THE TWO SPARROWS
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-  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."
 "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
"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
 "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."
 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
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
 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
"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-  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
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
"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-  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
"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
 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
"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
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
 evidently had no other feeling than one of extreme
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
"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
 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
"Is this nitrogen, then, such a terrible poison?" asked
"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,
 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
 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:
 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
 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."