ISO 5520:1981

After incineration of the product at 525 +/- 25 degrees centigrade the method consists in a) in the case of total ash: addition of an excess of standard volumetric sulphuric acid solution and back titration with standard volumetric sodium hydroxide solution, b) in the case of water-soluble ash: extraction of the ash with hot water and neutralization of the aqueous extract with standard volumetric sulphuric acid solution.