THE PLATINUM' METALS 891 



ammotoiacal salts.; consequently, the ammonlacal compounds produced 

 from PtX 2 will be salts in which X will be replaceable by various 

 other haloids, just as the metal is replaced in the cyanogen salts ; such 

 is the nature of the platino-ammonium compounds. PtX 2 forms com- 

 pounds with 2NH 3 and with 4NH 3 , and so also PtX 4 gives (not 

 directly from PtX 4 and ammonia, but from the compounds of PtX 2 by 

 the action of chlorine, <fec.) similar compounds with 2NH 3 and with 

 4NH 3 . 12 



(F) No less characteristic are the plat inonitrites formed by platinous oxide. They 

 correspond with nitrous acid, whose salts, ENO 2 , contain the univalent radicle, NO 2 , 

 which is capable of replacing chlorine, and therefore the salts of this kind should form a 

 common type PtR 2 (NO 2 ) 4 , and such a salt of potassium has actually been obtained by 

 mixing a solution of potassium platinosochloride with a solution of potassium nitrite, 

 when the liquid becomes colourless, especially if it be heated, which indicates the change 

 in the chemical distribution of the elements. As the liquid decolorises it gradually 

 deposits sparingly soluble, colourless prisms of the potassium salt K 2 Pt(NO 2 ) 4 , which 

 does not contain any water. With silver nitrate a solution of this salt gives a precipitate 

 of silver platinonitrite, PtAg 2 (tf 2 ) 4 . The silver of this salt may be replaced by other 

 metals by means of double decomposition with metallic chlorides. The sparingly soluble 

 barium salt, when treated with an equivalent quantity of sulphuric acid, gives a soluble 

 acid, which separates, under the receiver of an air-pump, in red crystals ; this acid has 

 the composition PtH 2 (N0 2 ) 4 . To the potassium salt, K 2 Pt(NO 2 ) 4 , there correspond 

 (Vezes, 1892) K 2 Pt(NO 2 ) 4 Br 2 and K 2 Pt(NO 2 ) 4 Cl 2 and other compounds of the same type 

 K 3 PtX 6 , where X is partly replaced by Cl or Br and partly by (NO 2 ), shpwing a 

 transition towards the type of the double salts like the platino-ammoniacal salts. (The 

 corresponding double sodium nitrite salt of cobalt is soluble in water, while he K,NH 4 

 and many other salts are insoluble in water, as I was informed by Prof. K. Winkler 

 in 1894). 



In all the preceding complex compounds of Pt we see a common type PtX 2) 2MX 

 (i.e. of double salts corresponding to PtO) or PtM 2 X 4 = Pt(MX 2 ) 2 , corresponding to 

 Pt(HO) 2 with the replacement of O by its equivalent X 2 . Two other facts must also be 

 noted. In the first place these X's generally correspond to elements (like chlorine) or 

 groups (like CN, NO 2 , SO 3 , &c.), which are capable of further combination. In the 

 second place all the compounds of the type PtM 2 X 4 are capable of combining with 

 chlorine or similar elements, and thus passing into compounds of the types PtX 3 or PtX 4 . 



12 The platinum salt and ammonia, when once combined together, are no longer 

 subject to their ordinary reactions but form compounds which are comparatively very 

 stable. The question at once suggests itself to all who are acquainted with these pheno- 

 mena, as to what is the relation of the .elements contained in these compounds. The first 

 explanation is that these compounds are salts of ammonium in which the hydrogen is 

 partially replaced by platinum. This is the view, with certain shades of difference, held 

 by many respecting the platino-ammonium compounds. They were regarded in this 

 light by Gerhardt, Schiff, Kolbe, Weltzien, and many others. If we suppose the hydro- 

 gen in 2NH 4 X to be replaced by bivalent platinum (as in the salts PtX 2 ), we shall 



obtain JJ^Pt^ that is, the compound PtX 2 ,2NH 3 . The compound with 4NH 3 will 



then be represented by a 'further substitution of the Hydrogen in ammonia 'by ammo- 

 nium itself i.e. as NH 2 (NH 4 X) 2 Pt or PtX 2 ,4NH 3 . A modification of this view is found 

 in that representation of compounds of this kind which is based on atomicity. As 

 platinum in PtX 2 is bivalent, has two affinities, and ammonia, NH 3 , is also bivalent, 

 because nitrogen is quinquivalent and is here only combined with H 3 , it is evident what 

 bonds should be represented inPtX 2> 2NH 3 and inPtX 2 ,4NH 3 . In the former, Pt(NH 3 Cl) 2 , 

 the nitrogen of each atom of ammonia is united by three affinities with H 3 , by one with 



*F 



