Q. Why do two pieces of wood burn better than one?
A. 1st—Because they help to entangle the heat of the passing smoke, and throw it on the fuel: and
2ndly—They help to entangle the air that passes over the fire, and create a kind of eddy or draught.
Q. Why does salt crackle when thrown into a fire?
A. Salt contains water; and the cracking of the salt is owing to the sudden conversion of the water into steam.
Q. Why will not wood or paper burn, if they are steeped in a solution of potash, phosphate of lime, or ammonia (hartshorn)?
A. Because any “al’kali” (such as potash) will arrest the hydrogen (as it escapes from the fuel), and prevent its combination with the oxygen of air.
Q. What is an al’kali?
A. The con’verse of an acid; as bitter is the con’verse of sweet, or insipid the con’verse of pungent.
Q. Why does a jet of flame sometimes burst into the room through the bars of a stove?
A. The iron bars conduct heat to the interior of some lump of coal: and its volatile gas (bursting through the weakest part) is kindled by the glowing coals over which it passes.
Q. Why is this jet sometimes of a greenish yellow colour?
A. When a lump of coals lies over the hot bars, or the coals below it are not red hot, the gas which bursts from the lump escapes unburnt, and is of a greenish colour.
Q. Why does the gas escape unburnt?
Q. Why does a bluish flame sometimes flicker on the surface of hot cinders?
A. Gas from the hot coals at the bottom of the grate mixing with the carbon of the coals above, produces an inflammable gas (called carbonic oxide), which burns with a blue flame.
Q. Why is the flame of a good fire yellow?
A. Because both the hydrogen and carbon of the fuel are in a state of perfect combustion. It is the white heat of the carbon, which gives the pale yellow tinge to the flaming hydrogen.
Q. What is light?
A. Rapid undulations of a fluid called ether, striking on the eye.
Q. How does combustion make these undulations of light?
A. The atoms of matter (set in motion by heat) striking against this ether, produce undulations in it; as a stone thrown into a stream, would produce undulations in the water.
Q. How can undulations of ether produce light?
Q. What is ether?
A. A very subtile fluid, which pervades and surrounds every thing we see.
Q. Mention a simple experiment to prove that light is produced by rapid motion.
A. When a fiddle-string is jerked suddenly, its rapid vibration produces a grey light; and when a carriage wheel revolves very quickly, it sends forth a similar light.
Q. Does heat always produce light?
A. No: the heat of a stack of hay, or reeking dunghill, though very great, is not sufficient to produce light.
Q. Why is a yellow flame brighter than a red hot coal?
A. Because yellow rays always produce the greatest amount of light; though red rays produce the greatest amount of heat.
A. The intensity of fire-light depends upon the whiteness to which the carbon is reduced, by combustion. If the carbon be white hot, its combustion is perfect, and the light intense; if not, the light is obscured by smoke.
Q. Why will not cinders blaze, as well as fresh coals?
A. The flame of coals is made chiefly by hydrogen gas. As soon as this gas is consumed, the hot cinders produce only an invisible gas, called carbonic acid.
Q. Where does the hydrogen gas of a fire come from?
A. The fuel is decomposed (by combustion) into its simple elements, carbon and hydrogen gas. (see p. 33)
Q. Why does not a fire blaze on a frosty night, so long as it does upon another night?
A. The air (being very cold) rushes to the fire so rapidly, that the coals burn out faster, and the inflammable gas is sooner consumed.
Q. Why does a fire burn clearest on a frosty night?
Q. Why does a fire burn more intensely in winter than in summer time?
A. Because the air is colder in winter, than in summer-time.
Q. How does the coldness of the air increase the heat of a fire?
A. For two reasons: 1st—Because cold air being more condensed than hot air, contains a greater body: and
2ndly—Cold air rushes more quickly to the fire, and supplies more oxygen.
Q. Why does the sun, shining on a fire, make it dull, and often put it out?
A. 1st—When the sun shines, the air is rarefied; and, therefore, flows more slowly to the fire.
2ndly—As the air is rarefied, even that which reaches the fire, affords less nourishment.
Q. Why does the air flow to the fire more tardily for being rarefied?
Q. Why does rarefied air afford less nourishment to fire, than cold air?
A. Because it is spread out, (like a piece of gold beaten into leaf); and as a square inch of gold leaf will not contain so much gold as a square inch of bullion—so, a square inch of rarefied air has less body, than a square inch of cold air.
Q. Why does a fire burn more fiercely in the open air?
A. 1st—Because the air out-of-doors is more dense, than the air in-doors: and
2ndly—Because air is more freely supplied to a fire out-of-doors.
