218 ELECTROLYSIS. 



He obtained the following results : 



1st. With the saturated solution of sulphate acidulated to 

 ^, the loss in weight of the copper electrode at the positive pole 

 is always greater than the increase in weight of the cathode. 

 This difference has varied between T f^ and yf ^ of the weight 

 of the deposition (or an average of 0'033). Care was taken 

 after withdrawing the electrodes from the solution to dry them 

 in vacuo, so as to prevent the alteration of the copper. 



2nd. With the solution of sulphate of copper neutralised in 

 a cold state by the carbonate, the loss at the positive pole has 

 been sometimes greater and sometimes smaller than the gain 

 at the negative pole, but the differences did not amount to T -J^- 

 part of the weight of the deposition. On an average, the loss of 

 weight was smaller than the weight of the deposition by a few , 

 thousandths only. The deposition in the two first solutions 

 (acid and ordinary) was very close and cohesive, and could be 

 taken off in bands ; whereas in the two last (pure and neutral) 

 the copper was crystallised and more cohesive. 



But the experiments, especially with the fourth solution, 

 are not satisfactory in this respect, that some blackish scales 

 produced by the formation of subsalts drop from the positive 

 pole ; which does not occur in the first ones, owing to the 

 acidity of the solution. In the same neutral solution the 

 negative cupreous deposit is pink-tinted, and probably contains 

 some protoxide, for it loses a part of its weight if it is heated in 

 hydrogen. 



These results illustrate the influence of the liquids and of 

 the electrodes on the effects produced and on the cohesion 

 of the deposition. If, however, the results obtained with the 

 three first solutions are considered, it may be admitted that the 

 differences in the loss of weight of the soluble anode is prin- 

 cipally due to the acidity of the solution, since the sulphate of 

 copper sold in the trade is always acid, and with the pure 

 sulphate this difference is very small. 



If we describe in detail M. Becquerel's experiments, it is not 

 only to warn the refiners against a loss of work amounting to 

 from 3 to 4 per cent., which loss can easily be avoided by using 

 sulphates as pure as possible, but more particularly to call their 



