CHAP. IX.] 



ELECTRO-PLA TING. 



705 



M. Jacobi. A solution of nitrate of silver in alcohol may also be 

 used. The surface of the mould moistened with this is exposed to a 

 stream of hydrosulphuric acid, when an extremely thin black layer of 

 sulphide of silver is formed, which is an excellent conductor. This 

 second method is chiefly employed in the reproduction of delicate 

 objects, as flowers and fruits, or objects in glass or crystal. 



The mould being obtained, and male ready to receive the metallic 

 deposit, the bath and other electro -plating apparatus must be prepared. 

 What is called the simple apparatus is just the bath itself, which 

 forms, in truth, a constant cell, like Daniell's. Suppose we want to 

 reproduce an object in copper, which is the metal most frequently 



PIG. 454. Simple apparatus for electro-plating. 



employed, we place in a tub or glass vessel a solution of sulphate 

 of copper. 



In the centre of the tub is placed a porous vessel filled with 

 water acidulated with sulphuric acid, and into this is plunged a plate 

 or cylinder of zinc, which forms the negative pole of the battery. To 

 this pole is suspended the mould of the object to be reproduced, by 

 means of a metallic wire which wraps it round so as to be in contact 

 with the conducting layer (plumbago or sulphate of silver). Fig. 454 

 shows the arrangement of the apparatus, which will serve equally 

 well for gold or silver electro-plating. In this case the nature of the 

 bath is altered, as we shall soon see. 



z z 



