HISTORY OF ELECTRO-METALLURGY. 17 



copy a wood engraving by a similar method, provided the wood 

 would bear the requisite pressure. Knowing that wood engravings 

 are executed on the end of the block, I had better hopes of succeed- 

 ing, the wood being less likely to sustain injury. 



" I accordingly procured a small wood block, and placed its en- 

 graved surface in contact with a piece of sheet lead made very clean, 

 and subjected it to pressure, as in the former instance. I had now, 

 as before, the gratification of perceiving that a perfect mould of the 

 little block had been obtained, and no injury done to the original. 

 Several wood engravings and copper plates were subjected to similar 

 treatment, and are now in process of being deposited on in the 

 apparatus before me. 



" I now come to the third and concluding portion of the experi- 

 ments on this subject. The object being to deposit a metallic surface 

 on a model of clay, wood, or other non-metallic body, as, otherwise, 

 I imagined the application of this principle would be extremely 

 limited. Many experiments were made to attain this result, which 

 I shall not detail, but content myself with describing those which 

 were ultimately most successful. 



" I procured two models of an ornament, one made of clay, and 

 the other of plaster of Paris, soaked them for some time in linseed- 

 oil, took them out, and suffered them to dry first getting the oil 

 clean off the surface. When dry, I gave them a thin coat of mastic 

 varnish. When the varnish was nearly dry, but not thoroughly so, I 

 sprinkled some bronze powder on that portion I wished to make a 

 mould of. This powder is principally composed of mercury and sul- 

 phur, or it may be chemically termed a sulphuret of mercury. There 

 is a sort that acts much better, in which is a portion of gold. I had, 

 however, a complete metalliferous coating on the surface of the 

 model, by which I was enabled to deposit a surface of copper on it, 

 by the voltaic method I have already described. I have also gilt 

 the surface of a clay model with gold leaf, and have been successful 

 in depositing copper on its surface. There is likewise another, and, 

 as I trust it will prove, a simpler method of attaining this object ; 

 but as I have not yet sufficiently tested it by experiment, I shall take 

 another opportunity of describing it." 



[At the close of the paper, several specimens of coins, medals, and 

 copper plates, some of them in the act of formation by the voltaic 

 process, were exhibited by Mr. Spencer to the Society.] 



Plumbago as a Coating. -^-Shortly after Mr. Spencer's paper was 

 published, several important improvements were introduced, one 



C 



