﻿in Gaseous Mixtures hy Rontgen Radiation. 319 



Apparatus. 



Various pieces of apparatus were used in the following 

 experiments to measure the ionization in gases. The ioniza- 

 tion-chamber itself was usually cylindrical in shape. One 

 flat end was provided with a thin aluminium window to 

 admit the ionizing radiation ; the opposite end was made 

 of brass or lead, with an internal facing of thick aluminium, 

 upon which the radiation fell after traversing the gas. The 

 sides of the cylinder were also aluminium-lined. The terminal 

 in this ionization-cbamber was in some cases axial, in others 

 circular in a plane parallel to the ends. This terminal was 

 connected by a vertical wire passing through a brass con- 

 necting-tube with an electroscope of the type used in many 

 previous experiments. Deflexions of the gold-leaf were, as 

 usual, observed by means of a microscope with micrometer 

 eyepiece, and the rate of deflexion was taken as a measure 

 of the ionization in the vessel above, when the saturation- 

 current was obtained. 



The radiations used were the homogeneous fluorescent 

 Rontgen radiations* emitted by elements when these were ex- 

 posed to ordinary primary Rontgen radiations. Two ioni- 

 zation-chambers and connected electroscopes were invariably 

 usod, each receiving a beam of homogeneous Rontgen radiation 

 from the same sheet of substance placed in the primary beam. 

 One chamber contained air, and was used to standardize the 

 intensity of fluorescent X-radiation from the particular sub- 

 stance used ; while the gas in the other chamber was varied in 

 order to study the relative ionizations in various gases. 



The following experiments were performed : — 



Ionization in SH 2 and S0 2 . 

 In experiments by one of us f on the gases sulphuretted 

 hydrogen and sulphur dioxide, it had been found that the 

 ionization in the former gas produced by beams of X-rays 

 was invariably greater than the ionization in sulphur dioxide 

 at the same temperature and pressure, whatever the pene- 

 trating power of the ionizing radiation. As the absorption 

 in oxygen is much greater than that in hydrogen, and as it 

 lias always been found that absorption is a purely atomic 

 phenomenon, the results suggested that the greater absorp- 

 tion of X-rays in S0 2 was accompanied by less ionization 

 than that in SH 2 , indicating that ionization is not propor- 

 tional to absorption, and that the process of ionization is not 

 purely atomic, but depends on chemical combination. Those 

 conclusions had been arrived at by various experimenters, 



* Phil. Mag. Sept. 1911. f Results not yet published. 



