The Story of Alchemy and the Beginnings of Chemistry

This proof was not forthcoming until about a century after the publication of Mayow's work. The experiments which furnished the proof were rendered possible by a notable discovery made on the 1st of August 1774, by the celebrated Joseph Priestley. Priestley prepared many "airs" of different kinds: by the actions of acids on metals, by allowing vegetables to decay, by heating beef, mutton, and other animal substances, and by other methods. He says: "Having procured a lens of twelve inches diameter and twenty inches focal distance, I proceeded with great alacrity to examine, by the help of it, what kind of air a great variety of substances, natural and factitious, would yield.... With this apparatus, after a variety of other experiments.... on the 1st of August, 1774, I endeavoured to extract air from mercurius calcinatus per se; and I presently found that, by means of this lens, air was expelled from it very readily. Having got about three or four times as much as the bulk of my materials, I admitted water to it, and found that it was not imbibed by it. But what surprised me more than I can well express was, that a candle burned in this air with a remarkably vigorous flame.... I was utterly at a loss how to account for it." The apparatus used by Priestley, in his experiments on different kinds of air, is represented in Fig. XVI., which is reduced from an illustration in Priestley's book on Airs. Priestley had made a discovery which was destined to change Alchemy into Chemistry. But he did not know what his discovery meant. It was reserved for the greatest of all chemists, Antoine Lavoisier, to use the fact stumbled on by Priestley.