Disappearance of Gas in the Electric Discharge. 931 



those with which they were filled, are H 2 0, C0 2 , PH 3 , 

 and (when nitrogen was used) NH 3 . Since ihe ''con- 

 densation point " of all these gases is above liquid-air 

 temperature, they can be detected certainly if their partial 

 pressure is above *0005 mm. in the presence of O'l mm. of 

 non-condensible gas. No other gases with condensation 

 points above that temperature were present. This conclusion 

 is important, for it seems to dispose of the hypothetical 

 compounds of extraordinary constitution that have sometimes 

 been imagined to account for the absorption. 



If the process of absorption was interrupted after the first 

 stage of Par. 13 (which cannot be subdivided), no gas was 

 ever found except hydrogen or nitrogen. The phosphorus 

 vapour disappears during the first st;ige, and no compounds 

 are present in the gas in appreciable amount. This observa- 

 tion does not prove that compounds are not formed, but only 

 that, if they are formed, they are absorbed as fast as they 

 are formed. 



The restoration of the absorbed gas on heating the vessel 

 was partially described in (II.). Much more complete 

 observations have now been taken, the results of which will 

 be summarized. The great difficulties in drawing certain 

 conclusions from these experiments are (1) that at the 

 temperatures necessary for the permanent restoration of the 

 gas, there is an almost inexhaustible evolution of water and 

 C0 2 from the vessel, even if it has been thoroughly baked 

 and exhausted beforehand and no discharge has passed. 

 through it * ; (2) that the temperature necessary for restora- 

 tion mav change the nature of the gas restored. (1) can 

 be avoided to a great extent by always comparing the 

 gas obtained from the vessel in which gas has been 

 absorbed with that from a precisely similar vessel treated 

 similarlv in which no gas has been absorbed. 



At room temperatures the absorption is quite permanent ; 

 vessels have been kept for a year (without the passage of a 

 discharge which might absorb again the gas restored), and 

 at the end of that period have shown no signs of the restora- 

 tion of gas to the most sensitive tests. Heating the vessel 

 to 100-120° C. causes some restoration of gas, which 

 disappears again w T hen the vessel cools. The first permanent 

 evolution of gas occurs at about 180° C, but the evolution is 

 not rapid until 300° is attained ; at 350° the restoration is 

 effected in a few seconds. Permanent restoration is 

 always accompanied by the appearance of phosphorus 

 * R. G. Sherwood, Phys. Eev. xii. p. 448 (1918). 



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