BAXTER AND JONES. — ATOMIC WEIGHT OF PHOSPHORUS. 141 



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- 

 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 hydrobromic 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 purity of the hydrobromic acid was tested by a quantitative 

 synthesis of silver bromide. The silver used, which was kindly fur- 

 nished by Mr. G. S. Tilley, had been prepared with all the necessary 

 precautions for work on the atomic weights of silver and iodine. 16 

 The procedure used by Baxter 17 for the synthesis of silver bromide 

 from a weighed amount of silver was followed in detail. In this experi- 

 ment 6.02386 grams of silver yielded 10.48627 grams of silver bromide ; 

 hence, silver bromide contains 57.4452 per cent of silver, while Baxter 

 found as the mean of 18 determinations 57.4453 per cent. The hydro- 

 bromic acid was evidently pure. 



Silver Nitrate. Crude silver nitrate was reduced with ammonium 

 formate, made by passing ammonia gas into redistilled formic acid. 

 The reduced silver was washed with the purest water, until the wash 

 waters no longer gave a test for ammonia with Nessler's reagent, and 

 was fused on sugar charcoal. The buttons were then scrubbed with 

 sea-sand and thoroughly cleansed with ammonia and nitric acid. 

 They were then dissolved in redistilled nitric acid, in a platinum dish. 

 After the silver nitrate solution had been evaporated on a steam bath 

 until saturated, an equal volume of redistilled nitric acid was added 

 and the solution was cooled. The precipitated silver nitrate was very 

 completely drained in a centrifugal machine, provided with platinum 

 Gooch crucibles to retain the salt. 18 A similar recrystallization fol- 



16 Baxter and Tilley, Jour. Amer. Chem. Soc, 1909, 31, 201. 



17 Baxter, These Proceedings, 1908, 42, 208. 



18 Baxter, Jour. Amer. Chem. Soc, 190S, 30, 286. 



