Gooch and Bosworth — Silver as the Chromate. 



243 



experiments no silver was found in the nitrate, but the pre- 

 cipitate was not so coarsely crystalline and easily washed as 

 when deposited by removal of ammonia from an ammonia- 

 cal solution. In the other experiments of Table I, therefore, 

 the first precipitate was dissolved in ammonia and reprecipi- 

 tated by boiling the solution : in those of B the evaporation 

 was carried to dryness, and in those of C the concentration 

 was stopped when a volume of 10-15 cm3 had been reached. 

 In all these experiments precipitation was complete, the fil- 

 trates giving no test with hydrochloric acid for a dissolved sil- 

 ver salt. 



The high results obtained in the experiments of B are no 

 doubt due to the inclusion of foreign matter in the silver chro- 

 mate, which is left in caked condition by the process of complete 

 evaporation. The better results in the experiments of C are 

 apparently due to the fact that in them the evaporation was 

 not pushed too far. The experiments of D show that the pres- 

 ence of a gram of sodium nitrate has no appreciable effect 

 upon the solubility of the silver chromate. It is plain that 

 the precipitation by potassium chromate in neutral solution is 

 practically complete and that accurate determinations may be 

 made by filtering at once, or by dissolving the precipitate in 

 ammonia, reprecipitating by boiling to a volume of 10-1 5 cm3 , 

 and then filtering, drying, and weighing. 



In many cases it is desirable to determine silver present -in 

 solutions containing free nitric acid. t The effect of free nitric 

 acid upon the process was therefore next studied. A few 

 qualitative experiments showed that the solvent action of nitric 

 acid may be obviated by taking care to use the precipitant, 

 potassium chromate, in such amounts that an excess of it shall 

 be present after taking up the nitric acid to form potassium 

 dichromate. The details of a few of these experiments are 

 giving in the accompanying table. 









Table II. 













• 



K 2 CrO 



4 













To form 



Theo- 



s 





Agin 





To form 



K 2 O 2 7 



retically 





Ag 



AgN0 3 



HN0 3 



AgaCrO* 



with HNO3 



required 



Present 



in filtrate 



grin. 



grm. 



grm. 



grm. 



grm. 



grm. 





0-1376 



0-063 



0-1241 



0-1946 



0-3187 



0-3172 



Found 



0-1376 



0-063 



0-1241 



0-1946 



0-3187 



0-3172 



Found 



0-0550 



0-063 



0-0496 



0-1946 



0-2442 



0-3172 



None 



0-0550 



0-063 



0-0496 



0-1946 



0-2442 



0-3172 



None 



0-1376 



0-063 



0*1241 



0-1946 



0-3187 



0-3806 



None 



0-1376 



0-063 



0-1241 



0-1946 



0-3187 



0-4758 



None 



0*1376 



0-095 



0-1241 



0-2919 



0-4160 



0*4758 



None 



0-1376 



0-126 



0-1241 



0-3892 



0-5133 



0-6344 



None 



0-1376 



0-158 



0-1241 



0-4865 



0-6106 



0-7930 



None 



