24 ROYAL SOCIETY OF CANADA 
It can be readily shown that if 
K = coefficient of diffusion of the emanation into air. 

f = duration of diffusion experiments in secs. 
a = total length of cylinder, — 
S = amount of emanation in tube A at end of diffusion. 
S, = amount of emanation in tube B at end of diffusion, then 
—_nKt — rKt 
— age oun BLUE 2 anaes 
rte ae | 
See Stefan and Loschmidt, Berichte Wien. Akad., 63, 1871. 
From this equation K can be determined, if S, and S, are known. 
An uncertainty however arises in estimating S, and S, for the rate 
of leak in A and B is made up of the current due to emanation alone 
and the current produced in the gas by the excited radioactivity on the 
electrodes. As the amount of excited radioactivity increases with the 
time, the ratio of the current due to the emanation and to the excited ; 
radiation varies with the time allowed for diffusion. The ratio of the 
current due to the excited radiation can be determined by removing the 
central electrode and finding the amount of current immediately after 
the introduction of a new electrode. 
When the emanation is allowed to diffuse for half an hour, the 
current due to excited radioactivity was about ‘4 of the whole. 
The calculated value of K was found to be about 20 per cent greater 
when the correction for the amount of excited radioactivity was applied. 
The value of AK deduced from the experiments was found to be 
between *08 and -15. All the later observations gave a value about ‘08. 
This variation in the value of A deduced from the experiments is not 
altogether due to errors of experiment, the values obtained at first with 
a new specimen of radium were in all cases higher than when it had 
been laid by for several months. It appears as if the emanation were 
not simple in character, and that part of the emanation first given off 
was of lower molecular weight than that emitted after severul months 
exposure to the air. Further experiments are now being carried out to 
see if the radium emanation undergoes a progressive change with time. 
For the purpose of comparison, we will now give a few of the coefficients 
of interdiffusion of gases, compiled from Landolt and Bernstein’s tables. 


Coefficient of 
diffusion into air. Molecular weight 
Gas or vapour 

Matter VADOUTE UE TRS EN ER ENR Rte 0°198 18 
Carboniciacid\asieeeate ee eee ee 0°142 44 
INIGOHOR SAN. AA eee PAC PRE TEA 0°101 46 


À EH D UE SR PNP oe ud eT | 0:077 74 

