THE PLATINUM METALS 887 



Ammonia, like potassium cyanide, has the faculty of easily reacting 

 with platinum dichloride, forming compounds similar to the platino 



with five molecules of water of crystallisation, (PtH 2 (CN) 4> 5H 2 0), confirms the opinion 

 that platinum is able to form compounds of still higher types than that expressed 

 in its saline compounds, and, moreover, the combination of hydroplatinocyanio acid 

 with water does not reach the limit of the compounds which appears in 



A whole series of glatinocyanides of the common type PtB 2 (CN) 4 wH 2 is obtained 

 by means of double decomposition with the potassium or hydrogen or silver salts. For 

 example, the salts of sodium and lithium contain, like the potassium salt, three molecules 

 of water The sodium salt is soluble in water and alcohol. The ammonium salt has the 

 composition Pt(NH 4 ) 2 (CN) 4 ,2H20 and gives crystals which reflect blue and rose-coloured 

 light. This ammonium salt decomposes at 800, with evolution of water and ammonium 

 cyanide, leaving a greenish platinum dicyanide, Pt(CN) 3 , which is insoluble in water 

 and acid but dissolved in potassium cyanide, hydrocyanic acid, and other cyanides. The 

 eatne platinous cyanide is, obtained by the action of sulphuric acid on the potassium 

 salts in the form of a reddish-brown amorphous precipitate. The most characteristic of the 

 platinocyanides are those of the alkaline earths. The magnesium salt PtMg(CN)4,7H 2 O 

 crystallises in regular prisms, whose side faces are of a metallic green colour and terminal 

 planes dark blue. It shows a carmine-red colour along the main axis, and dark red 

 along the lateral axes ; it easily loses water, (2H 2 O), at 40, and then turns blue (it then 

 contains 5H 2 0, which is frequently the case with the platinocyanides). Its aqueous 

 solution is colourless, and an' alcoholic solution deposits yellow crystals. The remainder 

 of the water is given off at 280. It is obtained by saturating platinocyanio acid with 

 magnesia, or else by double decomposition between the barium salt and magnesium sul 

 phate. The strontium salt, SrPt(CN) 4 ,4jH 2 O crystallises in milk-white plates having 

 a violet and green iridescence. When it effloresces in a desiccator, its surfaces have 

 a violet and metallic green iridescence. A colourless solution of the barium salt 

 PtBa(CN) 4 ,4H 2 is obtained by saturating a solution of hydroplatinocyanio acid with 

 baryta, or by boiling the insoluble copper platinocyanide in baryta water It crystallises 

 in nronoclinic prisms of a yellow colour, with blue and green iridescence ; it loses half its 

 water at 100, and the whole at 150. The ethyl salt, Pt(C 2 H 5 ) 2 (CN) 4) 2Ho v O, is also 

 very characteristic ; its crystals are isomotphous with those of the potassium salt, and 

 are obtained by passing hydrochloric acid into an alcoholic solution of hydroplatino- 

 cyanic acid. The, facility with which they crystallise, the regularity of their forms, 

 and their remarkable play of colours, renders the preparation of the platinocyanides one 

 of the most attractive lessons of the laboratory. 



By the action of chlorine or dilute nitric acid, the platinocyanides are converted into 

 salts of the composition PtM3(CN) 5 , which corresponds with Pt(CN) 3 ,2KCN that is, 

 they express the type of a non-existent form of oxidation of platinum, PtX$ (i.e. oxide 

 PtsOj), just as potassium ferricyanide (FeCy 3 ,8KCy) corresponds with ferric oxide, and 

 the ferrocyanide corresponds with the ferrous oxide. The potassium salt of this series 

 contains PtK^CN^SHgO, and forms brown regular prisms with a metallic lustre, and is 

 soluble in water but insoluble in alcohol. Alkalis re-convert this compound into the 

 ordinary platinocyanide K 2 Pt(CN)fc. taking up the excess of cyanogen. It is remarkable 

 that the salts of the type J?tMjjCy 5 contain the same amount of water of crystallisation 

 as those of the type PtM 2 Cy 4 . Thus the salts of potassium and lithium contain three, 

 and the salt of magnesium seven, molecules of water, like the corresponding salts of the 

 type of platinous oxide. Moreover, neither platinum nor any of its associates gives any 

 cyanogen compound corresponding with the oxide, i.e. having the composition PtK 2 Cy6, 

 just as there are no compounds higher than those which correspond to BCy 5 wMCy for 

 cobalt or iron. This would appear to indicate the absence of any such cyanides, and 

 indeed, for no element are there yet known, any poly-cyanides containing more than three 

 equivalents ol cyanogen for one equivalent of the element. The phenomenon, is perhapa 



