text:
Joseph Priestley

Joseph Priestley (24 March 1733 – 6 February 1804) was an English chemist, natural philosopher, separatist theologian, grammarian, multi-subject educator, and liberal political theorist. He published over 150 works, and conducted experiments in several areas of science.

Priestley is credited with his independent discovery of oxygen by the thermal decomposition of mercuric oxide, having isolated it in 1774. During his lifetime, Priestley's considerable scientific reputation rested on his invention of carbonated water, his writings on electricity, and his discovery of several "airs" (gases), the most famous being what Priestley dubbed "dephlogisticated air" (oxygen). Priestley's determination to defend phlogiston theory and to reject what would become the chemical revolution eventually left him isolated within the scientific community.

Priestley's science was integral to his theology, and he consistently tried to fuse Enlightenment rationalism with Christian theism. In his metaphysical texts, Priestley attempted to combine theism, materialism, and determinism, a project that has been called "audacious and original". He believed that a proper understanding of the natural world would promote human progress and eventually bring about the Christian millennium. Priestley, who strongly believed in the free and open exchange of ideas, advocated toleration and equal rights for religious Dissenters, which also led him to help found Unitarianism in England. The controversial nature of Priestley's publications, combined with his outspoken support of the American Revolution and later the French Revolution, aroused public and governmental contempt; eventually forcing him to flee in 1791, first to London and then to the United States, after a mob burned down his Birmingham home and church. He spent his last ten years in Northumberland County, Pennsylvania.

A scholar and teacher throughout his life, Priestley made significant contributions to pedagogy, including the publication of a seminal work on English grammar and books on history; he prepared some of the most influential early timelines. The educational writings were among Priestley's most popular works. Arguably his metaphysical works, however, had the most lasting influence, as now considered primary sources for utilitarianism by philosophers such as Jeremy Bentham, John Stuart Mill, and Herbert Spencer.

Early life and education (1733–1755)

Priestley was born in Birstall (near Batley) in the West Riding of Yorkshire, to an established English Dissenting family who did not conform to the Church of England. He was the oldest of six children born to Mary Swift and Jonas Priestley, a finisher of cloth. Priestley was sent to live with his grandfather around the age of one. He returned home five years later, after his mother died. When his father remarried in 1741, Priestley went to live with his aunt and uncle, the wealthy and childless Sarah (d. 1764) and John Keighley, 3 mi from Fieldhead.

Priestley was a precocious child – at the age of four, he could flawlessly recite all 107 questions and answers of the Westminster Shorter Catechism – and his aunt sought the best education for him, intending him to enter ministry. During his youth, Priestley attended local schools, where he learned Greek, Latin, and Hebrew.

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, the Independent Upper Chapel of Heckmondwike, near Leeds, refused him admission as a full member.

Priestley's illness left him with a permanent stutter and he gave up any thoughts of entering the ministry at that time. In preparation for joining a relative in trade in Lisbon, he studied French, Italian, and German in addition to Aramaic, and Arabic. He was tutored by the Reverend 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.

Daventry Academy
Priestley eventually decided to return to his theological studies and, in 1752, matriculated at Daventry, a Dissenting academy. Because he was already widely read, Priestley was allowed to omit 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 emphasised rational analysis of the natural world and the Bible.

Priestley later wrote that the book that 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 that would occupy Priestley for his entire life. In his third year at Daventry, Priestley committed himself to the ministry, which he described as "the noblest of all professions".

Needham Market and Nantwich (1755–1761)

Robert Schofield, Priestley's major modern biographer, 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, whereas 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. Although Priestley's aunt had promised her support if he became a minister, she refused any further assistance when she realised he was no longer a Calvinist. 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" that was more successful.

Priestley's Daventry friends helped him obtain another position and in 1758 he moved to Nantwich, Cheshire, living at Sweetbriar Hall in the town's Hospital Street; his time there was happier. The congregation cared less about Priestley's heterodoxy and he successfully established 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 grammar books, Priestley wrote his own: The Rudiments of English Grammar (1761). His innovations in the description of English grammar, particularly his efforts to dissociate it from Latin grammar, led 20th-century scholars to describe him as "one of the great grammarians of his time". After the publication of Rudiments and the success of Priestley's school, Warrington Academy offered him a teaching position in 1761.

Warrington Academy (1761–1767)

In 1761, Priestley moved to Warrington in Cheshire 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 fitted in well at Warrington, and made friends quickly. These included the doctor and writer John Aikin, his sister the children's author Anna Laetitia Aikin, and the potter and businessman Josiah Wedgwood. Wedgwood met Priestley in 1762, after a fall from his horse. Wedgwood and Priestley met rarely, but exchanged letters, advice on chemistry, and laboratory equipment. Wedgwood eventually created a medallion of Priestley in cream-on-blue jasperware.

On 23 June 1762, Priestley 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. On 17 April 1763, they had a daughter, whom they named Sarah after Priestley's aunt.

Educator and historian
All of the books Priestley published while at Warrington emphasised 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".

In his Essay on a Course of Liberal Education for Civil and Active Life (1765), Lectures on History and General Policy (1788), and other works, Priestley argued that the education of the young should anticipate their future practical needs. 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. Priestley's lectures on history were particularly revolutionary; he narrated a providentialist and naturalist account of history, arguing that the study of history furthered the comprehension of God's natural laws. Furthermore, 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 that the study of history allowed people to perceive and to advance this progress. Since the study of history was a moral imperative for Priestley, he also promoted the education of middle-class women, which was unusual at the time. Some scholars of education have described Priestley as the most important English writer on education between the 17th-century John Locke and the 19th-century Herbert Spencer. Lectures on History was well received and was employed by many educational institutions, such as New College at Hackney, Brown, Princeton, Yale, and Cambridge. Priestley designed two Charts to serve as visual study aids for his Lectures. These charts are in fact timelines; they have been described as the most influential timelines published in the 18th century. 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. During this period Priestley also regularly delivered lectures on rhetoric that were later published in 1777 as A Course of Lectures on Oratory and Criticism.

History of electricity

The intellectually stimulating atmosphere of Warrington, often called the "Athens of the North" (of England) during the 18th century, encouraged Priestley's growing interest in natural philosophy. He gave lectures on anatomy and performed experiments regarding temperature with another tutor at Warrington, his friend John Seddon. Despite Priestley's busy teaching schedule, he decided to write a history of electricity. Friends introduced him to the major experimenters in the field in Britain—John Canton, William Watson, Timothy Lane, and the visiting Benjamin Franklin who encouraged Priestley to perform the experiments he wanted to include in his history. Priestley also consulted with Franklin during the latter's kite experiments. In the process of replicating others' experiments, Priestley became intrigued by unanswered questions and was prompted to undertake experiments of his own design. (Impressed with his Charts and the manuscript of his history of electricity, Canton, Franklin, Watson, and Richard Price nominated Priestley for a fellowship in the Royal Society; he was accepted in 1766.) In 1767, the 700-page The History and Present State of Electricity was published to positive reviews. 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. The volume also contains extensive comments on Priestley's views that scientific inquiries be presented with all reasoning in one's discovery path, including false leads and mistakes. He contrasted his narrative approach with Newton's analytical proof-like approach which did not facilitate future researchers to continue the inquiry. 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. 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. This and other experiments on the electrical properties of materials and on the electrical effects of chemical transformations demonstrated Priestley's early and ongoing interest in the relationship between chemical substances and electricity. Based on experiments with charged spheres, Priestley was among the first to propose that electrical force followed an inverse-square law, similar to Newton's law of universal gravitation. He did not generalise or elaborate on this, and the general law was enunciated by French physicist Charles-Augustin de Coulomb in the 1780s.

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). He marketed the book with his brother Timothy, but unsuccessfully.

Leeds (1767–1773)

Perhaps prompted by Mary Priestley's ill health, or financial problems, or a desire to prove himself to the community that had rejected him in his childhood, Priestley moved with his family from Warrington to Leeds in 1767, and he became Mill Hill Chapel's minister. Two sons were born to the Priestleys in Leeds: Joseph, Junior, 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, of whom he wrote: "I never chose to publish any thing of moment relating to theology, without consulting him." Although Priestley had extended family living around Leeds, they do not appear to have communicated. Schofield conjectures that they considered him a heretic. Each year, Priestley travelled to London to consult with his close friend and publisher, Joseph Johnson, and to attend meetings of the Royal Society.

Minister of Mill Hill Chapel
When Priestley became its minister, Mill Hill Chapel was one of the oldest and most respected Dissenting congregations in England; however, during the early 18th century the congregation had fractured along doctrinal lines and was losing members to the charismatic Methodist movement. Priestley believed that he could strengthen the bonds of the congregation by educating the young people there.

