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ELEMENTARY

AGRICULTURAL CHEMISTRY

CHARLES GRIFFIN & CO. LTD., Publishers

In Crown 8vo. Cloth. Fully Illustrated. 5s net
A MANUAL OF

PRACTICAL AGRICULTURAL BACTERIOLOGY

By PROF. DR. F. I^OHNIS.

Translated by W. Stevenson, B.Sc.,of the West of Scotland Agricultural College,

and J. Hunter Smith, B.Sc, Assistant in the I^aboratory of Dr. F. I^ohnis.

In I^arge Crown 8vo. Cloth. Beautifully Illustrated. Ts 6d net

THE PLANT CELL :

Its Vital Processes and Modifications

By HAROIvD AXFI. HAIG, M.B., B.S., M.R.C.S., I,.R.C.P.
This volume contains a unique and beautiful series of micro-photographs
and many illustrations from drawings by the author.

With many F^ngravings and Photographs. Cloth. 4$ 6d net

FOOD SUPPLY

By ROBERT BRUCE, Agricultural Superintendent to the Royal Dublin Society.
With Appendix on Preserved Foods by C. A. MlTCHEI.1., B.A., F.I.C.

'' The work is one which will appeal to those intending to become farmers at
home or in the Colonies, and who desire to obtain a general idea of the true
principles of farming in all its branches." — Joumalof-the-Royal Colonial Inst.

Third Edition. With Numerous Tables. Fully Illustrated. At Press.

DAIRY CHEMISTRY
For Dairy Managers, Chemists, and Analysts

A Practical Handbook for Dairy Chemists and others
having Control of Dairies

By H. DROOP RICHMOND, F.I.C, Chemist to the Aylesbury Dairy Co.
"... In our opinion the book is the best contribution on the subject
THAT HAS YET APPEARED in the English language." — Lancet.

Second Edition, Revised. In Crown 8vo, Fully Illustrated. 3s net
THE LABORATORY BOOK OF

DAIRY ANALYSIS

By H. DROOP RICHMOND, F.I.C.

" Without doubt the best contribution to the literature of its subject that
has ever been written." — Medical Times.

Illustrated. With Photographs of Various Breeds of Cattle, &c. 7s 6d net

MILK : ITS PRODUCTION AND USES

With Chapters on Dairy Farming, The Diseases''of Cattle, and on the Hygiene
and Control of Supplies

By EDWARD F. WII,I.OUGHBY, M.D., D.P.H.

" We cordially recommend it to every one who has anything at all to do
with milk." — Dairy World.

London : Charles Griffin & Co. Ltd., Exeter St., Strand, W.C.2

ELEMENTARY

ACIRICULTUliAL CHEMISTRY

. A HANDBOOK FOR JUNIOR AGRICULTURAL

STUDENTS AND FARMERS ^^ '•>■' '''

BY

HERBERT INGLE, BSc,

FELLOW OF THE ROYAL SOCIETY OF SOUTH AFRICA, OF THE INSTITUTE

OF CHEMISTRY AND OF THE CHEMICAL SOCIETY, MEMBER OF

THE BRITISH AND SOUTH AFRICAN ASSOCIATIONS FOR THE

ADVANCEMENT OF SCIENCE, AND OF THE SOCIETY OF

CHEMICAL INDUSTRY; LATE CHIEF CHEMIST TO TUB

TRANSVAAL DEPARTMENT OP AGRICULTURE,

FORMERLY LECTURKR ON AGRICULTURAL

CHEMISTRY AT THE LEEDS UNIVERSITY.

mnb 5llu6tratfon3

THIRD EDITION, REVISED

LONDON:

CHARLES GRIFFIN AND COMPANY LTD.

EXETER STREET, STRAND, W.0.2

1920

[All rights reserve.]

/

u

PREFACE TO THE THIRD EDITION

With the exception of a few corrections and additions, this is
a reprint of the last edition. In an elementary book of this
kind the introduction of the results of recent work on the
constitution and digestion of proteids may safely wait until
the main facts and principles are more fully elaborated by the
active investigations which are now being made. Doubtless,
in the near future, a conception of the whole process of diges-
tion will be reached, clear enough for easy presentment to
even elementary students.

Leeds, October 1919.

PREFACE TO THE FIRST EDITION

This little volume is based upon the writer^s long experience
in teaching agricultural students, among whom there are,
unfortunately, many who cannot devote the time necessary to
acquire sufficient knowledge of pure chemistry to profitably
read such works as the author's "Manual of Agricultural
Chemistry." *

It is true that any attempt to combine, in one book,
instruction in the principles of general chemistry with the
somewhat technical information concerning the chemistry of
agriculture, must be in many ways a failure, and the author
would strongly recommend the user of this work to read some
good, modern text-book on the former ; or, better perhaps, to
ask his teacher to explain, at greater length, the very incom-
plete and sketchy accounts which are given of the jirinciple°
of chemistry and of the properties of the elements and com-
pounds important in agriculture.

While fully realising that a satisfactory knowledge of

agricultui-al chemistry cannot be acquired without a previous

training in pure chemistry, he is aware that there are many

agricultural students and farmers who have, perforce, to do

♦ Scott, Greenwood & Son, London.

47i)27

vi PREFACE

\vithout tliis preliminary chemical knowledge, and it is for
such that this Vook is mainly' intended. " ^ ' .' T

Since the work is written for the agriculturist rather than
for the chemist, few references to chemical literatiire afS
given. i w ■ •

The book, was prepared while the author was in to ch with
many of the crops and ngricultural practices of South Africa,
and it was thought advisable to give some account of the
products of tropical and sub tropical agriculture in addition to
the matters relating to ordinary English farming.

In these days of- frequent travels and emigiution, such
inclusions may be of service to many agricultural students
who, in the future, may becr.me Colonists, while it may render
the book more suited to the needs of the Colonial reader, aid
to all a comparison of tropical with temperate conditions
cannot fail to be useful.

Every writer is apt to give undue prominence to the
particular subjects upon which he has himself woiked, and
perhaps some examples of this weakness: may be found iri the
present volume.

The importance of the composition as well as the amount of
the ash constituents of the food of animals, to which leference
is made in chap, ix., though perhaps not strongly felt in
Europe where diet is varied,, is considerable in such countries
as South Africa, where the usual food of draught animals is
composed almost entirely of cereals.

In chap. iii. a brief account is given of the main causes of
tli6 motion of water in a Foil, intended to clear away the
confusion which is apt to attend the usual " explanation " as
to its being due to "capillarity."

Chap. X. deals with the variations in the composition of
cows' milk in greater detail, perhaps, than the elementary
character of the book justifies ; but here again the popular
interest at present shown in the subject must be the excuse.

..There are, doubtless, other re ^jpects in which the work is^
"out of balance," but for these the reader's indulgence is
solicited.

The author hopes that, in spite of this, the book may prove
of service to those for whom it is intended, .

October 1908.

CONTENTS

CHAPTER I
INTRODUCTION

Outline of Modern Chemical Theory— Atomic Theory— Properties of
Oxygen, Hydrogen, Carbon, Nitrogen, Sulphur, Phosphorus, Cal-
cium, Potassium, Sodium, Magnesium, Iron, Chlorine, Silicon

Pp. 1-23

CHAPTER II
THE ATMOSPHERE

Physical and Chemical Properties of the Air— Variations in its
Constituents Pp. 24-32

CHAPTER III
THE SOIL

Soil and Sub-soil — Transported and Sedentary Soils— Formation of
Soils — Various Agencies leading to Formation of Soils — The
Constituents of Soils — Chemical Changes occurring in Soils —
Movements of Water in Soils — Nitrification — Fixation of Nitrogen
in Soils — Soil Gases — Losses by Drainage — Analysis of Soils

Pp. 33-83

CHAPTER IV
NATURAL WATERS

Rain Water— Spring Water — Hard and Soft Water— River Water— Sea
Water— Relations of Water to Heat — Specific Heat— Latent Heat

Pp. 62-75
^ b

vm CONTENTS

CHAPTER Y
THE PLANT

Germination — Roots — Stems — Leaves — Flowers — Seeds— Conditions
affecting Growth — Constituents of Plants — Carbohydrates — Fats
— Essential Oils — Organic Acids — Ash Constituents — Proteids —
Amides— Alkaloids— Chlorophyll » » « -i .Pp. 76-95

CHAPTER VI
MANURES

Farm-yard Manure — Excreta — Litter — Preservation of Manure— Other
Organic Manures — Guano — Sea-weed — Fish Manure — Blood —
Shoddy — Bones— Soot — Oil-cakes — Night-soil — Green Manuring —
Fixation of Nitrogen by Leguminosse — Artificial Manures —
Analysis and Valuation of Manures . . . Pp. 96-118

CHAPTER VII

CROPS

Classification — Cereals— Leguminous Seeds — Miscellaneous Seeds —
Fruits — Root Crops — Forage Crops — Hay-making — Ensilage —
Rotation of Crops Pp. 119-1536

CHAPTER VIII

THE ANIMAL BODY

Constituents of the Body— Digestion— Destination of Digested Food

Pp. 154-163

CHAPTER IX
THE FEEDING OP ANIMALS

Constituents of Food— Digestibility of Foods— Albuminoid Ratio

Feeding Standards— Functions of Ash Constituents of Foods^
Money-value of Food Constituents— Manuri^ Value of Foods

Pp. 164-181

CONTENTS ix

CHAPTER X
THE DAIRY

Constituents of Cows' Milk — Physical Properties and Chemical Com-
position of Cows' Milk — Variations in Composition — Milk of other
Animals — Preservation of Milk — Milk Products . Pp. 182-210

CHAPTER XI
MISCELLANEOUS

Disinfectants and Antiseptics — Fungicides — Insecticides — Plant
Poisons s Pp. 211-234

APPENDIX Pp. 235-241

INDEX Pp. 243-250

CHAPTER 1.

INTRODUCTION.

Agricultural Chemistry concerns itself with the chemical
composition of the food of plants and animals and with the
chemical changes involved in the processes of life. It has thus
to deal with the composition of soil, air and water, of the bodies
of plants and animals, of manures and other materials, and
with the chemical changes which these substances undergo.

Before commencing the study of agricultural chemistry a
student should devote some time to acquiring a knowledge of
general chemistry. In this little work it is difficult to impart
such knowledge, and the reader should, if he has not already
had some training in the science, supplement what he reads
here by referring to some good modern text-book of chemistry.
This chapter will be devoted to a brief and necessarily very
incomplete sketch of the modern theory of chemistry, and of
the more characteristic properties of those elements which are
of importance in agriculture.

According to present views, all matter (by which is meant
everything that possesses weight and which affects our senses) is
composed of minute particles, which are incapable of being sub-
divided and which cannot be destroyed. In view of the electron
theory of matter, and of some of the recent discoveries with
respect to radium and its conversion into helium, this statement
may have to be modified, but so far as the great majority of sub-
stances is concerned it may be accepted as true. Thus to the
mental vision of the chemist all materials, whether solid,
liquid or gaseous, are guanular, inasmuch as they are com-
posed of countless multitudes of these indivisible particles.
Those particles are known as atoms (from two Greek words

2 ELEMJENTARY AGRICULTURAL CHEMISTRY

>ii8anin§; indiyfeible.), and the theory is known as the atomic
THEORY. It is of very ancient origin, but was first applied in
its modern sense to chemistry by John Dalton about the
beginning of the nineteenth century. There are about eighty-
three different kinds of atoms, and a substance containing
only one kind is said to be an element. The whole earth, so
far as is known, is made up of these eighty-three (or there-
abouts) elements. The atoms diflfer in weight, but those of
any one element are alike in weight and in all other properties.
The properties of any substance reside in its molecules, not in
its atoms. Thus, there may be two substances possessed of
entirely different properties and yet containing exactly similar
atoms, but, in such cases, the molecules are different. For
example, ordinary oxygen, consisting of molecules each con-
taining two atoms of the element, is essentially different from
ozone, which consists of molecules each containing three atoms
of the element. The actual weight of an atom is so small
that it is practically impossible to determine it, but the
relative weight compared with an atom of another kind can be
determined with considerable accuracy. The methods used in
the determination of the atomic loeight of an element cannot
here be described. The table on p. 3, giving the names (in
alphabetical order) of the elements and their relative atomic
weights, may be useful. It is the table published annually
by the International Committee on Atomic Weights and gives
the figures to be accepted for 1920,

The numbers are calculated on the assumption that the atom
of oxygen has a weight represented by 16*000. Formerly
it was usual to take as the unit of atomic weight that of
hydrogen, but for several reasons it is now preferred to
refer the values to the one-sixteenth of the atomic weight
of oxygen. After the name of each element in the table is
given a symbol^ consisting of a capital letter with or without
another letter. By a symbol is indicated one atom of the
element referred to, and thus a symbol has a quantitative as
well as a qualitative meaning.

INTRODUCTION

International Atomic "Weights for 1920.

Aluminium

Antimony

Argon .

Arsenic .

Barium .

Bismuth

Boron .

Bromine

Cadmium

Cajsium .

Calcium

Carbon .

Cerium .

Chlorine

Chromium

Cobalt .

Columbium

Copper .

Dysprosium

Erbium .

Europium

Fluorino

Gadolinium

Gallium

Germanium

Glucinum

Gold .

Helium .

Holmium

Hydrogen

Indium .

Iodine .

Iridium .

Iron

Krypton

Lanthanum

Lead

Lithium

Lutecium

Magnesium

Manganese

Mercury

0 = 16

0 = 16

Al 271

Molybdenum

. Mo 96-0

Sb 120-2

Neodymium

. Nd 144-3

A 39-9

Neon

. Ne 20-2

As 74-96

Nickel .

. Ni 58-68

Ba 137-37

Niton .

. Nt 222-4

Bi 208-0

Nitrogen

. N 14008

B 10-9

Osmium

. Os 190-9

Br 79-92

Oxygen .

. 0 16-00

Cd 112-40

Palladium

. Pd 106-7

Cs 132-81

Phosphorus

. P 31-04

Ca 40-07

Platinum

. Pt 195-2

C 12-00

Potassium

. K 3910

Ce 140-25

Praseodjniium

. Pr 140-9

CI 35-46

Radium

. Ra 226-0

Cr 520

Rhodium

. Rh 102-9

Co 58-97

Rubidium

. Rb 85-45

Cb 93-1

Ruthenium

. Ru 101-7

Cu 63-57

Samarium

. Sa 150-4

Dy 162-5

Scandium

. Sc 44-1

Er 167-7

Selenium

. Se 79-2

Eu 152-0

Silicon .

. Si 28-3

F 19-0

Silver .

. Ag 107-88

Gd 157-3

Sodium .

. Na 23-00

Ga 70-1

Strontium

. Sr 87-63

Ge 72-5

Sulphur

. S 3200

GI 91

Tantalum

. Ta 181-5

Au 197-2

Tellurium

. Te 127-5

He 4-00

Terbium

. Tb 159-2

Ho 163 5

Thallium

. Tl 204-0

H 1-008

Thorium

. Th 232-15

In 114-8

Thulium

. Tml68-5

I 126-92

Tin

. Sn 118-7

Ir 1931

Titanium

. Ti 48-1

Fe 55-84

Tungsten

. W 184-0

Kr 8202

Uranium

. U 238-2

La 139-0

Vanadium

. V 51-0

Pb 207-20

Xenon .

. Xe 130-2

Li 6-94

Ytterbium

. Yb 173-5

Lu 1750

Yttrium

. Yt 89-33

Mg 24-32

Zinc

. Zn 65-37

Mn 54-93

Zirconium

. Zr 90-6

Hg 200-6

4 ELEMENTAKY AGRICULTURAL CHEMISTRY

When two elements combine together to form a chemical
compound they do so by the union of a certain number of atoms
of one with a certain number of atoms of the other element,
and the proportion between these numbers is usually a very
simple one, and is always the same for a given compound. To
take an example, water is composed of hydrogen and oxygen,
and the numbers of atoms are in the proportion of two and
one respectively. This can be briefly expressed by the formula
HjjO, which conveys the information that a molecule of water
consists of two atoms (having a relative weight of 2) of hydro-
gen and one atom (with a relative weight of 16) of oxygen.

It is important to realise the essential differences between
a mechanical mixture and a chemical compound.

From the theoretical aspect this may be stated thus : In
a mixture the molecules of the constituents remain intact,
and by a suflBciently delicate means might conceivably be
detected lying side by side, and each constituent retains its own
characteristic properties, so that the mixture has properties
intermediate between those of its components. In a compound,
on the other hand, all the molecules are alike, and no investi-
gation, however searching, would be able to detect the original
components in the compound without destroying its charac-
teristic properties. From the practical aspect it is to be noted
that the mixing of the two subjects generally produces no
evolution or absorption of heat, and yields a product inter-
mediate in properties between its components, and capable,
by merely mechanical means, of being separated into its
constituents ; whilst with the formation of a compound there
is uaually much heat evolved, and the product has properties
totally unlike those of its constituents. No mechanical means,
however delicate, can separate, or even delect the existence of,
ihe constituents.

The following experiment will perhaps help to render the
distinction clear. If about 10 grammes of fine copper filings
are mixed in a mortar with half their weight of sulphur,
a dirty orange powder results. Under the microscope red

INTRODUCTION 5

particles of copper and lemon-yellow fragments of sulphur can
be distinguished lying side by side. Moreover, by throwing
some of this powder into water the constituents separate out
according to their relative specific gravities : the copper par-
ticles sink to the bottom, while the lighter sulphur particles
rest above the copper ; or complete separation may be eflfected
by treating a portion of the mixture with carbon disulphide,
when the sulphur is removed in solution and the copper left.
On allowing the carbon disulphide to evaporate, the sulphur is
recovered in small crystals. In this case a niere mixture of
sulphur and copper has been made, capable of separation by
mechanical means and partaking of the properties of its
constituents.

If some of the mixture be heated in a test-tube a chemical
union between the copper and sulphur takes place, attended
by the production of heat and light, and there results a black
substance totally unlike, in all its properties, either of its
constituents. If this black substance be ground to powder and
examined under the microscope all the particles will be alike
black in colour, and neither sulphur nor copper can be detected.
If a portion of the mixture be treated with carbon disulphide
the substance is not changed in appearance, and the liquid, if
filtered off, deposits on evaporation no sulphur (or at most a
small trace, due to imperfect mixing or heating of the powder).
If the powder be thrown upon water it all sinks together.
The substance is evidently neither copper nor sulphur, but by
appropriate means it can be shown to contain both. If some
of the powder be treated with strong nitric acid a violent action
takes place, and a dirty yellow mass floats on the top, the
liquid becoming blue in colour. If the liquid be filtered and
brought into contact with a bright iron or steel blade or some
scrap zinc, a deposit of red metallic copper will be obtained-
If the dirty yellow residue be heated in air, it will burn with
the blue flame and emit the characteristic odour of burning
sulphur. The black substance obtained by heating the mixture
of copper and sulphur is a chemical compound called sulphide

6 ELEMENTARY AGRIOCTLTURAL CHEMISTRY

of copper, and, like almost all compounds, was formed from its
constituents with the evolution of heat.

A consideration of the meaning of the term, atom, will clearly
show that it cannot be applied to even the smallest conceivable
portion of water or other compound substance, since such a
portion of matter must contain at least two atoms, and there-
fore can be further subdivided. Another term, molecule, is
therefore used for the smallest conceivable portion of a sub-
stance which can exist alone. Indeed, even with elementary-
substances it is usually the case that separate atoms do not
exist, but that the molecules of elements contain two or more
atoms. Thus, free oxygen exists as molecules, each containing
two atoms, and though molecules composed of three atoms of
oxygen are known, they are entirely different in their properties
from ordinary oxygen, and constitute the substance known
as ozone. It is only in the case of some few elements that
separate atoms exist in the free state. One of the best
examples is afforded in the recently discovered element, argon.
This substance consists entirely of separate atoms, so that in
this and similar cases the molecule and the atom are identical.
When chemical action takes place no creation or destruction
of matter occurs, but new molecules are formed by some re-
arrangement of the elements present. The chemist endeavours
to investigate fully the changes which take place, and in many
cases is able to represent the whole of the changes which occur
by means of chemical equations. To take a simple case, con-
sider the union of hydrogen with oxygen to form water. In
hydrogen gas there are only molecules of hydrogen, each
molecule represented by the formula H«, while in oxygen there
are only molecules, Oa. "When union occurs, two molecules
of hydrogen unite with one molecule of oxygen to form two
molecules of water. This can be represented thus :

2H2 + 02= 2H2O.

A chemical equation is like an algebraical equation, in that
there must be the same quantities of each element on each side

INTRODUCTION 7

of the equation ; but it is not like an algebraic equation, in
that it cannot necessarily be written either way. An equation,
to a chemi-t, is a concise statement of a chemical change,
given in addition to information as to its qualitative character,
full details of the quantities of the various substances taking
part in the reaction. The student, however, must not over-
look the fact that before an equation can be relied upon
actually to represent a given reaction, a complete and careful
experimental investigation of the reaction must have been
made. By the beginner particularly, equations must not be
used as a means of predicting the interaction of two or more
substances, but should be regarded as records of facts which
have been ascertained by careful experiment.

Before giving a brief description of the elements which are
of importance in agriculture it may be advisable to explain
the meaning of some of the commoner terms used in chemistry
As these explanations cannot claim to be other than frag'
mentary and disconnected, no attempt at a logical arrange-
ment is made. For convenience in reference an alphabetical
order has been adopted.

Acid* — a substance generally possessing a sour taste and
the property of changing vegetable blues, e.g.y blue litmus, to
red, and containing one or more atoms of hydrogen, which can
be replaced by a metal. As types of acids, sulphuric acid,
HjSO^, nitric acid, HNO,, hydrochloric acid, HOI, acetic acid,
HCjHjOj, may be mentioned. By replacement of the hydrogen
of these substances by a metal, e.g., sodium, the salts sodium
sulphate, Na,SO<, sodium nitrate, NaNO,, sodium chloride,
NaCl, and sodium acetate, NaC^HgOj, are obtained. The
possession of the sour taste and the power of changing vege-
table blues to red is indicated by saying that the substance
has an acid reaction, but is not a proof that it is an acid ; e.g.y
copper sulphate, CuSO^, has an acid reaction, yet it is a time
salt.

Alkali: — a . substance opposed in its properties to an acid,
capable of neutralising and destroying the characteristics of

8 ELEMENTARY AGRICULTURAL CHEMISTRY

an acid, forming, in doing so, a salt and water. The most im-
portant alkalies are soda, NaOH, potash, KOIT, and lime, CaO
or CaHgOj. Ammonia, NII3, or in solution (NHJOH, also acts
as an alkali. A substance is said to have an alkaline reaction
if it turns certain vegetable colours — e.g., litmus — which have
been reddened by an acid, back to blue again.

Base: — a substance, generally an oxide or hydroxide of a
metal, which can partially or wholly neutralise the acidity of
an acid, forming thereby a salt and water. The alkalies are
bases soluble in water, but many bases are insoluble.

Basicity of an acid is the number of atoms of replaceable
hydrogen present in a molecule of the acid. Thus the basicity
of nitric acid, HNO3, or hydrochloric acid, HCl, is 1 ; or these
acids are said to be monobasic. Sulphuric acid, HgSO^, has a
basicity of 2, or is dibasic; phosphoric acid, H3PO4, of 3, or is
tribasicy and so on. Monobasic acids can only form one kind
of salt with a metal, since the hydrogen must be wholly replaced,
if replaced at all. Thus there can only be one sodium nitrate
— the substance NaNOg. Dibasic acids, or acids of higher
basicity, can, however, form more than one salt with a metal.
Thus the sodium salt of sulphuric acid might be NaHSO^ or
NajSO^, according to whether one or both the atoms of hydrogen
in the acid have been replaced by sodium. The former salt
belongs to a class called the acid salts, and would be more
correctly named sodium hydrogen sulphate.

Destructive Distillation : — the change produced when a
substance, generally a carbonaceous compound, is submitted to
a high temperature with exclusion of air, and when gases and
vapours are emitted, the original substance being permanently
destroyed by the process. A good example is afforded in the
preparation of gas from coal. In most cases a black residue,
consisting largely of carbon, is left behind.

Endothermic and Exothermic Compounds.— By an

exothermic compound is understood a substance in whose
formation heat was evolved — e.g., carbon dioxide. Most com-
pounds are exothermic. An endothermic compound, on the

INTRODUCTION 9

other hand, is one in whose formation heat or energy was
absorbed. Consequently exothermic compounds are stable
and require some power to decompose them, while endothermic
compounds are unstable and give out heat or energy when
they decompose ; they are often explosive. A chemical change
evolving heat is described as an exothermic reaction, while
one in which heat or other form of energy is absorbed is called
an endothermic reaction.

Orgfanic Matter is, strictly speaking, matter which has
been produced by organisms — 2.e., animals or plants — but the
term is used in a wider sense in chemistry for any compound
of carbon, whether produced by life-processes or artificially.
Almost all forms of organic matter, when strongly heated out
of contact with air, blacken, owing to the liberation of carbon;
with free access of air combustion occurs, and carbon dioxide
and other products are formed.

Oxidation and Reduction.— By oxidation, literally

speaking, is meant union with oxygen, but in a chemical
sense the term is given a wider significance, viz., combination
with more oxygen or with some substance playing the part of
oxygen. Thus the conversion of a ferrous compound, e.g.^
ferrous chloride, FeCl,, into a ferric compound, ferric chloride,
FeClj, is often called by chemists a process of oxidation, though
no oxygen may be concerned in it.

Reduction is used in exactly the opposite sense. A sub-
stance which brings about oxidation of others is called an
'* oxidising agent," while one which removes oxygen or any-
thing which plays the part of oxygen is called a " reducing
agent." Common oxidising agents are air, nitric acid and
nitrates, chlorates, chlorine, &c. ; common reducing agents
are easily oxidisable metals, e.g., zinc, partially oxidised sub-
stances such as sulphurous acid, HjS03, many forms of deca,ying
organic matter (especially when under water), <fec.

Putrefaction: — a process of decomposition, sometimes
accompanied by oxidation, of carbonaceous matter, produced
by the life-processes of bacteria, yeasts, moulds, &c,, and result-

10 ELEMENTARY AGKICULTURAL CHEMISTRY

ing in the production of evil-smelling gases or vapours. When
oxidation by the air occurs, heat is evolved.

Valency. — Elements differ in their power of combining
with other elements. Thus chlorine can only combine with
hydrogen atom for atom, or one atom of chlorine is chemically
equivalent to one atom of hydrogen, as is seen in the com-
pound HCl ; oxygen has usually twice the combining power
of hydrogen, or one atom of oxygen is chemically equivalent
to two atoms of hydrogen, as seen in the compound H^O ;
nitrogen is possessed of even greater value in combination :
one atom of it can combine with three atoms of hydrogen, as
NH3; lastly, carbon forms a compound CH^, showing that
one atom of carbon is equivalent to four of hydrogen. The
number of atoms of hydrogen which one atom of a given
element can combine with or replace is called the valency of
the element. The valency of chlorine is 1, that of oxygen 2,
that of nitrogen 3, and that of carbon 4. Or chlorine is
said to be monovalent, oxygen divalent, nitiogen trivalent, and
carbon tetravalent. The valency of an element varies in
different compounds, and generally those compounds of an
element in which it has one particular valency possess many
properties in common, but quite distinct from the properties
which it has in another class of compounds in which its
valency is higher or lower. Thus divalent iron, which occurs
in all ferrous compounds, gives quite a distinct set of re-
actions from trivalent iron, which occurs in all fen^ic com-
pounds.

Volatile*. — capable of being converted from a liquid or solid
into a vapour or gas by heat. The term is somewhat loosely
used in two senses :

(1) (the proper use) When a substance on heating is con-
verted into a vapour or gas without undergoing any chemical
change. In this case, on cooling, the gas or vapour is trans-
formed again into the original solid or liquid — e.g.j camphor,
water.

(2) When a substance, on being heated, is converted into gas

INTRODUCTION 11

or vapour, and at the same time a chemical change, either
decomposition or oxidation, takes place. In this case the body-
is permanently altered, and on cooling, the gas or vapour does
not yield the original substance.

Of the eighty-three elements in the list on p. 3, by far
the larger proportion play little or no part in the ordinary
processes of plant and animal life. Indeed, a considerable
number are found in only extremely small quantities. From
the standpoint of the agriculturist, therefore, they possess
little interest. The bodies of animals and plants are mainly
built up of compounds of tho following elements :

Oxygen.

Potassium.

Hydrogen.

Sodium.

Carbon.

Magnesium,

Nitrogen.

Iron.

Sulphur.

Chlorine

Phosphorus,

Silicon.

Calcium.

A short account of these elements will now be given.

Oxygfen is the most abundant and most important of the
elements. It forms about half the weight of the solid crust
of the earth, eight-ninths of the water, and nearly one-fourth
of the atmosphere. In the first and second instances the oxygen
is in a combined state ; in the atmosphere it exists as the free
element, merely mixed with the other constituents.

Oxygen can be prepared in many ways. One of the most
usual laboratory methods is by the action of heat on potassium
chlorate, a substance having the composition expressed by
the formula KCIO,. The proportions of the elements present
in this substance are thus one atom of potassium, with a
relative weight of 39, one atom of chlorine, weighing 35*46,
and three atoms of oxygen, each weighing 16, so that in
39 + 35-46 + 48, i.e., 122-46 parts by weight of the salt, there
are 48 parts of oxygen. The final action of heat upon

12 ELEMENTARY AGRICULTURAL CHEMISTRY

potassium chlorate is to expel all the oxygen and to leave a
residue of potassium chloride, KCl. The reaction is therefore
represented by the equation

2KC103=2K01 + 30,.

The operation can be conducted in a hard glass flask or retort,
and the gas collected over water, in which it is only sparingly
soluble. If manganese dioxide, Mn02, be mixed with the
potassium chlorate the latter yields its oxygen at a much lower
temperature, and without fusion. A curious fact is that in
such a case the potassium chlorate is alone affected, the
manganese dioxide remaining unchanged at the end of the
operation. Oxygen compressed into steel cylinders is now
an article of commerce. Most of the oxygen so supplied is
prepared from the air by a process known as Erin's. This is
based upon the behaviour of barium monoxide, BaO, when
heated in air. Under proper conditions oxygon is absorbed
and barium dioxide or peroxide, BaOj, is formed, the other con-
stituents of the air passing away unchanged. By the action
of a higher temperature or lower pressure the barium dioxide
decomposes into the monoxide and free oxygen. The barium
monoxide is then again ready to absorb a fresh portion of
oxygen from the air, and so the process can go on almost in-
definitely. The reactions involved may be thus represented : —

(l)2BaO + 03 = 2BaO,

from the air
(2) 2BaO, = 2BaO + 0,

the equations in this case being simply reversed. The appa-
ratus employed on the large scale is ingenious and somewhat
complicated.

Oxygen is a colourless, odourless gas, very slightly soluble in
water, 100 volumes of water under ordinary conditions dis-
solving about 4 volumes of the gas. It shows a great tendency
to combine with other substances, and the act of union is usually

INTRODUCTION

13

attended with the production of much heat. Burning or com-
bustion is nearly always due to the heat produced by the
combination of the substance burnt with the oxygen of the
air. It is found, therefore, that any substance which will
burn in air (containing its 21 per cent, of free oxygen) will
do so with increased brilliancy in pure oxygen. The tem-
perature attained and the intensity of the light emitted are
always greater in the latter case, though the total quantity
of heat evolved by the union of a definite weight of a sub-
stance with oxygen is constant, and independent of the
circumstances under which the union takes place.

Quantity of heat is measured by the weight of water which
it can raise in temperature through 1° 0. It is therefore
possible to determine the amount of heat which is evolved by
the union of the unit weight (1 pound or 1 gramme) of a
substance with oxygen, and this value will be true under
whatever circumstances the union may take place. The
number which expresses the number of units of mass (pounds
or grammes) of water which are raised in temperature through
1* C. by the union of the unit mass (one pound or gramme)
of a substance with oxygen is called the heat of comhustion^
or the caloinfic power of the substance. The following
table gives the calorific power of a number of important
substances :

Charcoal .

8080

Fat of butter .

9216

Hydrogen.

34460

Olive oil .

9400

Wood

2800

Grape sugar

3750

Average coal ,

■ 7500

Cane sugar

3955

Coke

7050

Milk sugar

3952

Albumin .

5900

Malt sugar

3949

Casein

6860

Cellulose .

4185

Urea

2542

Starch .

4182

Fat of sheep ,

9494

In ordinary cases of burning, the evolution of heat is
readily evident, but in some cases of slow combination with
oxygen the heat is evolved so slowly that conduction and
convection carry it away almost as rapidly as it is produced,

14 ELEMENTARY AGRICULTUKAL CHEMISTRY

and very slight or no elevation of temperature is apparent.
In some cases, however, of slow oxidation, when the escape
of heat is hindered from any cause, the temperature rises so
as to be perceptible, or even dangerous. Under particularly
favourable conditions the rise of temperature may be sufficient
to start rapid combination with oxygen, and flame then results.
Such cases of " spontaneous combustion," as they are called,
not infrequently occur. Among the chief causes may be
mentioned absorption of oxygen by drying oils, e.g.^ linseed or
cotton-seed oil, especially when spread on cotton waste, as in
mills; fermentative changes in vegetable matter, e.g,^ hay,
lobacco ; slow oxidation of certain minerals, e.g.^ iron pyrites
m coal.

Hydrogfen is also very abundant in nature, though, because
of its low atomic weight (1-008), the proportion by weight
present on the earth's surface is small. Its most abundant
compound is water, H,0, It can leadily be obtained from
water by the removal of the oxygen by the aid of metals.
Some will set hydrogen free at the ordinary temperature on
contact with water, e.g.^ potassium or sodium, the reaction
being

Na, + 2H,0 = 2NaOII + H,,

only half the hydrogen being thus evolved. Other metals
liberate hydrogen from the v/ater at about the boiling-point,
e.g.^ magnesium :

Mg+2H,0 = MgH,0,+ H,;

while others require a red heat, e.g.^ iron. The reaction in the
last case is

3Fe + 4H,0 = ^efi^ + 4H,.

A more convenient method of preparing hydrogen is by the

action of a dilute acid upon a metal, e.r/., dilute sulphuric acid

upon zinc :

Zn + H,St), = ZnSO, + H,.
Zinc sulphate.

INTRODUCTION 15

The reaction commences at the ordinary temperature, and the
gas can be collected over water.

The characteristic properties of hydrogen are its h'ghtness
and the high temperature produced by its union with oxygen.
The former led to its employment for filling balloons, and
though now the more easily obtained coal-gas is generally em-
ployed for the purpose, it is not nearly so ej0&cienfc, and only
about half of it is hydrogen, the remaining half being made up
of heavier gases. Although the flame of hydrogen burning in
air or oxygen is intensely hot and can be used to melt refrac-
tory substances, e.^., silica and platinum, it possesses practically
no illuminating powers. When mixed with air or oxygen and
heated to a high temperature, e.g.^ by contact with a flame or
electric spark, hydrogen, like all inflammable gases, explodes
violently. With hydrogen and air the temperature required
to start the explosion is about 650° C, and any mixture con-
taining from 5 to 80 per cent, of hydrogen is explosive. Free
hydrogen is very rarely found in any quantity in nature,
though certain fermentative changes to which vegetable
matter is liable, produce it, and ib has been found in the gases
escaping from volcanoes. In a state of combination, however,
it occurs in a very large number of compounds, particularly
when combined with carbon, oxygen and nitrogen.

Carbon is the element most closely associated with plant
and animal life. It forms a large portion of the solid matter
of all living beings, and the chemical processes of animal and
plant life are mainly those in which carbon plays an important
part. It exists in the combined state in many minerals, e.g.,
the carbonates of calcium, magnesium, iron, zinc and lead, and
also in a small but important constituent of the air, carbon
dioxide. The element occurs in three distinct forms: the
diamond, graphite or plumbago, and the amorphous forms as
charcoal, lampblack, <fec. These allotropic forms as they are called,
though identical in composition (being elementary carbon),
are possessed of very different physical properties. Thus the

16 ELEMENTARY AGRICULTURAL CHEMISTRY

diamond is crystalline, transparent, and about three and a half
times as heavy as an equal bulk of water ; graphite is crystalline,
opaque, and about two and a half times as heavy as water ;
while amorphous carbon is, of course, non-crystalline, opaque,
and (when its pores are filled with water) about one and a half
times as heavy as watei* ' The black colour which is produced
when animal or vegetable wabstances are strongly heated with-
out access of air ("charring") is due to the separation of free
carbon from the various carbonaceous compounds present;
indeed, the charring of a substance when it is heated can
usually be taken as an indication that it contains organic or
carbonaceous matter. Chemically, carbon is remarkable for
its power of uniting in a vast number of different proportions
with hydrogen and with hydrogen and oxygen. Of such com-
pounds thousands are known, and their study comprises that
branch of science known as organic chemistry, which, though
of comparatively recent origin, has already attained vast
dimensions.

NitFOg"en is much less abundant in nature than the elements
already described. A peculiarity of its occurrence is the
fact that it appears to be present only in the outermost portion
of the earth, the greater portion being free in the air. No
true minerals containing it, except those which owe their
origin directly to plant or animal life, e.g., coal and Chili
saltpetre, are known. All living matter, however, contains it
as an essential constituent.

It can readily be obtained from its compound with hydrogen,
ammonia, by removing the hydrogen either by means of oxygen
or chlorine. Its properties are chiefly of a negative character,
for it shows little tendency to combine with other elements.
Although in the free state it is so inert, the nitrogen compounds
are as a rule, possessed of great chemical activity, and many of
them are very important substances. Many powerful drugs
and poisons contain nitrogen, e.g., quinine, C^oHj^NgO^, strych-
nine, O^HjjN^O, prussic acid, HCN ; while most explosives,

INTRODUCTION 17

e.g., nitroglycerine, C3H5N3O9, gun-cotton, CJI^NjO,!, and
many others, are also nitrogen compounds. It is an essential
ingredient in the food of both animals and plants. To the
former it must be supplied in combination with carbon
hydrogen, oxygen and other elements in the complex com-
pounds known as albuminoids, while plants require it chiefly
in the form of nitrates. Only under very special conditions
can some species of plants obtain the nitrogen they require
from the free nitrogen of the air. As will be seen in sub-
sequent chapters, although plants are surrounded with air,
which contains about three-quarters of 'its weight of nitrogen,
comhinedi nitrogen is one of the essential and most valuable
constituents of manures. A large portion of the nitrogen in
the food consumed by men and animals is eliminated in the
form of urea and other compounds in the excreta. Unfortu-
nately these are in many cases sent down the sewers into the
rivers, which are thereby polluted, and finally are discharged
into the sea. The valuable combined nitrogen is thus wasted
80 far as its utilisation in agriculture is concerned.

Sulphur is found both free and combined in nature. The
free element is found in volcanic districts, particularly in
Sicily ; while in the combined state it occurs as sulphuretted
hydrogen, H^S, in many mineral waters ; as sulphides of many
metals, e.g., of iron, as iron pyrites, FeS,, of lead, as galena, PbS,
of zinc, as blende, ZnS; and also as sulphates of certain
metals, e.g., of calcium, as gypsum or selenite, CaS0^.2HgO,
and anhydrite, CaSO^ and of barium, as barytes or heavy spar^
BaSO^. Calcium sulphate is very widely distributed, and
being soluble in water is to be found in most spfing and river
waters.

Sulphur can be obtained by the partial oxidation of sul-
phuretted hydrogen :

2H,S+0, = 2H,0 + 2S.

In this way large quantities of sulphur are now obtained, the

B

18 ELEMENTARY AGKICULTURAL CHEMISTRY

sulphuretted hydrogen being produced from bye-products in
the manufacture of " soda ash " (sodium carbonate) from
common salt.

Sulphur (" brimstone ") is a yellow, brittle substance which
is very inflammable. It burns in air with a pale blue flame
and forms the suflTocating gas, sulphur dioxide, SOg, while' small
quantities of sulphur trioxide, SO3, are also produced. The
latter by its union with the water vapour always present in
the air, forms sulphuric acid, HgSO^. Sulphur, like carbon, is
capable of existing in three modifi(!ations, possessing difierent
physical properties. Unoxidised or partially oxidised sulphur
compounds are very inj urious to plants, while sulphates are
not only harmless, but necessary. Sulphur is present in the
albuminoids of both animals and plants, and when putrefaction
of these substances occurs is often liberated as sulphuretted
hydrogen. This substance is perceptible by its disagreeable
odour as one of the chief products of the decay of albumin in
eggs.

Phosphorus always occurs in a state of combination.
Phosphorus compounds, chiefly phosphates, are very widely
distributed, but in small proportion, in the rocks of the earth.
Deposits of calcium phosphate, Ca3P208, occur in certain
localities, and are highly ■prbieA for manurial purposes. All
fertile soils contain small quantities of phosphates, which are
taken up by plants, and through plants find their way into
animals, where they accumulate in the bones or other hard-
parts {e.g.f teeth and shells). The element itself is somewhat
difficult to obtain, because of its strong aflinity for oxygen. It
is prepared by the action of carbon upon metaphosphoric acid
at a very high temperature, the chief reaction being —

4:HP03 + 12C = 12CO + 2H3 + P,.

Phosphorus, as usually prepared, is a yellowish, waxy
substance which has the power of emitting a faint light when
exposed to air. This property was the origin of its name,

INTRODUCTION 19

which is derived from the Greek and means "the light-bearer."
The emission of light is due to slow oxidation, and although the
glow occurs at low temperatures, heat is evolved, and often raises
the temperature to a point high enough to start rapid combus-
'tion (about 60° C), and actually to set fire to the phosphorus.
Phosphorus burns in air with a dazzling white light, evolving
dense clouds of phosphorus pentoxide, PjO^, which readily dis-
solve in water, forming phosphoric acid, HgPO^. Phosphorus
is a violent poison. It is largely used in the manufacture of
lucifer matches, and occasionally as a rat-poison. From an
agricultural standpoint its chief importance lies in the use of
its compounds, the phosphates, as manures, and its occurrence
in association with fats and albuminoids in feeding stuffs and
in the bodies of animals.

Calcium is very abundant in nature, always occurring
in a combined state. Calcium carbonate, CaCOg, is found in
enormous quantities in chalk, limestone and marble ; the sul-
phate is very abundant as gypsum or selenite, CaSO^ .2Kfl;
and the silicate is found as a constituent of many minerals.
The element itself is an easily oxidisable metal, difficult to
prepare, and of little importance. Its oxide, CaO, is the
important substance quicklime. Calcium is an essential con-
stituent of plant food, but in soil its compounds fulfil other
more important functions, which will be described hereafter.

Potassium occurs in many minerals. Most silicates con-
tain it in smaller or larger amount, and in some, e.^., oriho-
clase, AlgOg.KjO.GSiOg, and mica, K20.3Alj,03.4SiOj„ potassium
is an essential ingredient. It also occurs in sea-water, from
which sea- weeds accumulate large quantities of potassium
compounds. The huge saline deposits at Stassfurt furnish a
large proportion of the potassium required in the arts and for
manurial purposes. The character of these deposits will be
described later.

The element can be prepared by the action of carbon at a

20 ELEMENTARY AGRICULTURAL CHEMISTRY

very high temperature upon the carbonate or hydroxide of
potassium. It, is a bright, lustrous metal, very soft, and so
susceptible to oxidation that it has to be kept from contact
with air or moisture; this is often effected by means of
naphtha, a hydrocarbon. By contact with water it yields
potassium hydroxide and liberates hydrogen :

K, + 211,0 = 2K0H + H,.

The heat evolved by this reaction is so great that the metal
melts to a globule, which floats on the surface of the water
with a hissing sound ; the hydrogen is ignited, and burns with
a flame coloured violet by the vapour of the potassium.

Potassium compounds are of great importance in agriculture
and essential constituents of all fertile soils. They appear to
be closely associated with the growth and increase of plants,
and are always found in greatest abundance in the twigs,
young leaves, and other rapidly growing portions. In the
plant the potassium is in combination with various acids,
nitric, hydrochljric, and very often with organic acids —
e.g., oxalic, HgO^O^, citric, HgCgH^Oy, tartaric, HgC^H^Og,
and malic, HgC^H^Oj. In the ash of plants, however, it
generally occurs as carbonate, and this is the chief constituent
in the ash of the twigs and leaves of trees. Potassium salts
are very soluble in water, but are absorbed and retained by
certain constituents of the soil, so that their loss by drainage
from soil is little to be feared.

Sodium is very widely distributed in nature, and is a
constituent of many silicates. In the form of chloride, NaCl,
it is very plentiful as rock-salt and as the largest saline in-
gredient in sea-water. The element is prepared by the action
of carbon upon the carbonate or hydroxide, or by electrolysis
of common salt. Its properties resemble those of potassium.
Sodium compounds are very largely used in the arts, and the
preparation of sodium carbonate is one of the largest and most
important of the chemical industries.

INTRODUCTION 21

Sodium is found in the ashes of most plants, but, except
in the case of certain species, does not appear to be essential
to their welfare. A striking diflference between sodium and
potassium compounds, which are so much alike in most of
their properties, is in their behaviour towards the soil when
applied in solution. The potassium salts are retained by the
clay and organic matter in an insoluble form, but the sodium
salts are easily washed out by water and escape into the
drains.

Magfnesium is widely met with in nature as carbonate and
silicate. The metal itself is a bright, silvery substance, very
light, and capable of burning in air or oxygen with an intense
and dazzling white light. Magnesia, MgO, magnesium,
carbonate, MgCO,, and Epsom salts, MgSO^.THjO, are the
compounds most commonly used in the arts.

Magnesium is found in the ash of plants, and appears to be
essential, but as it is rare to find a soil deficient in magnesium
it is of little practical importance from an agricultural
standpoint.

Iron occurs in a large number of compounds. ITcematite,
Fe^O,, magnetite^ FejO^, and spathic iron ore, FeCO,, are
abundant minerals, valued as ores of iron. The element
occurs in two states of oxidation, as ferrous or divalent iron,
and as ferric or trivalent iron. The former forms salts which
are white or green in colour ; the latter, compounds which are
red and yellow. Ferrous compounds are often present in rocks
or minerals deep underground, but when they are brought to
the surface they combine with the oxygen of the air to form
ferric compounds. The change of state of the iron is indicated
by a change in colour in the rock or mineral, often from
green or grey to red or yellow. Only ferric compounds should
occur in good Soils. Iron is essential to plants, but a small
quantity is all that is required, and in most soils more than
this is present.

22 ELEMENTARY AGRICULTURAL CHEMISTRY

Chlorine is very abundant, especially in combination with
sodium, as rock-salt^ in the sea and in spring- watei . Othei
compounds of chlorine also occur as minerals. The element
is usually obtained by oxidising hydrochloric acid, HCl, when
the hydrogen is removed to form water and the chlorine
evolved. Many substances may be used to bring about this
oxidation. Black oxide of manganese, MnO„ is often used.
When this substance is heated with a solution of hydrochloric
acid (the usual hydrochloric acid, or " spirits of salt ") about
half the chlorine present is evolved, and the gas, being nearly
two and a half times as heavy as air, can be collected by leading
it to the bottom of upright vessels.

MnO, i- 4HC1 = MnCl, + CI, + 2H,0.

Chlorine is a yellowish-green gas, possessed of an irritating
and suffocating smell, very soluble in water, and of great
chemical activity. It readily unites with most metals, and
shows a particularly strong tendency to combine with hydrogen.
By pressure and cold, chlorine can be liquefied. The properties
of chlorine which are most valued in the arts are its bleaching,
disinfecting and deodorising powers. It readily destroys
most organic colouring matters, and is largely employed in
bleaching vegetable textile fabrics, e.^,, cotton or linen, lb
cannot be used for woollen or silk fabrics, as it injures the
fibres themselves. Chlorine only bleaches in the presence of
water, and it really acts by oxidation. Of itself it does not
decompose in water, except in the presence of strong light (sun-
light), but the combined effect of the organic colouring matter
tending to combine with oxygen and the attraction of chlorine
for hydrogen bring about the decomposition of water, with the
production of some oxidised organic matter, which is generally
colourless, and hydrochloric acid. Its action as a disinfectant
is probably due to the same process, the oxygen of water com-
bining with the organic matters, and micro-organisms and
destroying them.

Silicon is extremely abundant in the rocks of the earth's

INTRODUCTION 23

crust, anfl, though it forms a very important ingredient in soil
•and occurs in many plant ashes, it does not appear to be
essential as a plant food. Recently it has been shown that
soluble silica in a soil enables plants to subsist in the presence
of a smaller quantity of phosphoric acid than would be neces-
sary without the silica.

The element itself is of little importance. It is prepared
from the oxide, silica, SiO,, by the action of some substance
having a very strong affinity for oxygen, the most suitable re-
ducing agents being the alkali metals, potassium or sodium, or
magnesium powder. It is usually a brown solid, but, like
carbon or sulphur, can be obtained in several allotropic
forms.

The oxide, silica, SiOj, is a very abundant substance, occur-
ring free as quartz, flint and sand, and, in combination, as the
very numerous and important class of minerals, the silicates.
It has been estimated that nearly half the solid mass of the
outer crust of the earth consists of silica.

CHAPTER II.
THE ATMOSPHERE.

Physical Properties. — Most terrestrial plants and animals
live surrounded by air, and many of the processes of life are
directly dependent upon chemical actions in which the con^
stituents of air take part. Air also plays an important part
in the formation of soils and in the changes which occur iij
their constituents. It is therefore essential that the student
should have some knowledge of the properties and composition
of the atmosphere if he is to understand the nature of the
themical processes which are concerned in the life and growth
if plants and animals.

That air is a material substance only becomes apparent under
certain conditions. The space around us is apparently empty,
for air is invisible and seems to permit of bodies moving freely
within it. It is well known, however, that when a body of
considerable area is. moved rapidly in air great resistance is
ofiered, thus proving that air is a material substance. More-
over, by depressing a glass vessel, e.g., a beaker or tumbler,
mouth downwards beneath the surface of water it v/ill be
observed that the water only enters the vessel to a slight
extent, and that it is kept back by the air within the vessel.
These simple phenomena and many others prove the material
nature of air. It is quite easy, too, to show that air hab
weight. If a spherical flask be provided with an india-rubber
stopper fitted with a short piece of glass tubing to which a
piece of rubber tubing and a pinch-cock is fitted, it is possible
\o extract a large portion of the air, either by means of an

24

THE ATMOSPHERE 25

air-pump or more simply by placiDg some, water in the flask
and heating il to boiling. The steam from the water drives
the air out of the flask, and if the pinch-cock be closed and the
flame removed from under the flask the st^am within will
gradually condense. When quite cold the flask can be
accurately weighed. If the pinch-cock be then opened for a
moment air will be heard to enter the flask to take the place
of the steam which has condensed, and the flask will then be
found to have increased in weight, the increase being the
weight of the air which has entered. In this way it can be
shown that a litre of air weighs, under ordinary conditions,
about IJ grammes, or 1000 cubic feet weigh about 80 lb.

In consequence of its weight, air is pulled down towards the
surface of the earth, and those portions nearest the surface are
compressed by the weight of those above; consequently all
bodies on the earth are subjected to the pressure of the air
above and around them, for air, like other fluids, transmits
pressure in all directions. The pressure exerted is very high,
amounting on the average at the sea-level to about 14| lb.
per square inch, or 1033 grammes per square centimetre.
This pressure is a direct measure of the weight of the air.
On every square foot of surface at the sea-lev«l, therefore,
there rests 14-75 x 144 = 724 lb. of air, or upon an acre the
total weight of air would be about 41,300 tons.

The Barometer. — The pressure of the air is measured by
means of an instrument called a barometer. In its simplest
form it consists of a glass tube (preferably rather wide in bore)
about 32 or 33 inches long, closed at one eiid, open at the
other, filled completely with mercury and inverted into a
trough of mercury. It is then found that the mercury sinks
in the tube only a few inches, and comes to rest with the
mercury surface in the tube about 30 inches above that in the
trough. Equilibrium is reached when the weight of the
mercury column is equal to the weight of an air column of
the same sectional area whose base is at the mercury surface in
the trough or cistern and wliich extends to the utmost limits of

26 ELEMENTARY AGRICULTURAL CHEMISTRY

the atmosphere. This simple form of barometer is the best,
and, with proper means for accurately measuring the vertical
distance between the two mercury surfaces, is the most
accurate. The ordinary weather-glass^ or wheel barometer,
though it can be made very sensitive — i.e., capable of showing
even a small change in pressure — has no claims to accuracy.

The aneroid barometer depends for its action upon the elas-
ticity of a steel box which has been completely emptied of air.
The pressure of the air causes the lid of the box to collapse
partially, and the amount of the indentation will be greater or
less as the pressure varies. The motion of the lid is indicated
by the rotation of a pointer moved by a chain attached to the
centre of the lid, and controlled by a light spring.

As the height of the barometer measures the pressure,
which depends upon the weight of the air above, it is obvious
that the pressure, and therefore the barometric reading, will
diminish as the altitude above the sea-level increases. Hence
it is possible to measure this by means of the barometer.
The relation between the difference in the vertical heights of
the two stations and the difference in the barometric readings
depends upon several conditions. Roughly speaking, it is found
that near sen level for an ascent of about 900 feet the barometer
falls one inch, while from a height of 5000 feet an ascent of
about 1100 feet is accompanied by a fall of an inch in baro-
metric pressure.

Air, like other gases, is altered in volume by changes in
temperature or pressure. If the former remain constant tho
volume of a given quantity of gas is inversely proportional ta
the pressure. This relation was discovered by Boyle in 1661,
and is nearly true for all gases between small limits of pressure.

