英文科學讀本 第二冊·Lesson 37 Zinc

Lesson 37 Zinc

Father has given me these pieces of zinc, said Fred, "so suppose we have a chat about zinc tonight.

Let us begin with this piece. It looks new, and has a bright surface. We may say that zinc is a bluish-white metal, with a high metallic lustre. Now look at this piece. Can we call this bright?"

No, said Will and Norah together, "it is dull and tarnished."

It is not only tarnished, said Fred, "it is rusted. There is a thin coating of rust on the surface. But teacher asked us to remember that, when zinc once becomes covered with a thin coat of rust, it will not rust any further. The rust does not eat into the metal, as it does into iron. Take it in your hand, Norah, and scrape it lightly with the knife, and you will find it quite bright inside."

Norah did so, and found it just as Fred said.

But I say, Fred, she cried, "how light it seems."

Yes, said Fred, "it is light. It is the lightest of all the metals.

This piece, he added, "is sheet zinc. How was that made?"

It was rolled or hammered out, said Norah, "so zinc must be malleable."

Yes, said Fred, "it is like lead and tin in this respect. And, like them too, it is not good for making wire. It is neither ductile nor tenacious."

It is mostly used as sheet zinc. The reasons are that it is malleable, and can be easily rolled out; it is lighter and harder than lead, and, at the same time, cheaper, and it bends easily. It is largely used for the roofs and gutters of houses, and for rainwater pipes, as well as for baths, cans, and vessels of all kinds for holding water. The reason is that water and air do not rust zinc, except on the surface."

Do you know, Norah, that zinc saws are always used for sawing up blocks of salt? said Fred. "Iron or steel saws would rust, but zinc does not rust.

Now look at mother's new pail. It looks exactly like zinc; it is the colour of zinc. But it is not zinc. It is made of iron. We call it galvanized iron. It was made just as the 'tinned ware' was made. The iron was dipped into melted zinc, and this formed a coat all over it, to keep the iron from rusting."

SUMMARY

Zinc is a bluish-white metal. It rusts very slightly, and only on the surface. It is the lightest of the metals. It is malleable. Sheet-zinc is used for many purposes, but it is neither ductile nor tenacious. Iron that has been dipped in melted zinc is called galvanised iron. It will not rust.