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the heating power of coal is its most important property, this is often tested by means of an apparatus known as a 'calorimeter.' (See CALORIMETRY.) The principle of the test depends on the determination of the weight of water which can be converted into steam at 212° F. under atmospheric pressure with one pound of coal. (See also HEAT.) In addition to the varieties of coal given above, there may be mentioned semibituminous coal and cannel coal. The properties of the different varieties are as follows:

Anthracite contains 84 per cent. or more of fixed carbon, and also little ash, sulphur, and moisture. It has great heating power, and burns with a smokeless flame. Owing to its comparative scarcity, it commands a higher price than the bituminous. Anthracite is dense, has a shining lustre, and usually breaks with a smooth conchoidal fracture. It is estimated by some geologists that abo ten inches of peat is required to make one inch of anthracite coal. In the United States anthracite coal is confined chiefly to the eastern edge of the Appalachians in Pennsylvania, where the folding of the rocks has been very intense, and where the coal-seams have been subjected to great pressure. It is also known in Colorado, near Crested Butte, where the bituminous coals have been locally changed to anthracite by the heat of basalt intrusions. It is mined extensively in England, and large quantities are known in China.

Bituminous Coal contains 50 to 75 per cent. of fixed carbon, and 25 to 30 per cent. volatile hydrocarbons. It burns with a rather long and smoky flame, and is also much used for steaming purposes. Many bituminous coals have the property of coking or caking (see COKE) when heated to redness. Most of the Carboniferous and many of the Mesozoic coals of the United States are bituminous.

Semi-Bituminous Coal resembles bituminous coal in appearance, but is intermediate between it and anthracite. It contains from 70 to 84 per cent. of fixed carbon, and is considered of superior value for steaming purposes. This variety is obtained from Pennsylvania, Maryland, and West Virginia.

Cannel Coal is a variety of coal very rich in volatile hydrocarbons, and found sparingly in parts of Kentucky, Ohio, and Indiana. Its chief use is as a gas-enricher, since it yields 8000 to 15,000 cubic feet of gas per ton. Cannel coal is so called because it burns with a bright flame like a candle, and the name parrot coal was given to it in Scotland, from the crackling or chattering noise it makes while burning. It is very compact in texture and may even have an oily look; certain forms found in England admit of being polished, and ornamental articles have been made from them and sold under the name of jet.

land was the first European country in which coal was used in any considerable quantities. In America the deposits near Richmond, Va., were discovered in 1701, and mining was begun in 1750, while anthracite was first produced in 1793. Extended coal-mining in the United States did not really begin, however, until about 1820. Since that time up to the present, the increase has been very rapid. In 1822 the amount of coal mined in Virginia was about 48,000 long tons. Now the production for the United States is over 350,000,000 short tons, greater than that of any other country of the world.

Coal is used largely for domestic purposes, either as fuel or, in the form of gas, for illumination. Its use for the latter purpose is, however, not so widespread as formerly, water-gas having superseded it to a considerable extent. In the production of steam for motive power it also finds important applications. It is furthermore widely employed in the metallurgical industry in the form of either coal or coke, and in this connection may serve both as a fuel and as a reducing agent. Coke (q.v.) is made only from bituminous coal. Lignite seldom has much value as a fuel, owing to the large percentage of moisture that it contains. Because of this moisture it tends to crack in drying, and must therefore be used soon after mining, and in localities where it does not require long transportation from mine to market. This is true, for instance, of some of the lignite deposits in Colorado which are near the Denver market, and therefore possess commercial value. Lignite has sometimes been successfully used in the manufacture of producer gas, and peat has been found adaptable for this purpose.

COAL AREAS. The leading coal-producing countries of the present day are the United States, Great Britain, Germany, France, Belgium, Austria-Hungary, and Russia. The Russian coalfields are probably the most extensive in Europe. In the Far East coal is known in India, the Malay Archipelago, Japan, and China. The coal-fields of China are probably the greatest in the world, and may become a source of European supply. Up to the present time they have not been developed in a systematic manner. Italy, Spain, Sweden, Australia, New Zealand, Borneo, the Philippine Islands, and many countries in Africa, also produce coal; while in America deposits are worked in Canada, Mexico, Chile, and Argentina, and are known to occur in Colombia and Peru.

