will now be further described in more detail in connection with the examples which follow which are set forth for purposes of illustration only to an aqueous solution which contains per liter 20 grams of hydrogen peroxide hydrofluoric acid in an amount corresponding to 73 2 grams of total fluorine 29 3 grams of total iron 5 98 grams of total chromium 0 13 grams of total manganese 0 07 gram of total nickel and 0 0086 gram of total copper and in which the average rate of decomposition of the hydrogen peroxide measured at 26 u00b0 c over a period of 2 hours is 0 90 millimole per minute and per liter there is added sodium hydroxide naoh so as to give a concentration of 0 44 mole of naoh per liter of solution the mean rate of decomposition of the hydrogen peroxide determined as above is thereafter no more than 0 48 millimole per minute and per liter that is to say about half that found without addition of sodium hydroxide the same result is obtained if the sodium hydroxide is replaced by the same molar amount of potassium hydroxide koh or ammonium hydroxide nh 4 oh to the same solution as in example 1 there is added sodium hydroxide so as to give 0 66 mole of naoh per liter of solution the mean rate of decomposition.