My understanding of how the (c) law works is as follows. Please keep in mind, however that this post is not legal advice and does not establish a lawyer-client relationship. It is strictly private opinion.

If the copyright was not renewed, a work published in 1931 in the U.S. is in the U.S. public domain (though it may still be under copyright elsewhere). If the copyright was renewed, the work remains under copyright until the last day of 2026, unless the recent copyright extension is finally declared unconstitutional (the forces of truth, justice, and short-term copyright lost in the discrict court; an appeal is being prepared) in which case the copyright will presumably last until December 31, 2006.

The renewal of a 1931 copyright would have been in 1958 or 1959, or possibly 1960. To find out if the copyright was renewed you'll need to check the Catalog of Copyright Entries for those years. Some of the CCE is on line. If you go here you'll find some of it, but I don't think they're up to 1958 yet. Another site is here. Further useful information is here.

T.