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OCR for page 53
53 NAS/CWTC 025-82 Name: SODIUM SILICOFLUORIDE, SODIUM FLUOSILICATE CAS No.: 16893-85-9 Chemical Formula: Na2SiF6 Description: Formula Weight: 132 White, yellowish-white, or Nile blue crystalline powder, odorless, acidic taste, and hydroscopic. Use: Used as source of fluoride. Purity Requirements: Analyses of available grades of sodium silicofluoride 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 anal- yses are desired, the following protocol is recommended. Bulk Sample Collection: Sample in accordance with Standard for Sodium Silico- fluoride, AWWA B702-74, American Water Works Association, Denver, Colorado (1974). Analytical Sample Preparation Weigh out 2.5 g of sodium silicofluoride. In a 150-ml acid-washed beaker, dissolve the sample with 100 ml of deionized distilled water. Under a hood, acidify the solution with concentrated EC1 to a pH of less than 2. Add hydroxylamine hydrochloride until the solution turns clear. Gently heat the solution to reduce the volume

OCR for page 53
54 below 100 ml, making certain that it does not boil. Quan- titively transfer to a 100-ml acid-washed volumetric flask and make to volume with deionized distilled water. Pro- cess a reagent blank by the same procedure. Sample Analyses: The analyses are to be performed on the sodium silico- fluoride 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