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The Wonder Book of Chemistry by  Jean Henri Fabre


 

 

THE TWO SPARROWS

[109]

T
HE two sparrows had been caught. Spring-traps, hidden under a thin layer of earth amid the rows of sprouting peas, and each baited with a piece of bread, had soon accomplished their purpose. Extricated from their entanglement in time to prevent strangling, the two captives were now moving about, full of life, in a cage. The boys were impatient to know what their uncle proposed to do with them, eagerly looking forward to some highly interesting and important experiment. A course of study having for them the keenest interest, and carrying with it the fun of catching sparrows, was real play in their eye,—a circumstance highly pleasing to their uncle, who was convinced that in order to learn well one must enjoy learning.

"Ever since yesterday," said he to them, "the bell-glass full of gas, in which the phosphorous would no longer burn, has been standing in the bowl of water. The white smoke left after the experiment, and of which a little might have continued to linger all the afternoon, has now had ample time to disappear, to become absorbed in the water, so that at present there is nothing in the glass but perfectly pure nitrogen. Notice, the transparency, the com- [110] plete invisibility of this gas. Wouldn't you take it for ordinary air, air such as filled the bell-glass in the beginning? It looks just the same, and yet how different are its properties! In this gas nothing will burn, no matter what we try. After what has occurred, this is plain enough without further demonstration. Some phosphorous—a good deal of it, in fact—was left inside the bell-glass, as was proved when we burned this residue out in the garden. If this remnant of phosphorous could not burn under the glass, but did burn very readily in the open air, the reason must be that it no longer had around it the gas needed to support combustion, having consumed what was originally contained in the bell-glass. In the open air is found an unlimited supply of what it had lacked under the glass, and that is why it began to burn again more brightly than ever and continued to do so until the last particle of the phosphorous was used up.

"Hence it is plain enough that as phosphorous could not go burning in the gas now remaining in the bell-glass, no other substance whatever can burn there. Where the most inflammable of substances stops burning how could one less inflammable remain on fire?"

"That is very clear," admitted Jules; "what the strongest cannot do, certainly the weakest cannot. Then this gas—this nitrogen, as you call it—would immediately quench any fire that could be plunged into it?"

"Certainly. No burning substance plunged into it could go on burning for a single moment."

[111] "It would be the same as when the candle stopped burning in the bottle? Emile, with all his care, couldn't make it stay alight."

"Yes, that's it, except that it falls short of the truth. I told you a candle-flame hasn't energy enough to use all the oxygen in the air. A considerable part is left over in any such experiment as we performed at first; that is to say, in the experiment with the candle burning inside the bottle turned upside down, what is left of the gas is not pure nitrogen; there is still a little oxygen mixed with it, but not enough to keep a second candle alight where the first one ceased to burn. We found, in fact, that we couldn't put a lighted candle in there without its going out immediately. But a more inflammable substance, such as phosphorous, would find what it needed in the residue of oxygen there, and would go on burning for some time where the candle could not."

"One might, then, put it this way," suggested Jules: "phosphorus is so hungry for oxygen that it licks up the leavings of the candle, which has a more delicate appetite."

"Yes, that would express it admirably. If there are any remnants of oxygen, phosphorous, with its robust appetite, will be sure to devour them; but if there are no such leavings, it must go without, and in that case it ceases to burn just as any other combustible material would have to do."

"That seems clear enough," said Emile, in his turn; "but, all the same, I should like to see it proved by experiment."

[112] "What you desire is exactly what I propose to do," replied his uncle; "only we must first transfer a little of the gas from the bell-glass to a wide-mouthed bottle, in which our tests can be made more conveniently. So now is the time for us to put into practice the little I have told you about the transfusion of gases. As our bowl is too small and too shallow for this purpose, we will use this large tub filled with water."

So saying, Uncle Paul lowered the bowl with the bell-glass into the tub without disarranging them, and as soon as the rim of the glass was immersed he withdrew the bowl. A wide-mouthed bottle full of water, inverted and with only its mouth immersed, was held in position by Jules. His uncle tilted the bell-glass a little, and made some of the gas pass into the bottle and fill it. The the bowl was again slipped under the bell-glass, and the whole thing was replaced on the table. Finally, the bottle, filled with nitrogen and stopped with the palm of the hand, was set upright on the table and a piece of glass laid over its mouth. In these various operations, harder to describe than to execute, care was taken never to leave the containers of nitrogen open to the outer air, an indispensable precaution and one easy to observe by keeping the mouths immersed and operating under water.

