|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 |
PLANTS AT WORK
SHALL never forget," Uncle Paul resumed, "how rudely
one of my friends was treated by a noted cook. One
gala day he found the kitchen artist meditating on the
triumphs of his profession, as he stood watching the
various processes going on in his steaming pots and
pans. Broad of face, with a wealth of chins one under
another, an opulent nose richly adorned with pimples, a
majestic stomach, napkin tucked under his waistband,
cap of snowy linen—such was the man.
"The saucepans were simmering on the stove, and from
under the lids came whiffs of odors so delicious that
one could almost have dined by smelling them. A fat
capon stuffed with truffles and a young turkey
decorated with slices of bacon were roasting on the
spit. At one side a fat thrush redolent of juniper was
bestowing a part of its succulence on a slice of
"'Well,' said my friend, after the customary greetings,
pointing to one of the saucepans, 'what masterpiece of
your art have we here?'
"'Ragout of hare with plovers' replied the artificer of
tempting dishes, beaming with satisfaction and licking
his fingers as he lifted the lid. Immediately there
was wafted through the room a
 smell fit to awaken the demon of sensuality in the most
"My friend uttered words of high praise, and then
"'You are clever, as every one admits; but zounds! It's
not so very difficult a matter to cook good dishes when
you have good materials to start with, to make the
mouth water when you have a fat capon at your disposal,
or to create a most appetizing odor with a brace of
plovers. The ideal achievement would be to produce a
roast or a ragout with no capon, no hare, no bird or
beast of any kind. The old recipe, to make a hare pie,
first catch your hare, is too exacting. Hares are not
running about for every one to catch. It would be more
convenient if we could take something else, something
common and easy to get, and make our roast or ragout
out of that.'
"The cook was at a loss how to reply, so evidently
serious were my friend's words.
" 'What!' he exclaimed, 'a real hare ragout without any
hare, a real roast capon without any capon? And you
mean to say that you could do that?'
" 'No, not I; I am far from clever enough. But I know
some one who is clever enough, and compared with whom
you and your fellow artists are nothing but clumsy
"The cook's eyes flashed; the artist's self-esteem was
wounded to the quick.
" 'And what, if you please, does this master of masters
use? For I suppose he can hardly produce
 his delectable dishes with nothing at all to work
" 'He uses rather poor materials. Would you like to see
them? Here they are, all complete.'
"My friend drew three small vials from his pocket. The
cook took one. It contained a black powder, which the
culinary artist felt of, tasted, and held to his nose.
" 'It is charcoal,' he declared. 'You are fooling me.
Your charcoal capons must be fine eating! Let me see
another of your vials. Ha, this is water, or I am much
" 'You are right; it is water.'
" 'Now for your third vial. Why, there's nothing in
" 'Not so fast; there is something in it— air.'
" 'Air! Your air capons ought not to lie very heavy on
the stomach. Are you in earnest?'
" 'Very much in earnest.'
" 'No joking?'
" 'Not the slightest.'
" 'Your artist makes his capons out of charcoal, water,
air, and nothing else?'
"The cook's nose turned blue.
" 'With water, charcoal, and air you say he could make
this skewer of thrushes?'
" 'Yes, yes.'
"The cook's nose passed from blue to violet.
" 'And with charcoal, air, and water he could make this
pasty of fat goose-livers, and this pigeon stew?'
 " 'Yes, a hundred thousand times yes!'
"The nose, now attaining its last phase, turned
crimson. The bomb burst. The cook decided that the
man was a maniac who was making fun of him.
Accordingly he took my friend by the shoulders, spun
him round, and propelled him through the doorway,
throwing his three vials after him. Then the irascible
nose gradually returned from crimson to violet, from
violet to blue, and from that to its normal tint; but
the demonstration to prove that a capon can be made out
of charcoal, air, and water was never carried through."
"Of course your friend was only in fun, wasn't he, with
those three vials?" asked Jules.
"Not at all. His three vials really contained the
wherewithal to make the dishes the cook was preparing.
