370 Mr. R, W. Boyle on the Absorption of 



In consequence of the delicacy of electrical tests for 

 determining the presence of minute quantities of emanations 

 from radioactive substances, it is possible to carry out 

 experiments with quantities of emanation far too small 

 for examination by chemical or other known physical 

 methods, yet the measurements are capable of a high degree 

 of accuracy. 



Radium Emanation. 



a few preliminary expe- 

 emanation from vessels 

 with air to vessels con- 

 apparatus used (fig. 1) 



Fur. 1. 



Fboa// te 



A short account may be given of 

 riments on the diffusion of radium 

 containing the emanation mixed 

 taining coconut charcoal. The 

 was an emanation electroscope; 

 which consists of two chambers, 

 one above the other. The lower 

 chamber is an air-tight cylin- 

 drical vessel of brass, of about 

 1 litre cubical capacity, serving 

 as an emanation reservoir, while 

 the upper is a vessel covering 

 the gold-leaf system which can 

 be observed through a mica 

 window by a microscope with 

 a scale in the eyepiece. The 

 gold leaf is at the upper end of 

 a brass rod which extends down 

 into the lower chamber and 

 is well insulated. The lower 

 chamber is fitted with tubes and stopcocks, through which air 

 charged with emanation can be admitted or withdrawn at will 

 by means of a pump. Connected with the emanation reservoir 

 by a short tube of large cross-sectional area was a glass bulb 

 containing a few grammes of coconut charcoal in granulated 

 form. The outside of the electroscope was earthed, and the 

 ionization currents measured by the rate of movement of the 

 gold leaf. The ionization current, or activity, at any time is 

 proportional to the amount of emanation present in the 

 emanation reservoir. 



When radium emanation was admitted into and retained 

 in the electroscope, it w T as found that the decay of activity 

 did not follow an exponential law, for while at the first the 

 activity fell to half-value in 1*0 days, in the course of five or 

 six days the rate was half- value in 1'6 or 1'7 days. 



When the emanation reservoir was refilled with emanation 

 and the charcoal vessel removed, so that the emanation could 



