Summary The mesomorphic or “liquid crystalline” neat and middle phases encountered in aqueous systems of soaps and synthetic detergents differ considerably in plasticity. Nevertheless, in fundamental phase studies or the examination of commercial products and processes, identification of these two phases has hitherto been uncertain, particularly when they are mixed with each other or with other phases; even under the polarizing microscope, their identification has not been positive since, by the classical criteria for identifying mesomorphic phases, both are “smectic.” The present work reveals additional criteria by which the two phases may be satisfactorily distinguished. In the first place, there are non‐geometric textures exhibited by middle but not by neat. Conversely, there are planar textures exhibited by neat but not by middle. Furthermore there are important systematic differences even among the focal conic textures upon which the smectic nature of the two phases has previously been predicated. While the microscopic method now makes possible the identification of phase mixtures, it serves also as a rapid method even where one‐phase compositions are concerned. This study is primarily descriptive in its present state of development, but the existence of systematic microscopic differences between these two nominally smectic phases, coupled with their well‐known and pronounced difference in consistency, suggests a fundamental structural distinction between them. Much of the present subject‐matter applies also to such materials as certain wetting agents and dyes, as well as phosphatides and certain other biological substances.

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X-ray powder patterns on anhydrous sodium palmitate show that the five phases already known to occur between crystal and isotropic melt can be grouped into two basic structures. Both structures are liquid crystalline, i.e., crystalline in the direction of the long spacing and liquid-like laterally. Between the lower temperature "waxy" structure, which includes the previously known subwaxy, waxy, and superwaxy phases, and the higher temperature "neat" structure, which includes subneat and neat, there is a pronounced break in the curve of long spacing vs. temperature; in addition, the three waxy phases exhibit two diffuse short spacing rings, whereas the neat phases exhibit only one. These pattern differences lead to the interpretation that the waxy phases contain structural restraints on molecular position and motion not present in the neat phases.

The Phase Nature of Beta Sodium Palmitate 141 method in rats proved to be identical. An explanation for this was found in the ability of the rat to convert neovitamin A to vitamin A.5. Catalytic interconversion of the anthra-quinone carboxylate esters of the two vitamins was accomplished in vitro by the action of iodine in benzene solution.

CLINICAL tests have shown that topical application of fluorides to erupted teeth will reduce dental caries.1 Stannous fluoride has been found to be more effective than sodium fluoride in reducing decay when applied topically.2, 3,4 In an attempt to elucidate the mechanisms by which the fluoride exerts its protective action, extensive studies5' 6, 7 have been made of the effects of inorganic salts on rate of solution of enamel in acid solutions. Since many salts, and particularly the fluorides, reduce the solution rate, studies of the nature of the chemical and physical changes which occur in the enamel have been made using electron microscopy and x-ray and electron diffraction.8-13 It has been shown that treatment of enamel with sodium fluoride results in the formation of calcium fluoride. The diffraction studies have shown no such changes after treatment with stannous fluoride, but have suggested the presence on the enamel surface of an amorphous layer of unknown composition. The prior work does not include a comparative study of the visible effects of the reagents on the structure and properties of intact enamel surfaces.The present work shows the effects on whole enamel surfaces of treatments with aqueous solutions of stannous fluoride, sodium fluoride, and nonfluoride stannous salts, over a range of pH values. In addition, the effects resulting from the exposure of these treated surfaces to acid buffer solutions are described. EXPERIMENTAL METHODThe teeth used in this investigation were human maxillary first incisors which were stored in a 0.5 per cent formaldehyde solution. No prior history of the teeth was available. Rectangular pieces of whole enamel from these teeth were cut from the labial surface. The area of the enamel surface varied between 4 and 16 sq. mm., and generally it was possible to cut 9 such specimens from a single tooth. The cutting was done with a circular jeweler's slotting high-speed steel saw operated at low speeds under water to prevent heating and drying of the tooth.