Joseph Louis Gay-Lusac, French chemist and physicist, 1824.
© Science Museum / Science & Society Picture Library
Engraving by Ambroise Tardieu of Gay-Lusac (1778-1850) who made balloon ascents to investigate the laws of terrestrial magnetism. In 1805 he and Alexander von Humboldt observed that hydrogen and oxygen combine to form water. He was the first to prepare hydriodic and iodic acids, and isolated cyanogen. Investigating sulphuric acid, he introduced the Gay-Lusac tower. He also investigated the centesimal alcoholometer, the manufacture of bleaching chlorides and the asaying of silver.