Sulfuric acid, sulfuric also spelled Sulphuric (H2 SO4), also called Oil Of Vitriol , or Hydrogen Sulfate , dense, colourless, oily, corrosive liquid; one of the most important of all chemicals, prepared industrially by the reaction of water with sulfur trioxide (see sulfur oxide), which in turn is made by chemical combination of sulfur dioxide and oxygen either by the contact process or the chamber process.