still further obligation by sending me these two candles, which are from
Japan, and, I presume, are made of that substance to which I referred in a
former lecture. You see that they are even far more highly ornamented than
the French candles; and, I suppose, are candles of luxury, judging from
their appearance. They have a remarkable peculiarity about them—namely, a
hollow wick,—that beautiful peculiarity which Argand introduced into the
lamp, and made so valuable. To those who receive such presents from the
East, I may just say that this and such like materials gradually undergo a
change which gives them on the surface a dull and dead appearance; but
they may easily be restored to their original beauty, if the surface be
rubbed with a clean cloth or silk handkerchief, so as to polish the little
rugosity or roughness: this will restore the beauty of the colours. I have
so rubbed one of these candles, and you see the difference between it and
the other which has not been polished, but which may be restored by the
same process. Observe, also, that these moulded candles from Japan are
made more conical than the moulded candles in this part of the world.
I told you, when we last met, a good deal about carbonic acid. We found,
by the lime-water test, that when the vapour from the top of the candle or
lamp was received into bottles, and tested by this solution of lime-water
(the composition of which I explained to you, and which you can make for
yourselves), we had that white opacity which was in fact calcareous
matter, like shells and corals, and many of the rocks and minerals in the
earth. But I have not yet told you fully and clearly the chemical history
of this substance—carbonic acid—as we have it from the candle, and I
must now resume that subject. We have seen the products, and the nature of
them, as they issue from the candle. We have traced the water to its
elements, and now we have to see where are the elements of the carbonic
acid supplied by the candle. A few experiments will shew this. You
remember that when a candle burns badly, it produces smoke; but if it is
burning well, there is no smoke. And you know that the brightness of the
candle is due to this smoke, which becomes ignited. Here is an experiment
to prove this: so long as the smoke remains in the flame of the candle and
becomes ignited, it gives a beautiful light, and never appears to us in
the form of black particles. I will light some fuel, which is extravagant
in its burning. This will serve our purpose—a little turpentine on a
sponge. You see the smoke rising from it, and floating into the air in
large quantities; and, remember now, the carbonic acid that we have from
the candle is from such smoke as that. To make that evident to you, I will
introduce this turpentine burning on the sponge into a flask where I have
plenty of oxygen, the rich part of the atmosphere, and you now see that
the smoke is all consumed. This is the first part of our experiment; and
now, what follows? The carbon which you saw flying off from the turpentine
flame in the air is now entirely burned in this oxygen, and we shall find
that it will, by this rough and temporary experiment, give us exactly the
same conclusion and result as we had from the combustion of the candle.
The reason why I make the experiment in this manner is solely that I may
cause the steps of our demonstration to be so simple that you can never
for a moment lose the train of reasoning, if you only pay attention. All
the carbon which is burned in oxygen, or air, comes out as carbonic acid,
whilst those particles which are not so burned shew you the second
substance in the carbonic acid—namely, the carbon—that body which made
the flame so bright whilst there was plenty of air, but which was thrown
off in excess when there was not oxygen enough to burn it.
I have also to shew you a little more distinctly the history of carbon and
oxygen, in their union to make carbonic acid. You are now better able to
understand this than before, and I have prepared three or four experiments
by way of illustration. This jar is filled with oxygen, and here is some
carbon which has been placed in a crucible, for the purpose of being made
red-hot. I keep my jar dry, and venture to give you a result imperfect in
some degree, in order that I may make the experiment brighter. I am about
to put the oxygen and the carbon together. That this is carbon (common
charcoal pulverised), you will see by the way in which it burns in the air
[letting some of the red-hot charcoal fall out of the crucible]. I am now
about to burn it in oxygen gas, and look at the difference. It may appear
to you at a distance as if it were burning with a flame; but it is not so.
Every little piece of charcoal is burning as a spark, and whilst it so
burns it is producing carbonic acid. I specially want these two or three
experiments to point out what I shall dwell upon more distinctly
by-and-by—that carbon burns in this way, and not as a flame.
Instead of taking many particles of carbon to burn, I will take a rather
large piece, which will enable you to see the form and size; and to trace
the effects very decidedly. Here is the jar of oxygen, and here is the
piece of charcoal, to which I have fastened a little piece of wood, which
I can set fire to, and so commence the combustion, which I could not
conveniently do without. You now see the charcoal burning, but not as a
flame (or if there be a flame, it is the smallest possible one, which I
know the cause of—namely, the formation of a little carbonic oxide close
upon the surface of the carbon). It goes on burning, you see, slowly
producing carbonic acid by the union of this carbon or charcoal (they are
equivalent terms) with the oxygen. I have here another piece of charcoal,
a piece of bark, which has the quality of being blown to pieces—exploding
as it burns. By the effect of the heat, we shall reduce the lump of carbon
into particles that will fly off; still every particle, equally with the
whole mass, burns in this peculiar way: it burns as a coal, and not like a
flame. You observe a multitude of little combustions going on, but no
flame. I do not know a finer experiment than this, to shew that carbon
burns with a spark.
