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Reading Selection, Lesson 23

Making Metals by Mistake

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Mochica mask

This Mochica mask from northern Peru is made of copper. Although the Mochica civilization lasted for 1000 years, its smiths never mastered the production of iron. Why did early cultures make objects from less reactive metals such as copper, silver, and gold?

Are you the sort of person who does things by trial and error? For example, if you get a new video game, do you put it in your machine and then try to play without reading the instruction manual? If so, you are in good company. Trial and error is a technique that has been used since prehistoric times. It is still used today because it works.

Consider the way people figured out how to make metals. Before about 5000 b.c., the only metals that people used came from nuggets of gold, silver, and copper. Nobody knew that metals were locked inside rocks. Nobody, that is, until someone probably made a very hot fire on top of some greenish rocks and saw molten copper trickling out.

Today, it is known that those greenish rocks contained copper combined with oxygen and other elements. Heating the rocks with a wood fire to several hundred degrees caused a chemical reaction. The rock turned to copper oxide, and the oxygen broke loose from the copper and combined with carbon from the wood. Carbon dioxide floated away. The copper stayed behind.

Of course, early people didn't know any of this. But that didn't stop them from experimenting. How much rock should be used? Which rocks work? Where are the rocks found? How hot does the fire have to be? Does the type of wood matter? Does the phase of the moon make a difference? Would it help to add some dirt? If rocks can be changed to copper, can copper be turned into gold? After a few centuries of trials—and almost as many errors—people knew a lot about making copper and it became widely available.

The copper was not very hard. It could be made into pots and pans. It could be shaped into fancy jewelry. But it was too soft to make good tools or weapons. People needed tools and weapons, and more trial and error eventually led to the next big discovery.

Bronze armor for the upper body

Early armor, such as these pieces of armor, was made from alloys of less reactive metals. Bronze, an alloy of tin and copper, was used to make this armor.

In about 3800 b.c., a copper maker in the Middle East mixed tin ore with copper ore and heated them up. The resulting metal was very different from tin and from copper. This new metal, an alloy called bronze, was lighter in color than copper. It was also much harder than either copper or tin. This new alloy was used to make axes, spears, knives, armor, and other tools.

The secrets of making bronze soon spread to the Far East. By 1500 b.c., Chinese bronze makers had discovered, by trial and error, that the hardest bronze is exactly 85 percent copper and 15 percent tin. They had no idea why this particular mixture was so hard. But by experimenting, watching carefully, and recording results, they found the best way to make bronze.

Iron was probably discovered by mistake, in much the same way as copper. However, iron ore requires a much hotter fire than that used to extract copper from ore. Can you think of the reason why the fire needs to be so hot?

Iron is much harder than bronze. Tools and weapons made of iron were much harder than those made from bronze. The techniques for extracting and improving the quality of iron were refined through trial and error, and the new technology spread quickly. The Iron Age had begun.

 

Two gladiators fighting with bronze weapons.

Bronze is harder than either tin or copper—hard enough to use for armor in battle.

Question

Iron was discovered after copper and tin because it is more difficult to extract from its ore. What are the modern processes for extracting iron metal from its ores? Use information from the library and the Internet to find out more about these processes. Write a paragraph about the techniques involved, and illustrate your answer with a diagram.



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