=George Ernest Stahl=, who developed Becher’s notion into the theory of _phlogiston_ (φλογιοτός—burnt), and thereby created a generalisation which first made chemistry a science, was born at Anspach in 1660, became Professor of Medicine and Chemistry at Halle in 1693, physician to the King of Prussia in 1716, and died in Berlin in 1734. Stahl contributed little or nothing to practical chemistry; and no new fact or discovery is associated with his name. His service to science consists in the temporary success he achieved in grouping chemical phenomena, and in explaining them consistently by a comprehensive hypothesis. The theory of phlogiston was originally broached as a theory of combustion. According to this theory, bodies such as coal, charcoal, wood, oil, fat, etc., burn because they contain a combustible principle, which was assumed to be a material substance and uniform in character. This substance was known as phlogiston. All combustible bodies were to be regarded, therefore, as compounds, one of their constituents being phlogiston: their different natures depended partly upon the proportion of phlogiston they contain, and partly upon the nature and amount of their other constituents. A body, when burning, was parting with its phlogiston; and all the phenomena of combustion—the flame, heat, and light—were caused by the violence of the expulsion of that substance. Certain metals—as, for example, zinc—could be caused to burn, and thereby to yield earthy substances, sometimes white in colour, at other times variously coloured. These earthy substances were called _calces_, from their general resemblance to lime. Other metals, like lead and mercury, did not appear to burn; but on heating them they gradually lost their metallic appearance, and became converted into calces. This operation was known as calcination. In the act of burning or of calcination phlogiston was expelled. Hence metals were essentially compound: they consisted of phlogiston and a calx, the nature of which determined the character of the metal. By adding phlogiston to a calx the metal was regenerated. Thus, on heating the calx of zinc or of lead with coal, or charcoal, or wood, metallic zinc or lead was again formed. When a candle burns, its phlogiston is transferred to the air; if burned in a limited supply of air, combustion ceases, because the air becomes saturated with phlogiston.