1."Where there's reek there's heat,"is an old Scottish proverb,and a true one ;for while there may be heat without "reek"or smoke,smoke is never found without heat.
2.Smoke,smoke,smoke-where can we go to escape from it?Look how it rolls in black clouds from the tall factory chimneys,or curls in thinner wreaths above the tops of our houses.In the cities it covers our faces and our clothes with smuts,it blackens or kills our flowers,and even hides the sun from our sight at mid-day.
3.Smoke comes from almost everything that burns,and although these things may be very different,the smoke that comes from them is very much alike.When a lamp or a candle or a gas flame is burning well,you do not see any smoke coming from it,but the smoke is there all the same.
4.Pass a white card through the top of the flame just quickly enough to keep it from being singed.Look at it now,and you will find it slightly blackened with smoke.
Now pass it through the flame again,lower down this time:it is blacker still.So you see there is smoke in the flame of the candle,though very little comes from it.
5.Now let us see what happens when anything burns.Every substance that burns easily contains a great deal of carbon.When we hold a lighted match to any thing of this kind,such as a bit of wood,the little particle.of carbon in it turn hotter and hotter,until a strange thing happens to them:they unite with particles of oxygen from the air,and suddenly disappear!
6.But as the particles of carbon join with the oxygen they become very hot indeed,white-hot,and it is these white-hot bits of carbon that rise up in a stream like a waterfall flowing upwards,and form what we call flame.The heat of the flame warms the particles of carbon near it,and they too join in the dance.
7.But what has all this to do with smoke?Well,some of these little specks of carbon do not find any oxygen to join with-it has all been used up-and so they do not turn white-hot,but sail away in their old form of little black specks of carbon,or soot,or smoke.They have been of no use in giving us light or heat.
8.When a fire is smoking,we may be sure that there is no enough oxygen to make the carbon give out all its light and heat.What it wants is a good draught--more air and more oxygen.This is why we sometimes blow the fire with the bellows,or stir it up with the poker so as to let in more air.
9.Did you ever wonder why smoke rises?It is because the air when heated becomes lighter,and floats upwards through the cold heavy air like a cork set free at the bottom of a basin of water.The colder air from below takes its place,and this also becomes heated and rises;so a constant stream of hot air goes upwards,carrying the smoke along with it.
10.Did you ever see white smoke?Look at the white clouds coming puff,puff,puff from the funnel of that railway engine.They are made of smoke mixed with steam,Each little speck of soot gets a coatin.of moisture from the steam,and so it looks like a white cloud or mist.
11.The same thing often happens with the smoke that hangs over our large towns on a calm day.If the air is very moist,the smoke and the moisture together turn into a thick fog.In London,Glasgow,Manchester,and other manufacturing places,the fog is often so thick that people must use gas light even at mid-day.In the streets they can scarcely see a yard before them.
