Production and Origin of Radium. 743 



actinium R ? with periods of half transformation of 19*5 days, 

 10 days, 3*9 seconds, 34 minutes and 1*5 minutes respectively. 

 Is radium the final product of actinium, i. e. is radium formed 

 from actinium B ? There are two methods of attacking this 

 question : 



(1) To examine whether the active deposit of radium (com- 

 posed of actinium A and B) produces radium, or 



(2) To test whether the rate of growth in actinium is 

 initially altered by the removal from it of actinium X 

 or radioactinium. 



Experiments using the method (1) are described later in 

 § 9 of this paper, but we shall here only consider the second 

 method. If radium is produced directly from actinium B, 

 the rate of production of radium should be nearly proportional 

 to the amount of actinium X, since after a few hours the 

 rapidly transformed products actinium A and B are in equili- 

 brium with it. Consequently, if actinium X is removed from 

 an actinium solution in equilibrium, the rate of growth of 

 radium in the latter should at first be very small, but should 

 gradually increase as fresh actinium X is formed. JSince the 

 half period of actinium X is 10 days, the rate of growth of 

 radium should reach half value in 10 days and be within less 

 than two per cent, of the final constant value in about 60 

 days. 



In order to test this point accurately, it is necessary that 

 the solution under examination should initially contain 

 an amount of radium small compared with the growth per 

 week. In the case of actinium I., the initial content of radium 

 was too large to be quite certain that the rate of growth in 

 the first few days was identical with that determined later. 



A part of the actinium preparation of weight 0*32 gram, 

 discussed iu § 2, was used for this purpose. It was dissolved 

 in hydrochloric acid and twice precipitated with ammonium 

 sulphide and finally with ammonia, in order to be sure that 

 the actinium X as well as the radium was almost completely 

 removed. These operations were successful, for a solution 

 of actinium was obtained whose initial content of radium 

 corresponded to only *02 division per minute in the electro- 

 scope, while the rate of growth per week was *26 division. 

 A careful examination of the radium content was made at 

 successive intervals of four days until it was clear that the rate 

 of growth was constant. The results are shown in the 

 following table, and are arranged in the same way as the 



results in the table for actinium I; ■' 



■'•'• ; 3D2 ■ '•' 



