In Lord of The Flies, when in chapter 8 does Jack leave?
The boys in Lord of the Flies become obsessed by thoughts of the Beast, convinced of its existence. Ralph maintains that "the beast had teeth... and big black eyes." Ralph is the leader of the group, as voted for, even though Jack had been certain, "as head chorister", that he should be leader. He does have his own group of "hunters," initially the choir and he enjoys the status this gives him. The beast is close to the location of their signal fire so Ralph feels "we're beaten" as without a fire they cannot be rescued. When Jack offers his hunters as a means to fight off the beast and secure the fire, Ralph mocks them, calling them "Boys armed with sticks." Jack is angry about that and storms off (all at the beginning of chapter 8). He then summons all the boys by blowing the conch from the platform. At this stage, the conch gets everyone's attention. Jack now has everyone's attention and wants to talk about the beast and tries to use this opportunity to try and take over as chief, calling Ralph "a coward."
Jack is again defeated as the boys do not support him so he runs away into the forest, suggesting that "anyone who wants to hunt when I do can come too." This is significant as chaos is already beginning to replace order and, although Piggy thinks it may be better without Jack and his hunters, the problem of teh beast remains.
This all takes place in the first few pages of chapter 8. Different books have different page numbers so it would be unwise to quote a page number unless it relates to the same published edition.