Fig. 2.—DIAGRAM SHOWING THE COMBUSTION OF A CANDLE.
Fig. 2.—DIAGRAM SHOWING THE COMBUSTION OF A CANDLE.
246.Why does the lower part of the flame of a candle(D)burn of a blue colour?
Because thehydrogenof the tallow, having a stronger affinity for theoxygenof the air thancarbonhas, ignites first. Pure hydrogen burns with a bluish flame.
247.Why does the middle of the flame(C)look dark?
Because it is occupied with gaseous vapours, derived from the tallow, which have not yetignited.
248.Why does the upper part of the flame(B)produce a bright yellow light?
Because it is in this part of the flame that thehydrogenof the candle, and theoxygenof the air, combine, and there is just sufficientcarbonmixed with thehydrogento improve itsilluminating power.
249.Why is there a fringe of pale light(A)around the upper part of the flame?
Because some of thecarbonescapes in a state ofincandesence, and as soon as it reaches the air it combines withoxygen, and so formscarbonic acid gas.
If any dark body, such as the blade of a knife, be held between the eye and the flame of the candle, so as to shut off the light of the more luminous part, the pale fringe around the flame will be found distinctly perceptible.Incandesencemeansheated to whiteness.
"How oft is the candle of the wicked put out? and how oft cometh their destruction upon them?"—Job xxi.
250.Why does the flame terminate in a point?
Because cold air rushes towards the flame in every direction, and is carried upward. At the point where the flame terminates the cold currents have soreduced the temperaturethat combustion can no longer be sustained.
251.Why, if you hold anything immediately over the flame, will the flame lengthen?
Because, by preventing the rapid escape of the heated air, you maintain a temperature whichincreases the combustionat the point of the flame.
252.Why should persons whose clothes take fire, throw themselves down?
Because flame spreads most rapidly in anupwarddirection.
253.Why should persons whose clothes are on fire roll slowly about when they are down?
Because they therebypress outthe fire.
254.Why does pressing a flame or a spark put it out?
Because it prevents the contact of the flame or spark with theoxygenof the air.
Extinguishers put out the flame of candles in the same manner. A person dies from "suffocation" through the absence of oxygen; and it is literally practicable to"suffocate" a fire.
255.Why does the wick turn black as it burns?
Because it consists principally ofcarbon.
256.Why, when the point of the wick turns out and meets the air, does it exhibit a bright spark?
Because thecarbonof the wick comes into immediate contact with theoxygenof the air.
257.Why does holding a candle "upside down" put it out?
Because the melted grease runs down too rapidly, and at too low a temperature to undergo combustion. It thereforereduces the heat, and extinguishes the flame.
"Lord, what is man that thou takest knowledge of him! or the son of man, that thou makest account of him."—Psalms cxliv.
258.Why is it more difficult to blow out the flame of a candle with a cotton wick than one with a rush wick?
Because the cotton wick imbibes more of the combustible materials, and holds in its loose texture the inflammable gases in a state ready for combustion.
259.Why does blowing sharply at a candle flame put it out?
Because the breath drives away the vapour of the grease which, becoming gaseous, supports the flame.
And because too rapid a flow of cold air reduces the temperature below the point at which combustion can be maintained.
260.Why will a gentle puff of breath, if given speedily after the flame is extinguished, rekindle it?
Because theoxygenof the air combines with thecarbonandhydrogenthat are still escaping from theheated wick, and re-lights it.
261.Why will not a similar puff rekindle the flame of a rushlight?
Because its wick retains butlittle heat, and holds a comparatively small amount of combustible matter in avolatile state.
262.Why is a fire, when it is very low, sometimes put out by blowing it?
Because the too rapid flow of cold airreduces the temperatureof the burning mass.
263.Why will a piece of paper twisted like an extinguisher put out a candle?
Because, before the flame of the candle can ignite the paper,the oxygen contained within it is consumed, and the flame is suffocated.
"When his candle shined upon my head, and when by his light I walked through darkness."—Job xxix.
264.Why do tallow candles require snuffing?
Because theoxygenof the air cannot reach the wick through the body of flame—therefore theunconsumed carbonaccumulates upon the wick.
