THE
FOOD OF PLANTS
A. P. LAURIE
i
THE FOOD OF PLANTS
THE
FOOD OF PLANTS
AN INTRODUCTION
TO AGRICULTURAL CHEMISTRY
BY
A. P. LAURIE, M.A., B.Sc.
Fellow of King s College ', Cambridge
WITH ILLUSTRATIONS
MACMILLAN AND CO.
AND NEW YORK
1893
A II rights reserved
PEEFACE
THIS little book has been written as an experimental
introduction to Agricultural Chemistry for beginners,
and I have therefore not assumed any knowledge of
chemistry on the part of the reader. On the other
hand, he will have, in the course of carrying out the
experiments described in the text, occasionally to
perform operations which he cannot fully understand
the meaning of without some little knowledge of
chemistry. It would, therefore, be advisable to
combine the study of the Chemistry Primer with the
study of this book.
I have been long convinced that science can be
taught only in the laboratory or in the field, and
that it is of educational value only in so far as it
presents a logical course of reasoning based on ex-
periment to the young student. Accordingly I have
tried, as far as possible, to keep this method of
instruction in view, though I have been compelled,
especially in the last chapter, to give a good deal
of general information for which experimental proof
vi THE FOOD OF PLANTS
is wanting in the text. On the whole, however, an
experimental course has been developed in the series
of lessons.
The book is intended neither for reading in the
study, nor for supplying suitable experiments for
the lecture table. The student is supposed to himself
perform the experiments under the guidance of a
teacher. With this in view, I have taken pains to
make the experiments simple, and the materials
required inexpensive, so that all classes of schools
might find the course of instruction within their
capacity and their means.
A student who has been carefully through the
experiments will find that he can read a work such
as Fream's book on Agriculture with intelligence.
He will not, however, be able to pursue the study of
the chemistry of agriculture further, in a thorough
and scientific sense, without first mastering the
principles at least of chemistry. He should, accord-
ingly, be familiar with Eoscoe's Elementary Chemistry,
or a work of similar character, before involving
himself in the chemistry of agriculture.
I cannot conclude without thanking Mr. Wallace,
Professor of Agriculture in the Edinburgh University,
for the valuable assistance he has given me with the
pr°°fs- A. P. LAURIE.
CONTENTS
CHAPTER I
-•-•
THE PLANT AND WATER
PAOE
Introduction . . . . . 1
The Root ..... .2
The Plant requires Water . . . . .3
The Plant Drinks through the Roots . . .4
The "Water passes up from the Roots through the Stem
and into the Leaves . . . . .4
The Water passes off from the Plant into the Air by
Openings in the Leaves . . . .7
CHAPTER II
THE FOOD OBTAINED BY THE PLANT FROM THE SOIL
Some Substances are Soluble in Water . . .11
Soluble Substances can pass into the Roots . .13
The Food is left in the Plant when the Water evaporates 14
The Soil is partly Soluble in Water . . .15
The Plant Food in the Soil is only slightly Soluble . 17
vin THE FOOD OF PLANTS
CHAPTER III
THE NATURE OF THE SOIL
PAGE
The Soil contains Sand and Clay . . . .21
The Improvement of Clay Soils . . . .22
The Amount of Water in the Soil . . . .22
The Soil should not contain too much Water . . 24
The Soil contains decaying Remains of Plants called
Humus . . . . . .25
The Subsoil contains little Vegetable Matter . .26
The Way the Soil has been Formed . . 27
CHAPTER IV
THE SUBSTANCES OF WHICH A LEAF IS COMPOSED
Four-fifths by Weight of the Leaf is Water . . 30
The Leaf contains Water, Charcoal, and Ash . .31
Part of the Food of Plants from broken-down Rocks . 31
The Effect of Farming on the Soil . . . .31
How the Exhaustion of the Soil is Prevented . . 33
The Ash contains among other Substances Potash and
Phosphoric Acid . . . . .34
CHAPTER V
HOW PLANTS OBTAIN FOOD FROM THE AIR
The Seed obtains Food from the Air ... 40
The Food obtained from the Air is Charcoal . . 40
The Air is Altered by Burning Substances . . .43
The Air is Changed by the Breathing of Animals . . 44
Vitiated Air restored by Plants in Sunlight . . 45
CONTENTS ix
CHAPTER VI
THE COMPOSITION OF THE AIR AND THE PREPARATION
OF CARBONIC ACID GAS
PAGE
The Action of Vitiated Air on Lime Water . . 48
Vitiated Air is Produced by burning Charcoal . . 48
The Charcoal combines with the Air to form a Gas . 50
The Action of burning Phosphorus on Air . . .51
The Phosphorus removes Part of the Air . . .52
The Air contains two Gases, Oxygen and Nitrogen . 55
Oxygen set Free by Plants in Sunlight . . .56
CHAPTER VII
THE NITROGEN REQUIRED BY PLANTS
Ammonia contains Nitrogen . . . .58
Plants cannot absorb Nitrogen directly . . .59
The Natural Order, Leguminosse, and the Absorption of
Nitrogen . . . . . .59
Nitrogen Compounds obtained from the Decay of Plants . 60
Nitrogen Manures . . . . . .60
CONCLUSION . 61
APPENDICES
I. NOTES ON THE EXPERIMENTS
II. ON THE USE OF THE BALANCE
List of Apparatus and Chemicals required . . .74
CHAPTER I
THE PLANT AND WATER
Introduction
WHEN we walk through the country we see the
flowers growing in the gardens, the trees growing in
the forest, the grass growing in the meadow, the
corn growing in the field. All these different plants
require food or they would not live and grow ; and
yet they do not feed in the same way as animals,
for they cannot walk about in search of food, nor
have they a mouth and teeth to eat with.
Let us try and. find out where a plant gets its
food, and what sort of meat and drink it requires.
If we take a seed and put it in the ground, we
shall find after a few days that the seed has begun to
sprout and throw out little green leaves. The
young plajit has begun to grow, and must be getting
food in some way to build up leaves and stem.
Now pull it up, and you will find that besides push-
ing up leaves above ground into the open air it is
THE FOOD OF PLANTS
CHAP.
pushing a root covered with fine hairs down into
the ground. The young plant must be getting its
food either through the roots
or through the leaves; or
perhaps by means of both.
We have then one part
of the plant, the root, below
ground, and another part, the
stem and leaves, above ground.
We shall look at each of
these parts by themselves, and
try and find out if they have
anything to do with getting
food for the plant.
The Root
Let us begin by looking
at the root. You will notice at once that it is
covered with little branch roots or hairs, pushing
their way into the earth in all directions, as if in
search of something. We do not yet know, how-
ever, if this root is searching for and obtaining food
for the plant. Let us try and find out, by making
a few simple experiments.
Experiment 1
Pull up a plant, cut the root off, and then plant it
again. In a short time the plant will wither and
i THE PLANT AND WATER 3
die, showing that the root was probably getting food for
the plant out of the earth. In some cases, it is true,
if we cut a slip from a plant and put it in the ground,
it will live and grow, but this is because fresh roots
are formed at the end of the slip under the earth,
and pushed out into the soil. We may therefore
conclude that without a root a plant cannot live.
The Plant requires Water .
In order to live we require both food and drink,
and would soon die if deprived of water. Let us
see if water is required by the plant.
Experiment 2
In order to find out if a plant requires water,
place one in a flower -pot, and keep it without
water for a few days. It will soon wither and die,
showing that it cannot live without water. If a flower
is placed under shelter where the rain cannot fall on
it or moisture reach it, you must water it every day,
or it will die. In England the trees and grass and
flowers get all the water they require from the rain,
but in some countries where there is little or no rain,
canals have to be dug, bringing water from a river
or some other source, to supply the plants.
4 THE FOOD OF PLANTS CHAP.
The Plant Drinks through the Roots
Having found out that the plant must have a root
and be supplied with water, we now wish to know
whether the plant drinks up the water through the
roots or gets it through the leaves.
Experiment 3
In order to find this out, place a plant in a
flower-pot, under shelter, and water it every day,
taking care not to wet the leaves, but only the earth
round the roots. The plant will grow well, showing
that the roots, and not the leaves, suck in the water that
the plant requires.
This water is obtained by the roots from the
soil, which is nearly always moist a little below the
surface, holding the water just as a sponge does.
The Water passes up from the Roots through
the Stem and into the Leaves
Let us try some more experiments, so that we
may make sure that the water is drawn up by the
roots and find out what becomes of it.
Experiment 4
Pull a young plant up by the roots, and shake
it gently so as to remove the earth, and then place
I THE PLANT AND WATER 5
it in a vessel containing some water in which a
little eosine red * has been dissolved.
The water, you will notice, is coloured a bright
red by the eosine, and we shall therefore be able to
tell if the water is sucked up by the roots, because if
it is we should be able to follow its path through the
plant by means of the red dye.
We cannot see anything going on at first, but if
we examine the plant after some twelve hours we
shall find all the fine veins in the leaves stained
red, showing that the water, carrying with it the dye,
has passed through the roots, up the stem, and into
the leaves.
Let us now vary this experiment, and see what
we can learn from it.
Experiment 5
Take a young plant as before, and shake off the soil
from the roots. Next take a bottle with a fine tube
fixed in near the bottom, and rising up the side of
the bottle, as shown in the drawing. Then boil
some water, cool it, and pour it into the bottle, so
as to fill it up to the neck. Next place the roots
of the plant in the bottle, and run some melted
bees'-wax into the neck of the bottle round the stem
of the plant.
The plant is now cemented into the bottle.
Place the plant out in the sun, taking care to shade
1 A penny packet of aniline dye will do.
THE FOOD OF PLANTS
CHAP.
FIG. 2.
i THE PLANT AND WATER 7
the bottle from the sun's rays. In a short time you
will notice that the water is falling in the side tube,
showing that the plant is rapidly drawing up water.
You will find that the plant will live for some days,
the water sinking meanwhile lower and lower in the
tube and in the bottle.
