moment they were made to explode. If, for instance, we were to put in
this bottle a mixture of hydrogen gas and atmospheric air; and if, after
corking the bottle, we should kindle the mixture by a very small
orifice, from the sudden dilatation of the gases at the moment of their
combination, the bottle must either fly to pieces, or the cork be blown
out with considerable violence.
CAROLINE.
But in the experiment which we have just seen, if you did not kindle the
hydrogen gas, would it not equally combine with the oxygen?
MRS. B.
Certainly not; for, as I have just explained to you, it is necessary
that the oxygen and hydrogen gases be burnt together, in order to
combine chemically and produce water.
CAROLINE.
That is true; but I thought this was a different combination, for I see
no water produced.
MRS. B.
The water resulting from this detonation was so small in quantity, and
in such a state of minute division, as to be invisible. But water
certainly was produced; for oxygen is incapable of combining with
hydrogen in any other proportions than those that form water; therefore
water must always be the result of their combination.
If, instead of bringing the hydrogen gas into sudden contact with the
atmosphere (as we did just now) so as to make the whole of it explode
the moment it is kindled, we allow but a very small surface of gas to
burn in contact with the atmosphere, the combustion goes on quietly and
gradually at the point of contact, without any detonation, because the
surfaces brought together are too small for the immediate union of
gases. The experiment is a very easy one. This phial, with a narrow
neck, (PLATE VIII. fig. 5.) is full of hydrogen gas, and is carefully
corked. If I take out the cork without moving the phial, and quickly
approach the candle to the orifice, you will see how different the
result will be----
EMILY.
How prettily it burns, with a blue flame! The flame is gradually sinking
within the phial--now it has entirely disappeared. But does not this
combustion likewise produce water?
MRS. B.
Undoubtedly. In order to make the formation of the water sensible to
you, I shall procure a fresh supply of hydrogen gas, by putting into
this bottle (PLATE VIII. fig. 6.) iron filings, water, and sulphuric
acid, materials similar to those which we have just used for the same
purpose. I shall then cork up the bottle, leaving only a small orifice
in the cork, with a piece of glass-tube fixed to it, through which the
gas will issue in a continued rapid stream.
CAROLINE.
I hear already the hissing of the gas through the tube, and I can feel a
strong current against my hand.
MRS. B.
This current I am going to kindle with the candle--see how vividly it
burns----
EMILY.
It burns like a candle with a long flame. But why does this combustion
last so much longer than in the former experiment?
MRS. B.
The combustion goes on uninterruptedly as long as the new gas continues
to be produced. Now if I invert this receiver over the flame, you will
soon perceive its internal surface covered with a very fine dew, which
is pure water----
CAROLINE.
Yes, indeed; the glass is now quite dim with moisture! How glad I am
that we can see the water produced by this combustion.
EMILY.
It is exactly what I was anxious to see; for I confess I was a little
incredulous.
MRS. B.
If I had not held the glass-bell over the flame, the water would have
escaped in the state of vapour, as it did in the former experiment. We
have here, of course, obtained but a very small quantity of water; but
the difficulty of procuring a proper apparatus, with sufficient
quantities of gases, prevents my showing it you on a larger scale.
The composition of water was discovered about the same period, both by
Mr. Cavendish, in this country, and by the celebrated French chemist
Lavoisier. The latter invented a very perfect and ingenious apparatus to
perform, with great accuracy, and upon a large scale, the formation of
water by the combination of oxygen and hydrogen gases. Two tubes,
conveying due proportions, the one of oxygen, the other of hydrogen gas,
are inserted at opposite sides of a large globe of glass, previously
exhausted of air; the two streams of gas are kindled within the globe,
by the electrical spark, at the point where they come in contact; they
burn together, that is to say, the hydrogen combines with the oxygen,
the caloric is set at liberty, and a quantity of water is produced
exactly equal, in weight, to that of the two gases introduced into the
globe.
CAROLINE.
And what was the greatest quantity of water ever formed in this
apparatus?
MRS. B.
Several ounces; indeed, very nearly a pound, if I recollect right; but
the operation lasted many days.
EMILY.
