Mr M c Glung, On Ionization produced in Air and Hydrogen. 375 



Relative Amount of Ionization produced in Air and Hydrogen 

 by Rontgen Rays. By R. K. McClung, B.A., Trinity College, 

 1851 Exhibition Science Scholar. 



[Read 1 February 1904.] 



The question of the relative amount of ionization produced 

 in different gases by means of Rontgen rays has been investigated 

 by different experimenters. Professors Thomson 1 , Rutherford' 2 , 

 and Perrin 3 have each made independent determinations on this 

 question. In the case of most of the gases experimented upon 

 the results obtained by the different observers were in very fair 

 agreement, but hydrogen proved to be a marked exception. In 

 the case of hydrogen there was a very considerable difference in 

 the values obtained by the three experimenters. The conditions 

 under which these different experiments were carried out differed, 

 of course, somewhat in the different instances, and no doubt the 

 results were influenced thereby. The experiments described in 

 the present paper were undertaken therefore to determine, if 

 possible, what are the conditions which cause variations in this 

 particular gas. 



The method adopted for comparing the amount of ionization 

 in the two gases was a balance method. This promised to be 

 the most satisfactory, as the ionization in hydrogen is so much 

 less than in air that comparisons could be more easily made in 

 this manner than by separate and direct measurements. 



The gases to be ionized were contained in two similar metal 

 cylinders which were made gas-tight. Inside each of these 

 cylinders were placed two parallel plates between which the 

 Rontgen rays passed, in the direction parallel to the length of 

 the plates, and ionized the gas between them. These vessels 

 were placed symmetrically with regard to the source of the rays 

 so that the same amount of ionization was produced in each of 

 them when they were both filled with air at atmospheric pressure. 

 In one vessel one of the plates was connected to the positive 

 pole of a battery, while the corresponding plate in the other 

 vessel was connected to the negative pole, the centre of the 

 battery being connected to earth. The other two plates were 

 connected together and to the electrometer. When the gas was 

 ionized in both cylinders the plate connected to the electrometer 



1 J. J. Thomson, Proc. Camb. Phil. Soc. x. p. 10, 1900. 



2 Eutherford, Phil. Mag. v. 43, p. 241, 1897. 



3 Perrin, Annates de Physique et de Ghimie, xi. p. 496, 1897. 