The plant is evidently then taking up a great deal
of water, and constantly doing so. Where does this
water go to ? Does it remain in the plant, or pass
off into the air 2
We can easily find out if the water remains in the
plant or not, by weighing the plant and bottle full
of water at the beginning of the experiment, and
again at the end of the experiment. If it weighs
the same at the end as it did at the beginning, the
water has evidently passed from the bottle into the
plant and stayed there. If it weighs less, the water
must be in some way escaping from the plant.
The Water is passing off from the Plant into
the Air by Openings in the Leaves
Experiment 6
In order to find this out, we can repeat the last
experiment in a slightly different way. Break a
small branch covered with leaves from a bush, and
take a wide -mouthed bottle fitted with a cork.
Drill a hole in the cork large enough for the branch
THE FOOD OF PLANTS
CHAP.
to pass through.
Cut the cork in half through the
middle of this hole. Fit
the cork closely round the
branch. Nearly fill the
bottle with water, and
insert the cork with the
branch. Place the bottle
on a balance, weigh it,
and note the weight.
Then take the bottle off
the balance and place it
out in the sun as before.
In a short time the. water
will begin to sink in the
bottle, showing that the
broken end of the stem
is able to draw up the
water. After it has been
for a few hours in the
sun weigh again. It now
weighs much less, show-
ing that the water has
escaped into the air.
If we now pick off the
leaves, the water will practically cease sinking in
the bottle, and the bottle will no longer lose weight
appreciably.
Evidently then the water is escaping from the
surface of the leaves, and as it is not dripping from
them, it must be passing off in the form of vapour.
i THE PLANT AND WATER 9
That water- vapour is escaping from the leaves
can further be shown by a very simple experiment.
Experiment 7
Pick a fresh green leaf, and lay it lightly lack
PIG. 4. — Section of leaf showing stomata.
downwards on a polished piece of metal (the lid of a
tin can). After a few seconds pick it up again.
The metal surface under the leaf is covered with
little drops of water, owing to the escaping vapour
condensing on the cold surface.
Now turn the leaf over, and place the front or
10 THE FOOD OF PLANTS CHAP, i
upper surface en the metal surface. Very little water
will now be found on the metal, showing that most
of the water-vapour is escaping from the under surface
of the leaf.
In order to find out why the water escapes from
the under surface more than from the upper surface,
you must examine the leaf under a microscope, so as
to magnify it. We then see that the under surface
is covered with tiny little openings or mouths called
stomata, from which the water-vapour escapes.
These stomata, however, have something else to
do as well as to breathe out water -vapour, as we
shall find out later on.
We now know that water is sucked in by
the roots, passes up the stem, and into the
leaves, and then passes off from the leaves as
water- vapour ; and that in this way the plant
gets what drink it needs to keep it alive and
growing.
CHAPTER II
THE FOOD OBTAINED BY THE PLANT FROM THE SOIL
WE must next try and find out whether the roots
obtain any other food for the plant besides water j
whether the stream of water passing through the
plant carries anything else with it which the plant
requires.
We have noticed in a former experiment that
when the water was coloured red, the water took the
red colouring with it into the plant. Let us try
and understand how this came about.
Some Substances are soluble in Water
Experiment 8
Take five small flasks, and place in one some
sugar, in the next some salt, in the next some blue
crystals of sulphate of copper,1 in the next some sand,
1 Sulphate of copper is poisonous.
12 THE FOOD OF PLANTS CHAP.
in the next some whiting, and then add some water
to each and warm them gently over a spirit-lamp.
The salt, the sugar, and the sulphate of copper dis-
appear from sight ; the sand lies at the bottom un-
changed ; and the whiting mixes with the water,
but the water does not become clear. Now taste
the sugar water and the salt water. Evidently
from the taste the sugar and salt are still there, and
the blue colour of the sulphate of copper water shows
that the sulphate of copper also is still there. These
three substances have dissolved in the water. The
sand and whiting have not done so.
Now place five glass funnels in
a row, and fit a piece of filter-paper
into each, and empty the flasks,
each into a separate funnel.
The water comes through clear
in each case; but on tasting the
sugar water and salt water, we find
that the sugar and salt have passed
through the paper with the water.
The sulphate of copper water is still
blue in colour, showing that the
sulphate of copper has passed through.
But the sand and the whiting have been left behind on
the paper. It is now clear what we mean when we
say a substance dissolves or is soluble in water.
ii FOOD OBTAINED BY THE PLANT FROM SOIL 13
Soluble Substances can Pass into the Roots,
but Insoluble Substances cannot Pass
into the Roots.
Experiment 9
Now mix a little eosine red in water and filter.
The eosine red dissolves and passes through the
filter-paper. We thus see that the eosine red which
we already know can pass into the roots is also soluble in
water. Let us then see if a colour which does not
dissolve can pass into the roots also.
Experiment 10
Take a little red lead and mix it with water and
filter it. The red lead remains behind on the filter-
paper, showing that it does not dissolve. Now mix
some more red lead with water and dip the roots of
a plant into it, as you did in the case of the eosine
experiment. When we look at the plant next day
the veins of the leaves have not been coloured red,
showing that the roots cannot take up the red lead
because it does not dissolve in the water.
We thus see that some things dissolve in
water, and can then pass through filter-paper
and pass into the roots of the plants ; and that
other things do not dissolve in water, and
cannot pass through filter-paper or into the
roots of the plants.
14
THE FOOD OF PLANTS
CHAP.
The Pood is left in the Plant when the
Water evaporates
We now understand that any food the plant
obtains from the soil must first be dissolved in the
water, and that it can then pass up into the plant.
We also have learnt that the water evaporates from
the surface of the leaves. Let us see what will
become of the sub-
stances dissolved in the
water when this hap-
pens.
Experiment 11
To find this out,
pour the water con-
taining the salt, the
sugar, and the sul-
phate of copper into
three porcelain eva-
porating basins, and
place the basins over
a lamp. The water
will soon boil away, leaving the salt, sugar, and
sulphate of copper behind in the porcelain dishes.
We may see from this experiment that substances
dissolved in the water that is always passing into
the roots will remain behind when the water evapo-
rates from the leaves.
FIG.
ii FOOD OBTAINED BY THE PLANT FROM SOIL 15
Now if we suppose the soil to contain food for
the plant, which food is soluble in water, we can
understand how the plant may be fed by this
means.
The roots are always sucking up water,
which passes through the plant and evapo-
rates from the leaves, and this continuous
stream of water leaves behind the food it
brings with it, so that the plant is continu-
ally being supplied with fresh food.
The Soil is found to be partly Soluble in
Water
Let us now examine the soil itself to see if any
part of it is soluble in water or no.
Experiment 12
In order to find out what part of the soil is
soluble in water, take a little garden mould and
shake it up for some time with distilled water, and
let it settle. The clear water contains the part of
the soil which is soluble dissolved in it, and the rest
has settled down.
Pour off the clear water into a small evaporat-
ing basin and place the basin over a spirit-lamp.
The water will soon boil away, leaving a powder
in the bottom of the dish. This powder is the
16 THE FOOD OF PLANTS CHAP.
soluble portion of the soil, a portion of which passes
through the roots of the plant and forms part of
its food.
We have now found out not only that the
roots suck up water for the use of the plant,
but that this water contains certain parts of
the soil dissolved in it which are used by the
plant as food.
In the last experiment we used distilled water to
dissolve part of the soil. Why did we not use
ordinary tap water ? and what do we mean by dis-
tilled water ?
Take some tap or well or river water, place it
in the porcelain dish and boil it away. There is,
you notice, a residue left. Evidently the water was
not pure. Some things were dissolved in it which
were left behind when it was boiled away. We
could not therefore use this water for our former
experiment, as it is not sufficiently pure, and must
therefore obtain some pure water.
You have noticed that in boiling the water the
substances dissolved are left behind. If, then, we
could collect the steam which is passing away and
condense it — that is, bring it back into liquid again
— we should obtain pure water.
We can do this quite easily by the following
arrangement : —
ii FOOD OBTAINED BY THE PLANT FROM SOIL 17
Experiment 14
Place water in the retort A, and push the neck
of the retort into the condenser B. This condenser is
FIG. 7.
arranged so as to allow a stream of cold water to
flow in at (a) and out at (b), through the outer tube,
while the steam from the water in the retort passes
down the inner tube and is thus cooled and condensed.
Now place a lamp under A and let the water
boil vigorously. Soon drops of water will fall from
the end of the condenser into the flask. This is
pure or distilled water, obtained by condensing the
steam coming from the retort by means of the con-
denser.
The Plant Pood in the Soil is only slightly
Soluble
On boiling away the water which had been shaken
up with the garden mould, very little residue, we
found, was left (Experiment 12).
0
18 THE FOOD OF PLANTS CHAP.
From this it would seem that there was very
little store of plant food in the soil ; and it is true
that the greater part of the soil is useless as plant
food. But there is another reason why so little is
dissolved by the water. Some things dissolve easily
in water, while others dissolve only to a small extent.
Experiment 15
We can certainly dissolve almost as much sugar
as we please in water. But supposing instead of
sugar we take some gypsum, shake it up with dis-
tilled water, and filter. Apparently the gypsum has
not dissolved at all. However, we must make sure.
Boil the filtered water away, and notice that a slight
deposit is left, showing that the water has dissolved
a very little, but only a very little, of the gypsum.
If we continued to shake up the gypsum, always
adding fresh water, each supply of water would dis-
solve a little more, until all the gypsum was dissolved.
In the same way the soil contains a store of plant
food which is only dissolved little by little, year by
year. Furthermore, there are slow changes going on
in the soil which are changing valuable plant food
from an insoluble into a soluble state, and so making
it available for use by the plant.
We can now understand how the roots are
supplied with food from the soil.
The rain soaking into the earth dissolves such
soluble substances as it contains, and these are sucked
ii FOOD OBTAINED BY THE PLANT FROM SOIL 19
up by the roots along with the water. Some of them
may be of no use to the plant, but others are used by
the plant in building up root, stem, and leaves.
While a vigorous growth is taking place on the
soil this dissolved food is made good use of ; but in
autumn and winter, when the ground is bare, certain
kinds of valuable food are washed through the soil
and into the drains.
