Treatment of Gases and Vapors

A volatile substance may exist in one of three broad classes that can be loosely termed gases, vapors and liquids. 

A gaseous substance such as oxygen at normal environmental conditions exists at a temperature exceeding its critical temperature of 155 K. No vapor pressure can be defined or measured under this super-critical condition, thus no Henry s law constant can be calculated. Empirical data are required. 

A substance such as propane with a critical temperature of 370 K has a measurable vapor pressure of 998000 Pa, or approximately 10 atm at 27°C, which exceeds atmospheric pressure of 101325 Pa, the boiling point being -42 C or 231 K. It is thus a vapor at normal temperatures and pressures. A Henry s law constant can be calculated from this vapor pressure and a solubility as described earlier. 

Most substances treated in this handbook are liquids or solids at environmental conditions thus their boiling points exceed 25°C. Benzene, for example, has a critical temperature of 562 K, a boiling point of 80°C and a vapor pressure of 12700 Pa at 25°C. 

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There are many excellent books and articles describing collection and analytical methods for specific gases and vapors. Below, are listed only a few of the many possible sources that treat the subject of collection and treatment of gases and vapors [6-10],... 

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