OUTLINES OF POPULAR SCIENCE FOR CHILDREN OF ALL AGES. minutes of anxious suspense, during which, many an impatient eye was ever and anon directed towards the dial of the clock, the hand of which at last points to three, faintly strikes one, (as all unobtrusive clocks in lecture theatres are wont to (A SKETCH OF PROFESSOR FARADAY'S LECTURES TO do), and the lecturer walks in. Well, CHILDREN.) UNDER this title we mean to present to our young readers from time to time, (as frequently, indeed, as an opportunity occurs,) a working abstract of many lectures, which, being delivered in the metropolis to a favoured few, have hitherto been lost to the multitude. We intend to make this abstract plain as plain can be never using learned words when common words will serve; never taking anything for granted that has not been told. Never describing any experiment which a child cannot perform. Now there is a good deal in the proper beginning of a subject, as everybody knows. The witty Lucian of old said "the beginning, indeed, is half of all." The modern Spanish Proverb says:-"A thing well begun is in a manner finished;" a proverb, indeed, which in our opinion, overshoots the mark. We do not want to think, and we should not like our young friends to think, that our outlines just begun from which we hope to have so much pleasure,-which we hope will give our young readers so much pleasure,- -was already in a manner finished. But to the point: What can be so fortunate a beginning for us as a sketch of Professor Faraday's Lectures on Chemistry, addressed especially to children, and now in the course of delivery at the Royal Institution? What can be so lucky a time for the beginning, as the new year? Let our juvenile readers picture to themselves the Royal Institution lecture theatrewhen the first juvenile lecture of this course began. Let them picture to themselves a large amphitheatre of rising seats -tier after tier upwards extending,-the whole looking down upon the lecturer's table. Let them picture to themselves all the front seats, usually occupied by the greatest philosophers, now exclusively reserved for little boys and girls, each of whom sat half hidden behind note-books, almost bigger than the tiny individuals who held them. Let them fancy some the first thing Professor Faraday does is to assure his little friends that he is neither going to do or to say anything which they may not all perfectly understand,-nothing which they cannot do at home as well as here. He bids them to join him in a sort of Christmas game,―he admonishes mamma and papa, that long before he has finished, they will probably say to themselves "Dear me, the man is childish."-Childish? to be sure, said Professor Faraday. I mean to be childish-I try to be childish-I am bound to be childish; and why?-Because I talk to children. Professor Faraday now commenced his lecture by selecting for discussion the theme or proposition "WHY DO CER TAIN BODIES BURN?" Aye, now-Why do certain bodies burn? How very simple does the answer to this question seem. What answer would most children be likely to give?-Because of their touching fire, one would say. Stop then, let us see. Doesn't a lucifer-match burn when you rub it, and without touching fire? Doesn't the percussion-cap of a gun explode when you strike it, and without touching fire? It is quite clear then, that although certain burnable substances will burn when they touch fire, others will burn without any such contact. I can't tell why substances do burn, another child may say, but I can tell when Fig. 1. they will not burn. They won't burn when water is thrown upon them, that's very sure. P Indeed? Then just regard Professor I Faraday's first experiment. He takes a pointed wire, fixes on to its point a soft, shiny something, very much like silver to look at, and he brings this something in contact with the falling water of a fountain; when, strange to behold, a burst of flame results, the shining body, which is | potassium, and the water both take fire. (Fig. 1.) Well, now, is it not quite clear, that at least one body, will even burn on coming into contact with water? At this point let us pause. Is it not evident, children, that you do not know why it is that certain substances, combustibles, burnables as I will term them, in themselves, take fire?-How are you to know ?-How does the philosopher know ?-How do we all know?