Diffusion of the Emanation into Liquids.
164. Experiments have been made by Wallstabe[[259]] on the coefficient of diffusion of the radium emanation into various liquids. The radium emanation was allowed to diffuse into a closed reservoir, containing a cylinder of the liquid under observation. The cylinder was provided with a tube and a stop-cock extending beyond the closed vessel, so that different layers of the liquid could be removed. The liquid was then placed in a closed testing vessel, where the ionization current due to the escape of the emanation from the liquid was observed to rise to a maximum after several hours, and then to decay. This maximum value of the current was taken as a measure of the amount of emanation absorbed in the liquid.
The coefficient of diffusion K of the emanation into the liquid can be obtained from the same equation used to determine the diffusion of the thorium emanation into air,
where λ is the constant of decay of activity of the radium emanation and x the depth of the layer of water from the surface.
Putting
it was found that
for water α = 1·6,
for toluol α = ·75.
The value of λ expressed in terms of a day as the unit of time is about ·17.
Thus the value of K for the diffusion of the radium emanation into water = ·066 cm.2 / day.
The value of K found by Stefan[[260]] for the diffusion of carbon dioxide into water was 1·36 cm.2/day. These results are thus in harmony with the conclusion drawn from the diffusion of the radium emanation into air, and show that the radium emanation behaves as a gas of high molecular weight.