COAL, in the sense of a piece of glowing fuel (and hence a piece of fuel, whether dead or alive), is a word common to all the languages of the Gothic stock (Ice]. ka/, Ger. kdde), and seems allied to the Lat. ealeo, to be hot; as also to glow, and kiln. The dif ferent sorts of fuel are distinguished by prefixes, as charcoal, pit-coal, sea-coal; but in England, owing to time absorbing importance of mineral or pit-coal, the word C. alone has come to be used in this special signification (Ger. steinkoklen, Fr. charbon de tern).
C. is one of the most important of all minerals; it consists chiefly of carbon, and is universally regarded as of vegetable origin. Its geological relations are noticed in the article CARBONIFEROUS SYSTEM. It generally occurs in strata or beds; it is always of a black or blackish-brown color; some of the varieties have a very considerable degree of vitreous or resinous luster, and some arc very destitute of luster; some have a shell-like fracture, and some have a sort of slaty structure, and arc readily broken into cubical or rhomboidal fragments. The nreciso characters of C. as a mineral species are not easily defined, and both in Britain and other countries important cases have occupied courts of law, in which this difficulty was strongly felt, as in the great Scottish lawsuit concerning the Torbanehill Mineral (q.v.). C., indeed, is rather a commercial than a scientific term, but in a general way we may define it as a fossil fuel of black color and stony consistency, which, when heated in close vessels, is converted into coke with the escape of volatile liquids and gases. The variety known as blind C. or anthracite no doubt gives off scarcely any volatile matter, but this is because it has undergone a natural distillation through metamorphism or other cause. We may therefore divide C. into two primary divisions, namely, (1) An thracite, which does not, and (2) Bituminous a, which does flame when kindled. An thracite (q.v.) sometimes contains as much as 94, and if we exclude the ash, 98 per cent of carbon, and as this element decreases in amount it graduates into a bituminous Coal. The term anthracite is, however, still applied to some coals which do not con tain more than 80 per cent of carbon. Various synonyms, such as stone C., glance C..
culm, and Welsh C., are also used to designate this substance, which is used chiefly for Smelting purposes and for raising steam. It is difficult to kindle, but gives out a high heat in burning. Bituminous G. includes an almost endless number of varieties, one of the best marked being cannel or parrot C. Cannel C. is so called from burning with a bright flame like a candle, and the name parrot C. is given to it in Scotland from the or chattering noise it makes when burned. That of different localities varies much in appearance, but it is most commonly dull and earthy, or with only a slight luster; some examples are, however, bright and shining. In texture it is nearly always compact, and certain beds of it admit of being polished in slabs of consider able size, which approach black marble in appearance. Of this material vases, ink stands, boxes, etc., are made. Cannel C., from the large percentage of ash which it contains, is not suitable for house fires, and is for the most part consumed in making gas, of which it yields from 8,000 to 15,000 cubic ft. per ton. When distilled at a low red-heat it yields paraffin oil. The other varieties of bituminous C. are so numer ous that, as an admiralty report states, there are as many as 70 denominations of it imported into London alone. Still, among these there are three leading kinds—I. Caking G'., which cakes or fuses into one mass in the fire. It breaks into small uneven fragments, and is found largely at Newcastle and some other localities. 2. Splint or hard C., occurring plentifully in Scotland, which is hard, and has a kind of slaty fracture. It is not very easily kindled, but when lighted makes a clear lasting fire. 'J. Cherry or soft C., which breaks easily into small irregular cubes, has a beautiful shining luster, is readily kindled, and gives out a cheerful flame and heat. It is common in Staffordshire. Brown C. or lignite (q.v.), though inferior to true C., is nevertheless an important fuel in some countries in default of a better kind.