Joseph Priestley

Priestley by Ellen Sharples (1794)^[1]

Joseph Priestley (March 26,1733 – February 8, 1804) was an eighteenth-century British natural philosopher, Dissenting clergyman, political theorist, theologian, and educator. He is usually credited with the discovery of oxygen gas, although Carl Wilhelm Scheele and Antoine Lavoisier also have such a claim.^[2]

A member of marginalized religious groups throughout his life, Priestley advocated religious toleration and equal rights for religious Dissenters. He argued for the extension of civil rights, because he believed that individuals could bring about progress and eventually the Christian Millennium.^[3] In his metaphysical works, Priestley attempted to combine theism, materialism, and determinism, a project that has been called "audacious and original".^[4] The controversial nature of these works combined with Priestley's outspoken support of the French Revolution aroused public and governmental suspicion; he was eventually forced to flee to the United States after a mob burned down his home and church in 1791.

Priestley made significant contributions to pedagogy, including the publication of a seminal work on English grammar, the promotion of a liberal arts curriculum, and the advocacy of the study of modern history.

During his lifetime, Priestley's scientific reputation rested on his invention of soda water, his writings on electricity, and his discovery of several "airs" (gases), the most famous being what Priestley dubbed "dephlogisticated air" (oxygen). However, Priestley's determination to reject Lavoisier's "new chemistry" and to cling to the phlogiston theory of heat eventually left him isolated within the scientific community. Priestley's science was never divorced from his theology, and he consistently tried to fuse Enlightenment rationalism with Christian theism.^[5]

Early life and education (1733–55)

Priestley's birthplace (since demolished) in Fieldhead, Birstall, West Yorkshire (about six miles southwest of Leeds)^[6]

Priestley was born to an established Dissenting family (i.e., they did not conform to the Church of England) in West Yorkshire. He was the oldest of the six children born to Mary Swift and Jonas Priestley, a finisher of cloth. To ease his mother's burdens, Priestley was sent to live with his grandfather around the age of one; after his mother died five years later, he returned home. When his father remarried in 1741, Priestley was sent to live with his aunt and uncle, the wealthy and childless Sarah and John Keighley. Because Priestley was precocious—at the age of four he could perfectly recite all 107 questions and answers of the Westminster Shorter Catechism—she sought the best education for the boy, intending him for the ministry. During his youth, Priestley attended local schools where he learned Greek, Latin, and Hebrew.^[7]

Around 1749 Priestley became seriously ill and believed he was dying. Raised as a devout Calvinist, he believed a conversion experience was necessary for salvation, but doubted he had had one. This emotional distress eventually led him to question his theological upbringing, causing him to reject election and to accept universal salvation. As a result, the elders of his home church refused him admission as a full member.^[8]

Priestley's illness left him with a permanent stutter and he gave up any thoughts of entering the ministry. In preparation for joining a relative in trade in Lisbon, he studied French, Italian, and German in addition to Chaldean, Syrian, and Arabic. He was tutored by the Rev. George Haggerstone, who first introduced him to higher mathematics, natural philosophy, logic, and metaphysics through the works of Isaac Watts, Willem 's Gravesande, and John Locke.^[9]

Daventry Academy

Priestley eventually decided to return to his theological studies, and in 1752 matriculated at Daventry, a Dissenting academy.^[10] Because he had already read widely, Priestley was allowed to skip the first two years of coursework. He continued his intense study; this, together with the liberal atmosphere of the school, shifted his theology further leftward and he became a Rational Dissenter. Abhorring dogma and religious mysticism, Rational Dissenters emphasized the rational analysis of the natural world and the Bible.^[11]

Priestley later wrote that the book which influenced him the most, save the Bible, was David Hartley's Observations on Man (1749). Hartley's psychological, philosophical, and theological treatise postulated a material theory of mind. Hartley aimed to construct a Christian philosophy in which both religious and moral "facts" could be scientifically proven, a goal which would occupy Priestley for his entire life. In his third year at Daventry, Priestley committed himself to the ministry, what he described as "the noblest of all professions".^[12]

Needham Market and Nantwich (1755–61)

Title page from Rudiments of English Grammar (1791)

