Chem.
an oily, hygroscopic, corrosive liquid, H 2 S 2 O 7 , that, depending on purity, is colorless or dark brown: used chiefly as a dehydrating agent in the manufacture of explosives and as a sulfating or sulfonating agent in the manufacture of dyes. Also called fuming sulfuric acid, oleum .
[ 1870-75 ]