Nothing is created, nothing is destroyed — a chemist proved it with a sealed scale

Before Lavoisier, chemists rarely tracked gases produced or consumed during a reaction, letting mass seem to vanish or appear from nowhere. By sealing reactions in closed vessels and weighing everything before and after, Lavoisier showed in the 1770s and 80s that total mass never actually changes, it only rearranges into new substances. His 1789 textbook summarised the principle as 'nothing is lost, nothing is created, everything is transformed,' a foundation of modern chemistry.

— Antoine Lavoisier, Antoine Lavoisier — Traité Élémentaire de Chimie, 1789