If the pressure be constant the volume of gas varies
directly as the temperature, measured from the absolute zero of
temperature. The absolute zero is apparently at a point
273° C, or 491° F., below the melting-point of ice — i.e.,
- 273° C, or - 459° F. By the application of this generalisa-
tion the calculation of the volume which a known quantity of a

THE ATMOSPHERE 27

gas would occupy under new conditions of temperature and

pressure becomes simple. To take an example : Suppose a

gas measures 1000 c.c. at a temperature of 15° 0. and under

a pressure of 740 mm. of mercury, and it is desired to

calculate the volume it will occupy at 20° 0. and 7G0 mra.

Consider the effect of change of temperature. Tlie absolute

temperature of 15° is 273 + 15 = 288. The absolute

temperature of 20° is 273 + 20 = 293. The volume is

directly proportional to the absolute temperature; .*. the

203
volume will be 1000 x ^r^ if the pressure were constant. Next

Zoo

ronsider the influence of pressure. The pressure changes from

740 to 760 mm. ; therefore the volume will be diminished ; it

29S 740
will thus be 1000 x -^^ x ^tttt, = 1004-3 c.c.
Zoo / bU

Chemical Composition of the Air.— Air is a mechanical

mixture of several gases, some of which are invariably present,
though in variable proportion, while others are sometimes
practically absent.

The chief gases are : —

Nitrogen. Ammonia.

Oxygen. Nitric acid or oxides

Argon. of nitrogen.

Carbon dioxide. Ozone.

Water vapour.
m

Nitrogen is the largest and least variable constituent, its
amount in dry air being about 78 per cent, by volume, or
75-5 per cent, by weight. Although so abundant, it plays very
little part in the processes going on in the air ; indeed, its
chief function may almost be said to be that of a diluent.
Certain crops have been proved to assimilate the free
nitrogen by the aid of tubercles on their roots, and some very
low forms of plant-life are believed to be able directly to
utilise free nitrogen, but the great majority of plants have

28 ELEMENTARY AGRICULTURAL CHEMISTRY

apparently no power of utilising nitrogen, except when it is in
a state of combination, best in the form of nitrates.

Oxygen is the most active and perhaps most variable con-
stituent. Its average proportion in dry air is nearly 21 per
cent, by volume, or 23*2 per cent, by weight. In consequence
of the large number of processes of oxidation taking place, the
proportion of oxygen is liable to local variations, but these are
not so great as might be expected, because of t^e influences of
diffusion, convection, and wind, and the compensating action of
vegetation. In towns and over marshy places the amount of
oxygen is generally found to be slightly less than in the open
country or over the sea. The limits of variation in the outside
air are not wide, perhaps from 20*5 to 21*03 per cent.

Argon, a recently discovered constituent, is of little im-
portance from an agricultural or, indeed, from any practical
standpoint. The gas, which is about 19*9 times as heavy as
hydrogen, is remarkable for its inert character ; so far as is
known, it takes no part in any chemical processes, and appears
to be incapable of uniting with any other element, or even with
itself. Its molecule, unlike that of most gases, consists of one
atom. Its amount in the atmosphere is about 0'94 per cent.
by volume, or 1*3 per cent, by weight. Helium, neon, krypton
and xenon are other new elements which have been found in
air in excessively small quantities. So far as is known, they
play no part in any chemical change. •

Carbon Dioxide is a small but important constituent. Its
percentage amount is very variable, being increased by the
combustion and decay of all organic bodies and by respira-
tion. The average amount in the air as a whole is estimated
at about 0-03 per cent, by volume, but the tendency of recent
.investigations has been to give somewhat lower numbers. On
the land its proportion is greater during the night than in
the daytime* but over the sea this daily variation cannot be

THE ATMOSPHERE 29

detected. The quantity present in the atmosphere is increased
by many processes, among the most important being ;

(1) Emission from volcanoes, deep springs, and other sub-
terranean sources.

(2) Oxidation of carbonaceous matter — e.g., the combu&tion
of most fuels, the decay of animal and vegetable matter, and
the respiration of animals and plants. •

(3) The dissociation of carbonates by heat — e.g., in lime-
burning.

CaCOj = CaO + CO,.

The chief process tending to diminish its quantity is its
decomposition by the green portions of plants under the influ.
enc3 of sunlight. In this case the carbon is retained, being
converted into various complex organic compounds, and used
in forming the tissues of the plant, while the oxygen is returned
in the free state to the atmosphere.

The magnitude of this process of removal of carbon dioxide
from the air by plants is enormous. Some conception of it
can be formed when it is remembered that about half the dry
portion of most plants consists of carbon, and that the whole
of this is obtained from the atmosphere. Thus an acre of
an average crop of mangolds will abstract from the aii* before
reaching maturity about 3500 lb. of carbon, which repre-
sents the carboa dioxide in a 200-feet layer of air covering
some 180 acres. The amount of carbon dioxide present in the
atmosphere is continually being affected by the two kinds of
actions described, oxidation of carbon compounds and decom-
position of carbon dioxide by plants, and these processes
approximately balance each other.

Ammonia and Nitric Acid, or some oxide of nitrogen, are
often present in the air, but in exceedingly small quantities.
Near Paris the average amount of ammonia is estimated at
1-7 milligrammes per 100 cubic metres in winter, and 2*1 milli-
grammes per 100 cubic metres in summer. Other observers
have found three times as much in June as in February.

30 ELEMENTARY AGRICULTURAL CHEMISTRY

The nitric acid is probably present as ammonium nitrate (or a
portion of that reported as nitric acid may really be nitrous
acid as ammonium nitrite). The source of the ammonia is
probably the putrefaction of nitrogenous organic matter, as
the amount is generally larger near towns than in the open
country.

The quantities of these substances are generally so small
that they can only with great difficulty be estimated, and
since they are readily soluble in water they are largely re-
moved from the air by rain. In rain-water, therefore, they
become more concentrated, and analyses of rain are of much
interest as indicating the quantities of these and other sub-
stances present in the air. Many analyses have been pub-
lished— e.g., those made by Angus Smith in 1872, of which
the following is an abstract : the figures represent parts per
million of the rain water.

o

2

"3

-d

"2

^i

i

•^

IS

w to

eS

O c«

'D

d^g

riace of Collection.

2s

'i
%

CO

'3
o

a
s

.2 "5

a 9
<<

<

HI

Ireland, Valentia

48-67

2-73

6

None

•18

•03

•37

•06

Scotland, 8 coast

places .

12-91

7-66

59

2-44

•99

•11

•47

•65

„ 12 inland

places .

3-38

2-06

61

•31

•53

-04

-31

•26

England, 12 inland

places .

3-99

5-52

138

None

1-07

•11

-75

•47

Scotland, 6 towns

6-86

16-50

282

3-16

3-82

•21

1-16

1-86

„ Glasgow .

8-97

70-19

782

15-13

9-10

•30

2-44

10-04

England, 6 towns

8-70

3t-27

394

8-40

4-99

•21

-85

2-74

„ London

1-25

20-49

1645

3-10

3-45

•21

•84

—

„ Manchester.

5-83

44-82

768

10-17

5-96

•25

1-01

3-22

Experiments at Rothamsted in 1880-89 showed a mean of
0'426 part of nitrogen as ammonia and 0*1 31^ part of nitrogen
as nitrates per million of rain, which, with a total annual
rainfall of 29 -27 inches, gave a total of 2*823 lb. of nitrogen
as ammonia and 0-917 lb. of nitrogen as nitrates brought

THE ATMOSPHERE 31

down by the rain on each acre. To these must be added
about 0*8 lb. of nitrogen as organic matter, giving a total of
about 4*5 lb. of nitrogen per acre per annum.

As the mean of investigations carried on at seven Conti-
nental stations between 1864 and 1872, 0"47 part of nitrogen
as nitric acid and 1*26 parts of ammonia per million of rain
were found, equivalent to a total of 10*18 lb. of combined
nitrogen per acre per annum. These results are much higher
than the English figures, probably because some of them were
obtained in or near towns. In tropical countries the amounts
are generally much higher. Thus in Pretoria in the year
July 1, 1904, to June 30, 1905, the writer found a mean of
1-194 parts per million of nitrogen as ammonia and 0-196 part
per million of nitrogen as nitric acid in the rain, equivalent,
with a total rainfall of 24-31 inches, to 767 lb. of combined
nitrogen per acre per annum. It is also noteworthy that in
the Transvaal the whole of this is brought down during the
active growing season — the summer, September to April — for
the winter months are almost absolutely rainless.

The combined nitrogen of the air in the rain is of consider-
able importance to plants. The amount given above for
Rothamsted, 4*5 lb. combined nitrogen per acre per annum,
is equivalent to the application of about 27 lb. of nitrate of
soda, while that for Pretoria corresponds to 47*6 lb. of nitrate
of soda, or 36*2 lb. of sulphate of ammonia.

Ozone is an active form of oxygen obtained from ordinary
oxygen by the action of the electric discharge, especially the
form known as the silent discharge, or by the slow action of
certain readily oxidisable substances — e.g.j phosphorus — upon
oxygen or air • It is a gas with a peculiar odour, capable of
oxidising most organic substances and many metals. It is
doubtful if its presence in air has any beneficial effect upon
people breathing it, but it aflfords a proof that the air is free
from oxidisable organic matter, and probably from micro-
organisms. Its amount in the air is very variable, but always

32 ELEMENTARY AGRICULTURAL CHEMISTRY

very small ; in towns or over marshes it is rarely found. It
is most abundant in Europe during May or June, especially
after violent thunderstorms or gales.

In addition to the substances already mentioned as occurring
in air^ there are others which may be described as accidental.
Near towns or wherever much coal is burnt, air is found to
contain sulphur dioxide ^ which, on oxidation, passes into sul-
phuric acid. The rain of towns is usually distinctly acid from
this cause, and to this acidity is mainly attributable the diffi-
culty of growing plants, particularly grasses, in towns.

Air also contains suspended matter of various kinds. Parti-
cles mainly composed of common salt, NaCl, are very abundant,
resulting from the evaporation of the tiny droplets of sea- water
sent up as spray from breaking waves. These particles are
carried immense distances hy the wind, and are the chief source
of the chlorides found in rain-water. The amount is greatest
at places near the coast, but even far inland rain often contains
considerable quantities of chlorides.

In addition to the inanimate solid matter, air usually con-
tains micro-organisms or their spores. These are most abundant
in towns or wherever organic substances are undergoing decay ;
on mountain- tops they are very rare. The existence of these
micro-organisms is very important, since to them are attribut-
able many diseases and many forms of putrefaction and fer-
mentation. They are of particular interest and importance
with reference to dairy work, fermentation in breweries, the
manufacture of wines and spirits, and the preservation of all
forms of organic matter.

CHAPTER IIL
THE SOIL

Soil is the layer of disintegrated rock, mixed with the
remains of plants (and animals), which covers a large portion
of the land. It also contains living organisms of various
kinds, and variable quantities of water and air. The depth of^
soil varies greatly, being usually from six to twelve inches, but
sometimes is as great as several feet. Beneath it is the sub-
soil, which differs from it in being less oxidised and less rich
in organic matter. In many cases the line of separation
between the soil and subsoil is very clearly marked, often by
a difference in colour, the subsoil being generally the lighter
coloured.

Soils, consisting so largely of disintegrated rock fragments,
naturally depend for their chemical nature mainly upon the
character of the rocks beneath. Rocks are often classified by
geologists, according to their origin, into three classes :

(1) Igneous rocks — i.e., those which have resulted from the
cooling of intensely heated fluid matter.

(2) Sedimentary rocks — i.e., those produced by the settling
out of particles suspended (or in some few cases dissolved) in
water.

(3) Metamorphic rocks — i.e., those which have been essentially
altered in character since their deposition.

Rocks are rarely homogeneous — i.e., alike in all parts — but
are generally made up of several components mingled together,
often lying side by side in separate crystals. These com-
ponents, which have a more or less definite molecular struc-

83 0

34 ELEMENTARY AGKICULTtJRAL CHEMISTRY

ture and composition, are called minerals. Distinctly separate
minerals are most frequently to be found in the igneous rocks.

Minerals and Rocks. — The following minerals are ex-
ceedingly abundant, and are of importance in agriculture :

Quartz is chemically the oxide of silicon, SiOa, It has
been estimated that 35 per cent, of the solid crust of the earth
is composed of quartz. It is one of the hardest and most
durable of substances, being almost insoluble in water and
little affected by weather. In many cases, however, the other
constituents of rocks are acted upon by atmospheric agencies,
and the quartz crystals, being thus loosened, are removed by
► running water. Fragments of quartz consisting of crystals
rounded and worn by mechanically rubbing against each other
form the largest constituent of many soils. Such sand is
devoid of plant food.

Felspar is probably the most abundant of all minerals, con-
stituting, it is estimated, 48 per cent, of the earth's crust.
Chemically felspar is a double silicate of alumina and potash,
soda, or lime. The chief varieties of felspar are ;

Orthoclase, KgO.AiPg.eSiO, ;
Albite, NajO.AiPj.eSiOj; and
Lahradorite (Naj,.Ca)O.Al,03.3SiO,.

Orthoclase, or potash felspar, is the most important. It is a
hard mineral, often coloured pink or green, though sometimes
tvhite. Although hard, it is easily attacked by water and
carbon dioxide, the potash being largely removed in solution
as carbonate and silicate, while the final residue left is kaolin,
or china clay, Al3O8.2SiOj.2HjO. Orthoclase furnishes a con-
siderable quantity of the potash found in soils.

Mica, another abundant mineral, characterised by its
tendency to split into thin elastic plates, is essentially a
iilicate of alumina and potash, SAljOj-KjC-iSiOj, though

THE SOIL 35

ferric oxide is usually present, replacing a portion of the
alumina, and the potash is often partially replaced by magnesia,
lime, or soda. Mica also suffers decomposition under the in-
fluence of the weather, but not so readily as felspar. It
furnishes plant food in the potash, iron and lime which it con-
tains. Its amount in the earth's crust has been estimated at
8 per cent.

Silicates of Magnesia are also very abundant, the magnesia
generally being partially replaced by lime, ferrous oxide, or man-
ganese oxide. Talc and steatite may be taken as typical, their
composition being represented by the formula GMgO.^SiOj.HjO
Hornblende and augite, (Mg.0a.Fe.Mn)0Si02, are also very
abundant. They usually contain alumina and ferric oxide.
These minerals are easily acted upon by air and water,
and often yield brightly coloured (due to presence of iron)
clays.

Calcium Carbonate occurs in a great many crystalline
forms in the varieties of calcite (rhombohedral),and aiTagonite
(rhombic), also in the massive form as chalky Iwiestone and
marble. These are all essentially OaCO,, but the calcium is more
or less replaced by magnesium, and, moreover, most forms of
calcium carbonate contain notable quantities of phosphoric
acid. Calcium and magnesium carbonates, though only slightly
soluble in pure water,* are readily soluble in water containing,
as is the case with nearly all forms of natural water, carbon
dioxide. Rocks containing these substances, therefore, are
quickly eroded by exposure to the atmosphere. Calcium car-
bonate is of great importance in soils, both on account of its
providing plant food and because of its relationship to many
of the processes which go on in soils.

Clay in its pure form is hydrated silicate of alumina,
AljO3.2SiO3.2H2O, and is therefore devoid of plant food.
Ordinary clay, however, contains iron oxide and potash, the
latter remaining from the felspar from which most clays have

86 ELEMENTARY AGRICULTURAL CHEMISTRY

been formed. It therefore supplies potash to plants. Its
physical properties are very important, and greatly influence
soils in which it is abundant,

ROCKS '

The igneous rocks are the oldest, and it was from the debris
of igneous rocks that sandstones, shales and (indirectly)
limestones were formed.

Sandstones, Grits and Conglomerates consist of the larger
fragments of the waste resulting from the denudation of
igneous rocks — e.g., granite — which, in consequence of their
size and weight, have been deposited at or near the mouths
of rivers. Their main ingredient is silica, the grains of sand
consisting largely of quartz crystals, but in many cases frag-
ments of felspar, mica and other minerals are present. The
grains are cemented together either by calcium carbonate (in
" calcareous sandstone"), clay ("argillaceous sandstone"), ferric
oxide (" ferruginous sandstone "), or colloidal silica (" siliceous
sandstone"). Soils produced by the decay of sandstones are
light and friable and poor in plant food, unless there be
present potash-containing minerals, e.g., felspar and mica.

Shales consist essentially of the plastic, Jiydrated aluminium
silicate, kaolin, Al2O3.2SiO3.2H3O, but may contain any other
extremely finely divided matter obtain^ by the erosion of
the original rock. Particles of undecomposed or partially
decomposed felspar are often present, and these are important
because of the potash they contain. Soils formed from shale
are "heavy" and clayey, generally sufficiently rich in potash,
but poor in phosphates and in calcium carbonate.

Limestones, in which term chalk and magnesian limestone
may also be included, have been formed largely by the abstrac-
tion from solution by living organisms — e.g., coral polyps and
shellfish — of calcium and magnesium carbonates. They often
contain small quantities of clay, ferric oxide, silica and nearly
always calcium phosphate in comparatively large quantities

THE SulL 87

The soil left on limestone or chalk consists mainly of these
foreign substances, most of the calcium carbonate itself having
been dissolved out by the combined action of water and carbon
dioxide. It sometimes happens that the soil on limestones
would be benefited by the application of manures containing
lime.

Limestone only exerts its characteristic and important
functions in a soil when in a very finely divided state; in the
form of gravel or sand it is little better than ordinary siliceous
sand. In the finely divided condition it has two very valuable
functions — as a source of plant food, by virtue of the phosphates,
sulphates, and calcium which it contains, and, what is more
important, as a basic material necessary for the processes of
nitrification.

Sedentary and Transported Soils. — These terms are con-
venient in distinguishing between soils which are made up of
the debris resulting from the weathering of the particular
rock on which they rest (sedentary soils), and those which owe
their origin, fiot to the rock below them, but to matters brought
from a distance and deposited there (transported soils). The
rich alluvial soil in the lower reaches of river valleys consists
largely of matter which has been brought down by the river
from the higher parts of the valley, and since the materials have
in many cases, been brought from various rock formations the
resulting soil generally possesses a greater fertility than would
be shown by a soil formed exclusively by the weathering of
any one kind of rock.

Other excellent examples of transported soils are afforded by
the " warp " soils of the Humber and Trent. In these cases
the soil itself is transported, and not merely the materials out
of which it is (afterwards) formed.

Glaciers are also the means of transporting large quantities
of materials out of which soils may be formed. Large tracts of
country are covered with a thick deposit of clay and rock frag-
ments which have been brought from a great distance bj

88 ELEMENTARY AGRICULTtTIlAL CHEMISTRY

glaciers. Such deposits are known as glacial drift, and often
quite obscure the actual rock strata beneath. In this case the
transportation of the soil took place many ages ago.

Wind also sometimes acts as a means of transporting sand,
volcanic ashes, &c., from a distance and depositing them in a
new position, there to form a soil.

Formation of Soils.— In the formation of a soil the first
step is the mechanical breaking down of the rock into small
fragments. The chief agencies by which this is accomplished
are:

1. Water, which acts in several ways.

(a) Mechanically —

(i) By Liquid IVater, — The flow of water over the surface
of a rock abrades it slightly. The action is greatly increased
by the attrition of pebbles, gravel, <kc., urged by the current
over the rock. In this way streams in the rapid portions of
their course carry away large quantities of sand, gravel, (fee, and
deposit them in the lower and quieter portions of their course
as alluvial deposits.

(ii) By Glaciers. — Glaciers are slowly moving masses of ice
formed by the compression of snow by its own weight. In
their descent glaciers, aided by fragments of rocks imbedded in
them, grind away the rock over which they pass, and the stream
which issues from the snout of a glacier is always heavily
charged with the finest mud, while the termination of a
glacier is marked by huge piles of rock fragments of all sizes
(" moraines ") carried down on the surface of the moving ice.
This agency has been very active in past ages, even in countries
— e.g.., Britain — where no glaciers are now to be found.

{h) By Alternate Frost and Thaw. — Ice occupies a greater
volume than the water from which it is formed. The increase
in volume in the act of freezing amounts to about 10 per cent.,
and unless this increase be allowed to occur water cannot freeze,
however much it be cooled. In the disintegration of rocks
this agency is very powerful. During the warm part of a wet

THE SOIL S9

winter's day the crevices of a rock become filled with water.
If the temperature falls, the water begins to freeze, at first on the
surface, so that every crevice becomes plugged with ice. As
the liquid within continues to lose heat it tends to solidify.
This it can only do if it be allowed to expand, and in order to
do this it must either widen or lengthen the crevice which con-
tains it. When the next thaw comes the enlarged crevice again
fills with water ; the next frost repeats the action, and so the
process goes on, and in this way a rock, even the hardest, is soon
broken up into fragmenta Continuous frost appears rather to
hinder denudation by cementing the parts of a rock more firmly
together. In addition to the effect of expansion just described,
ice formation probably acts as a disintegrating agent upon soils
and rocks by virtue of crystallisation ; the mere growth of
crystals of ice, apart altogether from the expansion which
accompanies their formation, exerts a disruptive effect upon
the material in which they are formed.

(c) Chemically. — Many minerals when exposed to the action
of water are acted upon in such a way as to lead to their dis-
integration. A portion is often carried away in solution, while
the remainder crumbles away and is removed by rain or
running water. In many rocks the cementing material which
holds the grains of silica together is thus acted upon, when the
silica, though perhaps not appreciably dissolved by water,
becomes loosened and easily removed. Calcium, ferrous and
magnesium carbonates are particularly liable to be thus removed,
for though they are only very slightly soluble in pure water
they readily dissolve if carbon dioxide be present, owing to
the formation of bicarbonates ; thus —

CaCO, + H^CO, = Ca(HC03),.

2. Air. — This also acts in various ways.

(a) Mechanically. — "Wind actually detaches large projecting
pieces of rock in mountainous districts^ and sends them crashing
down on to the rocks or screes below. In addition, by hurling
sand and small pebbles against the surface of rocks it brings

40 ELEMENTARY AGRICULTURAL CHEMISTRY

%bout the erosion of the latter. In most cases the effects of
this form of erosion are masked and hidden by those of other
denuding agents, but occasionally — e.g.^ at Brimham Rocks, in
Yorkshire — the curious undercuttings produced by this action
are very clearly shown.

{h\ Chemically. — In many rocks are minerals capable of
taking up oxygen — e.g., ferrous carbonate. On exposure to air
oxidation occurs, and the mineral swells up, and often crumbles
to powder, thus loosening the other minerals in the rocks. The
oxidation is in many cases accompanied by a change in colour,
from green or grey to yellow or red. The carbon dioxide in the
air also acts corrosively on carbonates in the presence of water.

3. Animals. — Burrowing animals — e.g., rabbits and moles
— admit air into soil or sand, and thus favour the changes which
air produces. The part played by the humbler creatures,
earthworms, is probably much more important. They bring
portions of the subsoil to the surface, they draw dead leaves
and other vegetable refuse into their burrows, and they pass
large quantities of the soil through their bodies and deposit it
on the surface at a rate which has been estimated, on the
average, to be about ten tons per acre per annum. -

Ants in some hot countries — e.g., Africa — perform much the
same work as earthworms, though perhaps even on a larger
scale. In many parts of South Africa the veld is thickly
studded with the hills of the white ant, usually about two feet
high and about two or three feet in diameter, though much larger
ones are often found. The ant hills are full of cavities and
chambers inhabited by the insects, and much vegetable matter
is stored in them. The material of the ant-hills consists of
the smaller parts of the surrounding soil, the particles being
cemented together and the whole made practically water-tight.
When the veld is ploughed and sown it is always noticed that
where ant-hills had formerly been, the crop is heavier than else-
where. The following analyses of ant-heap material and the
adjacent soil, taken by the writer near Christiana, in the
Transvaal, will show the richness of such substances :

THE SOIL 41

Ant-heap. Veld soil
Per cent. Per cent.

Stones removed by 3 mm. sieve . • . None 8'66

The fine portion contained —

Moisture 3*28 1*98

Loss on ignition * 13-03 4 '14

Insoluble matter (sand, &c.) . . . 74-59 82-86

Iron oxide and alumina . . .8*79 9-89

Lime 0-30 0*12

Magnesia 0-40 0-18

Potash 0-39 0*25

Phosphoric acid (PgOg) . . . .0-06 0-06

100-84 99-48

♦ Containing nitrogen ..... 0-343 0'080

"Available "potash ... 0-0482 0-0121

"Available "phosphoric acid .... 0-0102 0-00^7

4. Plants. — These act in several ways: —

(a) Mechanically. — The roots penetrate the rocks or soils,
rendering them porous, and thus admitting air and water.
Plants growing on rocks also tend to keep the surface moist,
and thus favour erosion.

{h} Chemically : —

(i) During life. — By the corrosive action of the liquid
seci eted by the roots and root-hairs.t

(ii) After death. — By producing carbon dioxide and
various vegetable acids which have solvent properties
upon certain constituents of soils.

The formation of a mass of pulverised rock, however, is not
all that is necessary for producing a fertile soil. Ordinary
plants require the presence of organic nitrogen compounds
of the nature of *' humus," and the chief source of such matter
is the remains of previous plants. The question at once
suggests itself, how did the soil first obtain its organic matter
necessary for plant growth ? According to recent researches,

"f Recent work seems to point to carbon dioxide evolved by the root-
hairs as the corrosive agent, not any vegetable acid.

42 ELEMENTARY AGRICULTURAL CHEMISTRY

micro-organisms capable of assimilating free nitrogen from the
air and carbonaceous matter from carbon dioxide are to be
found on rock surfaces even near the summits of mountains.
Certain lichens and algae are also apparently able to grow
without combined nitrogen. Such growths, when they die,
furnish organic matter to the soil, and gradually fit it for
sustaining the life of higher plants.

The Constituents of SoiL— A popular and convenient
classification of soil constituents is the following :

1. Sandj — mainly silica, but containing small fragments of
felspar, mica, limestone, &c.

2. Clay — mainly kaolin, but containing also finely divided
silica, felspar, &c.

3. Ldmestone — finely divided calcium carbonate.

4. Humus — ^the somewhat indefinite nitrogenous and car-
bonaceous material resulting from fche decay of plants.

These constituents have great infiuence upon both the
physical and chemical properties of soil. The physical pro-
perties of the constituents themselves can be gathered from
the following table :

Real
Specific
Gravity.

Apparent
Specific
Gravity.

Specific
Heat,
Equal

Weights.

Specific
Heat,
Equal
Vols.

Con-
ductivity
for Heat.

Water
held by
100 Parts
by Weight
of Sub-
stance.

Sand .

Clay .
Limestone .
Humus .

2-62
2-50
2-6
1-30

1-45
1-01

0-34

•189
•233
•206
•477

•499
•668
•561
•687

100
90-7
85-2
90-7

25

70

85

181

It may be desirable to explain the meaning of the terms in
fche above table.

Real specific gravity is the weight of any volume of the
solid material compared with that of an equal volume of water.
Apparent specific gravity is the weight of any volume of the

THE SOIL 48

powdered material, with its enclosed air spaces, compared with
that of an equal volume of water.

Specific heat, eqvxxl weights^ is the ratio of the amount of
heat necessary to raise the temperature of a certain quantity
of the substance through, say, 10°, compared with that required
to raise an equal weight of water through the same range of
temperature. (See also chap, iv.)

Specific heat, equal volumes, is easily understood — the relative
amounts of heat required to raise equal volumes of the material
and of water through a given range of temperature.

Conductivity for heat is the quantity of heat which passes
through a cube of the substance when its opposite faces are
kept at different but constant temperatures, compared with
that which passes through a similar cube of another substance
under exactly similar conditions. In the table the numbers re-
ferred to silica =100 are given. The meaning of the figures
in the last column is suflficiently explained in its heading.

It is to be noted that some of the above values will vary
with difference in degree of fineness of the material and other
circumstances.

Sand is seen to have the greatest conductivity for heat and
the highest specific gravity, but the lowest specific heat and
lowest water-retaining power of all soil constituents. As a
plant food sand is practically valueless, except for the small
amounts of potassium, iron, and calcium sometimes present in
fragments of minerals occurring mixed with the true sand. Its
physical properties have great and often valuable effects upon
the character of a soil, particularly with regard to friability
and its relations towards water and heat.

Clay, if pure, is free from plant food, but is usually well
supplied with potash because of the felspar present. Common
clay, however, often contains quartz and calcium carbonate
(as in marls) in addition to felspar, the true clay, or kaolin,
Al,03.2SiO,.2HjO, acting as a kind of cement to the grains of
other minerals.

It is thought that even in the purest clay there is a small

44 ELEMENTARY AGRICULTURAL CHEMISTRY

quantity of aluminium silicate more hydrated than the rest,
to which the tenacity and plasticity of the clay is due. If
this constituent be fully swollen with water the clay is
sticky and impervious, while if it be shrunken or coagulated
the clay becomes more friable and less plastic. Coagulation is
easily brought about by the addition of acids or of many salts ;
calcium compounds are particularly effective in this respect,
and it is to this cause that the improvement in the texture of
heavy clay soils produced by the application of lime is due.
It can be illustrated by shaking up some pure clay with dis-
tilled water .and pouring the muddy liquid into two cylinders;
if to one some lime-water be added, the clay will be coagulated
or flocculated, and will settle to the bottom in a short time,
leaving a clear liquid above it, while the other will fail to
clarify even after standing a day or two.

The plasticity of clay is permanently destroyed by hekt,
which expels the two molecules of v/ater of hydration, the
anhydrous aluminium silicate left (e,^.,in the making of bricks
or tiles) not being capable of again combining with water.

Limestone. — Calcium carbonate is present in a soil in a
finely divided state disseminated among the other constituents,
but in addition there are often small fragments which are
clashed with the " sand." The former condition, however, is
the one which is of importance. It furnishes plant food by
virtue of the calcium, magnesium and phosphoric acid present,
but it plays other, perhaps more important, functions. It
modifies the plasticity of the clay in the manner characteristic
of calcium compounds, and acts as a weak base, for, though it
is a true salt, the carbonic acid is so weak an acid that it
is readily displaced by stronger acids^ which unite with the
calcium, and thus lose their acidity. Acids are produced by
the decay and fermentation of vegetable matter, and if large
quantities of such material are present in a soil there is often
a great tendency for the production and accumulation of free
acid, and the conditions then become unfavourable for the
growth of most useful plants. Such land is often spoken of as

THE SOIL 45

" sour," and can best be restored to fertility by the application
of free lime or of calcium carbonate. In soils containing an
abundance of calcium carbonate such sourness never occurs.

Another important function performed by the calcium car-
bonate is that of acting as a basic material necessary for the
important process known as nitrification ; this will be explained
hereafter. It is also important in the chemical changes which
are produced by the application of certain manures to soil —
e.^., in the case of ammonium sulphate, when the sulphuric
acid radical unites with calcium and runs off in the drainage
water, the ammonia being retained by the soil.

Humus, the characteristic organic matter of soil, is of great
importance on account of its chemical and physical properties.
The chemical nature is little understood, despite many investi-
gations. Many analyses of humus extracted from soils have
been made, but no definite constitution has yet been assigned
to it. Thus four samples gave the following ;

Carbon 44-60 per cent.

Hydrogen 3-6 „

Nitrogen 6-5-10 „

Oxygen 28-35

Ash 4-12

The ash was found to contain 7*5 per cent, of potash, 12-4 per
cent, of phosphorus pentoxide, together with silica, ferrit
oxide, alumina, soda, and other substances. According to
other investigations, humus contains several distinct and
complicated acids : huniict ulmic, crenic and apocrenic acids ;
but the nature of these bodies, which are said to be compounds
of carbon, hydrogen and oxygen, is not known, though several
formulae have been suggested for them.

Humus seems to be of an acid nature, and the calcium
compound is insoluble in water. The ash constituents asso-
ciated with humus are thought to be of considerable import-
ance, because they are apparently easily available for plants.
The nitrogen is of the utmost value to plants, though in most
cases it canaot be directly utilised, but must first be inverted

46 ELEMENTARY AGRICULTURAL CHEMISTRY

into nitrates by oxidation brought about under the influence
of the micro-organisms in the soil.

The physical properties of humus are also of importance. It
is a dark-coloured, bulky, porous substance, possessing con-
siderable tenacity or cementing power and a great capacity for
holding water, also for absorbing and retaining many import-
ant items of plant food — e.g,, ammonia, potash and lime.
The dark colour causes soils rich in humus to become heated
by the sun's rays more rapidly than light-coloured ones. The
bulkiness and porosity permit of freer admission of air, and
BO promote oxidation. In clay soils these properties confer
lightness and permeability. The cementing power is particu-
larly important in sandy soils, to which it imparts coherence
and water-retaining power, while its absorptive power is of
great value in retaining for the use of the plant many soluble
substances which might otherwise be removed in the drainage.

By the decay of humus, which is always going on, the
proportion of carbon dioxide in the soil water is increased,
and thus the solvent powers of the latter for plant food existing
in the mineral portions of the soil are enhanced.

Chemical Changes occurring" in Soils.— The reactions

taking place in a soil are very numerous, and of a type not
familiar to a student of elementary chemistry, the direction
of the change being largely dependent upon the conditions of
temperature, concentration, relative quantities of the reacting
substances, and other ciicumstances.

The inorganic matter is subjected to the same influences as
lead to its breaking down in the formation of the soil from the
rock, but the changes go on at an accelerated rate, because of
the greater quantity of carbon dioxide produced by the decay
of the organic matter. Fragments of felspar, for example, are
probably decomposed in accordance with the equation

AlA^»0.6SiO, + CO, + lOH.O = Al,03.2SiO,.2H,0
+ KjCOj + 4H,SiO„

THE SOIL 47

the silicic acid and potassium carbonate being dissolved and
either carried away in the drainage, or the latter may be
absorbed by the roots of a plant or by some of the ab-
sorptive constituents of the soil. The calcium carbonate is
dissolved by the carbon dioxide solution —

OaCO, + H,0 + CO, = Oa(HCO,),

— and is either carried away or absorbed, or perhaps acts upon
felspar or other silicate :

Al,0,.K,0.6SiO, + Ca(HC03), + 2'Bfl = K.CO, + CaCO,
+ Al,03.2SiOj.2H,0 + 4H,SiO,.

The phosphoric acid in minerals probably exists largely as
tricalcium phosphate, CajPgOg. This substance is nearly
insoluble in water, but by the action of carbon dioxide may be
changed thus :

Oa,P,08 + 200, + 2H,0 - Ca^H,P,08 + Oa(HC03),.

The dihydrogen dicalcium phosphate, dT, as it may be called,
the monocalcium monohydrogen phosphate, CallPO^, is
slightly soluble in water, and therefore available for plants.
In contact with ferric hydrate or aluminium hydrate it is
converted into ferric phosphate, FePO^, or aluminium
phosphate, AlPO^, and held back in the soil in a very finely
divided state, and, though then insoluble in water, is capable
of being dissolved by the acid juices of plants' roots. In fact,
many of the substances which become soluble owing to the
action of carbon dioxide, water, or other reagents do not
necessarily remain in a soluble form. If they did they would
be to a great extent washed out in the drainage water.

Most soils contain substances which have the power of uniting
with potassium, ammonium, and, to a less extent, calcium com-
pounds, and with phosphates, converting them into insoluble
compounds. If solutions of potassium or ammonium sulphate
or of sodium phosphate be filtered through a thick layer
j)f soil, the filtrate will be found to be almost free from

48 ELEMENTARY AGRIOtTLTURAL CHEMISTRY

potassium, ammonium, or phosphoric acid, though the sulphuric
acid may be present in the filtrate in the form of calcium sul-
phate. The substances which exert this retentive power in the
soil are believed to be :

1. The humus J which, in addition to acting as an acid, has
Jie absorptive power characteristic of extremely porous sub-
stances— e.g., charcoal.

2. Hydrated double silicates ^ probably transition bodies,
produced by the weathering of felspar, &c., possessing a com-
position similar to the minerals known as zeolites (so called
from a Greek word meaning,* to boili" and applied to them
because of their frothing up — due to the escape of steam —
when they are heated before the blowpipe). In many cases
if one metal be absorbed an equivalent quantity of another
metal (often calcium or magnesium) is given up to take its
place, and is carried away by the drainage water^

3. Ferric and Aluminium Hydrates. — These substances can
combine with phosphoric acid, forming the very insoluble
phosphates of iron or aluminium ; they can also retain lime,
potash and ammonia, probably owing to the fact that they
have weak acidic functions. The bases, however, are not
retained very tenaciously, and can be removed by prolonged
washing with water.

Phosphoric acid is retained most tenaciously by nearly all
soils, and the loss of this substance in the drainage is usually
insignificant.

The dissolved matter in soil water is distributed in two
ways :

1. By diffusion — i.e., the motion of the dissolved substance
from one part of the solvent to another. This process,
which tends to make the liquid uniform in concentration,
takes place more rapidly with some substances than others.
Colloidal bodies, or those which resemble glue or gum in
character, have the lowest rate of diffusion, whilst small diffe-
rences are shown by the various acid radicals and the metals
of salts ; thus chlorides diffuse more rapidly than nitrates or

THE SOIL 49

sulphates, and potassium salts than ammonium or calcium
compounds.

2. The Motion of the Liquid itself, — The solution in a soil
moves from two causes :

(i) Gravitation. — This is the attraction of the earth for
water, and only acts vertically downwards, tending to make the
solution sink into the soil.

(ii) Surface Pressure. — Every liquid surface exerts a
pressure upon the liquid within it. This is readily understood
when it is remembered that in a liquid every particle is
attracted by its neighbours, with a considerable force by those
particles nearest to it, and with less and less force by particles
more and more distant. Those at the surface are only
affected by the attraction of those within the liquid ; the
surface, therefore, is under a pressure acting inwards. A
liquid free to move always arranges itself so as to have the
smallest possible surface. If no other forces were acting it
would always assume a spherical form. Under ordinary con-
ditions gravitation far overpowers the effects of surface pres-
sure, but if the quantity of liquid be small the gravitation effect
becomes small and surface pressure asserts itself ; the liquid
thus tends to become spherical. Solid substances often exert
an attractive force (adhesion) upon liquids, so that when they
touch a liquid they become wetted.

The pressure exerted by a liquid surface depends upon its
form ; it is less than that of a plane if the surface be concave,
greater if convex. This can be understood by reference to the
diagram.

Let A B (Fig. 1) represent a plane surface of a liquid, and
consider any particle, C, well below the surface. The particles
whose attractive forces for C have any appreciable magnitude
may be assumed to lie within an imaginary sphere encircling
(7, and represented in section by the circle. It is evident that
the resultant of all the attractive forces acting upon G will be
nil^ since it will bo attracted equally in all directions. It
therefore remains in equilibrium. Now consider a particle, i),

0

50 ELEMENTARY AGRICULTURAL CHEMISTRY

at the surface. The imaginary limit of the particles which
have any appreciable effect on D would be represented by a
similar sphere, or, rather, by a hemisphere, since above the
surface there are no liquid particles. The resultant of the

B

Fia. 1.

forces acting upon D will be a considerable force acting towards
the body of the liquid and at right angles to the surface. The
same would apply to all particles on the surface, and to a less
degree upon all particles nearer to the surface than the radius

B

l!

uj

D

'^■V

Fig. 2.

of the imaginary hemisphere. Hence a plane surface exerts a
pressure upon the liquid within it.

Now take a surface which is concave, and consider a
particle, A (Fig. 2), on the surface. Draw a circle, with
A as centre, to represent the imaginary limit beyond which
the attraction of particles for A becomes inappreciable.

THE SOIL 51

Through A draw a horizontal line, BC. It is evident now
that the downward pressure exerted by the forces acting upon
A are less if the surface be concave than if it were horizontal,
because there is, in the former case, the upward resultant of
the forces exerted by the particles in the shaded spaces. Let
this upward attraction be represented by p, and the downward
force, if the surface were plane, be represented by P. The
final resultant will be P for the plane surface and P-p for the
concave, acting upon each particle on the surface. It is also
evident that the more concave the surface is, the greater will
be p and the less will he P-p,

Hence when a tube which is wetted by a liquid, and which
therefore has within it a concave surface of the liquid, is im-

Fig. 8.

merged in a liquid the latter rises until the hydrostatic pressure
in the tube is capable of balancing the difference betweam the
pressure exerted by the liquid surface outside the tube (which
will be approximately P if the area of the vessel be large) and
that exerted by the surface in the tube — i.e., P-p. This is the
cause of capillarity ^ as the rise of liquid iti hair-like tubes is
called.

Many writers on soils appear to think that in soils there are
such tubes, and they ascribe the rise of water to this action.
It is extremely improbable that this assumption is correct, for
the interstices of a soil are not filled with water, but, as is well
known, are largely occupied by air. True capillarity may per-
haps operate to a small extent, in some of the composite particles
of soil where the interstices among the cohering fragments
become entirely filled with water. But, in the great mass of
the soil, the motion of the water must be due to the action of
surface pressure exerted in the manner described. The rise of

52 ELEMENTARY AGRICULTURAL CHEMISTRY

water is due to the same cause as that which produces capillarity,
but acting in a different way. If two particles of soil, each
covered with a thin film of closely adherent water, be caused to
touch, the water films at the point of contact must take up a
concave surface. At this point the pressure exerted by the
liquid surface is less than elsewhere. Consequently water
moves from the films around the particles and tends to accu-
mulate at the space between them until the curvature becomes
less, indicated by the dotted line (Fig. 3). The water is thus
held between the particles by a surface tension efiect of the
same kind as that which causes capillarity. Now suppose three

particles to be in contact,
each with its film of moisture,
and assume that the amount
of water held between B and
C (Fig. 4) is greater than

that between A and B. The

Pjq^ ^ water surfaces at the line

of contact between A and B
will be more concave than those between B and C, and conse-
quei^ly the surface pressure exerted there will be less. Water
will therefore move round B in the direction of A until the
pressure exerted by the concave surface between A and B is
equal to that exerted between B and G, This action will occur
at every surface between neighbouring particles, and will account
for the movements of water from particle to particle, even
though there be many interstices filled w^ith air.

It is to be noted that the movements of water due to this
cause may be in any direction ; it will practically always be
from a more wet to a less wet part of the soil. The structure
of soil, therefore, in respect to the cause of the rise of water
from below is to be regarded in this way, and not by assuming
that the sol' particles form hair-like tubes filled with water.
The quantity of water which is held by a soil and the readiness
with which the water is raised from below is thus largely
dependent upon the number of points of contact of the soil

THE SOIL

53

particles, each contact giving rise to the formation of a concave
surface of the water layer, thus determining the movement of
water to that part. The number of these re-entering angles
or concave surfaces of water will increase with the fineness of
subdivision of the soil. At the same time excessive fineness of

Fig. 5.

the particles will tend to make the process slower, by increasing
the friction ofi*ered to the motion of the water.

If all the particles are already wet the action described will
occur rapidly, but if some of the pai tides are dry, then the
action will not occur until the dry particles become wetted by a
slow, creeping movement of the water over them. Hence,
although stirring a soil increases the rapidity of evaporation

54 ELEMENTARY AGRICULTURAL CHEMISTRY

from its surface, the total loss of water may be diminished if
the upper layers be frequently stirred ; they thus become dry,
the particles have fewer points of contact, and the flow of
water from below is greatly impeded by abolishing, for a time,
the production of the concave surfaces of water films (at the
contacts of the particles), which, as described above, are so
powerful in assisting the movements of the water.

NitPification. — Perhaps the most important reactions
going on in a soil are those connected with the decay of
organic matter and the change in the state of combination of
the nitrogen. The organic matter is continually being oxidised,
the carbon being mainly converted into carbon dioxide, though
certain organic acids are also formed, and may be injurious if
the soil be deficient in limestone or other substance capable of
acting as a base. The nitrogen originally present as complex
organic bodies is eventually converted into nitrates, and this
change is known as nitrification. It is really a process of oxida-
tion, and may be divided into three stages :

1. The conversion of the complex nitrogenous organic
compound into ammonium compounds.

2. The oxidation of ammonia into nitrites.

3. The oxidation of nitrites into nitrates.

The first step is very easily brought about in some cases ; e.g.,
urea, the characteristic constituent of urine, only requires to
combine with water to give ammonium carbonate :

CO(NH,), + 2H2O = (NHJ^CO,.
Urea Water Ammonium

carbonate

This occurs very readily, and is the cause of the strong
ammoniacal smell perceptible in stables. With other nitro-
genous compounds the change does not occur so readily. In
almost all cases, the reaction is brought about by the life
processes of some micro-organisms ; in some cases, moulds, in
othei»s, bacteria are the agents which do the work.

The ammonium compounds thus formed are absorbed by the

THE SOIL 55

constituents of the soil, until another set of organisms act upon
them. The chemical reaction involved is very simple :

(NH,),CO,

+ 30, = CO, +

2HN0, + 3H,0.

Ammonium

Oxygen Carbon

Nitrous Water

carbonate

dioxide

acid

This change, however, can only occur if some basic material
be present to neutralise the nitrous acid, probably calcium
carbonate —

OaCO, + 2HN0, « Ca(NO,), + CO, + H,0

Calcium Nitrous Calcium Carbon Water

carbonate acid nitrite dioxide

— and is accomplished by the action of a micro-organism, which
may conveniently be called the nitrous organism^ or Nitroso'
coccus. Lastly, the nitrite is converted by oxidation into a
nitrate —

0a(N0,), + 0, - Ca(NO,),

Calcium Oxygen Calcium

nitrite nitrate

— by the action of the nitrio o^'ganism, or Nitrohacter.

The conditions favourable for nitrification, assuming the
necessary organisms to be present, are :

1. Suitahh Food. — Mineral matters, especially potassium,
calcium, sulphates and phosphates must be present. Carbon
dioxide, either as gas, in solution, or as bicarbonates, appears
also to be essential. Organic matter is not required for either
the nitrous or nitric organism.

2. The Presence of some hasic material, — As already stated,
calcium or magnesium carbonate generally acts as the base^
The medium must not be more than slightly alkaline, or it maybe
neutral, but if strongly alkaline or acid the process is stopped.

3. Suitable temperature. — Nitrification ceases about the
freezing temperature, is most active about SO^C, and stops at
about 50° or 55° 0.

4. Prenevce of moiahirf..

5G ELEMENTARY AGRICULTURAL CHEMISTRY

5. Absence of Strong Light, — Sunlight stops the action of,
and, if continued, destroys the organisms.

6. Abundance of Oxygen,

DenitrificatiOM. — This is a process resulting in the libera-
tion of free nitrogen from nitrates, brought about by micro-
organisms which are probably nearly always present in soil,
but which can only act when free oxygen is absent — that is, the
organisms are anaerobic. If a soil be consolidated, water-
logged, or highly charged with oxidisable carbonaceous matter
the conditions become favourable for denitrification. The
application of very large dressings of dung along with nitrate
of soda sometimes causes a considerale loss of nitrogen from
this cause.

Fixation of Atmospheric Nitrogen in Soils.— Certain

micro-organisms, able to absorb free nitrogen from the
air and to convert it into compounds capable of being
utilised by plants, have been discovered. Indeed, some years
ago cultures of such organisms were prepared for sale under
the name of Alinit, but the success attending their employ-
ment was doubtful, and their manufacture has ceased.
Recently further attention has been directed to the subject,
and other organisms possessed of similar powers have been dis-
covered. Among others, a large bacterium, which has been
named Azotobacter^ is said to possess this power, in soils rich
in /)rganic matter, the necessary energy being believed to
be derived from the oxidation of the carbonaceous material. It
is thought that the fertility and richness in nitrogen of forest
or prairie soil is largely due to the activity of this and similar
organisms, which would find suitable conditions for growth in
the large quantity of organic carbonaceous matter contained in
f.uch soils.

Gases in a SoiL — The interstices of a soil are usually
occupied by air, but, in consequence of the chemical changes
going on in the f^oil, this air becomes robbed of some of its

THE SOIL 57

Oxygen and enriched with carbon dioxide. The air is not
stagnant, but undergoes constant renewal by diffusion from the
air above. The gases sucked out from soil vary considerably
in composition ; the oxygen may be anything between 10 and
20 per cent., the carbon dioxide from 1 to 10 per cent., while
the nitrogen usually differs very little in amount from that in
the atmosphere — about 78 per cent. The amount of carbon
dioxide is greater and of oxygen less during the summer and
autumn than in the winter or spring.

The Water in a Soil. — This is normally present as a
liquid film enclosing the particles composing the soil, and
contains, in dilute solution, the soluble matter of the soil, and
also dissolved gases. Its origin is usually rain, and it therefore
retains any dissolved substances — chlorides, sulphates, &c. —
which the rain contained. The actual composition of the water
in a soil must necessarily vary greatly, according to the amount
of rain which has recently fallen and other circumstances.

Of the rain which falls a large proportion sinks into the soil
by the action both of gravitation and surface pressure. Some
of this runs oflf in the drains, carrying with it a proportion of
dissolved matter ; the rest remains in the interstices, and of this
a proportion is brought up to the surface by surface pressure,
and is there evaporated. It consequently becomes more con-
centrated, and, in dry weather particularly, the water in the
upper portion of a soil may contain very many times the
amount of dissolved substances which is found in drainage
water. As the liquid becomes more concentrated, doubtless
many of its constituents are absorbed by the soil. Evapora-
tion from the top layers thus causes the soil water, by the
surface pressure phenomenon already described, to bring up
into the upper parts of the soil considerable quantities of plant
food and other dissolved matter. In extreme cases in some-
what arid regions, the soil may become so charged with dis-
solved substances from this cause that it is unfit for plant
growth. Such soils are known as " alkali " or " brak " soils.

58 ELEMENTARY AGRICULTURAL CHEMISTRY

The proportion of the rainfall which drains away varies with
many circumstances — the distribution of the rainfall, the re-
tentiveness of the soil, the rapidity of evaporation from the
surface, and others. The amount evaporated depends largely
upon whether the soil is bare or covered with vegetation, being
very much greater in the latter case.

At Rothamsted, as the average of twenty years (1877-78 to
1896-97) with a rainfall of 29 '5 inches, the drainage through
5 feet of bare soil amounted to 14*7 inches. In very wet
seasons the amount and proportion of drainage is greater ;
e.g., in 1878-79 the total rainfall was 41 inches and the drainage
24*4 inches, while in the very dry year 1897-98 the numbers
were 19*5 and 6 5 respectively.

From cultivated soil bearing a crop the drainage is much
less. In experiments conducted in France, fallow soil gave a
total drainage of 11*5 inches, while similar soil with a crop of
potatoes gave only 5*83 inches.

Losses caused by Drainage. — The water draining from
land always carries with it dissolved matter. The substances
whose removal in this way is the most important are the
nitrates. The loss is greatest from uncropped soil, for several
reasons —

(1) Because of the greater amount of drainage ;

(2) Because no absorption of nitrates by the roots of plants
occurs ;

(3) Because the land, being free from crops, dries more
slowly, and so the moisture favourable for nitrification is
retained for a longer period, especially in dry weather, when
the temperature is often high, and, therefore, most favourable
for nitrification.

The average annual loss of nitrogen as nitrates from un-
cropped land at Rothamsted for the twenty years 1877-78 fco
1896-97 amounted to 33*8 lb. per acre (equivalent to 216 lb.
of commercial nitrate of soda). The loss, of course, will vary
greatly with the nature of the soil. At Grignon, near Paris*
in the year 1896-97 the loss of nitrogen from fallow soil was

THE SOIL 59

found to bo about 1 90 lb. per acre, while from plots of the
same soil bearing crops the loss was in some cases very small —
e.g.y with i^e grass only 2*3 lb.*

The other substances carried off in drainage water, though
considerable in quantity, are of less importance from a prac-
tical standpoint. The largest is the calcium carbonate, and
this naturally varies very much in different soils. From soils
on igneous rocks its amount is estimated by Continental
observers at 500 lb. per acre per annum, while from the
chalk soils as much as 2700 lb. per acre may be removed
in a year. The amount is increased when ammonium com-
pounds are used as manure. English estimates are lower.

The loss of phosphoric acid is probably very small, except in
the case of peaty soils, which, though often very deficient in
this constituent, generally lose much in the drainage, probably
because of the solvent action of the vegetable acids and the
carbon dioxide produced by the decay of organic matter. In
German experiments the annual loss per acre varied from about
8 lb. from clay to 19*6 lb. from peaty soils.

The loss of potash is very variable, but seldom of much
importance in this country. Of course, under exceptional
circumstances drainage water may be very rich in dissolved
matter ; e.g.^ the drainage water from gardens, when excessively
large quantities of manure are used, may contain as much as
8*4 parts per million of potash and 33 parts of nitrogen
pentoxide.

Analysis of Soils. — The presence of an adequate store of

constituents of plant food in a soil is not sufficient to ensure

fertility, and this is true even when the physical condition of

the soil is suitable, for it is necessary that the constituents of

plant food should be in such a state that they can readily be

assimilated by the plant, A complete analysis of a soil, stating

• These losses refer to nitrate, &c., carried off in the drainage water.
In some cases, a soil may, in spite of such losses, actually become
richer in combined nitrogen owing to fixation of atmospheric nitrogen
by micro-organisms, e.g., A^iotobacter {seep. 56).

GO ELEMENTARY AGRICULTUKAL CHEMISTRY

the percentage amount of each constituent present, is often of
little use in leading to any judgment as to its fertility or
manurial requirements. A case illustrating this point may be
quoted. Ta70 pasture soils, A and B, gave the following
results on analysis :

A. B.

Per cent. Per cent.

