1892.] on Electro-Metallurgy. 627 



some solution of the same kind, which, to save time, has been pre- 

 pared beforehand, and immerse in it, a little apart from each other — 

 the positive and negative wires coming from some generator of 

 electric current — this will happen : metallic copper will come out of 

 the solution, and attach itself as a coating to the negative wire, and 

 consequently that wire will grow in thickness. At the other wire — 

 the positive — exactly the reverse action will take place. There, if 

 the positive wire be copper, it will gradually dissolve, and become 

 thinner. The quantity of metal deposited on the negative wire will 

 almost exactly equal the quantity dissolved from the positive, and 

 therefore the solution will contain the same quantity of metal at the 

 end of the experiment as at first, but it will not be the same metal ; 

 it will be fresh metal dissolved from the positive wire, and the metal 

 originally contained in the solution will have been deposited as 

 metallic copper. 



I will show on the screen this process in operation. Here are the 

 two wires I spoke of. The electric circuit, which includes these two 

 wires, is so arranged that on its completion the thick wire will be 

 the positive^ and the thin wire the negative. Now please complete 

 the circuit. One wire (the positive) is carrying an electric current 

 into the copper solution, and the other (the negative) is carrying the 

 current away. The solution is conveying the current between the 

 wires, and one of the incidents of the transport of current from wire 

 to wire by the solution, is electro-chemical decomposition, or electro- 

 lysis ; and the result of that is, the deposition, out of the solution, 

 of copper, upon one wire, and the dissolving away, or entering into 

 solution, of copper, from the other. Now it can be clearly seen that 

 the wire that was thick is now thin, and the wire that was thin is now 

 thick. 



Imagine the growing wire to be an electrotype mould, and that 

 the deposit of copper which formed on the wire has spread over the 

 surface, and formed a nearly uniform film, and that by continuing the 

 process it has become thick, that deposit, stripped from the mould, 

 would be an electrotype. 



Or imagine the negative wire to be a thin sheet of pure copper, and 

 the positive wire to be a thick sheet of impure copper, and suppose 

 the action carried on so far that the thin sheet has become thick, by 

 the deposition of copper upon it from the solution, and the thick 

 one thin, by its copper entering into solution, that case would 

 represent the condition of things in electrolytic copper refining. 



Allow your imagination to take one more short flight, and suppose 

 that this is not a solution of copper, but one of silver, and that the 

 growing wire is a teapot, to be silvered ; and further, suppose that 

 the dissolving electrode is silver, and you will then understand the 

 principle of electro-plating. 



It requires very little explanation to make the ordinary arrange- 

 ment of electrotyping intelligible. Here is a trough containing 

 sulphate of copper solution. Here is a mould, that, through the 



