Ex.1 Think and answer
1 Why was nickel considered troublesome?
2 What is the origin of the word “nickel”?
3 Where can nickel be found?
4 What country is the greatest producer of nickel?
5 How is nickel produced?
6 What are the main properties of nickel?
7 What is called “nickel plate”?
8 Where are nickel alloys used?
9 What is the main quality of nickel steel?
10 Where is nickel steel used?
Text What is marble?
Nature is a master baker. Deep inside the earth is her oven, heated thousands of years ago by great rising masses of molten rock. In this oven she baked, and with tremendous pressure turned limestone into hard marble.
In its purest form, marble is white. Different impurities often give it shades of pink, red, yellow, or brown, or form wavy lines or patches in it. Different colored crystals caught in the marble sparkle and flash in the sun’s rays. In some marble the remains of fossils add to its beauty.
Many other kinds of rock that take on a high polish and are used in building, such as granite, onyx, and porphyry, are often called marble. Real marble, however, is limestone that has been crystallized by nature’s process.
When marble is quarried a machine called a “channeler” cuts a series of channels or slots in the face of the rock. Some of these slots may be 8 to 12 feet deep and run from 60 to 80 feet in length. Blasting cannot be used because it would damage or shatter the marble. The blocks are lifted out carefully by large derricks.
A great toothless saw is set to work on the rough stone, while a stream of water containing sand is kept running over it. The friction of the steel blade and the sand soon cuts the marble into the desired sizes. Sometimes a wire saw is used instead of a solid blade.
Pieces of marble are then placed on a circular rubbing bed and held stationary. Sand and water flow over the rotating bed surface, rubbing away the marble to an even level. Then still more grinding is done to give it a smooth surface.
The last fine polishing is done by a mixture of tin oxide and oxalic acid applied to the surface of the marble by means of a buffer wheel.
Ex.1 Think and answer.
1 Why can nature be called a “master baker”?
2 How does limestone differ from marble?
3 Why is a machine used for marble quarrying called “a channeler”?
4 Can blasting be used when marble is quarried? Why?
5 How are blocks of marble produced?
6 What are the main industrial processes used in the marble producing?
7 Where is marble used?
Text What is silver?
The mining of silver has been carried on from ancient times. In Europe, kings depended on it as their source of wealth. In fact, when the Spanish silver mines began to run low, the King of Spain was delighted that the discovery of America led him to obtain the great silver mines of Mexico and Peru. The mines at Potosi in Peru produced $4,000,000 worth of silver every year for 250 years for the kings of Spain!
During the gold rush days in California, people cursed the “black earth” that struck to their gold dust. It was only by accident that they discovered it was silver ore!
Silver is one of the most widely distributed of all metals. Sometimes it is found in solid pieces. About 2,000,000 tons of it float about in solution in the sea, but it would not pay to get it out. In the main, silver comes only in ores from which it must be separated. In this ore, silver is usually combined with sulphur as silver sulphide, or is a part of other sulphides, chiefly those of copper, lead, or arsenic. In the United States, it is found mostly in connection with lead. In fact, silver occurs in so many combinations that there are a great many different methods of separating it from the other elements.
Silver is too soft to be used in its pure state, so it is combined with other metals. Silver coins, for instance, contain 90 per cent silver and 10 per cent copper. The sterling silver of which jewelry and silverware are made contains 92.5 per cent silver and 7.5 per cent copper. The name “sterling”, by the way, has a curious origin. It comes from a North German family called Easterling. The Easterlings were such honest traders that King John of England gave them the job of making the English coins in 1215. They did it so well and truly that their name is still used as a sign of solid worth. All sterling silver is stamped with a hallmark, either the word “sterling” or a symbol, depending on the country. The English symbol is a lion. Pure silver doesn’t tarnish in pure air. When it turns black, that’s a sign there is sulphur in the air, as from city smoke or oil wells. Next to gold, silver is the easiest metal to work with. One ounce of silver can be drawn into a wire more than 30 miles long! It is also the most perfect known conductor of electricity and heat.
Ex.1 Think and answer.
1 How old is the process of the silver mining?
2 Why did Kings in Europe depend on silver?
3 What were “gold rush days”?
4 What is “the black earth”?
5 Why did people curse it?
6 How and where is silver distributed?
7 What is it difficult to use silver in its pure state?
8 What is “the sterling silver”?
9 What is the origin of the name “sterling”?
10 What are the most important physical properties of silver?