NICKEL-PLATING. 109 



the use of a bath composed of two litres of sulphuric acid, one 

 litre of nitric acid, one-tenth litre of calcined soot, and pne- 

 tenth litre of sodic chloride. 



To prepare it, the nitric acid is first poured in an earthen- 

 ware jar, then the sulphuric acid and the soot, and finally the 

 salt ; stir slowly, avoid breathing the fumes which are given off, 

 and particularly the projections in the face resulting from the 

 ebullition due to the temperature of the mixture. 



This bath is only ready for use six hours after having been 

 prepared, and should be revived once a week with a little of 

 the four substances of which it is composed. 



Hydrochloric Acid Bath. For nickel-plating pieces of iron 

 or steel, a bath composed of a solution of one part of hydro- 

 chloric acid for every five volumes of water can be substituted 

 for the potassic cyanide solution. 



Dipping Copper Bath. This bath is used for covering the 

 pieces with a first metallic coating previous to the nickeling ; it 

 is composed of 



Sulphate of copper 100 grammes. 



Sulphuric acid 100 



Distilled water 10 litres. 



The sulphate is dissolved in hot water and the acid is poured 

 in the mixture. 



Coppering Bath for Zinc. This bath is composed as 

 follows : 



Crystallised acetate of copper 200 grammes. 



Carbonate of soda 200 



Crystallised bisulphide of soda 200 



Potassic cyanide 300 



Distilled water 10 litres. 



This solution should be energetically boiled before being used. 

 PREPARATION OF PIECES FOR NICKEL-PLATING. Before 

 being put into the electrolytic bath, the pieces should be pre- 

 pared with the greatest care ; upon this preliminary step often 

 depends the final success, and we beg to insist upon that point, 

 the more so that we have always seen it very much neglected 

 by beginners. 



