Active Deposits of Radium, Thorium, and Actinium. 603 
deposit was obtained, was suspended so as to hang symme- 
trically within the glass vessel V which was silvered on the 
inside, connexion to a battery o£ cells being made by means o£ 
a piece of platinum fused in the side of the vessel. 
The usual method of experimenting was as follows : — 
The whole system, with the exception of the vessel con- 
taining the radium emanation evolved from a solution of 
radium bromide, was exhausted firstly by means of a JETeuss 
pump and then by a charcoal tube immersed in liquid air (not 
shown in diagram). When the desired pressure had been 
obtained the tap D was closed, and by turning the tap E the 
small capillary tube C ('2 c.c. volume) was filled with the 
emanation at atmospheric pressure. 
The tap B was then closed and the glass spiral S surrounded 
by liquid air, E was then turned and the emanation contained 
In the capillary C was allowed to pass over a tube containing 
P 2 5 for drying purposes, after which it condensed in the 
spiral S. 
A few trials showed that nearly all of the emanation had 
condensed in 15 minutes. The tap A was then closed, 
B opened, the liquid air removed from the spiral, and the 
emanation allowed to diffuse into the vessel V and a McLeod 
gauge which was in connexion with it. The resulting pressure 
was then read. 
As the volume of the P 2 5 tube was several times that of 
the spiral, quite low pressures were obtainable in the spiral 
although the capillary C had been filled, at atmospheric 
pressures. The wire W was made either a cathode or anode 
as desired and exposed to the emanation for 1 hour. It was 
then removed from the vessel V, and its activity tested in the 
usual way by making it the central electrode of a cylinder 
connected with a Dolezalek electrometer and measuring the 
ionization produced by the a. rays emitted from it. The 
electrometer leak obtained in a measured interval of time 
14 minutes after the removal of the wire from the emanation 
was taken as a measure of the activity obtained on the wire. 
The variation in activity with change of pressure is seen 
from Table I., also from fig. 2, where the abscissae represent 
pressures and the ordinates the corresponding activities of 
the wire. It will be seen from the diagram that there is a 
very large decrease in the activity of the cathode as the 
pressure is diminished, while the anode shows if anything a 
small increase; the amount obtained by diffusion alone, 
i. e. to a neutral rod, being practically constant over this 
range of pressure. 
It will be observed that whereas at a pressure of about 
