IBRARY OF THE UNIVERSITY OF CALIFORNIA BRARY OF THE UNIVERSITY OF CALIFORNIA . LIBRARY tx IVERSITY OF CALIFORNIA IVERSITY OF CALIFORNIA LIBRARY OF THE UNIVERSITY L2866J ^n^-' LIBRARY OF THE UNIVERSITY . A GUIDE TO THE SCIENTIFIC KNOWLEDGE OF THINGS FAMILIAR; BY REV. DR. BREWER, TRINITY HALL, CAMBRIDGE, Head Master of King's College School, Norwich in union with King-* College, London. ;',. . . .268 XXV. BAROMETER .296 Ten Special Rules, &c. XXVI. SNOW. HAIL. RAIN ... 309 XXVII. WATER . . . . . .319 XXVIII. ICE 325 Freezing mixtures. Frost. Swimming, &c. XXIX. LIGHT 338 Reflection. Telescopes. Refraction. Spectacles. Rainbows. Color. XXX. SOUND .377 Ear trumpets. Echoes, &c. PART III. -MISCELLANEOUS. Attraction. Anti-putrescents. Dreams. Color. Ink. Iron. Bread. Horn. India-rubber. Starch. Meat. Butter. Mirrors. Bricks. Milk. Steel. Manure. Soap, etc. ... 387 Antidotes to Poisons 452 Glossary 454 Index 455 Index to Part III. Miscellaneous Ques- tions . . 485 PART I. HEAT. INTRODUCTION. Q. What is HEAT 1 A. The sensation of warmth. Q. How is this sensation produced ? A. When we touch a substance hot- ter than ourselves, a subtile invisible stream flows from the hotter substance, and produces on our nerves the " sensa- tion of warmth." Q. What is that "subtile invisible stream" CALLED, which flows from the hotter substance ? A. CALO'RIC. Caloric, therefore, is the agent, which produces the sensation of warmth; but HEAT is the sensation itself. Q. What are the four principal SOURCES of heat? A. 1. The Sun. 2. Electricity. 3. Chemical Action ; and 4. Mechan- ical Action. (1*) 9 10 HEAT. Q. What are the principal EFFECTS of heat ? A. Expansion, Liquefaction, Vapor- ization, and Ignition. CHAPTER I. THE SUN. Q. What is the PRINCIPAL source of heat ? A. The SUN. Q. Why do BURNING GLASSES set fire to sub- stances submitted to their power ? A. Because, when the rays of the Sun pass through the burning glass, thejr are bent toward one point, called the " focus;" in consequence of which, the light and heat at this point are very greatly increased. Q. Why is there a DARK RIM round this focus ? A. Because the rays of light are bent from the rim into the focus; and, as the rim is deprived of these rays, it is darkened. Q. Are ALL the rays bent into one point ? A. Not quite all : and, therefore, the rim round the focus is not quite black, but only dim. ELECTRICITY. 11 CHAPTER II. ELECTRICITY. Q. What is the SECOND chief source of heat ? A. ELECTRICITY. Q. What is LIGHTNING ? A. Lightning 1 is accumulated elec- tricity discharged from the clouds. Like that from a " Leyden jar." Q. What CAUSES the discharge of an electric cloud ? A. When a cloud, overcharged with electric fluid, approaches another which is undercharged, the fluid rushes from the former into the latter, till both con- tain the same quantity. N. B. It is generally supposed that there are two dif- ferent sorts of Electricity one Vitreous, and the other Resinous. Q. Is there any OTHER, cause of lightning, be- sides the one just mentioned ? A. Yes ; sometimes mountains, trees, and steeples, will discharge the light- ning from a cloud floating near ; and sometimes electric fluid rushes out of the earth into the clouds. Q. What produces ELECTRICITY in the CLOUDS ? A. 1st The evaporation from the earth's surface ; 12 ELECTRICITY. 2dly The chemical changes, which take place on the earth's surface ; and 3dly Currents of air of unequal temperature, which excite electricity by friction, as they pass by each other. Q. How HIGH are the LIGHTNING CLOUDS from the earth ? A. Sometimes they are elevated 4 or 5 miles high ; and sometimes actually touch the earth with one of their edges : but they are rarely discharged in a thun- der storm, when they are more than 700 yards above the surface of the earth. Q. How high are the clouds GENERALLY ? A. In a jine day, the clouds are often 4 or 5 miles above our heads ; but the average height of the clouds is from li to 2 miles. Q. Why is lightning sometimes FORKED ? A. Because the lightning-cloud is a long way off ; and the resistance of the air is so great, that the electrical cur- rent is diverted into a zig-zag course. Q. How does the resistance of the air make the lightning zig-zag ? A. As the lightning condenses the air in the immediate advance of its path, it flies from side to side, in order to pass where there is the least resistance. LIGHTNING. 13 Q. Why are there sometimes TWO flashes of forked lightning at the same moment ? A. Because (in very severe storms) the flash will divide into two or more parts ; each of which will assume the zig-zag form. Q. Why is the FLASH sometimes quite STRAIGHT ? A. Because the lightning-cloud is near the earth ; and, as the flash meets with very little resistance, it is not diverted; (in other words) the flash is straight. Q. What is SHEET LIGHTNING ? A. Either the reflection of distant flashes not distinctly visible ; or else several flashes intermingled. Q. What OTHER for m does lightning occasion- ally assume ? A. Sometimes the flash is globular ; which is the most dangerous form of lightning. Q. What are those BALLS of FIRE, which sometimes fall to the earth in a thunder-storm ? A. Masses of explosive gas, formed in the air : they generally move more slowly than lightning. Q. Why are BALLS of FIRE so very DANGER- OUS? A. Because, when they fall, they 14 ELECTRICITY. explode like a cannon ; 'and occasion much mischief. Q. Do these BALLS of FIRE ever run along the ground ? A. Yes ; sometimes they run a con- siderable way along* the ground, and explode in a mass : At other times they split into nume- rous smaller balls, each of which explodes in a similar manner. Q. What MISCHIEF will these balls of fire produce ? A. They will set houses and barns on fire ; and kill all cattle and human being's, which happen to be in their Q. Why does LIGHTNING sometimes KILL men and beasts ? A. Because (when the electric cur- rent passes throug-h a man or beast) it produces so violent an action upon the nerves, that it destroys life. Q. WHEN is a person struck DEAD by light- ning^ A. Only when his body forms a part of the lightning's path ; i. e. when the electric fluid (in its way to the earth) actually passes through his body. Q. Why- are MEN sometimes MAIMED by light* ning ? THUNDER; 15 A. Because the electric fluid pro- duces an action upon the nerves sufficient to injure them, but not to destroy Ufe. Q. What is THUNDER ? A. The noise made by the concussion of the air when it closes again, after it has been parted by the lightning* flash. A part of the noise is owing to certain physical and chem- ical changes produced in the air by the electric fluid. Q. Why does LIGHTNING part the air through which it passes ? it does not part a rod of iron. A. As iron is a conductor, it allows the fluid to pass freely over it ; but air (being* a non-conductor) resists its pas- sage. Q. Why is THUNDER sometimes ONE VAST CRASH ? A. Because the lightning-cloud is near the earth ; and as all the vibrations of the air (on which sound depends) reach the ear at the same moment, they seem like one vast sound. Q. Why is the PEAL sometimes an IRREGULAR, broken ROAR ? A. Because the lightning-cloud is a long way off; and as some of the vibra- tions of the air have much further to travel than others, they reach the ear at different times, and produce a continuous sound. 16 THUNDER. Q. Which vibrations will be soonest heard? A. Those produced in the lowest por- tions of the air. Q. Why will those vibrations be heard FIRST, which are made LAST ? A. Because the flash (which produces the sound) is almost instantaneous, but sound takes a whole second of time to travel 380 yards. Q. If a thunder-cloud were 1900 yards off, how long would the peal last ? A. Five seconds : we should^rsZ hear the vibrations produced in those portions of the air contiguous to the earth ; then those more remote ; and it would be 5 seconds before those vibrations reached us, which were made in the immediate vicinity of the cloud. 380 X 5 = 1900. A popular method of telling how far the storm is off is fiiis Immediately you see the flash, put your hand upon your pulse, and count how many times it beats before you hear the thunder: if it beats 6 pulsations, the storm is 1 mile off; if 12 pulsations, it is 2 miles off, and so on. Q. Why is the THUNDER sometimes like a deep GROWL ? A. Because the storm is far distant, and the sound of the thunder indistinct. Q. Is not the sound of thunder affected by LOCAL circumstances ? A. Yes; \heflatter the country, the more unbroken the peal. Mountain THUNDER-BOLTS. 17 scenery breaks the peal, and makes it harsh and irregular. Q. What is the cause of ROLLING THUNDER ? A. The vibrations of air (having- dif- ferent lengths to travel) reach the ear at successive intervals. The .reverberation (or echo) amongst the massive clouds contributes in some measure to this effect. Q. Why is a flash of lightning generally fol- lowed by POURING RAIN ? A. The flash produces a change in the physical condition of the air, rendering it unable to hold so much water in solu- tion as it could before ; in consequence of which, a part is given off in heavy rain. ^ Q. Why is a flash of lightning generally fol- lowed by a GUST OF WIND ? A. Because the physical condition of the air is disturbed by the passage of the lightning, and wind is the result of this disturbance. Q. Why is there NO THUNDER to what is called SUMMER LIGHTNING ? A. Because the lightning-clouds are so far distant, that the sound of the thun- der is lost, before it reaches the ear. Q. Do THUNDER-BOLTS ever drop from the clouds ? A. No ; the notion of thunder-bolts 18 ELECTRICITY. arises, either from the globular form which lightning" sometimes assumes ; or else from the gaseous flre-balls, which sometimes fall from the clouds. See page 13. Q. Why is the THUNDER often several moments AFTER the FLASH ? A. Because it has a long- way to come. Lightning- travels nearly a mil- lion times faster than thunder ; if, there- fore, the thunder has a long way to come, it will not reach the earth, till a consi- derable time after the flash. Q. Can we not tell the DISTANCE of a thunder- cloud, by observing the interval which elapses between the flash and the peal ? A. *Yes ; the flash is instantaneous* but thunder will take a whole second of time to travel 380 yards : hence, if the flash be 5 seconds before the thunder, the cloud is 1900 yards off. (See note, p. 16.) i. e. 380 X 5 = 1900 yards. Q. What PLACES are most DANGEROUS during a STORM ? A. It is very dangerous to be near a tree, or lofty building ; and also to be near a river, or any running water. * The speed of lightning is so great, that it would go 480 times round the earth in one minute : whereas thun- der would go scarcely 13 miles in the same space of time. LIGHTNING. 19 Q. Why is it DANGEROUS to be NEAR a TREE, or lofty building, during a thunder-storm ? A. Because a tall pointed object (like a tree or spire) will frequently discharge a lightning-cloud ; and if any one were standing near, the lightning might di- verge from the tree, and pass through the fluids of the human body. Q. How can a TREE or SPIRE DISCHARGE a lightning-cloud ? A. A lightning-cloud (floating over a plain) may be too far off to be dis- charged by it ; but, as a tree or spire would shorten this distance, it might no longer be too far off to be discharged. For example. If a lightning-cloud were 700 yards above the earth, it would be too far of to be discharged : but a tree or spire 50 yards high would make the cloud only 650 yards off a conductor ; in consequence of which, the cloud would be instantly discharged. Q. Is not AIR a CONDUCTOR of lightning ? A. No ; dry air is not a conductor of lightning. Q. Why would lightning fly from a tree or spire, into a, MAN standing near ? A. Because the electric fluid (called lightning) always chooses for its path the best conductors ; and, if the human fluids proved the better conductor, would pass through the man standing near the tree, rather than down the tree itself. 20 ELECTRICITY. There would be no danger if the tree or spire were made of metal ; because metal is a better conductor than the human fluids. Q. Does lightning go through the inside, or down the OUTSIDE of a tree ? A. It runs down the outside of a tree ; but passes through the inside of a man. Q. Why does lightning pass down the OUTSIDE of a tree ? A. Because it always makes choice of the best conductors ; and the outside of a tree is a better conductor than the inside. Q. Why does lightning pass through the IN- SIDE of a man ? A. Because the fluids of the human body make a better conductor than the skin ; therefore, lightning* passes through a man, and not down his skin. Q. Wh,y is it DANGEROUS to be near a deep RIVER, or any other running water, during a thun- der-starm ? A. Because running water is a good conductor ; and lightning always takes in its course the best conductors. Q. Why is it dangerous for a man to be NEAR. WATER in a thunder-storm ? A. Because the height of a man may be sufficient to discharge a cloud : and (if there were no taller object nigh) the LIGHTNING. 21 lightning- might make the man its con- ductor to the water. See note on p. 19. Q. Why is it DANGEROUS to RING CHURCH BELLS during a thunder-storm ? A. For two reasons : 1st Because the steeple may discharge the lightning- cloud, merely from its lieiglit ; and 2dly As the swinging of the bells puts the air in motion, it diminishes its resistance to the electric fluid. Q. Why is it unsafe to RUN or DRIVE FAST during a thunder-storm ? A.N Because it produces a current of air ; and, as air in motion affords less resistance to the flash, it is a better con- ductor than air in a state of rest. Q. What PARTS of a DWELLING are most DAN- GEROUS during a thunder-storm ? A. The fire-place, especially if the fire be lighted; the attics and cellar. It is also imprudent to sit close by the walls, to ring the bell, or to bar the shut- ters, during a thunder-storm. Q. Why is it DANGEROUS to sit BEFORE A FIRE during a thunder-storm ? A. Because the heated air and soot are conductors of lightning ; especially when connected with such excellent 22 ELECTRICITY. conductors as the stove, fender and fire- irons. Q. Why are ATTICS and CELLARS more DAN- GEROUS in a thunder-storm^ than the middle story of a house ? A. Because lightning* some ti mes pass- es from the clouds to the earth, and some- times from the earth to the clouds ; in either cases the middle story would be the safer place. Q. When does lightning pass FROM THE EARTH to the CLOUDS ? A. When the clouds are in a "nega- tive 77 state of electricity. Q. When does lightning pass FROM THE CLOUDS to the EARTH ? A. When the clouds are in a " posi- tive" state of electricity. Q. What is meant by the clouds being in a "positive state of electricity?" A. When the clouds contain more electric fluid than they generally do, they are said to be in a "positive state of elec- tricity." Q. What is meant by the clouds being in a " negative state of electricity . ? " A. When the clouds contain less electric fluid than they ought to do, they are said to be in a " negative state of electricity." LIGHTNING. 23 Q. Does the flash proceed from a negative or POSITIVE body ? A. Always from a positive body ; that is, from one over-charged with elec- tric fluid. It is generally thought that there are two sorts of elec- tricity, one called VITREOUS, corresponding to positive elec- tricity ; and the other called RESINOUS, corresponding to negative electricity. Q. When lightning flashes from the earth to the clouds, what is the flash called ? A. It is popularly called the "return- ing 1 stroke ;" because the earth (being over-charged with electric fluid) returns the surplus quantity to the clouds. Q. Why is it DANGEROUS to lean AGAINST A WALL during a thunder-storm ? A. Because the electric fluid will sometimes run down a wall ; and (as a man is a better conductor than a wall) would leave the wall, and run down the man. Q. Why is it dangerous to RING a BELL dur- ing a thunder-storm ? A. Bell- wire is an excellent conduc- tor ; and (if a person were to touch the bell-handle) the electric fluid, passing down the wire, might run through his hand and injure it. Q. Why would the lightning run through a man touching a bell- handle ? 24 ELECTRICITY. A. Because the human body is a better conductor than the wall (between the. bell-handle and the floor) ; and as lightning* always choos63s the best con- ductor for its path, it would (in this case) pass through the man, and injure him. Q. Why is it DANGEROUS 'to BAR a SHUTTER during a thunder -storm ? A. Because the iron shutter-bar is an excellent conductor ; and the electric fluid might run from the bar through the per- son touching it, and injure him. Q. Why is it dangerous to be in a CROWD during a thunder-storm? A. For two reasons : 1st Because a mass of people forms a better conductor than an individual ; and 2dly Because the vapor arising from a crowd increases its conducting power. Q. Why is a MASS of bodies a better conductor than a single body ? A. Each living body is a conductor of electricity; and a connected mass of such conductors is more likely to be struck, than a single individual. Q. Why is the danger increased by the VAPOR which rises from a crowd ? A. Because vapor is a conductor , and the more conductors there are, the greater the danger will be. LIGHTNING. 25 Q. Why is a THEATRE dangerous during a thunder-storm ? A. Because the crowd, and great va- por arising from so many living bodies, render it an excellent conductor of light- ning. Q. Why is a FLOCK of sheep in greater dan- ger than a smaller number ? A. 1st Because each sheep is a con- ductor of lightning 1 , and the conducting power of the flock is increased by its numbers : and 2dly The very vapor arising from a flock of sheep increases its conducting poiver, and its danger. Q. Why is a HERD of cattle in danger during a storm 1 A. 1st Because the number of living- bodies increases the conducting power of their animal fluids : and 2dly The very vapor arising from a herd increases its conducting power. Q. If a person be ABROAD in a thunder-storm, what place is the SAFEST ? A. Any place about 20 or 30 feet from some tall tree or building ; except it be near to running water. Q. Wh.y would it be safe to stand 20 or 30 feet from some tall tree, in a thunder-storm ? A. Because the lightning would al- 2 26 ELECTRICITY. ways choose the tall tree as a conductor ; and we should riot be sufficiently near the tree, for the lightning to diverge from it to us. Q. If a person be in A CARRIAGE in a thun- der-storm, in what way can he travel most SAFELY ? A. He should not lean against the carriage ; but sit upright, without touch- ing any of the four sides. Q. Why should not a person lean AGAINST the carriage in a storm ? A. Because the electric fluid might run down the sides of the carriage ; and (if a person were leaning against them) would make choice of him for a conduct- or, and perhaps destroy life. Q. If a person be in A HOUSE during a thun- der-storm, what place is SAFEST ? A. Any room in the middle story. The middle of the room is best ; espe- cially if you place yourself on a mat- tress, bed, or hearth-rug. Q. Why is the MIDDLE STORY of a house SAF- EST in a thunder-storm ? A. Because the fluid (if it struck the house at all) would be diffused among the several conductors of the upper part of the house, before it reached the midr dle story ; in consequence of which, its force would be weakened. LIGHTNING. 27 Q. Why is the MIDDLE of the ROOM more SAFE than any other part of it, in a thunder-storm ? A. Because the lightning 1 (if it struck the room at all) would come down the chimney, or walls of the room ; and, therefore, the further distant from these, the better. Q. Why is a MATTRESS, BED, or HEARTH-RUG a good security against injury from lightning? A. Because they are all non-conduct- ors ; and, as lightning* always makes choice of the best conductors, it would not choose for its path such things as these. Q. Is it better to be WET or dry during a storm ? A. To be wet : if a person be in the open field, the best thing he can do, is to stand about 20 feet from some tree, and get completely drenched to the skin. Q. Why is it better to be WET than dry ? A. Because wet clothes form a better conductor than the fluids of our body ; and, therefore, lightning would pass down our wet clothes, without touching our body at all. Q. What is the SAFEST thing a person can do^ to avoid injury from lightning? A. He should draw his bedstead into the middle of the room, commit 28 ELECTRICITY. himself to the care of God, and g*o to bed ; remembering 1 that our Lord has said, " The very hairs of your head are all numbered." N. B. No great danger needs really to be apprehended from lightning, if you avoid taking- your position near tall trees, spires, or other elevated objects. Q. What is a LIGHTNING-CONDUCTOR ? A. A metal rod fixed in the earth, running- up the whole height of a build- ing 1 , and rising 1 in a point above it. Q. What metal is the best for this purpose ? A. Copper makes the best conductor. Q. Why is COPPER belter than iron ? A. 1st Because copper is a better conductor than iron : 2dly It is not so easily fused or melted: and 3dly It is not so much injured by weather. Q. What is the USE of a lightning-conductor ? A. As metal is a most excellent con- ductor, lightning 1 (which makes choice of the best conductors) will run down a metal rod, rather than the walls of the building. Q. How FAR will the beneficial influence of a lightning-conductor extend ? A. It will protect a space all round, LIGHTNING. ffd 4 times the length of that part of the rod which rises above the building. Q. Give me an example. A. If the rod rise 2 feet above the house, it will protect the building for (at least) 8 feet all round. Q. Why are not lightning-conductors more generally used ? A. Because many accidents have arisen from conductors of defective con- struction. Q. How can lightning-conductors be produc- tive of HARM ? A. If the rod be broken by weather or accident, the electric fluid (being obstructed in its path) will damage the building. Q. Is there any other evil to be apprehended from a lightning-rod ? A. Yes ; if the rod be not big enough to conduct the whole current to the earth, the lightning will fuse the metal, and injure the building. The conducting rod should be (at least) one inch in di- ameter. Q. How does LIGHTNING sometimes KNOCK DOWN HOUSES and churches ? A. The steeple or chimney is first struck ; the lightning then* darts to the iron bars and cramps, employed in the 30 ELECTRICITY. building ; and (as it darts from bar to bar) shatters to atoms the bricks and stones which oppose its progress. Q. Can you tell me how St. Bride's Church (London) was nearly destroyed by lightning , about 100 years ago ? A. The lightning first struck the metal vane, and ran down the rod ; it then darted to the iron cramps, employed to support the building ; and (as it flew from bar to bar) smashed the stones of the church which lay between. . Q. Why did the Lightning fly about from place to place, and not pass down in a straight course ? A. Because it always takes in its course the best conductors ; and will fly both right and left, in order to reach them. Q. Why does LIGHTNING turn milk SOUR ? A. Lightning causes the gases of the air (through which it passes) to combine, and thus produces a poison, called nitric acid ; some small portion of which, mix- ing with the milk, turns it sour.* > * The air is composed of two gases, called oxygen and nitrogen, mixed together, but not combined. Oxygen com- bined with nitrogen, produces five deadly poisons, viz. nitrous oxide, nitric oxide, hyponitrous acid, nitrous acid, and nitric acid, according to the proportion of each gas in the combination. LIGHTNING. 31 N. B. Sometimes the mere heat of the air, during the btorm, turns milk sour. Q. What is the difference, "between COMBINING and MIXING ? A. When different ingredients are mingled together without undergoing any chemical change, they are said to be mixed ; but when the natural properties of each are altered by the union, then those ingredients are said to be combined. Q. Give me an example. A. Different colored sands (shaken to- gether in a bottle) will mix together, but not combine: but water poured on quick- lime, will combine with the lime, and not mix with it. Q. Why are different grains of sand said to be MIXED, when they are shaken together ? A. Because (though mingled togeth- er) the property of each grain remains the same as it was before. Q. Why is water ^ poured on lime, said to COMBINE with it ? A. Because the properties of each are altered by the mixture ; the lime al- ters the character of the water, and the water that of the lime. Q. Do oxygen and nitrogen COMBINE, or only MIX together, in common atmospheric air ? A. They only mix together, as grains 32 ELECTRICITY. of sand would do when shaken in a bot- tle. When oxygen arid nitrogen com- bine, they do not constitute air, but acid poisons. (See note on p. 30.) . Q. Why does LIGHTNING turn BEER SOUR, al- though contained in a close cask ? A. Because, if beer be new and the process of fermentation incomplete, light- ning will so accelerate the process, as to turn the sugar into acetic acid at once, without passing through the interme- diate state of alcohol. Q. Why is NOT OLD beer and strong PORTER made SOUR by lightning ? A. Because the fermentation is more complete ; and, therefore, is less affected by electrical influence. Q. Why is METAL sometimes FUSED by light' ning ? A. Because the dimension of the metal is too small to afford a path for the electric current. Q. Why does LIGHTNING PURIFY the AIR ? A. For two reasons : 1st Because the electric fluid produces " nitric acid" in its passage through the air : 2dly Because the agitation of the storm stirs up tfie air. LIGHTNING. 33 The " nitric acid" is produced by the combination of some portions of the oxygen and nitrogen of the air.* Q. How does the production of nitric acid PURI- FY the air ? A. Nitric acid acts very powerfully in destroying the exhalations, which arise from putrid vegetable and animal matters. Q. Why is LIGHTNING more common in SUM- MER and in AUTUMN, than in spring and winter ? A. Because the heat of summer and autumn produces great evaporation ; and the conversion of water into vapor always developes electricity. Q. Why does a THUNDER-STORM generally fol- low very dry weather ? A. Because dry air (being- a non- conductor) will not relieve the clouds of their electricity ; so the fluid accumulates, till the clouds are discharged in a storm. Q. Why does a THUNDER-STORM rarely suc- ceed WET weather ? A. Because moist air or falling rain (being a conductor) carries down the electric fluid gradually and silently to the earth. Q. What is the general DIRECTION of a THUN- DER-STORM ? * The oxygen and nitrogen are not combined, but simply mixed, in the ordinary air; but lightning causes some portions of the mixed elements to combine. See note, p. 30. 2* 34 ELECTRICITY. A. Either from east to west ; or from north to south. Q. Why is ELECTRICITY excited by FRICTION ? A. Electricity, like heat, exists in all matter ; but is often in a latent state : friction disturbs it, and brings it into active operation. " Latent," see p. 37. Q. Why is a TREE sometimes SCORCHED by lightning, as if it had been set on fire ? A. Lightning scorches by its own positive heat, just the same as fire would. Q. Why is the BARK of a TREE often ripped quite off by a flash of lightning ? A. Because the latent heat of the tree (being very rapidly developed by the electric fluid) forces away the bark in its impetuosity to escape. Some part of this is probably due to the simple mechan- ical force of the lightning. Q. Why are BOUGHS of TREES broken off by lightning ? A. Because the mechanical force of lightning is very great; and, as the boughs of a tree are imperfect conduct- ors, they will often be broken off by this force. Q. Why is an electric shock felt MOST at the \ ELBOW JOINT? A. Because the path of the fluid is LIGHTNING. 35 obstructed by the joint ; and the shock (felt at the elbow) is caused by the fluid leaping from one bone to another. Q. Is electricity accompanied with any ODOR 1 A. Yes ; near a large electrical ma- chine in good action, there is always a peculiar odor, resembling* sulphur and 2)Iiosphorus ; this odor is called -" OZONE." Pronounce O-ZONE, in two syllables. Q. Has this peculiar odor, called " OZONE," "been observed in thunder-storms ? A. Yes ; sometimes the sulphurous odor prevails, and sometimes the phos- phoric. If the gaseous body disengaged by lightning, reaches us in a concentrated form, the odor is SULPHUROUS ; if in a diluted form, it is PHOSPHORIC. Q. What are FUL'GURITES ? A. Hollow tubes produced in sandy soils by the action of lightning 1 . Q. How does lightning produce fulgurites ? A. When it enters the earth, it fuses the flinty matter of the soil into a vitre- ous (or glassy) substance, called a ful- gurite. Q. Does not lightning sometimes affect the character of IRON and STEEL ? A. Yes ; bars of iron and steel are sometimes rendered magnetic by light- ning. 36 CHEMICAL ACTION. Q. Give me an instance of the magnetic effects of lightning. A. Sometimes it will reverse the mag- netic needles of the electric telegraph, and sometimes destroy their magnetism altogether. Q. What is meant by the magnetic needles being REVERSED ? A. That part of the needle which ought to point toward the nortk, is made to point toward the south ; and that part which ought to point south, is made to point toward the north. Q. How does lightning act upcm the magnetic needles of the electric telegraph ? A. The electric fluid is conveyed along the conducting wires to the tele- graphic needles. CHEMICAL ACTION. CHAPTER III. Q. What is the THIRD chief source of heat ? A. CHEMICAL ACTION. Q. What is meant by chemical action being the source of heat ? A. Many things, when their chemical constitution is changed (either by the LATENT HEAT. 37 abstraction of some of their- gases, or by the combination of others not before unit- ed) evolve heat, while the change is go- ing 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 intense heat. Q. Why does COLD WATER, poured on LIME, make it intensely HOT ? A. Because heat is evolved by the chemical action which takes place, when the cold water combines with the lime. N. B. Heat is always evolved, when a fluid is converted into a solid form. Heat is always absorbed^ when a solid is changed into a liquid state. As the water is changed from its liquid form when it is taken up by the lime, therefore, heat is given off. Q. Where does the heat come from ? A. It was in the water and lime be- fore ; 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 ? A. Yes ; but it is latent (i. e., not per- ceptible to our senses.) Latert, from the Latin word Lateo, (to lie hid.) 38 CHEMICAL ACTION. Q. How do you KNOW there is heat, if you cannot PERCEIVE it ? A. Thus: Ice is 32 by the ther- mometer ; but if ice be melted over a fire, (though 140 of heat are absorbed by the process,) it will feel no hotter than before. i. e., it will be only 32, and not 172.* 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 1 140 of heat be added to water, without bein^ perceptible to our feelings? A. 1st 140 of heat are hidden in water, when ice is melted by the sun or fire. 2dly -1000 more of heat are secret- ed, when water is converted into steam. Thus, before ice is converted into steam, 1140 of heat become latent. One pint of boiling water, (212 according to the ther- mometer,) 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 * 32, i. e., 32 degrees ; 140, i. e., 140 degrees, &c. COMBUSTION. 39 of heat become latent. Hence, before ice is converted into 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 hands into the liquid ; and it will feel so in- tensely cold, that the snow itself will seem warm in comparison to it. Q. Is SALT and SNOW really COLDER than snow ? A. Yes, many degrees ; and by dip- ping your hand into the mixture first, and into snow afterward, the snow will seem to be comparatively warm. CHAPTER IV. . COMBUSTION. Q. What is FIRE? A. Heat and light, produced by the combustion of inflammable substances. Q. How is HEAT evolved by combustion? A. By chemical action. As latent heat is liberated, when water is poured upon lime, by chemical action ; so latent heat is liberated in combustion, by chemical action also. 40 CHEMICAL ACTION. Q. What CHEMICAL ACTION takes place in combustion? A. The elements of the fuel combine with the oxygen of the air. Q. What is meant by the "ELEMENTS OF FUEL?'' A. As bread is a compound of flour 7 yeast, and salt ; so fuel is a compound of hydrogen and carbon. Q. What are the ELEMENTS of atmospheric AIR? A. Oxygen and nitrogen, mixed toge- ther in the following proportions ; 4 gallons of nitrogen and one of oxygen will make 5 gallons of common air. Q. What is CARBON? A. The solid part of fuel. Carbon abounds in all animal bodies, earths, and even in some minerals. Q. Mention some different species of CARBON. A. Common charcoal, lamp-black^ coke, and the diamond. Q. What is HYDROGEN ? A. An inflammable gas. The gas used in our streets is hydrogen driven out of coals by heat. Coal gas (more correctly speaking) is carburetted hy- drogen, i. e., carbon and hydrogen. See p. 262. Q. What are the peculiar characteristics of hydrogen gas? A. 1st It is the lightest of all known substances : COMBUSTION. 41 2dly It will burn immediately it is ignited: and 3dly A lighted candle (immersed in this gas) will be instantly extinguished.* Q. What is OXYGEN ? A. A gas, much heavier than hydro- gen ; it gives brilliancy to flame, and is essential to animal life.t * 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. EXPERIMENTS. 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 a 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. f Oxygen gas is much more troublesome to make than hydrogen. The cheapest plan is to put a few ounces of manganese (called the black oxide of manganese) into an iron bottle, furnished with a bent tube ; set the bottle on a fire till it becomes red hot, and put the end of the tube into a pan of water. In a few minutes, bubbles will rise through the water ; these bubbles are oxygen gas. These bubbles may be collected thus : Fill a common bottle with water ; hold it inverted 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, 42 CHEMICAL ACTION. Q. What is NITROGEN ? A. An invisible gas, which abounds in animal and vegetable substances. The following are its peculiar characteristics : 1. It will not burn ; 2. An animal cannot live in it ; 3. It is the principal ingredient in common air. % Nearly 4 gallons out of every 5 being nitrogen gas. and half an ounce of chlorate of potassa. Put the mix- ture 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. (Chloride 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 ham- mer ; 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.) * 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 it. (Be sure the edge of the glass stands in the water.) In a few minutes the oxygen of the air will be taken up by the burning phosphorus ; and nitrogen alone will be left 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.) COMBUSTION. 43 Q. Why is there so MUCH nitrogen in the air ? A. In order to dilute the oxygen. [f the oxygen were not thus diluted, [ires would burn out too quickly, and life would be too rapidly exhausted. Q. What three elements are necessary to pro- duce 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 match), unites with the oxygen of the air, and makes a yellow flame ; this flame heats the carbon of the fuel, which (also uniting with oxygen of the air) produces car- bonic acid gas. Q. What is CARBONIC ACID GAS? A. -Only carbon (or charcoal) com- bined with oxygen gas. Q. Why does FIRE produce HEAT? A. Because it liberates latent heat from the air and fuel. Q. What CHEMICAL CHANGES in air and fuel are produced by COMBUSTION ? A. 1st Some of the oxygen of the air, combining with the hydrogen of the fuel, condenses into water : and 44 CHEMICAL ACTION. 2dly Some of the oxygen of the air, combining* with the carbon of the fuel, forms carbonic acid gas. Q. Why is a FIRE (after it has been long burning) RED HOT ? A. Because the whole surface of the coals is so thoroughly heated, that every part of it is undergoing a rapid union with the oxygen of the air. Q. In a BLAZING fire, why is the TIPPER sur- face of the COALS BLACK, and the LOWER surface RED ? A. Because carbon (being solid) re- quires a great degree of heat to make it unite with the oxygen of the air. In consequence of which, the hot under surface of coals is frequently red from its union with oxygen, while the cold upper surface remains black. Q. Which burns the more quickly , a BLAZING fire, or a RED HOT one ? A. Fuel burns quickest in a blazing fire. Q. Why do BLAZING COALS BURN QUICKER than red hot ones ? A. Because the inflammable gases of the fuel (which are then escaping) great- ly assist the process of combustion. Q. Why do the coals of a CLEAR BRIGHT fire burn out more slowly than blazing coals ? A. Because most of the inflammable COMBUSTION. 45 gases, and much of the solid fuel, have been consumed already ; so that there is less food for combustion. Q. What is SMOKE ? A. Unconsumed parts of fuel (prin- cipally carbon) separated from the solid mass, and carried up the chimney by currents of hot air. Q. Why is there MORE SMOKE when COALS are FRESH added, than when they are red hot ? A. Because carbon (being- solid) re- quires a great degree of heat to make it unite with oxygen, (or, in other words, to bring it into a stateof perfect combustion:) when coals are fresh laid on, more carbon is separated than can be reduced to com- bustion, and the surplus flies off in smoke. Q. Why is there so LITTLE SMOKE with a RED HOT FIRE? A. Because the entire surface of the coals is in a state of combustion ; and, as very little carbon remains unconsumed, there is but little smoke. Q. Why are there DARK and BRIGHT SPOTS in a CLEAR cinder FIRE ? A. Because the intensity of the com- bustion is greater in some parts of the fire, than it is in others. Q. Why is the intensity of the combustion so UNEQUAL ? 46 CHEMICAL ACTION. 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 combus- tion is 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 unburnt coal), produce strange and fanciful resemblances. Q. Why does PAPER BURN more readily than wood ? A. 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) very readily catches fire. Q. Why is WOOD laid on the top of the paper ? A. Because wood (being more sub- stantial") burns longer than paper ; and, COMBUSTION. 47 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 rap- idly, that it would not afford sufficient contact of flame to heat the coals to com- bustion. Q. Why will 'not wood do WITHOUT shavings, straw, or paper ? A. Because wood is too substantial to be heated into combustion by the fee- ble flame issuing- from a match. Q. Why would not the paper do as welL if placed on the TOP of the coals ? A. Because every blaze tends up- ward; if, therefore, the paper were placed on the top of the coals its blaze ' would afford no contact of flame to the fuel lying* below. Q. Why should COAL be placed ABOVE the wood ? A. Because otherwise, the flame of the fuel would not rise through the coal, to heat it. Q. Why is a FIRE KINDLED at the LOWEST BAR of a grate? A. That the flame may ascend through the fuel, to heat it. If the fire were kindled from the top, the flame would not come in contact with the fuel placed below. 48 CHEMICAL ACTION. Q. Why does COAL make such EXCELLENT FUEL ? A. Because it contains a large amount of carbon and hydrogen gas, in a very compact and convenient form. Q. Why will CINDERS become RED HOT more quickly than COALS 1 A. Because they are sooner reduced to a state of combustion, as they are more porous and less solid. Q. Why will not IRON CINDERS burn ? A. Because they contain impurities, which are not so ready to combine with oxygen, as carbon and hydrogen are. Q. Why are CINDERS lighter than COALS ? A. Because they are full of little holes ; from which vapor, gases, and other 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, and little or no carbon. Q. Why will not WET KINDLING light afire ? A. 1st Because the moisture of the wet kindling prevents the oxygen of the air from getting to the fuel ; and 2dly The heat of the fire is perpetu- ally drawn off, by the conversion of water into steam. COMBUSTION. 49 Q. Why does DRY wood burn BETTER than GREEN ? A. 1st Because none of its heat is earned away by the conversion of water into steam ; and 2dly The pores of dry wood (being filled with air) supply the fire with oxygen. Q. Why do TWO pieces of WOOD burn BETTER than ONE ? A. 1st Because they help to entan- gle the heat of the passing smoke, and throw il on the fuel; and 2diy The air 7 impinging against the pieces of wood, is thrown upon the fire in a kind of eddy or draught. Q. Why does SALT CRACKLE, when thrown into a FIRE ? A, Salt contains water; and the crackling of the salt is owing to the sud- den conversion of this water into steam. Q. Why will not wood or paper bwrn if steeped in a solution of POTASH, phosphate of LIME, or AM- MONTA (hartshorn) ? A. Because any " alkali " (such as potash) will arrest the hydrogen which escapes from the fuel, and prevent its Combination with the oxygen of air. Q. What is an alkali ? A. The con'verse of an acid; as 3 50 CHEMICAL ACTION. bitter is the con'verse of sweet, or insijjid the con'verse of pungent. Q. Why does a JET of FLAME sometimes burst into the room THROUGH THE BARS OF A STOVE ? A. Because 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 color ? A. Either because some lump of coal lies over the hot bars ; or else the coals below it are not red hot : in consequence of which, some of the g*as escapes unburnt, and is of a greenish color. 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. Because the g-as 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. 51 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 undula- tions of LIGHT ? A. The atoms of matter (set in mo- tion by heat) striking against this ether, produce undulations in it ; as a stone thrown into a stream, produces undula- tions in the water. Q. How can UNDULATIONS of ether produce LIGHT? A. As sound is produced by undula- tions of air striking on the ear ; so light is produced by undulations of ether strik- ing on the eye. Q. What is ETHER ? A. A very subtle fluid, which per- vades and surrounds everything we see. N. B. This theory of LIGHT is not altogether satisfactory ; but has been retained, as the most plausible hitherto pro- * jected. 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 ? 62 CHEMICAL ACTION. A. Because yellow rays 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 it is at others? A. The intensity of fire-light depends upon the whiteness to which the carbon is reduced by combustion. If 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 has been consumed, the hot cinders pro- duce only a gas, called carbonic acid, which is neither luminous nor visible. Q. Where does the hydrogen gas of afire come from? A. All fuel is composed of carbon and hydrogen gas, which are separated from each other by the process of combustion. (See p. 40.) Q. Why does not a FIRE BLAZE on a FROSTY NIGHT, so long as it does upon another night ? A. 1st Because air condensed by the cold contains more oxygen than the same quantity of warmer air ; and COMBUSTION. 53 2dly Air condensed by the cold is heavier. In consequence of which, it- falls more quickly on the fire, to supply the place of the hot ascending air. Q. Why does a FIRE burn CLEAREST on a FROSTY night ? A. Because the volatile gases are more quickly consumed ; and the solid carbon is plentifully supplied with oxygen from the air, to make it burn brightly and intensely. Q. Why does a FIRE burn more intensely in WINTER than in SUMMER ? A. Because the air is colder in winter, than it is in summer. Q. Why does the COLDNESS of the air increase the HEAT of a fire? A. 1st Because air condensed by the cold, supplies more oxygen than a similar volume of warmer air ; and 2d!y Condensed air, being heavy, falls more rapidly into the place of the hot ascending air, to supply the fire with nourishment. Q. Why does the SUN, shining on a FIRE, it DULL ; and often put it out ? A. 1st Because the air (being rare- fied by the sunshine) flows 'more slowly to theflre ; and 54 CHEMICAL ACTION. 2dly Even that which reaches the fire, affords less nourishment. Sunshine produces also some chemical eject upon the air or fuel detrimental to combustion. Q. Why does the airflow to the fire more TAR- DILY for being RAREFIED? A. Because the greater the contmst (between the external air and that which lias been heated by the fire), the more rapid will be the current of air toward that fire. Q. Why does rarefied air afford LESS NOURISH- MENT to fire than cold air ? A. Because rarefied air contains less oxygen than the same quantity of con- densed air. Inasmuch as the same quantity of oxygen is diffused over a larger volume of 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 2dly It has freer access to the fire. Q. Why is the air out-of-doors more DENSE than that in-doors ? A. Because it has freer circulation ; and, as soon as any portion has been rarefied, it instantly escapes, and is sup- plied by colder currents. Q. Why does not a FIRE burn so freely in a THAW as in a FROST I COMBUSTION. 