Phlogiston

Phlogiston (flo*jis"ton; 277) , noun

[New Latin, from Greek flogisto`s burnt, set on fire, from flogi`zein to set on fire, to burn, from flo`x, flogo`s, a flame, blaze. See Phlox.]

(Old Chemistry) The former hypothetical principle of fire, or inflammability, regarded by Stahl as a chemical element; it is now known to be nonexistent.

This was supposed to be united with combustible (phlogisticated) bodies and to be separated from incombustible (dephlogisticated) bodies, the phenomena of flame and burning being the escape of phlogiston. Soot and sulphur were regarded as nearly pure phlogiston. The essential principle of this theory was, that combustion was a decomposition rather than the union and combination which it has since been shown to be. This theory is now discredited and superseded by the theory of chemical reaction between oxidizable substances and oxidants as an explanation of combustion