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LXXXI. On the Activity of freshly-formed Radium Emanation, 

 By Horace H/ Poole *. 



AS there is no very satisfactory theoretical explanation of 

 the exponential law of radioactive decay, it is not 

 unreasonable to suppose that variations from it might occur 

 under certain conditions. For instance, as has been suggested 

 by Dr. Joly, it is possible that the rate of decay and hence 

 the activity of a body might be anomalous when the body 

 is freshly formed so that its age is only a very small fraction 

 of its average life. Accordingly an attempt has been made 

 to compare the activity of radium emanation a few seconds 

 old with that of the same body at the age of a few minutes. 

 If the exponential law holds the activities should be the same, 

 as the decrease in the total quantity of emanation during 

 the interval would be negligible. 



The continuous flow method was employed. An air blast 

 from a Roots blower was passed successively through a gas 

 meter, a pressure regulator, and a drying-tube ; it then 

 passed over a thin film of impure radium chloride formed by 

 evaporation on the upper surface of a small platinum ribbon, 

 similar to that used in the Apophorometer, which was 

 maintained at a white heat by means of an electric current. 

 Thence the air current passed through a long plug of cotton 

 wool, and after traversing a cooling tube entered the first 

 testing vessel, from which it passed through a long wide lead 

 pipe before entering the second testing vessel, which was 

 exactly similar to the first in all respects. After leaving this 

 the current was discharged in the open air by means of a 

 tube leading out the window. Knowing the volume of air 

 passing per second and the volumes of the various parts of 

 the apparatus, it was easy to calculate the average age of the 

 emanation entering the two testing vessels on the assumption 

 that the emanation was liberated from the white hot strip 

 as soon as formed. This seems to be the most doubtful 

 point connected with the experiment, but it Avould seem 

 probable that, as the strip was only slightly below the 

 melting point of platinum, and the film of radioactive matter 

 very thin, a very large percentage of the emanation must 

 have been liberated within a few seconds of its formation. 



In order to avoid trouble with the growth of active deposit 

 in the testing vessels the air current was allowed to flow 

 steadily over the heated strip for at least three hours before 

 readings were taken, so that the active deposit might attain 

 equilibrium with the emanation passing through. During 



* Communicated by the Author. 



