50 ATOMIC WEIGHT DETERMINATIONS. 



J. Dumas : 63.5 (O = 16). 



Dumas says that experiments on the reduction of cupric 

 oxide and on the sulphidation of copper have shown him 

 that the atomic weight of copper lies between 31.5 and 82, 

 near 31.75, but that his experiments cannot be regarded as 

 decisive. {Annal. de Chimie et de Physique, (3,) S5, 1859, 129.) 



MiLLON and Commaille : 63.128 (0 = 16); 394.55 

 (O = 100). 



These (three) experiments were in most respects a repeti- 

 tion of Erdmann and Marchand's. The value is the mean; 

 the extreme diflference is 0.49 for O = 100, or 0.0784 for O 

 = 16. The sulphate was prepared free from iron or zinc 

 by dissolving copper in ammoniacal sulphate or nitrate. 

 The oxide was obtained by heating the nitrate. (Paris 

 Comptes Pcndus.SS, 1863, 1249; and 57, 1863, 145.) 



Fresenius sees no reason for preferring this to Erdmann 

 and Marchand's value. [Fresenius^ Zeitschr. filr Anal. Chem.y 

 ^, 1863, 474.) 



W. Hampe : 63.3296 (0 = 16). 



In three experiments cupric oxide was reduced in a cur- 

 rent of hydrogen with all possible precautions. The hydro- 

 gen was displaced by air before weighing, though it was 

 shown by experiment tliat porous copper does not condense 

 hydrogen. The metal was heated till incipient melting was 

 observed. The reduction and melting were repeated with- 

 out altering the weight. Hampe attempted to control his 

 results by reconverting the metal into oxide, but was unable 

 to effect complete oxidation. The water produced by the 

 reduction was found to be perfectly pure. The mean result 

 was Cu = 31.6696, maximum,, 31.6729, minimum, 31.6648. 

 The oxide was prepared from metallic copper. To obtain 

 pure metallic copper, sulphate free from bismuth was elec- 

 trolytically decomposed, the iinely divided metal well washed, 

 then melted, lirst in a current of carbon di-oxide, afterwards 

 in hydrogen, and then again in carbon di-oxide. From the 

 metal, basic nitrate was formed and from this salt, by heat- 

 ing first in air and then in oxygen, oxide. In two experi- 

 ments the atomic weight of copper was determined by 

 decomposing cupric sulphate by electrolysis, and weighing 

 the metal. The residual fluid was evaporated, and a minute 

 amount of copper, which had escaped decomposition, was 



