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Methods of chemical analysis invariably involve physical measurements. In the simplest cases this may be a measurement of weight, volume, or density. By these means the mass of a sample may be determined as well as the mass of any of its ingredients, usually after chemical conversion to a form that will permit its actual physical separation. More frequently, the amount of the element or compound sought is estimated by measurement of the quantity of another substance required to react chemically with it. Still another method consists of direct observation of one of the physical properties of the material, such as color or some other characteristic of the substance sought and not held in common with the other ingredients. In this manner the actual isolation of the substance is avoided along with difficult and time-consuming procedures. Most modern instrumentation methods fall into the direct observation class, and a wide variety of physical properties of matter is utilized. Typical examples include absorption of ultraviolet or infrared radiation, radiant emission at high temperatures, electrical, optical, and nuclear effects. These properties may differ widely in their selectivity, precision, requirements for instrumentation, and, of course, in their applicability to specific analytical problems. Generally, thermal effects have been of little use for analytical purposes. Accurate measurement is difficult, and selectivity is often lacking. It is apparent, however, that a broad field exists here, since aside from the ordinary thermal properties that may be used to differentiate between substances, every chemical reaction is attended by an energy effect, usually thermal. Specifically, in the field of atmospheric analysis and control, heats of combustion of hydrocarbon and organic vapors in air could be used as a measure of concentration, if a convenient and accurate method of measurement were available. Frequently there is little or no need for selectivity in the usual analytical sense. In industrial processes where fumes are liberated, such as the volatile solvents in the drying or baking of finishes, concentration determinations of total combustible matter, without discrimination between the actual chemical compounds present, serve adequately for design of full-scale, disposal equipment. Measurement of heat release through catalytic oxidation appears to have considerable usefulness in other related atmospheric analysis and control problems. This paper will describe such analytical applications as have been made and discuss avenues for further refinement.
Ruff, R. J.
President, Catalytic Combustion Corp., Detroit, Mich.