ygen. 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.

"... I had so little suspicion of the air from the mercurius calcinatus,
etc., being wholesome, that I had not even thought of applying it to
the test of nitrous air; but thinking (as my reader must imagine I
frequently must have done) on the candle burning in it after long
agitation in water, it occurred to me at last to make the experiment;
and, putting one measure of nitrous air to two measures of this air, I
found not only that it was diminished, but that it was diminished quite
as much as common air, and that the redness of the mixture was likewise
equal to a similar mixture of nitrous and common air.... The next day I
was more surprised than ever I had been before with finding that, after
the above-mentioned mixture of nitrous air and the air from mercurius
calcinatus had stood all night,... a candle burned in it, even better
than in common air."

A little later Priestley discovered that "dephlogisticated air... is a
principal element in the composition of acids, and may be extracted by
means of heat from many substances which contain them.... It is likewise
produced by the action of light upon green vegetables; and this seems to
be the chief means employed to preserve the purity of the atmosphere."

This recognition of the important part played by oxygen in the
atmosphere led Priestley to make some experiments upon mice and insects,
and finally upon himself, by inhalations of the pure gas. "The feeling
in my lungs," he said, "was not sensibly different from that of common
air, but I fancied that my breathing felt peculiarly light and easy for
some time afterwards. Who can tell but that in time this pure air may
become a fashionable article in luxury?... Perhaps we may from these
experiments see that though pure dephlogisticated air might be useful as
a medicine, it might not be so proper for us in the usual healthy state
of the body."

This suggestion as to