See also: Joseph Priestley and education

Priestley's major modern biographer, Robert Schofield, describes his first "call" in 1755 to the Dissenting parish in Needham Market, Suffolk as a "mistake" for both Priestley and the congregation. Priestley yearned for urban life and theological debate and Needham Market was a small, rural town with a congregation wedded to tradition. Attendance and donations dropped sharply when they discovered the extent of his heterodoxy. While Priestley's aunt had promised her support if he became a minister, she refused any further assistance when she realized he was no longer a Calvinist. In order to earn extra money, Priestley proposed opening a school, but local families informed him that they would refuse to send their children. He also presented a series of scientific lectures titled "Use of the Globes", which was more successful.^[13]

Priestley's Daventry friends helped him obtain another position in Nantwich, Cheshire; his time there was happier. The congregation cared less about Priestley's heterodoxy and he opened a school. Unlike many schoolmasters of the time, Priestley taught his students natural philosophy and even bought scientific instruments for them. Appalled at the quality of the available English grammars, Priestley wrote his own: The Rudiments of English Grammar (1761).^[14] His innovations in the description of English grammar, particularly his efforts to disassociate it from Latin grammar, have led twentieth-century scholars to describe him as "one of the great grammarians of his time".^[15] After the publication of Rudiments and the success of Priestley's school, Warrington Academy offered him a teaching position in 1761.^[16]

Warrington Academy (1761–67)

Mary Priestley, the daughter of ironmaster Isaac Wilkinson and sister of industrialist John Wilkinson, in later life by Carl F. von Breda (1793)^[17]

In 1761 Priestley moved to Warrington and assumed the post of tutor of modern languages and rhetoric at the town's Dissenting academy, although he would have preferred to teach mathematics and natural philosophy. He fit in well at Warrington and quickly made friends. On 23 June 1762 he married Mary Wilkinson of Wrexham. Of his marriage, Priestley wrote:

This proved 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. Also, greatly excelling in every thing relating to household affairs, she entirely relieved me of all concern of that kind, which allowed me to give all my time to the prosecution of my studies, and the other duties of my station.^[18]

On 17 April 1763 they had a daughter, whom they named Sarah after Priestley's aunt.^[19]

Educator and historian

See also: Joseph Priestley and education

All of the books Priestley published while at Warrington emphasized the study of history; Priestley considered it essential for worldly success as well as religious growth. He wrote histories of science and Christianity in an effort to reveal the progress of humanity and, paradoxically, the loss of a pure, "primitive Christianity".^[20]

A redacted version of Chart of Biography (1765); Priestley believed his Charts would "impress" upon students "a just image of the rise, progress, extent, duration, and contemporary state of all the considerable empires that have ever existed in the world".^[21]

In his Essay on a Course of Liberal Education for Civil and Active Life (1765), Priestley argued that the education of the young should anticipate their future practical needs.^[22] This principle of utility guided his unconventional curricular choices for Warrington's aspiring middle-class students. He recommended modern languages instead of classical languages and modern rather than ancient history. Furthermore, because Priestley viewed education as one of the primary forces shaping a person's character and the basis of morality, he, unusually for the time, promoted the education of middle-class women.^[23] Some scholars of education have described Priestley as the most important English writer on education between the seventeenth-century John Locke and the nineteenth-century Herbert Spencer.^[24]

In his Lectures on History and General Policy (1788), Priestley encouraged the study of modern history, rarely studied at the time. The lectures cover a wide array of topics—everything from forms of government to commerce to manners. He narrated a providentialist and naturalist account of history, arguing that the study of history furthered the comprehension of God's natural laws. His millennial perspective was closely tied to his optimism regarding scientific progress and the improvement of humanity. He believed that each age would improve upon the previous and the study of history allowed people to see and further this progress. Priestley also presented a new method for historical research that emphasized the primacy of original documents and material objects. Lectures on History was well-received and was employed by many educational institutions, such as New College at Hackney, Brown, Princeton, Yale, and Cambridge.^[25] Priestley also designed two Charts to serve as visual study aides for his Lectures on History.^[26] Both were popular for decades and the trustees of Warrington were so impressed with Priestley's lectures and charts that they arranged for the University of Edinburgh to grant him a Doctor of Law degree in 1764.^[27]

History of Electricity

Priestley's electrical machine for amateur experimentalists, illustrated in the first edition of his Familiar Introduction to Electricity (1768), which he unsuccessfully marketed with his brother Timothy.^[28]

