Steampunk public domain source material
Knowing that Arthur Conan Doyle and HG Wells works are public domain, I was wondering what other classic works out there are public domain?
I've been considering writing a story about a young teenager named Watson who accidentally inhales some mind-alteting chemicals while cleaning out the attic of a historical society. The chemicals mix in his mind to create a facsimile of Sherlock Holmes as a form of enhanced intelligence as he tries to stop other Victorian/gothic/steampunk horrors get unleashed!
Any ideas would be appreciated.