55 A. Because the air is laden with vapor ; in consequence of which, it both moves too slowly, and is too much rarefied to nourish the fire. Q. Why does a FIRE burn so fiercely in WINDY weather ? A. Because the air is so rapidly changed, and affords plentiful nourish- ment to the fire. Q. Why does a pair of BELLOWS get afire up ? A. Because it drives the air more rap- idly to tliefire ; and the plentiful supply of oxygen soon makes the fire burn in- tensely. Q. Why is the flame of a CANDLE EXTINGUISHED when blown by the breath ; and not made more in- tense like afire? A. Because the flame of a candle is confined to a very small wick, from which it is severed by the breath ; and (being unsupported) must go out. Q. Why is a SMOULDERING WICK sometimes RE-KINDLED by blowing it ? A. Because air is carried to it by the breath with great rapidity ; and the oxy- gen of the air kindles the red hot wick t as it would kindle charred wood. Q. Why is not the red hot wick kindled by the air AROUND &, without BLOWING ? A. Because oxygen is not supplied 56 CHEMICAL ACTION. with sufficient freedom, unless air be blown to the wick. Q. When is this experiment most likely to suc- ceed ? A. In frosty weather ; because the air contains more oxygen when it is 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 2dly Air is arrested in the narrow aperture between the poker and the coals, and a draught created. See p. 49. Q. Why are STOVES fixed on the FLOOR of a room ? A. In order that the air on the lower part of tlie 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 tlie level of tlie grate; and, therefore, every grate should be as near to the floor as possible. Q. Our FEET are very frequently COLD when we sit dose by a good fire. Explain the reason of this. COMBUSTION. 57 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 cur rents 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. Because the carbon of a clear fire, being- sufficiently hot to unite with the oxygen of the air, produces carbonic acid fas, which soon envelops the paper laid at upon the cinders : but carbonic acid gas will not blaze. Q. If you BLOW the paper, it will BLAZE im- mediately. Why so ? A. Because by blowing or opening a door suddenly, the carbonic acid is dissi- pated^ and the paper fanned into flame. Q. Why does WATER EXTINGUISH a FIRE ? A. 1st Because the water forms a coating over the fuel, which keeps it from the air ; and 2dly The conversion of water into steam, draws off the heat of the burning fuel. Q. A LITTLE WATER mcikes a fire FIERCER, while a LARGER quantity of water puts it OUT.. Explain how this is. 3* 58 CHEMICAL ACTION. A. Water is composed of oxygen and hydrogen; when, therefore, the fire can decompose the water into its simple ele- ments, it serves for fuel to the flame. Q. How can WATER serve for FUEL to fir el A. Because the hydrogen of the water burns with aflame ; and the oxygen of the water increases the intensity of that flame. Q. When a house is on fire, is too LITTLE water worse than NONE ? A. Certainly. Unless water be sup- plied so plentifully as to quenck the fire, it will increase its intensity, like fuel. Q. When will water EXTINGUISH FIRE ? A. When the supply is so rapid and abundant that the fire cannot decompose it. Q. Does not a very LITTLE water SLACKEN the heat of fire ? A. Yes, till it is decomposed ; it then increases the intensity of fire, and acts like fuel. Q. Why does the WICK of a candle (when the flame has been blown out) very readily CATCH FIRE? A. Because the wick is already hot, and a very little extra heat will throw it into flame. Q, Why does the EXTRA heat revive the flame? COMBUSTIOX. 59 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. Because the heat of the fire drives out the hydrogen gas of the wood ; which gas is inflamed by contact with the red hot coals. Q. Why will a NEIGHBOR'S HOUSE sometimes CATCH FIRE, though no flame of the burning house ever touches it ? A. Because the heat of the burning house sets at liberty the hydrogen gas of the neighboring wood- work ; and this gas is ignited by the flames or red hot bricks of the house or fire. Q. What is COKE ? A. Coal freed from its volatile gases by the action of artificial heat. Q. Why do STOVES sometimes SMELL very strongly ^SULPHUR? A. Because coal and coke contain sulphur ; and whenever the draught is not rapid enough to drive the sulphur up the flue, it is emitted into the room. 60 CHEMICAL ACTION. Q. What is meant by SPONTANEOUS COMBUS- TION ? A. Combustion produced without the application of flame. Q. Give an example of spontaneous combustion. A. Coals stowed in the hold of a vessel, and goods packed in a warehouse, will often catch fire of themselves espe- cially 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 large masses in a damp state or place. Q. Why does this produce spontaneous combus- tion ? A. The damp produces dzcay, 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 COM- BUSTION ? 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. Wh.y is the HEAT of a LARGE MASS of goods GREATER than that of a smaller quantity ? A. Because the carbonic acid cannot COMBUSTION. 61 escape through the massive pile ; and the products of decomposition being con- fined, hasten further changes. Q. Why do HAY-STACKS sometimes CATCH FIRE of themselves ? A. Either because the hay was got up damp ; or else because rain has pen- etrated the stack. Q. Why will a HAY-STACK CATCH FIRE if the hay be damp ? A. Because damp hay soon decays, and undergoes a state of fermentation ; during which, carbonic acid gas is given off, and the stack catches fire. Q. Roasted COFFEE sometimes CATCHES fire spontaneously. Explain the reason of this. A. The heat of coffee is greatly in- creased by being roasted; and the car- bon of the coffee, uniting with the oxygen of the air, produces carbonic acid gas, and bursts \ntoflame. Q. Why do old RAGS, used for CLEANING LAMPS and CANDLESTICKS, sometimes set a HOUSE on fire? A. Because they very readily fer- ment, 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. . 62 CHEMICAL ACTION. CHAPTER Y. / . SMOKE. Q. Why does SMOKE ASCEND the chimney ? A. Because the air of the room (when it passes over the fire) becomes lighter for being* heated ; and (being- thus made lighter') ascends the chimney, carrying the smoke with it. Q. What is SMOKE? A. Small particles of carbon, separat- ed by combustion from the fuel, but not consumed. Q. Why do SMOKE and steam CURL as they ascend ? A. Because they are pushed round and round by the ascending and de- scending currents of air. Q. Why does a CLOSE STOVE DRAW up more fiercely than an OPEN GRATE ? A. Because the air which supplies the stove must pass through the fire ; and, as it becomes exceedingly heated, rushes up the flue with great violence. Q. What produces the ROARING noise made by the fire in a close stove? A. Air rushing rapidly through the crevices of the iron door, and up the chimney flue. SMOKE. 63 Q. Why is the ROAR LESS if the stove DOOR be thrown OPEN? 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. Because fresh air is not admitted into a room so fast as it is consumed by the fire ; in consequence of which, a cur- rent of air rushes down the chimney to supply the deficiency, driving* the smoke along- with it Q. Explai7i this by an illustration. A. If water be taken with a pail out of a river, other water will rush toward 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 g*oes up the chimney), other air will rush toward the void to fill it up. Q. What prevents air being supplied so fast as it is consumed by the fire ? A. Leather and curtains round the doors: sand-bag's at the threshold and on the window-frames; and other con- trivances to keep out the draug-ht. Q. Why will the air come down the CHIMNEY ? A. Because it can g-et into the room 64 CHEMICAL ACTION. ,n no other way, if the doors and win- dows are all made air -tight. 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 plenti- fully supplied with air by the tube : the doors and windows may all remain air- tight ; and we may enjoy a warm fire- side, without the inconvenience of draughts and cold feet. Q. Why is a CHIMNEY raised so high above the ROOF? A. That it may not 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. Q. Why does a CHIMNEY SMOKE, if the funnel be very short ? 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 than that of a long one ? SMOKE. A. 1st Because the fire is always dull and sluggish, if the chimney be too short : 2dly Because the smoke rolls out of the chimney, before it has acquired its full velocity ; and 3dly Because 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 SLUG- GISH, if the CHIMNEY-FLUE be very SHORT? A. Because the draught is bad ; and, as the rarefied air passes very tardily up the chimney fresh air flows as tardily toward the fire, to supply it with oxygen. Q. On what does the INTENSITY of fire depend? A. The intensity of fire is always in proportion to the quantity of oxygen with which it is supplied. Q. Why does not SMOKE acquire its full VELO- CITY in a SHORT funnel* A. Because the higher smoke as- cends, (provided the flue be clear and hot,) the faster it goes : 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 66 CHEMICAL ACTION. cold air will rush toward the fire to supply the place ; and, therefore, the longer the flue, the greater the draught. Q. Why are the CHIMNEYS of MANUFACTORIES made so very LONG ? A. To increase the intensity of the fire. Q. Why is the INTENSITY of a fire increased by LENGTHENING the FLUE ? A. Because the draught being* great- er, more fuel is consumed in the same time ; and, of course, the intensity of the heat is proportionally greater. Q. If a SHORT CHIMNEY cannot be lengthened, what is the best REMEDY to prevent smoking ? A. To contract the opening of tlie chimney contiguous to the stove. Q. Why will a SMALLER OPENING against the stove PREVENT the chimney's SMOKING ? A. Because the air will be compelled to pass nearer the fire ; and (being more heated) will rise through the chimney more rapidly. This increase of heat will therefore compensate for the slwrtness of the flue. Q. Why will a ROOM SMOKE if there be TWO FIRES in it ? A. Because the fiercer fire will ex- haust the most air, and draw from the smaller one, to supply its demand. SMOKE. 67 Q. Why will a chimney SMOKE if there be a FIRE in TWO ROOMS communicating with each other? A. Because (whenever the d'jor be- tween 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 best REMEDY in this case ? A. Let a tube be carried from the hearth of each stove into the external air ; and then each fire will be so well supplied, that neither will need to bor- row from the other. Q. Why does a HOUSE in a VALLEY or by the side of higher buildings very often SMOKE ? A. Because the wind (striking* against the surrounding* hills or building's) bounds back again upon the chimney : and destroys its draug-ht. Q. What is the REMEDY in 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. Because if the wind be strong, it will keep the opening of the cowl toward the higher building or hill ; and then the reflected wind will blow into the cowl, and down the chimney. 68 CHEMICAL ACTION. Q. As a cowl is suck a poor remedy, can any OTHER be suggested ? A. Yes. If the chimney-flue can be carried higher than the other building's or hills, no wind can enter the flue. Q. If a chimney -flue be carried up HIGHER than the buildings or hill, why cannot the wind enter it ? A. Because the reflected wind would strike against the sides of the chimney- flue, and not pass over the opening at all. Q. In what OTHER cases will a CHIMNEY SMOKE ? A. If the door and stove are both 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 (whenever the door is opened) a current of air will blow ob- liquely 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-place, or nearly so; and then the draught from the door wUl blow the smoke up the chimney, and not into the room. Q. Why will a CHIMNEY SMOKE if it NEEDS SWEEPING ? A. Because loose soot obstructs the SMOKE. 69 free passage of the smoke, delays its current, and prevents the draught. Q. Why will a CHIMNEY SMOKE if it be OUT OF REPAIR ? A. 1st Because the loose mortar and bricks obstruct the smoke ; and 2dly Cold air (oozing- through the chinks) chills the air in the chimney, and prevents its ascent. Q. Why will a STOVE SMOKE, if the joints of the flue do not Jit air-tight? A. Because cold air (oozing through the joints) chills the air in the flue, and prevents its ascent. Q. Why does an old-fashioned FARM CHIMNEY- PLACE generally 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 hot) 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 the current of air up the chimney is not powerful enough to buoy up the smoke through the flue. Q. If the opening of a chimney be TOO LARGE, what REMEDY can be applied ? 70 CHEMICAL ACTION. A. The chimney-place must be con- tracted. Q. Why will CONTRACTING the chimney -place PREVENT itS SMOKING ? A. Because the air will then pass nearer the fire ; and (being more heated) fly faster up the chimney. Q. Why do almost all CHIMNEYS SMOKE in GUSTY weather ? A. Because the column of smoke is suddenly chilled by the wind, and (be- ing* unable to ascend) rushes back into the room. Q. What is the use of a CHIMNEY-POT? A. It serves to increase the draught, when the opening of a chimney is too large. 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 smaller opening, it must pass through more quickly. Q. Why do BLOWERS help to get afire up ? A. Because they compel the air to go through the fire, and not over it; in consequence of which, the fire is well supplied with oxygen, and the draught greatly increased. Q. Why does a BLOWER INCREASE the DRAUGHT ? SMOKE. 71 A. Because the air (by passing through the fire) is made much hotter, and ascends the chimney more rapidly. Q. Why is a fire better supplied with oxygen while the blower hangs before it ? A. Because the blower increases the draught ; and the faster the hot air flies up the cliimney, the faster will cold air rush toward the fire, to supply it with oxygen. Q. WTiy does a parlor often SMELL disagreeably Of SOOT in SUMMER,-TIME? A. Because the air in the chimney (being colder than the air in the parlor) descends into the room, and leaves a dis- agreeable smell of soot behind. Q. Why are the CEILINGS of PUBLIC OFFICES generally BLACK and filthy ? A. Because the heated air of the office buoys up the dust and fine soot ; which (being unable to escape through the plaster) is deposited on the ceiling. Q. Why are SOME parts of the ceiling BLACKER and more filthy than others? A. Because the air, being unable to penetrate the thick joists of the ceiling passes by those parts, and deposits its soot and dust on others more penetrable. N. B. The site of this deposit of soot and dust is fre- quently determined by draughts and currents of air. 72 CHEMICAL ACTION. 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 charcoal is very pure carbon ; and, as it is the carbon of fuel which produces the glowing* heat of combustion, therefore, the purer the car- bon, the more intense will the heat of the fire be. Q. Why does charcoal REMOVE the TAINT of meat ? A. Because it absorbs all putrescent effluvia, whether they arise from animal or vegetable matter. Q. Why is WATER PURIFIED by being filtered through charcoal ? A. Because charcoal absorbs the im- purities of the water, and removes all disagreeable tastes and smells, whether they arise from animal or vegetable matter. Q. Why are water and wine CASKS CHARRED inside ? A. Because charring the inside of a cask reduces it to a kind of charcoal ; and charcoal (by absorbing animal and SMOKE. 73 vegetable impurities) keeps the liquor sweet and good. Q. Why does a piece of BURNT BREAD make impure WATER fit to drink ? A. Because the surface of the bread (which has been reduced to charcoal by being- burnt) absorbs the impurities of the water, and makes it palatable. Q. Why should TOAST and WATER, placed by the side of the sick, be made of BURNT BREAD? A. Because the charcoal surface of burnt bread prevents the water from being affected by the impurities of the sick room, Q. Why should sick persons eat DRY TOAST rather lhan bread and butter ? A. Because the charcoal surface of the dry toast helps to absorb the acids and impurities of a sick stomach, There are other reasons which belong to the science of medicine. Q. Why are TIMBERS which are to be exposed to damp CHARRED ? A. Because charcoal undergoes no change by exposure to air and water ; in consequence of which, timber will resist weather much longer after it has been charred. 74 CHEMICAL ACTION. CHAPTER VI. LAMPS AND CANDLES. Q. Of what are OIL, TALLOW, and WAX com posed ? A. Principally of carbon and hydro- gen gas. The solid part is carbon, the volatile part is hydrogen gas. Q. What is CARBON ? A. A solid substance, generally of a black color; well known under the forms of charcoal, lamp-black, coke, &c. Q. What is HYDROGEN GAS ? A. The principal ingredient of water. It burns so readily that it used to be called " inflammable air."* Common coal gas is a mixture of carbon and hydrogen, called " carburetted hydrogen." See p. 262. Q. A CANDLE BURNS when lighted. Explain how this is. A. The heat of the lighted wick de- composes the tallow into its elementary parts of carbon and hydrogen ; and the hydrogen of the tallow, combining with the oxygen of the air, produces flame. Q. WHERE is. the tallow or wax of a candle decomposed ? A. In the wick. The melted tallow, * To make hydrogen gas, see p. 41. LAMPS AND CANDLES. 75 or wax, rises up the wick by capillary attraction, and is rapidly decomposed by the heat of the flame. Q. What is capillary attraction ? A. The power which very minute tubes possess of causing a liquid to rise in them above its level. "Capillary." from the Latin word "capillaris" (like a hair} ; the tubes referred to are almost as fine and delicate as a hair. Water ascends through a lump of sugar, or piece of sponge, by capillary attraction. N. B. The smaller a tube, the higher will a liquid be attracted by it. Q. Why is the FLAME of a candle HOT? A. Because the flame liberates latent heat from the air and tallow. Q. How is LATENT HEAT liberated by the flame of a CANDLE? A. When the elements of the tallow combine with the oxygen of the air, latent heat is liberated by the chemical changes. Q. Why does the flame of a CANDLE produce LIGHT ? A. Because the chemical changes made by combustion excite undulations of ether, which (striking the eye) produce light. See p. 51. Q. Why is theflame^ of a CANDLE YELLOW ? A. It is not so altogether ; only the outer coat of the flame is yellow the 76 CHEMICAL ACTION. lower part is violet ; and the inside of the flame 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. See p. 50. Q. Why is the BOTTOM part of the flame pur- ple? A. Because it is overladen with hydro- gen, raised from the tallow by the burn- ing- wick ; and this gas (which burns with'a blue flame) gives the dark tinge to the bottom of the candle-flame. Q. Why is the INSIDE of the flame HOLLOW? A. Because it is fllled with vapor, raised from the* candle by the Jieat of the wick, and not yet reduced to a state of combustion. 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 inter- mediate one of a dingy purple hue; and the outside cone is yellow. Q. Why is the intermediate cone of a flame PUHPLE as well as the BOTTOM of the flame? A. Because the gases are not in a state of perfect combustion ; but contain LAMPS AND CANDLES. 77 an excess of hydrogen, which gives the flame a purple tinge. Q. Why is not the MIDDLE cone in a state of perfect combustion as well as the outer one ? A. Because the outer cone prevents the oxygen of the air from getting to the middle of the flame ; 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 UP- WARDS ? A. Because it heats the surrounding air, which (being hot) rapidly ascends, driving the flame upwards at the same time. Q. Wh.y is the FLAME of a candle POINTED at the lop like a cone ? A. Because the upper part of a flame is more volatile than the lower; and, as it affords less resistance to the air, is re- duced to a mere point. Q. Why are the LOWER parts of a flaine less VOLATILE than the upper? A. Because they are laden with un- consumed gas and watery vapor, which present considerable resistance to the air. Q. Why is the FLAME of a candle BLOWN OUT by a puff of breath ? A. Because it is severed from the wick, and goes out for want of support. 78 CHEMICAL ACTION. Q. Why does the FLAME of a candle make A GLASS (which is held over it) DAMP ? A. Because a " watery vapor " is made by the combination of the hydrogen of the tallow with the oxygen of the air ; and this " vapor " is condensed by the cold glass held above the flame. Q. Why does our hand, held ABOVE a candle, suffer more from heat 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. Radiation: i. e., emission of rays. The candle-flame throws out rays of light and heat in all directions ; but when the hand is held above the flame, it not only feels the heat of the rays, but also of the ascending current of hot air, &c. Q. Why is a RUSH LIGHT extinguished more quickly than a cotton-wick candle ? A. Because a hard rush imbibes the melted fat or wax much more slowly than porous, cotton ; as it imbibes less fat, it supplies a smaller volume of com- bustible gases ; and, of course, the light is more easily extinguished. Q. Why is it more difficult to blow out a COT- TON wick thai/i a rush light? A. Because porous cotton imbibes LAMPS AND CANDLES. 79 the melted fat, or wax, much more quick- ly than hard rush ; as it imbibes more fat, it supplies the flame with a larger volume of combustible gases; and, of course, the light is with more difficulty extinguished. Q. Why is a GAS FLAME more easily extin- guished when the jet is very slightly turned on^ than when it is in full stream ? A. Because there is less volume of combustible gases in the small flame than in the full blaze. Q. Why does an EXTINGUISHER put a candle out? A. Because the air in the extin- guisher is soon exhausted of its oxygen by the flame : and when there is no oxy- gen, 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 oxygen contained in the pa- per extinguisher : and 2dly 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. 80 CHEMICAL ACTION. Q. A LONG WICK is covered with an EFFLORES- CENCE at the top. . What doas this arise from ? A. The knotty or flowery appear- ance of the top of a wick arises from an accumulation of particles partly separat- ed but still loosely hanging* to the wick. Q. Why is not the END of a long wick BURNT OFF as it hangs over the fame ? A. Because the length of the wick diminishes the heat of the flame ; so that it is no longer hot enough to consume the wick. Q. Why do PALMER'S METALLIC WICKS never need SNUFFING ? A. Because the wick is divided into two parts, each of which bends toward the outside of the flame, where the end is intensely heated, and separated from the wick by the current of air up the candle. N. B. The small wire twisted in the wick greatly assists the process. 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 SNUFF- ING? A. Because the wick of wax candles LAMPS AND CANDLES. 81 is made of very fine thread, which the heat of the flame is sufficient to consume. The wick of tallow candles (on the other 1 hand) is made of coarse cotton, which is 1 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 s EXTINGUISH it? , A. Because a pin (being 1 a good ] conductor) carries away the heat of the \ fiame from the ivick, and prevents the 1 combustion of the tallow. Q. What is the SMOKE of a CANDLE ? A. Solid particles of carbon, separat- ed from the wick and tallow, but not consumed. Q. Why are SOME particles consumed and not OTHERS ? A. The combustion of the carbon de- pends upon its combining with the oxygen of the air : now, as the outer surface of the flame prevents the access of air to the interior parts, 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. 4* 82 CHEMICAL ACTION. Q. Why does a LAMP SMOKE when the WICK is Wbt UNEVENLY ? A. 1st Because the points of the jagged edge (being 1 very easily separated from the wick) load the flame with more carbon than it can consume ; and 2dly As the heat of the flame is greatly diminished by these bits of wick, at is unable to consume even the usual ^quantity of smoke. Q. Why does a LAMP SMOKE when the WICK is turned up too HIGH? A. Because more carbon is separated from the wick than can be consumed by .the flame. Q. Why do not " ARGAND BURNERS " smoke ? A. Because a current of air passes through the middle of the flame ; in con- sequence of which, 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. 1st Because it increases the supply of oxygen to the flame, by produ- cing* a draught ; and 2dly It concentrates and reflects the heat of the flame ; in consequence of which, the combustion of the carbon is ANIMAL HEAT. 83 more perfect, and very little escapes unconsumed. CHAPTER VII. AIWMAL HEAT. Q. What is the cause of ANIMAL HEAT ? A. Animal heat is produced by the combustion of hydrogen and carbon in the capillary vessels. Q. What are CAPILLARY VESSELS ? A. Vessels as small as hairs running* all over the body ; they are called capil- lary from the Latin word " capilla ris" (like a hair}. Q. Do these CAPILLARY VESSELS run all over the human body ? A. Yes. Whenever blood flows from a wound, some vein or vessel must be divided ; and as you can bring" blood from any part of the body by a very slight wound, these little vessels must run through every part of the human frame. Q. How do HYDROGEN gas and CARBON get into these very little vessels ? A. The food we eat is converted into 84 CHEMICAL ACTION. blood ; and blood contains both hydrogen and carbon. Q. How does COMBUSTION take place in the car pillary vessels ? A. The carbon of the blood combines with 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 ? A. The lungs throw off almost all of it into the air, by the act of respiration. Q. What GAS is generated in a common FIRE by COMBUSTION? A. Carbonic acid gas formed by the union of the carbon of fuel with the oxy- gen of the air. Q. What GAS is generated by a lighted CANDLE or LAMP ? A. Carbonic acid gas formed by the union of the carbon of the oil or tal- low with the oxygen of the air. Q. What is the cause of SPONTANEOUS COM- BUSTION? A. The piled-up goods ferment from heat and damp ; and (during fermenta- tion) carbonic acid gas is formed^ which is attended with combustion. Q. Does the HEAT of the HUMAN BODY arise from the SAME CAUSE as the heat of FIRE ? A. Yes, precisely. The carbon of ANIMAL HEAT. 85 the blood combines with the oxygen of the air inhaled, and 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 ? A. It actually does so. Every mus- cle, nerve, and organ of the body, actu- ally wastes away like a burning candle ; and (being* reduced to air and ashes) is rejected from the system as useless. 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 icere perpetually renewed: but as a lamp will not go out, so long 1 as it is supplied with fresh oil neither will the body be consumed, so long- as it is supplied with sufficient food. Q. What is the principal DIFFERENCE between the combustion of a FIRE or LAMP and that of the HUMAN BODY ? A. In the human body, the combus- tion is effected at a much lower temper- ature ; and is carried on more slowly, than it is in a lamp or fire. Q. How is it that carbon can be made to burn at so LOW a temperature in the human body ? A. Because the carbon in the blood 86 CHEMICAL ACTION. is reduced to very minute particles ; and these particles are ready 'to undergo a rapid change as soon as oxygen is supplied. Q. WTien 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. Because after the fat and muscles of the body have been consumed by ani- mal combustion, the brain is next attack- ed ; and (unless the patient dies) mad- ness ensues. Q. Why does a man SHRINK when STARVED ? A. Because the capillary fires feed upon the human body when they are not supplied with food-fuel. A starved man shrinks just as a fire does, when it is not supplied with fuel. Q. What is the FUEL of the BODY ? A. Food is the fuel of the body. 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? ANIMAL HEAT. 87 A. Because the capillary vessels run through every part of the human body, and the combustion of blood takes place in the capillary vessels. See p. 84. Q. Why does RUNNING make us WARM ? A. Because we inhale air more ra- pidly when we run, and cause the blood to pass more rapidly through the lungs in contact with it. Running acts upon the capillary vessels as a pair of bellows on a common fire. Q. Why does INHALING AIR RAPIDLY make the, body feel WARM ? A. Because more oxygen is intro- duced into the body. In consequence of which, the combustion of the blood is more rapid the blood itself more heated and every part of the body is made warmer. Q, Why does HARD WORK produce HUNGER ? A. Because it produces quicker respi- ration ; by which means, a larger amount of oxygen is introduced info 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 ? 88 CHEMICAL ACTION. A. Because it increases respiration ; and, as more oxygen is introduced into the lung-s, our food-fuel is more rapidly consumed. Q. Why does READING ALOUD make us feel HUNGRY ? A. Because it increases respiration; and, as more oxygen is introduced into the lungs, our foodrfael is more rapidly consumed. Q. Why do we feel less HUNGRY in the night than in the DAY ? A. Because we breathe more slowly during sleep ; therefore, less oxygen is introduced into the lung's, to consume our food-fuel. Q. Why do we need WARMER CLOTHING by NIGHT than by DAY ? A. 1st Because the night is gener- ally colder than the day ; and 2dly Our bodies are colder also ; be- cause we breathe more slowly, and our animal combustion is retarded. Q. Why do we PERSPIRE when very hot ? A. The pores of the body are like the safely valves of a steam-engine ; when the heat of the body is very great, some of the combustible matter of the blood is thrown off in perspiration; and the heat of the body kept more temperate. ANIMAL HEAT. 89 Q. Why do persons feel LAZY and averse to exercise when they are HALF-STARVED or ILL-FED? A. Animal food contains great nou- rishment, 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 labor 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 Because the air they inhale is less pure, being deprived of some of its oxygen : and A. 2dly Their respiration is neither so quick, nor so 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. Because strong meat and grease 90 CHEMICAL ACTION. contain large portions of carbon and hy- drogen; 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 ? A. Because the body requires more fuel in cold weather p , to keep up the same amount of animal tieat ; and as w r e put more coals on a fire on a cold day, to keep our room warm ; so we eat more food on a cold day, to keep our body warm. Q. Why does COLD produce HUNGER ? A. 1st Because the air contains more oxygen in cold weather; and, there- fore, fires burn more fiercely, and animal combustion is more rapid : and 2dly As we are more active in cold weather, our increased respiration acts like a pair of bellows on the capillary combustion. Q. Why does rapid DIGESTION produce a cra- ving APPETITE? A. This is a wise providence to keep our bodies in health ; they give notice (by hunger) that the capillary jires need re- plenishing, in order that the body itself may not be consumed. Q. Why do we feel a desire for ACTIVITY in cold weather ? ANIMAL HEAT. 91 A. 1st Because activity increases the warmth of the body, by fanning the combustion of the blood : and 2dly The strong food we eat creates a desire for muscular exertion. Q. Why are the Esquimaux so passionately fond of TRAIN OIL and WHALE BLUBBER ? A. Because oil and blubber contain large quantities of carbon and hydrogen, which are 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 food in very HOT weather ? A. Because strong 1 meat and grease contain so much carbon and hydrogen, that they would make us intensely hot : we therefore, instinctively refuse them in hot weather. Q. Why -do we like FRUITS and VEGETABLES most in hot weather ? A. Because they contain less hydro- gen and carbon than meat; and, there- fore, produce both less blood, and blood of a less combustible nature. Q. Why is the blood of a less COMBUSTIBLE na- ture, if we live chiefly upon FRUITS and VEGETABLES ? A. Because fruits and vegetables 92 CHEMICAL ACTION. supply the blood with a very large amount of water ; which is not combusti- ble, like the carbon and hydrogen of strong* meat. Q. How do FRUITS and VEGETABLES COOL the BLOOD? A. 1st They diminish the amount of carbon and liydrogen in the blood, which are the chief causes of animal heat : and 2dly They supply the blood with a large amount of water, which exudes through the skin, and leaves the body cool. Q. Why do ice feel LAZY and averse to activity in very HOT WEATHER ? A. 1st Because muscular activity increases the heat of the body, by quick- ening the respiration : and 2dly The food we eat in hot wea- ther (not being- greasy} naturally abates our desire for bodily activity. Q. . Why do the inhabitants of TROPICAL coun- tries live chiefly upon RICE and FRUIT? A. Because rice and fruit (by diges- tion) are mainly converted into ivater ; and (by cooling the blood) prevent the tropical heat from feeling so oppressive. Q. Why are the ILL-FED instinctively AVERSE tO CLEANLINESS? ANIMAL HEAT. 93 A. Because cleanliness increases hun- ger, which they cannot allay by food. Q. Why are the ILL-CLAD also instinctively averse to CLEANLINESS ? A. Because dirt is warm, (thus pigs, who love warmth) are fond of dirt) ; to those, therefore, who are very ill-dad, the warmth of dirt is agreeable. Q. Why are very POOR PEOPLE instinctively AVERSE to VENTILATION ? A. 1st Because ventilation increases the oxygen of the air the combustion of food and the cravings of appetite : and 2dly Ventilation cools the air of our rooms : to poor people, therefore, who are ill-clad, the warmth of an ill-ventilated apartment is agreeable. Q. Why does FLANNEL, <^c., make us WARM ? A. Flannel and warm clothing do not make us warm, but merely prevent our body from becoming cold. Q. How does FLANNEL, <^c., prevent our body from becoming cold ? A. Flannel (being a bad conductor) will neither carry off the heat of our body into the cold air, nor suffer the cold of the air to come in contact with our ivarm body : arid thus it is, that flannel clothing keeps us warm. 94 MECHANICAL ACTION. Q. WJiy are FROGS and FISHES COLD-BLOODED animals ? A. Because they consume very little air ; and, without a plentiful supply of air. combustion is too slow to generate much animal heat. Q. Why is a DEAD BODY COLD ? A. Because air is no longer conveyed to the lungs, after respiration has ceased ; and, therefore, animal heat is no longer generated by combustion. MECHANICAL ACTION. CHAPTER VIIL 1. PERCUSSION. Q. How is heat produced by MECHANICAL AC- TION 1 A. 1. By Percussion. 2. By Fric- tion. And 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. Q. Why does STRIKING IRON make it RED HOT ? A. Because it condenses the particles PERCUSSION. 95 of the metal, and makes the latent heat sensible. Q. Does COLD iron contain HEAT ? A. Yes ; everything 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 feelings. When anything contains heat without feeling the hotter for it, that heat is called " latent heat." See p. 37. Q. Does COLD iron contain latent HEAT ? A. Yes ; and when a blacksmith compresses the particles of iron by his hammer, he brings out latent heat ; and this makes the iron red hot. Q. How used blacksmiths 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. Q. How can a NAIL (beaten by a hammer) IGNITE a brimstone MATCH ? A. The particles of the nail being compressed by the hammer, can no longer contain so much heat in a latent state, as 96 MECHANICAL ACTION. they did before; some of it, therefore, becomes sensible, and increases the tem- perature of the iron. Q. Why does STRIKING a FLINT against a piece of STEEL produce a SPARK ? A. Because it compresses those parts of the flint and steel which strike toge- tlier. In consequence of which, some of their latent heat is disturbed, and exhi- bits itself in a spark. Q. How does this development of HEAT produce a SPARK and set TINDER on fire? 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. In order that the increased sup- ply of air may furnish the tinder with more oxygen to assist combustion. Q. Where does the OXYGEN of the, air 'COME FROM, which is blown to the lighted tinder ? A. From the air itself, which is com- posed of two gases (nitrogen and oxygen) mixed together. Every 5 gallons of common air contain nearly 4 gallons of nitrogen, and 1 of oxygen. Q. What is the USE of OXYGEN GAS to lighted tinder ? FRICTION. 97 A. It supports tlw combustion of the tinder. Blowing lighted tinder carries oxygen to it and quickens it, in the same way as a pair of bellows quickens a dull fire. Q. Why do HORSES sometimes STRIKE FIRE with their FEET ? A. Because when their iron shoes strike against the flint stones of the road, very small fragments (either of the shoe or stones) are knocked off red hot, and look like sparks. Q. WTiat makes these fragments RED HOT? A. The percussion condenses the part struck : In consequence of which, some of its latent heat is rendered sensible, and exhibits itself in these red hot fragments. CHAPTER IX. 2. FRICTION. Q. What is meant by FRICTION ? A. The act of rubbing two things to- gether ; as the Indians rub two pieces of wood together to produce fire. Q. How do the Indians produce FIRE by merely RUBBING TWO PIECES of dry WOOD TOGETHER? 5 98 MECHANICAL ACTION. A. They take a piece of dry wood, sharpened to a point, which they rub quickly up and down a flat piece, till a groove is made ; and the dust (collected in this groove) catches fire. Q. Why does the dust of the WOOD CATCH FIRE by RUBBING ? A. Because latent heat is developed from the wood by friction. The best woods for this purpose are boxwood against mulberry, or laurel against poplar or ivy. Q. Do not CARRIAGE WHEELS SOmetWUS CATCH FIRE? A. Yes ; when the wheels are dry or fit too tightly or revolve very rapidly. Q. Why do wheels catch fire in such cases ? A. Because the friction of the wheels against the axle-tree disturbs their latent heat, and produces ignition. Q. What is the use of GREASING CART WHEELS ? A. Grease lessens the friction ; and, because there is less friction, the latent heat of the wheels is less disturbed. Q. WTty does RUBBING our HANDS and FACES make them feel WARM? A. 1st Because friction excites the latent heat of our hands and faces, and makes it sensible to our feeling : and 2dly The blood is made to circulate more quickly ; in consequence of which, FRICTION. 99 the quantum of heat (left in its passage) is increased. Q. When a man has been almost DROWNED, why is suspended animation RESTORED by RUBBING 1 A. 1st Because friction excites the latent heat of the half-inanimate body : and 2dly It makes the blood circulate more quickly, which increases the animal heat. Q. Why do two pieces of ICE (rubbed together) MELT? A. Ice contains 140 degrees of latent Iwat, and (when two pieces are rubbed together) some of this latent heat is made sensible, and melts the ice. Q. Are not FORESTS sometimes SET on FIRE by friction ? A. Yes ; when two branches or trunks of trees (blown about by the wind) rub violently against each other , their latent heat is developed, and sets fire to the forests. Q. Why do carpenters 1 TOOLS (such as gimlets, saws, files, fyc.) become HOT when used ? A. Because the friction of the tools against the wood disturbs its latent heat, and makes it sensible. Q. Give an ILLUSTRATION of this. A. When cannon is bored, the borers 100 MECHANICAL ACTION. become so intensely hot from friction, that they would blister the hands, if touched. Q. Why do these BORERS become so i?ite?iscly HOT? A. Because the friction of the borers ag-ainst the metal is so great, that it sets free a large quantity of latent heat. CHAPTER X. 3. CONDENSATION or COMPRESSION.* Q. What is meant by COMPRESSION ? A. The act of bringing parts nearer together ; as a spong*e is compressed by be- ing* squeezed in the hand. Q. Cannot HEAT be evolved from common air merely by COMPRESSION ? A. Yes ; if a piece of German tinder be placed at the bottom of a glass tube, and the air in the tube compressed by a piston, the tinder will catch fire. In a common syringe or squirt, the Handle part (which contains the sucker, and is forced up and down) is called " the Piston." * N. B. The reduction of matter into a smaller com- pass by any external or mechanical force is called COM- PRESSION. The reduction of matter into a smaller compass by some internal action (as by the escape of caloric) is called CON- DENSATION. CONDENSATION OR COMPRESSION. 101 Q. Why will the tinder catch fire ? , A. Because the air is compressed, and its latent heat being squeezed out-, sets fire to the tinder at the bottom of the tube. Q. When an AIR-GUN is discharged in the dark, why is it accompanied with a slight FLASH ? A. Because the air is very rapidly condensedj and its latent heat developed in a flash of light. N. B. If a glass lens be fixed in the copper ball, (where the air of the gun is condensed?) a flash of light may be distinctly discerned at the stroke of the piston. Q. Why do DETONATING salt and powder EX- PLODE on being rubbed or struck ? A. Because the mechanical action of rubbing- or striking, produces sufficient heat to ignite the explosive materials of which they are composed. Q. Why are SHOT and CANNON-BALLS HEATED by being discharged from a gun or cannon ? A. Because the air is so rapidly con- densed, when the discharge is made, that sufficient latent heat is developed to make the shot or balls hot. Q. Why does the HOLE made by a shot or can- non-ball in a wall or timber, look as if it were BURNT ? A. Because the shot or cannon-balls were so heated by the discharge, as ac- tually to scorch the material into which they penetrated. 102 EFFECTS OF HEAT. EFFECTS OF HEAT. CHAPTER XL 1. EXPANSION. Q. What are the principal EFFECTS of HEAT ? A. 1. Expansion. 2. Liquefac- tion. 3. Vaporization. 4. Evapora- tion ; and 5. Ignition. Q. DOES HEAT EXPAND AIR 'I A. Yes ; if a bladder (partially filled with air) be tied up at the neck, and laid before the fire, the air will expand till the bladder bursts. Q. Why will the AIR SWELL if the bladder be laid before the fire? A. Because the heat of the fire will drive the particles of air apart from each other, and cause them to occupy more room than they did before. Q. Why do unslit CHESTNUTS CRACK with a loud noise when ROASTED ? A. Because they contain a great deal of air which is expanded by the heat of the fire ; and not being able to escape, bursts violently through the thick rind, slitting it) and making a great noise. EXPANSION. 103 Q. What occasions the loud CRACK or report which we hear ? A. 1st The sudden bursting of the rind makes a report ; in the same way as a piece of wood or glass would do, if snapped in two : and 2dly The escape of hot air from the chestnut makes a report also ; in the same way as gunpowder, when it escapes from a gun. Q. Why does the sudden BURSTING of the rind^ or SNAPPING of a piece of wood, make a REPORT ? A. Because a violent jerk is given to the air, when the attraction of cohe- sion is thus suddenly overcome. This jerk produces rapid undulations in the air, which (striking* upon the ear) give the brain a sensation of sound. Q. Why does the ESCAPE of AIR from the chest- nut, or the EXPLOSION of GUNPOWDER, produce a REPORT? A. Because the sudden expansion of the imprisoned air produces a partial vacuum ; the report is caused by the rushing of fresh air to fill up this vacuum. See Thunder, p. 15. Q. If a, CHESTNUT be SLIT, it will NOT CRACK ; why is this ? A. Because the heated air of the 104 EFFECTS OF HEAT. chestnut can then freely escape through the slit in the rind. Q. Why does an APPLE split and SPURT about when roasted? A. Because it contains a vast quanti- ty of air, which (being expanded by the heat of the fire) bursts through the peel, carrying the juice of the apple along with it. Q Does an APPLE contain MORE AIR in 'propor- tion than a CHESTNUT 1 A. Yes, much more. There is as much condensed air in a common apple, as would fill a space 48 times as large as the apple itself. Q. How can all this AIR %e stowed in an APPLE ? A. The inside of an apple consists of little cells (like a honey-comb), each of which contains a portion of the air. Q. When an APPLE is ROASTED, why is one part made SOFT, while all the rest remains hard ? A. Because the air in those cells next the Jire is expanded, and flies out ; the cells are broken, and their juices mixed together; so the apple collapses (from loss of air arid juice), and feels soft in those parts. Q. IVTiat is meant by the " apple COLLAPSING?" A. It means that the plumpness gives EXPANSION. 105 way, and the apple becomes flabby and shrivelled. Q. Why do SPARKS of fire start (with a crack- ling noise) from pieces of WOOD laid upon a FIRE ? A. Because the air (expanded by the heat)/orces its way through the pores of the wood; and carries along 1 with it the covering of the pore, which resisted its passage. Q. What is meant by the " PORES of the WOOD ?" A. Very small holes in the wood, through which the sap circulates. Q. What are the SPARKS OF FIRE which burst from the WOOD ? A. Very small pieces of wood made red hat, and separated from the log- by the force of the air, when it bursts from its confinement. Q. Why does DRY PINE make more snapping than any OTHER WOOD ? A. Because the pores of pine are very large, and contain more air than wood of a closer grain. Q. Why does GREEN WOOD make LESS SNAP- PING than DRY ? A. Because the pores being* filled with sap, contain very little air. Q. Why does DRY WOOD make MORE SNAPPING than green ? 5* 106 EFFECTS OF HEAT. A. Because the sap is dried up, and the pores are filled with air instead. Q. Why does DRY wood BURN more easily than GREEN or wet wood ? A. Because the pores of dry wood are filled with air which supports com- bustion ; but the pores of green or wet wood are filled with moisture, which ex- tinguishes flame. Q. Why does MOISTURE EXTINGUISH FLAME ? A. 1st Because it prevents the hy- drogen of the fuel from mixing 1 with the oxygen of the air, to form carbonic acid gas; and 2dly Because heat is perpetually carried off, by the formation of the sap or moisture into steam. Q. Why do STONES SNAP and fly about when heated in the FIRE ? A. Because the close texture of the stone prevents the hot air from escaping- ; in consequence of which, it bursts forth ivith great violence, tearing* the stone to atoms, and forcing- the frag-ments into the room. Probably some part of this effect is due to the setting free of the water of crystallization. Q. Wh.en bottled ALE or PORTER is set before a PIRE, why is the CORK FORCED OUT sometimes ? A. Because the carbonic acid of the EXPANSION. 