-Simply by trying experiments; and remember that whatever in chemistry has once occurred, will always, under the same circumstances, occur again; be sure of that. Potassium will always burn when you touch it with water, as I touched it just now. Lucifer-matches well made, will always inflame when rubbed under similar circumstances, with equal force. Percussion - caps will always explode if, being equally good, they be struck with equal force. This way of getting knowledge by trying experiments, and seeing in what they end, is called the practice of inductive philosophy-what can be more natural than such a plan of proceeding? What more natural? do we not all follow it, almost unknown to ourselves; old and young, are we not all inductive philosophers? What boy purchases a top without liking to try beforehand, whether it will spin or not; or a kite, without liking to see whether it will fly ?-or what girl buys a doll, warranted to speak, without trying whether she will speak? However little we know it, then, we are all inductive philosophers. Under what circumstances, again to put the question, will a combustible body burn ?-what is the reason of its burning? Let us all be inductive philosophers, and think. "I will try one experiment upon that matter,"-let us fancy an interlocutor to say; one thing I noticed was, that the potassium although touching water, also, when it burned touched the air.-Suppose, then, try the experiment—I will scoop out the end of a little stick so; but much deeper, (Fig. 2;) and and in the scoopedout depression, I will squeeze the bit of potassium; I will take the stick and plunge its armed end down through a glass of water, so. (Fig. 3.) Fig.2. then Fig. 3. one reason at any rate, why bodies burnthey must be in contact with air-for the potassium now does not burn until it escapes from the hollow stick and floats on the water. Bravo! I have found out That is quite true, all exclaim; of course it is, how could we be so stupid. I'll prove it another way, says a young gentleman, as follows. I will take a short wax taper, light it, put it on a table and cover it with a tumbler, so. (Fig. 4.) Fig. 4. Ah, there it goes; dim and more dim burns the flame, and see, now the flame goes out. Isn't it quite certain that combustible bodies won't burn without air? "Be very careful of what you consider proved," remarked Professor Faraday; this is the essence of philosophy." Now it may be proved that a candle won't burn without air, but it is not proved from anything we have as yet seen, that all substances are thus limited; on the contrary. I shall now show an experiment which will prove that we may get bodies to burn without air. Into this glass I pour first Fig. 5. under water. some water, then some crystals of a salt, called the chlorate of potash-a substance, which although soluble in water, is not soluble all at once. Upon this, I drop some fragments of phosphorus; then through a small glass tube, with funnel mouth, I pour a little oil of vitriol. (Fig. 5.) See what now takes place, there is fire Nor is it absolutely necessary to take this trouble to arrive at our conclusion. If the firework, called a serpent, be ignited and plunged under water, it will still continue to burn. Indeed, this provision is necessary, not only as regards fireworks for amusement, but as applied to the more terrible applications of war. We are none of us warriors here, we are philosophers; yet I shall not hesitate, remarked Professor Faraday, to illustrate my subject by reference to what is termed a shell or carcase fuse,-a contrivance which being thrust into the aperture of a bomb-shell, or a carcase (which is a variety of bomb-shell), filled with slow-burning materials, ignites with the blast of the mortar and burns. Now it is necessary, that not only provision be made for the continuous burning of this carcase bomb-shell fuse in air, but also that it shall not be extinguished even if it come into contact with water. Hence when ignited and held under water it does not go out. (The experimenter may try this experiment with a serpent). or "We have not only learned by our experiments," remarked Professor Faraday, "that certain bodies can burn without air, but we also begin to see certain gleamings of our general truth. We shall presently see what it is in air that makes things burn. Because, reflect on this. Even limiting our remarks to the candle, which placed burning under an inverted glass soon went out, it cannot be correct to say that the flame went out for want of air. At the period of extinction of flame there is air left, as can be seen. We must limit our remark, then, to the expression that it went out for want of fresh air. That would be correct. But let us go a little further. Does the candle, by burning, remove any of the air; and what Let us see: (Fig. 6.) "If I take the same wax-candle, and ignite it, put it to stand in the middle of a soup-plate, containing water, invert over it a glass and allow the whole to stand at rest; the candle after a time goes out, and water runs in the glass,-thus proving that one portion of the air has been burned away. But the demonstration may be still better effected by employing some Fig. 6. sort of air