Reproducibility of the Boiling Point of Equilibrium Hydrogen

Abstract

Accuracy of calibration of platinum resistance thermometers against vapour pressure of 20°K equilibrium hydrogen has been examined with a comparison cryostat made of a copper block enclosed in an atmosphere of helium and immersed in liquid hydrogen. After being condensed in a glass bulb filled with Nd₂O₃ powder as a catalyser and circulated for complete contact with the catalyser, sample hydrogen is introduced to the vapour pressure measuring system. This procedure is proved to be satisfactory for producing equilibrium condition for ortho-para composition of hydrogen. About 30 calibrations obtaind for each of two platinum thermometers in a range from 760 to 840 mmHg of pressure shows that the reproducibility of the point is ±0.27 mdeg in terms of standard deviation.