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188 PRANK A. PATTY C. CONDENSATION AT LOW TEMPERATURES Most vapors may be collected successfully by drawing them through a sditf able chamber immersed in a low-temperature bath, the temperature required being that at which the vapor pressure of the liquid or solid to be collected approachezero. A metering device for the air mixture is necessary, and the rate must hr slow enough to permit condensation and avoid loss of mist or dust of the co. densed material. The design of the condensation chamber must be such as to avSjp choking with either ice or solid contaminant condensed from the air sampled. Tl. condensed material may be weighed, measured by . volume, or determined !u quantitative chemical analysis. Ice, solid carbon dioxide, and liquid air have 'eat: been employed as the refrigerating medium. D. COLLECTION BY ABSORPTION OR ADSORPTION FOR LABORATORY ANALYSIS The collecting device here may be any of several types of scrubbers or im pingers, and the collecting medium may be granulated silica gel or a liquid of Id volatility, either of which must be a tenacious adsorbent or absorbent for the cot taminant or else it must fix the contaminant by chemical combination. The .cfi lectors may be used singly or in series depending upon their established efficieiify The collected samples are transported to the laboratory and evaluated by varirn means, which include colorimetric, volumetric, polarographic, or spectrograph; analyses, the use of the ultraviolet or infrared spectrometer, and combustion''! also4>ageaJ.82_and..l83).i____________ ____________________________ E. SAMPLING IN EVACUATED BOTTLES 1. Vacuum Bottle Samples Samples are conveniently collected in vacuum bottles for the determination oxygen, carbon dioxide, and combustible gases in the analysis of mine gases? means of the Haldane88 or Orsat10 gas burets; for the determination of radon means of especially constructed electrometers (page 731); for the determinant of nitrogen oxides by the phenoldisulfonic acid method; and for many other del ruinations. Usually this type of sample is not larger than 1 liter. The sample readily taken upon opening the bottle to the atmosphere, either by opening^"' stopcock or. a; pinchcpcEnon :a shorriengfirbf'lieavy-walle3"tubingi or off the tip of 4vsbAlfediimVet orifice, being careful not to warm thei.bottle byicS with the hands, and. then closing or sealing the orifice. ........~-%rSamples"in~Partially Evacuated BottlesSamples may be conveniently taken in partially evacuated bottles of, ai|p up to 20 liters. A measured volume of a suitable absorbent liquid is adPeds " L. B. Berger and H. H. Schrenk, V. S. Bur. Mines Circ. No. 7017, 1938. "q ff&jk-shv (few SAMPLING AND ANALYSIS OF CONTAMINANTS 189 !|;bottle and the bottle is partially evacuated by a hand pump or other f ifiefresidual partial pressure being recorded. The bottle is opened in the tm`osph|re to be sampled. It should then be taken to the laboratory, or to an un listed zone, shaken well, and the contents washed into a suitable container ISsuccessive portions of wash solution. After this, analysis may be made Ifmtte methods. jllratene of the sample is computed as follows: V.= [V-A)*fh Wpdr: sample volume, V = volume of bottle, A -- volume of absorbent to'-ithe' bottle, Px = residual partial pressure in the bottle, and P2 = ('pressure at the time and place of sampling. i F. SPECTROMETRY * 1. Infrared -.infrared spectrometer84 is a relatively new tool with great possibilities (miindustrial hygiene as a means of recognizing and evaluating organic fp$fi,the air. The basis of application is that practically all organic sub- ipniiss selective absorption at certain frequencies in the infrared portion to1um. The essential parts of the apparatus are a heat source emitting a iF,range of the wave lengths desired; a means of dispersing the radiation jj^narrow wave length bands'aTaoeiiratery Known wave length posiiispurpose prisms of sodium chloride, potassium- bromide, and so '.sugglied); cells for placing a suitable thickness of material for analysis tlupMhe radiation; and a detector, such as a sensitive thermocouple and pr|,accurately measuring the radiation. Absorption cells of various have been.used, from 0.05 mm. for liquids and solids to several meters for biie,,size,(weight, and complexity of the apparatus domot make it attractive 'tabje instrument; and the length of absorption path must be many meters to-make the instrument suitable for measuring a few p.p.m. of most gases >"-L"te((;air. However, when the material to be analyzed is absorbed or J-riSjguid, analysis is readily accomplished, providing a .liquid, .vehicle 'hc^'^^t'MknbTntreffOTingnbsbiTtibh'bRndFiFtKe significant range for &iattp|b.e analyzed. The absorption pattern furnishes positive identifica- igie compounds having a known pattern; furnishes helpf^i),,cj.uesftt.o the wTOfromplex mixtures (superimposed patterns); and identifies linkages, |&S|ps4n obscure-compounds;-It 4s- a- quantitative tool - as welly since |jl^|een found true for this region of the spectrum (the., absorption is lalgdlihe concentration of absorbent in the solution). Many ranges of WSin^th'e spectrum, between visible and ultra short radio waves, hav,e Pi B irnes, U. Liddel, and V. Z. Williams, Ind. Eng. Chem., Anal. Ed_ 15, .659 (1943). ,1 Jir*; 1 ,