The Chemical History of a Candle
Chapter 1 · 1/4
The Chemical History of a Candle
Chapter 1
1THE CHEMICAL HISTORY OF A CANDLE A COURSE OF LECTURES DELIVERED BEFORE A JUVENILE AUDIENCE AT THE ROYAL INSTITUTION BY MICHAEL FARADAY, D.C.L., F.R.S. 2EDITED BY WILLIAM CROOKES, F.C.S. 3A NEW IMPRESSION, WITH ILLUSTRATIONS LONDON CHATTO & WINDUS 1908 PREFACE From the primitive pine-torch to the paraffin candle, how wide an interval! 4between them how vast a contrast! 5The means adopted by man to illuminate his home at night, stamp at once his position in the scale of civilisation. 6The fluid bitumen of the far East, blazing in rude vessels of baked earth; the Etruscan lamp, exquisite in form, yet ill adapted to its office; the whale, seal, or bear fat, filling the hut of the Esquimaux or Lap with odour rather than light; the huge wax candle on the glittering altar, the range of gas lamps in our streets,—all have their stories to tell. 7All, if they could speak (and, after their own manner, they can), might warm our hearts in telling, how they have ministered to man’s comfort, love of home, toil, and devotion. 8Surely, among the millions of fire-worshippers and fire-users who have passed away in earlier ages, _some_ have pondered over the mystery of fire; perhaps some clear minds have guessed shrewdly near the truth. 9Think of the time man has lived in hopeless ignorance: think that only during a period which might be spanned by the life of one man, has the truth been known. 10Atom by atom, link by link, has the reasoning chain been forged. 11Some links, too quickly and too slightly made, have given way, and been replaced by better work; but now the great phenomena are known—the outline is correctly and firmly drawn—cunning artists are filling in the rest, and the child who masters these Lectures knows more of fire than Aristotle did. 12The candle itself is now made to light up the dark places of nature; the blowpipe and the prism are adding to our knowledge of the earth’s crust; but the torch must come first. 13Among the readers of this book some few may devote themselves to increasing the stores of knowledge: the Lamp of Science _must_ burn. 14“_Alere flammam. 15_” W. 16CROOKES. 17CONTENTS. 18LECTURE I. 19A CANDLE: THE FLAME—ITS SOURCES—STRUCTURE—MOBILITY—BRIGHTNESS LECTURE II. 20BRIGHTNESS OF THE FLAME—AIR NECESSARY FOR COMBUSTION—PRODUCTION OF WATER LECTURE III. 21PRODUCTS: WATER FROM THE COMBUSTION—NATURE OF WATER—A COMPOUND—HYDROGEN LECTURE IV. 22HYDROGEN IN THE CANDLE—BURNS INTO WATER—THE OTHER PART OF WATER—OXYGEN LECTURE V. 23OXYGEN PRESENT IN THE AIR—NATURE OF THE ATMOSPHERE—ITS PROPERTIES—OTHER PRODUCTS FROM THE CANDLE—CARBONIC ACID—ITS PROPERTIES LECTURE VI. 24CARBON OR CHARCOAL—COAL-GAS—RESPIRATION AND ITS ANALOGY TO THE BURNING OP A CANDLE—CONCLUSION LECTURE ON PLATINUM. 25NOTES. 26THE CHEMICAL HISTORY OF A CANDLE LECTURE I. 27A CANDLE: THE FLAME—ITS SOURCES—STRUCTURE—MOBILITY—BRIGHTNESS. 28I purpose, in return for the honour you do us by coming to see what are our proceedings here, to bring before you, in the course of these lectures, the Chemical History of a Candle. 29I have taken this subject on a former occasion; and were it left to my own will, I should prefer to repeat it almost every year—so abundant is the interest that attaches itself to the subject, so wonderful are the varieties of outlet which it offers into the various departments of philosophy. 30There is not a law under which any part of this universe is governed which does not come into play, and is touched upon in these phenomena. 31There is no better, there is no more open door by which you can enter into the study of natural philosophy, than by considering the physical phenomena of a candle. 32I trust, therefore, I shall not disappoint you in choosing this for my subject rather than any newer topic, which could not be better, were it even so good. 33And before proceeding, let me say this also—that though our subject be so great, and our intention that of treating it honestly, seriously, and philosophically, yet I mean to pass away from all those who are seniors amongst us. 34I claim the privilege of speaking to juveniles as a juvenile myself. 35I have done so on former occasions—and, if you please, I shall do so again. 36And though I stand here with the knowledge of having the words I utter given to the world, yet that shall not deter me from speaking in the same familiar way to those whom I esteem nearest to me on this occasion. 37And now, my boys and girls, I must first tell you of what candles are made. 38Some are great curiosities. 39I have here some bits of timber, branches of trees particularly famous for their burning. 40And here you see a piece of that very curious substance taken out of some of the bogs in Ireland, called _candle-wood_,—a hard, strong, excellent wood, evidently fitted for good work as a resister of force, and yet withal burning so well that where it is found they make splinters of it, and torches, since it burns like a candle, and gives a very good light indeed. 