The Collaborative International Dictionary of English v.0.48:

Fuming \Fum"ing\, a.
   Producing fumes, or vapors.
   [1913 Webster]

   Cadet's fuming liquid (Chem.), alkarsin.

   Fuming liquor of Libavius (Old Chem.), stannic chloride;
      the chloride of tin, SnCl4, forming a colorless, mobile
      liquid which fumes in the air. Mixed with water it
      solidifies to the so-called butter of tin.

   Fuming sulphuric acid. (Chem.) Same as Disulphuric acid,
      uder Disulphuric.
      [1913 Webster]