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Copper by Voltaic Electricity. 
A very convenient form and arrangement is the following : 
A is a glass or earthen vessel containing a quantity of a sa- 
turated solution of sulphate of cop- 
per; E a piece of gut or tubular 
membrane formed into a bag by be- 
ing tightly tied at the lower end and 
secured in a vertical position in the 
middle of the jar A, by means of a 
stick, which passing through two 
holes in it, rests upon the top of 
the jar. This bag is filled with 
dilute sulphuric acid, and contains 
the zinc rod C, which is likewise 
supported by the stick. D is the 
mould to be copied, and E the me- 
tallic wire connecting it with the 
zinc. Matters being thus arranged 
the precipitation goes on rapidly, 
and all that is requisite is to take 
care that the solution of sulphate 
of copper does not become too 
weak; when this happens, the cop- 
per comes down in a pulverulent and finely divided state, 
without any cohesion ; falling off from the surface of the 
mould in the form of a bulky powder, and rapidly reoxidizing. 
This effect also happens when the surface on which copper is 
to be precipitated is very small, compared with the size of the 
zinc and the strength of the acid. In the first case it is easily 
prevented by always keeping excess of undissolved sulphate of 
copper in the solution to supply that which is decomposed. 
When the deposited metal has acquired sufficient thickness, 
it is easily removed from the surface of the mould, by gently 
loosening its edge all round with any sharp instrument, after 
which it may be readily separated. Mr. Spencer has ingeni- 
ously availed himself of the different expansibility by heat of 
different metals, in removing the deposited metal from the 
mould. When copper is to be precipitated in a copper 
mould, he recommends rubbing into the surface of the mould 
a very small quantity of beeswax, the copper being previously 
warmed. In similar cases I have found that a small quantity 
of plumbago well rubbed over the surface completely pre- 
vented adhesion. 
The form of apparatus above described, has I believe an 
advantage over that first proposed by Mr. Spencer, in the 
vertical position of the mould. When the mould is placed 
horizontally beneath the zinc rod, it is more liable to become 
