Sulphuric acid was an acidic compound.
The Second Doctor used sulphuric acid to defeat the Krotons on the Gond planet. (TV: The Krotons)
It rained sulphuric acid on Kaalann. (GAME: City of the Daleks)
The seas of 16 Alpha Leonis One were made of sulphuric acid. Agent Yellow freed sulphur compounds which combined with water to form sulphuric acid. (PROSE: Eternity Weeps)
The Eleventh Doctor recommended using it to dissolve the TARDIS' translation circuits. (COMIC: Sticks & Stones)