The present Part continues the study of ion movements in an oxide matrix enclosed between two heated core pieces. Ions are divided into two classes—residual gas ions (probably carbon monoxide) resulting from imperfections of processing technique, and oxygen ions resulting from electrolysis of the oxide matrix. The different influences of the two classes of gas on matrix conductivity are distinguished by characteristic reactions, which are examined in both d.c. and a.c. fields. The effect of electrolytic oxygen on matrix resistance may be profound, and the action is probably a fundamental aspect of cathode operation.