82 THE ATOMIC WEIGHTS. 



Stas,* working by essentially the same method, with from 56 to 83 

 grammes of sulphate at a time, found these percentages : 



69.200 

 69.197 

 69.204 

 69.209 

 69.207 

 69.202 



Mean, 69.203, .0012 



Combining this mean with that from Struve's series, we get a general 

 mean of 69.205, 0011. 



The third sulphur ratio with which we have now to deal is one of 

 minor importance. When silver chloride is heated in a current of sul- 

 phuretted hydrogen the sulphide is formed. This reaction was applied 

 by Berzelius f to determining the atomic weight of sulphur. He gives 

 the results of four experiments ; but the fourth varies so widely from the 

 others that I have rejected it. I have reason to believe that the varia- 

 tion is due, not to error in experiment, but to error in printing ; never- 

 theless, as I am unable to track out the cause of the mistake, I must 

 exclude the figures involving it entirely from our discussion. 



The three available experiments, however, give the following results : 

 The last column contains the ratio of silver sulphide to 100 parts of 

 chloride. 



6.6075 grm. AgCl gave 5.715 grm. Ag. 2 S. 86.478 



9.2323 " 7-98325 " 86.471 



10.1775 " 8.80075 " 86.472 



Mean, 86.4737, db .0015 



We have also a single determination of this value by Svanberg and 

 Struve.J: After converting the chloride into sulphide they dissolved the 

 latter in nitric acid. A trifling residue of chloride, which had been 

 enclosed in sulphide, and so protected against change, was left undis- 

 solved. Hence a slight constant error probably affects this whole ratio. 

 The experiment of Svanberg and Struve gave 86.472 per cent, of silver 

 sulphide derived from 100 of chloride. If we assign this figure equal 

 weight with the results of Berzelius, and combine, we get a general mean 

 of 86.4733, .0011. 



The work done by Richards relative to the atomic weight of sulphur 

 is of a different order from any of the preceding determinations. Sodium 

 carbonate was converted into sodium sulphate, fixing the ratio Na 2 CO s : 

 Na a S0 4 : : 100 : x. The data are as follows, with vacuum weights : 



* Aronstein's translation, pp. 214-218. 



f Berzelius' Lehrbuch, sth ed., vol. 3, p. 1187. 



t Journ. Prakt. Chem., 44, 320. 1848. 



I Proc. Amer. Acad., 26, 268. 1891. 



