Ternary Mixtures

When a mixture of three liquids gives rise, on distillation, to the formation of a ternary mixture of minimum boiling point, the separation may, theoretically, take place in twelve different ways, and, in addition to these, if the original mixture has the same composition as the ternary mixture, its behaviour on distillation would be precisely that of a pure liquid.

Ethyl Alcohol - Benzene - Water

As an example we may consider mixtures of ethyl alcohol, benzene, and water. For convenience, the components are represented by the initial letters A, B, and W.

The possible cases are as follows :-

The first six cases, and on redistillation of the first fraction the thirteenth, would be those commonly met with. Of the first six, the third is unrealisable in practice, owing to the very small difference between the boiling points of the second fraction (A.W.) and the residue (ethyl alcohol).

Mixtures, however, tending to separate in the other five ways specified were distilled in order to determine the composition of the ternary mixture.

For the calculation it is necessary to know not only the composition of the original mixture, but also that of the binary mixture forming the second fraction.

Data Required

The boiling points of all possible components and the percentage composition of the three binary mixtures are given in Table 69.

Table 69

The middle points are therefore as follows: Table 70

Experimental Results

In Table 71 are given - (a) the actual weight of the components in the mixtures distilled, (b) the weights of distillate below and between the middle points, (c) the calculated percentages of the components in the ternary mixture.

Table 71. (a) Mixtures taken