Improved Gravimetric Vapor-Sorption Apparatus

Abstract

This improved gravimetric vapor-sorption apparatus was designed for vapor-sorption measurements at 20–50°C with condensable vapors, e.g., water and organic vapors on inorganic and organic adsorbents, such as minerals and resins. The apparatus can be readily adapted to low-temperature adsorption of noncondensable gases, e.g., N2, Kr, and Ar. The system consisted of a helical spring (quartz or tungsten) sorption balance. A Pirani gauge and a mercury manometer permitted the measurement of vapor pressures from several microns to more than 100 mm. Important considerations relevant to the design of helical springs (quartz or metal) were summarized, and a comparative evaluation was made of the advantages and limitations of tungsten and quartz helices. A practical high-vacuum Teflon seal for use in place of greases and waxes on ground glass joints was developed. This seal was designed for use with organic vapors. The aqueous vapor pressures at 20°C were measured for a wide range of concentrations of aqueous sulfuric acid solutions. These data were in excellent agreement (of the order of 1%) with the published data down to pressures of 1 mm of mercury, and they provided a reliable indication of the accuracy of the vapor pressures measured with this apparatus.