From Alchemy to Chemistry

The Aristotelian theory dominated scientific thought until the time of Robert Boyle in the middle of the seventeenth century. Its implication of the possibility of changing, or transmuting, one element into another was particularly important. As an example of this conception, it appeared that water, the cold-wet element, could be transmuted by the application of heat into air, the hot-wet element, through the displacement of the cold quality by the hot one. In modern terms, of course, this process of vaporisation is considered as a purely physical one. Solid water (ice), liquid water, and gaseous or vaporised water (steam) are different physical forms of the same substance, and there is no question of transmutation of one kind of matter into another being concerned in interconversions of these three forms.

It would be unjustifiable, in the light of present knowledge, to dismiss the theory of the Four Elements as ill-conceived or useless.