It contains a large proportion
of moisture, and yet has the power of drying any substance which is
heated to near its own temperature. A mass of cold metal placed in
the oven is instantly bedewed with moisture, which dries up as the
temperature of the metal rises. This is, for many purposes, an
objection, and the remedy is to close the bottom of the oven and place
burners underneath. If for drying purposes and a current of air is
necessary, the simplest way is to place in the bottom of oven the a
number of tubes hanging downward in such a position that the heat of the
flame acts both on the bottom of the oven and the sides of the tubes,
which, of course, must be long enough for the lower opening to be well
below the level of the flame. The exit may be at any level, but for
drying purposes it is better at the top, and it should be controlled
by a damper to prevent cooling by excessive currents of air. If not
otherwise objectionable, the arrangement of flames inside the oven is
far the most economical in use.
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