Joseph Priestley. Coloured engraving of Joseph Priestley (1733-1804), British chemist. Priestley began by inventing soda water using 'fixed air' (carbon dioxide). He discovered 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. He also discovered that animals consume oxygen and plants produce it. A religious and political radical, Priestley emigrated to America in 1794 to satisfy his need for intellectual and spiritual freedom.