continued
to teach for twenty-two years. His most important work was his
_Fundamenta chymiae dogmaticae et experimentale_. His theoretical
views are contained in the last part of this work. He there treats
of _zymotechnia_, or fermentation; _halotechnia_, or the production
of salts; and _pyrotechnia_, or the doctrine of combustion. It is
the last of these sections which gives an account of the doctrine of
_phlogiston_.

The fundamental conception of this doctrine is that all combustible
bodies are compounds. During combustion one of these constituents,
common to all, was dissipated and escaped, while the other, sometimes
an acid, sometimes an earthy powder or calx, remained behind. Thus
sulphur and phosphorus, when burnt, give acids; and the metals form
_calces_. Non-combustible substances, such as lime, were imagined to
be _calces_, and it was supposed that if phlogiston were restored
to them, they too would be converted into metals. This combustible
principle was thought to be inherent in all combustible bodies
whatsoever; it corresponds in kind with the “sulphur” of more ancient
writers, but differs from the latter inasmuch as no very precise ideas
were entertained of the identity of the “sulphur” which conferred on
the substances containing it as a constituent, or possessing it as a
property, their power of combustion. It was also made more definite by
Stahl that substances capable of burning or conversion into calces are
compounds containing phlogiston in combination with other substances.

Stahl can hardly be credited with more than the invention of the term
“phlogiston,” and with bringing the subject in a clear and definite
form before his contemporaries. For Stahl wrote in 1720; and we find
Mayow, in 1674, entering into an elaborate argument to prove that
sulphuric acid is not contained in sulphur, but that it is produced
by the union of the sulphur with his fire-air particles. But Stahl
amplified the doctrine which Mayow had controverted, in pointing
out that if such substances as phosphorus,