Collection of Mist and Dust for Particle Size Measurement Electrostatic Precipitation o n Hemacytometer H. G. BOURNE, JR., AND LEE B. FOSDICK Division of Industrial Hygiene, Ohio Department of Health. Columbus, Ohio IJsing commercially available apparatus, air-borne particulate matter is precipitated electrostatically upon a bright-line hemacytometer with the aid of two simple fixtures described by the authors. The diameter of individual particles is measured in the customary manner with a filar micrometer. The size range of atmospheric dust and in-plant dust and mist as ascertained by the proposed method is compared with results obtained using the Owens jet dust counter, and with that of factory dust in general as reported in the literature. Advantages of method are: Density of deposits may be controlled; solution of dust and mist is avoided; and particles are precipitated in their original state.
C
OXTAMINATION of the atmosphere and its potential adverse effect on health are causing wide concern. hleasurement of the size of air-borne particulate matter is an important phase in the study of atmospheric pollution, because toxicity evaluation and methods of control are based, in part, upon a knowledge of particle size. Furthermore, the degree of obscuration of light during smog conditions has been shown to be largely dependent upon the particle size of the air contit minan ts (12). In a study of the working environment of a plant manufacturing sodium bichromate it was necessary to collect many samples of air-borne dust and mist for particle size measurement. High dust concentration, the presence of chemically reactive soluble sodium monochromate and bichromate dust and mist, and suspected wide range of particle size presented an unusual collection problem. Preliminary trials using the Owens jet dust counter (If) showed this instrument to be unsatisfactory because the dust tkposit was of such density that individual particles could not IF visually isolated for microscopic measurement. Moreover, liquid droplets disintegrated when they impinged upon the slide. It has been reported ( 2 ) that this device s h o m a selectivity triward particles of 2 microns or less. The Greenburg-Smith
impinger (9) necessitates a liquid collecting medium. Use of this apparatus would require the selection of a liquid in which the chromate dust or mist was insoluble and with which it would not rcact. Furthermore, liquid droplets for size measurement cannot be collected with the impinger, as their size would t)e :iltCred by impact. Seither the cascade impactor (10)nor the thermal precipitator (fb) was available for this study. The expansion of the air through the jets of the cascade impactor causes condensation of moisture] sometimes resulting in agglomeration of the particles. The commercially available thermal precipitator deposits the dust in a narrow line on the collecting slide. The dense deposit. especially in a heavily contaminated atmosphere, renders it impossible to distinguish individual particles. T o alleviate this condition by a drastic reduction in the manufacturer’s prescribed air flow (7 cc. per minute) would appear impractical. Stokingcr and Laskin (IS) employ an oscillating slide to spread out the thermal precipitator deposit. Electrostatic precipitation a p peared to he the most logical solution to this problem. Drinker et al. ( 7 , 8) and Barnes and Penny (1) have established that electrostatic precipitation is a satisfactory means of collecting :+borne particles for size measurement. However, the apparatus employed by these earlier investigators is not conimercially available nor readily constructed. The authors have succeeded in precipitating air-borne particulate matter on a hemacytometer having a metallic conductive surface. The hemacytometer then may be transferred to a microscope stage where the particles are measured using the filar micrometer method (2). APPARATUS
6 ’\ Figure 1.
Two Fixtures Adapting Hemacytometer to Electrostatic Precipitator Electrode
The apparatus consists of a Spencer No. 1483 bright-line hemacytometer, the Mine Safety Appliances electrostatic precipitator, and two simple fixtures which are shown schematically in Figure 1. One fixture serves the dual purpose of supporting the hemacytometer in a horizontal position and preventing air from flowing in the space beneath the hemacytometer. It consists of an Lshaped piece of sheet copper, A , the short side of which is curved to fit the inner periphery of the outer electrode. The other fixture is a frame-shaped piece of copper, B, placed about the conductive surface of the hemacytometer, C , and provided with ears a t each end n-hich extend downward to make contact with the copper sheet beneath. D shows the unit as it would appear in the outer electrode; the electrode is represented by the dotted lines. Figure 2 shows the sampling head of the electrostatic precipitator containing the described equipment. Two minor alterations of the electrostatic precipitator are necessary, The normal rate of air flow (2.0 cubic feet per minute) through the precipitator will usually produce an excessive deposit of dust on the hemacytometer in less than a minute. It is therefore necessary to reduce the flow to approximately 0.1 cubic foot per minute by providing an adjustable “air bleeder hole” in the
1563
ANALYTICAL CHEMISTRY
1564 Table I.
Size Distribution of Air-Borne Nonindustrial Dust Percentage Less Than Stated Siec 50.00 84.13 15.87 50.00 84.13 Orens Jet Method, Hemacytometer Method. Mioron Micro" 0.3 0.6 1.0 0.3 0.5 0.9 0.3 0.6 1.0 0.4 0.6 0.9 0.3 0.6 0.9
15.87
Bample'
No. 1
2
3 200 wrtioles mehawed in o ~ d ~i s m p l e .
