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diff --git a/old/14474-0.txt b/old/14474-0.txt new file mode 100644 index 0000000..617a857 --- /dev/null +++ b/old/14474-0.txt @@ -0,0 +1,3938 @@ +The Project Gutenberg eBook of The Chemical History Of A Candle, by Michael Faraday + +This eBook is for the use of anyone anywhere in the United States and +most other parts of the world at no cost and with almost no restrictions +whatsoever. You may copy it, give it away or re-use it under the terms +of the Project Gutenberg License included with this eBook or online at +www.gutenberg.org. If you are not located in the United States, you +will have to check the laws of the country where you are located before +using this eBook. + +Title: The Chemical History Of A Candle + +Author: Michael Faraday + +Release Date: December 21, 2020 [eBook #14474] +[Most recently updated: October 21, 2023] + +Language: English + +Character set encoding: UTF-8 + +Produced by: Clare Boothby, Richard Prairie and +the PG Online Distributed Proofreading Team +Revised by Richard Tonsing. + +*** START OF THE PROJECT GUTENBERG EBOOK THE CHEMICAL HISTORY OF A CANDLE *** + + + + + THE 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. + + EDITED BY + + WILLIAM CROOKES, F.C.S. + + A NEW IMPRESSION, WITH ILLUSTRATIONS + + LONDON + + CHATTO & WINDUS + + 1908 + + + + +PREFACE + +From the primitive pine-torch to the paraffin candle, how wide an +interval! between them how vast a contrast! The means adopted by man to +illuminate his home at night, stamp at once his position in the scale of +civilisation. The 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. All, 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. + +Surely, 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. Think +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. + +Atom by atom, link by link, has the reasoning chain been forged. Some +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. + +The 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. + +Among the readers of this book some few may devote themselves to +increasing the stores of knowledge: the Lamp of Science _must_ burn. +“_Alere flammam._” + +W. CROOKES. + + + + +CONTENTS. + + +LECTURE I. + +A CANDLE: THE FLAME—ITS SOURCES—STRUCTURE—MOBILITY—BRIGHTNESS + + +LECTURE II. + +BRIGHTNESS OF THE FLAME—AIR NECESSARY FOR COMBUSTION—PRODUCTION OF WATER + + +LECTURE III. + +PRODUCTS: WATER FROM THE COMBUSTION—NATURE OF WATER—A COMPOUND—HYDROGEN + + +LECTURE IV. + +HYDROGEN IN THE CANDLE—BURNS INTO WATER—THE OTHER PART OF WATER—OXYGEN + + +LECTURE V. + +OXYGEN PRESENT IN THE AIR—NATURE OF THE ATMOSPHERE—ITS PROPERTIES—OTHER +PRODUCTS FROM THE CANDLE—CARBONIC ACID—ITS PROPERTIES + + +LECTURE VI. + +CARBON OR CHARCOAL—COAL-GAS—RESPIRATION AND ITS ANALOGY TO THE BURNING +OP A CANDLE—CONCLUSION + + +LECTURE ON PLATINUM. + + +NOTES. + + + + +THE CHEMICAL HISTORY OF A CANDLE + +LECTURE I. + +A CANDLE: THE FLAME—ITS SOURCES—STRUCTURE—MOBILITY—BRIGHTNESS. + + +I 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. I 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. There 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. There 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. I +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. + +And 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. I claim the privilege of speaking to juveniles as a juvenile +myself. I have done so on former occasions—and, if you please, I shall do +so again. And 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. + +And now, my boys and girls, I must first tell you of what candles are +made. Some are great curiosities. I have here some bits of timber, +branches of trees particularly famous for their burning. And 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. And in this +wood we have one of the most beautiful illustrations of the general nature +of a candle that I can possibly give. The 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. + +But we must speak of candles as they are in commerce. Here are a couple of +candles commonly called dips. They 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. +In 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. They are, or were, the candles used by the miners in coal +mines. In 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. They have been replaced since then by the steel-mill, and then by +the Davy-lamp, and other safety-lamps of various kinds. I have here a +candle that was taken out of the _Royal George_[1], it is said, by Colonel +Pasley. It has been sunk in the sea for many years, subject to the action +of salt water. It 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. + +Mr. Field, of Lambeth, has supplied me abundantly with beautiful +illustrations of the candle and its materials. I shall therefore now refer +to them. And, 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. A 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. This 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. +Glycerin—absolutely a sugar, or a substance similar to sugar—comes out +of the tallow in this chemical change. The 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. The candle I have in my hand is a +stearin candle, made of stearin from tallow in the way I have told you. +Then here is a sperm candle, which comes from the purified oil of the +spermaceti whale. Here also are yellow bees-wax and refined bees-wax, from +which candles are made. Here, too, is that curious substance called +paraffin, and some paraffin candles made of paraffin obtained from the +bogs of Ireland. I 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. + +And how are these candles made? I have told you about dips, and I will +shew you how moulds are made. Let us imagine any of these candles to be +made of materials which can be cast. “Cast!” you say. “Why, a candle is a +thing that melts; and surely if you can melt it, you can cast it.” Not so. +It 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. Candles cannot always be cast. A +wax candle can never be cast. It is made by a particular process, which I +can illustrate in a minute or two: but I must not spend much time on it. +Wax is a thing which, burning so well, and melting so easily in a candle, +cannot be cast. However, let us take a material that can be cast. Here is +a frame, with a number of moulds fastened in it. The first thing to be +done is to put a wick through them. Here is one—a plaited wick, which +does not require snuffing[3]—supported by a little wire. It 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. At the +upper part there is a little bar placed across, which stretches the cotton +and holds it in the mould. The tallow is then melted, and the moulds are +filled. After 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. The 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. In the same way are made +these candles of stearin and of paraffin. It is a curious thing to see how +wax candles are made. A 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. These are carried to a heater, where +the wax is melted. As 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. When 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. When they have been thus clothed, or +fed, or made up to that thickness, they are taken off, and placed +elsewhere. I have here, by the kindness of Mr. Field, several specimens of +these candles. Here is one only half-finished. They 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. This 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. + +We must not, however, take up more time about the mere manufacture, but go +a little further into the matter. I have not yet referred you to luxuries +in candles (for there is such a thing as luxury in candles). See how +beautifully these are coloured: you see here mauve, magenta, and all the +chemical colours recently introduced, applied to candles. You observe, +also, different forms employed. Here is a fluted pillar most beautifully +shaped; and I have also here some candles sent me by Mr. Pearsall, 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. All, however, +that is fine and beautiful is not useful. These fluted candles, pretty as +they are, are bad candles; they are bad because of their external shape. +Nevertheless, 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. + +Now, as to the light of the candle. We will light one or two, and set them +at work in the performance of their proper functions. You observe a candle +is a very different thing from a lamp. With 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. When the flame runs +down the cotton to the oil, it gets extinguished, but it goes on burning +in the part above. Now, 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? We shall presently examine that; but there is a much +more wonderful thing about the burning of a candle than this. You 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? How is it +that this solid gets there, it not being a fluid? or, when it is made a +fluid, then how is it that it keeps together? This is a wonderful thing +about a candle. + +We 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? Here 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. +I have very often admired it. They 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. By 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. + +You see, then, in the first instance, that a beautiful cup is formed. As +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. If 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. You 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. No 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. You 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. I hope you will now +see that the perfection of a process—that is, its utility—is the better +point of beauty about it. It is not the best looking thing, but the best +acting thing, which is the most advantageous to us. This good-looking +candle is a bad burning one. There 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. You 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. As 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. Now, 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. We +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? Why does it occur?” and you will in the course of time find +out the reason. + +Then, 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. You 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. They are fenced off from the fluid below, and do +not encroach on the cup at the sides. I 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. A 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. + +But how does the flame get hold of the fuel? There is a beautiful point +about that—_capillary attraction_[4]. “Capillary attraction!” you +say,—“the attraction of hairs.” Well, never mind the name: it was given +in old times, before we had a good understanding of what the real power +was. It 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. Now, I am going to give you one or two +instances of capillary attraction. It is that kind of action or attraction +which makes two things that do not dissolve in each other still hold +together. When 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. This is by that kind of attraction of which I am about to speak. And, +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. I 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. +We may consider the plate to be the candle, and the salt the wick, and +this solution the melted tallow. (I have coloured the fluid, that you may +see the action better.) You 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. + +[Illustration: Fig. 1.] + +If 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. It 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. When 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. I 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.[5] 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. In fact, wicks are sometimes made of +a kind of wire gauze. You 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. +You 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? The vessel is full +of water, and yet you see the water goes in and runs out as if it were +empty. In order to prove this to you, I have only to empty it. The 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. In 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. + +Here is another application of the same principle. You see this bit of +cane. I 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. They are enabled to do so by the permeability of the cane in +one direction, and by its capillarity. If 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. There +being no pores at the side, the fluid cannot go in that direction, but +must pass through its length. Already the fluid is at the top of the cane: +now I can light it and make it serve as a candle. The fluid has risen by +the capillary attraction of the piece of cane, just as it does through the +cotton in the candle. + +Now, the only reason why the candle does not burn all down the side of the +wick is, that the melted tallow extinguishes the flame. You know that a +candle, if turned upside-down, so as to allow the fuel to run upon the +wick, will be put out. The 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. + +There 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. In order that you may +understand that, let me shew you a very pretty, but very common-place +experiment. If you blow a candle out cleverly, you will see the vapour +rise from it. You 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. I 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. +I 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. + +Now, as to the shape or form of the flame. It 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. + +[Illustration: Fig. 2.] + +You 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. What diamond can shine like flame? It owes +its lustre at night-time to the very flame shining upon it. The 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. The candle +alone shines by itself, and for itself, or for those who have arranged the +materials. Now, let us look a little at the form of the flame as you see +it under the glass shade. It 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. It 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 +part above. + +[Illustration: Fig. 3.] + +I have a drawing here, sketched many years ago by Hooke, when he made his +investigations. It is the drawing of the flame of a lamp, but it will +apply to the flame of a candle. The cup of the candle is the vessel or +lamp, the melted spermaceti is the oil, and the wick is common to both. +Upon that he sets this little flame, and then he represents what is +true—a certain quantity of matter rising about it which you do not see, +and which, if you have not been here before, or are not familiar with the +subject, you will not know of. He has here represented the parts of the +surrounding atmosphere that are very essential to the flame, and that are +always present with it. There is a current formed, which draws the flame +out—for the flame which you see is really drawn out by the current, and +drawn upward to a great height—just as Hooke has here shewn you by that +prolongation of the current in the diagram. You may see this by taking a +lighted candle, and putting it in the sun so as to get its shadow thrown +on a piece of paper. How remarkable it is that that thing which is light +enough to produce shadows of other objects, can be made to throw its own +shadow on a piece of white paper or card, so that you can actually see +streaming round the flame something which is not part of the flame, but is +ascending and drawing the flame upwards. Now, I am going to imitate the +sunlight, by applying the voltaic battery to the electric lamp. You now +see our sun, and its great luminosity; and by placing a candle between it +and the screen, we get the shadow of the flame. + +[Illustration: Fig. 4.] + +You observe the shadow of the candle and of the wick; then there is a +darkish part, as represented in the diagram, and then a part which is more +distinct. Curiously enough, however, what we see in the shadow as the +darkest part of the flame is, in reality, the brightest part; and here you +see streaming upwards the ascending current of hot air, as shewn by +Hooke, which draws out the flame, supplies it with air, and cools the +sides of the cup of melted fuel. + +I can give you here a little further illustration, for the purpose of +shewing you how flame goes up or down; according to the current. I have +here a flame—it is not a candle-flame—but you can, no doubt, by this +time, generalise enough to be able to compare one thing with another. What +I am about to do is to change the ascending current that takes the flame +upwards into a descending current. This I can easily do by the little +apparatus you see before me. The flame, as I have said, is not a candle +flame, but it is produced by alcohol, so that it shall not smoke too much. +I will also colour the flame with another substance[6], so that you may +trace its course; for with the spirit alone you could hardly see well +enough to have the opportunity of tracing its direction. By lighting this +spirit-of-wine, we have then a flame produced; and you observe that when +held in the air, it naturally goes upwards. + +[Illustration: Fig. 5] + +You understand now easily enough why flames go up under ordinary +circumstances—it is because of the draught of air by which the combustion +is formed. But now, by blowing the flame down, you see I am enabled to +make it go downwards into this little chimney—the direction of the +current being changed. Before we have concluded this course of lectures, +we shall shew you a lamp in which the flame goes up and the smoke goes +down, or the flame goes down and the smoke goes up. You see, then, that we +have the power in this way of varying the flame in different directions. + +There are now some other points that I must bring before you. Many of the +flames you see here vary very much in their shape by the currents of air +blowing around them in different directions; but we can, if we like, make +flames so that they will look like fixtures, and we can photograph +them—indeed, we have to photograph them—so that they become fixed to us, +if we wish to find out everything concerning them. That, however, is not +the only thing I wish to mention. If I take a flame sufficiently large, it +does not keep that homogeneous, that uniform condition of shape, but it +breaks out with a power of life which is quite wonderful. I am about to +use another kind of fuel, but one which is truly and fairly a +representative of the wax or tallow of a candle. I have here a large ball +of cotton, which will serve as a wick. And, now that I have immersed it in +spirit and applied a light to it, in what way does it differ from an +ordinary candle? Why, it differs very much in one respect, that we have a +vivacity and power about it, a beauty and a life entirely different from +the light presented by a candle. You see those fine tongues of flame +rising up. You have the same general disposition of the mass of the flame +from below upwards; but, in addition to that, you have this remarkable +breaking out into tongues which you do not perceive in the case of a +candle. Now, why is this? I must explain it to you, because when you +understand that perfectly, you will be able to follow me better in what I +have to say hereafter. I suppose some here will have made for themselves +the experiment I am going to shew you. Am I right in supposing that +anybody here has played at snapdragon? I do not know a more beautiful +illustration of the philosophy of flame, as to a certain part of its +history, than the game of snapdragon. First, here is the dish; and let me +say, that when you play snapdragon properly, you ought to have the dish +well-warmed; you ought also to have warm plums and warm brandy, which, +however, I have not got. When you have put the spirit into the dish, you +have the cup and the fuel; and are not the raisins acting like the wicks? +I now throw the plums into the dish, and light the spirit, and you see +those beautiful tongues of flame that I refer to. You have the air +creeping in over the edge of the dish forming these tongues. Why? Because, +through the force of the current and the irregularity of the action of the +flame, it cannot flow in one uniform stream. The air flows in so +irregularly that you have what would otherwise be a single image, broken +up into a variety of forms, and each of these little tongues has an +independent existence of its own. Indeed, I might say, you have here a +multitude of independent candles. You must not imagine, because you see +these tongues all at once, that the flame is of this particular shape. A +flame of that shape is never so at any one time. Never is a body of flame, +like that which you just saw rising from the ball, of the shape it appears +to you. It consists of a multitude of different shapes, succeeding each +other so fast that the eye is only able to take cognisance of them all at +once. In former times, I purposely analysed a flame of that general +character, and the diagram shews you the different parts of which it is +composed. They do not occur all at once: it is only because we see these +shapes in such rapid succession, that they seem to us to exist all at one +time. + +[Illustration: Fig. 6.] + +It is too bad that we have not got further than my game of snapdragon; but +we must not, under any circumstances, keep you beyond your time. It will +be a lesson to me in future to hold you more strictly to the philosophy of +the thing, than to take up your time so much with these illustrations. + + + + +LECTURE II. + +A CANDLE: BRIGHTNESS OF THE FLAME—AIR NECESSARY FOR +COMBUSTION—PRODUCTION OF WATER. + + +We were occupied the last time we met in considering the general character +and arrangement as regards the fluid portion of a candle, and the way in +which that fluid got into the place of combustion. You see, when we have a +candle burning fairly in a regular, steady atmosphere, it will have a +shape something like the one shewn in the diagram, and will look pretty +uniform, although very curious in its character. And now, I have to ask +your attention to the means by which we are enabled to ascertain what +happens in any particular part of the flame—why it happens, what it does +in happening, and where, after all, the whole candle goes to: because, as +you know very well, a candle being brought before us and burned, +disappears, if burned properly, without the least trace of dirt in the +candlestick—and this is a very curious circumstance. In order, then, to +examine this candle carefully, I have arranged certain apparatus, the use +of which you will see as I go on. Here is a candle: I am about to put the +end of this glass tube into the middle of the flame—into that part which +old Hooke has represented in the diagram as being rather dark, and which +you can see at any time, if you will look at a candle carefully, without +blowing it about. We will examine this dark part first. + +[Illustration: Fig. 7.] + +Now, I take this bent glass tube, and introduce one end into that part of +the flame, and you see at once that something is coming from the flame, +out at the other end of the tube; and if I put a flask there, and leave it +for a little while, you will see that something from the middle part of +the flame is gradually drawn out, and goes through the tube and into that +flask, and there behaves very differently from what it does in the open +air. It not only escapes from the end of the tube, but falls down to the +bottom of the flask like a heavy substance, as indeed it is. We find that +this is the wax of the candle made into a vaporous fluid—not a gas. (You +must learn the difference between a gas and a vapour: a gas remains +permanent, a vapour is something that will condense.) If you blow out a +candle, you perceive a very nasty smell, resulting from the condensation +of this vapour. That is very different from what you have outside the +flame; and, in order to make that more clear to you, I am about to produce +and set fire to a larger portion of this vapour—for what we have in the +small way in a candle, to understand thoroughly, we must, as philosophers, +produce in a larger way, if needful, that we may examine the different +parts. And now Mr. Anderson will give me a source of heat, and I am about +to shew you what that vapour is. Here is some wax in a glass flask, and I +am going to make it hot, as the inside of that candle-flame is hot, and +the matter about the wick is hot. [The Lecturer placed some wax in a glass +flask, and heated it over a lamp.] Now, I dare say that is hot enough for +me. You see that the wax I put in it has become fluid, and there is a +little smoke coming from it. We shall very soon have the vapour rising up. +I will make it still hotter, and now we get more of it, so that I can +actually pour the vapour out of the flask into that basin, and set it on +fire there. This, then, is exactly the same kind of vapour as we have in +the middle of the candle; and that you may be sure this is the case, let +us try whether we have not got here, in this flask, a real combustible +vapour out of the middle of the candle. [Taking the flask into which the +tube from the candle proceeded, and introducing a lighted taper.] See how +it burns. Now, this is the vapour from the middle of the candle, produced +by its own heat; and that is one of the first things you have to consider +with respect to the progress of the wax in the course of its combustion, +and as regards the changes it undergoes. I will arrange another tube +carefully in the flame, and I should not wonder if we were able, by a +little care, to get that vapour to pass through the tube to the other +extremity, where we will light it, and obtain absolutely the flame of the +candle at a place distant from it. Now, look at that. Is not that a very +pretty experiment? Talk about laying on gas—why, we can actually lay on a +candle! And you see from this that there are clearly two different kinds +of action—one the _production_ of the vapour, and the other the +_combustion_ of it—both of which take place in particular parts of the +candle. + +[Illustration: Fig. 8] + +I shall get no vapour from that part which is already burnt. If I raise +the tube (fig. 7) to the upper part of the flame, so soon as the vapour +has been swept out, what comes away will be no longer combustible: It is +already burned. How burned? Why, burned thus:—In the middle of the flame, +where the wick is, there is this combustible vapour; on the outside of the +flame is the air which we shall find necessary for the burning of the +candle; between the two, intense chemical action takes place, whereby the +air and the fuel act upon each other, and at the very same time that we +obtain light the vapour inside is destroyed. If you examine where the heat +of a candle is, you will find it very curiously arranged. Suppose I take +this candle, and hold a piece of paper close upon the flame, where is the +heat of that flame? Do you not see that it is _not_ in the inside? It is +in a ring, exactly in the place where I told you the chemical action was; +and even in my irregular mode of making the experiment, if there is not +too much disturbance, there will always be a ring. This is a good +experiment for you to make at home. Take a strip of paper, have the air in +the room quiet, and put the piece of paper right across the middle of the +flame (I must not talk while I make the experiment), and you will find +that it is burnt in two places, and that it is not burnt, or very little +so, in the middle; and when you have tried the experiment once or twice, +so as to make it nicely, you will be very interested to see where the heat +is, and to find that it is where the air and the fuel come together. + +This is most important for us as we proceed with our subject. Air is +absolutely necessary for combustion; and, what is more, I must have you +understand that _fresh_ air is necessary, or else we should be imperfect +in our reasoning and our experiments. Here is a jar of air. I place it +over a candle, and it burns very nicely in it at first, shewing that what +I have said about it is true; but there will soon be a change. See how the +flame is drawing upwards, presently fading, and at last going out. And +going out, why? Not because it wants air merely, for the jar is as full +now as it was before; but it wants pure, fresh air. The jar is full of +air, partly changed, partly not changed; but it does not contain +sufficient of the fresh air which is necessary for the combustion of a +candle. These are all points which we, as young chemists, have to gather +up; and if we look a little more closely into this kind of action, we +shall find certain steps of reasoning extremely interesting. For instance, +here is the oil-lamp I shewed you—an excellent lamp for our +experiments—the old Argand lamp. I now make it like a candle [obstructing +the passage of air into the centre of the flame]; there is the cotton; +there is the oil rising up it; and there is the conical flame. It burns +poorly, because there is a partial restraint of air. I have allowed no air +to get to it, save round the outside of the flame, and it does not burn +well. I cannot admit more air from the outside, because the wick is large; +but if, as Argand did so cleverly, I open a passage to the middle of the +flame, and so let air come in there, you will see how much more +beautifully it burns. If I shut the air off, look how it smokes; and why? +We have now some very interesting points to study. We have the case of the +combustion of a candle; we have the case of a candle being put out by the +want of air; and we have now the case of imperfect combustion; and this is +to us so interesting, that I want you to understand it as thoroughly as +you do the case of a candle burning in its best possible manner. I will +now make a great flame, because we need the largest possible +illustrations. Here is a larger wick [burning turpentine on a ball of +cotton]. All these things are the same as candles, after all. If we have +larger wicks, we must have a larger supply of air, or we shall have less +perfect combustion. Look now at this black substance going up into the +atmosphere; there is a regular stream of it. I have provided means to +carry off the imperfectly burned part, lest it should annoy you. Look at +the soots that fly off from the flame: see what an imperfect combustion it +is, because it cannot get enough air. What, then, is happening? Why, +certain things which are necessary to the combustion of a candle are +absent, and very bad results are accordingly produced; but we see what +happens to a candle when it is burnt in a pure and proper state of air. At +the time when I shewed you this charring by the ring of flame on the one +side of the paper, I might have also shewn you, by turning to the other +side, that the burning of a candle produces the same kind of +soot—charcoal or carbon. + +But, before I shew that, let me explain to you—as it is quite necessary +for our purpose—that, though I take a candle and give you, as the general +result, its combustion in the form of a flame, we must see whether +combustion is always in this condition, or whether there are other +conditions of flame; and we shall soon discover that there are, and that +they are most important to us. I think, perhaps, the best illustration of +such a point to us, as juveniles, is to shew the result of strong +contrast. Here is a little gunpowder. You know that gunpowder burns with +flame—we may fairly call it flame. It contains carbon and other +materials, which altogether cause it to burn with a flame. And here is +some pulverised iron, or iron filings. Now, I purpose burning these two +things together. I have a little mortar in which I will mix them. (Before +I go into these experiments, let me hope that none of you, by trying to +repeat them, for fun’s sake, will do any harm. These things may all be +very properly used if you take care; but without that, much mischief will +be done.) Well, then, here is a little gunpowder, which I put at the +bottom of that little wooden vessel, and mix the iron filings up with it, +my object being to make the gunpowder set fire to the filings and burn +them in the air, and thereby shew the difference between substances +burning with flame and not with flame. Here is the mixture; and when I set +fire to it, you must watch the combustion, and you will see that it is of +two kinds. You will see the gunpowder burning with a flame, and the +filings thrown up. You will see them burning too, but without the +production of flame. They will each burn separately. [The Lecturer then +ignited the mixture.] There is the gunpowder, which burns with a flame; +and there are the filings—they burn with a different kind of combustion. +You see, then, these two great distinctions; and upon these differences +depend all the utility and all the beauty of flame which we use for the +purpose of giving out light. When we use oil, or gas, or candle, for the +purpose of illumination, their fitness all depends upon these different +kinds of combustion. + +There are such curious conditions of flame, that it requires some +cleverness and nicety of discrimination to distinguish the kinds of +combustion one from another. For instance, here is a powder which is very +combustible, consisting, as you see, of separate little particles. It is +called _lycopodium_[7], and each of these particles can produce a vapour, +and produce its own flame; but, to see them burning, you would imagine it +was all one flame. I will now set fire to a quantity, and you will see the +effect. We saw a cloud of flame, apparently in one body; but that rushing +noise [referring to the sound produced by the burning] was a proof that +the combustion was not a continuous or regular one. This is the lightning +of the pantomimes, and a very good imitation. [The experiment was twice +repeated by blowing lycopodium from a glass tube through a spirit-flame.] +This is not an example of combustion like that of the filings I have been +speaking of, to which we must now return. + +Suppose I take a candle, and examine that part of it which appears +brightest to our eyes. Why, there I get these black particles, which +already you have seen many times evolved from the flame, and which I am +now about to evolve in a different way. I will take this candle and clear +away the gutterage, which occurs by reason of the currents of air; and if +I now arrange a glass tube so as just to dip into this luminous part, as +in our first experiment, only higher, you see the result. In place of +having the same white vapour that you had before, you will now have a +black vapour. There it goes, as black as ink. It is certainly very +different from the white vapour; and when we put a light to it, we shall +find that it does not burn, but that it puts the light out. Well, these +particles, as I said before, are just the smoke of the candle; and this +brings to mind that old employment which Dean Swift recommended to +servants for their amusement, namely, writing on the ceiling of a room +with a candle. But what is that black substance? Why, it is the same +carbon which exists in the candle. How comes it out of the candle? It +evidently existed in the candle, or else we should not have had it here. +And now I want you to follow me in this explanation. You would hardly +think that all those substances which fly about London, in the form of +soots and blacks, are the very beauty and life of the flame, and which are +burned in it as those iron filings were burned here. Here is a piece of +wire gauze, which will not let the flame go through it; and I think you +will see, almost immediately, that when I bring it low enough to touch +that part of the flame which is otherwise so bright, that it quells and +quenches it at once, and allows a volume of smoke to rise up. + +I want you now to follow me in this point,—that whenever a substance +burns, as the iron filings burnt in the flame of gunpowder, without +assuming the vaporous state (whether it becomes liquid or remains solid), +it becomes exceedingly luminous. I have here taken three or four examples +apart from the candle, on purpose to illustrate this point to you; because +what I have to say is applicable to all substances, whether they burn or +whether they do not burn,—that they are exceedingly bright if they retain +their solid state, and that it is to this presence of solid particles in +the candle-flame that it owes its brilliancy. + +Here is a platinum-wire, a body which does not change by heat. If I heat +it in this flame, see how exceedingly luminous it becomes. I will make the +flame dim, for the purpose of giving a little light only, and yet you will +see that the heat which it can give to that platinum-wire, though far less +than the heat it has itself, is able to raise the platinum-wire to a far +higher state of effulgence. This flame has carbon in it; but I will take +one that has no carbon in it. There is a material, a kind of fuel—a +vapour, or gas, whichever you like to call it—in that vessel, and it has +no solid particles in it; so I take that because it is an example of flame +itself burning without any solid matter whatever; and if I now put this +solid substance in it, you see what an intense heat it has, and how +brightly it causes the solid body to glow. This is the pipe through which +we convey this particular gas, which we call hydrogen, and which you shall +know all about next time we meet. And here is a substance called oxygen, +by means of which this hydrogen can burn; and although we produce, by +their mixture, far greater heat[8] than you can obtain from the candle, +yet there is very little light. If, however, I take a solid substance, and +put that into it, we produce an intense light If I take a piece of lime, a +substance which will not burn, and which will not vaporise by the heat +(and because it does not vaporise, remains solid, and remains heated), you +will soon observe what happens as to its glowing. I have here a most +intense heat, produced by the burning of hydrogen in contact with the +oxygen; but there is as yet very little light—not for want of heat, but +for want of particles which can retain their solid state; but when I hold +this piece of lime in the flame of the hydrogen as it burns in the oxygen, +see how it glows! This is the glorious lime-light, which rivals the +voltaic-light, and which is almost equal to sunlight. I have here a piece +of carbon or charcoal, which will burn and give us light exactly in the +same manner as if it were burnt as part of a candle. The heat that is in +the flame of a candle decomposes the vapour of the wax, and sets free the +carbon particles—they rise up heated and glowing as this now glows, and +then enter into the air. But the particles when burnt never pass off from +a candle in the form of carbon. They go off into the air as a perfectly +invisible substance, about which we shall know hereafter. + +Is it not beautiful to think that such a process is going on, and that +such a dirty thing as charcoal can become so incandescent? You see it +comes to this—that all bright flames contain these solid particles; all +things that burn and produce solid particles, either during the time they +are burning, as in the candle, or immediately after being burnt, as in the +case of the gunpowder and iron-filings,—all these things give us this +glorious and beautiful light. + +I will give you a few illustrations. Here is a piece of phosphorus, which +burns with a bright flame. Very well; we may now conclude that phosphorus +will produce, either at the moment that it is burning or afterwards, these +solid particles. Here is the phosphorus lighted, and I cover it over with +this glass for the purpose of keeping in what is produced. What is all +that smoke? That smoke consists of those very particles which are produced +by the combustion of the phosphorus. Here, again, are two substances. This +is chlorate of potassa, and this other sulphuret of antimony. I shall mix +these together a little, and then they may be burnt in many ways. I shall +touch them with a drop of sulphuric acid, for the purpose of giving you an +illustration of chemical action, and they will instantly burn[9]. [The +Lecturer then ignited the mixture by means of sulphuric acid.] Now, from +the appearance of things, you can judge for yourselves whether they +produce solid matter in burning. I have given you the train of reasoning +which will enable you to say whether they do or do not; for what is this +bright flame but the solid particles passing off? + +[Illustration: Fig. 9.] + +Mr. Anderson has in the furnace a very hot crucible,—I am about to throw +into it some zinc filings, and they will burn with a flame like gunpowder. +I make this experiment because you can make it well at home. Now, I want +you to see what will be the result of the combustion of this zinc. Here it +is burning—burning beautifully like a candle, I may say. But what is all +that smoke, and what are those little clouds of wool which will come to +you if you cannot come to them, and make themselves sensible to you in the +form of the old philosophic wool, as it was called? We shall have left in +that crucible, also, a quantity of this woolly matter. But I will take a +piece of this same zinc and make an experiment a little more closely at +home, as it were. You will have here the same thing happening. Here is the +piece of zinc, there [pointing to a jet of hydrogen] is the furnace, and +we will set to work and try and burn the metal. It glows, you see: there +is the combustion, and there is the white substance into which it burns. +And so, if I take that flame of hydrogen as the representative of a +candle, and shew you a substance like zinc burning in the flame, you will +see that it was merely during the action of combustion that this substance +glowed—while it was kept hot; and if I take a flame of hydrogen, and put +this white substance from the zinc into it, look how beautifully it glows, +and just because it is a solid substance. + +I will now take such a flame as I had a moment since, and set free from it +the particles of carbon. Here is some camphine, which will burn with a +smoke; but if I send these particles of smoke through this pipe into the +hydrogen flame, you will see they will burn and become luminous, because +we heat them a second time. There they are. Those are the particles of +carbon re-ignited a second time. They are those particles which you can +easily see by holding a piece of paper behind them, and which, whilst they +are in the flame, are ignited by the heat produced, and, when so ignited, +produce this brightness. When the particles are not separated, you get no +brightness. The flame of coal-gas owes its brightness to the separation, +during combustion, of these particles of carbon, which are equally in that +as in a candle. I can very quickly alter that arrangement. Here, for +instance, is a bright flame of gas. Supposing I add so much air to the +flame as to cause it all to burn before those particles are set free, I +shall not have this brightness; and I can do that in this way:—If I place +over the jet this wire-gauze cap, as you see, and then light the gas over +it, it burns with a non-luminous flame, owing to its having plenty of air +mixed with it before it burns; and if I raise the gauze, you see it does +not burn below[10]. There is plenty of carbon in the gas; but, because the +atmosphere can get to it, and mix with it before it burns, you see how +pale and blue the flame is. And if I blow upon a bright gas-flame, so as +to consume all this carbon before it gets heated to the glowing point, it +will also burn blue: [The Lecturer illustrated his remarks by blowing on +the gas-light.] The only reason why I have not the same bright light when +I thus blow upon the flame is, that the carbon meets with sufficient air +to burn it before it gets separated in the flame in a free state. The +difference is solely due to the solid particles not being separated before +the gas is burnt. + +You observe that there are certain products as the result of the +combustion of a candle, and that of these products one portion may be +considered as charcoal, or soot; that charcoal, when afterwards burnt, +produces some other product; and it concerns us very much now to ascertain +what that other product is. We shewed that something was going away; and I +want you now to understand how much is going up into the air; and for that +purpose we will have combustion on a little larger scale. From that candle +ascends heated air, and two or three experiments will shew you the +ascending current; but, in order to give you a notion of the quantity of +matter which ascends in this way, I will make an experiment by which I +shall try to imprison some of the products of this combustion. For this +purpose I have here what boys call a fire-balloon. I use this fire-balloon +merely as a sort of measure of the result of the combustion we are +considering; and I am about to make a flame in such an easy and simple +manner as shall best serve my present purpose. This plate shall be the +“cup,” we will so say, of the candle; this spirit shall be our fuel; and I +am about to place this chimney over it, because it is better for me to do +so than to let things proceed at random. + +[Illustration: Fig. 10.] + +Mr. Anderson will now light the fuel, and here at the top we shall get the +results of the combustion. What we get at the top of that tube is exactly +the same, generally speaking, as you get from the combustion of a candle; +but we do not get a luminous flame here, because we use a substance which +is feeble in carbon. I am about to put this balloon—not into action, +because that is not my object—but to shew you the effect which results +from the action of those products which arise from the candle, as they +arise here from the furnace. [The balloon was held over the chimney, when +it immediately commenced to fill.] You see how it is disposed to ascend; +but we must not let it up, because it might come in contact with those +upper gas-lights, and that would be very inconvenient. [The upper +gas-lights were turned out, at the request of the Lecturer, and the +balloon was allowed to ascend.] Does not that shew you what a large bulk +of matter is being evolved? Now, there is going through this tube [placing +a large glass tube over a candle] all the products of that candle, and you +will presently see that the tube will become quite opaque. Suppose I take +another candle, and place it under a jar, and then put a light on the +other side, just to shew you what is going on. You see that the sides of +the jar become cloudy, and the light begins to burn feebly. It is the +products, you see, which make the light so dim, and this is the same thing +which makes the sides of the jar so opaque. If you go home and take a +spoon that has been in the cold air, and hold it over a candle—not so as +to soot it—you will find that it becomes dim, just as that jar is dim. If +you can get a silver dish, or something of that kind, you will make the +experiment still better. And now, just to carry your thoughts forward to +the time we shall next meet, let me tell you that it is _water_ which +causes the dimness; and when we next meet. I will shew you that we can +make it, without difficulty, assume the form of a liquid. + + + + +LECTURE III. + +PRODUCTS: WATER FROM THE COMBUSTION—NATURE OF WATER—A +COMPOUND—HYDROGEN. + + +I dare say you will remember that when we parted we had just mentioned the +word “products” from the candle. For when a candle burns we found we were +able, by nice adjustment, to get various products from it. There was one +substance which was not obtained when the candle was burning properly, +which was charcoal or smoke; and there was some other substance that went +upwards from the flame which did not appear as smoke, but took some other +form, and made part of that general current which, ascending from the +candle upwards, becomes invisible, and escapes. There were also other +products to mention. You remember that in that rising current having its +origin at the candle, we found that one part was condensable against a +cold spoon, or against a clean plate, or any other cold thing, and another +part was incondensable. + +We will first take the condensable part, and examine it; and, strange to +say, we find that that part of the product is just water—nothing but +water. On the last occasion I spoke of it incidentally, merely saying that +water was produced among the condensable products of the candle; but +to-day I wish to draw your attention to water, that we may examine it +carefully, especially in relation to this subject, and also with respect +to its general existence on the surface of the globe. + +Now, having previously arranged an experiment for the purpose of +condensing water from the products of the candle, my next point will be to +shew you this water; and perhaps one of the best means that I can adopt +for shewing its presence to so many at once, is to exhibit a very visible +action of water, and then to apply that test to what is collected as a +drop at the bottom of that vessel. I have here a chemical substance, +discovered by Sir Humphrey Davy, which has a very energetic action upon +water, which I shall use as a test of the presence of water. If I take a +little piece of it—it is called potassium, as coming from potash,—if I +take a little piece of it, and throw it into that basin, you see how it +shews the presence of water by lighting up and floating about, burning +with a violent flame. I am now going to take away the candle which has +been burning beneath the vessel containing ice and salt, and you see a +drop of water—a condensed product of the candle—hanging from under the +surface of the dish. + +[Illustration: Fig. 11.] + +I will shew you that potassium has the same action upon it as upon the +water in that basin in the experiment we have just tried. See, it takes +fire, and burns in just the same manner. I will take another drop upon +this glass slab, and when I put the potassium on to it, you see at once, +from its taking fire, that there is water present. Now, that water was +produced by the candle. In the same manner, if I put this spirit-lamp +under that jar, you will soon see the latter become damp, from the dew +which is deposited upon it—that dew being the result of combustion; and I +have no doubt you will shortly see by the drops of water which fall upon +the paper below, that there is a good deal of water produced from the +combustion of the lamp. I will let it remain, and you can afterwards see +how much water has been collected. So, if I take a gas-lamp, and put any +cooling arrangement over it, I shall get water—water being likewise +produced from the combustion of gas. Here, in this bottle, is a quantity +of water—perfectly pure, distilled water, produced from the combustion of +a gas-lamp—in no point different from the water that you distil from the +river, or ocean, or spring, but exactly the same thing. Water is one +individual thing—it never changes. We can add to it by careful +adjustment, for a little while, or we can take it apart, and get other +things from it; but water, as water, remains always the same, either in a +solid, liquid, or fluid state. Here, again [holding another bottle], is +some water produced by the combustion of an oil-lamp. A pint of oil, when +burnt fairly and properly, produces rather more than a pint of water. +Here, again, is some water, produced by a rather long experiment from a +wax candle. And so we can go on with almost all combustible substances, +and find that if they burn with a flame, as a candle, they produce water. +You may make these experiments yourselves. The head of a poker is a very +good thing to try with, and if it remains cold long enough over the +candle, you may get water condensed in drops on it; or a spoon or ladle, +or anything else may be used, provided it be clean, and can carry off the +heat, and so condense the water. + +And now—to go into the history of this wonderful production of water from +combustibles, and by combustion—I must first of all tell you that this +water may exist in different conditions; and although you may now be +acquainted with all its forms, they still require us to give a little +attention to them for the present, so that we may perceive how the water, +whilst it goes through its Protean changes, is entirely and absolutely the +same thing, whether it is produced from a candle, by combustion, or from +the rivers or ocean. + +First of all, water, when at the coldest, is ice. Now, we philosophers—I +hope that I may class you and myself together in this case—speak of water +as water, whether it be in its solid, or liquid, or gaseous state,—we +speak of it chemically as water. Water is a thing compounded of two +substances, one of which we have derived from the candle, and the other we +shall find elsewhere. Water may occur as ice; and you have had most +excellent opportunities lately of seeing this. Ice changes back into +water—for we had on our last Sabbath a strong instance of this change, by +the sad catastrophe which occurred in our own house, as well as in the +houses of many of our friends,—ice changes back into water when the +temperature is raised: water also changes into steam when it is warmed +enough. The water which we have here before us is in its densest +state[11], and although it changes in weight, in condition, in form, and +in many other qualities, it still is water; and whether we alter it into +ice by cooling, or whether we change it into steam by heat, it increases +in volume,—in the one case very strangely and powerfully, and in the +other case very largely and wonderfully. For instance, I will now take +this tin cylinder, and pour a little water into it; and seeing how much +water I pour in, you may easily estimate for yourselves how high it will +rise in the vessel: it will cover the bottom about two inches. I am now +about to convert the water into steam, for the purpose of shewing to you +the different volumes which water occupies in its different states of +water and steam. + +Let us now take the case of water changing into ice: we can effect that by +cooling it in a mixture of salt and pounded ice[12]; and I shall do so to +shew you the expansion of water into a thing of larger bulk when it is so +changed. These bottles [holding one] are made of strong cast iron, very +strong and very thick—I suppose they are the third of an inch in +thickness; they are very carefully filled with water, so as to exclude all +air, and then they are screwed down tight. We shall see that when we +freeze the water in these iron vessels, they will not be able to hold the +ice, and the expansion within them will break them in pieces as these +[pointing to some fragments] are broken, which have been bottles of +exactly the same kind. I am about to put these two bottles into that +mixture of ice and salt, for the purpose of shewing that when water +becomes ice, it changes in volume in this extraordinary way. + +In the mean time look at the change which has taken place in the water to +which we have applied heat—it is losing its fluid state. You may tell +this by two or three circumstances. I have covered the mouth of this glass +flask, in which water is boiling, with a watch-glass. Do you see what +happens? It rattles away like a valve chattering, because the steam rising +from the boiling water sends the valve up and down, and forces itself out, +and so makes it clatter. You can very easily perceive that the flask is +quite full of steam, or else it would not force its way out. You see, +also, that the flask contains a substance very much larger than the water, +for it fills the whole of the flask over and over again, and there it is +blowing away into the air; and yet you cannot observe any great diminution +in the bulk of the water, which shews you that its change of bulk is very +great when it becomes steam. + +I have put our iron bottles containing water into this freezing mixture, +that you may see what happens. No communication will take place, you +observe, between the water in the bottles and the ice in the outer vessel. +But there will be a conveyance of heat from the one to the other; and if +we are successful—we are making our experiment in very great haste—I +expect you will by-and-by, so soon as the cold has taken possession of the +bottles and their contents, hear a pop on the occasion of the bursting of +the one bottle or the other; and, when we come to examine the bottles, we +shall find their contents masses of ice, partly enclosed by the covering +of iron which is too small for them, because the ice is larger in bulk +than the water. You know very well that ice floats upon water: if a boy +falls through a hole into the water, he tries to get on the ice again to +float him up. Why does the ice float?—think of that, and philosophise. +Because the ice is larger than the quantity of water which can produce it; +and therefore the ice weighs the lighter, and the water is the heavier. + +To return now to the action of heat on water. See what a stream of vapour +is issuing from this tin vessel! You observe, we must have made it quite +full of steam to have it sent out in that great quantity. And now, as we +can convert the water into steam by heat, we convert it back into liquid +water by the application of cold. And if we take a glass, or any other +cold thing, and hold it over this steam, see how soon it gets damp with +water; it will condense it until the glass is warm—it condenses the water +which is now running down the sides of it. I have here another experiment +to shew the condensation of water from a vaporous state back into a liquid +state, in the same way as the vapour, one of the products of the candle, +was condensed against the bottom of the dish, and obtained in the form of +water; and to shew you how truly and thoroughly these changes take place, +I will take this tin flask, which is now full of steam, and close the top. +We shall see what takes place when we cause this water or steam to return +back to the fluid state by pouring some cold water on the outside. [The +Lecturer poured the cold water over the vessel, when it immediately +collapsed.] You see what has happened. If I had closed the stopper, and +still kept the heat applied to it, it would have burst the vessel; yet, +when the steam returns to the state of water, the vessel collapses, there +being a vacuum produced inside by the condensation of the steam. I shew +you these experiments for the purpose of pointing out that in all these +occurrences there is nothing that changes the water into any other +thing—it still remains water; and so the vessel is obliged to give way, +and is crushed inwards, as in the other case, by the further application +of heat, it would have been blown outwards. + +[Illustration: Fig. 12.] + +And what do you think the bulk of that water is when it assumes the +vaporous condition? You see that cube [pointing to a cubic foot]. There, +by its side, is a cubic inch, exactly the same shape as the cubic foot, +and that bulk of water [the cubic inch] is sufficient to expand into that +bulk [the cubic foot] of steam; and, on the contrary, the application of +cold will contract that large quantity of steam into this small quantity +of water. + +[Illustration: Fig. 13.] + +[One of the iron bottles burst at that moment.] Ah! There is one of our +bottles burst, and here you see is a crack down one side an eighth of an +inch in width. [The other now exploded, sending the freezing mixture in +all directions.] This other bottle is also broken; although the iron was +nearly half-an-inch thick, the ice has burst it asunder. These changes +always take place in water: they do not require to be always produced by +artificial means,—we only use them here because we want to produce a +small winter round that little bottle, instead of a long and severe one. +But if you go to Canada, or to the North, you will find the temperature +there out of doors will do the same thing as has been done here by the +freezing mixture. + +To return to our quiet philosophy. We shall not in future be deceived, +therefore, by any changes that are produced in water. Water is the same +everywhere, whether produced from the ocean or from the flame of the +candle. Where, then, is this water which we get from a candle? I must +anticipate a little, and tell you. It evidently comes, as to part of it, +from the candle; but is it within the candle beforehand? No. It is not in +the candle; and it is not in the air round about the candle which is +necessary for its combustion. It is neither in one nor the other, but it +comes from their conjoint action, a part from the candle, a part from the +air; and this we have now to trace, so that we may understand thoroughly +what is the chemical history of a candle when we have it burning on our +table. How shall we get at this? I myself know plenty of ways, but I want +_you_ to get at it from the association in your own minds of what I have +already told you. + +I think you can see a little in this way. We had just now the case of a +substance which acted upon the water in the way that Sir Humphrey Davy +shewed us[13], and which I am now going to recall to your minds by making +again an experiment upon that dish. It is a thing which we have to handle +very carefully, for you see, if I allow a little splash of water to come +upon this mass, it sets fire to part of it; and if there were free access +of air, it would quickly set fire to the whole. Now, this is a metal—a +beautiful and bright metal—which rapidly changes in the air, and, as you +know, rapidly changes in water. I will put a piece on the water, and you +see it burns beautifully, making a floating lamp, using the water in the +place of air. Again, if we take a few iron filings or turnings, and put +them in water, we find that they likewise undergo an alteration. They do +not change so much as this potassium does, but they change somewhat in the +same way; they become rusty, and shew an action upon the water, though in +a different degree of intensity to what this beautiful metal does: but +they act upon the water in the same manner generally as this potassium. I +want you to put these different facts together in your minds. I have +another metal here [zinc], and when we examined it with regard to the +solid substance produced by its combustion, we had an opportunity of +seeing that it burned; and I suppose, if I take a little strip of this +zinc and put it over the candle, you will see something half-way, as it +were, between the combustion of potassium on the water and the action of +iron,—you see there is a sort of combustion. It has burned, leaving a +white ash or residuum, and here also we find that the metal has a certain +amount of action upon water. + +By degrees we have learned how to modify the action of these different +substances, and to make them tell us what we want to know. And now, first +of all, I take iron. It is a common thing in all chemical reactions, where +we get any result of this kind, to find that it is increased by the action +of heat; and if we want to examine minutely and carefully the action of +bodies one upon another, we often have to refer to the action of heat. You +are aware, I believe, that iron-filings burn beautifully in the air; but I +am about to shew you an experiment of this kind, because it will impress +upon you what I am going to say about iron in its action on water. If I +take a flame and make it hollow;—you know why, because I want to get air +to it and into it, and therefore I make it hollow—and then take a few +iron-filings and drop them into the flame, you see how well they burn. +That combustion results from the chemical action which is going on when we +ignite those particles. And so we proceed to consider these different +effects, and ascertain what iron will do when it meets with water. It will +tell us the story so beautifully, so gradually and regularly, that I think +it will please you very much. + +I have here a furnace with a pipe going through it like an iron +gun barrel, and I have stuffed that barrel full of bright iron-turnings, +and placed it across the fire, to be made red-hot. We can either send air +through the barrel to come in contact with the iron, or we can send steam +from this little boiler at the end of the barrel. Here is a stop-cock +which shuts off the steam from the barrel until we wish to admit it. There +is some water in these glass jars, which I have coloured blue, so that you +may see what happens. Now, you know very well that any steam I might send +through that barrel, if it went through into the water, would be +condensed; for you have seen that steam cannot retain its gaseous form if +it be cooled down. + +[Illustration: Fig. 14.] + +You saw it here [pointing to the tin flask] crushing itself into a small +bulk, and causing the flask holding it to collapse; so that if I were to +send steam through that barrel, it would be condensed—supposing the +barrel were cold: it is, therefore, heated to perform the experiment I am +now about to shew you. I am going to send the steam through the barrel in +small quantities; and you shall judge for yourselves, when you see it +issue from the other end, whether it still remains steam. Steam is +condensable into water, and when you lower the temperature of steam, you +convert it back into fluid water; but I have lowered the temperature of +the gas which I have collected in this jar, by passing it through water +after it has traversed the iron barrel, and still it does not change back +into water. I will take another test and apply to this gas. (I hold the +jar in an inverted position, or my substance would escape.) If I now apply +a light to the mouth of the jar, it ignites with a slight noise. That +tells you that it is not steam. Steam puts out a fire—it does not burn; +but you saw that what I had in that jar burnt. We may obtain this +substance equally from water produced from the candle-flame as from any +other source. When it is obtained by the action of the iron upon the +aqueous vapour, it leaves the iron in a state very similar to that in +which these filings were after they were burnt. It makes the iron heavier +than it was before. So long as the iron remains in the tube and is heated, +and is cooled again without the access of air or water, it does not change +in its weight; but after having had this current of steam passed over it, +it then comes out heavier that it was before, having taken something out +of the steam, and having allowed something else to pass forth, which we +see here. And now, as we have another jar full, I will shew you something +most interesting. It is a combustible gas; and I might at once take this +jar and set fire to the contents, and shew you that it is combustible; but +I intend to shew you more if I can. It is also a very light substance. +Steam will condense: this body will rise in the air, and not condense. + +[Illustration: Fig. 15] + +Suppose I take another glass jar, empty of all but air: if I examine it +with a taper, I shall find that it contains nothing but air. I will now +take this jar full of the gas that I am speaking of, and deal with it as +though it were a light body. I will hold both upside-down, and turn the +one up under the other; and that which did contain the gas procured from +the steam, what does it contain now? You will find it now only contains +air. But look! Here is the combustible substance [taking the other jar] +which I have poured out of the one jar into the other. It still preserves +its quality, and condition, and independence, and therefore is the more +worthy of our consideration, as belonging to the products of a candle. + +Now, this substance which we have just prepared by the action of iron on +the steam or water, we can also get by means of those other things which +you have already seen act so well upon the water. If I take a piece of +potassium, and make the necessary arrangements, it will produce this gas; +and if, instead, a piece of zinc, I find, when I come to examine it very +carefully, that the main reason why this zinc cannot act upon the water +continuously as the other metal does, is because the result of the action +of the water envelopes the zinc in a kind of protecting coat. We have +learned in consequence, that if we put into our vessel only the zinc and +water, they by themselves do not give rise to much action, and we get no +result. But suppose I proceed to dissolve off this varnish—this +encumbering substance—which I can do by a little acid; the moment I do +this, I find the zinc acting upon the water exactly as the iron did, but +at the common temperature. The acid in no way is altered, except in its +combination with the oxide of zinc, which is produced. I have now poured +the acid into the glass, and the effect is as though I were applying heat +to cause this boiling up. There is something coming off from the zinc very +abundantly, which is not steam. There is a jar full of it; and you will +find that I have exactly the same combustible substance remaining in the +vessel, when I hold it upside-down, that I produced during the experiment +with the iron barrel. This is what we get from water—the same substance +which is contained in the candle. + +[Illustration: Fig. 16.] + +Let us now trace distinctly the connection between these two points. This +is hydrogen—a body classed among those things which in Chemistry we call +elements, because we can get nothing else out of them. A candle is not an +elementary body, because we can get carbon out of it; we can get this +hydrogen out of it, or at least out of the water which it supplies. And +this gas has been so named hydrogen, because it is that element which, in +association with another, generates water. [Footnote: [greek: hudos], +“water,” and [greek: gennao], “I generate.”] Mr. Anderson having now been +able to get two or three jars of gas, we shall have a few experiments to +make, and I want to shew you the best way of making these experiments. I +am not afraid to shew you, for I wish you to make experiments, if you will +only make them with care and attention, and the assent of those around +you. As we advance in Chemistry, we are obliged to deal with substances +which are rather injurious, if in their wrong places—the acids, and heat, +and combustible things we use, might do harm if carelessly employed. If +you want to make hydrogen, you can make it easily from bits of zinc, and +sulphuric or muriatic acid. Here is what in former times was called the +“philosopher’s candle.” It is a little phial with a cork, and a tube or +pipe passing through it. + +[Illustration: Fig. 17.] + +And I am now putting a few little pieces of zinc into it. This little +instrument I am going to apply to a useful purpose in our +demonstrations—for I want to shew you that you can prepare hydrogen, and +make some experiments with it as you please at your own homes. Let me here +tell you why I am so careful to fill this phial nearly, and yet not quite +full. I do it because the evolved gas, which, as you have seen, is very +combustible, is explosive to a considerable extent when mixed with air, +and might lead to harm, if you were to apply a light to the end of that +pipe before all the air had been swept out of the space above the water. I +am now about to pour in the sulphuric acid. I have used very little zinc, +and more sulphuric acid and water, because I want to keep it at work for +some time. I therefore take care in this way to modify the proportions of +the ingredients, so that I may have a regular supply—not too quick, and +not too slow. Supposing I now take a glass and put it upside-down over the +end of the tube, because the hydrogen is light I expect that it will +remain in that vessel a little while. We will now test the contents of our +glass to see if there be hydrogen in it. I think I am safe in saying we +have caught some [applying a light]. There it is, you see. I will now +apply a light to the top of the tube. There is the hydrogen burning. There +is our philosophical candle. It is a foolish feeble sort of a flame, you +may say; but it is so hot that scarcely any common flame gives out so much +heat. It goes on burning regularly, and I am now about to put that flame +to burn under a certain arrangement, in order that we may examine its +results and make use of the information which we may thereby acquire. +Inasmuch as the candle produces water, and this gas comes out of the +water, let us see what this gives us by the same process of combustion +that the candle went through when it burnt in the atmosphere; and for that +purpose I am going to put the lamp under this apparatus, in order to +condense whatever may arise from the combustion within it In the course of +a short time you will see moisture appearing in the cylinder, and you will +get the water running down the side; and the water from this hydrogen +flame will have absolutely the same effect upon all our tests, being +obtained by the same general process as in the former case. This hydrogen +is a very beautiful substance. It is so light that it carries things up: +it is far lighter than the atmosphere; and I dare say I can shew you this +by an experiment which, if you are very clever, some of you may even have +skill enough to repeat. Here is our generator of hydrogen, and here are +some soap-suds. I have an india-rubber tube connected with the hydrogen +generator, and at the end of the tube is a tobacco-pipe. + +[Illustration: Fig. 18.] + +I can thus put the pipe into the suds, and blow bubbles by means of the +hydrogen. You observe how the bubbles fall downwards when I blow them with +my warm breath; but notice the difference when I blow them with hydrogen. +[The Lecturer here blew bubbles with hydrogen, which rose to the roof of +the theatre.] It shews you how light this gas must be in order to carry +with it not merely the ordinary soap-bubble, but the larger portion of a +drop hanging to the bottom of it. I can shew its lightness in a better way +than this; larger bubbles than these may be so lifted up; indeed, in +former times balloons used to be filled with this gas. Mr. Anderson will +fasten this tube on to our generator, and we shall have a stream of +hydrogen here with which we can charge this balloon made of collodion. I +need not even be very careful to get all the air out, for I know the power +of this gas to carry it up. [Two collodion balloons were inflated, and +sent up, one being held by a string.] Here is another larger one made of +thin membrane, which we will fill and allow to ascend. You will see they +will all remain floating about until the gas escapes. + +What, then, are the comparative weights of these substances? I have a +table here which will shew you the proportion which their weights bear to +each other. I have taken a pint and a cubic foot as the measures, and have +placed opposite to them the respective figures. A pint measure of this +hydrogen weighs three-quarters of our smallest weight (a grain), and a +cubic foot weighs one-twelfth of an ounce; whereas a pint of water weighs +8,750 grains, and a cubic foot of water weighs almost 1,000 ounces. You +see, therefore, what a vast difference there is between the weight of a +cubic foot of water and a cubic foot of hydrogen. + +Hydrogen gives rise to no substance that can become solid, either during +combustion or afterwards as a product of its combustion. But when it +burns, it produces water only; and if we take a cold glass and put it over +the flame, it becomes damp, and you have water, produced immediately in +appreciable quantity; and nothing is produced by its combustion but the +same water which you have seen the flame of the candle produce. It is +important to remember that this hydrogen is the only thing in nature which +furnishes water as the sole product of combustion. + +And now we must endeavour to find some additional proof of the general +character and composition of water; and for this purpose I will keep you a +little longer, so that at our next meeting we may be better prepared for +the subject. We have the power of arranging the zinc which you have seen +acting upon the water by the assistance of an acid, in such a manner as to +cause all the power to be evolved in the place where we require it I have +behind me a voltaic pile, and I am just about to shew you, at the end of +this lecture, its character and power, that you may see what we shall have +to deal with when next we meet. I hold here the extremities of the wires +which transport the power from behind me, and which I shall cause to act +on the water. + +We have previously seen what a power of combustion is possessed by the +potassium, or the zinc, or the iron-filings; but none of them shew such +energy as this. [The Lecturer here made contact between the two terminal +wires of the battery, when a brilliant flash of light was produced.] This +light is, in fact, produced by a forty-zinc power of burning: it is a +power that I can carry about in my hands, through these wires, at +pleasure—although, if I applied it wrongly to myself, it would destroy me +in an instant, for it is a most intense thing, and the power you see here +put forth while you count five [bringing the poles in contact, and +exhibiting the electric light] is equivalent to the power of several +thunder-storms, so great is its force[14]. And that you may see what +intense energy it has, I will take the ends of the wires which convey the +power from the battery, and with it I dare say I can burn this iron file. +Now, this is a chemical power, and one which, when we next meet, I shall +apply to water, and shew you what results we are able to produce. + + + + +LECTURE IV. + +HYDROGEN IN THE CANDLE—BURNS INTO WATER—THE OTHER PART OF WATER—OXYGEN. + +I see you are not tired of the candle yet, or I am sure you would not be +interested in the subject in the way you are. When our candle was burning, +we found it produced water exactly like the water we have around us; and +by further examination of this water we found in it that curious body, +hydrogen—that light substance of which there is some in this jar. We +afterwards saw the burning powers of that hydrogen, and that it produced +water. And I think I introduced to your notice an apparatus which I very +briefly said was an arrangement of chemical force, or power, or energy, so +adjusted as to convey its power to us in these wires; and I said I should +use that force to pull the water to pieces, to see what else there was in +the water besides hydrogen; because, you remember, when we passed the +water through the iron tube, we by no means got the weight of water back +which we put in, in the form of steam, though we had a very large quantity +of gas evolved. We have now to see what is the other substance present. +That you may understand the character and use of this instrument, let us +make an experiment or two. Let us put together, first of all, some +substances, knowing what they are, and then see what that instrument does +to them. There is some copper (observe the various changes which it can +undergo), and here is some nitric acid, and you will find that this, being +a strong chemical agent, will act very