Separation of Three Liquids by Fractional Distillation. 19 



may therefore be saved if, instead of adding all the first 

 portions of the lowest fractions together (and the same remark 

 applies to the residues from the last fractions), we collect 

 them in six or more different quantities. The final fractiona- 

 tions will then be in a forward state when the preliminary 

 one is completed. 



We shall in this manner obtain two quantities of B, one by 

 the final fractionation of the first portions of the distillates 

 from the lowest fractions of the preliminary fractionations, 

 the other by that of the residues from the preliminary frac- 

 tionations, and we can test the purity of the substance by 

 comparing the boiling-points and the specific gravities of the 

 two samples so obtained. 



In order to test the value of this method, a mixture of 

 200 cub. cent, of methyl acetate (B.P. 57*1), 250 cub. cent, 

 of ethyl acetate (B.P. 7 7' 15), and 200 cub. cent, of propyl 

 acetate* (B.P. 101*55) was distilled from a flask provided 

 with a still-head one metre in length. The distillate was 

 collected in four approximately equal fractions, numbered 5, 

 8, 11, and 14 under F in the table (I.) below. The observed 

 temperatures (reduced to 760 millim.), the range of tem- 

 perature for each fraction (Atf), the weight of each fraction 

 (Aw), and the ratio of the weight to the temperature-range 



I -r- J are also given in the tables. The second fractionation 



(II.) was carried out in the following manner : — the first frac- 

 tion from I. (No. 5, B. P. 63°-8 to 71°'3) was distilled and 

 the distillate collected in a separate receiver (No. 4) until the 

 temperature rose to 63°' 8 f? when receiver No. 5 was substi- 

 tuted for it and the distillation continued until the tempera- 

 ture rose to 71 o, 0. The gas was then turned out, and the 

 second fraction from I. (No. 8, B. P. 71°'3 to 77°-8) added to 

 the residue in the flask. Heat was again applied and the 



* The esters had previously been purified with great care, and were 

 distilled separately from phosphorus pentoxide immediately before being 

 mixed. Special precautions were also taken to avoid absorption of 

 moisture during the fractionations. The methods of preparation and 

 purification and proofs of the purity of the esters are fully described in 

 the Trans. Chem. Soc. lxiii. p. 1194. 



t The actual temperature was 63°-5, the barometric pressure being 



751*1 millim. ; the value of -r, at the boiling-point is 27 millim. per 



degree for methyl acetate, 25 millim. for ethyl acetate, and 23 millim. 

 for propyl acetate. All the temperatures are corrected to 760 millim, 

 by means of these constants. 



C2 



