Phlogiston theory

The phlogiston theory is an obsolete scientific theory that postulated that a fire-like element called phlogiston is contained within combustible bodies and released during combustion. The name comes from the Ancient Greek φλογιστόν phlogistón (burning up), from φλόξ phlóx (flame). It was first stated in 1667 by Johann Joachim Becher. The theory attempted to explain burning processes such as combustion and rusting, which are now collectively known as oxidation.

Theory

Phlogisticated substances are substances that contain phlogiston and dephlogisticate when burned.

Thus, Becher described phlogiston as a process that explained combustion through a process that was opposite to that of oxygen.

Joseph Black's student Daniel Rutherford discovered nitrogen in 1772 and the pair used the theory to explain his results. The residue of air left after burning, in fact a mixture of nitrogen and carbon dioxide, was sometimes referred to as phlogisticated air, having taken up all of the phlogiston. Conversely, when oxygen was first discovered, it was thought to be dephlogisticated air, capable of combining with more phlogiston and thus supporting combustion for longer than ordinary air.