292 Boltwood — Radio-activity of Uranium Minerals. 



erals. The difficulty was due chiefly to the fact that most of 

 the chemical properties attributed to tins element by Debierne* 

 are not possessed by it, but are characteristic for two quite 

 different substances, namely, thorium and ionium. 



The fact that actinium is precipitated with the rare earths 

 was noted by Giesel,f and its further property of not being pre- 

 cipitated with thorium by sodium thiosulphate has been observed 

 by Marckwaldlj: and by Giesel.§ In the experiments which will 

 next be described advantage was taken of these properties, and 

 the actinium was precipitated from the solutions of the rare 

 earths after the removal of the thorium. 



Experiment 1. The filtrates obtained after removing the 

 thorium and ionium precipitated by sodium thiosulphate as 

 described under " Activity of Ionium," "Experiment 3," were 

 combined and concentrated by evaporation. An excess of 

 hydrochloric acid was added and, after boiling to decompose 

 the sodium thiosulphate present, the separated sulphur was 

 removed by filtration. The solution was still further concen- 

 trated, and finally in a volume of about 50 cc the rare earths 

 were precipitated as hydroxides by ammonia. The hydroxides 

 were filtered off and intensely ignited to form the oxides. 

 From the oxides, having a total weight of 0*0068 g., a film 

 weighing 0*0037 g. was prepared. The activity of the film 

 when freshly prepared was less than 0*10 div. per min. The 

 activity rose slowdy and at the end of 128 days reached a value 

 of 7*55 div. per min. This corresponded to 13*9 div. per 

 minute for the total oxide. Dividing this by the activity of 

 the uranium in the gram of mineral taken gives 0*14 X IT for 

 the relative activity of the actinium separated. That the active 

 substance was certainly actinium was demonstrated by the rate 

 of rise of the activity, which is shown in figure 4. In this 

 diagram the ordinates represent the activity and the abscissas the 

 time in days. The maximum activity is taken as 100. The 

 crosses give the activities as measured and the curve is the 

 recovery curve for actinium from which all active products have 

 been removed.|| The slight irregularity at the start was prob- 

 ably due to the presence of small amounts of products in the 

 fresh oxide. 



Experiment 2. In this experiment the filtrates obtained in 

 Exp. 1, •" Ionium," were treated as described in Experiment 1 

 of this series (Actinium). The ignited oxides of the rare earths 

 were made into a film weighing 0*0065 gram. The activity of 

 the film at the start was 0*15 div. per min., and the activity 



*C. R., cxxix, 593, 1899; ibid., cxxx, 206, 1900. 

 fBer. d. chera. Ges., xxxv, 3608, 1902. 

 |Ber. d. chem. Ges., xxxviii, 2264, 1905. 

 §Ber. d. chem. Ges., xl, 3011, 1907. 

 |[Hami, Phil. Mag., xiii, 165, 1907. 



