CHARCOAL, is wood burnt through, and suddenly extinguished by being co. vered with fresh earth. It is perhaps one of the most durable substances with which we are acquainted, not being de composed either by the air or the water. It is of great use in many processes where a strong heat is required: it is an antisep tic; but very dangerous as fuel in confin ed places. In chemistry, the terms car bon and charcoal were long confounded, and supposed to mean the same thing ; but the experiments by Morveau and others have pointed out the precise dis tinction. See CARBON.
When charcoal is prepared in the usual way, by exposing wood in close vessels to a red heat, it always contains a portion of hydrogen. For if a quantity of this char coal be exposed to a strong heat in a re-. tort of porcelain, iron, or coated glass, a great quantity of gas is obtained. The gas which comes over first is a mixture of car bonic acid and heavy inflammable gas ; but the proportion of carbonic acid di minishes, and at last it ceases to come over at all ; yet the inflammable gas con tinues as copious as ever. The evolution of these gases was long ascribed by che mists to the water which charcoal usually contains, and which it is known to absorb from the atmosphere with considerable avidity. If that were the case, the pro portion of inflammable gas ought to dimi nish at the same rate with the carbonic acid ; the hydrogen of the one being equally derived from the decomposition of water with the oxygen of the other. But as the evolution of inflammable gas conti nues after that of carbonic acid has ceased, it is scarcely possible to deny, that the hy drogen which thus escapes constituted a component part of the charcoal.
lf, therefore, we consider the experi ments of Morveau on the combustion of the diamond as decisive,we must conclude that common charcoal is composed of three ingredients, namely, carbon, hy drogen, and oxygen. It is of course a triple compound.
When common charcoal is exposed for an hour, in a close crucible, to the strong est heat of a forge, it ceases to emit gas; and no temperature is sufficient to expel gas from charcoal thus treated. Desormes and Clementhave endeavoured to demon. strate, that by this treatment common charcoal is deprived of the whole of its hydrogen. The same chemists tried the combustion of charcoal obtained frotn a variety of other substances exposed to the heat of a forge, as pitcoal, animal sub, stances, and various vegetable substan ces, and found the products exactly the same. Hence they conclude that char. coal is in all cases the same, provided it be exposed to a heat strong enough ; and they conclude too, that by this strong heat the whole hydrogen of common charcoal is expelled.
These facts enable us to conclude, that there are two species of charcoal, name. ly, common and prepared charcoal. The first contains three ingredients, carbon, hydrogen, and oxygen ; the second is de, prived of a portion of its hydrogen and oxygen. It consists chiefly of carbon and oxygen united.; but it still retains a small portion of hydrogen, and is not, there fore, strictly speaking, a pure oxyde of carbon, though it approaches very nearly to such an oxide.