As we start celebrating the International Year of Chemistry, let's think about chemistry and beauty. What makes an experiment beautiful? Does it have to be clever, or prove something unbelievable? And which is the most beautiful of them all?
Sometimes, a theory sounds so good and full of common sense that we think it must be true. Then someone comes along and does a simple experiment. And does it carefully, weighing and measuring everything. It comes up with results that go against the theory. Other scientists do the same experiment, and get the same result. Such experiments, which let the truth triumph, are often thought of as the most beautiful experiments in science.
Let's take the example of the theory of why some things burn and some don't. When you burn a piece of wood, it gives a bright flame and leaves a pile of ash. So there must be something in the wood that was lost, and which made it burn. Something that did not exist in things that do not burn, like water. This was called phlogiston in old times.
If things really had phlogiston in them, they should weigh less after they have been burned. When you burn a piece of wood, the ash is lighter. So the phlogiston theory seems to hold, right? But wait. To be really sure, you also have to weigh the air. If phlogiston had been released into it, the air should become heavier, shouldn't it?
That's the question the French scientists Antoine & Marie-Anne Lavoisier asked. To answer it, they came up with an experiment. They mixed mercury with air, sealed the container and weighed it. They then heated it. The mercury reacted with air to form a red material (called calx). When no more calx was being formed, they weighed the container. It weighed the same as before heating. So nothing had escaped.
Now if phlogiston had released into the air, the air should be denser, and escape when the container was opened. But the opposite happened - air rushed in. That meant nothing had been released. He then weighed the red calx - and it was heavier than the original mercury! In one stroke, the Lavoisiers had killed the phlogiston theory. Beautiful isn't it?
You see, instead of releasing phlogiston into air, mercury was actually removing something from it. Now we know that this something is oxygen. Later on, Lavoisier, and Joseph Priestley did many more experiments to prove the existence of oxygen, and to prove that it caused burning.
Here's a video of the science writer George Johnson describe some more experiments, and tell you why he thinks Lavoisier's experiment is the most beautiful of them all: