Jean Servais Stas (21 August 1813 – 13 December 1891) was a Belgian analytical chemist who accurately measured the atomic weight of carbon.

These careful, accurate atomic weight measurements of Stas helped lay the foundation for the periodic system of elements of Dmitri Mendeleev and others.

[1] 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,[2] even though they were carried out with other intentions.

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

He was presented with a medal in his honor sculpted by Belgian engraver Alphonse Michaux and with an album containing accolades authored by scientific societies from around the world.