Cryolite, natural and artificial -- Determination of fluorine content -- Modified Willard-Winter method
This standard was last reviewed* in 2015.
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.
Document published on: 1976-09-01 Edition: 1 (Monolingual) ICS: 71.060.50 Status: Published Stage: 90.93 (2015-01-05) TC/SC: ISO/TC 226 Number of Pages: 6
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