|The Wonder Book of Chemistry|
|by Jean Henri Fabre|
|Starting with a mixture of iron filings and sulphur, Uncle Paul awakens in his young nephews an eagerness to learn more about the properties of the elements. Through a series of carefully-devised experiments and conversations about the experiments, he leads the boys to an understanding of some of the basic principles of chemistry. Excellent as a follow-on to 'The Story Book of Science' and 'The Secret of Everyday Things' by the same author. Ages 11-15 |
MIXING AND COMBINING
 No sooner said than done. Uncle Paul went to his neighbor
the locksmith and from among the files on the artisan's
work-bench selected something and wrapped it up in a
piece of paper. Then he visited the apothecary and for
a few cents bought a drug which he also wrapped in a
bit of old newspaper, after which he returned home with
his two packages.
"What is this?" he asked, opening one of the parcels
before the children.
"It is a yellow powder that makes a little crackling
sound when you rub it between your fingers," replied
Emile. "I think it must be sulphur."
"And I," added Jules, "am sure it is sulphur. But we'll
So saying he took a pinch of the yellow powder and
dropped it on some live coals from the kitchen fire,
whereupon it began to burn with the blue flame and the
suffocating odor of a sulphur match.
"That proves it, I hope," cried the lad, much pleased
with himself at having found a quick way to demonstrate
the nature of the substance offered by his uncle. "It
is sulphur and nothing else, for that
 is the only thing that burns with that blue flame and
that smell that makes you cough."
"Yes, my boys," assented their uncle, "it is sulphur
powdered very fine and called flowers of sulphur. And
now what is this?"
He opened the second package and displayed its
contents, consisting of a powdered metal, the fact of
its being a metal showing clearly in its glittering
"That looks very much like iron filings," declared the
younger of the two observers.
"It does more than look like them," asserted the other;
"it really is iron filings. Uncle Paul, you must have
got them from the locksmith's".
"Though I must congratulate Jules on his cleverness and
quickness," rejoined Uncle Paul, "I ought at the same
time to warn him against jumping to conclusions. In the
studies we are about to take up together it is best to
exercise careful scrutiny before venturing on any
assertions, as otherwise one would run the risk of
making frequent mistakes. You say these metallic
particles are iron filings; but lead filings, tin
filings, zinc filings, iron filings—all are of
very much the same appearance, being all light in color
and having a bright luster. You declared the yellow
powder to be sulphur after you had proved it by
dropping a pinch on burning coals. Now find an equally
decisive proof that these filings are of iron."
The boys put on their thinking-caps and looked at each
other in mutual questioning, but no happy
 thought came at their bidding. To what test could they
put those filings to prove that they were indeed of
iron? It was a puzzling problem, that was certain. But
at last Uncle Paul started the boys on the right track.
"How about the magnet," said he, "that horse-shoe
shaped piece of iron bought by Jules at the last fair
and added to his little cabinet of apparatus for making
experiments in physics? Wouldn't it be just the thing
to help you out in your present perplexity? Many a time
I've seen you amusing yourselves with that magnet by
making it draw to itself bits of iron, nails, needles.
Does it have the same effect on lead?"
"No," replied Jules; "I have never been able to make it
take up the least little bit of lead, though it will
lift much heavier weights of iron,—a key, for
"Does it attract tin?"
"No; no more than lead."
"And zinc and copper—does it have any effect on
"No more than on lead or tin. Ah! Now I have it. The
magnets attracts only iron. That's the test we're
after. Now we'll see."
Thereupon Jules ran upstairs, two steps at a time, and
hastened to his cupboard where, on a pine shelf, were
arranged his books and his little pieces of
apparatus,—simple appliances and mostly of his
own make. Eagerly catching up his magnet, he ran
downstairs and brought it almost in contact with the
filings. Immediately there were clusters of them
 clinging to the two ends of the magnet, forming long
beards of bristling appearance.
