182 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the salt was recrystallized four times in platinum. Enough ammonia 

 to form disodium ammonium arsenate was added to a solution of this 

 salt before the precipitation of the silver arsenate. 



Sample F. A portion of the disodium arsenate prepared for Sample 

 B was converted into trisodium arsenate by means of recrystallized 

 sodium carbonate, and the trisodium arsenate was recrystallized six 

 times in platinum vessels. 



Sample G. Arsenic trioxide was twice resublimed in a current of 

 pure dry air and then once crystallized from dilute hydrochloric acid 

 solution. Next the arsenious acid was oxidized to arsenic acid exactly 

 as described under Sample C. Finally the arsenic acid was converted 

 into trisodium arsenate by means of pure sodium carbonate, and the 

 salt was crystallized four times in platinum. 



In all the foregoing crystallizations the crystals were thoroughly 

 drained in a centrifugal machine employing large platinum Gooch 

 crucibles as baskets,^ and each crop of crystals was once rinsed with a 

 small quantity of pure water and subsequently drained in the centrifugal 

 machine. 



Silver nitrate. — The silver nitrate used in the preparation of the 

 different samples of silver arsenate was recrystallized several times in 

 platinum vessels, with centrifugal drainage, until the mother liquor 

 gave no opalescence upon dilution when tested in the nephelometer. 



Hydrobromic acid. — One quarter pound of commercial bromine 

 was converted into potassium bromide by addition to recrystallized 

 potassium oxalate. In the concentrated solution of this bromide, in a 

 distilling flask cooled with ice, three pounds of bromine were dissolved, 

 in several separate portions, each portion being distilled from the 

 solution into a flask cooled with ice before the addition of the next 

 succeeding portion. A portion of the purified bromine was then con- 

 verted into potassium bromide with pure potassium oxalate as before, 

 and the remainder of the bromine was distilled in small portions from 

 solution in this pure potassium bromide. The product obtained was 

 thus twice distilled from a bromide, the bromide in the second distilla- 

 tion being essentially free from chlorine. This treatment has already 

 been proved sufficient to free bromine from chlorine. 5 



Hydrobromic acid was synthesized from the pure bromine by bub- 

 bling hydrogen gas (made by the action of water on "hydrone") 

 through the bromine warmed to 40°-44° and passing the mixed gases 

 over hot platinized asbestos in a glass tube. The apparatus was con- 



4 Baxter, Jour. Amer. Chem. Soc, 30, 286 (190S). 

 6 Baxter, These Proceedings, 42, 201 (190G). 



