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.