THE PLATINUM METALS 889 



metals, and as ammonia itself is able to combine -with acids, the 

 PtX 2 plays, as it tfere, the part of an acid with reference to the* 



like Pt(OH) 2 ; and such a salt as PtK 2 Cy 5 as PtCy(Cy a K) 2 , the analogue of PtX(OH) 2 , 

 or A1X(OH) 2 , and other compounds of the type RXj. 'Potassium ferricyanide and the 

 analogous compounds of cobalt, iridium, and rhodium, belong to the same'type, with the 

 same difference as there is between KX(OH) 3 and R(OH) S , since FeK3Cy 6 =Fe(Cy 2 K) 5 . 

 Limiting myself to these considerations, which may partially elucidate the nature 

 of double salts, I will now pasa 'again to the complex saline compounds known for 

 platinum. 



(A) On mixing a solution of potassium thiocyanate with a solution of potassium 

 platinosochloride, K 2 PtCl 4 , they form a double thiocyanate, PtB^CNS)^ which is easily 

 soluble in water and alcohol, crystallises in red prisms, and gives au orange-coloured 

 solution, which precipitates salts of the heavy metals. The action of sulphuric acid 

 on the lead .salt of the same 'type gives the acid jtself, PtH 2 (SCN)4, which corre- 

 sponds with these salts. The type of these compounds is evidently the same as that of 

 the cyanides. 



(J5) Platinous chloride, PtCl 2> which is insoluble fn water, forms double $alt$ .with 

 the metallic chlorides. These double chlorides are soluble in water, and capable of. 

 crystallising. Hence when a hydrochloric acid solution of platinous chloride is mixed 

 with solutions of metallic salts and evaporated it forms crystalline salts of a red or 

 yellow colour. Thus, for example, the potassium salt, PtKjjCl^ is red, and easily 

 soluble in water; the sodium salt is also soluble in alcohol;' the barium salt, 

 PtBaCl 4 ,8H 2 O, is soluble hi water, but the silver salt^ PtAg 2 Cl4, is insoluble in water, 

 and may be used for obtaining the remaining salts by means of double decomposition 

 with their chlorides. 



(0) A remarkable example of the complex compounds of platinum was observed by 

 Schiitzenberger (1868). He showed that finely-divided platinum in the presence of 

 chlorine and carbonic oxide at 250-800 gives phosgene and a volatile compound con- 

 taining platinum. The same substance is formed by the action of carbonic oxide on 

 platinous chloride. It decomposes with an explosion in contact with water. Carbon 

 tetracbloride dissolves a portion of this substance, and on evaporation gives crystals of 

 2PtCl 2 ,8CO, whilst the compound PtCl 2 ,2CO remains undissolved. When fused and 

 sublimed it gives yellow needles of PtCl^CO, and in the presence of an excess of 

 carbonic oxide PtCl 2 ,2CO is formed. These compounds are fusible (the first at 250, the 

 second at 142, and the third at 195). In this case (as in the double cyanides) com- 

 bination takes place, because both carbonic oxide and platinous chloride are unsaturated 

 compounds capable of further combination. The carbon tetrachloride solution absorbs 

 NH 5 and gives PtCl 2 ,CO,2NH 3 , and PtCl5,2CO,2NH 5 , and these substances are analo- 

 gous (Foerster, Zeisel, Jorgensen) to similar compounds containing complex amines (for 

 instance, pyridine, C 5 H 5 N), instead of NH$, and ethylene, &c., instead of CO, so that here 

 we have a whole series of comple? platino-compounds. The compound PtC^CO 

 dissolves in hydrochloric acid without change, and the solution disengages all the 

 carbonic oxide when KCN is added to it, which shows that those forces which bind 

 9 molecules of KCN to PtClj can also bind the molecule CO, or 2 molecules of CO. 

 When 'the hydrochloric acjd solution of PtCLjCO is mixed with a solution of sodium 

 acetate or acetic acid, it gives a precipitate of PtOCO, i.e, the C1 2 is replaced by oxygen 

 (probably because the acetate is decomposed by water). This oxide, PtOCO, splits up 

 into Pt+ C0 2 at 850, PtSCO is obtained by the action of sulphuretted hydrogen upon 

 PtCl 2 CO. All this leads to the conclusion that the group PtCO is able to assimilate 

 X 2 =C1 2 , S, O, &c. (Mylius, FperstSlr, 1891). Pullinger (1891), by igniting spongy 

 platinum at 250, first in a stream of chlorine, and then in a stream of carbonic oxide, 

 obtained (besides volatile products) a non-volatile yellow substance which remained 

 unchanged in air and disengaged chlorine and phosgene gas when ignited ; its compo- 

 sition was PtCl$(CO) 2 , which apparently proves it to be a compound of PtCl 2 and 