Moisture 3*13 1-70

Loss on ignition 10-85 7-79

(Nitrogen 0-274 0 247)

Insoluble matter 67-38 80-28

Ferric oxide and alumina . . . 15*61 8-16

Lime 029 0-13

Magnesia 031 ' 0-21

Potash 0-86 0-48

Phosphorus pentoxide .... 0-15 0*12

Not determined 1-42 1-13

100-00 100-00

From these numbers A is evidently better provided with lime
and phosphorus pentoxide than B, and since there is also
more nitrogen present it would seem that B needed phosphoric
acid and lime more than A. Actual trial shows just the
opposite ; for basic slag (containing chiefly calcium phos|^hate
and free lime) gives a decided increase of crop on soil A, but
has no marked effect on soil B.

Evidently the phosphoric acid and lime in B, though less in
amount, are more available to the roots of plants than those in
^oil A . Dr. Dyer suggested the determination of the amounts
of phosphoric acid and of potash which a soil could yield to a
solution of citric acid containing 1 per cent, of the acid, as a
means of estimating the amounts of these ingredients present
in an available form. This strength of acid was suggested
because it corresponds to the acidity of the sap contained in
the roots and root-hairs of many plants. By the application,
of this process to the two soils mentioned the following results
were obtained :

A. B.

Per cent. Per cent.

"Available" potash 00062 00060

« Available " phosphorus pentoxide . 00049 00205

THE SOIIi 61

The superiority of soil B in " available " phosphates is thus
evident ; it contains more than four times as much as A.
0*01 per cent. *' available " phosphates and 0005 per cent,
" available " potash are suggested as the lower limits foi
fertility for most crops. If less be found the soil requires
manure. It is obvious that the limits will be different for
different crops, since both their requirements and power of
assimilating food materials differ greatly. The amounts of
potash and phosphoric acid extracted by 1 per cent, citric
acid solution, though not claimed to be an accurate measure of
that which plants are able to obtain from the soil, probably
furnish one of the best chemical means of estimating their
fertility so far as their requirements are concerned. Another
point to consider in this connection is the rate at which the
" unavailable " plant food becomes " available." In some cases
it has been found that a soil deprived of all "available " plant
food by prolonged treatment with a one per cent, solution
of citric acid soon acquires, when kept moist, additional
quantities of the former. There seems little doubt that in
warm climates the renewal of the available plant food in soil
occurs more rapidly than in colder ones. In tropical soils,
therefore, the occurrence of smaller quantities of " available "
plant food may suffice for the requirements of crops, owing to
the greater rapidity with which it is renewed. This is one of
the reasons why such soils, which appear poor on analysis when
compared with English soils, often prove very fertile.

For details of analytical processes which cannot be given
here, a manual of agricultural analysis should be consulted.

CHAPTER IV.
NATURAL WATERS,

Pure water — i.e., the substance hydrogen oxide, H^O — practi-
cally never occurs in nature. Owing to its remarkable solvent
properties, water dissolves smaller or larger quantities of every
substance with which it comes in contact.

The purest form of natural water is rain, although, as
shown by the analysis on p. 30, rain-water is never pure, but
contains varying quantities of dissolved matter. In addition
to those mentioned in the Table, rain-water contains dissolved
gases. When it reaches the earth the water at once com-
mences to dissolve the substances upon which it falls. In dis-
tricts where the surface is composed of hard, igneous rocks the
quantity dissolved is small, while on limestone or chalk large
amounts of calcium carbonate particularly go into solution.
The water which drains away from a soil amounts in England
to about half the annual rainfall. Part of it finds its way
into the nearest watercourse, thence to a stream or river, and
finally to the sea. Another portion sinks into the earth until
stopped by some impervious layer of rock — e.g,, shale— when
it accumulates, and eventually finds an outlet at some lower
level in the form of a spring.

The chief forms of natural waters may be classed as follows..

1. Rain water, 8. River water.

2. Spring water. 4. Sea water.

1. Rain Water. — The composition and character of this
has already been described in chap. ii. The acidity of the

62

MINERAL WATERS 63

rain in districts where much coal is burnt is of great impor-
tance as affecting the growth of plants, particularly of the
grasses and certain trees. In addition to its direct injurious
effect upon the foliage, it exerts a deleterious action upon the
soil, tending to remove the calcium carbonate or other basic
material, to interfere with the growth of micro-organisms, e.g.^
those of nitrification, and to promote " sourness," so unfavour-
able to the growth of most useful plants. Grass land under
such circumstances often becomes almost sterile, the last plants
to succumb to the unfavourable conditions being the " sorrel "
or '* sour dock."

The combined nitrogen brought down by the rain has been
already referred to (see Chap. II, p. 80).

Spring* Water. — The water issuing from springs varies
greatly in the amount and nature of the dissolved matter
which it contains. If this be small, and not possessed of strong
taste or odour, the water is described as fresh water ; but if a
large quantity of dissolved matter be present, or if the water
possess pronounced taste, odour, or medicinal properties, it is
known as a mineral water.

Most spring-waters contain the following substances, but in
very varying amounts :

(1) Calcium and magnesium carbonates dissolved in excess
of carbon dioxide.

(2) Calcium or magnesium sulphate.

(3) Sodium or potassium chloride.

(4) Alkaline silicates.

(5) Dissolved gases — oxygen, nitrogen, and especially carbon
dioxide.

Calcium and magnesium carbonates are almost insoluble in
water, but if the water contain carbon dioxide the readily
soluble bicarbonates are formed :

CaCO, + H,0 + CO, = Ca(HC03V

Calcium bicarbonate

Such action occurs largely in all limestone or chalk districts,

64 ELEMENTARY AGRICULTURAL CHEMISTRY

the removal of the rock in solution giving rise to the cavea
and underground watercourses so common in these districts.
When such water is boiled the bicarbonates are decomposed,
the normal carbonater being again formed and precipitated :

Ca(HC03)2 = CaCOj + H,0 + CO,.
Calcium bicarbonate

In many cases the precipitated calcium or magnesium carbonate
forms a firmly adherent coating (" fur " or *' crust ") upon the
bottom and sides of the kettle or boiler.

Calcium and magnesium sulphates are soluble in water, the

former to the extent of about 1*7 grammes per litre. Waters

containing calcium or magnesium compounds are known as

"hard" waters, and have a peculiar and well-known action

on soap. The latter is essentially the sodium salt of a fatty

acid — e.g., stearic acid, HCigHg-O,, the calcium and magnesium

salts of which are insoluble in water. For water to form a

lather with soap or properly exercise its cleansing power it is

necessary that the water should contain some dissolved sodium

stearate. When a small quantity of soap is dissolved in hard

water, the calcium or magnesium present in the water, by

double decomposition with the soap, gives a curdy, flocculent

precipitate of the calcium or magnesium salts of the fatty

acid^ e.g.,

SNaC.gHg-O^ + CaSO, = Ca(0,3H3P,), + Na.SO,.
Sodium Calcium Calcium Sodium

stearate sulphate stearate sulphate

The dissolved soap is thus removed, and more has to be dis-
solved before the proper cleansing action can be exerted.
Hence hard waters are unsuitable for domestic use, especially
for laundry purposes ; they involve the consumption of large
quantities of soap, and contaminate the articles washed with
the precipitated " lime " or " magnesia soaps."

Hard waters are also unsuited for steam-raising, since the
deposit of calcium carbonate or of calcium sulphate upon the

NATURAL WATERS 65

boiler plates greatly increases the consumption of fuel required
for the production of a certain quantity of steam.

A distinction is often made between waters which contain
their calcium and magnesium as bicarbonates and those in
which the salts present are the sulphates. The former are
known as "temporarily," the latter as "permanently" hard
waters. By the removal of the excess of carbon dioxide from*
the former the calcium and magnesium carbonates are pre-
cipitated, while with the latter the salts are dissolved per se,
and cannot conveniently be removed. The usual plan adopted
to eflfect the softening of temporarily hard water is to add lime,
CaHjOj, in sufficient quantity to combine with the free carbon
dioxide and that present as bicarbonates, when the precipi-
tate formed contains the calcium (and magnesium) carbonate
originally present, together with that formed from the added
lime :

Ca(HC03)3 + CaH^Oa = 2CaC03 + 3H,0.

On standing the precipitate settles out, and the clear liquid is
then almost free from calcium and magnesium and is " soft."
It is much improved both for washing and for steam-raising
purposes.

In a drinking water the presence of calcium compounds,
except in excessive amounts, is not very objectionable — indeed,
is often advantageous, furnishing a portion of the lime neces-
sary for the building up of the hard parts (bones or shells) of
the animal. Moreover, in many cases water is delivered
through leaden pipes, and soft waters, especially if they con-
tain vegetable acids — e.g.., from peat — attack and dissolve lead,
often to such an extent as to cause lead poisoning in those
who drink them. The presence of calcium sulphate renders
water incapable of this dangerous action upon lead, for the
metal becomes coated with a film of the very insoluble lead
sulphate, which protects it from further contact with the water.

Of greater importance than the mineral matter in drinking
water is the amount and nature of the organic matter.

E

66 ELEMENTARY AGRICULTURAL CHEMISTRY

This in itself is comparatively harmless ; its importance lies
in the influence it has upon the kinds of micro-organisms
which accompany it. Animal excreta is the most dan-
gerous contamination, since the micro-organisms which cause
various diseases — e.g., typhoid and cholera — are liable to be
thus introduced into the water. Animal organic matter is
richer in nitrogen than most vegetable refuse, so that in
practice the detection of much combined nitrogen, whether as
organic matter, ammonium salts, or nitrates, is regarded as
sufficient to indicate that the water has been contaminated
with sewage or other animal matter. If much organic matter
of animal origin be present there must always be considerable
risk of pathogenic (disease-producing) organisms finding their
way into the bodies of those who drink it ; and though such
contaminated water may be, and often is, drunk for years with
impunity its consumption is decidedly dangerous.

Another substance characteristic of sewage is common salt ;
consequently the presence of much chlorine in a water is
generally indicative of sewage contamination, unless the water
is derived from some rock containing salt or is collected near
the sea.

Analyses of typically good and bad drinking waters are
given by Roscoe and Schorlemmer as follows :

Constituents

Good water.

1
Bad water.

Parts per
million.

Grains per
gallon.

Parts per
million.

Grains per
gallon.

Total solids ....
N as nitrites and nitrates .
"Free" ammonia .
"Albuminoid" ammonia .
Chlorine . . . .
Temporary hardness .
Permanent hardness .
Total hardness

63 0
0-25
0 03
0-07

11-4

4-4

0017

0-002

0-005

08

0-1

2-4

2-5

530
7-8
4-32
0-9
69

37-1
0-546
0-303
0063
4-8
7-2

14-4

21-6

NATURAL WATERS 67

By hardness is meant the number of grains of calcium
carbonate equivalent to the total amount of calcium and
magnesium salts present in one gallon of the water. The
meanings attached to " temporary " and " permanent " have
already been given. Numerically they too are expressed in
terms of the equivalent amount of calcium carbonate in grains
^er gallon.

By albuminoid ammonia in the above table is meant the
quantity of ammonia which is evolved from the water by the
decomposition of organic nitrogenous substances by distillation
with an alkaline solution of potassium permanganate.

River Water. — Most rivers originate in springs, so that
at first their water resembles that of their source. A con-
siderable influx of surface-water, however, generally enters
the river and alters its composition. The surface-water usually
contains less dissolved matter than spring water, but often
more organic matter and suspended particles. The composi-
tion of the river water greatly depends upon the character of
the rocks from which it is collected. When the surface con-
sists of igneous rocks or of sandstones the water is usually
soft, while in chalk or limestone districts it will be hard.
Some rivers — e.g., the Trent— are very rich in calcium sul-
phate, and to this fact the excellence of the Burton ales has
been ascribed.

Tlie table on page 68 is given by Roscoe and Schorlemmer as
representing the average composition of the waters of several
well-known rivers. The remarkable softness of the water of the
Dee, collected from the granite district in Aberdeenshire, will
be noted.

River water rarely contains excessively large quantities of
calcium carbonate, such as occur in some springs, since, owing
to its free contact with air, it never retains very large
quantities of dissolved carbon dioxide. Calcium sulphate in
river water is usually accompanied by sodium chloride and by
magnesium salts,

68 ELEMENTARY AGRICULTURAL CHEMISTRY

In thickly populated and manufacturing districts the rivers
are contaminated with the sewage and trade eflfluent of the
towns and villages, and thus often become foul and cvil-
smelling. This is to be deplored both on account of the
annoyance and injury to health which they cause, and also
because of the serious loss to the community of the valuable

CONSTITDENTS.

*

Grains per gallon.

Thames.

Trent.

Dec.

Total solids .
Calcium carbonate
Calcium sulphate .
Calcium nitrate .
Magnesium carbonate .
Sodium chloride .
Silica ....
Iron oxide and alumina
Calcium phosphate
Organic matter .
Hardness

20-81

10-80
3-00
0-17
1-25
1-80
0-56
0-27

Trace
2-36

14-0

50-06

0-32

21-55

6-66
17-63

0-72

0-50
Trace

3-68
26 5

3-89
0-85
012

0-36
0-72
014
0-06
Trace
1-54
1-5

combined nitrogen and other manurial constituents contained
in the sewage.

The amount of suspended matter in river water varies
enormously, depending upon the rainfall, the character of the
surrounding soil, and other circumstances. Soft waters or
those containing carbonate of soda are often muddy, while
hard waters tend to deposit their suspended clay and become
clear. The very muddy nature of many South African
streams is believed by the writer to be due to their containing
sodium carbonate. In some cases, the quantity of suspended
matter is very great, and the dense, muddy river-water, if it
overflows the banks, deposits upon the soil a layer of finely-
divided particles of materials brought down from higher up
the valley. The sediment is often rich in plant food and
forms an important fertiliser. In some few^ places in England
— e.gr., on the Humber and Trent — land is systematically

NATURAL WATERS 69

treated with the flood-water in order to increase the thickness
of the soiL . The process is known as " warping," and the
" warp *' soils are extremely rich and fertile. The Nile in
Egypt affords a still better example of a river used in this
manner.

In countries of limited or unevenly distributed rainfall
irrigation is often practised. In this case, since there is very
little drainage, the composition of the water used is of im-
portance. If the water be chai'ged with common salt, sodium
sulphate, or sodium carbonate, there is a gi'ave danger of the
surface soil, by the prolonged concentration of the water,
becoming charged with the soluble matter to such an extent
as to seriously interfere with plant growth. The soil is then
said to become " brak " or " alkali." The usual causes of this
sterile condition are sodium sulphate and chloride ("white
alkali ") or sodium carbonate ('* black alkali ") derived either
from the soil itself, or partly from the water used for irriga-
tion.

Different crops are possessed of different resistant powers to
these salts. As a rule, sodium carbonate is the most effective
in causing injury to plants, and sodium sulphate the least.
Fortunately, however, " black alkali " — i.e., sodium carbonate
— can be rendered almost innocuous by the application of
gypsum to the soil, when by double decomposition calcium
carbonate and sodium sulphate are formed :

CaSO, + Na.COg = Na^SO, -f CaCOj.

If ** white alkali " be due to common salt it cannot be cured,
except by drainage.

According to American results (and in various parts of the
United States large areas of alkali soils exist), the following
table gives the highest proportions of sodium chloride, sodium
sulphate, and sodium carbonate which may be present in soils
without injury to the plants named. The figures represent
the amounts in pounds of the various constituents present in
the upper four feet of soil per acre ;

70 ELEMENTARY AGRICULTURAL CHEMISTRY

Plant.

Sodium

So;liuin

Sodium

Chloride.

Sulphate.

Carhoaatc.

Grape

9,G40

40,800

7,550

Fig . . .

800

24.480

1,120

Orange

3,360

18,000

3,840

Pear .

1,360

17,800

1,760

Apple .

1,240

14,240

640

Peach .

1,000

9,600

680

Apricot

960

8,640

480

Lemon .

800

4,480

480

Mulberry .

2,240

3,360

160

Eucalyptus .

2,960

34,720

2,720

Oriental sycamor

e

20,320

19,240

3.200

Date palm .

—

5,500

2,800

Salt bush .

12,520

125,640

18,560

Lucerne, old

6,760

102,480

2,360

» young .

760

11.120

—

Sugar beet .

5,440

52,640

4,000

Sunflower .

5,440

52,640

1,760

Radish.

2,240

51.880

8,720-

Carrot .

2,360

24,880

1.240

Rye .

1,720

9,800

960

Wheat .

1,160

15,120

1.480

Barley .

5,100

12,020

12,170

Lupine.

3,040

5,440

2,720

Celery .

9,600

4,080

—

Sorghum

9,680

61,840

9,840

III the above table it is assumed that the weight of soil to
a depth of four feet per acre is 16,000,000 lb. — i.e., that
each foot depth of soil per acre weighs 4,000,000 lb. 1 per
cent, of any constituent would thus correspond to 40,000 lb.
per acre in a depth of one foot, one-tenth per cent, to 4000 lb.,
and so on.

Sea water varies locally in composition, being affected by
the intlux of fresh water from large rivers, (tc., but far out
from land it is very constant in composition. The average
amount of total solid matter is about 3G grammes per litre,
or 2520 grains per gallon. Thorpe found as the constituents
of 1000 grammes of water of the Irish Sea, in 1870, the
following : —

l^ATURAL WATERS

71

Grammes.

26-439

0-746

3-150

0-071

2-066

Traces

•002

1-332

0 048

0-0004

0005

Traces

Sodium chloride
Potassium chloride .
Magnesium chloride.
Magnesium bromide
Magnesium sulphate
Magnesium carbonnte
Magnesium nitrate .
Calcium sulphate .
Calcium carbonate .
Ammonium chloride
Ferrous carbonate ,
Silicic acid

33-859
In certain lakes having no communication with the ocean
the concentration of the water becomes much greater, and the
total solid matter may reach seven or eight times that found
in the ocean. Examples of such waters are found in the Dead
Sea and the Great Salt Lake of Utah.

Belations of Water to Heat.— The physical properties of
water, especially in its relations towards heat, are remarkable
in many ways, and of the utmost importance. It is therefore
desirable that the student should be familiar with these pro-
perties, in order that he may realise the parts played by water
in nature.

Pure water is usually described as colourless, but careful
examination will show that when seen in sufficiently thick
layers it has a bluish -green colour. It is a bad conductor of
heat — i.e., heat travels slowly from one particle of water to
another — but usually a mass of water is warmed readily, espe-
cially if the source of heat be below. In this case the distri-
bution of heat is effected by a process distinct from conduction,
known as convection. The particles of water nearest the source
of heat become warmed, expand, and consequently rise, the
cooler, and therefore heavier, particles above or around them
taking their place. A circulation is thus set up, the warmer
water continually rising and the colder sinking.

Specific Heat. — Water has a high specific heat. By this is
meant that to raise the temperature of a given mass of water

7b ELEMENTARY AGRlCITLTURAL CHEMISTRY

through a certain interval a relatively large amount of heat is
necessary. The specific heat of water is much higher than
that of mercury. The meaning of this statement can be readily
understood by considering two experiments. If 1 kilogramme
of water at 100° C. be mixed with 1 kilogramme of water at 0°
the temperature of the mixture will be approximately 50°.
The heat lost by the hot water in cooling from 100° to 50°
has just been sufficient to raise the temperature of the same
weight of cold water from 0° to 50°. If a kilogramme of water
at 100° be stirred with a kilogramme of mercury at 0° the tem-
perature of the mixture will be approximately 96*7° C. In
this case the water in cooling through only 3-3° C. gave out
enough heat to raise an equal weight of mercury through
96*7° C. From this result it follows that water requires about
thirty times as much heat to raise its temperature through any
specified interval as an equal weight of mercury. The specific
heat of water is taken as unity, so that the specific heat of
mercury will be ^^^j^, or -033.

The specific heat of a substance is thus the quantity of heat
required to raise the temperature of any weight of the sub*
stance through any interval, compared with the amount of
heat necessary to raise the temperature of the same weight of
water through the same interval.

Since water has the highest known capacity for heat, the
specific heats of other substances are represented by numbers
less than 1 . The following is a list of specific heats of various
common substances :

Table of Specific Heats

Water

. 1-000

Glass

. 0-198

Alcohol .

. 0-620

Silica

. 0-189

Turpentine

. 0-426

Steel

. 0-118

Glycerine .

. 0-555

Copper

. 0-094

Sulphuric acid .

. 0-355

Brass

. 0-094

Humus

. 0-477

Tin

. 0-056

Clay

. 0-233

Mercury

. 0-033

Aluminium

. 0-214

Lead

. 0-031

Calcium carbonate

. 0-206

NATURAL WATERS 78

Water is remarkable with respect to the influence of changes
of temperature upon its volume. Like most substances, it
expands when heated and contracts when cooled ; but a care-
ful examination will reveal the fact that this statement, though
roughly correct, is too general, and that at a certain tempera-
ture water is most dense and expands whether it be heated or
cooled. This temperature of maximum derisity is about 4° C.
When water changes into ice an expansion occurs (see chap. iii.).
In this respect water is unlike most other substances. It is
owing to water being most dense at 4° C. that the tempera-
ture of the water in deep lakes or ponds even in the coldest
weather is usually found to be about 4° at considerable depths
below the ice.

Latent Heat. — When a liquid changes into a solid heat is
evolved, and, conversely, when a solid becomes liquid heat
is absorbed.

If a quantity of ice or snow, say at - 10° C, be placed in
a vessel and heat be applied, a thermometer placed in the
material will show a slow rise in temperature until 0° C. is
reached, when, although the supply of heat be maintained,
no further rise will ensue until all the ice or snow is melted.

The amount of heat thus absorbed is very considerable, and
is exactly equal to that which was evolved when the ice was
formed from liquid water.

If akilogramme of waterat 80°O. be mixed with a kilogramme
of ice at 0° it will be found that the ice will be melted but the
temperature of the resulting liquid will only be 0°. It is thus
evident that to melt a kilogramme of ice without producing any
change of temperature as much heat is required as would raise
a kilogramme of water through 80° C, or 80 kilogrammes of
water through 1° C. Heat so absorbed is called latent, since it is
hidden, so far as a thermometer is concerned. Conversely, when
water freezes, each kilogramme converted into ice gives out
as much heat as would raise 80 kilogrammes of water through
1°0. It is for this reason that during cold weather ice onlv

74 ELEMENTARY AGRICULTURAL CHEMISTRY

forms slowly on the surface of water, and that snow and ice
melt so slowly when a thaw sets in.

The latent heat of ice, or of the fusion of ice, is thus said
to be 80.

Another change of state occurs when liquid water becomes
gaseous. If a quantity of water at the ordinary temperature
be gradually and regularly supplied Avith heat, a thermometer
placed in the liquid will indicate a steady rise of temperature.
It is evident that the heat supplied is being used in raising
the temperature of the water. Tliis will go on almost regu-
larly until a temperature of about 100° C. is reached. No
further rise will occur, and even if the rate of supply of heat
be doubled or quadrupled no effect upon the thermometer will
be observed ; the water, however, will now be slowly changing
into steam, which, as it leaves the liquid, has the same tem-
perature (100° C). Evidently the heat supplied is now being
used up in converting the liquid into vapour without producing
any rise in temperature. The quantity of heat required to
change the unit weight of water at 100° into steam at 100° is
called the latent heat of steam, or of the vaporisation of water.
It is very large, being 536 times as great as the amount required
to raise the same weight of water through 1° in temperature.

The quantity of heat necessary to raise 1 gramme of water
from 0° to 1° is called the thermal unit, unit of heat, or
calorie.

Now water evaporates into dry air (or into any gas or space
not already saturated with aqueous vapour) at any temperature,
and since that which is converted into vapour requires its latent
heat, a considerable absorption of heat ensues. This is the reason
why wetted things are cooled when exposed to air; it is not
because the water is cooler than other substances, but because
it evaporates and absorbs the heat necessary for its conversion
into vapour. The more rapid the evaporation, the greater is
the reduction of temperature. The rapidity is increased by
higher temperature and by quicker renewal of the atmosphere in
contact with the wet surface, e»g., by a draught of air or wind.

NATURAL WATERS 75

The conversion of a liquid into a vapour is always attended
by an absorption of heat. Though the amount of heat required
to convert a gramme of the liquid into vapour varies with the
nature of the liquid, in no case is it so great as with water.
The following experiment furnishes a striking proof of this
heat absorption :

A small, thin glass beaker is placed on a few drops of water
on a wooden block ; a little ether is placed in the beaker, and
by means of a tube and bellows a cuirent of air is blown into
the beaker so as to cause the ether to evaporate rapidly. In
being converted into vapour it absorbs heat from the beaker ;
this cools the water below, and in a short time the loss of heat
becomes so great that the water freezes, and the little beaker
is cemented to the block of wood by a thin film of ice.

The high specific and latent heats of water lead to important
consequences in nature. The former explains the temperate
character of the climate of places near large masses of water.
Islands or places near the coasts of large areas of water have
much smaller ranges of temperature than places far inland.

A wet soil is cold because of both these causes. The heat of
the sun shining on the soil can only warm it slightly, because
(1) of the high specific heat of the water present, and (2) a
large portion of the heat is absorbed by the evaporation of a
portion of the water. The magnitude of this second effect is
greatly increased if a wind be blowing, since the rate uf
evaporation is thereby accelerated.

CHAPTER V.

THE PLANT.

A BRIEF account of the functions of the various parts of a
plant will be given in this chapter, followed by a short de-
scription of the chief chemical compounds existing as its
constituents. For detailed accounts of the structure and life-
history of plants a treatise on botany wOuld naturally be
consulted.

Germination. — A seed is essentially a germ, with a store
of material, out of which the future plant is to be formed.
All seeds contain complex nitrogenous compounds (proteids)
and either cai-bohydiates or fats, together with mineral
matter.

Seeds may be kept unchanged for some time, provided they
be protected from moisture. In order that germination may
occur, the access of moisture and oxygen, a suitable tempera-
ture, and the removal of evolved carbon dioxide are necessary.
If these conditions are complied with, seeds will germinate
readily without requiring any mineral or other food. Oxygen
is absorbed, heat is produced and carbon dioxide is evolved.

Unorganised ferments, or enzymes — i.e., substances which
are soluble in water, and which have the power of bringing
about chemical changes apparently without themselves being
altered — are produced, and the starch or other insoluble con-
stituents of the seed are converted by the enzymes into sugars
or other soluble compounds capable of being transported to
the pluir.ule (the rudiment of the stem) and radicle (eventually

76

THE PLANT 77

the root), and so permitting of their growth. "When the
plumule reaches the surface, and on exposure to light becomes
green in colour from the formation of chlorophyll, it is then
capable of assimilating carbon dioxide. The radicle soon
develops root-hairs, through which mineral substances and
nitrates, if present in the solution outside, can enter the
plant.

The main parts of a plant are the roots, the stem, the leaves,
the flowers, and the seeds.

The Roots. — The radicle, growing from the seed, at first
extends vertically downwards, its direction being determined
by gravitation or other force acting upon it. It afterwards
branches and sends out lateral roots. Near every growing
part of the root thin-walled root-hccirs extend among the
particles of soil. As the root thickens the root-hairs die off;
they ai'e only found in abundance near the growing ends of
roots. The thin walls of the root-hairs probably play a most
important part in the growth of the plant. In order to under-
stand their action it is necessary that some knowledge should
be possessed of the peculiar phenomena of diffusion and osmotic
pressure.

Some reference to the former has already been made (see
chap. iii.). Colloidal^ or glue-like substances diffuse very
slowly when dissolved in water, and have no power of diffusing
through insoluble colloidal bodies — e.g.^ parchment — while
crystallisable bodies diffuse rapidly, and can readily penetrate
a colloidal membrane if it be saturated with water. This
passage of dissolved crystalloids, as they are called, through a
colloidal membrane is a process of diffusion, and will always
take place from a stronger to a weaker solution, apparently
(but only apparently) ceasing when the solutions on either
side are equal in concentration.

Certain substances, when arranged as a partition between
two solutions of different concentration, permit of the passage
of the solvent only, and prevent that of the dissolved substance.

78 ELEMENTARY AGRICULTURAL CHEMISTRY

Such substances are termed semi-permeable^ smd though perfect
semi-permeable membranes are not known a near approach to
them can be obtained. If such a membrane be arranged as a
closed cell connected with a manometer, it can be shown
that when filled with a solution and immersed in water the
water enters the cell, while practically none of the solution
leaves it. The consequence is that a pressure, amounting in
some cases to several atmospheres, is set up within the cell.

^Jhis pressure is known as osmotic pressure, and is found to
increase with the concentration and to become greater with a
rise of temperature. The cells of which a plant is composed
(or rather the protoplasm within them) are probably approxi-
mately semi-permeable. If they be surrounded by a solution
of less concentration than their contents they will receive more
liquid than they lose and the pressure within will increase,
while if surrounded by a solution of greater concentration than
their contents more liquid will pass out than passes in and
the cells will shrink. The cellulose walls of the cells are not
semi-permeable, but permit of free diffusion and are nearly
rigid. The shrinking of the protoplasm from the walls of
plant cells can be seen under the microscope when they are
immersed in salt solution of proper strength. The phenomena
is known as plasmolysis, and results in the death of the plant.
Most vegetable tissues contain while alive a large proportion
of water, but in spite oi this they are rigid and firm, because
of the swollen and turgid state of their cells. The stems and
leaves of plants largely depend for their erectness and rigidity
upon the strain set up between the rigid cellulose walls of
their cells and the water-distended state of their protoplasmic
contents. If the distension relaxes — e.g.^ by evaporation — the
plant wilts or flags, becoming quite flaccid.

Diftusion of dissolved matter through a membrane and the
setting up of osmotic pressure within the membrane are pro-
cesses which are opposed to each other, though they may to
some extent occur simultaneously. They probably do so occur

in the case of a plant's roots. The protoplasm admits of a

THE PLANT 79

Blight diffusion, whereby some of the dissolved matters in the
soil water enters, while some of the dissolved matter of the
plant juice leaves the plant, though at the same time, because
of its approximately semi-permeable character, osmotic pressure
is set up, owing to the liquid within being more concentrated
in dissolved matter (though of different nature) than the
liquid without. This latter effect is evident in the root-
p-essure which is shown by plants, and which causes the sap
to escape when a stem is cut. In some cases the magnitude
of this root-pressure has been measured, and found to amount
to two or three atmospheres.

Hence by diffusion through the roots and root-hairs of a
plant the mineral matter and nitrates are taken in and forced
mainly by osmotic pressure (set up, not by these inorganic
substances, but by the sugar and other carbonaceous consti-
tuents of the sap) into the stem and leaves. At the same
time a portion of the acid juice probably escapes by diffusion
from the root-hairs and exerts an important solvent action
upon insoluble phosphates and potash compounds present in
the soil.* Some of the dissolved phosphates, «fec., can then
enter the plant again by diffusion.

The Stem may here be regarded as the mere means of
communication between the roots and the leaves. It, however,
often plays other parts, in some cases acting as a storehouse
for reserve materials or for useless matters taken in by the
plant.

The Leaves perform a very important part in the chemical

processes of plant-life. It is through the leaves that the

assimilation of carbonaceous matters takes place, and probably

the albuminoids and amides are here formed out of the carbon

compounds and the nitrates, phosphates, and sulphates taken

in by the roots. Another important function of the leaves is

* As stated in the footnote on page 41, it is now believed that carbon
dioxide is the main agent tending to bring into solution the constituents
of the soil which are insoluble in water, and that the acid juices referred
to play very little, if any, part in the process,

80 ELEMENTARY AGRICULTURAL CHEMISTRY

transpiration, by which the surplus water taken in ^by the
roots is got rid of by evaporation.

The chemical change so characteristic of plant-life (the
absorption of carbon dioxide and the elimination of oxygen), ip
an endothermic reaction — i.e., one which requires energy to
bring it about. The necessary energy is derived from light,
for it is only in the presence of light that the change takes
place. The light is absorbed by the green colouring-matter of
the leaves, chlorophyll, and it has been shown that it is just
that kind of light which is most absorbed by chlorophyll —
red light — which produces the largest amount of assimilation
of carbon dioxide. The process takes place in spaces below the
outer covering (the epidermis) of the leaf, the carbon dioxide
entering these spaces by diffusion through the stomata, minute
apertures which are exceedingly numerous on all leaves,
particularly on their under surfaces. The nature of the change
by which carbon dioxide is absorbed and oxygen evolved by
green leaves in sunlight is not thoroughly known. It has been
suggested that the first step is the formation of formaldehyde,
CH,0, by the union of carbon dioxide and water and the
evolution of oxygen —

CO3 + H,0 = CH^O + O,

— and that the formaldehyde then immediately polymerises, i.e.,
several molecules combine together, to form sugar :

6CH,0 = C,H,A.

However, the matter cannot be said to be definitely settled.
It appears probable that in many plants, cane sugar, G^JI^fl^^,
is first formed, and when its concentration in the sap attains a
certain value starch granules begin to form. The change
is empirically a very simple one, but how it occurs is not
known :

C),,H,,0„ = 2C,H,,0, + H,0.
Cane sugar Starch

THE PLANT 81

The starch granules are attacked by diastase and converted
into sugar whenever the sugar in the sap falls below a certain
concentration. This is important, as only dissolved crystal-
loids can pass from one portion of the plant to another.

In addition to the formation of carbohydrates, the leaves of
plants fulfil other important functions.

Transpiration of water takes place chiefly through the
stomata, but probably all exposed parts of a plant allow of
the escape of some aqueous vapour. The rapidity with which
water is evaporated from a plant depends upon several factors —
the temperature, the humidity of the air, the amount of light
received, and other circumstances. In consequence of the
evaporation of water from the leaves, a diminished pressure is
often set up in the upper parts of a plant, so that the rise of
water from below becomes easier. Thus a steady stream of
dissolved substances taken in by the roots rises into the
leaves, where, by transpiration, the water is largely evaporated,
and the dissolved substances are elaborated into nutritive
materials. If the soil water be very dilute, more water will be
evaporated than when the liquid is more concentrated. Thus
oats were found to evaporate 688 grammes of water for each
gramme of dry substance formed, when grown in a solution
containing 0'25 per cent, of nutritive substances, but only
515 grammes when in a 3 per cent, solution.

It is not known how the formation of albuminoids takes
place, but it probably occurs in the leaves. The first step
appears to be the formation of amino-compounds from the carbo-
hydrates and nitrates, and the subsequent conversion of these
into albuminoids. It has been shown that with many plants,
leaves cut in the morning contain much less starch and nitro-
genous matter than similar leaves cut in the evening, indicating
that during the night a transference of the starch and albu-
minoids formed during the day takes place from the leaves to
other parts of the plant. The albuminoids probably have to be
converted into amides or amino-acids and the starch into sugar
before any movement from cell to cell can occur.

I?

82 ELEMENTARY AGRICULTURAL CHEMISTRY

The Flowers and Seeds. — In mcany plants the formation
of flowefs and seeds is the last act in their life. During
flowering the process of true respiration — i.e., the absorption of
oxygen and the production of carbon dioxide — takes place more
rapidly than at other times during the growth ; indeed, in
some cases a distinct rise of temperature has been noted.
Respiration occurs during the whole period of a plant's existence,
but in daylight it is concealed by the opposite process of
assimilation, already described. In biennial plants — e.g.^ turnips
and mangolds — the first year of growth is devoted to the
formation of a large store of nutritious material, intended to
serve during the second year for the formation of flower and
seed.

During the production of seed a concentration of nutritive
material, including always albuminoids, phosphates, sulphur,
potassium, chlorine, and the other elements essential to plant
life, takes place, the stem, leaves and roots being robbed of
much of their important constituents. The carbonaceous
material in a seed may be either mainly carbohydrates
(generally starch), or fats. Most seeds contain mainly one of
these classes, but some contain both.

Conditions affecting" Plant Growth.— Apart from the

obvious necessity of a proper supply of food and water, the
most important factor in growth is undoubtedly temperature.
For every plant three important temperatures may be found —
the minimum, optimum, and maximum temperatures at which
growth occurs. Temperatures below the minimum or above
the maximum, though not necessarily fatal to the plant, cause
its growth to cease, and in most cases seriously retard its rate
of growth for some time after the temperature has risen or
fallen above or below these limits. The cardinal temperatures
vary considerably with difierent plants. The minima are
usually about 7° or 8° C, the optima about 32° C, and the
maxima about 39° to 43° C.

In all cases the rate of growth increases with a rising

THE PLANT 83

'*^ temperature from the minimum, slowly at first, then more
rapidly, until the optimum temperature is reached, af t§r which
it diminishes rapidly to the maximum temperature.

Now, in temperate climates the maximum temperature for
most plants is rarely, if ever, reached, and as a rule the growth
is greater the higher the temperature. Fortunately, too, in
such climates the daily range of variation in temperature is not
great. Thus during the growing season the plant is rarely
cooled to the minimum or heated to the maximum temperature,
and its growth will be greater the longer the time at which it
is near the optimum temperature. Moreover, the disturbi'^g
effect of excessive heat and cold will be absent.

But in tropical countries, especially at considerable elevation
and far inland, the conditions are different. The daily range
of temperature is much greater. In the night, and especially in
the early morning, the ground temperature may sink below
the minimum, while in the hot midday sun it may rise con-
siderably above the maximum temperature of growth. Conse-
quently plaijts, though they may pass through the optimum
temj)erature perhaps twice in the twenty-four hours, are kept
near that temperature for but a short period each day, and
even then are not able to take advantage of it, because of their
being disturbed by the rapidity of the change. It has been
alleged that in such countries — South Africa, for example — the
screening off of the early morning sun has a very injurious
effect upon many plants, and has led to the belief that there is
something peculiarly favourable to plant-life in the rays at
sunrise. But the influence can be explained by the tempera-
ture effect produced. The following experiment by the writer
will show this. In the case of a thermometer on the ground
Fcreened from the sunrise rays from 6.30 to 9.30 a.m. the
temperature, at first about 6' C, rose very slowly to about 16°
at 9.30, and then rapidly (after direct sunshine fell upon it) to
28°, and subsequently gradually to 37° C. at 11 a.m. At the
same time a plant receiving the direct rays of the morning
sun rose from 6° C. at 6.30 a.m. to 11° at 7.15, attained 16° at

84 ELEMENTARY AGRICULTURAL CHEMISTRY

8.0, 21° at 8.45, and 25-5° at 9.15, 28° about 9.30, and there-
after gradually rose to 37° at 11 a.m.

Obviously an unshaded plant would not only pass more
gradually through the transition from the too low night to
the too high day temperature, but would be maintained at a
temperature near its optimum for a much longer period than
the screened plant. Consequently the conditions for its growth
would be much more favourable. In fact, there can be little
doubt that in countries like the Transvaal many plants
actually suffer from excessive sunshine, with its attendant
heat, while in less sunny lands — e.^., England — they rarely
attain even their optimum temperature, and probably never
exceed their maximum temperature of growth.

The Constituents of Plants— The elements present in
plants have been enumerated in the first chapter, but of far
greater importance are the chemical compounds actually
existent in the plant. These compounds may conveniently
be grouped as follows :

^

Non-nitrogenous
substances.

I. Carbohydrates.
II. Fats and waxes.

III. E^scntial oils and resins.

IV. Oiganic acids and their salts.
V. Inorganic salts.

( VI. Albuminoids or proteids.
Nitrogenous sub- J VIT. Amides and amino-compounds.
stances. jVlII. Alkaloids.

\ IX. Chlorophyllandothercolouring-matters.

A brief account will now be given of these substances.

I. The Carbohydrates. — This is a large group of substances,
each of which contains carbon, hydrogen and oxygen, the two
latter present in the ratio by weight of 1 : 8, the same ratio as
they have in water. Most of them contain some multiple of
five or six atoms of carbon in a molecule. They can be sub-
divided into two classes —

(1) the starches, amyloses, or poly saccharoses ;

(2) the sugars.

THE PLANT 85

(1) The Starches. — These have the composition expressed by
the formula OgHj^O^^jbut tlieir molecules aremuch more complex
than the formula indicates ; (CgHj^Oj)^, where 7i is a large
number, more correctly expresses their constitution. Among
the most important members of this group are :

Starch. Glycogen.

Dextrin. Cellulose.

Starch is very abundant in vegetable products, acting as a
reserve material for the nourishment of the growing portions.
It possesses ari organised structure, being in the form of
granules, which possess difl'erent forms and sizes in different
plants. It is insoluble in cold water, but when heated to about
G0° or 70° C. with water the granules burst, and their contents
form with the water a viscid, translucent liquid known as
starch paste. Starch is coloured intensely blue by free iodine.

Glycogen has the same composition as starch, and occurs in
animals, especially in their livers. It is therefore sometimes
known as animal starch. It gives a red colour with iodine.
It is a white solid, soluble in water.

Dextrin is formed when starch is heated to about 220° C.
It is easily soluble in water, and gives no blue with iodine. It
is made commercially for adhesive purposes, and is sometimes
known as " British gum."

Cellulose is very abundant in the leaves, stems, and roots of
plants. It is mingled with other substances, from which it can
usually be separated because of its resistance to most reagents.
By treating the tissues of a plant successively with chlorine,
caustic alkalies, dilute acid, water, alcohol, and ether a residue
of almost pure cellulose is left. It is a white substance, in-
soluble in most solvents, but soluble in zinc chloride or
ammoniacal copper oxide solutions. By the action of nitric
acid cellulose is converted into nitro-celluloses — e.g., gun-
cotton, CeHj(N03)30„ colk)dion, C6H,(N03),0,.

S6 ELEMENTARY AGRICULTURAL CHEMISTRY

Parchment paper is another product obtained from cellulose.
It is prepared by immersing unsized paper in strong sulphuric
acid and then washing it with water. The chief alteration
appears to be in the physical propeities.

By long boiling with dilute sulphuric acid, cellulose — e.g.,
filter paper, linen or cotton rags — is converted into dextrin and
dextrose.

Similar in many respects to the starches are the bodies
known as pentosans, of which arahan and xylan may be taken
as typical. These substances have the composition (C^HgOJ,,,
and by boiling with dilute acids yield arahinose or xylose,
CjHj^jOj, sugar-like bodies known under the general name of
pentoses. The pentosans are very abundant in many plants,
especially in wood-gums (of which they constitute from 60 to
92 per cent.), in straw (lG-27 per cent.), bran (22-25 per
cent.), brewer's grains (27-31 per cent.), and meadow hay
(16-18 per cent.). The pentosans and pentoses are probably
not digestible. When treated with strong boiling hydrochloric
acid they yield furfurol, C^H^Og ; e.g.,

G^U,fi, = C,H30.CH0 + SH^O.

Arabinose Fuifurol Water

Lignose or lignone is another ingredient in the stems
and woody portions of plants. It exists in association with
cellulose, from which it may be regarded as resulting by the
removal of water :

2C,H,A = C,,H,30, + H,0.

Cellulose Ligno-ceilulcse

The Pectin substances are bodies of unknown constitution
which exist as coagulable substances in fruit juices, stems,
roots, &c. They resemble the carbohydrates, though whether
the oxygen and hydrogen are in the ratio of exactly 8 to 1
seems somewhat uncertain. They readily pass into substances
which have the power of gelatinising.

THE PLANT 87

(2) The Sugars. — Of these there are many varieties for an
account of which a text-book on organic chemistry should be
consulted. Only a brief mention of the following can be
made here :

Cane sugar, saccharose^ 0^^1i^fl^^, occurs in many plants,
generally in the sap ; it is especially abundant in the juice of
the sugar cane (16 or 18 per cent.) in the sugar beet (10 to 18
per cent.), and in the sap of the sugar maple. It melts at
1G0°C. and becomes brown at about 190° 0. It does not
reduce copper salts, but rotates the plane of polarised light to
the right. By the action of certain enzymes, e.g., invertase.
present in yeast, or by boiling with dilute acids, it is converted
into a mixture of levulose and dextrose {^* inversion ").

Milk sugar, lactose, CjjII,,Oj, + IT^O. see p. 185.

Dextrose, glucose, grape sugar, CgHjgOg, occurs in many fruits
and can be obtained by boiling starch or cellulose with dilute
sulphuric acid. It reduces copper salts in alkaline solution and
rotates polarised light to the right.

Levulose, fructose or fruit sugar, has the same empiric com-
position as dextrose, but rotates the plane of polarised light
strongly to the left. It occurs in many fruits, and, like
glucose, lactose and maltose (Cj^HgjOn + 11^,0, formed by the
action of diastase upon starch), reduces copper salts to red
cuprous oxide in alkaline solution.

Milk sugar, dextrose and levulose are much less sweet to the
taste than cane sugar.

II. Fats and Waxes.— Fats are substances whose constitu-
tion has been fairly completely investigated. They, like the
carbohydrates, contain only the elements carbon, hydrogen,
and oxygen, but the latter element is present in comparatively
small quantities, and consequently fats are capable of uniting
with considerably more oxygen, thus producing much heat or
energy by their oxidation.

Ail true fats may be regarded as compounds of organic acids
with an organic basic radical, glyceryl (GjHj). This radical is
trivalent, having the constitution :

88 ELEMENTARY AGRICULTURAL CHEMISTRY

H

I
H— C—

I
H— C—

I
H— C—

I
H

Thus glyceryl stearate would be Os^ii^is^sflz)^'

Glyceryl is present in all true fats. The organic acids,
however, vary in different fats, and are usually of high mole-
cular weight. Many of them belong to the saturated series of
fatty acids, of which formic acid is the simplest example :

H

I
0 = C— 0— H

From this first member a series of fatty acids arises by the
successive substitutions of CH3 groups for hydrogen. Thus :

H

I
H— C— H

I
0«=C — 0 — H is acetic acid.

H

I
H— C— H

I
H— C— H

I
H— C— H

I
0 = C— 0 — H is butyric acid

THE PLANT 89

All acids of this series have the general formula

and are saturated, because each carbon atom is united by four
combining affinities with other atoms, and the compound is
incapable of uniting by addition with other substances.

The oils contain chiefly acids of high molecular weight. Thus
capric acid, CgHj^COOH, occurs in cocoa-nut oil ; myristic
acid, CjoHgjCOOH, also in cocoa-nut oil ; palmitic acid,
OijHgjCOOH, in palm oil ; stearic acid, Cj^Hg^COOH, in many
oils. These various acids are in combination with glyceryl.
But many oils contain also unsaturated fatty acids — i.e., acids
in which two or more carbon atoms are linked together by two
combining affinities. Such acids can combine hy addition with
other substances — e.g.^ oxygen, chlorine, or iodine.
The following are examples of unsaturated acids :

Crotonic acid, C3H5COOIT, in croton oil.

Oleic acid, Q^^ll^QOOH, in olive and other oils.

Brassic acid, CjiH^iCOOH, in colza oil.

Ricinoleic acid, C,yH32(OH)COOH, in castor oil.

All these have the general formula CnHjn_jCOOH and con-
tain one pair of doubly linked carbon atoms. Another acid,
linoleic acid, Cj^IlgiCOOH — i.e., C„H2n_3COOH — and containing
two pairs of doubly linked carbon atoms, occurs in linseed and
other oils ; while a still more unsaturated acid, linolenic acid,
0„H2,C0()H (i.e., C„H2^_.C00H), containing three pairs of
doubly linked carbon atoms, also occurs in linseed oil.

Oils containing glyceryl compounds of unsaturated acids
tend to absorb oxygen from the air and to become converted
into solid or stiff, viscid substances. This property is the more
marked the larger the number of doubly linked carbon atoms,
there are in the molecule.

Oils which contain only saturated acids or acids contain-
ing only one pair of doubly linked carbon atoms (e.g.., oleic
acid) are known as non-drying oih^ while those containing
much of the unsaturated acids are known as drying oils, Tho0

90 ELEMENTARY AGRICULTURAL CHEMISTRY

former — e.g., olive oil — are used for lubricating purposes, while

the latter — e.g., linseed oil — are used in the manufacture of

paints, linoleum, oil-cloth, varnishes. Oils and fats, both

vegetable and animal, are also largely used in the manufacture

of soap.

Hard soap consists of sodium salts of various fatty acids,

soft soap of corresponding potassium compounds. Soap is

made by boiling the oil or fat with a solution of an alkali,

whereby the metal of the alkali replaces the glyceryl of the

oil, yielding the soap and glycerine (or glycerol, as it is now

more systematically called). Thus, to take an example, if soda

be boiled with glyceryl oleate (the largest constituent of olive

oil) the following reaction occurs :

C3H,(C,,Il33COO)3 + SNaOH
Glyceryl oleate Sodium

hydroxide

- 3C3H,(OH)3 + 3NaCj,H33COO.

Glycerol or Sodiuro oleate

glyceryl hydroxide or soap

Both the soap and the glycerine remain dissolved in the

water, from which the soap can be separated in the solid

state by adding common salt. Glycerine can be recovered

from the remaining brine.

Oils may be present in various parts of a plant, but it is
always accumulated in the seed. Many seeds contain large
proportions of oil, sometimes up to half their weight. As a
rule, if a seed contains a high proportion of oil it is devoid of
starch, but many seeds — e.g., maize — which are rich in starch
contain a small quantity of oil.

Oil is a concentrated source of energy, one part of oil being
equivalent to about two and a half parts of starch or sugar.

Waxes are similar to the fats and oils in constitution, but
instead of the trivalent radical glyceryl, they contain mono-
valent radicals, of more complex character.

III. Essential Oils and Resins. — Essential oils are

usually volatile and possessed of characteristic odours. They

gbear no resemblance chemically to the true oils. Many of

THE PLANT 91

tliein are hydrocarbons — i.e., compounds of hydrogen and
carbon; others contain, in addition, oxygen or jsulphur. Tlie
hydrocarbon essential oils or terpenes have the general
formula (C^Hg)". Many vegetable perfumes consist mainly of
these terpenes — e.g., oil of turpentine, of lemon,of orange, or of
eucalyptus. Of oxygenated essential oils, many diflferent vari-
eties are known, e,(j., oil of bitter almonds contains benzoic alde-
hyde, CgH^CHO ; camphor has the empirical formula Cj„HjgO ;
oil of lavender contains linalyl acetate, C^oH^jC^Hfi^. Of essen-
tial oils containing sulphur, allyl isotbiocyanate, CjH^NCS,
found in oil of nmstard, and allyl sulphide, (03115)28, present
in oil of garlic, may be taken as typical.

The Resins may be regarded as oxidation products of ter-
penes. Their constitution is complex and not well under-
stood. In plants they oft^n occur associated with terpenes.

IV. Organic Acids and their Salts. — Many organic acids
have been detected in various vegetable products. They
generally occur as potassium, sodium, or calcium salts, though
sometimes as free acids. All organic acids contain the group
COOH, "carboxyl."

Among those commonly occurring in plants the following
may be mentioned :

Oxalic acid, COOH.COOH.

Tartaric acid, COOH.CHOH.OHOH.COOH.

Malic acid, COOH.CHOH.CH^.COOH.

Citric acid, CH,(COOH).C(OH)(COOH).CH,(COOH).

Gallo-tannic acid, C,ll^{0}i),.C0.0.C,U.XOIL),.C001I.

Gallic acid, C,H,(0H)3.C00H.
The acidity of fruits is often due to the presence of free
acids — e.g., malic acid, which occurs in apples, gooseberries, red
currants, blackberries, and sour cherries — but sometimes to
the occurrence of acid potassium or calcium salts ; thus grapes
contain acid potassium tartrate, sweet cherries acid potassium
malate. In many fruits two or more acids may occur to-
gether ; thus gooseberries contain both malic and citric acids.

92 ELEMENTARY AGRICULTURAL CHEMISTRY

Calcium oxalate is very frequently found in plants, often in
the form of crystals of CaCgO^-SH^O. Acid potassium oxalate
also often occurs in solution in the sap of plants.

Tannic acid is present in many plants, often associated
with glucose.

Organic acids occur in the sap of the roots and root-hairs of
plants, and possibly aid in promoting the solubility of the
mineral matter of the soil. The nature of these acids has not
been much investigated, though it has been shown that in a
large number of plants the average acidity of the sap, expressed
in terms of hydrogen, is about -013 per cent., corresponding to
about 0*91 per cent, of crystallsed citric acid.*

V. Inorganic Elements. — Many of the inorganic constituents
of plants, the metals in particular, occur in combination with
organic acids, as already stated. Others — phosphorus and
sulphur — are associated with complex organic compounds, e.g..,
albuminoids. A few words may be said about the mode of
occurrence and functions of each of the inoi'ganic elements
found in plants.

Sulphur^ though existent in a living plant chiefly as a con-
stituent of albuminoids, is left in the ash as sulphate, or some-
times as sulphide. It is probably obtained by the plant from
the sulphates in the soil, and can often be detected in that form
in the sap.

Phosphmms is undoubtedly absorbed as phosphates, and exists
in that form in the ash. In the living plant, however, it exists
partly in union with organic compounds, and appears to move
about in association with the albuminoids.

Silicon is probably taken into the plant in the form of
alkaline silicates. There is considerable evidence that though
silicon is often present, generally as deposits of silica in the
outer walls of the stem and leaves (particularly in cereals), it
is not indispensable.

Chlorine is found in all plants, but does not appear of much
* Vide footnote on p. 79.

THE PLANT 9^

importance, except in the case of a few plants — e.gr., buckwheat,
mangolds and cabbages.

Potassium is absorbed as various soluble salts. It generally
occurs in the plant in union with organic acids, which decompose
on burning, leaving potassium carbonate in the ash. In some
plants the sap contains nitrate, chloride and sulphate of potash.
Potash compounds appear to be necessary for the production
of starch, sugar and other carbohydrates, and are always most
abundant in the leaves and young shoots.

