英文科學(xué)讀本 第二冊·Lesson 39 Silver

Lesson 39 Silver

You remember, Norah, that silver and gold do not rust?

Oh yes, said Norah. "We call them precious metals."

I want you to look at mother's silver spoon. What can you tell me about it?

It is white, said Norah, "and has a very high polish."

Yes, said Fred, "and now let us put the spoon by the side of these pieces of tin and zinc. The whiteness of the silver is not the yellowish-white of the tin, nor the bluish-white of the zinc. Silver is pure white.

I must not let you scratch mother's nice spoon, he added, "but you could easily do it with a knife, for silver is a very soft metal. Pure silver would not be fit for use. It is too soft and would wear away. This spoon itself is not all silver; neither is this shilling. Some copper is always mixed with the silver to make it hard enough."

Don't let us forget those thin leaves of silver that teacher showed us, said Will. "Why, they were so thin you could blow them away, Norah. They were ever so much thinner than the tin-foil. You know that a thousand leaves of tin-foil, one on the other, make a pile an inch high. But you would want just ten thousand of these silver leaves to make a pile that height."

Then, said Norah, "what a very malleable metal silver must be."

It is, said Fred. "Teacher says it is more malleable than any of the common metals. It is so easily malleable, that it can be beaten into any shape, for making spoons, forks, trays, cups, tea and coffeepots, and many other things for use and ornament, as well as the money, with which we buy what we want.

Look now at this very thin silver wire, added Fred. "I pulled it out of an old piece of fringe. What do you learn by looking at the wire, Norah?"

I learn, replied his sister, "that silver must be very ductile, or it could not be drawn out into fine wire like this."

Quite right, said Fred. "This silver wire is used for making lace and fringe.

We said just now that silver does not rust, he went on, "but the fumes of our fires and gas will soon cause silver to tarnish. Sulphur too will quickly tarnish it, and turn it dull and black, like a dirty piece of lead. But a rub with the leather soon cleans it again, and brings back its beautiful white lustre."

SUMMARY

Silver is a pure-white metal, with a very high, metallic lustre. It does not rust. It is a precious metal. It is very malleable, ductile, and tenacious. It is made into money, and many beautiful articles for use and ornament.