Is applicable to products having a minimum KCl content of about 95 % (m/m). The principle consists in dissolution of a test portion taken from the laboratory sample, previously ground and sifted. Acidification to pH 1 after suitable dilution, and atomization of the resultant solution in the burner of a flame spectrophotometer. Measurement of the intensity of the 766 nm ray, compared with the intensity obtained for standard potassium chloride solutions acidified in the same way. Replaces ISO Recommendation R 2050-1971.