Section 184.1769a - Sodium metasilicate(a) Sodium metasilicate (CAS Reg. No. 6834-92-0) is a strongly alkaline white powder. It does not occur naturally but rather is synthesized by melting sand with sodium carbonate at 1400 °C. The commercially available forms of sodium metasilicate are the anhydrous form (Na2SiO3), the pentahydrate (Na2SiO3·5H2O), and the nonahydrate (Na2SiO3·9H2O).(b) The ingredient must be of a purity suitable for its intended use.(c) In accordance with § 184.1(b)(1) , the ingredient is used in food with no limitation other than current good manufacturing practice. The affirmation of this ingredient as generally recognized as safe (GRAS) as a direct human food ingredient is based upon the following current good manufacturing practice conditions of use: (1) The ingredient is used as a processing aid as defined in § 170.3(o)(24) of this chapter.(2) The ingredient is used to treat the following foods at levels not to exceed current good manufacturing practice: for use in washing and lye peeling of fruits, vegetables, and nuts when used in accordance with § 173.315 of this chapter; for use as a denuding agent in tripe; for use as a hog scald agent in removing hair; and for use as a corrosion preventative in canned and bottled water when used in accordance with § 165.110 of this chapter.(d) Prior sanctions for this ingredient different from the uses established in this section do not exist or have been waived.50 FR 38781, Sept. 25, 1985; 50 FR 42011, Oct. 17, 1985, as amended at 72 FR 10357 , Mar. 8, 2007; 73 FR 8608 , Feb. 14, 2008