We shall have to pay a little more attention to the forces existing
in water before we can have a clear idea on the subject. Besides
the attraction which there is between its particles to make it hold
together as a liquid or a solid, there is also another force, different
from the former--one which, yesterday, by means of the voltaic battery,
we overcame, drawing from the water two different substances--which,
when heated by means of the electric spark, attracted each other, and
rushed into combination to reproduce water. Now, I propose to-day to
continue this subject, and trace the various phenomena of chemical
affinity; and for this purpose, as we yesterday considered the
character of oxygen, of which I have here two jars (oxygen being those
particles derived from the water which enable other bodies to burn),
we will now consider the other constituent of water; and, without
embarrassing you too much with the way in which these things are made,
I will proceed now to shew you our common way of making _hydrogen_.
(I called it hydrogen yesterday--it is so called because it helps to
generate water.)[A] I put into this retort some zinc, water, and oil
of vitriol, and immediately an action takes place, which produces an
abundant evolution of gas, now coming over into this jar, and bubbling
up in appearance exactly like the oxygen we obtained yesterday.
[A] ὕδωρ, “water,” and γενναω, “I generate.”
[Illustration: Fig. 27.]
The processes, you see, are very different, though the result is the
same, in so far as it gives us certain gaseous particles. Here, then,
is the hydrogen. I shewed you yesterday certain qualities of this gas;
now let me exhibit you some other properties. Unlike oxygen, which
is a supporter of combustion, and will not burn, hydrogen itself is
combustible. There is a jar full of it; and if I carry it along in this
manner, and put a light to it, I think you will see it take fire, not
with a bright light--you will at all events hear it, if you do not see
it. Now, that is a body entirely different from oxygen: it is extremely
light; for although yesterday you saw twice as much of this hydrogen
produced on the one side as on the other, by the voltaic battery,
it was only one-eighth the weight of the oxygen. I carry this jar
upside-down. Why? Because I know that it is a very light body, and that
it will continue in this jar upside-down quite as effectually as the
water will in that jar which is not upside-down; and just as I can pour
water from one vessel into another in the right position to receive
it, so can I pour this gas from one jar into another when they are
upside-down. See what I am about to do. There is no hydrogen in this
jar at present, but I will gently turn this jar of hydrogen up under
this other jar (fig. 28), and then we will examine the two. We shall
see, on applying a light, that the hydrogen has left the jar in which
it was at first, and has poured upwards into the other, and there we
shall find it.
[Illustration: Fig. 28.]
You now understand that we can have particles of very different kinds,
and that they can have different bulks and weights; and there are two
or three very interesting experiments which serve to illustrate this.
For instance, if I blow soap bubbles with the breath from my mouth,
you will see them fall, because I fill them with common air, and the
water which forms the bubble carries it down. But now, if I inhale
hydrogen gas into my lungs (it does no harm to the lungs, although it
does no good to them), see what happens. [The Lecturer inhaled some
hydrogen, and after one or two ineffectual attempts, succeeded in
blowing a splendid bubble, which rose majestically and slowly to the
ceiling of the theatre, where it burst.] That shews you very well how
light a substance this is; for, notwithstanding all the heavy bad air
from my lungs, and the weight of the bubble, you saw how it was carried
up. I want you now to consider this phenomenon of weight as indicating
how exceedingly different particles are one from the other; and I
will take as illustrations these very common things--air, water, the
heaviest body, platinum, and this gas: and observe how they differ in
this respect; for if I take a piece of platinum of that size (fig. 29),
it is equal to the weight of portions of water, air, and hydrogen of
the bulks I have represented in these spheres. And this illustration
gives you a very good idea of the extraordinary difference with regard
to the gravity of the articles having this enormous difference in bulk.
[The following tabular statement having reference to this illustration
appeared on the diagram board.]
+------------+----------+-------+------+
| Hydrogen, | 1 | | |
+------------+----------+-------+------+
| Air, | 14.4 | 1 | |
+------------+----------+-------+------+
| Water, | 11943 | 829 | 1 |
+------------+----------+-------+------+
| Platinum, | 256774 | 17831 | 21.5 |
+------------+----------+-------+------+
Whenever oxygen and hydrogen unite together they produce water; and you
have seen the extraordinary difference between the bulk and appearance
of the water so produced, and the particles of which it consists
chemically. Now, we have never yet been able to reduce either oxygen
or hydrogen to the liquid state; and yet their first impulse, when
chemically combined, is to take up first this liquid condition, and
then the solid condition. We never combine these different particles
together without producing water; and it is curious to think how often
you must have made the experiment of combining oxygen and hydrogen to
form water without knowing it. Take a candle, for instance, and a clean
silver spoon (or a piece of clean tin will do), and if you hold it
over the flame, you immediately cover it with dew--not a smoke--which
presently evaporates. This perhaps will serve to shew it better. Mr.
