A N A L Y T I C A L CHEMISTRY
1782
are readily ground; and the method can be adapted to very small quantities such as those appropriate for manipulations under low-power microscopes. This possibility is of interest in criminology and for electron and x-ray diffraction work. For infrared mulls, the sample is ground in an appropriate oil that does not need removal, but if an oil-free sample is desired, the oil may be flooded off with a volatile selective solvent like hexane. Preliminary results suggest that this procedure may be useful in the preparation of samples for the potassium bromide wafer method (8, 9); however, the usual advantages from grinding in an oil medium seemed to be decreaed with substances like potassium bromide and sodium chloride that fracture into cubes, probably because the surface of the cubical crystals is relatively low.
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LITERATURE CITED
(1) ilrd, J. S., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, 1951, ANAL.CHEM.,23, 680 (1951)
(Abstract).
(2) Blout, E. R., and Fields, hi., J . Am. Chem. SOC.,72, 479 (1950). (3) DuBois, E., Ed., Better AnaEysis, 4 (No. l), 6 (1953). (4) Forriati, F. H., Stone, W. K., Rowen, J. W., and Appel, W. D., Bur. Standards J . Research, 45, 109 (1950). (5) Garlock, E. A., Jr., and Grove, D. C., J . A m . Pharm. Assoc., Sci. Ed., 37, 409 (1948). (6) Randall, H. &I., Fowler, R. G., Fuson, N., and Dangl, J. R.. “Infrared Determination of Organic Structures,” pp. 92-5, New York, D. Van Nostrand Co., 1949. (7) Sands, J. D., and Turner, G. S., ANAL.CHEhr., 24, 791 (1952). (8) Schiedt, U., 2. Naturfonsch., 8b, 66 (1953). (9) Schiedt, C . . and Reinwein, H., Ibid., 7b, 270 (1952). (10) Cmbreit, IT-. W., Burris, R. H., and Stauffer, J. F., “Llanometric Techniques and Tissue Metabolism,” pp. 114, 126, 136-8, Minneapolis, Alinn., Burgess Publishing Co., 1949. PRESESTED in part before the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 5 t o 7, 1961. Mention of names is intended for convenience and must not be construed am a n endorsement or recommendation by the United States Department of Agriculture over others not mentioned.
Device for Rapid Measurement of Chromatographic Rb Values. Anthony J. Glazko and Wesley A. Dill, Research Laboratories, Parke, Davis and Co., Detroit, Mich. for measuring chromatographic Rb A values, which hasdivider been used in this laboratory for more than PROPORTIONAL
3 years, appears to offer certainadvantagesover similar devices recently described in the literature [Rockland, L. B., and Dunn, hf. S., Science, 111, 332-3 (1950); Nettleton, R. hl., and Mefferd, R. B., ANAL.CHEM.,24,1687 (1952)]. As the scale is longer than the paper strip itself, the accuracy of measurement is as good as that obtained by manual measurements with a ruler, and the R, values are read off directly from the end of the pointer. No difficulty is experienced with proper orientation of the paper strip, since the device is transparent and can be laid down directly over the paper strip, holding it firmly in place. This device was first described by the authors a t aSymposiumon Chromatographyconducted by the Division of Medicinal Chemistry of the AMERICAK CHEMICAL SOCIETY in Chicago, September 1950. The device shown consists of a transparent triangular sheet of plastic material, such as ‘/le-inch Lucite or Plexiglas. An R, scale is inscribed on the hypotenuse, and a series of.lines parallel to the scaleisinscribed about 1inch apart on the rest of the triangle. One end of a movable arm having an index line drawn down the middle is attached to the angle opposite the Rb scale with a metal pivot. All lines can be inscribed with a sharp knife or razor blade, and filled with India ink, colored crayon, or enamel to render them easily visible. Approximate dimensions are 18 X 18 X 24 inches. The movable arm is 0.5 X 18 inches. I n use the scale is placed over the paper strip and oriented so that the paper strip is parallel to the scale, with the starting point of the chromatogram on the left-hand leg of the triangle and
the limit of solvent travel on the right-hand leg. The movable arm is then shifted to intersect the spot on the paper strip whose location is being measured, and the Ra value is read directly from the scale. This proportional divider is based on the principal of similar triangles, and has proved to be the most rapid and practical means of Rb measurement used to date.
Simple Method for DBerentiating between Borosilicate and Soft Glass. AI, I
