ELECTROTYPE PROCESSES. 



49 



current of electricity passing will be too much for the strength of 

 the solution, which will then give a deposit of a sandy consistence, 

 without tenacity. 1 It is therefore necessary, while the deposition 

 is going on, to suspend some crystals of sulphate of copper at 

 the top of the solution, which, being dissolved, will maintain its 

 strength. 



Forms of Apparatus. It will be observed that no particular form 

 of apparatus is required for electrotyping, but certain modifications 

 may be adopted for convenience and economy. As every portion 

 of the zinc in the acid is capable of giving off electricity, by placing 

 the cell that contains the zinc in the centre of the copper solution, 

 moulds may be suspended on each side of that cell. We have also 

 observed that the zinc plate should not be allowed to touch the cell, 

 as the copper will be reduced upon it and the cell destroyed. To 

 avoid this, the zinc may be suspended by a small wooden peg, put 

 through it and made to rest upon the edges of the cell. (See figure 13.) 

 Figures 29, 30, 31, represent several convenient forms of apparatus 

 for electrotyping. 



31. 



Instead of porous vessels made of earthenware, a bladder may 

 be used, in which the acid and zinc are placed. We have also seen 

 a vessel divided by a porous partition, being either a plate of biscuit 

 porcelain, or of plaster of Paris, or very thin sycamore wood, or 

 dressed skin. The porcelain, as before mentioned, is the best: 

 plaster is too porous, and the solution soon destroys it: wood is 

 too close, and the deposit is consequently very slow : skin does 

 very well for a short time, but it is soon destroyed. When porous 

 cells were not convenient, we have made electrotypes by wrapping 

 the zinc plates in two or three folds of stout cartridge paper, 

 moistened with a solution of salt, and placing this in the copper 

 solution with the mould. Of course, this is only to be adopted 

 when a porous vessel cannot be obtained. The paper lasts but a 

 short time, and has, therefore, to be frequently renewed; besides 



1 See laws, page 19. 

 E 



