A Simple Means of Retaining Oil between Slide and Condenser.

case n > 3. In a related field, that of the natural polyenes, the C40-carotenoids, methods have been used in some laboratories2 for the preparation of stereoisomers, viz., reversible isomerization by refiuxing solutions, by iodine or HCl catalysis, and by melting crystals. Irradiation can also be effective. As the adsorption affinity of stereoisomers varies with the configuration, they can be separated by chromatographic analysis. We have now found that the methods mentioned are applicable to the diphenylpolyenes, in particular diphenyloctatetraene, and that the stereoisomers can be separated by developing the chromatogram with benzene-petroleum ether mixtures on calcium hydroxide. The reversibility of the trans-cis shift becomes manifest by spontaneous reisomerization, each of the separated isomers yielding a mixture in which the all-trans compound prevails. So far two new partially cis-isomers of diphenyloctatetraene have been observed below the zone of the starting material. They are followed by several minor zones which are under investigation. Since the adsorbates mentioned are almost colorless, the developing of the chromatogram has been followed by their fluorescence in ultraviolet light. We expect to study other synthetic polyenes by the methods indicated. L. ZECHmEISTER A. L. IERosEN GATES AND CRELLIN LABORATORIES OF CHEMISTRY, CALIFORNIA INSTITUTE OF TECHNOLOGY