NICKEL-PLATING. 133 



some factories. They are suitable if the solutions are neutral 

 or slightly alkaline, and if care is taken to well insulate them 

 and not introduce them into circuit. 



M. Brandely, in his handbook on electroplating, recom- 

 mends the following recipe for rendering wooden vats water- 

 tight : 



Dissolve some indiarubber and guttapercha in sulphide of 

 carbon, reducing the solution until it is in a slightly semi-liquid 

 state, and spread it on the wall of the vat with a large flat 

 brush. The angles should be coated to a thickness of nearly 

 half an inch, so as to cover any defect in the joints which often 

 negligently occurs. In our opinion, all these coating mixtures 

 constitute remedies which it would be better to avoid the use 

 of, as they are not required when the work is well executed. 

 The best vat is that which is made of thick pine well joined 

 and lined inside with lead, ultimately covered by a thin wooden 

 lining, the latter being held in position by means of wooden 

 cross-bars without any screw or bolt. For small baths only, 

 we recommend stoneware vessels, but they must be selected 

 with care, and without any crack. 



NICKEL-PLATING OP ZINC. Zinc being easily dissolved by 

 the solutions used for nickel-plating, it is necessary to take 

 certain precautions for preventing pieces or fragments of zinc 

 getting detached in the bath ; otherwise the objects suspended 

 opposite the anodes become streaked and black, and it is utterly 

 impossible to improve them after. As soon as a solution con- 

 tains zinc, even in small quantities, it must be thrown away 

 and a fresh one must be prepared, as the cost of extracting 

 the zinc would be greater than that of a new bath. 



It will be understood from the foregoing how carefully the 

 nickel-plating of zinc has to be performed. The objects must 

 first be covered with a solid copper coating, not one single 

 point of it remaining uncovered, as without this precaution the 

 operation fails and the bath is lost. When thus prepared, the 

 objects can be plated without any difficulty and without any 

 danger to the bath. When the cost is not an obstacle, it is 

 preferable to polish the pieces before coppering them, because 

 polishing with steel or bloodstone closes the pores of the zinc 



