Does crystals have a place in histroy?

Question

Science project

Answer 1

When gallium was first discovered, chemists made the oxide and chloride and determined the equivalent (combining) weight very exactly. In order to know the atomic weight very exactly, they had to multiply the equivalent weight by the valence. They way to do that in those days was to use the Law of Dulong & Petit: That the atomic weight of a metal times its heat capacity (cal/gram-deg) is approximately 6.3. So they determined the heat capacity, got an estimated atomic weight, and divided that by the equivalent weight. The result was 2.5, which meant that they couldn't know whether the valence was 2.0 or 3.0.

So they made gallium ammonium sulfate. If the formula was NH4Ga(SO4)2, then the compound was an alum, and the valence of Ga was 3. If the formula was (NH4)2Ga(SO4)2, then the compound was a schoenite, and the valence of gallium was 2. It turns out that crystals of alums and schoenites have different appearances under a microscope. The chemists looked at their crystals: They were alum. The valence of Ga was 3.

In 1848, Louis Pasteur was looking at crystals of sodium ammonium tartrate, NaNH4C4H4O4, under a microscope. The crystals were of the size of salt or sugar. He saw that they were unsymmetrical and in two shapes that were mirror images of one another (like right and left hands).

Curious, he spent a few hours with a tweezers, looking at each crystal, and putting it into a different pile depending on whether it was "left" or "right." At the end, he had two tiny piles of crystals.

On a hunch, he dissolved one pile in a little water and looked at the solution in what is called a polarimeter. He found that "right" and "left" crystals rotated the plane of plane-polarized light equally, in opposite directions.

Today we know that this is because the molecules themselves are "left" or "right" handed. And the handedness of molecules has led to great discoveries in sugars, carbohydrates, amino acids, proteins, and drugs.

Answer 2

Sure. Blood diamonds, for example. Lots of action and history, go watch the movie.