265.Why do composite and wax candles not require snuffing?
Because their wicks are made by a series of plaits, by which they are bent to meet theoxygenof the air, and consumed.
266.Why does setting a glass upon a lamp increase its brilliancy, though it shortens the flame?
Because it conducts an increase of air to the flame, and the greater supply ofoxygencauses the escaping vapour of oil to be all rapidly consumed.
267.Why does a candle burn dimly when the wick has become loaded with carbon?
Because the carbonradiatesthe heat, and disperses it, and reduces the heat of the flame below that temperature which is essential to itsluminosity.
268.What differences characterise the combustion of carbon and of hydrogen?
The combustion ofcarbontakes place without the production of flame. The charcoal (or carbon in any other form) being heated to redness, enters directly into combination with theoxygenof the surrounding air, and the carbonic acid gas, being invisible, passes away unobserved.
But in the combustion ofhydrogenthe heat developed is so intense as to renderthe gas itself luminous, just as iron may be heated to a red or white heat.
269.What has become of the candle when it has been burnt?
It has been resolved partly intocarbonic acid gaswhich, though unperceived, has diffused itself through the surrounding air; and partly intowater, which escaped in the form of thin vapour.
270.Has any part of the candle been consumed or lost?
No; there is no such thing as "loss" in the operations of nature. Every particle of the candle, now invisible, exists either in the form ofgas,vapour, orwater, with, perhaps, a few solid particles that may be calledashes, but which are too minute to excite attention.
"I know that whatsoever God doeth, it shall be for ever: nothing can be put to it, nor anything taken from it; and God doeth it that men should fear before him."—Eccles. iii.
The economy of nature should teach us a very impressive lesson—nothing is suffered to be wasted, not even the slightest atom. As soon as any body has fulfilled its purpose in one state of being, it is passed on to another. The candle, existing no longer as a candle, is flying upon the wings of the air ascarbonic acid gas, and aswater. These probably find their way to the garden or the field, where the carbonic acid gas forms thefood of the plant, and the water affords it a refreshingdrink. And can it be supposed that the Almighty Being, who has thus economised the existence of thematerialcreation, should be less mindful of the immaterialsoulof man? Thereisan eternity before us, the certainty of which is evidenced even by the laws of the material creation.
271.What is coal?
Coal is a "vegetable fossil."
272.What is meant by a vegetable fossil?
It is a substanceoriginally vegetable, which, by pressure and other agencies within the earth, has been brought to a condition approaching that ofmineralor earthy matter.
273.Why do we know that coal is of vegetable origin?
By thechemical componentsof its substance; and also by thevegetable formsthat are found abundantly in coal beds.
Professor Buckland, in hisBridgewater Treatise, speaking of the impressions of plants found in the coal mines, says; "The finest example I have ever witnessed is that of the coal mines of Bohemia. The most elaborate imitations of living foliage upon the painted ceilings of Italian palaces bear no comparison with the beauteous profusion of extinct vegetable forms with which the galleries of these instructive coal mines are overhung. The roof is covered as with a canopy of gorgeous tapestry, enriched with festoons of most graceful foliage, flung in wild irregular profusion over every part of its surface. The effect is heightened by the contrast of the coal-black colour of these vegetables with the light ground-work of the rock to which they are attached. The spectator feels himself transported, as if by enchantment, into the forests of another world; he beholds trees, of forms and characters now unknown upon the surface of theearth, presented to his senses almost in the beauty and vigour of their primeval life; their scaly stems and bending branches, with their delicate apparatus of foliage, are all spread forth before him, little impaired by the lapse of countless ages, and bearing faithful records of extinct systems of vegetation which began and terminated in times of which these relics are the infallible historians."
"Surely every man walketh in a vain show; surely they are disquieted in vain: he heapeth up riches, and knoweth not who shall gather them."—Ps. xxxix.
274.What are the chemical components of coal?
