CONTRIBUTIONS FllOM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



A REVISION OF THE ATOMIC WEIGHT OF BROMINE. 

 By Gregory Paul Baxter. 



Presented by T. W. Richards. Received May 28, 1906. 



In numerous investigations in this laboratory upon the atomic 

 weights of certain metals, in which metallic bromides were first 

 titrated against the purest silver, and then the precipitated silver 

 bromide was collected and weighed, the relation between the silver 

 used in the titrations and the silver bromide obtained has yielded 

 data from which the atomic* weight of bromine may be calculated. 

 Furthermore, in all these investigations, as a check upon the purity 

 of the silver and bromine employed, silver bromide was synthesized 

 directly from weighed quantities of silver and an excess of ammonium 

 bromide or hydrobromic acid. Many of these results have already 

 been collected and discussed by Richards,^ nevertheless they are cited 

 in the following table together with a few more recent determinations. 



From the first of these ratios the atomic weight of bromine, referred 

 to silver 107.930, is found to be 79.956, and from the second 79.955. 



Very recently, in experiments in which silver iodide was heated 

 first in a current of air and bromine until the iodine was completely 

 displaced, and then in a current of chlorine to displace the bromine, 

 the ratio of silver bromide to silver chloride was determined in six 

 cases. From the results of these experiments the atomic weight of 

 bromine was calculated to be 79.953,2 if the atomic weight of chlorine 

 is assumed to be 35.473.*^ 



These values for bromine are in close agreement with those of Stas.* 

 In his experiments weighed quantities of pure silver and bromine were 



1 Proc. Amer. Phil. Soc, 43, 119 (1904). 



2 Baxter, These Proceedings, 41, 82 (1905). 



3 Richards and Wells, Puhiications of the Carnegie Institution, No. 28 (1905). 

 * CEuvres Completes, 1, 003. 



