with a cause
Joseph Priestley was born in Yorkshire,
the eldest son of a maker of wool cloth. His mother died
after bearing six children in six years. Young Joseph
was sent to live with his aunt, Sarah Priestley Keighley,
until the age of 19. She often entertained Presbyterian
clergy at her home, and Joseph gradually came to prefer
their doctrines to the grimmer Calvinism of his father.
Before long, he was encouraged to study for the ministry.
And study, as it turned out, was something Joseph Priestley
did very well.
Aside from what he learned in the local
schools, he taught himself Latin, Greek, French, Italian,
German, and a smattering of Middle Eastern languages,
along with mathematics and philosophy. This preparation
would have been ideal for Oxford or Cambridge, but as
a Dissenter (someone who was not a member of the Church
of England) Priestley was barred from England's great
universities. So he enrolled at Daventry Academy, a celebrated
school for Dissenters, and was exempted from a year of
classes because of his achievements.
After graduation, he supported himself, as he would for
the rest of his life, by teaching, tutoring and preaching.
His first full-time teaching position was at the Dissenting
Academy in Warrington. (Although obviously brilliant,
original and outspoken-and by one report, of "a gay and
airy disposition" Priestley had an unpleasant voice and
a sort of stammer. That he made a living through lectures
and sermons is further evidence of his extraordinary nature.)
1762, he was ordained and married Mary Wilkinson, the
daughter of a prominent iron-works owner. She was, he
noted, "of an excellent understanding, much improved by
reading, of great fortitude and strength of mind, and
of a temper in the highest degree affectionate and generous;
feeling strongly for others and little for herself."
Priestley traveled regularly to London, and became acquainted
with numerous men of science and independent thought,
including an ingenious American named Benjamin Franklin,
who became a lifelong friend. Franklin encouraged Priestley
in his research, one result of which was The History
and Present State of Electricity. For that work, and
his growing reputation as an experimenter, Priestley was
made a Fellow of the Royal Society in 1766.
The history book was too tough for a popular audience,
and Priestley determined to write a more accessible one.
But he could find no one to create the necessary illustrations.
So, in typical fashion, he taught himself perspective
drawing. Along the way, he made many mistakes, and discovered
that India rubber would erase lead pencil lines-a
fact he mentioned in the preface.
By the age of 34, Priestley was a well-established and
respected member of Britain's scientific community. He
was still paying a price for his religious nonconformity,
however. When the intrepid explorer Captain James Cook
was preparing for his second voyage, Priestley was offered
the position of science adviser. But the offer was rescinded
under pressure from Anglican authorities who protested
his theology, which was evolving into a strongly Unitarian
position that denied the doctrine of the trinity.
In retrospect, the Cook affair may have been all for the
best. In 1773, the Earl of Shelburne asked Priestley to
serve as a sort of intellectual companion, tutor for the
earl's offspring, and librarian for his estate, Bowood
House. The position provided access to social and political
circles Priestley could never have gained on his own,
while leaving ample free time for the research that would
earn him a permanent place in scientific history.
He systematically analyzed the properties of different
"airs" using the favored apparatus of the day: an inverted
container on a raised platform that could capture the
gases produced by various experiments below it. The container
could also be placed in a pool of water or mercury, effectively
sealing it, and a gas tested to see if it would sustain
a flame or support life.
the course of these experiments, Priestley made an enormously
important observation. A flame went out when placed in
a jar in which a mouse would die due to lack of air. Putting
a green plant in the jar and exposing it to sunlight would
"refresh" the air, permitting a flame to burn and a mouse
to breathe. Perhaps, Priestley wrote, "the injury which
is continually done by such a large number of animals
ã is, in part at least, repaired by the vegetable creation."
Thus he observed that plants release oxygen into the airthe
process known to us as photosynthesis.
On August 1, 1774, he conducted his most famous experiment.
Using a 12-inch-wide glass "burning lens," he focused
sunlight on a lump of reddish mercuric oxide in an inverted
glass container placed in a pool of mercury. The gas emitted,
he found, was "five or six times as good as common air."
In succeeding tests, it caused a flame to burn intensely
and kept a mouse alive about four times as long as a similar
quantity of air.
Priestley called his discovery "dephlogisticated air"
on the theory that it supported combustion so well because
it had no phlogiston in it, and hence could absorb the
maximum amount during burning. (The year before, Swedish
apothecary Carl Wilhelm Scheele isolated the same gas
and observed a similar reaction. Scheele called his material
"fire air." But his findings were not published 1777.)
Whatever the gas was called, its effects were remarkable.
"The feeling of it in my lungs," Priestley wrote, "was
not sensibly different from that of common air, but I
fancied that my breast felt peculiarly light and easy
for some time afterwards. Who can tell but that in time,
this pure air may become a fashionable article in luxury.
Hitherto only two mice and myself have had the privilege
of breathing it."
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