amount adsorbed per gram of solid influenced by the specific area of the solid, the equilibrium solute concentration in the solution or pressure in the case of adsorption from the gas phase, the temperature, and the nature of the molecules involved. From measurements at constant temperature, one can obtain a plot of N, the number of moles adsorbed per gram of solid, versus c, the equilibrium solute concentration. This is called an adsorption isotherm.