Pierre Louis Dulong (1785-1838), French chemist. Dulong was born and educated at Rouen before moving to Paris to study at the Ecole Polytechnique. He enrolled as a medical student, but later moved into chemistry as the assistant to Thenard. In 1812 he discovered the dangerously unstable explosive nitrogen trichloride, losing an eye and two fingers in the process. From 1815 he worked with A.T. Petit on thermometry; and in 1819 they published Dulong and Petit's Law. This stated that the specific heat capacity of a solid element when multiplied by its atomic weight, gives a constant which they called the atomic heat. The law is only approximately observed, but it had some use in estimating atomic weights for new metals. Dulong succeeded Petit as professor of physics at the Ecole Polytechnique, where he taught until shortly before his death.