of July, when the plant had
been growing in the burned air from the 8th of the same month. Besides,
the plant which I have found to be the most effectual of any that I have
tried for this purpose is _spinach_, which is of quick growth, but will
seldom thrive long in water. One jar of burned air was perfectly
restored by this plant in four days, and another in two days. This last
was observed on the 22d of July.

In general, this effect may be presumed to have taken place in much less
time than I have mentioned; because I never chose to make a trial of
the air, till I was pretty sure, from preceding observations, that the
event which I had expected must have taken place, if it would succeed at
all; lest, returning back that part of the air on which I made the
trial, and which would thereby necessarily receive a small mixture of
common air, the experiment might not be judged to be quite fair; though
I myself might be sufficiently satisfied with respect to the allowance
that was to be made for that small imperfection.

FOOTNOTES:

[3] The supposition, mentioned in this and other passages of the first
part of this publication, viz. that the diminution of common air, by
this and other processes is, in part at least, owing to the
precipitation of the fixed air from it, the reader will find confirmed
by the experiments and observations in the second part.

SECTION III.

_Of INFLAMMABLE AIR._

I have generally made inflammable air in the manner described by Mr.
Cavendish, in the Philosophical Transactions, from iron, zinc, or tin;
but chiefly from the two former metals, on account of the process being
the least troublesome: but when I extracted it from vegetable or animal
substances, or from coals, I put them into a gun-barrel, to the orifice
of which I luted a glass tube, or the stem of a tobacco-pipe, and to the
end of this I tied a flaccid bladder in order to catch the generated
air; or I received the air in a vessel of quicksilver, in the manner
represented Fig. 7.

There is not, I believe, any vegetable or animal substance whatever, nor
any mineral substance, that is inflammable, but what will yield great
plenty of inflammable air, when they are treated in this manner, and
urged with a strong heat; but, in order to get the most air, the heat
must be applied as suddenly, and as vehemently, as possible. For,
notwithstanding the same care be taken in luting, and in every other
respect, six or even ten times