either gained or lost by the
calcination of tin in a close glass vessel; but I purposely deferred
making any more experiments on the subject, till we should have some
weather in which I could make use of a large burning lens, which I had
provided for that and other purposes; but, in the mean time, I was led
to the discovery in a different manner.

Having, by the last-recited experiments, been led to consider the
electric matter as phlogiston, or something containing phlogiston, I was
endeavouring to revivify the calx of lead with it; when I was surprized
to perceive a considerable generation of air. It occurred to me, that
possibly this effect might arise from the _heat_ communicated to the
red-lead by the electric sparks, and therefore I immediately filled a
small phial with the red-lead, and heating it with a candle, I presently
expelled from it a quantity of air about four or five times the bulk of
the lead, the air being received in a vessel of quicksilver. How much
more air it would have yielded, I did not try.

Along with the air, a small quantity of _water_ was likewise thrown out;
and it immediately occurred to me, that this water and air together must
certainly be the cause of the addition of weight in the calx. It still
remained to examine what kind of air this was; but admitting water to
it, I found that it was imbibed by it, exactly like _fixed air_, which I
therefore immediately concluded it must be[12].

After this, I found that Mr. Lavoisier had completely discovered the
same thing, though his apparatus being more complex, and less accurate
than mine, he concluded that more of the air discharged from the calces
of metals was immiscible with water than I found it to be. It appeared
to me that I had never obtained fixed air more pure.

It being now pretty clearly determined, that common air is made to
deposit the fixed air which entered into the constitution of it, by
means of phlogiston, in all the cases of diminished air, it will follow,
that in the precipitation of lime, by breathing into lime-water the
fixed air, which incorporates with lime, comes not from the lungs, but
from the common air, decomposed by the phlogiston exhaled from them, and
discharged, after having been taken in with the aliment, and having
performed its function in the animal system.

Thus my conjecture is more confirmed, that the cause of the death of
animals in confined air is not owing to the want of any _pabulum vitae_,
wh