ANALYTICAL EDITION
February 15, 1941
justing “Bias Control”. Start pump, set valve on “Standard Air” and “Concentration Index” on zero. Bring meter to midscale by adjusting light slit for coarse adjustment and “Standardize” for fine adjustment. After meter reaches equilibrium, shift valve to “Test Air”. Turn “Concentration Index” dial until meter returns to mid-scale. Return valve t o “Standard Air” t o check zero. Determine concentration by applying average readings to calibration curves. The motor-driven pump should not be operated in explosive atmos heres because of sparking brushes, A hand pump is provided for such conditions. Table I1 indicates the detailed data that can be obtained in less than one hour in a survey of the concentrations of trichloroethylene near a degreasing unit. The abnormally high peaks of concentration would not appear in other analytical methods listed above, except possibly with the interferometer.
Miscellaneous Applications for Analyzer I n addition to the routine analyses of air for solvent concentration, this instrument has many potential applications because of its sensitivity and speed of response. Some of these are determination of efficiency of solvent absorbents, checking efficacy of gas masks, determination of concentrations of certain vapors in gaseous products from chemical reactions, determination of concentrations of certain flammable vapors, and checking performance of fume-disposal systems. The instrument may be modified to operate continually and may be adapted for automatic control of chemical processes or for use with other vapors. By using selective absorbents, i t is possible to determine the concentration of various components of mixtures of vapors.
Acknowledgment The writer wishes to acknowledge the technical assistance of P. M. Hackett of this company and F. H. Shepard, Jr.,
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electronics consultant, in developing the instrument. He also wishes to thank F. A. Patty of the Fidelity and Casualty Company of New York, Leonard Greenburg of the New York Department of Labor, Philip Drinker of Harvard University, William P. Yant of the Mine Safety Appliances Company, A. D. Brandt of the Willson Products Company, C. R. Williams of the Liberty Mutual Insurance Company, Allan L. Coleman of the State of Connecticut Department of Health, and H. D. McKinley, M. Marean, A. A. Levine, and B. H. Vollertsen of E. I. du Pont de Nemours & Company, Inc., for sponsoring this development and for conducting field tests on the instrument.
Literature Cited (1) Barrett, H. M., J . Znd. Hug. Tozicol., 18, 341-8 (1936). (2) Cook, Warren, American Public Health Association Year Book. 1936-36 and 1936-37. (3) Couchman, C. E., and Schule, TI;. H , J . Ind. Hug. Tosicol.,21 256-63 (1939). (4) Dargie, A., Analyst, 62, 730 (1937). ( 5 ) Edwards, J. D., Bur. Standards, Tech. Paper 89 (1917) (6) Harrold, G. C.. and Gordon, L. E., J . Ind. Hug. Tosicol.,21, 491-7 (1939). (7) Kay, K., Reese. G . M.,and Drinker, P., Ibid., 21, 264-9 (1939). (8) Kohn-Abrest, E., and Mafi, Ann. hug. pu bl. ind. sociale, 1937, 373-84. (9) Olsen, J. C., Smyth, H. F., Jr., Ferguson, G . E., and Scheflan, Leopold, IND. ENG.CHEM.,Anal. Ed., 8,260-3 (1936). (10) Patty, F. A., J . Znd. Hug. Toxicol., 21,469-74 (1939). (11) Silverman, L., Reese, G . M.,and Drinker, P., Zbid., 21, 27GS (1939). (12) Smyth, H. F., Jr., IND.ENG.CHEM.,Anal. Ed., 8, 379 (1936). (13) Stenger, V. A., et at., Ibid., 11, 121-4 (1939). (14) Weaver, E. R., and Palmer, P. E., J. IND. ENG.CHEM,12,894-9 (1920). (15) Woodson, T. T., Rev. Sci. Instruments, 10, 308-11 (1939).
PRESENTED before the Division of Physical and Inorganic Chemistry a t the 100th Meeting of the American Chemical Society, Detroit, Mich.
Simply Constructed Color Comparator RICHARD H. WILHELM, Princeton University, Princeton, N. J.
T
H E object of a color comparator is to bring color images from reflecting or luminous surfaces into closely adjacent fields, thereby enabling the eye to compare the colors with sensitivity. These instruments are generally constructed with optical prisms. During the course of a rate study in which the progress of the process was followed by color changes, the inexpensive color comparator herein described was constructed. Its operation depends upon the fact that curved bars of certain resins will transmit light without a p preciable loss through the curved surfaces. Although Plexiglas was used, any acrylate or methacrylate resin with similar optical properties would be equally satisfactory.
FIG^ 1. PARTS AND ASSEMBLY OF COMPARATOR
The component parts and the assembly of the comparator &1p shown in Figure 1. Two straight cylindrical rods of resin, A , 6 inches long and 0.75 inch in diameter, were softened by heating to about 1:’ C. and one end of each was bent through an angle of about 30 . One half of the remaining straight portion of each rod was removed by milling, leaving flat surfaces, B, as shown. With a strip of reflecting aluminum foil, C, between them the two surfaces were cemented together by an adhesive made from same of the resin dissolved in equal parts of carbon tetrachloride and chloroform. A strong bond and excellent internal reflection at the surface of the bond %’erethus obtained. To prevent stray light from entering the lateral surfaces of the instrument, it became necessary to coat these with an opaque lacquer which still allowed internal reflection to take place. A coating made from aluminum powder dispersed in the abovementioned resin solution was satisfactory. Flat surfaces, perpendicular to the resin rod at each point, were ground with h e emery at D,where the light enters the comparator, and at E, the eyepiece, where it emerges. A final polish on these surfaces was obtained with a finely divided abrasive metal olish. A small convex lens in a brass tube (not showny was fitted to the eyepiece of the comparator. By focusing this lens u on the resin surface, E, the two half-circle fields appeared to e! uniformly illuminated with diffused light. In using the comparator the usual care was taken to provide illumination of equal intensity upon both colored surfaces.
An angle of 60” between incident light sources was the only one tried and is not necessarily the maximum practical angle for a comparator of this type.
