The Separation of the Hydrogen Isotopes by Electrolysis. Part I

The equilibrium constants of the reactions H2O+2D =D2O+2H and H2O+D2O=2HDO are calculated and from these an expression is obtained for the electrolytic separation coefficient, valid when zero-point energy and tunnelling are negligible in the activated state. The change in this coefficient with increase in concentration of the heavy isotope is calculated. Experimental values have been determined for the separation coefficient at different metallic cathodes, ranging from 7.6 to 2.8. Local concentration disturbances round the cathode are not in general important, but may be the cause of the poor separation found with platinum black. The importance of half-quanta in the activated state is discussed. The experimental results considered in the light of the calculations indicate that tunnelling is not very important in the electrolytic separation. The vapor pressures of liquids containing isotopes are considered.