A video showing a Chicago police officer attempting to escort a man off a Chicago Transit Authority bus is the focus of a police department internal affairs review.

Chemistry is the study of matter and energy and the interactions between them. Get facts for the elements in the periodic table. Find chemistry demonstrations and experiments and science fair projects. Get chemistry homework help with worked example problems and a glossary. Grow your own crystals. Browse molecular structures. Find articles on chemistry. Find out how things work and get answers to

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The Library of Congress. The Library of Congress is the nation's oldest federal cultural institution, and it serves as the research arm of Congress. It is also the largest library in the world, with more than 120 million items. The collections include books, sound recordings, motion pictures, photographs, maps, and manuscripts.