Q. Why is the air out-of-doors more dense than that in-doors?
A. Because the circulation is more free; and as soon as any portion has been rarefied, it instantly escapes, and is supplied by colder currents.
A. During a thaw, the air is filled with vapour; and, both moves too slowly, and is too much diluted to nourish the fire.
Q. Why does a fire burn so fiercely in windy weather?
A. In windy weather the air is rapidly changed, and affords plentiful nourishment to the fire.
Q. Why do a pair of bellows get a fire up?
A. A pair of bellows, (like the wind), drives the air more rapidly to the fire; and the plentiful supply of oxygen soon makes the fire burn intensely.
Q. Why is a candle blown out by the breath, and not made more intense, like a fire?
A. As the flame of a candle is confined to a very small wick, it is severed from it by the breath; and (being unsupported) must go out.
Q. Why is a smouldering wick sometimes rekindled by blowing it?
Q. Why is not the red hot wick kindled by the air around it, without blowing it?
A. Because oxygen is not supplied with sufficient freedom, unless it be blown to the wick.
Q. When is this experiment most likely to succeed?
A. In frosty weather; because the air contains more oxygen then, being condensed by the cold.
Q. Why does a poker, laid across a dull fire, revive it?
A. For two reasons. 1st—Because the poker concentrates the heat, and therefore increases it: and
2ndly—Because the poker arrests the air which passes over the fire, and produces a draught.
Q. Why do several pieces of wood or coal burn better than one?
A. When there are two or three pieces of wood on a fire, the air (circulating round them) produces an eddy or draught, which draws up the fire.
A. In order that the air, on the lower part of the room, may be heated by the fire.
Q. Would not the air of the lower part of a room be heated equally well, if the stoves were fixed higher up?
A. No; the heat of a fire has a very little effect upon the air below the level of the grate; and, therefore, every grate should be as near to the floor as possible.
Q. Why are our feet so cold when we sit close by a good fire?
A. As the fire consumes the air which passes over it, cold air rushes through the crevices of the doors and windows along the bottom of the room to supply the deficiency; and these currents of cold air, rushing constantly over our feet, deprive them of their warmth.
Q. If a piece of paper be laid flat on a clear fire, it will not blaze, but char. Why so?
Q. If you blow the paper, it will blaze immediately. Why so?
A. By blowing, or opening the door suddenly, the carbonic acid is dissipated, and the paper is instantly fanned into flame.
Q. Why does water extinguish a fire?
1st—Because the water forms a coating over the fuel, and keeps it from the air:
2ndly—The conversion of water into steam, draws off the heat of the burning fuel.
Q. Why does a little water make a fire fiercer, while a larger quantity of water puts it out?
A. Water is composed of oxygen and hydrogen; when, therefore, the fire can decompose the water into its simple elements, it serves for fuel to the flame.
Q. How can water serve for fuel to fire?
Q. If a house be on fire, is too little water worse than no water at all?
A. Certainly. Unless the water be supplied so plentifully as to quench the fire, it will increase the intensity, like fuel.
Q. When will water extinguish fire?
A. When the supply is so rapid and abundant, that the fire cannot convert it into steam.
Q. Does not a very little water slacken the heat of fire?
A. Yes, till it is converted into steam; but then it increases the intensity of fire, and acts like fuel.
Q. Why does the wick of a candle (when the flame has been blown out) catch fire so readily?
A. As the wick is already very hot, a little extra heat will throw it into flame.
Q. Why does the extra heat revive the flame?
A. Because it again liberates the hydrogen of the tallow, and ignites it.
Q. Cannot wood be made to blaze without actual contact with fire?
Q. Why will wood blaze, even if it does not touch the fire?
A. The heat of the fire drives out the hydrogen gas of the wood; which is inflamed by contact with the red-hot coals.
Q. Why will a neighbour’s house sometimes catch fire, though no flame of the burning house ever touches it?
A. The heat of the burning house sets at liberty the hydrogen gas of the neighbouring wood-work, which is ignited by the flames or red-hot bricks of the house on fire.
Q. What is coke?
A. Coal freed from its volatile gases, by the action of artificial heat.
Q. Why do arnott’s stoves sometimes smell so strong of sulphur?
A. The fire is made of coke, which contains sulphur; and, whenever the draught is not rapid enough to drive the sulphur up the flue, it is emitted into the room.
A. Ignition produced by the action of one uninflamed body on another.
Q. Give an example of spontaneous combustion.
A. Goods packed in a warehouse will often catch fire of themselves; especially such goods as cotton, flax, hemp, rags, &c.
