X-ray emission spectrography, while based on Moseley's work, as a generally useful analytical method had its genesis in the work of Friedman, Birks, and Brooks 30 years ago. The central theme of this conference, quantitative methods in X-ray spectrometric analy sis, and the large number of papers on that subject attest to the growth of the application and usefulness of X-ray emission. It is a privilege to have as an invited speaker Laverne Birks, one of the original group that put X-ray emission into analytical chemistry. Determination of elements above titanium in the periodic table was considered the province of X-ray fluorescence, and most of the early development was aimed at the analy sis of alloys. The papers in this volume on metals analysis accept most operational features as routine and have concentrated on the improved treatment of the observed data in order to convert them to more accurate results. As the treatment of matrix effects, geometry, and stability have been better understood, corrections have become routine. For most elements that are present in amounts greater than a few parts per million, determinations can now be done with accuracies rivaling wet methods. Trace quantities are being determined to lower and lower amounts, largely owing to improvement of equipment and development of concentration techniques. For most trace elements, X-ray spectrography has become the preferred analytical method. The develop ment of improved methods for separating signals from noise should lead to major reduc tions in minimum detection levels.

The featured subject of the 1966 Denver X-Ray Conference was X-Ray Diffraction Topography and Dynamical X-Ray Phenomena. One of the chairmen of the featured ses sions, Professor R. A. Young, made the following remarks at the conclusion of his session. We think they are quite appropriate to the occasion and with his permission we reproduce them here.

The University of Denver and its staff members deserve much credit for organizing and operating this Denver X-ray Conference year after year, for there seems to be no doubt that it and the yolumes that result from it are filling a need. The interests covered by the papers at one of these conferences vary from year to year and as a whole cover a wide spread of topics. This is as it should be. Old problems that have been with us for many years are being attacked again with new and more effective tools, new problems are continually arising, and new methods of great power are being developed. These developments are occurring in each of the fields covered, as may readily be seen by a glance at this twelfth volume and other recent volumes of this series. It seems clear that the policy of having these conferences and these volumes cover a wide field rather than a single one such as, for example, structure determination, or fluorescence analysis, is a policy that meets with general approval and should be continued. I understand there is every intention to do so. C. S. Barrett It is customary to acknowledge in each volume the invited session chairmen of the three-day meeting. They and the sessions at which they presided (21-23 August 1968) were as follows: CRYSTALLOGRAPHY AND DIFFRACTION. C. S. Barrett, University of Chicago, Chicago, Illinois. METHODS AND THEIR APPLICATIONS. B. C. Giessen, Massachusetts Institute of Technology, Cambridge, Massachusetts.