3 10 Mr. E. Solly, Jim., 07i the Precipitation of 



perfect contact with the surface on which it is thrown down; and 

 thus we here have the first element of the process of copying, 

 or obtaining a cast by precipitation, but extremely crude and 

 imperfect. The film of copper so thrown down would be so 

 thin and fragile that it would be impossible to remove it from 

 the surface of the tin ; or if it should acquire any thickness it 

 would of course do so at the expense of a considerable quan- 

 tity of tin, because for every portion of copper precipitated 

 a corresponding quantity of tin must have been dissolved; the 

 smoothness of the surface would become destroyed ; and as 

 this corrosion does not act equally all over the surface, if any 

 design had been traced upon it, it would be much weakened, 

 and in some parts wholly obliterated. 



Both these difficulties are easily overcome in consequence 

 of the facilities which electricity gives us, of, as it were, making 

 chemical action portable ; of genei'ating it in one place, convey- 

 ing it along metallic conductors, and making use of its power 

 in another. Hence we are enabled to employ at pleasure one 

 of the most powerful known deoxidizing 'agents, hydrogen. 

 By means of electricity, we are able to give to any piece 

 of metal, the power of evolving hydrogen, under the most 

 favourable circumstances, from its surface, whilst immersed 

 in a cupreous solution ; and to continue that action, until the 

 coat of deposited copper, precipitated by the action of the 

 nascent hydrogen, has acquired any degree of thickness. 



In order to effect this, a piece of some highly oxidizable 

 metal, such as zinc, is connected by a wire soldered to its one 

 end with the plate of lead, tin, or other metal, on the surface 

 of which is engraved the design proposed to be copied. A 

 vessel of any shape and material is divided into two portions 

 by a partition or diaphragm of membrane, unglazed earthen- 

 ware, or any other porous substance; the one division being 

 filled with a strong solution of sulphate of coppei', and the 

 other with dilute sulphuric acid. The zinc is then placed in 

 the dilute acid, and the mould or form to be copied, in the 

 solution of copper. The zinc continues to dissolve in the 

 acid, and generate the power, which being conveyed through 

 the solutions to the surface of the mould, there causes the 

 precipitation of copper, whilst the wire joining the zinc with 

 the metallic mould, forms the connexion necessary to com- 

 plete the galvanic circle. 



The apparatus for this purpose is exceedingly simple, 

 cheap, and easy of management ; and when once arranged, 

 and set in action, requires no further attendance until the ope- 

 ration is complete, when the mould is to be removed and 

 the copy separated from it. 



