SPCCKSSIMN OF CHANC1.S IN RADIOACTIVE BOPTKS. 



1R9 



By substitution in the curve, the value <>l tin- other constant is found to be 

 77 X 10~ 3 (half transformed in 1*5 minutes). 



As in the case of thorium, a difficulty arises as to which value of X applies to the 

 rayless change, but the question in the case of actinium can at once be settled by 

 means of electrolysis. 



100 



15 20 



Time in Minutes. 

 Fig. 10. 



35 



I'.KIMIKS |irrt'niifi| tlic tulle .win- e\|.ri inn-ill : A platinum jil.-iti- \\ .,* nmdr 

 active in the presence of actinium and the active matter was dissolved off by 

 hydrochloric acid and then electrolysed. The activity of the anode, after removal, 

 fell very rapidly according to an exponential law, reaching half value in 1 '5 minutes. 

 The corresponding value of X is 77 X 10~ 3 . There is thus no doubt that the second 

 change is the most rapid of the two. We may thus conclude that the active deposit 

 from actinium undergoes two distinct successive transformations : 



(1) A rayless change, in which half the matter is transformed in 41 minutes; 



(2) A change giving rise to a rays, in which half the matter is transformed in 



I '5 minutes.* 



It can readily be shown that, for a very short exposure of a Ixxiy in the presence 

 of the actinium emanation, the activity I< at any time t is given by 



1,/Ir =1-1 4 (-*' -e-*), 

 where I T is the maximum value of I which occurs at time T = 7'5 minutes. 



* The radiations from the products have not yet been examined to see whether ft and y rays are 

 present. 



