Free Chess Books?

A quick return trip to the Lifeline Book Fair didn't turn up many more chess books than yesterday. However, in the "Collectibles" section, I spied a copy of "Lasker's Chess Primer" for $5. I'm not sure how collectible a $5 book really is, but I bought it nonetheless.
I have quite a few chess books written by authors long since passed away, and I have often wondered what the copyright status is on these works. I have always assumed that copyright exists for 50 years from the death of the author and after that the work is in the public domain. Recently copyright terms have been extended to 70 years from death of author, but I assume that this hasn't been applied retrospectively.
So I wonder whether "Lasker's Chess Primer" is now in the public domain, as Lasker died in 1941, and is anyone entitled to republish or distribute the original text? If so, it may be a project worth pursuing. Converting chess works in the public domain to electronic format and making them available free of charge on the net. Any advice from those with greater legal knowledge than I would be appreciated.