filled with quicksilver, and kept inverted in a basin of the same
.... With this apparatus, after a variety of experiments .... on
the 1st of August, 1774, I endeavored 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 express was that a candle
burned in this air with a remarkably vigorous flame, very much
like that enlarged flame with which a candle burns in nitrous
oxide, exposed to iron or liver of sulphur; but as I had got
nothing like this remarkable appearance from any kind of air
besides this particular modification of vitrous air, and I knew
no vitrous acid was used in the preparation of mercurius
calcinatus, I was utterly at a loss to account for it."[4]


The "new air" was, of course, oxygen. Priestley at once
proceeded to examine it by a long series of careful experiments,
in which, as will be seen, he discovered most of the remarkable
qualities of this gas. Continuing his description of these
experiments, he says:

"The flame of the candle, besides being larger, burned with more
splendor and heat than in that species of nitrous air; and a
piece of red-hot wood sparkled in it, exactly like paper dipped
in a solution of nitre, and it consumed very fast; an experiment
that I had never thought of trying with dephlogisticated nitrous
air.