Anderson will put a candle under that jar, and you will see how soon
the water is produced (fig. 30). Look at that dimness on the sides of
the glass, which will soon produce drops, and trickle down into the
plate. Well, that dimness and these drops are _water_, formed by the
union of the oxygen of the air with the hydrogen existing in the wax of
which that candle is formed.
[Illustration: Fig. 30.]
And now, having brought you in the first place to the consideration
of chemical attraction, I must enlarge your ideas so as to include
all substances which have this attraction for each other--for it
changes the character of bodies, and alters them in this way and that
way in the most extraordinary manner, and produces other phenomena
wonderful to think about. Here is some chlorate of potash, and there
some sulphuret of antimony.[17] We will mix these two different sets
of particles together; and I want to shew you in a general sort of way
some of the phenomena which take place when we make different particles
act together. Now, I can make these bodies act upon each other in
several ways. In this case I am going to apply heat to the mixture; but
if I were to give a blow with a hammer, the same result would follow.
[A lighted match was brought to the mixture, which immediately exploded
with a sudden flash, evolving a dense white smoke.] There you see the
result of the action of chemical affinity overcoming the attraction of
cohesion of the particles. Again, here is a little sugar[18], quite a
different substance from the black sulphuret of antimony, and you shall
see what takes place when we put the two together. [The mixture was
touched with sulphuric acid, when it took fire and burnt gradually,
and with a brighter flame than in the former instance.] Observe this
chemical affinity travelling about the mass, and setting it on fire,
and throwing it into such wonderful agitation!
I must now come to a few circumstances which require careful
consideration. We have already examined one of the effects of this
chemical affinity; but to make the matter more clear we must point
out some others. And here are two salts dissolved in water[19]. They
are both colourless solutions, and in these glasses you cannot see
any difference between them. But if I mix them, I shall have chemical
attraction take place. I will pour the two together into this glass,
and you will at once see, I have no doubt, a certain amount of change.
Look, they are already becoming milky, but they are sluggish in their
action--not quick as the others were--for we have endless varieties
of rapidity in chemical action. Now, if I mix them together, and stir
them, so as to bring them properly together, you will soon see what
a different result is produced. As I mix them, they get thicker and
thicker, and you see the liquid is hardening and stiffening, and before
long I shall have it quite hard; and before the end of the lecture
it will be a solid stone--a wet stone, no doubt, but more or less
solid--in consequence of the chemical affinity. Is not this changing
two liquids into a solid body a wonderful manifestation of chemical
affinity?
There is another remarkable circumstance in chemical affinity, which
is, that it is capable of either waiting or acting at once. And this
is very singular, because we know of nothing of the kind in the forces
either of gravitation or cohesion. For instance, here are some oxygen
particles, and here is a lump of carbon particles. I am going to put
the carbon particles into the oxygen; they _can_ act, but they _do_
not--they are just like this unlighted candle. It stands here quietly
on the table, waiting until we want to light it. But it is not so in
this other case. Here is a substance, gaseous like the oxygen, and if
I put these particles of metal into it, the two combine at once. The
copper and the chlorine unite by their power of chemical affinity, and
produce a body entirely unlike either of the substances used. And in
this other case, it is not that there is any deficiency of affinity
between the carbon and oxygen; for the moment I choose to put them in
a condition to exert their affinity, you will see the difference. [The
piece of charcoal was ignited, and introduced into the jar of oxygen,
when the combustion proceeded with vivid scintillations.]
