ATOMIC WEIGHTS 131 



away in a current of carbon dioxide, and the resulting silver sulphide 

 was weighed. 



I subjoin Dumas' weighings, and also the quantit}^ of AggS propor- 

 tional to 100 parts of Ag, as deduced from them: 



.0029 



Dumas used from ten to thirty grammes of silver in each experiment. 

 Stas/ however, in his work employed much larger quantities. Three 

 of Stas' determinations were made by Dumas' method, while in the 

 other two the sulphur was replaced by pure sulphuretted hydrogen. In 

 all cases the excess of sulphur was expelled by carbon dioxide, purified 

 with scrupulous care. Impurities in the dioxide may cause serious error. 

 The data are as follows, with vacuum weights : 



Mean, 114.8522, ± .0007 



The experiments made by Professor Cooke " with reference to this 

 ratio were only incidental to his elaborate researches upon the atomic 

 weight of antimony. They are interesting, however, for two reasons: 

 they serve to illustrate the volatility of silver, and they represent, not 

 syntheses, but reductions of the sulphide by hydrogen. Cooke gives three 

 series of results. In the first the silver sulphide was long heated to full 

 redness in a current of hydrogen. Highly concordant and at the same 

 time plainly erroneous figures were obtained, the error being eventually 

 traced to the fact that some of the reduced silver, although not heated to 

 its melting point, was actually volatilized and lost. The second series, 

 from reductions at low redness, are decidedly better. In the third series 

 the sulphide was fully reduced below a visible red heat. Rejecting the 

 first series, we have from Cooke's figures in the other two the subjoined 

 quantities of sulphide corresponding to 100 parts of silver : 



^ Oeuvres CJompl&tes, 1, 349. 



2 Proc. Amer. Acad., 13, 47-52. 1877. 



