It is a black, brittle, insoluble, inodorous,
tasteless substance, and, when newly-made, possesses the remarkable
property of absorbing certain quantities of the different gases. Its
dust, when used as a polishing powder, gives great brilliancy to metals.
It consists of wood half-burned, and is manufactured by cutting pieces
of timber into nearly the same size, then disposing them in heaps, and
covering them with earth, so as to prevent communication with the air,
except when necessary to make them burn. When they have been
sufficiently charred, the fire is extinguished by stopping the vents
through which the air is admitted. Of _coal_ there are various species;
as, pit, culm, slate, cannel, Kilkenny, sulphurous, bovey, jet, &c.
These have all their specific differences, and are employed for various
purposes; but are all, more or less, used as fuel.
The use of coal for burning purposes was not known to the
Romans. In Britain it was discovered about fifty years before
the birth of Christ, in Lancashire, not tar from where
Manchester now stands; but for ages after its discovery, so long
as forests abounded, wood continued to be the fuel used for
firing.
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