Geoscience Reference
In-Depth Information
giston accumulated in air. This explanation, however, was likely insuf-
ficient to Scheele, and he realized that the real key to understanding the
burning processes was to understand the nature of air.
One can follow Scheele's thought process in his topic
Chemical Treatise
on Air and Fire,
published in 1777 and now translated into English. In
early experiments, Scheele burned, among other things, a variety of
sulfurous compounds to reaffirm one property of air that was already
known. That is: “Substances which are subjected to putrefaction or to
destruction by means of fire diminish, and at the same time consume,
a part of the air
.
” From this Scheele concluded that “air must be com-
posed of elastic fluids of two kinds.” But what was the nature of these
two kinds of fluids? The experiments continued. The real breakthrough
came when Scheele distilled potassium nitrate (saltpeter) in a mixture
of nitric and sulfuric acids (nasty stuff indeed!) and collected gases near
the end of distillation, when “blood red vapours are produced.”
2
Lo
and behold, if a candle is introduced into this gas, “not only will it con-
tinue to burn, but this will take place with a much brighter light than
in ordinary air.” He produced the same product in a variety of other
ways and called this product “ire-air.” He then estimated that it makes
up about one-third of our atmosphere.
3
hat Scheele found, of course,
was oxygen. Through a variety of further ingenious experiments with
plants, rats, and bugs, he went on to surmise that “ire-air” is replaced
by (converted to in his view) carbon dioxide through respiration, and
that “ire-air” is absorbed by the lungs of animals and is transported by
blood through the body.
Scheele discovered that air consists of oxygen, carbon dioxide, and
a major portion of an unreactive substance; he called this “vitiated air,”
which we now know to be nitrogen gas. As for “ire-air,” Scheele mused,
“I am inclined to believe that ire-air consists of a subtle acid substance
united with phlogiston.” This conclusion, however, must have seemed
wanting because in September 1774 Scheele sent a letter to the world-
renowned French chemist Antoine Lavoisier explaining his experiments
and asking for advice.
Ironically, at the same time and unknown to Scheele, the Englishman
Joseph Priestley was in Paris discussing his own experiments on oxygen
production face to face with Lavoisier.
4
Lavoisier apparently listened
closely, because he quickly produced oxygen on his own; not bound to