Here, then, is carbonic acid formed from its elements. It is produced at
once; and if we examined it by lime-water, you will see that we have the
same substance which I have previously described to you. By putting
together 6 parts of carbon by weight (whether it comes from the flame of a
candle or from powdered charcoal) and 16 parts of oxygen by weight, we
have 22 parts of carbonic acid; and, as we saw last time, the 22 parts of
carbonic acid, combined with 28 parts of lime, produced common carbonate
of lime. If you were to examine an oyster-shell, and weigh the component
parts, you would find that every 50 parts would give 6 of carbon and 16 of
oxygen, combined with 28 of lime. However, I do not want to trouble you
with these minutiæ—it is only the general philosophy of the matter that
we can now go into. See how finely the carbon is dissolving away [pointing
to the lump of charcoal burning quietly in the jar of oxygen]. You may say
that the charcoal is actually dissolving in the air round about; and if
that were perfectly pure charcoal, which we can easily prepare, there
would be no residue whatever. When we have a perfectly cleansed and
purified piece of carbon, there is no ash left. The carbon burns as a
solid dense body, that heat alone cannot change as to its solidity, and
yet it passes away into vapour that never condenses into solid or liquid
under ordinary circumstances; and what is more curious still, is the fact
that the oxygen does not change in its bulk by the solution of the carbon
in it. Just as the bulk is at first, so it is at last, only it has become
carbonic acid.
There is another experiment which I must give you before you are fully
acquainted with the general nature of carbonic acid. Being a compound
body, consisting of carbon and oxygen, carbonic acid is a body that we
ought to be able to take asunder. And so we can. As we did with water, so
we can with carbonic acid—take the two parts asunder. The simplest and
quickest way is to act upon the carbonic acid by a substance that can
attract the oxygen from it, and leave the carbon behind. You recollect
that I took potassium and put it upon water or ice, and you saw that it
could take the oxygen from the hydrogen. Now, suppose we do something of
the same kind here with this carbonic acid. You know carbonic acid to be a
heavy gas. I will not test it with lime-water, as that will interfere with
our subsequent experiments; but I think the heaviness of the gas and the
power of extinguishing flame will be sufficient for our purpose. I
introduce a flame into the gas, and you will see whether it will be put
out. You see the light is extinguished. Indeed, the gas may, perhaps, put
out phosphorus, which, you know, has a pretty strong combustion. Here is a
piece of phosphorus heated to a high degree. I introduce it into gas, and
you observe the light is put out; but it will take fire again in the air,
because there it re-enters into combustion. Now, let me take a piece of
potassium, a substance which, even at common temperatures, can act upon
carbonic acid, though not sufficiently for our present purpose, because it
soon gets covered with a protecting coat; but if we warm it up to the
burning point in air, as we have a fair right to do, and as we have done
with phosphorus, you will see that it can burn in carbonic acid; and if it
burns, it will burn by taking oxygen, so that you will see what is left
behind. I am going, then, to burn this potassium in the carbonic acid, as
a proof of the existence of oxygen in the carbonic acid. [In the
preliminary process of heating, the potassium exploded.] Sometimes we get
an awkward piece of potassium that explodes, or something like it, when it
burns. I will take another piece; and now that it is heated, I introduce
it into the jar, and you perceive that it burns in the carbonic acid—not
so well as in the air, because the carbonic acid contains the oxygen
combined; but it does burn, and takes away the oxygen. If I now put this
potassium into water, I find that, besides the potash formed (which you
need not trouble about), there is a quantity of carbon produced. I have
here made the experiment in a very rough way; but I assure you that if I
were to make it carefully, devoting a day to it, instead of five minutes,
we should get all the proper amount of charcoal left in the spoon, or in
the place where the potassium was burned, so that there could be no doubt
as to the result. Here, then, is the carbon obtained from the carbonic
acid, as a common black substance; so that you have the entire proof of
the nature of carbonic acid as consisting of carbon and oxygen. And now, I
may tell you, that _whenever_ carbon burns under common circumstances, it
produces carbonic acid.
Suppose I take this piece of wood, and put it into a bottle with
lime-water. I might shake that lime-water up with wood and the atmosphere
as long as I pleased, it would still remain clear as you see it; but
suppose I burn the piece of wood in the air of that bottle. You, of
course, know I get water. Do I get carbonic acid? [The experiment was
performed.] There it is, you see—that is to say, the carbonate lime,
which results from carbonic acid, and that carbonic acid must be formed
from the carbon which comes from the wood, from the candle, or any other
thing. Indeed, you have yourselves frequently tried a very pretty
experiment, by which you may see the carbon in wood. If you take a piece
of wood, and partly burn it, and then blow it out, you have carbon left.
