The Polymorphism of Higher Fatty Acids

Abstract

IN continuation of former work, I have extended the study of the polymorphism of such substances (Piper, Malkin, and Austin, Jour. Chem. Soc., 1926, 2310; J. Thibaud, Comptes-rendus, 184, 24 and 96, 1927 ; de Boer, NATURE, Jan. 8, 1927) to the even and odd series of saturated acids of higher molecular weight. Thin films are prepared on a glass slip either by melting or by evaporating from a solution in ether, or better in carbon disulphide, and examined with respect to the Ka rays of copper by the turning crystal method. The result is as follows: the long spacing measured for an evaporated film differs from that obtained from a melted acid, the latter being smaller than the former. This property is quite general: for every acid which contains more than 16 carbon atoms in the molecule, the magnitude of the long spacing depends on its manner of preparation and the two kinds thus possible both seem very durable. For stearic acid I have been able to obtain upon one and the same evaporated film, two coexistent crystalline modifications.