powerfully when I add it to the +copper. It is now sending forth a beautiful red vapour; but as we do not +want that vapour, Mr. Anderson will hold it near the chimney for a short +time, that we may have the use and beauty of the experiment without the +annoyance. The copper which I have put into the flask will dissolve: it +will change the acid and the water into a blue fluid, containing copper +and other things; and I propose then shewing you how this voltaic battery +deals with it; and in the mean time we will arrange another kind of +experiment for you to see what power it has. This is a substance which is +to us like water—that is to say, it contains bodies which we do not know +of as yet, as water contains a body which we do not know as yet. Now, this +solution of a salt[15] I will put upon paper, and spread about, and apply +the power of the battery to it, and observe what will happen. Three or +four important things will happen which we shall take advantage of. I +place this wetted paper upon a sheet of tinfoil, which is convenient for +keeping all clean, and also for the advantageous application of the power; +and this solution, you see, is not at all affected by being put upon the +paper or tinfoil, nor by anything else I have brought in contact with it +yet, and which, therefore, is free to us to use as regards that +instrument. But first let us see that our instrument is in order. Here are +our wires. Let us see whether it is in the state in which it was last +time. We can soon tell. As yet, when I bring them together, we have no +power, because the conveyers—what we call the electrodes—the passages or +ways for the electricity—are stopped; but now Mr. Anderson by that +[referring to a sudden flash at the ends of the wires] has given me a +telegram to say that it is ready. Before I begin our experiment I will get +Mr. Anderson to break contact again at the battery behind me, and we will +put a platinum-wire across to connect the poles, and then if I find I can +ignite a pretty good length of this wire, we shall be safe in our +experiment. Now you will see the power. [The connection was established, +and the intermediate wire became red-hot.] There is the power running +beautifully through the wire, which I have made thin on purpose to shew +you that we have those powerful forces; and now, having that power, we +will proceed with it to the examination of water. + +I have here two pieces of platinum, and if I lay them down upon this piece +of paper [the moistened paper on the tinfoil], you will see no action; and +if I take them up, there is no change that you can see, but the +arrangement remains just as it was before. But, now, see what happens: if +I take these two poles and put either one or the other of them down +separately on the platinum-plates, they do nothing for me, both are +perfectly without action; but if I let them both be in contact at the same +moment, see what happens [a brown spot appeared under each pole of the +battery]. Look here at the effect that takes place, and see how I have +pulled something apart from the white—something brown; and I have no +doubt, if I were to arrange it thus, and were to put one of the poles to +the tinfoil on the other side of the paper—why, I get such a beautiful +action upon the paper, that I am going to see whether I cannot write with +it—a telegram, if you please. [The Lecturer here traced the word +“juvenile” on the paper with one of the terminal wires.] See there how +beautifully we can get our results! + +You see we have here drawn something, which we have not known about +before, out of this solution. Let us now take that flask from Mr. +Andersen’s hands, and see what we can draw out of that. This, you know, is +a liquid which we have just made up from copper and nitric acid, whilst +our other experiments were in hand; and though I am making this experiment +very hastily, and may bungle a little, yet I prefer to let you see what I +do rather than prepare it beforehand. + +Now, see what happens. These two platinum-plates are the two ends (or I +will make them so immediately) of this apparatus; and I am about to put +them in contact with that solution just as we did a moment ago on the +paper. It does not matter to us whether the solution be on the paper or +whether it be in the jar, so long as we bring the ends of the apparatus to +it. If I put the two platinums in by themselves, they come out as clean +and as white as they go in [inserting them into the fluid without +connecting them with the battery]; but when we take the power and lay that +on [the platinums were connected with the battery and again dipped into +the solution], this, you see [exhibiting one of the platinums], is at once +turned into copper, as it were: it has become like a plate of copper; and +that [exhibiting the other piece of platinum] has come out quite clean. If +I take this coppered piece and change sides, the copper will leave the +right-hand side and come over to the left side; what was before the +coppered plate comes out clean, and the plate which was clean comes out +coated with copper; and thus you see that the same copper we put into this +solution we can also take out of it by means of this instrument. + +Putting that solution aside, let us now see what effect this instrument +will have upon water. Here are two little platinum-plates which I intend +to make the ends of the battery, and this (C) is a little vessel so shaped +as to enable me to take it to pieces, and shew you its construction. In +these two cups (A and B) I pour mercury, which touches the ends of the +wires connected with the platinum-plates. In the vessel (C) I pour some +water containing a little acid (but which is put only for the purpose of +facilitating the action; it undergoes no change in the process), and +connected with the top of the vessel is a bent glass tube (D), which may +remind you of the pipe which was connected with the gun barrel in our +furnace experiment, and which now passes under the jar (F). I have now +adjusted this apparatus, and we will proceed to affect the water in some +way or other. In the other case, I sent the water through a tube which was +made red-hot; I am now going to pass the electricity through the contents +of this vessel. Perhaps I may boil the water; if I do boil the water, I +shall get steam; and you know that steam condenses when it gets cold, and +you will therefore see by that whether I do boil the water or not. +Perhaps, however, I shall not boil the water, but produce some other +effect. You shall have the experiment and see. There is one wire which I +will put to this side (A), and here is the other wire which I will put to +the other side (B), and you will soon see whether any disturbance takes +place. Here it is seeming to boil up famously; but does it boil? Let us +see whether that which goes out is steam or not. I think you will soon see +the jar (F) will be filled with vapour, if that which rises from the water +is steam. But can it be steam? Why, certainly not; because there it +remains, you see, unchanged. There it is standing over the water, and it +cannot therefore be steam, but must be a permanent gas of some sort What +is it? Is it hydrogen? Is it anything else? Well, we will examine it. If +it is hydrogen, it will burn. [The Lecturer then ignited a portion of the +gas collected, which burnt with an explosion.] + +[Illustration: Fig. 19] + +It is certainly something combustible, but not combustible in the way that +hydrogen is. Hydrogen would not have given you that noise; but the colour +of that light, when the thing did burn, was like that of hydrogen: it +will, however, burn without contact with the air. That is why I have +chosen this other form of apparatus, for the purpose of pointing out to +you what are the particular circumstances of this experiment. In place of +an open vessel I have taken one that is closed (our battery is so +beautifully active that we are even boiling the mercury, and getting all +things right—not wrong, but vigorously right); and I am going to shew you +that that gas, whatever it may be, can burn without air, and in that +respect differs from a candle, which cannot burn without the air. And our +manner of doing this is as follows:—I have here a glass vessel (G) which +is fitted with two platinum-wires (IK), through which I can apply +electricity; and we can put the vessel on the air-pump and exhaust the +air, and when we have taken the air out we can bring it here and fasten it +on to this jar (F), and let into the vessel that gas which was formed by +the action of the voltaic battery upon the water, and which we have +produced by changing the water into it,—for I may go as far as this, and +say we have really, by that experiment, changed the water into that gas. +We have not only altered its condition, but we have changed it really and +truly into that gaseous substance, and all the water is there which was +decomposed by the experiment. As I screw this vessel (GH) on here (H), and +make the tubes well connected, and when I open the stop-cocks (HHH), if +you watch the level of the water (in F), you will see that the gas will +rise. I will now close the stop-cocks, as I have drawn up as much as the +vessel can hold, and being safely conveyed into that chamber, I will pass +into it an electric spark from this Leyden jar (L), when the vessel, which +is now quite clear and bright, will become dim. There will be no sound, +for the vessel is strong enough to confine the explosion. [A spark was +then passed through the jar, when the explosive mixture was ignited.] Did +you see that brilliant light? If I again screw the vessel on to the jar, +and open these stop-cocks, you will see that the gas will rise a second +time. [The stop-cocks were then opened.] Those gases [referring to the +gases first collected in the jar, and which had just been ignited by the +electric spark] have disappeared, as you see: their place is vacant, and +fresh gas has gone in. Water has been formed from them; and if we repeat +our operation [repeating the last experiment], I shall have another +vacancy, as you will see by the water rising. I always have an empty +vessel after the explosion, because the vapour or gas into which that +water has been resolved by the battery explodes under the influence of the +spark, and changes into water; and by-and-by you will see in this upper +vessel some drops of water trickling down the sides and collecting at the +bottom. + +We are here dealing with water entirely, without reference to the +atmosphere. The water of the candle had the atmosphere helping to produce +it; but in this way it can be produced independently of the air. Water, +therefore, ought to contain that other substance which the candle takes +from the air, and which, combining with the hydrogen, produces water. + +Just now you saw that one end of this battery took hold of the copper, +extracting it from the vessel which contained the blue solution. It was +effected by this wire; and surely we may say, if the battery has such +power with a metallic solution which we made and unmade, may we not find +that it is possible to split asunder the component parts of the water, and +put them into this place and that place? Suppose I take the poles—the +metallic ends of this battery—and see what will happen with the water in +this apparatus (fig. 20), where we have separated the two ends far apart. + +[Illustration: Fig. 20.] + +I place one here (at A), and the other there (at B), and I have little +shelves with holes which I can put upon each pole, and so arrange them +that whatever escapes from the two ends of the battery will appear as +separate gases; for you saw that the water did not become vaporous, but +gaseous. The wires are now in perfect and proper connection with the +vessel containing the water; and you see the bubbles rising: let us +collect these bubbles and see what they are. Here is a glass cylinder (O); +I fill it with water and put it over one end (A) of the pile; and I will +take another (H) and put it over the other end (B) of the pile. And so now +we have a double apparatus, with both places delivering gas. Both these +jars will fill with gas. There they go, that to the right (H) filling very +rapidly; the one to the left (O) filling not so rapidly; and though I have +allowed some bubbles to escape, yet still the action is going on pretty +regularly; and were it not that one is rather smaller than the other, you +would see that I should have twice as much in this (H) as I have in that +(O). Both these gases are colourless; they stand over the water without +condensing; they are alike in all things—I mean in all _apparent_ things; +and we have here an opportunity of examining these bodies and ascertaining +what they are. Their bulk is large, and we can easily apply experiments to +them. I will take this jar (H) first, and will ask you to be prepared to +recognise hydrogen. + +Think of all its qualities—the light gas which stood well in inverted +vessels, burning with a pale flame at the mouth of the jar—and see +whether this gas does not satisfy all these conditions. If it be hydrogen, +it will remain here while I hold this jar inverted. [A light was then +applied, when the hydrogen burnt] What is there now in the other jar? You +know that the two together made an explosive mixture. But what can this +be which we find as the other constituent in water, and which must +therefore be that substance which made the hydrogen burn? We know that the +water we put into the vessel consisted of the two things together. We find +one of these is hydrogen: what must that other be which was in the water +before the experiment, and which we now have by itself? I am about to put +this lighted splinter of wood into the gas. The gas itself will not burn, +but it will make the splinter of wood burn. [The Lecturer ignited the end +of the wood, and introduced it into the jar of gas.] See how it +invigorates the combustion of the wood, and how it makes it burn far +better than the air would make it burn; and now you see by itself that +every other substance which is contained in the water, and which, when the +water was formed by the burning of the candle, must have been taken from +the atmosphere. What shall we call it, A, B, or C? Let us call it O—call +it “Oxygen:” it is a very good distinct-sounding name. This, then, is the +oxygen which was present in the water, forming so large a part of it. + +We shall now begin to understand more clearly our experiments and +researches; because, when we have examined these things once or twice, we +shall soon see why a candle burns in the air. When we have in this way +analysed the water—that is to say, separated, or electrolysed its parts +out of it—we get two volumes of hydrogen, and one of the body that burns +it. And these two are represented to us on the following diagram, with +their weights also stated; and we shall find that the oxygen is a very +heavy body by comparison with the hydrogen. It is the other element in +water. + +I had better, perhaps, tell you now how we get this oxygen abundantly, +having shewn you how we can separate it from the water. Oxygen, as you +will immediately imagine, exists in the atmosphere; for how should the +candle burn to produce water without it? + + _____________________ + | | | + | 1 | 8 | + | | | + | | Oxygen. | Oxygen, . . . . 88.9 + | | | + | |_________| Hydrogen, . . . 11.1 + | Hydrogen. | ————— + | | 9 Water,. . . . . 100.0 + | | + | | + | | + |___________| + +Such a thing would be absolutely impossible, and chemically impossible, +without oxygen. + +[Illustration: Fig. 21.] + +Can we get it from the air? Well, there are some very complicated and +difficult processes by which we can get it from the air; but we have +better processes. There is a substance called the black oxide of +manganese: it is a very black-looking mineral, but very useful, and when +made red-hot it gives out oxygen. Here is an iron bottle which has had +some of this substance put into it, and there is a tube fixed to it, and a +fire ready made, and Mr. Anderson will put that retort into the fire, for +it is made of iron, and can stand the heat. Here is a salt called chlorate +of potassa, which is now made in large quantities for bleaching, and +chemical and medical uses, and for pyrotechnic and other purposes. I will +take some and mix it with some of the oxide of manganese (oxide of copper, +or oxide of iron would do as well); and if I put these together in a +retort, far less than a red heat is sufficient to evolve this oxygen from +the mixture. I am not preparing to make much, because we only want +sufficient for our experiments; only, as you will see immediately, if I +use too small a charge, the first portion of the gas will be mixed with +the air already in the retort, and I should be obliged to sacrifice the +first portion of the gas, because it would be so much diluted with air; +the first portion must therefore be thrown away. You will find in this +case, that a common spirit-lamp is quite sufficient for me to get the +oxygen, and so we shall have two processes going on for its preparation. +See how freely the gas is coming over from that small portion of the +mixture. We will examine it, and see what are its properties. Now, in this +way we are producing, as you will observe, a gas just like the one we had +in the experiment with the battery, transparent, undissolved by water, and +presenting the ordinary visible properties of the atmosphere. (As this +first jar contains the air, together with the first portions of the oxygen +set free during the preparation, we will carry it out of the way, and be +prepared to make our experiments in a regular, dignified manner.) And, +inasmuch as that power of making wood, wax, or other things burn, was so +marked in the oxygen we obtained by means of the voltaic battery from +water, we may expect to find the same property here. We will try it You +see there is the combustion of a lighted taper in air, and here is its +combustion in this gas [lowering the taper into the jar]. See how brightly +and how beautifully it burns! You can also see more than this,—you will +perceive it is a heavy gas, whilst the hydrogen would go up like a +balloon, or even faster than a balloon, when not encumbered with the +weight of the envelope. + +[Illustration: Fig. 22.] + +You may easily see that although we obtained from water twice as much in +volume of the hydrogen as of oxygen, it does not follow that we have twice +as much in weight—because one is heavy, and the other a very light gas. +We have means of weighing gases or air; but without stopping to explain, +that, let me just tell you what their respective weights are. The weight +of a pint of hydrogen is three-quarters of a grain; the weight of the same +quantity of oxygen is nearly twelve grains. This is a very great +difference. The weight of a cubit foot of hydrogen is one-twelfth of an +ounce; and the weight of a cubit foot of oxygen is one ounce and a third. +And so on we might come to masses of matter which may be weighed in the +balance, and which we can take account of as to hundredweights and as to +tons, as you will see almost immediately. + +Now, as regards this very property of oxygen supporting combustion, which +we may compare to air, I will take a piece of candle to shew it you in a +rough way, and the result will be rough. There is our candle burning in +the air: how will it burn in oxygen? I have here a jar of this gas, and I +am about to put it over the candle for you to compare the action of this +gas with that of the air. Why, look at it: it looks something like the +light you saw at the poles of the voltaic battery. Think how vigorous that +action must be! And yet, during all that action, nothing more is produced +than what is produced by the burning of the candle in air. We have the +same production of water, and the same phenomena exactly, when we use this +gas instead of air, as we have when the candle is burnt in air. + +But now we have got a knowledge of this new substance, we can look at it a +little more distinctly, in order to satisfy ourselves that we have got a +good general understanding of this part of the product of a candle. It is +wonderful how great the supporting powers of this substance are as regards +combustion. For instance, here is a lamp which, simple though it be, is +the original, I may say, of a great variety of lamps which are constructed +for divers purposes—for light-houses, microscopic illuminations, and +other uses; and if it were proposed to make it burn very brightly, you +would say, “If a candle burnt better in oxygen, will not a lamp do the +same?” Why, it will do so. Mr. Anderson will give me a tube coming from +our oxygen reservoir, and I am about to apply it to this flame, which I +will previously make burn badly on purpose. There comes the oxygen: what a +combustion that makes! But if I shut it off, what becomes of the lamp? [The +flow of oxygen was stopped, and the lamp relapsed to its former dimness.] +It is wonderful how, by means of oxygen, we get combustion accelerated. +But it does not affect merely the combustion of hydrogen, or carbon, or +the candle; but it exalts all combustions of the common kind. We will take +one which relates to iron, for instance, as you have already seen iron +burn a little in the atmosphere. Here is a jar of oxygen, and this is a +piece of iron wire; but if it were a bar as thick as my wrist, it would +burn the same. + +[Illustration: Fig. 23.] + +I first attach a little piece of wood to the iron, I then set the wood on +fire and let them both down together into the jar. The wood is now alight, +and there it burns as wood should burn in oxygen; but it will soon +communicate its combustion to the iron. The iron is now burning +brilliantly, and will continue so for a long time. As long as we supply +oxygen, so long can we carry on the combustion of the iron, until the +latter is consumed. + +We will now put that on one side, and take some other substance; but we +must limit our experiments, for we have not time to spare for all the +illustrations you would have a right to if we had more time. We will take +a piece of sulphur—you know how sulphur burns in the air—well, we put it +into the oxygen, and you will see that whatever can burn in air, can burn +with a far greater intensity in oxygen, leading you to think that perhaps +the atmosphere itself owes all its power of combustion to this gas. The +sulphur is now burning very quietly in the oxygen; but you cannot for a +moment mistake the very high and increased action which takes place when +it is so burnt, instead of being burnt merely in common air. + +[Illustration: Fig. 24.] + +I am now about to shew you the combustion of another +substance—phosphorus. I can do it better for you here than you can do it +at home. This is a very combustible substance; and if it be so combustible +in air, what might you expect it would be in oxygen? I am about to shew it +to you not in its fullest intensity, for if I did so we should almost blow +the apparatus up—I may even now crack the jar, though I do not want to +break things carelessly. You see how it burns in the air. But what a +glorious light it gives out when I introduce it into oxygen! [Introducing +the lighted phosphorus into the jar of oxygen.] There you see the solid +particles going off which cause that combustion to be so brilliantly +luminous. + +Thus far we have tested this power of oxygen, and the high combustion it +produces by means of other substances. We must now, for a little while +longer, look at it as respects the hydrogen. You know, when we allowed the +oxygen and the hydrogen derived from the water to mix and burn together, +we had a little explosion. You remember, also, that when I burnt the +oxygen and the hydrogen in a jet together, we got very little light, but +great heat. I am now about to set fire to oxygen and hydrogen, mixed in +the proportion in which they occur in water. Here is a vessel containing +one volume of oxygen and two volumes of hydrogen. This mixture is exactly +of the same nature as the gas we just now obtained from the voltaic +battery: it would be far too much to burn at once; I have therefore +arranged to blow soap-bubbles with it, and burn those bubbles, that we may +see by a general experiment or two how this oxygen supports the combustion +of the hydrogen. First of all, we will see whether we can blow a bubble. +Well, there goes the gas [causing it to issue through a tobacco-pipe into +some soap-suds]. Here I have a bubble. I am receiving them on my hand: and +you will perhaps think I am acting oddly in this experiment; but it is to +shew you that we must not always trust to noise and sounds, but rather to +real facts. [Exploding a bubble on the palm of his hand.] I am afraid to +fire a bubble from the end of the pipe, because the explosion would pass +up into the jar and blow it to pieces. This oxygen then will unite with +the hydrogen, as you see by the phenomena, and hear by the sound, with the +utmost readiness of action, and all its powers are then taken up in its +neutralisation of the qualities of the hydrogen. + +So now I think you will perceive the whole history of water with reference +to oxygen and the air, from what we have before said. Why does a piece of +potassium decompose water? Because it finds oxygen in the water. What is +set free when I put it in the water, as I am about to do again? It sets +free hydrogen, and the hydrogen burns; but the potassium itself combines +with oxygen; and this piece of potassium, in taking the water apart—the +water, you may say, derived from the combustion of the candle—takes away +the oxygen which the candle took from the air, and so sets the hydrogen +free; and even if I take a piece of ice, and put a piece of potassium upon +it, the beautiful affinities by which the oxygen and the hydrogen are +related are such, that the ice will absolutely set fire to the potassium. +I shew this to you to-day, in order to enlarge your ideas of these things, +and that you may see how greatly results are modified by circumstances. +There is the potassium on the ice, producing a sort of volcanic action. + +It will be my place, when next we meet, having pointed out these anomalous +actions, to shew you that none of these extra and strange effects are met +with by us—that none of these strange and injurious actions take place +when we are burning, not merely a candle, but gas in our streets, or fuel +in our fireplaces, so long as we confine ourselves within the laws that +Nature has made for our guidance. + + + + +LECTURE V. + +OXYGEN PRESENT IN THE AIR—NATURE OF THE ATMOSPHERE—ITS PROPERTIES—OTHER +PRODUCTS FROM THE CANDLE—CARBONIC ACID—ITS PROPERTIES. + + +We have now seen that we can produce hydrogen and oxygen from the water +that we obtained from the candle. Hydrogen, you know, comes from the +candle, and oxygen, you believe, comes from the air. But then you have a +right to ask me, “How is it that the air and the oxygen do not equally +well burn the candle?” If you remember what happened when I put a jar of +oxygen over a piece of candle, you recollect there was a very different +kind of combustion to that which took place in the air. Now, why is this? +It is a very important question, and one I shall endeavour to make you +understand: it relates most intimately to the nature of the atmosphere, +and is most important to us. + +We have several tests for oxygen besides the mere burning of bodies. You +have seen a candle burnt in oxygen, or in the air; you have seen +phosphorus burnt in the air, or in oxygen; and you have seen iron-filings +burnt in oxygen. But we have other tests besides these, and I am about to +refer to one or two of them for the purpose of carrying your conviction +and your experience further. Here we have a vessel of oxygen. I will shew +its presence to you: if I take a little spark and put it into that oxygen, +you know, by the experience you gained the last time we met, what will +happen; if I put that spark into the jar, it will tell you whether we have +oxygen here or not. Yes! We have proved it by combustion; and now here is +another test for oxygen, which is a very curious and useful one. I have +here two jars full of gas, with a plate between them to prevent their +mixing; I take the plate away, and the gases are creeping one into the +other. “What happens?” say you: “they together produce no such combustion +as was seen in the case of the candle.” But see how the presence of oxygen +is told by its association with this other substance[14]. What a +beautifully coloured gas I have obtained in this way, shewing me the +presence of the oxygen! In the same way we can try this experiment by +mixing common air with this test-gas. Here is a jar containing air—such +air as the candle would burn in—and here is a jar or bottle containing +the test-gas. I let them come together over water, and you see the result: +the contents of the test-bottle are flowing into the jar of air, and you +see I obtain exactly the same kind of action as before, and that shews me +that there is oxygen in the air—the very same substance that has been +already obtained by us from the water produced by the candle. But then, +beyond that, how is it that the candle does not burn in air as well as in +oxygen? We will come to that point at once. I have here two jars; they are +filled to the same height with gas, and the appearance to the eye is alike +in both, and I really do not know at present which of these jars contains +oxygen and which contains air, although I know they have previously been +filled with these gases. But here is our test-gas, and I am going to work +with the two jars, in order to examine whether there is any difference +between them in the quality of reddening this gas. I am now going to turn +this test-gas into one of the jars, and observe what happens. There is +reddening, you see; there is then oxygen present. We will now test the +other jar; but you see this is not so distinctly red as the first: and, +further, this curious thing happens,—if I take these two gases and shake +them well together with water, we shall absorb the red gas; and then, if I +put in more of this test-gas and shake again, we shall absorb more; and I +can go on as long as there be any oxygen present to produce that effect. +If I let in air, it will not matter; but the moment I introduce water, the +red gas disappears; and I may go on in this way, putting in more and more +of the test-gas, until I come to something left behind which will not +redden any longer by the use of that particular body that rendered the air +and the oxygen red. Why is that? You see in a moment it is because there +is, besides oxygen, something else present which is left behind. I will +let a little more air into the jar, and if it turns red you will know that +some of that reddening gas is still present, and that consequently it was +not for the want of this producing body that that air was left behind. + +Now, you will begin to understand what I am about to say. You saw that +when I burnt phosphorus in a jar, as the smoke produced by the phosphorus +and the oxygen of the air condensed, it left a good deal of gas unburnt, +just as this red gas left something untouched,—there was, in fact, this +gas left behind, which the phosphorus cannot touch, which the reddening +gas cannot touch, and this something is not oxygen, and yet is part of the +atmosphere. + +So that is one way of opening out air into the two things of which it is +composed—oxygen, which burns our candles, our phosphorus, or anything +else; and this other substance—nitrogen—which will not burn them. This +other part of the air is by far the larger proportion, and it is a very +curious body, when we come to examine it; it is remarkably curious, and +yet you say, perhaps, that it is very uninteresting. It is uninteresting +in some respects because of this—that it shews no brilliant effects of +combustion. If I test it with a taper as I do oxygen and hydrogen, it +does not burn like hydrogen, nor does it make the taper burn like oxygen. +Try it in any way I will, it does neither the one thing nor the other: it +will not take fire; it will not let the taper burn; it puts out the +combustion of everything. There is nothing that will burn in it in common +circumstances. It has no smell; it is not sour; it does not dissolve in +water; it is neither an acid nor an alkali; it is as indifferent to all +our organs as it is possible for a thing to be. And you might say, “It is +nothing; it is not worth chemical attention; what does it do in the air?” +Ah! then come our beautiful and fine results shewn us by an observant +philosophy. Suppose, in place of having nitrogen, or nitrogen and oxygen, +we had pure oxygen as our atmosphere; what would become of us? You know +very well that a piece of iron lit in a jar of oxygen goes on burning to +the end. When you see a fire in an iron grate, imagine where the grate +would go to if the whole of the atmosphere were oxygen. The grate would +burn up more powerfully than the coals—for the iron of the grate itself +is even more combustible than the coals which we burn in it. A fire put +into the middle of a locomotive would be a fire in a magazine of fuel, if +the atmosphere were oxygen. The nitrogen lowers it down and makes it +moderate and useful for us, and then, with all that, it takes away with it +the fumes that you have seen produced from the candle, disperses them +throughout the whole of the atmosphere, and carries them away to places +where they are wanted to perform a great and glorious purpose of good to +man, for the sustenance of vegetation; and thus does a most wonderful +work, although you say, on examining it, “Why, it is a perfectly +indifferent thing.” This nitrogen in its ordinary state is an inactive +element; no action short of the most intense electric force, and then in +the most infinitely small degree, can cause the nitrogen to combine +directly with the other element of the atmosphere, or with other things +round about it; it is a perfectly indifferent, and therefore to say, a +safe substance. + +But before I take you to that result, I must tell you about the atmosphere +itself. I have written on this diagram the composition of one hundred +parts of atmospheric air:— + + Bulk. Weight. + Oxygen, . . . . . 20 22.3 + Nitrogen, . . . . 80 77.7 + ——— ————— + 100 100.0 + +It is a true analysis of the atmosphere, so far as regards the quantity of +oxygen and the quantity of nitrogen present. By our analysis, we find that +5 pints of the atmosphere contain only 1 pint of oxygen, and 4 pints, or 4 +parts, of nitrogen by bulk. That is our analysis of the atmosphere. It +requires all that quantity of nitrogen to reduce the oxygen down, so as to +be able to supply the candle properly with fuel, so as to supply us with +an atmosphere which our lungs can healthily and safely breathe; for it is +just as important to make the oxygen right for us to breathe, as it is to +make the atmosphere right for the burning of the fire and the candle. + +But now for this atmosphere. First of all, let me tell you the weight of +these gases. A pint of nitrogen weighs 10⁴⁄₁₀ grains, or a cubic foot +weighs 1⅙ ounce. That is the weight of the nitrogen. The oxygen is +heavier: a pint of it weighs 11⁹⁄₁₀ grains, and a cubic foot weighs 1¾ +ounce. A pint of air weighs about 10⁷⁄₁₀ grains, and a cubic foot 1⅕ +ounce. + +[Illustration: Fig. 25.] + +You have asked me several times, and I am very glad you have, “How do you +weigh gases?” I will shew you; it is very simple, and easily done. Here is +a balance, and here a copper bottle, made as light as we can consistent +with due strength, turned very nicely in the lathe, and made perfectly +air-tight, with a stop-cock, which we can open and shut, which at present +is open, and therefore allows the bottle to be full of air. I have here a +nicely-adjusted balance, in which I think the bottle, in its present +condition, will be balanced by the weight on the other side. And here is a +pump by which we can force the air into this bottle, and with it we will +force in a certain number of volumes of air, as measured by the pump. +[Twenty measures were pumped in.] We will shut that in and put it in the +balance. See how it sinks: it is much heavier than it was. By what? By +the air that we have forced into it by the pump. There is not a greater +_bulk_ of air, but there is the same bulk of _heavier_ air, because we +have forced in air upon it. And that you may have a fair notion in your +mind as to how much this air measures, here is a jar full of water. We +will open that copper vessel into this jar, and let the air return to its +former state. All I have to do now is to screw them tightly together, and +to turn the taps, when there, you see, is the bulk of the twenty pumps of +air which I forced into the bottle; and to make sure that we have been +quite correct in what we have been doing, we will take the bottle again to +the balance, and, if it is now counterpoised by the original weight, we +shall be quite sure we have made our experiment correctly. + +[Illustration: Fig. 26.] + +It is balanced; so, you see, we can find out the weight of the extra +volumes of air forced in, in that way, and by that means we are able to +ascertain that a cubic foot of air weighs 1⅕ ounce. But that small +experiment will by no means convey to your mind the whole literal truth of +this matter. It is wonderful how it accumulates when you come to larger +volumes. This bulk of air [a cubic foot] weighs 1⅕ ounce. What do you +think of the contents of that box above there, which I have had made for +the purpose? The air which is within that box weighs one pound—a full +pound; and I have calculated the weight of the air in this room,—you +would hardly imagine it, but it is above a ton. So rapidly do the weights +rise up, and so important is the presence of the atmosphere, and of the +oxygen and the nitrogen in it, and the use it performs in conveying things +to and fro from place to place, and carrying bad vapours to places where +they will do good instead of harm. + +Having given you that little illustration with respect to the weight of +the air, let me shew you certain consequences of it. You have a right to +them, because you would not understand so much without it. Do you remember +this kind of experiment? Have you ever seen it? Suppose I take a pump +somewhat similar to the one I had a little while ago to force air into the +bottle, and suppose I place it in such a manner that by certain +arrangements I can apply my hand to it: my hand moves about in the air so +easily that it seems to feel nothing, and I can hardly get velocity enough +by any motion of my own in the atmosphere to make sure that there is much +resistance to it. + +[Illustration: Fig. 27.] + +But, when I put my hand here [on the air-pump receiver, which was +afterwards exhausted], you see what happens. Why is my hand fastened to +this place, and why am I able to pull this pump about? And see! how is it +that I can hardly get my hand away? Why is this? It is the weight of the +air—the weight of the air that is above. I have another experiment here, +which I think will explain to you more about it. When the air is pumped +from underneath the bladder which is stretched over this glass, you will +see the effect in another shape: the top is quite flat at present, but I +will make a very little motion with the pump, and now look at it—see how +it has gone down, see how it is bent in. You will see the bladder go in +more and more, until at last I expect it will be driven in and broken by +the force of the atmosphere pressing upon it. + +[Illustration: Fig. 28.] + +[The bladder at last broke with a loud report.] Now, that was done +entirely by the weight of the air pressing on it, and you can easily +understand how that is. The particles that are piled up in the atmosphere +stand upon each other, as these five cubes do. You can easily conceive +that four of these five cubes are resting upon the bottom one, and if I +take that away, the others will all sink down. So it is with the +atmosphere: the air that is above is sustained by the air that is beneath; +and when the air is pumped away from beneath them, the change occurs which +you saw when I placed my hand on the air-pump, and which you saw in the +case of the bladder, and which you shall see better here. I have tied over +this jar a piece of sheet india-rubber, and I am now about to take away +the air from the inside of the jar; and if you will watch the +india-rubber—which acts as a partition between the air below and the air +above—you will see, when I pump, how the pressure shews itself. See where +it is going to—I can actually put my hand into the jar; and yet this +result is only caused by the great and powerful action of the air above. +How beautifully it shews this curious circumstance! + +Here is something that you can have a pull at, when I have finished +to-day. It is a little apparatus of two hollow brass hemispheres, closely +fitted together, and having connected with it a pipe and a cock, through +which we can exhaust the air from the inside; and although the two halves +are so easily taken apart, while the air is left within, yet you will see, +when we exhaust it by-and-by, no power of any two of you will be able to +pull them apart. Every square inch of surface that is contained in the +area of that vessel sustains fifteen pounds by weight, or nearly so, when +the air is taken out; and you may try your strength presently in seeing +whether you can overcome that pressure of the atmosphere. + +Here is another very pretty thing—the boys’ sucker, only refined by the +philosopher. We young ones have a perfect right to take toys, and make +them into philosophy, inasmuch as now-a-days we are turning philosophy +into toys. Here is a sucker, only it is made of india-rubber: if I clap it +upon the table, you see at once it holds. Why does it hold? I can slip it +about, and yet if I try to pull it up, it seems as if it would pull the +table with it I can easily make it slip about from place to place; but +only when I bring it to the edge of the table can I get it off. It is only +kept down by the pressure of the atmosphere above. We have a couple of +them; and if you take these two and press them together, you will see how +firmly they stick. And, indeed, we may use them as they are proposed to be +used, to stick against windows, or against walls, where they will adhere +for an evening, and serve to hang anything on that you want. I think, +however, that you boys ought to be shewn experiments that you can make at +home; and so here is a very pretty experiment in illustration of the +pressure of the atmosphere. Here is a tumbler of water. Suppose I were to +ask you to turn that tumbler upside-down, so that the water should not +fall out, and yet not be kept in by your hand, but merely by using the +pressure of the atmosphere. Could you do that? Take a wine-glass, either +quite full or half-full of water, and put a flat card on the top, turn it +upside-down, and then see what becomes of the card and of the water. The +air cannot get in because the water by its capillary attraction round the +edge keeps it out. + +I think this will give you a correct notion of what you may call the +materiality of the air; and when I tell you that the box holds a pound of +it, and this room more than a ton, you will begin to think that air is +something very serious. I will make another experiment, to convince you of +this positive resistance. There is that beautiful experiment of the +popgun, made so well and so easily, you know, out of a quill, or a tube, +or anything of that kind,—where we take a slice of potato, for instance, +or an apple, and take the tube and cut out a pellet, as I have now done, +and push it to one end. I have made that end tight; and now I take another +piece and put it in: it will confine the air that is within the tube +perfectly and completely for our purpose; and I shall now find it +absolutely impossible by any force of mine to drive that little pellet +close up to the other. It cannot be done. I may press the air to a certain +extent, but if I go on pressing, long before it comes to the second, the +confined air will drive the front one out with a force something like that +of gunpowder; for gunpowder is in part dependent upon the same action that +you see here exemplified. + +I saw the other day an experiment which pleased me much, as I thought it +would serve our purpose here. (I ought to have held my tongue for four or +five minutes before beginning this experiment, because it depends upon my +lungs for success.) By the proper application of air I expect to be able +to drive this egg out of one cup into the other by the force of my breath; +but if I fail, it is in a good cause; and I do not promise success, +because I have been talking more than I ought to do to make the experiment +succeed. + +[The Lecturer here tried the experiment, and succeeded in blowing the egg +from one egg-cup to the other.] + +You see that the air which I blow goes downwards between the egg and the +cup, and makes a blast under the egg, and is thus able to lift a heavy +thing—for a full egg is a very heavy thing for air to lift. If you want +to make the experiment, you had better boil the egg quite hard first, and +then you may very safely try to blow it from one cup to the other, with a +little care. + +I have now kept you long enough upon this property of the weight of the +air, but there is another thing I should like to mention. You saw the way +in which, in this popgun, I was able to drive the second piece of potato +half or two-thirds of an inch before the first piece started, by virtue of +the elasticity of the air—just as I pressed into the copper bottle the +particles of air by means of the pump. Now, this depends upon a wonderful +property in the air, namely, its elasticity; and I should like to give you +a good illustration of this. If I take anything that confines the air +properly, as this membrane, which also is able to contract and expand so +as to give us a measure of the elasticity of the air, and confine in this +bladder a certain portion of air; and then, if we take the atmosphere off +from the outside of it, just as in these cases we put the pressure on—if +we take the pressure off, you will see how it will then go on expanding +and expanding, larger and larger, until it will fill the whole of this +bell-jar, shewing you that wonderful property of the air, its elasticity, +its compressibility, and expansibility, to an exceedingly large extent, +and which is very essential for the purposes and services it performs in +the economy of creation. + +We will now turn to another very important part of our subject, +remembering that we have examined the candle in its burning, and have +found that it gives rise to various products. We have the products, you +know, of soot, of water, and of something else which you have not yet +examined. We have collected the water, but have allowed the other things +to go into the air. Let us now examine some of these other products. + +Here is an experiment which I think will help you in part in this way. We +will put our candle there, and place over it a chimney, thus. I think my +candle will go on burning, because the air-passage is open at the bottom +and the top. In the first place, you see the moisture appearing—that you +know about. It is water produced from the candle by the action of the air +upon its hydrogen. But, besides that, something is going out at the top: +it is not moisture—it is not water—it is not condensable; and yet, after +all, it has very singular properties. You will find that the air coming +out of the top of our chimney is nearly sufficient to blow the light out I +am holding to it; and if I put the light fairly opposed to the current, it +will blow it quite out. You will say that is as it should be; and I am +supposing that you think it ought to do so, because the nitrogen does not +support combustion, and ought to put the candle out, since the candle will +not burn in nitrogen. + +[Illustration: Fig. 29.] + +But is there nothing else there than nitrogen? I must now anticipate—that +is to say, I must use my own knowledge to supply you with the means that +we adopt for the purpose of ascertaining these things, and examining such +gases as these. I will take an empty bottle—here is one—and if I hold it +over this chimney, I shall get the combustion of the candle below sending +its results into the bottle above; and we shall soon find that this bottle +contains, not merely an air that is bad as regards the combustion of a +taper put into it, but having other properties. + +Let me take a little quick-lime and pour some common water on to it—the +commonest water will do. I will stir it a moment, then pour it upon a +piece of filtering paper in a funnel, and we shall very quickly have a +clear water proceeding to the bottle below, as I have here. I have plenty +of this water in another bottle; but, nevertheless, I should like to use +the lime-water that was prepared before you, so that you may see what its +uses are. If I take some of this beautiful clear lime-water, and pour it +into this jar, which has collected the air from the candle, you will see a +change coming about. Do you see that the water has become quite milky? +Observe, that will not happen with air merely. Here is a bottle filled +with air; and if I put a little lime-water into it, neither the oxygen nor +the nitrogen, nor anything else that is in that quantity of air, will make +any change in the lime-water. It remains perfectly clear, and no shaking +of that quantity of lime-water with that quantity of air in its common +state will cause any change; but if I take this bottle with the +lime-water, and hold it so as to get the general products of the candle in +contact with it, in a very short time we shall have it milky. There is the +chalk, consisting of the lime which we used in making the lime-water, +combined with something that came from the candle—that other product +which we are in search of, and which I want to tell you about to-day. This +is a substance made visible to us by its action, which is not the action +of the lime-water either upon the oxygen or upon the nitrogen, nor upon +the water itself, but it is something new to us from the candle. And then +we find this white powder, produced by the lime-water and the vapour from +the candle, appears to us very much like whitening or chalk, and, when +examined, it does prove to be exactly the same substance as whitening or +chalk. So we are led, or have been led, to observe upon the various +circumstances of this experiment, and to trace this production of chalk to +its various causes, to give us the true knowledge of the nature of this +combustion of the candle—to find that this substance, issuing from the +candle, is exactly the same as that substance which would issue from a +retort, if I were to put some chalk into it with a little moisture, and +make it red-hot: you would then find that exactly the same substance would +issue from it as from the candle. + +But we have a better means of getting this substance, and in greater +quantity, so as to ascertain what its general characters are. We find this +substance in very great abundance in a multitude of cases where you would +least expect it. All limestones contain a great deal of this gas which +issues from the candle, and which we call _carbonic acid_. All chalks, all +shells, all corals contain a great quantity of this curious air. We find +it fixed in these stones; for which reason Dr. Black called it “fixed +air”—finding it in these fixed things like marble and chalk. He called it +fixed air, because it lost its quality of air, and assumed the condition +of a solid body. We can easily get this air from marble. Here is a jar +containing a little muriatic acid, and here is a taper which, if I put it +into that jar, will shew only the presence of common air. There is, you +see, pure air down to the bottom; the jar is full of it Here is a +substance—marble[17], a very beautiful and superior marble—and if I put +these pieces of marble into the jar, a great boiling apparently goes on. +That, however, is not steam—it is a gas that is rising up; and if I now +search the jar by a candle, I shall have exactly the same effect produced +upon the taper as I had from the air which issued from the end of the +chimney over the burning candle. It is exactly the same action, and caused +by the very same substance that issued from the candle; and in this way we +can get carbonic acid in great abundance—we have already nearly filled +the jar. We also find that this gas is not merely contained in marble. +Here is a vessel in which I have put some common whitening—chalk, which +has been washed in water and deprived of its coarser particles, and so +supplied to the plasterer as whitening. Here is a large jar containing +this whitening and water, and I have here some strong sulphuric acid, +which is the acid you might have to use if you were to make these +experiments (only, in using this acid with limestone, the body that is +produced is an insoluble substance, whereas the muriatic acid produces a +soluble substance that does not so much thicken the water). And you will +seek out a reason why I take this kind of apparatus for the purpose of +shewing this experiment. I do it because you may repeat in a small way +what I am about to do in a large one. You will have here just the same +kind of action; and I am evolving in this large jar carbonic acid, exactly +the same in its nature and properties as the gas which we obtained from +the combustion of the candle in the atmosphere. And no matter how +different the two methods by which we prepare this carbonic acid, you will +see, when we get to the end of our subject, that it is all exactly the +same, whether prepared in the one way or in the other. + +We will now proceed to the next experiment with regard to this gas. What +is its nature? Here is one of the vessels full, and we will try it, as we +have done so many other gases, by combustion. You see it is not +combustible, nor does it support combustion. Neither, as we know, does it +dissolve much in water, because we collect it over water very easily. +Then, you know that it has an effect, and becomes white in contact with +lime-water; and when it does become white in that way, it becomes one of +the constituents to make carbonate of lime or limestone. + +The next thing I must shew you is, that it really does dissolve a little +in water, and therefore that it is unlike oxygen and hydrogen in that +respect I have here an apparatus by which we can produce this solution. In +the lower part of this apparatus is marble and acid, and in the upper part +cold water. The valves are so arranged that the gas can get from one to +the other. I will set it in action now, and you can see the gas bubbling +up through the water, as it has been doing all night long, and by this +time we shall find that we have this substance dissolved in the water. If +I take a glass and draw off some of the water, I find that it tastes a +little acid to the mouth: it is impregnated with carbonic acid; and if I +now apply a little lime-water to it, that will give us a test of its +presence. This water will make the lime-water turbid and white, which is +proof of the presence of carbonic acid. + +Then it is a very weighty gas—it is heavier than the atmosphere. I have +put their respective weights at the lower part of this table, along with, +for comparison, the weights of the other gases we have been examining:— + + Pint. Cubic Foot. +Hydrogen, . . . . ¾ grains. ¹⁄₁₂ ounce. +Oxygen, . . . . 11⁹⁄₁₀ „ 1½ „ +Nitrogen, . . . . 10⅒ „ 1¼ „ +Air,. . . . . . 10⁷⁄₁₆ „ 1⅜ „ +Carbonic acid, . . 16⅓ „ 1⁹⁄₁₀ „ + +A pint of it weighs 16⅓ grains, and a cubic foot weighs 1⁹⁄₁₀ ounce, +almost two ounces. You can see by many experiments that this is a heavy +gas. Suppose I take a glass containing nothing else but air, and from this +vessel containing the carbonic acid I attempt to pour a little of this gas +into that glass; I wonder whether any has gone in or not. I cannot tell by +the appearance, but I can in this way [introducing the taper]. Yes, there +it is, you see; and if I were to examine it by lime-water, I should find +it by that test also. I will take this little bucket, and put it down into +the well of carbonic acid—indeed, we too often have real wells of +carbonic acid—and now, if there is any carbonic acid, I must have got to +it by this time, and it will be in this bucket, which we will examine with +a taper. There it is, you see; it is full of carbonic acid. + +[Illustration: Fig. 30.] + +There is another experiment by which I will shew you its weight. I have +here a jar suspended at one end of a balance—it is now equipoised; but +when I pour this carbonic acid into the jar on the one side which now +contains air, you will see it sink down at once, because of the carbonic +acid that I pour into it. And now, if I examine this jar with the lighted +taper, I shall find that the carbonic acid has fallen into it, and it no +longer has any power of supporting the combustion. If I blow a +soap-bubble, which of course will be filled with air, and let it fall into +this jar of carbonic acid, it will float. + +[Illustration: Fig. 31.] + +But I shall first of all take one of these little balloons filled with +air. I am not quite sure where the carbonic acid is; we will just try the +depth, and see whereabouts is its level. There, you see, we have this +bladder floating on the carbonic acid; and if I evolve some more of the +carbonic acid, the bladder will be lifted up higher. There it goes—the +jar is nearly full; and now I will see whether I can blow a soap-bubble on +that, and float it in the same way. [The Lecturer here blew a soap-bubble, +and allowed it to fall into the jar of carbonic acid, when it floated in +it midway.] It is floating, as the balloon floated, by virtue of the +greater weight of the carbonic acid than of the air. And now, having so +far given you the history of the carbonic acid—as to its sources in the +candle, as to its physical properties and weight—when we next meet I +shall shew you of what it is composed, and where it gets its elements +from. + + + + +LECTURE VI. + +CARBON OR CHARCOAL—COAL-GAS—RESPIRATION AND ITS ANALOGY TO THE BURNING +OF A CANDLE—CONCLUSION. + + +A lady, who honours me by her presence at these Lectures, has conferred a +still further obligation by sending me these two candles, which are from +Japan, and, I presume, are made of that substance to which I referred in a +former lecture. You see that they are even far more highly ornamented than +the French candles; and, I suppose, are candles of luxury, judging from +their appearance. They have a remarkable peculiarity about them—namely, a +hollow wick,—that beautiful peculiarity which Argand introduced into the +lamp, and made so valuable. To those who receive such presents from the +East, I may just say that this and such like materials gradually undergo a +change which gives them on the surface a dull and dead appearance; but +they may easily be restored to their original beauty, if the surface be +rubbed with a clean cloth or silk handkerchief, so as to polish the little +rugosity or roughness: this will restore the beauty of the colours. I have +so rubbed one of these candles, and you see the difference between it and +the other which has not been polished, but which may be restored by the +same process. Observe, also, that these moulded candles from Japan are +made more conical than the moulded candles in this part of the world. + +I told you, when we last met, a good deal about carbonic acid. We found, +by the lime-water test, that when the vapour from the top of the candle or +lamp was received into bottles, and tested by this solution of lime-water +(the composition of which I explained to you, and which you can make for +yourselves), we had that white opacity which was in fact calcareous +matter, like shells and corals, and many of the rocks and minerals in the +earth. But I have not yet told you fully and clearly the chemical history +of this substance—carbonic acid—as we have it from the candle, and I +must now resume that subject. We have seen the products, and the nature of +them, as they issue from the candle. We have traced the water to its +elements, and now we have to see where are the elements of the carbonic +acid supplied by the candle. A few experiments will shew this. You +remember that when a candle burns badly, it produces smoke; but if it is +burning well, there is no smoke. And you know that the brightness of the +candle is due to this smoke, which becomes ignited. Here is an experiment +to prove this: so long as the smoke remains in the flame of the candle and +becomes ignited, it gives a beautiful light, and never appears to us in +the form of black particles. I will light some fuel, which is extravagant +in its burning. This will serve our purpose—a little turpentine on a +sponge. You see the smoke rising from it, and floating into the air in +large quantities; and, remember now, the carbonic acid that we have from +the candle is from such smoke as that. To make that evident to you, I will +introduce this turpentine burning on the sponge into a flask where I have +plenty of oxygen, the rich part of the atmosphere, and you now see that +the smoke is all consumed. This is the first part of our experiment; and +now, what follows? The carbon which you saw flying off from the turpentine +flame in the air is now entirely burned in this oxygen, and we shall find +that it will, by this rough and temporary experiment, give us exactly the +same conclusion and result as we had from the combustion of the candle. +The reason why I make the experiment in this manner is solely that I may +cause the steps of our demonstration to be so simple that you can never +for a moment lose the train of reasoning, if you only pay attention. All +the carbon which is burned in oxygen, or air, comes out as carbonic acid, +whilst those particles which are not so burned shew you the second +substance in the carbonic acid—namely, the carbon—that body which made +the flame so bright whilst there was plenty of air, but which was thrown +off in excess when there was not oxygen enough to burn it. + +I have also to shew you a little more distinctly the history of carbon and +oxygen, in their union to make carbonic acid. You are now better able to +understand this than before, and I have prepared three or four experiments +by way of illustration. This jar is filled with oxygen, and here is some +carbon which has been placed in a crucible, for the purpose of being made +red-hot. I keep my jar dry, and venture to give you a result imperfect in +some degree, in order that I may make the experiment brighter. I am about +to put the oxygen and the carbon together. That this is carbon (common +charcoal pulverised), you will see by the way in which it burns in the air +[letting some of the red-hot charcoal fall out of the crucible]. I am now +about to burn it in oxygen gas, and look at the difference. It may appear +to you at a distance as if it were burning with a flame; but it is not so. +Every little piece of charcoal is burning as a spark, and whilst it so +burns it is producing carbonic acid. I specially want these two or three +experiments to point out what I shall dwell upon more distinctly +by-and-by—that carbon burns in this way, and not as a flame. + +Instead of taking many particles of carbon to burn, I will take a rather +large piece, which will enable you to see the form and size; and to trace +the effects very decidedly. Here is the jar of oxygen, and here is the +piece of charcoal, to which I have fastened a little piece of wood, which +I can set fire to, and so commence the combustion, which I could not +conveniently do without. You now see the charcoal burning, but not as a +flame (or if there be a flame, it is the smallest possible one, which I +know the cause of—namely, the formation of a little carbonic oxide close +upon the surface of the carbon). It goes on burning, you see, slowly +producing carbonic acid by the union of this carbon or charcoal (they are +equivalent terms) with the oxygen. I have here another piece of charcoal, +a piece of bark, which has the quality of being blown to pieces—exploding +as it burns. By the effect of the heat, we shall reduce the lump of carbon +into particles that will fly off; still every particle, equally with the +whole mass, burns in this peculiar way: it burns as a coal, and not like a +flame. You observe a multitude of little combustions going on, but no +flame. I do not know a finer experiment than this, to shew that carbon +burns with a spark. + +Here, then, is carbonic acid formed from its elements. It is produced at +once; and if we examined it by lime-water, you will see that we have the +same substance which I have previously described to you. By putting +together 6 parts of carbon by weight (whether it comes from the flame of a +candle or from powdered charcoal) and 16 parts of oxygen by weight, we +have 22 parts of carbonic acid; and, as we saw last time, the 22 parts of +carbonic acid, combined with 28 parts of lime, produced common carbonate +of lime. If you were to examine an oyster-shell, and weigh the component +parts, you would find that every 50 parts would give 6 of carbon and 16 of +oxygen, combined with 28 of lime. However, I do not want to trouble you +with these minutiæ—it is only the general philosophy of the matter that +we can now go into. See how finely the carbon is dissolving away [pointing +to the lump of charcoal burning quietly in the jar of oxygen]. You may say +that the charcoal is actually dissolving in the air round about; and if +that were perfectly pure charcoal, which we can easily prepare, there +would be no residue whatever. When we have a perfectly cleansed and +purified piece of carbon, there is no ash left. The carbon burns as a +solid dense body, that heat alone cannot change as to its solidity, and +yet it passes away into vapour that never condenses into solid or liquid +under ordinary circumstances; and what is more curious still, is the fact +that the oxygen does not change in its bulk by the solution of the carbon +in it. Just as the bulk is at first, so it is at last, only it has become +carbonic acid. + +There is another experiment which I must give you before you are fully +acquainted with the general nature of carbonic acid. Being a compound +body, consisting of carbon and oxygen, carbonic acid is a body that we +ought to be able to take asunder. And so we can. As we did with water, so +we can with carbonic acid—take the two parts asunder. The simplest and +quickest way is to act upon the carbonic acid by a substance that can +attract the oxygen from it, and leave the carbon behind. You recollect +that I took potassium and put it upon water or ice, and you saw that it +could take the oxygen from the hydrogen. Now, suppose we do something of +the same kind here with this carbonic acid. You know carbonic acid to be a +heavy gas. I will not test it with lime-water, as that will interfere with +our subsequent experiments; but I think the heaviness of the gas and the +power of extinguishing flame will be sufficient for our purpose. I +introduce a flame into the gas, and you will see whether it will be put +out. You see the light is extinguished. Indeed, the gas may, perhaps, put +out phosphorus, which, you know, has a pretty strong combustion. Here is a +piece of phosphorus heated to a high degree. I introduce it into gas, and +you observe the light is put out; but it will take fire again in the air, +because there it re-enters into combustion. Now, let me take a piece of +potassium, a substance which, even at common temperatures, can act upon +carbonic acid, though not sufficiently for our present purpose, because it +soon gets covered with a protecting coat; but if we warm it up to the +burning point in air, as we have a fair right to do, and as we have done +with phosphorus, you will see that it can burn in carbonic acid; and if it +burns, it will burn by taking oxygen, so that you will see what is left +behind. I am going, then, to burn this potassium in the carbonic acid, as +a proof of the existence of oxygen in the carbonic acid. [In the +preliminary process of heating, the potassium exploded.] Sometimes we get +an awkward piece of potassium that explodes, or something like it, when it +burns. I will take another piece; and now that it is heated, I introduce +it into the jar, and you perceive that it burns in the carbonic acid—not +so well as in the air, because the carbonic acid contains the oxygen +combined; but it does burn, and takes away the oxygen. If I now put this +potassium into water, I find that, besides the potash formed (which you +need not trouble about), there is a quantity of carbon produced. I have +here made the experiment in a very rough way; but I assure you that if I +were to make it carefully, devoting a day to it, instead of five minutes, +we should get all the proper amount of charcoal left in the spoon, or in +the place where the potassium was burned, so that there could be no doubt +as to the result. Here, then, is the carbon obtained from the carbonic +acid, as a common black substance; so that you have the entire proof of +the nature of carbonic acid as consisting of carbon and oxygen. And now, I +may tell you, that _whenever_ carbon burns under common circumstances, it +produces carbonic acid. + +Suppose I take this piece of wood, and put it into a bottle with +lime-water. I might shake that lime-water up with wood and the atmosphere +as long as I pleased, it would still remain clear as you see it; but +suppose I burn the piece of wood in the air of that bottle. You, of +course, know I get water. Do I get carbonic acid? [The experiment was +performed.] There it is, you see—that is to say, the carbonate lime, +which results from carbonic acid, and that carbonic acid must be formed +from the carbon which comes from the wood, from the candle, or any other +thing. Indeed, you have yourselves frequently tried a very pretty +experiment, by which you may see the carbon in wood. If you take a piece +of wood, and partly burn it, and then blow it out, you have carbon left. +There are things that do not shew carbon in this way. A candle does not +shew it, but it contains carbon. Here also is a jar of coal-gas, which +produces carbonic acid abundantly. You do not see the carbon, but we can +soon shew it to you. I will light it, and as long as there is any gas in +this cylinder it will go on burning. You see no carbon, but you see a +flame; and because that is bright, it will lead you to guess that there is +carbon in the flame. But I will shew it to you by another process. I have +some of the same gas in another vessel, mixed with a body that will burn +the hydrogen of the gas, but will not burn the carbon. I will light them +with a burning taper, and you perceive the hydrogen is consumed, but not +the carbon, which is left behind as a dense black smoke. I hope that by +these three or four experiments you will learn to see when carbon is +present, and understand what are the products of combustion, when gas or +other bodies are thoroughly burned in the air. + +Before we leave the subject of carbon, let us make a few experiments and +remarks upon its wonderful condition as respects ordinary combustion. I +have shewn you that the carbon in burning burns only as a solid body, and +yet you perceive that, after it is burned, it ceases to be a solid. There +are very few fuels that act like this. It is, in fact, only that great +source of fuel, the carbonaceous series, the coals, charcoals, and woods, +that can do it. I do not know that there is any other elementary substance +besides carbon that burns with these conditions; and if it had not been +so, what would happen to us? Suppose all fuel had been like iron, which, +when it burns, burns into a solid substance. We could not then have such a +combustion as you have in this fireplace. Here also is another kind of +fuel which burns very well—as well as, if not better, than carbon—so +well, indeed, as to take fire of itself when it is in the air, as you see +[breaking a tube full of lead pyrophorus]. This substance is lead, and you +see how wonderfully combustible it is. It is very much divided, and is +like a heap of coals in the fireplace; the air can get to its surface and +inside, and so it burns. But why does it not burn in that way now, when it +is lying in a mass? [emptying the contents of the tube in a heap on to a +plate of iron]. Simply because the air cannot get to it. Though it can +produce a great heat, the great heat which we want in our furnaces and +under our boilers, still that which is produced cannot get away from the +portion which remains unburned underneath, and that portion, therefore, is +prevented from coming in contact with the atmosphere, and cannot be +consumed. How different is that from carbon. Carbon burns just in the same +way as this lead does, and so gives an intense fire in the furnace, or +wherever you choose to burn it; but then the body produced by its +combustion passes away, and the remaining carbon is left clear. I shewed +you how carbon went on dissolving in the oxygen, leaving no ash; whereas +here [pointing to the heap of pyrophorus] we have actually more ash than +fuel, for it is heavier by the amount of the oxygen which has united with +it. Thus you see the difference between carbon and lead or iron: if we +choose iron, which gives so wonderful a result in our application of this +fuel, either as light or heat. If, when the carbon burnt, the product went +off as a solid body, you would have had the room filled with an opaque +substance, as in the case of the phosphorus; but when carbon burns, +everything passes up into the atmosphere. It is in a fixed, almost +unchangeable condition before the combustion; but afterwards it is in the +form of gas, which it is very difficult (though we have succeeded) to +produce in a solid or a liquid state. + +Now, I must take you to a very interesting part of our subject—to the +relation between the combustion of a candle and that living kind of +combustion which goes on within us. In every one of us there is a living +process of combustion going on very similar to that of a candle; and I +must try to make that plain to you. For it is not merely true in a +poetical sense—the relation of the life of man to a taper; and if you +will follow, I think I can make this clear. In order to make the relation +very plain, I have devised a little apparatus which we can soon build up +before you. Here is a board and a groove cut in it, and I can close the +groove at the top part by a little cover. I can then continue the groove +as a channel by a glass tube at each end, there being a free passage +through the whole. Suppose I take a taper or candle (we can now be liberal +in our use of the word “candle,” since we understand what it means), and +place it in one of the tubes; it will go on, you see, burning very well. +You observe that the air which feeds the flame passes down the tube at one +end, then goes along the horizontal tube, and ascends the tube at the +other end in which the taper is placed. + +[Illustration: Fig. 32] + +If I stop the aperture through which the air enters, I stop combustion, as +you perceive. I stop the supply of air, and consequently the candle goes +out. But, now, what will you think of this fact? In a former experiment I +shewed you the air going from one burning candle to a second candle. If I +took the air proceeding from another candle, and sent it down by a +complicated arrangement into this tube, I should put this burning candle +out. But what will you say when I tell you that my breath will put out +that candle? I do not mean by blowing at all, but simply that the nature +of my breath is such that a candle cannot burn in it. I will now hold my +mouth over the aperture, and without blowing the flame in any way, let no +air enter the tube but what comes from my mouth. You see the result. I did +not blow the candle out. I merely let the air which I expired pass into +the aperture, and the result was that the light went out for want of +oxygen, and for no other reason. Something or other—namely, my lungs—had +taken away the oxygen from the air, and there was no more to supply the +combustion of the candle. It is, I think, very pretty to see the time it +takes before the bad air which I throw into this part of the apparatus has +reached the candle. The candle at first goes on burning, but so soon as +the air has had time to reach it, it goes out. And, now, I will shew you +another experiment, because this is an important part of our philosophy. +Here is a jar which contains fresh air, as you can see by the circumstance +of a candle or gas-light burning it. I make it close for a little time, +and by means of a pipe I get my mouth over it so that I can inhale the +air. By putting it over water, in the way that you see, I am able to draw +up this air (supposing the cork to be quite tight), take it into my lungs, +and throw it back into the jar. + +[Illustration: Fig. 33.] + +We can then examine it, and see the result. You observe, I first take up +the air, and then throw it back, as is evident from the ascent and descent +of the water; and now, by putting a taper into the air, you will see the +state in which it is, by the light being extinguished. Even one +inspiration, you see, has completely spoiled this air, so that it is no +use my trying to breathe it a second time. Now, you understand the ground +of the impropriety of many of the arrangements among the houses of the +poorer classes, by which the air is breathed over and over again, for the +want of a supply, by means of proper ventilation, sufficient to produce a +good result. You see how bad the air becomes by a single breathing; so +that you can easily understand how essential fresh air is to us. + +To pursue this a little further, let us see what will happen with +lime-water. Here is a globe which contains a little lime-water, and it is +so arranged as regards the pipes, as to give access to the air within, so +that we can ascertain the effect of respired or unrespired air upon it. Of +course, I can either draw in air (through A), and so make the air that +feeds my lungs go through the lime-water, or I can force the air out of my +lungs through the tube (B), which goes to the bottom, and so shew its +effect upon the lime-water. + +[Illustration: Fig. 34.] + +You will observe that, however long I draw the external air into the +lime-water, and then through it to my lungs, I shall produce no effect +upon the water—it will not make the lime-water turbid; but if I throw the +air _from_ my lungs through the lime-water, several times in succession, +you see how white and milky the water is getting, shewing the effect which +expired air has had upon it; and now you begin to know that the atmosphere +which we have spoiled by respiration is spoiled by carbonic acid, for you +see it here in contact with the lime-water. + +I have here two bottles, one containing lime-water and the other common +water, and tubes which pass into the bottles and connect them. The +apparatus is very rough, but it is useful notwithstanding. + +[Illustration: Fig. 35.] + +If I take these two bottles, inhaling here and exhaling there, the +arrangement of the tubes will prevent the air going backwards. The air +coming in will go to my mouth and lungs, and in going out, will pass +through the lime-water, so that I can go on breathing and making an +experiment, very refined in its nature, and very good in its results. You +will observe that the good air has done nothing to the lime-water; in the +other case nothing has come to the lime-water but my respiration, and you +see the difference in the two cases. + +Let us now go a little further. What is all this process going on within +us which we cannot do without, either day or night, which is so provided +for by the Author of all things that He has arranged that it shall be +independent of all will? If we restrain our respiration, as we can to a +certain extent, we should destroy ourselves. When we are asleep, the +organs of respiration, and the parts that are associated with them, still +go on with their action—so necessary is this process of respiration to +us, this contact of the air with the lungs. I must tell you, in the +briefest possible manner, what this process is. We consume food: the food +goes through that strange set of vessels and organs within us, and is +brought into various parts of the system, into the digestive parts +especially; and alternately the portion which is so changed is carried +through our lungs by one set of vessels, while the air that we inhale and +exhale is drawn into and thrown out of the lungs by another set of +vessels, so that the air and the food come close together, separated only +by an exceedingly thin surface: the air can thus act upon the blood by +this process, producing precisely the same results in kind as we have seen +in the case of the candle. The candle combines with parts of the air, +forming carbonic acid, and evolves heat; so in the lungs there is this +curious, wonderful change taking place. The air entering, combines with +the carbon (not carbon in a free state, but, as in this case, placed ready +for action at the moment), and makes carbonic acid, and is so thrown out +into the atmosphere, and thus this singular result takes place: we may +thus look upon the food as fuel. Let me take that piece of sugar, which +will serve my purpose. It is a compound of carbon, hydrogen, and oxygen, +similar to a candle, as containing the same elements, though not in the +same proportion—the proportions being as shewn in this table:— + +SUGAR. + + Carbon, . . . . 