In his three-volume Institutes of Natural and Revealed Religion (1772–74), Priestley outlined his theories of religious instruction. More importantly, he laid out his belief in Socinianism. The doctrines he explicated would become the standards for Unitarians in Britain. This work marked a change in Priestley's theological thinking that is critical to understanding his later writings—it paved the way for his materialism and necessitarianism (the latter being the belief that a divine being acts in accordance with necessary metaphysical laws).

Priestley's major argument in the Institutes was that the only revealed religious truths that could be accepted were those that matched one's experience of the natural world. Since his views of religion were tied deeply to his understanding of nature, the text's theism rested on the argument from design. 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." 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 in 1782. 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 defence of religion and religious readers dismissed the application of science to religion.

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", but as Schofield points out Priestley rarely altered his opinion as a result of these debates. 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.

Priestley 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 submitted articles. He was, therefore, obliged to provide much of the journal's content himself. This material also became the basis for many 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. However, he did revive it briefly in 1784 with similar results.

Defender of Dissenters and political philosopher

Many of Priestley's political writings supported 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.

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). An early work of modern liberal political theory and Priestley's most thorough treatment of the subject, it—unusually for the time—distinguished political rights from civil rights with precision and argued for expansive civil rights. Priestley identified separate private and public spheres, contending that the government should have control only over the public sphere. Education and religion, in particular, he maintained, were 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.

Priestley also defended the rights of Dissenters against the attacks of William Blackstone, an eminent legal theorist, whose Commentaries on the Laws of England (1765–69) had become the standard legal guide. Blackstone's book 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 interpretation of the law, his grammar (a highly politicised subject at the time), and history. Blackstone, chastened, 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.

Natural philosopher: electricity, Optics, and carbonated water
Although Priestley claimed that natural philosophy was only a hobby, he took it seriously. In his History of Electricity, he described the scientist as promoting the "security and happiness of mankind". Priestley's science was eminently practical and he rarely concerned himself with theoretical questions; his model was his close friend, 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 neighbouring brewery). Between 1767 and 1770, he presented five papers to the Royal Society from 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 focused on chemistry and pneumatics.

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. He 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. He followed the (corpuscular) particle theory of light, influenced by the works of Reverend John Rowning and others. Furthermore, he did not include any of the practical sections that had made his History of Electricity so useful to practising natural philosophers. 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. The hastily written text sold poorly; the cost of researching, writing, and publishing the Optics convinced Priestley to abandon his history of experimental philosophy.

Priestley was considered for the position of astronomer on James Cook's second voyage to the South Seas, but was not chosen. Still, he contributed in a small way to the voyage: he provided the crew with a method for making carbonated water, which he erroneously speculated might be a cure for scurvy. He then published a pamphlet with Directions for Impregnating Water with Fixed Air (1772). Priestley did not exploit the commercial potential of carbonated water, but others such as J. J. Schweppe made fortunes from it. For his discovery of carbonated water Priestley has been labelled "the father of the soft drink", with the beverage company Schweppes regarding him as "the father of our industry". In 1773, the Royal Society recognised Priestley's achievements in natural philosophy by awarding him the Copley Medal.

Priestley's friends wanted to find him a more financially secure position. 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. Although Priestley was reluctant to sacrifice his ministry, he accepted the position, resigning from Mill Hill Chapel on 20 December 1772, and preaching his last sermon on 16 May 1773.

Calne (1773–1780)

In 1773, the Priestleys moved to Calne in Wiltshire, 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". 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. 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.

Materialist philosopher
Priestley wrote his most important philosophical works during his years with Lord Shelburne. In a series of major metaphysical texts 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), 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 that incorporates four concepts: determinism, materialism, causation, and necessitarianism. By studying the natural world, he argued, people would learn how to become more compassionate, happy, and prosperous.

Priestley strongly suggested that there is no mind-body duality, and put 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. He also contended that discussing the soul is impossible because it is made of a divine substance, and humanity cannot perceive 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.

Responding to Baron d'Holbach's Système de la Nature (1770) and David Hume's Dialogues Concerning Natural Religion (1779) as well as the works of the French philosophers, Priestley maintained that materialism and determinism could be reconciled with a belief in God. He criticised those whose faith was shaped by books and fashion, drawing an analogy between the scepticism of educated men and the credulity of the masses.

Maintaining that humans had no free will, Priestley argued that what he called "philosophical necessity" (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 contended, but because a benevolent God created these laws, the world and the people in it will eventually be perfected. Evil is therefore only an imperfect understanding of the world.

Although Priestley's philosophical work has been characterised as "audacious and original", it partakes of older philosophical traditions on the problems of free will, determinism, and materialism. For example, the 17th-century philosopher Baruch Spinoza argued for absolute determinism and absolute materialism. Like Spinoza and Priestley, Leibniz argued that human will was completely determined by natural laws; unlike them, Leibniz argued for a "parallel universe" of immaterial objects (such as human souls) so arranged by God that its outcomes agree exactly with those of the material universe. Leibniz and Priestley share an optimism that God has chosen the chain of events benevolently; however, Priestley believed that the events were leading to a glorious millennial conclusion, whereas for Leibniz the entire chain of events was optimal in and of itself, as compared with other conceivable chains of events.

Founder of British Unitarianism
When Priestley's friend Theophilus Lindsey decided to found a new Christian denomination that would not restrict its members' beliefs, Priestley and others hurried to his aid. On 17 April 1774, Lindsey held the first Unitarian service in Britain, at the newly formed Essex Street Chapel in London; he had even designed his own liturgy, of which many were critical. Priestley defended his friend in the pamphlet Letter to a Layman, on the Subject of the Rev. Mr. Lindsey's Proposal for a Reformed English Church (1774), claiming that only the form of worship had been altered, not its substance, and attacking those who followed religion as a fashion. Priestley attended Lindsey's church regularly in the 1770s and occasionally preached there. He continued to support institutionalised 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.

Experiments and Observations on Different Kinds of Air
Priestley's years in Calne were the only ones in his life dominated by scientific investigations; they were also 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). 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. According to that 18th-century theory, the combustion or oxidation of a substance corresponded to the release of a material substance, phlogiston.

Priestley's work on "airs" is not easily classified. As historian of science Simon Schaffer writes, it "has been seen as a branch of physics, or chemistry, or natural philosophy, or some highly idiosyncratic version of Priestley's own invention". Furthermore, the volumes were both a scientific and a political enterprise for Priestley, in which he argues that science could destroy "undue and usurped authority" and that government has "reason to tremble even at an air pump or an electrical machine".

Volume I of Experiments and Observations on Different Kinds of Air outlined several discoveries: "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, most famously, "dephlogisticated air" (oxygen, O2) as well as experimental findings that showed plants revitalised enclosed volumes of air, a discovery that would eventually lead to the discovery of photosynthesis by Jan Ingenhousz. Priestley also developed a "nitrous air test" to determine 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. After a small history of the study of airs, he explained his own experiments in an open and sincere style. As an early biographer writes, "whatever he knows or thinks he tells: doubts, perplexities, blunders are set down with the most refreshing candour." Priestley also described his cheap and easy-to-assemble experimental apparatus; his colleagues therefore believed that they could easily reproduce his experiments. Faced with inconsistent experimental results, Priestley employed phlogiston theory. This led him to conclude that there were only three types of "air": "fixed", "alkaline", and "acid". Priestley dismissed the burgeoning chemistry of his day. Instead, he focused on gases and "changes in their sensible properties", as had natural philosophers before him. He isolated carbon monoxide (CO), but apparently did not realise that it was a separate "air".

Discovery of oxygen

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, Priestley replicated the experiment for others, including French chemist Antoine Lavoisier. After returning to Britain in January 1775, he continued his experiments and discovered "vitriolic acid air" (sulphur 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 the Society's journal Philosophical Transactions. Priestley called the new substance "dephlogisticated air", which he made in the famous experiment by focusing the sun's rays on a sample of mercuric oxide. He first tested it on mice, who surprised him by surviving quite a while entrapped with the air, and then on himself, writing that it was "five or six times better than common air for the purpose of respiration, inflammation, and, I believe, every other use of common atmospherical air". 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 did not emphasise his discovery of "dephlogisticated air" (leaving it to Part III of the volume) but instead argued in the preface how important such discoveries were to rational religion. His paper narrated the discovery chronologically, relating the long delays between experiments and his initial puzzlements; thus, it is difficult to determine when exactly Priestley "discovered" oxygen. 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" (that is, the first to explain oxygen without phlogiston theory).

In his paper "Observations on Respiration and the Use of the Blood", Priestley 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. Lavoisier's work began the long train of discovery that produced papers on oxygen respiration and culminated in the overthrow of phlogiston theory and the establishment of modern chemistry.

