Lavoisier, Antoine-Laurent (1743-1794), a French chemist. By 1777 Lavoisier had concluded that combustion, or burning, is the chemical union of the burning substance with a gas that he named oxygen. This theory soon overthrew the earlier phlogiston theory of combustion. Lavoisier was one of the first chemists to recognize the importance of accurately weighing the substances used in experiments. He extended and reinterpreted the work of earlier chemists and is considered the founder of modern chemistry.

Lavoisier's research led him to explain the role of combustion in the respiration of animals and plants. Experiments with guinea pigs convinced him that body heat is produced by the slow combustion of food. These studies helped lay the foundation for the study of metabolism. Through experiments on humans, Lavoisier determined that carbon dioxide and water are given off during respiration. Lavoisier also investigated problems of heat, fermentation, and the liquefaction of gases. In 1787 he published an improved system for naming elements and compounds, and in 1789 he reclassified the elements.

Lavoisier was the son of a wealthy merchant. He studied astronomy, botany, chemistry, geology, and mathematics at the Collge Mazarin in Paris, where he graduated in 1763. In 1768 he was admitted to the Academy of Sciences, and later served as its director (1785) and treasurer (1791). His activities were never limited to chemistry—he was active in local government and in education and agriculture, and served as a tax collector. At the height of the French Revolution's Reign of Terror Lavoisier was unjustly accused of cheating the government. He was tried, convicted, and guillotined the same day.