Pierre Louis Dulong (February 12, 1785 - July 19, 1838) was a French physicist and chemist, remembered today largely for the law of Dulong and Petit. He worked on the specific heat capacity and the expansion and refractive indices of gases. In chemistry, he contributed to knowledge on: the double decomposition of salts (1811), nitrous acid (1815), the oxides of phosphorus (1816), the oxides of nitrogen and catalysis by metals (1823, with Th矇nard). Dulong also discovered the dangerously sensitive nitrogen trichloride in 1812, losing two fingers and an eye in the process. In 1819 Dulong collaborated with Petit to show that the mass heat capacity of metallic elements are inversely proportional to their atomic masses, this being now known as the Dulong-Petit law. Dulong worked on the elasticity of steam, on the measurement of temperatures, and on the behavior of elastic fluids. He made the first precise comparison of the mercury and air-temperature scales. At the time of his death, he was working on the development of precise methods in calorimetry. He is one of the names of 72 scientists inscribed on the Eiffel Tower.