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70 MECHANICAL DENTISTRY AND METALLURGY.
quantity of water may be introduced into the tank before
applying- heat.
Fig. 40 represents a modeHng or packing machine of the
class here spoken of, and is designated as the " Best." The
inside chamber is of cast iron, surrounded by a sheet-iron
casing. The lid, of cast-iron, forming a part of the clamp,
is pierced for the passage of three wrought-iron screw-bolts
—the nuts being on the upper side and easy of access.
Fig. 40.
When these nuts are turned for the purpose of closing the
clamp, the bottom portion of the clamp is drawn up by
each revolution away from the flame, thus avoiding the
danger of overheating the plate, and securing a uniform
heat.
The bottom of the cast-iron chamber and the lid are
pierced with holes to allow a circulation through the cham-
