How do I know if the text of a book can be used in an application?

Question

Copyright

I am writing an application that uses the text of an old book by Mark Twain both in original and in translation. How do I know if I'm infringing copyright, and how not to infringe if I suddenly do?)

Answer 1

www.marktwainproject.org/copyright.shtml
(ahtung: translations and adaptations may have different licenses!)
If you're wondering where I got this link from: I just googled "mark twain public domain" and followed the first link.