72 + _ + Hydrogen, . . . 11 | + | 99 + Oxygen, . . . . 88_| + +This is, indeed, a very curious thing, which you can well remember, for +the oxygen and hydrogen are in exactly the proportions which form water, +so that sugar may be said to be compounded of 72 parts of carbon and 99 +parts of water; and it is the carbon in the sugar that combines with the +oxygen carried in by the air in the process of respiration—so making us +like candles—producing these actions, warmth, and far more wonderful +results besides, for the sustenance of the system, by a most beautiful and +simple process. To make this still more striking, I will take a little +sugar; or, to hasten the experiment, I will use some syrup, which contains +about three-fourths of sugar and a little water. If I put a little oil of +vitriol on it, it takes away the water, and leaves the carbon in a black +mass. [The Lecturer mixed the two together.] You see how the carbon is +coming out, and before long we shall have a solid mass of charcoal, all of +which has come out of sugar. Sugar, as you know, is food, and here we have +absolutely a solid lump of carbon where you would not have expected it. +And if I make arrangements so as to oxidize the carbon of sugar, we shall +have a much more striking result Here is sugar, and I have here an +oxidizer—a quicker one than the atmosphere; and so we shall oxidize this +fuel by a process different from respiration in its form, though not +different in its kind. It is the combustion of the carbon by the contact +of oxygen which the body has supplied to it. If I set this into action at +once, you will see combustion produced. Just what occurs in my +lungs—taking in oxygen from another source, namely, the atmosphere—takes +place here by a more rapid process. + +You will be astonished when I tell you what this curious play of carbon +amounts to. A candle will burn some four, five, six, or seven hours. What, +then, must be the daily amount of carbon going up into the air in the way +of carbonic acid! What a quantity of carbon must go from each of us in +respiration! What a wonderful change of carbon must take place under these +circumstances of combustion or respiration! A man in twenty-four hours +converts as much as seven ounces of carbon into carbonic acid; a milch cow +will convert seventy ounces, and a horse seventy-nine ounces, solely by +the act of respiration. That is, the horse in twenty-four hours burns +seventy-nine ounces of charcoal, or carbon, in his organs of respiration, +to supply his natural warmth in that time. All the warm-blooded animals +get their warmth in this way, by the conversion of carbon, not in a free +state, but in a state of combination. And what an extraordinary notion +this gives us of the alterations going on in our atmosphere. As much as +5,000,000 pounds, or 548 tons, of carbonic acid is formed by respiration +in London alone in twenty-four hours. And where does all this go? Up into +the air. If the carbon had been like the lead which I shewed you, or the +iron which, in burning, produces a solid substance, what would happen? +Combustion could not go on. As charcoal burns, it becomes a vapour and +passes off into the atmosphere, which is the great vehicle, the great +carrier for conveying it away to other places. Then, what becomes of it? +Wonderful is it to find that the change produced by respiration, which +seems so injurious to us (for we cannot breathe air twice over), is the +very life and support of plants and vegetables that grow upon the surface +of the earth. It is the same also under the surface, in the great bodies +of water; for fishes and other animals respire upon the same principle, +though not exactly by contact with the open air. + +Such fish as I have here [pointing to a globe of gold-fish] respire by the +oxygen which is dissolved from the air by the water, and form carbonic +acid; and they all move about to produce the one great work of making the +animal and vegetable kingdoms subservient to each other. And all the +plants growing upon the surface of the earth, like that which I have +brought here to serve as an illustration, absorb carbon. These leaves are +taking up their carbon from the atmosphere, to which we have given it in +the form of carbonic acid, and they are growing and prospering. Give them +a pure air like ours, and they could not live in it; give them carbon with +other matters, and they live and rejoice. This piece of wood gets all its +carbon, as the trees and plants get theirs, from the atmosphere, which, as +we have seen, carries away what is bad for us and at the same time good +for them,—what is disease to the one being health to the other. So are we +made dependent, not merely upon our fellow-creatures, but upon our +fellow-existers, all Nature being tied together by the laws that make one +part conduce to the good of another. + +There is another little point which I must mention before we draw to a +close—a point which concerns the whole of these operations, and most +curious and beautiful it is to see it clustering upon and associated with +the bodies that concern us—oxygen, hydrogen, and carbon, in different +states of their existence. I shewed you just now some powdered lead, which +I set burning[18]; and you saw that the moment the fuel was brought to the +air, it acted, even before it got out of the bottle—the moment the air +crept in, it acted. Now, there is a case of chemical affinity by which all +our operations proceed. When we breathe, the same operation is going on +within us. When we burn a candle, the attraction of the different parts +one to the other is going on. Here it is going on in this case of the +lead; and it is a beautiful instance of chemical affinity. If the products +of combustion rose off from the surface, the lead would take fire, and go +on burning to the end; but you remember that we have this difference +between charcoal and lead—that, while the lead can start into action at +once, if there be access of air to it, the carbon will remain days, weeks, +months, or years. The manuscripts of Herculaneum were written with +carbonaceous ink, and there they have been for 1,800 years or more, not +having been at all changed by the atmosphere, though coming in contact +with it under various circumstances. Now, what is the circumstance which +makes the lead and carbon differ in this respect? It is a striking thing +to see that the matter which is appointed to serve the purpose of fuel +_waits_ in its action: it does not start off burning, like the lead and +many other things that I could shew you; but which I have not encumbered +the table with; but it waits for action. This waiting is a curious and +wonderful thing. Candles—those Japanese candles, for instance—do not +start into action at once, like the lead or iron (for iron finely divided +does the same thing as lead), but there they wait for years, perhaps for +ages, without undergoing any alteration. I have here a supply of coal-gas. +The jet is giving forth the gas, but you see it does not take fire—it +comes out into the air, but it waits till it is hot enough before it +burns. If I make it hot enough, it takes fire. If I blow it out, the gas +that is issuing forth waits till the light is applied to it again. It is +curious to see how different substances wait—how some will wait till the +temperature is raised a little, and others till it is raised a good deal. +I have here a little gunpowder and some gun-cotton; even these things +differ in the conditions under which they will burn. The gunpowder is +composed of carbon and other substances, making it highly combustible; and +the gun-cotton is another combustible preparation. They are both waiting, +but they will start into activity at different degrees of heat, or under +different conditions. By applying a heated wire to them, we shall see +which will start first [touching the gun-cotton with the hot iron]. You +see the gun-cotton has gone off, but not even the hottest part of the wire +is now hot enough to fire the gunpowder. How beautifully that shews you +the difference in the degree in which bodies act in this way! In the one +case the substance will wait any time until the associated bodies are made +active by heat; but in the other, as in the process of respiration, it +waits no time. In the lungs, as soon as the air enters, it unites with the +carbon; even in the lowest temperature which the body can bear short of +being frozen, the action begins at once, producing the carbonic acid of +respiration: and so all things go on fitly and properly. Thus you see the +analogy between respiration and combustion is rendered still more +beautiful and striking. Indeed, all I can say to you at the end of these +lectures (for we must come to an end at one time or other) is to express a +wish that you may, in your generation, be fit to compare to a candle; that +you may, like it, shine as lights to those about you; that, in all your +actions, you may justify the beauty of the taper by making your deeds +honourable and effectual in the discharge of your duty to your fellow-men. + + + + +LECTURE ON PLATINUM. + +[_Delivered before the_ ROYAL INSTITUTION, _on Friday, February 22, +1861._] + + +Whether I was to have the honour of appearing before you this evening or +not, seemed to be doubtful upon one or two points. One of these I will +mention immediately; the other may or may not appear during the course of +the hour that follows. The first point is this. When I was tempted to +promise this subject for your attention this evening, it was founded upon +a promise, and a full intent of performing that promise, on the part of my +friend Deville, of Paris, to come here to shew before you a phenomenon in +metallurgic chemistry not common. In that I have been disappointed. His +intention was to have fused here some thirty or forty pounds of platinum, +and so to have made manifest, through my mouth and my statement, the +principles of a new process in metallurgy, in relation to this beautiful, +magnificent, and valuable metal; but circumstances over which neither he +nor I, nor others concerned, have sufficient control, have prevented the +fulfilment of that intention; and the period at which I learned the fact +was so recent, that I could hardly leave my place here to be filled by +another, or permit you, who in your kindness have come to hear what might +be said, to remain unreceived in the best manner possible to me under the +circumstances. I therefore propose to state, as well as I can, what the +principles are on which M. Deville proceeds, by means of drawings, and +some subordinate or inferior experiments. The metal platinum, of which you +see some very fine specimens on the table, has been known to us about a +hundred years. It has been wrought in a beautiful way in this country, in +France, and elsewhere, and supplied to the consumer in ingots of this +kind, or in plates, such as we have here, or in masses, that by their very +fall upon the table indicate the great weight of the substance, which is, +indeed, nearly at the head of all substances in that respect. This +substance has been given to us hitherto mainly through the philosophy of +Dr. Wollaston, whom many of us know, and it is obtained in great purity +and beauty. It is a very remarkable metal in many points, besides its +known special uses. It usually comes to us in grains. Here is a very fine +specimen of native platinum in grains. Here is also a nugget or ingot, and +here are some small pieces gathered out of certain alluvial soils in +Brazil, Mexico, California, and the Uralian districts of Russia. + +It is strange that this metal is almost always found associated with some +four or five other metals, most curious in their qualities and +characteristics. They are called platiniferous metals; and they have not +only the relation of being always found associated in this manner, but +they have other relations of a curious nature, which I shall point out to +you by a reference to one of the tables behind me. This substance is +always native—it is always in the metallic state; and the metals with +which it is found connected, and which are rarely found elsewhere, are +palladium, rhodium, iridium, osmium, and ruthenium. We have the names in +one of the tables arranged in two columns, representing, as you see, two +groups—platinum, iridium, and osmium constituting one group; and +ruthenium, rhodium, and palladium the other. Three of these have the +chemical equivalent of 98½, and the others a chemical equivalent of +about half that number. Then the metals of one group have an extreme +specific gravity—platinum being, in fact, the lightest of the three, or +as light as the lightest. Osmium has a specific gravity of 21.4, and is +the heaviest body in nature; platinum is 21.15, and iridium the same; the +specific gravity of the other three being only about half that, namely, +11.3, 12.1, and 11.8. Then there is this curious relation, that palladium +and iridium are very much alike, so that you would scarcely know one from +the other, though one has only half the weight of the other, and only half +the equivalent power. So with iridium and rhodium, and osmium and +ruthenium, which are so closely allied that they make pairs, being +separated each from its own group. Then these metals are the most +infusible that we possess. Osmium is the most difficult to fuse: indeed, I +believe it never has been fused, while every other metal has. Ruthenium +comes next, iridium next, rhodium next, platinum next (so that it ranks +here as a pretty fusible metal, and yet we have been long accustomed to +speak of the infusibility of platinum), and next comes palladium, which is +the most fusible metal of the whole. It is a curious thing to see this +fine association of physical properties coming out in metals which are +grouped together somehow or other in nature, but, no doubt, by causes +which are related to analogous properties in their situation on the +surface of the earth, for it is in alluvial soils that these things are +found. + +Now, with regard to this substance, let me tell you briefly how we get it. +The process used to be this. The ore which I shewed you just now was +taken, and digested in nitro-muriatic acid of a certain strength, and +partly converted into a solution, with the leaving behind of certain +bodies that I have upon the table. The platinum being dissolved with care +in acids, to the solution the muriate of ammonia was added, as I am about +to add it here. A yellow precipitate was then thrown down, as you perceive +is the case now; and this, carefully washed and cleansed, gave us that +body [pointing to a specimen of the chloride of platinum and ammonium], +the other elements, or nearly all, being ejected. This substance being +heated, gave us what we call platinum sponge, or platinum in the metallic +state, so finely divided as to form a kind of heavy mass or sponge, which, +at the time that Dr. Wollaston first sent it forth, was not fusible for +the market or in the manufacturers’ workshops, inasmuch as the temperature +required was so high, and there were no furnaces that could bring the mass +into a globule, and cause the parts to adhere together. Most of our metals +that we obtain from nature, and work in our shops, are brought at last +into a mass by fusion. I am not aware that there is in the arts or +sciences any other than iron which is not so. Soft iron we do not bring +together by fusion, but by a process which is analogous to the one that +was followed in the case of platinum, namely, welding; for these divided +grains of spongy platinum having been well washed and sunk in water for +the purpose of excluding air, and pressed together, and heated, and +hammered, and pressed again, until they come into a pretty close, dense, +compact mass, did so cohere, that when the mass was put into the furnace +of charcoal, and raised to a high temperature, the particles, at first +infinitely divided—for they were chemically divided—adhered the one to +the other, each to all the rest, until they made that kind of substance +which you see here, which will bear rolling and expansion of every kind. +No other process than that has hitherto been adopted for the purpose of +obtaining this substance from the particles by solution, precipitation, +ignition, and welding. It certainly is a very fine thing to see that we +may so fully depend upon the properties of the various substances we have +to deal with; that we can, by carrying out our processes, obtain a +material like this, allowing of division and extension under a rolling +mill—a material of the finest possible kind, the parts being held +together, not with interstices, not with porosity, but so continuous that +no fluids can pass between them; and, as Dr. Wollaston beautifully shewed, +a globule of platinum fused by the voltaic battery and the oxyhydrogen +blowpipe, when drawn into a wire, was not sounder or stronger than this +wire made by the curious coalescence of the particles by the sticking +power that they had at high temperatures. This is the process adopted by +Messrs. Johnson and Matthey, to whose great kindness I am indebted for +these ingots and for the valuable assistance I have received in the +illustrations. + +The treatment, however, that I have to bring before you is of another +kind; and it is in the hope that we shall be able before long to have such +a thing as the manufacture of platinum of this kind, that I am encouraged +to come before you, and tell you how far Deville has gone in the matter, +and to give you illustrations of the principles on which he proceeds. I +think it is but fair that you should see an experiment shewing you the way +in which we get the adhesion of platinum. Probably you all know of the +welding of iron: you go into the smith’s shop, and you see him put the +handle of a poker on to the stem, and by a little management and the +application of heat he makes them one. You have no doubt seen him put the +iron into the fire and sprinkle a little sand upon it. He does not know +the philosophy he calls into play when he sprinkles a little sand over the +oxide of iron, but he has a fine philosophy there, or practises it, when +he gets his welding. I can shew you here this beautiful circumstance of +the sticking together of the particles up to the fullest possible +intensity of their combination. If you were to go into the workshops of +Mr. Matthey, and see them hammering and welding away, you would see the +value of the experiment I am about to shew you. I have here some +platinum-wire. This is a metal which resists the action of acids, resists +oxidation by heat, and change of any sort; and which, therefore, I may +heat in the atmosphere without any flux. I bend the wire so as to make the +ends cross: these I make hot by means of the blowpipe, and then, by giving +them a tap with a hammer, I shall make them into one piece. Now that the +pieces are united, I shall have great difficulty in pulling them apart, +though they are joined only at the point where the two cylindrical +surfaces came together. And now I have succeeded in pulling the wire +apart, the division is not at the point of welding, but where the force of +the pincers has cut it, so that the junction we have effected is a +complete one. This, then, is the principle of the manufacture and +production of platinum in the old way. + +The treatment which Deville proposes to carry out, and which he has +carried out to a rather large extent in reference to the Russian supply of +platinum, is one altogether by heat, having little or no reference to the +use of acids. That you may know what the problem is, look at this table, +which gives you the composition of such a piece of platinum ore as I +shewed you just now. Wherever it comes from, the composition is as +complicated, though the proportions vary:— + +Platinum, . . . . . 76.4 +Iridium,. . . . . . 4.3 +Rhodium,. . . . . . 0.3 +Palladium,. . . . . 1.4 +Gold, . . . . . . . 0.4 +Copper, . . . . . . 4.1 +Iron, . . . . . . . 11.7 +Osmide of Iridium,. 0.5 +Sand, . . . . . . . 1.4 + ————— + 100.5 + +This refers to the Uralian ore. In that state of combination, as shewn in +the table, the iridium and osmium are found combined in crystals, +sometimes to the amount of 0.5 per cent., and sometimes 3 or 4 per cent. +Now, this Deville proposes to deal with in the dry way, in the place of +dealing with it by any acid. + +I have here another kind of platinum; and I shew it to you for this +reason. The Russian Government, having large stores of platinum in their +dominions, have obtained it in a metallic state, and worked it into coin. +The coin I have in my hand is a twelve silver rouble piece. The rouble is +worth three shillings, and this coin is, therefore, of the value of +thirty-six shillings. The smaller coin is worth half that sum; and the +other, half of that. The metal, however, is unfit for coinage. When you +have the two metals, gold and silver, used for coinage, you have a little +confusion in the value of the two in the market; but when you have three +precious metals (for you may call platinum a precious metal) worked into +coin, they will be sure to run counter to one another. Indeed, the case +did happen, that the price of platinum coin fixed by the Government was +such, that it was worth while to purchase platinum in other countries, and +make coin of it, and then take it into that country and circulate it. The +result was, that the Russian Government stopped the issue. The composition +of this coin is—platinum, 97.0; iridium, 1.2; rhodium, 0.5; palladium, +0.25; a little copper, and a little iron. It is, in fact, bad platinum: it +scales, and it has an unfitness for commercial use and in the laboratory, +which the other well-purified platinum has not. It wants working over +again. + +Now, Deville’s process depends upon three points,—upon intense heat, +blowpipe action, and the volatility of certain metals. We know that there +are plenty of metals that are volatile; but this, I think, is the first +time that it has been proposed to use the volatility of certain +metals—such as gold and palladium—for the purpose of driving them off +and leaving something else behind. He counts largely upon the volatility +of metals which we have not been in the habit of considering volatile, but +which we have rather looked upon as fixed; and I must endeavour to +illustrate these three points by a few experiments. Perhaps I can best +show you what is required in the process of heating platinum by using that +source of heat which we have here, and which seems to be almost +illimitable—namely, the voltaic battery; for it is only in consequence of +the heat that the voltaic battery affects the platinum. By applying the +two extremities of the battery to this piece of platinum-wire, you will +see what result we shall obtain. You perceive that we can take about this +heating agent wherever we like, and deal with it as we please, limiting it +in any way. I am obliged to deal carefully with it; but even that +circumstance will have an interest for you in watching the experiment. +Contact is now made. The electric current, when compressed into thin +conducting-wires offering resistance, evolves heat to a large extent; and +this is the power by which we work. You see the intense glow immediately +imparted to the wire; and if I applied the heat continuously, the effect +of the current would be to melt the wire. As soon as the contact is +broken, the wire resumes its former appearance; and now that we make +contact again, you perceive the glow as before. [The experiment was +repeated several times in rapid succession.] You can see a line of light, +though you can scarcely perceive the wire; and now that it has melted with +the great heat, if you examine it, you will perceive that it is indeed a +set of irregularities from end to end—a set of little spheres, which are +strung upon an axis of platinum running through it. It is that wire which +Mr. Grove described as being produced at the moment when fusion of the +whole mass is commencing. In the same manner, if I take a tolerably thick +piece of platinum, and subject it to the heat that can be produced by this +battery, you will see the brilliancy of the effect produced. I shall put +on a pair of spectacles for the experiment, as there is an injurious +effect of the voltaic spark upon the eyes, if the action is continued; and +it is neither policy nor bravery to subject any organ to unnecessary +danger; and I want, at all events, to keep the full use of my eyes to the +end of the lecture. + +You now see the action of the heat upon the piece of platinum—heat so +great as to break in pieces the plate on which the drops of metal fall. +You perceive, then, that we have sufficiently powerful sources of heat in +nature to deal with platinum. I have here an apparatus by which the same +thing can be shewn. Here is a piece of platinum, which is put into a +crucible of carbon made at the end of one pole of the battery, and you +will see the brilliant light that will be produced. There is our furnace, +and the platinum is rapidly getting heated; and now you perceive that it +is melted, and throwing off little particles. What a magnificent +philosophical instrument this is. When you look at the result, which is +lying upon the charcoal, you will see a beautifully fused piece of +platinum. It is now a fiery globule, with a surface so bright, and smooth, +and reflecting, that I cannot tell whether it is transparent, or opaque, +or what. This, then, will give you an idea of what has to be done by any +process that pretends to deal with thirty, or forty, or fifty pounds of +platinum at once. + +Let me now tell you briefly what Deville proposes to do. First of all, he +takes this ore, with its impurities, and mixes it (as he finds it +essential and best) with its own weight of sulphuret of lead—lead +combined with sulphur. Both the lead and the sulphur are wanted; for the +iron that is there present, as you see by the table, is one of the most +annoying substances in the treatment that you can imagine, because it is +not volatile; and while the iron remains adhering to the platinum, the +platinum will not flow readily. It cannot be sent away by a high +temperature—sent into the atmosphere so as to leave the platinum behind. +Well, then, a hundred parts of ore and a hundred parts of sulphuret of +lead, with about fifty parts of metallic lead, being all mingled together +in a crucible, the sulphur of the sulphuret takes the iron, the copper, +and some of the other metals and impurities, and combines with them to +form a slag; and as it goes on boiling and oxidising, it carries off the +iron, and so a great cleansing takes place. + +Now, you ought to know that these metals, such as platinum, iridium, and +palladium, have a strong affinity for such metals as lead and tin, and +upon this a great deal depends. Very much depends upon the platinum +throwing out its impurities of iron and so forth, by being taken up with +the lead present in it. That you may have a notion of the great power that +platinum has of combining with other metals, I will refer you to a little +of the chemist’s experience—his bad experience. He knows very well that +if he takes a piece of platinum-foil, and heats a piece of lead upon it, +or if he takes a piece of platinum-foil, such as we have here, and heats +things upon it that have lead in them, his platinum is destroyed. I have +here a piece of platinum, and if I apply the heat of the spirit-lamp to +it, in consequence of the presence of this little piece of lead which I +will place on it, I shall make a hole in the metal. The heat of the lamp +itself would do no harm to the platinum, nor would other chemical means; +but because there is a little lead present, and there is an affinity +between the two substances, the bodies fuse together at once. You see the +hole I have made. It is large enough to put your finger in, though the +platinum itself was, as you saw, almost infusible, except by the voltaic +battery. For the purpose of shewing this fact in a more striking manner, I +have taken pieces of platinum-foil, tinfoil, and lead-foil, and rolled +them together; and if I apply the blowpipe to them, you will have, in +fact, a repetition on a larger scale of the experiment you saw just now +when the lead and platinum came together, and one spoiled the other. When +the metals are laid one upon the other, and folded together and heat +applied, you will not only see that the platinum runs to waste, but that +at the time when the platinum and lead are combined there is ignition +produced—there is a power of sustaining combustion. I have taken a large +piece, that you may see the phenomenon on a large scale. You saw the +ignition and the explosion which followed, of which we have here the +results—the consequence of the chemical affinity between the platinum and +the metals combined with it, which is the thing upon which Deville founds +his first result. + +When he has melted these substances and stirred them well up, and so +obtained a complete mixture, he throws in air upon the surface to burn off +all the sulphur from the remaining sulphuret of lead; and at last he gets +an ingot of lead with platinum—much lead, comparatively, and little +platinum. He gets that in the crucible with a lot of scoriæ and other +things, which he treats afterwards. It is that platiniferous lead which we +have to deal with in our future process. Now, let me tell you what he does +with it. His first object is to get rid of the lead. He has thrown out all +the iron, and a number of other things, and he has got this kind of +compound indicated in the table. He may get it as high as 78 per cent. of +platinum, and 22 of lead; or 5, or 10, or 15 of platinum, and 95, or 90, +or 85 of lead (which he calls weak platinum), and he then places it in the +kind of vessel that you see before you. Suppose we had the mixture here; +we should have to make it hot, and then throw in air upon the surface. The +combustible metal—that is, the lead—and the part that will oxidise, are +thoroughly oxidised; the litharge would flow out in a fused state into a +vessel placed to receive it, and the platinum remains behind. + +[Illustration: Fig. 36.] + +Here is the process which Deville adopts for the purpose of casting off +the lead, after he has got out the platinum from the ore. (Having made use +of your friend, you get rid of him as quickly as you can.) He gets his +heat by applying the combination of oxygen and hydrogen, or of carburetted +fuel, for the purpose of producing a fire. I have here a source of +coal-gas; there I have a source of hydrogen; and here I have a source of +oxygen. I have here also one of the blowpipes used by Deville in his +process for working platinum in the way I have spoken of. There are two +pipes, and one of them goes to the source of coal-gas, and the other to +the supply of oxygen. + +[Illustration: Fig. 37.] + +By uniting these we obtain a flame of such a heat as to melt platinum. You +will, perhaps, hardly imagine what the heat is, unless you have some proof +of it; but you will soon see that I have actually the power of melting +platinum. Here is a piece of platinum-foil running like wax under the +flame which I am bringing to bear against it. The question, however, is +whether we shall get heat enough to melt, not this small quantity, but +large masses—many pounds of the metal. Having obtained heat like this, +the next consideration is what vessel is he to employ which could retain +the platinum when so heated, or bear the effects of the flame? Such +vessels are happily well supplied at Paris, and are formed of a substance +which surrounds Paris; it is a kind of chalk (called, I believe, by +geologists, _calcaire grossière_), and it has the property of enduring an +extreme degree of heat. I am now going to get the highest heat that we can +obtain. First, I shew you the combustion of hydrogen by itself. I have not +a large supply, because the coal-gas is sufficient for most of our +purposes. If I put a piece of lime obtained from this chalk into the gas, +you see we get a pretty hot flame, which would burn one’s fingers a good +deal But now let me subject a piece of it to the joint action of oxygen +and hydrogen. I do this for the purpose of shewing you the value of lime +as a material for the furnaces and chambers that are to contain the +substances to be operated on, and that are consequently to sustain the +action of this extreme heat. Here we have the hydrogen and the oxygen, +which will give the most intense heat that can be obtained by chemical +action; and if I put a piece of lime into the flame, we get what is called +the lime-light. Now, with all the beauty and intensity of action which you +perceive, there is no sensible deterioration of the lime except by the +mechanical force of the current of gases rushing from the jet against the +lime, sweeping away such particles as are not strongly aggregated. “Vapour +of lime” some call it; and it may be so, but there is no other change of +the lime than that under the action of heat of this highly-exalted +chemical condition, though almost any other substance would melt at once. + +Then, as to the way in which the heat is applied to the substance. It is +all very well for me to take a piece of antimony, and fuse it in the flame +of a blowpipe. But if I tried this piece in the ordinary lamp flame, I +should do nothing; if I tried a smaller piece, I should do little or +nothing; and if I tried a still smaller piece, I should do little or +nothing; yet I have a condition which will represent what Deville carries +to the highest possible extent, and which we all carry to the highest +extent, in the use of the blowpipe. Suppose I take this piece of antimony: +I shall not be able to melt it in that flame of the candle by merely +holding it there; yet, by taking pains, we can even melt a piece of +platinum there. This is a preparation which I made for the purpose of +proving the fusibility of platinum in a common candle. There is a piece of +wire, drawn by that ingenious process of Dr. Wollaston’s, not more than +the three-thousandth part of an inch in diameter. He put the wire into the +middle of a cylinder of silver, and drew both together until the whole +compound was exceedingly thin; and then he dissolved away the silver by +nitric acid. There was left in the centre a substance which I can scarcely +see with an eye-glass, but which I know is there, and which I can make +visible, as you see, by putting it into the candle, where the heat makes +it glow like a spark. I have again and again tried this experiment +up-stairs in my own room, and have easily fused this platinum-wire by a +common candle. You see we have, therefore, heat enough in the candle, as +in the voltaic battery, or in the highly-exalted combustion of the +blowpipe, but we do not supply a continuous source of heat. In the very +act of this becoming ignited, the heat radiates so fast that you cannot +accumulate enough to cause the fusion of the wire, except under the most +careful arrangement. Thus I cannot melt that piece of antimony by simply +putting it into the candle; but if I put it upon charcoal, and drive the +fiery current against it, there will be heat enough to melt it. The beauty +of the blowpipe is, that it sends hot air (making hot air by the +combustion of the flame) against the thing to be heated. I have only to +hold the antimony in the course of that current, and particle by particle +of the current impinges upon the antimony, and so we get it melted. You +now see it red-hot, and I have no doubt it will continue to burn if I +withdraw it from the flame and continue to force the air on it. Now, you +see it burning without any heat but that of its own combustion, which I am +keeping up by sending the air against it. It would go out in a moment if I +took away the current of air from it; but there it is burning, and the +more air I give it, by this or any other action, the better it is. So, +then, we have here not merely a mighty source of heat, but a means of +driving the heat forcibly against substances. + +Let me shew you another experiment with a piece of iron. It will serve two +purposes—shewing you what the blowpipe does as a source of heat, and what +it does by sending that heat where it is wanted. I have taken iron in +contrast with silver or other metals, that you may see the difference of +action, and so be more interested in the experiment. Here is our fuel, the +coal-gas; and here our oxygen. Having thus my power of heat, I apply it to +the iron, which, as you see, soon gets red-hot. It is now flowing about +like a globule of melted mercury. But observe, I cannot raise any vapour: +it is now covered with a coat of melted oxide, and unless I have a great +power in my blowpipe, it is hardly possible to break through it. Now, +then, you see these beautiful sparks: you have not only a beautiful kind +of combustion, but you see the iron is being driven off, not producing +smoke, but burning in a fixed condition. How different this is from the +action of some other metals—that piece of antimony, for instance, which +we saw just now throwing off abundance of fumes. We can, of course, burn +away this iron by giving plenty of air to it; but with the bodies which +Deville wants to expose to this intense heat he has not that means: the +gas itself must have power enough to drive off the slag which forms on the +surface of the metal, and power to impinge upon the platinum so as to get +the full contact that he wants for the fusion to take place. We see here, +then, the means to which he resorts—oxygen, and either coal-gas or +water-gas[19], or pure hydrogen, for producing heat, and the blowpipe for +the purpose of impelling the heated current upon the metals. + +I have two or three rough drawings here, representing the kind of furnaces +which he employs. They are larger, however, than the actual furnaces he +uses. Even the furnace in which he carries on that most serious operation +of fusing fifty pounds of platinum at once is not much more than half the +size of the drawing. It is made of a piece of lime below and a piece of +lime above. You see how beautifully lime sustains heat without altering in +shape; and you may have thought how beautifully it prevents the +dissipation of the heat by its very bad conducting powers. + +[Illustration: Fig. 38] + +While the front part of the lime which you saw here was so highly ignited, +I could at any moment touch the back of it without feeling any annoyance +from the heat So, by having a chamber of lime of this sort, he is able to +get a vessel to contain these metals with scarcely any loss of heat. He +puts the blowpipes through these apertures, and sends down these gases +upon the metals, which are gradually melted. He then puts in more metal +through a hole at the top. The results of the combustion issue out of the +aperture which you see represented. If there be strips of platinum, he +pushes them through the mouth out of which the heated current is coming, +and there they get red-hot and white-hot before they get into the bath of +platinum. So he is able to fuse a large body of platinum in this manner. +When the platinum is melted, he takes off the top and pours out from the +bottom piece, like a crucible, and makes his cast. This is the furnace by +which he fuses his forty pounds or fifty pounds of platinum at once. The +metal is raised to a heat that no eye can bear. There is no light and +shadow, no chiaro-oscuro there; all is the same intensity of glow. You +look in, and you cannot see where the metal or the lime is; it is all as +one. We have, therefore, a platform with a handle, which turns upon an +axis, that coincides with the gutter that is formed for the pouring of the +metal; and when all is known to be ready, by means of dark glasses, the +workmen take off the top piece and lift up the handle, and the mould being +then placed in a proper position, he knows that the issue of the metal +will be exactly in the line of the axis. No injury has ever happened from +the use of this plan. You know with what care it is necessary to carry +such a vessel of mercury as we have here, for fear of turning it over on +one side or the other; but if it be a vessel of melted platinum, the very +greatest care must be used, because the substance is twice as heavy: yet +no injury has been done to any of the workmen in this operation. + +I have said that Deville depends upon intense heat for carrying off +vapour; and this brings me to the point of shewing how vapours are carried +off. Here is a basin of mercury, which boils easily, as you know, and +gives us the opportunity of observing the facts and principles which are +to guide us. I have here two poles of the battery, and if I bring them +into contact with the mercury, see what a development of vapour we have. +The mercury is flying off rapidly; and I might, if I pleased, put all the +company around me in a bath of mercury vapour. And so, if we take this +piece of lead and treat it in the same way, it will also give off vapour. +Observe the fumes that rise from it; and even if it was so far enclosed +from the air that you could not form any litharge, you would still have +those abundant fumes flying off. I may also take a piece of gold, and shew +you the same thing. I have here a piece of gold which I put upon a clean +surface of Paris limestone. Applying the heat of the blowpipe to it, you +see how the heat drives off the vapour; and if you notice at the end of +the Lecture, you will observe on the stone a purple patch of condensed +gold. Thus you see a proof of the volatilisation of gold. It is the same +with silver. You will not be startled if I sometimes use one agent and +sometimes another to illustrate a particular point. The volatility of gold +and silver is the same thing, whether it be effected by the voltaic +battery or by the blowpipe. [A lump of silver was placed in a charcoal +crucible between the poles of a voltaic battery.] Now, look at the fumes +of silver, and observe the peculiar and beautiful green colour which they +produce. We shall now shew you this same process of boiling the silver, +cast on a screen from the electric lamp which you have before you; and +while Dr. Tyndall is kindly getting the lamp ready for this purpose, let +me tell you that Deville proposes to throw out in this way all these +extraneous things that I have spoken of, except two—namely, iridium and +rhodium. It so happens, as he says, that iridium and rhodium do make the +metal more capable of resisting the attacks of acids than platinum itself. +Alloys are compounded up to 25 per cent. of rhodium and iridium, by which +the chemical inaction of the platinum is increased, and also its +malleability and other physical properties. [The image of the voltaic +discharge through vapour of silver was now thrown upon the screen.] What +you have now on the screen is an inverted image of what you saw when we +heated the silver before. The fine stream that you see around the silver +is the discharge of the electric force that takes place, giving you that +glorious green light which you see in the ray; and if Dr. Tyndall will +open the top of the lamp, you will see the quantity of fumes that will +come out of the aperture, shewing you at once the volatility of silver. + +I have now finished this imperfect account. It is but an apology for not +having brought the process itself before you. I have done the best I could +under the circumstances; and I know your kindness well, for if I were not +aware that I might trust to it, I would not appear here so often as I have +done. The gradual loss of memory and of my other faculties is making +itself painfully evident to me, and requires, every time I appear before +you, the continued remembrance of your kindness to enable me to get +through my task. If I should happen to go on too long, or should fail in +doing what you might desire, remember it is yourselves who are chargeable, +by wishing me to remain. I have desired to retire, as I think every man +ought to do before his faculties become impaired; but I must confess that +the affection I have for this place, and for those who frequent this +place, is such, that I hardly know when the proper time has arrived. + + + + +NOTES. + + +[Footnote 1: Page 16. The Royal George sunk at Spithead on The 29th of +August, 1782. Colonel Pasley commenced operations for the removal of the +wreck by the explosion of gunpowder, in August, 1839. The candle which +Professor Faraday exhibited must therefore have been exposed to the action +of salt water for upwards of fifty-seven years.] + +[Footnote 2: Page 17. The fat or tallow consists of a chemical combination +of fatty acids with glycerine. The lime unites with the palmitic, oleic, +and stearic acids, and separates the glycerine. After washing, the +insoluble lime soap is decomposed with hot dilute sulphuric acid. The +melted fatty acids thus rise as an oil to the surface, when they are +decanted. They are again washed and cast into thin plates, which, when +cold, are placed between layers of cocoa-nut matting, and submitted to +intense hydraulic pressure. In this way the soft oleic acid is squeezed +out, whilst the hard palmitic and stearic acids remain. These are further +purified by pressure at a higher temperature, and washing in warm dilute +sulphuric acid, when they are ready to be made into candles. These acids +are harder and whiter than the fats from which they were obtained, whilst +at the same time they are cleaner and more combustible.] + +[Footnote 3: Page 19. A little borax or phosphorus salt is sometimes +added, in order to make the ash fusible.] + +[Footnote 4: Page 27. Capillary attraction or repulsion is the cause which +determines the ascent or descent of a fluid in a capillary tube. If a +piece of thermometer tubing, open at each end, be plunged into water, the +latter will instantly rise in the tube considerably above its external +level. If, on the other hand, the tube be plunged into mercury, a +repulsion instead of attraction will be exhibited, and the level of the +mercury will be lower in the tube than it is outside.] + +[Footnote 5: Page 29. The late Duke of Sussex was, we believe, the first +to shew that a prawn might be washed upon this principle. If the tail, +after pulling off the fan part, be placed in a tumbler of water, and the +head be allowed to hang over the outside, the water will be sucked up the +tail by capillary attraction, and will continue to run out through the +head until the water in the glass has sunk so low that the tail ceases to +dip into it.] + +[Footnote 6: Page 37. The alcohol had chloride of copper dissolved in it: +this produces a beautiful green flame.] + +[Footnote 7: Page 54. Lycopodium is a yellowish powder found in the fruit +of the club moss (_Lycopodium clavatum_). It is used in fireworks.] + +[Footnote 8: Page 58. Bunsen has calculated that the temperature of the +oxyhydrogen blowpipe is 8061° Centigrade. Hydrogen burning in air has a +temperature of 3259° C., and coal-gas in air, 2350° C.] + +[Footnote 9: Page 60. The following is the action of the sulphuric acid in +inflaming the mixture of sulphuret of antimony and chlorate of potassa. A +portion of the latter is decomposed by the sulphuric acid into oxide of +chlorine, bisulphate of potassa, and perchlorate of potassa. The oxide of +chlorine inflames the sulphuret of antimony, which is a combustible body, +and the whole mass instantly bursts into flame.] + +[Footnote 10: Page 63. The “air-burner,” which is of such value in the +laboratory, owes its advantage to this principle. It consists of a +cylindrical metal chimney, covered at the top with a piece of rather +coarse iron-wire gauze. This is supported over an argand burner, in such a +manner that the gas may mix in the chimney with an amount of air +sufficient to burn the carbon and hydrogen simultaneously, so that there +may be no separation of carbon in the flame with consequent deposition of +soot. The flame, being unable to pass through the wire gauze, burns in a +steady, nearly invisible manner above.] + +[Footnote 11: Page 74. Water is in its densest state at a temperature of +39.1° Fahrenheit] + +[Footnote 12: Page 74. A mixture of salt and pounded ice reduces the +temperature from 32° F. to zero—the ice at the same time becoming fluid.] + +[Footnote 13: Page 82. Potassium, the metallic basis of potash, was +discovered by Sir Humphrey Davy in 1807, who succeeded in separating it +from potash by means of a powerful voltaic battery. Its great affinity for +oxygen causes it to decompose water with evolution of hydrogen, which +takes fire with the heat produced.] + +[Footnote 14: Page 98. Professor Faraday has calculated that there is as +much electricity required to decompose one grain of water as there is in a +very powerful flash of lightning.] + +[Footnote 15: Page 101. A solution of acetate of lead submitted to the +action of the voltaic current, yields lead at the negative pole, and brown +peroxide of lead at the positive pole. A solution of nitrate of silver, +under the same circumstances, yields silver at the negative pole, and +peroxide of silver at the positive pole.] + +[Footnote 16: Page 129. The gas which is thus employed as a test for the +presence of oxygen, is the binoxide of nitrogen, or nitrous oxide. It is a +colourless gas, which, when brought in contact with oxygen, unites with +it, forming hyponitric acid, the red gas referred to.] + +[Footnote 17: Page 152. _Marble_ is a compound of carbonic acid and lime. +The muriatic acid being the stronger of the two, takes the place of the +carbonic acid, which escapes as a gas, the residue forming muriate of lime +or chloride of calcium.] + +[Footnote 18: Page 186. _Lead pyrophorus_ is made by heating dry tartrate +of lead in a glass tube (closed at one end, and drawn out to a fine point +at the other) until no more vapours are evolved. The open end of the tube +is then to be sealed before the blowpipe. When the tube is broken and the +contents shaken out into the air, they burn with a red flash.] + +[Footnote 19: Page 216. _Water-gas_ is formed by passing vapour of water +over red-hot charcoal or coke. It is a mixture of hydrogen and carbonic +oxide; each of which is an inflammable gas.] + + + + +Poster’s note: “combustion that makes!” was corrected from a misprint +“combusion that makes!” in the original. + + + + +*** END OF THE PROJECT GUTENBERG EBOOK THE CHEMICAL HISTORY OF A CANDLE *** + +***** This file should be named 14474-0.txt or 14474-0.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/1/4/4/7/14474/ + +Updated editions will replace the previous one—the old editions will +be renamed. + +Creating the works from print editions not protected by U.S. copyright +law means that no one owns a United States copyright in these works, +so the Foundation (and you!) can copy and distribute it in the +United States without permission and without paying copyright +royalties. 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Thus, we do not +necessarily keep eBooks in compliance with any particular paper +edition. + +Most people start at our website which has the main PG search +facility: www.gutenberg.org. + +This website includes information about Project Gutenberg™, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. diff --git a/old/14474-0.zip b/old/14474-0.zip Binary files differnew file mode 100644 index 0000000..55886f9 --- /dev/null +++ b/old/14474-0.zip diff --git a/old/old/14474-8_2005-10-01.txt b/old/old/14474-8_2005-10-01.txt new file mode 100644 index 0000000..170482a --- /dev/null +++ b/old/old/14474-8_2005-10-01.txt @@ -0,0 +1,3952 @@ +Project Gutenberg's The Chemical History Of A Candle, by Michael Faraday + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Chemical History Of A Candle + +Author: Michael Faraday + +Release Date: December 26, 2004 [EBook #14474] +[Date last updated: October 1, 2005] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE CHEMICAL HISTORY OF A CANDLE *** + + + + +Produced by Clare Boothby, Richard Prairie and the PG Online +Distributed Proofreading Team + + + + + + + THE 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. + + EDITED BY + + WILLIAM CROOKES, F.C.S. + + A NEW IMPRESSION, WITH ILLUSTRATIONS + + LONDON + + CHATTO & WINDUS + + 1908 + + + + +PREFACE + +From the primitive pine-torch to the paraffin candle, how wide an +interval! between them how vast a contrast! The means adopted by man to +illuminate his home at night, stamp at once his position in the scale of +civilisation. The 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. All, 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. + +Surely, 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. Think +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. + +Atom by atom, link by link, has the reasoning chain been forged. Some +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. + +The 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. + +Among the readers of this book some few may devote themselves to +increasing the stores of knowledge: the Lamp of Science _must_ burn. +"_Alere flammam._" + +W. CROOKES. + + + + +CONTENTS. + + +LECTURE I. + +A CANDLE: THE FLAME--ITS SOURCES--STRUCTURE--MOBILITY--BRIGHTNESS + + +LECTURE II. + +BRIGHTNESS OF THE FLAME--AIR NECESSARY FOR COMBUSTION--PRODUCTION OF WATER + + +LECTURE III. + +PRODUCTS: WATER FROM THE COMBUSTION--NATURE OF WATER--A COMPOUND--HYDROGEN + + +LECTURE IV. + +HYDROGEN IN THE CANDLE--BURNS INTO WATER--THE OTHER PART OF WATER--OXYGEN + + +LECTURE V. + +OXYGEN PRESENT IN THE AIR--NATURE OF THE ATMOSPHERE--ITS PROPERTIES--OTHER +PRODUCTS FROM THE CANDLE--CARBONIC ACID--ITS PROPERTIES + + +LECTURE VI. + +CARBON OR CHARCOAL--COAL GAS--RESPIRATION AND ITS ANALOGY TO THE BURNING +OP A CANDLE--CONCLUSION + + +LECTURE ON PLATINUM. + + +NOTES. + + + + +THE CHEMICAL HISTORY OF A CANDLE + +LECTURE I. + +A CANDLE: THE FLAME--ITS SOURCES--STRUCTURE--MOBILITY--BRIGHTNESS. + + +I 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. I 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. There 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. There 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. I +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. + +And 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. I claim the privilege of speaking to juveniles as a juvenile +myself. I have done so on former occasions--and, if you please, I shall do +so again. And 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. + +And now, my boys and girls, I must first tell you of what candles are +made. Some are great curiosities. I have here some bits of timber, +branches of trees particularly famous for their burning. And 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. And in this +wood we have one of the most beautiful illustrations of the general nature +of a candle that I can possibly give. The 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. + +But we must speak of candles as they are in commerce. Here are a couple of +candles commonly called dips. They 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. +In 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. They are, or were, the candles used by the miners in coal +mines. In 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. They have been replaced since then by the steel-mill, and then by +the Davy-lamp, and other safety-lamps of various kinds. I have here a +candle that was taken out of the _Royal George_[1], it is said, by Colonel +Pasley. It has been sunk in the sea for many years, subject to the action +of salt water. It 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. + +Mr. Field, of Lambeth, has supplied me abundantly with beautiful +illustrations of the candle and its materials. I shall therefore now refer +to them. And, 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. A 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. This 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. +Glycerin--absolutely a sugar, or a substance similar to sugar--comes out +of the tallow in this chemical change. The 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. The candle I have in my hand is a +stearin candle, made of stearin from tallow in the way I have told you. +Then here is a sperm candle, which comes from the purified oil of the +spermaceti whale. Here also are yellow bees-wax and refined bees-wax, from +which candles are made. Here, too, is that curious substance called +paraffin, and some paraffin candles made of paraffin obtained from the +bogs of Ireland. I 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. + +And how are these candles made? I have told you about dips, and I will +shew you how moulds are made. Let us imagine any of these candles to be +made of materials which can be cast. "Cast!" you say. "Why, a candle is a +thing that melts; and surely if you can melt it, you can cast it." Not so. +It 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. Candles cannot always be cast. A +wax candle can never be cast. It is made by a particular process, which I +can illustrate in a minute or two: but I must not spend much time on it. +Wax is a thing which, burning so well, and melting so easily in a candle, +cannot be cast. However, let us take a material that can be cast. Here is +a frame, with a number of moulds fastened in it. The first thing to be +done is to put a wick through them. Here is one--a plaited wick, which +does not require snuffing[3]--supported by a little wire. It 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. At the +upper part there is a little bar placed across, which stretches the cotton +and holds it in the mould. The tallow is then melted, and the moulds are +filled. After 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. The 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. In the same way are made +these candles of stearin and of paraffin. It is a curious thing to see how +wax candles are made. A 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. These are carried to a heater, where +the wax is melted. As 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. When 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. When they have been thus clothed, or +fed, or made up to that thickness, they are taken off, and placed +elsewhere. I have here, by the kindness of Mr. Field, several specimens of +these candles. Here is one only half-finished. They 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. This 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. + +We must not, however, take up more time about the mere manufacture, but go +a little further into the matter. I have not yet referred you to luxuries +in candles (for there is such a thing as luxury in candles). See how +beautifully these are coloured: you see here mauve, magenta, and all the +chemical colours recently introduced, applied to candles. You observe, +also, different forms employed. Here is a fluted pillar most beautifully +shaped; and I have also here some candles sent me by Mr. Pearsall, 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. All, however, +that is fine and beautiful is not useful. These fluted candles, pretty as +they are, are bad candles; they are bad because of their external shape. +Nevertheless, 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. + +Now, as to the light of the candle. We will light one or two, and set them +at work in the performance of their proper functions. You observe a candle +is a very different thing from a lamp. With 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. When the flame runs +down the cotton to the oil, it gets extinguished, but it goes on burning +in the part above. Now, 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? We shall presently examine that; but there is a much +more wonderful thing about the burning of a candle than this. You 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? How is it +that this solid gets there, it not being a fluid? or, when it is made a +fluid, then how is it that it keeps together? This is a wonderful thing +about a candle. + +We 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? Here 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. +I have very often admired it. They 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. By 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. + +You see, then, in the first instance, that a beautiful cup is formed. As +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. If 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. You 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. No 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. You 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. I hope you will now +see that the perfection of a process--that is, its utility--is the better +point of beauty about it. It is not the best looking thing, but the best +acting thing, which is the most advantageous to us. This good-looking +candle is a bad burning one. There 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. You 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. As 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. Now, 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. We +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? Why does it occur?" and you will in the course of time find +out the reason. + +Then, 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. You know that the flames on +these burning wicks in candles made of beeswax, 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. They are fenced off from the fluid below, and do +not encroach on the cup at the sides. I 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. A 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. + +But how does the flame get hold of the fuel? There is a beautiful point +about that--_capillary attraction_[4]. "Capillary attraction!" you +say,--"the attraction of hairs." Well, never mind the name: it was given +in old times, before we had a good understanding of what the real power +was. It 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. Now, I am going to give you one or two +instances of capillary attraction. It is that kind of action or attraction +which makes two things that do not dissolve in each other still hold +together. When 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. This is by that kind of attraction of which I am about to speak. And, +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. I 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. +We may consider the plate to be the candle, and the salt the wick, and +this solution the melted tallow. (I have coloured the fluid, that you may +see the action better.) You 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. + +[Illustration: Fig. 1.] + +If 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. It 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. When 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. I 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.[5] 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. In fact, wicks are sometimes made of +a kind of wire gauze. You 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. +You 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? The vessel is full +of water, and yet you see the water goes in and runs out as if it were +empty. In order to prove this to you, I have only to empty it. The 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. In 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. + +Here is another application of the same principle. You see this bit of +cane. I 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. They are enabled to do so by the permeability of the cane in +one direction, and by its capillarity. If I place this piece of cane on a +plate containing some camphin (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. There +being no pores at the side, the fluid cannot go in that direction, but +must pass through its length. Already the fluid is at the top of the cane: +now I can light it and make it serve as a candle. The fluid has risen by +the capillary attraction of the piece of cane, just as it does through the +cotton in the candle. + +Now, the only reason why the candle does not burn all down the side of the +wick is, that the melted tallow extinguishes the flame. You know that a +candle, if turned upside down, so as to allow the fuel to run upon the +wick, will be put out. The 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. + +There 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. In order that you may +understand that, let me shew you a very pretty, but very common-place +experiment. If you blow a candle out cleverly, you will see the vapour +rise from it. You 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. I 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. +I 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. + +Now, as to the shape or form of the flame. It 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. + +[Illustration: Fig. 2.] + +You 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. What diamond can shine like flame? It owes +its lustre at night-time to the very flame shining upon it. The 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. The candle +alone shines by itself, and for itself, or for those who have arranged the +materials. Now, let us look a little at the form of the flame as you see +it under the glass shade. It 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. It 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 +part above. + +[Illustration: Fig. 3.] + +I have a drawing here, sketched many years ago by Hooke, when he made his +investigations. It is the drawing of the flame of a lamp, but it will +apply to the flame of a candle. The cup of the candle is the vessel or +lamp, the melted spermaceti is the oil, and the wick is common to both. +Upon that he sets this little flame, and then he represents what is +true--a certain quantity of matter rising about it which you do not see, +and which, if you have not been here before, or are not familiar with the +subject, you will not know of. He has here represented the parts of the +surrounding atmosphere that are very essential to the flame, and that are +always present with it. There is a current formed, which draws the flame +out--for the flame which you see is really drawn out by the current, and +drawn upward to a great height--just as Hooke has here shewn you by that +prolongation of the current in the diagram. You may see this by taking a +lighted candle, and putting it in the sun so as to get its shadow thrown +on a piece of paper. How remarkable it is that that thing which is light +enough to produce shadows of other objects, can be made to throw its own +shadow on a piece of white paper or card, so that you can actually see +streaming round the flame something which is not part of the flame, but is +ascending and drawing the flame upwards. Now, I am going to imitate the +sunlight, by applying the voltaic battery to the electric lamp. You now +see our sun, and its great luminosity; and by placing a candle between it +and the screen, we get the shadow of the flame. + +[Illustration: Fig. 4.] + +You observe the shadow of the candle and of the wick; then there is a +darkish part, as represented in the diagram, and then a part which is more +distinct. Curiously enough, however, what we see in the shadow as the +darkest part of the flame is, in reality, the brightest part; and here you +see streaming upwards the ascending current of hot air, as shewn by +Hooke, which draws out the flame, supplies it with air, and cools the +sides of the cup of melted fuel. + +I can give you here a little further illustration, for the purpose of +shewing you how flame goes up or down; according to the current. I have +here a flame--it is not a candle flame--but you can, no doubt, by this +time, generalise enough to be able to compare one thing with another. What +I am about to do is to change the ascending current that takes the flame +upwards into a descending current. This I can easily do by the little +apparatus you see before me. The flame, as I have said, is not a candle +flame, but it is produced by alcohol, so that it shall not smoke too much. +I will also colour the flame with another substance[6], so that you may +trace its course; for with the spirit alone you could hardly see well +enough to have the opportunity of tracing its direction. By lighting this +spirit-of-wine, we have then a flame produced; and you observe that when +held in the air, it naturally goes upwards. + +[Illustration: Fig. 5] + +You understand now easily enough why flames go up under ordinary +circumstances--it is because of the draught of air by which the combustion +is formed. But now, by blowing the flame down, you see I am enabled to +make it go downwards into this little chimney--the direction of the +current being changed. Before we have concluded this course of lectures, +we shall shew you a lamp in which the flame goes up and the smoke goes +down, or the flame goes down and the smoke goes up. You see, then, that we +have the power in this way of varying the flame in different directions. + +There are now some other points that I must bring before you. Many of the +flames you see here vary very much in their shape by the currents of air +blowing around them in different directions; but we can, if we like, make +flames so that they will look like fixtures, and we can photograph +them--indeed, we have to photograph them--so that they become fixed to us, +if we wish to find out everything concerning them. That, however, is not +the only thing I wish to mention. If I take a flame sufficiently large, it +does not keep that homogeneous, that uniform condition of shape, but it +breaks out with a power of life which is quite wonderful. I am about to +use another kind of fuel, but one which is truly and fairly a +representative of the wax or tallow of a candle. I have here a large ball +of cotton, which will serve as a wick. And, now that I have immersed it in +spirit and applied a light to it, in what way does it differ from an +ordinary candle? Why, it differs very much in one respect, that we have a +vivacity and power about it, a beauty and a life entirely different from +the light presented by a candle. You see those fine tongues of flame +rising up. You have the same general disposition of the mass of the flame +from below upwards; but, in addition to that, you have this remarkable +breaking out into tongues which you do not perceive in the case of a +candle. Now, why is this? I must explain it to you, because when you +understand that perfectly, you will be able to follow me better in what I +have to say hereafter. I suppose some here will have made for themselves +the experiment I am going to shew you. Am I right in supposing that +anybody here has played at snapdragon? I do not know a more beautiful +illustration of the philosophy of flame, as to a certain part of its +history, than the game of snapdragon. First, here is the dish; and let me +say, that when you play snapdragon properly, you ought to have the dish +well-warmed; you ought also to have warm plums and warm brandy, which, +however, I have not got. When you have put the spirit into the dish, you +have the cup and the fuel; and are not the raisins acting like the wicks? +I now throw the plums into the dish, and light the spirit, and you see +those beautiful tongues of flame that I refer to. You have the air +creeping in over the edge of the dish forming these tongues. Why? Because, +through the force of the current and the irregularity of the action of the +flame, it cannot flow in one uniform stream. The air flows in so +irregularly that you have what would otherwise be a single image, broken +up into a variety of forms, and each of these little tongues has an +independent existence of its own. Indeed, I might say, you have here a +multitude of independent candles. You must not imagine, because you see +these tongues all at once, that the flame is of this particular shape. A +flame of that shape is never so at any one time. Never is a body of flame, +like that which you just saw rising from the ball, of the shape it appears +to you. It consists of a multitude of different shapes, succeeding each +other so fast that the eye is only able to take cognisance of them all at +once. In former times, I purposely analysed a flame of that general +character, and the diagram shews you the different parts of which it is +composed. They do not occur all at once: it is only because we see these +shapes in such rapid succession, that they seem to us to exist all at one +time. + +[Illustration: Fig. 6.] + +It is too bad that we have not got further than my game of snapdragon; but +we must not, under any circumstances, keep you beyond your time. It will +be a lesson to me in future to hold you more strictly to the philosophy of +the thing, than to take up your time so much with these illustrations. + + + + +LECTURE II. + +A CANDLE: BRIGHTNESS OF THE FLAME--AIR NECESSARY FOR +COMBUSTION--PRODUCTION OF WATER. + + +We were occupied the last time we met in considering the general character +and arrangement as regards the fluid portion of a candle, and the way in +which that fluid got into the place of combustion. You see, when we have a +candle burning fairly in a regular, steady atmosphere, it will have a +shape something like the one shewn in the diagram, and will look pretty +uniform, although very curious in its character. And now, I have to ask +your attention to the means by which we are enabled to ascertain what +happens in any particular part of the flame--why it happens, what it does +in happening, and where, after all, the whole candle goes to: because, as +you know very well, a candle being brought before us and burned, +disappears, if burned properly, without the least trace of dirt in the +candlestick--and this is a very curious circumstance. In order, then, to +examine this candle carefully, I have arranged certain apparatus, the use +of which you will see as I go on. Here is a candle: I am about to put the +end of this glass tube into the middle of the flame--into that part which +old Hooke has represented in the diagram as being rather dark, and which +you can see at any time, if you will look at a candle carefully, without +blowing it about. We will examine this dark part first. + +[Illustration: Fig. 7.] + +Now, I take this bent glass tube, and introduce one end into that part of +the flame, and you see at once that something is coming from the flame, +out at the other end of the tube; and if I put a flask there, and leave it +for a little while, you will see that something from the middle part of +the flame is gradually drawn out, and goes through the tube and into that +flask, and there behaves very differently from what it does in the open +air. It not only escapes from the end of the tube, but falls down to the +bottom of the flask like a heavy substance, as indeed it is. We find that +this is the wax of the candle made into a vaporous fluid--not a gas. (You +must learn the difference between a gas and a vapour: a gas remains +permanent, a vapour is something that will condense.) If you blow out a +candle, you perceive a very nasty smell, resulting from the condensation +of this vapour. That is very different from what you have outside the +flame; and, in order to make that more clear to you, I am about to produce +and set fire to a larger portion of this vapour--for what we have in the +small way in a candle, to understand thoroughly, we must, as philosophers, +produce in a larger way, if needful, that we may examine the different +parts. And now Mr. Anderson will give me a source of heat, and I am about +to shew you what that vapour is. Here is some wax in a glass flask, and I +am going to make it hot, as the inside of that candle-flame is hot, and +the matter about the wick is hot. [The Lecturer placed some wax in a glass +flask, and heated it over a lamp.] Now, I dare say that is hot enough for +me. You see that the wax I put in it has become fluid, and there is a +little smoke coming from it. We shall very soon have the vapour rising up. +I will make it still hotter, and now we get more of it, so that I can +actually pour the vapour out of the flask into that basin, and set it on +fire there. This, then, is exactly the same kind of vapour as we have in +the middle of the candle; and that you may be sure this is the case, let +us try whether we have not got here, in this flask, a real combustible +vapour out of the middle of the candle. [Taking the flask into which the +tube from the candle proceeded, and introducing a lighted taper.] See how +it burns. Now, this is the vapour from the middle of the candle, produced +by its own heat; and that is one of the first things you have to consider +with respect to the progress of the wax in the course of its combustion, +and as regards the changes it undergoes. I will arrange another tube +carefully in the flame, and I should not wonder if we were able, by a +little care, to get that vapour to pass through the tube to the other +extremity, where we will light it, and obtain absolutely the flame of the +candle at a place distant from it. Now, look at that. Is not that a very +pretty experiment? Talk about laying on gas--why, we can actually lay on a +candle! And you see from this that there are clearly two different