FURTHER EXPERIMENTS WITH AIR
UR experiment with the candle burning in a bottle turned
upside down in water, is one of the easiest to perform,
calling for nothing that is not readily procurable.
But, unfortunately, it is an incomplete experiment, for
the reason that I have already indicated. It shows us
that air is composed of two different gases, one that
will keep a flame burning and is called oxygen, and
another of a contrary nature in this respect and known
as nitrogen; but it does not tell us how much there is
of each, because what is left after the candle goes
out, still retains a good proportion of oxygen instead
of being reduced to pure nitrogen.
"A candle-flame is delicate; a moderate puff of wind
will blow it out. In the bottle, I admit, it is
sheltered from any current of air, but its weakness
prevents its using up all the gas on which it could
feed. It turns dim and then goes out altogether when
this gas begins to get scarce. If the comparison is
not too far-fetched, one might call the candle-flame a
guest at table with a poor appetite, leaving on his
plate the greater part of the food served to him. Let
us, then, call in a guest with a stronger stomach and
able to eat his food to the
 last morsel, leaving nothing but the uneatable, the
bare bones. I mean, let us find a kind of fuel that
burns with enough energy to consume all the oxygen to
the last trace and leave only the useless gas, the
"What shall this fuel be? Shall it be coal? No; that
would not do any better than candle-grease, burning
less freely, in fact, because needing the heat of a
glowing furnace to keep it going, and that is out of
the question in our experiment, which owes more than
half of its value to its very simplicity. Shall it be
sulphur? There, assuredly, we have a strong stomach
needing no second invitation when oxygen is offered.
Once set fire to, it burns vigorously. But it has its
faults,—its suffocating fumes. Nevertheless, I should
be glad to avail myself of it if there were not
something better at hand. You are familiar enough with
the common match, the little stick of wood tipper with
sulphur, and lightly coating the sulphur we find—See
who can tell me first."
"Phosphorous!" cried the two listeners at the same
"Yes, phosphorous, which is inflammable to a degree not
attained by any other substance in common use;
phosphorous, which takes fire by being merely rubbed
against the sandpaper cover of the match-box or against
a rough wall. Nothing equals it in the vigor and
persistence with which it burns. Here, truly, we have
the greedy guest who will leave nothing on his plate.
But first let us get a little better acquainted with
 is not very well known to you, as hitherto you have
seen it only on the tips of matches."
"Sometimes," said Emile, "the tips are red, and
sometimes blue, or yellow, or almost black. Does
phosphorus have all those colors?"
"No; of itself phosphorus has only one color, which is
nearly that of yellow wax. But the match manufacturer
adds colored powder, sometimes of one hue, sometimes of
another, according to his facy, for the sake of giving
a little variety to his wares and thus pleasing the
purchaser's eye. Glue is also mixed with the
phosphorus to make it stick to the sulphur. So what
you are used to seeing is not pure phosphorus; but I
will show you some that is perfectly pure.
"A few days ago, being called to town on business, I
bought a number of things that our laboratory was much
in need of. A laboratory, let me explain to you , is a
place devoted to scientific research; it is the
scientist's workshop. Modest though our workshop is,
it must have some equipment, certain implements and
supplies; otherwise we should have nothing but our ten
fingers for an outfit, and what could we do with them?
We should simply have to content ourselves with talking
and nothing else. But that I will not have, for I do
not think much of chemistry carried on in words only.
I wish to give you facts, things that you can see over
and over again, substances that you can feel of, taste,
examine, handle for yourselves, as that is the only
true way to learn.
 "What could the blacksmith do without his anvil and
hammer? Nothing. Equally helpless is the chemist
without the various appliances and drugs of his
laboratory. We will furnish ours, then, little by
little, but in a very modest way, I assure you
beforehand, as your uncle's resources do not permit
luxury. We will have the indispensable, but nothing
more. Nor is it altogether a misfortune to be thus
forced to use one's wits a little, in devising ways and
means to make what one has suffice, and in getting
along without what one does not have. Our earthen dish
borrowed from the kitchen, our old medicine-bottles and
preserve-jars—did they not play their part well?
