Cryolite, natural and artificial — Determination of fluorine content — Modified Willard-Winter method
NORMA vydána dne 1.9.1976
Označení normy: ISO 1693:1976
Datum vydání normy: 1.9.1976
Počet stran: 6
Přibližná hmotnost: 18 g (0.04 liber)
Země: Mezinárodní technická norma
Kategorie: Technické normy ISO
Description / Abstract: Specifies the determination for natural and synthetic materials having a molar ratio sodium fluoride/aluminium trifluoride between 3 and 1,7 approximately. The principle consists in fusion of a test portion with sodium carbonate, separation of fluorine by distillation with sulphuric acid or perchloric acid. Titration with thorium nitrate solution in presence of sodium alizarinsulphonate/methylene blue as indicator. Alternatively, the thorium nitrate titration may be made using only sodium alizarinsulphonate, the end-point being*spectrophotometrically determined at 525 nm.