608 Drs. Geiger and Kovarik on Relative Number of Ions 



Radium B. — A wire was exposed to radium emanation in 

 an electric field for 5-10 minutes, in which time a sufficient 

 amount o£ Ra A was collected. Ra B was then obtained by 

 recoil from the Ra A, exposures being made from 5 to 25 

 seconds. The /3-ray measurements were then made imme- 

 diately, and were carried on for only 3 minutes. The correc- 

 tions that had to be made for the growth of: Ra C within that 

 time were relatively small. The number of atoms breaking np 

 was obtained by measuring the a-ray activity of the Ra C. Both 

 the /3-ray and the a-ray activities were reduced to the time 

 of the maximum (33 minutes), at which time the two sub- 

 stances are in equilibrium. The values obtained in the 

 different experiments did not show the same agreement as 

 was obtained in the case of other substances. 



Radium C. — This was obtained in two different ways, 

 namely, by the growth from Ra B and by chemical sepa- 

 rations from the active deposit, using Lerch^s method of 

 separation. The absorption curve of the /3 rays is complicated, 

 as is well known, due to the fact that groups of /3 rays of 

 different absorption coefficients are present. According to 

 our experiments about 60 per cent, of the total activity, when 

 corrected for absorption, is due to soft /3 rays with an 

 absorption coefficient fi about 50, and 40 per cent, due to 

 hard /3 rays with an absorption coefficient /i = 13*5 about. 

 It is, however, possible that the whole of the /? radiation of 

 Ra C is heterogeneous *. 



Radium E. —Radium "emanation was allowed to decay in a 

 sealed glass tube containing a thin aluminium foil carefully 

 protected on one side by means of paraffin. The /3-ray 

 activity and the a-ray activity were observed over a period of 

 nearly a year, and from the latter measurements the number 

 of RaE atoms breaking up was calculated. Two such spe- 

 cimens were used, their relative activities being in the ratio 

 of 40 to 1. Other experiments were made using Ra E 

 chemically separated from pitchblende residues by Prof. 

 Boltwood. 



Uranium X. — This is the only case in which the number 

 of atoms breaking up was determined in a different way from 

 that explained above. The number was calculated from the 

 weight of uranium, knowing that 1 gram of uranium is in 

 equilibrium with 3*4 xl0~ 7 gram of radium-}-, and that 

 1 gram of radium emits 3*4 x 10 10 a particles. The actual 

 number of U X atoms breaking up is the product of the 

 weight of the uranium and the above two numbers. 



* See also H. W. Schmidt, Phys. Zeits. vii. p. 764 (190G). 

 t B. B. Boltwood, Am. J. Sci.'xxv. p. 296 (1008). 



