Dumas, Jean Baptiste André (1800–1884)

French chemist. He made contributions to organic analysis and synthesis, and to the determination of atomic weights (relative atomic masses) through the measurement of vapour densities. In 1833 Dumas worked out an absolute method for the estimation of the amount of nitrogen in an organic compound, which still forms the basis of modern methods of analysis. He went on to correct the atomic masses of 30 elements – half the total number known at that time – referring to the hydrogen value as 1.

In 1826, Dumas began working on atomic theory, and concluded that ‘in all elastic fluids observed under the same conditions, the molecules are placed at equal distances’ – that is, they are present in equal numbers. His theory of substitution in organic compounds, which he proved by experiments, established that atoms of apparently opposite electrical charge replaced each other. This refuted the dualistic theory of chemistry proposed by Swedish chemist Jöns Berzelius.

Studying blood, Dumas showed that urea is present in the blood of animals from which the kidneys have been removed, proving that one of the functions of the kidneys is to remove urea from the blood, not to produce it.

Dumas was born in Gard département and apprenticed to an apothecary. He moved to Geneva, Switzerland, and continued his studies there. In 1822 he went to Paris, where he became professor of chemistry first at the Lyceum and 1835 at the Ecole Polytechnique. After the political upheavals of 1848 Dumas abandoned much of his scientific work for politics, and held ministerial posts under Napoleon III.