They consist ofcarbon,hydrogen,oxygen, andnitrogen. The proportions of these elements vary in different kinds of coal. Carbon is the chief component; and the proportions may be stated to be, generally,carbon, 90 per cent.;hydrogen, from 3 to 6 per cent.; the other elements enter into the compound in such small proportions, that, for all ordinary purposes, it is sufficient to say that coal consists ofcarbonandhydrogen, but chiefly ofcarbon.
275.What is charcoal?
Charcoal consists almost entirely ofcarbon. It is made fromwoodby the application of heat, without the admission of air. The hydrogen and oxygen of the wood are expelled, and that which remains is charcoal, orcarbonin one of its purest states.
276.What is animal charcoal?
Animal charcoal, like vegetable charcoal, consists ofcarbonin a state approaching purity. It is made from thebones of animals, heated in iron cylinders. It is commonly calledivory black.
277.What is the purest form of carbon known?
The purest form ofcarbonis thediamond, which may be said to be absolutely pure.
Hence we derive another of the beautiful lessons of science—a lesson which teaches us todespise nothing that God has given. The soot which blackens the face of a chimney-sweep, and the diamond that glistens in the crown of the monarch, consist of the same element in merely a different atomic condition. What a lesson of humility this teaches to Pride! The haughty beauty as she walks the ball-room, inwardly proud of the radiance of her gems as they rise and fall upon her breast, little thinks or knows thatevery breath that is expired around her wafts away the like element of which her treasures are composed. That even in our own flesh and bones the same abounding substance lies hid; and that the buried tree of the primitive world, and the little flower of to-day, are both the instruments of giving this singular element to man!
278.What is coke?
Coke is coal, divested of its hydrogen and other volatile parts, bya similar process to that by which charcoal is produced. It forms the residue after hydrogen gas has been made from coals. It consists almost entirely ofcarbon.
"Oh that men would praise the Lord for his goodness, and for his wonderful works to the children of men."—Psalm cvii.
279.Why do burning coals produce yellow flame?
Because thehydrogenwhich they contain is combined with some proportion ofcarbon, which imparts a bright yellow colour to the flames.
280.Why do some of the flames of a fire appear much whiter than others?
Because the quality of coals, and the conditions under which they are burnt, are liable to variation. Some coals yield aheavyhydrogen, calledbi-carburetted hydrogen, which burns with a much brighter flame thancarburetted hydrogen.
281.Why does bi-carburetted hydrogen burn with a whiter flame than the common coal gas?
Because it is combined with a larger proportion ofcarbon, to which it owes its increased luminosity.
282.Why do some of the flames of a fire appear blue?
Because the hydrogen which is escaping where those flames occur ispure hydrogen, destitute of carbon.
283.Why does the fire sometimes appear red, and without flame?
Because the volatile gases have been driven off and consumed, and combustion is continued by thecarbonof the coals and theoxygenof the air.
284.What effect has the burning of a fire upon the composition of the air?
It is found that in burning 10lb. of coal the oxygen contained in 1,551 cubic feet of air is altogether absorbed. It is therefore necessary to keep the atmosphere of a room, in which a coal fire is burning, fresh and pure, to supply 155 cubic feet of fresh air for every pound of coal that is consumed.
"O Lord how manifold are thy works, in wisdom hast thou made them all: the earth is full of thy riches."--Psalm civ.
285.Why does wood which is "green" hiss and steam when it is burnt?
Because it contains a large amount of water, which must be evaporated before combustion can proceed.
286.What is the effect of this evaporation?
A great deal of heat is unprofitably expended in driving off the water of the fuel.
287.Why does poking a fire cause it to burn more brightly?
Because it opens avenues through which the air may enter to supplyoxygen.
288.Why do "blowers" improve the draft of air through a fire?
Because, by obstructing the passage of the current of airoverthe fire, they cause additional air to passthroughit, and therefore a greater amount ofoxygenis carried to the coals.
289.What is smoke?
Unconsumed particles ofcoal, rendered volatile by heat, and driven off.
290.What is soot?
Carbonin minute particles, driven off with other volatile matters and deposited on the walls of chimneys.
291.Why do fresh coals increase the quantity of smoke?
Because they contain volatile matters which are easily driven off; and because, also, they reduce momentarily the heat, so that those matters that first escape cannot be consumed.
