
42 IONIZATION THEORY OF GASES [CH. 
the rate of discharge of the electrode A varies directly as the 
potential of A, provided that the value of V is not large enough to 
remove all the ions from the gas as it passes by the electrode. 
This was found experimentally to be the case. 
In the comparison of the velocities, the potential V was adjusted 
to such a value that p, was about one half, when uranium oxide 
was placed in the tube at ZL. The active substance was then 
removed, and an aluminium cylinder substituted for the brass 
tube. X rays were allowed to fall on the centre of this aluminium 
cylinder, and the strength of the rays adjusted to give about the 
same conductivity to the gas as the uranium had done. Under 
these conditions the value of p, was found to be the same as for 
the first experiment. 
This experiment shows conclusively that the ions produced 
by Rontgen rays and by uranium move with the same velocity 
and are probably identical in all respects. The method described 
above is not very suitable for an accurate determination of the 
velocities, but gave values for the positive ions of about 1-4 cms. 
per second per volt per centimetre, and slightly greater values for 
the negative ions. 
33. The most accurate determinations of the mobility of the 
ions produced by Réntgen rays have been made by Zeleny! and 
Langevin”. Zeleny used a method similar in principle to that 
explained above. His results are shown in the following table, 
where K, is the mobility of the positive ion and K, that of the — 
negative ion. 






; 
| Gas Ky hg eddy Ee Temperature | 
| | ky 
DN arc We a a ses estan) walgsi (pcs i745 13°5 C. 
SSNNOIStM a. si Sih koi: 1:10 14° 
Oxygen, dry Mes 1:36 | 1:80 132 Le 
iy pMROIStY scoot LOO debe oul eelals 16° 
| Carbon dioxide, dry | 076 | 0:81 1:07 Vis 
x » moist | 0-81 | 075 | 0915 | 17° 
Hydrogen, dry one 6-70 | 7:95 1:15 20° 
i. moist ... 5°30 | 5°60 NO) ji BO 
| | 

1 Phil. Trans. 195, p. 193, 1900. 
* C. R. 134, p. 646, 1902, and Thesis, p. 191, 1902. 
