain small amounts of a vflatile hydride of 
lead of unknown composition, which can be condensed by liquid 
air and which re-evaporates without decomposition. When 
j)assed througji a heated Marsh tube, it is decomposed, with the 
formation of a dull grey deposit of lead.^ 

Lead Fluoride, PbF 2 .-”-This compound is obtained by heating 
lead oxide or carbonate with hydrofluoric acid, or by preci- 
pitating a lead salt with a soluble fluoride. It is a white powder, 
almost insoluble in water and in hydrofluoric acid, but fairly 
soluble in hydrochloric and nitric acids. When treated with 
ammonia, an easily soluble basic fluoride is fqrrned. If a solution 
of lead chloride be precipitated with sodium fluoride, the com- 
pound PbOlF is formed. The fojmatioii of this compound 
has been confirmed by the thermal analysis of the system 
PbCli-PbJfg/ and a second compound, PbC'lg.IPbFg, detected. 
The chloro-fluorido of lead (PbClF) is shghtly soluble in water, 
dissolving without decomposition (Berzelius). 

Lead Tetrafluoride, PbF 4 .— This compound is probably *iormed 
by the action oftdrong suljdiuric acid on the acid plumbifluoride, 
SKFjHFjPbF^, but has not been obtained in the pure state. 
The foregoing double salt, which is isomorphous with the analo- 
gous tin derivative, is obtained by the action of hydrofluoric 
acid and potassium fluoride on lead tetracetate, or by fusing 
lead dioxide with potassium fluoride and treating the product 
with hydrofluoric acid. It forms monoelinic needles which 
evolve hydrogen fluoride at 230®, and at a higher temperature 
yielcLfree fluorine.® 

ZAm? Chloride, PbClg.—Dioscorides mentions that yellow 
oxide of lead when brought in contact with common salt and 
warm water becomes white. After the discovery of silver 
chloride, to which the name of horn-silver was given, thi cor- 

^ iU«>«<rl920, 68, [H], 1093. See also Paneth, Matthiea. and Schmidt-Hebbel, 
- Her,, f922, 66 . [H], 776. 

* Sandonnini, AUi B. Acead. Lineei, 1911, [6], 20, i., 172. , 

* Brauiier, Joum. Chem, Soe., 1894, 06, 393. . 



USAP Alfe HYDROGEN AND THE HALOGENS 923 


responding lead compound was termed horn-lead (plumbum 
comeum). Lead chloride occurs native in the craters of vol- 
canoes as the mineral cotunnite. Lead combines with chlorine, 
but slowly, and without incandescence. Dilute hydrochloric 
acid dissolves the metal only in the presence of air, and then 
but slowly. The boiling concentrated acid, however, con- 
verts it into chlcyide with* evolution of •hydrogen gas. Lead 
chloride is easily* prepared by the action of hydrochloric acid on 
the oxide or carbonate, and also by the precipitation of a toler- 
ably concentrated solution of a lead salt by means of hydro- 
chloric acid or a soluble chloride. It is thus obtained in the 
form of a white, crystalline precipitate, of which 100 parts ojh 
water dissolve 0*909 part at 15°, and 3*2 parts at 100°. The 
salt crystallises, when a boiling solution is cooled, in white, 
silky, rhombic needles, having a specific gravity of 5*8. It 
is less soluble in dilute hydrochloric acid and solutions of 
chlorides than in pure water, but dissolves more frijely in 
concentrated hydrochloric acid; hence a precipitate may be 
obtained by addiifg water to the latter solution* • whilst the 
aqueous solution is precipitated by hydrochloric acid. It also 
dissolves readily in the solutions of the acetates and thiosul- 
phates of the alkali metals. AVhen heated in abseqee of air, lead 
chloride melts at about 485°, solidifying on cooling fo a white, 
translucent, horny mass; it volatili.ses at a temperature of, 
861 “934°, the vapour having a density of 5*8, corresponding 
to the formula PbClj-^ 

Lead yields a large number of oxychlorides.* The compound 
PbCljjPbO occurs as the mineral matlockite, and may be obtained 
artificially igniting the chloride in the air till no further 
fumeS are evolved. The mineral iiiendipite has the composition 
PbCt 2 , 2 PbO, and numerous others, some of which contain water 
of crystallisation, have been prepared. liuer^ has examined 
the freezing points of mixtures of lead oxide and lead chloride, 
and has obtained evidence of the existence of the compounds, 
PbClj,PbO, PbCl 2 , 2 PbO, and Pba2,4PbO. The hydrate 
PbCl 2 ,Pb 0 ,H 20 , which may also be formulated as lead hydroxy- 
chloride, Pb(OH)Cl, and occurs as the mineral laurionite, was 
formerly prepared by a process patented by Pattinson in 1849. 
In fills process chloride of lead is first prepared from finely 
pulverised galena and concentrated hydrochloric acid,^his is 

* Roscoe, Proc. Roy. 8oc., 1878, 87, 428. 

' ZtiU anorg. 1906, 48 , 365. 



924 


fTHE GERMANIUM GROUP 


then dissolved in water and mixed with lime-water in certain 
definite proportions; a snow-white precipitate having the 
composition given above is thrown down, which was at one 
time used as a paint in place of white lead. 

A hydrated oxychloride is likewise obtained by warming 
lead oxide with a solution of common salt (Scheele), caustic soda 
being produced at tlfc same time. * In the ^ear 1787 Turner 
took out a patent for the purpose of prcparingfcaustic soda by 
the reaction, and found that the residue when heated became 
anhydrous and possessed a yellow colour. This oxychloride is 
known under the name of Turner's yellow or 'patent yellow. 
J/auquelin theft showed that when lead chloride and lead oxide 
arc fused together, a yellow-coloured body is obtained. This is 
known as Cassel yelloiv, and is prepared by fusing together 
1 part of ammonium chloride and about 10 parts of massicot, 
minium, or white lead ; a part of the ammonium chloride sub- 
limes i^ndecomposed, and the resulting compound contains 
about one molecule of chloride to seven molecules of oxide, 
part of the45ad being at the same time reducdU by the ammonia. 

Lead chloride also yields a number of double salts with the 
chlorides of other metals. • 

Lead Telrafhloride, rbCl 4 . — A .solution of this con) pound is 
obtained by di.ssolving the dioxide fn well-cooled hydrochloric 
acid, but it is best prepared by passing chlorine into lead di- 
chlorido suspended in hydrochloric acid. On addition of 
ammonium chloride, ammonium plumbichloride, (NU 4 ) 2 pbClg, 
crystallises out, and the same compound is also formed by 
acting on lead tctracetate with concentrated hydrochloric acid 
and then adding ammonium chloride.^ It may also* be obtained 
by thef action of hydrochloric acid and anunouium persul|)hate 
on lead chloride in the cold,^ or by the electrolysis of concentfh-ted 
hydrochloric* acid with lead electrodes, the cathode being 
placed in a porous pot, when an orange solution of H^PbClg 
is formed, and this on addition of ammonia yields the above 
corap<|und.* AVhen this compound is added to well-cooled 
sulphuric acid, it yields the tetrachloride, as a yellow, refractive, 
fuming liquid, which readily decomposes into the dichloride and 
chlorin^. It has a specific gravity of 3*18 at 0°, solidifies at 
—15° to a yellowish, crystalline mass, and yields a hydrate with 

** ' Hutchinson and Pollard, Joum. Chem. 5oc., 1896, 69 , 212, 

■ Seyewet* and Trawitz, Compt. m»d., 1903, 136 , 086. , 

» ^Ibs and Nttbling, Zeit. Elektrochem., 1903, 9. 776. 



LEAD AND HYDROGEN AND THE HALOGENS 926 


a small quantity of water, but in presence of an excess is decon^- 
posed into lead dioxide and hydrochloric acid.^ 

Lead Bromide^ PbBrj. — This compoimd closely resembles the 
chloride. It is obtained by treating lead oxide with aqueous 
hydrobromic acid, or by precipitating a leafl salt with a solution 
of potassium bromide, when it is thrown down in the form of 
white, shining negdles. It ‘dissolves in Ifot water, and has a 
specific gravity tf 6*6. When heated in a closed vessel it fuses, 
forming a red liquid which on cooling solidifies to a white, horny 
mass. Fused in contact with the air, it emit^j white fumes and 
leaves a residue of oxybromide, PbBro.PbO, forming a pearly, 
yellow mass, whilst the hydrated oxyhromidey IM)Br 2 ,PbO,H 20 » 
or PbBrOII, has been prepared by heating a mixture of sfdutions 
of sodium bromide and lead acetate.^ 

Leml Iodide, PbL. -Hydriodic acid easily dissolves lead, and 
the iodide separates out from a concentrated solution in beauti- 
ful yellow crystals (Dcvillc). When a solution of le^d salt 
is mixed with a soluble iodide, a yellow precipitate of lead iodide 
is formed. This isWuble in 1,235 parts of cold arfd 194 parts 
of boiling water, giving rise to a colourless solution from which 
the iodide separates out on*cooling in yellow laminae resembling 
those of mosaic gold. The specific gravity of this ^compound is 
G’l; on heating, it becomes reddish-yellow, then bright red, 
and lastly brownish-black ; it melts in a closed tube to a reddish- ^ 
brownjiquid which solidifies to a yellow, crystalline mass, and 
may be sublimed unchanged by heating in carbon dioxide.® 
Like the chloride and bromide, it forms basic salts. 

A number of mixed halogen compounds of lead have been 
described, which are mostly prepared by the action of the 
halogAi salts of potassium or ammonium on those of lead. In 
this way the compounds PbFBr, PbICl, and PbBrCl are stated 
to be formed, as well as double compounds of th&e with the 
halogen salts of ammonia.* There is, however, some doubt as to 
whether these are true compounds or isoinorphous mixtures.® 

« 

^ Friedrich, ifomtsh., 1893, 14, 505; ClaHtien, Zeit, anorg, Chem,, 1203, 4, 
100 . 

* de Schulten, Bull. Soc.frart^. Min., 1897, 20, 186. 

* SchttfoherbakolT, J. Russ. Phys. Chem. Soc., 1905, 37, 682. 

* Tk)raM, Compt. rend., 1898, 128, 1349; 1899, 128, 12.34; 132f, BuU. 
Soc. chitn., 1898, [3], 19, 598; Fonzcs-Dijwon, ibid., 1897, [3], 17, 340. 

* Hcrty and Bogg, fT. Amer. Chem. Soc., 1897, 19, 820. ' 




926 


rrHE GERMANIUM GROUP 


» Lead AND Sulphur.'’ 

407 Lead Sulphide, PbS, occurs in nature as galena, crystallised 
in cubes or in other (jombinations of the regular system. It pos- 
sesses a bluish-grey colour, and has a specific gravity varjdng 
from 7*25 to 7*7. This mineral was known to the ancients 
under its present name, but the fact that it contained sulphur 
was not recognised until after some time. Tlfas even Kunkel 
was unacquainted with this fact, though Boyle ^ was aware that 
when galena is hehted with scrap iron metallic lead is formed, 
and recommended this mode of producing lead. 

When sulphur vapour is led over metallic lead it takes fire 
and burns, forming a crystalline sulphide ; even tolerably thick 
strips of lead take fire in sulphur vapour, depositing half-fused 
globules of lead sulphide. It can also be prepared by fusing 
lead oxide with an excess of sulphur. When sulphuretted hydro- 
gen is passed into a solution of lead nitrate, an amorphous, black 
precipitate is formed, but if the gas be passed into a dilute solution 
of the salt containing nitric acid a crystalline precipitate is 
obtained, consisting of microscopic cubes (Muck). 

Sulphide of lead fuses at a strong red heat -at 1120° i 10° 
according to Juried rich and when heated in a current of many 
gases sublimes in cubes which often Iiave a diameter of 1*5 him. 
Crystals of galena are often obtained in lead works in a similar 
way. On the other hand, octahedral crystals may be obtained 
by fusing 1 pai;j; of the precipitated sulphide with 6 parts 
of potash and 6 parts of sulphur (Schneider). Nitric acid 
converts galena, with separation of sulphur, partly into the 
nitrate and partly into the sulphate, the latter coinpound being 
formed in the largest quantity when tlie acid is strongest.** Hoi 
concentrated hydrochloric acid dissolves it \^h evolution 0: 
sulphuretted hydrogen. 

When an aqueous solution of a lead salt containing an exces; 
of hydrochloric acid is treated with a small quantity of sul 
phuretted hydrogen a yellowish- to dark-red precipitate is obtainec 
which consists of a double chloride and sulphide of lead 
According to HUnenfeld,® this precipitate has the compositioi 
3PbS,2PbCl2, whilst Parmentier * found the compoeitioi 
PbS,^Cl2 ; it is converted by an excess of sulphuretted hydrogel 

> A hydroatatical way of estimating ores of leai. 

• Metalhrgie, 1907, i 479,- 1908, 6, 23. 

• J. pr, Jhem., 1836, 7, 27. « Compt. rend., 1892, lli 299. 



mn AND SUI<PHUB • 

t « 


927 


t — ■ 

into lead sulphjde, and loses lead chloride on treatment with hot 
water. The compoiAd PbS,4PbCl2 has been obteined by diluting 
a solution of lead sulphide in concentrated hydrochloric acid, 
whilst similar compounds with lead bromide and iodide have 
also been prepared.^ • 

A polysulphide of lead, PbSg, is formed by the action of 
calcium polysulp^^ide on Idad nitrate at*0°, as a purplish-red 
precipitate whiob decomposes rapidly at ordinary temperatures 
into the monosulphide and sulphur.^ 

Lead Sulphate^ PbS04.— This substance ig found native as 
lead vitriol or anglesite in transparent, rhombic crystals, iso- 
morphous with those of celestine and heavy-spar, • or as pseudo-* 
morphs of galena. It is obtained as a white powder by pre- 
cipitating a lead salt with sulphuric acid or a soluble sulphate. 
If a layer of water be poured on to a saturated solution of potass- 
ium sulphate, and a platinum wire on which some lead chloride 
has been fused allowed to dip into the water, crystals pf lead 
sulphate are gradually formed.® It may also be formed by the 
action of sulphur dtoxide on lead peroxide.^ Lead rflilphate has 
a specific gravity of 6*2 to 6*3. It melts at about 1 100° withou 
decomposition. One part #f the salt dissolves in 21,739 part 
of cold water, 12,135 parts according to Schnal,® £jpd in 3G,50< 
parts of dilute sulphuric acid, whilst concentrated sulj^iunc aci( 
can take up about 6 per cent, of the compound. It also dissolvei 
in war^ ammonia and caustic potash, and in hot hydrochloric 
acid with formation of lead chloride. Sulphate of lead is likewise 
very readily soluble in ammoniacal salts, especialTy in the acetate ; 
calcium acetate and many other salts also dissolve it. 

When lead Sulphate is boiled with concentrated sulphuric acid, 
it is dissolved and is afterwards deposited in crystals, and*if the 
mother-liquor b% allowed to stand in contact with moist air 
crystals of the acid sulphate, PbS04,HaS()4,Il20, similar to those 
of the corresponding barium salt, are formed. 

When the normal salt is treated with ammonia the basic 

sulphate, PbjSO^ or 0<p|^ q>S 02, is formed. The same^ salt 

is obtained in microscopic needles when an excess of a hot solu- 
tion of sodium sulphate is added to basic lead formate (Barfoed). 

^ Lenher, J. Amer, Chm. Soc.^ 1895, 17, 511 ; 1901, 23, 680. 

* Bodroux, q^pt, rend., 1900. 130, 1397. 

* Manross, AnnaUn, 1852. 82, 360. 

Haiino, Zeit. anorg. Chem., 1907, 06, 233. 

* C<mfit,^end„ 1909, 148, 1394. 

VOl. n. (n.) 


H 



ITHE GERMANIUM GROUP 


The basic sulphates, PbSO,, 2 PbO and PbSOi.SPbO* also 
exist.^ • * 

Lead Persulyhalej Pb(S04)2, is obtained at the anode as a 
greenish-yellow, crystalline precipitate wdien a solution of sul- 
phuric acid is electro^scd below 30 “ with an anode of lead placed 
in a porous pot. It is decomposed by water with formation of 
sulphuric acid and load dioxide, and a powerfjd oxidising agent. ^ 

Lead Sahsxdphate, PboS()4, has been prepareij^^ 

Lead and Nitrogen and Phosphorus. 

408 Lead Imide, PbNH, k obtained by the action of potass- 
^mide on leadjodide in liquid ammonia, and is a reddish-brown, 
explosive substance. If the lead iodide be in excess, the white 
basic salt, NPb2l,NIl3, is obtained. Lead imide reacts with 
potassamide in liquid ammonia at low temperatures to form 
potassium ammono-idumbite, KNPb,2JNH3, which loses half 
a molecule of ammonia at — 40 “ to form the compound 
KPb(jfH2)3. At. (Kf, a further molecule of ammonia is lost 
with the p/nduction of the explosive compoimd KNPbjNHj. If 
these substances are treated with ammonium iodide in liquid 
ammonia the successive products arc Jead imide, an ammonobasic 
lead iodide, Pb2(Nlf2)3l, and lead iodide. Lead imide is an 
amphbterk electrolyte in liquid ammonia.* 

Lead Nitrite, i’b(N02)2.‘“This substance is most readily 
* obtained by decomposing silver nitrite with lead chloride 
and concentrating the solution in a vacuum, when yellow prisms 
separate out whUdi are easily soluble in water. On evaporating 
the solution, nitric oxide is evolved, and a basic salt remains 
behind. If lead nitrate be digested with water in- contact with 
finely-divided metallic lead for a few hours at a tempwrature 
of 75°, a yellow solution is formed, which 01^ cooling deposits 
the basic double salt, Pb(N03)01I,Pb(N02)0H, in glittering 
yellow plates. Proust, wlio first obtained this compound, 
considered it to be a nitrate of a suboxide of lead, whilst Berzelius 
viewed it as a simple basic nitrite. If its solution be boiled 
with*metallic lead and a large quantity of water, orange-yellow 
prisms separate out on cooling, having the composition 
Pb(N02)2,Pb(N03)2,5Pb0,3H20. This salt was formerly termed 

* Sohenck and Kaasbach, Ber., 1908, 2917. 

* SSlbi-and Fischer, Zeit. Klehrochem., 1900, 7, 343. 

* Denham, Jaum, Chem. Soc., 1919, 115. 109. 

* Franklin, J. Amer. Chem, Soc,, 1906, J!7i 820; and J. Physical Chei^., 1911, 

15. 609. « • 



LEAD AND NITROGEN AND PH()SPHORCrS 

f 

lead hyponitrate. If lead nitrate be boiled with one and a hall 
times its weight of* lead and fifty times its weight of water for 
twelve hours in a long-necked flask, pale red needles of basic 
nitrite of lead, Pb(N02)2,3Pb0,H20, are formed. Otlier basic 
nitrites of lead are known.^ • 

Lead Nitrate, Pb(N 03 ) 2 .— Lead nitrate is first mentioned 
in the Alcfiymia of Libaviiis. It is hye termed calx plumb, 
dulcis. Fit aquam fortem comminuto plumbo affusam 
vase in aqua irigida locato. Fit instar crystallorum.** Lead 
dissolves slowly in warm dilute nitric acid. Ijead nitrate, or 
lead saltpetre, as it is sometimes called, is prepared on the large 
scale by dissolving lead scale or litharge in hot dilute nitric acicL 
having a specific gravity of 1*35. Tlic solution is evajwratea 
until it attains a specific gravity of 1*0, and is then allowed to 
cool in earthenware vessels, when the salt .se])arates out in milk- 
white, regular octahedra exhibiting a combination of the regular 
dodecahedron. If a cold solution of the salt be allowed to under- 
go spontaneous evaporation, transparent octahedral crystals 
are formed (Knop^ It has a specific gravity of 1-5,^ and on dis- 
solving in water gives rise to a reduction of temperatun} ; 100 
parts of water dissolve, according to Mulder, as follows : 

At 0® 10® 20® 40® GO® 80® 100® 

r^NOj), 36-5 444. 52-3 034 88-0 107*6 •12r'0 

It scarcely dissolves in strong alcohol and is only slightly soluble^ 
in aqueous alcohol. Its aqueous solution is precipitated by 
nitric acid. It has an astringent, metallic ^aste, decrepitates 
when heated, detonates with brilliant sparks when thrown upon 
red-hot charcoal, and deflagrates when triturated with sulphur. 
When heated in a sealed tube at 357°, it decomposes partially 
according to the equation ; ^ • 

" PbfNOala PbO -f- 0 + ‘2N( Ig. . 

The salt is largely used in dyeing and calico-printing, for the 
preparation of mordants and of chrome-yellow. 

WTien the normal salt is boiled with an equal weight of lead 
oxide and water, crystals of a basic nitrate, Pb(N 03 ) 0 H, are 
thrown down on cooling. These are sparingly soluble in cold 
and^ more readily soluble in hot water. When gently^heated 
it is converted into red lead. If 'a solution of the normal salt 

* Compare Chiteefttti, Atti B. Accad. Lincei, 1908, [G], 17, it., 377 474. 

* lakeland, J. Arner. Chem. Svc., 1904, 26, 391; Morgan, J. Physical 
Chem., 1904, 8,^416. 




930 


GERUANIDM GROUP 


be precipitated with a slight excess of ammonia, and the solution 
heated in a closed vessel with the addition ofisome of the normal 
salt until the smelf of ammonia has almost disappeared, a basic 
nitrate is formed, having the composition 2Pb(N03)0H,Pb0. 
It is a white powder aiigbtly soluble in water. When an excess 
of ammonia is employed the compound Pb(N03)0H,2Pb0 is 
thrown down as a whil^ powder. 

Phosphates of Lead. — When common sodiui^ phosphate is 
precipitated by acetate of lead a white precipitate of normal 
lead orthophosphate^ Pb3( 1^04)2, is formed. If a boiling solution 
of lead nitrate be precipitated by phosphoric acid, a glittering 
^hite, crystalline precipitate of HPbP04 produced, and the 
same compound is obtained in the form of crystalline needles 
when lead pyrophosphate is heated with water to 250 °. The 
pyrophosphate and metaphosphate of lead are white precipitates. 
The following minerals are lead phosphates and arsenates 

• isomorphous with apatite : 

Pyromorphite, Pb3(P04)2,Pb2Cl(P04), 

I'olysphairite, (Pb,Ca)3(P04)2,(Pb,Ca)5Cl(P04), 

Mimctite, Pb3(A804)2,Pb2CI(A804), 

• 0 ampylite,Pb 3 [(As,P)O 4 ] 2 ,PbiCl[(A 8 ,P)O 4 ]. 

Som^of the^hlorine is usually replaced by fluorine. 

Borates of Lead.-Ai boron trioxide* and lead oxide be fused 

• together in the proportion of two molecules of the former to three 
of the latter, a yellowish soft glass is obtained, which s(rftens 
when exposed to the action of hot oil. If double the weight 
of boron trioxide be employed the glass obtained is harder and 
less coloured, and if three times the weight be used a colourless 
glass is obtained, which possesses the hardness of flint glass 
and reffacts light much more powerfully.^ When a lead salt 
is precipitated with borax, a compound having the composition 
PbjBgOjijdHjO is formed, and this when warmed with strong 
ammonia is converted into a heavy, w'hite powder having the 
composition PbB204,H20, wliich again, when boiled with a 
solution of boric acid, yields amorphous PbB407,4H20.2 

Lead and Carbon and Siucon. 

409 Qarbonates of I^ad.— Normal Lead Carbonate, PbQOg, 
occurs as cerussite or white carbonate of lead in rhombic crystals 

* F»raSi^, '* On the Manufacture of Optical Glass," Tram., 1830, 
UW.1. 

* But seetilso, Thompson, Traiu. Kngl. Ceram. Soc., 18, 51U. 



IJ8AD AHD OARBON AKD SiSiCON 


931 


isomorphous with ajagonite, and also as pseudomorphs of galena 
and lead sulphate. The same compound is formed by precipi- 
tating a cold solution of lead acetate by ammonium carbonate 
(Berzelius), or by passing carbon dioxide ^into a dilute solution 
of lead acetate (Rose). Cerussite forms colourless, transparent, 
lustrous crystals, having a specific gravity of 6*46, whilst the 
precipitated carbonate has a specific gravity of 6*43. It is 
scarcely solublJ in water, one part dissolving in 60,500 parts of 
water at the ordinary temperature, but in presence of ammoniacal 
salts it is somewhat more soluble (Fresenflis). A solution of 
carbon dioxide in water also dissolves it slowly. 

Lead forms several basic carbonates, among which whh 
lead is the most important, since it is manufactured on a very 
large scale. In the pure state this compound consists of 
2 PbC 03 ,Pb( 0 H) 2 , but the commercial product usually contains 
the normal carbonate in addition. 

White Lead has long been known, being called yjft/ji$iop by 
Theophrastus. The process of manufacture as described by him 
consisted in the action of vinegar on lead, the maferial foimcd 
being scraped off after a time from the surface of the metal. 
Pliny mentions the same subject under the name of cemsm* 
and describes the above method of manufacture. •He also states 
that it may be obtained by dissolving lead in vinegar and evaporat- 
ing to dryness. Thus it would appear that the difference between * 
whit^lead and sugar of lead was not known. The Latin Gebcr 
describes the manufacture as follows: “plumbum ponendo 
super vaporem aceti fit cerussa,” a description which accords 
with the method employed even' up to the present day. For 
some time white lead was supposed to be a compound of calx 
of lead with vinegar, and it was not until 1774 that Bergman 
showed that white lead contained lead calx and fixe^air, and gave 
to it the name of “ luftsaurcr blei-kalk ” or “ calx plumbi a)rata.** 

The oldest process for the manufacture of white lead is known 
as.the Dutch process. In this method conical glazed earthenware 
pots, 8 inches wide, are filled to one-fourth of their dep^ with 
malt vinegar. At one-third of the height of the pot from the 
bottom are three projecting points on which a cross-piece of 
wood is laid, and on this are placed vertically a number^of thin 
leaden plates rolled up into a spiral, and the whole is covmd with 
a leaden plate, ^hich often has holes punched in it. Tne pots 
are then placed under a shed in rows upon horse dun^ or spent 
taimery barl^and covered with boards: another layer of dung 




^ OERHANIDM OKOCP 


or decomposing bark is laid upon the boards, ^and on this another 
row of pots, many rows of pots being thus placed above one 
another, and the whole covered by the tan or dung. By the 
slow oxidation of th^^ dung heat is evolved, which assists the 
evaporation of the vinegar and causes basic lead acetate to be 
formed, and this in contact with the carbon dioxide evolved 
from the putrefaction of the organic matter is converted into 
white lead. In the course of from four to five wieks the greater 
portion of the lead is converted into white lead, the change 
taking place from 'without inwards. The white lead is then 
detached, ground into a fine paste whilst moist, washed well 
io free it from adhering acetate, and dried in small round pots. 
Unwashed white lead contains a considerable quantity (from 2 
to 12 per cent.) of the normal acetate. 

To reduce the risk of poisoning attending the drying of the 
, white lead pulp, formed by the treatment of the corroded lead 
with water, it is customary in some works to dry the pulp in 
ovens in which a vacuum is maintained. A further improve- 
ment, appli6able in the manufacture of paint, is that described 
by Tsmay (English Batent 23969, 1895) in which the white lead 
’ pulp is mixed with oil in a pug mill* in this way the greater 
portion of thoi' water is displaced by the oil, and the last portion 
is driven off from the paint by surrounding the mill with a 
' heating jacket so arranged that the contents are heated in a 
partial vacuum. In this way the use of drying stoves aal the 
dangers attending it are completely obviated. 

According to the German method of manufacture, plates of lead 
are hung up in wooden boxes placed in an atmosphere of carbon 
dioxide in heated chambers containing a stratum of acetic acid, 
or the plates are suspended in heated chambers having their 
floors covered with tan and acetic acid. 

The French method, introduced by Th6nard, and the English 
methodf suggested by Benson, do not furnish a white lead which 
possesses the same covering power as that prepared by the 
other methods. The process in these cases consists in passing 
carbon dioxide through a solution of a basic acetate of lead, 
obtained by boiling a solution of lead acetate with litharge. 

Another method, which yields a white lead of excellent covering 
power, ij the process patented by Dale and Milner. This con- 
sists id carefully grinding between millstoneS a mixture of 
litharge, or any insoluble basic lead salt, with water and sodium 
bicarbonate. Milner has improved upon this method by grindi:^ 



LEAD AND CARBON AND SILICON 


933 


a mixture of 4 parts of finely-divided litharge with 1 part of 
common salt and l6 parts of water. After ajbout 4J hours the 
reaction is complete. The mixture of basic lead chloride and 
caustic soda is then broiight into a leaden vessel, well stirred 
with a wooden pestle and a current of dhrbon dioxide passed 
through it until the liquid is neutral. If the carbon dioxide 
be passed in too Jong the product is spoifed.^ 

Another process, called, after its discoverer, the Bischof 'process ^ 
is now employed on a large scale at Mond’s works at Brimsdown 
in Middlesex.^ Metallic lead is converted* into litharge, and 
the latter is heated at 250-300"^ in a stream of water gas. It 
is thereby reduced to a black suboxidc of unknown compositioi^ 
and this is treated with water, when a yellow hydrate is formed 
with evolution of heat, which is further converted into white 
lead by treatment with carbon dioxide. This process, besides 
being rapidly completed, has the advantage of being carried out 
mechanically, and in such a manner that there is no (^st, and • 
thus a great source of danger to the Avorkers is avoided. The 
product has a confposition practically identical with .that formed 
by the German process. 

Several electrolytic processes have been proposed, but only a* 
very small amount of white lead is produced by ^lis means.* 

White lead is a white, earthy, heavy, amorphous *powder 
which appears under the microscope to consist of round, trans-, 
parent globules of the size of from 0*00001 to 0*00004 of an inch 
in diameter. The specific gravity of that prepared by the Dutch 
method is somewhat greater than that propafed by the French 
method, and it therefore absorbs less oil or varnish and gives 
rise to a thicker colour. 

Although it acts as a powerful poison, and is turned black by 
sulphuretted hydrogen, white lead is stiU almost exclusively 
used as the basis of paint, and has been replaced bnly to a very 
small extent by zinc- white or baryta- white. This is accounted 
for by the fact that it possesses a much greater covering power 
and is much more opaque than either of the other two, 

White lead is often mixed with heavy-spar and gypsum. A 
mixture of equal parts of white lead and barium sulphate is 
known as Venetian whitCy whilst Hamburg white is a mixture of 

^ Patent No. 40^, 22nd November, 1876. 

* Caro, Verh. dea Vtrtins zur Btfdrderung des OtwerbfieiMesy Berlin^ 1906. 

• Auckow, D.R..P., 91707 end 106143; Browe and Chaplin U.8.P., 561361, 

1896 and 666232, 1896. • 



934 


TOE germanium group 


one part of white lead to two of barium sulphate, and Dutch 
white of one part Jbo three of barium sulphate. The amount of 
this admixture may be readily ascertained by treating a weighed 
portion of the powder with warm dilute nitric acid, when the 
barium sulphate remains behind. 

Ijead Cyanide, Pb(CN)2, is obtained as a white powder when 
a solution of a normal lead salt is mixed with pptassium cyanide. 

It is not soluble in the cyanides of the alkaK metals and is 
decomposed on the addition of an acid. When heated in a 
closed vessel a mi; 5 cture of lead and charcoal remains behind 
which, if it has not been too strongly heated, is p 3 nrophoric. 

Lead Cyanata, Pb(CNO) 2 , is obtained by mixing solutions of a 
syanate and of a soluble lead salt. A dense white precipitate is 
thrown down, which soon assumes the form of slender needles 
ike chloride of lead. Under the action of boiling water lead 
jyanato is readily and quantitatively hydrolysed into lead 
•arbona;fc and urca.^ 

Silicates of Zcod.-— Silica fuses with lead oxide to form a yellow 
[lass, and silicates obtained by ** fritting ” lAd oxide with sili- 
ious material arc used by potters for preparing glazes. Glass 
ormed of equal parts of lead oxide and silica does not become 
lull when it is exposed to the action of sulphuretted hydrogen, 
out if '8 ports of the glass are fused' with one part of potash, 
the glass produced becomes tarnished on exposure.* In a similar 
manner it has been found by Thorpe and Simmonds * th^ the 
extent to which lead silicates are attacked by dilute hydrochloric 
acid depends up6n the proportion of acidic to basic oxides 
present. When there are present in the silicate two or more 
molecules of acidic oxides to one of basic oxide, dilute acid 
dissolves out very little lead, whereas when this propoltion 
falls below two, the silicates are readily attacked. Lead silicate 
forms a constituent of flint glass. The existence of the definite 
compounds 2 Pb 0 ,Si 02 and PbOjSiOg has been proved by various 
methods of investigation, and the existence of the compound 
3Pb0,2Si02 is probable.* 

^ Curoining, Joum. Ckem. 8bc., 1903, 88, 1391. 

* Faradav, “ On tho Manufaotnie of Optical Qlaac,” Phil, Trans,, 1830, . 

mi. , 

« Journ, Chem, Soe., 1901, 79 , 791. 

* Hilpert and Weiller, Btr,, 1909, 42, 2969; Cooper, Shaw and Loomia, ibid,, 
3991; llUpert and Naoken, ibid., 1910, 48 , 2565; Cooper, Kraua and Klein, 
Amer. Chem. J., 1912, 47 , 273. 



THE ACTION OF WATER UPON^LEAD 


980 


PoisoNflus Action op Lead Salts. 

4x0 The soluble lead salts are strongly poisonous and are em- 
ployed in medicine. The normal or basic ^etate given in doses 
containing 1 to 4 grams of lead mostly produces symptoms of 
acute lead poisoning, whilst 10 grams are i^id to be a fatal dose. 

When taken fox* a considerable time in small doses, especially 
in the case of tfe oxides and carbonates, chronic lead poisoning 
is observed. The disease called painters* colic is the chronic 
form of poisoning by carbonate of lead. The symptoms are 
pain in the abdomen, constipation, loss of appetite, thirst, and 
general emaciation, followed by a complex of nervous symptoms^ 
^own as lead-palsy, epileptic fits, and total paralysis. 

A very characteristic phenomenon accompanying chronic lead 
poisoning is the appearance of a blue line at the edges of the 
gums due to the deposition of lead sulphide. This line is often 
seen in the case of house-painters and the workmen engrfged in 
white lead works, well as those occupied -in manyfactures in 
which white lead is employed, as, for instance, in the manu- 
facture of glazed cards. Plumbers and others who have to 
handle metallic lead are also subject to lead poisoning. 

A serious source of lead^ poisoning is the materia^ used by 
potters for compounding their glazes. This generally consists 
of litharge, white lead, and red lead, which are readily dissolved • 
by tho^ acids of the gastric juice, and the use of suitable lead 
silicates has been suggested in place of these sub^itances.^ 


The Action of Water upon Lead. 

4ii^ince lead acts as a cumulative poison, its salts produce 
serious results if taken into the system even in very minute 
quantities for a length of time. Drinking water is often collected 
in lead-lined cisterns and passes through leaden pipes, and as 
water in certain circumstances can take up notable quanti- 
ties of lead it becomes of great importance to determini the 
conditions under which the solvent action is exerted. A fresh 
bright surface of lead does not tarnish in a perfectly dry atmo- 
sphere, nor when sealed up in a vessel filled with pure distilled 
water from which all air has been expelled by boiling. If, 
however, it be ex^Kxsed to the united action of air and \^ater 
the le|d is oxidised to hydroxide, which dissolves. After a 
Tboip^ and Simmonda, Jmwn, Cheitk 0^., 1901, 79, 791. 



•the germanium group 


time, this is converted by the action of the atmospheric carbon 
dioxide into an insoluble basic carbonate. l!ead hydroxide is then 
again formed, and thus the corrosive action may be continued.^ 

Potable waters always contain a certain amount of salts in 
solution and the corrosive action on lead depends upon the 
nature and quantity of the salts thus present. The ammoniacal 
salts act most prejudicially on water in this respect; this is 
especially the case with ammonium nitrate, whi^h greatly assists 
the oxidation and solution of the lead. Other nitrates do not, 
however, appear t<5 possess this power, and sulphates, phosphates, 
carbonates, and silicates either retard or altogether prevent this 
'action, and hdnce water containing carbonic acid in solution or 
temporarily hard water consisting of a solution of calcium car- 
bonate in carbonic acid gives rise to the formation of insoluble 
basic lead carbonate ; * if, however, an excess of carbon dioxide 
be present, this is dissolved, the water taking up lead in con- 
siderable quantity. 

The following table (p. 937) contains the results of experi- 
ments on* the solubility of lead in water containing various 
salts in solution. Bright plates of lead having a surface of 
5,600 sq. mm. were placed in flasks*containing 500 c.c. of water 
in which theisalts were dissolved, and the saline solutions allowed 
to act upon the lead for different periods of time.® 

Many jictable waters act as a solvent of lead, especially waters 
of a peaty nature which contain organic acids (ulmic anok humic 
acids) and waters containing little or no free carbonic acid, 
and destitute of calcium and magnesium salts. Occasionally 
otherwise pure waters are found to contain a trace of free sul- 
phuric acid sufficient to render the water plumbo-solvent and 
liable to cause lead poisoning. 

Epidemics of lead poisoning from such sources have neces- 
sitated the treatment of the water by the addition of calcium 
carbonate (precipitated chalk) alone, if such water contains 
suffi(!ient free carbonic acid to enable 1*5 grains CaC 03 per 
gallon to be dissolved, or if the water will not dissolve this amount 
the addition of fnmi 1 to 5 grains of sodium carbonate (NajCOj) 
per gallon also. 

» Slo also Thresh, Amhpt^ 1921, 270; Liverseego and Knapp, J. Soc. 

1920,89, 27. 

* ^ also Antony and Beneili, Gazt., 1896, 86, ii., 97 f 1898, 86, u., 136. 

* Muir, Proc, Maneh. Phil. Soe., 1876, 15, 31 ; Joum, Chem. Soc., 1877, i., 
560. Sec^Iso Camelley and Frew, J. Soc, Chttn. Ind., 1888, 7, 16, 78 ; l6&ichardt. 
Arch. Pharm., 1887, [3], 85, 868, 1069; Mflllcr, J. pr. Ghem.! 1887, [2J, 86, 317. 



DETECTION AND ESTIMATION of LEAD 


937 


Salt. 


NH4NO3 

063 . 

NaNOg 

KNO3 . 

K3SO4 
KNO3 . 

K2CO3 
CaCla . 

NH4NO3 
CaClg . 

Na2S04 

K2CO3 

CaClj . 

K2CO3 
Distilled water w 
bon dioxide at 


Grams per 
litre. 


ith 
ordinary 


0-02 
0-04 
0-02 \ 
0-05 ) 
0*07 \ 
0*50 I 
0-045i 
0-308/ 
0-26 
0-02 ] 
0-06 • 
0-02 j 

0-04 \ 
MO I 
0-31 

C4ir- I 


pressure . . . . ^ . 

Ditto with carbon dioxide 
at a pressure of about 
6 atmospheres 
Distilled water .... 


• 

Milligrams per Litre of I^ead 
dissolved. 

• 

24 hours. 

48 hours. 

72 hours. 

13 - 0 * 

15-0 

— 

25-0 

32-0 

2-0 

. 2-0 

— 

— 

• 

0-5 

— 

— 

0-3 

0-5 

0-5 

0-5 

— 

-- 

1-8 

• 



0-1 

— 

— 

0-2 

3-0 

• 

3-0 

• • 

M -8 

21-0 

— 

20 

2-0 

a 

3-0 


In testing for the presence of lead in water it is important to 
avoid any form of filtration, inasmuch as lead salts mordant 
with the filtering paper, and only a small amount of the original 
soluble lead is found in the filtrate.^ 


Detection and Estimation of Lead. 

412 The soluble lead salts possess a sweet, astringent taste, 
whence the name “ sugar of lead ” has been given to the achate, 
and are very poisonous. These two properties of the lead com- 
pounds have been long known, and it became in early times of 
importtmce to detect the presence of lead, inasmuch as the^om- 
pounds of this metal were largely employed for a great variety 
of purposes. Thus, for instance, the Romans were in the'^fobit 
of boii^g their poor wines in leaden vessels, and Pliny mentions 
^ SSe. Kolthoff, Pham Wtemad, 1991, M 132. 





938 •the germanium GROUP 


the fact that the point at which the wine^ becomes sour can be 
detected by harfging a strip of lead in it and then observing 
when this undergoes any change in its appearance. In later 
times the addition pf metallic lead to a cask of sour wine was 
said to render it drinkable. At a still later date, litharge 
appears to have been employed for the same purpose. It was 
observed that the treatment of wine with lead could be detected 
by tlie addition of sulphuric acid, and in 1707^Zeller suggested 
that an extract of orpiment and lime water (containing, there- 
fore, sulphide of chlcium) was an invaluable test for the presence 
of lead, inasmuch as this liquid turns all lead salts black. This 
'reaction led to the simultaneous suggestion, in 1787, by Four- 
croy and Hahnemann, of the application of water acidified with 
hydrochloric acid and then saturated with sulphuretted hydro- 
gen for the detection of lead, and thus the most important 
reagent which we now employ in analytical chemistry for the 
detectton and separation of the metals was introduced. 

Potable yrater may be examined in this w^y for lead by pass- 
ing sulphuretted hydrogen through water slightly acidified with 
hydrochloric acid. It is, however, to be remembered that 
many other metals, such as mercury, copper, and bismuth, also 
produce Ijlaek precipitates. The absence of these metals must, 
therefore, be ascertained before the presence of lead can be cer- 
tainly proved. Black lead sulphide can be readily distin- 
guished from other black sulphides insoluble in dilute •hydro- 
chloric acid by dissolving it in w'arm dilute nitric acid and filtering 
the solution ; on addition of sulphuric acid to the filtrate, from 
which the excess of acid should be removed by evaporation, 
a white precipitate of lead sulphate is obtained. By m^ns of 
this reliction lead may bo detected in the presence of all the 
other metajs and separated from them. 

Lead compounds, heated before the blowpipe on charcoal, yield 
a malleable bead of lead readily soluble in warm nitric acid, and 
the solution yields a precipitate with sulphuric acid. 

Another characteristic test for lead is, that when present in 
not too dilute solution, a crystalline precipitate of the chloride 
is obtained on the addition of hydrochloric acid. This is soluble 
in bailing water, and separates out on cooling in crystalline 
needle^. Potassium chromate gives, in the presence of free 
nitric* acid, a fine, yellow precipitate of chronfe yellow, PbCrOi. 
In order to detect small quantities of lead in presence oif large 
masses of organic matter, as is necessary in cases* of lea^ poison- 


DSTEOnON AMD ESTDIATION OlilBAD 


939 


ing, the mass is evaporated to dryness with sodium carbonate^ 
the residue ignited gently, and the carbonised mass rubbed 
fine and carefully lixiviated, when small, glittering, heavy spiculjB 
of metallic lead remain behind. These can be examined as 
already described. • 

Lead is easily estimated gravimetrically in the form of sul- 
phate, being precipitated by adding dilute# sulphuric acid and 
then two volum^i of absolute alcohol. For certain separations 
lead is also estimated as the chloride. In this case the solution 
is precipitated by hydrochloric acid, evaporateel on a water-bath, 
and the concentrated liquid treated with a mixture of ether and 
alcohol, in which the chloride is insoluble. Lead carbonate and 
lead oxalate are also occasionally used for the cstiriiatioii of lead, 
being converted by ignition into lead oxide. 

Volumetrically, lead is determined by tlic titration of the 
solution of lead sulphate in ammonium acetate solution with a 
standard solution of ammonium molybdate, the end point Jbeing 
detected on a spot plate by means of tannin solution.^ 

Lead is also estinfated electrolytically. When a i^ution of 
lead salt, to which 6 to 7 per cent, of nitric acid has been added, 
is electrolysed, lead peroxide is deposited at the anode. 

liCad compounds impart a pale tint to the non-lujiinous gas- 
flame, and this exhibits charaeteristic lines in the green (Werflier). 
The spark spectrum of lead contains a large number of lines 
betweei^the orange and violet. The brightest and most char- 
acteristic of these are a violet line (4058), a somewhat less bright 
one in the green (5608), and a fainter one lyinf near the less 
refrangible of the “ D ” lines of Fraunhofer (5875) (Lecoq de 
Boisbaudran). 

The Mtomte Weight of lead was determined by Berzelius, ^ by 
the reduction of pure lead oxide in hydrogen, his results giving 
the number 207*06; later,® during his experimentar work on 
the determination of the atomic weight of sulphur, he converted 
lead first into nitrate and then into sulphate, and from his 
results the number 206*96 is obtained. Turner* by a sinjlar 
method obtained 207*04, and Stas ® 206*92. Baxter and Wibon ® 
determined the atomic weight by analyses of lead chloride which 

‘ Seeal«oSa8M,PAann.ZeiM920,M,569,688;KoIthoff,/>A<im. Weemad, 
1920, 67 » 934; Simmons, Gordon, and Boehmer, Canad. Chm. J., 1920, 4 , 139. 

* Lehrbuch, 8, 1218. * Ibid., 5th cd., 3, 1187. 

* Pha. Tram,, 1833, 138 , 527. 

* BuU. 9 iead, ray, Bdg., 1860, [2J, 10 , 298. 

* J. Armr, CheM,^oc., 1907, 80 , 187. 




m 


Ithb gebmakiuh group 


bad been previously fused in an atmosphere of hydrogen chloride ; 
from the ratio pf lead chloride to silver ,• the number 207 088, 
and from the ratio to silver chloride, 207*096 was obtained. 
More recently Baxter and Thorvaldsen ^ have obtained the number 
207-19 by analysis %)f the bromide : while Baxter and Grover ^ 
found the numbers 207-21 and 207-19 by analysis of the chloride 
and bromide. The# weight of silver nece^ry to precipitate 
the. halogen from a known weight of lead haudrj, and the weight 
of silver halide produced, were both determined. It was shown 
that lead from ^pn-radioactive sources (‘ normal ” lead) always 
has the same atomic weight, since the lead used was derived 
from several different minerals and from sources widely separated 
geographically. The mean of these last numbers, 207-20, is 
now (1922) adopted as the atomic weight of lead, though later 
determinations, having as their object the comparison of the 
atomic weiglits of normal lead with that of lead from radioactive 
80 ur(;jB 8 , rather than the absolute value of the atomic weight, 
indicate a slightly lower number. By analysis of the chloride, 
Honigschmid and Horowitz ® obtain the nmi^er 207-18 ; Richards 
and Lembert* 207-15 : Richards and Wadswortli^ 207-18 : and 
Richards and Hall ® 207-19. • 

Isotopes op Lead. 

413 The study of radioactivity leads to the belief that there 
are nine isotopes {q,v.) of lead; of these, the final disintegration 
product of uranium (238), by loss of eight a-particles, should 
be lead of atomic weight 206 ; while the final product of thorium 
(232), by the loss of six a-particles, should be lead of atomic 
weight 208. , 

Confirmation of this was first obtained by Soddy and Hyman,’ 
who found lead derived from thorite, a radioactive mineral 
from Ceylon consisting chiefly of hydrated thorium silicate, 
has an atomic weight of 208-4. It has since been amply confirmed 
tha}. lead from a radioactive source in which thorium predominates 
harfa higher atomic weight tlian normal lead, though the number 
208-4 is probably too high. Honigschmid ® obtained the number 
207-90 for lead from Norwegian thorite. Richards and his 
collaborators, and Honigschmid, have shown that lead derived 

» Amer. Chm, 80 c., 1915, 87. 1021. * Ibid,, 1916, 87, 1027. 

* Monatsh., 1915, 86, 355. « J. Amer, Chem. ioc., 1914, 86, 1329. 

* Jbid., 1916, 88, 227 and 2013. • Ibid,, 1917, 88, 537. t 

* Jotm. Chem, Soc., 1914, 106, 1402. * Zeit, Elekirfchm., 1919, 26. 91. 



ISOTOPES OP LEAD 


941 


from a radioactive source in which uranium predominates has 
a lower atomic weight than normal lead; ihe lowest value 
yet obtained, 206-05, is for lead from a crystallised uranium 
mineral from Morogoro in Tanganyika territory. 

It has been shown that different isotopes Ifave the same melting 
point within the limits of experimental error; ^ that their atomic 
volumes are the s^e, for their densities ai% proportional to their 
atomic weights^ that the solubilities of their nitrates are the 
same, if the results are expressed in moles per litre,* that they 
cannot be separated by fractional crystallisation of their nitrates ; 
and that the refractive indices for sodium light of their nitrates 
are the same. Only a slight difference in tlie position of one line* 
in the spectra of different isotopes was detected by Soddy and 
Hyman, and has been confirmed by Merton.* 

A possible partial separation of the isotopes of lead by a 
chemical method has been described;* but the results require 
confirmation. • 

The lead content of radioactive minerals is regarded as a 
valuable indication* of their age. Since there is evidence 
fhat all the lead present in a mineral is derived from radioactive 
disintegration, the lead content can only give an upper limit 
to its age.® 

t 

‘ Richards and Hall, J, Avier, Cliem. Soc,, 1920, 4C, 1560; Lembert, Zeit. 
Khktrochem., 1920, 26, 59. * 

• ScK^iJy, Naiurf, 1921, 107, 41. 

• Richards and Sohurab., J, Amer. Chem. •SV>c., 1918, 40, 1403. 

• Proc. Roy, Soc., 1920, 96. [A], 388; 1921, 100. j. 84f 

® Dillon, Clarke, and Hinchy, Sci. Proc. Roy. Dublin Soc.^ 1922, 17, 53. 

• Lawson, Silzungnher. Akwl. Wias. IKicn, 1917, 126, 2a, 721. 



GROUP V. 


Sub-group (a). Sub-group^), 

Nitrogen. Phosphorus. 

Vanaflium. Arsenic. 

Columbium (Niobium). Antimony. 

•Jantalum. Bismuth. 

413 As in the preceding group (p. 831 ), the members of the 
two sub-groups resemble one another, especially in chemical 
properties, very closely, although they differ in certain respects. 

All Ahe elements of the group are characterised by the exist- 
ence of acid-forming oxides of the empirical formula R2^6» 
the acidity*'of the resulting acid diminishing &s the atomic weight 
of the element rises. Thus it is doubtful whether any salts 
of bismuthic acid exist, whereas the vanadates, arsenates, etc., 
are well-defined and stable salts. 

The elements vanadium, columbmm, and tantalum, which, 
with nitrogen, belong to the even series, combine so readily with 
oxygen that it is difficult to obtain them pure. They all have a 
metallic appearance, and melt and boil only at very higlx tem- 
peratures. They do not form volatile compounds with hydrogen 
or the alcohol radicles. 

The elements of the odd series, phosphorus, arsenic, antimony, 
and bismuth, on the other hand, are easily reduced froifi their 
oxides, melt at moderate temperatures, and can all readily be 
volatilised. ‘ They exhibit in their external characteristics the 
gradual passage from a well-marked non-metallio elem^t 
(phosphorus) to a well-defined metal (bismuth), and the same 
progression is to be traced also in their chemical properties. 
Thus the lower oxide of phosphorus, of the empurical formula 
PiOj, is the anhydride of a well-marked acid, but does not yield 
salts^even with strong acids. Arsenious oxide yields unstable 
salts with strong acids, such as sulphuric acid ; the correspondr 
ing dxide of antimony yields more stable saltr., and the trioxide 
of bismuth is entirely devoid of acid-forming properties, and 
reacts with acids to form a whole series of salts of the type RX^«. 
m 



VANADIUM 


943 


The same increase in basicity is observable in the sulphides of 
these elements, as vkU as in the pentoxides. ^ 

Phosphorus, arsenic, and antimony, as well as nitrogen, yield 
very characteristic volatile hydrogen coinpoimds; a hydride 
of bismuth has also been prepared. They all form organo- 
metallic derivatives. 

The group is further cliaracterised b}* the large number of 
oxides and h<^[j 0 §en derivatives formed by its members. In 
many of thesfe the valency of the elements varies considerably. 
They are all distinguished by a tendency to form two series of 
compounds of the types RX '3 and RX ‘5 (or^^gX^s, R 2 X" 6 )» 
in addition to this, some of them act also as dy^ds and tetrads. 
Thus nitrogen is divalent in nitric oxide, NO, and tetra valent 
in nitrogen peroxide, NOg, whilst vanadium forms a dichlorido, 
VClj, and a tetrachloride, VCI4. 

The elements nitrogen, phosphorus, and arsenic, and their 
chief derivatives, have already been described in Vol. 1. 


THE VANADIUM GROUP. 

VANADIUM. V«sro. At. No. 23. 

4 x 4 In 1801, Del Rio pointed out the existence of a new 
metal in a lead ore found at Zimapan, in Mexico,^ and gave to* ’ 
it thi name erythronium, from the fact that its salts became 
red when heated with acids. In 1805, Colkt-Descotils * ex- 
pressed his opinion that this supposed new metal was an impure 
oxide of chromium, and Del Rio accepted this conclusion as 
corr^t. In 1830, Sefstrom^ described a new metal which he 
found in the celebrated iron of Taberg, and for this he proposed 
the name of Vanadium, from Fanodw, a cognqmen of the 
Scandinavian goddess Freia. In the same year Wohler ^ showed 
that Del Rio's discovery was a true one, and that the Zimapan 
ore was a vanadate of lead. Unable to carry out the further 
investigation of the new metal, Sefstrom handed the materials, 
amounting only to a few grams, to Berzelius, and in 1831 this 
chemist^ published the result of an exhaustive investigation 
on the subject, in which he described a large number oP vana- 
dium compound^ and came to the conclusion that va^diiun 

1 OilbtTet Ann., 1801 , 71 , 7 . * Ann. Chim. Phys., 1805 , [ 1 ], 53 , 260 . 

• PSn. Ann., 1830 , 21 , 48 . ‘ Ibid., 1831 , 22 , 1 . ‘ Ibid. 

VJL. n. (R.) I 



M4 |THE vanadium GROUP 

closely resembled chromium and molybdenum, yielding, lik< 
these metals, an acid-forming trioxide. Chis view was uni 
versally adopted until the year 1867 , when Roscoe showed that 
the substance supposed by Berzelius to be vanadium was, 
according to the mode of its preparation, either an oxide or a 
nitride; that the volatile trichloride of Berzelius contained 
oxygen and possessed composition analogous to that of phos- 
phonw oxychloride; and that the metal, insteirA of belonging, 
as was supposed, to the chromium group, was a member of the 
antimony group and intimately connected with the nitrogen, 
phosphorus, and arsenic family. ‘ 

415 Vanadii^m is a somewhat rare substance, forming an 
essential constituent of only comparatively few scarce minerals. 
Traces of this clement are, however, tolerably widely dis- 
tributed throughout terrestrial matter; it is found in meteorites 
of the stony type,- and it exists in the sun. 

The principal vanadium minerals are vanadinite, or lead 
vanada 1 ;e, 3Pb3(V04)2,PbCl2; dechenite, (Pb,Zn)( ¥03)2 ;' 
cloizite, PbjVjO^; pucherite, BiV04; psittacmite, 
(Pb,Cu)3(V04)2,3Cu(0H)4,6Il20; 

volborthite, (Cu,Ca)3( ¥64)2,1120 ; roscoelite (vanadium mica), a 
vanadium muscovite, containing the metal as the basic oxide,® 
VjOg;' mpttfamite, (Pb,Cu)3(V04)2^(Pb,Cu)(0H)2; sulvanite, 
SCUjSjVjSg; carnotite, a jwtassium uranium vanadate found 
' in Colorado ; and patronite, an impure sulphide of vanadium, 
which occurs in considerable quantity in Peru. Mottramite 
has been found' in tolerable quantity in the copper-bearing 
beds of the kciiper, worked at Alderley Edge and Mottram 
St. Andrews in Cheshire, and it is from this source that 
the vanadic acid of commerce was at one time obtained. 
Small amounts of vanadium have also been found in a large 
number of relays, in trap and basalt,^ in certain iron ores, 
especially magnetite,'^ and cast-iron, in larger quantities in the 
slag from the basic steel process at Creuzot, in rutile, in the ash 
« 

' A •bibliography has been oonipilecl by Praijdtl (liepaig, 1906, VoM). 
More complete information concerning the compounds of vanadium may b# 
obtained from the monograph by Ephraim (Stuttgart, Enke, 1904). 

* Hasrelbeig, K. Vet. Akad. F6rh. Stockholm, 1899, 66, 131. 

* HiUcbrand, Turner and Clarke, Amr. J. Sci., 1899, [4]^ 7, 461. It Odenri 
in fairly large quantities associated with gold and gold tellorides in Eldondo 
Co. inUhlifomia; also in Colorado and at Kalgoorlie in tVestem Australia. 

* See HUlobrand, Amer. J. Sci., 1898, [4], 6. 209; 7, 294. 

* See Vqpe, Joum. Ohm. Soe., 1900, 78, it., 409. .> 




VANADIUM 


m 


-.it— 

'ol trees, in certain coals, lignites, and peats, and also in soda- 
ash, as well as in socfium phosphate. # 

. Extractim and Preparaiion of Vanadium Compound!^— In 
order to prepare vanadium salts from mottramite, the keiiper- 
sandstone, which contains the mineral dej^osited as a film on 
the surface of the grains of sand, is digested with strong hydro- 
chloric acid, t^aoid liquor drawn off, and^the sand well washed 
with water. Ae acid solution, together with the waslrings, 
is evaporated down with an excess of ammonium chloride, wJien 
ammonium meta vanadate separates out, and •this is repeatedly 
crystallised to free it from copper and iron. The crude ammonium 
metavanadate is then gently roasted in porceltfin, by which 
means the vanadium pentoxide is obtained in a tolerably pure 
condition. In order to purify this it is suspended in water and 
ammonia gas passed into the liquid. A solution of ammonium 
vanadate is thus formed, which is separated by filtration from 
the residue containing silica, phosphates, etc., and then ciystal- 
lised by evaporation in platinum vessels ; the pentoxide obtained 
by several rep^titioifs of this treatment is free from ^osphorus. 

Vanadio acid may be prepared in a similar manner from 
carnotite, which is an impoflant mineral commercially, being a 
source of uranium and radium. It is preferable, Jiowever, to 
boil the mineral with an Excess of sodium carbonrfle, when 
practically all the uranium and about two-thirds of the vanadium 
pass iijfo solution as sodium uranate and vanadate, and the 
radioactive matter remains in the residue. filtering the 
solution and concentrating until it is saturated with sodium 
carbonate, most of the uranium separates out as a yellow double 
salt, U02C03,2Na2C03, and on cooling the hot filtrate from this 
salt nflich of the excess of sodium carbonate crystallises out. 
The filtrate then contains sodium vanadate together with excess 
of sodium carbonate and a little uranium, which may* be precipi- 
tated as sodium diuranate, NagUgOy.GIIgO, by addition of caustic 
soda.^ 

416 MetaUio Vanadium. — Berzelius obtained brilliant metallic 
scales by heating the oxytrichloride in an atmosphere of ammo- 
nia. These do not, however, consist of metallic vanadium, but 
of vanadium nitride. Pure metallic vanadium was first obtained 
by the reduction of the dichloride in perfectly pure hydrogen. 
Although this pro(»w appears simple enough, there is no fifhtal 
more difficult to prepare in this way than vanadium. This 
‘SfePIum, J. Awer. 191C,a7, 1797. * 



946 


^ THE VANADIUM GROUP 


arises from the fact that whilst vanadium is stable at the ordinary 
atmospheric temperatures, it absorbs oxygfen at a red heat with 
the greatest avidity, so that every trace of air or moisture must 
be excluded during its preparation. Moreover, the dichloride 
itself cannot be readily obtained in quantity. 

Roscoe’s apparatus is shown in Fig. 189. The hydrogen 
generator (a) yields a*fetrcam of hydrogen whifh can be kept con- 
stantly passing through the wash-bottles for a/veek at a time, 
by occasionally adding fresh acid to the upper bottle and draw- 
ing oil the zinc sulphate solution from the lower bottle. The 
first wash-bottle contains a solution of lead acetate, the second 
one of silver ifitrate, and the three others contain boiled sulphuric 
acid. Traces of oxygen arising either from diffusion or from 
air absorbed in the dilute acid used are removed in the tube 
(cn) attached to the last washing-bottle ; the first portion of the 
tube contains red hot platinum sponge (c), whilst the further 
portian of the tube (d) is filled with phosphorus pentoxide 
and plugs of cotton-wool. The greatest care must be taken to 
have all rtibbcr stoppers and joints made*as tight as possible 
with copper-wire and paraffin. At right angles to the drying 
tube (cd) is placed the reducing arrangement shown in the lower 
part of thq drawing. This consists of a porcelain tube (ee') 
place(l iff a Hofmann’s furnace and protected in the central 
portions, where it is heated by an outer casing of sheet-iron. 
The porcelain tube is connected with the hydrogen apparatus 
by means of the wide glass tube {fp') provided with the tubulus 
(o) and narrowed down to join the drying tube at p'. The 
joint between the porcelain and glass tubes is made of seamless 
rubber, well wired and covered by an outer short glass cylinder, 
the space between the tubes and the cylinder being filled^ either 
with mercury or fused paraffin, and a similar joint is placed at 
the further*end of the porcelain tube. 

The dichloride is contwned in the bent tube (h) in which it 
was prepared and sealed up in hydrogen. It is fitted through 
the tubulus (o). The platinum boat being in position, as shown 
in the figure, hydrogen is allowed to pass through the apparatus 
for twelve hours to dry it completely and clear out the air; 
the rubber stopper of the tubulus is then withdrawn and the 
end of the tube containing the dichloride cut of, and the tube 
and*stopper are quickly replaced, so that th» crystals lie in the 
horizontal portion of the tube, which is then so turned, in the 
stopper' that the crystals of diohloride fall into the platinum 



VANADIUM 


947 


boat below. This bc^t, charged with dichloride, is then drawn 
into the centre of the porcelain tube by mean^ of the platinum 
wire, the end of which (w) passes tightly through a small hole 



in the rubber tube at the end of the apparatus; the wire is 
then cut off short at the end of the glass tube, a propei^joint 
made, and an exit tube attached dipping under sulphuric acid. 

The rubber stopper of the tubulus is surrounded by a bath of 
paraifih and the hydrogen is allowed to bubble through for six 
hours. *The porcelain tube is then gradually raised to the highest 


Fio. 189. 



THE VAHADIUM OROUP 


m 

temperature (a bright red heat) the Ho^ann’s furnace wiU 
yield, and kept dbustant until some hours after the last trace of 
hydrogen chloride can be detected in the issuing hydrogen. 
The process lasts frpm forty to eighty hours, according as the 
quantity of dichloride employed varies from 1 to 3 or 4 grams. 

Reduction of vanacjium pentoxide with carbon in the electric 
furnace yields only an impure metal, containk^a large amount 
of carbon.^ Pure vanadium can be prepared oy reducing the 
pentoxide with a mixture of the metals of the rare earths, known 
as mischmetal I, obtained by the reduction of the waste oxides 
from the manufacture of thoria.^ The oxide is mixed with the 
• finely divided ^netal in a magnesia crucible and the mass ignited, 
as in the aluminium thermite process ; a violent reaction occurs 
and a regulus of pure vanadium is produced. The metal has 
been prepared also by passing the electric current through thin 
rods of V 2 O 3 contained in a vacuum,® by heating the trioxide 
and carbide in a zirconia crucible to 1950°,* and by passing the 
vapour of vanadium chloride over heated sodium hydride.® A 
regulus of crude vanadium, probably consisting of a mixture of 
the metal and the dioxide, can be obtained from vanadic oxide 
by Goldschmidt’s aluminium reduction method. It can be used 
for tlif. preparation of the tetrachloride.® 

Metallic vanadium jireparcd by reduction from the dichloride 
in hydrogen, is a light whitish-grey coloured powder, which 
under the microscope reflects light most poweifully, and Appears 
as a brilliant crystalline, metallic ina.ss possessing a silver-white 
lustre. The surface of a regulus of the metal is covered with 
twinned rhombohedral crystals, and the metal has a hardness 
greater than that of steel or quartz. It is of a brilliant silver- 
white colour and takes a splendid polish which is not affected 
by air. Vanadium doas not decompose water at the ordinary 
temperature and is neither volatile nor fusible when heated to 
redness in hydrogen. When the powdered metal is thrown into 
a flame, or rapidly heated in an e.xcess of oxygen, it burns with 
brilliant scintillations. The specific gravity of vanadium at 
15° is 5-5, and the atomic heat, as deduced from the specific heat 


Moiuian, rend., 1803, 116 , 1225. 

* Weiss and Aichel, Annakn, 1904, 887, 380. 

• Wemcr von Bolton, Zeit. Elektrochem., 1905, li, 45. 

* Ruff and Martin, Zelf. angew. Chm., 1912, 85, 49. 

* Billy, Com pi. rend., 1914, 158 , 578. 

* koppel and Kaufmonn, Zeit. anorg. Chern., 1905, lb, .352. 



m 


VANADIUM AND 0XYGe3 


qf its alloys^ is nornjal.^ The metal is not attacked by hydro- 
chloric acid either when cold or hot, and neither strong nor 
dilute sulphuric acid acts upon it in the cold, but when heated 
with the strong acid it slowly dissolves, gi^ng a greenish-yellow 
solution. Hydrofluoric acid dissolves the metal slowly with 
evolution of hydrogen and formation of ^ green solution, whilst 
nitric acid of strengths oxidises it with violence, evolving 
nitrous fumes and forming a blue liquid. Vanadium also 
dissolves readily in chloric acid, perchloric acid, and ammonium 
persulphate, vanadic acid being produced. ^ *Both hot and cold 
solutions of caustic soda are without action onjihe metal, but 
when fused with the hydroxide, hydrogen is evolved and a* 
vanadate formed. Metallic vanadium precipitates platinum, 
gold, and silver from solutions of their salts, and reduces mercuric, 
cupric, and ferric salts to the corresponding lower salts (Marino). 
When heated in an atmosphere of pure nitrogen, it is converted 
into the mononitride (Roscoe). * 

Alloys of vanadium can be prepared in the eleqtric furnace 
by reducing vanadic anhydride in the presence of *the second 
metal or one of its oxides.^ It also forms an alloy with platinum. 
Ferrovanadium is manufactured on a commercial scale in the 
electric furnace in France and also in Colorado. "It^is aised in 
the production of vanadium steel (see Steel). 

COMPOUNDS OF VANADIUM. 

Vanadium and Oxyuen. 

4x7 Vanadium forms five compounds with oxygen, analogous 
to tljp oxides of nitrogen, namely ; 

Vanadium suboxide V2O. 

Vanadium monoxide, hyjwvaimdious oxide VO or VgOg. 

Vanadium sesquioxide, vanadium trioxide . V^Oy. 

Vanadium dioxide, hypo vanadic oxide . VOg or V2O4. 

Vanadic anhydride, vanadium i)entoxide . V2O5. * 

All these oxides form salts, the tlireo first acting only as basic 
oxides, the two highest both as acid-forming oxides and as weak 
basic oxides. ** 

Some confusion exists as to the nomenclature of the y|irious 

' Matignon and Monnet, Compt. rend., 1002, 134 , 342. 

* Marino, Zeil. anorg. Chem., 1004, 38 , 152. 

• Mdlssan, Compt. rend., 1896, 128 , 1297. 



900 


rHB VANADIUM GROUP 


oxides of vanadium and the series of compounds derived from 
them. Boscoe, mark the analogy with arsenic and phos> 
phorus, termed the sesquioxide, VgOg, vanadious oxide, and its 
salts the vanadious ^Its, and to the lower oxide, VO or VgOg, 
he gave the name hypovanadious oxide. The fact that VjOg 
acts entirely as a ba^c oxide, and the close analogy existing 
between the derivatives of VgOg and of VO aild ^e correspond- 
ing chromium compounds, have led more recent investigators ^ 
to term the compounds derived from VgOg the vanadic salts, 
and those derived Ifrom VO the vanadious salts, corresponding 
with the chromic and chromous salts respectively. The salts 
formed by the oxide VOg with bases, termed by Boscoe hypo- 
vanadates, are now usually called vanadites, and the salts with 
acids containing the divalent radicle VO (or the tetravalent 
radical VgOg) are known as vanadyl (or divanadyl) compounds. 
The more modern nomenclature has been adopted here. 

418 Vanadic Anhydride^ VgOg. — The preparation of this oxide 
from mottr^mite Las already been described.. In the pure state 
it is best prepared by decomposing the oxytrichloride, VOCI3, 
with water and fusing the residue, but it can also be obtained 
pure by heating pure ammonium rneta vanadate and avoiding any 
reductinn.2 Vanadic anhydride crystallises in splendid yellowish- 
red, rhombic prisms (Nordenskiold), which have a specific gravity 
’of 3-35 (J. J. Watts), and dissolve in about ],0CM} times their 
weight of water, giving a yellowish solution, which doH^ not 
possess any taste but turns blue litmus paper red. Vanadic 
anhydride fuses without decomposition in absence of organic 
reducing matter to a red liquid, which on cooling yields brilliant, 
transparent, reddish-yellow needles, and at the moment of^rys- 
tallisation exhibits the phenomenon of incandescence. 

Vanadic (anhydride exists in several different modifications, 
which differ in solubility ami other properties. When it is pre- 
pared by igniting ammonium vanadate, evaporating with nitric 
acid, and gently heating the residue, it forms a yellow, hygroscopic 
powder, which unites with water to form hydrates containing 
1, 2, and 8 molecules of water, and dissolves in cold w^ater to the 
extent of 8 grama per litre. When the oxide is heated for a long 
time At 440 ® or fused, it is converted into two different sparingly 
soluble modifications.^ 

0 * 

* Piocini and Marino, Zeit. anorg. Chem.^ 1902, 32 , 67. 

Matignon, Chem. ZtiU 1906, 29 , 080. 

• Ditto, Com/rf. rend.t 1886, 101 , 698. 




THE VANADIO ACIDS AND THEIR SALTS m 


Vanadic anhydride acts as a weak basic oxide as well as an 
acid-forming oxide. Thus it dissolves in strong acids, forming 
red or yellow solutions yielding crystalline compounds, which 
separate out on spontaneous evaporation oi cooling. 

Vanadic anhydride is reduced by sulphurous acid in presence 
of sulphuric acid, and by evaporation with hydrochloric acid, 
to VO2 ; magn^iiftn and hydrochloric acid, or evaporation^ with 
hydriodic acid, reduce it to V2O3, whilst zinc and hydrochloric 
acid carry the reduction to VO. 

Vanadic anhydride has been used in the preparation of aniline 
black, and its use has been suggested in the electrolytic oxida- 
tion and reduction of various organic compounds in an acid 
batE, e.g., the manufacture of quinone from aniline, etc.^ It 
also greatly accelerates certain oxidation processes, such as the 
action of nitric acid on sugar, the oxidation of alcohol by 
atmospheric oxygen, etc.^ 

The VllNADic Acids and their Salts.** 

419 Normal Vanadic Acid, H3VO4, is not known. 

Metavanadic Acid, IIVOJ, was discovered by Gerland.® It 
forms a fine yellow pigment, sometimes termed vanadium ^J)ronze, 
and is employed in place of gold bronze. It is obtained in the 
form of brilliant scales of a golden or orange colour by boiling 
aqueous sulphurous acid with copper vanadate, prepared by the 
double decomposition of ammonium raetavana(Jate and copper 
sulphate. A mixture of brown and orange-yellow crystals is 
obtained, and on continuing the ebullition with more sulphurous 
acid, the brown crystals dissolve, the yellow metavanadic acid 
being insoluble. 

Vanadium bronze may also be prepared by adding a solution 
of ammonium vanadate to one of copper sulphate containing 
excess of ammonium chloride until a permanent precipitate is 
formed, and then gently heating to 75 °, when the yellow scales 
are slowly deposited, and after the lapse of a few hours nearly 
the whole of the vanadium is precipitated. The larger the 
quantity of material employed and the slower the action takes 
place, the finer is the colour of the bronze.* 

‘ German Patent, 172054 (15/9/03). 

* Moeaer and Lindchbaum, J. pr, Chem., 1907, [2], 76, 146; German Atent, 
183022418/8/05). 

» Proc, Manch.J>hil Soc., 1873, 12, 60. 

« Hef.,*1876.9. 874. 




THE VANADIUM GROUP 


If the freshly prepared solution of coppej vanadate be quickly 
evaporated in a flat dish, a crystalline residue is obtained which 
is soluble in water, and when this solution is dialysed for some 
days a clear solutiqp of pure vanadic acid is obtained which 
remains clear when heated, and deposits the red amorphous 
pentoxide on evaporf^ion. 

A solution of vanadic acid is decomposed yi heating with 
sulphuric acid.^ 

Pyramnadic Acid, II4V207, is a brown precipitate closely 
resembling ferric Ifydroxide, obtained by treating a solution of an 
acid vanadate with nitric acid. When air-dried it possesses the 
’ above composition. It is, however, unstable and loses half its 
water when dried over sulphuric acid (v. Hauer). 

Hexamnadic Acid, =: 6V205,2H20.— AVhen a solution 

of pervanadic acid is allowed to stand it loses oxygen and forms 
an acid yellow licpiid, which probably contains hexavanadic acid. 
The sClution is uastable and soon dc|X)sits a brown precipitate 
of vanadium pentoxide.* ^ 

The The so-called normal vanadates prepared by 

Berzelius correspond to the metaphosphates ; it is also possible 
to prepare ortho- and p3n’o-vanadates analogous to the corre- 
8 pondingj)h«sphates. v. Hauer’s so-plled di- and tri-vanadates * 
are most simply formulated as tetra- and hexa-vanadates, 
NajV/In and Na2VQO,5, but it is probable from the researches 
of Diillberg on the molecular weights and conductivities 9 t these 
salts that thej^ are in reality acid salts derived from hexa- 
vanadic acid, H4Vg047, the normal salt of which, Na4VgOi7, 
is also known. Thus we have : 


( 1 ) Sodium Metii vanadate . . . NaVOj. 

( 2 ) Sodium Orthovanadate . Na3V04. 

( 3 ) Sodfum Pyrovanadate . . . Na4V207. 

( 4 ) Sodium Tetravanadate (v. Hauer) . Na3HVgOi7. 

( 5 ) Sodium Hexavanadate „ . . Na2H2V30i7. 


Other more complicated polyvanadates are known.^ 

The order of stability of the soluble vanadates in aqueous 
solution differa remarkably from that of the phosphates, the 

* Auger, Compt. rend,, 1921, 178, 306. 

* t^ttllberg, Zeif. phyeiktU. Chem., 1903, 46 , 170. • 

* J, pr, Chan., 1B66, 68, 385; 1859, 76 , 156, 929; 1860, 80 , 324. ^ 

* Cemelley, Joum. Chem, Soc„ 1873, 86, 323; Rosenjieiin, Zeit. anorg, 

1916, 96, 139; ibid., 98, 223. 



THE VANADK) ACIDS AND THElS SALTS 


053 


metavanadates being the most stable and the orthovanadates 
the least stable, whereas in the phosphorus sferies the order of 
stability is the reverse of this. At a high temperature, on the 
other hand, the orthovanadate is the most stable, being formed 
when vanadium pentoxide is fused with an alkali carbonate, the 
meta-salt being produced when a solution^of an alkali carbonate 
is boiled with yawdiura pentoxide. 

The propert3rwhich serves best to distinguish the ortho-* from 
the meta-vanadates is the colour of the respective copper salts. 
Copper orthovanadate possesses a blue-green* colour, whilst the 
metavanadate is a light yellow, crjrstalline powder. 

The alkali pyrovanadates are soluble, and dan be readily 
obtained by fusing one molecule of vanadium pentoxide with two 
molecules of the carbonate of an alkali metal, dissolving, and 
crystallising. They are likewise obtained by the decomposition 
of an aqueous solution of the corresponding orthovanadate. 
The pyrovanadates of the heavy metals are usually insoluble 
in water, and possess properties generally similar to those of 
the corresponding orthovanadates. ** 

yhe metavanadates are usually yellow : some of them, 
especially those of the alkaline earths, zinc, cadmium, and lead, 
are converted into colourless isomeric modifications, jn the 
solid state under water, in' aqueoas solution, and es^cially in 
the presence of alkali carbonates. The metavanadates of the i 
alkali 4netals are colourless, and on treatment with an acid give 
rise to anhydro-salts, which have a fine yelloji^'ish-red colour. 
The metavanadates of ammonium, potassium, sodium, barium, 
and lead are but sparingly soluble in water. The other meta- 
vanadates are more soluble. It is probable that sodium meta- 
vanacFate has the molecular formula NagVgOQ, thus correspond- 
ing with the triraetaphosphate (DUllberg). The following are 
the properties of the most important members of these three 
classes pf vanadates. 

Potassium Melmninadate, KVO3, dissolves slowly in cold and 
readily in hot water, and with difficulty in caustic potash. 
When it is boiled with water and vanadium pentoxide, or fused 
with ^the latter, 'potassium tetravanadaie^ ^3^4011,31140, or 
K3HV40 i 7,4H,0 (DUllberg), is obtained, crystallising in broad, 
reddish-yellow tablets. This salt is slightly soluble in cold and 
very easily soluble in hot water. 

Sodium Orthovanadatef Na3V04.— This salt crystallises with 
16 , 12 , p, and^SHgO, and in the form with 12 H ,0 is isonlorphous 



964 


. ^rm VANADIUM GROUP 


with sodium orthophosphate. It has a stroi^ly alkaline reaction, 
and in aqueous Solution is completely hydrolysed to caustic 
soda and sodium pyrovanadatc : 

2Na3V04 H2O - NaJgO; + 2NaOH. 

Sodium Pyrovanadatc^ Na4V207,18H20, crystallises in large, 
six-sided tablets, is easily soluble in water, and^s precipitated 
by alcohol from its aqueous solution in pearly scales. It fuses 
more easily than the orthovanadatc, and is first formed in the 
preparation of the*latter salt. 

Sodium MeUivanndate, NaVOg, resembles the potassium salt, 
^ind is converfed in a similar manner into sodium tetravana- 
date^ Nag V4O1 4,911.20, or NaallYgOj 7,131120 (DUllberg), which 
separates out in beautiful large orange-red crystals. This salt 
is only slightly soluble in water, but possesses such powerful 
colouring properties that 1 part of it is sufficient to impart a 
yellow 1.int to 200,000 parts of water. It effloresces on exposure 
to the air, becoming of a reddish-brown tint, and melts at a dark 
red heat, jfolidifying to a dark red, amorphous mass. 

Ammonium Metavanadate ^ NH4VO3, is the most important 
vanadate. It is obtained by dissolving the pentoxide in an 
excess, of ^ammonia and evaporatinfj, or by precipitating with 
alcohol, in which it is insoluble. It forms colourless, transparent, 
• crystalline crusts, and is insoluble in concentrated solution of 
ammonium chloride, and accordingly is precipitated wiien a 
lump of ammonium chloride is allowed to remain in a solution 
of a metavanadate or pyrovanadatc : 

Na4Vg07 -h 4NH4a - 2Nfl4V03 |- 2NH3 4- HgO + 4NaCl. 

The solution of this salt becomes of a deep black tintVhen 
treated with tincture of galls, and Berzelius originally sug- 
gested the use of this liquid as an ink. This ink is, however, 
not permanent, “ for letters thu.s written by Berzelius are now 
quite illegible.” (Wohler), It was once used in dyeing with 
aniline black, since it-s presence greatly facilitates the oxidation 
of the aniline hydrochloride on which the formation of the 
colouring matter depends. 

Ammnium Teiravanadatey (NH4)2V40ii,4H20, or 

is obimned by the addition of acetic acid to a Iboiling solution of 
the metavanadate until the precipitate redissolves. Tlfe salt 
separates out from the yellowish-red bquid on cooling qj laige, 



THE VANADIC ACIDS AND THeA SALTS 966 


transparent, orange-red crystals. If it be recrystallised from 
water containing acetic acid, splendid red crystals of ammonium 
hexavanadcUe, (NH4)2Vfl0ij,6H20 or (NH4)2H2Vg0i7,5H20 are 
obtained. ^ 

Calcium Pyrovanadate, 2Ca2V207,5H20, is a white, amor- 
phous p?ecipitate obtained by double Recomposition of the 
corresponding sodium salt with calcium chloride. If the 
solution of somum orthovanadate be precipitated by calcium 
chloride, the same salt is obtained mixed with calcium hydr- 
oxide, the orthovanadate being at once dec( 5 mposed according 
to the equation ; 

Ca3(V04)2 + H 2 O = Ca 2 V 207 + Ca(OH)2. 

Lead Orthovanadate, Pb3(V04)2, is a nearly white, insoluble 
precipitate obtained by adding a solution of lead acetate to 
one of sodium orthovanadate. This salt occurs in nature com- 
bined with lead chloride as vanadinite, 3Pb3(V04)2,Pl5Cl2 or 
Pb3(V04)2,Pb2(V04)Cl. This mineral crystallises in hexagonal 
prisms, having a reddish-brown colour, and is isbmorphous 
wijh apatite. It has a specific gravity of from 6*6 to 7 * 2 , and 
frequently contains some phosphoric acid. It was found by 
Del Rio in Zimapan in Mexico, and occurs also atiLeacj^ills in 
Scotland, in Carinthia, and* in the Urals. It may be obtained 
artificially by fusing together lead oxide, vanadium pentoxide, 
and l^d chloride, in the right proportions. The fused mass 
contains druses, in which thin, needle-shaped (yystals are con- 
tained. If boiled with water it falls to a crystalline powder 
consisting of microscopic, hexagonal prisms, possessing the 
waxy lustre and the yellowish colour of natural vanadinite, and 
havin| a specific gravity of 6-7 (Roscoe). 

Lead Pyr<mnadatei is found in South ^America as 

descloizite in rhombic crystals, which have an orange-green or 
black colour, a bronze lustre, and a specific gravity of 5 ’ 839 . 
It usually contains zinc, iron, manganese, and copper as im- 
purities. If a solution of sodium p3rrovanadate be precipilated 
with lead acetate, the basic salt, Pb3V40j5, is thrown down as 
a ligh^yellow precipitate. 

Lead Metavanadate, (Pb(V03)2, is obtained as a yellow preci- 
pitate when a solution of a metavanadate is mixed with one of 
lead acetate. Tlte mineral dechenite consists chiefly of* this 
oompcymd, a portion of the lead, however, being usually replaced 
by zinc. It dccuis t(^ether with lead ores, forming* yellow, 




056 


^THE VANADIUM GRpUP 
brown, or deep-red reniform masses, having a specific gravity 

offi' 6 to 5 -a • 

Lead Tetramnadale, Pb2V40ji, is obtained by precipitating 
the corresponding pytassium salt with lead nitrate in the form 
of a reddish-yellow precipitate slightly soluble in water. 

Copper Orthomnadc^ey Cu3(V04)2,H20, occurs as the mineral 
volborthite, in which a part of the copper is roplyed by calcium ; 
it crystallises in small yellow or green hexagonal tablets having a 
specific gravity of 3 * 55 , and is found in Thuringia and in the 
Urals. Copper P^rovanadatey CU2V2O7, is a yellow, crystalline 
precipitate, whilst copper inelavanadale is an apple-green 
• precipitate. * 

Silver OrihovanudatCy k^^O^y is obtained by precipitating a 
freshly prepared solution of the sodium salt with silver nitrate. 
It is a deep orange-red coloured precipitate, which is easily 
soluble in nitric acid and in ammonia. 

Sih^ Pyrovanadaley AggVjO,, is a heavy, yellow powder. 
Silver Metavanadate y AgVOs, forms a pale yellow, gelatinous 
precipitate. 

Vanadio acid, like phosphoric acid, yields complex compounds 
with Btannates,^ tungstates, and molybdates, as well as with 
phosphates and arsenates.^ 

PervatMic Acid and the Pervanadates.— The alkali meta- 
vanadatea are readily converted by hydrogen peroxide into 
pcr-salts of the formula RTO4, many of which hava been 
prepared pure.. They are decomposed by dilute acids with 
evolution of one atomic proportion of oxygen.® 

Pervanadic Acid, HVO4, is formed when vanadium pentoxide 
is added to hydrogen peroxide in dilute sulphuric acid solution. 
A deep-red coloured liquid is formed,^ which deposits unstable 
yellow crystals of the per-acid.® 

Potassium Pervanadatey KVO4, is a yellow, microcrystalline 
precipitate, obtained by dissolving potassium metavanadate in 
a solution of hydrogen peroxide containing sulphuric acid, and 
precipitating with alcohol. 

Barium Metapervanadatey Ba(y04)|, is obtained as an amor- 
> Prandtl, Ber,, 1907, 40, 2126. 

* ^ an account of these complex derivatives, see the monograjd! by 
Ephraim quoted on p. 944. 

* Sbheuer, ZtU, onsfy. Chm., 1S98, 16, 284; Pissarjawsky, J, Bu*i, Phys, 
Chm. 80 c., 1902, 84, 210, 472. See also Auger, CompL rend., 1921, 178, 1356. 

« Werther, J. pr. Chm., 1861, 88, 196. 

* PisMUjewaky, Zeit. fAyeihaL Chm., 1903, 48 , 173. 



TMlfi liUWJSR OXIDES OP VANAT)IUM 


957 


phous, yellow precipitate, when a solution of barium chloride is 
added to a saturate# solution of ammonium Aietavanadate in 
30 per cent, hydrogen peroxide. Other salts have been prepared 
in a similar manner; they are characterised by being bright 
yellow or deep orange. 

More complex compounds are formed bv the action of alkalis 
and hydrogen oer^xide on the pervanadates, and these are 
probably salts ot a p)n‘opervanadic acid with the peroxides of 
the alkali metals. The ammonium salt, and the 

potassium salt, K8V502e,2H20, have been prep&red in this way.^ 
Complex oxygenated products have also been obtained by the 
action of hydrogen peroxide on the compoimd* of vanadyl 
trifluoride with potassium fluoride, ^ VOF3,2KF. 


The Lower Oxides of Vanadium. 

420 Vanadium Suhoxide^ V2O, is formed by the prolinged 
exposure of finely divided metallic vanadium to the air. It is 
a brown substance, which, when heated in the air, is^gradually 
converted into the higher oxides. No salts of this oxide have 
been prepared. • 

Vanadium Monoxide or Hypovanadious Oxide, VO of V20j|.— In 
its power of uniting with oxygen vanadium surpasl^s even 
uranium,^ and, like uranium, it can be separated from its last 
portions of oxygen only with extreme difficulty. The oxide VO 

is, moreover, found to enter as a radicle into many compounds, 
so that the name vanadyl (VO) may appropriately be given to 

it. This substance, which was regarded by Berzelius as metallic 
vanadium, may be prepared by reducing the higher oxides with 
potassium, or by passing the vapour of vanadyl trichloride, 
VOC18, mixed with excess of hydrogen, through a combustion 
tube containing red-hot carbon.^ Thus obtained it forfns a light- 
grey, glistening powder or a lustrous, metal -bke crust, having a 
specific gravity of 3 * 64 . It is brittle, difficultly fusible, and 
conducts electricity. Heated to redness, it takes fire in the*air 
and bums to the sesquioxide, V8O3, whilst when heated in chlorine 
the oj^richloride, VOCI3, is formed. It is insoluble in water, but 
dissolved in acids, yieldi^ the corresponding salts. These Qjay 

» MelikoS tiid PuaarjewBky, Zeit, atwrg. Chem., 1809, 19, 405; Pwttr. 
jeviky, ibid., 1903, 82,^1. 

• Melikofi and Kaaanezky, Zeit. anorg. Chem., 1001, 98, 942. 

» P41igdl, Ann. Chim. Phys,, 1842. [3], 5, 5; 1844 [3], 19 , 549. 

* Sohalarik. Anndkn, 1869, 198, 86. 



058 


• the vanadium group 


also be obtained in solution by the action of nascent hydrogen, 
evolved by metallic zinc, cadmium, or sodium amalgam, upon a 
solution made by dissolving vanadium pentoxide in hot con- 
centrated sulphuric acid and then diluting with water, or bji 
the electrolytic reduction of a similar solution. The liquid 
rapidly changes colour, passing through all shades of blue and 
green until after some time it assumes a perpianent lavender oi 
violet tint. This solution of the sulphate absrfbs oxygen with 
such avidity as to bleach indigo and other vegetable colouring 
matters as quickly as chlorine. The solution in hydrochloric 
acid has been suggested as a reagent for removing arsenic from 
• liydrochloric licid, the whole of the arsenic being precipitated in 
the free state when the impure hydrogen chloride is passed 
through the solution.^ On allowing the neutralised lavender- 
coloured solution to stand exposed to the air for a few seconds, 
the colour changes to a deep chocolate-brown. The changes 
in colour which the yellow sulphuric acid solution of vanadium 
pentoxide undergoes on reduction are exceedingly characteristic! 
and may**be divided into eight stages as Mows : 


Stage. 

^ Colour, 

i 

• 

Rci^otion. 

• 

Stato of Oxida- 
tion of the Metal. 

I. 

Yellow 

Acid 

v.o,. 

II. 

Greoq 

Acid 

V,0.-V0,. 

III. 

Bluish-green 

Acid 

V,Oj-VO,. 

IV. 

Blue 

Acid 

VO,. , 

V. 

Greenish-blue 

Acid 

vo,-VA. 

VI. 

Green 

Bleaches slightly 

VgOj— VO. 

VII. 

Bluish-violet 

Bleaches strongly 

VjOa-VO. 

VIII. 

— m. 

Lavender or violet 

i Bleaches strongly 

VO. 


Thus the salts derived from the pentoxide are yellow; the 
divanadyl salts blue ; the sesqui-salts green and the vanadions 
salts lavender-coloured. 

' i German Patent, 164356 (15/4/04). ^ 




Axii!. ijKiyYXM ^^JSS UJT VAMADXUM 958 

Vanadium Sesquioxide or Vanadium Trioxidey VjOg, is obtained 
by heating the pentoiide in hydrogen, or by igniting the same 
oxide in a carbon crucible. It is also formed when vanadyl tri- 
chloride and hydrogen are passed through a red-hot tube, and 
when the pentoxide is heated in the oxy-hydrogen flame.^ It is a 
black powder which under pressure for^is a coherent mass 
which conducts deotricity. It oxidises when exposed to the air, 
not only being pjn*ophoric when warm, but also slowly talcing 
up oxygen when exposed in the air at ordinary temperatures, 

. and being converted into small dark indigo-coh)urcd crystals of 
the dioxide VOj. It has a specific gravity of 4 - 7 . When ignited 
in chlorine gas it is converted into vanadium o^cytrichloride, 
VOCI3, and vanadium pentoxide : 

3VA+6Cl3 = VA+ 4VOOI3. 

It is insoluble in most acids, but the corresponding sulphate 
may be obtained in solution by the reducing action of nascent 
hydrogen, evolved from metallic magnesium, on a solution of 
vanadium pentoxide*in sulphuric acid. A green liquid is thus 
obtained, the further reduction observed with zinc, cadmium, 
and sodium amalgam not tnking place with magnesium. The 
green solution may likewise be obtained by the partijjJ oxidation 
of the lavender-coloured solution of vanadious sulphat^;:^804. 
If a current of air be passed through such a solution, in which 
the free^acid has been neutralised by an excess of zinc and the 
remaining metallic zinc removed, the liquid attains a permanent 
brown colour, which with a few drops of acid turns green ; the 
solution then contains the sesquisulphate. 

Vanadium Dioxide or Hypovanadic Oxide, VOg or V2O4. — This 
oxide (All be prepared either by the oxidation of the monoxide, 
VO, in the air, or by the partial reduction of the pentoxide. It is 
readily converted by jx)tassium permanganate into the t^entoxidc, 
and advantage is taken of this fact in the volumetric estimation 
of vanadium. It is a lustrous, steel-coloured powder and dis- 
solves in acids, forming solutions of the vanadyl salts, winch 
possess a bright blue colour. Solutions of these saltsr are also 
produced by the action of moderate reducing agents, such as 
sulphur dioxide and sulphuretted hydrogen or oxalic acid, uj^n 
solutions of vanadic acid in sulphuric acid. They may also be 
obtained by passing a current of air through acid solutions* of 
the van|uiious salts until a permanent blue colour is attained. 

^ Itbad, Journ, Chtm. Soc., ISM, 65, 314. 

VOL. n. (U.) 


K 



^ THE VANADIUM GROUP 


MO 

The oxide may likewise be prepared by the electrolysis oi 
the fused pentoxide, or by the ignitioi! of the oxychloride, 
in a current of carbon dioidde : 

V2O2OI4 4 - 5H2O - 2VO2 + 4 HC 1 + 3H2O. 

Divanadyl Hydroxjfle or Hypovanadic Hydrate^ or 

011)4, 5H2O, a greyish-white pfec^itate, obtained 

when a solution of vanadyl sulphate or chloride is cautiously 
precipitated with a cold solution of sodium carbonate. When 
dried it is a blaek, amorphous mass, having a glassy fracture. 
This on heating to 100 ° loses four molecules of water, leaving the 
hydrate, ¥2(^4,31120. A hydrate containing 2H2O is obtained 
as a pink, crystalline powder by boiling a solution of the dioxide, 
VOg, in sulphurous acid.^ Vanadium dioxide acts both as a 
basic, and as an acid-forming oxide. When dissolved in acids the 
vanadyl salts are formed, ^ whilst with alkalis the vanadites or 
hypotanadates are produced. 

The vanadites or liypovanadales are all insoluble except those 
of the aftali metals, which are not derived from the normal 
hypovanadic acid, H4V20fl, but from the partial anhydrides, 
HgVjOg and II2V4O2. The alkali vanadites are obtained by 
addii)gan excess of caustic alkali to a concentrated solution of. 
vanadyTsulphate or chloride.® The dark-brown solution thus 
obtained with potash deposits polassiim vanadites 
in reddish-brown, crystalline scales which, after washmg first 
with potash solution, and then with alcohol, may be dried 
between filter-paper. This salt is permanent in the air, and 
very soluble in water, yielding a dark brown solution. 

Sodium Vafiaditey is prepared in a ^similar 

way to the potassium salt, and exhibits analogous properties. 

Ammonium Vanadile, (NH4)2V402,3H20, is obtained as a 
dark-brown, crystalline precipitate by adding a vanadyl sulphate 
solution to ammonia ; it dissolves in water, yielding an almost 
black solution (Oow). 

Vanadium and Fluorine. 

^1 The oxides, V1O3, VOg, and VjOg, all dissolve in hydro- 
fluoric acid, but only the trifluoride, VF3,3H20, and the oxy- 
diflj'ioride, VOFg, have been isolated. A ve^ large number of 

^ Gain, Compt. reiul., 1900, 148 , 823. 

« Os^yard, Butt. Soc, cAim., 1876, [2J, 85 , 350. 

* See also Koppel and Ooldmann, Zeit. wwrg. Chm,, 1003, 86^ 881. 



VANADXy|[ AND CHLOBIN% Ml* 

double salts of these compounds and of the oxyfluorides YOgF 
and VOF3 with hydrofluoric acid, metallic fluorides, and 
vanadium pentoxide have been described.^ Only a few of the 
most characteristic are mentioned here. 

Vanadium Trijluoride, VFgjSHgO, crystaflises from the dark 
green solution of vanadium trioxido in hydrofluoric acid, in 
dark green, rejidily soluble octahedra. The double 'potassium 
salt, 2KF,VF3,rf20, is a bright green, crystalline powder, which 
is precipitated when a solution of potassium fluoride is added to 
one of vanadium trifluoride. • 

Vanadium Oxydijluoride, VOFj, is formed when the tetroxido 
is dissolved in hydrofluoric acid, and separates in Blue, prismatic 
crystals containing water. Several double salts with the fluor- 
ides of sodium, potassium, and ammonium may be prepared by 
adding solutions of these fluorides to the blue solution of the 
oxydifluoride (Petersen). 

Potassium Vanadium Dioxyjluoride, 2KF,V()2F, is ob#ained 
by evaporating a solution of vanadium pentoxide in hydrofluoric 
acid almost to dryness, and adding it to potassium flfloride. It 
crystallises in golden-yellow, six-sided prisms. 

Vanadium pentoxide alsd dissolves easily in a solution of 
hydrogen potassium fluoride with evolution of h^t, and on 
cooling yellowish globular masses separate out con^Sffng of 
pearly, probably hexagonal crystals, which have the composition 
3KF,2V02F,H20. 

Ammonium Vanadium Dioxyjluorulc, 3NH4F,y02F, is formed 
when a solution of vanadium pentoxide in hydrofluoric acid is 
nearly neutralised with ammonia; it separates in large, golden- 
yellow crystals. 

Zinc Vanadium Dioxyjluoride, ZnF2,V02F,7Ha0, is formed by 
dissolving zinc carbonate and vanadium pentoxide in hydro- 
fluoric acid. The salt crystallises in hard, yellow, tridinic prisms. 


Vanadium and Chlorine. 


The following chlorides and oxychlorides of vanadium* are 
known : 


Chlorides. 


Vanadium tetrachloride . . VCI4. 

„ tricliloride . . . VCI3 or VgClg. 

„ • dichloride . , VCl2orV2Cl4. 

* BBteraon, J, Chem., 1889, [2], 40, 193, 271. Sec al«o Piccini and 
Gioigis, i^inirn. Ctitm. Soc., 1889, 06, 214; and Baker, Joum» cttm, Noc., 
1878, 86, 388. 



THE VANADIUM QKOUP 


Oxychlorides. ^ 

Vanadium oxytricbioride . . VOC18. 

„ oxydichloride . . VOClg. 

„ oxymonochloride . VOCl. 

Divanad/I monochloride . . Va02Cl. 

„ tfctracMoride . . V202Cl4,6Ha0. 

. Oivanadium trioxydichloride Vj(t3(3i,4HjO. 

Vanadium Tetrachloride^ VCI4, is formed when metallic vana- 
dium or the rnoflonitride is heated to redness in an excess of 
chlorine. It may be prepared by repeatedly passing the vapour of 
vanadium oxj^trichloride, together with an excess of dry chlorine, 
over a long column of pure sugar-charcoal heated to dull redness ; 
also, by treating the crude vanadium, prepared as already 
described by the aid of aluminium, with chlorine and removing 
the oxy trichloride, which is also formed, by fractional distillation 
or by heating ferrovanadimn in chlorine.*^ Vanadium tetrachloride 
is a dark brownish-red, thickish liquid, which^evolves white fumes 
when exp6sed to moist air. It boils at 154° with partial decomposi- 
tion, losing chlorine and leaving a residue of the trichloride. This 
decomposition takes place also at the ordinary temperature, especi- 
ally otLgxpoBure to light. It does not solidify at — 18° ; its specific 
gravity at 0° is 1*8584, and its vapour density at 205° is 6*69, the 
calculated vapour density being 6*()75. When thrown into water 
the tetrachloride is at once decomposed, yielding a blue Solution 
of vanadyl chlcyide. It is soluble in carbon tetrachloride. 

Vanadium Trichloride^ VCI3.— The foregoing compound easily 
decomposes, as has been stated, into this body and chlorine. 
The trichloride is obtained either by the slow decomposition of 
the tetrachloride at the ordinary temperature or at its boiling 
point, or, together with the dichloride, when the vapour of the 
tetrachloride mixed with hydrogen is passed through a red hot 
tube, as well as w^hen the trisulphide is heated in chlorine.® It 
crystallises in fine peach-blossom coloured, shining tablets of 
density 3*0, closely resembling in appearance tl\e crystals of 
chromium trichloride. It is non-volatile when heated in hydrogen, 
which reduces it to the dichloride, and decomposes to the*pent- 
oxido when heated in the air. It is extremely hygroscopic, 

instantly deliquescing on exposure to moist air to a dark brown 

« •> 

* Koppcl, Uoliitiiaiin and Kaufmann, Zeit. anorg. Chem., 1005, 45. 345. 

■ Mertea, J. Amo'. Chem, Soc., 1913, 36, S7l. 

* H&lberstadt, Ber., 1S82, 11^ 1619. 


