STLEY AND BY
SCHEELE--THE OVERTHROW OF THE PHLOGISTIC THEORY BY LAVOISIER


We have seen that Stephen Hales must have prepared oxygen, among the
numerous gases and mixtures of gases which he extracted from various
substances; for, among the many materials which he heated, one was
red-lead. The red-lead of that day, however, must have contained
carbonate, because, as we shall see, Priestley always obtained a
mixture of oxygen and carbon dioxide from that source. In the account
of his researches, Hales only incidentally mentions the collection of
gas from minium; and he appears to have made no experiments with the
object of ascertaining its properties.

The discovery of oxygen was made nearly simultaneously by Priestley and
Scheele, though it appears from the recent publication of Scheele’s
laboratory notes by Baron Nordenskjöld that Scheele had in reality
anticipated Priestley by about two years. His researches, however,
were not published until a year after Priestley had given to the world
an account of his experiments. Priestley had no theory to defend; his
experiments were undertaken in an almost haphazard manner, probably
as a relaxation. “For my own part,” he says,[4] “I will frankly
acknowledge that, at the commencement of the experiments recited in
this section, I was so far from having formed any hypothesis that led
to the discoveries made in pursuing them, that they would have appeared
very improbable to me had I been told of them; and when the decisive
facts did at length obtrude themselves upon my notice, it was very
slowly, and with great hesitation, that I yielded to the evidence of
my senses.” On the other hand, Scheele was engaged in forming a theory
of the nature of fire. He writes:[5]--“I perceived the necessity of a
knowledge of fire, because without this it is impossible to make any
experiment; and without fire or heat, it is impossible to utilise
the action of any solvent. I began, therefore, to dismiss from my
mind all explanations of fire, and undertook a series of experiments
in