ISO 2223:1972

Formaldehyde solutions for industrial use — Limit test for heavy metals (excluding iron)

The method detects only the heavy metals present in non-complex form, the sulphides of which are precipitated in acid solution. The method is not specific for any one heavy metal. The principle consists in conversion of heavy metal, such as lead and copper, in acid solution to their sulphides, and comparison of the colour produced with that given by an aliquot volume of standard lead solution treated with hydrogen sulphide in the same way.