278 Boltwood — Radio-activity of Uranium Mineral*. 



methods, and the results of all determinations were in good 

 agreement. 



Preparation of the Uranium Standard. 



The iirauoso-uranic oxide used as a standard of the uranium 

 activity was made from some very pure uranium nitrate which 

 was a portion of that prepared some years ago for experiments 

 on the growth of radium in uranium compounds.* A fraction 

 of a gram of this nitrate was dissolved in 50 cc of water, an excess 

 of a solution of pure, yellow ammonium sulphide was added, 

 and the mixture was digested for an hour at the temperature 

 of boiling water. The uranous oxide formed was filtered off 

 and ignited over the blast-lamp in oxygen. After the weight 

 of the uranoso-uranic oxide had been determined it was again 

 ignited, this time in hydrogen, and converted into the uranous 

 oxide. After weighing the uranous oxide this was again con- 

 verted into uranoso-uranic oxide and again weighed. The 

 weight of the U 3 8 in both cases was the same and was in per- 

 fect agreement with the weight obtained for the uranous 

 oxide. It was therefore assumed that the uranoso-uranic 

 oxide finally obtained was pure and this material was used in 

 preparing the standard. Two films of this material on alu- 

 minium sheets were made. The following table (Table III) 

 gives the data obtained from their measurement. 



Table III. 





Weight 

 U 3 6 g. 



Activity 

 div. per ruin. 



Activity 





Activity 



Film No. 



Weight 



per g. Uranium 



50 



0-0061 



0-64L 



105 





124 div, per min. 



51 



0-0063 



0-663 



105 





124 " " " 



In calculating the 



activity of 



one gram 



of 



uranium it was 



assumed that the oxide (U 3 O g ) contained 84 - 8 per cent of 

 uranium. 



At the beginning of the investigation some uranium oxide 

 supposed at that time to be pure TJ 3 8 was prepared by ignit- 

 ing pure uranium oxalate first in air and then in oxygen at the 

 highest temperature attainable with an ordinary Bunsen 

 burner. This was the oxide used in the preparation of the 

 films included in Table I. A duplicate sample of this oxide 

 was preserved and when examined later it was found to con- 

 tain only 82*1 per cent of uranium. Film jSTo. 3 of this series 

 was the film used throughout the investigation for determining 

 the sensitiveness of the electroscope. 



The Activity of the Minerals. 



In attempting to reach any definite conclusions from data 

 derived from the measurement of the activity of a uranium 

 *This Journal, xx, 239, 1905. 



