George Ernest Stahl was born at Anspach in 1660; he studied and graduated in medicine at Halle, and in 1694 he was appointed second professor of medicine at that University, where he 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, sulphur, or metals are heated, they burn, and are changed into phosphoric acid, sulphuric acid, or “calces”; and reciprocally, if phosphoric acid, sulphuric acid, or a calx such as that of tin or lead, is heated with matter rich in phlogiston, such as charcoal, pitcoal, sugar, flour, etc., phlogiston is restored to the burnt substance, and the original material, phosphorus, sulphur, tin, or lead, is reproduced. The idea at once captivated the minds of the chemists of that age, who received it with approbation, and devised experiments designed to extend the applications of the theory and to confirm its truth.