124 PROCEEDINGS OP THE AMERICAN ACADEMY. 



prominence with circumstances, vitiates the electrochemical equivalent 

 of copper as it is ordinarily determined. Even a cursory study of these 

 careful investigations shows that the complication arises at the point of 

 contact of the copper cathode with the solution, and that the side reaction 

 has the effect of lessening the amount of copper deposited by the current. 

 With this in mind, we made a systematic investigation of the behavior 

 of copper plates in cupric solutions, which led us to precisely the same 

 conclusions as those attained by Foerster and Seidel in the paper already 

 mentioned. Since these gentlemen have described their work in great 

 detail, an abbreviated statement of our results will suffice. 



1. Metallic copper slowly dissolves in an acid solution of cupric sulphate, 

 even when the solution has been freed from air and has been protected by 

 an atmosphere of hydrogen. This conclusion was tested many times, and 

 the losses of weight of the plates were found to be roughly proportional 

 to the respective areas of the plates, if the volume of solution was large. 



2. A strongly acid solution does not differ materially in its action from 

 a weakly acid solution ; hence neither hydrogen nor SO4 ions can be 

 responsible for the phenomenon. 



3. Other things being equal, the action is proportional to the concen- 

 tration of the cupric sulphate, being very slight when this is absent, even 

 if much sulphuric acid is present. Hence the cupric ions must be the 

 active agents, and they can only dissolve the copper according to the 

 reaction Cu + Cu++[+ SO/'] t.2 Cu+[+ SO"]. In a word, cuisrous 

 sulphate must be formed. 



4. In contact with the air this action naturally takes place more 

 rapidly than in the absence of oxygen. Instead of losing only about 

 0.004 milligram per square centimeter per hour in a normal solution 

 of cupric sulphate at 20", as before, the loss was nearly doubled. Evi- 

 dently the cuprous becomes cupric sulphate in the oxidizing environment, 

 and thus opportunity for further reduction is ottered. 



5. On the otlier hand, plates of copper immersed in neutral solutions 

 of cupric sulphate always gain in weight, becoming coated with a film 

 of cupi'ous oxide. This is a wholly separate phenomenon, due to tlie 

 hydrolysis of the cuprous sulphate. Of course this hydrolysis cannot 

 happen in an acid solution ; hence copper deposited electrolytically from 

 an acid solution is free from cuprous oxide. Obviously, too, the method 

 of Vaniii, which consists in adjusting the amount of acid so that the 

 plates neither gain nor lose, is a device for replacing dissolved coi)per 

 by an equal weight of cuprous oxide, and hence is very faulty from a 

 scientific point of view. 



