Section III, 1917 [7] Trans. R.S.C. 



The Solubilities of the Chloroplatinate Bromoplatinate and Chloriridate 

 of Ammonium and the Separation of Platinum and Iridium. 



By E. H. Archibald and John W. Kern. 



Presented by Dr. D. Mcintosh, F.R.S.C. 

 (Read May Meeting, 1917.) 



Since nearly all our platinum of commerce is an alloy of platinum 

 and iridium, the quantitative separation of these metals becomes a 

 problem of some importance. 



Previous Work on this Problem. 



Among the methods that have been suggested for the purpose 

 of this separation we should note that of U. Antony.^ He precipitates 

 the iridium by means of zinc from an acid solution of iridic chloride. 

 Treatment of this precipitate with aqua regia dissolves the platinum 

 together with some of the iridium. The residue is largely iridium. 

 This is fused with acid potassium sulphate and the iridic oxide ob- 

 tained is reduced with hydrogen, and the metal converted into potas- 

 sium chloriridate. The platinum still remaining with the iridium is 

 removed by passing a current of chlorine and carbon monoxide over 

 the compound, heated to 250°C, The platinum forms a volatile 

 product which escapes leaving supposedly pure indium. 



Another method for the separation of these metals, suggested 

 by Paul Bergsoe^, depends upon the insolubility of barium platino- 

 cyanide in a solution of barium chloride. The platinocyanide is 

 formed by adding to a solution of chloroplatinic acid the theoretical 

 quantity of barium hydroxide and hydrogen cyanide, and treating 

 the warm mixture with sulphurous anhydride until it becomes colour- 

 less. After removing the barium sulphate the barium platinocyanide 

 crystallizes out while the iridium remains in solution. 



For the separation of iridium from a solution also containing 

 platinum Leider^ adds to the solution an excess of sodium nitrite 

 and a considerable quantity of ammonium chloride. A double 

 ammonium iridium nitrite is thrown down. The mother liquor is 

 then heated with concentrated hydrochloric acid, to decompose the 



1 Gazzetta, 22 (1) 275. 



2Zeit. anorg. Chem., 19, 318, (1899). 



« Compt. rend., 131, 888, (1900). 



