At the official dinner of a· meeting in May 1939, I was seated next to Max Hansen. When I congratulated him on the well deserved success of his "Aufbau der Zweistoff-Legierungen", he smiled: "yes, it was a struggle with the hydra, and so it has taken me seven years", meaning that whenever he had thought to have finished the phase diagram of a particular system, new evidence would turn up like the new heads of the Greek monster. There is no need to point out the importance of assessed phase diagrams to metallurgists or even anyone concerned with the technology and applica tion of metals and alloys. The information contained therein is fundamental to considerations concerning the chemical, physical and mechanical properties of alloys. Hansen's German monograph was followed by a revised English edition in 1958 with K. Anderko and the supplements by R.P. Elliott (1965) and F.A. Shunk (1969). All those who have made use of these volumes will admit that much diligent labour has gone into this work, necessary to cope with the ever increasing number of publications and the consequent improvements.

With 505 evaluations under his belt, Okamoto (information management, Ashahi U., Japan) has personally evaluated and published phase diagrams and related data for more systems than any other living professional. Here he compiles phase diagrams of 2,335 systems, attempting to cover all binary systems

Evaluations of pure beryllium, plus 72 binary beryllium alloys. Bibliography through 1986. Required reference sources for engineers and scientists alike, each volume in the Phase Diagram Monograph Series presents the most complete, authoritative, and reliable phase equilibria information ever published on the alloys. Each volume comprises critical evaluations of individual alloy systems performed by experts under the ASM/NIST Data Program for Alloy Phase Diagrams. Evaluation involves searching the literature for all existing thermodynamic and related information on the system, assessing value and distilling the best data into a comprehensive report. Phase diagrams are plotted in atomic percent, but include a secondary weight percent scale. Important points are labeled with composition and temperature. Supplementary graphs provide enlargements of complex areas, solubilities and transformations on the phase diagrams, as well as ancillary drawings that show lattice parameters and thermodynamic data. The text includes discussion of stable and metastable phases, order-disorder and magnetic transitions, thermodynamic calculations and modeling, discrepancies in data values and controversial areas and uncertainties in the diagram. In addition, tables list invariant reactions, crystal structures, lattice parameters, experimental values and thermodynamic parameters.