Boltwood — Radio-activity of Uranium Minerals. 291 



removal of the insoluble matter and the sulphides precipitated 

 by hydrogen sulphide, the solution was evaporated to dryness. 

 The residue of nitrates was heated for some time at 110° to 

 remove all excess moisture and was then extracted with ether. 

 The oxalates precipitated from a dilute nitric acid solution of 

 the residue remaining after treatment with ether (as described 

 under the heading "Determination of Uranium," page 276), were 

 converted into the oxides and dissolved as sulphates after fusion 

 with sodium bisulphate. From the solution obtained, the rare 

 earths were precipitated as hydroxides by* ammonia and the 

 thorium was separated by treatment with sodium thiosulphate, 

 twice repeated. The final precipitate was dissolved in dilute 

 hydrochloric acid, the sulphur present was filtered off, and the 

 thorium was precipitated as hydroxide by ammonia. The 

 thorium hydroxide was finally ignited strongly to form the 

 oxide, and from this oxide a film weighing 0'00735 gram was 

 prepared. The activity of this film was 13*0 div. per min. at 

 the start; it rose slightly at first and then fell slowly like the 

 others; and at the end of 128 days amounted to 12*8 div. per 

 minute. This was equivalent to 33*3 div. per gram of mineral 

 and the amount to be deducted for the thorium present was 

 2'2 div. The activity of the ionium was therefore 31*1 div. 

 per minute and its relative activity was - 32 as compared with 

 the activity of the uranium present. 



Experiment 4. One gram of the same mineral used in 

 Experiment 3 was taken and the chemical treatment to which it 

 was submitted was identical, except that the thorium was not 

 separated from the other rare earths by precipitation with sodium 

 thiosulphate. Instead, the combined hydroxides precipitated 

 by ammonia were directly ignited to form the oxides and a film 

 was prepared from this material. The activity of this film rose 

 steadily from the start, and at the end of 129 days had increased 

 by 64 per cent of its initial value. It will be shown later that 

 the rise was due to the presence of actinium in the oxides and 

 that the activity due to the actinium in the freshly prepared 

 oxide was practically equal to zero. The initial activity of the 

 film, corrected for the thorium products present (radiothorium 

 only), was therefore due only to ionium and was equivalent to 

 an activity of 34*3 div. per minute for the ionium in the min- 

 eral taken. This gives a value of 035XU for the relative 

 activity of the ionium in the mineral. 



The values for the relative activity of the ionium obtained 

 in these four experiments were therefore 0*34, 0*32, - 32 and 

 0-35 XU. 



Activity of Actinium. 



The most difficult problem encountered in the course of this 

 investigation was the separation of the actinium from the min- 



