Cavendish, Henry (1731–1810)

English physicist and chemist. He discovered hydrogen (which he called ‘inflammable air’) in 1766, and determined the compositions of water and of nitric acid. The Cavendish experiment (1798) enabled him to discover the mass and density of the Earth.

Cavendish demonstrated in 1784 that water is produced when hydrogen burns in air, thus proving that water is a compound and not an element. He also worked on the production of heat and determined the freezing points for many materials, including mercury.

Cavendish was born in Nice, France, and left Cambridge without a degree. He spent the rest of his life in seclusion in London. Most of his work, especially his experiments with electricity, was unknown for 100 years or more. He believed electricity to be an elastic fluid.

In the late 1760s Cavendish began experimenting with ‘facticious airs’ (gases that can be produced by the chemical treatment of solids or liquids). He studied ‘fixed air’ (carbon dioxide) produced by mixing acids and bases; ‘inflammable air’ (hydrogen) generated by the action of acids on metals; and the ‘airs’ produced during decay and fermentation. He measured the specific gravities of hydrogen and carbon dioxide, comparing them with that of ‘common’ (atmospheric) air. In 1783 he found that the composition of the atmosphere is the same in different locations and at different times.