VATIAiriUm AXKJJ 

liquid, wWch on addition of a drop of hydrochloric acid becomes 
green. It readily dtesolves in absolute alcohol and in ether, 
forming green-coloured solutions. 

A hydrated compound of the composition VClajCHgO can be 
obtained as a green, crystalline powder by Svaporating in vacuo 
a solution of vanadium sesquioxide in hydrochloric acid,^ or by 
dissolving vanadiujn pentoxide in hydrochloric acid, reducing the 
solution electrol^tically with a platinum cathode, and satufating 
the green solution with hydrochloric acid.^ The salt decom- 
poses when heated before all the water hai been driven off. 
The aqueous solution rapidly oxidises in the air. Sparingly 
soluble double salts are formed with the chloridoB of the alkali . 
metals , 5 the potassium salt having the formula VCl3,2KCl,H20. 

Vanadium Bichloride or Vancidious Chloride^ VCIj.— This is a 
solid body, crystallising in fine apple-green coloured plates, having 
a micaceous lustre and a hexagonal form. It is prepared by 
passing vanadium tetrachloride, mixed with dry and pure hydro- 
gen, through a glass tube heated to dull redness, and is also 
formed together ^^ith silicon tetrachloride when ••vanadium 
silicide, VSig, is heated in chlorine.^ Its specific gravity at 18 ® 
is 3 * 23 . It is very deliquescent, yielding a lavender-coloured 
solution of vanadium dichloride, which possesses bleaching 
properties (p. 958 ). A violet solution containing thHShloride 
can be obtained by the electrolytic reduction of the trichloride. 
When* it is evaporated or when hydrochloric acid is added, 
hydrogen is evolved and the trichloride is formed, the reaction 
being extremely vigorous when a piece of platinum foil is placed 
in the acid liquid. Vanadious chloride is therefore a more 
vigorous reducing agent than chromoiLs chloride.® 

Vahxdium Oxytrichloride or Vanadyl Trichloride, VOCI3. 
—This compound, corresponding to phosphorus oxychloride, is 
obtained either by the action of chlorine on the oxides VO 
and V2O3 as already described, or by heating a mixture of the 
pentoxide and charcoal in a current of chlorine : 

V2O5 + 3 C -f 3CI2 = 2VOCI3 1- 3 CO. 

In the latter case, the resulting liquid is red-coloured from the 
presence of tetrachloride, and is best purified by rectification 

' Locke and Edwards, Amer. Chem, •/., 1808, 20, 504. 

^ Piccint %nd Brizzi, Zeit. anorg. Chem., 1890, 19, 304. 

• Stabler, Ber., 1904, 87. 4411. 

* Moissan and Holt, Compt. rend., 1902, 185, 78. 

' Picemi and Marino, Zeit. anorg. Chem., 1902, 82. 68. 



964 


THE VAKABIUM GROUP 


over clean sodium in a current of carbon dioxide. It is also 
formed ^ when dry hydrogen chloride is i^ssed over a mixture 
of vanadic and phosphoric anhydrides at 60—80°, and a solution 
in acetic acid may be obtained by treating vanadium pentoxide 
with a solution of ‘hydrogen chloride in glacial acetic acid.^ 
Vanadyl trichloride is a bright lemon-yellow, mobile liquid, 
boiling at ]26‘7° ancf having a specific gravity at 14° of 1*841. 
It dobs not solidify at —15°. The specific gravfty of its vapour 
is 6*108 at 186°, the calculated specific gravity being 6*003. 

On exposure ta. most air vanadyl trichloride emits vapoura 
of a cinnabar-red colour, and is soon decomposed in the presence 
, of moisture in^o vanadic and hydrochloric acids. When a small 
quantity of water is added it becomes thick and blood-red 
coloured owing to the formation of vanadic acid. A large 
quantity of water, however, yields a clear yellow solution.® 
When the oxychloride is ignited in a current* of dry ammonia 
gas, wuiadium mononitridc is obtained. Vanadium oxychloride 
condunes with ether at 70°, forming a compound crystallising 
in long, revl needles and having the composition VCl 3 (OC 2 H 5 ) 2 .* 

When vanadium oxychloride is heated with zinc to 400°, 
vanadium dioxide and vanadyl dicMoride, VOClg, are formed; 
the latter cjystallises in green tablets which deliquesce on ex- 
posure^ moist air. The same compound is formed when the 
vapour of vanadyl trichloride and hydrogen arc passed through 
a red hot tube. In this case vanadyl mnodiloride, VO(^, and 
divanadyl monochloridej VgOgCl, are likewise formed, the former 
as a flocculcnt, bVown powder insoluble in water, and the latter in 
the fonn of a yellow, crystalline powder resembling mosaic gold. 
Th(i molecular formulte of these bodies are not known. Vanadyl 
dichloride forms double conqmnds with two or four mofecules 
of the hydrochlorides of pyridine and qumoline.** 

Dminadyl Tetrachloride, V20A,5H20 or V0ei2,2*5H20. 
When vanadium i)entoxide is dissolved in hot concentrated 
hydrocliloric acid, chlorine is evolved and a green solution is 
obtained which becomes blue with deposition of sulphur when 
sulphuretted hydrogen is passed through the liquid. A brown, 
amorphous, deliquescent mass is obtained on evaporation, possess- 

«> 

* Ephroim, Zeit. anorg. Chem,, 1903, 35» 66. 

* K^oppcl and Katifmann, Zeit. anorg. Chem., 1906, 46i|362. 

* Sea AgafonofF, J. Jiues. Phge. Chem. Soc., 1903, 86, W9. 

* Bedson, Joum. Chem. Soc., 1876, i, 309. 

* KoppOl, Qoldmann and Kaufmann, Zeit. anorg. Chem., 1905, 45, ^6. 



VANADIUM AND SULPHUR 


905 


ing the above composition. It dissolves in water, yielding a blue 
solution; but when ^treated with strong hydrochloric acid or 
alcohol the solution is brown, and this change may possibly be 
due to the existence of two different hydrates.^ 

A compound of the formula V208Cl2,4ff2^ 
obtained as a dark green, deliquescent mass, by the action of 
hydrochloric acid qn vanadium pentoxide.^ 

Vanadium and Bromine and Iodine. 

423 Vanadium Tribromide, VBra.—Tliis is*the only known 
compound of the above elements. It condenses as a greyish- 
black, compact, amorphous sublimate when dry bromine vapour 
is passed in excess over vanadium nitride or over a mixture of 
vanadium trioxide and charcoal heated to redness. It is a very 
unstable compound, losing bromine even at the ordinary tem- 
perature in dry air, and deliquescing rapidly in moist air. 

The hydrated bromide, VBrgjGIIgO, and the corresponding 
iodide can be prej^ired in a similar manner to the^ hydrated 
chloride, which they closely resemble. 

Vanadyl Tribrmnide, VOEjfg, obtained by passing dry bromine 
vapour over vanadium sesquioxide heated to redness, is a dark red, 
transparent liquid, having a density of 2*967 at 0".* lypiay be 
distilled under diminished pressure, passing over without decom- 
position at a temperature of about 130° under a pressure of 
100 mA. When heated under the ordinary atmospheric pressure 
it suddenly solidifies at 180°, decom2)osing into free bromine and 
vanadyl dihromide, VOBrg, which is a brownish-yellow powder. 

Bivanadyl Tetra-iodide, V202l4,8H20, is formed by the action 
of hydriodic acid on the pentoxide as a dark, deliquescent mass.® 

Vanadium and Sulphur. 

424 The sulphides of vanadium correspond to the oxides.* 

Vanadium Monosulphide, VS, is formed when the sesqui- 

sulphide is strongly heated in a current of hydrogen. It forms 
a brownish-black powder or glistening brown scales, soluble 
slowly in dilute, quickly in strong nitric acid. It dissolves in 
alkali hydrosulphides, yielding a violet solution. ^ 

Vanadium Sesyuisulphide or Trmdphide, VgSg.— This was the 

* Crow, Jown. Chem, 8oe., 1870, ii., 453. 

* ' Ditto, Compt rend., 1880, RMS, 1310. 

4 Kay, Joum. Chem. 80c., 1880; 87* 728. 


* Ibid. 



966 


THE VANADIUM GROUP 


only vanadium salt free from oxygen prepared by Berzelius. He 
obtained it by heating the sesquioxide in a (torrent of sulphuretted 
hydrogen. It can in like manner be prepared from the pent- 
oxide, the oxychloride, or any of the chlorides, but it is best 
obtained by acting* on the ignited pentoxide with carbon di- 
sulphide vapour. It is a greenish-black powder possessing 
properties similar to Ihose of the monosulphide, VS. 

Va)fia(Uum Pentasulphide, VgSg, is formed by Seating the fore- 
going with sulphur to 400°. It is a black powder which on 
heating in a curw3nt of carbon dioxide yields sulphur and the 
sesquioxide (Kay). 

, Ammonium* Thiovanadate, (NH4)3VS4, is obtained by passing 

sulphuretted hydrogen into a cooled solution of ammonium 
metavanadate in ammonia of specific gravity 0-898. The 
crystals resemble those of potassium permanganate. If weaker 
ammonia be employed, ammonhnn kexa^ulpkopyrovatmlate^ 
(NH4)i4V28flO, is formed in dark green crystals. 

Several similar sodium and ].)otas.sium salts have been prepared 
from tlic «)rresponding meta- and pyro-vanadates.^ 

Vanadyl or Hypovanadic Sidphite, 6 VO.^, 4802,9110, is prepared 
by reducing barium vanadate with sftilphur dioxide, and filtering 
from the bajium sulphate : 

Ba(V 03)2 + H 2 SO 3 - BaS 04 -b lifi |- 2 VO 2 . 

When the filtrate is evaporated in an atmosphere of wilphur 
dioxide, the sulphite separates as a dark blue, crystalline powder, 
which spontaneously decomposes. It forms two scries of double 
salts with the alkali sulphites.^ 

Vanadious Sulphate, Y804,7H20, can be prepared by the 
electrolytic reduction of the blue solution obtained by the 
action of sulphur dioxide on vanadic anhydride in the presence 
of sulphuric acid. In order to obtfiin this salt in the pure state 
the greatest precautions must be taken to exclude oxygen. 
The blue solution gradually becomes green, then blue again, 
and finally violet as the reduction proceeds. It is then evaporated 
in vacuo, and the crystals are separated and dried with filter paper 
in an atmosphere of carbon dioxide. The salt is thus obtained 
in radish- violet, monoclinic crystals, which become bluish-violet 

^ IJjilss and Ohnmaia, Annaten, 1891, 863, 39; Kr^^, Zeit. anorg. Chem,, 
1893, 3» 264; Looke, Amer. Chem. J., 1898, 80, 373. 

* koppel and Berendt, Zeit, anerg. Chem., 1903, 36, 164: Gain,* 
rend., 1907, 1167. 



VANADIUM AND SULPHUR 


967 


on dr 3 dng and are very soluble in water, yielding a pure violet- 
coloiured solution, whifch becomes bluisb-violet in the presence of 
the slightest trace of oxygen. The solution at once reduces 
copper salts to metallic copper, the reaction proceeding quanti- 
tatively thus : * 

2 VSO 4 + CUSO 4 = ¥ 2 ( 80^3 + Cu. 

The salts of siJv?r, tin, gold, platinum, and mercury are also 
reduced to the metal. 

Vanadious sulphate appears to be isomorphous with ferrous 
sulphate, FeS 04 , 7 H 20 , and mixed crystals have been obtained 
both with ferrous sulphate and with magnesium ^sulphate. It 
readily forms double salts of the type with 

tlie alkali sulphates. Tlie.se can be prepared by adding the 
proper sulphate to the liquid to be reduced and crystallising, etc., 
as in the preparation of the pure sulphate. The ammonium salt, 
(NH 4 ) 2 ,S 04 ,VS 04 , 6 H 20 , forms reddish-violet, monoclinic crystals 
and is less easily oxidised than the pure sulphate, ana the 
potassium and rubidium salts closely resemble it.^ ^ 

Vanadium Sesquisulphate, ¥ 2 ( 804 ) 3 .™ Wlien the blue solution 
of vanadyl sulphate, prepp-red from 100 grams of vanadic 
anhydride, 200 c.c. of water, and 100 c.c. of concentrated sul- 
phuric acid, is reduced electrolytically until the vanaHiiui^ is pre- 
sent in the trivalent form, the compound ¥ 2 ( 804 ) 3 , 112804 , 121120 , 
known as vanadium sesquisulpkate sulphuric acidy separates * 
out green, crystalline powder. It readily forms a salt when 
evaporated with ammonium sulphate, green crystals separating 
out of the composition ¥ 2 ( 804 ) 3 ,(^ 14 ) 2804 , 121120 . 

When the acid salt is dissolved in a little water, sulphuric acid 
adde<i and the mass heated at 180° iA a current of carbon dioxide, 
the anhydrous sulphate separates out as a microcrystalline, 
yellow powder which is insoluble in water.® These compounds 
have a very close resemblance to the corresponding derivatives 
of titanium sesquioxide (p. 835). A solution of the sulphate 
acts as a vigorous reducing agent, and precipitates the ipetal 
from an acid solution of copper sulphate (Rutter). 

Vanadium i4fwww.—Several alums have been prepared by 
treating a metavanadate with sulphurous acid in the presence of 
sulphuric acid, and then reducing electrolytically. Ammdftium 

^ Picoini, Zeit. anor^. Chem., 1890, 19, 204 ; Picclni and Marino, Zeii. gnorg. 
Chm, 1902, 82, 55; Marino, Zeit. anorg. Chem., 1906, 60, 49; Rutter, Ztil. 
EkklroSbm., 1906, 12, 230; Z^t. anorg. Clwn., 1907, 52. 368. 

* St&h^er and Weithwein, Per., 1905, 89, 3978. 




068 


THE VANADIUM GROUP 


vanadium alum, crystallises in hemi- 

hedral forms of the regular system and is vif)let-coloiired. Alums 
containing potassium, rubidium, caesium, and thallium have 
also been prepared.^ A good yield of the alum is obtained by 
the electrolysis of ammonium metavanadate. The ammonium 
metavanadatc is placed in a porous cell with 50 per cent, 
sulphuric acid, a lead cathode being employed. The electrolysis 
is continued until the solution becomes green, ^hen on standing 
ammonium vanadium aliun crystallises out.^ 

The Vanadyl m llypavancdic Sulphates.— The blue solution 
obtained by the action of sulphur dioxide on a suspension of 
vanadic anhj^lride in dilute sulphuric acid contains sulphates 
of the radical or VO". These were termed hypovanadic 
sulphates by Roscoe, but are now generally known as the 
vanadyl siilpliates. From all solutions iii which the molecular 
ratio 112804 : VOg is greater than 1-5:1, acid sulphates are 
obtamed up to a temperature of about 201*5° ; from solutions in 
which the ratio is less than this normal salts are obtained, and 
these are/also formed by heating the acid* sulphates to about 
260”, or by treating them with water or alcohol. At the boiling 
point of sulphuric acid oxidation ocburs, vanadic anhydride and 
sulphur dioj^ide being formed (Koppel and Behrcndt). 

Vanoitj/l Sidphale, V202(804)2, is deposited as an insoluble, 

, blue, sandy powder by dissolving the dioxide, VOg, in excess of 
sulphuric acid and heating the solution for some time t(k 260°.^ 
If the dioxide be dissolved in sulphuric acid, the solution 
evaporated, and the residue treated with absolute alcohol, a 
sky-blue powder remains, which is a soluble form of the sulphate 
and deliquesces in moist air* This is also formed by heating the 
insoluble form with water at 130°. If the solution be allowed to 
e^'apo^ate spontaneously over sulphuric acid, fine, blue, rhombic 
prisms liaving the comimition Va02(S04)2, 41120 are deposited 
(Berzelius). In addition to this, hydrates with 13, 10, 7, 3, and 
2 molecules of water have been described. 

Wlien the acid solution containing more than 1*5 molecular 
proportions of sulphuric acid is evaporated, various hydrates of 
the acid salt, (V202)H2(S04)3 are obtained. The hydrate with 
* 

^ Piccini, Zeit. amrg. Chem., 189C, 11, 106; Chem. Cenir., 1897, i, 223; 
Bfll^mann, Zeit. Skktrochem., 1904, 9, 141. , 

* Renmhlor, Zeit. Ekcktrochem,, 1912, 18, 137. 

* Gerland, Ber., 1877, 10, 2109; Koppel and Behrendt, Zeit, anwrf. Chetfn,, 
1903, 86, *154. 



VANADItFBf AND ELBIBCEOTS OF NITROGEN GROUP 969 


5H2O is prepared by evaporating the solution on the water-bath, 
and washing the dried crystals with ether (Crow); at 125® the 
hydrate with is formed, and this can also be obtained 
by precipitating a concentrated solution of any of the vanadyl 
sulphates with concentrated sulphuric afid. At 150® the 
dihydrate is formed, at 175® a salt with 0-6 molecule of water, 
and at 190® the oiihydrous compound, 2Vl)2,3S03, which is a 
green powder, cAisisting of microscopic tetragonal tablets,* and 
is sparingly soluble in water (Koppel and Behrendt).^ 

Many double salts also of this series are known^nd are described 
in the memoirs cited above. 

Nornml Divanadyl Trisulphate, (¥0)2(804)3, ^is obtained, 
according to Berzelius, by dissolving the pentoxido in hot 
sulphuric acid which has been diluted with half its weight of 
water.2 On evaporating at a low temperature the salt crystallises 
out in reddish-brown, very deliquescent scales. The same 
compound is obtained in ruby-red octahedra by boiling the 
pentoxide with an excess of sulphuric acid. When these are 
heated to the melting point of lead, the basic salt, (V0)jj0(S04)2, 
remains as a red mass with small, bright, crystalline faces. 

If the pentoxide be dissolved in concentrated sulphuric acid 
and the solution evaporated, the basic salt, V0(pH)S04, 
formed 5 as a sandy, reddish-yellow powder. AccoflBTig to 
Gerland, this is identical with the preceding compound. 

Whe|^ potassium vanadate is dissolved in strong sulphuric 
acid and the excess of acid driven off by heat, the double salt, 
^2^^4>(¥0)2(S04)3, is obtained as a yellow, crystalline powder, 
(Berzelius), 

V^ADiUM AND Nitrogen, Phosphorus, and Arsenic. 

425 Vanadium Mononilride, VN. — The mononitride is obtained 
by strongly igniting the ammonio-oxychloride in a current of 
dry ammonia (or rather of its component gases) at a white heat 
as a greyish-brown powder, which does not undergo change at 
or^nary temperatures. It is likewise obtained when the black 
residue left on calcining ammonium metavanadate in the air is 
heated to whiteness in a current of dry ammonia. Other 
methods of obtaining the nitride are to expose the oxid% or 
dichloride to the action of ammonia gas at a white heat. 

• 

^ Seo also Gain, Comfit rtnd., 1906, 148» 1164. 

* See also Ditte, Qowfi. rertd., 1886, 106, 767. 

» Uerland, Btr., 1878. 11. 98. 



970 


THE VANADIUM GROUP 


When heated in the air, vanadium mononitride glows anc 
slowly oxidises to the blue oxide; when fceated with soda-lime, 
ammonia is produced. 

Vanadium Dinitnde, VNj, is obtained as a black powder by 
passing ammonia over vanadyl trichloride, heating the residue in 
a glass tube to expel ammonium chloride, washing with water, 
and drying in a vacuum over sulphuric acid. , 

426 Extended series of phosphovanadic atfd arsenovanadic 
acids and their derivatives have been described by Berzelius,^ 
Ditte,® and Gibbs.* According to Friedheim ^ these substances 
are phosphates and arsenates of vanadium (and double salts of 
these with the vanadates), in which vanadic anhydride acts 
as a weak base, the radical VOg replacing one or two hydrogen 
atoms of phosphoric or arsenic acid. They can be prepared by 
bringing the requisite salts together. 

Phosphovanadic Add, 2 (Y 02 )Vi 2 V 0 ^,dlJ.p — P205,V205,11H20, 
is foimed when vanadic anliydride is heated with syrupy phos- 
phoric acid, and crystallises in golden-yellow flakes. 

Arsenovanadic Acid, As2O5,V2O5,10ll2O, is'prcpared in a similar 
manner, and forms yellow crystals. 

VANADIiJM AND THE ELEMENTS OF THE CaRBON GrOUP. 

427 Vanadium Carbide, VC, is formed when vanadic an- 
hydride is heated with carbon in the electric furnace. It forms 
hard crystals of the specific gravity 5 * 405 , burns in oxygen, and 
becomes incandescent when heated in chlorine.'" It is silvery- 
white, very hard, and melts at 2750 ®.® 

Vanadium Cyanides.— I>o\ih\e salts of vanadium dicyanide 
and tricyanide with potassium cyanide of the f^rraulee 
K4V(CN)g,3HaO and KgVfCN)^ have been prepared.^ 

Potassium Vamdic Thiocyanate, V(SCN)3,3KSCN,4H20, is 
prepared in a similar manner to the cyanide (Locke and Edwards), 
and separates in dark red crystals, the solution of which in water 
rapidly decomposes. The ammonium and sodium salts have 
also been obtained.® 

> Lehrbuch, [6], 8, 1037. • Campi. rend., 1886, 102, 757. 

*Jmer. Chem. J, 1886-6, 7, 118, 209. * Btr., 1890, 23, 1630, 2600. 

' Moiasan, Cvmpt. rend., 1806, 122, 1297. 

* Ruff and Martin, Zeit. angew. Chem., 1912, 26, 49. 

’ Petersen, Zeit. anorg. Chem., 1904, 88, 342; Locke and Edwards, Jmer^ 
Chem. J„ 1898, 20, 694. 

* Cioofi Zeit. anorg. Chem., 1899, 19, 308. 



DETECTION AND ESTIMATION OF VANADIUM 971 


Complex ammonia vanadyl thiocyanates and oxalates have 
likewise been preparec?.^ 

Yanadium and Silicon . — Vanadium forms two compounds 
with silicon. The silicide^ VjSi, is prepared ^ by heating 120 
parts of the sesquioxide with 14 of silicon in the electric furnace, 
or better by heating this mixture with either carbon or copper. 
It forms hard, silvei-whitc prisms with a metallic lustre, and has 
the sp. gr. 5-48 at 17°. It is only attacked by fluorine when 
gently heated, and it is readily decomposed when heated in 
chlorine, bromine, or hydrogen chloride. It is msoluble in acids, 
with the exception of hydrofluoric acid, and is decomposed by 
fused potash. When it is fused with silicon it is (inverted into 
the disilidde, VSig, which can be obtained also by heating the 
sesquioxide with an excess of silicon in the electric furnace, or 
by igniting a mixture of the oxide and silicon with metallic 
magnesium.^ It forms hard prisms with a metallic lustre, has 
the sp. gr, 4*42, and melts and volatilises in the electric furnace. 
It is soluble in hydrofluoric acid, burns when heated in fluorine, 
chlorine, or bromine, and is attacked by gaseous ^lydrogen 
chloride. It is also decomposed by fused alkalis, and by molten 
copper, an alloy of this metal with vanadium being formed. 

Detection and Estimation of Vanadium. 

428 insoluble vanadium compounds can be brought into ' 
solution by treatment either with acids or with alkalis. The 
hydrochloric acid solution assumes a bright blue colour on the 
addition of zinc. A solution of vanadyl sulphate cannot be 
distinguished in colour from one of copper sulphate when diluted 
to the requisite extent with water. It, however, of course, does 
not become colourless in presence of metallic iron. Solutions 
of certain vanadates also closely resemble solutions of the chrom- 
ates. Thus, for instance, a solution of the tetravanadate of 
potassium does not differ in appearance from one of potassium 
dichromate. They may, however, be distinguished from •one 
another, inasmuch as the vanadate solution becomes blue, whilst 
the chromate assumes a green colour, on reduction. When 
a solution of vanadic acid or an acid solution of an ^kali 
vanadate is shaken up with ether containing hydrogen peroxide, 
the aqueous soluliion assumes a red colour like that of ierric 

* Koppel and Goldmann, Zeit, anorg. Chem.f 1903, 86, 281. 

• Moision and ftolt, Compt. rend.^ 1902, 186, 49.3. ■ Ibi^t 78. 



972 


T5E VANADIUM GROUP 


acetate. This reaction serves to detect 1 part of vanadic acid 
in 40,000 parts of the liquid, and is not aHected by the presence 
of chromic acid.^ 

For the quantitative estimation of vanadium in a soluble 
vanadate it may be treated with lead acetate, when basic lead 
vanadate is precipitated. The precipitate is insoluble in acetic 
acid but it dissolves readily in nitric acid| liberating vanadic 
acid* which separates out, but dissolves completely when the 
liquid is warmed. In the analysis of a soluble vanadate this 
insoluble lead salt is collected on a filter, dried at 100°, and 
weighed ; a given quantity of the dried salt is then dissolved in 
nitric acid, the lead precipitated by pure sulphuric acid, and the 
lead sulphate estimated with the usual precautions by evaporation, 
addition of alcohol, etc., or the filtrate is evaporated and the 
residue heated and weighed as vanadic anhydride.^ The lead 
sulphate thus obtained is quite free from vanadium, whilst the 
vanadium pentoxide in the filtrate is obtained perfectly pure 
and well crystallised on evaporation and ignition. The filtrate 
from thoTlead vanadate, freed from excess of lead by means 
of sulphuric acid and evaporated, yields the alkali sulphate, 
containing no trace of vanadiunf. Vanadium may be very 
readily est\juated volumetrically when no other reducible metals 
are p?58ent. For this purpose the solution of vanadic acid 
in sulphuric acid is diluted and reduced to a vanadyl salt by 
passing a current of sulphur dioxide through it and afl^.rwards 
boiling to expel the excess of this gas. Standard permanganate 
is then added until a permanent coloration is obtained. The 
inverse process may also be employed, and the acid solution of 
a vanadate titrated with decinormal ferrous sulphate solution, 
potassium ferricyanide being employed as indicator.® *Under 
these circumstances the acid is reduced to VOg and the process 
can be carried out in the presence of copper. The reduction 
may also be effected by repeated evaporation with hydrochloric 
acid.^ 

He Atomic Weight of vanadium has been determined in 
several ways. One is by igniting vanadium pentoxide in dry 


* Werthcr, J, pr. Chtm., 1863, 88» 195. 

* ConninibcDuf, Ann. Chim, anal.t !902, 7, 258. 

> WilliamB, J. Soc. Chem. Jnd., 1902, 21, 389. , 

* CampAgne, Ber., 1903, 88, 3164. See also Gooch and Stookey, Amr. J. 

Sci.t 1902, [4], lA 369; Qoooh and Gilbert, Zeit, anorg. Chem.^ 1903, 96, 420; 
Nakasona. J. Chm. Soc. Japant 1921, 42, 761. * 



OOLUHBIUM 


973 


hydrogen, when it is reduced to the sesquioxide, and the atomio 
weight of vanadium iaideduced the loss in weight. 

In this manner Roscoe ^ obtained the value 51*38. A second 
and more trustworthy method for the determination of the atomic 
weight of vanadium is the analysis of vanaJy^l trichloride. The 
chlorine in this compound was estimated by Roscoe both volu- 
metrically and gra^raetrically, the results Being 51*0(5 and 51*26 
respectively. T 8 e gravimetric analysis of vanadyl trichroride 
by Prandtl and Bleyer ^ yielded the value 51*07, while McAdam,® 
by the conversion of sodium vanadate into sodium chloride found 
50*97. A still further determination by Briscoe and Little, 
who analysed vanadyl trichloride, gave the value 60*90, in close 
agreement with that of McAdam. The value now ado[)ted 
(1922) for the atomic weight of vanadium is 51*0. 


COLUMBIUM. Cb = 93i* At. No. 41. 

429 This metal is*so closely connected with the ncjafc member 
of the same group, tantalum, that it will be most convenient to 
consider their history together. 

In the year 1801, Hatchett^ laid before the Rt^al Society 
an investigation on a mineral known as columbiff?^ from 
Massachusetts, which he believed to contain a new metal 
to whjph he gave the name coluinbwm. In the following 
year, Ekeberg,® in Sweden, investigating the yttrium minerals, 
discovered a new element in a mineral to which he afterwards 
gave the name of yttrotantalite, whilst the same element also 
(xxjurred in a mineral termed tantalite. In consequence of this 
he ndhied the metal tmtxihm^ partly because mythological 
names were frequently used, and partly also as pointing to the 
fact “that when placed in the midst of acids it is incapable 
of taking any of them up and saturating itself with them.” 

In 1809, Wollaston^ endeavoured to show that colurabium 
and tantalum were identical, and a few years later BerzeKus ® 
more carefully investigated the oiddes of the last-named metal 
obtained from tantalite, and prepared tantalic acid. After- 

» Phil Trans,, 1868, 168 , 6. * 

• Ztil anorg, Chem., 1909, 66 , 152; 1910, 67 , 267. 

* J, Amer. Chem. sSc., 1910. 88, 1603. « Joum. Chem. Soc., 1914, 106, "1310. 

» PhU. Trans., 1802, 98 , 49. • Ann. Chim., 1802, 48 , 276. 

^ Phil Trans., 1809, 99 , 246. • Pogg. Ann., 1820, 4 , 6. • 




974 


THE VANADIUM GROUP ^ 


wards, in 1839, WoMeri found that the acid-forming oxide 
contained in pyrochlor and in the Bavarian tantalites possessed 
peculiar properties ; and Rose ^ then observed that the colum- 
bites of Bodenmais contained the oxide of a new metal, to which 
he gave the name* of niobium (Nb), and in 1846 he thought 
that he had found a third new metal, to which he gave the name 
of j>el(ypium. In 1^53 he came to the cojiclusion on further 
investigation that niobic acid and pelopic acfd were different 
oxides of niobium, and to the first of these he gave the name of 
niobic acid, whilst the latter was designated as hyponiobic acid. 
These, however, exhibited “ a relationship so peculiar that the 
whole range of chemistry does not furnish an example of a similar 
kind.” ® In 1856-7 Hermann observed that niobium and 
tantalum usually occurred together, whilst in 1864-5, Blom- 
strand^ showed that Rose’s hyponiobic chloride contained 
oxygen, and was an oxychloride, and Marignac ^ almost at the 
saiuft time provcjd that the double salts which hyponiobic fluoride 
forms with metallic fluorides are isomorplious with similar 
double s«lts containing titanium fluoride, ' Tih^, and tungsten 
oxyfluoride, WOaFj. Inasmuch as the sum of the atoms in all 
these isomorplious compounds is c6nstant, and as, according to 
analysis, tlip hyponiobic fluoride contains three atoms of fluorine 
for on^f oxygen, Marignac concluded that it must be an oxy- 
fluoride of the composition NbOFg, and he succeeded in obtaining 
experimental evidence of the truth of this view. At the same 
time, ho showed that tantalic acid, which up to that time had 
been supposed to be analogous to titanic acid, and to which the 
formula TaOjj had been given, must, like the highest oxide of 
niobium, be a pentoxide, as these two oxides occur in isomor- 
phoub mixture in several minerals, and as both metals form 
isomorplious double fluorides, such as KgTaF^ and KgNbF^. 

The name columbiimi, originally proposed by Hatchett, has 
always been employed in America for Rose’s niobium, and has 
recently also been adopted in England, whilst in Germany the 
name uiobiiun is retained. 

The truth of this view of the composition of the columbium 
and tantalum compounds was confirmed by the experiments of 
De^le and Troost,® who in 1865 determined the vapour 

‘ Pogg, .4nn., 1839, 48 , 91. * IbuL, 1844, 63 , 307, 093; 1846, 69 , 118. 

» rbiti., 1863, 90 , 471. J. pr. Chim., 180l>, 97 , 37. 

* .4»». Chim, Phy9., 186ti, [4], 8, 6, 49. 

* rend., 1866. 60 . 1221. 



WJUJittUlUM 


975 


densities of columbium chloride, columbium oxychloride, and 
tantalum chloride, xvihich were found to correspond to tlie 
formulas CbClg, CbOCls, and TaCl5. investigations of 

Blomstrand and Marignac next showed that the metal dianium, 
supposed by v. Kobell to be contained in farious columbites, 
is in fact identical with columbium, and Marignac further showed 
. that ilmenium, whjph Hermaim believed h*e liad discovered in 
samarskite, is a* mixture of columbium and tantalum! It 
appears certain that neptiiniumf also discovered by Hermann, 
is a similar mixture.^ ^ 

■ 430 ^-The only tantalum ore of commercial importance is 
tanlalile, FeO.TajOj, of ferrous tantalate, whiclk is a black 
mineral the density of wliich varies from 6-5 to 7 * 3 . Tart of the 
tantalum is invariably replaced by columbium, and part of the 
iron by manganese, until in inanganolmUalite, Mn0,Ta206, 

• manganese is the chief metal present. Microlile^ or calcium 
tantalate, CaOjTagOg, is also known, while a very interesting 
mineral is siihiotanlalite, (Sb0)aTa(Cb)206. 

Colunibite, FeO,Cb2^6» most commonly occurring 

^ columbium tantalum mineral. Part of the columbium is 
always replaced by tantaluiif, and manganese accompanies the 
iron. The density varies from 5*3 to ()’ 5 , increasing with increase 
in the content of tantalum. Like tantalite, the mineral cry^^Ullises 

• in orthorhombic prisms. 

Coluigbite and tantalite have been found ip Scandinavia, 

“ Finland, Kussia, Greenland, Bavaria, Ceylon, Malay States, in 
Dakota and other parts of the United States, and particularly in 
^\estern Australia, in the Pilbara and Greenbushes gold-mining 
districts.’*^ The Pilbara district is the most important, and 
product almost entirely manganotantalitc. The accompanying 
table records the analyses of various samples of the minerals 
already mentioned. (See Table on p. 976 .) 

Of the numerous other coluinbium-tantalum minerals, several 
may be briefly mentioned, since they also contain the rare earths. 
^schynite, Ce2Cb40ji3,Ce2(TiTh)50i3, is essentially a columbo- 
titanate of the cerite earths, containing thorium in considerable 
quantity. It is found in Norway and the Urals. Fergusonite, 
(Y,Ce)(Cb,Ta)04, ^ ® metacolumbate of the yttrium earths 

^ See Smith. Proc. Apicr. Phil. Soc., 1905, 4i 151 ; HaU and Smith, J, 4mer. 
80c., 1905, 27, 1369; Barr, ibid., 1908, 30, 1668; Hildebrand, ibid., ftos. 

80, 1672. 

* See Si^peon. dhem. News, 1909, 99 , 49, 77. 

VOL. n. (n.) L 



m * THE VANABIHM GROUP 


Mineral. 

Tantalite. 

Columbite. 

Mangano- 

fantalite. 

Micro- 

lite. 

Stibio- 

tantalite 

Locality. 

Oreen- 

bushes. 

Sweden. 

Green- 

land. 

Massa- 

chu- 

setts. 

Pilbara. 

Pilbara. 

Green- 

bushes. 

Ta,0, . 

CbjOj . 

80'61 

2-50 

4^-64 

29'27 

1 77-97 

28-55 

51-53 

68-£5 
16- If 

1 77-16 

61-96 

4-49 

WO, . 

0*13 

— 

^ 0-13 

0-76 

— 

— 

— 

SnOa . 

1-51 

2-49 

0-73 

0-34 

0-48 



— 

TiO,. . 

0-71' 


— 


0-40 

— 

— 

ZrOj . 



0-13 

0-24 

— 




SiOj . 



— 

— 

— 


3-14 

FeO . 

10-89 

13-77 

17-33 

13-54 

1-63 

3-64 



Fe,0, . 


— . 

— 

— 

— 

— 

0-39 

MnO . 

3-78 

2-88 

3-28 

4-55 

14-15 

0-60 



CaO . 



— 

— 

— 

13-46 




0-19 


0-23 

0-42 

0-15 

0-42 

— 



0-12 

— - 







Na(K),0 



— 

- . 


1-86 



Sb,0, . 




... 


— 

38-04 

Bi203 . 






— 

0-79 

CuO . 


■ - 


• 

— 

— 

0-20 

H,0 . 

0*14 

— 

— 

0-16 

0-07 

1-28 

0-61 

Analyst, 

Simp- 

son. 

Uaramels- 

borg. 

Blomstrand. 


Simpson. 



oontdining also thorium and uranium. It occurs in Greenland, 
Scandinavia, and various localities in the United States. YUro- 
tanlalile and sarnarskite are columbo-tantalates of yttriuA, iron, 
and calcium, the latter mineral containing considerable amounts 
of uranium. Sarnarskite occurs massive in North Carolina, and 
has also been found in India. Euxenite is an orthorhombic 
:^umbo-titanate of yttrium, containing uranium; the iso- 
morphous mineral polycrase is similar in composition, but contains 
ess columbium and more titanium. 

Besides occurring in these and other minerals, columbium and 
4m^um are frequently found in small quantities in tinstone, 
volfram, pitchblende, monazite, and other minerals. 

||or the purpose of preparing columbium and tantalum com- 
>ounds, it is best to start with columbite or tantalite, which 
ontaip very little titanium, rather than to mploj^ one or 




COLtJMBIUM 


977 


other of the minerals rich in titanium, since no methods are 
yet known for the qiAntitative separation of columbium and 
tantalum from titanium, at any rate when operating on a fairly 
large scale. For decomposing the minera^ Giles ^ strongly 
recommends fusion of the finely powdered substance with 
2^ to 3 times its weight of potassium car^^onate in a steel or 
wrought-iron crucibte. The fusion is carried out in a reducing 
atmosphere by placing the crucible, covered with a lid, inside a 
larger crucible, the inner crucible being completely surrounded 
with charcoal. In this manner the columbiunl and tantalum 
are transformed into potassiiun columbatc and tantalate, which 
may be extracted from the fusion with water, leaVing behind 
the iron and manganese as monoxides in the form of a heavy, 
black sand. Small amounts of easily reducible metals such as 
tin and antimony (and tin is a constant constituent of the minerals) 
are completely removed in the metallic state, the metal usually 
alloying with the metal crucible. The aqueous extract is nlhde 
slightly acid with hy^ochloric acid and heated to boiling, when 
the hydrated pentoxides of columbium and tantalum Separate 
out as a white precipitate. The precipitate is thoroughly washed 
by decantation with hot water. 

The classic method for the decomposition of the »>inorals is 
fusion with acid potassium sulphate. For this purpose, the 
mineral is finely powdered and fused with three times its weight 
of the b«ulphate ; the fused mass is completely boiled out with 
water, when a residue of crude columbic and tantalic hydroxides 
is left. This is digested with ammonium sulphide for several 
days, in order to remove most of the tin and tungsten, which 
are always present. The residue is washed, boiled with a little 
dilute sulphuric acid, and again thoroughly washed with water. 

The columbium and tantalum are separated by taking advan- 
tage of the different solubibties of the double potassium fluorides, 
K^CbOF 5 ,HjO and KjTaF^, which dissolve in about 12 and 200 
times their weight of water respectively at the ordinary tempera- 
ture. The hydroxides are diwolved in hot hydrofluoric adid, 
filtered from any mineral residue or potassium silicofluoride, the 
solution treated with enough potassium fluoride to form the 
double tantalum salt, and concentrated if necessary. On cooling, 
fine, characteristic, needle-shaped crystals of the tantalum salt 
separate out, and aflre washed with water. On evaporating the 
tnother-liquor and wash-waters, more of the salt is obtainedi 



078 


THE VANADIUM GROUP 


which at last is mixed with scales of the columbium salt. The 
potassium tantalofluoride is purified from j^ractically all impurities 
but a trace of silicofluoride by one or two crystallisations, mixed 
with its own weight of concentrated sulphuric acid and heated 
gradually to 40()'' until the hydrofluoric acid and most of the excess 
of sulphuric acid arij expelled. The residue is then disintegrated 
by boiling with water, and thoroughly washcej, first with water, 
and finally with dilute ammonium carbonate, until all the 
potassium and sulphuric acid have been removed. The pure 
tantalic hydroxide is then ignited if it is desired to form the 
pentoxide. 

The filtrate from the tantalum salt is treated with a further 
quantity of potassium fluoride and concentrated, when, on cooling, 
the columbium salt, K2Cb0F5,H20, separates out. The salt 
thus obtained contains a little tantalum. It is therefore heated 
to 2(X)° for some hours and extracted with water, when a residue 
of ^iotassium tantalum oxyfluoride is obtained and removed 
by filtration. The solution is evaporated^ to dryness and the 
baking it 200 ' and extraction with water are repeated until all 
the tantalum has been removed. From the purified columbium 
salt the silica-free hydroxide and oxide may be obtained as has 
already b<>3n described for tantalum.^ 

Tlie oxides of columbium and tantalum obtained in the pre- 
ceding manner usually contain small quantities of oxides of tin 
and tungsten. These may be removed by Rose’s mithod of 
fusion with a mixture of sodium carbonate and sulphur, and 
extraction with water. The tin and tungsten pass into solution 
as thiostannate and tungstate, and the residual sodium 
columbate or tantalate is then washed with cold water, in which 
it is nearly insoluble, and fused with potassium bisulphate to 
recover the oxide. This treatment with sodium carbonate and 
sulphur may have to be repeated several times. 

The columbic oxide still contains small amounts of oxide of 
titanium, and no satisfactory separation of this impurity is 
kifown which does not remove also a considerable proportion of 
the columbium. The simplest procedure is to crystallise the 
double fluoride, K 2 CbF 7 , from fairly concentrated hydrofluoric 
aeid five or six times; this also eliminates tin and tungsten.^ 

\ Jlall, J. Amer. Chem. Soc., 1904, 80, 1236; Hall and Smith, ibid., 1906, 87. 
1309. See alao Rufif and Schiller, Zeit. anorg. Chem., 1911, 78, 329. 

* Balko and Smith, J. Amer. Ohm. Soc., 1908, 30, 163J; cf. Hall, Uk. cit.; 
Hlall aifd Smith, loc. cif. t 



COLUMBIUM 


979 


Ritff and Schiller prefer to eliminate titanium by fractional dis- 
tillation of the columijium pentachloride, the titanium chloride 
being much the more volatile. 

431 Columbium was first obtained by Blomstrand,^ by reducing 
the chloride in hydrogen, as a mirror-like d^iosit on the tube, 
but it was not certain whether this was the pure metal or a 
hydride. Roscoc ® pbtained it in the form bf a steel-grey crust, 
by passing the Vapour of the pure chloride together Vith 
hydrogen repeatedly through a red-hot tube; this was then 
more strongly heated in a porcelain tube, , through which 
hydrogen was passed. The metal contained only 0*27 j)er cent, 
of hydrogen as well as a small quantity of chloride and o.vide, 
the latter being derived from diffused air. It has been prepared 
in a somewhat impure condition as a metallic regulus by heating 
the pentoxidc with carbon in the electric furnace,® and by 
reducing the pentoxidc with the mixed metals of the cerite 
earths, the method being the same as that emjdoyed for '»na- 
dium (p. 918).'* It can be obtained in the pure condition by 
preparing fdaments*of the oxide, CbOg, by heating i% mixture 
of the pentoxidc and paraffin which has been pressed into 
threads, and then reducing this by passing through it an 
alternating curnmt in vacuo. The regulus obtained by the 
aluminium reduction of the pentoxidc may moreover be freed 
from aluminium by being heatixl in vacuo in an electric furnace.® 
The nij^tal has the specific heat 0-071 and the density 8-4, and 
melts at about lObO'^. The pure metal has a light grey colour, 
and is about as hard as wrought iron. It can be rolled into 
foil and then drawn into wire, and can be welded at a red heat. 
A regulus fused in a vacuum consists of crystals, apparently 
rhomlllc, several mm. in length. It combines only slowly with 
oxygen, even when it is strongly heated, and unites with hydrogen 
to form the hydride, Cbll. This compound, which has also 
been obtained by Marignac, resembles the metal in its behaviour 
to acids, and burns when heated in the air.® Columbium is 
not dissolved by hydrochloric or nitric acid or aqua regia, Qven 
when heated, but when alloyed wdth other metals is attacked 
by acids. It is attacked by fused alkalis and fused oxidising 
agents, and combines with nitrogen at 1200'^. 

^ J. pr, Chfm., 1800, 97, 37. ® Mem. Munch. Phil. Soc., [3], 0, 180. 

* Moiasan, Compt. rpnd.^ UK)!, 133, 20. 

* Weiss and Aichcl, Annalen, 1904, 337, 380. 

* Uoraer von Bolton, Zeit. Eleklrochem., 1907, 13, 145. 

* KrCiaf and ^JiTson, Ber., 1887, 20, 1091. 




THE VAiJADIUM GBOUP 


COMPOUNDS OF COLyMBIUM. 

COLUMBIUM AND OXYGEN. 

432 The two loTA^er oxides of columbium are usually known 
as the dioxide, Cb 202 , and the tetroxide, CbaO^, although they 
would more properly be termed the monoxide, CbO, and the 
dioxide, CbOj. ** f 

Coltimhinm Dioxide, CbO or CbgOj, is formed when dry 
potassium columbium oxyfluoride is heated with sodium under a 
layer of potassium chloride over a gas blow-pipe, and was thought 
by Rose to the metal. The fused mass is boiled with water, 
and tlic residue washed with water and afterwards with dilute 
alcohol. It then forms a white powder which on heating in the 
air oxidises with vivid incandescence. When gently warmed in 
chlorine gas, it burns with formation of oxychloride, and it dis- 
solves in the moist state in hydrochloric acid with evolution of 
hydrogen. If the vapour of the oxychloride be passed over 
heated n^gnesium wire, the same compound is formed in crystals 
which belong probably to the regiilar system. 

Cohtmbinm Tetroxide, CbOg or € 1 ) 304 , is obtained as a heavy, 
black powder, which appears blue by reflected light, by heating 
the j)entokide very strongly in hydrogen or with metallic 
magnesium.^ It is not attacked by acids, and burns in the air 
when heated to redness. 

Columbium Pentoxide, CbaO^. — The preparation of tins oxide 
has been already de.scribed. It is a white, amorphous, infusible 
powder having a sp. gr. of 4«5 to 5-0, according to its method 
of preparation, and becomes yellow and crystalline wlien strongly 
heated. It may be obtained in prismatic crystals of'sp. gr. 
4*568 by fusion with boron trioxide or borax. 

Colinnbic Acid or Cohwibium Hydroxide, HCbOa, obtained 
as already described on p. 977, and is also formed by the decom- 
position of the oxychloride or pentachloride in moist air or with 
water. It is a white powder which, when dried at 100 °, retains 
varying quantities of water, and is converted into the pentoxide 
it a red heat with incandescence. It is only slightly soluble in 
liot hydrochloric acid, but the residue, after this treatment, can 
dissolved in water. On the addition of zinc the solution 
becomes blue and a hydrated precipitate, probably of CbjOi, 
leparates out. The solution of columbic acid obtained by 
j ‘ Smith and Maas, Zeit. anorg. Chem., 1894, 96, 


COLUttBIUM AND OXYGEN 


treatment with hydrochloric acid gives, on the other hand, a 
brown colour with zin%, and a brown oxide separates out which 
has the composition Cb30fi(= Cb0,2Cb02). Columbic acid is 
easily soluble in caustic alkalis and their carbonates. 

C6lumhates.—T\\^ salts of columbic acid arelermcd columbates. 
Many of these salts were described by the early workers on 
columbium; but comparatively few were definite chemical 
individuals. The first definite sodium salt, 7Naa0,6Cb203,32'fT30, 
was prepared in 1905 by Bedford.^ Since then the columbates 
have been carefully studied by Balke and Smith, ^ who have 
shown that several series of these salts can be obtained. 

The 7 : 6 series^ 7M‘20,6Cb205,a;H20.— The sodiiifn salt of this 
series may be prepared by precipitating potassium columbium 
oxyfluoride in aqueous solution with three times its weight of 
caustic soda, washing the precipitate with cold water, and 
racrystallising from boiling water. The salt is not very soluble 
in hot, and almost insoluble in cold water. It may ah^ be 
obtained by fusing columbium pentoxide with four parts of 
caustic soda or 3 parts of sodium carbonate, extractii% most of 
the excess of alkali with cold water, and crystallising the residual 
sodium columbate. The salf is precipitated unchanged from its 
aqueous solution by the addition of alcoliol, and from it, by 
double decomposition, the corresponding barium, silver, and zinc 
salts have been obtained. The potassium, Ciesium, and lithium 
salts oh this series are also known. 

The 4 : 3 series^ 4M'20,3Cb206,a:H20.— The potassium, rubidium, 
and caesium salts are known. The last two salts crystallise with 
UHjO and are isoraorphous with each other and with the corres- 
ponding tantalates. The 'potassium salt crystallises with IfiHjO 
and is the easiest columbate of potassium to prepare, being 
obtained by fusing columbium pentoxide with twice its weight 
of potassium carbonate and crystallising the product from water 
(Marignac). Its aqueous solution yields the 7 : 6 salt when 
precipitated with alcohol. 

The 1 : 1 series^ M^2^,Cbj05,a;H20. — The sodium salt, 
Na20,Cb205,7H20, separates out when the mother-liquor from 
the crystallisation of the 7 : 6 salt is allowed to evaporate spon- 
taneously, and may be prepared by slowly evaporating ^an 
aqueous solution of the 7 : 6 salt on the water-bath while an 
atmosphere of carbon dioxide is maintained above the solution.* 

» J. Amer, Q^etn. Soc., 1905, 87, 1210, * Ibid., 1908, 80, 1637. 

• Snflth and van Haagen, J. Amr. Chtm. Soc., 1916, 87, 1783. * 




THE VANADIUM GROUP 


It is much more soluble than the 7 : 6 salt. It becomes anhydrous, 
hut is stable at a red heat From tiit aqueous solution, by 
double decomposition, the silver, magnesium, copper, cadmium, 
and aluminium salts have been prepared. 

The 3 : 4 series, ^M' 204 Cb 20 ^,xB 20 .— Only the rubidium salt 
is yet known. 

Numerous cryatalfiiie columbates have been prepared by fusing 
the ’precipitated salts with the corresponding* clilorides or with 
boric acid.^ 

Percohmbic Add is formed as an amorphous, yellow powder 
when columbic acid is warmed with hydrogen peroxide, or when 
sulphuric achl is added to a solution of potassium pcrcolumbate 
and the solution dialysed and evaporated. It has the composi- 
tion of a hydrated percolumbic acid, HCb 04 , and is decomposed 
by dilute sulphuric acid only on warming, thus differing from 
other per-acids.2 The percolumbic acid, Cb(OH)g or 
has also been prepared.® 

Ortliopcrcolumbat(;8 of the general formula MgCbOg, where 
M is a urfvalent metal, have been obtained Gy Balke and Smith ; * 
these represent some of the most highly oxidised series of salts 
known. They are prepared by adding an excess of hydrogen 
i)croxidc tq an aqueous solution of an alkali columbate, together 
with the corresponding alkali hydroxide, and precipitating with 
alcohol. The pota.ssium, sodium, rubidium, and cflcsium salts 
are anhydrous, white, crystalline solids,- quite stable intair and 
in warm aqueous solution ; they are decomposed, however, with 
liberation of oxygen, when the aqueous solutions are boiled. 
By double decomposition the following ])ercolumbates have also 
been prepared : 

ۥ 

MgNaCb()B,8H2() MgCsC’bOg.SHgO 

MgKCb()8,7II.20 CaNaCbOg,4H2() 

MgKbCb0g,7JH20 CaKCb08,4H20 

• COLUMDIUM AND THE HaLOGENS. 

433 Colvmbimn PentaJIuoride, CbFj, is prepared by treating 
the pentachloride with anhydrous hydrogen fluoride, and frac- 

^ liarsson, Zeit. atwnj. Chem.^ 1390, 12 , 188. Seo also Holmquist, Jovm, 
f Sm'., 1898, 74 , ii, 388. 

• Molikoff and I’issarjewsky, Zeit. amnj. Chan.^ 1899, 20 , 340. 

> Hall and ISmith, J. Amer. Chem. Soc., 1905, 27 , 1369. ^ 

• J. Amer. Chem. Soe„ 1908, 30 , 1637. ' \ 



COLUMBIUM AND THE HALOGENS 


983 


tionating out the product under reduced pressure. It is a 
colourless, crystalline toll'd of density 3*29, which melts at 76*6° 
and boils at 217—220®. It is rapidly decomposed by water, 
acids and alkalis, alcohol, and ether.^ • 

Cohmhium Oxiffluoride, CbOFa, is obtained by igniting n mix- 
ture of pentoxide and fluor-spar in a currentiof hydrogen chloride, 
in the form o4 Small crystals closely resembling zirconium 
fluoride. It forms double salts with other metallic fluorides, of 
which those of potassium and ammonium have been investigated 
by Marignac, who prepared the following : 

2NH4F,rhOF, * 
.3NH4F,ObOF, 
r)NTl4F.3Cb0F3,H20 
NH4F,CbOF3 
3NH4F,CbOF3.CbF5 

These are crystallishble, and are formed by dissolving columbic 
acid in a larger or smaller quantity of hydrofluoric acid and 
adding the other fluorides* in various proportions. The first 
salts of the two scries, which Marignac terms nornjal salts, are 
those which are readily formed. The normal potassium salt 
is formed whenever the others arc recrystallised, and is de- 
posited in the form of thin, monoclinic scales soluble in 12 parts 
of water at the ordinary temperature. It is isomorphous with 
potassium tungsten oxyfluoride, 2 KF,W 02 F 2 , and with potassium 
titanofluoride, KgTiFg. By dis.solving the normal oxyfluoride 
in hot hydrofluoric acid fotasdum cohmbifluoride, KgCbF^, is 
formed, which is deposited in glistening, rhombic needles. The 
normal ammonium salt crystallises in rhombic tablets, 
and is isomorphous with ammonium timgsten oxyfluoride, 
2NH4F,\V02F2. 

Rubidium, caesium, and thallous double fluorides of the type 
2 M’F,CbOF 3 are also known, and a sodium salt of the eom- 
position SNaFjCbOFg. Like the potassium compound, the 
rubidium and cfiesium salts are transformed into double fluorides 
of the type 2 M’F,CbF 5 when crystallised from fairly concentrated 
hydrofluoric acid (Balke and Smith). 

A double fluoride of the formula 2KF,3Cb02F is gradually 
deposited in small quantity as a white powder when a solution 

* ^ Kuff and Schiller, Zdt. anorg. Chm.t 191 J, 72i 329. 


2KF,CbOF3,ILO 

3KF,CbOF3 

5KF,3CbOF3JLO 

4KF,3Cb0F3,2TT20 

HF,3KF,CbbF3 



984 


THE VANADIUM GROUP 


of the normal potassium oxyfluoride is boiled for a considerable 
time : ^ ^ 

3(2KF,CbOF3)^+ 3 H 2 O = 2KF,3Cb02F + 4KF + 6HF. 

It is readily soluble in hydrofluoric acid. 

Hydrogen peroxidfe converts the oxyfluo^de into a peroxy- 
fluondc, CbOjFg, which crystallises in yellovAsh plates.^ The 
double sodium and rubidium peroxyfluorides have been similarly 
prepared (Balke^nd Smith). 

Cohmhium Trichloride, CbClg, is obtained when the vapour 
of the pentacliloride is slowly passed through a red hot glass tube, 
and when the oxide is heated with phosphorus pentachloride.® 
It cither forms crystalline crusts which have the appearance of 
iodine, or is found crystallised in long needles which are dichroic. 
It is neither volatile nor deliquescent, and is not decomposed by 
water or ammonia, but is easily oxidised by nitric acid. When ^ 
heated in the air it emits thick vapours, and when ignited in a 
current tf carbon dioxide it forma colufnbium oxychloride, 
ChOClg, and carbon monoxide, a reaction which is not exhibited 
by any other metallic chloride (Roscoe). 

Cohmhivjn PetUachloride, CbClg. — When an intimate mixture 
t)f columbium pontoxide and a large excess of sugar charcoal is 
heated in a current of chlorine perfectly free from air, yellow 
tieedles of the above compound are formed. The chlgride is 
ilao formed^ when the pentoxide is heated in the vapour of 
mlphur monochloride and chlorine, or carbon tetrachloride and 
'hlorine, or heated with carbon tetrachloride in a sealed tube 
it 200°; and, together with the oxychloride, when carbon 
^trachloride is passed over the heated pentoxide. It*has a 
ieiisity of 2-75, melts at 194°, and boils at 240*5°, but begins to 
lublime at 125°. The yellow' vapour has a specific gravity of 
1*6 (Deville and Troost), the formula requiring 9*38. The 
hloride is soluble in carbon tetrachloride, sulphur monochloride, 
hloroform, and alcohol. It dissolves in hydrochloric acid, 
erming a liquid which gelatinises on standing, and when diluted 
nth water or boiled almost all the columbic acid separates out. 

’•fCriiss and Nilson, Her., 1887, 20, 1676. 

° Ficcini, Z«it. anorg. Chem., 1892, 2, 22. 

’ ^nnington, Chem. News, 1807, 76, 38. 

* Smith, J. Amer. Chem. Soc., 1808, 20, 280; Hall and Smith, ibid,, 1906, 
f, 1360; Hall, ibid., 1004,26, 1235; Ruff and Schiller, ^eit. anorg. Chem., 
HI, 72,‘329. I 



HALIDE BASES OF COLUMBIUM 


985 


Metallic zinc brought into the solution turns it a deep blue 
colour. % 

Qdumhiim Oxychloride^ or Columbyl Chloride^ CbOClj, is formed 
by the direct union of the dioxide with chlorine, and also when a 
mixture of the pentoxide with a small quantity of carbon is heated 
in chlorine. It is best formed by heating the pentoxide in carbon 
tetrachloride valour, and eliminating the pentachloride also 
produced by repeatedly distilling the mixture in a current of 
carbon dioxide over the pentoxide (Hall and Smith). It is a 
colourless, fibrous, crystalline mass, which volatilises without 
melting at about 400°, giving rise to a colourless vapour, the 
specific gravity of which was determined by DeviHe and Troost 
to be 7*88, theory requiring 7*48. When heated in carbon 
dioxide, and still more readily in hydrogen, it decomposes into 
pentoxide and pentachloride. It deliquesces on exposure to 
moist air, with formation of crystalline columbic acid, whilst 
when brought into contact with water it decomposes viol/^tly, 
forming amorphous columbic acid. 

Double salts with various alkali chlorides and orgafiic hydro- 
chlorides have been prepared.^ 

When columbium oxide *is heated in hydrogen chloride a 
hydroxychloride, Cb 204 , 3 IT 20 ,HCl, is formed which is volatile at 
a high temperature.'-* Hydrogen bromide yields an analogous 
compound. 

Cohmbium Pentabromide, CbBr^, obtained by the direct union 
of its elements,® closely resembles the chloride in properties. It 
is a purple-red mass, wliich forms deep garnet-red, prismatic 
crystals. It melts at about 150° and boils at 270°. 

Cohmbium OxybromidCf CbOBr.,.— When a mixture of the 
pentoxide and double its weight of carbon is heated in bromine 
vapour a yellow, voluminous mass of the oxybromide is obtained, 
which sublimes without fusion in an inert atmosphere laden 
w^ith bromine vapour, and even at comparatively low tem- 
peratures begins to decompose into the pentabromide and 
pentoxide (Barr). • 


Halide Bases op Columbium. 

Chlorocolumbium Chloride^ (Cb^CIij)Cl2,7H20, is obtained*H)y 

heating columbium pentachloride with seven parts of 3 per cent. 

• 

^ Weinland and Storz, Ber., 1906, 89 , 3056; Zeit. anorg. Chem., 1007, 54 , 223. 

* Smith and M^, Zeit. anorg. Chem., 1894, 7, 96. 

• Barr#,/. Amer. Chem. 5oc., 1908, 80 , 1668. * 




THE VANADIUM GROUP 


fiodium amalgam in vacuo at a temperature just suJBQicient to 
propagate the initial reaction through the q^ass, and subsequently 
heating for an hour to a temperature at which Jena glass begins 
to soften. The mass is cooled in vacuo, extracted with boiling 
water, the solution filtered from brown residue, and concentrated 
after the addition of a little hydrochloric acid. The yield is 
very small. • 

TJie chloride separates in small, shining crysfals which appear 
black but give a gi*een powder. It is very slightly soluble in cold 
and not very 8(^uble in boiling water, the solution having an 
olive-green colour. It is not completely decomposed by ammonia 
even on longH)oiling, but boiling nitric acid decomposes it. The 
compound dissolves in concentrated alkalies to form a dark 
greenish-brown solution, from which, on adding excess of hydro- 
chloric acid, a brown chloride, CbfiClj4,9lT20, is obtained differing 
in constitution from the original chloride, although in composition 
it otlly differs in its water content. The brown chloride is 
re-converted into the green chloride when dissolved in water, 
the rate df change being rapid in boiling solution. 

A solution of chlorocolumbium chloride, when treated with the 
theoretical amount of sodium hydroxide, gives a black, crystalline 
precipitate .of chlorocolumbium hydroxide, (CbgCli2)(0H)2,8Il20, 
soluble in both acids and alkalis. From its solution in hydro- 
bromic acid, chlorocohmhhmi bromide, (Cb6Cli2)Br2,7H20, may 
be obtained in crystals which resemble the chloride but a^re more 
soluble in cold water.^ 

ConUMBllJM AND SULPIIUR. 

Columhium Sulphide— Vihan colunibium pentoxide is heated 
to redness for a sufficient period in hydrogen sulphide it pftduces 
a brown product containing only columbium and sulphur. The 
product is black when a mixture of hydrogen sulphide and carbon 
disulphide is employed. No definite sulphide or oxysulphide 
has yet been obtained.^ 

CoLUJjimiM AND Nitrookn. 

435 Columbium Nitride, CbaNg.- Metallic columbium forms 
i fellow nitride^ when it is heated in nitrogen at 1,200°. A 

‘ |famed, J. Amar. Chem. Soc., 1913, 35> 1078. 

“ BUt* and Oondor, lier., 1907, 40, 4963. 

* Moiasan, Compt. rmd., 1901, 138, 20; Miithniann, Weiss, and Reidelbauch, 
innalen^ 1907, 355, 58. * 



DETECTION AND ESTBUTION OF COLUMBIUM 987 


nitride also is presumably precipitated when dry ammonia gas is 
led into a solution of the pentachloride in carbon tetrachloride. It 
is separated from co-precipitated ammonium cliloride by washing 
with water, and is decomposed by caustic alkali with the evolu- 
tion of ammonia.^ When columbium pentoxide is heated to white- 
ness in ammonia it loses the half of its oxygen, and forms a black 
powder containiij^ fiitrogen. If the oxychloride be treated, with 
dry ammonia it becomes hot and turns yellow. This mass, 
when heated, gives off ammonium chloride, and a black powder 
remains behind, which, when melted with caustic potash, yields 
ammonia in large quantity, and on heating in the air burns with 
incandescence. It is not attacked either by boiliffg nitric acid 
or aqua regia, but dissolves readily in a mixture of hydrofluoric 
and nitric acids. 


Detection and Estimation oe Columbium and TantaIum. 

436 All columbatys and tantalates are decomposed when the 
finely powdered minerals are fused with six times their weight 
of potassium hydroxide in a nickel or silver crucible, and on 
extracting with water potassium columbate and tantalate pass 
into solution. On acidifying the solution, columbic and tantalic 
acids separate out as a white, amorphous precipitate somewhat 
soluble in excess of acid. After treating the washed precipitate • 
with atimoniura sulphide to remove any tungstic acid, it may 
be tested for tantalum by dissolving in hydrofluoric acid, adding 
potassium fluoride, concentrating to a small volume, and allowing 
it to cool; characteristic needles of potassium fluotantalate 
separi^Je out if tantalum is present. The filtrate is evaporated 
with excess of sulphuric acid to expel fluorine, cooled, diluted 
gradually with water, and treated with metallic zinc ; if colum- 
bium is present a blue coloration is developed, due to a compound 
in which columbium is quadrivalent or trivalent.^ For carrying 
out the colour test, Giles® recommends that the solution of 
potassium tantalate and columbate bo acidified with an excess 
of either oxalic or phosphoric acid, which holds the acid earths 
in solution, and the hot solution treated with zinc dust, when a 
yellow, brown, or nearly black colour is developed, according^ 

the amount of columbium present. Titanium, if present, gives 

• 

^ Hall and Smith, J. Amcr. Vhem. Soc.r 1905, 27, 1309. 

* See ^ St&hler, Ber., 1914. 47, 841. 

• * Chem. Ntw$, 1907, 05, 37. 



988 


THE VANADIUM GROUP 


a similar colour when oxalic acid is used, but a lilac or violet 
tint if excess of phosphoric acid is presenh 

In a reducing flame, the microcosmic salt bead is coloured blue, 
violet, or brown by columbic acid, and after the addition of a 
little ferrous sulphate becomes red. No colour is produced by 
tantalic acid. ^ 

For the quantitative estimation of columVium and tantalum 
there are several methods available fox decompoing the minerals. 
In some respects, the neatest method is to heat the finely di\aded 
mineral in a str^m of sulphur monochloride vapour.^ Colum- 
bium, tantalum, titanium, silicon, zirconium (?), tungsten, 
r antimony ( ?)*and most of the iron are thus removed as volatile 
chlorides and collected in a receiver charged with dilute nitric 
acid. This is treated with excess of ammonia, and hydrogen 
sulphide passed in until the separated sulphur has dissolved. 
Tungsten and antimony remain dissolved in the liquor, and, on 
filteflng and washing, the mixed hydroxides of columbium, 
tantalum, titanium, silicon, and zirconium are obtained, together 
with ferrSus sulphide. These are boiled with dilute sulphuric 
acid until the residual hydroxides of columbium, tantalum, 
titanium, and silicon are white. The small amount of the acid 
oxides which passes into the filtrate is rcprecipitated by making 
the solution nearly neutral and boiling while a current of hydrogen 
, sulphide passes through it to maintain the iron in the ferrous 
state. The titanium may now be removed from thei^ mixed 
hydroxides by boiling for several hours with excess of salicylic 
acid solution, in which it dissolves,^ forming a yellow solution. 

The method that has been most frequently used in decomposing 
columbium-tantalum minerals is fusion with an excess of pot- 
assium hydrogen sulphate, the mixed acid oxides being separated 
as has already been described on p. 977. According to Simpson,^ 
it is preferable to fuse with six parts of caustic potash, and extract 
with dilute hydrochloric acid, for opening up the minerals. In 
both these procedures, the presence of much titanium causes a 
considerable amount of the columbium and tantalum, particularly 
the former, to remain in solution.^ 

^ Hicks, J. Amer. CAm. Soe., 1911, 38, 1492. 

SJDittriob and Freund, Zeit, anorg, CAem., 1908, 56, 344, 346; Muller, 

Amtr, Chem, Soc., 1911, 33, 1506. 

• Wat Australia Qsd. Soc., 1906, 33, 71; Chsm. News, 1909, 99, 243. 

« Noyee, Tech. Quart., 1904, 17, 218; Wanen, Amer. J. Set., 1906, [41 
22, 520; Crook and Johnstone, iftn. Mag., 1912, 16, 244; Simpson, loc. ciU 
a,,,Uoa<iboiUK»adPotma.J(mn.Oliem.Stie.,mi,m,I»i7. 



DJfil'jfiOriON AND NSTIHATION OF OOLUMBIUM 969 


For the separate determination of the columbium and tantalum, 
it is simplest to weigh the mixed pentoxides and to determine 
the columbium by a vmumetric process, based upon its reduction 
to a state corresponding approximately with the oxide CbgOj 
and titration with potassium permanganate? The reduction is 
effected by means of zinc in a sulphuric acid solution, succinic 
acid being added tp maintain the columbiflm and tantalum in 
solution.^ • 

The only gravimetric process known is the classic procedure 
of Alarignac,^ or one of its modifications.® The mixed hydroxides 
are dissolved in a small excess of hydrofluoric acid, and the hot 
solution mixed with one of potassium fluoride, using about two 
parts of the latter for each part of mixed oxides estimated 
to be present. The solution is concentrated to a small volume 
(10 cubic centimetres per gram of mineral imder analysis) and 
set aside to cool. The bulk of the tantalum crystallises out as 
KjTaF,, which is washed several times with very little wjfter. 
Filtrate and washings are concentrated to half the previous 
volume and cooled, tvhen a further small crop of tantulurn salt 
is obtained, washed, and examined with a lens for flat plates of 
the columbium salt, which tnust be removed, if present, by 
further washing. A third crop of crystals is similarly obtained, 
examined, and washed. 

The final filtrate and washings, containing the columbium, is 
heated ^ith excess of sulphuric acid to expel the fluorine, diluted 
with water, made slightly alkahne with ammonia, and heated to 
boiling. The columbic hydroxide is filtered, washed, ignited, 
and weighed as (Jb^O^. The tantalum n similarly estimated in 
the combined crops of crystals, and the result increased by a 
small dbrrection based upon the volmnes of mother-liquor and 
vrash-hquor obtained from the third crop of crystals. This 
xnrection is, of course, subtracted from the weight of UbgO^. 

The Atomic Weight of columbium was determined by i:tose, 
Hermann, and Blomstrand, but their results are now of iiistorical 
nterest only; and the first fairly accurate value, 91, was deter- 
nined by Marignao in 18(>5, from analyses of KgUb0F7,H|0. 
Chis value was unchallenged for over fifty years, when in 1908 


^ Metzger and Taylor, Zeit. anorg. ChMk,, 1909, 62, 382; CAewt. A'euw, 
900, 100, 257, 270. See also Levy, Analyst^ 1915, 40, 204. 

• Ann, Chim. Phys., 1865. i;4J. S, 5, 49. 

* Meimbeig and Winzer, Zeit. angew. Chem., 1913, 96, 157; Kuff and 

oluller, Z^. anorf. Ghem., 1911, 72, 329. * 




990 


THE VANADIUM GROUP 


Bailee and Smith ^ determined the ratio 2 CbCl 5 : Cb 205 by 
decomposing the chloride with water ant^ igniting the columbic 
acid lo oxide. Tlieir results led to an atomic weight of 9*5'5. 
Subsequent work has shown that this method is not capable of 
giving results of fue liighcst degree of accuracy, and a more 
trustworthy metliod was found by Smith and \'an llaagen,^ who 
transformed sodiunf metacolumbate into sodiiun chloride by 
heating it in sulphur monochloride, and •from the ratio 
NaCb 03 ; NaCl obtained the value ‘J.M5. The number at 
present (1922) a 4 lopted is accordingly 92-1. 


TANTALUM. Ta - 181 - 5 . At No. 73 . 

437 Metallic tantalum wa.s first obUined in an impure state 
as a black ixiwder by Berzelius, who heated potiissium tantalo- 
lluoride with potassium. Moissan succeeded in preparing it as 
a fwsed regulus by reducing the pentoxide with carbon m the 
electric furnace, but the metal thus obtained contained carbon.^ 
It was Iv-st obtained pure by voii Bolton, wlio prepared it by 
carrying out Berzelius’s reaction, and then heating the com- 
prcs.scd powder of the metal iv an electric furnace in a 
vacuum, and also by passing a current through a iilament of 
Tag 04 in a vacuum, the oxygen being thus removed and a filament 
of the metal left.*^ It is also formed when the pentoxide is 
reduced by crude cerium (Weiss and Aichel), but the temjierature 
is not suilicicntly high to melt the tantalum, which is obtained 
as a silver-white, porous mass. It is manufactured by the 
action of sodium on sodium tantalotiuoride, or by the electrolysis 
of fused potassium tluotantalate, followed by melting the crude 
metal in mwo.” » 

The pure metal is silver- wliito in colour, has the sp. gr. 10*64 
(von Bolton), melts at 2,850'' (Pirani and Meyer), and has a 
normal atomic heat. Its compressibility is 0-54 x 10"^.' It' is 
as hard as soft steel, and when hot can be rolled, hammered, 
and drawn into wire. The tensile strength of the metal is very 
high, a fine wire giving a breaking test of 93 kilograms per 
square mm. 

^ J, Amer. Chem, Soc., 1008, 30. 1644. * Ibid., 1915, 37. 1788. 

■ CompL rend,, 1902, 134, 211. 

« Zeit, EUktrochm., 1905, 11, 45, 603, 722; Genuan Patents, 152848; 
162870; 153826; 156648; 161081; 163414; 171562. 

* Zeit, angtw. Chm., 1906, 36, 1, 537. « Mining Journal, 1906, 80, 363. 

» Ri&wds and Bartlett, J. Atner. Chm. Soc., 1916, S7,'470. 



TANTALUM AND OXYGEN 


Ml 


When heated in the air, thin wire bums, whilst more compact 
masses are oxidised siiperficially. The red hot powder decom- 
poses water, and in the form of wire readily absorbs nitrogen and 
hydrogen, 740 volimies of the latter being taken up at a yellow 
heat. About three-quarters of this is lost in a vacuum at a red 
heat, but the remainder, which renders thi^ metal brittle and 
increases its clect^dhl resistance, is lost only on fusion.^ Tan- 
talum is not attacked by aqua regia nor by any single acid except 
hydrofluoric acid, which dissolves it much more readily when 
the metal is in contact with platinum. It is attacked also by 
fused alkalis. It combines with nitrogen at a high temperature, 
more readily with sulphur. Carbon appears to form with it a 
carbide and renders the metal brittle. Alloys with iron, tungsten, 
and molybdenum can be obtained. 

The chief purpose for which metallic tantalum is employed 
is for the preparation of filaments for electric lamps. Wire of 
0*05 mm. diameter is employed, and as the resistance is much 
less than that of a ^arbon filament, a much longer filament is 
used than in a carbon lamp. The lamps require oiJy about 
half the energy needed by^a carbon lamp of equal candle- 
power. 

It has also been suggested to use tantalum in place of the more 
expensive platinum for crucibles, electrodes, etc., and for dental 
and surgical instruments. 


COMPOUNDS OF TANTALUM. 

Tantalum and Oxygen. 

438 tantalum Tetroxide, Ta 204 or TaOg, is formed when the 
pentoxide is heated in a very small carbon crucible, exposed to 
the highest heat of a wind furnace, or reduced by metallic mag- 
nesium. It is a porous, dark-grey mass which scratches glass, 
and when rubbed on a hone has a steel-grey colour. It gives a 
dark-brown non-raetallic powder, and is not attacked by acids, 
even by a mixture of hydrofluoric and nitric acids, but bums 
when heated, with formation of the pentoxide. 

Tantalum Penloxidet TajOj.— The preparation of this body hga^ 
already been described (p. 977). It is a white, amorphous, infus- 
ible powder which when strongly heated becomes crystalline, and 
when ignited with boron trioxide or melted with microcosmic 

^ » Piccini, ZeU. Skl^roehem., 190S, U, 555, 

VOL. n. (n.) 


M 




992 THE VANADIUM GROUP 


salt in a porcelain furnace is obtained in rhombic prisms. 
When gently heated it has a specific ^avity of 7-35, which 
after exposure to a white heat rises to 8*7. The ignited pentoxide 
does not dissolve ^n any acid. 

Tanlalic Acid or Tantalum Hydroxide^ HTaOg, is obtained in 
the form of a gclatij^ous mass when the chloride is quickly mixed 
with water. If, however, the same comp!u^id be exposed to 
moist air until it is decomposed, and then mixed with water 
containing ammonia, the hydroxide is obtained as a crystalline 
powder, which Vhen dried at 100° possesses the above composi- 
tion, and is converted with vivid incandescence into pentoxide 
when heated to low redness. The hydroxide obtained from the 
double fluoride by treatment with acid potassium sulphate does 
not exhibit this phenomenon. Tantalic acid dissolves in hydro- 
fluoric acid, and, when freshly precipitated, in other acids. 

The TaJitalales. — The normal tantalates, to which class the 
tantalum minerals belong, are all insoluble in water. Besides 
these, others are known, derived from the ui^nown hydrate, hexa- 
tantalio acid, HgTagOjg, or dlfgOjSTagOj, of wliich only the 
compounds of the alkali metals arc soluble in water. 

Potassimn llexataiUalate, 4K20,tlTa5,05,lGH20, is formed by 
dissolving •the acid in caustic, potash, and also by fusing the 
pentoxide with double its weight of caustic potash. The fused 
mass is dissolved in water and allowed to evaporate in a vacuum. 
Transparent, glistening, monoclinic crystals are thus 'obtained 
which dissolve in lukewarnx w*ater without decomposition. On 
boiling or eva])oratiiig in the air, salts containing more tantalum 
are formed. If it be repeatedly ignited with ammonium 
chloride and washed with water the normal salt, KTaOg, is 
obtained, ‘ 

SMm Ilexalantalate, 4Na20,3Ta205,25n20, is obtained in a 
similar way to the iK)tassium siilt, a vivid incandescence occurring 
when tlie mixture is heated to redness. The fused mass is 
boiled out with water, and the solution either allowed to cool 
or; inasmuch as the salt is insoluble in caustic soda, poured 
on to the top of a strong solution of this substance. It 
crystallises in small, hexagonal tablets which dissolve at 13-6° 

493, and at 100° in 162 parts of water. It is not decomposed 
by boiling water, and if the aqueous solution be mixed with 
alcohol a precipitate of NaTa03,H20 is formed, and this 
becomes anhydrous on ignition. The anhydrous salt is also 
formed by the ignition of the hexatantalate. 




TANTALUM AND THE HALOGENS 


Rubidium and Ccesium hexatantalates crystallise with liHgO 
and are isomorphous \^ith the corresponding colunibates.^ 

AVhen tantalum pentoxide is strongly ignited with the clilorides 
of calcimii, magnesium, and other metals, cr3istalliue tantalates 
of these metals are obtained.^ 

Pertanialic ^ci/i.—Wlien a large excess hydrogen peroxide 
is added to a solutioh of potassium hexatantalate and potassium 
hydroxide and the liquid mixed with an equal volume of alcoliol, 
a white, crystalline ^Tedintateof 2)olassium 2)ertanlala(e: KjTaOg, 
is obtained.® This salt is decomposed by sulpCuric acid with 
formation of a white precipitate of hydrated 2^<^rl(iiUalic aetdf 
HTa04. This substance is more stable tlian percolumbic acid, 
but yields hydrogen peroxide when heated for some time at 
100 ^ with dilute sulphuric acid, and evolves ozonised oxygen when 
treated with concentrated sulphuric acid. The salts appear 
to be derived from the unknown ortho-form of this acid, whjch 
would have the formula (IIODlaTaGg. The sodium, rubidium, 
and caesium salts are also known.* 

Tantalum anb the Halogens. 

439 Tantalum Pentajluoride^ TaF^, is prepared exactly like the 
columbium compound, which it closely resembles in pro2)erties. 
It forms large, colourless prisms of density 4 - 74 I, melts at 90 * 8 °, 
and boiljfat 229*2 to 229 * 5 ^"* 

Potassium Tanialojluorule, K2TaF7. — The mode of preparing 
this salt has been already described (p. 977 ). It forms small, 
rhombic needles which readily melt, but it docs not decompose 
when ignited even to w'hiteness in a i>latiuuni vessel. It is 
easily soluble in hot, though sparingly so in cold water (about 
1 part in 200 parts of Avater). WJien tlie solution is boiled 
decomposition takes {)lace rapidly, a white j^owder of the 
oxyjluoride, K4Ta405Fi4 = 4KF,2TaF5,Ta205, 8 ef)arating out. 
Hence the salt should be crystallised from dilute hydrofluoric 
acid. 

Sodium Tantalojlmride, Na2TaF7,H20, is obtained in a similar 
manner to the potassium salt, or by dissolving sodium hexa- 

* Balke and Smith. J. Afner. Chem. Soc„ 1908, 30 , 1637. 

* July, Compt. rend., 1876, 81 , 206, 1266. 

* MelikotT and Piasarjewsky, ZeU. anorg. Chem., 1899, 20 , 340. • 

* Balke, J. Amer. Chem. Sor., 1906, 27 , 1140; Balke and Smith, ibid., 1908, 
80 , 1637. 

* Ruff anh SchiMcr, Zeit. anorg. Chem., 1911, 72, 329, 




m 


THE VANADIUM GROUP 


tantalate in hydrofluoric acid. On evaporation, indistinct 
crystals of NagTaFg separate out, and tHen eight-sided rhombic 
tablets of the above salt, which lose their water below 100°, 

Amnioniurn, rubidium, and caesium salts of the type 2M^F,TaF5 
are also known, as well as the corresponding zinc and copper 
salts.^ Lithium, sodium, and caesium double fluorides of the 
type M'FjTaFg have also been described,^ * Hydrogen peroxide 
converts the potassium and rubidium salts, M^g^aF^, into the 
])eroxyJiuoridcs, 2M'F,Ta02F3,H20, which crystallise in colourless 
plates (Piccini, Balke and Smith). 

Tantalum Penlachloride, TaClg, is obtained by heating an 
intimate mixture of the pentoxidc and carbon in a current of 
chlorine, and is also formed when the pentoxide is heated with 
phosphorus pentachloride. It is best prepared by heating the 
pentoxide in a current of chlorine mixed with either sulphur 
monochloride or carbon tetrachloride.^ It forms light yellow 
needles and prisms of density 3-G8, which melt at 211° and boil 
at 212°,^but begin to volatilise at so low a. temperature as 144°, 
and may be readily sublimed in a current of carbon dioxide or 
chlorine. The specific gravity pf the vapour, according to 
Dcville and Troost, is 12*8, the calculated density being 12*42. 
It fumes in the air, and is converted into tantalic acid by water. 
It is reduced by aluminium in presence of aluminium chloride 
to a mixture of lower chlorides.'* 

lantalum PeiUabwniidef TaBrg, is prepared by l^ating a 
mixture of e(|ual parts of the pentoxide and carbon in a current 
of bromine vapour. It is best purified by sublimation in vacuo? 
It forms yellow, elonpited lamella), which melt at 240° to a 
ruby-red li<pud and boils at 320°. The vapour resemblesolilorine 
in colour. It fumes in air and is rapidly decomposed by water. 
The bromide may be sublimed in an atmosphere of hydrogen, 
but at high temperatures partial reduction to the metal takes 
place j also, traces of green bromotantalum bromide are produced. 
When the bromide has been exposed to traces of moisture and 
is* then sublimed in vacuo, tantalum oxybromide, TaOBrg, is 
left as a small residue. ' 

^ Alarignac, .4»». Chim. Vhyn., 1866, f4J, 9, 247; Balke, foe. cit. 

" ‘ * Balke, J, Amn. Chem, Soc., 1005, 87, 1140. 

• Hall and Smith, ibid,, 1905, 87, 1369; Balke, ibid,, 1910, 88, 1127; Ruflf 
and Schiller, Zeit. anorg. Chem., 1911, 72, 329. 

* Ruff and Thomas, Btr,, 1922, 55, [BJ, 1466. 

» v^Haageii, J. Amcr. Chem. Sve„ 1910, 32, 729; SmHh and (Jhapin, ibid., 



^ KAUDK BASES OF TANTALUM . 995 

Tantalum Pentaiodide, Talj, is prepared by distilling the 
pentabromide slowly several times in a brisk current of dry 
hydrogen iodide.^ It sublimes in nearly black lamell®, and fuses 
to a dark brown liquid which gives a vapour resembling bromine. 
The iodide closely resembles the chloride* and bromide in 
properties. 


Halide Bases of Tantalum. 

Bromolantahm Bromide^ (TagBrjglBrgJHgO, w prepared by 
heating tantalum pentabromide with four parts of 3 per cent, 
sodium amalgam in vacuo, the temperature being gradually 
raised to a red heat. The mass is cooled in wicuo, extracted 
with boiling dilute hydrobroraic acid, filtered from the residual 
brown powder (a lower oxide of tantalum), and concentrated 
on a water-bath. ^ 

The bromide forms small dark green crystals which are soluble 
in water, forming an emerald green solution, a one per cent, 
solution of which appears opaque in a half-inch layer. It is 
stable at 100°. From boiling- and freezing-point determinations, 
it has been found that the salt dissociates in solution into three 
ions, so that the formula should be written (TagBrijjBrg.THjO, 
the group Ta^Brjg behaving as a divalent radicle of considerable 
stability. In cold aqueous solution, silver nitrate precipitates 
only one-seventh of the total bromine. 

By the interaction of the bromide with the theoretical amount 
of caustic soda, a green, crystalline precipitate of bmnotantalum 
hydroxide, (TaQBri 2 )(OH) 2 , 10 H 2 O, is obtained, nearly insoluble 
in water. Solution of the hydroxide in hydrochloric and 
hydriodic acids leads to the formation of bromolanlalum chloride, 
(TajBrjjlCljjVHjO, and bromotanlahm iodide, (TaQBrj2)r2,7H2(), 
respectively. The former may also be obtained from the bromide 
by evaporation with hydrochloric acid, and in cold aqueous 
solution it gives a precipitate of silver chloride, free from bromide, 
upon the addition of silver nitrate.* 

Chlorotantalum Chloride, (TaflCli2)Cl2,7H20, is obtained by 
reducing tantalum pentachloride with sodium amalgam, as in 
the case of the bromotantalum bromide, which it resembles 
appearance and properties (Chapin). This salt was first obfiiinpd , 


^ van Maagen, loc. cit. 

* Chapin, J, Amtr. Chem. 8oc., 1010, 89- 323. 





THE VANADIUM GROUP 


in very small amount, by Chabri4, who mistook it for a dichloride, 
TaCl2,2H20.i 

Tantalum and Sulphur. 

440 Tantalum Cisulphide, TaSg, is produced in the crystalline 

form when the pentoxide is heated to 900° in a stream of 
hydrogen sulphide ind carbon disulphide. Jt begins to sublime 
at lS00° and is stable at 1300°.^ ^ 

* Tantalum and Nitrogen. 

441 Wheii tantalum chloride is heated in ammonia gas to a 
temperature not above the point of volatilisation of the ammon- 
ium chloride which is formed, an amorphous, yellowish-red 
mass of varying composition is obtained. If this is powdered 
and heated to redness in a stream of ammonia it is converted 
intft a briglit red, amorphous powder having the composition 
TayNg. AVhen this is raised to a full white heat in an 
atmospli^re of ammonia, an amorphoift, black powder of 
tantalum nilrkh% TaN, is produced which exhibits a metallic 
lustre on burnishing. IT. Rose, vvhe first obtained this compound, 
believed it to be the metal.® The nitride, Ta3N5, is also obtained 
when metallic tantalum is heated in nitrogen gas to a tem|)erature 
of 1000.° 


Tantalitm and Carbon. • 

Tantalum Carbide.'— Whvii G parts of Ta205, 1 part of sodium 
carbonate, and 1 ]>art of charcoal are heated to a temperature 
of about 1480°, tantalum carbide, TaC, is produced in the form of 
fine needles.'* 

Deteuiton and K.STIMAT 10 N OP Tantalum. 

442 The detection and estimation of tantalum have already 
been discussed under colunibium (p. 987). 

The Atomic ]Yeiijhi w'as determined by Marignac,® who 
analysed the potassium and ammonium tantalofluorides and 
obtained the number 183. For forty years the accepted value 

' rend.t 1907, 144, S()4. 

* Bilt* rtml Kirclu'r, Ber., 1910, 43, 1630. 

* .Miithniann, Weiss, ami Riwlolbauch, Annalcn, 1907, 866, 58. 

* July, Coinpt. rend., 1876, 82. 1195. 

J J»n. Chim. Phys., 1806, [4], 9, 251. 



ANTIMONY 


097 



which were by no means concordant; then, in 1906, by direct 
conversion of the metal into the pcntoxide Ilinrichsen and 
Sahlbom^ obtained the number 181. Later, by converting 
the pentachlorido into the oxide, Balke® fbund 181-52, arid 
Chapin and Smith found 181-8 by transforming the pentabromidc 
into the oxide.® "fhc number at presenff (1922) adopted is 
181-5, but the v?brk of Sears and Balke * indicates that* this 
result is probably in need of revision. 


ANTIMONY (STIBIUM). Sb - i20-2. A*. No. 51. 

443 This metal occurs in nature chiefly as stibnitc, aritimonite, 
or antimony sulphide, SbgSg, a mineral which w'as known in very 
early times, having been long employed, as indeed is yet the case, 
by women in the East for painting the eyebrows. In St. Jerome’s 
translation of the Hebrew of Ezeldel xxiii. 40, we rcad,“ circum- 
linisti stibio oculos taios ” ; and in the Second Book of^Kings ix. 
30, wo find, “ Form Jezebel introitu eius aiidito depixit ocidos 
suos stibio.” Of this latter passage Cheyne and Drover give as 
the translation of the Hebrew, “ set her ey(^s in paint (literally 
antiniony).” 

The name for this mineral in Hebrew and Arabic is “ Kohl,” 
and this word ])assed as “ alcool ” or alkohol ” into other 
languages ; thus in the Spanish traiLslation of the Bible the above 
passage from Ezekiel is thus rendered, “ Alcoholastc tus ojos.” 
In the middle ages the word alcohol indicated any fine powder ; 
it was only at a later period that it was employed to mean spirits 
of wdne. Dioscorides calls this metal and mentions that 

it is also knowm by other terms, such as TrXari/ot^^aX/ioi^, the 
eye-expander, ywaiKelov^ belonging to womankind, etc. Pliny, 
on the other hand, terms it stibium. The Latin Geber, who also 
was acquainted with this substance, termed it antiriwnium, and up 
to the time of Lavoisier both these words were made use of to 
signify sulphide of antimony. The German name was sfiessghst 
afterwards changed to spiessglanz. As already mentioned (Vol. I., 
p. 9), the works attributed to ** Basil Valentine,” which have 
hitherto been regarded as the earliest known records concernki^ 
antimony and its derivatives, were shown by Schorlemmer to be 

» J5er., 1906, 39, 2600. * J. Amer. Chem. Soc., 1910, 32, 1127. 

> Ibid.^ 1911, 33, 1497. * Ibid., 1915, 37. 833; 1917, Sg, 1682. 




THE VANADIUM GROUP 


forgeries dating from about 1600.^ There is no dotbt, however, 
that the iatro-cheraists, from the time of Paracelsus, were 
acquainted with many antimonial preparations, and numerous 
references to these are scattered throughout the chemical literature 
of those times. TBe statements of “ Basil Valentine ” may still 
serve to show the condition of knowledge concerning antimony 
in 1600. He rcmarlfs in his Triumphal Car jof Antiimny : “ In 
ordcf, as is most proper, that I may say somethiHg about the name 
of the material, it should be understood that this material was 
long known to the Arabians, and from ancient time was termed 
by them asinai. The Chaldeans entitled it stibium, and in the 
Latin toiigiH it has been called antimoniim ^ up to the latest 
times, and in our own German mother tongue the same material 
has been foolishly called spiessglas for this reason, that this 
material can be fluxed and a glass made from it.” 

Dioscorides mentions that in order to roast the crude antimony 
it must be heated in a current of air until it burns, for if more 
strongly ignited, it melts like lead. This passage has given rise 
to the supposition that the author was acqthinted with metallic 
antimony, and that this is probably the case is shown by the fact 
that an old Chaldean vase analysed by Berthelot consisted of pure 
antimony.^ Antimony was confounded with bismuth by some 
chemists, such as Libavius, even so late as the sixteenth century. 

The pre|)aration of the metal was described by “ Basil 
' Valentine,” who in his Wiederhohmg des Grossen Steins de\ uralten 
If mew terms it spmsylm rex and also plumbum anlwwnii. It 
has already been stated that the alchemists considered each 
semi-metal to be a variation of a true metal. 

444 Antimony occurs in many other minerals besides stibnite. 
The metal is found, though not frequently, in the native stale, and 
also as arseniferous antimony or allemontite (AsSb). Antimony 
also occurs as the trisulphide, 8 b 2 S 3 , combined with basic sulphides, 
and in these thioantimonites a portion of the antimony is usually 
replaced by arsenic. Amongst such compounds are berthierite, 
Fe^SbaSg; wolfsbergite or antimonial copper, CuaSjSbjSa; 

^ MSS. deposited in the library of the University of Manchester. Sec ako 
IMeroe, Science, 1808, 8. ICO, who conics to the same conclusion, chiefly from 
A study of the contents of Basil Valentine’s works. 

* The stoiy of the accidental poisoning of certain monks by spics^las having 
given rise to the name of the metal (antimoine) is on the face of it improbable, 
and must, as Kopp remarks, have been invented by a Frenchman, whereas 
Valentino wrote in German I 

* Comjaf. rend., 1887, 104, 265. 



AMXAiBLUXfX 


W» 


boulangerite, SPbSjSbjSj; jamesonite 2PbS,Sb2S3 ; bournonite, 
2PbS,Cu2S,Sb2S8; p3npargyrite or red silver ore, SAgjSjSbjSg, etc. 
In addition to these we have dyscrasite or antimonial silver, AggSb, 
breithauptite or antimonial nickel, NiSb, ullmannite or nickeli- 
ferous grey antimony, NiSbS; valentinite or antimony oxide, 
SbgOg ; cervanite or antimony ochre, Sb204 and stiblite, Sb204,H20. 
Antimony is also found in small quantity in iron ores, ferruginous 
waters, in the coaf formation, and in river sand . 

445 PrejHiration of MeiaUic Antbmny } — The preparation of 
the metal from the sulphide is a very simple opemtion. In order 
to free the ore from quartz or other earthy admixture, the mineral 
is either melted in vertical cylinders which have if hole at the 
bottom out of which the molten sulphide drops, or the pre- 
liminary fusion is carried on in reverberatory furnaces. The 
purified sulphide Is then fused with metallic iron, or roasted to 
convert it into oxide, which is reduced with carbon or crude 
tartar. Basil Valentine ” describes both of these methodfs in 
his account of the preparation of the philosopher's stone ; he states : 
“ Antimonium is a master in medicine, and from it by fneans of 
cream of tartar and salt a King (regulus) is made, steel-iron being 
added to the spiessglas during fusion. Thus by an artifice a wonder- 
ful star is obtained which the learned before my time have termed 
the philosophical ^gnet star. ” In the Triumphal Car of Antimony 
he gives the following receipt : “ Take good Hungarian spiessglas 
and witk the same quantity of crude tartar, and lialf as much 
saltpetre; rub these small and let them fuse well in a wind 
furnace ; afterwards pour out into a mould and allow to cool when 
a regulus is found.” 

In the English process, three operations are used for the pro- 
duction of the best star-antimony. The first of these is termed 
“ singling ” ; in this 40 parts of the liquated sulphide are mixed 
with about 18 parts of thin scrap iron and 4 parts of salt; and 
this is then melted in plumbago crucibles, when metallic antimony 
and iron sulphide are formed. The fusion lasts about an hour 
and a half, and when complete the charge is poured into conical 
moulds. The crude metal is then separated from the slag, 
consisting chiefly of sulphide of iron, which floats on the surface, 
and it is again melted in the second process of “ doubling,” with, 
an addition of a small quantity of liquated stibnite, sodium 
sulphate or salt, and slag obtained in the following operation. 
The charge for each pot is 80 lb. of crude antimony, 7 lb. of 

* For fun particulars, see Antimony , by C. Y. Wang (C. GriflSn k Cof, 1009). 




1000 


THE VANADIUM GROUP 


liquated stibnite, 2 lb. of salt-cake, and 2 lb. of slag, and the 
fusion lasts about an hour and a half. The metal is cast in moulds, 
allowed to cool, and broken into small pieces ready for the third 
process, termed “^lelting for star-metal.” For this purpose 
2 parts of pearl-ash and 5 parts of slag from a previous operation 
of the same kind are^ added to 60 parts of metal, and the fusion 
is repjeated. The molten metal is then poured ijto square moulds 
in which it is allowed to cool slowly, the surface being at the same 
time completely covered with slag in order that it may attain the 
peculiar crystallhie structure which is required in commerce. 

In the roast and reduction method for the extraction of anti- 
mony, two dNtinct processes are in use ; in the first, the sulphide 
ore is roasted to the stable tetroxide, generally in reverberatory 
or muffle furnaces at a temperature of about 350°. In the second 
process the volatile trioxide is formed by restricting the amount 
of air admitted, and working at a higher temperature, and is 
conflensed in ])ipcs and chambers. This process has several 
advantages, for low grade ores may be treated with success, arsenic 
oxide may be separated owing to its greater volatility, and in the 
case of OH'S containing precious metals, these may be extracted 
from the residues. * 

The oxide of antimony obtained by either process may be 
reduced to the metallic state by fusion with’*coal or charcoal, 
, together with alkaline fluxes such as potasli, soda, etc., in small 
reverberatory furnaces or crucibles. c 

It has bt‘en stated already that “ Basil Valentine ” was ac- 
quainted with the crystalline surface exhibited by pure antimony, 
but he specially mentions that the regulus which is not starred 
possesses exactly the same composition as that which ;^resents 
this [Kiculiarity. He, as well as some of his contemporaries, 
believ(;d that the stellated surface was produced only when iron 
was employed in the preparation, whilst other chemists taught 
that the preparation of the stellated antimony was connected with 
a favourable conjunction of the stars. Indeed this latter opinion 
was generally held until the time of Boyle, who, however, 
discredited both views. 

In his essay On the Unsncce^sfulness of Experiments, Boyle ^ 
.^-rsays : “ And it may perhaps also be from some diversity either 
in antimonies or irons, that eminent chemists have (as we have 
observed) often failed in their endeavours to make the starry 
regulus of Mars and antimony. Insomuch that divers artists 
» Opera, ed. 1772. 1, 325. 



AJNTIMONY 


1001 


fondly believe and teach (what our experience will not permit 
us to allow) that there is a certain respect to times and con- 
stellations requisite to the producing of this (I confess admirable) 
body. Upon this subject I must not omit^to tell you that a 
while since an industrious acquaintance of ours was working on 
an antimony, which unawares to him, was, as we then supposed, 
of so peculiar a ijature, that making a regulus of it alone without 
iron, the common way (for his mamier of operation I inquired 
of him), he found, to his w^onder, and showed me his regulus 
adorned wdth a more conspicuous star than I hate seen in several 
stellate rcguluses of both antimony and Mars'* Lemery, in liis 
Cours de Chyrnie, published in 1675, also argues stft)ngly against 
the supposition that the jdanet Mars has anything to do with the 
formation of the stellated surface. 

Commercial antimony often contains traces of silver, gold, 
arsenic, iron, lead, copper, and frequently some sulphur. In 
order to prepare the pure metal, 16 parts of the commercial inetal 
are fused with 2 ;^arts of sodium carbonate and 1 part of 
sulphide of antimony for an hour; on cooling, the fegulus is 
separated from the slag, and melted again for an hour with \\ 
parts of sodium carbonate, llnd the operation again performed 
with 1 part of this salt,^ a small quantity of nitre being added 
from time to tinie.^ The whole of the arsenic is thus separated, 
provided that a sufficient quantity of iron be originally present 
in the irietal ; should this not be the case, it is necessary to add 
about 2 per cent, of iron sulphide.® 

Another method for preparing pure antimony is as follow's.* 
Redistilled antimony trichloride or pentachloride is dissolved in 
concentrated hydrochloric acid, chlorine passed into the solution 
until it becomes greenish-yellow, and hydrogen chlorine then 
conducted into it, when chloroantimonic acid crystallises out. 
This is purified by rccrystallisation, decomposed by hot water to 
antimonic acid, and the latter reduced to the metal by fusion with 
potassium cyanide. 

446 Properties.— Antimony is a lustrous silver- white metal, 
which when slowly cooled exhibits a coarsely laminated crystal- 
line fracture. AVhen quickly cooled, on the other hand, the 
fracture is granular. It crystallises in obtuse rhombohedr^ 
which can scarcely be distinguished from cubes, and has a specific 

» Liebig, Annakn, 1857, 104 , 223. * Ibid., 1835, 19 , 22. 

* Bensch, ibid., 1847, 63, 273. See a]»o Meyer, ibid., 1848, 66, 238. 

* Grosokuff, Ztit. anorg. Chem., 1918, 103 , 104. 




