Joseph Priestley (1733-1804), English chemist and Presbyterian minister. Priestley isolated and examined many new gases including hydrogen chloride, nitrous oxide, ammonia, nitrogen and carbon monoxide. He was also the first to isolate oxygen but did not correctly recognize its role in combustion, believing instead that it played a part in the 'phlogiston' (combustible element) theory. However, he did discover oxygen's role in respiration, showing that animals consume oxygen and plants produce it. A Unitarian minister and political radical, Priestley's chapel and house in Birmingham were sacked by a mob in 1791 because of his support for the French Revolution. Painted by James Sharples c. 1797.