22 THE ATOMIC WEIGHTS. 



for estimating the atomic weight of l)romine. His results 

 are as follows : In the third column I give the weight of 

 AgBr equivalent to 100 parts of AgCl. 



2.028 grm. AgBr gave 1.547 AgCI. 131.092 



4.237 " 3.235 " 130-974 



5.769 " 4.403 " 131.024 



Mean, 131.030, dr .023 



This series is evidently of but little value. 



But the two ratios upon which, in connection with Stas' 

 analyses of silver bromate, the atomic weight of bromine 

 chiefly depends are those which connect silver with the 

 latter element directly and silver with potassium bromide. 



Marignac,* to effect the synthesis of silver bromide, dis- 

 solved the metal in nitric acid, precipitated the solution 

 with potassium bromide, washed, dried, fused, and weighed 

 the product. The following quantities of bromine were 

 found proportional to 100 parts of silver : 



74.072 



74-055 

 74.066 



Mean, reduced to a vacuum standard, 74.077, zh .003 



Much more elaborate determinations of this ratio are due 

 to Stas.f In one experiment a known weight of silver was 

 converted into nitrate, and precipitated in the same vessel 

 by pure hydrobromic acid. The resulting bromide was 

 washed thoroughly, dried, and weighed. In four other 

 estimations the silver was converted into sulphate. Then a 

 known quantity of pure bromine, as nearly as possible the 

 exact amount necessary to precipitate the silver, was trans- 

 formed into hydrobromic acid. This was added to the 

 dilute solution of the sulphate, and, after i)recipitation was 

 complete, the minute trace of an excess of silver in the clear 

 supernatant fluid was determined. All weighings were re- 



* E. Mulder's Overzigt, p. 116. Berzelius' Jahresbericht, 24, 72. 

 f Aronstein's Translation, pp. 154-170. 