Calcium exists in union with organic acids, and aids in the
conversion of starch into sugar. In many cases it appears to
act beneficially in converting vegetable acids into insoluble
compounds, which are deposited in the plant — e.g.., calcium
oxalate. It, too, is found largely in the leaves.

Magnesium is distributed over all parts of the plant, but
little is known of its functions. It has recently been shown to
be a constituent of chlorophyll.

/row, though indispensable, usually occurs in very small
quantities. It is essential for the production of chlorophyll.

Sodium^ though always present in the ash, does not appear
to be essential to the plant. It cannot replace potassium.

The metals above mentioned also act as carriers of nitric acid.
When nitrate is absorbed by a plant the nitrogen is used in the
formation of albuminoid substances, while the bases unite with
organic acids. When the plant is burnt the metals are left as
carbonates, and it is found that, the richer a plant is in nitrogen,
the larger is the amount of bases left as carbonate in the ash.

YI. Albuminoids or Proteids. — These are substances which
resemble albumin or white of e^g. They form a large class of
bodies, which differ in physical properties — e.g.., solubility and
coagulability — are of highly complex composition or consti-
tution, and contain carbon, hydrogen, oxygen, nitrogen and
sulphur. They occur in all living matter, being essential
constituents of protoplasm. Their composition varies some-
what, the following being the usual limits:

94 ELEMENTARY AGRICULTURAL CHEMISTRY

Carbon .

. 51-5 to 64-5 percent.

Hydrogen

. 6-9 „ 7-3 „

Oxygen .

. 20-9 „ 23-5

Nitrogen

. 15-2 „ 17-0

Sulphur .

. 0-3 „ 2-0 „

The constitution of proteicls is not yet fully known, though
recently they have been shown to consist of amino-acids.

As illustrating the complexity of albumin, for example, the fol-
lowing empirical formula, among many others, has been proposed
as most nearly representing its composition : C240II392N65O75S3.
That any definite compound really has such a composition is
extremely improbable. When hydrolysed, proteids split up
into their constitvient amino-acids.

Proteids all give a yellow colouration when heated with strong
nitric acid. This coloured substance becomes orange when
treated with ammonia. They also give a red colour when heated
with an acid solution of nitrate of mercury (Millon's reagent).
Id analysis it is usual to assume that proteids contain 16 per
cent, of nitrogen. The amount of nitrogen in a substance is
determined, and, by multiplying the percentage of this element
by ^^ or 6-25, the product is taken to represent the percentage
of albuminoids. The result can only be approximate, since, as
already stated, the percentage of nitrogen varies in different
albuminoids. The albuminoids are, as a rule, non-crystallisable,
colloidal bodies.

VII. Amides and Amino-acids. — These, also nitrogenous
compounds, have a much simpler constitution than the
albuminoids. An amide may be regarded as derived from an
organic acid by the replacement of the -OH by -NHj. Thus
from acetic acid,CH3.C00H, is derived acetamide, CH3.CONH,.
Amino-acids are derived from organic acids by the replacement
of one or more hydrogen atoms in the organic radical by -NH,,
thus, amino-acetic acid, or glycocoll, is CH2(NH2).COOH.

Amides occur widely distributed, especially in immature
plants, and since they apparently are incapable of forming flesh
when fed to animals it is important in food analysis to dis-
tinguish between them and the more valuable albuminoids.
Many amides have been found in various plants, but asparagine

THE PLANT 95

(amino-succinamic acid), CO.(NH2).C,n3(NH,).CO.OH, may be
taken as typical. This substance, which is both an amide and
an amino-acid, is soluble in water, and, like most amides, is
crystallisable. It occurs in asparagus, in the young shoots of
vetches, bean?, peas and many other plants.

VIII. The Alkaloids. — These substances may be regarded
as derived from ammonia, NH,, by the replacement of the
whole or part of the hydrogen by complex organic groups.
They are usually possessed of powerful medicinal properties, and
occur only in certain plants, sometimes in the seed, sometimes
in. the leaves, and sometimes in other parts of the plant. They
are of no value as direct foods, but are often valued in medicine.

Caffeine or tkeine, CgHjoN^O^, occurring in tea and cofiee,
and theobromine, CjH^fi^, found in cocoa, though by some
authorities not regarded as true alkaloids, may be mentioned ;
while as examples of undoubted alkaloids, quinine (in Peruvian
bark), C,oH,^N,0„ strijchnine (in nux vomica beans), C,iHj,N,Oj,
morphine (in poppy heads), C,yHj,NO,, and nicotine (in tobacco
leaves), C,,H,oN„ may be cited.

IX. Chlorophyll, also a nitrogenous body, has been much
investigated. It is the green colouring substance present in the
leaves and stems of almost all plants, and intimately connected
with the assimilation, under the influence of light, of carbon
from carbon dioxide. It has the composition represented by
the formula, C^sH^OgN^Mg, and contains, as its fundamental
constituent, chlorophyllin Cg^HjjOeN^Mg. It is easily extracted
by alcohol, ether, or carbon disulphide.

Though iron is essential for its production in the plant, the
coloured substance itself is free from iron. Except in this last
fact it appears to possess some similarity in composition and
constitution to the red colouring substance — haemoglobin — of
the blood of animals. Indeed, recent investigations tend to
show that the characteristic constituent of chlorophyll and of
hjematin (the coloured part of haemoglobin) have the same
constitution, except that in chlorophyll, magnesium replaces
the iron of haematin.

CHAPTER Yl.
MANURES.

For a soil to possess fertility — i.e., to be able to properly sup-
port the growth of plants — certain conditions are necessary.
The following may be mentioned as being perhaps the most
important :

1. Its mechanical or physical condition must be suitable.

2. It must contain sufficient plant food in a form which is
readily available to the crop.

3. It must not contain any appreciable quantity of poisonous
or injurious substances.

4. It must not contain injurious insects, fungi, or other
organisms which are destructive to the crop.

5. The temperature, sunshine, rainfall and other climatic
conditions must be suitable.

Of these, the second and third, and to a less extent, the
first, are matters in which chemistry may be of service.

Every crop removed from a soil robs the latter of materials
which have been used in building up the former's tissues. Soil
which annually bears a crop must, in time, become exhausted of
its store of plant food and unfitted to bear further crops.
Generally, one constituent of plant food becomes exhausted
first, and in many cases restoration of this constituent would
renew the fertility for some time longer. Substances which
are added to a soil in order to replace the ingredients which
have been removed by previous crops are called manures.

All constituents of plants present in a soil, except the
carbon, are diminished by the growth of crops upon it, but
the substances which usually first become deficient are com-
bined nitrogen, phosphates, calcium carbonate and potash.

96

MANURES

97

Consequently manures are usually valued according to the
quantities of these ingredients present in them, although in
many cases other constituents may exert an important in-
fluence upon the soil.

Farm -yard Manure.— This, formerly the only important
manure, is still the most popular.
It consists essentially of :

1. The excreta of the animals of the farm.

2. The litter and waste food.

The exci'eta of animals consists of undigested parts of their>
food, together with various waste products from the tissues
of their bodies. The composition of the excrement varies
greatly, some of the factors determining it being ;

1. The kind of animal.

2. The character and quantity of the food.

8. Whether the animals are growing, fattening, work-
ing, or milking.

Considerable discrepancies are therefore not surprising in
analyses of the excreta of animals.

The following table gives the average proportions of the
chief manurial ingredients found in the excreta of various
animals, according to American analyses : —

Nitrogen.

Potash.

Phosphorus
pentoxide.

Per cent.

Per cent.

Per cent.

Cattle : dung ....

0-20

0-10

0-17

urine .

0-58

0-49 ,

—

Horses: dung .

0-44

0-35

0-17

urine .

1-55

lv)0

—

Sheep : dung .

(y-55

0-15

0-81

urine .

1-95

2-26

0-01

Pigs : dung .

0-60

0-13

0-n

urine .

0-43

0-83

0-07

Man : dung .

1-UO

0-25

1-09

urine .

0-60

0-20

0-17

98 ELEMENTARY AGRICULTURAL CHEMISTRY

For many reasons, however, the proportions are liable to
very considerable variation. The excreta of sheep are less
watery than those of the other animals.

It will be noticed that in most cases the urine, though
almost free from phosphates, is richer in nitrogen and potash
than the dung. The substances found in the urine are those
which have been digested by the animal and produced by the
waste of tissue while those in the dung are chiefly derived
from the undigested food. In addition to the fertilising con-
stituents of the urine and dung, a notable quantity of nitrogen
and, particularly, of potash is contained in the perspiration
of some animals. Horses and sheep are remarkable in this
respect.

The litter renders the manure more bulky and porous,
absorbs and retains much of the liquid portion, increases the
carbonaceous matter which will eventually pass into humus
in the soil, and furnishes a small proportion of plant food.
It greatly influences the fermentation of the manure, both by
affecting the porosity and admission of air and also by furnish-
ing certain micro-organisms. The average proportions of the
chief manurial ingredients present in the various substances
used as litter are given in the following table : —

Name of substance.

Nitrogen.

Potash.

Phospliorus
pentoxlde.

Wheat straw .
Barley straw .
Oat straw .
Rye straw .
Peat-moss. ^ .
Dried bracken .
Dried leaves (autumn)
Sawdust ....
Tanners' refuse

Per cent.

0-48
0-57
0-72
0-57
0-85
0-90
0-75
1-00
0-16

Per cent.
0-9
1-2
1-2
1-4
0-01
0-13
0-10 to 0-50
0-10
0-08

Per cent.
0-25
0-26
0-19
0-28
0-03
0-20
0-18
0-05
0-04

The absorptive and retentive power of these substances for
water and ammonia are of much importance. Peat-moss

MANURES

99

excels in this respect, while leaves and bracken are probably
the poorest.

The composition of farm-yard manure is exceedingly
variable, and is always very complex. It usually contains
from two-thirds to three-quarters of its weight of water,
from 0*4 to 07 per cent, of total nitrogen, from 04 to 10
per cent, of potash, and from 0*3 to 0*4 per cent, of phosphorus
pentoxide. Very little of the nitrogen is present as ammonium
compounds and mere traces as nitrates, the main quantity
existing as complex organic compounds.

Various estimates of the amount of manure produced per
day by the animals of the farm have been made. According
to German authorities, the following are the figures :

Animal.

Horse
Cow.
Sh<iep
Pig -

Total

Straw

Total

Excrement.

required.

Manure.

lb.

lb.

lb.

28

6

33

73

8

81

3*8

0-6

4-4

8-3

4

12-3

American estimates give as the manure per day per 1000
lb. live weight, the animals being fed liberally and littered
sufiiciently :

Horse
Cow
Sheep
Pig

48-8 lb., valued at 3-8 pence.

74-1 „ ., 4-0 „

34-1 „ „ 3-6 „

83*6 „ ,, 8'3 ,.

Presepvation of Farm-yard Manure.— The best means

of using manure, whether fresh or rotted, and the best
methods of avoiding loss of valuable ingredients are matters
which have attracted much attention and given rise to much
discussion. The drainings from manure are very rich in
nitrogenous and potash compounds, and it is evident that
allowing them to run to waste is bad economy. They should

100 ELEMENTARY AGRICULTURAL CHEMISTRY

be preserved either by absorbents — e.g., peat-moss or dry
earth — or by being collected in a tank. Access of rain should
be prevented by storing the manure in a covered yard. Of
greater complexity is the question of losses* during fermenta-
tion. These losses are chiefly of importance as far as they
affect the nitrogen. Nitrogen is lost chiefly in two ways —
by volatilisation of ammonia from ammonium carbonate and
by the evolution of free nitrogen.

A characteristic constituent of the urine of most animals
is the substance known as urea, CO(NH2)2. This body is
by the action of micro-organisms converted into ammonium
carbonate :

COCNH^)^ + 2H2O = (NHJ2CO3.
Urea Water Ammonium

carbonate

Ammonium carbonate is a substance which smells of
ammonia; indeed, on exposure it is said to decompose into
ammonia and carbon dioxide :

(NH,),C03 = 2NH3 + CO2 + H,0.

Ammonium Ammonia Carbon Water
carbonate dioxide

This change is hindered by the presence in the atmosphere
of large quantities of carbon dioxide or of ammonia. To this
decomposition of urea is due the strong smell of ammonia
generally perceptible in stables.

In a manure heap numerous chemical changes produced
by micro-organisms take place, many of them attended
by absorptioil of oxygen and production of carbon dioxide.
Such changes evolve heat, and the temperature of the heap
often rises to a very high point. The oxidation of the
purely carbonaceous matter in the manure is rather ad-"
vantageous, since it diminishes the quantity of useless (from
a manurial standpoint) matter, and thereby increases the
proportion of manurial matter in the residue. The high tem-
perature produced, however, tends to increase the amount of
ammonia volatilised, especially if the mass becomes dry. On

MANCTRES *-^ ' '* ' *' ' 101

the other hand, the production of caibon'dic^idje^ln^t^i^'ipife^-i
stices of the manure tends to lessen the loss by volatilisation
of ammonia. In any case, it is desirable to regulate fermenta-
tion so that it goes on regularly, but slowly, and without any
excessive rise of temperature. This can be done by a careful
admixture of horse and sheep manure which are " hot ' (i.e.,
very prone to rapid fermentation) with cow and pig manura
which are " cold " (i.e., ferment slowly), and by keeping the
manure moist by occasionally pumping the drainings from thi
tank on to the heap.

The other way in which nitrogen is lost is by the decom-
position of the nitrogen compounds and the evolution of the
free element. This is the result of the action of micro-
organisms in the absence of air. A compact and a thoroughly
sodden state of the heap are the conditions favourable to this
action. The loss of nitrogen from a manure heap can be
greatly lessened by mixing or covering it with soil or peat
moss. Another even more effective plan is to add some acid
substance — e.g., superphosphate, or even sodium acid sulphate.
An objestion to these preservatives has been made on the score
that they act not merely as absorbents, but as antiseptics, and
prevent the decay of the litter.

Other Organic Manures. — The following substances are
also used as manure :

1. Guano. — This consists mainly of the dried dung of sea-
birds. It is found on the coasts of tropical seas. Two
varieties are now used, one rich in both nitrogen and phos-
phates, the other poor in nitrogen but very rich in phosphates.
Great variation in composition is shown by guano. An average
sample of the first class might contain 7 or 8 per cent, of
nitrogen and about 11 per cent, of phosphorus pentoxide,
vhile for the second variety 0*5 to 2 per cent, of nitrogen and
20 to 33 per cent, of phosphorus pentoxide would be fairly
representative. Potash is present in many samples of guano,
to the extent of about 2 or 3 per cent.

102 ELEMEMAF^Y AGRICULTUKAL CHEMISTRY

^vln .th<^ Tiitrogeno'Hi* Y^^'ieties the nitrogen is largely present
as ammonium salts, and some of the phosphoric acid as soluble
alkaline phosphates.

Bats' guaoio, consisting of the dried excrement of bats,
occurring in caves in some countries, is of variable composition,
being often mixed with fine silt. It always contains a con-
siderable amount of nitrates,.

2. Poultry and pigeon dung are rich manures, but seldom
abundant enough to have much importance in ordinary
farming.

3. Seaweed is a valuable manure, undergoing rapid decom-
position in the soil. In the fresh state it contains about
80 per cent, of water, from 0*3 to 0*7 per cent, of nitrogen,
from 0*3 to 2 per cent, potash, and from 01 to 0*4 per cent.*
of phosphorus pentoxide.

4. Fish Manure or Fish Guano. — This usually consists of
the dried refuse — heads, bones, and other oftal — of fish, and is
a rich manure, containing about 9 per cent, of nitrogen and
10 per cent, of phosphorus pentoxide. The presence of much
oil in this manure is objectionable, because it repels water and
hinders decay in the soil, and in some cases it is extracted by
means of volatile solvents.

5. Dried blood from slaughter-houses is a valuable manure,
easily decomposing in the soil. It contains 10 or 11 per cent,
of nitrogen, and nearly 2 per cent, of phosphorus pentoxide
Meat meal is similar in composition, but contains more phos
phates.

6. Shoddy manure or woollen waste is essentially the wool
fibres which have become so short by repeated spinning,
weaving, &c., that they will no longer hold together. Mixed
with the wool residue, however, is a variable quantity of cotton,
grease and dirt. The usual product contains about 7 or 8 per
cent, of nitrogen, and is remarkable for the slowness with
which it decomposes in the soil. It is essentially a nitrogenous
manure, but contains small quantities of potash (perhaps
0-5 per cent.) and phosphorus pentoxide (about 0-3 per cent.).

MANURES 103

It is largely.used for hops, and as a constituent in many mixed
manures. Hair, horn, and feathers resemble wool in com-
poation, and are occasionally employed as manure.

7. Bones consist of about 70 per cent, of mineral matter,
chiefly calcium phosphate, and 30 per cent, of organic matter,
containing 3 or 4 per cent, of nitrogen and a variable quantity
of fat. Coarse bones decay very slowly ; in some soils they
can be found almost unchanged several years after their
application. They are therefore now reduced to small frag-
ments, and are graded, according to their size, as " half-inch
bones," ** bone dust," " bone meal," and " bone flour." They
are often heated with steam under pressure before grinding, so
as to remove the fat and some of the nitrogenous matter.
They are then more easily ground and decay more quickly
when applied. Bone ash is sometimes used; it is free from
nitrogen and organic matter, and valuable only for its phos-
phates.

8. Soot consists largely of carbon, but that from house
chimneys contains about 3 per cent, of nitrogen, in the form
of ammonium salts and organic compounds.

9. Oil cakes consist of the husks and residue left after
expressing oil from certain seeds, and are rich in all the con*
stituents of plant food. Usually these residues are employed
as food, but in some cases they are unpalatable or poisonous,
IChey then form valuable manures, though somewhat slow in
action. * If the oil has been extracted by solvents the product
is improved. Rape seed and castor oil seed cakes are the chief
examples. They contain from 5 to 6 per cent, nitrogen,
about 1 per cent, of potash and 1*5 per cent, of phosphorus
pentoxide.

10. Human Excreta. — Where earth-closets are used the
night soil has considerable value as a manure, provided it can
be used locally. So, too, cess-pools yield a liquid manure rich
in fertilising materials. In large towns, however, the excreta
of the inhabitants usually passes into the sewers and becomes
mixed and diluted with much water and trade effluent. Its

104 ELEMENTARY AGRICULTURAL CHEMISTRY

utilisation then becomes very difficult, although highly desir-
able. Not only is valuable manure lost by the sewers dis-
charging into rivers, but the latter become so polluted as to be
a source of annoyance, and even danger.

Many attempts to extract a portable manure from sewage
have been made, but without success. A very popular
method, known as the ABC process, consists in adding alum,
blood, and clsiy, when the coagulum formed carries down most
of the suspended matter, which, when drained and dried, is
sold as *' native guano." The metliod, however, fails to remove
the large proportion of the nitrogenous matter of the sewage
which exists in solution.

Another plan is to utilise the sewage for irrigation purposes.
This is a better method, for a suitable soil extracts much
valuable fertilising matter from sewage, and will then yield
enormous crops. Great difficulty, however, is experienced in
obtaining a sufficient area of suitable land (light, sandy soils are
best) to deal efficiently with the enormous volume of sewage,
produced by a large town. Moreover, during frosty weather
difficulties arise in dealing with the outfall as rapidly as it is
delivered. The land, too, in time becomes so clogged with
matters derived from the sewage that it is rendered unfit for
further treatment — " sewage-sick." The composition of
sewage is naturally very variable, but it is always excessively
dilute, its manurial value, assuming that all its fertilising
ingredients are available, being about l^d. to 2d, per ton.

Green Manuring*. — Soil deficient in humus may be greatly
enriched in that substance by growing any quick-growing crop
and ploughing it in. By this practice not only is the soil
enriched with carbonaceous material derived from the air, but
a considerable amount of nitrates which have been formed by
nitrification during the growth of the crop is assimilated,
converted again into complex organic compounds, and restored
to the soil. Without the crop these nitrates would have
been to a large extent lost by drainage. The planting of

MANURES 105

" catch crops " for this purpose is best done in the autumn,
since nitrification is then very rapid, and loss by the washing
out of the nitrates by the winter rains is to a great extent
prevented. Rye and mustard are favourite crops for the pur-
pose ; and obviously the ploughing in of the crop must take
place before the seed is formed, or otherwise the land would be
fouled for the next year. If leguminous crops are grown
and the crop be ploughed in, a still greater accession to the
nitrogenous store of the soil may be secured, for in the pre-
sence of the appropriate nodule-forming bacteria such crops
draw supplies of nitrogen from the air.

In the case of most plants, the roots absorb from the soil
water, the phosphates, potash, nitrates, &c., present and the
plant is quite unable to obtain any sustenance from the free
nitrogen of the air. In the case of peas, beans, clover, lujwnes
and other leguminosae the roots often possess small nodular
swellings or tubercles, inhabited by micro-organisms (Bacillus
radicicola) which have the power of taking free nitrogen from
the air within the soil, building it up into complex organic
compounds, probably of an albuminoid nature, and handing it
on to the host plant.

When a leguminous plant possesses the nodules and their
micro-organisms, it becomes independent of combined nitrogen
in the soil, and can thus flourish under circumstances which
would induce nitrogen starvation in other plants. Moreover,
after such a crop, the soil is often left richer in nitrogen than
before, owing to the root-d6bris remaining after the removal
of the crop. These facts were discovered by Hellriegel and
Wilfarth in 1886-88, and artificial cultures of appropriate
micro-organisms for several crops were put on the market
under the name of " Nitragin."

In this connection attention may be called to the recent
improvements in the preparation of cultures of nodule-forming
bacteria for the various leguminous crops. Both in Germany
and in America modified preparations of "Nitragin" have
been prepared, which were said to be much more successful

106 ELEMENTARY AGRICULTURAL CHEMISTRY

than the previous cultures. The German products contained
their bacteria in dried agar-agar jelly, and were prepared for
use in a medium containing milk, peptone and grape sugar.
The American product consisted of cotton-wool impregnated
with a culture of the particular organism and dried. The
cotton-wool was introduced into a solution containing sugar,
potassium phosphate, magnesium sulphate and ammonium
phosphate. In this medium the organism developed. In both
cases it was claimed that if the seed be moistened with the
medium containing the appropriate organisms and dried, the
presence of the nitrogen-fixing bacteria when the seed is sown
would be ensured.

A considerable sensation was created by popular articles, in
which it has been stated that the use of these cultures of
nitrogen-fixing organisms, under the name of *'Nitro-bac-
terine," is destined to revolutionise agriculture, but it should
be remembered that the most that can be expected of these
methods is that the soils rich in the mineral elements of plant
food, but deficient in nitrogen, may be gradually enriched in
that constituent so as to become capable of supporting the
growth of ordinary crops. There seems to be little doubt that
the new cultures possess the power of inducing nodule-forma-
tions on the roots of leguminous plants, and that even in soils
in which nodules are spontaneously formed, inoculation of the
seed with the cultures ensures the formation of more numerous
and larger nodules. But, on the large scale, these preparations
have not been successful enough to secure their general adoption.

Artificial or Chemical Manures. — The organic manuies,

as a rule, contain all the ingredients necessary for plant life, and,
is general manures, are highly satisfactory. Cases often arise,
iiowever, in which a soil only requires the addition of one or two
fertilising substances in order to fit it to yield a full crop. In
such cases, by means of suitable artificial manures, it is possible
to add exactly what is required, without introducing other plant
food, with which the soil may be abundantly supplied.

MANURES 107

(A) Nitrogenous Manures. — The principal members of this
class are sodium nitrate and ammonium sulphate.

Sodium Nitrate. — " Chili saltpetre " or " cubic nitre " is
found in certain rainless districts in Peru, Chili, and Bolivia.
It occurs near the surface in layers varying in thickness from
a few inches to 12 feet. The crude deposit is known as caliche^
and varies greatly in composition. The different varieties
are mixed so as to yield a product containing :

Per cent.

Earth, stones, &c. 50

Sodium nitrate 35

Magnesium, calcium, and sodium chlorides . 10

Water, sulphates, and other substances . . 5

This mixture is treated with water and allowed to settle;

iodine, which is present as sodium iodate, NalOj, is extracted,

and the liquor evaporated and crystallised. The crystals

so formed, are dried by exposure to the sun, and exported.

The average composition of the commercial product is said

to be:

Sodium nitrate 9675

Water 2-10

Sodium chloride "75

Sulphates -SO

Insoluble matter "10

lOO-OO

During recent years much attention has been directed
to the presence of sodium perchlorate, NaClO^, in many
samples of nitrate, and to the injurious effects produced by
the application of such nitrate to many crops. Specimens
of nitrate of soda have been found to contain as much as 5
per cent, of this poisonous perchlorate, and in samples used
in Germany, an average of about 1 per cent, appears to be
present. English samples seem to be comparatively free from
this impurity. Pure sodium nitrate, NaNOj, is a white
crystalline salt, very soluble in water (100 parts of water dis-
solving about 80 parts of the salt at ordinary temperatures),
and deliquescent in moist air. It is not retained by any

108 ELEMENTARY AGRICULTURAL CHEMISTRY

constituent of the soil, and Is therefore very liable to be lost
in the drainage. Hence it should never be applied in heavy
dressings, nor much before the crop is sufficiently grown to be
able to absorb it.

It has recently been proposed to manufacture nitrates for
agricultural purposes by passing strong electric discharges
through air. By this means oxides of nitrogen are produced
by the union of nitrogen and oxygen, and if an alkali — e.g.^
soda — be present nitrite and nitrate of the alkali are formed.
Where large natural sources of power {e.g., Niagara) are
available for producing electricity this process might be
profitable.*

Ammonium Sulphate. — This substance is made from the
" ammoniacal liquor " of gasworks, coke ovens, or blast-furnaces.
When coal, which contains about 1*3 per cent, of nitrogen, is
distilled the nitrogen is partly evolved as ammonia, NH3, which
dissolves in the water condensed from the steam formed at
the same time. The " gas liquor " so obtained contains many
compounds of ammonia, the chief being carbonate, chloride,
sulphide, and thiosulphate. The total ammonia in the " gas
liquor" amounts usually to about 2 per cent. In order to
obtain sulphate of ammonia, the " gas liquor " is distilled
with lime, and the ammonia gas evolved is led into sulphuric

acid;

H3SO, + 2NH3 = (NH,),SO,.

The liquid is boiled down, and sulphate of ammonia crystallises
out. Important impurities sometimes found in commercial
ammonium sulphate are ammonium sulphocyanide, NH^CNS,
and arsenious sulphide, As^Sj. The former is derived from the
" gas liquor,^" the latter from the sulphuric acid, which some-
times contains arsenious oxide, Asfiy Both these substances
are plant poisons.

Ammonium sulphate crystallises in anhydrous crystals, which

♦ Recently at Notodden (Norway) by using lime as the alkali, a
basic nitrate of lime, capable of successfully competing as a nitrogenou9
manure with nitrate of soda, has been produced on a large scale.

MANURES 109

are easily soluble in water (100 parts of water at the ordinary
temperature will dissolve about 73 parts of the salt). When
it is applied to soil it undergoes decomposition, the acid radicle
uniting with calcium from the calcium carbonate in the soil and
finding its way into the drainage, whilst the ammonium is held
back by the humus and other constituents of the soil :

(NH,)3S0, + CaCOj = (NHJ.COg + CaSO,.

Before it is available for plants ammonia has to be converted
into nitrates by the nitrification process, and this involves a
further loss of calcium carbonate :

40^ + (NH,),C03 + CaCOj = Oa(NO,), + 2C0, + AKfl.
Oxygen Ammoniurn
(from carbonate

the air)

It is evident from these reactions that sulphate of ammonia
is only suited to soils containing at least a moderate amount of
calcium carbonate, and that its use is then attended with con-
siderable loss of calcium to the soil. It is also clear that
sulphate of ammonia ought to be applied some time before the
crop requires its nitrogen, so that the necessary nitrification
can take place. In these respects it difiers essentially from
nitrate of soda, which is already available for plants, has little
or no influence upon the calcium carbonate of the soil, and, as
already stated, should not be applied before it is wanted.

Ammonium sulphate has the advantage in a wet season, on
account of its retention in the soil. In a very dry season, when
nitrification may be checked and little loss of water by
drainage occurs, nitrate of soda often gives the better result.

PotcLsaium nitrate, KNOj, is of double value as a manure,
but its price is so high that it is not very largely employed in
agriculture.

Calcium cyanamide, CaCNj, has lately been proposed as a
nitrogenous manure. The substance is obtained by heating
calcium carbide, CaCj (now so largely produced by means of
the electric furnace from carbon and lime, chiefly for the

no ELEMENTARY AGRICULTURAL CHEMISTRY

manufacture of acetylene), in a current of air which has been
deprived of oxygen. The crude product, which contains about
20 per cent, of nitrogen instead of the theoretical 35 per cent.,
is a black powder, resembling basic slag in appearance. When
used as a manure it has in many cases yielded as good results
as the same amount of nitrogen applied as nitrate of soda or
sulphate of ammonia ; but on peaty soil it has been found to
be harmful to plants, owing, it is said, to the formation of
dicyandiamide by the action of the acids present in the soil.
This substance is a powerful plant poison.

Under ordinary conditions — i.e., in the absence of acids —
the substance probably decomposes thus :

CaCN^ + SRfi = CaCOj + 2NH3,

the whole of the nitrogen being obtained as ammonia, and
thus capable of nitrification.

(B) Phosphatic Manures. — Bones, especially steamed and
burnt bones, and guano are chiefly valued for the phosphates
they contain. These manures have already been described.
Other more important (because more abundant) sources of
phosphoric acid are known. Before dealing with them it may
be advisable to describe briefly the various forms in which
phosphoric acid occurs in fertilisers.

1. As Ft'ee phosphoric acid, HgPO^. — This, when pure, is a
thick, semi-solid mass, obtained by acting upon a phosphate
with sulphuric acid :

Csi^Vfi, + SH^SO, = 3CaS0, + 2H3PO,.

It is soluble to any extent in water. It is found in small
quantities in some superphosphates.

2. As Monocalcium tetrahydrogen phosphate, CaH^P^Og. —
This substance is obtained by the action of a smaller proportion
of sulphuric acid upon*calcium phosphate :

Ca,P,03 + 2H,S0, = CaH,P,0, + 2CaS0,.

MANURES 111

It is very soluble in water, and is the chief valuable consti-
tuent of superphosphates.

3. As Dicalcium hydrogen phosphate, CagH^P^Og, or CaHPO^,
a white solid, obtained by precipitating ordinary sodium phos-
phate, Na^HPO^, with calcium chloride, CaCI, :

CaCl^ + Na,HPO, = CaHPO, + 2NaCl.

It is almost insoluble in water, but dissolves in the presence
of certain salts — e.g., ammonium citrate. It is probably more
easily available for the roots of a plant than tricalcium
phosphate. It is found in superphosphates, especially if they
have been kept for some time.

4. As Tricalcium phosphate, CajP^Og. — This is a white sub-
stance, almost insoluble in water, but easily soluble in acid.
This is the form in which phosphoric acid occurs in bones,
mineral phosphates, and most guanos. Its solubility is greatly
increased by the presence of carbon dioxide. The solubility,
too, depends upon its degree of subdivision and physical state,
being much greater if finely divided, amorphous and porous
than if coarse, crystalline and compact.

Most mineral phosphates contain also calcium chloride,
CaClg, or calcium fluoride, CaF^.

5. As Tetra/ialcium phosphate, Ca^P^Og. This is practically
insoluble in water, but dissolves in many saline solutions. It
occurs in the slag formed in the dephosphorisation of cast iron
by the basic Bessemer or basic Siemens process.

6. As Ferric phosphate, FePO^, and Aluminium phosphate,
AlPO^, These are practically insoluble in water, and nearly
so in dilute vegetable acids. Consequently they are difficultly
available for plants, and unless extremely finely divided are
almost worthless as manures. When they are formed in the
soil by the action of ferric or aluminium hydrate upon soluble
phosphates, however, they appear to be capable of affording
phosphoric acid to the roots of plants, though not readily.

Generally it may be stated that if a substance is formed by
precipitation from solution in the soil itself it will be, as a

112 ELEMENTARY AGRICULTURAL CHEMISTRY

rule, much more available for plants than if it were applied
ready-formed to the soil, even in a finely divided condition.

The chief commercial forms in which phosphates are used as
manures are :

1. Mineral phosphates, consisting largely of tricalcium
phosphate, CasPaOs. Immense quantities of this material are
found in the United States of America, in Belgium, Algeria,
and Canada. Generally they are not used directly, but are
converted into superphosphate. If very finely ground, how-
ever, they are occasionally successful.

2. Mineral Superphosphates. — These are made by treating
the raw phosphates with sulphuric acid (chamber acid of sp. gr.
1 '55), which produces the reaction already described. A super-
phosphate contains a considerable portion of its phosphoric
acid in the form of monocalcium tetrah} drogen phosphate,
CaH4P208, some as unchanged CasP208, and generally some a,s
CaHP04.

3. Dissolved Bones.— -ThesQ are made by a process similar
to the last described, but the product contains nitrogenous
matter, and usually a larger propoi tion of unchanged tricalcium
phosphate.

4. Basic Slag, Thomas Slag, or Thomas Phosphate, — Tliis
product is formed in the basic Bessemer process of making
steel from cast iron. It contains its phosphorus pen^oxide
(usually from 16 to 18 per cent.) in the form of tetracalcium
phosphate, Ca3P208, together with free lime, and is particularly
suitable for soils rich in organic matter. It is only efiective if
applied in a finely divided state, so that its value largely
depends upon the thoroughness of the grinding ; 80 to 90 per
cent, should pass a sieve with 100 meshes to the linear or
10,000 meshes to the square inch. Its phosphoric acid, though
insoluble in water, is readily soluble in saline solutions — e.g.,
solution of ammonium citrate. The composition of the com-
mercial product varies considerably, but a good sample contains
about 18 per cent, of phosphorus pentoxide, 45 per cent, of
lime, 1 5 per cent, of ferric oxide, and small q^uantities of silica,
magnesia, alumina, &c.

MANURES 113

(C) Potash Manures. — Potash in England is less frequently
deficient in soils than nitrogen and phosphorus. Certain
crops, however, require more potash than they can readily
obtain from some soils, and are much helped by the application
of potash manures.

Plant ashes, which contain pobissium carbonate, were
formerly largely and still are, to some extent, used as a potash
manure, but the chief source of potash compounds has been the
immense deposit at Stassfurt, overlying huge beds of rock-salt.*
This is worked on an enormous scale, some of the products —
e.g., kainite — being sent into the market with no preparation
other than crushing, while others — e.g.., potassium sulphate —
are first purified by recrystallisation. The commercial products
contain their potassium either as chloride, KCl, or sulphate,
K2SO4. The former is the more soluble and diffusible, but
appears in the case of certain plants — e.g., tobacco, potatoes —
to produce ill-effects on the quality of the crops. The fol-
lowing are the chief forms in which potash is purchased for
manurial purposes :

Kainite, the most widely used form, is a mixture of several
salts, including potassium chloride and sulphate, magnesium
chloride and sulphate, sodium chloride and calcium sulphate.
It usually contains about 12 to 13 per cent, potash, KaO, and
from 25 to 45 per cent, common salt.

Muriate of Potash. — Under this, the old name for potassium
chloride, are sent out various qualities containing 70 to 95 per
cent. KCl (corresponding to from 44 to 58 per cent. KaO), the '
chief impurity being common salt.

Sulphate of potash is supplied generally either as of 90 or
96 per cent, purity — that is, containing about 49*6 or 52*5 per
cent, of K2O.

Double sulphate of potash ami magnesia is obtained by
calcining the crystallised salt, MgSO4.K2SO4.6H2O. It usually

♦ During the war several sources of potash have been proposed, the
most promising being the flue dust from the smelting of certain iron
ores.

9

114 ELEMENTARY AGRICULTURAL CHEMISTRY

contains about 50 per cent. K2SO4, 34 per cent. MgS04, and
11*5 per cent, water, corresponding to about 27 per cent, of
potash, K2O.

Potash is most needed on light sandy or calcareous soils,
particularly for potatoes, grasses, clovers, peas, and beans.
Potash manures are best applied in the autumn or winter, and
little loss need be feared from drainage.

(D) Miscellaneous Manures. — Common salt is generally
regarded as possessing no true manurial value, but as being
of service because of its action upon the potash, lime, and
magnesia compounds in the soil. It has a good effect on
mangolds and cabbages. It increases the solubility of phos-
phates and silicates.

Gypsum, Oai^O^.^^fi, is found to improve clover and
turnips. It perhaps acts as a source of sulphur, but probably
its good effects are indirect, partly by liberating potash from
insoluble silicates and partly by aiding nitrification.

Lime, CaO, slaked lime, CaH^Og, and chalk, marl, or limestone,
CaCOj, are very often useful as manures. They all contain
small quantities of phosphates, and thus provide plant food, but
their most important effect is that of acting as basic material,
and thus (1) neutralising the vegetable acids produced by the
decay of organic matter and (2) promoting nitrification.
Caustic lime — i.e., either quicklime, CaO, or slaked lime, CaH^O,
— always has a more decided effect than chalk or limestone,
.although within a very short time of its application to the soil
it is converted into the same compound, CaC03. This is due
to the solubility of calcium hydrate, leading to its more uniform
distribution throughout the soil than is possible with even the
finest ground chalk or limestone.

Another valuable action of lime is its flocculating effect upon
clay. It must be remembered that the too frequent applica-
tion of lime to a soil may exhaust the nitrogenous matter
contained in the humus. Lime from magnesian limestone,
which contains magnesia, MgO, is not so good for agricultural

MANURES 115

purposes as a purer lime, probably because magnesia does not
absorb carbon dioxide from the soil water and gases so qiiickly
as lime docs ; consequently the mcignesia retains its causticity
for a longer time, and this hinders the growth of plants.

Gas Lime. — This is a waste-product from gasworks, being the
residue left after passing coal-gas over slaked lime in order to
remove carbon dioxide, COj, and sulphuretted hydrogen, H^S.
It consists of a complex mixture containing calcium carbonate
and h3'drate, together with varying quantities of incompletely
oxidised sulphur compounds {e.g., calcium sulphite, CaSOg,
sulphide, CaS, thiosulphate, CaS^Oj). These latter substances
are powerful plant poisons, and fresh gas lime is very injurious
to plants. It should be kept for some time freely exposed to
air, in order to convert the unoxidised sulphur compounds into
sulphate, CaSO^.

Ferrous Sulphate, FeSO^.THgO, Green Vitriol; and Copper
Sulphate, CuS0^.5Il30, Blue Vitriol. — These substances are
rarely used as manures, but are often employed in spraying for
the destruction of charlock or of fungoid diseases. The iron
compound has been claimed to act as a useful manure for
grass, beans, potatoes, mangolds and cereals. It is applied at
the rate of about J cwt. per acre, and is said to kill moss and
to act as a plant food, increasing the amount of chlorophyll
in the crop and to a certain extent acting as a substitute for
potash manures.

Analysis and Valuation of Manures.

The value of a manure is usually estimated from the
quantities of nitrogen, phosphorus pentoxide, and potassium
which it contains.

In the trade the results of an analysis are often expressed
in percentages of "ammonia" (i.e., NH3), "phosphates" (by
which is meant tricalcium phosphate), and " potash." Now in
many manures — e.^., nitrate of soda — the nitrogen is not present
as ammonia ; so, too, " phosphates," meaning tricalcium phos-

116 ELEMENTARY AGRICULTURAL CHEMISTRY

phate, does not correctly describe the state of existence of the
phosphorus pentoxide in many manures ; while even " potash,"
which really means the substance KgO, is not correctly applied
as the name of a constituent of such a manure as " muriate of
potash " — i.e., KOI. The trade method of expressing the com-
position of a sample of superphosphate may be given.

Per cent.

Monocalcium phosphate, or monobasic phosphate of lime 15
(=tricalcium phosphate rendered soluble, or
" soluble phosphates," 23*5 per cent.)

Insoluble phosphates ....... 3

Hydrated calcium sulphate 54

Alkaline salts . . .2

Water 22

Silica 4

100

By " monobasic phosphate of lime " in such an analysis is
meant, not true monocalcium tetrahydrogen phosphate,
CaH^PgOg, but that substance less two molecules of water,
CaPgOg (though this is really calcium metaphosphate, which
does not occur in manures). The relation between this sub-
stance and the tricalcium phosphate is easily seen from their
formulas :

CaP.O, Ca3P,03

40 + 62-F96 = 198 120-1-62 + 128 = 310

i.e., the amount of " monocalcium phosphate "x310-rl98 = the
amount of tricalcium phosphate, or " tribasic phosphate of
lime," as it is sometimes called.

In many superphosphates a portion of the phosphorus pent-
oxide is in the form of calcium hydrogen phosphate, CaHPO^.
This substance, though insoluble in water, is soluble in many
salt solutions — e.^., ammonium citrate. It is sometimes referred
to as " reverted," " retrograde," or " reduced " phosphate ; it
would be better to call it " citrate soluble." In fact, since
phosphorus pentoxide is the really valuable ingredient, it would,

MANURES 117

in every sense, be better to report the analysis of a phospliatic

manure thus :

Per cent.
Total phosphorus pentoxide ;

Soluble phosphorus pentoxide ....

Citrate soluble phosphorus pentoxide

Insoluble phosphorus pentoxide ....

The meaning of these terms would be precise and definite.

In assessing the value of a manure from its analysis it is
usual to employ what are known as values " per unit " for the
three chief fertilising ingredients. These are the commercial
values (and therefore liable to fluctuation) of each per cent,
per ton, so that really they are the values of 22*4 lb. of the
particular ingredient. Thus, suppose nitrate of soda contain-
ing 15*75 per cent, of nitrogen be worth £8 per ton, then the
value of the nitrogen will be

Y^^ = 10'28., or 10s. 2^d. per « unit."

In sulphate of ammonia at £12 per ton, containing 24*5 per

14
cent, ammonia, equal to 24*5 x — = 20-2 per cent, nitrogen,

the value " per unit " of nitrogen will be --

12 X 20

2u-2

11-835. = lis. 10c?.

In a similar way the values " per unit " of phosphorus
pentoxide and of potash can be calculated from the market
prices of the various manures. In these cases, as with nitro-
gen, the values will vary with difierent manures. In most
tables of values "per unit," "ammonia" and "phosphates"
are the substances valued, but for reasons already given it is
preferable to give the figures for nitrogen and phosphorus
pentoxide.

The values "per unit," as already stated, are liable to

118 ELEMENTARY AGRICULTURAL CHEMISTRY

fluctuations, and differ somewhat with different manures, so
that the following figures are only to be taken as examples :

Value " Per Unit."

s. d. s. d.
Nitrogen 10 0 lo 12 0

(= ammonia, 8s. Zd. to 9s. lO^d.)
Soluble pliosphorus pentoxide . . . 4 1 to 5 5

(= soluble pliosphates, 2s. 3d. to 3-3.)
Insoluble pho.>phori'.s pentoxide . . . 2 6 to 2 9

(= insoluble phosphates. Is. id. to Is. 7d.)
Potassium 4 0 to 4 7

(= potash, 3s. id. to 3s. 9d.)

An example of the valuation of a manure from analysis may
be useful. Suppose it is desired to calculate the value per ton
of a mixed manure having the following proportions of fer-
tilising ingredients :

rer cent.

Ammonia 5

Soluble phosphates 15

Insoluble pho.sphatcs 7

Potash » . . 3

Assuming that the unit value for ammonia <s 9s., for soluble
phosphates 25. Gd., for insoluble phosphates Is. (jd., for
potash 3s. Qd.j the value per ton would be calculated thus :

Ammonia

Soluble phosphates .
Insoluble phosphates
Potash .

s.

d.

£ s.

d.

5

X 9

0

= 25

0

15

X 2

6

= 1 17

6

7

X 1

6

10

6

3

X 3

6

10

6

L5 3

CHAPTER VII.
CROPS.

In this chapter a brief account will be given of the compo-
sition and manurial requirements of the various crops grown
on a farm managed according to the usual English methods,
together with a few notes concerning the chief semi-tropical
and tropical crops grown in some of the British colonies.

Many methods of classifying crops might be used ; the
following is convenient, and will be adopted here :

I. Crops in which the seed or fruit is the portion most
valued.
11. Crops which are grown mainly for the sake of the
root or tuber.
III. Crops in which the foliage and stem are the most
important.

Class I. includes chiefly grain crops and fruits.
Class II. comprises turnips, potatoes, beets, (fee.
Class III. consists chiefly of gramineous (grasses), leguminous,
and other plants.

Class I. — Grain and Fruit Crops.
These may be subdivided into :

1. Cereals — wheat, barley, oats, rye, rice, maize, millet,

Kaftir corn, <kc.
2 Leguminous seeds — beans, peas, cow-pea, soy bean,

lentils, lupines, earth-nut.
119

120 eleMektahy agricultural chemistry

3. Miscellaneous seeds — buckwheat, cotton-seed, linseed,

hemp-seed, rape-seed, castor beans, sunflower-seed, <fec.

4. Fruits — apples, pears, plums, apricots, peaches^

oranges, melons, pumpkins, bananas, grapes.

1. The Cereals. — The seeds of these plants are character-
ised by their richness in starch. Their straw generally con-
tains a large amount of silica, which, however, does not appear
to be essential to the plant. The silica is probably absorbed
in the form of soluble silicates — e.g., of potassium, the metal
being used by the plant and the silica deposited, chiefly in the
stem, as an excretion.

Another characteristic of cereals is their richness in phos-
phoric acid and comparative poverty in lime. This is most
marked in the grain itself, but is also shared by the straw.

Wheat {Triticum vulgar e) in temperate climates is usually
autumn-sown, and therefore has a longer period of growth
than barley or oats. It is consequently better able to supply
itself with the necessary food from the soil. The land, how-
ever, loses the spriug tillage, which, by aerating the soil, is
conducive to nitrification, and nitrogenous manures are there-
fore more often required by wheat than by other common
cereals.

Wheat straw, when ripe, is remarkable for the large amount
of silica and the small proportion of nutritive matter which it
contains.

The wheat grain is particularly suited for the manufacture
of bread because of its large content (8 to 10 per cent.) of
gluten, and the richness of this gluten in the peculiarly sticky
gliadin. This enables wheat flour to furnish a light, porous,
ipongy, and palatable bread when the dough is inflated by
carbonic acid, as in baking. In warm climates, especially
when much rainy weather occurs in the summer, wheat (also
barley and oats) becomes very liable to the attacks of fun-
gous diseases — e.g., rust — and is in consequence only grown
for its seed during the dry season, and usually by the aid of

CROPS

121

irrigation. If intended for fodder, wheat, like other cereals,
should be cut while still unripe, as the straw is then more
palatable and digestible, and contains nutriment which, if the
plant were allowed to ripen, would be transferred to the seed.
Wheat does best generally with a firm seed-bed, and this
fact is to be borne in mind in preparing the land before
sowing. For the same reason soil containing a fair amount of
clay or humus is more suited to wheat than are open, sandy
soils.

Average Composition of Wheat and Wheat Straw.

1

Wheat.

Wheat Straw.

Moisture

Ash

Crude fibre

Carbohydrates

Protein

Fat

10-5

1-8

1-8

71-9

11-9

21

9-6
4-2
38-1
43-4
3-4
1-3

100-0

100-0

Barley {Hordeum distichum, two-rowed ; Hordeum vidgare,
six-rowed), of which there are many varieties, usually has a
shorter period of growth than wheat. The soil must therefore
be provided with a sufiiciency of plant food, although heavy
nitrogenous manuring is not desirable, since the crop is thereby
rendered rank and coarse, and the grain unsuited for malting
purposes. Barley straw is more palatable and digestible than
wheat straw, and is often used as food for cattle. The grain
contains less gluten than wheat, and this gluten is not so
tenacious as that of wheat. Consequently barley meal does
not furnish a satisfactory bread.

Barley is largely used for the preparation of malt. The grain
is soaked for some hours in water, and then laid in thick layers
on floors. The seed germinates and heat is evolved. When the
germination has proceeded far enough the sprouted barley is

122 ELEMENTARY AGRICULTURAL CHEMISTRY

dried in a kiln at a temperature liigh enough to destroy the
vitality of the embryo. The plumule and radicle are then re-
moved— they constitute rnalt culms — and the malt is then ready
for use in the preparation of wort. The most important change
produced by malting is the production of a considerable quantity
of a peculiar un(»'ganised ferment, or enzyme, known as diastase^
which has the power in the presence of warm water of con-
verting starch into sugar. When malt is mashed — i.e., treated
for some time with hot water — this change begins, and the
liquid gradually becomes charged with sugar, the starch of the
barley grain at the same time disappearing. The quantity uf
diastase in malt is so large that it is capable of converting
much larger quantities of starch into sugar than are contained
in the malt itself. Consequently unmalted barley or other
cereal is sometimes added with the malt. The resulting liquor,
known as wort, is then submitted to alcoholic fermentation by
means of yeast, hops are added to impart a bitter flavour, and
beer or cde results. Barley is also used as food for animals, in
England particularly for pigs.

"Pearl barley" is the grain divested of its outer fibrous
coat.

Average Composition of Barley and Barley Straw

Barley.

Barley Straw.

Moisture

Ash

Crude fibre ......

Carbohydrates . . . . .

Protein

Fat

10-9

2-4

2-7

69-8

12-4

]-8

14-2

5-7

36-0

39-0

3-6

1-5

100-0

100-0

Oats (Avena sativa) will ripen in a cooler "climate than wheat
or barley. The grain retains a large proportion of husk, and
varies in size and shape considerably in the different varieties.

CROPS

123

Oats are remarkable for the high proportion of fat and ash
which they contain. They also contain some constituent
capable of exerting a stimulating action upon horses. This
substance has been termed " aveiiin."

Oats in England are usually grown for seed, though occa-
sionally for fodder, especially if mixed with tares. But in
America and in South Africa enormous quantities are grown
as forage, partly to be eaten green, but mainly to be made into
oat hay. This product, which in some districts is the staple
food of horses, mules, (fee, should be made by cutting the oats
while still green and drying them in the sun. If allowed to
ripen before cutting, the grain robs the straw of most of its
nutritive properties, and the resulting hay is neither so palat-
able nor so digestible.

Oat straw, even when the grain has fully ripened, is more
suitable for feeding purposes than wheat or even barley straw.

AvERAQB Composition of Oats, Oat Fodder, Oat Straw
AND Oat Hay.

Oats.

Oat
Fodder.

Oat

Straw.

Oat
IIay.»

Moisture

Ash ....

Crude fibre .

Carbohydrates

Protein .

Fat

11-0

3-0

9-5

597

11-8

5-0

62 2

2-5

11-2

19-3

3-4

1-4

9-2
5-1
37-0
42-4
4-0
2-3

8-1
4-3
31-6
47-2
4-9
3-9

100-0

100 0

1000 ■ lOD-0

Rye {Secale cereale) resembles wheat in many respects. In
England rye is usually grown as a green crop for spring feed-

• Mean of several analyses of South African products. As the sole
food of horses or mules, oat hay is too rich in phosphoric acid and too
poor in lime for the healthy nutrition of the bones. Where it is used
as the exclusive food a disease known as osteoporosis is often pre-
valent.

124 ELEMENTARY AGRICULTURAL CHEMISTRY

ing. On the continent of Europe, however, rye is largely
grown for grain, being used for making rye-bread, the staple
food of the peasantry in many districts. The straw is long,
and valued for thatching. In composition the grain of rye
resembles that of wheat, but it does not yield so good a quality
Df bread.

Average Composition op Rye, Rye Straw and
Rye Fodder.

Eye.

Eye

Straw.

Rye

Fodder.

Moisture

Ash

Crude fibre

Carbohydrates ....

Protein

Fat

11 -6

1-9

17

72-5

10-6

1-7

7-1
3-2
38-9
46-6
3-0
1-2

76-6

1-8
11-6

6-8 •

2-6

0-6

100-0

100-0

100-0

Eice (pryzob sativa) forms the staple food of a large portion
of the human race. It is generally grown under irrigation.
It requires a warm climate, and generally has to be cultivated
under swampy and unhealthy conditions. Two crops per year
are usually grown. The rough rice, known as " paddy," ob-
tained from the plant is subjected to a process of milling, by
which the brown outer husk is removed and the familiar white
rice of commerce is obtained. The by-products of the mills
are chiefly rice polish, a fine, flour-like substance, and rice bran,
a coarser and less nutritious material. Sometimes these are
mixed and sold as "rice meal," "rice feed," or under some
other name. Organic nitrogenous matter — e.g., cotton-seed
cake — and superphosphates are recommended as manures.

Another variety, upland or mountain rice, will grow up to
elevations of 6000 feet, and without irrigation. It yields
excellent fodder. When ripened the grain is similar to ordi-

CROPS

1^5

nary rice, and it is even more prolific, but only one crop can
be obtained per annum instead of two.

Whole rice, or "paddy" — i.e., the seed with its husk — contains
a fair amount of ash constituents and protein, but the ordinary
white rice, deprived of its husk, consists very largely of starck
and contains very little ash. The " hulls " or husks, bran and
rice polish are much richer in ash, fat and protein.

Composition of Rice Grain, Husk, Bran and "Polish."

Kicc.

Husk.

Bran.

" Rice
Polish."

Moisture

Ash ....

Crude fibre .

Carbohydrates

Protein ....

Fat ... .