41And in this wood we have one of the most beautiful illustrations of the general nature of a candle that I can possibly give. 42The fuel provided, the means of bringing that fuel to the place of chemical action, the regular and gradual supply of air to that place of action—heat and light—all produced by a little piece of wood of this kind, forming, in fact, a natural candle. 43But we must speak of candles as they are in commerce. 44Here are a couple of candles commonly called dips. 45They are made of lengths of cotton cut off, hung up by a loop, dipped into melted tallow, taken out again and cooled, then re-dipped until there is an accumulation of tallow round the cotton. 46In order that you may have an idea of the various characters of these candles, you see these which I hold in my hand—they are very small, and very curious. 47They are, or were, the candles used by the miners in coal mines. 48In olden times the miner had to find his own candles; and it was supposed that a small candle would not so soon set fire to the fire-damp in the coal mines as a large one; and for that reason, as well as for economy’s sake, he had candles made of this sort—20, 30, 40, or 60 to the pound. 49They have been replaced since then by the steel-mill, and then by the Davy-lamp, and other safety-lamps of various kinds. 50I have here a candle that was taken out of the _Royal George_[1], it is said, by Colonel Pasley. 51It has been sunk in the sea for many years, subject to the action of salt water. 52It shews you how well candles may be preserved; for though it is cracked about and broken a good deal, yet, when lighted, it goes on burning regularly, and the tallow resumes its natural condition as soon as it is fused. 53Mr. 54Field, of Lambeth, has supplied me abundantly with beautiful illustrations of the candle and its materials. 55I shall therefore now refer to them. 56And, first, there is the suet—the fat of the ox—Russian tallow, I believe, employed in the manufacture of these dips, which Gay Lussac, or some one who entrusted him with his knowledge, converted into that beautiful substance, stearin, which you see lying beside it. 57A candle, you know, is not now a greasy thing like an ordinary tallow candle, but a clean thing, and you may almost scrape off and pulverise the drops which fall from it without soiling anything. 58This is the process he adopted[2]:—The fat or tallow is first boiled with quick-lime, and made into a soap, and then the soap is decomposed by sulphuric acid, which takes away the lime, and leaves the fat re-arranged as stearic acid, whilst a quantity of glycerin is produced at the same time. 59Glycerin—absolutely a sugar, or a substance similar to sugar—comes out of the tallow in this chemical change. 60The oil is then pressed out of it; and you see here this series of pressed cakes, shewing how beautifully the impurities are carried out by the oily part as the pressure goes on increasing, and at last you have left that substance which is melted, and cast into candles as here represented. 61The candle I have in my hand is a stearin candle, made of stearin from tallow in the way I have told you. 62Then here is a sperm candle, which comes from the purified oil of the spermaceti whale. 63Here also are yellow bees-wax and refined bees-wax, from which candles are made. 64Here, too, is that curious substance called paraffin, and some paraffin candles made of paraffin obtained from the bogs of Ireland. 65I have here also a substance brought from Japan, since we have forced an entrance into that out-of-the-way place—a sort of wax which a kind friend has sent me, and which forms a new material for the manufacture of candles. 66And how are these candles made? 67I have told you about dips, and I will shew you how moulds are made. 68Let us imagine any of these candles to be made of materials which can be cast. 69“Cast!” 70you say. 71“Why, a candle is a thing that melts; and surely if you can melt it, you can cast it.” 72Not so. 73It is wonderful, in the progress of manufacture, and in the consideration of the means best fitted to produce the required result, how things turn up which one would not expect beforehand. 74Candles cannot always be cast. 75A wax candle can never be cast. 76It is made by a particular process, which I can illustrate in a minute or two: but I must not spend much time on it. 77Wax is a thing which, burning so well, and melting so easily in a candle, cannot be cast. 78However, let us take a material that can be cast. 79Here is a frame, with a number of moulds fastened in it. 80The first thing to be done is to put a wick through them. 81Here is one—a plaited wick, which does not require snuffing[3]—supported by a little wire. 82It goes to the bottom, where it is pegged in—the little peg holding the cotton tight, and stopping the aperture, so that nothing fluid shall run out. 83At the upper part there is a little bar placed across, which stretches the cotton and holds it in the mould. 84The tallow is then melted, and the moulds are filled. 85After a certain time, when the moulds are cool, the excess of tallow is poured off at one corner, and then cleaned off altogether, and the ends of the wick cut away. 86The candles alone then remain in the mould, and you have only to upset them, as I am doing, when out they tumble, for the candles are made in the form of cones, being narrower at the top than at the bottom; so that what with their form and their own shrinking, they only need a little shaking, and out they fall. 87In the same way are made these candles of stearin and of paraffin. 