30 Separation of Three Liquids by Fractional Distillation. 



little water was present : in two fractionations, therefore, 

 phosphorus pentoxide was placed in the distillation-bulb, 

 which was heated by a water-bath. After the first frac- 

 tionation the first portion of the distillate from the first frac- 

 tion was taken as pure, the small residue in the still being 

 each time rejected. There were altogether nine fractionations, 

 and the amount of pure methyl acetate obtained was 88 grams, 

 or about 48 per cent, of that taken. (The loss of this ester 

 by evaporation would be greater than that of either of the 

 other two.) 



Propyl Acetate. — The flasks V to Z contained propyl acetate 

 with some ethyl acetate. It was found that the first two 

 residues were slightly acid, owing to hydrolysis of the esters 

 by the trace of water present. These two residues were 

 therefore collected separately and were shaken with a strong 

 solution of potassium carbonate ; the ester was then washed 

 with water, dried with phosphorus pentoxide, and again dis- 

 tilled. Five fractionations were found sufficient to purify the 

 propyl aceta*te, the residues being each time taken as pure 

 (except the first two, which were treated as described) . The 

 total weight of pure propyl acetate was 126*8 grams, or 72 per 

 cent, of that taken. (The loss by evaporation would be 

 smallest in this case.) 



The esters were then distilled from phosphorus pentoxide, 

 and their specific gravities at 0° determined by Sprengel's 

 method as modified by Perkin. The completeness of the 

 separation was proved by the close agreement of the results 

 with those obtained before mixing, as well as by the identity 

 of the boiling-points with those previously determined. 



The specific gravities are given below : — 



Specific Gravities at 0°. 





Previous 

 D eter min ations . 



After 

 Fractionation. 



Methyl acetate * {a) 



•95929 

 •95934 

 •92434 

 •92438 

 •91017 

 •91015 



•95937 



(1) -92438 



(2) -92437 

 •91008 



(b) 



Ethyl acetate * (a) 



(b) 



Propyl acetate * (a) 



(b) 





* Two different samples of each ester had been purified and their 

 specific gravities determined. The two results are given in each case, 

 in order to show what error of experiment might be expected. The two 

 samples of each ester were afterwards mixed together. 