107 liquor expands by the heat, and drives out the cork. Carbonic acid gas is a compound of carbon and oxygen. The carbon comes from the fuel, and the oxygen from the air. See p. 40. Q. Why does ALE or PORTER FROTH more after it has been set before the fire'} A. Because the heat of the fire sets free the carbonic acid of the liquor ; which is entangled as it rises through the liquor, and produces bubbles or froth. Q. When a boy makes a BALLOON, and sets fire to the cotton or sponge (which has been steeped in spirits of wine), why is the balloon INFLATED? A. Because the air of the balloon is expanded by the flame, till every crumple is inflated and made smooth. Q. Why does the BALLOON RISE after it has been inflated by the expanded air ? A. Because the same quantity of air is expanded to three or four times its ori- ginal volume; and made so much lighter, that even when all the paper, wire, and cotton are added, it is still lighter than common air. Q. Why does SMOKE RUSH UP a CHIMNEY ? A. Because the heat of the fire ex- pands the air in the chimney; which (being- thus made lighter than the air around) rises up the chimney, and carries the smoke in its current. 108 EFFECTS OF HEAT. Q. Why will a LONG chimney SMOKE, unless the FIRE be pretty FIERCE? A. Because the heat of the fire will not be sufficient to rarefy all the air in the chimney. Q. WHY will the chimney smoke, unless the fire be FIERCE enough to heat ALL the air in the CHIMNEY FLUE? A. Because the cold air ("condensed in the upper part of the flue) will sink from, its own weight ; and sweep the as- cending 1 smoke back into the room. Q. What is the use of a COWL upon a chim- ney-pot ? A. It acts as a screen, to prevent the wind from blowing* into the chimney. Q. What HARM would the WIND do if it were to BLOW into a CHIMNEY? A. 1st It would prevent the smoke from g'etting* out ; and 2dly The cold air (introduced into the chimney by the wind) would fall down the flue, and drive the smoke with it into the room. Q. Why are some things SOLID, others LIQUID, and others GASEOUS ? A. Because the particles which com- pose some thing's are nearer together than they are in others. Those in which the particles are closest are solid ; those EXPANSION. 109 in which they are furthest apart are gas- eous ; and *the rest liquid. Q. Why does heat change a SOLID (like ice) first into a LIQUID, and then into a GAS ? A. Because heat drives the compo- nent particles further asunder ; hence a certain quantity of heat changes solid ice into a liquid and a further addition of heat changes the liquid into steam. Q. Why does WATER SIMMER before it boi/.s ? A. Because the particles of water near the bottom of the kettle (being* form- ed into steam sooner than the rest) shoot upwards; but are condensed, again (as they rise) by the colder water, and pro- duce what is called " simmering." Q. What is meant by SIMMERING ? A. A gentle tremor or undidation on the surface of the water. When water simmers, the bubbles collapse beneath the surface, and the steam is condensed to water again ; but when water boils, the bubbles rise to the surface, and the steam is thrown off. Collapse, i. e., burst. Q. Why does a KETTLE SING when the water simmers ? A. Because the air (entangled in the water) escapes by Jits and starts through 110 EFFECTS OF HEAT. the spout of the kettle, which makes a noise like a wind instrument. Q. Wh,y does NOT a kettle SING when the water BOILS? A. Because all the water is boiling hot ; so the steam escapes in a continu- ous stream, and not by Jits and starts. Q. When does a kettle sing MOST? A. When it is set on the hob to boil. Q. Why does a kettle SING MORE when it is set on the SIDE of a fir e, than when it is set in the MIDST of the fire? A. Because the heat is applied so unequally, that one side is made hotter than the other ; in consequence of which, the steam is more entangled. Q. Why does a KETTLE sing, when the boiling water begins to COOL again ? A. Because the upper surface cools first ; and the steam (which rises from the lower part of the kettle) is again en- tangled, and escapes by Jits and starts. Q. Why does BOILING WATER SWELL ? A. Because it is expanded by the heat : i. e. The heat of the fire drives the par- ticles of water farther apart from each other: and (as they are not packed so close- ly together) they take up more room ; in other words, the water swells. EXPANSION. Ill Q. What is meant when it is said, that " HEAT drives the PARTICLES of water further APART from each other ?" A. Water is composed of little glo- bules, like very small grains of sand ; the heat drives these particles away from each other ; and (as they then require more room) the water swells. Q. Why does BOILING WATER BUBBLE? A. Because the vapor (rising through the water) is entangled, and forces up bubbles in its effort to escape. N. B. All the air of water is expelled at the commence- ment of its boiling. Q. Why does a KETTLE sometimes BOIL OVER ? A. Because the water is expanded by heal ; if, therefore, a kettle is filled icith cold water, some of it must run over, as soon as it is expanded by heat. Q. But I have seen a KETTLE BOIL OVER, al- though it has not been filled FULL of WATER ; how do you account for THAT? A. If a fire be very fierce, the air and vapor are expelled so rapidly, that the bubbles are very numerous ; and (tower- ering one above another) reach the top of the kettle, and fall over. Q. Why is a pot (which was full to OVER- FLOWING, while the water was boiling HOT) NOT PULL, after it has been taken off the fire for a short time? 112 EFFECTS OF HEAT. A. Because (while the water is boil- ing) it is expanded by the heat, and fills the pot even to overflowing : but, when it becomes cool, it contracts again, and occupies a much less space. Q. Why does the water of a KETTLE run out of the SPOUT when it BOILS ? A. Because the lid fits so tightly, that the steam cannot lift it up and escape : being confined, therefore, in the kettle, it presses on the water with great power, and forces it out of the spout. Q. What causes the RATTLING NOI&E, so often made by the LID of a saucepan or boiler ? A. The steam (seeking to escape) forces up the lid of the boiler, and the weight of the lid carries it back again : this being done frequently, produces a rattling noise. Q. If the steam COULD NOT LIFT UP THE LID of the boiler how would it escape ? A. If the lid fitted so tightly, that the steam could not raise it up, the boiler would burst into fragments , and the con- sequences might be fatal. Q. When steam pours out from the spout of a kettle, the STREAM begins apparently HALF AN INCH off the SPOUT ; why does it not begin CLOSE to the ut? A. Steam is really invisible ; and the EXPANSION. 113 half-inch (between the spout and the " stream of mist", is the real steam, before it has been condensed by air. Q. Why is not ALL the steam INVISIBLE as well as that half-inch ? A. Because the invisible particles are condensed by the cold air ; and, rolling one into another, look like a thick mist. Q. What BECOMES of the STEAM ? for it soon vanishes. A. After it has been condensed into mist, it is dissolved by the air, and dispers- ed abroad as invisible vapor. Q. And what BECOMES of the INVISIBLE VAPOR ? A. Being* lighter than air, it ascends to the upper regions of the atmosphere, where (being again condensed) it contri- butes to form clouds. Q. Why does a METAL SPOON (left in a sauce- pan) RETARD the process of BOILING ? A. Because the metal spoon (being an excellent conductor) carries off the heat from the water ; and (as heat is carried off by the spoon) the water takes a long- er time to boil. Q. Why will a POT (filled with water) NEVER BOIL, when immersed in ANOTHER vessel full of water also ? A. Because water can never be heat- ed above the boiling point ; all the heat 114 EFFECTS OF HEAT. absorbed by water after it boils, is em- ployed in generating steam. Q. How does the conversion of water into steam, prevent the INNER POT from BOILING? A. Directly the water in the larger pot is boiling Jwt (or 212), steam is form- ed and carries off some of its lieat ; there- fore, 212 of heat can never pass through it, to raise the inner vessel to boiling heat. Q. Why do SUGAR, SALT, tyc., RETARD the pro- cess of BOILING ? A. Because they increase the density of water ; and whatever increases the density of a fluid, retards its boiling. Q. If you want water to boil without COMING- IN CONTACT with the SAUCEPAN, what plan must you adopt ? A. We must immerse the pot (contain- ing the water to be boiled) in a sauce- pan containing strong brim, or sugar. Q Why ivould the INNER vessel boil, if the OUTER vessel contained strong BRINE ? A. Because brine will not boil, till it is raised to 218 or 220. Therefore, 212 of heat may easily pass through it, to raise the vessel immersed in it to boil- ing heat. Q. Why will brine impart to another vessel MORE than 212, and water NOT so MUCH ? EXPANSION. 115 A. Because no liquid can impart so high a degree of heat, as its own boiling temperature : As water boils at 212 it cannot impart 212 of heat : but, as brine will not boil without 21 of heat, it can impart enough to make water boil. Q. Why can liquids impart no EXTRA heat, after they boil ? A. Because all extra heat is spent in making steam. Hence water will not boil a vessel of water immersed in it, be- cause it cannot impart to it 212 of heat ; but brine will, because it can im- part more than 212 of heat, before it is itself converted into steam. Ether boils at - - 100 c Alcohol 173* Water 212 Water, with one- fifth salt - - 219 Syrup boils at - - 221 t Oil of turpentine - 314 Sulphuric acid - - 472 Linseed oil 640 Mercury 656 Any liquid which boils at a lower degree can be made to boil, if immersed in a liquid which boils at a higher degree. Thus a cup of ether can be made to boil in a saucepan of water. A cup of water in a saucepan of brine or syrup. But a cup of water will not boil, if immersed in ether ; nor a cup of syrup in water. Q. Why are CLOUDS HIGHER on a FINE DAY ? A. Because they are lighter, and more buoyant. Q. Why are CLOUDS LIGHTER on a FINE DAY ? A. 1st Because the vapor of the clouds is less condensed ; and 116 EFFECTS OF HEAT. 2dly The air itself (on a fine day) retains much of its vapor in an invisible form. Q. Why is a CUP put INVERTED into a FRUIT- PIE? A. Its principal use is to hold the, crust up, and prevent it from sinking, when the cooked fruit gives way under it. Q. Does not the cup PREVENT the FRUIT of the pie from BOILING OVER ? A. No it will rather tend to make it boil over, as there will be less room in the dish. Q. Explain this. A. When the pie is put into the oven the air in the cup will begin to expand, and drive every particle of juice from under it ; in consequence of which, the pie-dish will have a cup-full less room to hold its fruit in, than if the cup were taken out. Q. If the juice is driven OUT of the cup, why is the CUP always FULL of JUICE when the pie is cue up ? A. Because immediately the pie is drawn, the air in the cup begins to con- dense again, and occupy a smaller space ; and, as^ the cup is no longer full of air, juice rushes in to occupy the void. Q. Why does JUICE rush into the cup when the. CUp is NOT FULL of AIR ? EXPANSION FROM HEAT. 117 A. Because the external air presses upon the surface of the juice, which rushes unobstructed into the cup; as mercury rises through the tube of a barometer. N. B. Since the juice of the pie runs into the cup, as soon as it is taken out of the oven ; the cup prevents the juice from being spilt over the crust, when the pie is carried about from place to place ; although it does not prevent the fruit from boiling over. CHAPTER XII. EXPANSION FROM HEAT. (Continued.) Q. Does heat expand everything ELSE besides air and water ? A. Yes : every thing 1 (that man is ac- quainted with) is expanded by heat. Q, Wliy does a COOPER heat his HOOPS RED HOT when he puts them on a tub ? A. 1st As iron expands by heat, the hoops will be larger when they are red hot ; in consequence of which, they will fit on the tab more easily: and 2dly As iron contracts by cold, the hoops will shrink as they cool down, and girt the tub with a tighter grasp. Q. Why does a WHEELWRIGHT make the hoops RED HOT which, he fixes on the NAVE of a WHEEL? 118 EFFECTS OF HEAT. A. 1st That they may ft on more easily : and 2dly That they may girt the nave more tightly. Q. Why will the wheelwright's HOOP FIT the nave MORE BASIL Y,for being made RED HOT? A. Because it will be expanded by the heat ; and (being larger) will go on the nave more easily. Q. Why will the HOOPS which have been PUT ON HOT GIRT the nave more FIRMLY ? A. Because they will shrink when they cool down ; and, therefore, girt the nave with a tighter grasp. Q. Why does a STOVE make a CRACKLING NOISE when afire is very hot ? A. f Because it expands from the heat ; and the parts of the stove rubbing against each other, or driving against the bricks, produce a crackling noise. Q. Wh.y does a STOVE make a similar CRACK- LING NOISE when a large FIRE is TAKEN DOWN ? A. Because it contracts again, when the fire is removed ; in consequence of which, the parts rub against each other again, and the bricks are again disturbed. Q. Why does the PLASTER round a STOVE CRACK and fall away? A. Because (when the fire is light- ed) the iron-work expands more than EXPANSION FROM HEAT. 119 the brick-work and plaster, and pushes them away ; but (when the fire is put out) the metal shrinks again, and leaves the " setting 77 behind. The " setting" is a technical word for the plaster, &c., in immediate contact with the stove. Q. Why does the PLASTER FALL AWAY? A. As a chink is left (between the "setting' 7 and the stove), the plaster will frequently fall away from its own weight. Q. What OTHER cause contributes to BRING the PLASTER DOWN? A. As the heat of the fire varies, the size oftlie iron stove varies also ; and this swelling and contracting keep up such a constant disturbance about the plaster, that it cracks and falls off, leaving the fire-place very unsightly. Q. Why does the MERCURY of a THERMOMETER RISE in hot weather ? A. Because heat expands the metal, which (being increased in bulk) occupies a larger space ; and, consequently, rises higher in the tube. Q. Why is a GLASS BROKEN when HOT WATER is poured into it ? A. Because the inside of the glass is expanded by the hot water, and not the 120 EFFECTS OF HEAT. outside; so the glass snaps, in conse- quence of this unequal expansion. Q. Why is not the OUTSIDE of the GLASS ex- panded by the hot water as well as the INSIDE ? A. Because glass is a bad conductor of heat, and breaks before the heat of the inner surface is conducted to the outside. Q. Why does a GLASS snap because the INNER surface is HOTTER than the OUTER ? A. Because the inner surface is ex- panded and not the outer : in conse- quence of which, an opposing force is created, which breaks the glass. Q. Why is a CHINA CUP broken if HOT WATER be poured over it, or into it ? A. Because it is a bad conductor; and, as the inner surface expands from the heat, (and not the outer,") an opposing force is created, which breaks the cup. Q. If a GLASS BEAKER be set on a warm HOB, why does the BOTTOM COME OFF ? A. Because glass is a bad conductor; and (as the bottom of the glass expands from the warmth of the hot stove, before the sides are heated) the two parts sep- arate from each other. LIQUEFACTION. 121 ' CHAPTER XIII. 2. LlQJJEFACTION. 3. VAPORIZATION. Q. What is meant by LIQUEFACTION ? A. The staf'6 of being melted; as ice is melted by the heat of the sun., Q. Why is ICE MELTED by the HEAT of the SUN ? A. Because, when the heat of the sun enters the solid ice, it forces its par- ticles asunder ; till their attraction of cohesion is sufficiently overcome, to convert the solid ice into a liquid. See p. 109. Q. Why are METALS MELTED by the heat of FIRE ? A. Because, when the heat of the fire enters the solid metal, it forces Us par- tides asunder; till their attraction of cohesion is sufficiently overcome, to con- vert the solid metal into a liquid. Q. Why is WATER converted into STEAM by the heat of the FIRE ? A. Because, when the heat of the fire enters the water, it separates its globules into very minute bubbles ; which (being 1 lighter than air) fly off from the surface in the form of steam. Q. Why does not WOOD MELT like metal ? 6 122 EFFECTS OF HEAT. A. Because the heat of the fire de- composes the wood into gas, smoke, and ashes; and the different parts separate from each other. Q. What is meant by VAPORIZATION ? A. The conversion of a solid or liquid into vapor: as snow or water is con- verted into vapor by the heat of the sun. Q. What are CLOUDS ? A. Moisture evaporated from the earth, and again partially condensed in the upper regions of the air. Q. What is the difference between a FOG and a CLOUD ? A. Clouds and fogs differ only in one respect. Clouds are elevated above our heads : but fogs come in contact with the surface of the earth. Q. Why do CLOUDS FLOAT so readily in the air ? A. Because they are composed of very minute globules (called ves'icles) ; which (being lighter than air) float, like soap bubbles. Q. Why does VAPOR sometimes form into CLOUDS, and sometimes rest upon the earth as MIST or FOG? A. This depends on the temperature of the air. When the surface of the earth is warmer than the air, the vapor VAPORIZATION. 123 of the earth (being* condensed by the chill air) becomes mist or fog. Bat, when the air is warmer than the earth, the vapor rises through the air, and be- comes cloud. Q. Are ALL clouds ALIKE ? A. No. They vary greatly in density, height, and color. Q. What is the chief CAUSE of fog and CLOUDS ? A. The changes of the wind. Many local circumstances also favor the formation of clouds. Q. How can the CHANGES of the WIND affect the CLOUDS ? A. If a cold current of wind blows suddenly over any region, it condenses the invisible vapor of the air into cloud or rain : but if a warm current of wind blows over any region, it disperses the clouds, by absorbing their vapor. Q. What COUNTRIES are the MOST cloudy ? A. Those where the winds are most variable, as Britain. Q. What COUNTRIES are the LEAST cloudy ? A. Those where the winds are least variable, as Egypt. Q. What DISTANCE are the CLOUDS from the EARTH ? A. Some thin, light clouds are eleva- ted above the highest mountain-top ; 124 EFFECTS OF HEAT. some heavy ones touch the steeples, trees, and even the earth : but the aver- age height is between one and two miles. N. B. Streaky, curling clouds, like hair, are often 5 or 6 miles high. Q. WHAT CLOUDS are the LOWEST ? A. Those which are most highly elec- trified; lightning* clouds are rarely more than about 700 yards above the ground ; arid often actually touch the earth with one of their edges. Q. What is the SIZE of the CLOUDS? A. Some clouds are 20 square miles in surface, and above a mile in thickness ; while others are only a few yards or inches. Q. How can persons ascertain the THICKNESS of a cloud ? A. As the tops of high mountains are generally above the clouds, travellers may pass quite through them into a clear blue firmament ; when the clouds will be seen beneath their feet. Q. What produces the great VARIETY in the SHAPE of the CLOUDS? A. Three things : 1st The cause and manner of their formation : 2dly Their electrical condition : and 3dly Their relations to currents of wind. VAPORIZATION. 125 Q. How can ELECTRICITY affect the SHAPE of CLOUDS? A. If one cloud be 'full of electricity and another not, they will be attracted to each other, and either coalesce dimi- nish in size or vanish altogether. Q. WHAT CLOUDS assume the most FANTASTIC shapes ? A. Those that are the most highly electrified. Q. What effect have WINDS on the SHAPE of CLOUD ? A. They sometimes absorb them en- tirely ; sometimes increase their volume and density ; and sometimes change the position of their parts. Q. How can WINDS ABSORB CLOUDS altogether? A. Warm, dry winds will convert the substance of clouds into invisible vapor, which they will carry away in their own current. Q. How can WINDS INCREASE the bulk and density of CLOUDS ? A. Cold currents of wind will con- dense the invisible vapor of the air, and add it to the clouds with which they come in contact. Q. How can winds CHANGE the SHAPE of CLOUDS, by altering the position of their parts ? A. Clouds are so voluble and light, 126 EFFECTS OF HEAT. that every breath of wind changes the po- sition of their ves'icles or bubbles. Q. What are the general COLORS of the CLOUDS ? A. White and grey, when the sun is above the Jiorizon : but red, orange, and yellow, at sun-rise and sun-set. The blue sky is not cloud at all. Q. Why are thz LAST CLOUDS of EVENING gen- erally of a RED tinge? A. Because red rays (being the least refrangible of all) are the last to disap- pear. Suppose P A to be the red rays, P B the yellow, P C the blue. If the earth turns in the direction of P A D, it is quite manifest that a spectator will see A, (the red rays,) some time after P C and P B have passed from sight. Q. What is meant by being " LESS REFRANGI- BLE "? A. Being less able to be bent. Blue and yellow rays are more easily bent below the horizon by the resistance of the air : but red rays are not so much bent, VAPORIZATION. 127 down ; and, therefore, we see them later in the evening. As at A in the figure on p. 126. Q. Why are MORNING CLOUDS generally of a RED tinge? A. Because red rays are the least re- frangible of all; and not being bent so much as blue and yellow rays, we see them sooner of a morning. Thus (fig. on p. 126) if the earth turned in the direction of D A P, a spectator at D would see A (the red rays) long before he saw P B and P C. Q. Why is not the color of clouds always ALIKE 1 A. Because their size, density, and si- tuation in regard to the sun, are perpetu- ally varying ; so that sometimes one co- lor is reflected and sometimes another. Q. What regulates the MOTION of the CLOUDS ? A. Principally the winds ; but some- times electricity will influence their mo- tion also. Q. How do you know that CLOUDS move by OTHER influences besides WIND ? A. Because (in calm weather) we often see small clouds meeting each other from opposite directions. Q. How do you know that ELECTRICITY affects the motion of the clouds ? A. Because clouds often meet from opposite directions ; and, having discharg- 128 EFFECTS OF HEAT. ed their opposite electricities into each other, vanish altogether. Q. Into how many CLASSES are the different sorts of CLOUDS generally divided ? A. Into three classes : viz. Simple, Intermediate, and Compound. Q. How are SIMPLE CLOUDS sub-divided ? A. Into 1. Cirrus; 2. Cum'ulus ; and 3. Stra'tus clouds. Q. What sort of CLOUDS are called CIRRUS ? A. Clouds like fibres, loose hair, or thin streaks, are called " cirrus clouds." Q. Why are these clouds called CIRRUS ? A. From the Latin word cirrus (" a lock of hair, or curl "). Cirrus clouds are the most elevated of all. Q. What do CIRRUS clouds PORTEND? A. When the streamers point up- wards, the clouds are falling, and rain is at hand : but when the streamers point downwards, westerly winds or drought may be expected. Q. What sort of CLOUDS are called CUM'ULUS ? A. Cum'ulus clouds are lumps, like great sugar-loaves volumes of smoke or mountains towering over mountains. Q. Why are these monster masses called CUM'- ULUS CLOUDS ? A. From the Latin word cumulus (" a mass or pile "). VAPORIZATION. 129 Q What do CUM'ULTJS clouds FORESHOW 1 A. When these piles of cloud are fleecy, and sail against the wind, they indicate rain; but when their outline is very hard, and they come up with the wind, they foretell fine iveather. Cum/ulus clouds should be smaller towards evening than they are at noon. If they increase in size at sun-set, a thunder-storm may be expected in the night. Q. What sort of CLOUDS are calkd STRA'TUS ? A. Creeping mists, especially preva- lent in a summer's evening : these clouds rise at sun-set in low, damp places ; and are always nearer the earth than anjr other sort of cloud. Q. Why are, these, mists called STRA'TUS clouds ? A. From the Latin word stra'tus (" laid low," or " that which lies low "). Q. What produces CIRRUS CLOUDS 1 A. Moisture in a visible form, deposit- ed in the higher regions of the atmos- phere by ascending currents of heated air, Q. What produces CUM'ULUS CLOUDS ? A. Masses of visible vapor passing from the places where they were/ormed, to other places where they are about to be either dissolved, or deposited as falling rain. Q. What produces STRA'TUS CLOUDS ? A. Beds of visible moisture, formed 6* 130 EFFECTS OF HEAT. by some chilling- effects, acting- along- the direct surface of the earth. Q. How are the INTERMEDIATE CLOUDS sub-di- vided ? A. Into two sorts. 1. -The Cirro- Cum'ulus ; and 2. The Cirro-Stra'tus. Q. What are CIRRO-CUM'ULUS CLOUDS? A. Cirro-Cum'ulus clouds are cirrus clouds -springing- from a massy centre ; or heavy masses , edg-ed with long streaks g-enerally called "mares' tails." A system of small round clouds may be called cirro- the swallows fly low. Q. Why do these INSECTS seek the lower regions FOUL WEATHER. 145 of the air in WET weather, more than in FINE weather ? A. Because (in wet weather) the upper regions of the air are colder than the lower ; and, as insects enjoy warmth, they seek it near the earth. Q. Why does a DOWNWARD current of COLD AIR bring RAIN ? A. Because it condenses the warm vapor; which (being- condensed) de- scends in rain. Q. The proverb says, " A SINGLE MAGPIE in spring, FOUL WEATHER will bring:" Why is this the case ? A. Because in cold, stormy weather, one magpie alone will leave its warm, snug* nest in search of food, while the other stays with the eggs, or young ones; but in jine, mild weather (when their brood will not be injured by cold) both the magpies fly out together. Q. Why is it UNLUCKY for ANGLERS to see a SINGLE MAGPIE in spring ? A. Because when magpies fly abroad singly, the weather is cold and stormy ; but, when both birds fly out together, the weather is warm and mild, which is favorable for fishing. Q. Why do SEA-GULLS fly about the SEA in FINE weather ? 7 146 EFFECTS OF HEAT. A. Because they live upon the fishes, which are found near the surface of the sea in fine weather. Q. Why may we expect STORMY RAINS, when SEA-GULLS assemble on the land ? A. Because the fishes (on which they live) leave the surface of the sea in stormy weather, and are beyond the reach of the sea-gulls ; in consequence of which, they are obliged to feed on the worms and larvae^ which are driven out of the ground at such times. Larvas, little grubs and caterpillars. Q. WTiy do PETRELS fly to the SEA during a storm ? A. Because they live upon sea insects, which are always to be found in abun- dance about the spray of swelling leaves. N. B. Petrels are birds of the duck-kind, which live in the open sea. They run on the top of the waves, and are called Petrels, or rather Peter-els, from " St. Peter," in allusion to his walking on the sea, to go to Jesus. Q. Why do CANDLES and LAMPS SPIRT, when RAIN is at hand ? A. Because the air is filled with vapor which penetrates the wick; where (being formed into steam) it expands suddenly, and produces a little explosion. Q. Why does a DROP of WATER sometimes ROLL along a piece of hot iron, without leaving the least trace? VAPOR. 147 A. Because the bottom of the drop is turned into vapor, which buoys the drop up, without allowing* it to touch the iron. Q. Why does it ROLL 1 A. Because the current of air (which is always passing over a heated surface) drives it along. Q. Why does a LAUNDRESS put a little SALIVA on a FLAT-IRON, to know if it be hot enough ? A. Because when the saliva sticks to the box, and is evaporated, she knows it is not sufficiently hot ; but, when it runs along the iron, it is. Q. Why is the FLAT-IRON HOTTER if the saliva RUNS ALONG it, than if it adheres till it is evapor- ated ? A. Because when the saliva runs along the iron, the heat is sufficient to convert the bottom of the drop info vapor ; but, if the saliva will not roll, the iron is not sufficiently hot to convert the bottom of the drop into vapor. CHAPTER XIV. 4. EVAPORATION. Q. What is meant by EVAPORATION ? A. The dissipation of liquid by its conversion into vapor. 148 EFFECTS OF HEAT. Q. What EFFECTS are produced by evaporation ? A. The liquid vaporized absorbs heat from the body whence it issues ; and the body deprived of the liquid by evapora- tion, loses heat. Q. If you WET your FINGER in your mouth, and hold it up in the air^ why does it FEEL COLD ? A. Because the saliva quickly evap- orates ; and (as it evaporates) absorbs' heat from the finger, making- it feel cold. Q. If you BATHE your TEMPLES with ether, why does it allay INFLAMMATION and feverish heat 1 A. Because ether very rapidly evapo- rates ; and (as it evaporates) absorbs heat from the burning head, producing a sen- sation of cold. Q. Why is ETHER better for this purpose than WATER? A. Because ether requires less heat to convert it into vapor ; in consequence of which, it evaporates more quickly. N. B. Ether is converted into vapor with 100 of heat : "but water requires 212 of heat to convert it into steam. Q. Why does ETHER very greatly RELIEVE a SCALD Or BURN ? A. Because it evaporates very rapidly; and (as it evaporates) carries off the heat of the burn. Q. Why do we FEEL COLD, when we have WET FEET Or CLOTHES ? A. Because the wet of our shoes or DAMP CLOTHES. 149 clothes rapidly evaporates ; and (as it evaporates) absorbs heat from our body, which makes us feel cold. Q. Why do WET FEET or CLOTHES give us COLD ?" A. Because the evaporation absorbs heat so abundantly from the surface of our body, that its temperature is lowered below its natural standard; in conse- quence of which, health is injured. Q. Why is it DANGEROUS to SLEEP in a DAMP BED? A. Because the heat is continually absorbed from the surface of our body, to convert the damp of the sheets into va- . por ; in consequence of which, our ani- mal heat is reduced below the healthy standard. Q. Why is HEALTH INJURED, when the TEM- PERATURE of the BODY is REDUCED below its natural standard ? A. Because the balance of the circula- tion is destroyed. Blood is driven away from the external surface by the chill, arid thrown upon the internal organs, which are oppressed by this increased load of blood. Q. Why do we not feel the same sensation of cold, if we throw a MACINTOSH over our WET CLOTHES ? 150 EFFECTS OF HEAT. A. Because the macintosh (being* air tight) prevents evaporation; and (as the wet canrwt evaporate) no heat is absorbed from our bodies. Q. Why do NOT SAILORS get COLD, who are frequently wet all day with SEA- WATER ? A. 1st Because the salt of the sea retards evaporation ; and (as the heat of their body is drawn off gradually) the sensation of cold is prevented. 2dly The salt of the sea acts as a stimulant, and keeps the blood circulat- ing in the skin. Q. Why does SPRINKLING a HOT ROOM with water COOL IT ? A. Because the heat of the room causes a rapid evaporation of the sprin- kled water : and as the water evaporates, it absorbs heat from the room, which cools it. Q. Why does WATERING the STREETS and roads COOL THEM ? A. Because they part with their heat to promote the evaporation of the water sprinkled on them. Q. Why does a SHOWER of RAIN COOL the AIR in summer-time ? A. Because the wet earth parts with its heat to promote evaporation ; and when the earth is cooled, it cools the air also. EVAPORATION. 151 Q. Why is LINEN DRIED by being exposed to the WIND ? A. Because the wind accelerates evaporation, by removing the vapor from the surface of tlw wet /men, as fast as it is formed. Q. Why is LINEN DRIED sooner in the open AIR, than in a confined room ? A. Because the particles of vapor are more rapidly removed from the surface of the linen by evaporation. Q. Why are, WET SUMMERS generally SUC- CEEDED by COLD WINTERS? A. Because the great evaporation (carried on through the wet summer) reduces the temperature of the earth lower than usual, and produces cold. Q. Why is THIS COUNTRY WARMER and the winters less severe than formerly ? A. Because it is better drained and better cultivated. Q. Why does DRAINING land promote WARMTH ? A. Because it diminishes evaporation ; in consequence of which, less heat is ab- stracted from the earth. Q. Why does CULTIVATION increase the WARMTH of a country ? A. 1st Because hedges and belts of trees are multiplied : 2dly The land is better drained : and 152 EFFECTS OF HEAT. 3dly The vast forests are cut down. Q. Why do HEDGES and BELTS of TREES pro- mote WARMTH ? A. Because they retard evaporation, by keeping- off the wind. Q. If belts of trees promote WARMTH, why do FORESTS produce COLD ? A. 1st Because they detain and condense the passing clouds ; 2dly They prevent the access of both wind and sun ; 3dly The soil of forests is always covered with long, damp grass, rotting leaves, and thick brushwood ; and 4thly In every forest there are al- ways many hollows fall of stagnant water. Q. Why do LONG GRASS and ROTTING LEAVES promote COLD ? A. Because they are always damp ; and evaporation, which they promote, is constantly absorbing heat from the earth beneath. Q. Why are FRANCE and GERMANY WARMER now, than when the vine would not ripen there ? A. Chiefly because their vast forests have been cut doivn; and the soil is bet- ter drained and cultivated. Q. What becomes of the WATER of PONDS and TUBS in summer-time ? EVAPORATION. 153 A. Ponds and tubs are often left dry in summer-time, because their water is evaporated by the air. Q. How is this EVAPORATION PRODUCED and carried on ? A. The heat of the air changes the surface of the water into vapor, which (blending with the air) is soon wafted away ; and similar evaporation is repeat- edly produced, till the pond or tub is left quite dry. Q. Why are the WHEELS of some machines kept CONSTANTLY WET With WATER ? A. To carry off (by evaporation) the heat which arises from the rapid motion of the wheels. Q. Why is MOULD HARDENED by the SUN ? A. Because the moisture of the mould is exhaled by evaporation ; and, as the earthy particles are brought closer together, the mass becomes more solid. Q. Show the WISDOM of GOD in this arrange- ment. A. If the soil did not become crusty and hard in dry weather, the heat and drought would penetrate the soil, and kill both seeds and roots. Q. Why is TEA cooled FASTER in a SAUCER. than in a cup ? A. Because evaporation is increased 7* 154 EFFECTS OF HEAT. by increasing the surface ; and, as tea in a saucer presents a larger surface to the air, its heat is more rapidly carried off by evaporation. (The subject <*? " convection" will be treated of in a fu- ture chapter; it would scarcely be understood in this place. See p. 213.) Q. Why is not the VAPOR of the SEA SALT ? A. Because the salt is always left behind, in the process of evaporation. Q. What is that WHITE CRUST, which appears (in hot weather) upon CLOTHES wetted by sea water ? A. The salt of the water, left on the clothes by evaporation. Q. Why does this WHITE CRUST always DIS- APPEAR in WET weather? A. Because the moisture of tlie air dissolves the salt; in consequence of which, it is no longer visible. Q. Why should NOT persons, who take violent exercise, WEAR very THICK CLOTHING ? A. Because it prevents the perspira- tion from evaporating*. When the heat of the body is increased by exercise, per- spiration reduces the heat (by evapora- tion) to a healthy standard ; as thick clothing prevents this evaporation, it is injurious to health. CONDUCTION. 155 COMMUNICATION OF HEAT. CHAPTER XV. 1 CONDUCTION. Q. HOW is HEAT COMMUNICATED /TOM 0716 body to another ? A. 1. By Conduction. 2. By Ab- sorption. 3. By Reflection. 4 By Radiation. And 5. By Convection. Q. What is meant by CONDUCTION of heat ? A. Heat communicated from one body to another by actual contact. Q. Why does a PIECE of WOOD (blazing at ONE end) NOT feel HOT at the OTHER? A. Because ivood is so bad a conduct- or, that heat does not traverse freely through it ; hence, though one end of a stick be blazing- the other end may be quite cold. Q. Why do SOME THINGS feel COLDER than others ? A. Principally because they are bet- ter conductors ; and draw off heat from our body much faster. Q. What are the BEST CONDUCTORS of HEAT ? A. Dense, solid bodies, such as metal and stone. 156 COMMUNICATION OP HEAT. Q. Which METALS are the most RAPID CONDUCT- ORS 0/*HEAT? A. The best conductors of heat are 1. gold, 2. silver, 3. copper: The next best are 4. plat'inum, 5. iron, 6. zinc, 7. tin. Lead is a very inferior conductor to any of the preceding metals. Q. What are the WORST CONDUCTORS O/*HEAT ? A. All light and porous bodies; such as hair, fur, wool, charcoal, and so on. Two of the worst conductors known are hare's fur and eider down ; the two next worst are beaver's fur and raw silk ; then wood and lamp-black ; then cotton and fine lint ; -then charcoal, wood ashes, &c. Q. Why are COOKING VESSELS often furnished With WOODEN HANDLES? A. Because wood is not a good con- ductor, like metal ; and, therefore, wooden handles prevent the heat of the vessel from rushing into our hands, to burn them. Q. Why is the HANDLE of a METAL TEA-POT made of WOOD ? A. Because wood is a bad conductor ; therefore, the heat of the boiling water is not so quickly conveyed to our hand by a wooden handle, as by one made of metal. Q. Why would a METAL HANDLE BURN the HAND of the tea-maker ? A. Because metal is an excellent con- ductor ; therefore, the heat of boiling wa- KETTLE-HOLDERS. 157 ter would rush so quickly into the metal handle, that it would burn our hand. Q.' Prove that a METAL HANDLE would be HOT- TER than a WOODEN ONE. A. If we touch the metal collar into which the wooden handle is fixed, we shall find that the wooden handle feels cold, but the metal collar intensely hot. Q. Why do persons use paper or WOOLLEN KETTLE-HOLDERS? A. Because paper and woollen are both very bad conductors of heat ; in con- sequence of which, the heat of the kettle does not readily pass through them to the hand. Q. Does the heat of the boiling kettle NEVER get through the woollen or paper kettle-holder ? A. Yes ; but though the kettle-holder became as hot as the kettle itself, it would never feel so hot. Q. Why would not the kettle-holder FEEL so hot as the kettle, when both are of the same temperature ? A. Because it is a very bad conduct- or, and disposes of its heat too slowly to be perceptible ; but metal (being an ex- cellent conductor) disposes of its heat so quickly \ that the sudden influx is painful. Q. Why does HOT METAL FEEL MORE intensely WARM than HOT WOOL ? A. Because metal gives out a much 158 COMMUNICATION OP HEAT. greater quantity of heat in the same space of time ; and the influx of heat is, con- sequently, more perceptible. Q. Why does MONEY in our pocket feel very HOT when we stand BEFORE a FIRE 1 A. Because metal is an excellent con- ductor, and becomes rapidly heated. For the same reason, it becomes rapidly cold, whenever it comes in contact with a body colder than itself. Q. Why does a PUMP-HANDLE feel intensely COLD in WINTER ? A. Because it is an excellent conduct- or, and draws off the heat of our hand so rapidly, that the sudden loss produces a sensation of intense coldness. Q. Is the iron HANDLE of the pump really COLDER than the wooden PUMP itself? A. No ; every inanimate substance (exposed to the same temperature) pos- sesses in reality th6 same degree of heat. Q. Why does the IRON HANDLE seem so MUCH COLDER than the WOODEN PUMP ? A. Merely because the iron is a bet- ter conductor ; and, therefore, draws off the heat from our hand more rapidly than wood does. Q. Why does a STONE or marble HEARTH feel to the feet COLDER than a CARPET or hearth-rug? A. Because stone and marble are good CARPETS STONES. 159 conductors ; but woollen carpets and hearth-rugs are very bad conductors. Q. How does the STONE HEARTH make our FEET COLD ? A. As soon as the hearth-stone has absorbed a portion of heat from our foot, it instantly disposes of it, and calls for a fresh supply ; till the hearth-stone has be- come of the same temperature as the foot placed upon it. Q. Do not also the woollen CARPET and HEARTH- RUG conduct heat from the human body? A. Yes ; but being- very bad conduct- ors, they convey the heat away so slow- ly, that the loss is scarcely perceptible. Q. Is the COLD HEARTH-STONE in reality of the SAME TEMPERATURE as the WARM CARPET ? A. Yes ; every thing in the room is really of one temperature ; but some things feel colder than others, because they are better conductors. Q. How LONG will the hearth-stone feel cold to the feet resting on it ? A. Till the feet and the hearth-stone are both of the same temperature ; and then the sensation of cold in the hearth- stone will go off. Q. Why would not the HEARTH-STONE feel COLD, when it is of the SAME temperature as our FEET? 160 COMMUNICATION OP HEAT, A. Because the heat would no long- er rush out of our feet into the hearth- stone, in order to produce equilibrium, Q. Why does the HEARTH-STONE (when the fire is lighted) feel HOTTER than the HEARTH-RUG ? A. Because the hearth-stone is an excellent conductor, and parts with its heat very readily ; but the woollen hearth- rug* (being- a bad conductor) parts with its heat very reluctantly. Q. Why does PARTING with HEAT RAPIDLY make the H EARTH-STONE feel WARM? A. Because the rapid influx of heat raises the temperature of our body so sud- denly, that we cannot help perceiving the increase. Q. Why does the non-conducting power of the HEARTH-RUG prevent its feeling so HOT as it really is? A. Because it parts with its heat so slowly and gradually, that we scarcely perceive its transmission into our feet. Q. When we plunge our HANDS into a basin of WATER why does it produce a sensation of COLD ? A. Because water is a better conduct- or than air; and, as it draws off the heat from our hands more rapidly, it feels colder. Q. Why does the CONDUCTING power of water make it feel COLDER than AIR ? A. Because it abstracts heat from our WATER. 161 hands so rapidly, that we feel its loss; but the air abstracts heat so very slowly, that its gradual loss is hardly perceptible. Q. Is water a GOOD CONDUCTOR of heat ? A. No ; no liquid is a good conductor of heat ; but yet water is a much better conductor than air. Q. Why is WATER a BETTER CONDUCTOR of heat than AIR 1 A. Because it is less subtile ; and the conducting power of any substance de- pends upon its solidity, or the closeness of its particles. Q. How do you know that WATER is NOT a GOOD CONDUCTOR of heat ? A. Because it may be made to boil at its surface, without imparting sufficient heat to melt ice a quarter of an inch below the surface. Q. Why cure, NOT LIQUIDS GOOD CONDUCTORS of heat ? A. Because the heat (which should be transmitted) produces evaporation, and flies off in the vapor. , Q. Why does a POKER (resting on a fender) feel COLDER than the HEARTH-RUG, which is further off the fire? A. Because the poker is an excellent conductor, and draws heat from the hand much more rapidly than the woollen 162 COMMUNICATION OP HEAT. hearth-rug-, which is a very bad conductor: though both, therefore, are equally warm, the poker seems to be the colder. (See also p. 173.) Q. Why are HOT BRICKS (wrapped in cloth) employed in cold weather to KEEP the FEET WARM ? A. Because bricks are bad conductors of heat, and cloth or flannel still worse : in consequence of which, a hot brick (wrapped in flannel) will retain its heat a very long time. Q. Why is a TIN PAN (filled with HOT WATER) employed as a FOOT- WARMER ? A. Because polished tin (being 1 a bad radiator of heat) keeps hot a very long time ; arid warms the feet resting- upon it. Q. What is meant by being a " bad RADIATOR of heat .?" A. To radiate heat is to throw off heat by rays, as the sun ; a polished tin pan does not throw off the heat of boiling water from its surface, but keeps it in. Q. Why are TIN FOOT-WARMERS covered with FLANNEL ? A. 1st That the polish of the tin may not be injured : 2dly Because the flannel (being* a very bad conductor) helps to keep the tin hot longer : and FOOT-WARMERS STOVES. 163 3dly Lest the conducting* surface of the tin should feel painfully hot. Q. What disadvantage would it be, if the POL- ISH of the tin were injured ? A. If the tin foot- warmer were to lose its polish, it would get cold in a much shorter time. Q. Why would the tin foot-warmer get COLD SOONER, if the POLISH were INJURED ? A. Because polished tin throws off its heat very slowly; but dull, scratched, painted, or dirty tin, throws off its heat very quickly. Q. Why are FURNACES and stoves (where much HEAT is required) built of porous BRICK ? A. Because bricks are bad con- ductors, and prevent the escape of heat ; in consequence of which, they are em- ployed where great heat is required. Q. Why are FURNACE DOORS, fyc., frequently COVERED with a paste of CLAY and SAND? A. Because this paste is a very bad conductor of heat; and, therefore, pre- vents the escape of heat from the furnace. Q. If a stove be placed in the MIDDLE of a room should it be made of bricks or IRON ? A. A stove in the middle of a room should be made of iron ; because iron is an excellent conductor, and rapidly communicates heat to the air around. 