Radioactivity of Radium and Thorium. 451 



The amount of emanation stored up in a non-emanating 

 radium compound should therefore be nearly 500,000 times 

 the amount produced per second. This result was tested in 

 the following way. '03 gr. of solid radium chloride, of 

 activity 1000 times that of uranium, was placed in a Drechsel 

 bottle, and sufficient water drawn in to dissolve it. The 

 released emanation was swept out by a current of air into a 

 small gas-holder and thence into a large testing cylinder. 

 The maximum ionization current observed immediately after 

 the introduction of the emanation is proportional to N . 



A rapid current of air was then drawn through the radium 

 solution for a few minutes, and the Drechsel bottle was then 

 closed air-tight for a definite time, viz. 105 minutes. At the 

 end of this period the accumulated emanation was again swept 

 out as before and transferred to the testing vessel. The new 

 ionization current represents N^ the amount of emanation 

 produced in the time t. 



N , the amount occluded, gave 4'46 divisions of the electro- 

 meter per second with a capacity "494 microfarad in parallel. 



N*, the amount produced in 105 minutes, gave 5*48 divs. 

 with a capacity '00526 microfarad. 



Tims *p=-0131. 



N 



Assuming there is no decay during the interval, 

 N,= 105x60^0. 



Thus ^=480,000, 



go 



Making the small correction for the decay during the 

 interval t 



5? =477,000. 

 So 



We have previously shown that from theory 

 ?2 = 1=463,000. 



The agreement between theory and experiment is thus as 

 close as could be expected, and is an interesting example of 

 the way the processes occuring in radioactive bodies may be 

 brought to the test of quantitative experiment. 



This experiment proves conclusively that the production of 

 emanation occurs at the same rate in a solid non-emanating 

 radium compound as in the solution. In the former case ir is 

 occluded, in the latter it escapes as fast as it is produced. 



