Boltwood — Life of Radium. 505 



The average value for A, is 3*42 X 10 -4 , which is in good 

 agreement with the value 3 - 48xl0" 4 obtained directly from 

 the growth of radium in solution 5. 



Giesel has published* an account of some experiments with 

 a strong preparation of actinium in the course of which he 

 obtained results suggesting the existence of a very slowly 

 changing type of emanation, and has intimated that the pro- 

 duction of this new emanation would account for the results 

 which I had previously obtained and believed to indicate the 

 growth of radium in actinium compounds. It is therefore 

 desirable to state that in the course of the experiments 

 described in this paper I have been unable to obtain- any evi- 

 dence of the existence of an emanation in any way resembling 

 that described by Giesel. The emanation produced in the 

 solutions of ionium was in all respects identical with the 

 radium emanation, showing the characteristic rate of decay and 

 producing the readily identified radium active deposit. 



An interesting insight into the effectiveness of the method 

 used by Rutherford for separating the radium parent from 

 actinium can be gained from the data given in his later paper. f 

 He states that the actinium preparation used had an activity 

 about 250 times that of uranium, and on page 747;}: the total 

 constant activity of 0*32 gram of this material is given as 

 12900. This would correspond to an activity of about 160 per 

 gram of uranium. Now it can be readily shown that the 

 radium produced per year by a quantity of ionium having an 

 activity equal to that of one gram of uranium is about 

 3 - 3XlO -10 gram. From this it follows that in the crude 

 actinium preparation which Rutherford used about one-tenth 

 of the total activity was due to the ionium present. It can be 

 similarly shown that in his "Actinium I" and "Actinium II" 

 the activity due to the ionium was about 0*12 of the total in 

 the case of the former and about 0*18 of the total in the case 

 of the latter. By the chemical operations which he describes 

 the relative proportion of ionium to actinium was approxi- 

 mately doubled in his more concentrated preparation but was 

 still considerably below that in which these elements occur in 

 the uranium minerals.§ 



Discussion of Results. 



The results obtained in the different experiments indicate 

 that the growth of radium in the solutions of ionium was con- 

 stant within the limits of experimental error throughout the 

 periods during which the solutions were under examination. 



*Ber. d. chem. Ges., xl, 3011, 1907. 



f Phil. Mag., xiv. 733. 1907. \Loc.cit. 



§ Boltwood, this Journal, xxv, 269, 1908. 



