ABSTRACTThe porosity and particle spacing was determined for a number of plastic and non‐plastic materials under various conditions of wetness and pressure. This was done by pressing the material in a cylindrical mold and measuring the resultant density of both the freshly‐molded and the dried specimen. The results show that all of the materials at the lower pressures have a critical water content, beyond which the particles re‐orient themselves into a denser packing. This point corresponds to the pores being one‐half filled. The clays are differentiated from the nonplastic materials by their ability to hold a stable water film onto the surface of the particles. The maximum stable thickness of this film occurs at or beyond the point where the pores are filled, and for the clays tested averages about 3 × 10−6 Cm. in thickness. This film is so stable as not to be influenced by pressures as high as 800 kilograms per square centimeter. A size analysis of the particles of all the materials was made, and their average sue and diameter computed. All of the materials were found to have some elasticity when the pressure was relieved. These data taken as a whole allow the construction of a comparatively accurate picture of the clay structure.

Norton, F. H., & Hodgon, P. B. (1932). SOME NOTES ON THE NATURE OF CLAY1. Journal of the American Ceramic Society, 15(3), 191–205. Portico.