  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? A. The heat is evolved by the chemical action, produced by the cold water combining with the lime. 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 much heat may be thus secreted or made latent? A. All things contain a vast quantity of latent heat; but, as much as 1140° of heat may remain latent in water. 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] 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? A. Yes, many degrees; and by 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. A. Common charcoal, lamp-black, coke, black lead, and the diamond, are all varieties 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] 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] 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 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 [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? A. The hydrogen gas of the fuel being set free, and excited by a piece of lighted paper, instantly unites with the oxygen of the air, and makes a yellow flame: this flame heats the carbon of the 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 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? A. Carbon (being very solid) requires a great degree of heat to make it unite with the oxygen of the air. When fresh 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? A. Carbon (being solid), requires a great degree of heat to make it unite with oxygen, (or, in other words, to bring it 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? A. Because the intensity of combustion is so unequal, (owing to the gusty manner in which the air flies to the fuel; and the various shades of red, yellow, and white heat mingling with the black of the 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? A. Because paper burns out so rapidly, that it would not afford sufficient contact of flame to heat the coals to combustion. 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? A. As every flame tends upwards; when a flame is made at the bottom of a fire, it ascends through the fuel and heats it: whereas, if the fire were lighted from the top, the flame would not come into contact with the fuel piled below. 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? A. 1st—Because the moisture of the wet kindling prevents the oxygen of the air from getting to the fuel to form it into carbonic acid gas: and 2ndly—The heat of the fire is perpetually drawn off, by the conversion of water into steam. 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. 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? A. Because neither the bars nor coals (over which it passes) are red-hot. 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? A. As sound is produced by undulations 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. Q. Why is the light of a fire more intense sometimes than at others? 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? A. Because the volatile gases are 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? A. The greater the contrast (between the external air, and that which has 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. Q. Why does not a fire burn so freely in a thaw, as in a frost? 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? A. The breath carries the air to it with great rapidity; and the oxygen of the air kindles the red hot wick, as it kindles charred wood. 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. Q. Why are stoves fixed on the floor of a room? 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? A. The carbon of a clear fire, being sufficiently hot to unite with the oxygen of the air, produces carbonic acid gas, 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? A. The hydrogen of the water will burn with a flame; and the oxygen of the water will increase the intensity of that flame. 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? A. Yes; if a piece of wood be held near the fire for a little time it will blaze, even though it does not touch the 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. Q. What is meant by spontaneous combustion? 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? A. Because compression squeezes out 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. Q. Why do old rags, used for cleaning lamps and candles, sometimes set a house on FIRE? 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.) |
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