题目内容
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"It should be possible to make a precious stone that not only looks like the real thing, b
At first this did not seem like a particularly hard task. Scientists began to try making synthetic diamonds towards the end of the eighteenth century. It was at this time that a key scientific fact was discovered: diamonds are a form. of carbon, which is a very common element. Graphite, the black mineral that is used for the lead in your pencil, is made of it, too. The only difference, we know today, is that the carbon atoms have been packed together in a slightly different way. The chemists were fired with enthusiasm: Why not change a cheap and plentiful substance, carbon, into a rare and expensive one, diamond？
You have probably heard about the alchemists who for centuries tried to turn plain lead or iron into gold. They failed because gold is completely different from lead or iron. Transforming carbon into diamonds, however, is not illogical at all. This change takes place in nature, so it should be possible to make it happen in the laboratory.
It should be possible, but for one hundred and fifty years efforts failed. During this period, none the less, several people believed that they had solved the diamond riddle. One of these was a French scientist who produced crystals that seemed to be the real thing. After the man's death, however, a curious rumour began to go the rounds. The story told that one of the scientist's assistants had simply put tiny pieces of genuine diamonds into the carbon mixture. He was bored with the work, and he wanted to make the old chemist happy.
The first real success came more than sixty years later in the laboratories of the General Electric Company. Scientists there had been working for a number of years on a process designed to duplicate nature's work. Far below the earth's surface, carbon is subjected to incredibly heavy pressure and extremely high temperature. Under these conditions the carbon turns into diamonds. For a long time the laboratory attempt failed, simply because no suitable machinery existed. What was needed was some sort of pressure chamber in which the carbon could be subjected to between 800,000 and 1,800,000 pounds of pressure to the square inch, at a temperature of between 200°F and 2,200°F.
Building a pressure chamber that would not break under these conditions was a fantastically difficult feat, but eventually it was done. The scientists eagerly set to work again. Imagine their disappointment when, even with this equipment, they produce all sorts of crystals, but no diamonds. They wondered if the fault lay in the carbon they were using, and so they tried a number of difficult forms. They failed again and again but went on working. The idea was then brought forward that perhaps the carbon needed to be dissolved in a melted metal. The metal might act as a catalyst, which means that it helps a chemical reaction to take place more easily.
This time the carbon was mixed with iron before being placed in the pressure chamber. The pressure was brought up to 1,100,000 pounds to the square inch and the temperature to 900℉. At last the chamber was opened. A number of shiny crystals lay within. These crystals scratched glass, and even diamonds. Light waves passed through them in the same way as they do through diamonds. Carbon dioxide was given off when the crystals were burned. Their density was just 3.5 grams per cubic centimeter, as is true of diamonds. The crystals were analyzed chemically. They were finally studied under X-rays, and there was no longer room for doubt. These jewels of the laboratory were not like diamonds; they were diamonds. They even had the same atomic structure.
The main idea of Paragraph 2 is that______.
A．making artificial diamonds didn't seem very difficult at first sight
B．scientists began to try making synthetic diamond in the late 1700s
C．scientists discovered diamonds are a form. of carbon, a common element
D．the discovery of the diamonds' constitute impelled scientists to make a synthetic one
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