The English clergyman and chemist Joseph Priestley (1733-1804) contributed to the foundation of the chemistry of gases and discovered the role of oxygen in the animal-plant metabolic system.

Joseph Priestley was born on March 13, 1733, at Fieldhead. His mother died when he was 6, and he was reared by an aunt. Because of ill health he was unable to go to school and was educated partly by a Nonconformist minister and partly by private study. He had a gift for languages and learned about 10. He became a minister when he was 22.

Priestley moved about the country a great deal, preaching and teaching. About 1758 he began to add experiments in "natural philosophy" to his students' activities. In 1761 he moved to Warrington to teach languages in an academy established by Dissenters. There he began to take even more interest in science in general and had an opportunity to attend a few lectures in elementary chemistry.

On a trip to London in 1766 Priestley met Benjamin Franklin, who interested him in electricity. This led to fruitful experimentation--Priestley discovered the conductivity of carbon in 1766, found that an electrical charge stays on the surface of a conductor, and studied the conduction of electricity by flames--and his History and Present State of Electricity (1767), which at that time was definitive.

In 1767 Priestley moved to Leeds, where he lived next to a brewery. He became interested in the gases evolved during fermentation and soon discovered that carbon dioxide was being formed. He began preparing this gas at home for study and found that it could be absorbed by water. This discovery of "soda water" brought him much attention and the Royal Society's Copley Medal.

Thus stimulated, Priestley turned his attention to the preparation and study of other gases. He decided to collect them over mercury rather than water and was therefore able to prepare for the first time a variety of gases at random. His greatest discovery came in 1774, when he prepared oxygen by using a burning glass and solar heat to heat red oxide of mercury in a vacuum and collected the evolved gas over mercury. In accordance with the phlogiston doctrine, to which he remained loyal to his death, he called the new gas "dephlogisticated air," for he found that it greatly improved combustion. He realized that this gas must be the active component in the atmosphere and that the concept of air being a single substance was incorrect. Three years earlier he had discovered that plants had the capacity to restore to air the ability to support combustion after a candle had been burned in it. He could now identify oxygen as the agent involved in the animal-plant metabolic cycle.

Between 1772 and 1780 Priestley held the not very demanding post of librarian and companion to Lord Shelburne, and much of his best work was done through this patronage. Priestley then settled in Birmingham, where he became a member of the Lunar Club.

Priestley hated all oppression, openly supported the American and French revolutions, and denounced the slave trade and religious bigotry. As a result of his continued attacks on the government, public resentment rose against Priestley and in 1791 a mob sacked and burnt his house and laboratory. He and his family escaped to London, where he encountered harassment and snubs, and in 1794 he emigrated to the United States. He was offered various positions, including that of the presidency of the University of Pennsylvania, all of which he declined, but he did pass on much of his experimental techniques to American chemists and preached from time to time. President John Adams was among those who attended his sermons, and George Washington made him a welcome visitor to his home. Priestley died at his home in Northumberland, Pa., on Feb. 6, 1804.

Further Reading

• Among the biographies of Priestley are Anne Holt, A Life of Joseph Priestley (1931); John G. Gillam, The Crucible: The Story of Joseph Priestley (1954); and Frederick W. Gibbs, Joseph Priestley: Revolutions of the Eighteenth Century (1967). Bernard Jaffe's treatment of Priestley in his Crucibles: The Lives and Achievement of the Great Chemists (1930) is readable and interesting. There is also a study of Priestley in James G. Crowther, Scientists of the Industrial Revolution (1963).
• Clark, John Ruskin, Joseph Priestley, a comet in the system: biography, San Diego, Calif.: Torch Publications, 1990.
• McLachlan, John, Joseph Priestley, man of science, 1733-1804: an iconography of a great Yorkshireman, Braunton, Devon: Merlin Books, 1983.
• Priestley, Joseph, Memoirs of Dr. Joseph Priestley to the year 1795, written by himself; with a continuation to the time of his decease by his son, Joseph Priestley, and observations on his writings by Thomas Cooper and William Christi, Millwood, N.Y.: Kraus Reprint Co., 1978.
• Smith, Edgar Fahs, Priestley in America, 1794-1804, New York: Arno Press, 1980.
• Thorpe, Thomas Edward, Sir, Joseph Priestley, New York: AMS Press, 1976.