254 



Mr. E. Rutherford on the Electrification 



When the temperature of the vapour was raised above the 

 boiling-point of the liquid, the intensity of the radiation after 

 passing through 13 cm. of the vapour was only '4 of the 

 intensity when the vapour was removed. 



From experiments on the absorption of energy of different 

 lengths of the vapour of methyl iodide, and also of the gases 

 sulphuretted hydrogen and chlorine, the ratio of the intensity 

 of radiation after passage through the vapour or gas to the 

 intensity of the radiation when the gas was removed was found 

 to be in agreement with the theoretical ratio e~ Kl . For short 

 lengths of the gas the absorption is proportional to the length. 



It has been shown that for the vapour of methyl iodide 

 e~ Kl ~'A. when Z=13 cm.; therefore X=*07. The intensity of 

 the radiation after passing through a length of 1 metre of the 

 vapour is only one thousandth part of its value when the 

 vapour is removed. 



The absorption of energy varies with the pressure of the 

 gas. The vapour of methyl iodide was used, and it was found 

 that the values of X were roughly proportional to the pressures 

 down to a pressure of one quarter of an atmosphere. Results 

 of this kind, however, are difficult to determine with accuracy 

 on account of the variation of the Crookes tube during a 

 series of observations. 



The following table gives the values of \ and relative con- 

 ductivities of some of the gases : — 



Gas. 



\. 



Conductivities. 





(small) 

 001 



about -001 



•0025 

 •0037 

 •0065 

 •0095 



•5 



1 



12 

 •9 

 •8 



1-2 



4 



6 

 11 

 18 



Air 



Oxygen ] 



Nitrogen 1 





Sulphur dioxide 



Sulphuretted hydrogen ... 



Chlorine 



These experiments show that good conductors under the 

 .z-rays are good absorbers of the radiation. The absorbing 

 powers for the gases examined had the same relative order as 

 their conductivities. The absorption does not seem to depend 

 to any great extent on the molecular weight of the gas. 

 Hydrochloric acid is nearly twice as good an absorber as 

 sulphuretted hydrogen, although their densities are nearly 

 equal ; while it is more than ten times as good an absorber as 



