part of the firing-chamber, where they are
reverberated and passed down through the bricks in obedience to the pull of
the chimney. The "bags" may be joined together, forming an inner circular
wall entirely round the firing-chamber, except at the doorway; and a number
of kilns may be built in a row or group having their bottom flues connected
with the same tall chimney. Down-draught kilns usually give a more regular
fire and a higher percentage of well-fired bricks; and they are more
economical in fuel consumption than up-draught kilns, while the hot gases,
as they pass from the kiln, may be utilized for drying purposes, being
conducted through flues under the floor of the drying-shed, on their way to
the chimney. The method of using one tall chimney to work a group of
down-draught kilns naturally led to the invention of the "continuous" kiln,
which is really made up of a number of separate kilns or firing-chambers,
built in series and connected up to the main flue of the chimney in such a
manner that the products of combustion from one kiln may be made to pass
through a number of other kilns before entering the flue. The earliest form
of continuous kiln was invented by Friedrich Hoffman, and all kilns of this
type are built on the Hoffman principle, although there are a great number
of modifications of the original Hoffman construction. The great principle
of "continuous" firing is the utilization of the waste heat from one kiln
or section of a kiln in heating up another kiln or section, direct firing
being applied only to finish the burning. In practice a number of kilns or
firing-chambers, usually rectangular in plan, are built side by side in two
parallel lines, which are connected at the ends by other kilns so as to
make a complete circuit. The original form of the complete series was
elliptical in plan, but the tendency in recent years has been to flatten
the sides of the ellipse and bring them together, thus giving two parallel
rows joined at the ends by a chamber or passage at right angles. Coal or
gas is burnt in the chamber or section that is being fired-up, the air
necessary for the combustion being heated on its passage through the kilns
that are cooling down, and the products of combustion, before entering the
chimney flue, are drawn through a number of other kilns or chambers
containing unfired bricks, which are thus gradually heated up by the
otherwise waste-heat from the sections being fired. Continuous kiln