164 COMMUNICATION OF HEAT. Q. Why does the Bible say, that God " giveth BNOW like WOOL ?" A. Because snow (being- a very bad conductor of lieat) protects vegetables and seeds from the frost and cold. Q. How does the non-conducting power of SNOW PROTECT VEGETABLES from the FROST and cold? A. It prevents the heal of the earth from being- drawn off by the cold air which rests upon it. Q. Why are WOOLLENS and FURS used for CLOTHING in COLD weather ? A. Because they are very bad con- ductors of heat; and, therefore, prevent the warmth of the body from being drawn off by the cold air. Q. Do not woollens and furs actually IMPART heat to the body ? ^ A. No ; they merely prevent the heat of the body from escaping. Q. Where would the heat ESCAPE to, if the body were NOT wrapped in wool or fur ? A. The heat of the body would fly off into the air; for the cold air (coming in contact with our body) would gi*adu- ally draw away its heat, till it was as cold as the air itself. Q. What then is the PRINCIPAL USE of CLOTH- ING in winter-time ? A. 1st To prevent the animal heat from escaping too freely ; and AIR. 165 2dly To protect the body from the external air (or wind), which would carry away its heat too rapidly. Q. Why are BEASTS COVERED with FUR, HAIR or WOOL ? A. Because fur, hair and wool, are very slow conductors of heat; arid (as dumb animals cannot be clad, like human being's) God has given them a robe of hair or wool, to keep them warm. Q. Why are BIRDS covered with DOWN or FEATHERS ? A. Because down and feathers are very bad conductors of heat; and (as birds cannot be clad, like human beings) God has given them a robe of feathers, to keep them warm. Q. Why are WOOL, FUR, HAIR, and FEATHERS, such SLOW CONDUCTORS of heat ? A. Because a great quantity of air lurks entangled between the fibres; and air is a very bad conductor of heat. The warmest clothing is that which fits the body very loosely in every part except at the extremities: Because more hot air will be confined by a loose garment than by one which fits the body tightly. Q. If AIR be a BAD CONDUCTOR of heat, why should we not feel as warm WITHOUT clothing, as when we are wrapped in wool and fur ? A. Because the air (which is cooler than our body) is never at rest; and 166 COMMUNICATION OF HEAT. every fresh particle of air draws off a fresh portion of heat. Q. How does the ceaseless CHANGE of air tend to DECREASE the WARMTH of a naked body? A. Thus : the air (which cases the body) absorbs as much heat from it as it can, while it remains in contact ; being then blown away, it makes room for a fresh coat of 'air ', which absorbs more heat. Q. Does the ATR which encases a naked body become (by contact) as WARM as the BODY itself? A. It would do so, if it remained motionless ; but, as it remains only a very short time, it absorbs as much heat as it can in the time, and passes on. Q. Why do we feel COLDER in WINDY WEA- THER than in a CALM day ? A. Because the particles of air pass over us more rapidly ; pnd every fresh particle takes from us some portion of heat. Q. Show the wisdom of God in making the AIR a BAD CONDUCTOR. A. If air were a good conductor (like iron and stone) heat would be drawn so rapidly from our body, that we should be chilled to death. Similar evils would be felt also by all the animal and vegetable world. Q. Does not the bad conducting power of air STALE EGG FANNING. 167 enable persons to judge whether an EGG be NEW r STALE ? A. Yes ; touch the larger end of the shell with your tongue ; if it feels warm, the egg is stale ; if not, it is new-laid. Q. Why will the SHELL of a STALE EGG feel WARM to the tongue ? A. Because the thick end of an egg contains a small quantity of air (between the shell and the white) ; when the egg is stale the white shrinks, and the con- fined air accordingly expands. Q. Why does the expansion of air (at the end of 'an egg) make it feel WARM to the tongue ? A. Because air is a very bad conduct- or, and the more air an egg contains, the less heat will be drawn from the tongue when it touches the shell. Q. Why will a NEW-LAID egg feel COLDER to the tongue at the thick end than a stale one ? A. Because it contains more white ancl less air ; and as the white of an egg is a better conductor than air, the heat of the tongue will be drawn offmorera- pidly, and the egg feel colder. Q. Why does FANNING the face in summer make it COOL ? A. Because the fan puts the air in motion, and makes it pass more rapidly over the face ; and (as the temperature of 168 COMMUNICATION OP HEAT. the air is always lower than that of the human face) each puff of air carries off some portion of its heat. Q. Does FANNING make the AIR itself COOLER ? A. No ; fanning makes the air Iwtter and Jwtter. Q. How does FANNING the face increase the HEAT of the air ? A. By driving- the air more rapidly over the human body, and causing- it, consequently, to absorb more Iwat. Q. If fanning makes the AIR HOTTER, why can it make a PERSON feel COOLER ? A. Because it takes the heat out -of the face, and gives it to the air. Q. Why is BROTH COOLED by BLOWING it ? A. Because the breath causes a rap- id change of air to pass over the broth ; and (as the air is colder than the broth) it continually absorbs heat from it, and makes it cooler and cooler. Q. Would not the air absorb heat from the broth just as well WITHOUT BLOWING? A. No ; air is a very bad conductor ; unless, therefore, the change be rapid, the air nearest the surface of the broth would soon become as Iwt as the broth itself. Q. Would not hot air PART with its heat in- stantly to the CIRCUMJACENT air ? A. No ; not instantly. Air is so bad WIND. 169 a conductor, that it parts with its heat very slowly: unless, therefore, the air be kept in continual motion, it would cool the broil i very slowly indeed. Q. Why does WIND generally feel COOL ? A. Because it drives the air more rapidly over our body ; and this rapid change of air draws off a large quantity of heat Q. Why does AIR ABSORB heat more QUICKLY by being set in MOTION ? A. Because every fresh gust of air absorbs a fresli portion of heat ; and the more rapid the succession of gusts, the greater will be the quantity of heat ab- sorbed. Q. If the AIR were HOTTER than our body vsould the WIND feel COOL ? A. No ; the air would feel insuffera- bly hot, if it were /totter than our body. Q. Why would the AIR feel INTENSELY HOT, if it were WARMER than our BODY ? A. Because it would add to the heat of our body, instead of diminishing it. Q. Is the AIR EVER as HOT as the human BODY? A. Not in this country : in the hot- test, summer's day, the air is at least 10 or 12 degrees cooler than the human body. Q. Is the EARTH a good conductor of heat f 8 170 COMMUNICATION OF HEAT. A. No ; the earth is a very bad con- ductor of heat* Q. Why is the EARTH a BAD conductor of heat ? A. Because its particles are not con- tinuous : and the power of conducting heat depends upon the continuity of matter. Q. Why is the earth (BELOW the SURFACE) WARMER in WINTER than tJie surface itself? A. Because the earth is a bad con- ductor of heat; and, therefore, (although the ground be frozen,) the frost never penetrates more than a few inches below the surface. Q. Why is the earth (BELOW the SURFACE) COOLER in SUMMER than the surface itself? A. Because the earth is a bad con- ductor of heat ; and, therefore, (although the surface be scorched with the burning sun,) the intense heat cannot penetrate to the roots of the plants and trees. Q. Show the WISDOM of G-OD in making the EARTH a BAD CONDUCTOR ? A. If the heat and cold could pene- trate the earth (as freely as the heat of a fire penetrates iron), the springs would be dried up in summer, and fro- zen in winter ; and all vegetation would perish. SHADE COOL. 171 Q. Why is WATER from a SPRING always COOL even in SUMMER ? A. Because the earth is so bad a con- ductor, that the burning* rays of the sun can penetrate only a few inches below the surface ; in consequence of which, the springs of water are not affected by the heat of summer. Q. Why is it COOL under a SHADY tree in a hot summers day ? A. 1st Because the overhanging- fo- liage screens offtlie rays of the sun : 2dly As the rays of the sun are ward- ed off, the air (beneath the tree) is not heated by the reflection of the earth : and 3dly The leaves of the trees, being non-conductors, allow no heat to pene- trate them. Q. Why do the LAPLANDERS wear SKINS with the FUR INWARDS? A. Because the dry skin prevents the wind from penetrating to their body ; and the air (between the hairs of the fur) soon becomes heated by the body: in consequence of which, the Laplander in his fur is clad in a case of hot air, imper- vious to the cold and wind. Q. Why does a LINEN SHIRT feel COLDER than a COTTON ONE ? A. Because linen is a much better 172 COMMUNICATION OF HEAT. conductor than cotton ; and, therefore, (as soon as it touches the body) it draws away the heat more rapidly, and pro- duces a greater sensation of cold. Q. Why is the FACE COOLED by wiping the temples with a fine CAMBRIC HANDKERCHIEF ? A. Because the fine fibres of the cambric have a strong capillary attraction for moisture, and are excellent conductors of heat: in consequence of which, the moisture and heat are abstracted from the face by the cambric, and a sensation of coolness produced. " Capillary attraction," i. e., the attraction of a thread or hair. The wick of a candle is wet with grease, because the melted tallow runs up the cotton from capillary at- traction. Q. Why would not a COTTON handlcerchief do as well ? A. Because the coarse fibres of cot- ton have very little capillary attraction, and are very bad conductors ; in conse- quence of which, the heat of the face would be increased (rather than dimin- ished} by the use of a cotton handker- chief. ABSORPTION. 173 CHAPTER XVI. 2. ABSORPTION OF HEAT. Q. What is the difference between CONDUCTING heat, and ABSORBING heat ? A. To conduct heat is to transmit it from one body to another through a con- ducting medium. To absorb heat is to suck it up, as a sponge sucks up water. Q. Give me an example. A. Black cloth absorbs, but does not conduct heat ; thus, if black cloth be laid in the sun, it will absorb the rays very rapidly ; but if one end of the black cloth be made hot, it would not conduct the heat to the other end. Q. Are good CONDUCTORS of heat good AB- SORBERS also ? A. No ; every good conductor of heat is a bad absorber of it ; and no good ab- sorber of heat can be a good conductor also. Q. Is IRON a good ABSORBER of heat ? A. No ; iron is a good conductor, but a very bad absorber of heat. Q. Why do the FIRE-IRONS (which lie upon a FENDER) remain COLD, although they are before a good fire ? A. Because they are bad absorbers of 174 COMMUNICATION OP HEAT. heat; in consequence of which, they remain cold, unless they come in contact with the stove or fire. Q. Why are the FIRE-IRONS intensely HOT, when they REST AGAINST the STOVE which contains a good fire ? A. Because they are excellent conduct- ors ofheat, and draw it rapidly from the stove with which they are in contact. Q. Why does a KETTLE boil faster, when the bottom and back are COVERED with SOOT 1 A. Because the black soot absorbs heat very quickly from the fire, and the metal conducts it to the water. Q. Why will not a NEW KETTLE boil so fast as an OLD one ? A. Because the bottom and sides of a new kettle are clean and bright : but in an old kettle they are covered with soot. Q. Why will a KETTLE be SLOWER BOILING if the BOTTOM and BACK are CLEAN and bright ? A. Because bright metal does not ab- sorb heat, but reflects it ; and (as the heat is thrown off from the surface of bright metal by reflection) therefore, a new kettle takes a longer time to boil. Reflects heat, i. e., throws it off. Q. Why do we wear WHITE LINEN and a BLACK outer DRESS, if we want to be warm ? A. Because the black outer dress COLORS. 175 quickly absorbs heat from the sun ; and the white linen (being- a bad absorbent) abstracts no heat from the warm body. Q. Why do persons WEAR WHITE dresses in SUMMER time ? A. Because white throws off the heat of the sun by reflection, and is a very bad absorbent of heat; in consequence of which, white dresses never become so hot from the scorching sun as dark co- lors do. Q. Why do NOT persons WEAR WHITE dresses in WINTER time ? A. Because ivhite will not absorb heat y like black and other dark colors; and, therefore, white dresses are not so ivarm as dark ones. Q. What COLORS are WARMEST for dresses? A. For outside garments black is the warmest, and then such colors as ap- proach nearest to black, (as dark blue and green.) White is the coldest color for external clothing*. Q. Why are DARK COLORS (for external wear) so much WARMER than LIGHT ONES ? A. Because dark colors absorb heat from the sun more abundantly than light ones. Q. How can you prove that DARK colors are WARMER than LIGHT OWS? 176 COMMUNICATION OF HEAT. A. If a piece of black and a piece of white cloth were laid upon snow, in a few hotirs the black cloth will have melted the snow beneath; whereas, the white cloth will have produced little or no effect upon it at all. N. B. The darker any color is, the warmer it is, be- cause it is a better absorbent of heat. The order may be thus arranged: 1. Black (warmest of all). 2. Violet. 3. Indigo. 4. Blue. 5. Green. 6. Red. 7. Yellow: and 8. White (coldest of all). Q. Why are BLACK KID GLOVES unpleasantly HOT for summer wear ? A. 1st Because black absorbs tJie sola?' heat; and 2dly Kid will not allow the heat of our hand to escape through the glove. Q. Why are LISLE THREAD GLOVES agreeably COOL, for summer wear ? A. 1st Because thread absorbs per- spiration : and 2dly It conducts away the heat of our hot hands. Q. Are Lisle thread gloves ABSORBENTS of heat ? A. No ; Lisle thread gloves are gen- erally of a grey or lilac color ; and, there- fore, do not absorb solar heat. Q. Why is a PLATE-WARMER made of UN- PAINTED BRIGHT TIN ? A. Because bright tin reflects the heat REFLECTOR HOAR FROST. 177 (which issues from the fire in rays) upon the meat ; and, therefore, greatly assists the process of roasting-. Reflects the heat, i. e., throws it back upon the meat. Q. Why would not the tin REFLECTOR do as well, if it were PAINTED? A. Because it would then absorb heat, and not reflect it at all. A plate-warmer should never be painted, but should be kept very clean, bright, and free from all scratches. Q. Why should a REFLECTOR be kept so very CLEAN a?id free from all SCRATCHES? A. Because if a reflector were spotted, dullj or scratched, it would absorb heat, instead of reflecting it ; and, consequently, would be of no use whatsoever as a reflector. Q. Why does HOAR FROST remain on TOMB- STONES long after it has melted from the GRASS and GRAVEL- WALKS of a church-yard ? A. Because tomb-stones (being* white] will not absorb heat, like the darker grass and gravel ; in consequence of which, they remain too cold to thaw the frost congealed upon their surface. Q. If black absorbs heat, why have those who live in HOT climates BLACK SKINS, and not WHITE skins, which would not absorb heat at all ? A. Because black will not blister from 8* 178 COMMUNICATION OP HEAT. the heat of the sun. Although, therefore, the black skin of the negro absorbs heat more plentifully than the white skin of a European; yet the blackness prevents the sun from blistering or scorching it. Q. How is it known that the, BLACK color pre- vents the sun from either BLISTERING or SCORCHING the skin? A. If you put a white glove on one hand, and a black glove on the other (when the sun is burning* hot), the hand with the white glove will be scorched, but not the other. Q. WHICH hand will FEEL the HOTTER ? A. The hand with the black glove w'Mfeel the hotter, but will not be scorch- ed by the sun ; whereas, the hand with the white glove (though much cooler) will be severely scorched. Q. Why does the BLACK skin of a NEGRO NE- VER SCORCH or BLISTER with the hot sun ? A. Because the black color absorbs the heat conveys it below the surface of the skin and converts it to semible heat and perspiration. Q. Why does the WHITE EUROPEAN SKIN BLISTER and SCORCH when exposed to the hot sun? A. Because white will not absorb heat ; and, therefore, the hot sun rests on the surface of the skin, and scorches it. REFLECTION OF HEAT. 179 Q. Why has a NEGRO BLACK EYES ? A. Because the black color defends them from the strong* light of the tropi- cal sun. If a negro's eyes were not black, the sun would scorch them,, and every negro would be blind. Q. Why is WATER (in hot weather) KEPT COOLER in a BRIGHT TIN POT than in an EARTHEN one ? A. Because bright metal will not absorb heat from the hot air, like an earthen vessel ; in consequence of which, the water is kept cooler. Boiling water is also kept hot in bright metal better than in earthen vessels. See p. 187. CHAPTER XVII. 3. REFLECTION OF HEAT. Q. What is meant by REFLECTING HEAT ? A. To reflect heat is to throw it back in rays from the surface of the reflecting body towards the place whence it came. Q. What are the BEST REFLECTORS of heat ? A. All bright surfaces and light co- lors. Q. Are GOOD ABSORBERS of heat GOOD RE- FLECTORS also ? 180 COMMUNICATION OF HEAT. A. No; those thing's which absorb heat best, reflect heat worst; and those which reflect heat worst, absorb it best. Q. Why are those things which ABSORB HEAT unable to REFLECT it ? A. Because if anything* sucks in heat like a spong-e, it cannot throw it off from its surface ; and if anything 1 throws off heat from its surface, it cannot drink it in. Q. Why are REFLECTORS always made of LIGHT COLORED and highly POLISHED METAL ? A. Because light colored and highly polished metal makes the best of all re- flectors. ' Q. Why do not PLATE-WARMERS BLISTER and scorch the WOOD behind ? A. Because the brig-lit tin front throws the heat of the fire back again, and will not allow it to penetrate to the wood behind. Q. If metal be such an excellent CONDUCTOR of heat, how can it REFLECT heat, or throw it off? A. Polished metal is a conductor of heatj only when that heat is communi- cated by actual contact : But whenever heat falls upon bright metal in rays^ it is reflected back again, and the metal re- mains cool. Q. What is meant " by heat falling wpon meted IN RAYS," and not " by contact ?" TIN REFLECTORS. 181 A. If a piece of metal were thrust into a fire, it would be in actual contact with the fire ; but if it were held before a fire, the heat of the fire would fall upon it in rays. Q. What is the use of the TIN SCREEN or RE- FLECTOR used in ROASTING ? A. It throws the heat of the fire back upon the mmt ; and, therefore, both as- sists the process of roasting, and helps to keep the kitchen cool. Q. How does a tin REFLECTOR tend to keep the KITCHEN COOL ? A. By confining the heat of the fire to the hearth, and preventing its dispersion throughout the kitchen. Q. Why are SHOES HOTTER for being DUSTY ? A. Because dull, dusty shoes will absorb heat from the sun, earth, and air ; but shoes brightly polished throw off the heat of the sun by reflection. Q. Why does it always FREEZE on the TOP of 0, MOUNTAIN? A. 1st Because the air on a moun- tain is very rarefied ; and rarefied air re- tains more heat in the latent form than denser air does : and 2dly Air is heated by the reflection of the earth, and not by solar rays ; therefore a mountain-top (which is deprived of this reflection) remains intensely cold. 182 COMMUNICATION OF HEAT. CHAPTER XVIII. 4. RADIATION. Q. What is meant by RADIATION ? A. Radiation means the emission of rays: thus the sun radiates both light arid heat ; that is, it emits rays of liglti and heat in all directions. Q. WHEN is heat RADIATED from one body to another ? A. When the two bodies are separated by a non-conducting medium : thus the sun radiates heat towards the earth, be- cause the air (which is a very bad con- ductor) comes between. Q. On WHAT does RADIATION DEPEND ? A. On the roughness of the radiating surface : thus, if metal be scratched, its radiating- power is increased ; because the heal; has more points to escape from. Q. Does a FIRE RADIATE heat ? A. Yes ; and because burning fuel emits rays of heat, therefore we feel warm when we stand before a fire. Q. Why does our FACE FEEL uncomfortably HOT when ice approach a FIRE ? A. Because the fire radiates heat upon the face ; which (not being covered) feels the effect immediately. RADIATION BLACK LEAD. 183 Q. Why does the fire catch the FACE more than it does the REST of the body ? A. Because the rest of the body is covered with clothing 1 ; which (being* a bad conductor of heat) prevents the same sudden and rapid transmission of heat to the skin. Q. Do those substances which RADIATE heat ABSORB heat also ? A. Yes. Those substances which radiate most, also absorb most heat; and those which radiate least, also absorb the least heat. Q. Does anything ELSE radiate heat BESIDES the SUN and FIRE ? A. Yes : all thing's radiate heat in some measure, but not equally well. Q. WHAT things RADIATE 'heat the NEXT BEST to the sun and fire ? A. All dull and dark substances are good radiators of heat ; but all light and polished substances are bad radiators. Q. Why should the FLUES (connected with stoves, 4*c.,) be always BLACKENED with BLACK LEAD? A. In order that the heat of the flue may be more readily diffused throughout the room. Black lead radiates heat more freely than any other known substance. In heating a room with steam it would be ahsurd to use black pipes for conveying the steam, because they would tend to cool the hot vapor. 184 COMMUNICATION OF HKAT. Q. Why does a POLISHED METAL TEA-POT make BETTER TEA than a black earthen one ? A. Because polished metal (being* a very bad radiator of heat) keeps me water hot much longer ; and the hotter the wa- ter is, the better it " draws 77 the tea. Q. Why will not a DULL BLACK TEA-POT make good tea ? A. .Because the heat of the water flies off so quickly through the dull black surface of the tea-pot, that the water is very rapidly cooled, and cannot " draw " the tea. Q. Do not pensioners and aged cottagers gene- rally prefer the little BLACK EARTHEN TEA-POT to the bright METAL one ? A. Yes ; because they set it on the hob "to draw;" in which case, the little black tea-pot will make the best tea. Q. Why will a BLACK TEA-POT make better tea than a bright metal one, if it be set upon the HOB to DRAW? A. Because the black tea-pot will absorb heat plentifully from the fire, and keep the water hot: whereas, a bright metal tea-pot (set upon the hob) would throw off the heat by reflection. Q. Then sometimes a BLACK EARTHEN tea-pot is the best, and sometimes a bright metal one ? A. Yes ; when a tea-pot is set on the SAUCEPAN KETTLE. 185 hob "to draw" black earth is the best } because it absorbs heat : But, when a tea-pot is not set on the hob, bright met- al is the best ; because it radiates heat very slowly, and therefore keej}s the water hot. Q. Why does a SAUCEPAN which has been USED boil in a shorter time than a NEW ONE ? A. Because the bottom and back are covej^ed with soot ; and black soot rapidly absorbs tlie heat of the glowing 1 coals. Q. Why should the FRONT and LID of a SAUCE- PAN be dean and BRIGHT? A. Because they cannot absorb heat, as they do not come in contact with the fire ; and (being bright) they will not suffer the heat to escape by radiation. Q. In what state should a SAUCEPAN be in or- der that it may BOIL QUICKLY ? A. All those parts which come in contact with the fire, should be covered with soot, in order to absorb heat ; but all the rest of the saucepan should be as bright as possible, to prevent the escape of heat by radiation. Q. Why should NOT the BOTTOM and BACK of a kettle be CLEANED and polished ? A. Because, they come in contact with the fire, and (while they are covered with 186 COMMUNICATION OP HEAT. black soot) absorb heat freely from the burning* coals. Q. Why should the FRONT and TOP of a kettle be CLEAN and well polished ? A. Because polished metal will not radiate heat; and, therefore, (while the front and top of the kettle are well pol- ished) the heat is kept in, and not suffered to escape by radiation. Q. Why is the BOTTOM of a KETTLE nearly COLD when the WATER is BOILING HOT ? A. Because black soot is a very bad conductor of heat ; and, therefore, the heat of the boiling- water is some time before it gets through the soot which adheres to the bottom of the kettle. Q. Why is the LID of a KETTLE intensely HOT when the water boils ? A. Because the br%ht metal lid is an admirable conductor ; and, therefore, the heat from the boiling water pours into our hand the moment we touch it. Q. Show the benefit of SMOKE in COOKING ? A. The carbon of the fuel (which flies off in smoke) naturally blackens all culinary vessels set upon the fire to boil, and thus renders them fit for use. "Culinary vessels" are vessels used in kitchens for cooking, as saucepans, boilers, kettles, &c., (from the Latin word " Culina," a kitchen.) SMOKE BRIGHT METAL; 187 Q. How does SMOKE make culinary vessels FIT for USE ? A. By absorbing- heat. If it were not for the smoke (which gathers round a kettle or saucepan) heat would not be absorbed, and the process of boiling would be greatly retarded. Q. Why is boiling water KEPT HOT in a BRIGHT METAL pot better than in an earthen vessel ? A. Because bright metal (being a bad radiator} will not throw off from its surface the heat of the boiling water. Q. Would a metal pot serve to keep water hot if it were DULL and DIRTY ? A. No. It is the bright polish of the metal which makes it a bad radiator : if it were dull, scratched, or dirty, the heat would escape very rapidly. Water in hot weather is also kept cooler in bright metal than in dull or earthen vessels. See p. 179. Q. Why are DINNER-COVERS made of BRIGHT TIN or SILVER 1 A. Because light-colored and highly- polished metal is a very bad radiator of heat ; and, therefore, bright tin or silver will not allow the heat of the cooked food to escape through the cover by radiation. Q. Why should a MEAT-COVER be very brightly POLISHED ? A. To prevent the heat of the food 188 COMMUNICATION OP HEAT. from escaping- by radiation. If a meat- cover be dull or scratched, it will absorb heat from the food beneath ; and (instead of keeping- it hot) make it cold. Q. Why should a SILVER MEAT-COVER be PLAIN and not CHASED ? A. Because a chased meat-cover would absorb heat from tlw food; and (instead of keeping it hot) make it cold. Q. What is DEW? A. Dew is the vapor of tJie air con- densed by coming- in contact with bodies colder than itself. Q. Why is the GROUND sometimes COVERED with DEW? A. Because the surface of the earth (at sun-set) is made so very cold by radi- ation, that the warm vapor of the air is chilled by contact, and condensed into dew. Q. Why is the EARTH made colder than the AIR after the sun has set ? A. Because the earth radiates heat very freely, but the air does not ; in con- sequence of which, the earth is often 5 or 10 degrees colder than the air (after sun-set) ; although it was much warmer than the air, during the whole day. Q. Why is the EARTH WARMER than the AIR during the day ? DEW. 189 A. Because the earth absorbs solar heat very freely, but the air does not ; in consequence of which, it is often many de- grees warmer than the air, during the day. Q. Why is the surface of the GROUND COLDER in a FINE dear NIGHT than in a CLOUDY one ? A. Because, on a fine, clear star-light night, heat radiates from the earth freely, and is lost in open space : but on a dull night, the clouds arrest the process of ra- diation. Q. Why is DEW deposited only on a FINE, ckar NIGHT ? A. Because the surface of the ground radiates heat most freely on a fine night ; and (being cooled down by this loss of heat) chills the vapor of tlie air into dew. Q. Why is there NO DEW on a dull^ CLOUDY NIGHT ? A. Because the clouds arrest the radiation of heat from the earth ; and (as the heat cannot freely escape) the sur- face is not sufficiently cooled down to chill the vapor of the air into dew. Q. Why is a CLOUDY NIGHT WARMER than a FINE one ? A. Because the clouds prevent the radiation of heat from the earth ; in con- sequence of which, the surface of the earth remains warmer. 190 COMMUNICATION OF HEAT. Q. Why is DEW most ABUNDANT in situations most EXPOSED ? A. Because the radiation of heat is not arrested by houses, trees, hedges, or any other thing*. Q. Why is there scarcely any DEW under a shady TREE ? A. 1st Because the shady head of a tree arrests the radiation of heat from the earth : and 2dly A leafy tree radiates some of its own heat toicards the earth ; in conse- quence of which, the ground underneath a tree is not sufficiently cooled down to chill the vapor of the air into dew. Q. Why is there never much DEW at the foot of WALLS and HEDGES ? A. 1st Because they act as screens, to arrest the radiation of heat from the earth: and 2dly They themselves radiate some portion of heat towards the earth ; in consequence of which, the ground at the foot of walls and hedges is not sufficiently cooled down, to chill the vapor of the air into dew. Q. Why is there little or NO DEW beneath, a FLOWER-AWNING, although that awning be open on all four sides ? A. 1st Because the awning arrests FROST SNOW. 191 the radiation of heat from the ground beneath : and 2dly It radiates some of its own heat downwards ; in consequence of which, the ground beneath an awning- is not sufficiently cooled down, to chill the va- por of air into dew. Q. How can a thin covering of BASS or even MUSLIN protect trees from FROST ? A. Because any covering prevents the radiation of heat from the tree ; and if trees are not cooled down by radiation, the vapor of the air will not be frozen, as it comes in contact with them. Bass pronounce bas a kind of matting used by garden- ers. Q. Why is the BASS or CANVASS itself (which, covers the tree) always DRENCHED with DEW ? A. Because it radiates heat both up- wards and dowmcards ; in consequence of which, it is so cooled down that it rea- dily chills the vapor of the air into dew. Q. Why does SNOW (at the foot of a HEDGE or WALL) melt sootier than that in an open field? A. Because the hedg*e or wall radi- ates heat into the snow beneath, which melts it. Q. Why is there NO DEW after a WINDY NIGHT ? A. 1st Because the wind evaporates 192 COMMUNICATION OP HEAT. the moisture, as fast as it is deposited : and 2dly It disturbs the radiation of heat ; and thus diminishes the deposition of dew. Q. Why are VALLEYS and HOLLOWS often thickly covered with DEW, although they are sheltered ? A. Because the surrounding hills prevent the repose of air from being dis- turbed; but do not overhang and screen the valleys sufficiently to arrest their ra- diation. Q. Why does DEW fall more ABUNDANTLY on SOME -THINGS than on OTHERS ? A. Because some things radiate heat more freely than others ; and, therefore, become much cooler in the night. Q. Why are things which RADIATE HEAT MOST FREELY always the most THICKLY COVERED with DEW ? A. Because the vapor of the air is chilled into dew, the moment it comes in contact with them. Q. WHAT kind of things RADIATE HEAT most FREELY 1 A. Grass, wood, and the leaves of plants, radiate heat very freely : but pol- ished metal, smooth stones, and woollen cloth, part with their heat very tardily. Q. Do the Leaves of ALL plants radiate heat EQUALLY WELL ? VEGETABLES. 193 A. No. Rough, woolly leaves (like those of a holly-hock) radiate heat much more freely than the hard, smooth, polished leaves of a common laurel. Q. Show the WISDOM of GOD in making grass, the leaves of trees, and ALL VEGETABLES, EXCELLENT RADIATORS of heat ? A. As vegetables require much mois- ture, and would often perish without a plentiful deposit of dew, God wisely made them to radiate heat freely, so as to chill the vapor (which touches them) in- to dew. Q. Will polished' METAL, smooth STONES, and woollen CLOTH, readily collect DEW ? A. No. While grass and the leaves of plants are completely drenched with dew a piece of polished metal, or of * woollen cloth (lying on the same spot), will be almost dry. Q. Why would POLISHED METAL and WOOL- LEN CLOTH be DRY, while grass and leaves are drenched with DEW ? A. Because the polished metal and woollen cloth part with their heat so slow- ly, that the vapor of the air is not chilled into dew as it passes over them. Q. Why is a, GRAVEL WALK almost DRY, when a grass plat is covered thick with DEW ? A. Because grass is a good radiator , 9 194 COMMUNICATION OF HEAT. and throws off its heat very freely ; but gravel is a very bad radiator, and parts with its heat very slowly. Q. Is that the reason why GRASS is SATURATED \tilh DEW, and the GRAVEL is NOT 1 A. Yes. When the vapor of warm air comes in contact with the cold grass, it is instantly chilled into dew ; but it is not so freely condensed as it passes orer gravel, because gravel is not so cold as the grass. Q. Why does DEW rarely fall upon hard ROCKS and BARREN lands ? A. Because rocks and barren lands are so compact and hard, that they can neither absorb nor radiate much heat; and (as their temperature varies but very little) very little dew distils upon them. Q. Why does DEW fall more abundantly on CULTIVATED soils than on BARREN lands ? A. Because cultivated soils (being loose and porous) very freely radiate by night the heat which they absorbed by day ; in consequence of which, they are much cooled down, and plentifully con- dense the vapor of the passing air into dew. Q. Show the WISDOM of GOD in this arrange- ment. A. Every plant and inch of land, GIDEON'S MIRACLE. 195 which needs the moisture of dew, is adapted to collect it ; but not a single drop is wasted where its refreshing* mois- ture is not required. Q. Show the advantage to us in having pol- ished METAL and woollen CLOTH BAD RADIATORS of A. If polished metal collected dew as easily as grass, it could never be kept dry and free from rust. Again, if woollen garments collected dew as readily as the leaves of trees, we should be often soak- ing wet. and subject to constant colds. Q. Show how this affords a beautiful illustra- tion of GIDEON'S MIRACLE, recorded in the book of Judges, vi. 37, 38. A. The fleece of wool (which is a very bad radiator of heat) was soaking- wet with dew, when the grass (which is a most excellent radiator) was quite dry. Q. Was not this CONTRARY to the laws of NATURE ? , A. Yes ; and was, therefore, a plain demonstration of the power of God, who could thus change the very nature of things at his will. Q. Why do our CLOTHES FEEL DAMP, after walking in a fine evening in SPRING or AUTUMN ? A. Because the vapor (condensed by the cold earth) lights upon them like dew. 196 COMMUNICATION OF HEAT. Q. Why are WINDOWS often covered with thick MIST, and the frames wet with standing WATER? A. Because the temperature of the external air always falls at sunset, and chills the window-glass with which it comes in contact. Q. How does this account for the MIST and WA- TER on a WINDOW ? A. As the warm vapor of the room touches the cold glass it is chilled and con- densed into mist ; and the mist (collect- ing* into drops) rolls down the window- frame in little streams of water. Q. Does 'the GLASS of a window COOL down more RAPIDLY than the AIR of the room itself? A. Yes; because the air is kept warm by fires, and by the animal heat of the people in the room ; in consequence of which, the air of a room suffers vzry little diminution of heat from the setting of the sun. Q. Whence arises the VAPOR of a ROOM ? A. 1st The very air of the room contains vapor : 2dly The breath and insensible per- spiration of the inmates increase this vapor: and 3dly ffot dinners, the steam of tea } and so on ? increase it still more. MIST VAPOR. 197 Q. What is meant by " the INSENSIBLE PER- SPIRATION?" , A. From every part of the human body, an insensible and invisible perspi- ration issues all night and day ; not only in the hot weather of summer, but also in the coldest day of winter. Q. If the perspiration be both INSENSIBLE and INVISIBLE, how is it KNOWN that there is any such perspiration ? A. If you put your naked arm into a clean, dry glass tube, the perspiration will condense on the glass like mist. Q. Why are CARRIAGE WINDOWS very SOON covered with thick MIST ? A. Because the warm vapor of the carriage is condensed by the cold glass, and covers it with a thick mist. Q. WHY is the glass window COLD enough to condense the vapor of the carriage ? A. Because the inside of a carriage is much warmer than the outside ; and the glass window is made cold by con- tact with the external air. Q. WHERE does the WARM vapor of the car- riage come from ? A. The warm breath and insensible perspiration of the persons riding, load the air of the carriage with warm vapor. Q. What is the cause of the pretty FROST- WORK, seen on bed-room WINDOWS in winter-time ? 198 COMMUNICATION OF HEAT. A. The breath and insensible perspi- ration of the sleeper (coming* in contact with the ice-cold window) are frozen by the cold glass, arid form those beautiful appearances seen in our bed-rooms on a winter morning. Q. Why is the GLASS of a window colder than the WALLS of a room ? A. Because glass is so excellent a ra diator, that it parts with its heat more rapidly than the walls do. Q. Why is a TUMBLER of cold WATER made quite DULL with mist, when brought into a room FULL of PEOPLE ? A. Because the hot vapor of the room is condensed upon the cold tumbler, with which it comes in contact ; and changes its invisible and gaseous form into that of a thick mist. Q. Why is a GLASS made quite DULL by lay- ing a HOT HAND upon it ? A. Because the insensible perspiration of the hot hand is condensed upon the cold glass, and made perceptible. Q. WJiy are WINE-GLASSES made quite DULL, when they are brought into a room FULL O/*COMPANY? A. Because the hot vapor of the room (coming in contact with the cold wine-glasses) is condensed upon them,, and covers them with vapor, like dew. WINE GLASS WALLS. 199 Q. Why does this misty appearance GO OFF, after a little time ? A. Because the glass becomes of the same temperature as the air of the room ; and will no longer chill the vapor which touches it, and condense it into mist. Q. Why is a WINE GLASS (which has been brought out of a CELLAR into the AIR) covered with a thick MIST in summer-time ? A. Because the vapor of the hot air is condensed into a thick mist, by contact with the cold glass. Q. Why does BREATHING on a GLASS make it quite DULL ? A. Because the hot breath is con- densed by the cold glass ; and therefore covers it with a thick mist. Q. Why are the WALLS of a house covered with WET in a sudden THAW ? A. Because the walls (being thick) cannot change their temperature so fast as the air ; in consequence of which, they retain their cold after the thaw has set in. Q. How does " RETAINING their COLD" account for their being so WET ? A. As the vapor of the warm air touches the cold walls, it is chilled and condensed into water ; which either sticks to the walls or trickles down in little streams. 200 COMMUNICATION OF HEAT. Q. Why does a thick WELL-BUILT HOUSE con- tract more DAMP of this kind than an ORDINARY one ? A. Because the walls are much thicker ; and (if the frost has penetrated far into the bricks] they will be some time before they are reduced to the same temperature as the air. Q. Why are BALUSTERS, <^c., DAMP after a THAW ? A. Because they are made of some very close-grained varnished wood, which cannot change its temperature so 5 as the air. Balusters corruptly called banisters. Q. How does THIS account for the BALUSTERS being DAMP ? A. The vapor of the warm air (com- ing 1 in contact with the cold balusters) is chilled and condensed into water upon them. Q. Why is our BREATH VISIBLE in WINTER, and NOT in SUMMER ? A. Because the intense cold con- denses our breath into visible vapor; but in summer the air is not cold enough to do so. Q. Why are our HAIR and the BRIM of our HAT often covered with little drops of pearly DEW in winter -time ? A. Because our breath is condensed WINDS MOISTNESS. 201 as soon as it comes in contact with our cold hair or hat, and hangs there in little dew-drops. Q. Why does the STEAM of a RAILWAY BOILER often pour down, like fine rain, when the steam is let of?" A. Because in cold weather the steam from the chimney is condensed by the chill air and falls like fine rain. Q. Why is there LESS DEW when the WIND is WESTERLY, than when the wind is EASTERLY ? A. Because westerly winds cross the continent, and, (as they pass over land) are dry and arid: But easterly winds cross the Atlantic Ocean, and (as they pass over water] are moist and fall of vapor. Q. How does the DRYNESS of a westerly wind PREVENT DEW-FALLS ? A. As westerly winds are very dry, they imbibe the moisture of the air ; in consequence of which, there is very little left to be condensed into dew. Q. How does the MOISTNESS of an eastern wind PROMOTE dew-falls ? A. As easterly- winds are saturated with vapor, they require very little re- duction of heat to cause a copious deposi- tion of dew. Q. When is DEW most COPIOUSLY distilled ? 9* 202 COMMUNICATION OF HEAT. A. After a hot day in summer or autumn, especially if the wind be easterly. Q. Why is DEW distilled most COPIOUSLY af- ter- a HOT day ? A. Because the surface of the hot earth radiates heat very freely at sunset, and (being made much colder than the air) cfulls the passing vapor and con- denses it into dew. Q. Does not AIR radiate heat, as well as the i EARTH and its various plants ? A. No. The air never radiates heat ; nor is the air made hot by the rays of the sun. Q. How is the AIR made HOT or COLD ? A. By convection of hot or cold cur- rents. Q. Explain this. A. The air which has been heated by the surface of the earth ascends, warm- ing- the air through which it passes. Other air (being warmed in a similar way) also ascends, carrying heat; and this is repeated, till all the air is made hot. Q. How is the AIR made COLD ? A. The air resting on the earth is made cold by contact : this cold air makes the air above it cold; and cold currents (or winds) shake the whole together, till all becomes of one temperature. MOONLIGHT HONEY-DEW. 203 Q. Why is MEAT very subject to TAINT on a MOONLIGHT night ? A. Because it radiates heat vsry freely in a bright moonlight night; in conse- quence of which, it is soon covered with de-Wj which produces rapid decomposition. Q. How do MOONLIGHT nights conduce to the rapid GROWTH of PLANTS ? A. Radiation is carried on very rapidly on bright moonlight nights ; in consequence of which, dew is very plen- tifully deposited on young plants, which conduces much to their growth and vi- gor. Q. Why is evening DEW INJURIOUS to HEALTH 1 A. Because it is always laden with noxious exhalations from the earth; espe- cially in marshy countries. Q. Is HONEY-DEW a similar thing to DEW A. - No. Honey-dew is a sweet liquid shed by a very small insect (called the a'phis) and deposited in autumn on the under surface of favorite leaves. Frequently also on Lime Trees, in the Spring. Q. Does HONEY-D^W INJURE leaves, or do them good ? A. It injures them very much, by fill- ing the pores with a thick, clammy liquid ; in consequence of which, the leaf can 204 COMMUNICATION OF HEAT. neither transpire nor absorb its needful food. Q. What EFFECT has honey-dew upon tht APPEARANCE of a leaf? A. After a little time, the leaf (being- smothered and starved) begins to turn a dingy yellow. Q. Are not ANTS very FOND of HONEY-DEW? A. Yes ; and crawl up the loftiest trees in order to obtain it. Q. What is the cause of MIST (or earth-fog) ? A. If the night has been very calm, the radiation of heat from the earth has been very abundant ; in consequence of which, the air (resting- on the earth) has been chilled, and its vapor condensed into a thick mist. Q. Why does not the MIST become DEW ? A. Because the chill of the air is so rapid, that vapor is condensed faster than it can be deposited; and (covering- the earth in a mist) prevents any further radiation of heat from the earth. Q. When the earth can no longer RADIATE heat upwards, does it continue to CONDENSE the vapor of the air ? ^ A. No ; the air (in contact with the earth) becomes about equal in tempera- ture with the surface of the earth itself; for which reason, the mist is not con- DEW-DROPS. 205 densed into dew, but remains floating above the earth as a thick cloud. Q. This MIST seems to RISE HIGHER and. HIGHER, and yet remains quite as dense below as at first. Explain the cause of this. A. The air resting* on the earth is first chilled, and chills the air resting 1 on it ; the air which touches this new layer of mist being* a/so condensed, layer is added to layer : And thus the mist seems to be rising, when (in fact) it is only deepening' Q. Why do MIST and DEW VANISH, as the SUN rises ? A. Because the air becomes warmer at sun-rise, and absorbs the vapor. Q. Why is a DEW-DROP ROUND ? A. Because every part of it is equally balanced; and, therefore, there is no cause why one part of the drop should be further from the centre than anotJier. Q. Why is the DEW-DROP (on a broad leaf) sometimes FLATTENED ? A. Because two or more drops of dew roll together, and make one large spheroid (or flattened drop). Q. Why will DEW-DROPS ROLL ABOUT CAB- BAGE-PLANTS, POPPIES, <^c., without wetting the sur- face ? A. Because the leaves of cabbages 206 COMMUNICATION OF HEAT. and poppies are covered with a very fine waxen powder, over which the dew-drop rolls without wetting* the surface, as a drop of rain would over dust. Q. Why does not a drop of RAIN WET the DUST over which it rolls ? A. Because dust has no affinity for water, and, therefore, repels it. Q. Why does not the DEW-DROP WET the POW- DER of the CABBAGE-PLANT? A. Because the fine powder which covers the cabbage-leaves has no affinity for water, and, therefore, repels it. Q. Why will DEW-DROPS ROLL over a ROSE, <$fc., without wetting the petals ? A. Because the leaves of a rose con- tain an essential oil, which has no affinity for water, and, therefore, repels it. Q. Why can SWANS and DUCKS dive under water WITHOUT being WETTED ? A. Because their feathers are cover- ed with an oily secretion, which has no affinity for water, and, therefore, re- pels it. Q. What is the cause of MIST ? A. Currents of iur from the water coming- in contact with colder land cur- rents. Q. Why are the currents of air from the LAND COLDER than those blowing over WATER, 1 AIR AND WATER. 