The intellectually stimulating atmosphere of Warrington, dubbed the "Athens of the North", increased Priestley's interest in natural philosophy. He gave lectures on anatomy and, with his friend John Seddon, performed experiments regarding temperature.^[29] Despite his busy teaching schedule, Priestley wrote a history of electricity. Friends introduced him to the major experimenters in the field in Britain—John Canton, William Watson, and Benjamin Franklin—who encouraged Priestley to perform the experiments he wanted to include in his history. In the process of replicating others' experiments, Priestley became intrigued by unanswered questions and was prompted to undertake his own.^[30] (Impressed with the manuscript of his history of electricity and his Charts, Canton, Franklin, Watson, and Richard Price nominated Priestley for a fellowship in the Royal Society; he was accepted in 1766.)^[31]

In 1767, the 700-page The History and Present State of Electricity was published to positive reviews.^[32] The first half of the text is a history of the study of electricity to 1766; the second and more influential half is a description of contemporary theories about electricity and suggestions for future research. Priestley reported some of his own discoveries in the second section, such as the conductivity of charcoal and other substances, and the continuum between conductors and non-conductors.^[33] This discovery overturned what he described as "one of the earliest and universally received maxims of electricity", that only water and metals could conduct electricity. Such experiments demonstrated Priestley's early and ongoing interest in the relationship between chemistry and electricity.^[34] Based on experiments with charged spheres, Priestley was also the first to propose that electrical force followed an inverse-square law, although he did not generalize or elaborate on this.^[35]

Priestley's strength as a natural philosopher was qualitative rather than quantitative and his observation of "a current of real air" between two electrified points would later interest Michael Faraday and James Clerk Maxwell as they investigated electromagnetism. Priestley's text became the standard history of electricity for over a century; Alessandro Volta (who later invented the battery), William Herschel (who discovered infrared radiation), and Henry Cavendish (who discovered hydrogen) all relied upon it. Priestley wrote a popular version of the History of Electricity for the general public titled A Familiar Introduction to the Study of Electricity (1768).^[36]

Leeds (1767–73)

The earliest known portrait of Priestley, known as the "Leeds" portrait (c. 1763); Except for his membership on the Leeds Library Committee Priestley was not active in the town's social life.^[37]

In 1767, the Priestleys moved from Warrington to Leeds and Priestley became Mill Hill Chapel's minister. Two sons were born to the Priestleys in Leeds: Joseph, Jr. on 24 July 1768 and William three years later. Theophilus Lindsey, a rector at Catterick, Yorkshire, became one of Priestley's few friends in Leeds: "I never chose to publish any thing of moment relating to theology, without consulting him".^[38] Although Priestley had extended family around Leeds, it does not appear that they communicated. Schofield conjectures that they considered him a heretic.^[39] Each year Priestley traveled to London to consult with his close friend and publisher, Joseph Johnson, and to attend meetings of the Royal Society.^[40]

Minister of Mill Hill Chapel

See also: Joseph Priestley and education

Title page from the second edition of Institutes of Natural and Revealed Religion, a text he had been working on since his Daventry days.

When Priestley became its minister, Mill Hill Chapel was one of the oldest and most respected Dissenting congregations in England; however, during the early eighteenth century the congregation had fractured along doctrinal lines, and the Methodist movement was luring away Dissenters.^[41] Priestley believed that by educating the youth of the congregation, he could strengthen its bonds.^[42]

While Priestley outlined these theories of religious education in his Institutes of Natural and Revealed Religion (1772–74),^[43] he more importantly outlined his belief in Socinianism. The doctrines he laid out would become the standards for Unitarians in Britain. This work marked an important change in Priestley's theological thinking that is critical to understanding his later writings—it paved the way for his materialism and necessitarianism.^[44]

Priestley's major argument in the Institutes is that the only revealed religious truths that can be accepted are those that match one's experience of the natural world. Because his views of religion were deeply tied to his understanding of nature, the text's theism rests on the argument from design.^[45] The Institutes shocked and appalled many readers, primarily because it challenged basic Christian orthodoxies, such as the divinity of Christ and the miracle of the Virgin Birth. Methodists in Leeds penned a hymn asking God to "the Unitarian fiend expel / And chase his doctrine back to Hell."^[46] Priestley wanted to return Christianity to its "primitive" or "pure" form by eliminating the "corruptions" which had accumulated over the centuries. The fourth part of the Institutes, An History of the Corruptions of Christianity, became so long that he was forced to issue it separately. Priestley believed that the Corruptions was "the most valuable" work he ever published. In demanding that his readers apply the logic of the emerging sciences and comparative history to the Bible and Christianity, he alienated religious and scientific readers alike—scientific readers did not appreciate seeing science used in the defense of religion and religious readers dismissed the application of science to religion.^[47]

