The Typical Cellulose and the Cellulose Group 37 



The addition of iodine in relatively small proportion (^V p.ct.) 

 determines the solution of cellulose in acetic anhydride at 

 120-130. By this method an acetate is obtained free from 

 coloured by-products, and the yields of the product are remark- 

 ably uniform. In a series of experiments in which the propor- 

 tions of cellulose and anhydride were considerably varied, 

 the following yields were obtained per 100 parts cellulose : 



176, 175, 177,174; 



the yield calculated for the triacetate being 177. The uniformity 

 in these numbers, however, is somewhat illusory ; as in certain 

 cases the product is entirely soluble in acetone, and gives on 

 analysis the numbers calculated for a triacetate ; in other cases 

 the product is resolved into a soluble fraction giving high 

 saponification numbers (75 p.ct. acetic acid), and an insoluble 

 fraction giving low numbers (48 p.ct. acetic acid; calc. for 

 diacetate, 49). The evidence from these several processes 

 is somewhat conflicting, as to the composition of acetates 

 higher than the triacetate, and their relationship to the parent 

 molecule. 



(d) Cellulose regenerated from solution as thiocarbonate. 

 This form of cellulose has been found to react directly with 

 acetic anhydride, under what may be considered the normal 

 conditions. At 110-120 the cellulose is gradually dis- 

 solved, to a solution of quite extraordinary viscosity, which is 

 so marked that the limit of concentration is not higher than 

 10 p.ct. of the acetate (5 p.ct. cellulose), beyond which 

 point, i.e. the reaction is practically arrested. It is necessary, 

 therefore, to use a very much higher proportion of anhydride 

 to cellulose (20 : i) than in the reactions previously described. 

 The acetate thus obtained appears, from all its properties, to 

 be a true derivative of cellulose. Thus it may be prepared 

 in films of great tenacity and remarkable lustre ; and the 



