ust have arisen from the
bit of _cement_ diminishing the air to which it was exposed, I covered
all the inside of a glass tube with it, and one end of it being quite
closed with the cement, I set it perpendicular, with its open end
immersed in a bason of quicksilver; and was presently satisfied that my
conjecture was well founded: for, in a few days, the quicksilver rose so
much within the tube, that the air in the inside appeared to be
diminished about one sixth.

To change this air I filled the tube with quicksilver, and pouring it
out again, I replaced the tube in its former situation; when the air was
diminished again, but not so fast as before. The same lining of cement
diminished the air a third time. How long it will retain this power I
cannot tell. This cement had been made several months before I made
this experiment with it. I must observe, however, that another quantity
of this kind of cement, made with a finer and more liquid turpentine,
had not the power of diminishing air, except in a very small proportion.
Also the common red cement has this property in the same small degree.
Common air, however, which had been confined in a glass vessel lined
with this cement about a month, was so far injured that a candle would
not burn in it. In a longer time it would, I doubt not, have become
thoroughly noxious.

Iron that has been suffered to rust in nitrous air diminishes common air
very fast, as I shall have occasion to mention when I give a
continuation of my experiments on nitrous air.

Lastly, the same effect, I find, is produced by the _electric spark_,
though I had no expectation of this event when I made the experiment.

This experiment, however, and those which I have made in pursuance of
it, has fully confirmed another of my conjectures, which relates to the
_manner_ in which air is diminished by being overcharged with
phlogiston, viz. the phlogiston having a nearer affinity with some of
the constituent parts of the air than the fixed air which enters into
the composition of it, in consequence of which the fixed air is
precipitated.

This I first imagined from perceiving that lime-water became turbid by
burning candles over it, p. 44. This was also the case with lime-water
confined in air in which an animal substance was putrefying, or in which
an animal died, p. 79. and that in which charcoal was burned, p. 81.
But, in all these cases, there was a possibility of the fixed air being
discharged from th