Iodide ion was added in excess. Under these con- ditions, the fast reaction of chlorine dioxide and iodide ion is followed by a slower reaction between the chlorite ion formed and the excess I-. The latter reaction is slightly hydrogen ion dependent and results in the production of more iodine. It is a self-inhibited reaction;28as we discuss below, its rate decreases with [I-] over a wide range of [I-].