VARIETY AND CHARACTER OF COAL.
coals of the Carboniferous era, or " true coals," as they are frequently called, may be grouped under several heads, or names :—Cannel, Bitumi nous, Semi-Bituminous, and Anthracite. Cannel is a remarkable variety, the coarser kinds being called " parret" in Scotland, and splint-coal in England and our Western coal-fields.
Cannel contains from 40 to 60 per cent. of volatile matter, and the pro portion of carbon varies to the same extent. It takes fire like a candle, burns readily, and gives out much flame and smoke. The ash varies from 4 to 10 per cent. This is generally considered the best gas coal, since it produces large quantities and of a remarkably pure quality. It is found extensively in the Scotch coal-fields, and also exists to a limited extent in the Newcastle district ; in the Wigan portion of the Lancashire coal-field, and in the Yorkshire and Derbyshire coal-fields.
Cannel coal passes into jet and asphaltum. It may be worked into ornaments, but is brittle and not very hard. The seams are generally thin, though there are important exceptions. The coal of the Mons basin, Belgium, seems to be of this kind. Cannel exists, to a great extent, in our Western coal-fields, of the richest and purest variety.
Cannel is a bituminous coal, but differing so much from our common bituminous, that it seems more appropriate to designate them by different names. Common bituminous contains less volatile matter, and may be said to yield from 50 to 75 per cent. of carbon, and the semi-bituminous from 75 to 90 per cent. of carbon.
The rich caking, or coking, coals of Northumberland and Durham contain from 60 to 70 per cent. of carbon, and from 2.50 to 5 per cent. of ash; while the average yield of the Newcastle, or the Great Northern, coal-field, is from 70 to 75 per cent. of carbon. The variety known as "household coal" contains the largest amount of carbon, and those known as steam and gas coals the smallest amount of carbon, and, of course, the largest amount of volatile matter. The following analysis gives the approximate or average percentage of those coals, as presented on the authority of the North of England Institute of Mining Engineers.
The coking coal of this district leaves a red ash in an open fire, and requires to be deprived of its volatile matter before being exposed to a strong blast, owing to its tendency to cake or cement together in a solid mass, and thus prevent a free draught through the grate or furnace in which it may be used.
The coals of Staffordshire, Yorkshire, Derbyshire, Lancashire, North Wales, and many other districts, contain as much or more bituminous matter than those of Northumberland and Durham, but they do not cake or coke as well, and, consequently, may be used to a greater extent without coking. On account of its superior coking qualities, nearly half of the enormous coke production of Great Britain-6,000,000 tons—is made from the coals of the Great Northern coal-field. The coals of those dis
tricts named above burn freely, with much flame, and give out great heat, but they are considered inferior, for household as well as coke-making purposes, to the coals of the last-named field. They yield from 50 to 70 per cent. of carbon, and from 25 to 45 per cent. of volatile matter, with about 5 per cent. of ash, which is often white. Most of the coals of the inland counties show the presence of argillaceous earth by the white lines on the edges of the beds, and are, therefore, less adapted to general use than the Newcastle coals; but many of them are of excellent quality.
Next in order to the coals of the midland counties are those of North and South Wales, which contain a larger percentage of carbon generally than the coals named above, and, of course, less volatile matter and bitu men. They burn, however, freely, with but little smoke or residue, and are peculiarly adapted for steam purposes and the manufacture of iron, or where a strong blast is required. This character of coal is as extensively distributed as the coals before mentioned, and is found extensively in America, at Pittsburg in Pennsylvania, Ohio, Maryland, and elsewhere. It is also found and mined to some extent in France, Belgium, Saxony, and Austria.
The last variety among the true coals is anthracite, which consists almost exclusively of carbon. This is a non-bituminous coal, as the steam-coal is a semi-bituminous. We do not generally apply the term semi-bituminous in this country to the bituminous steam-coals of Cumberland and Bloss burg, or those of the eastern limits of the great Alleghauy coal-field; but they are nevertheless as genuine a semi-bituminous as the coals of Broad Top or Sullivan county.
Anthracite coal contains from 80 to 95 per cent. of carbon, with a small amount of ash generally, and sometimes a limited percentage of volatile matter. The anthracites are heavier than common coal, and take fire with difficulty, but burn with intense heat when fully ignited under a strong draft. This coal is found abundantly in South Wales and in Pennsylvania, and also exists in the south of Ireland, in France, Saxony, and Russia.
The use of this coal is greatly on the increase, though of late develop ment. It is adaptable to a variety of purposes, but its chief use of late years has been for the manufacture of iron and for steam purposes gene rally, in the vicinity of its production. It was used exclusively by our war-steamers during the Rebellion, with the exception of our gunboats on the Western rivers. This coal is generally lustrous, with a bright, shining, irregular or conchoidal fracture; hard, dense, and tenacious, or without fracture during combustion, but sometimes brittle and friable under a strong heat, and not available for use in the blast furnace.