Ionization oj Hydrogen by X-Rays. 



653 



mirror test for arsenic, the results showing that the amount 

 of arsenic present was certainly very small. 



Results. 

 In fig. 4 are shown two typical curves for hydrogen and 

 air. The observed points were found in the case of hydrogen 



Air H 2 

 315 7-0 



314 60 



c 



•5313 50 



'312 4-0 



311 30 



310 2-0 



> 











Air 







































1 







HT"" 



90 110 



Pressure (Cm.) 



130 



150 



to lie within the limits of experimental error on straight 

 lines. In the case of air it was necessary to correct for the 

 absorption by the air of the rays in passing through the 

 chamber ; after this correction had been applied the curves 

 for air became straight lines over the range of pressures 

 employed. 



Since air absorbs the rays, especially the soft copper rays, 

 much more than hydrogen, the mean intensity of the beam 

 traversing the chamber in the two cases was different. From 

 a knowledge of the absorption coefficient of air for the rays 

 used it is easy to correct for this absorption. 



If I is the intensity of the beam just after entering the 

 chamber, and if d is the length of the chamber, and X the 

 absorption coefficient for the gas, then the mean value of 

 the intensity throughout the chamber 





I e~^ x dx 



-&C 1 -' 



■kd~ 