Religious controversialist

Priestley engaged in numerous political and religious pamphlet wars. According to Schofield, "he entered each controversy with a cheerful conviction that he was right, while most of his opponents were convinced, from the outset, that he was willfully and maliciously wrong. He was able, then, to contrast his sweet reasonableness to their personal rancor."^[48] However, as Schofield points out, Priestley rarely altered his opinion as a result of these debates.^[49] While at Leeds he wrote controversial pamphlets on the Lord's Supper and on Calvinist doctrine; thousands of copies were published, making them some of Priestley's most widely-read works.^[50]

Priestley also founded the Theological Repository in 1768, a journal committed to the open and rational inquiry of theological questions. Although he promised to print any contribution, only like-minded authors ever submitted articles. He was therefore obliged to provide much of the journal's content himself (this material became the basis for much of his later theological and metaphysical works). After only a few years, due to a lack of funds, he was forced to cease publishing the journal.^[51] He revived it in 1784, with similar results.^[52]

Defender of Dissenters and political philosopher

Title page from Priestley's Essay on the First Principles of Government (1768); it influenced early nineteenth-century political philosophers such as Jeremy Bentham.^[53]

See also: Joseph Priestley and Dissent

Many of Priestley's political writings were aimed at supporting the repeal of the Test and Corporation Acts, which restricted the rights of Dissenters. They could not hold political office, serve in the armed forces, or attend Oxford and Cambridge unless they subscribed to the Thirty-nine Articles of the Church of England. Dissenters repeatedly petitioned Parliament to repeal the Acts, arguing that they were being treated as second-class citizens.^[54]

Priestley's friends, particularly other Rational Dissenters, urged him to publish a work on the injustices experienced by Dissenters; the result was his Essay on the First Principles of Government (1768).^[55] An early work of modern liberal political theory and Priestley's most thorough treatment of political theory, it—unusually for the time—precisely distinguishes between political and civil rights and argues for expansive civil rights. Priestley identifies separate private and public spheres, contending that the government should only have control over the public sphere. Education and religion, in particular, he maintains, are matters of private conscience and should not be administered by the state. Priestley's later radicalism emerged from his belief that the British government was infringing upon these individual freedoms. Essay on Government went through three English editions and was translated into Dutch.^[56]

In another attempt to champion the rights of Dissenters, Priestley defended their rights against the attacks of William Blackstone, an eminent legal theorist. Blackstone's Commentaries on the Laws of England, fast becoming the standard legal guide, stated that dissent from the Church of England was a crime and that Dissenters could not be loyal subjects. Furious, Priestley lashed out with his Remarks on Dr. Blackstone's Commentaries (1769), correcting Blackstone's grammar, his history, and his interpretation of the law.^[57] Blackstone, chastened, replied in a pamphlet and altered subsequent editions of his Commentaries: he rephrased the offending passages and removed the sections claiming that Dissenters could not be loyal subjects, but he retained his description of Dissent as a crime.^[58]

Natural philosopher: electricity, Optics, and soda water

Although Priestley claimed that natural philosophy was only a hobby for him, it was clearly one that he took seriously, for he believed that science could further human happiness. In his History of Electricity he describes the scientist as promoting the "security and happiness of mankind" and as one who is "a good citizen and a useful member of society".^[59] Priestley's science was always eminently practical and he rarely concerned himself with theoretical questions—his model was Benjamin Franklin. When he moved to Leeds, Priestley continued his electrical and chemical experiments (the latter aided by a steady supply of carbon dioxide from a neighboring brewery). Between 1767 and 1770, he presented five papers to the Royal Society out of these initial experiments; the first four papers explored coronal discharges and other phenomena related to electrical discharge, while the fifth reported on the conductivity of charcoals from different sources. His subsequent experimental work increasingly focused on chemistry and pneumatics.^[60]

