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Archive for the ‘metallurgy’ 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 7,000 years ago 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.

A thousand years went by and then 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.

About 3,500 years ago the Hittites in what is now Turkey discovered how to make and work iron, which requires a much hotter fire. Its alloy is steel, which is made of iron and carbon. Steel was discovered in India 3,000 years ago. 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.

Starting 2,000 years ago 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.

Alchemy became a proper science, chemistry, in the 1700s. 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 and 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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