"See there," cried the lad, "how it makes the filings
come to it! I am sure now they are iron, nothing but
"Yes, my boy, they are iron," assented his uncle; "and
it was the locksmith's work-bench that furnished me
with the filings. Now, with this iron and this sulphur,
which we have just proved to be iron and sulphur beyond
any doubt, we will enter upon our study of chemistry.
Give your attention to what I am about to do."
So saying, he emptied on a large sheet of paper both
the flowers of sulphur and the iron filings, after
which he mixed them thoroughly together by shaking the
paper like a sieve and stirring its contents with his
"Look, now," said he; "what have we on the paper?"
"Oh, that's easy enough," Jules made answer; "it's just
a mixture of sulphur and iron filings."
"Yes, a mixture; and could you still tell me the one
substance from the other, all mixed together as they
"Nothing easier," answered Emile, examining closely
what was on the paper. "Here, for instance, are some
grains of sulphur; I know them by their yellow color;
and here are some of the iron filings, as you can tell
by their shiny look."
"And would you undertake to separate the particles of
one kind from those of the other,—to sort them
 "Why not, if it really had to be done? I have good
eyes, and with the help of a pin I could gather all the
sulphur together on one side and all the iron on the
other. Only, I doubt whether my patience would hold out
to the end."
"Yes, it certainly would be a rather longer job than
picking over a plate of beans; and Emile's patience,
however great it may be, would be hardly equal to the
task. Still, the thing is not impossible. In that
little heap, which has now neither the yellow color of
pure sulphur nor the lustrous gray of pure iron, but
which has at once something of the two colors and is
consequently of a greenish appearance—in that
little heap of matter, I say, an eye of sufficient
patience and a hand of sufficient dexterity could,
between them, see and separate what is sulphur from the
iron. But there are other ways of making the
separation. Who will find one? Come, now, set your wits
"I have it!" cried Jules, passing the ends or poles of
his magnet back and forth through the mixture.
"Just what I was going to propose," said Emile, "if
Jules had given me a moment to think about it. Now that
Uncle has reminded us of the magnet, the rest comes of
"To hit on the way out of a difficulty after a moment's
reflection is all very well, my young friend," rejoined
his uncle; "but to hit on it immediately is still
better. However, you will get even with Jules very
soon, I am sure. Now let us see how his method of
sorting the two substances succeeds."
Jules went on passing his magnet through the
mix-  ture of iron filings and sulphur, with the result that
the metallic particles were attracted to the two poles
of the magnet and clung to them, while the sulphur was
left behind. Again and again the magnet was plunged
into the heap, and each time it was withdrawn loaded at
its two extemities with long and thick beards of
filings which the young operator detached with his
finger-tips, and placed at one side. Not a particle of
the sulphur clung to the magnet, or at least not by the
force of attraction, the magnet exerting no such force
on sulphur; and if any scattering particles were found
among the iron filings set aside by themselves, it was
simply because they had become enmeshed among the
grains of metal. A second, similar sorting very easily
"That's the way to do it!" exclaimed Jules, delighted
with the success of his operations. "That's the way,
see! The magnet comes out each time loaded with
filings, and the sulphur is left behind. If I went on,
it wouldn't take me more than ten minutes to separate
all the iron on the paper from the sulphur."
"It is unnecessary to continue, my dear child," said
Uncle Paul. "Your method is perfect, being both
expeditious and unfailing in its results. Now put the
iron filings back with the sulphur and mix the two well
together. Your magnet, so serviceable to us in this
process of sorting the two substances, is not at the
disposal of every one. Wouldn't it be possible to get
along without it, to make the desired separation in
some other way? It is well, it is even indispensable,
especially for us with our meager
 outfit, to learn how to do without what we do not
possess, and nevertheless to attain results. Let us,
then dispense with our magnet and find some other way
to separate the iron filings and the sulphur. Think a
moment. I will help you. Which is the heavier of the
two substances, the sulphur or the iron?"
"The iron," replied the two young chemists.
"And what would the iron do if we threw it into the
"It would sink to the bottom."
"And the sulphur—what would that do? I mean
finely powdered sulphur, flowers of sulphur, not
sulphur in the lump, for that too would sink in water."