Priestley published the first volume of his projected history of experimental philosophy, The History and Present State of Discoveries Relating to Vision, Light and Colours (referred to as his Optics), in 1772.^[61] Unlike his History of Electricity, it was not popular and had only one edition, although it was the only English book on the topic for 150 years. Priestley paid careful attention to the history of optics and presented excellent explanations of early optics experiments, but his mathematical deficiencies caused him to dismiss several important contemporary theories. Furthermore, he did not include any of the practical sections that had made his History of Electricity so useful to practicing natural philosophers. The text was hastily written and it sold poorly; the cost of researching, writing, and publishing the Optics convinced Priestley to abandon his history of experimental philosophy.^[62]

After the dual financial disasters of the Optics and the Theological Repository, Priestley was looking for ways to improve his finances. When offered the position of astronomer for James Cook's second voyage to the South Seas, he eagerly accepted and even informed his congregation at Mill Hill that he would be absent for several years; however, the offer was suddenly rescinded. Priestley claimed that he was denied the position because he was a Dissenter, but as Schofield explains, the organizing committee replaced him with a more qualified candidate. Schofield attributes the debacle to Joseph Banks's high-handedness in nominating Priestley in the first place.^[63]

Priestley contributed in a small way to the Cook voyage: he provided the crew with a method for making soda water, which he speculated might be a cure for scurvy (it is not). He then published a pamphlet with Directions for Impregnating Water with Fixed Air (1772).^[64] Priestley did not bother to exploit the commercial potential of soda water, but others such as J. J. Schweppe made fortunes from it.^[65] In 1773, the Royal Society recognized Priestley's achievements in natural philosophy by awarding him the Copley Medal.

Priestley's friends wanted to find him a more financially secure position, and in 1772, prompted by Richard Price and Benjamin Franklin, Lord Shelburne wrote to Priestley asking him to direct the education of his children and to act as his general assistant. Priestley debated whether to sacrifice his ministry and accept the position; after intense soul-searching, he resigned from Mill Hill Chapel on 20 December 1772 and preached his last sermon on 16 May 1773.^[66]

Calne (1773–80)

Engraving by Charles A. E. Turner (1836) of a Priestley portrait commissioned by his publisher and close friend Joseph Johnson from Henry Fuseli (c. 1783)^[67]

In 1773 the Priestleys moved to Calne and a year later Lord Shelburne and Priestley took a tour of Europe. According to Priestley's close friend Theophilus Lindsey, Priestley was "much improved by this view of mankind at large".^[68] Upon their return, Priestley easily fulfilled his duties as librarian and tutor. The workload was intentionally light, allowing him time to pursue his scientific investigations and theological interests (Shelburne even equipped a laboratory for him in Bowood House). Priestley also became a political adviser to Shelburne, gathering information on parliamentary issues and serving as a liaison between Shelburne and the Dissenting and American interests. When the Priestleys' third son was born on 24 May 1777, they named him Henry at the Lord's request. ^[69]

Materialist philosopher

See also: Joseph Priestley and Dissent

Title page from the first edition of Disquisitions relating to Matter and Spirit (1777); at least a dozen hostile refutations were published to it by 1782 and Priestley was branded an atheist.^[70]

Priestley wrote his most important philosophical works during his years with Lord Shelburne. In a series of major metaphysical works published between 1774 and 1780—An Examination of Dr. Reid's Inquiry into the Human Mind (1774), Hartley's Theory of the Human Mind on the Principle of the Association of Ideas (1775), Philosophical Necessity (1775), Disquisitions relating to Matter and Spirit (1777), The Doctrine of Philosophical Necessity Illustrated (1777), and Letters to a Philosophical Unbeliever (1780)—he argues for a philosophy which foregrounds four concepts: determinism, materialism, causation, and necessity. By studying the natural world, he argued, people would learn how to become more compassionate, happy, and prosperous.^[71]

Strongly suggesting that there is no mind-body duality, Priestley puts forth a materialist philosophy in these works, that is, one founded on the principle that everything in the universe is made of matter that we can perceive. However, he simultaneously contends that discussing the soul is impossible because it is made of a divine substance, and humanity cannot access the divine. Despite his separation of the divine from the mortal, this position shocked and angered many of his readers, who believed that such a duality was necessary for the soul to exist.^[72]

Responding to Baron d'Holbach's Système de la Nature and David Hume's Dialogues Concerning Natural Religion (1779) as well as the French philosophes, Priestley maintained that materialism and determinism could be reconciled with a belief in God. He criticizes those whose faith is shaped by books and fashion, drawing an analogy between the skepticism of educated men and the credulity of the masses.^[73]

