THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERTES.] 



f& 



NOVEMBER 1002. 



■ 

 LIX. On the Distillation of Binary Mixtures. 

 Bii Lord Ratlbigh, O.M., F.R.S.* 



AT various times during the past twenty years I havQr 

 turned my attention to the theory of distillation, and 

 have made experiments upon a question, as to which informa- 

 tion seemed to be almost entirely lacking, viz., the relation 

 between the strengths of liquid and vapour which are in 

 equilibrium with one another when a binary mixture is sub- 

 jected to distillation. In order to be intelligible I must set 

 forth a little in detail some matters which are now fairly well 

 known and understood, although they were not so at the time 

 when my notes were written. 



Distillation of a Pure Liquid. 

 The temperature of the saturated vapour just over the 

 liquid depends upon the pressure. If the end of the con- 

 denser-tube, e. g., of the Liebig type, be open, the pressure is 

 of necessity nearly atmospheric. Suppose that in this tube a 

 piston, moving freely, separates pure vapour from pure air. 

 Then the whole wall of the condenser on the vapour side is 

 almost at boiling-point. If we imagine the piston removed, 

 the air and vapour may mix, and it is now the total pressure 

 which is atmospheric. Wherever the temperature is below 

 boiling there must be admixture of air sufficient to bring up 

 the pressure. 



Two or more Liquids which press independently. 

 This is the case of liquids like water and bisulphide of 

 carbon whose vapour-pressures are simply added. So long 



* Communicated by the Author. 

 Phil. Mag. S. 6. Vol. 4. No. 23. Nov. 1902. 2 M 



