exceedingly pure,
so as to be almost wholly absorbed by water; whereas the other part, to
which I had put the mixture, was far from being so.

In one of these cases, in which fixed air was made immiscible with
water, it appeared to be not very noxious to animals; but in another
case, a mouse died in it pretty soon. This difference probably arose
from my having inadvertently agitated the air in water rather more in
one case than in the other.

As the iron is reduced to a calx by this process, I once concluded, that
it is phlogiston that fixed air wants, to make it common air; and, for
any thing I yet know this may be the case, though I am ignorant of the
method of combining them; and when I calcined a quantity of lead in
fixed air, in the manner which will be described hereafter, it did not
seem to have been less soluble in water than it was before.

FOOTNOTES:

[2] An account of Mr. Hey's experiments will be found in the Appendix to
these papers.

SECTION II.

_Of AIR in which a CANDLE, or BRIMSTONE, has burned out._

It is well known that flame cannot subsist long without change of air,
so that the common air is necessary to it, except in the case of
substances, into the composition of which nitre enters, for these will
burn _in vacuo_, in fixed air, and even under water, as is evident in
some rockets, which are made for this purpose. The quantity of air which
even a small flame requires to keep it burning is prodigious. It is
generally said, that an ordinary candle _consumes_, as it is called,
about a gallon in a minute. Considering this amazing consumption of air,
by fires of all kinds, volcanos, &c. it becomes a great object of
philosophical inquiry, to ascertain what change is made in the
constitution of the air by flame, and to discover what provision there
is in nature for remedying the injury which the atmosphere receives by
this means. Some of the following experiments will, perhaps, be thought
to throw light upon the subject.

The diminution of the quantity of air in which a candle, or brimstone,
has burned out, is various; But I imagine that, at a medium, it may be
about one fifteenth, or one sixteenth of the whole; which is one third
as much as by animal or vegetable substances putrefying in it, by the
calcination of metals, or by any of the other causes of the complete
diminution of air, which will be mentioned hereafter.

I have sometimes thought, that flame disposes the common air to de