It was pretty wild wild west, really. The idea that some some compounds didn't just contain some fire was still common when the first list of elements was put

It was pretty wild wild west, really. The idea that some some compounds didn't just contain some fire was still common when the first list of elements was put together. A big leap forward was realizing air had two principle components, burn-y air and not burn-y air. They figured out water wasn't an element when the burn-y air and some mystery gas burned to make it. Basically, everything was maybe an element until they either broke it into pieces, or made it out of other stuff.