"I see!" Emile made haste to answer, lest he should
again be outstripped in this race of wits by his elder
brother. "I see! I will throw the whole mixture into a
glass of water and the iron will sink to the bottom,
but the sulphur—wait a minute—the
"Hush, Jules!" cautioned his uncle, as the lad showed
signs of breaking in. "Let your brother finish."
"The sulphur," repeated Emile, his cheeks flushed with
animation, "will stay on the surface; or perhaps it
will sink, but not so fast as the iron, which is much
heavier. "Let's try it."
"I was confident, my good Emile" said his uncle,
approvingly, "that you would soon get even with Jules.
Yes, your idea is excellent, and if you hesistate a
little in putting it into words, that is only because
you are in some doubt as to how the sulphur
 will behave. I will put the thing to the test for you."
Uncle Paul thereupon took a large glass and filled it
with water, into which he dropped a handful of the
mixture, stirring the liquid at the same time with a
small wooden stick. Having thus started a brisk
movement in the glass, he paused and awaited results.
Very soon the iron filings, because of their weight,
had settled to the bottom, while the flowers of sulphur
continued to circle about in the liquid. This liquid
was next poured off into another glass, and when it
came to rest the sulphur held in suspension gradually
settled. Thus the two substances were collected, each
by itself, the iron in the first glass, the sulphur in
"You see, my young friends," said Uncle Paul, "it is
accomplished quite as expeditiously as with the magnet,
and the process calls for nothing that any one would
not have at hand. Let us learn, I repeat, to do without
what we lack and still to attain the end in view. It
would be easy, you understand, for us to separate the
two substances in the whole mixture by treating it a
handful at a time in the manner just shown to you; but
that is quite unnecessary for my present purpose. Let
us sum up briefly what we have just learned. Two or
more substances of different kinds form a mixture when
their union does not prevent their being separated by
the simple process of sorting, effected in one way or
another. The heap there before you is a mixture of
sulphur and iron, and these can be separated either
with the help of a magnet or with water, or given
sufficient time and patience, a grain at a time
 by hand. So much for that. Now let us pass on to
So saying, he put the mixture of iron filings and
sulphur into a bowl, added a little water, and kneaded
the mass with his fingers until it formed a thick
paste. Then he took a bottle of clear glass, an old
discarded bottle that had once contained some sort of
syrup or medicine, and filled it with the paste.
Finally, in order to heat the mass somewhat, the bottle
thus filled was set in the sun, and as it was a summer
day the result purposed by Uncle Paul was not long in
being attained, thanks to the temperature.
"Now pay close attention," he admonished his pupils,
"and you will see something curious."
The boys were all eyes, all attention, in their
eagerness to lose nothing of this their first
experiment in chemistry. What was going to happen in
the bottle? They did not have very long to wait. A
quarter of an hour had not passed before something
remarkable took place: the contents of the bottle, at
first greenish in color from the yellow of the sulphur
and the gray of the iron, began gradually to turn black
and present the appearance of soot, while at the same
time jets of vapor accompanied by hissing sounds
escaped from the mouth of the bottle and small
quantities of the black substance were ejected as if by
the force of an explosion.
"Jules," said his uncle, "take the bottle in your hand
a moment and, no matter what happens, don't loose your
 Unsuspectingly the boy approached and grasped the
bottle firmly in his hand.
"Oh, wow!" he cried, with a start of pain and surprise;
"it's hot, hot!" And all his self-control was needed to
prevent his dropping the burning bottle. Replacing it
on the ground more quickly than he had taken it up, he
turned to his uncle, shaking his fingers like one who
has inadvertently touched hot iron. "How it scorches,
Uncle!" he continued. "You can't hold it more than a
second, it's so hot. If the bottle had been over a fire
I should have expected to find it hot; but there is no
fire here to heat it, and yet it gets hot like that,
all by itself! Who would have thought it?"