207 A. Because the earth radiates heat after sun-set more freely than water; consequently the air which comes in con- tact with the land is more cold than that which comes in contact with water. For other questions respecting land and sea breezes see~ Chapter XXIV. Q. Why is not the AIR which passes over WATER so COOL as that which passes over LAND ? A. Because water does not cool down at sun-set so fast as land does ; and, therefore, the air in contact with it remains warmer. Q. Why does not WATER cool down so fast as LAND ? A. 1st Because the surface of water is perpetually changing ; and, as fast as one surface is made cold, another is pre- sented : and 2dly The moment water is made cold it sinks, and warmer portions of wa- ter rise to occupy its place : therefore, before the surface of water is cooled, the whole volume must be made cold : which is not the case with land. Q. What is the +use of a "pea-soup" LON- DON FOG? A. These fogs (which occur general- ly in the winter time) are occasioned thus : Some current of air (being sud- 208 COMMUNICATION OP HEAT. denly cooled) descends into the warm streets, forcing- back the smoke in a mass towards the earth. Q. Why are there not FOGS EVERY night ? A. Because the air will always hold in solution a certain quantity of vapor, (which varies according 1 to its tempera- ture :) and, when the air is not saturated, it may be cooled without parting- with its vapor. Q. When do FOGS occur at night ? A. When the air is saturated with vapor during 1 the day. When this is the case, it deposits some of its superabun- dant moisture in the form of dew or fog* as soon as its capacity for holding* vapor is lessened by the cold night. Q. Why is there very OFTEN a fog over MARSHES and RIVERS, at night-time? A. Because the air of marshes is almost always near saturation; and, therefore, the least depression of tempe- rature will compel it to relinquish some of its moisture in the form of dew or Q. What is the DIFFERENCE between DEW and RAIN? A. In dew, the condensation is made near the earth's surface. MIST AND FOG. 209 In rain, the drops fall from a consi- derable height. Q. What is the CAUSE of both dew and rain ? A. Cold condensing the vapor of the air when near the point of saturation. Q. Why do MIST and FOG VANISH at sun-rise? A. Because the condensed particles are again changed into invisible vapor by the heat of the sun. Q. What is the difference between a MIST and a FOG? A. MIST is generally applied to va- pors condensed on marshes, rivers, and lakes. FOG is generally applied to vapors condensed on land; especially if those vapors are laden with smoke. Q. What is the reason why condensed vapor sometimes forms into CLOUDS, and sometimes into FOG? A. If the surface of the EARTH is hotter than the air, the vapor of the earth is chilled by the cold air, and be- comes FOG: But if the AIR is hotter than the earth, the vapor rises through the air, and becomes cLout). Q. If cold air produces FOG, why is it not foggy on a FR.OSTY MORNING ? A. 1st Because less vapor is formed on a frosty day : and 210 COMMUNICATION OF HEAT. 2dly The vapor is frozen upon the ground, before it can rise from the earth, and becomes HOAR-FROST. Q. Why are FOGS more general in AUTUMN than in spring ? A. 1st Because the air in spring is generally much drier than it is in autumn ; in consequence of which, it is not so near the point of saturation: and 2dly The earth in spring- is not so hot as it is in autumn ; in consequence of which, its vapor is not chilled into fog as it issues into the air. Q. Why are FOGS more common in VALLEYS than on HILLS ? A. 1st Because valleys contain more moisture than hills : and 2dly They are not exposed to suffi- cient wind to dissipate the vapor. Q. How does WIND dissipate FOGS ? A. Either by blowing them away ; or else by dissolving them into vapor again. Q. What is HOAR-FROST ? A. Th^re are two sorts o' hoar-frost ; 1 . FROZEN- DEW : and 2. I JOZEN FOG. Q. What is the cause of the GROUND HOAR- FROST, or frozen DEW? A. Very rapid radiation of heat from the earth ; in consequence of which, the HOAR-FROST. 211 surface is so cooled down that it freezes the dew condensed upon it. Q. Why is HOAR-FROST seen only after a very CLEAR NIGHT ? A. Because the earth will not have thrown off heat enough by radiation to freeze the vapor condensed upon its sur- face, unless the night has been very clear indeed. Q. Why does HOAR-FROST very often COVER the GROUND and TREES, when the water of rivers is not frozen ? A. Because it is not the effect of cold in the air, but cold on the surface of the earth (produced by excessive radiation), which freezes the dew condensed upon it. Q. Why is the HOAR-FROST upon GRASS and VEGETABLES much thicker than that upon lofty TREES 1 A. Because the air (resting* on the surface of the ground) is much colder after sun-set than the air higher up ; in consequence of which, more vapor is condensed and frozen there. Q. Why is the AIR (resting on the surface of the EARTH) colder than that in the HIGHER regions ? A. Because the earth radiates more heat than the leaves of lofty trees ; and, therefore, more rapidly condenses and freezes the vapor of the air. 212 COMMUNICATION OF HEAT. Q. Why are EVERGREENS often FROST-BITTED when lofty trees are NOT? A. Because they do not rise far above the surface of the earth ; and (as the air contiguous to the earth is made colder by radiation than that in the higher regions), therefore, the low evergreen is often frost- bitten, when the lofty tree is uninjured. Q. Why is there little or NO HOAR-FROST un- der SHRUBS and shady TREES ? A. 1st Because the leafy top arrests the process of radiation from the earth : 2dly Shrubs and trees radiate heat towards the earth: and, therefore, the ground beneath is never cold enough to congeal the little dew which rests upon it. Q. What is the cause of that HOAR-FROST which arises from FROZEN FOG? A. The thick fog- which invested the earth during the night (being condensed by the cold frost of early morning), is con- gealed upon every object with which it comes in contact. CONVECTION. 213 CHAPTER XIX. 5. CONVECTION. Q. What is meant by the CONVECTION of HEAT? A. Heat communicated by being carried to another thing" or place ; as the hot water resting on the bottom of a ket- tle carries heat to the water through which it ascends. (See p. 226.) Q. Are LIQUIDS good CONDUCTORS of heat ? A. No ; liquids are bad conductors ; and are, therefore, made hot by convec- tion. Q. Why are LIQUIDS BAD CONDUCTORS of heat ? A. Because heat converts a liquid into steam ; and flies off with the vapor in- stead of being conducted through the liquid. Q. Explain how WATER is made HOT. A. The water nearest the fire is jirs* heated, and (being heated) rises to the top ; while its place is supplied by colder portions, which are 'heated in turn, till all the water is boiling hot. Q. Why is WATER in such continual FERMENT, when it is BOILING 1 A. This commotion is mainly produ- 214 COMMUNICATION OP HEAT. ced by the ascending and descending cur- rents of hot and cold water. The escape of steam from the water contributes also to increase this agitation. Q. How do these two currents PASS each other ? A. The hot ascending current rises up through the centre of the mass of water; while the cold descending currents pass down by the metal sides of the kettle. For other questions on the subject of boiling water, see from page 109 to 115. Q. Why is HEAT applied to the BOTTOM, and not to the top of a KETTLE ? A. Because the heated water always ascends to the surface, heating 1 the water through which it passes ; if, therefore, heat were applied to the top of a vessel, the water below the surface would never be heated. Q. As the lower part of a GRATE is made RED- HOT by the fire ABOVE, why would not the WATER boil, if fire were applied to the TOP of a kettle ? A. Tiie iron of a grate is an excellent conductor ; if, therefore, one part be heat- ed, the heat is conducted to every other part : But water is a very bad conductor, and will not diffuse heat in a similar way. Q. Prove that WATER is a BAD CONDUCTOR of heat. A. When a blacksmith immerses his red-hot iron in a tank of water, the water BOILING WATER SOUP. 215 which surrounds the iron is made boiling hot, while that below the surface remains quite cold. Q. If you wish to COOL LIQUIDS, where should the cold be applied? A. To the top of the liquid; because the cold portions will always descend, and allow the warmer parts to come in con- tact with the cooling* substance. Q. Does BOILING water get hotter by being KEPT on the FIRE 1 A. No : not if the steam be suffered to escape. Q. WHY does not boiling water get HOTTER. if the steam be suffered to ESCAPE ? A. Because the water is converted into steam as fast as it boils ; and the steam carries away the additional heat. Q. Why does SOUP keep HOT longer than boil- ing water ? A. Because the grease and various in- gredients floating- in the soup, oppose the ascending 1 motion of the hot particles, and prevent their rising- so freely to the surface. Q. If you wanted to keep WATER HOT for a long time, how could it be done ? A. By adding a little starch or flour to the water. Q. Why would a little STARCH, added to boil- ing water, serve to keep it HOT ? 216 COMMUNICATION OF HEAT. A. Because it would oppose the ascending- motion of the hot particles of water, and prevent their rising so freely to the surface. Q. Why do THICK MILK, RICE MILK, ^c., re- main HOT longer than water ? A. Because the ascending* motion of the hot particles is opposed by the flour or rice, and cannot so quickly reach the surface. Q. Is STEAM visible or INVISIBLE ? A. Steam is invisible; but when it comes in contact with the air (being* condensed into small drops) it instantly becomes visible. Q. How do you know that STEAM is INVISIBLE ? A. If you look at the spout of a boil- ing- kettle, you will find that the steam (which issues from the spout) is always invisible for about half an inch ; after which it becomes visible. Q. WHY is the steam INVISIBLE for HALF AN INCH ? A. Because the air is not able to condense it, as it first issues from the spout ; but when it spreads and comes in contact with a larger volume of air, the invisible steam is readily condensed into visible drops. Q. WHY do STEAM-ENGINES sometimes BURST ? HEATED AIR. 217 A. Because steam is very elastic; and this elasticity increases in a greater proportion than the heat which produces it ; unless, therefore, some vent be freely allowed, steam will burst the vessel which confines it. Q. Is AIR a good CONDUCTOR ? A. No; air is a very bad conductor; and is heated (like water) by convection. Q. How is a ROOM WARMED by a STOVE? A. The air nearest the fire is made hot first and rises ; cold air then descends, is heated, and ascends in like manner; and this interchange goes on till all the air of the room is warmed. (Ste p. 56.) Q. Why are FIRES placed on the FLOOR of & room, and not towards the CEILING ? A. Because heated air always as- cends. If, therefore, ihe fire were not near the floor, the air of the lower part of the room would never be heated by the fire at all. Q. If you take a POKER out of the fire, and hold the HOT END DOWNWARDS, why is the HANDLE intensely HOT'? A. Because the hot end of the poker heats the air around it ; and this hot air (in its ascent) scorches the poker and the hand which holds it. 10 218 COMMUNICATION OF HEAT. Q. How should a RED-HOT POKER be carried^ so as not to BURN our fingers? A. With the hot end upwards; for then the air (heated by the poker) would not pass over our hand and scorch it. PART II. AIR. CHAPTER XX. THE ATMOSPHERE. Q. Of what is atmospheric AIR composed ? A. Principally of two gases, oxygen and nitrogen, mixed together in the following proportion: viz., 1 gallon of oxygen to 4 of nitrogen. It must not be forgotten that the air contains small quantities of other gaseous substances also, as vapor of water, carbonic acid, and ammonia. Q. What do you mean by a GAS ? A. A permanent elastic fluid resem- bling air. N. B. MOST GASES ARE INVISIBLE OR COLORLESS, LIKE AIR. " PERMANENT," In this respect gas differs from vapor, which is not permanent; for vapor may be easily con- densed by cold into a liquid, but gas never changes its gaseous form. . " ELASTIC," In this respect gas differs from a liquid, which is almost inelastic; whereas gas is exceedingly elastic. "RESEMBLING AIR," or aeriform. The word "Gas" means air, but air is a compound of two gases. Some few gases are visible, as CHLORINE, which is a greenish yellow. 219 220 AIR. Q. What is the difference between a GAS and a LIQUID A. Gases arc elastic, but liquids not. Q. Illustrate what is meant by " the ELASTICITY of GAS." A. If from a vessel full of gas half were taken out the other half would im- mediately spread itself out, and fill the same space as was occupied by the whole. Q. Prove that a LIQUID is NOT ELASTIC. A. If from a gallon of water you take half, the remaining 1 4 pints will take up only half the room that the whole gallon previously did : a liquid, therefore, is not elastic like gas. Strictly speaking, a liquid is slightly elastic ; inasmuch as it may be compressed and will afterwards recover its former dimensions. Q. What are the uses of the OXYGEN of the air ? A. To support combustion and sus- tain life. Q. What is meant, when it is said, that the OXYGEN of the air "SUPPORTS COMBUSTION?" A. It means this : It is the oxygen of the air which makes fuel burn. Q. How does the OXYGEN of the air make FUEL A. The fuel is decomposed (by heat) into hydrogen and carbon; and these elements combining with the oxygen of the air produce combustion. GASES. 221 Q. What GAS is produced by the combination of carbon and oxygen ? A. CARBONIC ACID GAS. (/Steep. 43.) Q. What becomes of the HYDROGEN of the FUEL ? A. The hydrogen of the fuel combines with the oxygen of the air, and forms WATERY VAPOR ; but the combination is attended by the production of flame, owing* to the very inflammable nature of hydrogen gas. Q. What becomes of the NITROGEN of the air, amidst all these changes and combinations ? A. The nitrogen escapes unchanged, to be again mixed with oxygen, and con- verted into common AIR. Q. What is meant, when it is said, that OXY- GEN " SUSTAINS LIFE ?" A. It means this : If a person could not inhale oxygen, he would die. Q. What GOOD does this inspiration of OXYGEN do? A. 1st It gives vitality to the blood : and 2dly It is the cause of animal heat. Q. How is FOOD converted into BLOOD ? A. After it is swallowed, it is dis- solved in the stomach into a grey pulp, called CHYME ; it then passes into the in- testines, and is converted by the " bile" into a milky substance, called CHYLE. 222 AIR. Chyme pronounce kyme chyle pronounce kyle each as one syllable. Q. What BECOMES of the milky substance called CHYLE ? A. It is absorbed by the vessels call- ed " lacteals" and poured into the veins on the left side of the neck. Lac'teals -pronounce Lac'-te-als. Q. What becomes of the chyle, AFTER it is POURED into the VEINS ? A. It mingles with the blood, and is itself converted into blood also. Q. How does the OXYGEN we inhale MINGLE with the BLOOD ? A. The oxygen of the air mingles with the blood in the lungs, and converts it into a bright red color. Q. What color is the blood BEFORE it is oxi- dized in the lungs ? A. A dark purple. The oxygen turns it to a bright red. Oxidized, i. e., impregnated with oxygen. Q. Why are PERSONS so PALE, who live in CLOSE ROOMS and CITIES ? A. Because the blood derives its redness from the oxygen of the air inhal- ed ; but, as the air in close rooms and cities is not fresh, it is deficient in oxygen, and cannot turn the blood to a beautiful bright red. Q. Why are PERSONS, who live in the OPEN AIR and in the country, of a RUDDY complexion ? BLOOD. 223 A. Because they inhale fresh air which has its full proportion of oxygen : and the blood derives its bright red color from the oxygen of the air inhaled. Q. Why is not the air in CITIES so FRESH as that i?i the COUNTRY? A. Because it is impregnated with the breath of its numerous inhabitants, the odor of its sewers, the smoke of its fires, and many other impurities. Q. How does OXYGEN convert the color of blood into a bright RED? A. The coloring matter of the blood is formed by very minute globules float- ing in it ; the oxygen (uniting with the coats of these globules) makes them milky and the dark coloring matter of the blood (seen through this 'milky coat) appears of a bright red. Exp. : If you put some dark venous blood into a milky glass, and hold it up towards the light, it will appear of a bright florid color like arterial blood. Q. How does the COMBINATION of OXYGEN with the BLOOD produce animal HEAT ? A. The principal element of the blood is carbon; and this carbon (com- bining with the oxygen of the air inhaled) produces carbonic acid gas, in the same way as burning fuel. (See p. 43.) Q. What becomes of the NITROGEN of the air, after the oxygen enters the blood ? 224 AIR. t A. It is thrown out from the lungs unchanged, by the act of breathing ; to be again mixed with oxygen and con- verted into common AIR. Q. Why does the vitiated air (after the oxy- gen has been absorbed) COME OUT of the MOUTH, and not sink into the stomach ? A. Because a mechanical provision is made in the upper part of the wind- pipe and gullet for this purpose. N. B. The lungs are a hollow, spongy mass, capable of confining air and of being dilated by it. They are so situ- ated in the thorax (or chest), that the air must enter into them, whenever the cavities of the thorax are enlarged. The process of breathing is performed thus : When we INHALE, the thorax (or chest) is expanded ; in consequence of which, a vacuum is formed round the lungs, and heavy external air instantly enters (through the mouth and throat) to supply this vacuum. When we EXHALE, the thorax contracts again ; in conse- quence of which, it can no longer contain the same quan- tity of air as it did before ; and some of it is necessarily expelled. When this expulsion of air takes place, the lungs and muscular fibres of the wind-pipe and gullet contract, in order to assist the process. Q. If (both in combustion and respiration) the OXYGEN of the air is CONSUMED, and the NITROGEN REJECTED Why are not the PROPORTIONS of the AIR DESTROYED ? A. Because the under surface of vege- table leaves (during the day) gives out oxygen; and thus restores to the air the very element of which it has been de- prived. VEGETABLES. 225 Q. Whence do leaves OBTAIN the oxygen which they exhale ? A. From tfye carbonic acid absorbed by the roots from the soil, and carried to the leaves by the rising* sap. N. B. Carbonic acid (it must be remembered) is a compound of carbon and oxygen. Q. How do plants contrive to absorb carbonic acid from the soil ? A. It rises (by capillary attraction) through the small fibrous roots, after it has been dissolved in the soil by water. Q. Whence does the SOIL obtain carbonic acid ? A. 1st From the air ; from which it is driven by falling showers : 2dly From the decomposition of ve- g^etable and animal matters, which al- ways produces this gas in abundance : and 3dly All lime-stone, chalk, and cal- careous stones, contain vast quantities of carbonic acid in a solid state. Calcareous, i. e. 3 of a limy nature. Q. If leaves throw off the OXYGEN of the car- bonic acid, what becomes of the carbon? A. It is retained to give firmness and solidity to the plant itself. Q. Show how God has made ANIMAL life de- pendent on that of VEGETABLES. A. Animals require oxygen to keep them alive, and draw it from the air. by 10* 226 AIR. inspiration : The under surface of leaves gives out oxygen ; and thus supplies the air with the very gas required for the use of animals. Q. Show how God has made VEGETABLE life dependent on that of animal. A. Plants require carbonic acid, which is their principal food ; and all an- imals exhale the same gas from their lungs. Thus plants supply animals with oxygen, and animals supply plants with carbonic acid. Q. HOW is AIR HEATED ? A. By "convective currents." Q. Explain what is meant by " CONVECTIVE CURRENTS." A. When a portion of air is heated, it rises upwards in a current, carrying the heat with it ; other colder air succeeds, and (being heated in a similar way) as- cends also : TEhese are called " convective currents." (" Convective currents ;" so called from the Latin words, cum-vectus (earned with)] because the heat is "carried with " the current.) Q. Is AIR HEATED by the RAYS of the SUN ? A. No ; air is not heated (in any sen- sible degree) by the action of tlie sun's rays passing through it. Q. Why then is the AIR HOTTER on a SUNNY DAY, than on a CLOUDY one ? CONVECTION. 227 A. Because the sun heats the surface of the earth, and the air (resting- on the earth) is heated by contact : as soon as it is heated it ascends ; while its place is supplied by colder portions which are heated in turn also. Q. If AIR be a BAD CONDUCTOR, why does hot IRON become COLD by EXPOSURE to the AIR ? A. Because it is made cold 1st By " convection ;" and 2dly By " radi- ation." Q. How is hot iron made cold by CONVECTION ? A. The air resting on the hot iron (being- intensely heated), rapidly ascends with the heat it has absorbed ; colder air succeeding 1 absorbs more heat and as- cends also ; and this process is repeated till the hot iron is cooled completely down. Q. How is hot iron cooled by RADIATION ? A. While its heat is being- carried off by " convection/' the hot iron throws off heat (on all sides) by radiation also. Q. What is meant by RADIATION ? A. Heat emitted (in all directions) from any surface by rays. Q. How is BROTH COOLED by being left ex- posed to the AIR ? A. It throws off some heat by radia- tion ; but it is mainly cooled down by convection. 228 AIR. Q. How is hot BROTH cooled down by CONVEC- TION 'I A. The air resting on the hot broth (being heated) ascends ; colder air suc- ceeding* absorbs more heat, and ascends also ; and this process is repeated till the broth is made cool. The particles on the surface of the broth sink as they are cooled down, and warmer particles rise to the surface ; which gradually assists the cooling process. Q. Why is hot TEA and BROTH COOLED faster by being STIRRED about ? A. 1st Because the agitation assists in bringing its hottest particles to the surface. 2dly The action of stirring agitates the air, and brings it more quickly to the broth or tea : and 3dly As the hotter particles are more rapidly brought into contact with the air, therefore, convection is more rapid. Blowing tea or broth cools it also. (See p. 168.) Q. If a shutter be closed in the day-time, the stream of light (piercing through the crevice) seems in CONSTANT AGITATION. WflY is this ? A. Because little motes arid particles of dust (thrown into agitation by the violence of the convective currents) are made visible by the strong beam of light thrown into the room through the cre- vice of the shutter. PRESSURE OP AIR. 229 Q. Why is the GALLERY of a CHURCH or the- atre HOTTER than the AISLE or 'pit ? A. Because the hot air ascends from the bottom to the top of tlie building ; while cold air flows to the bottom from the doors and windows. Q. Why do persons who ascend in balloons feel intense pain in their eyes and ears ? A. Because the air of the upper regions is more rarefied than that on the earth ; and the air inside their bodies (seeking- to become of the same rarity) bursts through their eyes and ears, pro- ducing* intense pain. Q. Why is it often PAINFUL and difficult to BREATHE, On a MOUNTAIN-TOP ? A. Because the pressure of air on the mountain-top is not so great as it is on the plain; and the air inside our bodies (seeking to become of the same rarity) bursts through the pores of the body and produces great pain. Q. Why do we feel OPPRESSED just PREVIOUS to a storm ? A. Because the air is greatly rarejied by heat and vapor ; and the air inside us (seeking to become of the same rarity) produces an oppressive and suffocating feeling. 230 AIR. Q. Why do DIVERS, when they a>'e under water, suffer great pain in their eyes and ears ? A. Because the air at the bottom of the sea is more dense than the air on the surface ; and (till the air inside the diver's body is settled into the same density) he feels oppressed with pain, especially in the ears. Q. Why is this PAIN felt especially about the EARS of a DIVER ? A. Because the ear is fitted with a small membrane called the e/raw(ortym'- panum), through which the dense air bursts: The rupture of this membrane very often produces incurable deafness. When the 'diver is not in a bell the dense water bursts into his ears and ruptures the tympanum. Q. Why do our CORNS ache just previous to RAIN ? A. Because our feet swell from the sudden depression in the density of air ; and the hard corn (not being elastic) is painfully stretched and pressed. Some of this pain is due to electricity. Q. How do you know that the density of the air is lowered, previous to a storm ? A. Because the mercury of a barome- ter rapidly falls. Q. Why do CELLARS feel WARM in WINTER ? A. Because the external air has not RUST. 231 free access into them ; in consequence of which, they remain almost at an even temperature which (in winter time) is about 10 degrees warmer than the ex- ternal air. Q. Why do CELLARS/^ COLD in SUMMER? A. Because the external air has not free access into them ; in consequence of which, they remain almost at an even temperature which (in summer time) is about 10 degrees colder than the exter- nal air. Q. Why does AIR rust IRON ? A. Because the oxygen of the air combines with the surface of the metal, and produces oxide of iron; which is generally called " rust." An oxide of iron, copper, &c., is oxygen in combination with iron, copper, &c. Q. Why does hot iron SCALE and PEEL off^ when ,struck with a HAMMER? A. Because the oxygen oftJie air very readily unites with the surface of the hot iron, and forms a metallic oxide (or rust), which scales off when struck with a hammer. Q. Does iron RUST in DRY air ? A. No; iron undergoes no change in dry air. 232 AIR. Q. Why do STOVES and FIRE-IRONS become RUSTY in rooms, which are riot OCCUPIED ? A. Because the air is damp; and moist air oxidizes iron and steel. Oxidizes, i. e., rusts. Q. In, what part of the year is it most difficult to keep STOVES and FIRE-IRONS BRIGHT? A. In autumn and winter. Q. Why is it more difficult to keep STOVES and FIRE-IRONS bright in AUTUMN and WINTER than in spring and summer ? A. Because the capacity of the air for holding* water is constantly on the decrease, after the summer is over ; in consequence of which, vapor is deposited on everything with which the air comes in contact. Q. Why does GREASING iron prevent its be- coming RUSTY ? A. Because grease prevents the hu- midity of air from coming* in contact with the surface of the iron. Q. Why do not STOVES rust so frequently as POKERS and TONGS ? A. Because stoves are generally cov- ered with plumbago, or black lead. Q. W^hat is plumbago^ or black lead ? A. A mixture of charcoal and iron. Plumbago (strictly speaking) is a chemical union of caibon and iron, in the following proportions: 91 parts carbon and 9 iron. But the BLACK LEAD sold in shops is a mixture of charcoal and iron filings. METALS. 233 N. B. A most excellent varnish to prevent rust is made of 1 pint of fat oil varnish, mixed with 5 pints of highly rectified spirits of turpentine, rubbed on the iron or steel with a piece of sponge. This varnish may be ap- plied to bright stoves, and even mathematical instruments, without injuring their delicate polish. Q. Why does ornamental STEEL (of a purple or LILAC color) rust more readily than polished WHITE steel ? A. Because the lilac tinge is pro- duced by partial oxidation; and the process which forms rusts has, therefore, already commenced. Q. How can lilac STEEL be kept FREE from RUST ? A. By keeping- it in a very dry place. Q. If DRY AIR contains OXYGEN, why does it NOT RUST IRON, as well as MOIST air ? A. Because moisture is always need- ed, in order to bring* into action the affinity of oxygen for steel. Q. Do any OTHER metals (besides iron) com- bine rapidly with oxygen ? A. Yes ; copper, lead, mercury, and even silver to some extent. Q. Why does COPPER TARNISH ? A. The tarnish of copper is caused by its oxidation : that is, the oxygen of the air combines with the surface of the copper, and (instead of rusting it) covers it with -a dark tarnish. Q. Why does LEAD become of a DARKER hue, by being exposed to the air ? 234 AIR. A. Because the vapor of the air com- bines with the lead, and oxidizes its sur- face ; but instead of becoming- rusty, the surface assumes a darker hue. Q. Why does LEAD lose its BRIGHTNESS, and become DULL, by being exposed to the air ? A. The dullness of the lead is caused by the presence of a carbonate of the oxide. When the oxide is formed, it attracts carbonic acid from the air, and (combining 1 with it) produces a carbonate, which gives the dull tint to old lead. Q. Why is it difficult to keep SILVER BRIGHT 1 A. Because the vapor of the air oxi- dizes its surface, and tarnishes it. Q. Why do silver TEA-POTS and SPOONS tar- nish more quickly than silver ore or bullion ? A. Because alloy of some baser me- tal is used, to make them more hard and lasting ; and this alloy oxidizes more quickly than silver itself. Q. Why does GERMAN silver turn a dingy yelloio in a few hours ? A. Because German silver has a great affinity for oxyg*en ; and shows its oxidation by a sickly yellow tarnish, in- stead of rust. Q. If quicksilver (or mercury) will tarnish lik copper and lead why does it preserve its BRILLIANCY in BAROMETERS and THERMOMETERS ? OXIDATION PLATINUM. 235 A. Because the air is excluded ; and no moisture can come in contact with it, to oxidize (or tarnish) it. Q. Is GOLD affected by the atmosphere ? A. Not readily ; gold will never combine with oxygen of itself, (i. e., without aid.) Q. WHICH of the METALS is capable of resisting oxidation altogether ? A. Plat'inum ; in consequence of which, the graduated arcs of delicate " instruments-for-observation " are made of plat'inum instead of any other metal. Q. Why is PLAT'INUM used for the graduated arcs of delicate mathematical instruments^ instead of any other metal ? A. Because it will never oxidize; but retains its bright surface in all wea- thers, free from both rust and tarnish. Q. Before plat'inum was discovered, which of the metals was employed for the same purpose ? A. Gold. Plat'inum (a white metal), so called from " plata," the Spanish word for silver. It was introduced from South America into England hy Mr. Wood, (A. D. 1749.) Q. For what other SCIENTIFIC purpose is PI&T'- INUM now used ? A. For crucibles in which acids are employed : and for galvanic batteries. Q. Why are CRUCIBLES (in which acids are employed) made of PLAT'INUM ? 236 AIR. A. Because the acid would act upon other metals, or upon glass ; and prevent the experimenter's success. Q. Which of the METALS have the GREATEST affinity for OXYGEN? A. Those called potas'sium and so- dium. Potassium and so'dium derive their names from potash and soda. Potas'sa is the oxide of potas'sium ; and soda is the oxide of so'dium. Q. How is the affinity of potas'sium and so- dium for oxygen shown ? A. They decompose water immediately they are brought into contact with it. Q. What EFFECT has POTAS'SIUM on WATER ? A. It catches fire the moment it is thrown into water, and burns with a vivid flame which is still further in- creased by the combustion of hydrogen, separated from the water. N. B. Water is composed of oxygen and hydrogen ; and potas'sium separates the two gases. Q. What effect has SO'DIUM on WATER 1 A. It does not take^re, as potassium does ; but undergoes very rapid oxida- tion. Q. Is the FURR of KETTLES an oxide ? A. No ; the furr (or deposit of boil- ing water) is a precipitate of lime and mineral salt, separated from the water by the process of boiling. FURR. 237 Q. Is not this FURR of lolling water often DANGEROUS 1 A. Yes ; especially in tubular boilers, such as those employed in railways. Q. Why is this FURR especially TROUBLESOME in RAILWAY engines ? A. Because it is a bad conductor of heat; in consequence of which, it hin- ders the evaporating effect of the fire, and prevents the economy of fuel. Q. Why is this FURR especially DANGEROUS in RAILWAY engines ? A. Because, when it is deposited in the boilers, they are likely to become over-heated; and then explosion will take place, from the sudden generation of highly elastic steam. Q. Why cannot RAILWAY engines be fed with BRACKISH WATER ? A. Because brackish water contains mineral salt ; which makes a much lar- ger deposit of furr than water which contains only vegetable matters. 238 CARBONIC ACID GAS. CARBONIC ACID GAS. CHAPTER XXL Q. What is CARBONIC ACID GAS ? A. A gas formed by the union of carbon and oxygen : It used to be called " FIXED AIR." 3 Ibs. of carbon and 8 Ibs. of oxygen will form 11 Ibs. of carbonic acid. Q. Under what circumstances does CARBON most readily UNITE with OXYGEN ? A. 1st When its temperature is raised : Thus if carbon be red-hot, oxy- gen will most readily unite with it : and 2dly When it forms part of the fluid blood. Q. Why do oxygen and carbon so readily unite in the BLOOD ? A. Because the atoms of carbon are so loosely attracted by the other materials of the blood, that they unite very readily with the oxygen of the air inhaled. Q. Is carbonic acid WHOLESOME ? A. No; it is fatal to animal life; and (whenever it is inhaled) acts like a narcotic poison producing drowsiness, which sometimes ends in death. Q. How can any one KNOW, if a place be in* fested with CARBONIC ACID GAS ? VITIATED AIR. 239 A. If a pit or well contain carbonic acid, a candle (let down into it) will be insUmthj extinguished. The rule, there- fore, is this Where a candle will burn, a man can live ; but what will extinguish a candle, will also destroy life. Q. Why does a MINER lower a CANDLE into a mine, before he descends ? A. Because the candle will be extin- guished, if the mine contains carbonic acid gas : but if the candle is not extin- guished, the mine is safe, and the man may fearlessly descend. Q. Why does a CROWDED ROOM produce HEAD-ACHE ? A. Because we breathe air vitiated by the crowd. Q. Why is the AIR of a room VITIATED by a CROWD ? A. Because it is deprived of its due proportion of oxygen, and laden with carbonic acid. Q. How is the air of a room affected thus by a crowd ? A. The elements of the air inhaled are separated in the lungs : the oxygen is converted in the blood into carbonic add; and the carbonic acid (together with the nitrogen) is thrown back again by the breath into the room. 240 CARBONIC ACID GAS. Q. Is ALL the NITROGEN REJECTED by the _ t? A. Yes ; all the nitrogen of the air is always expired. Q. Why is a CROWDED ROOM UNWHOLESOME ? A. Because the oxygen of the air is absorbed by the lungs; and carbonic acid gas (which is a noxious poison) is substituted for it. Q. Mention, the historical circumstances, so well known in connexion with the " BLACK HOLE of CALCUTTA." A. In the reign of George II., the Raja (or Prince) of Bengal* marched suddenly to Calcutta, to drive the Eng- lish from the country ; as the attack was unexpected, the English were obliged to submit, and 146 persons were taken prisoners. Q. What became of these prisoners ? A. They were driven into a place about 18 feet square, and 15 or 16 feet in height, with only two small grated windows. 123 of the prisoners died in one night ; and (of the 23 who survived) the larger portion died of putrid fevers, after they were liberated. Q. Why were so many persons SUFFOCATED in * The Sur Raja, at Dowlat ; a young man of violent pas- sions, who had but just succeeded to the throne. A. D. 1756. JUNGLES. 241 & few hours, from confinement in this dose, hot PRIS- ON-HOLE ? A, Because the oxygen of the air was soon consumed by so many lungs, and its place supplied by carbonic acid, ex- haled by the hot breath. Q. ~tffhy did the captives in the BLACK HOLE die SLEEPING? A r 1st Because the absence of oxy- gen quickly affects the vital functions, depresses the nervous energies, and pro- duces a lassitude which ends in death : and 2dly Carbonic acid gas (being a narcotic poison) produces drowsiness and death, in those who inhale it. Q. Why are the JUNGLES of Java and Hin- dostan so FATAL to life ? A. Because vast quantities of car- bonic acid are thrown off by decaying vegetables in these jungles ; and (as the wind cannot penetrate the thick brush- wood to blow the pernicious gas away) it settles there, and destroys animal life. Q. Why do persons in a crowded CHURCH feel DROWSY ? A. 1st Because the crowded con- gregation inhale a large portion of the oxygen of the air, which alone can sus- tain vitality and healthy action : and 11 242 CARBONIC ACID GAS. 2dly The air of the church is im- pregnated with carbonic acid gas, which (being- a strong narcotic) produces drow- siness in those who inhale it. Q. Why do PERSONS who are much in the OPEN AIR enjoy the best HEALTH ? A. Because the air they inhale is much more pure. Q. Why is COUNTRY AIR more PURE than the, air in CITIES ? A. 1st Because there are fewer inhabitants to vitiate the air : 2dly There are more trees to restore the equilibrium of the vitiated air : and 3dly The free circulation of air keeps it pure and wholesome : (In the same way as running streams are pure and wholesome, while stagnant waters are the contrary.) Q. Why does the SCANTINESS of a country POPULATION render the COUNTRY AIR more PURE 1 A. Because the fewer the inhabitants, the less carbonic acid will be exhaled; and thus country people inhale pure oxygen, instead of air impregnated with the narcotic poison, called carbonic acid gas. Q. Why do TREES and FLOWERS help to make country AIR WHOLESOME ? A. 1st Because trees and flowers COUNTRY AND CITY AIR. 243 absorb the carbonic acid, generated by the lungs of animals, putrid substances, and other obnoxious exhalations : and 2dly Trees and flowers restore to the air the oxygen, which has been 'in- haled by man and other animals. Q. Why is the AIR of CITIES LESS wholesome, than COUNTRY air ? A. 1st Because there are more in- habitants to vitiate the air : 2dly The sewers, drains, bins, and filth of a city, very greatly vitiate the air: 3dly The streets and alleys prevent a free circulation : and 4thly There are fewer trees to ab- sorb the excess of carbonic acid gas, and restore the equilibrium. Q. Why are PERSONS, who live in CLOSE ROOMS and crowded CITIES, generally SICKLY ? A. Because the air they breathe is not pure, but is (in the 1st place) defec- tive in oxygen; and (in the 2d) is im- pregnated with carbonic acid gas. Q. Where does the CARBONIC ACID of close ROOMS and CITIES COME from? A. From the lungs of the inhabitants, the sewers, drains, and other like places, in which organic substances are under- going decomposition. 244 CARBONIC ACID GAS. Q. What BECOMES of the CARBONIC ACID of crowded cities ? A. Some of it is abswbed by vegeta- bles ; and the rest is blown away by the wind, and diffused through the whole volume of the air. Q. Does not this constant diffusion of carbonic acid affect the PURITY of the WHOLE AIR ? A. No ; because it is wafted by the wind from place to place, and absorbed in its passage by the vegetable world. Q. ' ""What is CHOKE DAMP? A. Carbonic acid gas accumulated at the bottom of wells and pits, which ren- ders them noxious, and often fatal to life. Q. Why is not this carbonic acid TAKEN UP by the AIR and DIFFUSED, as it is in cities ? A. Because (being heavier than com- mon air) it cannot rise from the well or pit : and no wind can get to it, to blow it away. Q. Why are PERSONS sometimes KILLED by leaning over BEER VATS ? A. Because vats (where beer has been made) contain a large quantity of carbonic acid gas, produced by the " vi- nous fermentation" of the beer ; and when a man incautiously leans aver a BEER VATS CHARCOAL. 245 beer vat, and inhales the carbonic acid, he is immediately killed thereby. Q. Why are PERSONS often KILLED, who enter BEER VATS to clean them? A. Because carbonic acid (being* hea- vier than atmospheric air} often rests upon the bottom of a vat : when, therefore, a person enters the vat, and stoops to clean the bottom, he inhales the pernicious gas, which kills him. Q. Why are PERSONS sometimes KILLED, by .having a CHARCOAL FIRE in their bedrooms ? A. Because the carbon of the burning charcoal unites with the oxygen of the air, and forms carbonic acid gas, which is a narcotic poison. Q. If carbonic acid settles at the BOTTOM of a, room, how can it injure a person LYING upon a BED, raised considerably above the jioqf ? A. Because all gases diffuse them- selves through each other, as a drop of ink would diffuse itself through a cup of water. If, therefore, a person slept for 6 or 8 hours in a room containing carbonic acid, quite enough of the gas will be diffused throughout the room to produce death. The heat of the fire assists the process of diffusion. Q. What are the chief SOURCES of CARBONIC ACID ? 246 CARBONIC ACID GAS. A. 1st The breath of animals. 2dly The decomposition of vegetable and animal matter. 3dly Lime-stone, chalk, and all cal- careous stones, in which it exists in a solid form. Q. From which of these sources is CARBONIC ACID most likely to ACCUMULATE to a noxious extent ? A. From the fermentation and putre- faction of decaying vegetable and ani- mal matters. Q. How can this ACCUMULATION of CARBONIC ACID be PREVENTED? A. By throwing quick-lime into pla- ces, where such fermentation and pu- trefaction are going on. Q. HOW Will QUICK-LIME PREVENT the OCCU- mulation of CARBONIC ACID ? A. Quick-lime will absorb the car- bonic acid ; and produce a combination called " carbonate of lime. 77 Q. Does not heavy RAIN prevent the ACCUMU- LATION of CARBONIC ACID, as well as quick-lime ? A. Yes ; an abundant supply of water will prevent the accumulation of carbonic acid, by dissolving it. N. B. Red heat (as a pan of red-hot coals, or a piece of red-hot iron) will soon absorb the carbonic acid gas, accumulated in a pit or well. Q. What effect has CARBONIC ACID on the WA- TER in which it is dissolved ? EFFERVESCENCE. 247 A.. It renders it slightly acid to the taste. Q. Can the CAPACITY of water for dissolving carbonic acid be increased ? A. Yes. Carbonic acid may be forced into water by pressure to a considerable extent. Q. To what practical USES has this capacity of water ( for dissolving carbonic acid) been applied ? A. Effervescing draughts are made upon this principle. Q. Explain the cause of EFFERVESCENCE in these beverages ? A. The carbonic acid of the beverage (being- prevented by the cork from es- caping] is forced into the liquor by pres- sure, and absorbed by it: but when the cork (or pressure) is removed, some of the carbonic acid flies off in bubbles or effervescence. Q. Why does AERATED WATER effervesce when the CORK is removed ? A. While the bottle remains cork- ed, carbonic acid is forced into the water by pressure, and absorbed by it : but, when the cork (or pressure) is removed, some of the carbonic acid flies off in effervescence. Q. Why does SODA WATER effervesce ? A. In soda water there is forced 8 248 CARBONIC ACID GAS. times its own bulk of carbonic acid gas, which makes its escape in effervescence, as soon as the cork is removed. Q. Why . does GINGER POP fly about in froth, when the string of the cork is cut ? A. Because it contains carbonic acid gas. While the cork is fast, the carbonic acid is forced into the liquor ; but when the pressure is removed the gas is given off in effervescence. N. B. All vinous fermentation produces carbonic acid. Q. Why does BOTTLED ALE froth more than DRAUGHT ale ? A. Because the pressure is greater in a bottle than in a tub which is contin- ually tapped ; and effervescence is al- ways increased by pressure. Q. What produces the FROTH of BOTTLED PORTER ? A. Carbonic acid generated by the vinous fermentation of the porter : This gas is absorbed by the liquor, so long as the bottle is well corked ; but is given off in froth, when the pressure of the cork is removed. Q. What gives the pleasant ACID taste to soda water, ginger beer, champagne, and cider ? A. The presence of carbonic acid, generated by fermentation ; and liberal- SPRING WATER ALCOHOL. 249 ed by effervescence, when the pressure of the cork is removed. Q. Why does fresh SPRING WATER SPARKLE, when poured from one vessel to another ? A. Because fresh spring- and pump water contain carbonic acid ; and it is the presence of this gas which makes the water sparkle. Much of the froth and bubbling of ale, beer, WATER, &c., when they are " poured high," is due to simple me- chanical action. Q. What is the FERMENTATION of BEER and WINE 1 A. The escape of carbonic acid, pro- duced by the change of sugar into alco- hol. Q. What is AL'COHOL ? A. The spirit of beer and wine, obtained by fermentation. Q. Of what ELEMENTS is AL'COHOL composed ? A. Of carbon, oxygen, and hydrogen. Of AL'COHOL, 4 parts are carbon, 2 oxygen, and 6 hydrogen. Q. What are the ELEMENTS of grape SUGAR ? A. Carbon, oxygen, and hydrogen, all in equal proportions. Q. What CHANGES does SUGAR undergo by FERMENTATION ? A. It is first decomposed, and then its elements re-unite in different propor- tions, producing alcohol, carbonic and water. 11* 250 CARBONIC ACID GAS. Of SUGAR, one portion is alcohol ; and another carbonic acid ; as may be seen by the following table. Garb. 0x7. Hyd. Every atom of anhydrous sugar contains 12 12 12 Two atoms of alcohol contain 8 4 12 Four atoms of carbonic acid contain 480 12 12 12 N. B. " Anhydrous sugar" is sugar dried at 300. Q . Ho w does s UG AR form AL' c OH OL by fermen- tation ? A. Two-thirds of its carbon and one- ifhird of its oxygen re-unite with the Ihydrogen^ and generate alcohol. Q. How does SUGAR form CARBONIC ACID by fermentation ? A. The remaining one-third of its carbon and two-thirds of its oxygen re- unite, arid generate carbonic acid. Q. What BECOMES of the AL'COHOL which is thus generated by fermentation ? A. It mixes with the water, and forms the intoxicating part of beer and wine. Q. What becomes of the CARBONIC ACID, which is generated by fermentation ? A. It makes its escape into the air. Q. Why is BARLEY MALTED ? A. Because germination is produced by the artificial heat; and in germina- tion, the starch of the grain is converted into sugar. BARLEY YEAST. 251 Q. How is barley malted ? A. It is moistened with water } and heaped up ; by which means, great heat is produced, which makes the b&rley sprout. (See " spontaneous combustion.") Q. Why is not the BARLEY suffered to GROW as well as SPROUT ? A. Because plants in the germ con- tain more sugar than in any other state : as soon as the germ puts forth shoots, the sugar of the plant is consumed, to sup- port the shoot. Q. HOW IS BARLEY PREVENTED from SHOOT- ING in the process of MALTING? A. It is put into a kiln, as soon as it sprouts ; and the heat of the kiln checks or destroys the young shoot. Q. What is YEAST ? A. The foam of beer (or of some similar liquor) produced by fermentation. Q. Why is YEAST used in BREWING ? A. Because it consists of a substance called glu'ten, undergoing putrefaction ; in which state it possesses the peculiar property of exciting fermentation. If the gluten were not in a putrefying state, it could not produce fermentation. Q. What is gluten ? A. A tough, elastic substance, com- 252 CARBONIC ACID GAS. posed of carbon, oxygen, hydrogen, and nitrogen. Q. Does MALT contain gluten ? A. Yes. The infusion of malt, called " sweet- wort" contains an abundance of glu'ten ; and the yeast (which converts its sugar into alcohol] converts this glu'- ten into yeast. Q. Why is YEAST needful in order to make malt into BEER ? A. Because the presence of a putre- fying body containing nitrogen is essen- tial, in order to convert sugar into al- cohol. Q. What EFFECT has yeast upon the SWEET- WORT? A. It causes the SUGAR to be con- verted into alcohol and carbonic acid; and its GLUTEN into yeast. Q. What change is produced in gluten by PU- TREFACTION ? A. Its elements are loosened from their former conditions of combination, and re-arranged (with the addition Af oxygen from the air) into a new series. Q. What is the DIFFERENCE between FERMEN- TATION and PUTREFACTION ? A. FERMENTATION is a change ef- fected in the elements of a body com- posed of carbon, oxygen, and hydrogen, PUTREFACTION. 