NICK KI.-I'l, ATI M.. 107 



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

 uvi.iiii'ter. Litmus paper should scarcely redden when dipped 

 nto a bath so composed. 



Wr could multiply the formula), but it would only result 

 in perplexing the operator, and perhaps prevent him succeed- 

 in-; 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 

 potassi.- 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.* 



When 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 

 d< -posit preserves its whiteness, but it adheres badly, swells, and 

 I'-i-ls 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, 



;:itini,' tin- red from the bine, without which precautions the vapours which 



nro constantly emitted in cKrtn>-pl:itiiig establishments would rapidly render i( 



