Potassium permanganate is added to a solution of graphite, sodium nitrate, and this compound in Hummers’ method for producing graphite oxide. An oxidized derivative of this compound is named for Heinrich Caro and exists transiently in an explosive oxidizing agent that is useful for removing organic matter from fritted glass. A mixture of this compound and (*) nitric acid is used to perform aromatic nitrations. This chemical, which is mixed with hydrogen peroxide in piranha solution, (10[1])is given a value of -12 for the Hammett function. Oleum is the concentrated “fuming” form of this substance formed from the contact process. Of the so-called strong acids, the only diprotic one is, for 10 points, what compound with formula H2SO4? ■END■