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The Wonder Book of Chemistry by  Jean Henri Fabre




[70] IMPRESSED by its glitter, the boys often talked to each other about the asses' gold which, despite its rich appearance, is made of just such sulphur and iron as go to make the black powder of the artificial volcano, but with a double quantity of suphur. The magnificent stone left with them by their uncle they took delight in striking with steel, in some dark place, so as to produce bright flashes of sparks. Furthermore, directed by Uncle Paul, they resolved to visit some of the neighboring mountains in search of more stones like this one. So successful was their quest that Jules's cabinet became filled with pieces of iron pyrites of all sizes and of varying degrees of brilliancy. There were some golden yellow, cut in facets as if a lapidary had taken it into his head to polish them, while others were shapeless and more of an iron gray. Uncle Paul told them that the former were crystals, and that the majority of substances can under favorable conditions take regular shapes in which smooth facets arrange themselves according to geometrical laws. Such substances are then said to be crystallized.

"We will return to this subject later if opportunity occurs," said he; "but to-day other things de- [71] mand our attention. So far we have been merely discussing, talking together, supporting our assertions by sundry facts picked up here and there. Your minds had to be prepared, had to become accustomed to certain ideas and expressions. But, now that you are ripe for it, we are going to have a little real chemistry; that is, we are going to perform some experiments. To see, touch, taste, handle, and smell for oneself, and to observe at leisure,—that is the only way to learn quickly and well. So, then, we will proceed with our experiments."

"Shall we have lots of them?" was the eager inquiry.

"As many as you please, my lads. Along that line, chemistry never comes to an end."

"Oh, that'll be splendid! We shall never get tired of experiments. And may we repeat them by ourselves just as we did with the artificial volcano? That will make twice as much fun."

"If they are not dangerous there is no reason why you should not perform the experiments yourselves. When there is any danger I will tell you beforehand what precautions are necessary. I count on Jules to take the lead, for I know how careful and how skilful he is."

At this word of praise a slight color flushed the older boy's pale cheeks.

"Now, what shall we begin with?" said Uncle Paul. "It shall be with a substance that plays a most important part, air. Let me tell you at the outset, if you do not already know it, that air forms around the earth an envelop known as the atmos- [72] phere and having a thickness of about fifteen leagues at the most moderate estimate. It is a substance of an extremely subtle nature, so intangible and invisible that one is at first surprised to hear it spoken of as matter. 'What! we exclaim; 'air is matter? Air has weight?' Yes, my boys, air is matter and can be weighed. With its delicate instruments physics can weigh air, and it teaches us that a liter of this invisible matter weighs one and three tenths grams. That is very little when compared with the weight of lead, it is true; but it is a good deal when compared with other substances that we shall soon learn about."

"Are there things lighter than air?" asked Jules in surprise. "Yet people say, 'as light as air,' as if there were nothing else of so little weight."

"Let them say it, but rest assured there are other things that in respect to weight are to air what wood is to lead. Air is colorless and, for that reason, invisible. Understand me correctly, however: when I say 'colorless' and 'invisible' I am speaking of air in small quantities; in large volumes that would no longer be true. Water will help us to understand this. Seen in a drinking-glass or in a bottle, it is colorless; seen in a deep body, as in a lake or the sea, it shows its blue color according to the depth of the water. Likewise with air: it is of blue tinge, but so pale that to become perceptible the body of air must have enormous thickness. That explains why the sky is blue: the thickness of the atmospheric envelop (some fifteen leagues, as I said before) [73] brings out its true color, which is imperceptible to the eye in a layer of moderate depth.

"Invisible, subtle, intangible, escaping the clutch of the fingers, air seems to present insurmountable difficulties to any one wishing to study it closely. If we desire to submit it to tests that will reveal its nature and properties, we must take a certain quantity of it, isolate it form the rest of the atmosphere, shut it up in some sort of container, make it flow out in this direction or that as we may choose, carry it from place to place, expose it to such and such conditions,—in short, make it obedient to our control as we should a piece of stone or a pebble. But how can we see the invisible, grasp the elusive, handle the intangible? The difficulty, you see, is no small one."

"It seems to me so great," replied Jules, "that I can't begin to guess how it is overcome. But I have too much confidence in you, Uncle, to doubt that we shall manage it somehow."

"We must; otherwise we should be held up at the very start. And that would be a pity, for air would not be the only thing to get the better of us. There are many other substances just as invisible, just as subtle, just as intangible as air, and of inestimable importance. They would all remain unknown to us if our present difficulty could not be overcome; and the great science of our day, chemistry, the mother of industrial wonders, would remain to be discovered in some ever-retreating future when the art of handling the intangible should have been mastered. All these substances, having the subtle [74] and elusive quality of air, are known by the general name of gases. Air itself is a gas."

"And there is the gas they use for lighting, too," said Emile. "I thought that was the only thing called gas."

