CONSTITUENTS OF COTTON-FIBRE. 103 



colouring-matter, which cannot be extracted by means of 

 boiling alcohol, not even when ammonia is added — a cir- 

 cumstance which is due either to the presence of some 

 colouring- matter distinct from those just referred to, or 

 perhaps to the latter being intimately combined with, or 

 firmly attached to, some other constituent of the mass. 

 I have reason to suppose that it contains also a small 

 quantity of some albuminous substance, the presence of 

 some such substance being rendered probable by an ex- 

 amination of the products of decomposition with caustic 

 alkali, as will be explained presently. Its chief consti- 

 tuent, however, is a body belonging to the pectine class, 

 generally either pectic or parapectic acid, or a mixture of 

 both. The presence of some such body is indicated by 

 the gelatinous appearance of the precipitate with acid, its 

 increasing in bulk and partially dissolving in water after 

 the precipitating acid has been removed^ and its shrinking 

 and curdling on the renewed addition of acid or of salts or 

 alcohol. Nevertheless the isolation and preparation, in a 

 state of purity, of this substance cannot be effected without 

 considerable difficulty, in consequence of the pertinacity 

 with which the colouring-matter adheres to, and accom- 

 panies it. If the precipitate, after exhaustion with boiling 

 alcohol, is treated with boiling water, the latter dissolves 

 a considerable quantity of the body in question, but on 

 evaporation it leaves a dark-brown residue, which, on an- 

 alysis, is found to contain no inconsiderable amount of 

 nitrogen, a proof of the presence of one or both of the 

 colouring-matters of cotton. I was unsuccessful in 

 all my attempts to remove this impurity by means of 

 animal charcoal, earths, metallic oxides, or salts of any 

 kind. I succeeded, however, in devising two methods of 

 preparing, in a state of tolerable purity, a body soluble in 

 water having the properties and composition of Fremy'a 

 parapectic acid, and thus proving that cotton contains a 



