Phlogiston

Phlogiston (Gr., 'combustible') was the term employed by Stahl, professor at Halle, in his Zymotechnia Fundamentalis (1697), to designate a hypothetical element which, by combining with a body, rendered it combustible, and which occasioned combustion by its disengagement, there being left, after its evolution, either an acid or an earth. Thus, sulphur, according to the phlogistic theory—which held undivided sway in chemistry until the time of Lavoisier, who substituted for it the theory of oxygenation (1775–81), and was maintained by a few chemists, especially Priestley, till the beginning of the 19th century—was composed of sulphuric acid and phlogiston; lead, of the calx or earth of lead and phlogiston; &c. In consequence of the general adoption of the phlogistic theory, when Priestley, in 1774, discovered oxygen, and when Scheele, a little later, discovered chlorine, the names these chemists gave to their discoveries were dephlogisticated air and dephlogisticated marine acid. According to modern views, mainly based on Lavoisier's experiments, the addition of oxygen takes place in the formation of acids and of earths, instead of the subtraction of phlogiston. The question whether the process was, in fact, one of addition or subtraction was finally decided by the balance, an instrument to which chemistry owes most of its marvellous progress during the last three-quarters of a century. See CHEMISTRY, Vol. III. p. 146.