Maintaining that humans had no free will, Priestley was the first to claim that what he called "philosophical necessity" (a position akin to absolute determinism) is consonant with Christianity, a position based on his understanding of the natural world. Like the rest of nature, man's mind is subject to the laws of causation, Priestley contends, but because a benevolent God created these laws, the world and the men in it will eventually be perfected. Evil is therefore only an imperfect understanding of the world. Priestley believed that mankind could be perfected through a study of nature.^[74]

Founder of Unitarianism

When Priestley's friend from Leeds, Theophilus Lindsey, decided to establish a new Christian denomination that would not restrict its members' beliefs, Priestley and others such as publisher Joseph Johnson hurried to his aid. On 17 April 1774, Lindsey held the first Unitarian service in Britain; he had even designed his own liturgy, of which many were critical. Priestley rushed to his defense with Letter to a Layman, on the Subject of the Rev. Mr. Lindsey's Proposal for a Reformed English Church (1774),^[75] claiming that only the form of worship had been altered, not its substance, and attacking those who only followed religion as a fashion. Priestley attended the church regularly in the 1770s and occasionally preached there.^[76] He continued to support institutionalized Unitarianism for the rest of his life, writing several Defenses of Unitarianism and encouraging the foundation of new Unitarian chapels throughout Britain and the United States.^[77]

Natural philosopher of air

A pneumatic trough designed by Stephen Hales. Priestley used a modified version of Hales' device to perform the nitrous air test and other experiments.^[78]

See also: Wikisource:An Inventory of the Furniture in Dr. Priestley's Study

Priestley's years in Calne were the only ones in his life dominated by scientific investigations, and the most scientifically fruitful. His experiments were almost entirely confined to "airs", and out of this work emerged his most important scientific texts: the six volumes of Experiments and Observations on Different Kinds of Air (1774–86).^[79][80] These experiments helped repudiate the last vestiges of the theory of four elements, which Priestley attempted to replace with his own variation of phlogiston theory.^[81] Priestley's work on "airs" is not easily classified. As historian of science Simon Schaffer points out, it "has been seen as a branch of physics, or chemistry, or natural philosophy, or some highly idiosyncratic version of Priestley's own invention".^[82] Also, the volumes were both a scientific and a political enterprise for Priestley; he argues in them that science could destroy "undue and usurped authority", writing that the government has "reason to tremble even at an air pump or an electrical machine".^[83]

Priestley's first volume of Experiments and Observations on Different Kinds of Air outlined several important discoveries, namely, experiments that would eventually lead to the discovery of photosynthesis and the discovery of several airs: "nitrous air" (nitric oxide, NO), "vapor of spirit of salt" (later called "acid air" or "marine acid air"; anhydrous hydrochloric acid, HCl), "alkaline air" (ammonia, NH₃), "diminished" or "dephlogisticated nitrous air" (nitrous oxide, N₂O), and "deplogisticated air" (oxygen, O₂). Priestley also developed the "nitrous air test", which tested for the "goodness of air". Using a pneumatic trough, he would mix nitrous air with a test sample, over water or mercury, and measure the decrease in volume—the principle of eudiometry.^[78] After a small history of the study of airs, he explained his own experiments in an open and sincere style; as Thorpe writes, "whatever he knows or thinks he tells: doubts, perplexities, blunders are set down with the most refreshing candour."^[84] Priestley also invented and described cheap and easy-to-assemble experimental apparatus. His colleagues therefore believed that they could easily reproduce his experiments in order to verify them or to answer the questions that had puzzled him.^[85]

Although many of his results puzzled him, Priestley used phlogiston theory to resolve the difficulties. This, however, led him to conclude that that there were only three types of "air": "fixed", "alkaline", and "acid". Priestley ignored the burgeoning chemistry of his day, indeed dismissing it in these volumes. Instead, he focused on gases and the "changes in their sensible properties", as had natural philosophers before him. He isolated carbon monoxide (CO) but seems not to have realized that it was a separate "air" from the others that he had discovered.^[86]

