CHAP, ix.] ELECTRO-PLATING. 709 



then trace the new lines, which are transferred to the plate and then 

 delivered to the engraver. 



It is well known that for printing plates by chromography, the 

 various colours must be rigorously fitted in their right places. Electro- 

 typing enables us to fit them perfectly in plates of this kind. The 

 National Press of France has thus been enabled to print many maps in 

 colours, and particularly the great geological Map of France, which is 

 itself based on the Staff Maps for all that regards the topographical 

 part. 



But electro-typing not only reproduces plates identical with 

 engraved ones, but it is applicable to direct engraving, such as copper- 

 plates and etching, only in this case it is not done by a metallic 

 deposit, and the plate on which the drawing to be reproduced is drawn, 

 instead of being placed in the bath as the negative pole, corresponds 

 to the soluble anode, In fact, its surface being cohered by a thin 

 layer of insulating varnish, and the drawing made by a fine point 

 having exposed the metal beneath, the latter is attacked by the 

 electrolytic action, and it is eaten into in the same way as in ordinary 

 etching, and the engraving is executed without the operator being 

 exposed to the injurious action of nitrous fumes." 



The processes of Duclot, Gillot, and Gamier, for engraving in 

 relief on copper or zinc, are also partly based on electrolysis ; but the 

 details of the operations necessary for these processes are too minute 

 to be reproduced here, we should be drawn, besides, beyond our 

 subject. 



We next coifle to the application of electro-plating to the 

 reproduction of objects in the round such for instance as busts, 

 statues, vases, capitals, and other architectural ornaments. The 

 principle is just the same, only the reproduction of objects of large 

 size offered at first certain difficulties that have been happily 

 surmounted. The object is to avoid all inequalities of thickness in 

 the deposits on different parts of the mould, and yet to obtain a 

 thickness all over which shall give a sufficient solidity to the object of 

 art reproduced. Suppose a mould of a statue, the parts of which 

 come together so as to leave a hollow which was occupied by the 

 model before the moulding. The question is how to obtain, all over 

 the interior, an equal and regular deposit of copper. At first a soluble 

 anode was placed inside the mould, but the rapid solution of this 



