606 Research Staff of the Gr.E. C, London, on the 



did not seem to bear any simple relation to the carbon 

 monoxide absorbed. 



An attempt was made to cause the gas to disappear without 

 the trap T cooled, but it was found that in these circumstances 

 the discharge caused little or no decrease of the pressure, 

 except perhaps when the pressure was less than 0*002 mm! 

 But if the trap is not cooled, mercury vapour has access to 

 the lamp, the glow potential is depressed, and the spectrum 

 of mercury is well developed : as was said on p. 599, it appears 

 that the glow is carried rather by the mercury than by the 

 carbon monoxide, so that the absence of action on that gas is 

 intelligible. Steps were therefore taken to exclude mercury 

 vapour otherwise than by the cooled trap, but it was not 

 easy to attain that condition. Gold-foil placed in the tube 

 between the lamp and T was quite ineffective in excluding 

 mercury vapour*. Cooling the trap to some temperature 

 above that necessary to condense C0 2 was an obvious course, 

 but the experiments on nitrogen to be described later make 

 it doubtful whether even at 200° K. the vapour-pressure of 

 mercury is inappreciable for the present purpose. Moreover, 

 it was decided to avoid having any part of the apparatus 

 appreciably colder than the rest. Some kind of stop-cock 

 seemed necessary, although it would involve the presence of 

 wax or grease vapour. A pinch-cock of rubber tube with 

 walls 1 cm. thick was actually used between the lamp and T ;. 

 but it was necessary to cement the ends of the tubing with 

 wax, which must have introduced some vapour. This vapour 

 (see p. 598) was sufficient to change somewhat the glow 

 potential of hydrogen, but it made no measurable difference 

 to the glow potential of CO. Moreover, it is known that the 

 discharge through wax vapour always produces CO, so that 

 it is less likely on this account that the vapour had any 

 prejudicial effect on the observations. 



When the absence of mercury vapour was thus secured 

 without giving the gas access to liquid air, it \\ as found that 

 under the glow discharge, carbon monoxide would still 

 disappear (though less rapidly than before) at the higher 

 pressures. But when a pressure between 0*008 and 

 0*009 mm. was reached, the decrease of pressure ceased 

 although the glow was continued. If fresh gas was admitted 



* It seems that gold-foil excludes mercury only when the gas is at 

 considerable pressure. Probably the mercury molecules stick to the 

 gold when they strike it, but they also tend to evaporate again. The 

 liigh pressure reduces the evaporation. It is not asserted that the gold 

 did not reduce the vapour-pressure somewhat, but only that it did not 

 reduce it enough for the present purpose. 



