Ortho and para hydrogen concentration determination based on vapor pressure

We have constructed a simple ortho-para hydrogen converter to generate para-hydrogen for our ongoing transport property measurement efforts. The apparatus utilizes hydrous ferric oxide as the catalyst. Conversion from normal hydrogen to para-hydrogen takes places at the boiling point of hydrogen. The heat due to condensation and conversion is removed by a liquid helium bath surrounding the vacuum jacketed apparatus. The temperature and the vapor pressure of the hydrogen inside the converter are used to determine the amount of the para content based on existing vapor pressure data. For verification purposes, we have also taken the more traditional approach to determine the para-hydrogen concentration by measuring the thermal conductivity of the converted gas in a flat plate calorimeter. The results from the thermal conductivity measurements have demonstrated that the composition of the gas can change significantly over the period of time needed to make the measurement.