Heat of Mixing ofHe3inHe4

The integral heat of mixing for an 8.6 percent solution of ${\mathrm{He}}^3$ in ${\mathrm{He}}^4$ at 1.0°K, measured by an adiabatic free-expansion process, is 0.17 cal/mol of solution. Combined with the free energy of mixing, obtained from vapor pressure data, this shows that at this temperature the bulk of the excess free energy of mixing is due to the heat of mixing.