Coal

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 (A.S. col, Icel. kol, Ger. kohle). The different sorts of fuel are distinguished by prefixes, as charcoal, pit-coal; but in England, owing to the absorbing importance of mineral or pit coal, the word coal alone has come to be used in this special signification (Ger. steinkohlen, Fr. charbon de terre).

Coal is one of the most important of all rocks; it consists chiefly of carbon, and is universally regarded as of vegetable origin. Its geological relations are noticed in the article CARBONIFEROUS SYSTEM. It occurs in layers or beds, and is always of a black or blackish-brown colour. Some of the varieties have a very considerable degree of vitreous or resinous lustre, while others are destitute of lustre; some have a shell-like fracture, and others have a highly cross-jointed structure, and are readily broken into cubical or rhomboidal fragments. The precise characters of coal as a rock 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 or Boghead Coal (q.v.). Coal, indeed, is rather a commercial than a scientific term, but in a general way we may define it as a fossil fuel of black colour 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 coal or anthracite no doubt gives off scarcely any volatile matter, but this is because it has undergone a natural distillation through the action of subterranean heat or of the proximity of intrusive igneous rock. We may therefore divide coal into two primary divisions—namely: (1) Anthracite, which does not, and (2) Bituminous coal, which does, flame when kindled. Anthracite (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 contain more than 80 per cent. of carbon. Various synonyms, such as stone coal, glance coal, culm, and Welsh coal, are also used to designate this substance, which is used chiefly for smelting purposes and for generating steam. In the United States it is also very largely used for domestic purposes—heating and cooking. It is difficult to kindle, but gives out a high heat in burning. Bituminous coal includes an almost endless number of varieties, one of the best marked being cannel or parrot coal. Cannel coal is probably so called from burning with a bright flame like a candle, and the name parrot coal is given to it in Scotland from the crackling 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 lustre; 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 considerable size, which approach black marble in appearance. Of this material vases, inkstands, boxes, &c. are made. Cannel coal contains a large percentage of ash, but the best cannels are in some places much used for open-grate fires in houses. Cannel is for the most part consumed in making gas, of which it yields from 8000 to 15,000 cubic feet per ton. When distilled at a low red-heat it yields paraffin oil. The other varieties of bituminous coal are so numerous that, as an Admiralty report states, there are as many as seventy denominations of it imported into London alone. Still, among these there are three leading kinds—1. Caking coal, 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 coal, occurring plentifully in Scotland, which is hard, and breaks into cuboidal blocks. This is often called block-coal; and locally it is very valuable, because it can be employed in smelting without being first coked. It is not very easily kindled, but when lighted makes a clear lasting fire. 3. Cherry or soft coal, which breaks easily into small irregular cubes, has a beautiful shining lustre, is readily kindled, and gives out a cheerful flame and heat. It is common in Staffordshire. Brown coal or Lignite (q.v.), though for the most part inferior to true coal, is nevertheless an important fuel in some countries in default of a better kind. There are, however, large deposits of lignites in some regions, as in North America, which coke well, and which are excellent substitutes for true coal.

The use of coal does not seem to have been known to the ancients; nor is it well known at what time it began to be used for fuel. Some say that it was used by the ancient Britons; and at all events it was to some extent an article of household consumption during the Anglo-Saxon period as early as 852 A.D. There seems to be reason for thinking that Britain was the first European country in which coal was used to any considerable extent. A coal-pit at Preston, Haddington, was granted to the monks of Newbattle between 1210 and 1219. Henry III. is said to have granted a license to dig coal in 1234. About the end of the 13th century it began to be employed in London, but at first only in the arts and manufactures; and the innovation was complained of as injurious to human health. In 1306 the parliament petitioned the king to prohibit the use of coal, and a proclamation was accordingly issued against it; but owing to the high price of wood, its use soon became general in London. It was for a long time known there as sea-coal, because imported by sea.

Several theories as to the mode of the origin of coal have been put forth from time to time. The one now generally believed in is that the rank and luxuriant vegetation which prevailed during the carboniferous age grew and decayed upon land but slightly raised above the sea; that by slow subsidence this thick layer of vegetable matter sunk below the water, and became gradually covered with sand, mud, and other mineral sediment; that then, by some slight upheaval or gradual silting up of the sea bottom, a land surface was once more formed, and covered with a dense mass of plants, which in course of time decayed, sank, and became overlaid with silt and sand as before. At length, thick masses of stratified matter would accumulate, producing great pressure, and this, acting along with chemical changes, would gradually mineralise the vegetable layers into coal. Microscopical examination shows that coal consists principally of the cortical portions of plants—more especially of the bark of such trees as Sigillaria—commingled with the debris of various other plants, amongst which the spore cases and spores of certain lycopodiaceous trees not infrequently occur in great abundance. It seems probable indeed that many coal-seams simply represent great swamps and marshy jungles.

As will be seen from the following table, wood, peat, lignite or brown coal, and true coal indicate by their composition the changes which vegetable matter undergoes by decay and pressure; and a table in which a considerable number of examples of each substance could be given would show how gradually these substances pass into each other:

In each of these bodies there is usually a small percentage of nitrogen, which in the above table has not been separated. In passing from wood or peat to coal, the proportion of oxygen and hydrogen decreases, these substances being given off in the form of marsh-gas and carbonic acid in the process of decay.