1002 


THE VANADIUM GROUP 


gravity of 6-71 to 6*86. Native antimony occurs in scaly masses, 
usually containing silver, iron, and arsenic. Its most important 
localities are at Sahl in Sweden, Andreasberg in the Harz, 
Przibram in ilohemia, in the Dauphiny, in Canada, the United 
States, Mexico, cliili, Sarawak, in Borneo and Queensland. 
Native antimony has a specific gravity of from 6*5 to 7. The 
metal has a normal atomic heat at ordinary Jemperatures ; at 
80° (Abs.) its atomic heat Ls 5*19.^ 

Antimony is hard, and so brittle that it can be powdered ; it 
melts at 630*3°,^ and volatilises at a bright red heat in the air, or 
in a current of a gas, but not when fused under a layer of common 
salt. It ma^ be distilled in a current of hydrogen at a white 
heat. The vapour density of antimony is 10*74 at 1572°, and 
9*78 at 1610° (Meyer and Biltz),® numbers which are inter- 
mediate between those required for the molecular formulae 
Sbj and Sb. It does not undergo any alteration on exposure to 
theTlir at the ordinary temperature; on heating it burns to form 
the oxide, and when lieated on charcoal before the blowpipe, the 
oxide is Evolved in thick, white fumes, and a portion of it is 
de]:>osited as a white incrustation on the charcoal. If the blast 
of air be stopped the globule of rftolten metal begins to glow, 
and is seen to be covered with a crystalline network of needles 
of oxide, and when the globule is thrown from some height on 
^ to a piece of j)aper, the edges of which are turned up, it breaks 
into many smaller glolmles which burn with a very brigli^ flame. 
Neither cold water nor dilute sulphuric acid acts upon the 
metal at the ordinary temperature, but at a red heat it decom- 
poses steam with formation of oxide. Nitric acid converts it 
into a white powder, the composition of which depends on the 
strength of the acid, nitrogen peroxide being evolved and no 
ammonia formed.* Pure antimony does not dissolve in strong 
hydrochloric acid in the absence of oxygen,^ but the ordinary 
metal is easily dis.solved by hot hydrochloric acid as .well as by 
cold aqua regia, and when heated with concentrated sulphuric 
acid is converted into antimony sulphate. Antimony combines 
directly with the elements of the chlorine group, with those of 
the sulphur group, and with phosphonis and arsenic. 

*> Gtinther, Ann, Phy^ik, 1920, [4], 63, 476. 

” Holbora and Day, ibid., 1900, [4j, 2, 505. See also Heyoock and 
Novice, Joum. Chtm. Soc., 1895, 67, 180; Grossohuff, Zeil. anorg. Chem , 1918, 
103 , 164. 

» Ber., 1899, 22 , 725. Seo also Antmlen, 1887, 240 , 317. 

* Montemariini, Oazz., 1892, 22, 384. 

* Ditto and Motzner, Compt. rend., 1892, 116, 936. 



ANnHONY 


1002 


Colloidal solutions of antimony may be obtained by acting upon 
a tartaric acid solution of potassium antimonate with potassium 
hyposulphite.^ 

AHotropic Modifications of Antimony . — (fhe grey, metallic 
form of antimony described above is the stable modification, 
although Cohen regards it as a mixture of S(weral allotropic forms 
the relative propwtions of which depend upon the previous history 
of the metal.* Unstable yellow and black modifications, corre- 
sponding with the unstable yellow and stable grey forms of 
arsenic (Vol. I., p. 691) also exist.* The yellow form is obtained 
by the action of oxygen on liquid stibine at —90", and by the 
action of chlorine on stibine, both dissolved in liquid ethane at 
—•100°. It is amorphous, appears to dissolve slightly in carbon 
disulphide, and passes very readily, when the temperature rises 
above — 90°, into the black variety. The latter can also be 
prepared by the rapid coobng of antimony vapour, and by^the 
action of oxygen on liquid stibine at — 10°. It is an amorphous 
black powder, has the specific gravity 5*3, oxidises spontaneously 
in the air, sometimes taking fire, and passes when heated into the 
stable metallic form with evqjution of heat. 

Explosive or Electrolytic Antimony. - peculiar substance, 
discovered by Gore,^ is obtained by electrolysis of an acid solution 
of antimony trichloride having a specific gravity of 135, or of a 
solution obtained by dissolving the trioxide in from five to six 
times Us w’eight of hydrochloric acid of specific gravity M2, 
metallic antimony being, in each case, used as the positive, and 
copper or platinum as the negative pole. The latter becomes 
covered with a grey, lustrous, metallic coating, having an amor- 
phous fracture and a specific gravity of 5*78. It contains from 
4‘8 to 7*9 per cent, of antimony chloride, together with a small 
quantity of free hydrochloric acid. When scratched with a 
metallic point or touched with a red hot wire it decomposes with 
evolution of heat and liberation of the chloride, and when heated 
to 200° it flies into powder with a loud explosion. If it be pre- 
served under cold water it does not immediately undergo any 
alteration, but when heated to 75° it decomposes with a hissing 
sound; hydrochloric acid is found in solution, and the water 
b^mes turbid owing to the formation of basic antimony 

^ See Gutbier and Krautle, Kotloid Zett., 1917, 20, 194. 

* Cohen and van den Bosch, Zeii. physikal. Chtm., 1910, 29, 707. 

• Stock and Guttmann, Ber., 1904, 87, 885; Stock and Sicberf, ibid., 1905, 
88, 3837.a 

« Pha. Trans., 1808, 118 , 185; 1859, 148 , 797; 1862, 182 , 323; Heifer, 
if«fialm;1881,808,61. 




1001 


THE VANADIUM GROD# 


chloride. Similar products are obtained by the electrolysis 
of acid solutions of the bromide and iodide (Gore), but not of the 
fluoride: 

This remarkable^substance is probably a solid solution of an 
antimony halogen compound in an allotropic form of antimony, 
and the explosion consists in the sudden transformation of the 
latter into the stable metallic form, the heat ewolved amounting 
to 20 cal. per gram ; tlie same change goes on slowly when the 
explosive material is preserved. ^ This form is possibly identical 
with the black amorphous form described above, but the identity 
has not been definitely proved. 

f/ses.—Antimony is employed for the preparation of tartar 
emetic, and of other products used in pharmacy and in many 
processes of calico printing and dyeing. Its alloys are also 
larg(;ly used in the arts. When antimony is precipitated by 
zin,o from a solution of the trichloride, the metal is obtained in 
a finely pulveriilent state, as antimony black; this is employed 
for the purpose of imparting to the surfaQp of gypsum figures 
and other objects the appearance of iron or steel. 

447 Antimwiy Alloys , — ** Basil ^Valentine ” mentions that 
antimony is valuable for the preparation of medicines, and that it 
is likewise employed for other purposes, such as for the prepara- 
tion of printers’ type. He adds that under certain favourable 
conjunctions of the planets alloys are made of antimony, and from 
tlicsc seals and amulets are. cast, which are said to possesf special 
virtues. These same alloys can, according to Valentine, be cast 
in the same way to form both bells and mirrors. 

Fnylish type metal is an alloy of lead, antimony, and tin. A 
small percentage of copper is sometimes added, but is found of 
little practical value. The value of antimony in these alloys is 
that it imparts to them hardness, and gives them the property 
of expanding in the act of solidification so necessary in order to 
obtain an accurate cast of the letter. The tin gives toughness 
and coherence to the metal, The following are analyses of 


English type metal : 

I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

Lead . . , 

, 50 

60-0 

61-3 

96*2 

85-7 

83-5 

80*0 

-irntimony . 

. 25 

30-0 

18-8 

19-5 

14-3 

13-5 

15-0 

Tin . . . 

. 25 

10-0 

20-2 

9-1 

— 

3‘0 

5-0 

Copper . . 

. — 

— 

— 

1-7 


— 

— 


1 Coh^n aiid Kinger, Zeit. phifsikai Chetn., 1904, 47 , 1 ; Cohon, Collins, and 
Strongors, i6id., 1905, 60 , 291; Cohen and Strengors, i6id., 1905, 6 ^ 129. 




ANTIMONY 


1005 


No. I is supposed to give the best results for high class work, 
but owing to the high price of tin No. II. is generally used. 
No. V is used for stereotype plates, No. VI is linotype metal, 
and No. VII. monotype metal. • 

Britannia Metal and Peivter . — This silver-white metal is largely 
used for the preparation of spoons, cups, and other article's. It 
consists mainly tin and antimony, but frequently contains 
other metals, as is shown by the following analyses : 



Britannia Metal. 

Plate 

Pewter. 

w 

Ashbury 

Mot«l. 

Metal 

Argen- 

tum. 

Tin ... . 

85-7 

81-9 

89-3 

77-8 

85-5 

Antimony . 

10-4 

16-2 

7-1 

19-4 

14-5 

Copper . . . 

1-0 

— 

1-8 

— 


Zinc .... 

2-9 

1-9 


2*8 


Bismuth . . . 

• 

— 

1-8 

— 

• 


White or anti-frictimi metal ts chiefly used for lining the brasses 
of various parts of locomotive engines and for the solid bushes 
for the coupling-rods. Several alloys arc used for this purpose, 
as is seen by the following analyses : 


I. II. III. 

Copper 5-3 1-5 — 

Antimony 10-5 13-0 20 

Tin. . ‘ 81-2 45-r> 20 

Lead — 44-0 GO 


The alloy employed for the manufacture of ship’s nails con- 
sists of 3 parts of tin, 2 of lead, and 1 of antimony. 

Brass articles can be covered with a tine, lustrous coating of 
antimony by dipping them into a hot solution of 1 part of tartar 
emetic, 1 of tartaric acid, and 3 of water, to which 3 or 4 paints 
of hydrochloric acid and as much powdered antimony have been 
added. 

Antimony forms a beautiful purple alloy with copper which 
has the composition CujSb, and is known as Regulus of Venus. 
With tellurium it forms a continuous series of mixed crystals.' 

* Dreifuss, Zeit, Klektrochem., 1022, 28, 100, 224, 





1006 


THE VAKADIUM GROOT 


COMPOUNDS OF ANTIMONY. 

Antimony and Hydrogen. 

448 Anlimmiy Hydride or Stilnne, SbH 3 . — This substance 
was, first prepared in 1837 by Lewis Thompson/ and also 
independently by Pfaf! ^ and other chemists. It is formed when 
nascent hydrogen is brought into contact with a soluble anti- 
mony compound, or when an alloy of potassium or sodium with 
antimony is decomposed by water, or an alloy of zinc and antimony 
by dilute Itydrochloric or sulphuric acid. It is also formed 
when antimony oxide is added to an acid solution wliich is evolving 
hydrogen. All these methods, however, furnish a gas which is 
largely mixed with free hydrogen,^ and the preparation of pure 
stibinc is a matter of some difficulty. The liquefied gas was first 
obThined by Olszewski * in 188(5, and the pure gas itself by Stock 
and Doht ® in 1901. A gas containing as much as 14 per cent, 
of stibint is first prepared by gradually bringing a powdered alloy 
of 1 part of antimony and 2 parts of magnesiimi, prepared by heat- 
ing the constituents to redness in aft atmosphere of hydrogen, into 
hydrochloric acid of sp. gr. 1-OG at 0*^, which has been previously 
boiled. When this gas is washed through water, dried over 
^ calcium chloride and phosphoric oxide, and cooled by liquid air, 
it yields a white mass of solid stibine, and this on evaporation 
gives pure stibine, free from admixed hydrogen. The gas thus 
prepared can be collected over mercury, and when dry can be 
preserved for some hours without undergoing decomposition. It 
is a colourless gas with a characteristic odour, faintly resembling 
that of sulphuretted hydrogen, and is very poisonous. It con- 
denses to a colourless liquid, which boils at —17^^, and solidifies 
to a white mass, melting at — 88°. The density of the gas is 
4-3C at 15° and 760 mm., this being about 2-95 per cent, greater 
than the calculated normal density. The density of the liquid 
is*2*26 at —25°, Water dissolves about 0-2 vol. of the gas, and 
in the absence of iinpiurities the solution is stable for some time, 
whilst in the presence of mere traces of air decomposition sets in 
^^japidly. Alcohol dissolves 15 vols. of the gas, and carbon 

1 Phil. Mag.. 1837, [3]. 10, 303. * Pogg- 1837, 42, 339. 

* 8oe Jones, Joum, Chem. Hoc., 1876, 28> i.i 641. 

« Mmtash.. 1886, 7, 371; £er., 1901, 31 3592. 

« Ber., 1901, 31 2339; 1902, 36, 2270; Stock and Guttmann, ihid., 1904, 

37 , 886 . 



ANTIMONY AND HYDROGEN 1007 


disulphide 250 vols., but both these solutions are very unstable. 
Stibine decomposes slowly at the ordinary temperature into 
antimony and hydrogen, one volume yielding 1*544 vols. of 
hydrogen. The rate of decompo.sition has beei^carefully studied,^ 
and is greatly accelerated by the presence of water, of metallic 
antimony, or of hydrogen chloride. The gaj is formed from its 
elements with ab^rption of 84,500 cal.,® and explodes when a 
spark is passed through it, or when it is strongly heat^*d. Spon- 
taneous explosion also occurs occasionally and may extend to the 
liquid. * 

Stibine is very readily decomposed by oxygen and air, with 
formation of water and metallic antimony, and is also attacked 
by nitric and nitrous oxides, ami explodes when brought into 
contact with chlorine. It is easily inflammable, burning with a 
greyish flame, and evolving white fumes of antimony oxide. 
If passed through a glass tube heated above 150 ’ metallic antimony 
is deposited clo.se to the heated spot in the form of a lustrmis 
mirror, and if this be heated more strongly, microscopic metallic 
globules are formed. Concentrated sulphuric acid decomposes 
the gas. Caustic alkali solution becomes deep brown wlum the 
gas is pa.ssed through it, aiufat last a black powder H(q)arates 
out. The brown solution absorbs oxygen rapidly, and especially if 
it be shaken with air. The powder appears to ix)ssess the com- 
|K)8ition *Sb(()H) 3 . It rapidly decomposes on standing, b(?coming 
richer in antimony. AVhen antimony liydride is passed through a 
solution of silver nitrate, black silver antimonide, SbAgj,® is first 
formed ; the excess of silver nitrate present, however, causes a 
further reaction to take place, and the final precipitate consists 
of silver and antimony hydroxide, with a little metallic antimony.* 
Sulphur decomjwses the gas, becoming covered with a film of the 
orange-red antimony sulphide (Jones) : 

2SbH3 -f- GS-SlvS^ k SII^S. 

Sulphuretted hydrogen has no action on the pure gas, but readily 
iecoinjxises the impure mixture with hydrogen. 

> Stock and Guttmann, Btr., 1904, 37, 901, 1957; BodenaUdn, ibid., 1904, 
17, 1381; Stock, Gomolka, and Heynemann, ibid., 1907, 40, 532; Stock, 
Scheandia, and Voigt, ibid., 1908, 41, 1309. 

• Bertholot and Petit, C’twnpf, rend., 1889, 106, 548. 

• Laasaigne, J. Chim. Mi/l., 1840, 17, 443. 

« Reckleben, Bcr., 1909, 42, 1458; see al»<j ViUli, VOrosi, 1892, .397. 

VOL. n. (n.) 




1008 


THE VANADIUM GROUP 


Antimony and Oxygen. 

449 Considerable doubt formerly existed as to the number of 
the oxides formed by antimony. Thenard, in 1800, mentions 
several ; whilst Roust, in 1804, admitted the existence of only 
two. The exact number was ascertained by Berzelius in 1812 
to be as follows : • 

Antimony trioxide, Sb^Og^ 

Antimony tetroxidc, SbgO^, 

, Antimony pentoxidc, SbgOg. 

All these arc acid-forming oxides, the first acting also as a feebly 
basic oxide.* 

Antimony Trioxidey Sb^Og.— This occurs as the mineral valen- 
tinite with other ores of antimony, having been produced by 
the oxidation of these. It forms pearly-white, rhombic crystals 
which are sometimes coloured yellow or red by the presence of 
iron and other metals, and have a specific gravity of 5*566. 
Another, though less frecpient, form of antimony trioxide is 
senarmontite, which usually occurs together with other antimony 
ores, and crystallises in regular octahedra, having a specific 
gravity of 5*2 to 5*3. From this* it appears that antimony tri- 
oxide is isodiniorphous with arsenious oxide (p. 238). Both these 
crystalline forms can be artificially prepared. Thus when the 
metal or sulphide is heated in an inclined crucible a light, whi^ 
oxide is formed at a red heat, and this when more strongly heated 
is deposited on the upper part of the crucible in glistening needles, 
sometimes mixed with octahedra, and known as Jlores antinwnii, 
or flowers of antimony. This latter form is also observed when 
the rhombic oxide is sublimed, and the octahedra, when quickly 
heated, are converted into the rhombic crystals.^ Both forms are 
also obtained by crystallising a hot saturated solution of the oxide 
or chloride in sodium carbonate (Mitscherlich). Antimony tri- 
oxide is prepared by diluting an acid solution of the oxide with 
water, and washing the basic salts which are thrown down, first 
A^ith hot water, then with sodium carbonate solution, again with 
water, and finally converting the residue into oxide by ignition. 
Obtained in this way, the oxide is a pale buff-coloured, crystalline 
powder, which can also be obtained, but not perfectly pure, by 
oxidising the metal with very dilute nitric acid. It is scarcely* 
soluble in water, and becomes yellow when ignited, but assumes 
the pale bufi tint again on cooling. 

* Terreil, Comjd, rend,^ 1806, 62, 302. * 



ATiTXMONY AND OXYGEN 


1009 


At a dark red heat it tnelts, and the mass obtained on cooling 
is crystalline. It volatilises at 1500”, yielding a vapour having 
a specific gravity of 19*9, corresponding to the molecular formula 
Sb 405 .' It is insoluble in dilute sulphuric ^cid and in nitric 
acid, but is easily soluble in Iiydrochloric and tartaric acids and 
the caustic alkalis. The solution of antiiiim^ trioxide in cream 
of tartar yields jptassium andmonyl tartrate, or tartar emetic^ 
CiH^KSbOy. Heated in the air it absorbs oxygen, the tetroxide 
being formed at all temperatures between 390” and 775” ; at very 
high tem|)eratiires, however, tlie latter decompofles and the tri- 
oxide is again formed.® The trioxide is readily reduced when it 
is heated in hydrogen. According to Bunsen, the ‘presence of 
higher oxides can be easily detected by the addition of potassium 
iodide to the hydrochloric acid solution, when iodine is 8(?t free, 
as may be readily ascertained by shaking the liquid with a few 
drops of carbon disulpliide. 

The trioxide in solution is readily converted into antimonic 
acid by means of oxjdising agents such as iodine, chlorine, or 
potassium dichromate, but the change cannot be completely 
effected by bromine water, nitric acid, or potassium chlorate 
and hydrochloric acid.* It reduces the salts of many of the 
metals.® 

The mineral valentinite was probably known to the ancients. 
Pliny states that two kinds of stibium exist : “ Duo ejus genera 
mas ft femina. llorruUor esl ma^ scalrrmqne et minus porukrosuSy 
minusque radians el arsenosior ; femina contra niict^ fruibilis, 
fissurisque, non globis, dehiscem.''* Perhaps, however, under the 
feminine variety he may have understood the preparation ob- 
tained by roasting the sulphide, for this process is mentioned by 
Dioscorides, and Glauber also refers to it. The operation is 
more fully described by “ Basil Valentine.’* He says that by 
regulating the fire carefully “ from the common regulus of the 
spiessglas magnificently fine jlores may be prepared, both yellow, 
red, and white,” Valentine certainly knew that the mineral 
which we now call valentinite is an ore of antimony, for he dis- 
tinguishes between the black and the golden spiessglas. The oxide 
obtained by roasting the metal reduced by iron was formerly 

» V. and C. Moyer, 1879, 12, 1282. 

* Camclley and Walker, Joum. Chem. Hoc., 1887, 63» 8fi. 

• Road, ihid., 1894, $5, 314; Baubigny, C’ompl, rmd., 1897, 124, 499, 
MO. 

• Bo««k, m., 1896, 68, [1], 516. 

* Harding* Zeit. anorg. Chm,, 1899, 80, 235. 



1010 


THE VANADIUM GROUP 


called nixferrum, as it was believed that iron was necessary for 
its formation. 

Antimony trioxide acts as a weak acid-forming oxide and also 
as a weak basic oxi Je. The salts with strong acids are decomposed 
by water with formation of basic salts, which in contact with 
water arc gradually, converted into the oxide. 

AtUmmiioiis Acid. — Two hydrates of antinyjiiy trioxide have 
been described, which may be considered as the ortho- and 
pyro-acids, although it is not certain that they are definite com- 
pounds, since the amount of water contained in them varies 
gradually with the temperature at which they are dried. The 
ortho-acid, *11.^81)03, is obtained by adding nitric acid to anti- 
rnonyl tartaric acid or tartar emetic, and drying the precipitate 
at 100'". The pyro-acid, ir48b205, is formed by adding copper 
sulphate to a solution of antimony sulphide in caustic potash until 
no^ further orange-coloun*<l precipitate is thrown down, but a 
white preci])itate is formed. After filtration, the liquid, on 
addition of acetic acid, yields a precipitate having the above 
composition.^ 

Only sodium and potas.sium salts have as yet been obtained 
in the crystalline condition, and t*hese appear to be salts of the 
(unknown) meta-acid, ILSbOg. 

Sodium AntimnnifCy Na8b02,311.20, separates out from a hot 
solution of the oxide in camstic soda in glistening octahedra, which 
are sparingly sohdde in water. • 

Uydrmjen S(Klium Anlimonife, Na8b02,2ILSb()2, is obtained 
from very concentrated solutions in large crystals almost iiLsoluble 
in water, which, like those of the former compound, appear to 
belong to the monodinic .system.- 

PotOfiiiium Triantimonite, K20,38b2()3, is formed in crystals 
when the trioxide is boiled with caustic potash.® 

Antimmy Tetroxide or Anlifnonious-anti manic Oxule^ SbgO^. — 
This oxide is a white powder formed when cither of the two 
other oxides is strongly heated in the air. When heated it 
becomes temporarily yellow, and dissolves only with difficulty 
in acids. Antimony-ash, obtained by roasting the sulphide in 
the air, is an impure tetroxide, and was formerly employed for 
the preparation of the antimony compounds. Impure tetroxide 
also occurs ns tlie mineral cervantite, found together with other 

^ iSchafTner, Amahn, 1844, 51, 182. 

« Terroil, An». Chim. Phya., 1866, [4], 7, 380. 

* Cormiiubocof, Compt. rend.t 1892, 115, 1305. 



ANTIMONY PENTOXIDE AND ANTIMONIC ACIDS 1011 


antiiuony ores in Tuscany. Antimony tetroxide forms salts with 
basic oxides which have been termed hjpoantinwmtes. 

Potassium llyjmantmomite, KgSbgOj, obtained by fusing 
together the tetroxide and pot^ish and lixiviating with cold water, 
is a white mass soluble in hot water; addition of hydrochloric 
acid to this solution precipitates the salt K2Sb40{,. 

Other insolubl^ hypoantimonates can be*obtained by double 
decomposition with the corresponding salts. Some of these 
occur as minerals. Thus romeite, CaSb^Os, crystallises in tetra- 
gonal pyramids, and is found at St. Marcel, in dMedmont ; and 
ammiolite which occurs as a powder coloured red by the presence 
of cinnabar, found in Chili, is jirobably a copper liypountiinonate, 
CuSbgOs. 

Antimony Pkntoxidk and tiik Antimonic Acids. 

450 Antimony Pentoxide, Sb.,^)^, is obtained by rapidly (^vapo- 
ratiiig the powdered metal or its lower oxides with nitric Miid 
and gently heating the residue. This product usually contains 
a small amount of t!ie lower oxides, but the pure oxidfc may be 
prepared by gently heating the jirccipitatc produced by adding 
dilute nitric acid to a solution of potassium antimonate. It is 
a light yellow jiuwder, having a specific gravity of 5-0, jiractically 
insoluble in water, and turning blue litmus paper r(;d. Nitric 
acid does not dissolve it, w'hilst concentrated hydrochloric acid 
dis8olv« it only slowly, but completely; it volatilises comjiletely 
when lieated with sal-ammoniac. It is reduced to the trioxide 
when it is heated with hydriodic acid, or treated with stannous 
chloride solution. Antimony pentoxide acts as a stronger acid- 
forming oxide than the trioxide, and at the same time as a weaker 
base, the only stable salts being the sulphide, fluoride, and chloride, 
of the typical formula tSbR^^. 

Antimonic Acid . — Antimony pentoxide is said to form several 
distinct hydrates, which correspond in composition to the hydrates 
of phosphorus pentoxide, and are known by similar names. A 
certain amount of confusion exists in the nomenclature of tiiese 
acids since Berzelius gave the name of antimonic acid to the 
hydrate, IlSbOj, the tnie metantimonic acid, whereas the true 
pyroantimonic acid, H4Sb207, was termed metantimonic acid by 
Fremy, and the same system extended to the salts. 

The hydrated pentoxide which is formed by the action of 
cold water on the pentachloride, or by oxidising antimony tri- 
chloride with nitric acid, and Drecinitatinff bv wat^r is mndprafulv 




1012 


THE VANADIUM GROUP 


Holuble in water. According to Delacroix,^ this solution contains 
pyroantitnonic or tetfa-antimonic acid, which is converted by 
boiling into the ortho- or tri-antimonic acid, and yields salts of the 
types MgOjtSbjjOg and M2(),2Sb205, whereas Senderens ^ describes 
the preparation of* rnetantinionates from the same solution. 

The ortho-acid, HjSb04, is formed when potassium antimonate 
is d(,*composed by dilute nitric acid and the precipitate dried 
at 100 '^. The meta-acid, IlSbOg, is formed when this is heated 
to ITD"". These substances are white pow’ders which are soluble 
in aqueous potash, slightly soluble in water, and are converted 
into the pentoxide when heated. The meta-acid was formerly 
ertqdoyed af^a medicine under the name of materia perlata. 

The jnjro-acid, ]l4Sb207 (Fremy’s metantimonic acid), is 
formed by the decomposition of the peiitachloride by hot water. 
The air-dried preci[)itate ® possesses the formula H4Sb207,2H20, 
and has th(‘ sanui comfwsition as volgerite, a mineral which occurs 
inThe j)rovince of ( ■onstantine, in Algeria. 

The composition and properties of all the hydrates of antimony 
pentoxich? which have been prepared in tlfe solid state depend 
on the mode of preparation and the temperature at which they 
liave been dri(‘d, and according tft the recent investigations of 
Jander * no really definite hydrates exist. 

The Antimonates. Since the time of Berzelius, the antimonates 
have been chiefly investigated by Fremy,^ llelfter,® Beilstein and 
Bliise," Knorre and Olschew.sky,^ Ebel,® Delacroix, and St^iderens, 
Doubt still exists as to the constitution of these compounds, 
since most of t hem contain water, which may be water of constitu- 
tion or of crystallisation. 

Potafisinm Antimomite, KSbO^, is obtained by deflagrating 
1 part of metallic antimony with 4 parts of saltpetre and 
lixiviating with warm water. A white iK)wder is thus obtained, 
which when boiled for some time with water dissolves to a con- 
siderable extent. On concentrating the solution to a certain 
point, a crystalline mass separates, but if the liquid be further 

» J. Vhnrm., 18»7. fOJ. 6. 3,37; Bull Soc. chim., 1809, [3], 21, 1049; 1900, 
[3]. 26. 288. 

• Bull Soc. chim., 1899, [3], 21. 47. But sco also Tomula, Zdl anorg. Ckem., 
1021, 118. 81. 

• Danbmwa, Annahn, 1877, 180, 110. 

• Kolloid Zeit., 1918, 23, 122. 

‘ .-lua. Chim. Phtjs., 1844, [3], 12. 499; 1848, [3], 23, 497. 

• Pogg. Ann., 1862, 86, 418. ' Joum. Chem. Soc., 1889, 66, 1123. 

» Btr.\ 1887, 20, 3043. • /M., 1889, 22, SW4, 



AOTIMONATES 


1013 


evaporated, a gum-like mass, 2KSb03,nH20, is obtained which 
dissolves readily in warm water. When dried at 100° this salt 
contains SHgO, and at 185° still contains 2H2O. When a current 
of carbon dioxide is passed through a solution of the normal 
salt, a sparingly soluble acid salt is precipita*le(l which has the 
formula 2K20,3Sb205,7H20 at 100°, and still contains 21120 at 
350°. This salt ^as probably known to the* iatro-cheniists, and 
was much employed by quack doctors and known as antimonium 
diaphoreticmn ablutinn. The substance obtained by deflagrating 
the sulphide with saltpetre was employed at ;the end of the 
seventeenth century under the name antimonium diaphoreticum 
nmi ahluium, and Libavius and others treated this^’csidue with 
acids in order to obtain their diaphoreticum, which, therefore, 
consisted chiefly of antimonic acid. 

Normal Potassium Pifroantimotmte, K4Sb20-, was described 
by Fr^my (under the name of metantimonate), but the substance 
obtained by him was probably a mixture of caustic potusli 
and |)otassium antimonate. A sparingly soluble acid sally 
KgllgSbgO-jTIIgO, can, however, be prepared by oxidising an 
alkaline solution of potassium antimonite with potassium per- 
manganate and evaporating tlie filtrate.^ 

S(Hlium Antimonate, 2NaSb()3,7H20, is obtained when the 
metal or sulphide is deflagrated with (hili 8alt])ctre and the mass 
V ashed out with water. At 200° it loses two molecules of water, 
and becomes anhydrous at a red heat. 

A salt which is probably identical with this is formed as a 
voluminous white precipitate when sodium chloride is added to 
a solution of the gummy potassium antimonate. This changes 
on standing into the crystalline acid sodium pyroantimoruiley 
HjNagSbjO^jOHgO. It is only soluble in 350 parts of cold water, 
and is one of the least soluble of the inorganic salts of sodiurii. A 
solution of potassium antimonate can therefore be used as a 
reagent for the detection of sodium. Even when a solution con- 
tains only 0* 1 per cent, of sodium salt a crystalline powder separates 
out after standing for tw'elve hours. Addition of alcohol facili- 
tates the precipitation; free alkalis, on the other hand, retard 
its formation. The salts of lithium, ammonium, and the metals of 
the alkaline earths give precipitates with potassium metanti- 
monate, and hence these substances must be removed from 
solution before the above test for sodium can be applied. 

Ammonium ArUinumatey NH4Sb03, formed by dissolving the 
• ^ Knorre and Olgchewsky, Ber.t 188S, 18, 2363. • 



1014 


THE VANADIUM GROUP 


acid in warm ammonia, separates out on cooling as a crystalline 
powder, insoluble in water, and readily gives off ammonia. This 
is the only ammonium antimonate known.^ 

Many otlier salts have been prepared by the action of alkalis 
and metallic acetates on a solution of hydrated antimonic oxide 
in water (Delacroix, Senderens). 

The antimonates*of metals of the other groups are either 
sparingly soluble or insoluble in water. They may be obtained 
by double decomposition as crystalline precipitates, which are 
decomposed by ‘weak acids with formation of acid salts, whilst 
stronger acids, on t Ik; other hand , liberate antimonic acid. Almost 
all the antinfonates dissolve in strong hydrochloric acid. 

Nimnal Lend Antimonate^ rb(Sb()3)2, is a white, curdy precipi- 
tate, insoluble in water. The basic salt, Pb3(Sb03)2(0H)4,2H20, 
occurs as bleini<*rito, at Nertschinsk, in Siberia, and Endellion, 
in (V)rnwall, in roniforin or spheroidal masses, which possess a 
resthouH ajipeurance and a white, grey, brown, or yellowish colour. 
Another basic salt, used in oil painting under the name of Naples 
yellow, is obtained by heating a mixture of 1 part of tartar 
em(‘tie, 2 }>arts of lead nitrate, and 4 parts of common salt 
for two hours to the fusing point of sodium chloride, and li.\iviating 
with water. 


Antimony and thk Halookns. 

t 

451 Antimony Trijhioride, SbF3, is obtained as a dense snow- 
white mass by distilling antimony with mercury fluoride. If 
a solution of the oxide in an excess of hydrofluoric acid be 
eva[)orated, the fluoride is also obtained in rhombic pyramids. 
It is delicjuescent, and is not decomposed by water; but if the 
solution be. evaporated without an excess of hydrofluoric acid 
a basic fluoride is formed. Antimony trifluoride forms crystalline 
double salts with one, two, or three molecular proportions of 
the fluorides of the alkali metals. The potassium salt is used in 
calico printing. 

Antimony Pcmtafluoride, SbFg, is obtained by boiling antimony 
pentachloride with anhydrous hydrofluoric acid in a platinum 
retort pro\dded with a reflux condenser of platinum for three 
days and fractionally distilling the residue.* It is a thick, colour- 

^ Itaschig, Ber., 1885, 18, 2743. 

* Rut! and Plato, 16 ^., 1904, 37. 073. Soe also ibid., 1900, 89, 4310; 1909. 
49 , 4021.< 



AOTIMONY AND THE HALOGENS 1015 


less liquid of specific gravity 2*993 at 22-7°; it boils at 150°, 
solidifying when cooled. It attacks the skin, and dissolves 
paraffin, but has no action on dry glass. Exposed to air it unites 
with water, forming a hydrate with 2 H 2 O. It combines with 
antimony trifliioride, with evolution of heat and contraction, 
forming a series of additive compounds, varying in comjx)siti()n 
from 8 bF 5 , 2 SbF 3 | to SbF 5 , 5 SbF 3 . The pentafluoride forms 
difficultly crystallisable double salts with the fluorides of the alkali 
metals.^ Chlorine has no action on it, but bromine forms a viscid, 
dark brown mass, probably containing SbF^Br. Iodine also 
reacts on the ])entafluoride with development of heat and the 
formation of a bluish-green liquid or of a dark brown'solid. 

Antimouif Trichloride, SbClg.-- “ Basil Valentine’’ says : “ Take 
of fine white, well-sublimed corrosive sublimate, and of good 
spiessglas the same (piantity. Hub these up together and distil 
them. The oil which comes over is at first white, and congeals 
like ice or clots of butter.” This preparation was termed huiyrttm 
(inlimonii, and was supposed to contain quicksilver until Claulx^r, 
in 1G48, showed that\his was not the case, inasmuch as 'it could 
be prepared by distilling sj)iessglas with oil of vitriol and common 
salt or hydrochloric Jicid. Other methods of preparation are by 
heating sulphate of jiiitimony with sodiutn chloride, and by 
heating an (‘xcess of metallic antimony, or its sulphide, in a current 
of dry chlorine. 

Antimony trichloride is a crystalline mass, melting at 73-2° 
and boiling at 223-5^ (Kopj)).^ Its colourless vapour has the 
normal specific gravity of 7-8 and the salt dissolved in ether 
has the normal molecular weight.^ Its latent heat of fusion 
is 13-37 cal. On exposure to moist air the solid deliquesces to 
a clear li<pad, and this, on evaporation over suljdiuric acid, yields 
crystals of the anhydrous chloride. A solution of tlui chloride 
is best obtained by boiling the sulphide with strong hydrochloric 
acid. When ‘this is distilled in a retort, water conies over first, 
next the excess of hydrochloric acid, and lastly the anhydrous 
chloride. The concentrated solution, which has a specific gravity 
of 1*35, is known as liquid butler of antimony, and is employed for 
giving a brown surface to iron and steel wares, such, for instance, 
as gun-barrels (brown Bess); it is also sometimas used for 
pharmaceutical purposes. The anhydrous cliloride yields with 

^ Marignac, Annalen, 1868, 146* 239. 

* JSec also Beckmann, Zeit. atwrgi Chem., 1900, 61, 96. 

^ Lespiean, Compt. rend.,^ 1897, 126, 1094. 



1016 


THE VANADIUM GROUP 


dry ammonia the brittle white compound SbClgjNHg, which, on 
heating, gives off ammonia. It combines with hydrochloric acid 
to form the crystalline compound 2SbCl3,HCl,2H20, and also 
forms soluble crystalline double salts with a variety of metallic* 
chlorides.^ 

Pmvder of Algaroth. -Jl the acid solution of the chloride be 
diluted with water a white precipitate of the^ basic chloride is 
thrown down. This was known to l^aracelsus, who employed it 
as a medicine, and states in his Arckidoxa that in order to prepare 
it, corrosive suWimatc is to be distilled with antimony, and the 
product coagulated with water, when the memtrius vike is obtained. 
Towards the*end of the sixteenth century it was much employed, 
especially by the Veronese physician, Algarotus, and was termed 
by him pulvis angcliom^ although it has been generally known as 
fonder of Algaroth. The presence of tartaric or free hydrochloric 
acid prevents the precipitation of this substance. Its composition 
varies according to the method of its preparation. If ten parts of 
solid trichloride are mixed with seventeen parts of water, and 
allowed fo stand until the precipitate has become crystalline, the 
compound SbCK'l is dejiosited in small rhombohedra. These 
may be washed with ether in ordA to remove the excess of the 
chloride. Tlie same compound is o])taincd by lieating equal 
jiarts of the trichloride and absolute alcohol in sealed tubes to 
14 ()‘\ If oiK^ part of the trichloride be mixed with three parts 
of water, and the precipitate filtered off (juickly and mi^’ed with 
ether, the same body is obtained as an amorphous powder. When 
this substance is heated the trichloride is given off, and the 
oxychloride, Sb4()5('l2, remains behind. The last named com- 
pound is formed as an amorphous precipitate when the chloride 
is mixed with from five to fifty parts of water; on standing, it 
gradually forms silky prisms. If three times its bulk of hot water 
be added to the trichloride, and the liquid allowed to stand at 
60 '' for some hours, crystals are obtained resembling soda crystals, 
which also possess the compowsition Sb405Cl2.^ With larger 
quantities of water still more basic chlorides are formed, which 
if boiled repeatedly with water, are converted into the trioxide, 
this reaction taking place more quickly in the presence of sodium 
carbonate. If antimony oxide be dissolved in boiling antimony 
trichloride, a pearl-grey, crystalline mass is obtained having the 
composition SbOCbTSbClg, and this yields the substance 
2Sb0CbSb203 on treatment with absolute alcohol. 

^ Ephraim, Ber,, 1903, 36* 1816. * Sabauajew, Zeit, Cheim, 1871, 204. 



AJNTIMONY AND THE HALOGENS 


1017 


Antimony Pentachloride, SbClg, was discovered by H. Rose* 
in 1835, and is prepared by the direct union of antimony and 
chlorine, which takes place with evolution of light and heat. 
It is also readily formed by satiu-ating the fused trichloride with 
chlorine gas, Antimony pentachloride is a yellow, fuming, 
disagreeably-smelling liquid, which solidifies in a freezing mixture, 
forming crystals melting at 3"^.^ It is readily volatile, ])artially 
decomposing on distillation into chlorine and tricliloride, but 
under a pressure of 22 mm. it boils without decomposition at 
79°, whilst under the same conditions tlie trichloride boils at 
113‘5°.2 The vapour density^ under a pressure of 58 mm. 
at 218° is 10, the calculated number being 10-3. \V<^ien brought 
in contact with the requisite quantity of ice-cold wat(*r it forms 
the monohydrate,^ SbClg, HgO, crystallising from chloroform 
in tliin, deliquescent scales melting at iwr. if more water be 
added ^ a clear liquid is obtained, and this, on standing over 
sulphuric acid, deposits crystals of KSbCl 5 , 4 H 20 , which ffre 
insoluble in chloroform (Anschutz and Evans). Hot water 
produces antimonic acid. As it easily loses chlorine, atitimony 
pentachloride is employed in organic chemistry as a chlorine 
carrier in the chlorination of*many bodies. With hydrocyanic 
acid it forms the white, crystalline com])ound >Sb(l 5 , 3 HCN 
which volatilises under 100 ° with ])artial decomposition. It 
also forms solid compoimds with various chlorides, oxides, etc., 
such astSbClg, 8 Cl 4 ; SbClg,!^'!^; SbClg, POCI 3 ; 2 SbCl 5 , 5 NOCl; 
SbClg, NO; SSbCIg/iNOj; SbClg, N48,. Ry the interaction of 
antimony pentachloride and iodine the addition compounds 
SbClg, 2IC1 and SbCl 5 . 3 lCl have been obtained as bluish-black 
crystals melting at 62 63°.* 

Antimony pentachloride forms a very large number of double 
salts, many of which are derived from the complex niefnrhhro- 
antimonic acid, HSbCIg, which is obtained in greenish -yellow 
prisms containing 4 JH 2 O by the action of chlorine and hydrogen 
chloride on a solution of antimony trichloride.'^ 

Antimony Tetrachloride, SbC^, is probably present in the dark 
brown solution formed by the action of chlorine on an excess of 

» Molca, Anal FU. Quim., 1914, 12, 314. 

• AnHchtitz and Kvang, Ber., 1880, 19, 1994; Joum. Chem. Soc., 1886, 

708. 

• Anschutz and Evans, Annalen, 1889, 263, 96. ^ Ihid., 1887, 239, 239. 

‘ Weber, AnnaUn, 1863, 126, 86. • Ruff, Btr., 1915, 48, 2068. 

’ Weinland and Schmid, Ztil anorg. Chem., 1906, 44 , 37. See also Ber., 
1901, di 2683; 1903,86,244. * 




1018 


THE VANADIUM GROUP 


antimony trichloride. A number of salts have been prepared of 
the type which appear to be derived from the tetra- 

chloride and arc characterised by their dark colour. They are 
iHomorphouH with the corresponding salts of the tetrachlorides 
of lead, tin, and platinum.^ The rubidium salt, RbgSbClg, is 
obtained by adding rubidium chloride to a mixture of equal 
molecular proportions of the tri- and penta-chlyrides of antimony 
in presence of liydrochloric acid. It crystallises in lustrous, dark 
violet, microscopic octahedra, and is decomposed by water. 
Analogous bromine compounds appear also to exist. 

Antimony Tribromide, Sbllrj.- PowTlered antimony combines 
directly with bromine with evolution of light and heat. The 
tribroniidii sublimes in colourless, deliquescent needles, which 
melt at 05” and boil at 275” ; water decomposes it with forma- 
tion of a basic bromide. Another method of preparation con- 
sists in heating an excess of powdered antimony with a solution 
onjromine in carbon disul[)hide; the tribromide thus obtained 
on evaporation crystallises in octahedra. 

'Fhe 'jftmtdhromule is obtained in cornbinjAion with ether when 
the metal is covered with ether and treated with excess of 
bromine. The compound forms Jrey crystals and is very un- 
stable.- 

Antimony Tri-iodide, SbLj. - Antimony and iodine combine 
directly with evolution of so much heat that if large quantities 
are employed explosions may ensue. Tht‘ tri-iodide is a brownish- 
red mass, which crystallises in red, six-sided tablets from solution 
in carbon disul|)hide. It melts at ITT to a garnet-red liquid 
and forms a violet-red vapour, which at a higher temperature 
becomes scarlet. It sublimes at a temperature slightly above its 
melting point, boils between 411” and 427”, and is decomposed 
by water, with formation of a yellow oxy-iodide, which forms 
crystalline double salts with the various iodides. 

Doth the bromide and iodide form numerous double salts. 

Antimony and the Sulphur Group. 

452 Antimony Trisidphide, SbgSg, occurs crystallised as stibnite 
in the older stratified rocks. This is the most important ore 
of antimony, and it is found in considerable quantity, occurring 
in Cornwall, Hungary, Transylvania, in the Banat, in the Harz, 

' Settorberg, Oft'tr. K. Vdetutk. alcad. F6r., 1882, 23; Wclnland and Feige, 
Bcr.t 1903, 36, 269; Weinland and Schmid, ibid.t 1906, 1080. 

* RaVnaud, Bull. Soc. chim., 1920, 27, 411. ^ 



ANTIMONY AND THE SULPHUR GROUP 


1010 


in Westphalia, in the Black Forest, in Bohemia, in the Auvergne, 
in FiStramadura, Algiers, Corsica, Siberia, Nevada, New Bruns- 
wick, in Japan, where it is foimd in magnificently large and 
perfect crystals, and in Borneo in large quantities. It crystallises 
in prisms, but is usually found in columnar or striated masses, 
which soil the fingers like graphite. It is ^easily pulverisable, 
and readily fusiye, and has a specific gravity of 1-02. . The 
crude sulpliide occurring in commerce is obtained by melting 
the ore in the manner already described, and is sold in rounded 
masses having the form of the vessel in which the'inolten sulphide 
solidifies. It has a metallic lustre, steel-grey streak, and crystalline 
fracture. From early times this substance has beeif useil in the 
East under the name of Kohl. The alchemists occupied tliem- 
selves much with the properties of this body, as it was used for 
the purification of gold, and was tmned judex uJfiuius or lupus 
metallorum. Antimony trisulphide also exists in the amorphous 
state, and in this form was known to “ Basil V^alentine.” lie 
states that crude sp^essglas may be sublimed with formation of 
a red bo<ly when it is mixed with sal awutoniacum. * In this 
way antimony chloride and ammonium sulphide are formed, 
which again react on cooling, producing the original compounds, 
the antimony sulphide separating out as a red powd(^r. Glauber, 
and also Lemory, speak of the solution and the subseejuent 
precipitation of the s])iessglas with caustic alkalis; but it was 
not unfll 1711 that attention was directed to the red sulphide 
of antimony. In this year a Carthusian monk whose life had been 
despaired of by the Paris faculty w^as saved by a monk of the 
name of Simon administering to him a medicine which was first 
prepared by a German apothecary, a disciple of Glauber, and 
which was bought by the Parisian apothecary de la Ligere. This 
was soon known as the “ poudre des chartreux,” or Carthusian 
{)owder. Simon, however, gave to it the name of Alkerum 
mineral^ and such was the reputation which this medicine enjoyed 
that the French Government bought the receipt for its preparation 
in 1720 from de la Lig^rie. The process consisted in boiling 
the spiessglas with potashes and allowing the clear solution to 
cool, when the kermes was deposited as a red powder. In 1728 
Stabel found that when caustic potash was employed, a red 
powder was also obtained, which Mender in 1738 showed to be 
pure kermes, and C. J. Geoffroy in 1735 proved that the same 
preparation was obtained when spiessglas was fused with car- 
bonates the alkali metals, and the liver of antimofly thus 




1020 


THE VANADItM GROUP 


obtained boiled with water. This body was believed to be a 
compound of antimony, sulphur, and alkali, though chemists 
such as Haum6 denied that it contained any alkali, and assumed 
that in spiessglas rcjgulus of antimony was combined with sulphur, 
whilst in mineral kermes calx of antimony was combined with 
sulphur. Many oth^r views were held concerning the composition 
of this compound until Rose in 1825, and Fiicl\[S in 1833, showed 
that mineral kermes is merely amorphous antimony sulphide. 

Various methods may be adopted for the preparation of 
mineral kermes* which for fifty years was highly prized as a 
medicine, and even now is sometimes employed. All these 
processes yi^ld a preparation containing, as impurity, varying 
quantities of antimony oxide, both free and combined with the 
alkalis, and moreover on exposure to air oxidation occurs with 
formation of the oxide and free sulphur.^ Hence the prepara- 
tion of the kermes should be carried on exactly according to the 
prescription of the pharmacopoeia. 

In order to prepare the amorphous sulpljide free from oxide, 
the crystalline coinjiound is boiled with caustic potash in absence 
of air, the liquid filtered, and the hot diluted solution precipi- 
tated with sulphuric acid. The precipitate is then washed with 
very dilute acid, and afterwards with cold water; and to remove 
any oxide which may be present it is heated with a solution of 
• tartaric aid. Thus obtained, the precipitate becomes anhydrous 
whim dried at 1(X)° and forms a reddish-brown, light**powder 
which readily soils the fingers. This is more soluble in hydro- 
chloric acid, in the fixed alkalis and their carbonates than the 
crystalline compound into which it is converted on fusion. It 
may also be obtained by pouring fused stibnite into an excess 
of cold water. It then forms an amorphous, lead-grey mass 
which appears of a hyacinth-red colour when seen in thin films, 
has a specific gravity of 4*15, and when triturated is converted 
into a dark reddish-brown powder. 

If sulphuretted hydrogen is passed into an acid solution of 
the tricliloride or into an acidified solution of tartar emetic, an 
orange-red precipitate of amorphous hydrated sulphide is 
obtained, which after drying at 100—130° becomes black at 
200°. The precipitated sulphide also becomes black when it is 
boiled wth 2 parts of hydrochlono acid and 1 part of water in a 
current of carbon dioxide.* 

' PoUacci, BcU, C\im, farm,, 1906, 46 > 401. 

* Mitoiiell, CAm. AVuv?, 1893, 97, 291. See also do Baobo, ilan. ckim, 
applicata, 1919, 12 , 143; Wilson and MoCrosky. J, Amer, Chm, See,, 1921, 48 » 
2178. 



ANTIMONY AND THE SULPHUR GROUP 


1021 


When the sulphide is heated at 850"^ in nitrogen, and the 
vapours are rapidly condensed, black needles are formed accom- 
panied by lilac-coloured globules which appear to constitute a 
polymorphic variety of the sulphide.^ This f(^rm lias the specific 
gravity 4*278 at 0“, and passes at 220*^ into the black, crystallino 
form, of specific gravity 4*652 and melting - at 540^. 

When a dilute .^lution of tartar emetic is added to sulphiii>itted 
hydrogen water a colloidal solution of antimony sulphide is 
produced, which is orange-red by transmitted light, and can be 
boiled without undergoing change. Calcium chhiride and many 
other electrolytes cause an immediate precipitation of the 
sulphide.® On heating in a current of hydrogen tM^ trisulphide 
is reduced to metal, but it may be sublimed without decom- 
position in an atmosphere of nitrogen. The equilibrium between 
the sulphide and hydrogen at various temperatures has been 
examined by Pelabon.^ Crystalline antimony sulphide is used 
for the preparation of other antimony compounds, in pyroteclmy, 
in the heads of lucifer matches, and in the composition used for 
firing brcechloading firearms. The amorphous suljihide is 
largely used for vulcanising caoutchouc, to which it imparts a 
reddish-brown colour. 

The compound known as antimony cinnaJxir, which is obtained 
by warming a solution of the trichloride with sodium thiosuljihate, 
is the trisulphide. This substance is used in oil painting as well * 
as in water-colour painting and as a distemper. 

The Thioanlimonites or Livers of Antimony are formeil by the 
combination of the trisulphide with metallic sulphides.® Those 
of the alkali metals are prepared by fusing the constituents 
together. They are brown or black, and when they contain a 
large quantity of metallic sulphide they are easily soluble in 
water, but when the quantity of antimony increases, these livers 
of antimony become more sparingly soluble, and at last insoluble 
in water. They are also formed when the trisulphide is dissolved 
in a solution of a sulphide, or, mixed with antimonitc, when the 
trisulphide is fused with an alkali or alkali carbonate or treated 
with the solution of an alkali : 

2SbjS3 + 4KOH - SKSbSj -f KSbOa + 2 H 2 O. 

* Guinchant and Chretien, Compt. rend., 1904, 138 , 1200; 139 , 5J. 

* See also P(:iabon, ibid., 1904, 138 , 277; and Zani, BuU. Acad. ray. Iklg., 
1909, 1169. 

* Rcton, Joum. Ckem. Soc., 1892, 6L 142; BUtr and Geilx?!, Nachr. K, 

Get. Wist. ffoUingen, 1006, 141. • 

* Compt. rfnd., 1900, 130 , 911. 

« See Pooget, tbid., 1897, 12i 1443, 1518. 




1022 


THE VANADIUM GROUP 


Acids precipitate the amorphous trisulphide from these solutions, 
whicli also absorb oxygen rapidly from the air. Many of the 
thioantirnoriites occur as minerals, and the composition of some 
of these has beei^ already given.^ The alkali salts ^ belong to 
the types MSbSg, MjSbSa, M 2 Sb 4 S 7 , and M 4 Sb 2 S 5 . 

Antimony TelramJjihide^ Sb 2 S 4 , and Pmtasnlphide, SbgSg, do 
not occur in the native state. Basil Valcntipe ” mentions that 
when spiessglas is boiled with strong caustic ley, and acetic acid 
added to the liquor, a red body is precipitated, and Quercetanus 
in 11)03 mentK)ns in his pharmacopoeia a preparation from 
spiessglas and liver of sulphur by means of acids, terming it 
sulphur antimonii anralum. In 1054 Glauber mentions in the 
“ pharmacopoeia spagyrica ” the pre])aration obtained by 
precipitating the slag formed in the preparation of regulus of 
antimony by means of acetic acid, and recommends this pro- 
duct as panacea anlimonialis f)r sulphur purgans universale. 
This preparation, .which, as golden sulphuret of antimony, soon 
became a favourite medicine, was obtained from the more or 
less oxidised solution of liver of antimony, containing a thio- 
antijnonate. When fractionally precipitated by hydrochloric 
acid a brown kermes is first thrown down and afterwards a 
golden-coloured sulphide, termed sulphur auralum terlitv pracipi- 
tationis. Later, stibnite was boiled with alkali and sulphur and 
the solution precipitated with acid. At the present day pure 
sodium thioaiitimonate is first prepared; this is dissr)lved in 
from 10 to (K) parts of water and a cold mixture of 3-3 parts of 
sulphuric acid and 100 parts of water is gradually added; the 
precipitate is well washed with distilled water and dried at a 
moderate temperature in the dark. 

The sulphur aural um thus prepared has generally been regarded 
as antimony pentasulphide mixed with trisulphide and free 
sulphur. According to F. Kirchhoff,® however, it contains the 
tetrasulphide, Sb 2 S 4 , and no pentasulphide. The tetrasulphide 
may be obtained in the pure state by decomposing zinc thio- 
antimonate with dilute acids, and extracting free sulphur from 
the precipitate by means of carbon disulphide or acetone. The 
zinc salt is readily obtained from Schbppe's salt by double 
decomposition with zinc chloride, when it forms a chrome-yellow 

^ See also Soiiitnerlad, Zeit. anorg. Chtm.t 1897, 15, 173; Poiigot, Compt. 
rtwi., 1807, 124, 1518; 1903, 136. 1450. 

• Se« Pouget, Compt. rnuL, 1897, 124, 1445; 1898, 120, 1144, 1792; Stanek, 
Ztit. anorg. CAcm., 1808, 17, 117. 

* Zeijp. anorg. Cketn.t 1020, 112, 67 ; 114, 266. ' 



ANTIMONY AND THE SULPHUR GROUP 


1023 


precipitate which becomes bright orange-red when dried and 
powdered, and contains about 6*7 per cent, of free sulphur. 

The pure penta.sulphide is precipitated when an excess of 
sulphuretted hydrogen water is added to a solution containing 
the antimony in the form of antimonic acid at the ordinary 
temperature (Bunsen).^ When sulphuretted hydrogen is passed 
into the antimony solution a mixture of pentasulphide, , tri- 
sulphide, and sulphur is formed, the proportion of the penta- 
sulphide diminishing as the rate at which the gas is passed is 
lessened and as the tenn)erature is raised. Hydrochloric acid up 
to about 20 per cent, favours the production of the pentasulphide, 
but in larger amount hinders it.- • 

Antimony pentasulphide is a fine yellowish-red powder easily 
soluble in aqueous alkalis and their sulphides, and also, in 
absence of air, in warm ammonia. It likewise dissolves in the 
carbonates of the alkali metals, but not in ammonium carbonate. 
When exposed to sunlight, heated in water to 98'^, or sim^y 
heated in absence of air, it decomposes into the black trisulphide 
and sulphur, and is (Jccomposed by hot hydrochloric acid. 

Sodium Thioantimonaie, Na3SbS4,9H20. — Tliis is termed, 
from the discoverer, Schlippe's*saltj and is obt/ained by dissolving 
the trisulphide, sulphur, and caustic soda or a mixture of soda- 
ash and lime, in the requisite quantity of water; or by fusing 
together 16 parts of anliydrous sodium sulphate, 13 parts of 
stibnite, #nd 5 parts of carbon, dissolving, and boiling the solu- 
tion with 2*5 parts of sulphur. It crystallises in large, colourless 
or yellow, regular tetrahedra which have an alkaline reaction 
and a saline, cooling, metallic taste resembling that of liver 
of sulphur. It dissolves at 15"^ in 2-9 parts of water and is 
precipitated from aqueous solution by alcohol. The hydrated 
crystals on exposure to moist air soon become covered with a 
kermes-coloured coating, and when they are heated in absence 
of air water is given off and the anhydrous salt formed, which 
fuses at a dark red heat. 

Potassium Thioa^Uinwnale^ K3SbS4,9H20, is prepared in a 
similar way to the sodium salt and forms deliquescent crystals. 

Am^mnium Thioantimonaie^ (NHJgSbSi, formed when the 
trisulphide and sulphur are dissolved in red ammonium sulphide, 
crystallises in unstable pale yellow prisms.® 

^ AmaUn, 1878 , 192 , 305 . 

• Bosek, Jtmm. Chtm. Soc.t 1895, 67, 515; Brauner, ibid., 627. Soc also 
Klenker, J. fr. Chem., 1899, [2J. 59, 160, 353. 

• Stanok, Zeit. anorg. Chem., 1898, 17, 117. 

VOL, n. (n.) 




1024 


THE VANABIDM GROUP 


Barium Thioantimonate, Ba3{SbS4)2,r)H20, is prepared hj 
dissolving the freshly precipitated golden sulphide of antimony 
in barium monosulphide and precipitating by alcohol. In this 
way stellate groups of needles are obtained. 

The calcium saft is prepared in a similar way and is thrown 
down as an oily liquid on addition of alcohol. The thioanti- 
mon^tes of the alkali metals have been examined by Donk.^ The 
thioantimonatcs of the other metals are yellow, red, brown, or 
black precipitates, almost entirely insoluble in water and are 
obtained by double decomposition. 

AnliiYumy Oxysulphide^ Sb2S20, is found, together with stibnite, 
as kermesite or antimony blende in needle-shaped crystals or 
thin, six-sided prisms which have a cherry-red colour and an 
almost metallic lustre. It is obtained as a reddish-brown powder 
by adding antimony trisulphide to fused antimony iodide, and 
treating the mass with dilute hydrochloric acid, when a dark 
r^iddish-brown, lustrous powder of antimony thio-iodide, SbSI, 
remains behind. When boiled with water and oxide of zinc, 
this is c^onverted into the oxysulphide. * 

Glass of Antimony or Vitrum Antimmii is obtained by fusing 
oxidised stibnite with a small (Quantity of the sulphide. It 
forms a transparent, dark ruby-red mass, formerly largely em- 
ployed for obtaining the other antimony compounds, but now 
used only for imparting a yellow tint to glass and porcelain. 

Aniimmiial Saffron or Crocus Antwwnii.—li stibnite is de- 
flagrated with a quantity of saltpetre insufheient for complete 
oxidation a brownish-yellow powder is obtained on lixiviation 
which when heated melts to a yellow glass. 

Chlorosulphides of Antimony. — Two compounds of this class, 
SbSjCl and SbjSjCl, have been obtained as reddish-brown, 
crystalline substances by the action of sulphuretted liydrogen 
on antimony trichloride at its melting point.^ The compound 
SbSCl,7SbCl3 is obtained by heating the trichloride and tri- 
sulphide together. Alcohol converts it into 2SbSCl,3Sb2S2. 

lodosulphides of ilnfiwany.—Compounds of the formulse SbS 2 l 
and SbS 2 l 3 are formed when antimony trisulphide is heated wi^ 
iodine (Ouvrard). 

Antimony Trisulphaie, SbjiSO^jj, is obtained as a white 
mass by heating either the metal or the oxide with concentrated 
sulphuric acid. The composition of the salt depends on the 
concentration of the acid used, acid or basic salts being obtained 

^ Chem. Wtdthd, i90S, 5, 629, 629. 

* Ouvrard, Cmpt, rend., 1893, 1616; 117, 107. 



1085 


AOTDIONY AW) THB SULPHUR GROUP 


when the acid employed is stronger or weaker than that repre- 
sented by the formula The normal salt crystallises 

from a tolerably acid concentrated solution in long, glistening, 
silky needles,® and is decomposed by water into a soluble acid 
salt, and an insoluble basic salt. If antimonyVhloride be heated 
with fuming sulphuric acid a basic salt, 8^0(804)2, is produced 
in small, glistening crystals, which in contatt with alcohol are 
transformed into the salt Sb202S04, consisting of a white powder, 
which, when treated with boiling water, yields the salt Sb405S04. 
Several other salts have also been described. 

Antimony sulphate yields double salts with the alkali sulphates, 
such as KSb(S04)2, which crystallises in nacreous leaflets. These 
arc decomjX)sed by water, yielding antirnonious hydro.xide.® 

Antimony Thiosulphate —A. number of complex antimony 
thiosulphates have been prepared by Szilagyi.* 

453 Antimony Triselenide^ Sb2Se3, is formed when the two 
elements are fused together, a metallic, lead-grtjy, crystalfee 
mass being produced® which melts at 572 *^. When selenium 
hydride is passed iftto a solution of tartar emetic tlie same 
compound is precipitated as a black powder. 

Antimony Pentaselenide, is precipitated as a brown 

powder by adding dilute sulphuric acid to a solution of sodium 
seleno-antimonatc. 

Sodium Seleno-antimonale, Na3SbSe4,9H20, is isomorj)hous 
with thg corresponding thio-antimonate, and is obtained by 
fusing together sodium carbonate, antimony triselenide, selenium, 
and charcoal. The fused mass is boiled out with water in absence 
of air and the filtrate covered with a layer of strong alcohol. 
The salt separates out after some time in orange-red, transparent 
tetrahedra which arc soluble in two parts of cold water and 
become red in air, with separation of selenium. When a solu- 
tion of Schbppe’s salt is boiled with selenium, filtered, and 
the solution concentrated in absence of air yellow tetrahedra of 
Na3SbSeS3,9H20 are deposited. 

Antimony and tellurium ® when fused together yield only one 
definite compound, antimony irileUuride^ SbjTcj. 

» Adie, Cktm. News, 1890, 61, 58. 

> Schultz-SeUack, Ber., 1871, i 13. 

* Gutmaim, Arch. Pham., 1898, 236, 477; Metzl, Zeit. anorg. Chetn., 1900, 
48, 140; Gennan Patent 161776, Soo alao Kflhl, Zeit. anorg. Chem., 1907, 54, 
256; Gutmann, Arch. Pharm., 1908, 246, 187. 

* Zeit. anorg. Chem., 1920, 113, 69. 

* See P4^bon, Compt. rend., 1906, 142, 207; Cbi^ticn, ibid., 133|/, 1412; 
Chikaahi^ and Fujita, Mem. CoU. Set. Kyoto, 1917, 2, 233. 

* See Fay and Aj^ley, Amer. Chem. J., 1902, 27, 95. 




1U20 


THE VANADIUM mOUP 


Antimony and the Nitrogen Group. 

454 No definite nitrate of antimony is known, although the 
white powder obtained by the action of nitric acid on antimony 
contains nitrogenf and is converted by water into antimony 
pentoxide and nitric acid. 

If phosphorus be added to fused antimony a tin- white phosphide 
of antimony is obtained which when heated in*che air burns with 
a greyish flame. 

Anlimony Thiophosphate, SbPS 4 or SbgSgjPgSg, is formed when 
the trichloride or trisulphide is heated with phosphorus penta- 
sulphide. It is a fusible, insoluble, yellow, crystalline mass.^ 

Antimony combines directly with arsenic. The compound 
SbAsg occurs as allemontite in reniform or amorphous masses 
having a metallic lustre. 

. Medicinal Uses of Antimony. 

455 As we have seen, various antimony preparations are 
used as. important medicines. Paracelsus 'was one of the first 
to employ these for internal use, and his example was followed 
by the other iatro-chemists, many of whom worked diligently 
on antimony and its compounds. The disciples of the old 
Galenic school were violently opposed to the introduction of the 
antimony compounds into medicine, and they succeeded in 
inducing the Paris Parliament in 1566 to prohibit tl^ use of 
antimony and its compounds by all physicians on pain of having 
their licences withdrawn. In 1603 the medical faculty of Paris 
took a similar wstep, and this decree was not withdrawn until the 
year 1666. 

Metallic antimony itself was at one time employed for the 
preparation of goblets in which wine was allowed to stand 
overnight in order that it might be used as an emetic ; but this 
practice fell into disuse even during Boyle’s time. Pills made 
of metallic antimony were employed at a later period; these 
w-ero termed everlasting pills, because they, like the goblets, 
were believed only to act by contact and not to lose their weight. 
This error was first combated by Lemery and Vigani, a Veronese 
quack doctor who lived in England, and they showed that both 
antimony and fused stibnite became acted upon when placed in 
contact with wine. 

Whilst formerly a large number of antimony compounds were 
, 1 Glatzel, Btr.» 1891, 84, 3886. > 



DETECTION AND ESTTMATION OF ANTIMONY 1027 


employed in medicine,' the only ones which are used at the 
present day are tartar emetic or potasaiimi antimonyl tartrate, 
C 4 H 4 K(SbO)Ofl, and the trisulphide or antinionium sulphuraium. 
The first compound is given in doses of 0*0027 to 0*008 gram 
as a diaphoretic, and from 0*065 to 0*13 gram as an emetic. 
The dose of the second is from 0*065 to 0*13 gjam. 

In larger doseciit produces, like white arsenic, violent irrita- 
tion in the intestines, vomiting and purging. AVlien one large 
dose only is administered the case proceeds rapidly to recovery 
or death, generally the former, if the case be placed early under 
proper treatment, and in this respect acute antimonial is dis- 
tinguished from acute arsenical poisoning. 

In cases of clironic antimony poisoning the principal symptoms 
arc dryness of tlic throat, pain on swallowing, nausea and vomit- 
ing, diarrhoea, loss of flesh, giddiness, fainting, and albuminuria. 
Death takes place from exhaustion and wasting. Several cnjes 
have occurred in this country to show that tartar emetic has been 
tlius criminally and h^tally u.sed (Taylor). 

Detfction and Estimation of Antimony. 

• 

456 When a small quantity of an antimony compound is 
heated in the upi)er reduction zone of a JJunsen burner on a 
thread of asbestos the flame becomes of a bluish tinge, and 
when c small porcelain basin filled with cold water is held 
above it*a brownish-black deposit of metallic antimony is found 
upon the basin, and this is but slightly attacked by cold nitric 
acid, and is insoluble in sodium hypochlorite. Arsenic gives 
a very .similar reaction, but this may be distinguished from 
antimony by the fact that during the reduction a garlic-like 
smell of arsenic is noticed, and that the metallic film is readily 
soluble in sodium hypochlorite. If an antimony compound 
is heated on a carbonised match a l)rittle metallic bead is obtained, 
whilst arsenic is completely volatili.sed. Most of the antimony 
compounds are insoluble in water but di 8 .solve in hydrochloric 
acid. Those which do not thus dissolve may be obtained in 
solution by fusion with pota.ssium carlmnate and saltpetre, 
and subsequent solution in hydrochloric acid. Sulphuretted 
hydrogen produces in acid solutions a very characteristic orange- 
red coloured precipitate of antimony trisulphide. If other metals 
precipitable by sulphuretted hydrogen are present, the mixed 
sulphides, after washing, are treated with ammonium sulphide, 
filtered, and the filtrate acidified with hydrochloric acid. This 




1028 


THE VANADIUM GROUP. 


precipitate may contain, together with antimony, the sulphides 
of tin and arsenic. This last metal is removed by digesting with 
freshly prepared solution of ammonium carbonate, and washing 
the residue with Y^ater. This is then brought into solution by 
heating with hydrocliloric acid, and the liquid is placed in a 
platinum dish containing a piece of zinc; the antimony is 
deposited upon the platinum as a black, adhenent coating, which 
is readily soluble in nitric acid and can then be identified as 
antimony. A more satisfactory method consists in dissolving 
the mixed sulphides in caustic soda and a few drops of yellow 
ammonium sulphide and then boiling with sodium peroxide, 
which converts the metals into stannate, antimonate, and 
arsenate respectively. Tin is then detected by boiling with 
ammonium chloride, which precipitates stannic hydroxide, and 
arsenic and antimony are detected in the acidified filtrate by 
Bunsen’s method described below.^ A rapid method of detection 
is to boil the sulphides with a 5 per cent, solution of sodium 
carbonate, which leaves tin sulphide undi^olved; the solution 
deposits* antimony sulphide on cooling, whilst arsenic sulphide 
remains dissolved and can be detected as usual.^ 

Antimony may also be detected by means of Marsh’s test 
carried out as described under arsenic (Vol. T., p. 717). The mirror 
obtained is deposited much closer to the flame than that of 
arsenic, is formed at a lower temperature, does not yield a 
crystalline deposit of oxide when heated in the air, aid is not 
soluble in sodium hypochlorite. When the gas is passed into 
silver nitrate solution, silver antimonide is precipitated (p. 1007). 

Antimony trichloride gives a spark spectrum containing, 
among others, the following lines, mentioned in order of their 
relative brightness (Lecoq de Boisbaudran) : a 6005, 5568, 

7 6130, h 6070. 

Antimony is usually estimated gravimetrically either as 
the sulphide or the tetroxide. In the first case it is obtained 
as a hydrated precipitate, which may also contain sulphur 
and peutasulphide. It is necessary therefore, to dry this 
at 100^, to weigh it, and to bring a known fraction into a 
porcelain boat contained in a glass tube. Through the tube 
dry carbon dioxide is passed, and the sulphide is heated, the pure 
anhydrous trisulphide remaining behind. The sulphide may 
also be oxidised by means of nitric acid and the residue ignited 

, ‘ Walker, Joum, Chem, Soc., 1003, 88, 184. 

• Mateme, BvU. Soc, chim. Btlg., 1906, 80, 46. 



DETBCfnOH AKD ESTDCAIION OF AKmfOKT Vm 


and weighed as tetroxide, or it may be dissolved in a large 
excess of sodium Sulphide, potassium cyanide added, and the 
resulting solution electrolysed and the metal weighed.^ 
Antimony is also frequently estimated volqmetrically, the 
trioxide, in presence of sodium bicarbonate, l)eing converted by 
means of standard iodine solution into the ixmtoxide, or the 
trichloride being converted into the pentachloride by a standard 
solution of sodium broinate in presence of hydrochloric acid.* 

The quantitative separation* of antimony from other metals, 
with the exception of arsenic and tin, does not exhibit any 
difficulty. Should these three elements be present together 
their sulphides must be first converted into oxides by treatment 
with nitric acid, and these fused for some time with eight times 
their weight of caustic soda. The cooled mass is next allowed 
to soften in hot water until the sodium metantimonate has 
separated out as a white powder, and then one volume of alcohol 
of specific gravity 0*83 is added for every three volumes of the 
licpiid. After standing for some time the liquid is filtered and 
the precipitate welf washed with dilute alcohol, to which at 
last some caiLstic soda is added. The filtrate contains the 
stannate and arsenate, whilst* the whole of the antimony is con- 
tained ill the residue, and this is converted in the usual way 
into the sulphide (II. Rose). A more rapid method of separation 
depends on the fact that in presence of free oxaiic acid antimony 
is preeijiitated by sulphuretted hydrogen as the sulphide, whereas 
tin remains in solution.* Antimony and tin can also be separated 
electrolytically.* 

The separation of antimony from arsenic, which had previously 
been difficult and unsatisfactory, was first rendered exact by 
Bunsen. The moist and well-wa.shed mixture of sulphides 
obtained by precipitation with sul^ihuretted hydrogen is dis- 
solved on the filter in an excess of caustic potash, and the 

‘ Kohn and BanicH, British Assoc. Beports, 1890, 244. Sec also J^aw and 
Perkin, Trans. Faratlay Soc., 1905, 1, 202; Halm and Philippi, Zeit. aw^ry. 
Chem., 1921, 116, 201. 

* Nissenson and Siedler, Chem. Zeit., 1903, 27, 749; Rowell, J. Soc. Chem. 
/iMf., 1906.26, 1181. 

* See Darling, Chem. Zentr., 1919, ii., 890; 1920, ii., 760 tor a bibliography 
of the Bubject. 

* Clarke, Chem. News, 1870, 21, 124; Lesaer, Zeit. anal. Chem., 1888, 27, 
218; Warren, Chem. Nem, 1890, 62, 210; Clark, Joum. Chem. Soc., 1892, 
61. 424; Hen*, Zeit. onory. Chem., 1903, 87, 1. 

^ See Fischer, Zeit. anorg. Chem., 1904, 42, 363, where the literature of the 
subject is Quoted. Compare Cohen and Morgan, Analyst, 1909, 34, 3e 




1030 


THE VANADIUM GROUP 


diluted solution treated with chlorine until all the free alkali has 
combined. The excess of chlorine is then got rid of by repeated 
evaporation with hydrochloric acid, the solution diluted, and this 
treated with a freslily prepared solution of sulphuretted hydrogen 
until all the antimony is precipitated. A rapid current of air is 
then passed through the liquid in order to expel the excess of 
sulphuretted hydrogen, and the precipitate gashed first with 
water, then with alcohol, and at last repeatedly with carbon 
disulphide, in order to remove free sulphur. After drying at 
110'", pure pentoilphide of antimony remains, and this is after- 
wards weighed. The arsenic in the filtrate may be estimated 
by continual treatment with sulphuretted hydrogen when the 
pentasulphide is precipitated and treated as above described. 

A still simpler method of effecting this separation consists in 
adding ferrous sulphate or chloride to a solution of the chlorides 
of tlie two metals in hydrochloric acid, saturating with hydro- 
chloric acid gas, and distilling. The whole of the arsenic passes 
over and may be collected in dilute hydrochloric acid, whilst the 
antimony remains behind and may be precipitated in the usual 
way after the ferric salt has been reduced to the ferrous state.^ 

Atomic Weight . — The methods ^hich have at various times 
been employed for the determination of the atomic weight 
of antimony have led to somewhat divergent results. The 
number 120 obtained by Berzelius was long accepted as correct, 
until Schneider’s experiments on the reduction of the ^lulphide 
proved that 120-55 was nearer the truth. Dexter 5 then found 
the number 122-5 by treatment of the metal and trioxide with 
nitric acid, the resulting oxide being converted into the tetr- 
oxide by ignition. This was confirmed by Kessler,* who adopted 
a similar plan, and by Dumas,® who analysed the trichloride and 
obtained the number 121-8. On the other hand, a very carefully 
conducted scries of analyses of the bromide led Cooke ® to the 
number 119-80, while analysis of the iodide gave 119-8 and 
synthesis of the sulphide 120-55. The electrolysis of the chloride 
led in the hands of Pfeiffer^ and of Popper® to the number 
121-2, but it has been shown that the method applied is not 

' Fischer, Bn., 1880, 18 , 1778. See also Piloty and Stock, Ber., 1897, 
80 * 1649; Beck and Fisher, Chem. News, 1899, 80 , 259, where a critical 
discussion of the various methods is to lo found. 

* Pogg. Ann., 1856, 98 , 293. • Ibid., 1857, 100 . 563. 

* Ibid., 1861, 118 , 145. » Ann. Chim. Phys„ 1859, [ 3 ], 56 , 129. 

« Amn. J. Sci., 1878, 15 . 41, 107; 1880, 19 , 382. 

» Anntkn, 1881, 909, 173. • Ibid., 1886, 888. 153. 



BISMUTH 


1031 


accurate.^ A series of determinations made by Friend and 
Smith,* by the indirect method of heating j)otassiuni antimonyl 
tartrate in hydrogen chloride and weighing the potassium 
chloride produced, gave the number 120-34. ^ 

The value at present (1922) adopted is 120-2, which is based 
largely upon the work of Cooke. Nevertheless, it is quite 
possible that th(% older determinations, giving a value pound 
about 122, are more nearly correct. A number of cliemists have 
suggested that the higher value is preferable, basing their views 
upon the results of careful analytical investigations;* and, in an 
elaborate investigation into the preparation and analysis of j)ure 
antimony tribroinide, AVillard and Me Alpine hafe^ recently 
obtained the value 121-77. 


BISMUTH. Bi-2o8-o. At. No. 83. 

457 The word marmsite^ by which, up to recent times, the 
metal bismuth was (fften designated, is found in the authors of 
the thirteenth century. Hence it has been supposed tluit this 
metal was known at that time. This is, however, not the case, 
for tlie name rnarcasitc had in those days, an<l (‘ven at a much 
later period, a very indefinite meaning, Ixdng givi-n to any ore 
which had a metallic appearance, and especially to those ores 
which ar^ now classed as pyrites. 

.Bisrnutli was classed by Paracelsus amongst the semi-metals. 
On the other hand, Agricola mentions hmmutum or jjlumbum 
cineremn as a true metal wliich is usually added to tin in order 
to make it work better. Notwithstanding this clear statement, 
it was subsequently confounded by labaviiis with antimony, 
and by Lemery with zinc. Metallic bismuth was moreover 
described by ‘‘ Basil Valentine ” in his Last Testament : 
“ Antimonium must be placed between tin and lead, as bismuth 
or magnesia is placed under and between tin and iron,” and 
he also states that “ bismuth or marcasite is a bastard jom.” 
Pott, in 1739, was the first to make us acquainted with the special 
properties of bismuth, and its reactions were exactly studied by 
Bergman. 

' Cohen and Strengere, Proc. K. Akad. Wetensch. Amsterdam, 1903, 6, 543. 

* J. Amr. Chem. Soc., 1901, 28, 502. 

* Youtz, Zeit. anorg. Chem., 1903, 37, 337; Beckett, Inaugural Diasertation 

(Zurich, 1909}; von Bacho, MonaUh., 1916, 37, 106, ^ 

* J. Amer. Chem. Soc., 1921, 43, 797. 




1032 


THE VANADIUM GROUP 


Bismuth is a comparatively rare metal. It is found chiefly 
in the native condition, but also as the oxide or bismuth ochre, 
BigOg; less frequently it occurs as bismuthite, BigSg, whilst it 
is found still mort sparingly in the following minerals : telluric 
bismuth or tetradymite, Bi2{Te,S)3; emplectite, Cu2®^2^4‘» 
muthite, 3(Bi0)2C03,2Bi(()H)3,3H20 ; aikinite, Bi2S3,2PbS,Cu2S ; 
bisrmithosmaltite, Co(As,Bi)2; pucherite, Bi^04; eulytite or 
bismuth silicate, Bi4(Si04)3, etc., and occurs in traces in the 
pyrites of Agordo. Native bismuth is sometimes found nearly 
pure, but is usually alloyed with other metals or mixed with a 
variety of ores. It is found in veins traversing gneiss or clayey 
slate in Bolivia, Saxony, Australia, etc., usually associated with 
ores of silver and cobalt. 

468 The Metallurgy of Bismuth —VoTmerly bismuth was 
obtained by heating the ore in sloping iron tubes, when merely that 
portion of the metal present in the elementary state was obtained, 
and this in a very incomplete manner. The residue was em- 
ployed in the manufacture of smalt, anjl the bismuth again 
extracted from the cobalt speiss. 

This liquation process has now^ been superseded by smelting 
methods. Oxidised ores may be treated direct, but sulphides 
must be subjected to a preliminary roast. Reduction is carried 
out in crucible furnaces or in small reverberatory furnaces, the 
charge being made up of ore, carbon, slag, sodium carbonate, 
limestone, and sometimes fluorspar. It is essential to^^have an 
easily fusible slag so as to avoid loss by volatilisation. The 
products of this operation are generally crude bismuth, matte or 
speiss, and slag. For ores carrying sulphide of antimony and 
arsenic scrap iron is also added to the charge. 

Bismuthiferous litharge and other metallurgical by-products 
are sometimes treated with hydrochloric acid, and the bismuth 
precipitated by means of iron, or the solution is largely diluted 
with water in order to precipitate the oxychloride, which is dried 
and reduced. 

Crude bismuth, which generally contains lead, antimony, and 
arsenic, besides traces of iron, cobalt, nickel, silver, and sulphur, 
is refined by melting it in small iron kettles under a cover of 
salt, potassium chloride, caustic soda, and sufficient oxychloride 
of bismuth to take up the lead. The mass is constantly stined, 
and in from one to three hours the whole of the lead is converted 
into chloride, and a corresponding amount of bismuth separated 
from \he oxychloride. Antimony is removed in the *8ame way 



BISMUTH 


1033 


with a flux of soda, potash, and sulphur, sodium thioantimonate 
being formed, whilst for arsenic the flux used is caustic soda and 
nitre.^ A simple liquation process is also often Tised, the metal 
being melted on a slightly inclined iron plate. • 

Bismuth which contains 1 or more per cent, of lead melts 
at a lower temperature than pure bismuth. Such an impure 
metal exhibits oit cooling the peculiarity that the solid crust 
of pure crystallised bismuth is seen to be broken through by 
drops of a liquid alloy, and this property has been employed 
to separate bismuth from lead (Matthey). Silver behaves in a 
similar manner. Commercial bismuth frequently contains small 
quantities of gold, which, along with silver, may beVmoved by 
melting with 2 per cent, of zinc and skimming off the surface 
layer, which is found to contain the precious metals.^ 

When bismuth is required for pharmaceutical purposes it must 
be freed from traces of arsenic. For this purpose it is melted 
with nitre or other oxidising agent, fused with metallic iron, or 
the molten metal i^ well stirred and exposed to the air, any 
antimony being simidtaneously oxidised.® 

In order to prepare chemjpally pure bismuth, the commer- 
cially pure metal is dissolved in nitric acid and evaporated with 
hydrochloric acid. The chloride is then dissolved in hydro- 
chloric acid and the solution mixed with alcohol, which preci- 
pitates the greater portion of the lead in the form of chloride. 
The filtAte is poured into water and the precipitated oxychloride 
washed, redi.ssolved in hydrochloric acid, and again precipi- 
tated with water, this process being frequently repeated. 
The oxychloride is then again dissolved in hydrochloric acid 
and precipitated with ammonia and ammonium carbonate, 
this operation being repeated three times, after which it is 
finally reconverted into oxychloride, and the latter reduced to 
metal by fusion with potassium cyanide. The metal thus 
obtained still contains lead, from which it can only be freed by 
electrolysis. For this purpose it is dissolved in nitric acid 
and the solution slowly electrolysed, any lead being deposited 
as peroxide on the positive pole. The bismuth is then finally 
fused with potassium cyanide.* Another method is as follows. 
The fairly pure nitrate is dissolved in hhlf its weight of 8 per cent, 
nitric acid, mixed with an equal weight of the concentrated acid, 

* Borchere, Mineral Industry, 1899, 8, 62. 

« M»ttjiey. Proc. Roy. 8oc., 1881, 43, 89. » Ibid., 1893, 6«,,46. 

« ClaMen,Ber., 1890,38,940. 



1034 


THE VANADIUM GROUP 


and cooled to O'* to —10°. The pure nitrate which crystallises 
out is washed with a little ice-cold nitric acid, heated to convert 
it into oxide, and the oxide reduced by fusion with potassium 
cyanide. If necej^jiary, further purification may be carried out 
by melting the metal under paraffin, allowing it to crystallise 
in part, and removing the first and purest crystals by means of 
a glass spoon.^ • 

459 Properlm. -Umimth is a hard, brittle metal, having a 
bright, metallic lustre and a greyish-white colour, with a dis- 
tinctly reddish tinge. Its specific gravity at 15° is 9‘747 ; it melts 
at 271° and expands in the act of solidification, the specific 
gravity of flic solid at the temperature of the melting point 
being 9-673 and that of the liquid 10-004.2 Its boiling point 
lies in the neighbourhood of 1420° (Greenwood), and it can be 
distilled in a current of liydrogen. The vapour density between 
1600° and 1700° is about 11, a number which is intermediate 
between the values corres[)onding to the formulae Bi and Big.® 
When a large ([uantity is melted, allowed to^cool slowly until the 
surface begins to solidify, the crust then broken, and the liquid 
metal poured out, fine large crystals are obtained. Ihese are 
obtuse rhombohedra which have the appearance of cubes as their 
angles approach closely to 90°. Acicular needles consisting of 
elongated, hexagonal prisms have also been observed.* The 
crystals oxidise in the air, and frequently become covered with 
an irid(?scent film of oxide. The .same colours may be obtained 
when the metal is melted in the air, but if the heat be continued, 
the metal gradually becomes altogether converted into oxide; 
at a red heat steam is slowly decomposed by bismuth. This 
metal combines also directly with the elements of the chlorine 
group and with sulphur; hydrochloric and sulphuric acids do 
not act u]Km it in the cold, but the latter acid dissolves it on 
heating with evolution of sulphur dioxide. Hydrochloric acid 
dissolves it in the presence of dissolved oxygen. The best solvents 
for bismuth are nitric acid and aqua regia, both of which dissolve 
the metal readily in tlic cold. 

According to Cohen, bismuth is a mixture of two or more 
allotropes,® 

* Mylius and Gnjschuff, Zeit. anorg. Chem,^ 1916, 96. 237. 

* Vicontini, Jonm. Chm. Soc., 1891, 60. 618. 

» Meyer, Ber., 1889, 89, 720. 

* Heberdcy, Sitzungaber, K. Akad. 1805, 104, i. 264. 

* Cohgn, Proc. K. Akad. U'efoti^cA. Amsterdam, 1015, 17, 1236; Wafinschmidt, 
Jakrb. Min., 1917, i. Ref. 2. 



BISMUTH 


1035 


Colloidal bismuth is obtained by reducing the nitrate by stannous 
chloride in the presence of ammonia and ammonium citrate,^ or 
the oxychloride by hypophosphorous acid/-* 

Bismuth serves for the preparation of ma^y pliarmaceutical 
products and cosmetics, and is also employed for tlie manu- 
facture of alloys of low melting point, and in tlie construction 
of thermopiles. • 

460 Alloys of Bismuth . — Bismuth forms a number of alloys of 
low melting point, which are known by the general name of 
fusible metal. The temperature of the melting point de})end8 
on the proportion of the constituents, as is shown in the following 
table : * 



Newton'a 

]\retal. 

Rose's 

Metal. 

Lichteii- 

iKTg's 

Metal. 

Wood’s 

Metal. 

LIpowitz. 

• 

Bismuth . . 

8 

2 

5 

4 

15 

Lead . . . 

8 

1 

3 

2 

• 8 

Tin . . . 

3 

1 

0 

1 

4 

Cadmium 

0 

% 

0 

1 

3 

Melting point 

9-1-5° 

93-75" 

91-0" 

71° 

GO" 


The melting point can be still further lowered by the addition 
of mercury. Fusible metal is now largely used for stereotyping, 
obtaining copies of wood-cuts, etc., and is not only valuable on 
account of its low melting point, but also because it expands 
considerably in the act of solidification, and thus gives a perfect 
cast; it is important to make the cast when the metal is so 
far cooled that it is beginning to be viscid. If any of these 
liquid alloys be i)oured into a glass vessel this Hies to pieces 
when the metal cools. Bismuth is also used in the manufacture 
of solder, and the soldering can be effected under hot water 
when a few drops of hydrochloric acid have been added. Alloys 
of lead, tin, and bismuth mixed together in such proportion that 
the mixture fuses at some particular temperature above 100^ 
serve as safety plugs for boilers and automatic sprinklers. Bis- 
muth alloys, melting at a given temperature, are used for 

* Lottermoaer, J. pr. Ckem., 1899, [2], 60 , 489. ^ 

• (Hitbier and Hofmeier, Zeit. aimg. Chem., 1905, 44 , 225. 



1036 


THE VANADIUM GROUP 


tempering steel; the pencils used for writing on the so-called 
metallic paper likewise consist of an alloy of bismuth. 

Bismuth in very small quantities renders gold and silver 
brittle, and greajly diminishes the conductivity of copper for 
electricity. 

Molten bismuth, to which 0-05 per cent, of tellurium has been 
added, solidifies to a minutely crystalline raai^, entirely different 
in appearance, fracture, etc., from the pure metal. 

When bismuth is treated with a solution of sodium in liquid 
ammonia a compound of the formula BiNaj is formed as a 
bluish-black mass, which takes fire in the air, and decomposes 
water with*evolution of hydrogen.^ 


COMPOUNDS OF BISMUTH. 

^ BisxMuth and Hydrogen. 

461 It has long been suspected that bismuth forms a volatile 
hydrid^, and its existence has now been demonstrated by Paneth 
and Winternitz.* A bismuth-magnesium alloy is prepared by 
heating equal weights of powdered bismuth and silicon-free 
magnesium in an iron crucible in a rapid stream of dry hydrogen. 
When this is dissolved in 4iV-hydrochloric or sulphuric acid the 
evolved hydrogen contains traces of bismuth hydride, the presence 
of which may be established by a mirror test or a luminescence 
test. The former is made in the familiar Marsh’s appdiatus (see 
Vol. I. p. 717) ; the mirror obtained closely resembles an antimony 
mirror in appearance. The luminescence test is more delicate. 
The gas issuing from the Marsh’s apparatus is ignited and a piece 
of pure calcium carbonate held in the flame on a platinum loop. 
The carbonate is allowed to cool, and then placed at the edge of 
the hydrogen flame, when a cornflower-blue luminescence is 
observed, due to bismuth, and visible in bright daylight. 

Bismuth hydride is absorbed by water and dilute sulphuric 
acid to some extent ; a better absorbent is silver nitrate solution. 
It is also absorbed by anhydrous calcium chloride and soda-lime, 
and to a considerable extent by sodium carbonate and potassium 
hydroxide solutions. It is completely decomposed by concen- 
trated sulphuric acid. 

* Jo<mni«, Ccmplt r^., 1892, 114, 585. 

* Paneth, Ber., 1918, SI, 1704; Paneth and Wintemitz, Ber., 1918, 61, 
1728; Paneth, CA«m. Zef/., 1920, 44, 341; Ztit. Ekktrochem.^ 1920, 26, 452; 
Paneth, Mattbiee and Sohmidt-Uebbel, Bar., 1922, 6, [B], 775. 



BISMUTH AND OXYGEN 


1037 


Bismuth and Oxygen. 

Only two well-defined oxides of bismuth are known : 

Bismuth suboxide or dioxide, BiO mr Bi^Og. 

Bismuth trioxide, BigOg. 

The suboxide l^s only very feeble basic properties, whereas 
the trioxide is a well-marked, basic oxide and corresponds to the 
stable salts of bismuth of the general formula BiR^g. Higher 
oxides are formed by the oxidation of the trioxide, to which the 
formulae Bi 204 and BigOj have been ascribed. 

Bismuth Suboxid^f BiO. — The question as to tlie existence of 
an oxide of this comjwsition has given rise to much discussion,^ 
but the experimental evidence renders it probable that the 
suboxide is a definite chemical substance. 

The suboxide was first described by Berzelius. It is best 
obtained by gently heating basic bismuth oxalate, (BiO)g()a(J|, 
in absence of air (Tanatar) : 

(Bi0)2C204=2Bi0-f 2CO2, 

or by carefully adding an alkaBne solution of stannous hydroxide 
(1 mol.) to bismuth hydroxide (1 mol.) suspended in dilute 
potash, washing the suboxide first with dilute potash in absence 
of air until all traces of stannic oxide are removed, then washing 
with watpr, and finally drying at 120'^ in a current of carbon 
dioxide (Schneider). It is a black powder which is stable in 
the air and has the specific gravity 7-2, this being considerably 
less than that of a mixture of bismuth and its oxide having the 
same percentage composition as the suboxide (8-9). When 
heated in the air it passes into the trioxide with incandescence, 
and in absence of air is converted into a mixture of bismuth 
and bismuth oxide. 

The suboxide Ls converted by hydrochloric acid into bismuth 
chloride, which dissolves, and insoluble metallic bismuth. The 
heat evolved in this reaction is considerably less than that 
produced when a corresponding amount of the trioxide is dis- 
solved, and this affords a further proof of the individuality of the 

* Vanino and Treubert, Ber., 1808, 31, 1113,^287; 1809, 82, 1072; where 
the older literature is quoted. See also Schneider, J. pr. Chm., 1808, [2j, 68, 
662; 1899, [2J, 60, 624; Tanatar, Zeii, anorg. Chem,, 1901, 27, 437; Hera and 
Guttmann, Zeit. anorg. Chem.f 1907, 68, 63; Vanino and Zumbusch, Arch. 
Pharm.t 1910,248,666; Hen, Zeit. anal. Chem., 1916, 64 , 103, 413; Treubert 
and Vanino, 1914, 68, 664 ; 1916, 64 , 266. * 



THE VANADIUM GROUP 


suboxide (Tanatar). It reduces Fehling's solution and potassium 
permanganate, and is converted by excess of alkaline stannous 
chloride into metallic bismuth. 

Bismuth Triox^e^ Bi 203 , is found as bismuth ochre in 
Cornwall, Virginia, Siberia, and Erzgebirge, as a yellow or 
greenish-grey, amorphous mass or as a powder, and it usually 
contains ferric oxide and other impurities. Ii^order to prepare it 
artificially, the hydroxide, carbonate, or nitrate is heated Thus 
obtained, it is a yellow powder having a specific gravity of 8*2. 
It fuses at 820'\ forming a brown liquid, and when this is allowed 
to cool the solid which is first formed passes at 704° with evolution 
of heat int(f a second modification, which forms a yellow, crystal- 
line mass. When fused in porcelain a third form is produced 
which crystallises in long, yellow needles of specific gravity 8*55.^ 
When a boiling solution of a bismuth salt is precipitated with 
jK)tash the trioxide is obtained in microscopic needles, and if 
tfiis be melted with caustic potash the product is found to crystal- 
lise in rhombic prisms. When the oxide is prepared by adding 
potassitim cyanide to bismuth nitrate solution, boiling and heating 
the resulting grey powder in the air, it crystallises in tetrahedra 
belonging to the regular system. It is therefore isodimorphous 
with antimony oxide.^ The oxide j)repared by roasting the metal 
api)ears to have been employed as a yellow paint in Agricola’s 
time. 

Bismuth trioxide is a stronger base tlian the corresponding 
oxide of antimony, and forms a well-defined series of salts, which 
are characterised by the ease with which they are converted by 
water into insoluble basic salts. 

Bismuth Trihydroxide, Bi(()ll) 3 , is obtained as a white, amor- 
phous pow'der by precipitating a bismuth salt with cold caustic 
soda or ammonia. It is soluble in caustic potash in the presence 
of glycerol,® and when precipitated from this solution by acids 
is free from basic salts, which are always present in the Hydroxide 
prepared by precipitation with alkalis.* When dried at 100°, it 
has the composition Bi 203 ,H 20 or BiO OH. 

Higher Oxides of Bismuth , — AVhen a current of chlorine is 
passed into a boiling solution of caustic potash or soda containing 
bismuth hydroxide in suspension, a red powder separates out 
which contains alkali and yields chlorine on boiling with hydro- 

* (.itirtler, Zeit. anorg. Chm., 1903, 37, 222. 

* Muir and Hutchinson, Joum, CMem. Soe., 1889, 56, 143. 

„ * [i)we, Zeit. anal. Chem., 1883, 22, 408. 

« Thibault, J. Phann., 1900, [6], 12, 669. 



BISHtrrH AN£» THE HALOGENS 


1089 


chloric acid. Under varying conditions, the nature of the products 
obtained in this reaction also varies and substances described as 
bismuth tetroxide, lii204, a brown powder, and the dihydrate of 
this oxide, Bi204,2H20, an orange-yellow |)ow(l|ir, have also been 
prepared by meaas of it. Similar highly oxidised products are 
formed by the electrolytic oxidation of the trioxide, and by the 
action of persulplates, of hydrogen peroxide, and of potassium 
ferricyanide on the trioxide in the presence of alkali.^ According 
to (rutbier and Biinz,® none of these reactions leads in any case 
to a definite homogeneoiLs product. 

Worsley and Robertson,® however, claim that definite oxides 
may be obtained. Using 5 -10 jier cent, sodium hydroxide and 
oxidising with chlorine, the only product is bismuth tetroxule, 
Bi204, which is freed from trioxide and alkali by rcjieated grinding 
with glacial acetic acid. Two forms of tluj anliydrous oxide 
exist, brown and purplish-black in colour, and also two similarly 
coloured forms of the monoliydrate, Bi204,ll20. All are solubte 
in nitric acid, sp. gr. 1^*2, with liberation of oxygen, and decom]K)se 
at IGO^. When concentrated alkali solution is used, a* yellow 
dihydrate, Bi204, 21120, is formed together with a red petitoxkle, 
Bi205,lf20. When ammonium persuljihate or potassium ferri- 
cyanide are used as oxidising agents, the product is the tetroxide 
when the reaction proceeds in boiling dilute alkali, but with 
concentrated alkali a small amount of a hexoxide, 11120^, is also 
formed, which may be separated from the tetroxide owing to its 
insolubility in nitric acid, sp. gr. 1 - 2 . The hexoxide is an anhy- 
drous, pale brown powder which slowly loses oxygen and darkens 
in colour at the ordinary temperature. 

Bismuth and the HALotiENs. 

462 Bismuth sub-iodide, Bilg, is a volatile substance, crystal- 
lising in red orthorhombic needles.^ The sub-oxylodule, 
2Bil2,3BiO, is non-volatile and begins to decompose at 350 \ 

Bismuth Trijluoride, BiFg, is obtained as a white powder 

^»Seo Beichler. Zeit. anorg. Chem,, 1890, 80t 81, where a critical diucutwictn 
of the earlier literature will be found. Muir, Joum. Chem. Soc.^ 1887, 51 , 
77; Hollard, Compt. rend., 1003, 136 , 229; Hauser and Vanino, Zeit. anury. 
Chem., 1904, 39 , 381; Aloy and Fr6bault, BuU. Hoc. cltim., 1906, [3], 36 , 396; 
Moacr, Zeit. anorg. Chem., 1906, 50 , 33. 

* Zeit. anorg, Chem., 1906, 48 , 102, 294 ; 49 , 432; 50 , 210; 1007, 52 , 124; 
Chem. Centr., 1909, i., 732. 

» Trans. Chem. Hoc., 1920, 117 , 63. 

* Denhaii^ Amer. Chem. Hoc., 1921, 48 , 2367. 

voi- n. (n.) 


p 




1040 


THE VANADIUM GROUP 


by dissolving the oxide in hydrofluoric acid and evaporating the 
solution. An oxyjlnmde^ BiOF, is formed when the acid is 
completely neutralised by the oxide. The fluoride forms a 
double salt with ^mmonium fluoride, BiF 3 ,NH 4 F.^ 

Bismuth Dichloride, BiClj, is said to be formed when a slow 
current of chlorine is passed over the fused metal, or when the 
metal is heated with calomel to 250° or fifsed with the tri- 
chloride. Thermal investigation of the system Bi-BiClg, how- 
ever, does not indicate tlie formation of any dichloridc, but shows 
that within certain limits the metal and its trichloride form mixed 
crystals.® 

Bmmtlh ^Trichloride, BiClg, w'as first prepared by Boyle * by 
heating bismuth with corrosive sublimate. It is also formed 
when the metal is burnt in a stream of chlorine, or when a con- 
centrated solution of the oxide in hydrochloric acid is distilled, 
the receiver being changed after all the w’ater has come over, 
ifismuth trichloride is a granular, white inass, which melts at 
from 225° to 230°, boils at 435° to 441”,^ and yields a vapour 
having the normal specific gravity of 11‘35 (Jaquelain). Heated 
in a current of hydrogen, it is reduced to dichloride.* It forms 
a 'syrupy liquid when dissolved m a small quantity of w’ater, 
though a larger quantity of water decomposes it, witli formation 
of bismuth oxychloride, BiOCl, as a pure white pow’der, insoluble 
in water, but readily soluble in acids. It separates from a 
hot acid solution in tetragonal crystals ^ of the sp. gra 7-717 at 
15°, and is decomposed by excess of caustic potash.® Heated in 
air, bismuth oxycldoride loses chlorine and takes up oxygen ; in 
absence of air it becomes yellow-coloured, fusing without 
decomposition. 

