Actually, Grab, phlogiston was disproved in a much easier fashion. The theory required heat to be the result of released phlogiston. A scientist (can't remember the name) showed that a grindstone produced heat from friction. This would make phlogiston a non-conserved substance (i.e., it could be made or destroyed), which diproved the theory. Just like falling speed being dependent on weight, phlogiston required only a little common sense to refute.