"Here we have our bottle full of nitrogen," said Uncle Paul. "Now what shall we try first,—sulphur, phosphorous, or candle?"

"Let's begin with the weakest," was Emile's suggestion, "and try the candle first."

[113] The candle, tied to a wire, was lighted and slowly let down into the bottle. Scarcely had it passed the mouth when it suddenly went completely out, not retaining even for an instant that red glow on the wick which is wont to linger for some time after the candle-flame has been blown out. A plunge into water could not have caused a more instantaneous and complete extinction.

"Ha!" cried Emile, "that goes much better than when we tried it before. Yesterday the flame seemed to hesitate, sometimes, about going out; it had to be let down well into the bottle, and the wick appeared to want to keep its red spot; but to-day we see nothing of the sort. As soon as the candle was lowered into the neck of the bottle, flame and red spot both vanished at the same time. And now let's try phosphorous."

"Phosphorus will not burn there any better; you shall see."

The fragment of broken crockery again served as a cup the size of a five-franc piece. An iron wire was bent at one end into a ring for holding this cup, which in turn was to hold the piece of phosphorous. These arrangements completed, the phosphorus was first lighted, and then lowered by means of the iron wire into the bottle of nitrogen. It went out abruptly, as had been expected. What burned so furiously outside the bottle immediately refused to burn when put inside.

A similar test was made with sulphur, which Emile seemed to think might burn in the bottle because of its high inflammability; but it went out [114] as quickly as the candle and the phosphorus.

"Further tests are needless," declared Uncle Paul; "they would only lead to the same result. Nothing can burn in nitrogen; or, in other words, that gas will not support combustion.

"So now we will proceed to make use of your two sparrows, whose part in our study of chemistry is still a puzzle to you. They will teach us some very interesting things, to atone in part for our loss in the peas they have destroyed. In the first place, we must fill our bottle once more with nitrogen. What is still there has come into contact with phosphorous, sulphur, and candle-grease; therefore we are not certain that it is perfectly pure, as it should be for the purpose of our experiment. Accordingly, we will obtain a fresh supply from the bell-glass, first emptying out what is already in the bottle. But how shall we proceed to accomplish this?"

"To empty a bottle, all you have to do is to turn it upside down," Emile made haste to explain, without stopping to think.

"Yes, if the bottle contained water or some other liquid," replied his uncle; "but it contains a gas of about the same weight as air. If you should try to empty a bottle of air by turning it upside down, you would never succeed."

"That's so. Then let's blow as hard as we can into the bottle, and we shall drive out what is in it."

"Agreed; but first tell me how we are to know when we have driven it all out, there being nothing to show what goes out and what comes in. Further- [115] more, you will only replace the first gas with another, your breath, which will be just as hard to drive out; and so the thing will have to be done all over again, and after that still again, and so on without end."

"Really, the more I think of it, the harder it looks to me. I was a little too hasty when I said it was so easy to do. Jules says never a word, and I'll bet he doesn't know any better than I how to manage it."

"I own I am puzzled," said Jules. "This little matter, which seemed a mere nothing, brings me up short."

"It will not stop you very long. Here is how it is done."

His uncle took the bottle and plunged it into the tub, where it quickly filled with water.

"There you have the gas driven out completely."

"Yes," agreed the boys, "but now the bottle is full of water."

"And what is to prevent our replacing it with nitrogen from the bell-glass just as we did before?"

"Why, that's so! It's as easy as can be. The only hard part was to think of it in the first place, just as you said yesterday."

"I am reminded at this point," said Uncle Paul, "of something that may appropriately be mentioned here. In order to ascertain whether the composition of the air is everywhere the same, aeronauts and travelers sometimes bring back air taken at the height they have reached. Now, how can a sample of air taken at the summit of Mont Blanc, for in- [116] stance, or in the lofty altitudes attained by balloonists? How make sure that the air really comes from precisely such and such a place, from a given mountain-top, for example, or from a certain height in the heavens above? Imagine a series of bottles labeled: 'This is from the top of Mount Perdu,' 'This was taken at a height of eight thousand meters, by an aeronaut,' 'This was brought by vessel from such and such a latitude and longitude at sea.' How are specimens to be obtained from various distant points when they are desired for the purpose of chemical examination? Nothing easier. A bottle filled with water is emptied at the exact spot where it is proposed to take a sample of the air, and the air at this spot rushes in to take the place of the liquid poured out. Then the bottle, carefully corked, will hold henceforth, with no further precautions, the invisible substance that at first seemed so hard to collect in perfect purity.

