HISTORY OF CHEMISTRY: Phlogiston (cont.). Robert Hooke (1735-1603). John Mayow (1645-79).
The phlogistic theory of Stahl, though incorrect, was of no small assistance towards a true understanding of chemical phenomena. It was based upon experimental data, the interpretation of which served for the correlation of facts of which but vague and enigmatic explanation had formerly been given. The supposed subtraction of phlogiston in the calcinations of metals, though equivalent in reality to the addition of oxygen, was yet a loss of potential energy, by virtue of the combination of the metal with the gas; and the gain of phlogiston was an increase of potential energy, attendant on the removal of oxygen.
It was only in the latter part of the 18th century that the influence of the presence of air upon the formation of many chemical compounds was generally perceived, and that through the use of the balance the nature of gases began to be comprehended and such airy nothingness became commonly regarded as an intimate and necessary constituent of various solid and fluid bodies. The phlogistic theory gave to its adherents so plausible and moreover so circumstantial an account of the modes of chemical action, that facts and observations which caused at a latter time a complete revolution in the theory of chemistry, such, for instances, as regarded the existence and properties of oxygen, remained without explanation, and almost unheeded. Robert Hooke, so early as 1665, in his Micrographia, foreshadowed the discoveries of Priestley and his contemporaries, when he advanced the opinion that in common air there existed a substance like, if not the same as, that fixed in saltpeter, and which at an elevated temperature dissolved combustibles such as sulphurous bodies with a rapidly sufficient to occasion the motion of fire, and to create light; this solvent he considered to be far less for a given bulk of air than of saltpeter. The investigations of Mayow (1645-1679) are particularly interesting. In treatises published at Oxford in 1668 and 1674 oxygen is actually described by him under the name of fire-air, aerial spirit, and nitre-air; all acids are said to contain it, and it is necessary for combustion and respiration, processes which are therefore analogous; it is the nitre-air of the atmosphere that causes fermentation and the souring of wines, that produces sulphuric acid from sulphur, and effects the calcinations of metals.
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