This edition contains complete rewrites on every article contained in the previous edition. It includes updates of all information - revisions that reflect the progress achieved since the early 1980s, and an expanded range of topics expertly covered by leading authorities in science and industry. The fourth edition is in many ways an entirely new encyclopedia in a format similar to the earlier editions. This encyclopedia's key features include: an expanded analytical chemistry section, now with individual articles defining techniques and including nearly 800 pages on instrumentation and methods inclusion of CAS Registry Numbers as well as other convention enhanced electronic searching features over 5000 photos, charts and graphs, figures and tables - many new to this edition - that elaborate on and clarify textual material.