Measurement of gases

The addition of an accurately measured quantity of a gas is sometimes necessary, for example to obtain selective hydrogenation of a diene. Some convenient and reasonably accurate methods for measuring gases are described in this section. 

If a gas is soluble in a suitable solvent, and the concentration of the solution can be determined by a simple analytical technique, then accurately measured quantities of the gas can be dispensed by using the appropriate volume of the solution. For example solutions of the hydrogen halides in various solvents can be determined by simple acid/base titration and solutions of chlorine in carbon tetrachloride can be determined by addition of excess potassium iodide and back titration with sodium thiosulphate. Refer to textbooks of inorganic analysis for details of these methods. 

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Manipulations involving materials sensitive to air or water vapour can be carried out by these procedures. Vacuum-line methods make use of quantitative transfers, and P(pressure)-V(volume)-T(temperature) measurements, of gases, and trap-to-trap separations of volatile substances. 

Possible Measurements of Gases Characterising the State of Combustion 38... 

Most chemical flow-through sensors based on piezoelectric phenomena (measurements of gases or liquids) are of the regenerable type. 

The detection and measurement of gases has important applications in environmental monitoring (see section 3.5.9) and in the biological and medicinal helds, where much work is being carried out on both singlet oxygen and nitric oxide. 

To better understand the effects of atmospheric processes (reactions, gas-particle partitioning, etc.) on the size distributions of PAHs in ambient aerosols, Venkataraman and Friedlander (1994b) carried out measurements of gases and particles during winter and... 

As seen throughout this discussion of the measurement of gases in the atmosphere, a critical component is the accurate calibration of the technique for the gas(es) of interest. This clearly requires sources of such calibration gases, which however, vaiy depending on the particular gas. 

Measurements of fhe solubilify of gases in ILs are increasingly important as researchers explore the use of ILs for gas separation and gas storage, as well as a solvent media for reacfions involving permanent gases. Here we present several different methods that have been used to obtain these measurements. These include traditional synthetic and pressure drop methods, as well as gravimetric methods that are particularly well-suited for the measurement of gases in nonvolatile liquids. 

Depending on conditions, frozen substances in comet nuclei can be crystalline ices, amorphous ices, and clathrate hydrates (compounds in which cages in the water-ice lattice can host guest molecules). Compositions of the ices and associated organic materials in comets have been determined from both telescopic and spacecraft observations. Spectral line measurements of gases in a comet s coma allow the identification of molecules and radicals. An inherent difficulty in spectral measurements is that volatiles in the coma are commonly broken... 

Stable Isotope Ratio Measurements of Gases and Volatile Compounds... 

A typical example of such devices for the flow measurement of gases is shown in Fig. 4.4-3 [60]. 

When properly handled, a vacuum line is a true joy to use because it provides a closed reaction vessel with excellent exclusion of air, quantitative retention of all reaction products, and a ready means for the transfer and quantitative measurement of gases. 

F. PVT Measurement of Gases. One of the primary advantages of the vacuum line manipulation of gases is the ease with which quantitative measurements are made. If the problem simply requires dispensing measured amounts of gas, a procedure such as the following may be employed. The ideal gas law is sufficiently accurate for most chemical work if the compounds are well removed from their condensation temperatures and pressures. For example, the van der Waals equation of state for CO2 indicates that 1 mmol of this gas in 25 mL will exert 749.7 torr pressure versus the ideal gas value of 748.4 torr. This disparity in pressures amounts to a 0.2% error, which is less that the other errors involved in routine PVT measurements, and is perfectly adequate for most chemical problems. 

A. Mercury Manometers for Routine Work. The pressure-volume-temperature measurement of gases is the backbone of quantitative chemical vacuum line work. For these measurements an error of a few percent is frequently sufficient and may be attained by a simple U-manometer attached to a calibrated volume and read with ah inexpensive cathetometer. 

Developments in the 1970s and 1980s allowed the first measurements of gases to be made using automated measurement techniques. Good examples include the techniques developed for the measurement of oxides of nitrogen, O3, C02, particle mass and soot (black carbon). 

Nonlinear, pressure-dependent solubility and permeability in polymers have been observed for over 40 years. Meyer, Gee and their co-workers (5) reported pressure-dependent solubility and diffusion coefficients in rubber-vapor systems. Crank, Park, Long, Barrer, and their co-workers (5) observed pressure-dependent sorption and transport in glassy polymer-vapor systems. Sorption and transport measurements of gases in glassy polymers show that these penetrant-polymer systems do not obey the "ideal sorption and transport eqs. (l)-(5). The observable variables,... 

ASTM E 800 Standard Guide for Measurement of Gases Present or Generated during Fires. Annual Book of Standards, Vol. 04.07, ASTM International, West Conshohocken, PA. 

Measurement of Gases. Since it is difficult to weigh a body of gas, but comparatively easy to find its volume, the amounts of gases are almost invariably estimated by measuring the volume. But the volume of a definite amount of gas is very dependent on the conditions, and to make a volume measurement have an accurate meaning it becomes necessary to know exactly the conditions of pressure, temperature, and dryness under which the measurement is made. To make the results of all measurements comparable it is customary to calculate what the measured volume would become if so-called standard conditions prevailed. 

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