48 FORMS OF ELECTROTYPE APPARATUS. 



an inch of the mouth with a mixture of 24 parts water and 1 sul- 

 phuric acid, taking care that the copper solution is of the same 

 depth as the solution in the porous cell. 



Preparation of the Coin. A fine copper wire must now be put 

 round the edge of the coin and fastened by twisting. Then cover 

 the back part, upon which the deposit is not required, with bees'- 

 wax or tallow, or, what is better, imbed the back of the coin with 

 gutta percha. Have the fore part or face well cleaned, and the sur- 

 face moistened with sweet oil, by a camel's hair pencil, and then 

 cleaned off by a silk cloth, till the surface appears dry : or, instead 

 of oil, the surface may be brushed over with black lead, which will 

 impart to it a bronze appearance. The use of the oil or black lead 

 is to prevent the deposit adhering to the face of the coin. A very 

 common and excellent method to prevent the copper deposit adher- 

 ing to the copper mould is this : Take a gill of rectified spirits of 

 turpentine, and add to it about the size of an ordinary pea of bees'- 

 wax. When this is dissolved, wet over the surface of the mould 

 with it, and then allow it to dry : the mould is then ready to put 

 into the solution. Medals taken from moulds so prepared retain 

 their beautifully bright colour for a long time. But when fine line 

 engravings are to be coated, the little wax dissolved in the turpen- 

 tine may be objectionable ; so also is black lead, for both have a 

 tendency to fill up the fine lines. In this case, let the wash be wiped 

 off by a silk handkerchief, instead of drying it : but for ordinary 

 medals this objection will scarcely apply. This being done, the 

 opposite end of the copper wire round the penny piece is to be con- 

 nected with a piece of amalgamated zinc, either by means of a bind- 

 ing screw or a hole in the zinc. Then place the zinc in the acid 

 within the porous cell, and put the penny piece into the copper 

 solution : bring the face of the metal or coin parallel to the zinc, at 

 the distance of about half an inch or one inch from the porous vessel. 

 Deposition immediately begins, and the metal thickens according to 

 the length of time the action is kept up. In about twenty-four 

 hours, the deposit will be of the thickness of a common card, and it 

 may then be taken off. The zinc is to be brushed and washed, 

 before it is put aside. The wire round the coin is now to be un- 

 twisted, and by a slight turn will come off easily. The deposit is 

 also easily separated from the mould, which will be a perfect coun- 

 terpart of the face of the penny piece. 



This mould is next to be treated exactly as described for obtaining 

 it from the penny piece, and the deposit from it will be afac-simile 

 of the penny piece. With care, any number of duplicates may be 

 taken from this mould. 



It need hardly be remarked, that as copper is deposited the 

 solution becomes proportionally exhausted, and in a short time the 



