Page:Radio-activity.djvu/295

 The emanation divided itself between the two reservoirs in the same proportion as would a gas under the same conditions.

162. For the purpose of comparison, a few of the coefficients of interdiffusion of gases, compiled from Landolt and Bernstein's tables, are given below.

+-+++ +-+++ +-+++
 * Gas or vapour |  Coefficient of  |Molecular weight|
 * |diffusion into air|               |
 * Water vapour    |      0·198       |       18       |
 * Carbonic acid gas|     0·142       |       44       |
 * Alcohol vapour  |      0·101       |       46       |
 * Ether vapour    |      0·077       |       74       |
 * Radium emanation |     0·07        |        ?       |

The tables, although not very satisfactory for the purpose of comparison, show that the coefficient of interdiffusion follows the inverse order of the molecular weights. The value of K for the radium emanation is slightly less than for ether vapour, of which the molecular weight is 74. We may thus conclude that the emanation is of greater molecular weight than 74. It seems likely that the emanation has a molecular weight somewhere in the neighbourhood of 100, and is probably greater than this, for the vapours of ether and alcohol have higher diffusion coefficients compared with carbonic acid than the theory would lead us to anticipate. Comparing the diffusion coefficients of the emanation and carbonic acid into air, the value of the molecular weight of the emanation should be about 176 if the result observed for the simple gases, viz. that the coefficient of diffusion is inversely proportional to the square root of the molecular weights, holds true in the present case. Bumstead and Wheeler compared the rates of diffusion of the radium emanation and of carbon dioxide through a porous plate, and concluded that the molecular weight of the emanation was about 180. On the disintegration theory, the atom of the emanation is derived from the radium atom by the expulsion of one α particle. Thus, it is to be expected that its molecular weight would be over 200.

It is of interest to compare the value of K = ·07 with the value of K determined by Townsend (section 37) for the gaseous ions