Sulfuric acid, chemical compound (H2SO4) that is a colorless, oily liquid that corrodes materials. Exposure to it or its fumes can damage a person's nose, lungs, and skin. Sulfuric acid has been used since the 15th century. In the 19th century it was discovered that adding sulfuric acid to soil made the soil more fertile for plant growth; this discovery led to improved methods of manufacturing sulfuric acid. Besides being used in the manufacture of fertilizer, sulfuric acid is used in steel processing, petroleum refining, and the manufacture of other acids. Because it is so strong and potentially dangerous, great caution must be taken when handling sulfuric acid.