The Liquid-Solid Transformation in Helium from 1.6° to 4°K

The transformation from liquid to solid helium behaves quite differently above and below the intersection of the $\lambda$-point-pressure curve with the melting pressure curve. The experimental data given here extend previous work from below 1.8° to about 4°, and show the effect of the $\lambda$-transformation on the latent heat of melting, the change in molar volume on melting, and the melting pressure curve. When these data are combined with a new determination of the $\lambda$-point-pressure curve, the indication seems to be that the $\lambda$-transformation is not truly of second order; that is, that it does not obey the Ehrenfest equations.