118 ELECTROLYSIS. 



baths on to the pieces will not be replaced. It will be at once 

 seen that the electric energy whose duty, with soluble anodes, 

 was confined to the equilibrium of the calorific action arising 

 out of the passage of the current through the resistances of 

 all kinds included in the circuit, will, with insoluble anodes, 

 have besides to equilibrate the work of decomposition of the 

 electrolyte. This supplementary expenditure of electrical 

 energy can be estimated by calculation when the heat of forma- 

 tion of the electrolyte is known, or by experience in working 

 sometimes with soluble and at other times with insoluble anodes, 

 and keeping identical in both cases all the other conditions of 

 the operation. 



But the influence of the nature of the electrodes is parti- 

 cularly felt in the constancy of the bath. If nickel plates are 

 exclusively used, it has been demonstrated in practice that 

 the solution grows more and more alkaline. This fact can 

 easily be verified by means of litmus paper: the bath, which is at 

 the beginning neutral or sensibly so, will, in a short time, colour 

 the red paper blue, and this coloration, which will grow deeper 

 and deeper, is a proof of an excess of alkali. If it is not 

 remedied the solution will thicken, and there will be formed a 

 yellow insoluble precipitate of suboxide of nickel. Nothing is 

 more simple than re-establishing the equilibrium of the bath by 

 pouring into it a little citric acid, at the same time stirring 

 the solution and testing it with litmus paper. 



When platinum or carbon anodes are used the nickel 

 deposited is entirely borrowed from the bath; the solution 

 grows metallically weaker and more acid. The effect produced 

 is therefore contrary to that which results from the use of soluble 

 anodes ; in the latter case the deposition will always be of a 

 good white but will not adhere freely, and it will be impossible 

 to obtain a thick coating of nickel. 



The remedy for that state of things is easy to be found : it 

 consists in introducing some carbonate of suboxide of nickel in 

 the bath, and its neutrality reappears.* 



* M. Pfanhauser recommends the following preparation for the carbonate of 

 suboxide of nickel : The carbonate of nickel, mixed with water, is pounded in 

 a mortar, and by successive additions of water reduced to a state of syrup, which 



