药学英语课文5

LESSON FIVE Chemistry and Matter

Why study chemistry? An important reason is indicated in the foregoing statement by Benjamin Franklin—it is through chemistry and her sister sciences that the power of man, of mind, over matter is obtained. Nearly two hundred years ago Franklin said that science was making rapid progress. We know that the rate of progress of science has become continually greater, until now the world in which we live has been greatly changed, through scientific and technical progress, from t hat of Frank1in’s time.

Science plays such an important part in the modern world that no one can now feel that he understands the world in which he lives unless he has an understanding of science.

The science of chemistry deals with substances. At this point in the study of chemistry we shall not define the word substance in its scientific sense, but shall, assume that you have a general idea of what the word means. Common examples of substances are water, sugar, salt, copper, iron, oxygen-you can think of many others.

A century and a half ago it was discovered by an English chemist, Sir Humphry Davy, that common salt can be separated, by passing electricity through it, into a soft, silvery metal, to which he gave the named sodium, and a greenish-yellow gas, which had been discovered some time earlier, named chlorine. Chlorine is a corrosive gas, which attacks many metals, and irritates the mucous membranes of the nose and throat if it is inhaled. That the substance salt is composed of a metal (sodium) and a corrosive gas (chlorine) with properties quite different from its own properties is one of the many surprising facts about the nature of substances that chemists have discovered.

A sodium wire will burn in chlorine, producing salt/. The process of combination of sodium and chlorine to form salt is called a chemical reaction. Ordinary fire also involves a chemical reaction, the combination of the fuel with oxygen in the air to form the products of combustion. For example, gasoline contains compounds of carbon and hydrogen, and when a mixture of gasoline and air burns rapidly in the cylinders of an automobile a chemical reaction takes place, in which the gasoline and the oxygen of the air react to form carbon dioxide and water vapor (plus a small amount of carbon monoxide), and at the same time to release the energy that moves the automobile.

Carbon dioxide and carbon monoxide are compounds of carbon and oxygen, and water is a compound of hydrogen and oxygen.

Chemists study substances in order to learn as much as they can about their properties (their characteristic qualities) and about the react ions that change them into other substances. Knowledge obtained in this way has been found to be extremely valuable. It not only satisfies man’s curiosity about himself and about the world in which he lives, but it also can be applied to make the world a better place to live in, to make people happier by raising their standards of 1ivng, ameliorating the suffering due to ill health, and enlarging the sphere of their activities.

Let us consider some of the ways in which knowledge of chemistry has helped man in the past and may help him in the future.

It was discovered centuries ago that preparations could be made from certain plants, such as poppies and coca, which, when taken by a human being, serve to deaden pain (are analgesics).

From these plants chemists isolated pure substances, morphine and cocaine, which have the pain deadening property. These substances have, however, an undesirable property, that of