Have I not already shown you that charcoal, or carbon,
goes to the making of bread, meat, milk, and countless
other things we use as food? Remember the slice of
bread left toasting too long, and the mutton-chop
forgotten on the broiler."
"I see now. Your friend was speaking of the chemical
elements. Carbon is one, and that was in the first of
the three vials. How about the other two?"
"The second is just as easy to account for. Hold a
pane of glass over the smoke rising from a slice of
bread when it is just beginning to burn on the stove,
and you will soon see the glass covered with a fine
film of moisture, exactly as if you had breathed upon
it. This moisture comes from the rising vapor, and the
latter from the bread. Therefore
 bread contains water, considerable water in fact,
however dry it may appear to be. If we could extract
all its moisture from a mouthful of bread, you would be
surprised at its quantity. It would astonish you to
learn how much water we eat at every meal."
"But we don't eat water, we drink it," objected Emile.
"I say we eat it, for as it is found in bread it does
not run, does not wet anything, does not quench thirst.
It is solid rather than liquid, dry rather than wet,
something to be chewed rather than drunk. Or, better,
it is no longer water, but something else that unites
with air and carbon to make bread."
"Well," assented the boy, "I'll admit there must be
water in bread because it shows on a piece of glass
held over a slice of toast that is beginning to burn.
But there is still another vial to account for, the one
"Here it will be impossible, with the simple means at
our disposal, to furnish proof. Of the three
substances named as being present in our food I have
accounted for two, carbon and water; the presence of
the third you must accept on faith."
"Agreed unanimously: there is air in bread. What other
wonderful things are you going to tell us about?"
"We will see. This much, first, is agree upon: bread
is composed of carbon, air, and water, which combine in
a certain way, merge into one another, and cease to be
merely carbon, air, and water, by becoming something
else quite different from any
 one of the three. White has come out of black, savor
out of insipidity, nutritive qualities out of
"Meat subjected to the action of fire teaches the same
lesson: it turns to carbon and emits fumes containing
the constituents of air and water. We will go no
farther, for our inquiries would always meet with the
same answer. All that we eat or drink, all that goes
to nourish us, is reducible to water, carbon, and air.
Everything found in an animal's body, everything in a
plant, is, with very few exceptions, made of nothing
that is not found in water, carbon, or air. Let us be
still more explicit. Carbon, being a simple substance,
an element, is always carbon and nothing else; but
water is composed of hydrogen and oxygen, and air of
oxygen and nitrogen. Hence the four elements, carbon,
oxygen, hydrogen, and nitrogen, are the materials of
which all things in the plant and animal world are
almost entirely made.
"So my friend with his three vials was speaking the
truth, for all the savory dishes prepared by the cook
were reducible to carbon, air, and water. In those
little bottles were actually the elements, the prime
ingredients, contained in roast capons, pigeon stews,
pasties of fat goose-livers, cream tarts, and so on;
but to put them together and make them into food, which
chemistry in its brutal operations knows only how to
destroy, the artist was lacking, the great artist of
whom my friend spoke."
"And who is this artist?"
"Vegetation, my young friends, or, more
par-  ticularly, grass. At the grand banquet spread for all the world,
three dishes only are served, though they take an
infinite variety of forms. From the epicure who dines
on the choicest of delicacies contributed by every
quarter of the globe, to the oyster that fills its
belly with slime washed up by the waves; from the oak
whose roots suck in nourishment from an acre of ground,
to the mold on a piece of cheese—all draw upon the
same source of supplies, all feed on carbon, air, and
water. The only difference lies in the way these
ingredients are prepared. Both wolf and man—the
latter not unlike a wolf in his kind of food and in
other respects also—eat their carbon as it is
served tot hem in sheep, while the sheep finds its
carbon in grass, and grass— Ah! Here we come to
the point that shows vegetation to be the feeder of the
world, with wolf, sheep, and man wholly at its mercy.