There are things that do not shew carbon in this way. A candle does not
shew it, but it contains carbon. Here also is a jar of coal-gas, which
produces carbonic acid abundantly. You do not see the carbon, but we can
soon shew it to you. I will light it, and as long as there is any gas in
this cylinder it will go on burning. You see no carbon, but you see a
flame; and because that is bright, it will lead you to guess that there is
carbon in the flame. But I will shew it to you by another process. I have
some of the same gas in another vessel, mixed with a body that will burn
the hydrogen of the gas, but will not burn the carbon. I will light them
with a burning taper, and you perceive the hydrogen is consumed, but not
the carbon, which is left behind as a dense black smoke. I hope that by
these three or four experiments you will learn to see when carbon is
present, and understand what are the products of combustion, when gas or
other bodies are thoroughly burned in the air.
Before we leave the subject of carbon, let us make a few experiments and
remarks upon its wonderful condition as respects ordinary combustion. I
have shewn you that the carbon in burning burns only as a solid body, and
yet you perceive that, after it is burned, it ceases to be a solid. There
are very few fuels that act like this. It is, in fact, only that great
source of fuel, the carbonaceous series, the coals, charcoals, and woods,
that can do it. I do not know that there is any other elementary substance
besides carbon that burns with these conditions; and if it had not been
so, what would happen to us? Suppose all fuel had been like iron, which,
when it burns, burns into a solid substance. We could not then have such a
combustion as you have in this fireplace. Here also is another kind of
fuel which burns very well—as well as, if not better, than carbon—so
well, indeed, as to take fire of itself when it is in the air, as you see
[breaking a tube full of lead pyrophorus]. This substance is lead, and you
see how wonderfully combustible it is. It is very much divided, and is
like a heap of coals in the fireplace; the air can get to its surface and
inside, and so it burns. But why does it not burn in that way now, when it
is lying in a mass? [emptying the contents of the tube in a heap on to a
plate of iron]. Simply because the air cannot get to it. Though it can
produce a great heat, the great heat which we want in our furnaces and
under our boilers, still that which is produced cannot get away from the
portion which remains unburned underneath, and that portion, therefore, is
prevented from coming in contact with the atmosphere, and cannot be
consumed. How different is that from carbon. Carbon burns just in the same
way as this lead does, and so gives an intense fire in the furnace, or
wherever you choose to burn it; but then the body produced by its
combustion passes away, and the remaining carbon is left clear. I shewed
you how carbon went on dissolving in the oxygen, leaving no ash; whereas
here [pointing to the heap of pyrophorus] we have actually more ash than
fuel, for it is heavier by the amount of the oxygen which has united with
it. Thus you see the difference between carbon and lead or iron: if we
choose iron, which gives so wonderful a result in our application of this
fuel, either as light or heat. If, when the carbon burnt, the product went
off as a solid body, you would have had the room filled with an opaque
substance, as in the case of the phosphorus; but when carbon burns,
everything passes up into the atmosphere. It is in a fixed, almost
unchangeable condition before the combustion; but afterwards it is in the
form of gas, which it is very difficult (though we have succeeded) to
produce in a solid or a liquid state.
Now, I must take you to a very interesting part of our subject—to the
relation between the combustion of a candle and that living kind of
combustion which goes on within us. In every one of us there is a living
process of combustion going on very similar to that of a candle; and I
must try to make that plain to you. For it is not merely true in a
poetical sense—the relation of the life of man to a taper; and if you
will follow, I think I can make this clear. In order to make the relation
very plain, I have devised a little apparatus which we can soon build up
before you. Here is a board and a groove cut in it, and I can close the
groove at the top part by a little cover. I can then continue the groove
as a channel by a glass tube at each end, there being a free passage
through the whole. Suppose I take a taper or candle (we can now be liberal
in our use of the word “candle,” since we understand what it means), and
place it in one of the tubes; it will go on, you see, burning very well.
You observe that the air which feeds the flame passes down the tube at one
end, then goes along the horizontal tube, and ascends the tube at the
other end in which the taper is placed.