It is for this reason that the farmer often sows a
catch crop, as it is called, of Italian rye grass or some
other forage crop, which, coming up in September or
October, occupies the surface and sucks up the food
in the soil. In the spring this catch crop is ploughed
in as green manure, and, rotting, returns to the soil
the food, stored in it through the winter, in time to
feed the young plants which are sown in spring.
We have now learnt that there are certain
substances in the soil, soluble in water, which
are absorbed by the roots and are used as
food for the plant.
CHAPTEE III
THE NATURE OF THE SOIL
WE have now learnt that the plant obtains food
from the soil, and shall therefore next try a few
experiments with a view to finding out something
about the nature of the soil itself.
Experiment 16
Take a little dry garden soil and rub it down
in a mortar, and then sift it through some muslin.
Notice the small stones and pieces of root and
blackened portions of plants left in the muslin.
Clean the mortar and place the sifted soil back in it,
and half fill the mortar with water, and grind the
soil and water together ; then pour the muddy water
off into another vessel, taking care to leave the
soil that settles to the bottom in the mortar. Do
this several times with fresh water until the water
comes off clean and is no longer muddy. Examine
the soil left in the bottom of the mortar and you
will notice that it consists of sand.
CHAP, in THE NATURE OF THE SOIL 21
Allow the mud in the water you poured off to
settle, and then pour the water off. On examining
the mud you will find it to be a fine sticky clay.
"We have thus separated the soil roughly into
stones, remains of plants, sand, and clay.
If we examine soils brought from different
places we shall find different proportions of sand
and clay, some containing a large quantity of clay
being called heavy clay soils, others containing a
large proportion of sand being called light sandy
soils.1
Sand alone forms a very loose, powdery soil, in
which the roots of the plants get little hold. Water
also passes through it quickly, as we can easily prove
by fashioning the sand into a hollow cup and pouring
water into it.
Consequently sandy soil dries up quickly,
and the plants growing in it suffer from want of
water.
Clay, on the contrary, will not allow water to
pass through it easily. If we model a little cup out
of clay, and fill it with water, it will remain there
and not drain through, as is the case with the sand.
A clay soil does not let the water pass freely through
it, so that it may dissolve food for the plant, and
supply the roots.
A good soil, therefore, is a mixture of both these
bodies in suitable proportions.
1 " Heavy " here means difficult to plough, " light " easy to
plough. Bulk for bulk, sandy soils weigh more than clay soils.
22 THE FOOD OF PLANTS CHAP.
The Improvement of Clay Soils
If we take a piece of clay and heat it red hot,
when it cools it will no longer knead up with water
as before. A common red flower-pot, or a brick, is
such a piece of baked clay.
Pound a piece of brick into a fine powder in a
mortar and then mix it with water. It behaves like
sand, and allows the water to pass freely through.
Sometimes, therefore, when the soil contains too
much clay, the farmer pares off the surface, gathers
the clay of the subsoil into heaps, and burns it, and
then returns the baked clay to the soil.
This baked clay acts like a mixing of sand with
the clay, and keeps the soil open, so as to allow
water to pass more freely through, and dissolve
the food necessary for the plant.
The Amount of Water in the Soil
Experiment 17
Let us now take a moist piece of garden soil and
try and find exactly how much water it contains.
To do this properly, we must make it hot enough
to drive off all the water, but at the same time
we must not heat it too strongly, as you will see
presently.
THE NATURE OF THE SOIL
We had best, therefore, heat it to exactly the
temperature at which water boils. We shall then
be sure that the water is driven off, and at the same
time not make it hotter than is necessary. We can
do this most easily by drying it in a water-lath.
That is to say, you
place the mould in a
metal case surrounded by
water contained in an
outer case, and heat the
whole apparatus over a
flame.
The water in the outer
case boils and heats the
soil to just the right
temperature.
Weigh out about one ounce of the soil in a tin dish
(the round lid of a tobacco tin will do very well),
and place it in the inner case of the water-bath, and
heat it there for about an hour.
Then take it out, let it cool, and weigh again.
It will now weigh much less than before. We
cannot, however, be sure that all the water is gone.
Put it back in the water-bath, heat for another half
hour, and again weigh.
If the weight is the same as in the second
weighing, we may be sure that all the water is
gone. The soil will lose perhaps 15 or 20 per cent
of its weight, showing the amount of water it
contains.
FIG.
24 THE FOOD OF PLANTS CHAP.
The Soil should not have too much Water
In order that we may have a healthy growth of
plants, the soil should be moist, but not saturated
with water, so as to form a swamp. This condition
is best obtained when the natural surface of the
water is at some distance below the surface of the
soil.
A very simple experiment will enable us to
understand this.
Experiment 18
Fill a flower-pot with garden mould, first placing
some pieces of a broken pot in the bottom, and then
stand it in a pail. Now pour water into the pail
until it stands at the level of the top of the earth in
the flower-pot.
The water will quickly rise in the pot and turn
the earth to mud.
Now pour the water out of the pail, leaving only
two or three inches of water behind, and place the
flower-pot in the pail again.
A great deal of the water will then drain out
of the flower-pot, but the earth in it will remain
moist as long as there is any water in the pail.
The earth can evidently soak up the water
like a sponge or a piece of blotting-paper.
To make sure of this, take another pot and fill it
with dry earth, and place it in a pail with two inches
of water.
THE NATURE OF THE SOIL
25
In a short time the water will have soaked up
and moistened the dry soil to the top.
When, therefore, the natural level of the water is
too near the surface of the soil, thus making it
swampy, the farmer lays drains in the ground,
which drain away the water until it is at the level
of the drains.
The soil is then kept moist by the soaking up of
the water from this level, just as in the case of the
flower-pot placed in two inches of water.
The Soil contains Decaying Remains of Plants
We have already found that the soil contains
roots and portions of
plants. These decay,
forming a black substance
called humus, which will
burn away if the soil is
heated.
Experiment 19
Take a portion of
garden soil, dry it in a
water -bath, and sift it
through muslin. Next
take a crucible or a piece FIG. 9.
of platinum foil about three
inches by four inches, and bend up the edges so as to
26 THE FOOD OF PLANTS CHAP.
make a shallow tray, and put it on the balance and
weigh it carefully. Note the weight. Put some
of the dried soil in it and weigh again. Subtract
the first weight from the second, and thus get the
weight of dried earth.
Place the crucible or platinum dish on a pipeclay
triangle over a Bunsen flame or petroleum blowpipe, and
heat it strongly.
The soil begins to smoke and burn.
Keep up the heat until no more smoke is given
off, let it cool, and weigh it again. Again heat and
again weigh until the weight remains the same. It
is now much lighter than it was before, owing to the
loss of all the decaying remains of plants which
have been burnt away.
We thus find that the soil consists of
two portions, the decaying remains of plants
or vegetable portion which burn away, and
the mineral portion, consisting of sand, stones,
clay, and other things which does not burn
away.
The Subsoil contains little Vegetable Matter
If we now dig a hole in the garden, we shall find
that the dark surface soil is only a few inches deep, and
that underneath we come to earth of a different colour.
This is called the subsoil, and contains very little
decaying vegetable material.
in THE NATURE OF THE SOIL 27
Take a little of this subsoil, dry it, and repeat the
preceding experiment. It does not smoke, and loses
very little in weight, showing that it consists almost
entirely of mineral, and not of vegetable, substances.
If we dig deeper still, we shall find the rock by
the crumbling of which the soil was first formed.
The Way the Soil has been Formed
We can now understand how the soil has been
formed. We must imagine a hard surface of rock
where now there is soil. This rock has slowly
crumbled to powder, forming the mineral portion of
the soil (sand, clay, etc.). Plants sown by chance
seeds have sprung up, died, and decayed, forming the
vegetable portion of the soil. The mixture of the
two forming a soil suitable for future vegetable life.
The crumbling of this rock to form the soil has
been caused partly by the action of air and rain,
but also by the freezing of water which has soaked
into the pores of the rock.
When water freezes it expands slightly, and so
splits up the rock. When the thaw comes those
broken-off pieces fall apart. .
This action of freezing water can be easily tested.
Experiment 20
Take a small narrow-necked glass flask, and fill
it with water, and place it in a vessel containing a
28 THE FOOD OF PLANTS CHAP, in
mixture of ice and salt, and leave it there for a
few minutes. The water in the flask will soon
freeze, and on lifting it carefully out, you will find
the flask has been split in tiny pieces by the
expanding water.
Not only are the rocks thus broken up, but the
stones and coarser pieces of soil are crumbled finer
and finer every winter by the action of the frost.
The particles of dense clay are also separated, and
the surface is left in a powdery or tilthy condition
suitable for a seed-bed.
When the rain falls upon this finely-powdered
rock the water dissolves the soluble portions, and
the roots can penetrate more easily in all directions
in search of food.
We have learnt that the soil is a mixture
of broken-down rock and of decayed vegetable
stuff, and we have divided the mineral portion
roughly into sand and clay.
We have also learnt that the soil can suck
up moisture, and why it is drained.
We can now understand how the soil has
been slowly formed by the action of rain, air,
and frost, and the decaying of plants, passing
gradually from hard rock to rich garden
mould.
CHAPTER IV
THE SUBSTANCES OF WHICH A LEAF IS COMPOSED
WE can readily understand that the decaying vege-
table stuff supplies food for the plant, but we have
not yet decided whether the broken-down rock also
supplies it with food.
We can best decide the matter by examining a
leaf itself, and seeing of what it is composed.
Experiment 21
Pick a few leaves and weigh them. About one
quarter ounce is sufficient. Put them in a warm dry
place for a short time and weigh again. They are
now lighter than before, having lost some of the
water they contain. Place them in a water -bath
over a lamp, so that they may be heated to the
temperature at which water boils, and leave them
there for two or three hours; then remove and weigh
again. They are now dried up and will only weigh
30 THE FOOD OF PLANTS CHAP.
about one-fifth part of what they weighed before ;
all the water having been driven off in vapour.
We thus see that four-fifths, by weight, of
the leaf is water.