Q. Why do such goods sometimes catch fire of themselves?
A. Because they are piled together in very great masses in a damp state or place.
Q. Why does this produce spontaneous combustion?
A. The damp produces decay or the decomposition of the goods, and the great heat of the piled-up mass makes the decaying goods ferment.
Q. How does this fermentation produce combustion?
A. During fermentation, carbonic acid gas is given off by the goods,—a slow combustion ensues,—till at length the whole pile bursts into flame.
Q. Why is the heat of a large mass of goods greater than that of a smaller quantity?
Q. Why do hay-stacks sometimes catch fire of themselves?
A. Either because the hay was got up damp, or because rain has penetrated the stack.
Q. Why will a hay-stack catch fire if the hay be damp?
A. Damp hay soon decays, and undergoes a state of fermentation; during which, carbonic acid gas is given off, and the stack catches fire.
Q. Why does roasted coffee sometimes catch fire spontaneously?
A. The heat of coffee is greatly increased by being roasted; and the carbon of the coffee uniting with the oxygen of the air, produces carbonic acid gas, and bursts into flame.
A. Because they very readily ferment, and (during fermentation) throw off exceedingly inflammable gases.
(N.B. Lamp-black mixed with linseed oil is more liable to spontaneous combustion, than anything that servants handle.)
Q. Why does smoke ascend the chimney?
A. As the air of the room passes over the fire, it becomes heated; and (being thus made lighter,) ascends the chimney, carrying the smoke with it.
Q. What is smoke?
A. Small particles of carbon, separated by combustion from the fuel, but not consumed.
Q. Why do smoke and steam curl, as they ascend?
Q. What are blacks?
A. When the hot air of the chimney has been cooled by the external air, it can no longer buoy up the solid smoke; so it falls to the earth in condensed flakes, called “blacks.”
Q. Why are there no blacks in the smoke of a railway engine?
A. The smoke of a railway engine consists chiefly of watery vapour, which dissolves in air, as sugar does in water; but the smoke of a common chimney consists of small fragments of unburnt fuel.
Q. Why does a “COPPER HOLE” DRAW up more fiercely than an open stove?
A. As the air, which supplies the copper hole, must pass through the furnace, it becomes exceedingly heated, and rushes up the chimney with great violence.
Q. What produces the roaring noise made by a copper-hole fire?
A. Air rushing rapidly through the crevices of the iron door, and up the chimney flue.
A. Because fresh air gets access to the fire more easily; and as the air is not so intensely heated, its motion is not so violent.
Q. Why do some chimneys smoke?
A. If fresh air is not admitted into a room, as fast as it is consumed by the fire, a current of air will rush down the chimney to supply the deficiency, and bring the smoke along with it.
Q. What prevents air being supplied, as fast as it is consumed by the fire?
A. Leather and curtains round the doors; sand-bags at the threshhold and on the window-frames; and other contrivances to keep out the draught.
Q. Why is it needful for cold fresh air to be so constantly supplied?
A. If water be taken with a pail out of a river, other water will rush towards the hole, as soon as the pail is lifted out; and if air be taken from a room, (as it is, when some of it goes up the chimney) other air will rush towards the void to fill it up.
A. Because if doors and windows are all made air-tight, it can get to the room in no other way.
Q. What is the best remedy in such a case?
A. The speediest remedy is to open the door or window: but by far the best remedy is to carry a small tube from the hearth into the external air.
Q. Why is that the best remedy?
A. Because the fire will be plentifully supplied with air by the tube; the doors and windows may all remain air-tight; and we may enjoy a warm fireside, without the inconvenience of draughts and cold feet.
Q. Why is a chimney raised so high above the roof?
A. If it were not so, it would smoke; as all funnels do which are too short.
Q. What is meant by the funnel, or flue of a chimney?
A. That part of a chimney through which the smoke passes, is called the funnel, or flue.
A. Because the draught of a short flue is too slack to carry the smoke up the chimney.
Q. Why is the draught of a short flue more slack that that of a long one?
A. For many reasons. 1st—The fire is always dull and sluggish if the chimney be too short.
2ndly—The smoke rolls out of the chimney, before it has acquired its full velocity.
3rdly—The wind, rain, and air, have more influence over a short funnel, than over a long one.
Q. Why is the fire always dull and sluggish if the chimney-flue be very short?
A. Because the draught is so bad: and as the rarefied air passes up the chimney very tardily, fresh air flows as tardily towards the fire, to supply it with oxygen.
Q. On what does the intensity of fire depend?
Q. Why does not smoke acquire its full velocity in a short funnel?
A. Because the higher smoke ascends in a flue, (provided it be clear and hot) the faster it goes; (as a stone falls faster and faster the lower it descends): if, therefore, a funnel be very short, the smoke never acquires its full velocity.