"In animal flesh both man and wolf find carbon, air,
and water served up in compact form as a savory dish,
while in grass the sheep finds them just as skilfully
prepared, though less savory and less compact in form.
But vegetation itself, so nourishing to the sheep, so
well fitted to be made into sheep's flesh for the
sustenance of man and for the building of his
body—with what sauce does it eat its carbon and
air and water?
It eats them with no sauce whatever, but in their
natural state, or very nearly so. Blessed with a
stomach truly marvelous in its capabilities, the plant
digests carbon and takes in air and water, and out of
these three substances, which no other
 form of life will deign to touch as nutriment, makes
the forage that hands on to the sheep its needed supply
of carbon, oxygen, hydrogen, and nitrogen, all
thenceforth united in nutritious form. The sheep takes
up the preparation of these elements as found in the
blade of grass and carries it further, improving it a
little and turning it into flesh that finally, by the
slightest possible change, becomes man's or wolf's
flesh, according to the consumer."
"I begin to see how it all comes about," said Jules:
"man makes his flesh from sheep's flesh and from the
various other things he eats, the sheep makes its flesh
from the grass it browses, and grass is made of carbon
and the elements in air and water. So it is the plant
that, in the beginning, prepares all our food for us."
"Yes, the plant, and only the plant, has that important
task. Man gets the materials of his body either from
the plant itself or from the sheep and other animals
that contain those materials already prepared; the
sheep or other grazing animal gets them from the plant,
where they are found in an advanced stage of
preparation; and the plant alone gets them from the
original source, eating the uneatable, carbon and the
elements in air and water, and, by a marvelous process
of which it alone knows the secret, converting them
into nutriment fit for the sustenance of animal life.
So, then, it is vegetation, finally, that spreads a
table for all the earth's inhabitants. Were its work
to cease, all forms of animal life, absolutely all,
unable to derive nourishment from carbon in its natural
state or from air or
 water, would perish of hunger, the sheep for want of
grass, the wolf for want of sheep, and man for want of
any and every kind of food.
"I see now," said Emile, "why you called the plant the
great artist that knows how to make everything with
what was in your friend's vials. It does it all with
carbon, air, and water."
"The plant does not eat as we do: it soaks in its food;
that is, carbon, for example, is not consumed by it in
the natural state known to you as fine black powder,
but after it has first been changed from its solid form
and dissolved. Now, the solvent of carbon is oxygen,
which converts it into carbonic-acid gas, and that is
the plant's chief food."
"You say plants live on carbonic-acid gas, that fatal
gas that kills us if we breathe a few breaths of it?"
"Yes, my lad, it lives on what would kill us, prepares
our food by using what would be death to us if there
were enough of it around us. Remember that whatever
breathes, whatever burns, whatever ferments, whatever
decays, sends out carbonic-acid gas into the
atmosphere. The atmosphere, receiving these fatal
emanations, would therefore in the course of centuries
become unbreathable and suffocating to all animal life
on the earth if other agencies did not forestall this
accumulation of the deadly gas. Let us now see, to
begin with, what statistics have to say as to the
amount of carbonic-acid gas that is continually being
"The carbonic-acid gas exhaled by a man in twenty-four
hours is estimated at about four hundred
 and fifty liters, which would represent two hundred and
forty grams of burnt carbon and four hundred and fifty
liters of oxygen taken from the air to effect this
combustion. At this rate the carbonic-acid gas
produced in a year by the whole human family would
amount to about one hundred and sixty billion cubic
meters, which represents eighty-six billion, two
hundred and seventy million kilograms of burnt carbon.
Piled in one heap, this carbon would make a mountain a
league around at its base and from four hundred to five
hundred meters high. Such is the quantity of fuel
required for the maintenance of man's natural heat.
All of us together eat carbon to this extent, and in
the course of a year we breathe it out, a breath at a
time, in the form of carbonic-acid gas. Then we start
on the consumption of another pile of the same size.
