英國學(xué)生科學(xué)讀本 Lesson 88 冷凝(3)

When we change a liquid into vapour, and cool this vapour till it is liquid again,

將水加熱成水蒸氣, 然后對(duì)其進(jìn)行冷卻直至再次液化,

we are said to distil the liquid, and the apparatus for doing this is called a still.

這個(gè)過程就是對(duì)液態(tài)水進(jìn)行蒸餾, 而它所需要的設(shè)備就叫做蒸餾器。

You see in the picture a simple form of still.

通過這種方法,

By means of it we can turn salt water into fresh.

就能夠?qū)⒑宣}分的水轉(zhuǎn)化為淡水。

The salt itself does not turn into vapour, and when we cool the vapour of salt water we get perfectly fresh water.

而這其中的鹽分不會(huì)轉(zhuǎn)化為水蒸氣, 我們對(duì)這種水進(jìn)行冷卻, 就可以得到純凈的淡水。

Our own breath contains water-vapour.

我們的呼吸中就帶有水蒸氣。

We have only to breathe upon some cold object, such as a looking-glass, to condense the vapour in our breath.

只需朝著梳妝鏡這樣清涼的物體呼上一口氣便能夠冷凝我們呼吸中的水蒸氣。

The mist which we see upon the cold glass consists of thousands of tiny particles of water.

我們?cè)谇鍥龅牟Ａ峡吹降哪菍铀F包含有成千上萬顆小水珠。

On a frosty morning the cold air condenses the water-vapour in our breath as soon as it leaves the mouth, and makes it look like a puff of steam;

在嚴(yán)寒的清晨, 當(dāng)水蒸氣離開我們嘴巴的瞬間就會(huì)被冰冷的空氣冷凝, 形成一股蒸汽團(tuán);

so that each child looks like a little steam-engine, as he runs along the street on his way to school.

如此一來, 當(dāng)孩子們?cè)诮值郎媳寂苤巴鶎W(xué)校的時(shí)候, 每個(gè)人都像是一臺(tái)蒸汽機(jī)。

The little white clouds which come in puffs from the engines on the railway, or which rise from the kettle, or from our breath,

火車蒸汽機(jī)與我們的呼吸所噴出的白色蒸汽團(tuán)

are not made of true steam or water-vapour at all.

并非是真正的水蒸氣。

They really consist of a great many little specks of condensed water.

這其中實(shí)際上包含有很多冷凝水微粒。

We call them steam, but true steam or water-vapour cannot be seen.

我們稱之為水蒸氣, 然而, 肉眼根本無法看到真正的水蒸氣。

If you look quite close to the top of an engine's funnel, or to the spout of a kettle which is boiling on the fire,

仔細(xì)觀察蒸汽機(jī)煙囪的頂部或者火焰上正在沸騰的水壺噴口,

you will see a clear space between it and the white cloud.

就會(huì)發(fā)現(xiàn)它與白霧之間有一片明顯的空隙。

This clear space is filled with the true steam or water-vapour.

這片空隙就充滿了真正的水蒸氣。

Only after the cold air has condensed and changed the true vapour into little particles of water, or water-dust, can it be seen.

只有當(dāng)清冷的空氣對(duì)真正的水蒸氣進(jìn)行冷凝, 將其變?yōu)榧?xì)小的水分子或者水霧以后, 我們才能看到這種物質(zhì)。

This water-dust is what we commonly call steam.

這種水霧就是人們常說的蒸汽。

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