d without any alteration a whole night, and part of the following
day; when lime-water, being admitted to it, it presently became turbid,
and, after some time, the whole quantity of air, which was about four
ounce measures, was diminished one fifth, as before. In this case, I
carefully weighed the piece of charcoal, which was exactly two grains,
and could not find that it was sensibly diminished in weight by the
operation.

Air thus diminished by the fumes of burning charcoal not only
extinguishes flame, but is in the highest degree noxious to animals; it
makes no effervescence with nitrous air, and is incapable of being
diminished any farther by the fumes of more charcoal, by a mixture of
iron filings and brimstone, or by any other cause of the diminution of
air that I am acquainted with.

This observation, which respects all other kinds of diminished air,
proves that Dr. Hales was mistaken in his notion of the _absorption_ of
air in those circumstances in which he observed it. For he supposed that
the remainder was, in all cases, of the same nature with that which had
been absorbed, and that the operation of the same cause would not have
failed to produce a farther diminution; whereas all my observations shew
that air, which has once been fully diminished by any cause whatever, is
not only incapable of any farther diminution, either from the same or
from any other cause, but that it has likewise acquired _new
properties_, most remarkably different from those which it had before,
and that they are, in a great measure, the same in all the cases. These
circumstances give reason to suspect, that the cause of diminution is,
in reality, the same in all the cases. What this cause is, may, perhaps,
appear in the next course of observations.

SECTION VIII.

_Of the effect of the CALCINATION of METALS, and of the EFFLUVIA of
PAINT made with WHITE-LEAD and OIL, on AIR._

Having been led to suspect, from the experiments which I had made with
charcoal, that the diminution of air in that case, and perhaps in other
cases also, was, in some way or other the consequence of its having more
than its usual quantity of phlogiston, it occurred to me, that the
calcination of metals, which are generally supposed to consist of
nothing but a metallic earth united to phlogiston, would tend to
ascertain the fact, and be a kind of _experimentum crucis_ in the case.

Accordingly, I suspended pieces of lead and tin in given quantities