748 The Production and Origin of Radium. 



It is seen from the above table that for equal amounts of 

 actinium, the growth in actinium I. is very nearly the same 

 as for the *32 gram, examined over a period of 2*7 years. 

 The closeness of the agreement is no doubt accidental on 

 account of the uncertainty (see § 2) in regard to the initial 

 content of radium in the *32 gram of actinium preparation. 

 The table brings out clearly the differences in the growth of 

 radium in the three solutions for equal quantities of actinium. 



The solution actinium II. grows radium at 1*5 times the 

 rate of actinium I., while solution III., if it grows radium at 

 all, certainly does so extremely slowly. 



These experiments can all be readily explained on the 

 simple hypothesis that in ordinary actinium preparations 

 there exists a new substance of slow change which is directly 

 transformed into radium. This new substance is separated 

 with the actinium from the mineral by the methods ordinarily 

 employed for the removal of the actinium. It differs, how- 

 ever, in chemical properties both from radium and actinium, 

 and by special chemical methods can be separated from them 

 both. For example, the preparation actinium I. may be con- 

 sidered as possessing the normal quantity of the radium 

 producing substance ; while the preparation J I. contains an 

 excess over the normal. In the case of the solution II., the 

 treatment with ammonium sulphide precipitated all this new 

 substance, but only a fraction of the actinium. The filtrate 

 consequently contained actinium but no trace of the parent 

 of radium. Under such conditions, there was relatively a 

 large growth of radium in the solution II. but none in the 

 solution III. 



As far as the investigations have gone, there is no definite 

 evidence whether this new substance is itself produced by 

 actinium, or whether it is merely associated with the actinium 

 in the same sense that barium always appears with the radium. 

 In the former case, the solution III. is gradually producing 

 this new substance, and in the course of time there will be an 

 appreciable growth of radium in it. In the latter case, the 

 solution III. will never show any growth of radium com- 

 parable with that ordinarily observed. It is not unlikely 

 that this new substance is in reality an intermediate product 

 in the direct line between uranium and radium, and has no 

 direct genetic connexion with the actinium. 



The observed constant growth of radium in the solution 

 shows that the parent of radium has a slow rate of change. 

 At a minimum estimate, its period cannot be less than seveial 

 years and may be much longer. 



