This coal is very heavy, and yields a large proportion of ashes.
6. Calm Coal is of a dull black colour, small and dusty ; by some mineralogists it is reckoned a distinct kind of coal, at least such is said to be the case in Sweden. What is termed calm in Great Britain, is the refuse or small dusty coal produced in working the common coals ; it contains much earthy matter, will not kindle in an ordi nary fire place, but produces a considerable heat and flame in a furnace, where a strong current of air is intro duced ; it also produces a very great proportion of ashes. In England it is exempted from the high duty imposed on the other coals.
7. Bogey Coal, or bituminous wood, is found in alluvial land, though some mineralogists affirm that it is found in the rock stratification. It is composed of trees, reeds, and rushes, embedded in the alluvial earth, the form of the trees, the ligneous and fibrous texture, being, in most cases, distinct ; their texture. is impregnated with pet•o leum, and combinations of the sulphuric acid. 'When first dug up, the fibres are flexile ; in burning, it pro duces little heat, and a very unpleasant smell, and is only used where other kind of fuel is scarce and in high price. In England it is found in greatest abundance at glove', near Exe ter. from which it derives its name ; it also abt nods in many parts of the continent, particularly in Germany.
Two hundred grains of nosey coal, according to Ilat chm, yielded, Water turbid and mixed with Liftmen S 60 grains.
Thick brown oily bitumen . 21 Charcoal 90 Hydrogen gas, carbonated hy 29 drogcn, and cat bonic acid 200 According to Professor Jameson there are five sub species of this inflammable matter, classed under the name of Brcvn coal.
The foregoing arc the principal kinds of coal known in commerce, and used for economical purposes. In each kind various shades of difference exist, both with respect to texture and quality.
With regard to the economical uses of the coals be fore mentioned, we shall state them briefly : The cubi cal and slate coals are chiefly used as fuel in private huuses, and in all manufactodes where a strong heat is required ; the caking coals are most suitable for smith's fires ; when any of these coals are made into soaks, they produce an ii.tense heat in the blast furnace for the ma
king of iron, being used with success in place of charcoal ; the slate coals of the best kinds suit this purpose excel lently, us from their strong texture they bear a heavy load of iron stone, and a strong blast.
The coals of South Wales, employed in the making of iron, contain less volatile matter than either the Eng lish or Scotch coals ; so that in producing a ton of pig iron, only about half the quantity of coals is requisite, as a given quantity contains a great proportion of car bon. That able and practical chemist, Lord Dundonald. whose genius merited a high reward, invented a process by which the volatile parts of the coal were condensed, producing volatile alkali, oil, and tar; the coals thus distilled were converted into excellent coak, and applied for the purpose of making iron ; this beneficial plan has only been adopted in a few instances, particularly at Coal brookdalc in England, and at AI uirkirk in Scotland.
For the production of intense heat and flame in a fur nace, the slate coals are most suitable, as, by keeping open, they admit a constant supply of air, which preserves a vehement combustion ; on this account they are in great request by the Scotch and Irish distillers.
Glance coal is used in Ireland as common fuel, and sells at a high price. It is much used for drying grain and malt ; to these it imparts a fair colour ; it is for this latter purpose that the Welsh and Scotch coals, of this kind, arc chiefly used. It is also used for the burning of lime, for which it is very suitable.
Cannel coal is chiefly used for common fuel : that which is found in Lancashire admits of being turned on the lath, and is made into a variety of utensils and ornaments, being susceptible of a very high polish, nearly equal to that of jet ; and of the various coals it is said to be the most suitable for producing the coal gas used for light ing up large manufactories.