英文科學(xué)讀本 第一冊·Lesson 18 Putty—What it is

Lesson 18 Putty—What it is

The other day, said Fred, "we had a chat about putty, and we found out why it is so useful."

Teacher has been telling us today what putty is. Would you like to hear all about it, Norah?

Oh yes, please. said Norah.

Well then, said Fred, "think of the two plastic substances, clay and putty. Clay, you know, is dug out of the earth. It is a mineral. But we don't dig putty out of the ground."

It is made of two substances—whiting and linseed oil.

You know what whiting is. You have seen mother use it to clean the pots and pans. It is only chalk. But can you tell me how we get chalk?

I suppose it is dug out of the ground, like clay and stone and sand, said Norah.

Quite right, said Fred. "It is a mineral. Teacher showed us a piece of chalk, just as it was dug up, but it was mixed with bits of stone and dirt. To make whiting, we must get rid of all this. The chalk is broken up in little pieces, and put into water. When the water is stirred, it looks just like milk. This milky-looking water is poured through a sieve, and all the dirt and stones are kept back. The chalk or whiting sinks to the bottom, and is dried after the water is poured off."

Here is some linseed oil. Father gave it to me. This oil is made from linseed—the seed of the flax plant. You know we get linen from the flax plant.

Pour a drop into your hand. It feels sticky. It is the oil, you see, that makes the putty sticky.

If I drop a little of the oil on this sheet of paper, it will dry very quickly; and water will run off the oily paper, but will not go through it, because the oil makes the paper waterproof.

It is the linseed oil that makes the whiting into pliable, sticky, waterproof putty, and causes it to dry and harden quickly.

SUMMARY

Putty is made of whiting and linseed oil. Whiting is made from chalk, and chalk is dug out of the ground; it is a mineral. Linseed oil is made from linseed, the seed of the flax plant. Linseed oil makes the putty sticky, pliable, and waterproof.