Literature Cited Badger, W. L., and Associates Inc., Office of Saline Water Report No. 25, US. Dept. Interior, Washington, D.C., 1959. Bradstreet, S.W., Armour Research Foundation Final Report for US. Coast Guard No. 90-501G, January 31,1950. Buch, K., Acta Acad. Aboensis, Math Physica 11, 18 (1938). Cadwallader, E. A,, Znd. Eng. Chem., 59,42 (1967). Checkovich, A. (to Singmaster and Breyer, New York, N.Y.) U S . Patent 3,119,752, January 28, 1964. Checkovich, A. (to Singmaster and Breyer, New York, N.Y.) U S . Patent 3,218,241, November 16, 1965. Cockrell, C. M., ASME Meeting, Atlantic City, N.J., Paper No. 59-A-183, November 1959. “Desalting Digest,” Office of Saline Water, U.S. Dept. Interior, Vol. 2, No. 3, Fall 1968, p. 1. Elliot, M.N., Desalination 6, 87 (1969). Ellis, R., M.S. thesis, University of California, Los Angeles, School of Engineering, Los Angeles, Calif., 1969. Herrero, P., British Patent 203,886, October 11, 1923. Hickman, K., National Academy of Sciences-National Research Council, Publication 568, Washington, D.C., 1958. Hightower, J.V., Chem Eng. 58, 162 (1951).
Hillier, H., Proc. Znst. Mech. Eng. lB, 295 (1952). Langelier, W. F., J. Amer. Water Works Ass. 46,461 (1954). Langelier. W. F., Caldwell, D. H.. Lawrence, W. B.. Znd. Ena. ., Ciem. 42, 126’(1950). Liddell, R. W. (to Hagen Corp., Pittsburgh, Pa.), U S . Patent 2.782.162, February 19,1957. McCutchan, J. W., Glater, J., et a[., University of California Dept. of Engineering Report 65-1, 1965. McCutchan, J.W., Glater, J., et al., University of California Dept. of Engineering Report 66-1, 1966. McCutchan, J. W., Glater, J., University of California Dept. of Engineering Report No. 64-5, 1964. Payen, A,, Dingler’s Polytech. J. 10, 254 (1823). Sverdrup, H. U., Johnson, M. W., Fleming, R. H., “The Oceans,” Prentice-Hall, Englewood Cliffs, N.J., 1942, p 201, Zuckerman, N., Desalination 4, 167 (1 967). ’
Receiced for resiew March 25, 1970. Accepted September 2, 1970. Data for this paper are based on a M.S. thesis by R. Ellis (1969). This work was supported by State of California Saline Water Research Funds. These funds are administered by the Water Resources Cetifer at the Unisersity of California, Los Angeles, Calif. 90024.
COM M UN I CATIONS
Continuous Monitoring of Water Surfaces for Oil Films by Reflectance Measurements Alvin D. Goolsby Shell Development Co., Emeryville, Calif. 94608
rn Laboratory experimentation and plant tests have shown
that the use of reflectance measurement is a promising means of continuously monitoring water surfaces for oil contamination. The instrument resulting from these experiments is both simple and sensitive and can be used as a qualitative analyzer which would sound a n alarm if oil slicks of significant size are detected.
R
ecent concern over the possible pollution of public waters by floating oil has led to the need for an oil film detector which could be used at critical points on water streams or surfaces to announce the presence of an undesired slick. Simple first-order calculations, based on Snell’s law and the Fresnel equations (VaSiEek, 1960), reveal that the reflection of unpolarized light from an oil surface ( n = 1.40) should occur with about 50% greater intensity than from a water surface (n = 1.33), for angles of incidence in the 5” to 30” range. All hydrocarbon materials which may be considered “oils” have refractive indexes of at least 1.39, and a means for detecting oil on water is suggested therein. 356 Environmental Science & Technology
A laboratory arrangement consisting of a n incandescent lamp, collimating lens, and photodetector was used to generate a light beam incident on a water surface and to measure the intensity of the reflected beam. The measured average intensity, using an angle of incidence of 30”, increased 100% when a drop of “waste oil” was introduced on the water. Without filtration, the electrical signal was found to vary rapidly from zero V dc to a certain maximum value due to surface turbulence, which caused the reflected beam to swing back and forth across the detector. The actual intensity increase is significantly greater than the calculated value. This is possibly due to multiple internal reflections and light absorption in the oil film because thin films of oil o n water give rise to more reflected light than very thick films. The lower limit of detectability is not known, but it is probably a function of the oil’s color, its tendency to form a uniform film, and other properties. A prototype oil film monitor (Figure 1) was constructed for tests of the reflectance principle in a refinery effluent stream. The apparatus was constructed in a housing which was safe for refinery usage, and consisted of the components listed in Figure 1. The device was floated o n a waste water stream (flowing at 1 ftlsec) and the actual reflectance measurement was performed continuously at a point (B) beneath the
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