When a solution of the oxide in an excess of hydrochloric acid 
is evaporated, fine, needle-shaped crystals are deposited, having 
the composition BiC33,21lCI, whilst at 0° a saturated solution 
of the two deposits crystals of the compound 2 BiCl 3 ,HCl, 3 H 20 
which are stable at the ordinary temperature.’ Bismuth tri- 

* HclmhuU, Zeit. unorg. Chem., 1802, 3, 115. See also Muir, Hoffnicister and 
liobbs, Joum, Chem. Soc., 1881, 39, 

* Marino and Becarelli, AHi Jt, Accad. Lincet, 1915, [5], 24, ii, 625; 1910, 
5J, 26, i, 105. 171, 221, 320. 

* ExptrimnU and Considerations Touchi.jg Colours. 

* Muir, Journ. Chspn. Soc.f 1876, i., 144. 

* da Sohulton, Bull. Soc. chim., 1900, [3], 23, 156. 

* Herz and Muhs, Zeit. anerg, Chem., 1904, 89, 115. 

’ Krigel, Cmpt. rend., 1888, 106, 1797. 



BISMUTH AND THE HALOGENS 


1041 


chloride forms double salts with the chlorides of the alkali metals,^ 
the chlorides of many bivalent metals, ^ and with many organic 
bases. Amnioma yields three compounds — a very 
volatile, colourless substance; BiCl 3 , 2 NH 3 , a dirty-grey, non- 
volatile mass; and 2 BiCl 3 ,NH 3 , a red, crystalline body. They 
combine with hydrochloric acid to form double salts, which are 
also obtained when ammonium chloride is added to the solytion 
of bismuth in the right proportion and the mixture evaporated.® 
Bismuth trichloride combiners also with nitric oxide * to form 
the yellow compound 2 BiCl 3 ,N(), and with nitrosyl chloride to 
form an orange-coloured powder, Bi('l 3 ,N( K -l. 

Bismuth Tribromide, BiBrg.- -When bromine vapc^r is passed 
over {X)wdered bismuth aii energetic reaction takes place and a 
red liquid volatilises. This cools to a golden-yellow, glistening, 
deliquescent, crystalline mass, which melts at 210" and boils at 
403'. Bismuth tribroinidc crystallises from ether in prisms, 
and water decomposes it into the white insohdde oxyhromi&e, 
BiOBr. It forms crj'stalline double salts with the bromides of 
tlic alkali metals and also with the cyanides of various metals : ® 
with ammonia it yields compounds similar to those* of the cldoride. 

Bismuth Tri-iodide, Bifj, is (Tljtained by treating tlio ])owdered 
metal with iodine and heating the ])roduct; by precipitating 
a bismuth salt with ])otassium iodide solution, dissolving in 
hydriodic acid, and r(*[)recipit.ating with water; or, better, by 
adding Ijismuth oxide to a solution of iodine in stannous chloride 
saturated with hydrochloric acid.’ It subliine.s in greyish-black, 
metallic, glistening, six-sided tablets, which are not decomposed 
by cold water, though they are converted by hot water into an 
insoluble oxyiodide. If a solution of the iodide in hydriodic acid 
be evaporated, rhombic pyramids of lii 13,111,41120 are deposited. 
Bismuth iodide forms a large number of double salts.® 

Bismuth Oxyiodide, BiOl, is obtained by decomjwsition of the 

• See Brigham, Anur. Chem. J., 1892, 14, 104; Field, Journ. (.'hem. Soc., 
1893, 63» 540; Aloy and Fr^bault,, Hull. Soc. chim., UKMi, [3J, 35, 390. 

*\Vcinland, Albcr, and Schweiger, Arch. Phtmn., 1910, 354, 521. 

• Dehcrain, Compt. rend., 1802, 54, 924. 

• Thomas, Compt. rend., 1895, 121, 128. 

‘ SudboroMgh, Joum. Chem. Soc., 1891, 50, 602. 

• Voumazog, Compt. rend., 1921, 172, 535. 

’ BLrckcnbach, Ber., 1907, 40, 1404. 

• Nicklcg, Compt. rend., 1800, 50, 872; J. Phann., [3], 89, 116; Linau, 
Pogg. Ann., 1860, 111, 240; Wclla and Foote, Amcr. J. Sri., 1897, 3, 401; 

Zeii anorg. Chem., 1902, 31, 191 ; Canneri and Purina, Gazz., 1922, 62, 
i.. 241. - • 




1042 THE VANADITO GROUP 


tri’iodidc with boiling water, or by heating the same in the air,^ 
as a co[)per-red, crystalline mass, which can be sublimed when 
lioated in the absence of air, but is gradually converted in 
presence of air intj) a crystalline oxide. 


Hismutu and tjie Elements of the SiApiiur Grout. 

463 Bismuth Suhsulphide, BiS, was first described by Werther ^ 
and Lager j helm® as a grey, metallic, lustrous mass of needle- 
shaped crystals, obtained by fusing bismuth with sulphur and 
cooling quidkly, but this contained free bismuth and the sulphide, 
Bi^^Sy. The existence of the same compound has been deduced 
by P^labon,'* but (hmied by Aten,*'* from the study of the equi- 
librium curve for bismuth and sulphur and the behaviour of 
these two elements in the presence of hydrogen. 

^Bismuth Trisulphiile, BijjS.,, occurs as bismuthitc in rhombic 
crystals, and also massive with a foliated or fibrous structure; 
its specific gravity is 0* 1 . It is found at *Jb‘andy Gill, ('arrock 
Fells in Cumberland, at Redruth and Botallack and other localities 
in (jornwall, in the Erzgebirge, in Bolivia, and in other places. It 
is obtained artificially by fusing the metal with an excess of sulphur, 
or by precipitating a solution of bismuth chloride with sulphur- 
etted hydrogen or sodium ihiosulphaL;. Thus pre})ared, it forms 
a blackish-brown precipitate easily soluble in nitric acid and in 
boiling concentrated hydrochloric acid, but not in alkalis. Its 
solubility in pure water has been found by the conductivity 
method to*be O-.'ir) x 10*^ gnun-molecules (0-2 mgm.) per litre. 
When it is heated to 2(K)‘^ in a solution of an alkali it becomes 
crystalline, assuming the form of bismuthitc, and when heated 
in the electric furnace yields metallic bismuth.® 

The amorphou.s sulphide dissolves in potassium sulphide 
solution and very sparingly in sodium sul])hide solution,’ and 

‘CompHre Dubrisay, Compt. rend,^ 1909, 140, 451. 

* J, pr. Ch€m., 1842, 27, 05. 

* Schweigtjers Journ., 1810, 17, 416. 

* Ann. Chim. Vhya., 1902, [7], 25, 365; J. Chim. pftys., 1904, 2, 321 ; Compi. 
rend., 1903, 137, 648, 920. 

* Zeit, anorff. Chem., 1905, 47, 386. Oomparo Schneider, Pogg. Ann., 1866, 
97, 480; Herz and Guttmann, Zeit. ttno.y. Chem., 1907, 68, 63; 1908, 66, 
422. 

* Mourlot, Compt. rend., 1897, 12i 768. 

’ Bittc, Compt. rend., 1895, 120, 186. Soo also J. Atner. Chem. Soe., 1896, 
18, 683, 1091. 



BISMUTH AND THE SULPHUR- GROUP 


1043 


forms salts of the formulae BigSgjKjS and Bi2S3,Na2S when it is 
fused with sulphur and an alkali carbonate.^ 

Bismuth Oxysidjihides.-— The compound Bi4()3S occurs as kare- 
lilinite at the Savodinck Mine in the Altai ; it is a crystalline 
mass having a strongly metallic lustre. * 

Bismuth Chhrosulphide, Bi8Cl, is obtained by fusing together 
in the air 1 part of sulphur and 8 parts of ammonium bisjuuth 
chloride, or by heating the latter compound in a current of sul- 
phuretted hydrogen (Schneider), and also when the chloride is 
heated in dry sulphuretted hydrogen or the sulphide in dry 
chlorine. It is a reddish-brown solid, not decomposed by water. 
The corresponding sulphohromide is obtained similarly, whereas 
the sulphioduk can be ])repared only by h(*ating bismuth iodide 
w'ith the trisulphide. All three compounds are decomposed by 
sulphuretted hydrogen at a briglit red heat.- 

Bismuth Trisulphate, 1^2(804)3, is obtained as an anuu'phous, 
white nuiss by dissolving the metal or the suljdiide in eomu'ntrafhd 
sulphuric acid and evaporating. This salt is decomposed by 
water witli formatioh of tlie basics salt, Bigt >3,803, 21120# When 
this is heated it loses water, and on cooling a yellow’ mass, con- 
sisting of 1^203,803, is obtitlned. This salt is also obtained 
by heating the other sul|)hates. Another of these basic salts 
has the coiiiposition Bi203,2803.3H20, and is obtained in small 
needles by acting u])on the nitrate with sulphufio acid. 8everal 
other Ij^sic salts have also been descriljed.® Concentrated 
sulphuric acid yields the acid salt, 1^203/1803, several hydrates 
of which liave been obtained.* 

Bismuth Thiosulphate- (.’om])lex thiosulpliates arc obtained 
by the addition of the alkali thiosulphates to bismuth chloride 
solution. The potassium salt, KgBi (8203)3,11120, is s])aringly 
soluble in water, and the solution rapidly decomposes, bismuth 
sulphide being deposited. This solution does not react with 
iodine. The sodium, ammonium, and strontium salts are also 
known.® 

464 Bismuth Triselenide, BigScg, is obtained by fusing the 
elements together as a metallic, lustrous, brittle, crystalline 


* Schneider, Vogg, Ann., 1809, 138 , 400. 

• Muir and Eagles, Journ. Chem. Sac., 1896, 67 , 90. 

' • See Allan, Amer. Chem. J., 1902, 87, 284. 

* Adic, Proc. Chem. Soc., 1899, 16 , 226. ft 

• Carnot, Compt. rend., 1876, 88, 338; Hauser, Zeit. anorg. Chem., 1903, 36, 1. 

Vanino and Muaagnug, Arch. Pharm,, 1919, 257 , 264. • 




1044 


THE VANADIUM GROUP 


mass, having a specific gravity of 6*82, which is attacked only by 
nitric acid and aqua regia. 

Bismuth Tritelhiride, Bi 2 Te 3 , occurs as the mineral tetradymite, 
in which some of the tellurium is replaced by sulphur. It forms 
pale metallic steel-grey rhombohedra, or foliated or granular 
masses having a specific gravity of 7*2 to 7*9. Groth ^ considers 
this mineral to be an isomorphous mixture of ^be elements, as it 
is not isomorphous with bismuthite, Bi 2 ^ 3 ) aiid as bismuth and 
tellurium can be fused together in all proportions.^ Other 
bismuth tellurides of varying composition have been described, 
some of which occur as minerals. According to Monkemeyer® 
only one stable compound of these two elements exists, namely, 
Bi 2 Te.„ which melts at 57.‘V\ 


BlSMlJTir ANO THE ELEMENTS OF THE NiTROGEN GrOUP. 

•465 Bismuth Niirid(\ BiN, is formed as a brown precipitate 
when bismuth iodide dissolved in li<[uid ammonia is added to a 
solutiomof potassamide in tin*, same solvent.'^ 

Bismuth 7V/a//m/c, BifNOylg, 51120, is obtained in large, trans- 
parent, trichnic prisms by dissolving the metal in nitric acid 
and evaporating th(i solution, which corrodes paj)er, and must, 
therefore, be filtered through aslx’stos or pounded glass. The 
crystals, which are deli(|uesc(*nt, are decomposed on heating, 
losing their water, and then heaving a n^sidiie, first of basic 
salt, and lastly of the trioxid(‘. Hydrates with 2 and IJH 2 O 
also exist.^ 

Bismuth nitrate is isomorphous with the nitrates of yttrimn, 
lanthanum, and others of the rare earth metals,® and forms 
double salts which are isomorphous with the corresponding salts 
of the rare earths and have been utilised in the fractional crystal- 
lisation of mixtures of these.’ 

When hydrated bis?nuth nitrate is ground with mannitol and 
water added, a clear solution is formed which is not precipitated 

^ T'ahcU. Utherntchi d. Minemlien, p. 12 (Braunschweig, 1882, Vioweg). 

•See also Amadori, Atti H, Accad. Lincci, 1015, [5], 24, ii, 200; 1018, [5], 
27. i. 131. 

* Zrit. anorg, Chem., 1005, 46, 415. See also Gutbicr, ibid., 1002, 31, 331. 

• Franklin, J. Amer. Chem. Soc., 1005, 27, 820. 

» van Beinmelen and Rutten, Free. K. Akad. Wetensch. Amsterdam, 1000, 

8 . 100 . 

•Bwlman, Her., 1898, 81, 1237; Zeit anorg. Chem., 1001, 27, 254; Zeit. 
Kryst. Min., 1902, 36, 192. 

’ Urbdin, Compt, rend,, 1903, 187, 568; J. Chim. phijs., 1906, 4i 106. 



BISMUTH AND THE NITROGEN GROUP 


1015 


on dilution and serves as a means of preparing many insoluble 
bismuth salts by double decomposition.' 

Basic Bismuth Nitrate^ Bi(OH) 2 N() 3 .— Libavius was aware 
that the solution of bismuth in nitric acid is precipitated by 
water, and Leinery, who describes the preparation of tliis com- 
pound, states that water containing common salt slioukl be 
employed for tlii-j precipitation, j)ure water precipitating it, 
but much more slowly ; and he adds that the product obtained 
weighs more than the metal employed. The reason of this, he 
explains, is that a certain (piantity of sj)irit of nitre remains beliind 
even if the precipitate be well washed, lioyle states that the 
solution of bismuth in aqua-fortis is almost completely pre- 
cipitated by common water. In spite of this, many chemists, 
looking at the analogy between lead and bismuth, believed that 
salt water was necessar}" for the precipitation; indeed, the 
substance was for some time termed horn-bismuth. This (‘rror 
was definitely rectified by Pott, in 1739. ^ 

Basic nitrate of bismuth, formerly termed magisterij of biwwlh, 
is us(‘d as an important medicine, and many diflerent^ receipts 
are given for its preparation. According to the method formerly 
prescribed in the British PharmacopcBia (1874), bismuth subnitras 
is best obtained by dissolving 2 parts by weight of bismuth in a 
mixture of 4 parts of nitric acid of sj)ecilic gravity 1*42 with 3 
parts of water. The clear liquid is poured <>11 from any insoluble 
matter gnd evaporated to the })oint at which it occupitjs two 
volumes, and this is then poured into 80 parts of distilled water. 
The clear liquid is then decanted and the precipitate well stirred 
up with 80 parts of water, collected on a filter, and dried at a 
temperature not higher than 55”. The (rennan and French 
pharmacopoeias recommended somewhat similar processes. In 
all these methods a considerable quantity of bismuth remains in 
solution, and this may be obtained, as the hydroxide, by pre- 
cipitating with ammonia. The bismuth is completely precipitated 
when 50,tX)0 parts of water are pre.sent to one of the nitrate.* 

Basic bismuth nitrate is a crystalline powder which reddens 
moistened litmus paper. Its composition varies somewhat 
according to the quantity of water used in the preparation, and 
a large number of basic salts have bepn described, the conditions 
of formation and existence of which have been investigated by 

^ Vaniiu) and Hauser, Zdt. nnorg. Chem., IflOl, 28> 210; J. pr. Chem., 1906, 
[2], 74, 142. 

* Antony and Gigli, Gazz., 1808, 28* i.> 245. • 


1046 


THE VANADHTM GROUP 


van Bemmelen and Rutten,^ by Allan, * and by de Schulten.® 
When washed for a long time it becomes more basic, until at last 
the hydroxide is left. 

Basic bismuth nitrate is largely used as a medicine in cases 
of chronic diarrhA^a and cholera. It is also employed in con- 
sidtjrable quantities as a cosmetic ; and this use is due to Lemery, 
wlio recommends it for softening the skin, ^hen utilised for 
this purpose it was first tenned hlanc iVEspa{fne^ which name, 
however, served to designate many other white pigments. 
Another name for this cosmetic is hlanc de fard. 

The basic nitrate, as well as the oxide, is also used for giving 
a colourless^ iridescent glaze to porcelain. This is obtained by 
rubbing up basic nitrate with resin and gently heating the 
mixture with lavender oil, and can be coloured by the addition 
of oxides, such as oxide of chromium, which gives to it a sulphur 
or lemon-yellow colour. W'ith addition of 5 per cent, of gold 
to* the oxide of bismuth, a splendid copper-red colour with a 
reflected golden lustre is obtained. When a smaller quantity 
is emph^yed, the glaze assumes a violet or pilre blue colour, whilst 
with another treatment a rose-red tint is obtained. These glazes 
are also used in glass-staining. ♦ 

466 Bismuth Orthophosjdiate, BiPOj, is precipitated when 
solutions of bismuth nitrate and ])hosphoric acid are brought 
togidher in presence of nitric, acid. When slowly precipitated by 
water from acid solution it forms microscopic crystals of sp. gr. 

at 15 ‘' (de Schiilten). In the same way, an insolut)lepyro- 
phosphulv, 1113(1*207)3, is ])rcpared with pyrophosphoric acid. 
When the oxide and phosphorus pentoxide are fused together, 
a clear ghiss is obtained, which on slow cooling becomes crystab 
line, and probably consists of the tetrametaphosj)hate. 

Bismuth Arsenate, Bi4(As207)3, is a. white precipitate insoluble 
in W’ater and nitric acid, but soluble in hydrochloric acid. The 
ortho-arsenate, BiA804, forms monoclinic prisms of sp. gr. 7*142 
at IS*^ (de Schulten). 

* Phosphorus and arsenic do not readily combine with bismuth. 
The first of these forms a compoimd with molten bismuth, 
and if a current of phosphine be passed through a solution of 
bismuth, a black phosp^pde is precipitated, w^hich, however, 
decomposes in absence of air into its elements. An alloy of 
bismuth and arsenic gives up the whole of the latter when heated. 

> Froc. K. Akad, Wftmsch. Amterdam, 1000, 3, 190. 

' * Atn^. CAm. J., 1901, 307. » Bulk Soc. chim., 1903, ^3], 28 , 720. 



DETECTION AND ESTIMATION OF BISMUTH 1047 


Arsine produces a black precipitate in bismuth solutions which 
behaves in a precisely similar way. 

Bismuth and the Elements of the Carbon Groui*. 

• 

467 Basic Bismuth Carbomiie, 2(Bi0)2C0a.H20, is obtained 
as a white powder wlien amnioniuni carbonate is poured into a 
solution of bismuth nitrate and the precipitate dried at a g^ntle 
heat. It is employed as a medicine. At 100° it loses water; 
stronger heating converts it into the trioxide. 

The mineral bismuthitc, 3(Bi0)2C03,2Bi({)lI)3,3H.20, is another 
basic carbonate and is found at 8chneeberg, at Chesteifi(‘ld, 
South Carolina, and at other places, togetlier with bismuth ores. 
It is a white or siskin-green, earthy mass, and sometimes occurs in 
acicular pseudomorphous crystals. 

Bismuth SilicntCy Bi4(Si()j)3, is found as eulytite in small, 
glistening yellow' or brown regular tetrahedra and occurs yi 
the Erzgebirge together with pho.sphates of iron and manganese. 

41 

Pete(tion and Estimation of Bjsmu'I'h. 

468 AVTien a bismuth compotind is heated in the upper reduc- 
ing flame of the Jbinsen bunuT on an asb(‘stos thread, a cold 
porcelain dish, held above it, receives a brown or black deposit 
of metallic bismuth, which is only slowly di.ssolved by cold 
dilute nitric acid. A brittle metallic bead is obtaimsl when the 
compound is heated on the carbonised match, and this dissolves 
in nitric acid, yielding a brown precipitate of bismuth with 
excess of stannous chloride and caustic soda. A characteristic 
reaction of the bismuth salts is tlie precipitation of the blackish- 
browm sulphide with sulphuretted hydrogen, insoluble in ammo- 
nium sulphide, and easily soluble in nitric acid. In addition to 
this, w'ater produces, in solutions which are not too strongly acid, 
a white precipitate of an insoluble basic salt, and ammonia 
throws down a w'hite precipitate of the hydroxide insoluble in 
excess. These reactions serve to separate bismuth from other 
metals, as well as to detect its presence. If other metals pre- 
cipitable by sulphuretted hydrogen are present, the washed 
precipitate is first digested with ammonium sulphide, in order to 
separate arsenic, antimony, and tin. The precipitate is then 
well washed, dissolved in nitric acid, and dilute sulphuric acid 
added to the filtrate to separate lead ; the precipitate is filtered 
oSf and sa excess of ammonia added which throws down the 



1048 


THE VANADIUM GROUP 


bismuth as the hydroxide, whilst any copper or cadmium present 
remains in solution. The precipitate is dissolved in a small 
quantity of hydrochloric acid, the liquid concentrated by evapora- 
tion, and added to a large quantity of water, when the insoluble 
oxychloride is precipitated. Care must be taken that all the 
antimony is removed by long digestion of the sulphides with 
amnionium sulphide, and the residue well ^shed with water, 
for otherwise an insoluble oxychloride of antimony may be 
precipitated and mistaken for bismuth. 

Bismuth can be estimated in several ways. If the solution 
contains the nitrate only, it may be precipitated with ammonium 
carbonate, Jioated for some time almost to boiling, filtered, the 
precii)itate dried and converted by ignition into the trioxide, 
which is weighed. If other acids arc present, the bismuth is 
precipitated by sulphuretted liydrogen, the washed preci])itate 
dissolved in nitric acid, and treated as above ; or it may be dried, 
excess of sulphur removed by carbon disulphide, and the residual 
sulphide dried at KHf and weighed. The phosjhate may also be 
precipitated in the presence of phosphoric aetd or dilute nitric acid, 
ignited, and weighed.^ If the solution of the nitrate contains 
only a small ((uantity of free acM it may be precipitated with 
potassium dichrornate, or with arsenic acid, and the precipitate 
dried and weighed. Bismuth may also be estimated as the metal 
by reduction with })otassium cyanide. The metallic mass is 
well washed with water and alcohol, and weighed aft^r drying. 
Bismuth may also be separated elect roly tically from an acid 
solution of the nit rate in thi^ presence of alcohol, glycerol, or acid 
potassium sulpludv.- 

The Atomic Weight of bismuth has been determined by several 
chemists, but without very concordant results. In 1851 
Schneider,® by converting the nietnl into the oxide, obtained the 
number 208-05, and this was confirmed in 1883 by Lowe,^ who 
used the same method and obtained the number 207-8, and by 
Marignac,® who, in 1883, found the atomic weight to be 208-16 
by converting the oxide into the sulphate. Dumas,® on the 
other hand, in 1859, by the analysis of the chloride, obtained the 

‘Stilhler and Scharfculierg, Btr., 1905, 88, 3802, 3943; Chm. Ztit,^ 1907, 
81. 015. 

*Compt. rend., 1900, 131, 179; ZeU. anorg. C’Acm., 1901, 27 , 1; J. Amer. 
Chem. Soc., 1903, 25 , 83; Richardson, Zeit. anorg. Chem., 1913, 84 , 277. 

•Pogg. Ann., 1851, 82 , 303, * Zeit. anal. Chem., 1883, 22 , 498. 

» ZeU. anal. Chem., 1884, 23 , 120. • Ann. Chim., Phys. 1859, «f3], 65 , 177. 



DETECTION AND ESTIMATION OP BISMUTH 1049 


number 210*7, which is certainly too high, and Marignac, by 
analysing the oxide, obtained the value 208-6. In 1890 Classen ^ 
made a series of nine concordant experiments in which carefully 
purified bismuth was converted into the oxide and found the 
number 208-9. Schneider, in 1894,^ rcpeatecf his experiments 
and again obtained the number 208-05. The lower determinations 
have been confirm<^ by the results obtained by Gutbier ^ anjl his 
co-\vorkers, who obtained the values 208-02 — 208-15 by converting 
the metal into oxide, reducing the oxide to metal, converting the 
metal into sulphate, and determining the ratio Billrg : Agllr. 
The value 208-0 is therefore (1922) adopted. Nevertheless, it is 
possible that the higher results are more nearly c(tfrect, since 
Honigschmid,^ who has analysed the pure chloride with all 
modern precautions, has obtained the value 209-02. 

^ Bir., 1800, 23, 038. «./. pr. Chm., 1S!M, 56, -101. 

^ Ztit. Klecktnchan., 1005, 11. 831; J. pr. Chan., 1008, ii., 77, 157; ii. 78, 
400, 421. iS'C* also the Dissertations (Krlungi-n) of Birckonhach, 1005; 

I [105; and .lanssati, DHjO. 

^ Zelt. KUi'trorhcni., 102ll^, 26, 403. ,Sco also Hoiiigschniid and Birckcnlach, 
Ikr., 1021, 64, [71], 1873; Classen and Ney, Btr., 1020, 63, [77]. 2207* 




GROUP VI. 


Suh-grou]) (a). 
Oxygen. 
Sulphur. 
Selenium, 
Tellurium. 


Sub~groii'p 9 [b). 

Chromium. 

Molybdenum. 

Tungsten. 

Uranium. 


469 In this group, as in Croups I, II, and III, the elements 
may ])e divided into two well-defined sub-groups, as shown in 
the above list, the sub-group (a) consisting of non-metallic 
elements (Vol. 1 ), whilst those in the sub-group (b) are metals. 
Oxygen falls in the even series, and therefore strictly belongs 
to sub-group (b), but as in the case of glucinurn in Croup II, it is 
much more nearly allied to the members o^ the odd series. 

Oxygeti is gaseous at the ordinary teni})erature, whilst sul- 
j)hur, seleniutn, and tellurium arc* solids, the melting and boiling 
points of which rise with increasing atomic weight. The 
elements of the chromium group melt only at high temperatures, 
and are reduced from their oxides with dilliculty. 

All the metals unite with the elements of the oxygen group 
to form oxides, sul[)hides, selenides, and tellurides; and the 
dilTenmt series <»f compounds thus formed present strong 
analogies among themselves, as has already been seen in the 
description of the com|K)unds of the metals of the previous 
groups. The analogy which exists between the “oxy-salts’' 
obtained by the union of a basic and an acidic oxide, and the 
“ thio-salts ” formed in a similar manner from the acidic and 
basic sulphides, has also been frequently alluded to. 

The most characteristic compoimds formed by these elements 
(with, of course, the exception of oxygen) are the trioxides and 
their numerous derivatives. All these beliave as acid-forming 
oxides, and give rise to well-defined series of compounds having 
the general formula in which M* represents hydrogen, 

or a univalent metal, and R' ^ an element of the group under 
consideration. These possess strongly marked analogies with 
each other, and the salts of the same metal are as a rule 
isomorphous. These oxides also form salts containing from 
1050 



CHROMIUM 


1051 


two to eight equivalents of the acidic oxide to one of basic 
oxide, such as the djsulphates, M'20,2S03, and dichromates, 
M*20,2Gr03, the trichromates, M*2^,3Cr03, tlie octotungstates, 
M'20,8W03, etc. ^ 

The constitution of the normal acids corresponding to the 
trioxides is represented by the formula 02ll'’’(()ll)2, and the 
hydroxyl groups ia these acids may be replaced by negative 
radicles such as the halogeiLs. The compounds thus formed 
from the elements of lower atomic weight, such as sulphur and 
chromium, are acidic chlorides, and are at once decomposed 
by water with formation of the acid ; but as the atomic weight 
of the element increases, the basicity of the radicle*R''()2 also 
increases, and the compounds become more stable, until, in the 
case of uranium, the compounds formed by negative radicles 
with the group U()2 constitute the moat stable scries of salts. 

The elements of this group also form other oxides cr)ntainiiip 
a less amount of oxygen than the trioxide ; in the case, of sul])hur, 
selenium, and telluriuni, these oxides (1U)2) are acidic or neutral, 
whilst with the metals of the chromium group (KG, R2G3, a/ld ROg) 
they are usually basic, and give rise to series of salts which often 
have strong reducing proi)erties, owing to their tendency to unite 
with oxygen, forming derivatives of the trioxide. 

The elements of sub-group (a) combine with hydrogen and 
the alkyl radicles forming volatile compounds; the elements of 
8ub-grou|i (6) do not form similar derivatives. 

Oxygen is bivalent in almost all of its compounds, but })ossibly 
sometimes acts as a tetrad. The remaining elements are, as 
stated above, . sexa valent in their most characteristic oxyg<n 
compounds, but the valency in their other comi)ounds, especially 
with the halogens, varies very coasiderably ; the elements 
sulphur, selenium, and tellurium are always bivalent towards 
hydrogen and the alkyl radicles, and usually either bi-, quadri- 
or sexa-valent in their other compounds, but no such regularity is 
observed in sub-group (6). 


CHROMIUM. Ct^sz'o. At. No. 24. 

470 In 1762 Lehmann, in a letter to Buffon, “ de nova minerse 
plumbi specie crystalline rubra,” described a new mineral from 
Siberia, now termed crocoisite. Vauquelin and Macquart investi- 
gated the composition of this mineral in 1789, and came to the 
conclusion* that it contained lead, iron, alumina, and a *large 



1052 


CHROMIUM 


quantity of oxygen. However, when the former chemist re- 
investigated the subject in 1797 , lie found that the lead present 
was combined with a peculiar acid, which he recognised as the 
oxide of a new iq^tal. To this the name of chromium was given, 
because its compounds are usually coloured (from 
colour). Chromium was discovered in crocoisite simultaneously 
and* independently by Klaproth. • 

Chromium is not a very common substance, and except for 
its occurrence in very small amounts in certain meteorites it is 
not found in the free state. It is found in several other minerals 
besides crocoisite or lead chromate, rbCr04, especially as chrome 
iron stone ^ir chromite, FeOjCrgOj, a mineral which is the chief 
ore of chromium and is the one usually employed for the manu- 
facture of the chromium compounds. Deposits in Rhodesia 
and New C^aledonia are of special economic importance, but the 
miiH'.ral occurs also in a number of localities in Europe, Asia 
iWinor, North America, and New Zealand. Chromium is widely 
distributed amongst certain* classes of rocks, e.g.^ basalts, in 
many t)f which it occurs in small amounts. Chromitite, 
(b'e,Al)203,2Cro03, occurs as minute, lustrous crystals in the 
sand of some of the streams ifescending from the Kopaonik 
Mountains, Serbia.^ (.'cylonite, which occurs in AVestern Australia, 
contains nearly 23 per cent, of chromic oxide.^^ Uvarovite or 
chrome garnet is 3Ca0,Cr203,3Si02. Chromium also forms the 
colouring matter of several minerals; thus the green icolour of 
C!ueral(i, as was shown by Vauquelin, is due to chromium; 
whilst serpentine, pennine, chromic mica or fuchsite, possibly 
sapphire,® and other minerals owe their colour to the same 
metal. Attempts to imitate the uni(iuc spectra of s\ich natural 
substances have met with ])artial success only.* 

Metallic chromium is obtained by the reduction of the oxide 
or chloride; thus Deville obtained it by strongly heating the 
oxide with sugar charcoal in a lime crucible,** and AVohler by 
heating chromic chloride with zinc under a layer of sodium 
chloride, and treating the alloy of zinc and chromium thus 
obtained with nitric acid;® it then forms a grey powder 
consisting of minute octahedra.’ Jager and KrUss obtained 

» Jovitschitsoh, 1009, 80 , 30; Buli Hoc. f rave. 1012 (1013), 

85 . 511. 

* Simiwon, Min. Mag., 1020, 19, 00. * Duboin, Bcr., 1898, 31, 1977. 

* Moir, 2'mw. Roy. Soc. S. Africa, 1918, 7 . 129. 

* rend., 1857, 4#, 673. * Annakn, 1859, 111, 230. 

’ PnnZ) Compt. rend., 1893, 116, 392. 



CHROMIUM 


im 


the pure metal by this process in tin-white rhombohcdra.^ 
Magnesium and sodiiun have also been employed in place of 
metallic zinc, the first of these being specially suitable for a 
laboratory preparation.^ If a mixture of chropiic chloride with 
finely divided iron is heated at 700-1200*^, ferric chloride is 
volatilised, and the metallic chromiuni remains in a finely 
divided form.® Another method of preparation is that of 
Moissan,^ w’hich consists in he*ating a mixture of chromiuni 
sesqiiioxide and carbon in tiie electric furnace ; the first product 
contains large quantities of carbon, which is removed by first 
heating strongly with lime when the greater part of the carbon 
is converted into calcium carbide, and then elimhiating the 
remainder by fusing the jiurified product in a crucible brasqued 
with the double oxide of calcium and chromium. 

Metallic chromium, is easily prepared from chromic o.xide 
by the “ thermite ” process (p. 737), which consists in mixing 
finely divided aluminium w'itli chromic oxide in slight excess of 
the equivalent proportion and igniting the mixture.® 

CV)3 + 2AL -2(V 1 ALA. 

When oiicc started, the reduction proceeds rapidly wdth great 
t volution of heat, and produces a fused mass of metallic 
chromium of considerable purity. This is shown by the following 
analysis :® Or 99*55 per cent., FeO-l l per cent., Si 0*31 per cent. 

Metallig chromium finds its chief technical application in the 
form of its alloys; large quantities are used in the form of ferro- 
chronie, manufactured by the reduction of chromite in the 
electric furnace or by means of aluminium ; these ferro-chromes 
generally contain between 60 and 70 per cent, of chromium. 
Chromium has also been prej)ared by the electrolysis of a warm 
solution of chromic chloride or of a cold solution acidified with 
hydrochloric acid, and is thus obtained as a bright silver-white 
deposit."^ It can also be deposited from the violet solutions of 
chrome alum, but not from the green solutions. 

Pure chromium is somewhat harder than glass, and has a 

* Her., 1889. 22, 20r>2. * (ilatzcl. Her., 1890, 28, 3127. 

» Weber, U.S. Pat. 1373038. 

< Compt, remi., 1893, 116, 349; 1894, 119, 18«; Ann. Chim. Phyx., 1896, 
[7], 8, 6.59. 

* J. Soc. Chetn. Jnd., 1898, 17, 543. • J. Iron filed M., HW2, 1. 186. 

* Cowper-Colea, Chem. News, 1900, 81, 16; Feroe, BuU. Sor.. chim., llKll, 
[3J, 25, 617; Neumann, Zeit. Etekirochem., 1901, 7, 666; Carveth ami othera, 
J. Physical Chem., 1906, 9, 231, 363; Zeit. Eklctrochem., 1906, 12^ 329; 
Askonaay and R^vai, Zeit. ElelUrochem., 1913, 19, 344. 




1054 


CHROMIUM 


melting point considerably higher than that of platinum, prob- 
ably between 1520'’ and 1550'", whilst if.it contains 1*5—3 per 
cent, of carbon it melts at a lower temperature, but can be cut 
only by the diamond. It may be distilled in the electric furnace.^ 
Tlie polished metal resembles iron, but is brighter and has a 
somewhat whiter colour : it has a density of 0*92 at 20°, a 
speoific heat of 0*1080 at 50°, and burns wheA heated in the oxy- 
hydrogen flame more brilliantly than iron. It is attacked by 
dilute hydrochloric acid, slowly in the cold and rapidly on heating, 
and also dissolves slowly in dilute sulphuric and nitric acids. 
With concentrated sulphuric acid it evolves sulphur dioxide, with 
formation^)! a dee{)-coloured solution, but It is unaffected by 
hot concentrated nitric acid; its rate of solutioii in acids is 
charac.terised by periodic variations. Chromium, like iron, has 
been found to exist in a passive ” state.® Colloidal chromium 
has also been prepared,"* 

471 Chromium /( /%•'»*• v far the most important are those 
with iron and nickel, since tney are very jesistant to corrosion, 
cither tvilh acids or by heating in the air. “ Nichrome ” wire of 
the average composition : 58 G 2 j)er cent. Ni ; 8 - 4 per cent. Cr ; 
23- -20 per cent. Fe; 0*5- 2 per cent. Mn, Zn, vSiOg, and 0*2—1 
per cent. C, is largely used as a resistance wire for electrically 
heated apparatus. “ Htainless steel ” is an iron-chromium alloy.® 

Cliromiuui Amalgams, -liy electrolysis of chromic chloride 
under suitable conditions, using a mercury cathodt, a solid 
chromiuni amalgam is obtained having the composition llgsCr. 
Under pressure this loses mercury, yielding an amalgam of the 
composition HgCr. When either of these amalgams is heated 
in a vacuum at 300°, the whole of the mercury is driven off, 
leaving the chromium as a powder which is pyroplioric at the 
ordinary temperature, and also combines with nitrogen on 
heating.® 

* Moissan, Compt. rmht 142, 425. 

* 8cluiboI, Zeit. atwrg. Chem.^ 1014, 87» 81. See also Jagor and Kriiss, 
JBer., 1889, 22. 2028. 

> Hittorl, Zeit. physikal Chem., 1898, 26, 729; 1899, 80, 481; Ostwald, 
Zeit. jfhyeikal. Vhein.y 1900, 36, 33, Morgan and Duff, J. .4m<r. Chem, 
80 c,, 1900, 22, 331; Brauer, Zeit. jAysikal. Chem., 1901, 88, 441; Ddring, 
J. pr. Chem., 1902, [2], 88 , OS; BemouUi, Physikal Zeit., 1904, 6 , 032; Aten, 
Proe. K. Akad. Weten^. Amsterdam, 1918, 21, 138, 

‘ Kulel, Ger. Pat. 197379; Svedberg, " Uerstellung kolloider Ldsungen 
anorganischer Staffe,"** 1909, p. 413. 

* See J&ncoke, Zeit. Ekktrochem., 1917, 28, 49; Murakami, Set. Btp. 
TdAoH Imp. Vniv., 1918, 7, 217. 

* F6r^, Compt. rend., 1895, 121, 822. 



CHROMIUM AND OXYGEN 


1055 


COMPOUNDS OF CHROMIUM. 

Chromium and Oxygen. 

472 Cliroiiiiuni conibinos with oxygen to form the well-defined 
oxides, ehroniium sesqiiioxide, CrjOj, and chroiniuni trioxide, 
CrOa. The former is a basic oxide, corresponding to the chief 
series of chromiunf salts, in which the metal is tervulent ; w^iilst 
the latter is an acidic oxide, which combines with water to form 
chromic acid, H2Cr04, the salts of which resemble the correspond- 
ing siiljdiates, selenates, and telliiratea, and are frequently 
isomor])hoiis with them. 

In addition to these, chromium monoxide, Crrt, and the 
corresponding hydroxide? have been prepared, and the latter 
yields with acids the chromous salts, in which the metal is 
bivalent. A number of other oxides have been described which 
may be regarded as combinations of one or other of the basjp 
oxides with the trioxide; the best defined of these is chromium 
dioxide, which has r«ally tlie constitution CrgOj’CrO^-- SCrOg, 
and will be described with the other chromates. 

Chromium Monoxide, CrO. -^An oxide of this composition is 
obtained as a black powder by the oxidation of chromium 
amalgam by exposure to air or by treatment with dilute nitric 
acid. It cannot, however, be obtained by direct reduction of 
tlie sesquioxide. When heated in air or when struck with a 
hammer fl inflames and burns to the sesipiioxide. It is insoluble 
in nitric acid, but dissolves in hydrochloric acid with liberation 
of hydrogen and formation of chromous and chromic chlorides.' 
Hy the action of hydrogen at 1000^ it is reduced to the rnetal. 

Chromous Hydroxide, Cr(OH)2, is formed by the action of 
aqueous potash, freed from air, on chromous chloride solution, as 
a brownish-yellow precipitate, which is readily oxidised with 
evolution of hydrogen, and on drying in absence of air has a 
dark brown colour.**' On ignition, it decomposes thus : 

2Cr(0H)2-Cr203 h IL^O j- 11*. 

Chromium Sesquioxide, or Chromic Oxide, CVjOg, occurs in the 
hydrated form as chrome ochre, and is obtained artificially as a 
dull green, amorphous jxiwder by igniting the hydroxide or the 

* F^r^e, Bull. Soc. chim., 1901, [3], 25. 619; Dieckmann and Ifanf, Zeit. 
anorg. Chem., 1914, 86. 301. See also Field, J. Ind. Eng. Ckem., 1916, 8. 238. 

• Moberg, J. pr. Chtm., 1848, 43 . 114; 44 . 322; T^ligot, Compt. nnd., 

1844, 19, 606, 734; Ann. Chim. phy9., 1844, [3], 12. 628. • 

VOL. n. (n.) Q 



1056 


CHROMIttM 


trioxide, or by heating a mixture of potassium dichromate with 
sulphur or ammonium chloride, and lixiviating the residue. The 
colour of the oxide prepared by gently igniting mercurous chrom- 
ate, Hg 2 Cr 04 , in a covered crucible is a very fine green. It 
melts at the temperature of the oxy-hydrogen blowpipe, solidify- 
ing to a crystalline, almost black mass. Chromic oxide is also 
obtained in the crystalline state by fusing the amorphous sub- 
stance with calcium carbonate and boron trioxide, or by ignition 
in a stream of oxygen. Wohler^ considered that crystalline 
chromic oxide is formed by passing the vapour of chromyl di- 
chloride, CrOgClj, through a red hot tube, but the product 
appears to- contain a large though varying proportion of a 
magnetic oxide, CrgO^.^ Another method consists in heating 
potassium dichromate either alone, or, better, mixed with 
common salt; the ignited mass is dissolved in water, when 
chromic oxide remains in bright, iridescent spangles, which have 
if density of 5-01.® 

The amorphous oxide glows when heated at 500—610°;^ 
after strong ignition it is almost insoluble m acids, and in order 
to bring it into solution it must either be heated for a long time 
with strong sulphuric acid, or fused with potassium liydrogen 
sulphate. The heats of formation of the various forms of 
chromic oxide exhibit striking differences.® Chromic oxide is^ 
used in the preparation of coloured glass, enamels, and j)orcelain, 
imparting to them a fine green tint. ' It forms one of the most 
permanent green pigments, known as chrome-green; it also 
finds limited application as a cataly.st. 

Chromic Hydroxides , — Pure chromic hydroxide, Cr 203 ,a:H 20 ,® 
may be obtained by precipitation of boiling solutions of chromic 
salts, free from alkali, with ammonia. Several modifications 
are known; the first, which reacts directly with three equiva- 
lents of acid forming the normal chromic salts, is obtained by 
the action of alkalis on cold solutions of violet chromic salts, 
and has probably the coastitution Cr(OH) 3 . It is best prepared 

1 Anmkn, 1840, 60 , 203. 

> and Ishiwara, Sci. Rep. Tdhoku Imp. Univ., 1914, 3, 271; Wedekind 
and Horst, Ber., 1915, 48, 105. 

* Schroder, Pogg. Ann., 18^9, 108 , 220; 107 , 113. See also Pitte, Compt. 
rend., 1902, 184 , 336. 

* J^thaug, Zeit. anorg. Chem., 1913, 84 , 105; Endell and Rieke, Zentr. 
Min. Oeoi, 1914, 246; Mixter, Amer. J. Sci., 1915, [4], 30, 295. 

* Mixter, loc. eit. 

* Weiser, J. Phgeical Chem., 1922, 98, 401, considers that an indehnite 
number of hydrous oxides exbts. 



GHROHIUU AND OXYGEN 


1087 


bj adding ammonia to a solution of a violet chromic salt free 
from alkali, and forms a pale blue precipitate, which, after 
drjring over sulphuric acid, lias the composition Cr(0H)3,2H20. 
When heated in a current of hydrogen at 200 ° it yields the hydr- 
oxide, CrO(OH) ; some water is retained eveif on long heating 
in hydrogen at 420 °,^ but at a red heat it commences to glow 
strongly and pass^ into chromic oxide. A hydroxide of this 
composition, or OrgOgjIIgO, has also been obtained as a brown 
substance by tlie electrolysis of neutral solutions of chromic 
chloride.^ Another hydroxide, which has probably the con- 
stitution Cr20(01I)4, is obtained by dissolving the first-named 
hydroxide in sodium hydroxide solution and repjecipitating 
with hydrochloric acid, and is also formed by the action of 
alkalis on the green chromic salts of oxy-acids (p. 1082 ) ; when 
treated with acids it reacts with only two equivalents of the 
latter, yielding the above green salts, wliich, however, on keeping 
in contact with acid gradually combine with it, forming tl\e 
normal violet salts. Another hydroxide which behaves similarly 
is formed, according to Recoura, by the action of alkalis/in the 
chromic oxychloride obtained by oxidation of chromous chloride 
solution. It differs from the foregoing in the amount of heat 
evolved by the action of two equivalents of acid.^ Whilst 
chromic hydroxide, when freshly jirccipitated in the cold, is 
soluble in acids, it becomes insoluble when kept or heated. 

Uuigiid^s Green is obtained by fusing together potassium 
dichromate and crystallised boric acid in equal molecular 
proportions and lixiviating the fused mass with water. The 
residue after grinding is a fine green powder, and is largely used 
as a pigment. It is usually described as having the composition 
Cr20{0H)4, but it always contains boric acid, and may possibly 
have the composition 3Cr203,B2()3,4H20. 

Colloidal Chromic Hydroxide. — Freshly precipitated and 
washed chromic hydroxide dissolves in aqueous chromic chloride, 
and on dialysing this solution Graham obtained a liquid con- 
taining 33 molecules of CrgOg to one of HCl. If the dialysis is 
carried out with hot liquids, much pwer chromic hydroxide 
sols are obtained in a few hours instead of in as many weeks at 
the ordinary temperature,^ The dark, green solution does not 
undergo change on boiling or dilution, but at once coagulates 

1 Mixtor, loe, cit. * Bull Soc. chim., 1901, [3], 26, 020. 

• Ann. Chim. Phys., 1887, [6], 10 , 60. 

« Noidlo and Barab, J. Amer. Chem. Soc., 1916, 88. 1901; 1917, 80 , 71. 
See al«o WeuKr, loc. cit. • 




iUO» 


UHKOMIUM 


oii addition of the smallest quantity of a salt,^ or slowly on merely 
keeping at the ordinary temperature. The precipitated colloid 
has no constant composition between l5° and 280°.^ Violet 
and green jellies of chromic oxide can be produced by addition 
of caustic alkalih to stationary solutions of chromic salts con- 
taining a sufficient amount of sodium acetate.® 

(.'^rom//c.9.-—AlthougIi the solubility of clyomic hydroxide in 
aqueous alkalis is doubtless due largely to the action of the alkali 
in converting the gel into a true colloidal solution,* it must 
dcjpend in part on the fact that, like alumina, chromic oxide acts 
as an acidic oxide towards strong bases, yielding salts termed the 
chromites. J Thus a green compound of chromic oxide with an 
alkali is thrown down on the addition of potash or soda to a 
solution of a chromic salt, and the alkali cannot be removed 
even by boiling water. This precipitate is, however, easily soluble 
in an excess of the precipitant, but can be again thrown down 
•ither by partial neutralisation with acids or by boiling the 
solution. When caustic soda is added to a solution of a chromic 
salt aud a salt of magnesium (for instance), a precipitate is 
obtained of a compound of magnesia and chromic oxide wliich 
does not dissolve in an excess of alkali. In this way, “ chromites " 
or “ absorption compounds ” of sodium, potassium, calcium, 
barium, magnesium, zinc, lead, iron, cobalt, nickel, copper, and 
cerium have been obtained, in a gelatinous condition, or their 
existence has been indicated by physical measuremei^s. Their 
c()m[)osition depends upon the conditions of their preparation. 

The chromites may be obtained also by the action of boiling 
aqueous alkalis on the corresponding sulphochromites. 

Better defined compounds arc produced by fusion of the 
appropriate oxides, by strong ignition of metallic chromates, 
and by fusion of alkali chromates or dichroinates with metallic 


^ Ctraliani, iV«7. 2'raHs., 1801, 151 , 183; Meuriicr, J. Soc. Leather Trades 
Chm., 1921, 5 , 103. , 

* van Beinniclen, Rec. trav. rhim., 1887, 7, 114. Se6 also Biltz, Ber., 1902, 
85 , 4431 ; 1904, 37 , 1096; Paal, Ber., 1914, 47 , 2211 ; and Picton and Linder, 
J. Ckem. Soc., 1897, 71 , 072; I^ttermoser, liber anorg. Kolhide, Stuttgart, 
1901; Siewort, Z. ges. yat., 1801, 18 , 244; van Bemmelon, Die Absorption, 
Dresden, 1910; Baikow, J, Russ. Phys. Chem. Soc., 1907, 89 , OGO; Beinitzer, 
Mmnlsh., 1882, 8, 249. 

* Bunco and Finch, J. Physical Chem., 1913, 17 , 769; Nagel, ibid., 1916, 
19 , 331, 669. 

* Nngol, loc. cit., Fischer and Horz, Zeit. anorg. Chem., 1902, 81 , 362; 
1904, 40 . 39; Bancroft. Chem. News, 1916, 118 , 113. 

* Wood and Block, J. Chem. Soc., 1916, 109 , 164. 



CHROMnJM TRIO^B ♦ IW 


chlorides. In this way, chromites of lithium, barium, calcium, 
magnesium, zinc, copper, cadmium, manganese, iron, and cobalt 
have been prepared. 

Ferrous Chromite^ FeCrgO^. — This occurs in nature as chromite 
or chrome iron ore, a mineral of the spinel group, ]!lfF'0,M'''2^8» 
the proportions of ferrous oxide and chromic oxide exhibiting 
considerable variatfon within limits. Sometimes tlie composi- 
tion approximates to Fe2Cr205,Fe3Cr40jj ; ^ and alumina and 
magnesia frequently occur as isomorphous constituents. Chrom- 
ite is rarely found crystallised in regular octahedra, generally 
occurring massive, with a granular, crystalline fracture. It is 
largely used in the manufacture of “ neutral ” refractofy furnace* 
linings. 

Chromous ChromUe^ CrOjCrgOgjirllgO.— Tliis is stated to be a 
reddish-brown oxide, fairly stable in dry air.® 


Chromium Trioxide, Chromic Acid, and the Chromates. 

473 Chromic oxide is unchanged when heated alone ^n air; 
the hydroxide is not so stable^ and in presence also of certain 
metallic oxides under a})propriate conditions of pressure, oxygen 
is readily absorbed.® A mixture of chromic acid wdth an alkali 
or alkaline earth can be completely oxidised by oxygen at a red 
heat,wdiilst if oxygen is supplied to the alkali-fusion in the form 
of potasshim nitrate or chlorate, the reaction takes place even 
more readily, yielding a yellow, soluble mass of an alkali chromate. 

Alkaline solutions of chromic salts are easily oxidised to 
chromat/cs by chlorine, bromine, hydrogen peroxide?,* persul- 
phates, and a number of other oxidising agents : 

CV2O3 + lOKOH + 3Br2 = 2K2Cr04 + 6KBr d OllgO. 

Acid solutions arc also susceptible to oxidation, though less easily, 
by potassium permanganate, lead dioxide, manganese dioxide, 
ceric nitrate, and particularly by persulphates.® 

Electrochemical oxidation of chromic salts can be so success- 
fully carried out that this method is now largely used for the 

1 ChrUtomanos, Ber., 1877, 10, 343. 

» Moberg. J, pr, Chem., 1843, 29. 175; Pifigot, Cimpt. rend., 1844, 19, 
609, 734; i4nn, Chtm. Phys., 1884, [3], 12, 528; Baug6, Compt, rend., 1898, 
127, 661. 

* Millbauer, Chem. Zeit., 1916, 40, 687. 

* Bourion and S4n6ohal, Compt. rend., 1919, 168, 69, 89. 

* Salinger,* Zetl. anorg. Chem.,*\903, 88, 342. 




1060 


.CHROMIUM 


commercial regeneration of chromate solutions from the chromic 
salts into which they have become converted.^ 

The chromates are usually yellow, yellowish-red, or red in 
colour; basic salts are known, but acid salts do not appear to 
exist. The salts frequently termed acid salts are dichromates 
corresponding to the disulphates (pyrosulphates), and are salts 
of dichromic acid, HgCrgO;. Trichromatel and other poly- 
chromates are also known. 

Chromium Trioxide or Chromic Anhydride^ CrOg. — This com- 
pound is formed by the action of strong sulphuric acid on solu- 
tions of the chromates. According to Zettnow * the best yield 
is obtained when 300 grams of potassium dichromate are mixed 
with 500 c.c. of water, 420 c.c. of concentrated sulphuric acid 
added, and the mixture is kept for twelve hours in order that the 
potassium hydrogen sulphate may crystallise out. The mother- 
liquor is then heated to 80° or 90°, and 150 c.c. of sulphuric acid 
are added, together with enough water to dissolve the crystals of 
trioxide which at first separate out. After tj^'clve hours the liquid 
is poured off from the crystals which have separated, and a second 
and a third crop may be obtained by concentration. The liquid 
is drained from the crystals, which are then washed on a pumice- 
stone or asbestos filter with pure nitric acid, of density 1*46, the 
adhering nitric acid being removed by passing a current of dry 
air over the crystals heated in a tube at 60-80°.® 

Chromium trioxide may also be obtained by the acflon of an 
excess of nitric acid of density 1'38 on barium chromate, the 
barium nitrate being separated by crystallisation.^ 

Chromimn trioxide exists either as a red, woolly mass or as 
lustrous, scarlet, rhombic prisms; it has a deiLsity of 2*78, and 
melts at 198° to a dark red liquid, which solidifies to a reddish- 
black, crystalline mass, having a metallic appearance. At 
about 420° it is completely resolved into oxygen and the 
sesquioxide.® 

Chromium trioxide is easily converted into chromic oxide 
by reducing agents, such as sulphur dioxide, hydrogen sulphide, 
stannous chloride, ar8eniou.s oxide, ferrous salts, zinc, etc., and 
many organic compounds also act in the same way. Thus if 

^ Ankcnasy and R^vai, Zeit, Ekktrcihem., 1013, 19, 344; Bochringcr, 
Ger. Pat., 251604; Zeit. Elektrccketn., 1013, 19, 248; Goldberg, Gcr. Pat., 
303165. 

* Pogg. Ann.t 1871, 148i 471. * Bunacn, Awwa/en, 1868, 149, 200. 

* DiiJirilUer, Compt, fend., 1872, 76, 711. 

* Jaeger and Oerma, Zeit. anorg. Chm., 1081, 119, 145. 

* Honda and Son6, Sci. Sep. T6h<^ Imp. Univ., 1014, 8, 223. 



CHROMIUBi TRIOXIDE 1061 


strong alcohol be dropped on to the dry trioxide reduction takes 
place with incandescence; paper, sugar, oxalic acid, etc., also 
reduce the solution of the trioxide, especially on warming. 
When the trioxide is heated with aqueous hydrochloric acid, 
chlorine is liberated, the dry gas yielding •chromyl chloride 
(p. 1070), and when heated with sulphuric acid it decomposes 
with evolution offoxygen. The aqueous solution of chroinium 
trioxide as well as its solution in glacial acetic acid is often used 
in organic chemistry as an oxidising agent. Still more com- 
monly, a mixture of potassium dichromate and dilute sulphuric 
acid is employed for this purpose, in which case chrome alum is 
obtained as a by-product. Chromium trioxide dissolves without 
alteration in cold dilute alcohol and pure ether, and it is soluble 
also in concentrated sulphuric acid, apparently ^ with formation 
of the compounds CrQajSOg and Cr03,S03,Ha0, but least in acid 
containing 16-17 per cent, of water. It deliquesces in the air, 
forming a browm solution which on dilution with water becomes 
yellowish-red. This dyes the skin, as well as silk and wool, a 
yellow colour, and possesses an acid and astringent tastq. 

Chromic Acid, H2Cr04.- The existence in the solid condition 
of normal chromic acid has been asserted by Moissaii.^ From 
the conductivity, molecular refractivity, and molecular solution 
volume it has been concluded ^ that solutions of chromium trioxide 
contain only dichromic acid, HgCraO, ; on the other hand, Costa * 
and Del\p ® consider that both chromic and dichromic acids are 
present in a state of equilibrium. It is observed that in very 
dilute solutions, chromic acid, dichromates, and chromates have 
identical colour; the hydrolysis HjCrjO; b HgO 21l2Cr()4 
is then regarded as complete; more concentrated solutions 
contain both chromic and dichromic acids, whereas further 
increase of concentration or temperature api>arently dehydrates 
the molecules, forming trichromic acid, H2Cr30iQ, and tetra- 
chromic acid, H2Cr40i3, the salts of which may be represented 
as {M'0)Cr02*0-Cr02-0*Cr02(0M') and 

(M'0)Ci020Cr02-0Cr02'0Cr02(0M') 

respectively. 

1 Gilbert, Buckley and Masson, J. Chem. Soc., 1922, Igl, 1934; Meyer and 
Stateezny, Zeit. anorg. Chem., 1922, 122, 1. • 

■ Moissan, Compt. rend., 1884, 98, 1081. 

« Ostwald, Zeit. physikal. Chem., 1888, 2, 78; Datta and Dhar, J. Amer. 
Chem. Soc., 1916, 88, 1303. 

* Costa, Oazz., 1906, 86, 035. 

» Dohn, Amer. Chem. Soc., 1914, 86, 829; Dhar, Zeit. anorg. Chetg., 1921, 
DO, 69. 



CHROMIUM 


Chromic acid, Cr 02 ( 0 H) 2 , in its chemical properties resembles 
sulphuric acid, and the normal salts are usually isomorphous 
with the corresponding sulphates; similarly, dichromic acid 
corresponds to disulphuric (pyrosulphuric) acid. 

Ry direct solutfon of metals ^ or by reaction with bases, there 
are produced the normal chromates and dichromates, of which 
potassium dicliromate is the most important, i 

Normal Potassium Chromate^ K 2 Cr 04 , is obtained by the 
addition of potassium hydroxide to a solution of the dichromate, 
evaporation yielding yellow, rhombic pyramids wdiich are iso- 
morplious with potassium sulphate. Potassium chromate has a 
density of 5'71 at and does not undergo alteration in the 
air. On heating to G60'' it is converted into a second modifica- 
tion; it becomes red -coloured, and melts at 978° without 
decomposition, solidifying on cooling to a crystalline mass. It 
dissolves in water with a yellow colour which is perceptible even 
when very small quantities of the substance are present, one part 
of the salt imparting a distinct yellow tint to 400,000 parts of 
water, pne hundred parts of water dissofve^ at 

0" 30® . CO® 105-C®t 

54-57 57-11 05-13 74-00 88-8 parts. 

* Cryohydrii! jxdnt. t Boiling point of .saturated solution. 

The salt has a bitter, cooling taste and an alkaline reaction. 
On evaporating its solution, red crystals of the dicliromate are 
first deposited and afterwards the yellow crystals of the normal 
salt. It is decomposed by all acids, even by carbonic acid, with 
formation of the dichromate. It is insoluble in alcohol. 

Potassium Dichromatey or Bichromate of Potash, K 2 CT 2 O 7 , 
serves as the starting point for the preparation o{ almost all 
the other chromium compounds, and is prepared on the large 
scale from chrome iron ore. 

Up to the year 1820 potassium dichromate was used only 
for the purpose of making chrome yellow, and was prepared 
by the calcination of chrome iron ore with costly saltpetre. 
In the above year Kochlin introduced potassium dichromate 
into the process of Turkey-red dyeing, and it was soon employed 
for" a variety of other purposes, especially in wool dyeing. In 
its preparation, potashes were employed instead of saltpetre, 

' See van Name and Hill, Amer. J. Set., 1016, [4], 48, 301 ; 1918, [4], 45, 
64. ^ 

' Konpel and Blumenthal, Zeit. artorg. Chem., 1907, 58, 262. ^ 




CHROMIUM TRIOXIDE 


1063 


and the chrome iron stone was oxidised in reverberatory furnaces 
by means of atmospheric oxygen. An important improvement 
was made in the process by Stromeyer by the introduction of a 
certain quantity of lime together with the potash. Not only 
was a saving of alkali thus effected, but the oxidation was 
rendered easier, inasmuch as the whole mass did not fuse, and 
therefore remained® porous and more capable of absorbing* the 
atmospheric oxygen. The chrome iron ore is first roasted and 
4 J parts of the finely ground ore are mixed witli parts of 
potassium carbonate and 7 parts of lime. This mass after drying 
at 150° is heated to bright redness with an oxidising flame, the 
whole being constantly stirred. At the end of tlicf operation 
the charge is withdrawn from the furnace, and, after cooling, is 
lixiviated with the minimiun amount of hot water. If calcium 
chromate be found in solution, a hot saturated solution of potass- 
ium sulphate is added, when the calcium is thrown down as 
sulphate and potassium chromate remains in solution. The 
liquor is next treated with the requisite quantity of sulphuric 
acid, diluted with twice its volume of water, to convert the 
chromate into dichromate, and allo^ved to cool. The solution of 
chromate saturated at 16° contains nearly 1 part of salt to 
2 parts of water, whilst the dichromate requires 10 parts of water 
for its solution ; hence when the saturated solution of chromate 
is converted into dichromate, a precipitate of about 75 ])er cent, 
of the dichromate is formed on cooling. The precipitate is 
collected and recrystallised. The mother-liquor, which contains 
potassium sulphate, is used to lixiviate another portion of the 
roasted mass. 

An important modification of this procedure consists in the 
manufacture of sodium dichromate (p. 1065) by a similar process, 
and the final conversion of this into the potassium salt. 

This salt may be produced also by electrolysing a solution of 
potassium hydroxide or a potassium salt, using an anode of 
ferrochrome.^ 

Potassium dichromatc crystallises in splendid garnet-red 
tablets or prisms belonging to the triclinic system, having a 
density of 2*692 at 3-9°. It melts at 396°, forming a transparent, 
red liquid, which when slowly cooled •crystallises in the same 
form as from aqueous solution. It is unchanged in the air, 
and decomposes at a white heat into oxygen, chromic oxide, 

* I^rcnz, Zeif. anorg. Chem., 1896, 12, 396; C. F. Gricshcira-linektron, 
Ger. Pat., 14^20. 




1064 


CHROBOUM 


and the normal salt. One hundred parts of water dissolve^ 
at 


-0 63° ♦ 0® 

4*f)0 . 4-64 

• (Vyohydric [Kjint. 


30® 60® 104-8® t 

18*09 46*10 106*2 parts of salt. 

t Boiling point, of saturated solution. 


Potassium dichroinate has an acid reactioh, a cooling, bitter, 
metallic taste, and is insoluble in alcohol ; it acts as a powerfuj 
poison, probably on account of its oxidising properties. The 
commercial salt is usually almost chemically pure, and is 
employed for the preparation of other chromium compounds, 
as a reagcftt, and as an oxidising agent, as well as being largely 
used in dyeing and calico-printing. 

A film of organic matter saturated with a solution of potass- 
iimi dichromate acquires a dark colour on exposure to light 
owing to a reduction to chromic oxide taking place, and a solu- 
tion in gelatin is used as a ‘sensitive agent in the Autotype 
and other similar photographic printing ^processes, commonly 
ndcrred to as “ carbon printing.” These processes depend not 
merely upon the de-oxidation of^the dichromate, but also upon 
the fact that this reduction renders the gelatin insoluble in» ^ 
and non-absorbent of, water, so that those portions of the gelatin 
film which have been acted upon by the light remain unchanged 
when the film is immersed in hot water, whilst those parts which 
have been protected from the action of the light dissolve away 
entirely. A film is thus obtained in which the various shades 
of the original negative are represented by deposits of varying 
thickness of the insoluble gelatin, which can be coloured with 
a wide range of pigments; in this way the red or blue chalk 
drawings of the old masters can be reproduced wuth remarkable 
accuracy.^ 

Potassium dichromate forms a double salt with mercuric 
chloride, KaCrjjOyjHgClg, which separates in red, well-developed, 
rhombic crystals. 

Potassium Trichromate, KjCtjOio, is formed by the action of. 
chromic acid solution on the dichromate, but is best prepared 
by boiling the dichromate with nitric acid of density 1*19; on 
cooling, |)otas8ium nitrite separates almost completely, and 
the decanted liquor then deposits the trichromate in deep red, 

^ Koppel and Blunienthal, Zeit. anorg. Chtm,, 1907» 58» 262. 

* For a full and interesting desoription of these processes, see Abney’s 
Tttatm OK Photography, (Longmans.) • 



CHROMIUM TRIOXIDE 


1065 


monocUnic prisms of density 2*648. It is decomposed by hot 
water into chromic acid and the dichromate, and cannot there- 
fore be recrystallised in this manner.^ 

Potassium fetrachmnate, K2Cr40i3, is obtained by heating the 
dichromate with nitric acid of density 1*41, and separates out 
on cooling in brownish-red crusts consisting of small, rhombic 
plates. It has a density of 2*649, and, like the trichromate, is 
decomposed by water into chromic acid and the dichromate. 

Normal Sodium Chromate^ Na2Cr04, 101120, is obtained by 
direct oxidation of chromite in presence of lime and soda (p. 1059), 
by fusing chromic oxide and sodium nitrate together, and evapor- 
ating the solution at a low temperature, or by allo\fing a solu- 
tion of potassium chromate saturated with soda to evaporate 
at 0°. However, the only method of obtaining the pure salt is 
by addition of sodium carbonate to a solution of carefully purified 
sodium dichromate. The salt is deposited in deliquesccn^ 
transparent, yellow prisms, isomorphous with (llauber s salt. 
Wien the solution is heated to above 65° the anhydrous salt 
separates out. It has an alkaline reaction, and a bitter, ftietallic 
taste. Hydrates containing ^2^^ 6H2O have also been 
obtained.^ 

Sodium lyichrotnate, Na2Cr20 7,21120 crystallises in thin, 
triclinic, yellowish-red, deliquescent prisms. This salt is now 
manufactured on a large scale, since for many technical purposes 
it can replace the more expensive potassium salt. It is much 
more soluble than the latter, and for this reason is used as a 
depolariser in chromic acid cells in place of the potassium salt. 
Above 83°, aqueous solutions deposit the anhydrous salt, a deli- 
quescent substance which melts at 230° and decomposes at 
400°. 

The following salts are also known : sodium trichrmnate^ 
Na2Crg0iQ,H20, sodium telrachromale, Na2(V4043,4H20, and a 
basic chromate^ Na4Cr05,13ir20. 

Ammonium Chromate^ (NH4)2Cr04. — This salt can be obtained 
pure only from solutions containing excess of ammonia, as it 
readily loses the latter, forming the dichromate. It is obtained 
in golden-yellow, monoclinic needles by gently warming pure 
chromium trioxide with a quantity of ammonia just sufficient 
to dissolve the chromate formed, and cooling the solution in a 

* J&ger and Kruss, Eter., 1680, 22, 2038. 

* Salkowi^, Ber., 1001, 84, 1047; Richarda and Kelley, J. Amer. Chem. 

Boc., 1011, 88, 847. ' 




1066 


CHROMIUM 


freezing mixture. One hundred parts of water at 30° dissolve 
40-40 parts of the salt. The dichromatej (.NH 4 ) 2 Cr 207 , is readily 
obtained by adding the requisite quantity of chromium trioxide 
to ammonia, and, separates out on evaporation in orange-red,, 
monoclinic crystals of density 2-3G7. At 30°, 47*17 parts dissolve, 
in 100 parts of water. The substance is stable in air, even at 
100°,* but on ignition it decomposes into nitro^n, water, a bulky, 
leaf-like mass of chromium sesquioxidc, and generally a little 
ammonia. This salt forms a number of crystalline double salts 
with mercuric chloride.^ 

Tlie trichromale and telrachromate have also been prepared. 

'Chromate, dichromates, etc., of the other alkali metals are 
known, as well as a number of double salts; these are formed 
not only amongst the alkali cliromates themselves, and between 
the alkali chromates and chromates of otlier metals, but also 
b<?twe(m tlie alkali chromates and mercuric chloride and cyanide. 

474 Most of the other metals form chromates or basic chromates 
which arc for the most part coloured substances insoluble in 
water, diany of which are largely used as pigments. The most 
important of these are tlie following : 

Co'pji&t Chromates ~-C(ypper Bichromate^ CuCr 207 , 2 TT 20 , is ob- 
tained by the action of concentrated chromic acid solution 
on copper hydroxide. It forms blackish-brown, deliquescent 
crystals. The solution wlien boiled deposits the basic salt 
CuaCrOfl.SHgO'-^ as a brown precipitate, which is also obtained 
w hen boiling solutions of normal potassium chromate and copper 
sulphate are mixed ; cold solutions, on the other hand, yield a 
double salt. The mineral vauquelinite, ( 0 u,rb) 3 Cr 209 , occurs 
in small, glistening, monoclinic crystals or earthy masses, together 
with crocoisite. Normal copper chromate^ CuCrOi, forms mixed 
crystals wdth copper sulphate. 

Silver Chromate ^ is obtained as a brick-red, amor- 

])hous precipitate when a solution of potassium chromate is 
poured into excess of a concentrated solution of silver nitrate 
either cold or hot.® It is formed when silver dichromate is 
boiled for a long time with water as a deep green, crystalline 
powder,* which is insoluble in water, but dissolves with some 
difficulty in sidphuric heid, nitric acid, or ammonia. The 

^ J&ger and Krliss, Btr., 18.89, 22. 2047. 

^ Gruger, Monatsh,^ 1903, 2i, 483. ’ Autenrieth, Z?er., 1902, 85, 2057. 

* Margosohes, Zeit. anorg, Chem.t 1904, 41, 68; 1906, 51, 231; Kohler, 
ibid., 1(116,96,207. * 



CHROMIUM TRIOXIUE 


1067 


* • « * 
solution obtained by dissolving silver chromate in as small a 

quantity as possible of warm ammonia of density 0*94 deposits 

amraonio-silver chromate, Ag 2 Cr() 4 , 4 NH 3 , on cooling in long, 

yellow needles ^ which by beating yield green silver chromate. 

The red chromate may be converted into tlu? green form by 
heating in an atmosphere of carbon dioxide (Autenrietli). 

Silver Dichrmiwk, AggCVgO^, is obtained by the actioji of 
potassium dichromate on silver nitrate in acid solution ; it forms 
small, red, triclinic crystals, and is decomposed by boiling water 
into chromic acid and normal cliromate. It is also obtained by 
warming silver chromate with dilute nitric acul.^ 

Barium Chromate^ BaCr04, is a yellow precipitatt, insoluble 
in acetic, but easily souble in nitric, hydrochloric, and aqueous 
cliromic acids. From the last solvent, the salt BaCVgO 7 , 21101 ) 
may be obtained in yellow, stellar needles, which are decomj)osed 
by water with separation of the normal salt. Barium chromate 
is used as a pigment under the name of yellow ultramarim dT* 
lemon chrome. It is, however, now very little used, as the h'ad 
chromates have a brighter colour and more body. • 

Zinc -Potassium chromate gives with zinc sul])hal(‘- 

a yellow precipitate of basic zftic chromate, Zn2(OJl)jjCr04,ll2ll. 
A similar compound, 2Zn2(0II)2Cr04,n20, is formed when zinc 
carbonate is heated with a solution of chromic acid. The normal 
chromate and dichromate have also been prepared. 

If a sajf or oxide of zinc is boiled with potassium dichromate 
the yellow compound, Zn4(0iI)(.Cr04, is precij)itated. 

The chromate obtained by the addition of a hot neutral solu- 
tion of zinc sulphate to jwtassiurn chromate forms a stable 
yellow pigment sold under the name of 7Anc yellow or Buttercup 
yellow. 

Lead Chromate, PbCr04, occurs as crocoisitc in translucent, 
yellow, monocbnic prisms, having a density of 5*9 to 6 - 1 . The 
mineral is found in Siberia, in the Urals, Brazil, Hungary, and 
the Philippine Islands. Crystals of somewhat higher density are 
artificially obtained when lead chloride is strongly heated with 
potassium chromate, as well as when solutions of lead acetate 
and normal potassium chromate are allowed slowly to diffuse 
into one another.® A bright yellow precipitate of the normal 

* Muthmann, Bar., 1889, 22, 2051. 

* Autenrieth, Ber., 1902, 35, 2059; tiherrill, J. Amer. Chem. Soc., I(K)7, 

29, 1641; Spitalflky, Chem. ZetUr., 1914, ii, 376. ^ 

* DrcFenii8im, Annakn, 1853, 87, 121. * 



1068 


CHBOMUnf 


chromate is obtained when a solution of a lead salt is precipi> 
tated with potassium dichroniate. The reaction PbS04 4 - 
K2Cr04 r - PbC)r04 K2S()4 is practically complete, and can 
bo iisod ^ for the manufacture of the normal salt, which is known 
as chrome yellow, Paris yellow, or Ldpsig yellow, and is largely 
used as a pigment. It is insoluble in water, but is readily dis- 
solvfjd by nitric acid and potassium hydroxide solution. When 
strongly heated it fuses to a brown liquid, which on cooling 
solidifies to a crystalline mass.^ Since lead chromate at a red 
heat oxidises all organic substances, it is frequently employed 
in organic analysis, especially in the case of bodies which contain 
chlorine, stilphiir, etc. TJie chrome yellow of commerce often 
contains admixtures, especially lead sulphate. This, however, 
is not always to be considered as an adulteration, and it is used 
for the preparation of a light shade. This is termed Cologne 
yellow, and is obtained by the precipitation of a mixtiue of the 
titrates of lead and calcium with a mixture of sodium sulphate 
and potassium chromate, or more generally by heating lead 
sulphaio with a solution of potassium dich’romate. 

Calico is printed or dyed with chronic yellow by first mor- 
danting the cloth with a solutioft of a lead salt, and afterwards 
stee|)ing it in one of a soluble chromate. 

Basic JmuI ('hromate, Pb./h‘05, is known in commerce as 
chrome red and is obtained as a fine red powder by digesting 
chrome yellow with cold sodium hydroxide solution, ^boiling it 
with a solution of normal jxitassium chromate, or fusing it with 
potassium nitrati*. Another basic salt, Pl)3(h20jj, occurs as the 
mineral pha’iiicite, in hyacinth-red crystals of density 5 * 75 ; 
the salt 4Pb0,Cr03,Fl20 is known, as also® arc Pb^CrOg and 

Pb:Cr2()43. 

Jly making a suitable mixture of chrome yellow and chrome 
red, or by modifying the process of manufacture go as to obtain a 
mixture of these, pigments of any shade between the two may be 
obtained. These are known commercially as chrome orange. 

Lead dichromate and the chromate and dichromate of quad- 
rivalent lead have been prejiared by an electrolytic method.^ 

* Milbttuor and Kohn, ZeiL jihyaikal Chtm., 1910, 91 , 410. 

» Jaeger and (Jerins, ZtiU anorg. Chem., 1021, 119 , 145, find that lead 
chromate is triniorphous; the o-form is staHe below VOT"*, the j8-form between 
707® and 783®, and the 7-fonn above 788®, melting at about 844® with 
evolution of oxygen. 

* Jaeger and Germs, toe. cit. 

* ^be and Nttbling, Zeit. EUktrochem,., 1903, 9 , 776. Soe^also Mayer, 
Btr., 1903, 86, 1740; Ck>x, ZetV. anorg. CAm., 1906, 50, 226. 



CHBdMIUM miOXiDfi 


1069 


Bismuth Chromate, — Normal bismuth chromate is unknown, 
but a number of basic salts have been described. By addition 
of potassium chromate solution to a solution of bismuth nitrate, 
the compound K 20 ,Bi 203 , 4 Cr 03 is obtained as a yellow precipi- 
tate; on boiling this with water, the compound BigOg/JCrOg 
or bismuthyl dichromate, (BiOljCVjO^, is obtained as orange- 
yellow crystals, insoluble in water. 

Chrotnic Chromate, CrjOgjOrOg = SCrO^. -This compound, 
also known as chromium dioxide, is formed when chromic nitrate 
is gently heated, or when a solution of chromic oxide in nitric 
acid is evaporated to remove excess of acid and the residue 
dissolved in water and treated with ammonium hydroxide.^ 
It is likewise })repared by the partial reduction of the trioxide, 
and by the precipitation of a chromic salt with a soluble chromate. 
The brown powder thus obtained is easily soluble in acids. 
Alkalis precipitate chromic hydroxide from its solution, whilst a 
chromate remains in the liquid. If chromic chromate be washelT 
for some time with water, it is decomposed into soluble trioxide 
and insoluble sesquioxide; for these reasons the substance is 
regarded as a chromate. When nitric oxide is ])assed into a 
tolerably concentrated solution bf potassium dichromate, chromic 
chromate is obtained as a dark brown precipitate, which dries 
at 250"' to form a black, hygroscopic powder, and this, when 
heated in a current of hydrogen chloride, yields chromic oxide, 
water, an^l chlorine. 

A hygroscopic black powder has also been obtained by Manchot 
and Kraus 2 by heating chromic hydroxide in a current of 
oxygen. This contains a little water, which it gives off at a 
red heat along with some of its oxygen ; chromic oxide remains. 
WTien washed with water, no chromium trioxide is obtained, 
and these investigators therefore consider it to be a dioxide, 
CrOg, and not chromic chromate. 

When the vapour of chromyl chloride is passed through a 
red hot tube, violet, translucent prisms, having the comi^sition 
(i.e., 2 Cr 203 ,Cr 03 ), are obtained. These are magnetic, 
ftnd on ignition are gradually converted into chromic oxide.* 

An oxide of the formula Cr 40 g (i.e,, has been 

^ JovitschiUch. Hdv. Chxm. Acta, 1920, 3, *40. Seo alf»o Hooton, Proc, 
8oc., 1908, Si 27; OgaU, J. Pfiarm. Chitn., 1916, [7], 14, 144. 

* Ber., 1906, 89, liS 62 . S©e also Meerburg, Zeit. anorg. Chem., 1907, 
14,31. 

• Qeuther, AnnaUn, 1801, 118, 61; Son6 and Ishiwara, 8ci. Rep, Tdholeu 

fmp, Univ,, 1914, 3, 271. • 



1070 


CHROMIUM 


described as being the product of the ignition of the trioxide 
between 500 " and 510 ".i 

A number of crystalline double chromates have been described 
which have the general formula M'2M''(CrO4)2,0H2O, where 
M' is K, Rb, Nk4, or Cs, and M'' is Ni, Mg, or Cd, as w'ell as 
ammoniacal double chromates of the formula M'gM "(6^04)2, 2Nir3, 
wh(ire M' is K or NIf4, and M" is Cu, Zn, C(i, Ni, or Co.^ 


IFalooen and Amido-derivatives of Chromic Acid. 

475 Chromyl Dijlvoride, Cr02F2. — Tliis substance was first 
obtained by Unverdorben by the action of sulphuric acid on a 
mixture of lead chromate and fluorspar, and was regarded by 
him as chromium hexalluoridj; ; Oliveri ® has, however, character- 
ised it as chromyl fluoride, derived from chromic acid by the 
replac(!ment of the two hydroxyl groups by fluorine. Ruff’s ^ 
attempt to olitain a substance of definite composition by this 
method, or, better, by substituting fluorosulphonic acid for 
calciurti fluoride and sulphuric acid, and a mixture of ])otassium 
dichromatc and chromium trioxide for potassium dichromate 
alone, was, however, unsuccessful. The substance is obtained 
as a red gas, condensing in a freezing mixture to a very volatile, 
blood-red licpiid which attacks glass, and is converted by the 
moisture of the air into chromium trioxide and hydrogen fluoride. 

Flnorochromie (icid^ Cr02F(()}l), is unknown in the «free state, 
but its 2)otass'nini salt is formed by heating potassium dichromate 
with liydrofluoric acid in a platinum vessel; it crystallises in 
red, tetragonal pyramids, which are soluble in water, but the 
solution decomposes on boiling into potassium dichromate and 
hydrofluoric acid. The ammonmn salt is also known. 

Chmnijl DicJdoride, CrlX^Clj, appears to have been discovered 
by Thomson ^ ; it was also investigated by Berzelius,® Dumas,’ 
and AVohlcr.® It is prepared ® by treating a dry, finely divided 
mixture of five parts of common salt and eight parts of potass- 
ium dichromatc with fifteen parts of fuming sulphuric acid 

» Shukow, Compt. rend., 1908, 146 . 1300. 

• JJriggg, Joum. Chem. Soc., 1003, 88. 1391; 1004, 86, 072, 677. 

» Olivori, Gazz., 880, 18, 218, * Ruff, Bcr„ 1014, 47, 650. 

“ Phil Trans., 1827, U7, 160. - Berz. Jahresber., 1827, 8, 120. 

’ .Dw. Chim. Phifs,, 1820, [2J, 81 , 433; \Valn?r, ibid., 1837, 12J, 88 , 387. 

« Pogg. .4nn., 1834, 88. 343. 

* Moiea anil Comez, Zeit. phgsilal Chtm., 1012, 80 , 613; Anal Fis. 
Quimf, 1914, 18, 142. 



HALOGEN AND AMIDO DERIVATIVES 


1071 


added in small quantities, and finally gently warming the mixture ; 
in order to remove free chlorine, the distillate is repeatedly 
rectified in a current of carbon dioxide. It is also formed by 
heating chromium trioxide in a current of hydrogen chlorkie, 
when it distils over, and an oily liquid remains which has been 
thought to be chJorochromic add, (I'CrOj’OH. It may readily 
be obtained by dissolving chromic acid in concentrated hydro- 
chloric acid, and adding sulphuric acid to the cooled liquid in 
small quantities at a time. The heavier chromyl chloride is 
then run off, dry air is blown through, and the licpiid distilled.^ 
It may also be obtained ^ in 80 per cent, yield by addition of 
acetyl chloride to a solution of chromium trioxide^ in carbon 
tetrachloride. Chromyl dichloride is a mobile liquid of a 
splendid blood-red colour by transmitted, and nearly black by 
reflected light. It boils at 11 6*7'^, and has a density at 25'’ of 
1-012.^ The molecular weight of chromyl chloride, determined 
by the usual methods, gives values corresponding to the abo\x? 
formula. It absorbs chlorine readily, dissolves iodine, and wl “ii 
drop[)(Ml into water it remains unaltered for a few seco’vls, but 
is afterwards decompos(‘d with violent ebullition into chromic 
and hydrochloric acids. AVhen brought into contact with 
j)hosphorus it explodes, whilst it takes fire in contact with 
sulphur, hydrogen suljdiide, ammonia, alcohol, and many other 
organic bodies, and when diluted with acetic acid or carbon 
tetrachloride acts as an oxidising and chlorinating agent upon 
hydrocarbons. With phosphorus halides it yields additive 
compounds.'* When chromyl dichloride is heated in a cIoschI 
tube to 180'’ for three or four hours, trichfomyl chhridr., CVgO/’lg, 
is formed as a black powder, which delitjuesces on exposure 
to the air ; ^ another solid oxychloride is stated to have the 
composition (CrOglgClg.® 

Bromine and iodine do not form analogous chroiuyl derivatives ; 
a bromide or iodide, heated with sulphuric acid and 2 )ota 8 sium 
dichromate, yields free bromine or iodine. This reaction is 
made use of for the detection of chlorine in presence of bromine 
or iodine ; if chlorine be present the substance, when heated with 

^ I.AW and Perkin, Jonm. Chtm. Soc., 1907, 91t 191. 

* Fry, J, Amer, Chem. Soc., 1911, 38, 697. • 

* Moles and Gomez, loc. cit. See also Thorpe, Journ. Chem. Soc., 1880| 
17, 327. 

* Fry and Donnelly, J. Amer. Chem. Soc., 1916, 88, 1923; 1918, 40, 478. 

‘ Thorpe, Joum. Chem. Soc., 1870, 28, 31. 

* Pascal, Compl. rend., 1909, 148, 1463. 

VOL. 11. (II.) 


R 



1072 


CHROMIUM 


potassium dichromate and sulphuric acid, yields chromyl chloride, 
which is converted* by water into chromic acid, wdiich may be 
recognised by the usual tests. 

Chlorochmnic acid, CbCrOg'OH, analogous to chlorosulphonic 
acid, is unknown, but its potassium salt is formed ^ when three 
parts of j>otassiuni dichromatc are gently heated with four 
})arts of concentrated hydrochloric acid and a small quantity 
of w'at(‘r, or when chromyl dichloride is added to a saturated 
solution of potassium chloride : 

CrOgClg -f- Ka + HjjO - KCrO^Cl -j- 2HC1. 

It crystallises in flat, red, rectangular prisms, having a density 
of 2*107. The salt is partially decomposed by water, but may 
be recrystallised from water containing hydrochloric acid, or 
from glacial acetic acid. It decomposes at 100° with evolution 
of chlorine : 

4CrO.^(OK)01 4- Cr^ f 2KC1 + CL, + Og 

Othor chlorochromates have been described,^ as well as 
potassium bromo- and iodo-chromates. 

Aniidochromic acid, NH2*Cr()2^0H. — It is doubtful whether, 
by the action of dry ammonia on clilorochromates in solution 
or su.s])ension in organic media, salts of amidochromic acid are 
formed, as has been suggested;® liquid ammonia, however, 
apparently leads to the formation of salts of imidochrmic acid, 
NII:(H)(0H)2.^ 

Perckromic. Acid and the Perchroniates. — A deep indigo-blue 
coloured solution is obtained when hydrogen peroxide is added 
to an aqueous solution of chromium trioxide, or to a solution 
of a chromate acidified with sulphuric acid. If the freshly 
prepared solution be shaken with ether, this liq\ud takes up 
the perchromic acid and becomes of a dark blue colour. The 
ethereal solution is more stable than the aqueous solution, but 
on evaporation it leaves a residue of chromium trioxide. The 
same decomposition is effected by alkalis, a chromate being 
formed wuth evolution of oxygen. The colouring power of 

» IVligot, J. Pham., 1833, 19, 301. 

• Pt^igot, Ann. Chim. Phys\, 1833, [2], 62, 267; Praetorius, Annakn, 1880, 
201, 1 ; Loevrenthal, ZtiL aiiorg. Chem., 1804, 6, 355. 

• lleiiitzc, J. pr. Chem., 1871,121,4,212; Loewonthal, /oe. ci7. ; Wyrouboff, 
Bull. Soc. chim., 1894, [3], 11, 845; Wemer and Klein, Zeit. anorg. Chm., 
1895. 9, 201 ; Meyer and Best, ibid., 1900, 22, 192. 

• Ko^enheim and Jacobsohn, Zeit. anorg. Ckrm., 1906, 60, 297. 



HALOGEN AND AMIDO DERIVATIVES 


1073 


perchroniic acid is so great that its formation is employed as 
a most delicate test, l)oth for chromic acid and for hydrogen 
peroxide. The doei)est coloration is produced when two mole- 
cules of hydrogen peroxide are used to one molecule of chromium 
trioxide. The constitution of the sub.stance thus formed is as 
yet uncertain. It lias been variou.sly regarded as CrgO-.irlM)/ 
CrOe, 31120,2 CrOa.H.O^,^ and 2HCr04,If202/ etc. By .‘tlu^ 
action of sodium peroxide on a thin paste of chromic hydroxide 
and water Htiussermaim^ obtained a sodium salt having the 
comjKisition NagCrgO^j, 281120, which would be the salt of an 
acid deiB'ed from the anhydride CrOg. When this salt is treated 
w'itli sulphuric acid, the characteristic blue colour i» first pro- 
duced, but oxygen is soon evolved, and chromic sulphate remains 
in solution. Salts of a perchroniic acid, IlOrOg, [03Cr‘0-(0II), 
in which chromium is septavalent], with pyridine, quinoliiu', 
and other organic bases have been prepared by Wiede,® by adding 
the bases to the blue ethereal solution of perchroniic acid cooled' 
below 0*^. These arc explosive crystalline compounds, which 
evolve oxygen w'hen treated with strong acids. In a similar 
manner, he has obtained blue jiotassium and ammonium salts, 
which he regards as (NJf4)Crt)5,H202 and KCr()g,ll2()2, the 
hydrogen peroxide acting like water of crystallisation. On thi^ 
other hand, according to Riesenfeld,'^ the last two compounds 
are acid salts of the perchromic acid, JigCrO-, and have, therefore, 
formuluc (d the type ll’JIgCrO^. They are also formed by the 
action of hydrogen peroxide on chromates in cold, faintly acid 
solution; in alkaline solution red salts of a jiercliromic acid, 
HgCrOg, are obtained. The red ammonium salt, (NH4)3CrOR, 
with dilute acids, gives off oxygen and forms the blue salt, 
{NIl4)Il2Cr07, and both these compounds yield with pyridine 
Wiede’s salt of the acid IlCrOg; finally, all three compounds 
with excess of ammonia form triammine chromium tetroxide, 
Cr()4,3NH3. This compound® is a browm, explosive, crystalline 
substance which has density 1-964 at 15-8°. 

^ BarreswiI, Ann. Chim. PhffH,, 1847, [3], 20, 304. 

* Fairley, Chem. News, 1876, 33, 337. 

• Moissan, C(mpl. rend., 1883, 07, 90. 

« Berthelot, ibid., 1889, 108, 26. » J. pr, Chem., 1803, [2], 48, 70. 

• Her., 1897, 30, 2178; 1898, 31, 616, 3139; 1893, 32, 378. See alao 
Hofmann and Hiendlmaior, ibid., 1906, 38, 3069. 

» Ber., 1905, 38, 4068; 1908, 41. 2826; 1911, 4i 147; Zeit. anorg. Chem., 
1912, 74, 48. Compare Hofmann and Hiendlmaier, Ber., 1904, 37, 1663. 

* Wiede, Ber., 1897, 30, 2178; 1899, 32, 378; Rieaenfeld, Wohlers, Kutsch, 

and Ohl, Ber* 1006, 88, 1886, 3380. * 


1074 


CHROBOUM 


Jiiesenfold considers that when excess of hydrogen peroxide 
acts on a solution of chromic acid, th^ acid HgCrOg (which, 
tliougli blue, has a composition corresponding to the red per- 
ch roinatcs) is mainly produced, but at the same time a little 
of the acid IT/VO^ is also formed, whilst the blue ethereal solu- 
tion probably contains a mixture of several percliromic acids.^ 
When perch romic acid is prepared by the action of hydrogen 
p(Toxid(; on chroniyl chloride or upon chromium trioxide in 
Jiiethyl (sther solution at — 30 '’, it is found to possess the formula 
I lyf )y,‘J I f^O ; the water is water of constitution. Thus the blue 
acid may be regarded^ as having the formula (0H)4Cr(0'()n)3, 
whereas the red perchromates are anhydro-salts of the formula 

(M 0 - 0 )/V 0 .^. 


CiiROMOus Salts. 

% 476 By dissolving metallic chromium in acids, or by reduc- 
tion of chromic salts or chromates with metals or by an electro- 
lytic process,® compounds of bivalent chromium are obtained. 
It is essential that air should be excluded during the operation, 
since the chromous salts in solution are readily oxidised to 
chromic salts and chromic acid, with intermediate formation 
of unstable compounds.* They are powerful reducing agents.® 
'riie anhydrous salts are usually white, and yield solutions the 
colour of which is blue in the case of salts of strong acids, and 
yellow, brown, or red in other cases. 

Chromous Fluor kit' , CrFg, known only in the anliydroiis con- 
dition, is a green, lustrous substance. It is obtained by the 
interaction of chromium or chromous chloride with hydrogen 
fluoride. 

Chronwus Chloride, CrCI,^, is formed by the ignition of chromium 
in hydrogen chloride, or of chromic chloride in a current of hydro- 
gen gas free from'oxygen, and forms white, silky; lustrous needles 
which are stable in dry air. It dissolves in water with evolution 
of heat, forming a blue solution, which absorbs oxygen with 
extreme avidity, yielding basic chromic salts, and forms a power- 

> 800 also 8 pit«l 8 ky, Zeit. anorg. Chtm., 1907, 63 , 184; 1907, 54 , 265; 
1907, 56 . 72; 1910, 68 , 179;,Bfr., 1910, 43 , 3187. 

’ Uioscofold and Man, Ber.t 1914, 47 , 548. 

> Traube and Goodaon, Ber., 1916, 48 , 1679; Taylor, Geradorff and Tovrea, 
J. Amer. Chtm. Soc., 1922, 44 , 612. 

* Piccard, Ber., 1913, 46 , 2477; Traube and Passarge, Ber„ 1913, 46 , 1505, 
have found that double salts with hydrazine are much more stable. 

* fraube and Passarge, Ber., 1916. 48, 1692. 



CHROMOUS SALTS 


1075 


fill reducing agent. The solution is sometimes employed in gas 
analysis for the absorption of oxygen. It is found, however,^ 
that chromous chloride prepared by treating chronious acetate 
with hydrochloric acid is less stable than that prepared by reduc- 
tion of chromic chloride in solution with nascent hydrogen; 
the latter solutions, however, do not give complete absorption. 
Further, acid solutions of chromous chloride spontane- 
ously decompose with liberation of hydrogen : ^ 2Cr() HgO - = 
4- Hg. Recoura states that the solution may be obtained 
by adding a mixture of 3(X) c.c. of pure fuming hydrochloric acid 
with 200 c.c. of water to 300 100 grams of amalgamated granu- 
lated zinc and 50 grams of finely powdered potassiuni<lichromate 
in a flask of about 3 litres capacity. A violent action occurs, 
the li(|uid becoming first green, then sky-blue. 

Hydrates of chromous chloride are known as follows : OHgO, 
•lllgO (dark blue), IHgO (dark greeii),^ 3H2O, and 211./). With 
ammonia, white chromous chloride forms a violet triammine 
and an ashy-grey hexammine.^ 

The vapour density of chromous chloride at 13(X)^ was found 
by Nilson and Pettersson to be 7*8, considerably lower than is 
reipiired by the formula (-^2(14. At ICOO" the density is further 
reduced to 0 2, showing that probably at a higher temperature 
its density would finally reach 4*25, corresponding to Cr(32.® 

Vhromo\(S Bromide, CrBr2, is obtained by giuitly heating 
chromic ^irrjmide in hydrogen gas, and also l)y heating the metal 
in gaseous hydrobromic acid. It is a white, crystalline mass, 
yi<4ding a green basic chromic bromide on (*xposure to moist air. 

Chromous Iodide, Crig, is a crystalline mass obtained by heating 
chromium in gaseous hydriodic acid.^ 

(liromous Sulphide, CrS, is obtained by igniting chromous 
chloride in hydrogen sulphide, or by the long continued heating 
of chromic sulphide in hydrogen, and forms a black powder 
attacked only with difficulty by acids.® It may also be prepared 
by heating chromium to a high temperature in hydrogen sulphide, 

^ Anderson and Riffe, J. Iiul, Kiuj. Chf:m., 1910, 8, 24. 

’ Traube and Passarffc, lier.^ 1910, 49, 1092. 

» Recoura, Compt. reml., 1887, 100, 1227; Ann. Chim. Ph/in., 1887, (01, 

10 , 1 . 

* According to Werner’s views, these isomeric tetrahydrafes have tho 
formula* [Cr(OH,),]Cl, and [(’rCl{()H,) 3 j(JI,HjO n*sjx*ctively. See Knight and 
Rich. J. Chem. Soc., 1911, 99, 87. 

® Ephraim and Miilmann, Ber., 1917, 50, 529. 

• Journ. Chftn. Soc., 1888, 53, 830. 

’ Moissan, Compt. rend., 1881, 98, 1061. • Ibid., 1880, 90, 8l7. 



1076 


CHROMIUM 


when it is obtained in needles having a densitj of 4 * 08 , and suffi- 
ciently hard to scratch quartz.^ 

Chromoiis Sulphate, is prepared by dissolving 

the rnetal in dilute sulphuric acid. It is best obtained by dis- 
solving chrornous acetate in dilute sulphuric acid; on cooling 
it He[)arates in fine blue crystals isomorphous with ferrous 
sulphate. The aminoniacal solution absorbs oxygen, nitric 
oxide, and ac(‘-tylene. If potassium sulphate be dissolved in 
a cold saturated solution of the chloride, alcohol added until 
a precipitate begins to form, and the mass kept for some 
weeks in absence of air, fine blue rhombic prisms, having the 
composition K2S()4,(VS04,r)H20, and isomorphous with the 
corresponding ammonium salt, are deposited ; these soon become 
green in the air owing to absorption of oxygen. 

Chnmous Carhonale, CrCOg, is obtained by precipitating the 
chloride with potassium carbonate. A yellow to greenish-blue 
Jh-ecipitate is obtained in the cold, which becomes reddish-brown 
on warming. Several double salts of chrornous carbonate with 
the alk<ili carbonates have been prepared by the action of 
carbon dioxide on a mixture of solutions of chrornous acetate 
and the alkali carbonate.- These arc ])owerful reducing agents 
decomposing water at 10 (f with evolution of liydrogen. 

Chrornous Acetate is a red, crystalline prccii)itate obtained by 
addition of a concentrated solution of sodium acetate, saturated 
with carbon dioxide, to a solution of chrornous chloride, and 
wusliing th(‘ product with air-free water. 


CuROMir Salts. 

477 The normal chromic salts have a blue or violet colour, 
and allow red light to pass through their solutions. The cold 
solutions have a violet colour, which on heating changes to 
green; in some cases the solution immediately becomes violet 
on cooling, but in others this occurs only on keeping the cooled 
solution for some time. Only the violet solutions of the salts 
with oxy-acids yield crystalline salts, the green solutions deposit- 
ing an amorphous mass on evaporation. Many attempts have 
been made to explain th (5 changes which take place, and much 
light lias been thrown on the subject by the researches of Recoura 

1 Mourlot, Compt. rend.t 1895, 121, 943; Wedekind and Horet, Ber., 1915, 
». 105. 

» Badge, Compt rend,, 1896, 122, 474; 1897, 125, 1177; 1898, 12b, 1666. 



CHROMIUM AND THE HALOGENS 


1077 


and others. The salts which have been most closely examined 
are the chloride, bromide, and sulphate. 

A certain complexity is thus introduced into the chemistry 
of the chromic salts owing to the existence of isomeric com- 
pounds the constitution of which can best be investigated from 
the point of view of Werner’s ^ ideas of co-ordination compounds. 
Thus the cliloride •forms three distinct hexahydrates, and, the 
bromide two distinct hexahydrates. These ionise' differently in 
water, yielding solutions from which one-third, two-thirds, or 
the whole of the chlorine is precipitable by silver nitrate solution. 
The coiLstitution of such isomers will be discussed later. 

• 

Chromium and the Halooens. 

478 Chromic Fluoride, CrFg.— The anhydrous salt is obtained 
by passing hydrogen fluoride over heated chromic chloride, 
and sublimes at about 1200° in rhombohedra. Hydrates with* 
8’5, C, and 0 FfgO are known. The last named, [Ct( H2b)fi]K3,3HjjO, 
is obtained by adding ammonium fluoride to a cold solution of 
(chromic sulphate. It is sparingly soluble in water, but dissolves 
in hydrochloric acid, forming violet solution. When heated 
in the air it becomes green, and finally leaves a residue of 
chromium trioxide.- The salt is used to some extent in the dyeing 
of wool. 

Double fluorides with other metallic fluorides are known, as 
well as various complex salts.® In the case of the salt of the 
composition Cr 2 F. 2 Cl 4 , the fluorine is not precipitable by barium 
chloride.'* 

Chromic Chloride, CrCIg. — The anhydrous chloride is obtained® 
by heating metallic chromium or an intimate mixture of chromic 
oxide and carbon to dull redness in a stream of dry chlorine. 
It forms peach -blo.ssom coloured scales, which have a density 
of 2-7G. It volatilises at 10G5°, yielding a vapour of the density 
fi-l.So, the formula CrClg requiring 5-478, and CcgCle correspond- 
ing to a density twice jus great ; hence this latter compound cannot 
exist in the state of vapour. From 1190° up to 1 300° the density 

‘ For a detailed explanation of Werner’s theories, see A. Werner, “ Neuere 
Angckaunng auf dem Gebieie dtr anorganischen Ckcmie ” (4th edn., Braun* 
schweig, 1920). 

* Poulenc, Compt. rend.^ 1891, 116, 253; Fabris, Oazz. 1890, S0» 582. 

* Recoura, Compt. rend., 1913, 167, 1525; CosUchescu, Ann. Sci. Univ. 

1914, 8, 16. 

* Recoura, loc. cit. 

* From efiromit^, ace Badische Anilin- und Soda-Fabrik, Ger, Pat., 2ffl990. 


