Document Yjq5BDMx6aJOQLmDvbmZENnrk

204 FRANK A. PATTY significant size, this factor of unresolved particles may be of considerable imppg tance. Holden and Hyatt60 propose that in the evaluation of exposures to dustsi^f taining free silica, a sufficiently large sample of air-borne dust be collected ^ sized by allowing the suspension in alcohol to settle for a measured time.'.Tin larger particles settle out leaving in suspension the particles 5 n or less in -dip eter; the silica content of this latter fraction is determined in order to apprau the relevant silica dust exposure. C. WEIGHING THE SAMPLE It is possible to evaluate certain classes of particulate samples by w'gi|jjf This may be true of impinger samples (especially useful with soluble dustS" well as samples collected by filtration or by electrostatic precipitation. 3n 'iffj? manner the milligrams of toxic contaminants per cubic meter of air mayl determined, and by ignition the sample may be divided into combustible? incombustible matter. Bloomfield and DallaValle,61 by weighing 611 imping samples upon which counts had been made, found a certain amount of correfljp between the weight and count, as given in Table 5. Since particle-size distribut TABLE 5 Correlation between Particle Counts and Weights of Air-Borne Industrial Dusts|| ...... . Kind.of .dust.. ......... . ... Bituminous coal Anthracite coal Granite Metal grinding and polishing Cement' All dusts Coefficient of ..................... correlation .... 0.847 0.771 0.755 0.698 0.694 0.726 Millions of dust paghcj eauivalent t,r- :| 44 A-.4 31 .-}j& 19 is ; (.:ss 35 `:'s.SS M is a tremendous factor to be considered in any attempt to evaluate 'weil count in terms of the other, in most cases such a conversion is not practiBjJI if attempted is apt to be translated into erroneous conclusions. --- ---------------------------------------------D.- ANALY2INCJCHEDESI_____ __ 1. Chemical Analysis for Toxic Materials Dusts collected by the impinger, the paper thimble or other filtrate! dium. of the electric precipitator may be analyzed by chemical method^SOj consideration being given to the amount of sample "in relation to th'e^^^^^5 and precision of the method. Methods of analysis for the toxic elemenj|ffi 80 F. R. Holden and E. C. Hyatt, Annual Meeting Ind. Hyg. Foundation Amer.,-P:if' (11345). " J. J. Bloomfield and J. M. DallaValle, V. S. Pub. Health Bull. No. 217 (1935) `Jl sVh- iga?;-.: SAMPLING AND ANALYSIS OF CONTAMINANTS 205 fK'-V'."'!* j^l'ls'r-w-i-11 be discussed individually in Volume II of this book. Differ- fEge' silica (SiOs) from silicates cannot be accomplished satisfactorily However, the quartz content of dusts containing representa- |,,a"]0'^r more in diameter may be satisfactorily determined in samples lij^by combining chemical and petrographic techniques. For such ^pfe'^mly.representative of an exposure they should be collected in the ',^sp*^.j:f^',b1efipfcthe workman. Nevertheless, ledge or rafter samples are not to be when selected with due consideration to obtaining air-borne or sifted deposits, they offer useful information regarding '`(xtSCuJ` i'^ntly more reliable than the analysis of unselected deposits or 'j-Sf^vVn'^-liimiiterial. `l' B. Determination of Quartz KiadstiV&J'Shined Chemical and Petrographic Analysis. If one is interested only ti^^'.ea^mination of free silica, especially quartz, in a sample of dust ranging "'k 'vt/c&yvl1 'j.u:;'[/greater, it is only necessary to clean the dust, removing as much mmpW^J^i^b^iparJicles other than free silica, and to estimate the free silica in the l&useibf petrographic methods. The procedure may be simplified and ' ` $dj^;f|lk)ws. A portion of the dust, between 0.1000 and 0.5000 g., is ^doiusijfeable. organic matter is present the weighed sample should first jflwise it is placed directly in a pyrex beaker and 30 ml. of con- hjjdiiochl'pric acid plus 10 ml. of concentrated nitric acid are added. The Saker-are-heated-to-boiling-on-a-hot-platefor-20-minutes,diluted fmEjif hot water, heated to boiling, filtered through No. 42 What&i||ind washed with hot water. The paper and residue are then jgjj&ighed crucible, dried, ignited at about 600 C. until the carbon i|||b6i'ed, and weighed. To examine the residue with a petrographic ^wfparticles are transferred to a microscope slide by means of a ^<|||,(drop of immersion oil of nD 1.545 isj ^laced on the specimen, Bi&a opveJ" slip. ^'`inMmmeVsion oils may be prepared covering the refractive index range of 1.46 paraffin oil (1.46) with monochlorqnaphthalene (162). Simi- ^tt^'^mmi^thalene.(1,65) may be used. If the refractive.,ipdex of,eaph constituent ??Ji^1, A^.'Sri'>?i%.(i^6fe"0^:bl!l*ro''*' Present.'antl"those"'pfodubts-are-addedrthe sum v-j^the refractive index of the mixture. The oils should he thoroughly mixed linHex at 25' C. determined by means of an Abbe refractometer. examined at about 450x magnification: a iSx objective and ^.'l.ni^;'(;^|Kjlfave-proved very satisfactoryv-Should-the-particles-be large as cluar*'zi diatomaceous earth, chalcedony, cristobalite, or ica1 or an easily estimated mixture of these with other matg/,* . pn" may be completed by counting or estimating particles in ^U`V'i<.H!\Ql-iiss A 14.3x objective is very useful for such estimation. If the A3:*' m?-