The absorption of organic vapours by thin films of nitrocellulose

Abstract

To check modem theories of high-polymer solutions measurements have been made of the effect of dissolved nitrocellulose on the vapour pressure of each of the following compounds: acetone, five other aliphatic ketones, dioxane, ethyln-propyl ether, acetonitrile and nitromethane. All measurements were made at 20° C, the vapour pressures being directly observed and the mixtures analyzed by magnetic weighingin situ. The results for acetone confirm those by earlier workers, The isotherms for ethyl propyl ether, acetonitrile and nitromethane are satisfactorily described by the equation of Huggins (1942) with a different constant value of the parameter μ in each case. These μ values lead to a constant value of the ‘solubility parameter’ of nitrocellulose which is compatible with earlier data on the absorption of hydrocarbons and of diethyl ether. In contrast, the isotherms for the six ketones are not satisfactorily explained in that (a) the 11 values are not constant for any one isotherm , (b) the values predicted from ‘solubility parameters’ are incorrect. An alternative explanation is proposed, based on the Bronsted-Koefoed (1946) concept of ‘congruence’, which leads to an equation with one constant which is approximately the same for five of the ketones studied and for two ketones studied by previous workers. This equation is shown to be in agreement with previous work on (i) osm otic pressure, (ii) the absorption of carboxylate esters, (iii) the vapour pressure of acetone solutions of simple nitrate esters, and some further consequences are discussed. The results for dioxane and di-isopropyl ketone remain, however, anomalous on either interpretation. In an appendix vapour-pressure data are given for the compounds studied, and are compared with previous observations.