Emile in his turn had to handle the wonderful bottle
that of its own accord grew so hot as almost to burn
any one touching it. First feeling of it cautiously
with his finger-tips, then grasping it boldly in his
hand, he set it down again not less quickly than Jules
had done, while his looks showed the profound
astonishment, the utter bewilderment, caused by this
generation of heat from no apparent source.
"Water was poured on the mixture of iron filings and
sulphur," said he to himself; it was all wet with
water, which is not exactly the right sort of fuel for
a fire, and then the whole was set in the sunshine,
which isn't what you could call hot, and pretty soon,
for no reason that I can see, the mixture grew
scorching hot. I can't understand it."
Ah, my little lad, Uncle Paul's chemical
experi-  ments will give you many another surprise before they
are finished! He who enters on the study of chemistry
finds himself transported to a new world, where marvel
follows marvel in endless succession. But don't be too
bewildered; keep your eyes open, remember what you see,
and gradually light will dawn on these perplexing
operations which now seem rather to partake of magic
than of veritable science.
"We have now learned," resumed Uncle Paul, "at the cost
of some little pain to you, that the contents of the
bottle become heated, apparently of their own accord,
and that this heat is not slight, but very
considerable, even sufficient to give a burning
sensation. All the rest that happened we must regard as
merely resulting from this development of heat. The
water with which I moistened the mixture was turned to
steam, and hence produced the jets of white vapor that
escaped from the bottle. From this vaporized water came
also the hissing sounds, the little explosions, and the
throwing out of solid matter. If I had at my disposal a
larger quantity of iron filings and sulphur,—if
my mixture, instead of being limited to a handful or
two, had amounted to a full decaliter or more,—I
could have produced some far more remarkable results.
But I will content myself with describing to you a
curious experiment that used to afford no little
entertainment to the onlookers.
"A generous allowance of mingled iron filings and
sulphur was placed at the bottom of a large hole in the
ground, water was sprinkled over the mass, and
 a mound of damp earth was then heaped upon it. Soon
this little mound would begin to behave exactly like a
volcano in eruption: the ground would tremble all about
the base of the mound, the heaped-up mass would crack
open here and there, and through the cracks would spurt
jets of steam accompanied by hissing sounds,
explosions, and even tongues of flame. This was called
an artificial volcano; but I must not omit to add that
real volcanoes are set in action by something quite
different from what was going on in that buried mixture
of iron filings and sulphur, though this is not the
time or the place to explain the difference. However,
there is nothing to prevent your employing some of your
leisure moments in contructing a miniature volcano of
your own with a small quantity of iron filings and an
equal amount of powdered sulphur. Your molehill of
moistened earth, small though it must be, will not lack
interest for you: it will at least break open in cracks
and send out hot steam."
Emile and Jules resolved to gather up all the iron
filings they could at the locksmith's and to buy a few
sous' worth of flowers of sulphur, with which they
would, at the earliest opportunity, perform the
experiment of the artificial volcano. Meanwhile, as
they were discussing this project the agitation inside
the bottle was gradually subsiding and the temperature
rapidly falling, until the bottle became cool enough to
be handled without inconvenience. Uncle Paul took it up
and emptied its contents on a sheet of paper. What came
out was a very black powder resembling soot.
 "Now use your eyes," said he, "and see if you can find
any of the sulphur; try to discover even one little
grain of it if no more."
The boys rummaged through the heap, stirring it with a
pin and scrutinizing it very closely, but could not
point to a single particle of sulphur after all their
"Where can it be now?" queried the searchers. "What has
become of all that sulphur? It must be there somehow,
for we saw it put into the bottle, saw it plainly
enough. It is somewhere in that black heap; nothing
could be more certain. It hasn't been lost during the
experiment, for it didn't come out of the bottle;
nothing much except a little steam came out. It must be
here, and yet we can't find the tiniest grain of it."
"Perhaps," suggested Jules, "we can't see it even if it
is there because it has turned black; but we'll try it
with fire and that will settle the question."
And convinced that he now had the solution of the
mystery, Jules ran into the kitchen and fetched some
live coals, on which he dropped a pinch of the black
powder. But what was his disappointment when, after
waiting a while and then blowing on the coals to make
them burn more brightly, and after trying another pinch
of the powder and then still another, each time from a
different part of the heap, no ignition took place, no
blue sulphurous flame showed itself!
