390 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



argentic bromide determined. Thus from each of these analvses two 

 distinct ratios were obtained as a basis for the calculation of the molecular 

 weight of uranous bromide, — the ratio of uranous bromide to argentic 

 bromide, and that of uranous bromide to silver. 



As would naturally be expected from the complexity of operations 

 involved, determinations of the sodium in the filtrates from the argentic 

 bromide gave unsatisfactory results. The large quantity of filtrate and 

 wash waters had to be evaporated to small bulk, the uranium precipi- 

 tated, and the sodium determined in the residue. It seemed advisable to 

 make a series of separate analyses for sodium only, and use the average 

 percentage of sodium found as a constant correction. This method was 

 used in the work upon cobalt and nickel.* 



Accordingly three alkali determinations were made, wholly in platinum, 

 the material not coming in contact with glass at any time except during 

 the original collection and weighing of the sublimed bromide. The sub- 

 limate was dissolved in pure water, in a platinum dish, and the uranium 

 was precipitated with pure ammonium sulphide. The ammonium sul- 

 phide was freshly prepared for each analysis, wholly in platinum. It left 

 no residue on evaporation in platinum. The precipitated sulphide was 

 digested on the water bath to expel most of the excess of ammonium 

 sulphide, filtered through a platinum funnel, and the filtrate and wash 

 water evaporated to small bulk in a platinum dish. The sodium bro- 

 mide was then converted to sodium sulphate and weighed. The follow- 

 ing table contains the data and result : — 



The average of these three determinations, 0.095, per cent, is practically 

 identical with the amount of sodic bromide found in the cobalt and nickel 

 work, which was 0.10 per cent. The porcelain tubes used in this inves- 



* These Prcoeedings, 34, 339, 365 (1899). 



