Volume 8 of Developments in Applied Spectroscopy presents a collection of selected papers presented at special symposia and other sessions during the 20th Mid-America Symposium on Spectroscopy, held in Chicago, May 12-15, 1969. In general, these papers are those of the symposium type and not papers per- taining to a specific research topic that one would expect to find in the journals. The 20th Mid-America Symposium was sponsored by the Chicago Section in cooperation with the Niagara Frontier, Rocky Mountain, St. Louis, and Southeastern Sections of the Society of Applied Spectroscopy, and the Chicago Gas Chromatography Group. Although the Mid-America is still occasionally thought of as a regional meeting, its attendees and authors come from all parts of the United States and Canada. Both theoretical and applied principles were presented in sessions on emission, atomic absorption, x-ray, nuclear particle, Raman and infrared, nuclear magnetic resonance, and electron spin resonance spectroscopy; computer applications; air and water pollution, instrumental applications to biomedicine toxicology; spectra and characterization; matrix isolation and gas chromatography-mass spectrometry. In addition, there were symposia on trace element analyses, silicate analyses, Mossbauer spectroscopy, electron spectroscopy for chemical analyses (ESCA), spectroscopy of materials under high pressure, and reference spectra and retrieval systems. The various chairmen of the Symposium Committee, H. Bedell, Dr. Charles Bell, Dr. Eleanor Berman, Dr. Roy Bible, Sam Booras, James E. Burroughs, Adrian Chisholm, Dr. Paul Day, Tod Engelskirchen, G. A. Ettelt, Dr. L. S.