88It is a curious thing to see how wax candles are made. 89A lot of cottons are hung upon frames, as you see here, and covered with metal tags at the ends to keep the wax from covering the cotton in those places. 90These are carried to a heater, where the wax is melted. 91As you see, the frames can turn round; and as they turn, a man takes a vessel of wax and pours it first down one, and then the next and the next, and so on. 92When he has gone once round, if it is sufficiently cool, he gives the first a second coat, and so on until they are all of the required thickness. 93When they have been thus clothed, or fed, or made up to that thickness, they are taken off, and placed elsewhere. 94I have here, by the kindness of Mr. 95Field, several specimens of these candles. 96Here is one only half-finished. 97They are then taken down, and well rolled upon a fine stone slab, and the conical top is moulded by properly shaped tubes, and the bottoms cut off and trimmed. 98This is done so beautifully that they can make candles in this way weighing exactly four, or six, to the pound, or any number they please. 99We must not, however, take up more time about the mere manufacture, but go a little further into the matter. 100I have not yet referred you to luxuries in candles (for there is such a thing as luxury in candles). 101See how beautifully these are coloured: you see here mauve, magenta, and all the chemical colours recently introduced, applied to candles. 102You observe, also, different forms employed. 103Here is a fluted pillar most beautifully shaped; and I have also here some candles sent me by Mr. 104Pearsall, which are ornamented with designs upon them, so that as they burn you have as it were a glowing sun above, and a bouquet of flowers beneath. 105All, however, that is fine and beautiful is not useful. 106These fluted candles, pretty as they are, are bad candles; they are bad because of their external shape. 107Nevertheless, I shew you these specimens sent to me from kind friends on all sides, that you may see what is done, and what may be done in this or that direction; although, as I have said, when we come to these refinements, we are obliged to sacrifice a little in utility. 108Now, as to the light of the candle. 109We will light one or two, and set them at work in the performance of their proper functions. 110You observe a candle is a very different thing from a lamp. 111With a lamp you take a little oil, fill your vessel, put in a little moss or some cotton prepared by artificial means, and then light the top of the wick. 112When the flame runs down the cotton to the oil, it gets extinguished, but it goes on burning in the part above. 113Now, I have no doubt you will ask, how is it that the oil, which will not burn of itself, gets up to the top of the cotton, where it will burn? 114We shall presently examine that; but there is a much more wonderful thing about the burning of a candle than this. 115You have here a solid substance with no vessel to contain it; and how is it that this solid substance can get up to the place where the flame is? 116How is it that this solid gets there, it not being a fluid? 117or, when it is made a fluid, then how is it that it keeps together? 118This is a wonderful thing about a candle. 119We have here a good deal of wind, which will help us in some of our illustrations, but tease us in others; for the sake, therefore, of a little regularity, and to simplify the matter, I shall make a quiet flame—for who can study a subject when there are difficulties in the way not belonging to it? 120Here is a clever invention of some costermonger or street stander in the market-place for the shading of their candles on Saturday nights, when they are selling their greens, or potatoes, or fish. 121I have very often admired it. 122They put a lamp-glass round the candle, supported on a kind of gallery, which clasps it, and it can be slipped up and down as required. 123By the use of this lamp-glass, employed in the same way, you have a steady flame, which you can look at, and carefully examine, as I hope you will do, at home. 124You see, then, in the first instance, that a beautiful cup is formed. 125As the air comes to the candle it moves upwards by the force of the current which the heat of the candle produces, and it so cools all the sides of the wax, tallow, or fuel, as to keep the edge much cooler than the part within; the part within melts by the flame that runs down the wick as far as it can go before it is extinguished, but the part on the outside does not melt. 126If I made a current in one direction, my cup would be lop-sided, and the fluid would consequently run over,—for the same force of gravity which holds worlds together holds this fluid in a horizontal position, and if the cup be not horizontal, of course the fluid will run away in guttering. 