878 PEINCIPLES OF CHEMISTRY 



the lower compound platinoua chloride, PtCl 2 . That faculty "which 

 reveals itself in platinum tetrachloride of combining with water of 

 crystallisation and hydrochloric acid is distinctly marked in its pro* 

 perty, with which we are already acquainted, of giving precipitates 

 with the salts of potassium, ammonium, rubidium, &c. In general it 

 readily forma double salts, R 2 PtCl 6 =:PtCl4 + 2RCl, where R is a 

 univalent metal such as potassium or NH 4 . Hence the addition of a 

 solution of potassium or ammoniunj chloride to a solution of platinio 

 chloride is followed by the formation of a yellow precipitate, which is 

 sparingly soluble in water and almost entirely insoluble in alcohol and 

 ether (platinic chloride is soluble in alcohol, potassium iridiochloride, 

 IrK 8 Cl 6 , i.e. a compound of IrCl 8 , is soluble in water but not in alcohol), 

 It is especially remarkable in this case, that the potassium compounds 

 here, as in a number of other instances, separate in an anhydrous form, 

 whilst tjie sodium compounds, which are soluble in water and alcohol, 

 form red crystals containing water. -The composition NaaPtCl 6 ,6H 2 O 

 exactly corresponds with the above-mentioned hydrochloric compound. 

 The compounds with barium, BaPt01 6 ,4H 2 O, strontium, 8rPtCl 6 ,8H 2 0, 

 calcium, magnesium, iron, manganese, and many other metals are all 

 soluble in watfer. 8 



e Nilson (1877), who investigated the platmochlorides of various metals subsequently 

 to Bonsdorff, Topsoe, Cleve, Marignao, atjd others, found that univalent and bivalent 

 metals such as hydrogen, potassium, ammonium . . . beryllium, calcium, barium 

 give compounds of euch a composition that there is always twice as much chlorine in 

 the platinic chloride as in the combined metallic chloride; for example, K 2 Cl 8t PtCl4} 

 BeC^PtCl^SHaO, to. Such trivalent metals as aluminium, iron (ferric), chromium, di 

 dyrnium, cerium (cerou8)'form compounds of the type ECljPtCl^ in which the amounts of 

 chlorine are in the ratio 8 : 4. Only indium and yttrium-give salts of a different composi- 

 tionnamely, 2lnCl 5 ,5PtCl4,86H a O and 4YCl 5 ,5PtCl 4) 5lHaO. Such quadrivalent metato 

 as thorium, tin, zirconium give compounds of the type RCl^PtC^, in which the ratio of 

 the chlorine is 1:1. In this manner the valency of a metal may, to a certain extent, be 

 judged from the composition of the double salts formed with platinic chloride. 



Platinic bromide, PtBr 4 , and iodide, Ptl*, are analogous to the tetrachloride, but the 

 todide is decomposed still more easily than the chloride. If sulphuric acid be added to 

 platinic chloride, and the solution evaporated, it forms a black porous mass like char- 

 coal, which deliquesces in the air, and has the composition Pt(SOi) 2 . But this, the 

 only oxygen salt of the type PtXj, is exceedingly unstable. This is due to the fact that 

 platinum oxide, the oxide of the type PtO 2 , has a feeble acid character. This is shown 

 in a number of instances. Thus if a strong solution of platinic chloride treated with 

 sodium carbonate be exposed to the action of light or evaporated to dryness and then 

 washed with water, a sodium platinate, PtjNaaO^HsO, remains.. The composition ol 

 this salt, if we regard it in the same sense as we did the salts of silicic, titanic, molybdio 

 and other acids, will be PtO(ONa) 8 ,2PtO 2 ,6H 2 that is, the same type is repeated as 

 we saw in the crystalline compounds of platinum tetrachloride with sodium chloride, or 

 with hydrochloric acidnamely, the type PtX^SY, where Y is the molecule H 8 O,HC1, &c. 

 Similar compounds are also obtained with other alkalis. They will be platinates of the 

 alkalis in which the platinio oxide, PtQ 2 , plays the part of an acid oxide. Eousseaa 

 (1889) obtained different grades of combination BaOPt0 3> 8(BaO)2Pt0 8 , &c., by igniting 

 a mixture of PtCl^ and caustic b&ryta. If uch an alkaline compound of platinum be 



