Q. Why is a theatre dangerous, during a thunder-storm?
A. Because the crowd assembled there, and the great vapour arising from so many living bodies, render a theatre an excellent conductor of lightning.
Q. Why is a flock of sheep in greater danger than a smaller number?
A. Because each sheep is a conductor of lightning, and the greater the number, the better its conducting power; besides, the vapour arising from a flock of sheep increases its conducting power, and its danger.
Q. Why is a herd of cattle in danger during a storm?
Q. If a person be abroad in a thunder-storm, what place is the safest?
A. Any spot about 20 or 30 feet from some tall tree or building; unless that spot be near to running water.
Q. Why would it be safe to stand 20 or 30 feet from some tall tree, in a thunder-storm?
A. Because the lightning would always choose the tall tree as a conductor, rather than the shorter man; and he would not be sufficiently near the tree, to be injured by the electric current passing down it.
Q. If a person be in a carriage in a thunder-storm, in what way can he travel most safely?
A. He should not lean against the carriage; but sit upright, without touching any of the four sides.
Q. Why should not a person lean against the carriage in a storm?
Q. If a person be in a house during a thunder storm, what place is safest?
A. Any room in the middle story. The middle of the room is best; especially if you place yourself on a mattrass, bed, or hearth-rug.
Q. Why is the middle story of a house safest in a thunder-storm?
A. Because (even if the fluid struck the house), its strength would be exhausted before it reached the middle story.
Q. Why is the middle of the room more safe, than any other part of it, in a thunder-storm?
A. Because, if the lightning came into the room at all, it would come down the chimney or walls of the room; and therefore, the further distant from these, the better.
Q. Why is a mattrass bed, or hearth-rug a good security against injury from lightning?
Q. Is it better to be wet or dry during a storm?
A. To be wet: if a person be in the open field, the best thing he can do, is to stand about 20 feet from some tree, and get completely drenched to the skin.
Q. Why is it better to be wet than dry?
A. Because the wet clothes would form a far better conductor than the fluids of our body; and, lightning would roll down the wet clothes, without touching our body at all.
Q. What is the safest thing a person can do to avoid injury from lightning?
A. He should draw his bedstead into the middle of his room, commit himself to the care of God, and go to bed; remembering that our Lord has said, “The very hairs of your head are all numbered.”
Q. What is a lightning-conductor?
A. A metal rod fixed in the earth, running up the whole height of a building, and rising in a point above it.
Q. Why is copper wire better than iron?
A. 1st—Because copper is a better conductor than iron:
2ndly—It is not so easily fused or melted: and
3rdly—It is not so much injured by weather.
Q. What is the good of a lightning-conductor?
A. Metal wire is a most excellent conductor; and as the lightning makes choice of the best conductors, it would run down the metal wire, rather than the bricks of the building.
Q. How far will the beneficial influence of a lightning-conductor extend?
A. It will protect a circumference all round, the diameter of which is (at least) 4 times as long as that part of the rod, which rises above the building.
Q. Give me an example.
A. If the rod rise 2 feet above the house, it will protect the building for (at least) 8 feet all round.
Q. Why are not lightning-conductors more generally used?
Q. How can lightning-conductors be productive of harm?
A. If the rod be broken by weather or accident, the electric fluid (being obstructed in its path) will rend the building into fragments.
Q. Is there any other evil to be apprehended from a lightning rod?
A. Yes; if the rod be not big enough to conduct the whole current to the earth, the lightning will fuse the metal, and greatly injure the building.
Q. How stout is it needful for the copper wire to be, that it may conduct the fluid safely to the earth?
A. It should be (at least) one inch in diameter.
Q. Why does lightning sometimes knock down houses and churches?
A. The steeple, or chimney is first struck; the lightning then darts to the iron bars and cramps employed in the building; and (as it darts from bar to bar) shatters to atoms the bricks and stones, which oppose its progress.
Q. Can you tell me how St. Bride’s Church (London) was nearly destroyed by lightning, about 100 years ago?
A. The lightning first struck the metal vane, and ran down the rod; it then darted to the iron cramps, employed to support the building; and (as it flew from bar to bar) smashed the stones of the church, which lay between.
Q. Why did the lightning fly about from place to place, and not pass down in a straight course?
A. Because it always takes in its course the best conductors; and will fly both right and left, in order to reach them.
Q. Why does lightning turn milk sour?
A. Lightning causes the gases of the air (through which it passes) to combine, and thus produces a poison, called nitric acid; some small portion of which, mixing with the milk, turns it sour.[2]
(N. B. Sometimes, the mere heat of the air, during the storm, turns milk sour.)