I assure you in all sincerity, we could not have done
better if we had had the outfit of a costly laboratory.
Why shouldn't we continue our studies in this way, as
far as may be? If you ever chance to have access to a
real laboratory, and to work in it, my little lads, you
will take pleasure in recalling your uncle's poor
outfit and in reflecting how little it took to lay the
solid foundations of useful knowledge in your minds,
and how little it would need to do so for others even
in our smallest villages.
"It may well happen that we shall be halted now and
then by difficulties impossible for us to overcome;
then, and only then, we shall be forced to appeal to
the expert chemist for aid. Such is our position
to-day. We had need of phosphorus, and here it is,
bought recently at the druggist's in town."
 Uncle Paul here set before his nephews a bottle holding
in water a yellow substance in the form of a stick as
long and as thick as one's little finger.
"That," said he, "is pure phosphorus. It is
semi-transparent, which, with its color, makes it look
like a pretty piece of wax such as we have in the
honeycomb. It is like wax before being bleached at the
taper factory by long exposure to the sun."
"Why do you keep it in water?" asked Jules.
"I keep it in water because if exposed to the air it
would soon catch fire. So inflammable is it that the
slightest heat is enough to ignite it."
"But the phosphorus on matches doesn't catch fire like
that; you have to scratch it."
"I told you that in matches it is not used in a pure
state. It is mixed with certain other substances with
glue and colored powder, which lessen its
inflammability. But even so it sometimes occurs in
summer that matches take fire of their own accord.
This is a serious fault which, added to others, will
perhaps some day induce us to give up the use of
phosphorus, when science has discovered something
better to take its place."
"And why," asked Emile, "doesn't it catch fire in the
water, if it is so eager to burn?"
"Has Emile forgotten what I told him yesterday? In
order to have fire, two things are necessary, each as
indispensable as the other,—the thing that burns
and the thing that makes it burn, this latter being a
gas called oxygen, contained in the air. Combustion is
brought about when the two combine. Where there is no
air—or, rather, where
 there is no oxygen—combustion is impossible,
however inflammable the fuel may be. So I guard the
phosphorus from risk of taking fire by keeping it in
water, which protects it from the air. This being
excluded, we are sure the phosphorus will not catch
"Still another precaution is not out of place with this
dangerous substance. The bottle holding the
phosphorous in water might get broken, which would
expose the phosphorous to the air. Therefore we must
guard against any chance shock or fall, and to this end
the bottle is enclosed in a tin box which serves as a
shock-absorber. In this double enclosure and immersed
in water, phosphorus is kept indefinitely on the
druggist's shelf without any danger.
"It remains for me to add that a burn from phosphorus
is a serious accident, a most painful accident. There
is nothing that smarts more than a wound made by this
terrible stuff. Neither live coals nor red-hot iron
can cause so acute and lasting a pain. I will leave
you to imagine the fate of the thoughtless person who,
wrapping a piece of phosphorus in paper, should put it
into his pocket, proposing to amuse himself with it
later and make it shine in the dark. The heat of his
body would set fire to his perilous possession, and the
imprudent one would be burned to his very entrails,
while he filled the air with his shrieks of agony. Be
careful then, my boy, not to play with this terrible
substance. If the thirst for knowledge should tempt
you to handle it at all, do so with the utmost caution.
 I appeal here to Emile's obedience and Jules's
prudence. Had I not perfect confidence in you, did I
not know you to be incapable of reckless folly, I
should double-lock and triple-lock my arsenal of drugs
and banish phosphorus from our lessons forever.
"I should be all the more impelled to this course
because the risk of fire and serious burns is not the
only danger to be considered; there is another peril,
which you must be still more careful to guard against.
Phosphorous is a deadly poison, a few particles of it
being enough to cause death with frightful sufferings.
