Method of analysis hydrogen peroxide

A method of automatically controlling a supply of hydrogen peroxide supplied to an aqueous solution, the supply being based on a content of hydrogen peroxide in the aqueous solution, said content being automatically determined by a method comprising the steps of (a) bringing a sample of the solution to a pH below 3, (b) adding iodide reagent in excess to the sample, (c) thereafter irradiating the sample with light, (d) measuring the light absorbance and obtaining a value therefore at a predetermined wavelength which is so selected that the light is absorbed, at least partly, by iodine formed in the sample by reaction of the iodide with hydrogen peroxide, the absorbance value obtained being a measure of the hydrogen peroxide content of the sample prior to addition of iodide thereto, and (e) automatically supplying an amount of hydrogen peroxide based on said measurement of hydrogen peroxide content of the sample.