76 THE ATOMIC WEIGHTS. 



Now, one of these salts being formed by a bivalent and the other by a 

 univalent acid, we have to reduce both to a common standard. Doing 

 this, we have tiie following results for the ratio between the atomic 

 weight of silver and the molecular weight of CO, ; if Ag = 1.00 : 



From the acetate COj = .40724, zh .000076 



From the oxalate " = .40718, it .000185 



General mean COj = .40723, ± .000071 



Here the slight error due to the impurity of the oxalate becomes of 

 such trifling weight that it practically vanishes. 



As has already been said, the volatility of silver renders all the fore- 

 going results more or less uncertain. Far better figures are furnished by 

 the combustion of carbon directly, as carried out by Dumas and Stas ^ 

 in 1840 and by Erdmann and Marchandf in 1841. In both investiga- 

 tions weighed quantities of diamond, of natural graphite, and of artificial 

 graphite were burned in oxygen, and the amount of dioxide produced 

 was estimated by the usual methods. The graphite emplo^'ed was puri- 

 fied with extreme care by treatment with strong nitric acid and by fusion 

 with caustic alkali. I have reduced all the published weighings to a 

 common standard, so as to show in the third column the amount of 

 ox3'gen which combines with a unit weight (say one gramme) of carbon. 

 Taking Dumas and Stas' results first in order, we have from natural 

 gra phite : 



1. 000 grm. C gave 3.671 grm. COj. 2. 6710 



.998 " 3.660 " 2.6673 



.994 " 3-645 " 2.6670 



1. 216 " 4.461 " 2.6686 



1. 471 " 5.395 " 2.6676 



With artificial graphite : 



Mean, 2.6683, ± .0005 



Mean, 2.669S5, ± .0313 

 And with diamond : 



.708 grm. C gave 2.598 grm. CO.,. 2.6695 



' 2.6661 



2.6628 

 ' 2.6680 



' 2.6662 



Mean, 5.6665 rb .0007 



*Compt. Rend., 11, 991-1008. Ann. Chiiu. Phj's. (3), i, i. 

 t Jour, f Prakt. Chem., 23, 159. 



