166 Dr. 0. Halm on Radioactinium, 



anomalous behaviour, a large number of experiments were 

 undertaken to test the variation of activity under different 

 conditions and with different methods of preparation. 



As the general result it was seen, that the undissolved part 

 of the preparation contained a new radioactive product. 

 If, in addition, actinium X also remained in the insoluble 

 portion, the activity of the filter was nearly constant for 

 some time,, and then decayed slowly, finally diminishing 

 according to an exponential law with a period of about 

 20 days. 



If there was no actinium X in the insoluble part, the activity 

 of the latter at first increased, reached a maximum after about 

 two or three weeks, and later decaved with a period of about 

 20 days. 



This product with a decay period of about 20 days was 

 later called " radioactinium," when its position in the actinium 

 series had been settled. 



The method of preparation of this new product, previously 

 described, was not very satisfactory, and generally gave a 

 mixture of the whole series of actinium products together 

 with a surplus of radioactinium. 



The following two methods proved much more satisfactory 

 and rendered it possible to obtain the product radioactinium 

 free, or at least nearly free, from actinium and actinium X. 



Actinium, which had been standing for a few months in 

 solution in order to reach the equilibrium state of activity, 

 Avas precipitated several times with ammonia. By this method 

 Godlewski and, independently, Giesel have shown that 

 actinium X remains in solution, while actinium itself remains 

 in the precipitate. The precipitation had to be repeated 

 several times to make the separation of actinium X as com- 

 plete as possible. 



The actinium precipitate is dissolved in hydrochloric acid, 

 and to the acid solution is added a very little sodium thio- 

 sulphate solution. The latter is decomposed by the acid, and 

 amorphous sulphur soon appears. The sulphur in the cold 

 solution is allowed to settle down for some time and is then 

 filtered and washed. The surplus is then burnt in a porcelain 

 crucible. An appreciable residue is always observed because 

 some of the rare earths, like thorium, are precipitated with 

 the sulphur. 



This residue shows considerable activity, depending of course 

 on the amount of actinium taken for the experiment. The 

 activity increases to about twice the initial strength and then 

 decays slowly, finally diminishing according to an exponential 

 law with a period of about 20 days. 



