116 ELECTROLYSIS. 



taken not to let a single point be untouched, so as to prevent 

 any interruption in the metallic coating. 



Thus cleaned, the piece must be rinsed in order to remove 

 the pumice stone, dipped in the cyanide bath, rinsed again, and 

 at last taken to the nickel bath. 



Mr. Elmore recommends that pieces of Britannia metal 

 or tin should not remain too long in the potash bath, as this 

 bath is a powerful solvent of tin ; nor to suspend pieces of 

 Britannia metal or brass from the same bar in the potash bath, 

 as the alkaline solution might become charged with tin and 

 deposit some on the brass. 



Cast iron pieces must be rinsed in cold water after coming 

 out of the potash bath, then put in the dilute sulphuric 

 acid scouring bath for from 20 to 60 minutes, rinsed again, 

 cleaned with a very hard brush and sand and water, dipped in 

 the hydrochloric acid bath and rinsed. 



Although cast iron and iron can be directly nickel-plated, 

 there is, according to Mr. Elmore, an advantage in previously 

 coating them with a film of copper, because the nickel adheres 

 better on copper than on iron, and because defects in the 

 cleaning can be more easily detected on a coppered surface than 

 on the naked surface of iron or cast iron. 



The composition of the bath being known, the mode of pre- 

 paration of the pieces elucidated, there remains to be found 

 what are the most suitable conditions to be fulfilled in the 

 electrolytic operation proper, and to successively examine the 

 particularities which the anodes, the vats, the electric currents, 

 &c., should present. 



Nature of the Anodes. When a manufacturer installs in his 

 factory the necessary plant for nickel-plating pieces of his own 

 manufacture, in which case the nickel-plating occupies a position 

 secondary to the principal industry, the economy of motive 

 power, of the consumption of acids, and of the labour entailed 

 for the maintenance of the baths is not particularly sought 

 after. His only object must be always to obtain solid and 

 regular deposits. The economy which would result from a 

 careful study of all the operations of nickel-plating would be 

 very small compared to the total cost of the piece, and would, on 



