Sulfuric acid (chemical formula: H2SO4), an important oxyacid of sulfur. Anhydrous sulfuric acid is a colorless oily liquid that crystallizes at 10.36 ° C. Generally, its aqueous solutions of various concentrations are used, which are prepared by the tower method and the contact method. The former obtained crude dilute sulfuric acid, the mass fraction is generally about 75%; the latter can get concentrated sulfuric acid with a mass fraction of 98.3%, boiling point 338 ℃, relative density 1.84.