COTTON 



411 



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 pre- 

 sence 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 suit- 

 able as a surgical dressing 

 (absorbent wool). 



Description. 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 re- 

 maining undissolved. Solutions of iodine colour cotton wool yellow, 



FIG. 231. Cotton. Magnified. (Tschirch.) 



