When does copper turn green?


Although copper is highly resistant to the chemical action of the atmosphere and of sea water, it turns green if exposed to them for a long time. The colour is caused by the formation of a thin coating of green basic copper carbonate known as patina or verdigris. The latter name comes from the old French vert de Greece (green of Greece), but the reason for it is unknown. This beautiful green is often seen on copper roofs or statues, especially if they are near the sea.



     Copper was the first metal man learned to use. Five thousand years ago, when men discovered deposits of pure copper in what are now Iraq and Cyprus, they found that this fairly soft metal could be easily melted, cast in moulds and hammered into tools, weapons and ornaments.



      About half the copper produced today is used by the electrical industry. Pure copper is the best cheap conductor of electricity and can be drawn into threads one-thousandth of an inch thick.



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Why are some metals chromium plated?


Some metals are chromium-plated to make them look more attractive and to make them look more attractive and to prevent them from corroding or rusting. Chromium is a silver-white, hard, brittle metal which was discovered in 1798 by N.L Vauquelin. Its non-corrosive, high-strength, heat-resistant characteristics are utilized in alloys and as an electroplated coating.



        In electroplating, the article to be plated is connected to the negative terminal of a battery and placed in a solution known as electrolyte. Direct electric current is introduced through the anode or positive terminal, which usually consists of the metal with which the article is to be coated. Metal slowly leaves the anode and forms a deposit on the article. The electrolyte for chromium contains chromic acid and sulphuric acid. It deposits a bright top layer but this is not the only important part of the electroplating. The chromium is only about 0.00002 inches thick. Under it lies a thick layer of nickel and beneath that again may be a layer of copper.



      Many household appliances are chromium-plated and so are the bright parts of an automobile. Tools, chemical equipment, electric appliances, gears, packing machinery, and hundreds of other articles are similarly treated to give them brightness, beauty or resistance to wear and rust. Electroplated and polished chromium is bright bluish-white with a reflecting power which is 77% that of silver



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Important iron



 



 



The centre of the Earth is partly made of iron! Around the world, there is plenty of iron found in rocks. Some of the rocks look rusty and red. When the iron is taken out, it is dark grey. Iron is a useful and important metal.



 



 



 





 



Iron is strong and easy to shape.



In its ore, iron is mixed with many other materials. To extract the iron, the rocks are heated in extremely hot ovens, called blast furnaces. When other materials, such as coke and limestone, are added, runny iron is taken out. The purest iron is then used to make steel.



 



 


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Light and strong Metals



 



 



Many metals, such as iron and steel, are strong and heavy. They are used to make machines or buildings. There is also a need for metals that are strong and light. A car needs to be strong, but it uses up less petrol if it is also light.



 



 



 



 





 



 



Aircraft need to be strong and light.



A light aircraft is cheaper to fly than a heavy one because it uses less fuel. It is also faster. But aircraft must be strong too. Titanium is as strong as steel but nearly half as light! This aeroplane is made mainly out of the metals titanium and aluminium.



 



 



 





 



 



This metal was worth more than gold!



Aluminium used to be more valuable than gold! It was precious because it was hard to find and costly to make. Today, it is much cheaper and is used to make cans and kitchen foil.



 



 





 



 



 



 



 



 



There is metal in your body.



Inside your body, there are tiny natural traces of metal such as iron and zinc. These are not chunks of solid iron. Instead, these metals flow around your body in your blood. Metals in the body are called minerals. We get them from eating different foods.


Useful metals



 



 



You can see and touch metals used in things like drink cans and bikes. Metals also make it possible for you to switch on a light. Your computer uses metals to work and there is even metal in the paint on your walls.



 



 





 



 



Electricity flows easily through some metals.



Electricity only flows easily through some materials. It cannot flow through wood or plastic. But it can flow through some metals, such as copper. These metals are called conductors. Many electrical wires are made from copper. Without metals, we could not use electricity as we do today.



 



 



 





 



 



What would happen if you had a wooden saucepan?



Many materials catch fire easily. A wooden saucepan would burn if it was heated. A metal saucepan gets hot but does not melt. Metal is a good conductor of heat. It lets heat through, but doesn’t burn unless it is extremely hot.



 



 





 



 



 



Mercury is a runny metal.



Mercury is the only metal that stays as a liquid at room temperature. This silver-coloured metal used to be called quicksilver because of the way it runs and flows. Mercury changes shape when it heats up or cools down. Because of this it can be used in thermometers to measure temperature.