112 ELECTROLYSIS. 



process, it is advisable to get them lightly scoured after cleansing. 

 This will be effected by dipping them in a bath of dilute sul- 

 phuric acid, and rinsing them in pure water before immersing 

 them in the potassic cyanide solution which always precedes 

 their being put in the bath. 



M. Julius Weiss's Method. M. Weiss distinguishes the 

 case in which the metals to be nickel-plated have been previously 

 polished from the case in which they are in a rough state. He 

 says that in the first case the cleansing must be effected with 

 the greatest care, as the polishing is generally obtained by 

 means of oiled cloth, and it is important to remove every trace 

 of greasy matters. 



M. Weiss recommends, amongst other means, a lixivium of 

 boiling soda, or a dipping into benzine, or again the lixivium 

 of soda succeeding the dipping in benzine. When cleansing by 

 means of benzine, an iron vessel, provided with a hermetic cover 

 (owing to the liability to explosion of benzine), is used. It is 

 filled up to about three-quarters, and the objects, suspended 

 by wires, are immersed in it, and submitted to a stirring action 

 up to the time of taking out, so as to remove any trace of 

 grease. They are then rinsed in several waters, and separately 

 brushed with pulverised lime with a brush and a little water 

 over a flat wooden tub, and rinsed again. 



For the cleaning of rough articles, a scouring done with care 

 accompanied with a vigorous washing, and if necessary, with a 

 cleansing in benzine, are sufficient. Of course the result is not 

 so satisfactory as that obtained from a complete polishing opera- 

 tion, but in some cases it is found quite sufficient. 



Gaiffe's Method. Eub the pieces with a brush dipped into 

 a hot thick decoction of Spanish whiting, water, and carbonate 

 of soda. The cleansing is perfect when the pieces can easily be 

 wetted by ordinary water. 



For scouring copper and its alloys, it is sufficient to dip 

 them for a few seconds in a bath composed of 10 litres of water 

 and one kilogramme of nitric acid. Eough pieces require a 

 bath composed of two parts water, one part nitric acid, and one 

 part sulphuric acid. 



For scouring iron, steel, and cast iron, the piece must be 



