As for why it didn't disolve, what bastardsnow said. Ms. Smythe didn't give Alex his book, so Alex never read the trigger that would free Xander.

I'm a bit confused by how the alligators & elephants phrase, which Spike obviously believed to be the trigger before it failed to work, relates to the books from Ms Smythe. Was Spike's phrase an *expired* trigger? Did each book contain a new trigger? If each book contained a new trigger, how come Alex never triggered Xander back when he tried to read it, and what was the point of Ms Smythe giving him the books?

Sorry to be so dense, but I just can't work out how it all fits. Love the characterizations though, and experiencing this story through Alex's POV.