108 ELECTROLYSIS. 



We would also recommend the operator to pay attention to 

 the temperature of his baths, keeping the solutions, if not 

 at a uniform, at least at a sufficiently warm temperature during 

 the days and nights of winter. The hand being dipped in the 

 bath should not feel any impression of cold. If, for economical 

 reasons, the room is not heated at night, it is a good precaution 

 in the morning to heat to ebullition a portion of the solution 

 and pour it in the vats so as to raise the temperature of the 

 baths quicker than this would take place with the surrounding 

 air only. In a large establishment where the heating is 

 effected by means of steam, care must be taken not to introduce 

 any iron or lead pipes in the vats, as they would damage and 

 alter the solutions of nickel ; earthenware pipes should be used. 



AUXILIAKT BATHS. The baths of which we have given a 

 description are those in which the electrolytical work takes 

 place ; the industry of nickel-plating requires some other baths 

 for the preparation of pieces ; we will call them auxiliary baths, 

 and will describe them before enumerating the manifestations 

 which precede the coating proper. 



Scouring Bath. This bath, which is especially used for 

 rough cast iron, is composed of a solution of one quarter of a 

 litre of sulphuric acid in each 10 litres of hot water. 



Potash Bath. The composition of the potash bath is 

 almost the same in all the factories ; it consists of a solution of 

 one kilogramme of potash in each ten litres of water. As it 

 is necessary to use this solution in a hot state, an iron worm 

 tube through which steam circulates may be conveniently 

 arranged at the bottom of the vat. 



Cyanide Bath. The cyanide bath contains a solution of 

 potassic cyanide in the proportion of 500 grammes of cyanide 

 to every ten litres of water. This bath is used for the removal 

 of any trace of oxide which might have been formed after the 

 scouring of copper or brass. This bath is of great importance 

 in nickel-plating, particularly as the solution of nickel, contrary 

 to ordinary solutions of cyanide of silver, exerts no dissolving 

 action on oxidised surfaces. 



Whiting Bath. As a substitute for the preceding bath, 

 which is expensive and offers some danger, M. Perille advises 



