An extension of the Nelsen‐Eggertsen continuous flow method of surface area measurement

One of the simplest methods of surface area measurement is extended to include the size distribution of pores in the 10–300 Å radius range. This technique involves passing a mixture of 10% nitrogen in helium over the sample cooled in liquid nitrogen at a fixed rate and at various pressures to 150 p.s.i.a. causing the nitrogen partial pressure to reach its liquefaction point. Consequently the nitrogen relative pressure in the sample tube is varied in the range of about 0.16 to 1. Nitrogen adsorbed or desorbed by increasing or decreasing pressure in the sample tube is measured continuously at near atmospheric pressure by thermal conductivity. The thermal conductivity cell always ‘sees’ a reference of 10% nitrogen in helium. Hence the measured composition differences fall within a comparatively narrow range where the thermal conductivity cell output is linear. Isotherms developed by this method are compared with isotherms obtained by the pressure‐volume method of adsorption measurement and show good agreement. Simplicity of design and operation of the instrument provides fast and reliable results.