He was Berthollet’s teaching assistant and Fourcroy’s demonstrator. Laplace encouraged him; he worked on potassium and sodium with Thénard. He criticised Humboldt for a lack of precision, but they became friends and travelled together, climbed Vesuvius in full eruption, and showed that the composition of air does not change with altitude. Liebig, Pelouze and Regnault were all students of his. Biot and he made the first balloon ascent for scientific study; on another balloon flight he threw a chair overboard to gain height, causing locals to marvel that God owned such shabby furniture.