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24.03.2017 | Famous Chemists In History: Joseph Priestley (1733-1804)

Joseph Priestley

Few concepts "have laid firmer hold upon the mind," he wrote, than that air "is a simple elementary substance, indestructible and unalterable."
Joseph Priestley may not seem like a familiar name off the bat, but his contributions to science are monumental. Credited with the discovery of oxygen in 1774, Priestley found that "air is not an elementary substance, but a composition," or mixture, of gases." He found a colorless and highly reactive gas which he deemed "dephlogisticated air," or as it was dubbed later, oxygen.
His most famous experiment was conducted on August 1, 1774. He used a glass "burning lens" to focus sunlight on a lump of reddish mercuric oxide contained an inverted glass, and placed in a pool of mercury. He found that the gas emitted was "five or six times as good as common air." Successive testing found that it caused a flame to burn intensely, and "kept a mouse alive about four times as long as a similar quantity of air."

Through his experiments, Joseph Priestley was able to answer one of the many questions that had boggled scientists at the time: How and why do things burn?
Although his most famous discovery was oxygen, Joseph Priestley is famed for many other discovers. He isolated and characterized eight other gases. These included ammonia, sulphur dioxide, nitrous oxide and nitrogen dioxide. Priestly was also the creator behind carbonated water. He dubbed it "mephetic julep" and hoped that it would be of use for sailors undertaking long voyages to prevent scurvy.
He also invented the rubber eraser, and wrote an important paper early on about electricity which was encouraged by his friend, Benjamin Franklin.

A deep lover of politics, and known for being a Liberal political theorist, he also wrote heavily on these topics. In fact, his unorthodox writings, coupled with his ardent support for the American and French revolutions meant he was shunned by many his countrymen and was forced to flee England.
In 1794, he settled in Pennsylvania to continue his research. Although he was offered a position at University of Pennsylvania, founded by his friend Benjamin Franklin, Priestley refused. Instead he chose to live in Northumberland, Pennsylvania and continue his research. Although he never became an American citizen, he was close friends with both Thomas Jefferson and John Adams. Thomas Jefferson expressed that he saw Priestley as "one of the few lives precious to mankind."

Joseph Priestley continued his scientific work while settled in Pennsylvania, with his wife and son until his death in 1804.