Distillation of Liquid Air. 521 



This curve has also been drawn on the large scale, and the 

 following points read therefrom may be of interest : — 



Temperature 



Percentage of 



Temperature 



Percentage of 



(absolute). 



Oxygen. 



(absolute). 



Oxygen. 



o 





o 





77-54 



o-oo 



84-5 



69-31 



78-0 



810 



85-0 



72-27 



78-5 



15-25 



85-5 



7510 



790 



21-60 



86-0 



77 80 



795 



27-67 



865 



8044 



80-0 



33-35 



87-0 



82-95 



80-5 



38-53 



87-5 



85-31 



810 



43-38 



88-0 



87-60 



81-5 



4792 



88 5 



8982 



820 



52-17 



890 



91-98 



82-5 



55-94 



89-5 



94-09 



830 



59v>5 



90-0 



9615 



835 



62-93 



905 



98-16 



840 



66-20 



90-96 



100-00 



The two curves A and B represent the complete fractional 

 distillation of any mixture of oxygen and nitrogen under 

 760 mm. pressure. For they show the boiling-point of every 

 mixture of oxygen and nitrogen at 760 mm., and also the 

 temperature at which any mixture of oxygen and nitrogen 

 will liquefy and the composition of the liquid formed. It is 

 evident that the lines of equal temperature cut the two curves 

 at points of corresponding equilibria; that is to say, the com- 

 positions of liquid and vapour phases in equilibrium at each 

 temperature. In connexion with these corresponding com- 

 positions of liquid and vapour, F. D. Brown * suggested that 

 in a distillation of a mixture of two liquids under constant 

 pressure, the following formula might express the relation 

 between them : — 



where r' is the ratio of components in the vapour phase, and r 



P 



the corresponding ratio in the liquid phase, and ^ the ratio 



of the vapour-pressures of the two components. This formula, 

 however, assumes the validity of Kaoult's law for every 

 possible mixture. In an actual experiment, however, Brown 

 found that it did not hold good, but that in the equation 

 / = rxQ, C was remarkably constant. 



* Chemical Society's Transactions, xxxix. p. 304. 



Phil Mag. S. 5. Vol. '49. No. 301. June 1900. 



2 



