412 Boltwood — Salts of Radium. 



natural air-leak of the instrument, which averaged O038 division 

 per minute. 



Table I. 



n No. 



Initial 

 activity 



Activity 

 3d 22hrs 



Activity 



1 



'l-14 



3-02 









12 days 



31 days 



2 



1-20 



4-84 

 17 days 



5-21 



3 



1-12 



4-60 





When the last measurement given in the table was made, the 

 dish containing the film was quickly placed in the bottom of a 

 small copper can having a capacity of about 300 ce . The can 

 was closed with a tight-fitting cover provided with two open- 

 ings to which were fitted glass tubes. One of these tubes was 

 attached by a short piece of rubber tubing closed with a pinch- 

 cock to the lieichardt apparatus,* and from the other tube, 

 which extended nearly to the bottom of the can, about one- 

 half of the air in the can was exhausted by suction. About 

 150 cc of warm water containing a little hydrochloric acid was 

 introduced through the tube, and the tube was then connected 

 with a flask containing boiling water. A current of steam was 

 passed through the can, and the displaced gases were collected 

 in the Eeichardt apparatus. After passing steam for about 

 15 minutes the accumulated gases were introduced into the air- 

 tight electroscope. The activity of the emanation obtained 

 from the films is given in the following table (Table II) in 

 terms of the fall of the gold leaf in divisions per minute. The 

 percentage of the total emanation present in each film was 

 calculated by dividing the observed leak by the leak cansed by 

 the total, equilibrium quantity of emanation corresponding to 

 the amount of radium in the film (4 - 60 divisions per minute). 



Table II. 



-p., -^ Observed Per cent of 



leak emanation present 



1 1-65 35 9 



2 3-29 71-5 



3 3-07 66-5 



Knowing the length of time which had passed from the time 

 when the emanation had been wholly removed from the saltf 

 to the time when the emanation retained by the film was re- 

 moved and measured, it is possible to calculate what proportion 



* This Journal, xviii, 379, 1904. 



f A freshly prepared film was subjected to the same treatment as were the 

 older films, and the complete absence of emanation from the fresh films con- 

 clusively proven by experiment. 



