It is shown that the temperature dependence of Langmuir constants contains
all the information needed to determine spherically averaged intermolecular
potentials. An analytical ``inversion'' method based on the standard
statistical model of van der Waals and Platteeuw is presented which extracts
cell potentials directly from experimental data. The method is applied to
ethane and cyclopropane clathrate-hydrates, and the resulting potentials are
much simpler and more meaningful than those obtained by the usual method of
numerical fitting with Kihara potentials.Comment: 33 pages, 7 figures, to appear in Physica