253 without nitrogen. PUTREFACTION is a change effected in the elements of a body composed of carbon, oxygen, hy- drogen, and nitrogen. Q. What NEW COMPOUNDS are produced by the change called FERMENTATION ? A. Alcohol and carbonic acid. The alcohol is still further changed (unless the process be checked) injp acetic acid or vinegar. Q. What new compounds are produced by the change called PUTREFACTION ? A. The carbon, oxygen, hydrogen, and nitrogen, of the original substance (being separated by decomposition) re- unite in the following manner. 1. Carbon and oxygen unite to form carbonic acid. 2. Oxygen and hydrogen unite to form water. 3. Hydrogen and nitrogen unite to form ammonia. Hartshorn is a solution of ammonia in water. N. B. When bodies containing sulphur and phosphorus pntrefy, the sulphur and phosphorus unite with hydrogen, and form sulphuretted and phosphurctted hydrogen gases. Q. What BECOMES of these several products of putrefaction ? A. They are all elastic bodies, and escape into the air. N. B. Water is elastic and gaseous when in the condi- tion of vapor. Q. What is the cause of the OFFENSIVE SMELL which issues from putrefying bodies ? 254 CARBONIC ACID GAS. A. The evolution of ammonia, or of sulphuretted and phosp/iuretted hydrogen gases ; all of which have pungent and offensive odors. Q. Why do boiled EGGS DISCOLOR a SILVER SPOON ? A. Because they contain a small portion of sulphur, which unites with the silver (for which it has a great affinity) and tarnishes it. Both the white and yolk contain sulphur the latter more abundantly. Q. What causes the offensive smell of STALE hard boiled EGGS? A. The hydrogen of the egg combin- ing with the sulphur and phosphorus, form sulphuretted and pfiosphurctted hy- drogen; both of which gases have an offensive odor. Of an egg 55 parts are carbon, 16 nitrogen, 7 hydrogen, and the remaining 22 are oxygen, phosphorus, and sul- phur. Q. Why is it NOT needful to put YEAST into GRAPE juice, in order to produce fermentation, ? A. Because grape juice contains a sufficient quantity of a nitrogenized substance (like yeast) to produce fermen- tation. Nitrogenized, i. e., containing nitrogen. Q. Why do NOT GRAPES ferment, while they hang on the VINE ? FERMENTATION. 255 A. Because the water of the juice evaporates through the skin, and allows the grapes to shrivel and dry up, after they are ripe. Fermentation cannot occur unless the sugar be dissolved in a sufficient quantity of water. Q. What is the FROTH or SCUM of fermented LIQUORS ? A. Putrefying- glutinous substances (of a nature similar to yeast), which rise to the surface from their lightness. Q. Why is BEER FLAT if the cask be left open too long ? A. Because too much of the carbonic acid gas (produced by fermentation) is suffered to escape. Q. Why are BEER and PORTER made STALE by being exposed to the AIR ? A. Because too much of the carbonic acid gas (produced by fermentation) is suffered to escape. Q. Why does BEER turnFLAT if the VENT PEG be left out of the tub? A. Because the carbonic acid gas es- capes through the. vent hole. Q. Why will NOT beer RUN OUT of the tub till the VENT PEG is taken out ? A. Because the upward pressure of the external air (admitted through the tap) holds the liquor back not being 256 CARBONIC ACID GAS. counterbalanced by any pressure of air on the surface of the liquid. The upward pressure of air is illustrated by the follow- ing simple experiment: Fill a wine glass with water; cover the top of the glass with a piece of writing paper turn the glass upside down, and the water will not run out. The paper is used merely to give the air a medium sufficiently dense to act against. Q. Why does the BEER RUN FREELY, imme- diately the VENT PEG is taken out ? A. Because air rushes immediately through the vent hole at the top of the tub, to counterbalance the air admitted by the tap ; in consequence of which the liquid escapes by its own downward pressure. Q. Why does liquor flow reluctantly out of a, BOTTLE held upside down ? A. Because the upward pressure of the air prevents the liquor from flowing" out. Q. Why should a bottle be held OBLIQUELY in order to be emptied of its liquor ? A. Because air will then flow into the bottle, and help the liquor out, by counterbalancing the upward pressure. Q. Why does wine (poured from a bottle QUICKLY) SPIRT about, without going into the decanter ? A. Because it fills the top of the de- canter (like a cork), and leaves no room YEAST FERMENTATION. 257 for the air inside to escape ; the decanter, therefore, (being- full of air] refuses to admit the wine. Q. Why does the EFFERVESCENCE of soda water a?id ginger beer so soon go off? A. Because the carbonic acid, (which produced the effervescence) very rapidly escapes into the air. Q. Why is BOILED WATER FLAT and insipid ? A. Because the whole of the carbonic acid is expelled by boiling 1 , and escapes into the air. Q. Why does YEAST make BREAD LIGHT ? A. Because it produces a species of fermentation on the starch and glu'ten of flour, as it does in the sug*ar of malt. Q. How does FERMENTATION make the DOUGH RISE ? A. During* fermentation, carbonic acid gas is evolved ; but the sticky texture of the dough will not allow it to escape; so it forces up little bladders all over the doug-h. Q. Why is DOUGH placed BEFORE the FIRE ? A. 1st Because the heat of the fire increases the fermentation ; and 2dly It expands the gas. confined in the little bladders ; in consequence of which, the bladders are enlarged, and 258 CARBONIC ACID GAS. the dough becomes lighter and more po- rous. Q. Why is BREAD HEAVY, if the dough be re- moved from the fire? A. Because the dough gets cold, and then the air in the bladders condenses the paste falls and the bread becomes close and heavy. Q. What causes the HEAT of FIRE ? A. The carbon of fuel (when heated) combines with the oxygen of the air, and produces carbonic acid gas : Again, the hydrogen of the fuel combining with other portions of oxygen, condenses into water ; by which chemical actions heat is evolved. Q. What causes the HEAT of our own BODY ? A. The carbon of our blood combines with the oxygen of the air inhaled^ and produces carbonic acid gas ; which evolves heat in a way similar to burn- ing fuel. Q. WHience does the HEAT of a DUNGHILL arise ? A. As the straw, &c., of the dunghill decays, it undergoes fermentation, which produces carbonic acid gas ; and heat is evolved by a species of combustion, (as in the two former cases.) LIME WATER. 259 Q. How does the formation of CARBONIC ACID (in all these cases) produce HEAT ? A. Carbonic add has less power of holding latent heat than carbon and oxy- gen have : When, therefore, these ele- ments are changed into carbonic acid, latent heat is given off, arid made sensible.' Q. Why do persons throw LIME into BINS and SEWERS, to PREVENT their offensive SMELL, in sum- mer time ? A. Because they contain large quan- tities of carbonic acid gas, which readily combines with lime ; and producing " car- bonate of lime" neutralizes the offensive gases. Q. Why should WATER (used for washing] be exposed to the air ? A. Because it is made more soft by exposure to the air. Most spring water holds lime in solution as a bicarbon- ate, in consequence of the presence of abundant carbonic acid. Carbonic acid escapes by exposure to air and the lime is, consequently, deposited as a carbonate. Q. Why is hard WATER made more SOFT by exposure to air ? A. 1st Because the mineral salts (which cause its hardness) subside : and 2dly Because the carbonic acid of the water makes its escape into the air. Q. How is the carbonic acid of water duced ? 260 CARBONIC ACID GAS, A. From the presence of lime, which is frequently held in solution by hard water : When the carbonic acid escapes by exposure to the air, the lime is depos- ited as a carbonate. Q. Why is HARD WATER more agreeable to DRINK than soft water ? A. Chiefly- because it contains car- bonic acid. Q. Why is water FRESH from the pump more SPARKLING, than after it has been drawn some time ? A. Because water fresh from the pump contains carbonic acid, which soon escapes into the air, and leaves the wa- ter flat and stale. Q. Why is QUICK-LIME formed by burning chalk and marl in a KILN ? A. Because the carbonic acid (which rendered it mild) is driven off by the heat of the kiln : and the lime becomes quick or caustic. Q. What is MORTAR ? A. Quick-lime mixed with sand and water. Q. Wherein does LIME-STONE differ in appear- ance from quick-lime ? A. LIME-STONE is a hard, rocky sub- stance ; but QUICK-LIME a loose powder. Q. Why does MORTAR become HARD after a few days ? MORTAR CHOKE-DAMP. 261 A. Because the lime re-imbibes from the air the carbonic acid which had been expelled by fire ; and the loose pow- der again becomes as hard as the origi- nal lime-stone. Explain in what way MORTAR is adhesive. When the carbonic acid is expel- he hard lime-stone is converted into a loose powder , which (being* mixed with sand and water) becomes a soft and sticky plaster ; but as soon as it is placed between bricks, it imbibes carbonic acid again, and hardens into lime-stone. CARBURETTED HYDROGEN GAS. CHAPTER XXII. Q. What is CHOKE-DAMP ? A. Carbonic acid gas accumulated at the bottom of wells and pits. It is called CHOKE damp, because it chokes (or suffocates) every animal that attempts to inhale it. (Seep. 238;) It suffocates without getting into the lungs, by closing the outer orifice spasmodically. Q. What is marsh-gas or FIRE-DAMP ? A. Carburetted hydrogen gas accu- 262 CARBURETTED HYDROGEN GAS. mulated on marshes, in stagnant waters, and coal-pits ; it is frequently called " inflammable air." Q. What is CARBURETTED HYDROGEN GAS ? A. Carbon combined with hydrogen. Q. How may CARBURETTED HYDROGEN GAS be PROCURED on marshes? A. By stirring the mud at the bottom of any stagnant pool, and collecting- the gas (as it escapes upwards) in an in- verted glass vessel. Q. What is COAL GAS ? A. Carburetted hydrogen extracted from coals by the heat ofjire. Q. Why is carburetted hydrogen gas called FIRE-DAMP or inflammable air ? A. Because it very readily catclies fire and explodes, when a light is intro- duced to it. Provided atmospheric air be present. Q. Why is carburetted hydrogen gas frequent- ly called MARSH-GAS ? A. Because it is generated in mea- dows and marshes from putrefying vege- table substances. See ignis fatuus, p, 266. Q. What gas is evolved by the WICK of a turning CANDLE ? A. Carburetted hydrogen gas : The carbon and hydrogen of the tallow com- DAVY'S SAFETY LAMP. 263 bine into a gas from the heat of the flame; and this gas is called carbureUed hydrogen or inflammable air. Q. Why do COAL-MINES so frequently EX- PLODE ? A. Because the CMrburetted hydrogen gas (which is generated in these mines by the coals) explodes, when a light is incautiously introduced. Q. How -can miners SEE in the coal-pits if they may never introduce a LIGHT ? A. Sir Humphrey Davy invented a lantern for the use of miners, called " the Safety Lamp," which may be used with- out danger. Q. Who was SIR HUMPHREY DAVY? A. A very clever chemist, born in Cornwall, 1778, and died in 1829. Q. What kind of thing is the SAFETY-LAMP ? A. A kind of lantern, covered with a fine gauze wire, instead of glass or horn. Q. How does this fine GAUZE WIRE prevent an EXPLOSION in the coal-mine ? A. By preventing the flame of the lamp from communicating with the in- flammable gas of the mine. N. B. The interstices of the gauze wire must not ex- ceed the 7th of an inch in diameter. Q. Why will not FLAME PASS THROUGH very fine wire GAUZE ? 264 CARBURETTED HYDROGEN GAS. A. Because the metal wire is a very rapid conductor of heat ; and when the flame (of gas burning* in the lamp) reach- es the wire gauze, so much heat is con- ducted away by the wire, that the flame is extinguished. Q. Does the gas of the COAL-PIT get THROUGH the wire gauze INTO the LANTERN ? A. Yes ; and the inflammable gas ignites, and burns inside the lamp : As soon as this is the case, t/w miner is in danger, and should withdraw. Q. . Why is the miner in DANGER if the gas ig- nites and burns in the INSIDE of the safety lamp ? A. Because the heat of the burning gas will soon destroy the wire gauze ; and then the flame (being free) will set fire to the mine. N. B. When the carburetted hydrogen gas takes fire from the miner's candle, the miner sometimes perishes in the blastof the flame, and sometimes suffers suffocation from the carbonic acid which is thus produced. PHOSPHORUS. 265 PHOSPHURETTED HYDROGEN G-AS. CHAPTER XXIII. Q. From what do the, very OFFENSIVE EFFLU- VIA of CHURCH-YARDS arise ? A. From a gas called PHOSPHURET- TED HYDROGEN ; which is phosphorus combined with hydrogen gas. Q. What is PHOSPHORUS? A. A pale amber-colored substance, resembling* wax in appearance. The word is derived from two Greek words, which mean " to produce or carry light" (00)-0J9V). Q. HOW is PHOSPHORUS OBTAINED ? A. By heating- bones to a white heat ; by which means, the animal mat- ter arid charcoal are consumed, and a substance called "phosphate of lime" is left behind. Q. What is the PHOSPHATE OF LIME ? A. Phosphorus united to oxyg*en and lime ; when sulphuric acid is added, and the mixture heated, the lime is attracted to the acid, and pure phosphorus remains. If powdered charcoal be added, phosphorus may be procured by distillation. Q. Of what is the ignitible part of LUCIFER MATCHES made ? 12 266 PHOSPHURETTED HYDROGEN GAS. A. Of phosphorus : and above 250 thousand Ibs. are used every year in London alone, merely for the manufac- ture of lucifer matches. Q. Why does a PUTREFYING dead BODY SMELL so offensively ? A. Because phosphuretted hydrogen gas always rises from putrefying* animal substances. The escape of ammonia and sulphuretted hydrogen con- tributes also to this offensive effluvia. Q. What is the cause of the IGNIS FATUUS, Jack 0' Lantern, or Will o'the Wisp? A. This luminous appearance (which haunts meadows, bogs, and marshes) arises from the gas of putrefying animal and vegetable substances ; especially from decaying* fish. Q. What gases arise from these PUTREFYING substances ? A. Phosphuretted hydrogen from pu- trefying* animal substances : and Carburetted hydrogen, from decaying* vegetable matters. (See p. 262.) Q. How is the gas of the ignis fatuus IGNITED on bogs and meadows ? A. Impure phosphuretted hydrog*en bursts spontaneously into flame, whenever it mixes with air or pure oxygen g*as. Pure phosphuretted hydrogen will not ignite spontane- ously this spontaneous ignition is due to the presence c* IGNIS FATUUS. 267 a small quantity of the vapor of an exceedingly volatile li- quid-compound of phosphorus with hydrogen, which is occasionally produced with the gas itself. If phosphorus be boiled with milk of lime, and the beak of the retort be placed under water, bubbles of phosphuret- ted hydrogen will rise successively through the water, and (on reaching the surface) burst into flame. ^ Q. Why does an ignis faluus or Will oHhe Wisp FLY from us when we RUN to MEET it ? A. Because we produce a current of air in front of ourselves, (when we run towards the ignis fatuus) which drives the light gas forwards. Q. Why does an ignis fatuus run AFTEII us when we FLEE /raw it in a fright ? A. Because we produce a current of air in the way we run, which attracts the light gas in the same course; drawing it after us as we run away from it. Q. Is not a kind of Jack o* Lantern sometimes produced by an INSECT ? A. Yes ; swarms of luminous insects sometimes pass over a meadow, and produce an appearance similar to the ignis fatuus. Q. May not many GHOST stories have arisen from some ignis faluus lurking about church-yards ? A. Perhaps all the ghost stories (which deserve any credit at all) have arisen from the ignited gas of church- yards, lurking about the tombs ; to which fear has added its own creations. 268 WIND. WIND. CHAPTER XXIV. Q. What is WIND ? A. Wind is air in motion. Q. What PUTS the air in motion^ so as to pro- duce WIND? A. The principal causes are the variations of heat and cold, produced by the succession of day and night j and of the four seasons. Q. What effect has HEAT upon the air ? A. Heat rarejies the air and causes it to expand. Q. How do you KNOW that heat causes the air to EXPAND ? A. Thus, if a bladder half full of air (tied tight round the neck) be laid before a j^re, the air will expand by the heat, and fill the bladder. Q. What EFFECT is produced upon air by RAREFACTION ? A. It is made lighter and ascends through colder strata ; as a cork (put at the bottom of a basin of water) rises to the surface. Q. Prove that rarefied air ASCENDS. A. When a boy sets fire to the cotton or sponge of his balloon, the flame heats AIR. 269 the air ; which becomes so light, that it ascends, and carries the balloon with it. Q. What effect is produced upon AIR by COLD ? A. It is condensed, or squeezed into a smaller compass : in consequence of which, it becomes heavier, and descends towards the ground. Q. Prove that air is condensed by COLD. A. Lay a bladder half full of air before a fire, till it has become fully inflated; if it be now removed from the fire, the bladder will collapse again, be- cause the air condenses into its former bulk. Q. What is meant by the bladder " COLLAPS- ING ?" A. The skin becoming 1 wrinkled, shrivelled, and flabby ; because there is not sufficient air inside to Jill it. Q. How do you KNOW that CONDENSED air will DESCEND? A. Because afire balloon falls to the earth, so soon as the spirit in the cotton is burnt out, and the air of the balloon has become cold again. Q. Does the SUN HEAT the AIR as it does the EARTH ? A. No ; the air is not heated by the rays of the sun ; because air (like water) is a very bad conductor. 270 WIND. Q. How is the AIR HEATED 1 A. By convection, thus : The sun heats the earth, and the earth heats the air resting upon it ; the air thus heated rises, and is succeeded by other air, which is heated in a similar way ; till the whole volume is warmed by " convective cur- rents." Q. What is meant by "CONVECTIVE CURRENTS" of hot air ? A. Streams of air heated by the earth, which rise upwards, and carry heat with them. (See p. 226.) Q. Is the air in a ROOM in perpetual motion as the air ABROAD is ? A. Yes; there are always two cur- rents of air in the room we occupy; one of hot air flowing- out of the room, and another of cold air flowing- into the room. Q. How do you KNOW that there are these TWO currents of air in every occupied ROOM 1 A. If I hold a lighted candle near the crevice at the top of the door, the flame will be blown outward (towards the hall] ; but if I hold the candle at the bottom of the door, the flame will be blown inwards (into the room). N. B. This is not the case if a, fire be in the room. When a fire is lighted, an inward current is drawn through all the crevices. Q. Why would the flame be blown OUTWARDS CANDLE FLAME. 271 (towards the HALL), if a candle be held at the TOP of the door ? A. Because the air of the room being* heated, &c., ascends ; and (floating about the upper part of the room) some of it escapes through the crevice at the top of the door, producing* a current of air out- wards (into the hall), Q. Why would the flame be blown INWARDS (into the ROOM), if the ca?idle be held at the BOTTOM of the door ? A. Because a partial vacuum is made at the bottom of the room, as soon as the warm air of the room has ascended to the ceiling 1 , or made its escape from the room : and cold air from the hall rushes under the door, to supply the void. Q. What is meant by a "partial VACUUM be- ing made at the BOTTOM of the ROOM ?" A. A vacuum means a place from which the air has been taken: and a " partial vacuum " means a place from which a part of the air has been taken away. Thus, when the air on the floor ascends to the ceiling-, a partial vacuum is made on the floor. Q. And how is the VACUUM filled UP again ? A. It is filled up by colder air, which rushes (under the cfoor, and through the window crevices) into the room. 272 WIND. Q. Give me an ILLUSTRATION. A. If I dip a pail into a pond and fill it with water, a hole (or vacuum) is made in the pond as big as the pail ; but the moment I draw the pail out, the hole is filled up by the water around. Q. Show how this illustration APPLIES. A. The heated air, which ascends from the bottom of a room, is as much taken away as the water in the pail ; and (as the void was instantly supplied by other water in the pond) so the void of air is supplied by the air around. Q. What is the CAUSE of WIND ? A. The sun heats the earth, and the earth heats the air resting 1 upon it ; as the warm air ascends, the void is filled up by a rush of cold air to the place ; and this rush of air we call WIND. Q. Does the WIND ALWAYS blow ? A. Yes ; there is always some motion in the air ; but the violence of the motion is perpetually varying 1 . Q. Does the rotation of the earth upon its axis affect the motion of the air ? A. Yes, in two ways. 1st As the earth moves round its axis, the thin moveable air is left somewhat behind; and, therefore, seems (to a stationary" VERTICAL RAYS. 273 object) to be blowing- in the opposite di- rection to the earth's motion : and 2dly As the earth revolves, different portions of its surface are continually passing- under the vertical rays of the sun. Q. When are the rays of the sun called " VER- TICAL RAYS ?" A. When the sun is in a direct line above any place, his rays are said to be " vertical " to that place. Q. Illustrate the manner in which the earth's surface passes under the vertical sun. A. Suppose the brass meridian of a globe to represent the vertical rays of the sun ; as you turn the g-lobe round, different parts of it will pass under the brass rim, in constant succession. Q. Why is it NOON-DAY to the place over which the SUN is VERTICAL ? A. Because the sun is half-way be- tween rising* and setting- to that place. Q. Show how this ROTATION of the earth affects the AIR. A. If we suppose the brass meridian to be the vertical sun, the whole column of air beneath will be heated by the noon- day rays ; that part which the sun has left, will become gradually colder and colder ; and that part to which the sun 12* 274 WIND. is approaching, will grow constantly warmer and ivarmer. Q. Then there are THRE qualities of air about this spot ? A. Yes ; the air over the place, which has passed the meridian, is cooling; the air under the vertical sun is the hottest ; and the air, which is over the place about to pass under the meridian, is increasing in heat. See fig. on next page. The column A (which the sun has passed) is cooling B is under the vertical sun ; and -C is increasing in heat. Q. How does this VARIETY in the HEAT of AIR produce WIND ? A. The air always seeks to preserve .much as one-tenth part more or less. -Q. What USE is a BAROMETER to sailors ? A. It warns them to regulate their before squalls come on. Q. How can a BAROMETER warn SAILORS to regulate their SHIPS ? A. As it indicates when wind, rain, and storm are at hand, the sailor can make his ship trim before they overtake him. Q. Are there any RULES which can be depended on? BAROMETER. 299 A. Yes ; there are ten special, rules to direct us how to know the changes of weather, by marking the mercury of a barometer. Q. Mention the IST SPECIAL RULE with regard to the barometer ? A. The barometer is highest of all during a long frost; and it generally rises with a north-west wind. Q. Why is the barometer HIGHEST of all during a long FROST ? A. Because a long frost condenses the air very greatly ; and the move condensed air is, the greater is its pressure on the mercury of a barometer. Q. Why does the barometer generally RISE with NORTH WEST winds ? A. Because NORTH-WEST winds make the air both cold and dry : and being both condensed, and without vapor, it is much heavier, Q. Mention the 2o SPECIAL RULE with regard to the barometer ? A. The barometer is lowest of all during a thaw, which follows a long frost : and it generally falls with SOUTH or EAST wind. Q. Why does the barometer fall LOWEST of all ,g> Here the width between the trees A and B will seem to be as great as the line AB : 354 LIGHT. But the width between the trees C and D will seem to be no more than EF. Q. In a long, straight STREET, WHY do the houses on the opposite sides seem to APPROACH NEARER together as they are more DISTANT ? A. Because the more distant the houses are the more acute will be the an- gle which any opposite two make with our eye. Thus in the last figure, If A and B were two houses at the 'top of the street, the street would seem to be as wide as the line AB : And if C and D were two houses at the bottom of the street, the street there would seem to be no wider than EF. Q. In an AVENUE, WHY do the TREES seem to be SMALLER as their distance increases ? A. Because the farther tke trees are off, the more acute will be the angle made by their perpendicular height with our eye. - Here the first tree AB will appear the height of the line AB ; but the last tree CD will appear only as high as the line EF. Q. In a long, straight STREET, WHY do the houses seem to be SMALLER and smaller, the FURTHER they are OFF ? A. Because the further any house is off, the more acute will be the angle made by its perpendicular height with our eye. PERPENDICULAR HEIGHT. 355 Thus in the last figure, If AB be a house at the top of the street, its perpendic- ular height will be that of the line AB. If CD be a house at the bottom of the street, its perpen- dicular height will appear to be that of EF. Q. Why does a man on the TOP of a MOUN- TAIN, or church spire, seem to be no BIGGER than a CROW? A. Because the angle made in our eye by the perpendicular height of the man at that distance, is no bigger than that made by a crow close by. Let AB be a man on a distant mountain, or spire, and CD a crow close by : The man will appear only as high as the line CD, which is the height of the crow. Q. Why does the MOON appear to us so much LARGER than the STARS, though, in fact, it is a great deal SMALLER ? A. Because the moon is very much nearer to us than any of the stars. 356 LIGHT. Let AB represent a fixed star, and CD the moon. AB, though much the larger body, will appear no big- ger than EF ; whereas the moon (CD) will appear as large as the line CD to the spectator G. The moon is 240.000 miles from the earth, not quite a quarter of a million of miles. The nearest fixed stars are 20.000,000,000,000. (i. e., 20 billions.) If a ball went 500 miles an hour, it would reach the moon in twenty days : but it would not reach the nearest fixed star in 4,500,000 years. Had it begun, therefore, when Adam was created, it would be no further on its journey than a coach (which has to go from the Land's End, Cornwall, to the most northern parts of Scotland) after it has passed about three-quarters of a mile. Q. Why does the MOON (which is a sphere) APPEAR to be a FLAT surface ? A. Because it is so far off that we cannot distinguish any difference be- tween the length of the rays issuing* from the edge and those which issue from the centre. The rays AD and CD appear to be no longer than the ray BD ; but if all the rays seem of the same length, the part B will not seem to be nearer to us than A and C ; and therefore ABC will look like a flat or straight line. The rays AD and CD are 240.000 miles long. The ray BD is 238,910 miles long. Q. Why do the SUN and STARS (which are spheres) appear to be FLAT surfaces ? A. Because they are such an im- mense way off, that we can discern no difference of length between the rays which issue from the edge and those TELESCOPES. 357 which issue from the centre of these bo- dies. The rays AD and CD appear no longer than BD ; and as B appears to be no nearer than A or C, therefore A, B, C, must all seem equally distant; and ABC will seem a fiat or straight line. (See last figure, p. 356.) Q. Why does DISTANCE make an object IN- VISIBLE ? A. Because no visible perpendicular can be inserted between the lines which form the angle ; or because the lines actually cross before they meet our eye. ??r Here the tree AD would not be visible to the spectator C, even if he were to approach as far as B ; because no visi- ble perpendicular can be inserted between the two lines AC, DC, at the point B, and after B the lines would cross : Therefore, the tree would be invisible from C, till after the spectator had passed B. Q. Why do TELESCOPES enable us to SEE objects INVISIBLE to the naked eye? A. Because they gather tog-ether more luminous rays from obscure objects than the eye can ; and form a bright image of them in the tube of the tele- scope where they are magnified. As many times as the dimensions of the object-glass ex- ceed the dimensions of the pupil of the eye, so many times the penetrating powers of the telescope will exceed that of the naked eye. 358 LIGHT. Q. When a SHIP (out at sea) is approaching the shore, why do we SEE the small MASTS before we see the bulky HULL ? A. Because the earth is round ; and the curve of the sea hides the hull from our eyes after the tall masts have become visible. Here, only that part of the ship above the line AG can be seen by the spectator A ; the rest of the ship is hidden by the swell of the curve DE. Q. What is meant by REFRACTION ? A. Bending a ray of light, as it passes from one medium to another. Q. How is a ray of light BENT, as it passes from one medium to another ? A. When a ray of light passes into a denser medium it is bent towards the per- pendicular. When it passes into a rarer medium it is bent from the perpendicular. RIVERS. 359 Suppose DE to be a perpendicular line. If AB (a ray of light) enters the water, it will be bent towards the perpendicular to C. If (on the other hand) CB (a ray of light) emerges from the water, it would be bent away from the perpen- dicular towards A. Q. Why does a SPOON (in a glass of water) always appear BENT ? A. Because the light (reflected from the spoon) is refracted as it emerges from the water. See Fig. 2, p. 358. The spoon ABC will appear bent, like ABD. Q. Why does a river always appear more shallow than it really is ? A. Because the light of the bottom of the river is REFRACTED, as it emerges out of the water. See Fig. 2, p. 358. The bottom of the river will appear elevated like the bowl of the spoon D. Q. How much deeper is a river than it seems to be? A. About one-third. If, therefore, a river seems only 4 feet deep, it is really 6 feet deep. The exact apparent depth would be 4J. To find the real depth, multiply by 4 and divide by 3 thus 4X4-*-3 =6, real depth. N. B. Many boys get out of their depth in bathing, in consequence of this deception. Remember, a river is al- ways one-third deeper than it appears to be : thus, if a river seems to be 4 feet deep, it is in reality nearly 6 feet deep, and so on. Q. Why do fishes seem to be nearer the surface of a river than they really are ? 360 LIGHT. A. Because the rays of light from the fish are refracted, as they emerge from the eye : and (as a bent stick is not so far from end to end, as a straight one) so the fishes appear nearer to our eye than they really are. See Fig. 2, p. 358. Q. Why are some persons NEAR-SIGHTED ? A. Because the COR'NEA of their eye is so prominent, that the image of distant objects is formed before it reaches the RET'INA ; and, therefore, is not distinctly seen. Q. What is meant by the " COR'NEA of the EYE?" A. All the outside of the visible part of the eye-ball. The curve ABC is called the COR NBA. If this curve be too prominen (or convex), the eye is near-sighted If too flat (or concave), the eye far-sighted. Q. What is meant by the " RET'INA of th EYE?" A. The net-work, which lines th back of the eye, is called the ret'ina. The net-work ABC is called the ret ina, and the projecting part DBF is calle the cor'nea. ))D N. B. This net-work is composed o a spreading out of the fibres of th nerve of vision. SPECTACLES. 361 Q. What sort of GLASSES do NEAR-SIGHTED persons wear ? A. If the cornea be too convex (or projecting 1 ), the person must wear double concave glasses, to counteract it. Q. What is meant by "DOUBLE CONCAVE GLASSES?" A. Glasses hollowed-in on both sides. , \ / The figure A is double concave, or concave on 1 \ both sides. Q. Where is the IMAGE of objects formed^ if the cornea be too convex ? A. If the cor'nea be too convex ', the image of a distant object is formed in the vitreous humors of the eye, and not on the retina. Thus the image is formed at DB, and not on ABC (the retina). Q. What is the use of DOUBLE CONVEX SPEC TACLE glasses ? A. To cast the image farther back f in order that it may be thrown upon the ret'ina and become visible. Q. Why are OLD people FAR-SIGHTED ? A. Because the humors of their eyes are dried up by age ; in consequence of 16 362 LIGHT. which, the COR'NEA sinks in, or becomes flattened. Q. Why does the FLATTENING of the COR'NEA prevent persons seeing objects which are NEAR ? A. Because the cor'nea is too flat, and the image of near objects is not completely formed, when their rays reach the RET'INA ; in consequence of which, the image is imperfect and confused. The perfect image is made at DE j and not on ABC (the retina). Q. What sort of GLASSES do OLD people WEAR ? A. As their cor'nea is not sufficiently convex, they must use double convex glasses, to enable them to see objects near at hand. Q. What sort of glasses are " DOUBLE CONVEX SPECTACLE-GLASSES ?" A. Glasses which curve outwards on both sides. The figure A is double convex, or convex on both sides. Q. What is the use of DOUBLE CONVEX spec- tacle-glasses ? A. To shorten the focus of the eye. SIGHT. 363 and bring- the image of distant objects upon the ret'ina. Q. Why do NEAR-SIGHTED persons bring objects CLOSE to the eye, in order to SEE THEM ? A. Because the distance between the front and back of the eye is so great, that the image of distant objects is form- ed in front of the ret'ina ; but when ob- jects are brought near to the eye, their image is thrown further back, and made to fall on the ret'ina. Q. Why do OLD people HOLD objects FAR OFF, in order to see them better ? A. Because the distance between the front and back of tJieir eyes is not great enough : when, however, objects are held further off, it compensates for this defect ; and a perfect image is form- ed on the ret'ina. Q. Why are HAWKS able to see such an IM- MENSE way off? A. Because they have a muscle in the eye which enables them to flatten their cornea, by drawing back the crys- talline lens. See p. 362. This muscle is called the Marsnpium. Q. Why can HAWKS see objects within half-a7i- inch of their eye^ as well as those a long way off? A. Because their eyes are furnished with a flexible bony rim, which throws 364 LIGHT. the cor'nea foncard, and makes the hawk near-sighted. See p. 360. Q. Into how many PARTS may a RAY of LIGHT be DIVIDED ? A. Into three parts : BLUE, YELLOW, and RED. N. B. These three colors, by combination, make seven. 1. RED. 2. ORANGE (or red and yellow). 3. YELLOW. 4. GREEN (or yellow and blue). 5. BLUE. 6. INDIGO (a shade of blue) ; and 7. VIOLET (or blue and red). Q. How is it known, that a ray of light con- sists of several different colors ? A. Because, if a ray of light be cast upon a triangular piece of glass (called a prism), it will be distinctly divided into seven colors: 1. Red; 2. Orange; 3._ Yellow ; 4. Green ; 5.. Blue ; 6. Indigo ; and 7. Violet. Q. Why does a PRISM DIVIDE a ray of light into VARIOUS COLORS? A. Because all these colors have different refractive susceptibilities. Red is refracted least, and blue the most ; therefore, the blue color of the ray will be bent to the top of the prism, and the red will remain at the bottom. B Here the ray AB (received on a prism at B), would RAINBOW. 365 have the blue part bent up to C ; the yellow part to D ; and the red part no further than E. Q. What is meant by the REFRACTION of a ray ? A. Bending it from its straight line. Thus the ray AB of the last figure is refracted at B into three courses, C, D, and E. Q. What is the cause of a RAINBOW ? A. When the clouds opposite the sun are very dark, and rain is still falling from them, the rays of the bright sun are divided by the rain-drops^ as they would be by a prism. Let A, B, and C, be three drops of rain ; SA, SB, and SO, three rays of the sun. SA is divided into three col- ors ; the blue and yellow are bent above the eye D, and the red enters it. The ray SB is divided into the three colors ; the blue is bent above the eye, and the red falls below the eye D ; but the yellow enters it. The ray SC is also divided into the three colors. The blue (which is bent most) enters the eye ; and the other 366 LIGHT. two fall below it. Thus the eye sees the blue of C, and of all drops in the position of C ; the yellow of B, and of all drops in the position of B ; and the red of A, and of all drops in the position of A ; and thus it sees a rainbow. Q. Does EVERY person see the SAME colors from the SAME DROPS ? A. No ; no two persons see the same rainbow. To another spectator, the rays from SB might be red instead of yellow ; the ray from SC yellow ; and the blue might be reflected from some drop below C. To a third person, the red may issue from a drop above A, and then A would reflect the yellow, and B the blue, and so on. Q. Why are there often TWO RAINBOWS at one and the same time ? A. In one rainbow we see the rays of the sun entering the rain-drops at the top, and reflected to the eye from the bottom. In the other rainbow, we see the rays of the sun entering the rain-drops at the bottom, and reflected to the top, whence they reach the eye. Here the ray SA (of the primary rainbow) strikes the drop at A is" refracted or bent to B is then reflected COLORS OF THE RAINBOW. 367 to C, where it is refracted again, and reaches the eye of the spectator. (See below.) Here the ray of SB (of the secondary rainbow) strikes the drop at B is refracted to A is then reflected to C is again reflected to D, when it is again refracted or bent, till it reaches the eye of the spectator. Q. Why are the COLORS of the SECOND bow all REVERSED ? A. Because in one bow we see the rays, which enter at the top of the rain- drops, refracted from the bottom : But in the other bow we see the rays which enter at the bottom of the rain- drops (after two reflections), refracted from the top. See figure on next page. Here ABC represent three drops of rain in the SECON- DARY (or upper) RAINBOW. The least refracted line is RED, and BLUE the most. So the RED (or least refracted rays) of all the drops in the position of A the YELLOW of those in the position of B and the BLUE (or the most refracted rays) of the lowest drops, all meet the eye D, and form a rainbow to the spectator. The reason why the primary bow exhibits the stronger colors is this because the colors are seen after one refleo 368 LIGHT. ijj jif S 1 lion and two refractions ; but the colors of the secondary (or upper) rainbow, undergo tioo reflections and two re- fractions. (See figure on p. 365.) Here also the least refracted ray is RED, and the most refracted BLUE (as in the former case) ; but the position of each is reversed. Q. Why does a SOAP BUBBLE exhibit such a VARIETY of COLORS? A. Because the thickness of the film through which the rays pass, is con- stantly varying*. Q. How does the THICKNESS of the FILM affect the COLOR of the soap bubble ? A. Because different degrees of thick- ness in the film produce different powers of refraction ; and, therefore, as the thick- ness of the film varies, different colors reach the eye. Q. Why is a SOAP BUBBLE so constantly CHANGING its THICKNESS 1 RAYS. 369 A. Because the water runs down from the top to the bottom of the bubble, till the crown becomes so thin as to burst. Q. Why are the late EVENING CLOUDS RED ? A. Because RED rays, being- the least refrangible, are the last to disappear. Suppose PA to be a red ray, PB yellow, and PC blue if the earth turns in the direction of CBD, it is quite man- ifest that a spectator standing at C or B (carried round in the same direction), would lose sight of the red rays (A) last of all. Q. Why are the early MORNING clouds RED ? A. Because RED rays being the least refrangible are theirs/ to appear. See last figure. We must suppose the sun to be on the left side of the diagram or (what will answer the same purpose) suppose the earth to be turning in the direction of BAP, then it is quite clear, that every person on the earth's surface will pass under A (the red rays) before he passes under B or C, (and therefore his early morning rays will be red.) Q. Why are the EDGES of CLOUDS more LUMIN- ws than their CENTRES ? 16* 370 LIGHT. A. Because the body of vapor \s thin" nest at the edges of the clouds. Q. What is the cause of morning and evening TWILIGHT ? A. When the sun is below the hori- zon, the rays which strike upon the atmosphere or clouds are bent down towards the earth, and produce a little light called twilight. See figure on p. 369. Here the rays of PA will give somt light. Q. WHY is a ray of LIGHT composed of VARI- OUS COLORS ? A. To vary the color of different objects. If solar light were of one color only, all objects would appear of that one color, or else black. Q. Some things are of ONE COLOR, and some 0f ANOTHER.. JElxplain tlie cause of this. A. As every ray of light is composed of all the colors of the rainbow ; some things reflect one of these colors and some another. Q. WHY do some things reflect ONE COLOR, and some ANOTHER ? A. Because the surface of things is so differently constructed, both physically and chemically. Q. Why is a ROSE RED ? A. Because the surface of a rose ab- COLOR. 371 sorbs the blue and yellow rays of light, and reflects only the red. Q. Why is a VIOLET BLTJE ? A. Because the surface of the violet absorbs the red and yellow rays of the sun, and rejlects the blue only. Q. Why is a PRIMROSE YELLOW 1 A. Because the surface of the prim- rose absorbs the blue and red rays of solar light, and rejlects the yellow. The chief reason why some rays are absorbed and other? reflected is, because the corpuscles which compose the col- ored substance vary in magnitude : thus, for example, if the diameter of a corpuscle of equal density with air be 21 millionth of an inch, it will reflect purple; if, on the other hand, it be 29 millionth of an inch, it will reflect red, and so on. Q. Why are some things BLACK ? A. Because they absorb all the rays of light and reflect none. Q. Why are some things WHITE ? A. Because they absorb none of the rays of light, but reflect them all. Q. Why are COALS BLACK ? A. Because they absorb all the rays of the sun which impinge upon them. Q. Why are FROTH, and SPRAY, and many CLOUDS, WHITE ? A. Because they consist of an infinite number of small bubbles or vesicles, which act like prisms in dividing the 372 LIGHT. rays of light; which, by uniting again before they meet the eye, give the ap- pearance of white. Q. Why are SNOW, SUGAR, and SALT WHITE? A. (See page 312.) N. B. The combination of all colors makes WHITE. Q. Why are the LEAVES of plants GREEN ? A. Because a peculiar chemical prin- ciple, called chlo'rophyll, is formed within their cells ; which has the property of absorbing the red rays and of reflecting the blue and yellow ; which mixture produces green. Chlorophyll (^Awpoy v\\ov, a green leaf) is the green matter of vegetable substances. Pronounce klo-ro-fill. Q. Why are leaves a LIGHT green in SPRING ? A. Because the chlo'rophyll is not fully formed. Q. Why do leaves turn BROWN in AUTUMN ? A. Because the chlo'rophyll under- goes decay, and is not replaced as it is in spring. Q. Why are plants a PALE YELLOW, when kept in the DARK ? A. Because chlo'rophyll can be form- ed only by the agency of the surfs rays. Q. Why are POTATOES YELLOW ? A. Because they are grown under- ground ; and, therefore, can form no chlo'rophyll in their tubers. TRANSPARENCY. 373 Q. Why are potatoes which grow EXPOSED to the air arid light GREEN ? A. Because chlo'rophyll is formed in them under the influence of the sun's light. Q. Why are SOME things TRANSPARENT ? A. Because every part between the two surfaces has a uniform refracting power, or (in other words) has in every place the same density. And, therefore, the rays of light emerge on the opposite side. Q. Why are some things NOT TRANSPARENT? A. Because the particles which com- pose them are separated by minute pores or spaces, which have a different density from the particles themselves. Therefore, the rays of light are reflected and refracted too often to emerge. Q. Why are DRY PAPER and calico (which are OPAQUE) made transparent by being OILED? A. Because the pores are filled by the oil, which has nearly the same den- sity as the substance of the paper itself by which means a uniform density is effected, and the substance becomes transparent. Q. Why is GLASS (which is transparent) ren- dered OPAQUE by being ground or pulverized ? A. Because the whole substance 374 LIGHT. from surface to surface is no longer of one uniform density. Q. Why are SOME things SHINING, and others DULL? A. Because some thing's reflect rays, and are bright ; but others absorb them. Q. Why do DESERTS DAZT.UE. from sunshine? A. Because each grain of sand reflects the rays of the sun like a mirror. Q. If you move a stick (burnt at one end) pretty briskly AROUND, it seems to make a CIRCLE OF FIRE WHY is this ? A. Because the eye retains the image of any bright object, after the object itself is withdrawn ; and as the spark of the stick returns before the image has faded from the eye, it seems to form a complete circle. Q. If separate figures (as a man and a horse) be drawn on separate sides of a card, and the card TWISTED quickly^ the man will seem to be seated on the horse WHY is this? A. Because the image of the horse remains upon the eye till the man ap- pears. The Thaumatrope is constructed on this principle. Q. Why do the STARS TWINKLE ? A. Because the inequalities and un- dulations in the atmosphere produce un- equal refractions of light; and these ACCIDENTAL COLORS. 