Born in Fieldhead, near Leeds, Joseph Priestley became a Presbyterian minister after leaving school, but became interested in chemistry in about 1770. Initially, he examined carbon dioxide liberated in breweries during fermentation, and his first scientific publication was on the impregnation of water with fixed air, creating sparkling mineral water. For this he was presented with the prestigious Copley Medal of the Royal Society.
Priestley also simplified experimental techniques for the preparation and collection of gases. His pneumatic trough of 1772 allowed gases which were soluble in water to be isolated successfully over mercury. From this he went on to prepare and study new ‘airs’ (gases). Most important was his discovery, in 1774, of ‘dephlogisticated air’ (oxygen), obtained by heating red oxide of mercury. He found that animals could survive in a given quantity five times as long as in ordinary air, and that it supported combustion vigorously.
In later life, Priestley returned to his theological roots, becoming involved in numerous controversial theological societies. After threats of attack, he fled Birmingham to London in 1791, and then emigrated to America in 1794, where he later died in Philadelphia after several serious illnesses.