290 Boltwood — Madio-activity of Uranium Minerals. 



chlorides, which was then treated with water. The solution 

 was filtered to remove traces of silica. The filtrate, diluted 

 to a volume of about 100 cc , was heated to boiling, an excess 

 of sodium thiosulphate was added, and the mixture was boiled 

 until the free sulphurous acid was completely removed. The 

 precipitate, containing free sulphur, was filtered off and treated 

 with dilute hydrochloric acid. The solution was filtered and 

 the precipitation with sodium thiosulphate was repeated. The 

 second precipitate was ignited at a high heat in a platinum cru- 

 cible over the blast-lamp. The thorium oxide obtained in this 

 manner weighed 0*0878 gram. A film containing 0*0123 gram 

 of this oxide was prepared. 



The activity of the film when first prepared was 4*53 div. 

 per minute. The activity rose for about 30 days and then fell 

 very slowly.* At the end of 110 days the activity of the film 

 was 4*75 div. per minute. This was equal to 3 7* 7 div. per 

 min. per gram of the mineral taken. The correction for the 

 activity of the thorium and thorium products present was now 

 calculated and was found to be equal to 5*7 div. per min. for 

 the total activity. f The activity of the ionium from the min- 

 eral was therefore equal to 32*0 div. per minute. Dividing 

 this by the activity of the uranium in one gram of mineral 

 (0*758x124) gives the value 0*34 XU for the relative activity 

 of the ionium. 



Experiment 2. One gram of Branch ville uraninite (No. 2, 

 Table IY) was taken for this experiment. The material was 

 treated in the same manner as was the North Carolina urani- 

 nite in Experiment 1 and the film of thorium oxide finally pre- 

 pared showed the same proportionate variations in its activity. 

 The activity of the film at the end of 110 days was equal to 

 3*88 div. per min. This corresponded to 41*7 div. per min. for 

 the activity of the total oxide and the correction for the thorium 

 products present was 10*6 div. per min. The activity of the 

 ionium from one gram of the mineral was therefore 31*1 div. 

 per minute. When this is divided by the activity of the uranium 

 (0*777x124), the value 0*32 is found for the ratio of the 

 activity of the ionium to that of the uranium with which it is 

 associated. 



Experiment 3. In this experiment one gram of North Car- 

 olina uraninite (No. 3, Table IY) was taken. After the 



* The initial rise was due to the formation of thorium X and its products, 

 which had been removed by the chemical treatment. The subsequent fall 

 was due to the decay of the radiothorium present. 



f To determine this correction a film of thorium oxide was prepared from 

 the nitrate added to the mineral solution This film was measured in the 

 electroscope at the end of the 110 day period. The activity of the thorium 

 in the mineral was calculated directly from the rates of decay of radio- 

 thorium and mesothorium. 



