ISO 8660:1988

Equal volumes of potassium permanganate solution are added to a carpolactam test solution and to a blank (water). After standing for a specified time the absorbance, at a wavelength of 420 nm, of the test solution and of the blank are compared in cells of 5 cm thickness. The permanganat index is the difference between the absorbance of the test sample and that of the blank, multiplied by 100/3. It is a conventional measure of the content of oxidizable impurities.