Fig. 1. Degree of sorption nonsingularity, , of the measured naphthalene adsorption-desorption isotherms as a function of the initial concentration of naphthalene in the sorption experiment. I and II represent the defined types of sorption nonsingularity. Open symbol represents short-term (48 h adsorption and 48 h desorption step) and closed symbols longer-term (504 h adsorption and 48 h desorption step) experiments.