Appraisal of the Ethylene Glycol Monoethyl Ether Method for Measuring Hydratable Surface Area of Clays and Soils

Abstract

The development of the ethylene glycol monoethyl ether (EGME) method for measuring the “hydratable” surface area of soils and clays is reviewed. We have examined the EGME retention of 18 montmorillonites and compared the surface areas obtained in this way with those obtained using the b‐axis parameter and total chemical composition of each clay. The original hypothesis of Dyal and Hendricks (1950), that a monolayer of ethylene glycol (and presumably of EGME) forms on each of the opposing lamellae within a montmorillonite quasi‐crystal, is approximately correct. However, the existing evidence for beidellites suggests that this mineral species is intermediate in retention behavior between montmorillonites and vermiculites. For illites and kaolinites the surface areas measured with EGME are significantly greater than those measured with N. However, we have shown that there is much better agreement between the surface areas measured with N and those calculated from the amount of water adsorbed at a relative vapor pressure of about , using 0.108 nm2 as the molecular area of adsorbed water. Accordingly, we recommend that the amount of water adsorbed at (a saturated solution of CaBr2 at 20°C) be used as a single point determination for the routine examination of large numbers of soil samples as an indication of surface extent. We provide reasons why it is inappropriate to convert the water adsorption value to a surface area. We briefly discuss the significance of surface area measurements in studies of the chemical and physical aspects of soil and clay behavior.