A. Because they compel the air to go through the fire, and not over it; therefore the fire is well supplied with oxygen, and the draught greatly increased.
Q. Why does a tin blower increase the draught?
A. As all the air which enters the chimney has to pass through the fire, it is much hotter, and ascends the chimney very fast; and the faster the air flies up the chimney, the faster it rushes towards the fire also.
Q. Why does a parlour often smell disagreeably of soot in summer-time?
A. The air in the chimney (being colder than the air in the parlour) descends into the room, and leaves a disagreeable smell of soot behind.
Q. Why are the ceilings of public offices so black and filthy?
Q. Why are some parts of the ceiling blacker and more filthy than others?
A. As the air cannot penetrate the thick joists of the ceiling, it passes by those parts, and deposits its soot and dust on those which are more penetrable.
Q. What is charcoal?
A. Wood which has been exposed to a red heat, till it has been deprived of all its gases and volatile parts.
Q. Why is a charcoal fire hotter than a wood fire?
A. Because so large a quantity of water has been abstracted from the fuel, by the red heat to which it has been already exposed.
Q. Why does charcoal remove the taint of meat?
A. Because it absorbs all odoriferous effluvia, whether they arise from putrefying animal or vegetable matter.
Q. Why is water purified by being filtered through charcoal?
Q. Why are water and wine casks charred inside?
A. Charring the inside of the cask reduces it to a kind of charcoal; and charcoal (by absorbing animal and vegetable impurities) keeps the liquor sweet and good.
Q. Why does a piece of burnt bread, steeped in impure water, make it fit to drink?
A. The surface of the bread is reduced to charcoal by being burnt; and the charcoal surface of the bread abstracts all the impurities of the water, and makes it palatable.
Q. Why should the toast and water, placed by the side of the sick, be made of burnt bread?
A. The surface of the bread being reduced to charcoal by being burnt, prevents the water from being affected by the impurities of the sick room.
Q. Why are timbers, which are to be exposed to damp, charred?
A. Charcoal undergoes no change by exposure to air and water; therefore timber will resist weather much longer, after it has been charred.
Q. Of what are oil, tallow, and wax composed?
A. Principally of carbon and hydrogen gas. The solid part is carbon, the volatile part is gas.
Q. What is carbon?
A. A solid substance, generally of a black colour; well known under the forms of charcoal, lamp-black, coke, black-lead, &c.
Q. What is hydrogen gas?
Q. Why does a candle burn when lighted?
Q. Why is the flame of a candle hot?
A. 1st—Because the flame liberates latent heat from the air and tallow: and
2ndly—It throws into rapid motion the atoms of matter.
Q. How is latent heat liberated by the flame of a candle?
A. When the hydrogen of the tallow and oxygen of the air combine, they condense into water; and much of their latent heat is squeezed out.
Q. How are the atoms of matter disturbed by the flame of a candle?
A. 1st—When the hydrogen of the tallow and oxygen of the 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.
2ndly—When the carbon of tallow and oxygen of the air expand into carbonic acid gas, the air is again disturbed; in a similar way as by the explosion of gunpowder.
Q. Why does the flame of a candle produce light?
A. The chemical changes made by combustion, excite undulations of ether, which (striking the eye) produce light. (see p. 46.)
Q. Why is the flame of a candle yellow?
A. Only the outer coat of the flame is yellow; the lower part of the flame is violet; and the inside of the flame is hollow.
Q. Why is the outside of the flame yellow?
A. Because the carbon of the tallow (being in a state of perfect combustion) is made white-hot.
Q. Why is the bottom part purple of the flame of a candle?
A. The bottom part of the flame is overladen with hydrogen, raised from the tallow by the burning wick; and this half-burnt gas gives a purple tinge to the flame.
Q. Why is the inside of the flame of a candle hollow?
Q. Describe the different parts of the flame of a common candle.
A. The flame consists of three cones. The innermost cone is hollow; the intermediate cone of a dingy purple hue; and the outside cone is yellow.
Q. Why is the intermediate cone of a flame purple, as well as the bottom of the flame.
A. Because the gases are not in a state of perfect combustion; but contain an excess of hydrogen, which gives this cone a purple tinge.
Q. Why is not the middle cone in a state of perfect combustion, as well as the outer cone?
A. Because the outer cone prevents the oxygen of the air from getting freely to the middle of the cone; and without the free access of oxygen gas, there is no such thing as complete combustion.
