RATIONAL CONSTRUCTION OF FURNACES
are so well known in this industry that it will not be necessary to
devote much space to them.
Fig. 84 shows the same kiln (Fig. 83) reconstructed to work on
the downdraft principle. The distribution of the current's of hot
gases is very good, as the hottest gases rise to the arch of the
furnace and then divide themselves into uniformly descending
currents. One of the results of this reconstruction was the
reduction of the amount of defective brick turned out from
30 per cent to 1 per cent.
Fig. 85 shows a two-story kiln used in the manufacture of
porcelain. Such kilns are still actually in use. The upper
chamber works in an unsatisfactory manner, the hot gases being
divided into ascending currents; it is practically impossible to
regulate the distribution of the heat by changing the size of the
waste-gas opening. The lower chamber of the kiln, which works
on the downdraft principle, has a regular heat distribution.
Fig. 86 shows a kiln of this type correctly constructed, both
the upper and the lower chamber working upon the downdraft
principle. The firebox has been changed from the lower to the
Note ly English translator.—Downdraft "beehive" kilns are widely used
in the manufacture of refractory brick. In the silica brick plants it is well
known that only one-seventh of the kiln capacity can be used for coke oven
shapes, many of which require two burns. The prevailing tendency in