(From the Hebrew term charak, to burn, or charbah, burnt). But charcoal is generally understood by this word when fossilis is not joined with it. It is also a name of the curbunculus.

Carbo fossilis, (from charbah, burnt). Pitcoal, or Scotch coal. Hoffman says, that when it is analysed by distilling in a retort, over an open fire, it first yields a phlegm, then an acrid sulphureous spirit, then a subtile oil, then a grosser oil, which falls to the bottom of the receiver; then, by a brisker fire, an acidulated salt, like that of amber; in the retort there is left a black earth that is light, and which, on the application of fire, emits neither flame nor smoke. The gross empyreumatic oil contains a quantity of mineral sulphur: thus coal, as all bitumens are, is an oleo sulphureous acid, with a light calcareous earth.

These coals are only used for the advantage of their heat by burning them in stoves; but for purposes not connected with medicine, they undergo a process previous to their being used, that is, they are charred, or reduced to coaks or cinders: this is effected by a method similar to that of making charcoal of wood: by this operation they are deprived of their phlegm, their acid liquor, and much of their fluid oil.

Carbo vegetabilis, or charcoal of wood, is the coal into which wood is converted by the process of charring.

Pieces of wood are so disposed as to form a pile, generally conical; this pile is covered with turf, to prevent the too free draught of air, by which the wood would be reduced to ashes, and not to coal. The pile is then kindled, and the fire continued till the watery and the more volatile parts of the wood are dissipated, that is, till no more smoke arises, at which time the wood is thoroughly red hot. The external air is then to be totally excluded by covering the pile with earth, and thus the fire is extinguished.

In chemistry, by the word coal is understood any substance containing oil, which hath been exposed to fire in a close vessel so that it can sustain a red heat without further decomposition; but the use of these coals or coaks in smelting iron is scarcely a part of our subject, and must not detain us at this time. Charcoal is of very considerable service in many processes connected with diet. From the indestructible nature of charcoal, charring the inner surface of casks renders them more fit for preserving water; and, from some late experiments, it appears that water may be kept at sea without any change for an indefinite period, by this simple previous operation on the staves. Honey is cleared from its bad colour, and occasionally offensive taste, by its means; ardent spirits are deprived of an empyreumatic, or other bad flavour, and rancid oil by an admixture of charcoal is restored to its former state of purity. Vinegar concentrated by freezing, and afterwards distilled from powdered charcoal, becomes highly pure and fragrant. Crystals of tartar are whitened, and many of the neutral salts crystallize more perfectly, by previously digesting their solutions with this substance.

Heated charcoal absorbs air very completely, and forms a more perfect vacuum than the best air pump. In other circumstances it absorbs it in part only, preferring the oxygenous part to the azote. Cold charcoal absorbs atmospheric air without any decomposition. Fresh made charcoal absorbs water very copiously, and deposits a great part of the air it had taken up. It is an excellent conductor of electricity.

In medicine it is used as an application to cancers, and to putrid ulcers; occasionally also as a dentifrice, but it appears to possess little peculiar merit.

Charcoal from different woods are preferred in different arts, but its use in medicine and pharmacy is the same from whatever source it be obtained.

The vapours that arise from charcoal are extremely pernicious, producing a species of apoplexy in those persons who are exposed to them. They produce at first a sense of uneasiness, a chilliness, nausea, and headach. These are followed by a loss of sense, a fixed look, a rigidity of the whole body, a ghastly countenance, a small, frequent, and irregular pulse, and death.

In this case the noxious vapours act on the brain and nerves, through the medium of the lungs; these vapours, and those from fermenting vegetables, putrefying animal substances, or from caverns, operate in the same manner; and as accumulated and confined, their effect is more or less instantaneous. They attack the vital principle, and extinguish it at once if copious: a less quantity produces the symptoms of debility in the nervous system. To prevent suffering from this cause, close rooms where these substances are burning must be avoided; they are only safe when a candle will continue to burn in them. The vapours of deep wells arc of this kind, but those of mines are different, and consist of hydrogenous gas. In some kinds of azotic gas, which are highly deleterious, a candle will burn freely.

When affected, the patient must be exposed to the open air; if he can swallow, acidulated liquors may be given: if he is insensible, cold water must be thrown on his face; strong vinegar rubbed about his nostrils, and held under them; stimulating clysters are also necessary. To remove the spasms, the sps. aetheris vi-triolicus compositus will be useful. If these fail, let a strong healthy person breathe forcibly into the mouth of the patient so as to distend his lungs, or they may be distended more advantageously by oxygenous gas.