Lignite, or Brown Coal, is a partially formed coal, containing much moisture and volatile matter. It often shows the woody structure of peat and burns very easily, but gives off little heat.

HISTORY AND USE. The value 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; at all events, it was an article of household consumption to some extent during the Anglo-Saxon period as early as A.D. 852. There seems to be reason for thinking that Eng

UNITED STATES. The coal-fields of the United States are especially extensive; indeed, in some instances the deposits of a single State exceed those of Germany or France in area. Their total area is over 335,000 square miles. They are separable into several regions, the divisions being geographical and not geological. The geological ages of the coals in 1, 2, 3, 4, and 6 (table on next page) are all Carboniferous, except small Triassic areas in Virginia and North Carolina. Those of 5 are Cretaceous and Tertiary.

By far the most important of these regions is the Appalachian, which takes in portions of Pennsylvania, Ohio, West Virginia, Virginia, Maryland, Eastern Kentucky, Eastern Tennessee, Georgia, North Carolina, and Alabama. It is about 750 miles long, and 70 to 80 miles wide. The coals are all bituminous or semi-bituminous with the exception of those at the northeastern end, in Pennsylvania, where close folding of the rocks

[blocks in formation]

been described in the article CARBONIFEROUS SYSTEM, from which it may be seen that the coalbeds occupy more or less well-marked stratigraphic positions. The maximum thickness of strata is from 2500 to 3000 feet; the seams measuring 120 feet near Pottsville, 62 feet at Wilkesbarre, and 25 feet at Pittsburg, showing a gradual diminution in a westward direction. The most persistent coal deposit is the Pittsburg seam, which is known over an area measuring 225 by 100 miles, and has a thickness varying from 2 to 14 feet. In Alabama the deposits are distributed

among three districts-the Warrior, Cahawba, and Coosa, named after the rivers that drain them. The anthracite district of Pennsylvania occupies an area of about 470 square miles on the left bank of the Susquehanna. The strata between Pottsville and Wyoming, which belong to the lowest portion of the coal-measures, are probably about 3000 feet thick; but it is difficult to make an exact estimate, because of the numerous folds and contortions. There are from 10 to 12 seams, each over three feet in thickness. The principal one, known as the Mammoth or Baltimore vein, is 29 feet thick at Wilkesbarre, and in some places exceeds even 60 feet. Many of the Appalachian coals, notably those of western Pennsylvania, West Virginia, and Alabama, produce excellent coke. The Ohio coals do not yield good coke. In most of the other coal-fields of the country the coal-beds lie comparatively flat, and the basins are quite shallow.

The Michigan area is a small one in the lower peninsula of Michigan. It forms a circular basin with a diameter of about 50 miles. The coals are bituminous, non-coking, and are mined chiefly for local use. The seams range from a few inches to three feet in thickness.

The Central area includes parts of western Kentucky, Indiana, and Illinois, and lies chiefly within the latter State. These coals are all bituminous, of Carboniferous age, and are used chiefly for steaming. The thickness of the Carboniferous System varies from 1200 to 1400 feet in southern Illinois, to about 600 feet in Indiana, and the workable coal-seams vary in number from 7 to 12 in Illinois, and their thickness from three to eight feet. The block coal' of Indiana has quite a reputation. The Western Central area includes Iowa, Missouri, Arkansas, Indian Territory, Kansas, and part of Texas. Here again there is an abundance of bituminous coal, which has been developed chiefly in Iowa and Missouri, while Kansas and Indian Territory are becoming prominent. The coals of this area are chiefly adapted to smithing and steaming purposes, though Indian Territory yields coking varieties.

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The Cordilleran area comprises the coal regions of Colorado, New Mexico, Utah, Wyoming, North Dakota, Montana, California, Oregon, Washington, and Alaska. In this field are found many varieties grading between lignite and anthracite. They are all of either Tertiary or Cretaceous age, and their discovery showed the incorrectness of the old classification, which included all post-Carboniferous coals under lignite. Colorado is perhaps the most important producer, having a number of good bituminous seams. Those in the vicinity of

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