G8S Research Staff of the Gr. E. 0., London, on the 



by its action upon sodium, which results in the evolution of 

 hydrogen. It is not definitely known whether the water 

 is produced by the oxidation o£ the hydrogen * or evolved as 

 water from the glass walls (see § 17). Second, the quantity 

 that can be made to disappear is less than that which 

 will disappear if there is no discharge. If the walls are 

 saturated without the discharge, and the discharge is then 

 started, hydrogen is evolved and not absorbed. However, 

 in order that this effect may be observed, the hydrogen must 

 be perfectly pure : if traces of impurity are present, the 

 discharge may cause the disappearance of more hydrogeu. 

 Third, until the limit of absorption is reached, disappearance 

 is more rapid with the discharge than without it. 



As before, part of the hydrogen can be liberated again by 

 rise of temperature of the walls, whether they have been 

 cooled in liquid air or have been at room temperature. In 



some cases all the hvdrogen absorbed during the discharge 



. i ? 

 has been liberated in this manner. Any loss may be ex- 

 plained by the oxidation of the gas to water, and this expla- 

 nation receives some support from experiments in which the 

 original pressure was restored by allowing the gas access to 

 sodium or heated magnesium. But since it was not possible 

 in all cases so to restore the original pressure, possibilities 

 indicated by later experiments must be taken into account ; 

 the hydrogen may adhere to the walls in a way which cannot 

 be reversed by heating to the softening point of the glass. 



1-4. The disappearance of carbon monoxide. — In the first 

 paper (§ 10) it was said that, in the absence of a cooled tube 

 to remove the carbon dioxide formed, the absorption of this 

 gas reached a limit when a pressure of 0*009 mm. was 

 reached, although the discharge stili continued. It has been 

 found since that this observation was vitiated by the presence 

 of a trace of mercury vapour [cf. § 7). If mercury vapour 

 is completely removed f, the disappearance continues until 

 the discharge stops, owing to the rise of the glow potential — 

 at any rate, if a potential greater than 300 volts is not 

 employed. If fresh CO is admitted, it disappears again under 

 the discharge at a rate apparently unchanged ; a limit to the 



* If there are reducible substances present, e. g. copper oxide on the 

 "wires, they are certainly reduced by the discharge in hydrogen. But 

 the lamps used here were thought to be frefi from such substances. 



t The belief, apparently current, that mercury can be completely 

 removed by a trap cooled in solid C0 2 is erroneous (cf. M. Knudsen, 

 Ann. d Phys. 1. p. 472 (1916)). The glow potential can certainly detect 

 the yapour of mercury at that temperature. On the other hand, no test 

 has been found which will show the vapour at the temperature of liquid 

 air. 



