16 PROCEEDINGS OF THE AMERICAN ACADEMY 



Analyses of Antiimoniods Bromide. 

 Determination of Bromine. 



Theory Sb. 120 requires 66.667 ' 



The mean vahie of the percentage of bromine deduced from the 

 fifteen analyses previously made (see these Proceedings, Vol. XII.", 

 page 54) was 66.666, which differs only by an inappreciable quantity 

 from the mean of the above results. At the same time the results are 

 much sharper, the maximum difference from the mean value having 

 been reduced to less than one fifth of the previous amount, and to only 

 0.00025 of the quantity estimated, giving us with certainty the atomic 

 weight of antimony within one one-thousandth of its value. It must 

 be remembered, moreover, that, although these last results were ob- 

 tained with the same compound as before, the material was prepared 

 in a wholly different way. The material first used was purified by 

 repeated crystallization from sulphide of carbon, — that last used by 

 repeated fractional distillation and sublimation. 



Hoping to reduce the limit of error to a still greater degi-ee, we * 

 were led to devise a volumetric method of testing the atomic weight of 

 antimony, which, while it had all the advantages of the gravimetric 

 method 23reviously employed, is free from its sources of error. The 

 method has also this great advantage, that it brings the question of 

 the atomic weight of antimony down to a definite issue. 



If the atomic weight of antimony were 122.00, it would require 

 1.7900 grammes of pure silver to jirecipitate the bromine from a solu- 

 tion of 2.0000 grammes of antimony bromide, while if the atomic 

 weight of antimony were 120.00, it would require 1.8000 grammes of 



* Since publishing our " preliminary notice," our attention has been called to 

 the fact that a similar process was used by Professor J. W. Mallet of the Univcr- 

 Bity of Virginia in his investigation of the atomic weight of lithium, as it has 

 since been used by him in his admirable work on the atomic weight of aluminum. 



