disulphuric

from The Century Dictionary.

• Containing two sulphuric-acid radicals. Used only in the following phrase.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (Chem.) Applied to an acid having in each molecule two atoms of sulphur in the higher state of oxidation.
• adjective 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.