remains? Fig. 7. substance more combustible than a candle. Thus, if into a little tin dish I put a bit of phosphorus, place the dish to float upon the surface of water, ignite the phosphorus by touching it with a hot wire, and then invert over it the glass as before, combustion will proceed, the phosphorus will ultimately go out, and the water will rise to the extent of one fifth, or, in other words, one-fifth of the atmospheric air will have been burned away, leaving four - fifths behind, totally incapable of supporting combustion. (Fig. 7.) "It is evident then that for substances that burn in the air, not all the air is capable of supporting combustion but only a portion of it; and now comes a curious question, what becomes of that part which is burned away? What becomes, for instance, of that part which the phosphorus burned away? Evidently it did not escape, because the glass very carefully kept it in. What, then, became of it? -Why, in answer to that, you must take my word. I cannot demonstrate all things, I say, in the course of a rapid lecture, but must ask you to believe me. That portion of the air which the phosphorus burns away, unites with the phosphorus into the solid form, and constitutes the red-looking solid which remains. "Here, then, we appear to have some clue to the mystery. We learn that one portion of the air at least can be solidified -can exist in a solid; therefore, now we may begin to ask ourselves whether some material existing in our compound which we got to burn under water does not contain a portion of air solidified. Whether some material of serpents and carcase fuses does not contain the same. Let us then proceed to examine this subject. You will remember that in my experiment of getting phosphorus to burn under water, I used chlorate of potash-perhaps you know also that nitre, or nitrate of potash, is one of the ingredients of gunpowder, and consequently of serpents, portfires, carcase fuses and so forth. Let us examine these two substances :-First, as regards nitre, I am going to try an experiment which I am sure every boy knows. I am going to make some touch-paper. Paper is com. bustible we are all aware, that is to say, if lighted it flames and burns away. If the flame be blown out, the remaining coal soon becomes extinguished; but if I moisten the paper with a solution of nitre in water, and dry it, then ignite it, see what a remarkable effect takes place. If I cause it to burst into flame it burns like any other paper, but if I blow out the flame then combustion still proceeds; not a flaming combustion but a combustion in sparks. "If instead of nitre I make a solution of chlorate of potash and moisten another piece of paper in a similar way, I also make touch-paper. Is it not evident therefore that nitre and chlorate of potash both of them increase the combustibility of paper? "For aught we know from the evidence before us, they may both contain, in the solid form, that part of the air which has the power of supporting combustion." Fig. S. Now in order to do what Professor Faraday did (or something like it,-for we don't mean to pledge ourselves to be literal copyists), let our young readers proceed as follows. Into a retort made of German glass without lead, or English green glass, but not common English white flint glass, which too easily melts,-put about a teaspoonful of chlorate of potash; then plunge the back of the retort under the mouth of a bottle previously filled with water, inverted in a wash-basin full of water, and tilted up in such a manner, by means of two bits of brick, or any other heavy substance, that the back of the retort will easily be under the inverted mouth of the bottle. Now apply heat to the retort, by means of some lighted charcoal placed upon a fire-pan, or any other convenient support, we are not particular about that. Professor Faraday used a crucible of black Fig. 9. lead, perforated with holes; (Fig. 9.) supplied with an iron grating, firmly bound together with wire; a com mon clay flower-pot similarly fitted up, answers perfectly well; but as we said before, the fire- pan will serve for the nonce; presently an air or gas will come over and would fill the bottle if collected; it is better, however, to allow the first portions to escape. As soon as the bottle becomes full of gas, slide under its mouth a flat plate of glass; reverse the bottle and put it to stand on the table, thus. (Fig. 10.) Fig. 10. "So it appears," continued the lecturer," that we have actually succeeded in getting from this solid chlorate a gas or air, for gas is only another name for air. Let us see what sort of air it is, and what will it do. Remember we are hunting for a certain something that shall enable burnable substances to burn. Let us try it thus." And let the reader try it, let