270 Boltwood — Badio-artivHy of Uranium Minerals. 



that the experiments to be described in this paper were under- 

 taken. 



The problem was first brought to my attention in April, 

 1905, by Professor Rutherford, who suggested that an attempt 

 be made to determine the relative activity due to actinium 

 and its known products in a uranium mineral. At his sugges- 

 tion certain experiments were undertaken with the object of 

 measuring the rise with the time in the activity of a uranium 

 mineral from which the radium emanation and its immediate 

 products (radium A, radium B ' and radium C) had been 

 completely removed, and also of determining the relative 

 activities of the radium and actinium emanations which were 

 evolved by a solution containing a known amount of a uranium 

 mineral. 



In the former experiments a fraction of a gram of a pure 

 uraninite was dissolved in dilute nitric acid and the solution 

 was boiled to expel the radium emanation. The solution was 

 heated for a further period of several hours, and was finally 

 transferred to a shallow dish and evaporated to dryness. The 

 radium emanation and the products of rapid change formed 

 from it (RaA, RaB and RaC) having been completely 

 removed in this manner, the dish with the residue was placed 

 in an electroscope and the activity measured. The rise in the 

 activity with the time due to the accumulation of fresh quan- 

 tities of emanation and active products was then observed and 

 the final maximum activity attained at the end of about thirty 

 days was ultimately determined. Results were obtained which 

 indicated that the activity of the residue free from radium 

 emanation, radium A, B and C, was from 0*55 to 0*62 that of 

 the residue when the maximum amounts of emanation and 

 products were present. From these data and from other data 

 on the relative activity of uranium minerals and the uranium 

 contained in them, it was possible to calculate roughly the 

 activity of the radium and known radium products as com- 

 pared with the activity of the other active substances (includ- 

 ing the actinium products) present in the mineral. The 

 relative activity of the actinium products as calculated in this 

 maimer was found to be so low that it appeared highly improb- 

 able that actinium was an intermediate product in the main 

 line of descent in the uranium-radium disintegration series.* 

 This matter had been discussed in some detail by Rutherford. f 

 In the experiments in which it was. attempted to measure 

 the actinium emanation evolved by a solution of the mineral, 

 it was found that the amount of the emanation given out by a 



* Rutherford and Boltwood, this Journal, xx, 56, 1905. 

 f Radioactive Transformations, p. 177. 



