two days in the presence of the emanation. The rod was then removed, and the distribution of the excited activity along it determined by the electric method. It was found that the amount of excited activity fell off with the distance x according to an exponential law, falling to half value in about 1·9 cms. This is in agreement with the above theory.
Since the activity of the emanation falls to half value in 1 minute, λ = ·0115. The value K = ·09 was deduced from the average of a number of experiments. This is a slightly greater value than K = ·07, obtained for the radium emanation, but the results show that the two emanations do not differ much from one another in molecular weight.
Makower (loc. cit.) compared the rates of diffusion of the thorium and radium emanation through a porous plate, and concluded that the two emanations were of about the same molecular weight, thus confirming the results obtained by the above method.
Diffusion of the Emanation into Liquids.
164. Experiments have been made by Wallstabe29 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