How many mountains of carbon, then, since the world
began, must mankind have breathed out into the
"We have also to take into account the vast variety and
extent of animal life on land and in the sea, and its
requirements in the way of carbon, requirements that
would in the course of a year represent a mountain of
perhaps the size of Mont Blanc. Animals far outnumber
us, abounding as they do all over the earth, including
oceans as well as continents. What a quantity of
carbon to keep the flame of life burning! And to think
that it all sooner or later goes into the air as a
fatal gas, a few breaths of which would quickly kill
"Nor is that the whole story. Fermenting
sub-  stances, like the juice of the grape and like the dough
that is to be baked into bread, and all decaying
matter,—such as, for instance, is found in the
form of manure spread over a cultivated
field,—these, too, are rich sources of
carbonic-acid gas. Even if the manure is of no great
strength it will send out one hundred cubic meters or
more of carbonic-acid gas in a single day for every
acre of land on which it is spread.
"Coal, wood, charcoal, and other fuel used for heating
our houses, and the great quantities of coal needed for
running our factories-do not these also contribute to
the atmosphere their share of the harmful gas we are
speaking of? Just think of the quantity of
carbonic-acid gas vomited into the air from the
smoke-stack of a great factory that consumes coal by
the car-load! Think, too, of the volcanoes, those
giant natural chimneys that in a single eruption throw
up enough of this gas to make the belchings of a
factory furnace seem like a mere whiff on the breeze.
"It is evident that carbonic-acid gas is constantly
being poured into the atmosphere in torrents that defy
computation; and yet animal life has no reason to fear
suffocation, either new or in the future. The
atmosphere, continually being tainted, is as
continually being purified: as fast as it is laden with
carbon it is purged of it. Now, the health-office
charged with the safeguarding of the general physical
welfare is the plant, my little friends, the plant that
lives on carbonic-acid gas to prevent our dying by
breathing it, and with it prepares the food that
 is to sustain us. This fatal gas in which is taken up
so much of the putrefaction of all things is the
plant's chief sustenance. To the plant's wonderful
stomach, putrefaction is satisfaction. What death has
cut down, the blade of grass builds up again.
"It is plain enough that there is never any lack of
carbonic-acid gas in the air we breathe, and also that
it does not accumulate to the point of becoming a
menace to life, as one might at first infer from the
abundance in which it is produced. In this dish is
some lime-water that I poured out yesterday, when it
was perfectly clear. Look at the surface and you will
see a delicate transparent crust, which cracks and
breaks if you touch it with the point of a pin. It
might be taken for a thin sheet of ice. What can it
be? The answer is plain: the air, coming into contact
with lime-water, has yielded to the latter some of its
carbonic-acid gas, and carbonate of lime has
consequently formed, not in this instance as a white
chalky powder, but as a transparent crystalline sheet."
"I've often noticed," said Jules, "the same sort of
crust on water in which lime has been slaked for making
mortar. I should have taken it for ice, but as it
didn't melt in the summer sun I concluded it must be
"It was carbonate of lime, formed exactly like that in
this dish by the union of carbonic-acid gas from the
atmosphere with lime dissolved in the water. Now that
our talk has led to this subject, let us say a little
more about mason's mortar. You know how it is
prepared. The lime-burner first
 heats a mass of broken limestone very hot in a
lime-kiln, and the heat drives out the carbonic-acid
gas, leaving the lime by itself. This lime the mason
slakes with water and mixes with sand, thus producing
mortar, which is laid by the trowel between the stones
that go to make a building. At first a soft paste that
readily fills in all empty spaces, it gradually becomes
impregnated with carbonic acid from the atmosphere,
this process being aided by the loosely compacted
grains of sand in the mortar, and finally, in
consequence of the union of the carbonic acid with the
lime, turns to stone as hard and firm as that from
which the lime was originally produced. In course of
time, therefore, the hardening of the mortar being
accomplished, the entire structure of stone and mortar
becomes welded into one solid mass, so that often the
stones themselves, if one tries to separate them, will
break before the mortar will relax its hold. It is,
then, carbonic-acid gas from the atmosphere that
hardens the mason's mortar by turning the lime it
contains back into limestone.