1078 


CHROMIUM 


is 5*5 (Nilson and Pettersson). Chromic chloride is almost 
insoluble in cold water, but it is readily ^pluble in presence of a 
very small quantity (less than 0-001 per cent.) of chromous 
cliloride, cuprous chloride, stannous chloride, or other reducing 
agents.^ The dilute solutions of the chloride have a violet colour, 
whilst the concentrated solutions or those containing a large 
exce,ss of acid are gre(;n. Recoura ® has shown that the heat 
evolved by tlie action of an equivalent quantity of soda is nearly 
50 per cent, greater in the case of the green solutions, and that 
as the concentration of the solution increases, the evolu- 
tion of heat gradually increases from the value for the violet 
solution ( f 22-2 (.\il.) to that for the dark green ( [- 31-5 Cal.). 
The colour of the solution at the same time gradually changes 
from violet to pun; green, thus indicating a gradual transition 
of the violet into the green modification. It has also been shown ® 
that ecpiilibrium between the green and the violet salts is set up 
^n solution, either salt leading to the same final conditions, 
depending on the concentration. In dilute solutions, the salt 
is almost all j)resent in the violet form, [Cr(H 20 )glCl 3 , whilst as 
the concentration increases the equilibrium shifts more and more 
in favour of the green. The equilibrium is reached very slowly 
at the ordinary temperature, but may be attained in 24 hours at 
84'’, Roth modifications have been isolated in the crystalline 
condition bv Recoura, and both have the same composition, 

The dark green chloride, [CVC1.2(If.2t))4]Cl,2l[oO, s(*parat(!S 
in small, emerald-green crystals when a current of hydrogen 
chloride is passed through a well-cooled, saturated solution 
of chromic chloride*. If the crude chloride be dissolved in its own 
w»‘ight of wattT, warmed for a few minutes to SCr, and then cooled 
to O’, the solution contains both the dark green and the violet 
salt, and on passing in liydrogeii chloride, only the latter separates 
at first, and may be obtained free from the green modification 
if it be immediately filtered off. It forms greyish-blue crystals 
which dissolve in water, forming the characteristic bluish violet 
solution. Intermediate between the violet hexahydratc and the 
dark green liexahydrate is the light green hexahydrate, 

1 Rohland, Ztit. anorg. Chrm., 1899, 21 , 87: lUl., 1908, 29 , 159; Unickrr, 
Zeit, Chtm., 1901, 36. 173. 

Recoura, /!»«. Chim. Phijs., 1887, [6], 10 , 5. 

• Roo/.ebooni and Olie, Proc, K. Akad, Wrttnsch. Amnlerdam, 1905, 8. GO; 
Zrit. anorg. Chan., 190G, 61 , 29; Werner and Gubser, Ber., 1901, 34 , 1379. 

* MKrehetti, (hzz., 1882, 22 , 375. 



CHROMIUM AND THE HALOGENS 


1070 


• 

[CrCl(H20)5]Cl2,H20, obtained by Bjerrum' by adding ether 
saturated with hydrogep chloride to the solution left after precipi- 
tating the violet salt with hydrochloric acid. It forms a light 
green, niicrocrystalline powder which is even more hygF(^sco})ic 
than the otlier isomers; on attempted drying it passes gradually 
into the dark green compound.^ The latter substance, however, 
when kept in a desiccator, loses two molecules of water, fonwing 
a tetrahydiate, wliilst a decahydrate is also known.® The con- 
stitution of these hydrates will be discussed in conjunction with 
that of the ammoniacal compounds of chromium (q.v.). (Vt- 
tain lower liydrates are stated to possess a red colour, us also does 
the compound CrCl 3 , 3 C 2 n 5 ,OH. • 

Basic chromic chlorides have been prepanul,'* flu; composition 
of which varies according to the method of preparation.^ 

Double compounds of an oxychloride of chromium with the 
chlorides of the alkali metals have been described, in which the 
chromium aj)peara to be quinquevaleiit. Thus tlie ])otassium 
compound, rrOCl 3 , 2 KCl, is formed as a garnet-red, crystalline 
precipitate when a solution of potassium chloride is added to a 
concentrated solution of chromic acid which has previously been 
ti'eated with hydrochloric acid at and the mixture saturated 
at 0’ with hydrogen chloride. Similar exanij)les have b(M*n 
prepared with quinoline and pyridine hydrochlorides.^ 

Chromic Bromide, C’rBrg. -- The anhydrous .salt is prepared in a 
similar wa}' to the chloride. It ff»rms alnio.st black, semi-metallic, 
transluc(*nt, h(*xagonal scales which in thin sections appear green 
by transmitted and red by reflected liglit. In its properties it 

‘ njurruiu, liXMl, 39 , 1597; Zcil. jihi/Mtkal. (%m., 1(X»7, 59 , 5SI. 
See nlHo W'cinlancl and Suliumann, Zrit. anorg. Chem., IJKW, 58 , 175. 

2 Vor dfiijlilf Halts (if thcHC chloridcfi, w*c I^arsHtm, Zdf. anorg. Chnn., 
1920, 110 , 15,3; W'uinland and Koch, 1904, 39 , 29t); Wcinland and 
8<diuniaiin, ibid., 1907, 40 , ,3707. 

’ Werner and (iubser, Brr., 1901,34, 1.379; Olic, Zdt. anorg. Cltan., 19(i7, 
53, 208. 

* Molierj;, J. ytr. Chf tn., 1843, 29 , 175; ,SchifF, Annalrn, 1802, 124 , 108; 
Olie, ZeiL anorg. Chem., 1900, 52 , 02. 

* For further information regarding the chromic chlorides, H(i*e ; Klias, Anal. 
Fu. Quim., 1918, 16 , 407; Foytis, Compt. rend., 1913 , 156 , 880; WyroubofT, 
ibid., 1913 , 156 , 1072; Hcydwciller, Zeit. antwg^ Chem., 1915, 91 , 06 ; Ijanib 
and Fonda, J. Amer. Chem. Soc., 1921, 43 , 1154;* Hojifgartner, MnnaUh., 1919, 
40 , 2,59; Baldwin, J. Amer. Leather Chem. As/ioc., 1919, 14 , 10; Kurilov, Kolloid 
Zeit., 1914, 14 , 171. 

* Meyer and Beat, Zeit. anorg. Chem., 1899, 22, 92; Wcinland and Fridrich, 

Ber., 1905, 38 , 3784; Wcinland and Fiedcrer, Ber., 1906, 37 , 4042; 1007, 40 , 
2090. • • 



1080 


CHROMIUM 


closely resembles the chloride, and dissolves easily in water, when 
a small quantity of chromous bromide,. or any other reducing 
agent, such as tinfoil, is present. Solutions of chromic bromide 
behave in an analogous manner to those of the chloride, and yield 
two isomeric salts, the one forming bluish-grey, and the other 
green crystals, both of which have the composition CrBrgjGHaO.^ 
Thei former has the constitution [Cr(H20)g]Br3 and the latter is 
[CrBr2(H2())4]Br,2H20. An octahydrate also exists. 

Chromic Iodide, CrTgjOHgO, forms unstable violet crystals.® 

Chromium and Sulphur. 

479 Cfnhmiimi Sesqumdpkide, or Chro^nic Sidphide, CrgSg. — 
This is obtained by heating chromium with sulphur, or by igniting 
chromic chloride, or tin; trioxide, in a current of hydrogen sul- 
phide. It forms either a blackish-grey powder with a metallic 
Justre, or an elastic mass having a density of 3 - 77 . AVhen 
heated in the air it burns with formation of the green oxide, and 
in chlorine yields sulphur chloride and chromic chloride. This 
compound cannot be prepared in the wet way, as soluble sulphides 
precipitate the hydroxide from cjirornic salts, with liberation of 
sulphur(‘tt(‘d hydrogen : 

‘ 2 (^r(’Ig 1 m^O | . 3 (NI 14)28 . . 2Cr(OH)3 + 6NH4CI -f 3H2S. 

Chromic Sulphafe, (^(804)3, is obtained by mixing equal 
parts of concentrated sulphuric acid and chromium hydroxide 
dried at KKf. The mixture is allowed to stand in a loosely- 
st()])pered bottle, wlien the green solution becomes blue, and in 
some w'eeks deposits a violet-blue, crystalline mass, which is 
purified by solution in water and precipitation with alcohol. 
Thus obtained, it is a violet, crystalline ])ow'der ; with less alcohol, 
blue octahedra containing 18 molecules of water are deposited. 
Chromic sulphate and the sulphates of the alkali metals form 
double salts, corresponding to the alums, to which the name of 
chrome-idums is given. 

Potassium Chromic Sulphate, K2S04,Cr(S04)3, 241120, or Chrome 
Alum is best obtained by the reduction of a solution of 
potassium dichromate, KjCrgO-, by adding the requisite quan- 
tity of sulphuric acid, artd passing sulphur dioxide through the 
solution : 

f Ha804 + 380* == K2SO4 + II2O. 

' Recourft, Cmipt, remi., 1800, 110, 1020. See also Hein, Ber., 1019. 52i [R], 195. 

> Iltglcy, J. .-Imer. Chem, Soc„ 1904, 28, 613. 



- CHROmra AND SULPHUR 


1081 


In place of sulphur dioxide any other easily oxidisable substance 
such as alcohol, etc., may be employed, but in tliis case more 
sulphuric acid must be added. Chrome alum is now obtained in 
large quantity as a by-product in the manufacture of artificial 
alizarin from anthracene, OJ4H10, in which the hydrocarbon is 
treated with a mixture of sulphuric acid and potassium dichromate, 
when anthraquinone, Ci4Hg02, is formed, and this is then sulijeqted 
to further treatment. The salt crystallises in large, dark purple- 
red, almost black octahedra, which, when seen by transmitted 
light, exhibit a ruby-red colour. One litre of water at 25 ^^ dis- 
solves 243-9 grams of the crystalline salt ; the solution has a dingy 
blue colour, with a tinge of red, which when heated to 7(C becomes 
dark green. After standing for several months, however, it returns 
to its ordinary colour (see below). Chrome alum is used in dyeing 
and calico-printing as well as in tanning. 

Ammonimn Chromic Sulphate, (Nll 4 ) 2 S() 4 ,Cr 2 (S(),).,, 241 f. 2 (), is 
obtained by crystallising a mixture of the two salts, or by reducing ^ 
ammonium dichromate in ])resence of sulphuric acid. The salt 
is l(‘.ss soluble than the potassium compound, and cryst/illises 
readily in fine ruby-red octahedra, which effloresce in the air. 

A number of other crystalline*^ double chromic sulphates, both 
anhydrous and hydrated, have been descril)e<l.' 

Action of Heat on Chromic Sulphate and its Double Awaits. — When 
the cold violet solution of chromic sulphate is boiled, there is 
produced a gre(*n solution which contains a considerable quantity 
of hydrogen ions ; evid(*ntly hydrolysis has taken })lacc, with t ho 
formation of soluble basic sulphates, probably of a complex, or 
even polymeric character. In such modified solutions, the sul- 
jihate is only partially ionised, since precipitation with barium 
chloride yields only a proportion of the anticijiated quantity of 
barium sulphate. It is impossible to a.ssign definite formul'o 
to such hydrolytic products, of which the conqMisition is doubtless 
more complex than [Cr40(S04)4]S04 or [Cr4(H2())n(f )H).,(*S04)4]S( )4 
as suggested by Recoura and others.^ Ry keeinng at the ordinary 

^ *Schrottcr, Pogg. Ann., 1841, 53, 513; Caratanjen, ./. pr. Cham., 1807, 
lOSt fiS; Pettemon, Bar., 1870, 9> 1559; Mcyeringh, ibid., 1S77, 10, 1940; 
Klobb, Compt. rend., 1893, 117, 31 1 ; BiiU. Soc. chini., 1803, [3J, 9, 003 ; Sommer, 
Zait. anorg. Chem., 1910, 94, 70; Kpbraim and Wagner, Bar., 1917, 50, 1088. 

* Recoura, Ann. Chim. Phga., 1895, [7], 4, 494*; Favre and Valnon, Compf. 
rent1.,lH12, 74,1023; Whitney, Zeit. physihd. Chem., 1890, 20, 40; Dougal, 

J. Chem. Soc., 1896, M, 1526; Colson, Cojnpt. rend., 1905, 140, 42, .372, 1451 ; 
141, 119, 331, 1024; 1906, 142, 402; 1907, 144. 79. 206, 325, 637; 146, 250; 
Bull. Soc. chim., 1907 [4], 1. 438, 889; 1908, [4], 8, 90; Ann. Chim. Phya. 
1907, [8], 12, 133. See also Meunier and Caste, Compl. rend., 1921, 172, 4488. 


1082 


CHROMIUM 


temperature, these green solutions are gradually converted into 
the ordinary violet solutions. The double salts, such as chrome 
alum, undergo an analogous reaction when the soliitioas are 
heated. 

(ireen Modificalions of Chromic Sidfhate- addition to the 
above compl(‘X basic sulphate, a solid green salt of the same 
empirical formula as the normal violet salt is known, which, 
however, possesses entirely different properties.^ This is obtained 
by heating the crystals of the violet salt, Cr2(S04)3,l8H20,^ at 90 ° 
until they have the composition Cr2(»S04)3,6H20.® The resulting 
green compound is readily soluble in water, but the freshly pre- 
pared soluAion shows the ordinary reactions neither of a chromium 
salt nor of a sulphate; further, it is capable of “masking” the 
sulpliato-ion of other sulphates to a coasidcrable extent."* In 
the course of a few days the solution is gradually transformed 
into that of tfie normal violet sulphate. In dry air, the green 
^suli)hate yi(‘lds 0r2(804)3, .31120, and becomes anhydrous at 400 °. 
According to Werner’s views, green chromic sulphate hexahydrate 
is formulated, [012(804)3(1120)3], whereas the corresponding violet 
compound is formulated 

[(>2(H20)J](804)3,^H20. 

It would be anticipated that intermediate salts of the 
form [C>2(lh/))(804)2](804),aq. and [Cr2(H20)2804](S04)2,aq., in 
which resp(‘ctively one-third and two-thirds of the sulphate an* 
j)recipital)le by barium chloride would bo found to exist. Colson's 
t)bservat ion ^ that sucli salts may be prepared does not, however, 
appear to have received definite confirmation. Recoura® has 
reported the existence of a lilac-grey sulphate which appears to 
consist of 1 mol. of the green salt and 2 mols. of the normal violet 
salt. At first, the sulphate ions corresponding to the green 
sulphate are masked, whilst those corresponding to the violet 
salt are precipitable ; 011 keeping, however, the latter sulphate 
ions also become masked. In explanation, the polymerisation 
of the green salt is put forward. 

^ Hecoiira, .l«w. Chim. 1895, 17J, 4 , *505. Sec also CubaTa and 

Marquina, Anal. FU. Qnim., 1017, 15 , 109; Shibata and Matsuno, J, Coll. Set. 
Tokyo, 1920, 41 , 0. 1. 

• But »eo StMi^chal, Compt. rend., 1913, 166. 552. 

• Wyrouboff, Bull. Sor. chim., 1902, 27 , 070; Colson, Compt. rend., 1907, 144 , 
200; Kling, Flonuitin, and Huchet, ibid., 1914, 159 , 60; S^ncchal, ibid., 1914, 
169 . 243. 

* Rocoura, Compt. rend,, 1022, 174 , 1460. • Colson, loc. cit. 

* Rocouro, Compt. rend., 1920, 170, 1494. iSco also ibid., 1919*169, 1163. 



1083 


CHROMIUM AND NITROGEN 


Although acid chromic sulphates are known, ^ Recoura has 
shown - that when the green sulphate combines with one, two, or 
three molecules of sulphuric acid or a sulphate, substances are 
obtained from which no barium sulphate can be obtained by ])reci- 
pitation in the cold, neither are chromium ions present; tliese 
may be regarded as the complex acids, chromosulphuric acid, 
[Cr2(^04)4]H2, cliromodmdphuric acid, [Cr2(S04) JIf4, and chramo- 
trisiilphuric acid, [Cr2(S04)g]Ifg, or their salts. These are stabl(^ 
in dry air, but in solution tliey gradually undergo conversion into 
the normal chromium salts. The alkali chromosiilphates are 
isomeric with the chrome alums, from which they may be readily 
obtained by heating the crystals of the latter for some time at 
ixr. Potassium ckromosulphale, [Cr2(S04)4]K2,4If2(), is thus 
obtained as a green salt which dissolves slowly ])iit completely in 
cold water. 

The colloidal character of the chromosnlphuric acids has been 
demonstrated by Strong.^ 

An analogous series of acids has been prepared by the union 
of the green chromic sulphate with chromic acid. Tliese liave 
the compositions [CV2(‘^^4)3>^r^4]H2» [^**2(804)3, (Cr04)2]lf4, and 
[(>2(804)3,(Cr04)3]Hg, and are called the chromosulphochwmic 
acids} 

Various complex chromiseletiales have also been prepared.* 

fhlROMIUM AND NiTROOEN, PhoSPHORU.S, AND lioRON. 

480 Chromium Nitride, CrN, is formed by the direct union of 
its elements at a red heat ; ® and also by passing ammonia over 
heated chromic chloride. It is a brownish-black powder, which 
takes fire and burns when heated to 200"" in the air or in oxygen. 
Cold chlorine does not act upon it, but when heated in this gas 
small explosions first occur owing to formation of nitrogen chloride, 
and finally chromic chloride remains. It does not undergo change 
on ignition in hydrogen or in aqueous vapour, and is not attacked 

^ Weinland and Krebs, Zcil. anorg. Chem., 1906, 157. 

* Strong, Compt, rend., 1910, 150 , 1172. These cuin|)ound 8 , particularly 
tiiose composed of 1 mol. of (> 1 ( 804 ), with 4, 6 , and 0 inols. of HjSOi, can there- 
fore no longer be regarded as com{)ounds of the type called “ sulphochromio 
hydroxide ” by Kecoura, loc. cit.. See also olvert and Ewan, Proc. Chem. 
Soe., 1896, 12 , 160. 

» Recoura, BuU. Soc. chim., 1897, [3J, 17 , 934; Ann. Chim. Phj«., 1895, 
[7], 4 , 494. 

^ Meyer, Ztit. anorg. Chem., 1921, 118 , 1. 

* Brieglietf and Geuther, AnnnUn, 1862, 123 , 239. * 



[)S4 


CHROMIUM . 


y potassium hydroxide, hydrochloric acid, or nitric acid. Con- 
jntrated sulphuric acid converts it. into the sulphates of 
nmonium and chromium : 

2 CrN + 4H2SO4 = Cr2(S04)3 f (NH4)2S04. 

Chromic Azide^ Cr(N3)3, has been obtained^ as well as its 
uridine compound, Cr(N3)3,3Py, which is explosive, and the 
impound CrNgjSNaNg. Basic salts are known. 

Chromic Nitrate, Cr(N03)3,9H20, is obtained by dissolving the 
^droxide in nitric acid; it crystallises in oblique, purple-red 
isms. The solution, like that of the sulphate, turns green on 
)iling, apd on evaporation dries to a green, amorphous mass, 
le green solution immediately becomes violet on cooling. 
Chromium Phosphides. — By heating finely divided chromium 
th red phosphorus in a sealed tube, the phosphide, Cr2p3, is 
tained ; when this compound is heated in hydrogen, chromic 
osphide, CrP, is produced.^ Both arc grey substances which 
3 insoluble in acids. 

Chrgmic Hypophosphite, Cr(H 2 p 02 ) 3 , 2 H 20 , is a green mass, 
tained by dissolving freshly prepared chromic hydroxide in 
pophosphorous acid.^ • 

Ihromic Phosphates. — When a solution of sodium hydrogen 
osphate is added to an excess of chrome alum solution a 
^atinouB precipitate is formed which on keeping for forty-eight 
lUTs is transiormed into dark violet crystals of the phosphate,^ 
cP04,fill20 *, more prolonged contact with the precipitant yields 
green, amorphous tetrahydrate. By boiling the violet salt with 
ivater, the tetrahydrate is obtained in crystalline fonu, whereas 
treatment with acetic anhydride yields a dihydrate. On ignition 
of a hydrate, the anhydrous salt is obtained as a brown, amorphous 
powder. If chromic hydroxide is dissolved in excess of pliosphoric 
acid and the solution evaporated and heated to 316 °, chromic 
metaphosphale, Cr(P03)3, is obtained, which has been employed 
as a green pigment. Chromic pyrophosphate in alkaline solution 
gradually yields salts of the type M'(CrP207),MH20 (chrmni- 
pyrophos^phates)/* 

' Olivcri Mai)dal&, Oazz., 1019, 49. ii, 43; 1922, 52, i, 112; Wohler and 
Martin. JJff., 1917,60, 595. , 

* Dicckiiiann and Hanf, Zeit. anorg. Chm., 1914, 86, 291. See also Granger, 

rend., 1897, 124, 190; Maronneau, ibid., 1900, 130, 056. 

* Mawrow and Zonew, Zeit. anorg. Chem., 1915, 98, 311. 

* Schiff, Zeit. anorg. Chew., 1905,48,304; Joseph and Rae, Trans. Chtm. 
Soc„ 1917, Ul, 196. 

> ]!osenheim and Triantaphyllides, Rer., 1915, 48 , 582. 



Chromium Arsenides, — The compounds ^CrgAsg and CrAs have 
been prepared similarly to the phosphides.^ An arsenite^ arsenates, 
and a metantimoncUe have been described. 

Chromium Borides. — Two chromium borides have been prepared 
by heating the elements together in the electric furnace ; ^ these 
have the formulae CrB, and Cr 3 B 2 , and are grey, crystalline 
substances. 


Chromium and Carbon and Silicon. 


481 Chromium Carbides. — These fall into two groups:® (1) 
those containing up to 8*5 per cent. C, and ( 2 ) those containing 
a larger proportion of carbon. The former are completely soluble 
in hot 24 per cent, hydrochloric acid; the latter only partially. 
The carbide CrgCg forms silvery crystals of density 6*9. It melts 
at 1665® and is unattacked by aqua regia. The carbide CrgCo is 
darker in colour, has a density 6 * 68 , and melts at about 1890® with 
partial decomposition to Cr 4 C 2 and graphite. Moissan^ has 
described carbides of the composition CrgCg and Cr 4 C respectively. 

Chromium Carhomte . — Chromic hydroxide absorbs carbon 
dioxide from air, yielding a compound to which the formula 




^/Cr2(OH)4‘OxY^Q iQtj Q 


has been given.® 

Cyanogen Compounds of Chromium. — Chrmnous cyanide is 
unstable in air. Potassium chrotnocyanide, K4[Cr(CN)c],2Il20, is 
obtained by the action of potassium cyanide on chromous acetate, 
and forms blue crystals. It is soluble in water, and on exposure 
to air passes into 

Potassium Chromicyanide or Potassium Hexa-cyano-chromite, 
Kj[Cr(CN) J, light yellow, monoclinic crystals, obtained also by 
pouring a solution of chromic acetate into a boiling solution 
of potassium cyanide. 

A number of chromicyanides of other metals have also been 
prepared.® 


* Dieckmann and Hanf, Zeit. anorg. Cketn., 1914, 86, 291. 

* Tucker and Moody, Journ. Chtm. Soc., 1902, 10; Binel du Jassonneix, 

%mpt. rend., 1900, 143 , 897; Wedekind and Fctxer, Ber., 1907, 40 , 297. 

* Ruff and Foehr, Zeit. anorg. Chem., 1918, 104 , 27. 

* Moiaaan, Compt. rend., 1894, 119, 185. 

* Jovitschitech, Compl. rend., 1914, 158 , 872; Helv. Chim. Acta, 1920, 8. 40. 

* Fischer and Benzian, Chem. Zeit., 1902, 86 , 49; Cniser and Miller, J. Amer. 

7km. i8oc., 1«)6, 88, 1132. * 



1086 


CHROMIUM 


Chromic Thiocyanate, Cr(SCN)3. — Chromic hydroxide dissolves 
in thiocyanic acid solution yielding a greenish-violet solution 
which when concentrated over sulphuric acid dries to a dark-green 
amorphous, deliquescent mass. It forms a series of characteristic 
double salts, which are regarded as salts of complex acid radicles 
containing chromium.^ The complex ions present in such solu- 
tions are : 2 [Craqe]^+^ [Cr aq5(CNS)]++, [Cr aq4(CNS)2]^ 
[Cr aq3(CNS)3] (non-electrolyte), [Craq2(^NS)4]", [Craq(CNS)5]“ “» 
and [Cr(CNS)Q] . Of particular importance is the potassium 
salt of the last-mentioned ion. 

Potassium Chromithiocyanate or Potassium ^Jlemthiocyano- 
chromite, K3[Cr(SCN)e],4H20, is formed by heating a moderately 
concentrated solution of 6 parts of potassium thiocyanate and 
5 parts of chrome alum for two hours at the boiling point ; the 
sulphates formed are precipitated by the addition of alcohol, the 
filtrate evaporated, and the residues recrystallised from alcohol. 

‘ It forms tetragonal, almost black crystals, which appear ruby-red 
by transmitted light, and dissolve very readily in water and 
alcohol, forming wine-red solutions. It is decomposed by alkalis 
and warm hydrochloric acid. The solution gives precipitates 
of analogous compounds with le&d and silver salts.® 

Chromium and /Si 7 fcow.— Several silicides of chromium have 
been described ; these are all prepared by heating chromium with 
silicon, or a mixture of silica and chromic acid with carbon or 
copper and aluminium in the electric furnace. In this way the 
compounds SigCr, SigCrg, SiCrg, and SiCrg have been obtained.* 
The compound, Si2Cr3, is also formed when silicon chloride is 
heated for some time in contact with chromium.® 

Chromium and Tungsten. — Chromic tungstates and derivatives 
of tungsto-chroraic acid are known.® 

^ Rosier, Annalen, 1867, 141, 185. 

® Bjerrum, Det. K. Danske Vidensk. SeUkaha Skrifter, Nat. Ma*h.y 1916, 7, 
60; Zeit. anorg. Chm., 1921,118, 131; 119, 39, 54, 179; see also Bohart, 
J. Physical Chem.y 1916, 19, 637 ; Scagliarini, AtH R. Accad. Linceiy 1918, [5], 
27, i, 442. 

* Rosier, Annakriy 1867, 141, 186; Rosenheim and Cohn, Zeit. anorg. 
Chem.y 1901, 27, 293. 

^Moissan, Compt. rend.y 1896, 121, 621; de Chalmot, Amer. Chem. J., 1897, 
19, 69; Zottel, Compt. rend.^ 1898, 128, 833; Lebeau and Figueras, ibid., 1903, 
136, 1329. 

® Vigouroux, Compt. rend., 1907, 144, 83. 

* See Kantschoy, J. Russ, Phys. Chem. Soc., 1914, 46, 729. 



AMMONIACAL COilPOUNDS OP CHROMIUM 


1087 


Ammoniacal and Other Complex Compounds op Chromium. 

482 Tlie salts of chromium readily combine with ammonia or 
substituted ammonias to form complex salts. These contain, for 
each atom of chromium, up to six molecules of ammonia, and 
often other elements or groups of elements united with the metal 
to form a complex radicle, which usually acts like a uni-, bi-,*or 
ter-valent metal, but may in other cases have an acid function, 
or be neutral, that is, the complex is not ionised in aqueous 
solution. These complex salts are capable of undergong numerous 
double decompositions, giving rise to a large number of deriv- 
atives, among which many cases of isomerism occur. Analogous 
compounds are formed by other metals, in particular, cobalt and 
the metals of the platinum group, and these are to be regarded 
as included in the general statement which follows. 

These compounds do not give the ordinary reactions of the 
metal, and in many cases this is also true of some or all of the acid 
radicles which they contain. This is accounted for, as already 
explained (pp. 37-^38) by supposing that, in these latter cases, the 
acid radicle forms part of the pomplex group containing the 
metal, whereas those acid radicles which give the ordinary re- 
actions are not contained in this group. 

The constitution of these complex radicles is still under dis- 
cussion, two different views being held. According to one of 
these (Blomstrand, Jorgensen) the metal retains its characteristic 
valency in all the compounds, the molecules of ammonia being 
attached to the metal in open chains by virtue of the pcntavalent 
character of nitrogen. That portion of the acid radicles which 
does not retain its ordinary properties is directly connected with 
the metal, whilst the other portion is combined with nitrogen. 
Water may take the place of one or more of the ammonia groups, 
the oxygen atom being supposed to be quadrivalent. The com- 
pound Cr(NH 3 ) 5 Cl 3 , in which only two of the chlorine atoms are 
precipitable by silver nitrate in aqueous solution, would thus 
receive such a constitutional formula as 


a 


/ 

ClNHo-NH«NH3-Cr-NH,"NHoa. 


The existence of isomerides may be readily expressed by a varia- 
tion in the arrangement of the various groups. 

The second and more satisfactory view is that proposed Jby 
VOL. n. (n.l s 




1088 CHROMIUM 

Werner , 1 who classifies these compounds op the theory of principal 
and supplementary valency, an account of which has already 
been given (p. 37 ). The theory has naturally undergone modifica- 
tion in some details as experimental evidence has accumulated. 
According to this theory, in the compound [Cr(NH3)JCl3, for 
example, the ammonia groups are all united or co-ordinated with 
the chromium atom by means of its supplementary valencies, 
whilst the chlorine, according to Werner’s more recent view, is 
combined with the complex radicle as a whole, without being 
attached to any particular atom in it, and is said to be in indirect 
combination with this radicle. The ammonia groups may be 
either pe-rtially or entirely replaced by acid groups such as 
Cl, NOg, SON, etc., yielding a large number of compounds, which 
usually contain six groups in the complex radicle, although in 
some cases only four such groups can be present. The valency 
of the complex radicle is easily ascertained from the number 
and character of the groups within it. If the number of univalent 
acid radicles be less than the principal valency of the atom of 
the metal, the complex radicle is basic and capable of combining 
with a number of acid radicles equal to the difference. If, 
however, it be greater, the complex radicle has an acid character 
and is capable of combining with univalent basic radicles equal 
in number to the excess of the number of uniyalent acid radicles 
over the principal valency of the metal. When the number in 
the complex radicle is equal to the principal valency of the metal, 
the compound is a neutral substance. 

This is illustrated in the following series of compounds derived 
from tervalent chromium, X representing a univalent acid and 
K a univalent basic radicle : 

[Cr(NH3)e]X3 [Cr(NH3)3(SCN)3] 

[Cr(NH3)5(SCN)])Xg [Cr(NH3)2(SCN)J E 

[Cr(NH3)4(SCN)J X [Cr(NH3)(SCN)6] Eg (unknown) 

[Cr(SCN)e]E3 

As already explained, the electrolytic dissociation and the 
reactions of these compounds in solution correspond with these 
formulae. 

^ Annaknf 1902, 22St, 261 ; Neuere Anschauungen auf dem Qd)iek der 
anorganischen Chemie (Vieweg & Sohn , ' Braunschmigt 1920). See also 5ef., 
1 907, 40, 15, whore an account of the literature on the subject is given. Recent 
investigations on the subject are described in papers by Jovitschitsch, Monatsh.t 
1913,84,225; Dubsky, pr. Chem.t 1914, [2], 80, 61; Werner and others, 
Annalen, 1914; 406, 212 ; 406, 261; Mandal, Ber., 1916, 49, 1307; Briggs, 
Joum. Chem. Soc.^ 1919, 116, 67 ; Mandal, Bcr., 1919, 62, [B\ 330, 489;Frowein, 
ZtiU anorg. Chem., 1920, 110, 107. 




' AMMONIAC^. COMPOUNDS OP CHROMIUM 1089 

- , - : 

In many cases, hydrated compounds of chromium may be 
formulated in a similar manner; instances have already been 
quoted in the cases of chromous chloride, chromic chloride, and 
chromic sulphate; Werner’s formulation is in agreement with 
the behaviour of these substances in solution, when the whole 
*or part only of the chloride or sulphate radicles is ionised. 
Examples may also be quoted of cases in which the ammonia 
groups in the complex radicle are only partially replaced by the 
“ aquo ” group, (OHg), thus : 

[Cr(NH3)elCl3; [Cr(OH3)(NH3)ja3, etc. [Cr(OH3)elCl3. 

The bluish-violet chromic chloride hexahydrate is, ‘of course, 
the final stage in such a substitution. 

Compounds are also known, derived from the bivalent atom of 
the metal, in which the complex radicle contains six univalent 
acid groups, and is therefore capable of uniting with four basic 
radicles, examples being potassium chromocyanide, [Cr"(CN)Q]K4, 
and potassium ferrocyanide, [Fe''(CN)g]K4. 

The ammonia compounds are known as the ammines^ this 
spelling of the word being adopted to avoid confusion with the 
organic amines, which have an entirely different constitution. 
The nomenclature of these compounds was originally founded 
on the colours characteristic of the various compounds, terms 
such as roseo-, praseo-, luteo-, croceo-, fusco-, xantho-, etc., 
having been employed. A much more rational method is due to 
Werner, the principle of which is that the names of the various 
groups contained within the complex radicle precede that of the 
metal, whereas those of the external group follow it, this being 
nothing more than an adaptation of the nomenclature frequently 
employed for organic compounds. 

Thus the well-known cobalt compound, [Cl(NH3)5Co]Cl2, 
formerly known as purpureocobaltic chloride, receives the name 
chloro-pentammine-cobaltic dichloride, whilst the compound 
[(OH2)(NH3)5Co]Cl3 (roseocobaltic chloride) becomes aquo- 
pentammine-cobaltic trichloride,^ 

^ Some of the metals from more than one series of complex derivatives, 
corresponding to\he different series of simple salts. In order to distinguish 
these compounds, a special nomenclature has been introduced by Werner 
(i^eitere Anschauungen, 1020, p. 92), according to which the valency of the 
metal is designated by the letters a-, o-, i-, e-, an-, on-, in-, en-, for uni-, bi-, 
ter-, quadri-, quinque-, sexa-, septa-, and octa-valent elements respectively. 
Thus amon^ the complex halogen derivatives of the platinum meta|^, the 
compound K|[PtCl 4 ] is known as potassium tetrachloroplatinoate, K,[RhCl 4 ] 




1090 


CHROMIUM 


Only a few examples of the chromium ammines are here 
described.^ Amongst salts containing the chromium complex 
as the anion are : 

Q-(Hem)ammino-chr(mium salts, [Cr(NH3)JX^3 (luteo-salts), 
which are prepared by addition of ammonium chloride and 
ammonia to a solution of chromous chloride and allowing the 
cold mixtures to oxidise slowly.^ Other members of this group 
are the ammino-aquo-chromium salts, in which some of the 
(NH3) groups are replaced by (OHg) groups. 5 -Ammino-l- 
aquo (or aquopentamminej-chromium salts, formerly called 
roseo-salts, are included. 

1- A(ddo-p-ammino-chr(mium salts, e.g., [CrC^NHalgJClg (pur- 
pureo-salts). This compound is obtained, together with its mono- 
aquo-substitution derivative, [Cr(OH2)Cl(NH3)4]Ol2, by the 
action of liquid ammonia on violet chromic chloride. This 
group includes thiocyano-, nitrito-, nitrato-, etc., salts. 

2 - AcidoA-ammino-cliTomium salts, e.g, , [CrClg en2]Cl,® obtainable 
in several different' ways. 

^-Acido-^-ammino-chromium compounds, e.g., [CrCl3(NH3)3], 
are not ionised in aqueous solution. The compound given as an 
example of this class may be pr(Jpared by adding the compound 
Cr04‘3NH3 (see p. 1073 ) to cooled concentrated hydrochloric 
acid, filtering from a bluish-green precipitate, keeping the filtrate 
for two days, and separating the greenish-blue precipitate. 

Compounds containing the chromium complex as the kation. 
4 :-Acido- 2 -ammino-chromites, e.g., [Cr(SCN)4(NH3)2]R'. — When 
finely divided potassium dichromate is added to fused ammonium 
thiocyanate, ammonia is evolved, and the whole mass solidifies. 
When this is treated with water, filtered, and a few lumps of 


as potassium hexachlororhodi’ate and Kj[PtCl8] as potassium hexachloro- 
platineate. This system has been adopted to some extent in Germany, but 
has not come into general use in England. The neutral compounds are named 
as in the following examples: [Co(NOg) 3 (NH,) 3 ], trinitrotetramminocobalt ; 
[PtClj(NHa) 2 ], dichlorodiamminoplatinum. 

^ For a full account of the compounds which have so far been prepared, 
reference must be had to Werner, Neuere Anschauunqen, 1920; Abegg’s 
“ Handbuch dor anorganischen Chemie, Vol. IV, (1), 2nd half; the literature 
quoted on page 1088, and the following papers: Weinland and Reihlen, 
Zeit. anorg. Chem., 1913, 426; Ber., 1913, 46, 3144; Weinland and 

Ensgraber, Zeit. anorg. Chem.^ 1913- 84, 368; Barbieri, Atti R. Accad. 
Lincei, 1915, [5], 84, i, 910; Weinland and Spanagel, Ber., 1916, 49, 1003. 

* Jorgensen, J. pr. Chem., 1884, [2], 30, 1. 

* The symbol “ en ” is used for the ethylenediamine group, 

corresponding to two ammonia groups. t 



ISOMERISM OP COMPLEX CHROMIUM COMPOUNDS 1091 


ammonium chloride are added, garnet-red scales of the salt 
[Cr(SCN)4{NH3)2]NH4 separate. 

^-Acido-hmnmino-chromiles are unknown. 

Q-Acido chromites, M'3[CrX6], no longer “ ammines ” since they 
contain no ammonia groups, include such compounds as the 
chromicyanides, chromioxalates, chromisulphates, etc. 

A number of compounds have been described which contain 
organic amines, particularly ethylenediaminc, and compounds 
such as pyridine, in the complex radicle in place of ammonia. 


Isomerism of Complex Chromium Compounds. 

A number of different types of isomerism ^ are known to which 
the complex chromium compounds are subj ect . It will be possibl e 
to mention each of these only very briefly. 

1 . Polymerism. — Certain complexes may be regarded as , 
polymers of simpler ones, although widely different in constitu- 
tion. Thus there are seven distinct compounds which possess 
the composition Cr(NH3)3(SCN)3 or some multiple thereof. 

2 . Co-ordination womemm.— Coinpoimds with the same mole- 
cular formula may possess entirely different structural formulse 
from the point ( of view of their ionisation and co-ordination 
relationships, e.g., 

[Co(NH 3 )e]"^*[Cr(CN)er” and [Cr(NH3)3]”' [Co(CN)e]^" i 

[Cr(NH3)6]-[Cr(C204)3] and [Cr(NH3)4(C304)]‘[C\(C304)2(NH3)3]. 

3 . Hydrate isomerism, 'as exhibited and already described in 
the case of chromic chloride, of which three isomeric forms 
exist, namely, [Cr(OH2)o]Cl3 (violet), [CrCl{0H2)5]Cl2,H20 (light 
green), and [CrCl2(0H2)4]Cl,2H20 (dark green). 

4 . Imisation metamerism, when different ions are furnished 
in aqueous solution, e.g,, the sulphate, [Co(N03)(NH3)q]S 04, and 
the nitrate, [Co(S04)(NH3)5]N03. 

5 . Salt isomerism in which the differences exhibited are those 
between the salts of tautomeric acids, e.g., nitrito- (-O-NiO) and 

nitro- groups. 

6 . Structural isomei'ism, e.g., [(NH2)2CS]2’Co(SCN) 2 and 

(NH4SCN)2*Co(SCN) 2, in which case the distinction is that 
between the thiocarbimido- and thicyano-groups. 

^ This subject is discussod at some length in Weraer’s ” Nemre An^clmU’ 
ungtn," 1920, p. 327 et seq. 




1092 CHROMICM 

: 1 c i 

7. Co-ordinative position isomerism^ e.g., 

[c1(NH3)3Co<2^Co(NH3),Ci]c1j and 

[(NH3)^Co^Q^^Co(NH3)2Cl2jci2. A similar difference exists 

between symmetrical and unsymmetrical dichloroethane, 
CH.Cl CHgCl and 

8. Geometrical isomerism. — ^As an example, complex radicles 
of the type [ME 4 Xa] may be cited. The metal atom is regarded 
as situated at the centre of a regular octahedron the corners of 
which are occupied by the co-ordinated groups. Two isomerides 
are then possible — the symmetrical or trans-form in which the 
groups X, X, are situated at opposite ends of a diagonal of the 
figure, and the asymmetrical or m-form, in which they are at 
adjacent corners, thus : 


11 


R. 




R. 


,R 


RT 


R 


"X 


R" 


■R 


m-Form. Asymmetric. frows-Form. Symmetric. 

Of the same class are the platinous complexes, e.g.j 


R X 

\/ 

Pt 

/\ 

R X 


and 


R X 

\/ 

Pt 

/\ 

X R 


9. Optical isomerism. — There is no difference between the 
configuration of a trans-form and its mirror-image, but in the 
case of a as-form it is possible to obtain two distinct configurations 
which are not identical, but bear to one another the relationship 
of mirror-images, thus : ^ 



» The symbol “ en ” is used for ethylenediamine, which 

corresponds to two ammonia groups. 



SETEOHON AND ESTIMATION OF GHROMIUU lUVi* 


10 . Valency isomerism, e.g., 

Cr[(NH,)s]X3 • Cr[(NH3)JX3 

^OH and \o--HX 

Cr[(NH3)6]Xj Crt(NH3)5]X3 

rhere certain of the molecular components may be linked to a 
entral atom by either of the two types of valency (principal* or 
uxiliary). 

Detection and Estimation of Chromium. 

483 Chromous salts in solution are unstable, readily becoming 
jonverted to green chromic salts with evolution of hydrogen; 
he solutions are therefore strong reducing agents. Chr&mic 
salts and the corresponding sesquioxide have a characteristic 
jreen or violet colour ; with borax or microcosmic salt, both in 
oxidising and reducing flames, an emerald-green bead is produced, 
[n aqueous solution, ammonia ^ gives a gelatinous precipitate of 
the hydroxide, Cr(OH)3, which partially dissolves in excess of 
ammonia, yielding a violet solution which contains complex 
ammines ; complete precipitatiqn of the hydroxide is, however, 
attained from boiling solutions. By substitution of sodium or 
potassium hydroxide for ammonia, a solution of the chromic 
hydroxide, at first precipitated, in excess of the alkali is obtained ; 
this is regarded both as a solution of a chromite and as a colloidal 
solution. On boiling, almost complete precipitation takes place : 
Cr(OH)3 -f KOH ^ 2H2O -f CrO(OK). 

Oxidation of green chromic salts to chromates having a char- 
acteristic yellow colour is readily effected. For qualitative 
purposes, it is sufficient to boil a solution of the salt with excess of 
sodium peroxide, sodium hypochlorite, or with nitric acid and 
lead dioxide, 2 but oxidation by fusion with a mixture of sodium 
carbonate and sodium peroxide conveniently admits of quantita- 
tive application. 

The chromium salts do not impart any colour to the non- 
luminous gas flame. The spark spectrum of the metal is a com- 
plicated one, the brightest lines being 6208*8, 6207*4:, 6204*7 in 
the green, and 4289*9, 4276*0, 4264*6 in the dark blue.® 

^Ammonium sulphide, or a mixturo of potassium iodide and potassium 
iodate, may also be employed. 

• Temi, Qazz., 1913, ii, 63. See also Browning, J. Amer. Chem. 80 c., 1921, 
43 , 114. 

*The infra-red speotrum has been examined by*Bandall and Barker, 
Astrophys. J., 1919, 48 , 54, and the J-ray spectrum by Fricke, PhysicMBev., 
iflf. 202. 




1094 


CHROMIUM 


( * 

Chromates.— 11 ^ after fusion of a chromic compound with 
sodium carbonate and sodium peroxide pr potassium nitrate the 
melt is dissolved in water, the whole of the chromium is present, 
in solution as yellow sodium chromate, Na2Cr04 ; on acidification, 
such a solution darkens in colour owing to production of the 
dichromate, NagCrgO^. The reverse reaction, of course, takes 
place when alkali is added to solutions of dichromates. From 
solutions of soluble chromates, barium chloride and lead nitrate 
precipitate the respective chromates which are yellow in colour ; 
mercurous nitrate yields brown, amorphous, mercurous chromate 
which on boiling is converted into a red, crystalline form, some 
basic chromate also being produced. With normal chromates 
silver nitrate yields a brick-red precipitate, Ag2Cr04, whereas 
cold concentrated solutions of dichromates yield Ag2Cr207) which 
is darker in colour. In presence of hydrogen sulphide, sulphurous 
acid, alcohol,^ etc., chromates suffer reduction to green chromic 
salts, whilst in presence of hydrogen peroxide they are oxidised 
to perchromates. The latter reaction is very sensitive when 
carried out in dilute solutions in presence of sulphuric acid, blue 
perchromic acid being formed; although unstable in aqueous 
solution, the blue compound may be extracted with ether, in 
which it somewhat less rapidly decomposes. Another charac- 
teristic reaction of the chromates consists in the formation of 
red vapours of chromyl chloride, condensing to a red liquid, when 
a chromate is heated with a chloride and concentrated sulphuric 
acid. An intense blue coloration is, moreover, produced by 
a-naphthylaraine in presence of tartaric acid,^ 

Estimation of Chromium . — Chromium may be estimated 
gravimetrically — ^in the case of the chromic salts as chromic 
oxide, and in the case of the chromates as mercurous chromate — or 
volumetrically by taking advantage of the oxidising action of 
chromates on ferrous salts, potassium iodide, etc. In view of 
the ease with which chromic salts are converted into chromates 
and vice versd, the choice of the method suitable in any particular 
case is of the widest. 

In order to estimate chromium gravimetrically in the chromic 
salts, a hot solution is precipitated with a very small excess of 
ammonia,® the solution ‘boiled till the free ammonia is nearly 

' For the photochemistry of this reaction, see Plotnikow, Zeit. mss, 
Photochem., 1919, 19, 40. 

* Van Eck, Chem. WeekbM, 1915, 12, 6. 

* The addition of 2 c.c. of 2^ per cent, tannic acid solution ^to the liquid 
before the addition of the ammonia greatly facilitates the subsequent filtration. 



DETECTION AND ESTIMATION OF CHROMIUM. 1096 


all expelled, and the precipitate well washed with hot water, 
dried, ignited in a platinum crucible,^ and weighed. Calcium 
and magnesium salts, if present, take part in the reaction with 
formation of insoluble chromites, but it has recently been stated ® 
that these elements may be removed by washing the precipitate 
with a boiling 5 per cent, solution of ammonium nitrate. 

In the chromates, the gravimetric estimation of chromiilm is 
usually carried out by addition of mercurous nitrate to a solution 
made slightly acid with nitric acid, and boiling the mixture. 
The red, crystalline precipitate of mercurous chromate so ob- 
tained yields on ignition a residue of chromic oxide. Methods 
depending on the precipitation and weighing (as sudh) of silver, 
barium, and lead chromates have also been employed. 

Soluble chromates may be estimated volumetrically by direct 
titration with ferrous salts, using potassium ferricyanide as an 
external indicator, or by an iodometric method, 

K2Cr207 + 6KI + UHCl = 8Ka + 2Cra3 + 7 H 2 O + 3 I 2 , 

the liberated iodine being titrated in the usual way with sodium 
thiosulphate solution. The 'valuation of chrome iron ore is 
commonly carried out by this method, the mineral being 
previously fused with an alkali and an oxidising agent, in order 
to convert the chromium into a soluble chromate. 

It is possible to differentiate between chromate and dichromate 
when present together in solution by an acidimetric method.® 

Atomic Weight of The older atomic weight 

determinations gave varying results, owing to the inexact 
methods and impure material employed. Berlin* obtained 
the number 52-5 by the analysis of silver chromate, whilst 
Kessler obtained 52-3 from the determination of the equivalent 
quantities of potassium dichromate and potassium chlorate 
required to oxidise arsenious oxide to pentoxide.^ Siewert® 
found 52*07 by the analysis of violet chromic chloride and of 
silver dichromate, and Baubigny’ got 52*14 by the conversion 
of chromic sulphate into the trioxide. Rawson,® by the conver- 

1 Rothang, ZeiLanorg. Chem,, 1913, 84, 166; Schwarz, Helv. Chim. Acta^ 
1920, 3, 33P. It is necessary to avoid formation^ not only of complex ammines, 
but also of chromic chromate. 

* Toporescu, Compt. rend., 1921, 172, 600. 

* Sacher, Farhenzeit., 1916, 22, 213. 

* Annakn, 1844, 68, 207; 1846, 60, 182. 

» Pogg. A^n., 1861, 118, 137. • Zeit. ges. Naturwiss., 1861, ^7, 630. 

’ Compt. rend., 1884, 98, 146. ® Joum. Chem. Soc.t 1889, 66, 213. 



1090 


MOLYBDENtJM 


sion of pure ammonium dichromate into chromium trioxide, 
found the value 52*15, and Meineke^ obtained the* average 
figure 52*12 by estimating (1) the quantity of silver and chromiiun 
in silver chromate and ammonio-silver chromate ; ( 2 ) the quantity 
of oxygen in these two compounds ; (3) the quantity of oxygen 
in potassium dichromate; and (4) the quantity of oxygen and 
of chromium in ammonium dichromate. More recently, Baxter 
and others , 2 by reducing silver chromate or dichromate with 
sulphurous acid or hydrazine sulphate, and then precipitating 
the silver as chloride or bromide, have found 62*01 ± 0*01 for 
the atomic weight of chromium. The value now (1922) adopted 
is 62*0. 


MOLYBDENUM. Mo = 96*o. At. No. 42. 

V 484 The name Molybdcena, which occurs in the writings of 
Dioscorides and Pliny, is derived from the Greek word fi6Xv08o<!f 
lead, and was originally employed for the designation of a variety 
of substances containing lead. At a later time the name was 
used to signify galena or substapces similar in appearance to 
this body, and to these the name of plumbago or black lead was 
also given. Even antimony sulphide and pyrolusite, to which 
latter mineral Linnaeus gave the name molybdcenum magnesiiy 
were also classed among the same group of bodies. At a still 
later period this word was applied solely to graphite and to the 
mineral sulphide of molybdenum, which are very similar in 
appearance. 

The difference between plumbago and the sulphide of 
molybdenum was first pointed out by Scheele in his treatise on 
“ Molybdaena ’’ in 1778, and in another on “ Plumbago ” in 
1779.^ By heating the former mineral with nitric acid he obtained 
sulphuric acid, together with a peculiar white earth which he 
recognised as an acid-forming oxide, and termed acidum molyb- 
dcmaSi and he assumed that the mineral was a compound of this 
acid with sulphur. In 1781 Bergman suggested that the earth 
was probably a calx of a metal, and in 1782 he wrote that Hjelm 
had succeeded in preparing the metal, though the details of the 
experiments were first known in 1790. 

Another mineral containing molybdenum is the yellow molyb- 
date of lead or wulfenite first found in Carinthia. This was 
investigated by the elder Jacquin, and he showed that it contained 

1 Annakn, 1891, 261, 339. > J, Amer. Chem. Soc., 1909, 31, 629, 541. 

’ Vetensk. Acad. Handl, 



MOLYBDENUM 


1097 


lead, but was doubtful as to the nature of the acid with which 
this metal was combined. Salzwedel, who analysed it in 1790, 
believed that it was a lead tungstate, but Klaproth in 1797 
ascertained its true composition. Later Berzelius more closely 
examined the molybdenum compounds. 

Molybdenum is usually found as molybdenite, MoSg, which 
occurs chiefly in Queensland and the United States; also as 
wulfenite, PbMo 04 . It occurs more rarely as molybdic ochre, 
which was for a long time believed to be molybdenum trioxide, 
M 0 O 3 . Schaller,^ however, from the analysis of a pure sample 
from Westmorland, New Hampshire, has shown it to be a 
hydrated ferric molybdate, Fe 203 , 3 Mo 03 , 7 iH 20 . 'Iron ores 
frequently contain traces of molybdenum, and hence this metal 
is also found in pig-iron as well as in the slag. Thus the iron 
slag obtained in the process of melting the cupreous schist at 
Mansfield is said to contain from 9 to 28 per cent, of molybdenum.^ 
Chillagite ® has the composition PbOWOgjPbOMoOg and 
powellite, CaMo 04 , in which a portion of the molybdenum is 
usually replaced by tungsten. 

Metallurgy of -Metallic molybdenum is obtained 

(either electrically or by the ‘‘ thermite ** process. 

By the electrical method, molybdenite is heated in a carbon 
tube with an arc of 350 amperes at 60 volts, when sulphur dioxide 
is evolved; the current is then increased to 900 amperes at 
60 volts, when complete fusion takes place and the sulphur is 
entirely expelled. The metal prepared in this way, however, 
contains from 5 to 7 per cent, of carbon, which may be removed 
by heating with molybdic oxide. Molybdenum melts at 2450"“ ± 
30 ^^ 

A metal of 98 to 99 per cent, purity, containing some iron and 
very small quantities of silicon, is obtained by the reduction of 
molybdic oxide by means of aluminium powder. 

Molybdenum is chiefly used in the form of rich ferromolyb- 

denum alloys for the manufacture of special steels.® It 

also finds employment in the construction of certain electrical 

apparatus, and, in the form of molybdic acid, is used in analytical 

laboratories for the estimation of phosphorus. 

^ » 

1 Amer. J. Sci., 1907, [4], 28, 297. * Heine, J. pr. Chem., 1836, 9, 177. 

* UUmann, J. Roy. 80 c. N. 8 .W., 1912, 46, 186; see also Cook, Amer. J. Sci.t 
1922, [6], 4, 60. 

*Von Firani and Moyer, Zeit. Elektrochem.f 1912, 18, 137; Wolf, Chem. 
Zentr.f 1918, i, 608, gives the freezing point as 2250°. , 

* See Mennioke, Elekirochem. Zeit.t 1913, 20, 181, 215, 250, 271 ; Aitchison, 

ChAm. Soc.. 1915. 107, 1631. 



1098 


MOLYBDENUM 


Metallic molybdenum may be obtained on the small scale as 
a grey powder, which assumes a silver-white appearance under 
pressure, by heating the trioxide or one of the chlorides in a 
current of hydrogen, but is best prepared by heating a mixture 
of molybdenum dioxide with one-tenth of its weight of sugar 
charcoal in a carbon crucible in the electric furnace, the action 
of the arc being stopped before the portions in contact with the 
crucible have had time to fuse. It is thus obtained free from 
carbon, whereas if too strongly heated it takes up the latter in 
considerable quantities. The pure metal is as malleable as iron, 
and is not hard enough to scratch glass, has a density ^ of 10-281, 
and can b6 forged when hot ; it scarcely undergoes oxidation at 
the ordinary temperature, but is superficially attacked at a dull 
red heat, and rapidly at 600°, molybdenum trioxide subliming. 
It is rapidly attacked by fused potassium chlorate and nitrate. 
^ It may be distilled in the electric furnace, giving a vapour which 
solidifies in crystals.^ When coarsely powdered it is attacked 
by fluorine at the ordinary temperature, by chlorine at a dull-red, 
and by bromine at a cherry-red heat, but not by iodine at the 
softening point of glass. When molybdenum filaments are heated 
in nitrogen, nitrides are probably formed.® 

The metal is insoluble in dilute acids with the exception of 
nitric acid, but dissolves in concentrated sulphuric acid, the solu- 
tion being first blue, but finally becoming colourless with forma- 
tion of the trioxide, sulphur dioxide being also evolved. It is 
slowly attacked by fused alkalis. At high temperatures it is 
attacked by water vapour with liberation of hydrogen and 
formation of the dioxide.^ In the potential series, molybdenum 
falls between Hg^ and Sb^^'. 

Molybdenum forms amalgams which may be obtained by the 
electrical method. When these amalgams are distilled in vacuo, 
molybdenum is left behind in the pyrophoric state.** 

Although not obtainable by reduction of its compounds, 
molybdenum in a colloidal form has been prepared by an electrical 
dispersion method.® 


iMiiller, J. Amer. Chem. Soc., 1915, 37, 2046; but Wolf, Chem. Zenlr., 
1918, i, 608, gives 8*95. « 

* Moissan, Compt. rend,, 1906, 142, 425. 

* Langmuir, J. Amer. Chem, Soc., 1919, 41, 167. 

* See Chaudron, Compt. rend., 1920, 170, 182, 1056. 

■ F6r4e, Compt. rend., 1896, 122, 733. 

* Svgdberg, “ Herstellung kolloider L5sungen anorganisch^r Stoffe *' 
(Dresden, 1909). 



MOLYBDENUM AND OXYGEN 


1099 


MOLYBDENUM COMPOUNDS. 

Molybdenum and Oxygen. 

485 Molybdenum combines with oxygen to form : 

Molybdenum sesquioxide, MogOg, 

Molybdenum dioxide, MoOg, 

Molybdenum trioxide, M0O3. 

The first two are basic oxides, but very little is known of 
their salts other than the halogen derivatives, the complex 
thiocyanates of the first, and the complex cyanides of fhe second. 
The trioxide is the most important, and like the analogous 
chromium oxide is an acid-forming oxide giving rise to the impor- 
tant scries of molybdates, A blue oxide, which is usually regarded 
as a combination of the dioxide with the trioxide, is also known, 
but its composition is not definitely settled, whilst an oxide, 
MogOg, and a peroxide have also been described. 

The compound formerly described as a hydrated monoxide 
has been shown to be the hy^oxide of molybdenum sesqui- 
oxide; nor are simple salts of the hypothetical monoxide 
known, but only polymolecular complexes. 

Molybdenum Sesquioxide, M02O3, is stated to be formed as 
a black substance when one of the higher oxides is treated with 
sodium amalgam, zinc, etc., but it is doubtful whether the pro- 
duct really has the composition MogOj. It is also formed by 
heating the metal in air or water vapour. The hydroxide, Mo(OH)3, 
is first obtained as a brownish-black powder by precipitating 
with ammonia, washing with dilute ammonia, and drying in 
a current of hydrogen at 100 °. When gently ignited in absence 
of air, the water evolved causes partial oxidation. A black 
precipitate of this hydroxide is also produced when molybdenum 
dichloride is boiled with caustic potash, hydrogen being evolved 
during the reaction.^ The hydroxide is also reported to have been 
prepared by an electrolytic method,^ and by reduction of ammo- 
nium paramolybdate in solution by hydrogen in presence of 
colloidal palla^um.^ Molybdenum ses(^uioxide is insoluble in 
acids, and even the hydroxide dissolves only with difficulty. 

^ Muthmann and Nagel, J?er., 1898, 31> 2009. 

> Smith and Hoskinson, Amer. Chem. J., 1885, 7, 90; Wolf, Chem. Zenir., 
1918, i, 608. 

* Paal and Btittner, Ber., 1916, 48, 220. 



1100 


MOLYBDENUM 


t • 

Salts of the Sesquioxide. — ^With the exception of the metaphos- 
phate, simple salts are not known in ^ the crystalline form, 
although solutions of the hydroxide in acids yield amorphous 
residues on evaporation. A complex pyrophosphate ^ and oxalate 
containing tervalent molybdenum have, however, been prepared. 

Molybdenum Dioxide, MoOg, is formed when the sesquioxide 
is gently heated in a current of air, or when sodium trimolybdate 
is ignited for several hours in a current of hydrogen. It is the 
only oxide formed when molybdenum trioxide is reduced by 
heating in hydrogen, ^ and may be prepared pure by heating 
this oxide first at 470° in a stream of the gas, and then in a 
current ofi dry hydrogen chloride, when any unchanged trioxide 
is converted into a volatile oxychloride and thus removed.^ 
It is formed also when ammonium molybdate is heated alone or 
fused with molybdenum trioxide, ^ and the product may be 
purified by washing successively with caustic soda, hydrochloric 
acid, and water, and then dried at 110°. The pure oxide is a 
brown or violet-brown, crystalline powder, and is reduced 
directly to the metal when heated at 600° in hydrogen. It is 
obtained in dark blue prisms resembling indigo by fusing sodium 
trimolybdate with one-third of its weight of zinc, and extracting 
the mass alternately with caustic potash and hydrochloric acid ; ^ 
this product, however, always contains a little admixed zinc 
molybdate, but it may be obtained pure by fusing together 
8 grams of fused ammonium molybdate, 14 grams of potassium 
carbonate, and 7 grams of boron sesquioxide, and extracting 
the cooled melt with water. It then forms opaque tetragonal 
crystals, having a violet reflex, and is insoluble in boiling 
hydrochloric acid and caustic potash.® 

Molybdenum Tetrahydroxide, Mo(OH) 4 . — It is probable that 
by interaction of alkalis with solutions of the reduction products 
of molybdic acid, only impure molybdenyl. hydroxide, Mo(OH) 3 , 
has been obtained, and not the tetrahydroxide as claimed. If, 
however, ammonium paramolybdate in aqueous solution is 
reduced at ordinary temperatures with hydrogen in presence of 
colloidal palladium, a greenish-black precipitate is obtained 
which has a composition corresponding approximately to 

' Rosenheim and ll^antaphyllides, Ber., 1916, 48 , 682. 

* Guiohaxd, Compt, rend., 1899, 129 > 722. 

^ Friedheim and Hofifmann, Ber., 1002, 36, 791. 

< Guichard, Compt. rend., 1899, 129 , 722; 1900, 181 , 998. 

» Ullik, Annalen, 1867, 144 , 227. 

* Muthmann, Annalen, 1887, 888, 114. 




MOLYBDENUM TBIOXIDE AND MOLYBDIC ACID 1101 

MoO(OH) 2.^ By a modification of the procedure, the compound 
can be prepared in a colloidal form.^ 

Salts of the Dioxide. — ^With the exception of the chloride, 
bromide, and sulphide, which are prepared by dry methods, 
and possibly the fluoride and iodide, these are known with but 
little certainty; even in solution there is liability of confusion 
between the salts in question and a mixture of those of quin- 
quevalent and tervalent molybdenum. On the other hand, a 
fairly large number of complex cyanides containing quadrivalent 
molybdenum have been prepared. 

Molybdenum Pentahy dr oxide and the Oxide^ MogOg. — It has 
already been mentioned that claims of the earlier investi- 
gators to have prepared the tetrahydroxide by interaction of 
alkalis with the reduction products of molybdic acid have not 
been substantiated, but that more or less impure molybdenyl 
hydroxide, MoO(OH)3, the hydroxide of quinquevalent molyb- 
denum, results. Klason^ prepared the compound, by treating 
ammonium molybdenum oxychloride, (NH4)2Mo^,OCl5, with 
ammonia, as a brown substance which gives a colloidal solution 
with water. It is insoluble in alkali hydroxide solutions, but 
soluble in those of alkali cafbonates, though it possesses no 
acid properties.* 

When the hydroxide is heated in a stream of carbon dioxide, 
a residue of the oxide, MogOg, is obtained as a violet-black powder. 
The existence of pure compounds of this composition is, how- 
ever, doubtful. 

Among other compounds containing quiquevalent molybdenum 
must be mentioned the pentachloride, the double thiocyanates, 
the sulphate, Mo203(S04)2, and a series of complex oxalates. 
Barbieri ® has prepared double molybdyl formates and oxalates 
containing the radicle Mo'Og. 


Molybdenum Trioxide and Molybdic Acid. 

486 Molybdenum Trioxide, M0O3, was supposed to occur as 
molybdic ochre, but this has been shown to be hydrated ferric 

^ Paal and Brunjes, Ber.f 1914v 47> 2214; Paal and Biittner, Bejr., 1015, 48, 
220 . 

* See also Freundlich and Leonhardt, Roll. Chem, Beihefte^ 1916, 7, 172. 

» Klason, Bcr., 1901, 84, 148. 

* Mawrow and Nikolow, Zeit. an^g. Chem., 1916, 92, 135, disagree with 
this statement. 

* Barbieri, Atti R. Accad. Lincei, 1916, [6], 25, i, 776. 



1102 


MOLYBPBNUM 


e r 

molybdate. Gagarine^ states, however, that he has found 
pure molybdic oxide as white or grey pseudomorphs after molyb- 
denite in specimens from the Ilmen Mountains. It has a pearly 
lustre and is semi-transparent. It has probably been obtained 
by the oxidation of molybdenite which occurs there as pure 
sulphide without a trace of iron. 

• In, order to prepare the trioxide in the pure state on the small 
scale the native sulphide may be heated in a combustion tube 
in a current of air until it is all oxidised and the trioxide sub- 
limed.^ On the larger scale, it may be obtained by mixing the 
same powdered mineral with an equal weight of pure quartz 
sand, and i;oasting the mixture on a flat iron plate. The roasted 
product is then boiled with dilute ammonia, and a small quan- 
tity of ammonium sulphide added to the solution in order to 
precipitate the copper. The filtered liquid is then evaporated 
to dryness, and the residue again dissolved in dilute ammonia. 

‘'Crystals of ammonium molybdate are obtained from the filtrate 
on concentration. ' These are decomposed by nitric acid, evapor- 
ated to dryness, and the residual trioxide well washed with 
water. Molybdenum trioxide can also be obtained from native 
lead molybdate by first treating the mineral with dilute hydro- 
chloric acid in order to remove iron, zinc, etc., then decomposing 
it with hot concentrated hydrochloric acid, evaporating down 
and digesting with dilute ammonia, when ammonium molyb- 
date remains in solution and can be crystallised out as already 
described.® The ammonium molybdate may also be converted 
into the trioxide by being ignited in a platinum dish and sub- 
sequently heated to a dull red heat in a current of oxygen.* 

Molybdenum trioxide is a white, impalpable powder, which 
when heated becomes yellow; it melts ® at 7%^ to a dark yellow 
liquid, which, on cooling, solidifies to a y^lowish-white, fibrous, 
crystalline mass, having a density of 4*696. It volatilises at 
very high temperatures when heated in closed vessels, but in 
the air it sublimes more easily, depositing small, colourless, 
transparent, rhombic tablets. It dissolves in 600 parts of cold, 
and in about 960 parts of hot water. The solution reddens 
litmus paper, turns turmeric paper brown, and possesses a sharp 
metallic taste. 

Molybdic Add, H2Mo04,H20 or Mo03,2H20, crystallises out 
in yellow crusts when three parts of ammonium molybdate are 

1 BuU. Acad. Sci. 8t. Petersbourg, 1907, 287. ^ 

* Wohler, Annakn, 1866, 100, 376. * Wohler, Mineralamlyse, 146. 

* Muihmann, Annakn, 1887, 238, 117. 

* Jaeger and Germs, Zeit. anorg. Chem., 1921, 119, 145. 




MOLYBDENUM TRIOXIDE AND MOLYBDIC ACID 1103 


dissolved in twenty parts of water, the same quantity of nitric 
acid of specific gravity. M6 is added, and the whole set aside. 
The deposition of the acid frequently takes place only very 
slowly, and the addition of a crystal of the compound renders 
its separation more easy.^ 

When the solution of the trioxide in nitric acid is allowed to 
evaporate spontaneously, a white, crystalline powder separates, 
which on heating loses water (Berzelius). This consists of the 
anhydrous acid, H2M0O4, which was once obtained by Ullik in 
the form of thin, prismatic crystals by the decomposition of 
magnesium molybdate with nitric acid. It is also formed when 
the yellow acid is heated at 60°, or its solution in water con- 
centrated at 40-50°, and is thus obtained in white needles which 
are very sparingly soluble in cold, but more readily in hot water.^ 
Two forms are distinguished as the a- and j5-forms respectively. 

Colloidal Molyhdic Add . — When the hydrochloric acid solution 
of ammonium molybdate is dialysed, a yellow, strongly acid, 
astringent solution of molybdic acid remains, which on evapora- 
tion yields a deliquescent, gummy mass.® After drying over 
sulphuric acid for several weeks it has the empirical formula 
H2M02O7, but the determination of the .molecular weight by 
Raoult’s method indicates that it contains four M0O3 groups.* 
If ordinary ammonium molybdate is precipitated with barium 
chloride, and the washed precipitate decomposed with the exact 
quantity of sulphuric acid, a colourless solution is obtained, 
possessing an acid reaction and metallic taste. When dried 
over sulphuric acid for several months it has the composition 
HgMogOy, and on heating at 100°, 120°, and 160-170°, the 
residues have the compositions HgMogO^, H2M04O13 and IlgMogOgs 
respectively ; at 250° pure molybdenum trioxide remains behind. 
Colloidal molybdic acid is rapidly reduced to the blue oxide by 
alcohol. 

Molybdenum trioxide generally behaves as an acid-forming 
oxide analogous to chromium trioxide, and unites with bases to 
form molybdates. The normal molybdates are unstable, and 
show a great tendency to form polymolybdates corresponding to 
the polychromates by uniting with further molecules of the 

^ Gmelin-Kraut, 2, 171 ; Rosenheim and Berthoim, Zeit. anorg. Clwn,, 1903, 
84, 427 ; 1006, 50, 320; Qrabam, Journ. Franklin Inst, 1607, 164, 69. 

® Rosenheim and Davidsohn, Zeit. anor^. Chem., 1903, 87, 314; Burger, ihid.t 
1922, m. 240. 

• Graham, Chem. 8oc.t 1864, 19, 326; See, however, Bruni ^nd 

Pappadjt, Ga»., 1901, 81, i, 244; Rosenheim and others, he. cit. 

* Saban4el, Jaum. Chm. Soc., 1890, 58, 1215. 

VOL. n. (n.) 


T 



1104 


MOLYBDENUM 


trioxide, as many as ten molecules of M0O3 combining with one 
equivalent of a basic oxide. 

The molybdates also combine with other acidic oxides, forming 
the series of salts known under the general term of the complex 
molybdates. The best known of these are the phosphomolybdic 
acids, in which a varjdng number of molecules of molybdenum 
trioxide and of phosphoric anhydride are combined with a 
basic oxide ; similar compounds are formed by the acidic oxides 
of arsenic, sulphur, vanadium, antimony, and also of iodine, tin, 
silicon, and manganese.^ The exact constitution of these salts 
is not yet known. 

Molybdenum trioxide acts towards strong acids as a basic 
oxide; thus it combines with two molecules of hydrochloric 
acid to form a volatile crystalline compound, which is probably 
the hydroxychloride, MoO(OH)2Cl2 ; with sulphuric acid it yields 
the compound ^ M0O2SO4, analogous to the salts formed by the 
trioxides of tungsten and uranium. 

Salt formation between molybdenum trioxide and bases is. 
attended by the formation of a series ® of compounds of complex 
constitution. Thus there may be formed substances of the type : 

R20*Mo 03 (normal molybdates) 

R20‘2Mo 03 (di-molybdates) 

6R20*12Mo 03 (para-molybdates) * 

R20*3Mo 03 (tri-molybdates) 

R20*4Mo 03 (tetra-molybdates) 

R20‘8Mo 03 (octa-molybdates) ® 

R2O*10MoO 3 (deca-molybdates) 

R20* 1 6M0O3 (hexakaideca-molybdates) 

1 Pechard, Compt. rend.j 1901, 132 , 628; Rosenheim and Itzig, Ze.it. anorg. 
Chem.f 1898, 16 , 76; Friedheim and Saraelon, Zeit. anorg. Chem., 1900, 24 , 66; 
Rosenheim and Liebknecht, AnnaUnt 1899, 304 , 40 ; Asch, Zeit. anorg. Chem.t 
1901, 28 , 273. See also : Rosenheim and Jaenicke, Zeit. anorg. Chem., 1912, 
77 , 239; Copaux, Compt. rend., 1913, 166 , 1771; Mazzucohelli and Ranucci, 
Qazz., 1914, 44 , ii, 116; Rosenheim, Weinberg, and Pinsker, Zeit. anorg. 
Chem., 1913, 84 , 217 ; Rosenheim andTraube, ibid., 1915, 91 , 76; Prandtl and 
von Blochin, ibid., 1916, 93 , 46; Mawrow and Nikolow, ibid., 1916, 93 , 170; 
Weinland and Gaisser, ibid., 1919, 108 , 231 ; Weinland and Zimmermann, ibid., 
1919, 108 , 248; Fors^n, Compt. rend., 1921, 172 , 681; Darmois, ibid., 1921, 
172 , I486 ; Postemak, ibid., ,1921, 172 , 697 ; Tanret, ibid., 1921, 173 , 43. 

* Compare Guichard, Cempt. rend., 1906, 143 , 744. 

* Foreign, Compt. rend., 1921, 172 , 216, 327. 

* Rosenheim, Zeit. anorg. Chem., 1916, 96 , 139; but Copaux, Compt. rend., 
1913, 166 , 1771 ; Postemak, ibid., 1920, 171 , 1068, regard paramolybdates as 
of the form 3 R| 0 * 7 Mo 04 . 

Rosenheim, Felix, and Pinsker, Zeit. anorg. Chem., 1913, 79, 292, regard 
octamolybdates as hydrogen-tetramolybdates. 



MOLYBDATES 


1105 


The di-, para-, and tri-salts are sometimes called ** isopoly ” 
salts; tetra- and octa-salts, possibly derived from a sexabasic 
heteropoly-acid, are grouped as “ meta ’’ salts. 

Sodium Molybdates, normal molybdate, Na2Mo04, is 
formed by fusing the trioxide with the requisite quantity of 
sodium carbonate, and crystallises from water in acute rhombo- 
hedra, containing two molecules of water; below 6° prisms con- 
taining 10 molecules of water separate, resembling Glauber’s 
salt in appearance ; these effloresce in the air, forming the first 
named salt. The dimdybdate^ NagMogO,, is formed when sodium 
carbonate and the trioxide are fused in the requisite proportions, 
and is a crystalline mass soluble with difficulty in cold and only 
slowly in hot water. A solution yields the hexahydrate. Sodium 
paramolybdate, 5Na20,12Mo03,36H20, to which Kosenheim 
ascribes the formula^ Na5H5[H2(Mo04)e],15-5H20 is obtained 
by allowing a solution of the calculated quantity of the trioxide 
in sodium carbonate or sodium hydroxide solution to evaporate 
spontaneously. On heating it loses water, with eventual loss of 
its individuality. The irimolybdate^ Na2Mo30ioJH20, obtained 
in a similar manner, crystallises in large needles, 3*9 parts of which 
dissolve in 100 parts of water £Pt 20 °, and in 137 parts at 100°. 
Other hydrates have been described. The tetramolyMate^ 
Na2Mo40j3,6H20,2 is prepared by the action of the calculated 
quantity of hydrochloric acid on the normal salt, and forms small, 
glistening crystals soluble with difficulty in cold, but readily in hot 
water. Sodium octamolybdate, Na2Mo8025,17H20, is formed as 
clear, lustrous, monoclinic crystals when a solution of the normal 
molybdate spontaneously evaporates in presence of the calculated 
quantity of hydrochloric acid. A sodium octamolybdate 
crystallising with I5H2O is said to be obtained by the action of 
sulphur dioxide on a solution of the tetramolybdate.® The 
decaynolybdate, Na2MoiQ03i,12H20, is a white, crystalline powder 
obtained by heating the normal salt on the water-bath with 
sufficient hydrochloric acid to saturate the requisite quantity 
of sodium. It is sparingly soluble in water. Salts containing 
GHgO and 22H2O have also been prepared.^ The compound 

^ Rosenheim, Zeit. anorg. Chem., 1916, 96, 139; various other formulie 
have, however, been ascribed; in particular, 3 NajO, 7 Mo 05 , 22 H, 0 . 

* But see Rosenheim and Felix, Zeit. anorg, Chem., 1913, 79, 292. See also 
Wempe, ihid., 1912, 78, 298. 

* Rosenheim, Zeit. anorg. Chem., 1897, 16, 180. 

* Ullik, Annalen, 1870, 163. 373; Rosenheim and Davidsohn, Zeit. anorg. 
Chm.t 1903, 87, 314; Rosenheim, and Felix, he. cit; Rosenheim, Felif and 
Pinsker, loc. cit. 



1106 


HiOLYBDEKUM 


Na2Moig049,9H26 was obtained Iby Ullik ^ by boiling a solution 
of the normal molybdate with nitric acid. It may probably 
be regarded as an acid salt of a lower type. 

Potassium Molybdates normal salt, K2M0O4, obtained in 
a similar manner to the sodium salt, crystallises in microscopic 
four-sided crystals, which are readily soluble in water. It is 
triiQorphous.2 When hydrochloric acid is added drop by drop 
to a solution of the trioxide in potassium carbonate until a 
permanent turbidity is produced, the 'paramolyhdate of the com- 
position K8 Mo 7024,4H20 (or 5K20,12 Mo 03,8H20) separates 
out on standing, in monoclinic prisms; it is decomposed by 
water intq the trimolybdate, K 2 Mo 30 jo, 3 H 20 , which forms silky, 
pliable needles.^ By heating a solution of sodium octa- 
molybdate with potassium chloride, the tetramolybdate, 
K2Mo40i 3,7H20, is obtained. A crystalline octamolybdate, 
K2Mog025,13H20, and hydrates of the decamolybdaie, EgMo^oOgi, 
are also known (Rosenheim). 

Ammonium Molybdates. — The normal molybdate, (NH4)2Mo04, 
is produced when molybdenum trioxide or an ammonium poly- 
molybdate is heated with excess of concentrated ammonia, and 
crystallises in four-sided prisms which are decomposed by water. 
The dimolybdate, (NH4)2Mo207, separates out on evaporating 
the mother-liquor of the normal salt, in the form of a white,- 
crystalline powder.^ When a solution of the trioxide in ammonia 
is evaporated, the compound (NH4)6Mo 7024,41120 (Delafontaine) 
crystallises out in large, colourless, monoclinic crystals. This 
is the salt usually known as ammonium molybdate. According 
to Klason,'^ however, the molecular weight in aqueous solution, 
taking into account the degree of dissociation indicated by the 
electrical conductivity, shows that this salt is probably a double 
salt, (NH4)3H3 Mo3042,(NH4)2H4Mo 30]2, wMch is resolved into its 
constituents, triammonium and diammonium trimolybdates, 
when dissolved in water. On the other hand, Junius® gives 
the formula as (NH4 )jqMoi204i. Results of physico-chemical 
measurements show that in aqueous solution the anion is 

1 Ullik, loc. cit. 

* Hiittner and Taramann, Zeit. anorg. Chem., 1905, <3, 215; Amadori, Atti 
B. Accad. lAncei, 1914, [5] 26, i, 800; van Klooster, Zeit. anorg. Chem., 1914, 
86,49. 

* For86n, Compt. rend., 1921, 172, 215, 327, reports the existence of two 
potassium trimolybdates of the same degree of hydration. 

^ Compare Klason, Ber., 1901, 34, 153. 

« Ber., 1901, 34 , 163. * Zeit. anorg. Chem., 1905, 46 , 428. 



MOLYBDATES 


1107 


consequently this would appear to be the correct formula.^ 
The irimolyhdatet (NH4)2Mo3Oi0,H2^> is frequently formed by 
the decomposition of a solution of the ordinary salt at a low 
temperature, when it separates out in silky needles, sparingly 
soluble in cold, but readily so in hot water. It may also bo 
formed by interaction of a solution of the ordinary paramolyb- 
date with a suitable quantity of hydrochloric acid. Other 
crystalline ammonium salts have been described, which contain 
a larger proportion of molybdenum trioxide.^ 

Calcium Molybdate, CaMo04, is obtained by precipitating a 
solution of the ordinary ammonium salt containing an excess 
of ammonia with calcium chloride. It forms a white precipi- 
tate consisting of microscopic tetragonal pyramids. If calcium 
carbonate is boiled with an excess of the trioxide and water, 
and the solution allow'ed to evaporate spontaneously, calcium 
trimolyhdale, CaMogOiQjGHaO, is deposited. The salt 
HgCaMogOgojlTHgO crystallises from a solution of the normal 
salt in the requisite quantity of hydrochloric acid. It is deposited 
in small, oblique, glistening prisms which arc scarcely soluble in 
cold but readily dissolve in hot water. 

Barium Molybdate, BaMo04, obtained in tetragonal pyramids 
by fusing together sodium molybdate, barium chloride, and 
common salt, and is difficultly soluble in acids. 

When the ordinary ammonium salt is precipitated with 
barium chloride, a flocculent precipitate of BagMo 7024,91120 or 
possibly 5BaO,12Mo03,a::H20, is thrown down, which is slightly 
soluble in water. A compound, BaMo30io,3H20, having pro- 
perties similar to the last salt, is obtained by precipitating a 
soluble trimolybdate. When barium carbonate is dissolved 
in soluble molybdic acid and the solution kept, oblique prisms 
of the salt H 2 BaMo 8023 , 17 H 20 are deposited; and if the 
normal salt be treated with dilute nitric acid the compound 
BaMogOggjIIIgO is formed. This is insoluble in water and is 
not completely decomposed by acids, even by sulphuric acid. 

Magnesium Molybdate, MgMo04,5Il20, is obtained by boiling 
magnesia with water and molybdenum trioxide, and evaporating 
the solution, when the salt separates out in long, glistening, 

^ Sand and Kisenlohr, Zeit. anorg. Chem., 1007, 52, 08; Rosenheim, ibid.^ 
1910, 96, 139 ; Posternak, Compt. rend., 1920, 171, 1068. 

* Klason, Ber., 1901, 34, 153; Roaerihcim, Zeit. anorg. Chem., 1897, 15, 
180; 1903, 34, 427; Mylius, Ber. 1903, 36, 038; Wompe, Zeit. anorg. Chem., 
1912, 78 , 298; Barbieri, AUi R. Accad. Lincei, 1919, [6], 88 , i, 390; Posternak, 
he. cit, 



1108 


MOLYBDENUM 


transparent prisms. A heptahydrate is also known. Magnesium 
molybdate forms with the molybdates of potassium and sodium 
double salts such as K2Mo04,MgMo04,2H20, which appear to 
be isomorphous with the corresponding manganese and ferrous 
salts. Magnesium forms para-, tri-, octa-, and 16-molybdates. 

Lead Molybdate^ PbMo04, occurs native as wulfenite in orange- 
red; transparent, tetragonal tablets and octahedra, which have a 
specific gravity varpng from 6 to 7. When one part of sodium 
molybdate is fused with six parts of lead chloride and four of 
sodium chloride in a closed crucible, bright yellow, translucent 
pyramids or tablets of the artificial compound are obtained, 
which have a specific gravity of 6-811. If a solution of a molyb- 
date be added to one of lead nitrate the same compound is obtained 
in the form of . a white precipitate of high melting point. The 
only other lead molybdate known ^ has the formula PbgMoOg. 

Molybdenum Molybdates . — ^When molybdic acid is reduced in 
solution by hydrogen sulphide, sulphur dioxide, stannous chloride, 
zinc, 2 alcohol,® etc., a blue solution is obtained, and this reaction 
forms one of the most characteristic tests for molybdenum. 
This is due to the formation of an oxide or oxides intermediate 
between the di- and the tri-oxide, and the solutions deposit a 
blue precipitate of this oxide which contains water and is termed 
molybdenum blue. It may also be obtained by adding a cold 
dilute hydrochloric acid solution of molybdenum dioxide 
to one of ammonium molybdate, and in several other ways. 
The solubility in water of the blue oxide varies with the conditions 
of precipitation. It is colloidal in nature, and behaves as a 
negative colloid. 

Much doubt exists as to the composition of this oxide ; Ram- 
melsberg assigned to it the formula MogOg = MoOgjMoOg, and 
others have regarded it as MogOg = Mo02,2MoOg, whilst accord- 
ing to Guichard* it has the composition Mo50i4,6H20 = 
Mo02,4Mo0g,6H20. On the other hand, Klason® states that 
more than one compound exists, and regards these as complex 
derivatives of an oxide, MogOg, and molybdic acid, analogous 
to phosphomolybdic acid. Junius ® has obtained it at the cathode 

1 Jooger and Gorms, Zeit. anorg. Chem., 1921, 110, 145. See, however, 
Dittler, Zeit. Kryst. Min., 1913, 6^ 168; 1914, 64, 332. 

2 Scott, J. Ind. Eng. Chem., 1920, 12, 678. 

2 Benrath, Zeit. wise. Photochem., 1917, 16, 253. 

* Cmpt. rend., 1899, 129, 722; Rogers and Mitchell, J. Amer. Chem. Soc., 
1900, 22, 360; Junius, Zeit. anorg. Chem., 1905, 46, 426. 

» Mer., 1901, 34 , 148. See also Bailhaohe, Cmpt. rend., 1901, 133 , 1210, 

* Zeit. anorg. Chem., 1906, 46 , 428. 



PHOSPHOM0LYBDIO ACID 


1109 


by the electrolysis of molybdic acid m strong hydrochloric acid, 
and gives to it the formula, The composition of the 

single individual compound— if, indeed, the substance is such— 
is known only approximately ; it is possible therefore to ascribe 
to it various formula) in which it may be regarded as a simple 
or complex molybdate of molybdenum or of the molybdenyl 
radicle. 

Several crystalline ammoniacal double molybdates have been 
described ^ of the general formula M*2M*^(Mo04)2,2NH3, where 
= K or NH4, and = Cu, Zn, Cd, Ni, or Co. 

Molybdates exhibit catalytic activity in several interesting 
ways, e.g., in influencing the oxidation of thiosulphates by hydro- 
gen peroxide to sulphates instead of, as normally, to tetra- 
thionates.2 

487 Phosjphomolybdic Addy P205,21Mo03,63H20 or 
H7[P(Mo207)g],28H20.— This yellow complex acid is obtained 
by the repeated treatment of the ammonium salt with small 
quantities of aqua regia, and crystallises out on evaporation 
of the combined solutions. It forms also crystalline hydrates 
containing 22H2O and I2H2O. 

The composition of these bodies has been investigated by 
Eosenheim and others.^ In common with a number of other 
complex acids, such as those containing molybdic acid in asso- 
ciation with silicic, oxalic, formic, arsenic, sulphurous, etc., acids, 
they are classed as heteropoly-acids y* the complex anion being 
composed of several anionogen radicles, of which at least one 
differs from the remainder.^ Such compounds are subject to 


^ Briggs, Journ. Chem. Soc.^ 1904, 85 , 072. 

^ Abel, Zeit. Elektrochem., 1912, 18 , 706; Abel and Baum, Monatsh., 1913, 
34 , 425, 821. See also Schilow, Zeit. physikal Chem,, 1898, 27, 613 ; Brode, 
ibid., 1901, 37 , 299; Titoff, ibid,, 1903, 46 , 641 ; MUbauor, ibid., 1907, 57 , 649. 

* See Abegg, Handbuch der anorganischen Chemie, IV, [ 1 ], ii ; also Friedheim, 
Zeit. anorg. Chem., 1893, 4 , 274; Friedheim and Meschoirer, ibid., 1894, 6 » 
33; Kehrmann, tbid., 1894, 7 , 406; Levi and Spelta, Gazz„ 1903, 33 , i, 207; 
Miolati,' ibid., 1903, 33 , ii, 336; J. pr. Chem., 1908 [2], 77 , 417; Kosenheim 
and Pinsker, Zeit. anorg. Chem., 1911, 70 , 79; Rosenheim, Zeit, Elektrochem., 
1911, 17 , 694; Rosenheim and Traube, Zeit. anorg. Chem., 1916, 91 , 96; Rosen- 
heim and Jaenicke, ibid,, 1912, 77 , 239; 1917, 101 , 247 ; Mawrow and Nikolow, 
ibid., 1916, 93 , 170; Rosenheim and Triantaphyllides, Ber., 1916, 48 , 682; 
Ephraim and Herschfinkel, Zeit. anorg. Chem., 1909, 65 , 233, 237 ; Ephraim and 
Brand, ibid., 1910, 65 , 233. 

* See Copaux, Compt. rend., 1913 , 156 , 1771 ; Barbieri, AUi R. Accad. lAncei, 
1913 , [6], 22, i, 781 ; Rosenheim, Weinberg, and Pinsker, Zeit. anorg. Chem., 
1913 , 84 , 217 ; Rosenheim and Traube, loc. cit. ; Rosenheim and Sohwer, ibid.^ 
1914 , 89 , 224 . 




1110 


MOLTfSBD3SNUM 


certain types of ‘isomerism* as have already been described in 
the case of the chromiammines. 

The phosphomolybdic acids and their derivatives fall into two 
main groups : (a) the more complex compounds, of a yeUow 
colour, are derivatives of the anions [POg]'^“ and [Mo207]^S 
(b) the less complex compounds, colourless, are derivatives of 
the anions and [MoOJ^^. The yellow compound already 

mentioned belongs to the first class. A solution of this substance 
on long keeping undergoes hydrolysis, resulting in the produc- 
tion of a complex phosphomolybdic acid of the formula 
Hi2[P202(Mo 207)9]24 to SOHgO. Further hydrolysis of salts 
of this acid yields salts of an unstable acid containing the anion 

If the yellow phosphomolybdates are treated with alkalis, 
e.g., ammonia solution, white salts of the second class are obtained ; 
the latter can also be produced directly from suitable proportions 
of their components, but no free acid corresponding to this group 
of salts has yet been prepared. 

Atmnoniim Phosfhomolyhdaie^ (NH4)3P04,12Mo03. — This salt 
is formed as an insoluble, canary-yellow precipitate when a solu- 
tion of a molybdate is mixed with ammonia, and a small quantity 
of phosphoric acid in nitric acid solution added, or when the free 
acid is added to a strongly acid solution of the ammonium salt. 
Pyro- and meta-phosphates do not yield this precipitate; it 
is formed only when they are converted into orthophosphates, 
and when this change takes place slowly the compound is obtained 
in glistening yellow crystals (Debray). It is almost insoluble 
in water and in dilute acids and is also insoluble in a nitric acid 
solution of ammonium molybdate. The presence of hydro- 
chloric acid and chlorides, as well as of many organic acids, 
with the exception of acetic acid, retards the formation, whilst 
in presence of an excess of phosphoric acid no precipitation 
occurs. Phosphates are commonly estimated by this method, 
so that the recovery of molybdic acid from the filtrate is a matter 
worthy of attention.^ It is usually effected by precipitation with 
sodium phosphate, solution of the precipitate in ammonia, and 
removal of the phosphoric acid with magnesium salts. The 
molybdenum may, howeyer, be recovered as sulphide. 

^ See Broivn, J. hid. Eiuj. Chcm., 1916, 7, 213; Armstrong, ibid.^ 1916, 7, 764; 
Kinder, Stahl u. Eisen, 1916, 36 , 1094 ; Rudnick and Cooke, J. Ind. Eng. Chem.t 
1917, 9 , 109; Lehner and Schultz, ibid., 1917, 9 , 684; Lynas, CAem, Met. Eng, 
1918,169; NeubauerandWolferts, Zeif. anal. Chm., 1919, 68, 446; Malowan, 
Ghem^Zeit., 1918, 49, 410. 




PERMOLYBDIC ACID 


1111 


When dried above 130°, the salt always has the composition 
given above, in which the ratio P2O5 : MoOg is 1 : 24, but accord- 
ing to Gibbs the hydrated precipitate, has the composition 
(NH4)3P04,12 Mo 03,(NH4)2HP04,11 Mo 03,8H20; it is commonly, 
however, regarded as (NH4)3P04,12Mo03,2HN03,H20. It dissolves 
in 10,000 parts of distilled water, in 6,600 parts of one per cent, 
nitric acid, and in 650 parts of hydrochloric acid of specific 
gravity 1*12. It is readily soluble in alkalis, and on allowing 
the ammoniacal solution to stand, glistening needles or prisms 
having the composition 2(NH4)3p04,5Mo03,7H20 separate. 
These are sparingly soluble in cold, readily in hot water, forming 
a slightly acid liquid. 

Phosphomolybdic acid also precipitates strongly acid solutions 
of the salts of rubidium, caesium, thallium, and the organic alka- 
loids, but not solutions of sodium or lithium salts. The heavy 
metals are also not precipitated if a sufficient amount of free 
acid be present. This acid is used as a reagent for the alkaloids 
or, in place of this, a liquid prepared by saturating a solution 
of sodium carbonate with molybdenum trioxide, and adding 
one part of sodium phosphate to every part of the trioxide, may 
be employed ; this solution is evaporated to dryness, the residue 
fused, dissolved in water, filtered, and nitric acid added until 
the liquid becomes yellow. 

Complex Arsenomolybdic acids likewise exist. 

Permolybdic Acid. — The molybdates when treated with hydro- 
gen peroxide in acid solution give a yellow coloration, but the 
yellow substance cannot be extracted with ether. If molybdenum 
trioxide be treated with hydrogen peroxide on the water-bath, 
and the mixture evaporated under diminished pressure, per- 
molybdic or ozomolybdic add} HgMoOgjnHgO, is obtained as an 
orange-red, amorphous substance. Potassium trimolybdate dis- 
solves in hydrogen peroxide, yielding an orange-yellow solution, 
which on concentration at a moderate heat yields yellow crystals of 
potassium permolybdate; this, according to Muthmann and Nagel, ^ 
has the composition K20,2Mo0g,Mo04,3H20. These chemists 
have shown that the molybdates of the alkali metals, when 
dissolved in hydrogen peroxide, can take up more oxygen to the 
extent of one atom or less per atom of molybdenum ; in this way 
they have prepared a number of per molybdates, which readily 
lose oxygen on heating. 

^ Muthmann and Nagel, Ber., 1898, 31» 1830. 

* Zeit. anorg. Ohem., 1898, 17, 73. Compare Pochard, Compt. rend.^ 1891, 
m 720« 



1112 


MOLYBDENUM 


, (' 

A compound, KgOjjMoOgjHgOg, is formed by the action of 
hydrogen peroxide at -“2° on a solution of potassium per- 
molybdate containing potassium hydroxide, followed by alcohol 
at — 12 *^. This is a brick-red mass which explodes spontaneously 
when preserved in quantity, and loses oxygen on exposure to the 
air, or on treatment with water.^ 

There are also known both red and h\e.ckferthi(ymlyhdales of the 
composition RMoSg and RMoSg respectively, and oxyfluoro- 
fermolyhdates, c.p., K2[F4Mo0(02)],H20. 


Molybdenum and the Halogens. 

488 Normal salts of bivalent molybdenum are unknown ; corre- 
sponding poly;nolecular complexes exist, but these do not yield 
the simple doubly-charged molybdenum ion. 

Molybdenum Dichloride, MogClg, is prepared by heating the 
" trichloride in a current of dry carbon dioxide : 

2MoCl3=MoCl2+MoCl4. 

The tetrachloride volatilises, leaving the dichloride as a sulphur- 
yellow, amorphous powder, which does not alter in the air, and 
does not dissolve in water but is soluble in alcohol or ether, 
separating from these solutions in the amorphous condition. ^ 
The dichloride is conveniently obtained ® by passing carbonyl 
chloride over powdered molybdenum at 700 - 800 °, when a small 
quantity of the pentachloride sublimes, and the metal gradually 
becomes coated with a heavy, protective layer of the dichloride, 
which is removed by extracting it with concentrated hydro- 
chloric acid. It is also produced when chlorine, mixed with a large 
excess of carbon dioxide, is passed over gently heated molybdenum 
in absence of oxygen.^ It is soluble in the hydracids, in hot sul- 
phuric acid, and in the alkalis, yielding compounds which must 
be regarded as salts of the radicle (M03CI4). Thus the hydrate. 
[Mo3Cl4]Cl2,3H20, crystallises from the hydrochloric acid solution, 
on keeping, in pale-yellow plates insoluble in water, but when 
the solution is evaporated long prisms having the formula 
Mo3Cl3,HCl,4H20, are deposited. Similarly, the solutions in 
alkalis contain compoiujds of the type [Mo3ClJ(OH)2. The 

^ Melikofif and Pissarjewsky, Ber., 1898, 31, 632. 

* Liechti and Kempe, Annalm, 1873, 169, 361. 

’ Lindner and others, Ber., 1922, 66, [.0], 1458. 

*Blomstrand, J. pr. Chem., 1869, 77, 96; Wolf, Chem. Zentr., 1918, i, 608; 
Lindner and others, loc. cit. 




1113 


MOLYBDENUM AND THE HALOGENS 

# 

molecular weight of the dichloride in alcohol corresponds to the 
formula MogCl^.^ 

Molybdenum Dihromidej MogBr^, is formed by the decomposition 
of the tribromide by heat. It is a yellowish-red, infusible mass 
which does not dissolve in water or in acids. 

Molybdenum Di-iodide^ Molg, or Mogig ( ?), is formed by heating 
the pentachloride in a current of hydrogen iodide. It is a brown, 
amorphous substance of density 4*3, and is insoluble in water.^ 

Chloromolybdic Hydroxide, [Mo3Cl4](OH)2, 21120, precipitated by 
acetic acid from a solution of the dichloride in alkali, possesses 
amphoteric properties, and forms well-defined salts with acids.^ 

Chloromolybdic Bromide, Mo3Cl4Br2,3H20, is obtained by heat- 
ing the hydroxide or the chloride with hydrobromic acid. It 
crystallises on cooling in glistening reddish-yellow plates which 
scarcely dissolve in water or in dilute hydrochloric acid. Hydriodic 
acid forms a corresponding compound. 

Bromomolybdic Hydroxide, Mo3Br4(0n)2,8H20. — When molyb- 
denum dibromide is dissolved in dilute alkali and the solution 
allowed to remain exposed to the air, or when ammonium chloride 
is added to the hot solution, the above compound is deposited 
in the form of golden-yellow*, glistening rhombohedra closely 
approximating in form to the cube. These lose six molecules 
of water on drying over sulphuric acid, and assume a dark red 
colour. At 100° they lose all their water, a fine red powder 
remaining behind.^ 

Bromomolybdic Fluoride, Mo3Br4F2,3H20, is prepared with 
hydrofluoric acid in the same way as the chloride, which it closely 
resembles. 

Bromomolybdic Chloride, Mo3Br4Cl2>*^H20, is obtained as a 
pale-yellow powder on adding an excess of hydrochloric acid to 
the alkaline solution of the hydroxide. 

Bromomolybdic Sulphate, Mo3Br4S04,3H20, can be obtained in 
the same way in the form of a yellow precipitate, whilst when 
the solution of the hydroxide is treated with ammonium molyb- 
date and acetic acid, bromomolybdic molybdate, Mo3Br4Mo04,2H20, 
is thrown down as a reddish-yellow precipitate. 

Molybdenum Trifluoride has not been isolated, except in the form 

^ Muthmann and Nagel, B&r., 1908, 31, 2009. See also Koppel, Ztit. anorg, 
Chern,, 1912, 77, 289. 

® Guichard, Compt, rend,, 1896, 123, 821. 

* Blomstrand, J, pr. Chein., 1869, 77, 100. 

*Atterberg, Ber„ 1873, 6f 1464. 



IIU 


MOLYBDENUM 


of double salts, but it is known to exist in solutions of molybdenum 
trihydroxide in hydrofluoric acid. 

Molybdenum Trichloride^ MoClg, is formed when the pure 
pentachloride is volatilised in a current of carbon dioxide, the 
tube being heated strongly at one point only. The trichloride is 
deposited as a copper-red, crystalline crust. ^ If the pentachloride 
is hpated in a current of hydrogen to 250*^ the trichloride is 
obtained in a form closely resembling red phosphorus.^ The 
trichloride is the main product of the reaction of carbonyl 
chloride and molybdenum at about 600°.® Heated in the 
air it forms a white, woolly sublimate, whilst impure di- 
chloride remains behind. It is insoluble in cold water and is 
decomposed by boiling water. It likewise does not dissolve in 
hydrochloric acid, though it is easily soluble in hot nitric acid, 
whilst sulphuric acid dissolves it, forming a blue solution which 
on heating becomes green. If the hydroxide is dissolved in hydro- 
chloric acid a. brown liquid is obtained which on evaporation dries 
to a black, pitch-like mass. By interaction with ammonia, a 
series of amido-compoimds is obtained. 

Molybdenum Tribromide^ MoBrg, is formed by the action of 
bromine vapour on the heated metal; it can also be prepared 
electrolytically.^ It sublimes as a mass of fine blackish-green 
needles which are insoluble in water though soluble in cold dilute 
nitric, and in boiling hydrochloric, acids. On boiling with alkalis 
the hydroxide is formed (Blomstrand). 

