16 THE ROYAL SOCIETY OF CANADA 



ium chloride or bromide increases. This seems to be in conformity 

 with the mass action law, the high concentration of the ammonium ion 

 preventing the dissociation of the corresponding platinum or iridium 

 salt. For all three salts the solubility is practically the same for the 

 most concentrated solution of the precipitating agent. For the more 

 dilute solutions of the ammonium chloride the chloriridateis more than 

 four times as soluble as the chloroplatinate. As this is the condition 

 under which precipitation, for the purpose of separation, takes place, 

 it can be seen that fairly complete separation will certainly be attained. 

 It is of interest to note that the bromoplatinate is less soluble in the 

 dilute solutions than the chloroplatinate. 



Comparing the solubility of the ammonium chloroplatinate with 

 the corresponding potassium salt, we find that the ammonium com- 

 pound is much the less soluble both in water and in solutions of the 

 corresponding chloride. At 100°, 5-03 grams of potassium chloro- 

 platinate dissolve in 100 grams of twice normal potassium chloride 

 solution; the corresponding values for the ammonium salt being 

 3-365 grams and 0-0024 gram. It seems likely that if it were not 

 for the high price of platinum, ammonia could be estimated through 

 the chloroplatinate more accurately than potassium can, as its solu- 

 bility in alcohol must be very small. 



We may summarize as follows :— 



(1) The solubility in water of ammonium chloroplatinate, 

 bromoplatinate and chloriridate increases continually with the tem- 

 perature. The first two salts being approximately ten times as soluble 

 at 100° as at 0°. 



(2) Ammonium chloriridate being several times more soluble 

 than the chloroplatinate under the conditions of precipitation, a 

 separation of platinum and iridium can be obtained by the precipita- 

 tion of the ammonium chloroplatinate. 



(3) The solubility of all three salts in solutions of their corres- 

 ponding halide salt is very small. 



(4) The ammonium chloroplatinate is appreciably less soluble 

 than the potassium salt. 



University of British Columbia. 

 Syracuse University. 



