SULPHUR. 81 



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 quan- 

 tities of sulphide corresponding to 100 parts of silver : 



7.5411 grm. Ag 2 S lost .9773 grm. S. Ratio, 114.889 



5.0364 .6524 " " 114.882 



2.5815 -3345 " " 114.886 



2.6130 .3387 " " 114.892 



2.5724 .3334 " " 114.891 



Mean, 114.888, .0012 



I - I 357 S rm - A S2$ lost -1465 S. Ratio, 114.810 



1.2936 .1670 " " 114.823 



Mean, 114.8165, db .0044 



Now, combining all four series, we get the following results : 



Dumas 1 14.8234, .0029 



Stas '.'-.. 114.8522,^.0007 



Cooke's 2d 114.888, .0012 



Cooke's 3d 1 14.8165, d= .0044 



General mean 1 14.8581, d= .0006 



Here again we encounter a curious and instructive compensation of 

 errors, and another evidence of the accuracy of Stas. 



The percentage of silver in silver sulphate has been determined by 

 Struve and by Stas. Struve t reduced the sulphate by heating in a cur- 

 rent of hydrogen, and obtained these results : 



5.1860 grm. Ag ? SO 4 gave 3.5910 grm. Ag. 69.244 per cent. 



6.0543 4.1922 " 69.243 



8.6465 " 5.9858 " 69.228 " 



11.6460 8.0608 " 69.215 " 



9.1090 6.3045 " 69.212 " 



9.0669 " 62778 " 69.239 " 



Mean 



* Proc. Ainer. Acad. of Arts of Sciences, vol. 12. 1877. 

 f Ann. Chem. Pharm., 80, 203. 1^51. 



