Ellen Gleditsch — Life of Radium. 121 



was added. The solution was now heated and hydrofluoric 

 acid added. The fluorides were treated as already told for 

 cleveite and a second solution for measuring the growth of 

 radium was obtained : test solution from brdggerite. 



Table 7. 



Growth of radium in test solution from Broggerite 1. 



Radium emanation found 

 Time from start expressed in Growth of radium 



Test in days terms of radium per day 



1 4- 0-129 X lO- 9 



2 97- 0-265 X 10~ 9 0-0002 X 10" 9 



3 226- 0-347 X 10~ 9 0-0004 X iO" 9 



Here is perhaps a very small augmentation of radium ; in 

 every case it does not amount to as much as one per cent. 

 The average growth of radium is 



per day: 0-047 X 10~ 9 gram 

 or per year: 17-155 x 10 -9 gram 



The amount of radium in 200 grams of mineral was found to be 

 4-07 X 10~ 5 . The constant of change of radium then is 



17-16 x 10~ 9 



= 4-22 x 10~ 4 (year)- 1 



4 07 X 10- 5 VJ ' 



and the half-value period is 



/ log e 2 \ 



( 5! ) 1642 years. 



\4-22 X IO- 4 / J 



The residue insoluble in nitric acid weighed about 5 grams and 

 had an activity corresponding to 2 grams of mineral. It was 

 treated with hydrofluoric acid, then evaporated to dryness with 

 sulphuric acid. To the residue was added hydrochloric acid ; 

 and the solution filtered off; it contained no uranium; the 

 residium still had the initial activity ; it was boiled with an 

 excess of sodium bicarbonate and filtered ; the undissolved part 

 was treated with hydrochloric acid, which dissolved the small 

 amount of carbonates found. Neither did this solution con- 

 tain any uranium. The residue, now nearly inactive, consisted 

 chiefly of niobic and tantalic acid ; it was treated with hydro- 

 fluoric acid which dissolved a large part of it. The remaining 

 part 0*9 gram only had a very slight activity and consisted, I 

 think, chiefly of unattacked columbite. 



Jf.. Ionium solution from Brdggerite 2, Norway. 



This broggerite was a very pure sample from the same local- 

 ity as the first one — Raade in Norway ; it was given to me by 



