The Adventures of Huckleberry Finn, essay topic?

I need to do a research on one of the novels we read in school this year. I chose The Adventures of Huckleberry Finn. As for a thesis, I was thinking about making a connection between the anti-slavery/ anti-racist views of Mark Twain and how he gets that point across in the book. My main problem is finding some sources. I can use the actual novel itself,as a primary source, but I also must use secondary sources. If any one knows of any books, biographies on Mark Twain, or websites that could help me, I would appreciate it very much. Thank you.