kinds +of action--one the _production_ of the vapour, and the other the +_combustion_ of it--both of which take place in particular parts of the +candle. + +[Illustration: Fig. 8] + +I shall get no vapour from that part which is already burnt. If I raise +the tube (fig. 7) to the upper part of the flame, so soon as the vapour +has been swept out, what comes away will be no longer combustible: It is +already burned. How burned? Why, burned thus:--In the middle of the flame, +where the wick is, there is this combustible vapour; on the outside of the +flame is the air which we shall find necessary for the burning of the +candle; between the two, intense chemical action takes place, whereby the +air and the fuel act upon each other, and at the very same time that we +obtain light the vapour inside is destroyed. If you examine where the heat +of a candle is, you will find it very curiously arranged. Suppose I take +this candle, and hold a piece of paper close upon the flame, where is the +heat of that flame? Do you not see that it is _not_ in the inside? It is +in a ring, exactly in the place where I told you the chemical action was; +and even in my irregular mode of making the experiment, if there is not +too much disturbance, there will always be a ring. This is a good +experiment for you to make at home. Take a strip of paper, have the air in +the room quiet, and put the piece of paper right across the middle of the +flame (I must not talk while I make the experiment), and you will find +that it is burnt in two places, and that it is not burnt, or very little +so, in the middle; and when you have tried the experiment once or twice, +so as to make it nicely, you will be very interested to see where the heat +is, and to find that it is where the air and the fuel come together. + +This is most important for us as we proceed with our subject. Air is +absolutely necessary for combustion; and, what is more, I must have you +understand that _fresh_ air is necessary, or else we should be imperfect +in our reasoning and our experiments. Here is a jar of air. I place it +over a candle, and it burns very nicely in it at first, shewing that what +I have said about it is true; but there will soon be a change. See how the +flame is drawing upwards, presently fading, and at last going out. And +going out, why? Not because it wants air merely, for the jar is as full +now as it was before; but it wants pure, fresh air. The jar is full of +air, partly changed, partly not changed; but it does not contain +sufficient of the fresh air which is necessary for the combustion of a +candle. These are all points which we, as young chemists, have to gather +up; and if we look a little more closely into this kind of action, we +shall find certain steps of reasoning extremely interesting. For instance, +here is the oil-lamp I shewed you--an excellent lamp for our +experiments--the old Argand lamp. I now make it like a candle [obstructing +the passage of air into the centre of the flame]; there is the cotton; +there is the oil rising up it; and there is the conical flame. It burns +poorly, because there is a partial restraint of air. I have allowed no air +to get to it, save round the outside of the flame, and it does not burn +well. I cannot admit more air from the outside, because the wick is large; +but if, as Argand did so cleverly, I open a passage to the middle of the +flame, and so let air come in there, you will see how much more +beautifully it burns. If I shut the air off, look how it smokes; and why? +We have now some very interesting points to study. We have the case of the +combustion of a candle; we have the case of a candle being put out by the +want of air; and we have now the case of imperfect combustion; and this is +to us so interesting, that I want you to understand it as thoroughly as +you do the case of a candle burning in its best possible manner. I will +now make a great flame, because we need the largest possible +illustrations. Here is a larger wick [burning turpentine on a ball of +cotton]. All these things are the same as candles, after all. If we have +larger wicks, we must have a larger supply of air, or we shall have less +perfect combustion. Look now at this black substance going up into the +atmosphere; there is a regular stream of it. I have provided means to +carry off the imperfectly burned part, lest it should annoy you. Look at +the soots that fly off from the flame: see what an imperfect combustion it +is, because it cannot get enough air. What, then, is happening? Why, +certain things which are necessary to the combustion of a candle are +absent, and very bad results are accordingly produced; but we see what +happens to a candle when it is burnt in a pure and proper state of air. At +the time when I shewed you this charring by the ring of flame on the one +side of the paper, I might have also shewn you, by turning to the other +side, that the burning of a candle produces the same kind of +soot--charcoal or carbon. + +But, before I shew that, let me explain to you--as it is quite necessary +for our purpose--that, though I take a candle and give you, as the general +result, its combustion in the form of a flame, we must see whether +combustion is always in this condition, or whether there are other +conditions of flame; and we shall soon discover that there are, and that +they are most important to us. I think, perhaps, the best illustration of +such a point to us, as juveniles, is to shew the result of strong +contrast. Here is a little gunpowder. You know that gunpowder burns with +flame--we may fairly call it flame. It contains carbon and other +materials, which altogether cause it to burn with a flame. And here is +some pulverised iron, or iron filings. Now, I purpose burning these two +things together. I have a little mortar in which I will mix them. (Before +I go into these experiments, let me hope that none of you, by trying to +repeat them, for fun's sake, will do any harm. These things may all be +very properly used if you take care; but without that, much mischief will +be done.) Well, then, here is a little gunpowder, which I put at the +bottom of that little wooden vessel, and mix the iron filings up with it, +my object being to make the gunpowder set fire to the filings and burn +them in the air, and thereby shew the difference between substances +burning with flame and not with flame. Here is the mixture; and when I set +fire to it, you must watch the combustion, and you will see that it is of +two kinds. You will see the gunpowder burning with a flame, and the +filings thrown up. You will see them burning too, but without the +production of flame. They will each burn separately. [The Lecturer then +ignited the mixture.] There is the gunpowder, which burns with a flame; +and there are the filings--they burn with a different kind of combustion. +You see, then, these two great distinctions; and upon these differences +depend all the utility and all the beauty of flame which we use for the +purpose of giving out light. When we use oil, or gas, or candle, for the +purpose of illumination, their fitness all depends upon these different +kinds of combustion. + +There are such curious conditions of flame, that it requires some +cleverness and nicety of discrimination to distinguish the kinds of +combustion one from another. For instance, here is a powder which is very +combustible, consisting, as you see, of separate little particles. It is +called _lycopodium_[7], and each of these particles can produce a vapour, +and produce its own flame; but, to see them burning, you would imagine it +was all one flame. I will now set fire to a quantity, and you will see the +effect. We saw a cloud of flame, apparently in one body; but that rushing +noise [referring to the sound produced by the burning] was a proof that +the combustion was not a continuous or regular one. This is the lightning +of the pantomimes, and a very good imitation. [The experiment was twice +repeated by blowing lycopodium from a glass tube through a spirit-flame.] +This is not an example of combustion like that of the filings I have been +speaking of, to which we must now return. + +Suppose I take a candle, and examine that part of it which appears +brightest to our eyes. Why, there I get these black particles, which +already you have seen many times evolved from the flame, and which I am +now about to evolve in a different way. I will take this candle and clear +away the gutterage, which occurs by reason of the currents of air; and if +I now arrange a glass tube so as just to dip into this luminous part, as +in our first experiment, only higher, you see the result. In place of +having the same white vapour that you had before, you will now have a +black vapour. There it goes, as black as ink. It is certainly very +different from the white vapour; and when we put a light to it, we shall +find that it does not burn, but that it puts the light out. Well, these +particles, as I said before, are just the smoke of the candle; and this +brings to mind that old employment which Dean Swift recommended to +servants for their amusement, namely, writing on the ceiling of a room +with a candle. But what is that black substance? Why, it is the same +carbon which exists in the candle. How comes it out of the candle? It +evidently existed in the candle, or else we should not have had it here. +And now I want you to follow me in this explanation. You would hardly +think that all those substances which fly about London, in the form of +soots and blacks, are the very beauty and life of the flame, and which are +burned in it as those iron filings were burned here. Here is a piece of +wire gauze, which will not let the flame go through it; and I think you +will see, almost immediately, that when I bring it low enough to touch +that part of the flame which is otherwise so bright, that it quells and +quenches it at once, and allows a volume of smoke to rise up. + +I want you now to follow me in this point,--that whenever a substance +burns, as the iron filings burnt in the flame of gunpowder, without +assuming the vaporous state (whether it becomes liquid or remains solid), +it becomes exceedingly luminous. I have here taken three or four examples +apart from the candle, on purpose to illustrate this point to you; because +what I have to say is applicable to all substances, whether they burn or +whether they do not burn,--that they are exceedingly bright if they retain +their solid state, and that it is to this presence of solid particles in +the candle-flame that it owes its brilliancy. + +Here is a platinum-wire, a body which does not change by heat. If I heat +it in this flame, see how exceedingly luminous it becomes. I will make the +flame dim, for the purpose of giving a little light only, and yet you will +see that the heat which it can give to that platinum-wire, though far less +than the heat it has itself, is able to raise the platinum-wire to a far +higher state of effulgence. This flame has carbon in it; but I will take +one that has no carbon in it. There is a material, a kind of fuel--a +vapour, or gas, whichever you like to call it--in that vessel, and it has +no solid particles in it; so I take that because it is an example of flame +itself burning without any solid matter whatever; and if I now put this +solid substance in it, you see what an intense heat it has, and how +brightly it causes the solid body to glow. This is the pipe through which +we convey this particular gas, which we call hydrogen, and which you shall +know all about next time we meet. And here is a substance called oxygen, +by means of which this hydrogen can burn; and although we produce, by +their mixture, far greater heat[8] than you can obtain from the candle, +yet there is very little light. If, however, I take a solid substance, and +put that into it, we produce an intense light If I take a piece of lime, a +substance which will not burn, and which will not vaporise by the heat +(and because it does not vaporise, remains solid, and remains heated), you +will soon observe what happens as to its glowing. I have here a most +intense heat, produced by the burning of hydrogen in contact with the +oxygen; but there is as yet very little light--not for want of heat, but +for want of particles which can retain their solid state; but when I hold +this piece of lime in the flame of the hydrogen as it burns in the oxygen, +see how it glows! This is the glorious lime-light, which rivals the +voltaic-light, and which is almost equal to sunlight. I have here a piece +of carbon or charcoal, which will burn and give us light exactly in the +same manner as if it were burnt as part of a candle. The heat that is in +the flame of a candle decomposes the vapour of the wax, and sets free the +carbon particles--they rise up heated and glowing as this now glows, and +then enter into the air. But the particles when burnt never pass off from +a candle in the form of carbon. They go off into the air as a perfectly +invisible substance, about which we shall know hereafter. + +Is it not beautiful to think that such a process is going on, and that +such a dirty thing as charcoal can become so incandescent? You see it +comes to this--that all bright flames contain these solid particles; all +things that burn and produce solid particles, either during the time they +are burning, as in the candle, or immediately after being burnt, as in the +case of the gunpowder and iron-filings,--all these things give us this +glorious and beautiful light. + +I will give you a few illustrations. Here is a piece of phosphorus, which +burns with a bright flame. Very well; we may now conclude that phosphorus +will produce, either at the moment that it is burning or afterwards, these +solid particles. Here is the phosphorus lighted, and I cover it over with +this glass for the purpose of keeping in what is produced. What is all +that smoke? That smoke consists of those very particles which are produced +by the combustion of the phosphorus. Here, again, are two substances. This +is chlorate of potassa, and this other sulphuret of antimony. I shall mix +these together a little, and then they may be burnt in many ways. I shall +touch them with a drop of sulphuric acid, for the purpose of giving you an +illustration of chemical action, and they will instantly burn[9]. [The +Lecturer then ignited the mixture by means of sulphuric acid.] Now, from +the appearance of things, you can judge for yourselves whether they +produce solid matter in burning. I have given you the train of reasoning +which will enable you to say whether they do or do not; for what is this +bright flame but the solid particles passing off? + +[Illustration: Fig. 9.] + +Mr. Anderson has in the furnace a very hot crucible,--I am about to throw +into it some zinc filings, and they will burn with a flame like gunpowder. +I make this experiment because you can make it well at home. Now, I want +you to see what will be the result of the combustion of this zinc. Here it +is burning--burning beautifully like a candle, I may say. But what is all +that smoke, and what are those little clouds of wool which will come to +you if you cannot come to them, and make themselves sensible to you in the +form of the old philosophic wool, as it was called? We shall have left in +that crucible, also, a quantity of this woolly matter. But I will take a +piece of this same zinc and make an experiment a little more closely at +home, as it were. You will have here the same thing happening. Here is the +piece of zinc, there [pointing to a jet of hydrogen] is the furnace, and +we will set to work and try and burn the metal. It glows, you see: there +is the combustion, and there is the white substance into which it burns. +And so, if I take that flame of hydrogen as the representative of a +candle, and shew you a substance like zinc burning in the flame, you will +see that it was merely during the action of combustion that this substance +glowed--while it was kept hot; and if I take a flame of hydrogen, and put +this white substance from the zinc into it, look how beautifully it glows, +and just because it is a solid substance. + +I will now take such a flame as I had a moment since, and set free from it +the particles of carbon. Here is some camphine, which will burn with a +smoke; but if I send these particles of smoke through this pipe into the +hydrogen flame, you will see they will burn and become luminous, because +we heat them a second time. There they are. Those are the particles of +carbon re-ignited a second time. They are those particles which you can +easily see by holding a piece of paper behind them, and which, whilst they +are in the flame, are ignited by the heat produced, and, when so ignited, +produce this brightness. When the particles are not separated, you get no +brightness. The flame of coal-gas owes its brightness to the separation, +during combustion, of these particles of carbon, which are equally in that +as in a candle. I can very quickly alter that arrangement. Here, for +instance, is a bright flame of gas. Supposing I add so much air to the +flame as to cause it all to burn before those particles are set free, I +shall not have this brightness; and I can do that in this way:--If I place +over the jet this wire-gauze cap, as you see, and then light the gas over +it, it burns with a non-luminous flame, owing to its having plenty of air +mixed with it before it burns; and if I raise the gauze, you see it does +not burn below[10]. There is plenty of carbon in the gas; but, because the +atmosphere can get to it, and mix with it before it burns, you see how +pale and blue the flame is. And if I blow upon a bright gas-flame, so as +to consume all this carbon before it gets heated to the glowing point, it +will also burn blue: [The Lecturer illustrated his remarks by blowing on +the gas-light.] The only reason why I have not the same bright light when +I thus blow upon the flame is, that the carbon meets with sufficient air +to burn it before it gets separated in the flame in a free state. The +difference is solely due to the solid particles not being separated before +the gas is burnt. + +You observe that there are certain products as the result of the +combustion of a candle, and that of these products one portion may be +considered as charcoal, or soot; that charcoal, when afterwards burnt, +produces some other product; and it concerns us very much now to ascertain +what that other product is. We shewed that something was going away; and I +want you now to understand how much is going up into the air; and for that +purpose we will have combustion on a little larger scale. From that candle +ascends heated air, and two or three experiments will shew you the +ascending current; but, in order to give you a notion of the quantity of +matter which ascends in this way, I will make an experiment by which I +shall try to imprison some of the products of this combustion. For this +purpose I have here what boys call a fire-balloon. I use this fire-balloon +merely as a sort of measure of the result of the combustion we are +considering; and I am about to make a flame in such an easy and simple +manner as shall best serve my present purpose. This plate shall be the +"cup," we will so say, of the candle; this spirit shall be our fuel; and I +am about to place this chimney over it, because it is better for me to do +so than to let things proceed at random. + +[Illustration: Fig. 10.] + +Mr. Anderson will now light the fuel, and here at the top we shall get the +results of the combustion. What we get at the top of that tube is exactly +the same, generally speaking, as you get from the combustion of a candle; +but we do not get a luminous flame here, because we use a substance which +is feeble in carbon. I am about to put this balloon--not into action, +because that is not my object--but to shew you the effect which results +from the action of those products which arise from the candle, as they +arise here from the furnace. [The balloon was held over the chimney, when +it immediately commenced to fill.] You see how it is disposed to ascend; +but we must not let it up, because it might come in contact with those +upper gas-lights, and that would be very inconvenient. [The upper +gas-lights were turned out, at the request of the Lecturer, and the +balloon was allowed to ascend.] Does not that shew you what a large bulk +of matter is being evolved? Now, there is going through this tube [placing +a large glass tube over a candle] all the products of that candle, and you +will presently see that the tube will become quite opaque. Suppose I take +another candle, and place it under a jar, and then put a light on the +other side, just to shew you what is going on. You see that the sides of +the jar become cloudy, and the light begins to burn feebly. It is the +products, you see, which make the light so dim, and this is the same thing +which makes the sides of the jar so opaque. If you go home and take a +spoon that has been in the cold air, and hold it over a candle--not so as +to soot it--you will find that it becomes dim, just as that jar is dim. If +you can get a silver dish, or something of that kind, you will make the +experiment still better. And now, just to carry your thoughts forward to +the time we shall next meet, let me tell you that it is _water_ which +causes the dimness; and when we next meet. I will shew you that we can +make it, without difficulty, assume the form of a liquid. + + + + +LECTURE III. + +PRODUCTS: WATER FROM THE COMBUSTION--NATURE OF WATER--A +COMPOUND--HYDROGEN. + + +I dare say you will remember that when we parted we had just mentioned the +word "products" from the candle. For when a candle burns we found we were +able, by nice adjustment, to get various products from it. There was one +substance which was not obtained when the candle was burning properly, +which was charcoal or smoke; and there was some other substance that went +upwards from the flame which did not appear as smoke, but took some other +form, and made part of that general current which, ascending from the +candle upwards, becomes invisible, and escapes. There were also other +products to mention. You remember that in that rising current having its +origin at the candle, we found that one part was condensable against a +cold spoon, or against a clean plate, or any other cold thing, and another +part was incondensable. + +We will first take the condensable part, and examine it; and, strange to +say, we find that that part of the product is just water--nothing but +water. On the last occasion I spoke of it incidentally, merely saying that +water was produced among the condensable products of the candle; but +to-day I wish to draw your attention to water, that we may examine it +carefully, especially in relation to this subject, and also with respect +to its general existence on the surface of the globe. + +Now, having previously arranged an experiment for the purpose of +condensing water from the products of the candle, my next point will be to +shew you this water; and perhaps one of the best means that I can adopt +for shewing its presence to so many at once, is to exhibit a very visible +action of water, and then to apply that test to what is collected as a +drop at the bottom of that vessel. I have here a chemical substance, +discovered by Sir Humphrey Davy, which has a very energetic action upon +water, which I shall use as a test of the presence of water. If I take a +little piece of it--it is called potassium, as coming from potash,--if I +take a little piece of it, and throw it into that basin, you see how it +shews the presence of water by lighting up and floating about, burning +with a violent flame. I am now going to take away the candle which has +been burning beneath the vessel containing ice and salt, and you see a +drop of water--a condensed product of the candle--hanging from under the +surface of the dish. + +[Illustration: Fig. 11.] + +I will shew you that potassium has the same action upon it as upon the +water in that basin in the experiment we have just tried. See, it takes +fire, and burns in just the same manner. I will take another drop upon +this glass slab, and when I put the potassium on to it, you see at once, +from its taking fire, that there is water present. Now, that water was +produced by the candle. In the same manner, if I put this spirit-lamp +under that jar, you will soon see the latter become damp, from the dew +which is deposited upon it--that dew being the result of combustion; and I +have no doubt you will shortly see by the drops of water which fall upon +the paper below, that there is a good deal of water produced from the +combustion of the lamp. I will let it remain, and you can afterwards see +how much water has been collected. So, if I take a gas-lamp, and put any +cooling arrangement over it, I shall get water--water being likewise +produced from the combustion of gas. Here, in this bottle, is a quantity +of water--perfectly pure, distilled water, produced from the combustion of +a gas-lamp--in no point different from the water that you distil from the +river, or ocean, or spring, but exactly the same thing. Water is one +individual thing--it never changes. We can add to it by careful +adjustment, for a little while, or we can take it apart, and get other +things from it; but water, as water, remains always the same, either in a +solid, liquid, or fluid state. Here, again [holding another bottle], is +some water produced by the combustion of an oil-lamp. A pint of oil, when +burnt fairly and properly, produces rather more than a pint of water. +Here, again, is some water, produced by a rather long experiment from a +wax candle. And so we can go on with almost all combustible substances, +and find that if they burn with a flame, as a candle, they produce water. +You may make these experiments yourselves. The head of a poker is a very +good thing to try with, and if it remains cold long enough over the +candle, you may get water condensed in drops on it; or a spoon or ladle, +or anything else may be used, provided it be clean, and can carry off the +heat, and so condense the water. + +And now--to go into the history of this wonderful production of water from +combustibles, and by combustion--I must first of all tell you that this +water may exist in different conditions; and although you may now be +acquainted with all its forms, they still require us to give a little +attention to them for the present, so that we may perceive how the water, +whilst it goes through its Protean changes, is entirely and absolutely the +same thing, whether it is produced from a candle, by combustion, or from +the rivers or ocean. + +First of all, water, when at the coldest, is ice. Now, we philosophers---I +hope that I may class you and myself together in this case--speak of water +as water, whether it be in its solid, or liquid, or gaseous state,--we +speak of it chemically as water. Water is a thing compounded of two +substances, one of which we have derived from the candle, and the other we +shall find elsewhere. Water may occur as ice; and you have had most +excellent opportunities lately of seeing this. Ice changes back into +water--for we had on our last Sabbath a strong instance of this change, by +the sad catastrophe which occurred in our own house, as well as in the +houses of many of our friends,--ice changes back into water when the +temperature is raised: water also changes into steam when it is warmed +enough. The water which we have here before us is in its densest +state[11], and although it changes in weight, in condition, in form, and +in many other qualities, it still is water; and whether we alter it into +ice by cooling, or whether we change it into steam by heat, it increases +in volume,--in the one case very strangely and powerfully, and in the +other case very largely and wonderfully. For instance, I will now take +this tin cylinder, and pour a little water into it; and seeing how much +water I pour in, you may easily estimate for yourselves how high it will +rise in the vessel: it will cover the bottom about two inches. I am now +about to convert the water into steam, for the purpose of shewing to you +the different volumes which water occupies in its different states of +water and steam. + +Let us now take the case of water changing into ice: we can effect that by +cooling it in a mixture of salt and pounded ice[12]; and I shall do so to +shew you the expansion of water into a thing of larger bulk when it is so +changed. These bottles [holding one] are made of strong cast iron, very +strong and very thick--I suppose they are the third of an inch in +thickness; they are very carefully filled with water, so as to exclude all +air, and then they are screwed down tight. We shall see that when we +freeze the water in these iron vessels, they will not be able to hold the +ice, and the expansion within them will break them in pieces as these +[pointing to some fragments] are broken, which have been bottles of +exactly the same kind. I am about to put these two bottles into that +mixture of ice and salt, for the purpose of shewing that when water +becomes ice, it changes in volume in this extraordinary way. + +In the mean time look at the change which has taken place in the water to +which we have applied heat--it is losing its fluid state. You may tell +this by two or three circumstances. I have covered the mouth of this glass +flask, in which water is boiling, with a watch-glass. Do you see what +happens? It rattles away like a valve chattering, because the steam rising +from the boiling water sends the valve up and down, and forces itself out, +and so makes it clatter. You can very easily perceive that the flask is +quite full of steam, or else it would not force its way out. You see, +also, that the flask contains a substance very much larger than the water, +for it fills the whole of the flask over and over again, and there it is +blowing away into the air; and yet you cannot observe any great diminution +in the bulk of the water, which shews you that its change of bulk is very +great when it becomes steam. + +I have put our iron bottles containing water into this freezing mixture, +that you may see what happens. No communication will take place, you +observe, between the water in the bottles and the ice in the outer vessel. +But there will be a conveyance of heat from the one to the other; and if +we are successful--we are making our experiment in very great haste--I +expect you will by-and-by, so soon as the cold has taken possession of the +bottles and their contents, hear a pop on the occasion of the bursting of +the one bottle or the other; and, when we come to examine the bottles, we +shall find their contents masses of ice, partly enclosed by the covering +of iron which is too small for them, because the ice is larger in bulk +than the water. You know very well that ice floats upon water: if a boy +falls through a hole into the water, he tries to get on the ice again to +float him up. Why does the ice float?--think of that, and philosophise. +Because the ice is larger than the quantity of water which can produce it; +and therefore the ice weighs the lighter, and the water is the heavier. + +To return now to the action of heat on water. See what a stream of vapour +is issuing from this tin vessel! You observe, we must have made it quite +full of steam to have it sent out in that great quantity. And now, as we +can convert the water into steam by heat, we convert it back into liquid +water by the application of cold. And if we take a glass, or any other +cold thing, and hold it over this steam, see how soon it gets damp with +water; it will condense it until the glass is warm--it condenses the water +which is now running down the sides of it. I have here another experiment +to shew the condensation of water from a vaporous state back into a liquid +state, in the same way as the vapour, one of the products of the candle, +was condensed against the bottom of the dish, and obtained in the form of +water; and to shew you how truly and thoroughly these changes take place, +I will take this tin flask, which is now full of steam, and close the top. +We shall see what takes place when we cause this water or steam to return +back to the fluid state by pouring some cold water on the outside. [The +Lecturer poured the cold water over the vessel, when it immediately +collapsed.] You see what has happened. If I had closed the stopper, and +still kept the heat applied to it, it would have burst the vessel; yet, +when the steam returns to the state of water, the vessel collapses, there +being a vacuum produced inside by the condensation of the steam. I shew +you these experiments for the purpose of pointing out that in all these +occurrences there is nothing that changes the water into any other +thing--it still remains water; and so the vessel is obliged to give way, +and is crushed inwards, as in the other case, by the further application +of heat, it would have been blown outwards. + +[Illustration: Fig. 12.] + +And what do you think the bulk of that water is when it assumes the +vaporous condition? You see that cube [pointing to a cubic foot]. There, +by its side, is a cubic inch, exactly the same shape as the cubic foot, +and that bulk of water [the cubic inch] is sufficient to expand into that +bulk [the cubic foot] of steam; and, on the contrary, the application of +cold will contract that large quantity of steam into this small quantity +of water. + +[Illustration: Fig. 13.] + +[One of the iron bottles burst at that moment.] Ah! There is one of our +bottles burst, and here you see is a crack down one side an eighth of an +inch in width. [The other now exploded, sending the freezing mixture in +all directions.] This other bottle is also broken; although the iron was +nearly half-an-inch thick, the ice has burst it asunder. These changes +always take place in water: they do not require to be always produced by +artificial means,--we only use them here because we want to produce a +small winter round that little bottle, instead of a long and severe one. +But if you go to Canada, or to the North, you will find the temperature +there out of doors will do the same thing as has been done here by the +freezing mixture. + +To return to our quiet philosophy. We shall not in future be deceived, +therefore, by any changes that are produced in water. Water is the same +everywhere, whether produced from the ocean or from the flame of the +candle. Where, then, is this water which we get from a candle? I must +anticipate a little, and tell you. It evidently comes, as to part of it, +from the candle; but is it within the candle beforehand? No. It is not in +the candle; and it is not in the air round about the candle which is +necessary for its combustion. It is neither in one nor the other, but it +comes from their conjoint action, a part from the candle, a part from the +air; and this we have now to trace, so that we may understand thoroughly +what is the chemical history of a candle when we have it burning on our +table. How shall we get at this? I myself know plenty of ways, but I want +_you_ to get at it from the association in your own minds of what I have +already told you. + +I think you can see a little in this way. We had just now the case of a +substance which acted upon the water in the way that Sir Humphrey Davy +shewed us[13], and which I am now going to recall to your minds by making +again an experiment upon that dish. It is a thing which we have to handle +very carefully, for you see, if I allow a little splash of water to come +upon this mass, it sets fire to part of it; and if there were free access +of air, it would quickly set fire to the whole. Now, this is a metal--a +beautiful and bright metal--which rapidly changes in the air, and, as you +know, rapidly changes in water. I will put a piece on the water, and you +see it burns beautifully, making a floating lamp, using the water in the +place of air. Again, if we take a few iron filings or turnings, and put +them in water, we find that they likewise undergo an alteration. They do +not change so much as this potassium does, but they change somewhat in the +same way; they become rusty, and shew an action upon the water, though in +a different degree of intensity to what this beautiful metal does: but +they act upon the water in the same manner generally as this potassium. I +want you to put these different facts together in your minds. I have +another metal here [zinc], and when we examined it with regard to the +solid substance produced by its combustion, we had an opportunity of +seeing that it burned; and I suppose, if I take a little strip of this +zinc and put it over the candle, you will see something half-way, as it +were, between the combustion of potassium on the water and the action of +iron,--you see there is a sort of combustion. It has burned, leaving a +white ash or residuum, and here also we find that the metal has a certain +amount of action upon water. + +By degrees we have learned how to modify the action of these different +substances, and to make them tell us what we want to know. And now, first +of all, I take iron. It is a common thing in all chemical reactions, where +we get any result of this kind, to find that it is increased by the action +of heat; and if we want to examine minutely and carefully the action of +bodies one upon another, we often have to refer to the action of heat. You +are aware, I believe, that iron-filings burn beautifully in the air; but I +am about to shew you an experiment of this kind, because it will impress +upon you what I am going to say about iron in its action on water. If I +take a flame and make it hollow;--you know why, because I want to get air +to it and into it, and therefore I make it hollow--and then take a few +iron-filings and drop them into the flame, you see how well they burn. +That combustion results from the chemical action which is going on when we +ignite those particles. And so we proceed to consider these different +effects, and ascertain what iron will do when it meets with water. It will +tell us the story so beautifully, so gradually and regularly, that I think +it will please you very much. + +I have here a furnace with a pipe going through it like an iron +gun-barrel, and I have stuffed that barrel full of bright iron-turnings, +and placed it across the fire, to be made red-hot. We can either send air +through the barrel to come in contact with the iron, or we can send steam +from this little boiler at the end of the barrel. Here is a stop-cock +which shuts off the steam from the barrel until we wish to admit it. There +is some water in these glass jars, which I have coloured blue, so that you +may see what happens. Now, you know very well that any steam I might send +through that barrel, if it went through into the water, would be +condensed; for you have seen that steam cannot retain its gaseous form if +it be cooled down. + +[Illustration: Fig. 14.] + +You saw it here [pointing to the tin flask] crushing itself into a small +bulk, and causing the flask holding it to collapse; so that if I were to +send steam through that barrel, it would be condensed--supposing the +barrel were cold: it is, therefore, heated to perform the experiment I am +now about to shew you. I am going to send the steam through the barrel in +small quantities; and you shall judge for yourselves, when you see it +issue from the other end, whether it still remains steam. Steam is +condensible into water, and when you lower the temperature of steam, you +convert it back into fluid water; but I have lowered the temperature of +the gas which I have collected in this jar, by passing it through water +after it has traversed the iron barrel, and still it does not change back +into water. I will take another test and apply to this gas. (I hold the +jar in an inverted position, or my substance would escape.) If I now apply +a light to the mouth of the jar, it ignites with a slight noise. That +tells you that it is not steam. Steam puts out a fire--it does not burn; +but you saw that what I had in that jar burnt. We may obtain this +substance equally from water produced from the candle-flame as from any +other source. When it is obtained by the action of the iron upon the +aqueous vapour, it leaves the iron in a state very similar to that in +which these filings were after they were burnt. It makes the iron heavier +than it was before. So long as the iron remains in the tube and is heated, +and is cooled again without the access of air or water, it does not change +in its weight; but after having had this current of steam passed over it, +it then comes out heavier that it was before, having taken something out +of the steam, and having allowed something else to pass forth, which we +see here. And now, as we have another jar full, I will shew you something +most interesting. It is a combustible gas; and I might at once take this +jar and set fire to the contents, and shew you that it is combustible; but +I intend to shew you more if I can. It is also a very light substance. +Steam will condense: this body will rise in the air, and not condense. + +[Illustration: Fig. 15] + +Suppose I take another glass jar, empty of all but air: if I examine it +with a taper, I shall find that it contains nothing but air. I will now +take this jar full of the gas that I am speaking of, and deal with it as +though it were a light body. I will hold both upside-down, and turn the +one up under the other; and that which did contain the gas procured from +the steam, what does it contain now? You will find it now only contains +air. But look! Here is the combustible substance [taking the other jar] +which I have poured out of the one jar into the other. It still preserves +its quality, and condition, and independence, and therefore is the more +worthy of our consideration, as belonging to the products of a candle. + +Now, this substance which we have just prepared by the action of iron on +the steam or water, we can also get by means of those other things which +you have already seen act so well upon the water. If I take a piece of +potassium, and make the necessary arrangements, it will produce this gas; +and if, instead, a piece of zinc, I find, when I come to examine it very +carefully, that the main reason why this zinc cannot act upon the water +continuously as the other metal does, is because the result of the action +of the water envelopes the zinc in a kind of protecting coat. We have +learned in consequence, that if we put into our vessel only the zinc and +water, they by themselves do not give rise to much action, and we get no +result. But suppose I proceed to dissolve off this varnish--this +encumbering substance--which I can do by a little acid; the moment I do +this, I find the zinc acting upon the water exactly as the iron did, but +at the common temperature. The acid in no way is altered, except in its +combination with the oxide of zinc, which is produced. I have now poured +the acid into the glass, and the effect is as though I were applying heat +to cause this boiling up. There is something coming off from the zinc very +abundantly, which is not steam. There is a jar full of it; and you will +find that I have exactly the same combustible substance remaining in the +vessel, when I hold it upside-down, that I produced during the experiment +with the iron barrel. This is what we get from water--the same substance +which is contained in the candle. + +[Illustration: Fig. 16.] + +Let us now trace distinctly the connection between these two points. This +is hydrogen--a body classed among those things which in Chemistry we call +elements, because we can get nothing else out of them. A candle is not an +elementary body, because we can get carbon out of it; we can get this +hydrogen out of it, or at least out of the water which it supplies. And +this gas has been so named hydrogen, because it is that element which, in +association with another, generates water. [Footnote: [greek: hudos], +"water," and [greek: gennao], "I generate."] Mr. Anderson having now been +able to get two or three jars of gas, we shall have a few experiments to +make, and I want to shew you the best way of making these experiments. I +am not afraid to shew you, for I wish you to make experiments, if you will +only make them with care and attention, and the assent of those around +you. As we advance in Chemistry, we are obliged to deal with substances +which are rather injurious, if in their wrong places--the acids, and heat, +and combustible things we use, might do harm if carelessly employed. If +you want to make hydrogen, you can make it easily from bits of zinc, and +sulphuric or muriatic acid. Here is what in former times was called the +"philosopher's candle." It is a little phial with a cork, and a tube or +pipe passing through it. + +[Illustration: Fig. 17.] + +And I am now putting a few little pieces of zinc into it. This little +instrument I am going to apply to a useful purpose in our +demonstrations--for I want to shew you that you can prepare hydrogen, and +make some experiments with it as you please at your own homes. Let me here +tell you why I am so careful to fill this phial nearly, and yet not quite +full. I do it because the evolved gas, which, as you have seen, is very +combustible, is explosive to a considerable extent when mixed with air, +and might lead to harm, if you were to apply a light to the end of that +pipe before all the air had been swept out of the space above the water. I +am now about to pour in the sulphuric acid. I have used very little zinc, +and more sulphuric acid and water, because I want to keep it at work for +some time. I therefore take care in this way to modify the proportions of +the ingredients, so that I may have a regular supply--not too quick, and +not too slow. Supposing I now take a glass and put it upside-down over the +end of the tube, because the hydrogen is light I expect that it will +remain in that vessel a little while. We will now test the contents of our +glass to see if there be hydrogen in it. I think I am safe in saying we +have caught some [applying a light]. There it is, you see. I will now +apply a light to the top of the tube. There is the hydrogen burning. There +is our philosophical candle. It is a foolish feeble sort of a flame, you +may say; but it is so hot that scarcely any common flame gives out so much +heat. It goes on burning regularly, and I am now about to put that flame +to burn under a certain arrangement, in order that we may examine its +results and make use of the information which we may thereby acquire. +Inasmuch as the candle produces water, and this gas comes out of the +water, let us see what this gives us by the same process of combustion +that the candle went through when it burnt in the atmosphere; and for that +purpose I am going to put the lamp under this apparatus, in order to +condense whatever may arise from the combustion within it In the course of +a short time you will see moisture appearing in the cylinder, and you will +get the water running down the side; and the water from this hydrogen +flame will have absolutely the same effect upon all our tests, being +obtained by the same general process as in the former case. This hydrogen +is a very beautiful substance. It is so light that it carries things up: +it is far lighter than the atmosphere; and I dare say I can shew you this +by an experiment which, if you are very clever, some of you may even have +skill enough to repeat. Here is our generator of hydrogen, and here are +some soap-suds. I have an india-rubber tube connected with the hydrogen +generator, and at the end of the tube is a tobacco-pipe. + +[Illustration: Fig. 18.] + +I can thus put the pipe into the suds, and blow bubbles by means of the +hydrogen. You observe how the bubbles fall downwards when I blow them with +my warm breath; but notice the difference when I blow them with hydrogen. +[The Lecturer here blew bubbles with hydrogen, which rose to the roof of +the theatre.] It shews you how light this gas must be in order to carry +with it not merely the ordinary soap-bubble, but the larger portion of a +drop hanging to the bottom of it. I can shew its lightness in a better way +than this; larger bubbles than these may be so lifted up; indeed, in +former times balloons used to be filled with this gas. Mr. Anderson will +fasten this tube on to our generator, and we shall have a stream of +hydrogen here with which we can charge this balloon made of collodion. I +need not even be very careful to get all the air out, for I know the power +of this gas to carry it up. [Two collodion balloons were inflated, and +sent up, one being held by a string.] Here is another larger one made of +thin membrane, which we will fill and allow to ascend. You will see they +will all remain floating about until the gas escapes. + +What, then, are the comparative weights of these substances? I have a +table here which will shew you the proportion which their weights bear to +each other. I have taken a pint and a cubic foot as the measures, and have +placed opposite to them the respective figures. A pint measure of this +hydrogen weighs three-quarters of our smallest weight (a grain), and a +cubic foot weighs one-twelfth of an ounce; whereas a pint of water weighs +8,750 grains, and a cubic foot of water weighs almost 1,000 ounces. You +see, therefore, what a vast difference there is between the weight of a +cubic foot of water and a cubic foot of hydrogen. + +Hydrogen gives rise to no substance that can become solid, either during +combustion or afterwards as a product of its combustion. But when it +burns, it produces water only; and if we take a cold glass and put it over +the flame, it becomes damp, and you have water, produced immediately in +appreciable quantity; and nothing is produced by its combustion but the +same water which you have seen the flame of the candle produce. It is +important to remember that this hydrogen is the only thing in nature which +furnishes water as the sole product of combustion. + +And now we must endeavour to find some additional proof of the general +character and composition of water; and for this purpose I will keep you a +little longer, so that at our next meeting we may be better prepared for +the subject. We have the power of arranging the zinc which you have seen +acting upon the water by the assistance of an acid, in such a manner as to +cause all the power to be evolved in the place where we require it I have +behind me a voltaic pile, and I am just about to shew you, at the end of +this lecture, its character and power, that you may see what we shall have +to deal with when next we meet. I hold here the extremities of the wires +which transport the power from behind me, and which I shall cause to act +on the water. + +We have previously seen what a power of combustion is possessed by the +potassium, or the zinc, or the iron-filings; but none of them shew such +energy as this. [The Lecturer here made contact between the two terminal +wires of the battery, when a brilliant flash of light was produced.] This +light is, in fact, produced by a forty-zinc power of burning: it is a +power that I can carry about in my hands, through these wires, at +pleasure--although, if I applied it wrongly to myself, it would destroy me +in an instant, for it is a most intense thing, and the power you see here +put forth while you count five [bringing the poles in contact, and +exhibiting the electric light] is equivalent to the power of several +thunder-storms, so great is its force[14]. And that you may see what +intense energy it has, I will take the ends of the wires which convey the +power from the battery, and with it I dare say I can burn this iron file. +Now, this is a chemical power, and one which, when we next meet, I shall +apply to water, and shew you what results we are able to produce. + + + + +LECTURE IV. + +HYDROGEN IN THE CANDLE--BURNS INTO WATER--THE OTHER PART OF WATER--OXYGEN. + +I see you are not tired of the candle yet, or I am sure you would not be +interested in the subject in the way you are. When our candle was burning, +we found it produced water exactly like the water we have around us; and +by further examination of this water we found in it that curious body, +hydrogen--that light substance of which there is some in this jar. We +afterwards saw the burning powers of that hydrogen, and that it produced +water. And I think I introduced to your notice an apparatus which I very +briefly said was an arrangement of chemical force, or power, or energy, so +adjusted as to convey its power to us in these wires; and I said I should +use that force to pull the water to pieces, to see what else there was in +the water besides hydrogen; because, you remember, when we passed the +water through the iron tube, we by no means got the weight of water back +which we put in, in the form of steam, though we had a very large quantity +of gas evolved. We have now to see what is the other substance present. +That you may understand the character and use of this instrument, let us +make an experiment or two. Let us put together, first of all, some +substances, knowing what they are, and then see what that instrument does +to them. There is some copper (observe the various changes which it can +undergo), and here is some nitric acid, and you will find that this, being +a strong chemical agent, will act very powerfully when I add it to the +copper. It is now sending forth a beautiful red vapour; but as we do not +want that vapour, Mr. Anderson will hold it near the chimney for a short +time, that we may have the use and beauty of the experiment without the +annoyance. The copper which I have put into the flask will dissolve: it +will change the acid and the water into a blue fluid, containing copper +and other things; and I propose then shewing you how this voltaic battery +deals with it; and in the mean-time we will arrange another kind of +experiment for you to see what power it has. This is a substance which is +to us like water--that is to say, it contains bodies which we do not know +of as yet, as water contains a body which we do not know as yet. Now, this +solution of a salt[15] I will put upon paper, and spread about, and apply +the power of the battery to it, and observe what will happen. Three or +four important things will happen which we shall take advantage of. I +place this wetted paper upon a sheet of tinfoil, which is convenient for +keeping all clean, and also for the advantageous application of the power; +and this solution, you see, is not at all affected by being put upon the +paper or tinfoil, nor by anything else I have brought in contact with it +yet, and which, therefore, is free to us to use as regards that +instrument. But first let us see that our instrument is in order. Here are +our wires. Let us see whether it is in the state in which it was last +time. We can soon tell. As yet, when I bring them together, we have no +power, because the conveyers--what we call the electrodes--the passages or +ways for the electricity--are stopped; but now Mr. Anderson by that +[referring to a sudden flash at the ends of the wires] has given me a +telegram to say that it is ready. Before I begin our experiment I will get +Mr. Anderson to break contact again at the battery behind me, and we will +put a platinum-wire across to connect the poles, and then if I find I can +ignite a pretty good length of this wire, we shall be safe in our +experiment. Now you will see the power. [The connection was established, +and the intermediate wire became red-hot.] There is the power running +beautifully through the wire, which I have made thin on purpose to shew +you that we have those powerful forces; and now, having that power, we +will proceed with it to the examination of water. + +I have here two pieces of platinum, and if I lay them down upon this piece +of paper [the moistened paper on the tinfoil], you will see no action; and +if I take them up, there is no change that you can see, but the +arrangement remains just as it was before. But, now, see what happens: if +I take these two poles and put either one or the other of them down +separately on the platinum-plates, they do nothing for me, both are +perfectly without action; but if I let them both be in contact at the same +moment, see what happens [a brown spot appeared under each pole of the +battery]. Look here at the effect that takes place, and see how I have +pulled something apart from the white--something brown; and I have no +doubt, if I were to arrange it thus, and were to put one of the poles to +the tinfoil on the other side of the paper--why, I get such a beautiful +action upon the paper, that I am going to see whether I cannot write with +it--a telegram, if you please. [The Lecturer here traced the word +"juvenile" on the paper with one of the terminal wires.] See there how +beautifully we can get our results! + +You see we have here drawn something, which we have not known about +before, out of this solution. Let us now take that flask from Mr. +Andersen's hands, and see what we can draw out of that. This, you know, is +a liquid which we have just made up from copper and nitric acid, whilst +our other experiments were in hand; and though I am making this experiment +very hastily, and may bungle a little, yet I prefer to let you see what I +do rather than prepare it beforehand. + +Now, see what happens. These two platinum-plates are the two ends (or I +will make them so immediately) of this apparatus; and I am about to put +them in contact with that solution just as we did a moment ago on the +paper. It does not matter to us whether the solution be on the paper or +whether it be in the jar, so long as we bring the ends of the apparatus to +it. If I put the two platinums in by themselves, they come out as clean +and as white as they go in [inserting them into the fluid without +connecting them with the battery]; but when we take the power and lay that +on [the platinums were connected with the battery and again dipped into +the solution], this, you see [exhibiting one of the platinums], is at once +turned into copper, as it were: it has become like a plate of copper; and +that [exhibiting the other piece of platinum] has come out quite clean. If +I take this coppered piece and change sides, the copper will leave the +right-hand side and come over to the left side; what was before the +coppered plate comes out clean, and the plate which was clean comes out +coated with copper; and thus you see that the same copper we put into this +solution we can also take out of it by means of this instrument. + +Putting that solution aside, let us now see what effect this instrument +will have upon water. Here are two little platinum-plates which I intend +to make the ends of the battery, and this (C) is a little vessel so shaped +as to enable me to take it to pieces, and shew you its construction. In +these two cups (A and B) I pour mercury, which touches the ends of the +wires connected with the platinum-plates. In the vessel (C) I pour some +water containing a little acid (but which is put only for the purpose of +facilitating the action; it undergoes no change in the process), and +connected with the top of the vessel is a bent glass tube (D), which may +remind you of the pipe which was connected with the gun barrel in our +furnace experiment, and which now passes under the jar (F). I have now +adjusted this apparatus, and we will proceed to affect the water in some +way or other. In the other case, I sent the water through a tube which was +made red-hot; I am now going to pass the electricity through the contents +of this vessel. Perhaps I may boil the water; if I do boil the water, I +shall get steam; and you know that steam condenses when it gets cold, and +you will therefore see by that whether I do boil the water or not. +Perhaps, however, I shall not boil the water, but produce some other +effect. You shall have the experiment and see. There is one wire which I +will put to this side (A), and here is the other wire which I will put to +the other side (B), and you will soon see whether any disturbance takes +place. Here it is seeming to boil up famously; but does it boil? Let us +see whether that which goes out is steam or not. I think you will soon see +the jar (F) will be filled with vapour, if that which rises from the water +is steam. But can it be steam? Why, certainly not; because there it +remains, you see, unchanged. There it is standing over the water, and it +cannot therefore be steam, but must be a permanent gas of some sort What +is it? Is it hydrogen? Is it anything else? Well, we will examine it. If +it is hydrogen, it will burn. [The Lecturer then ignited a portion of the +gas collected, which burnt with an explosion.] + +[Illustration: Fig. 19] + +It is certainly something combustible, but not combustible in the way that +hydrogen is. Hydrogen would not have given you that noise; but the colour +of that light, when the thing did burn, was like that of hydrogen: it +will, however, burn without contact with the air. That is why I have +chosen this other form of apparatus, for the purpose of pointing out to +you what are the particular circumstances of this experiment. In place of +an open vessel I have taken one that is closed (our battery is so +beautifully active that we are even boiling the mercury, and getting all +things right--not wrong, but vigorously right); and I am going to shew you +that that gas, whatever it may be, can burn without air, and in that +respect differs from a candle, which cannot burn without the air. And our +manner of doing this is as follows:--I have here a glass vessel (G) which +is fitted with two platinum-wires (IK), through which I can apply +electricity; and we can put the vessel on the air-pump and exhaust the +air, and when we have taken the air out we can bring it here and fasten it +on to this jar (F), and let into the vessel that gas which was formed by +the action of the voltaic battery upon the water, and which we have +produced by changing the water into it,--for I may go as far as this, and +say we have really, by that experiment, changed the water into that gas. +We have not only altered its condition, but we have changed it really and +truly into that gaseous substance, and all the water is there which was +decomposed by the experiment. As I screw this vessel (GH) on here (H), and +make the tubes well connected, and when I open the stop-cocks (HHH), if +you watch the level of the water (in F), you will see that the gas will +rise. I will now close the stop-cocks, as I have drawn up as much as the +vessel can hold, and being safely conveyed into that chamber, I will pass +into it an electric spark from this Leyden jar (L), when the vessel, which +is now quite clear and bright, will become dim. There will be no sound, +for the vessel is strong enough to confine the explosion. [A spark was +then passed through the jar, when the explosive mixture was ignited.] Did +you see that brilliant light? If I again screw the vessel on to the jar, +and open these stop-cocks, you will see that the gas will rise a second +time. [The stop-cocks were then opened.] Those gases [referring to the +gases first collected in the jar, and which had just been ignited by the +electric spark] have disappeared, as you see: their place is vacant, and +fresh gas has gone in. Water has been formed from them; and if we repeat +our operation [repeating the last experiment], I shall have another +vacancy, as you will see by the water rising. I always have an empty +vessel after the explosion, because the vapour or gas into which that +water has been resolved by the battery explodes under the influence of the +spark, and changes into water; and by-and-by you will see in this upper +vessel some drops of water trickling down the sides and collecting at the +bottom. + +We are here dealing with water entirely, without reference to the +atmosphere. The water of the candle had the atmosphere helping to produce +it; but in this way it can be produced independently of the air. Water, +therefore, ought to contain that other substance which the candle takes +from the air, and which, combining with the hydrogen, produces water. + +Just now you saw that one end of this battery took hold of the copper, +extracting it from the vessel which contained the blue solution. It was +effected by this wire; and surely we may say, if the battery has such +power with a metallic solution which we made and unmade, may we not find +that it is possible to split asunder the component parts of the water, and +put them into this place and that place? Suppose I take the poles--the +metallic ends of this battery--and see what will happen with the water in +this apparatus (fig. 20), where we have separated the two ends far apart. + +[Illustration: Fig. 20.] + +I place one here (at A), and the other there (at B), and I have little +shelves with holes which I can put upon each pole, and so arrange them +that whatever escapes from the two ends of the battery will appear as +separate gases; for you saw that the water did not become vaporous, but +gaseous. The wires are now in perfect and proper connection with the +vessel containing the water; and you see the bubbles rising: let us +collect these bubbles and see what they are. Here is a glass cylinder (O); +I fill it with water and put it over one end (A) of the pile; and I will +take another (H) and put it over the other end (B) of the pile. And so now +we have a double apparatus, with both places delivering gas. Both these +jars will fill with gas. There they go, that to the right (H) filling very +rapidly; the one to the left (O) filling not so rapidly; and though I have +allowed some bubbles to escape, yet still the action is going on pretty +regularly; and were it not that one is rather smaller than the other, you +would see that I should have twice as much in this (H) as I have in that +(O). Both these gases are colourless; they stand over the water without +condensing; they are alike in all things--I mean in all _apparent_ things; +and we have here an opportunity of examining these bodies and ascertaining +what they are. Their bulk is large, and we can easily apply experiments to +them. I will take this jar (H) first, and will ask you to be prepared to +recognise hydrogen. + +Think of all its qualities--the light gas which stood well in inverted +vessels, burning with a pale flame at the mouth of the jar--and see +whether this gas does not satisfy all these conditions. If it be hydrogen, +it will remain here while I hold this jar inverted. [A light was then +applied, when the hydrogen burnt] What is there now in the other jar? You +know that the two together made an explosive mixture. But what can this +be which we find as the other constituent in water, and which must +therefore be that substance which made the hydrogen burn? We know that the +water we put into the vessel consisted of the two things together. We find +one of these is hydrogen: what must that other be which was in the water +before the experiment, and which we now have by itself? I am about to put +this lighted splinter of wood into the gas. The gas itself will not burn, +but it will make the splinter of wood burn. [The Lecturer ignited the end +of the wood, and introduced it into the jar of gas.] See how it +invigorates the combustion of the wood, and how it makes it burn far +better than the air would make it burn; and now you see by itself that +every other substance which is contained in the water, and which, when the +water was formed by the burning of the candle, must have been taken from +the atmosphere. What shall we call it, A, B, or C? Let us call it O--call +it "Oxygen:" it is a very good distinct-sounding name. This, then, is the +oxygen which was present in the water, forming so large a part of it. + +We shall now begin to understand more clearly our experiments and +researches; because, when we have examined these things once or twice, we +shall soon see why a candle burns in the air. When we have in this way +analysed the water--that is to say, separated, or electrolysed its parts +out of it--we get two volumes of hydrogen, and one of the body that burns +it. And these two are represented to us on the following diagram, with +their weights also stated; and we shall find that the oxygen is a very +heavy body by comparison with the hydrogen. It is the other element in +water. + +I had better, perhaps, tell you now how we get this oxygen abundantly, +having shewn you how we can separate it from the water. Oxygen, as you +will immediately imagine, exists in the atmosphere; for how should the +candle burn to produce water without it? + + _____________________ +| | | +| 1 | 8 | +| | | +| | Oxygen. | Oxygen, . . . . 88.9 +| | | +| |_________| Hydrogen, . . . 11.1 +| Hydrogen. | ----- +| | 9 Water,. . . . . 100.0 +| | +| | +| | +|___________| + +Such a thing would be absolutely impossible, and chemically impossible, +without oxygen. + +[Illustration: Fig. 21.] + +Can we get it from the air? Well, there are some very complicated and +difficult processes by which we can get it from the air; but we have +better processes. There is a substance called the black oxide of +manganese: it is a very black-looking mineral, but very useful, and when +made red-hot it gives out oxygen. Here is an iron bottle which has had +some of this substance put into it, and there is a tube fixed to it, and a +fire ready made, and Mr. Anderson will put that retort into the fire, for +it is made of iron, and can stand the heat. Here is a salt called chlorate +of potassa, which is now made in large quantities for bleaching, and +chemical and medical uses, and for pyrotechnic and other purposes. I will +take some and mix it with some of the oxide of manganese (oxide of copper, +or oxide of iron would do as well); and if I put these together in a +retort, far less than a red heat is sufficient to evolve this oxygen from +the mixture. I am not preparing to make much, because we only want +sufficient for our experiments; only, as you will see immediately, if I +use too small a charge, the first portion of the gas will be mixed with +the air already in the retort, and I should be obliged to sacrifice the +first portion of the gas, because it would be so much diluted with air; +the first portion must therefore be thrown away. You will find in this +case, that a common spirit-lamp is quite sufficient for me to get the +oxygen, and so we shall have two processes going on for its preparation. +See how freely the gas is coming over from that small portion of the +mixture. We will examine it, and see what are its properties. Now, in this +way we are producing, as you will observe, a gas just like the one we had +in the experiment with the battery, transparent, undissolved by water, and +presenting the ordinary visible properties of the atmosphere. (As this +first jar contains the air, together with the first portions of the oxygen +set free during the preparation, we will carry it out of the way, and be +prepared to make our experiments in a regular, dignified manner.) And, +inasmuch as that power of making wood, wax, or other things burn, was so +marked in the oxygen we obtained by means of the voltaic battery from +water, we may expect to find the same property here. We will try it You +see there is the combustion of a lighted taper in air, and here is its +combustion in this gas [lowering the taper into the jar]. See how brightly +and how beautifully it burns! You can also see more than this,--you will +perceive it is a heavy gas, whilst the hydrogen would go up like a +balloon, or even faster than a balloon, when not encumbered with the +weight of the envelope. + +[Illustration: Fig. 22.] + +You may easily see that although we obtained from water twice as much in +volume of the hydrogen as of oxygen, it does not follow that we have twice +as much in weight--because one is heavy, and the other a very light gas. +We have means of weighing gases or air; but without stopping to explain, +that, let me just tell you what their respective weights are. The weight +of a pint of hydrogen is three-quarters of a grain; the weight of the same +quantity of oxygen is nearly twelve grains. This is a very great +difference. The weight of a cubit foot of hydrogen is one-twelfth of an +ounce; and the weight of a cubit foot of oxygen is one ounce and a third. +And so on we might come to masses of matter which may be weighed in the +balance, and which we can take account of as to hundredweights and as to +tons, as you will see almost immediately. + +Now, as regards this very property of oxygen supporting combustion, which +we may compare to air, I will take a piece of candle to shew it you in a +rough way, and the result will be rough. There is our candle burning in +the air: how will it burn in oxygen? I have here a jar of this gas, and I +am about to put it over the candle for you to compare the action of this +gas with that of the air. Why, look at it: it looks something like the +light you saw at the poles of the voltaic battery. Think how vigorous that +action must be! And yet, during all that action, nothing more is produced +than what is produced by the burning of the candle in air. We have the +same production of water, and the same phenomena exactly, when we use this +gas instead of air, as we have when the candle is burnt in air. + +But now we have got a knowledge of this new substance, we can look at it a +little more distinctly, in order to satisfy ourselves that we have got a +good general understanding of this part of the product of a candle. It is +wonderful how great the supporting powers of this substance are as regards +combustion. For instance, here is a lamp which, simple though it be, is +the original, I may say, of a great variety of lamps which are constructed +for divers purposes--for light-houses, microscopic illuminations, and +other uses; and if it were proposed to make it burn very brightly, you +would say, "If a candle burnt better in oxygen, will not a lamp do the +same?" Why, it will do so. Mr. Anderson will give me a tube coming from +our oxygen reservoir, and I am about to apply it to this flame, which I +will previously make burn badly on purpose. There comes the oxygen: what a +combustion that makes! But if I shut it off, what becomes of the lamp? [The +flow of oxygen was stopped, and the lamp relapsed to its former dimness.] +It is wonderful how, by means of oxygen, we get combustion accelerated. +But it does not affect merely the combustion of hydrogen, or carbon, or +the candle; but it exalts all combustions of the common kind. We will take +one which relates to iron, for instance, as you have already seen iron +burn a little in the atmosphere. Here is a jar of oxygen, and this is a +piece of iron wire; but if it were a bar as thick as my wrist, it would +burn the same. + +[Illustration: Fig. 23.] + +I first attach a little piece of wood to the iron, I then set the wood on +fire and let them both down together into the jar. The wood is now alight, +and there it burns as wood should burn in oxygen; but it will soon +communicate its combustion to the iron. The iron is now burning +brilliantly, and will continue so for a long time. As long as we supply +oxygen, so long can we carry on the combustion of the iron, until the +latter is consumed. + +We will now put that on one side, and take some other substance; but we +must limit our experiments, for we have not time to spare for all the +illustrations you would have a right to if we had more time. We will take +a piece of sulphur--you know how sulphur burns in the air--well, we put it +into the oxygen, and you will see that whatever can burn in air, can burn +with a far greater intensity in oxygen, leading you to think that perhaps +the atmosphere itself owes all its power of combustion to this gas. The +sulphur is now burning very quietly in the oxygen; but you cannot for a +moment mistake the very high and increased action which takes place when +it is so burnt, instead of being burnt merely in common air. + +[Illustration: Fig. 24.] + +I am now about to shew you the combustion of another +substance--phosphorus. I can do it better for you here than you can do it +at home. This is a very combustible substance; and if it be so combustible +in air, what might you expect it would be in oxygen? I am about to shew it +to you not in its fullest intensity, for if I did so we should almost blow +the apparatus up--I may even now crack the jar, though I do not want to +break things carelessly. You see how it burns in the air. But what a +glorious light it gives out when I introduce it into oxygen! [Introducing +the lighted phosphorus into the jar of oxygen.] There you see the solid +particles going off which cause that combustion to be so brilliantly +luminous. + +Thus far we have tested this power of oxygen, and the high combustion it +produces by means of other substances. We must now, for a little while +longer, look at it as respects the hydrogen. You know, when we allowed the +oxygen and the hydrogen derived from the water to mix and burn together, +we had a little explosion. You remember, also, that when I burnt the +oxygen and the hydrogen in a jet together, we got very little light, but +great heat. I am now about to set fire to oxygen and hydrogen, mixed in +the proportion in which they occur in water. Here is a vessel containing +one volume of oxygen and two volumes of hydrogen. This mixture is exactly +of the same nature as the gas we just now obtained from the voltaic +battery: it would be far too much to burn at once; I have therefore +arranged to blow soap-bubbles with it, and burn those bubbles, that we may +see by a general experiment or two how this oxygen supports the combustion +of the hydrogen. First of all, we will see whether we can blow a bubble. +Well, there goes the gas [causing it to issue through a tobacco-pipe into +some soap-suds]. Here I have a bubble. I am receiving them on my hand: and +you will perhaps think I am acting oddly in this experiment; but it is to +shew you that we must not always trust to noise and sounds, but rather to +real facts. [Exploding a bubble on the palm of his hand.] I am afraid to +fire a bubble from the end of the pipe, because the explosion would pass +up into the jar and blow it to pieces. This oxygen then will unite with +the hydrogen, as you see by the phenomena, and hear by the sound, with the +utmost readiness of action, and all its powers are then taken up in its +neutralisation of the qualities of the hydrogen. + +So now I think you will perceive the whole history of water with reference +to oxygen and the air, from what we have before said. Why does a piece of +potassium decompose water? Because it finds oxygen in the water. What is +set free when I put it in the water, as I am about to do again? It sets +free hydrogen, and the hydrogen burns; but the potassium itself combines +with oxygen; and this piece of potassium, in taking the water apart--the +water, you may say, derived from the combustion of the candle--takes away +the oxygen which the candle took from the air, and so sets the hydrogen +free; and even if I take a piece of ice, and put a piece of potassium upon +it, the beautiful affinities by which the oxygen and the hydrogen are +related are such, that the ice will absolutely set fire to the potassium. +I shew this to you to-day, in order to enlarge your ideas of these things, +and that you may see how greatly results are modified by circumstances. +There is the potassium on the ice, producing a sort of volcanic action. + +It will be my place, when next we meet, having pointed out these anomalous +actions, to shew you that none of these extra and strange effects are met +with by us--that none of these strange and injurious actions take place +when we are burning, not merely a candle, but gas in our streets, or fuel +in our fireplaces, so long as we confine ourselves within the laws that +Nature has made for our guidance. + + + + +LECTURE V. + +OXYGEN PRESENT IN THE AIR--NATURE OF THE ATMOSPHERE--ITS PROPERTIES--OTHER +PRODUCTS FROM THE CANDLE--CARBONIC ACID--ITS PROPERTIES. + + +We have now seen that we can produce hydrogen and oxygen from the water +that we obtained from the candle. Hydrogen, you know, comes from the +candle, and oxygen, you believe, comes from the air. But then you have a +right to ask me, "How is it that the air and the oxygen do not equally +well burn the candle?" If you remember what happened when I put a jar of +oxygen over a piece of candle, you recollect there was a very different +kind of combustion to that which took place in the air. Now, why is this? +It is a very important question, and one I shall endeavour to make you +understand: it relates most intimately to the nature of the atmosphere, +and is most important to us. + +We have several tests for oxygen besides the mere burning of bodies. You +have seen a candle burnt in oxygen, or in the air; you have seen +phosphorus burnt in the air, or in oxygen; and you have seen iron-filings +burnt in oxygen. But we have other tests besides these, and I am about to +refer to one or two of them for the purpose of carrying your conviction +and your experience further. Here we have a vessel of oxygen. I will shew +its presence to you: if I take a little spark and put it into that oxygen, +you know, by the experience you gained the last time we met, what will +happen; if I put that spark into the jar, it will tell you whether we have +oxygen here or not. Yes! We have proved it by combustion; and now here is +another test for oxygen, which is a very curious and useful one. I have +here two jars full of gas, with a plate between them to prevent their +mixing; I take the plate away, and the gases are creeping one into the +other. "What happens?" say you: "they together produce no such combustion +as was seen in the case of the candle." But see how the presence of oxygen +is told by its association with this other substance[14]. What a +beautifully coloured gas I have obtained in this way, shewing me the +presence of the oxygen! In the same way we can try this experiment by +mixing common air with this test-gas. Here is a jar containing air--such +air as the candle would burn in--and here is a jar or bottle containing +the test-gas. I let them come together over water, and you see the result: +the contents of the test-bottle are flowing into the jar of air, and you +see I obtain exactly the same kind of action as before, and that shews me +that there is oxygen in the air--the very same substance that has been +already obtained by us from the water produced by the candle. But then, +beyond that, how is it that the candle does not burn in air as well as in +oxygen? We will come to that point at once. I have here two jars; they are +filled to the same height with gas, and the appearance to the eye is alike +in both, and I really do not know at present which of these jars contains +oxygen and which contains air, although I know they have previously been +filled with these gases. But here is our test-gas, and I am going to work +with the two jars, in order to examine whether there is any difference +between them in the quality of reddening this gas. I am now going to turn +this test-gas into one of the jars, and observe what happens. There is +reddening, you see; there is then oxygen present. We will now test the +other jar; but you see this is not so distinctly red as the first: and, +further, this curious thing happens,--if I take these two gases and shake +them well together with water, we shall absorb the red gas; and then, if I +put in more of this test-gas and shake again, we shall absorb more; and I +can go on as long as there be any oxygen present to produce that effect. +If I let in air, it will not matter; but the moment I introduce water, the +red gas disappears; and I may go on in this way, putting in more and more +of the test-gas, until I come to something left behind which will not +redden any longer by the use of that particular body that rendered the air +and the oxygen red. Why is that? You see in a moment it is because there +is, besides oxygen, something else present which is left behind. I will +let a little more air into the jar, and if it turns red you will know that +some of that reddening gas is still present, and that consequently it was +not for the want of this producing body that that air was left behind. + +Now, you will begin to understand what I am about to say. You saw that +when I burnt phosphorus in a jar, as the smoke produced by the phosphorus +and the oxygen of the air condensed, it left a good deal of gas unburnt, +just as this red gas left something untouched,--there was, in fact, this +gas left behind, which the phosphorus cannot touch, which the reddening +gas cannot touch, and this something is not oxygen, and yet is part of the +atmosphere. + +So that is one way of opening out air into the two things of which it is +composed--oxygen, which burns our candles, our phosphorus, or anything +else; and this other substance--nitrogen--which will not burn them. This +other part of the air is by far the larger proportion, and it is a very +curious body, when we come to examine it; it is remarkably curious, and +yet you say, perhaps, that it is very uninteresting. It is uninteresting +in some respects because of this--that it shews no brilliant effects of +combustion. If I test it with a taper as I do oxygen and hydrogen, it +does not burn like hydrogen, nor does it make the taper burn like oxygen. +Try it in any way I will, it does neither the one thing nor the other: it +will not take fire; it will not let the taper burn; it puts out the +combustion of everything. There is nothing that will burn in it in common +circumstances. It has no smell; it is not sour; it does not dissolve in +water; it is neither an acid nor an alkali; it is as indifferent to all +our organs as it is possible for a thing to be. And you might say, "It is +nothing; it is not worth chemical attention; what does it do in the air?" +Ah! then come our beautiful and fine results shewn us by an observant +philosophy. Suppose, in place of having nitrogen, or nitrogen and oxygen, +we had pure oxygen as our atmosphere; what would become of us? You know +very well that a piece of iron lit in a jar of oxygen goes on burning to +the end. When you see a fire in an iron grate, imagine where the grate +would go to if the whole of the atmosphere were oxygen. The grate would +burn up more powerfully than the coals--for the iron of the grate itself +is even more combustible than the coals which we burn in it. A fire put +into the middle of a locomotive would be a fire in a magazine of fuel, if +the atmosphere were oxygen. The nitrogen lowers it down and makes it +moderate and useful for us, and then, with all that, it takes away with it +the fumes that you have seen produced from the candle, disperses them +throughout the whole of the atmosphere, and carries them away to places +where they are wanted to perform a great and glorious purpose of good to +man, for the sustenance of vegetation; and thus does a most wonderful +work, although you say, on examining it, "Why, it is a perfectly +indifferent thing." This nitrogen in its ordinary state is an inactive +element; no action short of the most intense electric force, and then in +the most infinitely small degree, can cause the nitrogen to combine +directly with the other element of the atmosphere, or with other things +round about it; it is a perfectly indifferent, and therefore to say, a +safe substance. + +But before I take you to that result, I must tell you about the atmosphere +itself. I have written on this diagram the composition of one hundred +parts of atmospheric air:-- + + Bulk. Weight. +Oxygen, . . . . . 