I don’t know how many are aware of Google Books, but a number of old classic books on the Papacy have been made available. They’ve been scanning them in for a few years now. I didn’t realize this until I went searching for old copies of books. These are fully available as PDF downloads:
The Pope and the Council (pdf) by "Janus"
Anti-Janus: A Reply to “The Pope and the Council” (pdf)
Roman Catholic Claims by Charles Gore (not available as PDF but I recently got this old book)
Bishop Gore and the Catholic Claims (pdf) a reply by Dom John Chapman
Plain Reasons Against Joining the Church of Rome (pdf) by Littledale
Catholic Controversy, a reply to Littledale (pdf)
The Infallibility of the Church, A Refutation (pdf) by George Salmon
The Church and Infallibility, a reply to the “Abridged” Salmon by B.C. Butler (typing this one in as HTML)
St. Peter, His Name and His Office (pdf) by Thomas Allies
Studies on the Early Papacy by Dom John Chapman (HTML edited by me)
The Primitive Church and the See of Peter (pdf) by Luke Rivington
I scanned this last one in myself then I realized Google has a cleaner and smaller PDF scan. But Google’s scan was missing a couple pages which I filled in.
These are good representatives of the “battle of the books” that went back and forth between Anglicans and Catholics in the late 19th, early 20th century. Advanced stuff, they get pretty deep into Church history and the Fathers.