英國學生科學讀本 Lesson 70 蒸發(fā)作用(2)

The finger which is wet with alcohol will be dry before you can count ten, while the finger which is wet with water may take a minute or more to dry.

在你數(shù)到十之前, 那根沾有酒精的手指就會變得干燥, 而另外一根沾有水的手指, 則需要一分多鐘才能變干。

How do your fingers feel after the two liquids have evaporated? They feel cold; for the heat which was needed to make both the alcohol and the water evaporate has been taken chiefly from your hand. This is the reason why one gets a cold so readily by sitting in damp clothes. The clothes dry gradually, but in so doing they rob the body of some of its heat.

當這兩種液體蒸發(fā)之后, 你的手指有何感覺? 你會感到清涼, 因為手指釋放了一部分用來蒸發(fā)酒精與水的熱量。穿著潮濕的衣服, 容易感冒, 原因就在于此。衣服會逐漸變干, 但是在這個過程中, 人體的大量熱量就被消耗掉了。

If you try such liquids as milk and treacle, you will find that they evaporate more slowly than water. I daresay you may have noticed that milk also takes a little longer to boil than water does.

用牛奶與糖蜜來做上述的實驗, 就會發(fā)現(xiàn), 它們比水的蒸發(fā)速度要慢很多。我相信, 你肯定發(fā)現(xiàn)了這樣一種現(xiàn)象：與水相比, 牛奶沸騰所需的時間比水稍微長一點。

Now you can tell why liquids are kept in bottles, and why the bottles are fitted with good stoppers, or with corks. It is to prevent the liquids from evaporating, as well as to keep dust from them.

現(xiàn)在你一定明白了, 為什么我們要把液體裝在瓶子里, 而瓶子還需要蓋上嚴實的瓶蓋或者軟木塞。這樣做就是為了防止液體蒸發(fā)或者沾染上灰塵。

If we leave the stopper out of a bottle full of spirit of wine, for instance, we shall find, after a few days or weeks, that the bottle is empty, although no one has touched it. The alcohol will have changed from a liquid into a vapour or gas, and this vapour will have escaped through the open mouth of the bottle.

比如, 把一瓶酒精的瓶蓋取下, 就會發(fā)現(xiàn)：雖然沒人去碰這個酒瓶, 但是經(jīng)過幾天或幾周, 瓶子一定會變得空空如也。因為酒精會從液體狀態(tài)變成蒸汽, 從瓶子的開口處揮發(fā)出去。

Some solids, too, can evaporate, though much more slowly than liquids. Ice and snow are solids; and yet lumps of both ice and snow get smaller and smaller in even the driest and the coldest weather. They slowly change into water-vapour without first melting into liquid water, and this vapour mingles with the air and is lost to our sight.

有些固體也能蒸發(fā), 當然了, 其速度比液體要慢上許多。冰與雪都是固體;然而, 即便是在最為寒冷的日子里, 一塊冰雪也會逐漸變小。它們沒有融化成液態(tài)水, 而是慢慢變成水蒸氣并混入空氣之中, 我們就看不見了。

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