Joseph Priestley: The man who discovered Oxygen

One of the founding fathers of chemistry, Joseph Priestley (1733-1804) stumbled across photosynthesis, is credited with the discovery of oxygen and accidentally brought us soda water. He was also a member of BRLSI's predecessor, the Bath Philosophical Society.

Joseph Priestley (picture: Wikipedia)

2004 marked the two hundredth anniversary of the death of Joseph Priestley one of the most influential and colourful scientists of the eighteenth century. He had a Bath connection since he was a member of the Bath Philosophical Society, a forerunner of the BRLSI, when he lived and worked at Bowood House in Calne, Wiltshire. There he was the librarian and scientific guru for Lord Shelburne, the 1st Marquis of Lansdowne, and it was here that he first identified oxygen. It is for this discovery that he is best remembered today.

Priestley was born in Birstal Fieldhead near Leeds in 13th March 1733, the eldest son of a cloth-dresser. His mother died when he was seven years old and his aunt mainly brought him up. He was educated for the dissenting ministry and spent much of his life both as a teacher and a preacher. Priestley was a true polymath, writing books and articles on theology, history, education, aesthetics and politics as well as science. During his lifetime he was as well known for his views on theology and politics as for his work in science.

Priestley married Mary Wilkinson in 1762. She was the daughter of Isaac and sister to John and William Wilkinson. All three men were prominent iron masters in the eighteenth century.

His scientific interests began around the middle of the 1760s. It was during this time that he began to write his book History and Present State of Electricity. For this work he received the help from several people. These included Benjamin Franklin (The American academic, politician and scientist who was present at the signing of the American Declaration of Independence), William Watson (An apothecary who lived in Bath and was also a member of the Bath Philosophical Society; he was also a friend of William Herschel) and John Canton (Another scientist born in the West country at Stroud in Gloucester in whose honour the Institute of Physics recently erected a blue plaque on his schoolhouse in Stroud).

While writing the book he carried out several experiments. Among them was an ingenious demonstration of the inverse square law of electrostatics. This is generally known as Coulomb's law but the work of Priestley in fact predates that of Coulomb by nearly twenty years. Mainly as a result of his work on electricity, he was elected to Fellowship of the Royal Society in 1766.

In part as a result of financial problems stemming from his increasing family responsibilities, Priestley resigned a teaching position that he had to become the minister of Mill-Hill Chapel, which was a major Presbyterian congregation in Leeds. It was here that he completed History and Present State of Electricity (1767) and also wrote the History of Optics (1772). While living and working in Leeds he became a founder member of the Leeds Library, becoming both its Secretary and later President. In 1989 the Leeds Library was prominent in setting up the Association of Independent Libraries, to which the BRLSI also belongs.

The Leeds Library holds important archival material on Priestley's time there. It was while he was in Leeds that he began his most important scientific researches namely those connected with the nature and properties of gases. A bizarre consequence of this is that Priestley can claim to be the father of the soft drinks industry. He found a technique for dissolving carbon dioxide in water to produce a pleasant "fizzy" taste. Over a hundred years later Mr Bowler of Bath benefited from this when he formed his soft drinks industry.

Discovery of Oxygen

Priestley entered the service of the Earl of Shelburne in 1773 and it was while he was in this service that he discovered oxygen. In a classic series of experiments he used his 12inch "burning lens" to heat up mercuric oxide and observed that a most remarkable gas was emitted. In his paper published in the Philosophical Transactions of the Royal Society in 1775 he refers to the gas as follows: "this air is of exalted nature…A candle burned in this air with an amazing strength of flame; and a bit of red hot wood crackled and burned with a prodigious rapidity, exhibiting an appearance something like that of iron glowing with a white heat, and throwing sparks in all directions. But to complete the proof of the superior quality of this air, I introduced a mouse into it; and in a quantity in which, had it been common air, it would have died in about a quarter of an hour; it lived at two different times, a whole hour, and was taken out quite vigorous."

Although oxygen was his most important discovery, Priestley also described the isolation and identification of other gases such as ammonia, sulphur dioxide, nitrous oxide and nitrogen dioxide.

By 1780 the working relationship between Priestley and the Earl of Shelburne had cooled somewhat and he decided to move with his family to Birmingham, where he became preacher at the New Meeting House. This was one of the most liberal congregations in England. For Priestley his time at Birmingham was among the happiest in his life.

He soon became involved with the Lunar Society - a small group of academics, scientists and industrialists with wide ranging interests who were prominent in spearheading the Industrial Revolution in England. The Lunar Society was so named because its members met at full moon thereby facilitating travelling home in the dark after the meetings. Fellow members of the Lunar Society included Matthew Boulton, Erasmus Darwin (grandfather of Charles and also a pioneer in the theory of evolution), James Watt and Josiah Wedgwood.

Although Priestley played an active role in the Lunar Society his interests turned more and more towards theology. He became an active dissenter with outspoken criticism of the established church. These were dangerous times to be alive with the French Revolution (1789-91), which Priestley supported, sending shock waves around Europe. In 1791 on the second anniversary of the storming of the Bastille a "Church and King" mob in Birmingham destroyed the New Meeting House as well as Priestley's house and laboratory. He barely escaped with his life and most of his equipment and records were lost. Priestley briefly joined a dissenting group in London at Hackney but after renewed vitriol against him and his family he emigrated to the United States of America in 1794.

He was warmly welcomed in America and offered the chair of chemistry at the University of Pennsylvania, which had been founded by Benjamin Franklin. Priestley declined and settled in Northumberland, Pennsylvania in an area intended for British émigrés fleeing political persecution. He was befriended by Thomas Jefferson, who became President of the United States in 1800. However, Priestley's final years were sad and lonely; his favourite son died in 1795 and his wife a year later. He himself died on the 5th February 1804 aged seventy-one and is buried in Northumberland where his house has now been turned into a museum.

Priestley should be included in any pantheon of scientists. The bicentenary of his death is an opportune time to reassess his life and work and several events are planned during the year. He possessed enormous scientific skills and originality of thought as well as having the courage to promote unpopular views. He was a man of rare insight and talent.

Dr Peter J. Ford
Department of Physics, University of Bath

Jan. 2004