12-4
0-4
0-2

79-2

7-4
0-4

8-2

13 2

35-7

38-6

3-6

0-7

9-7
10-0

9-6
49-9
12-1

8-8

10-0

6-7

6-3

59-0

11-7

7-3

100-0

100-0

100-0

100-0

Maize, Indian corn, m' ^* mealies" (Zea mays) is perhaps,
next to rice, the most extensively cultivated of all the cereals.
It was grown by the aborigines of America ; hence the name
" Indian corn," by which it is widely known in England. In
the United States of America it is usually called corn, the
other cereals being known as grain. In South Africa it is
always known as "mealies." In England maize (imported) is
chiefly used for fattening animals, but in America and other
countries it is also largely used for human food. The grain,
when crushed or ground, can be fed to horses, mules, or cattle,
can be ground to meal and flour and used as porridge for
human food, while the unripe grain on the cob is boiled and
considered a dainty by some people. The green leaves and
stalks can be used as fodder for animals or made into excellent
silage, while the spathes or sheaths of the ear can be made
*n.to paper. By fine grinding and removal of the bran-like

126 ELEMENTARY AGRICULTURAL CHEMISTRY

portions of the grain a product known as maizena or corri/lour
is obtained, largely used as a substitute for arrowroot and for
culinary purposes.

Maize is a fine plant, attaining a height of from five to
twelve or fifteen feet. The male flower is borne at the top of
the stem in a feathery panicle, while the female flowers, of
which there are usually three or four spikes on each plant,
grow out from the axils of the leaves, enveloped in membranous
sheaths or spathes, the long pink styles hanging out from the
tops of the sheaths as silky tassels. The pollen from the male
flowers either drops or, more usually, perhaps, is carried by the
wind into contact with the styles (*' tassels "), and fertilisation
is thus effected. Each spike of female flowers then becomes
an ear, consisting of a central fibrous woody core of conical
form, with the seeds arranged regularly around it, and the whole
enveloped in several spathes or husks. An enormous number
of varieties of maize have been produced. Great difierencesin
size, shape, colour and chemical composition, are presented by
the various varieties, also in the number of rows on the cob.
Thus the ear may be from an inch to sixteen inches in length,
and have six to forty rows of grains. In practice the varieties
may be classed into five types.

(a) Bent Corn. — If a grain of this variety be split longi-
tudinally there will be seen the germ, horny or glossy starch
at the sides, and white, floury starch in the centre, extending to
the top of the grain. Owing to the shrinking of the white
starch on drying being much greater than that of the horny
starch, the grains have an indentation at the top, giving then
a supposed resemblance to a tooth ; hence the name dent.

(6) Flint Corn. — In this type the horny starch entirely
surrounds the white, floury starch. The top of the grain,
therefore, remains smooth, hard, and convex. It has a trans-
lucent appearance.

(c) Fop-corn, in which almost all the starch is glossy or
horny.

{d) Soft ^orn, or ** bread mealie," in which all the starch is

CROPS

127

white and floury. The top of the grain is smooth, since the
contraction on drying is uniform. The grain is opaque.

(e) Sweet corn, or " sugar mealie," in which the starch is
partially converted into glucose. Such grains are translucent,
and, owing to the shrinkage in drying, very wrinkled.

Maize will grow well in any warm climate, but will not ripen
without abundant sunshine. Its manurial needs in many soils
appear to be phosphates, lime, potash, and nitrogen, in the
order given. Varieties attain maturity in from 90 to 150
days from sowing, but much depends upon temperature and
climate.

Average Composition of Maize (American Results).

Dent.

Flint.

Sweet.

Moisture

10-6

11-3

8-8

Ash

1-5

1-4

1-9

Crude fibre

2-2

1-7

2-8

Carbohydrates ....

70-4

70-1

66-8

Protein

10-3

10-5

11-6

Fat

5-0

6-0

8-1

100-0

100-0

100-0

1

The following represents the results of analyses of Transvaal-
grown mealies :

Soft or
Bread

Mealies.

Dent
Mealies.

Flint
Mealies.

Moisture

Ash

Crude fibre

Carbohydrates ....

Protein

Fat . ....

7-72
1-14

1-51

76-26

9-00

4-37

6-97
1-27
1-94
75-87
9-42
4-63

7-40
1-85
1-87
72-74
10-89
5-25

100-00

100-00

100-00

128 ELEMENTARY AGRICULTURAL CHEMISTRY

From the above figures it is seen that the average sweet
or sugar maize is richest in protein and ash, while the soft or
bread mealies is lowest in these constituents, but richest it
starch ; also that the flint varieties are richer in protein, ash,
and water than the dent.

Queensland- (Australia) grown maize is apparently richer in
protein than American-grown maize. But it must be remem-
bered that considerable differences are shown by the various
varieties of the same type. Asa rule, too, the smaller-grained
varieties are more nitrogenous than the larger.

In good soil crops of from 50 to 80 or even 100 bushels of
maize per acre can be obtained. Maize is sometimes grown for
forage, being either eaten green or made into ensilage. In
both cases it should be cut while still unripe, and before the
seed has fully formed.

Analyses of Maize Silage,

American.

Transvaal.

Moisture

79-1

76-66

Ash

1-4

1-91

Crude fibre

6-0

8-38

Carbohydrates

11-0

1089

Protein

1-7

2-31

Fat

•

0-8

0-85

100-0

100-00

Millet. — Under this term are included many plants. The
following may be mentioned as the most important : Common
millet {Panicum miliaceum), grown in America for fodder ;
this is an annual. Pearl millet j or Kaffir manna-hoorn {Penni-
setum spicatum), also an annual, growing to a height of from
three to six feet, bears its seed in a " head " or spike six to
ten inches long, and is chiefly used for^resn forage in America.
/talian, or golden millet, German millet^ or Hungarian grass^
and Japanese millet are varieties of Setaria italica. They have

CROPS 129

long and broad leaves, and a spike-like " head," four to six
inches long. They grow to a height of three or four feet.

Boer manna, or foxtail millet {Ghoetochloa italica), is also
useful as a forage crop. A sample of hay grown near Johan-
nesburg gave 1 he following figures on analysis ;

Moisture 8 '3

Ash 78

Crude fibre 30-9

Carbohydrates 46-2

Protein 6*0

Fat 1-8

100-0

Sorghum. — Belonging to this genus are several varieties
which bear a general resemblance to the millets. In America
both saccharine and non-saccharine sorghums are largely
grown for forage. The non- saccharine sorghums are most
important from our present standpoint, since they are largely
grown for seed. The most important are :

Kaffir corn {Andropogon sorghum or Sorghum vulgare), of
which there are several varieties. It is largely grown in South
Africa, the grain being used as food for horses, cattle, poultry,
and to some extent by the natives. It is also used in the
manufacture of Kaffir beer.

Durra or Dhoura, Egyptian cm'n, Egyptian rice-corn, Jeru-
salem cmm, Guinea com, broom corn (so-called because the
panicles after the removal of the seed are used in the manu-
facture of brooms and clothes-brushes), and Jowarine are names
given in various hot countries to varieties of this crop. It haa
the advantage of growing and thriving in hot, arid districts.

In reference to all plants of the millet and sorghum type,
an important point to notice is the occurrence of a glucoside,
tapable of yielding by the action of water hydrocyanic acid
(prussic acid), especially in the immaijure plants. This has
given rise to poisoning in animals fed upon second cuttinga of
sorghum fodder.

The amount of hydrocyanic acid is apparently greater in

130 ELEMENTARY AGRICULTURAL CHEMISTRY

immature crops. Up to two or more grains per pound of the
green material have been found, and it is suggested that any-
thing above half a grain of hydrocyanic acid per pound (i.e.,
about 0-007 per cent.) of green material indicates the prob-
ability of poisoning resulting from the use of the fodder.
Small quantities of hydrocyanic acid . have also been found in
young maize plants and Kaffir corn, as well as in other millets
and sorghums. The danger of poison is, Iiowever, probably
7iil with maize, slight with matured millets or sorghums, but
great with immature sorghums and millets.

Composition of Seeds of Millets and Sorghums.

Sorghum.

Broom
Corn.

Kaffir
Corn.

Millet.

Hun-
grarian
Grass.

Moisture

Ash ... .

Crude fibre

Carbohydrates

Protein

Fat ... .

12-8
2-1
2-6

69-8
9-1
3-6

11-7

3-4

7-1

64-6

10-2

3-0

9-3
1-5
1-4
74-9
9-9
3-0

14-0

3-3

9-5

57-4

11-8

4-0

9-5
5-0
7-7
63-2
9-9
4-7

100-0

100-0

100-0

100-0

100-0

2. Leguminous Seeds. — Many plants of the "Legumi-
nosse," or pod-bearing family, are grown as farm crops. They
differ in composition from the cereals mainly in containing
more nitrogenous matter. The stems and leaves, too, are much
poorer in silica and phosphoric acid, but richer in lime than
those of the cereals.

Beans. — Several plants go under this general name. The
common field -bean fVicia faba or Faba vulgaris) is largely
grown in some districts. The Scotch horse-bean and the tick-
bean, or English horse-bean, are varieties. As a rule beans do
best in a clayey soil, and yield about 30 bushels of seed and
1 to 1 J tons of " straw " per acre. French or kidney beans

CROPS 131

and haricot beans (Phaseolus vuli^arit)^ Lima beai»5 (Phaseolus
luiiatiis), and a Japanese plant, Adzuki beans (Phaseolus
radiatuf), are also grown, chiefly as vegetables. Boy or Soja
beans {Soja hispida or Glycine hispida) are largely cultivated
in Japan, and have been introduced into America >.nd South
Africa. The velvet bean (Mucuna utills) also does \> ell in hot
climates, and is a useful food for cattle, pigs and poultry.
Beans a»e always rich in protein, and furnish valuable /ood for
man or animals. Phaseolus lunatus, however, contains a
cyanogenetic glucoside, known as phaseolunatin, which some-
times leads to fatal poisoning when these beans are eaten.

Peas. — The field-pea (Pisum arvense), the garden-pea (Pisum
sativum) and the edible -podded pea (Pisum macrocarpon) are
the principal species, each including many varieties. As a
field crop, peas are very uncertain in yield. They require the
soil to contain a considerable proportion of lime. On rich
soils they grow luxuriously, but yield little seed.

The chick-pea (Cicer arietinum) yields a seed of similar com-
position to the field-pea, and can be used for similar purposes.
It is known as " gram " in India, The haulms, however, are
of little use as forage. It is well adapted for dry climates.

The cow-pea (Vigna catjang or Dolichos sinensis) rather
resembles the bean than the pea. The seed may be used as
food for pigs, or the whole plant may be made into hay.

The pea-nut (Arachis hypogcea) does well in hot countries.
After flowering, the stalk bends over and enters the ground,
where the seed grows and ripens. A light, porous soil is there-
fore best. In harvesting, the crop is ploughed up and the vines
and pods forked out of the ground. The seed is used for human
consumption, as "ground-nuts" or " monkey-nubs," as a source
of oil (for salads, <kc.), of which the kernels contain from 40
to 45 per cent., and is a valuable food for pigs, who enjoy
harvesting it for themselves. The foliage makes good hay.

Ijentils (Lens esculenta) are highly valued as a rich nitro-
genous item of diet for culinary purposes. The vines, too, when
cut early, form an excellent fodder or hay for cattle.

132 ELEMENTARY AGHICULTUIIAL CUKMIJSTKY

Lupines are somewhat too shrubby and woody to yield good
fodder, though sometimes used for sheep. Three species are
chiefly used — the white {Lupinus albus), the blue (Lujnnus
hirsutus or angustif alius) , and the yellow {Lupinus luteus)^
Lupines contain a bitter alkaloidal constituent, and are not
readily eaten by cattle or sheep ; moreover, they are sometimes
poisonous. The poisonous property can be destroyed by
steaming under pressure. They grow well on light, sandy soils,
and are often used as green manures.

Average Composition op Leguminous Seeds.

Horse-
bean.

Soy
Bean.

Pea.

Cow-
pea.

Pea-
nut.

Lupines.

Moisture .

11-3

10-8

10-5

14-8

7-3

14-0-

Ash .

3-8

4-7

2-6

3-2

2-0

3-0

Crude fibre

7-2

4-8

14-4

4-1

}-{

12-2

Carbohydrates

501

28-8

51-1

55-7

34-2

Protein .

26-6

34-0

20-2

20 8

29-9

30-4

Fat .

1-0

16-9

1-2

14

44 7

6-2

100-0

100-0

100-0

100-0

100-0

100-0

Though leguminous seeds (and also the leaves, stems, and
roots) are so rich in nitrogen, they usually can grow well in
soils comparatively poor in nitrogenous matter, provided
mineral plant food be abundant. This is due to the power which
they have of obtaining nitrogen from the air by the aid of
micro-organisms in tubercles on their roots (see chap. vi.
p. 105).

3. Miscellaneous Seeds. — Buckwheat {Polygonum fago-
pyrum) is grown in certain parts of Europe, being largely used
as poultry food, and also for pig- and cow-feeding. Its flowers
furnish excellent pasturage for bees. When sown with a
cereal — e.g,, oats or barley — it furnishes an excellent green
fodder.

CHOPS 133

Cotton (Gossypium Jterhaceum^ &c.). — This crop, which is
largely grown for its lint, yields also seeds which are valuable
both on account of the oil they contain and also because of
their richness in nitrogenous matter and ash constituents.
Cotton requires a warm climate, and succumbs rapidly to frost.
Frequent rain and a damp atmosphere are wanted during the
early stages of its growth until the formation of seed com-
mences, then dry weather is favourable to the formation of
seed. The lint envelops the seed, and is contained in a boll,
which attains the size of a hen's e^^, and then bursts into three
or five cells. In America about 300 lb. of lint and 600 to
650 lb. of seed per acre are usually obtained. The seed is
highly nitrogenous, and also rich in phosphoric acid. The
manurial needs of cotton in most soils are phosphoric acid,
nitrogen, and potash, in the order given.

The seed is mainly used for the manufacture of oil, which is
extracted by pressure. Sometimes the whole seeds are crushed
and pressed, but more generally their outer coating is first
removed. In the former case, the residue from the press is
sold as ** undecorticated cotton cake," in the latter as " decor-
ticated cotton cake" or " cotton-seed meal," but cotton-seed
itself — best after steaming — is an excellent food for milch cows
or fattening oxen and is largely used in the cotton -growing
districts.

Linseed^ Flax (^Liiium). — The usual species, Linum usitatis-
simum, can be grown either for fibre or for seed, sometimes,
though not very successfully, for both. For fibre the plant
apparently does best in moist, temperate climates — e.g.^ Ireland,
Belgium, certain parts of Russia and Canada. For seed, how-
ever, warmer climates are more favourable, much linseed
coming from Russia, India, the United States, Canada, and the
Argentine. Any soil which will grow wheat will apparently do
well for linseed ; a friable, loamy, alluvial soil with a clay sub-
soil is probably best. A fair supply of phosphates, potash, and
lime is important. If grown for fibre the object is to obtain
as tall and little-branched plants as possible, while for seed

134 ELEMENTARY AGRICULTURAL CPIE^ISTRY

the more branches and flowers the plants produce the better.
In the former case thick seeding, say 100 lb. per acre, is
employed, while for the latter from a quarter to half that
amount suffices. A fair yield of linseed in America is about
15 bushels of seed (of 56 lb. per bushel) and about 2000 lb.
of straw. The usual species {L. itsttoiisszwiitm) attains a height
of about two feet, and has blue flowers ; another species
{L. americanum album) is somewhat taller, and has white
flowers ; while a third (L. crepitans), which produces much
seed but little fibre, scatters its seeds by the explosive bursting
of its capsules.

Linseed is chiefly valuable for the oil which it contains
(from 30 to 40 per cent.) and for the large amounts of nitro-
genous and mineral matter, particularly phosphates, which are
also present in the seed, and which are left in the " cake " after
the oil is expressed. Linseed cake is thus highly prized foi?
cattle-feeding.

Oil expressed from the seed obtained from the Baltic ports
is usually preferred for the manufacture of linoleum, paints,
&c., since it has the power of absorbing the largest quantity of
oxygen. Oil is obtained from the seed by crushing it, and
then either expressing the oil by heat and pressure (old
process) or by extraction with volatile solvents — carbon
disulphide or naphtha (new process), in which the oil readily
dissolves. In the latter case the solvent is separated from the
oil by distillation and from the "meal" by steaming. The
"old process" meal usually retains from 8 to 12 per cent,
of oil, while the " new process " sometimes contains not
more than 1 or 2 per cent. Tho former is generally pre-
ferred for feeding purposes, as it is the more digestible.

Hempseed {Cannabis sativa)^ related to the hop {Humulus
lupulus) and to ramie, is cultivated both for the fibre yielded
by its stem and for its oily seeds. It is an annual, growing to
a height of eight or ten feet. It thrives best in a temperate
climate, and in any soil suited to maize. The yield of fibre
is from 500 to 1500 lb. per acre, of seed from 10 to 30

CROPS

135

bushels. The seed is used for feeding poultry, and as a source
of oil which is sometimes used to adulterate linseed oil.

Average Compositiox of Hemp- seed and of Hemp-seed
Cake.

Hemp-seed.

Hemp-seed Cake.

Moisture

Ash

Crude fibre

Carbohydrates

Protein

Fat

122
4-5
22-1
11-3
16-3
33-6

11-9

7-8
24-7
173
29-8

8-5

100-0

100-0

In hot countries the hairs on the stems and leaves secrete a
resinous substance, which has powerful narcotic qualities. In
colder climates this secretion does not occur.

Rape^ or Cole {Brassica napas and Brassica campesiris). —
A plant belonging to the turnip family, grown either as a
fodder crop or for seed. The seed is valued for the oil (about
42 per cent.) which it contains. The oil, either expressed or,
more generally, extracted by volatile solvents, is sold as rape
oil or colza oil. The plant resembles the turnip plant, except
that it has not a fleshy "root" and bears yellow flowers.
Several varieties are known, some being sown in the autumn
and harvested in the middle of the next summer, others sown
in the spring and reaped in the autuD^n. The residue after
extraction of the oil from the seeds is chiefly used for manurial
purposes, as it is not readily eaten by cattle. The plant
resembles in composition and manurial requirements the
turnip or swede.

Castor-seed {Ricinus commiuiis). — The castor-oil plant, some-
times called " Palma christi," id well known as an ornamental
plant in England. In many warm countries it is almost a
weed. In temperate climates it is only an annual, but in

156 ELEMENTAKY AGRICULTURAL CHEMISTRY

tropical countries it becomes a perennial tree, growing to a
height of twenty or thirty feet. The plant will grow in
almost any soil, but does best on rich sandy soils. If culti-
vated the land should be cleared, ploughed deeply, and the
seeds planted in groups of three or four about six or eight feet
apart. The ground should be kept clear of weeds, and when
the plants are well up all but one of each group should be
destroyed. They usually commence to bear about four or five
months after sowing. The main stem may be nipped off so as
to favour the growth of lateral branches, and thus increase
the yield of seed. The spikes of seed should be gathered
before they are quite ripe, and dried in the sun, as the seeds
shoot out from the capsules when ripe. The cleaned seeds,
whose resemblance to a tick has given rise to the botanical
name of the plant, are then sent to be pressed.

Castor oil is a valuable lubricant, and is also largely used as
an illuminant and for medicinal purposes. The residue after
reparation of the oil is suitable for use as a manure. It cannot
well be used for feeding purposes, as it contains a poisonous
ingredient which is difficult to remove. In America from 15
to 25 bushels of seed per acre are usually obtained. The seeds
contain about 50 per cent, of oil. A bushel of seed usually
weighs about 46 lb.

Sunflower-seed (Uelianihus annuus). — The plant is an annual,
growing to a height of ten or twelve feet. It can be sown in
groups of four at distances of about three or four feet apart.
The yield of seed is about 50 bushels per acre ; and the dried
seeds contain about ^ per cent, of oil. Sunflower-seed is
employed as a poultry and cattle food, and also as a source of
oil, used as a substitute for olive oil. The " cake " left after
the expression of the oil furnishes a valuable cattle food.

4. Fruits. — Most fruits are obtained from plants which
are perennial in habit, and are therefore hardly to be classed
with ordinary farm crops. Orchard management is a distinct
branch of agriculture, and reference to it would not be

CROPS

187

appropriate here. Broadly speaking, it may be said that
fruit-trees, owing to their far-reaching roots, will succeed in
finding sufficient nutriment in soils which may be too poor in
plant food to yield payable crops of ordinary farm produce.

Average Composition op Miscellaneous Seeds.

Sun-

Buck-

Cotton-

Linseed

Eape-

Castor-

flower-

wheat.

seed.

sced.

seed.

seed.

Moisture .

13-2

11-4

12-3

11-8

6-1

8-6

Ash .

. 1-8

4-3

3-4

3-9

2-7

2-6

Crude fibre

15-0

18-9

7-2

10-3

15-0

29 9

Carbohydrates

58-4

20-2

19-6

12-1

12-6

21-4

Protein .

101

19-9

20-5

19-4

17-9

16-3

Fat . . .

1-6

25-3

37-0

42-5

46-7

21-2

100-0

100 0

100 0

100-0

100-0

100-0

Average Composition of Products prom Above.

Buck-
wheat
Bran.

Undecor-

ticated

Coiton-

seed

Cake.

Decorti-
cated

Cotton-
seed
Cake.

Old

Process

Linseed

Cake.

New
Process
Linseed

Cake.

Sun-
flower-
seed
Cake.

Moisture .
Ash .

Crude fibre
Carbohydrates
Protein .
Fat .

10-5
3-0
31-9
38-9
12-4
3*3

10-6
7-2
24-9
26-0
24-7
6-6

8-9

7-2

5-7

19-7

43-6

14-9

11-8
7-3
9-4

32-1

28-7
10-7

9-7
7-3

8-8
38-7
33-2

2-3

10-8
6-7
13-5
27-1
32-8
9-1

100-0

100-0

100 0

100-0

100-0

100 0

Nevertheless it must be remembered that the large growth of
a tree locks up in the wood a considerable amount of plant
food, and if the tree is to continue to bear fruit additional
supplies from the soil must be maintained. In fruit-trees, as
in other plants, abundant supplies of nitrogen from the soil

138 ELEMENTARY AGRICULTURAL CHEMISTRY

tend to favour the growth of leaves and twigs rather than
fruit. Fruits are, as a rule, very rich in water, contain sugar
and generally some vegetable acid, to which their characteristic
taste is partly due. We can only very briefly consider the
chemical character of some of the principal typical fruits.

Ap2)l€s (Pf/rus malus). — An immense number of varieties
of this fruit are known, diftering very much in size, shape,
colour, and flavour. Doubtless their composition will also
vary greatly. They usually contain about 85 per cent.
of water, about 12 per cent, of carbohydrates (chiefly sugar),
about 0*4 per cent, of ash, 1 per cent, of crude fibre, and 0*2
per cent, of albuminoids. The acidity is due to malic acid
^HgC^H^O/). which may amount to from 02 to 1 per cent, of
the juice. The diflference in " sweetness " of different apples
is mainly due to the propoition of malic acid present. The
sugar present is partly cane sugar (sucrose), partly invert
sugar, which is a mixture of dextrose and levulose. In green,
immature apples starch is found, sometimes to the extent of
5 per cent., but as the fruit ripens the starch disappears and
the sugars increase. Cellulose is present to the extent of
about 1 per cent., pentosans up to about 0 5 per cent., and
pectin, or perhaps more accurately pectose, from 0*2 to 0*6
per cent. The gelatinising property of pectin is of importance
in the preparation of apple jelly.

The following analyses of American Baldwin apples will
show the changes which occur during ripening :

Very Green.

Green.

Eipe.

Over-ripe.

per cent.

per cent.

per cent.

per cent.

Water ....

81-33

79-81

80-36

80-30

Solids .

18-67

20-19

19-64

19-70

Invert sugar

6-40

6-46

7-70

8-81

Sucrose

1-63

4-05

6-81

5-26

Starch

4-14

3-67

0-17

Free malic acid

1-14

—

0-65

0-48

Ash .

0-27

—

0-27

0-28

CROPS 189

Different varieties ghow considerable differences in composi-
tion ; thus the solids in the ripe fruit have been noticed to
vary from 134 to 23-4 per cent., the invert sugar from 5 "3
to 117 per cent., the free malic acid from 0*26 to 1*11 per
cent., the ash from 0*17 to 0-37 per cent.

As an average of recent American analyses of several
varieties the following is given as the typical composition of
ripened apples ;

Per cent.

Water . . * 840

Ash 0-3

Invert sugar 8 0

Cane sugar 4 0

Starch O'O

Cellulose 0 9

Lignin 0*4

Pentosans 0*5

Pectin matter 0*4

Malic acid (free) 0*6

„ „ (in combination) . . . 0-2

Oil •. . 0-3

Protein 0-1

Undetermined (tannin, &c.) . . . . 0*3

100-0

The ash consists chiefly of potassium carbonate, magnesium
and potassium phosphates, calcium sulphate, free lime, with
traces of common salt, silica, iron oxide, and alumina.

Pears {Pyrus communis) resemble apples in their chemical
composition, but contain less acid and more "crude fibre." As
a rule the trees have deeper roots, and thus range over a larger
volume of soil for their sustenance.

Plums {Pi'unus spj).). — Belonging to this genus are many
species, including sloes or blackthorn {P. spinosa), bullace and
Jamsons (P. insititia), various true plums {P. domestica),
apricots (P. Armeniaca)^ wild dwarf cherry (P. ceo'asus), wild
cherry {P. avium) j almond (P, amygdcdus or Amygdalus
communis), nectarine and peach {P, persica). The fruit con-
sists of a central kernel (the true seed), a hard, bony layer
surrounding the kernel (known as the " stone " or " pit ") and

UO ELEMENTARY AGRICULTUHAL CHEMISTRY

a fleshy pulp (the edible portion), the whole being covered
with a thin skin. The kernel, and in some cases the bark and
leaves, contains a glucoside known as amygdalin, Q^^l.^^'^O^^,
which under the influence of an enzyme — emulsin — generally
present in the kernel, decomposes in the presence of water,
thus :

C,,H,,NO,, + 2Hp = CJI.CIIO + HON + 20,H,30„

the products being benzaldehyde, hydrocyanic or prussic acid»
and glucose. The flesh of all fruits of the plum family is
rich in sugar and faintly acid with various organic acids, of
which malic {Kfififi^ and citric acid (HgCgH^Oy) are the
principal.

The following are partial analyses of the fruits :

Apricots.

Peaches.

Cherries.

Nec-
tarines.

Plums.

Moisture

Ash . . .

Crude fibre

Carbohydrates

^Protein

Sugar in juice
Acid (as SOJ in
fruit

81-12

0-82

' 5-27

12-30

0-49

80-03
0-69
6-06

12-57
0-65

80-26
0-73
6-07

12-32
0-62

79-00
0-50

0-73

81-18
0-71
5-41

11-92
0-78

100-00

100 00

100-00

—

100-00

11-10
0-68

17-00
0-24

12-89
0-48

14-10 ■
0-24

—

Cities Fruits. — The chief varieties are the orange, the
lemon, the lime, the citron, and the shaddock or pompelmous.
All members of this family thrive only in warm climates.
Frost is very liable to cause death to the trees. They do best
in rich, deep, mellow soil, with porous subsoil. The fruits
contain sugar, citric acid, and comparatively small quantities
of cellulose and ash constituents, while the rind contains
considerable quantities of essential oils.

CROPS 141

Average Composition of Oranges and Lemons.

Oranges.

Lemons.

Moisture

Ash

Crude fibre

Carbohydrates ....

Protein

Fat

Sugar ......

Citric acid

85-2
0-4

1-2

83-8
0-6
1-1

12-7
0-9
0 9

100-0

9-7
1-3

2-1

7-2

Grapes (Vitis spp.). — Yines are best suited by a damp
wititer and spring, and a dry, fine summer for the ripening of
the fruit. Climate is of more importance than the soil in
most cases. Their manurial requirements are not great, but
an open, deep, friable soil is advantageous. Great differences in
composition of grapes are shown, according to the variety, soil,
season, and climate. The grape is characterised by containing
grape sugar (dextrose) and tartaric acid (H^C^H^Og).

Average Composition of Grapes.

Per cent.

Water 78-17

Ash 0-63

Crude fibre 3'60

Carbohydrates 17-11

Protein 0-59

Fat —

100-00

Tlie Banana (Musa sapientum) is one of the most character-
istic and imposing products of the tropics. If the climate be
suflaciently warm and moist almost any soil will support the
plant, but the best cro'ps are obtained on deep loams with a
plentiful supply of humus. The plants are propagated by

142 ELEMENTARY AGRIOULTURAL CHEMISTRY

Slickers out of the parent stem. These are planted about
15 feet apart, and under favourable conditions fruit will be
produc'ed in about a year. In successive years suckers from
the original plants replace the first stem, which is cut down
after the fruit is gathered.

Average Composition of Bananas.

Per cent

Moisture ....

. 66-25

Ash

. 1-15

Crude fibre ....

. 0-96

Carbohydrates

. 28-88

Protein

. 1-41

Fat

. 1-35

100 00

According to American estimates, the following table repre-
sents the amounts of the chief fertilising materials contained
ill various fruits and removed by an average crop from an
acre of land :

Potash.

Pliosphoric
Acid.

Nitrogen.

lb.

lb.

lb.

Grapes, per cent. .

0-50

0-15

0-17

10,000 lb. per acre

50

15-2

17

Oranges, per cent.

0-28

0-07

0-27

20,000 lb. per acre

55-6

13-4

53-8

Pears, per cent.

018

0-05

0 06

20,000 lb. per acre

36-0

10

12

Plums, per cent.

0-17

0 04

0-42

30,000 lb. per acre

51-6

13-2

127-7

Apples, per cent.

0-08

0-03

0-06

20,000 lb. per acre

16

6

12

The heavy demands upon nitrogen made by plums and the
small amounts required by apples and pears are noticeable
features.

Class II. — Root Crops.

The principal members of this class are the turnip, the beet
and the potato.

CROPS 113

The Tuniij) (Brassica rapa) is a biennial, producing in its

first year a large store of material in its " root," intended to

serve as food for production of stem, flowers, and seed during

. the second season. There are many varieties, differing in the

shape and colour of their " bulbs " or roots.

The Swede Tuimip {Brassica rutabaga) closely resembles the
ordinary turnip in composition and habit, but is distinguished
by the possession of a distinct " neck," from which the leaves
sprir g. The foliage of swedes is generally bluer and less grass-
green than that of the turnip. Tlie flesh is firmer and less
watery than that of the turnip, and the roots generally keep
better after being dug.

Turnips do best on open, loamy soils and in somewhat dull,
damp climates. They are usually drilled in rows from 20 to
27 inches apart, and " singled " so as to be from 11 to 13 inches
apart in the rows.

Turnips re^ond readily to applications of phosphatic
manures. They also require to be well supplied with nitro-
genous material. From 15 to 25 tons per acre is a fair yield
of turnips.

The Beet {Beta vulgaris). — There are many varieties,
obtained by careful selection. Mangel-wurzel^ or field-beets^
include many varieties, which may be classified into long,
tankard, and globe formp. Differences in colour of the flesh are
also shown. Mangolds, or mangels, as they are often called,
require a warm, fairly dry climate and a deep, somewhat
clayey soil. The usual yield is from 18 to 25 tons per
acre. Mangolds require much nitrogen, and readily respond
to applications of nitrate of soda. Being descended from
a maritime plant, they also appreciate chlorides, and are
benefited by applications of common salt. They form excel-
lent food for cattle, but should not be used until they have
been stored for a few months.

Tha Sugar-beet is a variety of the mangold, which has been
developed especially for its richness in sugar. Many varieties
are grown, but they are usually conical in shape, grow with

144 ELEMENTARY AGRICULTURAL CHEMISTRY

the root entirely underground, and should be, compared with
ordinary mangolds, small in size. The best probably weigh
about 2 lb. each. They thrive in a warm and moderately
damp summer and dry, hot autumn. A deep, medium loam
with a fair proportion of lime is the soil best suited for their
growth. Late nitrogenous manuring should be only sparingly
done. The seed is usually sown in rows 14 or 15 inches
apart, and the plants are afterwards singled so as to stand 6
or 8 inches apart in the rows. The usual yield is from 12 to
16 tons per acre.

Turnips and mangolds are very watery, and in nearly all
cases the large roots are much more watery, and therefore less
valuable, -weight for weight, than the small ones of the same
variety.

The sugar-beet is now a most important crop, especially
in Germany, Russia, France, Austria, and the United States.
Beet sugar is gradually replacing cane sugar. In 1903-4, for
example, it was estimated that the European production of
beet sugar amounted to 5,910,000 tons, while the world's
production of cane sugar was estimated at 3,535,000 tons.

Average Composition of Turnips, Swedes, Mangolds,
AND Beets.

Turnip.

. Swede.

Mangold.

Sugar-beet.

Water ....

92-0

87-0

88-0

81-6

Ash , . . .

0-7

1-0

0-8

0-7

Crude fibre . . .

0-8

M

0-9

1-3

Carbohydrates

.5-3

9-5

91

15-4

Protein.

1-1

1-3

1-1

10

Fat ... .

o-i

0-1

0-1

0-1

1000

1000

100-0

100 0

The Potato {Solanum tuberosum). — The valued product of
this plant is the underground stem, known as a tubev. Usually
the crop is grown from the tubers or " sets,"

CROPS 145

The best soil is a deep, warm one, with good drainage and
free from acidity, well supplied with potash and nitrogen.
Heavy manuring is generally done for this crop, and farmyard
manure is especially useful for its water-retaining power in
dry seasons, though open to the objection that it favours
" scab." On soils rich in lime, superphosphate, potassium sul-
phate and sulphate of ammonia are suitable artificial manures,
applied before planting, while on soils poor in lime, basic slag
should be substituted for the superphosphate and nitrate of
soda (ps top-dressing to the growing crop) for the sulphate of
ammonia. From 12 to 15 cwt. of "sets " per acre are usually
required. In wet districts these are sown in the ridge, in
dry ones on the flat. The rows are usually 20 to 30 inches
apart, and the " sets " are placed from 12 to 18 inches apart.
Potatoes about the size of a hen's egg should be used as "sets";
if larger, they should bo cut, care being taken to leave at least
two " eyes " on each piece. The cut surfaces are often dusted
with quicklime before planting.

The fruit of the potato — " apple " or "berry " — is poisonous,
as are also, though to a less extent, the leaves or " haulms.V
Potatoes consist largely of starch, with very small amounts of
protein and ash constituents. The amount of water present is
subject to considerable variation — from about 75 to as high as
83 per cent. Potatoes are largely used as food for men and
animals ; also, especially on the continent of Europe, for the
manufacture of alcohol and of fusel oil.

Average Composition of Potatoes,

Per cent.

Water 78-9

Ash 1-0

Crude fibre 0*6

Carbohydrates , 17 '3

Protein ,..21

Fat .*.•...... 0-1

100-0

UG ELEMENTARY AGRICULTURAL CHEMISTRY

Ihe Sweet Potato (Iponioea batatas or Batata edalis). — This
is a convolvulus-like plant, usually with purple flowers, pro-
ducing tubers on its roots, sometimes of great size, up to 121b.
or more in weight. It is essentially a tropical or sub-tropical
crop, and does best in light, friable soils rich in organic matter.
It is propagated by cuttings, and once established on land will
yield several crops in succession. A fair crop is four or five
tons to the acre.

The tubers are used in the same way as the ordinary
potatoes, but are sweeter and more nutritious. The leaves
and stems are eaten greedily by horses, cattle, and sheep,
but it has recently been shown that they sometimes contain
a glucoside which decomposes and yields hydrocyanic acid
(prussic acid). Amounts varying from 0014 to 0019 per
cent, of the green material were found. Numerous cases of
death in pigs fed on sweet potato vines were observed in
Queensland in 1905.

Average Composition of Sweet Potatoes and their Vines.

Water .

Ash .
Crude fibre .
Carbohydrates
Protein
Fat .

Tubers.

100-0

Vines.

71-1

41-6

1-0

5-8

1-3

13-6

24 7

29-3

1-5

7-6

0-4

2-1

1000

The Cannot {Daucus carota) and the Parsnip {Pastinaca
sativa) are also sometimes grown as farm crops. The roots are
used as vegetables, and as an excellent food for horses and cattle.
Also belonging tc this family of Umbellifera? are Celery {Apium
graveolens)^ Parsley {Petroselinum sativum)^ and Caraway
{fiarwm carui).

CROPS 117

Average Composition of Carrots and Parsnips.

•

Carrots.

Parsnips.

Water

Ash

Crude fibre

Carbohydrates

Protein . ....
Fat

88-6
1-0
1-3
7-6
1-1
0-4

80-3
1-0
0-5

16-1
1-4
0-7

1000

100-0

Class III.— Fodder Crops.

These, which include some of the crops already mentioned,
are grown to provide bulky food for cattle. They are used in
three principal forms :

1. In the fresh, green state, being either pastured or

cut, and fed green to animals — " soiling"

2. In the dried (and generally fermented) state, as hay»

3. In the fermented state, as ensilage.

In the case of all forage crops it is desirable to cut or use
the plant some time before it ripens its seed, otherwise the
Btems and leaves become woody and indigestible, and^o a great
extent robbed of their nutriment.

The principal forage crops may be classed in three main
groups :

1. Gramineous crops.

2. Leguminous crops.

3. Miscellaneous forage crops,

1. Gramineous Crops. — These are used for pasturing, and
fof hay-making or for soiling. Some of the cereals already
described are used in this way.

Pasture and meadow grasses usually consist of a complex

148 ELEMENTA.RY AGRICULTURAL CHEMISTRY

mixture of plants. The grasses:, which usually predominate,
resemble the cereals in general chemical composition, being
rich in silica and potash and comparatively po©r in nitrogenous
organic matter. Grasses are usually surface -feeders, and the
root debris gradually imparts a peaty character to the upper
portion of the soil, thus leading to nitrification and loss
of calcium compounds. Hence phosphatic and calcareous
manures — basic slag, bones, lime — are beneficial. Heavy
dressings of nitrogenous manures favour the growth of coarse
grasses at the expense of clovers and some of the finer grasses.
Grasses are used on the farm either as permanent pastures
and meadows, or in the rotation in the form of " small seeds"
• — rye-grass usually mixed with clover. There are numerous
species of grass, differing in chemical composition and
palatability.

Average Composition of Various Green Fodders.

-

Pasture
Grasses.

Timothy.

Meadow
Fescue.

Italian
Rye-
grass.

Green
Oats.

Water ....

Ash

Crude fibre
Carbohydrates
Protein ....
Fat ^ . . .

80-0
2-0
4 0
9-7
3-6
0-8

61-6

2-1

11-8

20-2

3-1

1-2

69-9

1-8

10-8

U-3

2-4

0-8

73-0
2-5
6-8

13-3
3-1
1-3

62-2

2-5

11-2

19-3

3-4

1-4

100-0

100-0

100-0

100-0

100-0

2. Leguminous Fodder Crops.— Some leguminous plants
are usually present in pastures and meadows. Their growth
is favoured by additions of potash, lime and phosphates, and
by stinting the nitrogenous manuring ; the clovers, &c., having
their own peculiar supply of nitrogen (see chap, vi.), are
thus able to hold their own in competition w^ith the grasses,
which in the presence of abundant supplies of nitrogen would
probably outgrow and smother the Leguminosse.

CROPS

149

As already stated, the leguminous plants are remarkable
for the large amounts of nitrogenous matter, potash and lime
which they contain. Their power of collecting nitrogen from
the air by the aid of the micro-organisms in the nodules on
their roots renders their af ter-eflfect on land of great value (see
p. 105).

Lucerne {Medicago sativa), known as alfalfa in America, is
particularly valuable in hot, somewhat dry climates, since
when once established its deep-reaching roots enable it to
bring up water from the subsoil and to stand long drought.
It will then yield repeated cuttings of valuable forage for many
years. Other valuable leguminous fodder crops are red clover
{THfolium pratense), crimson clover (T. incai-natum), white
clover {1\ repens), alsike clover (T. hyhridum), sainfoin {Ono-
hrychis saliva), trefoil [Medicago lupulina)^ vetches or tares
{Vicia saliva) and serradella {Ornilhopus sativus). The charac-
teristic of the leguminous crops is their ability to grow on
soils poor in nitrogen, provided mineral constituents are
sufficiently abundant.

Composition of Green Leguminous Fodder.

Lucerne.

Ked
Clover.

White
Clover.

Alsike.

Serra-
della.

Vetches.

Water .
Ash .

Crude fibre
Carbohydrates
Protein .
Fat .

74-0
2-0
9-5
9-2
4-5
0-8

80-4
1-3
5-8
8-9
30
0-6

80-5
'•2-0
6-0
7-2
3-5
0-8

82-0
1-8
6-0
63
33
0-6

81-0
1-8
5-8
6-9
3-7
0-8

82-0
1-8
5-5
6-6
3-5
0-6

1000

100-0

100-0

100-0

100 0

1000

8. Miscella

{Symphylum as^
to time highly
much public J

neous

perrimu
praised
avour.

Fodde

m).—T\

as a fo

It is

r Cro]

lis plan

rage cro

a shi-L

3S. — - t

t has 1
p, but
ibby, p

Sickly
3een frc
las not
erennia

Comfrey
)m time
received
[ plant,

150 ELEMENTARY AGPJCtJLTURAL CHEMISTRY

generally propagated by root cuttings, planted two or three
feet apart. It may be cut several times in a season, and
the total weight per acre amounts to about 30 tons per
annum. It is not readily eaten by cattle until they acquire
the taste for it.

Rape {Brassica napus) has already been described (p. 135).
It is often grown as green fodder, especially for sheep. If
used in large quantities as food for milch cows it is liable to
taint the milk.

Buckwheat is also grown for green forage.

Sugar-cane (Saccharum offlcinarum) is also grown, for the
sake of the young shoots, which are greatly relished by stock.
They are either eaten green or made into ensilage.

Pumpkins {Cucurhita spp.) are sometimes grown in warm
countries as cattle food, being excellent for dairy cows and for
pigs. They are necessarily very watery.

Cabbages {Brassica oleracea) with abundant manuring or on
rich land yield large crops of excellent green food for cattle
and sheep. Cabbages are gross feeders, and are greatly bene-
fited by nitrate of soda. Common salt also seems to be bene-
ficial to this crop.

Sugar-beet leaves are sometimes used as food for cattle ; but
they contain a considerable proportion of oxalic acid, which pro-
hibits their use except in small quantities. By sprinkling lime
over them and keeping them in heaps for some time the oxalic
aeid may be neutralised and ils injurious effect diminished.

Composition of Miscellaneous Forage Crops.

Water.

Ash.

Crude
Fibre.

Carbo-
hydrates.

Protein.

Fat.

Prickly comfrey
Buckwheat .
Rape .
Cabbage
Pumpkin

Beet leaves .

877
85-0
85-9
89-0
90-9

82-6

2-2
1-4
1-3
1-2
0-5

3-4

1-7
4-2
3-5
2-0
17

5-0

5-7
5-9
5-2

3-0
2-4
2-8
1-5
1-3

3-6

0-4 ■

0-6

0-8

0-4

04

0-3

)

i6-i

CROPS ]5i

Hay making". — When green forage has to be preserved for
the winter or future use it is either made into hay or into
ensilage. Hay-making consists essentially in drying the plants
by exposure to sun and air to a sufficient extent to prevent
excessive fermentation when the material is bulked together.
The most important change is the removal of water. Ordinary
meadow grass contains nearly 75 per cent, of water, while the
hay from it will contain about 15 or 16 per cent. The yield
of hay from a given weight of grass must obviously vary
greatly ; it will usually be between 30 and 40 per cent. The
plants should always be cut while flowering, for if left longer
the resulting hay will be poorer in albuminoids and ash,
though richer in carbohydrates and crude fibre.

Grass and other green plants are always well supplied with
micro-organisms, which at once attack the sap as soon as the
grass is cut, producing carbon dioxide and promoting oxidation^
with its resulting evolution of heat. If the green material
be spread out the heat is quickly dissipated and 'no rise of
temperature occurs, and as the water evaporates the activity of
the micro-organisms is soon checked ; but if the green vego-
table matter be piled together in large masses, so as to prevent
the escape of heat by convection currents, the temperature
rises and the processes of fermentation proceed more and more
rapidly. The rise of temperature may be so great as to start
direct chemical oxidation and finally to set fire to the material.
Such an occurrence is often observed when imperfectly dried
hay is collected in stacks or barns. The presence of too much
moisture is one of the most powerful causes tending to set up
dangerous heating of haystacks. Thorough drying of the hay
is obviously the best method of minimising the risk, but this
is open to the objection that the proper aroma, flavour and
colour of hay is not produced unless a certain amount of
fermentation occur in the stack. If somewhat green hay has
to be stacked, danger of overheating may be lessened either
by mixing Fait with it or by allowing free ventilation in
the stack. The first method checks fermentation, and so

152 ELEMENTARY AGRICULTURAL CHEMISTRY

prevents the evolution of heat ; the second is eflicacious chiefly
by carrying the heat away as it is evolved, and thus keeping
down the temperature.

The pleasant odour of hay, upon which its palatability
chiefly depends, is partly due to compound ethers and other
fragrant products of fermentation, and partly to coumarin,
CgHgOg, which is present in wood-Yxif^ {Asperula odoraia), in
Bokhara clover (Melilotus alba), and in sweet-scented vernal
grass (Anthoxanthum odoratum). Though the odour of
coumarin is generally considered pleasant, there is some
reason to think that horses and cattle are not very fond of it.

AvEBAGE Composition op Hay.

Crude

Carbo-

Water.

Ash.

Fibre.

hydrates.

Proteiu.

Fat.

Meadow hay

U-1

6-2

26-3

41-4

9-5

2-5

Rye-grass .

14 -3

6-5

36-2

36-1

8-2

2-7

Timothy

U-3

4 5

22-7

45-8

9-7

3-0

Sainfoin

15-8

6-7

24-9

34-0

15-4

3-2

Lucerne

16-0

6-2

23 '0

37 9

14-4

2-5

Red clover

160

6-3

26-0

38-2

12-3

2-2

Serradella

16-7

8-1

25-6

30-3

16-2

3-1

Alsike .

16-0

6-0

27-0

32-7

15-0

3-3

Lupines

16-7

4-6

28-5

30-9

17-1

2-2

Rye .

14-1

5-1

23-1

44-5

10-4

2-8

Oats .

11-5

6-1

30-1

42-4

7-5

2-4

Natal blue grass .

8 0

6-0

38-5

41-8

4-4

1 3

Boer manna hay

8-3

7-8

30-9

46-2

6-0

1-8

Ensilage, or Silage. — When green fodder is closely com-
pacted so as to prevent access of air as much as possible,
fermentation is hindered and restricted, and the fodder may
be kept for some time. Originally all silos were pits or
buildings of stone or wood, intended to be air-tight, in which
the fodder could be rfubjected to great pressure. The simpler
plan of merely stacking the green fodder in the open, treading
it well, and finally weighting it with stones or earth is now
often adopted.

CROPS 153

In a silo fermentation is limited by exclusion of air, while
in a haystack it is chiefly lack of moisture which determines
the cessation of change. If the silo be filled slowly the tem-
perature rises so high (to about G0° C.) that the micro-
organisms which produce acetic, lactic, and butyric acids are
killed, and only the other organisms remain. The resulting
silage is known as ** sweet silage." On the other hand, when
the silo is rapidly built and pressed as soon as possible the
temperature attained is not so high, and the acid-forming
organisms have opportunity for full development, and " sour
silage " results.

The chief changes produced by conversion of fodder into
ensilage are a diminution of the albuminoids and of the
carbohydrates, while the "crude fibre" seems to be increased.
A more serious loss, however, is a considerable diminution in
the digestibility of the albuminoids. In the case of red clover
it was found that 100 lb. of dry matter containing

Ash.
9-5

Fibre.
23-8

Carbolijdratcs. Albumiuolds. Amides.
4G-3 16-5 3-9

gave 90*5 lb. of dry matter in the ensilage, containing

Ash.
9-5

Fibre.
27-4

Carbohydrates. Albuminoids. Amides.
33-9 15-7 4-0

It would appear, therefore, to be most economical to make
ensilage of fodders low in albuminoids, and to convert legu-
minous plants into hay.

AVEI?

AGE Composition of

Silage

Water.

Ash.

Crude
Fibre.

Carbo-
liydrates.

Protein.

Fat.

Maize .

79-1

1-4

6-0

11-0

17

0-8

Sorghum

76-1

1-1

6-4

15-3

0-8

0-3

Rye . . .

SO -7

1-6

5-8

9-2

2-4

0-3

Grass

G8-0

2-7

9-9

12-9

3-8

2-7

Buckwheat .

72-3

2-2

7-7

14-1

2-8

0-9

Lucerne

72-5

3-5

10-7

6-1

4-0

2-2

Red clover .

70 0

2-3

8-5

11-6

5-G

2-0

Lupines

80-3

1-4

95

4-9

2-9

10

153a ELEMENTARY AGRICULTURAL CHEMISTRY

Rotation of Crops.

In all countiies where farming has been long established,
the plan of alternating different crops on any particular portion
of land has become general. It is only in the first few years
after virgin soil has come into cultivation, that the same crop
is grown, year after year, on the same land.

The practice of rotation of crops has many advantages; some
with respect to the practical operations of cultivation, seeding
and reaping, some in diminishing the ravages of plant diseases,
insect pests, weeds and other troubles, and some in connection
with the power of the soil to supply the needs of plants. The
obvious advantages of distributing the labour involved in the
ploughing, drilling, harrowing and reaping of the crops, more
evenly over the year, which a variety of crops affords, need not be
discussed here. So, too, the benefits derived from changing the
crop from time to time, in preventing the continuance of any
particular disease or blight which may attack a certain kind of
crop, or in destroying the weeds which may accompany it,
hardly require more than passing mention.

With the efiect of rotation upon the soil's ability to supply
plant food, however, chemistry has more to deal, and a short
account of the advantages of rotation, from this aspect, may
appropriately be given.

These advantages mainly depend upon the following :

1. Differences in the root range. Some crops, e.g.., barley,
have only shallow roots which draw their sustenance from the
uppermost layers of soil, while others, e.g,, mangolds, depend
chiefly for their food, upon the matters present in the lower
parts of the soil. By alternating shallow-rooted and deep-
rooted plants, all parts of the soil, in turn, are called upon tc
contribute plant food.

2. Utilisation of crop residues. The root debris^ stubble
and waste left in the field after the removal of any crop, afford,
on decay, good food for another kind of crop, while such
residues are often of little benefit, indeed, in some instances,

CROPS 1536

are actually injurious, to a second crop of the same species.
The debris of leguminous crops, e.g.^ clover, is particularly rich
in combined nitrogen, owing to the power which such crops
possess, of absorbing nitrogen from the air, and afford im-
portant supplies of this material, slowly (as nitrification occurs)
to a crop of, say, wheat, which follows.

3. Variations in the relative requirements as to plant food.
Some crops require relatively large supplies of one particular
item of plant food. Thus an average crop of wheat or potatoes
consumes only about 50 lb. of nitrogen per acre, while an
average crop of mangolds removes about 150 lb. per acre.

Again, too liberal a supply of nitrogen may do actual harm
to one crop, e.g.^ barley for malting purposes, but after the
addition of farmyard manure, barley may safely follow, if the
too abundant nitrogen be depleted by first taking off a crop of
some nitrogen-loving plant, e.g.j mangolds.

4. The obtaining of suitable mechanical conditions in the
soil. Some crops do best when the soil is loose and open at
seed time, c^r., barley, which often follows roots; the land is then
loose and friable and free from weeds, owing to the posbi-
bility of hoeing during the growth of the turnips or mangolds.
Other seeds, e,^., wheat, grow best in a firm, compact soil,
and in this condition the land is left after a crop of clover,
which can be harvested early in the summer, giving ample time
for preparation of the land for the autumn sowing of wheat.

Many systems of rotation are in vogue in difl'erent parts of
the country, various modifications being introduced to suit the
local conditions and requirements. For details of such systems,
reference to some manual of agriculture should be made. The
most generally adopted system is known as the Norfolk four-
course rotation, which in its simplest form, consists of —

1. Roots, eaten on the land by sheep.

2. Barley.

3. Clover, generally made into hay, or sometimes grazed.

4. Wheat.

the farmyard manure being applied before the root crop.

CHAPTER VIII.

THE CHEMISTRY OF THE ANIMAL BODY.

The compounds present in the body of an animal are numerous,
and in many cases, very complex. Only a very brief and super-
ficial survey of the principal ones can be made here. The
elements present in animal tissues are the same as those found in
vegetable matter, but their relative proportions differ materially.
Calcium, phosphoric acid, fluorine, chlorine and sodium appear
to be of much more importance to animals than to plants.
The constituents of the animal body may be divided into.:

1. Inorganic compounds, including water, various acids,
and numerous salts : some in the solid state — e.g.^ calcium
phosphate ; others in solution — e.^., sodium chloride,

2. Organic compounds —

,.x xT-j. fProteids — e.o'., albumin.

(A) Nitrogenous (Amides-e.^Vvrea.

(B) Non-nitrogenous {o^fbohydrates.

According to Lawes and Gilbert, the composition of the
whole bodies of various animals is, on the average :

Contents

Animal.

Water.

Fat.

Proteids.

Ash.

of Sto-
mach, &c.

Fat calf

63-0

14-8

15-2

3-8

3-2

Half-fat ox

51-5

19-1

16-6

4-6

8-2

Fat ox

45-5

30-1

14-5

3-9

6-0

Fat lamb .