Now, this chemical action is set going exactly as it would be if I
had lighted the candle, or as it is when the servant puts coals on
and lights the fire: the substances wait until we do something which
is able to start the action. Can anything be more beautiful than this
combustion of charcoal in oxygen? You must understand that each of
these little sparks is a portion of the charcoal, or the bark of the
charcoal, thrown off white-hot into the oxygen, and burning in it most
brilliantly, as you see. And now let me tell you another thing, or you
will go away with a very imperfect notion of the powers and effects of
this affinity. There you see some charcoal burning in oxygen. Well, a
piece of lead will burn in oxygen just as well as the charcoal does,
or indeed better; for absolutely that piece of lead will act at once
upon the oxygen as the copper did in the other vessel with regard to
the chlorine. And here also a piece of iron: if I light it and put
it into the oxygen, it will burn away just as the carbon did. And I
will take some lead, and shew you that it will burn in the common
atmospheric oxygen at the ordinary temperature. These are the lumps of
lead which, you remember, we had the other day--the two pieces which
clung together. Now these pieces, if I take them to-day and press them
together, will not stick; and the reason is, that they have attracted
from the atmosphere a part of the oxygen there present, and have
become coated as with a varnish by the oxide of lead, which is formed
on the surface by a real process of combustion or combination. There
you see the iron burning very well in oxygen; and I will tell you the
reason why those scissors and that lead do not take fire whilst they
are lying on the table. Here the lead is in a lump, and the coating of
oxide remains on its surface; whilst there you see the melted oxide
is clearing itself off from the iron, and allowing more and more to
go on burning. In this case, however [holding up a small glass tube
containing lead pyrophorus.[20]], the lead has been very carefully
produced in fine powder, and put into a glass tube, and hermetically
sealed, so as to preserve it; and I expect you will see it take fire
at once. This has been made about a month ago, and has thus had time
enough to sink down to its normal temperature. What you see, therefore,
is the result of chemical affinity alone. [The tube was broken at
the end, and the lead poured out on to a piece of paper, whereupon it
immediately took fire.] Look, look at the lead burning; why, it has set
fire to the paper! Now, that is nothing more than the common affinity
always existing between very clean lead and the atmospheric oxygen; and
the reason why this iron does not burn until it is made red-hot is,
because it has got a coating of oxide about it, which stops the action
of the oxygen--putting a varnish, as it were, upon its surface, as we
varnish a picture, absolutely forming a substance which prevents the
natural chemical affinity between the bodies from acting.
I must now take you a little further in this kind of illustration--or
consideration, I would rather call it--of chemical affinity. This
attraction between different particles exists also most curiously in
cases where they are previously combined with other substances. Here
is a little chlorate of potash, containing the oxygen which we found
yesterday could be procured from it. It contains the oxygen there
combined and held down by its chemical affinity with other things; but
still it can combine with sugar, as you saw. This affinity can thus
act _across_ substances; and I want you to see how curiously what we
call combustion acts with respect to this force of chemical affinity.
If I take a piece of phosphorus and set fire to it, and then place a
jar of air over the phosphorus, you see the combustion which we are
having there on account of chemical affinity (combustion being in all
cases the result of chemical affinity). The phosphorus is escaping in
that vapour, which will condense into a snow-like mass at the close of
the lecture. But suppose I limit the atmosphere, what then? why, even
the phosphorus will go out. Here is a piece of camphor, which will burn
very well in the atmosphere, and even on water it will float about and
burn, by reason of some of its particles gaining access to the air. But
if I limit the quantity of air by placing a jar over it, as I am now
doing, you will soon find the camphor will go out. Well, why does it go
out? Not for want of air, for there is plenty of air remaining in the
jar. Perhaps you will be shrewd enough to say, for want of oxygen.
This, therefore, leads us to the inquiry as to whether oxygen can do
more than a certain amount of work. The oxygen there (fig. 30) cannot
go on burning an unlimited quantity of candle, for that has gone
out, as you see; and its amount of chemical attraction or affinity
is just as strikingly limited: it can no more be fallen short of or
exceeded than can the attraction of gravitation. You might as soon
attempt to destroy gravitation, or weight, or all things that exist,
as to destroy the exact amount of force exerted by this oxygen. And
when I pointed out to you that 8 by weight of oxygen to 1 by weight
of hydrogen went to form water, I meant this, that neither of them
would combine in different proportions with the other; for you cannot
get 10 of hydrogen to combine with 6 of oxygen, or 10 of oxygen to
combine with 6 of hydrogen--it must be 8 of oxygen and 1 of hydrogen.
Now, suppose I limit the action in this way: this piece of cotton wool
burns, as you see, very well in the atmosphere; and I have known of
cases of cotton-mills being fired as if with gunpowder, through the
very finely-divided particles of cotton being diffused through the
atmosphere in the mill, when it has sometimes happened that a flame
has caught these raised particles, and it has run from one end of the
mill to the other, and blown it up. That, then, is on account of the
affinity which the cotton has for the oxygen; but suppose I set fire
to this piece of cotton, which is rolled up tightly, it does not go on
burning, because I have limited the supply of oxygen, and the inside
is prevented from having access to the oxygen, just as it was in the
case of the lead by the oxide. But here is some cotton which has been
imbued with oxygen in a certain manner. I need not trouble you now with
the way it is prepared; it is called gun-cotton.[21] See how that burns
[setting fire to a piece]; it is very different from the other, because
the oxygen that must be present in its proper amount is put there
beforehand. And I have here some pieces of paper which are prepared
like the gun-cotton[22], and imbued with bodies containing oxygen. Here
is some which has been soaked in nitrate of strontia--you will see the
beautiful red colour of its flame; and here is another which I think
contains baryta, which gives that fine green light; and I have here
some more which has been soaked in nitrate of copper--it does not burn
quite so brightly, but still very beautifully. In all these cases the
combustion goes on independent of the oxygen of the atmosphere. And
here we have some gunpowder put into a case, in order to shew that it
is capable of burning under water. You know that we put it into a gun,
shutting off the atmosphere, with shot, and yet the oxygen which it
contains supplies the particles with that without which chemical action
could not proceed. Now, I have a vessel of water here, and am going to
make the experiment of putting this fuse under the water, and you will
see whether that water can extinguish it. Here it is burning out of the
water, and there it is burning under the water; and so it will continue
until exhausted, and all by reason of the requisite amount of oxygen
being contained within the substance. It is by this kind of attraction
of the different particles one to the other that we are enabled to
trace the laws of chemical affinity, and the wonderful variety of the
exertions of these laws.
