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The Wonder Book of Chemistry by  Jean Henri Fabre

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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
379 pages $14.95   





NCLE PAUL took a rather deep dish and in the center he fixed a candle with a few drops of melted wax. Then he lighted the candle and covered it with a large, wide-mouthed bottle of clear glass. After this he poured water into the dish until it was quite full.


Meanwhile the children looked on, chattering between themselves and wondering what their uncle was up to with his lighted candle all surrounded with water and burning in a bottle upside down in the middle of the dish. What curious experiment was he about to perform? They were not left long in doubt. Everything being ready, Uncle Paul began thus:

"What is there in the bottle?"

"A lighted candle," Emile hastened to answer.

"Is there nothing else there?"

"No, nothing. I don't see anything but the candle."

"You forget that there are some things we cannot [84] see. You must here the eyes of the mind, not those of the body."

Emile scratched behind his ear with the tip of his finger and winked hard, as was his wont when puzzled. He was trying to think what the invisible thing could be that his uncle referred to. Jules came to his aid.

"It is air," declared the older boy. "There is air in the bottle where the candle is burning."

"But Uncle Paul didn't put any there," Emile rejoined.

"It is necessary to put any there, little giddypate?" his uncle demanded. "Is not the bottle full of it without any help from us? All the vessels we use, all our flasks, jars, bottles, glasses, containers of whatever kind, being immersed in the atmosphere, in the very depths of this ocean air, are filled with this gas as they would be with water if they were plunged uncorked into that liquid. If it does not contain anything else, every bottle, whether right side up or wrong side up, is full of air, which gets in of itself, usually without our paying any heed to it. When a bottle of wine is drained to the last drop, we say it is empty. Should we really call it empty if we chose our words with extreme care? Certainly not, for the so-called empty bottle is as full as ever, full to the top; it is filled with the air that has taken the wine's place. And so it is with all vessels when we empty them of their contents: if they were full before, they remain full afterward, though the nature of their contents has changed. Nothing is abso- [85] lutely empty, nothing can be empty, when air is free to enter it. We can, it is true empty a vessel in the literal sense; we can create a void or vacuum, as the learned men say; but that is an elaborate operation, and its success demands proper appliances."

"You mean an air-pump?" asked Jules.

"Yes, my boy, an air-pump, a special kind of pump that sucks the air from a tightly closed vessel and discharges it into the outer atmosphere. But as nothing of the sort has been used here, my bottle is full of air exactly like the air around us. Consequently the candle is burning in the midst of the air contained in the bottle. Now, why did I fill the dish with water? For this reason: The air in the bottle is the substance I propose to study with you by subjecting it to certain experiments, particularly this experiment with the lighted candle. And so we must separate this air from the rest of the atmosphere, isolating it in a closed container, as otherwise our experiment could not be carried through; and, furthermore, we should be unable to tell what portion of the atmosphere we had been experimenting with. The bottle alone does not furnish complete isolation, for, between its mouth and the bottom of the dish, air could easily slip in and mix with that already in the bottle. A barrier must be interposed to separate the inner from the outer air, and this barrier is furnished by the bed of water in the dish. Thus we obtain perfect isolation; and you will also see that the water serves a second purpose, being an indicator of what takes place in the bottle. [86] But I must not distract your attention by too much explanation. Now watch closely what is going on in the bottle."

Behold, in a few minutes the candle-flame, which at first was full and bright like that of a candle burning in the open air instead of in a bottle, began to get dimmer little by little, becoming shorter, shrinking in width, and looking dull and smoky. Soon it had diminished to a mere point, and finally to nothing at all. The flame was quite extinguished.

"Look!" cried Emile. "The candle has gone out without any one's blowing it out."

"Wait a moment, Emile, and we will presently talk the thing over. Just now keep your eyes open and watch what is happening in the water, the indicator I spoke about."

Emile and Jules watched attentively and saw the water gradually rise in the neck of the bottle, completely fill it, and go still farter, so that an appreciable part of the bottle , at first filled with air, was occupied by the liquid coming form the dish and slipping in form beneath. Its ascent was slow, and when at last it was finished Uncle Paul broke the silence.

"Now," said he, "you may ask all the questions you please."

"I should like to have one thing explained," said Emile. "When a candle is burning and you want to put it out, you have to blow on it. But here no one blew out the candle, and if we had wanted to we couldn't have done it on account of the bottle [87] over it. Not a breath of air came, that is certain; no puff of wind. Under cover of the bottle no breath of air or puff of wind could get at it. The flame was perfectly still; it stood up straight and calm; and yet, without any reason that can see, it got dim and dwindled to nothing but a point, and then at last went out altogether."

