OF ARTS AND SCIENCES. 343 



ever, closely agree with one another, — found the relation, CuO : Cu = 

 100 : 79.7787; and calculating from this relation the atomic weight of 

 copper, the value 62.979 is obtained. Dumas* made several determi- 

 nations of the reduction of cupric oxide and the synthesis of cuprous 

 sulphide ; and calculates the value Cu = 63.5. 



HampCjt whose work gave the most concordant results thus far 

 secured, obtained from three determinations of the percentage of cop- 

 per in cupric oxide the mean value of 79.8347 ± .0013 ; and from two 

 analyses of anhydrous cupric sulphate by electrolytic precipitation he 

 found the proportion CuSO^ : Cu = 100 : 39.725 ± .0007. The atomic 

 weights of copper from these two methods are respectively 63.197 and 

 63.173. 



This was in 1874; and the subject has rested undisturbed until last 

 year, when W. N. Shaw, in the paper before referred to, sought 

 to prove the accuracy of Faraday's law of electrolysis in atomic pro- 

 portions, by means of the actual weights of silver and copper deposited 

 in cells in the same circuit. For the particulars of his method the 

 Report of the Committee on Electrolysis should be consulted ; it is 

 sufficient here to say that as the mean of many determinations he 

 finds the ratio of the silver and copper precipitated to be 3.39983 : 1. 

 Correcting this result for variations in current density, he obtains the 

 value 3.39888, and finally adopts the practically identical value 3.400, 

 which makes the ratio Ag : Cu = 17 : 10. This last value makes 

 Cu = 63.333, while the corrected value gives as the atomic weight the 

 quantity 63.360. 



Below is a summary of all the results : — 



Berzelius, from CuO . . . . 63.153 



Erdmann and Marchand, from CuO 63.316 



Millon and Commaille, from CuO 62.979 



Dumas, from CuO and Cu^S 63.5 



Hampe, from CuO 63.197 



fromCuSO^ 63.173 



W. N. Shaw, by relation to silver 63.333 



" " « corrected 63.360 



The most obvious chemical method for the determination of the 

 relation of the atomic weights of silver and copper, is by the precipi- 



* Ann. d. Chim. et Pliys., (3,) Iv. 129. 

 t Fresenius' Zeitschrift, xiii. 352. 1874. 