Around 1779 Priestley and Shelburne – soon to be the 1st Marquess of Landsdowne – had a rupture, the precise reasons for which remain unclear. Shelburne blamed Priestley's health, while 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.

Both Priestley and Shelburne's families upheld their Unitarian faith for generations. In December 2013, it was reported that Sir Christopher Bullock – a direct descendant of Shelburne's brother, Thomas Fitzmaurice (MP) – had married his wife, Lady Bullock, née Barbara May Lupton, at London's Unitarian Essex Church in 1917. Barbara Lupton was the second cousin of Olive Middleton, née Lupton, the great-grandmother of Catherine, Duchess of Cambridge. In 1914, Olive and Noel Middleton had married at Leeds' Mill Hill Chapel, which Priestley, as its minister, had once guided towards Unitarianism.

Birmingham (1780–1791)
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 religiously motivated mob violence in what became known as the Priestley Riots. 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. Because Priestley's New Meeting salary was only 100 guineas, friends and patrons donated money and goods to help continue his investigations. He was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1782.

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. The core of the group included men such as the manufacturer Matthew Boulton, the chemist and geologist James Keir, the inventor and engineer James Watt, and the botanist, chemist, and geologist William Withering. Priestley was asked to join this unique society and contributed much to the work of its members. As a result of this stimulating intellectual environment, he published several important scientific papers, including "Experiments relating to Phlogiston, and the seeming Conversion of Water into Air" (1783). The first part attempts to refute Lavoisier's challenges to his work on oxygen; the second part describes how steam is "converted" into air. After several variations of the experiment, with different substances as fuel 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". This discovery, along with his earlier work on what would later be recognised as gaseous diffusion, would eventually lead John Dalton and Thomas Graham to formulate the kinetic theory of gases.

In 1777, Antoine Lavoisier had written Mémoire sur la combustion en général, the first of what proved to be a series of attacks on phlogiston theory; it was against these attacks that Priestley responded in 1783. While Priestley accepted parts of Lavoisier's theory, he was unprepared to assent to the major revolutions Lavoisier proposed: the overthrow of phlogiston, a chemistry based conceptually on elements and compounds, and a new chemical nomenclature. Priestley's original experiments on "dephlogisticated air" (oxygen), combustion, and water provided Lavoisier with the data he needed to construct much of his system; yet Priestley never accepted Lavoisier's new theories and continued to defend phlogiston theory for the rest of his life. Lavoisier's system was based largely on the quantitative concept that mass is neither created nor destroyed in chemical reactions (i.e., the conservation of mass). By contrast, Priestley preferred to observe qualitative changes in heat, colour, and particularly volume. His experiments tested "airs" for "their solubility in water, their power of supporting or extinguishing flame, whether they were respirable, how they behaved with acid and alkaline air, and with nitric oxide and inflammable air, and lastly how they were affected by the electric spark."

By 1789, when Lavoisier published his Traité Élémentaire de Chimie and founded the Annales de Chimie, the new chemistry had come into its own. Priestley published several more scientific papers in Birmingham, the majority attempting to refute Lavoisier. Priestley and other Lunar Society members argued that the new French system was too expensive, too difficult to test, and unnecessarily complex. Priestley in particular rejected its "establishment" aura. In the end, Lavoisier's view prevailed: his new chemistry introduced many of the principles on which modern chemistry is founded.

Priestley's refusal to accept Lavoisier's "new chemistry"—such as the conservation of mass—and his determination to adhere to a less satisfactory theory has perplexed many scholars. Schofield explains it thus: "Priestley was never a chemist; in a modern, and even a Lavoisierian, sense, he was never a scientist. He was a natural philosopher, concerned with the economy of nature and obsessed with an idea of unity, in theology and in nature." Historian of science John McEvoy largely agrees, writing that Priestley's view of nature as coextensive with God and thus infinite, which encouraged him to focus on facts over hypotheses and theories, prompted him to reject Lavoisier's system. McEvoy argues that "Priestley's isolated and lonely opposition to the oxygen theory was a measure of his passionate concern for the principles of intellectual freedom, epistemic equality and critical inquiry." Priestley himself claimed in the last volume of Experiments and Observations that his most valuable works were his theological ones because they were "superior [in] dignity and importance".

Defender of English Dissenters and French revolutionaries

Although Priestley spent much of this time defending phlogiston theory from the "new chemists", most of what he published in Birmingham was theological. For example, in 1782, he published the fourth volume of his Institutes, An History of the Corruptions of Christianity, describing how he thought the teachings of the early Christian church had been "corrupted" or distorted. Schofield describes the work as "derivative, disorganized, wordy, and repetitive, detailed, exhaustive, and devastatingly argued". The text addresses issues ranging from the divinity of Christ to the proper form for the Lord's Supper. In 1786, Priestley published its provocatively titled sequel, An History of Early Opinions concerning Jesus Christ, compiled from Original Writers, proving that the Christian Church was at first Unitarian. Thomas Jefferson later wrote of the profound effect that these two books had on him: "I have read his Corruptions of Christianity, and Early Opinions of Jesus, over and over again; and I rest on them ... as the basis of my own faith. These writings have never been answered." Although a few readers such as Jefferson and other Rational Dissenters approved of the work, many others reviewed it harshly because of its extreme theological positions, particularly its rejection of the Trinity.

In 1785, while Priestley was engaged in a pamphlet war over Corruptions, he also published The Importance and Extent of Free Enquiry, claiming that the Reformation had not really reformed the church. In words that would boil over into a national debate, he challenged his readers to enact change: Let us not, therefore, be discouraged, though, for the present, we should see no great number of churches professedly unitarian .... We are, as it were, laying gunpowder, grain by grain, under the old building of error and superstition, which a single spark may hereafter inflame, so as to produce an instantaneous explosion; in consequence of which that edifice, the erection of which has been the work of ages, may be overturned in a moment, and so effectually as that the same foundation can never be built upon again .... Although discouraged by friends from using such inflammatory language, Priestley refused to back down from his opinions in print and he included it, forever branding himself as "Gunpowder Joe". After the publication of this seeming call for revolution in the midst of the French Revolution, pamphleteers stepped up their attacks on Priestley and he and his church were even threatened with legal action.

In 1787, 1789, and 1790, Dissenters again tried to repeal the Test and Corporation Acts. Although they might have succeeded initially, by 1790, with the fears of revolution looming in Parliament, few were swayed by appeals to equal rights. Political cartoons, one of the most effective and popular media of the time, skewered the Dissenters and Priestley. In Parliament, William Pitt and Edmund Burke argued against the repeal, a betrayal that angered Priestley and his friends, who had expected the two men's support. Priestley wrote a series of Letters to William Pitt and Letters to Burke.

Dissenters such as Priestley who supported the French Revolution came under increasing suspicion as scepticism regarding the revolution grew. In its propaganda against "radicals", Pitt's administration used the "gunpowder" statement to argue that Priestley and other Dissenters wanted to overthrow the government. Burke, in his famous Reflections on the Revolution in France (1790), tied natural philosophers, and specifically Priestley, to the French Revolution, writing that radicals who supported science in Britain "considered man in their experiments no more than they do mice in an air pump". Burke also associated republican principles with alchemy and insubstantial air, mocking the scientific work done by both Priestley and French chemists. He made much in his later writings of the connections between "Gunpowder Joe", science, and Lavoisier—who was improving gunpowder for the French in their war against Britain. Paradoxically, a secular statesman, Burke, argued against science and maintained that religion should be the basis of civil society, whereas a Dissenting minister, Priestley, argued that religion could not provide the basis for civil society and should be restricted to one's private life.

Priestley also supported the campaign to abolish the British slave trade and published a sermon in 1788 in which he declared that nobody treated enslaved people "with so much cruelty as the English".

Birmingham riots of 1791

The animus that had been building against Dissenters and supporters of the American and French Revolutions exploded in July 1791. Priestley and several other Dissenters had arranged to have a celebratory dinner on Bastille Day, the anniversary of the storming of the Bastille, a provocative action in a country where many disapproved of the French Revolution and feared that it might spread to Britain. Amid fears of violence, Priestley was convinced by his friends not to attend. Rioters gathered outside the hotel during the banquet and attacked the attendees as they left. The rioters moved on to the New Meeting and Old Meeting churches, and burned both to the ground. Priestley and his wife fled from their home; although their son William and others stayed behind to protect their property, the mob overcame them and torched Priestley's house "Fairhill" at Sparkbrook, destroying his valuable laboratory and all of the family's belongings. Twenty-six other Dissenters' homes and three more churches were burned in the three-day riot. Priestley spent several days hiding with friends until he was able to travel safely to London. The carefully executed attacks of the "mob" and the farcical trials of only a handful of the "leaders" convinced many at the time—and modern historians later—that the attacks were planned and condoned by local Birmingham magistrates. When George III was eventually forced to send troops to the area, he said: "I cannot but feel better pleased that Priestley is the sufferer for the doctrines he and his party have instilled, and that the people see them in their true light."

