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Joseph Priestley (1733 - 1804)

Portrait Joseph Priestley

Joseph Priestley by Ellen Sharples (1794)

Joseph Priestley was the eldest son of Jonas Priestley, a wool trader, and his first wife, Mary. The family lived in Birstall in the West Riding of Yorkshire. The Priestley's had six children over the same number of years. Joseph was sent to live with his grandfather when he was just one year old, only returning to the family home in 1739, aged six, following the death of his mother.

Two years later Jonas Priestly married for a second time and Joseph, now aged eight, was sent to live with his aunt, Sarah Priestley Keighley and her husband. Joseph's uncle died in 1745 but Joseph remained with his Aunt Sarah. Sarah Keighley was a wealthy widow, having been left money and property on the death of her husband.

Religion played an important part in Joseph Priestley's life from an early age. The Priestley's were Calvinist Dissenters. These were people who rejected the Church of England and adhered to the austere teachings of John Calvin. Sarah Keighley's ambition was that Joseph would become a minister of the Calvinist church and she made sure that he received a good, all-round education. He attended the best local school and had a private tutor at home. In 1749 Joseph Priestley was struck by a serious illness. Although he recovered (against all expectations) he was left with a permanent stutter.

Joseph's private tutor, Reverend George Haggerstone, instructed him in mathematics and Natural Philosophy. Joseph was also a talented linguist having been taught Latin, Greek and Hebrew in school and self-taught in French, Italian, German and Arabic. Priestley entered Daventry Dissenting Academy in Northampton in 1752 to study theology. He rejected Calvinism (much to the dismay of his Aunt Sarah who would have nothing more to do with him) and became a Rational Dissenter. Rational Dissenters rejected a church based on tradition and authority and believed in a benevolent God as opposed to Calvin's vengeful deity. (Later in life, around 1773, Priestley was one of the founders of the Essex Street Chapel, a Unitarian Church in London).

After his graduation, Priestley worked as a Unitarian Minister, first in Suffolk and then in Cheshire. After successfully founding a school in Nantwich, Cheshire, he was offered a teaching post at Warrington Academy in Lancaster in 1761 to teach modern languages. The following year Priestley was both ordained and married. His wife was Mary Wilkinson, daughter of the industrialist Isaac Wilkinson and brother of the iron master, John. Mary gave birth to their first child, a daughter, named Sarah after Priestley's Aunt Sarah, in 1763.

Warrington life provided Priestley with intellectual stimulation and the opportunity to pursue his interest in Natural Philosophy. His encounter with Benjamin Franklin in London in 1765 encouraged Priestley to complete his publication 'History of Present State of Electricity with Original Experiments'. Priestley's work so impressed the scientists of the day that he was a fellow of the Royal Society in 1766.

Priestley and his family moved to Leeds in 1767 where he took up the ministry at Mill Hill Chapel. During their time in Leeds the Priestley's added two sons to their family, Joseph in 1768 and William in 1771. Priestley continued his experiments and presented five papers to the Royal Society over the next three years. He was an experimental scientist first and foremost, prioritizing facts over hypotheses. Priestly discovered that carbon conducts electricity and made the distinction between conductors and non-conductors of electricity.

The Priestley's house in Leeds was close to a brewery and Joseph Priestley became interested in carbon dioxide gas that was given off during the fermentation process. He bubbled carbon dioxide through water and produced soda water. It was mistakenly believed that soda water could prevent scurvy and it was taken, in quantity, on Captain James Cook's second voyage to the Antipodes. It was for an entrepreneur, a certain Johann Jacob Schweppe, to realise the potential of soda water a fizzy drink! Priestley's work on soda water earned him the Royal Society Copely medal.

In 1773 the Priestley family was on the move again, this time to Calne in Wiltshire. This move was by invitation of William Petty, Earl of Shelburne. Priestley was employed as a tutor for the Petty children and as librarian in Bowood House, the Shelburne residence. It was during their time at Calne that their third son, Henry, was born in 1777.

