Applicable to the determination of Fe contents, expressed as Fe2 O3 , of more than 0.020 % (m/m). Covers the dissolution of a test portion by alkaline fusion by means of sodium carbonate and boric acid. Dissolving of the residue with nitric acid solution and reduction of iron(III) by means of hydroxylammonium chloride. Formation of the iron(II)-1,10-phenanthroline complex in a buffered medium at a pH between 3.5 and 4.2. Photometric measurement of the coloured complex at a wavelength of about 510 nm.