Take a piece of platinum foil about four inches by
three inches, and bend up the edges so as to make
a little platinum dish.
Weigh it and note the weight.
Place the dried leaves in it and weigh again.
By subtracting the first weighing from the second
we find the weight of the leaves. Place the
platinum tray on a pipeclay triangle over a Bunsen
burner or petroleum blowpipe, and light the gas.
The leaves will burst into flame and burn for a
short time. When the flame has died away remove
the burner and notice the charred bits of leaf in the
tray. This charred leaf is charcoal. We have now
reduced the leaf to charcoal.
Replace the lamp, and arrange it under the dish
so that the platinum becomes red hot.
The pieces of leaf glow, the charcoal burns
away, and a pinkish ash is left behind.
This ash is the unburnable or mineral part of the
leaf.
Allow the platinum dish to cool and weigh again,
and subtract the weight of the empty dish. This
gives us the weight of the ash, which is a very small
fraction of the weight of the dried leaves.
We see from these experiments that the
leaf consists of —
iv SUBSTANCES OF A LEAF 31
Water, about four-fifths.
A portion that burns away with flame.
Charcoal.
Ash.
Part of the Food of the Plant is derived from
broken-down Rocks
These experiments have shown us that the plant
consists of a portion that can be burned away, and
another or mineral portion, the ash, which cannot
be burned away.
The material contained in the ash (which is a
mixture of several things, as we shall see presently)
must come from the mineral portion of the soil, the
broken-down rocks, of which that portion of the soil
is composed.
Let us consider, just now, only this part of the
food of the plant, — the part derived from the crumbled
rock of which the soil is partly composed, and con-
veyed in solution in water into the plant.
If we search in the soil for the mineral substances
contained in the ash of the plant, we find that they
are present in an available form in very small quanti-
ties, so that they will be temporarily used up if plants
are grown repeatedly on the same soil, and then removed.
The Effect of Farming on the Soil
Now let us try and understand what will happen
on a piece of wild uncultivated land. The plants
32 THE FOOD OF PLANTS CHAP.
growing there — grass, trees, bracken, gorse, and
numerous weeds — will suck up through their roots
the mineral food they require, and which exists along
with the sand and clay of the soil. And when they
die, they will decay upon the soil, and replace the
mineral food they have taken from it, ready to be
used again by fresh plants. The soil will therefore
remain rich in the food the plant requires, whether
it be mineral or decaying vegetable matter.
Let us now suppose this land to be brought under
cultivation by the farmer.
He grows crops upon it of wheat, grass, turnips,
and other things. When these are ripe, he does not
leave them to decay on the land, but takes a large
part of them away. In the case of wheat he takes
away the straw and ear, but leaves the roots. In
the case of potatoes he takes away the tubers, but
burns the leaves and stems on the field and re-
turns the ashes left by them to the soil. If he is
using land for grazing, the cattle eat the grass and
return' a great portion of the food to the soil as
dung, but some they keep for building up their own
flesh and bone. Thus we find that when soil is
being cultivated, a certain amount of the plant food
it contains is removed every year, and consequently
the soil may get temporarily exhausted. It no longer
contains sufficient food to grow good crops.
iv SUBSTANCES OF A LEAF 33
How the Exhaustion of the Soil is
Prevented
In order to prevent the soil thus becoming
temporarily exhausted, the farmer does several
things.
(1) He digs or ploughs the land, thus turning
up fresh earth for the roots to feed on.
(2) He has found that different crops do not
require the same food, and he therefore grows one
crop one year and another the next year, rotating
his crops.
(3) He allows the land to lie fallow, that is, grows
nothing on it at all during a summer season. By
doing this he gives time for fresh plant food to
become soluble. At the same time a certain amount
of food is permanently lost through the drains.
(4) He manures the land, that is, adds to it the
food which he believes to be deficient in quantity,
for the health and luxuriant growth of his crops.
While he is thus trying to make up for the ex-
haustion of the soil, he is being assisted by changes
taking place in the soil itself.
The earthworms are bringing up fresh soil to the
surface from below, and the wind is blowing fresh
soil or dust upon the top.
The stones and rocks also are gradually breaking
down and supplying the soil with fresh mineral food.
This natural process goes on all the more freely if
the cultivation is deep, thorough, and frequent.
D
34 THE FOOD OF PLANTS CHAP.
The Ash contains many mineral Substances,
among -which Potash and Phosphoric Acid
are of Special Importance
The ash of the plant contains some substances
necessary to the life of the plant and some that are
not necessary, as has been proved by experiments, in
which plants have been grown in water, in which
the various substances found in the ash, have been
dissolved.
You cannot hope to understand the nature and
properties of all these different substances until you
are able to study a more advanced book than this.
Let us, however, look at two of these substances,
and learn how we can recognise them, namely, Potash
and Phosphoric Acid.
(1) The Potash, or " Pearl Ashes" as it is some-
times called, can be easily recognised by the following
experiment : —
Experiment 22
Dip a fine platinum wire in some hydrochloric
acid and then in the ash, and then hold the
wire in the flame of a spirit-lamp. The flame is at
once coloured violet by the potash. Compare this
with the flame produced by dipping the wire into
the solution in water of a little potash obtained from
the chemists, and the same coloration is produced.
The potash can be easily separated from the ash
of the plant by boiling water. Take some wood
iv SUBSTANCES OF A LEAF 35
ashes, boil them in water, filter, and then boil the
water away. A white powder will be left, which is
potash or pearl ashes.
(2) The Phosphoric Acid can be easily recognised
in the ash by the following experiment : —
Experiment 23
Warm the ash with a little strong nitric acid, add
a little water, filter, add a little more strong nitric
acid, and some molybdate of ammonia, and warm
the liquid gently. A yellow powder is slowly formed
in the liquid, thus indicating the presence of phos-
phoric acid.
Warm in a test-tube in the same way a little phos-
phate of soda (which contains phosphoric acid), with
nitric acid and molybdate of ammonia, and the
same yellow powder will be formed.
While these two substances (potash and phosphoric
acid) are quite necessary for the plant, they exist in
an available form in very small quantities in the soil,
and have therefore often to be supplied in manure
of different kinds.
For instance, place a little dried horse dung on
the platinum foil and heat it strongly. Some ash is
left. On testing this in the way already explained
(in Experiments 22, 23), it will be found to contain
both potash and phosphoric acid.
Potash is also often supplied in the form of kainit,
sulphate of potash, wood ashes, ashes of plants and
36 THE FOOD OF PLANTS CHAP.
weeds, etc. etc. ; and phosphoric acid in many
common manures.
For instance, bones in all the various forms used
in agriculture contain large quantities of phosphoric
acid in combination with lime. Take a piece of
bone, heat it red hot on the platinum foil, and then
Mrarm it with nitric acid and test it as before, and
phosphoric acid will be found in it.
Another common source of artificial manure are
earth phosphates, such as apatite and coprolites ; the
latter are the fossil remains of fish, and on warming
with nitric acid and testing as before, will show
the presence of phosphoric acid.
Phosphate slag (formed in certain methods of
making steel), will also show the presence of phos-
phoric acid in the same way.
Sometimes the farmer prefers to have his phos-
phate soluble in water, in which case the bones or
coprolites are treated with sulphuric acid. The
experiment may be carried out as follows : —
Take some powdered ignited bone and warm it
with a few drops of dilute sulphuric acid and heat
till dry. The dry powder left is now soluble in
water. Boil with water, filter, and test as before.
Phosphoric acid will be found in the solution, while
on boiling the bone dust with water, before it has
been treated with acid, nothing will be dissolved.
We have now learnt that the plant con-
tains water, charcoal, and a mineral ash, and
that this ash contains among other things
iv SUBSTANCES OF A LEAF 37
potash and phosphoric acid. We also know
that this ash is derived from the broken-down
rocks in the soil, and that the available
materials supplying it may be temporarily
used up if not restored to the soil as manure.
CHAPTER V
HOW PLANTS OBTAIN FOOD FROM THE AIR
WE have seen that plants obtain both food and
water from the soil by means of the roots. Is this
the only way in which they obtain food, or are they
also able to feed on air ?
We have often seen mustard or cress grown
upon a piece of moist flannel, the tiny seeds spring-
ing in a rich mass of green foliage. How have those
plants been supplied with food 1
Let us try a few experiments with a view to
understanding exactly what happens when cress is
grown in this way.
But in the first place, let us examine a seed itself,
with a view to finding what it contains, and whether
it plays any part in feeding the young plant.
If we select a large seed, such as a bean, and cut
it neatly in half, we notice in one corner near the
margin a small speck. This is the young plant
which, if the seed be kept warm and moist, will
begin to grow. The rest of the seed is 'merely a store
CHAP, v HOW PLANTS OBTAIN FOOD FROM AIR 39
of food, from which the seedling is supplied until it can
obtain food for itself.
This food store may be largely oil, as in linseed,
or starch and other vegetable substances.
Experiment 24
Let us take, for instance, some linseed and crush
them in a mortar. Now place the crushed seed in a
bottle, pour a little ether upon it, cork the bottle
and shake it vigorously. After shaking it for a few
minutes, empty the contents of the bottle on a filter-
paper, and collect the ether running through. Place
the ether out in the sun, exposed in a shallow dish.
In a short time the ether will evaporate and leave
behind a yellow oil. This oil has been dissolved by
the ether from the seed, leaving behind a brown-
coloured substance, similar to that of which linseed
cake is made by pressing hot seed.
A store of food is therefore contained in the
seed, and with this and with water the cress grow-
ing on flannel has been supplied. Can we regard
such a store of food as sufficient, or must we search
elsewhere to find other sources from which the
plant has been fed 1
Let us try to find out the answer to this question
by another experiment.
40 THE FOOD OF PLANTS CHAP.
The Seed obtains Pood from the Air
Experiment 25
Pour a little distilled water into a saucer.
Weigh out one gramme of mustard or cress seed,
and scatter it on some water placed in the saucer.
Place the saucer in the window, and keep it well
.supplied with water. Let the water used be distilled,
so that it may contain no food for the young plant.