[2] The air is composed of two gases, called oxygen and hydrogen, mixed together, but not combined. If oxygen is combined with nitrogen, it produces five deadly poisons, viz.—nitrous oxide, nitric oxide, hyponitrous acid, nitrous acid, and nitric acid, according to the proportion of each gas in the combination.
Q. What is the difference between combining and mixing?
Q. Give me an example.
A. If different coloured sands be shaken together in a bottle, the various grains will mix together, but not combine: but if water be poured on quick lime, the water will combine with the lime, and not mix with it.
Q. Why are the different grains of sand said to be mixed, when they are shaken together?
A. Because they are mingled together, but the property of each grain remains the same as it was before.
Q. Why is water poured on lime, said to combine with it?
A. Because the properties, both of the water and the lime, are altered by the mixture: the lime alters the character of the water, and the water alters the character of the lime.
A. They only mix together, as grains of sand would do, when shaken in a bottle. When oxygen and nitrogen combine, they do not constitute air, but acid poisons.
Q. Why does lightning turn beer sour, although contained in a close cask?
A. If the beer be new, and the process of fermentation not complete, lightning will so accelerate the process, as to turn the liquor sour.
Q. Why is not old beer and strong porter made sour by lightning?
A. Because the fermentation is complete already; and, therefore, is not affected by electrical influence.
Q. Why is metal sometimes fused by lightning?
A. Because the dimension of the metal is too small, to afford a path for the electric current.
Q. Why does lightning purify the air?
A. For two reasons: 1st—Because the oxygen and nitrogen of the air combine,[3] and produce “nitric acid:”
2ndly—Because the agitation of the storm stirs up the air.
[3] The oxygen and hydrogen are not combined, but simply mixed in the ordinary air; but the lightning causes the mixed elements to combine.
Q. How does the production of nitric acid purify the air?
A. Nitric acid acts very powerfully in destroying exhalations, arising from putrid vegetable and animal matters.
Q. Why is lightning more common in summer and autumn, than in spring and winter?
A. The heat of summer and autumn produces great evaporation; and the conversion of water to vapour, always develops electricity.
Q. Why does a thunder-storm generally follow very dry weather, and rarely succeeds continued wet?
A. The clouds are always charged with electricity; but dry air (being a non-conductor), will not conduct the surplus fluid from the clouds to the earth: so it violently rends the dry air with a flash, in order to relieve the cloud, and reach the earth.
Q. What is the general direction of a thunder-storm?
Q. Why is electricity excited by friction?
A. Electricity, like heat, exists in all matter; but is often in a latent state: friction disturbs it, and brings it into active operation. (see p. 31.)
Q. Why is a tree sometimes scorched by lightning, as if it had been set on fire?
A. Lightning scorches it by its own positive heat, just the same as fire would.
Q. Why is the bark of a tree often ripped quite off by a flash of lightning?
A. As the lightning runs down the tree, it develops the latent heat so rapidly, that it carries the bark of the tree along with it, while it seeks to escape.
Q. Why are boughs of trees broken off by lightning?
A. The mechanical force of lightning is very great; and when the flash strikes a tree, it will often break off the boughs by the force with which it strikes against it.
Q. Why is an electric shock felt most at the elbow joint?
A. Because the path of the fluid is obstructed by the joint: and the shock felt at the elbow is caused by the fluid leaping from one bone to another.
CHAPTER III.
Q. What is the third chief source of heat?
A. Chemical Action.
Q. What is meant by chemical action being the source of heat?
A. Many things, when their chemical constitution is changed, (either by the abstraction of some of their gases, or by the combination of others not before united,) evolve heat, while the change is going on.
Q. Explain by illustration what you mean.
A. Water is cold, and sulphuric acid is cold; but if these two cold liquids be mixed together, they will produce boiling heat.
Q. Why will cold water, mixed with sulphuric acid, produce heat?
A. Because water (being lighter than sulphuric acid), is condensed by the heavier liquid; and its heat is squeezed out, as water from a sponge.
Q. Why does cold water, poured on lime, make it intensely hot?
Q. Where does the heat come from?
A. It was in the water and lime before; but was in a latent state.
Q. Was there heat in the cold water and lime, before they were mixed together?
A. Yes. All bodies contain heat; the coldest ice, as well as the hottest fire.
Q. Is there heat even in ice?
Q. How do you know there is heat, if you cannot perceive it?
Q. What becomes of the 140°, which went into the ice to melt it?
A. It is hidden in the water; or (to speak more scientifically) it is stored up in a latent state.
Q. How can 1140° of heat be added to water, without being perceptible to our feelings?
A. 1st—140° of heat are hidden in the water, when ice is melted by the sun or fire.
2ndly—1000° more of heat are secreted, when water is converted into steam. Thus, before ice is converted into steam, 1140° of heat become latent.[6]
[6] Thus, one pint of boiling water, (212° according to the thermometer,) will make 1800 pints of steam; but the steam is no hotter to the touch than boiling water, both are 212°: therefore, when water is converted into steam, 1000° of heat become latent. Hence, before ice is converted to steam, it must contain 1140° of latent heat.
