EXPERIMENTS WHICH SERVE TO SHOW THE ANALOGY 7
while the temperature at the solo is less than that which exists
immediately below the roof of the kiln.
Note by /ra//,.s7<7/or.—A considerable portion of the equalization of the heat
in the updraft kiln is due to conduction of the heat, through the kiln structure
and the brick set iu the kiln. This heat is carried downward in this manner
and imparted to the cooler layers of j^aseH at the bottom of the kiln, healing
them and promoting eddy currents. The updraft kiln, however, heats very
slowly at the bottom, and the upper portion of the sotting will he overburned
while the lower portion is underburned. As compared with the downdmft
kiln, the updraft kiln consumes a larger amount of fuel per unit of output,
and requires a longer time to complete a kiln round.
Direct or updraft brick kilns were the only ones built up to
about twenty years ago. They are still found in many potteries,
as in the works of Korniloff Brothers, at Petrognul. A brie.k
kiln of this type is still in use at the Oboukoff works, and it is
only a short (line since one* was in use at the Poutiloff works.
These arc not the last updraft kilns in use, but most of thorn have
been replaced by downdraft kilns.
tiecond Experiment.—VonimMud study of updraft kiln. Method
of operating downdraft kiln. For this experiment the smoke
hole at the top of the kiln is completely closed. The; chimney
of the apparatus, as shown in Fig. 4, is filled with kerosene, which