The adsorption process can be characterized by determining what amount of the ions or molecules are adsorbed to the surface. This amount can be determined experimentally by the construction of an adsorption isotherm. An adsorption isotherm is a graph of Γ(P,T) versus partial pressure of the adsorbate(P/P) for a given constant temperature, where Γ(P,T) is the number of molecules adsorbed per surface area. As the partial pressure of the adsorbate increases, the number of molecules per area also increases.