The occurrence of mixtures of maximum boiling point (or minimum vapour pressure) is comparatively rare ; in most of the known cases one of the substances is an acid and the other a base or a compound of basic character - formic, acetic and propionic acid with pyridine (Zawidski),2 hydrochloric acid with methyl ether (Friedel) 3 ; or the liquids are water and an acid - formic, hydrochloric, hydrobromic, hydriodic, hydrofluoric, nitric or perchloric acid (Roscoe)4; but Ryland finds that such mixtures are formed by chloroform and acetone =4.8°) and by chloroform and methyl acetate = about 4.3°) ; the first observation has been confirmed by Zawidski and by Kuenen and Robson,5 and the second by Miss Fortey (unpublished).
The number of known mixtures of maximum boiling point has been greatly increased by Lecat.
Benzene and water are practically non-miscible, whilst benzene and ethyl alcohol and ethyl alcohol and water form mixtures of minimum boiling point. It was observed by Young 6 in 1902 that when any mixture of the three liquids is distilled, a ternary azeotropic mixture comes over at a temperature lower than the boiling point of any of the binary mixtures or of any of the pure substances. It was found that by the distillation of strong spirit with benzene the water came over in the first fraction and anhydrous alcohol was left as the residue.
1 Speyers, "Some Boiling Point Curves," Amer. Journ. Set., 1900, IV., 9, 341.
2 Loc. cit.
3 Friedel, " On a Combination of Methyl Oxide and Hydrochloric Acid," Bull. Soc. Chim., 1875, 24, 160.
4 Roscoe, " On the Composition of Aqueous Acids of Constant Boiling point," Trans. Chem. Soc, 1861, 13, 146; 1862, 15, 270; "On Perchloric Acid and its Hydrates," Proc. Roy. Soc, 1862, 11, 493.
5 Kuenen and Robson, "Observations on Mixtures with Maximum or Minimum Vapour Pressure," Phil. Mag., 1902, VI., 4, 116.
6 " The Preparation of Absolute Alcohol from Strong Spirit," Trans. Chem. Soc, 1902, 81, 707.
Ternary azeotropic mixtures of several of the lower alcohols with benzene and water and with n-hexane and water were obtained and examined by Young and Fortey.1 The formation of other ternary azeotropic mixtures has since been observed by several chemists, Lecat having added a considerable number to the list.
In the following tables data which are not regarded as well established are printed in italics. When any mixture has been examined by more than one observer, the initial letters of the names of those observers whose data are regarded as less well established than the others are printed in italics.
1 Trans. Chem. Soc, 1902, 81, 739.