170 Dv. 0. Halm on Radioactinium, 



ammonia filtrate was evaporated, heated and tested in the 

 electroscope, the filter was burnt, and the small residue also 

 tested in a similar way. 



Both preparations showed considerable a. ray activity, while 

 the filter also showed considerable /3 ray activity. 



The activity of these two preparations varied, however. 

 in a very different way. The activity of the filter increased 

 in exactly the same way as that of the initial radioactinium. 

 when first prepared ; the activity of the filtrate, however, 

 steadily decreased according- to an exponential law with a 

 period of about 11 days. 



There is no doubt that this decaying product was actinium X, 

 for which Godlewski found a period of 102 days. 



On repeating the above-described experiment, the activity 

 of the ammonia filtrate was found to decay to half value in 

 about 12 days and then slightly slower, indicating that the 

 product consisted mainly of actinium X but also contained 

 a little radioactinium. 



For comparison, some actinium X was now prepared after 

 the method of Godlewski and of Giesel from actinium solution 

 itself and not from radioactinium. On account of the great 

 number of other preparations under investigation, care could 

 not be taken to avoid slight irregularities of the activity 

 arising from the effect of moisture and other influences on the 

 actinium X. The period found for actinium X was therefore 

 not very accurate ; 11 days, or even a little longer, was 

 found instead of 10*2 days, as found by Godlewski. It is 

 intended at an early date to repeat these experiments in order 

 to determine with greater accuracy the decay and rise curves 

 of the products actinium, radioactinium, and actinium X. 



The separation of actinium X from decaying radioactinium, 

 which originally was almost entirely free from actinium X, 

 shows clearly that actinium X is continuously produced by 

 radioactinium. This is confirmed by the fact that old radio- 

 actinium, from which the actinium X has been removed, again 

 increases in activity in exactly the same way as a newly 

 prepared specimen. This increase of activity is due to the 

 formation of actinium X and its successive products ; after 

 reaching a maximum, the actinium X and radioactinium are 

 in approximate radioactive equilibrium, and the activity finally 

 decays according to the period of radioactinium. 



In order to prove this connexion beyond question, the 

 ionization curves of the a. particles of radioactinium were 

 determined at different intervals after preparation. 



In my paper en " The Ionization Eanges of the « Particles 

 of Actinium/' I described the methods of preparing a thin 



