red upon being brought
into the common air. A snail treated in the same manner died presently.

Fixed air is presently fatal to vegetable life. At least sprigs of mint
growing in water, and placed over the fermenting liquor, will often
become quite dead in one day, or even in a less space of time; nor do
they recover when they are afterwards brought into the common air. I am
told, however, that some other plants are much more hardy in this
respect.

A red rose, fresh gathered, lost its redness, and became of a purple
colour, after being held over the fermenting liquor about twenty-four
hours; but the tips of each leaf were much more affected than the rest
of it. Another red rose turned perfectly white in this situation; but
various other flowers of different colours were very little affected.
These experiments were not repeated, as I wish they might be done, in
pure fixed air, extracted from chalk by means of oil of vitriol.

For every purpose, in which it was necessary that the fixed air should
be as unmixed as possible, I generally made it by pouring oil of vitriol
upon chalk and water, catching it in a bladder fastened to the neck of
the phial in which they were contained, taking care to press out all the
common air, and also the first, and sometimes the second, produce of
fixed air; and also, by agitation, making it as quickly as I possibly
could. At other times, I made it pass from the phial in which it was
generated through a glass tube, without the intervention of any bladder,
which, as I found by experience, will not long make a sufficient
separation between several kinds of air and common air.

I had once thought that the readiest method of procuring fixed air, and
in sufficient purity, would be by the simple process of burning chalk,
or pounded lime-stone in a gun-barrel, making it pass through the stem
of a tobacco-pipe, or a glass tube carefully luted to the orifice of it.
In this manner I found that air is produced in great plenty; but, upon
examining it, I found, to my very great surprise, that little more than
one half of it was fixed air, capable of being absorbed by water; and
that the rest was inflammable, sometimes very weakly, but sometimes
pretty highly so.

Whence this inflammability proceeds, I am not able to determine, the
lime or chalk not being supposed to contain any other than fixed air. I
conjecture, however, that it must proceed from the iron, and the
separation of it from the calx may