Production and Origin of Radium. 



747 



activity of: 24.00 divisions. Consequently the amount of 

 radium to be expected on the platinum plate is 1*6 of the 

 growth of radium in the solution in the time of exposure of 

 the platinum plate to the constant supply of actinium 

 emanation. Now this solution grew per week an amount of 

 radium corresponding to '56 division per minute of the 

 electroscope. Consequently, on this hypothesis, the platinum 

 plate exposed for two weeks should contain an amount of 

 radium corresponding to 1*8 divisions per minute. The actual 

 amount observed was not more than *01 division, or less than 

 1/180 of the theoretical amount. Such a result conclusively 

 shows that actinium B does not change directly into radium. 

 It is not inconsistent, however, with the possibility that a 

 slowly changing product exists between actinium B and 

 radium. In such a case radium, in the course of time, should 

 appear in the solution containing the platinum plate. 



§ 10. Discussion of Results. 



In the following table are given the collected results of the 

 experiments on the growth of radium in the various solutions. 

 In column II. is given the total activity of the preparations 

 when in radioactive equilibrium, expressed in divisions per 

 minute of the a. ray electroscope. This activity was deter- 

 mined in each case by taking a definite small fraction of the 

 preparation in solution and evaporating it to dryness on a 

 watch-glass. Column III. gives the observed rate of growth 

 per week expressed in grams of radium. Column III. gives 

 the rate of growth per year, on the assumption that it is 

 constant over that interval. Column V. shows the relative 

 growth of radium for equal quantities of actinium, taking 

 the rate of growth in the solution actinium I. as unity. 



I. 



II. 



III. 



[Total constant Rate of growth 

 Preparation. activity of j of radium 



Actinium I , 



Actinium II 



Actinium III. .. 



32 gram of ac- 

 tinium tested 

 over a period I 

 of 2"7 years ... I 



preparation. 



9900 

 3000 

 6000 



12900 



per week. 



4-9x10-11 gram 

 2-3x10-11 „ 

 not measurable 



5-0x10 



11 



gri 



IV 



V. 



Eate of growth I Eelative 

 of radium ; growth of 

 per year. vadium. 



2 - 55 X 10 ' gram 1 



9 



1-2 X10 



2-9 XlO ' gram 



1'55 



not greater 

 than -002 



•97 



