An alternative way of measuring the specific heat of superttuid 4He and dilute 3He-4He mixtures is described. Specific heat data are derived from the measured resonance curves for the temperature amplitude in a second-sound Helmholtz resonator. It is shown that the nature of the losses that govern the shape of these curves, need not to be known for the analysis. The applicability of the method is first demonstrated by a series of measurements on pure 4He in the temperature range between 1.4-2.0 K; the results are in good agreement with existing specific heat data. Next, some measurements performed in the range from 0.3 K to 0.7 K on two mixtures of molar concentrations X= 6.0 x 10 -3 and X = 8.5 x 10 -3 are presented. Although the thermal anchoring of the resonator to the mixing chamber of the Leyden dilution refrigerator did not appear to be optimal, so that the precision of the results was not high, the feasibility of the method also for the case of mixtures could be shown. It is further shown that the analysis of the data is somewhat more difficult for mixtures than for pure 4He; this is due to less direct coupling between the amplitudes of the energy and the temperature, caused by the accompanying oscillations in the concentration X.
The connection between second-sound resonances and the specific heat