Charcoal

Made by heating wood in a closed ve el without admittance of air, so that the water and volatile matters it contains are driven off, leaving the fixed carbon and ash. This may be done in large ovens or retorts and the products of the distillation condensed; or else the wood is charred in an open pile, the heat developed by the complete combustion of part of the wood being used to char the rest. The latter method is the original one used in the forests by the charcoal burners, and is conducted as follows: a level piece of ground is selected in a sheltered spot, and in the center a large stake is driven. Around this the pieces of wood in ab. 4-foot lengths are piled, either on end or flat, the spaces between the large pieces being filled with small branches, twigs,etc.(fig. 1). A pile may be 20 to 60 ft.in diameter, and 5 to12 ft. high. The outside is covered with wet leaves and earth. The stake in the center is then pulled out, leaving a chimney, into which some shavings and light wood are dropped and Fig. 1.-Charcoal Pile; vertical section. fired. Openings to let in air are now made around the outside edge of the pile against the ground. The fire burns very slowly, at first giving off a thin, yellow smoke, which consists of the volatile matter from the wood. After several days the smoke becomes gray, and then the openings admitting air are closed and the pile left to burn slowly with a very small admi ion of air, such as leaks in through the cracks in the outer covering. The pile shrinks as the wood chars, and needs continual watching to prevent it firing and being entirely consumed. Toward the end of the charring the openings around the edge are again opened to draw the draft that way and char the outer layers of wood. Small piles are carbonized in 6 to 14 days; large piles require a month or more. Wood gives 15 to 25 per cent of its weight of charcoal, according to the slowne with which it is charred, and the care with which the pile is extinguished. Sometimes the pile is made rectangular, with stakes around the sides to keep it in shape (fig.2). These methods of charring, while cheap and capable of being conducted out in the forest, have the disadvantage of allowing Fig.2.-Charcoal-burning; rectangular heap. all the volatile matter to escape. In the U. S. charcoal-burn ing is done in kilns connected with condensers. The ovens are either rectangular, cylindrical, or conical, with a capacity of 50 to 100 cords of wood, yielding 1,000 to 4,000 bushels of charcoal. The wood is fired and part allowed to burn in order to char the rest, as in an open pile, but the gases coming off are all condensed. Both rectangular and cylindrical kilns are hard to keep air-tight, and have been largely displaced by the conical one (fig. 3). Sometimes the retorts are made small and the heat applied from without, thus allowing a IMG:content-0826.png:[graphic] IMG:content-0827.jpg:[graphic] IMG:content-0828.jpg:[graphic] more perfect condensation of the volatile matters, but producing an inferior quality of charcoal. In this case, the gases coming from the condensers are burnt to heat the retorts. The volatile matters condensed contain tar, pyro IMG:content-0829.png:[ocr errors] ligneous acid, naphtha, Fig. 3.-Charcoal Kiln; vertical section. wood spirits, acetic acid, and ammonia salts, and are often of more value than the charcoal obtained. Charcoal is very light because of the porous structure, but its density in powder is 1 to 2. Light woods give the lightest charcoal. The chemical composition is 90 to 95 per cent of carbon and 5 to 10 of ash, when fresh, but it can absorb 10 to 20 per cent of moisture on standing in the air. Practical use has shown that an equal volume of hard charcoal produces a greater heat than soft coal, or, that charcoal is equal to about 1 times its volume of soft coal in heating power; also that it is 3 to 4 times that of an equal weight of wood. In evaporative effect, charcoal will turn into steam 8 to 12 times its own weight of water. When freshly burned and finely powdered, it is used to relieve accumulations of gas in the stomach and to correct the odor arising from offensive wounds, being incorporated in poultices or placed in small bags which are loosely packed around the wound.