The seeds will soon begin to sprout and grow.
When they have grown to a full crop remove the
young plants, place them in the platinum tray, add
the water the saucer contains, and then place them
in the water oven, dry them completely, so as to
remove the water they contain, and then weigh.
The dried plants will weigh more than the seed,
showing that the seeds cannot have supplied
all of the material used in the growth of the
plant.
The seeds themselves contain a little water, losing,
on drying, about 15 per cent of their weight. Con-
sequently, in order to compare exactly the weight of
the seed with the weight of the plants, this should
be allowed for.
The Food Obtained from the Air is Charcoal
Now let us go a step farther, and try and deter-
mine the nature of the food obtained by the plant
from the unknown source.
HOW PLANTS OBTAIN FOOD FROM AIR
41
We noticed before, on heating some dried leaves,
that they were largely composed of charcoal.
If we heat the cress seed strongly we can also
change it into charcoal.
The best way to do this is to place half a
gramme of the cress seed in a test-tube, and lead
into the test-tube a stream of gas obtained by
pouring an acid on chalk. This gas passing
through the test-tube will prevent the charcoal
formed from burning away and so leaving nothing
but ash when the test-tube is strongly heated.
In order to obtain this
gas, take a wide-mouthed
bottle fitted with an india-
rubber cork in which two
holes have been bored.
Fit a bent glass tube into
one hole, and a thistle
funnel into the other.
Place in the bottle some FIG. 10.
pieces of broken marble
and a little water. Fit into the bottle the cork.
Take another piece of glass tubing about nine inches
long and connect it by a piece of india-rubber tubing
to the bent tube through the cork.
Now pour some strong hydrochloric acid down
the thistle funnel. The acid at once begins to attack
the marble, and bubbles of gas rise from it, which
pass out of the bottle along the glass tube.
Now push the glass tube into the test-tube so as
42 THE FOOD OF PLANTS CHAP.
to fill the test-tube with this gas, and hold the test-
tube in the flame of a lamp.
The cress seed begins to smoke. Continue
heating it till the smoke ceases to come off, then let
it cool, and empty the contents on to a watch-glass.
The seeds have been reduced to charcoal. Weigh.
Let us now heat the dried cress in the platinum
dish for a few seconds over a spirit lamp, so as to
reduce it to charcoal, and weigh.
The charcoal obtained from the seed weighs a good
deal less than that obtained from the dried plants.
We have found by this experiment, not
only that the dried plants weigh more than
the seeds, but also that the dried plants con-
sist partly of charcoal, and that only some of
this charcoal has come from the seeds.
Let us search on every side, and try and find
from what source this charcoal can have come.
We have seen that plants are largely composed of
charcoal. Are animals also largely composed of this
substance 1
Let us find out by repeating on a piece of meat
the experiment we made with the dried cress.
Smoke is given off, and a mass of charcoal is left
behind.
Animals as well as vegetables then can be trans-
formed in part into charcoal.
We have still, however, to find out where the plant
obtains the charcoal from, and with a view to helping
you towards that discovery, I would ask you to
v HOW PLANTS OBTAIN FOOD FROM AIR 43
notice some curious facts about the burning of
different substances.
The Air is Altered by Burning Substances
You must have often observed that when a fire is
burning, the air in the room is drawn into the fire
through the bars and then passes up the chimney,
and that, if deprived of a plentiful supply of air, the
fire would go out.
Let us look into this matter more closely, and try
and determine what part the air plays when the
wood or coal. is burning.
We do not yet know if this air is in any way
changed by passing through the flame, and so must
try by a simple experiment
to find out if any change
has taken place.
Experiment 26
Light a candle and then
cover it over with a bell-jar,
so as to shut in with the
flame a fixed amount of air.
At first the flame burns
^/ [ | \
brightly, but soon begins Fio n
to burn feebler and feebler,
and then goes out. Now light a match and plunge
it into the bell-jar. The match also goes out at once.
44 THE FOOD OF PLANTS CHAP.
The burning candle has so altered the air that
substances can no longer burn in it. We may
call this air spoiled, or vitiated air. Having tested
the effect of the candle, we can try the effect of
spirits of wine, burning paper, burning oil, burning
hay, wood, or dried leaves. In each case the result
is the same. The air is so altered that it no longer
supports combustion.
We find then by these experiments that sub-
stances when burnt alter the air in such a way that
it will no longer support combustion, that is to say,
that nothing will burn in it.
Let us see now if we can obtain vitiated air in
any other way.
The Air is Changed by the Breathing of
Animals
Experiment 27
Take a wide -mouthed stoppered bottle, remove
the stopper, fill it with water, and turn it upside
down in a basin of water. Then by means of a
piece of tubing blow air coming from the lungs
into the bottle. When the bottle is full of air
breathed out from the lungs, put in the stopper
and lift the bottle out of the basin. Light a
match, open the bottle, and plunge in the match.
The match goes out at once, showing that the
HOW PLANTS OBTAIN FOOD FROM AIR
45
air coining from the lungs is also vitiated
air. We have thus learnt that both the air acted
upon by burning bodies and the air coming from the
lungs will not support combustion.
If we were to place a living animal in this
vitiated air it would quickly die, showing that the
vitiated air will not support life.
We see then from all these experiments that
breathing animals and burning fires are all preparing
this vitiated air, so that we should expect that by
this time all the air on the earth would be unbreath-
able, unless there is some way in which the air can be
purified and restored to its former state.
Vitiated Air restored by Plants in Sunlight
Let us see whether it is growing plants that
exercise such an influence
on the air as to purify it.
Experiment 28
Place the wide-mouthed
bottle, full of water, upside
down in the basin as be-
fore and fill it with viti-
ated air from the lungs,
and then, leaving it standing upside down in the
basin, put a young vigorous plant up into it, with the
46 THE FOOD OF PLANTS CHAP, v
roots remaining in the water outside, and expose
the whole to the sun.
After exposing all day, remove the plant, stopper
the bottle, lift it out, and test the air in it with a
lighted match. The match will now burn, showing
that the plant acting in sunlight has been able
to restore the air to its former state.
We can now easily find out if exposure to sun-
light had anything to do with the action of the
plant.
Repeat the last experiment, only keep the plant
in the dark instead of in the sunlight, and test with
the match. The air will remain unaltered and the
match will go out, showing that the plant cannot
restore the air without the assistance of light.
"We have now found that the plant does
not obtain all its food from the soil through
the roots, but also obtains food from the air,
and that we find this food in the form of
charcoal when we heat the plant. We also
know that charcoal enters into the substance
of animals as well as vegetables.
We have further discovered that air is
altered in some way by burning bodies, and the
breathing of animals, and is restored to its
former condition by the action of plants in
sunlight.
CHAPTER VI
THE COMPOSITION OF THE AIR AND THE PREPARA-
TION OF CARBONIC ACID GAS
WE have now learnt two facts about the plant. We
know that it obtains charcoal from the air, and we
also know that it can restore air, which has been
vitiated by burning substances or by passing through
the lungs, to its former state.
There is surely some connection between these
facts which we should be able to find out.
And first, take note that the substances burnt,
whether they be the spirits of wine prepared from
fermented corn, or the candle prepared from animal
or vegetable fat, were all of animal or vegetable origin,
and would probably contain charcoal as one of their
parts.
Let us then burn some charcoal and see whether
that also produces vitiated air, which can be restored
to its pure state by the plant. But before doing so,
let us try another test for the presence of vitiated
air.
48 THE FOOD OF PLANTS CHAP.
The Action of Vitiated Air on Lime-Water
Experiment 29
We have noticed that a candle or match will not
burn in vitiated air. It has another property which
will be useful in identifying it when we come
across it.
If we shake up some lime with water and then
filter, we obtain a clear solution of lime in water.
Pour a little of this clear lime-water into a wide-
mouthed bottle, and lower a lighted candle into the
bottle and then cover up the mouth. The candle
soon goes out.
Remove the candle, replace the stopper in the
bottle, and shake up the lime-water with the vitiated
air. A white powder is formed, the lime-water
becoming milky in appearance.
Now take a fresh supply of lime-water in another
bottle, and blow through it. This also becomes
milky in appearance, owing to the vitiated air from
the lungs.
We have here then a simple means of testing for
the presence of vitiated air.
Vitiated Air is produced by burning Charcoal
We have seen that various different bodies in
burning produce vitiated air : let us now see whether
burning charcoal also does so.
VI
THE COMPOSITION OF THE AIR
49
Experiment 30
Fill a little brazier with lumps of charcoal and
set the charcoal on fire. When it is burning brightly
arrange over it a tin funnel with a glass tube passing
away at the top to a bell-jar through a cork, and
arrange another tube from the top of the bell-jar and
connected through a cork with a tin can full of water,
with a tap at the bottom. Place a lighted candle on
FIG. 13.
a ground glass plate and fit the bell-jar, rubbed
round the edge with vaseline, over it, and draw a
stream of air through the whole apparatus by turn-
ing on the tap of the tin can.
As long as ordinary air is passing through, the
candle burns ; but as soon as the tin funnel is placed
over the brazier, so as to collect the air from the
burning charcoal, the candle goes out.
In order that we may be sure of the nature of
E
50 THE FOOD OF PLANTS CHAP.
the air coming from the charcoal, place on the ground
glass plate a little beaker containing clear lime-
water, with the tube from the funnel dipping into
it, and draw the air through as before. The lime-
water quickly becomes milky, showing that the
burning charcoal is producing the same
vitiated air as the burning candle and the
breathing animal,
The Charcoal is combining with the Air to
form a Gas
Now let us watch the charcoal burning, and try
and understand what is happening.
We notice that the charcoal disappears, leaving a
little ash behind, and that the air passing through it
is at the same time altered. We see no smoke rising
from the charcoal, and must suppose that the charcoal
passes away with the air as a gas of some kind.
We know the air is an invisible gas or mixture of
gases. We know that by heating coal in a retort,
another invisible gas — coal-gas — is formed. Here
also the charcoal and the air seem to form an in-
visible gas of such a kind that it puts out a burning
flame and turns lime-water milky in appearance.