On the continent of Europe, productive coal-fields occur in Belgium, France, Prussia, Spain, Silesia, and in Russia—the only important Russian coal-field being that of Donetsk, on the north shore of the Sea of Azov. Coal is also found in India, China (where several extensive coal-fields occur, in which coal has been worked from a very early period), Japan, and the Malayan Archipelago, in Australia and New Zealand, and in Africa. There is evidence of promising coal-deposits in several South American countries, but, owing to the great supply of wood in their forests, there is little temptation to work them. Considerable importance already attaches, however, to the mines of Chili (q.v.). In Canada there are small, though valuable, coal-fields; but in the United States enormous fields of fossil fuel are found. The entire area of these is about 200,000 sq. m., being 83 times greater than the area of the coal-fields of Great Britain. But although the coal-measures of the States are of vast extent, and contain many valuable coal-seams—a few of them 40 and even 50 feet thick at certain places—it has been doubted whether the amount of workable coal in them has not been exaggerated. In proportion to the extent of the seams, the quantity of coal annually raised in the States is small, and amounted to 160,000,000 short tons of 2000 lb. each in 1892. The distribution of the coal-fields of Britain and North America is discussed at CARBONIFEROUS SYSTEM.

Coal-supply of Britain.—The probable duration of the British coal-supply is a question which until recent years rarely excited any public anxiety. Early in the 19th century attention had been called to the subject by Sir John Sinclair, Mr Robert Bald, and Dr Buckland, but the existing store of coal was generally believed to be practically inexhaustible—its exhaustion at all events seemed to be relegated to so remote a date as to relieve the nation from all anxiety on the matter. In recent years, however, Professor Hull, from a more accurate survey of British coal-fields than was possible before the map of the Geological Survey had been published, came to the conclusion in 1860, that at the then rate of production we had enough coal to last for 1000 years. But as the rate of consumption was yearly increasing, it was obvious that our coal-supply might not last nearly so long. In 100 years, as Professor Jevons showed, if the same rate of increase continued, the annual consumption would be 415,000,000 tons, and our coal-fields by that time would be nearly exhausted. A Royal Commission was appointed in 1866 to consider the whole question, and came to the conclusion in 1871 that at the then rate of consumption there was enough coal to last for 1273 years, but with a constantly increasing consumption this term would necessarily be reduced. The amount of coal at all depths down to 4000 feet was estimated at the date of the Royal Commissioners' Report to be 90,207 million tons, while including the coals at greater depths, the total was 146,480 millions of tons. Although, therefore, we know approximately the extent of available coal, we cannot tell how long that coal will last, for we cannot say whether the present rate of consumption will be maintained, increased, or diminished in the future. It seems most probable, however, that the rate of increase of coal used per head of the population will follow a diminishing ratio, and that it will be 300 or 400 years before the coal-supplies of these islands begin to fail.

Coal-trade.—The production and sale of coal, like every other important branch of industry, was long fettered with legislative regulations. At a very early period, the corporation of the city of London undertook the duty of either weighing or measuring the coal brought into the port, and by a series of statutes commencing with 7 Edward VI. chap. 7, the mayor and aldermen of London, and the justices of the counties, were empowered to fix the price of coal to be sold by retail; and in case of refusal by the parties to sell at the prices fixed, to enter their wharves, or other places of deposit, and to cause it to be sold at the prices which they had set. In addition to the general supervision which they thus possessed, and the sums which they were empowered to exact for their trouble, the corporations of London and other towns have exacted, and still continue to exact, dues on coal for local purposes. These were first imposed in London in 1667, after the great fire, in order to enable the corporation to repair the ravages which it had committed; and they have been since continued as a fund for civic improvements, though, as McCulloch has remarked, no improvement could be equal to a reduction in the price of coal. In the reign of William III. a general tax, payable to government, was laid on all sea-borne coal—a tax which was in the highest degree unjust to places which were dependent for their supply on the coasting trade, and oppressive to the whole country, inasmuch as it amounted to more than 50 per cent. on the price paid to the owner at the pit's mouth. The tax varied in amount, not only at different periods, reaching its highest point of 9s. 4d. per chaldron during the great war, but also in different parts of the country, being higher in London and the south of England, and lower in Ireland and Wales, whilst Scotland for a considerable period was altogether exempt. The tax itself, with all its inequalities, was abolished in 1830; and the tax on coal, long collected for local purposes in London, was abolished in 1889. The repeal, in 1845, of the duty on coal exported to foreign countries was a measure of much more doubtful policy. The quantity of coal exported from Great Britain (excluding coke and patent fuel) in 1895 was 31,756,368 tons; in 1899, 41,180,332 tons.—For the regulation and inspection of mines, explosions, &c., see MINING; where also mention is made of the varying arrangements as to the proprietorship of mines. The condition of colliers and salters in Britain is discussed at SLAVERY. For coal-tar products, see COALTAR, DYEING. See also the articles FUEL, GAS, PETROLEUM.

Coal-whipping is the name given to a mode of unloading coal from vessels at anchor to barges, which convey them to the wharves. When the number of these men at work on the Thames was about 2000, public-house keepers got into the habit of acting as middlemen; the trade fell into such a state, that the men were virtually slaves to the publicans. They asked for the interference of the legislature. An act was passed in 1843, and a Coal-whippers' Board was formed, which contracted for the whipping of ships of coal, and employed the men; and other acts were passed in 1846 and 1851. But in 1856 the coal-owners agreed with the Board of Trade to maintain a Whipping Office, to give the men a refuge from the publicans, but without interfering with the liberty of coal-shippers. The necessity for coal-whippers has been much lessened by the use of hydraulic or steam machinery in discharging.

See Green and Miall, Coal: History and Uses (1878); Galloway, History of Coal-mining in Great Britain (1882); Hull, Coal-fields of Great Britain (1880); Pameley, The Colliery Manager's Handbook (1891); Meldola, Coal and what we get from it (1891); H. W. Hughes, A Text-book of Coal-mining (1892); D. M. D. Stuart, Coal Dust an Explosive Agent (1894).