HISTORY OF ELECTRO-METALLURGY. 15 



" Being aware of the apparent natural law which limits metallic 

 deposition by voltaic electricity, excepting in the presence of a 

 metallic body, I perceived that the uses of the process would in 

 consequence be extremely limited, except in the .multiplication of 

 already engraved plates, as, whatever ornament it might produce, it 

 would only be done by adhering to the condition of a metallic mould. 



" I accordingly determined to make an experiment on a very pro- 

 minent copper medal. It was placed in a voltaic circuit as already 

 described, and deposited a surface of copper on one of its sides, to 

 about the thickness of a shilling. I then proceeded to get the depo- 

 sition off. In this I experienced some difficulty, but ultimately suc- 

 ceeded. On examination with a lens, every line was as perfect as 

 the coin from which it was taken. I was then induced to use the 

 same piece again, and let it remain a much longer time in action, 

 that I might have a thicker and more substantial mould, in order to 

 test fairly the strength of the metal. It was accordingly put again 

 in action, and let remain until it had acquired a much thicker coat- 

 ing of the metallic deposition ; but on attempting to remove it from 

 the medal, I found I was unable. It had, apparently, completely 

 adhered to it. 



" I had often practised, with some degree of success, a method 

 of preventing the oxidation of polished steel, by slightly heating it 

 until it would melt fine bees' wax ; it was then wiped, apparently 

 completely off, but the pores or surface of the metal became impreg- 

 nated with the wax. 



" I thought of this method, and applied it to a copper coin. 



" I first heated it, applied wax, and then wiped it so completely off, 

 that the sharpness of the coin was not at all interfered with. I pro- 

 ceeded as before, and deposited a thick coating of copper on its sur- 

 face. Being desirous to take it off, I applied the heat of a spirit- 

 lamp to the back, when a sharp crackling noise took place, and I had 

 the satisfaction of perceiving that the coin was completely loosened. 

 In short, I had a most complete and perfect copper mould of one 

 side of a half-penny. 



" I have since taken some impressions from the mould thus 

 taken, and, by adopting the above method with the wax, they are 

 separated with the greatest ease. 



" By this experiment it would appear that the wax impregnates 

 the surface of the metal to an inconsiderable depth, and prevents 

 a chemical adhesion from taking place on the two surfaces ; and I 

 can only account for the crackling noise, on separation, by sup- 

 posing it probable that the molecular arrangement of the voltaic 

 metal is different from that subjected to percussion, and this dif- 

 ference causes an unequal degree of expansibility on the application 

 of heat. 



