THE PLATINUM METALS 893 



PtCl 2 ,2NH 3 , insoluble in water and hydrochloric acid. But, judging 

 by its reactions, this salt has twice this formula. Thus, Gros (1837), 

 on boiling Magnus's salt with nitric acid, observed that half the chlorine 

 was replaced by the residue of nitric acid and half the platinum was 

 disengaged : 2PtCl 2 (NH 3 ) 2 + 2HNO 3 ==PtCl 2 (NO 3 ) 2 (NH 3 ) 4 + 2PtCl 2 . 

 The Gros's salt thus obtained, PtCl 2 (NO 3 ) 2 4NH 3 (if Magnus's salt 



Judging from the most complex platino-ammonium compounds PtCl 4 ,4NH 3 , we 

 should admit the possibility of the formation of compounds of the type PtX 4 Y 4 , where 

 Y 4 = 4X 2 = 4NH 3 ,' and this shows that those forces which form such a characteristic 

 Series of double platinocyanides PtK 2 (CN) 4 ,3H 2 O. probably also determine the formation 

 o! the higher ammonia derivatives, as is seen on comparing 



PtCl 2 NH 3 C1 2 8NH 3 

 Pt(CN) 2 KCN KCN 3H 2 0. 



Moreover, it is obviously much more natural to ascribe the faculty for combination 

 with nY to the whole of the acting elements that is; to PtX 2 or PtX 4 , and not to 

 platinum alone. Naturally such compounds are not produced with any Y. With 

 certain X's there only combine certain Y's. The best known and most frequently-;', 

 formed compounds of this kind are those with- water that is, compounds with water of 

 crystallisation. Compounds with salts are double salts; also we know that similar 

 compounds are also frequently formed by means of ammonia. Salts of zinc, ZnXj, 

 copper, CuX 2 , silver, AgX, and many others give similar compounds, but these and many 

 other ammonio-metallic saline compounds are unstable, and readily part with their 

 combined ammonia, and it is only in the elements of the platinum 'group and in the 

 group of the analogues of iron, that we observe the faculty to form stable ammonio- 

 metallic compounds. It must be remembered that the metals of the platinum and iron 

 groups are able to form several high grades of oxidation which have an acid character, 

 .and consequently in the lower degrees of combination there yet remain affinities capable 

 of retaining other ' elements, and they probably retain ammonia, and hold it the more 

 stably, because all the properties of the platinum compounds are rather acid than basic 

 that is, PtX n recalls rather HX or SnX or CX n than KX, CaX 2 , BaX 2 , &c., and 

 ammonia naturally will rather combine with an acid than with a basic substance. 

 Further, a dependence, or certain connection of the forms of oxidation with the ammonia 

 compounds, is seen on comparing the following compounds : 



PdClo,2NH 3 ,H 2 PdCl 2 ,4NH 3 ,H 2 



PtCl 2 ,2NH 3 PtCl 4 ,4NH 3 



BhCl 3 ,5NH 3 BuCl 2 ,4NH 3 ,8H 2 O 



IrCl 3) 5NH 3 OsCl 2 ,4NH 3 ,2H 2 O 



We know that platinum and palladium give compounds of lower types than iridium 

 and rhodium, whilst ruthenium and osmium give the highest forms of oxidation ; this 

 shows itself in this case also. We have purposely cited the same compounds with 4NH 5 

 for^osmium and ruthenium as we have for platinum and palladium, and it is then seen 

 that Eu and Os are capable of retaining 2H. 2 O and 8H 2 O, besides C1 2 and NH 3 , which 

 .the compounds of platjnum and palladium are unable to do. The same ideas 

 which were developed in Note 85, Chapter XXII. respecting the cobaltia compounds are 

 perfectly applicable to the present case, i.e. to the platinia compounds or ammonia 

 compounds of the platinum metals, among which Bh and Ir give compounds which are 

 perfectly analogous to the cobaltia compounds. 



Iridium and rhodium, which easily give compounds of the type RX 3 , give compounds 

 (Claus) of the type IrX 3 ,6NH 3 , of a rose colour, and BhX 3 ,5NH 3 , of a yellow colour. 

 .Jbrgensen, in his researches on these compounds, showed their entire analogy with the 

 .cobalt compounds, as was to be expected from the periodic system. 



