Here's a
link to the copyright info page at Cornell. Assuming this information is correct and up-to-date it looks like your book falls under...
Date of Publication: 1923 through 1963
Conditions: Published with notice and the copyright was renewed
Copyright Term: 95 years after publication date
I'd guess the book won't enter the public domain for another 15 years or so depending on the actual publication date. Author + 70 years doesn't seem to apply in this case.