That water was composed of earth and air seemed easily proven by the simple process of boiling it in a tea-kettle, for the residue left was obviously an earthy substance, whereas the steam driven off was supposed to be air.

The fact that pure water leaves no residue was not demonstrated until after alchemy had practically ceased to exist.

It was possible also to demonstrate that water could be turned into fire by thrusting a red-hot poker under a bellglass containing a dish of water.

Not only did the quantity of water diminish, but, if a lighted candle was thrust under the glass, the contents ignited and burned, proving, apparently, that water had been converted into fire.

These, and scores of other similar experiments, seemed so easily explained, and to accord so well with the "four elements" theory, that they were seldom questioned until a later age of inductive science.
But there was one experiment to which the alchemist pinned his faith in showing that metals could be "killed" and "revived," when proper means were employed.