Linus Pauling: In the old days it was possible to make discoveries without spending much money and
a great many very important discoveries were made. Pasteur, for example, laid the
basis for modern three-dimensional chemistry with spending very little money. He was
being paid to check up on problems connected with making wine. One of the substances
present in wine is cream of tartar, which is potassium hydrogen tartrate, a salt of
tartaric acid, well-known chemical compound. Chemists had discovered that there were
two kinds of tartaric acid that looked just the same; you looked at them, they had
the same solubility, they, really, properties essentially the same as one another.
But the tartaric acid that you got in the laboratory had a peculiar property that
when you dissolved it in water and passed a plane polarized beam of light, such as
you get by passing ordinary light through a Polaroid film, invented by Mr. Land when
he was an undergraduate at Harvard. You pass the beam of light through that.
Of course in the old days you didn't have a Polaroid film; you used a crystal of calcite,
specially cut crystal of calcium carbonate. When you pass this plane polarized beam
of light through the solution of ordinary tartaric acid it just goes on through, synthetic
tartaric acid. If you make tartaric acid from grapes it rotates the plane of polarization
of the light in one direction. And it's possible, in fact, to get a kind of tartaric
acid that seems identical but rotates the plane of polarization in the opposite direction.
Pasteur didn't understand this. He knew he had made a discovery. He could take the
inactive tartaric acid, look at the crystals and separate out right-handed crystals
and left-handed crystals. The right-handed crystals twisted the plane of polarization
to the right and the left-handed ones twisted it to the left. Well, he didn't know
why and about thirty years later the explanation was discovered by a young Dutchman
named van't Hoff, about 23 years old. He had the idea that the carbon atom is a tetrahedral
carbon atom. It forms four bonds that are pointed in four different directions in
space. Molecules have a three-dimensional structure. Some molecules can be built so
that the atoms are arranged in ways that look like the right hand and some built in
exactly the same way except the mirror image, so that they look like the left hand.
They interact with the plane polarized light in different ways. This led, of course,
to tremendous advances in chemistry. It was the start of the golden era of analytic
and synthetic organic chemistry, of structural chemistry.
Chemists were able then to determine by interpreting their experiments just how the
atoms were arranged relative to one another. In a qualitative way they didn't know
how far apart the atoms were in the late 19th century but they knew their relative
positions in this qualitative way and they could begin to explain the properties of
chemicals in terms of the molecular structure as determined by these chemical methods.
They could then synthesize new compounds, new drugs. Drugs that would be better than
quinine for controlling malaria and many other drugs that had specific purposes. They
could do it in quite an efficient way because they understood pretty well what they
were doing.
When I was a boy, 18 years old, I became interested in the question of just why are
atoms held a certain distance apart. How far apart are they when they are bonded
together and what is it that holds them at this distance? What is the chemical bond
between atoms? What are the structures of molecules? They were just beginning to be
determined.
