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                              JOSEPH PRIESTLEY

The great men of science of today stand on the shoulders of giants. Joseph
Priestley was one such intellectual "giant" whose works laid the foundation
for that branch of science which we now call Chemistry. Although Priestley
is best known for his experiments with gases especially that which we now
call oxygen, he was extraordinarily prolific in his writings on other areas
of intellectual endeavors. He had important contributions in the fields of
education, moral philosophy, theology, metaphysics, political economy,
history and physical science.

Joseph Priestley was born at Fieldhead, in the parish of Birstal, not far
from Leeds, in the northern English county of Yorkshire, on March 13, 1733
according to the Old Style Calendar, the Gregorian calendar not coming into
use until 1751, after which he celebrated on March 24. He was the oldest of
the six children - four sons and two daughters - of Jonas Priestley, a
dresser and finisher of cloth and Mary Swift, a farmer's daughter. Mary,
having children so fast, sent Joseph as an infant to live at his maternal
grandfather's farm some miles away, returning to his father's house after
his mother's death only to be adopted by his childless Aunt Sarah (Mrs. John
Keighly, his father's sister) when he was nine. It was at the Keighly
household that he was exposed to discussions of theological questions and to
liberal political attitudes for many of the dissenting ministers of the
neighborhood were welcome there. He remained with his aunt until her death
in 1764.

During his boyhood, Joseph went to the local schools where he learned Greek
and Latin at an early age, and during school holidays, Hebrew. In his mid
teens he fell seriously ill with tuberculosis of the lungs, was forced to
drop out of school, and for a time abandoned his plan of entering the
ministry. As he gathered strength after his illness, he taught himself
French, Italian, and German and learned Chaldean, Syrian and Arabic.
Privately, he also learned the rudiments of geometry, algebra and

Soon he was ready to pursue the goal of his boyhood, the ministry. By this
time, however, he had started to question some of the orthodox tenets of the
Calvinist faith. He decided not to go to the Academy at Mile End, where he
would have been required to profess his loyalty every six months to ten
printed articles of the faith. He went instead to the more liberal Daventry

At this time, Dissenting Academies became the center of liberal education
since the doors of the great universities were closed to believers of
nonconformist doctrines. The academy at Daventry offered Joseph the
opportunity of learning the traditional subjects as well as natural and
experimental philosophy. It was here that his interest in natural phenomena
and experimentation was encouraged. But his dominant inclination was still
towards theology. After Daventry, Priestley accepted his first position with
a poor congregation at Needham Market in Suffolk where he remained for three
years. He was not very successful in his ministry as his preaching was
hampered by a serious speech impediment, and his popularity was diminished
by his Unitarian tendencies. He was invited to preach at Nantwich, in
Cheshire. The congregation there was more accepting of his unorthodox
theology so he felt more welcome. His responsibilities expanded to that of
schoolmaster and private tutor. The increased income enabled him to buy
instruments that he needed for his original researches.

His success as a teacher in Nantwich opened the door to a post as tutor in
"polite" and classical languages at a new Dissenting Academy in Warrington
where he spent six happy years.

     For the first time since his academic days, he found himself in
     sympathetic surroundings. His colleagues held the same opinions
     and shared the same ideals with him. If disagreement arose on any
     point, they looked on controversy as a means of discovering the
     truth, and not as a sign of moral reprobation. (3)

> It was there in 1762 that Priestley married Mary Wilkinson, daughter of
John Wilkinson, one of the leading figures of the emerging Industrial
Revolution in England. He described his marriage as

     a very suitable and happy connexion, my wife being a woman 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. (6)

A month before his wedding, in anticipation of impending financial
obligations, he applied for and was conferred ordination to the Dissenting
ministry. His lectures on History and General Policy were his most important
work while at Warrington. Through his lectures he attempted to introduce his
students to wider realms. He expected his students to become familiar with
political theory, laws, grammar, oratory and criticism. He acquainted them
with Shakespeare, Milton, and other writers and poets of that time.

