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)
