BAXTER, — ATOMIC WEIGHT OF PHOSPHORUS. 595 



corrected weight of the bulb and the tribromide, the weight of the tri- 

 bromide in vacuum was obtained. 



In order to make sure that this method of finding the weight of the 

 glass was a satisfactory one, it was tested by several blank experiments 

 with bulbs containing no tribromide. These bulbs were first weighed 

 in the air unsealed, and then were treated in exactly the same way as 

 bulbs containing tribromide. In two cases the fi-agments of the bulbs 

 were collected upon a weighed Gooch-Munroe-Neubauer crucible. In 

 the first three, however, the glass was collected upon a small filter 

 paper as in the analyses. 



Weight of Bulb. Weight of Glass recovered. Difference, 



grams. grams. gram. 



1.20098 1.20097 -0.00001 



0.99814 0.99813 -0.00001 



1.01851 1.01846 -0.00005 



1.12986 1.12994 +0.00008 



1.0843S 1.08441 +0.00003 



Since in every experiment the weight of the glass collected agrees with 

 that of the bulb within 0.00008 gram and is never more than 0.00005 

 gram less than that of the bulb, it is evident that no important 

 amount of glass is lost either by passing through the filter paper or 

 by solution in the ammoniacal liquid. 



The filtrate containing ammonium bromide was next acidified by the 

 addition of about 40 cc. of concentrated nitric acid diluted to about 

 300 cc. Since bromine was sometimes temporarily set free during the 

 addition of the acid, the acid solution was poured into the bromide 

 through a thistle tube the stem of which extended to the bottom of 

 the flask. Thus, although bromine might be set free at the dividing 

 surface between the bromide and the nitric acid, no bromine ever 

 reached the upper surface of the liquid, owing to unoxidized phosphor- 

 ous compounds in the bromide solution. The thistle tube was thor- 

 oughly rinsed into the flask, the stopper of the flask was moistened 

 and put in place, and the flask was gently agitated to mix the solutions. 

 It was then allowed to stand for forty-eight hours. In no case was 

 there any evidence that bromine was permanently set free by the nitric 

 acid, for after the mixing of the solutions they were always colorless, 

 and when the flasks were opened after two days' standing no odor of 

 bromine could be detected, although 0.00001 gm. is readily perceptible 

 in 3 liters of air.^ 



* Baxter, Thorvaldson and Cobb, Jour. Amer. Chem. Soc, 33, 329 (1911). 



