\Phlo*gis"ton\, n. [NL., fr. Gr. ? burnt, set on
fire, fr. ? to set on fire, to burn, fr. ?, ?, a flame,
blaze. See {Phlox}.] (Old Chem.)
The hypothetical principle of fire, or inflammability,
regarded by Stahl as a chemical element.
Note: 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.