BAXTER. — ATOMIC WEIGHT OF CHROMIUM. 409 



asbestos. From the drying apparatus the air passed into the tube 

 in which the boat containing the silver chromate was placed. 



The Determination of Silver in Silver Chromate. 



During the drying of the silver chromate it was contained in a plat- 

 inum boat which had been weighed, in a weighing bottle, by substitu- 

 tion for a similar bottle which with its contents displaced the same 

 amount of air as the bottle with the boat. The boat was placed in a 

 hard glass tube connected by a carefully ground joint with a bottling 

 apparatus by means of which the boat could be transferred to the 

 weighing bottle, after being heated, without the slightest exposure to 

 moist air. 24 The tube was heated by means of two solid aluminum 

 blocks which were grooved to contain the tube, by means of which the 

 temperature could be maintained constant within a very few degrees. 25 

 After two hours' heating at 225° the boat was transferred* to the 

 weighing bottle and was allowed to stand in a desiccator near the bal- 

 ance for several hours before being weighed. 



Next, the weighed quantity of silver chromate was transferred to a 

 three-liter glass stoppered Jena flask with a carefully ground stopper 

 and, after the boat and bottle had been cleaned with hot dilute nitric 

 acid and water, the rinsings were poured into the flask and the silver 

 chromate dissolved by the application of gentle heat. If the salt 

 had not been heated above 225°, the solution was absolutely clear. 

 Specimens heated above this temperature always showed more or less 

 turbidity. 



The chromate was next reduced to the chromic state by the addition 

 of a very slight excess of sulphur dioxide w T hich had been freshly dis- 

 tilled into pure water. The slight excess of sulphurous acid was soon 

 oxidized under the combined influence of heat and nitric acid. In 

 Analyses 1, 2, 3, 12, 13, and 14 the reduction was effected by means 

 of recrystallized hydrazine sulphate, in order to avoid to a large 

 extent the presence of sulphuric acid, for Richards and Jones 26 found 

 that silver chloride occludes silver sulphate very tenaciously. This 

 method of reduction, however, was without effect on the results. 



Since in the reduction of the chromate by hydrazine, nitrogen gas is 

 evolved, the flask in which the reduction took place was protected from 

 loss by spattering by means of a long column of bulbs fitting loosely 

 into the neck of the flask. The solution of hydrazine sulphate was 



24 Richards and Parker, These proceedings, 32, 59 (1896). 



25 Baxter and Coffin, These proceedings, 44, 184 (1909). 



26 Jour. Amer. Chem. Soc, 29, 831 (1907). 



