46 
POPULAR SCIENCE REVIEW. 
sists of amalgamated zinc in dilute sulphuric acid, and copper in 
a solution of sulphate of copper, the two liquids being separated 
by a porous partition, is not much used for electro-plating; and 
the preference of one battery over another for electro-deposition 
depends partly upon the bias of the plater in favour of that 
particular battery, but chiefly upon the special purpose for 
which the battery is intended ; in cases where great resistance 
is offered to the passage of the electric current, as in solutions 
for coating articles of iron, &c., with brass, the more power- 
ful batteries of Grove and Bunsen are used. Whichever of 
these batteries is employed, and whatever may be the metal 
intended to be deposited, the article to receive the coating is 
always connected with the zinc plate of the battery, and the 
metal to be dissolved is connected with the copper, silver, 
carbon, or platinum, as the case may be. 
All metallic articles that are to be coated with silver or other 
metals by electro-process require to be perfectly cleaned and pre- 
pared before being placed in the plating-liquid, otherwise the 
metal deposited upon them will not adhere properly. To clean 
them they are at first immersed in a boiling solution of caustic 
potash to remove greasy and tarry matters ; then, if they are 
formed of German silver, brass, or copper, they are washed in 
water, dipped momentarily into aquafortis, again washed in 
water, then dipped into a very dilute solution either of nitrate 
of mercury, or of cyanide of mercury and potassium, and im - 
mersed in the silver-plating vat. In cases where it is desired 
to know the quantity of silver deposited upon them, they are 
weighed after cleansing, and also at intervals during the process 
of deposition. Articles formed of Britannia metal, lead, tin, 
and similar metals or alloys, are not dipped into aquafortis, but 
immersed in a weak silver solution immediately from the 
caustic potash liquid, to receive a thin preparatory electro-coating, 
and then transferred to the ordinary silver vat. The thickness of 
silver deposited upon articles is frequently very minute, as may 
be judged from the fact that full-sized iron snuffers are some- 
times wholly coated with silver for two-pence each pair, and 
other common articles at proportionate prices. 
After receiving the coating of silver, much remains to be 
done to the articles before they assume a saleable condition, they 
have to be “scratched” by a bundle of revolving fine brass wires to 
remove asperities ; burnished to make them bright ; in some 
cases, they have to be “ oxidized ” in particular parts. This 
consists in wetting those parts with a solution of bichloride of 
platinum, which blackens those portions ; and, in other cases, 
different parts, as, for instance, the interior of cream-jugs, 
sugar-basins, &c., have to be electro-gilded. And in cases 
where portions of the exterior have to be gilded, the remaining 
