Ions and Electrons through Gases. 41 



were allowed to stand undisturbed for a few hours in the 

 measuring vessel, which was presumably air-tight. This 

 effect is illustrated in the curves of fig. 5 : curve A refers to 

 C0 2 at 79 mm. pressure, the readings being taken quickly- 

 after the introduction of the gas ; curve B exhibits the 

 values after the gas had been allowed to remain 2J hours in 

 the closed vessel. 



For lower pressures of the gas this effect practically 

 vanishes; with C0 2 at a pressure of 4^ mm. the EI curve 

 obtained after the gas had remained undisturbed in the vessel 

 for two dajs was identical with that obtained immediately 

 after the introduction of the gas. 



It is probable that the above effect arose from a very slow 

 leak of oxygen into the vessel from the outside atmosphere ; 

 actual experiments were performed to test this point, and it 

 was found that traces of air added to C0 2 or H 2 at relatively 

 high pressures resulted in a marked decrease of the number 

 of free electrons, whereas when these gases were at low 

 pressures the number of electrons was not appreciably 

 affected by the admixture. 



It should, however, be mentioned that a similar though 

 much more intense effect was found in experimenting with 

 the free electrons in the vapour of petroleum ether (y. sec. 4D) ; 

 in this instance the diminution in the number of electrons was 

 very rapid, and could not reasonably be ascribed to a small 

 leak of air into the apparatus. AH the indications pointed to 

 the appearance in the vapour of a constituent capable of 

 absorbing electrons at ordinary temperatures. It is con- 

 venient to refer to nuclei, whether molecules or aggregations, 

 which possess this property, as "electron sinks"; the 

 electrons cannot remain in the free state during their motion 

 through a gas which contains these sinks other than in 

 excessively small quantity. All the experimental evidence 

 indicates that the molecules of oxygen do not belong to this 

 class of impurities, and that the larger electron velocities 

 attendant upon the act of ionization are necessary for the 

 formation of negative oxygen ions. 



It is of course possible that the decay of the electrons in 

 C0 2 and H 2 does not arise from an air leak but is due to an 

 ageing effect similar to that in petroleum ether. In this 

 connexion several unsuccessful attempts were made to remove 

 possible nuclei from C0 2 which had been allowed to remain 

 for several hours at a pressure of 81 mm. in the measuring- 

 vessel. In one experiment the gauze electrode was main- 

 tained for several hours at a potential of —160 volts in the 

 hope that the electrons which were being continually produced 