[Illustration: Fig. 32]
If I stop the aperture through which the air enters, I stop combustion, as
you perceive. I stop the supply of air, and consequently the candle goes
out. But, now, what will you think of this fact? In a former experiment I
shewed you the air going from one burning candle to a second candle. If I
took the air proceeding from another candle, and sent it down by a
complicated arrangement into this tube, I should put this burning candle
out. But what will you say when I tell you that my breath will put out
that candle? I do not mean by blowing at all, but simply that the nature
of my breath is such that a candle cannot burn in it. I will now hold my
mouth over the aperture, and without blowing the flame in any way, let no
air enter the tube but what comes from my mouth. You see the result. I did
not blow the candle out. I merely let the air which I expired pass into
the aperture, and the result was that the light went out for want of
oxygen, and for no other reason. Something or other—namely, my lungs—had
taken away the oxygen from the air, and there was no more to supply the
combustion of the candle. It is, I think, very pretty to see the time it
takes before the bad air which I throw into this part of the apparatus has
reached the candle. The candle at first goes on burning, but so soon as
the air has had time to reach it, it goes out. And, now, I will shew you
another experiment, because this is an important part of our philosophy.
Here is a jar which contains fresh air, as you can see by the circumstance
of a candle or gas-light burning it. I make it close for a little time,
and by means of a pipe I get my mouth over it so that I can inhale the
air. By putting it over water, in the way that you see, I am able to draw
up this air (supposing the cork to be quite tight), take it into my lungs,
and throw it back into the jar.
[Illustration: Fig. 33.]
We can then examine it, and see the result. You observe, I first take up
the air, and then throw it back, as is evident from the ascent and descent
of the water; and now, by putting a taper into the air, you will see the
state in which it is, by the light being extinguished. Even one
inspiration, you see, has completely spoiled this air, so that it is no
use my trying to breathe it a second time. Now, you understand the ground
of the impropriety of many of the arrangements among the houses of the
poorer classes, by which the air is breathed over and over again, for the
want of a supply, by means of proper ventilation, sufficient to produce a
good result. You see how bad the air becomes by a single breathing; so
that you can easily understand how essential fresh air is to us.
To pursue this a little further, let us see what will happen with
lime-water. Here is a globe which contains a little lime-water, and it is
so arranged as regards the pipes, as to give access to the air within, so
that we can ascertain the effect of respired or unrespired air upon it. Of
course, I can either draw in air (through A), and so make the air that
feeds my lungs go through the lime-water, or I can force the air out of my
lungs through the tube (B), which goes to the bottom, and so shew its
effect upon the lime-water.
[Illustration: Fig. 34.]
You will observe that, however long I draw the external air into the
lime-water, and then through it to my lungs, I shall produce no effect
upon the water—it will not make the lime-water turbid; but if I throw the
air _from_ my lungs through the lime-water, several times in succession,
you see how white and milky the water is getting, shewing the effect which
expired air has had upon it; and now you begin to know that the atmosphere
which we have spoiled by respiration is spoiled by carbonic acid, for you
see it here in contact with the lime-water.
I have here two bottles, one containing lime-water and the other common
water, and tubes which pass into the bottles and connect them. The
apparatus is very rough, but it is useful notwithstanding.
[Illustration: Fig. 35.]
If I take these two bottles, inhaling here and exhaling there, the
arrangement of the tubes will prevent the air going backwards. The air
coming in will go to my mouth and lungs, and in going out, will pass
through the lime-water, so that I can go on breathing and making an
experiment, very refined in its nature, and very good in its results. You
will observe that the good air has done nothing to the lime-water; in the
other case nothing has come to the lime-water but my respiration, and you
see the difference in the two cases.
Let us now go a little further. What is all this process going on within
us which we cannot do without, either day or night, which is so provided
for by the Author of all things that He has arranged that it shall be
independent of all will? If we restrain our respiration, as we can to a
certain extent, we should destroy ourselves. When we are asleep, the
organs of respiration, and the parts that are associated with them, still
go on with their action—so necessary is this process of respiration to
us, this contact of the air with the lungs. I must tell you, in the
briefest possible manner, what this process is. We consume food: the food
goes through that strange set of vessels and organs within us, and is
brought into various parts of the system, into the digestive parts
especially; and alternately the portion which is so changed is carried
through our lungs by one set of vessels, while the air that we inhale and
exhale is drawn into and thrown out of the lungs by another set of
vessels, so that the air and the food come close together, separated only
by an exceedingly thin surface: the air can thus act upon the blood by
this process, producing precisely the same results in kind as we have seen
in the case of the candle. The candle combines with parts of the air,
forming carbonic acid, and evolves heat; so in the lungs there is this
curious, wonderful change taking place. The air entering, combines with
the carbon (not carbon in a free state, but, as in this case, placed ready
for action at the moment), and makes carbonic acid, and is so thrown out
into the atmosphere, and thus this singular result takes place: we may
thus look upon the food as fuel. Let me take that piece of sugar, which
will serve my purpose. It is a compound of carbon, hydrogen, and oxygen,
similar to a candle, as containing the same elements, though not in the
same proportion—the proportions being as shewn in this table:—
SUGAR.
Carbon, . . . . 72
_
Hydrogen, . . . 11 |
| 99
Oxygen, . . . . 88_|