ELECTROPLATING AND ELECTROTYPING. 169 



These pieces must be conductors; they act in the same 

 manner as the copper electrode in the ordinary Daniell cell. 

 The simple bath is nothing but a real Daniell cell closed on 

 itself on a very short circuit, and in which the internal instead 

 of the external current is used. 



FIG. 27. 



Simple Bath. 



The bath is electrolysed as soon as the circuit is closed by 

 the connection of the objects to the zincs ; the zinc becomes 

 oxidised, and the copper is slowly and in a very regular and 

 uniform manner deposited upon the objects to be reproduced. 

 When the coating of precipitated metal is sufficiently thick, 

 the pieces are taken out of the bath and detached from the 

 copper mould thus formed. These moulds are then placed in 

 the bath and connected with the zinc. After a longer or 

 shorter immersion in the cupric sulphate solution the moulds 

 become coated with a deposit of copper, and perfectly true 

 reproductions of the original objects are obtained. 



It is easy to understand that the moulds of galvanic copper 

 can only be used for taking impresses on objects having a 

 sufficient taper, and that only objects which cannot be attacked 

 by acid can be placed in the bath. If, for example, it is pro- 

 posed to reproduce iron castings, it will be necessary to pre- 

 viously copper them, so as to prevent their being attacked by 

 the acid solution. It is also necessary to rub the metallic 

 surfaces with a pad soaked with turpentine, so as to prevent 

 the adherence of the deposit against the pieces themselves. 