292.Why do charcoal and coke fires burn clearly and without flame?
Because thehydrogenhas been previously driven off from those substances.
293.Why is it difficult to light charcoal and coke fires?
Because they contain nohydrogento produceflame, and assist combustion.
"He hath made his wonderful works to be remembered: the Lord is precious and full of compassion."—Psalm cxl.
A new plan of kindling fires has lately been recommended. Coals are to be laid in thebottomof the fire-place to a considerable depth, then the paper and wood are to be laid on, and then a little coals and cinders over them. This plan of "laying in" the fire is precisely thereverseof that which has been pursued for many years. The theory is, that when the coals in the bottom are ignited, a more even combustion is kept up, whilst the smoke and gas which would otherwise escape, and become as so much waste fuel, is burnt up, and produces heat. We have heard the plan strongly recommended by persons who have tried it, and who testify to the great economy of fuel to which it conduces.
294.Why does paper ignite more readily than wood?
Because its texture is lessdensethan that of wood; its particles are therefore morereadily heatedand decomposed.
295.But if articles of loose texture are bad conductors of heat, why do they so easily ignite?
The fact that they arebad conductorsassists their ignition. The heat which would pass from particle to particle of the dense substance of iron, and beconducted away, accumulates in the interspaces of paper, and ignites it.
296.Why does wood ignite less readily than paper?
Because its substance isdenserthan that of paper; it therefore requires a higher degree of heat to inflame its substance.
297.Why does wood, when ignited, burn longer than paper?
Because, being a denser substance, it submits alarger number of particles, within a given space, to the action of the heat, and the formation of gases.
298.Why do we, in lighting a fire, first lay in paper, then wood, and lastly coals?
Because the paper is more easily ignited than wood, and wood than coals; therefore thepaperassists the ignition of thewood, and thewoodassists the ignition of thecoals.
"It is a good thing to give thanks unto the Lord, and to sing praises unto thy name, O Most High."—Psalm xcii.
299.Why will not wood ignite by the flame of a match?
It will do so, unless there is a great disproportion between the size of the wood and the flame of a match. Athinpiece of wood will ignite, but a square block will not, because the heat of the flame is insufficient to raise the temperature of alarge surfaceto the point that will drive out its gases.
300.Why do we place the paper under the wood, and the wood under the coals?
Because heat and flame, when surrounded by air, have a strong tendency to spread themselvesupwards.
301.Would it be possible to light the coals by putting the paper and the wood upon the top?
It would be possible; but the loss of heat would be so great, that amuch larger quantityof paper and wood would be required.
302.Why does a poker laid across the top of a dull fire revive it?
Because the pokerradiatesthe heat it receives from the fire downward upon the fuel.
Because, also, it divides the ascending air, and therebycreates currents.
The amount of good which the poker does to the fire is very slight indeed. Generally, the housewife stirs the fire first, and blows or brushes away the ashes that prevent the influx of air. She then places the poker upon the top, and the popular mind supposes that the poker "draws" the fire. The custom of placing a poker over the fire is of very remote antiquity. It was once believed that forminga cross, by placing the poker over the bars, protected the fire from the hostility of malignantwitches!
303.Why should fire-places be fixed as low as possible in rooms?
Because heatascends, and when the fire-places are high the lower parts of the room areinadequately warmed.Also, as currents of air fly towards the fire, elevated fire-placescause draftsabout the persons of the inmates to a much greater extent than they would if they were lower down.
"Unto thee, O God, do we give thanks: for that thy name is near thy wondrous works declare."—Psalm lxxv.
304.Why, if a piece of paper be laid with its flat surface upon the fire, will it "char," but not ignite?
Because, as in the case of the proper candle-extinguisher, thecarbonic acid gasaccumulating beneath it prevents its igniting.
305.Why, if you direct a current of air towards the paper, will it burst into a blaze?
Because the carbonic acid gas is displaced by a current of air containingoxygen.
306.Why does water extinguish fire?
Because itsaturates the fuel, and prevents the gases thereof from combining with the oxygen of the air.
307.As water contains oxygen, why does not the oxygen of the water support the fire?
