Document 5k57Vwd7dGVX5DjjNjGorvkN5

IH Pi 194 FRANK A. PATTY average being 90 per cent. The results indicate that the two impingers in serid were 10 per cent more efficient than the precipitator for fluoride fume. No attem| was made to determine what percentage of the fluorides existed in the gasegt phase, but, inasmuch as some of the fluoride was disseminated into the air -b| contact of ammonium bifluoride with hot sand molds and molten magnesium, it reasonable to suppose that some of the fluoride existed as hydrogen fluoride . g. This gas, of course, would not be caught by the precipitator, but some would^ caught by the impingers, thus increasing their efficiency ratio and indicatinj falsely high collection efficiency, when compared with that of the precipitator'.'" This precipitator has been found satisfactory for collecting silica dust sam| for quantification by counting.41 Another electrostatic collector for dusts for lig field counting techniques was devised by Barnes.42 This device consists of| aluminum cylinder 9 inches in diameter and 12 inches long holding about V ft. of air. The ends can be closed with micarta disks that support an ionising wj axially through the center of the cylinder. A slide adapter in the side of the cylin|J| holds a special microscope slide with conducting surface. In use, the cylinder" opened and moved to the sample location, the ends are closed, the slide is covered, and the dust is deposited electrostatically in about 15 seconds. Seve samples can be taken on the same slide if desired. It has been stated that the is nearly 100 per. cent' efficient and that the slide receives a uniformly distribilg proportionate share of the dust in the air in the.cylinder at the time the curreht' turned on. ....... c: filtration---------- Paper thimbles48 have been used successfully for collecting various dusts eluding explosives. They have a very high efficiency and at an air flow of 2 c\i| per minute have been found to collect nearly 100 per cent of most dustsj|^ around 50 per cent of tobacco smoke. Filters made of salicylic acid,44 sugaiij other material to be dissolved later in a liquid medium leaving the dust in i sion, have also been used. Filter-paper disks have been, used for sampling^ blackening of the paper, after a measured volume of air has been drawn throu maybe compared with standards; or the samples obtained may be used for coiin ing, with results comparable to results obtained by the impinger method.4?^ filter-paper48 cups, with inverted cones, have been used for rapid .sampjing^ particulate matter from,large air. volumes. Molecular (membrane! filterggMMHji ful for the collection and examination of .aerosols. They are highly effici?nt| "E. C. Barnes and J. W, Penney, J. Ind. Hyg. Toxicol, 20, 259 (1938). "H. H^Schrenk, Am. J. Pub. Health, 30, 1183 (1940). "E. C. Barnes, Am. J. Pub. Health, 26, 274 (1936). **L. T. Trostel and H. W. Frevert, Ind. Eng. Chem., 15, 232 (1923). 44 F. R. Holden, W. C. L. Hemeon, and E. C. Hyatt, Seventh Annual Meeting Hyg. Assoc., Chicago (1946). 45 C. E. Brown, U. S. Bur. Mines Kept. Invest. No. 3788, 1944. Silverman and C. R. Williams, J. Ind, Hyg. Toxicol, 28, 21 (1946). SAMPLING AND ANALYSIS OP CONTAMINANTS 195 mleigipthe 0.1-^ range.47 A high-efficiency large-volume sampler that collects v".pacles' from air at the rate of 1000 c.f.m. has been constructed.48 iSas * D. THERMAL PRECIPITATION teen And Watson49 devised a thermal precipitator that draws air by water about 7 ml. per minute through a 0.051 X .0.95 cm. slot. A ni- Stj'ite ^025 cm. in diameter, heated to 100 C., is held centrally in the slot |||||||| of the slot are cover slips backed by brass blocks for cooling. As ^^^|,>between the hot wire and the cool surface of the cover glass any .jSsPy particles are deposited upon the cover slips. The efficiency of the per ent' deposit is suitable for microscopic examina- igllllljpldique includes counts and particle-size determinations with the E. SEDIMENTATION ^ jV.'^b.ciimentation cell, as devised by Green,81 is a brass cylinder 6 cm. deep Ji'if3.b(cmr|p diameter closed at the top with a swivel lid and at the bottom by a two V2-inch cover slips. The cylinder is filled with atmosIpjjjSy dosed at the point where the sample is desired, and left to stand ^^|jThen the cover slips are removed and examined under a microscope Tr||l|||p!Ying power. The method is suitable for determining the count and i6.oj|^oi dusts down to 0.2 /a in diameter (3 hours settling time). The sediSlP^i^ntended-as-aiaboratory or-research-instrument and not for field II. Evaluation of Dust Samples a samP^e may be made on. a weight basis, with or of chemical analyses, or it may be accomplished for all insoluble "^m^4&ilS'produoing and nuisance dusts by determining the number of -^-TWffM8urd volume of air. -Particles from a known volume of air.are collected, an aliquot counted in order to compute the number of particles , suspended u`)*^^^^^lP-a'losRjiMe-sampled,-the cubic foot-being-the-a.ccepted unit ttisonsm'1' " " ' .,, Arch' Ind- Hvg- and Occupational Med., 8, 412 (1953). M. W. First and Ind. Hyg,.and Occupational Medv 7, 1 (1953). a^Mgj|ytonfJ.,Jt.aAmold,.and.:F. A. Patty, Science,-122,.75M4955), and-Am-./nd '"effiOMn.. 1166.- 229933 n(1o9u55n). and H- H- Wats0D' Med Research Council, Special Reprint No. 199, '.ioiSIW Office, London, 1935. 'atson, Can. J. Research, 21, 89 (1943), , aSSpSCn. J.lnd. Hyg. Toxicol., 16, 29 (1934). MjaKs?!: ' - \ * - ' v ' >v' , 7> '