Hackney (1791–1794)
Unable to return to Birmingham, the Priestleys eventually settled in Lower Clapton, a district in Hackney, Middlesex where he gave a series of lectures on history and natural philosophy at the Dissenting academy, the New College at Hackney. Friends helped the couple rebuild their lives, contributing money, books, and laboratory equipment. Priestley tried to obtain restitution from the government for the destruction of his Birmingham property, but he was never fully reimbursed. He also published An Appeal to the Public on the Subject of the Riots in Birmingham (1791), which indicted the people of Birmingham for allowing the riots to occur and for "violating the principles of English government".

The couple's friends urged them to leave Britain and emigrate to either France or the new United States, even though Priestley had received an appointment to preach for the Gravel Pit Meeting congregation. Priestley was minister between 1793 and 1794 and the sermons he preached there, particularly the two Fast Sermons, reflect his growing millenarianism, his belief that the end of the world was fast approaching. After comparing Biblical prophecies to recent history, Priestley concluded that the French Revolution was a harbinger of the Second Coming of Christ. Priestley's works had always had a millennial cast, but after the beginning of the French Revolution, this strain increased. He wrote to a younger friend that while he himself would not see the Second Coming, his friend "may probably live to see it ... It cannot, I think be more than twenty years [away]."

Daily life became more difficult for the family: Priestley was burned in effigy along with Thomas Paine; vicious political cartoons continued to be published about him; letters were sent to him from across the country, comparing him to the devil and Guy Fawkes; tradespeople feared the family's business; and Priestley's Royal Academy friends distanced themselves. As the penalties became harsher for those who spoke out against the government, Priestley examined options for removing himself and his family from England.

Joseph Priestley's son William was presented to the French Assembly and granted letters of naturalisation on 8 June 1792. Priestley learned about it from the Morning Chronicle. A decree of 26 August 1792 by the French National Assembly conferred French citizenship on Joseph Priestley and others who had "served the cause of liberty" by their writings. Priestley accepted French citizenship, considering it "the greatest of honours". In the French National Convention election on 5 September 1792, Joseph Priestley was elected to the French National Convention by at least two departments, (Orne and Rhône-et-Loire). He declined the honour, on the grounds that he was not fluent in French.

As relations between England and France worsened, a removal to France became impracticable. Following the declaration of war of February 1793, and the Aliens Bill of March 1793, which forbade correspondence or travel between England and France, William Priestley left France for America. Joseph Priestley's sons Harry and Joseph chose to leave England for America in August 1793. Finally Priestley himself followed with his wife, boarding the Sansom at Gravesend on 7 April 1794. Five weeks after Priestley left, William Pitt's administration began arresting radicals for seditious libel, resulting in the famous 1794 Treason Trials.

Pennsylvania (1794–1804)

The Priestleys arrived in New York City on 4 June 1794, where they were fêted by various political factions vying for Priestley's endorsement. Priestley declined their entreaties, hoping to avoid political discord in his new country. Before travelling to a new home in the backwoods of Northumberland County, Pennsylvania, at Point township (now the Borough of Northumberland), Priestley and his wife lodged in Philadelphia, where he gave a series of sermons which led to the founding of the First Unitarian Church of Philadelphia. Priestley turned down an opportunity to teach chemistry at the University of Pennsylvania.

Priestley's son Joseph Priestley Jr. was a leading member of a consortium that had purchased 300000 acre of virgin woodland between the forks of Loyalsock Creek. This they intended to lease or sell in 400 acre plots, with payment deferred to seven annual instalments, with interest. His brothers, William and Henry, bought a 284 acre plot of woodland which they attempted to transform into a farm, later called "Fairhill", felling and uprooting trees, and making lime to sweeten the soil by building their own lime kilns. Henry Priestley died 11 December 1795, possibly of malaria which he may have contracted after landing at New York. Mary Priestley's health, already poor, deteriorated further; although William's wife, Margaret Foulke-Priestley, moved in with the couple to nurse Mary 24 hours a day, Mary Priestley died 17 September 1796. Priestley then moved in with his elder son, Joseph Jr., and his wife Elizabeth Ryland-Priestley. Thomas Cooper, whose son, Thomas Jr., was living with the Priestleys, was a frequent visitor.

Since his arrival in America, Priestley had continued to defend his Christian Unitarian beliefs; now, falling increasingly under the influence of Thomas Cooper and Elizabeth Ryland-Priestley, he was unable to avoid becoming embroiled in political controversy. In 1798, when, in response to the Pinckney affair, a belligerent President Adams sought to enlarge the navy and mobilise the militia into what Priestley and Cooper saw as a 'standing army', Priestley published an anonymous newspaper article: Maxims of political arithmetic, which attacked Adams, defended free trade, and advocated a form of Jeffersonian isolationism. In the same year, a small package, addressed vaguely: "Dr Priestley in America," was seized by the Royal Navy on board a neutral Danish boat. It was found to contain three letters, one of which was signed by the radical printer John Hurford Stone. These intercepted letters were published in London, and copied in numerous papers in America. One of the letters was addressed to "MBP", with a note: "I inclose a note for our friend MBP—but, as ignorant of the name he bears at present among you, I must beg you to seal and address it." This gave the intercepted letters a tinge of intrigue. Fearful lest they be taken as evidence of him being a 'spy in the interest of France', Priestley sent a clumsy letter to numerous newspaper editors, in which he naively named "MBP" (Member of the British Parliament) as Mr. Benjamin Vaughan, who "like me, thought it necessary to leave England, and for some time is said to have assumed a feigned name." William Cobbett, in his Porcupine's Gazette, 20 August 1798, added that Priestley "has told us who Mr MBP is, and has confirmed me in the opinion of their both being spies in the interest of France."

Joseph Priestley Jr. left on a visit to England at Christmas 1798, not returning until August 1800. In his absence, his wife Elizabeth Ryland-Priestley and Thomas Cooper became increasing close, collaborating in numerous political essays. Priestley allowed himself to fall too heavily under Elizabeth and Cooper's influences, even helping hawk a seditious handbill Cooper had printed, around Point township, and across the Susquehanna at Sunbury. In September 1799, William Cobbett printed extracts from this handbill, asserting that: "Dr Priestley has taken great pains to circulate this address, has travelled through the country for the purpose, and is in fact the patron of it." He challenged Priestley to "clear himself of the accusation" or face prosecution." Barely a month later, in November and December 1799, Priestley stepped forward in his own defence, with his Letters to the inhabitants of Northumberland.

Priestley's son, William, now living in Philadelphia, was increasingly embarrassed by his father's actions. He confronted his father, expressing John and Benjamin Vaughan's unease, his own wife's concerns about Elizabeth Ryland-Priestley's dietary care, and his own concerns at the closeness of Elizabeth Ryland-Priestley and Thomas Cooper's relationship, and their adverse influence on Dr Priestley; but this only led to a further estrangement between William and his sister-in-law. When, a while later, Priestley's household suffered a bout of food poisoning, perhaps from milk sickness or a bacterial infection, Elizabeth Ryland-Priestley falsely accused William of having poisoned the family's flour. Although this allegation has attracted the attention of some modern historians, it is believed to be without foundation.

Priestley continued the educational projects that had always been important to him, helping to establish the "Northumberland Academy" and donating his library to the fledgling institution. He exchanged letters regarding the proper structure of a university with Thomas Jefferson, who used this advice when founding the University of Virginia. Jefferson and Priestley became close, and when the latter had completed his General History of the Christian Church, he dedicated it to President Jefferson, writing that "it is now only that I can say I see nothing to fear from the hand of power, the government under which I live being for the first time truly favourable to me."

Priestley tried to continue his scientific investigations in America with the support of the American Philosophical Society, to which he had been previously elected a member in 1785. He was hampered by lack of news from Europe; unaware of the latest scientific developments, Priestley was no longer on the forefront of discovery. Although the majority of his publications focused on defending phlogiston theory, he also did some original work on spontaneous generation and dreams. Despite Priestley's reduced scientific output, his presence stimulated American interest in chemistry.

By 1801, Priestley had become so ill that he could no longer write or experiment. He died on the morning of 6 February 1804, aged seventy and was buried at Riverview Cemetery in Northumberland, Pennsylvania.

Priestley's epitaph reads:

"Return unto thy rest, O my soul, for the Lord hath dealt bountifully with thee. I will lay me down in peace and sleep till I awake in the morning of the resurrection."