"There is always, as I have said, carbonic-acid gas in
the air around us: the hardening of mortar and the
forming of a brittle crust on lime-water when exposed
to the air prove this sufficiently. But there is not
much of this gas thus floating about us; for if the
chemist subjects the air to delicate tests such as are
beyond the resources of our modest laboratory, he finds
that never and nowhere is there more than one liter of
carbonic-acid gas in two thousand liters of air. What
becomes, then, of the
 enormous volumes of this gas continually being added to
the atmosphere? Vegetation feeds upon it and thus
causes it to disappear, as we shall soon see.
"The surface of a leaf is riddled with numerous
excessively small holes called stomata, or mouths. On
a single leaf more than a million can be counted; but,
being so thickly assembled in so small a space, they
are of course too small to be seen without a
magnifying-glass, a microscope. I cannot show them to
you in their natural state, but only as represented in
this picture. Well, through these tiny mouths the
plant breathes, not pure air as we do, but poisoned
air, fatal to the animal, but life-giving to the plant.
It inhales, through these millions of myriads of
stomata, the carbonic-acid gas dispersed throughout the
atmosphere, receiving it into the substance of the
leaves, where under the action of the sun's rays an
incomprehensible process is accomplished. Stimulated
by the light of the sun, the leaves work upon the fatal
gas and rid it completely of its carbon. In other
words, they decompose the carbonic-acid gas, undo what
combustion has done, separate the carbon from the
oxygen combined with it.
STOMATA, HIGHLY MAGNIFIED.
"You must not think it is any easy task to restore to
their original condition two substances combined by
burning, by oxidizing. The chemist will have to
exercise his utmost ingenuity and use his most
po-  tent drugs if he wishes to break the hold that carbon
and oxygen have on each other in carbonic-acid gas.
Well, it is just this task, which would tax the
resources of a chemical laboratory, that the leaves
accomplish quietly, without effort, instantaneously,
but only on the express condition that the sun gives
"If the sun does not shine, the plant can do nothing
with carbonic-acid gas, which is its chief food. Then
it languishes in a half-starved condition, reaching out
as if seeking the much-needed light and losing the
green color, the hue of health, from its leaves and
stems, until finally it perishes. This sickly state
caused by lack of light is called etiolation, or
bleaching. In market-gardening it is resorted to for
the purpose of making certain vegetables more tender
and their flavor less strong. Thus it is customary to
tie closely together the stems or stalks of a plant
used for salad, in this way keeping the sunlight from
the central portion and causing it to turn white and
tender. So, too, it is usual to heap up the earth
around the stalks of artichokes and celery, as their
flavor would be unbearable without this treatment of
darkness. Lay a tile flat on the grass, or invert a
flower-pot over a plant, and after a few days you will
find the matted grass of the shaded plant yellow and
"But when, on the other hand, a plant receives the
sun's rays in full force, carbonic-acid gas is
decomposed in no time, the carbon and the oxygen
separating and each resuming its original attributes.
Freed of its load of carbon, the oxygen becomes
 again what it was before the union took place; it is
once more a breathable gas, if diluted with nitrogen, a
gas that will support life and make a fire burn. In
this pure state it is given out by the stomata to take
its part again in combustion and respiration. It
entered the leaves a fatal gas, it departs a vivifying
gas. It will find its way back some day with a fresh
load of carbon, deposit its burden in the plant's
storehouse, and, once more purified, recommence its
atmospheric round. Bees go and come, one after
another, from the hive to the fields and from the
fields to the hive, by turn, in the one instance
lightened of their heavy load and eager for a fresh
burden, and in the other laden with honey and winging
their way heavily back to the hive. Oxygen is the
swarm of the plant hive: it reaches the stomata with a
load of carbon taken from the veins of animals, from
burning fuel, or, it may be, from substances undergoing
decay, and it gives this carbon to the plant and then
departs on its untiring round.
