L36 PROCEEDINGS OF THE AMERICAN ACADEMY. 



U to be noticed that the value (68.54) obtained from Gray's observa- 

 tions I >\ our method oi correction is near these figui 



It' the absolute accuracy of Faraday's law is assumed, these results 

 show either that the Bilver voltameter must yield nearly 0.1 per cent too 

 mucb Bilver, or else that the value of the atomic weight of copper found 

 chemically in this Laboratory (63.604) must be ".1 percent too high. 



Convincing as these conclusions seemed, the attempt was made to ob- 

 tain yet further light upon the copper voltameter by varying the conditions. 

 For example, several experiments were made with a mercury cathode, 

 in the hope that the amalgam of copper might be less easily influenced 

 by side reactions than the metal itself; but the difficulties in the waj of 

 determining accurately the weight of the large volume of metal which 

 was needed to contain the copper, soon led to the abandonment of this 

 attempt. Moreover other chemical difficulties, due to the po sible dis- 

 solving of mercury, added complications. 



It seemed now worth while to make a few determinations of the 

 amount ol copper deposited from a solution saturated with cuprous salt, 

 in order to fix the highest possible limit for the electrochemical equiva- 

 lent in a fashion wholly free from any correction, as well as to test 

 experimentally our criticism of Foerster and Seidel's remarks about 

 such a Bolution. In order to saturate the liquid with cuprous ions, the 

 weighed platinum cathode was raised above the solution by means of its 

 sliding BUpport, and the current was run backward and forward for an 

 hour or more between the two coils of copper (wrapped in 61ter paper, 

 B and C, Fig. 4) which were to serve as anodes. Instead of the large 

 bottle of the earlier experiments, a test tube just large enough to contain 

 the electrodes was used, so that the small amount of necessary solution 

 could be more easily saturated. In due time the cathode was lowered, 

 and the quantitative electrolysis commenced. Of course the Bolution had 

 been boiled, and was protected by a current of hydrogen throughout 

 the experiment. The silver voltameter used was an improved arrai 

 meiit. but its results are reduced to the standard used in the earlier 

 experiments for the sake of ready comparison. This matter will be 

 fully explained in the sequel. 



This value of the atomic weight, 63.573, is 0.06 per cent higher 



* Gray in his first paper reports that with plates of 240 Bq. cm. ares bi 

 0.29803 gram of copper for every gram of silver, while with plates ol 50 sq. cm. area 



he obtained 0.29 107 L:ram. Hence with plates of zero ana lie W ould ha\ . obtained 



0.29434, corn sponding to the atomic weight given above. (Phil. Mag., [5], 22, J07 

 [IbbGJ. Last three determinations in table.) 