Legacy
By the time he died in 1804, Priestley had been made a member of every major scientific society in the Western world and he had discovered numerous substances. The 19th-century French naturalist George Cuvier, in his eulogy of Priestley, praised his discoveries while at the same time lamenting his refusal to abandon phlogiston theory, calling him "the father of modern chemistry [who] never acknowledged his daughter". Priestley published more than 150 works on topics ranging from political philosophy to education to theology to natural philosophy. He led and inspired British radicals during the 1790s, paved the way for utilitarianism, and helped found Unitarianism. A wide variety of philosophers, scientists, and poets became associationists as a result of his redaction of David Hartley's Observations on Man, including Erasmus Darwin, Coleridge, William Wordsworth, John Stuart Mill, Alexander Bain, and Herbert Spencer. Immanuel Kant praised Priestley in his Critique of Pure Reason (1781), writing that he "knew how to combine his paradoxical teaching with the interests of religion". Indeed, it was Priestley's aim to "put the most 'advanced' Enlightenment ideas into the service of a rationalized though heterodox Christianity, under the guidance of the basic principles of scientific method".

Considering the extent of Priestley's influence, relatively little scholarship has been devoted to him. In the early 20th century, Priestley was most often described as a conservative and dogmatic scientist who was nevertheless a political and religious reformer. In a historiographic review essay, historian of science Simon Schaffer describes the two dominant portraits of Priestley: the first depicts him as "a playful innocent" who stumbled across his discoveries; the second portrays him as innocent as well as "warped" for not understanding their implications better. Assessing Priestley's works as a whole has been difficult for scholars because of his wide-ranging interests. His scientific discoveries have usually been divorced from his theological and metaphysical publications to make an analysis of his life and writings easier, but this approach has been challenged recently by scholars such as John McEvoy and Robert Schofield. Although early Priestley scholarship claimed that his theological and metaphysical works were "distractions" and "obstacles" to his scientific work, scholarship published in the 1960s, 1970s, and 1980s maintained that Priestley's works constituted a unified theory. However, as Schaffer explains, no convincing synthesis of his work has yet been expounded. More recently, in 2001, historian of science Dan Eshet has argued that efforts to create a "synoptic view" have resulted only in a rationalisation of the contradictions in Priestley's thought, because they have been "organized around philosophical categories" and have "separate[d] the producers of scientific ideas from any social conflict".

Priestley has been remembered by the towns in which he served as a reforming educator and minister and by the scientific organisations he influenced. Two educational institutions have been named in his honour—Priestley College in Warrington and Joseph Priestley College in Leeds (now part of Leeds City College)—and an asteroid, 5577 Priestley, discovered in 1986 by Duncan Waldron. In Birstall, the Leeds City Square, and in Birmingham, he is memorialised through statues, and plaques commemorating him have been posted in Birmingham, Calne and Warrington. The main undergraduate chemistry laboratories at the University of Leeds were refurbished as part of a £4m refurbishment plan in 2006 and renamed as the Priestley Laboratories in his honour as a prominent chemist from Leeds. In 2016 the University of Huddersfield renamed the building housing its Applied Sciences department as the Joseph Priestley Building, as part of an effort to rename all campus buildings after prominent local figures.

Since 1952 Dickinson College, Pennsylvania, has presented the Priestley Award to a "distinguished scientist whose work has contributed to the welfare of humanity". Priestley's work is recognised by a National Historic Chemical Landmark designation for his discovery of oxygen, made on 1 August 1994, at the Priestley House in Northumberland, Penn., by the American Chemical Society. Similar recognition was made on 7 August 2000, at Bowood House in Wiltshire, England. The ACS also awards their highest honour, the Priestley Medal, in his name.

Several of his descendants became physicians, including the noted American surgeon James Taggart Priestley II of the Mayo Clinic.

Archives
Papers of Joseph Priestley are held at the Cadbury Research Library, University of Birmingham.

Selected works

 * The Rudiments of English Grammar (1761)
 * A Chart of Biography (1765)
 * Essay on a Course of Liberal Education for Civil and Active Life (1765)
 * The History and Present State of Electricity (1767)
 * Essay on the First Principles of Government (1768)
 * A New Chart of History (1769)
 * Institutes of Natural and Revealed Religion (1772–74)
 * Experiments and Observations on Different Kinds of Air (1774–77)
 * Disquisitions Relating to Matter and Spirit (1777)
 * The Doctrine of Philosophical Necessity Illustrated (1777)
 * Letters to a Philosophical Unbeliever (1780)
 * An History of the Corruptions of Christianity (1782)
 * Lectures on History and General Policy (1788)
 * Theological Repository (1770–73, 1784–88)

Short online biographies

 * "Joseph Priestley: Discoverer of Oxygen" at the American Chemical Society
 * Joseph Priestley at the Woodrow Wilson National Fellowship Foundation
 * Joseph Priestley from the Encyclopædia Britannica
 * ExplorePAHistory.com
 * ExplorePAHistory.com
 * ExplorePAHistory.com

title: Joseph Priestley


text:
550s BC

This article concerns the period 559 BC–550 BC.

Events and trends

 * Carthage conquers Sicily, Sardinia, and Corsica.
 * 559 BC—King Cambyses I of Anshan dies and is succeeded by his son Cyrus II the Great.
 * 558 BC—Hegesias is removed as Archon of Athens.
 * 558 BC—The Chinese state of Jin defeats its rival state of Qin in battle.
 * 557 BC—The Persians besiege Larissa (Calah) but fail to capture it until a solar eclipse occurs.
 * 556 BC—Pisistratus is exiled from Athens to Euboea.
 * 556 BC—Labashi-Marduk succeeds Neriglissar as king of Babylon.
 * 556 BC—Nabonidus succeeds Labashi-Marduk as king of Babylon.
 * c. 550 BC—Colonisation of Greeks ends.
 * 550 BC—Abdera is destroyed by the Thracians.
 * 550 BC—Mago I begins his rule of Carthage.
 * 550 BC—The Temple of Artemis is completed in Ephesus.
 * 553-550 BC—Medo-Persian conflict, the Persian king Cyrus II overthrows the Median king Astyages, establishing the First Persian Empire.
 * c. 550 BC—The Temple of Hera I is built in what is now Paestum, Italy.
 * 550 BC—Siddhartha Gautama founds Buddhism in Northern India after achieving enlightenment after six years of practicing penance and meditation.

Significant people

 * 556 BC—Rule of Labashi-Marduk as king of Babylon
 * 556 BC—Rule of Nabonidus as king of Babylon
 * 558 BC—Death of Solon, Athenian statesman, poet.
 * c. 556 BC—Birth of Simonides of Ceos.
 * 555 BC—Death of Stesichorus, Greek lyric poet.
 * September 28, 551 BC—Birth of Confucius, Chinese philosopher (traditional date).
 * c. 551 BC—Commonly accepted date of death of Zoroaster, founder of Zoroastrianism.
 * 550 BC—Birth of Epicharmus, Greek poet (d. 460 BC).

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: 550s BC


text:
7th millennium BC

The 7th millennium BC spanned the years 7000 BC to 6001 BC (c. 9 ka to c. 8 ka). It is impossible to precisely date events around this millennium, and all dates mentioned here are estimates mostly based on geological and anthropological analysis.

Towards the end of this millennium, the islands of Great Britain, and Ireland were severed from continental Europe by rising seawater.

Population
Neolithic culture and technology were established in the Near East by 7000 BC and there is increasing evidence through the millennium of its spread or introduction to Europe and the Far East. In most of the world, however, including north and western Europe, people still lived in scattered Palaeolithic hunter-gatherer communities. The Mehrgarh chalcolithic civilization began around 7000 BC. The world population is believed to have been stable and slowly increasing. It has been estimated that there were perhaps ten million people worldwide at the end of this millennium, growing to forty million by 5000 BC and 100 million by 1600 BC, an average growth rate of 0.027% p.a. from the beginning of the Neolithic to the Middle Bronze Age.

Europe
Neolithic culture and technology reached modern Turkey and Greece c. 7000 BC; and Crete about the same time. The innovations, including the introduction of farming, spread from the Middle East through Turkey and Egypt. There is evidence of domesticated sheep or goats, pigs, and cattle, together with grains of cultivated bread wheat. The domestication of pigs in Eastern Europe is believed to have begun c. 6800 BC. The pigs may have descended from European wild boar or were probably introduced by farmers migrating from the Middle East. There is evidence, c. 6200 BC, of farmers from the Middle East reaching the Danube and moving into Romania and Serbia. Farming gradually spread westward and northward over the next four millennia, finally reaching Great Britain and Scandinavia c. 3000 BC to complete the transition of Europe from the Mesolithic to the Neolithic.

