CHARCOAL. A form of carbon, ob tained by burning wood with the imper fect access of air, or by heating or dis tilling it in iron cylinders so constructed as to allow of the collection of the vola tile products ; among which are tar, and pyrolioneous acid, which is impure vinegar. Charcoal, exclusive of its im portant use as a fuel, is possessed of some curious and valuable properties. It is a very bad conductor of heat ; and hence powdered charcoal is used to surround tubes and vessels 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 care fully excluded, it undergoes no change in most intense heats. It absorbs air and moisture, and also the coloring and odoriferous parts of many animal and ve getable substances. Tainted flesh and putrid water are thus sweetened by the action of powdered charcoal, especially by what is called animal charcoal, ob tained by burning bone, or the clippings of hides, leather, &c. Colored vegetable solutions filtered through well burned charcoal are materially decolored by it : when burned in oxygen or air, it is con verted into carbonic add. (See DIAMOND and CARBON.) Common charcoal, in tended merely for fuel, is prepared by cutting pieces of wood from 1 mch to 8 inches in diameter, into lengths of from 1 foot to 3 feet, forming them into a coni cal pile, and covering them with turf or clay ; leaving two or three small holes, close to the ground, for lighting 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 turf is removed. In the case of very
high winds, the holes to the windward are stopped, to prevent combustion from going on with too great rapidity. Char coal 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 now always so prepared.
It is not, however, by any means as good as that prepared by the burning of peat or turf. More charcoal is obtained by the slow combustion of the wood than by the quick. The quantity of charcoal obtainable from wood varies from 12 to 25 per cent.
Animal charcoal is superior in its de colorizing power to vegetable charcoal. In filtering ale through it, it was found to abstract all the bitter principle ; it has also the property of separating sulphate df quina, many salts of the alkaloids, as well as other saline matters from their solutions.
Its absorbing power over gases is great est when it is fresh. It acts with differ ent energy on different gases ; one cubic inch of charcoal will absorb of Ammoniacal Gas 90 cubic inches.
Muriatic Acid 85 Sulphurous Acid 65 Sulphuretted Hydrogen 55 Carbonic Acid 35 Oyxgen 9 it Hydrogen I it Hence the great value of charcoal thrown into cesspools and privies, to ab sorb odors ; hence its use, added to gua na, fcecal matter, urine, or any substance giving off gases valuable for growth of vegetation. Its chief value as a manure depends on this property. Charcoal is occasionally used as a polishing powder.