Today, let's look at alchemy. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

When we think of alchemy, we think of magicians trying to change lead into gold. Yet alchemy was actually the study of chemistry from the 3rd century BC all the way through the next 2000 years. The word probably comes from the Greek chemeia, which meant to transmute or change matter; and that's what alchemy, like chemistry itself, has always been concerned with.

Alchemy originated when Aristotle took up an older idea that all matter combined the four elements of earth, air, fire, and water. He guessed that these elements could be changed -- transmuted -- by the action of heat and cold, or dampness and dryness.

Aristotle's ideas were developed first by the Greeks after him, and then by Arab scientists. From time to time, alchemy mired itself in metaphysical razzle-dazzle. The practical Romans had no taste for it at all. So, as civilization spread north into Europe, alchemy all but vanished until the 13th and 14th centuries, when scholars began to reread the old Greek and Arabic texts.

Of course, alchemy promised great wealth to anyone who figured out how to transmute other metals into gold. It might seem a waste that so many alchemists devoted their lives to that, but the spin-off was enormous. By trying to understand transmutation, they learned about practical metallurgy, about extracting metals from ores, and about chemical reaction. Their results were reported in terms alien to our ears, but the late medieval chemists were suprisingly able metallurgists.

Late-17th-century chemists saw matter as made up of three elements, or "earths," as they were called: Vitreous earth gave solidity to matter; fluid earth gave it liquidity; and fatty earth, which was later called phlogiston, gave it combustibility. These were the old Aristotelian elements of earth, water, and fire -- without air! Air was thought to be inert and not a part of other materials.

All the while, a more and more analytical science was being built on these ideas. The alchemical view of matter didn't give way to an atomic theory until less than two hundred years ago. And then it didn't give way completely. When people realized that heat wasn't a part of matter, they replaced phlogiston with caloric. Caloric was another Aristotelian substance that occupied all matter and flowed from hot bodies to cold ones. Even after the atomic theory of matter replaced the various earths, caloric was still being used to describe heat when my grandfather was a little boy.

So before we write alchemy off as voodoo magic, we'd better ask what our own chemistry will look like in the 22nd century.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

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This episode has been substantially rewritten as Episode 1508.