"We now come to the sparrows, whose part in all this I see you are impatient to learn. From the contents of the bell-glass I once more fill our bottle with nitrogen in the manner already shown. A second bottle of the same size and shape, but full of air, is placed on the table beside the first. There they both are, with pieces of glass over their mouths as stoppers. In the appearance of their contents there is no difference, each bottle showing the same clearness, the same invisibility, as to what is inside. Now I will put these two sparrows into our bottles, which are large enough to hold them for the short time required by the experiment. But [117] first I will ask Emile which bottle, if he were a bird, he would prefer to go into, the one with air or the one with nitrogen."

"A week ago," replied the boy, "I should have said it didn't matter which I chose, for there is nothing to be seen in the one any more than in the other; but now, to tell the truth, I'm beginning to be afraid of these invisible things. That rascally nitrogen that puts out a candle is not to be trusted. I don't know much about it, and I do know a little more about air, and so I'd rather trust air than nitrogen. If I were a sparrow, then, I'd choose the bottle filled with air."

"And you would choose very wisely, as you shall soon see."

Taken from the temporary cage, the sparrows were put, one into the bottle full of air, the other into the bottle of nitrogen. The piece of glass laid over the mouth of each bottle shut in its occupant completely. The young observers looked on, deeply interested in what was to come next. In the bottle of air nothing unusual occurred. The captive fluttered about, pecking at its prison-wall of glass, that mysterious obstruction which it could not see and yet could not pass through. It tried to take flight, fell back, rose again, and recommenced its vain attempts. All this was simply the agitation of a bird seeking to regain its lost liberty, a desperate attempt to escape from the prison, and nothing more. Vigorously alive, struggling with beak, claw, and wing, the bird [118] evidently had no other feeling than one of extreme fright.


[Illustration]

Quite otherwise did the sparrow in the bottle filled with nitrogen behave. No sooner was it placed in its glass cage than it was overcome as if with stupor. Staggering, beak open, breast heaving, it appeared almost at its last gasp. Seized with convulsions, it fell sidewise, struggled aimlessly, opened its beak again and again as it panted for breath, and then ceased to move. The bird was dead. The other, on the contrary, was still comporting itself in a very lively fashion.


[Illustration]

"This experiment," Uncle Paul confessed, "is one that I have no liking for; nor does it please you any better, my dear children. The sight of a creature in pain, suffering as the victim of our curiosity, like this sparrow dying to afford us instruction, is as repugnant to your kindly nature as it is to mine. It is a thing to see once, the pursuit of knowledge having its cruel necessities; but it is not to be repeated. Let us hasten to liberate the survivor. For the sake of its fellow, dead in the cause of chemistry, I forgive it for pilfering my peas."

The two sparrows were taken out of the bottles, the one from that containing air being as lively as a cricket. Emile held it in his hand a moment, bade it good-by, took it to the open window, and let it go, whereupon it flew away like an arrow, with a cry of supreme joy. The other, its poor little claws [119] stiff in death, remained on the table, breast upward. Emile and Jules gave it occasional side glances, puzzled to understand the cause of so sudden a death, and perhaps hoping to see it come back to life. Their uncle perceived what was in their minds.

"Do not hope for the sparrow's revival," said he. "It is dead—poor little thing!—dead for good and all."

"Is this nitrogen, then, such a terrible poison?" asked Jules.

"No, my young friend. Far from being a poison, nitrogen is perfectly harmless. It must be harmless or we could not live in an atmosphere of which it constitutes four fifths. We all breathe it incessantly, and not one of us ever has any reason to complain of it. Nitrogen is quite harmless; that is not what killed the bird."

"Then why did it die?"

"The candle which burns in the air goes out in nitrogen. Is it because of this gas? No, for if that were so, the candle could not burn in an atmosphere abounding in nitrogen. Where this gas is present all by itself the candle goes out, not on account of the nitrogen, but because it lacks the element essential to combustion, and that is oxygen. It is not the presence of the one gas, but the absence of the other, that makes combustion impossible.