Because the affinity between thehydrogenandoxygenof the water is so strong that fire cannot separate them.
Water may be decomposed byheat, as will be hereafter explained. But the heat of an ordinary fire is insufficient. There is, however, some reason for believing that, in cases of very large fires, such as the accidental burning of houses, &c., when the supply of water thrown upon the fire is very deficient, the waterdoesbecomedecomposed, and add to the fury of the flames.
308.Why does the blacksmith sprinkle water upon the coals of his forge?
The blacksmith usessmall coalsbecause the small pieces thereof are more easily ignited than large lumps would be, and they convey heat better by completely surrounding the articles put into the fire. He sprinkles water on the coal dustto hold its particles together by cohesion, until the heat forms it into a cake. A strong blast of hot hair drives the vapour of the water away, and leaves a porous mass to the action of the fire.
309.Why, when the blacksmith thrusts a heated iron into a tankard of water, do we recognise a peculiar smell?
Because the intense heat disengages a small volume of the gases of which water is formed.
"Oh the depth of the riches both of the wisdom and knowledge of God! how unsearchable are his judgments, and his ways past finding out."—Rom. xi.
310.Which gas do we (in this instance) recognise by the smell?
Thehydrogengas. Oxygen gas possesses no odour.
311.What is Spontaneous Combustion?
Spontaneous combustion is that which occurs in various bodies when they become highly heated bychemical changes.
312.Why is heat developed during chemical changes?
Because, as all bodies containlatent caloric, the disturbance of the atoms of which those bodies are composed, during the new combinations that constitutechemical changes, frequently sets the caloric free, and anaccumulation of caloricproduces spontaneous combustion.
313.Does a match ignite spontaneously when drawn over a rough surface?
No. Because in this case the combustion arises from heatapplied by friction.
314.Does phosphorous ignite spontaneously when held in a warm hand?
Phosphorous will ignite when held in a warm hand, but it does not then produce spontaneous combustion, because it ignites through the agency ofapplied heat.
315.But if a piece of dry phosphorous be sprinkled with powdered charcoal it will ignite, without the application of heat. Why is this?
Because thecarbon(charcoal) absorbsoxygenfrom the air, and conveys it to thephosphorous. Here arechemical changeswhich develope heat, and producespontaneous combustion.
316.Why do hay-stacks sometimes take fire?
Because the hay, having become damp, decays, and passes on to a state offermentation, in whichchemical changes occur, duringwhich heat is evolved. Hay, taking fire under these circumstances, would exhibitspontaneous combustion.
"Who hath woe? who hath sorrow? who hath contentions? who hath babbling? who hath words without cause? who hath redness of the eyes? * * * They that tarry long at the wine."—Prov. xxiii.
317.What substances are liable to produce spontaneous combustion?
All substances which contain sugar, starch, and other components liable tofermentation. All bodies that evolve, under low degrees of temperature,inflammable gases. And all organic bodies undergoing decay.
Grain, cotton, hemp, flax, coals, oily and greasy substances.
318.What is the Ignis Fatuus (sometimes called "Will-o'-the-Wisp", "Corpse Candles," and "Jack-o'-Lantern")?
It is a flame produced by spontaneous combustion, caused by the decay of animal or vegetable bodies, which evolvephosphoretted hydrogengas, under circumstances attended by a low degree of heat, sufficient to ignite the gases. It is mostly seen over marshy places, and burial-grounds.
Many a "Ghost Story" has owed its origin to these singular but harmless appearances. People, ignorant of the cause, have been terrified at the effect. To the fancy of an affrighted mortal, the simple flame of theIgnis Fatuushas assumed the form of a departed friend, and even found a supernatural voice. If, excited by a momentary daring, the beholder moved towards the light upon which he gazed, it fled from him. If he turned from it and walked away, it followed him, step by step. The darkness of a lonely road, or the sacred solitude of a burial-place, have been sufficient accessories to authenticate the appearance of a spirit. And yet how simple the phenomenon? Matters so volatile as those which produce theIgnis Fatuuswould naturally be driven back by the motion in the air caused by an advancing body; and, on the other hand, a body moving from them would create a current in which theIgnis Fatuuswould follow. Poisonous gases, escaping from decaying bodies, pass into the air and take fire. They are thereby converted into harmless compounds. Thus we see that the "ghost" which terrifies the mind of the ignorant, becomes a "guardian angel" to the educated.
