Stas, Jean Servais (1813-1891)

Belgian analytical chemist who made the first accurate determinations of atomic weights (relative atomic masses).

Stas was born in Louvain and studied medicine there. He went to Paris 1837 as assistant to French chemist Jean Baptiste Dumas. From 1840 to 1869 Stas was professor at the Ecole Royale Militaire in Brussels, and he advised the Belgian government on military topics. He was also commissioner of the Mint, but disagreed with the monetary policy of the government and retired 1872. He was openly critical of the part played by the Christian church in education.

While he was working with Dumas in Paris, Stas helped to redetermine the atomic weights of oxygen and carbon. In the 1850s and 1860s, Stas measured the atomic weights of many elements, using oxygen = 16 as a standard. His results discredited English physicist William Prout's hypothesis that all atomic weights are whole numbers, provided the foundation for the work of Dmitri Mendeleyev and others on the periodic system, and remained the standard of accuracy for 50 years.