Abstract
The boiling point of equilibrium hydrogen on the thermodynamic scale of temperature as realized at the National Physical Laboratory was found to be 20.2705° K. The mean value of all the determinations since 1930, recalculated to be consistent with the best values of the reference temperatures, is shown to be 20.267° K. The triple point of equilibrium hydrogen was found to be 13.816°K at a vapour pressure of 52.95 mmHg. The vapour pressure of equilibrium hydrogen was measured at ten temperatures over the range from the triple point to the boiling point. Second power and fourth power equations of (log p,T) were fitted by least mean square deviation. The average deviations of the observations were 1.8 millidegrees for the second power equation and 0.6 millidegree for the fourth power equation.
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