time consume, a part of the air;
sometimes it happens that they perceptibly increase the bulk of the air,
and sometimes finally that they neither increase nor diminish a given
quantity of air; phenomena which are certainly remarkable. Conjectures
can here determine nothing with certainty, at least they can only bring
small satisfaction to a chemical philosopher, who must have his proofs
in his hands. Who does not see the necessity of making experiments in
this case, in order to obtain light concerning this secret of nature?

+7. General properties of ordinary air.+

(1.) Fire must burn for a certain time in a given quantity of air. (2.)
If, so far as can be seen, this fire does not produce during combustion
any fluid resembling air, then, after the fire has gone out of itself,
the quantity of air must be diminished between a third and a fourth
part. (3.) It must not unite with common water. (4.) All kinds of
animals must live for a certain time in a confined quantity of air. (5.)
Seeds, as for example peas, in a given quantity of similarly confined
air, must strike roots and attain a certain height with the aid of some
water and of a moderate heat.

Consequently, when I have a fluid resembling air in its external
appearance, and find that it has not the properties mentioned, even when
only one of them is wanting, I feel convinced that it is not ordinary
air.

+8. Air must be composed of elastic fluids of two kinds.+

+First Experiment.+--I dissolved one ounce of alkaline liver of sulphur
in eight ounces of water; I poured 4 ounces of this solution into an
empty bottle capable of holding 24 ounces of water, and closed it most
securely with a cork; I then inverted the bottle and placed the neck in
a small vessel with water; in this position I allowed it to stand for 14
days. During this time the solution had lost a part of its red colour
and had also deposited some sulphur: afterwards I took the bottle and
held it in the same position in a larger vessel with water, so that the
mouth was under and the bottom above the water-level, and withdrew the
cork under the water; immediately water rose with violence into the
bottle. I closed the bottle again, removed it from the water, and
weighed the fluid which it contained. There were 10 ounces. After
subtracting from this the 4 ounces of solution of sulphur there remain 6
ounces, consequently it is apparent from this experiment that of 20
parts of air 6 parts have been