Q. Can we be made to feel the heat of ice or snow?
A. Yes. Into a pint of snow put half as much salt; then plunge your hand into the liquid; and it will feel so intensely cold, that the snow itself will seem quite warm in comparison to it.
Q. Is salt and snow really colder than snow?
Q. What is fire?
A. Combustion is another instance of heat, arising from chemical action.
Q. What two things are essential to produce combustion?
A. Fuel and air.
Q. What are the elements of fuel?
A. As bread is a compound of flour, yeast, and salt; so fuel is a compound of hydrogen and carbon.
Q. What are the elements of atmospheric air?
A. The air is a compound of oxygen and nitrogen mixed together; in the proportion of five gallons of nitrogen, to one of oxygen.
Q. What is carbon?
A. The solid part of fuel. It abounds also in all animal bodies, earths, and minerals.
Q. Mention some different species of carbon.
Q. What is hydrogen?
A. An inflammable gas. The gas used in our streets, is only the hydrogen gas driven out of coals by heat.
Q. What are the peculiar characteristics of hydrogen gas?
A. Though this gas itself will burn, yet a candle will not burn when immersed in it; nor can an animal live in it. Hydrogen gas is the lightest of all known substances.[7]
[7] Hydrogen gas may be made thus:—Put some pieces of zinc or iron filings into a glass: pour over them a little sulphuric acid (vitriol), diluted with twice the quantity of water; then cover the glass over for a few minutes, and hydrogen gas will be given off.
Exp. If a flame be put into the glass, an explosion will be made.
If the experiment be tried in a phial, which has a piece of tobacco-pipe run through the cork; and a light held a few moments to the top of the pipe, a flame will be made.
If a balloon be held over the phial, (so that the gas can inflate it,) the balloon will ascend in a very few minutes.
Q. What is oxygen?
A. A gas, much heavier than hydrogen; which gives brilliancy to flame, and is essential to animal life.[8]
[8] Oxygen gas is much more troublesome to make than hydrogen. The cheapest plan is to put a few ounces of manganese (called the black oxide of manganese) into an iron bottle, furnished with a bent tube; set the bottle on a fire till it becomes red hot, and put the end of the tube into a pan of water. In a few minutes, bubbles will rise through the water; these bubbles are oxygen gas.
These bubbles may be collected thus:—Fill a common bottle with water; hold it topsy-turvy over the bubbles which rise through the pan, but be sure the mouth of the bottle be held in the water. As the bubbles rise into the bottle, the water will run out; and when all the water has run out, the bottle is full of gas. Cork the bottle while the mouth remains under water; set the bottle on its base; cover the cork with lard or wax, and the gas will keep till it be wanted.
N. B. The quickest way of making oxygen gas, is to rub together in a mortar half an ounce of oxide of copper, and half an ounce of chlorate of potassa. Put the mixture into a common oil flask, furnished with a cork which has a bent tube thrust through it. Heat the bottom of the flask over a candle or lamp; and when the mixture is red hot, oxygen gas will be given off. Note—the tube must be immersed in a pan of water, and the gas collected as before.
(Chlorate of potassa may be bought at any chemist’s; and oxide of copper may be procured by heating a sheet of copper red hot, and when cool, striking it with a hammer: the scales that peel off, are oxide of copper.)
Exp. Put a piece of red hot charcoal, (fixed to a bit of wire,) into your bottle of oxygen gas; and it will throw out most dazzling sparks of light.
Blow a candle out; and while the wick is still red, hold the candle (by a piece of wire,) in the bottle of oxygen gas; the wick will instantly ignite, and burn brilliantly.
(Burning sulphur emits a blue flame, when immersed in oxygen gas.)
Q. What is nitrogen?
A. Nitrogen is another invisible gas. It will not burn, like hydrogen; and an animal cannot live in it: it abounds in animal and vegetable substances, and is the chief ingredient of the common air.[9]
[9] Nitrogen gas may easily be obtained thus:—Put a piece of burning phosphorus on a little stand, in a plate of water; and cover a bell glass over. (Be sure the edge of the glass stands in the water.) In a few minutes the air will be decomposed, and nitrogen alone remain in the bell glass.
(N.B. The white fume which will arise and be absorbed by the water in this experiment, is phosphoric acid; i. e. phosphorus combined with oxygen of the air.)
Q. Why is there so much nitrogen in the air?
A. In order to dilute the oxygen. If the oxygen were not thus diluted, fires would burn out, and life would be exhausted too quickly.
