hyposulphurous acid

from The Collaborative International Dictionary of English v.0.48

Hyposulphurous \Hy`po*sul"phur*ous\, a. [Pref. hypo- +
   sulphurous.] (Chem.)
   Pertaining to, or containing, sulphur, all, or a part, in a
   low state of oxidation.
   [1913 Webster]

   {Hyposulphurous acid}.
   (a) Thiosulphuric acid. [Obs.]
   (b) An acid, {H2SO2}, obtained by the reduction of sulphurous
       acid. It is not obtained in the free state, but in an
       orange-yellow water solution, which is a strong reducing
       and bleaching agent. Called also {hydrosulphurous acid}.
       [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Thiosulphuric \Thi`o*sul*phur"ic\, a. [Thio- + sulphuric.]
   (Chem.)
   Of, pertaining to, or designating, an unstable acid,
   {H2S2O3}, analogous to sulphuric acid, and formerly called
   {hyposulphurous acid}.
   [1913 Webster]