phlogiston

A hypothetical substance formerly thought to be a volatile constituent of all combustible substances, released as flame in combustion.

In old chemistry, the supposed principle of inflammability; the matter of fire in composition with other bodies.

The hypothetical principle of fire, or inflammability, regarded by Stahl as a chemical element.

The hypothetical fiery principle formerly assumed to be a necessary constituent of combustible bodies and to be given up by them in burning.

a hypothetical substance once believed to be present in all combustible materials and to be released during burning