1-1 PROCEEDINGS OP l Hi: AMERICAN ACADEMY. 



prominence with circumstances, vitiates the electrochemical equivalent 

 of copper as it is ordinarily determined. Even :t cursor} Btudj ol th 

 careful investigations shows that the complication arises at the point 

 contact of the copper cathode with the solution, and that the Bid Lion 



has the effect of lessening the amount of copper deposited l>y the current 

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

 •pper plates in cupric solutions, which led us to precisely the Batne 

 conclusions as those attained by Foerster and Seidel in 1 1 » « - paper already 

 mentioned. Since these gentlemen have described their work in great 

 detail, an abbreviated statement of our results will Buffice. 



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

 even when the Bolution has been freed from air and has been p i by 



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

 the losses >>! weight of the plates were found to he roughly proportional 

 t<> the respective area- of the plates, if the volume of solution was large. 



■_'. A strongly acid solution does not differ materially in its action from 

 a weakly acid Bolution J hence neither hydrogen nor S< >, ions can he 



responsible for the phenomei 



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

 tration df the cupric Bulphate, being u-n slight when this is abs< at, i een 

 it much sulphuric acid is present. Hence the cupric ions must he the 

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

 reaction Cu + Cu ++ [-f S0 4 "] ±; 2 Cu + [+S0 4 "]. in a word, cuprous 

 Bulphate must be formed. 



■1. 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 . us before, the I oss was nearly doubled. Evi- 

 dently the cuprous becomes cupric sulphate in the oxidizing environment, 

 and thus opportunity lor further reduction is otfered. 



5. ( )n the other hand, plates of copper immersed in neutral solutions 

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

 of cuprous oxide. This is a wholly separate phenomenon, due to the 

 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 Vanni, which consists in adjusting the amount of acid so thai the 

 plates neither gain nor h><e. is a device for replacing dissolved copper 

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

 scientific point of view. 



