RICHARDS AND MERIGOLD. — ATOMIC WEIGHT OF URANIUM. 391 



tigation were of the same manufacture as those used in the nickel and 

 cohalt work, and since the method of preparation of the three bromides 

 was practically the same, probably the quantity of sodium extracted from 

 the tubes by the action of the hot bromine vapor was the same, — on the 

 average, — in all three cases, and not far from 0.10 per cent. Conse- 

 quently, in calculating the following results, this value was used as a 

 constant correction. The effect of applying the correction is to raise the 

 calculated atomic weight about two tenths of a unit. Of course by this 

 method the quantity of sodic bromide calculated will vary somewhat from 

 the exact quantity present, in individual determinations. The average 

 result, however, will undoubtedly vary but little from the result obtained 

 if the alkali could be determined in each sample. It certainly is very 

 much nearer the truth than the results to be obtained by the cumber- 

 some method of determining the alkali in the filtrate from each precipita- 

 tion of argentic bromide. 



Analysis No. 2 was rejected on account of contamination of the 

 uranous bromide by shreds of asbestos from the packing of the jacket, and 

 No. 4 was not used because the combustion tube cracked during sublima- 

 tion, rendering probable the formation of some oxybromide. The silver 

 required in analysis No. 6 was determined for practice preparatory to 

 the final series, being 0.9087 gram when all corrections were applied. It 

 is not included in the table, since its nature was essentially preliminary. 

 As usual, all weighings were reduced to the vacuum standard. While all 



THE ATOMIC WEIGHT OF URANIUM. 



O = 16.000 ; Ag = 107.93 ; Br = 79.955. 

 First Series (preliminary). UBr 4 : 4AgBr. 



