342 PROCEEDINGS OF THE AMERICAN ACADEMY 



XVII. 



CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 



HARVARD COLLEGE. 



Presented by Josiah P. Cooke, Director, March 9, 1887. 



A DETERMINATION OF THE RELATION OF THE 

 ATOMIC WEIGHTS OF COPPER AND SILVER. 



By Theodore W. Richards. 



In the Report of the Committee on Electrolysis made to the Brit- 

 ish Association at Birmingham, of which an advance copy has been 

 received by Professor Cooke through the kindness of Dr. Oliver 

 Lodge, a direct determination is given of the ratio between the atomic 

 weight of copper and that of silver, based on the electrolytic experi- 

 ments of W, N. Shaw. As the value of the ratio thus obtained is 

 quite different from that usually accepted, it seemed to Professor 

 Cooke desirable that the results should be confirmed by a direct 

 chemical method, and the writer was intrusted with this investigation. 



Of the work worthy of consideration which has thus far been done 

 upon the atomic weight of copper, first in chronological order comes 

 that of Berzelius,* who made two determinations of the weight of cop- 

 per formed by the reduction of pure cupric oxide by hydrogen. He 

 found the percentage of copper in this compound to be 79.823 ± .002. 

 This corresponds to an atomic weight of 63.153, taking oxygen 

 = 15.963, with Clarke. The next determination was by Erdmann 

 and Marchand,t who used the same method. They found the per- 

 centage of copper in cupric oxide to be 79.8645 ± .0038 as a mean 

 of four determinations, — a value which makes Cu = 63.316. Mil- 

 Ion and Commaille.l in three determinations, — which did not, how- 



* Poggend. Annal., viii. 177. 



t Journ. fur Prakt. Cliem., xxxi. 389. 1844. 



$ Fresenius' Zeitschrift, ii. 475. 1863. 