This experiment must have convinced all the world of the truth of the
discovery. Pray, if improper proportions of the gases were mixed and set
fire to, what would be the result?
MRS. B.
Water would equally be formed, but there would be a residue of either
one or other of the gases, because, as I have already told you, hydrogen
and oxygen will combine only in the proportions requisite for the
formation of water.
EMILY.
Look, Mrs. B., our experiment with the Voltaic battery (PLATE VIII. fig.
2.) has made great progress; a quantity of gas has been formed in each
tube, but in one of them there is twice as much gas as in the other.
MRS. B.
Yes; because, as I said before, water is composed of two volumes of
hydrogen to one of oxygen--and if we should now mix these gases together
and set fire to them by an electrical spark, both gases would entirely
disappear, and a small quantity of water would be formed.
There is another curious effect produced by the combustion of hydrogen
gas, which I shall show you, though I must acquaint you first, that I
cannot well explain the cause of it. For this purpose, I must put some
materials into our apparatus, in order to obtain a stream of hydrogen
gas, just as we have done before. The process is already going on, and
the gas is rushing through the tube--I shall now kindle it with the
taper----
EMILY.
It burns exactly as it did before---- What is the curious effect which
you were mentioning?
MRS. B.
Instead of the receiver, by means of which we have just seen the drops
of water form, we shall invert over the flame this piece of tube, which
is about two feet in length, and one inch in diameter (PLATE VIII.
fig. 7.); but you must observe that it is open at both ends.
EMILY.
What a strange noise it makes! something like the Æolian harp, but not
so sweet.
CAROLINE.
It is very singular, indeed; but I think rather too powerful to be
pleasing. And is not this sound accounted for?
MRS. B.
That the percussion of glass, by a rapid stream of gas, should produce a
sound, is not extraordinary: but the sound here is so peculiar, that no
other gas has a similar effect. Perhaps it is owing to a brisk vibratory
motion of the glass, occasioned by the successive formation and
condensation of small drops of water on the sides of the glass tube, and
the air rushing in to replace the vacuum formed.*
[Footnote *: This ingenious explanation was first suggested by
Dr. Delarive. --See Journals of the Royal Institution, vol. i.
p. 259.]
CAROLINE.
How very much this flame resembles the burning of a candle.
MRS. B.
The burning of a candle is produced by much the same means. A great deal
of hydrogen is contained in candles, whether of tallow or wax. This
hydrogen being converted into gas by the heat of the candle, combines
with the oxygen of the atmosphere, and flame and water result from this
combination. So that, in fact, the flame of a candle is owing to the
combustion of hydrogen gas. An elevation of temperature, such as is
produced by a lighted match or taper, is required to give the first
impulse to the combustion; but afterwards it goes on of itself, because
the candle finds a supply of caloric in the successive quantities of
heat which results from the union of the two electricities given out by
the gases during their combustion. But there are other circumstances
connected with the combustion of candles and lamps, which I cannot
explain to you till you are acquainted with _carbon_, which is one of
their constituent parts. In general, however, whenever you see flame,
you may infer that it is owing to the formation and burning of hydrogen
gas*; for flame is the peculiar mode of burning hydrogen gas, which,
with only one or two apparent exceptions, does not belong to any other
combustible.
[Footnote *: Or rather, _hydro-carbonat_, a gas composed of
hydrogen and carbon, which will be noticed under the head
_Carbon_.]
EMILY.
You astonish me! I understood that flame was the caloric produced by the
union of the two electricities, in all combustions whatever?
MRS. B.
Your error proceeded from your vague and incorrect idea of flame; you
have confounded it with light and caloric in general. Flame always
implies caloric, since it is produced by the combustion of hydrogen gas;
but all caloric does not imply flame. Many bodies burn with intense heat
without producing flame. Coals, for instance, burn with flame until all
the hydrogen which they contain is evaporated; but when they afterwards
become red hot, much more caloric is disengaged than when they produce
flame.
CAROLINE.
But the iron wire, which you burnt in oxygen gas, appeared to me to emit
flame; yet, as it was a simple metal, it could contain no hydrogen?
MRS. B.
It produced a sparkling dazzling blaze of light, but no real flame.
EMILY.
And what is the cause of the regular shape of the flame of a candle?
