Dr. 0. Halm on Radioactinium. 167 



The other method, which proved satisfactory for the separa- 

 tion o£ radioactinium, is described already in nry paper on 

 " The Ionization Ranges of Actinium " * . A small quantity oE 

 ammonia is added to an actinium solution in radioactive 

 equilibrium in amount sufficient to produce only a partial 

 precipitation. The ammonia filtrate is redissolved and part 

 again precipitated. After repeating this process several 

 times, all the actinium X and the greatest part of the actinium 

 remain in solution, while the radioactinium remains in the 

 precipitate. The latter is then treated in the same manner 

 as the sulphur precipitate described above. 



The methods of separation of radioactinium, which we 

 have outlined, are not altogether as satisfactory or reliable as 

 could be wished. In some cases a very complete separation 

 is obtained, but in others some actinium is carried down or 

 other difficulties are encountered. The right conditions are 

 not always easily found, but, in general, the separation can 

 be effected by the methods described above. 



Some recent experiments of Levin seem to show that radio- 

 actinium can also be separated to some extent by electrolysis. 



II. Radioactive Properties of Radioactinium. 

 a. Nature of the Radiations. 



Radioactinium emits a rays. In the previous paper f I 

 described the methods of preparing a thin film of this radio- 

 active product, sufficiently active for the determination of 

 the range of its a, particles by the electric method. It was 

 shown that freshly prepared radioactinium emits one homo- 

 geneous type of a. rays, which are able to ionize the air for a 

 distance of 4*8 cms. at ordinary pressure and temperature. 



While newly prepared radioactinium always shows a very 

 considerable a ray activity, the j3 ray effect at first is very 

 weak, and is probably due to the presence of a slight amount 

 of actinium B. This is in accordance with the results of 

 Levin obtained in Rutherford's laboratory, for he has shown 

 that actinium B is the only product of actinium which emits 

 /3 rays. 



A small amount of actinium emanation is also present. 

 Since actinium X is the direct parent of the emanation, the 

 amount of emanation in the preparation is a measure of the 

 amount of actinium present. 



As we shall prove later in this paper, actinium X is formed 

 by the radioactinium : it is therefore very difficult to obtain a 



* Phil. Mag. Sept. 1906. f Loc. cit. 