Q. Does the draught of a chimney depend on the speed of the smoke through the flue?
A. Yes. The more quickly hot air flies up the chimney, the more quickly cold air will rush towards the fire to supply the place; and, therefore, the longer the flue, the greater the draught.
Q. Why is the draught of a long flue greater than that of a short one?
A. Because the higher smoke ascends, the faster it goes; (as a stone falls faster and faster, the nearer it approaches to the earth): if, therefore, a funnel be long, the smoke acquires great velocity, and the draught is great.
A. To contract the opening of the chimney contiguous to the stove.
Q. Why will a smaller opening against the stove prevent the smoking?
A. As all the air (which enters the chimney) must pass near the fire, it will become greatly heated, and rise rapidly through the funnel; and this increase of heat will compensate for the shortness of the flue.
Q. Why will a room smoke, if there be two fires in it?
A. Because the fiercer fire will exhaust the most air; and draw from the smaller one, to supply its demand.
Q. Why will a chimney smoke if there be a fire in two rooms communicating with each other?
A. Whenever the door between the two rooms is opened, air will rush from the chimney of the inferior fire, to supply the other; and both rooms will be filled with smoke.
Q. What is the remedy in this case?
Q. Why do vestry chimneys so often smoke?
A. Because the wind (striking against the steeple) is reflected back; and tumbles down the vestry chimney, forcing the smoke into the room.
Q. what winds make vestry chimneys smoke?
A. Those from the north-east or south-east; according to the position of the vestry.
Q. Why will the eastern winds make vestries smoke, more than those from the west?
A. Because they strike against the steeple, and bound back to the vestry chimney: but western winds cannot rebound over the roof of a church.
(N. B. The steeple of a church is always due west, and the other end of the church due east; if, therefore, a western wind rebound, it would rebound to the west, or away from the church, and not towards it.)
Q. Why does a house in a valley very often smoke?
Q. What is the common remedy in both these cases?
A. To fix a cowl on the chimney top, to turn like a weather-cock, and present its back to the wind.
Q. Why will not a cowl always prevent a chimney smoking?
A. If the wind be strong, it will keep the opening of the cowl towards the steeple or hill; and then the reflected wind will blow into the cowl, and down the chimney.
Q. As a cowl is such a poor remedy, can any other be devised?
A. If the chimney flue can be carried higher than the steeple or hills, no wind can enter the flue.
Q. Why cannot the wind enter a chimney flue, if it be carried up higher than the steeple or hills?
A. Because the reflected wind would strike against the sides of the chimney-flue, and not pass over the opening at all.
A. If both door and chimney be placed on the same side of a room, the chimney will often smoke.
Q. Why will a chimney smoke, if the door and stove are both on the same side?
A. Because when the door is opened, a current of air will blow into the chimney-place, and drive the smoke into the room.
Q. What remedy can be applied to this evil?
A. The door must be set opposite to the chimney, or nearly so; and then the draught from the door will blow the smoke up the chimney, and not into the room.
Q. Why will a chimney smoke if it needs sweeping?
A. Because the obstruction in the chimney (presented by the loose soot, to the free passage of the smoke) delays its current, and prevents the draught.
Q. Why will a chimney smoke, if out of repair?
Q. Why will an arnott’s stove smoke, if the joints of the flue do not fit air-tight?
A. Because the cold air (which gets through the joints) chills the air in the flue, and prevents its ascent.
Q. Why does an old fashioned farm chimney-place so often smoke?
A. Because the opening is so very large, that much of the air which goes up the chimney, has never passed near the fire; and this cold air mixing with the other, so reduces its temperature, that it ascends very slowly, and the draught is destroyed.
Q. Why does a chimney smoke, if the draught be slack?
A. Because, unless the current of air up the chimney be very powerful, it cannot buoy the smoke up through the flue.
Q. If the opening of a chimney be too large, what remedy can be applied?
Q. Why will contracting the chimney-place prevent its smoking?
A. As the air will then pass nearer the fire, it will be more heated, and fly up the chimney much faster.
Q. Why do almost all chimneys smoke in gusty weather?
A. The gust (blowing the air away from the top of the chimney) removes (for a time) all resistance to the smoke: but when the wind lulls again, the resistance of the air suddenly returns—the draught is checked—and a puff of smoke rushes into the room.
Q. What is the use of a chimney-pot?
A. When the opening of a chimney is large, the top must be contracted by a chimney-pot, in order to increase the draught.
Q. How does a chimney-pot increase the draught of a chimney?
A. As the same quantity of hot air has to escape through a much smaller opening, it must pass through more quickly.