Joseph Priestley | Biography

Born into a poor family in a village near Yorkshire, England, Priestley lost his mother at an early age and was sent to live with his aunt, a devout Protestant. He was educated at religious schools that endorsed nonconformist beliefs; he never formally studied science, but he did excel as a scholar of languages, logic, and philosophy. Priestley became a country preacher, but eventually turned to teaching. While employed at the Warrington Academy in the 1760s, he argued that school curriculums should reflect contemporary discoveries, rather than following outdated classical models. In 1762 Priestley married Mary Wilkinson, the sister of one of his schoolmates.

In 1766 Priestley visited London, England, and met Benjamin Franklin, who was trying to settle a dispute between the American colonies and the British government.

Soon after meeting Franklin, Priestley took over a pastorate in Leeds, England. Next door to his home was a brewery, and Priestley's scientific curiosity was aroused by the layer of heavy gas hovering over the huge fermentation vats. Priestley began experimenting with this gas, which we know today as carbon dioxide. Finding that the gas was heavier than air and that it could extinguish flames, Priestley realized he had isolated the same gas Joseph Black had designated as fixed air. Conducting various experiments with this gas, he found that when dissolved in water, a bubbly drink was produced. Priestley had invented soda water, or seltzer.

During this period Priestley also wrote a history of optics and an immensely successful history of electrical research. He discovered that carbon conducts electricity, for example, and he learned that an electrostatic charge collects on the outer surface of a charged object. As the first scientist to predict a relationship between electricity and chemistry, Priestley anticipated the new field of electrochemistry. At this time, Priestley also gave the modern name rubber to a Brazilian tree-sap product that had just been introduced to Europe. It was Priestley who told draftsmen that the material could be used to erase, or "rub out, " pencil marks on their drawings.

Soon Priestley turned to chemistry, particularly the study of gases. During the early 1770s he developed new methods of collecting gases in the laboratory and prepared several gases unknown to chemists at the time. Priestley adapted a device called the pneumatic trough, filling it with liquid mercury instead of water to obtain samples of gases. In this way, he was able to isolate gases such as sulfur dioxide, ammonia, and hydrogen chloride. (Ammonia and hydrochloric acid were known earlier, but only as liquids.)

Priestley also discovered nitrous oxide (N₂O) years before Sir Humphry Davy popularized the gas's properties. Other gases isolated and identified by Priestley include nitrogen dioxide and silicon fluoride. As a result of these accomplishments, Priestley was elected to the French Academy of Sciences.

In 1773 Priestley won a lucrative post as librarian and companion to Lord Shelburne (1737-1805), a liberal politician. Priestley and his employer both sympathized with the colonial American rebels, who were then ready to begin the American Revolution, and an essay on government published by Priestley in 1768 provided Thomas Jefferson (1743-1826) with ideas for writing the Declaration of Independence.

Priestley's most famous scientific research was done during his eight years with Lord Shelburne. Because most of the gases he had studied were created by heating various substances, Priestley obtained a large magnifying lens. In 1774 Priestley used this lens to discover oxygen. Although Swedish chemist Carl Wilhelm Scheele had discovered the gas just a few years earlier, Priestley's results were reported first, and he usually gets the credit for the discovery. Priestley found that mercuric oxide, when heated, breaks down to form shiny globules of elemental mercury, while giving off a gas with unusual properties. A smoldering ember of wood, for example, burst into flames when exposed to the gas. Also, a mouse trapped in a container of the gas became frisky and survived for a longer time than it would when trapped in ordinary air. And when Priestley inhaled the gas, he reported feeling "light and easy." Priestley realized that this same gas was produced by plants, enabling them to restore "used-up " air to its original freshness.

In keeping with the scientific theory accepted at that time, Priestley named the gas dephlogisticated air because it absorbed phlogiston so readily. Phlogiston was thought to be the substance that gives materials their ability to burn. Supposedly, during combustion, phlogiston is released from burning material and absorbed by the surrounding air or gas. When Priestley reported his findings, he unknowingly gave Antoine-Laurent Lavoisier the key to a new theory of combustion that contradicted the phlogiston theory. It was Lavoisier who later expanded on Priestley's work, re-named the gas oxygen, and explained how substances burn by combining chemically with oxygen.

While conducting his experiments, Priestley continued to speak out aggressively on political and religious issues. He not only supported the American colonists' war with England, but also sympathized with supporters of the French Revolution. Priestley's religious allegiance had shifted toward the Unitarian Church, which was also unpopular in England at the time. Priestley eventually settled in Birmingham, England, where he served as a chapel minister and joined the Lunar Society, a club of respected scientists and inventors, but in 1791 an angry "Church and King" mob retaliated against France's supporters and burned down Priestley's home and laboratory, destroying much of his research.

Priestley escaped to London, but even there, his beliefs were barely tolerated. After the French people beheaded their king, declared war on England, and offered to make Priestley a citizen, Priestley gave in to public outrage and left for America. There he became a personal friend of Jefferson and of other politicians.