Near East
The Ubaid period (c. 6500–3800 BC) began in Mesopotamia, its name derived from Tell al-'Ubaid where the first significant excavation took place.

By the end of this millennium, Jericho had become a large agricultural settlement with some eight to ten acres within its walls. Kathleen Kenyon reckoned that it was home to about three thousand people. Construction was done using stone implements to mould clay into bricks. The main crop was wheat.

The Steppe
“Sheep and goats were domesticated in South West Asia, probably in the region of eastern Anatolia and northern Syria between 8000 and 7500 BC, and were part of the agricultural package that was transmitted to Greece and the Balkans during the pioneering movements in the seventh millennium. From there the herding of domesticated sheep and goats was gradually taken up by foraging communities in the Pontic-Caspian steppe during the sixth and fifth millennia and became an essential part of the herder economy.”

The Northgrippian
In the geologic time scale, the "Northgrippian" succeeded the "Greenlandian" c. 6236 BC (to c. 2250 BC). The starting point for the Northgrippian is the so-called 8.2 kiloyear event, which was an abrupt climate change lasting some four centuries in which there was a marked decrease in global temperatures, possibly caused by an influx of glacial meltwater into the North Atlantic Ocean.

Creation of Great Britain and Ireland
The influx is believed to be one factor in the creation of Great Britain and Ireland as islands separate from the European continent. After the Last Ice Age ended c. 9700 BC, increasing sea levels gradually inundated Doggerland, a land bridge which linked Great Britain to Denmark and the Netherlands. This process began the formation of the North Sea and the English Channel. Further west, another low-lying land area was being flooded to form the Irish Sea and create Ireland. Sometime in the second half of the 7th millennium, the Storegga Slides occurred off Norway to generate a huge tsunami which completely overwhelmed Doggerland and its Mesolithic community of an estimated 5,000 hunter-gatherers. By about 6100 BC, Great Britain had become an island.

Astronomy
Jupiter occulted Saturn in 6857 B.C.E. This is one of the rarest astronomical events in the solar system, with the next occurrence on February 17, 7541.

title: 7th millennium BC


text:
6th millennium BC

The 6th millennium BC spanned the years 6000 BC to 5001 BC (c. 8 ka to c. 7 ka). It is impossible to precisely date events that happened around the time of this millennium and all dates mentioned here are estimates mostly based on geological and anthropological analysis. The only exceptions are the felling dates for some construction timbers from Neolithic wells in Central Europe.

This millennium is reckoned to mark the end of the global deglaciation which had followed the Last Glacial Maximum and caused sea levels to rise by some 60 m over a period of about 5,000 years.

Overview
Neolithic culture and technology had spread from the Near East and into Eastern Europe by 6000 BC. Its development in the Far East grew apace and there is increasing evidence through the millennium of its presence in prehistoric Egypt and the Far East. In much of the world, however, including Northern and Western Europe, people still lived in scattered Palaeolithic/Mesolithic hunter-gatherer communities. The world population is believed to have increased sharply, possibly quadrupling, as a result of the Neolithic Revolution. It has been estimated that there were perhaps forty million people worldwide at the end of this millennium, growing to 100 million by the Middle Bronze Age c. 1600 BC.

Europe
It has been estimated that humans first settled in Malta c. 5900 BC, arriving across the Mediterranean from both Europe and North Africa.

Use of pottery found near Tbilisi is evidence that grapes were being used for winemaking c. 5980 BC.

Evidence of cheese-making in Poland is dated c. 5500 BC.

Four identified cultures starting around 5300 BC were the Dnieper-Donets, the Narva (eastern Baltic), the Ertebølle (Denmark and northern Germany), and the Swifterbant (Low Countries). They were linked by a common pottery style that had spread westward from Asia and is sometimes called "ceramic Mesolithic", distinguishable by a point or knob base and flared rims.

North Asia
- According to Vasily Radlov, among the Paleo-Siberian inhabitants of Central Siberia and Southern Siberia were the Yeniseians, of whom the Kets are considered the last remainder of these peoples. The Yeniseians were followed by the Uralic Samoyeds, who came from the northern Ural region. Proto-Uralic is the unattested reconstructed language ancestral to the modern Uralic language family. The hypothetical language is thought to have been originally spoken in a small area in about 7000–2000 BC, and expanded to give differentiated Proto-Languages. Some newer research has pushed the "Proto-Uralic homeland" east of the Ural Mountains into Western Siberia.

- Polities harbouring the Uralic peoples thrive. The shores of all Siberian lakes, which filled the depressions during the Lacustrine period, abound in remains dating from the Neolithic age. Countless kurgans (tumuli), furnaces, and other archaeological artifacts bear witness to a dense population. Some of the earliest artifacts found in Central Asia derive from Siberia. Large scale constructions occur as early as 6000 BC. Prehistoric settlements in remote Siberia, Russia have revealed that 8,000 years ago construction of complex defensive structures, such as the Amnya complex, occurred with political warfare. They are the oldest fortresses in the world. Finding such ancient fortifications challenges previous understanding of early human societies. It suggests that agriculture wasn’t the only driver for people to start building permanent settlements.

- Large scale backwards migrations occur with Native American populations migrating back into Asia, settling in areas such as the Altai Mountains several times over a span of thousands of years, earliest dated to 5500 BC. This is potentially linked to the environmental changes at the time (see Mount Mazama), which remained preserved in oral history of the North American cultures to this day.

- Na-Dené-speaking peoples finally entered North America starting around, reaching the Pacific Northwest by , and from there migrating along the Pacific Coast and into the interior. Linguists, anthropologists, and archeologists believe their ancestors constituted a separate migration into North America, later than the first Paleo-Indians. They migrated into Alaska and northern Canada, south along the Pacific Coast, into the interior of Canada, and south to the Great Plains and the American Southwest.

- Indo-European cultures descended from Ancient North Eurasians long ago, continue to expand Westwards from Central Russia. It provides linguistic evidence for the geographical location of these languages around that time, agreeing with archeological evidence that Indo-European speakers were present in the Pontic-Caspian steppes by around 4500 BCE (the Kurgan hypothesis) and that Uralic speakers may have been established in the Pit-Comb Ware culture to their north in the fifth millennium BCE (Carpelan & Parpola 2001:79).

Such words as those for "hundred", "pig", and "king" have something in common: they represent "cultural vocabulary" as opposed to "basic vocabulary". They are likely to have been acquired along with a novel number system and the domestic pig from Indo-Europeans in the south. Similarly, the Indo-Europeans themselves had acquired such words and cultural items from peoples and cultures to their south or west, including possibly their words for "ox", *gʷou- (compare English cow) and "grain", *bʰars- (compare English barley). In contrast, basic vocabulary – words such as "me", "hand", "water", and "be" – is much less readily borrowed between languages. If Indo-European and Uralic are genetically related, there should be agreements regarding basic vocabulary, with more agreements if they are closely related, fewer if they are less closely related.

- Indo-European cultures in Central Asia flourish, these cultures are the: Middle Volga culture (followed by the Samara culture at the turn of the millennium), the contemporary Dnieper–Donets culture. From around 5200 BC, the patriarchal Dnieper-Donets culture leaves the Mesolithic hunter-gatherer lifestyle and begins keeping cattle, sheep and goats. Other domestic animals kept included pigs, horses and dogs.

South Asia
Junglefowl were domesticated around c. 5500 BC in Southeast Asia.

East Asia
- The Zhaobaogou culture in China began c. 5400 BC. It was in the north-eastern part of the country, primarily in the Luan River valley in Inner Mongolia and northern Hebei.

- The 'Yangshao culture (仰韶文化, pinyin: Yǎngsháo wénhuà) was a Neolithic culture that existed extensively along the middle reaches of the Yellow River in China from around the end of this millennium, from 5000 BC to 3000 BC. Excavations found that children were buried in painted pottery jars. Pottery style emerging from the Yangshao culture spread westward to the Majiayao culture, and then further to Xinjiang and Central Asia along a proto-Silk Road.

Oceania
Indigenous Australians in what is now southwestern Victoria were farming and smoking eels as a food source and trade good using stone weirs, canals, and woven traps around 6000 BC.

Environmental changes
The 6th Millennium features widespread dramatic climatic events: The early Holocene sea level rise (EHSLR), which began c.10,000 BC, tailed off during the 6th millennium. Global water levels had risen by about 60 metres due to deglaciation of ice masses since the end of the Last Ice Age. Accelerated rises in sea level rise, called meltwater pulses, occurred three times during the EHSLR. The last one, Meltwater Pulse 1C, which peaked c. 6000 BC, produced a rise of 6.5 metres in only 140 years. It is believed that the cause was a major ice sheet collapse in Antarctica.

