been absorbed is the vital air, and what remains, the azote, which
is incapable of supporting flame. If an animal be immersed in a
given quantity of common air, it will live only a certain time; at
the end of this time, the air will be found diminished, about one
fourth being extracted from it, and the remainder will neither
support flame nor animal life; this experiment might easily be made,
but it seems a piece of unnecessary cruelty.

By similar experiments to those I have mentioned, we get the azote
pure; here is some, in which a candle has burnt out, and in which
nothing but azote, or the impure part of the atmosphere is left. [4] I
shall plunge a lighted match into it, and you see it is instantly
extinguished.

Some metals, and particularly manganese, when exposed to the
atmosphere, attract the vital air from it, without touching the
azote; and it may be procured from these metals by the application
of heat, in very great purity. Here is a bottle of that kind of air,
which I have expelled by heat from manganese; I shall plunge a taper
into it, and you will perceive that it burns with great brilliancy.
An animal shut up in it, would live about four times as long as if
shut up in an equal quantity of atmospheric air.

If I take three parts of azote, and one of vital air, I shall form a
compound which is similar to the atmosphere, and which is the
mixture best suited to support the health of the body; for if there
were a much greater proportion of vital air, it would act too
powerfully upon the system, and bring on inflammatory diseases; it
would likewise by its stimulus exhaust the excitability, and bring
us sooner to death; and in the same manner that a candle burns