MRS. B.
The regular stream of hydrogen gas which exhales from its combustible
matter.
CAROLINE.
But the hydrogen gas must, from its great levity, ascend into the upper
regions of the atmosphere; why therefore does not the flame continue to
accompany it?
MRS. B.
The combustion of the hydrogen gas is completed at the point where the
flame terminates; it then ceases to be hydrogen gas, as it is converted
by its combination with oxygen into watery vapour; but in a state of
such minute division as to be invisible.
CAROLINE.
I do not understand what is the use of the wick of a candle, since the
hydrogen gas burns so well without it?
MRS. B.
The combustible matter of the candle must be decomposed in order to
emit the hydrogen gas, and the wick is instrumental in effecting this
decomposition. Its combustion first melts the combustible matter,
and . . . .
CAROLINE.
But in lamps the combustible matter is already fluid, and yet they also
require wicks?
MRS. B.
I am going to add that, afterwards, the burning wick (by the power of
capillary attraction) gradually draws up the fluid to the point where
combustion takes place; for you must have observed that the wick does
not burn quite to the bottom.
CAROLINE.
Yes; but I do not understand why it does not.
MRS. B.
Because the air has not so free an access to that part of the wick which
is immediately in contact with the candle, as to the part just above, so
that the heat there is not sufficient to produce its decomposition; the
combustion therefore begins a little above this point.
CAROLINE.
But, Mrs. B., in those beautiful lights, called _gas-lights_, which are
now seen in many streets, and will, I hope, be soon adopted every where,
I can perceive no wick at all. How are these lights managed?
MRS. B.
I am glad you have put me in mind of saying a few words on this very
useful and interesting improvement. In this mode of lighting, the gas is
conveyed to the extremity of a tube, where it is kindled, and burns as
long as the supply continues. There is, therefore, no occasion for a
wick, or any other fuel whatever.
EMILY.
But how is all this gas procured in such large quantities?
MRS. B.
It is obtained from coal, by distillation. --Coal, when exposed to heat
in a close vessel, is decomposed; and hydrogen, which is one of its
constituents, rises in the state of gas, combined with another of its
component parts, carbon, forming a compound gas, called _Hydrocarbonat_,
the nature of which we shall again have an opportunity of noticing when
we treat of carbon. This gas, like hydrogen, is perfectly transparent,
invisible, and highly inflammable; and in burning it emits that vivid
light which you have so often observed.
CAROLINE.
And does the process for procuring it require nothing but heating the
coals, and conveying the gas through tubes?
MRS. B.
Nothing else; except that the gas must be made to pass, immediately at
its formation, through two or three large vessels of water, in which it
deposits some other ingredients, and especially water, tar, and oil,
which also arise from the distillation of coals. The gas-light
apparatus, therefore, consists simply in a large iron vessel, in which
the coals are exposed to the heat of a furnace,--some reservoirs of
water, in which the gas deposits its impurities,--and tubes that convey
it to the desired spot, being propelled with uniform velocity through
the tubes by means of a certain degree of pressure which is made upon
the reservoir.
EMILY.
What an admirable contrivance! Do you not think, Mrs. B., that it will
soon get into universal use?
MRS. B.
Most probably, as to the lighting of streets, offices, and public
places, as it far surpasses any former invention for that purpose; but
as to the interior of private houses, this mode of lighting has not yet
been sufficiently tried to know whether it will be found generally
desirable, either in regard to economy or convenience. It may, however,
be considered as one of the happiest applications of chemistry to the
comforts of life; and there is every reason to suppose that it will
answer the full extent of public, expectation.
I have another experiment to show you with hydrogen gas, which I think
will entertain you. Have you ever blown bubbles with soap and water?
EMILY.
Yes, often, when I was a child; and I used to make them float in the air
by blowing them upwards.
MRS. B.
We shall fill some such bubbles with hydrogen gas, instead of
atmospheric air, and you will see with what ease and rapidity they will
ascend, without the assistance of blowing, from the lightness of the
gas. --Will you mix some soap and water whilst I fill this bladder with
the gas contained in the receiver which stands on the shelf in the
water-bath?
CAROLINE.
