Just as you will use WorldCat for identifying and locating books as secondary sources, you will use WorldCat to identify and locate books as primary sources.
Follow these steps:
So, looking for primary source books on the Baltimore Riots:
In addition to the Historical Newspapers database, be sure to check for additional sources by clicking on the
Historical Newspapers and Periodicals Historical (pre 1990)
Note the dates covered.
American Periodical Series ( 1740 - 1900)
Nation Digital Archive (1865 - present)