Pressure on the Excess Properties

However this agreement must not be taken too seriously owing to the con derable uncertainity in the theoretical estimate (19.6.2). 

The lack of information on the thermal properties of the helium isotopes in the solid state prevents us from calculating the excess functions for solid mixtures. 

Let us consider bri y the influence of the difference in statistics on the excess functions of liquid He — He mixtures. 

The considerations which we have presented in Qx. XVIII, 5 on the influence of quantum statistics lead us to suggest that those of the excess functions which are mainly concerned with the change of the ground state at mixing may be paore or less independent of the statistics whereas the excess functions which depend on the excitation will strongly depend on the difference in statistics. 

To the first category belong the excess free energy, the excess volume and to the second the excess specific heat. Available experimental data are not sufficient for a serious test of this conjecture. To separate the effects depending on statistics the study of solid mixtures would also be extremely interesting. 

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