GAY-LUSSAC, ga' lu'sale, Louis JOSEPH (1778-1850). One of the most distinguished chemists and physicists of the nineteenth cen tury. He was born at Saint Leonard le Noblat (Haute-Vienne). In 1794 he was sent to Paris, and was admitted to the Ecole Polytechnique in 1797. After three years' study, Berthollet, who was then professor of chemistry in the Ecole Polytechnique, selected him as his assistant at Arcueil, where the Government chemical works were situated. In 1801 the young chemist pub lished his first memoir, which treated of the dila tation of gases and vapors, and which was speed ily followed by others, on the improvement of thermometers and barometers, on vapor-tensions and the determination of vapor-densities, and on capillary action. In association with Biot, he was commissioned by the Institute of France to make a balloon ascent, with the view to ascer taining whether magnetic force existed at con siderable heights above the surface of the earth, or only on the surface, as had been asserted by some physicists. Alexander von Humboldt in vestigated with him the properties of air brought down from a height of more than 23,000 feet, and their joint memoir to the Academy of Sciences (read on October 1, 1804) contained the first announcement of the fact that oxygen and hydrogen unite to form water in the simple pro portion of one volume of the former to two vol umes of the latter. The simplicity of the ratio in which these gases stood to each other in their combining proportions induced Gay-Lussac to study the combining volumes of other gases, and thus led him to the important discovery of the law of volumes, which was announced in 1808, and is one of the most general and important laws in the whole domain of chemistry. In 1809 he was made professor of chemistry at the Ecole Polytechnique. Davy's discoveries of potassium and sodium, by the decomposing action of the electric current, having excited much attention in France, Napoleon directed Gay-Lussac and Thenard to pursue this class of researches. The
results of their investigations appeared in two volumes, under the title Recherches physico chimiques, in 1811. Among the most important of the discoveries announced in these volumes were a new chemical process which yielded po tassium much more abundantly than the electro lytic method, the isolation of boron, and new and improved methods of analyzing organic com pounds. Gay-Lussac was also the first to obtain bydriodic and iodic acids and cyanogen. He also investigated the manufacture of hydrated sul phuric acid, bleaching chlorides, alcohols, and alkalies employed in commerce. In 1805 he was chosen a member of the Committee of Arts and Manufactures, established by the Minister of Commerce. In 1818 he was appointed to super intend the Government manufactory of gunpow der and saltpetre, and in 1829 lie received the lu crative office of chief assayer to the mint, where he introduced several important improvements. In 1831 he became a member of the Chamber of Deputies; in 1832 professor of chemistry at the Jardin des Plantes; and in 1839 lie was made a peer of France. lie never took an active part in politics, and was diligently engaged in scien tific research until his last illness. From 1816 he was of the Annales de chimie et de physique, in which many of his original memoirs were published. He also wrote: Cours de physique (1827) ; Lecons de chimie (2 vols., 1828) ; and other works. Consult: American Journal of Science (1850) ; Biot and Gardeur le Brun, No tices biographiques sur Gay-Lussac (Chalons, 1850). See CHEMISTRY; AVOGADBO'S RULE. .