Heat of Fusion of Solid Parahydrogen

The heat of fusion of solid parahydrogen has been measured for the first time at pressures above that of the triple point. The measurements were carried out up to a pressure of 338 atm. The heat of fusion was found to be a linear function of the pressure, and its values are well reproduced by the equation ΔHf = 0.04415 P+28.04, in which ΔHf is the heat of fusion in calories per gram mole and P the pressure in atmospheres. The value given by this equation for the triple point of hydrogen is 28.04, which compares with literature values of 28.03, 28.08, and 28.3 cal/mole. A few independent measurements were also made of temperatures corresponding to various pressures along the melting line for parahydrogen; most of the measured temperatures agree within 0.1°K of those previously reported in the literature.