There are to be found in those
bodies particular substances, which abound more or less with one of
those species of phlogistic matter, but never is the one species of
those burning substances to be found naturally, in animal and vegetable
bodies, without being associated with the other; and it is all that the
chemical art can do to separate them in a great degree upon occasion.
Pure ardent spirit may perhaps be considered as containing the one, and
the most perfect coal the other; the chemical principle of the one
is proper carbonic matter; and of the other it is the hydrogeneous
principle, or that of inflammable air.
Thus we so far understand the composition of animal and vegetable
substances which burn or maintain our fires; we also understand the
chemical analysis of those bodies, in separating the inflammable from
the combustible substance, or the volatile from the fixed matter, the
oil from what is the proper coal. It is by distillation or evaporation,
the effect of heat, that this separatory operation is performed; and we
know no other means by which this may be done.
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