The Collaborative International Dictionary of English v.0.48:

Pyrosulphuric \Pyr`o*sul*phu"ric\, a. [Pyro- + -sulphuric.]
   (Chem.)
   Pertaining to, or designating, an acid called also
   disulphuric acid) obtained by distillation of certain
   sulphates, as a colorless, thick, oily liquid, H2S2O7
   resembling sulphuric acid. It is used in the solution of
   indigo, in the manufacture of alizarin, and in dehydration.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Disulphuric \Di`sul*phu"ric\, a. [Pref. di- + sulphuric.]
   (Chem.)
   Applied to an acid having in each molecule two atoms of
   sulphur in the higher state of oxidation.
   [1913 Webster]

   Disulphuric acid, a thick oily liquid, H2S2O7, called
      also Nordhausen acid (from Nordhausen in the Harts,
      where it was originally manufactured), fuming sulphuric
      acid, and especially pyrosulphuric acid. See under
      Pyrosulphuric.
      [1913 Webster]