BAXTER. — ATOMIC WEIGHT OF PHOSPHORUS. 587 



diately before use. A quantity of bromine which had been thus 

 treated was evaporated on a steam bath in a glass dish, which was 

 then tested for residual phosphoric acid with negative results. 



Phosphorus. — The method used for purifying the phosphorus was 

 distillation with steam. In the case of the phosphorus from which 

 the tribromide for the first series of analyses was prepared, the dis- 

 tillation was assisted by a current of carbon dioxide, and was not 

 repeated. The phosphorus used for the second and third series of 

 analyses was twice distilled with steam, the greater portion at atmos- 

 pheric pressure, a small portion at reduced pressure, in an apparatus 

 constructed wholly of glass. The purified material was preserved 

 under water until used. Portions of these specimens were carefully 

 tested for arsenic by the Berzelius-Marsh method and were found 

 to contain less than one part in one million of the latter element. 

 We are indebted to Mr. W. A. Boughton for carrying out these 

 tests. 



Silver. — Pure silver was prepared by methods which have already 

 been found to be very effective. Since these methods have been de- 

 scribed in detail several times in papers from this laboratory,* only a 

 brief outline of the procedure is given here. Heterogeneous silver re- 

 sidues were reduced with zinc and sulphuric acid, and thoroughly 

 washed with water. The metal was dissolved in nitric acid, and silver 

 chloride was precipitated by a large excess of hydrochloric acid. 

 After the precipitate had been washed it was dissolved in ammonia and 

 reprecipitated with hydrochloric acid. The resulting chloride was 

 reduced with alkaline sugar solution and the metal was fused on 

 charcoal. After cleansing with sand and etching with nitric acid, the 

 buttons were dissolved in nitric acid, and the metal was precipitated 

 with pure ammonium formate. The thoroughly washed product was 

 fused with a blowpipe on a crucible of the purest lime. Electrolytic 

 deposition with silver nitrate as the electrolyte and with a dissolving 

 anode of the pure silver buttons followed, and the electrolytic crystals 

 were fused in a current of pure hydrogen on a boat of the purest lime 

 provided with compartments so that the resulting buttons weighed from 

 two to ten grams. After the buttons had been etched with nitric acid 

 until their surfaces were uniformly crystalline, they were thoroughly 

 washed with ammonia and pure water, and finally heated to 400° in a 

 vacuum. The pure silver was preserved in a desiccator over fused 

 potassium hydroxide. 



* See especially Richards and Wells, Pub. Car. Inst., No. 28, 16 (1905); 

 Jour. Amer. Chem. Soc, 27, 472; Zeit. anorg. Chem., 47, 70. 



