158 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



This result is practically identical with that of Hampe, whose work 

 receives excessive weight, as does also that of Berzelius. The oxide of 

 copper is evidently of doubtful value in the measurement of this atomic 

 weight. 



The composition of copper sulphate has been studied, not only by 

 Hampe, but also by Baubigny ' and by Richards." Baubigny merely 

 ignited the anhydrous salt, weighing both it and the residual oxide, as 

 follows : 



4.022 grm. CuSO^ gave 2.0035 CuO. 49.813 per cent. 

 2.596 " 1.293 " 49.807 



Mean, 49.810, ± .002 



Hence Cu = 63.460. 



The same ratio, in reverse — that is, the synthesis of the sulphate 

 from the oxide — was investigated by Richards, who shows that the 

 results obtained are vitiated by the same errors which affect the copper 

 oxide experiments previously cited. The weights given are reduced to 

 vacuum standards. The percentage of oxide in the sulphate is stated in 

 tlie third column of figures: 



1.0084 grm. CuO gave 2.0235 grm. CuSO,. 49.835 per cent. 



2.7292 " 5.4770 " 49.830 



1.0144 " 2.0350 " 49.848 



Mean, 49.838, ± .0036 



Hence Cu = 63.550. 



The two series combine thus ; 



Baubigny 49.810, ± .0020 



Richards 49.838, ± .0036 



General mean 49.816, ± .0017 



Here, plainly, the rigorous discussion gives Baubigny's work weight 

 in excess of its merits. 



In the memoir by Richards now under consideration, his fourth upon 

 copper, the greater part of his attention is devoted to the sulphate, 

 Hampe being followed closely in order to ascertain what sources of 

 error affected the work of the latter. Crystallized sulphate, CUSO4.5H2O 

 was purified with every precaution and made the basis of operations. 

 Three series of experiments were carried out, the water being determined 

 by loss of weight upon heating, and the copper being estimated electro- 

 lytically. In the first series the following data were found, the weights 

 being reduced to a vacuum, as in all of Richards' determinations: 



iCompt. Rend., 97, 906. 1S83. 

 ''Proc. Amer. .\cad., 26, 240. 1S91. 



