REGNAULT, HENRI VICTOR French chemist and physicist, was born on July 21, 181o, at Aix-la Chapelle. His early life was a struggle with poverty, he worked in a drapery establishment in Paris until 1829. Then he entered the Ecole Polytechnique, and passed in 1832 to the Ecole des Mines. A few years later, after studying under Liebig (q.v.), he was appointed to a professorship of chemistry at Lyons. His most important contribution to organic chemistry was a series of researches, begun in 1835, on the halogen and other derivatives of unsaturated hydrocarbons. He also studied the alkaloids and organic acids, introduced a classification of the metals and effected a comparison of the chemical composition of atmospheric air from all parts of the world. In 184o he became professor of chemistry in the Ecole Polytechnique, Paris; he was elected a member of the Academie des Sciences, and in 1841 he succeeded Dulong (q.v.), professor of physics in the College de France. In 1847 he published a four-volume treatise on Chemistry which has been translated into many languages. Regnault's work in physics was remarkably accurate and painstaking. He designed apparatus for a large number of measurements which is the stand ard apparatus of the present.
Regnault executed a careful redetermination of the specific heats of many solids, liquids and gases. (See CALORIMETRY.) He
investigated the expansion of gases by heat, and showed that, contrary to previous opinion, no two gases had precisely the same coefficient of expansion. By delicate experiments he proved that Boyle's law is only approximately true for real gases. He studied the subject of thermometry (q.v.) critically; he introduced the use of an accurate air-thermometer, and compared its indications with those of a mercurial thermometer, determining the absolute expansion of mercury as a step in the process. He also paid atten tion to hygrometry and devised Regnault's hygrometer.
In 1854 he was appointed as director of the porcelain manufac tory at Sevres. He carried on his great research on the expansion of gases in the laboratory at Sevres, but all the results of his latest work were destroyed during the Franco-German War, in which also his son Henri (noticed above) was killed. Regnault never recov ered from the double blow, and, although he lived until Jan. 19, 1878, his scientific labours ended in 1872. Regnault's most im portant work is collected in vols. 21 and 26 of the Memoires de l'Academie des Sciences.