CHARCOAL

A form of carbon, obtained by burning wood with the imperfect acce of air, or by heating or distilling it in iron cylinders so constructed as to allow of the collection of the volatile products; among which are tar, and pijroligneous acid, which is impure vinegar. Glial coal, exclusive of its important use as a fuel, is po e ed of some curious and valuable properties. It is a very bad conductor of heat; and hence powdered charcoal is used to surround tubes and ve els which are required to retain their heat. It is not injured by air and moisture; hence stakes and piles are superficially charred to preserve them. It is infusible; and provided air be carefully excluded, it undergoes no change in most intense heats. It absorbs air and moisture, and also the colouring and odoriferous parts of many animal and vegetable substances Tainted flesh and putrid water are thus sweetened by the action of powdered charcoal, especially by what is called animal charcoal, obtained by burning bone, or the clippings of hides, leather, . Coloured vegetable solutions filtered through well burned charcoal are materially decoloured by it: when burned in oxygen or air, it is converted into carbonic acid. (See Diamond and Carbon.) Common charcoal intended merely for fuel is prepared by cutting pieces of wood from 1 in. to 3 in. in diameter into lengths of from 1 ft. to 3 ft., forming them into a conical pile, and covering them with turf or clay; leaving two or three small holes, close to the ground, for li'dit in" the wood, and boring through the turf in the upper part of the cone, a few other small holes for the escape of the smoke. The pile being lighted at the several holes along the bottom, continues burning with a slow smouldering flame for a week or two, and is allowed to cool before the iurf is removed. In the case of very hish winds, the holes tc the windward are stopped, to prevent combustion from going on with too great rapidity. Charcoal obtained by distilling beech-wood, log-wood, willow, and other woods.which are free from resin, is called cylinder charcoal. The charcoal employed in the manufacture of gunpowder is njw always so prepared. [s. 230]