Richard Melson

September 2006

Michael Faraday

Faraday:
Chemical History of a candle

• Chemical Manipulation, being Instructions to Students in Chemistry (1 vol., John Murray, 1st ed. 1827, 2nd 1830, 3rd 1842);

• Experimental Researches in Electricity, vols. i. and ii., Richard and John Edward Taylor, vols. i. and ii. (1844 and 1847); vol. iii. (1844); vol. iii. Richard Taylor and William Francis (1855);

• Experimental Researches in Chemistry and Physics, Taylor and Francis (1859);

• A Course of Six Lectures on the Chemical History of a Candle (edited by W. Crookes) (Griffin, Bohn & Co., 1861);

• On the Various Forces in Nature (edited by W. Crookes) (Chatto & Windus, 1873).

• A Course of 6 lectures on the various forces of matter and their relations to each other. edited by William Crookes(1861).

• His Diary edited by T. Martin was published in eight volumes (1932 - 36)
  
  The Chemical History Of A Candle, by Michael Faraday 1861
  
  Title: The Chemical History Of A Candle
  
  Author: Michael Faraday
  
  THE CHEMICAL HISTORY OF A CANDLE
  
  A COURSE OF LECTURES DELIVERED BEFORE A JUVENILE
  AUDIENCE AT THE ROYAL INSTITUTION 1861
  
  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 Hooker, 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 Hooker 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
  Hooker, 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 Hooker 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?nd 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 grossi?_), 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