from these metals by the application of
heat, in very great purity.

Because this air is essential to the formation of acids, it has been
called by chemists the acidifying principle, or oxygen gas.

On plunging a combustible body into the remaining air, it is
instantly extinguished; an animal in the same situation is
immediately deprived of life: from this latter circumstance this air
has been called azote, or azotic gas. If we take three parts of azote
and one of oxygen, and mix them together, we shall form an air in
every respect similar to that of the atmosphere.

If I plunge a piece of iron, previously heated, into oxygen gas, it
will burn with great brilliancy, the gas will be diminished in
quantity, and the iron augmented in weight, and this increase of
weight in the metal will be in proportion to the oxygen which has
disappeared: at the same time a great quantity of heat is given out.
This is the heat which was combined with the oxygen in the state of
gas, and which now becomes free, when the oxygen becomes solid and
joins with the iron.

The same phenomena take place when phosphorus is burned in oxygen
gas; the gas becomes diminished, the phosphorus increased, in weight,
and converted into an acid, and a great quantity of heat is given
out. The same is the case when charcoal is burned in this gas. In
short, in every instance of combustion, the oxygen combines with the
combustible body, and at the same time gives out its heat, which
supported it in the form of gas. This is the case of the combustion
of coal in a common fire, as well as in other cases of combustion;
the heat comes from the air, and not from the coal.

When we examine the phenomena of respiration with attention, we shall
find them very analogous to those of combustion. A candle will not
burn in an exhausted receiver: an animal in the same situation ceases
to live.

When a candle is confined in a given quantity of atmospheric air, it
will burn only for a certain length of time. On examining the air in
which it has been burned, the oxygen is found to be all extracted,
nothing remaining but azotic gas, and a quantity of carbonic acid
gas, produced by the union of the charcoal of the candle with the
oxygen of the atmospheric air.

In the same manner, if an animal be confined in a given quantity of
atmospheric air, it will live only a short time; on examining the air
in which it has ceased to live, it will be found to have lost its
oxygen: wha