Q. Why does the flame of a candle point upwards?
A. The flame heats the surrounding air, which (being hot) rapidly ascends, and drives the flame upwards at the same time.
A. The upper part of a flame is more volatile than the lower parts; and as it affords less resistance to the air, is reduced to a mere point.
Q. Why is the upper part of a flame more volatile than the lower parts?
A. The lower parts of the flame are laden with unconsumed gas and watery vapour; which present considerable resistance to the air.
Q. Why is the flame of a candle blown out by a puff of breath?
A. As the flame of a candle is attached to a very small wick, a puff of breath severs the flame from the wick; and it goes out for want of support.
Q. Why does the flame of a candle make a glass damp, which is held over it?
A. The hydrogen of the tallow combining with the oxygen of the air, produce a “watery vapour,” which is condensed by the cold glass held above the flame.
Q. Why does our hand, held above a candle, suffer from the heat of the flame so much more, than when it is placed below the flame, or on one side of it?
A. Because the hot gases and air (in their ascent) come in contact with the hand placed above the flame: but when the hand is placed below the flame, or on one side, it only feels heat from radiation.
Q. Why is a rush light extinguished so much more quickly than a cotton-wicked candle?
A. As the rush wick is smooth and hard, the mere motion of the air (produced by carrying the candle from one place to another,) is sufficient to sever the flame from the rush.
Q. Why is it more difficult to blow out a cotton wick?
A. The cotton wick is quite full of small threads or filaments, which help to hold the flame on the wick, like the roots of a tree.
Q. Why does an extinguisher put a candle out?
A. Because the air in the extinguisher is soon exhausted of its oxygen by the flame: and when there is no oxygen to support it, the flame goes out.
Q. Why does not a candle set fire to a piece of paper twisted into an extinguisher, and used as such?
A. 1st—Because the flame very soon exhausts the little oxygen contained in the paper extinguisher: and
2ndly—The flame invests the inside of the paper extinguisher with carbonic acid gas, which prevents it from blazing.
Q. Why is a long wick never upright?
A. Because it is bent by its own weight.
Q. Why is a long wick covered with an efflorescence at the top?
A. The knotty or flowery appearance of the top of a wick arises from an accumulation of particles partly separated, but still loosely hanging to the wick.
Q. Why is not the end of a long wick burnt off, as it hangs over the flames?
A. Because the length of the wick so diminishes the heat of the flame, that it is not hot enough to burn it off.
Q. Why do palmer’s metallic wicks never need snuffing?
Q. Why do common candles require to be snuffed?
A. Because the heat of the flame is not sufficient to consume the wick; and the longer the wick grows, the less heat the flame produces.
Q. Why do wax candles never need snuffing?
A. The wick of wax candles is made of very fine thread, which the heat of the flame is sufficient to consume: but the wick of tallow candles is made of coarse cotton, which is too substantial to be consumed by the heat of the flame, and must be cut off by snuffers.
Q. Why does a pin, stuck in a rush-light, extinguish it?
A. Because a pin (being a good conductor), carries away the heat of the flame from the wick, and prevents the combustion of the tallow.
Q. What is the smoke of a candle?
Q. Why are some particles consumed and not others?
A. The combustion of the carbon depends upon its combining with the oxygen of the air: but as the outer surface of the flame prevents the access of air to the interior parts, therefore much of the carbon of those parts passes off in smoke.
Q. Why do lamps smoke?
A. Either because the wick is cut unevenly, or else because it is turned up too high.
Q. Why does a lamp smoke when the wick is cut unevenly?
A. 1st—Because the points of the jagged edge (being very easily separated from the wick,) load the flame with more carbon than it can consume: and
2ndly—As the heat of the flame is greatly diminished by these bits of wick, it is unable to consume even the usual quantity of smoke.
Q. Why does a lamp smoke when the wick is turned up too high?
Q. Why do not “Argand burners” smoke?
A. Because a current of air passes through the middle of the flame; and therefore the carbon of the interior is consumed, as well as that in the outer coating of the flame.
Q. Why does a lamp-glass diminish the smoke of a lamp?
A. Because it both concentrates and reflects the heat of the flame; in consequence of which, the heat is so greatly increased, that very little carbon escapes unconsumed.
Q. What is the cause of animal heat?
Q. What are capillary veins?
A. Veins as small as hairs running all over the body; so called from the Latin word “capilla’ris” (like a hair).
Q. Do these capillary veins run all over the human body?
A. Yes. Whenever blood flows from a wound, some vein must be divided; and as you cannot insert a needle into any part of the body without bringing blood, therefore these little veins must run through every part of the human frame.
