Solutions of Helium Isotopes

The relevant thermodynamic properties of liquid He and He are summarized in Table 19.6.1 

Unfortunately the value of is not known. For this reason we have replaced / by in (19.4.8), which gives an upper limit for 

This is of the correct order of magnitude (cf. 19.1.1) and shows that one may account for the excess free energy of mixtures of He — He by the difierence in masses. 

The experimental data on pure isotopes do not permit the estimation, of the excess volume. We shall indicate in 8 a simplified method which predicts a negative excess volume for this mixture. 

It seems that the second term in the expression (19.4.9) of the excess entropy gives the principal contribution due to the negative thermal dilatation coefficient of He. N ecting the contribution of the first term (cf. Table 19.6.1), we have 

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Solutions of Helium Isotopes 410. 7. Influence of Pressure on the Excess... 

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