1. H.K. Henisch, Crystal Growth in Gels, 2nd printing, Pennsylvania state university press, Pennsylvania, 1973, p. 43.
2. J.J. Bikerman, Surface Chemistry: Theory and Applications, 2nd ed., Academic Press, New York, 1958, p. 343.
3. A.E. Scheidegger: In: The Physics of Flow Through Porous Media, 3rd ed., University of Toronto press, Toronto, 1974.