The Library of Congress has a great tool for helping you evaluate potential primary sources:
Primary source research requires a slightly different approach to searching. Here are a few tips/strategies:
Start by doing some background reading or "pre-research": The more you know about key events, people, laws, and especially common terminology used during the time period you are researching the more successful your research will be. See the "Getting to Know Your Topic" page in this guide for help.
Limit to specific time periods: When searching for primary sources online always remember to use date ranges (usually on the advanced search page) to focus your search.
Use primary source keywords to find primary sources: Use search terms that reflect the types of primary sources you’re looking for, such as: diaries, pamphlets, correspondence, speeches, manuscripts, personal narratives, interviews, firsthand, eyewitness, sources, etc.
For example: slave AND diary | suffrage AND pamphlets | united states and race relations AND sources
The Accessible Archives collection within History Commons includes text primary sources from 18th and 19th century America, mainly newspapers, including the Pennsylvania Gazette, the Virginia Gazette, Godey's Lady's Book, Frederick Douglass Paper, a collection of South Carolina Newspapers, and a collection of African American newspapers
The full text of hundreds of U.S. newspapers from more than 35 states published by African Americans, dating from 1827 to 1998.
Coverage: 1827-1898
The full text of 52 books and pamphlets published by 19th-century black women writers.