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CELLULOID AS A DENTAL BASE. 69

selected, allowing of course for some little surplus, and this
should he as evenly distrihuted as possihle.
The selected hlank should he conformed as nearly as
possible to the shape of mold by heating it in boiling water
and pressing it with the fingers into the section containing
the teeth; after which, if there is found to be more surplus
than is necessary, it may be dressed away, either with a
file, knife, or small saw, first softening the blank in boiling
water before using them.
When plaster is used for the cast, it should be given a
thin coat of oil, liquid soap, or liquid silex, or its surface
should be rubbed with powdered soapstone or French chalk,
to prevent the adhesion of the plaster to the plate. More
perfect results, however, can be obtained by using a metal-
faced model.
Molding.—Various heaters are used for molding celluloid
into dental plates. There are machines designed to use
glycerin or oil and others for steam or dry heat; and while
with careful and intelligent manipulation satisfactory re-
sults may be obtained with all, some of them may possess
special points of merit which the others do not. The limits
of this work, however, will only permit of the introduction
of one method, the one in most general use.
Hot Moist Air Machines.*—Richardson says of this
method : In the use of these heaters, the water with which the
plaster is impregnated is relied upon to produce the steam
necessary to carry off all excess of camphor from the cellu-
loid in the process of molding. An essential point by this
method is to have the plaster in the flask thoroughly wet,
and this may be better attained by setting the flask in a
vessel of water before placing it in the heater. To provide
against insufficiency of moisture in the plaster, a small
* So-called " Dry Heat."