20 22.3 +Nitrogen, . . . . 80 77.7 + ---- ----- + l00 100.0 + +It is a true analysis of the atmosphere, so far as regards the quantity of +oxygen and the quantity of nitrogen present. By our analysis, we find that +5 pints of the atmosphere contain only 1 pint of oxygen, and 4 pints, or 4 +parts, of nitrogen by bulk. That is our analysis of the atmosphere. It +requires all that quantity of nitrogen to reduce the oxygen down, so as to +be able to supply the candle properly with fuel, so as to supply us with +an atmosphere which our lungs can healthily and safely breathe; for it is +just as important to make the oxygen right for us to breathe, as it is to +make the atmosphere right for the burning of the fire and the candle. + +But now for this atmosphere. First of all, let me tell you the weight of +these gases. A pint of nitrogen weighs 10-4/10 grains, or a cubic foot +weighs 1-1/6 ounce. That is the weight of the nitrogen. The oxygen is +heavier: a pint of it weighs 11-9/10 grains, and a cubic foot weighs 1-3/4 +ounce. A pint of air weighs about 10-7/10 grains, and a cubic foot 1-1/5 +ounce. + +[Illustration: Fig. 25.] + +You have asked me several times, and I am very glad you have, "How do you +weigh gases?" I will shew you; it is very simple, and easily done. Here is +a balance, and here a copper bottle, made as light as we can consistent +with due strength, turned very nicely in the lathe, and made perfectly +air-tight, with a stop-cock, which we can open and shut, which at present +is open, and therefore allows the bottle to be full of air. I have here a +nicely-adjusted balance, in which I think the bottle, in its present +condition, will be balanced by the weight on the other side. And here is a +pump by which we can force the air into this bottle, and with it we will +force in a certain number of volumes of air, as measured by the pump. +[Twenty measures were pumped in.] We will shut that in and put it in the +balance. See how it sinks: it is much heavier than it was. By what? By +the air that we have forced into it by the pump. There is not a greater +_bulk_ of air, but there is the same bulk of _heavier_ air, because we +have forced in air upon it. And that you may have a fair notion in your +mind as to how much this air measures, here is a jar full of water. We +will open that copper vessel into this jar, and let the air return to its +former state. All I have to do now is to screw them tightly together, and +to turn the taps, when there, you see, is the bulk of the twenty pumps of +air which I forced into the bottle; and to make sure that we have been +quite correct in what we have been doing, we will take the bottle again to +the balance, and, if it is now counterpoised by the original weight, we +shall be quite sure we have made our experiment correctly. + +[Illustration: Fig. 26.] + +It is balanced; so, you see, we can find out the weight of the extra +volumes of air forced in, in that way, and by that means we are able to +ascertain that a cubic foot of air weighs 1-1/5 ounce. But that small +experiment will by no means convey to your mind the whole literal truth of +this matter. It is wonderful how it accumulates when you come to larger +volumes. This bulk of air [a cubic foot] weighs 1-1/5 ounce. What do you +think of the contents of that box above there, which I have had made for +the purpose? The air which is within that box weighs one pound--a full +pound; and I have calculated the weight of the air in this room,--you +would hardly imagine it, but it is above a ton. So rapidly do the weights +rise up, and so important is the presence of the atmosphere, and of the +oxygen and the nitrogen in it, and the use it performs in conveying things +to and fro from place to place, and carrying bad vapours to places where +they will do good instead of harm. + +Having given you that little illustration with respect to the weight of +the air, let me shew you certain consequences of it. You have a right to +them, because you would not understand so much without it. Do you remember +this kind of experiment? Have you ever seen it? Suppose I take a pump +somewhat similar to the one I had a little while ago to force air into the +bottle, and suppose I place it in such a manner that by certain +arrangements I can apply my hand to it: my hand moves about in the air so +easily that it seems to feel nothing, and I can hardly get velocity enough +by any motion of my own in the atmosphere to make sure that there is much +resistance to it. + +[Illustration: Fig. 27.] + +But, when I put my hand here [on the air-pump receiver, which was +afterwards exhausted], you see what happens. Why is my hand fastened to +this place, and why am I able to pull this pump about? And see! how is it +that I can hardly get my hand away? Why is this? It is the weight of the +air--the weight of the air that is above. I have another experiment here, +which I think will explain to you more about it. When the air is pumped +from underneath the bladder which is stretched over this glass, you will +see the effect in another shape: the top is quite flat at present, but I +will make a very little motion with the pump, and now look at it--see how +it has gone down, see how it is bent in. You will see the bladder go in +more and more, until at last I expect it will be driven in and broken by +the force of the atmosphere pressing upon it. + +[Illustration: Fig. 28.] + +[The bladder at last broke with a loud report.] Now, that was done +entirely by the weight of the air pressing on it, and you can easily +understand how that is. The particles that are piled up in the atmosphere +stand upon each other, as these five cubes do. You can easily conceive +that four of these five cubes are resting upon the bottom one, and if I +take that away, the others will all sink down. So it is with the +atmosphere: the air that is above is sustained by the air that is beneath; +and when the air is pumped away from beneath them, the change occurs which +you saw when I placed my hand on the air-pump, and which you saw in the +case of the bladder, and which you shall see better here. I have tied over +this jar a piece of sheet india-rubber, and I am now about to take away +the air from the inside of the jar; and if you will watch the +india-rubber--which acts as a partition between the air below and the air +above--you will see, when I pump, how the pressure shews itself. See where +it is going to--I can actually put my hand into the jar; and yet this +result is only caused by the great and powerful action of the air above. +How beautifully it shews this curious circumstance! + +Here is something that you can have a pull at, when I have finished +to-day. It is a little apparatus of two hollow brass hemispheres, closely +fitted together, and having connected with it a pipe and a cock, through +which we can exhaust the air from the inside; and although the two halves +are so easily taken apart, while the air is left within, yet you will see, +when we exhaust it by-and-by, no power of any two of you will be able to +pull them apart. Every square inch of surface that is contained in the +area of that vessel sustains fifteen pounds by weight, or nearly so, when +the air is taken out; and you may try your strength presently in seeing +whether you can overcome that pressure of the atmosphere. + +Here is another very pretty thing--the boys' sucker, only refined by the +philosopher. We young ones have a perfect right to take toys, and make +them into philosophy, inasmuch as now-a-days we are turning philosophy +into toys. Here is a sucker, only it is made of india-rubber: if I clap it +upon the table, you see at once it holds. Why does it hold? I can slip it +about, and yet if I try to pull it up, it seems as if it would pull the +table with it I can easily make it slip about from place to place; but +only when I bring it to the edge of the table can I get it off. It is only +kept down by the pressure of the atmosphere above. We have a couple of +them; and if you take these two and press them together, you will see how +firmly they stick. And, indeed, we may use them as they are proposed to be +used, to stick against windows, or against walls, where they will adhere +for an evening, and serve to hang anything on that you want. I think, +however, that you boys ought to be shewn experiments that you can make at +home; and so here is a very pretty experiment in illustration of the +pressure of the atmosphere. Here is a tumbler of water. Suppose I were to +ask you to turn that tumbler upside-down, so that the water should not +fall out, and yet not be kept in by your hand, but merely by using the +pressure of the atmosphere. Could you do that? Take a wine-glass, either +quite full or half-full of water, and put a flat card on the top, turn it +upside-down, and then see what becomes of the card and of the water. The +air cannot get in because the water by its capillary attraction round the +edge keeps it out. + +I think this will give you a correct notion of what you may call the +materiality of the air; and when I tell you that the box holds a pound of +it, and this room more than a ton, you will begin to think that air is +something very serious. I will make another experiment, to convince you of +this positive resistance. There is that beautiful experiment of the +popgun, made so well and so easily, you know, out of a quill, or a tube, +or anything of that kind,--where we take a slice of potato, for instance, +or an apple, and take the tube and cut out a pellet, as I have now done, +and push it to one end. I have made that end tight; and now I take another +piece and put it in: it will confine the air that is within the tube +perfectly and completely for our purpose; and I shall now find it +absolutely impossible by any force of mine to drive that little pellet +close up to the other. It cannot be done. I may press the air to a certain +extent, but if I go on pressing, long before it comes to the second, the +confined air will drive the front one out with a force something like that +of gunpowder; for gunpowder is in part dependent upon the same action that +you see here exemplified. + +I saw the other day an experiment which pleased me much, as I thought it +would serve our purpose here. (I ought to have held my tongue for four or +five minutes before beginning this experiment, because it depends upon my +lungs for success.) By the proper application of air I expect to be able +to drive this egg out of one cup into the other by the force of my breath; +but if I fail, it is in a good cause; and I do not promise success, +because I have been talking more than I ought to do to make the experiment +succeed. + +[The Lecturer here tried the experiment, and succeeded in blowing the egg +from one egg-cup to the other.] + +You see that the air which I blow goes downwards between the egg and the +cup, and makes a blast under the egg, and is thus able to lift a heavy +thing--for a full egg is a very heavy thing for air to lift. If you want +to make the experiment, you had better boil the egg quite hard first, and +then you may very safely try to blow it from one cup to the other, with a +little care. + +I have now kept you long enough upon this property of the weight of the +air, but there is another thing I should like to mention. You saw the way +in which, in this popgun, I was able to drive the second piece of potato +half or two-thirds of an inch before the first piece started, by virtue of +the elasticity of the air--just as I pressed into the copper bottle the +particles of air by means of the pump. Now, this depends upon a wonderful +property in the air, namely, its elasticity; and I should like to give you +a good illustration of this. If I take anything that confines the air +properly, as this membrane, which also is able to contract and expand so +as to give us a measure of the elasticity of the air, and confine in this +bladder a certain portion of air; and then, if we take the atmosphere off +from the outside of it, just as in these cases we put the pressure on--if +we take the pressure off, you will see how it will then go on expanding +and expanding, larger and larger, until it will fill the whole of this +bell-jar, shewing you that wonderful property of the air, its elasticity, +its compressibility, and expansibility, to an exceedingly large extent, +and which is very essential for the purposes and services it performs in +the economy of creation. + +We will now turn to another very important part of our subject, +remembering that we have examined the candle in its burning, and have +found that it gives rise to various products. We have the products, you +know, of soot, of water, and of something else which you have not yet +examined. We have collected the water, but have allowed the other things +to go into the air. Let us now examine some of these other products. + +Here is an experiment which I think will help you in part in this way. We +will put our candle there, and place over it a chimney, thus. I think my +candle will go on burning, because the air-passage is open at the bottom +and the top. In the first place, you see the moisture appearing--that you +know about. It is water produced from the candle by the action of the air +upon its hydrogen. But, besides that, something is going out at the top: +it is not moisture--it is not water--it is not condensible; and yet, after +all, it has very singular properties. You will find that the air coming +out of the top of our chimney is nearly sufficient to blow the light out I +am holding to it; and if I put the light fairly opposed to the current, it +will blow it quite out. You will say that is as it should be; and I am +supposing that you think it ought to do so, because the nitrogen does not +support combustion, and ought to put the candle out, since the candle will +not burn in nitrogen. + +[Illustration: Fig. 29.] + +But is there nothing else there than nitrogen? I must now anticipate--that +is to say, I must use my own knowledge to supply you with the means that +we adopt for the purpose of ascertaining these things, and examining such +gases as these. I will take an empty bottle--here is one--and if I hold it +over this chimney, I shall get the combustion of the candle below sending +its results into the bottle above; and we shall soon find that this bottle +contains, not merely an air that is bad as regards the combustion of a +taper put into it, but having other properties. + +Let me take a little quick-lime and pour some common water on to it--the +commonest water will do. I will stir it a moment, then pour it upon a +piece of filtering paper in a funnel, and we shall very quickly have a +clear water proceeding to the bottle below, as I have here. I have plenty +of this water in another bottle; but, nevertheless, I should like to use +the lime-water that was prepared before you, so that you may see what its +uses are. If I take some of this beautiful clear lime-water, and pour it +into this jar, which has collected the air from the candle, you will see a +change coming about. Do you see that the water has become quite milky? +Observe, that will not happen with air merely. Here is a bottle filled +with air; and if I put a little lime-water into it, neither the oxygen nor +the nitrogen, nor anything else that is in that quantity of air, will make +any change in the lime-water. It remains perfectly clear, and no shaking +of that quantity of lime-water with that quantity of air in its common +state will cause any change; but if I take this bottle with the +lime-water, and hold it so as to get the general products of the candle in +contact with it, in a very short time we shall have it milky. There is the +chalk, consisting of the lime which we used in making the lime-water, +combined with something that came from the candle--that other product +which we are in search of, and which I want to tell you about to-day. This +is a substance made visible to us by its action, which is not the action +of the lime-water either upon the oxygen or upon the nitrogen, nor upon +the water itself, but it is something new to us from the candle. And then +we find this white powder, produced by the lime-water and the vapour from +the candle, appears to us very much like whitening or chalk, and, when +examined, it does prove to be exactly the same substance as whitening or +chalk. So we are led, or have been led, to observe upon the various +circumstances of this experiment, and to trace this production of chalk to +its various causes, to give us the true knowledge of the nature of this +combustion of the candle--to find that this substance, issuing from the +candle, is exactly the same as that substance which would issue from a +retort, if I were to put some chalk into it with a little moisture, and +make it red-hot: you would then find that exactly the same substance would +issue from it as from the candle. + +But we have a better means of getting this substance, and in greater +quantity, so as to ascertain what its general characters are. We find this +substance in very great abundance in a multitude of cases where you would +least expect it. All limestones contain a great deal of this gas which +issues from the candle, and which we call _carbonic acid_. All chalks, all +shells, all corals contain a great quantity of this curious air. We find +it fixed in these stones; for which reason Dr. Black called it "fixed +air"--finding it in these fixed things like marble and chalk. He called it +fixed air, because it lost its quality of air, and assumed the condition +of a solid body. We can easily get this air from marble. Here is a jar +containing a little muriatic acid, and here is a taper which, if I put it +into that jar, will shew only the presence of common air. There is, you +see, pure air down to the bottom; the jar is full of it Here is a +substance--marble[17], a very beautiful and superior marble--and if I put +these pieces of marble into the jar, a great boiling apparently goes on. +That, however, is not steam--it is a gas that is rising up; and if I now +search the jar by a candle, I shall have exactly the same effect produced +upon the taper as I had from the air which issued from the end of the +chimney over the burning candle. It is exactly the same action, and caused +by the very same substance that issued from the candle; and in this way we +can get carbonic acid in great abundance--we have already nearly filled +the jar. We also find that this gas is not merely contained in marble. +Here is a vessel in which I have put some common whitening--chalk, which +has been washed in water and deprived of its coarser particles, and so +supplied to the plasterer as whitening. Here is a large jar containing +this whitening and water, and I have here some strong sulphuric acid, +which is the acid you might have to use if you were to make these +experiments (only, in using this acid with limestone, the body that is +produced is an insoluble substance, whereas the muriatic acid produces a +soluble substance that does not so much thicken the water). And you will +seek out a reason why I take this kind of apparatus for the purpose of +shewing this experiment. I do it because you may repeat in a small way +what I am about to do in a large one. You will have here just the same +kind of action; and I am evolving in this large jar carbonic acid, exactly +the same in its nature and properties as the gas which we obtained from +the combustion of the candle in the atmosphere. And no matter how +different the two methods by which we prepare this carbonic acid, you will +see, when we get to the end of our subject, that it is all exactly the +same, whether prepared in the one way or in the other. + +We will now proceed to the next experiment with regard to this gas. What +is its nature? Here is one of the vessels full, and we will try it, as we +have done so many other gases, by combustion. You see it is not +combustible, nor does it support combustion. Neither, as we know, does it +dissolve much in water, because we collect it over water very easily. +Then, you know that it has an effect, and becomes white in contact with +lime-water; and when it does become white in that way, it becomes one of +the constituents to make carbonate of lime or limestone. + +The next thing I must shew you is, that it really does dissolve a little +in water, and therefore that it is unlike oxygen and hydrogen in that +respect I have here an apparatus by which we can produce this solution. In +the lower part of this apparatus is marble and acid, and in the upper part +cold water. The valves are so arranged that the gas can get from one to +the other. I will set it in action now, and you can see the gas bubbling +up through the water, as it has been doing all night long, and by this +time we shall find that we have this substance dissolved in the water. If +I take a glass and draw off some of the water, I find that it tastes a +little acid to the mouth: it is impregnated with carbonic acid; and if I +now apply a little lime-water to it, that will give us a test of its +presence. This water will make the lime-water turbid and white, which is +proof of the presence of carbonic acid. + +Then it is a very weighty gas--it is heavier than the atmosphere. I have +put their respective weights at the lower part of this table, along with, +for comparison, the weights of the other gases we have been examining:-- + + Pint. Cubic Foot. +Hydrogen, . . . . 3/4 grains. 1/12 ounce. +Oxygen, . . . . 11-9/10 " 1-1/2 " +Nitrogen, . . . . 10-1/10 " 1-1/4 " +Air,. . . . . . 10-7/16 " 1-3/8 " +Carbonic acid, . . 16-1/3 " 1-9/10 " + +A pint of it weighs 16-1/3 grains, and a cubic foot weighs 1-9/10 ounce, +almost two ounces. You can see by many experiments that this is a heavy +gas. Suppose I take a glass containing nothing else but air, and from this +vessel containing the carbonic acid I attempt to pour a little of this gas +into that glass; I wonder whether any has gone in or not. I cannot tell by +the appearance, but I can in this way [introducing the taper]. Yes, there +it is, you see; and if I were to examine it by lime-water, I should find +it by that test also. I will take this little bucket, and put it down into +the well of carbonic acid--indeed, we too often have real wells of +carbonic acid--and now, if there is any carbonic acid, I must have got to +it by this time, and it will be in this bucket, which we will examine with +a taper. There it is, you see; it is full of carbonic acid. + +[Illustration: Fig. 30.] + +There is another experiment by which I will shew you its weight. I have +here a jar suspended at one end of a balance--it is now equipoised; but +when I pour this carbonic acid into the jar on the one side which now +contains air, you will see it sink down at once, because of the carbonic +acid that I pour into it. And now, if I examine this jar with the lighted +taper, I shall find that the carbonic acid has fallen into it, and it no +longer has any power of supporting the combustion. If I blow a +soap-bubble, which of course will be filled with air, and let it fall into +this jar of carbonic acid, it will float. + +[Illustration: Fig. 31.] + +But I shall first of all take one of these little balloons filled with +air. I am not quite sure where the carbonic acid is; we will just try the +depth, and see whereabouts is its level. There, you see, we have this +bladder floating on the carbonic acid; and if I evolve some more of the +carbonic acid, the bladder will be lifted up higher. There it goes--the +jar is nearly full; and now I will see whether I can blow a soap-bubble on +that, and float it in the same way. [The Lecturer here blew a soap-bubble, +and allowed it to fall into the jar of carbonic acid, when it floated in +it midway.] It is floating, as the balloon floated, by virtue of the +greater weight of the carbonic acid than of the air. And now, having so +far given you the history of the carbonic acid--as to its sources in the +candle, as to its physical properties and weight--when we next meet I +shall shew you of what it is composed, and where it gets its elements +from. + + + + +LECTURE VI. + +CARBON OR CHARCOAL--COAL GAS--RESPIRATION AND ITS ANALOGY TO THE BURNING +OF A CANDLE--CONCLUSION. + + +A lady, who honours me by her presence at these Lectures, has conferred a +still further obligation by sending me these two candles, which are from +Japan, and, I presume, are made of that substance to which I referred in a +former lecture. You see that they are even far more highly ornamented than +the French candles; and, I suppose, are candles of luxury, judging from +their appearance. They have a remarkable peculiarity about them--namely, a +hollow wick,--that beautiful peculiarity which Argand introduced into the +lamp, and made so valuable. To those who receive such presents from the +East, I may just say that this and such like materials gradually undergo a +change which gives them on the surface a dull and dead appearance; but +they may easily be restored to their original beauty, if the surface be +rubbed with a clean cloth or silk handkerchief, so as to polish the little +rugosity or roughness: this will restore the beauty of the colours. I have +so rubbed one of these candles, and you see the difference between it and +the other which has not been polished, but which may be restored by the +same process. Observe, also, that these moulded candles from Japan are +made more conical than the moulded candles in this part of the world. + +I told you, when we last met, a good deal about carbonic acid. We found, +by the lime-water test, that when the vapour from the top of the candle or +lamp was received into bottles, and tested by this solution of lime-water +(the composition of which I explained to you, and which you can make for +yourselves), we had that white opacity which was in fact calcareous +matter, like shells and corals, and many of the rocks and minerals in the +earth. But I have not yet told you fully and clearly the chemical history +of this substance--carbonic acid--as we have it from the candle, and I +must now resume that subject. We have seen the products, and the nature of +them, as they issue from the candle. We have traced the water to its +elements, and now we have to see where are the elements of the carbonic +acid supplied by the candle. A few experiments will shew this. You +remember that when a candle burns badly, it produces smoke; but if it is +burning well, there is no smoke. And you know that the brightness of the +candle is due to this smoke, which becomes ignited. Here is an experiment +to prove this: so long as the smoke remains in the flame of the candle and +becomes ignited, it gives a beautiful light, and never appears to us in +the form of black particles. I will light some fuel, which is extravagant +in its burning. This will serve our purpose--a little turpentine on a +sponge. You see the smoke rising from it, and floating into the air in +large quantities; and, remember now, the carbonic acid that we have from +the candle is from such smoke as that. To make that evident to you, I will +introduce this turpentine burning on the sponge into a flask where I have +plenty of oxygen, the rich part of the atmosphere, and you now see that +the smoke is all consumed. This is the first part of our experiment; and +now, what follows? The carbon which you saw flying off from the turpentine +flame in the air is now entirely burned in this oxygen, and we shall find +that it will, by this rough and temporary experiment, give us exactly the +same conclusion and result as we had from the combustion of the candle. +The reason why I make the experiment in this manner is solely that I may +cause the steps of our demonstration to be so simple that you can never +for a moment lose the train of reasoning, if you only pay attention. All +the carbon which is burned in oxygen, or air, comes out as carbonic acid, +whilst those particles which are not so burned shew you the second +substance in the carbonic acid--namely, the carbon--that body which made +the flame so bright whilst there was plenty of air, but which was thrown +off in excess when there was not oxygen enough to burn it. + +I have also to shew you a little more distinctly the history of carbon and +oxygen, in their union to make carbonic acid. You are now better able to +understand this than before, and I have prepared three or four experiments +by way of illustration. This jar is filled with oxygen, and here is some +carbon which has been placed in a crucible, for the purpose of being made +red-hot. I keep my jar dry, and venture to give you a result imperfect in +some degree, in order that I may make the experiment brighter. I am about +to put the oxygen and the carbon together. That this is carbon (common +charcoal pulverised), you will see by the way in which it burns in the air +[letting some of the red-hot charcoal fall out of the crucible]. I am now +about to burn it in oxygen gas, and look at the difference. It may appear +to you at a distance as if it were burning with a flame; but it is not so. +Every little piece of charcoal is burning as a spark, and whilst it so +burns it is producing carbonic acid. I specially want these two or three +experiments to point out what I shall dwell upon more distinctly +by-and-by--that carbon burns in this way, and not as a flame. + +Instead of taking many particles of carbon to burn, I will take a rather +large piece, which will enable you to see the form and size; and to trace +the effects very decidedly. Here is the jar of oxygen, and here is the +piece of charcoal, to which I have fastened a little piece of wood, which +I can set fire to, and so commence the combustion, which I could not +conveniently do without. You now see the charcoal burning, but not as a +flame (or if there be a flame, it is the smallest possible one, which I +know the cause of--namely, the formation of a little carbonic oxide close +upon the surface of the carbon). It goes on burning, you see, slowly +producing carbonic acid by the union of this carbon or charcoal (they are +equivalent terms) with the oxygen. I have here another piece of charcoal, +a piece of bark, which has the quality of being blown to pieces--exploding +as it burns. By the effect of the heat, we shall reduce the lump of carbon +into particles that will fly off; still every particle, equally with the +whole mass, burns in this peculiar way: it burns as a coal, and not like a +flame. You observe a multitude of little combustions going on, but no +flame. I do not know a finer experiment than this, to shew that carbon +burns with a spark. + +Here, then, is carbonic acid formed from its elements. It is produced at +once; and if we examined it by lime-water, you will see that we have the +same substance which I have previously described to you. By putting +together 6 parts of carbon by weight (whether it comes from the flame of a +candle or from powdered charcoal) and 16 parts of oxygen by weight, we +have 22 parts of carbonic acid; and, as we saw last time, the 22 parts of +carbonic acid, combined with 28 parts of lime, produced common carbonate +of lime. If you were to examine an oyster-shell, and weigh the component +parts, you would find that every 50 parts would give 6 of carbon and 16 of +oxygen, combined with 28 of lime. However, I do not want to trouble you +with these minuti--it is only the general philosophy of the matter that +we can now go into. See how finely the carbon is dissolving away [pointing +to the lump of charcoal burning quietly in the jar of oxygen]. You may say +that the charcoal is actually dissolving in the air round about; and if +that were perfectly pure charcoal, which we can easily prepare, there +would be no residue whatever. When we have a perfectly cleansed and +purified piece of carbon, there is no ash left. The carbon burns as a +solid dense body, that heat alone cannot change as to its solidity, and +yet it passes away into vapour that never condenses into solid or liquid +under ordinary circumstances; and what is more curious still, is the fact +that the oxygen does not change in its bulk by the solution of the carbon +in it. Just as the bulk is at first, so it is at last, only it has become +carbonic acid. + +There is another experiment which I must give you before you are fully +acquainted with the general nature of carbonic acid. Being a compound +body, consisting of carbon and oxygen, carbonic acid is a body that we +ought to be able to take asunder. And so we can. As we did with water, so +we can with carbonic acid--take the two parts asunder. The simplest and +quickest way is to act upon the carbonic acid by a substance that can +attract the oxygen from it, and leave the carbon behind. You recollect +that I took potassium and put it upon water or ice, and you saw that it +could take the oxygen from the hydrogen. Now, suppose we do something of +the same kind here with this carbonic acid. You know carbonic acid to be a +heavy gas. I will not test it with lime-water, as that will interfere with +our subsequent experiments; but I think the heaviness of the gas and the +power of extinguishing flame will be sufficient for our purpose. I +introduce a flame into the gas, and you will see whether it will be put +out. You see the light is extinguished. Indeed, the gas may, perhaps, put +out phosphorus, which, you know, has a pretty strong combustion. Here is a +piece of phosphorus heated to a high degree. I introduce it into gas, and +you observe the light is put out; but it will take fire again in the air, +because there it re-enters into combustion. Now, let me take a piece of +potassium, a substance which, even at common temperatures, can act upon +carbonic acid, though not sufficiently for our present purpose, because it +soon gets covered with a protecting coat; but if we warm it up to the +burning point in air, as we have a fair right to do, and as we have done +with phosphorus, you will see that it can burn in carbonic acid; and if it +burns, it will burn by taking oxygen, so that you will see what is left +behind. I am going, then, to burn this potassium in the carbonic acid, as +a proof of the existence of oxygen in the carbonic acid. [In the +preliminary process of heating, the potassium exploded.] Sometimes we get +an awkward piece of potassium that explodes, or something like it, when it +burns. I will take another piece; and now that it is heated, I introduce +it into the jar, and you perceive that it burns in the carbonic acid--not +so well as in the air, because the carbonic acid contains the oxygen +combined; but it does burn, and takes away the oxygen. If I now put this +potassium into water, I find that, besides the potash formed (which you +need not trouble about), there is a quantity of carbon produced. I have +here made the experiment in a very rough way; but I assure you that if I +were to make it carefully, devoting a day to it, instead of five minutes, +we should get all the proper amount of charcoal left in the spoon, or in +the place where the potassium was burned, so that there could be no doubt +as to the result. Here, then, is the carbon obtained from the carbonic +acid, as a common black substance; so that you have the entire proof of +the nature of carbonic acid as consisting of carbon and oxygen. And now, I +may tell you, that _whenever_ carbon burns under common circumstances, it +produces carbonic acid. + +Suppose I take this piece of wood, and put it into a bottle with +lime-water. I might shake that lime-water up with wood and the atmosphere +as long as I pleased, it would still remain clear as you see it; but +suppose I burn the piece of wood in the air of that bottle. You, of +course, know I get water. Do I get carbonic acid? [The experiment was +performed.] There it is, you see--that is to say, the carbonate lime, +which results from carbonic acid, and that carbonic acid must be formed +from the carbon which comes from the wood, from the candle, or any other +thing. Indeed, you have yourselves frequently tried a very pretty +experiment, by which you may see the carbon in wood. If you take a piece +of wood, and partly burn it, and then blow it out, you have carbon left. +There are things that do not shew carbon in this way. A candle does not +shew it, but it contains carbon. Here also is a jar of coal-gas, which +produces carbonic acid abundantly. You do not see the carbon, but we can +soon shew it to you. I will light it, and as long as there is any gas in +this cylinder it will go on burning. You see no carbon, but you see a +flame; and because that is bright, it will lead you to guess that there is +carbon in the flame. But I will shew it to you by another process. I have +some of the same gas in another vessel, mixed with a body that will burn +the hydrogen of the gas, but will not burn the carbon. I will light them +with a burning taper, and you perceive the hydrogen is consumed, but not +the carbon, which is left behind as a dense black smoke. I hope that by +these three or four experiments you will learn to see when carbon is +present, and understand what are the products of combustion, when gas or +other bodies are thoroughly burned in the air. + +Before we leave the subject of carbon, let us make a few experiments and +remarks upon its wonderful condition as respects ordinary combustion. I +have shewn you that the carbon in burning burns only as a solid body, and +yet you perceive that, after it is burned, it ceases to be a solid. There +are very few fuels that act like this. It is, in fact, only that great +source of fuel, the carbonaceous series, the coals, charcoals, and woods, +that can do it. I do not know that there is any other elementary substance +besides carbon that burns with these conditions; and if it had not been +so, what would happen to us? Suppose all fuel had been like iron, which, +when it burns, burns into a solid substance. We could not then have such a +combustion as you have in this fire-place. Here also is another kind of +fuel which burns very well--as well as, if not better, than carbon--so +well, indeed, as to take fire of itself when it is in the air, as you see +[breaking a tube full of lead pyrophorus]. This substance is lead, and you +see how wonderfully combustible it is. It is very much divided, and is +like a heap of coals in the fireplace; the air can get to its surface and +inside, and so it burns. But why does it not burn in that way now, when it +is lying in a mass? [emptying the contents of the tube in a heap on to a +plate of iron]. Simply because the air cannot get to it. Though it can +produce a great heat, the great heat which we want in our furnaces and +under our boilers, still that which is produced cannot get away from the +portion which remains unburned underneath, and that portion, therefore, is +prevented from coming in contact with the atmosphere, and cannot be +consumed. How different is that from carbon. Carbon burns just in the same +way as this lead does, and so gives an intense fire in the furnace, or +wherever you choose to burn it; but then the body produced by its +combustion passes away, and the remaining carbon is left clear. I shewed +you how carbon went on dissolving in the oxygen, leaving no ash; whereas +here [pointing to the heap of pyrophorus] we have actually more ash than +fuel, for it is heavier by the amount of the oxygen which has united with +it. Thus you see the difference between carbon and lead or iron: if we +choose iron, which gives so wonderful a result in our application of this +fuel, either as light or heat. If, when the carbon burnt, the product went +off as a solid body, you would have had the room filled with an opaque +substance, as in the case of the phosphorus; but when carbon burns, +everything passes up into the atmosphere. It is in a fixed, almost +unchangeable condition before the combustion; but afterwards it is in the +form of gas, which it is very difficult (though we have succeeded) to +produce in a solid or a liquid state. + +Now, I must take you to a very interesting part of our subject--to the +relation between the combustion of a candle and that living kind of +combustion which goes on within us. In every one of us there is a living +process of combustion going on very similar to that of a candle; and I +must try to make that plain to you. For it is not merely true in a +poetical sense--the relation of the life of man to a taper; and if you +will follow, I think I can make this clear. In order to make the relation +very plain, I have devised a little apparatus which we can soon build up +before you. Here is a board and a groove cut in it, and I can close the +groove at the top part by a little cover. I can then continue the groove +as a channel by a glass tube at each end, there being a free passage +through the whole. Suppose I take a taper or candle (we can now be liberal +in our use of the word "candle," since we understand what it means), and +place it in one of the tubes; it will go on, you see, burning very well. +You observe that the air which feeds the flame passes down the tube at one +end, then goes along the horizontal tube, and ascends the tube at the +other end in which the taper is placed. + +[Illustration: Fig. 32] + +If I stop the aperture through which the air enters, I stop combustion, as +you perceive. I stop the supply of air, and consequently the candle goes +out. But, now, what will you think of this fact? In a former experiment I +shewed you the air going from one burning candle to a second candle. If I +took the air proceeding from another candle, and sent it down by a +complicated arrangement into this tube, I should put this burning candle +out. But what will you say when I tell you that my breath will put out +that candle? I do not mean by blowing at all, but simply that the nature +of my breath is such that a candle cannot burn in it. I will now hold my +mouth over the aperture, and without blowing the flame in any way, let no +air enter the tube but what comes from my mouth. You see the result. I did +not blow the candle out. I merely let the air which I expired pass into +the aperture, and the result was that the light went out for want of +oxygen, and for no other reason. Something or other--namely, my lungs--had +taken away the oxygen from the air, and there was no more to supply the +combustion of the candle. It is, I think, very pretty to see the time it +takes before the bad air which I throw into this part of the apparatus has +reached the candle. The candle at first goes on burning, but so soon as +the air has had time to reach it, it goes out. And, now, I will shew you +another experiment, because this is an important part of our philosophy. +Here is a jar which contains fresh air, as you can see by the circumstance +of a candle or gas-light burning it. I make it close for a little time, +and by means of a pipe I get my mouth over it so that I can inhale the +air. By putting it over water, in the way that you see, I am able to draw +up this air (supposing the cork to be quite tight), take it into my lungs, +and throw it back into the jar. + +[Illustration: Fig. 33.] + +We can then examine it, and see the result. You observe, I first take up +the air, and then throw it back, as is evident from the ascent and descent +of the water; and now, by putting a taper into the air, you will see the +state in which it is, by the light being extinguished. Even one +inspiration, you see, has completely spoiled this air, so that it is no +use my trying to breathe it a second time. Now, you understand the ground +of the impropriety of many of the arrangements among the houses of the +poorer classes, by which the air is breathed over and over again, for the +want of a supply, by means of proper ventilation, sufficient to produce a +good result. You see how bad the air becomes by a single breathing; so +that you can easily understand how essential fresh air is to us. + +To pursue this a little further, let us see what will happen with +lime-water. Here is a globe which contains a little lime-water, and it is +so arranged as regards the pipes, as to give access to the air within, so +that we can ascertain the effect of respired or unrespired air upon it. Of +course, I can either draw in air (through A), and so make the air that +feeds my lungs go through the lime-water, or I can force the air out of my +lungs through the tube (B), which goes to the bottom, and so shew its +effect upon the lime-water. + +[Illustration: Fig. 34.] + +You will observe that, however long I draw the external air into the +lime-water, and then through it to my lungs, I shall produce no effect +upon the water--it will not make the lime-water turbid; but if I throw the +air _from_ my lungs through the lime-water, several times in succession, +you see how white and milky the water is getting, shewing the effect which +expired air has had upon it; and now you begin to know that the atmosphere +which we have spoiled by respiration is spoiled by carbonic acid, for you +see it here in contact with the lime-water. + +I have here two bottles, one containing lime-water and the other common +water, and tubes which pass into the bottles and connect them. The +apparatus is very rough, but it is useful notwithstanding. + +[Illustration: Fig. 35.] + +If I take these two bottles, inhaling here and exhaling there, the +arrangement of the tubes will prevent the air going backwards. The air +coming in will go to my mouth and lungs, and in going out, will pass +through the lime-water, so that I can go on breathing and making an +experiment, very refined in its nature, and very good in its results. You +will observe that the good air has done nothing to the lime-water; in the +other case nothing has come to the lime-water but my respiration, and you +see the difference in the two cases. + +Let us now go a little further. What is all this process going on within +us which we cannot do without, either day or night, which is so provided +for by the Author of all things that He has arranged that it shall be +independent of all will? If we restrain our respiration, as we can to a +certain extent, we should destroy ourselves. When we are asleep, the +organs of respiration, and the parts that are associated with them, still +go on with their action--so necessary is this process of respiration to +us, this contact of the air with the lungs. I must tell you, in the +briefest possible manner, what this process is. We consume food: the food +goes through that strange set of vessels and organs within us, and is +brought into various parts of the system, into the digestive parts +especially; and alternately the portion which is so changed is carried +through our lungs by one set of vessels, while the air that we inhale and +exhale is drawn into and thrown out of the lungs by another set of +vessels, so that the air and the food come close together, separated only +by an exceedingly thin surface: the air can thus act upon the blood by +this process, producing precisely the same results in kind as we have seen +in the case of the candle. The candle combines with parts of the air, +forming carbonic acid, and evolves heat; so in the lungs there is this +curious, wonderful change taking place. The air entering, combines with +the carbon (not carbon in a free state, but, as in this case, placed ready +for action at the moment), and makes carbonic acid, and is so thrown out +into the atmosphere, and thus this singular result takes place: we may +thus look upon the food as fuel. Let me take that piece of sugar, which +will serve my purpose. It is a compound of carbon, hydrogen, and oxygen, +similar to a candle, as containing the same elements, though not in the +same proportion--the proportions being as shewn in this table:-- + +SUGAR. + +Carbon, . . . . 72 + _ +Hydrogen, . . . 11 | + | 99 +Oxygen, . . . . 88_| + +This is, indeed, a very curious thing, which you can well remember, for +the oxygen and hydrogen are in exactly the proportions which form water, +so that sugar may be said to be compounded of 72 parts of carbon and 99 +parts of water; and it is the carbon in the sugar that combines with the +oxygen carried in by the air in the process of respiration--so making us +like candles--producing these actions, warmth, and far more wonderful +results besides, for the sustenance of the system, by a most beautiful and +simple process. To make this still more striking, I will take a little +sugar; or, to hasten the experiment, I will use some syrup, which contains +about three-fourths of sugar and a little water. If I put a little oil of +vitriol on it, it takes away the water, and leaves the carbon in a black +mass. [The Lecturer mixed the two together.] You see how the carbon is +coming out, and before long we shall have a solid mass of charcoal, all of +which has come out of sugar. Sugar, as you know, is food, and here we have +absolutely a solid lump of carbon where you would not have expected it. +And if I make arrangements so as to oxidize the carbon of sugar, we shall +have a much more striking result Here is sugar, and I have here an +oxidizer--a quicker one than the atmosphere; and so we shall oxidize this +fuel by a process different from respiration in its form, though not +different in its kind. It is the combustion of the carbon by the contact +of oxygen which the body has supplied to it. If I set this into action at +once, you will see combustion produced. Just what occurs in my +lungs--taking in oxygen from another source, namely, the atmosphere--takes +place here by a more rapid process. + +You will be astonished when I tell you what this curious play of carbon +amounts to. A candle will burn some four, five, six, or seven hours. What, +then, must be the daily amount of carbon going up into the air in the way +of carbonic acid! What a quantity of carbon must go from each of us in +respiration! What a wonderful change of carbon must take place under these +circumstances of combustion or respiration! A man in twenty-four hours +converts as much as seven ounces of carbon into carbonic acid; a milch cow +will convert seventy ounces, and a horse seventy-nine ounces, solely by +the act of respiration. That is, the horse in twenty-four hours burns +seventy-nine ounces of charcoal, or carbon, in his organs of respiration, +to supply his natural warmth in that time. All the warm-blooded animals +get their warmth in this way, by the conversion of carbon, not in a free +state, but in a state of combination. And what an extraordinary notion +this gives us of the alterations going on in our atmosphere. As much as +5,000,000 pounds, or 548 tons, of carbonic acid is formed by respiration +in London alone in twenty-four hours. And where does all this go? Up into +the air. If the carbon had been like the lead which I shewed you, or the +iron which, in burning, produces a solid substance, what would happen? +Combustion could not go on. As charcoal burns, it becomes a vapour and +passes off into the atmosphere, which is the great vehicle, the great +carrier for conveying it away to other places. Then, what becomes of it? +Wonderful is it to find that the change produced by respiration, which +seems so injurious to us (for we cannot breathe air twice over), is the +very life and support of plants and vegetables that grow upon the surface +of the earth. It is the same also under the surface, in the great bodies +of water; for fishes and other animals respire upon the same principle, +though not exactly by contact with the open air. + +Such fish as I have here [pointing to a globe of gold-fish] respire by the +oxygen which is dissolved from the air by the water, and form carbonic +acid; and they all move about to produce the one great work of making the +animal and vegetable kingdoms subservient to each other. And all the +plants growing upon the surface of the earth, like that which I have +brought here to serve as an illustration, absorb carbon. These leaves are +taking up their carbon from the atmosphere, to which we have given it in +the form of carbonic acid, and they are growing and prospering. Give them +a pure air like ours, and they could not live in it; give them carbon with +other matters, and they live and rejoice. This piece of wood gets all its +carbon, as the trees and plants get theirs, from the atmosphere, which, as +we have seen, carries away what is bad for us and at the same time good +for them,--what is disease to the one being health to the other. So are we +made dependent, not merely upon our fellow-creatures, but upon our +fellow-existers, all Nature being tied together by the laws that make one +part conduce to the good of another. + +There is another little point which I must mention before we draw to a +close--a point which concerns the whole of these operations, and most +curious and beautiful it is to see it clustering upon and associated with +the bodies that concern us--oxygen, hydrogen, and carbon, in different +states of their existence. I shewed you just now some powdered lead, which +I set burning[18]; and you saw that the moment the fuel was brought to the +air, it acted, even before it got out of the bottle--the moment the air +crept in, it acted. Now, there is a case of chemical affinity by which all +our operations proceed. When we breathe, the same operation is going on +within us. When we burn a candle, the attraction of the different parts +one to the other is going on. Here it is going on in this case of the +lead; and it is a beautiful instance of chemical affinity. If the products +of combustion rose off from the surface, the lead would take fire, and go +on burning to the end; but you remember that we have this difference +between charcoal and lead--that, while the lead can start into action at +once, if there be access of air to it, the carbon will remain days, weeks, +months, or years. The manuscripts of Herculaneum were written with +carbonaceous ink, and there they have been for 1,800 years or more, not +having been at all changed by the atmosphere, though coming in contact +with it under various circumstances. Now, what is the circumstance which +makes the lead and carbon differ in this respect? It is a striking thing +to see that the matter which is appointed to serve the purpose of fuel +_waits_ in its action: it does not start off burning, like the lead and +many other things that I could shew you; but which I have not encumbered +the table with; but it waits for action. This waiting is a curious and +wonderful thing. Candles--those Japanese candles, for instance--do not +start into action at once, like the lead or iron (for iron finely divided +does the same thing as lead), but there they wait for years, perhaps for +ages, without undergoing any alteration. I have here a supply of coal-gas. +The jet is giving forth the gas, but you see it does not take fire--it +comes out into the air, but it waits till it is hot enough before it +burns. If I make it hot enough, it takes fire. If I blow it out, the gas +that is issuing forth waits till the light is applied to it again. It is +curious to see how different substances wait--how some will wait till the +temperature is raised a little, and others till it is raised a good deal. +I have here a little gunpowder and some gun-cotton; even these things +differ in the conditions under which they will burn. The gunpowder is +composed of carbon and other substances, making it highly combustible; and +the gun-cotton is another combustible preparation. They are both waiting, +but they will start into activity at different degrees of heat, or under +different conditions. By applying a heated wire to them, we shall see +which will start first [touching the gun-cotton with the hot iron]. You +see the gun-cotton has gone off, but not even the hottest part of the wire +is now hot enough to fire the gunpowder. How beautifully that shews you +the difference in the degree in which bodies act in this way! In the one +case the substance will wait any time until the associated bodies are made +active by heat; but in the other, as in the process of respiration, it +waits no time. In the lungs, as soon as the air enters, it unites with the +carbon; even in the lowest temperature which the body can bear short of +being frozen, the action begins at once, producing the carbonic acid of +respiration: and so all things go on fitly and properly. Thus you see the +analogy between respiration and combustion is rendered still more +beautiful and striking. Indeed, all I can say to you at the end of these +lectures (for we must come to an end at one time or other) is to express a +wish that you may, in your generation, be fit to compare to a candle; that +you may, like it, shine as lights to those about you; that, in all your +actions, you may justify the beauty of the taper by making your deeds +honourable and effectual in the discharge of your duty to your fellow-men. + + + + +LECTURE ON PLATINUM. + +[_Delivered before the_ ROYAL INSTITUTION, _on Friday, February 22, +1861._] + + +Whether I was to have the honour of appearing before you this evening or +not, seemed to be doubtful upon one or two points. One of these I will +mention immediately; the other may or may not appear during the course of +the hour that follows. The first point is this. When I was tempted to +promise this subject for your attention this evening, it was founded upon +a promise, and a full intent of performing that promise, on the part of my +friend Deville, of Paris, to come here to shew before you a phenomenon in +metallurgic chemistry not common. In that I have been disappointed. His +intention was to have fused here some thirty or forty pounds of platinum, +and so to have made manifest, through my mouth and my statement, the +principles of a new process in metallurgy, in relation to this beautiful, +magnificent, and valuable metal; but circumstances over which neither he +nor I, nor others concerned, have sufficient control, have prevented the +fulfilment of that intention; and the period at which I learned the fact +was so recent, that I could hardly leave my place here to be filled by +another, or permit you, who in your kindness have come to hear what might +be said, to remain unreceived in the best manner possible to me under the +circumstances. I therefore propose to state, as well as I can, what the +principles are on which M. Deville proceeds, by means of drawings, and +some subordinate or inferior experiments. The metal platinum, of which you +see some very fine specimens on the table, has been known to us about a +hundred years. It has been wrought in a beautiful way in this country, in +France, and elsewhere, and supplied to the consumer in ingots of this +kind, or in plates, such as we have here, or in masses, that by their very +fall upon the table indicate the great weight of the substance, which is, +indeed, nearly at the head of all substances in that respect. This +substance has been given to us hitherto mainly through the philosophy of +Dr. Wollaston, whom many of us know, and it is obtained in great purity +and beauty. It is a very remarkable metal in many points, besides its +known special uses. It usually comes to us in grains. Here is a very fine +specimen of native platinum in grains. Here is also a nugget or ingot, and +here are some small pieces gathered out of certain alluvial soils in +Brazil, Mexico, California, and the Uralian districts of Russia. + +It is strange that this metal is almost always found associated with some +four or five other metals, most curious in their qualities and +characteristics. They are called platiniferous metals; and they have not +only the relation of being always found associated in this manner, but +they have other relations of a curious nature, which I shall point out to +you by a reference to one of the tables behind me. This substance is +always native--it is always in the metallic state; and the metals with +which it is found connected, and which are rarely found elsewhere, are +palladium, rhodium, iridium, osmium, and ruthenium. We have the names in +one of the tables arranged in two columns, representing, as you see, two +groups--platinum, iridium, and osmium constituting one group; and +ruthenium, rhodium, and palladium the other. Three of these have the +chemical equivalent of 98-1/2, and the others a chemical equivalent of +about half that number. Then the metals of one group have an extreme +specific gravity--platinum being, in fact, the lightest of the three, or +as light as the lightest. Osmium has a specific gravity of 21.4, and is +the heaviest body in nature; platinum is 21.15, and iridium the same; the +specific gravity of the other three being only about half that, namely, +11.3, 12.1, and 11.8. Then there is this curious relation, that palladium +and iridium are very much alike, so that you would scarcely know one from +the other, though one has only half the weight of the other, and only half +the equivalent power. So with iridium and rhodium, and osmium and +ruthenium, which are so closely allied that they make pairs, being +separated each from its own group. Then these metals are the most +infusible that we possess. Osmium is the most difficult to fuse: indeed, I +believe it never has been fused, while every other metal has. Ruthenium +comes next, iridium next, rhodium next, platinum next (so that it ranks +here as a pretty fusible metal, and yet we have been long accustomed to +speak of the infusibility of platinum), and next comes palladium, which is +the most fusible metal of the whole. It is a curious thing to see this +fine association of physical properties coming out in metals which are +grouped together somehow or other in nature, but, no doubt, by causes +which are related to analogous properties in their situation on the +surface of the earth, for it is in alluvial soils that these things are +found. + +Now, with regard to this substance, let me tell you briefly how we get it. +The process used to be this. The ore which I shewed you just now was +taken, and digested in nitro-muriatic acid of a certain strength, and +partly converted into a solution, with the leaving behind of certain +bodies that I have upon the table. The platinum being dissolved with care +in acids, to the solution the muriate of ammonia was added, as I am about +to add it here. A yellow precipitate was then thrown down, as you perceive +is the case now; and this, carefully washed and cleansed, gave us that +body [pointing to a specimen of the chloride of platinum and ammonium], +the other elements, or nearly all, being ejected. This substance being +heated, gave us what we call platinum sponge, or platinum in the metallic +state, so finely divided as to form a kind of heavy mass or sponge, which, +at the time that Dr. Wollaston first sent it forth, was not fusible for +the market or in the manufacturers' workshops, inasmuch as the temperature +required was so high, and there were no furnaces that could bring the mass +into a globule, and cause the parts to adhere together. Most of our metals +that we obtain from nature, and work in our shops, are brought at last +into a mass by fusion. I am not aware that there is in the arts or +sciences any other than iron which is not so. Soft iron we do not bring +together by fusion, but by a process which is analogous to the one that +was followed in the case of platinum, namely, welding; for these divided +grains of spongy platinum having been well washed and sunk in water for +the purpose of excluding air, and pressed together, and heated, and +hammered, and pressed again, until they come into a pretty close, dense, +compact mass, did so cohere, that when the mass was put into the furnace +of charcoal, and raised to a high temperature, the particles, at first +infinitely divided--for they were chemically divided--adhered the one to +the other, each to all the rest, until they made that kind of substance +which you see here, which will bear rolling and expansion of every kind. +No other process than that has hitherto been adopted for the purpose of +obtaining this substance from the particles by solution, precipitation, +ignition, and welding. It certainly is a very fine thing to see that we +may so fully depend upon the properties of the various substances we have +to deal with; that we can, by carrying out our processes, obtain a +material like this, allowing of division and extension under a rolling +mill--a material of the finest possible kind, the parts being held +together, not with interstices, not with porosity, but so continuous that +no fluids can pass between them; and, as Dr. Wollaston beautifully shewed, +a globule of platinum fused by the voltaic battery and the oxy-hydrogen +blowpipe, when drawn into a wire, was not sounder or stronger than this +wire made by the curious coalescence of the particles by the sticking +power that they had at high temperatures. This is the process adopted by +Messrs. Johnson and Matthey, to whose great kindness I am indebted for +these ingots and for the valuable assistance I have received in the +illustrations. + +The treatment, however, that I have to bring before you is of another +kind; and it is in the hope that we shall be able before long to have such +a thing as the manufacture of platinum of this kind, that I am encouraged +to come before you, and tell you how far Deville has gone in the matter, +and to give you illustrations of the principles on which he proceeds. I +think it is but fair that you should see an experiment shewing you the way +in which we get the adhesion of platinum. Probably you all know of the +welding of iron: you go into the smith's shop, and you see him put the +handle of a poker on to the stem, and by a little management and the +application of heat he makes them one. You have no doubt seen him put the +iron into the fire and sprinkle a little sand upon it. He does not know +the philosophy he calls into play when he sprinkles a little sand over the +oxide of iron, but he has a fine philosophy there, or practises it, when +he gets his welding. I can shew you here this beautiful circumstance of +the sticking together of the particles up to the fullest possible +intensity of their combination. If you were to go into the workshops of +Mr. Matthey, and see them hammering and welding away, you would see the +value of the experiment I am about to shew you. I have here some +platinum-wire. This is a metal which resists the action of acids, resists +oxidation by heat, and change of any sort; and which, therefore, I may +heat in the atmosphere without any flux. I bend the wire so as to make the +ends cross: these I make hot by means of the blowpipe, and then, by giving +them a tap with a hammer, I shall make them into one piece. Now that the +pieces are united, I shall have great difficulty in pulling them apart, +though they are joined only at the point where the two cylindrical +surfaces came together. And now I have succeeded in pulling the wire +apart, the division is not at the point of welding, but where the force of +the pincers has cut it, so that the junction we have effected is a +complete one. This, then, is the principle of the manufacture and +production of platinum in the old way. + +The treatment which Deville proposes to carry out, and which he has +carried out to a rather large extent in reference to the Russian supply of +platinum, is one altogether by heat, having little or no reference to the +use of acids. That you may know what the problem is, look at this table, +which gives you the composition of such a piece of platinum ore as I +shewed you just now. Wherever it comes from, the composition is as +complicated, though the proportions vary:-- + +Platinum, . . . . . 76.4 +Iridium,. . . . . . 4.3 +Rhodium,. . . . . . 0.3 +Palladium,. . . . . 1.4 +Gold, . . . . . . . 0.4 +Copper, . . . . . . 4.1 +Iron, . . . . . . . 11.7 +Osmide of Iridium,. 0.5 +Sand, . . . . . . . 