"Well, I declare," exclaimed the bewildered lad, "that
beats me! With all that sulphur somewhere in the
powder, it won't burn."
 "And the iron," said Emile, "I can't see that, either.
There's nothing there but a sort of black soot, nothing
at all that shines like iron. Let's try the magnet and
see if it will separate any of the filings from the
But the magnet produced as little effect as had the
live coals; no more bristling beards, no more strings
of iron filings clinging to the poles of the magnet,
after these had been passed to and fro through the
black powder. Nothing was attracted, nothing showed any
tendency to adhere to the piece of magnetized iron.
"Well, that's strange," declared Emile, still pushing
the magnet into the inert heap, now here, now there.
"There's plenty of iron there, that's certain, and yet
not a particle of it will stick to the magnet. If I
hadn't seen the iron put there I should say there
wasn't any in the whole heap."
"And I," chimed in Jules, "should say there wasn't a
particle of sulphur there, if I hadn't seen it mixed
with the iron. Yet of the two substances that certainly
went into the heap, it now seems to contain not an
atom; not a speck of sulphur, not a speck of iron can
be found in what was made out of sulphur and iron."
Uncle Paul let his two nephews have their say,
convinced that ideas thus born of personal observation
and worth far more than those adopted on the authority
of another. To see is to know. But after the boys had
become thoroughly persuaded of their powerlessness to
find and separate either the sulphur or the iron, then
at last he intervened.
 "Well," said he, "would you now undertake to sort the
two substances, particle by particle?"
"It's no use," was the reply; "we can't find the least
trace of either of them."
"How about using the magnet?"
"That's no good, either; it won't attract anything."
"Well, then, try water."
"I haven't much hope it will help us," answered Jules,
"for the whole heap seems to be all of a kind, nothing
heavy and nothing light. Still it may be worth trying."
A pinch of the black stuff was dropped into water and
stirred into the liquid, but it all sank very soon to
the bottom of the glass, without the slightest tendency
to any separation.
"So, then," resumed Uncle Paul, "sorting is no longer
possible by any of the methods that at first succeeded
so well. And that is not all: the appearance and the
properties of the mass before us have undergone such a
change that, if you did not know beforehand what was
there, you would never suspect the presence of the two
"But who in the world would ever imagine this black
stuff was made of sulphur and iron?" the boys
"The appearance of the mass is changed, as I say,"
their uncle admitted. "The sulphur had a beautiful
yellow color, the iron a lustrous gray, whereas the
substance resulting from their combination is neither
yellow nor gray nor lustrous; it is, on the contrary,
of a deep, dull black. And the
 properties are likewise altered: the sulphur was found
to take fire readily and to burn with a blue flame
accompanied by stifling fumes, but this black substance
refuses to ignite when it is placed on glowing coals;
and the iron filings were attracted by the magnet,
which has no effect on the black powder here. Hence we
must conclude that this powder is neither sulphur nor
iron, but some third substance of a wholly different
nature. Shall we call it a mixture of sulphur and iron?
Certainly not, for it is no longer possible to divide
the mass into those two ingredients by any process of
sorting, the properties of sulphur and of iron having
given place to others showing nothing in common with
the first two. We have, then, to do with an association
far more intimate than that known as
'mixture,'—with one that is known in chemistry as
'combination.' Mixture leaves to the mingling
substances their distinctive qualities intact;
combination causes them to disappear, and substitutes
others in their place. After mixture it is always
possible to separate the ingredients by some simple
process of sorting applicable to the given case; after
combination this is never possible. Hence we may say
that two or more substances are combined when they can
no longer be separated by the process of sorting, in
the customary sense of that word; when, in short, their
characteristic properties have disappeared and given
place to others.
