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ARTIFICIAL DENTURES. 99

then coated with horax, i^ToiiiKh nr ruhl)e(l in clean, soft
water to ahout the consistenc}' of cream;* after which small
pieces of solder arc placed along the joints and over the
points of the platinnm pins. The piece thus prepared is
now placed in the furnace or ordinary fire-place in order to
heat the entire mass preparatory to soldering.
The heating process should be conducted gradually until
the case acquires a visible red heat, when it should be re-
movetl, placed on a suitable holder, and the solder fused
with the blowpipe. A broad, spreading flame should first
be thrown over the entire surface of the plate and invest-
ment until the temperature of the entire mass is nearly that
required to fuse the solder, which is indicated by the latter
settling and contracting upon itself; the flame may then be
concentrated upon a particular point, as at the heel of the
plate on one side, passing around from tooth to tooth until
all the parts are completely united and the solder is well and
uniformly ditYused.
Having united the teeth to the plate, the piece may be
allowed to cool gradually, or it may be plunged after the
lapse of a few minutes into boiling water wdthout risk of
injury to the teeth. When cool, the plaster is removed
and the plate placed in the acid bath (a solution of ecjual
parts of sulphuric acid and water), where it may be allowed
to remain until the discoloration of the plate and the re-
mains of the vitrified borax, incident to the soldering, are
removed, or it may be put into a small copper vessel, partly
filled with the same solution, and boiled for a few' minutes.
After removing the plate from the acid, it should be boiled

* Slate is often used for this purpose, but is unfit, as, in rubbing the
borax, loosened particles of the former become mixed with the latter
and impede the flow of the solder, and becoming entangled render it
unclean and porous. Ground glass or a porcelain slab is the best for
the purpose.