Coal

(kol.) [A.S. col.] (Min. and Geol.) A name under which are cla ed together various solid inflammable mineral substances, capable of being used as fuel, and characterized by the presence of carbon as a largely predominant constituent, a ociated with smaller quantities of hydrogen oxygen, nitrogen, sulphur, and certain mineral matters which compose the ashes. Coal appears to have been formed by a peculiar decomposition or fermentation of buried vegetable matter, resulting in the separating of a large proportion of its hydrogen in the form of marsh-gas (C2H4), and similar compounds, and of its oxygen in the form of carbonic acid (CO2), the carbon accumulating in the residue. The examination of a peat-bog is very instructive with reference to the formation of coal, as attording examples of vegetable matter in every stage of decomposition, from that in which the organized structure is still clearly visible, to the black carbonaceous ma which only requires consolidation by pre ure in order to resemble a true coal. The three principal varieties of coal lignite, bituminous coul, and anthracite-present us with the material in different stages of carbonization; the lignite, or brown coal, presenting indications of organized structure, and containing considerable proportions of hydrogen and oxygen, while anthracite often contains little else than carbon and the mineral matter or ashes. The lignites furnish amuch larger quantity of gas under the action of heat, and therefore burn with more flame than the other varieties, leaving a coke which retains the form of the original coal; while bituminous coal,softens and cakes together, a useful property, since it allows even the dust of such coal to be burnt, if the fire be judiciously managed. Anthracite is much le easily combustible than either of the others, since it yields but little gas when heated, and it usually burns with little flame or smoke. Coal has been in course of formation since the existing state of the world began; and it is probably so still. It is therefore found in all geological ages. It is chiefly found in the Lia ic and Oolitic members of the secondary formation; but the Carboniferous series, which belongs to the Primary or Palæozoic formation, is that which yields the chief supplies in Western Europe and Eastern N. America. The most remarkable coal-fields of Europe at present in actual work are those of England, Belgium, France, Rhenish Pru ia, Silesia, Bohemia,Spain, and Ru ia. The productive coalfields of the U. States are of enormous extent, embracing an area of 125,000 sq. m. The most remarkable is the great Appal a chi an coal-field, which covers parts of Pennsylvania, Ohio, Virginia, E. Kentucky, E. Tenne ee, and Alabama. The whole thickne of the formation is 2,500 to 3,000 ft.; aggregate thickne of the included coal-beds, over 120 ft. in the Pottsville and Tamaqua valley, abt. 62 ft. near Wilkesbarre, and 25% ft. at Pittsburg. In the centre of Pennsylvania, between Pottsville and Wyoming, are the famous anthracite beds, divided into many distinct patches. The total product of coal in the U. States in the year 1869 (excluding Anthracite, q. v.) was abt. 16,000,000 tons. During the fiscal year ending June 30, 1871, there were imported into the U. States 443,955 tons of bituminous coal, valued at $1,132,775; while our exportation during the same period was: bituminous coal 133,380 tons, valued at $564,067; and other coals 134,571 tons, valued at $805,169. See ANTHRACITE. [s. 200]