Priestley, Joseph (1733–1804)

PRIESTLEY, JOSEPH (1733–1804)

PRIESTLEY, JOSEPH (1733–1804), English cleric, chemist, historian, theologian, philosopher, and social and political critic. Joseph Priestley, the eldest son of a maker and dresser of woolen cloth, was born in Fieldhead near Leeds, Yorkshire. As a boy, Joseph was exposed to strict Calvinism and tutored by local clergymen. Because his religious Nonconformity barred him from Oxford and Cambridge, his formal education was completed at the dissenting academy at Daventry. However, it was largely through his own efforts that Priestley learned Latin, Greek, French, Italian, German, Hebrew, Chaldean, Syriac, and Arabic.

Over the course of his life, Priestley's religious beliefs evolved from Calvinism to Socinianism (Unitarianism), but religion always remained of pivotal importance. His chief formal occupation was as a minister, and he served liberal congregations in various parts of England. In addition, he taught for six years at the dissenting academy in Warrington, and he tutored private students. During all this time, his prolific pen seldom stopped moving. His collected works fill over twenty-five volumes and include such titles as A Chart of Bibliography, Rudiments of English Grammar, A Course of Lectures on Oratory and Criticism, An Essay on the First Principles of Government, History of the Corruptions of Christianity, Disquisitions Relating to Matter and Spirit, Institutes of Natural and Revealed Religion, and Experiments on Air.

Although today Priestley is best known for his contributions to chemistry, he was only an amateur scientist. His first scientific publication, The History and Present State of Electricity (1767), was stimulated and encouraged by his friend Benjamin Franklin. Priestley reported in his posthumously published memoir that his interest in chemistry was a consequence of living adjacent to a brewery during his ministry at Leeds (1767–1773). His first publication on pneumatic chemistry (1772) provided directions for impregnating water with the "fixed air" generated by fermenting beer. In modern terms, Priestley described the carbonation of water. In addition, he isolated and identified ten gases, most of them previously unknown, and he discovered photosynthesis independently of Jan Ingenhousz.

Joseph Priestley's most famous discovery occurred on 1 August 1774, while he was serving as the "literary companion" of William Petty, the second Earl of Shelburne. On that date, Priestley used a burning glass to focus the rays of the sun on a sample of the red calx of mercury, which evolved a colorless, odorless, and tasteless gas. He ultimately found that this new gas was "between five and six times as good as the best common air" in supporting combustion. The name he chose, "dephlogisticated air," reflects the Phlogiston Theory, an explanation of combustion widely held in the eighteenth century. According to this theory, flammable substances contained phlogiston, the principle of combustibility, which escaped during burning. Air was necessary as a reservoir to absorb the escaping phlogiston, and when the air became saturated with it, burning ceased. Because the newly isolated gas had an enhanced capacity for supporting combustion, Priestley concluded that its phlogiston content must be lower than that of air.

Unbeknown to Priestley, Karl Wilhelm Scheele (1742–1786), a Swedish apothecary, had prepared the same gas in 1771. But the correct interpretation of the essential role of this gas in combustion and in chemistry was one of the major contributions of the French chemist, Antoine Laurent Lavoisier (1743–1794). Lavoisier gave the name "oxygen" to Priestley's dephlogisticated air and included it among the thirty-three simple substances listed in his Elements of Chemistry (Traitéélémentaire de chimie, 1789). Oxygen was literally a key element in the revolution that transformed chemistry and established the modern science, but Priestley never accepted the new "French chemistry."

Priestley's chemical conservatism seems to stand in stark contrast to his religious, political, and social radicalism. He was a severe critic of traditional Trinitarian Christianity, an outspoken advocate of freedom of religion and speech, and an ardent supporter of the American and French Revolutions. It was especially his espousal of the latter cause that led to criticism and caricature in the popular press and to the sacking of his Birmingham home in 1791. Continuing opposition in England contributed to Priestley's decision to move to Pennsylvania in 1794. He and his family settled in the village of Northumberland, where he lived quietly until his death in 1804.

Most modern scholars have found considerable consistency in the great diversity of Priestley's work. The unifying themes are his materialistic world view, his acceptance of a benign form of determinism known as philosophical necessity, his commitment to the power of reason, and his Unitarian beliefs. From this foundation Priestley inferred (in his own words) that "a wise Providence [disposes] everything for the best"; "the human species itself is capable of . . . unbounded improvement"; "the great instrument in the hand of divine providence of this progress of the species towards perfection, is society and consequently government"; and, "the good and happiness of the . . . majority of the members of any state is the great standard by which everything relating to that state must finally be determined." Ultimately, even Priestley's refusal to accept the chemical revolution that he helped start is consistent with his status as an "honest heretic."

See also Chemistry ; Lavoisier, Antoine ; Petty, William .

BIBLIOGRAPHY

Primary Sources

Priestley, Joseph. Autobiography of Joseph Priestley. Introduction by Jack Lindsay. Bath, U.K., 1970.

——. Experiments and Observations on Different Kinds of Air. 2nd ed. London, 1775.

——. The Theological and Miscellaneous Works of Joseph Priestley, L.L.D., F.R.S., etc. 25 vols. Edited by J. T. Rutt. London, 1817–1835.

Secondary Sources

Schofield, Robert E. The Enlightenment of Joseph Priestley: A Study of His Life and Work from 1733 to 1773. University Park, Pa., 1997.

Schwartz, A. Truman, and John G. McEvoy, eds. Motion Toward Perfection: The Achievement of Joseph Priestley. Boston, 1990.

A. Truman Schwartz