70 ELECTROTYPE PROCESSES. 



an odds-and-ends battery and raw zinc, there would be, for every 

 pound of copper deposited, 



s. d. 



16 oz. of zinc used ..04 



16 oz. of copper dissolved 1 



1 4 



And when iron is used, the expense of depositing lib. of copper 

 would be, 



16 oz. of iron, say ..02 



16 oz. of copper ... 1 



Notwithstanding these results, Mr. Smee proves, by several fractional 

 formulEe and an algebraic equation, that the cost of depositing a 

 pound of copper is 



By iron, Is. 6d. 



By odds-and-ends battery, Is. 1 



To this it may be replied by the manufacturer, that, in the first place, 

 raw zinc or spelter used in the way described for an odds-and-ends 

 battery would lose two or three times the quantity that is stated for 

 every equivalent of copper ; and, secondly, that this form of battery 

 is altogether unsuitable for manufacturing purposes, even when 

 amalgamated scrap zincs are used ; and, as regards the calculation, 

 it is not easy to see that, while a pound of copper, dissolved from 

 the positive electrode, originally costs Is., it could, notwithstanding, 

 be deposited by the destruction of 1 Ib. of zinc, not including acid, 

 &c., at the expense of only Is. It ought always to be remembered, 

 that, for manufacturing purposes, the surface upon which the metal 

 is to be deposited in general amounts to several square feet. The 

 article may be, for example, a large ornamental vase, having four 

 square feet of surface. An odds-and-ends battery, or an iron single 

 pair battery, would be too weak. To deposit, with a separate 

 battery, upon a surface such as that of the vase, it requires two or 

 three pairs of plates to give what we may call economical power. 



Recovery of Mercury from Waste Zinc. The general practice of 



manufacturers, when the scraps of zinc become small, is either to 

 treat them as referred to at page 26, to distil the mercury from the 

 zinc, or to sell the scraps to parties who do distil them. This is 

 done by putting the scraps into an iron retort, subjecting it to a red 

 heat, and allowing the beak of the retort to pass into a condenser, 

 which has a tube dipping into water. The mercury distils over, and 

 condenses in, the water. The zinc left in the retort is found to be so 



1 Smee's Elements of Electro-metallurgy, 3rd edit. p. 112. 



