414 Boltwood — Salts of Badium . 



was determined and the dish was then allowed to remain in a 

 desiccator over sulphuric acid for about six weeks. At the end 

 of this period the activity was again determined, and was found 

 to have risen to 3*1 times the initial activity. It is evident 

 that this film retained only about 45 per cent of the emanation 

 formed within it. For the solution from which it was pre- 

 pared I am indebted to Mr. A. S. Eve of McGill University. 



Conclusions. 



The ranges in air at atmospheric pressure of the a particles 

 from radium and its disintegration products of rapid change 

 have been determined by Bragg and Kleeman.* The ranges 

 which they found were the following : 



1 Radium 3-5 cm 



2 Emanation or Radium A 4*23 



3 Radium A or Emanation 4 - 83 



4 Radium C 7*06 



The sum of these numbers is equal to 19*62 and this number 

 is 5*60 times the range of the a particle from radium itself. 

 The value found for the relative ionization or activities of the 

 different products, namely 5"64,f agrees so closely with the ratio 

 of the relative ranges of the same products that it appears highly 

 probable that the a-ray activities of the different products are 

 proportional to the ranges of their a particles. Moreover, 

 since according to the disintegration theory when the parent 

 substance and the products are in radio-active equilibrium the 

 same number of atoms of each are undergoing disintegration 

 per second and the same number of a particles are projected 

 from each exploding atom, it would appear probable that the 

 ionization produced by each a particle is proportional to its 

 range. That the ionization measured was produced almost 

 wholly by the a particles was demonstrated by covering one of 

 the films which had attained its maximum activity with a sheet 

 of aluminium 0"l mm in thickness. The ionization then pro- 

 duced was only about 0*3 per cent of the ionization produced 

 by the bare film. 



New Haven, Conn., April, 1906. 



*Phil. Mag. (6), viii, 719, 1905. 



f The value for the ratio was also determined in an electroscope having an 

 ionization chamber 16 c,n long, 8'5 cm wide and 7 cm high. The charged plate, 

 13 cm long and 5 cm wide, was suspended 3 - 5 c ™ from the bottom. The ratio of 

 the activity of the emanation-free salt to the activity of the same substance 

 containing all of its emanation as determined in this smaller electroscope 

 was 5 - 35, and this lower value is to be attributed to the fact that a portion 

 of the a particles of longer range were stopped by the walls and plate before 

 they had completed their full paths, which resulted in a corresponding 

 reduction in the total ionization. 



