\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.