Jean Stas

Jean Servais Stas (21 August 1813 to 13 December 1891) was a Belgian analytical chemist who accurately measured the atomic weight of carbon. Born in Leuven and trained at first as a physician, he switched to chemistry and worked at the École Polytechnique in Paris under Jean-Baptiste Dumas, with whom he established the atomic weight of carbon by weighing a pure sample, burning it in pure oxygen and weighing the carbon dioxide produced. Appointed professor at the Royal Military School in Brussels in 1840, he became internationally known for determining atomic weights more accurately than anyone before him, using oxygen as 16 for his standard. His results disproved William Prout's hypothesis that all atomic weights are integer multiples of that of hydrogen and helped lay the foundation for Mendeleev's periodic system, and his exhaustive experiments also supported the strict accuracy of the conservation of mass in chemical reactions. In 1850 he gave the evidence that Count Hippolyte Visart de Bocarmé had killed his brother-in-law with nicotine. He retired in 1869 because of a throat ailment, served briefly as commissioner of the mint, and received the Davy Medal in 1885.