For anyone looking for another book to reference for the essay, The Invention of Journalism by Jean K. Chalaby has been helpful for me so far. It's pretty dense but the whole book revolves around the period from 1850 onwards so there's a lot of good quotable bits, particularly in the Third Part.
And the last chapter contains some interesting theories on the function of journalism, in particular the 'magic mirror' effect.
Don't let the intoduction put you off reading this book, I didn't know half the words in there but I found some good facts in the rest of the book.
Good luck everybody!