Abstract
The rate of conversion of parahydrogen and of orthodeuterium is measured on paramagnetic crystals, viz., CuSO4, NiCl2 and neodymium oxalate. In the last case, crystals of approximately uniform size were used so that the total converting area was known. The conversion rate has a maximum at 0°C and it is shown that below this temperature the desorption rate of the H2 and the D2 is rate‐determining. Hence, the ratio of the rates for H2 and D2 is not far from unity. The rate of desorption increases with increasing temperature and at higher temperatures, the rate of conversion on the surface becomes the slow process. The ratio of the rates for H2 and D2 becomes nearly 11 in this region. The heat of adsorption of the hydrogen on neodymium oxalate is about 2.4 kcal./mole.

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