Joseph Priestley

In the 18th century the great British scientist Joseph Priestley helped found the science of chemistry, and discovered several important gases. He was also one of the first people in history to understand the importance of conducting experiments.

A RELIGIOUS BACKGROUND

Joseph was born on March 13, 1733, in Fieldhead, Yorkshire. His father was a Calvinist minister, and his mother died when he was seven. He was brought up by his equally religious aunt, but because he was a sickly child he received little education. Both Joseph’s parents and his aunt had wanted him to become a religious minister in the Dissenting Church, which was made up of various churches that had separated from the Church of England. He seemed destined for this life when he entered the Dissenting Academy at Daventry, Northamptonshire, at the age of 19. Joseph questioned much of the religious teaching there, but he later served at ministries at Needham Market in Suffolk from 1755 to 1758, and at Nantwich in Cheshire from 1758 to 1761. Later he became a teacher at the Warrington Academy in Lancashire, where he helped to create practical courses for students planning to enter industry and commerce, and not the Church. He was ordained a minister in the Dissenting Church in 1762.

Joseph Priestley had not been educated in science but he had always shown an interest in the subject, and throughout his years in the Church this interest grew.

SCIENCE IN THE 18TH CENTURY

This period in history was known as the Age of Enlightenment. There was a growing interest in science, but little had been discovered. For hundreds of years before this time, many people had attempted to discover more about chemical compounds and reactions, but they were hardly scientists or chemists as we now think of them. They were known as “alchemists” and they studied alchemy, which was a combination of science, art and magic. Alchemists believed that the world was made up of four “elements” known as earth, air, fire and water, and that these four contained something called phlogiston, a substance produced during a process known as combustion, or burning. Priestley also believed in phlogiston and wanted to know more about it.

In the mid-1760s Priestley began attending a series of lectures being given in London by some of the greatest names in science. In 1766 the American statesman and scientist Benjamin Franklin encouraged Priestley to conduct experiments in the new science of electricity. The following year, Priestley wrote a history of electricity, and also discovered that charcoal can conduct electricity. In 1767 he became a minister at Leeds in Yorkshire, and began research on gases. His innovative experimental work resulted in his election to the French Academy of Sciences in 1772. He was also employed as a librarian and literary companion to William Petty Fitzmaurice, 2nd Earl of Shelburne. This arrangement allowed Joseph the time and money to be able to continue with his experiments.

PRIESTLEY’S DISCOVERIES

On August 1, 1774, Priestley was heating red mercury oxide when he obtained a colourless gas in which a candle would burn with a “remarkably vigorous flame”. Priestley had discovered the gas oxygen. He realized that this gas was a component of ordinary air and he then attempted to investigate its role in combustion and in respiration (breathing). He discovered that plants produce oxygen.

Priestley believed in the phlogiston theory and called the new gas “dephlogisticated air”. He had not completely understood the future importance of his discovery. Nor had he realized that oxygen was a separate chemical element. His discovery was still a great breakthrough though, and he had begun the revolution that established modern chemistry. However, it was French chemist Antoine Lavoisier who became the first person to isolate and name the element as oxygen a few years later. Lavoisier also correctly described its role in combustion and respiration. Priestley disagreed with Lavoisier’s view throughout his life and continued to believe in phlogiston.

Later, Priestley isolated and described the properties of several other gases, including ammonia, nitrous oxide, sulphur dioxide and carbon monoxide.

POLITICS, SCIENCE AND RELIGION

In 1780, Priestley fell out with the Earl of Shelburne because of religious and political differences, and he became a minister in Birmingham. Priestley was becoming very radical in his religious thinking and was now turning towards Unitarianism, which rejected most of the basic doctrines of Christianity. His book, History of the Corruptions of Christianity (1782), was considered so dangerous that it was officially burned in 1785. Because of his open support of the French Revolution, and his belief in religious and political freedom, his house and laboratory were destroyed by a mob in 1791. He left Birmingham and went to live in London where he believed he would be safe.

In 1794 Joseph emigrated to the United States, which had only recently achieved independence and freedom from Britain in the American War of Independence. While there he freely pursued his religious, political and scientific writing for the remainder of his life.

Priestley died in Northumberland, Pennsylvania, on February 6, 1804.

Did you know?

• In olden times pencil errors were rubbed out using balls of moist bread. It was Joseph Priestley who discovered that rubber can be used to erase pencil marks.

• Priestley was a member of the Lunar Society, the 18th-century group of thinkers and inventors that met at each other's homes in or near Birmingham at the time of a full moon. Its members contributed to the progress of the Industrial Revolution and the Enlightenment through discussion, correspondence, mutual support, observation and experiment.

• The Swedish chemist Carl Wilhelm Scheele may have discovered oxygen in 1773, a year before Joseph Priestley, but he did not make his work known in time to be credited with its discovery.

• In 1772, while living next door to a brewery, Joseph invented soda water. It is used as the basis for the soft drinks industry.

• Priestley discovered eight different gases in his life, more than any other scientist in history has done.