Scientists once believed that all combustible objects contain an element called phlogiston that is released during burning. But in 1779, the chemist Antoine Lavoisier (1734–1794) demonstrated that when metals such as mercury are burned, they don’t get lighter, as the phlogiston theory said they must. Lavoisier (left) and his theory-killing apparatus (right).
SEFANO BIANCHETTI/CORBIS
INTERFOTO/ALAMY
INTERFOTO/ALAMY