On August 1,1774, Joseph Priestly, a British clergyman and author, discovered oxygen. Priestley maintained a scientific lab where he studied the composition of gases. In a series of experiments, Priestley found that “air is not an elementary substance,” as it was thought but a mixture of gases. Because of his friendship with men like Benjamin Franklin and John Adams, some Englishmen set fire to his laboratory. Priestley then moved to the U.S., settling in Pennsylvania.
