32 Cellulose 



tion the part played by the water. It may be noted that a 

 i p.ct. solution of cellulose (as thiocarbonate) will ' set ' to 

 a firm jelly of hydrate, of the volume of the containing vessel; 

 and that even at 0*25 p.ct. cellulose, gelatinisation of the 

 liquid occurs in decomposition. We have also pointed out 

 that a hydrate containing only 10 p.ct. cellulose is a sub- 

 stantial solid which gives up water with extreme slowness. 



Cellulose, therefore, affords conspicuous illustrations of the 

 property which the ' colloids ' have, as a class, of ' fixing ' water, 

 and of the modes in which this property takes effect. In regard 

 to the causes underlying this peculiar relationship to water, we 

 know as yet but little. It is to be noted that the group of 

 colloids comprises bodies of very various chemical function, 

 acids, bases, salts and compounds of mixed function, as in the 

 complex carbohydrates and proteids ; the only possible feature 

 common to so varied a group would be that of molecular 

 arrangement, favouring the aggregation of the molecules, to- 

 gether with those of water, to groups of indefinite magnitude. 

 On this subject, however, conjectures must, for the present, do 

 duty for a theory which can only be shaped by further in- 

 vestigation. 



Cellulose Benzoates. The alkali celluloses also react 

 with benzoyl chloride, according to Baumann's method, to form 

 the corresponding benzoates. 



(a) Mercerised cellulose. This form of alkali cellulose, 

 treated with benzoyl chloride in the cold and in presence of 

 excess of alkali, gives a mixture of products, the numbers 

 obtained indicating that reaction occurs in the ratios, 



C 6 H 10 5 : C 6 H 5 .COOH and C 6 H 10 O 5 : 2 C 6 H 5 COOH. 



Cellulose Benzoic acid 



Within the limits of Concentration, producing the specific 

 'mercerising' action the lower limit being at about 12*5 

 p.ct. NaOH the degree of benzoylation is inversely as the 