During his annual month-long visits to London, he joined the company of men
who were known for their liberal politics and their rational dissent.
Foremost among these were Richard Price, whose pamphlet, Civil Liberty, is
said to have influenced the Declaration of Independence of the American
Colonies, and Benjamin Franklin, whose friendship was crucial to his
emerging scientific career. He was introduced to scientific society and
encouraged to write The History and Present State of Electricity, which
included original experiments and illustrations in copperplate. This led to
his election as a Fellow of the Royal Society in 1766. Priestley's History
was found to be too difficult for ordinary readers so he prepared a version
that was more popular. This necessitated the inclusion of some drawings, but
he could not find anyone who could do the work. Consequently he forced
himself to learn the rules of perspective drawing, and since there was no
book to help him with these, he published one himself. In the course of this
work, he stumbled on the use of India rubber as an eraser of lead-pencil
marks. The preface to his book contains the first printed reference to India
rubber erasers.

Soon after, confronted with the obligations of a growing family, he decided
to accept the invitation to minister to the concregation at Mill Hill. In
1767, he moved his family to Mill Chapel in Leeds, close to his birthplace.

Joseph Priestley is best known as the discoverer of oxygen. Perhaps a more
appropriate description of this accomplishment would be to credit Priestley
with the isolation of dephlogisticated air. Our thorough understanding today
of the chemical reactivity of oxygen comes from Antoine Lavoisier's
systematic theory of combustion. Priestley was an industrious and clever
investigator, not a sweeping theoretician with a guiding program of
research. In the realm of theory, Priestley's expertise lay in his
disputatious and prodigious command of theology, rather than in his chemical
prowess. His adherence to the phlogiston theory was persistent.

Priestley's work on electricity is eclipsed by his memorable experiments on
air, which began in 1767 and peaked in 1774. The proximity of his house to a
public brewery set the stage for many experiments on fixed air (carbon
dioxide). Access to an abundant source of fixed air eventually led to an
understanding of the nature of the effervescence found in mineral waters
such as those of Spa, a resort in Belgium. Restorative sparkling beverages
and baths were simply water containing fixed air. His first scientific
publication was on the impregnation of water with fixed air. This
achievement won for him the prestigious Copley Medal of the Royal sociecty.
The carbonated beverages of today trace their origin to Priestley's initial

Experiments on air in the eighteenth century posed challenges to the natural
philosopher. Today we unhesitatingly regard air as a solution of gases and
confidently understand the chemical and physical properties that distinguish
one colorless gas from another. However, centuries ago there was
considerable confusion. In Priestley's time air was subjected to only simple
tests of appearance, odor, and solubility. Any differences could have been
real or, depending on the purity of the samples, caused by contamination.
Modern gaseous elements and compounds were known as types of air: nitrous
air (NO), phlogisticated air (N2O), acid air (HCl), and reduced fixed air
(CO). The "goodness" of air, a measure of its respirability, interested
Priestley. In 1771 he noted the restoration of "injured" or depleted air by
green plants. He wrote,

     The injury which is continually done to the atmosphere by the
     respiration of such a large number of, in part at
     least, repaired by the vegetable creation. (5)

This balance between animal and plant kingdoms is particularly relevant to
our present environmental concerns over global warming and rainforest

Joseph Priestley simplified experimental techniques for the preparation and
collection of gases. His pneumatic trough of 1772 was an admirable
apparatus. Gases soluble in water, previously difficult to collect, were
collected successfully over mercury. In Wiltshire, England, on August 1,
1774 Priestley focused sunlight through a lens in order to heat a sample of
mercuric oxide (red calx). The resulting gas supported the burning of a
candle with a vigorous flame, was essentially insoluble in water, and
accommodated a mouse under glass for some time. In Priestley's own words,

     I have discovered an air five or six times as good as common air.

This "good" air, which accounted for about twenty per cent of atmospheric
air, he named dephlogisticated air. In addition, he concluded that
calcination imparted to a metal the ability to take this "good" air from the
atmosphere. In 1874, one hundred years after this prominent experimental
contribution to chemistry, Joseph Priestley was honored by a meeting which
led to the founding of the American Chemical Society in 1876.

