Gay-Lussac, Joseph Louis
Aiton's Encyclopedia (1910)
ga-lu-sak', Joseph Louis (1778-1850), a brilliant French chemist. As a student of the Polytechnic School of Paris he attracted the attention of the professor of chemistry, and a few years later he was appointed to a chair in that institution. He also subsequently held various positions under the French government. In 1804 Gay-Lussac made a balloon ascent for the French Institute to ascertain how a magnetic needle would act above the surface of the earth. He found no perceptible difference. He reached a height of 23,000 feet and brought down a supply of upper air which was found to be identical with surface air. Gay-Lussac took an active interest in the making of gunpowder and the working of the French mint. As chemist of the Jardin des Plantes, the French botanical garden , he took an active interest in botany; the Gaylussacia or huckleberry of our northeastern woodlands and swamps was named for him. The final claim of Gay-Lussac to scientific renown rests on an enunciation of a law to the effect that, when certain volumes of gases are combined, the result will be even and not fractional volumes. For instance, if two volumes of one gas be united with one volume of some other gas the result may be a heavy gas of one volume or a gas of two or it may be a gas of three volumes, but it will not be fractional, as a volume and a half or two and a half volumes, etc. Stated more scientifically, "When chemical action takes place between gases, the volume of the gaseous product bears a simple relation to the volumes of the reacting gases." See Chemistry
What Has Changed in the Last Century
The chemistry in Aiton's 1910 account still stands: Gay-Lussac's law of combining volumes, announced in 1808, remains textbook material, and the genus Gaylussacia (the huckleberries) is still a valid name. What has been filled in is the reason behind the law — Amedeo Avogadro's 1811 hypothesis that equal volumes of gas hold equal numbers of molecules, which was largely ignored until Cannizzaro pressed it on chemists at the Karlsruhe congress of 1860 and it became the basis of modern molecular weights. His 1804 balloon ascent of about 23,000 feet held the altitude record until Glaisher and Coxwell went higher in 1862, and his finding that upper air matches surface air holds good: the atmosphere is now known to stay well mixed to roughly 50 miles up, apart from water vapour and ozone.
Written for this edition, 2026.