Is this the song you're looking for? Click here
Copyright comes up so often, that while the questions aren't dumb, the ones with answers won't do it all again. Try putting copyright in the box under the word filter on the Forum page, set the age for anything more than 30 days & you'll find something.
A short answer is that copyright laws vary from country to country and are constantly be changed & updated. Here's a timeline of significanat changes. The most important was the change in 1976, that set copyright to life of author +50 years instead of the max of 56 years from creation. The 50 years has since been changed to 75. That law change affected materials from the 1920's forward. Pre 1920's material was not affected by the law change.