Q. How do hydrogen gas and carbon get into these very little veins?
A. The food we eat is converted into blood, and blood contains both hydrogen and carbon.
Q. How does combustion take place in the veins?
A. The carbon of the blood combines with the oxygen of the air we breathe, and forms into carbonic acid gas.
Q. What becomes of this carbonic acid gas formed in the human blood?
Q. What is the cause of the combustion of fire?
A. The carbon of fuel unites with the oxygen of the air, and forms carbonic acid gas.
Q. What is the cause of the combustion of a candle or lamp?
A. The carbon of the oil or tallow unites with the oxygen of the air, and forms carbonic acid gas.
Q. What is the cause of spontaneous combustion?
A. The piled-up goods ferment from heat and damp; and (during fermentation) carbonic acid gas is formed, as in the two former cases.
Q. Does the heat of the human body arise from the same cause as the heat of fire?
A. Yes, precisely. The carbon of the blood, combining with the oxygen of air inhaled, produces carbonic acid gas, which is attended with combustion.
Q. If animal heat is produced by combustion, why does not the human body burn up like a coal or candle?
Q. If every bone, muscle, nerve, and organ, is thus consumed by combustion, why is not the body entirely consumed?
A. It would be so, unless the parts destroyed were perpetually renewed: but as a lamp will not go out, so long as it is supplied with fresh oil; neither will the body be consumed, so long as it is supplied with sufficient food.
Q. When a man is starved, what parts of the body go first?
A. First the fat, because it is the most combustible; then the muscles; last of all the brain; and then the man dies, like a candle which is burnt out.
Q. Why does want of sufficient nourishment often produce madness?
A. After the fat and muscles of the body have been consumed by animal combustion, the brain is next attacked; and (unless the patient dies) madness must ensue from starvation.
A. A starved man shrinks just as a fire does, unless it be supplied with sufficient fuel.
Q. What is the fuel of the body?
A. Food is the fuel of the body; and the carbon of the food mixing with the oxygen of the air, evolves heat in the same way that a fire or candle does.
Q. Why is every part of the body warm?
A. As the capillary veins run through every part of the human body, and the combustion of blood takes place in the capillary veins, therefore every part of the body is warm.
Q. Why does running make us warm?
A. When we run, we inhale air more rapidly; and the rapidity with which we inhale air fans the combustion of our body, as a pair of bellows quickens the flame of a common fire.
Q. How does inhaling air rapidly make the body feel warm?
Q. Why does hard work produce hunger?
A. Because it produces quicker respiration; by which means a larger amount of oxygen is introduced into the lungs, and the capillary combustion increased. Hunger is the notice (given by our body) to remind us, that our food-fuel must be replenished.
Q. Why does singing make us hungry?
A. Singing increases respiration; and as more oxygen is introduced into the lungs, our food-fuel is more rapidly consumed.
Q. Why does reading aloud make us feel hungry?
A. Reading aloud increases respiration; and as more oxygen is introduced into the lungs, our food-fuel is more rapidly consumed.
Q. Why do we feel more hungry in the day-time than in the night-time?
Q. Why do we need warmer clothing by night than by day?
A. 1st—Because the night is generally colder than the day.
2ndly—As our respiration is slower, our animal combustion is slower also; in consequence of which, our bodies are more cold.
Q. Why do we perspire when very hot?
A. The pores of the body are like the safety valves of a steam-engine; when the heat of the body is too great, the combustible gas and grease flow out in perspiration, instead of burning in the blood.
Q. Why do persons feel lazy and averse to exercise, when they are half-starved or ill-fed?
A. Animal food contains great nourishment, and produces a desire for active occupations; but when the body is not supplied with strong food, this desire for muscular action ceases, and the person grows slothful.
Q. Why have persons, who follow hard out-of-doors occupations, more appetite than those who are engaged in sedentary pursuits?
A. Hard bodily labour in the open air causes much oxygen to be conveyed into the lungs by inspiration; the combustion of the food is carried on quickly; animal heat increased; and need for nutritious food more quickly indicated by craving hunger.
Q. Why have persons who follow sedentary pursuits less appetite than ploughmen and masons?
A. 1st—The air they inhale is not so pure, because its oxygen is partly exhausted: and
2ndly—Their respiration is neither so quick nor strong, and therefore the combustion of their food is carried on more slowly.
