What a find. A recording of an all black quartette singing the longest version of the "Bonnie Blue Flag" I've ever heard. The recording is very scratched and poorly done, sounds like it was made about WWI or earlier. It's on Rhapsody so I can't give you the link to the audio but here is the cover of the album.

http://rhap-app-4-0.real.com/rhapsody/musicguide/album/image/pop?URL=http://image.listen.com/img/500x500/9/7/2/0/1750279_500x500.jpg&title=The%20Earliest%20Negro%20Vocal%20Quartets%20(1894-1928)