THE COAL. A good gas-coal should contain only a small percentage of ash and sulphur, and should yield, upon distillation, a comparatively large percentage of volatile matter of good illu urinating value, and a good coke amounting to from 55 per cent. to 65 per cent. of the original weight of the coal. A gas-coal showing the fol lowing analysis by weight may be considered as the standard for the United States: Volatile matter, 33 per cent. to 35 per cent.; fixed carbon, 55 per cent. to 60 per cent.; ash, 4 per cent.
are of varying dimensions, a very common size for the United States being 16" X 26" X 9' in side, and are set in groups of from three to nine, there being usually six in a group. The to 6 per cent.; sulphur, 0.4 per cent. to 0.6 per cent. A pound of such coal will yield, upon distillation, about five cubic feet of gas, possess ing an illuminating value of from 15 to 17 candle power when burned in an Argand burner.
Under proper conditions, a falling off in any direction may compensate for a proportionate betterment in another. Thus an extra amount of sulphur may be offset by an increased yield of gas, or a harder, better coke. Comparative cheapness of price may also turn the scale in favor of an otherwise in ferior local coal. Good gas coals of practically the above composition arc found in Penn sylvania, in the Pittsburg fields; in West Virginia, in the West Virginia and Kanawha fields; and also in Tennessee, Indian Territory, and Colorado; while others not so good are found in Alabama, Kansas, and Washington. In Europe the coal-fields of England furnish the best gas-coals, these English coals being of very nearly the composition given above, except that they contain less ash. but more sulphur.