The principle consists in conversion of heavy metals, such as lead, copper and iron, to their sulphides by treatment with sodium sulphide in ammoniacal solution, and visual comparison of the colour produced with that of a standard lead solution similarly treated. The method detects only the heavy metals present in non-complex form. Using a test portion of 25 g, the method is applicable directly to products having heavy metal contents in the range 0,00044 % (m/m) to 0,04 % (m/m). This range can be extended by adjusting the mass of the test portion. It has also been approved by the International Union of Pure and Applied Chemistry (IUPAC). ISO 753/1 to ISO 753/11 cancel and replace ISO Recommendation R 753-1968.