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CELLULOID AS A DKXTAL BASE. 73
gradually, stopping occasionally if the resistance is very
great. If the temperature is kept at 300', the ilask can
usually be closed in about ten minutes. As soon as the
flask is closed, the flame should be extinguished and the
oven door opened to permit the case to cool.
W Fig. 41.
The Finishing Process.—After the flask has become per-
fectly cold the sections should be carefully separated by
passing a knife-blade between them; a gentle movement
will cause one or the other to leave the plaster, when the
remaining one is easily detached by a few blows from the
hammer on its edge. Now trim off the plaster from around
the case, wash freely, cut away the surplus, and remove the
tin-foil. The case is then ready for finishing, which is
7
