1 8 Cellulose 



basic and { acidic/ present in the colouring matter or mordant 

 and the substance with which it combines. 



This explanation certainly covers a wide range of such re- 

 actions, but we shall find that the molecular constitution of the 

 fibre-substance is also an important factor. This point will 

 be discussed subsequently. 



Capillary Phenomena. The absorption and trans- 

 mission of solutions by cellulose is attended by a number of 

 special effects. Schonbein appears to have been the first to 

 observe that strips of unsized paper, of which one end was 

 placed in an aqueous solution, e.g. of a metallic salt, will 

 absorb and transmit the water more rapidly than the dissolved 

 salt, which is therefore ' filtered out ' ; further, that to the 

 various salts, cellulose manifests varying degrees of re- 

 sistance to transmission in solution. These phenomena have 

 been further studied by Lloyd (Chem. News, 51, 51) for 

 metallic salts, 1 and byF. Goppelsroeder (Berl. Ber. 20, 604) for 

 various colouring matters ; the results of their observations 

 constituting the beginnings of a method of * capillary analysis 

 or separation.' The subject is comparatively new and not yet 

 systematised, but the method is undoubtedly capable of con- 

 siderable extension. 



Contrasted with the relatively feeble attractions of cotton 

 cellulose for the acids and bases of low molecular weight there are a 

 number of cases of special combinations which take place in much 

 higher proportions. 



Thus the fibre removes a considerable quantity of barium 

 hydrate on digestion with the solution ; and from solutions of the 

 basic salts of lead, zinc, copper, tin, aluminium, iron, chromium, 

 &c. the fibre takes up considerable but variable ^proportions of the 

 respective basic oxides. The formation of these compounds 

 underlies the well-known processes of ' mordanting' practised by 

 the dyer and printer of textiles. The theory of these processes will 



1 More recently by E. Fischer and Schmidmer, Lieb. Ann. 272, 156. 



