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.