IN AN ELECTRIC FIELD. HENDERSON. 131 



In hytlrogen at a potential gradient of 150 volts per cm. 

 more of the rest-atoms can be collected on the cathode than 

 in air while at 4000 volts per cm. a smaller percentage is 

 collected by the cathode than in air with the same field. 

 With this intense electrical field it is difficult completely to 

 eliminate brush discharge. This would produce water vapor 

 by causing the h3^drogen to combine with the traces of oxygen 

 present. That some moisture was present seemed evident 

 from the fact that the P2O5 in the vessel was affected to a 

 much greater extent than under a low potential-gradient, or 

 n any other gas tried, though the same precautions were taken 

 in all cases to dry the gas before admitting it tathe vessel. Very 

 small quant s of moisture are known to lower considerably 

 the percentage cathode activity. This would seem to explain 

 the low values of this percentage found in hydrogen with 

 h gh potential gradients. If the effect of moisture could be 

 eliminated it seems probable that a higher percentage cathode 

 activity would be obtained in hydrogen than in air at all 

 potential gradients. In hydrogen as in air the conclusion 

 seems justified that at a sufficiently high potential-gradient 

 all the rest-atoms could be collected on the cathode. 



In carbon dioxide and in sulphur dioxide, it is much more 

 difficult to bring over the rest-atoms to the cathode than in 

 air. It will be noticed that both carbon dioxide and sulphur 

 dioxide at room temperatures are on the border line between 

 vapors and gases. To test if any abrupt change in the be- 

 havior of tie 5(st-atoms takes place near the critical tem- 

 perature, experiments were carried out in carbon dioxide at 

 temperatures of 4°C., 19°C., and 36°C. It seemed a little 

 more difficult to bring the rest-atoms over to the cathode at 

 the lowest temperature, but the difference was very slight. 



The fact that the percentage cathode activity is increas- 

 ing .so slowly when it is as low as 93% should perhaps make 



Pboc. & TRAN3 N. S. Inst. Sci., Vol XI /. 23 .\i?. 'IG. Trans.— 



