292 PROCEEDINGS OF THE AMERICAN ACADEMY 



unnecessary. The amount of hydrogen absorbed even by copper 

 reduced from the oxide is exceedingly small. Erdmann and Marchand 

 found that one gram of copper absorbed three one-hundredths of a 

 milligram of hydrogen, and Dumas's results were essentially the same.* 

 Hampe was unable to find a trace of the gas in the copper remaining 

 from his experiments. While this correction may have a sensible 

 effect upon the old atomic weight of oxygen, it cannot seriously eiFect 

 the atomic weight of copper. 



No method for the preparation of pure copper has been suggested 

 which is not open to possible objections. The present standard of 

 reference has the merit of simplicity. Moreover, the results of the 

 analysis of cupric sulphate, unless concealing some unknown error, 

 show that electrolytic copper cannot be very different from the typical 

 element as it exists in combination, otherwise the summation of the 

 results would not so nearly equal one hundred per cent. Again, cupric 

 oxide gives essentially identical results, whether analyzed by reduction 

 or by electrolysis. It must be remembered that, while some of the 

 copper used in the present series of researches came from Lake Su- 

 perior, the greater part was prepared from " chemically pure " Ger- 

 man cupric sulphate. Some unknown constant impurity may have 

 vitiated all the preparations, but the present evidence seems to show 

 that pure electrolytic copper is as definite a substance as most of 

 the other " elementary substances " to which our atomic weights are 

 referred.! A more elaborate comparison of copper from different 

 sources and different modes of preparation would neverthless be one 

 of considerable interest. 



* Ann. Chira. Phys., [3], VIII. 189, 205. See also Thudichum and Hake, 

 Jahresber. 1876, p. 966; and Johnson, Jahresber. 1878, p. 286. 



t Griinvvald and Brauner have independently come to the conclusion that 

 copper is a compound. If this is the case, the compound must be a very defi- 

 nite one. See Chem. Soc. Abstracts, 1890, p. 434. 