"We ourselves perish quickly in water. Why? Can it be that water is a poison? Certainly not; such an idea would never occur to us. We die in the water for want of air, water itself having nothing to do with the death of the person drowned, [120] which is due solely to the lack of breathable air. In like manner we may say the sparrow met its death by drowning in nitrogen. It cannot truly be said that air was wholly lacking, for the bird had a plenty of one of the two gases composing the atmosphere; it was merely deprived of that part which alone is breathable, which alone promotes in the animal, for the purpose of sustaining life, an action comparable in ever way to that set up in the candle-flame to cause it to burn.

"It is the lack of oxygen, then, that caused the sparrow's death and the going out of the candle. Where there is no oxygen, neither life nor combustion is possible. No animal can live where a candle cannot burn, for life and combustion are closely akin, as I will show you at the proper time. But first we must study carefully this partner of nitrogen in our atmosphere, this gas called oxygen; and then you will be in a position to see the close resemblance between life and fire."

The boys exchanged glances of surprise at hearing their uncle thus associate these two things.

"I am saying nothing," he continued, "that does not agree with the most careful scientific observations; that has not, indeed, to some extent, become a part of our every-day thinking, so obvious is it to every one. We say of a fire that has gone out, that it is dead. The famous song that Harlequin  sings under his friend Pierrot's  window tells us that the candle is dead. In order to die it must first have lived. The dead fire, the dead candle, had, while they burned, I will not say life, for that would be [121] going too far, but at least a state not unlike life in respect to the chemical action concerned. A lighted candle and a live animal consume oxygen in order to continue burning in the one case and living in the other. Both candle-flame and animal die in nitrogen because this oxygen is lacking there. That is the whole secret of the end of the poor sparrow."

"And other animals?" asked Emile. "Would they die in the nitrogen as the sparrow did?"

"All would die there, some sooner, some later, according to their different kinds—absolutely all, since no creature, however small, can live without oxygen, for which nitrogen will not in the least serve as a substitute. If it were not a cruelty as repugnant as it would be useless, we might repeat our experiment with all the inhabitants of our garden,—with its birds, field-mice, moles, insects, snails, and so on,—and we should see them all succumb in nitrogen, some quickly, others after a long enough time to try our patience; for I must tell you that though all animals without exception need oxygen if they are to live, they do not feel its need with equal urgency. There are some that are overpowered instantly in nitrogen: such was the case with our sparrow; others can live in it for hours or even for days, but are sure to die at last. The rule is universal; the length of the victim's resistance alone varies. First to succumb are the birds, their breathing being very rapid. The follow the fur-bearing animals,—the cat, the dog, the rabbit, etc.,—in short, the mammals, as naturalists call them. Reptiles have a much greater power of resistance: [122] a lizard, a snake, or a frog would perhaps not be quite dead even at the end of an hour. Finally, insects, snails, and other small forms of animals life are the last to perish.

"This is something so important that I must not refuse to illustrate it by experiment, despite our pity for suffering. Besides, I have in mind a poor victim that would otherwise perish miserably under a cat's claws. Better that it should meet with a gentle death in nitrogen than endure the cruel suffering a cat's claws would inflict. We shall be doing it a kindness to spare it that torture. It is a mouse caught in the mouse-trap. I saw it this morning on one of the pantry shelves. Emile, go and get it."

Emile came back with the mouse-trap and its captive. From the nitrogen left in the bell-glass, the bottle in which the sparrow had died was refilled. Opening the trap a little, Uncle Paul dropped the mouse into the bottle. Finding itself in this glass prison, the animal first circled around several times, hugging the wall and seeking an outlet, with no further appearance of discomfort than fright. Then it crouched down, began to tremble, and seemed to go to sleep. Finally, a sudden convulsion announced that it was dead. Only a few minutes had passed, but it was clear the animal had taken longer to die than the bird.

"Give the mouse to the cat," said Uncle Paul, "and that shall end our experiments with animals. Now let us sum up what we have just learned. Nitrogen forms four fifths of our atmosphere. It [123] is a colorless, odorless, invisible gas in which nothing can burn. A lighted candle goes out the moment it is lowered into this gas. Nor can animal life sustain itself in nitrogen: any animal that breathes it unmixed with oxygen dies sooner or later, not on account of the nitrogen itself, which has no harmful properties, but for lack of oxygen, the only part of the atmosphere that will sustain life."


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