Expansion by Heat.
How does heat generally affect substances?
Heat expands them or makes them larger.
Does heat expand all metals?
Yes; all metals are expanded by heat.
When a rod of iron is heated, is it longer or shorter than when cold?
It is longer than when it is cold.
How do we know this?
We know it by measuring the rod when it is cold, and again when it is heated.
Will the rod be larger, as well as longer?
The rod will be larger.
How can we prove this?
The rod, when red-hot, will not go through as small a hole as when it is cold.
How do heat and cold affect most substances?
Heat expands most substances, and cold contracts them.
Do all metals expand alike by heat?
No; some metals expand much more than others.
How does heat expand substances?
Heat pushes the parts or atoms of an object farther from each other, and thus its size is increased.
What does a blacksmith do with a tire before putting it on a wheel?
He heats the tire red-hot.
Why does he heat the tire red-hot?
So that it will be increased in size, and will go on the wheel more easily.
What takes place as the tire cools?
It becomes smaller, and thus binds the parts of the wheel tightly together.
When a fire is made in a room, why does the furniture often make a snapping noise?
Because heat expands the wood, and the particles make a snapping noise upon separating.
Why does a stove make a crackling noise as it grows hot?
The particles of the iron make the noise in expanding.
If a piece of glass be held in the hand, will the glass become warm?
The glass will become as warm as the hand.
What part of the glass will be warmed first?
The part touching the hand will be warmed first.
What part of the glass will be warmed last?
The part farthest from the hand will be warmed last.
Which part of the glass will be expanded first?
The part touching the hand, because it is first warmed.
Which part will be expanded last?
The part farthest from the hand, because it is the last part warmed.
If any other warm substance touch the glass, will the glass be heated in the same manner?
The glass will be heated in the same manner.
What often results from this unequal heating?
The glass is broken.
Why are glass plates or tumblers broken when placed in hot water?
They are broken because the part next to the hot water is expanded more than that farther away.
Why will a cloth dipped in hot water and wrapped around the neck of a bottle loosen its stopper?
Because the heat from the cloth expands the neck of the bottle before it does the stopper, so that the stopper is loosened.
Why do stove-plates often break?
Because they are fitted together in the stove so that they have not room to expand without breaking.
What effect has cold upon substances?
Cold causes them to contract or grow smaller.
Things expand unequally; do they also contract unequally?
They do contract unequally, and in this way may be broken.
Why are lamp chimneys often broken while the lamp is burning?
Because the heat of the flame causes them to expand unequally.
In what other way are they broken?
By a draught of cold air, or a drop of cold water, touching them, thus causing them to contract unequally.
Why are they sometimes broken when the lamp is not burning?
Because a current of cold air from a window or a door, blows upon them.
Does quicksilver expand when heated?
Like other metals, quicksilver expands as it grows warmer, and contracts as it grows cooler.
Is quicksilver in the form of a solid or a fluid?
It is a fluid as we usually see it.
For what is quicksilver used?
It is used for filling the tubes of thermometers.
What is a Thermometer?
It is an instrument used for measuring the degree or quantity of heat in any substance.
How does heat affect the quicksilver?
Heat expands the quicksilver, and causes it to rise in the tube.
How does cold affect the quicksilver?
Cold contracts the quicksilver, and causes it to fall in the tube.
Does heat expand liquids more than solids?
Heat does expand liquids more than solids.
Why are liquids expanded more than solids?
Because the particles of which they are formed are more easily separated or pushed apart by the heat.
If we continue to apply heat to a liquid, what becomes of it?
The liquid is changed into a gas or vapor.
What common example have we of vapor?
Water, when heated, is turned into steam.
Mention some gas.
The air we breathe is a gas.
How does heat affect the air?
Heat warms the air and causes it to expand.
Do solids all expand equally when heated?
No; some solids expand more than others; thus, zinc expands more than iron, and iron more than glass.
Do liquids all expand equally when heated?
No; liquids, although more sensitive to heat, do not expand as equally as solids.
Do gases expand equally when heated?
Yes; gases expand uniformly; thus, 491 cubic inches of any gas, if heated one degree, will become 492 cubic inches.
If one cup be filled with lead, and another cup of the same size with water, which will weigh the more, the lead or the water?
The lead will weigh more than the water.
Which is the heavier substance, lead or water?
Lead is heavier than water.
Why do we say lead is heavier than water?
Because a cup full of lead will weigh more than the same cup fall of water, or any bulk of lead will weigh more than an equal bulk of water.
