160 THE ROYAL SOCIETY OF CANADA 
of the contradictory evidence of Wellisch, one seems justified in con- 
cluding that all the rest-atoms could be brought to the cathode in a 
sufficiently strong field and hence that all the rest-atoms of radium 
are initially positively charged. 
In hydrogen at a potential gradient of 150 volts per cm. a larger 
percentage of the rest-atoms was collected on the cathode than in air, 
while at 4,000 volts per cm. a smaller percentage was collected in 
hydrogen than in air. With this intense electrical field it is difficult 
to completely eliminate brush discharge. This would produce 
water vapor by causing the hydrogen to combine with the traces of : 
oxygen present. That some moisture was present seemed evident 
from the fact that the P.O; in the vessel was affected to a much greater 
extent in hydrogen under a high potential gradient than in hydrogen 
under low potential gradients, or in any other gas tried, though the 
same precautions were taken in all cases to dry the gas before admitting 
it to the vessel. Small quantities 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 
high 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 the rest-atoms 
are all initially positively charged. 
In carbon dioxide and in sulphur dioxide it is much more difficult 
to bring the rest-atoms over to the cathode than in air. It will be 
noticed that both carbon dioxide and sulphur dioxide are, at room: 
temperatures, either vapors or on the border line between vapors 
and gases. To see if any abrupt change in the behaviour of the rest- 
atoms takes place near the critical temperature, experiments were 
carried out in carbon dioxide at temperatures of about 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 in- 
creasing so slowly when it is as low as 93%, perhaps should make one 
hesitate to conclude that with a sufficiently high potential gradient, 
all the rest-atoms could be collected on the cathode. However, 
it seems unnatural to suggest any other limit than 100% for the 
percentage cathode activity, especially in view of the fact that with 
the highest obtainable voltages the percentage was still increasing. 
Therefore, in the absence of contradictory evidence, it does not seem 
unreasonable to conclude that in sulphur dioxide and in carbon 
dioxide all the rest-atoms of radium are initially positively charged. 
This brings the behaviour of the radium rest-atoms in agreement 
