CORE is the fuel generally used in locomotive engines, and is obtained by the beat ing of coal in ovens, or other arrangements where little air is admitted. Caking coal is most suitable for the manufacture of coke. The process is conducted either (1) in heaps or ridges, or (2) in ovens. The coking in heaps is called the Yeller method, and consists in placing the coal in round stacks, or in long ridges, occasionally to the length of 200 feet. During the building of the coal, wooden stakes are driven in, which are afterwards taken out, and lighted coal introduced at numerous places at the same time. As the coal becomes heated, much smoke and vapor are evolved, which mainly consist of tar, water, and coal-gas. Whenever the smoke ceases to be evolved, the process of coking is regarded as concluded, and the mound or ridge of red-hot cinder, or C., is covered over with fine coal-dust, which, excluding the air, extinguishes the combustion. At places where the operation of coking is conducted regularly on the large scale, it is customary to erect brick chimneys or columns, about the height of the proposed mound, and to build the coal round these, placing the larger masses in the center, the smaller pieces outside, and ultimately covering the whole with fine coal or dross.
A more economical plan of preparing C. is to introduce the coal into fire-brick ovens. The coal is introduced by the top, and being lighted, a little air is admitted by
openings in front. Whenever the coal ceases to evolve smoky vapor, every opening is closed, and the oven is allowed to cool down for 12 to 24 hours. A door in front is then opened, and the C. being raked out whilst still hot, water is thrown upon it, to stop the combustion. Small coal may be used if it belongs to the caking kind; and a little water sprinkled over it, causes the caking operation to proceed more completely. The proportion of C. obtained from coal in Great Britain ranges from. 54 to 73 per cent, so that in round numbers the better class of coal for this purpose loses a fourth of its weight. At the same time, the coal increases in volume to the extent of about one fourth.
C. is a hard, brittle, porous solid, with a color varying from iron-gray to blackish gray, and more or less of a metallic luster, and does not soil the fingers. It absorbs moisture from the air, sometimes to the extent of 30 per cent, end contains an amount of ash ranging from up to 15 per cent. It gives off no smoke in burning, is of great value as a fuel, evolving a very large amount of heat, and is used, not only in locomotive and other furnaces, but also in the smelting of metallic ores.