Dulong, Pierre (1785-1838)

French chemist and physicist. In 1819 he discovered, together with physicist Alexis Petit, the law that now bears their names. Dulong and Petit's law states that, for many elements solid at room temperature, the product of relative atomic mass and specific heat capacity is approximately constant. He also discovered the explosive nitrogen trichloride 1811. Dulong concluded 1829 that, under the same conditions of temperature and pressure, equal volumes of all gases evolve or absorb the same quantity of heat when they are suddenly expanded or compressed to the same fraction of their original volumes. He also deduced that the accompanying temperature changes are inversely proportional to the specific heat capacities of the gases at constant volume. Dulong was born in Rouen and studied medicine at the Ecole Polytechnique in Paris. He was professor of chemistry at Paris 1820-30, and then director of studies at the Ecole Polytechnique. He collaborated with Petit 1815-20, and continued on his own to work on specific heat capacities, publishing his findings in 1829.