Regnault, Henri Victor (1810–1878)

German-born French physical chemist who showed that Boyle's law applies only to ideal gases. He also invented an air thermometer and a hygrometer, and discovered carbon tetrachloride (tetrachloromethane).

Regnault was born in Aachen and studied in Paris at the Ecole Polytechnique and the Ecole des Mines as well as in various parts of Europe. He returned to the Ecole Polytechnique in 1836 as an assistant to Joseph Gay-Lussac and in 1840 succeeded him as professor of chemistry. He became professor of physics at the Collège de France in 1841. From 1854 Regnault was director of the porcelain factory at Sèvres. During the Franco-Prussian war, his son was killed, and Prussian soldiers destroyed his books and instruments. He never recovered from these losses.

In chemistry, Regnault studied the action of chlorine on ethers, leading to the discovery of vinyl chloride (monochloroethene), dichloroethylene (dichloroethene), trichloroethylene (trichloroethene), and carbon tetrachloride (tetrachloromethane).

In 1842 Regnault was commissioned to redetermine all the physical constants involved in the design and operation of steam engines. This led him to study the thermal properties of gases. He measured the coefficients of expansion of various gases and by 1852 had shown how real gases depart from the behaviour required by Boyle's law.

Regnault also calculated that absolute zero is at −273°C/−459°F. He redetermined the composition of air, and performed experiments on respiration in animals.