132 



ELECTROLYSIS. 



pole, and the pieces with the positive pole of the battery or the 

 dynamo. The basic salts which are the cause of the yellowish 

 tint will, by this operation, be dissolved, and the coating will 

 become white. 



VATS. The nickeling vats must be of a capacity greater by 

 10 per 100 than that really required for the work to be executed. 

 These vats are generally made of pine or pitch pine, two or 

 three inches thick, and well joined, as shown in Fig. 22. 



FIG. 22. 



Vat for Nickel-plating. 



Some vats are not lined internally ; others are lined with 

 sheets of lead soldered together by a homogeneous soldering ; 

 others are lined with guttapercha. 



Mr. Sprague recommends lining the inside walls of a vat 

 with a mixture composed of 4 parts of rosin and 1 part of 

 guttapercha with a small quantity of boiled oil. 



M. Berthoud* lines his vats with a mixture composed of 

 150 parts of Burgundy pitch, 25 parts of guttapercha, and 75 

 parts of pumice powder. 



For small baths, stoneware, glass or china vessels may be 

 used ; they are more expensive and fragile, but are watertight, 

 and easily kept clean. 



Enamelled cast-iron or iron vats are also generally used in 

 * ' Formulaire de 1'Electricien,' by E. Hospitaller. 