Q. Why do we like strong meat and greasy food when the weather is very cold?
A. Strong meat and grease contain large portions of hydrogen, which (when burned in the blood) produce a larger amount of heat than any other kind of food.
Q. Why do persons eat more food in cold weather, than in hot?
Q. Why does cold produce hunger?
A. 1st—The air contains more oxygen in cold weather; and as fires burn fiercer, so animal combustion is more rapid: and
2ndly—We are more active in cold weather; and increased respiration acts like a pair of bellows on the capillary combustion.
Q. Why does rapid digestion produce a craving appetite?
A. This is a wise providence to keep our bodies in health; in order that the body itself may not be consumed, it gives notice (by hunger) that the capillary fires need replenishing.
Q. Why do we feel a desire for activity in cold weather?
Q. Why are the Esquimeaux so passionately fond of train oil and whale blubber?
A. Oil and blubber contain a very large amount of hydrogen, which is exceedingly combustible; and as these people live in climates of intense cold, the heat of their bodies is increased by the greasy nature of their food.
Q. Why do we feel a dislike to strong meat and greasy foods in very hot weather?
A. Strong meat and grease contain so much hydrogen, that they would make us intensely hot; and therefore we refuse them in hot weather.
Q. Why do we like fruits and vegetables so very much in hot weather?
A. Fruits and vegetables contain less carbon than meat, and therefore produce less blood: instead of blood, they combine into water as they are digested, and keep the body cool.
Q. Why do people say that fruits and vegetables cool the blood?
Q. Why do we feel lazy and averse to activity in very hot weather?
A. 1st—Because muscular activity would increase the heat of the body, by quickening the respiration: and
2ndly—The food we eat in hot weather, not being greasy, naturally abates our desire for bodily activity.
Q. Why do the inhabitants of tropical countries live chiefly upon rice and fruit?
A. Rice and fruit by digestion are mainly converted into water, and (by cooling the blood) prevent the tropical heat from feeling so oppressive.
Q. Why are poor people generally averse to cleanliness?
Q. Why are poor people generally averse to ventilation?
A. 1st—Because ventilation increases the oxygen of the air,—the combustion of food,—and the cravings of appetite: and
2ndly—Ventilation cools the air of our rooms: poor people, therefore, (who are generally ill-clad) love the warmth of an ill-ventilated apartment.
Q. Why does flannel, &c. make us warm?
A. Flannel and warm clothing do not make us warm, but merely prevent the body from becoming cold.
Q. How does flannel, &c. prevent the body from becoming cold?
A. Flannel (being a bad conductor) will neither carry off the heat of the body into the cold air, nor suffer the cold of the air to come into contact with our warm bodies; and thus it is that flannel clothing keeps us warm.
Q. Why are frogs and fishes cold-blooded animals?
Q. Why is a dead body cold?
A. Air is no longer conveyed to the lungs after respiration has ceased; and, therefore, animal heat is no longer evolved by combustion.
Q. How is heat produced by mechanical action?
A. 1.—By Percussion. 2.—By Friction. 3.—By Condensation.
Q. What is meant by percussion?
A. The act of striking; as when a blacksmith strikes a piece of iron on his anvil with his hammer.
A. Beating the iron condenses the particles of the metal; and squeezes out its latent heat, as water from a sponge.
Q. Does cold iron contain heat?
A. Yes; every thing contains heat; but when a thing feels cold, its heat is latent.
Q. What is meant by latent heat?
A. Heat not perceptible to our feeling. When anything contains heat without feeling the hotter for it, that heat is called “latent.” (See p. 31.)
Q. Does cold iron contain latent heat?
A. Yes; and when a blacksmith compresses the particles of the iron by his hammer, he squeezes out this latent heat, and makes the iron red-hot.
Q. How did blacksmiths use to light their matches before the general use of lucifers?
A. They used to place a soft iron nail upon their anvil; strike it two or three times with a hammer; and the point became sufficiently hot to light a brimstone match.
A. As the particles of the nail are compressed by the hammer, it cannot contain so much heat as it did before; so some of it flies out (as water flows from a sponge when it is squeezed).
Q. Why does striking a flint against a piece of steel produce a spark?
A. The blow condenses those parts of the flint and steel which strike together, and squeezes out their latent heat.
Q. How does this development of heat produce a spark?
A. A very small fragment (either of the steel or flint) is knocked off red-hot, and sets fire to the tinder on which it falls.
Q. Why is it needful to keep blowing the tinder with the breath?
A. Because blowing the tinder, drives the oxygen of the air towards it.