1.4 + ----- + 100.5 + +This refers to the Uralian ore. In that state of combination, as shewn in +the table, the iridium and osmium are found combined in crystals, +sometimes to the amount of 0.5 per cent., and sometimes 3 or 4 per cent. +Now, this Deville proposes to deal with in the dry way, in the place of +dealing with it by any acid. + +I have here another kind of platinum; and I shew it to you for this +reason. The Russian Government, having large stores of platinum in their +dominions, have obtained it in a metallic state, and worked it into coin. +The coin I have in my hand is a twelve silver rouble piece. The rouble is +worth three shillings, and this coin is, therefore, of the value of +thirty-six shillings. The smaller coin is worth half that sum; and the +other, half of that. The metal, however, is unfit for coinage. When you +have the two metals, gold and silver, used for coinage, you have a little +confusion in the value of the two in the market; but when you have three +precious metals (for you may call platinum a precious metal) worked into +coin, they will be sure to run counter to one another. Indeed, the case +did happen, that the price of platinum coin fixed by the Government was +such, that it was worth while to purchase platinum in other countries, and +make coin of it, and then take it into that country and circulate it. The +result was, that the Russian Government stopped the issue. The composition +of this coin is--platinum, 97.0; iridium, 1.2; rhodium, 0.5; palladium, +0.25; a little copper, and a little iron. It is, in fact, bad platinum: it +scales, and it has an unfitness for commercial use and in the laboratory, +which the other well-purified platinum has not. It wants working over +again. + +Now, Deville's process depends upon three points,--upon intense heat, +blowpipe action, and the volatility of certain metals. We know that there +are plenty of metals that are volatile; but this, I think, is the first +time that it has been proposed to use the volatility of certain +metals--such as gold and palladium--for the purpose of driving them off +and leaving something else behind. He counts largely upon the volatility +of metals which we have not been in the habit of considering volatile, but +which we have rather looked upon as fixed; and I must endeavour to +illustrate these three points by a few experiments. Perhaps I can best +show you what is required in the process of heating platinum by using that +source of heat which we have here, and which seems to be almost +illimitable--namely, the voltaic battery; for it is only in consequence of +the heat that the voltaic battery affects the platinum. By applying the +two extremities of the battery to this piece of platinum-wire, you will +see what result we shall obtain. You perceive that we can take about this +heating agent wherever we like, and deal with it as we please, limiting it +in any way. I am obliged to deal carefully with it; but even that +circumstance will have an interest for you in watching the experiment. +Contact is now made. The electric current, when compressed into thin +conducting-wires offering resistance, evolves heat to a large extent; and +this is the power by which we work. You see the intense glow immediately +imparted to the wire; and if I applied the heat continuously, the effect +of the current would be to melt the wire. As soon as the contact is +broken, the wire resumes its former appearance; and now that we make +contact again, you perceive the glow as before. [The experiment was +repeated several times in rapid succession.] You can see a line of light, +though you can scarcely perceive the wire; and now that it has melted with +the great heat, if you examine it, you will perceive that it is indeed a +set of irregularities from end to end--a set of little spheres, which are +strung upon an axis of platinum running through it. It is that wire which +Mr. Grove described as being produced at the moment when fusion of the +whole mass is commencing. In the same manner, if I take a tolerably thick +piece of platinum, and subject it to the heat that can be produced by this +battery, you will see the brilliancy of the effect produced. I shall put +on a pair of spectacles for the experiment, as there is an injurious +effect of the voltaic spark upon the eyes, if the action is continued; and +it is neither policy nor bravery to subject any organ to unnecessary +danger; and I want, at all events, to keep the full use of my eyes to the +end of the lecture. + +You now see the action of the heat upon the piece of platinum--heat so +great as to break in pieces the plate on which the drops of metal fall. +You perceive, then, that we have sufficiently powerful sources of heat in +nature to deal with platinum. I have here an apparatus by which the same +thing can be shewn. Here is a piece of platinum, which is put into a +crucible of carbon made at the end of one pole of the battery, and you +will see the brilliant light that will be produced. There is our furnace, +and the platinum is rapidly getting heated; and now you perceive that it +is melted, and throwing off little particles. What a magnificent +philosophical instrument this is. When you look at the result, which is +lying upon the charcoal, you will see a beautifully fused piece of +platinum. It is now a fiery globule, with a surface so bright, and smooth, +and reflecting, that I cannot tell whether it is transparent, or opaque, +or what. This, then, will give you an idea of what has to be done by any +process that pretends to deal with thirty, or forty, or fifty pounds of +platinum at once. + +Let me now tell you briefly what Deville proposes to do. First of all, he +takes this ore, with its impurities, and mixes it (as he finds it +essential and best) with its own weight of sulphuret of lead--lead +combined with sulphur. Both the lead and the sulphur are wanted; for the +iron that is there present, as you see by the table, is one of the most +annoying substances in the treatment that you can imagine, because it is +not volatile; and while the iron remains adhering to the platinum, the +platinum will not flow readily. It cannot be sent away by a high +temperature--sent into the atmosphere so as to leave the platinum behind. +Well, then, a hundred parts of ore and a hundred parts of sulphuret of +lead, with about fifty parts of metallic lead, being all mingled together +in a crucible, the sulphur of the sulphuret takes the iron, the copper, +and some of the other metals and impurities, and combines with them to +form a slag; and as it goes on boiling and oxidising, it carries off the +iron, and so a great cleansing takes place. + +Now, you ought to know that these metals, such as platinum, iridium, and +palladium, have a strong affinity for such metals as lead and tin, and +upon this a great deal depends. Very much depends upon the platinum +throwing out its impurities of iron and so forth, by being taken up with +the lead present in it. That you may have a notion of the great power that +platinum has of combining with other metals, I will refer you to a little +of the chemist's experience--his bad experience. He knows very well that +if he takes a piece of platinum-foil, and heats a piece of lead upon it, +or if he takes a piece of platinum-foil, such as we have here, and heats +things upon it that have lead in them, his platinum is destroyed. I have +here a piece of platinum, and if I apply the heat of the spirit-lamp to +it, in consequence of the presence of this little piece of lead which I +will place on it, I shall make a hole in the metal. The heat of the lamp +itself would do no harm to the platinum, nor would other chemical means; +but because there is a little lead present, and there is an affinity +between the two substances, the bodies fuse together at once. You see the +hole I have made. It is large enough to put your finger in, though the +platinum itself was, as you saw, almost infusible, except by the voltaic +battery. For the purpose of shewing this fact in a more striking manner, I +have taken pieces of platinum-foil, tin-foil, and lead-foil, and rolled +them together; and if I apply the blowpipe to them, you will have, in +fact, a repetition on a larger scale of the experiment you saw just now +when the lead and platinum came together, and one spoiled the other. When +the metals are laid one upon the other, and folded together and heat +applied, you will not only see that the platinum runs to waste, but that +at the time when the platinum and lead are combined there is ignition +produced--there is a power of sustaining combustion. I have taken a large +piece, that you may see the phenomenon on a large scale. You saw the +ignition and the explosion which followed, of which we have here the +results--the consequence of the chemical affinity between the platinum and +the metals combined with it, which is the thing upon which Deville founds +his first result. + +When he has melted these substances and stirred them well up, and so +obtained a complete mixture, he throws in air upon the surface to burn off +all the sulphur from the remaining sulphuret of lead; and at last he gets +an ingot of lead with platinum--much lead, comparatively, and little +platinum. He gets that in the crucible with a lot of scori and other +things, which he treats afterwards. It is that platiniferous lead which we +have to deal with in our future process. Now, let me tell you what he does +with it. His first object is to get rid of the lead. He has thrown out all +the iron, and a number of other things, and he has got this kind of +compound indicated in the table. He may get it as high as 78 per cent. of +platinum, and 22 of lead; or 5, or 10, or 15 of platinum, and 95, or 90, +or 85 of lead (which he calls weak platinum), and he then places it in the +kind of vessel that you see before you. Suppose we had the mixture here; +we should have to make it hot, and then throw in air upon the surface. The +combustible metal--that is, the lead--and the part that will oxidise, are +thoroughly oxidised; the litharge would flow out in a fused state into a +vessel placed to receive it, and the platinum remains behind. + +[Illustration: Fig. 36.] + +Here is the process which Deville adopts for the purpose of casting off +the lead, after he has got out the platinum from the ore. (Having made use +of your friend, you get rid of him as quickly as you can.) He gets his +heat by applying the combination of oxygen and hydrogen, or of carburetted +fuel, for the purpose of producing a fire. I have here a source of +coal-gas; there I have a source of hydrogen; and here I have a source of +oxygen. I have here also one of the blowpipes used by Deville in his +process for working platinum in the way I have spoken of. There are two +pipes, and one of them goes to the source of coal-gas, and the other to +the supply of oxygen. + +[Illustration: Fig. 37.] + +By uniting these we obtain a flame of such a heat as to melt platinum. You +will, perhaps, hardly imagine what the heat is, unless you have some proof +of it; but you will soon see that I have actually the power of melting +platinum. Here is a piece of platinum-foil running like wax under the +flame which I am bringing to bear against it. The question, however, is +whether we shall get heat enough to melt, not this small quantity, but +large masses--many pounds of the metal. Having obtained heat like this, +the next consideration is what vessel is he to employ which could retain +the platinum when so heated, or bear the effects of the flame? Such +vessels are happily well supplied at Paris, and are formed of a substance +which surrounds Paris; it is a kind of chalk (called, I believe, by +geologists, _calcaire grossire_), and it has the property of enduring an +extreme degree of heat. I am now going to get the highest heat that we can +obtain. First, I shew you the combustion of hydrogen by itself. I have not +a large supply, because the coal-gas is sufficient for most of our +purposes. If I put a piece of lime obtained from this chalk into the gas, +you see we get a pretty hot flame, which would burn one's fingers a good +deal But now let me subject a piece of it to the joint action of oxygen +and hydrogen. I do this for the purpose of shewing you the value of lime +as a material for the furnaces and chambers that are to contain the +substances to be operated on, and that are consequently to sustain the +action of this extreme heat. Here we have the hydrogen and the oxygen, +which will give the most intense heat that can be obtained by chemical +action; and if I put a piece of lime into the flame, we get what is called +the lime-light. Now, with all the beauty and intensity of action which you +perceive, there is no sensible deterioration of the lime except by the +mechanical force of the current of gases rushing from the jet against the +lime, sweeping away such particles as are not strongly aggregated. "Vapour +of lime" some call it; and it may be so, but there is no other change of +the lime than that under the action of heat of this highly-exalted +chemical condition, though almost any other substance would melt at once. + +Then, as to the way in which the heat is applied to the substance. It is +all very well for me to take a piece of antimony, and fuse it in the flame +of a blowpipe. But if I tried this piece in the ordinary lamp flame, I +should do nothing; if I tried a smaller piece, I should do little or +nothing; and if I tried a still smaller piece, I should do little or +nothing; yet I have a condition which will represent what Deville carries +to the highest possible extent, and which we all carry to the highest +extent, in the use of the blowpipe. Suppose I take this piece of antimony: +I shall not be able to melt it in that flame of the candle by merely +holding it there; yet, by taking pains, we can even melt a piece of +platinum there. This is a preparation which I made for the purpose of +proving the fusibility of platinum in a common candle. There is a piece of +wire, drawn by that ingenious process of Dr. Wollaston's, not more than +the three-thousandth part of an inch in diameter. He put the wire into the +middle of a cylinder of silver, and drew both together until the whole +compound was exceedingly thin; and then he dissolved away the silver by +nitric acid. There was left in the centre a substance which I can scarcely +see with an eye-glass, but which I know is there, and which I can make +visible, as you see, by putting it into the candle, where the heat makes +it glow like a spark. I have again and again tried this experiment +up-stairs in my own room, and have easily fused this platinum-wire by a +common candle. You see we have, therefore, heat enough in the candle, as +in the voltaic battery, or in the highly-exalted combustion of the +blowpipe, but we do not supply a continuous source of heat. In the very +act of this becoming ignited, the heat radiates so fast that you cannot +accumulate enough to cause the fusion of the wire, except under the most +careful arrangement. Thus I cannot melt that piece of antimony by simply +putting it into the candle; but if I put it upon charcoal, and drive the +fiery current against it, there will be heat enough to melt it. The beauty +of the blowpipe is, that it sends hot air (making hot air by the +combustion of the flame) against the thing to be heated. I have only to +hold the antimony in the course of that current, and particle by particle +of the current impinges upon the antimony, and so we get it melted. You +now see it red-hot, and I have no doubt it will continue to burn if I +withdraw it from the flame and continue to force the air on it. Now, you +see it burning without any heat but that of its own combustion, which I am +keeping up by sending the air against it. It would go out in a moment if I +took away the current of air from it; but there it is burning, and the +more air I give it, by this or any other action, the better it is. So, +then, we have here not merely a mighty source of heat, but a means of +driving the heat forcibly against substances. + +Let me shew you another experiment with a piece of iron. It will serve two +purposes--shewing you what the blowpipe does as a source of heat, and what +it does by sending that heat where it is wanted. I have taken iron in +contrast with silver or other metals, that you may see the difference of +action, and so be more interested in the experiment. Here is our fuel, the +coal-gas; and here our oxygen. Having thus my power of heat, I apply it to +the iron, which, as you see, soon gets red-hot. It is now flowing about +like a globule of melted mercury. But observe, I cannot raise any vapour: +it is now covered with a coat of melted oxide, and unless I have a great +power in my blowpipe, it is hardly possible to break through it. Now, +then, you see these beautiful sparks: you have not only a beautiful kind +of combustion, but you see the iron is being driven off, not producing +smoke, but burning in a fixed condition. How different this is from the +action of some other metals--that piece of antimony, for instance, which +we saw just now throwing off abundance of fumes. We can, of course, burn +away this iron by giving plenty of air to it; but with the bodies which +Deville wants to expose to this intense heat he has not that means: the +gas itself must have power enough to drive off the slag which forms on the +surface of the metal, and power to impinge upon the platinum so as to get +the full contact that he wants for the fusion to take place. We see here, +then, the means to which he resorts--oxygen, and either coal-gas or +water-gas[19], or pure hydrogen, for producing heat, and the blowpipe for +the purpose of impelling the heated current upon the metals. + +I have two or three rough drawings here, representing the kind of furnaces +which he employs. They are larger, however, than the actual furnaces he +uses. Even the furnace in which he carries on that most serious operation +of fusing fifty pounds of platinum at once is not much more than half the +size of the drawing. It is made of a piece of lime below and a piece of +lime above. You see how beautifully lime sustains heat without altering in +shape; and you may have thought how beautifully it prevents the +dissipation of the heat by its very bad conducting powers. + +[Illustration: Fig. 38] + +While the front part of the lime which you saw here was so highly ignited, +I could at any moment touch the back of it without feeling any annoyance +from the heat So, by having a chamber of lime of this sort, he is able to +get a vessel to contain these metals with scarcely any loss of heat. He +puts the blowpipes through these apertures, and sends down these gases +upon the metals, which are gradually melted. He then puts in more metal +through a hole at the top. The results of the combustion issue out of the +aperture which you see represented. If there be strips of platinum, he +pushes them through the mouth out of which the heated current is coming, +and there they get red-hot and white-hot before they get into the bath of +platinum. So he is able to fuse a large body of platinum in this manner. +When the platinum is melted, he takes off the top and pours out from the +bottom piece, like a crucible, and makes his cast. This is the furnace by +which he fuses his forty pounds or fifty pounds of platinum at once. The +metal is raised to a heat that no eye can bear. There is no light and +shadow, no chiaro-oscuro there; all is the same intensity of glow. You +look in, and you cannot see where the metal or the lime is; it is all as +one. We have, therefore, a platform with a handle, which turns upon an +axis, that coincides with the gutter that is formed for the pouring of the +metal; and when all is known to be ready, by means of dark glasses, the +workmen take off the top piece and lift up the handle, and the mould being +then placed in a proper position, he knows that the issue of the metal +will be exactly in the line of the axis. No injury has ever happened from +the use of this plan. You know with what care it is necessary to carry +such a vessel of mercury as we have here, for fear of turning it over on +one side or the other; but if it be a vessel of melted platinum, the very +greatest care must be used, because the substance is twice as heavy: yet +no injury has been done to any of the workmen in this operation. + +I have said that Deville depends upon intense heat for carrying off +vapour; and this brings me to the point of shewing how vapours are carried +off. Here is a basin of mercury, which boils easily, as you know, and +gives us the opportunity of observing the facts and principles which are +to guide us. I have here two poles of the battery, and if I bring them +into contact with the mercury, see what a development of vapour we have. +The mercury is flying off rapidly; and I might, if I pleased, put all the +company around me in a bath of mercury vapour. And so, if we take this +piece of lead and treat it in the same way, it will also give off vapour. +Observe the fumes that rise from it; and even if it was so far enclosed +from the air that you could not form any litharge, you would still have +those abundant fumes flying off. I may also take a piece of gold, and shew +you the same thing. I have here a piece of gold which I put upon a clean +surface of Paris limestone. Applying the heat of the blowpipe to it, you +see how the heat drives off the vapour; and if you notice at the end of +the Lecture, you will observe on the stone a purple patch of condensed +gold. Thus you see a proof of the volatilisation of gold. It is the same +with silver. You will not be startled if I sometimes use one agent and +sometimes another to illustrate a particular point. The volatility of gold +and silver is the same thing, whether it be effected by the voltaic +battery or by the blowpipe. [A lump of silver was placed in a charcoal +crucible between the poles of a voltaic battery.] Now, look at the fumes +of silver, and observe the peculiar and beautiful green colour which they +produce. We shall now shew you this same process of boiling the silver, +cast on a screen from the electric lamp which you have before you; and +while Dr. Tyndall is kindly getting the lamp ready for this purpose, let +me tell you that Deville proposes to throw out in this way all these +extraneous things that I have spoken of, except two--namely, iridium and +rhodium. It so happens, as he says, that iridium and rhodium do make the +metal more capable of resisting the attacks of acids than platinum itself. +Alloys are compounded up to 25 per cent. of rhodium and iridium, by which +the chemical inaction of the platinum is increased, and also its +malleability and other physical properties. [The image of the voltaic +discharge through vapour of silver was now thrown upon the screen.] What +you have now on the screen is an inverted image of what you saw when we +heated the silver before. The fine stream that you see around the silver +is the discharge of the electric force that takes place, giving you that +glorious green light which you see in the ray; and if Dr. Tyndall will +open the top of the lamp, you will see the quantity of fumes that will +come out of the aperture, shewing you at once the volatility of silver. + +I have now finished this imperfect account. It is but an apology for not +having brought the process itself before you. I have done the best I could +under the circumstances; and I know your kindness well, for if I were not +aware that I might trust to it, I would not appear here so often as I have +done. The gradual loss of memory and of my other faculties is making +itself painfully evident to me, and requires, every time I appear before +you, the continued remembrance of your kindness to enable me to get +through my task. If I should happen to go on too long, or should fail in +doing what you might desire, remember it is yourselves who are chargeable, +by wishing me to remain. I have desired to retire, as I think every man +ought to do before his faculties become impaired; but I must confess that +the affection I have for this place, and for those who frequent this +place, is such, that I hardly know when the proper time has arrived. + + + + +NOTES. + + +[Footnote 1: Page 16. The Royal George sunk at Spithead on The 29th of +August, 1782. Colonel Pasley commenced operations for the removal of the +wreck by the explosion of gunpowder, in August, 1839. The candle which +Professor Faraday exhibited must therefore have been exposed to the action +of salt water for upwards of fifty-seven years.] + +[Footnote 2: Page 17. The fat or tallow consists of a chemical combination +of fatty acids with glycerine. The lime unites with the palmitic, oleic, +and stearic acids, and separates the glycerine. After washing, the +insoluble lime soap is decomposed with hot dilute sulphuric acid. The +melted fatty acids thus rise as an oil to the surface, when they are +decanted. They are again washed and cast into thin plates, which, when +cold, are placed between layers of cocoa-nut matting, and submitted to +intense hydraulic pressure. In this way the soft oleic acid is squeezed +out, whilst the hard palmitic and stearic acids remain. These are further +purified by pressure at a higher temperature, and washing in warm dilute +sulphuric acid, when they are ready to be made into candles. These acids +are harder and whiter than the fats from which they were obtained, whilst +at the same time they are cleaner and more combustible.] + +[Footnote 3: Page 19. A little borax or phosphorus salt is sometimes +added, in order to make the ash fusible.] + +[Footnote 4: Page 27. Capillary attraction or repulsion is the cause which +determines the ascent or descent of a fluid in a capillary tube. If a +piece of thermometer tubing, open at each end, be plunged into water, the +latter will instantly rise in the tube considerably above its external +level. If, on the other hand, the tube be plunged into mercury, a +repulsion instead of attraction will be exhibited, and the level of the +mercury will be lower in the tube than it is outside.] + +[Footnote 5: Page 29. The late Duke of Sussex was, we believe, the first +to shew that a prawn might be washed upon this principle. If the tail, +after pulling off the fan part, be placed in a tumbler of water, and the +head be allowed to hang over the outside, the water will be sucked up the +tail by capillary attraction, and will continue to run out through the +head until the water in the glass has sunk so low that the tail ceases to +dip into it.] + +[Footnote 6: Page 37. The alcohol had chloride of copper dissolved in it: +this produces a beautiful green flame.] + +[Footnote 7: Page 54. Lycopodium is a yellowish powder found in the fruit +of the club moss (_Lycopodium clavatum_). It is used in fireworks.] + +[Footnote 8: Page 58. Bunsen has calculated that the temperature of the +oxyhydrogen blowpipe is 8061 Centigrade. Hydrogen burning in air has a +temperature of 3259 C., and coal-gas in air, 2350 C.] + +[Footnote 9: Page 60. The following is the action of the sulphuric acid in +inflaming the mixture of sulphuret of antimony and chlorate of potassa. A +portion of the latter is decomposed by the sulphuric acid into oxide of +chlorine, bisulphate of potassa, and perchlorate of potassa. The oxide of +chlorine inflames the sulphuret of antimony, which is a combustible body, +and the whole mass instantly bursts into flame.] + +[Footnote 10: Page 63. The "air-burner," which is of such value in the +laboratory, owes its advantage to this principle. It consists of a +cylindrical metal chimney, covered at the top with a piece of rather +coarse iron-wire gauze. This is supported over an argand burner, in such a +manner that the gas may mix in the chimney with an amount of air +sufficient to burn the carbon and hydrogen simultaneously, so that there +may be no separation of carbon in the flame with consequent deposition of +soot. The flame, being unable to pass through the wire gauze, burns in a +steady, nearly invisible manner above.] + +[Footnote 11: Page 74. Water is in its densest state at a temperature of +39.1 Fahrenheit] + +[Footnote 12: Page 74. A mixture of salt and pounded ice reduces the +temperature from 32 F. to zero--the ice at the same time becoming fluid.] + +[Footnote 13: Page 82. Potassium, the metallic basis of potash, was +discovered by Sir Humphrey Davy in 1807, who succeeded in separating it +from potash by means of a powerful voltaic battery. Its great affinity for +oxygen causes it to decompose water with evolution of hydrogen, which +takes fire with the heat produced.] + +[Footnote 14: Page 98. Professor Faraday has calculated that there is as +much electricity required to decompose one grain of water as there is in a +very powerful flash of lightning.] + +[Footnote 15: Page 101. A solution of acetate of lead submitted to the +action of the voltaic current, yields lead at the negative pole, and brown +peroxide of lead at the positive pole. A solution of nitrate of silver, +under the same circumstances, yields silver at the negative pole, and +peroxide of silver at the positive pole.] + +[Footnote 16: Page 129. The gas which is thus employed as a test for the +presence of oxygen, is the binoxide of nitrogen, or nitrous oxide. It is a +colourless gas, which, when brought in contact with oxygen, unites with +it, forming hyponitric acid, the red gas referred to.] + +[Footnote 17: Page 152. _Marble_ is a compound of carbonic acid and lime. +The muriatic acid being the stronger of the two, takes the place of the +carbonic acid, which escapes as a gas, the residue forming muriate of lime +or chloride of calcium.] + +[Footnote 18: Page 186. _Lead pyrophorus_ is made by heating dry tartrate +of lead in a glass tube (closed at one end, and drawn out to a fine point +at the other) until no more vapours are evolved. The open end of the tube +is then to be sealed before the blowpipe. When the tube is broken and the +contents shaken out into the air, they burn with a red flash.] + +[Footnote 19: Page 216. _Water-gas_ is formed by passing vapour of water +over red-hot charcoal or coke. It is a mixture of hydrogen and carbonic +oxide; each of which is an inflammable gas.] + + + +Poster's note: "combustion that makes!" was corrected from a misprint +"combusion that makes!" in the original. + + + +End of the Project Gutenberg EBook of The Chemical History Of A Candle +by Michael Faraday + +*** END OF THIS PROJECT GUTENBERG EBOOK THE CHEMICAL HISTORY OF A CANDLE *** + +***** This file should be named 14474-8.txt or 14474-8.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/1/4/4/7/14474/ + +Produced by Clare Boothby, Richard Prairie and the PG Online +Distributed Proofreading Team + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Chemical History Of A Candle + +Author: Michael Faraday + +Release Date: December 26, 2004 [EBook #14474] +[Date last updated: October 1, 2005] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE CHEMICAL HISTORY OF A CANDLE *** + + + + +Produced by Clare Boothby, Richard Prairie and the PG Online +Distributed Proofreading Team + + + + + + + THE 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. + + EDITED BY + + WILLIAM CROOKES, F.C.S. + + A NEW IMPRESSION, WITH ILLUSTRATIONS + + LONDON + + CHATTO & WINDUS + + 1908 + + + + +PREFACE + +From the primitive pine-torch to the paraffin candle, how wide an +interval! between them how vast a contrast! The means adopted by man to +illuminate his home at night, stamp at once his position in the scale of +civilisation. The 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. All, 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. + +Surely, 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. Think +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. + +Atom by atom, link by link, has the reasoning chain been forged. Some +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. + +The 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. + +Among the readers of this book some few may devote themselves to +increasing the stores of knowledge: the Lamp of Science _must_ burn. +"_Alere flammam._" + +W. CROOKES. + + + + +CONTENTS. + + +LECTURE I. + +A CANDLE: THE FLAME--ITS SOURCES--STRUCTURE--MOBILITY--BRIGHTNESS + + +LECTURE II. + +BRIGHTNESS OF THE FLAME--AIR NECESSARY FOR COMBUSTION--PRODUCTION OF WATER + + +LECTURE III. + +PRODUCTS: WATER FROM THE COMBUSTION--NATURE OF WATER--A COMPOUND--HYDROGEN + + +LECTURE IV. + +HYDROGEN IN THE CANDLE--BURNS INTO WATER--THE OTHER PART OF WATER--OXYGEN + + +LECTURE V. + +OXYGEN PRESENT IN THE AIR--NATURE OF THE ATMOSPHERE--ITS PROPERTIES--OTHER +PRODUCTS FROM THE CANDLE--CARBONIC ACID--ITS PROPERTIES + + +LECTURE VI. + +CARBON OR CHARCOAL--COAL GAS--RESPIRATION AND ITS ANALOGY TO THE BURNING +OP A CANDLE--CONCLUSION + + +LECTURE ON PLATINUM. + + +NOTES. + + + + +THE CHEMICAL HISTORY OF A CANDLE + +LECTURE I. + +A CANDLE: THE FLAME--ITS SOURCES--STRUCTURE--MOBILITY--BRIGHTNESS. + + +I 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. I 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. There 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. There 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. I +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. + +And 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. I claim the privilege of speaking to juveniles as a juvenile +myself. I have done so on former occasions--and, if you please, I shall do +so again. And 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. + +And now, my boys and girls, I must first tell you of what candles are +made. Some are great curiosities. I have here some bits of timber, +branches of trees particularly famous for their burning. And 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. And in this +wood we have one of the most beautiful illustrations of the general nature +of a candle that I can possibly give. The 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. + +But we must speak of candles as they are in commerce. Here are a couple of +candles commonly called dips. They 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. +In 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. They are, or were, the candles used by the miners in coal +mines. In 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. They have been replaced since then by the steel-mill, and then by +the Davy-lamp, and other safety-lamps of various kinds. I have here a +candle that was taken out of the _Royal George_[1], it is said, by Colonel +Pasley. It has been sunk in the sea for many years, subject to the action +of salt water. It 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. + +Mr. Field, of Lambeth, has supplied me abundantly with beautiful +illustrations of the candle and its materials. I shall therefore now refer +to them. And, 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. A 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. This 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. +Glycerin--absolutely a sugar, or a substance similar to sugar--comes out +of the tallow in this chemical change. The 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. The candle I have in my hand is a +stearin candle, made of stearin from tallow in the way I have told you. +Then here is a sperm candle, which comes from the purified oil of the +spermaceti whale. Here also are yellow bees-wax and refined bees-wax, from +which candles are made. Here, too, is that curious substance called +paraffin, and some paraffin candles made of paraffin obtained from the +bogs of Ireland. I 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. + +And how are these candles made? I have told you about dips, and I will +shew you how moulds are made. Let us imagine any of these candles to be +made of materials which can be cast. "Cast!" you say. "Why, a candle is a +thing that melts; and surely if you can melt it, you can cast it." Not so. +It 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. Candles cannot always be cast. A +wax candle can never be cast. It is made by a particular process, which I +can illustrate in a minute or two: but I must not spend much time on it. +Wax is a thing which, burning so well, and melting so easily in a candle, +cannot be cast. However, let us take a material that can be cast. Here is +a frame, with a number of moulds fastened in it. The first thing to be +done is to put a wick through them. Here is one--a plaited wick, which +does not require snuffing[3]--supported by a little wire. It 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. At the +upper part there is a little bar placed across, which stretches the cotton +and holds it in the mould. The tallow is then melted, and the moulds are +filled. After 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. The 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. In the same way are made +these candles of stearin and of paraffin. It is a curious thing to see how +wax candles are made. A 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. These are carried to a heater, where +the wax is melted. As 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. When 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. When they have been thus clothed, or +fed, or made up to that thickness, they are taken off, and placed +elsewhere. I have here, by the kindness of Mr. Field, several specimens of +these candles. Here is one only half-finished. They 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. This 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. + +We must not, however, take up more time about the mere manufacture, but go +a little further into the matter. I have not yet referred you to luxuries +in candles (for there is such a thing as luxury in candles). See how +beautifully these are coloured: you see here mauve, magenta, and all the +chemical colours recently introduced, applied to candles. You observe, +also, different forms employed. Here is a fluted pillar most beautifully +shaped; and I have also here some candles sent me by Mr. Pearsall, 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. All, however, +that is fine and beautiful is not useful. These fluted candles, pretty as +they are, are bad candles; they are bad because of their external shape. +Nevertheless, 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. + +Now, as to the light of the candle. We will light one or two, and set them +at work in the performance of their proper functions. You observe a candle +is a very different thing from a lamp. With 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. When the flame runs +down the cotton to the oil, it gets extinguished, but it goes on burning +in the part above. Now, 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? We shall presently examine that; but there is a much +more wonderful thing about the burning of a candle than this. You 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? How is it +that this solid gets there, it not being a fluid? or, when it is made a +fluid, then how is it that it keeps together? This is a wonderful thing +about a candle. + +We 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? Here 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. +I have very often admired it. They 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. By 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. + +You see, then, in the first instance, that a beautiful cup is formed. As +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. If 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. You 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. No 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. You 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. I hope you will now +see that the perfection of a process--that is, its utility--is the better +point of beauty about it. It is not the best looking thing, but the best +acting thing, which is the most advantageous to us. This good-looking +candle is a bad burning one. There 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. You 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. As 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. Now, 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. We +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? Why does it occur?" and you will in the course of time find +out the reason. + +Then, 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. You know that the flames on +these burning wicks in candles made of beeswax, 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. They are fenced off from the fluid below, and do +not encroach on the cup at the sides. I 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. A 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. + +But how does the flame get hold of the fuel? There is a beautiful point +about that--_capillary attraction_[4]. "Capillary attraction!" you +say,--"the attraction of hairs." Well, never mind the name: it was given +in old times, before we had a good understanding of what the real power +was. It 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. Now, I am going to give you one or two +instances of capillary attraction. It is that kind of action or attraction +which makes two things that do not dissolve in each other still hold +together. When 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. This is by that kind of attraction of which I am about to speak. And, +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. I 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. +We may consider the plate to be the candle, and the salt the wick, and +this solution the melted tallow. (I have coloured the fluid, that you may +see the action better.) You 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. + +[Illustration: Fig. 1.] + +If 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. It 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. When 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. I 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.[5] 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. In fact, wicks are sometimes made of +a kind of wire gauze. You 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. +You 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? The vessel is full +of water, and yet you see the water goes in and runs out as if it were +empty. In order to prove this to you, I have only to empty it. The 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. In 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. + +Here is another application of the same principle. You see this bit of +cane. I 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. They are enabled to do so by the permeability of the cane in +one direction, and by its capillarity. If I place this piece of cane on a +plate containing some camphin (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. There +being no pores at the side, the fluid cannot go in that direction, but +must pass through its length. Already the fluid is at the top of the cane: +now I can light it and make it serve as a candle. The fluid has risen by +the capillary attraction of the piece of cane, just as it does through the +cotton in the candle. + +Now, the only reason why the candle does not burn all down the side of the +wick is, that the melted tallow extinguishes the flame. You know that a +candle, if turned upside down, so as to allow the fuel to run upon the +wick, will be put out. The 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. + +There 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. In order that you may +understand that, let me shew you a very pretty, but very common-place +experiment. If you blow a candle out cleverly, you will see the vapour +rise from it. You 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. I 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. +I 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. + +Now, as to the shape or form of the flame. It 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. + +[Illustration: Fig. 2.] + +You 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. What diamond can shine like flame? It owes +its lustre at night-time to the very flame shining upon it. The 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. The candle +alone shines by itself, and for itself, or for those who have arranged the +materials. Now, let us look a little at the form of the flame as you see +it under the glass shade. It 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. It 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 +part above. + +[Illustration: Fig. 3.] + +I have a drawing here, sketched many years ago by Hooke, when he made his +investigations. It is the drawing of the flame of a lamp, but it will +apply to the flame of a candle. The cup of the candle is the vessel or +lamp, the melted spermaceti is the oil, and the wick is common to both. +Upon that he sets this little flame, and then he represents what is +true--a certain quantity of matter rising about it which you do not see, +and which, if you have not been here before, or are not familiar with the +subject, you will not know of. He has here represented the parts of the +surrounding atmosphere that are very essential to the flame, and that are +always present with it. There is a current formed, which draws the flame +out--for the flame which you see is really drawn out by the current, and +drawn upward to a great height--just as Hooke has here shewn you by that +prolongation of the current in the diagram. You may see this by taking a +lighted candle, and putting it in the sun so as to get its shadow thrown +on a piece of paper. How remarkable it is that that thing which is light +enough to produce shadows of other objects, can be made to throw its own +shadow on a piece of white paper or card, so that you can actually see +streaming round the flame something which is not part of the flame, but is +ascending and drawing the flame upwards. Now, I am going to imitate the +sunlight, by applying the voltaic battery to the electric lamp. You now +see our sun, and its great luminosity; and by placing a candle between it +and the screen, we get the shadow of the flame. + +[Illustration: Fig. 4.] + +You observe the shadow of the candle and of the wick; then there is a +darkish part, as represented in the diagram, and then a part which is more +distinct. Curiously enough, however, what we see in the shadow as the +darkest part of the flame is, in reality, the brightest part; and here you +see streaming upwards the ascending current of hot air, as shewn by +Hooke, which draws out the flame, supplies it with air, and cools the +sides of the cup of melted fuel. + +I can give you here a little further illustration, for the purpose of +shewing you how flame goes up or down; according to the current. I have +here a flame--it is not a candle flame--but you can, no doubt, by this +time, generalise enough to be able to compare one thing with another. What +I am about to do is to change the ascending current that takes the flame +upwards into a descending current. This I can easily do by the little +apparatus you see before me. The flame, as I have said, is not a candle +flame, but it is produced by alcohol, so that it shall not smoke too much. +I will also colour the flame with another substance[6], so that you may +trace its course; for with the spirit alone you could hardly see well +enough to have the opportunity of tracing its direction. By lighting this +spirit-of-wine, we have then a flame produced; and you observe that when +held in the air, it naturally goes upwards. + +[Illustration: Fig. 5] + +You understand now easily enough why flames go up under ordinary +circumstances--it is because of the draught of air by which the combustion +is formed. But now, by blowing the flame down, you see I am enabled to +make it go downwards into this little chimney--the direction of the +current being changed. Before we have concluded this course of lectures, +we shall shew you a lamp in which the flame goes up and the smoke goes +down, or the flame goes down and the smoke goes up. You see, then, that we +have the power in this way of varying the flame in different directions. + +There are now some other points that I must bring before you. Many of the +flames you see here vary very much in their shape by the currents of air +blowing around them in different directions; but we can, if we like, make +flames so that they will look like fixtures, and we can photograph +them--indeed, we have to photograph them--so that they become fixed to us, +if we wish to find out everything concerning them. That, however, is not +the only thing I wish to mention. If I take a flame sufficiently large, it +does not keep that homogeneous, that uniform condition of shape, but it +breaks out with a power of life which is quite wonderful. I am about to +use another kind of fuel, but one which is truly and fairly a +representative of the wax or tallow of a candle. I have here a large ball +of cotton, which will serve as a wick. And, now that I have immersed it in +spirit and applied a light to it, in what way does it differ from an +ordinary candle? Why, it differs very much in one respect, that we have a +vivacity and power about it, a beauty and a life entirely different from +the light presented by a candle. You see those fine tongues of flame +rising up. You have the same general disposition of the mass of the flame +from below upwards; but, in addition to that, you have this remarkable +breaking out into tongues which you do not perceive in the case of a +candle. Now, why is this? I must explain it to you, because when you +understand that perfectly, you will be able to follow me better in what I +have to say hereafter. I suppose some here will have made for themselves +the experiment I am going to shew you. Am I right in supposing that +anybody here has played at snapdragon? I do not know a more beautiful +illustration of the philosophy of flame, as to a certain part of its +history, than the game of snapdragon. First, here is the dish; and let me +say, that when you play snapdragon properly, you ought to have the dish +well-warmed; you ought also to have warm plums and warm brandy, which, +however, I have not got. When you have put the spirit into the dish, you +have the cup and the fuel; and are not the raisins acting like the wicks? +I now throw the plums into the dish, and light the spirit, and you see +those beautiful tongues of flame that I refer to. You have the air +creeping in over the edge of the dish forming these tongues. Why? Because, +through the force of the current and the irregularity of the action of the +flame, it cannot flow in one uniform stream. The air flows in so +irregularly that you have what would otherwise be a single image, broken +up into a variety of forms, and each of these little tongues has an +independent existence of its own. Indeed, I might say, you have here a +multitude of independent candles. You must not imagine, because you see +these tongues all at once, that the flame is of this particular shape. A +flame of that shape is never so at any one time. Never is a body of flame, +like that which you just saw rising from the ball, of the shape it appears +to you. It consists of a multitude of different shapes, succeeding each +other so fast that the eye is only able to take cognisance of them all at +once. In former times, I purposely analysed a flame of that general +character, and the diagram shews you the different parts of which it is +composed. They do not occur all at once: it is only because we see these +shapes in such rapid succession, that they seem to us to exist all at one +time. + +[Illustration: Fig. 6.] + +It is too bad that we have not got further than my game of snapdragon; but +we must not, under any circumstances, keep you beyond your time. It will +be a lesson to me in future to hold you more strictly to the philosophy of +the thing, than to take up your time so much with these illustrations. + + + + +LECTURE II. + +A CANDLE: BRIGHTNESS OF THE FLAME--AIR NECESSARY FOR +COMBUSTION--PRODUCTION OF WATER. + + +We were occupied the last time we met in considering the general character +and arrangement as regards the fluid portion of a candle, and the way in +which that fluid got into the place of combustion. You see, when we have a +candle burning fairly in a regular, steady atmosphere, it will have a +shape something like the one shewn in the diagram, and will look pretty +uniform, although very curious in its character. And now, I have to ask +your attention to the means by which we are enabled to ascertain what +happens in any particular part of the flame--why it happens, what it does +in happening, and where, after all, the whole candle goes to: because, as +you know very well, a candle being brought before us and burned, +disappears, if burned properly, without the least trace of dirt in the +candlestick--and this is a very curious circumstance. In order, then, to +examine this candle carefully, I have arranged certain apparatus, the use +of which you will see as I go on. Here is a candle: I am about to put the +end of this glass tube into the middle of the flame--into that part which +old Hooke has represented in the diagram as being rather dark, and which +you can see at any time, if you will look at a candle carefully, without +blowing it about. We will examine this dark part first. + +[Illustration: Fig. 7.] + +Now, I take this bent glass tube, and introduce one end into that part of +the flame, and you see at once that something is coming from the flame, +out at the other end of the tube; and if I put a flask there, and leave it +for a little while, you will see that something from the middle part of +the flame is gradually drawn out, and goes through the tube and into that +flask, and there behaves very differently from what it does in the open +air. It not only escapes from the end of the tube, but falls down to the +bottom of the flask like a heavy substance, as indeed it is. We find that +this is the wax of the candle made into a vaporous fluid--not a gas. (You +must learn the difference between a gas and a vapour: a gas remains +permanent, a vapour is something that will condense.) If you blow out a +candle, you perceive a very nasty smell, resulting from the condensation +of this vapour. That is very different from what you have outside the +flame; and, in order to make that more clear to you, I am about to produce +and set fire to a larger portion of this vapour--for what we have in the +small way in a candle, to understand thoroughly, we must, as philosophers, +produce in a larger way, if needful, that we may examine the different +parts. And now Mr. Anderson will give me a source of heat, and I am about +to shew you what that vapour is. Here is some wax in a glass flask, and I +am going to make it hot, as the inside of that candle-flame is hot, and +the matter about the wick is hot. [The Lecturer placed some wax in a glass +flask, and heated it over a lamp.] Now, I dare say that is hot enough for +me. You see that the wax I put in it has become fluid, and there is a +little smoke coming from it. We shall very soon have the vapour rising up. +I will make it still hotter, and now we get more of it, so that I can +actually pour the vapour out of the flask into that basin, and set it on +fire there. This, then, is exactly the same kind of vapour as we have in +the middle of the candle; and that you may be sure this is the case, let +us try whether we have not got here, in this flask, a real combustible +vapour out of the middle of the candle. [Taking the flask into which the +tube from the candle proceeded, and introducing a lighted taper.] See how +it burns. Now, this is the vapour from the middle of the candle, produced +by its own heat; and that is one of the first things you have to consider +with respect to the progress of the wax in the course of its combustion, +and as regards the changes it undergoes. I will arrange another tube +carefully in the flame, and I should not wonder if we were able, by a +little care, to get that vapour to pass through the tube to the other +extremity, where we will light it, and obtain absolutely the flame of the +candle at a place distant from it. Now, look at that. Is not that a very +pretty experiment? Talk about laying on gas--why, we can actually lay on a +candle! And you see from this that there are clearly two different kinds +of action--one the _production_ of the vapour, and the other the +_combustion_ of it--both of which take place in particular parts of the +candle. + +[Illustration: Fig. 8] + +I shall get no vapour from that part which is already burnt. If I raise +the tube (fig. 7) to the upper part of the flame, so soon as the vapour +has been swept out, what comes away will be no longer combustible: It is +already burned. How burned? Why, burned thus:--In the middle of the flame, +where the wick is, there is this combustible vapour; on the outside of the +flame is the air which we shall find necessary for the burning of the +candle; between the two, intense chemical action takes place, whereby the +air and the fuel act upon each other, and at the very same time that we +obtain light the vapour inside is destroyed. If you examine where the heat +of a candle is, you will find it very curiously arranged. Suppose I take +this candle, and hold a piece of paper close upon the flame, where is the +heat of that flame? Do you not see that it is _not_ in the inside? It is +in a ring, exactly in the place where I told you the chemical action was; +and even in my irregular mode of making the experiment, if there is not +too much disturbance, there will always be a ring. This is a good +experiment for you to make at home. Take a strip of paper, have the air in +the room quiet, and put the piece of paper right across the middle of the +flame (I must not talk while I make the experiment), and you will find +that it is burnt in two places, and that it is not burnt, or very little +so, in the middle; and when you have tried the experiment once or twice, +so as to make it nicely, you will be very interested to see where the heat +is, and to find that it is where the air and the fuel come together. + +This is most important for us as we proceed with our subject. Air is +absolutely necessary for combustion; and, what is more, I must have you +understand that _fresh_ air is necessary, or else we should be imperfect +in our reasoning and our experiments. Here is a jar of air. I place it +over a candle, and it burns very nicely in it at first, shewing that what +I have said about it is true; but there will soon be a change. See how the +flame is drawing upwards, presently fading, and at last going out. And +going out, why? Not because it wants air merely, for the jar is as full +now as it was before; but it wants pure, fresh air. The jar is full of +air, partly changed, partly not changed; but it does not contain +sufficient of the fresh air which is necessary for the combustion of a +candle. These are all points which we, as young chemists, have to gather +up; and if we look a little more closely into this kind of action, we +shall find certain steps of reasoning extremely interesting. For instance, +here is the oil-lamp I shewed you--an excellent lamp for our +experiments--the old Argand lamp. I now make it like a candle [obstructing +the passage of air into the centre of the flame]; there is the cotton; +there is the oil rising up it; and there is the conical flame. It burns +poorly, because there is a partial restraint of air. I have allowed no air +to get to it, save round the outside of the flame, and it does not burn +well. I cannot admit more air from the outside, because the wick is large; +but if, as Argand did so cleverly, I open a passage to the middle of the +flame, and so let air come in there, you will see how much more +beautifully it burns. If I shut the air off, look how it smokes; and why? +We have now some very interesting points to study. We have the case of the +combustion of a candle; we have the case of a candle being put out by the +want of air; and we have now the case of imperfect combustion; and this is +to us so interesting, that I want you to understand it as thoroughly as +you do the case of a candle burning in its best possible manner. I will +now make a great flame, because we need the largest possible +illustrations. Here is a larger wick [burning turpentine on a ball of +cotton]. All these things are the same as candles, after all. If we have +larger wicks, we must have a larger supply of air, or we shall have less +perfect combustion. Look now at this black substance going up into the +atmosphere; there is a regular stream of it. I have provided means to +carry off the imperfectly burned part, lest it should annoy you. Look at +the soots that fly off from the flame: see what an imperfect combustion it +is, because it cannot get enough air. What, then, is happening? Why, +certain things which are necessary to the combustion of a candle are +absent, and very bad results are accordingly produced; but we see what +happens to a candle when it is burnt in a pure and proper state of air. At +the time when I shewed you this charring by the ring of flame on the one +side of the paper, I might have also shewn you, by turning to the other +side, that the burning of a candle produces the same kind of +soot--charcoal or carbon. + +But, before I shew that, let me explain to you--as it is quite necessary +for our purpose--that, though I take a candle and give you, as the general +result, its combustion in the form of a flame, we must see whether +combustion is always in this condition, or whether there are other +conditions of flame; and we shall soon discover that there are, and that +they are most important to us. I think, perhaps, the best illustration of +such a point to us, as juveniles, is to shew the result of strong +contrast. Here is a little gunpowder. You know that gunpowder burns with +flame--we may fairly call it flame. It contains carbon and other +materials, which altogether cause it to burn with a flame. And here is +some pulverised iron, or iron filings. Now, I purpose burning these two +things together. I have a little mortar in which I will mix them. (Before +I go into these experiments, let me hope that none of you, by trying to +repeat them, for fun's sake, will do any harm. These things may all be +very properly used if you take care; but without that, much mischief will +be done.) Well, then, here is a little gunpowder, which I put at the +bottom of that little wooden vessel, and mix the iron filings up with it, +my object being to make the gunpowder set fire to the filings and burn +them in the air, and thereby shew the difference between substances +burning with flame and not with flame. Here is the mixture; and when I set +fire to it, you must watch the combustion, and you will see that it is of +two kinds. You will see the gunpowder burning with a flame, and the +filings thrown up. You will see them burning too, but without the +production of flame. They will each burn separately. [The Lecturer then +ignited the mixture.] There is the gunpowder, which burns with a flame; +and there are the filings--they burn with a different kind of combustion. +You see, then, these two great distinctions; and upon these differences +depend all the utility and all the beauty of flame which we use for the +purpose of giving out light. When we use oil, or gas, or candle, for the +purpose of illumination, their fitness all depends upon these different +kinds of combustion. + +There are such curious conditions of flame, that it requires some +cleverness and nicety of discrimination to distinguish the kinds of +combustion one from another. For instance, here is a powder which is very +combustible, consisting, as you see, of separate little particles. It is +called _lycopodium_[7], and each of these particles can produce a vapour, +and produce its own flame; but, to see them burning, you would imagine it +was all one flame. I will now set fire to a quantity, and you will see the +effect. We saw a cloud of flame, apparently in one body; but that rushing +noise [referring to the sound produced by the burning] was a proof that +the combustion was not a continuous or regular one. This is the lightning +of the pantomimes, and a very good imitation. [The experiment was twice +repeated by blowing lycopodium from a glass tube through a spirit-flame.] +This is not an example of combustion like that of the filings I have been +speaking of, to which we must now return. + +Suppose I take a candle, and examine that part of it which appears +brightest to our eyes. Why, there I get these black particles, which +already you have seen many times evolved from the flame, and which I am +now about to evolve in a different way. I will take this candle and clear +away the gutterage, which occurs by reason of the currents of air; and if +I now arrange a glass tube so as just to dip into this luminous part, as +in our first experiment, only higher, you see the result. In place of +having the same white vapour that you had before, you will now have a +black vapour. There it goes, as black as ink. It is certainly very +different from the white vapour; and when we put a light to it, we shall +find that it does not burn, but that it puts the light out. Well, these +particles, as I said before, are just the smoke of the candle; and this +brings to mind that old employment which Dean Swift recommended to +servants for their amusement, namely, writing on the ceiling of a room +with a candle. But what is that black substance? Why, it is the same +carbon which exists in the candle. How comes it out of the candle? It +evidently existed in the candle, or else we should not have had it here. +And now I want you to follow me in this explanation. You would hardly +think that all those substances which fly about London, in the form of +soots and blacks, are the very beauty and life of the flame, and which are +burned in it as those iron filings were burned here. Here is a piece of +wire gauze, which will not let the flame go through it; and I think you +will see, almost immediately, that when I bring it low enough to touch +that part of the flame which is otherwise so bright, that it quells and +quenches it at once, and allows a volume of smoke to rise up. + +I want you now to follow me in this point,--that whenever a substance +burns, as the iron filings burnt in the flame of gunpowder, without +assuming the vaporous state (whether it becomes liquid or remains solid), +it becomes exceedingly luminous. I have here taken three or four examples +apart from the candle, on purpose to illustrate this point to you; because +what I have to say is applicable to all substances, whether they burn or +whether they do not burn,--that they are exceedingly bright if they retain +their solid state, and that it is to this presence of solid particles in +the candle-flame that it owes its brilliancy. + +Here is a platinum-wire, a body which does not change by heat. If I heat +it in this flame, see how exceedingly luminous it becomes. I will make the +flame dim, for the purpose of giving a little light only, and yet you will +see that the heat which it can give to that platinum-wire, though far less +than the heat it has itself, is able to raise the platinum-wire to a far +higher state of effulgence. This flame has carbon in it; but I will take +one that has no carbon in it. There is a material, a kind of fuel--a +vapour, or gas, whichever you like to call it--in that vessel, and it has +no solid particles in it; so I take that because it is an example of flame +itself burning without any solid matter whatever; and if I now put this +solid substance in it, you see what an intense heat it has, and how +brightly it causes the solid body to glow. This is the pipe through which +we convey this particular gas, which we call hydrogen, and which you shall +know all about next time we meet. And here is a substance called oxygen, +by means of which this hydrogen can burn; and although we produce, by +their mixture, far greater heat[8] than you can obtain from the candle, +yet there is very little light. If, however, I take a solid substance, and +put that into it, we produce an intense light If I take a piece of lime, a +substance which will not burn, and which will not vaporise by the heat +(and because it does not vaporise, remains solid, and remains heated), you +will soon observe what happens as to its glowing. I have here a most +intense heat, produced by the burning of hydrogen in contact with the +oxygen; but there is as yet very little light--not for want of heat, but +for want of particles which can retain their solid state; but when I hold +this piece of lime in the flame of the hydrogen as it burns in the oxygen, +see how it glows! This is the glorious lime-light, which rivals the +voltaic-light, and which is almost equal to sunlight. I have here a piece +of carbon or charcoal, which will burn and give us light exactly in the +same manner as if it were burnt as part of a candle. The heat that is in +the flame of a candle decomposes the vapour of the wax, and sets free the +carbon particles--they rise up heated and glowing as this now glows, and +then enter into the air. But the particles when burnt never pass off from +a candle in the form of carbon. They go off into the air as a perfectly +invisible substance, about which we shall know hereafter. + +Is it not beautiful to think that such a process is going on, and that +such a dirty thing as charcoal can become so incandescent? You see it +comes to this--that all bright flames contain these solid particles; all +things that burn and produce solid particles, either during the time they +are burning, as in the candle, or immediately after being burnt, as in the +case of the gunpowder and iron-filings,--all these things give us this +glorious and beautiful light. + +I will give you a few illustrations. Here is a piece of phosphorus, which +burns with a bright flame. Very well; we may now conclude that phosphorus +will produce, either at the moment that it is burning or afterwards, these +solid particles. Here is the phosphorus lighted, and I cover it over with +this glass for the purpose of keeping in what is produced. What is all +that smoke? That smoke consists of those very particles which are produced +by the combustion of the phosphorus. Here, again, are two substances. This +is chlorate of potassa, and this other sulphuret of antimony. I shall mix +these together a little, and then they may be burnt in many ways. I shall +touch them with a drop of sulphuric acid, for the purpose of giving you an +illustration of chemical action, and they will instantly burn[9]. [The +Lecturer then ignited the mixture by means of sulphuric acid.] Now, from +the appearance of things, you can judge for yourselves whether they +produce solid matter in burning. I have given you the train of reasoning +which will enable you to say whether they do or do not; for what is this +bright flame but the solid particles passing off? + +[Illustration: Fig. 9.] + +Mr. Anderson has in the furnace a very hot crucible,--I am about to throw +into it some zinc filings, and they will burn with a flame like gunpowder. +I make this experiment because you can make it well at home. Now, I want +you to see what will be the result of the combustion of this zinc. Here it +is burning--burning beautifully like a candle, I may say. But what is all +that smoke, and what are those little clouds of wool which will come to +you if you cannot come to them, and make themselves sensible to you in the +form of the old philosophic wool, as it was called? We shall have left in +that crucible, also, a quantity of this woolly matter. But I will take a +piece of this same zinc and make an experiment a little more closely at +home, as it were. You will have here the same thing happening. Here is the +piece of zinc, there [pointing to a jet of hydrogen] is the furnace, and +we will set to work and try and burn the metal. It glows, you see: there +is the combustion, and there is the white substance into which it burns. +And so, if I take that flame of hydrogen as the representative of a +candle, and shew you a substance like zinc burning in the flame, you will +see that it was merely during the action of combustion that this substance +glowed--while it was kept hot; and if I take a flame of hydrogen, and put +this white substance from the zinc into it, look how beautifully it glows, +and just because it is a solid substance. + +I will now take such a flame as I had a moment since, and set free from it +the particles of carbon. Here is some camphine, which will burn with a +smoke; but if I send these particles of smoke through this pipe into the +hydrogen flame, you will see they will burn and become luminous, because +we heat them a second time. There they are. Those are the particles of +carbon re-ignited a second time. They are those particles which you can +easily see by holding a piece of paper behind them, and which, whilst they +are in the flame, are ignited by the heat produced, and, when so ignited, +produce this brightness. When the particles are not separated, you get no +brightness. The flame of coal-gas owes its brightness to the separation, +during combustion, of these particles of carbon, which are equally in that +as in a candle. I can very quickly alter that arrangement. Here, for +instance, is a bright flame of gas. Supposing I add so much air to the +flame as to cause it all to burn before those particles are set free, I +shall not have this brightness; and I can do that in this way:--If I place +over the jet this wire-gauze cap, as you see, and then light the gas over +it, it burns with a non-luminous flame, owing to its having plenty of air +mixed with it before it burns; and if I raise the gauze, you see it does +not burn below[10]. There is plenty of carbon in the gas; but, because the +atmosphere can get to it, and mix with it before it burns, you see how +pale and blue the flame is. And if I blow upon a bright gas-flame, so as +to consume all this carbon before it gets heated to the glowing point, it +will also burn blue: [The Lecturer illustrated his remarks by blowing on +the gas-light.] The only reason why I have not the same bright light when +I thus blow upon the flame is, that the carbon meets with sufficient air +to burn it before it gets separated in the flame in a free state. The +difference is solely due to the solid particles not being separated before +the gas is burnt. + +You observe that there are certain products as the result of the +combustion of a candle, and that of these products one portion may be +considered as charcoal, or soot; that charcoal, when afterwards burnt, +produces some other product; and it concerns us very much now to ascertain +what that other product is. We shewed that something was going away; and I +want you now to understand how much is going up into the air; and for that +purpose we will have combustion on a little larger scale. From that candle +ascends heated air, and two or three experiments will shew you the +ascending current; but, in order to give you a notion of the quantity of +matter which ascends in this way, I will make an experiment by which I +shall try to imprison some of the products of this combustion. For this +purpose I have here what boys call a fire-balloon. I use this fire-balloon +merely as a sort of measure of the result of the combustion we are +considering; and I am about to make a flame in such an easy and simple +manner as shall best serve my present purpose. This plate shall be the +"cup," we will so say, of the candle; this spirit shall be our fuel; and I +am about to place this chimney over it, because it is better for me to do +so than to let things proceed at random. + +[Illustration: Fig. 10.] + +Mr. Anderson will now light the fuel, and here at the top we shall get the +results of the combustion. What we get at the top of that tube is exactly +the same, generally speaking, as you get from the combustion of a candle; +but we do not get a luminous flame here, because we use a substance which +is feeble in carbon. I am about to put this balloon--not into action, +because that is not my object--but to shew you the effect which results +from the action of those products which arise from the candle, as they +arise here from the furnace. [The balloon was held over the chimney, when +it immediately commenced to fill.] You see how it is disposed to ascend; +but we must not let it up, because it might come in contact with those +upper gas-lights, and that would be very inconvenient. [The upper +gas-lights were turned out, at the request of the Lecturer, and the +balloon was allowed to ascend.] Does not that shew you what a large bulk +of matter is being evolved? Now, there is going through this tube [placing +a large glass tube over a candle] all the products of that candle, and you +will presently see that the tube will become quite opaque. Suppose I take +another candle, and place it under a jar, and then put a light on the +other side, just to shew you what is going on. You see that the sides of +the jar become cloudy, and the light begins to burn feebly. It is the +products, you see, which make the light so dim, and this is the same thing +which makes the sides of the jar so opaque. If you go home and take a +spoon that has been in the cold air, and hold it over a candle--not so as +to soot it--you will find that it becomes dim, just as that jar is dim. If +you can get a silver dish, or something of that kind, you will make the +experiment still better. And now, just to carry your thoughts forward to +the time we shall next meet, let me tell you that it is _water_ which +causes the dimness; and when we next meet. I will shew you that we can +make it, without difficulty, assume the form of a liquid. + + + + +LECTURE III. + +PRODUCTS: WATER FROM THE COMBUSTION--NATURE OF WATER--A +COMPOUND--HYDROGEN. + + +I dare say you will remember that when we parted we had just mentioned the +word "products" from the candle. For when a candle burns we found we were +able, by nice adjustment, to get various products from it. There was one +substance which was not obtained when the candle was burning properly, +which was charcoal or smoke; and there was some other substance that went +upwards from the flame which did not appear as smoke, but took some other +form, and made part of that general current which, ascending from the +candle upwards, becomes invisible, and escapes. There were also other +products to mention. You remember that in that rising current having its +origin at the candle, we found that one part was condensable against a +cold spoon, or against a clean plate, or any other cold thing, and another +part was incondensable. + +We will first take the condensable part, and examine it; and, strange to +say, we find that that part of the product is just water--nothing but +water. On the last occasion I spoke of it incidentally, merely saying that +water was produced among the condensable products of the candle; but +to-day I wish to draw your attention to water, that we may examine it +carefully, especially in relation to this subject, and also with respect +to its general existence on the surface of the globe. + +Now, having previously arranged an experiment for the purpose of +condensing water from the products of the candle, my next point will be to +shew you this water; and perhaps one of the best means that I can adopt +for shewing its presence to so many at once, is to exhibit a very visible +action of water, and then to apply that test to what is collected as a +drop at the bottom of that vessel. I have here a chemical substance, +discovered by Sir Humphrey Davy, which has a very energetic action upon +water, which I shall use as a test of the presence of water. If I take a +little piece of it--it is called potassium, as coming from potash,--if I +take a little piece of it, and throw it into that basin, you see how it +shews the presence of water by lighting up and floating about, burning +with a violent flame. I am now going to take away the candle which has +been burning beneath the vessel containing ice and salt, and you see a +drop of water--a condensed product of the candle--hanging from under the +surface of the dish. + +[Illustration: Fig. 11.] + +I will shew you that potassium has the same action upon it as upon the +water in that basin in the experiment we have just tried. See, it takes +fire, and burns in just the same manner. I will take another drop upon +this glass slab, and when I put the potassium on to it, you see at once, +from its taking fire, that there is water present. Now, that water was +produced by the candle. In the same manner, if I put this spirit-lamp +under that jar, you will soon see the latter become damp, from the dew +which is deposited upon it--that dew being the result of combustion; and I +have no doubt you will shortly see by the drops of water which fall upon +the paper below, that there is a good deal of water produced from the +combustion of the lamp. I will let it remain, and you can afterwards see +how much water has been collected. So, if I take a gas-lamp, and put any +cooling arrangement over it, I shall get water--water being likewise +produced from the combustion of gas. Here, in this bottle, is a quantity +of water--perfectly pure, distilled water, produced from the combustion of +a gas-lamp--in no point different from the water that you distil from the +river, or ocean, or spring, but exactly the same thing. Water is one +individual thing--it never changes. We can add to it by careful +adjustment, for a little while, or we can take it apart, and get other +things from it; but water, as water, remains always the same, either in a +solid, liquid, or fluid state. Here, again [holding another bottle], is +some water produced by the combustion of an oil-lamp. A pint of oil, when +burnt fairly and properly, produces rather more than a pint of water. +Here, again, is some water, produced by a rather long experiment from a +wax candle. And so we can go on with almost all combustible substances, +and find that if they burn with a flame, as a candle, they produce water. +You may make these experiments yourselves. The head of a poker is a very +good thing to try with, and if it remains cold long enough over the +candle, you may get water condensed in drops on it; or a spoon or ladle, +or anything else may be used, provided it be clean, and can carry off the +heat, and so condense the water. + +And now--to go into the history of this wonderful production of water from +combustibles, and by combustion--I must first of all tell you that this +water may exist in different conditions; and although you may now be +acquainted with all its forms, they still require us to give a little +attention to them for the present, so that we may perceive how the water, +whilst it goes through its Protean changes, is entirely and absolutely the +same thing, whether it is produced from a candle, by combustion, or from +the rivers or ocean. + +First of all, water, when at the coldest, is ice. Now, we philosophers---I +hope that I may class you and myself together in this case--speak of water +as water, whether it be in its solid, or liquid, or gaseous state,--we +speak of it chemically as water. Water is a thing compounded of two +substances, one of which we have derived from the candle, and the other we +shall find elsewhere. Water may occur as ice; and you have had most +excellent opportunities lately of seeing this. Ice changes back into +water--for we had on our last Sabbath a strong instance of this change, by +the sad catastrophe which occurred in our own house, as well as in the +houses of many of our friends,--ice changes back into water when the +temperature is raised: water also changes into steam when it is warmed +enough. The water which we have here before us is in its densest +state[11], and although it changes in weight, in condition, in form, and +in many other qualities, it still is water; and whether we alter it into +ice by cooling, or whether we change it into steam by heat, it increases +in volume,--in the one case very strangely and powerfully, and in the +other case very largely and wonderfully. For instance, I will now take +this tin cylinder, and pour a little water into it; and seeing how much +water I pour in, you may easily estimate for yourselves how high it will +rise in the vessel: it will cover the bottom about two inches. I am now +about to convert the water into steam, for the purpose of shewing to you +the different volumes which water occupies in its different states of +water and steam. + +Let us now take the case of water changing into ice: we can effect that by +cooling it in a mixture of salt and pounded ice[12]; and I shall do so to +shew you the expansion of water into a thing of larger bulk when it is so +changed. These bottles [holding one] are made of strong cast iron, very +strong and very thick--I suppose they are the third of an inch in +thickness; they are very carefully filled with water, so as to exclude all +air, and then they are screwed down tight. We shall see that when we +freeze the water in these iron vessels, they will not be able to hold the +ice, and the expansion within them will break them in pieces as these +[pointing to some fragments] are broken, which have been bottles of +exactly the same kind. I am about to put these two bottles into that +mixture of ice and salt, for the purpose of shewing that when water +becomes ice, it changes in volume in this extraordinary way. + +In the mean time look at the change which has taken place in the water to +which we have applied heat--it is losing its fluid state. You may tell +this by two or three circumstances. I have covered the mouth of this glass +flask, in which water is boiling, with a watch-glass. Do you see what +happens? It rattles away like a valve chattering, because the steam rising +from the boiling water sends the valve up and down, and forces itself out, +and so makes it clatter. You can very easily perceive that the flask is +quite full of steam, or else it would not force its way out. You see, +also, that the flask contains a substance very much larger than the water, +for it fills the whole of the flask over and over again, and there it is +blowing away into the air; and yet you cannot observe any great diminution +in the bulk of the water, which shews you that its change of bulk is very +great when it becomes steam. + +I have put our iron bottles containing water into this freezing mixture, +that you may see what happens. No communication will take place, you +observe, between the water in the bottles and the ice in the outer vessel. +But there will be a conveyance of heat from the one to the other; and if +we are successful--we are making our experiment in very great haste--I +expect you will by-and-by, so soon as the cold has taken possession of the +bottles and their contents, hear a pop on the occasion of the bursting of +the one bottle or the other; and, when we come to examine the bottles, we +shall find their contents masses of ice, partly enclosed by the covering +of iron which is too small for them, because the ice is larger in bulk +than the water. You know very well that ice floats upon water: if a boy +falls through a hole into the water, he tries to get on the ice again to +float him up. Why does the ice float?