Dr Fenton and Mr Berry, Studies on Cellulose Acetate 19 



experiments originated in connexion with our determinations of 

 tlie water contained in commercial samples of cellulose acetate. 

 As is well known, the water is readily expelled by exposure of the 

 material over concentrated sulphuric acid in a desiccator or by 

 heating to 100°. It has frequently been supposed that the approxi- 

 mately constant proportion of 5 or 6 per cent, of water usually 

 met with indicates a definite hydrate. In order to obtain positive 

 information on this point, we determined the pressure-concentra- 

 tion relationship in the manner originally adopted by van Bemmelen 

 in his well known researches on silicic acid {Zeitsch. anorg. Chem. 

 1896, XIII. 233). Weighed quantities of the material were exposed 

 in a series of exhausted desiccators over sulphuric acid of various 

 determined concentrations, and the corresponding vapour pressures 

 were found by reference to Landolt and Bornstein's tables. The 

 weights were found to be constant after 24-48 hours, and the 

 pressure concentration relationship showed that no chemical 

 hydration occurs. The phenomenon is to be regarded as one of 

 adsorption, probably with subsequent difiusion, and is precisely 

 similar to the absorption of water by cellulose itself. (Compare 

 Masson and Richards (Proc. Roy. Soc. 1906, lxxviii. 421), Trouton 

 and Pool {Ibid. 1906, lxxvii. 292) and Travers {Ibid. 1906, lxxviii. 

 21, and 1907, lxxix. 204).) 



Characterization and Analysis of cellulose acetate. 



In the technical analysis of cellulose acetate, it is usual to 

 examine the product by the heat test, solubility, acidity, and 

 viscosity of the solutions, in addition to the determinations of 

 acetyl (as acetic acid), copper reducing power, water, ash, and 

 impurities. We have made an exhaustive investigation of various 

 methods of carrying out these determinations, especially of the 

 acetyl number, and have also carried out many ultimate analyses 

 for carbon and hydrogen in some commercial specimens of the 

 material. 



The methods of determining the acetyl group may be classified 

 under the two heads of alkaline saponification and acid hydrolysis. 

 In the former the substance is saponified by excess of standard 

 alkali, either at the ordinary temperature or at some higher tem- 

 perature, and the excess of alkali determined by titration. In the 

 latter, the substance is hydrolysed by strong acid, usually sulphuric 

 or phosphoric, and the resulting acetic acid separated by steam 

 distillation (Ost), or alcohol is added and the resulting ethyl acetate 

 distilled off and collected in excess of standard alkali (Green and 

 Perkin). The following is a summary of the principal results 

 obtained in our experiments. 



(1) Cold alkaline saponification (Ost and Katayama, Zeitsch. 

 angew. Chem. 1912 (25), 1467). A known weight of the substance 



2 2 



