Pierre Louis Dulong (12.02.1785-19.07.1838) was a French physicist and chemist, a member of the Paris Academy of Sciences (1823) and its president (1828). He was born in Rouen. In 1801-03 he studied at the École Polytechnique. In 1811—20 he worked at the École Normale and at the Veterinary School in Paris. From 1820 he was professor at the University of Paris and in 1920—30 at the École Polytechnique.
His work in physics concerned heat. Together with A. Petit he established in 1819 that the product of the specific heat capacity and the atomic weight of simple bodies in the crystalline state is an almost constant quantity (the law of Dulong and Petit). He studied the thermal conductivity and the elasticity of gases and the thermal expansion of solids, and invented (1816) the cathetometer (with A. Petit). In 1829 he calculated the heat capacity of various gases at constant volume, and in 1830 he built a water calorimeter and determined the heats of combustion of a large number of substances. He was the first to obtain nitrogen chloride and hypophosphorous acid.