844 Prof. Barkla and Mr. Philpot : Ionization in Gases and 



from the gas leaving through the ends of the chamber. The 

 net result may be either a gain or a loss. By selection of 

 the material forming the ends of the chamber, it is possible 

 to make these effects calculable from observations which 

 have already been made on secondary radiations of the three 

 types. Aluminium ends were used, as Sadler had made 

 a fairly exhaustive study of the corpuscular radiation 

 from aluminium under the action of various homogeneous 

 radiations. 



When the gases nitrogen, oxygen, carbonic acid, nitrous 

 oxide, coal-gas were used, the net gain of corpuscles from 

 the ends was, within a small error, equal to that when air 

 was used as the gas being ionized. When sulphuretted 

 hydrogen and sulphur dioxide were ionized, the gain or loss 

 became inappreciable, first because the total ionization was 

 very great and the end effect proportionately smaller ; 

 secondly, because the corpuscular radiation from sulphur, 

 an element of atomic weight near to that of aluminium, 

 being lost by the gas, would tend to neutralize the gain from 

 aluminium. When combined with hydrogen the balance 

 would be fairly good ; when combined with oxygen in 

 sulphur dioxide there would probably be a net gain from 

 aluminium, for the oxygen would intercept and prevent 

 about half of the corpuscles from sulphur which would 

 otherwise escape from getting away, while the oxygen would 

 contribute little to the corpuscular radiation. 



When heavier vapours were ionized and the incident radia- 

 tion was sufficiently penetrating to produce comparatively 

 large corpuscular radiations from the aluminium ends, the 

 net result would be a loss of ionization due to the ends. 

 This loss, however, was small compared with the total 

 ionization, for the thickness of the layer from which they 

 emerged was small compared with the total length of the 

 ionization-chamber. In these, then, the end effect was 

 negligible. 



The end effect due to gain or loss of corpuscular radiation 

 was thus corrected in the calculation of the ionization in 

 some gases, and was negligible in others. 



From a knowledge also of the penetrating powers of the 

 fluorescent and scattered X-radiations from the elements 

 constituting the gas, it may readily be shown which d these 

 was absorbed in the gas itself in the particular experiment 

 the results of which are given. When an appreciable 

 fraction of the primary radiation absorbed was re-emitted as 

 scattered radiation, this was of so penetrating a type that 

 it produced a negligible ionization compared with that 



