Studies of Aluminum Soaps

I t has been shown by McBain and collaborators I that aluminum soaps present characteristics somewhat akin to proteins in their lyophilic colloidal behavior. These soaps, particularly the aluminum disoaps AIOHR~, are solids which can be prepared relatively pure. No macroscopic crystals have yet been obtained but powder x-ray diffraction patterns show structures varying from almost amorphous to quite crystalline. These soaps are inert in water but swell and dissolve in hydrocarbons. Depending on conditions, a brittle non-homogeneous gel of discrete lumps may be formed, or a stringy viscous elastic and transparent jelly. The jelly passes imperceptibly into a sol of low viscosity as the temperature is raised or dilution increased. Many additives have a peptizing effect changing the gel to jelly or even to sol. All forms show marked hysteresis in phase change and in viscosity, the latter depending both on prior flow (thixotropy) and prior heating (calotropy). The non-volatile soaps may be easily recovered from a mixture or solution in more volatile hydrocarbons such as isooctane or cyclohexane without change of composition. Properties of recovered soaps depend on the method of recovery. By rapid freezing of a dilute sol and removal of solvent by sublimation, the soap is obtained in its most amorphous form as an extremely fluffy and light mass, which is readily and rapidly redissolved by the solvent and thus may be properly considered to be a lyophilized form. In the course of the study of these soaps, electron microscope pictures of the lyophilized forms were obtained with Dr. L. Marton's kind help using the Stanford electron microscope. They showed a peculiar, fine structure of films and fibers. In view of the practical importance of hydrophilized proteins and the apparent absence of published electron microscope pictures of lyophilized colloids, the method of preparing specimens and the accompanying photomicrographs (Figs. 1 and 2) are of interest. Preparation of Samples.--Transfer of particles of prepared lyophilized soap onto the electron microscope object holder failed to give good pictures. The soap was therefore prepared directly on the object holder which was of the type