12 HISTORY OF ELECTRO-METALLURGY. 



stance attending these experiments, which was, that when I heated 

 the plates to get off the covering of cement, the meshes of copper 

 net-work occasionally came off with it. I at one time imagined this 

 difficulty inseparable, as it appeared that I had cleared the cement 

 entirely from the surface of the copper that I meant to have exposed ; 

 and I concluded that there must be difference in the molecular 

 arrangement of copper prepared by heat and that prepared by 

 voltaic action, which prevented their chemical combination. How- 

 ever, I determined, should this prove so, to turn it to account in 

 another manner, which I shall relate in the second portion of the 

 paper. 



" I now occupied myself for a considerable period in making ex- 

 periments on this latter section of the subject. 



" In one of them I found, on examination, that a portion of the 

 copper deposition, which I had been forming on the surface of a coin, 

 adhered so strongly that I was quite unable to get it off, indeed, 

 a chemical combination had apparently taken place. This was only 

 on one or two spots on the prominent parts of the coin. I imme- 

 diately recollected that, on the day I put the experiment in action, I 

 had been using nitric acid, for another purpose, on the table I was 

 operating on, and that in all probability the coin might have been 

 laid down where a few drops of the acid had accidentally fallen. 

 Bearing this in view, I took a piece of copper, coated it with cement, 

 made a few scratches on its surface until the copper appeared, and 

 immersed it for a short time in dilute nitric acid, until I perceived, 

 by an elimination of nitrous gas, that the exposed portions were 

 acted upon sufficiently to be slightly corroded. I washed the copper 

 in water, and put it in action as before described. In forty-eight 

 hours I examined it, and found the lines were entirely filled with 

 copper. I applied heat, and then spirits of turpentine, to get off 

 the cement, and, to my satisfaction, I found that the voltaic copper 

 had completely combined itself with the sheet on which it was 

 deposited. 



" I then gave a plate a coating of cement to a considerable thick- 

 ness, and sent it to an engraver ; but when it was returned, I found 

 the lines were cleared out so as to be wedge-shaped, or somewhat in 

 the form of a v> leaving a hair line of the copper exposed at the 

 bottom, and a broad space near the surface ; and where the turn of 

 the letters took place, the top edges of the lines were galled and ren- 

 dered rugged by the action of the graver. This, of course, was an 

 important objection, which I have since been able to remedy in 

 some degree by an alteration in the shape of the graver, which 

 should be made of a shape more resembling a narrow parallelogram 

 than those in common use : some engravers have many of their tools 

 so made. I did not put this plate in action, as I saw that the lines, 



