Observations on the use of a thermal conductivity cell to measure the para hydrogen concentration in a mixture of para and ortho hydrogen gas

This paper describes the use of a thermal conductivity cell to measure the para hydrogen concentration in a mixture of para and ortho hydrogen gas. The device was calibrated over its entire range and the output compared with the theoretically expected form. The output of this device had been previously assumed to be linear, this assumption can lead to systematic errors of up to 5.6% in the determination of the para hydrogen concentration. A simple calibration procedure is described.