704 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



which had to be very feeble. Various improvements were introduced 

 to the process of M. de la Eive by several savants as MM. Eisner, 

 Bsettger, Perrot, and Sinee ; but soon after, a new method, discovered 

 almost simultaneously by an Englishman, Mr. Wright, and patented 

 by Mr. Elkington (September 1840), and a Frenchman, M. de Euolz 

 (1841), gave to this application of electro-chemistry a fertile impulse. 

 Electro-plating from this moment became a true industrial art in the 

 hands of M. Ghistofie, who acquired the patents of M. de Euolz. 



Without entering into the detailed history of the phases through 

 which electro-plating has passed during thirty years, we will describe 

 the various processes a they are now generally carried on. 



Electro-typing, viz., the art of reproducing by a homogeneous, 

 but a non-adherent and sufficiently thick metallic deposit, the relief 

 of any object such as medals, statues, bas-reliefs, architectural orna- 

 ments, jewellery, &c., may first be referred to. 



Electro-type reproduction is performed in two different ways, 

 according to the object in .view. If an identical reproduction is 

 required, in which the reliefs and intaglios of the copy shall be the 

 same as those of the model, a mould must first be made whose 

 intaglios correspond to the reliefs of the model, and vice versd. The 

 ordinary processes of moulding are then employed ; but it is plain that 

 the mould or cast might be first obtained by electro-typing, and then 

 by a second operation made on the counterpart, the object would be 

 reproduced. The first of these operations only is required if a repro- 

 duction in intaglio of the reliefs of the model is to be made. 



In any case, the surface of the mould on which the current is to 

 deposit the desired metal must be a good conductor of electricity ; and 

 this is the case when the mould is metallic. If however, as often 

 happens in practice, the mould is of wax, sulphur, plaster, or even of 

 gelatine or gutta-percha, the surface must first be metallized. This 

 is accomplished in several ways. The simplest plan is to cover the 

 mould with a uniform thin coat of powdered plumbago by means of a 

 pencil or brush. 



This method of rendering the mould a good conductor is due to 



