288 Bolt-wood — Radio-activity of Uranium Minerals. 



one gram of uranium being 124 div. per minute, the relative 



55 - 7 

 activity of the polonium was ^^ = 0*45 XU. 



A second similar experiment made shortly after the first one 

 was completed gave 041 XU for the relative activity of the 

 polonium. A third experiment made with 10 cc of the same 

 solution after it had stood for 2 days gave the value 0-32 xU 

 for the activity of the polonium, indicating that in this solution 

 also the polonium was slowly separating out in an insoluble 

 form. 



The precipitate of lead sulphate removed in preparing the 

 polonium solution was dissolved by warming with some dilute 

 hydrochloric acid to which a few crystals of potassium chlorate 

 had been added,* a little sulphuric acid was then added and the 

 solution was heated until white fumes appeared. The solution 

 obtained by treating the residue of lead sulphate with a drop 

 or two of dilute hydrochloric acid and a little water, was placed 

 in the cell and stirred in contact with a copper plate for about 

 an hour. The activity of the polonium obtained on the plate 

 was equal to 0*80 div. per min. Correcting the activity of the 

 polonium obtained in the first experiment by this amount gives 

 the value of its relative activity as 0'46X U". It would appear 

 that but little of the polonium remains with the lead when the 

 latter is removed as the sulphate. 



Attempts were also made to separate the polonium on a plati- 

 num plate from a nitric acid solution by electrolysis. The acid 

 solutions tried were of various strengths but the results were 

 very unsatisfactory, the chief difficulty lying in the fact that a 

 greater proportion of the polonium was deposited on the anode 

 than on the cathode. It was also found that in general the 

 chemical separation of the polonium was incomplete when 

 some bismuth salt was not added to the solution of the mineral 

 before the sulphides were precipitated. 



The activity of the polonium separated in the three series of 

 experiments varied with the conditions, and the maximum 

 value obtained wasO - 46xU. The value to be expected from 

 the theory is somewhat greater than this, namely, about 0*49 XU, 

 when the relative ranges of the a particles from radium (3*5 cm ) 

 and polonium (3*8 cm ) are taken into consideration and the activ- 

 ity of the radium is assumed to be 0*45 XU- That the experi- 

 mental results should come out somewhat low (about 6 per cent) 

 is not surprising in view of the difficulties attending the separa- 

 tion of so minute an amount of matter, f 



* Considerable quantities of lead sulphate can be decomposed by this 

 treatment. 



f The weight of polonium, in one gram of the uraninite is probably of 

 the order of 5 x 10 -u gram. 