--think of that, and philosophise. +Because the ice is larger than the quantity of water which can produce it; +and therefore the ice weighs the lighter, and the water is the heavier. + +To return now to the action of heat on water. See what a stream of vapour +is issuing from this tin vessel! You observe, we must have made it quite +full of steam to have it sent out in that great quantity. And now, as we +can convert the water into steam by heat, we convert it back into liquid +water by the application of cold. And if we take a glass, or any other +cold thing, and hold it over this steam, see how soon it gets damp with +water; it will condense it until the glass is warm--it condenses the water +which is now running down the sides of it. I have here another experiment +to shew the condensation of water from a vaporous state back into a liquid +state, in the same way as the vapour, one of the products of the candle, +was condensed against the bottom of the dish, and obtained in the form of +water; and to shew you how truly and thoroughly these changes take place, +I will take this tin flask, which is now full of steam, and close the top. +We shall see what takes place when we cause this water or steam to return +back to the fluid state by pouring some cold water on the outside. [The +Lecturer poured the cold water over the vessel, when it immediately +collapsed.] You see what has happened. If I had closed the stopper, and +still kept the heat applied to it, it would have burst the vessel; yet, +when the steam returns to the state of water, the vessel collapses, there +being a vacuum produced inside by the condensation of the steam. I shew +you these experiments for the purpose of pointing out that in all these +occurrences there is nothing that changes the water into any other +thing--it still remains water; and so the vessel is obliged to give way, +and is crushed inwards, as in the other case, by the further application +of heat, it would have been blown outwards. + +[Illustration: Fig. 12.] + +And what do you think the bulk of that water is when it assumes the +vaporous condition? You see that cube [pointing to a cubic foot]. There, +by its side, is a cubic inch, exactly the same shape as the cubic foot, +and that bulk of water [the cubic inch] is sufficient to expand into that +bulk [the cubic foot] of steam; and, on the contrary, the application of +cold will contract that large quantity of steam into this small quantity +of water. + +[Illustration: Fig. 13.] + +[One of the iron bottles burst at that moment.] Ah! There is one of our +bottles burst, and here you see is a crack down one side an eighth of an +inch in width. [The other now exploded, sending the freezing mixture in +all directions.] This other bottle is also broken; although the iron was +nearly half-an-inch thick, the ice has burst it asunder. These changes +always take place in water: they do not require to be always produced by +artificial means,--we only use them here because we want to produce a +small winter round that little bottle, instead of a long and severe one. +But if you go to Canada, or to the North, you will find the temperature +there out of doors will do the same thing as has been done here by the +freezing mixture. + +To return to our quiet philosophy. We shall not in future be deceived, +therefore, by any changes that are produced in water. Water is the same +everywhere, whether produced from the ocean or from the flame of the +candle. Where, then, is this water which we get from a candle? I must +anticipate a little, and tell you. It evidently comes, as to part of it, +from the candle; but is it within the candle beforehand? No. It is not in +the candle; and it is not in the air round about the candle which is +necessary for its combustion. It is neither in one nor the other, but it +comes from their conjoint action, a part from the candle, a part from the +air; and this we have now to trace, so that we may understand thoroughly +what is the chemical history of a candle when we have it burning on our +table. How shall we get at this? I myself know plenty of ways, but I want +_you_ to get at it from the association in your own minds of what I have +already told you. + +I think you can see a little in this way. We had just now the case of a +substance which acted upon the water in the way that Sir Humphrey Davy +shewed us[13], and which I am now going to recall to your minds by making +again an experiment upon that dish. It is a thing which we have to handle +very carefully, for you see, if I allow a little splash of water to come +upon this mass, it sets fire to part of it; and if there were free access +of air, it would quickly set fire to the whole. Now, this is a metal--a +beautiful and bright metal--which rapidly changes in the air, and, as you +know, rapidly changes in water. I will put a piece on the water, and you +see it burns beautifully, making a floating lamp, using the water in the +place of air. Again, if we take a few iron filings or turnings, and put +them in water, we find that they likewise undergo an alteration. They do +not change so much as this potassium does, but they change somewhat in the +same way; they become rusty, and shew an action upon the water, though in +a different degree of intensity to what this beautiful metal does: but +they act upon the water in the same manner generally as this potassium. I +want you to put these different facts together in your minds. I have +another metal here [zinc], and when we examined it with regard to the +solid substance produced by its combustion, we had an opportunity of +seeing that it burned; and I suppose, if I take a little strip of this +zinc and put it over the candle, you will see something half-way, as it +were, between the combustion of potassium on the water and the action of +iron,--you see there is a sort of combustion. It has burned, leaving a +white ash or residuum, and here also we find that the metal has a certain +amount of action upon water. + +By degrees we have learned how to modify the action of these different +substances, and to make them tell us what we want to know. And now, first +of all, I take iron. It is a common thing in all chemical reactions, where +we get any result of this kind, to find that it is increased by the action +of heat; and if we want to examine minutely and carefully the action of +bodies one upon another, we often have to refer to the action of heat. You +are aware, I believe, that iron-filings burn beautifully in the air; but I +am about to shew you an experiment of this kind, because it will impress +upon you what I am going to say about iron in its action on water. If I +take a flame and make it hollow;--you know why, because I want to get air +to it and into it, and therefore I make it hollow--and then take a few +iron-filings and drop them into the flame, you see how well they burn. +That combustion results from the chemical action which is going on when we +ignite those particles. And so we proceed to consider these different +effects, and ascertain what iron will do when it meets with water. It will +tell us the story so beautifully, so gradually and regularly, that I think +it will please you very much. + +I have here a furnace with a pipe going through it like an iron +gun-barrel, and I have stuffed that barrel full of bright iron-turnings, +and placed it across the fire, to be made red-hot. We can either send air +through the barrel to come in contact with the iron, or we can send steam +from this little boiler at the end of the barrel. Here is a stop-cock +which shuts off the steam from the barrel until we wish to admit it. There +is some water in these glass jars, which I have coloured blue, so that you +may see what happens. Now, you know very well that any steam I might send +through that barrel, if it went through into the water, would be +condensed; for you have seen that steam cannot retain its gaseous form if +it be cooled down. + +[Illustration: Fig. 14.] + +You saw it here [pointing to the tin flask] crushing itself into a small +bulk, and causing the flask holding it to collapse; so that if I were to +send steam through that barrel, it would be condensed--supposing the +barrel were cold: it is, therefore, heated to perform the experiment I am +now about to shew you. I am going to send the steam through the barrel in +small quantities; and you shall judge for yourselves, when you see it +issue from the other end, whether it still remains steam. Steam is +condensible into water, and when you lower the temperature of steam, you +convert it back into fluid water; but I have lowered the temperature of +the gas which I have collected in this jar, by passing it through water +after it has traversed the iron barrel, and still it does not change back +into water. I will take another test and apply to this gas. (I hold the +jar in an inverted position, or my substance would escape.) If I now apply +a light to the mouth of the jar, it ignites with a slight noise. That +tells you that it is not steam. Steam puts out a fire--it does not burn; +but you saw that what I had in that jar burnt. We may obtain this +substance equally from water produced from the candle-flame as from any +other source. When it is obtained by the action of the iron upon the +aqueous vapour, it leaves the iron in a state very similar to that in +which these filings were after they were burnt. It makes the iron heavier +than it was before. So long as the iron remains in the tube and is heated, +and is cooled again without the access of air or water, it does not change +in its weight; but after having had this current of steam passed over it, +it then comes out heavier that it was before, having taken something out +of the steam, and having allowed something else to pass forth, which we +see here. And now, as we have another jar full, I will shew you something +most interesting. It is a combustible gas; and I might at once take this +jar and set fire to the contents, and shew you that it is combustible; but +I intend to shew you more if I can. It is also a very light substance. +Steam will condense: this body will rise in the air, and not condense. + +[Illustration: Fig. 15] + +Suppose I take another glass jar, empty of all but air: if I examine it +with a taper, I shall find that it contains nothing but air. I will now +take this jar full of the gas that I am speaking of, and deal with it as +though it were a light body. I will hold both upside-down, and turn the +one up under the other; and that which did contain the gas procured from +the steam, what does it contain now? You will find it now only contains +air. But look! Here is the combustible substance [taking the other jar] +which I have poured out of the one jar into the other. It still preserves +its quality, and condition, and independence, and therefore is the more +worthy of our consideration, as belonging to the products of a candle. + +Now, this substance which we have just prepared by the action of iron on +the steam or water, we can also get by means of those other things which +you have already seen act so well upon the water. If I take a piece of +potassium, and make the necessary arrangements, it will produce this gas; +and if, instead, a piece of zinc, I find, when I come to examine it very +carefully, that the main reason why this zinc cannot act upon the water +continuously as the other metal does, is because the result of the action +of the water envelopes the zinc in a kind of protecting coat. We have +learned in consequence, that if we put into our vessel only the zinc and +water, they by themselves do not give rise to much action, and we get no +result. But suppose I proceed to dissolve off this varnish--this +encumbering substance--which I can do by a little acid; the moment I do +this, I find the zinc acting upon the water exactly as the iron did, but +at the common temperature. The acid in no way is altered, except in its +combination with the oxide of zinc, which is produced. I have now poured +the acid into the glass, and the effect is as though I were applying heat +to cause this boiling up. There is something coming off from the zinc very +abundantly, which is not steam. There is a jar full of it; and you will +find that I have exactly the same combustible substance remaining in the +vessel, when I hold it upside-down, that I produced during the experiment +with the iron barrel. This is what we get from water--the same substance +which is contained in the candle. + +[Illustration: Fig. 16.] + +Let us now trace distinctly the connection between these two points. This +is hydrogen--a body classed among those things which in Chemistry we call +elements, because we can get nothing else out of them. A candle is not an +elementary body, because we can get carbon out of it; we can get this +hydrogen out of it, or at least out of the water which it supplies. And +this gas has been so named hydrogen, because it is that element which, in +association with another, generates water. [Footnote: [greek: hudos], +"water," and [greek: gennao], "I generate."] Mr. Anderson having now been +able to get two or three jars of gas, we shall have a few experiments to +make, and I want to shew you the best way of making these experiments. I +am not afraid to shew you, for I wish you to make experiments, if you will +only make them with care and attention, and the assent of those around +you. As we advance in Chemistry, we are obliged to deal with substances +which are rather injurious, if in their wrong places--the acids, and heat, +and combustible things we use, might do harm if carelessly employed. If +you want to make hydrogen, you can make it easily from bits of zinc, and +sulphuric or muriatic acid. Here is what in former times was called the +"philosopher's candle." It is a little phial with a cork, and a tube or +pipe passing through it. + +[Illustration: Fig. 17.] + +And I am now putting a few little pieces of zinc into it. This little +instrument I am going to apply to a useful purpose in our +demonstrations--for I want to shew you that you can prepare hydrogen, and +make some experiments with it as you please at your own homes. Let me here +tell you why I am so careful to fill this phial nearly, and yet not quite +full. I do it because the evolved gas, which, as you have seen, is very +combustible, is explosive to a considerable extent when mixed with air, +and might lead to harm, if you were to apply a light to the end of that +pipe before all the air had been swept out of the space above the water. I +am now about to pour in the sulphuric acid. I have used very little zinc, +and more sulphuric acid and water, because I want to keep it at work for +some time. I therefore take care in this way to modify the proportions of +the ingredients, so that I may have a regular supply--not too quick, and +not too slow. Supposing I now take a glass and put it upside-down over the +end of the tube, because the hydrogen is light I expect that it will +remain in that vessel a little while. We will now test the contents of our +glass to see if there be hydrogen in it. I think I am safe in saying we +have caught some [applying a light]. There it is, you see. I will now +apply a light to the top of the tube. There is the hydrogen burning. There +is our philosophical candle. It is a foolish feeble sort of a flame, you +may say; but it is so hot that scarcely any common flame gives out so much +heat. It goes on burning regularly, and I am now about to put that flame +to burn under a certain arrangement, in order that we may examine its +results and make use of the information which we may thereby acquire. +Inasmuch as the candle produces water, and this gas comes out of the +water, let us see what this gives us by the same process of combustion +that the candle went through when it burnt in the atmosphere; and for that +purpose I am going to put the lamp under this apparatus, in order to +condense whatever may arise from the combustion within it In the course of +a short time you will see moisture appearing in the cylinder, and you will +get the water running down the side; and the water from this hydrogen +flame will have absolutely the same effect upon all our tests, being +obtained by the same general process as in the former case. This hydrogen +is a very beautiful substance. It is so light that it carries things up: +it is far lighter than the atmosphere; and I dare say I can shew you this +by an experiment which, if you are very clever, some of you may even have +skill enough to repeat. Here is our generator of hydrogen, and here are +some soap-suds. I have an india-rubber tube connected with the hydrogen +generator, and at the end of the tube is a tobacco-pipe. + +[Illustration: Fig. 18.] + +I can thus put the pipe into the suds, and blow bubbles by means of the +hydrogen. You observe how the bubbles fall downwards when I blow them with +my warm breath; but notice the difference when I blow them with hydrogen. +[The Lecturer here blew bubbles with hydrogen, which rose to the roof of +the theatre.] It shews you how light this gas must be in order to carry +with it not merely the ordinary soap-bubble, but the larger portion of a +drop hanging to the bottom of it. I can shew its lightness in a better way +than this; larger bubbles than these may be so lifted up; indeed, in +former times balloons used to be filled with this gas. Mr. Anderson will +fasten this tube on to our generator, and we shall have a stream of +hydrogen here with which we can charge this balloon made of collodion. I +need not even be very careful to get all the air out, for I know the power +of this gas to carry it up. [Two collodion balloons were inflated, and +sent up, one being held by a string.] Here is another larger one made of +thin membrane, which we will fill and allow to ascend. You will see they +will all remain floating about until the gas escapes. + +What, then, are the comparative weights of these substances? I have a +table here which will shew you the proportion which their weights bear to +each other. I have taken a pint and a cubic foot as the measures, and have +placed opposite to them the respective figures. A pint measure of this +hydrogen weighs three-quarters of our smallest weight (a grain), and a +cubic foot weighs one-twelfth of an ounce; whereas a pint of water weighs +8,750 grains, and a cubic foot of water weighs almost 1,000 ounces. You +see, therefore, what a vast difference there is between the weight of a +cubic foot of water and a cubic foot of hydrogen. + +Hydrogen gives rise to no substance that can become solid, either during +combustion or afterwards as a product of its combustion. But when it +burns, it produces water only; and if we take a cold glass and put it over +the flame, it becomes damp, and you have water, produced immediately in +appreciable quantity; and nothing is produced by its combustion but the +same water which you have seen the flame of the candle produce. It is +important to remember that this hydrogen is the only thing in nature which +furnishes water as the sole product of combustion. + +And now we must endeavour to find some additional proof of the general +character and composition of water; and for this purpose I will keep you a +little longer, so that at our next meeting we may be better prepared for +the subject. We have the power of arranging the zinc which you have seen +acting upon the water by the assistance of an acid, in such a manner as to +cause all the power to be evolved in the place where we require it I have +behind me a voltaic pile, and I am just about to shew you, at the end of +this lecture, its character and power, that you may see what we shall have +to deal with when next we meet. I hold here the extremities of the wires +which transport the power from behind me, and which I shall cause to act +on the water. + +We have previously seen what a power of combustion is possessed by the +potassium, or the zinc, or the iron-filings; but none of them shew such +energy as this. [The Lecturer here made contact between the two terminal +wires of the battery, when a brilliant flash of light was produced.] This +light is, in fact, produced by a forty-zinc power of burning: it is a +power that I can carry about in my hands, through these wires, at +pleasure--although, if I applied it wrongly to myself, it would destroy me +in an instant, for it is a most intense thing, and the power you see here +put forth while you count five [bringing the poles in contact, and +exhibiting the electric light] is equivalent to the power of several +thunder-storms, so great is its force[14]. And that you may see what +intense energy it has, I will take the ends of the wires which convey the +power from the battery, and with it I dare say I can burn this iron file. +Now, this is a chemical power, and one which, when we next meet, I shall +apply to water, and shew you what results we are able to produce. + + + + +LECTURE IV. + +HYDROGEN IN THE CANDLE--BURNS INTO WATER--THE OTHER PART OF WATER--OXYGEN. + +I see you are not tired of the candle yet, or I am sure you would not be +interested in the subject in the way you are. When our candle was burning, +we found it produced water exactly like the water we have around us; and +by further examination of this water we found in it that curious body, +hydrogen--that light substance of which there is some in this jar. We +afterwards saw the burning powers of that hydrogen, and that it produced +water. And I think I introduced to your notice an apparatus which I very +briefly said was an arrangement of chemical force, or power, or energy, so +adjusted as to convey its power to us in these wires; and I said I should +use that force to pull the water to pieces, to see what else there was in +the water besides hydrogen; because, you remember, when we passed the +water through the iron tube, we by no means got the weight of water back +which we put in, in the form of steam, though we had a very large quantity +of gas evolved. We have now to see what is the other substance present. +That you may understand the character and use of this instrument, let us +make an experiment or two. Let us put together, first of all, some +substances, knowing what they are, and then see what that instrument does +to them. There is some copper (observe the various changes which it can +undergo), and here is some nitric acid, and you will find that this, being +a strong chemical agent, will act very powerfully when I add it to the +copper. It is now sending forth a beautiful red vapour; but as we do not +want that vapour, Mr. Anderson will hold it near the chimney for a short +time, that we may have the use and beauty of the experiment without the +annoyance. The copper which I have put into the flask will dissolve: it +will change the acid and the water into a blue fluid, containing copper +and other things; and I propose then shewing you how this voltaic battery +deals with it; and in the mean-time we will arrange another kind of +experiment for you to see what power it has. This is a substance which is +to us like water--that is to say, it contains bodies which we do not know +of as yet, as water contains a body which we do not know as yet. Now, this +solution of a salt[15] I will put upon paper, and spread about, and apply +the power of the battery to it, and observe what will happen. Three or +four important things will happen which we shall take advantage of. I +place this wetted paper upon a sheet of tinfoil, which is convenient for +keeping all clean, and also for the advantageous application of the power; +and this solution, you see, is not at all affected by being put upon the +paper or tinfoil, nor by anything else I have brought in contact with it +yet, and which, therefore, is free to us to use as regards that +instrument. But first let us see that our instrument is in order. Here are +our wires. Let us see whether it is in the state in which it was last +time. We can soon tell. As yet, when I bring them together, we have no +power, because the conveyers--what we call the electrodes--the passages or +ways for the electricity--are stopped; but now Mr. Anderson by that +[referring to a sudden flash at the ends of the wires] has given me a +telegram to say that it is ready. Before I begin our experiment I will get +Mr. Anderson to break contact again at the battery behind me, and we will +put a platinum-wire across to connect the poles, and then if I find I can +ignite a pretty good length of this wire, we shall be safe in our +experiment. Now you will see the power. [The connection was established, +and the intermediate wire became red-hot.] There is the power running +beautifully through the wire, which I have made thin on purpose to shew +you that we have those powerful forces; and now, having that power, we +will proceed with it to the examination of water. + +I have here two pieces of platinum, and if I lay them down upon this piece +of paper [the moistened paper on the tinfoil], you will see no action; and +if I take them up, there is no change that you can see, but the +arrangement remains just as it was before. But, now, see what happens: if +I take these two poles and put either one or the other of them down +separately on the platinum-plates, they do nothing for me, both are +perfectly without action; but if I let them both be in contact at the same +moment, see what happens [a brown spot appeared under each pole of the +battery]. Look here at the effect that takes place, and see how I have +pulled something apart from the white--something brown; and I have no +doubt, if I were to arrange it thus, and were to put one of the poles to +the tinfoil on the other side of the paper--why, I get such a beautiful +action upon the paper, that I am going to see whether I cannot write with +it--a telegram, if you please. [The Lecturer here traced the word +"juvenile" on the paper with one of the terminal wires.] See there how +beautifully we can get our results! + +You see we have here drawn something, which we have not known about +before, out of this solution. Let us now take that flask from Mr. +Andersen's hands, and see what we can draw out of that. This, you know, is +a liquid which we have just made up from copper and nitric acid, whilst +our other experiments were in hand; and though I am making this experiment +very hastily, and may bungle a little, yet I prefer to let you see what I +do rather than prepare it beforehand. + +Now, see what happens. These two platinum-plates are the two ends (or I +will make them so immediately) of this apparatus; and I am about to put +them in contact with that solution just as we did a moment ago on the +paper. It does not matter to us whether the solution be on the paper or +whether it be in the jar, so long as we bring the ends of the apparatus to +it. If I put the two platinums in by themselves, they come out as clean +and as white as they go in [inserting them into the fluid without +connecting them with the battery]; but when we take the power and lay that +on [the platinums were connected with the battery and again dipped into +the solution], this, you see [exhibiting one of the platinums], is at once +turned into copper, as it were: it has become like a plate of copper; and +that [exhibiting the other piece of platinum] has come out quite clean. If +I take this coppered piece and change sides, the copper will leave the +right-hand side and come over to the left side; what was before the +coppered plate comes out clean, and the plate which was clean comes out +coated with copper; and thus you see that the same copper we put into this +solution we can also take out of it by means of this instrument. + +Putting that solution aside, let us now see what effect this instrument +will have upon water. Here are two little platinum-plates which I intend +to make the ends of the battery, and this (C) is a little vessel so shaped +as to enable me to take it to pieces, and shew you its construction. In +these two cups (A and B) I pour mercury, which touches the ends of the +wires connected with the platinum-plates. In the vessel (C) I pour some +water containing a little acid (but which is put only for the purpose of +facilitating the action; it undergoes no change in the process), and +connected with the top of the vessel is a bent glass tube (D), which may +remind you of the pipe which was connected with the gun barrel in our +furnace experiment, and which now passes under the jar (F). I have now +adjusted this apparatus, and we will proceed to affect the water in some +way or other. In the other case, I sent the water through a tube which was +made red-hot; I am now going to pass the electricity through the contents +of this vessel. Perhaps I may boil the water; if I do boil the water, I +shall get steam; and you know that steam condenses when it gets cold, and +you will therefore see by that whether I do boil the water or not. +Perhaps, however, I shall not boil the water, but produce some other +effect. You shall have the experiment and see. There is one wire which I +will put to this side (A), and here is the other wire which I will put to +the other side (B), and you will soon see whether any disturbance takes +place. Here it is seeming to boil up famously; but does it boil? Let us +see whether that which goes out is steam or not. I think you will soon see +the jar (F) will be filled with vapour, if that which rises from the water +is steam. But can it be steam? Why, certainly not; because there it +remains, you see, unchanged. There it is standing over the water, and it +cannot therefore be steam, but must be a permanent gas of some sort What +is it? Is it hydrogen? Is it anything else? Well, we will examine it. If +it is hydrogen, it will burn. [The Lecturer then ignited a portion of the +gas collected, which burnt with an explosion.] + +[Illustration: Fig. 19] + +It is certainly something combustible, but not combustible in the way that +hydrogen is. Hydrogen would not have given you that noise; but the colour +of that light, when the thing did burn, was like that of hydrogen: it +will, however, burn without contact with the air. That is why I have +chosen this other form of apparatus, for the purpose of pointing out to +you what are the particular circumstances of this experiment. In place of +an open vessel I have taken one that is closed (our battery is so +beautifully active that we are even boiling the mercury, and getting all +things right--not wrong, but vigorously right); and I am going to shew you +that that gas, whatever it may be, can burn without air, and in that +respect differs from a candle, which cannot burn without the air. And our +manner of doing this is as follows:--I have here a glass vessel (G) which +is fitted with two platinum-wires (IK), through which I can apply +electricity; and we can put the vessel on the air-pump and exhaust the +air, and when we have taken the air out we can bring it here and fasten it +on to this jar (F), and let into the vessel that gas which was formed by +the action of the voltaic battery upon the water, and which we have +produced by changing the water into it,--for I may go as far as this, and +say we have really, by that experiment, changed the water into that gas. +We have not only altered its condition, but we have changed it really and +truly into that gaseous substance, and all the water is there which was +decomposed by the experiment. As I screw this vessel (GH) on here (H), and +make the tubes well connected, and when I open the stop-cocks (HHH), if +you watch the level of the water (in F), you will see that the gas will +rise. I will now close the stop-cocks, as I have drawn up as much as the +vessel can hold, and being safely conveyed into that chamber, I will pass +into it an electric spark from this Leyden jar (L), when the vessel, which +is now quite clear and bright, will become dim. There will be no sound, +for the vessel is strong enough to confine the explosion. [A spark was +then passed through the jar, when the explosive mixture was ignited.] Did +you see that brilliant light? If I again screw the vessel on to the jar, +and open these stop-cocks, you will see that the gas will rise a second +time. [The stop-cocks were then opened.] Those gases [referring to the +gases first collected in the jar, and which had just been ignited by the +electric spark] have disappeared, as you see: their place is vacant, and +fresh gas has gone in. Water has been formed from them; and if we repeat +our operation [repeating the last experiment], I shall have another +vacancy, as you will see by the water rising. I always have an empty +vessel after the explosion, because the vapour or gas into which that +water has been resolved by the battery explodes under the influence of the +spark, and changes into water; and by-and-by you will see in this upper +vessel some drops of water trickling down the sides and collecting at the +bottom. + +We are here dealing with water entirely, without reference to the +atmosphere. The water of the candle had the atmosphere helping to produce +it; but in this way it can be produced independently of the air. Water, +therefore, ought to contain that other substance which the candle takes +from the air, and which, combining with the hydrogen, produces water. + +Just now you saw that one end of this battery took hold of the copper, +extracting it from the vessel which contained the blue solution. It was +effected by this wire; and surely we may say, if the battery has such +power with a metallic solution which we made and unmade, may we not find +that it is possible to split asunder the component parts of the water, and +put them into this place and that place? Suppose I take the poles--the +metallic ends of this battery--and see what will happen with the water in +this apparatus (fig. 20), where we have separated the two ends far apart. + +[Illustration: Fig. 20.] + +I place one here (at A), and the other there (at B), and I have little +shelves with holes which I can put upon each pole, and so arrange them +that whatever escapes from the two ends of the battery will appear as +separate gases; for you saw that the water did not become vaporous, but +gaseous. The wires are now in perfect and proper connection with the +vessel containing the water; and you see the bubbles rising: let us +collect these bubbles and see what they are. Here is a glass cylinder (O); +I fill it with water and put it over one end (A) of the pile; and I will +take another (H) and put it over the other end (B) of the pile. And so now +we have a double apparatus, with both places delivering gas. Both these +jars will fill with gas. There they go, that to the right (H) filling very +rapidly; the one to the left (O) filling not so rapidly; and though I have +allowed some bubbles to escape, yet still the action is going on pretty +regularly; and were it not that one is rather smaller than the other, you +would see that I should have twice as much in this (H) as I have in that +(O). Both these gases are colourless; they stand over the water without +condensing; they are alike in all things--I mean in all _apparent_ things; +and we have here an opportunity of examining these bodies and ascertaining +what they are. Their bulk is large, and we can easily apply experiments to +them. I will take this jar (H) first, and will ask you to be prepared to +recognise hydrogen. + +Think of all its qualities--the light gas which stood well in inverted +vessels, burning with a pale flame at the mouth of the jar--and see +whether this gas does not satisfy all these conditions. If it be hydrogen, +it will remain here while I hold this jar inverted. [A light was then +applied, when the hydrogen burnt] What is there now in the other jar? You +know that the two together made an explosive mixture. But what can this +be which we find as the other constituent in water, and which must +therefore be that substance which made the hydrogen burn? We know that the +water we put into the vessel consisted of the two things together. We find +one of these is hydrogen: what must that other be which was in the water +before the experiment, and which we now have by itself? I am about to put +this lighted splinter of wood into the gas. The gas itself will not burn, +but it will make the splinter of wood burn. [The Lecturer ignited the end +of the wood, and introduced it into the jar of gas.] See how it +invigorates the combustion of the wood, and how it makes it burn far +better than the air would make it burn; and now you see by itself that +every other substance which is contained in the water, and which, when the +water was formed by the burning of the candle, must have been taken from +the atmosphere. What shall we call it, A, B, or C? Let us call it O--call +it "Oxygen:" it is a very good distinct-sounding name. This, then, is the +oxygen which was present in the water, forming so large a part of it. + +We shall now begin to understand more clearly our experiments and +researches; because, when we have examined these things once or twice, we +shall soon see why a candle burns in the air. When we have in this way +analysed the water--that is to say, separated, or electrolysed its parts +out of it--we get two volumes of hydrogen, and one of the body that burns +it. And these two are represented to us on the following diagram, with +their weights also stated; and we shall find that the oxygen is a very +heavy body by comparison with the hydrogen. It is the other element in +water. + +I had better, perhaps, tell you now how we get this oxygen abundantly, +having shewn you how we can separate it from the water. Oxygen, as you +will immediately imagine, exists in the atmosphere; for how should the +candle burn to produce water without it? + + _____________________ +| | | +| 1 | 8 | +| | | +| | Oxygen. | Oxygen, . . . . 88.9 +| | | +| |_________| Hydrogen, . . . 11.1 +| Hydrogen. | ----- +| | 9 Water,. . . . . 100.0 +| | +| | +| | +|___________| + +Such a thing would be absolutely impossible, and chemically impossible, +without oxygen. + +[Illustration: Fig. 21.] + +Can we get it from the air? Well, there are some very complicated and +difficult processes by which we can get it from the air; but we have +better processes. There is a substance called the black oxide of +manganese: it is a very black-looking mineral, but very useful, and when +made red-hot it gives out oxygen. Here is an iron bottle which has had +some of this substance put into it, and there is a tube fixed to it, and a +fire ready made, and Mr. Anderson will put that retort into the fire, for +it is made of iron, and can stand the heat. Here is a salt called chlorate +of potassa, which is now made in large quantities for bleaching, and +chemical and medical uses, and for pyrotechnic and other purposes. I will +take some and mix it with some of the oxide of manganese (oxide of copper, +or oxide of iron would do as well); and if I put these together in a +retort, far less than a red heat is sufficient to evolve this oxygen from +the mixture. I am not preparing to make much, because we only want +sufficient for our experiments; only, as you will see immediately, if I +use too small a charge, the first portion of the gas will be mixed with +the air already in the retort, and I should be obliged to sacrifice the +first portion of the gas, because it would be so much diluted with air; +the first portion must therefore be thrown away. You will find in this +case, that a common spirit-lamp is quite sufficient for me to get the +oxygen, and so we shall have two processes going on for its preparation. +See how freely the gas is coming over from that small portion of the +mixture. We will examine it, and see what are its properties. Now, in this +way we are producing, as you will observe, a gas just like the one we had +in the experiment with the battery, transparent, undissolved by water, and +presenting the ordinary visible properties of the atmosphere. (As this +first jar contains the air, together with the first portions of the oxygen +set free during the preparation, we will carry it out of the way, and be +prepared to make our experiments in a regular, dignified manner.) And, +inasmuch as that power of making wood, wax, or other things burn, was so +marked in the oxygen we obtained by means of the voltaic battery from +water, we may expect to find the same property here. We will try it You +see there is the combustion of a lighted taper in air, and here is its +combustion in this gas [lowering the taper into the jar]. See how brightly +and how beautifully it burns! You can also see more than this,--you will +perceive it is a heavy gas, whilst the hydrogen would go up like a +balloon, or even faster than a balloon, when not encumbered with the +weight of the envelope. + +[Illustration: Fig. 22.] + +You may easily see that although we obtained from water twice as much in +volume of the hydrogen as of oxygen, it does not follow that we have twice +as much in weight--because one is heavy, and the other a very light gas. +We have means of weighing gases or air; but without stopping to explain, +that, let me just tell you what their respective weights are. The weight +of a pint of hydrogen is three-quarters of a grain; the weight of the same +quantity of oxygen is nearly twelve grains. This is a very great +difference. The weight of a cubit foot of hydrogen is one-twelfth of an +ounce; and the weight of a cubit foot of oxygen is one ounce and a third. +And so on we might come to masses of matter which may be weighed in the +balance, and which we can take account of as to hundredweights and as to +tons, as you will see almost immediately. + +Now, as regards this very property of oxygen supporting combustion, which +we may compare to air, I will take a piece of candle to shew it you in a +rough way, and the result will be rough. There is our candle burning in +the air: how will it burn in oxygen? I have here a jar of this gas, and I +am about to put it over the candle for you to compare the action of this +gas with that of the air. Why, look at it: it looks something like the +light you saw at the poles of the voltaic battery. Think how vigorous that +action must be! And yet, during all that action, nothing more is produced +than what is produced by the burning of the candle in air. We have the +same production of water, and the same phenomena exactly, when we use this +gas instead of air, as we have when the candle is burnt in air. + +But now we have got a knowledge of this new substance, we can look at it a +little more distinctly, in order to satisfy ourselves that we have got a +good general understanding of this part of the product of a candle. It is +wonderful how great the supporting powers of this substance are as regards +combustion. For instance, here is a lamp which, simple though it be, is +the original, I may say, of a great variety of lamps which are constructed +for divers purposes--for light-houses, microscopic illuminations, and +other uses; and if it were proposed to make it burn very brightly, you +would say, "If a candle burnt better in oxygen, will not a lamp do the +same?" Why, it will do so. Mr. Anderson will give me a tube coming from +our oxygen reservoir, and I am about to apply it to this flame, which I +will previously make burn badly on purpose. There comes the oxygen: what a +combustion that makes! But if I shut it off, what becomes of the lamp? [The +flow of oxygen was stopped, and the lamp relapsed to its former dimness.] +It is wonderful how, by means of oxygen, we get combustion accelerated. +But it does not affect merely the combustion of hydrogen, or carbon, or +the candle; but it exalts all combustions of the common kind. We will take +one which relates to iron, for instance, as you have already seen iron +burn a little in the atmosphere. Here is a jar of oxygen, and this is a +piece of iron wire; but if it were a bar as thick as my wrist, it would +burn the same. + +[Illustration: Fig. 23.] + +I first attach a little piece of wood to the iron, I then set the wood on +fire and let them both down together into the jar. The wood is now alight, +and there it burns as wood should burn in oxygen; but it will soon +communicate its combustion to the iron. The iron is now burning +brilliantly, and will continue so for a long time. As long as we supply +oxygen, so long can we carry on the combustion of the iron, until the +latter is consumed. + +We will now put that on one side, and take some other substance; but we +must limit our experiments, for we have not time to spare for all the +illustrations you would have a right to if we had more time. We will take +a piece of sulphur--you know how sulphur burns in the air--well, we put it +into the oxygen, and you will see that whatever can burn in air, can burn +with a far greater intensity in oxygen, leading you to think that perhaps +the atmosphere itself owes all its power of combustion to this gas. The +sulphur is now burning very quietly in the oxygen; but you cannot for a +moment mistake the very high and increased action which takes place when +it is so burnt, instead of being burnt merely in common air. + +[Illustration: Fig. 24.] + +I am now about to shew you the combustion of another +substance--phosphorus. I can do it better for you here than you can do it +at home. This is a very combustible substance; and if it be so combustible +in air, what might you expect it would be in oxygen? I am about to shew it +to you not in its fullest intensity, for if I did so we should almost blow +the apparatus up--I may even now crack the jar, though I do not want to +break things carelessly. You see how it burns in the air. But what a +glorious light it gives out when I introduce it into oxygen! [Introducing +the lighted phosphorus into the jar of oxygen.] There you see the solid +particles going off which cause that combustion to be so brilliantly +luminous. + +Thus far we have tested this power of oxygen, and the high combustion it +produces by means of other substances. We must now, for a little while +longer, look at it as respects the hydrogen. You know, when we allowed the +oxygen and the hydrogen derived from the water to mix and burn together, +we had a little explosion. You remember, also, that when I burnt the +oxygen and the hydrogen in a jet together, we got very little light, but +great heat. I am now about to set fire to oxygen and hydrogen, mixed in +the proportion in which they occur in water. Here is a vessel containing +one volume of oxygen and two volumes of hydrogen. This mixture is exactly +of the same nature as the gas we just now obtained from the voltaic +battery: it would be far too much to burn at once; I have therefore +arranged to blow soap-bubbles with it, and burn those bubbles, that we may +see by a general experiment or two how this oxygen supports the combustion +of the hydrogen. First of all, we will see whether we can blow a bubble. +Well, there goes the gas [causing it to issue through a tobacco-pipe into +some soap-suds]. Here I have a bubble. I am receiving them on my hand: and +you will perhaps think I am acting oddly in this experiment; but it is to +shew you that we must not always trust to noise and sounds, but rather to +real facts. [Exploding a bubble on the palm of his hand.] I am afraid to +fire a bubble from the end of the pipe, because the explosion would pass +up into the jar and blow it to pieces. This oxygen then will unite with +the hydrogen, as you see by the phenomena, and hear by the sound, with the +utmost readiness of action, and all its powers are then taken up in its +neutralisation of the qualities of the hydrogen. + +So now I think you will perceive the whole history of water with reference +to oxygen and the air, from what we have before said. Why does a piece of +potassium decompose water? Because it finds oxygen in the water. What is +set free when I put it in the water, as I am about to do again? It sets +free hydrogen, and the hydrogen burns; but the potassium itself combines +with oxygen; and this piece of potassium, in taking the water apart--the +water, you may say, derived from the combustion of the candle--takes away +the oxygen which the candle took from the air, and so sets the hydrogen +free; and even if I take a piece of ice, and put a piece of potassium upon +it, the beautiful affinities by which the oxygen and the hydrogen are +related are such, that the ice will absolutely set fire to the potassium. +I shew this to you to-day, in order to enlarge your ideas of these things, +and that you may see how greatly results are modified by circumstances. +There is the potassium on the ice, producing a sort of volcanic action. + +It will be my place, when next we meet, having pointed out these anomalous +actions, to shew you that none of these extra and strange effects are met +with by us--that none of these strange and injurious actions take place +when we are burning, not merely a candle, but gas in our streets, or fuel +in our fireplaces, so long as we confine ourselves within the laws that +Nature has made for our guidance. + + + + +LECTURE V. + +OXYGEN PRESENT IN THE AIR--NATURE OF THE ATMOSPHERE--ITS PROPERTIES--OTHER +PRODUCTS FROM THE CANDLE--CARBONIC ACID--ITS PROPERTIES. + + +We have now seen that we can produce hydrogen and oxygen from the water +that we obtained from the candle. Hydrogen, you know, comes from the +candle, and oxygen, you believe, comes from the air. But then you have a +right to ask me, "How is it that the air and the oxygen do not equally +well burn the candle?" If you remember what happened when I put a jar of +oxygen over a piece of candle, you recollect there was a very different +kind of combustion to that which took place in the air. Now, why is this? +It is a very important question, and one I shall endeavour to make you +understand: it relates most intimately to the nature of the atmosphere, +and is most important to us. + +We have several tests for oxygen besides the mere burning of bodies. You +have seen a candle burnt in oxygen, or in the air; you have seen +phosphorus burnt in the air, or in oxygen; and you have seen iron-filings +burnt in oxygen. But we have other tests besides these, and I am about to +refer to one or two of them for the purpose of carrying your conviction +and your experience further. Here we have a vessel of oxygen. I will shew +its presence to you: if I take a little spark and put it into that oxygen, +you know, by the experience you gained the last time we met, what will +happen; if I put that spark into the jar, it will tell you whether we have +oxygen here or not. Yes! We have proved it by combustion; and now here is +another test for oxygen, which is a very curious and useful one. I have +here two jars full of gas, with a plate between them to prevent their +mixing; I take the plate away, and the gases are creeping one into the +other. "What happens?" say you: "they together produce no such combustion +as was seen in the case of the candle." But see how the presence of oxygen +is told by its association with this other substance[14]. What a +beautifully coloured gas I have obtained in this way, shewing me the +presence of the oxygen! In the same way we can try this experiment by +mixing common air with this test-gas. Here is a jar containing air--such +air as the candle would burn in--and here is a jar or bottle containing +the test-gas. I let them come together over water, and you see the result: +the contents of the test-bottle are flowing into the jar of air, and you +see I obtain exactly the same kind of action as before, and that shews me +that there is oxygen in the air--the very same substance that has been +already obtained by us from the water produced by the candle. But then, +beyond that, how is it that the candle does not burn in air as well as in +oxygen? We will come to that point at once. I have here two jars; they are +filled to the same height with gas, and the appearance to the eye is alike +in both, and I really do not know at present which of these jars contains +oxygen and which contains air, although I know they have previously been +filled with these gases. But here is our test-gas, and I am going to work +with the two jars, in order to examine whether there is any difference +between them in the quality of reddening this gas. I am now going to turn +this test-gas into one of the jars, and observe what happens. There is +reddening, you see; there is then oxygen present. We will now test the +other jar; but you see this is not so distinctly red as the first: and, +further, this curious thing happens,--if I take these two gases and shake +them well together with water, we shall absorb the red gas; and then, if I +put in more of this test-gas and shake again, we shall absorb more; and I +can go on as long as there be any oxygen present to produce that effect. +If I let in air, it will not matter; but the moment I introduce water, the +red gas disappears; and I may go on in this way, putting in more and more +of the test-gas, until I come to something left behind which will not +redden any longer by the use of that particular body that rendered the air +and the oxygen red. Why is that? You see in a moment it is because there +is, besides oxygen, something else present which is left behind. I will +let a little more air into the jar, and if it turns red you will know that +some of that reddening gas is still present, and that consequently it was +not for the want of this producing body that that air was left behind. + +Now, you will begin to understand what I am about to say. You saw that +when I burnt phosphorus in a jar, as the smoke produced by the phosphorus +and the oxygen of the air condensed, it left a good deal of gas unburnt, +just as this red gas left something untouched,--there was, in fact, this +gas left behind, which the phosphorus cannot touch, which the reddening +gas cannot touch, and this something is not oxygen, and yet is part of the +atmosphere. + +So that is one way of opening out air into the two things of which it is +composed--oxygen, which burns our candles, our phosphorus, or anything +else; and this other substance--nitrogen--which will not burn them. This +other part of the air is by far the larger proportion, and it is a very +curious body, when we come to examine it; it is remarkably curious, and +yet you say, perhaps, that it is very uninteresting. It is uninteresting +in some respects because of this--that it shews no brilliant effects of +combustion. If I test it with a taper as I do oxygen and hydrogen, it +does not burn like hydrogen, nor does it make the taper burn like oxygen. +Try it in any way I will, it does neither the one thing nor the other: it +will not take fire; it will not let the taper burn; it puts out the +combustion of everything. There is nothing that will burn in it in common +circumstances. It has no smell; it is not sour; it does not dissolve in +water; it is neither an acid nor an alkali; it is as indifferent to all +our organs as it is possible for a thing to be. And you might say, "It is +nothing; it is not worth chemical attention; what does it do in the air?" +Ah! then come our beautiful and fine results shewn us by an observant +philosophy. Suppose, in place of having nitrogen, or nitrogen and oxygen, +we had pure oxygen as our atmosphere; what would become of us? You know +very well that a piece of iron lit in a jar of oxygen goes on burning to +the end. When you see a fire in an iron grate, imagine where the grate +would go to if the whole of the atmosphere were oxygen. The grate would +burn up more powerfully than the coals--for the iron of the grate itself +is even more combustible than the coals which we burn in it. A fire put +into the middle of a locomotive would be a fire in a magazine of fuel, if +the atmosphere were oxygen. The nitrogen lowers it down and makes it +moderate and useful for us, and then, with all that, it takes away with it +the fumes that you have seen produced from the candle, disperses them +throughout the whole of the atmosphere, and carries them away to places +where they are wanted to perform a great and glorious purpose of good to +man, for the sustenance of vegetation; and thus does a most wonderful +work, although you say, on examining it, "Why, it is a perfectly +indifferent thing." This nitrogen in its ordinary state is an inactive +element; no action short of the most intense electric force, and then in +the most infinitely small degree, can cause the nitrogen to combine +directly with the other element of the atmosphere, or with other things +round about it; it is a perfectly indifferent, and therefore to say, a +safe substance. + +But before I take you to that result, I must tell you about the atmosphere +itself. I have written on this diagram the composition of one hundred +parts of atmospheric air:-- + + Bulk. Weight. +Oxygen, . . . . . 20 22.3 +Nitrogen, . . . . 80 77.7 + ---- ----- + l00 100.0 + +It is a true analysis of the atmosphere, so far as regards the quantity of +oxygen and the quantity of nitrogen present. By our analysis, we find that +5 pints of the atmosphere contain only 1 pint of oxygen, and 4 pints, or 4 +parts, of nitrogen by bulk. That is our analysis of the atmosphere. It +requires all that quantity of nitrogen to reduce the oxygen down, so as to +be able to supply the candle properly with fuel, so as to supply us with +an atmosphere which our lungs can healthily and safely breathe; for it is +just as important to make the oxygen right for us to breathe, as it is to +make the atmosphere right for the burning of the fire and the candle. + +But now for this atmosphere. First of all, let me tell you the weight of +these gases. A pint of nitrogen weighs 10-4/10 grains, or a cubic foot +weighs 1-1/6 ounce. That is the weight of the nitrogen. The oxygen is +heavier: a pint of it weighs 11-9/10 grains, and a cubic foot weighs 1-3/4 +ounce. A pint of air weighs about 10-7/10 grains, and a cubic foot 1-1/5 +ounce. + +[Illustration: Fig. 25.] + +You have asked me several times, and I am very glad you have, "How do you +weigh gases?" I will shew you; it is very simple, and easily done. Here is +a balance, and here a copper bottle, made as light as we can consistent +with due strength, turned very nicely in the lathe, and made perfectly +air-tight, with a stop-cock, which we can open and shut, which at present +is open, and therefore allows the bottle to be full of air. I have here a +nicely-adjusted balance, in which I think the bottle, in its present +condition, will be balanced by the weight on the other side. And here is a +pump by which we can force the air into this bottle, and with it we will +force in a certain number of volumes of air, as measured by the pump. +[Twenty measures were pumped in.] We will shut that in and put it in the +balance. See how it sinks: it is much heavier than it was. By what? By +the air that we have forced into it by the pump. There is not a greater +_bulk_ of air, but there is the same bulk of _heavier_ air, because we +have forced in air upon it. And that you may have a fair notion in your +mind as to how much this air measures, here is a jar full of water. We +will open that copper vessel into this jar, and let the air return to its +former state. All I have to do now is to screw them tightly together, and +to turn the taps, when there, you see, is the bulk of the twenty pumps of +air which I forced into the bottle; and to make sure that we have been +quite correct in what we have been doing, we will take the bottle again to +the balance, and, if it is now counterpoised by the original weight, we +shall be quite sure we have made our experiment correctly. + +[Illustration: Fig. 26.] + +It is balanced; so, you see, we can find out the weight of the extra +volumes of air forced in, in that way, and by that means we are able to +ascertain that a cubic foot of air weighs 1-1/5 ounce. But that small +experiment will by no means convey to your mind the whole literal truth of +this matter. It is wonderful how it accumulates when you come to larger +volumes. This bulk of air [a cubic foot] weighs 1-1/5 ounce. What do you +think of the contents of that box above there, which I have had made for +the purpose? The air which is within that box weighs one pound--a full +pound; and I have calculated the weight of the air in this room,--you +would hardly imagine it, but it is above a ton. So rapidly do the weights +rise up, and so important is the presence of the atmosphere, and of the +oxygen and the nitrogen in it, and the use it performs in conveying things +to and fro from place to place, and carrying bad vapours to places where +they will do good instead of harm. + +Having given you that little illustration with respect to the weight of +the air, let me shew you certain consequences of it. You have a right to +them, because you would not understand so much without it. Do you remember +this kind of experiment? Have you ever seen it? Suppose I take a pump +somewhat similar to the one I had a little while ago to force air into the +bottle, and suppose I place it in such a manner that by certain +arrangements I can apply my hand to it: my hand moves about in the air so +easily that it seems to feel nothing, and I can hardly get velocity enough +by any motion of my own in the atmosphere to make sure that there is much +resistance to it. + +[Illustration: Fig. 27.] + +But, when I put my hand here [on the air-pump receiver, which was +afterwards exhausted], you see what happens. Why is my hand fastened to +this place, and why am I able to pull this pump about? And see! how is it +that I can hardly get my hand away? Why is this? It is the weight of the +air--the weight of the air that is above. I have another experiment here, +which I think will explain to you more about it. When the air is pumped +from underneath the bladder which is stretched over this glass, you will +see the effect in another shape: the top is quite flat at present, but I +will make a very little motion with the pump, and now look at it--see how +it has gone down, see how it is bent in. You will see the bladder go in +more and more, until at last I expect it will be driven in and broken by +the force of the atmosphere pressing upon it. + +[Illustration: Fig. 28.] + +[The bladder at last broke with a loud report.] Now, that was done +entirely by the weight of the air pressing on it, and you can easily +understand how that is. The particles that are piled up in the atmosphere +stand upon each other, as these five cubes do. You can easily conceive +that four of these five cubes are resting upon the bottom one, and if I +take that away, the others will all sink down. So it is with the +atmosphere: the air that is above is sustained by the air that is beneath; +and when the air is pumped away from beneath them, the change occurs which +you saw when I placed my hand on the air-pump, and which you saw in the +case of the bladder, and which you shall see better here. I have tied over +this jar a piece of sheet india-rubber, and I am now about to take away +the air from the inside of the jar; and if you will watch the +india-rubber--which acts as a partition between the air below and the air +above--you will see, when I pump, how the pressure shews itself. See where +it is going to--I can actually put my hand into the jar; and yet this +result is only caused by the great and powerful action of the air above. +How beautifully it shews this curious circumstance! + +Here is something that you can have a pull at, when I have finished +to-day. It is a little apparatus of two hollow brass hemispheres, closely +fitted together, and having connected with it a pipe and a cock, through +which we can exhaust the air from the inside; and although the two halves +are so easily taken apart, while the air is left within, yet you will see, +when we exhaust it by-and-by, no power of any two of you will be able to +pull them apart. Every square inch of surface that is contained in the +area of that vessel sustains fifteen pounds by weight, or nearly so, when +the air is taken out; and you may try your strength presently in seeing +whether you can overcome that pressure of the atmosphere. + +Here is another very pretty thing--the boys' sucker, only refined by the +philosopher. We young ones have a perfect right to take toys, and make +them into philosophy, inasmuch as now-a-days we are turning philosophy +into toys. Here is a sucker, only it is made of india-rubber: if I clap it +upon the table, you see at once it holds. Why does it hold? I can slip it +about, and yet if I try to pull it up, it seems as if it would pull the +table with it I can easily make it slip about from place to place; but +only when I bring it to the edge of the table can I get it off. It is only +kept down by the pressure of the atmosphere above. We have a couple of +them; and if you take these two and press them together, you will see how +firmly they stick. And, indeed, we may use them as they are proposed to be +used, to stick against windows, or against walls, where they will adhere +for an evening, and serve to hang anything on that you want. I think, +however, that you boys ought to be shewn experiments that you can make at +home; and so here is a very pretty experiment in illustration of the +pressure of the atmosphere. Here is a tumbler of water. Suppose I were to +ask you to turn that tumbler upside-down, so that the water should not +fall out, and yet not be kept in by your hand, but merely by using the +pressure of the atmosphere. Could you do that? Take a wine-glass, either +quite full or half-full of water, and put a flat card on the top, turn it +upside-down, and then see what becomes of the card and of the water. The +air cannot get in because the water by its capillary attraction round the +edge keeps it out. + +I think this will give you a correct notion of what you may call the +materiality of the air; and when I tell you that the box holds a pound of +it, and this room more than a ton, you will begin to think that air is +something very serious. I will make another experiment, to convince you of +this positive resistance. There is that beautiful experiment of the +popgun, made so well and so easily, you know, out of a quill, or a tube, +or anything of that kind,--where we take a slice of potato, for instance, +or an apple, and take the tube and cut out a pellet, as I have now done, +and push it to one end. I have made that end tight; and now I take another +piece and put it in: it will confine the air that is within the tube +perfectly and completely for our purpose; and I shall now find it +absolutely impossible by any force of mine to drive that little pellet +close up to the other. It cannot be done. I may press the air to a certain +extent, but if I go on pressing, long before it comes to the second, the +confined air will drive the front one out with a force something like that +of gunpowder; for gunpowder is in part dependent upon the same action that +you see here exemplified. + +I saw the other day an experiment which pleased me much, as I thought it +would serve our purpose here. (I ought to have held my tongue for four or +five minutes before beginning this experiment, because it depends upon my +lungs for success.) By the proper application of air I expect to be able +to drive this egg out of one cup into the other by the force of my breath; +but if I fail, it is in a good cause; and I do not promise success, +because I have been talking more than I ought to do to make the experiment +succeed. + +[The Lecturer here tried the experiment, and succeeded in blowing the egg +from one egg-cup to the other.] + +You see that the air which I blow goes downwards between the egg and the +cup, and makes a blast under the egg, and is thus able to lift a heavy +thing--for a full egg is a very heavy thing for air to lift. If you want +to make the experiment, you had better boil the egg quite hard first, and +then you may very safely try to blow it from one cup to the other, with a +little care. + +I have now kept you long enough upon this property of the weight of the +air, but there is another thing I should like to mention. You saw the way +in which, in this popgun, I was able to drive the second piece of potato +half or two-thirds of an inch before the first piece started, by virtue of +the elasticity of the air--just as I pressed into the copper bottle the +particles of air by means of the pump. Now, this depends upon a wonderful +property in the air, namely, its elasticity; and I should like to give you +a good illustration of this. If I take anything that confines the air +properly, as this membrane, which also is able to contract and expand so +as to give us a measure of the elasticity of the air, and confine in this +bladder a certain portion of air; and then, if we take the atmosphere off +from the outside of it, just as in these cases we put the pressure on--if +we take the pressure off, you will see how it will then go on expanding +and expanding, larger and larger, until it will fill the whole of this +bell-jar, shewing you that wonderful property of the air, its elasticity, +its compressibility, and expansibility, to an exceedingly large extent, +and which is very essential for the purposes and services it performs in +the economy of creation. + +We will now turn to another very important part of our subject, +remembering that we have examined the candle in its burning, and have +found that it gives rise to various products. We have the products, you +know, of soot, of water, and of something else which you have not yet +examined. We have collected the water, but have allowed the other things +to go into the air. Let us now examine some of these other products. + +Here is an experiment which I think will help you in part in this way. We +will put our candle there, and place over it a chimney, thus. I think my +candle will go on burning, because the air-passage is open at the bottom +and the top. In the first place, you see the moisture appearing--that you +know about. It is water produced from the candle by the action of the air +upon its hydrogen. But, besides that, something is going out at the top: +it is not moisture--it is not water--it is not condensible; and yet, after +all, it has very singular properties. You will find that the air coming +out of the top of our chimney is nearly sufficient to blow the light out I +am holding to it; and if I put the light fairly opposed to the current, it +will blow it quite out. You will say that is as it should be; and I am +supposing that you think it ought to do so, because the nitrogen does not +support combustion, and ought to put the candle out, since the candle will +not burn in nitrogen. + +[Illustration: Fig. 29.] + +But is there nothing else there than nitrogen? I must now anticipate--that +is to say, I must use my own knowledge to supply you with the means that +we adopt for the purpose of ascertaining these things, and examining such +gases as these. I will take an empty bottle--here is one--and if I hold it +over this chimney, I shall get the combustion of the candle below sending +its results into the bottle above; and we shall soon find that this bottle +contains, not merely an air that is bad as regards the combustion of a +taper put into it, but having other properties. + +Let me take a little quick-lime and pour some common water on to it--the +commonest water will do. I will stir it a moment, then pour it upon a +piece of filtering paper in a funnel, and we shall very quickly have a +clear water proceeding to the bottle below, as I have here. I have plenty +of this water in another bottle; but, nevertheless, I should like to use +the lime-water that was prepared before you, so that you may see what its +uses are. If I take some of this beautiful clear lime-water, and pour it +into this jar, which has collected the air from the candle, you will see a +change coming about. Do you see that the water has become quite milky? +Observe, that will not happen with air merely. Here is a bottle filled +with air; and if I put a little lime-water into it, neither the oxygen nor +the nitrogen, nor anything else that is in that quantity of air, will make +any change in the lime-water. It remains perfectly clear, and no shaking +of that quantity of lime-water with that quantity of air in its common +state will cause any change; but if I take this bottle with the +lime-water, and hold it so as to get the general products of the candle in +contact with it, in a very short time we shall have it milky. There is the +chalk, consisting of the lime which we used in making the lime-water, +combined with something that came from the candle--that other product +which we are in search of, and which I want to tell you about to-day. This +is a substance made visible to us by its action, which is not the action +of the lime-water either upon the oxygen or upon the nitrogen, nor upon +the water itself, but it is something new to us from the candle. And then +we find this white powder, produced by the lime-water and the vapour from +the candle, appears to us very much like whitening or chalk, and, when +examined, it does prove to be exactly the same substance as whitening or +chalk. So we are led, or have been led, to observe upon the various +circumstances of this experiment, and to trace this production of chalk to +its various causes, to give us the true knowledge of the nature of this +combustion of the candle--to find that this substance, issuing from the +candle, is exactly the same as that substance which would issue from a +retort, if I were to put some chalk into it with a little moisture, and +make it red-hot: you would then find that exactly the same substance would +issue from it as from the candle. + +But we have a better means of getting this substance, and in greater +quantity, so as to ascertain what its general characters are. We find this +substance in very great abundance in a multitude of cases where you would +least expect it. All limestones contain a great deal of this gas which +issues from the candle, and which we call _carbonic acid_. All chalks, all +shells, all corals contain a great quantity of this curious air. We find +it fixed in these stones; for which reason Dr. Black called it "fixed +air"--finding it in these fixed things like marble and chalk. He called it +fixed air, because it lost its quality of air, and assumed the condition +of a solid body. We can easily get this air from marble. Here is a jar +containing a little muriatic acid, and here is a taper which, if I put it +into that jar, will shew only the presence of common air. There is, you +see, pure air down to the bottom; the jar is full of it Here is a +substance--marble[17], a very beautiful and superior marble--and if I put +these pieces of marble into the jar, a great boiling apparently goes on. +That, however, is not steam--it is a gas that is rising up; and if I now +search the jar by a candle, I shall have exactly the same effect produced +upon the taper as I had from the air which issued from the end of the +chimney over the burning candle. It is exactly the same action, and caused +by the very same substance that issued from the candle; and in this way we +can get carbonic acid in great abundance--we have already nearly filled +the jar. We also find that this gas is not merely contained in marble. +Here is a vessel in which I have put some common whitening--chalk, which +has been washed in water and deprived of its coarser particles, and so +supplied to the plasterer as whitening. Here is a large jar containing +this whitening and water, and I have here some strong sulphuric acid, +which is the acid you might have to use if you were to make these +experiments (only, in using this acid with limestone, the body that is +produced is an insoluble substance, whereas the muriatic acid produces a +soluble substance that does not so much thicken the water). And you will +seek out a reason why I take this kind of apparatus for the purpose of +shewing this experiment. I do it because you may repeat in a small way +what I am about to do in a large one. You will have here just the same +kind of action; and I am evolving in this large jar carbonic acid, exactly +the same in its nature and properties as the gas which we obtained from +the combustion of the candle in the atmosphere. And no matter how +different the two methods by which we prepare this carbonic acid, you will +see, when we get to the end of our subject, that it is all exactly the +same, whether prepared in the one way or in the other. + +We will now proceed to the next experiment with regard to this gas. What +is its nature? Here is one of the vessels full, and we will try it, as we +have done so many other gases, by combustion. You see it is not +combustible, nor does it support combustion. Neither, as we know, does it +dissolve much in water, because we collect it over water very easily. +Then, you know that it has an effect, and becomes white in contact with +lime-water; and when it does become white in that way, it becomes one of +the constituents to make carbonate of lime or limestone. + +The next thing I must shew you is, that it really does dissolve a little +in water, and therefore that it is unlike oxygen and hydrogen in that +respect I have here an apparatus by which we can produce this solution. In +the lower part of this apparatus is marble and acid, and in the upper part +cold water. The valves are so arranged that the gas can get from one to +the other. I will set it in action now, and you can see the gas bubbling +up through the water, as it has been doing all night long, and by this +time we shall find that we have this substance dissolved in the water. If +I take a glass and draw off some of the water, I find that it tastes a +little acid to the mouth: it is impregnated with carbonic acid; and if I +now apply a little lime-water to it, that will give us a test of its +presence. This water will make the lime-water turbid and white, which is +proof of the presence of carbonic acid. + +Then it is a very weighty gas--it is heavier than the atmosphere. I have +put their respective weights at the lower part of this table, along with, +for comparison, the weights of the other gases we have been examining:-- + + Pint. Cubic Foot. +Hydrogen, . . . . 