after having been exposed to a considerable degree of _cold_, and
likewise after having been compressed in bladders, (for the cold had
been supposed to have produced this effect by nothing but
_condensation_) I repeated those experiments, and did, indeed, find,
that when I compressed the air in _bladders_, as the Count de Saluce,
who made the observation, had done, the experiment succeeded: but having
had sufficient reason to distrust bladders, I compressed the air in a
glass vessel standing in water; and then I found, that this process is
altogether ineffectual for the purpose. I kept the air compressed much
more, and much longer, than the Count had done, but without producing
any alteration in it. I also find, that a greater degree of cold than
that which he applied, and of longer continuance, did by no means
restore this kind of air: for when I had exposed the phials which
contained it a whole night, in which the frost was very intense; and
also when I kept it surrounded with a mixture of snow and salt, I found
it, in all respects, the same as before.

It is also advanced, in the same Memoir, p. 41. that _heat_ only, as the
reverse of _cold_, renders air unfit for candles burning in it. But I
repeated the experiment of the Count for that purpose, without finding
any such effect from it. I also remember that, many years ago, I filled
an exhausted receiver with air, which had passed through a glass tube
made red-hot, and found that a candle would burn in it perfectly well.
Also, rarefaction by the air-pump does not injure air in the least
degree.

Though this experiment failed, I have been so happy, as by accident to
have hit upon a method of restoring air, which has been injured by the
burning of candles, and to have discovered at least one of the
restoratives which nature employs for this purpose. It is _vegetation_.
This restoration of vitiated air, I conjecture, is effected by plants
imbibing the phlogistic matter with which it is overloaded by the
burning of inflammable bodies. But whether there be any foundation for
this conjecture or not, the fact is, I think, indisputable. I shall
introduce the account of my experiments on this subject, by reciting
some of the observations which I made on the growing of plants in
confined air, which led to this discovery.

One might have imagined that, since common air is necessary to
vegetable, as well as to animal life, both plants and animals had
affected it in the same