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36 Name: FLUOSILICIC ACID, HYDROFLUOSILICIC ACID CAS No.: 16961-83-4 Chemical Formula: H2SiF~ v Description . NAS/CWIC 015-82 Formula Weight: 88.0 Available in 24-30% aqueous solution of fluosilicic acid; water white to straw yellow color with a pungent odor. Use . Used as source of fluoride. Purity Requirements: Analyses of available grades of fluosilicic acid show the presence of arsenic and lead but at levels far below that which would necessitate RMIC values based on a maximum dosage of 1.2 mg of fluoride ion/liter. If analyses are desired, the following protocol is recommended. Bulk Sample Collection: Sample in accordance with Standard for Fluosilicic Acid, AWWA B703-71, American Water Works Association, Denver, Colorado (1971). Analytical Sample Preparation . Weigh out 2.5 g of fluosilicic acid. In a 150-ml acid- washed beaker, dissolve the sample with 100 ml of deion- ized distilled water. Under a hood, acidify the solution with concentrated HC1 to a pH of less than 2. Add hydrox- ylamine hydrochloride until the solution turns clear. Gently heat the solution to reduce the volume below 100 ml, making certain that it does not boil. Quantitively
37 transfer to a 100-ml acid-washed volumetric flask and make to volume with deionized distilled water. Process a reagent blank by the same procedure. Sample Analyses: The analyses are to be performed on the fluosilicic acid sample in accordance with: Standard Methods for the Examination of Water and Waste- water, 15th Edition, American Public Health Association, Washington, D.C. (1981). Arsenic Lead Section 304 Section 304