BAXTER AND COFFIN. — ANALYSIS OF SILVER ARSENATE. 187 



to the weighing bottle in which it was always weighed without expo- 

 sure to moist air. The boat and bottle were weighed by substitution 

 by comparison with a counterpoise similar both in shape and 

 volume. 



After the silver arsenate had been weighed, the boat with its con- 

 tents was transferred to a flask, and the salt was dissolved in warm 

 nitric acid of density about 1.15. The weighing bottle was rinsed with 

 acid, and the rinsings were added to the main solution ; then the solu- 

 tion was carefully transferred to a large glass-stoppered precipitating 

 flask and diluted to a volume of about one litre. 



From the weight of silver arsenate the amount of either hydrochloric 

 or hydrobromic acid necessary to precipitate the silver was calculated. 

 A slight excess of one acid or the other was then diluted to about six 

 hundred cubic centimeters, and the solution was slowly poured into the 

 solution of silver arsenate in the precipitating flask. After a few 

 moments' shaking the precipitate was allowed to stand for several 

 days, with occasional agitation. 



The precipitated silver chloride or silver bromide was next col- 

 lected upon a weighed Gooch crucible, after it had been washed by 

 decantation about ten times with dilute hydrochloric acid in the case 

 of silver chloride, with water in the case of silver bromide. After 

 several hours' heating in an electric air bath at 150° C, and about two 

 hours' heating at 200° C, the precipitate was cooled in a desiccator 

 and weighed. 



In order to determine the moisture retained by the precipitate it was 

 transferred as completely as possible to a small porcelain crucible and 

 weighed. Then the salt was fused by heating the small covered cru- 

 cible contained in a large crucible and was again weighed. 



The asbestos mechanically detached from the Gooch crucible, to- 

 gether with a small quantity of silver chloride or silver bromide which 

 escaped the crucible, was collected upon a small filter through which 

 the filtrate and wash waters were passed, and the filter paper was ig- 

 nited in a small weighed porcelain crucible. Before being weighed 

 the ash was treated with a drop of nitric and a drop of either hydro- 

 chloric or hydrobromic acid and again heated. 



The filtrate and wash waters were evaporated to small bulk. The 

 precipitating flask was rinsed with ammonia, and the rinsing was 

 added to the evaporated filtrate and wash water. Then the solution 

 was diluted to definite volume, and the silver content was determined 

 by comparison with standard silver solutions in the nephelometer. 



The operations of precipitating and collecting the silver halides 

 were all carried out in a room lighted only with ruby light. 



