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.

Source: Webster's Revised Unabridged Dictionary (1913)
 

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.

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.

Source: Webster's Revised Unabridged Dictionary (1913)