Synonyms: silicic acid, magnesium saltcas number: 14987-04-3 (39365-87-2 for hydrate), molecular weight: 260.86, chemical formula: mg2o8si3, einecs ec number: 239-076-7, fema: ----, magnesium trisilicate bp ph eur grade definitionit has a variable composition corresponding approximately to mg2si3o8, xh2o. Content:magnesium oxide: minimum 29.0 per cent (ignited substance), silicon dioxide: minimum 65.0 per cent (ignited substance). Charactersappearance: white or almost white powder.Solubility: practically insoluble in water and in ethanol (96 per cent). Identificationa. 10.25 g gives the reaction of silicates.B. 1 ml of solution s (see tests) neutralized with dilute sodium hydroxide solution gives the reaction of magnesium. Testssolution s: to 2.0 g add a mixture of 4 ml of nitric acid and 4 ml of distilled water. Heat to boiling with frequent shaking. Add 12 ml of distilled water and allow to cool. Filter or centrifuge to obtain a clear solution and dilute to 20 ml with distilled water.Alkalinity: to 10.0 g in a 200 ml conical flask, add 100.0 g of water and heat on a water-bath for 30 min. Allow to cool and make up to the initial mass with water r. Allow to stand and filter or centrifuge until a clear liquid is obtained. To 10 ml of this liquid add 0.1 ml of phenolphthalein solution. Not more than 1.0 ml of 0.1 m hydrochloric acid is required to change the colour of the indicator.Water-soluble salts: maximum 1.5 per cent. In a platinum dish, evaporate to dryness on a water-bath 20.0 ml of the liquid obtained in the test for alkalinity. The residue, ignited to constant mass at 90050c, weighs a maximum of 30 mg.Chlorides: maximum 500 ppm.Sulphates: maximum 0.5 per cent.Arsenic: maximum 4 ppm, determined on 2.5 ml of solution s.Heavy metals: maximum 40 ppm.
Upington, South Africa
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