ISO 6229:1980

Covers a method, the principle of which is based on the extraction from a test portion of compounds soluble in acetic acid solution and weighing of the residue after heating at 600 °C, removal from the residue, of silica by evaporation with hydrofluoric acid solution and of residual fluorides by heating with ammonia solution, and reweighing of the residue after heating at 600 °C. Is applicable to products having free silica contents equal to or greater than 0,05 % (m/m).