Approximately 8,000 years ago (c. 6000 BC), a massive volcanic landslide off Mount Etna, Sicily, caused a megatsunami that devastated the eastern Mediterranean coastline on the continents of Asia, Africa and Europe.

In South America, a large eruption occurred at Cueros de Purulla c. 5870 BC, forming a buoyant cloud and depositing the Cerro Paranilla Ash in the Calchaquí Valleys. A cataclysmic volcanic eruption occurred c. 5700 BC in Oregon when 12000 ft high Mount Mazama created Crater Lake as the resulting caldera filled with water. Another major eruption occurred c. 5550 BC on Mount Takahe, Antarctica, possibly creating an ozone hole in the region.

The carbon-14 content in tree rings created c. 5480 BC indicates an abnormal level of solar activity.

Astronomy and calendars
The epoch of the Byzantine calendar, used in the Byzantine Empire and many Christian Orthodox countries, is equivalent to 1 September 5509 BC on the Julian proleptic calendar (see image right).

The 6th millennium BC falls entirely within the Astrological Age of Gemini (c. 6450 BC to c. 4300 BC) according to some astrologers.

According to Gregory of Tours God created the world 5597 years prior to the death of Martin of Tours, which would be 5200 BC.

title: 6th millennium BC


text:
Bessemer process

The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation with air being blown through the molten iron. The oxidation also raises the temperature of the iron mass and keeps it molten.

Related decarburizing with air processes had been used outside Europe for hundreds of years, but not on an industrial scale. One such process (similar to puddling) was known in the 11th century in East Asia, where the scholar Shen Kuo of that era described its use in the Chinese iron and steel industry. In the 17th century, accounts by European travelers detailed its possible use by the Japanese.

The modern process is named after its inventor, the Englishman Henry Bessemer, who took out a patent on the process in 1856. The process was said to be independently discovered in 1851 by the American inventor William Kelly though the claim is controversial.

The process using a basic refractory lining is known as the "basic Bessemer process" or Gilchrist–Thomas process after the English discoverers Percy Gilchrist and Sidney Gilchrist Thomas.

China
A system akin to the Bessemer process has existed since the 11th century in East Asia. Economic historian Robert Hartwell writes that the Chinese of the Song Dynasty (960–1279 CE) innovated a "partial decarbonization" method of repeated forging of cast iron under a cold blast. Sinologist Joseph Needham and historian of metallurgy Theodore A. Wertime have described the method as a predecessor to the Bessemer process of making steel. This process was first described by the prolific scholar and polymath government official Shen Kuo (1031–1095) in 1075, when he visited Cizhou. Hartwell states that perhaps the earliest center where this was practiced was the great iron-production district along the Henan–Hebei border during the 11th century.

Europe
In the 15th century, the finery process, another process which shares the air-blowing principle with the Bessemer process, was developed in Europe. In 1740, Benjamin Huntsman developed the crucible technique for steel manufacture, at his workshop in the district of Handsworth in Sheffield. This process had an enormous impact on the quantity and quality of steel production, but it was unrelated to the Bessemer-type process employing decarburization.

The Japanese may have made use of a Bessemer-type process, which was observed by European travellers in the 17th century. The adventurer Johan Albrecht de Mandelslo describes the process in a book published in English in 1669. He writes, "They have, among others, particular invention for the melting of iron, without the using of fire, casting it into a tun done about on the inside without about half a foot of earth, where they keep it with continual blowing, take it out by ladles full, to give it what form they please." According to historian Donald Wagner, Mandelslo did not personally visit Japan, so his description of the process is likely derived from accounts of other Europeans who had traveled to Japan. Wagner believes that the Japanese process may have been similar to the Bessemer process, but cautions that alternative explanations are also plausible.

Bessemer's patent
In the early to mid-1850s, the American inventor William Kelly experimented with a method similar to the Bessemer process. Wagner writes that Kelly may have been inspired by techniques introduced by Chinese ironworkers hired by Kelly in 1854. The claim that both Kelly and Bessemer invented the same process remains controversial. When Bessemer's patent for the process was reported by Scientific American, Kelly responded by writing a letter to the magazine. In the letter, Kelly states that he had previously experimented with the process and claimed that Bessemer knew of Kelly's discovery. He wrote that "I have reason to believe my discovery was known in England three or four years ago, as a number of English puddlers visited this place to see my new process. Several of them have since returned to England and may have spoken of my invention there." It is suggested Kelly's process was less developed and less successful than Bessemer's process.

Sir Henry Bessemer described the origin of his invention in his autobiography written in 1890. During the outbreak of the Crimean War, many English industrialists and inventors became interested in military technology. According to Bessemer, his invention was inspired by a conversation with Napoleon III in 1854 pertaining to the steel required for better artillery. Bessemer claimed that it "was the spark which kindled one of the greatest revolutions that the present century had to record, for during my solitary ride in a cab that night from Vincennes to Paris, I made up my mind to try what I could to improve the quality of iron in the manufacture of guns." At the time, steel was used to make only small items like cutlery and tools, but was too expensive for cannons. Starting in January 1855, he began working on a way to produce steel in the massive quantities required for artillery and by October he filed his first patent related to the Bessemer process. He patented the method a year later in 1856. William Kelley was awarded priority patent in 1857.

Bessemer licensed the patent for his process to four ironmasters, for a total of £27,000, but the licensees failed to produce the quality of steel he had promised—it was "rotten hot and rotten cold", according to his friend, William Clay —and he later bought them back for £32,500. His plan had been to offer the licenses to one company in each of several geographic areas, at a royalty price per ton that included a lower rate on a proportion of their output in order to encourage production, but not so large a proportion that they might decide to reduce their selling prices. By this method he hoped to cause the new process to gain in standing and market share.

He realised that the technical problem was due to impurities in the iron and concluded that the solution lay in knowing when to turn off the flow of air in his process so that the impurities were burned off but just the right amount of carbon remained. However, despite spending tens of thousands of pounds on experiments, he could not find the answer. Certain grades of steel are sensitive to the 78% nitrogen which was part of the air blast passing through the steel.

The solution was first discovered by English metallurgist Robert Forester Mushet, who had carried out thousands of experiments in the Forest of Dean. His method was to first burn off, as far as possible, all the impurities and carbon, then reintroduce carbon and manganese by adding an exact amount of spiegeleisen, an alloy of iron and manganese with trace amounts of carbon and silicon. This had the effect of improving the quality of the finished product, increasing its malleability—its ability to withstand rolling and forging at high temperatures and making it more suitable for a vast array of uses. Mushet's patent ultimately lapsed due to Mushet's inability to pay the patent fees and was acquired by Bessemer. Bessemer earned over 5 million dollars in royalties from the patents.

The first company to license the process was the Manchester firm of W & J Galloway, and they did so before Bessemer announced it at Cheltenham in 1856. They are not included in his list of the four to whom he refunded the license fees. However, they subsequently rescinded their license in 1858 in return for the opportunity to invest in a partnership with Bessemer and others. This partnership began to manufacture steel in Sheffield from 1858, initially using imported charcoal pig iron from Sweden. This was the first commercial production.

A 20% share in the Bessemer patent was also purchased for use in Sweden and Norway by Swedish trader and Consul Göran Fredrik Göransson during a visit to London in 1857. During the first half of 1858, Göransson, together with a small group of engineers, experimented with the Bessemer process at Edsken near Hofors, Sweden before he finally succeeded. Later in 1858 he again met with Henry Bessemer in London, managed to convince him of his success with the process, and negotiated the right to sell his steel in England. Production continued in Edsken, but it was far too small for the industrial-scale production needed. In 1862 Göransson built a new factory for his Högbo Iron and Steel Works company on the shore of Lake Storsjön, where the town of Sandviken was founded. The company was renamed Sandviken's Ironworks, continued to grow and eventually became Sandvik in the 1970s.

Industrial revolution in the United States
Alexander Lyman Holley contributed significantly to the success of Bessemer steel in the United States. His A Treatise on Ordnance and Armor is an important work on contemporary weapons manufacturing and steel-making practices. In 1862, he visited Bessemer's Sheffield works, and became interested in licensing the process for use in the US. Upon returning to the US, Holley met with two iron producers from Troy, New York, John F. Winslow and John Augustus Griswold, who asked him to return to the United Kingdom and negotiate with the Bank of England on their behalf. Holley secured a license for Griswold and Winslow to use Bessemer's patented processes and returned to the United States in late 1863.

The trio began setting up a mill in Troy, New York in 1865. The factory contained a number of Holley's innovations that greatly improved productivity over Bessemer's factory in Sheffield, and the owners gave a successful public exhibition in 1867. The Troy factory attracted the attention of the Pennsylvania Railroad, which wanted to use the new process to manufacture steel rail. It funded Holley's second mill as part of its Pennsylvania Steel subsidiary. Between 1866 and 1877, the partners were able to license a total of 11 Bessemer steel mills.

