In what chapter does Bob Ewell spit in Atticus' face?

This event occurs after the verdict in the trial, and is first mentioned at the very end of Chapter 22. It is described in detail in Chapter 23, where we learn that Bob Ewell has not only spat on Atticus, but threatened to kill him and attempted to goad him into a fight. Atticus bears his threats with dignity, claiming that he is "too old" to fight despite Bob's unseemly insults. Jem and Scout are understandably upset about the incident, and Atticus tries to explain by asking them to see things from Ewell's perspective. Bob lost all his credibility in the trial, Atticus said, and he had to be seen to retaliate in some way. In any case, he tells them, "if spitting in my face and threatening me saved Mayella Ewell one extra beating," then it was worth it to Atticus. This extraordinary act of empathy is among Atticus's finest moments in the book, and one which is consistent with what he always preaches to the children--one has to be able to walk in the shoes of others to treat them fairly and with dignity.