72 MOLECULAR WEIGHT OF ARGENTIC SULPHATE, ETC. 



assumption that the deviations from Boyle's law diminish as the pressure is 

 lowered. They obtained 32.01 as the atomic weight of sulphur. After- 

 wards Jaquerod and Scheuer determined the compressibility of sulphur 

 dioxide through the ranges 400 to 800 mm. and 200 to 400 mm. by a 

 method similar to Lord Rayleigh's. They found, as was to be expected, 

 that the deviation from Boyle's law was smaller at the lower pressure. 

 Nevertheless, in calculating the molecular weight of sulphur dioxide, they 

 assumed that the deviation from Boyle's law per centimeter of pressure 

 between and 760 mm. was the same as between 400 and 800 mm. They 

 obtained 64.036 for sulphur dioxide and hence S = 32.036. If their meas- 

 urement of the compressibility through the range 200 to 400 mm. is used, 

 the result becomes 32.052, and it seems probable that yet a higher value 

 is the true outcome of their experiments. These different conclusions em- 

 phasize the uncertainty of the method. 



Probably the adsorption of sulphurous oxide and hydric sulphide on the 

 glass of the containing globes introduces an error in both the density and 

 compressibility determinations, and hence in facts to which the assumption 

 above mentioned are applied. This possibility of adsorption seems to have 

 been not sufficiently heeded by any of the experimenters on sulphur com- 

 pounds. It adds yet another uncertainty to the results. 



The upshot of these considerations is the conclusion that none of the 

 work heretofore done upon the atomic weight of sulphur decides its value. 

 Hence further investigation is imperative. The problem, for complete 

 solution, must be approached from many sides, and the work must involve 

 many compounds of sulphur. The following contribution describes one 

 section of a comprehensive program by which it is hoped the question may 

 be answered. 



PRELIMINARY EXPERIMENTS. 



The sulphate of silver was selected as the most suitable starting-point 

 for the present investigation, because it seemed probable that this salt 

 could be prepared in a pure condition and accurately analyzed. A further 

 reason for studying argentic sulphate lies in the possibility of later com- 

 bining the results with some ratio involving the sulphide and thus fur- 

 nishing evidence on the even more important question as to the atomic 

 weight of silver. Balanced against the advantages is the disadvantage 

 that only about 10 per cent of its weight is sulphur, causing the experi- 

 mental errors to be greatly multiplied in the calculations ; but the advan- 

 tages more than outweigh the disadvantage. 



A tentative preliminary plan of operations was to fuse argentic sulphate 

 in a platinum crucible, dissolve it, precipitate as chloride, and collect and 

 weigh the precipitate. This plan was thwarted by numerous obstacles. 