319.Has spontaneous combustion ever occurred in living bodies?
It has occurred in numerous instances to persons habituated to the excessive use of spirits.
320.Why should spontaneous combustion occur in the case of the drunkard?
Because spirituous drinks contain a large proportion of ALCOHOL, one of the constituents of which ishydrogen. The vital energies of the drunkard, being destroyed by excess, chemical agencies obtain an ascendancy, and it is supposed that thehydrogenof the alcohol combines with thephosphorousof the body to formphosphoretted hydrogen, which ignites spontaneously, and literally consumes the living temple.
"Drought and heat consume the snow waters; so doth the grave those which have sinned."—Job xxiv.
Cases of spontaneous combustion are of rare occurrence. But they are sufficiently well authenticated by high medical authority, in many parts of the world, to present an awful warning to the inveterate drunkard. The cases of which we have read the particulars present details of the most appalling description. How signally the Almighty displeasure at intemperance is expressed, when the very drink which imparts the mad pleasure of intoxication is made thedirectinstrument by which the drunkard is destroyed!
321.Why does friction produce heat?
Because all bodies containlatent heat, that is, heat that lies hid in their substance, and the rubbings of two bodies against each otherdraws the latent heat to the excited surfaces.
322.Why does the rubbing of two surfaces together attract latent heat to those surfaces?
Because it is a law of nature thatheatshall always attendmotion; and it is generally found that theintensity of heatbears a specific relation to thevelocity of motion.
323.What are the sources of heat?
Theraysof thesun, thecurrentsofelectricity, theactionofchemicals, and themotionofsubstances.
324.Why does water freeze?
Because its latent heat is partlydrawn offby the surrounding air.
325.Why does ice melt?
Because the heat, once latent in the water, but drawn off by the air,has returnedto it, and restored the water to its former condition.
"So teach us to number our days, that we may apply our hearts unto wisdom."Psalm xc.
326.Why does water become steam?
Because a larger amount of heat has entered into it than can remain latent in water. The water therefore expands and rises in the form of vapour, orwater attenuated by heat.
327.How many degrees of heat are latent, or hidden, in the different states of water?
In thawingice, 140 deg. of caloric become latent; and in converting the water into steam, 1,000 deg. more of caloric are be taken up. Therefore,icerequires to take up 1,140 deg. of latent caloric before it becomes steam.
328.What is the most modern theory of heat?
It is this—that caloric, which produces heat, is an extremelysubtile fluid, of so refined a nature that it possesses no weight, yet is capable of diffusing itself among the particles of the most solid bodies.
It is also believed that—all bodies are subject to the action of two opposing forces: one, themutual attractionof theirparticles; the other, therepulsive forceofcaloric—and that bodies exist in theæriform,fluid, orsolid state,according to the predominance of either the one or the other of these opposing forces.
329.How do we measure the quantity of caloric in any substance?
It is impossible to determine the amount of caloric which any body contains. Oursensationswould obviously be deceptive, since, if we dipped the right hand in snow, and held the left hand before the fire, and then immersed both hands in cold water, the water would feelwarmto theright handandcoldto theleft hand.
But, ascaloricuniformly expands substances that are under its influence, one of the bodies most sensitive tocalorificeffects has been selected to be theindicatorof the amount ofcaloric. This substance isquicksilver; and the scale of measurement, and the apparatus for exhibiting the rise or fall of the quicksilver, constitute thethermometer.
330.If it is impossible to measure the amount of caloric in any substance, how can it be said that ice absorbs140.deg. in becoming water?
Those figures simply record the amount of calorie indicated by thethermometer. The instrument will show with sufficient accuracy therelative amountof caloric in various bodies, or in the same bodiesunder different circumstances, but it can never determine theprecise amount of caloricin any one body.
