I love researching knitting history and copyright, so I have uploaded the following knitting books to various public domain repositories. There will certainly be more to come!

Jack Frost Blouse Book Volume 43
Published 1945 by Gottleib Bros.
I walked through the process of researching the copyright in the aptly titled post Is this knitting pattern public domain?

Hand Knits By Beehive, Book No. 137: Dress and Sweater Fashions
Published in 1949 by Patons & Baldwins, Inc.
- Internet Archive
- Stitch Book coming soon

Coat’s & Clark O.N.T. Book No. 506: Knit and Crochet Style Parade
Published 1954 by Coats & Clark, Inc.
- Internet Archive
- Stitch Book coming soon

Minerva, volume 74: Fashions in Hand Knits
- Internet Archive
- Stitch Book coming soon

Columbia, volume 112: Hand Knit Fashions
- Internet Archive
- Stitch Book coming soon

Columbia, Volume 114: Hand Knit Fashions
- Internet Archive
- Stitch Book coming soon