309 
Mr. E. Solly, Jun., on Voltaic Precipitation. 
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. RoGET. 
March 20th, 1840. 
LII. Observations on the Precipitation of Copper by Voltaic 
Electricity. By Edward Solly, Jun. In a Letter to 
Richard Taylor^ Esq. ^c. 
'^HE 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 the mode in which this precipitation is caused, 
it follows that the metal precipitated must be everywhere in 
