英文科學(xué)讀本 第三冊(cè)·Lesson 21 Mercury

Lesson 21 Mercury

We have had a lesson today on a new substance, Norah, said Fred. "It is a metal, but it is not solid, like iron, copper, lead, or any of those which we have talked about before. It is a liquid."

Teacher showed us some of it in a bottle. It flows about, and can be poured out like water. It is a liquid metal. It is the only liquid metal that exists. Its name is mercury.

I think I have some mercury in a bottle upstairs, said his father. "I will go and bring it down for you; only be very careful with it."

Presently back father came with the bottle of mercury, and they were soon ready to start.

Fred poured some of it into a saucer, and pointed out its silvery white color and its bright metallic lustre.

Teacher says mercury never tarnishes when it is exposed to the air, but always keeps its bright surface, said he.

Now look what happens when I let fall a drop of the mercury on this slate. It breaks up at once into an immense number of tiny round drops. If I tilt the slate ever so slightly, the little drops run about rapidly over the slate.

Then I suppose that is the reason why it is sometimes called quicksilver, said Norah.

Yes, you are quite right, said Fred.

Now, you shall take a saucer in each hand, while I pour the liquid metal into one and water into the other. What do you notice?

I am surprised to find the mercury so heavy, said she.

Yes, said Fred, "it is heavy. It is heavier than any of the metals we have seen, except gold. Teacher says it is nearly fourteen times as heavy as water; gold is nineteen times as heavy as water."

Can you tell me a property which all metals have?

All the metals are fusible, said Norah. "They all melt with heat, although they do not require the same amount of heat."

Gold, silver, copper, iron, and steel are all fusible, said Will, "but they require intense heat before they will become liquid. Lead and tin we can melt for ourselves over the fire. They are more easily fused than any of those metals."

Quite right, said Fred. "But mercury, you see, is a metal—the only metal, which is always melted, always in the liquid form, in this country."

Remember, however, that in some very cold parts of the world mercury always becomes solid in the winter. In its solid state it is malleable, and can be beaten and rolled out like other metals.

I thought it was very curious to see teacher boil the mercury in the tube, as if it were water, said Will. "We saw the liquid metal boil, and we saw the vapor from it condense into tiny little silvery balls, on the cool sides of the tube."

SUMMARY

Mercury is a liquid metal. It flows about, and readily breaks up into tiny drops. It is silvery-white, and has a bright metallic lustre. It is nearly fourteen times as heavy as water.