ANALYTICAL CHEMISTRY
576 analytical data on them. The cooperation given this research by Frank MacNiven, chief chemist, Noranda Mines, LM., was greatly appreciated. LITERATURE CITED
(1) Claassen,A.,andWesterveld,W., Rec. trav. chim., 67,720 (1948). (2) Davies, W. C., and Key, C., Ind. Chemist, 19, 555 (1943). (3) Furman, iY,H., Bricker, C. E., and McDuffie, B., J . Wash.
Acad. Sci., 38, 159 (1948). (4) Haywood, F. W., and Wood, A. A. R., J . SOC.Chem. Ind., 62, 37 (1943). (5) Hiilebrand, W ,F., and Lundell, G. E. F., “Applied Inorganic Analysis,” New York, John Wiley & Sons, 1929. (6)
Lingane, J. J., and Kerlinger, H., IND.EXG.CHEM.,AIAL. En., 13, 77 (1941).
(7) Pieters, H. A. J., Anal. Chim. Acta, 2, 411 (1948). A v a L . ED., (8) Reed, J. F., and Cummings, R. W., IND.ENG.CHEM., 12, 489 (1940). (9) Ringbom, A., and Torn, L., Finska Kemistsamfundets Medd., 56, 12 (1947). (10) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 1st ed., p. 202, New York, Interscience, Publishers, 1944. (11) Taylor, J. K., ANAL. CHEM.,19, 368 (1947). (12) Taylor, J. K., and Smith, R. E., Ibid., 22, 495 (1950). ESG. CHEM.,BXAL. ED., (13) Willard, H. H., and Kaufman, S., IND. 19,505 (1947).
RECEIVED for review July 30, 1951. Accepted October 17, lQ51. Abstracted from a thesis submitted by Paul J. Mattern in partial fulfillment of the requirements for the degree of master of science, University of Wisconsin, June 1951.
Detection of Micron and Submicron Chloride Particles B E N K . SEELY New Mexico Institute of Mining and Technology, Socorro, N.‘Wf.
S
IGNIFICAXT quantities of chlorides exist as particulate matter in the atmosphere, particularly in air that has been recently over the ocean. These chloride particles are recognized as a principal constituent of sea haze, and meteorologists consider them to be very effective nuclei for the condensation of atmospheric moisture. The chemical method covered in this paper has enabled individual identification and counting of these air-borne chloride particles in collections made from air that has traveled more than a thousand miles from the ocean. An example of this kind of study has been reported by Crozier and Seely ( 2 ) . A number of investigators have been concerned with air-borne chlorides, but very few have dealt with the individual particles. The work of Woodcock and Gifford ( 4 ) is a noteworthy exception: They used an “isopiestic” method, as well as a titration procedure, to estimate chlorinity in sea salt nuclei. Zworykin and others ( 5 )briefly describe the use of the electron microscope for the study of aerosols. Cadle, Rubin, Glassbrook, and Magill ( 1 ) have contributed significant microchemical techniques for the study of air-borne particulate matter during their investigation of Los Angeles smog. These methods apparently have not yet been used in any systematic, broad scale studies for the detection of chlorides. The chloride identification method described is simple, and it permits picking out and counting individual chloride particles in the presence of vastly greater numbers of particles of other materials. It also is readily applicable to systematic study of a long series of collections, such as those made on an airplane flight or a t a ground station for study of the day by day abundance of chlorides. The term “chloride particle’’ in this paper is not intended to imply concern only with chlorides in the solid state. In atmospheric chlorides, for example, the “particles” will range all the way from droplets of dilute solution to practically dry crystals, depending on the nature of the salts involved and upon the ambient humidity. The identification method is equally applicable to chloride-bearing droplets and solid chloride particles, and it is by no means restricted to study of chlorides collected from the atmosphere. The work on chloride identification is one of the activities carried on under the program of air-borne particle study of the New Mexico Institute of Mining and Technology, sponsored by the Office of Naval Research (Contract No. N70NR-405/1). The method was mentioned briefly in a report to the First National Air Pollution Symposium (3). The present paper first describes the method, and then discusses sensitivity, limitations, and various applications.
GENERAL RlETIIOD
Procedure. The pi ocedure developed for identifying mici on and submicron chloride particles is basically a modified spot test. Essentially, it consists of bringing a chloride particle into contact, by impaction or otherwise, with a gelatin-glycerol film sensitized with a Epecific reagent that reacts with the particle. The reaction product then forms a persistent spot or halo which can be recognized under the microscope. In this manner the disadvantages of micromanipulation are eliminated and particle identification is rapid and very selective. Gelatin-glycerol was selected as a suitable medium upon which to make the collection because it is compatible with the chloride reagent and is stable over a wide range of atmospheric conditions. Other materials, such as agar, gum arabic, polyvinyl alcohol, and isinglass, were investigated and found to be definitely inferior. The chloride reagent is a mercurous salt. Qf all the mercurous salts tried, mercurous fluosilicate, dissolved in fluosilicic acid, proved to be the most stable when incorporated in the gelatin film. Before the development of the mercurous fluosilicate reagent, a considerable amount of work was done with mercurous nitrate and mercurous acetate. These proved fairly satisfactory for many studies, but they are very susceptible to decomposition, which leaves an objectionable background of small particles dispersed throughout the gelatin film. Silver salts, the conventional chloride reagents, are not suitable
A method was developed to detect the presence and to study the concentration of individual chloride particles in the atmosphere, in order to add to the meteorological data concerning the relative origin and behavior of certain air masses. This procedure proved to be capable of detecting and recording the presence of individual chloride particles approximately 0.2 micron in diameter and representing a gram. This method has been mass of about used extensively for the past three years and has produced reliable data. A n extremely sensitive microchemical test has been developed which can be applied to other fields of study, and with slight modifications is applicable to the detection of many ions other than chlorides. In most cases a permanent record is obtained.
V O L U M E 24, N O . 3, M A R C H 1 9 5 2
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in the form of a fairly dense nucleuus of feathery crystals in the center of the mercurous chloride halo. Such nuclei are not evident in the smaller halos that are only a. few microns in diameter, horever. The characteristics of the halo under the microscope depend somewhat on the halo size. Halos larger than 10 or 15 microns are white and are composed of comparatively coarse, highly refractive crystals. Halos smaller than 10 or 15 microns in diameterusuallyexhibitTyndal1blue with dark-field illumination. The blue color results from the well-known diffraction effect and signifies that the individual crystals of the precipitate me approximately 0.1 micron in diameter Figure 1 gives photomicrographs of some of these halos with dark-field illumination. MATERIALS AND APSARATUS
Mercurous Fluosilicate. Because of the difficulty in obtaining mercurous fluosilicate from chemical supply houses a brief description of the prepemtion of this reagent is presented.
A solution of C.P. mercurous nitrate is treated with a solution of potassium bicarbonate to precipitate the mercury as mercurous csrbonate. The mercurous carbonate is filtered in an atmosphere of carbon dioxide and washed with distilled water saturated n-ith carbon dioxide. While the mercurous carbonate is still moist it is dissolved in 29.9% hydrofluasilicic acid. This solution the; is evamraied to recover