3/4 grains. 1/12 ounce. +Oxygen, . . . . 11-9/10 " 1-1/2 " +Nitrogen, . . . . 10-1/10 " 1-1/4 " +Air,. . . . . . 10-7/16 " 1-3/8 " +Carbonic acid, . . 16-1/3 " 1-9/10 " + +A pint of it weighs 16-1/3 grains, and a cubic foot weighs 1-9/10 ounce, +almost two ounces. You can see by many experiments that this is a heavy +gas. Suppose I take a glass containing nothing else but air, and from this +vessel containing the carbonic acid I attempt to pour a little of this gas +into that glass; I wonder whether any has gone in or not. I cannot tell by +the appearance, but I can in this way [introducing the taper]. Yes, there +it is, you see; and if I were to examine it by lime-water, I should find +it by that test also. I will take this little bucket, and put it down into +the well of carbonic acid--indeed, we too often have real wells of +carbonic acid--and now, if there is any carbonic acid, I must have got to +it by this time, and it will be in this bucket, which we will examine with +a taper. There it is, you see; it is full of carbonic acid. + +[Illustration: Fig. 30.] + +There is another experiment by which I will shew you its weight. I have +here a jar suspended at one end of a balance--it is now equipoised; but +when I pour this carbonic acid into the jar on the one side which now +contains air, you will see it sink down at once, because of the carbonic +acid that I pour into it. And now, if I examine this jar with the lighted +taper, I shall find that the carbonic acid has fallen into it, and it no +longer has any power of supporting the combustion. If I blow a +soap-bubble, which of course will be filled with air, and let it fall into +this jar of carbonic acid, it will float. + +[Illustration: Fig. 31.] + +But I shall first of all take one of these little balloons filled with +air. I am not quite sure where the carbonic acid is; we will just try the +depth, and see whereabouts is its level. There, you see, we have this +bladder floating on the carbonic acid; and if I evolve some more of the +carbonic acid, the bladder will be lifted up higher. There it goes--the +jar is nearly full; and now I will see whether I can blow a soap-bubble on +that, and float it in the same way. [The Lecturer here blew a soap-bubble, +and allowed it to fall into the jar of carbonic acid, when it floated in +it midway.] It is floating, as the balloon floated, by virtue of the +greater weight of the carbonic acid than of the air. And now, having so +far given you the history of the carbonic acid--as to its sources in the +candle, as to its physical properties and weight--when we next meet I +shall shew you of what it is composed, and where it gets its elements +from. + + + + +LECTURE VI. + +CARBON OR CHARCOAL--COAL GAS--RESPIRATION AND ITS ANALOGY TO THE BURNING +OF A CANDLE--CONCLUSION. + + +A lady, who honours me by her presence at these Lectures, has conferred a +still further obligation by sending me these two candles, which are from +Japan, and, I presume, are made of that substance to which I referred in a +former lecture. You see that they are even far more highly ornamented than +the French candles; and, I suppose, are candles of luxury, judging from +their appearance. They have a remarkable peculiarity about them--namely, a +hollow wick,--that beautiful peculiarity which Argand introduced into the +lamp, and made so valuable. To those who receive such presents from the +East, I may just say that this and such like materials gradually undergo a +change which gives them on the surface a dull and dead appearance; but +they may easily be restored to their original beauty, if the surface be +rubbed with a clean cloth or silk handkerchief, so as to polish the little +rugosity or roughness: this will restore the beauty of the colours. I have +so rubbed one of these candles, and you see the difference between it and +the other which has not been polished, but which may be restored by the +same process. Observe, also, that these moulded candles from Japan are +made more conical than the moulded candles in this part of the world. + +I told you, when we last met, a good deal about carbonic acid. We found, +by the lime-water test, that when the vapour from the top of the candle or +lamp was received into bottles, and tested by this solution of lime-water +(the composition of which I explained to you, and which you can make for +yourselves), we had that white opacity which was in fact calcareous +matter, like shells and corals, and many of the rocks and minerals in the +earth. But I have not yet told you fully and clearly the chemical history +of this substance--carbonic acid--as we have it from the candle, and I +must now resume that subject. We have seen the products, and the nature of +them, as they issue from the candle. We have traced the water to its +elements, and now we have to see where are the elements of the carbonic +acid supplied by the candle. A few experiments will shew this. You +remember that when a candle burns badly, it produces smoke; but if it is +burning well, there is no smoke. And you know that the brightness of the +candle is due to this smoke, which becomes ignited. Here is an experiment +to prove this: so long as the smoke remains in the flame of the candle and +becomes ignited, it gives a beautiful light, and never appears to us in +the form of black particles. I will light some fuel, which is extravagant +in its burning. This will serve our purpose--a little turpentine on a +sponge. You see the smoke rising from it, and floating into the air in +large quantities; and, remember now, the carbonic acid that we have from +the candle is from such smoke as that. To make that evident to you, I will +introduce this turpentine burning on the sponge into a flask where I have +plenty of oxygen, the rich part of the atmosphere, and you now see that +the smoke is all consumed. This is the first part of our experiment; and +now, what follows? The carbon which you saw flying off from the turpentine +flame in the air is now entirely burned in this oxygen, and we shall find +that it will, by this rough and temporary experiment, give us exactly the +same conclusion and result as we had from the combustion of the candle. +The reason why I make the experiment in this manner is solely that I may +cause the steps of our demonstration to be so simple that you can never +for a moment lose the train of reasoning, if you only pay attention. All +the carbon which is burned in oxygen, or air, comes out as carbonic acid, +whilst those particles which are not so burned shew you the second +substance in the carbonic acid--namely, the carbon--that body which made +the flame so bright whilst there was plenty of air, but which was thrown +off in excess when there was not oxygen enough to burn it. + +I have also to shew you a little more distinctly the history of carbon and +oxygen, in their union to make carbonic acid. You are now better able to +understand this than before, and I have prepared three or four experiments +by way of illustration. This jar is filled with oxygen, and here is some +carbon which has been placed in a crucible, for the purpose of being made +red-hot. I keep my jar dry, and venture to give you a result imperfect in +some degree, in order that I may make the experiment brighter. I am about +to put the oxygen and the carbon together. That this is carbon (common +charcoal pulverised), you will see by the way in which it burns in the air +[letting some of the red-hot charcoal fall out of the crucible]. I am now +about to burn it in oxygen gas, and look at the difference. It may appear +to you at a distance as if it were burning with a flame; but it is not so. +Every little piece of charcoal is burning as a spark, and whilst it so +burns it is producing carbonic acid. I specially want these two or three +experiments to point out what I shall dwell upon more distinctly +by-and-by--that carbon burns in this way, and not as a flame. + +Instead of taking many particles of carbon to burn, I will take a rather +large piece, which will enable you to see the form and size; and to trace +the effects very decidedly. Here is the jar of oxygen, and here is the +piece of charcoal, to which I have fastened a little piece of wood, which +I can set fire to, and so commence the combustion, which I could not +conveniently do without. You now see the charcoal burning, but not as a +flame (or if there be a flame, it is the smallest possible one, which I +know the cause of--namely, the formation of a little carbonic oxide close +upon the surface of the carbon). It goes on burning, you see, slowly +producing carbonic acid by the union of this carbon or charcoal (they are +equivalent terms) with the oxygen. I have here another piece of charcoal, +a piece of bark, which has the quality of being blown to pieces--exploding +as it burns. By the effect of the heat, we shall reduce the lump of carbon +into particles that will fly off; still every particle, equally with the +whole mass, burns in this peculiar way: it burns as a coal, and not like a +flame. You observe a multitude of little combustions going on, but no +flame. I do not know a finer experiment than this, to shew that carbon +burns with a spark. + +Here, then, is carbonic acid formed from its elements. It is produced at +once; and if we examined it by lime-water, you will see that we have the +same substance which I have previously described to you. By putting +together 6 parts of carbon by weight (whether it comes from the flame of a +candle or from powdered charcoal) and 16 parts of oxygen by weight, we +have 22 parts of carbonic acid; and, as we saw last time, the 22 parts of +carbonic acid, combined with 28 parts of lime, produced common carbonate +of lime. If you were to examine an oyster-shell, and weigh the component +parts, you would find that every 50 parts would give 6 of carbon and 16 of +oxygen, combined with 28 of lime. However, I do not want to trouble you +with these minuti3/4--it is only the general philosophy of the matter that +we can now go into. See how finely the carbon is dissolving away [pointing +to the lump of charcoal burning quietly in the jar of oxygen]. You may say +that the charcoal is actually dissolving in the air round about; and if +that were perfectly pure charcoal, which we can easily prepare, there +would be no residue whatever. When we have a perfectly cleansed and +purified piece of carbon, there is no ash left. The carbon burns as a +solid dense body, that heat alone cannot change as to its solidity, and +yet it passes away into vapour that never condenses into solid or liquid +under ordinary circumstances; and what is more curious still, is the fact +that the oxygen does not change in its bulk by the solution of the carbon +in it. Just as the bulk is at first, so it is at last, only it has become +carbonic acid. + +There is another experiment which I must give you before you are fully +acquainted with the general nature of carbonic acid. Being a compound +body, consisting of carbon and oxygen, carbonic acid is a body that we +ought to be able to take asunder. And so we can. As we did with water, so +we can with carbonic acid--take the two parts asunder. The simplest and +quickest way is to act upon the carbonic acid by a substance that can +attract the oxygen from it, and leave the carbon behind. You recollect +that I took potassium and put it upon water or ice, and you saw that it +could take the oxygen from the hydrogen. Now, suppose we do something of +the same kind here with this carbonic acid. You know carbonic acid to be a +heavy gas. I will not test it with lime-water, as that will interfere with +our subsequent experiments; but I think the heaviness of the gas and the +power of extinguishing flame will be sufficient for our purpose. I +introduce a flame into the gas, and you will see whether it will be put +out. You see the light is extinguished. Indeed, the gas may, perhaps, put +out phosphorus, which, you know, has a pretty strong combustion. Here is a +piece of phosphorus heated to a high degree. I introduce it into gas, and +you observe the light is put out; but it will take fire again in the air, +because there it re-enters into combustion. Now, let me take a piece of +potassium, a substance which, even at common temperatures, can act upon +carbonic acid, though not sufficiently for our present purpose, because it +soon gets covered with a protecting coat; but if we warm it up to the +burning point in air, as we have a fair right to do, and as we have done +with phosphorus, you will see that it can burn in carbonic acid; and if it +burns, it will burn by taking oxygen, so that you will see what is left +behind. I am going, then, to burn this potassium in the carbonic acid, as +a proof of the existence of oxygen in the carbonic acid. [In the +preliminary process of heating, the potassium exploded.] Sometimes we get +an awkward piece of potassium that explodes, or something like it, when it +burns. I will take another piece; and now that it is heated, I introduce +it into the jar, and you perceive that it burns in the carbonic acid--not +so well as in the air, because the carbonic acid contains the oxygen +combined; but it does burn, and takes away the oxygen. If I now put this +potassium into water, I find that, besides the potash formed (which you +need not trouble about), there is a quantity of carbon produced. I have +here made the experiment in a very rough way; but I assure you that if I +were to make it carefully, devoting a day to it, instead of five minutes, +we should get all the proper amount of charcoal left in the spoon, or in +the place where the potassium was burned, so that there could be no doubt +as to the result. Here, then, is the carbon obtained from the carbonic +acid, as a common black substance; so that you have the entire proof of +the nature of carbonic acid as consisting of carbon and oxygen. And now, I +may tell you, that _whenever_ carbon burns under common circumstances, it +produces carbonic acid. + +Suppose I take this piece of wood, and put it into a bottle with +lime-water. I might shake that lime-water up with wood and the atmosphere +as long as I pleased, it would still remain clear as you see it; but +suppose I burn the piece of wood in the air of that bottle. You, of +course, know I get water. Do I get carbonic acid? [The experiment was +performed.] There it is, you see--that is to say, the carbonate lime, +which results from carbonic acid, and that carbonic acid must be formed +from the carbon which comes from the wood, from the candle, or any other +thing. Indeed, you have yourselves frequently tried a very pretty +experiment, by which you may see the carbon in wood. If you take a piece +of wood, and partly burn it, and then blow it out, you have carbon left. +There are things that do not shew carbon in this way. A candle does not +shew it, but it contains carbon. Here also is a jar of coal-gas, which +produces carbonic acid abundantly. You do not see the carbon, but we can +soon shew it to you. I will light it, and as long as there is any gas in +this cylinder it will go on burning. You see no carbon, but you see a +flame; and because that is bright, it will lead you to guess that there is +carbon in the flame. But I will shew it to you by another process. I have +some of the same gas in another vessel, mixed with a body that will burn +the hydrogen of the gas, but will not burn the carbon. I will light them +with a burning taper, and you perceive the hydrogen is consumed, but not +the carbon, which is left behind as a dense black smoke. I hope that by +these three or four experiments you will learn to see when carbon is +present, and understand what are the products of combustion, when gas or +other bodies are thoroughly burned in the air. + +Before we leave the subject of carbon, let us make a few experiments and +remarks upon its wonderful condition as respects ordinary combustion. I +have shewn you that the carbon in burning burns only as a solid body, and +yet you perceive that, after it is burned, it ceases to be a solid. There +are very few fuels that act like this. It is, in fact, only that great +source of fuel, the carbonaceous series, the coals, charcoals, and woods, +that can do it. I do not know that there is any other elementary substance +besides carbon that burns with these conditions; and if it had not been +so, what would happen to us? Suppose all fuel had been like iron, which, +when it burns, burns into a solid substance. We could not then have such a +combustion as you have in this fire-place. Here also is another kind of +fuel which burns very well--as well as, if not better, than carbon--so +well, indeed, as to take fire of itself when it is in the air, as you see +[breaking a tube full of lead pyrophorus]. This substance is lead, and you +see how wonderfully combustible it is. It is very much divided, and is +like a heap of coals in the fireplace; the air can get to its surface and +inside, and so it burns. But why does it not burn in that way now, when it +is lying in a mass? [emptying the contents of the tube in a heap on to a +plate of iron]. Simply because the air cannot get to it. Though it can +produce a great heat, the great heat which we want in our furnaces and +under our boilers, still that which is produced cannot get away from the +portion which remains unburned underneath, and that portion, therefore, is +prevented from coming in contact with the atmosphere, and cannot be +consumed. How different is that from carbon. Carbon burns just in the same +way as this lead does, and so gives an intense fire in the furnace, or +wherever you choose to burn it; but then the body produced by its +combustion passes away, and the remaining carbon is left clear. I shewed +you how carbon went on dissolving in the oxygen, leaving no ash; whereas +here [pointing to the heap of pyrophorus] we have actually more ash than +fuel, for it is heavier by the amount of the oxygen which has united with +it. Thus you see the difference between carbon and lead or iron: if we +choose iron, which gives so wonderful a result in our application of this +fuel, either as light or heat. If, when the carbon burnt, the product went +off as a solid body, you would have had the room filled with an opaque +substance, as in the case of the phosphorus; but when carbon burns, +everything passes up into the atmosphere. It is in a fixed, almost +unchangeable condition before the combustion; but afterwards it is in the +form of gas, which it is very difficult (though we have succeeded) to +produce in a solid or a liquid state. + +Now, I must take you to a very interesting part of our subject--to the +relation between the combustion of a candle and that living kind of +combustion which goes on within us. In every one of us there is a living +process of combustion going on very similar to that of a candle; and I +must try to make that plain to you. For it is not merely true in a +poetical sense--the relation of the life of man to a taper; and if you +will follow, I think I can make this clear. In order to make the relation +very plain, I have devised a little apparatus which we can soon build up +before you. Here is a board and a groove cut in it, and I can close the +groove at the top part by a little cover. I can then continue the groove +as a channel by a glass tube at each end, there being a free passage +through the whole. Suppose I take a taper or candle (we can now be liberal +in our use of the word "candle," since we understand what it means), and +place it in one of the tubes; it will go on, you see, burning very well. +You observe that the air which feeds the flame passes down the tube at one +end, then goes along the horizontal tube, and ascends the tube at the +other end in which the taper is placed. + +[Illustration: Fig. 32] + +If I stop the aperture through which the air enters, I stop combustion, as +you perceive. I stop the supply of air, and consequently the candle goes +out. But, now, what will you think of this fact? In a former experiment I +shewed you the air going from one burning candle to a second candle. If I +took the air proceeding from another candle, and sent it down by a +complicated arrangement into this tube, I should put this burning candle +out. But what will you say when I tell you that my breath will put out +that candle? I do not mean by blowing at all, but simply that the nature +of my breath is such that a candle cannot burn in it. I will now hold my +mouth over the aperture, and without blowing the flame in any way, let no +air enter the tube but what comes from my mouth. You see the result. I did +not blow the candle out. I merely let the air which I expired pass into +the aperture, and the result was that the light went out for want of +oxygen, and for no other reason. Something or other--namely, my lungs--had +taken away the oxygen from the air, and there was no more to supply the +combustion of the candle. It is, I think, very pretty to see the time it +takes before the bad air which I throw into this part of the apparatus has +reached the candle. The candle at first goes on burning, but so soon as +the air has had time to reach it, it goes out. And, now, I will shew you +another experiment, because this is an important part of our philosophy. +Here is a jar which contains fresh air, as you can see by the circumstance +of a candle or gas-light burning it. I make it close for a little time, +and by means of a pipe I get my mouth over it so that I can inhale the +air. By putting it over water, in the way that you see, I am able to draw +up this air (supposing the cork to be quite tight), take it into my lungs, +and throw it back into the jar. + +[Illustration: Fig. 33.] + +We can then examine it, and see the result. You observe, I first take up +the air, and then throw it back, as is evident from the ascent and descent +of the water; and now, by putting a taper into the air, you will see the +state in which it is, by the light being extinguished. Even one +inspiration, you see, has completely spoiled this air, so that it is no +use my trying to breathe it a second time. Now, you understand the ground +of the impropriety of many of the arrangements among the houses of the +poorer classes, by which the air is breathed over and over again, for the +want of a supply, by means of proper ventilation, sufficient to produce a +good result. You see how bad the air becomes by a single breathing; so +that you can easily understand how essential fresh air is to us. + +To pursue this a little further, let us see what will happen with +lime-water. Here is a globe which contains a little lime-water, and it is +so arranged as regards the pipes, as to give access to the air within, so +that we can ascertain the effect of respired or unrespired air upon it. Of +course, I can either draw in air (through A), and so make the air that +feeds my lungs go through the lime-water, or I can force the air out of my +lungs through the tube (B), which goes to the bottom, and so shew its +effect upon the lime-water. + +[Illustration: Fig. 34.] + +You will observe that, however long I draw the external air into the +lime-water, and then through it to my lungs, I shall produce no effect +upon the water--it will not make the lime-water turbid; but if I throw the +air _from_ my lungs through the lime-water, several times in succession, +you see how white and milky the water is getting, shewing the effect which +expired air has had upon it; and now you begin to know that the atmosphere +which we have spoiled by respiration is spoiled by carbonic acid, for you +see it here in contact with the lime-water. + +I have here two bottles, one containing lime-water and the other common +water, and tubes which pass into the bottles and connect them. The +apparatus is very rough, but it is useful notwithstanding. + +[Illustration: Fig. 35.] + +If I take these two bottles, inhaling here and exhaling there, the +arrangement of the tubes will prevent the air going backwards. The air +coming in will go to my mouth and lungs, and in going out, will pass +through the lime-water, so that I can go on breathing and making an +experiment, very refined in its nature, and very good in its results. You +will observe that the good air has done nothing to the lime-water; in the +other case nothing has come to the lime-water but my respiration, and you +see the difference in the two cases. + +Let us now go a little further. What is all this process going on within +us which we cannot do without, either day or night, which is so provided +for by the Author of all things that He has arranged that it shall be +independent of all will? If we restrain our respiration, as we can to a +certain extent, we should destroy ourselves. When we are asleep, the +organs of respiration, and the parts that are associated with them, still +go on with their action--so necessary is this process of respiration to +us, this contact of the air with the lungs. I must tell you, in the +briefest possible manner, what this process is. We consume food: the food +goes through that strange set of vessels and organs within us, and is +brought into various parts of the system, into the digestive parts +especially; and alternately the portion which is so changed is carried +through our lungs by one set of vessels, while the air that we inhale and +exhale is drawn into and thrown out of the lungs by another set of +vessels, so that the air and the food come close together, separated only +by an exceedingly thin surface: the air can thus act upon the blood by +this process, producing precisely the same results in kind as we have seen +in the case of the candle. The candle combines with parts of the air, +forming carbonic acid, and evolves heat; so in the lungs there is this +curious, wonderful change taking place. The air entering, combines with +the carbon (not carbon in a free state, but, as in this case, placed ready +for action at the moment), and makes carbonic acid, and is so thrown out +into the atmosphere, and thus this singular result takes place: we may +thus look upon the food as fuel. Let me take that piece of sugar, which +will serve my purpose. It is a compound of carbon, hydrogen, and oxygen, +similar to a candle, as containing the same elements, though not in the +same proportion--the proportions being as shewn in this table:-- + +SUGAR. + +Carbon, . . . . 72 + _ +Hydrogen, . . . 11 | + | 99 +Oxygen, . . . . 88_| + +This is, indeed, a very curious thing, which you can well remember, for +the oxygen and hydrogen are in exactly the proportions which form water, +so that sugar may be said to be compounded of 72 parts of carbon and 99 +parts of water; and it is the carbon in the sugar that combines with the +oxygen carried in by the air in the process of respiration--so making us +like candles--producing these actions, warmth, and far more wonderful +results besides, for the sustenance of the system, by a most beautiful and +simple process. To make this still more striking, I will take a little +sugar; or, to hasten the experiment, I will use some syrup, which contains +about three-fourths of sugar and a little water. If I put a little oil of +vitriol on it, it takes away the water, and leaves the carbon in a black +mass. [The Lecturer mixed the two together.] You see how the carbon is +coming out, and before long we shall have a solid mass of charcoal, all of +which has come out of sugar. Sugar, as you know, is food, and here we have +absolutely a solid lump of carbon where you would not have expected it. +And if I make arrangements so as to oxidize the carbon of sugar, we shall +have a much more striking result Here is sugar, and I have here an +oxidizer--a quicker one than the atmosphere; and so we shall oxidize this +fuel by a process different from respiration in its form, though not +different in its kind. It is the combustion of the carbon by the contact +of oxygen which the body has supplied to it. If I set this into action at +once, you will see combustion produced. Just what occurs in my +lungs--taking in oxygen from another source, namely, the atmosphere--takes +place here by a more rapid process. + +You will be astonished when I tell you what this curious play of carbon +amounts to. A candle will burn some four, five, six, or seven hours. What, +then, must be the daily amount of carbon going up into the air in the way +of carbonic acid! What a quantity of carbon must go from each of us in +respiration! What a wonderful change of carbon must take place under these +circumstances of combustion or respiration! A man in twenty-four hours +converts as much as seven ounces of carbon into carbonic acid; a milch cow +will convert seventy ounces, and a horse seventy-nine ounces, solely by +the act of respiration. That is, the horse in twenty-four hours burns +seventy-nine ounces of charcoal, or carbon, in his organs of respiration, +to supply his natural warmth in that time. All the warm-blooded animals +get their warmth in this way, by the conversion of carbon, not in a free +state, but in a state of combination. And what an extraordinary notion +this gives us of the alterations going on in our atmosphere. As much as +5,000,000 pounds, or 548 tons, of carbonic acid is formed by respiration +in London alone in twenty-four hours. And where does all this go? Up into +the air. If the carbon had been like the lead which I shewed you, or the +iron which, in burning, produces a solid substance, what would happen? +Combustion could not go on. As charcoal burns, it becomes a vapour and +passes off into the atmosphere, which is the great vehicle, the great +carrier for conveying it away to other places. Then, what becomes of it? +Wonderful is it to find that the change produced by respiration, which +seems so injurious to us (for we cannot breathe air twice over), is the +very life and support of plants and vegetables that grow upon the surface +of the earth. It is the same also under the surface, in the great bodies +of water; for fishes and other animals respire upon the same principle, +though not exactly by contact with the open air. + +Such fish as I have here [pointing to a globe of gold-fish] respire by the +oxygen which is dissolved from the air by the water, and form carbonic +acid; and they all move about to produce the one great work of making the +animal and vegetable kingdoms subservient to each other. And all the +plants growing upon the surface of the earth, like that which I have +brought here to serve as an illustration, absorb carbon. These leaves are +taking up their carbon from the atmosphere, to which we have given it in +the form of carbonic acid, and they are growing and prospering. Give them +a pure air like ours, and they could not live in it; give them carbon with +other matters, and they live and rejoice. This piece of wood gets all its +carbon, as the trees and plants get theirs, from the atmosphere, which, as +we have seen, carries away what is bad for us and at the same time good +for them,--what is disease to the one being health to the other. So are we +made dependent, not merely upon our fellow-creatures, but upon our +fellow-existers, all Nature being tied together by the laws that make one +part conduce to the good of another. + +There is another little point which I must mention before we draw to a +close--a point which concerns the whole of these operations, and most +curious and beautiful it is to see it clustering upon and associated with +the bodies that concern us--oxygen, hydrogen, and carbon, in different +states of their existence. I shewed you just now some powdered lead, which +I set burning[18]; and you saw that the moment the fuel was brought to the +air, it acted, even before it got out of the bottle--the moment the air +crept in, it acted. Now, there is a case of chemical affinity by which all +our operations proceed. When we breathe, the same operation is going on +within us. When we burn a candle, the attraction of the different parts +one to the other is going on. Here it is going on in this case of the +lead; and it is a beautiful instance of chemical affinity. If the products +of combustion rose off from the surface, the lead would take fire, and go +on burning to the end; but you remember that we have this difference +between charcoal and lead--that, while the lead can start into action at +once, if there be access of air to it, the carbon will remain days, weeks, +months, or years. The manuscripts of Herculaneum were written with +carbonaceous ink, and there they have been for 1,800 years or more, not +having been at all changed by the atmosphere, though coming in contact +with it under various circumstances. Now, what is the circumstance which +makes the lead and carbon differ in this respect? It is a striking thing +to see that the matter which is appointed to serve the purpose of fuel +_waits_ in its action: it does not start off burning, like the lead and +many other things that I could shew you; but which I have not encumbered +the table with; but it waits for action. This waiting is a curious and +wonderful thing. Candles--those Japanese candles, for instance--do not +start into action at once, like the lead or iron (for iron finely divided +does the same thing as lead), but there they wait for years, perhaps for +ages, without undergoing any alteration. I have here a supply of coal-gas. +The jet is giving forth the gas, but you see it does not take fire--it +comes out into the air, but it waits till it is hot enough before it +burns. If I make it hot enough, it takes fire. If I blow it out, the gas +that is issuing forth waits till the light is applied to it again. It is +curious to see how different substances wait--how some will wait till the +temperature is raised a little, and others till it is raised a good deal. +I have here a little gunpowder and some gun-cotton; even these things +differ in the conditions under which they will burn. The gunpowder is +composed of carbon and other substances, making it highly combustible; and +the gun-cotton is another combustible preparation. They are both waiting, +but they will start into activity at different degrees of heat, or under +different conditions. By applying a heated wire to them, we shall see +which will start first [touching the gun-cotton with the hot iron]. You +see the gun-cotton has gone off, but not even the hottest part of the wire +is now hot enough to fire the gunpowder. How beautifully that shews you +the difference in the degree in which bodies act in this way! In the one +case the substance will wait any time until the associated bodies are made +active by heat; but in the other, as in the process of respiration, it +waits no time. In the lungs, as soon as the air enters, it unites with the +carbon; even in the lowest temperature which the body can bear short of +being frozen, the action begins at once, producing the carbonic acid of +respiration: and so all things go on fitly and properly. Thus you see the +analogy between respiration and combustion is rendered still more +beautiful and striking. Indeed, all I can say to you at the end of these +lectures (for we must come to an end at one time or other) is to express a +wish that you may, in your generation, be fit to compare to a candle; that +you may, like it, shine as lights to those about you; that, in all your +actions, you may justify the beauty of the taper by making your deeds +honourable and effectual in the discharge of your duty to your fellow-men. + + + + +LECTURE ON PLATINUM. + +[_Delivered before the_ ROYAL INSTITUTION, _on Friday, February 22, +1861._] + + +Whether I was to have the honour of appearing before you this evening or +not, seemed to be doubtful upon one or two points. One of these I will +mention immediately; the other may or may not appear during the course of +the hour that follows. The first point is this. When I was tempted to +promise this subject for your attention this evening, it was founded upon +a promise, and a full intent of performing that promise, on the part of my +friend Deville, of Paris, to come here to shew before you a phenomenon in +metallurgic chemistry not common. In that I have been disappointed. His +intention was to have fused here some thirty or forty pounds of platinum, +and so to have made manifest, through my mouth and my statement, the +principles of a new process in metallurgy, in relation to this beautiful, +magnificent, and valuable metal; but circumstances over which neither he +nor I, nor others concerned, have sufficient control, have prevented the +fulfilment of that intention; and the period at which I learned the fact +was so recent, that I could hardly leave my place here to be filled by +another, or permit you, who in your kindness have come to hear what might +be said, to remain unreceived in the best manner possible to me under the +circumstances. I therefore propose to state, as well as I can, what the +principles are on which M. Deville proceeds, by means of drawings, and +some subordinate or inferior experiments. The metal platinum, of which you +see some very fine specimens on the table, has been known to us about a +hundred years. It has been wrought in a beautiful way in this country, in +France, and elsewhere, and supplied to the consumer in ingots of this +kind, or in plates, such as we have here, or in masses, that by their very +fall upon the table indicate the great weight of the substance, which is, +indeed, nearly at the head of all substances in that respect. This +substance has been given to us hitherto mainly through the philosophy of +Dr. Wollaston, whom many of us know, and it is obtained in great purity +and beauty. It is a very remarkable metal in many points, besides its +known special uses. It usually comes to us in grains. Here is a very fine +specimen of native platinum in grains. Here is also a nugget or ingot, and +here are some small pieces gathered out of certain alluvial soils in +Brazil, Mexico, California, and the Uralian districts of Russia. + +It is strange that this metal is almost always found associated with some +four or five other metals, most curious in their qualities and +characteristics. They are called platiniferous metals; and they have not +only the relation of being always found associated in this manner, but +they have other relations of a curious nature, which I shall point out to +you by a reference to one of the tables behind me. This substance is +always native--it is always in the metallic state; and the metals with +which it is found connected, and which are rarely found elsewhere, are +palladium, rhodium, iridium, osmium, and ruthenium. We have the names in +one of the tables arranged in two columns, representing, as you see, two +groups--platinum, iridium, and osmium constituting one group; and +ruthenium, rhodium, and palladium the other. Three of these have the +chemical equivalent of 98-1/2, and the others a chemical equivalent of +about half that number. Then the metals of one group have an extreme +specific gravity--platinum being, in fact, the lightest of the three, or +as light as the lightest. Osmium has a specific gravity of 21.4, and is +the heaviest body in nature; platinum is 21.15, and iridium the same; the +specific gravity of the other three being only about half that, namely, +11.3, 12.1, and 11.8. Then there is this curious relation, that palladium +and iridium are very much alike, so that you would scarcely know one from +the other, though one has only half the weight of the other, and only half +the equivalent power. So with iridium and rhodium, and osmium and +ruthenium, which are so closely allied that they make pairs, being +separated each from its own group. Then these metals are the most +infusible that we possess. Osmium is the most difficult to fuse: indeed, I +believe it never has been fused, while every other metal has. Ruthenium +comes next, iridium next, rhodium next, platinum next (so that it ranks +here as a pretty fusible metal, and yet we have been long accustomed to +speak of the infusibility of platinum), and next comes palladium, which is +the most fusible metal of the whole. It is a curious thing to see this +fine association of physical properties coming out in metals which are +grouped together somehow or other in nature, but, no doubt, by causes +which are related to analogous properties in their situation on the +surface of the earth, for it is in alluvial soils that these things are +found. + +Now, with regard to this substance, let me tell you briefly how we get it. +The process used to be this. The ore which I shewed you just now was +taken, and digested in nitro-muriatic acid of a certain strength, and +partly converted into a solution, with the leaving behind of certain +bodies that I have upon the table. The platinum being dissolved with care +in acids, to the solution the muriate of ammonia was added, as I am about +to add it here. A yellow precipitate was then thrown down, as you perceive +is the case now; and this, carefully washed and cleansed, gave us that +body [pointing to a specimen of the chloride of platinum and ammonium], +the other elements, or nearly all, being ejected. This substance being +heated, gave us what we call platinum sponge, or platinum in the metallic +state, so finely divided as to form a kind of heavy mass or sponge, which, +at the time that Dr. Wollaston first sent it forth, was not fusible for +the market or in the manufacturers' workshops, inasmuch as the temperature +required was so high, and there were no furnaces that could bring the mass +into a globule, and cause the parts to adhere together. Most of our metals +that we obtain from nature, and work in our shops, are brought at last +into a mass by fusion. I am not aware that there is in the arts or +sciences any other than iron which is not so. Soft iron we do not bring +together by fusion, but by a process which is analogous to the one that +was followed in the case of platinum, namely, welding; for these divided +grains of spongy platinum having been well washed and sunk in water for +the purpose of excluding air, and pressed together, and heated, and +hammered, and pressed again, until they come into a pretty close, dense, +compact mass, did so cohere, that when the mass was put into the furnace +of charcoal, and raised to a high temperature, the particles, at first +infinitely divided--for they were chemically divided--adhered the one to +the other, each to all the rest, until they made that kind of substance +which you see here, which will bear rolling and expansion of every kind. +No other process than that has hitherto been adopted for the purpose of +obtaining this substance from the particles by solution, precipitation, +ignition, and welding. It certainly is a very fine thing to see that we +may so fully depend upon the properties of the various substances we have +to deal with; that we can, by carrying out our processes, obtain a +material like this, allowing of division and extension under a rolling +mill--a material of the finest possible kind, the parts being held +together, not with interstices, not with porosity, but so continuous that +no fluids can pass between them; and, as Dr. Wollaston beautifully shewed, +a globule of platinum fused by the voltaic battery and the oxy-hydrogen +blowpipe, when drawn into a wire, was not sounder or stronger than this +wire made by the curious coalescence of the particles by the sticking +power that they had at high temperatures. This is the process adopted by +Messrs. Johnson and Matthey, to whose great kindness I am indebted for +these ingots and for the valuable assistance I have received in the +illustrations. + +The treatment, however, that I have to bring before you is of another +kind; and it is in the hope that we shall be able before long to have such +a thing as the manufacture of platinum of this kind, that I am encouraged +to come before you, and tell you how far Deville has gone in the matter, +and to give you illustrations of the principles on which he proceeds. I +think it is but fair that you should see an experiment shewing you the way +in which we get the adhesion of platinum. Probably you all know of the +welding of iron: you go into the smith's shop, and you see him put the +handle of a poker on to the stem, and by a little management and the +application of heat he makes them one. You have no doubt seen him put the +iron into the fire and sprinkle a little sand upon it. He does not know +the philosophy he calls into play when he sprinkles a little sand over the +oxide of iron, but he has a fine philosophy there, or practises it, when +he gets his welding. I can shew you here this beautiful circumstance of +the sticking together of the particles up to the fullest possible +intensity of their combination. If you were to go into the workshops of +Mr. Matthey, and see them hammering and welding away, you would see the +value of the experiment I am about to shew you. I have here some +platinum-wire. This is a metal which resists the action of acids, resists +oxidation by heat, and change of any sort; and which, therefore, I may +heat in the atmosphere without any flux. I bend the wire so as to make the +ends cross: these I make hot by means of the blowpipe, and then, by giving +them a tap with a hammer, I shall make them into one piece. Now that the +pieces are united, I shall have great difficulty in pulling them apart, +though they are joined only at the point where the two cylindrical +surfaces came together. And now I have succeeded in pulling the wire +apart, the division is not at the point of welding, but where the force of +the pincers has cut it, so that the junction we have effected is a +complete one. This, then, is the principle of the manufacture and +production of platinum in the old way. + +The treatment which Deville proposes to carry out, and which he has +carried out to a rather large extent in reference to the Russian supply of +platinum, is one altogether by heat, having little or no reference to the +use of acids. That you may know what the problem is, look at this table, +which gives you the composition of such a piece of platinum ore as I +shewed you just now. Wherever it comes from, the composition is as +complicated, though the proportions vary:-- + +Platinum, . . . . . 76.4 +Iridium,. . . . . . 4.3 +Rhodium,. . . . . . 0.3 +Palladium,. . . . . 1.4 +Gold, . . . . . . . 0.4 +Copper, . . . . . . 4.1 +Iron, . . . . . . . 11.7 +Osmide of Iridium,. 0.5 +Sand, . . . . . . . 1.4 + ----- + 100.5 + +This refers to the Uralian ore. In that state of combination, as shewn in +the table, the iridium and osmium are found combined in crystals, +sometimes to the amount of 0.5 per cent., and sometimes 3 or 4 per cent. +Now, this Deville proposes to deal with in the dry way, in the place of +dealing with it by any acid. + +I have here another kind of platinum; and I shew it to you for this +reason. The Russian Government, having large stores of platinum in their +dominions, have obtained it in a metallic state, and worked it into coin. +The coin I have in my hand is a twelve silver rouble piece. The rouble is +worth three shillings, and this coin is, therefore, of the value of +thirty-six shillings. The smaller coin is worth half that sum; and the +other, half of that. The metal, however, is unfit for coinage. When you +have the two metals, gold and silver, used for coinage, you have a little +confusion in the value of the two in the market; but when you have three +precious metals (for you may call platinum a precious metal) worked into +coin, they will be sure to run counter to one another. Indeed, the case +did happen, that the price of platinum coin fixed by the Government was +such, that it was worth while to purchase platinum in other countries, and +make coin of it, and then take it into that country and circulate it. The +result was, that the Russian Government stopped the issue. The composition +of this coin is--platinum, 97.0; iridium, 1.2; rhodium, 0.5; palladium, +0.25; a little copper, and a little iron. It is, in fact, bad platinum: it +scales, and it has an unfitness for commercial use and in the laboratory, +which the other well-purified platinum has not. It wants working over +again. + +Now, Deville's process depends upon three points,--upon intense heat, +blowpipe action, and the volatility of certain metals. We know that there +are plenty of metals that are volatile; but this, I think, is the first +time that it has been proposed to use the volatility of certain +metals--such as gold and palladium--for the purpose of driving them off +and leaving something else behind. He counts largely upon the volatility +of metals which we have not been in the habit of considering volatile, but +which we have rather looked upon as fixed; and I must endeavour to +illustrate these three points by a few experiments. Perhaps I can best +show you what is required in the process of heating platinum by using that +source of heat which we have here, and which seems to be almost +illimitable--namely, the voltaic battery; for it is only in consequence of +the heat that the voltaic battery affects the platinum. By applying the +two extremities of the battery to this piece of platinum-wire, you will +see what result we shall obtain. You perceive that we can take about this +heating agent wherever we like, and deal with it as we please, limiting it +in any way. I am obliged to deal carefully with it; but even that +circumstance will have an interest for you in watching the experiment. +Contact is now made. The electric current, when compressed into thin +conducting-wires offering resistance, evolves heat to a large extent; and +this is the power by which we work. You see the intense glow immediately +imparted to the wire; and if I applied the heat continuously, the effect +of the current would be to melt the wire. As soon as the contact is +broken, the wire resumes its former appearance; and now that we make +contact again, you perceive the glow as before. [The experiment was +repeated several times in rapid succession.] You can see a line of light, +though you can scarcely perceive the wire; and now that it has melted with +the great heat, if you examine it, you will perceive that it is indeed a +set of irregularities from end to end--a set of little spheres, which are +strung upon an axis of platinum running through it. It is that wire which +Mr. Grove described as being produced at the moment when fusion of the +whole mass is commencing. In the same manner, if I take a tolerably thick +piece of platinum, and subject it to the heat that can be produced by this +battery, you will see the brilliancy of the effect produced. I shall put +on a pair of spectacles for the experiment, as there is an injurious +effect of the voltaic spark upon the eyes, if the action is continued; and +it is neither policy nor bravery to subject any organ to unnecessary +danger; and I want, at all events, to keep the full use of my eyes to the +end of the lecture. + +You now see the action of the heat upon the piece of platinum--heat so +great as to break in pieces the plate on which the drops of metal fall. +You perceive, then, that we have sufficiently powerful sources of heat in +nature to deal with platinum. I have here an apparatus by which the same +thing can be shewn. Here is a piece of platinum, which is put into a +crucible of carbon made at the end of one pole of the battery, and you +will see the brilliant light that will be produced. There is our furnace, +and the platinum is rapidly getting heated; and now you perceive that it +is melted, and throwing off little particles. What a magnificent +philosophical instrument this is. When you look at the result, which is +lying upon the charcoal, you will see a beautifully fused piece of +platinum. It is now a fiery globule, with a surface so bright, and smooth, +and reflecting, that I cannot tell whether it is transparent, or opaque, +or what. This, then, will give you an idea of what has to be done by any +process that pretends to deal with thirty, or forty, or fifty pounds of +platinum at once. + +Let me now tell you briefly what Deville proposes to do. First of all, he +takes this ore, with its impurities, and mixes it (as he finds it +essential and best) with its own weight of sulphuret of lead--lead +combined with sulphur. Both the lead and the sulphur are wanted; for the +iron that is there present, as you see by the table, is one of the most +annoying substances in the treatment that you can imagine, because it is +not volatile; and while the iron remains adhering to the platinum, the +platinum will not flow readily. It cannot be sent away by a high +temperature--sent into the atmosphere so as to leave the platinum behind. +Well, then, a hundred parts of ore and a hundred parts of sulphuret of +lead, with about fifty parts of metallic lead, being all mingled together +in a crucible, the sulphur of the sulphuret takes the iron, the copper, +and some of the other metals and impurities, and combines with them to +form a slag; and as it goes on boiling and oxidising, it carries off the +iron, and so a great cleansing takes place. + +Now, you ought to know that these metals, such as platinum, iridium, and +palladium, have a strong affinity for such metals as lead and tin, and +upon this a great deal depends. Very much depends upon the platinum +throwing out its impurities of iron and so forth, by being taken up with +the lead present in it. That you may have a notion of the great power that +platinum has of combining with other metals, I will refer you to a little +of the chemist's experience--his bad experience. He knows very well that +if he takes a piece of platinum-foil, and heats a piece of lead upon it, +or if he takes a piece of platinum-foil, such as we have here, and heats +things upon it that have lead in them, his platinum is destroyed. I have +here a piece of platinum, and if I apply the heat of the spirit-lamp to +it, in consequence of the presence of this little piece of lead which I +will place on it, I shall make a hole in the metal. The heat of the lamp +itself would do no harm to the platinum, nor would other chemical means; +but because there is a little lead present, and there is an affinity +between the two substances, the bodies fuse together at once. You see the +hole I have made. It is large enough to put your finger in, though the +platinum itself was, as you saw, almost infusible, except by the voltaic +battery. For the purpose of shewing this fact in a more striking manner, I +have taken pieces of platinum-foil, tin-foil, and lead-foil, and rolled +them together; and if I apply the blowpipe to them, you will have, in +fact, a repetition on a larger scale of the experiment you saw just now +when the lead and platinum came together, and one spoiled the other. When +the metals are laid one upon the other, and folded together and heat +applied, you will not only see that the platinum runs to waste, but that +at the time when the platinum and lead are combined there is ignition +produced--there is a power of sustaining combustion. I have taken a large +piece, that you may see the phenomenon on a large scale. You saw the +ignition and the explosion which followed, of which we have here the +results--the consequence of the chemical affinity between the platinum and +the metals combined with it, which is the thing upon which Deville founds +his first result. + +When he has melted these substances and stirred them well up, and so +obtained a complete mixture, he throws in air upon the surface to burn off +all the sulphur from the remaining sulphuret of lead; and at last he gets +an ingot of lead with platinum--much lead, comparatively, and little +platinum. He gets that in the crucible with a lot of scoriae and other +things, which he treats afterwards. It is that platiniferous lead which we +have to deal with in our future process. Now, let me tell you what he does +with it. His first object is to get rid of the lead. He has thrown out all +the iron, and a number of other things, and he has got this kind of +compound indicated in the table. He may get it as high as 78 per cent. of +platinum, and 22 of lead; or 5, or 10, or 15 of platinum, and 95, or 90, +or 85 of lead (which he calls weak platinum), and he then places it in the +kind of vessel that you see before you. Suppose we had the mixture here; +we should have to make it hot, and then throw in air upon the surface. The +combustible metal--that is, the lead--and the part that will oxidise, are +thoroughly oxidised; the litharge would flow out in a fused state into a +vessel placed to receive it, and the platinum remains behind. + +[Illustration: Fig. 36.] + +Here is the process which Deville adopts for the purpose of casting off +the lead, after he has got out the platinum from the ore. (Having made use +of your friend, you get rid of him as quickly as you can.) He gets his +heat by applying the combination of oxygen and hydrogen, or of carburetted +fuel, for the purpose of producing a fire. I have here a source of +coal-gas; there I have a source of hydrogen; and here I have a source of +oxygen. I have here also one of the blowpipes used by Deville in his +process for working platinum in the way I have spoken of. There are two +pipes, and one of them goes to the source of coal-gas, and the other to +the supply of oxygen. + +[Illustration: Fig. 37.] + +By uniting these we obtain a flame of such a heat as to melt platinum. You +will, perhaps, hardly imagine what the heat is, unless you have some proof +of it; but you will soon see that I have actually the power of melting +platinum. Here is a piece of platinum-foil running like wax under the +flame which I am bringing to bear against it. The question, however, is +whether we shall get heat enough to melt, not this small quantity, but +large masses--many pounds of the metal. Having obtained heat like this, +the next consideration is what vessel is he to employ which could retain +the platinum when so heated, or bear the effects of the flame? Such +vessels are happily well supplied at Paris, and are formed of a substance +which surrounds Paris; it is a kind of chalk (called, I believe, by +geologists, _calcaire grossiere_), and it has the property of enduring an +extreme degree of heat. I am now going to get the highest heat that we can +obtain. First, I shew you the combustion of hydrogen by itself. I have not +a large supply, because the coal-gas is sufficient for most of our +purposes. If I put a piece of lime obtained from this chalk into the gas, +you see we get a pretty hot flame, which would burn one's fingers a good +deal But now let me subject a piece of it to the joint action of oxygen +and hydrogen. I do this for the purpose of shewing you the value of lime +as a material for the furnaces and chambers that are to contain the +substances to be operated on, and that are consequently to sustain the +action of this extreme heat. Here we have the hydrogen and the oxygen, +which will give the most intense heat that can be obtained by chemical +action; and if I put a piece of lime into the flame, we get what is called +the lime-light. Now, with all the beauty and intensity of action which you +perceive, there is no sensible deterioration of the lime except by the +mechanical force of the current of gases rushing from the jet against the +lime, sweeping away such particles as are not strongly aggregated. "Vapour +of lime" some call it; and it may be so, but there is no other change of +the lime than that under the action of heat of this highly-exalted +chemical condition, though almost any other substance would melt at once. + +Then, as to the way in which the heat is applied to the substance. It is +all very well for me to take a piece of antimony, and fuse it in the flame +of a blowpipe. But if I tried this piece in the ordinary lamp flame, I +should do nothing; if I tried a smaller piece, I should do little or +nothing; and if I tried a still smaller piece, I should do little or +nothing; yet I have a condition which will represent what Deville carries +to the highest possible extent, and which we all carry to the highest +extent, in the use of the blowpipe. Suppose I take this piece of antimony: +I shall not be able to melt it in that flame of the candle by merely +holding it there; yet, by taking pains, we can even melt a piece of +platinum there. This is a preparation which I made for the purpose of +proving the fusibility of platinum in a common candle. There is a piece of +wire, drawn by that ingenious process of Dr. Wollaston's, not more than +the three-thousandth part of an inch in diameter. He put the wire into the +middle of a cylinder of silver, and drew both together until the whole +compound was exceedingly thin; and then he dissolved away the silver by +nitric acid. There was left in the centre a substance which I can scarcely +see with an eye-glass, but which I know is there, and which I can make +visible, as you see, by putting it into the candle, where the heat makes +it glow like a spark. I have again and again tried this experiment +up-stairs in my own room, and have easily fused this platinum-wire by a +common candle. You see we have, therefore, heat enough in the candle, as +in the voltaic battery, or in the highly-exalted combustion of the +blowpipe, but we do not supply a continuous source of heat. In the very +act of this becoming ignited, the heat radiates so fast that you cannot +accumulate enough to cause the fusion of the wire, except under the most +careful arrangement. Thus I cannot melt that piece of antimony by simply +putting it into the candle; but if I put it upon charcoal, and drive the +fiery current against it, there will be heat enough to melt it. The beauty +of the blowpipe is, that it sends hot air (making hot air by the +combustion of the flame) against the thing to be heated. I have only to +hold the antimony in the course of that current, and particle by particle +of the current impinges upon the antimony, and so we get it melted. You +now see it red-hot, and I have no doubt it will continue to burn if I +withdraw it from the flame and continue to force the air on it. Now, you +see it burning without any heat but that of its own combustion, which I am +keeping up by sending the air against it. It would go out in a moment if I +took away the current of air from it; but there it is burning, and the +more air I give it, by this or any other action, the better it is. So, +then, we have here not merely a mighty source of heat, but a means of +driving the heat forcibly against substances. + +Let me shew you another experiment with a piece of iron. It will serve two +purposes--shewing you what the blowpipe does as a source of heat, and what +it does by sending that heat where it is wanted. I have taken iron in +contrast with silver or other metals, that you may see the difference of +action, and so be more interested in the experiment. Here is our fuel, the +coal-gas; and here our oxygen. Having thus my power of heat, I apply it to +the iron, which, as you see, soon gets red-hot. It is now flowing about +like a globule of melted mercury. But observe, I cannot raise any vapour: +it is now covered with a coat of melted oxide, and unless I have a great +power in my blowpipe, it is hardly possible to break through it. Now, +then, you see these beautiful sparks: you have not only a beautiful kind +of combustion, but you see the iron is being driven off, not producing +smoke, but burning in a fixed condition. How different this is from the +action of some other metals--that piece of antimony, for instance, which +we saw just now throwing off abundance of fumes. We can, of course, burn +away this iron by giving plenty of air to it; but with the bodies which +Deville wants to expose to this intense heat he has not that means: the +gas itself must have power enough to drive off the slag which forms on the +surface of the metal, and power to impinge upon the platinum so as to get +the full contact that he wants for the fusion to take place. We see here, +then, the means to which he resorts--oxygen, and either coal-gas or +water-gas[19], or pure hydrogen, for producing heat, and the blowpipe for +the purpose of impelling the heated current upon the metals. + +I have two or three rough drawings here, representing the kind of furnaces +which he employs. They are larger, however, than the actual furnaces he +uses. Even the furnace in which he carries on that most serious operation +of fusing fifty pounds of platinum at once is not much more than half the +size of the drawing. It is made of a piece of lime below and a piece of +lime above. You see how beautifully lime sustains heat without altering in +shape; and you may have thought how beautifully it prevents the +dissipation of the heat by its very bad conducting powers. + +[Illustration: Fig. 38] + +While the front part of the lime which you saw here was so highly ignited, +I could at any moment touch the back of it without feeling any annoyance +from the heat So, by having a chamber of lime of this sort, he is able to +get a vessel to contain these metals with scarcely any loss of heat. He +puts the blowpipes through these apertures, and sends down these gases +upon the metals, which are gradually melted. He then puts in more metal +through a hole at the top. The results of the combustion issue out of the +aperture which you see represented. If there be strips of platinum, he +pushes them through the mouth out of which the heated current is coming, +and there they get red-hot and white-hot before they get into the bath of +platinum. So he is able to fuse a large body of platinum in this manner. +When the platinum is melted, he takes off the top and pours out from the +bottom piece, like a crucible, and makes his cast. This is the furnace by +which he fuses his forty pounds or fifty pounds of platinum at once. The +metal is raised to a heat that no eye can bear. There is no light and +shadow, no chiaro-oscuro there; all is the same intensity of glow. You +look in, and you cannot see where the metal or the lime is; it is all as +one. We have, therefore, a platform with a handle, which turns upon an +axis, that coincides with the gutter that is formed for the pouring of the +metal; and when all is known to be ready, by means of dark glasses, the +workmen take off the top piece and lift up the handle, and the mould being +then placed in a proper position, he knows that the issue of the metal +will be exactly in the line of the axis. No injury has ever happened from +the use of this plan. You know with what care it is necessary to carry +such a vessel of mercury as we have here, for fear of turning it over on +one side or the other; but if it be a vessel of melted platinum, the very +greatest care must be used, because the substance is twice as heavy: yet +no injury has been done to any of the workmen in this operation. + +I have said that Deville depends upon intense heat for carrying off +vapour; and this brings me to the point of shewing how vapours are carried +off. Here is a basin of mercury, which boils easily, as you know, and +gives us the opportunity of observing the facts and principles which are +to guide us. I have here two poles of the battery, and if I bring them +into contact with the mercury, see what a development of vapour we have. +The mercury is flying off rapidly; and I might, if I pleased, put all the +company around me in a bath of mercury vapour. And so, if we take this +piece of lead and treat it in the same way, it will also give off vapour. +Observe the fumes that rise from it; and even if it was so far enclosed +from the air that you could not form any litharge, you would still have +those abundant fumes flying off. I may also take a piece of gold, and shew +you the same thing. I have here a piece of gold which I put upon a clean +surface of Paris limestone. Applying the heat of the blowpipe to it, you +see how the heat drives off the vapour; and if you notice at the end of +the Lecture, you will observe on the stone a purple patch of condensed +gold. Thus you see a proof of the volatilisation of gold. It is the same +with silver. You will not be startled if I sometimes use one agent and +sometimes another to illustrate a particular point. The volatility of gold +and silver is the same thing, whether it be effected by the voltaic +battery or by the blowpipe. [A lump of silver was placed in a charcoal +crucible between the poles of a voltaic battery.] Now, look at the fumes +of silver, and observe the peculiar and beautiful green colour which they +produce. We shall now shew you this same process of boiling the silver, +cast on a screen from the electric lamp which you have before you; and +while Dr. Tyndall is kindly getting the lamp ready for this purpose, let +me tell you that Deville proposes to throw out in this way all these +extraneous things that I have spoken of, except two--namely, iridium and +rhodium. It so happens, as he says, that iridium and rhodium do make the +metal more capable of resisting the attacks of acids than platinum itself. +Alloys are compounded up to 25 per cent. of rhodium and iridium, by which +the chemical inaction of the platinum is increased, and also its +malleability and other physical properties. [The image of the voltaic +discharge through vapour of silver was now thrown upon the screen.] What +you have now on the screen is an inverted image of what you saw when we +heated the silver before. The fine stream that you see around the silver +is the discharge of the electric force that takes place, giving you that +glorious green light which you see in the ray; and if Dr. Tyndall will +open the top of the lamp, you will see the quantity of fumes that will +come out of the aperture, shewing you at once the volatility of silver. + +I have now finished this imperfect account. It is but an apology for not +having brought the process itself before you. I have done the best I could +under the circumstances; and I know your kindness well, for if I were not +aware that I might trust to it, I would not appear here so often as I have +done. The gradual loss of memory and of my other faculties is making +itself painfully evident to me, and requires, every time I appear before +you, the continued remembrance of your kindness to enable me to get +through my task. If I should happen to go on too long, or should fail in +doing what you might desire, remember it is yourselves who are chargeable, +by wishing me to remain. I have desired to retire, as I think every man +ought to do before his faculties become impaired; but I must confess that +the affection I have for this place, and for those who frequent this +place, is such, that I hardly know when the proper time has arrived. + + + + +NOTES. + + +[Footnote 1: Page 16. The Royal George sunk at Spithead on The 29th of +August, 1782. Colonel Pasley commenced operations for the removal of the +wreck by the explosion of gunpowder, in August, 1839. The candle which +Professor Faraday exhibited must therefore have been exposed to the action +of salt water for upwards of fifty-seven years.] + +[Footnote 2: Page 17. The fat or tallow consists of a chemical combination +of fatty acids with glycerine. The lime unites with the palmitic, oleic, +and stearic acids, and separates the glycerine. After washing, the +insoluble lime soap is decomposed with hot dilute sulphuric acid. The +melted fatty acids thus rise as an oil to the surface, when they are +decanted. They are again washed and cast into thin plates, which, when +cold, are placed between layers of cocoa-nut matting, and submitted to +intense hydraulic pressure. In this way the soft oleic acid is squeezed +out, whilst the hard palmitic and stearic acids remain. These are further +purified by pressure at a higher temperature, and washing in warm dilute +sulphuric acid, when they are ready to be made into candles. These acids +are harder and whiter than the fats from which they were obtained, whilst +at the same time they are cleaner and more combustible.] + +[Footnote 3: Page 19. A little borax or phosphorus salt is sometimes +added, in order to make the ash fusible.] + +[Footnote 4: Page 27. Capillary attraction or repulsion is the cause which +determines the ascent or descent of a fluid in a capillary tube. If a +piece of thermometer tubing, open at each end, be plunged into water, the +latter will instantly rise in the tube considerably above its external +level. If, on the other hand, the tube be plunged into mercury, a +repulsion instead of attraction will be exhibited, and the level of the +mercury will be lower in the tube than it is outside.] + +[Footnote 5: Page 29. The late Duke of Sussex was, we believe, the first +to shew that a prawn might be washed upon this principle. If the tail, +after pulling off the fan part, be placed in a tumbler of water, and the +head be allowed to hang over the outside, the water will be sucked up the +tail by capillary attraction, and will continue to run out through the +head until the water in the glass has sunk so low that the tail ceases to +dip into it.] + +[Footnote 6: Page 37. The alcohol had chloride of copper dissolved in it: +this produces a beautiful green flame.] + +[Footnote 7: Page 54. Lycopodium is a yellowish powder found in the fruit +of the club moss (_Lycopodium clavatum_). It is used in fireworks.] + +[Footnote 8: Page 58. Bunsen has calculated that the temperature of the +oxyhydrogen blowpipe is 8061 deg. Centigrade. Hydrogen burning in air has a +temperature of 3259 deg. C., and coal-gas in air, 2350 deg. C.] + +[Footnote 9: Page 60. The following is the action of the sulphuric acid in +inflaming the mixture of sulphuret of antimony and chlorate of potassa. A +portion of the latter is decomposed by the sulphuric acid into oxide of +chlorine, bisulphate of potassa, and perchlorate of potassa. The oxide of +chlorine inflames the sulphuret of antimony, which is a combustible body, +and the whole mass instantly bursts into flame.] + +[Footnote 10: Page 63. The "air-burner," which is of such value in the +laboratory, owes its advantage to this principle. It consists of a +cylindrical metal chimney, covered at the top with a piece of rather +coarse iron-wire gauze. This is supported over an argand burner, in such a +manner that the gas may mix in the chimney with an amount of air +sufficient to burn the carbon and hydrogen simultaneously, so that there +may be no separation of carbon in the flame with consequent deposition of +soot. The flame, being unable to pass through the wire gauze, burns in a +steady, nearly invisible manner above.] + +[Footnote 11: Page 74. Water is in its densest state at a temperature of +39.1 deg. Fahrenheit] + +[Footnote 12: Page 74. A mixture of salt and pounded ice reduces the +temperature from 32 deg. F. to zero--the ice at the same time becoming fluid.] + +[Footnote 13: Page 82. Potassium, the metallic basis of potash, was +discovered by Sir Humphrey Davy in 1807, who succeeded in separating it +from potash by means of a powerful voltaic battery. Its great affinity for +oxygen causes it to decompose water with evolution of hydrogen, which +takes fire with the heat produced.] + +[Footnote 14: Page 98. Professor Faraday has calculated that there is as +much electricity required to decompose one grain of water as there is in a +very powerful flash of lightning.] + +[Footnote 15: Page 101. A solution of acetate of lead submitted to the +action of the voltaic current, yields lead at the negative pole, and brown +peroxide of lead at the positive pole. A solution of nitrate of silver, +under the same circumstances, yields silver at the negative pole, and +peroxide of silver at the positive pole.] + +[Footnote 16: Page 129. The gas which is thus employed as a test for the +presence of oxygen, is the binoxide of nitrogen, or nitrous oxide. It is a +colourless gas, which, when brought in contact with oxygen, unites with +it, forming hyponitric acid, the red gas referred to.] + +[Footnote 17: Page 152. _Marble_ is a compound of carbonic acid and lime. +The muriatic acid being the stronger of the two, takes the place of the +carbonic acid, which escapes as a gas, the residue forming muriate of lime +or chloride of calcium.] + +[Footnote 18: Page 186. _Lead pyrophorus_ is made by heating dry tartrate +of lead in a glass tube (closed at one end, and drawn out to a fine point +at the other) until no more vapours are evolved. The open end of the tube +is then to be sealed before the blowpipe. When the tube is broken and the +contents shaken out into the air, they burn with a red flash.] + +[Footnote 19: Page 216. _Water-gas_ is formed by passing vapour of water +over red-hot charcoal or coke. It is a mixture of hydrogen and carbonic +oxide; each of which is an inflammable gas.] + + + +Poster's note: "combustion that makes!" was corrected from a misprint +"combusion that makes!" in the original. + + + +End of the Project Gutenberg EBook of The Chemical History Of A Candle +by Michael Faraday + +*** END OF THIS PROJECT GUTENBERG EBOOK THE CHEMICAL HISTORY OF A CANDLE *** + +***** This file should be named 14474-8.txt or 14474-8.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/1/4/4/7/14474/ + +Produced by Clare Boothby, Richard Prairie and the PG Online +Distributed Proofreading Team + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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