英文科学读本 第二册·Lesson 12 Soap

Lesson 12 Soap

I didn't think, said Willie, "that greasy oil bottle and the soda could have anything to do with soap. Did you, Fred?"

No, said Fred, "I didn't. Suppose we have our lesson all over again now."

As soon as tea was over Fred said, "Do you remember that greasy oil-bottle, Norah?"

Oh yes, said Norah. "The soda dissolved the oil, although the water would not dissolve it."

Now look, said Fred; "this bottle is half-full of oil. Smell it and see that it is oil. I have got here a strong solution of soda. What does that mean?"

A solution of soda is some soda dissolved in water, said Norah. "I suppose you call it a strong solution, because you have put a lot of soda in it."

Now I will fill the bottle up with the solution, said Fred, "and well give it a good shaking. Tell me what you see."

The oil seems to be mixing with the Soda, said Norah.

Quite right, said Fred. "If I shake it a little more, the soda will dissolve all the oil. It will form a new substance.

We will stand it down for a minute or two and let it rest. Look at the bottle now. The watery part of the mixture is at the bottom, a new substance is floating on the top. This is not oil, but oil dissolved in soda.

Let us take some of it out and rub it in our hands. It is not greasy or oily now. It is soft and smooth.

It feels just like soap, said Norah, as she rubbed her hands.

So it does, said Fred; "and it is soap, although it is not hard soap fit for use. It contains a great deal of water.

How could we get rid of the water in it, Norah?

I suppose, said Norah, "we should have to boil it."

Quite right, said both the boys. "When the water boils away, the soap becomes solid. And now, Norah, you know how soap is made."

It is not always made of oil, added Fred. "Tallow, suet, fat, and grease of all kinds are used to make soap."

SUMMARY

Soda dissolves tallow, suet, fat, oil, and grease of all kinds, and makes soap.