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 soon see."
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 particles.
"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 example."
"Does it attract tin?"
"No; no more than lead."
"And zinc and copper—does it have any effect on them?"
"No more than on lead or tin. Ah! Now I have it. The magnet 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 iron."
"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 fingers.
"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 are?"
"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 all out?"
"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 to work."
"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 itself."
"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 mixture 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 extremities 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 separated them.
"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 water?"
"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 sulphur—"
"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 hesitate 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 the second.
"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 something else."
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 hold."
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 experiments 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 mole-hill 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 pains.
"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 rest."
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 are 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 ingredients."
"But who in the world would ever imagine this black stuff was made of sulphur and iron?" the boys exclaimed.
"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 combining 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 it?"
"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 combination?"
"Precisely; you cause two different substances to combine."
"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 brings about."
"And will you tell us all about these wonderful things?"
"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 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 volcano."
"My dear young friends," their uncle admonished them, "don't let your 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 bonds; they 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 'sulphid.' "