  Q. Of what is atmospheric air composed? A. Principally of two gases, oxygen and nitrogen; mixed together in the following proportion: viz. 1 part of oxygen, to 4 parts of nitrogen. Q. What are the uses of the oxygen of the air? A. It is the oxygen of the air which supports combustion, and sustains life. Q. What is meant when it is said, that the oxygen of the air “supports combustion?” A. It means this; that it is the oxygen of the air which makes fuel burn. Q. How does the oxygen of the air make fuel burn? A. The fuel being decomposed (by heat) into hydrogen and carbon; the carbon combines with the oxygen of the air, and produces combustion. Q. What does the combination of carbon and oxygen produce? Q. What becomes of the hydrogen of the fuel? A. Hydrogen (being very inflammable) burns with a blaze, and is the cause of the flame which is produced by combustion. (see p.34). Q. What becomes of the nitrogen of the air, amidst all these changes and combinations? A. The nitrogen of the air escapes, and is absorbed by the leaves of grass, trees, and various other vegetables. Q. What is meant when it is said, that oxygen “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 2ndly—It is the cause of animal heat. Q. How is food converted into blood? A. After it is swallowed, it is dissolved in the stomach into a grey pulp; it then passes into the intestines, and is converted by the “bile” into a milky substance (called chyle). Q. What becomes of the milky substance, called chyle? A. It is absorbed by the vessels called “lacteals,” and poured into the veins on the left side of the neck. Q. What becomes of the chyle after it is poured into the veins? A. It then mingles with the blood, and is itself converted into blood. 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 colour. Q. What colour is the blood before it is oxydized in the lungs? A. A dark purple. The oxygen turns it to a bright red. Q. Why are persons so pale who live in close rooms and cities? A. The blood derives its redness from the oxygen of the air inhaled; 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? A. As the blood derives its bright red colour from the oxygen of the air inhaled, therefore, country-people (who inhale fresh air) are more ruddy than citizens. Q. Why is not the air in cities so fresh as that in the country? A. Because it is impregnated with the breath of its numerous inhabitants, the odour of its sewers, the smoke of its fires, and many other impurities. Q. How does the combination of oxygen with the blood produce animal heat? Q. What becomes of the nitrogen of the air, after the oxygen enters the blood? A. The nitrogen is exhaled, and taken up by the leaves of trees and other vegetables. (see p.35). Q. Why does the vitiated air (after the oxygen has been absorbed) come out of the mouth, and not sink into the stomach? A. The vitiated air (being heated by the heat of the body) ascends naturally, and passes by the heavier fresh air (which we inhale) without obstruction or injury. Q. If (both in combustion and in respiration) the oxygen of the air is consumed, and the nitrogen rejected—Why are not the proportions of the air destroyed? A. Because the upper surface of vegetable leaves (during the day) gives out oxygen and absorbs nitrogen, and thus the proper balance is perpetually restored. Q. Show how God has made animal and vegetable life dependent on each other? A. Animals require oxygen to keep them alive, and draw it from the air by inspiration; the upper surface of leaves (all day long) gives out oxygen, and thus supplies the air with the very gas required by man and other animals. Q. Do not animals exhale the very gas needed by vegetables? A. Yes; animals reject the nitrogen of the air (as not suited to the use of animal life), but vegetables absorb it, as it is the food they live on; and thus the vegetable world restores the equilibrium of the air, disturbed by man and other animals. Q. Is air a good conductor? A. No; air is a very bad conductor. Q. How is air heated? A. By “convective currents.” Q. What are meant by “convective currents?” A. When a portion of air is heated, it rises upward in a current, carrying the heat with it: other colder air succeeds, and (being heated in a similar way) (“Convective currents;” so called from the Latin words, cum-vectus (carried 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 sensible degree) by the action of the sun’s rays passing through it. Q. Why then is the air hotter on a sunny day, than on a cloudy one? A. On a fine day, 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, and other air succeeding is heated in a similar way, till all is heated by convection. Q. If air be a bad conductor, why does hot iron get cold, by being exposed to the air? A. A piece of hot iron exposed to the air, is made cold—1st—By “convection;” and 2ndly—By “radiation.” Q. How is hot iron (exposed to the air) made cold by convection? A. The air around the iron (being intensely heated by contact) rapidly ascends, carrying some of its heat with it: Q. How is hot iron cooled by radiation? A. While the heat of the iron is being carried off by “convection,” it is throwing off heat (on all sides) by radiation. Q. What is meant by radiation? A. Heat emitted (in all directions) from any surface, by innumerable rays. Q. Why is broth cooled by being left exposed to the air? A. Hot broth throws off some heat by radiation; but it is mainly cooled down by convection. Q. How is hot broth cooled down by convection? A. The