Dr Fenton and Mr Berry, Studies on Cellulose Acetate 21 



excess of standard alkali. The ester is then saponified and the excess 

 of alkali determined by titration. In our experiments phosphoric 

 acid was used instead of sulphuric acid for the reason already 

 mentioned. The results varied from 52-2 to 54-4 per cent, of acetic 

 acid. 



In our opinion, preference should be given to the method of 

 cold alkaline saponification of Ost. Not only are the results more 

 uniform, but they agree well with those obtained by acid hydro- 

 lysis. The latter methods are exceedingly tedious to carry out. 

 We have also carried out some experiments with the use of hot 

 baryta water as a saponifying agent and subsequent gravimetric 

 determination of the barium, the results averaging 57-58 per cent, 

 of acetic acid. 



The materials met with in commerce known as cellulose acetate 

 are most probably mixtures or solid solutions of various acetates, 

 not definite chemical individuals. If, however, it were desired to 

 represent cellulose acetate as a chemical individual, the results of 

 our analyses of a number of specimens do not correspond with the 

 formula of the triacetate C6H7O2 (0C0CH3)3 which is commonly 

 supposed. They agree better with the formula of a pentacetyl 

 derivative of C12H20O10 and still better with that of a heptacetyl 

 compound of CjgHgQOig. 



Thus 



Carbon Hydrogen Acetic acid 



CcH-Oa (OCOCH3)3 requires 50-0 5-5 62-1 per cent. 



C12H15O5 (OCOCH3)5 „ 49-4 5-6 560 



C.sHaA (OCOCHs)^ „ 49-2 5-64 53-8 



Our most reliable results average carbon 49-2, hydrogen 5-5, and acetic 

 acid 54 per cent. 



Certain authors have stated that sodium ethylate may be used 

 for the determination of acetyl in cellulose acetates. In investi- 

 gating this reaction, we were surprised to find that ethyl acetate 

 was always produced along with a yellow sodium derivative of 

 cellulose. Quantitative experiments were performed in which the 

 ethyl acetate was distilled into an excess of standard sodium 

 hydroxide, and after saponification determined with standard 

 acid. The residue was washed with alcohol to remove the unaltered 

 sodium ethylate and this solution was titrated with standard 

 acid. The residue was then treated with water to decompose the 

 sodium compound and titrated also. It was found that the quantity 

 of acetic acid converted into ethyl acetate to that becoming sodium 

 acetate appears to depend to some extent on the proportion of 

 sodium ethylate employed. The results can be explained, if the 

 average commercial cellulose acetates are represented by the 

 formula C12H15O5 (OCOCH3)5, by the equation: 



