﻿306 Mr. H. G-. J. Moseley and Dr. W. Makower on 



In order to prepare pure radium emanation in sufficient 

 quantity to carry out the desired experiment, about 30 milli- 

 curies of emanation mixed with air were exposed at atmo- 

 spheric pressure to a strong electric field for 3 hours, to 

 render it as free from active deposit as possible. The 

 emanation was then quickly forced through a plug of glass 

 wool into a glass tube which was sealed off in a blow-pip^. 

 The tube was placed in position near the electroscope and 

 measurements begun. The activity was at first so small as to 

 be incapable of detection, and then rapidly rose as measure- 

 ments were continued till the activity became too great for 

 lurther observations. The tube was then moved further from 

 the electroscope and measurements continued till the emanation 

 had attained its maximum activity. In order to deduce 

 a complete curve showing the rise of activity of the 

 emanation, a careful comparison was made of the ionizations 

 produced in the two positions by the active deposit left in the 

 tube after removing the emanation and waiting for the 

 activity to decay to a convenient amount. The results 

 obtained for the first few minutes through 2*3 cm. of lead 

 are marked with crosses in fig. 3, in which the activities are 

 expressed in percentages of the maximum reached after about 



Rise of activity from pure emanation. 



four hours. The fact that the activity was too small to 

 measure at the beginning ol the experiment shows that the 

 emanation contained not more than about O'Ol per cent, of the 

 equilibrium amount of active deposit. This fact is some- 

 what remarkable. It will further be noticed that the 

 experimental results lie closely on curve E, fig. 3. This 