127You see, therefore, that the cup is formed by this beautifully regular ascending current of air playing upon all sides, which keeps the exterior of the candle cool. 128No fuel would serve for a candle which has not the property of giving this cup, except such fuel as the Irish bogwood, where the material itself is like a sponge, and holds its own fuel. 129You see now why you would have had such a bad result if you were to burn these beautiful candles that I have shewn you, which are irregular, intermittent in their shape, and cannot therefore have that nicely-formed edge to the cup which is the great beauty in a candle. 130I hope you will now see that the perfection of a process—that is, its utility—is the better point of beauty about it. 131It is not the best looking thing, but the best acting thing, which is the most advantageous to us. 132This good-looking candle is a bad burning one. 133There will be a guttering round about it because of the irregularity of the stream of air and the badness of the cup which is formed thereby. 134You may see some pretty examples (and I trust you will notice these instances) of the action of the ascending current when you have A little gutter run down the side of a candle, making it thicker there than it is elsewhere. 135As the candle goes on burning, that keeps its place and forms a little pillar sticking up by the side, because, as it rises higher above the rest of the wax or fuel, the air gets better round it, and it is more cooled and better able to resist the action of the heat at a little distance. 136Now, the greatest mistakes and faults with regard to candles, as in many other things, often bring with them instruction which we should not receive if they had not occurred. 137We come here to be philosophers; and I hope you will always remember that whenever a result happens, especially if it be new, you should say, “What is the cause? 138Why does it occur?” 139and you will in the course of time find out the reason. 140Then, there is another point about these candles which will answer a question,—that is, as to the way in which this fluid gets out of the cup, up the wick, and into the place of combustion. 141You know that the flames on these burning wicks in candles made of bees-wax, stearin, or spermaceti, do not run down to the wax or other matter, and melt it all away, but keep to their own right place. 142They are fenced off from the fluid below, and do not encroach on the cup at the sides. 143I cannot imagine a more beautiful example than the condition of adjustment under which a candle makes one part subserve to the other to the very end of its action. 144A combustible thing like that, burning away gradually, never being intruded upon by the flame, is a very beautiful sight; especially when you come to learn what a vigorous thing flame is—what power it has of destroying the wax itself when it gets hold of it, and of disturbing its proper form if it come only too near. 145But how does the flame get hold of the fuel? 146There is a beautiful point about that—_capillary attraction_[4]. 147“Capillary attraction!” 148you say,—“the attraction of hairs.” 149Well, never mind the name: it was given in old times, before we had a good understanding of what the real power was. 150It is by what is called capillary attraction that the fuel is conveyed to the part where combustion goes on, and is deposited there, not in a careless way, but very beautifully in the very midst of the centre of action which takes place around it. 151Now, I am going to give you one or two instances of capillary attraction. 152It is that kind of action or attraction which makes two things that do not dissolve in each other still hold together. 153When you wash your hands, you wet them thoroughly; you take a little soap to make the adhesion better, and you find your hand remains wet. 154This is by that kind of attraction of which I am about to speak. 155And, what is more, if your hands are not soiled (as they almost always are by the usages of life), if you put your finger into a little warm water, the water will creep a little way up the finger, though you may not stop to examine it. 156I have here a substance which is rather porous—a column of salt—and I will pour into the plate at the bottom, not water, as it appears, but a saturated solution of salt which cannot absorb more; so that the action which you see will not be due to its dissolving anything. 157We may consider the plate to be the candle, and the salt the wick, and this solution the melted tallow. 158(I have coloured the fluid, that you may see the action better.) 159You observe that, now I pour in the fluid, it rises and gradually creeps up the salt higher and higher; and provided the column does not tumble over, it will go to the top. 160[Illustration: Fig. 1611.] 162If this blue solution were combustible, and we were to place a wick at the top of the salt, it would burn as it entered into the wick. 163It is a most curious thing to see this kind of action taking place, and to observe how singular some of the circumstances are about it. 164When you wash your hands, you take a towel to wipe off the water; and it is by that kind of wetting, or that kind of attraction which makes the towel become wet with water, that the wick is made wet with the tallow. 