NICKEL-PLATING. 107 



The bath should be of from 6 to 8 degrees of Baume's 

 areometer. Litmus paper should scarcely redden when dipped 

 into a bath so composed. 



We could multiply the formulae, but it would only result 

 in perplexing the operator, and perhaps prevent him succeed- 

 ing before a long series of trials. We prefer to remind him 

 that it is neither the prescription nor the bath by themselves 

 which insure satisfactory results, but the conscientious work of 

 the operator, the purity of the chemical substances, the con- 

 duct of the electric current, the maintenance of the plant in good 

 working order, and particularly the most minute cleanliness. 



Contrary to almost all the other electro-plating solutions, 

 such as those of gold, silver, copper, or brass, which contain 

 potassic cyanide, the solution of a nickel bath should be ab- 

 solutely free from that salt. 



After a certain time the nickel baths become altered 

 according to the anodes in use, turning either alkaline or acid. 

 At the beginning we prefer the solutions having a very slightly 

 acid reaction, this can be ascertained with the litmus paper, 

 which should take a slightly pink-red colour.* 



W T hen the solution becomes too alkaline or too ammoniacal, 

 a kind of greenish sediment is produced, which thickens the 

 bath and gives the pieces a disagreeable yellow appearance. 

 In the contrary case, when the solution becomes too acid, the 

 deposit preserves its whiteness, but it adheres badly, swells, and 

 peels off. In order to avoid these annoyances the operator 

 must test his baths every morning before using them, and, if 

 necessary, bring them to that state of slight acidity which we 

 recommended. 



Should the solution not reach the above-mentioned degree 

 of concentration of 8 degrees, the deposition would take place 

 too slowly; should it be higher than 10 degrees, the salts of 

 nickel would crystallise, and crystals of an emerald green hue 

 would be deposited on the walls of the vat and on the anodes. 



* Litmus paper being continually used in the preparation of baths must 

 always be kept in proper working condition. It must be kept in a closed vessel, 

 separating the red from the blue, without which precautions the vapours which 

 are constantly emitted in electro-plating establishments would rapidly render it 



