SILVER, POTASSIUM, ETC. 45 



When silver bromide is heated in chlorine gas, silver chloride is formed. 

 In 1860 Dumas* employed this method for estimating the atomic weight 

 of bromine. 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 AgCl. 131.092 



4.237 " 3. 2 35 " i3 -974 



5.769 4-403 " 131.024 



Mean, 131.030, .023 



This series is evidently of but little value. 



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,f to effect the synthesis of silver bromide, dissolved the 

 metal in nitric acid, precipitated the solution with potassium bromide, 

 washed, dried, fused, and weighed the product. The following quanti- 

 ties of bromine were found proportional to 100 parts of silver : 



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



Much more elaborate determinations of this ratio are due to Stas.J 

 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 neces- 

 sary to precipitate the silver, was transformed into hydrobromic acid. 

 This was added to the dilute solution of the sulphate, and, after precip- 

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

 supernatant fluid was determined. All weighings were reduced to a 

 vacuum. From these experiments, taking both series as one, we get 

 the following quantities of bromine corresponding to 100 parts of silver: 



74.0830 



74.0790 



74.0795 

 74.0805 

 74.0830 



Mean, 74.081, db .0006 



*Ann. Chem. Phartn., 113, 20. 



f E. Mulder's Overzigt, p. 116. Berzelius' Jahresbericht, 24, 7; 



I Aronstein's translation, pp. 154-170. 



