The Specific Surface and Density of Some Soils and Their Colloids

It has long been recognized that the magnitude of the surface area may bear an important relationship to other properties of soils and soil colloids. While many attempts (5) have been made to obtain the specific surface area, the results obtained so far can be considered, at best, only as approximations or estimates. Emmett, Brunauer, and Love (?) pointed out that the measurement of physical adsorption of nitrogen at -183°C. offers means for calculating the surface area of colloidal solids, and have demonstrated the applicability of the method to soils by applying it to Barnes and Cecil soils and to the colloids derived from them. The work described in the present paper is an extension of this method to a number of representative soils and colloids of the great soil groups, and to a few minerals known to occur in the soils. Measurements were also made of the adsorptive capacity of the soils and soil colloids for nitrogen, oxygen, and carbon dioxide at 0°C. A slight modification of the adsorption apparatus made possible measurement of the density of the soils and colloids by the use of helium gas, a non-adsorbable gas at. 0°C. The use of helium gas has certain advantages over the commonly used pyknometer method employing liquids because it assures a more complete penetration of the interstices of the solid and precludes the possibility of any chemical or physical changes during the measurement.