Potassium Nitrate

• TESTS Solution S: Dissolve 10.0 g in carbon dioxide-free water prepared from distilled water and dilute to 100 ml with the same solvent.
• Appearance of solution: Solution S is clear and colourless.
• Acidity or alkalinity: To 10 ml of solution S add 0.05 ml of bromothymol blue solution. Not more than 0.5 ml of 0.01 M hydrochloric acid or 0.01 M sodium hydroxide is required to change the colour of the indicator.
• Reducible substances: To 10 ml of solution S, add 0.5 ml of dilute sulphuric acid and 2 ml of zinc iodide  and starch solution. The solution does not become blue within 2 min.
• Chlorides: If intended for ophthalmic use, it complies with the test for chlorides. Dissolve 2.5 g in water and dilute to 15 ml with the same solvent. The solution complies with the limit test for chlorides (20 ppm).
• Sulphates: Dilute 10 ml of solution S to 15 ml with distilled water. The solution complies with the limit test for sulphates (150 ppm).
• Ammonium: 1 ml of solution S complies with the limit test (A) for ammonium (100 ppm). If intended for ophthalmic use, not more than 50 ppm of ammonium.
• Calcium: Dilute 10 ml of solution S to 15 ml with distilled water. The solution complies with the limit test for calcium (100 ppm). If intended for ophthalmic use, not more than 50 ppm of calcium.
• Iron: Dilute 5 ml of solution S to 10 ml with water. The solution complies with the limit test for iron (20 ppm). If intended for ophthalmic use, not more than 10 ppm of iron.
• Sodium: Not more than 0.1 per cent of Na, determined by atomic emission spectrometry.
• Heavy metals: 12 ml of solution S complies with limit test A for heavy metals (10 ppm).
• Loss on drying: Not more than 0.5 per cent determined on 1.000 g by drying in an oven at 100°C to 105°C.

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