76 RESEARCHES UPON ATOMIC WEIGHTS. 



PURIFICATION OF OTHER MATERIALS. 

 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, 3 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 converted 

 into potassium bromide with pure potassium oxalate as before, and the re- 

 mainder 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 distillation being essentially free from 

 chlorine. This treatment has already been proved sufficient to free bromine 

 from chlorine.^ 



Hydrobromic acid was synthesized from the pure bromine by bubbling hy- 

 drogen 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 constructed wholly of glass. The hydrogen 

 was cleansed by being passed through two wash bottles containing dilute sul- 

 phuric 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 permanganate was added 

 to the hydrobromic-acid solution, and the bromine 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 pro- 

 vided with a ground-glass stopper. 



The purification of the hydrobromic acid was carried on in conjunction with 

 Dr. Grinnell Jones, who was engaged in a parallel research upon the atomic 

 weight of phosphorus. Using this acid, he found that 10.48627 gm. of silver 

 bromide were obtained from 6.02386 gm. of the purest silver. This ratio of 

 silver bromide to silver, 100.0000 to 57.4452, is in close agreement with the 

 most probable value, 100.0000 to 57.4453.^ 



' Ba.xteT: Proc. Amcr. Acad., 42, 201 {igo6); Jour. Amer.Chem. Soc, 2S, 1322; Zeit.anorg. 

 Chem., 50, 389. (See page 59.) ^ Baxter: Loc. cit. 