47-8

28-5

12-3

2-9

8-5

Store sheep

57-3

18-7

14-8

3-2

6-0

Half-fat sheep

60-2

23-5

14-0

3-2

9-1

Fat eheep .

43-4

35 6

12-2

2-8

6-0

Store pig .

55-1

23-3

13-7

2-7

5-2

Fat pig .

41-3

1

42-2

10-9

re

4-0

154

THE CHEMISTRY OF THE ANIMAL BODY 155

The nitrogenous matter shows the least variation, while

the water and fat are more or less complementary to each

other — i.e. J as the one increases the other decreoFes. The

ash is dependent chiefly upon the proportion of bono present.

The chief parts of an animal's body are :

1 . Blood. 4. Fatty tissue.

2. Bones, 5. Connective tissue.

3. Muscular tissue.

Blood consists of a colourless liquid — " plasma" — holding, in
suspension, enormous numbers of small solid particles — the red
and white corpuscles. When taken from an animal, the plasma
quickly deposits one of its nitrogenous constituents— ^6W?i —
which, entangling the corpuscles, causes them to separate as a
clot from the yellowish liquid — the serum. Blood plasma is
thus the liquid portion of fresh blood, blood serum the liquid
portion after clotting. The latter differs from the former by
having lost its fibrin, ov fibrinogen^ as it is now called, and a
portion of its lime, magnesia, and phosphoric acid. Blood
serum contains about 9 per cent, of total solids, of which
7*5 are albuminoid. Its ash amounts to about 0 8 5 per
cent., and consists chiefly of common salt, with small quan-
tities of potash, lime, and magnesia.

The clot of blood consists of red and colourless corpuscles
entangled in a network of fibrin. The red corpuscles consist
of circular, biconcave discs, though their shape and size vary
in different animals. They are largest in reptiles. In birds,
fishes, and in the camel they are elliptical and biconvex.
In man, the average diameter of a blood corpuscle is -OC? '^^m.
(about g^^QQ of an inch), and its thickness about '0019 mm.
(t^Itti^ of an inch). When blood corpuscles are treated with
water, ether, or other solvents they lose their colouring-matter
and leave a nitrogenous residue, which retains the shape of
the original corpuscles.

The colour of blood is due to hcemoglobin and oxyhcemoglobin.
These are extremely complex in chemical constitution, and

156 ELEMENTARY AGRICULTURAL CHEMISTRY

contain carbon, hydrogen, oxygen, nitrogen, sulphur, and
iron. Haemoglobin contains about 16 to 17 per cent, of
nitrogen and about 0'4 to 0*45 per cent, of iron. It is a dark
purplish-red coloured substance, which readily combines with
oxygen to form the oxy compound, which is bright red in
colour. The haemoglobin of the red corpuscles plays an
important part in respiration. In the lungs the blood is
brought into contact with air, oxygen is absorbed by the
haemoglobin, thus causing the purplish red colour of the venous
blood to become bright red, almost scarlet. At the same time
a considerable quantity of carbon dioxide, mosfc of which is in
solution in the blood plasma, probably as bicarbonates, is given
up to the air within the lungs. When blood is put under a
vacuum, gases are given off. On the average 100 volumes of
blood yield :

Arterial Blood.

Venous Blood.

Oxygen

Nitrogen and argon ....
Carbon dioxide . . . .

20

1 to2

40

8 to 12

I to 2

46

A change in the composition of the air is produced by
respiration. The average composition of air before and after
respiration is as follows:

Nitrogen .
Argon and neon
Oxygen

Carbon dioxide .
Water vapour .
Temperature

Inspired Air.

78-00

0-97

21-00

0-03

Variable

Variable

Expired Air.

78-09
0-98

16-50

4-43

Saturated

36° C.

The chief changes produced on air by respiration are the
removal of oxygen, the addition of carbon dioxide, and its
saturation with aqueous vapour. When oxygen combines

THE CHEMISTRY OF THE ANIMAL BODY 157

with carbon it yields its own volume of carbon dioxide, but
in respiratioil the increase in volume of the carbon dioxide
is less than the decrease in that of oxygen, being generally
about 90 per cent, of that decrease. This is probably due
to some of the oxygen being used to oxidise some hydrogen of
the food or tissues to water. Though the absorption of oxygen
takes place almost wholly in the lungs, it is not there that the
act of combination of the carbon and hydrogen of the body
with the oxygen takes place. The blood, by the haemoglobin
of the red corpuscles, acts as a carrier of oxygen, and the actual
combustion of the products derived from the food occurs in the
tissues themselves.

Bones consist essentially of an earthy framework composed
mainly of calcium phosphate, permeated by an albuminoid
known as ossein, and by nerves, blood-vessels, &c. In the
hollow centre of many bones is the maiTow^ which consists
largely of fat and albuminoids. The relative proportions of
mineral and organic matter in bones vary considerably. The
latter usually varies from 30 to 50 per cent, of the weight
of the whole bone. The proportions of nitrogen and phos-
phate of lime in avernge bones have already been discussed
in the chapter on manures.

The ash of bones, however, is not entirely phosphate of
lime, but contains also carbonates, fluorides, chlorides and
magnesia. An analysis of the ash of ox-bones gave :

Calcium phosphate 86*0

Magnesium phosphate 1-0

Calcium as carbonate, chloride and fluoride . 7'3

Carbcn dioxide 6 2

Chlorine . . . . . . . .0-2

Fluorine 0-3

101-0

Muscular tissue consists largely of albuminoids and water,
but contains also small quantities of fat, glycogen (or animal
starch), '* nitrogenous extractives " of which creatirte, C^Hj^NjOa,
sarcine, C^H^N^O, xanthine, C^H^N^Oj, guanine^ CjII^N^O and

158 ELEMENTARY AGRICULTURAL CHEMISTRY

carnine, OjE^p^, are the chief, and sugar. The ash of
muscle consists largely of potash and phosphoric acid com-
pounds, but sodium, magnesium, calcium, chlorine and iron are
also present. Muscle usually contains from 75 to 78 per cent,
of water, and 22 to 25 per cent, of solids. Living muscle has
an alkaline reaction, but after death it becomes acid, probably
owing to the formation of sarcolactic acid, CHg.CHOH.COOH.
When a muscle does work the glycogen and sugar, and
possibly the fat, are oxidised at an increased rate, and the
blood which bathes the muscle receives increased quantities of
carbon dioxide. The nitrogenous waste of muscle, which is
not now believed to be increased by exertion, is excreted in
the form of urea and uric acid.

Fatty tissue consists of cells, the walls of which are composed
of a membrane of albuminjids, filled with fat, which during
life is fluid. The fat, which resembles in constitution the
vegetable oils already described, contains stearic, oleic and
palmitic acids combined with glyceryl.

Fatty tissue contains water, membranes and fat. in about
the following proportions :

From the ox.

From the sheep.

From the pig.

Water .
Membrane
Fat .

9-96
1-16

88-88

10-48
1-64

87-88

6-44

1-35

92-21

Fat is stored in the body as a reserve from which the animal
can draw in times of scarcity of food. It is the most concen-
trated form in which energy can be stored.

Connective tissue, of which tendons, ligaments, cartilage and
skin are mainly composed, consists of substances which yield
gelatin when heated with water. Three different substances
have been recognised, viz,, elastin, collagen and keratin. The
first is almost free from sulphur, the second contains about

THE CHEMISTRY OF THE ANIMAL BODY 159

0*6 per cent., while the last usually has about 4 or 5 per cent,
of sulphur. Keratin is the main constituent of horns, hoofs,
skin, feathers, hair, wool, nails, &c. It is insoluble in water,
alcohol, or ether, but by heating with water under pressure to
150° or 200° 0. it can be rendered soluble, and then constitutes
glue.

Digestion. — An important process by which the food of an
animal is rendered capable of being absorbed into the system
and utilised in building up or renewing the tissues of the body.
It is accomplished partly by mechanical means, but mainly by
chemical changes, which are produced chiefly by the action of
enzymes.

The first step is mastication, by which the food is subdivided
and crushed by the action of the teeth and thoroughly mixed
with saliva^ a special secretion poured by glands into the
mouth. Saliva is a highly dilute liquid of faint alkaline re-
action, and contains an enzyme, ptyalinj or salivary diastase,
which has the power of bringing about the same changes as
are produced by plant diastase, viz., the conversion of starch
into sugar (maltose). Ruminants, whose food usually con-
tains much starchy material, secrete enormous quantities of
saliva — estimated in the case of the ox at about 1 cwt. per day.

The foqd, after mastication, passes into the stomach, though
In the case of ruminants it is brought back from the paunch
or rumen into the mouth to undergo a second mastication
(" chewing the cud "). It then passes into the stomach, where
it meets with the characteristic secretion — the gastQ'ic juice.
The gastric juice contains various salts (chlorides and phos-
phates of calcium, magnesium, sodium, and potassium), free
hydrochloric acid, and two enzymes, pepsin and rennet (or
chymosin). The former has the power of converting insoluble
proteids into soluble and diffusible albumoses and peptones,
the latter of coagulating casein. . These properties are pos-
sessed in acid, but not in alkaline solutions. Pepsin acts best
in a liquid containing from 0*1 to 0*3 per cent, of free hydro*

h

160 ELEMENTARY AGRICULTURAL CHEMISTRY

chloric acid. The gastric juice of sheep contains about the
lower, that of the dog the higher of these amounts.

The walls of the stomach move about when food is present,
and knead and incorporate it with gastric juice, producing a
pulpy mass known as chyme. In this process the proteids are
largely dissolved, being converted ultimately into amino-
acids, the fat is melted, and the cell walls of the fatty tissue
are removed. A certain amount of hydrolysis of starch (i.e.,
conversion of this substance into sugar) also occurs in the
stomach. The chyme then passes into the intestines, the
secretion of which has an alkaline reaction. The acidity due
to the gastric juice is therefore neutralised, and the chyme
then receives the secretions of the pancreas and liver.

Pancreatic juice is a viscid, alkaline liquid containing various
organic substances and inorganic salts. Its specific constituents,
however, are three enzymes: (1) a diastatic one, amylopsin,
acting rapidly upon starch and converting it into dextrin and
maltose ; (2) a fat-splitting one, steapsin or pialyn, possessing
the power of decomposing fats into glycerol and free fatty
acids, at the same time emulsifying the unchanged fat ; and
(3) a proteolytic enzyme, trypsin, which resembles pepsin in
its properties, except that it works best in an alkaline liquid.
Pancreatic juice is thus capable of completing the work com-
menced by the saliva and the gastric juice, and, in addition,
has the power of bringing about the emulsification of the fat.
This latter process, however, is greatly aided by the hile, the
alkaline secretion of the liver.

Bile is a reddish-yellow (in carnivorous animals) or green
(in herbivora) liquid, with an alkaline reaction and intensely
bitter taste. It contains alkaline salts of bile acids, bile
pigments, fats, soaps and mineral matter. The bile acids
are mainly glycocholic acid, CggH^jNOg, and taurocholic acid,
Q^^^.^0^^, and to these substances the bitter taste of bile
is mainly due. The bile pigments consist chiefly of bilirubiny
CjgHjgNgOj, a reddish-yellow substance, insoluble io water

THE CHEMISTRY OF THE ANIMAL BODY 161

but soluble in alcohol, chloroform, or alkalies. It is found
especially in the bile of the carnivora, and by exposure to ail
in alkaline solution absorbs oxygen and passes into hiliverdin,
CjgHjgNgO^, an amorphous green substance, insoluble in water,
but soluble in alcohol and alkalies. This substance is found
in bile and in the shells of many birds' eggs.

Bile has a slight power of dissolving fats (a familiar appli-
cation of this is afforded by the use of ox-gall for removing
grease, &c., from carpets and other textile fabrics), and has a
distinct antiseptic effect upon the contents of the intestines.
Bile is to a large extent reabsorbed in the intestines.

In the intestines many chemical changes occur, many being
induced by bacteria, which grow freely in the alkaline contents,
producing various putrefactive decompositions. Carbohydrates
produce lactic acid, cellulose splits into carbon dioxide and
marsh gas, while butyric acid, C3Hy.C00H, and valeric acid,
C^Hg.COOH, result from the bacterial hydrolysis of fats. Two

characteristic substances — indol, ^6^4\ 7CH, and skatol,

^NH/

or methyl indol, CgH^^ /CH, crystalline substances

^ NH /
with very unpleasant odours, have been extracted from the
contents of the intestines, and it is to the presence of these
substances that the unpleasant smell of faeces is largely due.

Destination of Dig^ested Food.— Some few constituents

of the food can be absorbed without undergoing chemical
changes ; this is the case with water and common salt, perhaps
also with some soluble proteids. Absorption commences in
the stomach, but is mainly accomplished in the intestines by
the lacteals and lymphatics.

The carbohydrates are probably entirely absorbed in the
form of maltose or glucose, being converted into these com-
pounds by the enzymes of the saliva, pancreatic juice, und
intestines. Some of these eiiter the blood stream and are

162 ELEMENTARY AGRICULTURAL CHEMISTRY

conveyed to the tissues, while another portion is stored in
the liver in the form of glycogen, CellioOs, an amorphous white
powder occurring in the liver to the ext3nt of from very little
or none in starvation to 10 or 12 per cent, under a rich carbo-
hydrate diet.

Only a small portion of the fat is saponified (^.e., decomposed
into glycerol and fatty acids), the greater portion being merely
emulsified by the action of the pancreatic fluid and the bile.
The minute globules of fat apparently pass through the walls of
the intestines into the lacteals, and thus into the blood. The
proteids are chiefly absorbed as peptones and albumoses,
though apparently they are transformed back into proteids in
the act of absorption, for no peptones can be found in the
blood.

According to recent researches proteids are hydrolysed by
the digestive juices into amino-acids, and in this form entfer
the blood stream. The amino-acids are then used by the
animal in building up the proteids required in its tissues.
Unless all the amino-acids necessary for forming animal
proteids are present in sufticient quantities in the proteids of
the food proper nutrition cannot occur. In the case of the
proteids of certain food-stuffs — e.g., of maize — all the neces-
sary amino-acids are not present, and such food-stuffs cannot,
of themselves, support life for long. The subject is at present
receiving much attention from biological chemists, and, in
the near future, much new light will doubtless be thrown
upon it.

The digestion of the food thus commences in the mouth
and is completed in the stomach and intestines, while the
digested materials are absorbed by the lacteals and poured
into the blood stream from which they are extracted in the
building up of tissue.

The carbohydrates and fats which are oxidised in keeping up
the animal heat or in furnishing energy, are exhaled as carbon
dioxide and water from the blood in the lungs, while the
nitrogenous waste products of the breaking down of muscle,

THE CHEMISTRY OF THE ANIMAL BODY 163

&c., and the mineral matter are chiefly excreted from the
blood, by the kidneys and appear in the urine.

Urine. — Urine vaiies greatly in composition, being affected
by the food, amount of exercise, water consumed and other
circumstances. In carnivorous animals it is usually acid, in
herbivora alkaline or neutral. The characteristic constituent
is urea^ or carhamide^ C0(NH8)a, of which there is usually more
in the urine of carnivora than in that of herbivora.

Uric acid, H2C6H2N4OS, occurs very largely in the excre-
ments of birds and reptiles, also in the urine of carnivora, and
to a small extent in that of herbivora. In certain diseases —
e.g., gout and rheumatism — deposits of uiic acid and urates
are formed in the body.

In the urine of herbivorous animals, uiic acid is replaced
by hippuric acid (benzoyl-amino- acetic acid), C9H9NO3, which
occurs to the "extent of about 2 per cent, in the mine of horses
and catt'e. By hydrolysis (taking up of water) hippuric acid
readily p isses into benzoic acid, CeHs.COOH, and amino-
acetic acid, or glycocoll, CH2(NH2).COOH :

CeHsCO.NH.CHa.COOH + H2O
=C6H6.COOH 4-CH2(NHa).COOH.

CHAPTER IX.

THE FEEDING OF ANIMALS.

The food of the animals of the farm consists mainly of various
vegetable products, being either a part or the whole of the
plant, or some bye-product resulting from the utilisation of the
vegetable matter for some other purpose {e.g.^ oil-cakes).

The actual essentials of the food of animals can be deduced
from the composition of their first natural food— rtheir mother's
milk.

All animals are alike in requiring, as ingredients of their
food, the following classes of constituents :

1. Nitrogenous organic compounds — proteids.

2. Richly carbonaceous, non-nitrogenous compounds— /c< is

or carbohydrates.

3. Mineral com2:>ounds, including especially lime, iron,

potash, sodium, phosphates, sulphates, &c.

In addition, almost all food-stuffs contain more or less
woody, fibrous matter, which is usually known as ''crude
fibre."

The composition of mos': substances used as food has been
given in chap. vii. A little explanation of the meaning of
the terms used in stating the composition of a food may, how-
ever, be useful.

The common method of expressing the results of the ana-
lysis of a food-stuff is to give the amounts of the following
constituents :

164

THE FEEDING

OF ANIMALfS

Moisture.

N-free extract.

Ash.

Protein.

Crude fibre.

Fat.

1G5

By nioistitre is meant the loss which the food-stuflf undergoes
when heated in a steam-bath until constant. This may be
taken without much error to be water, though other volatile
constituents of the material may be lost. An error in the
opposite direction may be introduced by the oxidation of some
constituent, unless the heating is done, as it sometimes is, in a
current of hydrogen or of nitrogen. Certain oils — e.g.^ lin-
seed— absorb a considerable quantity of oxygen when heated,
in air.

Ash is the amount left by heating the material to redness in
air until all black portions of carbon have disappeared. The
residue obtained does not necessarily contain the true mineral
constituents of the food-stuft' in the same form as they were
actually present. Indeed, it almost invariably happens that
the various constituents are left in an entirely different state;
e.g.^ potassium and calcium are left in the ash largely as
carbonates, though in the plant they are doubtless present as
organic salts (malates or oxalates). The sulphates in the ash,
too, are often derived from sulphur existing as albuminoids.

Crude fibre is determined by the somewhat arbitrary method
of boiling a weighed portion of the material successively with
dilute sulphuric acid and a solution of caustic soda. The
organic matter which resists this treatment is reported as crude
fibre. It consists generally of woody matter, but it is quite
empiric to assume, as is sometimes done, that it is a measure
of the material which would resist digestion if fed to an
animal.

N-free Extract, or Soluble Carbohydrates. — This is always
determined by difference — by subtracting the sum of all the
other constituents from 100. The result, which includes the .
accumulated errors of all the other items, is assumed to consist
of starch, sugar, and other carboh^^drates. This is not very

166 ELEMENTARY AGRICULTURAL CHEMISTRY

satisfactory, but is still the usual way of expressing analytical
results.

Protein. — This is obtained by multiplying the percentage of
total nitrogen present by 6*25, on the assumption that all the
nitrogen is present as albuminoids and that the latter contain
IB per cent, of nitrogen. Both these assumptions are generally
wrong. Many food-stuffs contain a considerable portion of
their nitrogen in the form of amides, which are less valuable
for feeding purposes than albuminoids (see chap. v.). How-
ever, in recent analyses distinction is made between albu-
minoids and amides.

Fat, or ether extract, as it is sometimes more accurately
called, is, as the latter name indicates, the proportion of the
material which is soluble in ether. It generally includes true
fat or oil, chlorophyll, and other colouring substances and
resinous bodies.

The value of a food depends partly upon its composition,
but also upon its palatability and digestibility. The last can
be determined experimentally by experiments with animals.
"Weighed quantities of the food are fed to animals kept in such
a way that their excrement can be collected and analysed for
a considerable period of time. In this way the proportion of
each food constituent digested out of 100 parts by weight
supplied can be determined. This proportion is known as the
" digestion coefficient," but diff'ers with the kind of animal, and
even with different individuals of the same kind. ,

The ** digestibility " of a food constituent, however, in this
sense, has no reference to the ease or rapidity of its assimilation,
nor to its effect upon the health or comfort of the animals
consuming it.

Animals diflTer in their power of digesting any given food or
food-constituent. Thus ruminants, by their more thorough
and repeated mastication, are better able to digest bulky fodder
than are pigs and horses.

In the following table are given the average digestion
coefficients of the constituents of various foods according to

THE FEEDING OF ANIMALS 167

American and German experiments. Jt must be remembered
that the figures have no pretensions to accuracy, since in any
given case differences may be produced by variations (1) in the
food or (2) in the animals consuming it.

Average Digestion Coefficients in Various Foods.

Pro-

Carbo-

Fat.

Crude

Total

dry

matter.

tein.

hydrates.

fibre.

I*— Fob Ruminants.

Maize » . . . .

76

93

86

68

91

Gluten meal

89

93

93

—

88

Gluten feed

85

87

83

72

84

Wheat bran

79

• 69

68

• 22 *

61

Wheat sharps

82

85

85

36

79

Rye meal ,

84

92

64

—

87

Barley i

70

92

89

60

86

Malt sprouts or culms

80

69

100

34

67

Brewers' grains, wet

73

62

86

40

63

» M dry .

79

69

91

63

62

Oats* , . . .

78

76

83

20

70

Rice meal

•63

86

85

26

76

Linseed ,

91

55

86

61

77

Linseed oil, rich in oil

89

78

89

67

79

„ „ poor in oU

85

84

93

74

80

Cotton seed

68

50

87

76

66

Cotton cake, decorticated

88

64

93

32

76

„ „ undecorticated .

62

54

85

46

55

Pea meal .

83

73

86

—

79

Meadow hay .

57

64

53

60

61

Timothy hay .

48

63

57

52

67

Red clover hay

62

69

62

49

61

Alsike hay

66

71

60

53

62

White clover hay

73

70

61

61

66

Lucerne hay .

74

66

39

43

60

Sainfoin hay .

70

74

66

36

62

Wheat straw .

11

38

81

52

43

Rye straw

21

37

32

60

46

Oat straw

30

44

•33

64

48

Barley straw .

20

54

42

56

63

Pasture grass, green

70

73

63

76

71

Timothy grass, green

50

64

47

52

58

Green oats, in bloom

75

63

70

60

64

Red clover, green w

67

78

65

53

66

Crimson clover, green

77

74

66

56

69

Lucerne, green

81

76

52

45

67

1G8 ELEMENTARY AGKTCULTURAL CHEMISTRY

Average Digestion Coefficients in Vaiuous
Foods — continued.

Pro-

Carbo-

Crude

Total

tein.

hydrates.

Fat.

fibre.

dry
mutter.

I.— Foe 'Ruminants— conihiued.

Potatoes ! ? s ! .

61

90

__

85

Mangolds . . . i ,

77

96

—

—

88

Turnips .....

90

97

98

100

93

Swedes ......

80

95

84

74

87

Cows' milk ....

94

98

100

—

98

II.— For Pigs.

Maize meal .8 ? ...

86

95

76

40

92

Pea meal .- ;

89

95

50

78

90

Barley meal

76

90

65

15

82

Wheat s

70

74

60

30

7?

Wheat bran

75

66

72

34

61'

Wheat sharps .

73

87

37

77

Potatoes .

73

98

—

55

93

Dried blood

72

92

72

Flesh meal

.97

—

87

92

Sour milk

96

99

95

—

95

By combining such results with a table of the composition
of food-stuffs it is possible to construct a table giving the
digestible constituents of various foods, which, though not
necessarily accurate in any particular case, is very useful as a
guide in framing rations for animals. The following is such
a table, compiled from American and German experiments;,
appended to it are the fertilising constituents present in the
various foods, which enable the manurial value of the foods to
be gauged.

Of the "digestible protein" given in the above table a
portion only consists of true albuminoids. In cakes, grain, <fec.,
the proportion of true albuminoids to total " protein " is high,
while with grasses, and especially with roots, it is very small.
Thus in cakes, peas, beans, wheat, barley, oats, maize, &c., the
proportion is 80 per cent, or over, in barley straw and meadow

THE FEEDING OF AJSIMALS 169

Digestible and Fertilising Constituents op Various
Food-stuffs.

Digestible constituents.

Fertilising constituents. |

Dry

matter

per

rci-ccntag

es.

Perceutay

cs.

Food.

Carbo-

I'hos-

Nitro-

cent.

Protein.

hy-

Fat.

Potash.

phoric

drates.

aci.l.

gen.

Maize .

■ 89-1

7-9

66-7

4-3

0-40

0-70

1-82

Maize bran

90-9

7-4

59-8

4-6

0-68

1-21

1-63

Gluten meal .

91-8

25-8

43-3

11-0

0-05

0-33

5-03

Germ meal

89-6

9-0

61-2

6-2

0-50

0-80

2-65

Wheat .

89-5

10-2

69-2

1-7

0-50

0-79

2-36

Flour

87 -^

8-9

62-4

0-9

0-15

0-22

1-89

Wheat bran .

88-1

12-2

39-2

2-7

1-61

2-89

2-67

Sharps or

shorts .

88-2

12-2

50-0

3-8

0-59

1-35

2-82

Rye . .

88-4

9-9

67-6

1-1

0-54

0-82

1-76

Rje bran

88-4

11-5

50-3

2-0

1-40

2-28

2-32

Barley .

89-1

8-7

65-6

1-6

0-48

0-79

1-51

Malt culms

89-8

18-6

37-1

1-7

1-63

1-43

3-55

Brewers'

grains, wet .

24-3

3-9

9-3

1-4

0-05

0-31

^•89

Brewers'

grains, dry .

91-8

15-7

36-3

5-1

0-09

1-03

3-62

Oats

89-0

9-2

47-3

4-2

0-62

0-82

2-06

Oat meal

92-1

11-5

52-1

5-9

Rice

87-6

4-8

72-2

0-3

0-09

0-18

1-08

Rice bran

90-3

5-3

4o-l

7-3

0-24

0-29

0-71

Buckwheat

87-4

7-7

49-2

1-8

0-21

0-44

1-44

Linseed .

90-8

20-6

17-1

29-0

1-03

1-39

3-61

Linseed meal,

pressure

90-8

29-3

32-7

7-0

1-37

1-66

5-43

Linseed meal,

solvent

89-9

28-2

40-1

2-8

1-39

T83

5-78

Cotton seed .

89-7

12-5

30-0

17-3

l']7

1-27

3.13

Cotton - seed

meal .

91-8

37-2

16-9

12-2

0-87

2-88

6-79

Palm-nut meal

89-6

16-0

52-6

9-0

0-50

1-10

2-69

Sunflower seed

92-5

12-1

20-8

29-0

0-56

1-22

2-28

Sunflower cake

91-8

31-2

19-6

12-8

1-17

2-15

6-55

Pea-nut meal .

89-3

42-9

22-8

6-9

1-50

1-31

7-56

Rape-seed meal

90-0

25-2

23-7

7'5

1-30

2-00

4-96

Peas

89-5

16-8

51-8

0-7

0-99

0-82

3-08

Horse-beans .

85-7

22-4

49-3

1-2

1-29

1-20

4-07

« Pasture grass .

20-0

2-5

10-2

0-^

0-75

0-23

0-91

Timothy grass

38-4

1-2

19-1

0-G

0-76

0-26

0-48

1 Green oats

37-8

2-6

18-9

ro

0-38

0-13

0-49

i Meadow fescue

30-1

1-5

16-8

0-4

—

i Green barley .

21-0

11-9

10-2

0-4

—

—

—

170 ELEMENTARY AGRlCULTtJRAL CHEMISTRY
Digestible Constituents, (fee. — continued.

Digestible constituents.

Fertilising constituents.

Dry

Percentages.

Percentages.

iii3rtt6r

Food.

per

Carbo-

Ph"s-

Nitro-

cent.

Protein.

hy-

Fat.

Potash.

plioric

drates.

acid.

gen.

Timothy hay .

86-8

2-8

43-4

1-4

0-90

0-53

1-26

Mixed grass

hay *

87-1

5-9

40-9

1-2

1-55

0-27

1-41

Meadow fescue

hay

80-0

4-2

43-3

1-7

2-10

0-40

0-99

Wheat straw .

90-4

0-4

36-3

0-4

0-51

0-12

0-59

Rye straw

92-9

0-6

40-6

0-4

0-79

0-28

0-46

Oat straw

90-8

1-2

38-6

0-8

1-24

0-20

0-62

Barley straw .

85-8

0-7

41-2

0-6

2-99

0-30

1-31

Red clover,

green .

29-2

2-9

14-8

0-7

0-46

0-13

0-53

Al&ike clover .

25-2

2^7

13-1

0-6

0-20

0-11

0-44

Crimson clover

19-1

2-4

9-1

0-5

0-49

0-13

0-43

Lucerne *

28-2

3-9

12-7

0-5

0-56

0-13

0-73

Red clover hay

84-7

6-8

35-8

1-7

2-20

0-38

2-07'^

Alsike clover

hay . .

90-3

8-4

42-5

1-5

2-23

0-67

2-34

White clover

hay I

90-3

11-0

42-2

1-5

1-81

0-52

2-75

Crimson clover

hay s

90-4

10-5

34-9

1-2

1-31

0-40

2-05

Lucerne hay .

91-6

11-0

39-6

1-2

1-68

0-51

2-19

Clover silage .

28-0

2-0

13-5

1-0

—

—

—

Lucerne silage

27-5

3-0

8-5

1-9

—

'—

—

Grass silage .

32-0

1-9

13-4

1-6

—

—

—

Maize silage .

20-9

0-9

11-3

0-7

0-37

0-11

0-28

Potatoes .

21-1

0-9

16-3

0-1

0-46

0-12

0-32

Mangolds

9-1

M

5-4

0-1

0-38

0-09

0-19

Turnips *

9-5

1-0

7-2

0-2

0-39

0-10

0-18

Swedes .

11-4

1-0

8-1

0-2

0-49

0-12

0-19

Carrots .

11-4

0-8

7-8

0-2

0-51

0-09

0-15

Parsnips .

11-7

1-6

11-2

0-2

0-44

0-20

0-18

Artichokes

20-0

2-0

16-8

0-2

0-47

0-14

0-26

Cabbages

15-3

1-8

8-2

0-4

0-43

0-11

0 38

Spurrey .

20-0

1-5

9-8

0-3

0-59

0-25

0-38

Prickly com-

frey

11-6

1-4

4-6

0-2

0-75

0-11

0-42

Acorns, fresh .

44-7

2-1

34-4

1-7

—

—

—

Rape

14-0

1-5

8-1

0-2

0-36

0-15

0-45

Dried blood .

91-5

52-3

0-0

2-5

0-77

1-35

13-50

Cows' milk .

12-8

3-6

4-9

3-7

0-18

0-19

0-53

Separated milk

9-4

2-9

5-2

0-3

0-19

0-20

0-56

Butter-milk .

9-9

3-9

4-0

1-1

0-16

0-17

0-48

Whey .

6-6

0-8

4-7

0-3

0-18

0-14

0-15

THE FEEDING OF ANIMALS 171

hay about GO 1o 65 per cent., in potatoes and carrots less than
50 per cent., in mangolds, turnips, and swedes about 25 per
cent., while in some specimens of maize silage it may be as
little as 12 per cent.

Albuminoid Ratio. — It is found in practice that the food
of an animal may be varied considerably without any detri-
ment to the well being of the animal, providing the ratio of
albuminoids to non-albuminoids in the food be kept within
certain limits.

In order to get this ratio it is necessary that some definite
carboliydrate be taken in which to express the non-albuminoids.
Starch is the substance always chosen, and it becomes necessary,
in order to express the fat and the other carbohydrates in terms
of starch, to obtain the equivalents in heat-producing power
of these other food constituents. This has been done (1) by
burning weighed portions of the various materials in calori-
meters and (2) by direct experiments upon animals placed in
large respiration calorimeters and fed with known weights of
the various food-stufis.

As the mean of several experiments it may be taken that
100 parts of fat evolve as much heat as 230 parts of sugar,
starch, or cellulose, or of protein.

To express the percentage of total non-albuminoids of a
food, therefore, in terms of starch it is necessary to multiply
the percentage of fat by 2-3 and add the product to the per-
centage of soluble carbohydrates. The albuminoid ratio thus

albuminoids

becomes — , , i — : ; — 77-7 o77\> the digestible consti-

carbohydrates + (tat x Z'dy ^

titents being taken in all cases. Suppose, for example, it is

desired to calculate the albuminoid ratio, or nutritive ratio, as

it is sometimes called, of red clover hay. From the table it

appears that the digestible constituents are as follows :

Per cent.

Protein 6*8

Carbohydrates . . . 358

Fat . . . . . 1-7

J 72 ELEMENTARY AGRICULTURAL CHEMISTRY

The albuminoid ratio is : *

G-8 ^ 6-8 ^ 6-8^ = _1_

35-8 + (1-7 X 2-3) 35-8 + 3*91 3971 5-84*
1 :5-84

For the reasons already stated, unless the distinction between
true albuminoids and amides is made in the analyses, the
albuminoid ratio calculated from the " protein " {i.e., the per-
centage of nitrogen x 6*25) may in certain cases — e.g., roots,
grasses, and silage — be very misleading. If the amides present
are considered, the best plan is probably to class them with the
non-albuminoids and consider them as about equal to half
their weight of starch. With a ration consisting of several
foods the calculation of the albuminoid ratio is somewhat
more complex. Thus, if it is desired to calculate the albuminoid
ratio of a ration composed of the following mixture :

Oat straw

Beans ....

Bran ....

. 10 1b.
. . 2 „
. . 2 „

First find the total digestible protein :

In the oat straw ....

1-2 X ;,', - -12

In the beans

22-4 X ^^,^--45

In the bran

12-2 X 3|-o=-24 ,

•81

Next the carbohydrates :

In the oat straw ....

38-6 X ^^^ - 3-83
100

In the beans

49-3 X — = -99
100

In the bran

39-2 x^= -78

5-63

* Digestible crude fibre should really be included in the calculation
and be reckoned as of equal value to starch. It is of importance in
fodder crops, and when it is taken into account the albuminoid ratio
will be " wider," e.^., about X : 77 in the example givea,

THE FEEDING OF ANIMALS

173

Next the fat : in the oat slfaw .

10
• 0-8 X ^ = -08

In the beans

. 1-2 X ~ = -02

2
In the bran . . . 27 X Jqq = 'Oo

T5
0-15 of fat X 2-3 = 0-34 of caibohydratos
5-64

5 "97 total carbohyd rotes

.'. Albuminoid ratio

=0-81 : r,-97
= 1 : 7-37

The albuminoid ratio in a ration most suitable for the food of
animals depends largely upon the kind of animal and the con-
dition under which it is living. The following are suggested
as suitable for the various capes :

For very young animals the food should have an

albuminoid ratio of about
For oxen at rest .

„ moderalely worked

„ heavily worked
For horses moderately worked

„ heavily worked .
For milch cows .
For sheep, for wool-prod uring
For fattening cattle, sheep, or pigs

4-0
11-0
8-7
6-0
7-0
5-5
5 0
8-0
5-5

It is probable, however, that in the past, too mucli impor-
tance has been attached to the albuminoid ratio of rations,
especially in the case of fattening animals. When real albu-
minoids only are considered, the albuminoid ratio of fattening
rations may, with economy, be much wider than has hitherto
been recommended. A study of many feeding trials shows that,
provided sufficient proteid be supplied — and much less than was
thought necessary, suffices — the increase of a fattening animal
becomes proportional to the amount of digestible non-nitro-
genous matter which it consumes. A general recognition of
this fact would lead to much economy in the cost of fattening
for proteid-^ are the most expensive constituents of food-stufTs,

Thermal Value of Foods. — Provided foods contain suffi.
cient nitrogenous matter to replenish waste of muscular tissue,

174 ELEMENTARY AGRICULTURAL CHEMISTRY

&c., and to maintain the animal in health, it is possible to assess
their relative values as sources of mechanical power when con-
sumed by the animal by a determination of their heat-producing
power. The amount of heat produced by the burning of Ipart by
weight of the three classes of food constituents may be stated
in terms of the weight of water which that heat would raise
through 1° C. These are found to be :

Fat . . . 9300

Protein 4100

Starch 4100

Amides {e.g., asparagine) ..... 3500

If it is desired to calculate the heat-producing or calorific

power of a food, the proportions of the digestible constituents

in 1 part by weight should be multiplied by their respective

heats of combustion. The sum of these products will give the

calorific power of the food when fed to animals — i.e., the

quantity of water which will be raised 1°C. in temperature by

the heat evolved from 1 part by weight of the food consumed

in the animal. Suppose, for example, we wish to calculate the

calorific power of oats.

1 part by weight of oats contains *092 part digestible protein

„ „ „ '473 „ „ carbohydrate*

•0i2 „ „ fat

-, ,,. , . , ^, ,. , ^.- ,, 4100 = 377-2

Multiplying by the respective J .473 ^ 4100 = 1939-0
heats of combustion, I .q^2 x 9300= 390*6

r-092 X
-{•473 X
1-042 X

The calorific power of oats thus is 2706*8

Calculated in this way, the heat-producing powers of food-
stuff's show great variation, maize being nearly 3500, while
roots are very low, turnips being about 300.

In an animal, food is used chiefly in three ways :

1. To promote growth and increase.

2. To repair and renew tissue.
8. To furnish heat and energy.

The proportion used in these three ways varies greatly with
the animal. Thus in young and growing animals, as also in
fattening animals, kept quiet, the first will consume a larger
proportion of the total food than in adult animals doing hard

THE FEEDING OF ANIMALS 175

work. The proper quantity of food to be provided for an
animal will therefore vary considerably with conditions.

As long ago as 18G4, Wolff proposed certain feeding
standards, which, with various modifications, have been largely
used in framing rations. In order to eliminate the influence
of the size of the animal, the proportions of the various food
constituents to be supplied daily per 1000 lb. of body weight
are given.

Wolff's Feeding Standards.
Per day per 1000 lb. live weight.

Approxi-

Digestible food-stults.

mate fuel

Total

value iu

organic
matter.

lb. of
water

Pro-

Carbo-

Fat.

raised

tein.

hydrates.

I'C.

lb.

lb.

lb.

lb.

Ox, at rest ....

17-5

0-7

80

0-15

37,000

„ moderately worked

24-0

1-6

11-3

0-30

63,500

„ heavily worked .

26-0

2-4

13-2

0-50

68,500

Horse, moderately worked .

22-5

1 8

11-2

0-60

59,000

„ heavily worked

25-5

2-8

13-4

0-80

74,000

Milch cow ....

24-0

2-5

12-5

0-40

65,000

Sheep, for wool, coarse

20 0

1-2

10-3

0-20

49,000

fine . .

22-5

\-r>

11-4

025

55,000

Fattening Cattle.

First period

27-0

2-5

15-0

0-50

76,000

Second period .

26-0

3-0

14-8

0-70

79,000

Third period

25 0

2-7

14-8

0-60

77,000

Fattening Sheep.

First period

26-0

3-0

15-2

0-50

79,000

Second period .

25-0

3-5

14-4

0-60

79,000

Fattening Pigs.

First period

36 0

5 0

27-

6

133,000

Second period .

31-0

4 0

24-

0

115,000

Third period

23-5

2-7

17-

5

82,500

In the case of the m*lch cow the ration ought to vary with
the milk-flow, or, better, with the amount of solids in the

176 ELEMENTARY AGRICULTURAL CHEMISTRY

milk. According to Lehnxann, the ration for cows should vary
in accordance with the following table ;

Milk per cow pfer . day.

Lehmann's Standard for Coics

qf 1000 lb. live xveight.

1

oa
2

Digestible
uutrients.

Fuel Value Caloiies,

i.e., kilos of ' water

throug^h 1° C.

<

1

1

5|

f-

Yielding 11 lb. of milk .

22
27i

Lb.
25
27
29
32

Lb.
1-6
20
2-5
3-3

Lb.

0-3
0-4
0-5
08

Lb.
10
11
13
13

22,850
25.850
30,950
33,700

1 :67
1 : 6 0

1 :5-7
1 :4-5

Another point of importance in connection with foods is the
supply of sufficient mineral matter, lime and phosphates parti-
cularly, for the requirements of the animal. Young animals
especially are liable to suffer in development should their food
be deficient in these constituents. Fortunately many of the
concentrated foods — e.g., oil-cakes — valued for their richness in
nitrogen and fat, are also rich in ash constituents. Maize and
rice are perhaps the worst foods in this respect.

Recent investigations show that the ratio of basic material
to acid radicals in the ash of a food is of much importance. In
cereals, for example, the amount of bases (lime and magnesia)
is small compared with the amount of phosphoric acid, and
there is reason to think that an exclusive cereal diet is not good
for horses, &c., and may encourage certain diseases of the bones.
From a study of the composition of bones of animals suffering
from certain bone diseases, the writer has recently come to the
conclusion that the diet of animals should contain at least as
much lime as phosphorus pentoxide, or otherwise the proper
nutrition of the bones is disturbed. The following table gives
the ratio of lime to one of phosphorous pentoxide in certain
food-stuffs :

THE FEEDING OF ANIMALS 177

Sced,<t.

Forage.

Kaffir corn

002

Whole wheat plant .

0-66

Maize

004

„ oat plant

0.77

Barley-

0 06

Boer manna hay

0 94

Wheat .

0 07

Natal blue grass hay

1-68

Oats .

0-16

English meadow hay

2-27

Moots.

Cabbages .

2-24

Potatoes .

0-15

Red clover hay

3-60

Turnips .

0-83

Lucerne hay .

4-78

The seeds of all plants are thus relatively poor in lime and rich
in phosphorus pentoxide as compared with the foliage, while
even the whole plant, in the case of the cereals, contains far
more of the latter than the former.

The importance of the diet being rich in ash constituents
in connection with bone formation has long been realised, but
the fact that it is the ratio of lime to phosphoric acid that is
important has not hithei'to been recognised. Thus5 bran is
widely regarded as being rich in "bone-forming " material,
but from the point of view here expressed it should be very-
unsuitable for the development of bone, since analysis shows
it to contain about 3*3 percent, of its dry weight of phosphorus
pentoxide, but only 0*3 per cent, of lime, i.e., only 009 of
lime to I'O of phosphorus pentoxide. Practical experience
shows that animals fed very largely upon bran are prone to
contract a curious bone disease known as "millers' horse
disease " or " bran rachitis."

The feeding of horses and mules upon a diet exclusively
composed of oat-hay or oat-hay and maize, a ration containing
a great excess of phosphorus pentoxide over lime, is believed,
by the writer, to be the main cause of the prevalence of a
bone disease, '* osteoporosis," in many parts of South Africa.

Another function of the ash constituents of food is the supply
of certain substances required by the animal in secreting various
digestive juices, e.g., chlorine for the production of hydrochloric
acid in the gastric juice, potassium compounds which are
present in the saliva, gastric juice and other secretions. In
some countries, these substances are deficient in the natural
food available, and it is then found necessary, in order to

178 ELEMENTARY AGRICULTURAL CHEMISTRY

preserve the health of animals, to supply them artificially in
the form of " licks," which generally consist chiefl}' of common
salt, often with a little sulphur and sometimes some compound
of iron — e.g., ferrous sulphate. With young ruminants, too,
it has been found that a certain quantity of bulky food is
essential, and that when entirely fed on rich, concentrated food
containing a sufficiency of all necessary constituents they died.
The proportion of water to dry food required by animals is
apparently greatest in cattle, smallest in sheep, while horses
are intermediate in their demands. With sheep the ratio of
water to dry matter is said to be about 2:1, with cattle
about 4:1. When roots which contain more water than this
are taken the economy of adding a little dry food in the shape
of cake or meal to the dietary is obvious. With horses in
France it was found that the ratio of water to dry food was
2*1 : 1 when at rest and 3'6 : 1 when working. With fattening
oxen the ratio was found to be from 1*6 to 3'4 lb. of water to
each pound of dry matter, the larger amount being consumed
when the food was richest in protein. Cows will usually drink
from eight to ten gallons of water per day, but much less if
roots be taken.

Money Value of Food Constituents.— It would be

convenient, if it were possible, to adopt, in valuing food-stuffs
from analysis, a method similar to that already described in
valuing manures — i.e., to give to the albuminoids, fats, and
carbohydrates ^* unit values," so that the value per ton could
be computed. Such methods, however, are not completely
successful, since some of the properties of food -stuffs — flavour,
palatability, &c. — cannot be taken into account, and since
animals are much more fastidious as to their food than are
plants.

By taking the market prices (which are necessarily fluctuat-
ing) of large numbers of foods it has been estimated that the
values of the digestible carbohydrates, fats, and protein are in
the ratio 1 : 2-5 : 2-5.

In England digestible carbohydrates may be taken as worth

THE FEEDING OF ANIMALS 179

approximately Is. Sd. " per unit " per ton. Thus the digestible
fat and protein become worth about 3s. 1J(Z. "per unit'* per
ton. To calculate the value per ton of a food-stuflf the per-
centages of digestible fat and protein should be added together,
their total multiplied by 2*5 and added tp the percentage of
digestible carbohydrates, thus giving the number of " food
units." The food units multiplied by Is. dd. will then give the
value. In practice, it will be found that if the total carbohy-
drates be taken as worth Is. per unit, and the total fat and
protein as worth 2s. Qd. per unit, the value per ton, calculated
on this basis, will be roughly correct.

Manurial Value of Foods.— Another factor of importance
in determining the relative values of foods is their eflfect in
enriching the excreta of animals fed upon them, in the valu-
able manurial constituents — nitrogen, phosphates and potash.
Many of the rich nitrogenous food-stuffs are rich too in
phosphates and potash ; oil-cakes, for example, have a marked
eflfect upon the manure of animals fed upon them, especially if
the animals are not growing rapidly or producing milk. A
variable proportion of the nitrogen, a smaller proportion of
the phosphates, but practically none of the potash is retained
"by the animal in order to build up new tissue ; the remainder
•eventually finds its way into the excreta.

Great importance is rightly attached to the manurial value
■of food-stuffs consumed on the farm, but it would be well for
the farmer to remember that combined nitrogen can often be
more cheaply purchased in the form of nitrates or ammonium
salts than as cake or other concentrated food-stuff.

Lawes and Gilbert made elaborate experiments upon the
manurial value of the common feeding-stuffs when supplied to
fattening sheep and oxen. Voelcker and Hall have published
a revised table, embodying the results of Lawes and Gilbert.
In this table it is assumed that half the nitrogen, three-quarters
of the phosphoric acid, and all the potash are voided in the
excrement, and that nitrogen is worth 12s. per unit per ton,
phosphoric acid Ss. per unit, and potash 4s, per unit.

180 ELEMENTARY AGRICULTURAL CHEMISTRY

ValuatiOxN per Ton as Manure.

Nitiogen.

rhosphoric

Acid.

Potash.

No.

Foods.

Per

Value

Half of

Per

Value

Three-
quarters
of V^alue

Per

Value
at 4s.

cent.

atl2s.

Value

cent.

at 3s.

cent.

per

iu

per

to

in

per

to

in

Unit,

Food.

Unit.

Manu-e

Food.

Unit.

Manure.

Food.

all to
Manure.

s. d.

8. d.

s. d.

s. d.

9. d.

1

Decorticated cot-
ton cake

6-90

82 10

41 6

3-10

9 4

7 0

2-00

8 0

2

Undecorticated
cotton cake

3-54

42 6

21 3

2-00

6 0

4 6

2-00

8 0

3

Linseed cake

4-75

57 0

28 6

2-00

6 0

4 6

1-40

5 7

4

Linseed

3-60

43 2

21 7

1-54

4 7

3 5

1-37

5 6

5

Palm-nut cake .

2-50

30 0

15 0

1-20

3 7

2 8

0-50'

2 0

6

Cocoanut cake .

8-40

40 10

20 5

1-40

4 2

3 1

2-00

8 0

7

Rape cake .

4-90

58 10

29 5

2-50

7 6

5 8

1-50

6 0

8

Beans .

4-00

48 0

24 0

1-10

3 4

2 6

1-30

5 2

9

Peas .

3 -GO

43 2

21 7

0-85

2 7

1 11

0-96

3 10

10

Wheat

1-SO

21 7

10 9

0-85

2 7

2 0

0-53

2 1

11

Barley

1-65

19 10

9 11

0-75

2 3

1 8

0-55

2 2

12

Oats .

2-00

24 0

12 0

0-60

1 10

1 5

0-50

2 0

13

Maize .

1-70

20 5

10 2

0-60

1 9

1 4

0-37

1 6

14

Kice meal .

1-90

22 10

11 5

0-60

1 9

1 4

0-37

1 6

15

Locust beans

1-20

14 5

7 2

0-80

2 5

1 10

0-80

3 2

16

Malt .

1-82

21 10

10 11

0-80

2 5

1 10

0-60

2 5

17

Malt culms .

3-90

46 10

23 5

2-00

6 0

4 6

2-00

8 0

18

Bran .

2-50

30 0

15 0

3-60

10 10

8 2

1-45

5 9

19

Brewers' grains,
dried

3-30

39 7

19 9

1-61

4 10

3 8

0-20

0 10

20

Brewers' grains,
wet

0-81

9 9

4 11

0-42

1 3

Oil

0-05

0 2

21

Clover hay .

2-40

28 10

14 5

0-57

1 9

1 4

1-50

6 0

22

Meadow hay

1-50

18 0

9 0

0-40

1 2

Oil

1-60

6 5

23

Wheat straw

0-45

5 5

2 8

0-24

0 9

0 7

0-80

3 2

24

Barley straw

0-40

4 10

2 5

0-18

0 6

0 4

1-00

4 0

25

Oat straw .

0-50

6 0

3 0

0-24

0 9

0 7

1-00

4 0

26

Mangolds .

0-22

2 8

1 4

0-07

0 3

0 2

0-40

1 7

27

Swedes

0-25

3 0

1 6

0-06

0 2

0 1

0-22

Oil

28

Turnips

0-18

2 2

1 1

0-05

0 2

0 1

0-30

1 2

THE FEEDING OF ANIMALS

181

Compensation Value for each Ton

of the Food Consumed.

Last

Last Year

Last Y'ear

Last Year

^

Year.

but cue.

but two.

but three.

Foods.

No.

s. d.

S. (I.

8. d.

s. d.

56 5

28 2

14 1

7 0

Decorticated cotton cake

1

33 9

16 10

8 5

4 2

Undecorticated cotton
cake

2

38 7

19 3

9 7

4 9

Linseed cake .

3

30 6

15 3

7 7

3 9

Linseed ....

4

19 8

9 10

4 11

2 5

Palm-nut cake

5

31 6

15 9

7 10

3 11

Cocoanut cake

6

41 1

20 6

10 3

5 1

Rape cake

7

31 8

15 10

7 11

3 11

Beans ....

8

27 4

13 8

6 10

3 5

Peas ....

9

14 10

7 5

3 8

1 10

Wheat ....

10

13 9

6 10

3 5

1 8

Barley ....

11

15 5

7 8

3 10

1 11

Oats ....

12

13 0

6 6

3 3

1 7

Maize ....

13

14 3

7 1

3 6

1 9

Rice meal

14

12 2

6 1

3 0

1 6

Locust beans .

15

15 2

7 7

3 9

1 10

Malt ....

16

35 11

17 11

8 11

4 5

Malt culms

17

28 11

14 5

7 2

3 7

Bran ....

18

24 3

12 1

6 0

3 0

Brewers' grains, dxied .

19

6 0

3 0

1 6

0 9

» „ wet

20

21 9

10 10

5 5

2 8

Clover hay

21

16 4

8 2

4 1

2 0

Meadow hay .

22

G 5

3 2

1 7

0 9

Wheat straw .

23

6 9

3 4

1 8

0 10

'Barley straw ,

24

7 7

3 9

1 10

Oil

Oat straw

25

3 1

1 6

0 9

0 4

Mangolds

26

2 6

1 3

0 7

0 3

Swedes ....

27

2 4

1 2

0 7

0 3

Turnips ....

28

tJaAPTER X.
THE DAIRY.

Milk is a valuable agricultural product, and both it and the
substances obtained from it are of considerable commercial and
industrial importance.

Milk is the secretion of special glands in the mammalian
female, adapted to the nourishment of the newly born
animal.

The milk of different animals differs considerably in com-
position and properties. That of the cow is the most
important.

The constituents of milk may be divided into the follow-
ing:

Water.

Sugar,

Fat.

Ash.

Albuminoids.

The Fat of Milk resembles in chemical constitution the
animal and vegetable oils and fats already described in
chap. y. — i.e., it consists of the glyceryl compounds of
fatty acids. It differs chiefly in containing acid radicals of
low molecular weight in addition to the heavy acids — oleic,
stearic, palmitic, &c, — which are present in other oils and fats.
Butter fat, like all natural oils and fats, is a complex mixture
of glyceryl salts of various acids.

According to recent investigations, 100 grammes of butter
fat yield 92*73 grammes of fatty acids, containing :

182

THE DAIRY

183

Dihydroxystearic acid, H.CigH33(OH)202

Oleic acid, H.CjsJIgsOa .

Stearic acid, H-CigHsjOo

Palmitic acid, H.C16H33O2

Myristic acid, H.C,4H2702

Laurie acid, H-CigHasbj

Capric acid, H-CioHigOg

Caprylic acid, E.G^HigOa

Caproio acid, H-CgHnOa

Butyric acid, H.C4H7O2

Grammes.

0-38

44-42

3-40

14-83

16-43

5-01

119

M6

1-64

4-27

92-73

The proportions, however, are variable, but the important
fact to notice is the occurrence in milk fat of the last three or
four acids in the above list, mere traces of which are present
in other fats. These acids differ from those of higher mole-
cular weight in being volatile in steam. The proportion of
volatile acids from butter fat varies from 7*5 to 9*7 per cent*
of the fat, while in suet, for example, there is usually about
0*4 per cent, of volatile acids.

