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XXXV. On Mr. Morris-Airey's Paper on Electrolytic 

 Conduction in Gases. 



To the Editors of the Philosophical Magazine. 



Cambridge, 



March 2, 1900. 

 GrBNTLEMBNj — 



MR. MORRIS-AIREY, in bis paper in the Philosophical 

 Magazine for March, describes an experiment which 

 shows that when the electric discharge passes through a 

 mixture of hydrogen and chlorine, though the chlorine lines 

 are bright at the anode and faint at the cathode, there is a 

 considerable quantity of chlorine in the half of the discharge- 

 tube next the cathode. From this he concludes that there is 

 no appreciable electrolytic transport of the chlorine through 

 the hydrogen. I do not think this conclusion can legitimately 

 be drawn from his experiments. It is evident, that if the 

 chlorine is transported to the anode, the increase in the partial 

 pressure of the chlorine in this region will cause a diffusion of 

 chlorine towards the cathode, and the steady state will be 

 reached when the backward flow due to diffusion is equal to 

 the forward flow due to electrolytic conduction, so that an 

 electrolytic flow is consistent with the existence of a con- 

 siderable amount of chlorine throughout the tube, and this 

 amount will be relatively more important as the amount of 

 chlorine in the tube increases. Mr. Morris- Airey worked 

 with large quantities of chlorine amounting to 6 or 7 per cent, 

 of the total amount of gas. In my experiments (Proc. Roy. 

 Soc. lviii. p. 244) a very small quantity of chlorine was 

 introduced into a tube filled with hydrogen, and the effects 

 observed were not merely the presence of the chlorine lines 

 at the anode and their absence at the cathode when the 

 current was steady, but it was found that on the reversal of 

 the current, so that the old anode became a cathode, the 

 chlorine lines at first flashed out brightly at the new cathode 

 and were faint at the anode, then there was a short interval 

 during which they were faint at both electrodes, and, finally, 

 they became bright at the new anode and invisible at the 

 cathode. This seems very complete proof of the transport. 



Yours very truly, 



J. J. Thomson. 



