10 Johnstone and Boltwood — Relative Activity 



transformation and may serve to suggest the nature of 

 the changes which are actually taking place. If the 

 transformations are all simple the activity of the ura- 

 nium (consisting of an equilibrium mixture of uranium 

 I and uranium II) should be to the activity of the radium 

 in the proportion 



(1-78 + 1-96) : 214 = 1-00 : 057. 



An experimental determination of this ratio was car- 

 ried out in the following manner : 



A quantity of radium was separated from Colorado 

 carnotite and was carefully freed from other radioactive 

 substances which can be separated by chemical opera- 

 tions. Since carnotite is free from thorium the speci- 

 men of radium obtained did not contain any appreciable 

 amounts of mesothorium or other products. A solution 

 of this radium in dilute hydrochloric acid was then 

 prepared and its approximate strength in radium was 

 determined by the emanation method. Using this first 

 solution as a basis, two other solutions (denoted here- 

 after as solutions B and C) were prepared which con- 

 tained about 0-025 g. of barium chloride and 24 X 10~ 8 g. 

 of radium in 10 cc. of solution. The quantities of 

 radium were so chosen that the radium films ultimately 

 obtained would have activities of the same order of mag- 

 nitude as the activities of the uranium films with which 

 they were to be compared. 



An accurate determination was then made of the 

 emanation in equilibrium with the radium in 10 cc. of the 

 radium-barium solutions. The results were recorded 

 in terms of the leak produced in the emanation electro- 

 scope in divisions per minute. 



The results were 



For 10 cc. of Solution B 81-7 div. per min. 



For 10 cc. of Solution C 71- div. per min. 



The radium emanation in equilibrium with the radium 

 contained in one gram of the uraninite was also deter- 

 mined and was found to correspond to 853-5 divisions 

 per minute in the same electroscope. Since the uraninite 

 contained 73-0% of uranium, the radium in equilibrium 

 with one gram of uranium in the mineral was equivalent 

 to a leak of 1170 divisions per minute. The quantity of 

 radium in 10 cc. of solution B, therefore, was the same 



