The Commonness of the Phenomenon of Azeotropy It is a well-known fact that azeotmpes occur in organic and inorganic systems, although most of the known azeotropes are formed by organic substances. The explanation of this is simple: the very large number of organic compounds boil without decomposition in the easily accessible ranges of temperature and pressure. At the end of last century W. Ostwald considered azeotmpy as an extremely rare phenomenon. This opinion has survived in same circles until today, despite convincing evidence that the phenomenon of azeotropy is defmitely a common one. The first book an azeotropy, published by Leeat1 appeared in 1918. This monograph showed that the appearance of minimum or maximum vapor pressures of binary and ternary mixtures should not be regarded as a rate phenomenon. On the contrary, the number of azeotropes known in 1918 was amazingly large. In 1949 Lecat2 published the azeotmpic data for 13,290 binary systems. The number of azeatmpes reached 6287 or 47% of the systems examined. In 1973 Horsley3 published his Azeotmpic Data-111. In this book 15,823 binary, 725 ternary, 21 quaternary and 1 quinary systems are reported. The number of azeotropic systems is as follows: binary 7945 (52%). ternary 371 (51%). quaternary 9 (43%) and quinary 1. It is interesting to see that 100 binary azeotmpes occur in the systems composed either of two inorganic compounds (elements) or an inorganic-organic compound mixture: 765 binary systems eontain water as one component (amongst them 637 (86%) are azeotropic). The ternary positive-negative (saddle) azeotropes occur in 34 systems; 267 (72%) ternary azeotropic systems contain water as one component. There is also one ternary negative azeotmpe. As far as quaternary systems are concerned, 8 systems form positive azeotmpes and one-a positive-negative. These figures indicate clearly that the opinion about azeatropy as a rarely encountered phenomenon is not justified and therefore should be abandoned. The term ousgeschnete Liisungen, referred to azeotrapy and suggested by Ostwald became meaningless and should not be used.
'Leeat, M., "A'orCotropisrne, donnes Experimentoles," Lamartin, Bruxelles, 1918. ZLecat, M., "TablesAzi.otropiques," Vol. I, Bruxelles, 1949. Horsley, L. H., Azeotropic Data-III, Advances in Chemistry Series No. 116, ACS monograph, Washington, D.C., 1973. 'Present address: 4/44 Bryants Road, Dandenong, Victoria 3175, Australia.
The Ahmadu Bello University Zaria, Nigeria
366 / Journal of Chemical Education
