mass, and moderately hard, which retains its solidity, when heated. Its component parts, according to Mr. Kirwan, are petrol, or asphaltum, mixed with a small portion of argillaceous earth, and frequently blended with pyrites, or fire-stone. A red tincture is extracted from this species of coal, by means of spirit of wine.
2. Culm-coal, which, together with a moderate quantity of petrol, has a larger proportion of argillaceous earth, and vitriolic acid, than the pit-coal, to which it bears a strong resemblance. Its texture is not so bright as that of the former species; and it burns with a flame, without being consumed, leaving a slate nearly of the same sise as the original volume of the coal.
3. Slate-coal, which contains so large a quantity of argillaceous earth, that it has the appearance of common slate. It, nevertheless, burns by itself, with a flame, and is found principally in the quarries near Purbeck; and in such abundance, that the poorer class of inhabitants in that neighbourhood are wholly supplied with it, for their common fuel.
4. The Ampelites, or Canal-coal, is of a dull black colour, and easily breaks in every direction. It burns with a bright flame, but frequently flies to pieces in the fire: it may, however, be divested of this property, by being immersed in water for several hours, previously to its being used. As this coal is of an uniform, hard texture, it is readily turned on a lath, and takes a good polish. Hence, it is used for making various toys, which greatly resemble those manufactured from the finest jet.
5. Kilkenny-coal is the lightest of the various species of this fossil. Although containing the largest proportion of asphaltum, it emits less smoke and flame, produces a more intense degree of heat, and is more slowly consumed than the canal-coal. This valuable coal is chiefly found in the county of Kilkenny, in Ireland.
These are the principal varieties of coal most commonly known; but they are not uniformly of the same kind or nature, in the different places where they are found. On the contrary, the various proportions and qualities of their ingredients, produce a great number of other varieties, which are calculated for different purposes, according to the quantity and quality of their contents. Hence it happens, that various kinds of coal are often found intermixed in one stratum, and some of the finer sorts frequently run like veins among the coarser species.
Coals are applied to various purposes, and are eminently useful in the smelting of ores, especially when burnt into coke (to which we refer); but, by these processes, considerable quantities of tar and pitch have hitherto been, inattentively, wasted. To obviate these losses, the ingenious Lord Dundonald erected ovens of a peculiar construction, for burning pit-coal into coke, and, at the same time, for collecting, in separate vessels, the volatile alkali, pitch, oil, and tar, which would otherwise have been dissipated. For this invention he obtained a patent, on the 30th of April, 1781, for 14 years; which term was afterwards, by an act of parliament, extended to 20 years, to commence from the 1st day of June, 1785. His ovens are so contrived, as to admit the
