ISO 1916:1972

The principle of the method consists in 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. In the same solution, titration of the boric oxide with standard volumetric solution of sodium hydroxide in the presence of mannitol or sorbitol, using phenolphthalein as indicator. Determination of the loss on ignition by weighing a test portion into a platinum crucible and heating in an electric furnace, maintained at (900 +- 50 ) °C, for 15 min. The loss on ingnition is expressed conventionally as the water content.