Now, I want you to observe that one great exertion of this power,
which is known as _chemical affinity_, is to produce HEAT and light.
You know, as a matter of fact, no doubt, that when bodies burn they
give out heat; but it is a curious thing that this heat does not
continue--the heat goes away as soon as the action stops, and you see
thereby that it depends upon the action _during the time_ it is going
on. It is not so with gravitation: this force is continuous, and is
just as effective in making that lead press on the table as it was
when it first fell there. Nothing occurs there which disappears when
the action of falling is over; the pressure is upon the table, and
will remain there until the lead is removed; whereas, in the action
of chemical affinity to give light and heat, they go away immediately
the action is over. This lamp _seems_ to evolve heat and light
continuously; but it is owing to a constant stream of air coming into
it on all sides, and this work of producing light and heat by chemical
affinity will subside as soon as the stream of air is interrupted.
What, then, is this curious condition of heat? Why is the evolution
of another power of matter, of a power new to us, and which we must
consider as if it were now for the very first time brought under our
notice? What is heat? We recognise heat by its power of liquefying
solid bodies and vaporising liquid bodies, by its power of setting in
action, and very often overcoming, chemical affinity. Then, how do we
obtain heat? We obtain it in various ways--most abundantly by means of
the chemical affinity we have just before been speaking about; but we
can also obtain it in many other ways. Friction will produce heat. The
Indians rub pieces of wood together until they make them hot enough to
take fire; and such things have been known as two branches of a tree
rubbing together so hard as to set the tree on fire. I do not suppose
I shall set these two pieces of wood on fire by friction; but I can
readily produce heat enough to ignite some phosphorus. [The Lecturer
here rubbed two pieces of cedar-wood strongly against each other
for a minute, and then placed on them a piece of phosphorus, which
immediately took fire.] And if you take a smooth metal button stuck on
a cork, and rub it on a piece of soft deal wood, you will make it so
hot as to scorch wood and paper, and burn a match.
[Illustration: Fig. 31.]
I am now going to shew you that we can obtain heat, not by chemical
affinity alone, but by the pressure of air. Suppose I take a pellet of
cotton and moisten it with a little ether, and put it into a glass tube
(fig. 31), and then take a piston and press it down suddenly, I expect
I shall be able to burn a little of that ether in the vessel. It wants
a suddenness of pressure, or we shall not do what we require. [The
piston was forcibly pressed down, when a flame, due to the combustion
of the ether, was visible in the lower part of the syringe.] All we
want is to get a little ether in vapour, and give fresh air each
time, and so we may go on again and again getting heat enough by the
compression of air to fire the ether-vapour.
This, then, I think, will be sufficient, accompanied with all you have
previously seen, to shew you how we procure heat. And now for the
effects of this power. We need not consider many of them on the present
occasion, because when you have seen its power of changing ice into
water and water into steam, you have seen the two principal results
of the application of heat. I want you now to see how it expands all
bodies--all bodies but one, and that under limited circumstances. Mr.
Anderson will hold a lamp under that retort, and you will see the
moment he does so that the air will issue abundantly from the neck,
which is under water, because the heat which he applies to the air
causes it to expand. And here is a brass rod (fig. 32) which goes
through that hole, and fits also accurately into this gauge; but if
I make it warm with this spirit-lamp, it will only go in the gauge
or through the hole with difficulty; and if I were to put it into
boiling-water, it would not go through at all. Again, as soon as the
heat escapes from bodies they collapse. See how the air is contracting
in the vessel, now that Mr. Anderson has taken away his lamp: the stem
of it is filling with water. Notice, too, now, that although I cannot
get the tube through this hole or into the gauge, the moment I cool
it by dipping it into water, it goes through with perfect facility;
so that we have a perfect proof of this power of heat to contract and
expand bodies.
[Illustration: Fig. 32.]