Jean Servais Stas

Belgian analytical chemist appointed professor at the Royal Military School in Brussels in 1840. He acquired international fame by determining the atomic weights of the elements more accurately than had ever been done before, using an atomic mass of 16 for oxygen as his standard. His results disproved the hypothesis of the English physicist William Prout that all atomic weights must be integral multiples of that of hydrogen. These careful, accurate atomic weight measurements of Stas helped lay the foundation for the periodic system of elements of Dmitri Mendeleev and others.

Following the pioneering work of Lavoisier and his statement of the conservation of mass, the prolonged and exhaustive experiments of Stas supported the strict accuracy of this law in chemical reactions, even though they were carried out with other intentions. His research indicated that in certain reactions the loss or gain could not have been more than from 2 to 4 parts in 100,000. The difference in the accuracy aimed at and attained by Lavoisier on the one hand, and by Morley and Stas on the other, is enormous.

In 1850 Stas gave the evidence that the Belgian Count Hippolyte Visart de Bocarmé killed his brother-in-law by poisoning with nicotine.

Stas retired in 1869 because of problems with his voice caused by a throat ailment. He became commissioner of the mint, but resigned in 1872 because he disagreed with the government's monetary policy. Jean Stas died in Brussels on 13 December 1891.