Production and Origin of Radium. 



741 



radium present in scale-divisions per minute (taken from 

 column V.), and the abscissae time in days. It will be seen 

 from the curve and also from column IV. that the rate of 

 growth of radium is constant within the limit of experimental 

 error over the time of observation, viz. 121 days. In that 

 interval, the amount of radium in the solution has increased 

 2*36 times the initial \alue. The equilibrium amount of 

 emanation from a standard solution of 10 — 9 gram of radium 

 gave 11*5 divisions per minute in the electroscope. The rate 

 of growth of radium in the solution thus was 4*9 x 10~ n gram 

 per week, and assuming the rate of growth constant, 

 2'55 x 10~~ 9 gram per year. 



§ 5. Activity Measurements. 



In ordpr to follow the results of the chemical operations, 

 the activity due to a definite fraction of the solution was 

 examined over a long interval. 1 '2000 of the solution was 

 taken and evaporated to dryness on a watch-glass. This 

 gave an extremely thin film of active matter from which the 

 a, rays escaped with little absorption. The a ray activity of 

 this film was tested in an a ray electroscope. The variation 



Fig. 2. 



J bo 



20 





















'V fiC Tlf 



MUM I . 





























RCTINlUt 



/J IT. 











r 









■ — -T~ 



ACT/ML 



/a; m . 





/ 















6o so 



TIME IN DAYS 



of activity is shown in fig. 2, where the ordinates represent 

 the activity in arbitrary units and the abscissae time in days. 

 Phil. Mag. S. 6. Vol. 14. No. 84. Dec. 1907. 3 D 



