英文科學(xué)讀本 第三冊(cè)·Lesson 07 Further Uses of Water

Lesson 07 Further Uses of Water

I wonder what can be the matter with Norah, said Willie, as the two boys came in at the garden gate one afternoon from school.

She was sobbing and crying, while the big tears rolled down her cheeks.

Oh, Fred, she cried, " look at my pretty window boxes. I forgot to water them yesterday, and the sun has been so hot today, that all my beautiful flowers look scorched up and dying. Can we do anything for them ? I am so sorry."

All right, little sister, said Fred, "crying won't do any good, so dry your eyes and let us see what can be done for them. Here, Will, you go and get a pail of water. The best way to revive them is to stand them in water just as they are, pot and all, for about ten minutes."

Fred took the flowerpots down, one by one, and stood them in the water. After giving them a soaking in this way, he put them back in their places, and then it was time to go in to tea. When tea was over, and they got out again, many of the plants were already holding up their heads, and the rest of them looked to be reviving rapidly.

Now, little girl, said Fred, "while we sit here and watch your plants, let us have a chat about them. Do you know why they were drooping and dying?"

I suppose, said Norah, "it was because they were thirsty and wanted water."

Yes, Fred replied, "that's right. But it was worse than that. They were not only thirsty through the great heat; they were dying, because they were actually being starved in the midst of plenty of food."

The soil in the flowerpots contained an abundance of food, of exactly the kind they required, but it was useless to the plants till it had been dissolved by water.

By soaking the pots a few minutes we dissolved some of the substances in the soil, and then the little roots were able to suck up those things in a state of solution.

You know that the root is the feeding organ of every plant. You will now understand that, but for this solvent power of water, no single plant could live and grow.

I have always noticed, said Norah, "how fresh and bright and beautiful the plants in the garden look after a shower of rain."

Yes, said Fred; "they do. But you must remember that it is not the rain itself that does this."

Teacher was very careful to show us that the rainwater is nearly pure, and contains no substances in solution. Such water could not feed the plant.

It is only after it falls, and sinks into the soil, that the rain becomes useful to the plant. It is useful then because it dissolves the plant-food in the soil.

Teacher explained to us, too, said Willie, "that this same rain, after passing through the soil, continues to sink down deep into the earth. It trickles through rocks of various kinds, and dissolves, on its way, all that is soluble."

By and by the same water bubbles up out of the ground again, and forms a spring.

Teacher says this spring water always contains some solid substances or other in a state of solution.

The waters of some springs contain such mineral substances as iron and sulphur in solution. These are known as mineral springs. The waters are used as medicines.

You remember, said Fred, "our talk about the glass of sparkling spring water. Does that spring water contain any substance in solution?"

Yes, it has lime dissolved in it, said Norah. "We cannot see the lime, but we can find it as a thick coating round the sides of the kettle, in which the water is boiled. We call it 'fur'; and we say that the kettle is getting 'furred.'"

Oh, Norah continued, "I remember, too, about the brine springs which supply us with salt for the table. The water of these springs fell at first as rain, and as it sank through the earth it dissolved the salt that was there, and carried it away in solution."

Then, again, said Will, "the sea is salt too, and it gets its salt in the same way."

Teacher says the sea is fed with water by the rivers, which are constantly flowing into it; but the water of all these rivers is fresh, not salt water. It fell in rain from the clouds. It got its salt by dissolving it out of the substance of the earth itself.

SUMMARY

Water feeds the growing plants by dissolving proper food for them out of the soil. Water dissolves many substances out of the earth as it soaks through. It forms mineral springs and brine springs, but all this water falls in rain from the clouds at first.