Illustration: GILDING RINGS.
By way of experiment, procure two vessels, A and B, fig. 1, in one
of them, A, put some dilute sulphuric acid and two plates, one of
zinc, Z, the other of copper, _c_, these must not touch each other,
but may be separated about half an inch by two or three pieces of
wood or cork, and bound round with string; each of these plates must
have a piece of wire fastened by soldering to their upper parts.
In the vessel B put some solution of sulphate of copper and a small
quantity of dilute sulphuric acid, and attach another copper plate to
the wire which comes from the copper plate in the acid; this second
copper plate is to be immersed in the solution of sulphate of copper,
and to the wire from the zinc plate is to be fixed the object to be
coated with copper. If a medallion or other object is plaster, it
should be soaked in very hot wax and then brushed over with blacklead
until the surface is perfectly blackened and bright; the wire should
be bound all round the margin and soldered (as it were) with melted
wax to the medallion, taking care that this wax also is well coated
with blacklead. If the object be now immersed in the sulphate of
copper solution and kept at a short distance from the plate (it
must not touch it), a coating of copper will soon cover the surface
and form a perfect cast, which when of sufficient thickness may be
removed by filing the edge all round (if instead of the plaster cast
a copper coin or other copper object be used, the blackleading is not
required, but the surface must be first made clean and bright). With
the same arrangement, but using instead of the sulphate of copper
a solution made by dissolving cyanide of silver in a solution of
cyanide of potassium, a coating of silver will be deposited, and the
same of gold (if cyanide of gold be used), but these coatings will
not adhere. If it be intended that the coatings shall adhere, to
plate the article with silver or gold, it should be first thoroughly
cleaned, then brushed over with a solution of nitrate of mercury,
washed in clean water, and put into the gold or silver solution;
the nitrate of mercury will cover the copper article with a thin
coating of mercury, which will be taken up as the gold or silver
is deposited, and this coating will adhere, the article being thus
“electro plated.” As in using the solution of sulphate of copper, a
copper plate was immersed in the solution and united by the wire to
the copper plate in the vessel A, so in using the solution of cyanide
of silver, a silver plate must be used, and in the gold solution a
gold plate, these plates being dissolved as the metal is deposited,
the liquid remaining pretty much the same and serving for future
operations. The gold and silver thus deposited are dull, but may be
burnished with a steel burnisher, all over or in parts as the design
may require. In manufacturing, these processes are much modified, and
powerful galvanic batteries or electro-magnets used; in the latter
case the electro-magnetic machine is often driven by a steam-engine
and the troughs of depositing liquids contain often many dozens of
articles, which are all receiving a coating at once.