Boltwood — Life of Radium. 503 



acid, the solution evaporated to dryness and the residue of 

 nitrates was treated with pure, dry ether to remove the uranium 

 nitrate. That portion of the residue undissolved by the ether 

 was treated with dilute hydrochloric acid, and to the resulting 

 solution about 5 grams of oxalic acid were added. An immedi- 

 ate precipitate of oxalates formed, but the mixture was allowed 

 to stand over night before filtering. The oxalates were then 

 removed, were added to the oxalates obtained by the first 

 precipitation with oxalic acid, and the whole was ignited gently 

 to form the oxides. The oxides were treated with hydrochloric 

 acid to form the chlorides, and the chlorides were thrice 

 precipitated with ammonia to form the hydroxides. The final 

 precipitate of hydroxides was dissolved in dilute hydrochloric 

 acid and the solution was tested for the growth of radium. 

 The results obtained with this solution are given in Table V. 







Table V. 







Growth of Radium in Solution 



5. 





Time from 



Ea Em found 



Growth of 



Test 

 No. 



start 

 in days 



expressed 

 in terms of Ea 



radium 

 per day 



1 

 2 

 3 



8-7 



2T7 



147-0 



0-097 X 10- 9 g. 

 0-240 X 10" 9 g. 

 1-51 X 10-°g. 



00110 x io- 

 0-0101 X 10" 



The average production of radium per day, calculated from 

 the results of tests 1 and 3 only, was 0-0102 X 10"" gram and 

 the amount of radium in the solution at the start was 

 0*067 X 10~ 9 gram. The amount of radium produced per 

 year would therefore be 3 - 72 X 10~ 9 gram. The amount of 

 radium contained in the 40 grams of mineral (78*5 per cent U) 

 taken was 1*07 X 10 -5 gram. The fraction (A.) of the radium 

 changing per year was therefore 3'48 x 10 -4 , which gives 1990 

 years for the half- value period of radium. 



Activity of Ionium in Solutions. 



The activity of the substances present in solutions 1, 2, 3 

 and 4 was determined in the manner which has been already 

 described.* Now it has been elsewhere shownf that the 

 activity of the ionium in radio-active equilibrium with uranium 

 is about 0'35 the activity of the uranium with which it is 

 associated in a mineral. From the activity of an ionium 

 preparation it is therefore possible to determine the weight of 

 uranium with which this quantity of ionium would be in radio- 

 active equilibrium. Since the amount of radium in equilibrium 

 with one gram of uranium is known, \ it is also possible to 



*This Journal, xxv, 374, 1908. flbid., xxv. 291, 1908. 

 Jlbid., xxv, 296, 1908. 



