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A simple and generalized method for calculating the composition of the Type I clathrate gas hydrates is discussed. It is suggested that the use of additive terms in the known temperature dependent molar volume values of hexagonal ice is useful in calculating the molar volume of the empty clathrate cage. Since the molecular weight of the gas hydrate is dependent on the occupation, the degree of occupation can be expressed by using the experimental density values of each hydrate. The results so obtained are in fair agreement with the results calculated from experimental density and X-ray lattice constants, and with the values of the experimentally measured compositions.

The minimal occupancy level (θmin) of the clathrate lattice of gas molecules is defined as the number of guest molecules in the host clathrate lattice, which can stabilize the thermodynamically unstable empty cage by covering the energy demand of the transformation of hexagonal ice into empty clathrate lattice (ΔHtrans). The θmin values for chlorine hydrate were determined from the n = f(p)T=const. relationship and the average molar intercalation heat of chlorine in the type I clathrate lattice was also calculated for both type of cavities.