Page 116 - My FlipBook

I04 MECHANICAL DENTISTRY AND METALLURGY.

plished by placing the zinc in a dish, pouring a small quan-
tity of acid over it, then, after having tied a small piece of
flannel over the end of a stick, proceed to brush the acid o\'er
the surface of the metal ; after which pour a little mercury
on the plate, and, with a similar little mop, rub it thoroughly
over and into the surface of the zinc, which will give it a
bright, silvery luster.
Preparation of the Plaster Cast.—Have the cast well
dried ; twist around it a piece of copper wire, then dip in
melted wax and allow to drain. The cast is then to be cov-
ered with finely powdered plumbago by briskly brushing it
over the surface with a soft brush, care being taken to brush
the powder well into every crevice.
The Deposition of the Metal.—The cast is now connected
to the large copper wire which supports the zinc plate, and is
gently lowered into the copper solution in the outer jar,
when the whole arrangement is complete. The cast should
remain in this position until the desired thickness of copper
has been deposited.

THE DEPOSITION OF SILVER.

In silver plating the solutions are formed from silver
nitrate. In preparing which, dissolve i oz. of fine silver in
2 ozs. of nitric acid and ^2 oz. of distilled water.
Method of Preparing Silver Nitrate.—This is best ac-
complished by first placing the silver in an evaporating dish,
then adding the water, and lastly the acid. A vigorous
ebullition then takes place, giving off red fumes of nitrous
gas, wdiich are injurious and should be allowed to escape
through the chimney or out the window.
After the action begins to quiet down a little, the dish
should l)e placed upon a warm sand-bath, \\dien the fumes
cease to appear the chemical action is at an end.