290 J. Dewar — Separation of Gases from Air. 



Art. XXXIII. — The Separation of the most Volatile Gases 

 from the Air without Liquefaction ; * by Sir James 

 Dewar. 



[Bead before the Royal Society of London, June 16, 1904.] 



From the time when liquid air came to be an ordinary 

 laboratory agent I have continually used it for the purpose of 

 producing high vacua in vessels that had been previously filled 

 with easily condensable gases, like sulphurous acid, carbonic 

 acid, vapor of water or benzol. 



I When the liquefaction of hydrogen was effected, 



n one of the first scientific uses to which it was put was 



[I that described in my paper on the u Application of 



\ Liquid Hydrogen to the Production of High Yacua, 

 u together with their Spectroscopic Examination. "f In 



that communication it was shown by theory and con- 

 firmed by experiment that the condensing power of 

 liquid hydrogen is so great relatively to that of liquid 

 oxygen or nitrogen, that any closed vessel, a part of 

 which is cooled to the boiling point of hydrogen, must 

 suddenly become a highly vacuous space. This was 

 proved by the great difficulty of getting electric dis- 

 charges to pass through specially prepared spectro- 

 scopic tubes when subjected to liquid hydrogen cool- 

 ing, and from the fact that when the current did pass 

 no lines of oxygen or nitrogen were seen, but only* 

 those of hydrogen, helium and neon. In order to 

 separate these latter gases from air it was necessary to 

 liquefy a quantity of air and to distill off the most 

 volatile portion at as low a temperature as possible 

 into a separate receiver placed in liquid hydrogen. 

 In this way many spectroscopic tubes were filled with 

 the uncondensable air gases and the results of their 

 examination is recorded in a paper entitled " On the 

 Spectra of the more Volatile Gases of Atmospheric 

 Air, which are not condensed at the Temperature of 

 Liquid Hydrogen," J by Professor Liveing and myself. 

 Some two years later I improved the method of separation 

 of the volatile air gases. The process is fully described and 

 illustrated in my paper on " Problems of the Atmosphere."§ 

 Its success depends upon the continuous direct liquefaction of 

 air at atmospheric pressure combined with a device which 



* From an advance proof sent by the author. 

 fProc. Eoy. Soc, vol. lxiv, 1898. 

 % Proc. Eoy. Soc, vol. lxvii, 1900. 

 §Proc. Roy. Inst., 1902. 



