英文科學(xué)讀本 第六冊(cè)·Lesson 06 Nature of an Element

Lesson 06 Nature of an Element

The other day I tried to make clear to you the meaning of the term compound, said Mr. Wilson, "and we must go back this morning to the experiments I showed you then. In our first experiment we made one compound body— red oxide of mercury—resolve itself into two distinct substances—the liquid metal, mercury, and a gas, oxygen.

No one has ever been able, by any treatment, to split up either of these substances into simpler kinds of matter. It is impossible to get anything from oxygen but oxygen, and it is equally impossible to get anything from mercury but mercury. Hence we say that oxygen and mercury are elements. In our second experiment we separated chalk into two distinct substances—lime and carbonic acid gas. The solid lime can be further split up into oxygen and a metal called calcium. This calcium, which is a metal somewhat resembling sodium, cannot, by any kind of treatment, be made to yield anything but calcium. Hence we say that calcium is an element, and lime is an oxide of calcium.

The other constituent of the chalk—carbonic acid gas—is, as we already know, a compound in itself. It is composed of the solid substance, carbon, and the element, oxygen. Carbon is a simple body, and will yield nothing but carbon. It cannot be split up or separated into anything else. Thus we know that carbon is an element. If you will now carry your mind back to some of our former lessons, I think you will be able to remember a very simple-looking substance, and, moreover, one of the commonest substances in nature, which is a compound, formed of two distinct bodies."

I suppose you mean water, sir, said Fred, "for I remember that water is formed of the two gases, hydrogen and oxygen. Hydrogen is an inflammable gas, and when it burns in oxygen or in the air, the product of the burning is water. Water, therefore, must be a compound body, made of the two substances, hydrogen and oxygen."

Yes, Fred, you are quite right; water was the very body I had in my thoughts. Now, as regards one of its constituents— oxygen—we already know that it is an element. Hydrogen, likewise, is a body in its simplest form. Nothing can, by any means, be got from hydrogen but hydrogen; we therefore place it among the elements. The chemist has been able, by experimenting on various substances—solid, liquid, and gaseous—which exist in, on, and around the earth, to find about sixty-four distinct elements or simple bodies. That is to say, the earth and all it contains are built up of these sixty-four elements.

Some of these elements, such as oxygen, hydrogen, nitrogen, and chlorine, are gases; mercury is a liquid, but most of them are solids. Among the solid elements, iron, silver, gold, copper, tin, lead, zinc are metals; carbon, sulphur, and phosphorus are known as non-metals. In all there are forty-nine metallic elements, and fifteen non-metallic elements.

These sixty-four elements combine to form compounds much in the same way as the twenty-six letters of our alphabet combine to form words. Nearly every word we use is a compound of two or more letters, and the letters make totally different words according to the manner in which they are combined. Just in a similar way the chemical elements may be called the alphabet of chemistry, and they form various compounds as they vary in their mode of combining. Thus, we might say that the red oxide of mercury is like a word of two letters—mercury and oxygen. Water, a compound of hydrogen and oxygen, and carbonic acid gas, a compound of carbon and oxygen, are two similar words. Chalk would then represent a word of three letters— calcium, carbon, and oxygen; and slaked lime—calcium, hydrogen, and oxygen—would be another similar word of three letters.

As we learn to read and understand these words better, we shall find that some of them are very long, and, like the hard words in our books and newspapers, contain a great many letters.