Why is cork lighter than water?
Because any bulk of cork is lighter than an equal bulk of water; a cup filled with cork will weigh less than when it is filled with water.
When lead is put in water, why does it sink to the bottom?
Because the lead is heavier than an equal bulk of water.
When cork is put in water, why does it rise to the surface?
Because the cork is lighter than an equal bulk of water.
Does heat increase the weight of any substance?
Heat does not increase the weight of any substance.
How do we know this?
Because a piece of iron when cold will weigh as much as when heated red-hot.
When a liquid is heated, does it become lighter or heavier?
It becomes lighter, bulk for bulk, when heated.
Why does a liquid become lighter when heated?
Because the same liquid is expanded and takes up more room, although it has no more weight.
Why will a gallon of cold water weigh more than a gallon of hot water?
Because a gallon of cold water, when heated, will make more than a gallon of hot water.
When do we get the most molasses, by buying it in hot or in cold weather?
We get the most by buying it in cold weather, because a gallon bought then will make more than a gallon when the weather becomes warmer.
Does heat expand the air and make it lighter?
Heat does expand the air and make it lighter.
What does the air do when heated?
It ascends or rises up, because it is lighter, and the cold or heavier air falls to take its place.
What part of a room, in which there is fire, is the warmest?
The part next to the ceiling is the warmest, because the heated air always ascends.
Why does a soap-bubble ascend?
Because it is filled with heated air from the lungs, and is, therefore, lighter than the air around it.
Why do balloons ascend?
Because they are filled with a gas lighter than the air around them.
Why does a chestnut split open when roasting?
Because the air in it is expanded by the heat, so that it bursts the shell.
Why does the chestnut not split open when a hole is made in the shell?
Because the air can then escape as it expands, without bursting the shell.
What becomes of the air in an apple, when the apple is roasted?
The air, upon being heated, bursts through the peel of the apple, carrying the juice with it.
Why does an apple become soft when roasted?
Because the air in the cells of the apple expands, and breaks those cells, so that the apple becomes soft.
What part of the apple first becomes soft?
The outside, because it is first heated.
Why do all fruits and vegetables become soft when cooked?
Because the heat expands the air in them, and thus breaks up their cells, so that they become soft.
Why does wood make a snapping noise when burning?
Because the air in the cells of the wood bursts them apart, thus making the noise.
Why are sparks of fire thrown out?
Because the heated air bursts the cells with such force as to throw off small pieces of the burning wood.
What kinds of wood snap the most?
The coarse-grained kinds, like chestnut; while the finer-grained kinds, like walnut, seldom snap much.
Why does dry wood snap more than green wood?
Because the sap in the pores of the green wood dries up as the wood becomes dry, and its place is filled with air, so that there is more air in dry wood than in green wood.
Why does smoke rise in a chimney?
Because the air in the chimney is heated by the fire, and as the air rises, it carries the smoke with it.
Why does a chimney smoke when the fire is first kindled?
Because the cold walls of the chimney cool the heated air so rapidly as to prevent its rising to the top, and the smoke then sinks back into the room.
How are houses heated with hot air?
By having the fires made in the cellar, so that the air when heated, may ascend through pipes to the different parts of the building.
Is there any substance that does not contract by cold?
Yes; water, when near freezing, does not contract by cold.
What takes place with the water?
When it is reduced nearly to the freezing point, it begins to expand, and when it freezes, it expands still more.
How much does water expand by freezing?
It expands about one-seventh of its bulk. That is, seven gallons of water will make eight gallons of ice.
Does freezing water expand with much force?
Yes; it expands with great force.
Why are vessels containing water often broken during a cold night?
As the water in them freezes, it expands and breaks the vessels.
Why do lead pipes and iron pipes often burst during the winter?
Because the water in them is permitted to freeze, and as there is not room for it to expand, the pipes are burst.
Is ice heavier or lighter than water?
Ice is lighter than the same bulk of water.
How much lighter is ice than water?
Eight gallons of ice weigh no more than seven gallons of water.
Does the ice protect the water beneath it from freezing?
Ice does protect the water from freezing, to a very great extent.
If ice were heavier than water, what would result?
The ice would sink as rapidly as formed, and our streams would, every winter, freeze to the bottom, thus destroying the fish and other creatures living in them. In this, as in many other ways, we may learn the lesson, that in the creation of the world, God wisely made all things to serve some useful purpose.