THREE years ago, Hüttig1 derived a multilayer adsorption isotherm which in most cases agrees with experiment up to higher relative pressures x = p/p0 (where p0 is vapour pressure of the liquid adsorbate) than the Brunauer–Emmett–Teller2 isotherm. Hüttig's formula, however, is not in accord with the kinetic assumptions implied in the derivation and does not explain the entire failure of the theory at very high pressures (x greater than 0.8).
Hüttig, G. F., Monatsh. Chem., 78, 177 (1948).
Brunauer, S., Emmett, P. H., and Teller, E., J. Amer. Chem. Soc., 60, 309 (1938).
Halsey, G., J. Chem. Phys., 16, 931 (1948).