air resting on the hot broth (being heated) ascends; colder air succeeding absorbs more heat, and ascends also; and this process is repeated, till the broth is made cool. Q. Why is hot tea and broth cooled faster, for being stirred about? A. 1st—The agitation assists the liquor in bringing its hottest particles to the surface: 2ndly—The action of stirring agitates the air, and brings it quicker to the broth or tea: and 3rdly—As the hottest particles are more rapidly brought into contact with the air, therefore convection is more rapid. Q. Why is hot tea, &c. cooled more rapidly by blowing it? A. Because the heated air is blown more rapidly away; in consequence of which, cold air more rapidly succeeds to absorb heat from the surface of the tea or broth. Q. If a shutter be closed in the day-time, the stream of light (piercing through the crevice) seems in constant agitation. Why is this? A. The air (in the sun-beam piercing through the shutter-crevice) is more heated, than that in its neighbourhood; the convective current, therefore, is distinctly seen, where little motes and particles of dust are thrown into agitation by the violence of the current. Q. Why is the gallery of a church or theatre hotter than the aisle or pit? A. The hot air ascends from the bottom to the top of the room, and cold air (from the doors and windows) flies to the bottom to supply its place. Q. Why does a crowded room produce head-ache? A. Because we breathe air vitiated by the crowd. Q. How does a crowd vitiate the air of a room? A. Whenever we breathe, the elements of the air are separated in the lungs, some of the oxygen is absorbed by the blood, and some of it is converted into carbonic acid gas, and exhaled with the nitrogen. Q. Is all the nitrogen rejected by the lungs? A. Yes; all the nitrogen of the air is always exhaled. Q. What is carbonic acid gas? A. As carbon has a very great affinity for oxygen, therefore, whenever they are exposed to heat, they combine, Q. Is carbonic acid gas wholesome? A. No; it is quite fatal to animal life; and whenever it is inhaled, it acts like a narcotic poison, (producing drowsiness which ends in death). Q. Why is a crowded room unwholesome? A. Because the oxygen of the air is either absorbed by the lungs, or substituted for carbonic acid gas, which is a noxious poison. Q. Mention the historical circumstances, so well known in connection with the “Black Hole of Calcutta.” A. In the reign of George II, the Raja (or Prince) of Bengal [12] The Sur Raja, at Dowlat; a young man of violent passions, who had but just succeeded to the throne. A. D. 1756. 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 in the morning. Q. Why were 123 persons suffocated in a few hours, from confinement in this close hot prison-hole? A. Because the oxygen of the air was soon consumed by so many lungs, and its place supplied by carbonic acid exhaled by the hot breath. Q. Why do persons in a crowded church feel drowsy? A. 1st—Because the crowded congregation inhale a large portion of the oxygen of the air, which alone can sustain vitality and healthy action: and 2ndly—The air of the church is impregnated with carbonic acid gas, which (being a strong narcotic) produces drowsiness in those who inhale it. Q. Why did the captives in the black hole die sleeping? A. 1st—Because the absence of oxygen quickly affects the vital functions, depresses the nervous energies, and produces a lassitude which ends in death: and 2ndly—The carbonic acid gas inhaled by the captives (being a narcotic poison) would also produce drowsiness and death. Q. Why do persons, who are so 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: 2ndly—There are more trees to restore the equilibrium of the vitiated air: and 3rdly—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? A. Because the fewer the inhabitants, Q. Why do trees and flowers help to make country air wholesome? A. Because trees and flowers absorb the carbonic acid generated by the lungs of animals, putrid substances, and other noxious exhalations. Q. Why is the air of cities less wholesome than country air? A. 1st—Because there are more inhabitants to vitiate the air: 2ndly—The sewers, drains, bins, and filth of a city, very greatly vitiate the air: 3rdly—The streets and alleys prevent a free circulation: and 4thly—Besides all this, there are fewer trees to absorb 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 both defective in oxygen, and impregnated 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 so on: besides, trees and gardens are not numerous enough to absorb the noxious gas as fast as it is generated. Q. What becomes of the carbonic acid of crowded cities? A. Some of it is absorbed by vegetables, 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 after it is thus diffused, it is carried to various lands, and absorbed in its passage by the vegetable world. 