immersed in the copper sulphate
solution.

Sec. 139. The process of copper-plating from sulphate or nitrate may,
according to Mr. Swan (Journal of the Royal Institution, 1892, p.
630), be considerably accelerated by the addition of a trace of
gelatine to the solution. As success appears to depend upon hitting
the exact percentage amount of the gelatine, which must in any case be
but a fraction of one per cent, and as Mr. Swan refrains from stating
what the amount is, I am unable to give more precise instructions. A
few experiments made on the subject failed, doubtless through the
gelatine content not having been rightly adjusted. Mr. Swan claims to
be able to get a hard deposit of copper with a current density of 1000
amperes per square foot, but seems to recommend about one-tenth of
that amount for general use.

The solution employed is a mixture of nitrate of copper and ammonium
chloride--proportions not stated. Electrolytic copper, as generally
prepared, is very pure, but this is a mere accident depending on the
impurities which, as a rule, have to be got rid of. Electrolysis
seems to have no effect in purifying from arsenic, for instance.

Roughly speaking, about 11 grms. of copper are deposited per ampere
hour from cupric salt solutions. When the current density is too high
the anode suffers by oxidation, and this introduces a large and very
variable resistance into the circuit.

Sec. 140. Alkaline Coppering Solution

Coppering Base Metals. It is often desirable to coat lead, zinc,
pewter, iron, etc, with a firm and uniform layer of copper
preparatory to gilding or silvering. If copper or brass articles are
soldered with soft solder it is found that the solder does not become
silvered or gilt along with the rest of the material, but remains
uncoated and of an ugly dark colour. This defect is got over by
giving a preliminary coating of copper.

This is done in an alkaline solution, generally containing cyanogen
and ammonia. The following method has succeeded remarkably well with
me. The receipt was taken originally from Gore's Electro-metallurgy,
p. 208. A solution is made of 50 grms. of potassium cyanide
(ordinary commercial, say, 75 per cent) and 30 grms. of sodium
bisulphite in I.5 litres of water. Thirty-five grammes of cupric
acetate are dissolved in a litre of water, and 20 cubic centimetres of
the strongest liquid ammonia are added. The precipitate formed must
be more or less disso