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.
