BRICK-KILNS may be temporary or permonent. The former are built up of the bricks themselves, generally in a munber of rows of parallel arches, which, may contain as ninny as 40,000 brick and be 40 courses in height. Burnt brick arc placed around the outer sides and on top of the kiln, the walls being daubed with mud. Openings are left at the top to permit the escape of steam arising from the liberated moisture in the brick. Fires are started in the windward end of each arch, then at the other end, and allowed to ap proach each other slowly, several days sometimes being required. doors are closed and sealed to prevent the entrance of air. Wood, coal, or oil may be used for fuel, the oil requiring special burners, and being used but comparatively little. Permanenl brick-kilns have fixed side walls. but may be open or closed at the top. If open, the fires extend beneath the whole length of the charge, the gases passing upward, much as in temporary kilns. if closed, the tires are at one end. Both up-draught and down-draught are used with the permanent, closed-top kilns. In up draught kilns the (•barging holes are above the level of the tire-holes, the latter being on the out side. In the down-draught kilns the gases enter through the flues ranged around the inside of the kilns. Continuous brick-kilns have a series of connecting chambers fired in succession, the gases passing from the first to the second, and so on.
placed at two points near the ends. A circum ferential rack on the shell enables the cylinder to be rotated by worm-gea•ing or by a sprocket chain. The head of the cylinder is inclosed by the chimney in such a manner as to be free to rotate. and is somewhat higher than the front,
which is covered by a movable cap. through which the crude oil or powdered coal is forced by air pressure. The raw material, either dry or wet, is fed into the upper end of the kiln, and grad ually works toward the bottom, in consequence of the inclination and the rotary movement of the eylinder. Calcination takes place during the passage.
All four of the classes of kilns described are used for horning Portland cement. Natural cement is burned in a dome kiln much resembling those used for burning Portland cement, hut smaller in size and somewhat fatter in shape, Filling, burning, and emptying goes on in differ ent chambers at the same time. Fire-brick and refractory ware are frequently burned in down draught kilns, which must be lined with fire-brick. Burning requires five or six days, and cooling several days more. Pariny-brick, in the Middle \Vest, are generally burned in the down-draught kilns. The temperature while burning ranges from 1600 to 2300 degrees Fahrenheit. The burn ing takes from six to ten days, and the cooling from six to twelve days.
CnAitcoAL-Kmxs, when of a permanent char acter (see CHARCOAL), are dome-shaped struc tures, with doors, a grate. ash-pit, and an out let mar the top for the volatile products.
1,111E-KILNs are similar to the dome kilns nscd for burning cement. Two types are shown in section herewith, one built of brick, and another of iron or steel, with a fire-brick lining.