Molybdenum Teiracldoride, M 0 CI 4 , is obtained together with 
the dichloride, as has been stated, by heating the trichloride in 
an atmosphere of carbon dioxide. The tetrachloride volatilises 
as a dark yellow vapour which condenses to a brown, crystal- 
line powder. A better method^ is to heat the dioxide with a 
solution of chlorine in carbon tetrachloride at 250°. When heated 
in moist air it is decomposed. It reacts readily with water, but 
is incompletely dissolved. It is only slowly soluble in hydro- 
chloric acid, and dissolves in concentrated sulphuric acid, giving 
a bluish-green colour. 

Molybdenum Tetrabromide, MoBr^, is formed in small quantities 

1 Blomstrand, J, pr. Chem., 1869, 77, 96. 

*Liechti and Kempe, Ann., 1873, 169 , 344; Wolf, Chem. Zentr., 1918, i, 
608. 

> Lindner and others, Ber., 1922, 65, [B], 1458. 

* Rosenheim and Braun, Zeit. anorg. Chtm.^ 1906, 46 , 311. 

> Michael and Murphy, Amr, Chm, J., 1910, 44 , 365. 




MOLYBDENUM AND THE HALOGENS 


1116 


in the preparation of the tribromide as black, glistening needles, 
which fuse when heated, volatilising in brownish-red vapours. 
These readily decompose into bromine and dibromide. In 
presence of air the compound deliquesces, forming a dark liquid 
giving with more water a yellowish-brown solution. 

Molybdenum Tetriodide, M 0 I 4 . — Liquid hydrogen iodide and 
molybdenum pentachloride yield black, insoluble crystals, 
probably of this compound. Double salts have also been 
described.^ 

Molybdenum Penlachloridey M 0 CI 5 . — This, the highest chloride 
of molybdenum, is formed ^ by heating molybdenum or molyb- 
denite in dry chlorine for some time, when bright, metallic, glisten- 
ing, black crystals are formed which melt at 194° and boil at 268°, 
giving a dark red vapour with a density of 9*4-9*53,^ correspond- 
ing to the above formula. The compound fumes on exposure to 
moist air, giving MoOgClg, and becomes coloured bluish-green, 
gradually deliquescing to a brown liquid which on dilution with 
water becomes colourless. Absolute alcohol, ether, and certain 
other solvents ^ yield green solutions, whilst chloroform, carbon 
disulphide, and nitrobenzene arc examples of solvents yielding 
red-brown solutions, which differ physically from the former; 
the chloride also dissolves in hydrochloric acid with evolution of 
•heat. It is decomposed by water with formation of the tetra- 
chloride, molybdic acid, and hydrochloric acid,'^ M 0 OCI 3 prob- 
ably being formed intermediately. 

When molybdenum trioxide is heated with phosphorus 
pentachloride to 170°, the compound MoCl 5 ,POCl 3 is formed. It 
crystallises in dark green prisms, and when further heated 
decomposes into its two constituents. 

Molybdenum Hexafluoride, M 0 F 3 , is obtained by passing 
dry fluorine over powdered molybdenum at 60-70°, the product 
being collected in a receiver cooled by a mixture of solid carbon 
dioxide and alcohol, and then purified by distillation. It is a 
snow-white, crystalline substance, melting at 17° to a colourless 
liquid, which boils at 35°, and is decomposed by water with 
formation of a blue oxide.® It is not acted upon by chlorine, 

^ Guiohard, "Ann. Chim, Phys., 1901, [7], 28, 498; Rosenheim and Koss, 
ZeiL anorg. Chem,, 1906, 49 , 148. • 

* Lindner and others, Ber., 1922, 65, [Bj, 1458. 

* Debray, Compt. rend., 1868, 68, 732. 

* Lloyd, J. Physical Chem., 1913, 17, 692. 

‘ Quichard, Bull, Soc. chim., 1901, [3], 25, 188. 

Ru6 and Eisner, Ber., 1907, 40, 2926. 



1116 


MOLYBDENUM 


but reacts with arsenic trichloride and antimony pentachloride ; 
it is reduced and turned blue by organic compounds. 


OxY-HALiDE Derivatives op Molybdenum. 

489 No oxyfluoride or oxychloride containing quinquevalent 
molybdenum is known with certainty to exist, although a con- 
siderable number of double salts, e,g.y MoOF3,2KF,H20 and 
K2(Mo0Cl5),2H20, have been prepared. The former class are 
blue or green, and the latter green, crystalline substances. The 
hydroxybromide, MoO(OH)Br2, 1-51120 yields double salts of 
the types K(MoOBr4),2H20 and K2(MoOBr5). 

Sexa valent molybdenum forms a large number of deriva- 
tives containing oxygen and the halogens, many of which are 
volatile and crystalline, and yield crystalline double salts with 
^ other metallic halides. 

Molyhdmyi Tetrajluoride^ M0OF4, is formed by the action of 
anhydrous liquid hydrofluoric acid on the corresponding oxy- 
cliloride as a white, hygroscopic body, melting at 97 ° and boiling 
at 180 °.^ It forms a double salt with potassium fluoride.^ 

Molybdenum Dioxydijluoride, MoOgFg, is obtained by heating 
the trioxide with cryolite or lead fluoride as an amorphous 
sublimate having a bluish tinge, which decomposes in the air 
into hydrogen fluoride and molybdenum trioxide; ® it is obtained 
in solution by dissolving the trioxide in hydrofluoric acid. It 
may also be obtained by the action of anhydrous liquid hydro- 
fluoric acid on the dioxydichloride as a white, hygroscopic mass, 
which sublimes at about 270 °, and turns blue in the air.^ Crystal- 
line double salts are formed by dissolving the normal and poly- 
molybdates in hydrofluoric acid; thus potassium molybdenum 
oxyfiucyride, K2Mo02F4,H20 = Mo02F2,2KF,Il20, forms lustrous 
plates or scales, and is soluble in water. 

Molybdenyl Tetrachloride^ M0OCI4, has been stated to be 
formed by the action of chlorine on a moderately-heated mixture 
of carbon and molybdenum dioxide. There is formed a dark 
green, crystalline mass, or, if obtained at a higher temperature, 
light-green plates having a metallic lustre. It is readily decom- 
posed by water, deliquesding in moist air to a blue liquid, and this 

* Ruff and Elsiner, Ber.i 1907, 40 , 2931. 

> Marohetti, Zeit. anorg. Chem.^ 1895, 10 , 66. 

* Sohultze, J. pr. Chem., 1880, 21 , 442. 

* Ruff and Eisner, Ber., 1907, 40 , 2933. 




OXY-HALIDE DERIVATIVES QE MOLYBDENUM 1117 


on addition of water gives a blue precipitate which becomes brown 
in presence of ammonia. It is probable, however, that it is not 
an individual compound, but a mixture of the pentachloride and 
dioxydichloride.^ 

Molybdenum Dioxydichloride^ MoOgClg. — This compound was 
originally supposed to be the hexachloride, its true composition 
being first ascertained by Rose. It is obtained by heating the 
dioxide in chlorine, and also, together with other chlorides, when 
a mixture of the trioxide and carbon is substituted for the dioxide. 
It sublimes usually as an amorphous mass, and melts only in 
closed vessels, in which it may be sublimed at low temperatures 
yielding thin tetragonal plates, or mossy aggregates. Jt dissolves 
readily in water and alcohol. 

The oxychloride, MoaCaClg, is obtained by the repeated sub- 
limation of the oxytetrachloride,*’ and forms well-developed 
violet prisms, which are decomposed on heating in the air into 
molybdenum dioxydichloride and chlorine. When heated to 
a temperature somewhat higher than that needed for its formation, 
it yields MogOgClg, which forms pale red needles and is stable 
in the air. Oxychlorides having the composition MogOgClg, 
M02O3CI4, and M03O3CI7 have also been described.^ 

Molyhdenyl Dihydroxydichloride, MoO(OH)2Cl2, is obtained 
by the action of hydrogen chloride on the trioxide at 150 - 200 °, 
and is a white, crystalline substance which is volatile without 
decomposition only in an atmosphere of hydrogen chloride.^ 

A number of salts of chloromolybdic acids, which may be 
regarded as molybdates in which the oxygen and the hydroxyl 
groups are partially replaced by chlorine, have been described. 
The acid, MoOCl3'OH,7H20, is obtained by the action of fmning 
hydrochloric acid on molyhdenyl hydroxide, and a number of its 
salts have been prepared.^ 

Molybdenum Dioxydibromide, Mo02Br2, is formed when 
bromine vapour is passed over the heated dioxide, or when a 
mixture of molybdenum trioxide and boron trioxide is heated 
with potassium bromide : 

M0O3 -f B2O3 + 2KBr = Mo02Br2 + 2KBO2. 

It forms yellow tablets which deliquescp on exposure to air. 

A hydroxybromide of the composition Mo(OH)3Br3 exists. 

1 See also Klason, Ber., 1901, 34, 148. * Annalen, 1880, 201, 123. 

* Debray, Compt. rend., 1858, 46, 1101. 

* Weinland and Knoll, Ber., 1904, 87, 669; Zeit anorg. Chem., 1906, 44, 81. 




1118 


> MOLYBDENUM 


A number of bromomolybdates have been described (Weinland 
and Knoll). 


Molybdenum and Sulphur. 

490 Molybdenum Sesquisulphide, MogSg, is obtained when the 
disulphide is heated in the electric furnace. It forms steel-grey 
needles of density 6*9 at 15 °, and is converted into metallic 
molybdenum when heated to a higher temperature than that 
at which it is formed.^ 

Molybdenum Disulphidey MoSg, is found native as molybdenite 
in Sweden, Norway, Bohemia, Saxony, the Urals, at Caldbeck 
Fells in Cumberland, in Connecticut, California, and elsewhere. 
It commonly occurs in foliated masses or in scales, and sometimes 
in tabular hexagonal prisms, and in its general appearance is 
very similar to graphite, since it possesses a metallic lustre and 
pure lead-grey colour, and leaves a grey trace on paper. It 
possesses interesting electrical properties, and between ordinary 
temperatures and a red heat it exists in two distinct states.^ 
Molybdenite generally occurs embedded in or disseminated 
through granite, gneiss, zircon-syenite, granular limestone, and 
other crystalline rocks. 

When the trioxide is fused with sulphur, or heated in a current 
of hydrogen sulphide, the same compound is obtained in the 
form of a glistening black, powder, easily distinguished from 
graphite by the facts that when heated before the blowpipe it 
is incombustible, that it oxidises when heated in the air with 
evolution of sulphur dioxide and formation of molybdenum 
trioxide, and that it is readily oxidised by nitric acid and aqua 
regia. 

Dimolybdenum Pentasul'phide^ MogSgjSHgO, is produced when a 
solution of ammonium molybdate containing sulphuric acid is 
reduced with zinc, the liquid filtered and treated with hydrogen 
sulphide. It is a brownish-black precipitate which on careful 
dehydration in a stream of carbon dioxide yields black M02S5. 
It is soluble in alkali sulphide to red solutions.® 

Molybdenum Trisulflitde^ M0S3, is formed when hydrogen 
sulphide is passed into the concentrated solution of a molybdate 
and hydrochloric acid is added to the liquid. It may likewise be 
prepared by boiling the molybdate of an alkali metal for a short 
time with ammonium sulphide, and then precipitating with 

* Guichard, Bull. Soe. chim., 1900, [3], 28, 147. 

» W..term»n, Phil. Mag., 1917, [6], 33, 226. * Krto, Amalen, 1884, 285, 1. 




MOLYBDENUM AND SULPHUR 


1110 


dilute sulphuric acid. Thus obtained, it is a reddish-brovn 
precipitate which dries to a blacldsh-brown powder. On heating 
in absence of air, it splits up into the disulphide and sulphur. 
With basic sulphides it forms soluble thio-salts. 

Potassium Thiormlyldate^ K2M0S4, is formed when potassium 
molybdate is saturated with hydrogen sulphide in presence 
of potassium hydroxide. On evaporating the solution, the com- 
pound crystallises out in ruby-red four- or eight-sided tablets 
which have a green, metallic lustre, and dissolve in water to form 
a yellowish-red solution. 

Ammonium Thiomilyhdate^ (NH4)2MoS4, is obtained by dis- 
solving the trisulphide in ammonium sulphide, and crystallises 
in cinnabar-red scales. 

A series of mono- and di-thiomolybdates has been described 
by Kriiss. 

Molybdenum Tetrasul'phide^ M0S4, is obtained by heating penta- 
thiomolybdic acid to 140 ° as a cinnamon-brown powder which 
undergoes slight oxidation in the air. Tlie pentathio-acid 
is obtained as a reddish-brown powder by the action of dilute 
hydrochloric acid on the potassium salt. 

Potassium Pentathiomolyhdate^ KHM0S5, is obtained ^ by 
evaporating a solution of potassium dimolybdate which has been 
saturated with hydrogen sulphide, and separates in sparingly 
soluble, blood-red prisms probably belonging to the rhombic 
system. A black powder consisting of molybdenum di- and tri- 
sulphides separates out at the same time.^ 

Perthiomolybdic Acid, HMoSg. — When a solution of normal 
ammonium thiomolybdate is mixed with a solution of ammonium 
polysulphides, ammonium hexathiomolybdate or 'perthiomolybdale 
separates out in black, lustrous needles, which are sparingly 
soluble in water or alcohol. By the action of caustic potash 
it yields the potassium salt, KMoSg, which crystallises in thin, 
dark-brown plates, more soluble in water than the ammonium 
salt. The free acid, HMoSg, is obtained by treating the am- 
monium salt with cold 10 per cent, hydrochloric acid and washing 
the product with carbon disulphide.® 

Sulphomolybdic Add, H2[MoO(S04)2(Mo04)], has also been 
prepared.^ 

^ KriiBs, Ann., 1884, 22(}, 1. Hofmann, 2eit. anorg. Chem., 1896, 12, 65, 
ascribes the formula KMoS^ to this compound. 

‘ Kriiss, he. cit. 

* Hofmann, he. eii. 

* Meyer and Stateezny, Zeit. anorg. Chem. 1922, X82, 1. 

VOL. II. (n.) 



1120 


MOLYBDENUM 


Molybdenum and Nitrogen, Phosphorus, Boron, Carboh 
AND Silicon. . 

491 Molybdenum 'Nitride . — When molybdenum oxide 
hydroxide, or mixtures of the two are heated to 500 - 600 ° wit] 
equal parts of nitrogen and hydrogen under a pressure of abou 
60 atmospheres a molybdenum nitride is formed. Direct inter 
action, with formation of a nitride, takes place at high tempera 
tures between molybdenum and nitrogen.^ It is also the fina 
product when molybdenum trichloride or pentachloride ii 
heated in a stream of ammonia. When heated in hydrogen oi 
water-vapour, M03N2 yields pure metallic molybdenum anc 
ammonia ; ^ its technical application as a catalyst for the unior 
of nitrogen and hydrogen has been the subject of investigation. 

Molybdenum Phosphide, MoP, is obtained by strongly 
heating molybdenum trioxide and metaphosphoric acid in a 
carbon crucible. It forms a grey, vesicular mass having a metallic 
lustre and containing crystals in the cavities. On ignition in the 
air, it oxidises slowly, and it takes fire when dropped into fused 
potassium nitrate. 

Molybdenum Metaphosphate, Mo(P03)3, formed when a solu- 
tion of molybdenum trioxide in metaphosphoric acid is reduced 
with hydrogen at a red heat.® 

Molybdenum Boride, probably MogB, has been prepared by an 
arc method. 

Molybdenum Carbides . — The carbide, MoC, is obtained by 
fusing in the electric furnace ^ a mixture of molybdenum, carbon, 
and aluminium, as a grey, crystalline powder of density 8-40 
at 20°, whilst the compound, MogC, is formed when calcium 
carbide is heated in the electric furnace with molybdenum 
dioxide .5 The carbonyl, Mo(CO)3, or more probably ® Mo5(CO)2e, 
is known. 

Molybdenum Cyanides and Thiocyanates . — Tervalent molyb- 
denum forms a series of complex molybdo-thiocyanates of the 
type K3Mo(CNS)g,4H20 ; quadrivalent molybdenum forms three 
distinct series of complex cyanides ’ ; quinquevalent molybdenum 

^ Lederer, 1911 ; Langmuir, J. Amer. Chem. Soc., 1919, 41, 1C7. 

* D.R.-P., 246554; Austr. Pat. 62524. 

» Colani, Compt. rend., 19f4, 158, 499, 794; ibid., 1917, 165, 185. 

* Moissan and HofFmann, Compt. rend., 1904, 138, 1558. 

• Moissan, Compt. rend., 1897, 125, 839. See also Hilpert and Omstein, 
Ber., 1913, 46, 1669. 

• Mond and WalUs, J. Chem. Soc., 1922, 121. 29. 

^ iSoe a review by Collenburg, Zeit. anorg. Chem. 1922, 121, 298. 




DETECTION AND ESTIMATION OP MOLYBDENUM 1121 


forms double hydroxythiocyanates of the form Mo(OH)2(CNS)3‘Py2 
as well as complex oxalp-derivatives. 

Molybdenum Silidde, Mo2Si3, is formed as a crystalline com- 
pound when the oxide obtained by calcining ammonium molyb- 
date is heated with silicon in the electric furnace.^ Silicides of the 
formulfle MoSi and MoSig have also been described. ^ 


Detection and Estimation of Molybdenum. 

492 Probably the most delicate qualitative test for molybdenum 
compounds consists in their reduction by means of stannous 
chloride or zinc, in the presence of a soluble thiocyanate; a 
blood-red coloration, due to the formation of moybdenum 
thiocyanate which is soluble in ether, indicates the presence of 
as little as 1 part in 6 millions.® Formation of a plum-coloured 
compound, Mo03{OEt‘CSSH)2, with xanthic acid is another 
sensitive reaction,^ as also is that of red ammonium permolybdate 
by means of hydrogen peroxide.® Acidified solutions of molyb- 
dates, when brought into contact with zinc or other suitable 
reducing agents, become blue, then green, and finally brown ; 
hydrazine, iodides, or quinol give a blue colour, whilst catechol 
yields an orange solution.® Reduction is effected by sulphurous 
acid only if the solutions are neutral or but slightly acid. When 
a trace of a molybdenum compound is evaporated nearly to dry- 
ness with a few drops of sulphuric acid, a blue colour develops. 
This reaction also is very sensitive. 

Molybdenum trisulphide is slowly precipitated from an acid 
solution of a molybdate by hydrogen sulphide, which first causes 
the development of a blue colour. The precipitate dissolves 
readily in ammonium sulphide solution, yielding ammonium 
thiomolybdate which on acidification again deposits the brown 
trisulphide. 

^ Vigouroux, Compt. rend., 1899, 129, 1238. 

• Honigsehmid, Monatsh.j 1907, 28, 1017 ; Watts, Chem. Zentr., 1908, i, 
698; Wedekind, D.R.-P. 294267. 

• Browning, Amer, J. Sci.t 1915, [4], 40, 349; Moir, J. Chem. Metall. Min. 
80c. 8. Africa^ 1916, 16, 191 ; St6rba B6hm and VostrSbal, Zeit. anorg. Chem.f 
1920, 110, 81. 

• Koppel, Chem. Zeit., 1919, 43, 777; Malowan, Zeit. anorg. Chem., 1919, 

108, 73. 

• Komarowsky, Chem. Zeit, 1913, 37, 967. 

• Moir, he. cit See also Kafka, Zeit anal. Chem., 1912, 51, 482; Poz/.i* 
Esoot, BuU. 80c. chim., 1913, [4], 13, 402, 1042. 



1128 MOLYBDBINDM 

'' ’< ' 

Fuchs/ describes a test for molybdenite whereby the mineral 
is dissolved in fused potassium hydroxidp, yielding a red double 
sulphide ; if this is dissolved in water, a series of colour changes, 
through blue, green, and yellow, takes place. 

A solution of ammonium molybdate in nitric acid becomes 
yellow-coloured on the addition of a few drops of sodium phos- 
phate solution, and on keeping or warming a heavy yellow pre- 
cipitate of ammonium phosphomolybdate “ separates out. 

Molybdenum compounds impart tb a bead of microcosmic 
salt or borax in the reducing flame a fine green colour; the 
bunsen flame is coloured green by molybdic acid. 

For the gravimetric estimation of molybdenum, the compoimd 
is converted into a neutral molybdate which is precipitated from 
aqueous solution as mercurous molybdate or lead molybdate, 
the latter method now being almost exclusively employed.® In 
the former case, mercury is removed during ignition, and the 
residual mcflybdenum trioxide, which must not be heated to more 
than 425°, is weighed.^ If the molybdenum is to be estimated by 
way of the sulphide,® the latter may be directly precipitated by 
hydrogen sulphide from a solution acidified preferably with 
formic acid, or the gas may be passed into an aramoniacal solu- 
tion containing the molybdic acid, and the resulting solution 
of ammonium thiomolybdate decomposed with acid. In either 
case the sulphide is usually converted into the trioxide by roasting 
and treatment with nitric acid, but it may be dried in carbon 
dioxide and weighed as such. 

It is also possible to estimate molybdenum by volatilisation 
of the trioxide in a current of carbon tetrachloride vapour.® 

Molybdenum trioxide can be separated from admixture with 
tungsten trioxide by dissolving it in a mixture of selenium 
oxychloride and sulphuric acid.^ 

Volumetric methods which have been proposed include the 
titration of the sesqui-compounds with potassium permanganate 
and methods based on the reactions : 2Mo08 + 2HI = HgO -f* 

^ Informaciones y mm,, soc. ing. Peru, 1918, 20^ 423. 

‘ Ardonates give a precipitate of similar appearance. 

* Raper, Biochem. J., 1914, 8» 649; Taylor and Miller, J. Biol Chetn., 1915, 
21, 255; Weiser, J. Physical f hem., 1916, 20, 640. 

* Treadwell, Zeii. Eleklrochem., 1913, 19, 219; Wolf, Zeit. angew. Chem., 1918, 
81, i, 140, 

‘Binder, Chem. Zeit, 1918, 42, 255; Wolf, he. cit; Stgrba-Bohm and 
V^ostrSbal, he. cit 

* Jannasch and Ijaubi, J. yr. Chem., 1918, [2], 97, 154. 

^ *Merrill, J. Amer, Chem. 8oc., 1921, 48, 2383. 



DETECTION AND ESTIMATION OP MOLYBDENUM 1123 


MoaOj+Ijj, and KIO 3 + MoA + 2Ha = KCl + M 02 O 5 + 
ICl+HaO.i 

Alomtc Weight of Jflolybdenim.—The determination of the 
atomic weight of molybdenum has been frequently made, but 
with varying results. After an inaccurate determination by 
Berzelius, Svanberg and Struve obtained the number 92-5, 
which was confirmed by Berlin, and then generally adopted. 
The investigation of Dumas ^ then showed that the number just 
quoted was distinctly too low, the average obtained by the 
reduction of the trioxide to the metal in a current of hydrogen 
being 95*9 ; the numbers in the different experiments varying, 
however, from 95-3 to 96*2. Debray ® obtained the number 95*5 
by the same method, whilst Liechti and Kempe ^ by the analysis 
of the di-, tri-, and penta-chlorides of molybdenum obtained 
the same average number as Dumas; but in this case also the 
numbers found in the different experiments varied considerably. 
Smith and Maas ® found the number 96-06, the method adopted 
being to heat pure sodium molybdate in a current of hydrogen 
chloride : 

Na^MoO^ + 4Ha = 2NaCl + Mo(OH) 20 Cl 2 + H^O. 

The last two being volatile, only pure sodium chloride remains 
beliind, and from the amount of this obtained from a given 
quantity of sodium molybdate, the abo\e number was obtained 
as the average of ten closely agreeing experiments. Seubert 
and Pollard,® by the acidimetric determination of molybdic 
acid, obtained the number 95-92, and by the reduction of the 
trioxide to the metal in a current of hydrogen the number 96-01. 
By a determination of the ratio Mo ; M 0 O 3 , Vandenberghe ^ 
obtained the value 96-06, whilst MUller,® employing the same 
ratio, found the value 96-029. The mean value of the best de- 
terminations is 96-04 ± 0-01. The atomic weight now adopted 
(1922) is 96-0.® 

^ JamioBon, J. Amer. Chem. Soc., 1917, 39, 246. For details of certain other 
methods, see Zinberg, Zeit. anal. Chem., 1913, 62, 629 ; Marbaker, J. Amer. Chem. 
Soc., 1916, 37, 86; Travers, Compt. rend., 1917, 166, 362 ; Hoepfnor and Binder, 
Chem. Zeit., 1918, 42, 316, 664 ; Scott, J. Ind. Rng. Chem., 1920, 12, 578 ; Camp 
and Marden, ibid., 1920, 12, 998 ; Nakazono, J. Chem. Soc. Japan, 1921, 42, 626. 

* Ann. Chim. Phya., 1869, [3], 66, 129. 

* Compt. rend., 1868, 66, 732. * Annalen, 1873, 169, 360. 

' Zeit. anorg. Chem., 1893, 6, 280. • Ibid., 1896, 8, 434. 

Mem. Acad. Belg., 1898, 66. • J. Amer. Chem. Soc., 1915, 37, 2046. 

* Gerber, Mon Set., 1917, [6], 7, 73, claims that molybdenum is not a simple 
substance, but is accompanied by neo-molybdenum of higher atomic weight. 




112S4 


TUNGSTEN 


TUNGSTEN. W=i84*o. At. No. 74. 

493 The minerals tungsten or heavy-stone, now termed 
scheelite or calcium tungstate, and wolfram (the lupi spuma 
of Agricola) were, up to the middle of the eighteenth century, 
both classed among the tin ores. In 1781 , Scheele proved that 
tungsten was composed of lime combined with a peculiar acid, 
and in the same year Bergmann stated that, in his opinion, this 
acid was a metallic calx. Two years later the Spanish chemists 
Juan, Jos 4 , and Fausto d’Elhujar,^ showed that this same acid 
is contained in the mineral wolfram, combined with iron and 
manganese. They also prepared metallic tungsten. 

Tungsten is not a common metal, being found only in a few 
minerals, some of which occur, however, in fairly large quan- 
tities. The most important of these are wolfjam, or wolframite, 
a tungstate of iron and manganese, (Fe,Mn)W04, found in 
Cornwall, in Cumberland, on Bona in the Hebrides, in County 
Wicklow, at Zinnwald, in many localities in the United States, 
in Burmah, and also in Austria-Hungary, Spain, Portugal, 
Queensland, New Zealand, Tasmania, Canada, and various parts 
of South America, and scheelite or calcium tungstate, CaW04. 
In addition to these, tungsten occurs in the following somewhat 
rare minerals: wolframochre, WO3; stolzite or lead tungstate, 
PbW04; ferberite, FeW04, which occurs in large quantities in 
Colorado; hubnerite, MnW04; cuproscheelite, or cuprotungstite, 
(Ca,Cu)W04; chillagite,^ PbW04,PbMo04, and tungstenite,® 
WS2(?). 

Metallic Tungsten is obtained from wolfram by a method 
which consists of three distinct stages.^ Sodium tungstate is 
first prepared by heating together a mixture of the ground ore 
and sodium carbonate. When this operation is carried out 
under proper conditions the extraction is complete, and at the 
same time any tin and silica present are left insoluble. The 
sodium tungstate thus formed is dissolved in water and separated 
from the oxides of iron, aluminium, manganese, tin, and silicon 
by filtration, and tungstic acid, HaW04, is then precipitated by 

^ A Chemical Analyais of Wolfram and Examination of a New Metal, which 
enters into its Composition^ Translated from the Spanish by C. Cullen, to 
which is prefixed a translation of Mr. Soheele’s analysis of the Tungsten, or 
heavy-stone, with Mr. Bergmann’s supplemental remarks. I^ondon, 1786. 

* Ullmann, J. Roy. Soe, New South Wales, 1912, 46, 186. 

® Wells and Butler, J, Washington Acad. Sci., 1917, 7, 696. 

* sSIadfield, J. Iron Steel Institute, 1903, 64, 38. 




TUNGSTEN 


1125 


means of acid. In this step care is necessary to prevent the 
formation of hydrated tungstic acid, which is soluble. The 
tungstic acid thus obtained is washed free from sodium salts 
and dried, and the resulting tungstic oxide is mixed with car- 
bonaceous materials and submitted to a high temperature in 
crucibles for reduction to metal. A well-fired crucible when 
opened should be uniform throughout, with the exception of 
a thin layer of tops or undecomposed tungstic oxide and carbon, 
which can be readily removed. 

Tungsten containing 99 per cent, of the metal has been obtained 
by fusing tungsten trisulphide with lime.^ 

Metallic tungsten may be prepared on the small scale by the 
reduction of the trioxide with carbon or in a current of hydrogen,*^ 
by the reduction of the chloride in hydrogen or sodium vapour, or 
by heating a mixture of the trioxide with one-tenth of its weight 
of sugar charcoal in the electric furnace ; if care be taken that 
complete fusion of the metal does not occur, the latter is free from 
carbon.® The metal thus obtained is as a rule fused on the 
surface, but is porous internally, and can be welded like iron. 
It has been obtained in the form of a regulus by reducing the 
oxide with aluminium turnings and at the close of the reaction 
adding aluminium foil, and blowing in a stream of oxygen, 
or by adding liquid air to a mixture of the oxide and aluminium 
and igniting as in the thermite process ^ The powdered metal 
can be prepared also by heating the oxide with zinc and extracting 
the product with caustic soda solution,® and by the action of 
dilute acids on the alloys of manganese and tungsten.® Electro- 
lysis of the fused trioxide or salts, or of the latter in solution, has 
been found to yield metallic tungsten. 

Powdered tungsten, or the massive form obtained from it by 
fusion (although this process is not simple, the metal attacking 
the receptacle at the high temperatures necessary and becoming 
impure) are used in the manufacture of alloys, particularly 
ferrotungsten. The massive form is not sufficiently ductile, nor 
indeed sufiiciently pure, for use in the manufacture of tungsten 
filaments for electric incandescence lamps, so that until recently 
it was necessary to form the filaments of the powdered metal 

^ Weiss, ZtU. anorg, Chem., 1910, 65, 279. 

* Davis, J. Ind. Eng. Chem., 1919, 11, 201. 

* Moissan, Compt. rend., 1896, 123, 13. See also Mennicke, “ Mctallurgie (’es 
Wolframs,” Berlin, 1911, 

* Stavenhagen, Ber., 1899, 32, 1513, 3064. 

* Del^pine, Compt. rend., 1900, 131, 184. • Arrivant, ibid., 1906, 143, 694, 



MOT TUNGSTEN 

together with an appropriate binding material. Now/ however, 
the finely divided metal is formed into rods by pressure alone, and 
heated in hydrogen by slowly drawing it through a small heated 
coil, whereby it is converted into elongated crystals; it then 
responds to the mechanical treatment necessary to give malle- 
ability and ductility. 

In the form of a regulus, tungsten has a slightly darker colour 
than zinc, shows a crystalline (cubic structure, is harder than 
glass, (its degree of hardness depends on its previous treatment, 
and is higher if the metal is impure); its density is above 19, 
but figures varying between 18*7 and 21*4 have been obtained. 
The metal is not magnetic, it has a mean specific heat 0*0340 
between 15° and 93°, 0-0375 between 15° and 423°, ^ melts * at 
3540° ± 30°, and can be volatilised in the electric furnace, but is 
more refractory than iron, molybdenum, or uranium.® 

Tungsten has the smallest compressibility of any substance 
hitherto studied.® It occupies a place in the potential series 
between antimony and mercury, and exhibits passivity under 
certain conditions.’ It is attacked by fluorine at the ordinary 
temperature with incandescence, and by chlorine at 250-300°, 
but has no action on nitrogen or phosphorus at a red heat; 
when heated with carbon, silicon, or boron in the electric furnace, 
it yields crystalline compounds having a metallic lustre which 
are hard enough to scratch rubies. It is slowly attacked by fum- 
ing sulphuric acid and by fused alkalis.® At a red heat, the 
powdered metal burns in air, forming the trioxide,® but it is not 
readily oxidised by moist air, although slowly attacked by water 
containing carbon dioxide it is readily oxidised when heated 
with oxidising agents such as lead dioxide or potassium chlorate. 
Sulphuric, hydrochloric, and hydrofluoric acids act upon it slowly, 
but it is more readily dissolved by a mixture of nitric and hydro- 
fluoric acids; the powdered metal is rapidly oxidised by aqua 

^ Gross, Jahrb. Radioakiiv. Ekktronik, 1918, 16, 270. , 

* Debye, Physikal Zeit„ 1917, 18 , 483. 

* Dofacqz and Guichard, Ann, Chim, Phys.^ 1901, [7], 24 , 139. See also 
Worthing, J. Franklin Inst., 1 918, 186 , 707. 

* Langmuir, Physical Rev., 1916, 6, 138. 

‘ Moissan, CornTpi. rend., 1906, 142 , 425. 

^ Richards and Bartlett, J.,Amer. Chtm. Soc., 1915, 87, 470. 

^ Fischer and Boderburg, Zeit. anorg. Chem. 1913, 81 , 170; Fischer and 
Rideal, i6W.; Koemer, Trane. Amer. Electrochem. Soc., 1917, 31 , 221. 

* Ruder, J. Amer. Chem. Soc., 1912, 34 , 387. 

* Langmuir, J. Amer. Chem., Soc., 1913, 86, 106. 

Wohler and Prager, Zeit. EUktrochem., 1917, 23, 199. 




TUNGSTEN AND OXYGEN 


1127 


regia, and dissolves in boiling potassium hydroxide solution with 
formation of potassium tungstate and evolution of hydrogen, 
whereas the fused metal is not attacked by aqua regia, but dis- 
solves slowly in fused potash (Stavenhagen). Tungsten is utilised 
for the production of filaments for incandescence electric lamps 
which have a very high efiiciency.^ It is also largely employed in 
the manufacture of tungsten steels, generally in the form of fcrro- 
tungsten. In the finely-divided form, it is a valuable catalyst 
in Haber’s process for the synthesis of ammonia. 

Alloy s.—Cert&m definite compounds of tungsten with other 
metals are believed to exist ; ferrotungsten is, however, the most 
important.^ Cobalt forms the alloys ® CogW and CoW. 


COMPOUNDS OF TUNGSTEN. 

Tungsten and Oxygen. 

494 Tungsten forms two definite oxides ^ : tungsten dioxide, 
WOg, and tungsten trioxide, WO3. These combine together to 
form compounds analogous to the blue oxides of molybdenum. 

A black gelatinous precipitate, considered to be the hydrated 
sesquioxidcy WgOg, is formed when potassium hydroxide solution, 
followed by a weak acid, is added to the product of reduction of 
tungsten hexachloride with sodium amalgam. It is unstable, 
being converted into the dioxide.^ 

Tungsten Dioxide, WOg.— This oxide is formed when a current 
of hy(bogen is passed over the trioxide, WO3, at a dull red heat. 
It may also be obtained in the wet way by reducing the trioxide, 
mixed with hydrochloric acid, by means of metallic zinc, or by 
the action of water on the tetrachloride. In preparing it in the 
dry way care is needed, as if the temperature be too high metallic 
tungsten is formed, whereas if the heat be not sufficient, the 
intermediate blue oxide is produced. Tungsten dioxide is a brown 
powder of density 12-1, which has a copper-red colour when 

^ J.filr QaMeuchtung, 1906, 49 , 766; Nature, 1907, 76 , 156; J. Inst. Elect. 
Engineers, 1907, 38, 211; Weber “Die elektrischen Metallfadengliihlarapen,” 
Leipzig, 1914; MtiUer, “ Metalldrahtlampe,’* Halle, 1914; Lummer, “ Grund- 
lagen, Ziele und Greazen der Leuchttechnik,” Berlin, 1918. 

* Honda and Murakami, 5ct. Rep. Tohdku Imp. IJniv., 1918, 6, 236, state 
that the only compound formed in tungsten steels has the formula fOgW. 

» Kreitz, Metall u. Erz, 1922, 19 , 137. 

* For the thermochemistry and vapour pressures of the oxides, see van 
Liempt, Zeit. anorg. Chem., 1921, 120, 267. 

» Hill, J. Amer. Chem. 80c., 1916, 88, 2383. 



1128 


TUNGSTEN 


crystalline trioxide is employed for its preparation. It is strongly 
pyrophoric, and must be cooled in hydrogen for some time before 
it is exposed to the air. It is slightly soluble in concentrated 
hydrochloric acid and sulphuric acid, pelding purple solutions. 
Oxidising agents convert it rapidly into the trioxide. It dissolves 
in potash to form hydrogen and potassium tungstate : 

WO 2 + 2KOH - K 2 WO 4 + Hg. 

Tungsten Trioxide, WO3. — This oxide occurs native as wolfram- 
ine, a yellow powder found together with other tungsten 
minerals in Cumberland, near Limoges, in Connecticut, and in 
North Carolina. In order to prepare the trioxide, the method 
already described may be adopted, or finely powdered 
wolfram may be digested for a long time with hydrochloric 
acid, the mixture frequently shaken, the acid renewed, and a 
little nitric acid added towards the end of the process to oxidise 
the iron. This is continued until the acid has dissolved out the 
whole of the iron and manganese and the brown powder has 
become yellow-coloured. The insoluble portion consisting of 
tungsten trioxide and undecomposed wolfram and quartz, after 
being well washed, is shaken up with a solution of ammonia 
which dissolves the liberated tungstic acid. The solution is 
crystallised and the crystals are converted into the trioxide by 
ignition in the air. Wohler converted the wolframite into 
calcium tungstate by fusing the finely powdered mineral for 
an hour with twice its weight of calcium chloride and then 
lixiviating, when calcium tungstate remained behind. This was 
then decomposed by nitric acid, and tungsten trioxide obtained 
by igniting the yellow precipitate formed. The native calcium 
tungstate (scheelite) can also be decomposed in this way. 

Tungsten trioxide is a bright canary-yellow coloured, amorphous 
powder which becomes dark orange on heating, but regains its 
bright yellow colour on cooling ; it melts at 1473°. A very slight 
admixture of sodium salt imparts to the oxide a greenish tint 
which no amount of oxidation can remove (Roscoe). It also 
becomes greenish on exposure to light.^ Tungsten trioxide has 
been obtained in the crystalline state by Debray, by igniting 
a mixture of sodium tujogstate and carbonate in a current of 
hydrochlpric acid, when the trioxide is obtained in olive-green 
rectangular prisms which sublime at a white heat. The crystal- 
line trioxide has also been prepared by heating hydrated tungstic 

1 8ee van Liempt, loc7cii.\ Burger, Zeit. anorg, Chem., 1922, 121, 240. 



TUNGSTIC ACID AND THE TUNGSTATES 


1129 


. • * 

acid with borax in a porcelain tube (Nordenskjold). The density 
of tungsten trioxide is 7*2. It is insoluble in water. Keduction 
to the metal is effected by hydrogen or carbon, various oxides of 
indefinite conposition being formed intermediately.^ The amor- 
phous oxide is soluble and the crystalline oxide insoluble in sulphur 
monochloride.® 


Tungstic Acid and the Tungstates. 

495 Tungsten trioxide is an acid-forming oxide, and yields two 
tungstic acids, the normal acid, H2WO4, and metatungstic or 
tetratungstic acid, the salts of which correspond to 

the tetrachromates and tetramolybdates. In addition to the 
salts corresponding to these acids, a large number of other 
tungstates analogous to the polychromates and polymolybdates 
have been prepared, the formulae ascribed to which are given in the 
following table : ^ 

M^2W04 =M^20,W03. 

= M^20,2W03. 

MW30 io = M^ 20,3W03. 

M^2W40i3 = M^ 20,4W03. 

MW50 i 6=M^20,5W03. 

MWi 9=M^20,6W03. 

Many of these crystallise with a number of molecules of 
water, forming well-developed crystals. The salts of the formula 
M^io^12^4i termed paratungstates. Copaux^ formulates 
the paratungstates as B6[n(W207)3],aq., whilst Rosenheim*' 
formulates them as R6H5[H2(^^4)6 ]j^T- 

The tungstates also 3deld complex salts with many other 
acidic oxides analogous to the complex molybdates. 

Tungstic Acid, H2WO4.— When a solution of a tungstate is 

^ Davis, J. Ind. Eng. Chem., 1919, 11, 201. 

® Smith and Fleok, J. Amer. Chem. Soc., 1899, 21, 1008. 

* See Schaefer, Zeit. anorg. Chem., 1904, 38, 142, where the literature is 
quoted. Acids containing a complex radicle composed of one kind of anionogen 
radicle only are termed “ iso-poly-acids ” ; those composed of two or more 
different anionogen radicles are termed “ Xetero-poly-acids,” The exact 
quantitative examination of these bodies is rendered difficult by the high atomic 
weight of tungsten ; for this and other reasons there is still considerable un- 
certainty regarding the formulation of the complex tungstic acids. 

* C(mpt. rend., 1913, 156, 1771. 

» Zeit. anorg. Chem., 1916, 96 , 139. See also Prandtl, Ber., 1916, 48,692. 


MW, 5 =M',0.8W03. 

=2M'20,6W03. 

M'jWjO,! = 3 M'jj0,7W03. 
M‘ 3 W 30 i 3 =4M"30,3W03. 

M'ioWi 304 i = 5M-30,12W03. 




TUNGOTBN 


1130 


precipitated by an acid in the cold, a white precipitate is gradually ^ 
thrown down consisting oi hydrated tungstic acid, H2W04,H20.® 
This is soluble in water, possesses a bitter taste, and reddens litmus. 
If, on the other hand, an excess of hot acid be used, anhydrous 
tungstic acid, H2WO4, separates as a yellow powder, insoluble in 
water and in all acids except hydrofluoric acii If pure tungsten 
hexj^chloride be exposed to the action of moist air, the red 
monoxychloride is first formed, and this soon passes into a fine 
flocculent mass of white tungstic acid. 

The tungstates are insoluble in water, except those of the alkali 
metals; and even of these, some tungstates of potassium and 
ammonium are only sparingly soluble. The tungstates of the 
alkaline-earth metals, and of the heavy metals are mostly amorph- 
ous powders, but they may be obtained crystalline by double 
decomposition at a high temperature. 

Metatungstic Addy 

H2W40i3,8(?8-5)TT20, i.e.y HeH4[H2(W207)6,]21H20. 

— The salts of this acid were discovered by Margueritte,® but 
the acid was first prepared by Scheibler.* For this purpose 
the barium salt is decomposed by dilute sulphuric acid or the 
lead salt with hydrogen sulphide. Metatungstic acid crystallises 
in small, yellow octahedra which effloresce in the air. On 
ignition it is converted into the trioxide. It is readily soluble 
in water and the solution possesses a harsh, bitter taste. When 
the solution is concentrated by boiling, a white hydrate is 
deposited and afterwards the trioxide separates. The meta- 
tungstates of the alkali metals are formed when the ordinary 
tungstates are boiled with timgstic acid until the filtrate gives 
no precipitate on addition of hydrochloric acid.^ The meta- 
tungstates of the other metals are, as a rule, easily soluble in 
water, and are best prepared by double decomposition of the 
barium salt with the corresponding sulphate or carbonate. The 
warm solutions usually yield the salts in amorphous masses when 
evaporated, but when concentrated over sulphuric acid they 
frequently crystallise. The metatungstates possess a bitter taste, 
and are not precipitated by acids; on long boiling ordinary 
tungstic acid is deposited* 

^ Lottermoser, KoUoid ZeU.y 1914, 16» 145. 

3 See, however, HUttig and Kurre, Zeit. anorg, Chem.y 1922, 122, 44; also 
Burger, ibid,, 1922, 121, 240. 

» Am, Chim, Phy8.y 1846, [3], 17, 476. « J. pr, Chm„ 1861, 88, 310. 

* Copaux, Ann. Chim. Phya., 1909, [8], 17, 207 ; Compi. rend., 1913, 156, 71. 

* 




TUNGSTIC ACID AND THE TUNGSTATES 1181 


Colloidal Tungstic Add, — This modification of tungstic acid 
was discovered by Gr,aham,^ and is obtained by dialysing a 
5 per cent, solution of sodium tungstate, to wbich sufficient 
hydrochloric acid has been added to combine with the sodium. 
The liquid remaining in the dialyser possesses a bitter, astringent 
taste and does not gelatinise on the addition of acids, even on 
boiling. On evaporating in a vacuum, a transparent, gum- 
like mass is obtained, and this can be heated to 200° without 
losing its solubility, whilst at a red heat it is transformed into 
tungsten trioxide, losing 2*4 per cent, of water. When 
moistened with water the colloidal acid becomes pasty and 
adhesive like gum, dissolving completely in one quarter of its 
weight of water. It can also be obtained by dialysing a solution 
of freshly precipitated tungstic acid in oxalic acid.^ The photo- 
chemical and other behaviour of colloidal tungstic acid suggest 
that it exists in two forms. 

Sodium Tungstates. — The nmmal salt, Na2W04,2H20, is 
prepared like the potassium salt, and is obtained on the large 
scale by fusing wolfram with soda ash. It crystallises in thin, 
lustrous, rhombic prisms which dissolve in four parts of cold and 
in two parts of boiling water.® The solution possesses a bitter 
taste and has an alkaline reaction. The crystals do not undergo 
alteration in the air, and they are insoluble in alcohol ; a deca- 
hydrate is also known. When heated to 200° the salt becomes 
opaque and loses its water, and fuses at 665°. 

Sodium Paratungstate, NaioWi204i,28H20.— This salt, which 
is the one known commercially as tungstate of soda, is prepared 
on the large scale by roasting wolframite with soda ash and lixivi- 
ating the fused mass. The boiling solution is nearly neutralised 
with hydrochloric acid and allowed to crystallise at the ordinary 
temperature, when the ^alt separates in large tri clinic crystals. 
At a higher temperature crystals containing 25 and 21 molecules 
of water are formed. The salt can also be prepared by electrolysis 
of solutions of the normal tungstate.* It is sometimes used in 
place of sodium stannate as a mordant in dyeing and calico 
printing, and is also employed for rendering cotton, linen, 
‘^flannelette,” etc., uninflammable.® Kosenheim® formulates 

' Joum. Chem. Soc., 1864, 19, 325. 

* Pappad&, Oazz., 1902, 88, ii, 22. Compare Saban<^ff, Zeit. anorg. Chem., 
1807, 14, 354. See also Wassiljewa, Zeit. wise. Photochem., 1013, 12, 1. 

* Marignao, Ann. Chim. Phys., 1863, [3], 69, 39. 

* Lottermoser, Kdloid Zeit., 1922, 30, 346. 

* Versmann, Reports of Ihe Juries of the Exhibition of 1862. 

* Zeit. anorg. Chem., 1916, 98, 139. Marignao considered that the para* 
tungstates obtained by him were of the form 3Na|0,7W0|. 



1132 


TUNGSTEN 


the compound : Na3oH4[H4(W04)e(W207)3],24H20. The anhy- 
drous salt melts at 705 ‘ 8 °. 

Sodium Metaiungstate {Tdmiungsiate), Na2W40i3,10H20, is 
formed by prolonged boiling of the normal salt with tungsten 
trioxide.^ It crystallises in efflorescent octahedra probably 
belonging to the regular system. Cold water dissolves 10*69 
times its weight of this salt ; there is a rapid increase in solubility 
with rise of temperature. It loses its water at a red heat 
(Marignac and Scheibler), fusing at 706 °. 

Tungstates typified by the salt, 4 Na 2 O, 10 WO 3 , 23 Il 2 O (which 
melts, when aidiydrous, at 680 * 8 °), have also been found to con- 
stitute a definite series.^ The salt, 9Na20,22W03, melts at 
683 * 3 °. 

Potassium Tungstates. — The normal salt. K2WO4,® is obtained 
by adding tungsten trioxide little by little to its own weight of 
fused potassium carbonate. On cooling a solution of the fused 
mass in hot water, normal potassium tungstate crystallises in 
large, acicular, anhydrous crystals, or in large, prismatic crystals, 
K2W0|,2H20 (Marignac). When the normal salt is treated in 
aqueous solution with an acid, or when tungsten trioxide is added 
to its boiling solution until no more dissolves, glistening scales 
of the paratungstatCy KioWi204i,l]H20, are deposited; meta- 
tungstate is formed at the same time. The paratungstate 
dissolves more readily in hot than in cold water, and the solu- 
tion has an acrid tavste and acid reaction. When alcohol is 
added to the aqueous solution a precipitate is formed; this 
dissolves on warming, but, on cooling, the solution deposits scales 
of potassium metatungstate, K2W40i3,5H20 ; a second hydrated 
salt containing SllgO, crystallising in octahedra, is obtained 
from the mother-liquor of the normal tungstate. The following 
compounds have also been described: K20,2W03,2H20; 
2K20,5W03,4Il20; K20,3W03,2H20 ; K 20 , 8 W 03 . 

Ammonium Tungstates.— The normal salt is extremely un- 
stable.^ When a solution of tungstic acid in ammonia is allowed 
to evaporate over calcium oxide, warty concretions of the salt 
2(NH4)20,3W03,3H20 are sometimes deposited, which easily give 
off ammonia. The usual product is, however, the paratungstate, 
5(NH4)20,12W03,llHa0 • [or possibly 3(NH4)20,7W03,6H20], 

^ See also Lottermoser, loc. cit., for an electrolytic method. 

* Smith, J. Amer. Chem. 80 c. » 1922, 44, 2027. 

* Potassium tungstate is trimorphous; see Amadori, Atti B. Accad. lAncei, 
1914, [6], 28, i, 800. 

* Bdsenheim and Jaoohsohn, Zeit. anorg. Chem., 1906, 60, 297. 



TUNGSTIC ACID AND THE TUNGSTATES 


1133 


formulated by Rosenheim as (NH4)ioH4[H4(W04)6(W207)3],7H20. 
If, liowever, the ammoniacal solution of the trioxide bo 
allowed to evaporate whilst warm, monoclinic crystals of 
(NH4 )iqWi204i, 5H20 separate out. When tungsten trioxide 
is boiled with ammonia, tetragonal prisms of ammmium meia- 
tungstate, (NH4)2W40i3,8H20, Le. (NH4)cH4[H2(W207)e],2lH20, 
are obtained. These are very soluble, and effloresce quickly on 
exposure to the air. A hexahydrate is also known. Besides 
these, many other ammonium tungstates have been prepared 
(Marignac), as well as compounds of these with ammonia, and 
ammoniacal derivatives of other tungstates.^ Commercial 
ammonium tungstate is stated ^ to possess the formula 
(NH4)4W30, 7,21120. 

Normal Calcium Tungstate, CaW04. — This occurs native as 
scheelite in vitreous, yellowish-white, tetragonal pyramids. 
Its chief source is Australia, but it is also met with in the following 
localities : Zinnwald, Caldbeck Fell in Cumberland, Piedmont, 
Dalecarlia, in the Vosges, at Huntingdon in Connecticut, and at 
the Mammoth mining district in Nevada. The crystals usually 
contain iron, and are found in crystalline rocks in connection 
with tin-ore, topaz, apatite, wolfram, etc. 

It is prepared artificially as a white, insoluble precipitate by 
mixing solutions of calcium chloride and a normal tungstate, and 
can be obtained in the crystalline form of scheelite by heating 
the precipitate mixed with lime in a current of hydrogen chloride. 
If a hot solution of metatungstic acid be saturated with calcium 
carbopate, calcium raetatungstate, CaW40j3,10H20, is obtained 
crystallising in small, tetragonal octahedra.® 

Lead Tungstate, PbW04, occurs as stolzite at Zinnwald in 
Bohemia, at Bleiberg in Carinthia, in Chili, and at Southampton, 
Massachusetts. It crystallises in translucent, tetragonal pyramids 
having a density of 7-87 to 8 - 13 . 

Ferrous Tungstate, FeW04, occurs as wolfram, (Fe,Mn)W04, 
which contains manganese as an isomorphous constituent, in 
Cornwall, Cumberland, France, the Erzgebirge, and various parts 
of the United States. Wolfram crystallises in the monoclinic 
' system in dark grey or brownish-black prisms having a metallic 
lustre and a density of 7 * 3 . 


^ Taylor, J. Amer, Chem. Soc., 1902, 24, 629; Briggs Joum. Chem. 8oc. 
1904, 85, 672. 

^ Arnold, Zeit. anorg. Chem., 1914, 88, 74. 

* See also Smith, J. Amer, Chem. 8oc., 1922, 44, 2027. 



1134 ' TUNGSTEN 

^ ^ 

Manganese TungstaiCt is found as hubnerite in 

Nevada in a vein from three to four feet yvide. 

Chromium Tungstates, — A number of such compounds have 
been described, but there is little doubt that some are merely 
mixtures of simpler compounds.^ 

Tungsten Tungstates, — By the partial reduction of tungsten 
trioxide a number of oxides of tungsten have been prepared, 
having a composition intermediate between that of the dioxide 
and trioxide. These have a blue or purple-red colour, and are 
probably combinations of the acidic trioxide with the more 
basic dioxide. Thus by^-the action of hydrogen on the trioxide 
at 250® the compound WsOg = 2 W 03 ,W 02 is formed, which has 
a deep blue colour ; the same oxide, when prepared by heating 
ammonium metatungstate to a red heat, has a purple-red colour 
and metallic reflex.^ Other blue oxides having the compositions 
W 2 O 5 =. - 3W03,W02; W 3 O 14 = 4W03,W03 

have been described; in addition, Desi has obtained oxides 
containing less oxygen than the dioxide, by the action of con- 
centrated sulphuric acid on metallic tungsten under suitable 
conditions. It is therefore uncertain whether the blue oxide is a 
chemical individual or an admixture. Hydrated blue oxides 
are readily obtained by reduction of tungsten trioxide or 
tungstic acid, e.g.^ with stannous chloride, hydrogen iodide, or 
alcohol.® 

496 Tungsten Bronzes,— remarkable compounds, ob- 
tained by the partial reduction of the alkali and alkaline-earth 
tungstates, are usually regarded as compounds of the tungstates 
with tungsten dioxide, but their exact constitution is as y^t 
unknown. Owing to their bronze-like appearance and insolubility 
in acids and alkalis, they have been employed ad bronze powder 
substitutes. 

They are scarcely affected by aqua regia, but are oxidised by 
aramoniacal silver nitrate solution, a reaction which is utilised 
for their analysis. Owing to their insolubility they can be 
freed from metallic tungsten and its oxides only by successive 

t ' Lotz, Ann,t 1864, 91, 49; Lefort, Ann. Chim. Phys., 1879, [6], 17, 470; 
Smith and Bieck, Zeit. anorj, Chem., 1894, 6, 13; Kantschov, J. Rubs, Phya, 
Cham. Soc., 1914, 46, 729. 

* Besi, J. Amer. Chem. Soc., 1897, 19, 213; see also Hallopeau, Cmpt, rend., 
1898, 127, 67; Bull. 80 c. chim., 1899, [3J, 21, 267; AUen and Gottschalk, 
Amer. Chem, J,, 1902, 27, 328. 

* and Gotisohalk, Amer. Chem. J., 1902, 27, 328 ; Benrath, Zeit. mas. 
Photochem., 1917, 16, 263. 



1135 


PHOSPHOTUNGSTIC ACID 

extractions with aqua regia, hydrochloric acid, potassium 
carbonate, and water. 

Twigsten Sodium Bronze was first obtained by Wohler by the 
reduction of sodium tungstate with hydrogen, and may also be 
obtained by substituting coal-gas, zinc, iron, or tin for hydrogen, 
or by means of electrolysis. It forms fine golden cubes, which 
have a specific gravity of 6*617, and conduct electricity well. 
On ignition in the air, it oxidises and fuses. It is not attacked 
by any acid except hydrofluoric acid, nor is it acted upon by 
alkalis except on fusion.^ According to Philipp,^ the products 
are a mixture of different compounds, the relative proportions of 
which vary according to the method of preparation and the 
nature of the original tungstate. The substance obtained by 
heating the ditungstate in hydrogen, which was formerly supposed 
to have the composition NagWgOg, is, according to Philipp, 
NagWgOig, and has a golden-yellow colour. By the electrolysis 
of fused sodium paratungstate a blue bronze, NagWgO^g, is 
obtained, which forms dark blue cubes or plates having a red 
reflex. A purple-red bronze, NagWgOg, is obtained by strongly 
heating a mixture of 12*9 grams of sodium carbonate and 68*9 
grams of tungsten trioxide with 20 grams of tinfoil, and a reddish- 
yellow bronze, Na^WgOis, by fusing 60-80 grams of a mixture of 
two molecular proportions of sodium tungstate and one of the 
trioxide with 30 grams of tinfoil for two hours. It forms reddish- 
yellow cubes and yields a brownish-yellow powder. 

Tungsten Potassium Brmze is obtained in a similar manner to 
the sodium bronzes, but only one compound ® appears to exist, 
K2W4O12. Bronzes containing lithium and rubidium have also 
been prepared as well as a number of mixed bronzes containing 
both sodium and potassium or an alkali metal along with one of 
the alkaline-earth metal groups.^ 

497 Phos'photungstic Acids . — Timgstic acid combines with 
phosphoric, arsenic, antimonic, and vanadic acids to form com- 
plex substances analogous to the corresponding molybdic 
derivatives. A very large number of these have been prepared, 
the relation • WO3 varying from 1 : 7 to 1 : 24. Phospho- 

^ Knorre, J. pr. Chem., 1883, [2], 27f 63. 

* J5cf., 1882, 15, 499. 

* Schaefer, Zeit. anorg. Chem.t 1904, 88, 142, where references to the 
literature are given ; Hallopeau, Compt. rend., 1898, 127, 67 ; Bull. 80 c. chim., 
1899, [3], a, 267. 

* See Engels, Zeit. anorg. Chem., 1903, 87f 126; Hallopeau, Compt, rend., 
1898, 127, 612. 

VOL. n. (n.) 


X 




1136 


TUNGSTEN 


f r 

duodedtungstic acid, H3PWi204o,a;H20, is obtained by evaporating 
a mixture of the requisite quantities of orthophosphoric acid and 
metatungstic acid, or by the exact decomposition of the barium 
salt with sulphuric acid or of the mercurous salt with hydro- 
chloric acid. It crystallises in tetragonal pyramids containing 
water of crystallisation, the amount of which is variously stated 
by different investigators. Phosphotungstic acid is largely used 
as a reagent for the precipitation of the alkaloids, proteins, and 
certain of their hydrolysis products, and also for the detection 
of potassium and ammonium salts, with which it yields insoluble 
precipitates. For this purpose it is prepared by acidifpng a 
solution of 4 parts of sodium tungstate and 1 of common sodium 
phosphate with sulphuric acid and extracting the concentrated 
solution with ether, in which phosphotungstic acid is readily 
soluble.^ Two sodium salts are known, having the formula) 
Na2HPWi204o,icH20 and Na3PWi204o,a:H20, and are obtained by 
heating together solutions of sodium hydrogen phosphate and 
tungstate. In presence of an excess of hydrochloric acid the 
former salt is obtained in yellow crystals, whilst when the acid is 
gradually added with stirring until crystallisation commences the 
latter salt separates in transparent colourless octahedra. 

The number of complex phosphotungstates and similar com- 
pounds is very large, and many of them crystallise well.^ 

498 Silicotungstic These peculiar compounds were 

discovered and investigated by Marignac,® but the composition 
of many of them is doubtful. 

Silicodecitungstic Acid, 

H8WioSi03e,3Il20 ( = 4H2O,SiO2,10WO3,3H2O). 

— To prepare this acid, gelatinous silica is boiled with ammo- 
nium poly tungstate and the solution evaporated, ammonia 

1 Winterstein, Chem. Zeit., 1898, 22, 639. 

• See Scheibler, fier., 1872, 5, 801; Sprenger, J. pr. Chem., 1880, [2], 22 
48; Gibbs, Amer. Chem. J., 1880, 2, 217, 281; 1882, 4, 377; 1883, 6, 361 
391; 1885, 7, 31, 392; Kehrmann, Ber., 1887, 20, 1806, 1811; 1891, 24 
2326; 1892, 25, 1966; Annalen, 1888, 245, 46; Zeit. anorg. Chem., 1891, 1 
428; Drechsol, Ber., 1887, 20, 1462; Pochard, Compt. rend., 1889, 109, 301 
1890, 110, 764; Hallopeau, Compt. rend., 1896, 123, 1066; Kehmann anc 
Rvittimann, Zeit, anorg. Chem., 1899, 22, 285 ; Rogers, J. Amer, Chem. 8oc. 
1903, 25, 298; Copaux, Ann. Chim. Phys., 1909, [8], 17, 261; Rosenheim 
Zeit. Elektrochem., 1911, 17, 694; Rosenheim and Jaenicke, Zeit. anorg 
Chem., 1912, 77, 239; 1917, 101, 264; Copaux, Compt. rend., 1913, 156, 71 
Prandtl and Heoht, Zeit. anorg. Chem., 1916, 02, 198 ; Sweeney, J. Amer. Chem 
Soc., 1916, 38, 2377. 

• linn. Chim. Phys., 1864, [4], 8, 5. 




SILICOTUNGSnC ACIDS 


1137 


being added from time to time. The amnumium salt, 
(NHJgSiWioO ggjSHgO, is thus obtained in short, rhombic prisms 
which are soluble in water ; the solution is then precipitated by 
silver nitrate, and the precipitate washed and decomposed by 
hydrochloric acid. On evaporating the filtrate in a vacuum the 
acid is left as a yellowish, glassy mass, and on exposure to air 
splits into fragments, which then deliquesce. Its salts have not 
been carefully examined. 

On dissolving it in water and evaporating the solution, some 
silicic acid separates out, and the thick mother-liquor 
yields short triclinic prisms of octabasio tungstosilicic acid, 
HgWi2SiO42,20H2O ( - 4H2O,SiO2,12WO3,20H2O), which are 
readily soluble in water and alcohol. It forms both normal and 
acid salts.i 

Silicoduodecitungstic or Silicotungstic Acid was formulated by 
Marignac as an octabasic acid, 

H8SiWi2022,29H20 ( = 4H20,Si02,12W03,29H20), 
but according to Wyrouboff ^ it is tetrabasic, and has the formula 
2H20,Si02,12W03,31H20, the normal salts of Marignac being 
basic salts and his acid salts in reality the normal salts. All 
the salts contain water of crystallisation, and in view of tlie 
uncertainty as to their constitution are at present best formulated 
in terms of the oxides. The salts of this acid are formed by 
boiling gelatinous silicic acid with the polytungstates of the 
alkali metals. To obtain the acid the salts are precipitated 
with mercurous nitrate and the washed precipitate is decomposed 
by hydrochloric acid. It crystallises below 40° in large tetragonal 
pyramids of the formula H8SiWia04a,29H20, above 40°, or in 
presence of hydrochloric acid, in rhombohedral forms, 
HgSiWia042,22H20, and readily dissolves in water, alcohol, 
or ether. Silicotungstic acid is a valuable reagent for alkaloids. 

The salts, with the exception of the mercurous salt and a few 
others, are soluble in water. Boiling hydrochloric acid converts 
the normal salts into acid salts without decomposing them 
further (Marignac), whilst alkalis decompose their solutions 
with the separation of silicic acid. They have been very 
thorougUy examined both by Marignac and by Wyroubofi. 

Potassium Silicotungstate. — Three distinct salts are known. ® The 

^ See, however, Kehrmann, Zeit. anorg. Chem., 1904, 39, 98 ; Rosenheim and 
Jaenioke, ibid., 1912, 77i 242; 1917, 101, 240; Gopaux, Compt. rend., 1913, 
166, 71. » Bull. 8oc. fran^. Min., 1896, 19, 219. 

» See also van Liempt, Zeit. anorg. Chem., 1922, 122. 176. 



1138 


TUNGSTEN 


> c 

salt 4K20,Si02,12W08,14H20 forms hard, granular crusts, consist- 
ing of prisms closely resembling cubes ; 2K20,Si02,12W03,18H20 
forms transparent, glistening, hexagonal crystals; and 
3K2O,2SiO2,24WO3,30H2O crystallises in monoclinic prisms. 

Marignac formulates the first of these as the normal 
salt, K8SiWi2042,14H20, and the others as acid salts, 
H4K4SiWi2042,16H20 and 2H5K3SiWi2042,25H20, whereas 
WyroubofE regards them as a basic salt, 
K4SiWj2O40,4KOH,12H2O, 

a normal salt, K4SiWi2043,18H20, and a double salt, 
K4SiWi204o,K2H2SiWi20.o.29H20. 

Zircono-,^ mangano-,^ Wo-,® bismutno-,^ and silico-vanadio- 
tungstates ^ have also been obtained. 

Pertmgslic Acid. — ^When a solution of sodium paratungstate 
is boiled for a few minutes with hydrogen peroxide, a yellowish 
solution is obtained, which no longer gives a precipitate with 
nitric acid.® When the solution is allowed to evaporate in a 
vacuum, small white crystals having the formula NaW04,H20 
are deposited, which are the sodium salt of the unknown per- 
tungstic acid, HWO4. The same salt is formed in solution by 
the electrolysis of slightly acid solutions of sodium tungstate.’ 
More highly oxidised compounds are formed by the action 
of caustic alkali and hydrogen peroxide on a solution 
of a pertungstate,® the unstable salts, Na202,W04,H202 ; 
Na202,W04,Il202,(Na202)2W04,7H20 ; and K204,W04,H20 
having been isolated in this way. Aqueous solutions of per- 
tungstic acid and hydrogen peroxide appear to contain the 
unstable acids ® W02(02H)2 and W02(02H)(0H). 


Tungsten and the Halogens. 

499 Tungsten Hexafluoride, WFg, is formed by the action of 
anhydrous hydrofluoric acid on timgsten hexachloride in the 
cold, and can also be prepared by the action of arsenic tri- 

^ Hallopeau, BuU. Soc.’chim., 1896, [3], 15, 917. 

* Just, j?cr., 1903, 86, 3619. 

» Rosenheim and Jaenicke, Zeit. anorg. Chem., 1912, 77» 239 ; Rosenheim and 
Schwor, ibid., 1914, 89, 224. 

* Sweeney, J. Amer. Chm) 80 c., 1916, 88, 2377. 

® Friedheim and Hendereon, Ber., 1902, 85, 3242. 

* Pc^ohaid, Coinpt. rend., 1891, 112, 1060. 

’ Thomas, J. Amer. Chem. 80 c., 1899, 21, 373. 

* MelikofI and Pissarjewsky, Ber., 1898, 81, 632. 

* Pissarjewsky, J. Russ. Phys, Chem. 80 c., 1002, 84, 472. 



TUNGSTEN AND THE HALOGENS 


1139 


• * 

fluoride or antimony pentafluoride on the hexachloride. The 
preparation by the last of these methods can be carried out in 
glass vessels and proceeds according to the equation : 

WClg + SSbFg = WFe + SSbFgCla. 

Antimony pentafluoride is gradually added to the tungsten 
hexachloride contained in a flask until no further reaction 
occurs, and the contents of the flask are finally heated to 90°. 
The hexafluoride volatilises, and is condensed in a receiver 
cooled by a freezing mixture of alcohol and solid carbon dioxide. 
A trace of chlorine is^ present, which can be removed by allowing 
the liquid in the receiver to boil for a moment.^ 

Pure tungsten hexafluoride is a colourless gas, which has the 
normal density corresponding with the formula WFg, and is 
therefore about ten times as heavy as air. It condenses to a 
faintly yellow liquid which boils at 19*5° and solidifies at 2-5° 
to a snow-white mass. It is at once decomposed by water and 
fumes in the air ; nearly all the commoner metals, except gold 
and platinum, are attacked by it. It is absorbed by alkali 
fluorides and reacts violently with ammonia. 

Tungsten Oxytetrafluoride^ WOF 4 , can be prepared by the 
action of anhydrous hydrofluoric acid on the oxytetrachloride 
in the cold, or by heating tungsten trioxide with lead fluoride 
to redness in an electric furnace. It sublimes in white i)lates, 
melts at 110 °, and boils at 185—190°. It is decomposed by 
water, and is soluble in chloroform, absolute alcohol, or 
benzene. It appears to unite with ammonia, forming an orange- 
coloured substance (Ruff). 

Tungsten Dioxydifluoride, WOgFg, has not been prepared pure, 
but is formed in small amount by the action of moisture on 
the vapour of the oxytetrafluoride. Double salts with the 
alkali fluorides, such as 2 KF,W 02 F 2 ,H 20 , have, however, been 
prepared by the action of hydrofluoric acid on the tungstates.^ 
A double salt of the formula is also known. 

500 Four compounds of tungsten and chlorine are known, 
viz. : 

Tungsten dichloride .... WClg. 

Tungsten tetrachloride . . . WCI 4 . 

Tungsten pehtachloride . . WCI 5 . 

Tungsten hexachloride . . . WCl^. 

1 Ruff and Eisner, J?cr., 1905, 88, 742; Ruff, Eisner, and Heller, Zeit. anorg. 
Chem., 1907, 62, 266. 

* Marignao, Ann, Chim. Phys., 1803, [3], 69, 70. 



1140 


TUNGSTEN 


' r. ■ 

Tungsten Dichloride, WClg.— This body may be obtained in 
pale grey crusts by reducing the hexachloride in hydrogen at a 
moderately high temperature, or by reduction in a stream of 
nitrogen with powdered aluminium and quartz.^ It is, however, 
best prepared by heating the tetrachloride in a current of carbon 
dioxide at the temperature of a moderately hot zinc bath. The 
dichloride is a non-volatile, loose, grey powder without lustre or 
crystalline structure. It alters perceptibly on short exposure 
to the air and dissolves slightly in water, forming a brown solu- 
tion. The remainder is converted into the brown oxide, a slow 
evolution of hydrogen occurring (Eoscoe). , In view of the fact 
that a compound of the formula WgClejHC^-bHgO has been 
prepared,^ the dichloride may perhaps be regarded as having the 
composition WgClg. . 

Tungsten Trichloride . — ^Although this compound has not been 
^ obtained, double salts of the form MgWgClg have been prepared by 
reduction of tungstic acid in hydrochloric acid solution in presence 
of alkali chloride.^ 

Tungsten Tetrachloride, WCI4, is produced by the incomplete 
reduction of the hexachloride or pentachloride by hydrogen, 
and forms the non-volatile residue obtained by the distillation 
of the hexachloride in hydrogen. In order to obtain it in the 
pure state a mixture of hexa- and penta-chloride is distilled at 
a low temperature from a bath of sulphuric acid in a current of 
dry hydrogen or carbon dioxide, and the volatile pentachloride 
poured back again once or twice over tlie residue to convert 
into the tetrachloride the lower chlorides or metal which arc 
also formed. Tungsten tetrachloride is a loose, soft, crystalline 
powder of a greyish-brown colour. It is highly hygroscopic, 
though not so much so as the pentachloride, and is partially 
decomposed by cold water into the brown oxide and hydrochloric 
acid. The tetrachloride is non-volatile and infusible under 
ordinary pressure, but on heating it decomposes into penta- 
chloride, which distils off, and dichloride, which remains behind. 
On heating in hydrogen to a temperature above the melting point 
of zinc the tetrachloride is reduced to metallic tungsten, some of 
which is deposited as a black, tinder-liko powder and undergoes 
spontaneous ignition on Exposure to air (Eoscoe). By reduction 
of an acidified solution of tungstic acid in presence of alkali 
chloride, Olsson* has prepared the compound K2W(OH)Cl5. 

1 Lindner and others, Ber., 1922, 65, [5], 1468. 

2 m\ J. Amur. Chem. Soc., 1917, 88, 2383. 

’ OlsBon, Ber., 1913, 46, 666; Eosenheim and Uehn, ibid., 1016, 48, 1167. 

* hoc. cit. 



1141 


TUNGSTEN AND THE HALOGENS 

Tungsten Pentachloridej WCI5. — This compound is formed by 
the incomplete reduction of the hexachloride in a current of 
hydrogen. If the temperature be kept but slightly above the 
boiling point of the hexachloride, the dark red colour of its 
vapour is seen to disappear and a light greenish-coloured vapour 
takes its place, and this soon condenses either to black drops 
or to long, lustrous, black, needle-shaped crystals. After two or 
three distillations in hydrogen a pure volatile product is 
obtained. For the production of the pentachloride, it is, how- 
ever, more convenient to reduce the hexachloride at a higher 
temperature, when a further loss of chlorine takes place, the 
solid non-volatile tetrachloride remaining behind and the volatile 
pentachloride distilling over. The latter compound only requires 
redistillation in order to be obtained in the pure state. Tungsten 
pentachloride crystallises in long, black, lustrous crystals, but if 
quickly condensed the crystalline powder possesses a dark green 
colour, resembling potassium manganate. It melts at 248”, 
boils at 275-6°, has the normal vapour density at 350°, and is 
extremely hygroscopic, the crystals becoming instantly covered 
with a dark golden-green film on exposure to air, whilst the 
small particles are converted into liquid. The crystals do not 
decrepitate on cooling like those of the hexachloride. On 
treatment with large quantities of water, the pentachloride 
forms an olive-green solution, although the greater part is at 
once decomposed into the blue oxide and hydrochloric acid. 

Electrolysis of a solution of the hexachloride^ in absolute 
alcohol gives a compoimd of quinquevalent tungsten of the 
formula [WCl 2 (OC 2 H,) 3 ] 2 . 

Although the oxychloride, WOCI3, is unknown, two series of 
chlorolungstites have been prepared, having respectively the 
formula) 2 MgWOClg and MWOCl^. 

Tungsten Eemchloride, WClg. — This substance is prepared by 
heating metallic tungsten in an excess of dry and pure chlorine ; 
platinum black may be employed as a catalyst.® It is necessaiy 
for the preparation of the pure compoimd that every trace of 
oxygen and of moisture be excluded, as otherwise some red 
oxychloride is invariably formed, and this cannot easily be 
separated from the hexachloride by distillation. Metallic tungsten 

^ Fischer and Roderbuig, ZtiU anorg. Chem., 1013, 81, 170; Fischer and 
Michiels, ibid., 1913, 81, 102. 

“ Collonberg, Zeit. anorg, Chem.t 1918, 102, 247; Arkiv Kern, Min. Gcol, 
1918, 7, No. 6, 1. 

® Hill, J, Amer. Chem. 8oc., 1916, 38, 2383. 



1142 


ITOGSTBN 


takes fire at a moderate heat in dry chlorine, and the action goes 
on by itself until all the chlorine has disappeared. 

In order to obtain the hexachldride *in quantity, the metal 
is first ignited in a current of dry hydrogen; then the hydro- 
gen is completely displaced by a current of dry carbon dioxide, 
and lastly chlorine free from air substituted, and the tube 
or retort moderately heated. At the commencement of the 
operation a slight sublimate of red, needle-shaped crystals of 
the oxychloride is frequently formed owing to the unavoidable 
presence of traces of oxygen, but this is easily driven to the end 
of the tube beyond the point at which it is intended to collect 
the hexachloride. On raising the temperature of the metal, a 
granular sublimate of dark violet, opaque crystals of the hexa- 
chloride makes its appearance, and if in large quantity the 
hexachloride collects as a blackish-red liquid. In order to 
saturate this liquid, it is slowly distilled in a current of chlorine. 
The dark violet crystals decrepitate on cooling, and the crystalline 
mass thus readily breaks up into a powder. 

Perhaps the simplest method of preparing the hexachloride 
consists in the interaction of tungsten trioxide and carbon 
tetrachloride at 280°.^ 

When pure, the solid hexachloride does not undergo any 
change even in moist air, but in the presence of the slightest trace 
of oxychloride it at once absorbs moisture, evolving copious fumes 
of hydrogen chloride and changing in colour from violet to brown. 
Water does not act upon the pure hexachloride, but on boiling 
decomposition occurs. If, however, the oxychloride be present 
the whole is suddenly decomposed by cold water into a greenish 
oxide. It is soluble in carbon disulphide and crystallises from 
the solution in six-sided plates. 

The melting point of the hexachloride is 275° ; it boils under 
a pressure of 759*5 mm. at 346*7°. The vapour density of 
tungsten hexachloride has been determined in sulphur vapour 
and in mercury vapour ; at 440°, the mean experimental density 
compared with that of hydrogen is 168*8, whilst at 350° the 
density is 190*9, the calculated density being 196*9. The 
alteration of the density from 191 at 360°, only 3° above the 
boiling point, to 169 at 440° points to the fact that dissociation 
occurs. That this is the case is shown by the fact that when 
a 'Current of dry carbon dioxide is passed through the fused 
hexachloride a continuous liberation of clilorine takes place, 

' Michael and Murphy, Amer. Chm, J., 1910, 44» 366. 




‘tungsten AND THE HALOGENS 1143 

whereas the pentachloride treated m the same way does not 
undergo a similar •decomposition. 

Tungsten Oxychloridk.—Tlie oxytetrachloride, WOCI4, and the 
dioxydichloride, WOgClg, have been studied by Blomstrand and 
Riche. The dioxydichloride is best obtained by passing chlorine 
over the brown oxide, WOg. Combination takes place at a 
moderate temperature, the oxide becoming covered with a 
whitish crust, which as the temperature increases sublimes 
without melting, condensing in small square scales of a light 
lemon-yellow colour. The dioxydichloride volatilises at a 
temperature approaching redness with partial decomposition; 
the crystals do not fuse, and are not acted upon by moist air or 
cold water. Even when boiled with water the dioxydichloride 
is not completely decomposed. 

The splendid red needle-shaped crystals of the oxytetra- 
chloride, prepared by Wohler, are obtained by passing the 
hexachloride vapour over heated oxide or dioxydichloride : 

W 03 + 2WCl6=3W0Cl4, 

and also by acting on the trioxide with phosphorus penta- 
chloride, ^ and by the interaction of tungsten trioxide with a 
solution of chlorine in carbon tetrachloride at 240°.^ Attempts to 
prepare tungsten dichloride by interaction of the metal with 
carbonyl chloride result in the formation of this compound.® The 
crystals melt at 210*4'’, and the liquid boils at 227*5°, forming a 
red vapour rather lighter coloured than that of the hexachloride, 
and having the normal density at 350° (Roscoe). On repeated 
distillation over red hot charcoal in a cun'ent of chlorine the 
hexachloride is formed.' On exposure to the air the oxytetra- 
chloride becomes at once covered with a yellowish crust of 
tungstic acid. 

501 Bromine acts rapidly on red-hot tungsten, forming dark, 
bromine-like vapours, which condense to a crystalline sublimate. 
Special precautions similar to those taken in the preparation of 
the chlorides must also be employed for the bromides, as the 
oxybromides formed in the presence of air and moisture possess 
almost the same colour as the bromide, and therefore the detection 
of the impurity is not so easy as with the chloride. 

Tungsten Dibromide, WBrg, is formed by the reduction in 
hydrogen of the pentabromide, heated in a bath of fused zinc 

1 Schiff, Ann., 1879, 197,,J86. * Michael and Murphy, loc. cii. 

* iandner and others, Ber„ 1922, 55> [-O]* H58. * 



1144 TUNGSTEN 

chloride. A residue of non-volatile dibromide remains in the 
form of a bluish-black, velvety, crystalline powder. 

Tungsten Pentahromide^ WBr^, is prepared by the action 
of an excess of bromine on tungsten, and is formed also when 
the hexachloride is heated in dry hydrogen bromide, but cannot 
be prepared pure in this way.^ The pentabromide forms dark 
crystals having a metallic lustre resembling iodine, melting at 
276°, and boiling at 333°. It is at once decomposed by an 
excess of water into hydrobromic acid and the blue oxide. 
When the pentabromide is heated in a current of hydrogen, 
the metal is formed in the state of pyrophoric powder. 

Tungsten Hembromide, WBrg, is obtained, according to 
Schaffer and Smith, ^ by gently heating tungsten in dry bromine 
vapour in an atmosphere of nitrogen. It can be sublimed, and 
forms bluish-black needles. It decomposes very readily when 
heated, fumes in the air, and is decomposed by water with 
• formation of a blue oxide. 

Liquefied hydrogen bromide converts the hexachloride at 
60 — 70° into a mass of olive-green crystals which melt at 232° 
and have the composition WClgjSWBrg, whilst at the ordinary 
temperature a similar substance of the composition WOlgjWBrg 
is formed (Defacqz). 

Tungsten oxybromideSy corresponding to the oxychlorides, exist. 
The dioxydibromidCy WOgBrg, is prepared by passing bromine 
vapour over red hoi tungsten dioxide. It forms light red, 
transparent crystals which yield a yellow powder. It does not 
melt, but volatilises at a temperature approaching a red heat, 
and is not acted upon by water. The oxytetrabromidey WOBr 4 , 
is formed in the same circumstances as the last-named com- 
pound in brownish-black, lustrous needles, which are readily 
fusible and can be separated from the dioxydibromide by gently 
heating, when the latter compound remains behind. It melts 
at 277°, boils at 327-f)°, and is decomposed by water. 

Tungsten Di-wdidCy Wig, is obtained in the form of green, 
metallic scales when iodine vapour is passed over the metal 
heated to redness ® (Roscoe), and is formed also by the action of 
hydrogen idoide on the hexachloride at 400° (Defacqz).^ 

Tungsten Teira-iodide^ WI 4 , obtained by Defacqz® by the 
action of liquefied hydrogen iodide on the hexachloride at 100 °, 

1 Defacqz, Ann. Chim. Phya., 1901, [7], 22, 247. 

» J. Amcr. Chem. Soc., 1897, 18, 1098. ^ Ann., 1872, 162, 349. 

♦ Ann. Chim. Phys.y 1901, [7], 22, 239. ' Loc, cit. 



TUNGSTEN AND NITROGEN/ ETC. 


1146 


is a black, infusible, crystalline mass, which is decomposed by 
water into the brown oxide and hydriodic acid. 

Tungsten and Sulphur. 

502 Tungsten Disulphidey WS2, is obtained by the action of 
sulphur, hydrogen sulphide, or carbon disulphide on ignited 
metallic tungsten. It may be prepared also by heating tung- 
sten trioxide in a crucible with six times its weight of cinnabar 
or with potassium carbonate and sulphur, and by heating the 
hexachloride in a current of hydrogen sulphide (Defacqz). It 
forms soft, black, needle-shaped crystals which soil the fingers 
like graphite. 

A chlorosulfhide, WClgjSWSg, is formed, by the action of licpu;- 
fied hydrogen sulphide on the hexachloride at 60 ° (Defacqz). 

Tungsten Trisulphide, WSg, is obtained only in the wet way 
by dissolving tungsten trioxide in ammonium sulphide and 
precipitating with an acid, or by saturating an aqueous solution 
of an alkali tungstate with hydrogen sulphide, and acidifying. 
When dry it is black, yielding a liver-coloured powder. It 
yields a colloidal solution with water, and is precipitated by 
ammonium chloride and acids. It is easily dissolved by potassium 
carbonate and also by ammonia. Heated witli potassium 
cyanide, it forms the disulphide ; this is unaltered by fusion with 
excess of the reagent. 

The Thiotungstates.^The thiotungstates of the alkali and 
alkaline-earth metals are prepared by dissolving the tri- 
sulphide in the corresponding hydrosulpliide, or by treating 
the corresponding tungstate with hydrogen sulphide. The 
ammonium salt, (NH4)2WS4, is deposited from concentrated 
solution in yellowish-red crystals; the potassium salt, K2WS4, 
forms anhydrous, yellow crystals, whilst the sodium salt, NagW S4, 
crystallises with difficulty. Salts of the form MgWOgSg and a 
salt of the composition KgWOgSjllgO are also known. 

Tungsten and Nitrogen, Phosphorus, Carbon, 
Silicon, and Boron. 

503 Tungsten does not combine directly under ordinary 
conditions with nitrogen, and neither tfie metal nor the dioxide 
is attacked when strongly heated in ammonia.^ By the action 

^ Langmuir, J. Anicr. Chem, Noc., 1913, 35, 931 ; 1915, 37, 1139, has, however, 
shown that under the conditions obtaining in a nitrogen-filled tungsten-filament 
electric incandescence lamp, a nitride, WN,, is formed. • 



TUNGSTEN 


1149 

of ammonia on the oxjrtetrachloride or the hexachloride in the 
cold, a black, semi-metallic powder is obtained, which has the 
composition WgNg. It is insoluble in caustic soda, nitric acid, 
or dilute sulphuric acid, but is converted by concentrated 
sulphuric acid into ammonia and tungstic .acid.^ 

By the action of ammonia on tungsten trioxide at a dull red 
heajb Wohler obtained a black, amorphous product which he 
termed tungsten nitretamidoxide'" the formula of which is 
WjNgHgOg (Kidcal). It is insoluble in acids and alkalis, but dis- 
solves in sodium hypochlorite solution, and on ignition decom- 
poses, ammonia, nitrogen, and hydrogen being evolved. Other 
compounds which have been described are: W4N4H2O4, W3NgH4, 
W3N4H4, and W3N2. 

Phosphides of Tungsten. — Phosphorus and tungsten combine 
directly when the finely powdered metal is heated to redness 
in phosphorus vapour, a dark green powder of the composition 
W3P4 being formed. Another compound, WgP, is obtained, 
when a mixture of phosphorus pentoxide and tungsten trioxide, 
in the proportion of two molecules of the former to one mole- 
cule of the latter, is reduced at a high temperature in a char- 
coal crucible,^ and forms a vesicular mass, the hollow portions 
of which contain large crystals. 

A black, amorphous diphosphide, WP2, is formed when the 
hexachloride is heated in phosphine, and this reacts with copper 
phosphide at a high temperature to form tungsten monophosphide, 
WP, which crystallises in grey prisms with a metajlic reflex, has 
density 8*5, and is oxidised to tungsten trioxide when heated 
in air (Defacqz). An arsenide, WAsg, has also been prepared in 
a similar manner to the diphosphide, which it resembles. 

Tungsten and Carbon.— Tungsten forms two carbides. The 
compound obtained by heating the oxide with carbon or calcium 
carbide ® has the forinula W2C, whilst in presence of a large 
amount of iron ^ the carbide WC is produced. They are both 
hard, iron-grey, crystalline substances. The compound W3C is 
also considered to be definite.® Several complex carbides 

1 Wohler, Ann., 1860, 78, 180; 1858, 105, 258; Rideal, Jowm. Chem. 
80 c., 1889, 55, 41. 

* Wohler, Jmm. Chem. 80 c., 1853, 8, 94. 

• Moiasan, Compt. rend., 1896, 128, 13; 1897, 125, 839. 

« Williams, Compt. rend., 1898, 126, 1722. 

» Ruff and Wunsch, Zeit. anorg. Chem., 1914, 85, 292. See also HUpert and 
Ornstein, Ber,, 1913, 46, 1669. 



DETECTION AND ESTIMATION OF TUNGSTEN 1147 


... • • 

containing iron or chromium have also been prepared,^ and the 

existence of a compound WCO is postulated. ^ 

Quadrivalent tungsten forms a series of double cyanides of 

the general formula R4[W(CN)8],a;H20 ; quinquevalent tungsten 

forms a series of double cyanides of the type R3[W(CN)8],a;H20, 

double thiocyanates, and double oxalates ; in none of these cases, 

however, is the constituent simple tungsten salt known. 

Tungsten Silicide, WgSig, is obtained by heating the trioxide 

with silicon in the electric furnace,® and freeing the product from 

metal by electrolytic oxidation. It forms beautiful, steel -grey 

plates with a metallic lustre, and burns in oxygen. It is attacked 

by a mixture of nitric and hydrofluoric acids, and by fused potash. 

Other silicides which have been described are WSig and WSig. 

Tungsten Boride, WBj, is obtained by fusing the two elements 

together by a convenient electrical method; it crystallises in 

hard octahedra of density 10 * 77 .* It is attacked by concentrated 

acids.® 


Detection and Estimation op Tungsten.® 

504 All the insoluble tungsten compounds can be converted 
into soluble tungstates by fusion, either with caustic alkali 
alone, or with the addition of nitre. The solution when brought 
into contact with zinc or aluminium and hydrochloric a(.ud 
becomes blue-coloured, owing to the formation of the blue 
tungsten oxides (or tungsten tungstates). When ammonium 
sulphide is added to the colourless solution of the tungstate, and 
then dilute Hydrochloric acid, a brown precipitate of tungsten 
sulphide is obtained, whereas hydrochloric acid alone precipitates 
tungstic acid, which on heating turns yellow. If the tungsten 
compounds are fused with a small quantity of tin in the reducing 
flame with microcosmic salt, a blue bead is obtained, whilst 

1 C'ompf.reiw?., 1898,127, 1410; 1899,128,207; 1903,187,292. 

* Langmuir, J, Amer. Chem. 80 c., 1916, 37, 1139. 

* Vigouroux, Compt. rend,, 1898, 127, 393. See also Warren, Chem. News, 

1QQQ tyo Qia 

< Wekind, Bcr., 1913, 46, 1198. 

‘ Tuoker and Moody, Joum. Chem. 8 oc., 1902, 81, 16. 

* The are spectrum of tungsten has’ been dkamined by Belke, Zeit. wUs. 

Photochem., 1917, 17, 132, 146, and the X-ray spectrum by Barnes, Phil, 
Mag., 1916, [6], 368; Ledoux-Lebard and DauvilUer, Compt. rend., 1917, 

164, 687; Siegbahn, Phil. Mag., 1919, [6], 88, 639; de Broglie, Compt. rend., 
1^1 9, 168, 962 ; Duane and Patteison, Phya. Rev., 1920, 16, 626. 

^ Torossian, Amer. J. Set., 1914, [4], 88, 637. 



1148 


TUNGSTEN 


tungsten compounds containing iron yield in tlie reducing flame 
a blood-red bead. Tungstic oxide can be very readily detected 
by fusing with potassium bisulphate anid adding sulphuric acid 
and a crystal of phenol or quinol (hydroquinone), when a blue or 
violet coloration is produced, by the aid of which the presence of 
0-002 ingm. of tungstic oxide can be recognised (Defacqz). 

Tungsten is estimated gravimetrically as the trioxide. For 
the purpose of ascertaining the quantity contained in wolfram, 
for instance, the finely powdered mineral is heated with aqua 
regia, evaporated to dryness, the residue treated with water, 
the soluble chlorides of iron and manganese are filtered ofl, and 
the insoluble tungstic acid is washed with alcohol and dissolved 
in ammonia. The solution is then evaporated down, and the 
residue heated gently, and afterwards ignited in presence of air, 
when the trioxide remains, and is weighed. Solutions of tung- 
states may also be precipitated with benzidine hydrochloride,^ 
mercurous nitrate, ^ or “ nitron,’^ ^ and the precipitate ignited 
and weighed as the trioxide (compare also Woltcr).^ Colori- 
metric methods, in which titanous chloride ® or stannous chloride ® 
are employed, may also be used. 

For recent investigations on the estimation of tungsten the 
original literature should be consulted.’ 

Atomic Weight of Tungsten , — The atomic weight of tungsten 
has been determined by numerous investigators. Schneider,® 
by the reduction of tungsten trioxide to metal and oxidation of 
the metal to trioxide, found the average value 184*11, whilst 

^ V. Rnorre, 5er., 1905, 38, 783; Kant8ohev,V."iJ?w5. Phys. Chem. 8oc., 
1914, 40, 729. 

2 Defacqz, Cofnpt rend., 1896, 123, 308. 

’ Gutbier and Woise, Zeit, anal. Chem., 1914, 53, 420. 

^ Chem. Zeit., 1910, 36, 2. 

^ Travers, Compt. rend., 1918, 160, 416. 

• Heath, Chem. Trade J., 1920, 00, 629. 

Hilpcrt and Dieokmann, Ber., 1913, 40, 152; Treadwell, Zeit. Elektrochem., 
1913, 19, 219, 381; Zinberg, Zeit. anal. Chem., 1013, 52, 529; Hermann, ibid.t 
1913, 62, 657 ; Kafka, ibid,. 1912, 52, 601 ; Wunder and Schapira, Ann. Chim. 
ami., 1913,-18, 257; Arnold, Zeit. anorg. Chem., 1914, 88, 74, 333; Dieckmann 
and Hilpcrt, Ber., 1914, 47, 2444 ; Marbaker, J. Amer. Chem. 8oc., 1916, 37» 
86 ; Dittler and Graffenried, Chem. Zeit., 1916, 40, 681 ; Guglialmelli and Hordh, 
Ami. 8oc. Quim. Argentim, 1917, 5, 81 ; Travers, Compt. rend., 1917, 105, 408; 
Sweeney, J. Amer. Chem, Sdc., 1916, 38, 2377 ; van Duin, Chem. Weekblad, 
1917, 14, 169; Fenner, Chem. Zeit., 1918, 42, 403; Jannasch and Leiste, J. pr. 
Chem., 1918, [2], 97, 141; Hodes, Zeit. angew. Chem., 1917, 30, 240; Erlieh, 
Arm. Chim. ami, 1920, [2], 2, 102; Corti, Ami Soc. Qulm. Argentina, 1917, 
5, 308 ; Lowy, Zeil angew. Chem., 1919, 32, 379. 

• A pr. Chem., 1850, 60, 162. 



URANIUM 


1149 


Marchand ^ found an almost identical value. Roscoe ^ by 
the same method obtained the number 183-48, and by the 
analysis of the hexachloride the number 184-02, whilst Waddell ® 
by the reduction of the trioxide found the higher number 
184-33. More recently Pemiington and Smith and Desi ^ have 
found the still higher number 184*8 by Schneider’s method, 
but their results have been criticised by Schneider ^ as , un- 
trustworthy. The investigations carried out by Smith and 
Exner,® who converted the hexachloride into the trioxide by the 
action of water and synthesised the trioxide from the metal, 
gave an average value for the atomic weight of 184*06. The best 
mean value is probably 184*1 ± 0 * 1 . The value now (1922) 
adopted is 184*0.'^ 


URANIUM. U = 238-2. At. No. 92. 

505 The mineral known as pitchblende was formerly believed 
by certain chemists to be an ore of either zinc or iron, whilst by 
others it was thought to contain tungsten. Klaproth, in 1789, 
was the first to point out the existence in this mineral of a peculiar 
metal, to which he gave the name of uranium, in remembrance 
of Herschel’s discovery of the planet Uranus in the year 1781. 
The substance obtained by Klaproth by the reduction of the calx 
of uranium was supposed by all the chemists who subsequently 
investigated the subject to be the metal, until Peligot ® in 1842 
proved it to be an oxide. Peligot likewise isolated the metal 
and determined its equivalent. 

Uranium is not a very abundant element, and its chief ore is 
pitchblende or uraninite. This consists of impure uranoso- 
uranic oxide, UgOg, and is found in Cornwall, at Joachimsthal, 
Johanngeorgenstadt, Adrianople, and other localities. Carnotite, 
potassium uranyl vanadate, is found in Colorado, Utah, and 
S. Australia ; autunite, uranyl calcium phosphate, is found in 
France, Portugal, the United States, and Madagascar. Varieties 
found in Cornwall are called bassetite and uranospathite.® 

1 Ann., 1861, 77, 261. 

* Mem. Manch. Phil 80 c., [3], 5, 77; Annalen, 1872, 168, 366. 

® Amer. Chem. J., 1886, 8, 280. « Zdl altorg. Chem., 1896, 8, 198, 206. 

^ J. pr. Chem., 1896, [2], 58 , 288. • J. Amer. Chem. Soc., 1904, 28 , 1082. 

’ Gerber, Mon. 8 ci., 1917, [6], 7, 73, claims that tungsten is not a simple 
substance, but is accompanied by neotungsten of higher atomic weight. 

^ Ann. Chim. Phya., 1842, [3], 5, 6. 

* HaUimond, Min. Mag., 1916, 17, 221. 



1160 


URANIUM 


f c 

^Uranium is found also as a double phosphate with copper in 
torbernite or uranium-mica, as carbonate in liebigite, voglite, 
and uranothallite, whilst as uranotantalite or samarskite it is 
found combined with columbium and tantalum. Other uranium 
minerals are gilpinite,^ brannerite,* becquerelite,® U08,2H20, 
and soddite,® 12U02,5Si02,14H30. Pitchblende is the best 
source of uranium, this mineral usually containing from 
40 to 90 per cent, of uranoso-uranic oxide, UgOg. The 
following analysis* gives the composition of a specimen of 
pitchblende from Connecticut: UOg, 26*48 per cent^; UOj, 
57*43; ThOg, 9*79; CeOg, 0*25; (La,Di)203, 0*13; (Y,Er)203, 
0*20; Fe203,0*40; PbO,3*26; MnO, trace; Ca0,0*08; alkaUes, 
trace ; HgO, 0*61 ; SiOg, 0*16 ; insoluble, 0*70. Total 99*49 per cent. 

The uranium minerals always contain the radioactive element 
radium, as well as helium, the occurrence of which is discussed 
under the heading of Radioactive Elements. Small amounts 
of compounds of copper, bismuth, silver, zinc, arsenic, and 
aluminium are often present. 

The process employed for the extraction of uranium from 
pitchblende is described by Meyer ® as follows : The finely 
ground mineral is first roasted and then calcined with sodium 
carbonate in a reverberatory furnace, the soluble uranium 
compound being extracted from the melt with water; alter- 
natively, the mineral may be decomposed by fusion with sodium 
sulphate, followed by extraction of the melt with dilute sulphuric 
acid, or the mineral may be decomposed with a mixture of 
sulphuric and nitric acids. In all cases the uranium compounds 
pass into solution, and in presence of excess of sodium carbonate 
remain in solution as sodium uranyl carbonate ; on boiling with 
a suitable excess of dilute sulphuric acid, a yellow precipitate 
of sodium uranate, Na2U207,6H20, is obtained. The insoluble 
residue contains the radium salt in admixture with a number 
of other compounds. 

The method recommended by Wohler® consists of the 
decomposition of the pitchblende with a mixture of sulphuric 
and nitric acids, volatilisation of the acid, and extractior 
with water, yielding a solution through which hydrogei 

^ Larsen and Brown, Ami', Min., 1917, 2* 76. 

* Hess and Wells, J. FranhUn Inst., 1920, 189, 226. 

3 Sohoep, Comvt. rend., 1922, 174, 1066, 1240. 

* Cilarke, ** The Data of Geochemistry,** U.S. Qtolt. Survey Bull., 1916, No. 616 

‘ Abegg’s “ Handbuch der anorganischen Chmie,** 1921, IV, [1], ii, p. 89! 

‘ Pogg. Ann., 1846, 64, 94. 



URANTOM 


1151 


sulphide is passed ; the filtrate, jafter being oxidised with nitric 
acid, is treated with ammonia, and the precipitate digested with 
a concentrated solution of ammonium carbonate containing 
excess of ammonia. Uranic hydroxide dissolves and yellow 
ammonium uranyl carbonate crystallises out on cooling. Peli- 
got’s ^ method depends on the facility with which uranyl nitrate 
crystallises, and on its ready solubility in ether. 

Metallic uranium was first prepared in the pure state by 
P^ligot, who obtained it by the action of sodium or potassium 
on uranium tetrachloride, a mixture of the tetrachloride, potass- 
ium chloride, and sodium being usually employed.^ It is also 
obtained by heating 600 parts of the oxide, U^Og, with 40 parts 
of sugar charcoal in the electric furnace in a carbon tube, closed 
at one end. The product contains a little carbon, which is 
partially removed by heating it in a crucible brasqued with 
uranium oxide, and enclosed in a larger crucible brasqued with 
titanium to protect the uranium from the action of nitrogen.® 
Uranium may also be obtained by heating the dioxide to redness 
with carbon and starting the reduction by means of a cartridge 
of magnesium and barium dioxide,^ or by reducing the trioxide 
with aluminium, a fused regulus of the metal containing a little 
aluminium being thus obtained.® A satisfactory method consists 
in first preparing the tetrachloride by passing chlorine over the 
heated dioxide mixed with carbon, or by heating the oxide in 
a stream of chlorine and sulphur chloride, and then reducing 
this with sodium or magnesium.® 

Pure uranium has a white colour, and takes a high polish ; it 
has a density of 18*7 at 14°, and a specific heat of 0*02765; in 
the powdered state it oxidises on exposure to the air and, if 
freshly prepared, may be spontaneously inflammable. It 
decomposes water slowly at the ordinary temperature, and 
more quickly at the boiling point. In the same condition it 
burns in oxygen at 170°, in fluorine at the ordinary temperature, 
in chlorine at 180°, in bromine at 210°, in iodine at about 260°, 
and in sulphur vapour at 600°. It melts at a high temperature, 

^ Ann. Chirn. Phys„ 1842, [3], 6, 5; 1844, 12, 549; 1848, 22, 329; 1869, 
[4], 17 , 368. 

