Document ZBzGbNQYDKY7w8ED5041DKZ8

TABLE 39-E. PHYSICAL METHODS USED IN AIR ANALYSIS Method Principle of Operation Type of Range Lower (ppm) tipper (ppm) Application and Remarks Absorption (oh)metric, gnaometric or maxtotnetrie) Measured volume of gmsolr mixture b absorbed by reagent and volume shrinkage determined Pres* ore reduetum may abo be mentored (maaometric) Grab <00 1.000,000 Selective. Oxygen deficiency determinator. Special forms will detect tower eoneentrstums U S Bu reau of Mines describes a portable form for Add use, and several compact models are available IN D U S TR IA L HYGIENE Adsorption (Gravimetric) Gu-tir or vaporair mixture b trapped on ad- Continuous orbent neb as activated charcoal or tQica gd Change in weight represents weight of contami nant tn known air volume* <1 `Depends Honselective Used primarily for total solvents on when a mixture of solvents is encountered Ab amount sorbed material when eluted ean fan measured by sampled gaa chromatography Electrical Conductivity Gas-ir tobrtare b absorbed la a eolulton whom Grab deetnesl conductivity b measured before and after or absorption Continuous 001 10,000 Selective Can bo oppbed to all sod or alkaline gnses and abo to vapors which con ba burned to COa. 80s, or HC1 Field instrument available Beat of Combustion 1 Bnud Indicator or Vapotcster Caa-atr or vapor mlxtoze b passed over a heated platinum wire which ts part of a hnlnnrril Wheat* stone bridge. Combustion of the gas on the wire unbalances the bridge Grab 80 1,000 Selective Field instrument was designed unmanly for benid but ean be applied to other combustible Buses not removed by water vapor absorbent whieb b provided for proper operation of the instrument Exphmmeter la a baa sensitive form of the above 8 Expknoiter instrument for explosive oaneentratsoas of Bam* (Flammable) matte gases Grab 10,000 and up <0.000 Water vapor absorbent not necessary of tower eensitmty Single meter calibrations for oil gnses the product of wboae mobeular heat of com bination and the tower explosive limit ta o ran- teat. 8 CO Indicator Gas b passed over a catalyst (Hopcalite) which Continuous (Hopcalite) convert* CO tn CO* Bast of combustion b mensurad by thermopile connected to a galvanometer. 10 10,000 Portable apparatus for field use Water vapor and ml fumes are removed eo they eannot poison catalyst.