him learn by experiment what sort of a gas he has got. Let him take a long slip of wood, and having set fire to one end, let him blow out the flame, so that only a little ignited charcoal point shall remain. Plunge this glowing end into the gas. and mark how the stick bursts into flame. How beautiful is this! how simple is all becoming! how clearly do appearances unveil themselves! From a solid body we have got out an air, a gas, for the terms are the same, and this gas is the same, the very same, test it as you will, that forms that part of the atmosphere, and enables bodies to burn. It is the very virtue of the air, so to speak,—we won't give it a name just yet, the very essence. Chlorate of potash contains much of it; nitre contains an equal quantity; therefore how easy is it to learn the reason why touch-paper burns so well. We may now put our knowledge together; burnable bodies burn, not universally because fire is applied to them, for some burn without, and some, as will be shown hereafter, don't burn even then; but they burn when they are heated to a certain extent in contact with a supporter of combustion in a convenient form. That is all our experiments warrant us in saying at present; by-and-by other points will be made out. Now don't imagine there is only one supporter of combustion there are several, but the most important, the grandest in its effects, the most glorious in its action, is what we will at present call the virtue of atmospheric air. And now one word more. Did we not say that bodies before they can burn must be heated to a certain extent ?—and was the potassium heated by coming into contact with cold water? Assuredly it was. That point can be demonstrated, and so on for the rest. Friction heats the lucifer-match; percussion heats the gun-cap; in every ease heating in one way or another must be applied. One thing more must here be remembered. Burnable bodies will not all burn under precisely similar circumstances. Potassium will burn if it touches water, but it won't burn under water. Phosphorus and chlorate mixed, will burn under water perfectly well; so will a firework serpent, or a carcase fuse. The wick of a candle and its contained oil will burn, but not the surrounding wax or grease, whereas a piece of camphor (try it) will burn all over. Thus burnable bodies have most of them different burning propensities; and many which you think won't burn at all, will burn perfectly well when their caprices are favoured, as we shall see hereafter. All combustible or burnable bodies have their caprices, or fancies, so to speak; not only must they be heated in contact with a supporter of combustion, but they must be heated under particular circumstances. As a special illustration of this fact we cannot do better than conclude this sketch by describing an experiment performed by Professor Faraday. The experiment is pretty, interesting and instructive; moreover, it shows the exact way of making lightning as adopted in plays and pantomimes. Lycopodium may be called a sort of seed of a sort of fern. Don't be too severe on the Editor, young gentlemen and ladies who know botany; he is perfectly aware that lycopodium is not a fern; he is also aware that neither ferns nor lycopodiums have any seeds but spores. He knows all this just as well as the facts that wheat, barley, and cats, are not seeds but fruits; that strawberries, pine-apples, and figs, are no fruits; or that cactus plants have no leaves. Lycopodium is a sort of seed with a mallet or hammer, or anything of that kind, so that the lycopodium may fill the air as a cloud. Hold now a lighted candle in the cloud, and see what takes place; the whole cloud burns with a vivid flash. Thus do we learn that the lycopodium, though perfectly willing to burn, will only burn when the air is mixed with it in a particular way. Children, put together all these facts. In a future Number we will proceed to learn something more about that distilled gas, which, for the present, shall still be called the virtue of atmospheric air. But DESIRE OF APPROBATION.-I am much less regardful of the approbation of man, and set much lighter by contempt or applause, than I did long ago. I am oft suspicious that this is not only from the increase of self-denial and humility, but partly from my being glutted and surfeited with human applause; and all worldly things appear most vain and unsatisfactory when we have tried them most. though I feel that this hath some hand in the effect, yet, as far as I can perceive, the knowledge of man's nothingness, and God's transcendent greatness, with whom it is that I have most to do, and the sense of the brevity of human things, and the nearness of eternity, are the principal causes of this effect; which some have imputed to self-conceitedness and morosity. |