* /6«^., 1869, [4], 17, 368. 

* Moissan, Compi. rend.f 1896, 122 , 1088. * 

* Aloy, BuU. 8oc. chirn,, 1901, [3], 25, 344. 

^ Stavenhagen, Ber., 1899, ^ 3065; Stavenhagen and Schuohard, ibid., 
1902, 25 , 909. 

* Rideal, J. 8oc, Chm. Ind., 1914, 88, 673; Lely and Hambniger, Zeit, 
anoTff, Chm., 1914, 87 , 209; Baragiola, 8chweiz. apoth. Zeit, 1915, 58 , 477. 

VOL. II. (n.) Y 



1152 


URANIUM 


and has a higher boiling point than iron, condensing in small, 
non-magnetic spheres, free from carbon.^ It readily combines 
with nitrogen at 1000°. Uranium has a potential between those 
of copper and hydrogen. ^ 

Several alloys with iron, manganese, and cobalt have been 
prepared by the aluminium reduction method. An amalgam ^ 
can be obtained by the electrolytic method, and leaves pyrophoric 
uranium when the mercury is distilled off at 242°. 

Metallic uranium and its compounds are radioactive (see the 
section on the Radioactive Elements). 

COMPOUNDS OF URANIUM. 

Uranium and Oxygen. 

506 Uranium combines with oxygen to form two ^ well-defined 
oxides, UO 2 and UO3, and these combine, forming intermediate 
oxides. Both these oxides are more magnetic than the metal.® 
The dioxide is a basic oxide, and gives rise to the uranous 
salts, in which the metal is quadrivalent. The trioxide, 
like the corresponding oxide of the other metals of this group, 
behaves as an acid-forming oxide, yielding salts known as the 
uranates, analogous to the chromates, molybdates, and tungstates. 
Like the other trioxides of the group, uranium trioxide also 
yields a large number of derivatives in which only one of the 
three oxygen atoms is replaced by negative groups ; these may 
be regarded as derivatives of .the bivalent compound radicle 
uranylf UOj. This radicle has more decidedly basic properties 
than the corresponding radicles derived from the other metals, 
and the derivatives, therefore, correspond to the salts of a basic 
oxide, whilst the similar compounds of the other metals are 
more nearly allied to the acid chlorides, such as sulphuryl 
chloride, SOaClg, and phosphoryl chloride, POClg. This view 
of the constitution of the uranyl salts is supported by the electro- 
chemical properties of their solutions. In aqueous solution the 
salts of strong acids, UOg’R'ai are hydrolysed to a small extent, 
corresponding in this respect to the analogous salts of aluminium 

^ Zimmermann, Annakrif 1883, 216, 1; Moisaan, Compt. rend,, 1803, 116, 
1429; 1896, 122, 1088; 19d6, 142, 425. 

‘ Eischer and Roderburg, Zeii. anorg. Chem., 1013, 81, 170; Fischer and 
.Eideal, ibid, 

* FeriSo, Bull. Soc. chim. 1901, [3], 25, 622. 

* See Lebeau, Compt. rend., 1922, 174, 388. 

^ Wedekind and Horst, Bet., 1915, 48, 105. 



1163 


URANIUM AND OXYGEN 

' I — ^ 

and glucinum. The non-hydrolysed portion of the salt dis- 
sociates in the normal ^manner, and on electrolysis the uranyl 
ion migrates to the cathode. Complex derivatives are, however, 
very readily formed, especially with salts of organic acids.^ 

Uranium Dioxide^ UOg. — This oxide, formerly mistaken for 
the metal uranium, is prepared on the technical scale by fusing 
35 parts of sodium chloride, 20 parts of sodium uranate, and 
1 part of powdered charcoal in a cast steel pot at a red heat, 
lixiviating with water and treating the residue with hydrochloric 
acid.2 It is obtained by heating uranoso-uranic oxide, UgOg, 
or uranic oxalate in a current of hydrogen, or by the electrolysis 
of uranyl nitrate solution under suitable conditions.® Thus 
prepared it is a p 3 n:ophoric powder, having a brown or copper- 
red colour, and a density of 10*95. When heated in the 
air it takes fire, and is completely converted into the oxide, 
UgOg.^ It dissolves in strong acids, forming the green uranous 
salts.® It may be obtained in jet black octahedra isomorphous 
with thoria by fusing with borax, and then removing the latter 
with dilute hydrochloric acid.® It is also formed in microscopic, 
black, non-pyrophoric crystals when crystalline uranic hydroxide 
is reduced in hydrogen,’ and is left as a brick-red mass, which 
becomes black on heating, when uranyl bromide is heated in 
the air.® 

Uranous oxide is oxidised to the trioxide by ammoniacal 
silver solutions.® 

Uranous Hydroxide^ U02,2H20 (?), is precipitated in reddish- 
brown flakes, which become black on ebullition, by adding an 
alkali to a uranous solution.^® In presence of alcohol, uranyl 
salts are reduced by light to uranous salts, or uranous 
hydroxide. It dissolves easily in dilute acids, whilst the 
calcined oxide is only slightly soluble in these liquids. The 

1 Dittrich, Zeit, phyaikal Chem., 1899, 29, 449; I/jy, tij'd., 1900, 30, 193; 
Ber., 1900, 33» 2658. Compare Kohlschtitter, AnnaUn, 1900, 811, 1. 

* Parsons, J, Ini. Eng. Chem., 1917, 9, 466. 

’ Oechsner de Coninck and Camo, Bull. Acad. roy. Bdg., 1901, 321. 

^ Jolibois and Bossoet, Compt. rend.^ 1922, 174, 386. Oechsner de Coninck, 
Bull Soc. chim.t 1912, [4], 11, 1037 states that the oxide U 40 iq is thus formed. 

^ See Colani, Compt. rend., 1912, 165, 1249; Raynaud, ibid., 1911, 153, 
1480; BuU. Soc. chim., 1912, [4], 11, 802. ' 

* Hillobrand, Zeit. anorg, Chem., 1893, 3, 240. 

’ Aloy, BuU. Soc, chim., 1900, [3], 28, 368. 

* Oechsner de Coninck, Compt. rend., 1902, 186, 900. 

* Smith and Shinn, Zeit. anorg. Chem., 1894, 7, 47. 

See Aloy, BuU. Soc. chim., 1899, [3], 21, 613. 



1154 


URANIUM 


substance has also been obtained electrolytically in a colloidal 
form.^ 

Uranic Oxide^ TJO3, or Uranyl Oxide^ (U02)0. — When uranyl 
nitrate is heated in a glass tube to 250° so long as acid fumes 
escape, this oxide is left behind in the form of a brownish-yellow 
powder, whereas, when the nitrate is rapidly decomposed, a red 
modification of the oxide is produced.^ It can also be prepared by 
heating ammonium uranyl carbonate or ammonium uranate in air. 

Uranic Hydroxide (Uranic Acid), UOgjHgO, cannot be obtained 
by precipitating a uranyl salt by an alkali, the precipitate thus 
formed consisting of an alkali uranate. It may, however, be 
prepared, according to Berzelius, by gently calcining the nitrate 
in a sand-bath as long as nitric acid is evolved. The residue 
contains uranic hydroxide mixed with a basic salt, which can be 
removed by washing with boiling water. It may likewise be 
, obtained by evaporating a solution of uranyl nitrate in absolute 
alcohol, at a moderate heat, until a yellow mass remains, con- 
sisting of the hydroxide, U02(0H)2,H20, or by the electrolysis 
of uranyl salts at a low current density.* This hydrate loses 
half its water at 80°,* or in a vacuum at the ordinary tempera- 
ture, but at a temperature of 400° it begins to lose oxygen, and 
is converted into uranoso-uranic oxide, UgOg. Uranic hydroxide 
is yellow, and has a density of 5*92. It does not undergo change 
in the air, nor does iib absorb carbon dioxide. 

An orange-coloured hydroxide, U03,H20, can be obtained by 
the electrolysis of the nitrate,® and is formed hi rhombic crystals 
when the violet hydrate of the oxide UgOg is boiled with water 
in the air,® 

This oxide, as mentioned above, yields by the action of acids 
the uranyl salts, whDst with bases it gives rise to the uramtes. 
The former have a yellow colour, and most of them possess a 
remarkable fluorescence,’ which they impart to glass. The 
absorption bands exhibited by these compounds have been 

^ Samsonow, KoUoid-Zeit., 1911, 8, 96. 

* Oechsner de Coninck, Compt, rend., 1901, 138, 204; BuU. Acad. roy. Belg., 
1904, 363, 448. 

* PierI4, J. Physical Chem., 1919, 88, 517. 

*■ de Foiprand, Compt. re^., 1913, 156 , 1954; 

‘ Oeohsuer de Coninck and Camo, BvU. Acad. roy. Belg., 1901, 8, 222; PierW, 
J. Physical Chem., 1919, 83, 517. 

* Aloy, BuU. 80 c. chim., 1900, [3], 88, 368. 

^ See Trttmpler, Zeit. physiM. Chem., 1915, 90 , 385; Bauer, Schweiz. Chem. 
Zeitj^, 1918,8,40; Nichols and Howes, PAywcaiBer., 1919, [2], 14 , 293; Nichols, 
Howes, and Wick, ibid., 1919, [2], 14 , 201 ; Nichols and others, Carnegie Inst, 
WasUngUm PvbUcaiiont 1919, 8W, 1* 



URANIIM AND OXYGEN 


1155 


studied by Becquerel and others. Aese salts are highly sensi- 
tive to light and have been employed for photographic purposes. 
The most important are described in the sequel, together with 
the other uranium salts. 

The Uranates, — The alkali uranates are obtained by precipi- 
tating a uranic salt with an alkali, those of the alkaline earths 
and other metals by precipitating a mixture of a uranyl salt and 
a corresponding metallic salt with ammonia. They are also 
formed when a mixture of a metallic uranate and the acetate or 
carbonate of the metal is heated in the air. The uranates gen- 
erally have the composition M20,2U03, and correspond to the 
dichromates. They are yellow, insoluble in water but soluble 
in acids, and are decomposed by heat, like uranic oxide itself. 
Normal uranates are, however, known, as well as potassium 
and sodium salts of tri-, tetra-, penta-, and hexa-uranic acids. 

Potassium Di-uranate^ K2U2O7. — This is obtained as a pale 
orange-yellow coloured powder by precipitating a uranyl salt 
with an excess of potash. Probably the hydroxide is first pre- 
cipitated and then two molecules unite by the elimination of 
water, forming uranic acid, which unites with the excess of alkali 
to form the potassium salt. The norrml salt can be produced by 
fusing uranyl chloride with potassium chloride and ammonium 
chloride, or by heating uranium trioxide with potassium chlorate. 
Potassium uranate can also be obtained by electrolysis of a 
neutral solution of potassiiun uranyl cyanide.^ 

Sodium Di-uranate, Na2U207, is obtained in a similar manner 
to the potassium salt, and is known as uranium yellow^ being 
used for painting on glass and porcelain, as well as for preparing 
the yellow glass known as uranium glass. It is prepared on 
a large scale by roasting 100 parts of pitchblende, containing 
45 per cent, of UgOg, with 14 parts of lime in a reverberatory 
furnace. The resulting calcium uranate is treated with dilute 
sulphuric acid, and the solution of uranic sulphate thus obtained 
is mixed with sodium carbonate. The uranium is precipitated, 
together with the other metals, but re-dissolves in an excess of 
the alkali. On treating this liquid with dilute sulphuric acid, a 
hydrated sodium uranate, Na2U207,6HaO, is obtained.^ 

Ammonium Uranate, — This salt sometimes occurs in commerce 
as a fine deep yellow-coloured precipitate, terined, like the 
sodium salt, uranium yellow. It is easily obtained by adding 
ammonium chloride or sulphate to a boiling solution of sodium 

* Pierl^, J. Physical Chm., 1919, 517. 

* Patera, J. pr, Chm., 1854, 61,' 397. 



1156 


URANIUM 


• • 

uranate, washing the resulting precipitate, and drying at a gentle 
heat. When heated to redness this salt yields pure uranoso- 
uranic oxide, and serves therefore as the raw material for the 
preparation of other uranium compounds. 

Uranoso-uranic Oxide or Green Oxide of Uranium^ 
U308(= 1102,21103), occurs more or less pure in pitchblende. 
The pure oxide can be obtained by gently heating the trioxide 
or the dioxide in the air in the form of a satiny, dark-green 
powder, having density 7 * 2 , and soluble in strong acids. It 
forms a violet hydroxide which can be prepared by the action 
of light on a solution of uranyl oxalate or an alcoholic solution 
of the acetate.^ A number of violet compounds of uranium are 
known, being obtained whenever a uranous and a uranic salt 
are present together at the requisite temperature in neutral or 
feebly acid medium. By loss of their acid radicles they yield 
hydrated uranoso-uranic oxide.^ 

Bloch Oxide of Uranium^ or Uranium Penioxide, 
^2^5 (== U02,U03), is formed when the other oxides, or am- 
monium uranate, are strongly ignited in the air, and when the 
nitrate is electrolysed. Zimmermann stated that it possesses 
no constant composition,^ but there seems to be no reasonable 
doubt regarding its individual existence. 

An oxide of the composition U30io,2H20 is stated to be formed 
when uranium salts are electrolysed.^ 

Uranium Peroxide, UO4. — ^When a very dilute , solution of 
hydrogen peroxide is added to one of uranyl nitrate, a yellowish- 
white precipitate of peruranic hydroxide, U04,a;Il20, is formed, 
which evolves chlorine when treated with hydrochloric acid.® 
Peruranates are formed by the action of alkali and hydrogen 
peroxide on the uranyl salts (Fairley). Two types of salt 
are known; in one of these the metal appears to be present 
as a peroxide and the salt can be hydrolysed by weak acids or 
bases into a peroxide and uranium peroxide ; the hydrolysis of 
salts of the second type yields uranium peroxide and an ordinary 
metallic oxide.® 

^ See Aloy, BmU. 80 c, chim., 1900, [3], 28, 368. 

* Aloy and Rodier, Bull 8 m. chim., 1920, [4], 27, 101. 

* Annalen, 1886, 282, 276. See also Lel^au, Compt. rend., 1922, 174, 388. 

* Pierl6, J. Physical Chem., 1919, 28, 617, 

* Fairley, Joum, Chem. 80 c., 1877, i., 127; HOttig and Sohroeder, Zeit, 
anorg. Chem., 1922, 121, 243. 

* Melikoff and Pissarjewaky, Ber., 1897, 80, 2902; Zeit. anorg. Chem., 1898, 
18, 69; Pissarjewaky, J. Russ. Phys. Chem. 8 oe., 1902, 84, 472. 



URANIUM AND THE HALOGENS 


1167 


Sodium Peruramiey (Na202)2U04,te20, is precipitated when 
alcohol is added to a solution of uranyl nitrate, sodium hydroxide, 
and hydrogen peroxide,’ and crystallises in golden-yellow needle- 
shaped crystals, which are somewhat more stable than the 
potassium salt. If the minimum quantity of caustic soda be 
employed, a red crystalline salt separates out, having the com- 
position Na202(U04)2,6H20. A red, crystalline salt, NagUO^jIIgO, 
is formed when peruranic hydroxide is added to hydrogen 
peroxide containing alcohol, sodium hydroxide being then 
gradually introduced. It slowly decomposes with evolution 
of oxygen.^ The formation of a salt of this type is the cause 
of the red coloration produced when hydrogen peroxide and 
solid potassium carbonate are added to a uranyl salt.^ 

Lead Perumnale is formed as a double salt with lead uranate, 
(Pb0)2U04,PbU04, by the action of sodium peruranate on lead 
acetate. Hydrogen peroxide is liberated in the reaction and 
the resulting lead salt, when treated with dilute acetic acid, 
yields lead acetate and peruranic hydroxide, but no hydrogen 
peroxide (Melikoff and Pissarjewsky). Other salts of the heavy 
metals are prepared in a similar manner; they are more stable 
than the corresponding salts of molybdenum and tungsten. 


Uranium and the Halogens. 

507 Uranium difluoridcy UF2,2H20, has been obtained by 
electrolytic reduction of uranyl chloride in presence of excess of 
hydrofluoric acid.® 

Uranium Tetrajluoride or Uranous FluoridCy UF4, is obtained 
in the form of a voluminous green powder when hydrofluoric 
acid is added to a solution of uranous chloride. It is insoluble 
in water and hydrofluoric acid, and when heated in the air it 
leaves a green residue of oxide. When ignited in hydrogen it 
loses hydrofluoric acid.^ The hexahydrate is obtained by 
electrolysis of potassium uranyl fluoride in acid solution.® 

Uranous fluoride forms double salts with the alkali fluorides. 
Potassium urano-fluoride, KF,UF4, is obtained by the action of 
^educing agents, such as formic and oxalic acids under the 
influence of light, upon the potassium urano-oxyfluoride, described 

1 Aloy, Bull 80 c, chim.y 1003, [Z], 292. * Ibid,, £7, 734. 

* Oiolitti and Agamennone, Atti B, Accad, Lincei, 1905, [5], 14, i., 114, 105. 

• Carrington Bolton, Ber. Akad, Wm. Berlin, 1866, 299; see also Smithells. 
J. Chem. 8 oc„ 1883, 43, 125. 

« PierW, J. Physical Chem,, 1919, 23, 517. 



1158 \ URAmtJM 

below. It is a* green powder, resembling uranous fluoride, 
insoluble in water and in dilute acids. 

The hexafluoride is also known. The reaction between fluorine 
and uranium is extremely vigorous and the product is mainly 
the tetrafluoride and small quantities of the hexafluoride, UF^. 
The hexafluoride is best prepared from fluorine and the penta- 
chloride cooled in an alcohol and carbon dioxide mixture. It 
forms glistening, colourless, fuming, monoclinic prisms, which 
sublime without melting at ordinary temperatures under reduced 
pressure.^ 

Uranyl Fluoride, UO2F2, is a green solid, obtained by the 
action of hydrofluoric acid on the oxide UgOg. It was con- 
sidered by Smithells ^ to exist in two modiflcations. It combines 
with potassium fluoride, yielding 'potassium uranyl fluoride, 
UOjFgjSKF, which is a lemon-yellow, crystalline precipitate, and 
is also formed when an excess of* potassium fluoride is added to 
' a solution of uranyl acetate. It is trimorphous (Baker).® 
Corresponding sodium, ammonium, and barium salts are known 
(Bolton). Hydrogen peroxide converts these salts into deep 
yellow-coloured perox3rfluorides.^ 

Uranous Oxjfluoride, UOFg, is formed by the electrolytic or 
photochemical reduction of uranyl salts.® 

Uranium Trichloride, UCI3, is obtained by heating the tetra- 
chloride in hydrogen,® or by the continued reduction of uranyl 
salts with zinc .and hydrochloric acid.’ It is a reddish-brown 
powder, and dissolves readily in water, forming a red solution, 
which gradually becomes green with evolution of hydrogen. 

Uranium Tetrachloride or Uranous Chiwide, UCI4.— This is 
produced with vivid incandescence, when chlorine is passed 
over metallic uranium, and is obtained also by igniting uranium 
dioxide in hydrogen chloride, and, in solution, by exposing a 
solution of uranic oxide in hydrochloric acid containing alcohol 
to sunlight ; ® other reduction methods may also be used. It 

^ Ruff, Zedner, Schiller, and Heinzelmann, Ber., 1909, 42, 492. 

‘ Loc. cit. See also Giolitti and Agamennone, 2oe. ciU 

* Joum. CAem. 8oc„ 1879, 861 763. 

*■ Lordkipanidz4, J. Rust. Phyt, Chm. Soc., 1900, 82> 283. 

^ Qiolitti and Agamennone, diU R. Accad, Ztncet\ 1905, [ 6 ], 14, i., 114, 165. 

* P^ligot, Ann. Chim. Fhys., 1842, 5, 20; Rosenheim and L^bel, Zeit. anory. 
Chem., 1908, 57. 234. 

^ Zimmermann, Annalen, 1882, 813, 320. 

* Aloy, BuU. 80c. chim., 1899, [3], 21» 613 ; Aley and Rodier, ibid., 1922, 
[4J, 81*246. 



URAimJM AND THE HALOGENS 1169* 

is best prepared by passing chlorine over a heated mixture of 
charcoal and any of the uranium oxides, or over uranium 
carbide.^ Some pentachloride is simultaneously formed, and 
may be removed by heating the product in a current of carbon 
dioxide. It can also be prepared by passing carbon tetrachloride 
over U3O3 at a red heat.^ It crystallises in splendid dark-green 
octahedra, having a metallic lustre, and volatilising at a* red 
heat to form red vapours with the normal density of 13 - 3 . It 
is extremely deliquescent, fumes strongly on exposure to the 
air, and dissolves readily in water, with evolution of heat 'and 
formation of a deep emerald-green solution. This, when con- 
centrated in a vacuum, leaves an amorphous, deliquescent mass 
of uranous chloride, but when evaporated by heat it decomposes, 
yielding a soluble residue, probably consisting of the oxychloride. 
Solutions of Uranous chloride yield with alkah’s a precipitate of 
uranous hydroxide. The solution acts as a powerful deoxidising 
agent, reducing gold and silver salts, and converting ferric 
chloride into f^rous chloride. It was by the analysis of this 
chloride that P( 51 igot ascertained that the supposed metal was 
in reality an oxide. 

Uranium tetrachloride combines directly with ammonia, 
forming the compound 3UCl4,4NH3, and unites with the heated 
chlorides of potassium, lithium, and the metals of the calcium 
group, forming green salts, UCl4,2M'Cl or UCl4,M^‘Cl2, which are 
decomposed by water (Aloy). 

Benrath ® considers that the greenish-yellow powder deposited 
when uranyl chloride dissolved in ether is exposed to sunlight 
is the oxychloride^ UOClg. 

Uranium PentachloridSy UCI5, is obtained by the direct union 
of the tetrachloride with chlorine. It eidsts in two distinct 
forms, according as it is produced slowly or quickly. When 
the current of chlorine is slow, the uranium pentachloride forms 
long, dark, needle-shaped crystals, which reflect light with a 
green, metallic lustre, but are of a splendid ruby-red colour 
when viewed by transmitted light. If the rate at which the 
chlorine passes be rapid, the pentachloride is deposited in the 

fown of a light brown, mobile powder. Both forms are hygro- 

• 

^ Aloy, BuU. Soc, chim., 1899, [3], 21, 264; Roderburg, Zeit. anorg. Chem., 
1913, 81, 122; Lely and Hamburger, ibid., 1914, 87, 209; Rideal, J. Soc. 
Vhem. Ind.y 1914, 33, 073. 

. * Colani, Ann. Chim. Phys.^ 1907, [8], 12, 69. 

* Zeit. wise. Photochem., 1917, 16, 253. 



1160 


URANTOM 


scopic, yielding yellowish-green liquids on exposure to the air 
for a few minutes, and hissing and giving off fumes of hydro- 
chloric acid when thrown into water. Uranium pentachloride 
cannot be volatilised without partial decomposition, since 
uranium tetrachloride and free chlorine are formed. The 
tetrachloride when similarly heated loses no chlorine.^ There 
are jeasons for regarding uranium pentachloride as possessing 
the constitution UCl 4 *UClg. The free hexachloride is not, how- 
ever, known. . 

Ufanyl Chloride or Uranium Oxychloride^ UOgClg, is formed 
when dry chlorine gas is passed over uranium dioxide at a red 
heat. The tube then becomes filled with the orange-yellow 
vapour of this compound, which solidifies to a yellow, crystalline 
mass, and is easily fusible, but not very volatile. When strongly 
heated in dry air, it yields chlorine and the dioxide, which then 
^ becomes oxidised.^ 

Uranyl chloride is soluble in water, alcohol, or ether, and 
its aqueous solution yields on evaporation crystals of the hydrate, 
U02Cl2,H20. This may be obtained in solution by acting 
upon uranic oxide with hydrochloric acid, or by oxidising a 
solution of uranous chloride with nitric acid.^ 

Uranyl chloride forms double chlorides with the chlorides of 
the alkali metals. The ammonium salt, 2NH4Cl,U02Cl2,2Il20, 
crystallises in rhombohedra from a syrupy solution of the mixed 
salts. The potassium salt, 2KCl,U02Cl2,2H20, is obtained by 
dissolving potassium uranate in excess of hydrochloric acid, 
adding potassium chloride, and evaporating, when large, rhombic 
tablets separate out, which have a yellowish-green colour, and 
are very soluble.* The anhydrous compound can be obtained 
by passing the vapour of the oxychloride over heated potassium 
chloride.® Uranyl chloride combines also with the hydro- 
chlorides of the organic bases (Greville Williams). Several basic 
chlorides have been described.® 

^ Roscoe, Joum. Chem. Soc.t 1874, 933; Ruff and Heinzolmann, Ber., 

1909, 4S> 492; Zeit. anorg. Chem., 1911, 72, 63; Camboulives, Compt. rend., 

1910, 160, 176. 

‘ Oeohsner de Coninok, Ar^n Chim. Phye., 1904, [8], 3, 500. 

® Sw Mylius and Dietz, Ber., 1901, 84, 2774. 

* See Rimbach, Ber., 1904, 87, 461. 

» Aloy, Bull. Soe. chim., 1901, [3], 26, 163. 

• Ibid., 1899, [3], 81, 613; Orloff, J. Ruse. Phye. Chem. 8oc., 1902, 34, 376; 
1903^ 86, 613. 



URANIUM AND SULPHUR 


1161 


^ — j 

Uranium Trihromide, UBrg, has been described as dark brown 
needles.^ 

Uranium Tetrabromide, UBr 4 , is obtained by heating in an 
atmosphere of bromine vapour a previously ignited mixture of 
uranous oxide and six times its weight of starch, or of the green 
oxide with sugar charcoal.^ The bromide is deposited in the 
more strongly-heated portions of the tube in lustrous brown 
tablets of density 4*838 at 21^/4^^. The density of its vapour 
is 19*5. It loses its lustre and becomes dull yellow on the surface 
in the presence of even traces of oxygen, fumes in the air, and 
is very deliquescent. 

Uranyl Bromide or Uranium OxybromidSy UOgBrg, is obtained 
by treating uranous oxide with bromine and water, or by dis- 
solving uranic oxide in hydrobromic acid. On evaporation, 
yellow needles are deposited, which have a styptic taste and 
decompose when heated.® 

Uranium Telraiodidey UI 4 , described by Rammelsberg, is 
obtained by dissolving uranous hydroxide in hydriodic acid. A 
green solution is thus formed which decomposes on evaporation. 
The solid substance is formed as a crystalline sublimate when 
iodine vapour is passed over uranium at a temperature of 500'^ 
in sealed vacuum tubes. It forms black needles melting at 
500°, and dissolves in water, giving a green acid solution.^ 

Uranyl Iodide^ UGglg, is formed when a slight excess of barium 
iodide is added to an ethereal solution of the nitrate, and separates 
in red, deliquescent, unstable crystals.® 

Uranyl chloratey perchhratey and iodatCy and double compounds 
of the last-named with potassium iodate, have been described. 

Uranium and Sulphur. 

508 Uranium SesquisulphidCy UgSg, is prepared by heating 
UBrg in hydrogen sulphide, and yields uranium monosulphidey 
US, when heated in hydrogen.® 

Uranous Sulphide, USg, is obtained, according to P61igot, 
when metallic uranium is heated in sulphur vapour. The mass 
takes fire and an amorphous, greyish-black powder is obtained 

^ Alibegoff, Annalm, 1882, 233, 104, 131, 135. 

* Richards and Merigold, Zeit. anorg. Chem., 1902, 31» 250. 

® See Oechsner de Coninok, BuU. Acad. roy. Belg.y 1902, 12, 1025. 

* Guiohaid, Compi. rend., 1907, 145, 921. 

* Aloy, Ann. Chim. Phya., 1901, [7], 24, 412. 

* Alibegoff, Annalm, 1886, 233, 117. 




1162 


URANIUM 


j j 

which becomes crystalline when ignited in absence of air. It 
may also be formed by passing a care^y dried mixture of 
hydrogen and sulphur vapour over sodium uranium chloride. 
The sulphide is thus obtained in small, flattened crystals.^ 

Ammonium sulphide always gives a black precipitate of tile 
hydrated sulphide with uranous salts. In moist air it loses 
hydrogen sulphide and forms uranyl sulphide, UOgS. 

An oxysulphide, UOS, is obtained when U02,U308 or am- 
monium uranate is heated in hydrogen sulphide. 

Uranyl Sulphide^ UOgS, is precipitated when ammonium 
sulphide is added to a solution of uranyl nitrate. It oxidises 
quickly on exposure to air, and dissolves easily in acids and in 
ammonium carbonate. When heated in the presence of water 
until all the ammonium sulphide has been driven off, it decom- 
poses into sulphur and the dioxide. If air be excluded the 
, ammonium sulphide acts as a reducing agent, ^ and the residual 
black powder has the composition Uranyl sulphide is 

formed in black, needle-shaped, tetragonal crystals when the 
green oxide is strongly heated with potassium thiocyanate and 
sulphur.* 

Uranium When hydrogen sulphide is passed into a 
solution of uranyl nitrate to which about 2*8 molecular propor- 
tions of potassium hydroxide have been added, an orange-yellow 
precipitate is produced which dries to a hard, amorphous, brick- 
red mass and has the composition 5UO3, 2X20,11282. When 
this substance is treated with potassium carbonate or hydroxide 
it is converted into uranium red, which is a blood-red precipitate 
and dries to a brittle, amorphous mass resembling potassium 
permanganate in appearance and yielding a carmine-red powder. 
This compound has notr been obtained free from water, but has 
the composition 6U03,2K20,HS2K,a;H20, and is converted into 
the orange-yellow substance by carbonic acid. Acids decompose 
it with liberation of half the sulphur as free sulphur and half 
as hydrogen sulphide.^ An analogous ammonium-red can be 
obtained by the action of ammonium sulphide on uranyl nitrate, 
and it was in this way that uranium red was first prepared.® 

1 Colani, Am. Chm. Phys., 1907, [8], 12, 69. 

* For conditions of formation of urantms sulphide, see Wilke-Ddrfurt, Chm, 
Zentr., 1921, i., 170. 

’ Milbaner, Zeit. amrg. Chem., 1904, 42, 448. 

* * KohlsohOtter, Annden, 1900, 814 , 311. 

* Patera, J. pr. Chem., 1850, 51 , 122; Bemel4, Annalen, 1865, 126 , 209; 
Zimnlermann, ibid., 1880, 804 , 204. 



URANIUM AiSfD SULPHUR 1163 

The sdenides, USej.and UgSej, and the telluride, UgTea, have 
been obtained iiT the crystalline state by heating the double 
chloride, UCl4,2NaCl, in hydrogen containing the vapour of 
, selenium or tellurium.^ A crystalline uranyl selenide, UOgSe, 
is obtained by heating the green oxide with potassium cyanide 
and sulphur.^ 

Uranyl Sulphite, — When sulphur dioxide is passed into a 
solution of uranyl acetate, a crystalline precipitate is produced 
which has the empirical composition U03'S02,4H20 and was 
regarded by Girard^ as the normal sulphite, UOa’SOaAHgO. 
Kohlschiitter,^ however, formulates it as a uranyl sulphurous 
acid, S03H’U02‘0H,3H20, and has prepared a number of 
complex alkali salts. A basic uranous sulphite, U0*S03,2H20, 
is also believed to exist. 

Uranous Sulphate, U(S04)2,9H20, crystallises from aqueous solu- 
tion in greenish, monoclinic, twinned prisms and is isomorphous 
with crystallised thorium sulphate.® It is, however, usually 
obtained with SHgO. In order to prepare this salt, the green 
oxide, UsOe, is dissolved in dilute sulphuric acid and the solution 
allowed to crystallise after addition of some alcohol. The 
mother-liquor, which contains uranyl sulphate, yields another 
crop of crystals of uranous sulphate after it has remained exposed 
to the light, inasmuch as the uranyl salt present in solution is 
reduced by the alcohol. 

Sodium thiosulphate has also been found a satisfactory 
reducing agent. Uranous sulphate forms a stable hydrate 
with 4H2O and several other hydrates, and is readily decomposed 
by water with formation of basic salts.® It forms double salts 
with the sulphates of the alkali metals;"^ as, for instance, 
U(S04)2,K2S04,2H20, and U(S04)2,4(NH4)2S04,3H20. 

An acid uranium sulphate, (US04)2H, containing tervalent 
uranium, has been obtained by an electrolytic method.® 

^ Colani, Compt. rend., 1903, 137^ 382. 

* Milbauer, Zeit. anorg. Chem., 1904, 42, 450. 

* Compt. rend., 1852, 84 ;, 22. 

« AnnaUn, 1900, 311 , 1. 

Rammelaboig, Zeit. Kryat. Min., 1889, 15 , 640. For a general discussion 
of the relation of uranous salts to those of thorium, see Fleck, J. Chem. 80 c., 
1914, 105 , 247. • • 

* Orloff, J. Jiuas. Phya. Chem. 80 c., 1902, 84 , 381 ; Oechsner de Goninok, 

BuU. Acad. roy. Belg., 1901, 483; Kohlschfltter, Ber., 1901, 34 , 3628; Giolitti 
and Bucoi, Qazx., 1905, 85 , ii., 151, 162 ; Giolitti and Libori, ibid., 1906, 36 , 
u., 443. 7 See KoblsohUtter, Ber., 1901, 34 , 3619. 

* Rosenheim and Loebel, Zeit, anorg. Chem., 1908, 57, 234. 



1164 


URANIUM 


Uranyl SulpJmte, 1102*804,31120, is obtained by heating 
uranyl nitrate with sulphuric acid, and does not crystallise 
readily. It dissolves in about 20 parts of water at the ordinary 
temperature.^ When dissolved in moderately concentrated 
sulphuric acid, fine, yellowish-green, fiuorescent crystals of 
U02*S04,H2S04 are deposited on cooling, whilst from a solution 
in concentrated sulphuric acid crystals of a disulphate, U02*S207, 
are deposited, which do not fluoresce. By the gradual oxidation 
of the pitchblende found in Joachimsthal, several new uranium 
minerals have been formed. Amongst the more important are 
certain sulphates, such as uranium-vitriol or johannite, and 
some basic sulphates. 

Uranyl sulphate forms double salts with the sulphates of the 
alkali metals, such as U02*S04,K2S04,2H20. This is very 
soluble, and crystallises in yellow crusts, whilst the sparingly 
soluble ammonium salt, U02*S04,(NH4)2S04,2H20, is deposited 
in monoclinic, lemon-coloured prisms.^ 

Uranyl selenitey selemle, chromates, molybdates, and tungstates 
have been studied, and their existence has been confirmed. 


Uranium and Nitrogen, Phosphorus, Arsenic, and Boron. 

509 Uranium Nitride.— Vmmum combines directly with 
nitrogen at 1000°, forming a yellow nitride,^ the composition of 
which is not stated. The nitride, U3N4, is obtained as a grey 
or black powder by heating the tetrachloride in ammonia, 
mixing the product with ammonium chloride, and again igniting 
in an atmosphere of ammonia.^ 

Uranyl Nitrate, U02(N03)2,6H20. — This salt, which is com- 
monly known as uranium nitrate, is prepared by dissolving any of 
the oxides of uranium in nitric acid. It crystallises in fine, lemon- 
yellow, fluorescent, rhombic ® prisms, which are soluble in half 
their weight of water ® and deliquesce on exposure. Icositetra-, 

^ Oechsner de Coninok, Bull, Acad. ray. Belg., 1901, 222, 340; 1902, 94, 161. 

* See also Oechsner de Coninck, Bull. Acad, roy, Belg., 1904, 1171; 1906, 
60, 94, 161, 182. 

* Moissan, Compt. rend., 1896, 122 » 274. 

* Kohlschiitter, Annalen, 1901, 817 . 168. See also Colani, Compt. rend., 
1903, 137 , 382; Haber and* Greenwood, Zeit. Elektrochem., 1916, 81 , 241; 
Ger. Pat, 229126. 

® See, however, Quercigh, Riv. min. criat. Ital., 1916, 44, 6. 

® See Oechsner de Coninck, Compt, rend., 1900, 181 , 1219, 1303; 1901, 
132 , 90, 204; Bull. Acad, roy, Belg., 1901, 222; Bull. 8oc, chim., 1916, [4], 



URANIUM AND NITROGEN, ETC. ^ 


1165 


tri-, di-, and mono-hydrates and the anhydrous salt are known 
to exist.^ The aqueous solution has an acid reaction owing to 
the partial hydrolysis of the salt.^ The nitrate is prepared 
commercially by igniting ammonium uranate, (Nn4)2U207, and 
dissolving the oxide in nitric acid.® When crystals of uran.yl 
nitrate are shaken or ground together, triboluminescenoe 
(emission of light under such conditions) is observed. .The 
explosive property of uranyl nitrate, which has in these circum- 
stances frequently been observed, is apparently not an inherent 
property of the salt, but is attributed to the presence of an 
imstable compound produced when nitric acid is present during 
its recrystallisation from ether.^ Uranyl nitrate readily forms 
double salts with the alkali nitrates.® 

Uranium phosphide^ U3P4, arsenide, U3AS4, and antimonide, 
U3Sb4, have been prepared by Colani ® in a similar manner to 
the telluride as black, crystalline powders, readily oxidised by 
nitric acid. 

Uranyl hypophosphite, U02(H2P02)2, and complex alkali salts 
have also been prepared.’ 

U ramus metaphosphate, U(P03)4, uranous pyrophosphate, 
UP2O7, and uranous orthophosphate, U3(P04)4, have been pre- 
pared by Colani,® as well as complex salts with alkali- and 
alkaline earth-metal phosphates. 

Uranyl Phosphates. — The normal orthophosphate is not known. 
The mono-hydrogen salt, H(U02)P04,4H20, is deposited in 
yellow, tetragonal plates from a solution of precipitated uranium 
phosphate in hot water acidified with hydrochloric acid.® When 
uranic oxide is treated with phosphoric acid, a crystalline 
powder is obtained which is partially soluble in water, and the 
solution deposits yellow crystals of the di-hydrogen salt, 

^ de Forcrand, Com'pt. rend., 1913, 156 , 1044, 1207 ; Ann. Chim., 1916, [9], 
3 , 6 ; Gormann, J. Amer. Chem. 80 c., 1922, 44 , 1466. 

* Ley, Zeit. physikal. Chem., 1899, 30 , 193; Ber., 1900, 33 , 2668; Dittrich, 
Zeit. physikal, Chem., 1899, 29, 449. See also Gomez, Ami. Fis. Quim., 1919, 
17 , 24. 

® Janda, Oeater. Zeit. Berg.-Hutt., 1901, 49 , 326. 

* Ivanov, J, Buss. Phys. Chem. Soc., 1912, 44 , 678; Chem. Zeit, 1912, 36 , 
2^, 499; Andrews, ibid., 1912, 36 , 1463; J. Amer. Chem. 80 c., 1912, 34 , 
1686; Eichhom, Chem. Zeit» 1914, 38 , 139; Mtiller, ibid., 1916, 40 , 38; 1917, 
41 , 439; Siemssen, ibid., 1919, 43 , 267; ibid., fk22, 46 , 460. 

» Meyer and Wendol, Ber., 1903, 36 , 4066; Rimbaoh, ibid., 1904, 37 , 461. 

* Cmpt rend., 1903, 137 , 382. 

’ Rosenheim and Trewendt, Ber., 1922, 56 , [B], 1967. 

® Ann. Chim. Phys., 1907, [8], 12 , 69, 

> Bourgeois, Bull. 80 c. /rang. Min., 1898, 21, 32. 



1166 ” URAKIUM . : ^ 

U02(H2P04)2,3H20. Both" the pyrophosphate and the meta- 
phosphate have been described. 

Uranyl Ammonium Phosphate^ UO2NH4PO4, is a greenish- 
yellow precipitate, insoluble in acetic acid, obtained by adding a, 
soluble phosphate to a solution of uranyl acetate containing 
ammonium chloride. This reaction is employed for the 
vobimetric estimation of uranium, or of phosphoric acid. 

Uranyl Arsenates. — Several of these compounds exist as minerals 
(Winkler). Trogerite has the composition (UQ2)3(As04)2,12H20 ; 
walpurgite is a basic arsenate of uranyl and bismuth; urano- 
spinite is an arsenate of uranium and calcium. Various simple 
and complex arsenates have been prepared artificially. 

Uranium Boride^ UBg. — ^When an electric arc is produced 
between electrodes of compressed powdered boron and uranium, 
a boride, UBj, is formed, having a metallic appearance. It is 
stable towards alkalis and acids with the exception of a nitriC” 
hydrofluoric acid mixture, but is readily attacked by fused 
alkali hydroxide.^ 


Uranium and Carbon. 

510 Uranium Oarbidey UCg, is obtained by strongly heating 
a mixture of 600 grams of green uranium oxide and 60 grams of 
charcoal in the electric furnace, and is a crystalline, lustrous 
solid, which scratches rock crystal but not corundum, and has a 
density of 11-28 at 18°. It was considered by Moissan to possess 
the formula U2C3. It is attacked by fluorine when gently 
warmed, by chlorine at 360°, and by oxygen at 370°. In contact 
with water, about one-third of the carbon is evolved as a gaseous 
mixture containing 0-2 -0*7 per cent, of acetylene, 6-0-7-0 per 
cent, of ethylene, 78-81 per cent, of methane, and 13-6-16-0 ^ 
per cent, of hydrogen, the remainder of the carbon being con- 
verted into a mixture of solid and liquid hydrocarbons.* When 
two pieces of the carbide are rubbed together, or even shaken 
in a bottle, brilliant sparks are given off. 

Uranyl Carbonates. ‘-Dovihle salts of uranyl carbonate and 
alkali carbonates are obtained by precipitating a uranyl salt with 
an alkali carbonate. The potassium salt, U02*C03,2K2C08, 

1 Wedekind, Ber.y 1913, 46, 1198. 

* Moissan, Compt. rend.^ 1896, 122 , 274; Lebeau, Ccmpt. rend.^ 1911, 162 , 
955; Bull. 8oe. ehim., 1911, [4], 8, 512; Lebeau and Damiens, Comp<. rend., 
1913, 166 , 1987 ; Polushkin, Iron and Steel Inet., Carnegie Schd. 'Mem.^ 1920, 
10,129. 



DEFECTION ESTIMATiON OF URANIUM 1167 

is obtained by dissolving potassium uranate in potassium 
bicarbonate, and evaporating at a moderate temperature, when 
the compound is deposited in silky, crystalline crusts^ Water 
dissolves at the ordinary temperature 7 per cent, of its weight 
of this salt. The corresponding sodium salt is obtained in a 
similar way, and possesses similar properties. The ammonium 
compound, U02*C03,2(NH4)2C03, is prepared by gently warming 
ammonium uranate with a solution of ammonium carbonate, 
and separates put on cooling in lemon-yellow, small, flat, mono- 
clinic prisms. It dissolves at the ordinary temperature in 
20 per cent, of water, but is less soluble in water containing 
ammonium carbonate. The mineral liebigite is a uranyl calcium 
carbonate, 1102*003, CaCO3,10H2O, which occurs as an apple- 
green, warty mass, together with other uranium minerals. 

Cyanides^ etc , — Potassium uranyl cyanide,^ K2[U02(CN)4], 
uranyl cyanate,® U02(CN0)2, and its complex salts, and uranyl 
thiocyanates,^ U02(CNS)2,8H20, and its double salts have been 
described. 

Organic CowipZearcs.— Complexes with formic, acetic, oxalic, 
and a number of other organic acids have been studied.® 

Uranium Silidde, USi2, has been prepared by an alumino- 
thermic method. It is a grey, lustrous powder which is not 
easily attacked by oxygen.® 

Detection and Estimation of Uranium. 

51 1 The uranous salts are green and pass rapidly by oxida- 
tion into the uranyl salts, which have a yellow colour, and yield 
with alkalis or alkali carbonates yellow precipitates of the 
alkj^li uranates. Although uranyl salts do not give precipitates 
with cupferron (nitrosophenyUiydroxylamine), uranous salts are 
completely precipitated by this reagent.^ Uranyl salts with 
ammonium sulphide yield a brown precipitate of uranyl sulphide, 

^ See also Oechsner de Coninck, BuU. Acad. roy. Belg.f 1904, 363, 448. 

* Aloy, Ann. Chim. Phys., 1901, [7], 24, 412. 

’ Pascal, Bull. 3oc. chim., 1914, [5], 16, 11. 

« Pascal, Compt. rend., 1914, 168, 1672. 

i For recent work, see MazzucchelU and d’Alceo, AUi R. Accad. Lined, 
1912, [51 21, ii., 620, 860; 1913, [6], 22, i., 41; Courtois, Compt rend., 1914, 
168, 161 i, 1688; Henri and Landau, ibid., 1914^ 168, 181; Mazzucchelli and 
Sabatini, Qazz., 1916, 45, [2], 226; Bauer, Schweiz. Chem. Zeit., 1918, 2, 40; 
Hatt, Zeit. physikal, Chem., 1918, 92, 613. 

• l^facqz, Compt. rend., 1908, 147, 1060. 

^ Auger, Compt. rend., 1920, 170, 996. See also Browning, J. Amer. Chem. 
80 c., 1921, 48, 114. 

VOL. II. (II.) 


Z 



1168 


URANIUM 


UOgS, soluble In dilute acids and in ammonium carbonate; 
potassium ferrocyanide also yields a brown precipitate. In the 
absence of sulphuric or hydrochloric acid, uranium compounds 
in nitric acid solution yield, after the addition of excess of zinc, 
^ yellow deposit on the metal, consisting of the hydrated trioxide.^ 

In the general separation of the metals, uranium is obtained 
together with iron. In order to separate these, advantage is 
taken of the solubility of uranium oxide and uranates in ammon- 
ium carbonate solution, a complex ammonium uranyl carbonate 
being formed. When a uranium compound is fused with 
microcosmic salt in the oxidising flame, a yellow bead is obtained 
which on cooling becomes green, and on re-heating attains a 
darker green colour. In the reducing flame, the bead is green. 

Most of the uranyl salts show a strong fluorescence, and give 
a characteristic absorption spectrum, which has been examined 
by Morton and Bolton, ^ whilst the fluorescence and phosphor- 
escence spectra have been described by E. Becquerel ^ and 
H. Becquerel.^ 

The uranium compounds do not impart any tint to the non- 
luminous gas flame. The spark spectrum of uranium is a 
complicated one, and has been mapped by Thalen. It consists 
of a large number of lines, of which five in the green are con- 
spicuous by their brightness, viz., 5495, 5482, 5480, 5478, and 
5475; there are also three specially bright lines in the more 
refrangible portions, viz., 4473, 4363, and 4341.^ 

In order to estimate uranium it is precipitated as uranyl 
ammonium phosphate and weighed finally as uranyl pyro- 
phosphate, (U 02 ) 2 P 207 , or it is converted into a uranyl salt, 
precipitate^ with ariimonia,® and the washed precipitate con- 

1 Buell, J, Ind, Eng, Cheni-f 1922, 14, 693. 

» American ChemisU 8, 360, 401. See also Vogel, Ber., 1876, 8, 1636; 1878, 
11, 916; Ziinmermann, Ann^^t 1882, 218, 286; Mazzuochelli and Ferret, 
Atti R, Accad. Linceh 1913, [6],x22, U., 446. 

* Compt. rend,f 1872, 76; 187S^88» 1237. 

* Ibid., 1885, 101, 1262; 1907, J44, 469. 

* See also Exner and Hasohek, \ Epektren der Elemente hei normalem 
Druck," Leipzig, 1911; Siegbahn anX^ Friman, Fhyaikal Zeit., 1916, 17, 17, 
61; Phil. Mag., 1916, [6], 81, 403;\1916, [6], 88, 39; Siegbahn, jP«r. 
phyaikal. Oea., 1916, 18, 160; DauvillieiV C(mpt. rend., 1921, 178, 1360; Moir, 
Trans. Ray. 8oc. South Africa, 1921, 10, 

* Schwarz, Helv. Chim, Acta, 1920, 8, 38^* A summary of the best methods 

is also given by Kern, J. Amer. Chem. Soc), 1901, 88, 686. Recent papers on 
the subject are: Konig, Chem. Zeit., 1913, \87, 1106; Wunder and Wenger, 
Zeit. anal. Chem., 1914, 68, 371; Turner, A^^^- 191 0» [4], 48, 109; 

SchoH, J. Jnd. Eng. Chem., 1919, 1^, 842; Pie#, ibid., 1920, 18, 60. 



BBTimON AND ESTDIATION OF URANIUM 11^9 


verted by ignition in hydrogen intfl the broWn oxide, UOg. 
Small quantities may be estimated colorimetrically by com- 
parison of the red coloration obtained when a uranyl salt is 
treated with sodium salicylate.^ Further, it may, like iron, be 
estimated volumetrically with a solution of potassium per- 
manganate, the uranyl compound being previously reduced to 
the uranous state by the action of zinc and sulpWic acid, or 
of titanous sulphate,^ or a solution of uranyl acetate may*be 
titrated with sodium phosphate. 

The Atomic Weight of uranium was determined by Peligot 
by the analysis of the tetrachloride, which he found to contain 
37*2 per cent, of chlorine, whence he calculated the atomic 
weight to be 237*6. He afterwards obtained the number 238*3 
by the conversion of the acetate, 1102(0211302)2, HgO, into the 
dioxide. Zimmermann, on the other hand, by the same method, 
obtained the number 237*7, whilst from a series of experiments 
in which he converted the dioxide into the green oxide and vice 
versa the number 237*8 was foimd.® Aloy,^ by the determination 
of the ratio UO2 : N in pure uranyl nitrate, obtained the value 
237*6 (N = 13*93), which becomes 237*1 when the more modern 
value N = 13*90 is adopted. Richards and Merigold,® by 
analysis of the very carefully purified tribromide, obtained the 
value 238*5, whilst Lebeau® found the same number by the 
reduction of uranyl nitrate dihydrate to .uranium oxide by 
heating the salt in a current of hydrogen to 1100°. Oechsner 
de Coninck,’ by igniting uranyl oxalate to the dioxide, obtained 
the value 238*4; that of Honigschmid,® by the conversion of 
the tetrabromide to silver bromide, was 238*175. Honigschmid 
and Horovitz,® by determinations of the same ratio, obtained 
an atomic weight of 238*043 ± 0*018 when the tetrabromide 
was finally sublimed in bromine vapour, and 238*159 ± 0*023 
when it was finally sublimed in nitrogen. The actual atomic 
weight appears, therefore, to be not higher than 238*2; hence 
this number is now (1922) adopted. 

^ MtiUer, Chem, Zeit., 1919, 48, 739. 

* Newton and Hughes, J. Amer, Chem. Soc., 1915, 37* 1711. 

. » Annakn, 1885, 218, 299. 

* Compt. rend.f 1901, 188, 551. Zeit. anorg. Chem.f 1902, 81, 235. 

” Compt, rend., 1912, 155, 163. ’ Ibid., 1511. 

B Ibid., 1914, 168, 2004. • Monatah., 1916, 87, 185. 



GROUP VII. 


^ Sub-group (a) Sub-group (b) 

Manganese. Fluorine. 

Chlorine. 

Bromine. 

Iodine. 

512 In the periodic system, manganese is the only repre- 
sentative of the even series of the seventh group known. 

The halogen elements have already been described in Vol. I. 
The analogy of manganese with these elements is almost entirely 
confined to the derivatives of its highest oxide, MngO^. To this 
oxide corresponds permanganic acid, HMn04, the salts of which 
are isomorphous with the perchlorates. 

In its general behaviour, however, manganese shows strong 
resemblances to chromium, iron, and its neighbours in the same 
horizontal series of the periodic table : 

Group. IV. V. VI. VII. VIII. I. II. 

Element Ti V Cr Mn (Fe Co Ni) Cu Zn 

Manganese, titanium, vanadium, chromium, iron, cobalt, and 
nickel are all hard, white metals of high melting point. Man- 
ganese, iron, cobalt, and nickel, or their alloys, have strong 
magnetic properties. The whole of the elements in the above 
series have a great tendency to form double or complex salts. 

They all form oxides nf the type RO, and a series of salts in 
which the metal is divalent; many examples of isomorphism 
between manganous and the corresponding ferrous, cobaltous, 
nickelous, cupric, and zinc compounds are known, but our 
knowledge of the divalent compounds of titanium, vanadium, 
and chromium is slight. 

With the exception of copper and zinc, all these elements form 
an oxide of the type R^Oa and salts in which they are trivalent, 
a well-known isomorphous series being the alums which are 
formed by titanium, vanadium, chromium, manganese, iron, and 
cobalt. Manganese, like chromium and iron, forms mbi:ed 
oxides with other elements of the t3rp6 R0,Mn20s; it also forms 
mo 



. MANGANESE 


1171 


an oxide, Mn304 or Mn0,Mn208, anatogous to the similar com- 
pounds of iron, cobalt and nickel. 

Manganese has a dioxide, MnOg, isomorphous with rutile, 

'TiOgi vanadium, chromium, cobalt, and nickel also form 
dioxides, all of which, except the chromium compound, can aQt 
as weak acidic oxides and form manganites {e,g,, CaMnOg), 
titanates, vanadites, cobaltites, and nickelites. Though ij-on 
dioxide is unknown, corresponding compounds {e.g., BaFeOg) 
are known. The dioxides of manganese, titanium, and vanadium 
can also act as basic oxides, and give rise to a series of salts in 
which the metals are tetravalent. 

Manganese, like chromium, has a trioxide, MnOg, which is a 
purely acidic oxide and forms manganates (e.^., K2Mn04), which 
are isomorphous with the corresponding chromates and ferrates. 

MANGANESE. Mn = 54-93. At. No. 25. 

513 Black oxide of manganese, manganese dioxide, or pyro- 
lusite was known in early times, but for a long period this com- 
pound was confounded with magnetic iron ore, and this fact 
explains the statement of Pliny that loadstone was employed 
in the manufacture of glass for the purpose of removing or 
attracting the impurities of colouring, matters out of the glass. 
He distinguished, moreover, special kinds of magnes; one of 
these, which is of the feminine gender, does not attract iron : 
“ magnes qui niger est et feminei sexus, ideoque sine viribus.” 

^ This probably was manganese dioxide. The derivation of the 
word magnet appears to be doubtful. In the Middle Ages 
loadstone was distinguished as magnes or magnesius hpis. 
Pyrolusite, however, was termed magnesia probably because 
Pliny had already pointed out the existence of two species of 
loadstone. Many of the alchemists, however, believed it to be 
an ore of iron. They likewise mention its use in glass-making, 
and in the Latin manuscripts of the sixteenth century it is termed 
hpis manganensis, or some similar name. 

' In 1740, Pott, in his treatise entitled Emmen chymicum 
magnesia vilrarmum, Germanis Braunsteiny* proved that the 
black oxide of manganese did not contain iron, and that from it 
a definite series of salts could be obtained. He did not, however, 
suggest that it contained a new metal. Scheele’s celebrated 
investigations on manganese were published in the year 1774. 
In these he showed that the mineral manganese possesses a strong 
attraction for phlogiston, and that it takes this substance up. 



1172 MANGANESE • 

uniting with acids to form colourless salts, this being explained, 
according to our present views, by the fact that it gives off 
oxygen. On the other hand, the solutions of manganese which 
did not contain phlogiston were shown to be coloured. Scheele 
believed that the earth contained in this mineral resembled lime ; 
but in the above-mentioned year Bergman, founding his deduc- 
tions upon Scheele’s experiments, came to the conclusion that 
manganese was probably the calx of a new metal, inasmuch as it 
coloured glass, and its solutions were precipitated by prussiate 
of potash, these being reactions common to the metallic calces. 
Gahn was, however, the first to isolate the new metal. In 
Germany, this was called braunstein-konig or braunstein-metal. 
In other languages, in which braunstein was termed magnesia 
niger^ in order to distinguish it from magnesia alba, the metal was 
called manganese or manganesium. 

Manganese occurs in nature chiefly as the dioxide or pyrolusite, 
MnOg. It is found also in the following minerals: braunite, 
MugOg) hausmannite, Mn304; psilomelane, (Mn,Ba)0,Mn02 ; 
manganite, MngOgjHgO ; rhodocrosite or manganese spar, 
MnCOg, which also frequently occurs as an isomorphous con- 
stituent in ferrous carbonate and other similar minerals. Man- 
ganese occurs also as alabandite or sulphide of manganese, MnS ; 
and hauerite, or manganese disulphide, MnSg. It likewise forms 
an essential constituent of many other minerals, although occur- 
ring in them only in small quantity. Thus, for instance, most 
silicates contain manganese, which frequently imparts to them 
their peculiar colour. By means of these minerals the metal 
manganese passes into the soil and into drainage water, whence 
it is absorbed in small quantities into the bodies of plants and 
animals. 

The natural oxides of manganese usually contain traces of 
potassium, rubidium, silver, and copper, whilst gallium, indium, 
and thallium are occasionally present.^ 

514 Preparation of Metallic Manganese.— The higher oxides of 
manganese can be reduced only to manganese monoxide at a 
red heat, the metal not being formed either when the oxide is 
heated alone or mixed with charcoal in a current of hydrogen 
until the temperature ri&es to white heat. The original method 
of preparing the metal, proposed by John,^ depends upon this 
fact. Finely divided oxide of manganese, obtained by the 

^ Hartley and Bamaget Jwm, Ghem. 80c., 1897, 71, 633. 

* Gehlen’s Joum. Chm. Phya., 8 , 462. 



MANGANESE 


1173 


calcination of the carbonate in a covered crucihle, is well mixed 
with carbon, and the mixture formed into a paste with oil ; the 
paste is then introduced into a crucible lined with charcoal, and 
the upper portion completely filled with powdered charcoal. 
The crucible is first heated to redness for half-an-hour to solidfy 
the mass, after which the cover is carefully luted down, and the 
whole exposed to a wind furnace for an hour-and-a-half to the 
highest temperature which the crucible can support without 
fusing. The regulus thus prepared contains both carbon and 
silicon derived from the ashes of the wood charcoal. By igniting 
the metal a second time in a charcoal crucible with some borax it 
was obtained by John in a more fusible and brilliant state, and 
so free from carbon that it left no black residue when treated 
with an acid. 

Deville’s method^ consists in mixing red manganese oxide, 
Mn 304 , prepared by heating the artificial dioxide, with sugar 
charcoal insufficient in quantity for complete reduction. The 
mixture is heated to whiteness in a doubly-lined crucible. The 
regulus obtained is coated with a violet, crystalline mass, appar- 
ently calcium-manganese spinel, CaOjMugOs. 

Jordan ^ describes a method of preparing metallic manganese 
on a large scale by treating manganese ores in a blast furnace. 
The metal obtained is really ferro-manganese, containing 85 per 
cent, of manganese, 6 per cent, of carbon, 8 per cent, of iron, and 
traces of silicon, sulphur, and phosphorus. 

Other processes of preparing the metal consist in igniting 
a mixture of fluor-spar and chloride of manganese with metallic 
sodium,^ or gradually adding 15 grams of metallic magnesium to a 
fused mixture of 100 grams of manganese chloride and 200 grams of 
potassium chloride.^ The metal may be obtained also by the 
electrolysis of a concentrated solution of the chloride according 
to the process described by Bunsen,^ or by heating the amalgam, 
which can be prepared electrolytically.® 

The method of reducing manganese oxide by aluminium is 
due to Greene and Wahl,’ who devised it for producing the 
pure metal cheaply. The metal they obtained contained 96-5 per 
cent, of manganese, 2*0 of iron, and 1’5 of silicon. 

A considerable amount of metallic manganese has been made 

» Ann. Chtm. Phys., 1860, [3], 46, 182. * Compt. rend., 1878, 86, 1374. 

* Brunner, Poyg. Ann^, 1867, 101, 264. * Glatzel, Ber„ 1889, 22, 2867 

» Pogg. Ann., 1864, 91, 619. • Prelinger, Monatsh., 1894, 14, 363. 

» J’rawfl. American Institute of Mining Engineers, 1893, gl, 887. 



1174 

by the Goldschmidt prbcesi (p. 737^ of a high degree of j)urity. 
Lebeau ^ has, however, shown that metal so produced may con- 
tain as much as 5-26 per cent, of silicon. ' 

With regard to the preparation of manganese in the electric 
furnace,® Moissan proved that by using excess of oxide, the 
reduced metal might be obtained free from carbon and silicon. 
This method has recently been put into commercial use, but the 
efficiency of the process is not such as to yield metal at a low 
cost, for Moissan has shown that manganese is highly volatile at 
electric furnace temperatures, and that as much as 400 grams 
of the metal may be volatilised in ten minutes in the electric 
arc. High grade ferro-manganese, and other alloys such as 
silico-manganese, are produced in large quantities in electric 
furnaces. 

Manganese has been obtained also by electrolysis. Ferro- 
manganese anodes are allowed to dip into fused sodium chloride, 
and an electric current is passed. Pure manganese is deposited 
at the cathode.® It has been prepared also by electrolysing 
manganese dioxide dissolved in fused fluorspar.^ 

Properties . — Small amounts of impurities influence the proper- 
ties of manganese considerably; since none of the methods of 
preparing the metal yield an absolutely pure product, its properties 
depend largely on how it has been prepared. Obtained by the 
reduction process, it is a grey or reddish-white metal, having the 
colour and appearance of cast iron. It is very hard and brittle, 
has a specific gravity of about 7*3, and oxidises so easily in the 
air that it must be kept under rock-oil or in well-sealed vessels. 
Ferro-manganese is, however, unalterable in the air. Manganese 
is readily dissolved by all dilute acids, yields sulphur dioxide 
with hot concentrated sulphuric acid,® and decomposes water 
with evolution of hydrogen, even in the cold, more rapidly when 
heated. It melts • at 1260° and boils under atmospheric pressure 
at about 1900° (Greenwood)^; its atomic heat increases from 
4*51 between the temperatures —188° and —79°, to 6*90 at 0°; 
6*29 at 100°, and 9*09 at 500° (Estreicher and Staniewski®; 
Lammel®): its average compressibility between 100 and 600 

1 Ann. Chim. Phya., 1904, 1 , 663. * Compt. rend., 1892, 118 , 1429. 

» Ger. Pat. 74959. r * Eng. Pat. 17190. 

» Adie, Proc. Chen, 8oc., 1899, 15, 133. 

Burgess and Waltenbeig, J, Washington Acad, Sci., 1913, 8, 371. 

» Proc. Roy. Soc., 1909, 82 , [A], 398. 

* BvU. intern. Acad. 8ci. Cracovie, 1912, [A], 834. 

• Ann. Physik., 1906, (iv), 18 . 661. 




manganese Alto 1175 

mega^iirs is 0*000,000,67 tBichardl and Stull )} It is para- 
magnetic, but becomes ferromagnetic on heating ; it is exceptional 
in that its magnetic properties are not intensified by cooling 
in solid hydrogen (Weiss and Kamerlingh Onnes).^ Manganese 
combines rapidly with nitrogen above 1210 °. 

515 Alloys of Manganese . — The alloys of manganese and copper 
closely resemble those of tin and copper.® Those which contain 
from 5 to 8 per cent, of manganese are malleable, but those in 
which a higher percentage of manganese is present become grey 
and brittle. 

Manganese bronze is made by adding cupro-manganese con- 
taining about 25 per cent, of manganese to molten brass. For 
industrial purposes it contains from traces to 2 per cent, of 
manganese, 39 to 41 per cent, of zinc, and less than 1 per cent, 
each of tin, iron and aluminium, the rest being copper. 

Manganin is a copper-manganese alloy containing small 
quantities of nickel. Its electrical resistance has a very low 
temperature coefficient, and it is largely used in the manufacture 
of electrical resistances. 

Alloys of manganese with aluminium, antimony, tin, bismuth, 
arsenic, and boron are noteworthy owing to the remarkable 
magnetic properties which they possess.* 

The alloys of manganese and iron, such as manganese steels, 
"" spiegel iron, and ferro-manganese, will be described under iron. 

Manganese Amalgam is prepared by electrolysing a saturated 
solution of manganous chloride, mercury being used as the 
negative pole. 

COMPOUNDS OF MANGANESE. 

Manganese and Oxygen. 

516 Manganese forms a series of oxides, of which the follow- 
ing are the best defined : 

Manganese monoxide, MnO, 

Trimanganese tetroxide, Mn 304 , 

Manganese sesquioxide, MngOj, 

Manganese dioxide, MnOa, 

Manganese trioxide, MnOs, 

Manganese heptoxide, MngOy. 

1 Pvb. Cam. Inst., 1907, 78, 66 . * Compt. rend., 1910, X60, 687. 

, • Valenciennes, Compt. rend., 1870, 70, 607. 

^ Hogg, Brit. Aaeoc. Reports, 1892, 671; Heusler, Ber. dent. physikalOes,, 

. 1903, 5, 220. 



1W6 


MANGANESE 


« 

The first of thfese is a poVerful bfllbic oxide, whilst the sesqui- 
oxide is feebly basic, giving rise to an unstable series of salts, 
and the oxide, Mn304, behaves in many respects as a compound 
of the two. The dioxide acts as a weak acidic oxide, yielding 
with strong bases salts known as the manganites. Manganese 
trioxide and the heptoxide are well-marked acid-forming oxides. 
Thq manganates, derived from manganic acid, H2Mn04, are very 
unstable, and as already mentioned are isomorphous with the 
sulphates and chromates. Permanganic acid, HMn04, ^ 
strong acid and pelds stable salts, which are isomorphous with 
the perchlorates. 

Manganese Monoxide^ or Manganms Oxide, MnO, is best 
prepared by fusing together a mixture of equal parts of anhydrous 
manganese chloride and sodium carbonate to which some 
ammonium chloride has been added, and lixiviating the fused 
mass with water.^ It is obtained also when a higher oxide 
or the carbonate is ignited in a current of hydrogen. Manganous 
oxide is a greyish-green powder, which fuses at 1650 ° ^ without 
loss of oxygen. It has a specific gravity of 6 - 09 . When the 
powdered oxide is heated in hydrogen containing a very small 
quantity of hydrogen chloride, it is obtained crystallised in trans- 
parent, regular octahedra of an emerald-green colour and an 
adamantine lustre.® It has been found in Sweden as the crystal- 
line mineral manganosite. 

Mav^ganoiis Hydroxide, Mn(OH)2, is obtained as a white pre- 
cipitate when caustic alkali is added to the solution of a manganese 
salt. As it oxidises rapidly in the air and assumes a brown 
colour, forming the oxide Mn304 and finally Mn203, it must be 
precipitated in an atmosphere free from oxygen, and dried at a 
.moderate heat in a current of hydrogen. The powder thus 
obtained is frequently ■p3n:ophoric and when touched with a 
piece of red-hot charcoal it begins to glow at the point of contact, 
the oxidation proceeding rapidly throughout the mass. It occurs 
in Sweden as the mineral pyrochroite. 

When ammonia is added to a solution of a manganous salt 
containing an ammonium salt, no immediate precipitation occurs, 
but on standing a precipitate separates out which consists of 
manganous hydroxide, iiair be excluded, but of a brown hydrated 
oxide in the presence of air. When manganous hydroxide is 
treated with an ammonium salt it dissolves to an extent pro- 

^ Liebig and Wohler, Pogg. Ann,, 1830, SI, 584. 

* Tiede and Bimbrauer, Z^ii, anorg. Chem., 1914, 87, 129. 

* BevUle, Compi, rend., 1861, 58, 199. 




MANGANESE AND OXYGEN 


im 


portioijal to the conceDtration of ammonium ions in the solution ; 
probably complex ions containing ammonium and manganese are 
formed.^ 

The manganous salts, MnR^g? usually faintly pink-coloured, 
although, according to some chemists, this coloration is due to 
the presence of a trace of a manganic compound. The halogen 
salts, as well as the nitrate and sulphate, are readily soluble in 
water. 

Mangano-Manganic Oxide, Red Oxide of Manganese, or Tri- 
manganese Tetroxide, Mn304, occurs with other manganese ores, 
and also by itself as the mineral hausmannite. This mineral 
crystallises in acute tetragonal pyramids, and one of its best 
localities is Ilmenau in Thuringia. Its specific gravity is 4 * 85 . 
If manganese monoxide is heated in contact with air, or if the 
higher oxides are strongly heated either in contact or out of 
contact with air, this same compound is obtained in the form of 
a brownish-red powder, which then has a specific gravity of 
4 * 72 , and is converted into crystals of hausmannite by being 
gently heated in a slow current of hydrogen chloride.® It is 
obtained in the crystalline form also by heating a mixture of 
manganese sulphate and potassium sulphate to bright redness,® 
or by treating a mixture of manganous oxide and calcium chloride 
in the same way.^ This oxide dissolves in cold concentrated 
sulphuric acid, giving rise to a red solution containing a mixture 
of manganous and manganic sulphates, whilst acetic acid dis- 
solves one-third of the manganese as manganous acetate and 
leaves the remainder in the form of the sesquioxide. Mixed 
oxides of the type Mn203,R0, which appear to be isomorphous 
with hausmannite (Gorgeu®), have been prepared by fusing the 
corresponding sulphates and by the ignition of the metal ic 
manganites. Hence the red oxide is often considered to be a 
compound having the formula Mn0,Mn203. On the other hand, 
other reactions suggest that it has the formula 2Mn0,Mn02; 
thus, on heating with dilute sulphuric acid, manganous sulphate 
and manganese dioxide are formed, and boiling nitric acid 
decomposes it in a manner similar to that in which it acts on 
r^ lead : 

Mn304 + 4HNO3 = 2Mn(N03)2 + MnOg + 2H2O. 

^ Herz, Zeit. anorg. Chetn., 1899, 21, 243; 22, 279. 

* DeviUe, Compt. rend.^ 1861, 58f 199, 

* Debray, Compt, rend., 1861, 52> 986. 

* Kuhlmann, Compt. rend., 1861, 52, 1283. 

» Bull. Soc. chim., 1903, [3], 29, 1111, 1167. 



1176 

Chlorine gas is* given off when this oidde is heated with hydro- 
chloric acid, and manganous chloride is formed : 

Mn304 + 8HCI = 3MnCla + 4H2O + 

^Manganic Oxide or. Manganese Sesquioxide, MngOg.—This 
oxide occurs as the mineral braunite in obtuse tetragonal pyr- 
amids. It possesses a sub-metallic lustre, has a dark brownish- 
black colour, and a specific gravity of 4*75. It may be obtained 
artificially by igniting any of the oxides of manganese in a mixture 
of oxygen and nitrogen containing not more than twenty-six 
per cent, of oxygen.^ It then forms a black powder, having a 
specific gravity of 4*32. 

Manganic Hydroxide^ MnO(OH), occurs in nature as manga- 
nite in steel-grey or arsenic-black crystals belonging to the 
tetragonal system, and having a specific gravity of 4*3. It is 
usually accompanied by other manganese ores, calc-spar, and 
heavy-spar. In general appearance it closely resembles pyrolusite 
but it may be distinguished from this compound by its giving a 
brown instead of a black streak when rubbed on an unglazed 
porcelain plate. When the mineral is heated at 270-310° in 
the air it is converted without change of form into the dioxide.^ 
Manganic hydroxide is formed when manganous hydroxide is 
allowed to oxidise in moist air. It may be prepared also by 
passing chlorine into water in which an excess of manganese 
carbonate is suspended, or by decomposing the corresponding 
manganic sulphate with water (Carius).® It forms a dark-brown 
powder which gives off its water at a temperature above 100°. 
It dissolves in hot nitric acid : 

2MnO(OH) + 2HNO3 = Mn{N03)a + MnOg + 2H2O. 

From this reaction it would appear that in constitution this body 
resembles lead sesquioxide and analogous compounds, having the 
constitution MnOjMnOg, but a other reactions it acts as a feebly 
basic oxide, the salts of which, with a few exceptions, are very 
unstable. 

The manganic salts, MnB 3 or MngR^s, are unstable, strongly 
coloured substances. The fluoride, sulphate, phosphates, and. 
salts of some’ organic acids are comparatively stable, as also are 
some double or complex salts, such as the double fluorides and 

^ Dittmar, Joum. Chem, Soe., 1864, 17, 294. 

* Goxgeu, Compi. rend., 1888, 106, 1101. 

* Annakn,im,9B,6^: 



jilANGANESE DIOXIDE AKD THE MANGAOTTES 1179 

- 

chlorides, the manganicyanides, and the alums. Manganic 
chloride, bromide, iodate, periodate, selenite, and arsenate have 
been prepared. 

Manganese Dioxide and the Manoanites. 

517 Manganese Dioxide^ Manganese Peroxide, or Bhck Oxide 
of Manganese, MnOg, is the most important ore of manganese. It 
occurs in rhombic crystals and in crystalline and amorphous 
masses, being known to the mineralogist as pyrolusite. It pos- 
sesses a metallic lustre, an iron-black or dark steel-grey colour, 
and a black streak. It is opaque and rather brittle, and has a 
specific gravity of 4*82. The most celebrated localities for this 
mineral are Ilmenau in Thuringia, near Flatten in Bohemia, near 
Mahrisch-Trubau in Moravia, on the Lahn, and in the Caucasus, 
France, Spain, and North America. It occurs in the United 
States, abundantly at Vermont, and in Red Island Bay at San 
Francisco ; and also in New Brunswick and Nova Scotia ; large 
quantities too are found in India. It is likewise found in Devon- 
shire. Pyrolusite seldom occurs in the pure state, but mixed 
with other manganese ores such as psilomelane, (Mn,Ba)0,2Mn02, 
and manganite. It almost always contains ferric oxide, silica, 
lime, carbonic acid, and traces of the oxides of cobalt and nickel. 
Pure manganese dioxide is obtained by melting about 600 grams 
of the crystallised nitrate and warming until red fumes appear ; 
the clear liquid is then decanted from the lower oxides which first 
separate out, and is heated in another vessel at 150-160° for 
40-60 houis.i If manganous carbonate is heated to 260° in 
presence of air, and the residue then treated with very dilute 
cold hydrochloric acid, pure manganese dioxide remains behind 
(Forchhammer), 

A brown precipitate approximating in composition to hydrated 
manganese dioxide can be obtained from the manganous salts by 
the aid of a large number of oxidising agents such as potassium 
permanganate (p. 1189), sodium hypochlorite, ammonia and 
bromine, nitric acid and sodium chlorate, ammonium persulphate 
tmd sulphuric acid,^ and ozone.^ 

It appears to be almost impossible prepare perfectly pure 
hydrated manganese peroxide,* since this substance very readily 

^ Ooigeu, Bull, 3oc. chim., 1890, [3], 4, 16. 

* Mamhall, Joum, Chm. 8oc„ 1891, 68 , 771. 

* Jannasoh and Gottscbalk, Ber., 1904, 37f 3111. 

* Go^u, Compt, rend,, 1890, UO, 1134. 



1180 


BliNGANESE 


loses a portion of its oxygen, forming mixtures of the com- 
position icMnO + yMnOg, and moreover readily combines with 
bases forming manganites. Products of constant composition 
appear to be obtainable only from solutions acidified with a 
mineral acid> Thus the oxide formed by the reduction of 
permanganic acid by manganese sulphate, and by the decom- 
position of permanganic acid in presence of hydrated manganese 
dioxide, varies in composition from bMnOg -f MnO to ISMnOg + 
MnO. On the other hand, the oxide precipitated from manganous 
sulphate by dilute potassium permanganate at 80° in presence of 
zinc sulphate contains all the manganese in the form of dioxide, 
but combined with alkali. The oxide precipitated from manganese 
nitrate by nitric acid and sodium chlorate contains 98 per cent, 
of the manganese as dioxide,^ and that obtained with ammonium 
persulphate also contains less than the theoretical amount of 
oxygen.® A similar oxide may also be prepared by treating 
manganic hydroxide with hot nitric acid,^ or by adding potassium 
permanganate to sodium thiosulphate solution. The hydroxide 
thus obtained, after washing with water, is soluble in water,* 
yielding a brown solution to which the name of manganous acid 
has been given. This solution turns blue litmus paper red, and 
does not undergo alteration on standing for many weeks, but 
small quantities of acid or alkali produce an instant precipitation. 
Manganous acid appears to be identical with a colloidal solution 
of manganese, dioxide, which can be conveniently prepared by 
the action of ammonia on a boiling solution of potassium 
permanganate.® Manganese dioxide, like lead dioxide, possesses 
at the same time feebly basic and feebly acid properties. Of 
the salts in which manganese behaves as a quadrivalent basic 
element, only the chloride, sulphate, and selenite have been 
isolated. Among the most stable are certain double or complex 
salts, KgMnFj, KjMnClg, K 2 Mn{I 03 )e. 

On heating, manganese dioxide loses oxygen and forms the 
sesqmoxide : 

4Mn02 = 2Mn208 + Og. 

The action is reversible ; when the pressure of oxygen is below 
a certain value depending on the temperature the reaction goes 
towards the right hand side of the equation, when it is above that 

^ Rupp, Zeit. anal. Chm., 1903, 42, 732. 

* Gooch and Austin, Amer. J. 8ci., 1898, [4], 5, 260. 

* von Knorre, Zeii. angew. Chem., 1901, 14, 1149. 

* Qoijgen, Awn. Chim. Phge., 1862, [8], 66» 165. 

* Guy, J. Physical Chm,, 1921» 85» 415. 



MANGANESE DIOXIDE AND THE MANGANITES 1181 

value towards the lef t.^ When heated to higher lemperatures the 
red oxide, Mn304, is produced. 

Manganese dioxide has long been used for the preparation 
of colourless glass, and hence pyrolusite has been known as 
savon des verriers. Its mineralogical name, indeed, has reference 
to this employment of the mineral (from ttO/), fire, and Xvw, 
I wash). It serves also for the preparation of the manganese 
compounds and of oxygen, but by far the largest quantity of the 
mineral is employed for making chlorine, used in the manufacture 
of bleaching powder. 

The Manganese dioxide combines with several 

basic oxides 1)0 form compounds which may be considered as 
salts of manganous acid. The composition of these compounds 
seems to depend on the amount of alkali which is present. A large 
number of them have been described. Potassium Manganitey 
KgMngOii, is obtained as a yellow precipitate when carbon 
dioxide is passed into a solution of potassium manganate, 
K2Mn04. Calcium Manganitey CaMngOu, is a blackish-brown 
precipitate formed when a solution of manganous nitrate is 
poured into an excess of bleaching powder solution. Many other 
compounds, such as Ca2Mn04, CaMnO^, CaMugOs, and CaMn307, 
have been prepared. 

518 Regeneration of Manganese Dioxide from the Chlorifie 
Residues . — Before the year 1856 the whole of the manganese 
chloride obtained in the manufacture of chlorine from manganese 
dioxide and hydrochloric acid was allowed to run to waste. In 
1821 Forchhammer ^ observed that when manganous carbonate 
is heated to 260° in an open vessel it is converted into dioxide. 
Charles Dunlop ® applied this reaction to the regeneration of man- 
ganese dioxide from the chlorine still liquors, the manganous 
carbonate being prepared by heating manganous chloride solution 
with calcium carbonate under pressure. In 1857 this process was 
adopted by Messrs, Charles Tennant and Co., at St. Kollox, but 
the process was not adopted elsewhere, 

A much less troublesome process was invented by Walter 
Weldon, in 1867, and first practically carried out at Messrs. 
Gamble’s works at St. Helens in 1868; it is now universally 
adopted wherever chlorine is made from’ manganese dioxide and 
hydrochloric acid. 

The crude manganese chloride solution remaining in the stills, 

^ Askenasy and Klonowski, Zeii, Ekkkochm., 1910, 16, 107. 

* Ann. Philyim, 17, SO. 

* Seport of Patent Jnventioniy March, 1850, p. 236. 



1182 MANOMBSE 

I (Pig. 190), which are fittd. for using native manganese dioxide, 
is run into the well, K, and treated with limestone dust, which 
neutralises the residual free hydrochloric acid, precipitates the 
sulphuric acid present as impurity in the hydrochloric acid 
in the form of calcium sulphate, and then precipitates the ferric 
chloride as ferric hydroxide; the muddy liquor is thrown by the 
pump, L, into the settling tanks. A, from which the clear manganous 
chloride solution is run into the oxidiser, B, while the sediment 
is run into the shute, H, and so to the drains. In the agitator, 
E, lime is slaked to form a thick cream which is run through a 
sieve into a store and measuring tank, whence it is pumped 
as required into the oxidiser, B. 

If exactly the theoretical amount of milk of lime be added 
according to the equation : 

MhCla + Ca(OH)2 = Mn(OH)2 + CaClg, 

it is foimd that the whole of the manganese is not precipitated 
and the mixture absorbs oxygen exceedingly slowly, only half 
the manganese being converted into dioxide; by adding ten 
per cent, more lime the liquor becomes free from manganese, 
but the most rapid absorption of oxygen and the most readily 
settling mud are obtained only by employing about sixty per 
cent, more lime (Weldon). When air is pumped by the pipe, C, 
through this mixture at 65®, the alkalinity disappears owing, 
to the formation of calcium manganite, Ca0,Mn02, and acid 
manganite, Ca0,2Mn02, whilst some of the manganous oxide 
is converted into manganous manganite, MnOjMnOg : 

lOOMnO + eOCaO + 860 == 12(Ca0,2Mn02) + 48(Ca0,Mn02) + 

14(Mn0,Mn02), 

at about which stage the oxidation practically ceases. An 
additional quantity of the manganous chloride is next added, 
which instantly reacts with the Ca0,Mn02, thus : 

48(Ca0,Mn02) + 24Mna2 = 24(Ca0,2Mn02) + 

24MnO + 24CaCl2, 

and the blowing being continued, the manganous oxide is oxidised 
to manganous manganite : 

24MnO + 120 = 12(Mn0,Mn02). 

The effect of the whole operation may be summarised thus : 

124Mna2 + 160CaO + 980 = 36(Ca0,2Mn02) + 
26(Mn0,Mn02) + 124CaCl2. 



MANGANESE DIOXIDE AND THE MANGANITES 1181 

value towards the lef t.^ When heated to higher lemperatures the 
red oxide, Mn304, is produced. 

Manganese dioxide has long been used for the preparation 
of colourless glass, and hence pyrolusite has been known as 
savon des verriers. Its mineralogical name, indeed, has reference 
to this employment of the mineral (from ttO/), fire, and Xvw, 
I wash). It serves also for the preparation of the manganese 
compounds and of oxygen, but by far the largest quantity of the 
mineral is employed for making chlorine, used in the manufacture 
of bleaching powder. 

The Manganese dioxide combines with several 

basic oxides 1)0 form compounds which may be considered as 
salts of manganous acid. The composition of these compounds 
seems to depend on the amount of alkali which is present. A large 
number of them have been described. Potassium Manganitey 
KgMngOii, is obtained as a yellow precipitate when carbon 
dioxide is passed into a solution of potassium manganate, 
K2Mn04. Calcium Manganitey CaMngOu, is a blackish-brown 
precipitate formed when a solution of manganous nitrate is 
poured into an excess of bleaching powder solution. Many other 
compounds, such as Ca2Mn04, CaMnO^, CaMugOs, and CaMn307, 
have been prepared. 

518 Regeneration of Manganese Dioxide from the Chlorifie 
Residues . — Before the year 1856 the whole of the manganese 
chloride obtained in the manufacture of chlorine from manganese 
dioxide and hydrochloric acid was allowed to run to waste. In 
1821 Forchhammer ^ observed that when manganous carbonate 
is heated to 260° in an open vessel it is converted into dioxide. 
Charles Dunlop ® applied this reaction to the regeneration of man- 
ganese dioxide from the chlorine still liquors, the manganous 
carbonate being prepared by heating manganous chloride solution 
with calcium carbonate under pressure. In 1857 this process was 
adopted by Messrs, Charles Tennant and Co., at St. Kollox, but 
the process was not adopted elsewhere, 

A much less troublesome process was invented by Walter 
Weldon, in 1867, and first practically carried out at Messrs. 
Gamble’s works at St. Helens in 1868; it is now universally 
adopted wherever chlorine is made from’ manganese dioxide and 
hydrochloric acid. 

The crude manganese chloride solution remaining in the stills, 

^ Askenasy and Klonowski, Zeii, Ekkkochm., 1910, 16, 107. 

* Ann. Philyim, 17, SO. 

* Seport of Patent Jnventioniy March, 1850, p. 236. 



1184 


MANGANESE 


the chlorine made entirely from the mud, and as this, unlike the 
native ores, contains no iron which requires to be eliminated by 
precipitation with limestone dust, it now becomes possible to 
avoid the use of the latter and to utilise the excess of acidVhich 
is invariably left in the chlorine still, even when the artificial 
mud is used But as crude hydrochloric acid always contains 
sulphuric acid, which was eliminated as calcium sulphate in the 
mud run off from the settling tanks. A, in the process so far 
described, it is necessary to provide a new outlet for this impurity, 
and this is done by treating the hydrochloric acid with a portion 
of the waste calcium chloride liquor, the calcium sulphate formed 
being separated by a sand-filter. The purified acid is then used 
to generate chlorine in the stone stills I, with thick manganese 
mud run from the settlers, G, by the pipe, N. When no more 
chlorine is evolved the residual liquor is treated with an excess 
of mud more than enough to neutralise all the residual free acid, 
amounting to about 0*7 per cent, of the liquor; the mixture is 
then allowed to settle, and the much richer manganese mud 
settling out forms part of the next batch to be treated with acid, 
the reaction being approximately : 

36(Ca0,2Mn02) + ISHQ = ISMnO^ + 27(Ca0,2Mn02) + 
9CaCl2 + 9H20. 

The Weldon operation thus converts 124MnCl2 into 
98Mn02 + 26MnO. The equations given above are intended to 
express the average results obtained.^ 


Manganese Trioxide and Heptoxide, Manganic Acid, 
Permanganic Acid, and their Salts. 

519 In his work entitled The Prosperity of Gefrrmny,^ pub- 
lished in 1656, Glauber mentions that when manganese is fused 
with fixed saltpetre (caustic potash) a mass is produced from 
which he obtained “a most dainty purple fiery liquor,’* this 
afterwards turning blue, red, and green. In 1705 an anonymous 
treatise appeared, entitled Key to the Secret Cabinet of Nature's 
Treasury ; in this it is stated that the product obtained by fusing 
saltpetre and manganese yields a solution of which the colour 
alters, first being grass-green, then sky-blue, violet-coloured, and 

^ A detailed description is to be fonnd in Lunge’s Svtphuric Add and Alkali 
Manufacturct Vol. III. 

* Faoke’s translation, 1687, p. 363. 




MANGfANESE TEIOXIDB AND HEPTOXIDE 1185 


lastly tose-red. The changes of colour which afe here given are 
exactly the opposite of those which Glauber noticed. Pott in 1740 
described these changes, believing that they had -not been 
previously noticed, and Scheele, who endeavoured to explain 
these phenomena, gave to the colouring material the name of 
mineral chameleon, a term which had previously been applied to 
other mineral colouring matters capable of undergoing chai\ges 
of tint. The properties of this mineral chameleon were after- 
wards investigated by many chemists, but it was not until the 
year 1817, when Chevillot and Edwards ^ investigated the subject, 
that a rational view of its composition was arrived at. They 
“showed that when much alkali is employed a green compound 
is formed ; that when, on the other hand, an excess of manganese 
is fused with potash a red body is produced, and they succeeded in 
preparing tlie substance obtained by the latter reaction in the 
crystalline form. They also showed that an absorption of 
oxygen takes place, and consequently they assumed that the 
potash salt forms with manganese a manganate, and that the 
green salt contains more base than the red. Forchhammer^ 
investigated the subject in 1820, and ascribed the difference in 
colour to the existence of two distinct acids ; but Mitscherlich ® 
first showed their exact composition. 

Manganese Trioxide, MnOs, is a deliquescent, amorphous, 
reddish mass, prepared by dropping a solution of potassium 
permanganate in concentrated sulphuric acid on to dry sodium 
carbonate : ^ 

2(Mn08)2S04 -f 2Na2C03 = 2Na2S04 + 4Mn03 + 2CO2 + Og. 

It is formed only in extremely small quantity, and is carried 
forward by the carbon dioxide as a pink fume, which may be 
caught on fragments of glass placed in a freezing mixture. 

\^en thrown into water it is decomposed as follows : ^ 

SMnOs + H2O = 2HMn04 + MnOg. 

The manganates have a green colour, and their solutions are 
stable only when they contain large quantities of free alkali. 
If carbon dioxide is passed through them, or if they are diluted 
with much water, or made slightly acid, the liquid passes from 

1 Ann. Chim. Phys.^ 1817, [2], ^ 287. 

* Ann. Phil, 1820, 16, 130; 1821, 17, 160. 

» Pogg. Ann., 1832, 25, 287. 

* Franke, J. pr. Chm., 1887, [2], 6, 893, 

^ Thorpe and Hambly, Joum. Ohem. 80c., 1888, 63, 176. 



1186 lONQimSSB . 

a green to a bltie and viSlet colour, the permanganate being 
formed, and the dioxide deposited : 

3K2Mn04 + 2 H 2 O = 2 KMn 04 + MnOg + 4KOH. 

The manganates are also converted by direct oxidation into 
permanganates when they are dissolved in a large quantity of 
water containing dissolved oxygen. 

Manganates are produced by the partial reduction of perman- 
ganates in alkaline solution, and this change occurs when small 
amounts of reducing agents such as alcohol and sodium thiosul- 
phate are added to the red, alkaline liquid. The latter also 
gradually turns blue and afterwards green simply on exposure* 
to air, this being caused by the reducing action of the organic 
matter contained in the atmosphere. These reactions explain 
the changes of colour of the mineral chameleon. In alkaline 
solution the manganates act as powerful oxidising agents. 

Potassium Manganate, K 2 Mn 04 . — The preparation of potassium 
manganate is important, since it is the first stage in the manufac- 
ture of potassium permanganate. Potassium hydrate or car- 
bonate is heated with manganese dioxide to dull redness in the 
presence of air ; in the laboratory it is quicker and therefore more 
convenient to use an oxidising agent such as potassium chlorate. 
According to Bahr and Sackur,^ the product is a complex 
manganite-manganate : 

8 K 2 CO 3 + SMnOa + 30 = 8K20,Mn60i3 + 8 CO 2 . 

The deep green-coloured mass is dissolved in water, when mangan- 
ese dioxide is precipitated and an alkaline solution of manganate 
is obtained : 

8Ka0,Mn50i3 + = 3K2Mn04 + 2Mn02 + lOKOH. 

By evaporation of the resulting deep green solution, after it has 
been separated from the precipitated dioxide by decantation and 
filtration, the salt is obtained in small crystals isomorphous with 
those of potassium sulphate. It may be prepared also by boiling 
a saturated solution of potassium permanganate with caustic 
potash solution of specific gravity 1-33 (Aschoff). 

On heating it is decomposed, potassium manganite and oxygen 
being formed: 

2 KaMn 04 = 2 KaMn 03 + 0 a. 

> Zeit. anorg. Chem., 1912, 78, 101. See also Askenasy and Klonowski, Zeit 
Elektrochm,, 1910, 16, 104. 


^ MAkOANATfiS 1187 

The reaction does not go to completion^ however, for the manganite 
forms a solid solution or complex manganite-manganate with the 
unchanged manganate of the composition SKgOjMnjOij or 
3K3Mn04,2K2Mn03; this does not decompose easily (Bahr and 
Sackur). 

Sodium Manganate^ Na2Mn04, is formed when a mixture of 
equal parts of manganese dioxide and caustic soda is heated, for 
sixteen hours ; the mass is then lixiviated with a small quantity 
of water and the solution cooled down, when the salt separates 
out in small crystals isomorphous with Glauber’s salt, and having 
the composition Na2Mn04,10H20. These dissolve in water with 
partial decomposition, yielding a green solution. Sodium 
manganate is now used largely as a deodoriser. 

Barium Manganate^ BaMn04, is formed when manganese 
dioxide is heated with baryta or barium carbonate or nitrate, or 
when barium permanganate is heated with baryta-water. It is 
an emerald-green powder, consisting of microscopic, four-sided 
prisms or six-sided plates. It has a specific gravity of 4 * 85 , and 
is insoluble in water, but is readily decomposed by acids. The 
employment of this salt in place of the poisonous &heele’s green 
has been suggested,^ and it has been employed in a few instances, 
though not so generally as might be wished. 

520 Manganese Heptoxide, Mn207, and Permanganic Acid, 
HMn04. — The first of these compounds, also termed perman- 
ganic anhydride, was noticed by Chevillot, and afterwards 
investigated by Th^nard,^ Aschoff,^ and Terreil.* In order to 
prepare this compound, pure potassium permanganate free from 
chlorine is gradually added to well-cooled, highly concentrated 
sulphuric acid. The salt dissolves with an olive-green colour, 

■ 2KMn04 + 2H2SO4 = (Mn03)2S04 + K2SO4 + 2H2O, 

and if the solution be cooled, and water carefully added, the 
heptoxide separates as a dark reddish-brown liquid ® which does 
not solidify at —20® : 

(Mn03)2804 + H3O = MngO^ + H2SO4. 

It is extremely unstable, constantly evolving bubbles of oxygen 
on exposure to the air. These carry with them a small quantity 

1 Sohad, DeuUch, Indiutriezeit., 1865, 118; Bosenstiehl, Dingl. Polyt, Joum., 
1865, m, 409. 

• Com^. rend., 1866, 42, 389. » Pogg, Ann,, 1860, 111, 217. 

* BuU. 80c, ehim,, 1862, 40. 

« Fnmke,'d. pr. Chm„ 1885, [2], 81, 166. 




1188 


hanganese 


of the heptoxide* and thus*violet fumes are emitted. It rapidly 
absorbs moisture, and dissolves in water^ yielding a deep violet- 
coloured solution, so much heat being thereby evolved that the 
liquid undergoes partial decomposition. It dissolves in con- 
centrated sulphuric acid with an olive-green colour. On heating, 
it decomposes, with evolution of light and heat, and with violent 
explosion. 

Perrmnganic Acid, HMn04, is obtained in aqueous solution 
by adding the requisite quantity of dilute sulphuric acid to 
the barium salt or by electrolysing the potassium salt in a special 
form of apparatus and removing the alkali from the cathode 
compartment.^ A deep red liquid is thus obtained, which 
exhibits a blue colour by reflected light, and possesses a bitter, 
metallic taste. It decomposes on exposure to light or when 
heated gently, and still more rapidly when boiled, with evolution 
of oxygen and separation of the hydrated dioxide. It acts as 
a most powerful oxidising agent. 

Permanganic acid is formed also when manganese nitrate or 
any manganous salt, with the exception of the halide compounds, 
is warmed with nitric acid and lead dioxide, with potassium 
bromate and dilute sulphuric acid,^ with the higher oxides of 
bismuth and nitric acid,^ or with ammonium persulphate, silver 
nitrate, and nitric acid.^ 

A weak solution of permanganic acid continually evolves 
oxygen at a very slow rate, manganese dioxide being deposited, 
and the rate of decomposition is greatly increased by the 
presence of hydrated manganese dioxide.® When such a solu- 
tion is shaken with hydrogen or carbonic oxide, the gas is rapidly 
absorbed and a considerable volume of oxygen evolved (Victor 
Meyer and Kecklinghausen).® It has been suggested that this 
is due to the fact that the hydrated manganese dioxide simul- 
taneously formed is at first present in a specially active con- 
dition and thus greatly increases the normal decomposition of 
the permanganic acid (Morse and Reese). 

Permanganic acid has been obtained in the form of violet- 

» Mowe and Olsen, Amer. Chem. J., 1900, 23, 431. 

* VitaU, Ml, Chim. Farm., 1898, 87 , 646. 

* Schneider, Dinffl. Pofyt. Joum., 1888, 869 , 224. 

* Marshall, CAem, Newt, 1901, 88, 76. 

* Morse, Hopkins, and Walker, Amer, Chem. J., 1896, 18 , 401; Morse, 
Ber., 1897, 80 , 48; Morse and Reese, Amer, Chem. J,, 1898, 80 , 621; Morse 
and Byers, ibid., 1900, 28 , 313; Olsen, ibid., 1903, 28 . 242. 

* Ber., 1896, 29 , 2649; Hirtz and Meyer, ibid,, 2828. 



PERMANGANATES lisft 

black crystals* by evaporating the ^solution Obtained by the 
action of barium permanganate and sulphuric acid. It decom- 
poses very rapidly.^ 

Potassium Permanganate^ KMn04, is prepared on the large 
scale as a disinfectant. The first stage is the preparation of an 
alkaline solution of potassium manganate (q.v.). This may be 
neutralised by carbon dioxide or sulphuric acid; mangan^tes 
are only stable in presence of alkali, and when this is removed 
they decompose according to the equation : 

3K2Mn04 + 2 H 2 O = 2 KMn 04 + Mn02 + ^^OH. 

This method involves the loss of two-thirds of the manganese 
and the neutralisation of the alkali. The loss of manganese is 
prevented by Stadeler’s method of passing chlorine into the solu- 
tion, but this method is just as wasteful of the alkali. 

2K2Mn04 + CI 2 2KMn04 + 2KC1. 

An electrolytic process of oxidation is now largely used. This 
involves no loss of manganese, nor is the alkali neutralised, and 
the resulting permanganate has only to be separated from the 
very soluble hydroxide. Numerous processes ^ have been 
described; in most the solution is electrolysed between iron 
electrodes separated by a diaphragm. Oxidation takes place at 
the anode, thus : 

2K2Mn04 + H 2 O + 0 == 2KMn04 + 2KOH. 

When the pure crystallised product is not required, the 
corresponding, difficultly crystallisable, but cheaper, sodium 
permanganate is prepared in an exactly similar manner ; solutions 
of this are sold as Condy’s Disinfecting Fluid, 

Potassium permanganate is isomorphous with potassium per- 
chlorate, with which it crystallises in all proportions. The 
crystals are almost black, and when freshly prepared possess a 
green, metallic lustre, which, however, on exposure to the air 
becomes of a steel-blue tint without any further alteration in 
the salt taking place. The crystals have a specific gravity of 
2’7, and yield a red powder. One hundred parts of water dissolve ® 
2*83 parts of the salt at 0°, 6*34 parts at 19*8°, 12*66 parts at 40°, 

i Muir, Joum. Chm, 80 c., 1907, 91 , 1485. 

* See Brand and Eamsbottom, J. pr, Chm„ 1910, [2], 82, 330; Askenasy 
and Klonowski, Zeii EUhtrochm, 1910, 16, 170. 

* Baxter, Boylston, and Hubbard, J, Amer, Chm, Soc., 1906, 28, 1336; 
Patterson, ibid., 1734. 



ligo^ BIANGANESi; 

and 25*03 parts At 65°, foi&ing a deep purple-coloured solution. 
On heating to 240° they decompose as follows : 

10 KMn 04 = 2 K 2 Mn 03 + (SKjjMnO* + SHnOg) + eOg. 

The final products are potassium manganite and a solid solu- 
tion or complex compound of potassium manganate with 
manganese dioxide.^ 

Jones 2 has shown that hydrogen and phosphine decompose 
potassium permanganate, and that oxygen is evolved together 
with carbon dioxide when sulphuric acid acts on permanganate 
in presence of oxalic acid. 

Mixed with sulphur or phosphorus, a material is obtained 
which takes fire or explodes violently on percussion, and a 
mixture of the salt with charcoal burijs like tinder. 