"What is burned in chandeliers in our cities is a gas, but not the only one. There are many others, each with its own peculiar qualities. The word gas, then, is a general term by which we designate all substances having a tenuity or thiness similar to that gas; and if we commonly restrict it to illuminating gas, it is because the latter is much better known to us all than any of the others except air. In ordinary language a general term is thus monopolized by one particular substance.

"But to return to our problem, how can we handle air, how subject any gas whatever to observation? I will show you. Suppose we wish to collect the air that comes from our lungs,—our breath, in short. I dip a tumbler into a bowl of water and fill it, after which I invert it in the bowl and raise it. As long as the brim remains completely submerged the water does not run out, but is held suspended above the general level of liquid in the bowl. I see by your looks that this lifting of water and holding it motionless above the level of the surrounding liquid excites some surprise. I will return to this in a moment and explain the cause; but just now let us proceed with our experiment. Here is the glass, full of water and held up by one hand, with the brim immersed. Now with a glass tube—or, if necessary, with a reed or a big straw—I blow under the glass, [75] and the air from my lungs makes the water bubble. Because of its superior lightness it makes it way upward in big globules through the contents of the glass until it reaches the inverted tumbler's bottom. As the breath—or, to express it better, the exhaled air—collects in the upper part of the glass, the water thus displaced descends and reenters the bowl. The thing is done: I have collected my breath; there it is in the glass ready to undergo any tests we choose to apply."


"How easy it is, after all!" exclaimed Emile, much impressed by what he had just seen.

"It is nearly always so, my child,—very easy when we know how, very difficult when we do not."

"Then this glass holds what we send out of our mouth when we blow out a candle; I mean, it is filled with breath. It certainly is a curious thing to collect like this what can't be seen or felt. When I let out my breath after puffing up my cheeks, I don't see anything at all; and yet I just now saw your breath [76] going up through the water and making it bubble."

"The commotion in the water made it seem to you as if you saw what is by its very nature invisible."

"Now that the water is still again, I see nothing, though I am sure the part of the glass that looks empty really has something in it; for I saw that something come and take the place of the water, which went down slowly in the glass. All the same, it seems to me very funny to have that glass full of Uncle Paul's breath. May I try filling it with mine?"

"Certainly; but first you must empty out what is now in the glass."

"Empty it out? But how?"

"In this way."

So saying, Uncle Paul took the glass and inclined it just enough to let a part of the brim come to the surface of the water, whereupon something escaped with a bubbling sound.

"It's gone," cried Emile. "Let who wants to, run after it and catch it in the air where it has disappeared."

The glass being refilled with water, Emile took the straw and blew as his uncle had done, controlling the muscles of his cheeks so that he might watch the bubbles as they rose one by one; and great was his delight to see so easily, and to shut up in a glass so securely, what he had thought must always remain invisible and unmanageable.

"That was soon done," said he, when the glass was full. "I could fill a big bottle with my breath just as easily as a tumbler. May I, Uncle Paul?"

[77] "You may, my boy. If you enjoy the experiment of bottling up your breath, I for my part enjoy your enthusiasm."

A large bottle of clear glass with a wide neck was standing on the table, having been placed there by Uncle Paul for later experiments. Emile took it up and went to the bowl, but soon saw that the latter was not deep enough to dip the bottle into so as to fill it and then admit of its being lifted up with the mouth under water as had just been done with the glass. "Look," said he, after a few vain attempts; "the way you did it with the tumbler won't work. What shall I do?"

"Since the difficulty does not yield to a frontal attack, let us turn its flank. Watch me."

Therewith Uncle Paul placed the bottle on the table and filled it from the carafe. Then, clapping the palm of his left hand over the mouth as a stopper, he took the bottle in his other hand, turned it upside down, and plunged it while stopped in this manner into the bowl of water. Then he removed his left hand, and the bottle with its neck immersed retained its liquid contents suspended above the exterior level, without losing a drop.

"You always find a way out, Uncle Paul," said Emile, delighted at this easy way of overcoming the difficulty.

"We must practise a little ingenuity, my child; for if we didn't, what could we accomplish with the poor apparatus our small village provides? Skill must make up for the defects of our appliances."

Emile blew, filling the bottle with his breath in a [78] few minutes. Then, after Jules also had performed the operation, so as to accustom himself a little to handling gas, their uncle continued thus:

"Why does the water in the glass and in the bottle remain above the level of that in the bowl? This is what we must now find out, though not in all its details, for to do so would take us out of chemistry into physics. A brief explanation, just enough to show you the cause of what now excites your surprise, is all that at present propose.

"Air, I told you, can be weighed just the same as any other substance; and its weight, as I said before, has been found to be one gram and three decigrams a liter. That is very little, but the atmosphere is at least fifteen leagues thick, which must make an enormous number of liters piled one on top of another. Since, then, the atmosphere has weight it must press on them from above, from below, from the right, from the left, from every direction. It presses, for instance, on the water in our bowl; and the pressure, being transmitted by the liquid to the mouth of the bottle, keeps the water in the latter suspended above the exterior level.

