Mr. E. Solly, Jiin., on Voltaic Preciintation. 309 



squares belonging to it ; and we, lastly, come to system A, 

 where we find no difficulty in ending the course at the given 

 terminal square. 



In No. 2, where the terminal square belongs to system L, 

 as well as the initial, we must, in going over that system, 

 omit that square, and also one connected with it. With 

 this exception, we are to proceed as before, traversing in suc- 

 cession the systems L, E, P and A ; and taking care to end 

 at a square of the latter, connected by a knight's move with 

 the other omitted square of system L. 



In No. 3, where the terminal square belongs to system P, 

 the same series of courses is to be pursued, excepting that the 

 squares to be omitted will belong to that system. 

 Your obedient servant, 



39, Bernard Street, Russell Square, P. M. RoaET. 



March 20th, 1840. 



LI I. Observations' on the Preciipitatioyi of Copper hy Voltaic 

 Electricity. By Edward Solly, Jun. In a Letter to 

 Richard Taylor^ Esq. Sfc. 



nnHE beautiful discoveries of Professor Jacobi and Mr. 

 •*- T. Spencer have, as it were, laid the foundation of an en- 

 tirely new art, namely, that of copying works in metal, with- 

 out heat, without pressure, and at a very small expense. As 

 many of your readers may not have seen either Mr. Spencer's 

 very interesting and ingenious pamphlet, or any detailed ac- 

 count of the process which he has so successfully employed 

 in copying medals, copper-plates, &c., I will briefly sketch 

 the principles of the process of voltaic precipitation, and de- 

 scribe the apparatus required for the purpose, introductory 

 to a short account of some experiments on the subject which 

 I have made. 



When a piece of tin or other similar metal is immersed in a 

 strong solution of sulphate of copper or blue vitriol, it soon be- 

 comes coated with metallic copper, which is said to be precipi- 

 tated or reduced ; the oxide of copper being decomposed by 

 the more oxidizable metal having a stronger affinity for oxygen 

 than the copper itself has. In this way the tin becomes ox- 

 idized and dissolved, and the copper is reduced and precipi- 

 tated in the form of a thin film. If the whole surface of the 

 tin were to become coated with copper, of course this action 

 would cease, because the former being entirely cased in cop- 

 per, would remain inert, and in fact represent a plate of that 

 metal. From iKr mode in which this precipitation is caused, 

 it follows that the metal precipitated must be everywhere in 



