Gay-Lussac is known to many of today’s students solely for his Law of Gaseous Combining Volumes. This does scant justice to a man who was, in the era when French science led the world, France’s leading chemist. Gay-Lussac was born on December 6, 1778, the son of a comfortably bourgeois lawyer. He received an excellent scientific education at the recently founded Ecole Polytechnique even though his specialty was formally civil engineering. On graduation Gay-Lussac was taken in hand by Claude Louis Berthollet, from whom he received training in chemical research. His first major publication involved a study of the thermal expansion of gases at constant pressure, a subject pursued at the same time, though less accurately, by John Dalton. Since Dalton and Gay-Lussac each have a different gas law named for them, students of chemistry should be eternally grateful that Gay-Lussac chose to name this particular relationship “Charles’ Law” in honor of a fellow countryman who had carried out a similar (but unpublished) investigation 20 years earlier. Charles and Gay-Lussac are linked in another way; they were both pioneer balloonists. In 1783 J.A.C. Charles made the second-ever ascent and in 1804 Gay-Lussac established an altitude record of over 6,000 meters that was to last for 50 years.

Gay-Lussac published his Law of Combining Volumes in 1809, the year after Dalton had proposed his atomic theory. He hesitated to embrace Dalton’s theories perhaps because his mentor, Berthollet, advocated variable composition (“berthollides”) while Dalton insisted on fixed composition (“daltonides”). It was left to Avogadro to take the first major step in rationalizing Gay-Lussac’s results two years later. Gay-Lussac made many less celebrated, but perhaps more important, contributions to chemistry. Along with his great rival, Humphry Davy, Gay-Lussac established the elemental nature of chlorine, iodine, and boron. He prepared pure sodium and potassium in large quantities and discovered potassium hydride and potassium amide. Later he was to systematize volumetric analysis, popularizing the terms titre, burette, pipette, and normalite, and make important contributions to industrial chemistry.

References
DSB, Vol. V, pp. 317-327.
M. Crosland, Gay-Lussac: Scientist and Bourgeois. Cambridge: Cambridge University Press, 1978.

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