250 Cellulose 



been noted that when dissolved in zinc chloride, more especially 

 in presence of hydrochloric acid, there is a progressive hydrolysis 

 of the molecule, with conversion into soluble products. 



It is evident, therefore, that the hydration of cellulose has 

 nothing in common with hydrolysis ; the cellulose molecule 

 appears to have an indefinite capacity for combining with water 

 and for undergoing an extensive series of hydration changes with- 

 out affecting its fundamental constitution. 



Cellulose is usually regarded as a * condensed ' derivative, pre- 

 senting more or less analogy with starch. But in resistance to 

 hydrolysis there is a marked and very important distinction, the 

 due interpretation of which will no doubt result in establishing for 

 the celluloses a special constitutional type. 



We write the cellulose unit as C 6 H 10 O 5 , remembering that this 

 merely represents the empirical facts of its ultimate elementary 

 composition. It is of course evident that at least one of the O 

 atoms is present as carbonyl oxygen. Further, we may regard 

 the constituent groups of the molecule as grouped around the CO 

 or negative, and a CH 2 or positive centre. There are many evi- 

 dences of a ' polarity ' of this character manifested by cellulose, as 

 by other * carbohydrates,' in reaction. The thiocarbonate reaction 

 proper we may regard as localised at the more negative OH groups, 

 i.e. those in proximity to CO, which are held in combination by the 

 alkali used in mercerisation or the formation of alkali cellulose. 



The attendant phenomena of mercerisation indicate a consider- 

 able degree of hydration of the cellulose (combination with water), 

 associated with the entrance of the alkaline groups. This gela- 

 tinous condition of the alkali cellulose hydrate conforms with the 

 characteristics of the earlier stages of the process of solution of 

 colloids. The completion of the process requires in this case the 

 additional strain of the carbon disulphide, evidently acting as an 

 acid group. It is certainly noteworthy, as already pointed out, 

 that all the solvents of cellulose (as cellulose) are of a saline cha- 

 racter, and may be regarded as forming with the cellulose, by 

 reciprocal combination with its acid and basic groups, compounds 

 analogous to the" double salts. The actual mechanism of solution 

 we cannot pretend to follow. The modern theory of solution in the 

 hands of its most advanced exponents confines itself to the inves- 

 tigation of the molecular condition of substances in solution ; and, 



