Cryolite, natural and artificial -- Determination of fluorine content -- Modified Willard-Winter method
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.
| SDO | ISO: International Organization for Standardization |
| Document Number | ISO 1693 |
| Publication Date | Not Available |
| Language | en - English |
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| Supercedes | |
| Committee | ISO TC 47/SC 7 |
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