es of copper coated with silver. The
silver employed should be as pure as possible; the thickness of the
plate is of little consequence, provided there be sufficient silver to
bear the cleaning and polishing--is free from copper spots, is
susceptible of a high polish, an exquisitely sensitive coating and a
pleasing tone. These qualities are possessed to an eminent degree by
the French plates.

Having already enumerated the various processes--and the apparatus
necessary for the manipulation, I will here give a list of the
chemicals to be used, and then proceed to explain them more fully. The
requisite chemicals are--

NITRIC ACID, ROUGE,
DRY IODINE, MERCURY,
DRYING POWDER, HYPOSULPHITE OF SODA,
CYANIDE OF POTASSIUM, CHLORIDE OF GOLD; OR
ROTTENSTONE, HYPOSULPHITE OF GOLD.
TRIPOLI, CHLORIDE OF SILVER.
CHLORIDE OF IODINE, } their compounds, or other
BROMINE } accelerating mixtures.

FIRST OPERATION.--Cleaning and polishing the plate.--For this purpose
the operator will require the--

Plate Blocks,

Plate Vice

Spirit Lamp,

Polishing Buffs,

Nitric Acid, diluted in fifteen times its bulk of water

Galvanic Battery, to galvanize the plate, if it is too imperfect to be
used without, previous cleaning it, as directed in the last chapter.

Rottenstone,

Tripoli, which is too often dispensed with.

Rouge, or lampblack--the first being most preferable. The English
operators mix the two together.

Prepared cotton Wool, or Canton flannel. If the first is used, it
should be excluded from the dust, as it is not so easily cleansed as
the latter.

The plate is secured, with its silver side upward, to the block, by the
means described on page 58--having previously turned the edges backward
all around. The amount of cleaning a plate requires, depends upon the
state it is in. We will suppose one in the worst condition; dirty,
scratched, and full of mercury spots, all of which imperfections are
more or less to be encountered. The mercury spots are to be removed by
burning the plate. To do this hold the plate over the flame of a
spirit lamp, more particularly under the mercury spots, until they,
assume a dull appearance, when the lamp is to be removed, and the plate
allowed to cool, after which it is attached to the block.

Place the block upon the swivle, and hold it firmly with the left hand;
take a small knot o