Q. What three elements are necessary to produce combustion?
A. Hydrogen gas, carbon, and oxygen gas; the two former in the fuel, and the last in the air which surrounds the fuel.
Q. What causes the combustion of the fuel?
Q. What is carbonic acid gas?
A. Only carbon (or charcoal) combined with oxygen gas.
Q. Why does fire produce heat?
A. 1st—By liberating latent heat from the air and fuel: and
2ndly—By throwing into rapid motion the atoms of matter.
Q. How is latent heat liberated by combustion?
A. When the oxygen of the air combines with the hydrogen of the fuel, the two gases condense into water; and latent heat is squeezed out, as water from a sponge.
Q. How are the atoms of matter disturbed by combustion?
A. 1st—When hydrogen of fuel and oxygen of air condense into water, a vacuum is made; and the air is disturbed, as a pond would be, if a pail of water were taken out of it: and
2ndly—When the carbon of fuel and oxygen of air expand into carbonic acid gas, the air is again disturbed, as it would be by the explosion of gunpowder.
Q. How does fire condense hydrogen and oxygen into water?
A. The hydrogen of fuel and oxygen of air (liberated by combustion) combining together, condense into water.
Q. How does fire expand carbon into carbonic acid gas?
A. The carbon of fuel and oxygen of air (combining together in combustion) expand into a gas, called carbonic acid.
Q. Why is a fire (after it has been long burning) red hot?
A. When coals are heated throughout, the carbon is so completely mixed with the oxygen of the air, that the whole surface is in a state of combustion, and therefore red hot.
Q. In a blazing fire, why is the upper surface of the coals black, and the lower surface red?
Q. Which burns the quicker, a blazing fire, or a red hot one?
A. A blazing fire burns out the fuel quickest.
Q. Why do blazing coals burn quicker than red hot ones?
A. In red hot coals, only the mere surface is in a state of combustion, because the carbon is solid; but in a blazing fire, (where the gases are escaping), the whole volume of the coal throughout is in a state of decomposition.
Q. What is smoke?
A. Unconsumed parts of fuel (principally carbon), separated from the solid mass, and carried up the chimney by the current of hot air.
Q. Why is there more smoke when coals are fresh added, than when they are red hot?
Q. Why is there so little smoke with a red hot fire?
A. When a fire is red hot, the entire surface of the coals is in a state of combustion; so a very little flies off unconsumed, as smoke.
Q. Why are there dark and bright spots in a clear cinder fire?
A. Because the intensity of the combustion is greater in some parts of the fire, than it is in others.
Q. Why is the intensity of the combustion so unequal?
A. Because the air flies to the fire in various and unequal currents.
Q. Why do we see all sorts of grotesque figures in hot coals?
Q. Why does paper burn more readily than wood?
A. Merely because it is of a more fragile texture; and, therefore, its component parts are more easily heated.
Q. Why does wood burn more readily than coal?
A. Because it is not so solid; and, therefore, its elemental parts are more easily separated, and made hot.
Q. When a fire is lighted, why is paper laid at the bottom, against the grate?
A. Because paper (in consequence of its fragile texture), so very readily catches fire.
Q. Why is wood laid on the top of the paper?
A. Because wood, (being more substantial), burns longer than paper; and, therefore, affords a longer contact of flame to heat the coals.
Q. Why would not paper do without wood?
Q. Why would not wood do without shavings, straw, or paper?
A. Because wood is too substantial to be heated into combustion, by the flame issuing from a mere match.
Q. Why would not the paper do as well, if placed on the top of the coals?
A. As every blaze tends upwards, if the paper were placed on the top of the fire, its blaze would afford no contact of flame to fuel lying below.
Q. Why should coal be placed above the wood?
A. As every flame tends upwards, if the wood were above the coal, the flame would not rise through the coal to heat it.
Q. Why is a fire kindled at the lowest bar of a grate?
Q. Why does coal make such excellent fuel?
A. Because it is so very hard and compact, that it burns away very slowly.
Q. Why will cinders become red hot, quicker than coals?
A. Because they are more porous and less solid; and are, therefore, sooner reduced to a state of combustion.
Q. Why will not iron cinders burn?
A. Iron cinders are cinders saturated with oxygen; they are unfit for fuel, because they can imbibe no more oxygen, being saturated already.
Q. Why are cinders lighter than coals?
A. Because their vapour, gases, and volatile parts, have been driven off by previous combustion.
Q. Why will not stones do for fuel, as well as coals?
A. Because they contain no hydrogen (or inflammable gas) like coals.
Q. Why will not wet kindling light a fire?
Q. Why does dry wood burn better than green?
A. 1st—Because no heat is carried away, by the conversion of water into steam: and
2ndly—The pores of dry wood are filled with air, which supply the fire with oxygen.