"I should like to ask something, too," put in the older boy. "The bottle was at first filled full of air; now, besides the air that is left, it has several fingers of water from the dish. I saw this water rise little by little as the flame dwindled. So something has been taken from what was in the bottle at first, for the water rose and took its place. But how did that something disappear, and where has it gone to? If you had not told us and made us understand that nothing is ever annihilated, I should say that a part of the air was annihilated while the candle burned."

"Jules's point shall have our attention first, as it will furnish us the explanation of Emile's difficulty. A part of the bottle's gascous contents has disappeared, apparently; the water's rising above its level in the dish to fill the vacancy would seem to prove it in a way to convince the most incredulous. Something, I repeat, has disappeared, so far as we can see; but we must not for a moment suppose it has been annihilated. Let us investigate further, and we shall discover what has become of this something that seems to be lacking.

"I have already told you that heat and light are [88] nearly always signs of the mingling of substances of different natures,—of chemical combination, in short."

"I remember," said Jules. "You called it the fireworks that celebrate chemical weddings. Can such weddings take place in a bottle?"

"Yes. The flame was hot and it gave out light; hence a chemical combination was going on, producing this heat and light; hence a chemical combination was going on, producing this heat and light. And what substances were they that were thus combining? One of them, beyond a doubt, was supplied by the fatty material of the candle as it melted under the heat from the lighted wick; the other could have come only from the air, since the bottle contained nothing else. From this combination sprang something new, something that was no longer either candle grease or air, something with properties that neither air nor candle possesses. The compound thus formed is an invisible substance, a gas just as air is a gas, and for that reason invisible."

"But if a gas is made out of air and candle grease," Jules objected, "this gas takes the place of the air that disappeared, and the bottle ought to be just as full as it was before. I don't see why the water rises."

"Wait; we are coming to that. The compound we are speaking of is readily soluble in water, somewhat as sugar and salt easily dissolve in that liquid. Once dissolved in this way, sugar and salt disappear, become invisible, and the only evidence we have of their presence is the sweet or the salt [89] taste of the water. In like manner, what is produced by the flame disappears: it enters the water and becomes incorporated with it. Similar but much richer gaseous solutions are familiar to you. I hardly need to remind you of beer, cider, sparkling wine, and soda-water, drinks that make the cork pop and that foam when poured into the glass. All these liquids hold quantities of gas in solution,—so much of it, in fact, that they cannot retain it when escape is possible; and therefore it thrusts out the cork and covers the drink with foam. Now, curiously enough, the gas that makes these beverages foam is precisely the gas that the candle-flame manufactures. Some day I will take this interesting subject up again. I mention it here in passing, but have not time to dwell on it.

"Since the compound produced by the candle grease and the air disappears from sight, being dissolved in the water, a vacant space must be left; and this it is that the water in the dish, under pressure of the atmosphere, rises in the bottle to occupy, showing us by the height to which it rises the amount of air that has disappeared."

"It hasn't risen far," said Emile. "See! It's only just above the neck."

"That shows that the candle burned up only a small part of the air in the bottle,—a tenth part, let us say, if the water that has made its way in fills a tenth part of the bottle's total capacity."

"But as there is still so much air in the bottle, why didn't the candle use that up just as it did the [90] other part? I don't see that it is any different form what that was. It is still transparent, invisible, and hasn't a particle of smoke."

"Here is where we come to your question, my boy, the question why the candle went out without being blown out. The candle-flame is caused by the combination of the material of the candle with certain other material contained in the air. Air and candle are equally necessary in feeding the flame. If either be lacking, the flame is extinguished. As to the candle's being necessary, that is plain enough: no fuel, no flame. But in regard to the air you don't feel quite so sure. And yet what you have just witnessed ought to give you food for reflection. If the candle went out of its own accord, there was certainly something wanting."

"I'm ready enough to admit that. Yes, that must have been the trouble; something was wanting, as no one blew out the candle and there wasn't a breath of wind. Now, what was it?"

"What was lacking must have been air, as the bottle contained nothing else to begin with. Air is indispensable for keeping a flame burning."

"But there is still air in the bottle,—lots of it, almost the whole bottleful."

