supposition that the more combustible a substance was the more
phlogiston it contained, and since free phlogiston sought always
to combine with some suitable substance, it was only necessary to
mix the phlogisticating agents, such as charcoal, phosphorus,
oils, fats, etc., with the ashes of the original substance, and
heat the mixture, the phlogiston thus freed uniting at once with
the ashes. This theory fitted very nicely as applied to the
calcined lead revivified by the grains of wheat, although with
some other products of calcination it did not seem to apply at
all.

It will be seen from this that the phlogistic theory was a step
towards chemistry and away from alchemy. It led away from the
idea of a "spirit" in metals that could not be seen, felt, or
appreciated by any of the senses, and substituted for it a
principle which, although a falsely conceived one, was still much
more tangible than the "spirit," since it could be seen and felt
as free phlogiston and weighed and measured as combined
phlogiston. The definiteness of the statement that a metal, for
example, was composed of phlogiston and an element was much less
enigmatic, even if wrong, than the statement of the alchemist
that "metals are produced by the spiritual action of the three
principles, salt, mercury, sulphur"--particularly when it is
explained that salt, mercury, and sulphur were really not what
their names implied, and that there was no universally accepted
belief as to what they really were.

The metals, which are now regarded as elementary bodies, were
considered compounds by the phlogistians, and they believed that
the calcining of a metal was a process of simplification. They