Evaporating water from hydrate compounds

[7hor]

Sorry if this has been asked before, we've got a lab tomorrow, we have to take some different hydrate compounds and heat them up with a bunsen burner. We are supposed to figure out a way to know if all the water has been driven off, I just can't think of anything...besides until the compounds start burning, and that isn't good Is there a trick with temperature? I'm very puzzled Thanks in advanced for some hints

 

Edit: So I've thought up heating it slowly, and by looking around on the net, keep weighing it till it stays at that constant weight...I think that's it. Might be a better way though.