CHAPTER VI.
Epoch of the Theory of Oxygen.—Lavoisier.
Sect. 1.—Prelude to the Theory.—Its Publication.
WE arrive now at a great epoch in the history of Chemistry. Few revolutions in science have immediately excited so much general notice as the introduction of the theory of oxygen. The simplicity and symmetry of the modes of combination which it assumed; and, above all, the construction and universal adoption of a nomenclature which applied to all substances, and which seemed to reveal their inmost constitution by their name, naturally gave it an almost irresistible sway over men’s minds. We must, however, dispassionately trace the course of its introduction. [276]
Antoine Laurent Lavoisier, an accomplished French chemist, had pursued, with zeal and skill, researches such as those of Black, Cavendish, and Priestley, which we have described above. In 1774, he showed that, in the calcination of metals in air, the metal acquires as much weight as the air loses. It might appear that this discovery at once overturned the view which supposed the metal to be phlogiston added to the calx. Lavoisier’s contemporaries were, however, far from allowing this; a greater mass of argument was needed to bring them to this conclusion. Convincing proofs of the new opinion were, however, rapidly supplied. Thus, when Priestley had discovered dephlogisticated air, in 1774, Lavoisier showed, in 1776, that fixed air consisted of charcoal and the dephlogisticated or pure air; for the mercurial calx which, heated by itself, gives out pure air, gives out, when heated with charcoal, fixed air,[27] which has, therefore, since been called carbonic acid gas.
[27] Mém. Ac. Par. 1775.
Again, Lavoisier showed that the atmospheric air consists of pure or vital air, and of an unvital air, which he thence called azot. The vital air he found to be the agent in combustion, acidification, calcination, respiration; all of these processes were analogous: all consisted in a decomposition of the atmospheric air, and a fixation of the pure or vital portion of it.
But he thus arrived at the conclusion, that this pure air was added, in all the cases in which, according to the received theory, phlogiston was subtracted, and vice versâ. He gave the name[28] of oxygen (principe oxygène) to “the substance which thus unites itself with metals to form their calces, and with combustible substances to form acids.”
[28] Mém. Ac. Par. 1781, p. 448.