Aw

At

rise of temperature during distillation, and is consequently 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

Aw for the sixth distillate (No. 9) is higher than for those

Aw

At

At 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 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 fractionation 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 Nos. 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 XII. represent the first twelve fractionations, 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 removed 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.

Final Fractionations.

The fractions into which the esters had been separated at the end of the 26th preliminary fractionation are given below :

The total weight was 490-8, so that 86 grams had been lost by evaporation and through adherence to the flasks and to the funnel through which the liquid was poured into the still.

The final separation of the esters was carried out in the following manner :—

Ethyl Acetate (1).-The fractions 5 to 10 consisted of ethyl acetate with some methyl acetate. The final fractionations in this case were a continuation of the preliminary ones and were carried out in the same manner. No. 10 was almost if not quite pure ethyl acetate, and was only distilled once more; the first portion was collected in No. 9, and the residue was taken as pure. In the remaining six fractionations the residue, after the distillation of No. 9, was each time taken as pure, and the total amount of ethyl acetate thus obtained was 56.1 grams.

Ethyl Acetate (2). The flasks Q to U contained ethyl acetate with some propyl acetate. In the six fractionations, which were carried out in the usual way, the first portion of the distillate from Q was each time taken as pure, the small residue in the still being rejected. The weight of pure ethyl acetate obtained from this series was 62.7, and the total weight was therefore 118-8 grams, or about 53 per cent. of that originally taken.

Methyl Acetate.-The flasks A to E contained methyl acetate with some ethyl acetate. Although special care had been taken to prevent absorption of moisture, it was found that a

:

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 fractionation the first portion of the distillate from the first fraction 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 distilled. Five fractionations were found sufficient to purify the propyl acetate, 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 :

*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.