Butter fat alsoi contains traces of a substance, cholesterol,
CJ5H43OH, present largely in wool fat, and of lecithin,
C3H,(C,8H3,0,)2[HPO,.N(CH3)3C3H,OH], present in certain
seeds, especially peas and beans, and of a colouring substance
of unknown composition known as " lacto-chrome." Milk fat
melts at about 30° to 33° 0., and has a specific gravity of "930

37*8° 39*5°

at 15° C, at ^yTyo (molten) = -9118, at g^:^ = -9113. Con-
traction occurs at the moment of solidification ; hence solid
milk fat is heavier, volume for volume, than the liquid fat at
the same temperature. Milk fat, however, varies considerably
both in composition and physical properties, being affected by
the food, period of lactation, and other circumstances under
which the cows are kept. It exists in milk in the form of
minute globules varying in diameter from 0016 to '010 mm.
In the milk of Jersey and Guernsey cows the average size of the
globules is considerably larger than in the milk of Ayrshire, also
in lecently calved cows than in those far advanced in lactation.

184 ELEMENTARY AGRICULTURAL CHEMISTRY

When milk fat becomes rancid the chief changes are the
hydrolysis of a portion of the fat into free acids and glycerol.
Thus the butyric acid glyceride may decompose in this way :

C3H,(O.HA)3 + SHp = 03H,(OH)3 + SHC^H^.

The glycerol sometimes oxidises to acrolein, CJlfi, or acrylic
acid, C3H4O2. The free volatile acids give rise to the charac-
teristic odour of rancid butter. -

The Albuminoids. — Various views are held as to the
character of the albuminoids present in milk, some investi-
gators believing that there are only two, or, at the most, three,
while others declare the existence of five or more. Two,
casein and albumin, undoubtedly occur, and are the most
important.

Casein is by far the most abundant. This substance is a
white, amorphous body, tasteless and odourless, insoluble in
water, alcohol, or ether, but soluble in dilute alkalies, and in
solutions of carbonates or phosphates. It is insoluble in
dilute, but dissolves in strong, acids.

Its composition is :

Per cent.

Carbon . . . . . . . . 53-30

Hydrogen 7*07

Oxygen 22-03

Nitrogen . . . . . . . . 15"91

Phosphorus 0-87

Sulphur 0-82

Casein can be coagulated in two ways — by the addition of an
acid, or by the action of an enzyme contained in rennet. With
dilute acids the casein is coagulated unchanged and the curd
is almost free from calcium compounds. With rennet, how-
ever, the casein is split into two compounds, one of which
unites with the calcium salts (chiefly phosphate) present in
the milk and forms a curd which entangles the fat ; the other
remains in solution in the whey, but can be coagulated by
heating to 95° or 100° C. In the absence of calcium salts

THE DAIRY 185

rennet will not curdle milk. The enzyme, known as rennin^
lab, chymosiriy or pixine, acts best at 35° and is destroyed at
70° 0. It is found in the stomachs of many animals, espe-
cially in young ones, while enzymes possessing similar pro-
perties have been found in birds, fishes, many plants, and !»-♦
the products of the action of certain bacteria.

Milk Albumin resembles blood albumin. It is in complete
solution in milk, but coagulates and precipitates when the
milk is heated to 72° 0. It is readily precipitated by lead,
copper, or mercury salts, or by tannin or alcohol. It resembles
casein in composition, but contains about twice as much
sulphur and no phosphorus.

Milk Sug'ar. — Lactose or lacto-biose occurs in the milk of
all animals, but is not present in plants. It is usually com-
bined with one molecule of water, as represented by the
formula Cj3H220ij + lift. This substance crystallises in large
rhombic or monoclinic crystals, which lose water at about 130'.
It possesses a faint sweet taste, and is very soluble in hot
water. Milk sugar, like glucose, has strong reducing pro-
perties, precipitating metallic silver from ammoniacal silver
nitrate or cuprous oxide from alkaline copper salts.

By the action of hot dilute acids it combines with a mole-
cule of water and yields a mixture of glucose and galactose,
isomeric bodies of the composition CIl20H(CH0H)^.CII0.

An enzyme known as lactase can bring about the same
change.

Milk sugar does not easily undergo alcoholic fermentation,
but very readily suffers the lactic fermentation under the
influence of certain micro-organisms. The change may be
represented thus:

Ci2H,,0„ + H^O = 4C2H,(OH).COOH;

but other products are simultaneously formed, and the reaction
is doubtless much more complex. This change in the milk
sugar is the cause of milk " going sour " when kept. The

186 ELEMENTARY AGKIOULTURAL CHEMISTRY

Qecessary lactic organisms are very abundant everywhere,
especially in the neighbourhood of dairies, cow-houses, <fec.,
and as they multiply, more and more lactic acid is produced.
As milk is usually sold, the acidity is less than 0*2 per cent, lactic
acid. When about 0*4 per cent, is present the milk acquires
a sour taste, and when the amount reaches about 0"7 per cent,,
coagulation or curdling commences. After long keeping, as
much as 2*0 per cent, of lactic acid may be present.

The Ash of Milk is white, and contains the basic mineral
matter and salts of the milk, together with sulphates, phos-
phates and carbonates produced by the oxidation of the
sulphur, phosphorus and carbon contained in organic con-
stituents. Its amount in cows' milk is usually about 07 per
cent.

It contains from 22 to

27

per

cent.

of potash.

^,

„ 10 „

12

,,

,, soda.

>»

19 ,.

. 24

,,

„ lime.

»»

» 1-8,.

3

'»

,, magnesia.

t»

,, traces „

0-2

»>

„ ferric oxide.

„ 3-8 „

4-4

,, sulpiiur trioxide.

»»

22 „

27

,,

,, phosphorus pentoxide.

»»

.. 13 „

16

, ,

„ chlorine.

The lime and other bases in the milk are associated with
the casein and citric acid. The latter substance appears to be
a general constituent of cows' milk, being present usually to the
extent of 0*1 per cent. Milk contains dissolved gases, chiefly
carbon dioxide, nitre gea and a little oxygen. When fresh,
oxygen and nitrogen are the chief, amounting to from 1 to
3 c.c. per litre, but on keeping, the oxygen diminishes and
carbon dioxide appears, probably from fermentation of the
milk sugar.

Cows' Milk. Physical Properties.- A white or yellowish-
white, opaque liquor, with a sweet taste, fc^pecific gravity varies,
usually from 1-027 to 1*034:. When fresh milk is quickly
cooled and its specific gravity taken at once, then again after

THE DAIRY

187

some hours, at the same temperature, a small but decided rise
in density is observable, usually amounting to about 00005.
This, which is known as Recknagel's phenomenon, has been
explained in various ways. It has been ascribed to the
presence of air bubbles in the quickly-cooled milk, which
gradually escape ; to a molecular change in the casein ; and,
lastly, which is more likely, to the fat globules, which are
liquid at the temperature of the cow, not solidifying at once in
cooling, but remaining for some time in a super-cooled liquid
state. Since contraction occurs as the liquid solidifies, a
gradual increase of density would result from the slow solidifi-
cation of the fat globules. The maximum density of milk is
at its freezing point, about - 0'4°O.

Milk expands when heated by about '0002 for each degree C,
while its specific heat is about 0*847.

Chemical Composition. — This varies considerably according
to race, food, age, period of lactation, and even individuality
of the cow.

The mean composition, according to many thousands of
analyses, is in England :

Water
Fat . .

Sugar
Casein
Albumin
Citric acid
Ash .

87-10

3-90

4-75

3-00

0-40

010

0-75

10000

But it must be remembered that these figures, being averages,
imply the existence of many values, some above, some below
them. As a rule the fat is most liable to variation, and the
ash perhaps the most constant. In considering the variations
in the composition of cows' milk it will be advisable to discuss
in detail the influence of various circumstances.

1. Period of Lactation. — Immediately after calving, the first
product of the udder, known as " colostrum " ox *' beestings,"

ISS ELEMENTARY AGRICULTURAL CHEMISTRY

is a yellow liquid of strong, pungent taste, very different from
normal milk. It is characterised by containing small clusters
of cells known as *' colostrum granules," varying from '005 to
•025 mm. in diameter. The fat of colostrum has a higher
melting-point than ordinary milk fat, and contains less butyric
and other volatile fatty acids. Milk sugar is accompanied by
glucose, and the ash is greater and much richer in phosphoric
acid (up to 41 per cent, of its weight) and poorer in potash
than that of ordinary milk.

Colostrum has been found to contain :

Per cent.

Fat 1-8 to 4-6

Casein 2-6 „ 7'1

Albumin ll'l „ 20*2

Sugar 1-3 „ 3-8

Ash 1-2 „ 2-3

Total solids 24-3 to 32*5

Specific gravity 1*059 to 1-079

After four or five days from calving the secretion becomes
like normal milk, but the colostrum granules can usually be
found in the milk for about fourteen days after calving. The
milk during the first month after calving is generally rich in
fat and total solids, and these diminish during the second
month. After the second or third month the proportion of fat
begins to increase, as does also the milk sugar, and this goes on
as long as the cow continues to give milk. The average size of
the fat globules diminishes with advancing lactation, but their
number per unit volume increases. The proportion of vola-
tile fatty acids in the fat has been found to diminish with
advancing lactation.

The following table gives the average composition of the milk
of seventeen cows (dairy shorthorns), arranged according to
the month of lactation, embodying the results of about 700
analyses by the writer in 1900.

THE DAIRY

189

Fat.

Solids not Fat.

1
Total Solids.

Period of Lactation.

Tor cent.

Per cent.

Per cent.

[ First rnont'i

4-11

8-91

13-02

Second

3-40

8-81

12-21

Third

3-65

8-99

12-64

Fourth „

—

—

—

1 Fifth

3-70

9-00

12-70

1 Sixth „

3-82

9-08

12-90

Seventh „

—

—

—

Eighth „

4-30

9-31

13-61

Ninth „

4-35

9-37

13-72

Tenth

—

—

—

Eleventh ,,

5-48

9-65

15-13

2. Food. — The influence of the food of the cows upon the
composition of their milk is a matter upon which many varied
opinions are held. There appears to be a widespread belief
that this influence is considerable, but all experimental evidence
shows it to be very small. The quantity of milk is more
affected than the quality by change of food. There appears,
however, to be distinct evidence that a change from a ration of
wide albuminoid ratio to one of narrow albuminoid ratio is, for
a time, attended with the production of milk slightly richer in
fat, but the change is apparently only transient ; and even if
the food with the high albuminoid ratio be continued, the milk,
after allowance is made for the effect of advancing Inctation,
shows a tendency to return to its previous composition.

In any case, it appears that, provided cows are sufficiently
fed, change of food has very little effect upon the composi-
tion of their milk.

Certain foods, however, affect the character of the fat in the
milk ; thus certain oil-cakes have been noticed to affect the
properties of the butter — e.g.^ melting-point, iodine value, and
proportion of volatile fatty acids.

8. Influence of Season. — Winter milk is richest, summer
milk poorest, while in autumn and spring it is of intermediate
quality. This, however, may be partly due to influence of food
and mode of life of the animals.

19U ELEMENTARY AGRICULTURAL CHEMISTRY

4. Influence of Time of and Intervals between Milking.— -In
most cases cows are milked twice a day, morning and evening.
The intervals between the milkings are usually very unequal,
the night intervals being generally the longer. Evening's
milk is, under these circumstances, much richer in fat than that
taken in the morning. With seventeen shorthorn cows, milked
at 6 A.M. and 3 p.m., the author found as an average of 1700
analyses 3*2 per cent, of fat in morning's milk and 4-5 per
cent, in evening's milk, the animals being stall-fed. In summer-
time, July to September, the same herd, milked at the same
hours, gave an average of 2 09 per cent, of fat in the morning's
milk and 4*03 per cent, in the evening. In a third series of
experiments the numbers obtained were in the summer 2 97 per
cent, of fat in the morning and 4*31 per cent, in the evening.

The yield of milk in the morning is considerably greater
than in the evening, the ratio of one to the other being in the
cases just cited approximately inversely as the ratio of the fat
content.

If, however, cows are milked at equal intervals of twelve
hours both the yield and the average fat content become
approximately equal at the two milkings.

The author proved this by experiment with some of the cows
of the herd just referred to.

The results were as follows :

Firet Period.
Intervals 15
and 9 Hours.

Second Period

(4 weeks).

Intervals 12^

and 11^ Hours.

Third Period.
Intervals 15
and 9 Hours.

Fat in milk of five cows
per cent. . »

Yield of milk in lb. .

A.M. P.M.
2-87 4-2G
98-7 66-1

A.M. P.M.
3-18 3-80
81-6 68-8

A.M. P.M.

2-94 4-40
77-6 56-2

But it was noticed that when the change from the usual
intervals to the 12 J and 11 J intervals was made the proportion
of fat in the morning's and evening's milk was at first little

THE DAIRY

191

affected, but became more and more so as the practice of
milking at the more nearly equal intervals was prolonged.
Taking the figures for the last weeks of each period, the follovr
ing are the results :

Intervals
15 and 9
Hours.

Intervals

12jand 11^

Hours.

Intervals
15 and 9
Hours.

Fat per cent.
Yield in lb. .

Ratio, fat .
„ yield. . .
„ interval

A.M. P.M.
2-94 4-50
970 64-1

1 : 1-630
1-513 : 1
1-66 :1

A.M. P.M.
3-20 3-63
78-0 66-7

1 : 1-134
1-169 : 1
1-09 :1

A.M. P.M.

2-90 4-48
76-9 64-0

1 : 1-644
1-424 : 1
1-66 : 1

The solids other than fat do not show this variation, but are
practically the same in evening's and morning's foilk. By
milking three cows at intervals of six hours for four successive
days the following average figures were obtained :

Time of Milking.

5 A.M.

11 A.M.

5 P.M.

11 P.M.

Milk yield (lb.) . . . .
Percentage of fat in milk .

40-0
2-8

23-5
36

24-0
3-5

24-0
3-0

f

The greater richness of the milk secreted during the day, and
the large secretion between 11 p.m. and 5 a.m., will be noted.
But it may be that the unequal intervals fifteen and nine hours
to which the cows had been long accustomed had some eftect
upon their manner of secretion, and that this influence affected
them for the four days of the experiment. .

It is well know n that the first milk drawn from the udder at
milking time is very low in fat (sometimes 1-0, or even 0*5 per
cent, has been observed), while the last portion (" strippings ")
is very rich (sometimes up to 10 per cent. fat). The " fore-

192 ELEMENTARY AGRICULTURAL CHEMISTRY '

milk," too, contains very small globules of fat, while the
" strippings " or " af terings " contain large globules.

5. Influence of Breed. — It is well known that the milk of
certain breeds of cows — e.^., Guernseys and Jerseys — is very
rich in fat, while that of others — e.^r., Holderness and Holstein
Friesians — is notoriously poor in fat.

The following table gives the composition of the milk of
certain breeds, according to various observers :

Breed.

Fat.

Solids not Fat.

Total Solids.

Per ceut.

Per cent.

Per cent.

Jersey

5-6

9-7

15-3

Guernsey .

51

9-5

14-6

Welsh

4-9

9-2

14-1

Sussex

4-8

9-3

14-1

Kerry

47

9-0

13-7 .

Red-polled

4-3

8-9

13-2

Devon

4-2

9-5

13-7

Shorthorn

4 0

8-8

12-8

Montgomery

3-6

9-0

12-6

Ayrshire ,

3-6

9-4

130

American Holderness

3-6

9-1

12-6

Holstein Friesian .

3-4

8-9

12-3

Another important difference in the milks of various breeds
is in the average size of fat globules. In any one sample of
milk there are great variations in the size of these. The
average diameters of the fat globules from milk of various
breeds of cows during the whole period of lactation are,
according to American experiments, as follows :

Inch. Millimetre.

Guernsey Wrr 0-00270

Jersey ^^Vt 0-00265

Devon Txrinr 0*00245

American Holderness . . yrirs 0-00225

• Holstein Friesian . . . nrigir 0-00210

Ayrshire Tirirff 0-00205

This has an important practical effect upon the speed at
which the cream rises. The milk of the Channel Island breeds
throws up its cream very rapidly aiid such cream is well

THE DAIRY 193

suited for butter-making, while from the milk of Ayrshire
cows the cream rises very slowly.

Morning's milk is said to have larger globules than evening's
milk. The change from dry winter food to pasture in spring
is said to increase the size of globules.

Milk with large fat globules, though preferable for butter-
making, is not so well suited for cheese-making as that with
small globules. The number of fat globules per cubic millimetre
of milk has been estimated to vary from two to eleven millions.

6. Other circumstances. — But even when all known disturb-
ing influences have been eliminated milk shows considerable
variation. There is little doubt that even the average composi-
tion of the milk yielded by a cow is dependent upon the indi-
viduality of the animal, and the proportion of fat in the milk
of any individual cow is often subject to enormous changes from
one milking to the next, even when the conditions are, so far
as is possible, kept constant. The writer suggested, some years
ago, that probably these variations were due to changes in the
mental condition of the animal — i.e., her relative contentedness
or otherwise with her surroundings, food, &c. — and though the
hypothesis has given rise to some ridicule and amusement, he
still adheres to the opinion. It is well known that sexual
excitement, for example, has a marked effect upon both the
composition and quantity of the milk secreted ; it certainly
seems probable that other mental influences should act in a
similar manner, though perhaps in a different degree. Enjoy-
ment of food, comfortable housing, freedom from fright or
annoyance, say by insects or dogs, and other circumstances
affecting the placidity of existence may very probably affect
the physiological processes going on in the cow, and thus have
an influence upon the composition and quantity of the milk
secreted.

Milk of other Animals.— The following table, compiled
from various authorities, gives the average composition of the
milk of other animals ;

194 ELEMENTARY AGRICULTURAL CHEMISTRY

Solids

)

Animal.

Specific
Gravity.

Fat.

not
Fat.

Sugar.
6-8

Casein.
1-5

Ash.
0-20

Woman ....

1-031

3-3

8-5

Ass - .

1-02

7-8

5-5

1-16

0-42

Goat .

6-5

10-2

.5-0

4-3

0-90

Ewe .

1-010

53

12-4

4-2

7-1

1-00

Mare .

1-7

8-6

6-0

2-2

0-40

Camel

1-012

2-9

10-2

5-7

3-8

0-66

Hippopotamus

4-5

4-5

4-1

Trace

0-n

Sow .

4-6

11-4

3-1

7-2

1-10

Bitch

1-035

9-6

13-8

3-2

9-9

0-73

Cat .

3-3

15-0

4-9

9-5

0-58

Rabbit

•0-5

20-1

2-0

15-5

2-58

Elephant .

19-6

12-6

8-8

3 1

0-65

Porpoise .

48-5

13-1

1-3

11-2

0-57

Whale

48-7

7-7

—

7-1

0-46

A considerable difference in the behaviour of the casein of
the milks of different animals when treated with rennet (the
coagulating enzyme present in the stomach, especially of young
animals) is observable. With cows' milk rennet gives a
coherent, curdy precipitate ; with human milk or asses' milk
the precipitate is much more finely divided, and of course
smaller in quantity. This fact has an important bearing upon
the feeding of infants, who for this reason often have great
difficulty in properly digesting cows' milk. It will also be
observed from the figures given in the table that cows' milk
differs from the natural food of the human infant in containing
much more ash and albuminoids and much less milk sugar.

Preservation of Milk. — Fresh milk is an important
article of diet, and it is a matter of great interest to be
able to supply it in a cleanly and uncontaminated state to
the consumer. This is rendered the more diflScult by the
fact that milk serves as an excellent medium for the growth
of micro-organisms, which by their life-processes effect pecu-
liar chemical changes in several of the constituents. Milk
sugar is particularly liable to undergo decomposition, being

THE DAIRY 195

changed into lactic acid by micro-organisms which are very
widely distributed.

In the udder, under normal conditions, milk is free from
micro-organisms, but, unless special precautions are taken, in
a short time after milking it becomes highly charged with
them. The micro-organisms find their way into the milk
from the air, the hands of the milker, the teats and hair
of the cow, and, too often, from the vessel in which the milk
is collected.

Milk, as drawn from the cow, is at a temperature highly
favourable to the multiplication of the micro-organisms, and
the number present after any given time is largely dependent
upon the temperature at which the milk is stored. Thus
milk stored for fifteen hours at 15° 0. was found to con-
tain about 100,000 bacteria per cubic centimetre j another
portion, stored for the same period at 25°, contained
72,000,000 organisms per cubic centimetre ; while a third
sample, kept at 35°, contained 165,000,000 per cubic centi-
metre.

The micro-organisms which find their way into milk are of
various kinds; generally the lactic organisms predominate, so
that, usually, the first evidence of change is the production of
lactic acid — i.e., the milk becomes " sour." As the quantity of
lactic acid increases the casein is coagulated, and the milk is
said to " curdle." This generally occurs when the amount of
lactic acid reaches about 0-7 per cent., or with less acid if the
milk be heated.

Other bacteria also sometimes find their way into milk,
some of them dangerous to the health of the drinker. Out-
breaks of typhoid, cholera, diphtheria, diarrhoea and other
diseases have been traced to contaminated milk. Tuberculosis
has also been proved to be conveyable by milk. Milk, too, has
a great aptitude to absorb gases and vapours, and, in conse-
quence, readily acquires odours and flavours from the air.

The necessity of perfect cleanliness in the cow-house and
dairy is thus evident, if the milk is to be kept sweet and pure.

196 ELEMENTAEY AGRICULTURAL CHEMISTRY

But it is impracticable to keep milk free from access of
micro-organisms, especially such widely distributed ones as the
lactic bacteria.

The methods to be adopted in preserving milk are, there-
fore, based upon either the destruction of the micro-organisms
which have entered it or the prevention of their growth.

The second of these methods, the prevention of the growth
of the micro-organisms, cannot be done perfectly, but if the
temperature of the milk can be kept low the growth is slow
and the milk will keep for some days. Rapid cooling, after
milking is of great importance, as multiplication of the
micro-organisms goes on very quickly in warm new milk.

In order to destroy the organisms which have gained access
to milk recourse may be made to either of two methods :

1. Sterilisation by heat.

2. The use of antiseptics.

To effect complete sterilisation — i.e., the destruction of all
bacteria and their spores — by heat requires a high temperature
(about 115° C), which can only be applied to milk under
pressure, and unfortunately this produces undesirable chemical
changes in the milk. Some of the sugar is turned brown, the
albumen and a portion of the calcium citrate are precipitated,
a peculiar burnt or cooked flavour is imparted and the casein
becomes less readily coagulable by rennet. The fat rises more
slowly and a very small quantity of richer cream is obtained.

In order to avoid these disadvantages a modified process
known as Pasteurisation is often substituted for sterilisation.
The milk is heated to only G0° or 80° C, whereby its flavour
is hardly affected and the active bacteria are killed, though
the spores are not. It fortunately happens that the micro-
organisms to which the souring of milk is due- viz., the
lactic bacteria — do not readily form spores, so that Pasteurised
milk will usually keep sweet and good for some days. Occa-
sionally, however, spore-forming bacteria are present in milk,
and it may happen in such cases that the milk very soon

THE DAIRY 197

curdles, and even putrefies, after Pasteurisation. A case of
this kind recently came under the writer's notice near Pretoria,
the injurious organisms being Bacillus subtilis and allied species.
The trouble arose from the very dusty condition of the kraals
in which the cows were milked, and after Pasteurisation the
milk did not keep as well as un-Pasteurised milk, becoming
curdled without the formation of acid. In this case the
destruction of the lactic organisms was apparently complete,
and in their absence the spores of Badllas subtilis multiplied
more rapidly than if they (the lactic organisms) had been
present, and thus led to the coagulation of the casein without
souring. In some cases the coagulum redissolved on further
standing, but the milk soon became repulsive in appearance
and flavour.

Fortunately, as most of the pathogenic organisms likely to
occur in milk do not form spores. Pasteurised milk is generally
safe from risk of conveying contagion.

The most satisfactory method of distinguishing sterilised or
Pasteurised milk from fresh milk is by a determination of the
soluble albumin. In fresh milk this amounts to about 0*4 per
cent., while in milk heated to about 70° 0. only about 0*25
per cent, will remain, and if the milk be heated to 80° C. the
whole of the albumin is coagulated and precipitated.

Fresh milk also contains an enzyme, which with para-
phenylene diamine, CgH4(NH2),, and hydrogen peroxide gives a
blue colour. In Pasteurised milk this enzyme is largely
destroyed, while in sterilised milk it is entirely absent.

Preservation by Antiseptics. — By adding various sub-
stances to milk the growth of the micro-organisms can be
greatly impeded, so that the milk becomes sour much more
slowly. The amounts of the antiseptics added, however, can
never be suflicient to destroy pathogenic organisms, and thus
render milk safe from a hygienic standpoint. Moreover, it is
probable that the presence of antiseptics in milk renders it
less digestible.

198 ELEMENTARY AGRICULTURAL CHEMISTRY

The chief *' preservatives " used are :

1. Boric acid, HBO3, or borax, NagBPy.lOHjO.

2. Salicylic acid, CeH,(OH).COOH.

3. Formaldehyde, H.CHO.

4. Sodium carbonate, NagCOj.

5. Glycerine, C3H,(OH)3.

6. Benzoic acid, C;H,.C00H.

7. Beta-naphthol, Ci^HfiK.

No. 4, sodium carbonate, is not a true preservative, since it
does not prohibit the activity of the lactic acid organisms, but,
indeed, rather favours their action. However, by neutralising
the lactic acid as fast as it forms it postpones the curdling of
the milk. Its presence is readily detected by ashing some of
the milk and adding hydrochloric acid, when an effervescence
will /show the presence of carbonates.

The favourite preservatives are formaldehyde and boric
acid.

Formaldehyde is a gas, very soluble in water. A solution
containing 4.0 per cent, of real formaldehyde is commercially
known as ** formalin," and is the origin or source of many
commercial milk preservatives. These substances usually
contain from 1 to 6 per cent, of real formaldehyde in water,
and they are generally added in the proportion of about
1 ounce to 10 gallons of milk. The milk thus receives 1 part
of the real preservative to from 20,000 to 50,000 of milk.
Even in these small proportions the preservative power is
remarkable, but this increases greatly as the quantity added is
increased; thus 1 part of formaldehyde in 50,000 of milk
extended the time required for curdling from 36 hours to 66
hours, the mi k being kept at 20° C. 1 part in 20,000
extended the time required for curdling to 96 hours, while 1 in
10,000 required 5J days, 1 in 5000 10| days, and 1 in 2500
kept the milk from curdling for 55 days. It is very doubtful
whether formaldehyde is as efficacious in destroying pathogenic
germs as it is in preventing the lactic fermentation.

THE DAIRY 199

Formaldehyde may be detected in milk by adding to a small
quantity of the milk an equal volume of strong hydrochloric
acid containing about 2 per cent, of a 10 per cent, solution of
ferric chloride. The mixture is heated gradually to the boiling-
point, when a violet colouration is produced if formaldehyde be
present. Pure milk slowly becomes brown under this treat-
ment. 1 part of formaldehyde in 250,000, it is said, can be
detected by this test.

Boric acid and borax have long been used for preserving
milk in hot weather. They are not nearly so effective as
formaldehyde, and have to be added in much larger propor-
tions; thus 1 part of a mixture of boric acid and borax
added to 2000 parts of milk had scarcely any preservative
action at 20°, 1 in 1500 extended the period before curdling
from 36 to 66 hours, 1 in 1000 to 72 hours, and 1 in 500 to
96 hours.

Boric acid can be detected by ashing the milk (best after
addition of lime), acidifying with a little dilute hydrochloric
acid, and immersing in the liquid a strip of turmeric paper. On
drying, the paper turns red if boric acid be present, and on
moistening with very little caustic soda, takes a greenish-black
colour.

The other preservatives are rarely used.

Products Derived from Milk.

The foUow^ing substances must be very 'briefly considered
here :

Cream,

Milk powder.

Skimmed milk.

Cheese.

Butter.

Whey.

Condensed milk.

Crc^m. — The fat, being specifically lighter than the aqueous
portion of milk (sp. gr. of fat at 15° =» 0-930, that of the rest
of the milk about 1*030), tends to rise to the surface. The
resistance to the motion of the small globules is large, while

200 ELEMENTARY AGRICULTURAL CHEMISTR^T
their buoyancy is small ; consequently the rise of the fat is a
slow process, slower in milk possessing very small globules — e.g.,
the milk of Ayrshire cows — quicker in milk with large fat
globules — e.g., Jersey or Guernsey milk.

The fat, however, in any case, does not separate completely
from the aqueous portions. The globules simply become more
crowded together near the surface than they are lower down
in the body of the milk. The upper layer on milk which has
stood at rest tor some time is known as cream, and is very
variable in composition, according to the state of accumulation
of the fat globules. There is, however, a fairly sharp line of
separation between the cream and the rest of the milk.
Cream can be separated from milk by gravitation, or by substi-
tuting for gravitation the much greater force produced by
rapid rotation.

There are two methods employed in the former, viz. :

Shallow setting.
Deep setting.

By the former the milk is placed in shallow vessels to a
depth of from 2 to 4 inches, cooled to about 15*5° C, and kept
at that temperature for twenty-four or thirty-six hours. The
cream layer is then removed, either by means of a shallow
spoon-like vessel, known as the skimmer, or sometimes by
running oflf the milk into another vessel through a hole at the
bottom of the creaming pan.

By the deep-setting system the milk, while still warm, is
placed in cylindrical vessels, usually about 8 to 12 inches in
diameter and 15 to 20 inches deep, which are then immersed in
ice-cold water. Under these conditions the creaming will be
practically complete in twelve hours.

The explanation of the effectiveness of deep setting is some-
what difficult. Since fat expands and contracts with changes
of temperature more rapidly than water, the effect of cooling
upon milk would be to lessen the difference in specific gravity
between the fat and water, and on that account would make

THE DAIRY 201

the rise of the cream slower. To ascribe, as has been done, the
effect to the difl'erence in conductivities for heat of fat and
water, and to assume that the fat globules remain at a higher
temperature than the watery liquid surrounding them, is
absurd. Neither is it due to a change in the viscosity of
the milk, for this is much greater at low than at high
temperatures.

The two causes which are probably most influential are the
setting up of gentle convection currents in the milk during the
time the temperature is falling, and the fact that the fat
globules remain liquid for some time after cooling, and while
liquid are of lower specific gravity than when solidified. The
milk in contact with the cooling wall of the can contracts,
becomes heavier, and sinks slowly to the bottom, the warmer
and therefore lighter milk rising in the central portion of the
can and flowing outwards near the surface towards the walls,
and again sinking. Thus a slow circulation takes place, nearly
all the milk rising in the centre, flowing outwards, and sinking
down near the walls. The fat globules are thus brought in
turn near the surface, and all the time, by virtue of their levity,
they tend to accumulate there, the very gentle currents pro-
duced by convection not being sufficient to drag them down.

The eflfect of super-cooling the liquid fat has already been
alluded to in the explanation of Recknagcl's phenomenon
(p. 187).

Separators. — By imparting very rapid rotation to milk, the
magnitude of the centrifugal force thus set up may be made
immensely greater than the force of gravity. Consequently
the separation of the heavier portion of the milk from the
lighter part takes place much more quickly. The construction
and details of the various forms of separators cannot be
described here, but they all depend upon the general principle
that by rotating milk, previously warmed so as to become more
mobile, at the rate of several thousand revolutions per minute
the aqueous portion of the milk accumulates near the walls of
the vessel furthest from the axis of rotation, while tlie fat

202 ELEMENTARY AGRICULTURAL CHEMISTRY

globules tend to accumulate on the inner surface of the
revolving mass — i.e., near the centre. By providing suitable
outlets the skimmed milk can be directed into one channel,
and the cream into another, and by adjustment of the size of
one of these openings, thick or thin cream can be obtained
at will.

Composition of Cream. — Cream varies enormously in com
position, the proportion of fat varying from as low as 10 per
cent, to as high as 60 or 70 per cent. By shallow setting a
product containing from 15 to 40 per cent, of fat is usually
obtained ; at low temperatures* about 20 per cent, of fat is
present. With the separator almost any desired proportion of
fat may be obtained. Usually the amount of the "solids not
fat" in the aqueous portion of the cream is slightly higher
than in milk, due probably to a slight loss of water by evapora-
tion during setting, though possibly also to the fat globules
holding around them by surface attraction a layer of liquid
slightly richer in casein, &c., than the rest of the aqueous
portion of the milk.

In Devonshire " clotted cream," prepared as it is by heating
the milk during setting, the amount of evaporation of the
water is probably considerable. Such clotted cream usually
contains about 58 per cent, of fat, 34 per cent, of water,,and
about 8 per cent, of solids not fat.

Although the specific gravity cannot conveniently be deter-
mined directly if the cream contains more than 30 per cent, of
fat, yet, according to Richmond, the proportion of fat can in
most cases be calculated from the specific gravity, thus :

F = 32-0 - 0-892^,

where F = per cent, of fat,

G = lactometer reading

(i.e., specific gravity x 1000 - 1000),
D = true specific gravity.

Separated cream is always thinner in consistency than

THE DAIRY 203

skimmed cream of the same fat content, and is sometimes
thickened by the addition of " viscogen," made by mixing
2 J parts of cane sugar, 1 of quicklime, and 8 of water. About
1 oz. of the clear solution will thicken a gallon of cream.

Skimmed Milk varies in composition according to the more
or less complete removal of the fat.

Skimmed milk from hand-skimming usually contains about
06 per cent, of fat, but may contain as much as 2 per cent.
Separated milk usually contains from 005 to 0-15 per cent, of
fat. In consequence of the removal of fat the percentage
amounts of the other constituents are slightly higher than in
the original milk. Thus milk of the average quality given on
p. 187 might be expected to yield with a good separator
skimmed milk of about the following composition :

Water 90-54

Fat 0-10

Sugar . . . . . . . . 4-91

Casein 3*11

Albumin 0'42

Citric acid 0*10

Ash 0-79

100-00

Skimmed milk contains a valuable amount of food-stuffs, and
should be utilised on the farm for feeding pigs or in other
ways. Separated milk, though poorer in fat, has the advan-
tage of being sweet and of keeping better ; by the addition of
cod-liver oil it has proved successful in calf-rearing.

Butter. — When cream or milk is agitated for some time the
fat globules coalesce and butter separates out in irregular
masses, which consist of almost continuous fat, very few of the
original globules remaining. The spherical globules visible in
butter under the microscope consist of minute drops of butter-
milk or water enclosed in the fat.

Churning is a purely mechanical process : the fat globules
collide, adhere, and the large, irregular masses thus formed in

204 ELEMENTARY AGRICULTURAL CHEMISTRY

turn knock against each other or against other fat globules
and cohere. Portions of the aqueous liquid, butter-milk, are
enclosed in the masses of fat. During the *' working " of the
butter the butter-milk is more and more pressed out.

The best temperature for churning depends upon the melting-
point of the fat in the particular sample of cream churned.
Thus when cotton-cake has been used as food for the cows the
melting-point of the butter-fat is raised, and churning should
be done at a higher temperature. So, too, with " ripened " or
sour cream a slightly higher temperature than with sweet
cream is suitable. From 8° to 18° C. (46° to 65° F.) is the
greatest range usually employed, and in most cases from 10°
to 15-5° 0. is chosen (50° to 60° F.). Churning takes place
more readily at the higher temperature, but the resulting
butter will not be so free from casein nor the butter-milk
so free from fat as when the operation is done at a lower
temperature.

Freshly separated cream is sometimes churned, but it is
generally admitted that the best flavour and aroma in butter
can only be obtained by the use of properly ripened cream — i.e.,
cream to which the lactic organisms have either gained access
spontaneously or, as is preferred in modern practice, have
been added in the form of a " starter " of sour skimmed milk
or some pure culture of the lactic organisms. The degree
of "ripeness" which is probably best corresponds to about
0-5 per cent, of lactic acid ; but the acidity most suitable
depends to some extent upon the flavour desired in the butter.
If the cream be over-ripe the casein present may be com-
pletely coagulated, and on churning is found as white specks
or flakes in the butter, thus spoiling its appearance, and also
rendering it liable to contract unpleasant flavours and rancidity
on keeping.

Salt is usually added to butter, serving both as a condiment
and as a preservative, the proportion varying from a mere
trace up to 6 or 7 per cent.

Composition of Butter. — The main constituent is, of course,

THE DAIRY 205

fat, but in addition water, casein, milk sugar, and ash are also
present.

The amount of fat is usually about 80 to 86 per cent., water
about 11 or 12 per cent., casein from 0*6 to 1*5 per cent., salt
from O'l to 4-0 per cent. Salt butter often appears to be wetter
than fresh butter, but is generally lower in water content.

" Pickled " butter is made in Ireland by warming and knead-
ing it in brine, when the resulting butter often contains a high
proportion — 16 to 20 per cent. — of water.

By the present Sale of Butter Regulations (Britiyh) it is
unlawful to sell butter containing more than 16 per cent, of
water.

So-called "milk-blended" butters, prepared by kneading
butter in milk, usually contain an excessive quantity of water
and a high proportion of casein.

In America rancid butter is sometimes converted into what
is known as "renovated," "process," "boiled," "aerated,"
or " sterilised " butter. This is done by melting the butter,
separating the fat from the casein, water, tkc, blowing air
through the fat to remove the unpleasant smell, and then
churning the liquid fat with milk until an emulsion is formed.
This is quickly cooled in ice, and a granular mass is obtained.
This is then "worked," salted, and made up ns butter.

" Oleo-margarine, " *' Margarine," or "Butterine." — This
product, which is intended as a substitute for butter, is made
by churning so-called "oleo oil" with lard, milk, sometimes a
little butter, and occasionally cotton-seed oil or pea-nut oil, in
a warm state, quick.'y chilling the mixture, salting, " working,"
and treating it like butter, colouring-matters — e.g.., annatto —
being sometimes added.

The " oleo oil " is made from beef fat by melting, carefully
clarifying, and aPowing it to stand at a temperature of about
30° C. The semi-solid mass which results is then separated
by a press into solid stearin and a liquid composed of olein
and palmitin.

Pure butter can be distinguished from ** renovated" butter

206 ELEMENTAKY AGRICULTURAL CHEMISTRY

and from margarine by its behaviour when heated, say in a
test-tube or basin, over a flame. Pure butter ** boils " quietly,
but with much frothing or foaming, while *' renovated " butter
and margarine bump and splutter violently, but do not froth.

The chief reliable chemical difference between genuine butter
and margarine is in the proportion of volatile fatty acids
present.

Butter-milk varies in composition ; in general it resembles
skimmed milk, but is usually sour. It contains from 0'3 to
3 '5 per cent, of fat, 4 to 5 per cent, of sugar, 3 to 4 per cent,
of albuminoids, and 0'7 to 0"8 of ash. It finds a limited use
in the kitchen, but the greater part is employed as food for
pigs.

Condensed Milk and Milk Powder.— Though the prepa-
ration of condensed milk forms no part of the work of the farm
or dairy, it may be of interest to explain briefly the character
and method of preparation of this and similar products.

Condensed milk is prepared by boiling milk in vacuum pans
until its volume is diminished to about one-third or one-fourth
of the original. In many brands cane sugar is added in large
proportion, whereby the product keeps better, even after the
tins are opened. In other brands, often known as " evapo-
rated cream,"* no cane sugar is added. The composition of
such products varies considerably, the fat especially being
liable to great fluctuation. The following analyses may be
taken as typical ;

Un-
Sweetened, sweetened.

Water 257 717

Fat 107 8-1

Proteids 8-5 87

Milk sugar 11-9 9-9

Cane sugar 41*9 —

Ash _1;3 1-6

1000 100-0

* The term " cream " cannot now b^ legalljr uged for such products.

THE DAIRY 207

Milk powder is made by evaporating milk in thin layers in
a current of warm air and scraping off the film. So far as
the writer can ascertain, the yellowish- white powder which is
sold as dry milk contains less fat in proportion to the other
constituents than would be present in the residue from whole
milk.

Cheese is produced from milk by the coagulation of the
casein, which carries down with it almost all the fat, leaving
the albumin and sugar in the whey. This curd is separated
from the whey as fully as possible, pressed and allowed to
" ripen."

The coagulation of the casein is usually effected by the
action of rennet, but it may be produced by acids — e.g., by
the lactic acid resulting from the action of the lactic organisms
on the milk sugar. This is sometimes done in the pre-
paration of cream cheese. The curd and whey produced from*
whole milk by rennet have approximately the following
composition :

Curd. Whey,

Water 50-0 92-04

Fat 26-7 0-35

Sugar 2-3 6-10

Casein 20-0 0*46

Albumin Trace 0-46

Ash 1-0 0-69

100-00 100-00

Rennet acts most rapidly at a temperature of about 39° or
40° C. (102° to 104° F.), and then gives a firm and hard curd,
while in cooler or hotter milk — up to 50° 0. ( = 122° F.) — the
curd formed is soft.

Sofl cheeses are made by coagulating the milk at 25° to 80° 0.
(77° to 86° F.), and always contain much moisture.

Hard cheeses result when the curd forms in milk at about

o

208 ELEMENTARY AGRICULTURAL CHEMLSTRY

35° C. (95° F.). Some of the better qualities of hard cheese
are made from enriched milk — i.e,, from a mixture of milk and
cream — others from whole milk, others from a mixture of whole
and skimmed milk, while some poor, horny cheeses are made
from skimmed milk.

It would be beyond the scope of the present volume to
attempt to describe the varieties of cheese and their methods
of manufacture.

The practice usually followed is to " ripen " the milk — i.e.,
to impart the necessary acidity, often corresponding to about
0*2 per cent, lactic acid — by adding to it a " starter " consisting
of sour milk or a pure culture of lactic organisms, then to
add the necessary amount of rennet, the milk being previously
warmed to the proper temperature. When coagulation occurs,
which should be in from twenty to forty minutes, the tempera-
ture is raised to the optimum temperature, about 37" or
38** C, and kept at that for some time, usually one or two
hours. The whey is then run off, the curd stirred and cut,
and lastly broken in a mill, salted and pressed into moulds.
The cheeses are then ripened at a temperature of 15**
to 20° 0.

^ During ripening many changes of complex character occur ;
the sugar is converted into lactic acid, water evaporates and
the casein is converted into more digestible nitrogenous
bodies of the nature of albumoses and peptones. These
changes, according to one view, are produced by the lactic
organisms, while another theory ascribes them to enzymic
action, the enzyme being probably mainly galactase^ which is
said to be present in all milk, and possesses the power of
peptonising casein.

Whatever may be the cause of the change, there can be
no doubt that in well-ripened cheese a considerable portion
of the casein is converted into albumoses, peptones, amides
and even ammonia. In most analyses, however, the
whole of the nitrogen present is expressed as being pre-
sent as casein, though in fully ripened cheese perhaps not

THE DAIRY

209

more than 14 or 15 per cent, is actually present in tViat form.
Pasteurised milk or sterilised milk cannot be used in cheese-
making. ^

The average composition of various cheeses, according to
American analyses, is given in the following table :

Water

Casein.

Fat.

Sugar.

Ash.

Per cent

l\r cent

Percent

Percent

Per cent

Cheddar ....

34-4

26-4

32-7

2-9

3-6

Cheshire ....

32-6

32-5

26-0

4-5

43

Stilton ....

30-4

2S 9

35-4

1-6

3-8

Edam ....

36-3

24-1

30-3

4-6

4-6

Roquefort (sheep's milk) .

31-2

27-(;

33-2

2-0

G-0

Swiss ....

35-8

24-4

37-4

—

2-4

Brie (cream cheese)

60-4

17-2

25-1

1-9

6-4

In some of the American States " standards" of fat content
for various classes of cheese were, some few years ago, estab-
lished by special law.

Thus "full cream" cheese must contain at least 32 per cent.
of milk fat, "three-fourths cream" cheese at least 24 per
cent., "one-half cream" cheese not less than 16 per cent.,
"one-fourth cream" cheese at least 8 per cent, of fat. All
cheeses containing less than 8 per cent, of milk fat must be
labelled " skimmed milk cheese."

In some cases cheese is adulterated by the addition of
foreign fat — e.g.^ lard — and such cheese is generally known as
" filled cheese." ~^

The characteristic ingredient of cheese is casein, but the
commercial value depends rather upon the percentage of fat
present than upon the richness in casein. Stilton cheese is
made from milk enriched with cream ; Cheddar, Cheshire,
Wensleydale, Gorgonzola and Gruy^re are made from whole
milk ; while Parmesan, Gloucester and Edam are made from
partially skimmed milk.

210 ELEMENTARY AGRICULTURAL CHEMISTRY

English cream cheese is usually made without rennet, and
varies greatly in composition — water from 20 to 55 per cent.,
fat from 40 to 80 per cent., casein from 3 to 19 per cent.

Whey. — As already stated, whey contains almost all the
milk sugar originally present in the milk, together with small
quantities of albumin, casein, fat and ash constituents.

It is usually utilised as food for pigs, but sometimes in the
manufacture of milk sugar.

CHAPTER XI.

MISCELLANEOUS.

In this chapter a description will be given of various sub-
stances used on the farm which do not come under the category
of the materials discussed in the preceding chapters.

The subjects to be dealt with are numerous and diverse, so
that no attempt can be made to attain any continuity or
logical order.

For convenience we may consider in turn the chemical
nature of the substances used as

I. Disinfectants and antiseptics ;
II. Fungicides;

III. Insecticides;

IV. Plant poisons ; and, lastly, those used for
V. Other purposes.

I. Disinfectants and Antiseptics.— A real disinfectant

is a substance which destroys the micro-organisms (and their
spores) which give rise to putrefaction, disease, or other chemical
changes. An antiseptic is a body which prevents their growth,
but may or may not destroy them. All disinfectants are thus
antiseptics, but all antiseptics are not disinfectants.

A great many substances act as disinfectants in strong solu-
tion, but obviously only those which by their presence in
relatively small quantity act destructively on micro-organisms
are worthy ^f consideration under this heading.

Powerf ul disinfectants are found among chemical compounds
of very different types, and no perfectly satisfactory method

211

212 ELEMENTARY AGKiCULTURAL CHEMISTRY

of correlating chemical and physical properties with germicidal
action is known. The following classification is perhaps one
of the best suggested :

1. Free acids or salts of acid reaction retard the growth of
micro-organisms.

2. Soluble salts of many heavy metals — e.g., mercury and
copper — precipitate albuminoid?. Such compounds probably
act upon the protoplasm in the organisms

3. Such salts or other substances — e.g., charcoal — by ren-
dering albuminoids insoluble, may deprive the bacteria of
food, and thus kill them by starvation.

4. Reducing agents — e.g., sulphites, ferrous salts — remove
oxygen from the medium, and thus destroy aerobic organisms
— i.e., those which require oxygen.

5. Oxidising agents — e.g., chlorine, ozone, hydrogen- per-
oxide, permanganates — destroy by oxidation both the
bacteria and their food, and thus form the most perfect
disinfectants.

6. Some metallic salts are assimilated by l^cteria, and the
metal is deposited within their tissues. In this way gold and
silver salts act as disinfectants, provided they are present in
sufficient quantity.

7. Some substances act as germicides for no apparent
chemical reason. To this class belong boric acid, the borates,
and some of the aromatic compounds.

By a disinfectant we usually mean a substance used for
killing noxious micro-organisms in substances which are not
used for food, while an antiseptic is used to arrest putrefactive
changes without rendering the substance to which it is applied
injurious to animals.

A large number of substances possessing disinfecting pro-
perties exists, and new ones are continually being introduced.
On the farm disinfectants are chiefly used for destroying the
ri:?k of infection after outbreaks of contagious diseases. The
following are among the most important substances which can
be used for this purpose.

MISCELLANEOUS 2l3

Bleaching Powdevj or " chloride of lime," Ca(OCl)Cl. This
substance may act in two ways :

1. By evolving hypochlorousacid, HCIO, which is a powerful
oxidising agent and readily destroys putrescible matter and
bacteria. The liberation of hypochlorous acid is effected by
the carbon dioxide of the air :

2Ca(0Cl)Cl + CO, + H,0 = 2HC10 + CaCl, + OaCO,.

2. By evolving chlorine, which is a powerful disinfectant.
The evolution of chlorine occurs when bleaching powder is
acted upon by any acid — e.g.^ dilute sulphuric acid :

Ca(OCl)Cl + H3SO, = CaSO, + H,0 + CI

If a building is to be disinfected by means of chlorine about
2 lb. of bleaching powder for each 1000 cubic feet of space should
be placed in an earthenware bowl or vessel, and then a pre-
viously cooled mixture of 1 J lb. of oil of vitriol and a gallon
of water poured upon it, and the windows and doors closed as
quickly as possible. This will yield gas enough to form nearly
0*5 per cent, of the atmosphere in the room, and this is suffi-
cient to kill micro-organisms, though possibly some spores may
escape destruction.

Sulphur Dioxide J SO,, is a much-used disinfectant. It gives
rise to the well-known smell of burning sulphur, and is soluble
in water, forming a solution of sulphurous acid, H3SO3. It is
a strong reducing agent, and acts upon many organic sub-
fctances, producing colourless compounds, and is therefore
often used for bleaching wool, straw, <fec. By strong pressure
it can be liquefied, and liquid sulphur dioxide, under a
pressuie of three or four atmo.'phares, is now commercially ob-
tainable in glass siphons or in metal cylinders. In this form
it can very conveniently be used for disinfecting purposes,
but the gas is usually made by burning sulphur in air. The
sulphur should be either in the form of " candles " — i.e., short
cylindrical cakes provided with a wick — or roll sulphur, which
can be readily set on fire if placed in metal dishes just pre-

214 ELEMENTARY AGRICULTURAL CHEMISTRY

viously moistened with the very inflammable carbon disul-
phide. About 1 lb. of sulphur to each 1000 cubic feet of space
will probably be the most suitable quantity to use for fumigation.

Carbon Bisulphide, a very volatile and inflammable liquid
of ofiensive odour, gives off a vapour which is very poisonous
both to animals and to micro-organisms, but its readiness to
catch fire and its explosibility when mixed with air render it
too dangerous for use on the large scale. Its temperature of
ignition is so low — about 150° C, that a glowing splint or a
burning cigarette is sufficient to ignite a mixture of its vapour
with air.

The above are gaseous disinfectants, and are thus readily
brought into contact with the material to be disinfected.
Many liquid preparations are in use for disinfecting purposes,
some of them volatile, and therefore giving off disinfecting
vapours.

/^/ie?zo?,CgH^OH,or*'carbolicacid,"andCre5oZ,CeH,(CH3)OH,
contained in coal-tar or wood-tar, have long been used as dis-
infectants. Pure phenol is a colourless, crystalline substance,
melting at 41° C. and boiling at 182** C. Often, however,
it is used in the form of a liquid (a hydrate), and is soluble
in about fifteen times its weight of water.

With alkalies phenol forms salts, " carbolates," which are
much more soluble in water, and are readily decomposed by
acids (even by carbonic acid), yielding free phenol again.
Many of the " disinfecting " powders of commerce consist of
gome indiflferent powder, silica, silicates, or sometimes of lime
or magnesia, to which about 15 per cent, of phenol has been
added.

Creasote is a mixture of cresol, C,II^{CH3)0H, xylenol,
CgH3(CIl2)20H, and other members of this series, and is largely
used for preserving timber.

Lysol is an alkaline (potash) compound of tar oils and fat.
It is soluble in water, and owes its disinfecting powers mainly
to cresol.

Wood Creasote is obtained from wood - tar, and con-

MISCELLANEOUS 215

tains phenol, cresol, guaiacol, C,H^(0CH3)0H, and creosol,
0,H,(CH3)OOH30H.

" FoTTnalin" the commercial name for a 40 per cent solution
of formaldehyde, HjCO, in water, is a very powerful disin-
fectant. Formaldehyde is a gas, and from strong solutions,
if exposed, it escapes into the air. A solution of 1 part of
this substance in 10,000 of water will prevent the growth
of many micro-organisms, while 1 in 100 gives absolute
sterility.

Formalin is too expensive to be used for true disinfecting
purposes, but is largely used for the prevention of decay in
food materials.

The above, though used in the liquid or solid form, are
volatile, and to some extent exert a disinfecting action upon
substances near but not actually in contact with them.

The following substances, used as disinfectants, are non-
volatile, and only affect those substances with which they
or their solutions actually come into contact :

Potassium Permanganate^ KMqO^, or the sodium salt,
NaMnO^, and the manganates — e.g., K,MnO^ — are extremely
powerful oxidising agents, and soon destroy organic matter and
micro-organisms. Solutions of these salts are the active ingre»
dients in " Condy's Fluid."

Zinc Chloride, ZnClj, is a caustic and deliquescent solid. A
strong solution (about 50 per cent.) constitutes " Bur-
nett's Disinfecting Fluid," and is often used as a wood-preser-
vative.

Copper Sulphate, "blue vitriol," or "blue-stone," CuSO^.SII^O,
is sometimes used as a disinfectant, but is somewhat expensive.

Mercuric Chloride, " corrosive sublimate," HgCl^, is a very
efficient disinfectant, but is very poisonous. It is largely
employed in surgical operations.

As antiseptics, several substances, in addition to those
described under " Disinfectants," are employed :

Boi-ic Acid, or Boracic Acid, HaBOs, is a sparingly soluble,
crystalline, solid substance, almost devoid of taste. It is often

irl6 ELEMENTARY AGRICULTURAL CHEMISTRY

employed as a preservative of food-stufFc>— e,^., milk, cream — -
and in surgery.

