771 



Mr. F. Soddy on the Productk 



The rates of leak are given in divisions of the scale in 

 seconds, and were those obtained after the emanation had 

 been left in the electroscope about 5 minutes, that is, at the 

 end of the initial period of rapid increase. It may be pointed 

 out that it is impossible to obtain strictly comparable 

 measurements of the quantity of radium emanation with the 

 electroscope. No attempt was made to arrive at more than 

 the order of magnitudes measured. If the observation of 

 January 7 is selected as the most accurate of the series, and 

 the rates of leak theoretically to be expected for the other 

 periods of accumulation calculated from it by means of the 

 equation given, the observed results are found to be in fair 

 agreement with the theoretical. 





Time of accumulation. 



Observed. 



Calculated. 



I 



9 months 



4 days 

 17 days 

 525 bours 



15 1 



10'2 



15-65 



67 



165 

 8-2 



15-65 

 5-3 



11 



Ill 



IV 





The agreement is as close as can be expected and, taken in 

 conjunction with the whole behaviour of the emanation, 

 leaves no doubt as to its identity with that of radium. 



III. — The quantity of emanation observed in the experi- 

 ments recorded after a period of eighteen months' production 

 of radium is far below that which is to be expected on the 

 assumption that the radium atom results directly by the change 

 of the uranium X atom. The diagram (fig. 1) represents 

 the course of change in a quantity of uranium represented 

 by 10 11 atoms for 150 days. Time in days is plotted 

 on the horizontal axis, w r hile the figures on the vertical 

 axis denote numbers of atoms. The straight line AB repre- 

 sents the number of atoms of uranium undergoing change, 

 primarily into uranium X atoms. The curve ACD repre- 

 sents the number of atoms of radium that would be formed 

 if the uranium X atom changed directly into the radium 

 atom. The area ABDC gives the number of uranium X 

 atoms present at any instant. AE is the average life of 

 the uranium X atom. The rate of change or radioactive 

 constant of uranium is taken to be 6 X 10~ 17 (sees. -1 ), and 

 is derived from that of radium by comparing the relative 



