372 PROCEEDINGS OF THE AMERICAN ACADEMY. 



assumes a dull, greenish yellow appearance, due to formation of the oxy- 

 salt. If not protected from further action of moist air, the salt liquifies 

 completely in a surprisingly short space of time. 



In an attempt to change the coating of oxybromide back to the 

 normal salt, recourse was had to the method which has been used suc- 

 cessfully in many atomic weight investigations carried on in this labora- 

 tory. The salt was transferred to a platinum boat and placed, with a 

 weighing bottle of suitable size, in a glass bottling apparatus* A 

 stream of dry hydrobromic acid gas was then passed over the bromide at 

 a temperature just below the subliming point of the salt. This treat- 

 ment, however, fails to restore the original brilliant appearance of the 

 freshly sublimed bromide. The yellow color of the oxybromide still 

 remains. Apparently the oxybromide, once formed, cannot, by this 

 method, be reduced to the normal uranous bromide. 



In the previous investigations upon zinc, magnesium, nickel, and 

 cobalt, in which this method of converting oxy-salts to the normal com- 

 pounds has been used, the presence of even minute quantities of oxy-salt 

 was made known by the opalescence of the solutions on account of the 

 insolubility of these salts. With uranium, however, this method of 

 detecting the presence of uranyl bromide cannot be used, for the oxy- 

 bromide of uranium is even more soluble than uranous bromide. 



The analysis of uranous bromide presents further difficulties. All 

 uranous salts reduce silver nitrate. When a solution of silver nitrate, 

 slightly in excess of the calculated amount, is added to a solution of 

 uranous bromide, the silver bromide first precipitated is probably mixed 

 with metallic silver; for if the silver bromide is filtered off, and the 

 filtrate set aside, finely divided metallic silver soon separates. If a 

 lar^e excess of silver nitrate is added to the uranous bromide, a brilliant 

 purple precipitate is obtained. It is possible that the precipitate 

 may be a mixture of finely divided metallic silver and argentic 

 bromide, or perhaps of normal argentic bromide and the long sought 

 sub-bromide. Although this is an interesting phenomenon, it was 

 not considered advisable to interrupt the research at this period for 

 the length of time necessary for an investigation. The addition of 

 nitric acid prevents the formation of this colored precipitate, but owing 

 to the danger of the loss of bromine, this is not an advisable expedient. 

 Of course it is possible to determine the bromine by first precipitating 

 the uranium and adding silver nitrate to the filtrate, but this introduces 



* For a description of this apparatus, see These Proceedings, 32, 59. 



