224 Professor Dewar [April 11, 



It is interesting to note in passing that the relative volatilities of 

 water and oxygen are in the same ratio as those of liquid air and 

 hydrogen, so that the analogy between the ocean of water and that of 

 liquid air has another suggestive parallel. The total uncondensable 

 gas separated in this way amounts to about 3-0^00^^ ^^ ^^® volume of 

 the air, which is about the same proportion as the air dissolved in 

 water. 



That free hydrogen exists in air in small amount is conclusively 

 proved, but the actual proportion found by the process described above 

 is very much smaller than Gautier has estimated by the combustion 

 method. The recent experiments of Lord Rayleigh show that air does 

 not contain more than 30^00^^' ^^ ^^^^ Gautier, who estimated the 

 hydrogen present as 5 oVo^-'^' ^^^ ^^ some way produced more hydrogen 

 than can be extracted from air by a repetition of the same process 

 conducted by an equally competent experimenter. 



The more volatile gases, helium, hydrogen and neon, can be 

 separated from liquid air without the use of liquid hydrogen. For 

 this purpose the arrangement of apparatus shown in Diagram 1 is 

 employed ; the primary object being to liquefy air uncontaminated 

 by compression pumps or the use of chemical reagents, at the pressure 

 of the atmosphere by cooling a vessel shaped like F to some — 210^ C, 

 by the evaporation in vacuo of liquid air covering its exterior. 



This is effected by connecting the tube D to a large air pump 

 and regulating a supply of liquid air from the vessel B by means 

 of the valve a. The external air freed from moisture by prelimin- 

 ary cooling on its way to the apparatus, is brought from the roof 

 of the laboratory through glass pipes to the tube A, with its re- 

 gulating stopcock. It rapidly liquefies and begins to fill up the 

 vessel F, which has a capacity of about 130 cc, while the more 

 volatile gases diffuse into the space above the liquid. In order 

 to prevent their re-solution a very light and rather tight-fitting 

 glass cylinder, shown in E, is used as a float to diminish the liquid 

 surface. As the liquid air accumulates the float K rises in the vessel 

 F, until finally a small amount of uncondensed gas is left at C. The 

 external supply of liquid air from B being shut off and the stopcock A 

 closed, the valve h connected with the tube d coming from the interior 

 vessel F is opened. This discharges all the air which was liquefied 

 directly to the outside of F ; thereby diminishing the amount required 

 to be supplied from the vessel B for the next operation of filling F, 

 and the float E falls to the bottom of the vessel. During this empty- 

 ing of the vessel the separated gas expands and fills the whole of F 

 under the given conditions of temperature and pressure. Care is 

 taken, however, to leave a layer of liquid air below the float to guard 

 against the gaseous contents in F being taken away in part by the air 

 pump. The valve b is now shut again and A opened so that the opera- 

 tion of filling may be repeated, and after five or six sequences of this 

 kind the accumulated gas in F is drawn off into a mercury receiver G. 

 The total volume of gas collected in this way amounted to about 