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 the air on the earth; and the air inside their bodies (seeking to become of the same rarity) bursts through their eyes and ears, producing an 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 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 rarefied by heat and vapour; and the air inside us (seeking to become of the same rarity) produces an oppressive and suffocating feeling. Q. Why do divers suffer great pain in their eyes and ears under water? A. Because the air at the bottom of the sea is more dense than the air on the surface; and while the air inside the diver’s body is settling 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. The ear is fitted with a small Q. Why do our corns ache just previous to rain? A. Previous to rain, the density of air is greatly lowered (as every one knows from the fall of the barometer); in consequence of an unequal pressure, our feet swell; but the hard corn, not being elastic, is painfully stretched and pressed. (Some of this pain is due to electricity.) Q. Why do cellars feel warm in winter? A. As the external air has not free access into cellars, they remain at a pretty even temperature, which (in winter time) is about 10 degrees warmer than the external air. Q. Why do cellars feel cold in summer time? A. As the external air has not free access into cellars, they remain at a pretty even temperature, which (in summer time) is about 10 degrees colder than the external air. Q. Why does lightning strike the oak-tree more frequently than any other tree? A. 1st—Because the grain of the oak, being closer than that of any other tree, renders it a better conductor: and 2ndly—The sap of the oak contains a large quantity of iron in solution, which is a most admirable conductor of lightning. Q. Why does air rust iron? A. The oxygen of the air combines with the surface of the iron, and produces oxide of iron, which is generally called rust. This rust is a species of combustion. Q. Why does hot iron scale and peel off, when struck with a hammer? A. The oxygen of the 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. Q. Why do stoves and fire-irons become rusty, in rooms which are not occupied? A. Because the air is damp; and moist air oxidizes (or rusts) iron and steel. Q. In what part of the year is it most difficult to keep stoves and fire-irons bright? A. In autumn and winter; because the capacity of the air for holding water being on the decrease, its vapour is deposited on every-thing with which it comes in contact. Q. Why does greasing iron prevent its becoming rusty? A. Because grease prevents the humidity 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 covered with plumbago, or black lead. Q. What is plumbago, or black lead? A. A mixture of charcoal and iron filings. 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 applied to bright stoves and even mathematical instruments, without injuring their delicate polish. Q. Why does ornamental steel (of a purple or lilac colour) rust more readily than polished white steel? A. Because the lilac tinge is produced by partial oxidation; and the process which forms rust has, therefore, already commenced. Q. How can lilac steel be kept free from rust? A. By keeping it in a very dry place; for then no additional oxygen will come in contact with it, to increase its amount of rust. Q. Do any other metals (besides iron) combine 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 lose its brightness, and become dull and of a darker hue, by being exposed to the air? A. The vapour of the air combines Q. Why is it difficult to keep silver bright? A. Because the vapour of the air oxidizes its surface, and tarnishes it. Q. Why do silver tea-pots and spoons tarnish more quickly than silver ore or bullion? A. Because alloy (of some baser metal) is used to make it more hard and lasting; and this alloy oxidizes more quickly than silver itself. Q. Why does German silver turn a dingy yellow in a few hours? A. German silver has a great affinity for oxygen, and shows its oxidation by a sickly yellow tarnish, instead of rust. Q. If quicksilver (or mercury) is tarnished like copper and lead,—Why does it preserve its brilliancy in barometers and thermometers? A. Because air is excluded from it, and no moisture comes in contact with it to oxidize (or tarnish it). Q. Is gold affected by the atmosphere? A. Not readily: gold will never 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 retain its bright surface in all weathers free from both rust and tarnish. Q. Before plat’inum was discovered, which of the metals was employed for the same purpose? A. Gold. Platinum, (a white metal), so called from “plata,” the Spanish word for silver. It was first introduced into England by Mr. Wood, (A. D. 1749) from South America. Q. For what other scientific purposes is plat’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? A. Because the acid would act upon Q. Which of the metals have the greatest affinity to oxygen? A. Those called potassium and sodium. Potassium and sodium derive their names from potash and soda. Potassa is the oxide of potassium; and soda is the oxide of sodium. Q. How is the affinity of potassium and sodium for oxygen shewn? A. They decompose water the moment they are brought into contact with it. Q. What effect has potassium on water? A. It catches fire the moment it is thrown into water, and burns with a vivid flame, which is still further increased by the combustion of hydrogen separated from the water. (N.B. Water is composed of oxygen and hydrogen; and potassium separates the two gases.) Q. What effect has sodium on water? A. It does not take fire as potassium does, but undergoes very rapid oxidation. Q. Is the furr of kettles an oxide? A. No; the furr (or deposit of boiling water) is a precipitate of lime Q. Is not this furr of boiling water often dangerous? 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 hinders 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 larger deposit of furr, than that which contains only vegetable matter. |
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