Your nearest federal depository library may have a set of the U.S. Copyright Catalog, showing both new copyrights and renewals. The renewal on that book was due in 1951. (Renewals are on-line from 1978 onward.)
Mind burp. For some reason I was thinking 17 years, which was the term for a patent, I believe.
Getting old. 
again, thank you all very much!
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