In "The Adventures of Huckleberry Finn," how do you know Huck and Jim are friends by the end of Chapter 9?

A reader can tell that Jim and Huck are friends by the end of chapter 9 very simply because Huck makes the decision to help Jim escape.  Huck knows that people will call him a 'low-down Abolitionist' if he helps Jim, and the decision to help Jim goes against everything Huck has ever been taught, but he makes the still decides to help him, and from then on, Huck and Jim stick together in their adventures.