of Radium and Uranium. IT 



activity of the actinium products in an equilibrium mix- 

 ture. 



In order to fulfill the conditions involved in Scheme II 

 it would be necessary for 14 out of every 100 atoms of 

 uranium to be transformed in the mode leading to the 

 production of actinium. Nor is there any apparent ad- 

 vantage gained by assuming that the transformation of 

 either U I or U II into the first member of the side series 

 is accompanied by the expulsion of a ^-particle instead 

 of an a-particle. 



It might, however, be assumed that the branching of 

 the series takes place at some other point, as at radium, 

 for example, and that 86 per cent of the radium atoms 

 disintegrate with the emission of «-rays to form the 

 emanation, etc., while 14 per cent disintegrate (emitting 

 /3-rays) to form actinium. Direct evidence of the emis- 

 sion of /3-rays by a specimen of radium has been obtained 

 by Halm and Meitner. 22 Under these conditions the 

 a-ray activity of ionium would be proportional to the 

 uranium radiation and would equal 0-53. The ac- 

 tivity of the actinium series would equal 0-56 and 

 the activity of the radium + emanation + radium A, C 

 and F would be 3-01 (the sum of the values given in 

 table V). The sum of all of these together with uranium 

 is 5-10 for the total activity of the uranium series 

 (as in uraninite). There are, however, serious objec- 

 tions to the assumption that the side branch arises at 

 radium, aside from the fact that the values mentioned 

 are widely different from those found in Boltwood's 

 experiments and the value found in the present experi- 

 ments for the total activity of the uranium products. 



The most significant objection is presented by the 

 agreement of the value found for the disintegration con- 

 stant or radium by Rutherford and Geiger 28 and the 

 value of this constant found by Miss Gleditsch. 24 The 

 Eutherford and Geiger estimate was based on the num- 

 ber of a-particles emitted per second by the radium C 

 in equilibrium with one gram of radium. If only eighty- 

 six out of every hundred of the radium atoms disinte- 

 grate to form radium C, then this estimate would be 14 

 per cent too low. The method employed by Miss 



22 Physik. Zeitschr., 10, 741, 1909. 



23 Eutherford, Phil. Mag., 28, 326, 1914. 



24 This Journal, 41, 112, 1916. 



Am. Jour. Sci.— Fourth Series, Vol. L, No. 295.— July, 1920. 



2 



