Hexamethylene In Galician Petroleum

Later on, a large quantity of Galician petroleum was fractionated by Miss E. C. Fortey,1 who obtained a considerable amount of liquid boiling quite constantly at 80.8°. A chemical examination of the liquid led to the conclusion that it consisted of pure hexamethylene 2 3; but it was afterwards found 4 that it could be partially, but not completely, frozen in an ordinary freezing mixture, and it was necessary to resort to fractional crystallisation to separate the hexamethylene (b.p. 80.85°) in a pure state. It is evident that there is another hydrocarbon present in small quantity, no doubt a heptane, and that the two substances cannot be separated by fractional distillation.

Mixtures Of Constant Boiling Point

Reference has been made in Chapter IV (Boiling Points Of Mixed Liquids). to the formation of mixtures of constant (minimum or maximum) boiling point. When a liquid contains two components which are capable of forming a mixture of constant boiling point, it is not possible to separate both components; all that can be done is to separate that component which is in excess from the mixture of constant boiling point, and even this is not possible when the boiling points are very near together. Thus, no amount of fractionation with the most perfect apparatus would make it possible to separate either pure normal hexane or pure benzene from a mixture containing, say, 2 per cent of benzene,1 because the boiling points of hexane and of the binary mixture differ, in all probability, by less than 04°. On the other hand, if the original mixture contained, say, 50 per cent of benzene, a small quantity of that component could be separated in a pure state from the mixture of constant boiling point.2

1 Fortey, "Hexamethylene from American and Galician Petroleum," Trans. Chem. Soc, 1898, 73, 932.

2 Baeyer, "On the Hydro-derivatives of Benzene," Berl. Berichte, 1893, 26, 229; " On the Reduction Products of Benzene," Liebigs Annalen, 1893, 278, 88.

3 Markownikoff, "On the Presence of Hexanaphthene in Caucasian Naphtha," Berl. Berichte, 1895, 28, 577; "On Some New Constituents of Caucasian Naphtha," ibid., 1897, 30, 974.

4 Young and Fortey, "The Vapour Pressures, Specific Volumes and Critical Constants of Hexamethylene," Trans. Chem. Soc., 1899, 75, 873.

American petroleum contains a relatively small amount of benzene, and the whole of it comes over with the hexanes; but Russian petroleum is much richer in aromatic hydrocarbons, and, consequently, some of the benzene comes over at its true boiling point, only a portion of it distilling with the hexanes.

When a liquid contains three components which are not closely related to each other it may happen that both a ternary and a binary mixture of constant boiling point are formed on distillation. In that case it is only possible to separate one of the original components in a pure state. These points will be considered more fully in Chapters XIII. and XV.

1 Loc. cit.

2 Jackson and Young, " Specific Gravities and Boiling Points of Mixtures of Benzene and Normal Hexane," Trans. Chem. Soc. 1898, 73 923.