An Etymological Dictionary of Astronomy and Astrophysics
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The product of the → specific heat and → atomic weight of most solid elements at room → temperature is nearly the same. In other words, specific heat is constant for a solid and independent of temperature. Experiment shows that at moderate temperatures this law is satisfied for → crystals with rather simple structure. However, the law fails for crystals with more complex structures. More specifically the law cannot explain the variation of specific heat with temperature. The specific heat drops to zero as the temperature approaches 0 K. This behavior is explained only with the quantum theory. → Debye model.

Named after Pierre L. Dulong (1785-1838) and Alexis T. Petit (1797-1820), French chemists, who proposed the law in 1819. They collaborated in several important investigations, including studies of thermal expansion of gases and of liquids and the specific heats of substances; → law.