Engraving made in 1801 by Caldwell after a painting by Opie and David showing portraits of English-American theologian and chemist Priestley (1733-1804), and French chemist Lavoisier (1743-1794). Priestley discovered various gaseous elements and compounds, and in an experiment in 1774 obtained a gas which he named 'dephlogisticated air'. This was in fact oxygen, although it was not named thus until Lavoisier repeated Priestley's experiment. Lavoisier is considered to be the founder of the modern science of chemistry. His major work, the 'Traite elementaire de Chimie' (1789), contained many of the ideas that set chemistry on its modern path. He was also a member of the commission which devised the metric system.
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