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I08 MECHANICAL DENTISTRY AND METALLURGY.

Ammonium Gold Cyanid Solution.—To the solution of
gold chlorid, acjua ammonia is added, a little at a time with
stirring, until all the gold is thrown down in the form of a
brown precipitate. The liquid is poured off and the precip-
itate or ammonia gold is washed several times with distilled
water. It is now dissolved in a strong solution of potas-
sium cyanid, which is then filtered.
Gold Bronze.—Take a solution of gold chlorid and pre-
cipitate with a solution of iron sulphate; wash thoroughly
and dry. This is then used as the gold bronze for coating
the cast, before attaching it to the battery.
Preparation of the Cast.—The cast, as directed for silver
and copper work, is encircled and well secured by a piece
of copper wire. It is then coated with gold bronze, and
attached to the negative wire of the battery ready for action.
Deposition of the Metal.—The Bunsen battery is em-
ployed. A piece of fine gold is soldered to a small platinum
wire, which is attached to the copper wire coming from the
carbon of the battery, as the anode ; the cast being attached
to the wire coming from the zinc, wdiich acts as the cathode.
These are gently lowered and left suspended in the vessel
containing the ammonia gold cyanid solution. If this solu-
tion is worked cold it requires about five days to deposit a
sufficient thickness of gold for an artificial denture. If,
however, it is kept at about 130° F. the result may be ac-
complished much quicker.
After the base plate is thus secured, the teeth are secured
by means of rubber or celluloid attachments. See chapter
upon the subject.