Today, we look for the universal solvent. 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.

You've heard the old remark, "Spit is the universal solvent." That mocks a very old idea that, somewhere, there might be found a solvent that will dissolve anything. Water is quite a good solvent. It dissolves the sugar in hot tea quite nicely, but it doesn't do as well in iced tea. It dissolves many materials, but, lucky for us, not the glass that holds it, nor our human tissue.

Dissolving is quite different from chemically decomposing a material. When water dissolves sugar, it leaves the sugar molecules intact -- it simply separates them from one another. When, on the other hand, nitric acid attacks copper, it reacts with it and creates a new salt -- one that's blue in color.

That distinction was far less clear before we had an atomic theory. And one of the holy grails sought by the alchemists was that of finding the universal solvent.

They called that unknown liquid the alkahest. Alkahest was a word made up by the sixteenth-century alchemist Paracelsus. Maybe it meant alkali est (or it is alkali). Or maybe he just wanted a term that sounded Arabic and mysterious. Paracelsus was one of the first to start moving away from pure old alchemical thinking. A later great alchemist named van Helmont picked up where Paracelsus had left off. But van Helmont also intensified the search for the universal solvent, alkahest. In fact he claimed to've found it.

Now here we need to look at van Helmont's work in the light of what we know today. Whatever he found was certainly not a solvent. It had to've been a reagent that attacked materials chemically. Of course a true alkahest could never be contained. He'd probably just found a chemical that could reduce many more materials than any previous agent.

And so chemical historian Ladislao Reti goes looking for van Helmont's alkahest. What he finds is a surprise. Van Helmont's writings point to even earlier medieval descriptions of a substance called sal alkali. Sal alkali, in turn, appears to've been a solution of caustic potash in alcohol, which reduces many substances.

Helmont describes a process in which his alkahest -- this sal alkali -- is applied to olive oil. The result was identified as a sweet oil, which would've been glycerol. The irony of that is that DuPont obtained a patent for that process in 1942. (One more example of how arbitrary the assignment of priority always is.)

So we strip away the hyperbole of the old alchemical language and find substance. We see modern chemistry taking form. Paracelsus's "universal solvent" was no such thing, but who ever thought it was? Paracelsus was no more excessive than nineteenth-century poet Sidney Lanier when he wrote these lovely lines:

Now in the sea's red vintage melts the sun,
As Egypt's pearl dissolved in rosy wine,
And Cleopatra night drinks all.

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

(Theme music)

Reti, L. Van Helmont, Boyle and the Alkahest. Some Aspects of Seventeenth-Century Medicine & Science, Los Angeles: UCLA, William Andrews Clark Memorial Library, 1969, Part I.

The Lanier quote is from his poem Evening Song.
 

Image of Alchimia, the embodiment of Alchemy
Woodcut published by Leonhard Thurneysser in 1574.
Thurneysser was a student of Paracelsus.