"As to the carbon that the leaves separate from the
oxygen, it remains in the plans and enters into the
composition of the sap, turning finally into sugar,
gum, oil, starch, wood, or some other vegetable
substance. Sooner or later these substances are
decomposed by the slow combustion of decay, or by the
less gradual combustion that takes place in animal
nutrition, and the carbon once more enters into the
formation of carbonic-acid gas and returns to the
atmosphere to feed another generation of plant life,
which will hand on to animal life the food products
 it has with the help of this carbon manufactured.
"Now I will ask Emile if he remembers that old tree
stump we were talking about that was some day, it might
be, to contribute its carbon to the making of a slice
of bread and butter to eat. Does he remember the oak
that was to give of its carbon to produce a loaf of
white bread or some other article of food? Was I not
right in saying it is quite possible that to-day we
eat, in the form of a buttered roll, what we some time
before burned on the hearth as a stick of wood?"
"I haven't in the least forgotten," replied Emile, "how
puzzled I was when you told us those things might some
day give us our bread and butter. Now I begin to see
how it might come about. A stick of wood burns in the
fireplace, and its carbon goes out of it combined with
oxygen, making carbonic-acid gas, which is scattered in
the air. Plants take in this gas as food and, the next
thing we know, the carbon has turned to flour in the
grains of wheat, or it may have become grass and been
eaten by cows to make butter; and so we have the slice
of bread and butter all complete. And then there's no
reason why this carbon from the stick of wood, after it
has traveled through the air, should not become a stick
of wood again and be burned once more in a fireplace,
so that it might go the same round again and again, no
one knows how many times."
"Yes, my boy, it can keep going back and forth in that
way indefinitely; for the same carbon is forever
passing from atmosphere to plant, from plant to animal,
and from animal to atmosphere,
 this last being the common storehouse whence all forms
of life derive the principal material of which they are
made. Oxygen is the common carrier of this material.
The animal gets its carbon from plants or from other
animals, in the form of food, and in the end makes
carbonic-acid gas out of it, with the help of oxygen,
and out it goes into the air. Plants take this
unbreathable gas from the air and give back pure oxygen
in return, using the carbon in making food for men and
animals. Thus the two kingdoms, animal and vegetable,
help each other, the former making carbonic-acid gas to
feed the latter, and this in turn making breathable air
and nutritious substances out of the fatal gas."
"Those are the most wonderful things you have told us
yet," declared Jules, deeply impressed by these
marvelous transformations. "When you began to tell us
about the vials that made the cook's nose turn blue, I
thought it was going to be just a funny story, and
never dreamed it would turn out to be so interesting
and so serious."
"Yes, my child, what I have just told you is indeed
interesting and serious, perhaps too serious for one so
young as you; but I could not resist the temptation to
acquaint you with the beautiful concord existing
between the plant that feeds the animal and the animal
that feeds the plant.
"Let us now descend from these heights and go on to
another experiment. We wish to prove that plants do
really decompose carbonic-acid gas. The simplest way
to do this is to let the operation go on under water, a
method that enables us to observe
 the release of the gas,—that is the oxygen,—and to
collect it. Ordinary water always contains a little
carbonic-acid gas in solution, obtained either from the
soil or from the atmosphere; therefore we shall not
have to supply this to the immersed plant.
"Into a wide-mouthed glass jar filled with ordinary
water we put a recently cut plant in full leaf. A
water-plant is preferable, as with it quicker and
longer-continued results are obtained. We next invert
the jar with its mouth in a bowl of water, and then set
the whole thing in the sunlight. Soon the leaves are
covered with tiny bead-like bubbles, which rise to the
upper end of the inverted jar and accumulate there,
forming a layer of gas. This gas, as has been proved
by trial, will rekindle a match that has just been
extinguished, provided by trial, will rekindle a match
that has just been extinguished, provided it has a
spark left; and thus the gas is shown to be oxygen.
