ISO 3237:1975 PDF

Applicable to the analysis of products manufactured by traditional methods provided that the impurities other than sulphates are well known. The gravimetric method shall be applied only in the case of doubt as to the accuracy of the calculated result. Principle of calculation: subtraction of the loss in mass at 110 °C, acid-insoluble matter, chlorides content (as NaCl), alkalinity (as Na2 CO3 ) or acidity (as H2 SO4 ), expressed as percentages by mass. The chemical analysis follows the principle: extraction of a test portion with dilute acid, separation of the insoluble matter, precipitation of the sulphate in the filtrate with barium chlorid and weighing of the precipitate formed after drying.