Georg Ernst Stahl
Stahl, Georg Ernst (1660-1734) was a German physician and chemist who developed the theory of phlogiston as the substance responsible for combustion and oxidation.
Stahl earned his degree in medicine in 1684, in Jena, Germany. In 1694, after serving for seven years as court physician to the duke of Sachsen-Weimar, he became a professor of medicine at the newly created University of Halle and spent the next two decades teaching, writing, and developing his theory of phlogiston. In 1715, he moved to Berlin to become the private physician of King Frederick William I of Prussia.
Building on the theory of combustion proposed by another German chemist, Johann Joachim Becher, Stahl put forth the theory that combustible materials and metals held an invisible substance that escaped during the process of combustion or oxidation. He called this substance “phlogiston,” which translates from the Greek to mean “inflammable.” For minerals, this process was reversible. As burning or oxidation occurred, Stahl believed phlogiston would be transferred into another form, such as ash or rust.
Like all other good chemical theories, the phlogiston theory provided an explanation for the results of a variety of experiments and offered clues to areas of study in which new discoveries could be made. For that reason, the theory was widely accepted in the 1700's and led to many findings in chemistry. In the 1770's, however, the French chemist Antoine Laurent Lavoisier began experiments that eventually refuted the idea of phlogiston. His experiments proved the oxygen theory of combustion, which replaced the phlogiston theory.