20 Dr Fenton and Mr Berry, Studies on Cellulose Acetate 



is soaked with alcohol, then a measured volume of normal alkali 

 is added and allowed to stand for 24 hours. The excess of alkali 

 is then determined by standard acid. The mean result was 54 per 

 cent, of acetic acid calculated for the dry substance. 



(2) Cold alkaline saponification (Boeseken, van der Berg and 

 Kerstjens, Rec. Trav. Chim. 1916, xxxv. 320). The substance is 

 treated with strong aqueous potash for one or two days. A measured 

 excess of normal hydrochloric acid is then added, the liquid then 

 boiled for a moment to expel carbon dioxide and the resulting 

 solution titrated with baryta water. The mean result calculated as 

 above was 53-5 per cent, of acetic acid. 



(3) Hot alkaline saponification (Barthelemy, Moniteur Scienti- 

 fique, 1913 (3), ii. 549). In this method the saponification is effected 

 by heating the substance with normal soda for about 16 hours at 

 85°. The excess of alkali is then determined by titration with 

 standard acid. Several experiments were made in which the condi- 

 tions were subjected to considerable variations as regards length 

 of heating and amount of excess of alkali. The extreme variations 

 in the acetyl number calculated as above were 60-0 and 62-1 per 

 cent. 



(4) Hot alkaline saponification (Green and Perkin, Trans. 

 Chem. Soc. 1906, 812). The saponification is carried out at the 

 boiling point with semi-normal alcoholic soda and the excess of 

 alkali titrated by standard acid. Our experiments yielded results 

 of 60 per cent, of acetic acid, the extreme variations being 58-2 

 and 61-9 per cent. These numbers are in agreement with those of 

 Green and Perkin (loc. cit.). 



It is evident that the methods of hot alkaline saponification 

 invariably yield results which are considerably higher than those 

 obtained by cold saponification. There can be little doubt that 

 the higher results are due to the action of alkali on the regenerated 

 cellulose. Support to this contention was obtained by digesting two 

 equal weights of filter paper with 50 c.c. of normal soda for two 

 days, one at the ordinary temperature, the other at 85°. In the 

 former case no alkali was consumed, while the heated product 

 showed a loss of nearly 2 c.c. of normal alkali on titration. 



(5) Acid hydrolysis (Ost, loc. cit.). The substance is first 

 digested with 50 per cent, (by volume) sulphuric acid. After 24 

 hours the liquid is diluted considerably and the acetic acid separated 

 by steam distillation, and titrated with baryta water. In our 

 experiments phosphoric acid was substituted for sulphuric acid in 

 order to avoid error due to possible formation of sulphur dioxide. 

 The results varied from 51-5 to 55-0 per cent, of acetic acid. 



(6) Acid hydrolysis (A. G. Perkin, Trans. Chem. Soc. 1905, 107). 

 In this method the cellulose acetate is treated with ethyl alcohol 

 and sulphuric acid, and the resulting ethyl acetate distilled into 



