Alchemy, ancient and modern . cognised The Birth of that jts ajm js neither the transmutation of Chemistry. *he meta^s nor the preparation of medi-cines, but the observation and generalisa-tion of a certain class of phenomena ; who denied thevalidity of the alchemistic view of the constitution ofmatter, and enunciated the definition of an elementwhich has since reigned supreme in Chemistry; andwho enriched the science with observations of theutmost importance. Boyle, however, was a manwhose ideas were in advance of his times, and inter-vening between the iatro-chemical period and the Ageof Mod
Alchemy, ancient and modern . cognised The Birth of that jts ajm js neither the transmutation of Chemistry. *he meta^s nor the preparation of medi-cines, but the observation and generalisa-tion of a certain class of phenomena ; who denied thevalidity of the alchemistic view of the constitution ofmatter, and enunciated the definition of an elementwhich has since reigned supreme in Chemistry; andwho enriched the science with observations of theutmost importance. Boyle, however, was a manwhose ideas were in advance of his times, and inter-vening between the iatro-chemical period and the Ageof Modern Chemistry proper came the period of thePhlogistic Theory—a theory which had a certainaffinity with the ideas of the alchemists. § 72, The phlogiston theory was mainly due toGeorg Ernst Stahl (1660-1734). Becher (1635-1682) had attempted to revive the once universallyaccepted sulphur-mercury-salt theory of the alchem-ists in a somewhat modified form, by the assump-tion that all substances consist of three earths—the n. $tp. /&W. //.V. i- JhUf j -;3<) ? ,/ „ , r»i/t*N/iJif. 4 /, A».-i /<?n«tttt iff, PORTRAIT OF ROBERT BOYLE. <7im,^oW/. To face page 94] §72] AGE OF MODERN CHEMISTRY 95 combustible, mercurial, and vitreous ; and herein is tobe found the germ of Stahls phlogistic theory. According to Stahl, all combustible bodies Tlie (including: those metals that change on Theory. heating) contain phlogiston, thfc principle of combustion, which escapes in the form offlame when such substances are burned. According tothis theory, therefore, the metals are compounds, sincethey consist of a metallic calx (what we now call theoxide of the metal) combined with phlogiston;and, further, to obtain the metal from the calx it isonly necessary to act upon it with some substancerich In phlogiston. Now, coal and charcoal are bothalmost completely combustible, leaving very littleresidue; hence, according to this theory, they mustconsist very largely of phlogiston ; and,
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