Boltwood — Radio-activity of Uranium Minerals. 287 



the polonium from a quantity of 1 gram of a nranmite, con- 

 taining 78*5 per cent of uranium, the process followed being 

 otherwise identical with that already outlined. The precipitate 

 of hydroxides obtained was very small, and w r as readily dis- 

 solved in a couple of drops of dilute hydrochloric acid. This 

 solution was diluted to exactly 50 cc and quantities of this, 10 cc 

 in volume, were taken for separate treatment with metallic 

 bismuth. In the first experiment the button was rotated in 

 the solution for ?j\ hours ; in the second the button previously 

 used was run for 4 hours, when a fresh button was put in and 

 run for one hour longer. The polonium on the second button 

 was only about 2*5 per cent of that obtained on the first. In 

 the third experiment, which was made on the day following, 

 a button was run in this solution for 7 hours and a fresh but- 

 ton was then put in and run for one hour longer. The amount 

 of polonium removed on the second button was an inappreciable 

 fraction of that deposited on the first. 



The activities of the total polonium obtained in the separate 

 experiments, expressed in terms of the activity of the uranium 

 in the original mineral, were 0"38, 0'34 and 0*22, respectively. 

 It was found, from these and from other experiments, that the 

 polonium was gradually precipitated from very dilute hydro- 

 chloric acid solutions on standing, even when the amount of 

 bismuth salts in the solution was inappreciable. 



Third Series. — Final experiments. One gram of uraninite 

 (78'5 per cent uranium) was used for these experiments and 

 about 10 milligrams of bismuth nitrate was added to the 

 solution of the mineral in nitric acid before the sulphides were 

 precipitated with hydrogen sulphide. The separation of the 

 polonium was conducted as before. The final hydrochloric 

 acid solution contained 5 C0 of concentrated HC1 and had a 

 volume of 100 cc . Portions of this solution 10 cc in volume were 

 introduced into a glass cylinder closed at the bottom by a 

 copper plate. The plate was about 2 inches square and was 

 held tightly to the cylinder by clamps; the joint between 

 cylinder and plate was made tight by a washer of thin sheet 

 rubber. The solution in the cell was diluted to about 30 cc and 

 was stirred by a small glass stirrer driven by a motor. In the 

 first experiment, conducted with the freshly prepared solution, 

 after a run of Z\ hours, the activity of the copper plate w T as 

 4*27 div. per minute. -A fresh copper plate treated with the 

 same solution for two hours longer had an activity of 0*10 div. 

 per minute. The total was therefore 4-37 div. per minute per 

 O'l gram of mineral, equivalent to 43*7 div. per gram. The 

 amount of uranium in 1 gram of the mineral was 0*785 gram 

 and the activity of the polonium obtained per gram of uranium 



43-7 



was therefore — — = 55'7 div. per minute. The activity of 



•78o r J 