One of the investors they attracted was Andrew Carnegie, who saw great promise in the new steel technology after a visit to Bessemer in 1872, and saw it as a useful adjunct to his existing businesses, the Keystone Bridge Company and the Union Iron Works. Holley built the new steel mill for Carnegie, and continued to improve and refine the process. The new mill, known as the Edgar Thomson Steel Works, opened in 1875, and started the growth of the United States as a major world steel producer. Using the Bessemer process, Carnegie Steel was able to reduce the costs of steel railroad rails from $100 per ton to $50 per ton between 1873 and 1875. The price of steel continued to fall until Carnegie was selling rails for $18 per ton by the 1890s. Prior to the opening of Carnegie's Thomson Works, steel output in the United States totaled around 157,000 tons per year. By 1910, American companies were producing 26 million tons of steel annually.

William Walker Scranton, manager and owner of the Lackawanna Iron & Coal Company in Scranton, Pennsylvania, had also investigated the process in Europe. He built a mill in 1876 using the Bessemer process for steel rails and quadrupled his production.

Bessemer steel was used in the United States primarily for railroad rails. During the construction of the Brooklyn Bridge, a major dispute arose over whether crucible steel should be used instead of the cheaper Bessemer steel. In 1877, Abram Hewitt wrote a letter urging against the use of Bessemer steel in the construction of the Brooklyn Bridge. Bids had been submitted for both crucible steel and Bessemer steel; John A. Roebling's Sons submitted the lowest bid for Bessemer steel, but at Hewitt's direction, the contract was awarded to J. Lloyd Haigh Co.

Technical details
Using the Bessemer process, it took between 10 and 20 minutes to convert three to five tons of iron into steel – it would previously take at least a full day of heating, stirring and reheating to achieve this.

Oxidation
The blowing of air through the molten pig iron introduces oxygen into the melt which results in oxidation, removing impurities found in the pig iron, such as silicon, manganese, and carbon in the form of oxides. These oxides either escape as gas or form a solid slag. The refractory lining of the converter also plays a role in the conversion — clay linings may be used when there is little phosphorus in the raw material, and Bessemer himself used ganister sandstone – this is known as the acid Bessemer process. When the phosphorus content is high, dolomite, or sometimes magnesite, linings are required in the basic Bessemer limestone process, see below. In order to produce steel with desired properties, additives such as spiegeleisen (a ferromanganese alloy), can be added to the molten steel once the impurities have been removed.

Managing the process
When the required steel had been formed, it was poured into ladles and then transferred into moulds while the lighter slag was left behind. The conversion process, called the "blow", was completed in approximately 20 minutes. During this period, the progress of the oxidation of the impurities was judged by the appearance of the flame issuing from the mouth of the converter. The modern use of photoelectric methods of recording the characteristics of the flame greatly aided the blower in controlling final product quality. After the blow, the liquid metal was recarburized to the desired point and other alloying materials were added, depending on the desired product.

A Bessemer converter could treat a "heat" (batch of hot metal) of 5 to 30 tons at a time. They were usually operated in pairs, one being blown while another was being filled or tapped.

Predecessor processes

By the early 19th century the puddling process was widespread. Until technological advances made it possible to work at higher heats, slag impurities could not be removed entirely, but the reverberatory furnace made it possible to heat iron without placing it directly in the fire, offering some degree of protection from the impurity of the fuel source. Thus, with the advent of this technology, coal began to replace charcoal fuel. The Bessemer process allowed steel to be produced without fuel, using the impurities of the iron to create the necessary heat. This drastically reduced the costs of steel production, but raw materials with the required characteristics could be difficult to find.

High-quality steel was made by the reverse process of adding carbon to carbon-free wrought iron, usually imported from Sweden. The manufacturing process, called the cementation process, consisted of heating bars of wrought iron together with charcoal for periods of up to a week in a long stone box. This produced blister steel. The blister steel was put in a crucible with wrought iron and melted, producing crucible steel. Up to 3 tons of expensive coke was burnt for each ton of steel produced. Such steel when rolled into bars was sold at £50 to £60 (approximately £3,390 to £4,070 in 2008) a long ton. The most difficult and work-intensive part of the process, however, was the production of wrought iron done in finery forges in Sweden.

This process was refined in the 18th century with the introduction of Benjamin Huntsman's crucible steel-making techniques, which added an additional three hours firing time and required additional large quantities of coke. In making crucible steel, the blister steel bars were broken into pieces and melted in small crucibles, each containing 20 kg or so. This produced higher quality crucible steel but increased the cost. The Bessemer process reduced the time needed to make lower-grade steel to about half an hour while requiring only the coke needed initially to melt the pig iron. The earliest Bessemer converters produced steel for £7 a long ton, although it initially sold for around £40 a ton.

"Basic" vs. acidic Bessemer process
Sidney Gilchrist Thomas, a Londoner with a Welsh father, was an industrial chemist who decided to tackle the problem of phosphorus in iron, which resulted in the production of low grade steel. Believing that he had discovered a solution, he contacted his cousin, Percy Gilchrist, who was a chemist at the Blaenavon Ironworks. The manager at the time, Edward Martin, offered Sidney equipment for large-scale testing and helped him draw up a patent that was taken out in May 1878. Sidney Gilchrist Thomas's invention consisted of using dolomite or sometimes limestone linings for the Bessemer converter rather than clay, and it became known as the 'basic' Bessemer rather than the 'acid' Bessemer process. An additional advantage was that the processes formed more slag in the converter, and this could be recovered and used very profitably as a phosphate fertilizer.

Importance

In 1898, Scientific American published an article called Bessemer Steel and its Effect on the World explaining the significant economic effects of the increased supply in cheap steel. They noted that the expansion of railroads into previously sparsely inhabited regions of the country had led to settlement in those regions, and had made the trade of certain goods profitable, which had previously been too costly to transport.

The Bessemer process revolutionized steel manufacture by decreasing its cost, from £40 per long ton to £6–7 per long ton, along with greatly increasing the scale and speed of production of this vital raw material. The process also decreased the labor requirements for steel-making. Before it was introduced, steel was far too expensive to make bridges or the framework for buildings and thus wrought iron had been used throughout the Industrial Revolution. After the introduction of the Bessemer process, steel and wrought iron became similarly priced, and some users, primarily railroads, turned to steel. Quality problems, such as brittleness caused by nitrogen in the blowing air, prevented Bessemer steel from being used for many structural applications. Open-hearth steel was suitable for structural applications.

Steel greatly improved the productivity of railroads. Steel rails lasted ten times longer than iron rails. Steel rails, which became heavier as prices fell, could carry heavier locomotives, which could pull longer trains. Steel rail cars were longer and were able to increase the freight to car weight from 1:1 to 2:1.

Obsolescence
As early as 1895 in the UK it was being noted that the heyday of the Bessemer process was over and that the open hearth method predominated. The Iron and Coal Trades Review said that it was "in a semi-moribund condition. Year after year, it has not only ceased to make progress, but it has absolutely declined." It has been suggested, both at that time and more recently, that the cause of this was the lack of trained personnel and investment in technology rather than anything intrinsic to the process itself. For example, one of the major causes of the decline of the giant ironmaking company Bolckow Vaughan of Middlesbrough was its failure to upgrade its technology. The basic process, the Thomas-Gilchrist process, remained in use longer, especially in Continental Europe, where iron ores were of high phosphorus content and the open-hearth process was not able to remove all phosphorus; almost all inexpensive construction steel in Germany was produced with this method in the 1950s and 1960s. It was eventually superseded by basic oxygen steelmaking.

In the U.S., commercial steel production using this method stopped in 1968. It was replaced by processes such as the basic oxygen (Linz–Donawitz) process, which offered better control of final chemistry. The Bessemer process was so fast (10–20 minutes for a heat) that it allowed little time for chemical analysis or adjustment of the alloying elements in the steel. Bessemer converters did not remove phosphorus efficiently from the molten steel; as low-phosphorus ores became more expensive, conversion costs increased. The process permitted only limited amount of scrap steel to be charged, further increasing costs, especially when scrap was inexpensive. Use of electric arc furnace technology competed favourably with the Bessemer process resulting in its obsolescence.

Basic oxygen steelmaking is essentially an improved version of the Bessemer process (decarburization by blowing oxygen as gas into the heat rather than burning the excess carbon away by adding oxygen carrying substances into the heat). The advantages of pure oxygen blast over air blast were known to Henry Bessemer, but 19th-century technology was not advanced enough to allow for the production of the large quantities of pure oxygen necessary to make it economical.

title: Bessemer process