"Great is the Lord, and greatly to be praised in the city of our God, in the mountain of his holiness."—Psalm xlviii.
331.Why, if a hot and a cold body were placed near to each other, would the cold one become warmer, and the hot one cooler?
Becausefree caloric(that is, caloric that is not latent,) always exhibits a tendency to establish anequilibrium. If twenty bodies, of different temperatures, were placed in the same atmosphere, they wouldall soon arrive at the same temperature. The caloric would leave the bodies of those of thehighest, and find its way to those of thelowesttemperature.
332.How does caloric travel?
It travels inparallel raysin all directions with a velocity approximating to that of light; and it passes through various bodies with a rapidity proportionate to their power ofconduction.
333.Why does melted metal run like a stream of fluid?
Becausecalorichas passed into its substance, and, repelling its particles, has separated them to that degree which produces fluidity.
334.How do we know that it is caloric passing into the substance of the metal which produces this effect?
Because, as soon as a bar of metal begins to be heated, itexpandsandlengthens. It continues to do so, until the heat arrives at that point whichcauses the metal to melt.
335.Why does the iron of an ironing-box sometimes become too large for the box to receive it?
Becausecalorichas passed into the substance of the iron, andrepelled its particles, by which it has become expanded.
336.Why does the iron enter the box when it has become partially cooled?
Because a portion of the caloric has left the iron, the particles of which havedrawn closer together, and contracted the mass.
"Cast thy burden upon the Lord, and he shall sustain thee; he shall never suffer the righteous to be moved."—Psalm lv.
This effect is frequently observed by females in domestic life, who, when they are ironing, or using the Italian irons, find that the heated metal has been too much expanded to enter the box or tube. They find it necessary to wait until the cooling of the iron has had the effect of reducing its dimensions. The expansion of bodies by heat is one of the grandest and most important laws of nature. We are indebted to it for some of the most beautiful, as well as the most awful, phenomena. And science has gained some of its mightiest conquests through its aid. Yet frequently, though quite unthought of, in the hands of the humble laundress, will be found a most striking illustration of this wonderful force of caloric.
337.Are there any instances in which the abstraction of latent heat will reduce the hulk of bodies?
Yes, there are several. But the most familiar one is that which is exhibited by mixing apintof theoil of vitriolwith apintofwater.A considerable amount of heat will be evolved; and it will be found that the two pints of fluidwill not afterwards fill a quart measure.
338.Is there any latent heat in air?
Yes: a considerable amount. In a pint measure of air, though in no way evident to our perceptions, there lurks sufficient caloric to raise a piece of metal several inches square to glowing redness.
339.How do we know that caloric exists in the air?
It has been positively demonstrated by the invention of a small condensing syringe, by which, through the rapid compression of a small volume of air, a spark is emitted which ignites a piece of prepared tinder.
340.What is the cause of the spark when a horse's shoe strikes against a stone?
Thelatent heatof the iron or the stone is set free by theviolent percussion. The same effect takes place whenflintstrikes againststeel, as in the old method of obtaining a light with the aid of the tinder-box.
"The waters are laid as with a stone, and the face of the deep is frozen."—Job xxxviii.
