François-Marie Raoult

François-Marie Raoult (10 May 1830 – 1 April 1901) was a French chemist who conducted research into the behavior of solutions, especially their physical properties.

Life and work
Raoult was born at Fournes, in the département of Nord. He became aspirant répétiteur at the Lycée of Reims in 1853, and after holding several intermediate positions was appointed in 1862 to the professorship of chemistry in Sens lycée. There he prepared a thesis on electromotive force which gained him a doctor's degree in Paris the following year.

In 1867 Raoult was put in charge of chemistry classes at the University of Grenoble, and three years later he succeeded to the chair of chemistry, which he held until his death in 1901. Raoult's earliest researches were physical in character, being largely concerned with the phenomena of the voltaic cell; later there was a period when more purely chemical questions engaged his attention.

Raoult's name is best known in connection with work on solutions, to which he devoted the last two decades of his life. His first paper describing how solutes depressed the freezing points of solutions was published in 1878. Further experiments 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 a solute and the freezing-point of a solution. He expressed the relationship as the loi générale de la congélation (general law of freezing), that if one molecule of a substance be dissolved in 100 molecules of any given solvent, the temperature of solidification of the latter will be lowered by 0.63 °C. Another relation on which Raoult worked was that concerning the depression of a solvent's vapor pressure, due to a solute, showing that the decrease is proportional to the solute's molecular weight. This relationships holds best in the limiting case of a dilute solution. Note:
 * Raoult first stated his law in terms of the reduction of the freezing points of solutions:
 * 1)  F.-M. Raoult (1882) "Loi de congélation des solutions benzéniques des substances neutres" (Law of freezing of solutions of neutral substances in benzene), Comptes rendus, 95 :  187-189.  From p. 189:  "Il est donc permis de dire, dès à présent:  Dans une multitude de cas, l'abaissement du point de congélation d'un dissolvant ne dépend que du rapport entre le nombres de molécules du corps dissous et du dissolvant; il est indépendant de la nature, du nombre, de l'arrangement des atomes qui composent les molécules dissoutes."  (It is thus allowable to say, as of now:  In the multitude of cases, the lowering of the freezing point of a solvent depends only on the relation between the number of molecules of the dissolved substance and of the solvent; it is independent of the nature, number, [or] arrangement of the atoms composing the dissolved molecules.)
 * 2)  In his next paper, Raoult specified (p. 1033) that in a solution containing one mole of solute per 100 moles of solvent, the freezing point is reduced by 0.62 °C, regardless of the nature of solute or solvent.  See:  F.-M. Raoult (1882) "Loi générale de congélation des dissolvants" (General law of the freezing of solvents), Comptes rendus, 95 :  1030-1033.  English translation available on-line at:  Le Moyne College
 * Raoult later stated his law in terms of the reduction of the vapor pressures of solutions:
 * 1)  F.-M. Raoult (1887) Loi générale des tensions de vapeur des dissolvants" (General law of vapor pressures of solvents), Comptes rendus, 104 :  1430-1433.
 * 2)  This reduction in vapor pressure had been predicted, via thermodynamic calculations, by two investigators:
 * Güldberg (1870) "Sur la loi des points de congélation des solutions salines" (On the law of freezing points of saline solutions), Comptes rendus, 70 : 1349-1352.
 * J. H. van 't Hoff (1885) "Lois de l'équilibre chimique dans l'état dilué, gazeux ou dissous" (Laws of chemical equilibrium in the dilute state, gaseous or in solution), Kongliga Svenska Vetenskaps-Akademiens Handlingar (Royal Swedish Science Academy Proceedings),  21 (17) : 1-42.  A condensed version of this article is available in English:   J. van't Hoff  (August 1888) "The function of osmotic pressure in the analogy between solutions and gases," Philosophical Magazine, 5th series, 26 :  81-105.  These two generalizations afforded a new method of determining the molecular weights of dissolved substances, and were  utilized by Jacobus van 't Hoff and Wilhelm Ostwald, among other chemists, in support of the hypothesis of electrolytic dissociation in solutions.  Raoult's freezing-point depression method became even more useful after it was improved by Ernst Otto Beckmann and became a standard technique for determining molecular weights of organic substances.

An account of Raoult's life and work was given by van 't Hoff in a memorial lecture delivered before the London Chemical Society on 26 March 1902.

Activities and honors

 * Prix International de Chimie LaCaze (1889)
 * Davy Medal (1892)
 * Prix de l'Institut (1895)
 * Commandeur de la Légion d'Honneur (1900)