This gas, formed of charcoal and air, seems
to act as a food to the plant, the plant taking
the charcoal to itself and restoring the air to
its former condition.
vi THE COMPOSITION OF THE AIR 51
We have yet to learn, however, if the whole or
only part of the air is consumed in this change as it
passes through the burning charcoal.
The Action of burning Phosphorus on the Air
In order to decide this point we shall try some
experiments with another substance which burns
readily, and which is used in the manufacture of
matches, namely, phosphorus.
Experiment 31
Phosphorus is sold in sticks which are always
kept under water, owing to their tendency to go on
fire when exposed to the air. Take one of these
sticks out of the bottle by means of a pair of nippers
or a sharp-pointed penknife, and, placing it under
water in a saucer, scrape it clean at one end with
the knife, and cut off a little piece, about a quarter
of an inch thick, and cut it into four bits. Re-
move one of these bits with the nippers and dab
it gently with blotting-paper to dry it, then place it
in a deflagrating spoon. Take the bell-jar used in
the last experiment and dry it thoroughly inside and
place it on a sheet of window glass carefully dried and
remove the stopper from the jar. Light the phos-
phorus in the deflagrating spoon by touching it with
a hot wire, and lower it into the bell-jar till the open-
52 THE FOOD OF PLANTS CHAP.
ing into the jar is closed by the brass disk attached to
the wire handle of the spoon. The phosphorus in burn-
ing gives off a copious white smoke, which presently
collects into flakes, which fall like snow to the
bottom of the bell-jar and collect on the glass plate.
When the phosphorus has gone out, remove the
deflagrating spoon and test the air left in the bell-
jar with a lighted taper. The taper goes out, show-
ing that the air has again been altered by the burn-
ing body. Lift off the bell-jar and the glass plate
is seen to be covered with a white snow-like powder.
During this experiment the phosphorus has dis-
appeared and this white powder has been formed,
which contains the phosphorus. It, however, must
contain something else besides phosphorus, as on
weighing it, it is found to weigh more than the phos-
phorus which was consumed. (This cannot be shown
without special arrangements.) Apparently, then,
the phosphorus in burning is joining with, or
combining with, some other body, which is
obtained from the air by which it is sur-
rounded ; and it is on account of the absence
of this body that nothing will burn in the
bell-jar afterwards.
The Phosphorus removes Part of the Air
We can now proceed to vary this experiment, so
as to decide definitely whether any part of the air
vi THE COMPOSITION OF THE AIR 53
is removed during the burning of the phosphorus or
not.
Experiment 32 l
Take a pear-shaped hard glass flask (such as is
sold for the preparation of oxygen) and clean and
dry it carefully, and fit it with a good tight-fitting
cork. Cut one of the quarter bits of phosphorus
in half. Examine it to see that it is perfectly clean,
dry it thoroughly, place it in the flask and cork it up.
We have now got air and phosphorus corked up
together.
Warm the flask gently over a spirit-lamp, keep-
ing it turning in the hand all the time. The
phosphorus will melt, catch fire, and run burn-
ing round the inside of the flask. As soon as the
phosphorus catches fire, remove the flask from the
flame and hold it out at arm's length, and turn your
head the other way, still turning the flask in your
hand. The flask is very apt to burst at this moment,
and should therefore be so held that if it does burst
it cannot injure the face.
When the phosphorus has gone out, examine the
flask. A streak of unburnt phosphorus will be
noticed, showing that the phosphorus has gone
out before it was completely consumed. We may
therefore assume that it has exhausted the supply of
the body in the air necessary for its combustion, or it
would not have gone out. The flask also contains
1 This experiment is the invention of Professor Armstrong, F. R. S.
THE FOOD OF PLANTS
CHAP.
the same white powder that was formed by the
burning phosphorus before (Experiment 31).
Take a pudding basin, nearly fill it with water, and
as'soon as the flask is cool, plunge the neck under
the water, and then carefully ease out the cork, keep-
ing the neck under water all the time. As soon
as the cork is removed the water rushes into the
flask.
Push the cork
back again into the
neck, lift the flask
out of the water,
shake it so as to
thoroughly cool it
FIG. 14. > J
by means of the
water which has rushed in, plunge the neck under
water again, remove the cork as before, and lower the
flask into the water until the level of the water inside
and outside the flask is the same. Again insert the
cork and lift out the flask.
The water has rushed in to occupy the space
formerly occupied by the part of the air which has
combined with the burning phosphorus. The greater
part of the air, however, has evidently remained
uncombined. Remove the cork and test with a
lighted taper the air which remains in the flask.
The lighted taper goes out, showing that this residual
air will not support combustion.
We are thus led to believe that the air is
a mixture of two gases, one which combines
vi THE COMPOSITION OF THE AIR 55
with the burning phosphorus, another which
does not so combine, and is left behind.
The gas which supports combustion is called
Oxygen
The gas which does not support combustion is
called
Nitrogen
We can now determine the volumes in which
these two gases are present in the air, as the water
which has rushed into the flask represents the
volume of oxygen which has disappeared. Pour
this water into a measuring glass and note the
amount. An ordinary ounce-measuring glass will do.
Next fill the flask with water, allowing a little for
the cork, and empty it into the measuring glass as
well, so as to determine the volume of the flask.
On doing this we shall find that the oxygen occu-
pied about one-fifth part of the volume of the flask.
The air therefore contains four- fifths by volume of
nitrogen mixed with one-fifth by volume of oxygen.
This experiment gives us an example of
what we mean by chemical combination, the
oxygen of the air combining with the phos-
phorus to form a third new body, which we
call oxide of phosphorus.
During this operation no substance has been lost
or gained, the flask and its contents weighing the
same at the beginning and the end of the burning
56 THE FOOD OF PLANTS CHAP.
of the phosphorus ; but at the same time heat has
been given out and has escaped. Chemical changes
then never result in loss of mass, but often result in
the giving out of heat.1
Oxygen set Free by the Plant in Sunlight
We can now understand what was happening
while the charcoal was burning. It was combining
with the oxygen of the air.
The compound thus formed is known as carbonic
acid gas, and is formed during the breathing of
animals and the burning of animal or vegetable stuff.
During sunlight, as we have seen, it is absorbed
by the plant, the charcoal retained, and the oxygen
restored.
That oxygen is thus formed can be easily shown
by the following experiment : —
Take a tall glass cylinder and fill it with tap
water (which contains a good deal of carbonic acid
1 This experiment can also be performed \vitli greater safety by
floating a watch-glass in some water in a dish, placing a piece of
phosphorus in the watch-glass, removing the stopper from the bell-
jar used before, lowering the bell-jar over the floating phosphorus
into the water, lighting the phosphorus with a piece of hot wire,
and inserting the stopper. The way given in the text is neater,
and gives a more accurate measurement of the volume of oxygen,
but should only be performed by a skilled manipulator.
THE COMPOSITION OF THE AIR
67
dissolved in it), and with fresh green leaves. Put a
glass funnel upside down inside the cylinder, and
over this an inverted test-tube full
of water.
Place the whole thing out in
sunlight.
Soon bubbles of gas will begin
to rise from the leaves and collect
in the test-tube. When enough
has been collected, remove the test-
tube, keeping it closed with the
thumb. Turn it up and lower into
it a piece of red-hot wood.
The wood will glow brightly,
owing to the presence of nearly
pure oxygen gas.
We have now learnt that the
air is a mixture of two gases, oxygen and
nitrogen. That burning bodies are combining
with the oxygen to form new substances.
That during the burning of animal or
vegetable substances, or the breathing of
animals, the charcoal they contain is being
converted into carbonic acid gas by combining
with oxygen.
That this carbonic acid gas is absorbed
by the leaves of plants, and during daylight
decomposed, the plant keeping the charcoal
and returning the oxygen.
FIG. 15.
CHAPTER VII
THE NITROGEN REQUIRED BY PLANTS
IN the last chapter we found that the air is a
mixture of two gases — nitrogen and oxygen — and
that nitrogen forms four-fifths of the air.
This gas is found combined with other substances
in both plants and animals, and can easily be recog-
nised.
One of the simplest compounds containing
nitrogen is ammonia, which has a peculiarly
pungent smell. (For instance, take a little sal-
ammoniac and mix it in a mortar with lime.
Ammonia is at once set free, and we can notice
the peculiar smell of the gas.)
If, then, we find that any substance can be made
to yield ammonia, we may take that as a proof that
it contains nitrogen combined with other substances.
Now take some seeds of corn, and mix them with
a little soda-lime, and heat them strongly in a test-
tube. Ammonia is set free, and we can smell it
coming from the tube.
CHAP, vii NITROGEN REQUIRED BY PLANTS 59
If we treat a piece of dried horse dung and a
piece of meat in the same way we shall in each case
obtain ammonia gas.
We should expect to find that as plants require
nitrogen they would absorb this gas from the air, as
they do carbonic acid gas, through the leaves.
Careful experiments, however, have shown that
they cannot do this, and have to obtain their
nitrogen in other ways.
There is, however, one natural order of plants
which can take up nitrogen from the air in a very
curious way indeed. These plants belong to the
order leguminosse, and some of the commonest
varieties of the order are vetches, peas, lupins, etc.
If we pull up one of these plants and examine
the roots we shall find them covered with little
lumps. On cutting through one of these lumps and
examining it under a powerful microscope, we find
it full of minute creatures, to which the name of
bacteria have been given. These bacteria are able
to absorb nitrogen gas, which surrounds the roots,
and make it up into such compounds as the plant
can absorb and use.
In this way the plant is fed by these bacteria
from the free or uncombined nitrogen of the air.
No other common crop plants have, however, so
convenient an arrangement, and, being unable to
obtain nitrogen direct from the immense stock of
free nitrogen in the air, they absorb the compounds
of nitrogen which are formed (in part by the action
60 THE FOOD OF PLANTS CHAP.
of another set of organisms which carry on the process
of nitrification), from the decay of vegetable stuff in
the soil. By their means insoluble compounds of
nitrogen are broken up and the nitrogen converted
into nitrous and nitric acids which combine with lime
and other bases in the soil.
