236 Barss — Ionization by Collision in Gases and Vapors. 

 As a further test the equation 



a/p =f(X/p) 



was shown to hold. Since this equation is a general one, if we 

 plot a curve for each pressure, taking as coordinates a/p and 

 X./p, the curves for different pressures should coincide. This 

 was tried for four different pressures in hydrogen. Values of 

 a/p and X./p are given in Table III, and the curve connecting 

 a/p and X/j? is shown in fig. 3. Points on the curve marked 







Table III 









1. 



P = 



15-5 







X 



a 







a/p 



X/p 



960 



0-80 







0-05 



61-9 



1100 



0-93 







0-06 



72-0 



1260 



1-08 







0-07 



81-3 



1660 



2"28 







0-14 



107-1 



1980 



4-88 







0-31 



127-7 





2. 



P = 



10- 







700 



0-60 







0-06 



70-0 



960 



1-08 







o-io 



96-2 



1080 



1-60 







0-16 



108-1 



1260 



3-28 







0-32 



1260 





3. 



P = 



4*2 cm 





400 



0-46 







o-ii 



98-0 



450 



0-63 







0-15 



107*4 



500 



1-0 







0-24 



119-1 



580 



2-0 







0-47 



138-2 





4. 



P = 



19-6 



cm 





1660 



1-37 







0-07 



84-7 



1800 



1-76 







0-09 



92-0 



1980 



2-30 







0-12 



101-0 



2240 



3-81 







0-19 



114-1 



1, 2, 3, and 4 correspond to pressures of 15-5 cm , 10 cra , 4/2 cm , and 

 19-6 cm respectively. It will be noticed that all the points cal- 

 culated are close to a common curve, which agrees with the 

 theory. 



From these results in air and hydrogen, we may conclude 

 that the negative ions generated in a gas by collisions with 

 alpha particles are identical with those generated by Rontgen 

 rays and ultra-violet light. In other words, the collision con- 

 stants are independent of the nature of the ionizing agent. 



Vapors. 



The method of experimenting was the same for all vapors 

 employed. The apparatus was evacuated to a low pressure 

 (•01 mm ) and vapor was admitted to a pressure depending on the 



