BAXTER. — A REVISION OF THE ATOMIC WEIGHT OF BROMINE. 203 



first titrated again&t each other, and then the precipitate of silver 

 bromide was collected and weighed. Of the four results by the first 

 method, one should be rejected according to his own statements, since 

 the bromine was not thoroughly dried. The remaining three, 79.959, 

 79.961, and 79.960, give as an average 79.960. From the weight of 

 silver bromide four values were obtained, 79.950, 79.952, 79,955, and 

 79.957, with an average of 79.954. 



Marignac^ also determined the ratio of silver to silver bromide, 

 with somewhat lower results, — 79.959, 79.941, and 79.952; average, 

 79.950. 



Scott,^ in his analyses of ammonium bromide, obtained six values 

 for the same ratio, varying between 79.936 and 79.948, with an 

 average of 79.943. One of his results is here rejected, since the silver 

 used in this experiment was known to be impure. 



Dumas'' by heating silver bromide in chlorine found the values 

 80.06, 79.89, and 79.96. 



In computing the atomic weight of bromine from these data, great 

 weight is always given to Stas's determinations, the value 79.955 

 being usually assumed as the most probable one for the constant in 

 question. Certainly, as pointed out by Richards,^ the true value 

 must lie between 79.95 and 79.96. Clarke calculates the value 79.949 

 as the weighted average of the dififerent investigations previous to 

 Scott's.9 



Considerable uncertainty exists as to the purity of the materials 

 employed in much of the foregoing work. Richards and Wells ^^ have 

 already exhaustively investigated the various methods of preparing 

 pure silver, and have found that while it is a comparatively simple 

 matter to free this substance from metallic impurities, the absence of 

 gaseous impurities is by no means so easy to secure. Oxygen may be 

 eliminated best by fusion in an atmosphere of pure hydrogen gas,^^ 

 or by prolonged fusion in a vacuum, while a lime boat was found to be 

 the most suitable support for the silver during fusion. 



In most of the experiments cited on page 202, one of the final steps 

 in the purification of the silver was fusion of electrolytic crystals on 

 lime, in many cases in a vacuum, but without especial care to prolong 



" CEuvres Completes, 1, 81. 



« Jour. Chein. Soc. Trans., 79, 147 (1901). 



f Ann. Chera. Pharm., 113, 20 (1860). 



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



9 A Recalculation of Atomic Weights, Smith. Misc. Coll., 1897. 

 1° Publications of the Carnegie Institution, No. 28, 16. 



" 13a.\ter, These Proceedings, 39, 249 (1903). 



