ring which
secured the bottle to the bladder, the full bottle could be conveyed
away. This process is obviously a clumsy one, although in Scheele’s
hands it yielded splendid results; and the methods which Priestley had
borrowed from Mayow have attested their superiority by their survival.

The first gas which Priestley investigated was “nitrous gas,” or, as it
is now named, nitric oxide. It had previously been prepared by Mayow
(see p. 25) by the action of nitric acid on iron; and Mayow had made
the important observation that when it was introduced into ordinary air
confined over water, the volume of the air was decreased, and a rise
of temperature occurred. But Mayow did not apply his discovery to the
analysis of air, though he rightly conjectured that the reason of the
decrease in volume of the latter was due to combination between the
nitric oxide and his “fire-air particles.” It was left for Priestley to
rediscover this fact, and to apply it to the analysis of air, or, as he
expressed it, to the determination of its “goodness.”

Priestley’s use of a mercurial trough enabled him to collect and
investigate various kinds of airs, among others “marine acid air” or
gaseous hydrogen chloride, a gas differing entirely in properties
from ordinary air. This made his mind familiar with the thought
that different kinds of air exist, not necessarily modifications
of atmospheric air. He had previously from his experiments come to
the conclusion that “atmospheric air is not an unalterable thing,
for that the phlogiston with which it becomes loaded from bodies
burning in it, and animals breathing it, and various other chemical
processes, so far alters and depraves it, as to render it altogether
unfit for inflammation, respiration, and other purposes to which it is
subservient; and I had discovered that agitation in water, the process
of vegetation, and probably other natural processes, by taking out the
superfluous phlogiston, restore it to its natural purity. But I own I
had no idea of the possibility