The structure of surface films. Part XV.—Amines

This paper describes observations on monomolecular surface films of the long chain amines, Cn H2n+1 NH2 , on aqueous solutions of different acidities. The lengths of the hydrocarbon chains were varied from 14 to 20 carbon atoms, five members of the series (with 14, 16, 17, 18 and 20 carbons) being used. The acidity of the solutions was varied from N/10 alkali to N/10 acid, using buffered solutions for most of the intermediate acidities. The dilution of the buffer solutions was also varied in some instances. The results indicate that the acidity of the solution is by no means the only factor affecting the structure of the films, and indeed theP H of the solution, on the acid side of neutrality, seems to be of little importance ; but the structure of the films depends very much indeed on the nature of the anions present in the buffer solutions. Entirely different results are obtained on phthalate and acetate buffers, and there is little doubt that the films measured on solutions on the acid side of neutrality are not those of the amines at all, but of their salts with whatever acid radicals are present in the water.