10 THE ROYAL SOCIETY OF CANADA 



chloroplatinate except that hydrobromic acid was now used as electro- 

 lyte. The platinum was precipitated from the bromoplatinic acid 

 solution by adding a solution of ammonium bromide. The resulting 

 precipitate was washed and dried as before. 



Ammonium chloriridate : — It is only recently that any work of 

 moment has been done on the double alkali chlorides and bromides of 

 iridium. In 1907 Rinbach and Korten^ prepared these salts and 

 important work has been done by A. Gutbier and M. Riess^ working 

 together, and by A. Gutbier^ working alone. These investigators 

 prepared Ammonium chloriridate through the sodium salt as 

 follows : — 



Sodium chloride and iridium black were mixed and heated in 

 a combustion tube, while chlorine was passing through. The sodium 

 chloriridate formed was dissolved in water and treated with Ammon- 

 ium chloride and chlorine forming ammonium chloriridate; this was 

 recrystallized and treated, at a low temperature, with chlorine. The 

 resulting solution was desiccated, in vacuo, over calcium oxide, at 

 40°, until crystals of iridium tetrachloride were formed. A hydro- 

 chloric acid solution of these crystals was prepared and to this was 

 added a saturated solution of ammonium bromide, precipitating 

 ammonium chloriridate. The method followed by us differed from 

 the above in this particular that the sodium chloriridate was treated 

 with a saturated solution of sodium iodide while free chlorine was 

 passed into the solution. This precipitated the iridium as iridium 

 tetraiodide. This precipitate was washed until free from sodium. 

 It was then digested in pure water and free chlorine until it was con- 

 verted into iridium tetrachloride and all the iodine driven out of the 

 solution, as shown by testing with starch. 



The solution was then made strongly acid with hydrochloric 

 acid and the iridium precipitated by adding drop by drop a cold 

 saturated solution of ammonium bromide. As the ammonium bromide 

 is added, bromine is set free and dark, brownish red crystals of am- 

 monium chloriridate are formed. Iridium from two sources was 

 used in this way for the preparation of the ammonium chloriridate. 

 In the first case, the residues obtained by evaporating the mother 

 liquors from a large number of platinum precipitations were reduced 

 in hydrogen, the mixture of platinum and iridium black obtained 

 treated with aqua regia and the insoluble residue converted into iridium 

 salt. This furnished only a small part of the total amount of salt, 



1 Zeit fur anorg, Chem., 52, 406 (1907). 



2 Ber. der deut. Chem. Ges. 42, 3905. 



3 Ibid. 42, 4770; Zeit, fur Physik. Chem., 69, 304. 