375 unequal refractions cause the twinkling or irregular brilliancy of the stars. Q. If we look at a RED-HOT FIRE for a few minutes, WHY does every thing seem TINGED with a BLUISH GREEN Color ? A. Because bluish green is the " ACCIDENTAL COLOR " of red ; and if we fix our eye upon any color whatsoever, we see every object tinged with its acci- dental color when we turn aside. The accidental color is the color which would be required to be added, in order to make up white light. See p. 360. Q. Why does the eye perceive the ACCIDENTAL COLOR when the fundamental one is removed? A. Because the nerve of the eye has become tired of the one, but still remains fresh for the perception of the other. Q. If we wear BLUE GLASSES, why does every thing appear tinged with ORANGE when we take them of? A. Because orange is the " accidental color " of blue ; and if we look through blue glasses, we shall see its " accidental color " when we lay our glasses aside. Q. If we look at the SUN for a few moments, every thing seems tinged with a VIOLET color Wnt is Ms ? A. Because violet is the " accidental color " of yellow ; ,and as the sun is yd- low, we shall see its " accidental color " violet when we turn from gazing at it. 376 LIGHT. Q. Does not the DARK SHADOW (which seems to hang over every thing after we turn from looking at the su?i) arise from our eyes being DAZZLED ? A. Partly so : the pupil of the eye is very much contracted by the brilliant light of the sun, and does not adjust itself im- mediately to the feebler light of terres- trial objects ; but, independent of this, the " ACCIDENTAL COLOR " of the sun be- ing dark violet, would tend to throw a shadow upon all things. (See p. 340.) Q. Why is BLACK glass for spectacles the BEST for wear in this respect ? A. Because white is the accidental color of black ; and if we wear black glasses, every thing will appear in ivhite light when we take them off. Q. Why does every thing seem shadowed with a BLACK MIST when we take off our common SPECTA- CLES ? A. Because the glasses are white ; and black being its " accidental color/ 7 every thing appears in a black shade when we lay our glasses down. The accidental color of red is bluish green. " of orange " blue. " of violet " yellow. " of black " white. And the converse of this is true : The accidental color of bluish green is red. " of blue ' " orange. " of yellow " violet. " " " of white "black. SOUND. 377 (The law of an accidental color is this The accidental color is always half the spectrum. Thus, if we take half the length of the spectrum by a pair of compasses, and fix one leg in any color, the other leg will hit upon its ac- cidental color.) N. B. The spectrum means the seven colors (red, or- ange, yellow, green, blue, indigo, and violet), divided into seven equal bands, and placed side by side in the order just mentioned. SOUND. CHAPTER XXX. Q. How is SOUND produced ? A. The vibration of some sonorous substance produces motion in the air, called SOUND-WAVES, which strike upon the drum of tlie ear and give the sensa- tion of sound. Q. What are MUSICAL SOUNDS ? A. Regular and uniform successions of vibrations. Q. How FAST does SOUND TRAVEL ? A. About 13 miles in a minute, or 1142 feet in a second of time. Light would go 480 times round the whole earth, while sound is going its 13 miles. Q. Why are SOME things SONOE.OUS and others NOT? A. The sonorous quality of any sub- stance depends upon its hardness and elasticity. 378 SOUND. Q. Why are COPPER ana IRON SONOROUS and. not LEAD ? A. Copper and iron are hard and clastic; but as lead is neither hard nor yet elastic, it is not sonorous. Q. Of what is BELL-METAL made ? A. Of copper and tin in the following* proportions : In every 5 pounds of bell- metal there should be 1 pound of tin, and 4 pounds of copper. Q. Why is this mixture of tin and copper used for BELL-METAL? A. Because it is much harder and more elastic than any of the pure metals. Q. Why is the SOUND of a bell STOPPED by TOUCHING the bell with our finger ? A. Because the weight of our finger stops t/ie vibrations of the bell ; and as soon as the bell ceases to vibrat,e, it ceases to make sound-waves in the air. Q. Why does a SPLIT BELL make a hoarse, dis- agreeable sound ? A. Because the split of the bell causes a double vibration : And as the sound-waves clash and jar, they impede each other's motion, and produce dis- cordant sounds. Q. Why does a FIDDLE-STRING give a musical sound ? A. Because the bow drawn across the string causes it to vibrate ; and this MUSICAL SOUNDS. 379 vibration of the string sets in motion the sound-waves of the air, arid produces musical notes. Q. Why does a DRUM sound ? A. Because the parchment head of the drum vibrates from the blow of the drum-stick, and sets in motion the sound- waves of the air. Q. Why do MUSICAL GLASSES give sounds 1 A. Because the glasses vibrate as soon as they are struck, and set in motion the sound-waves of the air. Q. Why do FLUTES, <^c., produce musical sounds ? A. Because the breath of the per- former causes the air in the flute to vi- brate ; and this vibration sets in motion the sound-waves of the air. Q. Why do PIANO-FORTES produce musical sounds ? A. Because each key of the piano (being struck with the finger) lifts up a little hammer which knocks against a string ; and the vibration thus produced sets in motion the sound-waves of the air. Q. Why are SOME notes BASS, and SCWl TRE- BLE ? A. Because slow vibrations produce bass or deep sounds ; but quick vibrations produce shrill or treble ones. 380 SOUND. Q. Why is an instrument FLAT when tht STRINGS are UNSTRUNG ? A. Because the vibrations are too slow ; in consequence of which, the sounds produced are not shrill or stiarp enough. Q. Why can per sons, living a mile or two from a town, HEAR the BELLS of the town churches SOME- TIMES and not at OTHERS ? A. Because fogs, rain, and snow, obstruct the passage of sound ; but when the air is cold and clear, sound is propa- gated more easily. Q. WHY can we NOT hear sounds (as those of distant church bells) in RAINY weather so well as in FINE weather? A. Because the falling rain interferes with the undulations of the sound-waves, and breaks them up. Q. Why can we not hear sounds (as those of distant church bells) in SNOWY weather so well as in FINE weather ? A. Because the falling snow inter- feres with the undulations of the sound- leaves, and stops their progress. Q. Why can we HEAR distant clocks MOST dis- tinctly in CLEAR COLD iveather ? A. Because the air is of more uniform density, and there are fewer currents of air of unequal temperature to interrupt the sound-waves. DISTANT SOUNDS. 381 Besides,, dense air can propagate sound-waves more readily than rarer air. Q. Why can persons (near the POLES) hear the, VOICES of men in conversation for a MILE distant in winter-time ? A. Because the air is very cold, clear, and still; in consequence of which, there are but few currents of air of unequal temperature to interrupt the sound- waves. Captain Ross heard the voices of his men in conversa- tion a mile and a half from the spot where they stood. Q. Why are not SOUNDS (such as those of dis- tant church bells) heard so distinctly on a HOT DAY as in FROSTY weather ? A. 1st Because the density of the air is less uniform in very hot weather : 2dly It is more rarefied ; and, conse- quently, a worse conductor of sound : and 3dly It is more liable to accidental currents, which impede the progress of sound. Q. Why can we not hear SOUNDS (such as those of distant clocks) so distinctly in a thick MIST or HAZE as in a CLEAR night ? A. Because the air is not of uniform density when it is laden with mist ; in consequence of which, the sound-waves are obstructed in their progress. Q. Why do we hear SOUNDS better by NIGHT than by DAY ? A. 1st Because night air is of more 382 SOUND. uniform density and less liable to acd~ denial currents : and 2dly Night is more still from the suspension of business and hum of men. Q. Why is the air of more UNIFORM DENSITY by NIGHT than it is by day ? A. Because it is less liable to acci- dental currents ; inasmuch as the breez- es (created by the action of the sun's rays) generally cease during- the night. Q. How should PARTITION WALLS be made, to PREVENT the voices in adjoining rooms from being HEARD ? A. The space between the laths should be filled with shavings or saw- dust; and then no sound would ever pass from one room to another. Q. Why would SHAVINGS, or saw-dust, PRE- VENT the transmission of sound from room to room ? A. Because there would be several different media for the sound to pass through: 1st the air; 2dly the laths and paper ; 3dly the saw-dust or sha- vings ; 4thly lath and paper again ; 5thly the air again : And every change of medium diminishes the strength of the sound-waves. Q. Why can DEAF people hear through an EAR-TRUMPET? A. Because the ear-trumpet restrains ECHO. 383 the spread of the voice and limits the dia- meter of the sound-waves : in consequence of which, their strength is increased. Q. Why are MOUNTAINS NOISELESS andyuiet ? A. Because the air of mountains is very rarejied; and, as the air becomes rarefied, sound becomes less intense. Q. How do you know that the RARITY of air DIMINISHES the intensity of SOUND ? A. If a bell be rung in the receiver of an air-pump, the sound becomes fainter and fainter as the air is exhaust- ed ; till at last it is almost inaudible. Q. What is the cause of ECHO ? A. Whenever a sound-wave strikes against any obstacle (such as a wall or hill), it is reflected (or thrown back) ; and this reflected sound is called an ECHO. The same laws govern echo as light. (See p. 338.) Q. What places are most famous for ECHO ? A. Caverns, grottoes, and ruined ab- beys ; the areas of halls ; the windings of long passages ; the aisles of cathedral churches ; mountains and icebergs. Q. Why are caverns, grottoes, and ruins , FA- MOUSjfor ECHOES ? A. 1st Because the sound-waves cannot pass beyond the cavern or grotto, and, therefore, must flow back : and 2dly The return-waves (being entan- 384 SOUND. gled by the cavern) are detained for a short time, and come deliberately to the ear. Q. Why are halls, winding passages^ and ca- thedral aisles, FAMOUS for ECHOES? A. Because the sound-waves cannot flow freely forward; but perpetually strike against the winding walls, and are beaten back. Q. Why are MOUNTAINS and icebergs FAMOUS for ECHOES ? A. Because they present a barrier to the sound-waves, which they cannot pass, and are sufficiently elastic to throw them back. Q. Why do not the WALLS of a ROOM or church produce ECHO ? A. Because sound travels with such velocity that the echo is blended with the original sound; and the two produce but one impression on the ear. Sound travels 13 miles in a minute; and no echo is heard, unless the surface (against which the sound strikes) is 65 feet from the place whence the sound originally pro- ceeded. x Q. Why do very LARGE buildings (as cathe- drals) often REVERBERATE the voice of the speaker ? A. Because the walls are so far off from the speaker that the echo does not get back in time to blend with the origi- ECHO. 385 nal sound ; and, therefore, each is heard separately. Q. Why do SOME echoes repeat only ONE sylla- ble? A. Because the echoing* body is very near. The further the echoing- body is off, the more sound it will reflect: If, therefore, it be very near, it will repeat but one syllable. Q. Why does an ECHO sometimes repeat TWO or more syllables ? A. Because the echoing* body is far off ; and, therefore, there is time for one reflection to pass away before another reaches the ear. N. B. All the syllables must be uttered, before the echo of the first syllable reaches the ear If, therefore, a per- son repeats 7 syllables in 2 seconds of time, and hears them all echoed, the reflecting object is 1142 feet distant; (because sound travels 1142 feet in a second, and the words take one second to go to the reflecting- object, and one second to return.) Q. Why are TWO or more ECHOES sometimes heard ? A. Because separate reverberating* surfaces receive the sound and reflect it in succession. 17 miles above Glasgow (Scotland) near a mansion called Rosneath, is a very remarkable echo. If a trumpeter plays a tune and stops, the echo will begin the same tune and repeat it all accurately : as soon as this echo has ceased, another will echo the same tune in a lower tone; and after the second echo has ceased, a third will succeed with equal fidelity, though in a much feebler tone. 17 386 WINDOWS. At the Lake of Kilkarney in IRELAND, there is an echo which plays an excellent " second " to any simple tune played on a bugle. Q. Why do WINDOWS RATTLE when CARTS pass by a house ? A. 1st Because glass is sonorous ; and the air communicates its vibrations to the glass, which echoes the same sound : and 2dly The window-frame being sha- ken, contributes to the noise. Window frames are shaken, 1. By sound-waves im- pinging against them ; 2. By a vibratory motion com- municated to them by the walls of the house. PART III. MISCELLANEOUS. *** This part is little else than a collection of various questions propounded by different correspondents, pupils, and private friends, set down, without regard to arrange- ment, in the order in which they were proposed ; together with a few leading questions to break up some which would have been otherwise too intricate, and others which naturally arose out of the subject under consideration. Q. Why do the BUBBLES in a CUP of TEA range round the SIDES of the CUP ? A. Because the cup attracts them. Q. Why do all the LITTLE BUBBLES tend to- wards the LARGE ones ? A. Because the large bubbles (being 1 the superior masses) attract them. Q. Why do the BUBBLES of a CUP OF TEA FOLLOW a TEA-SPOON ? A. Because the tea-spoon attracts them. Q. Why are the SIDES of a pond covered with LEAVES, while the MIDDLE of the pond is quite CLEAR ? 388 CAPILLARY ATTRACTION. A. Because the shore attracts the leaves to itself. * Q. Why do all fruits, fyc., (when severed from the tree.) FALL to the EARTH ? A. Because the earth attracts them. Q. Why do persons who water PLANTS very often 'pour the ivatcr into the SAUCER, and not aver the PLANTS ? A. Because the water in the saucer is drawn up by the mould (through the hole at the bottom of the flower-pot) and is transferred to the stem and leaves of the plant by CAPILLARY ATTRACTION. (Seep. 75.) Q. Why is vegetation on the MARGIN of a RIV- ER more LUXURIANT than in an open FIELD ? A. Because the porous earth on the bank draws up water to the roots of the plants by CAPILLARY ATTRACTION. Q. Why is a LUMP of SUGAR (left at the bottom of a cup) so LONG in MELTING? A. Because (as it melts) it makes the tea above it heavier ; and (so long- as it remains at the bottom) is surrounded by tea fully saturated with sugar ; in con- sequence of which, the same portions of liquid will hold no more sugar in solution. Q. Why does the LUMP of SUGAR MELT more QUICKLY when STIRRED ABOUT 1 A. Because fresli portions of unsatw- EFFLUVIA. 389 rated tea come in contact with the lump, and soon dissolve it. Q. Why does a PIECE OP SUGAR (held in a spoon at the TOP of our tea) melt very RAPIDLY? A. Because, as the tea becomes sweetened, it descends to the bottom of the cup by its own gravity ; and fresh por- tions of unsweetened tea are brought constantly into contact with the sugar till the lump is entirely dissolved. Q. How can a SICK ROOM be kept FREE from unhealthy EFFLUVIA? A. By sprinkling it with vinegar boiled with myrrh or camphor. Q. Why does LIME destroy the offensive smells Of BINS, SEWERS, C Water freezes at 32, but salt and water will not freeze unless the thermometer sinks below 7. Q. Why does HOT WATER FREEZE more quickly than cold ? A. Because there is a slight agitation 432 OIL FREEZING WATER. on the surface of hot water, which pro- motes congelation ; by assisting- the crystals to change their positions, till they take up that which is most favorable to their solidification. Other causes may have a minor influence, as for example : In hot water, the particles are subdivided into smaller globules by the heat, and offer less resistance to the action of cold than larger ones. 2dly. The air has been expelled from the water by the process of boiling hence the In- dians always used boiled water in their ice-pits. N. B. Air must be expelled from water before it can be frozen. Q. Why will a little OIL on the surface of water prevent its FREEZING ? A. Because oil is a bad conductor, and prevents heat from leaving* the wa- ter. The surface of water never freezes, till the whole mass is cooled down to 42. Q. Why does water in a very EXPOSED place freeze more rapidly than that which is under cover, or in places less exposed ? A. 1st Because evaporation goes on more rapidly, when water is exposed ; and carries away heat from the general mass: and 2dly Any covering will radiate heat into the water 'below, and prevent the mass from cooling down to 42. "Radiate heat" means, to send heat out in rays. Q. Why are GLUE, GUM, STARCH, and PASTE, adhesive ? RAIL-WAY TRAIN, ETC. 433 A. Because the water used with them rapidly evaporates, and leaves them solid. They lose their adhesiveness when dissolved in water ; and, therefore, must always be suffered to become dry, before they will hold with tenacity. Q. Why does a rail-way TRAIN make more NOISE, when It passes over a BRIDGE or MEADOW, than when it runs over SOLID GROUND ? A. Because the bridge (or meadow) is very elastic, and vibrates much more from the weight of the train, than the solid earth ; in consequence of which, it produces more definite sound-waves. The bridge acts as a sounding-board ; and the water or earth, below the bridge, repeats the sound. Q. Why does MILK BOIL more QUICKLY than water ? A. Because less steam is carried off from the thick liquid (milk), than from the thin liquid (water) ; in consequence of which, the heat of the whole mass rises more quickly. Q. Why will MILK BURN very easily, when boiled, while water will not do so ? A. 1st Because milk contains solid organic substances, capable of burning ; which water does not : and 2dly Because the heat of the fire coagulates the albu'men of the milk 19 jfe* 434 WAX STEEL, ETC. which falls to the bottom, and adheres to the boiler. Albu'men is a substance resembling the white of an egg-. Q. Why does WAX become SOFT, before it turns LIQUID ? A. Because it absorbs heat sufficient to loosen the contact of its particles, before it has absorbed sufficient to liquefy the mass. Q. If you heat STEEL RED HOT in the fire, and then plunge it suddenly into cold water, it becomes HARD and BRITTLE j why is this ? A. Because the sudden chill violently expels the latent heat, which would have settled in the steel, had it been al- lowed to cool slowly. The malleability and toughness of metals depend upon their power of absorbing heat. Q. Why are the ICE-PITS of India lined with straw and coarse blanketing stopped up with STRAW at the mouth, instead of a door and THATCHED on the roof, instead of being covered with slates or tiles ? A. Because straw and coarse blank- eting, being* very bad conductors indeed, prevent the external heat from getting to the ice-pits to dissolve the ice. Q. How do the natives of INDIA provide them- selves with ICE, when the temperature is much higher than the freezing point ? A. They make a hole in the earth about 2 feet deep, and 30 feet square : They cover the bottom of this hole, to WARM COUNTRIES, ETC. 435 the depth of a foot, with the stalks of Indian corn or sugar-canes : On this bed they place fleet unglazed earthern pans about an inch and a quar- ter deep, and pour into them (at sun-set) soft water, which has been boiled and suffered to cool. At sun-rise the water is found to be frozen, and is thrown into the ice-pit. The reason of this is : The vessels being porous, part of the water evaporates through the pans, and reduces the heat of the water sufficient for congelation. Q. Why is it customary, in very HOT COUN- TRIES, to sit in rooms separated by CURTAINS, instead of walls ; and to keep these curtains constantly sprinkled with WATER 1 A. Because curtains are bad conduct- ors of heat ; and the rapid evaporation of water reduces the temperature of the room 10 or 15 degrees. Q. Why is it impossible to WRITE on GREASY PAPER ? A. Because grease has no affinity for water or ink, and, therefore, will not mix with it. Q. Why is rain said to " bring down the cold ?" A. Because the change in the atmos- phere, which causes rain ,to fall, sets free latent heat, and makes it sensible. 436 TURPENTINE, ETC. Frost is broken up by the rains ; and the sharp, piercing wind, being laden with vapor, is much mitigated. Q. Why does TURPENTINE take out GREASE spots from doth ? A. Because it dissolves fixed oils. The fixed oils are all greasy oils, such as sperm oil, olivo oil, &/C. The other sort of oils, called volatile or essential oils, are those used in perfumery, &c. Q. Why does OXALIC acid take out INK spots ? A. Because it dissolves the tannate of iron, of which the black portion of the ink consists. " Tannate of iron " is tannic acid combined with iron. Tannic acid is the acid of tan, or oak bark. Q. When COPPER is exposed to moist air, it is incrusted with a green coating , called VERDIGRIS ; why is this ? A. Because the oxygen of the moist air combines with the copper, and forms what is called a hydrate of the carbonate of the protoxide of copper. " Protoxide " (wpwroj-oxide, the lowest or first state of oxidation) : The protoxide of copper is a combination of one portion of oxygen, and one of copper. Hydrate (from the Greek word v<$wp, water) is a compound containing water ; but in all hydrates, the substance forms so inti- mate a union with water, as to solidify it, and render it a component part. A " hydrate of the carbonate of copper," is a compound of water, carbonic acid, and copper; and " A hydrate of the carbonate of the protoxide of copper," is copper in its lowest state of oxidation, in which carbonic acid and water is so united, as to form a solid. Q. Why does ZINC TARNISH id the air ? A. Because the oxygen of the moist air combines with the zinc, and forms an oxide of zinc. SALT SILVER. 437 An " oxide of zinc " is oxygen in union with zinc. Q. WJiy does SALT turn silver BLACK ? A. Because it precipitates an oxide of silver on the surface of the spoon, the color of which is black. " Marking ink" is made of soda and the nitrate of sil- ver ; the black mark being due to the oxide, precipitated on the cloth. Q. How can the BLACK stain of SILVER, made by salt) be REMOVED ? A. By washing* the silver in harts- horn, or common ammonia ; by which means, the oxide will be re-dissolved and the blackness entirely disappear. Q. Why does WAXING cotton or thread make it STRONGER ? A. Because it cements the loose fila- ments to the cord ; and makes the strands of the thread more compact. The " filaments of the cotton," are the loose fibres hang- ing about it. The " strands " are the twists or single yarns twisted into a thread. Sewing cotton contains two, three, and occasionally more than three strands. Q. The cromb of walking-sticks is made by BOILING the end of the stick, and then bending it into an arch; why is a STICK made FLEXIBLE by BOILING? A. Wood contains many substances soluble in hot water, as starch, sug*ar, glim, &c., and several other substances which are softened by it : as, therefore, several substances are dissolved, and 438 MANURE GUANO. others softened by boiling water, the stick is rendered flexible. Cell'ular fibre and woody matter, when boiled in water, become soft and gelatinous. Q. Explain how MANURE makes LAND FER- TILE. A. As plants extract a certain amount of salts from the soil, which are entirely removed at harvest, it is obvious that the soil will become gradually impoverished, unless these matters are restored ; this restoration is made by manuring the soil. Q. Why is GUANO valuable as a MANURE ? A. Because it contains nitrogen and ammonia, both of which are essential to plants. Q. What is the use of LIME, MARL, $c. : as MANURE ? A. 1st They decompose vegetable substances : and 2dly They liberate the- alkalies in union with the silica of the soil. Silica (pronounce SilM-cah), from the Latin word Silex, flint one of the most common substances on the earth- containing the following varieties white chuckystone- violet amethysts red quartz yellow cairngorum Brazil pebbles for spectacle glasses rock crystal chalcedony agate blood-stonescornelian flint, &c. Q. Why do you see the reflection of TWO can- dles, or two fires, in a looking-glass or window-pane, though there is only ONE candle or fire in the room ? A. Because each surface of the look- SKY BLUE LIGHT. 439 ing-glass or window-pane makes a reflec- tion. N. B. In order to see these two reflections, you must not stand directly before the glass, but a little on" one side. Q. Why is the SKY BLUE on a fine day, and, not red or orange ? A. Because the momentum of red and orange rays (being 1 greater than that of blue) causes them to penetrate beyond the clouds ; but the blue rays are stop- ped on their passage, and reflected. Q. Why is it LIGHT when the heavens are covered with thick CLOUDS 1 A. Because the multiplied reflections of the sun in the atmosphere are suffi- cient to give light upon the earth, even when thick clouds are passing 1 over the disc of the sun. Q. Why are putrefying FISH LUMINOUS ? p. 266. A. Because the carbon of the fish, uniting* with oxygen, forms carbonic acid ; and the phosphoric acid of the fish (be- ing thus deprived of oxygen) is con- verted into phosphorus : as soon as this is the case, the phosphorus begins to unite with the oxygen of the air, and becomes luminous. Carbonic acid is a compound of carbon and oxygen. Phosphoric acid is a compound of phosphorus and oxy- gen. If you take the oxygen away from phosphoric acid, the residue, of course, is phosphorus. 440 SEA LUMINOUS. The luminousness spoken of is due to the slow combus- tion of the phosphorus, while it is uniting with the oxygen of the air. Q. Why is the SEA often LUMINOUS in summer- time ? p. 266. A. Because the small jelly fish decay ; the phosphoric acid which they contain (being* deprived of oxygen) is converted into phosphorus, unites with the oxygen of the air, and becomes luminous. Q. What causes the disease commonly called the itch ? A. It is produced by an insect called the " itch insect," which burrows in the skin, and is greatly encouraged by filth. Sulphur, corrosive sublimate, &c., will destroy the insect, and cure the disease. Corrosive sublimate is made of 200 parts of mercury with 72 of chlorine. It is plain to see how the disease is contagious. Q. Why does the use of SALT BEEF produce scurvy ? A. Because the soluble salts are re- moved from the beef by brine : in con- sequence of which, it cannot restore to the human system those salts, which are essential to preserve the blood in a healthy state. Q. Why is LIME-JUICE a perfect CURE for SCURVY ? A. Because it contains the very salts, VEGETABLES WOOD. 441 removed from the beef by the action of brine. Namdy alkaline phosphate and sulphate, chloride and phosphate of lime. "Alkaline phosphates" are such as these phosphate of soda, phosphate of potash, and phosphate of magnesia; i. e. soda, potash, or magnesia, in combination with phos- phoric acid. " Sulphate of lime," a compound of sulphuric acid and lime. " Chloride of lime," a compound of chlorine gas and lime. " Phosphate of lime," a compound of phosphoric acid and lime. Q. Iftniy does the use of VEGETABLES generally PREVENT SCURVY ? A. Because they contain the soluble salts removed from the beef by brine ; which being 1 restored by the vegetables, preserve the blood in a healthy state. Why does WOOD DECAY ? A. Because the oxygen of the air unites with the carbon and hydrogen of the wood, and forms carbonic acid and water. Q. When WINE is spilt on a TABLE-CLOTH, napkin, or handkerchief, how can the STAIN be REMOVED ? A. By dipping* it in a weak solution of chlorine. ^ Bleaching powder is only lime impregnated with chlo- rine. Q. When WINE is spilt on a tabk-cloth, 19* 442 INFECTIOUS DISEASES. why do persons generally cover the part immediately with SALT ? A. Because salt is a compound of chlorine and sodium ; and the chlorine of the salts acts as a bleaching powder. Q. When INFECTIOUS DISEASES prevail, how can the contagious matter be removed from bed-rooms, hospitals, houses, fyc. ? A. By using- a solution of chlorine, or of sulphurous acid ; which will not only remove the contagious matter, but also the offensive smell of a sick room. Q. What is an excellent remedy against RATS and MICE ? A. Sulphuretted hydrogen. All that is necessary is to introduce the beak of a retort into a rat-hole, while sulphuretted hydrogen is being given off. It will destroy the rats and make the hole unfit for others to frequent. Sulphuretted hydrogen is made thus. Put into a retort or glass bottle a quantity of sulphuret of iron, prepared by heating a rod of iron red hot ; bring it in contact with a roll of sulphur allow the sulphuret of iron formed to drop into water; pour over it a small portion of water, and then add an equal quantity of sulphuric acid ; sulphuretted hydrogen will be given off most copiously. Q. Why does GUNPOWDER EXPLODE? A. Because of the instantaneous pro- duction and expansion of carbonic acid, sulphurous acid, and nitrogen. Gunpowder consists of 76 parts of nitre, 13 charcoal, and 11 sulphur. SHADE, ETC. 443 Q. An object in the SHADE is not so bright and apparent, as an object in the sun ; why is it not? A. Because objects in the shade are seen by reflected light reflected, i. e. the light is twice reflected : and, as the rays of light are always absorbed in some measure by every substance on which they fall, therefore, some light is lost ; 1st Before the second reflection is made, and 2cily In the object that makes the second reflection : Part of the rays are absorbed, and part are scattered in all directions by irregular reflections ; so that rarely more than half is reflected, even from the most polished rnetals. Q. Why are GREEN GOOSEBERRIES, CURRANTS, <^c., HARD ; and RIPE ones SOFT ? A. Because they contain an infinite number of little cells, with thick walls ; these become thinner from day to day, as the fruit ripens, until they break ; when the fruit becomes soft. Q. Why is PORTER much DARKER than ale or beer ? A. Because the malt of which porter is made is dried at a higher temperature and slightly charred. Small beer is a weak wort fermented, and contains 1 per cent, of alcohol. Ale is a stronger wort, and contains 7 per cent, of alcohol. Porter contains 4 per cent, of alcohol. Brown stout contains 6| per cent, of alcohol. Burton ale contains 8i per cent, of alcohol. 444 WINE HAMS, ETC. Q. 7f WINE or BEER be imperfectly corked, why does it rapidly turn sour ? A. Because air gets into the liquor ; and the oxygen of the air, combining with the alcohol of the liquor, produces ace'tic acid. 1 alcohol and 4 oxygen, become 1 hydrous acetic acid and 2 water. Q. Why does pyroligneous acid PRESERVE MEAT and remove its taint ? (Pyroligneous acid, is vinegar extracted from wood.) A. Because it contains a small quan- tity of creasote, which is a great preser- vative of all animal substances. Creasote, pronounce Cre-a-sote (from two Greek words, *f)aj, flesh, and ?.) It is mado thus; 100 parts of nitrate of bary'tes well dried, 9 of sul- phur, 7 of chlorate of potash, 2 charcoal, 4 sulphuret of antimony, all well dried and mixed in a mortar. Q. How is the RED FIRE of fireworks pro- duced ? A. By the nitrate ofstroritian, which burns with a red hue. (Stron'tian is an earth, so called from a village in Argyleshire of the same name, where it was first dis- covered.) It is made thus ; 100 parts of dry nitrate of stron'tian, mixed with 12 parts of chlorate of potash, 30 sulphur, 10 sulphuret of antimony, and 3 charcoal, all dried and rubbed carefully in a mortar. N. B. Unless care be taken the mixture will explode. 452 POISONS. ANTIDOTES FOR POISONS. Q. If a person has swallowed a MINERAL poison, suck as ARSENIC, what is the best antidote ? A. A tea-spoonful of sulphur or half a tea-spoonful of pearl-ash or a ivine- glass of soap-suds : After a little while, give a table-spoon- ful of antimonial wine, and plenty of warm water. Q. If a person has swallowed a VEGETABLE poison, such as SULPHURIC ACID, AQUA-FORTIS, or OXALIC ACID, what is the best antidote ? A. Lime, chalk, pearl-ash, magnesia, carbonate of soda, or soap-suds, and a plenty of warm water ; a dessert-spoonful of antimonial wine should be added, if at hand. The chalk or lime, &c., unites with the oxalic acid, and forms oxalate of lime, which is quite innocuous. Q. If LAUDANUM has been taken, what is the best antidote ? A. A tea-spoonful of common mus- tard ; and to keep the patient walking. Q. If CHLORINE has been taken, what is the best antidote ? A. Ammonia, which will neutralize the ill effects of chlorine. Q. If IODINE has been taken in too large a quantity ', what is the best antidote ? ANTIDOTES FOR POISON. 453 A. Iron-filings are the best antidote for an over-dose of iodine. Q. If a person feels faint from the fumes of PRUSSIC ACID, what is the best antidote ? A. To smell the vapors of strong am- monia^ which will soon restore con- sciousness. Q. How can WARTS, <^c., be REMOVED 1 A. By rubbing 1 them with common solid potash. Q. What is the best antidote to VERDIGRIS ? A. Sugar, or white of egg. Q. What is the best antidote to CORROSIVE SUBLIMATE ? A. White of egg 1 , or milk ; which will combine with them, and neutralize their poisonous qualities. Q. If a person has eaten too much FRUIT, what is the best antidote ? A. Lime, chalk, pearl-ash, magnesia, carbonate of soda, or soap-suds. Great relief is often found by eating the hard part of cheese (cut close to the rind) thickly covered with com- mon salt ; the reason is plain. GLOSSARY. Acetic Acid. called Citric " " Nitric " " Oxalic " " Sulphuric " Sulph. of Alumina " Lime Iron Copper " Magnesia " Soda " Zinc Nitrate of Potash " Prussiate of Potash Tartrate of Potash Acetate of Copper Muriate of Soda Oxide of Lead Carb. of Ammonia top. Acetate of Lead " Distilled Vinegar. Juise of Lemons. Aqua Fortis. Salt of Lemons. Oil of Vitriol. Alum. Plaster of Paris. Green Copperas. Blue Vitriol. Epsom Salts. Glauber Salts. White Vitriol. Saltpetre. Lunar Caustic. Prussian Blue. Rochelle Salt. Verdigris. Table Salt. Goulard. Smelling Salts. Chalk, Marble, &c, Sugar of Lead. SUBLIMATES are chemical preparations, the basis of which is quicksilver. In CORROSIVE SUBLIMATES, the quicksilver is extinguished either by vitriol, potter's clay, or some other ingredient. SUBLIMATION is a similar process to distillation; only solids (such as metals) are employed, instead of liquids. Thus the fine blue used by painters is a sublimate, and made thus : Take 2 parts of quicksilver, 3 flower of brim- stone, 8 sal ammoniac; and (having ground them) put them with the quicksilver into a glass retort, luted at the bottom: place the retort in a sand-heat; and (when the moisture is given off) you will have a splendid blue sub- limate for painting. N. B. It may be profitable to remind the pupil that when the termination " ous" is used, it implies that the substance has less oxygen than when the termination " io " is added thus, sulphurous acid contains less oxygen than sulphuric acid, &c. INDEX, 1 Page Page Air dries linen . 151 not conductors 173 elements of 219 not reflectors. 179 radiators 182 expanded by heat 102, 268 full of smells 143 ABSORPTION of HEAT . . 173 not conduction 173 healthful 242 of light 339 heated 202 226 270 ACCIDENTAL COLORS .. 375 Acetate of copper . .. 454 not by the sun 181, 226 hotter when the sun shines 227 Acid of drinks 248 in a room . . 270 of fermentation . . 248 Acids dissolve ice 32 Activity affected by cold 90 inflammable, see hy- drogen. needful for fire 53 non-conductor 19 " by heat 92 of cities unhealthy Aerated water 247 223 242 Aeronauts feel pain 138, 229 Age affects power of of the country heal- thy 223 242 walking 392 on land colder than Aged people far-sighted on water 207 361, 363 AIR 219 268 on land cold at night 211 preserved normal 2^4 always in motion .. 270 ascends when hot . . 268 bad conductor 15, 165, 217 bad radiator 202 purified by lightning 32 radiates no heat 202 rarefied is noiseless. 139 rarefied bad conduc- cold 166 tor of sound 383 colder than blood . . 169 composed of two " by a crowd.. 239 rusts iron . . .' 231 gases . . 30 219 still before a temDest 139 condensed by cold . . 269 cooled by convection 202 cooled by rain 150 use of oxygen in 220 varies in tempera- ture 313 cools hot iron 227 Air-gun 101 density diminished by rain 315 Air-pump freezes water 335 Aisles famous for echoes 384 descends when cold 269 double current in a colder than galleries 229 Alcohol ! . . 249 room 270 from sugar .. ,. 250 (For Index to Part III, see page 485.) 456 INDEX. Page Alcohol, boiling point of 115 Am 107 Pag* Balloons 138 inflated 107 bottled 248 rise (sec aeronauts.) 107 Balls of fire . . . . 14 froth of . . 248 " increased by heat 107, 248 Alkali 50 Balusters wet 200 Banisters, see balusters. Barley malted 251 Anemometer 294 affected by cold . . 300 frost.. 299 " heat .. 302 " thaw.. 300 " wind.. 299 rules for its rise and fall . . 299, 308 sudden change in 302 use o f 298 Anglers hate a magpie 145 Angle of incidence .... 344 of reflection 344 Anhydrous sugar 250 Animal fluids conduc- tors 20 ANIMAL HEAT . . 83 258 caused by com- bustion 85 Animal and vegetable varies most in win- ter 306 " least in summer 306 when highest. . . 306 " lowest ... 307 Barren land collects no dew 194 Animals for bode rain . . 141 Ants love honey-dew . . 204 Appetite, see hunger. Apples full of air 104 roasted 103 Bass notes in music . . 379 Bass preserves flowers from frost 191 soft 104 April 'showers 288 Bathing, danger of 359 " with ether for in- flammation .... 148 Argand lamps 82 Ascent in balloons pain- ful 138 Beakers broken by hot Ashes soften water .... 322 Asses bray in wet wea- ther 141 Beasts covered with hair 165 Beds damp .... 149 Atmosphere (see air) . . 284 Aurora borealis 136 BEER, fermentation of 249 flat 255 colored 136 froth increased by bottling 248 white . . . 136 a prognostic .. 136 Autumn tints . . . 372 froth increased by heat 107, 248 Avenues . 353 stale 255 Azote, see nitrogen. Bales catch fire spon- taneously . . 60 soured by lightning 32 not old beer .... 32 spoiled, if the vent- peer be left out 255 INDEX. 457 Page. Beer, yeast added to make it work 251 (see vent peg*) Beer-vats dangerous . . 245 Bells heard at a distance 380 cracked, sound harsh 378 ringing dangerous . . 23 silenced by a touch 378 Bell-metal 378 Bellows 55 Bible explained.. 164, 195 311 Birds covered with fea- thers.., 165 Bins purified by lime, 259 BLACK 371 cloth warm 174 eyes 179 glass for spectacles 376 hat turns red at the sea-side 321 hole of Calcutta . . 240 Black kid gloves 176 lead 232 prevents rust . . 232 mist 137 skin 178 tea-pot 184 used by cotters 184 set on a hob to draw 184 will never blister '. . 178 Blacksmiths strike fire by nails 95 Bladders inflated by heat 102, 269 BLAZE, blue 50 green 50 yellow 50 between the bars of a grate.. .. 50 Blazing coals burn quickly 44 Blood 222, 238 purple 222 Blood, red 222, Blowers Blowing cools broth, tea &c 168, Blue sky spectacles sublimate Body, fuel of warm 84, Boiler, see saucepan. BOILING " WATER bubbles . . furrof makes it flat . . is in a ferment kept hot rattles runs over swells one pot will not boil in another retarded by a spoon " by salt, sugar without touching the boiler Boiling point Boots hot when dusty Bottled ale, &c. Brackish water unfit for railway engines .... Bracing weather Bread heavy made with yeast Breath exhaled inhaled visible in winter Breathing described . . difficult on a moun- tain previous to a storm BREEZE at watering evening . land ... Page 223 70 293 454 126 375 454 86 258 213 111 236 257 214 187 112 111 110 113 113 114 114 115 181 248 237 140 258 257 223 221 200 224 229 229 291 290 291 20 458 INDEX. Page Breeze, morning 289 of islands 291 sea 290, 291 speed of 293 (see wind.) Bricks for cold feet ... 162 Brick stoves 163 Bricklayers cannot work in a frost 334 cover work with straw 334 Bright day exhilarating 137 Brilliancy 339 Brine retards boiling. . 114 tested 335 Britain cloudy 123 Broth cooled by breath 227 by convection 228 by stirring . . 228 Bubbles in tea 387 of boiling water 111 Bulk for bulk 107 Burns cured.. 148 Buint stick twisted .. 374 Burning glasses 10 Calcutta, black hole of 240 Calcareous 225 Caloric 9 Cambric handkerchiefs cool 172 Camphor antiseptic . . . 389 CANDLES 74 burn 74 cotton, not easily blown out 78 easily blown out 65, 77 extinguished 79 by a pin 81 breath 77 paper 79 flame blown out . . 55 hot 76 hollow 76 pointed 77 Page Candle-flame purple be- low 76 tends upwards 77 yellow 76 Candles, gas of 84, 262 held at a door 270, 271 hottest above the flame 78 give light 75 make glass damp 78 need snuffing 80 Palmer's 80 prevent our seeing abroad 352 reflected in a win- dow 352 rekindle quickly . . 55 rush, easily go out 78 shadow cast by . . 352 smoke of 81 . spirt 146 suddenly introduced give pain 339 wax, need no snuf- fing 80 Candlestick rags catch fire spontaneously.. 61 Cannon balls hot 101 boring 100 Canvass flower-awning 191 Capillary attraction 75,172 388 vessels 83 Captain Ross 381 Capuchin 317 Carbon 40, 74 in the blood .... 238 Carbonate of ammonia 454 of lime .... 454 CARBONIC ACID GAS 43, 238 absorbed by leaves 225 accumulation of, prevented 246 deleterious 238 detected 239 INDEX. 459 Page Carbonic acid gas dis- sipated by red heat 246 in human bodies . . 84 ofthesoil 225 sources of 245 CARBURETTED HYDROGEN GAS 263 Carpenters' tools hot.. 99 Carpets warm 157 Carriage in a storm . . 26 wheels catch fire 98 windows misty . 197 Casks charred 72 Cart-grease 98 Cathedral aisles famous for echoes 384 CATS in wet weather . . 140 prowl by night . . . 342 rub their ears 142 see in the dark . . . 341 wink before a fire 342 Cattle low in wet wea- ther 140 in a storm 25 Caustic lime 390 lunar 454 Caverns famed for ech- oes 383 Ceilings sooty 71 Cellars cold in summer 231 warm in winter 231 Cerebellum 391 Cerebrum 391 Chalk 454 Champagne acid 248 CHARCOAL 72 bad conductor 156 fire very hot 72 " deleterious 245 purifies water 72 removes taint 72 Charring bread 73 casks 72 wood 73 Page CHEMICAL ACTION 3(i Chestnuts crack when roasted 102 not if slit 103 Chimney pots 70 flues long 64 '' short 64 raised above a house ... 64, 68 CHIMNEYS SMOKE 63 if a room be too close 63 remedy 64 in old farm houses 69 valleys ,, . 67 in wind 70. 108 if too long.. 64| 108 Chimneys smoke if too short 64 remedy 66 large 69 remedy 70 when the draught is slack 65, 69 when the door is on the same side . . 68 remedy 68 when they need re- pairing 69 sweeping 69 when two fires are in one room .... 67 remedy 67 China broken by hot water 120 Chlorophyll 372 Choke damp 244, 261 Church bells heard at a distance 139, 380 congregation drowsy 241 Churchyards smell offen- sively 265 Chyle 221 Chyme 221 460' INDEX. Page Cinders iron 48 Clouds distance from lighter than coals 48 the earth 123 soon heated 48 will not blaze.... 52 edges most lumi- nous 369 Cirro-cumulus clouds 130 electrical . . . 1^5 Cirro-stratus clouds . . . 130 Cirrus clouds . 128 fall in rainy wea- ther .. 315 Citizens pale 222 fantastic . ... 131 float. 1*?3 City air unhealthy 242 Clay for furnaces . 163 gather round hills 132 height of T' 1 - >4 Clean kettles 174 Cleanliness connected with the dietary 93 highest in a fine day 115 increased by wind 166 intermediate .... 130 Clear day overcast 285 lio-ht 115 fire burns slowly 44 lowest 124 nights exhilarat- morning red 1 27 ing 137 motion of . . 1^7 Clocks heard at a dis- nimbus 131 tance 380 rain indicated bv 131 Close rooms unhealthy 240 red 1 26 369 Cloth collects but little d ew 143 round mountain- tops 182 Clothes slather damp in simple ... .... 1^8 summer 195 size of 1*^4 wet . . . .., . . 148 s stratus 129 Clothing for workmen 154 loose warmest 165 sun-set 133 thickness of 1 24 promotes warmth 164 want of makes dirt how ascertained 124 thunder 15 agreeable . . . 93 vary in shape .... 1 "?4 Cloudiest countries 1^3 in color . 1^7 where most abund- absorbed bv wind 125 ant . 1 23 cause of 122 where least 123 cirro-cumulus 130 use of 1 32 cirro-stratus .... 1 30 velocity of 294 classes of 128 color of 124, 126 compound .... 130 wind affects them 123, 125 yellow 133, 134 cumulo-stratus 131 cumulus . . 129 Cloudy night warm ... 189 differ from fog 122, 209 dissinated . . . 125. 133 . oppressive ... 137 Coale:as.. . 74,262 INDEX. Page Coal mines explode . . . 262 Coals black 371 blazing 44 frotesque figures of 46 >r fuel . . . . 48 smoke 45 Coffee, spontaneous combustion of 61 Coke 59 for fuel 48 spontaneous com- bustion of 60 COLD WEATHER affects the barometer 299, 306 makes us love fafc 89 activity 90 out of doors 293 promotes hunger . 90 Colder some things than others 155 Colds from wet clothes 149 Collapsing ... 104, 269 Color of clouds 123 electricity ... 35 Colors 364 accidental 375 dark, warm .... 175 light, cold 175 vary 370 Combining not mixing 31 COMBUSTION (see fire).. 83 animal 84 cause of 43 chemistry of ... 40, 43 from fermentation 60 elements of 43 heat of 40 increased by wind 55 in the veins 84 produces light 51 spontaneous . .'. 60, 81 COMMUNICATION OF HE\T 155 Compound clouds 130 Page COMPRESSION 100 differs from con- densation 99 CONDENSATION 99 Condensed air 269 CONDUCTION 55 not absorption.. 173 CONDUCTORS, best 56 worst 56 animal fluids ... 20 not absorbers . . 1 73 of lightning .... 27 dangerous 29 CONVECTION 202. 213 Convective currents 226. 270 cool broth 228 iron 227 Cooking vessels with wooden handles 156 Cooper applies hot hoops 117 Copper for conductors 28 sonorous 378 tarnishes 233 Cork driven out by heat 106 Cornea 360 Corns ache in wet wea- ther 230 Corpse cold 94 Corrosive sublimates.. 396 Cotton bales catch fire 60 spontaneously. 