Gaseous Mixtures by Rontgenand Corpuscular Radiations. 853 



considerably greater than the third ; and the ionization in the 

 mixture, however, does not agree closely with that calculated 

 on the assumptions that all ionization by Rontgen radiation 

 is the result of the secondary corpuscular radiation and a 

 density law of energy absorption. 



In these experiments a cylindrical ionization-chamber 

 12 centimetres long and about 7 centimetres in diameter was 

 used. In order to obviate the difficulties and uncertainties 

 of the loss or gain of corpuscular radiation at the two ends 

 of the chamber, the soft homogeneous radiation characteristic 

 of copper (series K) was used as the ionizing radiation. In 

 such a case, the gain or loss of ionization owing to the 

 material of the ends differing from that of the ionized gas 

 was almost infinitesimal, the corpuscular radiation penetrating 

 only a small fraction of a millimetre of air under normal 

 atmospheric conditions for instance. It was found that the 

 ionization produced by the radiation in air and also in ethyl 

 bromide did not differ appreciably from proportionality with 

 the pressure, showing that neither corpuscular radiation lost 

 or gained at the ends nor fluorescent X-radiation from the 

 ends produced an appreciable portion of the observed 

 ionization. 



After a small correction for the absorption in the separate 

 gases and in the mixture, results were obtained of which the 

 following is typical. The ionizations are expressed in 

 arbitrary units. 



Ionization in C 2 H 3 Br at 2'6 cm. of mercury pressure = '728 i 



^ >3um=ri01 

 „ air at 61 \L cm. „ „ „ ='373! 



„ mixture of the above = '989. 



If / is the fraction of ionization in any gas due to cor- 

 puscular radiation, then assuming the absorption of energy 

 of corpuscular radiation proportional simply to the density 

 of the gas and independent of its quality, we may write the 

 direct ionization in C 2 H 5 Br-f-that due to its corpuscular 

 radiation 



(l-/)-728+ g/x -728X^5 + }J/x -728, 



i. e., direct ionization + ionization in air due to corpuscles 

 from C 2 H 5 Br + ionization in C 2 H 3 Br due to its own cor- 

 puscles : — 



[the relative densities of C 2 H 5 Br and air being 10 : 63 

 and the ratio of ionizations in C 2 H 5 Br and air due to equal 

 absorption of energy of corpuscular radiation being 1*5 : 1]. 



Phil. Mag. S. 6. Vol. 25. No. 150. June 1913. 3 M 



