

Dr. 0. Halm on Radioactinium. 179 



The peculiarities of such reactions are clearly brought out 

 when varying quantities of precipitating material are used. 

 For example, the following experiments were made : — An 

 excess of sulphuric acid was added to an actinium solution in 

 equilibrium. The clear dilute acid solution was divided into 

 three portions. 



Portion 1 was precipitated with O'l c.c. of barium chloride. 

 Portion 2 „ „ 1 c.c. „. .. . „ 



Portion 3 „ „ about 10 c.c. of barium 



chloride. 



The three solutions were treated in exactly the same 

 manner. ]n order to determine the amount of active matter 

 removed by the barium precipitates, it w^as not satisfactory 

 to determine the activity of the precipitates themselves, as 

 the amount of inactive matter contained in the three portions 

 varied in the ratio of about 1 : 100. Recourse was had in 

 the filtrates, from which thin films of active matter could be 

 obtained whose activity could be compared quantitatively. 

 For this purpose the acid filtrates were neutralized with 

 ammonia, then the solutions evaporated to dryness in equal 

 vessels and the ammonia-salts driven off by heating. Small 

 films of the active matter were left behind, and the a ray 

 activity of these thin layers of material could easily be 

 compared under identical conditions. 



It was found that the activities of the filtrates varied in 

 the following manner, the activity of portion 1 being taken 

 as 100 :— 



Activity of 

 Portion. filtrate. 



1 100 



2 63 



3 37-5 



The result thus shows that the filtrates get weaker the 

 more barium has been precipitated as sulphate. For this 

 special case the activities were approximately 1, 2, 3 for 

 quantities 1, 10, 100. 



This is in general agreement with the results of other 

 observers for other products, and again shows conclusively 

 that the reactions are not chemical in nature. 



Other properties of radioactinium have not so far been 

 studied in detail. 



Like radiothorium, radioactinium is not volatilized by 

 means of an ordinary blowpipe at a temperature where 

 actinium A and actinium B are freely volatile. Still higher 



