170 ELECTROLYSIS. 



MOULDS IN PLASTIC MATERIALS. In practice gutta-percha 

 is used for taking the impresses of metallic pieces, and gelatine 

 for taking those of plaster or wax pieces. 



The gutta-percha or gelatine moulds are rendered con- 

 ductors either by the dry or by the wet method. The dry 

 method consists in brushing the surfaces with plumbago until 

 they become bright black. The wet method consists in coating 

 the surfaces with a solution of argentic nitrate and alcohol, 

 letting them dry, and blowing on them some sulphuretted 

 hydrogen in a nascent state. 



MASSIVE ELECTROPLATING. In order to give the copper 

 reproductions great strength without immoderately increasing 

 the thickness of the deposition, Messrs. Christofle and Co. melt 

 in the interior of the moulds some pieces of brass, which solder 

 easily to each other, and give the electroplated depositions an 

 appearance similar to that of castings. The pieces thus ob- 

 tained can be worked exactly like cast copper; they possess 

 the artistic appearance of the model, which has been faithfully 

 preserved by electroplating, and, in the interior, a malleable 

 resisting body. 



RELIEVO ELECTROPLATING. In the reproduction of statues 

 or of large pieces in relievo the process consisted at first in 

 executing the work in parts and joining these parts together by 

 means of very careful solderings. 



Mr. Lenoir has discovered the means of distributing and 

 spreading the currents in the interior of a mould, whatever 

 may be its dimensions, and therefore of obtaining very large 

 pieces without soldering. 



His process consists in replacing the single metallic wire of 

 the negative pole of the battery by a platinum conductor made 

 of numerous platinum wires interwoven with each other, so as 

 to constitute a veritable carcase having grosso modo the shape of 

 the interior of the mould with a little play, so as to leave every- 

 where a thickness of liquid between the walls and the platinum. 

 The extreme wires are attached together, passing through a 

 glass tube which isolates them from the gutta-percha mould, 

 and are connected to the positive pole of an external battery. 



M. Plante has substituted lead for platinum in the construe- 