What is the use of the brass-stopper and turn-cock at the top of the
receiver?
MRS. B.
It is to afford a passage to the gas when required. There is, you see,
a similar stop-cock fastened to this bladder, which is made to fit that
on the receiver. I screw them one on the other, and now turn the two
cocks, to open a communication between the receiver and the bladder;
then, by sliding the receiver off the shelf, and gently sinking it into
the bath, the water rises in the receiver and forces the gas into the
bladder. (PLATE IX. fig. 1.)
[Illustration: Plate IX. Vol. I. p. 228
Fig. 1. Apparatus for transferring gases from a Receiver into a
bladder.
Fig. 2. Apparatus for blowing Soap bubbles.]
CAROLINE.
Yes, I see the bladder swell as the water rises in the receiver.
MRS. B.
I think that we have already a sufficient quantity in the bladder for
our purpose; we must be careful to stop both the cocks before we
separate the bladder from the receiver, lest the gas should escape.
--Now I must fix a pipe to the stopper of the bladder, and by dipping
its mouth into the soap and water, take up a few drops--then I again
turn the cock, and squeeze the bladder in order to force the gas into
the soap and water at the mouth of the pipe. (PLATE IX. fig. 2.)
EMILY.
There is a bubble--but it bursts before it leaves the mouth of the pipe.
MRS. B.
We must have patience and try again; it is not so easy to blow bubbles
by means of a bladder, as simply with the breath.
CAROLINE.
Perhaps there is not soap enough in the water; I should have had warm
water, it would have dissolved the soap better.
EMILY.
Does not some of the gas escape between the bladder and the pipe?
MRS. B.
No, they are perfectly air tight; we shall succeed presently, I dare
say.
CAROLINE.
Now a bubble ascends; it moves with the rapidity of a balloon. How
beautifully it refracts the light!
EMILY.
It has burst against the ceiling--you succeed now wonderfully; but why
do they all ascend and burst against the ceiling?
MRS. B.
Hydrogen gas is so much lighter than atmospherical air, that it ascends
rapidly with its very light envelope, which is burst by the force with
which it strikes the ceiling.
Air-balloons are filled with this gas, and if they carried no other
weight than their covering, would ascend as rapidly as these bubbles.
CAROLINE.
Yet their covering must be much heavier than that of these bubbles?
MRS. B.
Not in proportion to the quantity of gas they contain. I do not know
whether you have ever been present at the filling of a large balloon.
The apparatus for that purpose is very simple. It consists of a number
of vessels, either jars or barrels, in which the materials for the
formation of the gas are mixed, each of these being furnished with a
tube, and communicating with a long flexible pipe, which conveys the gas
into the balloon.
EMILY.
But the fire-balloons which were first invented, and have been since
abandoned, on account of their being so dangerous, were constructed,
I suppose, on a different principle.
MRS. B.
They were filled simply with atmospherical air, considerably rarefied by
heat; and the necessity of having a fire underneath the balloon, in
order to preserve the rarefaction of the air within it, was the
circumstance productive of so much danger.
If you are not yet tired of experiments, I have another to show you. It
consists in filling soap-bubbles with a mixture of hydrogen and oxygen
gases, in the proportions that form water; and afterwards setting fire
to them.
EMILY.
They will detonate, I suppose?
MRS. B.
Yes, they will. As you have seen the method of transferring the gas from
the receiver into the bladder, it is not necessary to repeat it. I have
therefore provided a bladder which contains a due proportion of oxygen
and hydrogen gases, and we have only to blow bubbles with it.
CAROLINE.
Here is a fine large bubble rising--shall I set fire to it with the
candle?
MRS. B.
If you please . . . .
CAROLINE.
Heavens, what an explosion! --It was like the report of a gun: I confess
it frightened me much. I never should have imagined it could be so loud.
EMILY.
And the flash was as vivid as lightning.
MRS. B.
The combination of the two gases takes place during that instant of time
that you see the flash, and hear the detonation.
EMILY.
This has a strong resemblance to thunder and lightning.
MRS. B.
