Allotropy dynamic

Dye wastewater, 9 431 Dynamic affinity chromatography, 6 398 Dynamic allotropy, 23 564 Dynamically formed membranes, 15 813t Dynamic coefficient, 15 205 Dynamic compressors, in refrigeration systems, 21 535... 

AUatropes. Some or the elements exist in two or more modifications distinct in physical properties, and usually in some chemical properties. Allotropy in solid elements is attributed to differences in the bonding of the atoms in the solid. Various types of allotropy are known. In ertuntiomorphic allotropy, the transition from one form to another is reversible and takes place at a definite temperature, above or below which only one form is stable, e.g., the alpha and beta forms of sulfur. In dynamic alloimpy. the transition from one form to another is reversible, but with no definite transition temperature. The proportions of the allotropcs depend upon the temperature. In monotropic allotropy, the transition is irreversible. One allotrope is mctastable at all temperatures, e.g.. explosive antimony. 

Solid selenium likewise exists m several allotropic forms. The i crystalline variety is labile, and may possibly occur in two modification both of which arc monoclmic.2 The grey crystalline form appears consist of two varieties, SeA and ScD, in dynamic equilibrium with ea other.1 Solid tellurium manifests allotropy, but to a much less pi nounccd degree. 

Tire first ease of dynamic allotropy, namely, that of liquid sulphur, was investiaated bv Alexander Smith and his collaborators (Joum. Amr. 

A number of facts lead to the view that in the case of phosphorus as in the case of sulphur, a condition of dynamic allotropy exists (Cohen and Olie, Z. pkysikaL Chem., 1910, 71, I Stock and Stamm, Ber., 1913, 46, 3497 Smits and Bokhorst, Z, pkysikaL Chem, 1916, 91, 249). The equilibrium relations would therefore be those of a pseudo-binary system or of a system of perhaps even higher order. For a discussion of the phosphorus systems from this point of view, see Smits, FersL K, Akad. Wetensch, Amsterdam, 1912, 21, 753 1914, 22, 1145 Smits and Bokhorst, Z, physikal. Chem., 1916, 91, 249,... 

A discussion of the phosphorus equilibria from the point of view of the existence of dynamic allotropy in the liquid as well as in the solid phase is given by Smits, Z. physikal. Chem., 19 ii, 76, 439. For an experimental investigation of the relationships, see Smits and de Leeuw, Z. physikal. Chem.. 1911, 77, 367 Smits and Bokhorst, Z. physikal. Chem., 1916, 91, 249. See also Marckwald and Helm-holz. Z. anorgan. Chem., 1922, 124, 81. 

On the basis of his theory of allotropy, according to which there separates from a liquid mixture in dynamic equilibrium, not a pure solid substance but a solid phase consisting also of an equilibrium mixture (a solid solution), Smits has suggested a diagram for the equilibrium relations of sulphur. This diagram, however, has not yet... 

---