514 



Dr. R. 8. Willows on the 



Fig. 7. 





A tube like the one shown in fig. 7 was used ; it was found 

 that when A was cathode, the rate of absorption 

 was about fifteen times greater than when it was 

 anode. If this be really due to more ions being- 

 shot into the glass in the first case, it should be 

 possible to increase the rate of running down 

 when B is cathode, by deflecting the negative 

 ions on to the glass by means of a magnetic field. 

 Although a strong electromagnet was used for 

 the purpose, no increase was found. 



The difference in the rates of absorption accord- 

 ing to the direction of the current may be ex- 

 plained by the difficulty of freeing a disk electrode 

 from occluded gas, as it cannot be made thoroughly 

 hot. This gas is given off in greater quantity 

 when B is cathode, on account of the greater 

 heating, and so masks the effect it is desired to 

 measure. This might also explain some of the 

 results of Section 7. 



10. It has been shown in Sees. 6, 7 that replacing a soda- 

 glass surface by one of silver or aluminium entails no differ- 

 ence in the rate of absorption : this would seem to show that 

 the gas penetrates the last two substances. That this pene- 

 tration was not due to cathode rays was shown as follows : — 

 Between the anode B (see fig. 6) and the glass was placed 

 some dry common salt, and a discharge was passed for some 

 days using A as cathode. It is known from the experiments 

 of Wiedemann and Schmidt and others that cathode rays 

 colour the salt blue, but no blue coloration was found after 

 several days, although in the meantime a large amount of gas 

 was absorbed. 



That some of the gas penetrates the walls is proved by an 

 observation of Gouy's *. It was noticed after bombarding a 

 piece of glass for some time with cathode rays, that when it 

 was strongly heated small bubbles of gas made their appear- 

 ance just in the surface, and when the glass was nearly 

 molten these escaped. The amount that can be driven off in 

 this manner does not, however, nearly account for the large 

 amount that can be absorbed ; several tubes were heated till 

 they were on the point of collapsing, and only small quantities 

 of gas were evolved. 



11. In order further to insure that the electrodes did not 

 produce the fall in pressure by combining with the gas, a 

 tube was used having platinum wire for electrodes. It was 



* Compt. Rend. vol. exxii. 1896, p. 775. 



