This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
The cotton plants, of which many varieties exist, are either herbs, shrubs, or small trees. They produce three to five-celled capsular fruits containing numerous seeds covered with a woolly mass of long white or yellowish hairs. These are separated from the seeds and freed from impurities by machinery specially designed for that purpose.
Each of the hairs thus separated is covered with a thin cuticle by which certain waxy and fatty substances are secreted; the presence of these is objectionable, as they repel moisture, and consequently the wool will only slowly absorb watery fluids. To remove them, the cotton wool is usually boiled under pressure with a dilute caustic alkali, after which it is washed, bleached by chlorinated lime and hydrochloric acid, again washed and then dried; finally the fibres are loosened by machinery, and separated by a current of air, from which they are collected as a fleecy wool. The wool thus freed from the wax and fat naturally present in it possesses much better absorbent properties and is in most cases more suitable as a surgical dressing (absorbent wool).
Each of the soft white filaments of which cotton wool consists is a single hair from the surface of the seed. They attain as much as 5 cm. in length, and appear, when examined under the microscope, as flattened, twisted bands with slightly thickened rounded edges. Cotton wool should readily sink in water, showing that the waxy coating with which it is naturally provided has been removed, as directed by the Pharmacopoeia; it should not, however, communicate to water either an acid or an alkaline reaction, as might be the case if it had not been completely freed from the acids and alkalies commonly used to remove the wax. Cotton wool is inodorous, tasteless and insoluble in water but almost completely soluble in an ammoniacal solution of cupric oxide, the cuticle remaining undissolved. Solutions of iodine colour cotton wool yellow, which is changed to deep blue by sulphuric acid. It burns easily, leaving less than 1 per cent. of ash.
Fig. 231. - Cotton. Magnified. (Tschirch).
Cotton wool consists principally of cellulose (C6H10O5)n, associated with traces of inorganic matter, albuminoids, etc. The fatty matter is partly a wax soluble in alcohol and ether, and melting at 86°, partly a mixture (apparently) of stearic and palmitic acids.
Cotton wool is best identified by microscopic examination. It may be distinguished from animal fibres by being insoluble in hot 8 per cent. solution of potassium hydroxide, by not being stained permanently yellow by a solution of picric acid, and by containing only traces of nitrogenous substances. It differs from many other vegetable fibres by the blue colour it yields with iodine and sulphuric acid, but its ultimate identification can be effected only by the microscope.
Cibotium or Penghwar Djambi is a brownish woolly substance consisting of the hairs from the bases of the fronds of Cibotium Barometz, Link, G. glaucum, Hooker and Arnold, Alsophila lurida, B1., etc. (N.O. Filicineoe), Java, Sumatra, etc.; it is used as a haemostatic (Pili haemostatici).