60 candles hard to bio v out 78 handkerchiefs hot 172 oiled transparent . 373 Countries most cloudy 123 least cloudy 123 Country air salubrious 223, 242 Countrymen enjoy health 242 ruddy 222 Cowls 67, 108 462 INDEX. Crowds dangerous in a Page Dark colors warm .... 175 radiate heat 183 produce drowsiness 242 Davy Sir H 263 head-ache . 239 vitiate air 239 Day - light produces hunger . . 88 unhealthy 240 mitigates cold 88 Crucibles made of pla- tinum 236 Dead bodies cold 94 smell 266 Culinary vessels 186 taller than livino- 390 have wooden handles 156 Deafness 382 should be sooty .... 186 Decanting liquor .... 256 Cultivation promotes dew 194 spirting.. 266 Decomposition . . . 246 warmth ... 152 Cumulo-stratus clouds 131 Deep water freezes slowly 331 Cumulus clouds 129 Depression of spirits . . 137 Cup in a pie 116 Descent in a diving bell use of 117 painful 138 why full of juice 117 Currents of air 270 Deserts hot and dazzling 374 Detonating powder . . . 101 DEW 188 Damp balusters 200 cause of 209 beds ... . 149 deleterious 203 clothes 195 differs from rain . . 209 house 200 distilled after a hot Dandelion forebodes dav 202 rain 142 especially if the DANGER IN A STORM ... 18 in attics and cellars 22 a crowd 25 wind be westerly 202 in fine nights only 189 distilled unequally 192 in a theatre, &c... 25 before a fire 25 in open places 190 in valleys and hollows 191 near a tree 19 in a river 19 cultivated lands . . 194 flocks and herds are grass 194 exposed to .... 25 hair 201 those who bar hat 201 shutters . . 24 leaves &c 193 those who drive fast 21 none beneath a tree. 190 a flower awning 191 lean against a wall 23 or carriage. 26 who ring bells 19, 23 run .. .21 a hedge or wall 191 none in a cloudy night 189 in a windy night 191 especially if easterly .... 201 INDEX. 463 Page Dew, none on stones, 191 cloth, deserts. grav- el metal rocks Page Dry wood burns best . . 106 snaps about.. 106 Driest months 307 'wool ' ' 194 Dew-drops round 205 flattened 205 Duck dry in water .... 206 noisy before rain 141 roll on. cabbasres 205 Dullness 339,371 K roses 206 Dunghills hot 258 Digestion .... . . 90 Dinner covers ... .... 187 Dirt warm 93 Ear trumpets 382 Distant bells heard 380 clocks . . . 381 EARTH, bad conductor. 170 cool in summer. . . 170 objects appear small 354 sight 361 363 cools after sun-set 189 in a fine night 189 spectacles for 362 Distance makes things cracks by frost ... 332 crumbles in spring 333 warm in winter. . . 170 warmer than air Divers suffer pain 138 230 by day 189 Diving bell 138 Earth-fog 204 Doors swell and shrink 143 Dogs uneasy in wet weather 140 Earthen tea-pots 184 set on a hob to draw 184 Eat more in cold wea- Dou2"h fermented 257 ther 90 set before a fire to rise 258 - Double concave glasses 361 less in warm wea- ther 90 convex fflasses 362 Echo .... 383 Down warm 165 Echoes, two or more . . 385 Draining lands promote remarkable . . 385 EFFECTS OF HEAT 101 DRAUGHT at a door .... 294 EFFERVESCENCE 247 key-hole. 294 window . . 294 slack 65 23 soon subsides 257 Effervescing draughts. 247 Egg, component parts of 254 Dreams 390 discolors silver spoons 254 Driving in a storm new-laid cold 167 stale warm 167 Drops of rain roll on dust 206 " smells offensively 254 tests brine 335 Drowned men restored 99 tested 167 Drowsiness at church . . 242 Drums 379 Egypt not cloudy 123 ELECTRICITY affects the Dry toast for invalids. 73 wood for kindling 49 clouds .... 125, 127 excited by friction 34 4G4 INDEX. Electricity felt at the elbow joints 34 hot 84 Page Eyes affected by sud- den light ". 339 affected by the sun 375 black 179 of clouds 11, 127 cornea of 360 positive and nega- retina of 360 tive 22 two use of 343 resinous and vitre- ous 11 23 " see single. . .. 343 source of heat .... 11 Electric telegraph .... 36 Face soon scorched ... 182 Fanning 167 293 Elements of air 40 Far sight 361 363 of fuel 40 spectacles for . . 362 Emetic tartar 45 i Farm-houses smoke . . 69 Epsom salts . . .... 454 Fat men swim best . . 337 Esquimaux love blubber 91 Equatorial current. . . . 278 ETHPR 51 Fat pleasant in winter 89 not in summer 91 Feathers warm 165 boilin " point of . 115 Feelin- 392 used for freezing . . 335 " inflammation, scalds burns, 148 Feet cold before a fire. 57 wet dangerous .... 148 differs from pu- European skin white . . 178 EVAPORATION 147 trefaction 252 of dough 257 freezes .... 335 of sea 276 produces corn- EVENING CLOUDS. . .126, 133 grey 135 requires water. . 155 Fender and fire-irons red 126 133 370 cold 173 yellow . 133, 234 Evergreens frost-bitten 212 Ewers broken by frost. 325 EXPANSION by HEAT 101, 117 Explosion of roasted chestnuts . . 102 Fiddle-strings musical 378 snap from wet 316 Fine weather braces . . 140 indications of 134 Finger feels cold when wet 148 of gunpowder 103 FlRF 39 of mines 263 air needful for .... 63 Extinguishers 79 bellows use of ... 55 made of paper 79 Eves adapt themselves black and red .... 44 to light 340 not in frost 62 affected by blue fflasses 375 affected bv fire-lip-ht 374 charcoal .. 72 INDEX. 465 Page Fire, charcoal danger- ous 245 Pag Fishes ascend and dive 338 seem nearer than clear . . 44 53 they are .... 359 damp .. 261 cold 93 differs from animal heat 85 FLAME of a CANDLE ... 75 described 76 dull, cause of 65 effect upon v " the blown out easily. . 77 eyes 341 374 extinguished . 57 hot 75 by water 57 106 fiercest in winter 53 hottest above .... 78 out of doors . 54 pointed 77 gas generated by 84 grotesque figures purple and yellow 76 in .... 46 Flame of a fire between heat of 258 the bars of a grate 50 how increased 53 63 blue 50 hot 44 kindled at the bot- Flame yellow 5O 1 tom 47 Flannel warm 93- lighted with paper i and wood 46 used for foot- warm- ers 93 ' li^ht dazzles .... 340 Flash sec li, cf 'fitfi'i r ti cr light variable .... 52 Flat beer &c 256 luminous 50 melts metal ... . 121 Flavor discerned by the mottled . 45 taste . 392 out of doors 45 poker draws up . . 56 Flax burns spontane- radiates heat .... 182 Flint and steel strike red hot 44 330 fire 96 reflected on win- dows 352 Flocks dangerous in storms . . ... 26 spotted . , 45 FLOWING WATFR freezes sun dulls it 53 slowly 329 thaw dulls it 55 makes rough ice . . 330 wind intenses it . 55 oscillates 324- See combustion. pure 324 Pire-irons cold 161, 174 hot 174 Flower awnings arrest dew 190 rust ... 231 purifv air . . 232 *' most in win- ter 232 Flowers sme!l sweetest at night and " prevented . 232 2 before ram 144 0* 466 INDEX. Page Flowers forebode rain 142 Flues 64 blacked 183 long, good for draught 66 short, bad " 65 See chimney. Flutes 379 Fly poison 390 Foam, white 371 FOGS 208 arrest sound 381 cause of 123 differ from cloud 122, 209 mist 209 dispersed by wind 210 dispersed by sun 209 frozen 212 in autumn 209 ";iacrease distance . 141 in marshes 208 in valleys 210 magnify 141 none m a frosty night 209 I Food concerted to blood 221 cooled by the breath 293 ! Food, want of, produces hunger 89 want of, produces laziness 89 aversion to clean- liness 93 " to ventilation 93 Foot-prints frozen .... 325 Foot warmers 162 Forked lightning 12 , Forests catch fire spon- taneously 99 cold 152 France warmer than of yore 153 FREEZING MIXTURES. .. 335 FRICTION {see riibbing) 97 Pag* Friction excites electri- city 34 sets forests on fire 99 Frogs cold 94 croak before rain 141 FROST affects barome- ter..,, 299 " sound . . 380 braces ,. 140 breaks ewers 325 " tiles, stones, rock 325 " pipes.. \. 327 cracks earth 332 " mortar 333 expands water 325 on windows ...... 220 prevents fog 209 stops work.. * 334 warmer than thaw 332 Froth of beer.... 107, 248 of fermentation . . 255 white 372 Frozen water warm . . 330 ruts and foot-prints 326 Fruits cool the blood . . 92 fall to the earth . . 388 pleasant in summer 91 Fuel, dry burns well , 49 elements of 40 for the body 86 wet burns badly . , 49 Fulgurites 35 Fumigation for sick rooms 389 Funnel (see flues} 64 FUR, bad conductor . . 156 for clothing 164 warm 165 Furnaces of brick .... 163 lined with clay 163 Furr of kettles 236 steam-engines dan- gerous 237 Gallery hot 229,296 INDEX. 46T Page (j as 74 109 19 195 225 283. 289. 328. ^ differs from liquid 220 elastic 220 Gold never tarnishes . . 235 Goodness (see wisdom). invisible ^19 jet of 79 Grape juice needs no of candles ^63 veast 254 Gau/e wire of safety- ferments 249 lamps 264 makes alcohol 250 prevents explosion 264 Geese noisy before rain 141 German silver tarnishes 235 tinder 100 " carbonic acid 250 Grapes never ferment . 254 Grass promotes cold . . 152 Germany war me?' than of yore . . . 153 Grate (see stoves). Gravel collects no dew 194 Germination 288 Gravity 387 Ghosts 266 Gray morning, sign of a fine dav 134 Ginger-pop 248 evening, sign of wet 135 acid 248 GLASSFS broken by hot GREASE liked in cold weather 89 water 119 loathed in hot .... 91 broken if set on a hob . 120 prevents rust .... 145 used for wheels . . 98 covered with mist 198 Green color 372 " if brought from cellar 199 wood does not burn 105 " does not snap dulled by a hot hand 198 when burned 205 Grottoes famous for " by breath &c 199 echoes 383 mist of soon sub- Ground frost 209 sides 198 Growth promoted by moonlight 203 Guinea fowls squall be- soon cools 196 198 ground not trans- Gulls fly to sea 145 parent 373 to land . . . 145 S?:e looking-glass. Glauber salts 454 Gunpowder explodes.. 103 Gusty weather makes a Gloves black kid 176 smoky house ... . 70 Lisle thread. . . 176 Glow-worms glisten by HAIL 312 night 342 accompanied with Gluten 251 thunder 313 ferments 252 Hail cause of 313 GOD'S WISDOM 153, 166 ; 193 falls in summer . . 313 468 INDEX. Page Hair, bad conductor . . 156 covered with dew 201 warm 165 Halls famous for echoes 384 Halo round the moon 136 Handles, wooden 156 metal 156 Hard work promotes hunger .*. 87 water bad for wash- ing 234 Hartshorn 253 Hat covered with dew 200 turned red at the sea-side 320 Hawks see near and far 363 Hay-stacks catch fire spontaneously 61 Haze round the sun. . . 136 " the inoon 136 affects sound 381 Head aches in a crowd 239 itches in wet weather 142 Hearth-rug warm .... 159 Hearth-stone cold 159 hot 160 HEAT 9 absorbed 37 and light 51 affects barometer . 302 " sound 380 animal ... 83 ; 223, 258 applied to the bot- tom of boilers ..214 communication of 155 conduction of .... 155 effects of ... 10 to 101 evolved 37 " by compres- ' sion 100 expands air 102 expands water .... 334 from beaten iron . 94 increased by accu- mulation 60 Page HEAT, LATENT 38, 95 of candles 75 dunghills 258 fire 258 ice 38 human bodies 84, 258 lime 265 radiates ... 182 reflection of 179 sensation of 9 sources of . . 10 to 101 Heating rooms by stoves 103, 183 by steam 183 Heavy bread 258 Hemp, spontaneous com- bustion of 60 Herds dangerous in storms 25 Hedges increase warmth 152 Hills larger in a fog. . . 141 seem more distant 141 HOAR FROST 211 not found on trees 212 under shrubs, &c. 212 of frozen fog 212 on clear nights only 211 " grass 211 " tombstones 177 very partial 211 HONEY-DEW 203 Honey-de v, ants fond of 204 * effects of 203 injures plants . . 203 Hoops iised red-hot ... 117 Horizontal sun and moon 350 Horses strike fire 97 snuff up air .... 144 uneasy in dull weather 141 Hot, cloudy night op- pressive 137 I Hot water 187 melts sugar .... 323 I INDEX. 469 Hot weather abates ac- tivity abates appetite, produces love of fruit " dislike of grease . . . Hottest place at church 229, Houses catch fire spon- taneously .... gather damp . . . 200 seem more dis- tant in a fog smoke in valleys 67 Hull of ships seen last 358 Hunger 87 t< promoted by cold " day-light " rapid digestion . " singing, speak- ing, work .... See appetite. Hydrogen gas 40, 74 of fuel 220 ICE contains heat 38 dissolved by acids 332 friction 99 salt . . . 332 sun . . . 121 grows thicker 329 lighter than water 325 Ice -bergs famous for echoes 384 IGNIS FATUUS .... 266, 267 cause of 266 Impure water purified 72 Indian mode of striking fire Inflammable air, 40, 74 Insects in wet weather 145 Insensible perspiration 197 Intermediate clouds . . . 130 Page 92 Page IRON affected by light- ning 36 91 cinders 48 cold 159 91 91 296 59 contains latent heat 95 cooled by air 227 " convection 227 " radiation . 227 good conductor ... 173 heated by blows . . 94 rust 231 200 " when most com- mon 231 141 " prevented . . 232 67 " scales 231 858 ) 91 90 Ironin 01 box 147 . 88 90 Islands equable in tem- perature 291 88 subject to wind . . . 290 ,74 220 Itching in wet weather 142 Jack o'-lantern (see ig- nis fatuus) 266 3^5 Java (WP jungles) .... 241 38 3?>? Jet of flame through bars 50 99 83? Judges vi. illustrated . 195 121 39q Jungles of Hindostan fatal 241 325 384 267 266 72 97 >, 74 145 KETTLE boils over 111 quickly if cover- ed with soot . 174 slowly if clean . . 174 " if new. .. 174 bottom should be sooty 185 cold when water boils 186 197 furr of 236 130 holder.. . 157 470 INDEX. Page Kettle-lid clean 1 85 T . Pa?e Leaves in a pond '5S7 hot . . . 186 light green in spring 372 pale in dark places 372 promote cold 152 yellow in autumn 372 Lemons, juice of. . . . 454 Kettle not full after boiling Ill runs over . . Ill through the spout 112 sin-s 109 salt of 454 steam of 216 Lid of kettle bright... 185 hot 186 rattles... 112 Light bread 257 top bright 185 Kilkarney, echo of 386 Kindlin " fires 46 colors cool 175 dry 49 LIGHT 51 338 wet 48 absorbed 339 Ladies fan 289 composed of vari- ous colors 364, 370 divided by a prism 364 from a flint 96 Lakes which never freeze 331 Lamps 74 compression .... 100 Argand 82 of candles 76 smoke 82 fire 50 5'> spirt 149 houses, trees, &c. 338 the sun '. 338 See candle. Lamp-glasses 82 Land air cold . . . . 207 reflected .... 339 speed of 337, 338 sudden, painful.. . 339 Lighting fires 46 Land breeze unhealthy 290 cools faster than water 207 LIGHTNING 11 Laplanders clad in skin 171 Larvae 146 affects iron & steel 35 ' electric tele- graph .... 36 LATENT HKAT 38, 95 Laundress 147 balls 13 Laziness caused by want of food .. 89 by heat .... 92 Lead, dullness of 234 barks & snaps trees 34 clouds 12 comes from clouds 22 " from earth. 22 conductors 28 tarnish of . . 234 Leanness from starva- tion 86 dangerous 29 followed by rain . . 17 by wind ... 17 follows dry weather, not wet 33 LEAVES absorb carbonic acid 225 collect dew une- quallv 192 forked 12 exhale oxygen . . . 224 green . . 372 fuses metal 32 kills animals . . 14 INDEX. 471 Page Lightning knocks down houses, churches, &c 29 magnetic 36 maims 14 odor of 35 passes down the out- side of a tree . . 20 passes through the inside of animals 20 produces fulgurites 35 purifies air 33 rare in winter 33 returning stroke . . 23 scorches trees .... 34 sheet 13 speed of 18 straight 13 summer 17 common in . . 33 turns beer sour . . 32 milk sour .... 30 not old beer.. 32 not porter ... 32 two flashes 13 See danger , safety. Lilac steel rusts 233 prevented 233 LIME and water... 31, 37 burned 260 hot 260 purifies bins 259, 389 " sewers 259, 389 quick or caustic . . 260 Lime-wash for rooms 389 Line of incidence 344 of reflection 344 Linen cool wear 171 dried 151,295 Linseed oil, boiling point of 115 LIQ.UEFACTION . . , 121 LIQUIDS 109 bad conductors. 213 cooled 215 Page Liquids heated 214 not elastic 220 Lisle thread gloves ... 176 LONDON FOG 208 Long flues 107 grass promotes cold 152 Logs, two burn better than one 49 See wood. Looking-glass 343 a reflector 343 reflects our image approaching, &c. 345 reflects our whole person 345 Lucifer matches 265 Lunar caustic 454 Lungs described 224 Mackarel scales, &c. . . 130 Mackintosh prevents cold 149 Madness from starva- tion 86 Magnetic effects of light- ning 36 Magpies indicate wea- ther 145 Malt 252 Malting 251 Man a swimmer 337 fat, swims best . . . 337 no bigger than a crow 355 Marble 454 MARCH comes in like a lion 287 goes out like a lamb 287 dry good, wet bad 288 flowers undesira- ble 288 use of 287 wind dry 287 472 INDEX. Mares' tails 131 Marsh gas 261 Marsupium 363 Mast of ships seen first 358 May flowers 288 MEAT covers 188 Meat liked in cold wea- ther 90 loathed in hot 91 roasted by reflect- ors 180 taint removed 389 tainted by moon- light 203 MECHANICAL ACTION. . . 94 Mercury of barometer. 297 boiling point of. 115 bright 235 concave 304 convex 304 Its rise & fall, 303 to 308 rises Bom heat. . . 119 METAL collects no dew 193 conductors 156 feels colder than wood 158 hotter than wool 157 fused by tire 121 by lightning 32 good conductor. . . 156 handles burn 156 reflectors 180 tea-pots , 184 Milk long in cooling . . 216 soured by lightning 30 Mineral springs 320 Miners' danger 264 prevented 239 Mirror 343 MIST arrests sound . . . 381 black 137 cause of 204, 206 differs from cloud 122 dew . 204 fog.. 209 Paje Mist increases distance. 141 magnifies 141 on windows 196 seems to rise 205 vanishes at sunrise 205, 209 white 137 Mixing not combining 30 Money hot in a pocket 15cS Monsoon 280, 282 Months, driest 307 wettest 307 MOON, distance and size 356 largest at horizon . 350 reflected in water. 349 seems flat 356 larger than stars 356 Moonlight makes plants grow 203 taints meat . . 203 MORNING breeze 290 gray . . .' 134 rainbow 135 red.... 127, 134, 369 streaks 127 MORTAR 260 adhesive 260 crumbles 333 hardens 260 Motes in a sunbeam . . 228 Mould hardened by sun 153 Mountains cloudy 132 cold 181 collect rain 316 famous for echoes 384 impede respiration 229 noiseless 383 Muriate of soda 454 Murky nights oppres- sive 1^7 Musical instruments . . 379 flat.. 380 glasses 379 notes.... 379 sounds 377 INDEX. 473 Myrrh antiseptic 389 Nails for matches 95 Naves fitted on hot ... 118 Near-sight 360, 363 spectacles for 360 Negative electricity ... 22 Negroes, why black. . . 178 with black eyes 179 New kettles boil slowly 174 Night allays hunger . . 88 exhilarating 137 oppressive 137 produces cold 88 rainbow at 135 warm, when cloudy 189 Nimbus clouds 131 Nitrate of silver 454 Nitric acid 30, 33, 454 Nitrogen 42 expired ....224, 239 of air 221 Nitrogenized 254 Non- transparency 373 North wind cold 284 dry 284 North-west wind dry 286 299 Northern lights 135 Notes, bass 379 flat 380 sharp 380 treble 379 November rainy 289 Odor of electricity 35 Oil, elements of 74 linseed, boiling point of 115 of turpentine .... 115 of vitriol 454 Oiled paper transparent 373 Old people far-sighted 361 hold objects at a distance 363 Page Old people lose their power of walking 392 spectacles for . . 362 One pot will not boil in another 113 how to make it boil 114 Out-of-door work pro- duces hunger 89 Owls prowl at night . . 342 see in the dark . . 341 sleep all day 341 screech before rain 1 41 Oxalic acid 396 Oxide of copper 233 iron 231 lead 234 Oxide of platinum 235 potassium . . . 236 silver 234 sodium 236 Oxidised 222 Oxygen 41 exhaled! by leaves 226 heats the blood . . . 223 in the blood 238 inhaled 222 makes blood red.. 223 " fuel burn.. 220 of air 96 'its use 220 supports combus- tion 97, 220 sustains life 221 Ozone 35 Paleness 222 Palmer's candles 80 Paper burns 46 not always 49, 57 extinguishers 79 oiled, transparent. 373 puckers from wet. 317 used for kindling . 46 Papillae 392 474 INDEX. Pa^e Paris plaster of 454 Page Poison for flies . . . 390 Parlors smell of smoke in summer 71 Partition walls to arrest sound 382 Poker draws up fire . . 56 hot against a stove 173 cold on a fender 161 , 173 how to carry it Pea-soup fog 207 when hot .... 217 Peacocks forebode rain 141 Poker rusts 232 Pearl divers deaf .... 139 rust of prevented 232 Polar current 278 Perspiration . . 88 197 Polish use of 163 petals 370 Polished metal tea-pots 184 Petrels 146 Ponds dried up 153 Petrifaction 320 Poor averse to cleanli- Phosphate of lime . . 265 ness 92 Phosphoric acid . . .... 43 Phosphorus 65 ^azy 89 PHOSPHURFTTED HYDRO- Pores of wood 105 GEN GAS 265 Porter froth of . . 107 248 Piano fortes 379 set before a fire 107 Pickle tested 335 Porter, stale 255 Pie with a cup .... 116 Porter vats dangerous 245 full of juice 116 Positive electricity . . , 22 Pigs squeak before rain 141 Potatoes green 372 Pimpernel forebodes yellow 372 rain 143 Potash, tartrate of 454 Pin puts a candle out 81 Potassium 236 Pine snaps in fire 105 Pipes broken by frost 327 burns in water 236 Primrose yellow .... 371 Piston 100 Prisms divide light . . . 364 PLANTS collect dew . . . 192 forebode rain 143 Psalm cxlvii. 16, illus- trated 164 311 grow out of walls 296 after moonlight 203 Plaster of Paris 454 Pump handle cold 158 water hard .... 320 Purple steel rusts 233 of stoves falls away 118 its rust prevent- ed 233 Plasterers cannot work in fro^t . 334 differs from Plate warmer 177, 180 Platinum its use .... 235 fermentation 253 Putrefying bodies smell never tarnishes 235 Ploughing promotes warmth 151 253, 266 Quadrupeds swim .... 337 Plumbago 232 Quick lime absorbs car- prevents rust 232 bonic acid 246, "260 INDEX. 475 Page Quicksilver bright .... '236 extinguished 454 Quiet precedes storm . . 139 RADIATION . 182, 228 cools iron .... 228 Radiators are absorb- ers 182 bad 162 Rags catch tire sponta- neously 60 especially candle- rags 61 Railway steamers 201 water for 237 RAIN 313 affected by wind . . 315 after lightning 17 arrests sound 380 cause of 209 clouds bode 134 cools air 150 differs from dew.. 208 dispels carb. acid . . 246 falls in drops 314 fertilizing.... 288, 315 from passing clouds 315 heaviest in summer 318 least at the poles . . 313 most in mountain- ous places 316 most in winter 289, 318 near the equator. . 318 not salt 323 on dust 206 cabbages 206 rose-leaves 206 prognostics of 134 from animals . . . L40 candles & fires 141 clouds 134 flowers 143 purifies air. : .- 315 sudden change . . . 302 RAINBOW 364, 365 Page Rainbow colors reversed 367 Rainbows, two 366 Rain drops 314 vary in size . . 314 Rain-water smells offen- sively 322 fertilizing 324 not salt 323 soft 321 stagnant 323 unpleasant . . . 322 Rainy months 318 Rare air bad for sound 383 Rattling of kettle-lid.. 112 Ray of light divided . . 364 Reading aloud produ- ces hunger 88 RED color 222, 371 rose 371 sky 126, 369 sun-rise 127, 134 sun-set 134 Reflected light 339 REFLECTION of HEAT . . 179 in a mirror 345 in water 346 REFLECTORS 179 help the roast ... 181 keep kitchen cool 181 not absorbers 180 should be clean and bright.. 177,179 " not be painted 177 REFRACTION 358 Refrangible 126 Resinous electricity. . . 23 Retina 360 Returning stroke 23 Reverberation 383 Rice for food 92 RIVERS flow slowest at sides 324 freeze unequally 328, 380 invert our image 3^6 476 INDEX. Page Rivers never frozen at bottom 328 not wholly frozen 329 shallow, freeze fastest 330 seem shallower than they are 359 warm if frozen 330 Roast apples 103 soft 103 chestnuts 102 Road dark from a light room 340 Rocks collect no dew . . 194 broken by frost . . . 326 Room cooled 150, 295 currents of air in a 270 ventilated 295 vitiated by a crowd 295 warmed by fire . . . 240 Rose red 371 Rosneath, echo of 385 Ross, Captain 381 Rotation of earth 272 Rotting leaves promote cold 152 Rubbing 98 Rubbing hands to warm them 98 melts ice 99 restores suspended animation 98 wood excites fire . . 98 See friction. Ruddiness 223 Ruins ftuned for echoes 383 Running promotes warmth 87 in a storm dan- gerous 21 water freezes slow- ly 329 water makes. rough ice 33 " oscillates 324 Page Running water pure. . . 324 Rush lights easily blown out 78 extinguished by a pin 81 RUST 231 prevented 232 when most trouble- some 232 Rustics healthy 242 Ruts frozen 326 SAFETY IN A STORM abroad 25 to 27 at a slight dis- * tance from a tree 25 best to be wet 27 in a carriage 26 in bed 27 indoors 26 Safety lamp 263 Sailors rarely catch cold 150 St. Bride's church de- stroyed bv lightning 30 SALT ". 454 and snow cold.. 39, 332 and water boils slowly 114 crackles in a fire . . 49 dissolves ice.. . . .\ 332 dissolved by water 322 especially by hot water 323 flavors water 322 of lemons 454 retards boiling.. . . 114 smelling 454 white 372 water unfit for rail- way engines . . 237 for washing 320 Salts, Epsom 396 Sand dazzling 374 Saucepan boils best when black 185 INDEX. 477 Page Saucepan boils slowly when new 185 lids should be clean and bright 185 rattle 112 Scald cured 14Q Scripture illustrated. . . 16-1 145, 311 Scum of fermentation.. 255 Sea-beach healthy in the morning .... 290 not healthy at night 290 Sea before storm 139 gives out heat .... 292 heaves and sighs . . 139 less hot than land. 275 not much heated by sun 275 Sea-gulls 146 Sea- vapor not salt 154 Sea-water easier to swim in than fresh ... 335 heavy and salt .... 323 rarely frozen 331 " gives cold.. 150 salt 323 Sea-waves 292 Sedentary pursuits abate hunger 89 SEEING in a glass 343 into a dark street. 352 " light room. 340 .ourselves in a small mirror .... .... 345 the same object. . . 339 when used to dark- ness 340 Sensation destroyed . . 391 of feeling ... 391 of taste 391 Sewers purified by lime 259 Shadocool...., 171 Shadow in water. . . 345, 346 Shadow larger as object . approaches a light. . 352 Page Shallow water soon freezes 330 bleat before rain 141 in a storm. 25 lie under hedges 140 Sheet lightning 14 Sheets wet 149 Ships out at sea 358 hull of, last seen 358 Shirts of linen 172 Shoes cold when wet . . 148 hot when dusty. 181 Shot hot 101 Shower cools air 150 Shutters dangerous ... 24 Sick rooms purified. . . 389 Sides of a pond covered with leaves 388 Sight affected by sud- den light 339 SILVER meat-covers . . . 188 should not be chased ... 188 nitrate of 454 tarnishes 234 Simmering 109 Simple clouds 128 Singing of a kettle 110 of boiling water 110 produces hunger 88 Single magpie unlucky 145 Size diminished by dis- tance 354 Skin, black, does not scorch 176 white does 179 itches before rain. 142 Sky blue 126 Sleep elongates the body 390 body feels not in . . 391 dreams in 391 , ears hear not in... 391 eyes see no' in . . . . 391 mind wills not in . . 3 ( ^1 478 INDEX. Page Sleep, tongue tastes not in 391 Sleet 310 Slit chestnuts 103 Smelling salts 454 SMELLS in wet weather H3 of bins and sewers 258 church-yards . . . 265 putrefying bodies 253 SMOKE 45, 62 ascends '.. 62 curls 62 falls 144 " down a chimney 65 of fresh coals 45 candles 81 lamps diminish- ed by a glass. 83 red : hot coals. .. 45 rises 107 useful in cooking . . 186 Smoky chimneys 63 See chimney. Smoke jacks 108 Smouldering wicks .... 56 SNOW 309 arrests sound 380 bad conductor. . . . 311 cause of. 310 falls in winter .... 310 " not in summer 312 like wool 164 nourishes the earth 311 on mountains 312 soon melts beneath a hedge or wall 191 use of 310 ^ warm 310 mixed with salt, cold 332 white 312 321 cleansing 321 hard, soft 321 .yellow 321 Soap-bubbles 368 ascend 325 change color . . . 368 Soapy water bubbles . . 325 Soda, muriate of 454 water 247 " acid 248 Sodium 236 decomposes water 236 Soft soap 321 water for washing 321 Solids 109 Sonorous things 377 Soot in summer 71 on ceilings 71 Sooty kettles 174 SOUND 377 affected by frost .. 381 heat.. 381 arrested by mist . . 381 wet... 380 diminished by rarity of air 383 heard best by night 381 in a frost 380 inaudible on moun- tains 383 velocity of 377 Sounds musical 377 prevented from passing from room to room 381 Soup long cooling 215 Sources- of heat . . 9 to 15 South wind rainy 285, 300 warm 285 South-east wind rainy 286 Sparks from a lire 105 aflint.... 196 a horse- shoe ... 97 Spectacles 361 black 376 blue 375 for aged 362 INDEX. 479 Page Spectacles for near sight 360 Spectrum 377 Split bells 378 Sponge swells when wet 316 SPONTANEOUS COMBUS- TION ... 60 3 84 of forests ... 99 Spoons become dull . . . 234 bent in water .... 359 discolored by eggs 254 retard boiling ... 113 Speaking produces hun- ger 88 Spray white 371 Spring, best late 288 crumbles the earth 333 bracing 140 verdure 372 Spring water cool .... 171 " " sparkles. 249 Springs prevent freez- ing 331 Sprinkling to cool rooms 150 Stagnant water 323 full of worms 323 Stale beer, &c. (see beer} 255 Stars, distance and size of 355 invisible by day . . 342 seem flat 356 seen in a well .... 342 seen on mountains 350 twinkle 374 Starvation 86 produces dirtiness 93 laziness 89 leanness 86 madness 86 STEAM 122 engines burst .... 217 invisible .... 112, 216 ofakettle 216 " locomotive.. . 201 pipes should not be black 184 Page Steam, why visible 112 what becomes of it 113 STEEL affected by light- ning 36 and flint make a spark 96 purple 233 rusts 233 prevented 233 Stick burnt makes a circle of light 374 Stillness before a storm 139 Stirring cools broth, &c. 228 Stockings difficult to draw on when wet . . 317 STONES broken by frost 326 cold 159 collect no dew 193 snap in fire 106 unfit for fuel . . 49 STORMS 139 direction of 34 distance of, told 16, 19 follow dry weather 33 places of danger in 19 " . safety in 26 prevail in summer and autumn 33 rare in wet weather 34 STOVES crack when lighted 118 when cooling . . 118 of bricks 163 on a floor 54, 217 rust 240 most in win- ter 232 not often 232 prevented 232 settings fall away 118 smell of sulphur . . 59 smoke 69 close 62 warm a room .... 21 Strataofair 1 480 INDEX. Fage Stratus clouds 129 Pare Summer allavs hunger 91 Straw covered, over brick- clothes for 175 work 334 creates dislike of over trees . 334 grease . . 91 " water-pipes 334 Streets dark from a li*lit " love of fruit 92 liffhtnin " . 17 room . ... 340 Sun-beams full of motes 228 seem to meet at bottom 354 -dazzles . . 340 watered . 150 dulls fire .... 53 Strikin " iron makes it hot 94 largest at horizon. 350 Struggling in water dan- gerous . .... 336 not seen in a well. 348 radiates heat 183 Stucco peels off in frost 333 Sublimates . . 454 reflected in water. 349 seems flat 356 Sublimation . . . 454 source of heat .... 10 Sudden li-ht painful . 339 Sun-rise red 127 134 SUG4R 249 Sun-set gray 135 anhydrous . 250 red 133 135 ferments 249 yellow 133 134 at top of tea melts quickly 389 Super-acetate of lead . . 454 Suspended animation flavors water . . . 322 left at tlie bottom. Swallows fly low 144 of a cup melts slowly . ... 388 Swan dry in water 206 Sweet-wort needs yeast 252 makes alcohol *^50 Swimmers sink . . . 33f> " carbonic acid ^50 Swimmin * 337 melted by water.. 322 " especially by hot water. 322 of lead 454 in the sea .... 335 Syrup, boiling point of 115 Table salt 454 retards boiling . . . 114 stirred melts quick- ly ... 388 Tainted meat cured 72, 389 in moonlight. 203 water 72 wh^te 372 Tallow 74 Sulphate of lime 320 454 Tarnish 233 magnesia 454 Tartar emetic 454 soda 454 Tartrate of potash 454 zinc 454 Tarts have a cup inside 116 Sulphuric acid 454 full of juice 117 arid water 37 Taste 892 boils 115 Sumn_er, air in . . . 293 TEA cooled by blowing 228 by stirring 228 INDEX. 481 Pa?e Tea cooled in a saucer 153 green, deleterious 390 poison for flies 390 TEA-POT, bright metal. 184 tarnishes 234 black earth 184 preferred by some 184 set on a hob .... 18'4 Tea-spoons tarnished . 234 by eggs 254 Telescopes 357 Tempest 139 affects weather 305 Sie storms. Thaumatrope .... .... 374 THAW affects barometer 308 cold 331 dulls fire 55 Theatre dangerous 25 Thermometer 119, 296 Thick clothing un- healthy 154 Thread gloves cool .... 176 THUNDER 15 after lightning .... 17 bolts (see fulgurites) 1 7 deep growl 16 distance of, told. 16, 18 followed by rain . . 17 wind. 17 irregular roar .... 15 one crash 15 rolling 17 See danger, safety, storm. Tigers prowl by night, 342 see in the dark. 341 sleep all day . . . 341 Tiles broken by frost. . 326 Timber charred 73 Tin-blowers 70 foot- warmers . '. . . 162 " covered with flannel 162 plate- warmer .... 177 21 Tin-blowers reflectors 181 See reflectors. Tinder blown 96 Toast and water 73 dry, for the sick . . 73 Tomb-stones frosted . . 177 Tongs rust 232 prevented.. 232 Tools hot from use ... 99 Trade winds 277, 280 Transparency 373 Treble 379 TREES barked by light- ning 34 collect dew 190 covered with bass, &c 334 look more dis- tant in a fog.. 141 not frost-bitten. 211 promote warmth 152 purify air 242 shade of, cool . . 171 Trefoil forebodes rain . 143 Tube of barometer 297 Tubs dried up 153 Tumblers (see glasses.) Twilight 370 Twinkling of stars 374 Two eyes 343 " see single .. 343 logs burn best 49 Unslit chestnuts 103 Use of barometers 298 clouds 132 smoke in cooking 186 snow 310 Valley chimneys smoke 67 VAPORIZATION 122 Vapor a conductor .... 25 forms fog and cloud 209 of a carriage . 197 482 INDEX. Page Vapor of a room 196 of sea not salt 154 Page WATER (see rain) 319 and lime 31 37 Varnish to prevent rust 232 Vats fatal 244 and sulphuric acid 37 ashes soften 3 4 ^1 Vegetable and animal life dependent 225 Vegetables absorb car- bonic acid . . . 225 bad conductor 161, 214 boiling.. 115, 213, 215 bubbles . Ill, 214 rattles 112 agreeable in sum- mer 91 runs over 111 sings 109 collect dew 192 cool the blood . . 92 cleans dirty linen . 321 cold 160 exhale oxygen . 224 Velocity of clouds .... 294 light 338 converted to steam 121, 319 cools slowly ... . 207 sound 384 deep freezes slowly 330 wind .... 294 dried up in summer 153 Vent peg 255 elastic 253 expands by frost . . 327 sought by the well-fed .... 93 by heat.. 327 extinguishes fire 57 106 sought not by the ill-fed 93 Verdigris 454 not always 57. 58 flat when boiled . . 257 fluid 319 Vertical sun 273 flowing pure .... 324 Vinegar antiseptic .... 389 distilled 454 for washing.. 259, 320 freezes at the sur- Violets blue 371 face 328 Violins musical 378 fresh, sparkles . . . 260 Vitreous electricity 11, 23 Vitriol oil of 454 frozen by ether . . 334 air-pump 335 white 454 fuel 58 furr of 237 Walls to arrest sound 382 hard 320 wet in winter .... 199 " in a thaw 199 Want connected with dirt 92 agreeable to drink 260 unfit for washing 320 how preserved cool 179 hot 179, 187 Warm clothes 175 heated 213 some things more than others. . . 155 Warming rooms ... 217 intenses fire 57 inverts images . . . 346 kept hot 215 Wash-hand basin 160 Washing water for 259 melts sugar, salt, &c 322 should not be hard 320 especially hot 373 INDEX. 483 Page Water mixed with salt, boils slower 115 needful for ferment- ation 255 not heated above boiling 215 of a spring cool .. 171 oscillates 324 pump, agreeable.. 260 hard 319 purified 72 purifies bins, &c. . 259 reflects sun by a spot 350 moon by a path 349 running, keeps pure 324 salt, bad for wash- ing 320 shallow, freezes fastest 330 simmers 109 slackens flame .... 58 soft 259, 321 best for washing 321 sparkles ; . . 249 stagnant 323 full of worms 323 stale 257 swells with boiling 110 will not bubble without soap . . . 324 warm when frozen 330 Water-pipes broken by frost 327 covered with litter 334 Watering plants by the saucer 388 streets 150 Waves 292 Wax 74 candles need no snuffing ...... 80 Weather affected by tempests 305 affected by weight of air 297 Page Weather, prognostics of 130 told by barometer 296 rules for 299 Weather-toys 317 Well, stars seen in .... 348 sun not seen in ... 348 West winds 201, 285 Wet clothes give cold 148 safe 27 feet dangerous ... 148 finger cold 148 indications of 134 to 136 kindling 48 night oppressive . . 137 sheets 149 summer, cold win- ter 151 weather offensive 137, 140 Wettest months 307 Wheels catch fire 98 greased 98 kept cool by water 153 Wheel-ruts frozen .... 325 Wheelwright 117 WHITK 371 blisters 178 body linen 174 crust on clothes.. 154 dresses for summer 175 " not fit for win- ter 175 mist.... 138 vitriol 454 WICKS, cotton, need snuffing 80 gas of 262 have a nob when long 80 not upright when long 80 Palmer's, need no snuffing 80 rekindled quickly 55, 58 smoke 81 484 INDEX. Page See candles. Will o' the wisp, (see ignis fatuus) 266 WIND 268, 296 affects barometer. 299 " clouds 125, 127 after lightning.... 17 altered by clouds . . 276 " by electricity 127 " by seas 275 always blows 272 brings clouds 182 " dry 286 " rain 286 cause of 268, 272 changes the shape of clouds.. 123,125 cold 171, 184 dispels clouds 125, 133 " fog... .... 210 draws up fire 55 dries linen 295 effects on air 268 feels hot sometimes 169 increases clouds . . 125 makes barometer fall 299 makes chimneys smoke "67, 108 near mountains. . . 276 of a morning 289 of an evening 290 prevents dew 191 velocity of 293 regular 277 See monsoon, north, south, west, fyc., trade-winds, tyc. Winding passages famed for echoes 384 Windows blazing with the sun 347 not at noon 347 covered with frost 197 " mist 196 carriage, dull 197 Windows rattle 387 Wine-glasses (see glasses. ) Wine, fermentation of 249 made without yeast 254 Winter clothing 164 Winters less severe . . . 157 Winter cold 151 promotes hunger 90 WISDOM or GOD 153, 166, 193, 195, 225, 283, 289. 328 ; 3*5 WOOD ashes soften water 322 burns 46 " spontaneously 59 charred 72 hot at one end, cold at the other 55 ignited by friction 97 kindling 47 " dry 49 wet .... 49 made incombustible 49 sends forth sparks 105 snaps 103 two logs burn best 49 will not melt 122 Wooden handles 156 Woodpeckers cry before rain 141 WOOL bad conductor . . 156 collects no dew .. 193 warm 165, 311 Woollen clothing 164 kettle holders.. 157 Work produces hunger 87 Yeast 215 makes light bread 275 not used in wine 215 used in brewing . . 215 Yellow flame gives best light 51 soap 321 sun-set sign of wet 133 Zig-zag lightning 12 INDEX TO PAET III. Page Above proof 449 Page Books discolored by Abundance of dew a age 423 sign of fine weather 392 Brazil pebbles 438 Bread ... . . 426 Acid stains removed.. 420 full of eyes 399 hard from a"e 410 Agate 438 mouldv 427 Air rots wood : . . . . 429 new indigestible 410 Bridges increase sound 433 Ale 443 Brine preserves meat 407 Alkali 420 Brown paper burns well 393 Alkaline phosphates . . 441 of meat 407 Amethyst 438 sticky from rubbing.. 405 Brown stout 443 ANTIDOTES FOR POISONS 452 Apples sour . . 446 Brushing hair makes the head il ch 395 Aqua-fortis, antidote for 452 Arsenic antidote for 452 Burning glass ignites paper 393 Burton ale 443 Baking dough into bread 426 Butter hard from cold 412 soft from heat. 412 Barometers measure heights 406 Cairngorum . 438 Bary tes 45 1 Candescence. 431 Beer 443 Candle flickering 395 sour from bad cork- ing 444 Candle-wick smell 447 Carbonic acid 439 Below proof 449 Caries 447 Binoxide 394 Casein 424 443 Birds kept in feathers 428 Black earth turns red 402 Caves increase sound. 413 Cellular fibre 438 Blackness from decay 419 Cellulin 414 Block-tin 451 Chalcedony 438 Bloodstones 438 Champagne ... . 448 Blue looks green by candle-light 393 Chandelier lustrous.. . 404 Chaps and chilblains.. 402 Blue sky 439 Cheese * 425 Boiled lobster red 419 shrimp red 429 Chlorate of potash .... 417 Chloride of lime 440 Boiler bursts . . . 395 Chlorine, antidote fop. 442 Boiling meat 402 Chlorophyll ... 411 stale milk curdles 424 Chiicky stone 438 Boiling'wood makes it soft... . 437 Churning makes butter 425 Claret . . , . 448 486 INDEX. Page Clothing warm if loose 399 Clouds do not hide light 439 Citric acid 446 Citrons sour 446 Cold affects skin 402 Color 396 destroyed by dark- ness 396 faded by sun 425 Contagion prevented.. 442 Copper bursting v 395 Copper cankers 436 Cork of soda- water flies 401 pops 401 Cornelian 438 shines, if wet 397 Corrosive sublimate. .. 440 antidote for 453 Court buttons 415 Cream made butter. .. 425 Creasote 444 for tooth-ache . . . 447 to remove taint. 444 Crombs made by boil- ing .. 437 Crystal 438 Cup filled beyond brim 455 not if edge be wet 415 Curdling milk 423 Curling paper with knives 418 Currants hard 443 ripe, soft 443 Curtains promote heat 397 Damp lucifers 417 of decay 410 Darkness spoils color. 396 Decanter-stopple sticks 418 Decanting liquor, gur- gles 416 Decay, see rot. black 402 Decay of teeth 447 theory of 403 Dentine 47 Dextrin 427 Diastase 427 Double doors increase heat 397 Double reflexions in glass 438 Dough 426 made bread 426 Drops of water spread. 406 Dust laid by night .... 401 Effervescing draughts. 420 Egg tarnishes silver. . . 423 tarnish removed by salt 422 Electricity sticky 405 Essential oils 436 Explosive lucifers 416 Explosion of gunpowder 442 Fat solid 411 Ficus 448 Filaments 437 Fire destroys steel-pol- ish 413 revived by brush 398 by poker 398 quenched by sul- phur 421 warps wood 425 Fire-works 451 Fish luminous 439 Fixed oils 436 Flag-stones loose in frost 396 Flickering of candles . . 395 Flint 438 Flowers bend to sun.. 429 Fog makes sun red .... 393 Frost loosens pavement 396 Fruit, antidote for 453 Fungus 427 Glasses filled above brim 415 not if wet 415 INDEX. 48T Page Glazed pictures some- times invisible .... 401 Glazier mending a win- Page Ink-spots removed 436 turn yellow 394 Interstices 406 dow 404 Iodine antidote for 453 Glue adhesive 432 Iris ornaments .... 415 Gooseberries hard .... 443 Iron bends 430 soft, if ripe 443 galvanized 450 hisses 430 Grapes sour 446 melts 431 Grease-spots removed. 436 rusts 398 Greasy paper unfit for* turns red 431 writing 435 ^turns white 431 Green fire- works 451 Itch 440 fruit hard 443 Itching caused by hair wood rots .... 413 brush 395 Grindstone wet 425 Guano 438 Jeweller's gold 45 f ) Gum adhesive 432 Gunpowder explosive. 442 Gurgling explained... 416 Knife sharpened by Gutta percha 448 Lactic acid 424 Hams smoked 444 Lamb soon taints .... 409 Hard bread 410 tender . . 408 soap 445 Larks roasted with lard 407 Hartshorn removes acid Lather 399 stains 420 Laudanum antidote for 452 Heat warps wood 425 Hock 448 Lead differs from solder 450 Leffumine . 445 Horn shavings opaque 404 Lemons sour 446 Humus 436 Hydrate 436 Light when cloudy 439 of the carbonate of copper .... 436 Lightning conductors pointed 421 Ice in India 434 Likeness reversed in a glass 417 Ice-^its .... % 434 Lime for manure . . . 438 Indian houses kept cool 435 Indian-rubber 448 Lime-juice cures scurvy 440 erases pencil marks 429 Linen starched 421 Indian- rubber sticky. . 405 Indigo blue, white 420 Infection prevented ... 450 Locomotive whistle. . . 412 Lucifer matches 416 Ink 394 spoilt by damp 417 Ink-spots black.. . 394 Lustres variegated .... 403 488 INDEX. Page Manure for land 438 Page Oxalic acid 445 Marking ink 449 antidote for 452 Marl for manure .... 438 removes ink-spots 436 Meadows reverberate. 433 Meat, directions for boiling 408 Oxide of potassium . . . 445 Paint blisters 409 preserved . . 444 preserves wood 413 tough when old 408 overcooked 408 boiled in cold water gJ08 putrefies from change 428 prevents rust. .. 398 Pannary fermentation. 410 Paper curls by scraping 418 discolored by age 423 Partridges roasted with lard . . . 409 damp . . 428 Paste adhesive . . . 432 heat... 427 Mice destroyed 442 Pencil marks erased.. 429 Peroxide 394 Milk boils over 400 of iron red 403 quickly . . . 433 Pewter 450 burns 432 Phosphate 407 curdles 423 of lime 440 by rennet 424 sour from boiling 424 of nieat 407 Phosphoric acid 439 heat... 424 keeping 424 Pictures glazed invisi- ble 451 Molecules 431 Plants bend to sun .... 429 Moon shadow strong . . 420 Mother of pearl 414 Plants white if kept in the dark. 411 Mouldy bread 437 Plaster of walls peals off 403 Mountains meted 406 Mutton fat hard . 411 Points discharge elec- tricity . . . 422 Oak bark contains iron 419 Oak struck by lightning 419 POISONS, antidotes for 452 Polish of steel destroy- ed by fire 413 Oar bent in water 392 Pop-guns pop 412 Oil liquid 411 Porter, dark 453 prevents water Port- wine 448 freezing 432 Potatoes boiled 422 thick in winter 411 Proof spirit 448 used on grind- Protoxide 394 of iron black 403 Oleine... 411 of copper . . 436 (Enanthate 447 Prussic acid antidote ofethyle.. 447 for 453 Putty dancing 404 Overboiled meat toue:h 408 Putrefaction. . . . 424 INDEX. 489 Page Putrid fish luminous . . 439 Pyroligneous acid , 444 Page Sesquioxide of iron. . . 394' Shadow of moon and sun 420 dark. 443 Quails roasted with lard 409 Shear steel 449 Quartz 438 Sherry 448 Shrill sounds 412 Railway whistle 412 Shrimps red 420 train passing a bridge Silent lucifers 416 or meadow .... 433 Silica 438 Rain brings .down cold 435 Rats destroyed 442 Silver hotter than nickel 448 tarnished by egg Red earth 403 ^.Ipanpd - 422 by salt cleaned 437 Reflection in a glass Sky blue 439 double 438 Small beer 443. reversed 417 Rennet 425 Smell of sick rooms re- moved . . 442' curdles milk. .. 424 Rhubarb sour 446 Smelling-bottle stopple sticks 418 Ripe fruit soft . . 443 Smoked meat . 444 Rock crystal 428 Soap made of fat . 445 Rooms kept warm by curtains 397 Soapy water lathers . . . 399 Soda in tea .... 444 Rot 413 429 441 Soda water cork flies out 402 Rotting leaves hot 410 Rust 398 pops . . 401 Soft soap.. 445 prevented by paint 398 Solder 450' Sorrel sour 445 Sails of mill turn ...... 396 Sound 412 Salt 423 p heard furthest beef produces scurvy 440 on sea 405 remedy. . . 440 meat not nutritious 407* meat needs vegetables 408 louder in caves. 413 silenced by touch 399 Sour milk 424 removes tarnish from silver 422 curdles 423 Sponge cleans a slate 400 wine stains. .... 442 Spores Sporules .... 427 tarnishes silver . . . 437 Stains removed 420 436 tarnishes removed.. 437 Salts preserve meat . . . 407 wood ... 414 Starch glazes linen .... 406 stiffens linen , . . 421 Stars twinkle 400 Sapid 409 Stearine 411 445 Scraped paper curls ... 418 Scurvy 440 441 Steel made from iron. 449 made brittle 434 Sea luminous. . . . . 440 Stirring: a fire.. . 399 , 490 INDEX. Page Stopples stick 418 : Page "Vegetables black from decay i . . 41 9 Strands 437 essential with salt meat . ... 408 Stucco falls off 403 Sulphate of lime .... 441 prevent scurvy . . . 407 wet from decay . . . 403 soda 423 Sulphur quenches fire. 421 Sulphuret of silver 423 Sulphuretted hydrogen 442 antidote for.. 433 Volatile oils 436 antidote for 452 ;Sulphurous acid 4^421 \yalking-stick crombs. 437 Water 388 .Sugar of dough : 410 ftSun fades colors 426 freezes if exposed . 431 sooner than milk 431 when boiled 432 hisses on fire 430 rots wood 429 red in fog 393 warps wood 425 'Tainted meat 428 spreads on cloth , . 406 used on grindstones 426 Tannate of iron 436 Tannic acid 394, 436 'Tanning leather 446 Wax hard 409 Tarnish of silver 437 removed, 423, 437 of zinc 436 liquid.. 409, 434 makes cotton strong 437 orff 424 'Tartaric acid 446 Tea 444 Wet sponge cleans slate 400 White lead 450 improved by soda 444 in Tartary 4^5 rushes to a spoon. 415 Teeth decav 447 Whistle of locomotive. 412 Windows mended 404 \TT-1 Ml CQ ilo ^QQ 'Teroxide..* 394 Tooth-ache, cause of.. 447 cure of. . . 447 Touch stills sound 399 Tough meat 408 sour from corking 444 stains removed 441 Turpentine removes W^ood decav of 441 flexible, if boiled. 437 preserved by paint 413 by salts 414 rotted by air 429 warped by heat.. 425 Twinklin " . 400 'Unseasoned wood rots 413 Veal soon taints 409 tender 408 Zinc tarnish. .' 436 Testable fibre.. ,. 414 14 DAY USE RETURN TO DESK FROM WHICH BORROWS: LOAN DEPT. 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