"I do not deny it; but listen a moment. It is not possible that air, instead of being made of only one substance, is made of two of different kinds, equally colorless, equally subtle and invisible, and very thoroughly mixed together? Is it not possible, too, that one of these gaseous substances can keep a [91] flame going, whereas the other cannot, and that the first-named forms but a small part of the atmosphere as compared with the second? If so, when this first part is used up in the bottle, the candle goes out of itself, as we say, the candle grease no longer finding what it needs for burning, and there will be left in the bottle, colorless and invisible, as it was in the first place, the other gaseous element, of no use for keeping a flame alive."

"How clear that makes everything, Uncle," said Jules. "Now I see it all perfectly. The candle went out of itself when there was no more of this gas material to keep it burning. By combining with a little burnt grease, this matter turned into something else, a gas that is dissolving disappeared in the water while the water in the dish rose and took its place. Now the bottle holds only the kind of gas of no use to a flame, and that is why the candle stopped burning."

"Yes, that's the way of it, with one slight correction. A candle-flame is not by any means a fire strong enough to use up all the gaseous element needed for the act of burning; there is still some of it left over, but too little to keep the candle alight. The air has become impoverished, but not deprived of all it contained of the element in question. Another day we will try to find a way to remove the last trace of this flame-supporting gas. At present let us rest content with our partial result. The contents of the bottle will no longer keep a candle burning, and a lighted candle put into the bottle would immediately be extinguished."

[92] "A candle would go out if put into that bottle?" asked Emile, still rather inclined to doubt.

"Certainly it would, and almost as quickly as if you plunged it into water. How can you expect it to burn? If the one that was there could not burn, why should another do any better? They are all made alike."

"All the same, I'd like to see it tried."

"Your curiosity shall be gratified."

With this Uncle Paul took a short candle-end and tied it to a wire bent up at the bottom. Then, raising the bottle a little with one hand, he slipped the palm of the other over the mouth, which was still under water, thus stopping it up. After this he set the bottle upright on the table without letting it lose any of its contents, liquid or gaseous, and withdrew the hand he had used as a stopper.

"But the air in the bottle will get out," objected Emile, "if you leave the bottle open."

"There is no danger of that," his uncle reassured him. "The invisible gas there, being as heavy as air will not escape. However, to make sure of it, here is a stopper we can use."

It was a little piece of glass from a broken window-pane. Uncle Paul placed it over the bottle's mouth.

"Now," said he, "let us proceed to our experiment."

The candle fastened the wire was lighted and allowed to burn until the flame was bright and full, after which Uncle Paul removed the piece of glass [93] and gently let down into the bottle the lighted candle, which almost immediately became dim and went out. A second attempt met with the same speedy result. If violently blown upon or plunged into water, the candle could not have gone out more promptly.

"Well, are you convinced now, Master Unbeliever? Here, try it for yourself, so as to be quite satisfied."

Emile took the candle and began the experiment over again, lowering the flame little by little, very gently, very cautiously, so as to keep it away from the sides of the bottle, thinking that careful management might accustom the flame to this unsuitable atmosphere. But it was of no use. Though several times repeated, the attempt invariably failed: a little higher or a little lower in the bottle, the flame always went out.


"It's no good, the candle won't burn there," declared the boy, tired of attempting the impossible. "I should be perfectly sure of it if I were certain the bottle had nothing to do with it. Couldn't the nearness of the glass and the want of space make the candle go out?"

"That is a very natural question, but it is soon answered. Here is a bottle like the first, of the same size and with the same wide neck. It is filled with air that has not been impoverished by anything [94] burning in it, the same kind of air as that all around us. Repeat your experiment with that."

Emile lowered the candle into the bottle, and it burned very well, exactly as if in the open air. Whether put in abruptly or gently, near to or away from the enclosing glass, it remained alight and burned as it had outside. His constant failure with the first bottle and his repeated success with the second dispelled Emile's last lingering doubt.

"I have nothing more to say," he declared. "The stuff in the bottle where the first candle burned doesn't suit it now at all."

"You are convinced, then?"




"Then I will continue. What we conclude from our experiment is that air is composed of two different gases, equally invisible but of so unlike a nature, each to the other, as to prevent our confusing them. One, the less abundant, suits the candle-flame and combustion in general; the other, more plentiful, does not. The first is called oxygen, the second nitrogen. They are two simple substances, two metalloids. As to air, which is a mixture of these two gases, we can no longer properly call it an element as did the ancients. It is a compound of two substances of very different natures. This has been known only a comparatively short time."

"I wonder why it took so long to find out about air," said Jules. "It would have been such a simple [95] thing to burn a candle in a bottle turned upside down in a dish of water."

"Very simple, undoubtedly; but it had to be thought of, and there was the difficulty."

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