594 PROCEEDINGS OF THE AMERICAN ACADEMY. 



fied with nitric acid and allowed to stand for a further period. Even 

 then it is probable that oxidation was not quite complete, for if the 

 bromine is precipitated with any considerable excess of silver nitrate, 

 even in the presence of much nitric acid, the silver bromide is percep- 

 tibly discolored. On the other hand, if the amount of silver salt used 

 is very nearly equivalent to the bromide present, the precipitate 

 retains its lemon-yellow color even when left for days under the 

 solution. 



Since the determination of the weight of the tribromide and its 

 analysis are so intimately connected, they are described together. 



The weight of the tribromide was found in each analysis by weigh- 

 ing the bulb with its contents, and then, after breaking the bulb, col- 

 lecting and weighing the glass. The bulb was first carefully cleaned 

 on the outside and dried, and left in a desiccator over sulphuric acid 

 for at least twenty-four hours. Its weight in air was then found by 

 substituting standardized weights for the bulb on the balance. The 

 buoyant effect of the air was estimated by finding the volume of the 

 bulb in the usual way from the loss in weight under water of known 

 temperature. The conditions of the atmosphere were taken into ac- 

 fcount in calculating the buoyant effect of the air on the bulb and 

 weights. Since the bulb was exhausted when sealed no correction is 

 necessary for the space in the bulb not filled with liquid. 



After the bulb had been weighed and its volume determined, it was 

 placed in a 300 cc. thick-walled Erlenmeyer flask together with some- 

 what over one hundred cubic centimeters of redistilled ammonia and 

 ten cubic centimeters of pure 30 per cent hydrogen dioxide. A glass 

 stopper which had been very carefully ground into the neck of the 

 flask, was inserted, and the flask was shaken violently enough to break 

 the bulb. The heavy tribromide reacted quietly at the bottom of the 

 aqueous solution, until at the end of about five minutes decomposition 

 was complete. The flask was then allowed to stand twenty-four hours, 

 ■with occasional shaking. This long standing was necessary to allow a 

 small quantity of ammonium bromide fumes to be collected in the 

 aqueous solution. 



The flask, cooled to produce inward pressure, was next carefully 

 opened and the solution was filtered into a three-liter ground-stoppered 

 precipitating flask, while the particles of glass were collected upon a 

 small filter paper. This filter was very thoroughly rinsed with pure 

 water until the filtrate and washings amounted to about 1200 cc. 



In order to find the weight of the glass the filter was burned at as 

 low a temperature as possible in a weighed platinum crucible. When 

 the weight of the glass, corrected to vacuum, was subtracted from the 



