696 GEOLOGY OF OHIO. 
# 
district, at Ironton, Logan, Akron, Cleveland and Zanesville. The next 
kiln in wide use is the circular down-draft. It is largely used for brick 
and still more largely for pipe, ete. It varies from 16 to 24 feet in 
diameter, with from 18 inches to 24-inch walls of the best fire-brick and 
with strong iron binding. Itis from 10 to 14 feet high to the top of the 
arched roof. The fireplaces are arranged around the base of the kiln 
each one separate, usually, but sometimes in a continuous block. They 
pass into; thegkiln and are deflected upward by a so-called fire-wall, 
which is a partition concentric to the outer wall of the kiln, about 10 
inches from it, and extending upwards to the spring of the arch. This 
wall is of the best quality of brick, as it has to stand the severest heat 
attainable inthe kiln. The fires being turned up between these two walls 
first reach the brick from above over the top of the inner wall. The 
draft now sucks the fire down through the bricks piled in open order, 
through the floor, which is built of perforated brick, into the flues beneath, 
which run into the base of a large stack. —The whole draft of a kiln may 
be stopped or retarded at will by blocking up the flue to the chimney, 
and these kilns owe their value over the up-draft kiln mainly to the ease 
with which they can be regulated. Burning takes a little longer, per- 
haps, than with an up-draft kiln, but the down-draft is more economical 
of fuel. These kilns do not attain such high heat, and consequently the 
brick are usually softer burned, but are rather more uniform. At the 
works of C. EH. Holden, Mineral Point, there are three large circular 
down-draft kilns whose tops are connected each to the other by a boiler- 
iron tube about 1 foot in diameter. When one kiln is hot and cooling, 
and another is just set with fresh brick, the flue to the stack from the 
hot kiln may be stopped, and the current of hot air directed through 
the second kiln and out of the stack, thus performing rapidly, uniformly 
and completely all that sweat-burn of a kiln usually does. By this 
means,a fire is not let into the kiln until all is ready to raise the heat 
at once tofa high point. Any of the kilns can thus be manipulated, 
being cut out or brought into the current by a movement of damper. 
The use of a real fire-wall is not as common in circular down-draft 
kilns as in rectangular; the same effect is obtained by inclosing the vent 
to each fireplace in a chimney which runs up the wall to the usual 
height, and delivers into the ware just as a fire-wall would. ‘These 
chimneys are called pockets. 
The rectangular, down-draft, end-fired kiln is in common use in 
