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Vol. 27 No. 3
May-June 2005

Joseph Priestly: Radical Thinker

Chemical Heritage Foundation’s Exhibit on Joseph Priestley Includes Rare Instruments and Papers

by Mary Ellen Bowden

Visiting Philadelphia before the end of July 2005? The Chemical Heritage Foundation is holding an exhibit, Joseph Priestley, Radical Thinker, that chemists should not miss.

Although Joseph Priestley (1733–1804) is best remembered for his contributions to chemistry, his many pursuits included theology, politics, education, and several areas of scientific inquiry. At the entrance to the exhibit, an air pump (on loan from the Franklin Institute) that belonged to Priestley when he lived in Northumberland, Pennsylvania, from 1794 to 1804, serves as a reminder of his fame as a natural philosopher. But nearby representations of a dozen or so of Priestley’s friends and foes give the visitor an early indication of Priestley’s importance in eighteenth-century politics and religion as well.

The exhibition entrance at the Chemical
Heritage Foundation.

A portrait of Antoine-Laurent Lavoisier, one of the two other contenders for title of “discoverer” of oxygen, is mounted on a wall near images and items related to members of the Lunar Society of Birmingham and founders of the Industrial Revolution. Their ranks include Matthew Boulton and James Watt as well as Josiah Wedgwood, who is represented by his famous jasperware plaques and a commemorative plate.

A portrait of King George III’s prime minister, William Pitt the Younger, is included because he was one of Priestley’s most resolute political foes. In one display case, Priestley’s Experiments and Observations on Different Kinds of Air, volume I (1774), open to its dedication page, acknowledges the patronage from 1773 to 1780 of another politician, William Petty, Earl of Shelburne. Great political thinkers were among Priestley’s sparring partners, including Edmund Burke and Thomas Paine, who, as different as their theories were from each other, were once Priestley’s admirers but eventually became his foes. Jeremy Bentham, another political theorist, once wrote that he owed to Priestley the famous phrase “the greatest happiness of the greatest number.”

Engraving from Expériences
et Observations sur differentes
espèces d’Air ; Roy G.
Neville Historical Chemical
Library; Chemical Heritage

Priestley’s fame and influence in America preceded his arrival there by decades. He maintained personal friendships with both Benjamin Franklin and John Adams from the days when those men were American diplomats in London (though his relationship with Adams soured over time). Priestley’s writings on religion, politics, education, and natural philosophy were well known to many more Americans, including Thomas Jefferson and various ministers leaning towards Unitarianism, as well as those religious leaders who were scandalized by doubts raised by Priestley concerning the divinity of Jesus.

In the main exhibit area beckon the brass and glass of Priestley’s career as a natural philosopher. On loan from Dickinson College, a reflecting telescope, microscope, surveyor’s compass, and voltaic pile (thought to be a gift from Alessandro Volta to Priestley) immediately alert the viewer that Priestley thoroughly pursued several sciences other than chemistry. His History and Present State of Electricity (1767), inspired by Benjamin Franklin, was Priestley’s first book in the sciences.

"Yours is one of the few lives precious to mankind, and for the continuance of which every thinking man is solicitous . . ." Thomas Jefferson to Joseph Priestley, 21 March 1801

The exhibit’s most eye-catching apparatus is the Smithsonian Institution’s reproduction of one of Priestley’s burning glasses, used to focus sunlight through lenses as a relatively clean way of heating substances to high temperatures. Magnificent original glassware (also from the Smithsonian) from Priestley’s Northumberland laboratory shines in a nearby exhibit cabinet. After his arrival in Northumberland—a 130-mile wagon ride over bumpy roads from Philadelphia —Priestley continued to obtain the bulk of his glassware from England. The pneumatic trough that is most emblematic of Priestley’s research on “airs” (gases) is depicted in blown-up illustrations from Experiments and Observations on Different Kinds of Air.

Double-lens burning glass
replica. Image courtesy of
the Smithsonian Institution,
National Museum of
American History, Behring

Modern chemists might be interested to follow the details of how Priestley originally discovered oxygen, which did not actually take place on the oft-cited date of 1 August 1774. On that date he thought he had produced “phlogisticated nitrous air” (N2O) from mercury calx (MgO) heated in a vessel set in a trough of mercury, since a lighted candle flared in the air so produced. It was in March 1775—months after his return from France, where he had mentioned this experiment to Lavoisier—that Priestley resumed his experimentation with mercury calx. This time, he carried out a succession of tests on the air produced. He observed that when he conducted his “nitrous air” (NO) test for the “goodness” of “common” or atmospheric air (the red fumes generated [NO2] indicated in reality the presence of oxygen), a candle would burn or a mouse could breathe in the remains of a sample of this air. Reiteration of the tests led him to the conclusion that he had produced an air five times better than atmospheric air. He named this new substance “dephlogisticated air.”

The exhibit attempts to give a sympathetic account of the appeal of “phlogiston” to Priestley, Scheele, Lavoisier (initially), and virtually all their chemical contemporaries. As a substance that could be transferred from one compound to another and dramatically changed the properties of the substances to which it united, phlogiston explained a number of important reactions. Despite Priestley’s frequently proclaimed distrust of the role of theories in natural philosophy and his declared willingness to give up the theory of phlogiston should it be disproved, he clung to it until his dying day. Contributing to that obstinacy may well have been his astuteness as an observer. Repeatedly he produced results that Lavoisier and other oxygen chemists could not explain—disregarding the fact that oxygen explanations seemed to work pretty well on the whole, if not in every circumstance.

