Peroxydisulfuric acid is defined as an inorganic compound having a chemical formula H2S2O8. It is also known as Marshall's acid, and after its inventor, Professor Hugh Marshall, it became a sulfur oxoacid. It can be written as HO3SOOSO3H in structural terms. It also contains sulfur in its +6 oxidation state, including a peroxide group. Its salts are commonly known as persulfates and are industrially essential as powerful oxidizing agents.