The properties of metals are determined by their structures which are produced or altered by transformation reactions. If the formation and preservation of these structures shall be control ed, the driving forces of the transformations must be known quantitatively. An estimate of these forces can be made by means of the thermodynamics of alloys. In detail it is shown that by suitable experiments the interatomic forces in alloys can be estimated; with these data and with the aid of simple statistical model calculations the ordered orland decomposed states in solid solution can be predicted. These states influence substantially the stabilities of the different structures in solid solutions; hence also predictions on trans- formations from one structure to another one can be made. Such theoretical results are compared with corresponding experimental data. Finally an ap- plication of the results to a technological problem is presented. Thermodynamik der Eisenmischkristalle 17 WEIGHT PERCENT TITANIUM 10 20 30 40 50 60 70 80 90, II I I I I I II 1117, . L 0 1700' 1665 bfi 0 '16 i..o-'7 160 - . 15'30" 1562 (r-Fe )., a-Fe) f"! 1- /, n 140 1358', (,9-Ti) . I e 8 "'J - ..: .