392 PRINCIPLES OF CHEMISTRY 



If ammonia acts on a boiling solution of platinous chloride in 

 hydrochloric acid, it produces the green salt of Magnus (1829), 



platinum, and by the fifth with chlorine. The other compound is Pt(NH 3 $ :NH 3 Cl)y that 

 is, the N is united by one affinity with the other N, whilst the remaining bonds are the 

 same as in the first salt. It is evident that this union or chain of ammonias has no 

 obvious limit, and the most essential fault of such a mode of representation is that it does 

 not indicate at all what number of ammonias are capable of being retained by platinum. 

 Moreover, it is hardly possible to admit the bond between nitrogen and platinum in such 

 stable compounds, for these kinds of affinities are, at all events, feeble, and cannot lead 

 to stability, but would' rather indicate explosive and easily-decomposed compounds. 

 Moreover, it is not clear why this platinum, which is capable of giving PtX 4 , does not act 

 with its remaining affinities when the addition of ammonia to PtXj takes place. These, 

 and certain other considerations which indicate the imperfection of this representation of 

 the structure of the platino-ammonium salts, cause many chemists to incline more to the 

 representations of Berzelius, Glaus, Gibbs, and others, who suppose that NH^is able to 

 combine with substances, to adjoin itself or pair itself with them (this kind of combination 

 is called ' Paarung ') without altering the fundamental capacity of a substance for further, 

 combinations. Thus, in PtX 2 ,2NH 3 , the ammonia is the associate of PtX 2 , as is 

 expressed by the formula N^HePtX-j. Without enlarging on the exposition of the details 

 of this doctrine, we will only mention that it, like the first, does not render it possible to 

 foresee a limit to the compounds with ammonia; it isolates compounds of this kind 

 into a special and artificial class ; does not show the connection between .compounds of 

 this and of other kinds, and therefore it essentially only expresses the fact of the com- 

 bination with ammonia and the modification in its ordinary reactions. For these 

 reasons we do not hold to either of these proposed representations of the ammonio- 

 platinum compounds, but regard them, from the point of view cited above with reference 

 to double salts and water of crystallisation that is, we embrace all these compounds 

 under the representation of compounds of complex types. The type of the compound 

 PtX2,2NH 3 is far more probably the same as that of PtX 2 ,2Z i.e. as PtX^ or, still more 

 accurately and truly, it is a compound of the same type as PtX2,2KX or PtX 2 ,2H 2 0, &c. 

 Although the platinum first entered into PtK 2 X 4 as the type PtX 2 , yet its character has 

 changed in the same manner as the character of sulphur changes when from SO 2 the com- 

 pound S0 2 (OH) 2 is obtained, or when KC10 4 , the higher form, is obtained from KC1. For us 

 as yet there is no question as to what affinities hold X 2 and what hold 2NH 3 , because this 

 is a question which arises from the supposition of the existence of different affinities in the 

 atoms, which there is no reason for taking as a common phenomenon. It seems to me 

 that it is most important as a commencement to render clear the analogy in the formation 

 of various complex compounds, and it is this analogy of the ammonia compounds with 

 those of water of crystallisation and double salts that forms the main object of the 

 primary generalisation. We recognise in platinum, at all events, not only the four. 

 affinities expressed in the compound PtCl 4 , but a much larger number of them, if only 

 the- summation of affinities is actually possible. Thus, in sulphur we recognise not two 

 but a much greater number of affinities; it is clear that at least six affinities can act. 

 So also among the analogues of platinum : osmic anhydride, Os04, Ni(CO) 4) PtH 2 Cl 6 , &o. 

 indicate the existence of at least eight affinities ; whilst, in chlorine, judging from the 

 compound KC1O 4 = C1O 3 (OK) = C1X 7 , we must recognise at least seven affinities, 

 instead of the one which is accepted. The latter mode of calculating affinities is a tribute 

 to that period of the development of science when only the simplest hydrogen compounds 

 were considered, and when all complex compounds were entirely neglected (they were 

 placed under the class of molecular compounds). This is insufficient for the present 

 state of knowledge, because we find that, in complex compounds as in the most simple, the 

 same constant types or modes of equilibrium are repeated, and the character of certain 

 elements is greatly modified in the passage from the most simple into very complex 

 compounds. 



