BAXTER AND COFFIN. — ANALYSIS OF SILVER ARSENATE. 183 



structed wholly of glass. The hydrogen was cleansed by being passed 

 through two wash bottles containing dilute sulphuric acid, and through 

 a tower filled with beads also moistened with dilute sulphuric acid. 

 The hydrobromic acid gas was absorbed in pure water contained in a 

 cooled flask. In order to remove iodine the solution of hydrobromic 

 acid was diluted with water and twice boiled with a small quantity of 

 free bromine. Then a small quantity of recrystallized potassium per- 

 manganate was added to the hybrobromic acid solution, and the bro- 

 mine set free was expelled by boiling. Finally the acid was distilled 

 with the use of a quartz condenser, the first third being rejected. It 

 was preserved in a bottle of Nonsol glass provided with a ground- 

 glass stopper. 



The purification of the hydrobromic acid was carried on in con- 

 junction with Dr. Grinnell Jones, who was engaged in a parallel re- 

 search upon the atomic weight of phosphorus. Using this acid, he 

 found that 10.48627 grams of silver bromide were obtained from 

 6.02386 grams of the purest silver. This ratio of silver bromide to 

 silver of 100.0000 to 57.4452 is in close agreement with the most prob- 

 able value, 100.0000 to 57.4453.6 



Hydrochloric acid. — A solution of this acid was purified by dis- 

 tillation after dilution. 



Hydrochloric acid gas was generated by dropping C. P. concen- 

 trated sulphuric acid into C. P. concentrated hydrochloric acid. The 

 acids were shown to be essentially free from arsenic. 



Water. — All the water used in the research was purified by dis- 

 tilling the ordinary distilled water of the laboratory, once with alkaline 

 permanganate and then once alone, in both cases with the use of block 

 tin condensers which required no cork or rubber connections to the 

 distilling flasks. 



Utensils. — Quartz or platinum vessels were always employed in 

 place of glass, whenever glass was unsuitable. 



Methods of Analysis. 



The first method of analysis employed was that of converting the 

 silver arsenate into silver chloride by heating in a current of hydro- 

 chloric acid gas. Since this process does not involve transfer of mate- 

 rial it should be capable of giving results of great accuracy. Glass 

 and porcelain are unsuitable for containing the arsenate during this 

 process on account of the certainty of their being attacked. The first 

 attempts at using quartz for the purpose resulted in slight etching of 



6 Baxter, These Proceedings, 42, 201 (1906). 



