The Superposition Approximation in Statistical Mechanics of Compressed Gases

The fifth virial coefficient of a fluid of hard spheres

The fifth virial coefficient of a fluid of hard spheres is a sum of 238 irreducible cluster integrals of 10 different types. The values of 5 of these types (152 integrals) are obtained analytically, the contributions of a further 4 types (85 integrals) are obtained by a com­bination of analytical and numerical integration, and 1 integral is calculated by an approximation. The result is E = (0·1093 ± 0·0007) b 4 , b = 2/3 πN A σ 3 , where σ is the diameter of a sphere. A combination of the values of 237 of the cluster integrals obtained in this paper with the value of one integral obtained independently by Katsura & Abe from a Monte Carlo calculation yields E = (0·1101 ± 0·0003) b 4 .