On the 1st of August, 1774, I endeavoured to extract air from mercurius calcinates per se [mercury oxide]; and I presently found that, by means of this lens, air was expelled from it very readily. … I admitted water to it [the extracted air], and found that it was not imbibed by it. But what surprized 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.