two desorption mechanisms can be distinguished: In pore blocking, the menisci retreat from the ends of the pore, and the amount adsorbed decreases gradually as pressure is reduced, until a point at which the remaining concave lens breaks, and the amount adsorbed decreases more rapidly, giving a knee in the isotherm. The second mechanism is cavitation, where the adsorbed fluid grows a vapour-like bubble which increases in size as pressure is reduced, due to the stretching of the fluid beyond its stability limit. In some cases, it is possible for desorption to switch from pore blocking to cavitation as the temperature is increased