Separation of Three Liquids by Fractional Distillation, 1 1 



been collected are represented as abscissa^ and the relative 

 quantities of the two liquids A and B in the distillate at any 

 moment as ordinates. 



It will be seen that the composition of the distillate alters 

 slowly at first, then more and more rapidly, also that while 

 the first portion of the distillate contains a considerable 

 amount of the less volatile substance B, the last portion is 

 very nearly free from the lower-boiling component A. These 

 points are fully confirmed by experiment. 



By fractionating a few times in the ordinary way, collect- 

 ing the distillates in six or eight fractions, we shall have a 

 very large excess of A in the first fraction, and of B in the 

 last. 



Suppose now that w r e have two of these fractions, one con- 

 taining A and B in the ratio of 9 : 1, and the other in the 



Fiar. 2. 



Fio-. 3 



ratio of 1 : 9, and that we distil these fractions separately and 

 completely ; the results will then be represented by figs. 2 

 and 3. 



In making use of this formula it is assumed that no con- 

 densation (and therefore no fractionation) goes on in the 

 still-head, but that the vapour reaches the condenser in the 

 same state as when first evolved from the liquid in the still. 

 It is obvious that by using a long still-head or a dephlegmator 

 a more rapid separation would be effected. 



In any case it is evident that after a sufficient number of 

 fractionations, the first portion of the distillate from the first 



