380 PROCEEDINGS OF THE AMERICAN ACADEMY. 



limate thereby, since there was always a constant outward pressure of 

 bromine during the sublimation. The outer end of L was connected 

 with the nitrogen supply of the desiccating apparatus. All glass joints 

 and stop-cocks were lubricated with syrupy phosphoric acid. 



The method of procedure was as follows : In the porcelain boat, E, 

 was placed an intimate mixture of urano-uranic oxide and pure carbon, 

 the carbon being about twenty per cent of the weight of the mixture, 

 thus insuring a large excess of carbon. The apparatus was then thor- 

 oughly swept out by nitrogen, which enters at B and L simultaneously. 

 After the air was completely expelled, the combustion tube was grad- 

 ually raised to a high temperature by the blast lamp. Heating in a 

 current of nitrogen was then continued for three hours at least, some- 

 times longer, in order to insure complete removal of all traces of air and 

 moisture. During this and subsequent operations, the outlet of the 

 stopper D of the inner tube was nearly closed by asbestos wool, thus 

 maintaining a constant and considerable pressure within the apparatus, 

 and hindering the diffusion of air. After this preliminary heating in 

 nitrogen, bromine vapor was passed in through B. During the first trials 

 of the apparatus it was our practice to keep a slow current of nitrogen 

 passing in at L during the sublimation. This kept the jacket entirely 

 free of bromine, a very slow current of nitrogen being sufficient to keep 

 any bromine from passing between the walls of the porcelain tubes. It 

 was found, however, that traces of air diffused through the permeable 

 asbestos packing, and were of course carried into the combustion tube by 

 the current of nitrogen, forming on the inner tube a coating of oxide, 

 and contaminating the sublimate. In order to avoid this, the nitroiren 

 was shut off from L sometime before turning on the bromine. After 

 turning on the bromine, the jacket slowly filled with dilute bromine 

 vapor. While the greater part of the sublimate collected within the 

 inner tube, a little collected between the walls of the two tubes, almost 

 sealing the annular space. This sublimate, which collected on the outside 

 of the inner tube, is a valuable indicator of the condition of the subli- 

 mate witliin. In the presence of mere traces of oxygen the lustrous 

 brown color of the urauous bromide gives place to a dull yellow color 

 easily distinguishable. Comparatively small quantities of oxygen form a 

 coating of black oxide. When the sublimation is conducted according to 

 the method described, the outside of the inner tube is free from any traces 

 of the supposed oxybromide or of oxide, thus showing that no appreciable 

 quantity of moist air could have reached the innermost portions of the 

 sublimate. The best proof of the purity of the sublimate is of course 



