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PIT  FURNACES

135

armor plate. Moreover, this furnace \vas intended to work with a
negative pressure in the heating' chamber, with the result that the
reheating of the armor plate had to be accomplished while it was
surrounded by a current of colder air drawn in through the door
of the furnace. The effects of such a method of operation are
obvious.

It had been planned to carbonize and heat two armor plates at
a time, placing one above the other and separating them by a layer
of charcoal. It may be stated that the lower plate was car-
bonized much more slowly than the upper; and it was necessary
to give up the idea of carbonizing two plates at a time. Actually,
the carbonizing was done one plate at a time, double the number
of furnaces were required with twice the expense for installation.

Moreover, the men in charge of the Russian works were so
thoroughly impressed with the prestige of the Krupp Company
that they would not consent to the cutting down of these heads
to the level of the hearth of the furnace.

XVII. PIT FURNACES

In   pit-reheating   furnaces   the   defect   which   is   commonly
encountered consists in the incorrect location of the waste-gas

FIG. 112.

ports. In these furnaces, by reason of the considerable height
of the heating chamber, it is very necessary that attention should
be paid to the locating of the waste-gas port at the level of the
hearth of the pits. Unless this is done, the lower parts of the