I will say no more; you are warned. Look on
phosphorous as one of the most formidable of foes, and
let no carelessness on your part lay you open to its
"After these warnings, dictated by prudence, I will now
explain how phosphorous may be used to show what air is
made of. We must burn a little in a certain volume of
air properly separated from the rest of the atmosphere.
Our container in this operation should be of
considerable size, so that the glass may be far enough
from the flame to escape the risk of being cracked or
broken by the heat. A common glass preserve-jar
holding two liters or more, and as large at the top as
at the bottom, would do very well if I had not
something better. This something better is a chemist's
bell-glass, a recent purchase of mine, which we shall
find to be one of the most useful appliances in our
laboratory. I will ask you to be especially careful of
it. It is, as you see, a simple container of
color-  less glass, cylindrical in form, with a dome-shaped top
surmounted by a little knob for taking hold of. Some
are made with flaring mouth, reminding one of the shape
of our bronze church bells, whence comes the name of
bell-glass. For certain delicate plants requiring
shelter and warmth gardeners use similar glass covers,
but they are commonly too large and cumbrous for
laboratory use. If one could find a medium-sized one,
it would do perfectly.
"A large bottle, a gardener's glass plant-protector of
suitable size, or the ordinary chemist's
bell-glass—any one of these that should chance to
fall into our hands would serve as a contain for
burning phosphorous; but Uncle Paul's purse has
procured for us a real laboratory bell-glass, so let us
be grateful for it and proceed with our experiment.
"The combustion, the burning of our bit of phosphorous,
must take place on water, to prevent any communication
between the air in the glass and that outside.
Consequently, the phosphorus has to be placed on a tiny
raft that will keep it dry, and for this purpose we can
use any small object that will float, as a piece of
cork or a bit of wood. But this float of ours would
catch fire if unprotected from the burning phosphorous.
Accordingly, we will put the latter in a tiny
earthenware cut resting on the float; and for our cup
we will simply take a concave fragment of some old
broken pot. Now all is ready and we will proceed to
 "First we must cut off a piece of our stick of
phosphorus. It is soft enough to cut with a knife,
being of about the hardness of rather firm wax; but it
is not a thing to be cut as carelessly as one might
whittle a stick of pine wood, the mere friction of the
knife being likely to prove sufficient to set fire to
the phosphorus if it were exposed to the air, with
consequent serious injury to the clumsy operator. The
inflammable stuff should not be held in the air except
by the finger-tips and for as short a time as possible,
and the cutting should take place under water. Watch
Uncle Paul put his fingers into the bottle and drew out
the phosphorous stick, which gave out a rather strong
smell of garlic, with some slight wisps of white smoke.
The children were told that this smell of garlic is the
natural odor of phosphorus, and that the white smoke
would be found to give out light if looked at in the
dark. Matches emit, to a lesser extent, these same
odorous fumes. The phosphorus was immediately plunged
into the bowl of water, and there, both hands under
water, Uncle Paul with a knife cut off a piece about as
large as two peas. This fragment was placed on a bit
of broken crocker, and that on a little wooden raft of
sufficient buoyancy to float its load; then the whole
thing was set on the surface of the water in the middle
of the bowl. A lighted match quickly started the
phosphorus to burning, and Uncle Paul hastened to cover
it with the bell-glass, which was, of course, full of
Behold, then, the phosphorous blazing away with
 a violence quite new to the boys, who up to this time
had seen no more of the inflammable stuff than the
minute quantity at the tip of a match. The flame
crackled, the light was brilliant, almost blinding. A
dense cloud of white smoke formed, giving the
appearance of milk to the contents of the bell-glass.
At the same time the water in the bowl rose so rapidly
in the glass that Uncle Paul was obliged to add more,
in order not to leave the bottom of the bowl dry, for
that would have let air into the bell-glass. So thick
was the milky-looking cloud that the phosphorus flame
could no longer be seen; or, if seen, it was only at
intervals, like lightning in a mass of clouds. But the
jets of light became more and more infrequent and
feeble, and finally ceased altogether.
