Joseph Priestley was an English theologian, philosopher, chemist, and educator who is best known for his discovery of oxygen. He was born on March 13, 1733, in Birstall Fieldhead, England, and died on February 6, 1804, in Northumberland, Pennsylvania.
Priestley was a prolific writer and researcher who published over 150 works in a variety of fields, including theology, history, and science. He was particularly interested in the study of gases and conducted extensive experiments on the properties of air.
In 1774, Priestley discovered oxygen while conducting experiments on the properties of air. He observed that a candle burned more brightly in a closed container of air, and that a mouse placed in the same container lived longer than a mouse in a container without air. He concluded that there was a gas in the air that supported combustion and respiration, which he called "dephlogisticated air."
Priestley's discovery of oxygen was a major breakthrough in the field of chemistry and laid the groundwork for the development of modern theories of combustion and oxidation. He also discovered several other gases, including nitrogen dioxide and ammonia, and made important contributions to the study of photosynthesis.
In addition to his work in science, Priestley was a noted theologian and political thinker. He was a proponent of Unitarianism, an influential religious movement that rejected the doctrine of the Holy Trinity, and he was also an advocate for political reform and religious toleration.
Priestley's scientific and philosophical contributions continue to be studied and celebrated today, and he is widely regarded as one of the most important thinkers of the 18th century.