286 Boltwood — Radio-activity of Uranium Minerals. 



After the small precipitate was filtered off and washed, it was 

 dissolved in a small volume of very dilute hydrochloric acid. 

 A button of metallic bismuth was suspended over the solution 

 so that its under side just clipped below the surface of the 

 liquid. The solutions were allowed to stand for about ten days, 

 when the bismuth buttons were removed and their activities 

 compared in an electroscope. The activities found were quite 

 closely proportional to the amounts of uranium in the minerals 

 taken.* The residues obtained when the solutions were evapo- 

 rated to dryness were found to be almost completely inactive. 



Rutherfordf has shown that polonium is a direct disintegra- 

 tion product of radium. As a consequence of this it is to be 

 expected that minerals will contain amounts of polonium in 

 proportion to the amounts of uranium and radium present. 

 If the mineral in its natural state loses an appreciable amount 

 of its radium emanation, the amounts of polonium present will 

 be correspondingly reduced. 



As the relative activities of the radium and the polonium in 

 a mineral are of some importance, the following experiments 

 were carried out to determine this relation : — 



First Series. — Early experiments. In these experiments the 

 polonium was separated from O100 gram of uraninite (contain- 

 ing 75*8 per cent of uranium) by the operations already 

 described. Instead, however, of allowing the bismuth buttons 

 to remain in contact with the solutions for a longer period of 

 10 days or so, the buttons were attached to a short, vertical 

 rod connected with a motor, and were rotated in the solutions 

 for periods of from one to three hours, or longer. The buttons 

 were then removed, washed, dried and their activity determined 

 in the electroscope. The activity of the polonium obtained in 

 this manner was compared with the activity of the uranium 

 present in the mineral taken, with the following results : — 



No. 1, 0-33 xU; No. 2, 0-37XU; No. 3, 0'44 xU. 



The periods that the buttons were treated were about one,, 

 two and four hours respectively. 



Second Series. — Later experiments. The addition of even 

 small amounts of bismuth to the mineral solution previous to 

 the separation of the sulphides introduced certain difficulties 

 later, the most serious of which was the necessity of having 

 considerable free hydrochloric acid present in the final solution 

 in order to prevent the precipitation of the bismuth as a basic 

 salt. When the basic salt was formed it carried with it a large 

 proportion of the polonium. The addition of the bismuth salt 

 was therefore omitted, and an attempt was made to separate 



* Eng. and Min. Jour., lxxvii, 756, 1904. 

 fPhil. Mag., viii, 636, 1904; ibid., x, 290, 1905. 



