Joseph Louis Gay-Lussac

Joseph Louis Gay-Lussac was born in 1778 at Saint-Léonard-de-Noblat in the Limousin. Educated at the École Polytechnique in its first years, he became an assistant to the chemist Claude Louis Berthollet and rose to professorships at the Polytechnique and the Sorbonne, becoming one of the most accomplished experimentalists in France.

In 1802 Gay-Lussac published the law that at constant pressure all gases expand by the same fraction per degree of temperature, generously crediting the unpublished work of Jacques Charles. In 1804 he made two balloon ascents — one reaching about 7,000 metres, a height record that stood for decades — to sample the air and measure the magnetic field at altitude, finding the atmosphere's composition unchanged. In 1808 he announced his law of combining volumes: gases react in simple whole-number ratios of volume, the very regularity Avogadro's hypothesis would explain.

Gay-Lussac's chemical work was prodigious. With Louis Thénard he isolated boron and studied the alkali metals; he developed precise methods of volumetric analysis still used in titration, characterised cyanogen and the cyanides, and contributed to industrial chemistry as an adviser on gunpowder and assaying. He served in the Chamber of Deputies and later as a peer of France.

Honoured across Europe and elected to the Académie des Sciences, Gay-Lussac died in Paris in 1850, his name attached both to the gas-expansion law and to the law of combining volumes.