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  3. "It should be possible to make a precious stone that not only looks like the real thing, but that is the real thing", said a che

"It should be possible to make a precious stone that not only looks like the real thing, but that is the real thing", said a che

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问题     "It should be possible to make a precious stone that not only looks like the real thing, but that is the real thing", said a chemist many years ago. "The only difference should be that one crystal would be made by man, the other by nature."
    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.
选项 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
答案D
解析 本题是主旨题。本段的大意是：科学家们在十八世纪末开始尝试制造人造钻石，他们之所以这样，是因为那时他们发现了一个很重要的科学事实：钻石是碳的一种形式，而碳是一种很普通的元素。一种黑色矿石：石墨—就是用于铅笔里的铅，也是碳构成的。两者的区别仅在于它们的碳原子排列的方式不一样。于是科学家们激情大发，要把便宜且量大的碳改变成稀有、昂贵的钻石。
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