Determination of Swelling and Foaming Index

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Many herbal drugs are of specific for the therapeutic or pharmaceutical utility because of their swelling properties − especially gums and drugs those are containing an appreciable amount of constituents like mucilage, pectin or hemicelluloses. The swelling index is defined as the volume in ml taken up by the swelling of 1 g of herbal material under specified conditions. Its determination is based on the addition of water or a swelling agent as specified in the test procedure for each individual herbal material (either whole, cut or pulverized). Using a measuring cylinder with glass-stopper, the material must be shaken repeatedly for 1 hour and then allowed the measuring cylinder to stand for a required period of time. The volume of the mixture (in ml) is then read. The mixing of whole herbal material with the swelling agent is easy to achieve, but cut or pulverized materials requires vigorous shaking at specified interval of time to ensure even distribution of the material in the swelling agent.1

Aim: The main objective of present experiment is to measure the swelling factor of the given sample i.e isapgol seeds.

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Apparatus:     Stoppered measuring cylinder – 25 ml

Conical flask – 500 ml

Volumetric flask

Stopper test tubes

Sample:         Isapgol (Plantago ovata) seed

               Water (q.s)

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Determination of swelling index

Transfer 1gm of isapgol seed to a 25 ml stoppered measuring cylinder. Fill the cylinder up to 20 ml mark with water. Agitate gently occasionally during 24 hour and allowed to stand. Measure the volume occupied by the swollen. The genuine seed of isapgol occupies a volume of not less than 10 ml.2

Determination of foaming index

The foaming ability of an aqueous decoction of plant materials & their extracts are measured in terms of a foaming index.


Weigh accurately about 1 g of coarsely powdered drug and transferred to 500 ml conical flask containing 100 ml of boiling water maintain at moderate boiling at 80- 900C for about 30 min. Then make it cold, filter into a volumetric flask and add sufficient water through the filter to make the volume up to 100 ml (V1).

Cleaned stopper test tubes 10 numbers are taken and marked with 1 to 10. Take the successive portions of 1, 2 ml up to 10 ml drug in separate tubes and adjust remaining volume with the liquid up to 10 ml in each test tube. After closing the tubes with stoppers, Shake them for 15 seconds and allowed to stand for 15 min. then measure the height.

If the height of the foam in each tube is less than 1cm, the foaming index is less than 100 (not significant). Here, if the foam is more than 1cm height after the dilution of plant material in the sixth tube, then corresponding number of the test tube is the index sought.

If the height of the foam in every tube is more than 1 cm, the foaming index is more than 1000. In this case, 10 ml of the first decoction of the plant material needs to be measured and transferred to a volumetric flask of 100 ml capacity (V2) and volume is to be maintained up to 100 ml and follow the same procedure.2

Foaming index is calculated by using the following formula

Foaming index = 1000/a in case of V1

Foaming index = 1000 × 10/a in case of V2

Where, a = Volume (ml) of decoction used for preparing the dilution in the tube where exactly 1 cm or more foam is observed.

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Swelling factor of supplied isapgol seeds is ________ and foaming index is ________.

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  1. Kokate CK. Practical Pharmacognosy, 4th edition, Vallabh Prakashan. Delhi; 1994: 127.
  2. Quality control methods for medicinal plants material by W.H.O. Guidelines : 34.