Priestley, Joseph (1733–1804)

English chemist and Unitarian minister. He identified oxygen in 1774 and several other gases. Dissolving carbon dioxide under pressure in water, he began a European craze for soda water.

Gases Swedish chemist Karl Scheele independently prepared oxygen in 1772, but his tardiness in publication resulted in Priestley being credited with the discovery.

Priestley discovered nitric oxide (nitrogen monoxide, NO) in 1772 and reduced it to nitrous oxide (dinitrogen monoxide, N2O). In the same year he became the first person to isolate gaseous ammonia by collecting it over mercury (previously ammonia was known only in aqueous solution). In 1774 he found a method for producing sulphur dioxide (SO2).

Life Priestley was born near Leeds and became a cleric; as a Dissenter, he was barred from English universities. A meeting with the US polymath Benjamin Franklin in 1766 aroused his interest in science. As librarian and literary companion to Lord Shelburne 1773–80, Priestley accompanied him to France in 1774 and there met the chemist Antoine Lavoisier. Priestley moved to Birmingham in 1780 and joined the Lunar Society, an association of inventors and scientists that included James Watt, Matthew Boulton, Josiah Wedgwood, and Erasmus Darwin. In 1791 Priestley's chapel and house were sacked by a mob because of his support for the French Revolution. He fled to London, then emigrated to the USA in 1794, settling in Pennsylvania.

Electrostatic charge Priestley's early work was in physics, particularly electricity and optics. He established that electrostatic charge is concentrated on the outer surface of a charged body and that there is no internal force. From this observation he proposed an inverse square law for charges, by analogy with gravitation.