KILN, a name applied to various kinds of furnaces, ovens, or other devices stone, brick, or iron, or of the material itself to be operated upon. They may be divided into intermittent and continuous, or perpetual; or into furnace-kilns, oven-kilos, and what may be termed mound-kilns, such as are used in making charcoal; and also a kind which are intermediate between oven and mound-kilns, as certain kinds of brick-kilns, where the raw brick is a part of the kiln, and forms a structure which cannot be called an oven.
The furnace-kiln, for burning limestone, may be of an intermittent or of a perpetual kind. An intermittent kiln is one in which the fire is ]et to go out after the charge is. burned; a continuous kiln is one which is so arranged that the charge may be removed and a fresh one put in while the fire is kept burning, and the furnace kept at its • reducing heat. An intermittent furnace-kiln may be made of stone or brick of amoval' form, like an egg standing on either end. That form resembling an egg standing on its larger end is perhaps the most common, although some lime kilns are shaped more deep bowls, without much contraction at the top. Where wood is very plentiful antL cheap, and the lime is burned for agricultural purposes, so that ashes is a desirabh ingredient, a common bowl shape is perhaps preferable, because it is readily charged: with both limestone and wood, and a mass of wood may be placed upon the top inaddi-. tion to what is used in the charge, by which thorough burning will be secured. In., a furnace-kiln a grating, of iron is placed at the bottom, or an arch of open brickwork, and then the charge is ingeniously placed, first with ,fuel, and then with the brokeir masses of limestone in such a manner as to allow the flame to pass through, and thor oughly perform the Work 'of beatitig. These- kihis may b8 from-1Ote 304't. high, or evens higher. Intermittent oval kilns are used in burning Portland and other kinds of hydraulic cement, and they are 40 or 50 ft. high, and employ coke or coal for fuel. The charge is usually composed of one part of coke or coal and two parts of raw cement. There are, however, several kinds of cement which do not require so prolonged high heat as Portland cement, and these may he burned in a kind of kiln so constructed as not to require the fire to go out when the burned contents are removed. These kilns are cylin drical, except at the bottom, where they have the shape of an inverted cone, and a chamber below and a kind of spout leading into it from the bottom of the cone, so that the charge when burned may be raked down from time to time with a suitable apparatus, and removed, while it may be renewed at the top. Cement-kilns should be
lined with fire-brick. A preferable form of continuous kiln is one in which the kiln cylinder is charged only with the material to be burned, and a current of flame or heated gas is introduced at the side near the bottom. The heat thus passing up through the material reduces it to the proper condition, without adding any of the ashes of the fuel to it.
Briek-kans are of three kinds: 1. That in which the raw brick are piled up in such a way as to form flues for the flame and hot gases of the fuel to.pass through, and which are in more common use than the others, and called by the workmen clamps. 2. That kind of kiln in which common stoneware is baked, which is a sort of reverberatory fur nace, and unlike the kiln in which the better kinds of earthenware arc baked. 3. An example of a third form of brick-kiln, now used to a considerable extent, is Hoffann's annular brick furnace, which was on exhibition at Paris in 1867. It consists of a large annular chamber, divided into sections, with openings on the periphery for the reception of the bricks or material to be baked. Movable partitions divide the sections. Each compartment of bricks is burned successively, the heat passing from one section to another, so that very little is lost. Kilns or furnaces of this kind are used for other purposes, as the degree of heat can be easily regulated. It is a very fine form of kiln for drying and seasoning lumber. Pottery-kilns are usually in the form of a tall cylin der of various dimensions, from 15 to 30 ft. in diameter, rising from 15 to 20 or more ft., and terminated by a truncated cone of about two-thirds the height of the cylindrical part. Coal-burning furnaces are placed at different parts of the circumference at the floor of the kiln and rather below it, the flues from all of them passing to a common •opening at the center of the floor, where the heat enters and passes through the con tents of the kiln, which are usually placed in receptacles called seggars. The porce lain-kiln differs from the earthenware-kiln in having two stories instead of one, the upper one being used for the first "firing," which is done at a lower beat than for earthenware. For the manner of using the various forms of kiln see Buten, POT