APPENDIX 291 



trated, answers nearly as well. The gaseous mercury 

 condenses by the intense cold of the liquid air on the 

 outside of the inner receiver and up to the height of the 

 liquid gas. This absolute vacuum (as regards gases) 

 nearly prevents the passage of Ether to the liquid air, 

 and thus the air retains its liquid condition or only 



Fig. 4. 



evaporates, i.e. becomes gaseous very slowly indeed ; 

 probably the small amount of Ether obtained by the 

 liquid is received via the glass, and not via the vacuum. 

 Liquid air, subject only to the pressure of the atmo- 

 sphere, can be kept, in such a receiver, for days. 



Now if we pour this liquid air into an open vessel, 

 say a saucer, what takes place? Each molecule, of its 

 own inherent energy, becomes gaseous, seizes the Ether 

 from the surrounding atmosphere while it is increasing 

 in volume, and cools it, and especially the saucer, 

 which becomes so intensely cold that the water vapour 

 in the atmosphere condenses on the outside in the 

 form of ice. 



