848 Prof. Barkla and Mr. Phil pot : Ionization in Gases and 



elements. Such a result would, however, be produced by 

 the presence o£ a small quantity of arseniuretted hydrogen 

 in the hydrogen. The ionization in hydrogen is worth 

 further investigation, for, if the results obtained are actually 

 those for hydrogen, they are important in indicating a 

 characteristic radiation of a hitherto undiscovered third 

 series. If, on the other hand, the deviation from propor- 

 tionality be due to an impurity in the hydrogen, this shows 

 that hydrogen has a remarkably low ionization coefficient 

 for the softer radiations — possibly of the order of xooo or 

 even a smaller fraction of the corresponding coefficients of 

 ionization in air. 



There is a general similarity between the relative ioniza- 

 tions in the gases and vapours, and the relative absorptions 

 of the ionizing radiations in these gases and vapours. The 

 light gases which absorb comparatively little of the primary 

 radiation are ionized to a small extent. There is not, how- 

 ever, exact proportionality between ionization and absorp- 

 tion *. This is clearly seen from the ionizations produced 

 in SH 2 and S0 2 , the ionization in SH 2 being greater than 

 that in S0 2 , whereas the absorptions of the ionizing radia- 

 tions are in the reverse order. This difference was shown 

 by Barkla and Simons f to be a true case of different energy 

 consumption for equal numbers of ions produced in these two 

 gases. 



If we compare the amount of energy truly absorbed in the 

 gases (by subtracting from the absorption coefficient that part 

 due to scattering) with the ionizations produced, we find 

 that the relative energy spent per ion produced varies to a 

 certain extent with the gas. This is shown in relative values 



of — ~. that is 

 i 



coefficient of absorption — coefficient of scattering 



relative coefficient of ionization 





for a particular radiation in a particular gas, which are given 

 below. In the cases here dealt with, the scattered radiation 

 was the only secondary radiation to escape. 



* Absorption of homogeneous X-rays by gases and vapours was 

 investigated by Barkla and Collier (Phil. Mag. June 1912, p. 987). 

 Absorption by elements had been previously studied by Barkla and 

 Sadler (Phil. Mag. May 1909, p. 739). 



t Phil. Mag. Feb. 1912, pp. 317-333. 



