Deaths on February 6

Joseph Priestley, English chemist and theologian (b. 1733)

Joseph Priestley: A Polymath of the Enlightenment

Joseph Priestley, born on March 24, 1733, and passing on February 6, 1804, was a profoundly influential English polymath whose intellectual curiosity spanned an astonishing array of disciplines. He was not only a pioneering chemist and natural philosopher but also a prolific separatist theologian, a meticulous grammarian, a multi-subject educator, and a liberal political theorist. His diverse pursuits led to the publication of more than 150 works throughout his lifetime, leaving an indelible mark on science, philosophy, and education.

Pivotal Scientific Discoveries and Reputation

Priestley's scientific reputation, though subject to later re-evaluation, was immense during his lifetime, largely cemented by three significant achievements:

• The Independent Discovery of Oxygen: While Swedish chemist Carl Wilhelm Scheele had isolated oxygen around 1772, Priestley independently discovered it on August 1, 1774. He meticulously isolated this new "air" by the thermal decomposition of mercuric oxide (also known as the "red calx of mercury"), observing that it made a candle burn brighter and allowed a mouse to live longer. He famously dubbed it "dephlogisticated air," a term rooted in the prevailing phlogiston theory of combustion that he staunchly defended.
• The Invention of Carbonated Water: Priestley's invention of carbonated water, born from his observations at a brewery where he noticed "fixed air" (carbon dioxide) hovering over vats, brought him widespread recognition. His 1772 publication, Directions for Impregnating Water with Fixed Air, detailed his method of dissolving carbon dioxide in water, laying the groundwork for the modern soft drink industry and companies like Schweppes.
• Discovery of Other "Airs" (Gases): Beyond oxygen, Priestley's tireless experimentation with gases led to the discovery and characterization of several other significant "airs," including nitrous oxide (or "laughing gas"), ammonia, hydrogen chloride, and sulfur dioxide.

However, Priestley's unwavering commitment to the phlogiston theory – which posited that a fire-like element called phlogiston was released during combustion – and his resistance to the emerging chemical revolution championed by Antoine Lavoisier, ultimately led to his isolation within the scientific community. Despite his pivotal role in isolating oxygen, he never fully embraced the new understanding of combustion that would fundamentally transform chemistry.

A Fusion of Science, Theology, and Philosophy

For Priestley, scientific inquiry was inseparable from his theological convictions. He dedicated considerable effort to fusing Enlightenment rationalism with Christian theism, believing that a deeper understanding of the natural world would not only promote human progress but also hasten the arrival of a Christian millennium.

His metaphysical texts, described as "audacious and original," explored complex ideas, attempting to reconcile:

• Theism: A belief in a personal God who creates and sustains the universe.
• Materialism: The view that reality, including consciousness and the soul, is fundamentally material. Priestley controversially argued that the human soul was not a separate, immaterial entity but rather a function of the brain, created by God.
• Determinism (Necessarianism): The belief that all events, including human actions, are causally determined. Priestley, a necessarian, reconciled this with moral responsibility by arguing that human choices, though determined, still have consequences that motivate ethical behavior.

A staunch advocate for the free and open exchange of ideas, Priestley passionately championed toleration and equal rights for religious Dissenters – Protestants who had separated from the Church of England. His advocacy was instrumental in the establishment of Unitarianism in England, a movement characterized by its rejection of the Trinity and its emphasis on reason and individual interpretation of scripture.

Political Controversy and Forced Exile

Priestley's intellectual courage and outspoken nature, particularly his fervent support for the ideals of the French Revolution, made him a controversial figure. His dissenting religious views combined with his radical political stance aroused widespread public and governmental suspicion.

This escalating tension culminated in the infamous Birmingham Riots of July 14-17, 1791, also known as the "Priestley Riots." Fuelled by anti-Dissenter and anti-revolutionary sentiment, a mob burned down Priestley's home, laboratory, and church in Birmingham. Fearing for his safety, he was compelled to flee, first to London, and eventually, in 1794, to the United States. He spent his final ten years peacefully in Northumberland County, Pennsylvania, where he continued his scientific and theological pursuits.

Enduring Legacy in Education and Philosophy

Throughout his life, Priestley remained a dedicated scholar and teacher, making significant contributions to pedagogy. His works included a seminal publication on English grammar, The Rudiments of English Grammar (1761), and numerous books on history. He also pioneered some of the most influential early timelines, such as A Chart of Biography (1765) and A New Chart of History (1769), which were highly popular and widely used educational tools.

While his educational writings enjoyed immediate popularity, it was Priestley's profound metaphysical works that exerted the most lasting influence. These texts, with their materialist psychology and associationist theories of mind, served as primary sources for the development of utilitarianism. Leading philosophers such as Jeremy Bentham, John Stuart Mill, and Herbert Spencer drew upon Priestley's ideas, particularly his understanding of human nature and motivation, to formulate their ethical theories centered on the pursuit of the greatest good for the greatest number.

Frequently Asked Questions About Joseph Priestley

What is Joseph Priestley most famous for?

Joseph Priestley is most widely recognized for his independent discovery of oxygen in 1774, which he termed "dephlogisticated air," and for his invention of carbonated water. He was also a prominent theologian and political theorist.

When did Joseph Priestley discover oxygen?

Joseph Priestley discovered oxygen on August 1, 1774, by heating mercuric oxide. Although Carl Wilhelm Scheele had isolated it earlier, Priestley was the first to publish his findings.

What was "dephlogisticated air"?

"Dephlogisticated air" was the name Joseph Priestley gave to oxygen. He believed that this gas was air that had been stripped of phlogiston, a hypothetical substance thought to be released during combustion, making it exceptionally effective at supporting burning and respiration.

Why was Joseph Priestley forced to leave England?

Joseph Priestley was forced to flee England in 1791 due to his outspoken support for the French Revolution and his dissenting religious views (Unitarianism). These beliefs sparked public outrage, leading to the "Birmingham Riots" where a mob burned his home, laboratory, and church.

What was Priestley's connection to Unitarianism?

Joseph Priestley was a key figure in the establishment and early development of Unitarianism in England. He strongly advocated for religious toleration and the rights of religious Dissenters, promoting Unitarian theology which rejects the Trinity and emphasizes the oneness of God.

How did Priestley influence utilitarianism?

Priestley's metaphysical works, particularly his materialist view of the mind and his theories on human psychology, laid foundational groundwork for utilitarianism. Philosophers like Jeremy Bentham and John Stuart Mill drew upon his ideas about human motivation and the association of ideas when developing their ethical frameworks centered on maximizing pleasure and minimizing pain.