Gaseous Mixtures by ilijntgen and Corpuscular Radiations. 845 



produced by the direct primary beam. We may therefore 

 neglect further consideration of this. The fluorescent radia- 

 tions from the ionized gas can only be dealt with individually 

 as we consider each gas. 



The radiation scattered from aluminium being of the same 

 penetrating power as the primary would produce relative 

 ionizations similar to those due to the primary, so that except 

 for a different correction for absorption due to divergence of 

 the scattered radiation, the ionization may be included with 

 that of the primary. The error introduced by neglecting 

 this is negligible. 



The very soft fluorescent X-radiation from aluminium 

 contains only a very small portion of the energy of the 

 primary radiation absorbed in the thin layer from which it 

 can emerge. It is also negligible i n its ionizing action : if 

 it had not been so it would have been included in the ionizing 

 effect of the soft corpuscular radiation studied hj Sadler, and 

 would have been corrected with the corpuscular radiation. 

 After correction for absorption, and where necessary for the 

 corpuscular radiation from the window and walls of the 

 ionization-chamber, the following results (Table IV.) w 7 ere 

 obtained for the coefficients of ionization in a number of 

 gases compared with the coefficients of ionization for the 

 corresponding radiations in air *. Beatty's values for the 

 ionization in H 2 and SeH 2 have been added |. 



Perhaps the simplest way of stating the conditions of the 

 experiments is that the ionization coefficients obtained for 

 air, coal-gas, H 2 , N 2 , 2 . C0 2 , N 2 0, SH 2 , S0 2 were those got 

 by complete absorption of all secondary radiations except the 

 scattered X-radiations. Only in the case of SeH 2 , C 2 H 5 Br, 

 and CH 3 I did the greater part of the characteristic radiation 

 (series K) from Se, Br, or I escape — when it was excited ; 

 and only in the case of the former two when ionized by Sr 

 and Mo characteristic radiations would the complete ab- 

 sorption of the fluorescent radiations have made any great 

 difference to the ionization coefficient. Of course, in many 

 cases the absorption of the scattered X-radiation or of the 

 fluorescent X-radiation produces no appreciable increase in 

 the total ionization ; so that we may say either that the 

 results include or do not include the scattered radiation 

 ionization. In the case of the ionization of light gases Im- 

 penetrating radiations, however, nearly all scattered radiation 



* E. A. Owen obtained values for C0 2 about 10 per cent, greater than 

 those given in Table IV. ? and for S0 2 values, within 1 or 2 per cent, of 

 our values in this table. 



t Phil. Mag. Aug. 1910; Proc. Eoy. Soc. A. lxxxv. p. 578 (1911). 