"A striking experiment will convince you of this thrust exerted by the atmosphere. Over the mouth of a bottle filled with water we place a piece of damp paper, and while this is held in position with one hand the bottle is turned upside down with the other. Then the hand holding the paper can be withdrawn without the escape of a drop of water from the inverted bottle. It is the atmosphere pushing in every

[79] direction, upward as well as downward, that holds the water in. The office of the paper is to keep the air from entering the liquid mass and breaking it up, which would immediately cause the escape of the water."

"And shall we try this wonderful experiment?" asked the boys, in eager curiosity.

"Shall we try it? you say. Do you think I should have told you about it if we were not going to try it? Up and at it then! Here is our bottle, and here are paper and water; nothing further is needed."

The bottle was filled to the brim and a piece of damp paper placed over its mouth. With his right hand Uncle Paul raised the bottle by its bottom, holding the fingers of his left hand meanwhile on the paper. Then he carefully turned the bottle upside down, let go of the paper, and the thing was done: not a drop of water escaped from the bottle, even though its neck pointed downward. Emile, more excited than ever, could not contain himself.


"That's fine!" he declared, "not a drop comes out of the bottle, and it's turned upside down, too. If it had a cork in it, the thing would be natural enough; but the paper doesn't cork the bottle; if you blew on it, it would come away. How long will the water stay in like that?"

"As long as you please; as long as one has patience to hold the bottle as I am holding it now."

[80] "But the water is trying all the time to get out? It presses down and would fall if it could?"

"Yes, it keeps pressing down, and tends to fall, but the stronger pressure of the atmosphere restrains it."

"And what if we took away the piece of paper?"

"Immediately the water would run out, just as we have so often seen it do from a bottle or carafe tipped sidewise, or, still more, from one turned upside down. This piece of paper closes the bottle's mouth so that water and air are placed in a position where one pushes squarely against the other. Without it the water would slip through the air, the air through the water, and in this mutual evasion the bottle would speedily empty itself. Put two iron rods together, end to end, and exert pressure; there will be mutual resistance. That is what happens when we put the piece of paper between the air and the water. But if the iron rods were made into two bundles of very fine needles pushing against each other, end to end, these same rods would slip into and through each other just as happens with the air and water when there is no paper to separate them.

"To return to the bottle that Emile used to hold the breath he blew into it: as long as its mouth is immersed in the bowl the water it contains does not run out, but is held above the surrounding level by the force of the air pushing against lit. Now, what would happen if instead of this bottle we used a very tall container,—a tube, for example, closed at its upper end? Would this tube, whatever its length, still remain full when raised out of the water except [81] its lower end? No. If the tube were raised so as to project only ten meters above the surface of the water, it would indeed remain full; but if it projected beyond this height the part of the tube above ten meters would be empty. The pressure of the atmosphere can hold up a column of water only ten meters high; that is the extreme limit. Our containers here, as you see, are well within this limit in their height. However big or tall our bottles may be, there is no danger of their being so tall that the pressure of the atmosphere cannot hold back the water that fills them.

"Finally, suppose we wish to transfer a quantity of gas from vessel to another, or to transfuse it as they say. This gas shall, again, be our breath, which will perfectly well serve the purpose of the demonstration I have in view. I fill a glass with it by blowing through a tube in the manner just shown; and now I propose to make this volume of gas pass into another container, or it may be I wish to transfer only half of it. I fill this second glass with water and invert ilt in the bowl so as to keep only the brim immersed. The first glass, with only its brim still in the water, is then tilted side-wise under the other, whereupon the air it contains escapes in bubbles and passes into the second glass, wholly or in part, as I choose.


"To decant a liquid—to pour wine, for example, [82] from one bottle into another—a funnel is used, as you know. The same utensil is often very useful for decanting gases; but a chemist's funnel, which is likely to come into contact with all sorts of corrosive liquids, is of glass, a very resistant substance. As long as only gas is to be transfused, it will suffice to add a modest tin funnel to our simple outfit; but if we had a glass funnel it would be better and more in keeping with chemical practice. Furthermore, glass has one inestimable advantage over tin: it is transparent, and thus allows us to see all that takes place within it. But with nothing beyond a common tin funnel we are not necessarily brought to a halt in our operations.

"A funnel of some sort is indispensable for transfusing a gas from a container of any kind to a bottle with a narrow neck such as bottles commonly have. Of course the transfusion is effected under water. The bottle, filled with water and held with its mouth immersed, has the funnel inserted into it by one hand operating under water. That done, the jar or whatever it may be that contains the gas is brought under the funnel and inclined little by little until bubbles of the gas escape into the flaring mouth of the funnel and pass thence into the bottle.

"That will do for to-day, my boys. You are now in a position to repeat these experiments by yourselves as often as you like, collecting your breath in a glass, transfusing it into another, or into a bottle turned upside down, thus getting your hand into practice. I shall soon need your assistance."

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