Archive for the ‘chemistry’ Category

The following is based on part four of Jacob Bronowski’s BBC series on the history of science and invention, “The Ascent of Man” (1973). It is about metals, alchemy and the rise of chemistry.

Man first used fire 400,000 years ago. It kept him warm, cooked his food, kept away wild animals. But he did not learn to use it to get the metal hidden in stone till -5000 somewhere in Persia or Afghanistan: put a certain green stone in the fire and out came a red, liquid metal: copper

Copper was the plastic of its day, an almost universal material that you could shape into anything. But copper had one drawback: it was too soft. It could not keep an edge; it would wear out too quickly.

By -4000 someone made a surprising discovery: if you add tin, an even softer metal, it made a new metal that was much stronger than either one: bronze. An impure metal, an alloy, is stronger than a pure one.

By -1500 the Hittites in what is now Turkey knew how to make and work iron, which requires a much hotter fire.

By -1000 people in India knew how to make steel from iron and carbon. It was used in swords but it was so hard to make that it did not become common till the 1800s.

And then there was gold. It was not terribly useful, but in a world that is constantly changing and falling apart, it stayed the same: wind and rain could not make it rust and fire could not destroy it but only make it purer. In every age and every city it is prized above all the rest.

By 100 in China the alchemists tried to make gold out of more common materials. After hundreds of years of trial and error they failed. But along the way they learned quite a bit about the stuff that makes up the world: the chemical elements.

In the 1700s alchemy became a proper science, chemistry. That was the work of three men in the West: Priestley, Lavoisier and Dalton:

  • Priestley discovered oxygen. It was because people did not know about oxygen that they thought fire was material, like air or water. Fire is not material – it is a process that takes other materials apart and puts them back together in new ways.
  • Lavoisier ran Priestley’s experiments but carefully weighed everything before and after, even the air. He found that elements like mercury and oxygen always go together in certain proportions – it was not just a matter of chance. That was true for any substance that could be broken down into simpler substances.
  • Dalton took Lavoisier’s numbers and asked “Why?” That is the essence of science: ask an impertinent question and you are on the way to the pertinent answer. Dalton’s question led him, in 1803, to discover that everything is made of atoms.

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Sir Humphry Davy (1778-1829) was a British scientist who discovered the elements potassium, sodium, barium, strontium, calcium and magnesium. He also discovered laughing gas, proved that iodine was an element and that diamonds are just a form of carbon.

But his greatest discovery was a man: Faraday, one of the greatest scientists of all time.

Davy’s big trick, the reason he discovered so many elements, was that he built the world’s biggest battery. That is why he could discover so many elements. With the electricity that it created he passed it through different substances to break them down into simpler ones. Some of these simpler substances were elements that no one had ever seen before.

For example, he thought potash had some kind of metal in it. He passed his electric current through the stuff and out came little shining balls of metal. He called the metal potassium.

Guy-Lussac was doing the same sort of thing in France. In one case he beat out Davy, finding boron nine weeks before he did.

When Davy was young he studied medicine and wanted to be a poet. He loved to fish and walk through the woods and look at the mountains. In one pocket he had his fishing hooks and in the other he had stones that he found along the way.

As a poet Davy was friends with Wordsworth, Coleridge and Southey, some of the best British poets of the time.

But he was not to become a famous poet: at age 19 he read Lavoisier’s book on chemistry. It hooked him for life. A friend of Davy’s let him use his library and chemistry laboratory, one of the best in England as it turned out.

Davy started out by trying to understand out how batteries work. Once he understood that he saw they could be used to break down substances into simpler ones.

Davy came to London. It turned out that he was a great speaker, even though his Cornish English sounded strange. The women liked his handsome looks. His talks on chemistry made him famous and helped to give science a good name. One person who came to see him was Faraday. Davy later hired him.

Davy did not believe in Dalton’s atoms. We take them for granted now, but it was a new idea then, one that was slow to catch on.

Davy was not all that careful: sometimes things blew up, one time he almost went blind.

He made a habit of breathing in any gas he created. He wanted to learn as much as possible about it. Once this paid off when he discovered laughing gas. Another time it almost killed him. But over the years it destroyed his health. He only lived to be 50.

One of the best things he did was to make mines safer with his invention of the safety lamp. He worked out a way for the lamp’s flame to burn without being in danger of blowing up inside the mine.

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