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142

RATIONAL CONSTRUCTION OF  FURNACES

other. This drop in the roof acts as a dam to arrest the -flow of
the gases for a sufficient length of time for the completion of
combustion. Fig. 120 shows the Morgan type of roof. The drop
in the roof simply checks the flow of the hot reacting gases; the
port through which the gases enter the heating chamber is located
some distance above the hearth. The author believes that these

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D      n      n      n      o       n



FIG. 121.

two methods of retarding the flow of the combining gases and
promoting combustion are equally good.

However, it is here necessary to call attention to an error often
made in the design of these furnaces. The working doors, A, B,
and C must not be located at different heights. If these doors are
placed at different heights, the highest door acts as a chimney in
conjunction with the lowest door. Cold air will be drawn into
the heating chamber at the lowest opening while a jet of flame

FIG. 122.

and smoke will escape from the highest opening. The sills for all
of the working openings should be placed at the same level.
The last three illustrations in this chapter show the recon-
struction, according to the direction of the author, of two very
costly furnaces of a Swedish type. These furnaces were installed
in a plant located in the Oural district.
Fig. 121 shows the longitudinal section of the furnace as
originally built. During its operation it became very apparent