Dr. Priestley’s House and Laboratory, Fair Hill .
Hulmondel after painting by Exted, lithograph; courtesy
of the Archives and special collections,
Dickinson College, Carlisle, PA; photograph by
Gregary Tobias.

Two items in the exhibit bracket Priestley’s long fight with the oxygen chemists. One is a manuscript copy of Priestley’s “Experiments Relating to Phlogiston and the Conversion of Water into Air” (read before the Royal Society in 1783), in which Priestley responded formally for the first time to Lavoisier’s attacks on phlogiston. The first presentation of Priestley’s research to the American Philosophical Society was a reading by Samuel Vaughan in 1784 of this manuscript. An inscribed copy of Priestley’s final chemical work, The Doctrine of Phlogiston Established, and that of the Composition of Water Refuted (Northumberland, 1800), demonstrates poignantly that Priestley never gave up.

The exhibit also delves into Priestley’s religion and politics. As a Dissenter, he vigorously argued in books, pamphlets, and sermons that established churches, such as the Church of England, had corrupted Christianity, that all people should enjoy religious freedom, and that the ideals of both the American and French revolutions should be applauded. As a consequence of these views, Priestley was made public enemy number one by political and religious leaders in Birmingham, where he served as minister of New Meeting from 1780 to 1791. Forewarned of possible violence, Priestley did not attend a dinner held 14 July 1791 to commemorate the second anniversary of the storming of the Bastille. Disappointed at not finding Priestley among the diners, the rioters set fire to New Meeting, Priestley’s home and laboratory, and a score of other buildings belonging to other Birmingham Dissenters.

This stretch of the exhibit is particularly enriched by a dozen eighteenth-century political cartoons given some years ago to the Chemical Heritage Foundation by Derek Davenport, professor emeritus of chemistry at Purdue University. In one cartoon, Priestley—with characteristic pointy nose and curly wig—breathes fire from a pulpit occupied by three Unitarian ministers. In another, he leads a toast with a chalice and calls for King George’s head to be placed on the empty Communion plate that he bears. In still another, he consoles the king, who is about to be beheaded, that by his execution he is doing a great service to the nation.

Like today’s political buttons, here, too, are medals lent by Roy Olofson, professor emeritus of chemistry at Pennsylvania State Uni-versity. Commissioned by friends and foes, these medals show Priestley as a scion of democratic ideals or a threat to public safety.

Lent by the Pennsylvania Historical and Museum Commission, the lock and key salvaged from Priest-ley’s house in Birmingham is a remarkable relic symbolizing the strife of this period in Priestley’s life. So, too, is Priestley’s letter of resignation to his Birmingham congregation, written from London, where he and his family fled immediately after the riots. He believed that his return to Birmingham could only bring further harm to his friends. This is the author-retained copy now held by the American Philosophical Society.

Dumourier Dining in State at St. James, on the
15th of May, 1793. James Gillray (British,
1757–1815), hand-colored etching. Derek A.
Davenport Collection, CHF.

In 1794, under threat of arrest, Priestley and his wife moved to the United States to join their three sons, who were planning to set up a utopian society in central Pennsylvania. Although the utopia did not materialize, the family settled there, and Priestley made very occasional trips to Philadelphia. Even in the United States he proved to be a controversial figure. In Philadelphia, only the Universalists—who like the Unitarians believed in universal salvation—permitted him to preach from their pulpit. His preaching was so effective that it inspired the founding in 1796 of the First Unitarian Church in Philadelphia. Off in the hinterlands of Pennsylvania, Priestley’s supposed sympathies with efforts to entangle the United States in an alliance with France against Britain almost landed him in prison under the terms of the Alien and Sedition Acts of 1798.

The exhibit also includes a corner with some of the textbooks written by Priestley. He spent many years as a teacher and educational adviser, usually combining such activities with preaching. Perhaps the most radical aspect of his pedagogy was his insistence that the study of modern history be part of the curriculum intended for young men preparing to become merchants or members of the gentry or for young women preparing to be their wives. In the United States, Priestley continued to enjoy a reputation as a great educator. The trustees of the University of Pennsylvania elected him professor of chemistry, a position that he declined. Among other signs of this veneration, Jefferson turned to him for advice in founding the University of Virginia.

The exhibit concludes with reflections on the Priestley heritage, including a proof for the American Chemical Society’s Priestley Medal. For browsing, there is an eight-foot shelf of books about Priestley, including the recently published second volume of Robert Schofield’s magnum opus, The Enlightened Joseph Priestley: A Study of His Life and Work from 1773 to 1804 (Pennsylvania State University Press, 2004).

Joseph Priestley, Radical Thinker is generously sponsored by the Lounsbery Foundation. CHF has contributed texts, images, and objects from its own collections, including the Roy G. Neville Historical Chemical Library and the Derek Davenport Collection, and gratefully acknowledges the loan of objects from the following people and institutions: Archives and Special Collections, Dickinson Col-lege, The American Philo-sophical Society, Edgar Fahs Smith Collection, University of Pennsylvania Library, Franklin Institute Science Museum, Joseph Priestley House, Pennsylvania Histor-ical and Museum Comm-ission, The Library Company of Philadelphia, Roy A. Olofson, Robert E. Schofield, Smithsonian Institution, National Museum of American History, Behring Center, Special Collections Library, The Pennsylvania State University Libraries.

The exhibit is open to the public weekdays between 10 a.m. and 4 p.m. at the Chemical Heritage Foundation, 315 Chestnut Street, Philadelphia, Pennsylvania. For more information or to arrange group visits or guided tours, please e-mail <[email protected]> or call +1 215-925-2222.

Mary Ellen Bowden is senior research historian at the Chemical Heritage Foundation, in Philadelphia, Pennsylvania.

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