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7.10 SWELLING INDEX

         The swelling index is the volume in ml occupied by 1 g of a drug, including any adhering mucilage, after it has swollen in an aqueous liquid for 4 hours.

         Place 1 g, accurately weighed, of the drug, whole or of the degree of comminution prescribed in the monograph, in a 25-ml ground-glass stoppered cylinder graduated over a height of 120 to 130 mm in 0.5-ml divisions. Unless otherwise specified, moisten the drug with 1.0 ml of ethanol, add 25 ml of water and close the cylinder. Shake vigorously every 10 minutes for 1 hour and then allow to stand for 3 hours. At 90 minutes after the beginning of the test, release any large volumes of liquid retained in the layer of the drug and any particles of the drug floating at the surface of the liquid by rotating the cylinder about a vertical axis. Measure the volume occupied by the drug, including any adhering mucilage. Carry out three tests at the same time. Calculate the swelling index from the mean of the three tests.