CONSTITUENTS OF COTTON-FIBRE. 105 



As soon as the liquid ceased to give a precipitate with 

 nitrate of silver, the mass was taken from the filter, pressed 

 between folds of blotting-paper in order to take up the 

 alcohol, and then treated with boiling water for some time. 

 A milky liquid was thus obtained, which was set aside for 

 some time in order to allow the flocculent matter sus- 

 pended in it, which prevented it from filtering readily, to 

 settle. The liquid having been decanted from the deposit, 

 was filtered and evaporated, when it left an amorphous 

 light-brown residue, resembling gum or gelatine, and 

 having the properties and composition of parapectic acid. 

 The flocculent deposit consisted of pectic acid ; but it was 

 contaminated with a considerable quantity of colouring- 

 matter, from which it could, in most cases, not be sepa- 

 rated without undergoing a change. If, for instance, it 

 was dissolved again in caustic soda, and the process just 

 described was repeated, it was usually converted for the 

 most part into a substance soluble in water — that is, into 

 parapectic acid. 



The second method of preparing the acid is far less 

 tedious, and yields a product much freer from colour than 

 the one just described. It difiers, however, from the latter 

 in one particular only, viz. in the use of a bleaching agent, 

 instead of caustic soda as a precipitant. To the watery 

 solution of impure pectate and parapectate of soda obtained 

 in the same manner as before, there was added a clear 

 solution of chloride of lime, which produced an abundant 

 precipitate, consisting mostly of pectate and parapectate 

 of lime. By adding an excess of the bleaching-solution, 

 the colour of the precipitate, Avhich was at first brown, 

 became gradually lighter. As soon as it had lost all its 

 colour, or retained only a yellowish tinge, it was filtered 

 off*, washed with water, and treated with dilute hydro- 

 chloric acid. The white flocks left undissolved by the acid 

 were filtered off, washed at first with water and then 



