
232 RADIO-ACTIVE EMANATIONS [CH. 
The emanation divided itself between the two reservoirs in the 
same proportion as a gas under the same conditions. 
153. For the purpose of comparison, a few of the coefficients 
of interdiffusion of gases, compiled from Landolt and Bernstein’s 
tables, are given below. 

Coefficient of 
diffusion into air Meson wieig.2 
Gas or vapour 

Water vapour re 07198 18 
Carbonic acid gas... 07142 44 
Alcohol vapour ens 0-101 46 
Ether vapour so5 | 0-077 74 
Radium emanation ... 0:07 2 





The tables, although not very satisfactory for the purpose of 
comparison, show that the coefficient of mterdiffusion 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. On the disintegration 
theory developed in chapter xX, it is to be expected that the 
atomic weight of the emanation should be slightly less than 225, 
the atomic weight of radium. 
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 
produced in air at ordinary pressure and temperature, by Rontgen 
rays or by the radiations from active substances. Townsend found 
that the value of J in dry air was ‘028 for the positive ions 