Potassium permanganate is largely used as an oxidising agent, 
both in analytical work and for the preparation of many organic ,, 
oxidation products. In alkaline solution it is first converted 
into manganate, which afterwards loses a further amount of 
oxygen and yields the hydrated dioxide, two molecules of the 
salt providing three atoms of oxygen. 

(1) 2KMn04 + 2KHO = 2K2Mn04 -f HgO + 0, 

(2) 2K2Mn04 + 2 H 2 O = 2Mn02 + 3KHO -f 20. 

It is in this way, for example, that potassium permanganate 
acts when it is brought into contact with a hot solution of 
manganous salt, the whole of the manganese being precipitated 
as dioxide (Volhard) ; three-fifths of this is therefore formed by 
the oxidation of the manganese salt added and the remaining 
two-fifths by the reduction of the permanganate : 

3 MnS 04 -f 2KMn04 -f 2H2O = SMnOa -f K2SO4 + 2H2SO4. 

In acid solution the manganese of the permanganate is finally 
converted into a salt corresponding to the monoxide MnO, five 
atoms of oxygen being rendered available : 

2KMn04 -f 3HaS04 = K2SO4 -f 2MnS04 -f 3H2O + 50. 

Thus the action of acid potassium permanganate solution on 
ferrous sulphate, in presence of sulphuric acid, is represented : 

2KMn04 + 10FeSO4 + 8H2SO4 = + 

2 MnS 04 -f 5Fe2(S04)3 + SEfi. 

^ Askenasy and Solberg Nemst-Festschrift, 1912, 63. 

* Jmm* Chm,f 8oe„ 1878, 88, 96. 



, ^ PERMAN0AKATE8 IM 

The acid solution of potassium permanganate is reduced by 
hydrogen peroxide wit{i evolution of oxygen,^ half of which is 
due to the peroxide, half to the permanganate : 

2KMn02 + 5H2O2 + 3H2SO4 = K2SO4 + 2MnS04 + 

8H2O + 5O2. 

The reduction of potassium permanganate by formic acid 
in slightly acid solution appears to take place in stages.^ 

When potassium permanganate is used as an oxi^sing agent 
in volumetric analysis, it is often noticed that the first portion of 
permanganate added only reacts slowly, further additions react 
more rapidly. The phenomenon is particularly noticeable in 
the titration of oxalic acid. This is an example of autocatalysis : 
manganous sulphate catalyses, and is itself a product of the 
reaction. Harcourt and Esson,^ and Schilow,^ have shown that 
the velocity of the reaction is proportional to the concentration 
of the manganous salt. Similar results have been obtained in 
the oxidation of sulphites, and in the titration of hydrogen 
peroxide. In the titration of ferrous salts in the presence of 
hydrochloric acid, besides the main reaction shown in the equa- 
tion above, a subsidiary reaction, induced by the presence of 
iron salts, occurs : 

2KMn04 + 16HC1 == 2KC1 -f 2MnCl2 + BHgO + SClg. 

This secondary reaction can be prevented by the addition of 
manganous sulphate, which greatly increases the velocity of the 
main, but not that of the secbndary reaction ; thus a negligible 
part of the permanganate only is used in the oxidation of the 
hydrochloric acid. 

Ammonium Permmganate, NH 4 Mn 04 , is obtained by the 
decomposition of the potassium salt with ammonium chloride. 
It is isomorphous with potassium permanganate, and decomposes 
readily when gently heated,^ forming ammonium nitrate, oxides 
of nitrogen, and an oxide of manganese of the composition 
22Mn02,Mn0. It explodes when rapidly heated, or when 
subjected to percussion. 

‘ On the nature of this reaction, see Baeyer and Villiger, Ber., 1900, 88, 
2488, where the literature is quoted j Bach, Ber., 1901, 84, 3851. 

* Holluta, Zeit. physikal Chem., 1922, 101, 34. 

> Phil Trans., 1866, 166, 201. 

* Christensen, Zeit, anorg. Chem., 1900, 84, 203. 


^ Ber., 1903, 86, 2735. 



liw MANGANESE 

^ jp— ^ 

Barium Permanganate, tfa(Mn04)2, forms hard, almost black 
prisms, soluble in water. It is obtained by passing carbon 
dioxide through water containing barium manganate in suspen- 
sion, ^ or by the action of barium chloride on silver permanganate. 

Silver Permanganate, AgMn04, separates out in large, regular 
crystals when warm solutions of silver nitrate and potassium 
permanganate are mixed. It dissolves in 190 parts of water at 
15°, and is much more soluble in warm water. The solution 
decomposes on boiling. 


Manganese and the Halogens. 

521 Manganous Fluoride, MnFg, is obtained by dissolving 
metallic manganese or the carbonate in hydrofluoric acid, the 
compound being deposited as a white, crystalline powder when 
the solution is boiled. According to Edminster and Cooper,^ how- 
ever, the compound thus formed is an acid salt, MnF2,5HF,6H20, 
of specific gravity 1*921. It is formed as a rose-coloured mass 
by the action of gaseous hydrogen fluoride on manganese. 
It is insoluble in water, but may be recrystallised from fused 
manganese chloride and then forms rose-coloured prisms of sp. 
gr. 3*98, melting at 856°. It dissolves in strong acids, yields 
an ox5dluoride when boiled with water, and is completely 
reduced by hydrogen at 1000°.® 

Manganic Fluoride, MnFg, is obtained by the action of fluorine 
on manganous iodide in purple pseudomorphs of sp. gr. 3*54. 
It decomposes, when heated, into manganous fluoride and 
fluorine, dissolves in strong acids, forming unstable dark brown 
solutions, and is decomposed by water.^ A hydrated trifluoride, 
MnF3,3H20, is obtained in ruby-red crystals by dissolving the 
sesqui- or the di-oxide in hydrofluoric acid. 

Potassium Manganifluoride, KgMnFe, is obtained by decofn- 
posing potassium manganate with water and dissolving the 
resulting potassium manganite in a mixture of hydrofluoric 
acid and potassium fluoride. It forms small, golden-yellow, 
hexagonal tablets and is decomposed by water, but may be 
recrystallised from hydroflx’oric acid. It yields a dark brown- 

1 Bottger, J. pr, Chem., 1863, 90, 166. 

* J. Amer, Chem. Soc., 1920, 49, 2419. 

* Moissan and Venturi, Compt. rend., 1900, 180, HOP. 

* Moiflsan, Convpt. rend., 1900, 180, 622. 


MANGANESE AND THE HALOGENS 1103 

coloured solution in hydrochloric acid which* evolves chlorine 
when gently heated. A rubidium salt of similar properties has 
also been obtained.^ 

Mangancm Chloride, MnClg, is formed when the metal is 
burned in chlorine gas, or when hydrogen chloride is passed oyer 
heated manganous carbonate. Prepared in this way, manganese 
chloride is a pale rose-coloured mass, having a lamino-crystalline 
structure. When heated to redness it fuses to an oily liquid, 
and decomposes in moist air at this temperature with formation 
of hydrochloric acid and the oxides of manganese. Manganous 
chloride is obtained in solution by dissolving the carbonate or any 
of the oxides in hydrochloric acid. For this purpose the residues 
from the preparation of chlorine by means of pyrolusite and 
hydrochloric acid may be utilised. These are always coloured 
yellow, from the presence of ferric chloride, and contain an 
excess of acid. They must be evaporated to drive off the acid, 
then diluted with water, and a tenth of the solution precipitated 
with sodiumr carbonate. The precipitate, consisting of manganese 
carbonate and ferric hydroxide, is then well washed with hot 
water and boiled with the remainder of the liquid for a long time. 
By this means the whole of the iron is precipitated as ferric 
oxide. The filtrate may contain copper, barium, and calcium, 
which are separated by the usual methods. On evaporation, a 
concentrated solution of manganous chloride deposits between 
15° and 20° light pink-coloured, monoclinic crystals of the hydrate 
MnClaj^HgO, This hydrate is transformed at 58*098° into 
the hydrate MnCl 2 j 2 H 20 , this temperature having been deter- 
mined with great accuracy by Kichards and Wrede as a suitable 
fixed point for use in thermometry.^ The dihydrate is stable up 
to 198° and then passes into the anhydrous salt. Below — 2° 
the hydrate MnCl2,6H20 is formed.® In addition to these an 
isomeric /3-tetrahydrate is known (Marignac) ^ which also forms 
monoclinic crystals, but of a different form from the ordinary 
tetrahydrate, being isomorphous with those of hydrated ferrous 
chloride, FeCl2,4H20. The dihydrate may be prepared by 
heating the tetrahydrate for some time at 60° or passing hydrogen 

^ Weinland and Lauenstein, Zdt. anorg. Chem., 1899, 20, 40. 

‘ Zeit. physikdl. Chem., 1907, 01, 313. 

’ Knznetzoif, J, Iktas. Phye. Chem. Soc., 1898, 30, 741; Dawson and 
William8> Zeit. physikal. Chem., 1899,81, 59. See also Richards and Briggs, 
m., 1898, 28, 313. 

‘ Compt, rend., 1857, 45, 660, 



1104 UANOiil^E 

; •' 

chloride into an alcoholic solution of the chloride. One hundred 
parts of water dissolve : 

At 8® 26“ 30“ 67-86“ 80“ 100“ 

MnClg 62 77-2 80-7 105-7 112-7 116 . 

This salt is also soluble in alcohol, forming a green sblution 
which burns on ignition with a red flame. Manganous chloride 
forms double salts with the chlorides of the alkali metals, such 
as K2MnCl4,2H20 and K4MnCl4, and with the chlorides of some 
other metals. The anhydrous salt combines readily with 
ammonia and similar compounds. With ammonia, it forms the 
hexammine, [Mn(NH3)g]Cl2, the diammine, (NH3)2,MnCl2, and 
the monammine, NH3,MnCl2.^ 

Manganese TriMmide^ MnClg, and Manganese Tetrachloride^ 
MnCl4, have only recently been obtained in the solid state. 
When any one of the oxides, Mn304, Mn203, or MnOg, is added to 
cold concentrated hydrochloric acid, a dark brown solution, is 
formed, chlorine being simultaneously produced when the dioxide 
is employed. This solution appears to contain the trichloride,^ 
and yields double salts of the type MnCl3,2RCl, with the chlorides 
of potassium and ammonium.® The addition of water to the 
solution precipitates a mixture of hydrated oxides (Pickering).^ 
When the dark brown solution is heated, chlorine is evolved, 

2MnCl3 = 2MnCL2+Cl2. 

When manganese dioxide is treated with ether saturated with 
hydrochloric acid, a deep green solution is obtained, which was 
considered by Nickl^s ® to contain the tetrachloride, MnCl4, and 
by Franke ® to contain the compound MnCl2,MnCl4. It is, how- 
ever, probable that this green liquid contains the trichloride 
and not the tetrachloride, since it yields double salts with the 
hydrochlorides of pyridine and quinoline of the type MnCl3,2RHCl ; 
almost the whole of the manganese in the solution can be 
precipitated in this form. More concentrated green solutions can 

^ Biltz and Huttig, Zeit anorg, Chem., 1919. 109f 88; Ephraim. Ber., 
1912. 45. 1322; Zeit. phyaikal. Chem., 1913. 81. 613. 

* Pickering, Joum. Ckem. /Sloe., i879, 85, 664. 

> Neumann. Momtsh., 1894. 15, 489; Rice. Joum, Chem. 8oc., 1898. 78, 268. 

*8ee also Fisher. Jaum, Chem. 8oc., 1878. 88, 409; Christensen. J, pr, 
Chem., 1887, [2], 85. 67, 161, 541. 

Ann. Chim. Phye., 1866, [4], 5, 169; 1867, [4]. 10. 318. 

• J. pr. Chem., 1888, [2], 86, 31. 463. 



• MANOA^ THE HALOGENS . ^1195' 

be prepared by the action of alcoholic hydrochloric acid on 
manganese dioxide or potassium permanganate.^ 

When dry hydrogen chloride is passed into carbon tetra- 
chloride in which manganese dioxide is suspended, a solid 
product is obtained which consists of manganese trichloride 
and tStrachloride. On treating this with anhydrous ether, the 
trichloride dissolves, forming a deep violet-coloured solution. 
A reddish-brown residue of the tetrachloride remains. The 
trichloride is a black solid, having a greenish tinge, which is 
decomposed by water. The tetrachloride is stable at ordinary 
temperatures, but is decomposed by moisture.^ 

Derivatives of the tetrachloride can be obtained by boiling 
potassium permanganate with glacial acetic aeid, and saturating 
the resulting reddish-brown solution with hydrochloric acid. 
A dark crystalline precipitate of potassium rmnganichloridef 
MnCl 4 , 2 KCl, is thus produced, which rapidly loses chlorine 
in moist air, but may be preserved in dry air for some time. 
If potassium acetate be added to the liquid before it is saturated 
with hydrochloric acid, Neumann’s salt, MnCl3,2KC), is obtained 
(Meyer and Best). 

Permanganic Oxychloride^ MnOjCl.— This -chloride of perman- 
ganic acid was first prepared by Dumas ; ® he did not, however, 
analyse the compound, but from its mode of decomposition con- 
sidered it to be manganese heptachloride, MnCly. It is obtained 
by gradually adding fused sodium chloride to a solution of 
potassium permanganate in concentrated sulphuric acid. A 
yellow gas is then evolved, which when passed through a freezing 
mixture condenses to a greenish-brown liquid. This when 
exposed to the air emits a purple-red vapour, which possesses the 
peculiar smell of the oxides of chlorine, and like them acts most 
violently upon the mucous membrane, so that the smallest 
quantity of the chloride contained in commercial permanganate 
can be thus readily detected.^ When heated, it explodes violently, 
and water decomposes it with formation of permanganic acid 
and hydrochloric acid. These substances, however, mutually 
decompose with formation of free chlorine and manganese 
dioxide. A corresponding oxyfluoride, MnOgF, exists, and 
.was first prepared by Wbhler.® • 

^ Meyer and Best, Zeit, anorg, Chm., 1900, 22» 169. 

» Holmes, J. Amer. Chm. 8oc., 1907, 29, 1277. 

» Ann. CMm, Phys., 1827, [2], 86, 81. 

« Aschoff, Pogg. Ann., 1860, lU, 217. 

* Pogg. Ann., 1827, 9 , 619. 




1196 Mi^OA^DSl: 


Manganous Btomide, MhBrg, is obtained by heating the 
powdered metal in bromine vapour, and when the compound is 
fused, it is obtained as a pale red mass. *It can also be obtained 
by the action of the calculated quantity of bromine on finely 
divided manganese suspended in ether, but not in other organic 
solvents. The crystalline compound MnBig, (02115)20 is first 
obtained; this readily loses its ether on being heated to 100°, 
leaving manganous bromide as a white powder (Ducelliez and 
Kajmaud).^ When the carbonate is dissolved in hydrobromic 
acid the hydrated bromide, MnBr2,4H20, is obtained, and this 
was found by Marignac to be isomorphous with the ordinary 
form of the chloride. Other hydrates are known. Unlike the 
chloride, it shows no tendency to form double salts with chlorides 
of the alkali metals. It behaves in a similar manner to the 
chloride towards ammonia (Biltz, Ephraim). 

Manganic Bromide^ MnBrg. — When finely divided manganese 
is treated with a large excess of bromine in ethereal solution, 
two liquid layers are formed ; from the lower of these Ducelliez 
and Eaynaud obtained by cautious evaporation a yellow, amor- 
phous mass of the composition MnBr3,3(C2H5)aO, from which 
the ether could not be removed without formation of manganous 
bromide. It is very soluble in water, and gives a black precipitate 
with sodium carbonate solution. 

Manganous Iodide, Mnl 2 , 4 H 20 , is obtained crystallised in 
colourless, deliquescent needles, which become coloured on 
exposure to air. Hydrates with GHgO and 9H2O are formed 
below — 2 * 7 ° and — 9 * 3 ° respectively.^ It has little tendency 
to form double salts, and forms a hexammine and a diammine 
(Biltz, Ephraim). 

Manganese Tetriodate, Mn(IOg)4, is not known in the free 
state, but a double salt with potassium iodate, Mn(I03)4,2KI03, 
is formed as a brownish-violet, insoluble, crystalline powder 
when hydrated manganese dioxide is boiled with iodic acid and 
potassium iodate.^ 

Manganese, Sulphur and Selenium. 

522 Manganese Monosulphide, MnS, occurs as the mineral 
manganese blende, or alSabandite, forming a steel-grey, crystal- 
line mass with a green streak, and sometimes observed in cubes 

1 Bull Soc. chim,, 19U, [4], 16 , 273, 408. 

* Kuznetzoff, J, Busb, Phys, Chm* 80 c., 1900, 82, 290. 

* Beig, Campl rend,, 1899, 128 , 673. 




MANGANESE, SULPHUR AND SELENIUM 1197 

, 

and octahedra. It has a specific gravity of 4*04, and occurs in 
veins in the coal mines in Transylvania, and in Freiberg and 
Mexico. It may be obtained artificially in the form of a dark 
grey powder, which melts at a high temperature, forming a 
steel-grey, crystalline mass, by heating the monoxide, the car- 
bonate, or the sulphate in a current of hydrogen sulphide 
(Arfvedson), or in green octahedra by heating manganous sul- 
phide with a little sulphur in the electric furnace.^ Ammonium 
sulphide and the other monosulphides of the alkali metals pre- 
cipitate anhydrous manganese sulphide from a solution of a 
manganous salt in the form of a light flesh-coloured precipitate, 
which dissolves readily in dilute acids and oxidises on exposure 
to the air, assuming a brown tint. When left in contact with 
ammonium sulphide, or heated to 300°,^ and when suspended 
in a dilute solution of sulphuretted hydrogen and exposed to a 
low temperature, it passes into the green, crystalline sulphide.® 
According to Olsen and Rapalje a grey form of the sulphide 
also exists and the sulphide precipitated by ammonium sulphide 
is a mixture of this and a red form. The sulphide precipitated 
by sodium sulphide does not contain the grey form,^ and does 
not become green in contact with excess of the precipitant. 

Manganese sulphide combines with the sulphides of the alkali 
metals to form salts.® The dark-red, crystalline potassium salt, 
KgSjSMnS, is formed when anhydrous manganese sulphate is 
gradually heated to redness with three parts of potassium 
carbonate, 0-2 part of lamp-black, and excess of sulphur. 

Manganese Disulphide, MnSg. — This substance is found as the 
mineral hauerite in crystals belonging to the regular system. 
They possess a metallic, adamantine lustre, and a reddish-brown 
colour, and occur in clay at Kalinka in Hungary, together with 
sulphur and gypsum. 

Manganous Sulphate, MnS04, is best prepared by mixing 
commercial black oxide of manganese to a paste with sulphuric 
acid and heating the mixture in a crucible to strong redness, 
when the greater part. of the iron sulphate is destroyed. The 
filtrate obtained after lixiviating the residue is then heated with 

1 Mourlot, Comp/, rend., 1895, 121, 202. 

* Antony and Donnini, Qazz., 1893, 28, i., 560. 

* Villiera, Comp/, rend., 1895, 120, 322; see also Hahn, ZeiU anorg. Chem., 
1922,121,209. 

* J. Am&r. Chem. Soc., 1904, 26, 1615, where the literature is quoted. 

* Vdlker, Annalen, 1846, 69, 35; Brunner, Arch. eci. pllps. na/., 1889, 22, 68. 



1198 - 


a small quantity of mangabous carbonate in order to precipitate . 
the last traces of iron. 

It has a specific gravity of 3*1, and is' decomposed at a bright 
red heat, leaving a residue of red oxide of manganese. Man- 
ganous sulphate forms a number of hydrates and the equilibrium 
cfurve for this substance and water is one of great complexity. 
Below 8°, the heptahydrate separates out, between 8® and 27° 
the pentahydrate is the stable form, and above 27° the mono- 
hydrate. The solubility of the latter decreases as the tempera- 
ture rises, so that a maximum of solubility exists at 27°. In 
addition to these stable forms, several labile hydrates exist, the 
most important of these being the tetrahydrate, which separates 
at about 30° in rose-coloured prisms of sp. gr. 2*097 (Kopp). 
Several other hydrates have been described, but it is doubtful 
whether they all exist.^ One hundred parts of water dissolve ; 

At 0® 9® 16® 27® 60® 70® 100® 

MnS04 53*2 -59*3 61*1 66 59*5 52 33*2 parts. 

The last trace of water is expelled from the monohydrate 
only at 450°. 

Manganous sulphate is insoluble in absolute alcohol, this"" 
liquid removing a portion of the water from the hydrates. 
Finely crystalline double sulphates * of the isomorphous series, 
K*2S04,R”S04,6H20, are formed when manganous sulphate and 
the alkali sulphates are crystallised together. 

Manganous Aluminium Sulphate, MnS04,Al2(S04)3,24H20.~ - 
This substance occurs as the mineral apjohnite found in Algoa 
Bay in South Africa.® 

. Manganic Sulphate, Mn2(S04)3,— Manganic oxide and hydroidde 
dissolve with difficulty in sulphuric acid. The red oxide, 
Mn304, on the other hand, dissolves readily, yielding a purple- 
red solution. If the finely divided precipitated’ dioxide is 
treated with sulphuric acid, oxygen is evolved, and at a tem- 
perature of 138° a green liquid is obtained from which the s^ 
phate is precipitated as a non-crystalline powder. In order " 
purify this salt it is brought on to a porous porcelain plate, when 
the greater part of the sulphuric acid is absorbed; the residue 

^ 8ohieber, Momtsh., 1808, 18, 280; Cottrell, J, Physical Chem., 1900, 4, 
637 ; BichaidB and Fraprie, Amer. Chm. J., 1901, 26, 75. 

* See aUb Scott, Jottm. Chm, 8oc., 1897, 71 , 1^7; Mallet, ibid., 1900, 77 » 
221; 1902,81, 1649. 

* PhiUfag.,im, 1^112, m. ' 




MAKGANISE, SUIJPHUR AND SELENIUM 1195 

1 —^ ^ ^ 

is then washed with pure nitric acid, the salt dried in absence 
of air on another plate, and then heated to 160®.^ 

Manganese Alums. — ^Manganese forms a series of alums, 
K*2804,Mn2(S04J3,24H20, which crystallise in pink or red, 
octahedral forms. They are decomposed by water, but are 
stable in a solution of 1 volume of sulphuric acid diluted with 
3 of water, provided that the temperature is kept low. ^he 
potassium and ammonium salts are extremely unstable and 
have not been obtained pure, but the caesium and rubidium salts 
can be prepared. The salts obtained by the addition of the 
sulphates of potassium and ammonium to manganic sulphate 
and evaporating are not true alums, but contain less water of 
crystajfisation.^ An anhydrous ammonium manganic sulphate 
has also been obtained and forms violet crystals which are 
decomposed by water.® 

Manganic Ccesium Alum, Cs2S04,Mn2(S04)3,24H20, may be 
prepared by dissolving caesium sulphate and manganic acetate, 
Mn 2 (C 2 H 302)3 (obtained by the action of potassium perman- 
ganate on manganous acetate dissolved in glacial acetic acid), in 
dilute sulphuric acid and cooling to —20° (Christensen). It can 
be obtained also by electrolysing at 10“16° a solution of 
manganous sulphate and caesium sulphate in dilute sulphuric 
acid placed in the anode compartment of an electrolytic cell.^ 
It forms coral-red crystals of the regular system (class 30, p. 209) 
and is decomposed by water. It Aelts at 40° in its water of 
crystallisation. . i 

The Rubidium Alum closely r#embles the caesium salt, but 
decomposes at about 15°, whilst the potassium and ammonium 
alums decompose at%till lower temperatures (Christensen). 

Manganese Dioxysulfhate &r Persul'phate, Mn(S 04 ) 2 , was first 
prepared by Fremy,® and can best be obtained by oxidising 
manganous sulphate in warm sulphuric acid with the calculated 
quantity of potassium permang|pate. When the solution is 
sufficiently concentrated, it is precipitated in the form of black 
crystals, which are soluble in sulphuric acid, forming a brown 
solution which is stable up to 80°, but above that temperature 
decomposes with the formation of manganic sulphate. On 
diluting the solution the salt is hydrolysed and manganese dioxide 

^ Carius, Annalen, 1856, 98» 53. 

* Christensen, Zeit. anorg. Ohm., 1901, 27, 328. 

’ Lepierre, Comyt. rend., 1895, 120, 924. 

* Picoini, Zeit. aiwrg. Ohm,, 1898, 17> 355; 1899, 20, 12. 

B Compt. rend;, 1876, 82, 475, 1231. 

VOL. n. (n.) 


BB 



1200 MAKGANBSB 

; — — T ' f ' — ;■ 

is precipitated. Electrolysis^ of a solution of manganese sul- 
phate' in sulphuric acjd yields a solution of it, which, however, 
is not free from manganic sulphate. It has been used as an. 
oxidising agent in organic chemistry. 

Manganous DithiovuUe, MnS 20 e, 3 H 20 . — This salt is of interest 
inasmuch as it is employed for the preparation of dithionic 
acid (Vol. L, p. 459). It is obtained by passing sulphur diojdde 
through water in which finely divided manganese dioxide is 
suspended. The solution always contains a small quantity of 
manganous sulphate, and for tWs reason baryta water is added 
as long as a precipitate of barium sulphate is formed. Manganous 
dithionate forms easily soluble rhombohedral crystals. 

Double selenates of manganese with potassium, rubidium,- 
ceesium and ammonium have been prepared.^ 


Manganese and the Elements op the Nitrogen Group. 

523 Manganese Nitride^ Mn 3 N 2 .— Nitrogen reacts vigorously 
with manganese at a red heat to produce this compound. It is a 
dark coloured powder, which yields ammonia when heated in 
hydrogen or fused with potash, and is attacked only with* 
difiiculty by acids.® 

Manganous NitratOy Mn(N 03 ) 2 . — The hydrate with GHgO • 
crystallises with difficulty in colourless, deliquescent needles 
which melt at 26*8°, and are readily soluble in alcohol. A hydrate 
with SHgO also exists ^ which is stable above 25° and melts at 
35*5°. The nitrate decomposes at 129*5°, at which temperature 
a black deposit of manganese oxides is formed. 

Manganese Phosphides— The freezing points of manganese- 
phosphorus mixtures have been determined by Zemczwznyj and 
Efremow ® : these prove the existence of two compounds. The 
first has the formula Mn 5 P 2 , the second probably has the formula 
MnP. The substance MngPg, described by many of the earlier 
workers, is really a eutectic mixture. The magnetic properties 
of the compound Mn^Pj have been studied by Wedekind and 
Veit.® 

^ Zeii. Elekirochm,y 1906, 11, 853. ^ 

* Tutton, Proc. Roy, Soc.y 1932, [A] 101, 225. 

’ Prelinger, MomUh., 1894, 15, 391 ; Hal>er and van Oordt, Zeii. anorg. 
Chem.f 1905, 44, 341 ; Shukow, J. Rues. Phye. Chem. 80 c., 1908, 40, 457. 

« Funk, Ber.y 1899, 82, 96. 

* Zeii. anorg. Chm.y 1908, 57, 241. 

* JBcr., 1907, 40, 1268. 



MANGANESB AND ELEMENTS OP NITROGEN GROUP 1201 

^ — - 

Manganous Phosphates.— These salts have been investigated 
by Heintz,^ Debray, ^ Bodecker,® and Erlenmeyer.^ The normal 
manganous orthophosphate, Mn3(P04)2,7H20, is a white, 
imperfectly crystalline precipitate. The monohydrogen salt, 
HMnP04,3H20, forms small, prismatic, rose-coloured, rhombic 
crystals slightly soluble in water, and the dihydrogen phosphate, 
H4Mn(P04)2,2Ha0, crystallises in red, four-sided prisms which 
deliquesce on exposure to the air, decomposing into free phos- 
phoric acid and the preceding salt.® 

Manganous salts are precipitated by ammonium phosphate 
as manganous ammonium phosphate,^ Mn(NH4)P04,H20, which 
is converted by ignition into the pyrophosphate, MuaPaO;. 

Manganic Phosphates. — Both manganic oxide and the dioxide 
dissolve in a concentrated solution of phosphoric acid, in the 
latter case with evolution of oxygen, with formation of a deep 
violet liquid, from which a violet-coloured, crystalline mass 
separates out (Gmelin). This decomposes in contact with 
water, and manganic hydroxide is precipitated from the solu- 
tion by alkalis. On evaporating the red solution a peach- 
blossom-coloured powder separates, consisting of manganic 
metaphosphate, Mn(P03)s,H20.'^ The normal phosphate 
MnP04,H20, an acid pyrophosphate, MnHPjO^, and the salts 
MnKPjO; and Mn4PQ02i,14H20,® have also been prepared.® 

Manganese Arsenides. — Two arsenides of manganese are 
known, the first of which, MnAs, is non-magnetic, but is con- 
verted by heating into the magnetic compound, MngAs. 

Manganous Arsenate.— When arsenic acid is saturated with 
manganese carbonate, a sparingly soluble salt having the com- 
position HMnA804,H20 is formed. This dissolves readily in 
arsenic acid with formation of the salt H4Mn(As04)2, which latter 
crystallises in rectangular plates. Several double salts with 
the alkali arsenates are also known.^ 

I Pogg. Ann., 1848, 74, 460. > Anmlen, 1849, 00, 208. 

* Ann. Chim. Phya., 1861, [3], 6X, 433. * Annahn, 1877, 190, 191. 

* See also Viard, Compt. rend., 1899, 129, 412. 

* Dakin, Zeit. anat. Ckem., 1900, 89, 784. 

^ Hermann, Pogg. Ann., 1848, 74, 303. See also Barbier, Compt. rend, 1902, 
138, 1054, 1109. 

* Auger, Compt. rend., 1901, 133, 94. , 

* Christensen, J. pr. Chm., 1883, [2], 28, 1 ; Sohjexning, J. pr. Chem., 1892, 
[2], 45, 616. 

Wedekind, Zeit. Elekirochem, 1906» 11, 860; Ber. deuiach. phyaik. Qea., 
1906, 4, 412. Sohoen, Metedlurgie, 1011, 8, 730. 

Lefdvre, Ctmpt. rend., 1800, 110,. 400. 



1202 


MANGAipSE 


TV" — *=7Ti? 

Manganese Antimonides, — ^Two compounds, MnjSb and 
MngSbg, exist, ^ and can be prepared by heatijag the elements in 
the right proportions; the former is strongly, the latter only 
weakly magnetic. 


Manganese and Boron. 

5*24 Manganese Dihoride^ MnBg, is produced when a mixture of 
manganese thermite and boron is ignited or the oxide reduced 
with boron, and may be purified by treatment with chlorine. 
It forms grey-black crystals, which, when pure, are non-magnetic, 
decompose in warm water, and dissolve in concentrated acids.^ 

Manganese Monohoride^ MnB, is prepared by the reduction 
of red oxide of manganese with boron at a white heat in a 
magnesia crucible, or by the direct union of its elements, and 
forms a black, crystalline powder of specific gravity 6*2, which 
r^eihbles the diboride in its properties, but is strongly magnetic 
and dissolves more readily in acids.® 

Manganese borate is used in the preparation of drpng oils 
and oil varnishes * ; it is made by adding manganous sulphate to 
a solution of borax, washing and drying the precipitate. It is a 
mixture of varying composition, not a definite compound.^ 
The compounds Mn(B02)2 and MnB407 have been prepared by 
melting manganese oxide or carbonate with boron trioxide.® 

Manganese and the Elements of the Carbon Group. 

525 Manganese Carbide, MngC, is formed when red oxide of 
manganese is heated with charcoal or calcium carbide in the 
electric furnace. It has the specific gravity 6 * 89 , and with water 
yields equal volumes of hydrogen and methane : 

MngC + 6H2O - CH4 + H2 + 3Mn(OH)2. 

It burns readily in oxygen, and is easily attacked by fluorine 
and chlorine.’ When very strongly heated it dissociates, the 
manganese volatilises, and the carbon remains as graphite.® 

^ Williame, Zeit. anorg, Chem., 1907, 55, 1. 

* Wedekind, Ber., 1905, 88, 1228; Wedekind and Fetzer, Ber., 1907, 40, 
1264; Binet du Jassonneix, Ber., 1907, 40, 3193. 

* Binet du Jsssonneiz, Compl. rend., 1904, 139, 1209; 1906, 142, 1330. 

^ Hartley and Eamage, J<mm, CJiem. Soc., 1893, 68, 129. 

‘ See Endemann and Paisley, Zeit. angew. Chem., 1903, 16, 175. 

* Guertler, Zeit. anorg. Chem., 1904, 40, 244. 

7 Moissan, Compt. rend., 1896, 122, 421; 1897, 125, 839. 

‘ Gin and Leleuz, Compt. rend., 1898, 1^ 749. 



AUAxivirAxijuajai Ai'Mi/ I'O UJ^' UAUISUN GROUP 1203 

;; ■' 

Manganese Garhomie^ MnCOg, occurs in the pure state in the 

rose-red crystals of manganese spar, rhodochrosite or dialogite, 
and also as an isomorphous mixture with chalybite. These 
minerals crystallise, like calc-spar, in rhombohedra, but mangano- 
calcite, (Mn,Ca,Mg)C 03 , is isomorphous with aragonite. • 
Hydrated manganese carbonate is obtained as a white pre- 
cipitate by mixing a solution of the chloride or sulphate of 
manganese with sodium carbonate. In the moist state it soon 
becomes brown-coloured on exposure to the air; it dissolves in 
8,000 parts of pure water, and in about half this quantity of 
water saturated with carbon dioxide. 

Manganese and Cyanogen, — When a concentrated solution 
of manganese acetate is warmed with solid potassium cyanide 
a green precipitate is thrown down of KCN,Mn(CN) 2 ; this 
gradually disappears, and in its place dark blue crystals of 
'potassium manganocyanide, K4Mn(CN)e,3H20, are formed.^ 
The manganocyanide is obtained also when manganous car- 
bonate is heated to a temperature of from 40° to 50° with a 
solution of potassium cyanide.^ The salt crystallises in deep 
violet-blue, efflorescent, tetragonal tablets. Its solution oxidises 
on exposure to air with formation of potassium rmnyanicyanide^ 
K 3 Mn(CN)e, which crystallises in dark-red prisms. This latter 
salt when brought into contact with potassium amalgam in 
aqueous solution is again transformed into manganocyanide. 
The constitution of these complex salts will be referred to under 
the corresponding iron compounds. 

Manganese Thiocyanate^ Mn(SCN) 2 , may be prepared from 
manganous sulphate and barium thiocyanate. The anhydrous 
salt is yellow, and forms a green hydrate with SHgO, which 
crystallises at the ordinary temperature. Concentrated aqueous 
solutions are green, but become pink when they are diluted.® 
Manganese Silicidesr—^m^ doubts exist as to the number 
of definite compounds formed by these elements. A study of 
the freezing-point curve for mixtures of the two ^ indicates the 
existence of the two compounds, MngSi and MnSi. The com- 
pounds MnSi 2 ® and Mn 3 Si 2 ® have also been described. 

The silicide, MngSi, is formed when the two elements are 

^ Eaton and Fittig, Annalen., 1898, 145) 167. 

‘ Descampg, Ann. Chim. Phys., 1881, [6], 24, 178. 

* Kumakoi!. Quoted by Grossmann, Ber., 1905, 87, 659. 

< Doerinckel, Zeit. anorg. Chm.t 1906, 50, 117. 

^ De Ghalmot. Amer. Chm. J,, 1896, 18, 536. 

* Gin, Compt. rend,, 1906, 143, 1220* 



.1204 MANOkiBSE 

^ T- — ''-r^ — 

heated together iQ the electric furnace/ by firing a mixture of 
silica, manganese oxide, and aluminium, or by heating a mixture 
of potassium silicofluoride, red oxide of manganese, copper, and 
sodium (Lebeau). It is a very hard, brittle mass, which has a 
metallic lustre and steel-grey colour and a specific gravity of 6 * 4 . 
It is not decomposed by water at the ordinary temperature, but 
it is attacked by steam, oxygen, or chlorine at a red heat, and 
dissolves in hydrochloric acid. Fluorine decomposes it Tat the 
ordinary temperature. 

The monosilicidej MnSi, forms hard, lustrous, tetrahedral 
crystals of specific gravity 5*9, whilst the disilidde, MnSig, forms 
dark-grey, octahedral crystals of- specific gravity 5*24. The 
compound described by Gin of the formula MugSig is probably 
impure MugSi (Lebeau).^ 

Manganous Silicates occur as isomorphous constituents of 
many minerals, and some naturally occurring manganese silicates 
are also known.' Thus, for instance, rhodonite, MnSiOg, occurs 
in light brownish-red, transparent, triclinic crystals, and tephroite, 
MngSiO^, crystallises in the tetragonal system in rose-red, brown, 
or grey masses, and usually occurs together with rhodonite. 


Detection and Estimation op Manganese. 

526 Manganese is distinguished by forming a flesh-coloured 
sulphide readily soluble in dilute acids. In the course of 
analysis manganese is thrown down with the sulphides and 
hydroxides of the metals which are precipitated by ammonium 
sulphide. If the precipitate be treated with very dilute cold 
hydrochloric acid, the sulphides of cobalt and nickel, if present, 
remain undissolved. The solution is heated in order to remove 
the sulphuretted hydrogen, oxidised with potassium chlorate, and 
an excess of caustic soda is added. Iron, manganese, and uranium 
are thus thrown down as hydroxides. The washed precipitate 
is then dissolved in hydrochloric acid, the liquid neutralised, 
and ammonia and ammonium chloride are added, when the whole 
of the metals, with the exception of manganese, are thrown 
down; the filtrate is then evaporated to dryness, and the 
residues heated to get rid of ammonium salts. The mass which 

^ Vigouroux, CompL rend,, 1806, 121, 771; 1906, 141, 722; Lebeau, Compt, 
rend,, 1903, IM, 89, 231; BuU, Soc, chim,, 1903, [3], 28, 797; Ann, Chim, 
Phye„ 1004, [8], 1, 663. 

* Compt, rend., 1907, 144, 86. , 



" i)ira^ OF MANGANESE 1205 

'' • ' ' 

remains can be treated in various ways for the detection of 
nanganese. The simplest plan is to fuse a sdiall quantity- of the 
residue with caustic soda and saltpetre, when the dark-green 
[)otassium manganate is formed, and this colour becomes deep 
blue on cooling. It dissolves in water with a green coloujr, which 
)n addition of a little nitric acid turns red. Other character- 
stic reactions for the manganese salts are the following. Potash 
md soda precipitate the white hydroxide, which soon becomes 
Drown on exposure to air. Ammonia in the presence of 
ammonium chloride produces no immediate precipitate, but 
}he solution rapidly absorbs oxygen from the air, brown man- 
ganic hydroxide being deposited. When a manganese com- 
pound is fused with borax an amethyst-coloured bead is 
Dbtained in the outer flame, and this in the inner flame becomes 
colourless. 

The non-luminous gas flame is coloured green by manganese 
chloride, and this exhibits a spectrum in which the lines in 
the green and yellow are : ^ 6587(a), 5392(/9), and 6195(7). The 
jpark spectrum of manganese contains a large number of bright 
lines, of which the most important are : 6022, 6017, and 6014 
in the orange; 4824 and 4784 in the green; 4766, 4762, and 
1754 in the blue; 4236 and 4228 in the indigo (Lecoq de 
Boisbaudran). 

The absorption spectrum of permanganic acid and its potass- 
ium salt exhibits in very dilute solution five distinct bands ; a 
more concentrated solution gives continuous absorption in the 
j^ellow and green ; and this is observed also in certain solutions 
of manganic salts. The latter, however, do not show the bands 
on dilution. The manganous salts also show a characteristic 
absorption spectrum, chiefly in the ultra-violet.^ 

In order to estimate manganese gravimetrically it may be 
precipitated as the carbpnate or, by the action of bromine water 
and ammonia or nitric acid and a chlorate, as the dioxide. These 
are both converted by ignition to the red oidde, Mn304, in which 
condition the manganese may be weighed ; a better method is to 
ignite the precipitate, dissolve it in sulphuric acid, drive off 
excess of acid, and weigh as .the sulphate, MnS04. Manganese 
may also be precipitated as the suljghide, and either weighed in 
this form by Eose’s method, or converted to the oxide by 
ignition, or to the sulphate. It may be precipitated as ammonium 

1 Hoppe-Seyler, J. Chm.t 1870, 110, 303. 

* Lambert, Comfl, rend., 1905, 141, 357, 



1300 MANGiINBISE 

manganese phosphate* and weighed as the pyrophosphate, 
Mn 2 P 207 . Electrolytic methods have been proposed. 

Manganese always occurs in nature together with iron. In 
order to separate these the solution is heated with ammonium 
chloride^ neutralised with the requisite quantity of ammonia, and 
. the iron precipitated with ammonium acetate. The manganese 
canrthen be estimated in the filtrate in the above way. An 
equally accurate method, but easier and more rapid, is to remove 
the iron by precipitation with “ cupferron.” ^ 

Manganese may be estimated volumetrically by titration with 
potassium permanganate in presence of zinc sulphate (p. 1190 ), 
or. by conversion into permanganate, which is then estimated 
by titration with standard oxalic acid, hydrogen peroxide, or 
some other reducing agent. When small quantities are con- 
cerned this is best done by boiling the manganese salt with 
concentrated nitric acid, solid lead peroxide, and a little dilute 
sulphuric acid, and filtering the resulting liquid through asbestos, 
or by digesting the salt with nitric acid and sodium bismuthate, 
or a persulphate, sulphuric acid, and silver nitrate. 

Manganese may also be precipitated as the hydrated dioxide 
by boiling with dilute sulphuric acid and ammonium persul- 
phate, and the dioxide either estimated volumetrically, or in 
the absence of other metallic salts, gravimetrically by conversion 
into the red oxide.^ 

Very small traces of manganese can be detected and esti- 
mated colorimetrically by oxidising it to permanganate and 
comparing its colour with potassium permanganate solutions of 
known concentration,® 

Valuation of Manganese Ores , — The most accurate and con- 
venient methods for the estimation of the quantity of man- 
ganese dioxide in manganese ores are those of Bunsen,^ and of 
Fresenius and Will.® By the former method, the quantity 
of chlorine evolved on treatment with hydrochloric acid is 
directly determined. The gas is collected in a solution of 
potassium iodide, and the liberated iodine estimated with a dilute 
solution of sulphurous acid or sodium thiosulphate. 

Fresenius and Will's method depends upon the action : 

MnOg + C202(0H)2 + H5SO4 = MnS04 + 2CO2 + 2H2O, 

^ See Fresenius, Zeit. anal. Chm., 1911, 60, 35. 

* von Knorre Zeit. angew. Chem.t 1901, 14 , 1149. 

* See Marshall, Chem. Nem, 1904, 88, 76. 

^ J<mm. Chm. Soc., 1856, ^ 219. * AnnaUnt 1843, 47, 87. 



DETECTION AND ESTIMATION OF MANGANESE 1207 

: \ ^ ^ 
ie. 88*00 parts of carbon dioxide corresj^ond to 86*93 parts of 
manganese dioxid^. The reaction is carried out in a weighed 
apparatus provided with a drying tube, the loss of weight being 
ascertained. 

Another method, based on the same reaction, is to start with 
a known amount of oxalic acid and to determine the excess of 
this, after the manganese dioxide has been reduced, by titration 
with standard potassium permanganate. 

The Atomic Weight of manganese has been determined by 
several chemists, among the earliest of whom were Berzelius,^ 
Dumas,2 and V. Hauer.® Dewar and Scott, by estimating the 
percentage of silver in silver permanganate, obtained 55*01 ; ^ 
and Marignac, by converting pure MnO into MnS 04 , obtained 
55*02.® Baxter and Hines from the analysis of the bromide 
and chloride have found 54*96.® The value at present (1922) 
adopted is 54*93. 

^ Pogg. Ann.f 1828, 14, 211. * Annalen, 1860, 113» 25. 

■ * Wien Akad. Ber.t 1867, 26j 124. * Proc. Roy. Soc., 1883, 35, 44. 

« Zeit. anal. Chem., 1884, 23, 123. » J. Amer. Chem. Soc., 1906, 28, 1660. 



GROUP VIII. 


Sub-group (a) Iron, Cobalt, Nickel. 

„ (6) Ruthenium, Rhodium, Palladium. 

' „ (c) Osmium, Iridium, Platinum. 

527 The metals placed by Mendeleev in the eighth vertical 
group form a very remarkable feature of his arrangement of the 
elements. They occur in three sub-groups, each containing three 
metals, forming the termination of the even horizontal series 
4 ,« 6^ and 10, each group being the connecting link between 
the elements of. the even series which precedes and those of 
the odd series which follows. The three metals which make up 
each horizontal sub-group resemble one another very closely, 
and differ much less in atomic weight, atomic volume, and 
general physical properties than is usual in the successive 
elements of a horizontal series, as may readily be seen by a 
reference to Lothar Meyer’s diagram (p. 62 ). 

This remarkable similarity is borne out by the chemical 
behaviour of these elements, the -various platinum metals, for 
example, being so similar that their separation from each other 
is a matter of the greatest difficulty, and this is true also of 
cobalt and nickel. 

At the same time, a certain degree of similarity can be traced 
between those metals which are in the same vertical column, 
more particularly in sub-groups b and c. Thus ruthenium and 
osmium, rhodium and iridium, palladium and platinum agree 
very closely in many of their most characteristic properties, 
such, for example, as the formation of a tetroxide, which is 
peculiar to ruthenium and osmium, etc. 

From the analogy of the preceding groups, it would be 
expected that the characteristic oxide of the metals of this 
group would have the formula MO4 or MaOa- Actually, how- 
ever, only ruthenium and osmium form such an oxide, and 
this is not an acidic oxide, whilst all the metals of the group 
form lower oxides, many of which correspond to series of stable 
salts. 


1208 



IRON 


1209 


All these metals, unlike the other members of the even 
series of the periodic system, form metallo-organic compounds.^ 
A very characteristic property of the metals of this group is 
their tendency to form complex radicles with other elements or 
groups, which then act as basic or acidic radicles, and thus give 
rise to extended series of compounds. These substances, as a 
rule, differ entirely in properties from the ordinary salts of » the 
metal, this being due to the fact that each radicle has its own 
characteristic properties, and those of the metal appear only 
when the radicle has been broken up. Some of the most 
important of these complex derivatives are the double cyanides, 
such as the ferrocyanides and their analogues, the complex 
halogen derivatives of the platinum metals, the ammoniacal 
derivatives of cobalt and of the platinum metals, the double 
nitrites, sulphites, etc. This tendency is shared by chromium 
and to some extent by manganese, copper, and other metals 
which either immediately precede or follow the metals of 
Group VIII in the periodic system. 


SUB-GKOUP (a). THE IRON GROUP. , 

Iron, Cobalt, Nickel. 

528 These three metals are all magnetic, melt at a high tem- 
perature, are oxidised when strongly heated in air or oxygen, 
and decompose steam at a red heat. They all form basic oxides of 
the formula M*^0, and a corresponding series of coloured salts 
in which the metal is divalent. The sesquioxides also 

act as basic oxides, but the corresponding salts of nickel and 
cobalt are so unstable that they speedily decompose with forma- 
tion of salts corresponding to the lower oxide. Those of iron, 
on the other hand, are much more stable, and are formed from 
those of the lower oxide on exposure to the air. These metals, 
moreover, all yield oxides of the formula M3O4, to which no 
stable salts correspond, and which are probably to be considered ^ 
as being themselves salts of the formulfi Cobalt, in 

addition to these, probably forms an unstable acidic dioxide, 
whilst derivatives of the corresponding nickel oxide are also 
known, but no such derivatives of iron have been prepared, 
although the corresponding sulphide exists as iron pyrites. Iron, 

1 Pope and Peachey, Proc. Chem. Soc.t 1907, 28, 86, 



1210 


IRON 


however, forms a seri^ of compounds known as the ferrates, 
which* are derived from a hypothetical acidic trioxide, FeOg, to 
which no analogue is known among the compounds of nickel and 
cobalt. 

Nickel and iron both unite with carbon monoxide to form 
volatile liquids, whereas cobalt forms a crystalline carbonyl. 

Nickel has much less tendency to form complex radicles than 
cobalt or iron, the most important of such derivatives formed 
by the last two being the cobaltammines and the cyanogen 
compounds of iron. 

IRON (FERRUM). Fe = S5*84. At. No. 26. 

529 Iron is the most important of all the metals. It seldom 
occurs in the metallic state in nature; the ores of iron are, 
however, found widely distributed. It is usually supposed that 
the iron age followed those of copper and bronze, although in 
many cases the art of working in iron became known at a very 
early period. It is, however, to be remembered that metallic 
iron is rapidly .destroyed by rusting, at any rate in damp 
situations, and this may to some extent account for the com- 
paratively rare occurrence of very early iron implements. 

It appears probable that iron was first obtained from its ores 
in India, and it is certain that both the Assyrians and the 
Egyptians employed iron implements many centuries before our 
era. In the Pentateuch the metal iron is mentioned, as well 
as the furnaces in which it was prepared ; the Hebrew name for 
iron, Barz 41 , is derived from the root Bazal, which signifies ‘‘ to be 
hard,*' whilst the derivation of the Greek word aiBrjpo^f which 
occurs in Homer, is unknown. The Greeks obtained their iron 
from the Chalybes, a nation dwelling on the south coast of the 
Black Sea, from whom the Asiatic nations also obtained the metal. 
The Romans, on the other hand, procured their iron, not only 
from this district, but also from Spain, Elba, and Noricum. The 
Elban iron mines, which are to this day renowned for their fine 
specular iron, were worked by the Etruscans. 

The word iron, which is identical with the Scandinavian 
“ iam ” (instead of “ isarn ”), and with the German “ Eisen ” 
(adjective, ** eisem ”), appears to be connected with the Sanscrit 
“ ayas ’’ (Latin ** aes ”), and chis, according to Grimm, is an indi- 
cation that bronze was in use among the Germans at a much 
earlier date than iron. The alchemists connected iron with 
Mars, the god of war, and gave to it the sign 



IRON 


1211 


— : — : — : 

Native iron occurs, according to Andrews,^ in small spiculsc 

distributed throughout the basalt of the Giant’s Causeway, as 
well as in the old lavas of the Auvergne. The occurrence of 
terrestrial iron in large lumps has also been observed; tliese 
masses have, however, probably been formed in the firing.of coal- 
pits when the burning mass has come in contact with ores of 
iron ; the product is termed natural steel. 

The native metal occurs more frequently in the form of 
meteoric iron. The meteorites falling in larger or smaller masses 
from extra-terrestrial sources may be divided into two groups : 
“ Earthy meteorites,” which consist chiefly of silicates, and 
“ Meteoric irons,” which consist of iron together with a larger 
or smaller quantity of nickel, the presence of this latter metal 
being characteristic of meteoric masses.^ Meteoric iron likewise 
usually contains small quantities of cobalt and other metals, as 
well as graphite, ferrous sulphide, and schreibersite, (Fe,Ni,0o)5P, 
this last compound being one which is not 
known to exist in any terrestrial mineral. 

When the surface of a meteoric iron is planed 
and polished, and then treated with dilute 
nitric acid, peculiar configurations make their 
appearance which were first noticed by Wid- 
manstatten in the year 1808. These consist 
of rhombic folia or crystalline markings (shown in Fig. 191) 
which have a metallic lustre; the spaces enclosed by these 
markings are somewhat raised, so that a surface of meteoric iron 
thus treated may be used as a plate from which an engraving 
can be obtained. Similar structures have been artificially ob- 
tained in iron, steel and other alloys by slow cooling. Meteoric 
iron frequently occurs in considerable masses ; thus, for instance, 
that which was discovered by Pallas in Siberia originally weighed 
800 kilos, [analysis (a)], whilst that found in Bahia weighed 
nearly 7,000 kilos. ; a still larger mass occurs at Chaco-Gualamba 
in Peru, which is said to weigh 16,000 kilos., and similar large 
masses have been found in other localities, both in North and 
South America, as well as in Africa. The largest known masses 
are those found at Ovifak on the Island of Disko, off Greenland, 
where fifteen blocks of meteoric iron occur, the weight of the 

^ Brit. Assoc. Beporis, 1862, 34. 

“ See Fletcher’s Introduction to the Study of Meteorites (published by the 
Trustees of the British Museum, 1904). See also Prior, Min. Mag., 1916, 18r 
26; 1920, 19i 61. 



Fig. 191. 



1212 


mm 

two largest being, according to Nordenskjold,^ 21,000 and 8,000 
kilos, '[analysis (6)]. 

The following table gives the composition of several meteoric 
irons : 



(a) 

(&) 

{c) 

id) 

Locality. 

Siberia. 

Ovifak. 

Brazil. 

Tennessee. 

Analyst. 

Berzelius. 

Nordenskjold. 

Damover. 

J. L. Smith. 

Iron . . 

. 88«04 

84*40 

63*69 

91*16 

Nickel . . 

. 10*73 

2*48 

33*97 

8*01 

Cobalt . . 

. 0*46 

0*07 

1*48 

0*72 

Copper 

. 0*07 

0*27 

0*05 

0*06 

Manganese 

0*13 

— 

— 

— 

Carbon 

. 0*04 

10*62 

0*02 


Sulphur . 

. trace 

1*52 

0*02 

— 

Phosphorus 

— 

0*20 

0*05 

— 

Chlorine . 

— 

0*72 


_ 

Silicate 

. 0*53 

0*09 

— 

— 


100*00 

100*46 

99*28 

99*94 


Finely divided meteoric iron is constantly falling from extra- 
terrestrial space on to the earth : the occurrence of this meteoric 
dust has been observed in Sweden and in the snow-fields of 
Northern Siberia, the snow enclosing black magnetic particles 
which contain cobalt as well as iron. Similar particles of 
meteoric dust, consisting of metallic iron, have been found 
by Murray, of the Challenger expedition, at great depths in mid- 
ocean. It is only under conditions such as the above that it is 
possible to detect this fine meteoric dust, in consequence of the 
enormous accumulation elsewhere of terrestrial dust. 

■ 530 Iron is usually found in combination either with oxygen 
or sulphur. Of the large Humber of minerals which contain iron 
only those will now be mentioned which occur most commonly 
and in the largest quantity; the ores will be specially described 
hereafter. The most important oxygen compounds of iron are 
red haematite, or specular iron ore, FcjOg; brown haematite, 
2Fe303,3H20 ; magnetic iron ore, Fe304 ; spathic iron ore, FeCb3, 
the latter containing other isomorphous carbonates. Again, 
iron pyrites, FeSg, occufs largely, whilst magnetic pyrites, 
Fe^Sg, is less common; iron sulphide also forms an important 
constituent of copper pyrites, CuFeSg, arsenical pyrites, FeAsS, 
and other minerals. Silicates of iron are found in most geological 
* Pogg. Am., 1874, m, 154. 




lEON 1213 

^ ^ ^ — 

formations) and from these iron oxide finds its way into the soil, 

in which it is usually present in considerable quantity, imparting 
to it a reddish or brown colour. This fact was known to Pliny, 
who mentions that the presence of iron may be recognised by 
the colour of the soil. Iron compounds are contained in solution 
in spring- and river-waters, as well as in the water of the ocean, 
and it is from one or other of these sources that plants obtain 
the iron which forms an essential constituent of their chlorophyll. 

In 1702 N. Lemery proved that the ashes of plants contained 
iron : this observation was confirmed by the experiments of 
Geo&oy in 1705, who, however, assumed that the iron was not 
originally contained in the plants, but that it was produced 
when they were burned. Other celebrated chemists, such as 
Becher, held the view that the iron which made its appearance 
when certain substances were subjected to chemical treatment 
was not contained in them, but was produced independently. 
This erroneous opinion was first disproved by Lemery. 

Iron likewise is a necessary constituent of the animal 
body ; for instance, haemoglobin, the red colouring matter of the 
blood, contains 0*336 per cent, of iron. Iron preparations have 
also long been employed as medicine, especially in anaemia. 
After the use of iron the number of red corpuscles is increased, 
and the amount of haemoglobin which they contain becomes 
larger. The presence of iron in the blood was first shown by 
Menghini of Bologna in 1747. 

The existence of iron in large quantities in meteoric masses 
indicates a wide cosmical distribution of the element, and this 
conclusion has been confirmed by spectrum analysis, which 
indicates the presence of iron in the sun and many fixed stars. 

531 Preparation of Pure Iron . — Iron is usually produced from 
its oxides by reduction with carbon, and is thus obtained on the 
large scale; thus prepared, however, iron is not pure, but 
contains carbon. In order to obtain chemically pure iron, the 
oxide, or oxalate, may be heated in a current of hydrogen at 
the lowest possible temperature; the metal is obtained by this 
process as a black powder which oxidises and becomes incandes- 
cei),t in the air ; if the reduction is carried on at a higher 
temperature the powdered iron is not jpyrophoric. Reduction at 
1000 ° of the oxide or basic nitrate made by heating very carefully 
purified ferric nitrate gives a product with a distinct metallic 
lustre and a light grey colour. The iron thus obtained is of 
exceptional purity and is remarkably inert.^ 

^ Lambert and Thomflon, Joum. Chem. 8oe,, 1010, 97, 2430. 



1214 


IROJSf 


Pure iron may be prefared also by electrolysis ; ^ this process 
has received considerable aittention during, recent years and 
deposits containing 99-98 per cent, of iron have been obtained. 
Two solutions from which satisfactory deposits can be obtained 
have been used on an industrial scale. One consists of a highly 
concentrated solution of ferrous and calcium chlorides, which is 
used at a temperature between 90° and 110° with a current 
density of 180 amperes per square foot of cathode area. The 
other solution consists of a concentrated solution of ferrous 
and sodium sulphates; it is used at a temperature near the 
boiling point with a high current density. Electrolytic deposition 
has also been used for making up worn surfaces of machinery 
to correct gauge. 

Properties — iron has a specific gravity of 7*86, pos- 
sesses an almost silver-white lustre, and takes a high polish; 
it^isf with the exception of cobalt and nickel, the most tenacious 
of all the ductile metals at the ordinary temperature, but 
becomes brittle at the temperature of liquid air.^ Its average 
specific heat over 15-100° is 0*10983, but this increases some- 
what rapidly with the temperature up to 850°, after which it 
decreases.^ 

Pure iron becomes soft at a red heat, and may be readily 
welded at a white heat, but above the welding point it becomes 
brittle under the hammer. It fuses less readily than commer- 
cial wrought iron, the melting point being 1505-1520°,^ and 
when heated in the electric furnace it readily distils, much 
frothing taking place in the boiling liquid owing to the 
evolution of occluded gases.^ It is attracted by the magnet and 
may also be rendered magnetic, but loses this property rapidly. 
Carbonised iron or steel, on the other hand, retains its magnetic 
property at the ordinary temperature, but loses it at a red 
heat. 

When iron is heated from the ordinary temperature to the 
melting point, it undergoes three changes. These changes are 

^ Maximowitsoh, Zeit. Ekklrochem.t 1905, 11, 52; Byss and Bogomolny, 
ibid., 1900, 12, 097. Compare Ambeig, ibid., 1908, 14, 320; 1910, 16, 125; 
Miiller, MetaUurgie, 1909, 6, 145: Pfaff, Zeit. EUdctrochem., 1910, 16, 217. 
Fischer and Quillet, J. Iron gnd Steel Inst., 1914, 90, 00; Hughes, The 
Electrician, 1920, 86, 530. 

> Dewar and Hadfield, Proc. Boy. Soc., 1905, 74, 320. 

® Barker, PhU. Mag., 1906, [0], 10, 430. 

* See Carpenter, J. Iron Steel Inst,, 1908, 78, 290. 

‘ Moissan, Compt, rend., 1900, 142, 425. 





1215 


lacGompani^ by an absorption of bea^ v^nd the cipre of heating 
0 a^bits corresponding breaks. Similaily, when molten iroi\ is 
looted, these changes occur in the reverse order, accompanied by 
t of heat, and the cooling curve exhibits similar breaks, 
g to an inertia on the part of the iron to undergo these 
the temperature at which each occurs is different 
as the metal is heated or cooled; the breaks on {he 
5 curve are slightly lower than the corresponding ones on 
. , pleating curve. The explanation of these changes lies in the 
iron exists in four allotropic forms/ distinguished as 
7 - and S-iron (ferrite), though some regard the /S-modifica- 
a solid solution of 7 - in a-ferrite.® The a-form, which is 
|||0 me constituent of pure soft iron and is capable of assuming 
hj^etic properties, is stable from the ordinary temperature up 
id ^bput 760°, when the first change occurs, coinciding with the 
lisappearance of magnetic properties ; the yS-form is stable from 
his point up to about 900°, when the second change takes place ; 
he 7 -form, which is the variety usually formed on solidification 
i the fused metal, is stable from this to about 1400°, when the 
bird change occurs ; the 8 -form is stable from here to the melting 
oint (1506°). The a-, j3-, and 7 -forms all crystallise in the 
Bgular system ; the a- and ) 8 -forms possess a space-centred and 
the 7 -form a face-centred cubic lattice.® 

Iron combines readily with the elements of the chlorine 
group, and when strongly heated burns in oxygen, forming 
the magnetic oxide, and at a red heat decomposes steam 
with formation of the same oxide; it also burns at a red 
heat in sulphur vapour, and combines with carbon at a high 
temperature. 

Iron readily occludes many gases, notably hydrogen, nitrogen, 
and the oxides of carbon. . The solubilities of hydrogen and 
nitrogen in iron have been studied * and found to be proportional 
to the square root of the pressure of the gas. The solubility 
increases with temperature, and shows a marked alteration near 
the transition point, namely, at 930°. The excess of gas is 


^ Osmond and Cartaud, Ann. des Mines, 1901, 1?* 110; 18, 113; Oompt. 
rend., 1006, 142, 1630; 14i^ 44; Buer and Qoeiens, Ferrum, 1915, 18, 1. 

* Benedioks, /. Iron Steel Inst., 1912, 86, 241^: Eigh^ Inter. Cong. App. 
Chem., 1912, 22, 13; Carpenter, Iron Steel Inst., 1913, i., 315; Sauver, J. 
Inst, Metals, 1913, 88, 171. 

* Westgren and Lindh, Zeit. pliyeikal, Chem., 1921, 98, 181 ; Westgren and 
Phragmdn, ibid., 1922, 102, 1. 

« SieverU, ibid., 1007, 60, 129; Jnrisoh, Stahl und Eisen, 1914, 84, 252. 

’ VOL. n. (II.) CO 


1216 IRON 


liberated on cooling the molten metal, and that retained by the 
sohd may be removed by heating it in vacuo. 

Iron is also permeable to hydrogen. If an iron tube is immersed 
in acid ^ or used as cathode in electrolysis ^ the liberated hydrogen 
diffuses through the metal to the inside. Diffusion of molecular 
hydrogen through iron begins at about 350 ° and rapidly increases 
with temperature.® During its passage it combines with any 
sulphur, carbon, or phosphorus which may be present, thus 
removing them and rendering the iron soft.* 

Iron dissolves in most dilute acids with evolution of hydrogen. 
Dilute nitric acid dissolves it in the cold without the evolution 
of any gas and with the formation of ferrous nitrate, Fe(N03)2, 
and ammonium nitrate; when heat is applied, or when a 
stronger acid is employed, oxides of nitrogen are evolved, and 
ferric nitrate, re(N03)3, is formed. 

Passive /row.— When iron is placed in concentrated nitric 
acid it appears to undergo a change, and is then not attacked 
by the acid.® It will then not precipitate metals, such as copper, 
from solutions of their salts, and is highly resistant to rusting. 
Iron in this state is termed ‘‘ passive.’^ This condition may be 
brought about by the action, not only of nitric acid, but also of ♦ 
other substances such as chloric, bromic, iodic, and chromic 
acids, and even hydrogen peroxide, as well as by electrolysis, the 
iron acting as anode in sulphuric acid solution.® 

The cause of this phenomenon has not yet been definitely 
ascertained, and many suggestions have been made to account 
for it. It is possible that there are more kinds of passivity than 
one, and that no theory will cover all cases. Schonbein, Faraday, 
and Beetz regarded it as due to the formation of a thin film of 
oxide on the surface of the iron, which protects it from further 
action, and this film, according to Haber and Goldschmidt,'^ 

■ possesses metallic conductivity. 

1 Fuller, Trans. Amer. Elect. Soc., 36. 

* Charpy and Bonnerot, Compt. rend., 1912, 164, 592; Fuller, loc. cit. 

* Charpy and Bonnerot, Compt. rend., 1913, 156, 394; Bcllati and Lussana, 
Nuovo Cim., 1913, [6], 5 , i.> 389. See also Smits, Stahl und Eisen, 1919, 39, 3, 
73, 406; Schmidt and Lhoke, Zeit. physikal. Chem., 1921, 98, 152. 

* Kier, Phil. Trarts., 1790, 80, 359. See also Young and Hogg, J. Physical 
Chem., 1915, 19, 617. 

^ See Gunther and Schulze, Zeit. Elektrochem., 1912, 18, 326 ; Flade and 
Koch, Zeit. physikal. Chem., 1914, 88, 307. 

* Friend, Joum. Chem. 8oc., 1912, 101, 50. 

* Zeit. Elektrochem., 1906, 18, 49. See also Gordon and Clark, J. Amer. 
Chem. Soc., 1906, 28, 1634; Byen, ibid., 1908, 30, 1718; Krassa, Zeit. 
Elektrochem., 1909, 15, 490; Dunstan and Hill, Joum. Chem. Soc., 1911, 99, 1853. 



IKON 


1217 


“ ' ~ i ^ m 

Fredenliageii 1 supports the hypoth’dsis that ip the passive 
condition the iron is coated with a thin layer of gas, and points 
out that iron rendered ‘passive by anodic polarisation ^s a 
different behaviour from that made passive by nitric acid, 
probably because the protective layer is oxygen in the one 
case, and nitric oxide in the other. Iron is readily rendered 
passive to a marked degree by nitrogen tetroxide and the presence 
of a film of this gas has also been suggested as the cause of 
passivity.2 Hittorf,® Hcathcote,* and Finkelstein,® on the other 
hand, regard the phenomenon as due to a chemical or electrical 
change taldng place in the molecules forming the surface of the 
iron, the last-named author suggesting that ordinary iron consists 
of both ferrous and ferric iron molecules, and that by the action 
of the above substances the ferrous iron molecules are dissolved 
or converted into ferric molecules, which are not capable of 
attack by the reagents.® A similar idea is found in the theory 
of Smits,’ who postulates two kinds of iron : a, base, and 
noble, which are in equilibrium. During anodic polarisation, or 
in nitric acid, the metal dissolves quicker than equilibrium can 
be established, and consequently there is produced on the surface 
•^n excess of /9 iron, the noble variety, so that the metal is resistant 
to attack or, in other words, is passive. Hydrogen (as also the 
halogens) tends to accelerate the change of to a. During 
anodic polarisation or when the metal is dipped in nitric acid 
the hydrogen it contains is completely removed from the surface 
by oxidation. In either case, therefore, the passivity produced 
will persist until hydrogen diffuses from the interior of the metal 
to the surface, when the equilibrium is accelerated, the a Variety 
being re-formed, and the metal becomes active again. 

liambert and Thomson® have prepared iron of exceptional 
purity and found it to be extremely resistant to chemical action, 
or, in other words, ** passive.*^ It would therefore appear that 
pure iron is passive,® and Lambert has proposed the following 

^ Zeit. physikal, Chem,, 1903, 43, 1; 1908, 63, 1. 

* Young and Hogg, loc. cit. * Zeit. physikaL Chem.t 1900, 34, 386. 

« IMd., 1901, 37, 368; J. Soc. Chem. Ind., 1907, 26, 899. 

» Ibid., 1902, 39, 91, 

® See also Smits and Lobry de Bruyn, Proc. K. Akad, Wetensch. Amierdam, 
1917, 19, 880; Brown, J. Phya. Chem., 1921, 26, 429. 

’ J. Soc. Chem. Ind., 1916, 35, 928; De Ingenieur, 1916, 357. See also 
Smits, The Theory of Allotropy (Longmans), 1922, p. ^2. 

^ Joum. Chem. Soc., 1910, 97, 2426. 

* See also Flade and Koeh, Zeit. Ekktrochem., 1911, 18, 335. 

‘ Joum. Chem. Soc., 1916, 107, 218. 



1218 IRON 

^ — ' 

definition of passivity : •The .production by some chemical or 
electrochemical means of a physically homogeneous layer on the 
surface of a metal of which the surface Vas originally phjrsically 
heterogeneous. 

Passive iron is rendered active again by chlorine, bromine, or 
iodine ions. Anodic polarisation by electrolysis of an iron salt 
can be made periodic by the addition of chlorine ions to the 
solution.' 

Findy Divided or Deduced Iron (ferrum redactum) has long 
been used in medicine. Spongy iron^ prepared by the reduction 
of burnt pyrites or other suitable iron ore, has been employed 
as filtering material for purifying water for domestic use. 

532 The Dusting of The formation of rust on exposed 
surfaces of iron was formerly supposed to be due to direct 
oxidation of the metal. However, contact with both air and 
water in the liquid state is necessary for the production of rust .2 

The investigations of Crace-Calvert ® and Crum Brown* 
indicated that carbon dioxide, too, plays an essential part in the 
reaction, and in most cases of rusting it is certainly an active 
agent. The feebly acid solution of carbon dioxide in water 
attacks the iron with considerable rapidity, yielding a solution 
of ferrous carbonate or bicarbonate. This is then oxidised by 
the oxygen with formation of hydrated ferric oxide and evolution 
of carbon dioxide, which is thus available for further attack, its 
action therefore being catalytic : 

Fe + 2H2O + 2CO2 = Fe(HC03)2 + 

' 4Fe(HC03)a + 2 H 3 O + 0 ^ = 4Fe(OH)3 + SCO^. 

Dunstan, Jowett, and Goulding^ have suggested that the 
presence of carbon dioxide is not essential, but that the iron acts 
on the water and oxygen with formation of ferrous oxide and 
hydrogen peroxide. These two substances then interact with 
formation of hydrated ferric oxide : 

Fe + O2 + HjO = FeO + Efi^ 

2Fe0 + H20a = Fe20a(0H)3, 

‘ Smits and Lobiy de hrayn, Proc, K. Akad, Weknsch. Amterdam, 1916, 
18, 807. 

* Bonstan, Jowett, and Oonlding, Joum, Chem, Soc.f 1905, 87, 1548; Pfoe, 
Chem. 8oc,t 1907, 88, 63. 

s Mm. Manch. Phil 80c., 1876, 5, 104. 

* J, Ir(m 8ted Insl, 1888, ii., 129. * Loc. cil 


iitpN 

the excess of hydrogen peroxide imme^ately reacting with iron^ 
to form a further quantity of rust. No evidench of the inter- 
mediate formation of hydrogen peroxide has been found, fhe 
authors basing their conclusion mainly on the fact that substances 
which destroy hydrogen peroxide appear also to prevent rusting. 

Water is itself dissociated into H and OH' ions, and Whitney ^ 
has suggested that iron combines directly with the OH' ions to 
form ferrous hydroxide while hydrogen is liberated. The function 
of the oxygen is to oxidise the ferrous hydroxide to rust and 
also the hydrogen, thus disturbing the equilibrium and allowing 
the reaction to proceed further. 

Whether pure oxygen and water in the complete absence of 
carbon dioxide or other acid will cause iron to rust has been the 
subject of much discussion. The researches of Moody ^ showed 
that under such conditions no rusting occurred. In his experi- 
ments, however, the iron was cleaned by means of chromic acid, 
and the criticism has been made that it was thereby rendered 
passive. Lambert and Thomson ® found that an exceptionally 
pure sample of iron made by the reduction of carefully purified 
ferric nitrate did not rust, and it is therefore probable that the 
I non-rusting of Moody’s iron can be accounted for by the thorough 
cleaning of the metal. Lambert ^ consequently concludes that 
only an impure iron will rust, and that rusting is due to differences 
of solution tension of different parts of a heterogeneous surface 
of impure metal. The process is an electrolytic one and the 
oxygen acts as a depolariser by oxidising the hydrogen.^ 

The formation of rust takes place to begin with but slowly, 
but as soon as a thin, superficial layer of rust has been formed » 
the process goes on rapidly. There is a difference of potential 
between rust and metal, so that electrolytic action is further 
increased.® Friend ’ has suggested that rusting itself is due to 
the catalytic action of a sol of a higher oxide of iron which oxidises 
the iron and is thus reduced, but is oxidised again by oxygen. 
He has shown that iron does not rust as quickly in moving 

^ J, Amer, Chan, Soc., 1903, 2(^, 394. 

* Joum. Chem. 8oc., 1906, 89, 720; Proc. Chm. Soc., 1907, 28, 84. 

* Joum, Chm. Soc.t 1910, 97, 2426. 

« Hid., 1912, 101, 2066; ibid., 1916, 107, 218 Proc. Chm. 8oc., 1912, 28, 
197; Tram. Faraday 8oc., 1913, 9, 108. 

* See also Aitchison, J. Iron Steel Inst., 1916, 1, 77; Goudriaan, Chm. 
Weekblad, 1919, 18, [40], 1270. 

* See Aston, Trane. Amer. Elect. 8oc., 1916, 29, 449. 

’ Joum. Chm. Soc., 1921, 119, 932; see also KoU. Zeit., 1921, 28, 207. 




’"water which would remgve the sol, and that those substances 
which precipitate, dehydrate, dissolve, or act as protective colloids 
to* the sol, also decrease rusting. 

Certain salts, especially those of ammonia,^ promote rusting, 
while alkalis and alkali carbonates inhibit it.^ 

Steel instruments may be kept bright by immersion in a 
solution of caustic soda, or, better, of sodium nitrate. In order 
to lessen the liability to rust, iron articles are coated with varnish 
or oil-paints, or the surface is covered with oil, grease, or graphite. 
A coating of magnetic oxide of iron, Fe 304 , is, however, the most 
efficient protection, and to obtain such a coating articles of iron 
are subjected to the action of superheated steam at a temperature 
of about 650°, this process being known, from the name of its 
inventor, as the Barff process. 

In contact with zinc, iron becomes electronegative, and is 
thereby to a considerable extent prevented from rusting. Iron 
articles are therefore often covered with a coating of zinc to 
protect them from atmospheric corrosion. This is usually done 
by immersing the cleaned iron article in a bath of molten zinc 
(galvanising) or by packing the iron round with zinc dust in a 
closed chamber and heating to just below the melting point of * 
zinc (sherardising). The former method is more extensively 
employed, but the latter gives a more resistant product.® Iron 
is also coated with tin by immersion in the molten metal (tin- 
plate) but in this case the protection lasts only as long as the 
layer of tin is intact. Once a portion of the iron becomes exposed 
it rusts much more rapidly than if no tin were present, because 
iron is electropositive in contact with tin. The coating of iron 
with nickel by electro-plating is another important method of 
protecting it from atmospheric action. 

By alloying chromium with steel, a product is obtained which 
is capable of resisting all ordinary corrosive agents. It is put on 
- the market as rustless or stainless steel. 

533 Iron amalgam does not form readily, but on acting with 
a 1 per cent, sodium amalgam upon a solution of ferrous 
sulphate a semi-solid mass is obtained which, when in small 
globules, is attracted by the magnet. On distilling this 
amalgam, metallic irop remains in a state of fine division 

1 See Vaubel, Chem. Zeit., 1913, 87» 693. 

* See Friend and Marshall, Jmm. Chem. Soc., 1914, 106, 2776; Pm. 
Chem. 8oc.t 1914, 30, 263. 

* Halla, Zeit, Ekktrochem., 1913, U, 221. 




METALLXmGY OF lEON , 1221 

(Bottger). The same amalgam can^be formed by rubbing 
powdered iron with mercuric chloride and water. If an iron 
wire be attached to the copper pole of a Daniell element, and 
dipped into a solution of ferrous sulphate, whilst another iron 
wire from the zinc pole touches a drop of mercury lying in 
the solution, amalgams of varying composition are obtained 
according to the intensity of the current.^ Those containing 
only small quantities of iron are liquid; those in which more 
iron is present are soft and crystalline. One containing 103*2 
of iron to 100 of mercury forms a hard, black mass, and is obtained 
by submitting the liquid amalgam to a pressure of 60 tons to the 
square inch. 


METALLURGY OF IRON.* 

534 Several mythical stories point to the fact that in very 
early times meteoric iron, which, falling from the heavens, was 
considered as a gift of the gods to man, was employed in the 
manufacture of iron weapons. Kumbary® relates that the 
chiefs in the Wadai country, in Central Africa, possess many 
weapons which have been worked up from meteoric masses. 
But meteoric iron occurs so sparingly upon the earth’s surface, 
and is, in fact, so unsuited to the manufacture of tough forgings, 
that at a comparatively early period in the history of Civilisation 
men set about the smelting of iron from its ores.^ 

The enormous deposits of ancient slag and furnace-cinder 
which are found spread over large areas in various districts of 
India point to the fact that the iron industry existed in that 
country in very early times, and even to the present day the 
manufacture of iron is carried on in India in the most primitive 
manner. It is also clear that the ancient Assyrians and 
Eg 3 q)tians were well acquainted with the uses of iron, and the 
remains of their iron works have been found near Sinai. But, 
independently of these sources, a knowledge of the methods of 
working iron ores also appears to have been gained by the 
tribes living in the North of Europe, whilst the inhabitants 
of the Western Hemisphere were not acquainted with these pro- 
cesses. Little is known respecting the method employed by the 

• 

^ Joule, Joum, Chem. Soc.^ 1803, 16, 378. 

* Further information on this subject may be obtained from the metal- 
lui^ioal works of Percy, Turner, Howe, Harbord, Sexton, and Carnegie. 

* Compt. rend., 1870, 70, 649. 

^ See “ The Early Use of Iron,*' Brough, J. Iron Steel Inst, 1900, 69, 233. 



ancients in the manufacture of iron ; the slight information which 
we possess has 'been collected together by Agricola in his works, 

De Veteribus et Novis Metallis,” and “ De Re Metallica.” ^ 
The apparatus employed was evidently of a primitive kind, and 
consisted of a small hearth or furnace to which was attached a 
bellpws or blowing arrangement driven by hand, similar indeed 
to that which is now in use among the hill-tribes in India and 
in Central Africa. Malleable iron and steel are both produced 
by igniting the iron ore with charcoal, the metal being obtained 
in the form of a porous lump or “ bloom,” which is pressed or 
hammered into a coherent metallic mass. 

The dexterity exhibited by the Hindus in the manufacture 
of wrought iron may be estimated from the fact of the existence 
near the Kutab Minar, Delhi, of a wrought iron pillar 24 feet in 
length.* This pillar stands about 22 feet out of the ground, and 
has an ornamental cap bearing an inscription in Sanskrit belonging 
to the fourth century. An analysis of specimens obtained from 
the actual pillar by Hadfield shows that the material is an 
excellent type of wrought iron, made with a very pure fuel, 
probably charcoal. 

535 Varieties of Iron and Steel.— hon which is obtained from 
its ores by metallurgical processes is never pure, but contains 
3ther constituents, which greatly afEect the properties of the 
netal and determine its value for various purposes. The most 
mportant of these constituents are carbon, silicon, phosphorus, 
lulphur, and manganese, and, in special cases, nickel, chromium, 
tungsten, vanadium, cobalt, and molybdenum. It is found that 
comparatively small variations in the amount of these substances 
exert an enormous influence on the properties of the metal. 

Four main varieties of commercial iron are usually dis- 
tinguished : 

(1) Cast iron contains 2*2-4*5 per cent, of carbon, besides 
varying quantities of the other elements mentioned above. 
This variety fuses readily, and when cold is brittle and cannot 
be worked under the hammer. 

(2) Wrought or malleable iron contains little carbon and 

^ See the translation from the Latin edition of 1656, by H. C. Hoover and 
L. H. Hoover; published by The Mining Magazine, 1912. 

* A cast of this pillar was formerly to be seen in the Architectural Court 
of the South Kensington Museum, but was destroyed during a fire in 1885. 
A drawing of the pillar is found in St. John Hay’s Prehistoric Vse of Iron 
and Steel, p. 144, and a reproduction from a photograph in the J. Iron Skel 
1912, 86, 168, Plate 14. 




1223 


BfBTALLURGY OF IRON 


fuses with difficulty, but is malleable aiyl can therefore be worked 
under the hammer, and can be welded at a red heat. The 
characteristic feature of malleable iron is that it is produced 
in a pasty state without having been melted, and consequently 
contains particles of slag, which cannot be completely removed 
from the unfused metal. 

(3) Steel comprises all malleable alloys of carbon and iron 
which have at any time been actually melted. It contains very 
little slag, but otherwise does not necessarily differ in composition 
from malleable iron. Steel possesses the valuable property of 
becoming hard when it is suddenly cooled from a high tempera- 
ture, the intensity of this effect depending largely upon the 
amount of carbon which it contains. 

(4) Special steels contain, besides carbon, varying quan- 
tities of one or more of the following elements : manganese, 
nickel, chromium, tungsten, silicon, vanadium, molybdenum, 
and cobalt. Some of these steels have valuable mechanical and 
physical properties not possessed by ordinary carbon steels. 

The general process of iron smelting consists essentially in 
the removal of the oxygen from the ores, and this is invariably 
carried out in practice by the action of carbon at a high tem- 
perature. In addition to the oxygen, the extraneous matter 
contained in the ore, such as silica, alumina, lime, sulphur, etc., 
must also be removed, and the resulting iron must be exposed to 
such conditions that it acquires the composition which will fit it 
for the special purpose to which it is to be applied. 

536 Ores of Iron . — The term iron ore includes only those 
minerals which contain iron both in sufficient quantity and also 
in a condition which enables them to be employed for the economic 
production of the metal. Thus, for example, iron pyrites, FeS 2 , 
which occurs in very large quantities and contains a high per- 
centage of iron, cannot properly be described as an iron ore, 
although it is used as a source of iron after the removal of sulphur 
for the manufacture of sulphuric acid. In like manner, arsenical 
P3rrites, although it also contains a large quantity of iron, is 
unfit for the production of the metal; and the same may be 
said of many other minerals which contain large quantities of 
iron. ^ 

” The various ores of iron are composed of, or yield, the oxides 
of iron in more or less pure condition, and the value of an iron 
ore is influenced by the nature of the impurities which it contains 
as well as by the percentage of iron. 




IRON 


im 


The ores of iron occur, in almost every geological formation; 
thus magnetic 'iron ore is found in the older rocks, as in the 
Laurentian beds of North America, and the old slates and 
gneisses of Sweden, whilst red haematite occurs in beds or 
pockets in the carboniferous limestone of Cumberland and 
North Lancashire, and spathic ore and clay iron stone in the coal 
measures. Again, the oolitic rocks furnish large deposits of 
brown haematite, and the Elba ore is probably a tertiary deposit. 
Still more recent formations of iron ore are seen in the bog ore 
of Germany and the North of Ireland, whilst “ lake ores ” are 
being formed in Scandinavia at the present day. Analyses of 
various ores are given on page 1227. 

Magnetic Iron Ore^ Magnetite^ or Loadstone, FegO^.— This ore, 
in the pure state, constitutes the richest ore of iron, containing 
724 per cent, of the metal. It occurs in the crystalline and 
massive state as well as in the form of sand, and is found in 
large deposits, especially in volcanic rocks, as well as in granite, 
gneiss, and mica-schist. The most important localities of 
magnetite are' Arendal, Dannemora, and other places in Norway, 
Sweden, and Lapland ; the island of Elba ; the Ural Mountains ; 
and several localities in the United States, especially near 
Lake Superior. In England, magnetic oxide of iron occurs on 
Dartmoor, at Brent in South Devon, and at Treskerby in 
Cornwall; but it cannot be said to be an important English 
ore. In Germany it is found in large quantities at Schmiedeberg, 
in Silesia, and a few other localities. 

Franklinite, (Fe,Mn) 203 ,(Fe,Zn) 0 , occurs in New Jersey, and is 
first worked for zinc, the residue being used as an iron ore for 
the production of spiegeleisen.^ 

Red Hcermtite, or Specnlar Iron Ore, FegOg.— This sub- 
stance occurs crystalline as specular iron ore, and also in a 
massive state having a columnar, granular, or botryoidal form, 
as well as in the earthy condition. Haematite occurs in veins as 
well as in beds and pockets. One of its most remarkable localities 
is the island of Elba, where it occurs finely crystallised between 
talcous schist and crystalline limestone. The Elba mines were 
worked by the Etruscans, and are still productive. A fine 
haematite occurs in the Puronian rocks on the southern shore of 
Lake Superior, whilst at Iron Mountain, near St. Louis, Missouri, 
enormous masses of this ore of iron are found. On the continent 
of Europe haematite occurs in Belgium, and deposits of this ore 
1 J. Iron Steel Inst., 18M, 45i 416. 




METALLURGY OF IRON 


122C 


are found also in the Devonian formation on the Lahn in West- 
phalia. The chief deposits of haematite in England are those 
near Ulverston in Lanoashire, and on the coast of Cumberland 
near Whitehaven; the ore here occurs in beds or pockets 
in the carboniferous limestone, sometimes existing as hard 
botryoidal masses exhibiting crystalline structure, and some- 
times in a soft or compact amorphous condition. 

Brmn Hcematite, or Limonite^ Fe203,2Fe(0H)3 = 2Fe203,3li20. 
— This substance occurs crystallised in rhombic prisms, but 
is more frequently found either in a fibrous, foliated, and 
scaly condition, or as a dark brown, reniform mass and commonly 
known as Brown and Yellow Haematite. In the massive state 
this ore occurs in large quantity, and, as it can be readily 
worked, it has been long employed as a source of iron. It is 
found in the carboniferous limestone as well as in the older 
rocks, in the Forest of Dean, and at Llantrissant in Glamorgan- 
shire in the lower coal measure sandstones. At Bilbao, in Spain, 
it occurs largely in the carboniferous limestone, whilst the newer 
and earthy brown haematite is found in the oolite and greensand 
in Northamptonshire and Lincolnshire. It is likewise largely 
worked in Germany and France, being the ore from which the 
greater part of the iron made in these countries is derived. The 
bog ores which are worked in the plains of North Germany and 
Canada and in other places, as well as the peculiar iron ore of 
the North of Ireland and the Swedish lake ore, belong to this 
class, and are of the most recent geological formation. 

Spathic Iron Ore, or Sideriie. — Spathic iron ore consists of 
ferrous carbonate, FeC03, invariably mixed with the isomor- 
phous carbonates of manganese, magnesium, and calcium. It 
possesses a yellowish-brown colour, and occurs often in globular 
or botryoidal forms having a silky, fibrous structure. It is usually 
found in Devonian rocks, occurring in England at Weardale in 
Yorkshire, at Brendon Hill in Somerset, and on Exmoor. 

Clay Iron-stone, or Argillaceons Iron Ore, is a spathic iron 
containing clay, and is chiefly found in nodules or bands inter- 
spersed throughout the clays and shales of the coal measures. 
It is the most important English ore of iron. The chief workable 
British beds occur in Yorkshire, Dopbyshire, Staffordshire, 
Warwickshire, South Wales, and Scotland. 

The black band iron-stone is an important variety of this 
ore. It contains from 20 to 26 per cent, of carbonaceous matter, 
and is found in Lanarkshire, North Staffordshire, and South 



im 


ism 


Waleft. The Scottish be^ were discovered by Mushet in 1800, 
but thejP were* not worked until the year 1830. In 1855 the 
same ore was discovered in Westphalia, and it is worked also in 
Lower Silesia. The coal measures of the Gard and of the 
Aveyron in France, and those in Pennsylvania and Maryland 
andjDther States, also contain large quantities of clay iron-stone. 
The same ore is found in strata in the lias and also in th^ 
oolitic and tertiary rocks, the Cleveland iron ore belonging to 
this last class. 

537 Preparation of Ores for Smelting,— In many cases iron ores 
require no preliminary treatment before smelting other than 
breaking to a size suitable for the furnace. The correct size will 
depend on the nature of the ore. In most cases it is not profitable 
to concentrate the ore or to separate it from associated impurities 
before smelting, but in the case of certain magnetites, magnetic 
separators are used which concentrate the ore and at the same 
time considerably reduce the amount of phosphorus which occurs 
as non-magnetic apatite. The concentrates, which have neces- 
sarily been crushed to a fine state, are afterwards briquetted in 
suitable presses and hardened by submitting to a high tem- 
perature. In some cases a binder is introduced before briquetting, 
the most common being lime, the briquettes in this case being 
submitted to the action of high pressure steam for hardening. 

Many methods of sintering, agglomerating or nodulising fine 
ores such as the residues of pyrites burners have been recently 
introduced, some of which are carried out in a similar manner to 
that used in the blast roasting of galena (p. 906). 

The carbonate ores, clay iron-stones and brown hsematites are 
submitted to a process of calcination prior to smelting. Cal- 
cination is carried out in kilns, and during the process water is 
expelled, carbonic acid driven off, sulphur reduced considerably, 
coaly matter burnt, and ferrous oxide converted into ferric oidde. 
The operation also results in a more porous material suitable for ^ 
reduction by the agency of carbon monoxide in the furnace. 

The Manufacjture of Iron.^ 

538 The application of the blast furnace to the manufacture 
of iron marks an era in the history of the iron industry, inasmuch 
as it was by its use that a continuous process of iron manufacture 

^ For further infonuation on this subject the reader is referred to Percy’s 
admirable “Sketch of the History of Iron,” Iron and 8ted, p. 873, and to 
Turner's Metallurgy of Iron, 1 tt etq. 





IRON 


became possible. The discovery of a process by which fusible 
iron can be prepared appears to have been made, probably 
accidentally, about the end of the fifteenth century, in Germany, 
where the Stuckofen had long, been in use for manufacturing 
blooms. No description of the process is, however, to be found 
in the older writers upon metallurgy. Thus Agricola, writing 
in J556, mentions only the older methods of iron making, 
although he appears to have been acquainted with cast iron; at 
any rate, the new method must have been at work in this 
country in 1543, for we find that in that year English cast iron 
cannons were used. The great demand for cast iron, which was 
all made with charcoal, soon leading to a destruction of our 
forests, it became necessary, in the first year of the reign of 
Elizabeth, to endeavour to replace charcoal by some other fuel. 
Tliis was accomplished by the employment of coke instead of 
charcoal, a practice which was carried out in England by Dudley 
as early as the first half of the seventeenth century, but which 
afterwards fell into abeyance. It was subsequently revived by 
Abraham Darby at Colebrookdale, about 1735'. 

The blast furnace consists of a shaft varying in height from 
50 to 100 feet, the largest diameter being 14 to 24 feet. The 
essential parts of the furnace are, first, the hearth or crucible, 
and, second, a shaft or chimney formed of two truncated cones 
joined at their bases, the upper being termed the “ body ” and 
the lower one the boshes.” Fig. 189 shows the construction 
of such a furnace on the scale of 1 : 180. 

The shaft. A, Fig. 192, is 75 feet high, the diameter at the 
widest part (the belly or bosh) being 20 feet, whilst at the 
throat, B, it is 16 feet, and at the hearth, c, 11 feet. The 
shaft is constructed of an outer shell of wrought iron or 
mild steel plates, supported by means of cast iron columns, 
D, and is lined with fire-brick. In the lining of the boshes, 
which is exposed to the highest temperature, cooling boxes 
are inserted. These consist of narrow, flat boxes made of bronze, 
which are built into the brickwork, and are cooled by a current 
of water, thus preventing the brickwork from becoming too hot. 
The wall of the hearth, which is also lined with fire-brick, is 
pierced by several openin^gs; the tapping hole, e, by means of 
which the molten iron is periodically withdrawn; the slag-notch 
(not shown in the diagram), which is situated at a higher level, 
and through which the lighter slag is allowed to flow away into 
trucks or ladles ; and, finally, the openings by which the blast o1 
air is introduced through the tuykes. 





mm 




The throat 9 ! the furniice is closed by a contrivance known as 
the cup and cone arrangement, first introduced by G. Parry at 
the Ebbw Vale works in 1850. It consists of a cast iron funnel, 
fixed at the mouth of the furnace, and closed by a cast iron cone, 
suspended at one end of a counterpoised lever, or by means of a 
chain and wheel. The charge is tipped from barrows on to 
the cone, and is introduced into the furnace by momentarily 
lowering the latter. When the cone is raised against the funnel 
(as shown in the figure) the throat of the furnace is closed, and 
the escape of gases into the air prevented; these then pass 
out of the furnace by the downcast, f, which is provided with 
a dust-catcher, G, and are, after further cleaning, conveyed 
through the main to the stoves for heating the blast, to the 
l)oilers, or to any other point where the heat produced .by 
their combustion can be made available. The gases are also 
frequently used direct in gas engines.^ 

The blast of air is introduced near the bottom of the furnace 
through tuyere holes, perforating the walls of the hearth. The 
tuykes are made of wrought iron, cast iron, or bronze, and have 
a double casing through which water circulates to keep them 
cool ; they vary in number from 8 to 16, according to the size 
of the furnace, are about 5 to 7 inches in diameter, and are 
fed from an annular pipe, h, which surrounds the lower part 
of the furnace, and is connected with the blowing engine. 

Hot and Cold Blast.~V^ to the year 1828 air was blown 
into the furnace at the ordinary atmospheric temperature, but 
in that year J. B. Neilson ^ patented a process for heating the 
air before it passed into the furnace, and this process, inasmuch 
as it saved from 16 to 26 per cent, of the fuel, and was also accom- 
panied by an increased productive power of the furnace, was 
soon generally adopted, although the cold blast is still employed 
in some works for the manufacture of certain brands of cold 
blast iron. For the purpose of heating the air, the waste gases 
from the furnace are burned in a Cowper’s or Whitwell’s stove 
or some modification of these, such as the Massick and Crookes, 
the Ford and Moncur, or the Cowper-Kennedy ; all these act 
on the principle of the Siemens regenerator, and after being heated 
sufficiently the gas supply is diverted and cold air passed through 
on its way to the furnace. The air is thus introduced at a 

^ Hubert, Keinhardt, and Webtgarth on Blast-furnace Gas Engines, J. Iron 
1906,71, 16-168. 

* Patent No. 6701, March 3id, 1828. 



xnjji JMLAJNUJJ’AUTUKJS OF IRON 


1231 


temperature of about 700® to 800®, and at a pressure of about 
5 lb. to the square inch. 

The total capacity of a furnace such as that described is about 
14,160 cubic feet, and it is capable of producing about 1,000 to 
1,300 tons of iron per week. 

Dry Air BhsL—kn important development in blast furnace 
practice is the drying of the air before passing it through the 
stoves.^ This is accomplished by drawing the air through 
refrigerators in which the moisture is removed. By this means 
it is possible imder certain climatic conditions to increase the 
burden and production of pig-iron by 20 per cent., to reduce 
the amount of coke per ton of iron by 18 per cent., and to diminish 
the duty on the blowing engines on account of the colder air 
being denser. The greatest advantage is, however, in the regu- 
larity of working the furnace, because the amount of moisture 
carried into the furnace by the blast varies very largely from day 
to day with change of atmospheric conditions, so that the burden 
of the furnace must have a safe margin of fuel to allow of a sudden 
loss of heat due to this cause. 

539 The Wwhing of the Furmce—'Eot the purpose of start- 
ing the newly-built blast furnace it is necessary that the whole 
should be gently heated by means of a fire, usually made by 
piling a quantity of rough dry timber in the hearth, on to the 
top of which charges of coke are placed. As soon as the shaft 
has become warm, regular charges of calcined iron-stone, Hme- 
stone, and coke are added, until the furnace is filled. The 
blast is then turned on to about one-fifth of the quantity usually 
employed, the size of the tuyeres being gradually increased 
until the furnace is in full work. 

The proportion of the materials employed, viz., iron ore, lime- 
stone, and fuel, termed the charge or burderiy varies consider- 
ably according to the nature of the ore. If it be sihceous or 
clayey, additions of Hme must be made ; whilst if the ore contain 
lime instead of silica, the addition of sihca may be required. 
The object of these additions is to form fusible slags, so that 
the gangue of the ore may be removed and the furnace kept open 
and in proper working. The slag consists of calcium and alu- 
minium silicates, and it is extremely important that it be kept 
of the right basicity and fusibility. If the supply of lime and 
alumina be insufficient to combine with the silica present, oxide 

^ Gayley, J. Iron Steel Inst.^ 1904, 66* 274; 1905, 67» 266. See also Daubing 
and Roy, J. Iron Steel Inet.f 1911, 88f 28. 

VOL. n. (II.) 


DD 




1282 JDROK 

of iron passes into the slag^ thus causing waste, whilst if an excess 
of these bases be used the lining of the furnace is attacked. 
The fusibility of the slag, moreover, determines the temperature 
which can be reached, and is therefore of great importance, 
as this has a great effect on the nature of the iron produced. 
The higher the temperature which is required for the reduction 
of the ore the less fusible must be the slag. As soon as the proper 
proportions between the fuel, ore, and limestone have been 
ascertained, it is of the greatest importance that these propor- 
tions should be strictly adhered to, and for this purpose the charges 
are regularly weighed or measured and supplied at the top of 
the furnace, into which they are charged by lowering the cone 
as already described. 

On the average about one ton of coke and 8 to 12 cwt. of lime- 
stone are required for each ton of iron produced, about 6 tons 
of heated air being used in the operation. When the furnace 
is in regular blast, a constant stream of slag passes out from the 
slag-hole, the iron collecting in the lower part of the hearth, 
and being from time to time tapped by piercing a plug of sand 
and clay by which the tap-hole has been closed. Before tapping, 
moulds are prepared for holding the metal; these are formed 
in the sand as a series of parallel trenches, which are placed 
in communication with the tap-hole. The blast of air is then shut 
off, and the tap-hole opened by piercing the plug with a long 
bar of iron. The molten iron flows into the channels communicat- 
ing with the moulds and assumes the form of semi-cylindrical 
bars or “ pigs ’’ united to one another by one of larger dimensions 
termed the “ sow.” 

If, owing to some accident to the machinery, a blast furnace 
is obliged to stand when hot, the operations may be suspended 
for several months if the throat and tuyke-holes are closed up 
with sand or clay. Should, however, serious damage have 
occurred, the furnace must be ** blown out.^’ This is accom- 
plished by reducing the burden, and thus increasing the tempera- 
ture for a time so as to remove any aggregations of solid matter 
which are fusible only at a high temperature. Finally only 
fuel is charged, the contents of the furnace are allowed to burn 
out, and the last tapping is made at a point as low down in 
the hearth as possible. The life of a blast furnace varies con- 
siderably, lasting from five to twelve years, or even for a longer 
time, according to circumstances. 

The size and shape of blast furnaces have been and continue 



1283 


r T!BM mm^AOrUlSiE OF IRON 

to be very different. When charcoal is employed, as was formerly 
universally the case, and is still so in countries where wood is 
plentiful, the furnace is usually only from 20 to 30 feet in height. 
The charcoal iron which is thus manufactured in Sweden, Russia, 
and America is especially valuable for the preparation of crucible 
steel. Blast furnaces in which the fuel used is either coke, 
anthracite, or splint coal, are, on the other hand, of much larger 
dimensions, the exact height and capacity of the furnace being 
regulated by the nature and amount of iron which has to be 
produced, as well as by the nature of the ore and fuel to be 
used. 

In the year 1750 each English blast furnace produced about 
300 tons of pig-iron per annum, whereas a large-size modern 
furnace yields up to 70,000 tons in the sa^e period. In the 
Cleveland district, where the blast furnaces are usually large, 
the average capacity of those built up to the year 1854 was 
about 7,000 cubic feet ; whilst those built during the years 1870 
and 1871 have an average capacity close upon 30,000 cubic 
feet; in some cases, however, the height rises to 105 feet, and 
the capacity to 50,000 cubic feet. The production of a blast 
furnace increases, of course, with its size, but not in a direct 
ratio; thus Lowthian Bell has shown that an old furnace of 
1853, having a capacity of 6,000 cubic feet, yielded one ton of 
iron per twenty-four hours for every 190 cubic feet of space; 
whilst in the high furnace built in 1870, 380 cubic feet of space 
are req