From Leeds, he had wanted to accompany Captain Cook, as a naturalist, on his
second voyage. He was refused because of objections to his religious
opinions. He subsequently accepted a position with William Petty, Earl of
Shelburne as librarian and tutor to his sons. He was offered a generous
compensation which provided for protection in case of his patron's death or
of a separation, the use of a house at Calne, the Shelburne residence at
Wiltshire during the summers, and as intellectual-in-residence, freedom and
resources to engage in his many interests. He published his two major
philosophical works, Disquisitions Relating to Matter and Spirit, a
materialistic view of man and Experiments and Observations, which contained
his major chemical achievements. The period from 1773 to 1780 were the most
fruitful years of Priesley's career as a chemist.

Priestley accompanied Lord Shelburne on a tour of the continent. In Paris he
met other members of the scientific world. With Lavoisier he spoke of his
recent isolation of the gas from the red oxide of mercury, unaware of the
importance of his discovery. This was the missing clue from which Lavoisier
developed the grand conceptual scheme of the role of oxygen in burning,
leading to the overthrow of the phlogiston theory and the revolutionizing of
the whole science of chemistry.

Priestley withdrew from his position with Lord Shelburne amicably, with an
annuity secure for the rest of his life. Wishing to resume his active
ministry he settled at Fairhill, on the outskirts of Birmingham with his
family, which now included three sons and a daughter. Among his benefactors
were his brother-in-law John Wilkinson, who provided a house for his family,
and Josiah Wedgwood, master potter, who supplied him with the funds he
needed for his experiments. Also in Birmingham were Matthew Boulton
(manufacturer of buckles and buttons) and James Watt, who together were
preparing to manufacture the steam engine, Erasmus Darwin, grandfather of
Charles Darwin, who is responsible for the theory of evolution, and William
Small, a tutor of Thomas Jefferson at the College of William and Mary.

When Priestley arrived in Birmingham in the autumn of 1780, he joined the
Lunar society which met at the home of James Keir. The Lunar Society was an
informal group of a dozen or so men, sometimes referred to as the
"Lunatics", who were interested in natural science and literature. Benjamin
Franklin was a frequent guest. The society met once a month in one another's
houses on the Monday nearest the full moon. This time was chosen so that the
members could return to their homes by moonlight. These meetings were
described in a note Darwin wrote to Boulton.

     . . . what inventions, what wit, what rhetoric, metaphysical,
     mechanical, and pyrotechnical, will be on the wing, bandied like a
     shuttlecock from one to another of your troop of philosophers! (1)

Among his accomplishments during his years in Birmingham were the
publication of the first part of Letters to a Philosophical Unbeliever, an
attempt to defend natural religion against the skepticism of David Hume; a
History of the Corruptions of Christianity, a direct attack on the central
tenets of orthodox religion, particularly the doctrine of the Trinity; and a
History of the Early Opinions Concerning Jesus Christ, where he set out to
prove that the doctrine of the Trinity was not according to Scripture. These
three works catalyzed storms of controversy. Priestley was attacked in
pamphlets and periodicals, denounced in pulpits and in the House of Commons,
and considered as an agent of the Devil because of his unorthodox views.

Under the Test and Corporation Acts in England, the Dissenter was deprived
of the rights of citizenship, and , by law, the Unitarian was not even
tolerated. When the French Revolution broke out, the sympathies of the
Dissenters lay with those who were strugggling under the yoke of corruption,
tyranny and opression. Two years later, festivities were planned to
celebrate the auspicious event. On the 11th of July, 1791 a local newspaper
printed an advertisement for a dinner to be held at a leading hotel on July

     to commemorate the auspicious day (Bastille Day) which witnessed
     the Emancipation of Twenty-six Millions of People from the yoke of
     Despotism . . .(1)

The dinner was attended by eighty one men and ended without incident. Dr.
Priestley had declined to attend, to the disappointment of the crowd that
had gathered to demonstrate their contrary views to Priestley's
revolutionary and heretical writings. By evening, the crowd reconvened and,
fueled by liquor, sacked and burned the New Meetinghouse where Priestley
preached. The Old Meetinghouse was sacked and burned, too. Warned of the
murderous multitude, Priestley and his wife left Fairhill, with nothing more
than the clothes we happened to have on. They did not realize the magnitude
of the danger they were in and stopped at a friend's house a mile away.
There they received information that the mob was now at their house looking
for them. They moved again a little farther away but not far enough for
Priestley to be spared the sight of the holocaust that engulfed his home,
his laboratory and especially his library which contained precious
manuscripts of works, some of which were as yet unpublished.