~~
ratus, measurements of the yart,ir:Ic s i i , of winter air-borne dust in a downtown office mdc! using oil immersion and H. inagniticittion of 960X. The data were plotted on logarithmic probibility paper (Codex Bcok Company, Inc., No. 3128) and the statistical parameters were dckrmined asexplained hy 1hIl;tVdle (5). The results appear in T:rhlr I. The median size of industrinl dust ia approximately double that. of nonindustrial dust or that encountered in nature. I n Trahle I1 the medim and size range of both dust and mist eneountcred in the various departments of ta plant manufacturing sodium bichromate are reported. These data were obtained by the hemacytometer method of oollecting and using the filar micrometer for measurement.s rrt a magnification of ahout S O X . niscussioN
Thr question may arise its to thr: phy~iological reason for uhtnining the Siee distribution of dusts. Brown et al. (4) have submitted that size distribution i x important because the retention of particuhtc matter in the lungs as well as the depth of penetration is dependent upon particle sine. The degree of health hazard in dusty working environments is thus related and its total evaluation, therefore, necessitates a knowledge of the pmticle size distribution. It is atatistically desirable, when determining particle siso dist.ribnt,ioir using the filar micrometer method, to base the lprults
Figure 2. Sampling Head of Electrostatic Precipitator Containing Hemaoytometer and Two Fixtures
vertical tube supporting the sampling herd. The air flow is measured by the method of Bourne and Wunderle (3). The wire attached to the inner eleotrode should be bent to a position a p proximrttely equidistant, from the hemacytometer and the upper inside surfaoe of the outer eleatrode. This alteration of the center electrode position ia required to prevent arcing. METHOD
Dust- and mist-laden air is drawn throueh the ureciuitator in the customary msnner, but a t a reduced &e, ana th; pnrtieulate matter is deposited electrostatically on the conductive surface of the hemacytometer. When a sufficient deposit has been obtained, a8 ascertained by visual inspection and experience, the hemacytometer is transferred to the stage of a microscope and the particles are measured using a filar miciameter as described by Drinker aud Hatch ( 6 ) . The deposit may be protected by 8. glass slide and the whole ulacod in a, dust-tieht container for tmnmortation if the size me&urements are notionduot.ed in the field.
Figure 3. Dust from Industrial ttmosphere Deposited h, Electrostatic 1'recipit.llion o n Hemacytometer
~
PARTICLE DISPERSION
The accurate measurement of individual particles is impossible if agglomeration occurs. In Figure 3 a photomicrograph of a typical industrial dust is shown to illustrate the absence of coalescence using the method proposed. The particles show a high degree of dispersion, and a similar conclusion can be drawn an the basis of visual observation of other samples. If, during sampling, the density of deposit becomes so great as to make particle size measurements impossihle, agglomeration might be anticipated. RESULTS
To compare the results obtained with the electrostatic PI.?cipitator-hemacytometer method and the Owen8 jet dust. nppa-
Table 11. Particle Sise Distribution in Sodium Bichromate I'lant (Microns)
Dust ore preparation Roast
1:iitering I\eutra1iring
Liquor Shipping Office and laboratory Maintenance Plant aversze, dust Mist
0.8
1.7
3.7
1.,5
3.8
9.8
Finishing LiWOr
Plant *verage, mist
zoo p.rtie1ea meaeured in endl ha,"/,lC.
1565 ~il:trit, samples collected in proximity tu dustproducing processes, wch as those carried on in the ore preparation department, had a nirdian size (2.2 microns) greater than those in the maintenanre liuilding (1.1 microns) which is more remote from the major w u r w c of dust pollution. This gr:itl:ition i b logic-a1
nL:CEI\-E." h l a r c h 1:i, 1930. This rirojccr was supported by a cancer control grant from t h e Xntional Cancer Institute, U. S. Public Health Service, CS-887, 'rl~ornasF , 11nnciiau. ?,l.lL, i~riijrr.1dirrrtor..
Coulometric Titration of 8-Quinolinol w'. Ti.CARSON,
JR.
Hariford F o r k s , General Elertrir Company, Rirhland, R'ash.
4 microtitration of 8-quiriolinol with electrolytically generated bromine is dcscrihed. The use of an improved electrometric indicator circuit permits direct titration of samples containing 0.4 to 2.0 mg. of 8-quinolinol with a precision of =tO..5%, in spite of the slowness of bromination. The amount of bromine used is measured by determining the number of coulombs of electricity passed through the electrolysis cell by electrolyzing at constant current and measuring the time. 1 simple, electronically controlled ronstant current source suitahle for use in the titration is described.
T
IIP: estimation of 8-quiiioliriol (&hydroxyquinoline, oxini,) is important in the determination of metals that form insoluble precipitates with it. In the volumetric method. thr metal quinolate precipitate is pu ti h y a suitable procedure and the 8-quinolinol content is det ined by dissolving in acid, adding : i n excess of brominating agent, and back-titrating with arsenite or thiosulfate. A direct titrxtioii with electrolytically generated tromiric was studied and found to bc practical. I n this method, t hr amount of bromine gener:ited is measured hy determining the iiumher of coulombs passed through the cell. The use of electrolytically generated bromine in analysis is well cbst:il)lishcd. It has been used for. the determination of arsenite lycols (3),mustard gas (4), thiocyanate, hydrazine, and imine ( 5 ) . It is espcinlly useful for microtitrations, as the amount of bromine added is easily controlled and accurately memured for rates :is low as lo-* equivalent per second. No standard solutions are required and the method lends itself to routine use. The principal reactions occurring in the analysis are those of I)romincr formation and bromination of oxine.
Formation of Br? :tt t~l~,c~tr(;tle. 2Br-
--+
Br?
+ 2e
Concurrently H?is formed at cathode. 2H"
+2 ~+ HZ
Bromination of 8-quinolinol. C9H,0S
+ 2Br2--+ (~pHaO?;Br?+ 2HBr
The bromination of onr mole of 8-q~iinolinolthus requires the passage of 4 f:irndays of elrctricity. APP4K \"bS
Constant Current Source. The clrruit of the constant current source used in these experiment^ I- bhown in Figure 1.
The output current flows through resistors R-1 and R-2, which are the input of a conventional voltage regulator circuit. The voltage regulator circuit holds the I R drop across R-1 and R-2 (.onstant and compensates for changes in the output current.
