Antoine Lavoisier (1514-1564). Caricature of the French chemist Antoine-Laurent de Lavoisier. Lavoisier is viewed as the father of modern chemistry. He was the first to state a law of the conservation of mass, that although the form of matter may change its mass is invariant. He recognised and named oxygen and hydrogen, and helped disprove the phlogiston theory. He used a calorimeter to show that respiration was a slow combustion of organic material using inhaled oxygen. He proposed that chemicals were simple combinations of elements and described them by their components, a system essentially as used today. He was executed during the French Revolution on trumped-up charges laid by Marat.