A great source to use if you are looking for books published before 1924 is HathiTrust. Over a million books (also some magazines and Parliamentary Papers) free of copyright are available full-text and can be downloaded as pdfs. Plus you can search through the entire text to find the information you seek.
The Advanced Catalog Search provides options to search for specific titles, authors and keywords and to limit your search by fulltext availability (full view only) and publication date.
Hathi Trust's collection includes books published in Britain, the United States and other countries.
Comprehensive indexing of the most popular general-interest periodicals published in the United States. Reflects the history of 20th century America.
The database covers the years 1890 through 1982. For access to current general periodicals indexing, see Academic Search Premier
Access to records drawn from the Research Libraries Information Network (RLIN) and the OCLC bibliographic database that describe archival and manuscript collections in research, college, university and public and special libraries, archives, museums and historical societies in North America and worldwide.
Libraries, Archives, Museums and other institutions are digitizing enormous amounts of primary source materials from their collections and making them freely available on the internet. It is always useful to conduct a web search, using Google or other search tools to locate primary sources.