Lavoisier Demonstrates Conservation of Mass

Antoine Lavoisier conducted a series of sealed-vessel combustion experiments in Paris in 1774, demonstrating that the total mass of reactants equals the total mass of products in a chemical reaction. His work, informed by Joseph Priestley's identification of a gas that vigorously supported combustion, led Lavoisier to identify oxygen as a distinct element and by 1777 to propose a new theory of combustion that displaced the phlogiston framework. The law of conservation of mass established quantitative measurement as the foundation of chemical analysis and is widely regarded as marking the beginning of modern chemistry as an exact science.