58 Messrs. J. H. L. Johnstone and B. B. Boltwood on the 



the two-thirds power of the ranges of the ^-particles emitted 

 by the respective elements, namely, the activities should be 

 proportional to 



(2-37)1, (2-75)1, (3-13)*, 



where the numbers in parentheses are the ranges at 0° C. of 

 the a-particles from uranium I., uranium II., and radium, 

 respectively. Any departure from this proportionality will 

 indicate an irregularity in the mode of 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 uranium (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) :2-14 = l-00:0-57. 



An experimental determination of this ratio was carried 

 out in the following manner : — 



A quantity of radium was separated from Colorado carno- 

 tite and was carefully freed from other radioactive substances 

 which can be separated by chemical operations. Since car- 

 notite is free from thorium, the specimen 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 hereafter as solutions B and C) were prepared, 

 which contained about 0*025 g. of barium chloride and 

 2*4 x 10 -8 g. of radium in 10 c.c. of solution. The quantities 

 of radium were so chosen that the radium films ultimately 

 obtained would have activities of the same order of magni- 

 tude as the activities of the uranium films with which they 

 were to be compared. 



An accurate determination was then made of the emana- 

 tion in equilibrium with the radium in 10 c.c. of the radium- 

 barium solutions. The results were recorded in terms of 

 the leak produced in the emanation electroscope in divisions 

 per minute. 



The results were : — 



For 10 c.c. of Solution B 81*7 div. per min. 



For 10 c.c. of Solution C 71*0 div. per min. 



The radium emanation in equilibrium with the radium 

 contained in one gram of the uraninite was also determined 

 and was found to correspond to 853*5 divisions per minute 

 in the same electroscope. Since the uraninite contained 



