56 The Philippine Journal of Science i9i4 



thirty minutes after introducing the emanation into the chamber. 

 The deflection of the aluminum leaf for the following thirty- 

 minutes was then recorded. By this method we always obtained 

 the reading over approximately the same part of the decay 

 curve for radium emanation, thereby making the electroscope 

 readings directly comparable. The air-solution tubes were then 

 heated and the radioactivity of the gas measured in exactly the 

 same way, correction in every case being made for the decay 

 of the emanation in the period of time intervening between the 

 collecting and testing of the gas. 



PRELIMINARY EXPERIMENTS 



The accuracy of the determination of the radium-emanation 

 content of the atmosphere by the charcoal method depends to 

 a large extent on the efficiency of the charcoal as an absorber of 

 the emanation under the conditions of the experiment. Satterly," 

 in the course of his work on the amount of emanation in the 

 atmosphere, made a careful investigation of the following : 



(a) Is the amount of emanation absorbed from the air always the same 

 fraction of the total amount in the air whatever that amount may be, other 

 experimental conditions remaining the same? 



(6) In the case when the air flowing to the charcoal contains a constant 

 percentage of emanation, is the amount absorbed by the charcoal propor- 

 tional to the time the air current is flowing, or does the charcoal show 

 signs of saturation? 



(c) Does the amount of emanation absorbed from the air depend on the 

 humidity of the air? 



(d) What is the percentage of emanation absorbed in any particular 

 case? 



From his results he drew the following conclusions: 



(a) That with weak solutions the amount of emanation absorbed in 

 short exposures of the same time for the same strength of air stream is 

 proportional to the strength of the solution. 



(6) That with the same solution and strength of air stream the amount 

 absorbed for exposures of different times does not increase in proportion 

 to the time of exposure but falls off, showing that the charcoal is getting 

 saturated. 



(c) That under the condition of the experiments the amount of emanation 

 absorbed does not depend on the humidity of the air. 



(d) That with tubes 8 sq. cm. in cross section containing a column 30 

 cms. long of coarsely powdered coconut charcoal the amount of emanation 

 absorbed when the air stream is 0.5 liter per minute and the exposure in 

 21 hours is only 62 per cent of the total amount of emanation carried to 

 the tube. 



"Pkil. Mag. (1910), 20, 778. 



