ATOMIC WEIGHT OF SILICON. 247 



liquor was free from chloride. This required from three to six crystal- 

 lizations according to the quality of the original material. 



Two other specimens of hydroxide were made by combining barium 

 hydroxide and sodium carbonate, after both substances had been 

 crystallized until free from chloride. The resulting solution was then 

 evaporated to crystallization, and the product was recrystallized. 



Bromine. This material had been purified by Mr. A. F. Scott 

 according to the method which has been frequently used at Harvard. 12 

 Crude bromine was first distilled from aqueous potassium bromide in 

 order to remove chlorine. Next one-fourth of the product was con- 

 verted to potassium bromide by means of recrystallized potassium 

 oxalate, and the remaining three-fourths of the bromine was distilled 

 from solution in this potassium bromide. All the product was then 

 converted to potassium bromide by means of potassium oxalate, and 

 the potassium bromide was fused in a platinum dish with enough 

 recrystallized potassium permanganate to oxidize all organic matter. 

 In order to obtain bromine the purified potassium bromide was dis- 

 solved in a solution of pure sulfuric acid. The excess of potassium 

 permanganate contained by the salt caused a small quantity of 

 bromine to be liberated. This bromine was removed by distillation 

 since it might have contained a trace of iodine. Enough pure per- 

 manganate to liberate the greater portion of the bromine was then 

 added, and the bromine was distilled into a receiver cooled with ice. 

 In this last step the bromine received a third distillation from a 

 bromide. The product was separated from the water, dried with 

 resublimed phosphorus pentoxide and once redistilled. 



Silver. This substance was prepared by standard methods. These 

 consisted in brief of the following processes: double precipitation as 

 chloride, followed by reduction with alkaline sugar solution, fusion of 

 the metal on charcoal, solution and reprecipitation with ammonium 

 formate, fusion on pure lime, electrolytic transport, fusion on pure 

 lime in hydrogen, etching, drying in a vacuum at 500°. Recent work 

 by Baxter and Parsons 13 and Baxter 14 as well as earlier work have 

 shown that these processes yield a product of adequate purity. 



Nitrogen. This gas was prepared by the Wanklyn process. Air was 

 charged with ammonia and passed over hot copper catalyst. The 



12 Baxter, Moore and Boylston, These Proceedings, 47, 585 (1912); Jour. 

 Amer. Chem. Soc, 34, 1644 (1912); Baxter and Grover, Jour. Amer. Chem. 

 Soc, 37, 1029 (1915). 



13 Baxter and Parsons, Jour. Amer. Chem. Soc, 44, 577 (1922). 



14 Baxter, Ibid., 44, 591 (1922). 



