SILVER, POTASSIUM, ETC. 29 



retted hydrogen. In all cases the excess of sulphur was ex- 

 pelled by carbon dioxide, purified with scrupulous care. 

 Impurities in the dioxide may cause serious error. The 

 five results come out as follows for 100 parts of silver : 



.0007 



The experiments made by Professor Cooke* with reference 

 to this ratio were only incidental to his elaborate researches 

 upon the atomic weiglit of antimony. They are interesting 

 however, for two reasons : they serve to illustrate the vola- 

 tility of silver, and they represent, not syntheses, but reduc- 

 tions 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 concord- 

 ant and at the same time plainly erroneous figures were ob- 

 tained ; the error being eventually traced to the fact that 

 some of the reduced silver, although not heated to its melt- 

 ing 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 : 



7.541 1 grm. Ag2S lost .9773 grm. S. Ratio, 114.889 



5.0364 " .6524 " " 114.882 



2.5815 " .3345 " " 114-886 



2.6130 " .3387 " «' H4.892 



2.5724 " .3334 " " 1 14.891 



Mean, 114.888, ± .OOI2 



I-I357 grm. AggS lost .1465 S. Ratio, 114.810 



1.2936 " .1670 " " 114.823 



Mean, 1 14.8165, ±: .0044 



* Proc. American Acad, of Arts and Sciences, v. 12. 1877. 