"It is over," Uncle Paul announced. "The phosphorus
has used up all the oxygen in the air contained in the
bell-glass, and there is nothing left but nitrogen,
which will not support combustion, although there is
still some combustible matter left on the bit of
crockery. We shall see it when the white smoke has
cleared away. Meanwhile let us talk a little about
this smoke, which seems to attract your attention by
reason of its beautiful milky appearance. It comes
from burned phosphorus—that is to say, from the
phosphorous combined with the oxygen of the atmosphere.
A brilliant light, of such intensity as to try our
 accompanied this act of combining, as it always does.
I say nothing of the heat, to which the bit of broken
crockery could testify if it could speak. These fumes
are easily dissolved in water, and thus there is left a
vacant space which the water from the dish rises to
fill, little by little, in this way showing how much
oxygen has disappeared. We should have to wait only
about twenty minutes, more of less, for the contents of
the glass to become as clear and transparent as at the
start. But to hasten the process and not to put your
patience to such a test, let us see what this will do:
we shake the bell-glass gently so that the moving water
washes the interior and takes up the smoke. By this
operation the contents will soon be made clear."
With a little careful management in shaking the glass,
the gas within was soon made to resume its original
transparency, and then there was revealed, on the bit
of broken earthenware, the residue of that had been
placed there, but now of a reddish color and, indeed,
so changed in appearance that the boys would not have
recognized it as phosphorous. Melted by the heat so
that it was spread out on the piece of earthenware, it
had quite an altered look. But to convince his hearers
that it was still phosphorous, their uncle tilted the
bell-glass slightly, so as to bring the little raft
near its edge, when it became an easy matter to
withdraw the raft and its load.
"What we have here," said he, "is really phosphorous
despite the reddish tinge that heat and melting have
given it. There is even more left over
 than there was burned. You shall judge for
The potsherd was taken out into the garden so as not to
mingle the disagreeable phosphorous fumes with the air
of the workroom, then with a match the reddish
substance was set fire to, and it burned with the
bright light and dense white smoke attending the
combustion under glass. Thus it was proved that there
remained some phosphorous, even a good deal, as it
burned for a considerable time; and in this instance
every particle of it was consumed, the last trace being
dissipated in the air as white smoke.
"If combustion stopped under the bell-glass," Uncle
Paul continued, "it was not for lack of something to
burn, for there was a good deal of it left at the end,
but for lack of the gas necessary to support
combustion—oxygen, in a word. It stopped when
the last trace of this gas was used up, phosphorous
being able to burn as long as there is any oxygen left,
however little it may be. Consequently, the bell-glass
now contains nothing but pure nitrogen, a gas in which
no substance whatever can burn.
"The phosphorous experiment tells us once again, but
more positively and more distinctly, what the candle
experiment; the atmosphere contains two gases, oxygen,
which supports combustion, and nitrogen, in which
neither candle nor phosphorous nor anything else can
burn. It tells us, also, in what proportions the two
gases, both simple substances, both metalloids, are
combined in the atmosphere. Our bell-glass is
cylindrical. If we divide
 its height into five equal parts, these will represent
equal capacities, equal volumes. Now we see that the
water that rose in the glass and took the place of the
departed oxygen has mounted to a fifth of the total
height, nitrogen occupying the other four-fifths. Thus
the air about us has four times as nitrogen as oxygen;
or, to express it differently, in five liters of air
there are four of nitrogen and one of oxygen.
"We will stop here for to-day. To-morrow, let me
notify you in advance, our chemical experiments will
call for two live and uninjured sparrows. Set your
snares and catch them. I must ask you also to be
careful not to molest any of the various species of
garden birds, industrious hunters of insects and worms
that are the scourge of agriculture; but I gladly give
you free rein in regard to those pillaging sparrows
that, eager to find some tender foliage to tickle their
palates in the spring, fly down from the neighboring
roofs and nip my peas as fast as they sprout. I must
have two of these birds for our instruction and to
serve as a lesson to their brother marauders."