RICHARDS AND MERIGOLD. — ATOMIC WEIGHT OF URANIUM. 381 



found in the agreement of analyses of substance formed under various 

 conditions of bromine supply. 



After the bromine had been run for about one and a half hours, the 

 sublimate was cooled for three hours in a current of nitrogen. "When 

 the tubes were thoroughly cold, nitrogen was finally passed into the 

 jacket through L, iu order to sweep out any traces of bromine that 

 might still remain. The inner tube, containing the sublimate, was then 

 carefully drawn out until the inner end reached a position over the 

 mouth of the weighing bottle, indicated in the diagram by the dotted 

 line. This can be done without seriously disturbing the asbestos pack- 

 ing, a rapid current of' perfectly dry nitrogen being admitted meanwlule 

 through L. By means of the glass rod, R, the sublimate was pushed 

 out of the tube and dropped into the weighing bottle, I. The tube 

 L, carrying the stopper, was then pushed down and the stopper in- 

 serted. The stopper was held by the platinum wires so lightly that 

 after pushing it into place the tube L could be withdrawn, leaving the 

 stopper inserted in the bottle. 



Thus uranous bromide was sublimed, collected, and bottled up in an 

 atmosphere of dry nitrogen ready for weighing, without once coming 

 in contact with the air of the laboratory. That the apparatus is effective 

 for the purpose intended, and capable of producing material of constant 

 composition, was shown by the first rough analyses of uranous bromide, 

 which yielded 57.41, 57.41, and 57.42 per cent bromine respectively. 

 These analyses were made with material that had not been purified, but 

 served to show the constancy of composition of the sublimate ; for not only 

 was the length of time occupied in the sublimation varied, but in one case 

 the sublimate was cooled in bromine instead of in nitrogen. Of course if 

 an appreciable amount of an oxygen compound were formed, by diffusion 

 of air or moisture, there would almost certainly be discrepancies in the 

 results, since it is hardly conceivable that under the varying conditions 

 exactly the same quantities of oxy-salt should be formed each time. 



Because the specific gravity of uranous bromide was unknown, the fol- 

 lowing determinations were made : 2.0328 grams of the salt displaced on 

 one occasion 0.3332 gram of kerosene at 21°, and at another trial 0.3322 

 gram. The kerosene had been redistilled, and only the high boiling 

 portion was used. The density of the kerosene at 21°, referred to 

 water at 4°, was 0.7919. Hence the specific gravity of the uranous 

 bromide was (1) 4.830 and (2) 4.846, giving as the mean 4.838. 

 This value was used in reducing the observed weights of bromide to 

 the vacuum standard. 



