Pierre Dulong was a French chemist and physicist who, with Alexis Thérèse Petit (1791–1820), discovered Dulong and Petit's law. This states that the specific heats of elements are inversely proportional to their atomic weights (see relative atomic mass) and is equivalent to the observation that the atomic heats of most elements is about 26.4 joules per mole per kelvin (J/K.mol). Dulong also discovered the explosive nitrogen trichloride.