(cyclic trimer) and 12.27 microns, Si(CH& methyl rocking mode (Bellamy, L. J. "The Infrared Spectra of Complex Molecules," pp. 334-9, Wiley, New York, 1960). If the flask were rinsed with benzene-CCL prior to the chromic acid treatment and then cleaned as described, the hands increased in intensity.
This is probably due to increased chromic acid oxidation of the very thin film of silicone grease deposited on the flask walls. To eliminate these infrared hands i t was necessary to remove the stopcock plugs and clean thoroughly the silicone grease from the stopcocks and then fill the flask with chromic acid
cleaning solution and allow it to soak several hours and finally complete the cleaning as described previously. We also find that with Kel-F grease i t is not necessary to remove all the grease from the stopcocks prior to chromic acid cleaning, and in no case " have . extraneous infrared bar . .
Dark-Field Microscopy at Elevated Temperatures on the Kofler Hot Stage Clinton D. Felton.' Stamford Research Laboratories, American Cyanamid Co., Stamford, Conn. HE
most common microscope hot
T stage in use in laboratories is the
Kofler hot stage. Usually the behavior of materials a t elevated temperatures on this hot stage is observed microscopically by bright-field and by polarized, transmitted illumination. Some systems, however, contain certain components which are not visible by such illumination due to transparency, size, isotropy, etc. Frequently these optical discontinuities may readily be made visible by transmitted, dark-field illumination. Yet dark-field is not generally used with the Kofler hot stage simply because it has not been considered or because the difficulties presented by the physical.design of the hot stage seem to preclude its use-Le., its small viewing port, the thickness of the heating block separating condenser and specimen, and the thickness of tkle heating chamber, requiring the use of long working distance objectives. These difficulties were overcome 1-,Y use of the basic central-stop methcId for obtaining dark-field illuminati0 n. First, the simple condenser in the h
