1660-1734

German chemist and physician remembered for developing phlogiston theory—combustion and calcination consist of phlogiston loss. Stahl postulated that ash from burnt wood and calx from heated metals are devoid of phlogiston, and heating calx with phlogiston-rich charcoal yields metal by calx re-absorbing phlogiston. Accounting for observed weight changes required phlogiston to have negative weight. Though incorrect, Stahl's theory greatly facilitated the shift from alchemy to Antoine Lavoisier's new chemistry. Within medical thought, Stahl's vitalism provided an alternative to Hermann Boerhaave's mechanist theories.