If there is not sufficient store of decaying plants
in the soil, the crops must be supplied with nitrogen
by putting on the soil farmyard manure, which we
have seen contains nitrogen, or any other vegetable or
animal refuse.
Two compounds of nitrogen are now also very
largely used for this purpose, and are prepared in
enormous quantities for the farmer — sulphate of
ammonia and nitrate of soda. Take a little dry
sulphate of ammonia, mix with lime, and notice the
smell of ammonia, showing that it contains nitrogen.
In order to prove the presence of nitrogen in nitrate
of soda we must treat it a little differently.
Dissolve a little sulphate of copper in water, and
put in it a strip of zinc. It is at once coated with
spongy copper.
Dissolve a little sodium nitrate in water, and put
in some pieces of zinc covered with spongy copper,
and warm gently for some time, then add some caustic
soda and warm. The smell of ammonia will soon be
quite distinct, showing that nitrate of soda also con-
tains nitrogen.
Nitrate of soda and sulphate of ammonia are
both very soluble in water (as we can easily see by
vii THE NITROGEN REQUIRED BY PLANTS 61
dissolving a little of each in a little cold water), and
are therefore very easily washed out of the soil.
For this reason they are often scattered over the
soil after the wheat has begun to grow, so that they
may be absorbed at once by the roots and not allowed
to wash into the drains*
We can, however, enrich a soil with nitrogen
suitable for plant food in another way.
We have learnt that leguminous plants can take
up the nitrogen from the air.
If, then, we sow a crop of lupins, and after they
have grown to maturity plough them in, we shall
add to the store of nitrogen in the soil the decaying
lupins yielding up to the next crop the nitrogen
they obtained from the air. Or we may encourage
the growth of clover by the application of lime or slag
phosphate powder, and the root residue from the
clover will enrich the soil for succeeding crops.
Conclusion
Let us now sum up what we know of the food of
plants.
We have learnt of what substances a plant is
composed.
We have found that it contains water, charcoal,
nitrogen, and ash.
62 THE FOOD OF PLANTS CHAP.
The charcoal is obtained from the air by decom-
posing carbonic acid gas.
The water is obtained from the soil.
The nitrogen is obtained entirely from the soil,
except in the case of leguminous plants, which can
also obtain it from the air, which surrounds their
roots in the soil.
The ash is obtained from the soil.
We have also learnt that the ash contains, among
other substances, potash and phosphoric acid, and
that these are apt to run short, as they exist in an
available form in the soil in very small quantities.
We know that when a seed first begins to sprout
it only requires to be supplied with water, as it
contains food for the young plant in the form of oil,
starch, and other substances. The young plant, how-
ever, develops in two directions — pushing a root into
the earth, and stem and leaves into the air.
The root sucks up water from the soil, which,
passing through the plant, evaporates from the leaves.
The water brings from the earth two kinds of
food in solution : mineral food derived from the
decayed rocks of which the soil is partly composed,
and vegetable food, the most valuable ingredient of
which is combined nitrogen in a soluble state, derived
from the decay of plants in the soil, or from the
organisms already described.
The leaves obtain food from the air in the form
of carbonic acid gas, keeping the carbon or charcoal
they require, and setting free oxygen again.
vn THE NITROGEN REQUIRED BY PLANTS 63
We have also learnt that when we remove from the
land the crops as fast as they grow up, we are taking
away from the soil the store of mineral and vegetable
food that the plant requires, and the soil becomes
temporarily exhausted, and we have seen how this
exhaustion of the soil can be remedied.
We have still much to learn about the nature of
the soil and the changes which take place in the
plants, for which purpose we must study very
carefully the science of chemistry and then more
advanced works on agricultural chemistry; for the
present we must be content that we have gained
some little insight into the way plants are fed.
APPENDICES
Notes on the Experiments
BEFORE performing an experiment the student should
write out carefully the question which he wishes to
have answered by the experiment. While performing
the experiment, he should note down what he does and
what he observes, making a rough sketch of the apparatus
used. When the experiment is completed, he should
state his conclusion. These notes should then be care-
fully copied into another book, with a neat drawing of
the apparatus. Several of the experiments in the text
extend over hours, days, and weeks. Some can only
be performed in spring or summer, and though many
can be managed during the winter, it would be best to
go through the book during spring and summer.
Experiment 5. A glass bottle with a wide tube,
as shown in the drawing, would probably have to be
specially made by a glass-blower. They can, however, be
made very cheaply, and will, of course, be supplied in sets
of apparatus. When such a bottle cannot be obtained,
a fine glass tube could be introduced through the neck
before the bees'-wax was poured in. This would do just
as well. The water must be boiled to remove all dis-
solved air, and care taken that no air-bubbles are enclosed
under the bees'-wax, as otherwise the water will not fall
66 THE FOOD OF PLANTS
in the side tube, bubbles of gas collecting in the neck
of the bottle instead. Any young healthy plant (flower
or weed) will do for this experiment.
Experiment 6. The cork should be cut in half and
fitted round the stem, so as not to injure the young bark.
Experiment 8. In some experiments where heating
is necessary a spirit-lamp is described as being used, in
others a Bunsen burner. If gas is available, a Bunsen
burner, provided with a rose, will be found the most con-
venient. When gas cannot be obtained, a spirit-lamp
will do instead for most of the experiments. When a
high temperature is required, as in the burning to ash of
the leaf, or the heating to redness of the soil, a spirit-
lamp will not do. Petroleum blowpipes can now be
obtained which are perfectly suitable for this purpose, or
a small charcoal fire will do as well.
Filter -paper is usually sold cut into circular disks.
One of these should be folded in half, and then folded
again into a quarter of the original size, then opened
with the finger so as to form a little cone-shaped bag, and
slipped into the glass funnel, and held there while it is
moistened with a little water. It will then stay in position.
Experiment 12. The soil may take several hours
to settle and leave the water clear, and is so finely divided
that some of it will pass through the filter-paper if we
try to filter it. This experiment therefore requires some
patience.
Experiment 14. Condensers of various forms, and
made of different materials, will do for this experiment.
The one shown in the diagram is made of glass. A
piece of stout block-tin tubing, surrounded by an outer
tube of sheet-tin, does very well. The can described in
Experiment 30 may be used to supply water to condense
the steam, the tap being connected to (a) by a piece of
india-rubber tubing.
Another tin can, with a block-tin tube passing through
a cork, can be used as a boiler. In fact, with the assist-
APPENDIX I 67
ance of the village tinsmith, a very satisfactory still can be
cheaply put together. Instead of a straight condenser, it is
sometimes convenient to coil the tin tube into a spiral,
and place it in a tub of water with the end of the tube
coming through the side of the tub near the bottom.
Experiment 16. With a little practice a very com-
plete separation of the sand and clay can be obtained
by this means. The process is the same as that used in
gold-washing, etc.
Experiment 17. The diagram in the text shows a
very simple and cheap form of apparatus for drying sub-
stances at the temperature of boiling water.
The dry, clean, empty dish should first be weighed and
the weight noted, then the soil introduced and the whole
weighed again. The dish of soil after drying must be
allowed to cool before being weighed again. It should
be placed to cool in a desiccator or under a bell-jar (see
Appendix II).
Experiment 19. A crucible made of platinum,
while very suitable for this experiment, is somewhat
expensive. A porcelain crucible, or platinum tray made
by bending up the edges of a piece of platinum foil, will
do very well. If a crucible is used, it should be left
uncovered when over the flame and tilted a little on one
side, so as to let the air freely circulate. Where gas is
available it can be heated over a Bunsen burner. Where
gas cannot be obtained, the petroleum blowpipe should
be used. The pipeclay triangle is easily made. Three
pieces of iron wire about 6 inches long and a clay to-
bacco pipe are required. Break off the stem of the pipe,
three short pieces about 2 inches long, slip a piece of
iron wire through each, and then twist together the ends
of the iron wires, so as to make a triangular support for
the crucible, with the twisted ends of the wires resting on
the ring of the retort-stand. Such a stand will endure
a high temperature for a long time, and will not injure
the platinum, as a metal support would do.
68 THE FOOD OF PLANTS
Experiment 21. The directions for drying, heating,
and weighing already given apply to this experiment.
The weight of ash obtained is, however, very small, and
care must be taken to weigh very accurately. The ash
should be kept, as it is required in Experiment 22.
Experiment 22. A very fine platinum wire should
be used here. It should be heated in the flame for some
time till it ceases to colour it, then moistened in a few
drops of hydrochloric acid in a watch-glass, then dipped
in the ash, and then placed in the flame again. It should
be held in the outer part of the flame. A pale violet tint
will be imparted to the flame, mixed with a yellow tint,
due to the presence of soda. With a little practice,
however, the potash violet flame will be easily recog-
nised.
Experiment 23. About as much of the ash as
would cover a sixpence will do for this experiment. It
should ba emptied into a test-tube, about half an inch
(measured on the side of the test-tube) of strong nitric
acid added, and the test-tube warmed gently over the
flame. Then add an inch of distilled water and filter
into another test-tube. Add to 1 inch of the filtrate
1 inch of strong nitric acid, and 2 inches of molybdate
of ammonia solution; shake up and warm gently, and
allow it to stand for a few minutes. The yellow pre-
cipitate will be slowly formed.
Experiment 25. The end of the tube of the
thistle funnel must of course dip below the water in
the bottle so as to prevent the gas escaping up it. Fresh
strong hydrochloric acid can be poured down the funnel
from time to time to keep up the supply of gas. The
marble should be broken up into pieces about the size of
filberts. The gas set free is carbonic acid gas. It
entirely prevents the charcoal from burning.
Experiment 28. This experiment and the two
preceding it are due to Priestley, who first proved the
exchange of carbon (charcoal) between the animal and
APPENDIX II 69
vegetable kingdom. His experiments are published in
his works, and are well worth reading.
Experiment 32. If an explosion is to be avoided
great care must be taken to follow exactly the directions
in the text. The beginner had better adopt the method
described in the Note, but a teacher will find the experi-
ment as described in the text very effective.
