Copper hy Voltaic Electricity. 313 
heating it and allowing it to cool slowly it becomes tough and 
flexible. 
In this process it is evident that a metallic surface is re- 
quisite for the commencement of any precipitation of copper ; 
‘the arrangement in fact forms a single cell of a Daniell’s bat- 
tery, and is incomplete with the presence of the surface of the 
second metal in the sulphate of copper. 
Mr. Spencer has shown, however, that moulds for the pre- 
cipitation of copper may be made of any substance by gild- 
ing them or otherwise covering their surface with a thin film 
of metal which affords a conducting surface for the first por- 
tions of copper to be precipitated upon. My attention w^as 
early directed to this part of the process, because it seemed to 
open a wide field for new and beautiful applications. I was 
induced to pay particular attention to the deposition of copper 
upon non-metallic surfaces, and in consequence made nu- 
merous experiments to ascertain the circumstances most fa- 
vourable to its precipitation under these conditions. My first 
experiments were made on surfaces of plaster of Paris, 
which I endeavoured to coat with copper, so as in fact to con- 
vert plaster casts into bronzes. 1 commenced by gilding the 
surface with different metals in the manner proposed by Mr. 
Spencer, but I found it exceedingly difficult to get a perfectly 
smooth and uniform surface ; the process succeeded best with 
gold-leafi but even that had its objections, and was besides 
very expensive. Subsequently I tried metals, such as bismuth 
and antimony in a state of very fine division, ground up with 
water and glutinous matters ; these attempts were however 
not much better than the first trials. 
In the course of these experiments I observed a curious 
fact, which I had not at all anticipated, and which very ma- 
terially assisted me in attaining the objects which I had in 
view. When I had endeavoured to precipitate lead from a 
solution of one of its salts, in the same way that I had been 
doing with copper, I found that small grey crystals of lead 
soon formed upon the most prominent parts of the metallic 
mould I was employing, and which happened to be a leaden 
cast of a medal : these crystals rapidly increased in size, extend- 
ing towards the membrane bag containing the zinc, which w^as 
about 3 inches distant from the mould. As soon as the cry- 
stals reached the surface of the membrane they bent about 
in various directions, crossing and recrossing each other until 
they had completely enveloped the membrane in a net-work 
of reduced lead. Again, when silver is precipitated from the 
fused nitrate, by electricity, the crystals formed at the one 
electrode extend across the fused electrolyte, until having 