"Observe, also, my young friends, that these new
properties resulting from combination can by no means
be predicted from the nature of the
com-  bining substances. Who would ever imagine, with no
previous study of these curious things, that sulphur,
yellow and readily combustible, could enter into the
formation of a black and incombustible powder? And who
would think that iron, with its metallic luster and its
quick response to the magnet, could be capable of
entering into the composition of a substance having a
dull black color and no tendency whatever to be
attracted by the magnet? Such things are impossible of
prediction without previous knowledge. Combination, as
you will have occasion to note again and again, works a
fundamental change in matter, turning white to black
and black to white, sweet to bitter and bitter to
sweet, harmless substances to deadly poison and deadly
poison to something entirely harmless. Watch well the
result when two or more substances combine.
"Still another point demands serious attention. In the
process of combining, our mixture of iron filings and
sulphur became much heated by spontaneous action; in
fact, it grew so burning hot that it was impossible to
hold the bottle in one's hands. Jules will long
remember the surprise caused him by this unexpected
heat. In this connection I must tell you that this rise
in temperature is nothing exceptional, nothing peculiar
to the combining of iron and sulphur. Every time two or
more substances enter into combination there is heat
generated, sometimes so slight as to be detected only
by the most delicate instruments; sometimes, and more
often, of a degree unbearable to the touch; and
 sometimes, again, of such intensity as to be apparent
to the eye in glowing redness or even blinding
incandescence. In short, whenever combination takes
place there is more or less heat; and, conversely,
whenever heat or light is manifested it is almost
always a sign that combination is going on."
"I should like to ask a question, Uncle Paul," Jules
interposed. "When coal burns in a furnace, is there a
combination going on between different substances?"
"Certainly there is."
"One of the substances, then, must be the coal, mustn't
"Yes, one is the coal."
"And the other?"
"The other is contained in the air. It is invisible,
but none the less it is there. We shall consider it at
length in its proper place."
"And the wood that burns in the fireplace and gives out
heat and light?"
"There too we have a combination that includes the
substance of the wood and that other substance
contained in the air."
"And lamps and candles that we use for light?"
"Combination there also."
"Then every time I set fire to anything I start a
"Precisely; you cause two different substances to
"What a funny thing it is, combination!"
"More than funny, my boy; it is useful beyond
 your power to imagine, and that is why I wish you not
to remain ignorant of the marvelous transformations it
"And will you tell us all about these wonderful
"So far as I am able I will tell you about them, if you
will both pay close attention."
"Oh, there's no danger of our not doing that. We won't
lose a word, and we'll remember it all, too. I like
this kind of lessons [should be lesson?] ever so much
better than long division and conjugation of verbs.
Don't you Emile?"
"I should say so!" was the emphatic reply. "I wish I
could have lessons like this all day and every day. I'd
leave my grammar any time to help make an artificial
"My dear young friends," their uncle admonished them,
"don't let you enthusiasm for chemistry cause you to
slight your grammar, if you wish to keep on good terms
with me. Chemistry has its place but so has language
and no small place, either. Don't neglect your
conjugations, hard though they may seem to you. But now
let us return to our subject of combination.
"It is, as I have said, always accompanied by heat,
sometimes by light. Explosions, detonations, flashes of
light, luminous outbursts, and brilliant
sparks—all the dazzling display of an exhibition
of fireworks, in short—are by no means
exceptional when two substances come together in
chemical combination. In the act of thus coming
together the two substances unite in the closest of
 marry, as we might say, and heat and light make haste
to celebrate the nuptials just as pinwheels and Roman
candles celebrate weddings with us. Do not laugh at my
comparison; it is apter than you think. Chemical
combination is like marriage; it makes one out of two.
"Now I have to tell you what this substance is that has
resulted from the marriage of sulphur and iron. We
cannot call it sulphur, as it is no longer sulphur; nor
can we call it iron, as it is no longer iron. Neither
would it do to call it a mixture of sulphur and iron,
for what was a mixture in the beginning has ceased to
be one now. Its name in chemistry is sulphid of iron, a
name that enables us to remember the two substances
united in the bonds of chemical matrimony,—iron,
which we here write out unchanged, and sulphur, which
appears somewhat disguised in the word
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