英國學(xué)生科學(xué)讀本 Lesson 88 冷凝(1)

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第88課 冷凝

When the water in a kettle boils, it boils first at the bottom.

當(dāng)水壺中的水沸騰時(shí), 首先開始沸騰的是底部的水。

We cannot see this in a kettle, because the kettle is made of iron.

我們無法看到水壺中的情況, 因?yàn)樗氰F做的。

Let us take a flask or bottle made of thin glass, and fill it half full of water.

我們拿起一個(gè)輕薄的玻璃燒瓶或瓶子, 然后裝入半瓶水。

We will set this flask on an iron stand, and under it we will place a spirit-lamp—that is, a lamp which burns alcohol or spirit of wine.

將燒瓶固定在鐵架子上, 然后在下面放一個(gè)酒精燈, 也就是燃燒酒精或者烈酒的燈。

Soon little bubbles appear on the sides of the warm flask.

很快, 溫?zé)岬臒勘谏暇蜁?huì)出現(xiàn)氣泡。

These are bubbles of the air which was dissolved in the water, and which the heat causes to expand and rise to the top.

這些溶于水的氣泡在熱量的作用下體積不斷增大, 最終浮到上方。

As the water gets hotter, we see larger bubbles form on the bottom of the glass flask.

當(dāng)水變得更熱時(shí), 我們便能看到玻璃燒瓶底部出現(xiàn)了許多更大的氣泡。

These bubbles are full of water-vapour, or steam as we call it.

這些氣泡含有大量的水蒸氣。

Soon these bubbles begin to rise to the top of the water, where they burst.

很快, 這些氣泡全部漂浮到了上面, 然后破裂。

Then we say that the water boils.

這時(shí), 我們就判斷說, 水沸騰了。

If we now fit into the neck of the flask a cork through which a glass tube passes,

這時(shí), 如果我們?cè)跓款i部放入一個(gè)中間裝了玻璃管的木塞,

we shall see a jet of steam or water-vapour rushing out of the upper end of the tube.

就會(huì)看到一股蒸汽從玻璃管的上方噴涌而出。

Let us hold a cold slate in the way of the water-vapour as it escapes. What do we see?

隨后, 我們用一塊冰冷的石板擋在蒸汽前方。你會(huì)看到什么?

At once the slate is covered with thousands of tiny drops of liquid water.

很快, 石板上就會(huì)出現(xiàn)成千上萬顆小水珠。

The cold slate has taken heat away from the water-vapour;

這塊冰冷的石板吸走蒸汽的熱量;

and as soon as this is done, the vapour returns to its old state of a liquid.

這過程一完成，蒸汽又變成了原來的液體水了。

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