the Active Deposit of Radium. 423 



the curves there given, and as in any case the actual shape of 

 any one of the curves depends upon the particular vessel em- 

 ployed, it was not thought desirable to reproduce the corrected 

 curves. 



Experiments ivith large amounts of Emanation. 



5. It was shown in Section 3 that when the emanation 

 mixed with any gas is introduced into a cylindrical vessel, 

 the amount of active deposit in the gas (i. e. gas activity) 

 when the steady state is established is inversely proportional 

 to the coefficient of diffusion (D) of the active particles in 

 the gas. If, therefore, we could determine the amount of 

 active deposit in the gas at any time, we would be able to 

 obtain the value of D. The determination of this coefficient 

 is of importance in the theory of diffusion because the 

 particles are of relatively large mass and also because they 

 are present in extremely small number. 



Before describing the method employed for determining 

 the amount of active deposit in the gas, it is of interest 

 to record that when relatively small amounts of emanation 

 were employed the gas activity was found to be a definite 

 fraction of the total activity. With larger amounts of 

 emanation, however, variations of such an exceptionally 

 large order were found to occur in the values of the gas 

 activity, that it became of interest to make a systematic 

 investigation. The results obtained in this connexion are 

 given in the present section ; the determination of D by the 

 use of relatively small amounts of emanation is described in 

 the next section. 



In the experiments now to be described it was not found 

 necessary to determine the total amount of the active deposit 

 present in the gas. The experimental procedure may be 

 briefly described as follows : approximately 2\ millicuries of 

 radium emanation * mixed with air was introduced through 

 drying-tubes and cotton-wool into the cylindrical testing 

 vessel, which was closed at the top with a rubber stopper, no 

 central rod being present. Several hours and occasionally a 

 few days were allowed to elapse in order that any dust 

 present in the gas might have a chance to subside. The 

 outer case was connected to any desired potential, but as 

 there was no inner electrode the electrical conditions inside 

 the cylinder were not disturbed. When conditions were 

 steady an electrode permanently connected to earth was 

 introduced for 1 minute and then withdrawn, the cylinder 



* Kindly supplied by Professor Boltwood. 



