Characters
a white, crystalline powder or colourless crystals, freely soluble in water, very soluble in boiling water, practically insoluble in alcohol.
identification
a. It gives the reaction of nitrates.
b. Solution s (see tests) gives the reactions of potassium.
tests
solution s
dissolve 10. 0 g in carbon dioxide-free waterprepared 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 waterand 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.