What an eloquent lecture might be delivered upon the old-fashioned tinder-box, illustrated by the one experiment of "striking a light." In that box lie, cold and motionless, the Flint and Steel, rude in form and crude in substance. And yet, within the breast of each, there lies a spark of that grand elementwhich influences every atom of the universe; a spark which could invoke the fierce agents of destruction to wrap their blasting flames around a stately forest, or a crowded city, and sweep it from the face of the world; or which might kindle the genial blaze upon the homely hearth, and shed a radiant glow upon a group of smiling faces; a spark such as that which rises with the curling smoke from the village blackmith's forge—or that which leaps with terrific wrath from the troubled breast of a Vesuvius. And then the tinder—the cotton—the carbon: What a tale might be told of the cotton-field where it grew, of the black slave who plucked it, of the white toiler who spun it into a garment, and of the village beauty who wore it—until, faded and despised, it was cast amongst a heap of old rags, and finally found its way to the tinder-box. Then the Tinder might tell of its hopes; how, though now a blackened mass, soiling everything that touched it, it would soon be wedded to one of the great ministers of nature, and fly away on transparent wings, until, resting upon some Alpine tree, it would make its home among the green leaves, and for a while live in freshness and beauty, looking down upon the peaceful vale. Then the Steel might tell its story, how for centuries it lay in the deep caverns of the earth, until man, with his unquiet spirit, dug down to the dark depths and dragged it forth, saying, "No longer be at peace." Then would come tales of the fiery furnace, what Fire had done for Steel, and what Steel had done for Fire. And then the Flint might tell of the time when the weather-bound mariners, lighting their fires upon the Syrian shore, melted silicious stones into gems of glass, and thus led the way to the discovery of the transparent pane that gives a crystal inlet to the light of our homes; of the mirror in whose face the lady contemplates her charms; of the microscope and the telescope by which the invisible are brought to sight, and the distant drawn near; of the prism by which Newton analysed the rays of light; and of the photographic camera in which the sun prints with his own rays the pictures of his own adorning. And then both Flint and Steel might relate their adventures in the battle-field, whither they had gone together; and of fights they had seen in which man struck down his fellow-man, and like a fiend had revelled in his brother's blood. Thus, even from the cold hearts of flint and steel, man might learn a lesson which should make him blush at the "glory of war;" and the proud, who despise the teachings of small things, might learn to appreciate the truths that are linked to the story of a "tinder-box."
341.Since all bodies expand by heat and contract by cold, why does water, when it reaches the freezing point, expand?
Because, in freezing, water undergoes crystallization, in which its particles assume a new arrangement occupyinggreater space.
342.Why does water never freeze to a great depth?
Because the covering of ice which is formed upon the surface ofthe water prevents the cold air from continuing to draw off thecaloricof the water.
"For he saith to the snow, Be thou on the earth; likewise to the small rain, and to the great rain of his strength."—Job xxxvii.
343.Why has this exceptional law of the expansion of water, when freezing, been ordained?
Because, but for this, deep waters might be frozen through their whole depth. This would destroy the myriads of fish and other living things that inhabit the water. Parts of the earth, now clad in verdure, would be lost in eternal winter; and even in the most temperate zones it would take months to effect a thaw; and thawing would be attended with such floods and subterranean commotion as are terrible to contemplate.
344.Why are bed-room windows sometimes covered with crystalline forms on winter mornings?
Because the vapour of the breaths of the inmates has condensed upon the window-panes, and formed water. The water has frozen with the cold, and exhibits the beautiful crystalline forms into which its particles are arranged.
Here we have another domestic illustration of the great laws of nature. It is the same law which locks the arctic regions in ice and decorates our window-panes. This beautiful phenomenon is usually witnessed by us on frosty mornings when we rise from our beds. It has a story which the observer of nature may read in its sparkling eyes. It tells that, although without the air is biting cold, God has wrapped a mantle around the face of nature to keep it from injury; and that the earth and the waters, though looking chilled and dead, have still the warmth of life preserved in their bosoms.
345.What is dew?
Dew iswatery vapourdiffused in the air,condensedby coming in contact with bodiescolder than the atmosphere.
346.Why does the air become charged with watery vapour?
Because, during the day, under the influence of the sun's rays, vapours areexhaledfrom all the moist and watery surfaces of the earth. These vapours areheld in suspensionin the atmosphere until, by a change in the temperature of the earth, and of bodies on the surface of the earth, they arecondensed, and deposited in translucid drops.
347.What causes the decline of temperature that favours the deposition of dew?
The earth, which during the dayreceived heatfrom the solar rays,radiates the heatback into the air, and therefore becomes itself colder. All the various objects upon the face of the earth alsoradiate heatin a greater or lesser degree. And dew will be found to be deposited upon the surfaces of such bodies in proportion to the fall of their temperature throughradiation.
"The Lord is my shepherd, I shall not want. He maketh me to lie down in green pastures."—Psalm xxiii.
348.Why is there little or no dew when the nights are cloudy?
Because clouds act as secondary radiators; and when theearthradiates its heat towards theclouds, the clouds againradiate it back to the earth.