Liquefaction of Gases. 195 



the spheroidal state : it is only when the cylinder has cooled 

 considerably that the ethylene comes into direct contact with 

 it ; a violent boiling of the liquid shows that this has taken 

 place. Henceforward a more abundant stream of ethylene 

 may be poured in until it fills the vessel m above the cylinder a; 

 afterwards the cock h is closed, and the smaller pump which 

 is connected with the vessel m by means of the tube i must be 

 kept working without interruption, by which the temperature 

 of the ethylene is continually lowered ; and when it has fallen 

 below the critical temperature of the gas contained in the 

 flask c (oxygen or air), the cock of this flask is slowly opened. 

 The gas enters the cooled cylinder a under the pressure in- 

 dicated by the manometer b, and becomes liquid speedily 

 enough, in consequence of which the index of the manometer 

 shows a constant fall ; when it becomes stationary, the cylinder 

 a is wholly filled with the liquefied gas. When this has been 

 done, the bottle c is closed, and by slowly opening the cock d 

 the liquefied gas is poured into the glass vessel placed under- 

 neath, which is secured from external heat by its triple walls. 

 Whilst the liquid oxygen is being poured from the cylinder a, 

 the pressure descends to 20 atin., and remains at this point 

 as long as any liquid oxygen remains in the cylinder : it is 

 only when there is no more that the pressure becomes less 

 than 20 atm. As the liquefied gas comes under the ordinary 

 atmospheric pressure, a considerable part of it resumes the 

 gaseous state, and only half or a third of the liquid remains 

 in the glass vessel after having cooled down to its boiling- 

 temperature. In order to prevent the collected liquid being- 

 blown out by the powerful jet, the thin copper tube through 

 which the stream flows is closed beneath, and provided with 

 four lateral openings. 



I mentioned above that the temperature of ethylene in the 

 vessel m must be lowered by pumping to less than the critical 

 temperature of the gas we wish to liquefy ; but it is not 

 necessary to measure the temperature of the ethylene. It is 

 sufficient to measure its pressure. According to my compu- 

 tations (3), the following relation exists between the pressure 

 and the temperature of the liquefied ethylene : — 



Pressure. Temperature, 



millim. Hg\ ° C. 



146 -122 



107 -126 



72 -129 7 



56 -132 



31 -139 



12 -148 



9-8 -150-4 

 02 



