, for reduction, upon the open
fire in a small retort, which was provided with a bladder empty of air.
As soon as the calx began to glow, the bladder became expanded, and
quicksilver rose into the neck. The fire-air obtained had some aerial
acid mixed with it.

(_b._) Mercury converted into calx by the acid of nitre, or red
precipitate, treated in the same way behaved similarly. In this case I
obtained a pure fire-air, without any aerial acid in it.

+41. Eighth Experiment.+--I have proved, in a treatise on arsenic
communicated to the Royal Swedish Academy of Sciences, that this
poisonous substance is compounded of a peculiar acid and an inflammable
substance. I also shewed in the same treatise how this acid can be
sublimed into ordinary arsenic simply by continued heat; and although I
clearly perceived the reason for this, even at that time, still I was
unwilling to mention it there in order to avoid prolixity. I placed some
of this fixed acid of arsenic in a small retort with a bladder attached,
for distillation. When the acid had gone into fusion, and glowed
brightly, it began to boil; during this ebullition arsenic rose into the
neck and the bladder became expanded; I continued with this heat as long
as the retort would hold out. The air collected was likewise fire-air.
In the same treatise I made mention of a peculiar explosion which took
place in the distillation of zinc with the acid of arsenic. How clear,
how manifest does the explanation of this phenomenon not become when one
is satisfied that in this case fire-air is present in the retort in its
greatest purity, and the zinc is in red hot fusion? What more is
necessary for its ignition?

I have very often regarded with pleasure the brightly glowing sparks
which are produced in a retort by heat alone, during the reduction of
metallic calces, when only a very little coal dust is mixed along with
it.

We shall now see whether this fire-air is not the same air which had
been lost without fire (Sec.Sec. 8-15), and with fire (Sec.Sec. 17-23).

+42. First Experiment.+--I filled a bottle which was capable of holding
16 ounces of water with pure fire-air according to the method which is
described in Sec. 30, letter e. I placed the bottle, inverted, in a glass
which was filled with a solution of liver of sulphur. The solution rose
a little into the bottle hour by hour, and after the lapse of 2 days the
bottle was filled with it.

+43. Second Experiment.+--I