urs which might pass over should not attack the bladder, I poured
into it some milk of lime (Sec. 30, letter _b_). As soon as the bottom of
the retort became red hot, an air passed over which gradually expanded
the bladder. This air had all the properties of a pure fire-air.

+33. Second Experiment.+--When I distilled two parts of finely
pulverised manganese with one part of the phosphorous acid of urine in
the same way as is indicated in the preceding paragraph, I likewise
obtained fire-air.

+34. Third Experiment.+--(_a._) I dissolved in _aqua fortis_ the white
magnesia employed in medicine; I evaporated this solution to dryness. I
then placed the salt in a small retort for distillation, as is described
in Sec. 32. Even before the retort was red hot the acid of nitre separated
from the magnesia, and that in blood-red vapours; and at the same moment
the bladder began to expand. The air thus obtained was my fire-air.

It is thus seen constantly that the acid of nitre goes off again
blood-red when separated by means of heat from the metals which had been
dissolved in this menstruum.

(_b._) I distilled mercurial nitre in the foregoing manner until the
acid of nitre had separated from the residual red precipitate. In this
case also I obtained our fire-air.... Whence comes the boiling of nitre,
fused in a crucible and obscurely red-hot? Neither smoke nor vapours are
seen to rise from it, and yet coal dust flying above the open crucible
takes fire, burning brilliantly. Whence comes it that such nitre
maintained in red-hot fusion in a glass retort for half an hour, becomes
moist in open air and deliquesces after cooling, and still does not
show any trace of alkali? (Sec. 27, letter _c._) What is the reason that
this liquefied nitre permits its volatile acid to escape immediately,
when rubbed or mixed with the vegetable acids?... If the chemists of the
preceding century had thought worthy of a more particular examination,
the elastic fluids resembling air which manifest themselves in so many
operations, how advanced should we now be! They desired to see
everything in corporeal form, and to collect everything as drops in the
receiver. This is now for the first time better inquired into, and the
air has begun to be carefully examined: and who is there who does not
perceive the advantage which the results of such experiments carry with
them?

* * * * *

+35. Fourth Experiment.+--I put an