Cahours, Auguste André Thomas

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Cahours, Auguste André Thomas

(b. Paris, France, 2 October 1813; d. Paris, 17 March, 1891),


Cahours’s father was a tailor on the rue de Provence in Paris. Cahours studied at the École Polytechnique from 1833 to 1835, graduating as a staff officer. He had already decided to study chemistry, however, and resigned his commission in 1836 in order to enter Chevreul’s laboratory at the Muséum d’Histoirc Naturelle as a préparateur. Cahours became docteur-és-sciences at the Faculty of Sciences in 1845 and was professor of chemistry at the École Polytechnique and the École Centrale.

At the Muséum, Cahours devoted himself, in 1839–1840, to the thorough study of potato oil, a substance analogous in composition to ethyl alcohol, which had been discovered by Scheele and analyzed by Dumas. Cahours suspected that it might well behave like a true alcohol because it was isomorphic with ethyl alcohol. Starting with only a liter of the substance, he succeeded in producing a great number of derivatives, all of which were quite analogous to the corresponding derivatives of ethyl alcohol. In this work he followed the method indicated by Dumas and Eugéne Péligot’s research on methyl alcohol (1839). He next used the research of Regnault and Faustino Malaguti on the action of chlorine on the ethers in order to study derivatives formed by substituting chlorine for hydrogen in the series, which he had named amyl.

Another important group of Cahours’s researches concerned abnormal vapor densities. He sought to elucidate the principle that the stability of a given density in a certain temperature interval characterized the molecular groupings. In 1845 he began to study the variation in the density of acetic acid vapor between 124° and 336°C., then that of phosphorus pentachloride; in 1863 he conducted the same type of study on the substitution derivatives of acetic acid, and in 1866 he made a more complete examination of acetic acid vapor. He established that it behaves as a perfect gas from 240° to 440°C. and then decomposes into methane and carbon dioxide. “These classic works,” wrote Armand Gautier in 1891, “have become one of the solid foundations on which we today base the fundamental proposition that as a perfect gas the [gram] molecular weight of most substances occupies the same volume in the vapor state.”

Among Cahours’s other accomplishments the most important are the discovery (1834) of toluene, identified among the products of the dry distillation of benzoin, and the study (1844) of the oil of Gaultheria procumbens, known to have the same composition and properties as methyl salicylate; Cahours demonstrated by synthesis that it was the same substance. Cahours also discovered anisic acid, anisole, and the polysulfides of alcohol; achieved the etherification of the phenols; and studied tetravalent sulfur. Finally, while preparing acid chlorides by using phosphorus pentachloride, he paved the way for Gerhardt’s discovery of the acid anhydrides.

Cahours became assayer at the Monnaie in 1853, replacing Auguste Laurent. In 1851 he had become Jean-Baptiste Dumas’s suppléant at the Sorbonne; and when Dumas became perpetual secretary of the Académie des Sciences in 1868, Cahours succeeded to his seat there.

The second half of Cahours’s life was marked by a series of sorrows: between 1866 and 1871 he lost his brother, his wife, and his two sons, who were hardly more than twenty years old. Although greatly affected by these ordeals, he did not give up his research, which then took on a more fragmentary and episodic character. A second marriage, late in life, brought some serenity to Cahours’s last years.

Among his honors were the Prix Jecker of the Institut de France in 1860 and 1867, corresponding membership in the Berlin Academy, the rank of commander in the Legion of Honor, and member shipin the Académie des Sciences in 1868.


I. Original Works. Most of Cahours’s research results were published in the Comptes rendus hebdomadaires des séances de l’Académie des sciences; lists can be found in Tables générates des Comptes rendus de t’Académie des sciences… tomes ler à XXXI… (Paris, 1853), p. 109; Tables générates… tomes XXXII à LXI… (Paris, 1870), pp.85 –86; Tables générales… tomes LXII à XCI… (Paris, 1888), pp. 98–99; and Tables généralestomes XCII à CXXI… (Paris, 1900). Among his most important works are “Mémoire sur l’huile volatile de pommes de terre et ses combinaisons,” in Annales de chimie, 70 (1839), 81– 104, and 75 (1840), 193–204; “Recherches chimiques sur le salicylate de méthylène et l’éther salicylique,” ibid.. 10 (1844), 327–369; “Recherches sur les acides volatils à six atomes d’oxygène,” ibid, 13 (1845), 87–115, and 14 (1845). 485–507; Recherches sur les huiles essentielles et sur une classification de ces produits en familles naturelles, fondé esur l’expérience (Paris, 1845), his doctoral thesis; Lemç onsde chimie générale élémentaire professées à l’École centrale des arts et manufactures, 2 vols. (Paris. 1855–1856), subsequent eds. entitled Traité de chimie générale élémentaire (2nd, ed., 3 vols., 1860; 3rd ed., 3 vols., 1874–1875; 4th ed., 3 vols., 1879); “Recherches sur les radicaux organoméialliques,” in Annales de chimie, 58 (1860), 5–82, and 62 (1861), 257–350; and “Recherches sur les densités de vapeur anomales,” in Comptes rendus hebdomadaires desséances de l’Académie des sciences, 56 (1863), 900–912, and 63 (1866), 14–21.

II. Secondary Literature. Cahours’s work is discussed in Maurice Delacre, Histoire de la chimie (Paris, 1920), pp. 441, 443. 497; Armand Gautier, “L’oeuvre de M. A. Cahours,” in Revue scientifique, 48 (Jan.-July 1891), 385–387 Edouard Grimaux,“L’oeuvre seientifique d’AugusteCahours,” ibid., 49 (Jan.-July 1892), 97–101; Raoul Jagnaux. Histoire de la chimie, 2 vols. (Paris, 1891), passim: Albert Ladenburg. Histoire du développement de la chimie depuis Lavoisier jusqu’à nos jours, trans, from the 4th German ed. by A. Corvigny, 2nd French ed. with a supplement by A. Colson (Paris, 1919), passim; and Notice surles travaux scientifiques de M. Auguste Cahours (Paris, 1868).

Jacques Payen