742 Prof. E. Kutherford on the 



It will be seen that the activity at first rises, passes through 

 a maximum in a little over 20 days, and then gradually decays 

 to a constant value about equal to that initially observed. 

 This decrease of the activity after rising to a maximum shows 

 clearly that some of the actinium had not been precipitated 

 by the ammonium sulphide. In addition, the rise of activity 

 to a maximum in about 20 days shows that an excess of the 

 normal amount of radioactinium was removed with the part 

 of the actinium precipitated. Most of the actinium was left 

 behind in the filtrate. The radioactinium in the precipitate 

 produced fresh actinium X and the activity rose. The 

 gradual fall of the activity to a constant value is due to the 

 decay of the excess of the radioactinium together with its 

 transformation products. The activity curve will be seen to 

 be very similar to the curves given by Hahn (Phil. Mag. 

 Jan. 1907) for cases where radioactinium is initially in excess. 

 It will be seen that the activity curve is of great value for 

 determining the effect of the chemical operation in removing 

 the various products associated with actinium. 



§ 6. Further Experiments with Actinium I. 



After an interval of 121 days, the solution was removed, 

 precipitated with ammonia, and the growth of radium in the 

 precipitated actinium again observed. The object of this 

 experiment was to test whether this reagent was as effective 

 as ammonium sulphide in removing radium from actinium, 

 and also whether the substance that produced radium was 

 precipitated completely with the actinium. Most of the 

 radium was removed by a single precipitation, while the rate 

 of growth of radium in the actinium was unaltered by the 

 process. Such a result is of importance in showing that 

 while radium is soluble in ammonia, the substance, that 

 produces it is not, but is precipitated with the actinium. 

 The observation of the growth of radium in the solution has 

 been tested over a further period of 184 days or 305 days in 

 all. There has been no certain change in the rate of growth 

 of radium in this interval. 



§ 7. Experiments with Actinium II. 



The experiments with actinium I. show that radium is 

 produced at a constant rate in a normal actinium solution, 

 but do not show whether radium is produced from actinium 

 itself or from another substance ordinarily separated with the 

 actinium. The products of actinium in order of sequence 

 are radioactinium, actinium X, emanation, actinium A and 



