Die Theorie der Allotropie

Abstract

AT one time the term allot ropy or allotropism was confined mainly to the chemical elements, such as oxygen, carbon, phosphorus, etc. In one of these cases—that of oxygen and ozone—the explanation of the allotropie forms was found in the existence of different molecular species, whereas in the case of diamond and graphite, for example, this could not be definitely proved. Another more striking case of the latter sort is presented by the rhombic and monoclinic forms of sulphur. As our knowledge increased concerning the different crystalline fbrms, in which both elements and compounds could occur, the idea of crystalline polymorphism was developed. In these cases it was supposed that one and the same molecular species only was involved, that the polymorphism was due to different crystalline arrangements of the same units, and that the vapours or solutions derived from the different polymorphic forms would, for the same values of pressure, temperature, and concentration, be chemically and physically identical. This explanation certainly gave a satisfactory account of the main facts involved—that is to say, the various substances appeared to behave as one-component systems. The curious facts relating to the behaviour of water suggested, however, to chemists that this substance was in reality complex, water consisting at any given temperature and pressure of a mixture of molecular species differing in the degree of association of the simplest (Avogadrian) molecular type.

Die Theorie der Allotropie.

By Prof. A. Smits. (Pp. xvi + 500. (Leipzig: Johann Ambrosius Barth, 1921.) 100 marks.