382 Prof. E. Rutherford and Mr. F. Soddy on 



Now this last equation has been theoretically developed in 

 other places (compare Rutherford, Phil. Mag. 1900, pp. 10 

 and 181) to express the rise of activity to a constant maxi- 

 mum of a system consisting of radiating particles in which 



(1) The rate of supply of fresh radiating particles is 

 constant. 



(2) The activity of each particle dies down geometrically 

 with the time according to equation (1). 



It therefore follows that if the initial irregularities of the 

 curves are disregarded and the residual activity of thorium is 

 assumed to possess a constant value, the experimental curve 

 obtained for the recovery of activity will be explained if two 

 processes are supposed to be taking place : 



(1) That the active constituent ThX is being produced at a 



constant rate; 



(2) That the activity of the ThX decays geometrically 



with time. 

 Without at first going into the difficult questions connected 

 with the initial irregularities and the residual activity, the 

 main result that follows from the curves given can be put to 

 experimental test very simply. The primary conception is 

 that the major part of the radioactivity of thorium is not due 

 to the thorium at all, but to the presence of a non-thorium 

 substance in minute amount which is being continuously 

 produced. 



V. Chemical Properties of ThX. 



The fact that thorium on precipitation from its solutions 

 by ammonia leaves the major part of its activity in the filtrate 

 does not of itself prove that a material constituent responsible 

 for this activity has been chemically separated. It is possible 

 that the matter constituting the non-thorium part of the 

 solution is rendered temporarily radioactive by its association 

 withe thorium, and this property is retained through the 

 processes of precipitation, evaporation, and ignition, and 

 manifests itself finally on the residue remaining. 



This view, however, can be shown to be quite untenable, 

 for upon it any precipitate capable of removing thorium 

 completely from its solution should yield active residues 

 similar to those obtained from ammonia. Quite the reverse, 

 however, holds. 



When thorium nitrate is precipitated by sodium or am- 

 monium carbonate, the residue from the filtrate by evapora- 

 tion and ignition is free from activity, and the thorium 

 carbonate possesses the normal value for its activity. 



The same holds true when oxalic acid is used as the 



