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When we change a liquid into vapour, and cool this vapour till it is liquid again,
将水加热成水蒸气, 然后对其进行冷却直至再次液化,
we are said to distil the liquid, and the apparatus for doing this is called a still.
这个过程就是对液态水进行蒸馏, 而它所需要的设备就叫做蒸馏器。
You see in the picture a simple form of still.
通过这种方法,
By means of it we can turn salt water into fresh.
就能够将含有盐分的水转化为淡水。
The salt itself does not turn into vapour, and when we cool the vapour of salt water we get perfectly fresh water.
而这其中的盐分不会转化为水蒸气, 我们对这种水进行冷却, 就可以得到纯净的淡水。
Our own breath contains water-vapour.
我们的呼吸中就带有水蒸气。
We have only to breathe upon some cold object, such as a looking-glass, to condense the vapour in our breath.
只需朝着梳妆镜这样清凉的物体呼上一口气便能够冷凝我们呼吸中的水蒸气。
The mist which we see upon the cold glass consists of thousands of tiny particles of water.
我们在清凉的玻璃上看到的那层水雾包含有成千上万颗小水珠。
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;
在严寒的清晨, 当水蒸气离开我们嘴巴的瞬间就会被冰冷的空气冷凝, 形成一股蒸汽团；
so that each child looks like a little steam-engine, as he runs along the street on his way to school.
如此一来, 当孩子们在街道上奔跑着前往学校的时候, 每个人都像是一台蒸汽机。
The little white clouds which come in puffs from the engines on the railway, or which rise from the kettle, or from our breath,
火车蒸汽机与我们的呼吸所喷出的白色蒸汽团
are not made of true steam or water-vapour at all.
并非是真正的水蒸气。
They really consist of a great many little specks of condensed water.
这其中实际上包含有很多冷凝水微粒。
We call them steam, but true steam or water-vapour cannot be seen.
我们称之为水蒸气, 然而, 肉眼根本无法看到真正的水蒸气。
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,
仔细观察蒸汽机烟囱的顶部或者火焰上正在沸腾的水壶喷口,
you will see a clear space between it and the white cloud.
就会发现它与白雾之间有一片明显的空隙。
This clear space is filled with the true steam or water-vapour.
这片空隙就充满了真正的水蒸气。
Only after the cold air has condensed and changed the true vapour into little particles of water, or water-dust, can it be seen.
只有当清冷的空气对真正的水蒸气进行冷凝, 将其变为细小的水分子或者水雾以后, 我们才能看到这种物质。
This water-dust is what we commonly call steam.
这种水雾就是人们常说的蒸汽。
