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Francois Marie Raoult

1911 Encyclopedia Britannica

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FRANCOIS MARIE RAOULT (1830-1901), French chemist, was born at Fournes, in the Departement du Nord, on the 10th of May 1830. He became aspirant repetiteur at the lycee of Rheims in 1853, and after holding several intermediate positions was appointed in 1862 to the professorship of chemistry in Sens lycee, where he prepared the thesis on electromotive force which gained him his doctor's degree at Paris in the following year. In 1867 he was put in charge of the chemistry classes at Grenoble, and three years later he succeeded to the chair of chemistry, which he held until his death on the 1st of April 1901. Raoult's earliest researches were physical in character, being largely concerned with the phenomena of the voltaic cell, and later there was a period when more purely chemical questions engaged his attention. But his name is best known in connexion with the work on solutions, to which he devoted the last two decades of his life. His first paper on the depression of the freezing-points of liquids by the presence of substances. dissolved in them was published in 1878; and continued investigation and experiment with various solvents, such as benzene and acetic acid, in addition to water, led him to believe in a simple relation between the molecular weights of the substances and the freezing-point of the solvent, which he expressed as the "loi generale de la congelation," that if one molecule of a substance be dissolved in loo molecules of any given solvent, the temperature of solidification of the latter will be lowered by 0.63° C. (See, however, the article Solution.) Another relation at which he worked was that the diminution in the vapour-pressure of a solvent, caused by dissolving a substance in it, is proportional to the molecular weight of the substance dissolved - at least ' when the solution is dilute. These two generalizations not only afforded a new method of determining the molecular weights of substances, but have also been utilized by J. H. van't Hoff and W. Ostwald, among other chemists, in support of the hypothesis of electrolytic dissociation in solutions. An account of Raoult's life and work was given by Professor van't Hoff in a memorial lecture delivered before the London Chemical Society on the 26th of March 1902.