HISTORY OF CHEMISTRY: Johann Kunckel (1630-1703). Johann Joachim Becher (1635-82). Georg Ernst Stahl (1660-1734). Phlogiston.

Of the labours of Kunckel (1630-1703) in the cause of chemistry it is impossible to give and account within the compass of the present sketch; but whilst the science was enriched by means of his numerous researches, amongst which may be mentioned those on phosphorus, it received no assistance from his theoretical views concerning the constitution of bodies; thus, for instance, he rejected the belief in the three principles of Paracelsus, yet maintained that all metals contained common quicksilver; and though their increase in weight by calcinations was not, according to him, due to the absorption of ponderable fiery material, the explanation he offered of this phenomenon was even less satisfactory.

To Becher (1635-1682) and to Stahl (1660-1734) chemistry owes the introduction of the first consistent theory of the constitution of compounds and of chemical action. Becher held that the primary ingredients of matter were water and earth, and that from these were produced three earths—the fusible or stony, the fatty, and the fluid earths, -- improperly called salt, sulphur, and mercury. Stahl, who developed the doctrines of Becher, enumerated four elements – water, acid, earth, and phlogiston. Becher had explained the calcinations of metals on the supposition that they consisted of an earth and a something of which they became deprived on ignition; the burning of brimstone was, in like manner, though to be its resolution into an acid and true sulphur, or that combustible part which was dispelled by heat. It was this supposed combustible body to which the name phlogiston (phlogiston, Gk., combustible) was applied by Stahl) -- the material aut principium ignis non ipse ignis. The phlogiston of Stahl answers in some measure to the souls and spirits assigned to metals and salts by the alchemists, or to what Geber called the "humidity," and Cardan the "celestial heat" of metals. When by means of charcoal a metallic calx was reduced, or a compound containing sulphur was obtained from fused sodium Sulphate, phlogiston was supposed to be absorbed from the charcoal, which with aemp black and other reducing agents came in time to be regarded as nearly pure phlogiston. Bodies that would not burn were thought to have already parted with their phlogiston. From a consideration of the insolubility of most combustible substances arose the idea that phlogiston was a dry and earthy body, capable of receiving a motion of great velocity -- the motus verticillaris -- manifested when ignition or flame was produced. John Rey had in 1630 remarked that metals grow heavier when calcined by the absorption of "thickened air," but had given no general theory of combustion, or explanation why many substances become lighter or are lost sight of when heated. Boyle, too, had noticed the increase of weight caused by the calcinations of metals, and had attributed it to the combination of the latter with heat particles; and Stabel and others were not slow to object that this fact negatived the supposition that calcinations consisted in a subtraction of phlogiston; the Stahlians, however, met the difficulty by declaring that substance to be the principle of levity or negative weight.

F. Hoffmann, who contributed greatly to the progress of analytical chemistry in Germany, held with Stahl that sulphur consisted of acid and phlogiston, and that combustible bodies contained something which might be described as phlogiston, but thought it possible that the calces of metals were formed, not by the subtraction of phlogiston, but by the combination of the metals with an acid material. Boerhaave, without directly attacking the phlogistic theory, casts doubts upon the assumption of the existence of a combustible principle and of earthy substances in the metals. The view of Homberg (1652-1715) was that the principle of combustibility in inflammable minerals and in vegetable substances was sulphur; and E. F. Geoffroy (1672-1731) regarded phlogiston as a sulphurous or oily principle. Amongst the most active supporters of the doctrines of Stahl were Neumann (1683-1737); J. H. Pott (1692-1777), distinguished for his researches on the behavior of mineral substances at high temperatures; Marggraf (1709-1782); and Macquer (1718-1784), the discoverer of arsenic acid. Other celebrated chemists who flourished during the phlogistic period were Réaumur (1683-1757), Hellot (1685-1766), and Duhamel du Monceau (1700-1782), who first proved the nature of the base of common salt.






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