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72 MECHANICAL DENTISTRY AND METALLURGY,
quired in any case until near the close of the operation,
when the mold is completely impacted, and the excess is
being forced into the grooves or gateways as the flask
comes together.
At this point considerable force will be necessary to close
the flask perfectly, and somewhat longer intervals of time
should occur between each turn of the screw or nuts.
During the progress of the molding the flask should be
withdrawn occasionally for inspection. If, in the case of
central pressure, the flask is found to be closing unevenly,
it should be loosened in the clamp and readjusted in such
manner as to correct the faulty approximation. No difti-
culty will be experienced in this respect in the use of clamps
provided with screw-bolts, as pressure may be applied at
any point, and the flask be made to close uniformly without
the necessity of shifting the latter.
The moment the flask is completely closed the heat should
be turned off and the piece allowed to cool gradually. In
no instance should the flask be removed from the clamp
until it is entirely cold. In cases where the material is of
extra thickness, or where the shape of the blank is totally
altered, longer seasoning is advisable, and the flask should
be placed near a stove or over a register (keeping it closed
by a clamp) for half a day or more, at a temperature of
not over 140^. If these directions are observed, no trouble
from warping plates will be experienced.
Dry Heat Apparatus.—The Seabury Celluloid Press
shown in Fig, 41. When the investment is thoroughly
dried the flask is placed in the oven immediately under the
screws as shown in the illustration. The screws are turned
down until they bear lightly upon the top of the flask, after
which the machine is closed and the heat applied. In Ave
minutes time the celluloid will be sufficiently softened to
permit the commencement of the molding. Close the flask