The varieties of coal are distinguished by their different manner of
burning; but, from appearances of this kind, no perfect judgement can be
formed with regard to the specific manner in which those strata had been
made; although, from chemical principles, some conclusion may be drawn
concerning certain changes which they have undergone since they had been
formed.
Thus we have one species of coal which is extremely fusible, abounds
with oil, and consequently is inflammable; we have another species again
which is perfectly fixed and infusible in the fire; therefore, we may
conclude upon principle, that, however, both those coals must have
undergone the operation of heat and fusion, in bringing them to their
present state, it is only the last that has become so much evaporated as
to become perfectly fixed, or so perfectly distilled, as to have been
reduced to a caput mortuum.
The argument here employed is founded upon this fact; that, from the
fusible species of coal, a caput mortuum may be formed by distillation,
and that this chemical production has every essential quality, or every
peculiar property, of the fixed and infusible species; although, from
the circumstances of our operation, this caput mortuum may not have
precisely the exterior appearance of the natural coal.
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