Discovery of oxygen

See also: Wikisource:The Mouse's Petition

After the publication of the first volume of Experiments and Observations, Priestley undertook another set of experiments. In August 1774 he isolated an "air" that appeared to be completely new, but he did not have an opportunity to pursue the matter because he was about to tour Europe with Shelburne. While in Paris, however, Priestley managed to replicate the experiment for others, including Antoine Lavoisier. After returning to Britain in January 1775, he continued his experiments and discovered "vitriolic acid air" (sulfur dioxide, SO₂). In March he wrote to several people regarding the new "air" that he had discovered in August. One of these letters was read aloud to the Royal Society, and a paper outlining the discovery, titled "An Account of further Discoveries in Air", was published in Philosophical Transactions. Priestley called the new substance "dephlogisticated air" and described it as "five or six times better than common air for the purpose of respiration, inflammation, and, I believe, every other use of common atmospherical air".^[87] He had discovered oxygen gas (O₂).

Priestley assembled his oxygen paper and several others into a second volume of Experiments and Observations on Air, published in 1776. He does not emphasize his discovery of "dephlogisticated air" (leaving it to Part III of the volume) but instead argues in the preface how important such discoveries are to rational religion. His paper narrates the discovery chronologically, relating the long delays between experiments and his initial puzzlements; thus, it is difficult to determine when exactly Priestley "discovered" oxygen.^[88] Such dating is significant as both Lavoisier and Swedish pharmacist Carl Wilhelm Scheele have strong claims to the discovery of oxygen as well, Scheele having been the first to isolate the gas (although he published after Priestley) and Lavoisier having been the first to describe it as purified "air itself entire without alteration" (not "dephlogisticated air").^[89]

William Petty, 2nd Earl of Shelburne

Priestley also connected oxygen to respiration. In his paper "Observations on Respiration and the Use of the Blood", he was the first to suggest a connection between blood and air, although he did so using phlogiston theory. In typical Priestley fashion, he prefaced the paper with a history of the study of respiration. A year later, clearly influenced by Priestley, Lavoisier was also discussing respiration at the Académie des sciences. His work began the long train of discovery that produced papers on oxygen respiration and culminated in the overthrow of phlogiston theory.^[90]

Around 1779 Priestley and Shelburne had a rupture, the reasons for which remain unclear. Shelburne blamed Priestley's health, and Priestley claimed Shelburne had no further use for him. Some contemporaries speculated that Priestley's outspokenness had hurt Shelburne's political career. Schofield argues that the most likely reason was Shelburne's recent marriage to Louisa Fitzpatrick—apparently, she did not like the Priestleys. Although Priestley considered moving to America, he eventually accepted Birmingham New Meeting's offer to be their minister.^[91]

Birmingham (1780–91)

In 1780 the Priestleys moved to Birmingham and spent a happy decade surrounded by old friends, until they were forced to flee in 1791 by mob violence. Priestley accepted the ministerial position at New Meeting on the condition that he be required to preach and teach only on Sundays, so that he would have time for his writing and scientific experiments. As in Leeds, Priestley established classes for the youth of his parish and by 1781, he was teaching 150 students. Although New Meeting supplied Priestley with an annual salary of 100 guineas, such a sum would never have supported his experimental interests. Happily, friends and patrons frequently offered him money and goods that allowed him to continue his scientific investigations.^[92]

Chemical revolution

See also: Chemical Revolution

Many of the friends that Priestley made in Birmingham were members of the Lunar Society, a group of manufacturers, inventors, and natural philosophers who assembled monthly to discuss their work. Matthew Boulton (manufacturer), Erasmus Darwin (naturalist, physician, poet, and grandfather to Charles Darwin), James Keir (chemist and geologist), James Watt (inventor and engineer), Josiah Wedgwood (manufacturer) and William Withering (botanist, chemist, and geologist) formed the core of the group. Priestley was asked to join this unique society and contributed much to the work of its members.^[93] In this stimulating intellectual environment, he published several important scientific papers. One of the most significant was "Experiments relating to Phlogiston, and the seeming Conversion of Water into Air" (1783). The first part of the paper attempts to refute Lavoisier's challenges to his work on oxygen; the second part describes how the steam that results from heated water is "converted" into air. After several variations of the experiment, with different substances as the fuel for the fire and several different collecting apparatuses which produced different results, he concluded that air could travel through more substances than previously surmised, a conclusion "contrary to all the known principles of hydrostatics".^[94] This discovery, along with his earlier work on what would later be recognized as gaseous diffusion, would eventually lead John Dalton and Thomas Graham to formulate the kinetic theory of gases.^[95]