Ionization of Hydrogen by X-Rays. 649 



avoid AsH 3 . In view of the difficulty of obtaining these 

 chemicals in an arsenic free condition, it is quite probable 

 that the sudden rise in ionization observed by Beatty was 

 due to the presence of AsH 3 . It is possible, also, that the 

 steep rise in Crowther's results was due in part at least to 

 some such impurity. 



Method and Apparatus. 



The method adopted in this investigation was, generally 

 speaking, that used by Beatty. The manner in which the 

 ionization in the chamber varied with the pressure was 

 observed, and from the curves obtained for hydrogen and 

 air the relative ionizations of the two gases were deduced. 

 The ionization pressure curves obtained are of the form I. in 

 fig. 2, and it is seen that only beyond a certain pressure does 



Fig. 2. 



Pressure 



the curve become a straight line. At this pressure the amount 

 of gas present was sufficient to absorb completely all the 

 electrons emitted by the walls and electrode. The admission 

 of more gas was not accompanied by an increase of ioniza- 

 tion due to end electrons, so that any increase in ionization 

 observed beyond this point must be due to the action, direct 

 or indirect, of the X-rays on the gas itself. Curve II. shows 

 the ionization pressure curve for the electrons from the walls, 

 or rather for the gain of electrons resulting from the inter- 

 change of electrons between the walls and the gas. Curve III. 

 gives the ionization produced by the action of the X-rays on 

 the gas. This last curve is a straight line, and the slopes of 



