experiments that the heat is really brought forth and produced in the
first place from fire-air and the phlogiston of the inflammable
substance....

* * * * *

+80.+ I had long wished to have some of the precipitate of mercury _per
se_, in order to see whether it also would yield fire-air during
reduction by means of heat alone. At length I obtained some from my much
esteemed friend Doctor Gahn. This so-called precipitate had the
appearance of small dark-red crystals resembling cinnabar. Now, as I
know that mercury cannot be dissolved in muriatic acid unless it has
lost its phlogiston, which takes place during its solution in acid of
nitre or in vitriolic acid; and as this is also the reason why nitre
must be present in a mixture of calcined vitriol, common salt, and
quicksilver, I therefore poured muriatic acid upon a part of this red
precipitate; the solution was soon formed and was somewhat hot; I
evaporated it to dryness and increased the heat. Everything sublimed,
and a true corrosive sublimate was formed. Hence this precipitate,
produced by heat alone, is a calcined mercury. I then placed the other
part of this precipitate over the fire in a small glass retort to which
I had fastened an empty bladder. As soon as the retort became red hot
the bladder became expanded, and at the same time the reduced mercury
rose into the neck. In this case no red sublimate arose as customarily
takes place with that calx which is prepared by the acid of nitre. The
air obtained was a pure fire-air. This is a remarkable circumstance,
that the fire-air which had previously removed from the mercury its
phlogiston in a slow calcination, gives this same phlogiston up to it
again when the calx is simply made red-hot. Still we have several such
phenomena, where heat similarly alters the attractive forces between
substances.

* * * * *

+83. Air is a Dulcified Elastic Acid.+

In the foregoing experiments I have demonstrated the two proximate
constituents of common air, because it was not necessary to know
anything more about it for a clear knowledge of fire. I shall now go
further, and see whether a still deeper decompounding of air is
possible.

+First Experiment.+--I placed a rat in a flask capable of holding 4
quarts of water; I gave it some bread softened in milk and closed the
flask with a wet bladder. It died 31 hours afterwards. I then held the
flask, inverted