26 Separation of Three Liquids by Fractional Distillation. 



At 



rise of temperature during distillation, and -— - is conse- 



quently small. 



It will be seen that the ratio for the highest fraction rises 

 rapidly, being 197 in the third fractionation and rising to 340 

 in the sixth, after which it diminishes again owing to removal 

 of propyl acetate in the residues. The value for the lowest 

 fraction increases much more slowly, reaching a maximum of 

 204 in the thirteenth fractionation, and afterwards diminishing 

 owing to removal of methyl acetate. 



The presence of the middle substance, ethyl acetate, is not 

 clearly shown until the fourth fractionation, when the value of 



-r— for the sixth distillate (No. 9) is higher than for those 



above and below it ; but the gradual accumulation of the 

 ethyl acetate in the middle fractions in subsequent fractionations 



is clearly shown by the rise in the values of -r— for fractions 



8 and 11, and after the tenth fractionation in fractions 9 

 and 10. The range of temperature for fractions 9 and 10 was 

 gradually diminished from 0°*2 each in the eleventh fractiona- 

 tion until no rise could be detected ; there was indeed no 

 perceptible rise of temperature during the collection of No. 11 

 in the twenty-second and twenty- third fractionations. It was 

 therefore certain that after the twenty-sixth fractionation the 

 tenth fraction was free from propyl acetate, and that the 

 remaining fractions ISTos. 5 to 10 contained only methyl and 

 ethyl acetates. 



The preliminary series of fractionations was therefore 

 completed, no fraction now containing more than two sub- 

 stances. 



The progress of the separation is well seen by mapping 

 the temperatures against the total weight of distillate 

 collected. The curves I. to XI I. represent the first twelve frac- 

 tionations, the weight of distillate being given in each case 

 as percentages. The dotted lines at the extremities of the 

 later curves represent the methyl and propyl acetates re- 

 moved in the first portions of the first distillates and in the 

 residues. 



The presence of the middle substance is clearly indicated in 

 the fourth curve, but not in the earlier ones. 