Chapter VII. Some valuable papers on the way in
which nitrogen is supplied to plants will be found in the
Journal of ike Royal Agricultural Society, vol. ii. part
iv. No. 8.
II
On the Use of the Balance
IN several of the experiments described in the text,
accurate weighing is required in order to obtain a satis-
factory result. In some cases the quantity to be weighed
is very small, as for instance the ash left on burning
leaves. It is indispensable, therefore, that an accurate
balance and a good set of weights be obtained. It is
almost impossible to weigh accurately unless the balance is
enclosed in a glass case. The French weights (grammes)
will be found the most convenient, as they are divided
into tenths, and consequently can be easily added and
subtracted.
Before trying any experiments in which weighing is
required the student should practise weighing, so as to
learn how to obtain an accurate result. On examining
the balance he will notice a little brass stud in front.
On turning this, tne beam of the balance is raised off
the brass pegs that support it, and is able to swing
freely.
70 THE FOOD OF PLANTS
Turn the brass stud slowly round, and bring the beam
gently on to its supports again. It is now off the knife
edges, and can no longer swing to and fro. It should
always be in this position when not in use, and when any-
thing is going to be placed on or removed from either pan.
Now open the glass front of the balance, dust the
pans with a soft brush, and again turn the brass stud.
The beam commences to swing to and fro, and the
pointer to move backwards and forwards in front of
the little ivory scale.
If the balance is equally weighted on both sides, the
pointer will swing to about equal distances on both sides
of the middle line of the scale. This can be accurately
tested by noting the divisions on the scale. As the
balance is slowly coming to rest, the pointer will swing
a little less each time, and therefore in order to tell if
the weights on each pan are exactly equal we should
have to note down each swing and take the mean.
For most purposes it is sufficient to note that the
pointer is very nearly equal in its swings on both sides
of the dividing line. For instance, it may swing 4
on one side, 3 on the other side, 2 on the first side,
and so on. Evidently the beam is equally balanced
but slowly stopping.
If you wish to increase the swing of the beam gently
fan the air with your hand near one of the pans. While
noting the swings of the beam, close the glass front,
otherwise currents of air entering the balance case will
disturb the weighing.
As a rule, on trying the balance you will find the
equilibrium imperfect. You will notice on the end of the
beam a little nut running on a screw. By screwing this
in or out the balance can be perfectly adjusted. Lower
the beam, wind in or out as the case may be the little
nut, raise the beam again, note the swings, and repeat
until the balance is in equilibrium. You are now ready
to weigh something.
APPENDIX II 71
Take a piece of metal, say a lead bullet or a penny,
see that it is clean and dry, and having lowered the
beam, place it on one pan of the balance. Open the
box of weights, and with the nippers provided for the
purpose lift out the heaviest weight in the box and
place it on the other pan. Now begin to raise the
beam, turning the brass stud very gently, and noting the
pointer. The pointer will probably move in one direction
as the beam is being raised. We need not therefore
raise the beam completely. Lower the beam, and if the
weight is too heavy, remove it and place on the pan the
next in order. If this is too light, add to it the next
again. If too heavy with this addition, remove the last
weight added and try the next. Do not try and guess at
the weight of an object, but go systematically through the
box. When you arrive at the tiny weights and are near
to the true weight of the object, you will have to raise
the beam completely and note the swings of the pointer.
The glass front should be closed during these final
observations. Having got the balance exactly in equi-
librium and lowered the beam, next look at the box of
weights.
The brass weights beginning with 100 or 50 grammes
go down to 1 gramme. The fractions of a gramme are
of aluminium or platinum, and are tenths, hundredths,
and thousandths of a gramme.
The tenths are marked '5, -2, •!, 1. The hundredths
are marked '05, "02, -01, '01 ; the thousandths or milli-
grammes are merely marked 5, 2, 2, 1, their size indicating
their weight, or in some cases they are made of wire,
which is bent to show the weight — thus, O V V - — ;
the number of bends indicating the number of milli-
grammes.
In the more expensive boxes each weight has its own
little pigeon-hole. In cheaper boxes the fractions of a
gramme are all mixed together. In the latter case it is
as well before beginning a weighing to take a piece of
72
THE FOOD OF PLANTS
paper and rule it into squares, marking each square as
shown in the text, and placing the corresponding weight
in it —
•5
•2
•1
•i
•05
•02
•01
•01
•005
•002
•002
•001
Supposing our weights to have been so arranged and
the weighing completed, before removing the weights
from the balance pan examine the box and the diagram,
and find the weight of the object by noting the weights
missing. For instance, we notice that 30 grammes, 5
grammes, 2 grammes, '5 gramme, '2 gramme, '1 gramme,
•05 gramme, '002 gramme are missing. Write these
down in the following way and add : —
30-000
5-000
2-000
•500
•200
•100
•050
•002
37-852 grammes.
Next remove the weights from the pan, noting down the
value of each as you return it to the box. On adding
these up they should also come to 37-852 grammes. In
this way a double check is obtained and mistakes in
weighing are avoided.
APPENDIX II 73
Every object must be clean, dry, and cool before
weighing. On removing crucibles from heating over
lamps, or objects from heating in a water -bath, they
are best placed under a bell-jar on a glass plate, and a
little dish of strong sulphuric acid should be placed
under the bell-jar beside them, or they may be placed in
an ordinary desiccator instead.
NOTE
For a class of twenty pupils, one balance and two drying
ovens will be sufficient. Certain experiments, such as 13, 18, 20,
25, 30, 31, 32, are best performed by the teacher before the class.
The rest should be performed by the pupils themselves. In the
list of apparatus those marked with a star should be provided for
each pupil. One set of the other things will be sufficient.
LIST OF APPAKATUS AND CHEMICALS
REQUIRED
Apparatus
Exper.
5. * Growing bottle 4 oz., with side tube to show level
of water absorbed.
6. Chemical balance, 30 gramme load, in glass case,
with set of weights from 30 grammes down to
1 milligramme.
,, Set of 3 cork borers.
„ * 3 blown glass bottles.
8. * 6 flat-bottomed flasks, 4 oz.
„ * 6 glass funnels, 2J in. diam.
„ * 100 cut filter-papers, 4f in. diam.
11. * 3 porcelain basins, 3 in. diam.
„ * 4 in. square wire gauze for supporting basins,
flasks, etc., on following retort stand.
„ * 1 spirit-lamp and 1 pint methylated spirit, or
Bunsen burner and 1 yard rubber tube where there
is town gas, same value.
14. Tubulated retort, 16 oz.
Note. — One of each of the articles marked with an
asterisk is sufficient for each student when several sets
for students are being made up.
APPARATUS AND CHEMICALS REQUIRED 75
Exper.
14. * Retort stand, with 2 rings and screws.
,, Liebig's condenser, all glass.
„ Condenser stand.
„ 2 yards india-rubber tube to supply condenser with
water.
16. * Mortar and pestle, 4^ in. diam.
17. Tin drying chamber, double walls, for hot water,
with tripod.
19. * Piece stout platinum foil, 4x3 in.
,, * Pipeclay-covered triangle.
„ Ignition burner for methylated spirit, latest design,
for use in rural districts, or where there is town
gas a foot blower and gas ignition burner will be
supplied instead, same value.
22. * Fine platinum wire, 4 in.
„ * 2 watch-glasses.
23. * 12 test-tubes, 5 x f.
„ * Test-tube stand for six.
25. Gas generating bottle, 20 oz., fitted with rubber
stopper, funnel tube and delivery tube.
26. Bell-jar with stopper at top, 8 x 4 in.
,, Ground glass plate, 6 in. square.
27. * Stoppered bottle with very wide mouth, 20 oz.
30. Aspirator fitted with brass tap.
Rubber stopper for top of it.
Rubber-jointed glass leading tubes.
Extra rubber stopper for the bell-jar.
Small beaker to hold lime water.
Small tin candle-holder and candle.
Charcoal chauffer on feet.
31. Deflagrating spoon and support.
32. 2 hard glass flasks for making oxygen, fitted with
solid corks.
33. * Cylindrical jar on foot, 8 x 2| in. inside.
76 THE FOOD OF PLANTS
Chemicals
In bottles.
\ oz. eosine red.
2 oz. bees'-wax.
4 oz. copper sulphate.
6 oz. red lead.
2 oz. calcium sulphate.
4 oz. hydrochloric acid, pure.
1 oz. ammonium molybdate.
6 oz. nitric acid, pure.
1 oz. sodium phosphate.
1 oz. potassium carbonate.
4 oz. sulphuric acid, pure.
6 oz. sulphuric ether.
1 Ib. hydrochloric acid, com.
1 oz. phosphorus.
1 oz. ammonium chloride.
4 oz. soda lime.
1 oz. ammonium sulphate.
1 oz. sodium nitrate.
1 oz. granulated zinc.
6 oz. lime water.
4 Ib. (parcel) charcoal.
1 oz. caustic soda.
Chemicals and bottles cost Us.
N.B. — If the case is sent by rail the chemicals in
italics must be omitted, and an allowance of 4s. will
be made for them.
Specimens
In 1 Ib. stoppered specimen bottles.
Kainite.
Sulphate of potash.
Pearl ash.
APPARATUS AND CHEMICALS REQUIRED 77
Bone meal.
Coprolites.
Apatite.
Phosphatic slag.
Soluble phosphate.
Guano.
Sulphate of ammonia.
Nitrate of soda.
Linseed.
Linseed oil.
Linseed cake.
The commercial names are used above.
Cost of specimens and bottles, 16s,
TOTAL COST
Apparatus . . £6 18 0
Chemicals and bottles . . . .0110
Specimens and bottles . . . .0160
Packing cases, internal and external . .096
£8 14 6
The above-mentioned Apparatus and Chemicals will
be forwarded, carriage paid, to any station in the United
Kingdom, when cash accompanies order} by
ME. WILLIAM HUME,
1 LOTHIAN STREET, EDINBURGH •
or
MESSRS. J. J. GRIFFIN AND SONS,
22 GARRICK STREET, COVENT GARDEN,
LONDON, W.C.
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