[Illustration: HOW A COAL MINE LOOKS ABOVEGROUND
All that shows on the surface is the machinery shed where the various engines work to keep the air fresh, and bring up the miners and the coal.]
That is the way mining used to be done. In these days a man with a small machine for cutting coal comes first. He puts his cutter on the floor against the wall of coal and turns on the electricity. _Chip, chip_, grinds the machine, eating its way swiftly into the coal, and soon there is a deep cut all along the side of the room. The man and his machine go elsewhere, and the first room is left for its next visitors. They come in the evening and bore holes for the blasting. Once these holes were bored by hand, but now they are made with powerful drills that work by compressed air. A little later other men come and set off cartridges. In the morning when the dust has settled and the smoke has blown away, the loaders appear with their shovels and load the coal into the cars. Then it is raised to the surface and made ready for market.
Did you ever notice that some pieces of coal are dull and smutty, while others are hard and bright? The dull coal is called bituminous, because it contains more bitumen or mineral pitch. This is often sold as "run-of-mine" coal,--that is, just as it comes from the mine, whether in big pieces or in little ones; but sometimes it is passed over screens, and in this process the dust and smaller bits drop out.
The second kind of coal, the sort that is hard and bright, is anthracite. Its name is connected with a Greek word meaning ruby. It burns with a glow, but does not blaze. Most of the anthracite coal is used in houses, and householders will not buy it unless the pieces are of nearly the same size and free from dirt, coal dust, and slate. The work of preparation is done in odd-shaped buildings called "breakers." One part of a breaker is often a hundred or a hundred and fifty feet in height. The coal is carried to the top of the breaker. From there it makes a journey to the ground, but something happens to it every little way. It goes between rollers, which crush it; then over screens, through which the smaller pieces fall. Sometimes the screens are so made that the coal will pass over them, while the thin, flat pieces of slate will fall through. In spite of all this, bits of coal mixed with slate sometimes slide down with the coal, and these are picked out by boys. A better way of getting rid of them is now coming into use. This is to put the coal and slate into moving water. The slate is heavier than the coal, and sinks; and so the coal can easily be separated from it. Dealers have names for the various sizes of coal. "Egg" must be between two and two and five eighths inches in diameter; "nut" between three fourths and one and one eighth inches; "pea" between one half and three fourths of an inch.