ELECTROMETALLURGY 213 



holes, of 0-1 in. in diameter, per 16 square inches, and are of oak or beech wood, and 

 about 0*2 in. thick. Before it is put together, the apparatus is plunged in a bath of 

 melted wax, and is covered with several coats of gum-lac varnish, in order to protect 

 the parts from the action of the acid, brass screws being used to connect it. 



The following practical hints will be of use in selecting scraps to fill the recep- 

 tacle : Choose pieces free from solder or rivets of brass or iron. Flatten out with a 

 hammer such bits as are curled up, and divide with shears those of irregular form, so 

 that all may fit closely upon each other. With these, pack the receptacle as uniformly 

 as possible. For the band of copper, which serves as a conductor, choose a long piece, 

 so that it may bury anew in the mass as its lower end becomes dissolved. Every four 

 or five days stir the pieces vigorously with a brass rod. 



The soluble anode, in its rectangular form as before described, acts as a plate, and 

 hence gives proofs of unequal thickness ; but if the active surface of the receptacle, 

 instead of being flat, be so disposed as to form a sort of counterpart, following the 

 contour of the mould, the deposit will have a uniform thickness. This is illustrated 

 in fig. 798. 



M N is the mould in section ; over it, at a distance of 0*3 in., is arranged a gutta- 

 percha box D P, of which the bottom is perforated with a large number of small holes. 

 This box first has its bottom covered with linen cloth, and is then filled with copper 

 scraps, and the copper conducting band is inserted. 



In order to localise or concentrate the galvanic action at certain places, it is only 

 necessary to heap up the copper pieces at the desired points ; and conversely, when a 

 part has become covered with a deposit of sufficient thickness, it is obviously unneces- 

 sary to employ the protecting coverings of wax or gutta-percha ordinarily used with 

 plate anodes. The- mode of forming the gutta-percha counterpart consists in coating 

 the interior of the mould with several layers of fine thin plaster for a thickness of 

 0'3 in. This is allowed to harden. Into the hollow cast the gutta-percha, softened 

 by warm water, is pressed by the hand, so as to cause it to conform to the indenta- 

 tions of the plaster, care being taken to keep it of uniform thickness. After cooling, 

 it is easily removed, and after perforation is ready for use as above described. It is 

 of course a reduced copy of the interior of the mould. 



With the exception of silver and gold, copper is the metal which has been most 

 extensively worked by these electro-metallurgical processes. 



Seals are copied by obtaining impressions in sealing-wax, pressing a warm wire 

 into the edge for a connection ; rubbing black-lead over the wax to make the surface 

 conducting ; fastening a slip of zinc to the other end of the wire ; wrapping the zinc 

 in brown paper, and putting the whole into a tumbler containing sulphate of copper, 

 a little salt-water having been poured into the brown paper cell. 



Plaster-of-Paris medallions may be saturated with wax or stearine, and then 

 treated, if small, like seals ; if large, in a distinct trough, as in fig. 794. In this case 

 the copy is in intaglio, and may be used as a mould for obtaining the facsimile of the 

 cast. More commonly, the cast is saturated with warm water, and a mould of it 

 taken in wax, stearine, or gutta-percha. This is treated with black-lead, and in other 

 respects the same as seals. 



Woodcuts are treated with black-lead, and a copper reverse is deposited upon 

 them. This is used as a mould to obtain electrotype duplicates, or as a die for 

 striking off duplicates. 



Stereotype plates are obtained in copper by taking a plaster copy of the type, 

 treating it plaster fashion, depositing a thin plate of copper upon it, and giving 

 strength by backing up with melted lead. 



Old brasses may be copied by the intervention of plaster. 



Embossed cards or paper may be copied by first saturating with wax and then using 

 black-lead. 



Fruit may be copied by the intervention of moulds, or may be covered with 

 copper. Leaves, twigs, and branches may have copper deposited upon them. The 

 same for statuettes, busts, and statues. 



Leaves and flowers are furnished with a conducting surface by dipping them into 

 a solution of phosphorus in bisulphide of carbon, and then into a solution of nitrate 

 of silver. Silver is thus released in a metallic state upon their surface. 



Plaster busts, &c., have been copied in copper, by first depositing copper on the 

 plaster prepared for this operation ; when thick enough, the original bust is destroyed, 

 the copper shell is filled with sulphate of copper, as in Jig. 794, and copper is deposited 

 on its inner surface till of sufficient thickness ; the outer shell is then removed. 



Tubes and vessels of capacity do not appear to have been profitably multiplied by 

 electrotype. 



Plates have been prepared for the engraver to work on by depositing copper on 

 polished copper-plates, and removing the deposits when thick enough, 



