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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：我們能夠通過加熱液體使得它們蒸發, 變成水蒸氣或氣體；
and by taking away heat from these gases, or cooling them, we turn them into liquids once more.
也能夠通過消除氣體中的熱量或者冷卻, 將它們再次變為液體。
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.
大家通過上一本書的學習了解到：當水變成水蒸氣之后就需要更多空間。
And so, when the water-vapour turns back into liquid water again, it takes up much less room.
那么當水蒸氣再次變成液體的時候, 它所占據的空間就會小很多。
It needs seventeen hundred pints of water-vapour or steam to produce one pint of liquid water.
1700品脫的水蒸氣只能轉化為1品脫的液態水。
It is certain, then, that the particles of the liquid must be very much closer together than the particles of the vapour;
毫無疑問, 水的分子比水蒸氣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.
所以一品脫的水遠比一品脫的水蒸氣要重很多。
Now when the particles of any substance are packed closely together, we say that the substance is dense.
不論是什么物質, 如果它的分子緊密地擁擠在一起, 我們就說這種物質密度很大。
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, 當我們冷卻水蒸氣, 將水蒸氣的分子緊壓到一起, 轉化為液態水時, 我們就是對它進行凝結, 或者說增加它的密度。
and the process of doing this we call condensation.
這個過程就被稱作冷凝。
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.
讓我們將來自沸水燒瓶的玻璃管, 連接到冷水之中的彎曲或螺旋狀玻璃管之上。
As the steam passes along the inside of this cold spiral tube it is condensed;
當水蒸氣沿著清涼的螺旋狀玻璃管前進時, 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.
隨著分子密度的增加, 水蒸氣變成了水, 從螺旋狀玻璃管的外端流下。