Priestley fled to London and was never to return to Birmingham. He moved to
Tottenham and then to Hackney. During the following months, Priestley was
verbally attacked in the House of Commons, burned in effigy, portrayed in
caricatures, denounced in pulpits and subjected to threatening letters.
Priestley had by now become an honorary citizen of France which was at war
with England. He was snubbed by the Royal Society and was forced to resign
his membership when several of his colleagues turned against him. His sons
were unable to find work in the area and decided to emigrate to America. He
and his wife decided to join them. They sailed from Gravesend on the Samson
on April 7, 1794, two weeks after Priestley's 61st birthday.

While the Priestleys were on their journey to America, Laviosier met his
death at the guillotine in the Place de la Revolution. The Priestleys landed
in New York and proceeded to the capital, Philadelphia. He refused the offer
of a chair in chemistry at the University of Pennsylvania, choosing instead
to join his son, Joseph, and friend, Thomas Cooper, who were establishing a
colony for English Dissenters in central Pennsylvania. He moved 130 miles to
the north and settled in the small town of Northumberland on the banks of
the Susquehanna River. Within the year, the youngest Priestley son, Harry,
died, as did Joseph's wife. Priestley remained active, writing, preaching
and experimenting in his newly established laboratory, but the old fire and
cheerfulness were gone.

Joseph Priestley missed his circle of friends and decided to spend the
winter months in Philadelphia. As the founder of the first Unitarian church
in America, his sermons were attended by then Vice President John Adams and
other luminaries. When Adams became president, Priestley sided with the
Jeffersonian opposition. Jefferson greatly admired Priestley and even
consulted him for advice on the curriculum for the University of Virginia
which he was planning to found. It was in Philadelphia, during Jeffereson's
term, in 1801, that he suffered his first serious illness and nearly died.

During his last journey to Philadelphia he was honored by the Americal
Philosophical Society in a testimonial dinner. He offered a benediction to
his scientific colleagues in a manner that turned prophetic.

     Having been obliged to leave a country which has been long
     distinguished by discoveries in science, I think myself happy by
     my reception in another which is following its example, and which
     already affords a prospect of its arriving at equal eminence. (7)

Although he never fully recovered his health, he continued work on his
latest manuscript even when he could no longer rise to dress and shave
himself. On February 5, 1804, he had all the children brought to his
bedside, and after prayers spoke to each of them separately. He exhorted
them all to continue to love each other .

     . . . I am going to sleep as well as you: for death is only a good
     long sleep in the grave, and we shall meet again. (6)

The next morning, he asked his son and Mr. Cooper to bring him the pamphlets
they had been working on and dictated clearly and distinctly the additions
and alterations he wished to have made. He objected to Mr. Cooper's putting
the corrections in his own language. He then repeated over again what he had
said before and when done he said

     That is right; I have now done. (6)

Half an hour later he was dead. He had put his hand to his face to prevent
his son and his wife from observing his quiet departure. The date was
February 6, 1804.


1. K. S. Davis, The Cautionary Scientists, G. P. Putnam's Sons, New York,
New York, 1966.

2. R.E. Schofield, Joseph Priestley, Dictionary of Scientific Biography, C.
C. Gillispie, Editor-in-chief, Vol XI, Scribner Publications, New York, New
York, 1975, pp. 139-147.

3. A. Holt, A Life of Joseph Priestley, Oxford University Press, London,
England, 1931.

4. A. J. Ihde, The Development of Modern Chemistry, Dover Publications,
Inc., New York, New York, 1984, pp. 40-50.

5. J. R. Partington, A Short History of Chemistry, 3rd ed., Dover
Publications, Inc., New York, New York, 1989, pp. 110-121.

6. J. Priestley, Autobiography of Joseph Priestley with an introduction by
J. Lindsay, Associated University Presses, Cranbury, New Jersey, 1970.

7. D.J. Rhees, Joseph Priestley, Enlightened Chemist, American Chemical
Society, Center for History of Chemistry, Publication No. 1, 1983.