Hence the carbonic-acid gas dissolved in the water must
have been resolved by the leaves into its original
elements, the oxygen being set free and the carbon
remaining in the leaves.
"But let us put aside our laboratory outfit and resort
to the simplest possible proof of the fact in question.
Let us go to the nearest pond, where, in some stretch
of still water, we shall find a population of tadpoles
living and flourishing, either lying in the sun at the
water's edge or swimming out into the deeper part,
where they frisk and play in freedom. In this pond,
also, are to be found various mollusks crawling slowly
along, and small shell-fish propelling themselves by
jerks as they lash the water with the end of their
tail; larvae, too, encased
 in little molds of fine sand, and black leeches lying
in wait for their prey; and finally, sticklebacks,
graceful little fish armed with spines on the back,
hence the name.
"All these creatures, of whatever sort, breathe oxygen
but it is oxygen held in solution by the water. If the
vivifying gas were lacking in the pond, all this
teeming population would infallibly perish. Another
danger menaces it, also. The bed of the pond is black
mud, being an accumulation of decaying matter such as
rotting leaves, dead plants, ejections from the aquatic
population, the lifeless bodies of various kinds of
tiny creatures, and other refuse. This bed of
decomposing matter is continually throwing off
carbonic-acid gas, as fatal for the stickleback and
the tadpole to breathe as for us. How, then, is the
water kept clear of this unbreathable gas and enriched
with life-giving oxygen for the maintainence of the
"Water-plants perform this office of sanitation by
feeding on the dissolved carbonic-acid gas, decomposing
it under the sun's rays, and giving out oxygen in its
place. Decay supports the plant, and the plant
supports the animal. Among the various kinds of plants
entrusted with the sanitation of stagnant water I will
mention the confervae, that is to say the delicate,
green, thread-like growths that overlay the floor of
the pond or other body of fresh water with a sort of
thick velvet carpet, or float
 about in jelly-like flakes. Put one of these plants
into a bottle of water, and after a short exposure to
the direct rays of the sun you will see the plant
covered with innumerable tiny beads of gas. These are
bubbles of oxygen from decomposed carbonic-acid gas.
Caught in the sticky network of the water-plant, these
bubbles increase until they finally buoy up the plant
and so raise it, all covered with foam, to the surface
of the water.
"This experiment calls for no special outfit. Break
off a green fragment from some aquatic plant, put it
into a glass of water, set the glass in the sun, and
soon you will see your little oxygen factory in full
operation. When the process is well under way, set the
glass in the shade, and the release of gas will stop at
once; but put the glass back in the sun, and the
formation of gas-bubbles will promptly begin again,
thus proving the need of the sun's rays in this
wonderful process. I cannot imagine a more beautiful
or lucid experiment. It is, too, so simple that I
leave you to perform it yourselves.
"The bit of green water-plant making breathable gas in
a glass of water set in the sun, will enable you to
understand the work of sanitation accomplished in large
bodies of water by aquatic vegetation just as a like
purification of the atmosphere is effected by
terrestrial vegetation. All the green plants of
various kinds growing in a standing body of fresh water
become covered with tiny beads of oxygen if they
receive the sun's rays to help them in their work, and
this oxygen dissolves in the water and gives it new
life. It is thus by means of the lowest
 forms of vegetation that standing water, instead of
becoming pestilential, may be kept in a condition to
support innumerable species of aquatic life.
"From all this you may learn a little lesson that will
perhaps be of use to you. How many times you have
tried to keep sticklebacks alive in a glass jar! But
the attempt has always failed. In water not frequently
renewed the little fish soon died, perishing as soon as
the small amount of oxygen contained in the water was
exhausted by their breathing. Hereafter, if you wish
to succeed, put a good-sized clump of confervae into a
jar. Plant and fish will help each other, the plant
supplying the stickleback with oxygen, and the
stickleback providing carbonic-acid gas for the plant;
so both will prosper even in unrenewed water. In
short, then, if you would keep your water animals
alive, do not forget to give them their indispensable
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