165I have known some careless boys and girls (indeed, I have known it happen to careful people as well) who, having washed their hands and wiped them with a towel, have thrown the towel over the side of the basin, and before long it has drawn all the water out of the basin and conveyed it to the floor, because it happened to be thrown over the side in such a way as to serve the purpose of a syphon.[ 1665] That you may the better see the way in which the substances act one upon another, I have here a vessel made of wire gauze filled with water, and you may compare it in its action to the cotton in one respect, or to a piece of calico in the other. 167In fact, wicks are sometimes made of a kind of wire gauze. 168You will observe that this vessel is a porous thing; for if I pour a little water on to the top, it will run out at the bottom. 169You would be puzzled for a good while if I asked you what the state of this vessel is, what is inside it, and why it is there? 170The vessel is full of water, and yet you see the water goes in and runs out as if it were empty. 171In order to prove this to you, I have only to empty it. 172The reason is this,—the wire, being once wetted, remains wet; the meshes are so small that the fluid is attracted so strongly from the one side to the other, as to remain in the vessel although it is porous. 173In like manner the particles of melted tallow ascend the cotton and get to the top; other particles then follow by their mutual attraction for each other, and as they reach the flame they are gradually burned. 174Here is another application of the same principle. 175You see this bit of cane. 176I have seen boys about the streets, who are very anxious to appear like men, take a piece of cane, and light it and smoke it, as an imitation of a cigar. 177They are enabled to do so by the permeability of the cane in one direction, and by its capillarity. 178If I place this piece of cane on a plate containing some camphine (which is very much like paraffin in its general character), exactly in the same manner as the blue fluid rose through the salt will this fluid rise through the piece of cane. 179There being no pores at the side, the fluid cannot go in that direction, but must pass through its length. 180Already the fluid is at the top of the cane: now I can light it and make it serve as a candle. 181The fluid has risen by the capillary attraction of the piece of cane, just as it does through the cotton in the candle. 182Now, the only reason why the candle does not burn all down the side of the wick is, that the melted tallow extinguishes the flame. 183You know that a candle, if turned upside-down, so as to allow the fuel to run upon the wick, will be put out. 184The reason is, that the flame has not had time to make the fuel hot enough to burn, as it does above, where it is carried in small quantities into the wick, and has all the effect of the heat exercised upon it. 185There is another condition which you must learn as regards the candle, without which you would not be able fully to understand the philosophy of it, and that is the vaporous condition of the fuel. 186In order that you may understand that, let me shew you a very pretty, but very common-place experiment. 187If you blow a candle out cleverly, you will see the vapour rise from it. 188You have, I know, often smelt the vapour of a blown-out candle—and a very bad smell it is; but if you blow it out cleverly, you will be able to see pretty well the vapour into which this solid matter is transformed. 189I will blow out one of these candles in such a way as not to disturb the air around it, by the continuing action of my breath; and now, if I hold a lighted taper two or three inches from the wick, you will observe a train of fire going through the air till it reaches the candle. 190I am obliged to be quick and ready, because, if I allow the vapour time to cool, it becomes condensed into a liquid or solid, or the stream of combustible matter gets disturbed. 191Now, as to the shape or form of the flame. 192It concerns us much to know about the condition which the matter of the candle finally assumes at the top of the wick—where you have such beauty and brightness as nothing but combustion or flame can produce. 193[Illustration: Fig. 1942.] 195You have the glittering beauty of gold and silver, and the still higher lustre of jewels, like the ruby and diamond; but none of these rival the brilliancy and beauty of flame. 196What diamond can shine like flame? 197It owes its lustre at night-time to the very flame shining upon it. 198The flame shines in darkness, but the light which the diamond has is as nothing until the flame shine upon it, when it is brilliant again. 199The candle alone shines by itself, and for itself, or for those who have arranged the materials. 200Now, let us look a little at the form of the flame as you see it under the glass shade. 201It is steady and equal; and its general form is that which is represented in the diagram, varying with atmospheric disturbances, and also varying according to the size of the candle. 202It is a bright oblong—brighter at the top than towards the bottom—with the wick in the middle, and besides the wick in the middle, certain darker parts towards the bottom, where the ignition is not so perfect as in the
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