374 Mr. R. W. Boyle on the Absorption of 



at the anode surface, and X the length of the last free run of 

 the ions at the end of which they reach the anode surface, 

 it is suggested that arcing commences when IEA, attains a 

 value sufficient to raise a part of the anode surface to such a 

 temperature that positive ions are somewhat freely emitted. 



The Physical Laboratory, 

 The. University of Sydney. 



XXXV. The Absorption of the Radioactive Emanations by 

 Charcoal. By k W. Boyle, M.Sc* 



[Plate VII.] 



THE experiments of Sir James Dewar in 1903 drew 

 attention . to the property possessed by the charcoal 

 of coconut of absorbing gases in a remarkable degree. 

 Since then this property has been investigated by several 

 experimenters t, and has been applied by Sir William Ramsay 

 in separating the inert gases helium and neon from the air, 

 and measuring the quantities in which they exist in the 

 atmosphere. The results in the papers mentioned below may 

 be summarized as follows : — 



(1) The absorption of gases by coconut charcoal is 



greatly increased by lowering the temperature of 

 the charcoal. 



(2) The charcoal has a greater " affinity " for some gases 



than for others, there beino- something of the nature 

 of a selective absorption. In consequence of this 

 property, it is possible to separate from one another, 

 in some degree, the constituents of a mixed gas. 



(3) Of the inert gases of the argon family, argon is 



absorbed about in the same degree as ordinary gases, 

 but helium and neon in a much less degree, and 

 helium less than neon. 



(4) The absorption is also influenced by the pressure of the 



gas in contact with the charcoal, the pressure-con- 

 centration-curves varying in a regular manner with 

 the temperature. 



* Communicated by Prof. E. Rutherford. 



t " The Absorption and Thermal Evolution of Gases occluded in 

 Charcoal of Low Temperature." Dewar, Proc. Roy. Soc. vol. lxxiv. p. 122. 



" The Separation of the most volatile Gases from Air without Lique- 

 faction." Dewar, Proc. Roy. Soc. vol. lxxiv. p. 122. 



" The Determination of the Amount of Neon and Helium in Atmo- 

 spheric Air." Ramsay, Proc. Roy. Soc. May 24th, 1905. 



" The Law of Distribution in the Case in which one of the Phases 

 possesses Mechanical Rigidity." " Absorption and Occlusion." Travers, 

 Proc. Roy. Soc. Julv 21st, 1905. 



