BAXTER. — A REVISION OF THE ATOMIC WEIGHT OF BROMINE. 207 



laboratory, and have shown evidence of great purity. For details con- 

 cerning the puritication the papers referred to should be consulted. 



Sample A was employed in a determination of the atomic weight of 

 iodine. ^^ This specimen had been twice precipitated as chloride and 

 once electrolyzed. 



Sample B was used in experiments upon the atomic weight of iodine ^^ 

 and of manganese. ■'^'^ It was precipitated once as chloride, electrolyzed 

 once, and finally precipitated as metal with ammonium formiate. 



Sample C also was employed in a determination of the atomic weight 

 of manganese, and was purified by recrystallizing silver nitrate, seven 

 times from nitric acid and five times from aqueous solution. Finally 

 the silver nitrate was reduced by means of ammonium formiate. 



Sample D was prepared for the determination of the atomic weights 

 of cadmium ^^ and manganese, by one precipitation as chloride, one 

 precipitation with ammonium formiate, and one electrolysis. 



Sample E was first purified in part by precipitation as chloride, in 

 part by precipitation with ammonium formiate. The combined mate- 

 rial was then subjected to two electrolyses. 



In all cases the electrolytic crystals were fused in a boat of the purest 

 lime, contained in a porcelain tube, in a current of electrolytic hydro- 

 gen. After the buttons had been cleansed with dilute nitric acid and 

 dried at 200°, they were cut into fragments of from four to eight grams 

 either by means of a clean chisel and anvil or with a fine jeweller's 

 saw. The latter method was employed in the case of Samples D and E, 

 because it proved easier completely to free the silver from surface con- 

 tamination with iron by etching the fragments with nitric acid, than 

 when a chisel was used. The cleansing process with nitric acid was 

 repeated until the solution thus obtained, after precipitation with 

 hydrochloric acid and evaporation, proved free from iron. That every 

 trace of iron could be removed by this treatment was proved by testing 

 for iron the evaporated filtrates from several of the analyses subse- 

 quently recorded in this paper. Negative results were obtained in all 

 cases. 



After thorough washing with water and drying at 100°, the pieces of 

 metal were heated to about 400° in a vacuum, and were preserved over 

 solid potassium hydroxide in a desiccator. 



" Baxter, These Proceedings, 40, 420 (1904). 



16 Baxter, Ibid., 41, 79 (1905). 



" Baxter and Ilines. Tliis paper will soon be publislied. 



18 Baxter and Ilines, Jour. Amer. Chem. Soc, 28, 772 (1906). 