These phenomena, however, are generally of an electrical nature. Yet
various meteorological effects may be attributed to accidental
detonations of hydrogen gas in the atmosphere; for nature abounds with
hydrogen: it constitutes a very considerable portion of the whole mass
of water belonging to our globe, and from that source almost every other
body obtains it. It enters into the composition of all animal
substances, and of a great number of minerals; but it is most abundant
in vegetables. From this immense variety of bodies, it is often
spontaneously disengaged; its great levity makes it rise into the
superior regions of the atmosphere; and when, either by an electrical
spark, or any casual elevation of temperature, it takes fire, it may
produce such meteors or luminous appearances as are occasionally seen in
the atmosphere. Of this kind are probably those broad flashes which we
often see on a summer-evening, without hearing any detonation.
EMILY.
Every flash, I suppose, must produce a quantity of water?
CAROLINE.
And this water, naturally, descends in the form of rain?
MRS. B.
That probably is often the case, though it is not a necessary
consequence; for the water may be dissolved by the atmosphere, as it
descends towards the lower regions, and remain there in the form of
clouds.
The application of electrical attraction to chemical phenomena is likely
to lead to many very interesting discoveries in meteorology; for
electricity evidently acts a most important part in the atmosphere. This
subject however, is, as yet, not sufficiently developed for me to
venture enlarging upon it. The phenomena of the atmosphere are far from
being well understood; and even with the little that is known, I am but
imperfectly acquainted.
But before we take leave of hydrogen, I must not omit to mention to you
a most interesting discovery of Sir H. Davy, which is connected with
this subject.
CAROLINE.
You allude, I suppose, to the new miner’s lamp, which has of late been
so much talked of? I have long been desirous of knowing what that
discovery was, and what purpose it was intended to answer.
MRS. B.
It often happens in coal-mines, that quantities of the gas, called by
chemists _hydro-carbonat_, or by the miners _fire-damp_, (the same from
which the gas-lights are obtained,) ooze out from fissures in the beds
of coal, and fill the cavities in which the men are at work; and this
gas being inflammable, the consequence is, that when the men approach
those places with a lighted candle, the gas takes fire, and explosions
happen which destroy the men and horses employed in that part of the
colliery, sometimes in great numbers.
EMILY.
What tremendous accidents these must be! But whence does that gas
originate?
MRS. B.
Being the chief product of the combustion of coal, no wonder that
inflammable gas should occasionally appear in situations in which this
mineral abounds, since there can be no doubt that processes of
combustion are frequently taking place at a great depth under the
surface of the earth; and therefore those accumulations of gas may arise
either from combustions actually going on, or from former combustions,
the gas having perhaps been confined there for ages.
CAROLINE.
And how does Sir H. Davy’s lamp prevent those dreadful explosions?
MRS. B.
By a contrivance equally simple and ingenious; and one which does no
less credit to the philosophical views from which it was deduced, than
to the philanthropic motives from which the enquiry sprung. The
principle of the lamp is shortly this: It was ascertained, two or three
years ago, both by Mr. Tennant and by Sir Humphry himself, that the
combustion of inflammable gas could not be propagated through small
tubes; so that if a jet of an inflammable gaseous mixture, issuing from
a bladder or any other vessel, through a small tube, be set fire to, it
burns at the orifice of the tube, but the flame never penetrates into
the vessel. It is upon this fact that Sir Humphry’s safety-lamp is
founded.
EMILY.
But why does not the flame ever penetrate through the tube into the
vessel from which the gas issues, so as to explode at once the whole of
the gas?
MRS. B.
Because, no doubt, the inflamed gas is so much cooled in its passage
through a small tube as to cease to burn before the combustion reaches
the reservoir.
CAROLINE.
And how can this principle be applied to the construction of a lamp?
MRS. B.
Nothing easier. You need only suppose a lamp enclosed all round in glass
or horn, but having a number of small open tubes at the bottom, and
others at the top, to let the air in and out. Now, if such a lamp or
lanthorn be carried into an atmosphere capable of exploding, an
explosion or combustion of the gas will take place within the lamp; and
although the vent afforded by the tubes will save the lamp from
bursting, yet, from the principle just explained, the combustion will
not be propagated to the external air through the tubes, so that no
farther consequence will ensue.
EMILY.
And is that all the mystery of that valuable lamp?
MRS. B.