among chemists, signifies any substance containing oil, which has been exposed to the fire in close vessels, so that all its volatile principles are expelled, and that it can sustain a red heat without further decomposition. Coal is commonly solid, black, very dry, and considerably hard. The specific character of perfect coal is its capacity of burning with access of air, while it becomes red-hot and sparkles, sometimes with a sensible flame which gives little light, with no smoke or fume capable of blackening white bodies.

Coal is capable of communicating its inflammable principle, either to the vitriolic acid with which it forms sulphur; or to the nitrous acid contained in nitre, which it inflames; or to metallic earths, which it reduces into metals. But the phlogiston cannot pass from coal to form these new combinations without the affluence of red-heat. Coal seems to be an unalterable compound in every instance but those mentioned, of burning in the open air, and of communicating its phlogiston to other bodies: for it may be exposed in close vessels to the most violent and long continued fire without suffering the least decomposition. No disposition to fuse, nor any diminution of weight, can be perceived. It is a substance exceedingly fixed, and perhaps the most refractory in nature. It resists the action of the most powerful menstrua, liver of sulphur alone excepted. Coal is evidently a result of the decomposition of the compound bodies from which it is obtained. obtained. It consists of the greatest part of the earthly principle of these compound bodies, with which a part of the feline principles, and some of the phlogiston of the decomposed oil, are fixed and combined very intimately. Coal can never be formed but by the phlogiston of a body which has been in an oily state; hence it cannot be formed by sulphur, phosphorus, metals, nor by any other substance the phlogiston of which is not in an oily state. Also every oily matter treated with fire in close vessels, furnishes true coal; so that whenever a charry residuum is left, we may be certain that the substance employed in the operation contained oil. Lastly, the inflammable principle of coal, although it proceeds from oil, certainly is not oil; but pure phlogiston; since coal added to vitriolic acid can form sulphur, to phosphoric acid can form phosphorus, &c., and since oil can produce none of these effects till it has been decomposed and reduced to the state of coal. Besides, the phenomena accompanying the burning of coal are different from those which happen when oily substances are burnt. The flame of charcoal is not so bright as that of oil, and produces no flame or foot.

All the phlogiston of coal is not burnt in the open air, particularly when the combustion is slow. One part of it exhales without decomposition, and forms a vapour, or an invisible and incombustible gas. This vapour, (which is, or at least contains a great deal of fixed air) is found to be very pernicious, and to affect the animal system in such a manner as to occasion death in a very short time. For this reason it is dangerous to remain in a close place, where charcoal or any other sort of coal is burnt. Persons struck by this vapour are stunned, faint, suffer a violent headache, and fall down senseless and motionless. The best method of recovering them is by exposure to the open air, and by making them swallow vinegar, and breathe its fumes.

Amongst coals, some differences are observable, which proceed from the difference of the bodies from which they are made: some coals, particularly, are more combustible than others. This combustibility seems to depend on the greater or less quantity of feline principle they contain; that is, the more of the feline principle it contains, the more easily it decomposes and burns. For example, coals made of plants and wood containing much feline matter capable of fixing it, the ashes of which contain much alkaline salt, burn vigorously and produce much heat; whereas the coals of animal matters, the feline principles of which are volatile, and cannot be fixed but in small quantity, and the ashes of which contain little or no salt, are scarcely at all combustible. For they not only do not kindle so easily as charcoal does, nor ever burn alone, but they cannot be reduced to ashes, without very great trouble, even when the most effectual methods are used to facilitate the combustion. The coal of bullocks blood has been kept for six hours very red in a shallow crucible, surrounded with burning charcoal, and constantly stirred all the time, that it might be totally exposed to the air; yet could it not be reduced to white, or even grey, ashes. It still remained very black, and full of phlogiston. The coals of pure oils are of concrete oily substances and foot, which is a kind of coal raised during inflammation, are as difficultly reduced to ashes as animal coals. These coals contain very little feline matter; and their ashes yield no alkali. The coals which are so difficultly burnt, are also less capable of inflaming with nitre than others more combustible; and some of them even in a great measure reflect the action of nitre.

Cannel-Coal. See Amplellites.

Fossil Coal, or Pit-coal. See Lithanthrax and Coalery.

Coal-Fish. See Gadus.

Coal-Mine. See Coalery.—Maliciously setting fire to coal-mines is felony, by stat. 10 Geo. II. c. 32. § 6.

Small-Coal, a sort of charcoal prepared from the sprigs and brushwood stripped off from the branches of coppice wood, sometimes bound in bairns for that purpose, and sometimes charred without binding, in which case it is called "coming it together."