ISO 1917:1972

Determination of the sodium oxide content by addition of an excess of a solution of hydrochloric acid and back titration with a standard volumetric solution of sodium hydroxide in presence of methyl red/bromocresol green as indicator. Subsequent titration of the boric oxide with the standard volumetric solution of sodium hydroxide in the presence of mannitol or sorbitol, using phenolphthalein as indicator. Determination of the available oxygen content in a test portion by titration in acid solution with a standard volumetric potassium permanganate solution. The equation for the reaction involved in the determination of available oxygen is given.