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Thus by heating liquids we cause them to evaporate, or change into vapours or gases;
因此, 可以看出：我们能够通过加热液体使得它们蒸发, 变成水蒸气或气体；
and by taking away heat from these gases, or cooling them, we turn them into liquids once more.
也能够通过消除气体中的热量或者冷却, 将它们再次变为液体。
We saw, in the Lesson on steam in your last book, that when water changes into water-vapour, it requires a great deal more room.
大家通过上一本书的学习了解到：当水变成水蒸气之后就需要更多空间。
And so, when the water-vapour turns back into liquid water again, it takes up much less room.
那么当水蒸气再次变成液体的时候, 它所占据的空间就会小很多。
It needs seventeen hundred pints of water-vapour or steam to produce one pint of liquid water.
1700品脱的水蒸气只能转化为1品脱的液态水。
It is certain, then, that the particles of the liquid must be very much closer together than the particles of the vapour;
毫无疑问, 水的分子比水蒸气的分子密度要大上很多；
and a pint of the liquid will therefore weigh a great deal more than a pint of the vapour.
所以一品脱的水远比一品脱的水蒸气要重很多。
Now when the particles of any substance are packed closely together, we say that the substance is dense.
不论是什么物质, 如果它的分子紧密地拥挤在一起, 我们就说这种物质密度很大。
So when we cool the steam, and bring its particles close together in the form of water, we are said to condense it, or make it dense;
因此, 当我们冷却水蒸气, 将水蒸气的分子紧压到一起, 转化为液态水时, 我们就是对它进行凝结, 或者说增加它的密度。
and the process of doing this we call condensation.
这个过程就被称作冷凝。
Let us connect the tube which leads from our flask of boiling water with a twisted or spiral piece of glass tubing which is surrounded by cold water.
让我们将来自沸水烧瓶的玻璃管, 连接到冷水之中的弯曲或螺旋状玻璃管之上。
As the steam passes along the inside of this cold spiral tube it is condensed;
当水蒸气沿着清凉的螺旋状玻璃管前进时, 它就被冷凝了；
its particles are brought closer together, and it therefore changes into liquid water, which falls in drops from the outer end of the spiral tube.
随着分子密度的增加, 水蒸气变成了水, 从螺旋状玻璃管的外端流下。
