Tuesday, June 15, 2010

Aristotle and Ancient Chemistry

Aristotle believed that earth, air, fire, and water were the fundamental elements of the universe. We scoff today at this naïve notion of the natural world, but the story beneath the story is still interesting.

In Aristotle’s time the known elements were ten:

Copper – discovered in 9000 B.C.
Lead – discovered in 7000 B.C.
Gold – discovered in 6000 B.C.
Silver – discovered in 5000 B.C.
Iron – discovered in 5000 B.C.
Carbon – discovered in 3750 B.C.
Tin – discovered in 3500 B.C.
Sulfur – discovered circa 2000 B.C.
Mercury – discovered in 2000 B.C.
Zinc – discovered in 1000 B.C.

Aristotle believed that all substances, such as the above, were made up of earth, air, fire, and water in differing proportions. Consider the burning of wood. It breaks down into fire and earth (ash). You can obtain fire from wood, but not wood from fire, so fire must be a component of wood.

He goes to great lengths in On the Heavens to derive the properties of the elements and how they are related to each other. He explains how they are subject to generation and destruction. For example, fire can be destroyed by two methods: by its contrary (water) when quenched and by itself when it burns out.

In his analysis of how the elements are generated, however, Aristotle gets off track. He proposes that the elements are either created from something incorporeal (non-material) or from themselves. He ruled out the former because it would require the space of a void to synthesize the element and voids do not exist. He simply could not accept the fact that there is space unoccupied by matter. If elements are created from themselves, how does this happen? To Aristotle, they cannot change shape so they must resolve themselves into planes. For example, when an object is burned it becomes spheres and pyramids because fire itself is spheres and pyramids. Several of the early Greek “chemists” talk about the forms of matter in geometric figures.

Yet there is still a more interesting case – that of the atomists Democritus and Leucippus. Predating Aristotle by a century, these two philosophers postulated the existence of tiny atoms that make up all substances in nature. The atoms of any substance are unique, indivisible, and infinite, the latter attribute being unacceptable to Aristotle. While he focused on the absurdity of infinite atoms, and used that to debunk the atomists theory, he never perceived how atoms could be small and in large quantity without being infinite. Man had to wait for centuries before he would be able to perfect his methods of experimentation and embrace the concepts of atomic physics.

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