NICKEL-PLATING. 113 



immersed in the bath of diluted sulphuric acid until they be- 

 come of a uniform grey hue, and then scrubbed with wet pumice 

 powder, which brings out the bare metal. When the pieces 

 are rough they must remain four hours in the scouring bath 

 and afterwards be scrubbed with well sifted wet sand. The 

 two operations are repeated until the complete disappearance 

 of the layer of oxide. 



This process is not complicated, and to those who know the 

 excellence of M. Gaiffe's products, it will appear quite unneces- 

 sary to look for further improved processes. 



Operations effected ly M. Perille. The objects dealt with by 

 M. Perille are mostly of polished steel, ordinary polished cast 

 iron, and polished malleable iron. 



His workshop is arranged as it is illustrated in Fig. 19, 

 page 114. The manipulations before the pieces are put in the 

 bath are as follow : 



1. Brush the pieces with petroleum, turpentine, or benzine, 

 then wipe in the sawdust of the left-hand bins 1 and 2 ; 



2. Suspend the pieces separately and dip them in a bath of 

 boiling potash ; after about 15 minutes' immersion, rinse them 

 in tub No. 3 ; 



3. Brush lightly all the pieces on all their faces in liquid 

 quicklime, then rinse well in tubs Nos. 3 and 2 ; 



4. Scrub the pieces lightly with some almost liquid pumice 

 powder, then rinse in tubs 3, 2, and 1, shake and drain dry, 

 always holding the pieces by their hooks ; 



5. Dip quickly in the whiting bath so that the pieces do not 

 remain in this bath more than one or two seconds ; then rinse 

 in tubs 2 and 1 and shake well. 



M. Perille prepares the pieces of copper in the same 

 manner as those of cast iron or steel, with the following 

 variations : 



1. Leave the pieces only a few minutes in the potash ; 



2. Do not rub with pumice powder the pieces which would 

 become unpolished or scratched by the powder or the brush ; 



3. When the pieces happen to be only partially polished, 

 dip them quickly in pure nitric acid and then dip them in the 

 whiting bath. 



