724 



Prof, A, F. Kovarik on 



curve was taken for the actinium D. The sensitiveness o£ 

 the electroscope was checked in each experiment by means 

 o£ the /3-rays from a uranium oxide standard. The ratio 

 of the activity of actinium D at zero time divided by the 

 activity of the standard, gave the measure of the number of 

 recoil atoms collected on the negative plate. 



In the experiments with the ionized air in the field, a small 

 glass a-ray tube containing radium emanation in equilibrium 

 with the active deposit was fixed in a definite and permanent 

 position between the plates. The average range of the 

 a-particles in the air outside the tube was about 3 cm., and 

 this was sufficient to traverse all the air between the plates. 



Actinium D drawn through Ionized Air. 

 In these experiments measurements were made from time 

 to time as the radium emanation in the a-ray tube decayed. 

 The strength of the emanation was a measure of the ionization 

 between the plates. Two series of measurements were made 

 and were found to be in good agreement. The one in which the 

 orioinal amount of the radium emanation used was the greater 

 is given in this paper. The initial amount of emanation in 

 this case was 10 mnlicuries. The distance between the plates 

 was 12'3 mm. The potential difference between the plates 

 was 115 volts, which was sufficient to produce an approximate 

 saturation of the current due to the radiations from the active 

 deposit. Table I. gives the results of the experiments. The 



Table I. 



Relative amount of 

 Emanation. 



Actinium D by recoil. 



ioo-o 



12 



94-2 



12 



80-5 



16 



55'3 



17 



46-5 



22 



40-4 



24 



263 



29 



16-1 



30 



130 



31 



11-5 



35 



96 



34 



7-5 



42 



5-2 



51 



3-7 



63 



2-2 



66 



1-8 



77 



1-27 



81 



0-65 



M 



~Ng emanation. 



100 



