THE PLATINUM METALS 895 



parative stability (for instance, as compared with AgCl and NH 3 ) of 

 such compounds, and the existence of many other compounds analogous 



and these hydroxides do not at once show the properties of alkalis, just as the chlorine 

 which stands in the same place does not react distinctly ; but still, after the prolonged 

 action of acids, this hydroxyl group is also replaced by acids. Thus, for example, the action 

 of nitric acid on Pt(N0 3 ) 2 Cl 2 ,4NH 3 causes the non-active chlorine to react, but in the 

 product all the chlorine is not replaced by NO 3 , but only half, and the other half is replaced 

 by the hydroxyl group : Pt(NO 3 ) 2 Cl 2 ,4NH 3 + HN0 3 + H 2 O = Pt(NO 3 ) 3 (OH),4NH 3 + 2HC1 ; 

 and this is particularly characteristic, because here the hydroxyl group has not reacted 

 with the acid an evident sign 1 of the non-alkaline character of this residue. I think it 

 may be well to call attention to the fact that the composition of the. ammonio-metalla- 

 salts very often exhibits a correspondence between the amount of X's and the amount 

 of NH 3) of such a nature that we find they contain either XNH 3 or the grouping 

 X2NH 3 ; for example, Pt(XNH 3 ) 2 and Pt(X2NH 3 ) 2 , Co(X2NH 3 ) 3 , Pt(XNH 3 ) 4 , &o. 

 Judging from this, the view of the constitution of the double cyanides of platinum 

 given in Note 11 finds some confirmation here, but, in my opinion, all questions 

 respecting the composition (and structure) of the ammoniacal, double, complex, and 

 crystallisation compounds stand connected with the solution of questions respecting the 

 formation of compounds of various degrees of stability, among which a theory of 

 solutions must be included, and therefore I think that the time has not yet come for a 

 complete generalisation of the data which exist for these compounds ; and here I again 

 refer the reader to Prof. Kournakoff's work cited in Chapter XXII., Note 85. However, 

 we may add a few individual remarks concerning the platinia compounds. 



To.the common properties of the platino-ammonium salts, we must add not only their 

 stability (feeble acids and alkalis do not decompose them, the ammonia is not evolved 

 by heating, &c.), but also the fact that the ordinary reactions of platinum are concealed 

 in them to as great ah extent as those of iron in the ferricyanides. Thus neither alkalis 

 nor hydrogen sulphide will separate the platinum "from them. For example, sulphuretted 

 hydrogen in acting on Gros's salts gives sulphur, removes half the chlorine by' means of 

 its hydrogen, and forms salts of Reiset's first base. This may be understood or explained 

 by considering the platinum in the molecule as covered, walled up by the ammonia, or 

 situated in the centre of the molecule, and therefore inaccessible to reagents. On this 

 assumption, however, we should expect to find clearly-expressed ammoniacal properties, 

 and this is not the case. Thus ammonia is easily decomposed by chlorine, whilst in 

 acting on the platino-ammonium salts containing PtX 2 and 2NH 3 or 4NH 3 , chlorine 

 combines and does not destroy the ammonia ; it converts Reiset's salts into those of. 

 Gros and Gerhardt. Thus from PtX 2 ,2NH 3 there is formed PtX 2 Cl 2 ,2NH 3 , and from 

 PtX 2 ,4NH 3 the salt of Gros's base PtX 2 Cl 2 ,4NH 3 . This shows that the amount .of 

 chlorine which combines is not dependent on the amount of ammonia present, but is due 

 to the basic properties of platinum. Owing to this some chemists suppose the ammonia 

 to be inactive or passive in certain compounds. It appears to me that these relations, 

 these modifications, in the usual properties of ammonia and platinum are explained 

 directly by their mutual combination. Sulphur, in sulphurous anhydride, SO 2 , and 

 hydrogen sulphide, SH 2 , is naturally one and the same, but if we, only knew of it in the 

 form of hydrogen sulphide, then, having obtained it in the form of sulphurous anhydride, 

 we should consider its properties as hidden. The oxygen in magnesia, MgO, and in 

 nitric peroxide, NO 2 , is so different that there is no resemblance. Arsenic no longer 

 reacts in its compounds with hydrogen as it reacts in its compounds with chlorine, and 

 in their compounds with nitrogen all metals modify both their reactions and their physical 

 properties. We are accustomed to judge the metals by their saline compounds with 

 haloid groups, and ammonia by its compounds with acid substances, and here, in the 

 platino-compounds, if we assume the platinum to be bound to the entire mass of the 

 ammonia to its hydrogen and nitrogen we shall understand that both the platinum 

 and ammonia modify their characters. Far more complicated is the question why a por- 



