1.Let us fill a small kettle with water，and place it on the fire.The water will soon begin to boil.After an hour or so we shall find the kettle quite empty，although no one has touched it since it was placed on the fire.
2.What has become of the water which we poured into the kettle？It has all been changed into a vapouror gas，called steam，which has passed out of the mouth of the kettle and mixed with the air in the room.Because the liquid water has changed into vapour，we say that it has evaporated.
3.But we need not put water on the fire to make it evaporate.
Let us place a saucer full of water on the mantel-piece，or out in the garden if the weather is fine.In a few hours the water will have changed into water-vapour and mingled①with the air，and the saucer will be quite dry.We cannot see the water-vapour in①Mingled，mixed together；united.
the air，for it has no colour，and is quite transparent①.The water in the saucer will evaporate much more slowly than that in the kettle，and we cannot see rising from it any of the white wreaths which we usually call steam.
4.The hotter the place is in which we put the water，the more quickly will it evaporate.On a hot，dry，and windy day，water placed in the open air evaporates very quickly indeed.Your mother will tell you that such days are the best for drying clothes that have been washed.The water soon evaporates，and leaves the clothes quite dry.
5.Some liquids evaporate more quickly than others.Alcohol，or spirit of wine，evaporates more quickly than water.Dip one finger into alcohol，and another finger into water，and then wave both in the air.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.
6.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 yourhand.This is the reason why one gets a cold so readily②by sittingin damp clothes.The clothes dry gradually③，but in so doing they rob the body of some of its heat.
7.If you try such liquids as milk and treacle④，you will find thatthey evaporate more slowly than water.I daresay you may have noticed that milk also takes a little longer to boil than water does.
8.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.
①Transparent，that can be seen through.
②Readily，quickly；easily.
③Gradually，by degrees；little by little.
④Treacle，a thick dark liquid like syrup drained off during the refining of sugar.
9.If we leave the stopper out of a bottle full of spirit of wine，for instance①，we shall find，after a few days or weeks，that the bottle is empty，although no one has touched it.The alcohol willhave changed from a liquid into a vapour or gas，and this vapour will have escaped through the open mouth of the bottle.
10.Some solids②，too，can evaporate，though much moreslowly 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.
SUMMARY
Evaporation is changing water into steam.Water evaporates if heated or left in the open air.Alcohol or spirit of wine evaporates more quickly than water，while other liquids，such as milk and treacle，do so more slowly.Damp clothes make one feel cold，as the water evaporating from them takes away heat from the body.To prevent liquids from turning into vapour，they are kept in well-corked bottles.Some solids，such as ice and snow，also evaporate.
【中文阅读】
1．我们找上一个水壶，灌满水，放在火上。很快，水就会沸腾起来。经过一个小时左右，我们会发现水壶已经空空如也。但是水壶放到火上之后，根本没有人动过。
2．那么，我们倒进去的水去了哪里呢？它们变成了水蒸气，经过壶嘴跑了出去，并且与房间里的空气混合在了一起。我们将这种液态水变成水蒸气的过程称为蒸发作用。
①Instance，example.
②Solids，hard and firm bodies.
3．不过呢，我们并不需要将水放在火上才能实现蒸发作用。现在，我们将一碟水放在壁炉架上，如果天气好，也可以放在花园中。几个小时之后，这一碟水就将变成水蒸气与空气混合在一起，而碟子也就变得完全干燥。我们无法看到空气中的水蒸气，因为它没有颜色而且完全透明。与水壶相比，碟子中的水蒸发速度要慢上很多，而且我们也无法观察到通常被称为水蒸气的那种白色气圈。
4．水放的地方越热，蒸发速度就越快。如果遇到炎热、干燥且有风的天气，放置在户外的水很快就会蒸发。妈妈一定会告诉你，这样的天气最适合晾晒刚刚清洗过的衣服。水分将会很快蒸发，而衣服就变得非常干爽。
5．不同液体的蒸发速度存在一定差异：酒精比水的蒸发速度要快上不少。你可以用一根手指沾一些酒精，另一根手指沾上水，然后分别在空气中挥动。在你数到十之前，那根沾有酒精的手指就会变得干燥，而另外一根沾有水的手指，则需要一分多钟才能变干。
6．当这两种液体蒸发之后，你的手指有何感觉？你会感到清凉，因为手指释放了一部分用来蒸发酒精与水的热量。穿着潮湿的衣服，容易感冒，原因就在于此。衣服会逐渐变干，但是在这个过程中，人体的大量热量就被消耗掉了①。
7．用牛奶与糖蜜来做上述的实验，就会发现，它们比水的蒸发速度要慢很多。我相信，你肯定发现了这样一种现象：与水相比，牛奶沸腾所需的时间比水稍微长一点。
8．现在你一定明白了，为什么我们要把液体装在瓶子里，而瓶子还需要盖上严实的瓶盖或者软木塞。这样做就是为了防止液体蒸发或者沾染上灰尘。
9．比如，把一瓶酒精的瓶盖取下，就会发现：虽然没人去碰这个酒瓶，但是经过几天或几周，瓶子一定会变得空空如也。因为酒精会从液体状态变成蒸汽，从瓶子的开口处挥发出去。
10．有些固体也能蒸发，当然了，其速度比液体要慢上许多。冰与雪都是固体；然而，即便是在最为寒冷的日子里，一块冰雪也会逐渐变小。它们没有融化成液态水，而是慢慢变成水蒸气并混入空气之中，我们就看不见了②。
译注
①一切液体的蒸发都会吸热，所以用凉水可以降温，中暑的病人还可以在皮肤上涂抹酒精来治疗。
②严格地说，固体直接变成气体的过程，不是蒸发而是“升华”（sublimation）。冬天晾在户外的衣服会结冰，但冰冻的衣服也会干，就是因为升华作用。
THE CHERRY-TREE AND ITS FRUIT