X-ray Evidence for the Existence of Different Modifications of Fatty Acids

Abstract

IN continuation of the work on the high order X-ray reflections of fatty acids done in this laboratory (J. A. Prins and D. Coster, NATURE, July 17, 1926), I tried to get the high orders with stearic acid. In determining the long spacing of a crystal of stearic acid obtained by slow crystallisation from acetone, I found the remarkable fact that the crystal showed a long spacing of 43.95 Å.U., whereas a thin layer obtained by melting the acid on a glass strip gave a spacing of 39.75 Å.U. Crystals obtained from alcohol and petrol also showed the larger spacing. A film obtained by evaporating an alcoholic solution on a glass strip gave the smaller spacing, but an acetonic film gave the two spacings, the relative intensities of which were altered by slight changes in the way of forming the film. Apparently these facts point at the existence of different modifications of stearic acid.¹