Priestley made his most important scientific discoveries under the employ of Lord Shelburne. He devised experiments to produce and to isolate ten different gases (that he termed 'airs'). Priestley's success was in part due to his designs of simple, easy to use apparatus. He ingeniously collected gases over mercury rather than water which meant that water-soluble gases could be isolated. Three of the gases Priestley produced and isolated were

  • NO (nitric oxide) that he called 'nitrous air'

  • HCl (hydrogen chloride gas) that he called 'acid air'

  • NH4 (ammonia) that he called 'alkaline air'

He concluded that there were three types of 'air' - fixed, alkaline and acid. However, Priestley was immovable in his adherence to the theory of phlogiston. This theory that dated from 1667, stated that anything that could be combusted (burnt) contains an ethereal-like substance called phlogiston. When combustion was complete it meant that all the phlogiston had been released into the air. Phlogiston had no substance - as one proponent described it, it could not be 'put in a bottle'.

In 1774 Priestley produced an unknown 'air' by hearting red mercury oxide in a vacuum and collecting the gas over mercury. This 'new' gas allowed a candle to burn brighter and supported the life of a mouse for longer than the same amount of atmospheric air would have done. Priestley even tried inhaling the gas himself (presumably after his experiment with the mouse!). He called this 'new' air 'dephlogisticated air' since it supported combustion five to six times better than atmospheric air (so, in his view, could not contain any phlogiston).


In fact a scientist named Carl Wilhelm Scheele was the first to discover oxygen, three years before Priestley, in 1772 but he did not publish his work until three years after Priestley had done so.


Later in 1774 Priestley accompanied Lord Shelburne on a tour around Europe. He met Antoine Lavoisier in Paris and shared his findings about the 'new' air. Lavoisier repeated Priestley's experiments and the results these provided allowed him to make sense of the results from his own investigations. Rejecting the phlogiston theory, Lavoisier recognised the 'new' gas as an element and named it oxygen (from the Greek meaning 'acid forming'). These different conclusions led to a lengthy dispute between the two researchers.

Although he was incorrect in promoting the phlogiston theory, Priestly did make important observations regarding air and oxygen. He was the first to realise the connection between air and the blood vascular system and he proved by experiment that plants give out oxygen in sunlight (photosynthesis).

In 1779 the Priestley's moved to Fair Hill, Birmingham by the suggestion of John Wilkinson. There had been a break up in the friendship between Joseph Priestley and Lord Shelburne. The reason for this break up is uncertain but it may have been something to do with Lord Shelburne's recent marriage to his second wide, Lady Louisa Fitzpatrick who considered Priestly too middle class and did not appreciate his religious views. The Priestley's spent ten years in Birmingham where Joseph Priestley was minister at the New meeting Chapel. Priestley became a member of the Lunar Society, a group of intellectuals that included Matthew Boulton, James Watt, Josiah Wedgewood and Erasmus Darwin.

Priestley religious views were politically extremely controversial. His publication entitled 'History of the Corruptions of Christianity' was banned in England. He was an outspoken advocate of both the American Civil War and the French revolution. As a Rational Dissenter he spoke out for the 'destruction of all earthly regimes' and he circulated seditious pamphlets around Birmingham. His views were not popular with the government and many of the population. This culminated in riots (known as the Priestley riots) on 14th July 1791 that resulted in his house, laboratory and the New Meeting Chapel being burnt to the ground. The Priestly family escaped to Hackney near London where they lived until their move to America.

Preistley Riots

Rioters Burning Dr. Priestley's House in Birmingham in 1791
by Johann Eckstein

In 1794, aged sixty one, Joseph and Mary Priestley moved to America to join two of their sons, Joseph and Henry, who had emigrated the previous year. The Priestley's made their home in Northumberland, Pennsylvania to be near their sons. Mary Priestly died in 1796 before their house, that included a laboratory, had been completed. Priestley continued to minister and spent a few weeks in Philadelphia each year to conduct morning services. Some of his influential friend and acquaintances during this time were John Adams, Benjamin Franklin and Thomas Jefferson. George Washington was a visitor to his home in Pennsylvania.

Joseph Priestley's health gradually declined during the last four years of his life and he died at his home in 1804. He was buried in Riverview Cemetery in Northumberland, Pennsylvania.


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