An excellent tool for looking for source material as well as ensuring you
have made proper citations is the Library of Congress Experimental Search
System.
It is available 7 days a week 24 hours a day!
http://lcweb2.loc.gov/resdev/ess/
IMPORTANT NOTICE: Files available through this search interface have not
been updated since September 1997. The Experimental Search System (ESS),
currently located in the LC WEB research and development area, searches
copies of LC catalog records, supports relevancy-ranked searching of
catalog records, and provides some sorting capabilities for search results.
Special search features include analyzing results by subject heading and
"browsing" the shelf for items with similar LC call numbers. Some of these
records have direct links to digitized materials, including selected
fulltext, image, video and audio files, at the Library of Congress and
elsewhere. This is a test system and results may not be all inclusive.