A History of Science, vol 4 | Page 9

that he
might not be disturbed, he desired to be left alone. His servant,
returning sooner than he had wished, was ordered again to leave the
chamber of death, and when be came back a second time he found his
master had expired.[3]
JOSEPH PRIESTLEY
While the opulent but diffident Cavendish was making his important
discoveries, another Englishman, a poor country preacher named
Joseph Priestley (1733-1804) was not only rivalling him, but, if
anything, outstripping him in the pursuit of chemical discoveries. In
1761 this young minister was given a position as tutor in a
nonconformist academy at Warrington, and here, for six years, he was
able to pursue his studies in chemistry and electricity. In 1766, while on
a visit to London, he met Benjamin Franklin, at whose suggestion he
published his History of Electricity. From this time on he made steady
progress in scientific investigations, keeping up his ecclesiastical duties
at the same time. In 1780 he removed to Birmingham, having there for
associates such scientists as James Watt, Boulton, and Erasmus
Darwin.
Eleven years later, on the anniversary of the fall of the Bastile in Paris,
a fanatical mob, knowing Priestley's sympathies with the French
revolutionists, attacked his house and chapel, burning both and

destroying a great number of valuable papers and scientific instruments.
Priestley and his family escaped violence by flight, but his most
cherished possessions were destroyed; and three years later he quitted
England forever, removing to the United States, whose struggle for
liberty he had championed. The last ten years of his life were spent at
Northumberland, Pennsylvania, where he continued his scientific
researches.
Early in his scientific career Priestley began investigations upon the
"fixed air" of Dr. Black, and, oddly enough, he was stimulated to this
by the same thing that had influenced Black--that is, his residence in
the immediate neighborhood of a brewery. It was during the course of a
series of experiments on this and other gases that he made his greatest
discovery, that of oxygen, or "dephlogisticated air," as he called it. The
story of this important discovery is probably best told in Priestley's own
words:
"There are, I believe, very few maxims in philosophy that have laid
firmer hold upon the mind than that air, meaning atmospheric air, is a
simple elementary substance, indestructible and unalterable, at least as
much so as water is supposed to be. In the course of my inquiries I was,
however, soon satisfied that atmospheric air is not an unalterable thing;
for that, according to my first hypothesis, the phlogiston with which it
becomes loaded from bodies burning in it, and the 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 the water, the process of vegetation, and probably other natural
processes, restore it to its original purity....
"Having procured a lens of twelve inches diameter and twenty inches
local distance, I proceeded with the greatest alacrity, by the help of it,
to discover what kind of air a great variety of substances would yield,
putting them into the vessel, which I filled with quicksilver, and kept
inverted in a basin of the same .... With this apparatus, after a variety of
experiments .... on the 1st of August, 1774, I endeavored to extract air
from mercurius calcinatus per se; and I presently found that, by means

of this lens, air was expelled from it very readily. Having got about
three or four times as much as the bulk of my materials, I admitted
water to it, and found that it was not imbibed by it. But what surprised
me more than I can express was that a candle burned in this air with a
remarkably vigorous flame, very much like that enlarged flame with
which a candle burns in nitrous oxide, exposed to iron or liver of
sulphur; but as I had got nothing like this remarkable appearance from
any kind of air besides this particular modification of vitrous air, and I
knew no vitrous acid was used in the preparation of mercurius
calcinatus, I was utterly at a loss to account for it."[4]
The "new air" was, of course, oxygen. Priestley at once proceeded to
examine it by a long series of careful experiments, in which, as will be
seen, he discovered most of the remarkable qualities of this gas.
Continuing his description of these experiments, he says:
"The flame of the candle, besides being larger, burned with more
splendor and heat than in that species of nitrous air; and a piece of
red-hot wood sparkled in it, exactly like paper dipped in a solution of
nitre, and it consumed very fast; an experiment that