Each of those sources allows you to filter results by publication date, so make sure you select and earlier to ensure they’re in the U.S. public domain.
-If you can’t find scans of your book at the above sources, and you’re using a Project Gutenberg transcription as source material, there’s a good chance that PGDP (the sister project of Project Gutenberg that does the actual transcriptions) has a copy of the scans they used accessible in their archives. You should only use the PGDP archives as a last resort; because their scans are not searchable, verifying typos becomes extremely time-consuming.
Please keep the following important notes in mind when searching for page scans: