158 THE ROYAL SOCIETY OF CANADA 
case of radium. In a mixed atmosphere of ether vapor and air, at a 
given potential, the fraction of the thorium rest-atoms collected on 
the cathode depended on the relative porportions of air and ether 
vapor. Ina given mixture of ether vapor and air the fraction of the 
rest-atoms which could be collected on the cathode seemed to reach 
a definite limiting value as the potential gradient was increased. 
In oxygen 98:5% of the total active deposit was collected on the 
cathode with a potential gradient of only 40 volts per cm. It seemed 
quite evident that at a sufficiently high potential gradient all the 
active deposit could be collected on the cathode. In carbon dioxide, 
with a potential gradient of only 150 volts per cm. 98-0% of the total 
active deposit was collected on the cathode. As this percentage 
was steadily rising with increase of potential gradient up to 150 
volts per cm. it seemed reasonable to suppose that with a sufficiently 
strong field all the rest-atoms could be collected on the cathode. 
In sulphur dioxide at a potential gradient of 4,000 volts per cm. 
98-5% of the total active deposit was collected on the cathode. 
As with carbon dioxide it appeared that with a high enough potential 
gradient all the rest-atoms could be collected on the cathode. On 
the other hand in ethyl bromide and in aceton vapors all the rest- 
atoms appeared to be uncharged just as in ether vapor. 
Thus it will be seen that, in those experiments in which the 
atmosphere surrounding the rest-atoms consisted of molecules of 
one kind, the rest-atoms were either all positively charged or all 
neutral. 
EXPERIMENTS WITH RADIUM. 
The thought immediately suggested itself that the behaviour 
of the active deposit of radium in air might be due to the fact that 
air is a mixture, since it resembled the behaviour of the thorium 
rest-atoms in a mixed atmosphere. Experiments carried out in 
pure nitrogen and in pure oxygen, however, gave approximately 
the same percentage cathode activies as in air, which disposed of this 
suggestion. 
While continuing experiments in air and other gases, it was found 
that a much higher potential gradient was required to bring over to 
the cathode any percentage of radium rest-atoms than was, needed 
to bring over the same percentage of thorium rest-atoms. A series 
of experiments was then made in dry air using high potential gradients. 
Above a gradient of 150 volts per cm. the potential were furnished 
by a Wimshurst machine. The results obtained are given in Table I. 
The first column gives the potential gradient in volts per cm. The 
second gives the percentage cathode activity, i.e., the percentage 