Borax, NagB^Oy.lOH^O, is used for similar purposes, and
sometimes as a poison for cockroaches.

Salicylic Acid, CgH^(OH).COOH, is also sometimes added as
a preservative to milk, cream, canned fruits, fruit syrups, &c.

II. Fungficides. — A fungicide is a plant poison — in fact,
a disinfectant — but used under such conditions that while
destructive to the low forms of plant-life — the fungi — it does
not injure the higher plants. In fact, a fungicide might be
defined as a differential plant poison, strong enough to kill
some forms of plant-life, bub too weak to destroy others.

A fungicide is usually employed to destroy micro-organisms
which are liable to attack cultivated plants, and may be applied
to the seed, stem, or foliage, as the case requires. Amongst
the substances used as fungicides the following are the most
important :

{a) Copper Salts. — These salts are, when in solution, very
injurious even to the higher plants. The starting-point of
nearly all copper fungicides is copper sulphate, or " blue
vitriol," CuSO^.SHgO. This is a blue crystalline substance
of specific gravity 2-28, readily soluble in water to a blue
solution.

100 parts of water at 0° 0. dissolve 31*6 parts of the salt.
10° „ 37-0 „

20" „ 42-3 „

100° „ 203-3 „■ „

A 2 per cent, solution of the salt has a specific gravity of
1-0126, a 4 per cent, solution 1-0254, and a 6 per cent, solution
1-0384.

A solution of copper sulphate has long been used ioi
** pickling " seed wheat for the prevention of the fungoid
diseases smut, rust and hunt. A common practice is to
thoroughly wet each quarter of wheat with 2 gallons of
water in which 2 lb. of "blue vitriol" has been dissolved.

MISCELLANEOUS 21 7

The grain is dressed with this liquid about twenty- four hours
before sowing. The spores of the fungi which niay be on the
grain are thus destroyed, and the thin film of sohible copper
sulphate which remains on the wheat is converted, probably
mainly by the calcium carbonate of the soil, into insoluble
compounds soon after sowing, and before the wheat germinates.
If this conversion of the copper into insoluble compounds did
not occur the wheat would probably be killed by the treat-
ment. In America the grain is soaked for twelve hours in a
solution of 1 lb. of copper sulphate in 24= gallons of water, and
then for five minutes in lime-water.

Copper sulphate is also employed for spraying the foliage of
plants for the prevention of fungoid diseases. For this purpose
a solution not stronger than 1 lb. of the salt in 20 gallons of
water should be used, or the leaves will be injured.

Copper sulphate has also been used for the destruction of
certain cruciferous weeds, especially charlock. If barley or
oats are badly infested with this plant it is found that if the
whole field be sprayed with a 2 or 3 per cent, solution of
sulphate of copper, using about 40 gallons to the acre, provided
the charlock plants are not above two or three inches high,
their leaves blacken, and they die, while the oats, barley, or
clover are not injured.

It is difficult to explain why the charlock should be killed,
while the cereal is uninjured, but it may be due to plasmolysis
(see chap, v., p. 78) occuriing more readily in the one case
than in the other. But copper sulphate is too corrosive in its
effect on foliage to be very suitable as a fungicide for many
plants, and a much more generally used substance is copper
hydroxide, CulJfi.^, or really basic copper sulphate, i.e., a com-
pound of 4 or 5 molecules of copper hydroxide with one of
copper sulphate, applied in suspension in water.

This is largely used under the name of Bordeaux mixture^
and is made as required by the action of slake<i lime upon
sulphate of copper :

218 ELEMENTARY AGRICULTURAL CHEMISTRY

CuSO, + CaH^^ = CuH^Og + CaSO,
Copper Lime Copper Calcium

sulphate hydroxide sulphate

Various strengths have been recommended — usually from 12
to 30 lb. of copper sulphate to 100 gallons of water, and from
8 to 20 lb. of quicklime. Of the pure substances, 239 parts
of sulphate of copper require only 56 parts of quicklime, but
in practice, as the lime is never pure and portions of it never
dissolve, much more lime has to be employed. The mixing of
the lime and copper sulphate must always be done in the cold,
and there should always be a slight excess of lime. This can
be ascertained by filtering the muddy blue liquid and testing
it for dissolved copper or lime. The simplest plan for the
former is to immerse a piece of polished steel — a knife blade,
for example — in the liquid for a few minutes. If there be
excess of copper sulphate a stain of metallic copper will appear
on the steel. To show excess of lime in the solution the
easiest plan is to breathe on the surface, when the carbon
dioxide in the air from the lungs will form a thin scum of
carbonate of lime.

A much-used formula is :

Copper sulphate . . , • , . 6 lb.

Quicklime . . , 6 „

Water 50 gallons.

Each of the solid constituents should be dissolved in 25 gallons
of water, and then thoroughly mixed together. The mixture
should be used as soon after its preparation as possible, since it
must be remembered that the effective ingredient, copper
hydroxide, or rather basic copper sulphate, is in suspension,
not in solution.

It has recently been shown that the active substance in
Bordeaux mixture is not copper hydroxide, but some basic
copper sulphate — (several are known to exist, e.g., 4CUO.SO3
5CuO.SOy and lOCuO.SOg)— which subsequently on exposure to

MISCELLANEOUS 219

air absorbs carbon dioxide and again forms sulphate, which
being soluble, exerts its fungicidal action —

4CUO.SO3 + 300j = SCuCO, + CuSO,.

Other copper preparations used as fungicides are :

Edu Celeste^ ammonio-copper sulphate, CuSO4.4NH3.H3O,
made by adding ammonia to a solution of copper sulphate.
This yields a magnificent blue solution. The usual proportions
are copper sulphate 5 lb., ammonia (strong) 6 or 7 pints,
water lOO gallons.

Ammoniacal Cojyper Carbonate, made by dissolving 10 ounces
of copper carbonate in about 6 pints of strong ammonia and
diluting to 100 gallons with water. A deep blue solution.

In the latter two preparations the copper is in solution, and
the liquids have the advantage of not discolouring the fruit and
foliage so much as Bordeaux mixture.

Mercuric chloride, HgCl,, "corrosive sublimate," is an
extremely powerful poison both to animals and plants. It *
has been used as a fungicide against bunt in wheat, and
for other purposes. A very dilute, solution suffices — ^about
1 lb. in 50 gallons of water. Its violent poisonous qualities
render it necessary to take every precaution in dealing with
this substance.

Foiimaldchydej H,CO, used in the form of a solution in
water, "formalin," containing about 40 per cent, of the real
substance. It is an excellent fungicide and disinfectant, and
is being more and more used ; but as it is also a violent poison
to plants it has to be used with care.

A solution containing 01 per cent, of the real substance —
i.e., about 1 quart of formalin to 100 gallons of water — has been
recommended as effective for destroying fungi and their spores
on grain, clover seed, &c. An hour's immersion of the seed in
this solution is recommended. As a preventative of scab in
potatoes, immersion of the "sets" for an hour in a solution
containing 1 pint of formalin in 30 gallons of water is said to

220 ELEMENTARY AGRICULTURAL CHEMISTRY

be effective. This solution would contain 0*1 67 per cent, of
the real formaldehyde.

in. Insecticides. — By this term is understood a substance
which can be used to kill insects or creatures similar to insects.
The destruction may be accomplished in three ways :

(A) By poisoning the food eaten by the insects, or by
absorption through their skin.

(B) By poisoning the air breathed by the insects.

(C) By suffocating the insects by stoppage of their
breathing apparatus.

(A) Poisoning the Food.

Under Class A large numbers of chemical compounds may be
included ; in fact, nearly all which are poisonous to the higher
animals are fatal to insects.

Among those most largely used for the purpose of destroying
objectionable insects are the following : —

Arsenic. — Tliis substance is never used in the pure elementary
state, but in the form of its oxide, arsenious oxide, ASgOg, or
some compound containing this. Indeed, in common language
"arsenic" or "white arsenic" is generally used to designate
what the chemist would call arsenious oxide. This is a hea'vy
white substance, not readily soluble in water, but dissolving
easily in alkalies — e.g., caustic soda or sodium carbonate solu-
tion, when the arsenious oxide is converted by the soda into
sodium arsenite, or arsenite of soda.

Arsenious oxide is used as a vermin poison, and is fatal to
most forms of animal and plant life. Certain low forms of
vegetables, however, can develop in presence of considerable
quantities of arsenic. This is the case with many moulds.
But to higher plants arsenical solutions are quickly fatal, even
when highly diluted.

In very small doses arsenic acts as a tonic upon animals, and

MISCELLANEOUS 221

confers by continued use an immunity to doses which under
ordinary conditions would be sufficient to cause death. The
adjainistration of arsenic in small doses often produces a
plumpness and sleekness of the skin, but is attended with the
danger of setting up chronic poisoning.

As an insecticide both for animal and plant parasites
arsenical compounds, are largely used. They enter into the
composition of many dips for sheep, cattle, &c.

Arse7iic in Dipping Compositions. — In these the arsenic is
usually in the soluble form of sodium arsenite. Though in
many commercial dips other substances are also present, in
the majority of arsenical dips the efficiency depends upon the
amount of arsenic alone.

In South Africa particular interest attaches to the destruc-
tion of ticks on cattle and sheep, because of the transmission
of disease by ticks. According to Lounsbury's experiments
in Cape Colony,* it appears that to ensure the killing of
all ticks the solution must contain about 1 lb. of arsenious
oxide in 30 gallons of water — i.e., 0*33 per cent. — though for
practical purposes 1 lb. in 40 or 45 gallons (0-25 to 0'22 per
cent.) is considered by him to be sufficient.

A preparation reported to be efficient in Queensland con-
tains 1 lb. in 50 gallons — i.e., 0 2 per cent.

In the same paper Lounsbury concludes that the addition
of tar or soap to the arsenical dips has little or no effect upon
their poisonous qualities.

He also gives a table from which it may be inferred
that two well known arsenical dips, Demuth's and Alder-
son's, contain about 11 and 46 per cent, of arsenious oxide
respectively, and that when diluted in accordance with
the makers' directions — viz., 1 lb. to 6 gallons and 1 lb.
to 14 — they yield a liquid containing arsenious oxide in
the proportions of 1 lb. to 65 gallons and 1 lb. to 30 gallons
respectively.

He also states that " Scrub exterminator," crude arsenite of
* Cape Agricultural Journal, March 1905, p. 390.

222 ELEMENTARY AGRICULTURAL CHEMISTRY

soda, contains about 66 per cent, of arsenious oxide.* If diluted
so as to contain about 1 lb. of arsenious oxide in 40 or 50
gallons of water it forms a thoroughly efficient destroyer of
ticks.

Later, in the same journal, a dip containing

Arsenite of soda 5 lb.

Aloes • . 12 ounces

Soft soap 5 lb.

Water 100 gallons

is recommended. The aloes are merely added to render the
dip distasteful, so as to lessen the risk of the animals drink-
ing it. This dip contains shout 0*3 per cent, of arsenious
oxide.

The soft soap is thought to increase the effect upon the
ticks by keeping the wool moist for a longer time after dipping,
and for long-wooled sheep it is recommended that the soap* be
omitted.

If the animals are dipped in too strong an arsenical solu-
tion, or too frequently, poisoning through absorption of the
arsenic by the skin may ensue. This is apparently most likely
to occur with long-haired or long-wooled animals. Thus it
occurs more readily with sheep than with cattle or horses. It
is also said to be more likely to occur if the animals be dipped
or sprayed while hot.

It is unnecessary, perhaps, to emphasise the need of care in
using so poisonous a substance as arsenic, but every pre-
caution should be taken to prevent animals drinking the dip,
or licking or eating anytliii g with which the arsenical prepara-
tion has been in contact.

Arsenic compounds are also largely used for the destruction
of insects injurious to plants or vegetable products. Thu^i
arsenious oxide is now strongly recommended for poisoning
white ants. The most successful plan of using it for this
purpose is to vapourise a mixture of sulphur and arsenious

* My experience is that commercial arsenite of soda frequently
contains about 56 per cent, of arsenious oxide.

MISCELLANEOUS 223

oxide in a suitable apparatus, and force the vapours by means
of a pump into the ants' nest. The vapour of arsenious oxide
is intensely poisonous, and as it cools it impregnates the
workings and their contents with a sublimate, which would
be fatal to any insect which might escape the effect of the
fumes and afterwards eat of the stores within the nest. An
apparatus designed for performing this operation has been
constructed. The material supplied with the machine consists
of about 11 per cent, of sulphur and 89 per cent, of arsenious
oxide, intimately mixed together. Arsenic, generally as
sodium arsenite, is the basis of many preparations for the
destruction of ants or preserving wood, (fee., from their
attacks.

Another important use of arsenic is for poisoning locusts.
The plan adopted is to spray the grass or other vegetation in
the neighbourhood of a swarm of " voet-gangers " with a
solution containing

Arsenite of soda . . . . " . . 1 lb.
Sugar . . . . I . . . 1 lb.
Water . . * 8 to 12 gallons

The grass so sprayed, if consumed by the locusts, soon poisons
them, or, if not, it quickly dies and dries. If eaten by cattle
or sheep soon after spraying injury might result, but after a
few showers of rain the arsenic is to a great extent washed off
into the soil. Even if no rain falls the danger of cattle eating
the poisoned grass is not great, as after a few days the grass
dies and withers, and, except under stress of hunger, would be
rejected by the animals. The poisoned insects are often eaten
by poultry, locusts, birds, <fec., and though they contain con-
siderable quantities of arsenious oxide (in one sample we
found 0-219 per cent, in the dried insects) they do not appear
to do much harm to the birds. Nevertheless animals should
be kept from access to the sprayed locality until after several
showers, and the poisoned insects should be supplied in small
quantities only, if at all, to poultry, (kc, as there is undoubtedly

?

224 ELEMENTARY AGRICULTURAL CHEMISTRY

some risk of poisoning, for arsenic is not a substance which is
readily eliminated from the carcass by decomposition, as some
poisonous substances are.

The arsenite of soda employed for this and other purposes
may be prepared by boiling "white arsenic" — i.e., arsenious
oxide — with one-third of its weight of caustic soda or four times
its weight of sodium carbonate (washing soda) and water until
it dissolves ; or it may more conveniently be procured already
prepared in the form of a white solid.

About 9 ounces of " white arsenic " is equivalent to 1 lb.
of sodium arsenite.

The sugar in the above formula is intended to make the
poisoned material more attractive to the insects, and aids also
in increasing the quantity' which adheres to the grass or other
vegetation.

Arsenic is also used for the destruction of caterpillars,
grubs, &c., particularly on fruit-trees. In this case the use of
arsenious oxide, arsenite of soda, or other readily soluble com-
pound is excluded, because of the injury which such substances
produce on the foliage.

Several almost insoluble compounds of arsenic are therefore
employed, the following being the favourites :

Paris Green, " Schweinfurth's Green," or " Emerald Green." —
An impure arsenite and acetate of copper, usually containing
from 30 to 50 per cent, of arsenious oxide (in combination),
but of very variable composition. Often a portion (2 per cent.
or more) of its arsenic is in a soluble form. The best samples
for spraying are those which contain the least soluble and the
most insoluble arsenic. It is used in suspension in water, and
applied by means of a spray pump, usually at a strength of
1 part of the solid in 2000 or 3000 of water. Obviously, to
ensure good results the liquid must be kept in constant agita-
tion, otherwise the Paris green will settle to the bottom. The
injury to foliage due to the presence of soluble arsenic may be
prevented by the addition of an equal weight of lime.

London Purple. — A mixture of arsenite of lime with colour-

MISCELLANEOUS 225

ing matter, obtained as a by-product in the manufacture of
certain coal-tar dyes. It, like Paris green, is very variable in
composition, but usually contains from 30 to 50 per cent, of
arsenious oxide, of which often a considerable proportion is
soluble in water. It is used in the same manner as Paris
green, but unless lime be also added it is even more liable to
injure foliage.

An arsenice of lime can be made by dissolving arsenite of
soda in water, diluting largely, and then stirring in milk of
lime containing about ten times the weight of lime as of the
arsenite of soda taken. The lime is in large excess, but does
no harm.

Lead Arsenate, which is insoluble in water, and therefore
does not injure foliage, is very valuable as a spraying material.
It can be bought ready prepared, or can be made as required
from " sugar of lead " (i.e., acetate of lead) and arsenate of soda
— 11 ounces of the former and bounces of the latter, dissolved
in separate portions of water. When mixed they give a fine
white precipitate of arsenate of lead, which, when suspended
in 150 gallons of water, can be sprayed on trees without fear
of injury. Arsenate of lead is supplied either as a paste
(usually containing about 12 per cent, arsenious oxide) or in
powder. The former gives the better results.

Scheele^s Green. — Copper hydrogen arsenite is also sometimes
used for spraying. Like lead arsenate, it is very slightly
soluble in water, and therefore has but little injurious
action on foliage. It is, however, not often used as an in-
secticide.

Caution as to Use of Arsenical Preparations. — Arsenic com-
pounds are so poisonous to man and the higher animals that
it is of the utmost importance that they be used with care.
Every precaution should be taken to prevent access of any of
the arsenical solutions to foods, water, (fcc, which may
afterwards be consumed by animals. The lethal dose of
arsenious oxide depends very largely upon the individual ; for
man it has been given as probably 1 or 2 grains, for a

226 ELEMENTARY AGRICULTURAL CHEMISTRY

horse perhaps 30 grains, for a cow 10 or 15 grains, for a dog
about 1 grain. A uthori'uies, however, differ very greatly as
to the lethal doses. In readily soluble form — e.g., sodium
arsenite — it is much more powerful than as the oxide. As anti-
dotes, emetics should be given, followed by a dose of recently
precipitated ferric hydrate, prepared, as required, by adding
ammonia or carbonate of soda to a solution of ferric chloride
(" perchloride of iron "). Milk, eggs, olive oil, and barley-
water are also useful.

Other poisonous substances sometimes used as insecticides
are:

Carbolic Add, phenol, CgHgOH (see p. 214) . This is a ^violent
poison, both to animals and plants, and as an insecticide has
to be used with care, in order to avoid injur}"^ to vegetation.

On dormant fruit trees a wash containing about 1 lb. of the
crude acid, 2 or 3 lb. of soft soap, and 2 gallons of watefr is
sometimes used to destroy boring insects. A solution of car-
bolic acid is also sometimes used for preventing the attacks of
insects — e.g., the warble fly on cattle.

On account of its poisonous action on plants, it is probably
not safe to use solutions stronger than 0'5 or at the most
1 per cent. It should not be allowed to touch the foliage.

Alkaline Sulphides.— These are very effective insecticides,
but are also poisonous to the roots of plants and corrosive to
foliage.

*' Sulphide of potash," or " liver of sulphur," is really a mix-
ture of sulphide and polysulphides of potassium, and is used
in solution for spraying trees at a strength of from 2 to 4 per
cent. More largely used is the sulphide of calcium, generally
prepared, as required, by boiling lime and sulphur with water.
The resulting yellow liquid contains in solution a mixture of
various sulphides of calcium, and often some free lime.

This " lime and sulphur " wash or dip is largely used both
by the horticulturist for the destruction of scale and other
insects on trees and by the sheep-farmer for killing insect
parasites, especially scab, on his animals.

MISCELLANEOUS 227

There are many forrnulte recommended, according to the
particular plant and kind of insect to be dealt with. Thus a
mixture for fruit trees is made by boiling 10 lb. of quicklime
with 20 lb. of sulphur in about 20 gallons of water for about two
hours, then mixing this with 40 gallons of water in which
30 lb. of lime and 15 lb. of common salt have been dissolved.
This wash must only be used in winter, when the leaves are off.

For scab in sheep the so called *' lime and sulphur dip " has
some strong partisans, especially in Cape Colony. However
it may be prepared (and the variations in the proportions of
lime, sulphur, and water appear to be very great ; thus, to
100 gallons of water quantities of lime varying from 4|- lb. to
20 lb., and of sulphur from 15 to 25 lb., are recommended
by various correspondents, and the ratio of lime to sulphur
varies from 1 : 1 to about 1:5), there can be little doubt that
the dip is injurious to wool. All alkalies and alkaline sul-
phides have a strong caustic action on such organic substances
as hair and wool, as is evidenced by the use of calcium sulphide
in strong solution for removing hair, both for toilet purposes
and also, on the larger scale, from skins prior to tanning. But,
if the injury to the quality of the wool can be excused, there
appears to be strong evidence in favour of the efficacy of the
dip as a remedy for and preventative of scab.

It is of importance, however, to understand the principles of
its preparation. As already stated, the really active ingredient
is the calcium sulphide and polysulphide, though the free
sulphur doubtless would be useful, especially as a preventative
of re-infection. This free sulphur, however, can only be
applied to the wool if the dip is well stirred during the
operation of dipping, since it is quite insoluble in water, and
this practice is rarely followed. When lime is boiled with
sulphur the reaction results in the formation of calcium sulphide
and calcium thiosulphate, as indicated by the equation :

3CaO

4- 4S =

2CaS

+ CaS,03,

Lime

Sulphur

Calcium

Calcium

sulphide

thiosulphate

228 ELEMENTARY AGRICULTURAL CHEMISTRY

The calcium monosulphide, CaS, can, however, dissolve an addi-
tional quantity of sulphur, to form, finally, calcium penta-
sulphide, CaS^, thus :

CaS + 4S = CaS^.

So the maximum amount of sulphur which can be dissolved by
boiling with lime and water is indicated by the equation :

3CaO + 12S = 2CaS5 + CaSp,.

Taking atomic weights Ca = 40, 0 = 16, S = 32,

3(40 + 16) = 168 lime. 12 x 32 = 384 sulphur.

168 parts of pure lime can thus bring about the solution of
384 parts of sulphur — i.e., 1 part by weight of lime suffices to
dissolve 2'28 parts of sulphur, or 1 lb. of sulphur requires
0'4375 lb. of pure lime. Now ordinary lime is never pure;
the proportion of real lime present varies from as low as
50 per cent., or even lower, to as high as 98 per cent.,
or higher. Hence those recipes which give lime to sulphur
in less proportion than 1 to 2, even if the lime be of good
quality, must leave a large proportion of the sulphur un-
dissolved. With the usual qualities of lime the amount of
sulphur in excess will be still greater, and when, as is generally
recommended, the liquid is allowed to settle and only the clear
portion used for dipping much sulphur is wasted. It is, on
the other hand, desirable to avoid excess of lime in the dip,
otherwise the injury to the wool becomes greater. The proper
propoitions of lime and sulphur to use will depend greatly
upon the purity of the former, If the lime be white, freshly
burnt, and slakes with considerable heat when water is added,
it is probably fairly pure, and 1 part of lime to about 2 J parts
of sulphur will be about the right proportion. But if '' blue
lime " be used, and especially if it be partly " air -slaked " — i.e.,
has been kept for some time — equal weights of lime and
sulphur will probably be better. In any case it will be safer
to see thafc there is at the end of the boiling a little sulphur

MISCELLANEOUS 229

undissolved, as this makes it less likely that there is excess of
lime in the liquid.

Of course, in preparing 100 gallons of the dip the lime
should be treated with only about 5 to 10 gallons of water,
heated to boiling, the sulphur added in fine powder little by
little, and the whole boiled for about two hours, or until most
of the sulphur has disappeared. The strong solution of calcium
sulphides and thiosulphate is then diluted to 100 gallons with
water.

The dip should be used as soon after preparation as possible,
as it absorbs carbon dioxide and oxygen from the air and the
calcium sulphide and pentasulphide are decomposed. Many
users have obtained better results by using the dip at a tern-
perature of about 100° to 1 10° F. (38° to 43° C). Each animal
should remain at least two minutes in the dip.

Hellebore ( Veratrum album). — The root of this plant contains
several alkaloids, of which veratrine, CggH^^NOg, protoveratrine
CjjHjjNOji, and jervine, C26H37NO3, are poisonous to animals.
It is occasionally ussed as an insecticide, either in the dry,
finely powdered state, often mixed with flour, or in water —
about an ounce to 3 gallons of water. It is efficacious against
leaf -gnawing insects, and is not so poisonous to animals or man
as the arsenites.

Iiisect-powder is the finely powdered flower-heads of a plant
Two species of plant are used — Pyrethrum roseum, the pro-
duct from which is known as Persian or Caucasian insect-
powder, and Pyrethrum cineraricBfolium^ which yields Dal-
matian insect-powder, or '' buhach," as it is called in California.
The Dalmatian product is said to be more effective than the
Persian. It can be used dry, often mixed with three times it.i
weight of flour, or in aqueous or alcoholic solution, also in
fumigation. The substance can be used to destroy aphides,
house insects of various kinds, and, especially by fumigation,
for driving away mosquitoes and flies. For spraying solution
1 ounce of the powder is mixed with 2 or 3 gallons of water.
A little alcohol is sometimes first added to the powder, and the

230 ELEMENTARY AGRICULTURAL CHEMISTRY

mixture then diluted with water. Additions of ammonia and
•of soap to the liquid are sometimes made, and are said to
increase efficiency. For fumigation the powder is scattered
on hot coals or on a hot metal plate ; this, of course, can only
be effective in a closed space.

Several other vegetable products — e.g., quassia chips — are
used as insecticides, but their importance is not sufficient to
justify detailed description here.

Other insecticides are substances which are more commonly
used as disinfectants or antiseptics. To this category belong
many coal-tar products — carbolic acid, Lysol, Izal, JejJ'es' dis
infectant, creasote, and many others.

Quicklime, calcium oxide, CaO, is sometimes used for killing
snails, slugs, caterpillars, &c. It is only effective for this pur-
pose when fresh and unslaked, and is best applied as fine
powder, dusted on to the slugs or caterpillars. Lime-water,
too, is useful as a destroyer of many caterpillars and worms.
Lime will only dissolve in water to the extent of about 0-13
per cent. — i.e., a gallon of water will only dissolve about one-
fifth of an ounce of quicklime. Lime-wash — i.e., about 2 lb.
of lime to the gallon of water — is also used as a remedy against
scale insects, being applied to the bark of trees.

(B) For Poisoning the Atmosphere breathed by the
Insects

the principal substances used are the following :

Carbon Disidphide, CSg, " bisulphide of carbon," a colourless,
heavy, very refractive liquid, possessed of a strong, disagreeable
odour recalling that of rotten cabbage. When perfectly pure,
however, it has a pleasant, ether-like smell. Carbon disulphide
is very volatile, and its vapour is very inflammable, becoming
ignited, when mixed with air, at temperatures much lower
than those required to set tire to most combustibles. A mix-
ture of air and carbon disulphide vapour is very explosive, and
may be ignited even by a glowing pipe or cigar. The vapour

MISCELLANEOUS 231

is heavy, and very poisonous to animals, including insects. On
this account its vapour is particularly well adapted for killing
subterranean insects or larvaB. It is often used for destroying
ants. One or two ounces of the liquid poured down the holes,
which should then be covered, will evolve a poisonous vapour
which may penetrate into all parts of the nest.

It can also be used for the destruction of weevils in mealies
or other grain. For this purpose the grain is placed in bins
or tanks, sufficient carbon disulphide is either poured on to
the grain or placed in a vessel on the top, and the bin or tank
closely covered.

Insects on low-growing shrubs or trees may be destroyed by
surrounding the trees with boxes to enclose the heavy vapour
given off from a small quantity — half an ounce to an ounce —
of the liquid placed in a saucer.

Sulphur Dioxide^ SO^ (see p. 213), cannot be used to
destroy insect pest on plants, but is often employed for the
destruction of bugs, cockroaches and other household insects.

Tobacco Smoke, or, better, the fumes from tobacco extract,
is often used as an insecticide in greenhouses, &c.

Hydrocyanic Acid J HON, "prussic acid," is a gas with a
curious and characteristic, though not strong, odour. It is in-
tensely poisonous to animals, but as, in small quantities, it is
not fatal to plants in the dark, it can be and is extensively
used for the destruction of insect pests on shrubs and trees.

The gas is made as required by the action of diluted sulphuric
acid upon potassium cyanide. The reaction is :

KCN + H,SO, = KHSO, + HON.

Potassium Sulphuric Potassium acid Hydrocyanic
cyanide acid sulphate . acid

Fairly pure cyanide is now easily obtainable (98 per cent,
potassium cyanide), and ordinary oil of vitriol is suitable for
the purpose. Before use the acid should be diluted with about
one and a half or twice its volume of water. The proportions
to use are about one part by weight of potassium cyanide to

232 ELEMENTARY AGRICULTURAL CHEMISTRY

one and a half parts of sulphuric acid and two or three parts of
water. The water should be placed in a glass or earthenware
vessel, the sulphuric acid poured gradually in, with continuous
stirring, and lastly, when all is ready, the cyanide should bo
dropped in, and the building or tent at once vacated.

For trees a tent made of canvas, rendered gas-tight by
treatment with boiled linseed oil, is used to retain the gas, and
the fumigation done at night. Usually from thirty to forty
minutes' exposure to the gas is sufficient. The greatest care
should be taken in dealing with such intensely poisonous sub-
stances as potassium cyanide and prussic acid. Caution to
avoid breathing air containing the acid is particularly neces-
sary. This method is also very successful in ridding houses,
mills, &c., of insect pests of all descriptions. For trees the
amount of cyanide to use is from 10 to 25 grams — i.e., from J to
J ounce — per 100 cubic feet of air space, depending upon the
kind of trees. For buildings about 1 ounce per lOQ cubic feet
will generally be sufficient.

(C) The so-called Contact Poisons.

These are intended particularly for sucking insects, which,
deriving their food from the interior of the host plant or
animals, cannot be killed by poisoning their food. They, there-
fore, are destroyed either by clogging the breathing pores by
some liquid or solid, or in some cases, perhaps, by absorption
of the poison through the skin. Soap of any kind, and parti-
cularly potash or soft soap, is effective, being usually applied
in from five to twenty times its weight of water.

Resin soaps are also employed, being made as required by
boiling resin with caustic soda or potash solution, or with
sodium carbonate (washing soda) solution. Generally some fish-
oil or tallow is also used. Thus a common wash is made by
taking :

Resin . , . ^ . . . 20 lb.

Fish-oil . g i to 1 gallon

Caustic soda 8 lb.

MISCELLANEOUS 233

These are placed in a boiler with a few gallons of water and
heated to boil^ig, cold water gradually added, and the boiling
kept up for about two hour?, until there aie about 30 gallons
and all is dissolved. Then dilute to 100 gallons with soft
water. Sometimes potash is substituted for soda, and tallow
for fish-oil, and occasionally petroleum is alf-o added. If the
potiish and soda are equally pure, 56 parts of potash are equal
to 40 of soda.

Paraffin or petroleum emulsion is also very effective. It
can be made with either soap solution or sour milk. For the
former 1^ lb. of soap are dissolved in 2^ gallons of hot water,
then 5 gallons of paraffin are added, and the whole violently
agitated by a spray pump until an emulsion is formed. 1
gallon of the emulsion is then diluted with from 9 to 12 gallons
of water.

The effect of the soap is merely mechanical, and the petro-
leum is not in any sense dissolved, but merely broken up into
minute droplets and suspended in the water.

1 gallon of sour milk to 2 gallons of paraffin may also
be emulsified, and afterwards diluted with water before
spraying.

Some of the substances described under (A) also act as contact
poisons, being probably absorbed by the insect through the
skin. This is often the case with arsenic dips, calcium sul-
phide, sulphur, (fcc, when used for blood- or sap-sucking
insects.

IV. Plant Poisons. — These are sometimes useful to kill
weeds. A large number of substances act as poisons to plants.
Among those which have been most largely used are the
following :

Arsenic and Arsenite of Soda. — These have been described
under "Insecticides." About 1 lb. of arsenious oxide or IJ lb.
of arsenite of soda to 10 gallons of water is the strength often
used. If arsenious oxide be used it should be dissolved by
boiling with water and about 2 lb. of soda. It should be

234 ELEMENTARY AGRICULTURAL CHEMISTRY

applied in dry weather, and care be taken to keep cattle off
the treated vegetation.

Salt. — Hot brine — 1 lb. of salt to 1 gallon of water — is
useful for killing weeds on paths, &c.

Calcium Sulphide (or any soluble sulphide — e.g., fresh gas-
lime") is a powerful plant poison. For this purpose it is
advisable to use excess of lime, so as to save waste of sulphur.
2 lb. of sulphur, 10 to 20 lb. of quicklime, and 10 gallons
of water, boiled for an hour or two, are suitable quantities to
use.

Sulphuric Acid. — Oil of vitriol, diluted with about 30 parts
of water, will kill weeds. Care must be taken that the acid
does not come into contact with iron vessels or be spilt on
clothing, &c.

Carbolic Acid, Phenol. — An ounce of the commercial, acid
to a gallon of water will kill plants as well as insects.

All these substances render the soil barren for some time
afterwards. With heavy rains, however, they will soon wash
out. Additions of lime to the soil would cure the acidity due
to sulphuric acid.

An example of a differential plant poison is afforded by the
so-called " lawn .sand " used for ridding lawns of daisies and
plantains. The essential ingredient in lawn sand is sulphate
of ammonia, and if it be applied in sufficient quantity — about
4 oz. per square yard — it will be found that broad-leaved
plants, daisies, plantains, &c., are turned brown and killed,
while the grasses, though, perhaps, at first slightly injured,
soon recover and grow vigorously.

APPENDIX

♦

Specific Gravities. — The most rational method of expressing
the specific gravity of a solid or liquid is in terms of water —
i.e., by a number which expresses the ratio of the weight of
any volume of the solid or liquid to that of an equal volume
of water at a specified temperature.

This plan is always adopted for solids, but for liquids for
technical purposes various empiric scales are employed.

In England Twaddle's hydrometers are often used for
liquids heavier than water.

These are so constructed that the relationship between true
specific gravity and degrees Twaddle is

-^+ 100
d = , or n = 200(cZ - 1),

where d = true specific gravity and n = degrees Twaddle.

The determinations are assumed to be made at 15*5° C.
(60° F.).

Other hydrometers, based upon purely arbitrary and empiric
systems, are also in use in various branches of industry, and it
is to be regretted that they do not give way to a more rational
method of expression of density.

Thus Baum6's hydrometer, for liquids heavier than water,
is so constructed that it sinks to 0° in pure water and to 10°
in a 10 per cent, solution of common salt, both at 17'5° C, and
the scale is continued in a uniform manner down the stem.

235

236 ELEMENTARY AGRICULTURAL CHEMISTRY

For liquids lighter than water a Baum^'s hydrometer is
constructed so that in a solution of 1 part by weight of
common salt in 9 parts by weight of water it sinks to 0°,
while in pure water it sinks to 10°, the scale being extended
further up the stem.

The following formulsB connect degrees Baume with true
specific gravity :

For Liquids Heavier
than Water.

At 12-5'* 0. .
At 16' O. .
Atn-S'O. .

d =

145-88

For Liquids Ligliter
than Water.

145-88

145-88 -n

135-88+n

146-3
146-3-n

146-3
"" 136-3 + n

146-78

146-78
d =

146-78-n

136-78 + n

Other empiric scales are also in use. The relationships to
real specific gravity of some of the principal ones are given
below :

For Liquids

Heavier than

Water.

For Liquids

Lighter than

Water.

Brix, atl2-5»R. (15-62»0.)

Balling

Gay-Lussac, at 4° 0. .

Beck, at 12-5° 0.

Cartier, at 12-5" O. .

d =

d =

d =

d =

400

400 -n

200

200 -n

100

100 -n

170

170 -n

136-8

126-1 -n

400

400 +n

200
200 +n

100
100 +n

170

170+n

13)-S
126-1 +n

d = true specific gravity.

n = degrees of the various hydrometers.

Thermometer Readings. — Though in modern science the
Centigrade thermometer is coming more and more into general

APPENDIX 237

use, the much less convenient Fahrenheit and Reaumur scales
are still often employed in ordinary life.

The relationships between the three scales is simple, it being
only necessary to remember that the interval between the
melting-point of ice and the boiling-point of water under a
barometric pressure of 760 mm. of mercury is divided into
100° on the Centigrade, 180° on the Fahrenheit, and 80° on
the Reaumur thermometers ; and that while the scales com-
mence at the lower temperature on the Centigrade and Reaumur
thermometers, on the Fahrenheit instrument it begins at a
point 32° below the melting-point of ice.

Hence

° C. = I- ° R. = I (° F. - 32),

or ° F. = I ° C. + 32 = I ° R. + 32,

or ° R. = I ° C. = f (° F. - 32).

On the continent of Europe many thermometers are
graduated on one side in Centigrade, on the other in Reaumur
degrees. With such an instrument an easy way of obtaining
the temperature in Fahrenheit degrees is to add the read-
ings in Centigrade and Reaumur degrees together, and then
add 32.

Units of Lengthy Area, Volume, and Weight. — Our British
system of weights and measures is absurdly cumbrous, com-
plex, and inconvenient, and it is to be hoped that the whole
of the civilised world will eventually resort to some simple
and rational method of expressing lengths, areas, volumes,
and weights. In agriculture, perhaps more than in other
branches of commerce, English units are inconsistent, for
there are such anomalies as selling grain nominally by volume
(bushels and quarters) and then fixing definite weights, which
necessarily differ with various products, for these volumes, and
which are so arbitrary that they differ in various parts of the
country.

Then even in our weights there are peculiar anomalies ; e.g.,
the hundredweight is 112 lb. in England, though usually

238 ELEMENTARY AGRICULTURAL CHEMISTRY

100 lb. (as its name implies) in America, South Africa, and
other places.

The metric system, which is gradually gaining in popularity
is free from many of the objections of our British units, and
has the great advantage that the various units are connected
together in a simple and uniform manner.

It is unnecessary to give here the fundamental units and
method of decimal multiples and sub-multiples of the metric
system, but the connection between metric and British units
may be useful.

Units of Length.

1 centimetre = 0'393708 inch.

1 metre = 39-3708 inches = 32809 feet = 1-0936 yards.

1 kilometre = 3208*9 feet = 1093-63 yards = 0-62138 mile.

Or

1 inch = 2-53995 centimetres.
1 foot = 0-30479 metre.
1 yard = 0-91438 metre.
1 mile = 1-609315 kilometres.

Units of Area.
1 square metre = 1550 square inches = 10*764 square feet

= 1*196 square yards.
100 square metres (1 are) = 1076*4 square feet = 1196

square yards = 0-0247 acre.
10,000 square metres (1 hectare) = 11,960 square yards =

2*4711 acres.

Or

1 square inch = 6*45137 square centimetres.

1 square foot = 9*290 square decimetres = 0*0929 square

metre.
1 square yard = 0-8361 square metre.
1 acre = 0*40467 hectare — 404 6- 7 square metres.

APPENDIX 239

Units of Volume.
1 cubic centimetre (c.c.) = 0*061 cubic inch.
1 cubic decimetre (1 litre) = 61-028 cubic inches = 1*76

pints = 0*22 gallon.
1 cubic metre (1 kilolitre or 1 stere) = 61,028 cubic inches

= 35-317 cubic feet = 1*308 cubic yards = 220-09

gallons = 27-512 bushels.

Or

1 cubic inch = 16*3862 cubic centimetres. «

1 cubic foot = 28*3153 litres = 6*24 gallons.

1 pint = 567*93 cubic centimetres.

1 gallon = 4*54346 litres = 277*274 cubio inches.

1 cubic yard= 0*7645 stere or 764*513 litres= 168*49 galls.

1 bushel— 36*3477 litres.

Units of Weight.

1 gramme = 15*43235 grains = 0035274 ounce avoirdu

pois.
1 kilogramme = 35*2739 ounces avoirdupois = 32*1507

ounces troy = 2*2046 pounds avoirdupois.
1000 kilogrammes (1 tonne) = 2204*621 pounds avoirdupois

= 0*98420 ton.

Or

1 ounce avoirdupois — 28*3495 grammes.

1 ounce troy = 31*1035 grammes.

1 pound avoirdupois = 453*593 grammes.

1 pound troy = 373*242 grammes.

1 hundredweight = 50*802 kilogrammes.

1 ton = 1016*05 kilogrammes.

On the Continent crop yields are usually expressed in kilo-
grammes per hectare, which is approximately equal to -^^ of
English pounds per acre.

In South Africa lengths, volumes, and area are usually
expressed in Cape or Dutch measures.

Q

240 ELEMENTARY AGEICULTURAL CHEMISTRY

Length.
The Cape foot = 1-033 English feet.
The Cape rood = 12 Cape feet = 12-396 English feet.
1 English mile (5280 English feet) = 5111-3 Cape feet =.

425- 944 Cape roods.
Approximately 1 Cape foot = 1^^ English feet.

1 English foot = 0-96786 Cape foot.

Area.

1 Cape square foot = 1'067 English square feet.
144 Cape square feet = 1 Cape square rood.
600 Cape square roods = 1 Cape morgen.
86,400 square Cape feet = 1 Cape morgen.
1 Cape morgen = 2*11654 English acres.

= 10244*054 square yards.

= 92196*486 English square feet.
1 acre = 0*47247 morgen = 283*48 Cape square roods.
1 square mile = 302*38 morgen.
1 hectare = 2*471 acres = 1*1675 morgen.

Volume.
1 muid = 3 bushels = 24 gallons.
1 Dutch gallon = -7895 English gallon.

= 6*316 English pints.
1 English gallon = 1-2666 Dutch gallons.
1 leaguer = 16 anker = 152 Dutch gallons = 126^ English
gallons.

Weight of a Bushel of Grain, dec.

The following are the approximate weights of a bushel
(8 gallons, or 4 pecks, or 2219*7 cubic inches) of various grains
of average density :

Wheat . . . . 63 lb. (varies from 60 to 65 lb.)

Oats . . . . 42 „ ( „ „ 35 „ 48 „ )

Barley . . . . 55 „ ( „ „ 52 „ 59 „ )

Rye 54 „

APPENDIX 241

Mealies (maize)

English beans

Peas

Lucerne seed

Russian linseed

Bombay and La Plata linseed

Buckwheat .

Sorghum

Castor beans

Pea-nuts

A bushel of the following substances weighs approximately
the number of pounds stated :

60 1b.

66

))

64

>»

61

>»

53

t>

52

»>

48

»

45

»

46

»

22

»

Salt

. 65 lb.

Turnips .

45 lb.

Lentils .

. 63 „

Brewers' grains, wet

40 „

Potatoes

. 56 „

Bran

17 „

Cotton-seed meal

. 51 „

Malt culms

14i„

Mangolds

. 45 „

Chaffed hay .

8 „

Swedes .

. 45 „

„ oat straw .

5 „

In South Africa, farm produce is often sold per 100 lb., and
the usual "ton " is the "short ton " of 2000 lb. Grain and
potatoes are usually sold per bag or " muid " of 3 bushels.

}d as 200 lb.
203 „
200 „
163 ,.

A bag of mealies is i

pec

„ Kaffir corn

j»

„ wheat

j>

„ barley, oats or potatoes

)}

INDEX

Absolute zero of temperature, 26
Acid, definition of, 7
Acids, organic, in plants, 91
Air, changes in, by respiration, 156

chemical composition of, 27

effect of, on rocks, 39

physical properties of, 24

suspended matter in, 32

weight of, 24
Albite, 34

Albumin in milk, 185
Albuminoid ammonia in water, 67

ratio of foods, 171
Albuminoid8,chemical nature of, 93

of milk, 182

formation of, in plants, 81
Alinit, 66
Alkali, '• black," 69

definition of, 7

soils, 57, 69

tolerance of plants to, 70

"white," 69
Alkaloids, 95
Allotropic forms, 16
Amides, 94
Amino-acids, 94
Ammonia, in the air, 29

in rain water, 30
Ammonium sulphate, 108
Amylopsin, 160
Anaerobic organisms, 56
Analysis of manures, 115

Analysis of soils, 59
Aneroid barometer, 26
Animals, action of, on soils, 40

composition of bodies of, 164
Antiseptics, 211, 216

in milk, 198
Ants, action of, in soil formation,
40

destruction of, 222
Apples, 138
Argon, 6

in the atmosphere, 28
Arsenic, as insecticide, 220

in sulphate of ammonia, 108
Artificial manures, 106
Ash in foods, 165

importance of, to animals, 176
Assimilation of carbon dioxide, 80
Atomic theory, 2

weights, 2
"Available" plant food in soils,

60
Avenine, 123
Azotobacter, 56

Bacteria, 54, 56, 105, 196

Bananas, 141
Barley, 121
Barometer, 25
Base, 8

Basic slag, 112
Basicity, 8
243 B

244

INDEX

Baum6 hydrometer, 235
Beans, 130

field, 130

haricot, 131

soy, 131

velvet, 131
Beck's hydrometer, 236
Beestings, 187
Beets, 143
Bile, 160
Bilirubin, 160
Biliverdin, 161
Bleaching powder, 213
Blood, 155

dried, as manure, 102
Blue vitriol, 216
Boer manna, 102
Boiler crusts, 64
Bone ash, 157
Bones, 157

as manure, 105
Boracic acid, 215
Borax, 216

Bordeaux mixture, 217
Boric acid, 215
Boyle's law, 26
Brak soils, 57, 69
Brewing, 121
Brix hydrometer, 236
Broom corn, 129
Buckwheat, 132
Burnett's fluid, 215
Butter, 203
Butterine, 205
Butter-milk, 206

Cabbages, 150

Calcium, functions of, in plants,
occurrence of, 19
carbonate, forms of, 35

in soils, 44
cyanamide, 109
nitrate, 108

Caliche, 107
Calorific power, 13

power of foods, 173
Capillarity, 51
Carbohydrates, in food, 165

in plants, 84
Carbolic acid, 214, 226, 234
Carbon, occurrence of, 15
dioxide, in air, 28

assimilation of, 80
in decay, 100
respiratory, 156
in soil gases, 56
asasolvent,39, 41,63, 79
Carbon disulphide, 214, 230
Carnine, 158
Carrots, 146

Cartier's hydrometer, 236
Cartilage, 158
Casein, 184
Castor oil seeds, 135
Celery, 146
Cellulose, 85
Cereals, 120
Cheese, 207

Chemical changes in soil, 46
Chemical manures, 106
Chili saltpetre, 107
Chlorine, bleaching action of,
22
as a disinfectant, 213
functions of, in plants, 92
occurrence of, 22
Chlorophyll, 95
Churning, 204
Citrus fruits, 140

Clay, occurrence and composition
of, 35
physical and chemical pro-
perties of, 42
Clovers,* 149
Cole, 135
Collagen, 158

INDEX

245

Colloids, 77
Colostrum, 187
Comfrey, prickly, 149
Combustion, heat of, 13

spontaneous, 13
Compounds, chemical, 3
Concave surfaces of water, 50
Condensed milk, 206
Condy's fluid, 215
Conglomerates, 86
Connective tissue, 158
Constituents of plants, 84
Copper sulphate, 115, 216
Cotton, 133
Coumarin, 152
Cream, 199
Creasote, 214
Creatine, 157
Cresol, 214

Crops, classification of, 119
Crops, rotation of, 153a
Crude fibre in plants, 105
Crystalloids, 77
Cubic nitre, 107

Dairy, the, 182

Denitrification, 56

Density, maximum, of water^ 73

Dent maize, 126

Dextrin, 77

Dextrose, 87

Diastase, 77, 122

Diffusion of liquids, 77

in soils, 48
Digestibility of foods, 166
Digestible constituents of foods,

169
Digestion, 159
Dips, arsenical, 221

lime and sulphur,'227
Disinfectants, 211
Dissolved bones, 112
Distillation, destructive, 8

Drainage, amount of, 58

losses by, 58
Durra, 129
Dyer's method in soil analysis,

60

Eau celeste, 219

Elastin, 158

Elements, 2

Emerald green, 224

Endothermic compounds, 8

Ensilage, 152

Enzymes, 76, 121, 159, 197, 208

Equations, chemical, 6

Ether extract in foods, 166

Excreta, animal, 97

human, 103
Exothermic compounds, 8

Fahrenheit thermometer, 237
Farmyard manure, 97

decomposition of, 100

preservation of, 99
Fat in foods, 166

in milk, 182
Fat globules in milk, 192
Fats, nature of, 87
Fatty acids, saturated, 88 ,

unsaturated, 89
Fatty tissue, 158
Feeding of animals, 164
Felspar, 34

Ferrous sulphate as manure, 115
Fish manure, 102
Flax, 133
Flint maize, 126
Flowers, 82
Fodder crops, 147
Food of animals, 164
Foods, manurial value of, 179

money value of, 178

thermal value of, 173
Formaldehyde, 80, 198, 215, 219

246

INDEX

Formalin, 215
Frost, action of, 38
Fruits, 136

Fumigation, by hydrocyanic acid.
231

by pyrethrum, 230

by sulphur dioxide, 213, 231

by tobacco, 231
Fungicides, 216

Gas lime as manure, 115
Gases, expansion of, by heat, 26

in soil, 56
Gastric juice, 159
Gay-Lussac hydrometer, 236
German millet, 128
Germination of seeds, 76
Glaciers, action of, 37, 38
Glucose, 87
Glycerol, 90
Glyceryl radical, 87
Glycocholic acid, 160
Glycocoll, 163
Glycogen, 85, 162
Granularity of matter, 1
Grapes, 141
Grasses, 148
Gravitation, effect of, on water in

soils, 49
Green manuring, 104
Green vitriol as manure, 115
Grits, 36

Ground nuts, 131
Guano, 101

bats', 102

fish, 102

"native," 104
Guinea corn, 129
Gypsum, 114

Hsemoglobin, 155

Hair, 105

Hardness of water, 64, 67

Haymaking, 151

Hays, composition of, 152

Haystacks, firing of, 151

Heat, latent, 73

Heat of combustion, 13

quantity of, 13

specific, 43, 72-
Heating value of foods, 173
Helium, 28
Hellebore, 229
Hempseed, 134
Hippuric acid, 162
Hoofs, 159
Horn>', 105, 159
Humus, functions of, in soil, 45

physical properties of, 42
Hungarian grass, 128
Hydrated silicates, 48
Hydrocyanic acid fumigation, 231

in plants, 129
Hydrogen ignition temperature,
15

occurrence of, 14
Hydrometer, 235
Hydroxides of iron and aluminium,

48

Igneous rocks, 33

Indian corn, 125

Indole, 161

Insect powder, 229

Insecticides, 220

Iron, functions of, in plants, 93

occurrence of, 21
Irrigation, water used in, 69
Italian millet, 128

Japanese millet, 128

Jerusalem corn, 129

Kaffir corn, 129
Kaffir manna-koorn, 128
I Kainite, 113

INDEX

247

Keratin, 158
Krypton, 28

Labpadorite, 34

Lactic acid fermentation, 185
Latent heat of ice, 74

of steam, 74
Lead, action of water on, 65

arsenate, 225
Leaves, functions of, 79
Lentils, 131
Ligaments, 158
Light, importance of, to plants,

80
Lignone, lignose, 86
Lime, as a manure, 114 •
Lime and sulphur wash, 226
Limestone, comp(»sition of, 36

functions of, in soil, 44

as manure, 114

physical properties of, 42
Linseed, 133

Locusts, destruction of, 223
London purple, 224
Lucerne, 149
Lupines, 132
Lysol, 214

Magfnesium, functions of, in
plants, 93

occurrence of, 21

silicates, 35
Maize, 125

silage, 128
Mangolds, 143
Manure, farmyard, 97

functions of, 96

yield of, by animals, 99
Manures, artificial, 106
Manurial value of foods, 179
Margarine, 205
Marl, as manure, 114
Marrow of bones, 157

Mealies, 125
Metamorphic rock?, 33
Mica, 19, 34

Micro-organisms in milk, 195
Milk albumin, 185

ash of, 186

cows', 186

fat, 182

physical properties of, 186

powder, 207

preservation, 194

souring of, 185

sugar, 185

of various animals, 193
Millet, 128

Mineral superphosphates, 112
Minerals, 34

Miscellaneous manures, 114
Mixtures, difference of, from com-

pounds, 4
Molecule, definition of, 6
Money value of foods, 178
Monkey nuts, 131
Muriate of potash, 113
Muscular tissue, 157

Neon in the air, 28
Nitragin, 105
Nitrate of potash, 109
Nitrate of soda, 107
Nitric acid in the air, 29
Nitric organisms, 55
Nitrification, 54
Nitro-bacter, 55
Nitro-bacterine, 106
Nitrogen in the air, 29

assimilation, 27

fixation of, 55

loss by drainage, 58

occurrence of, 16
Nitrosococcus, 55
Nitrous organism?, 55
Nodules on leguminosee, 105

24$

INDEX

Oat hay, 123

straw, 123
Oats, 122
Oil cakes, 133, 135, 137

as manure, 105
Oils, drying and non-drying, 89

essential, 90

nature of, 88
Oleo-margarine, 205
Organic acids in plants, 91
Organic chemistry, 16
Orthoclase, 19, 36
Osmotic pressure, 77
Osteoporosis, 177
Oxidation, 9

slow, 13
Oxygen in the air, 28

occurrence of, 11
Ozone, 6, 31

Pancreatic juice, 160

Paraffin emulsion, 233
Parchment paper, 86
Paris green, 224
Parsley, 146
Parsnips, 146
Pea nuts, 131
Pearl barley, 122

millet, 126
Pears, 139
Peas, 131

chick, 131

cow, 131
Pectins, 86
Pentosans, 86
Pentoses, 86
Pepsin, 159
Perchlorates in nitrate of soda

107
Permanganates, 215
Persian insect powder, 299
Petroleum emulsion, 233
Phosphates, loss of, by drainage, 59

Phosphatic manures, 110
Phosphorus, functions of, in plants,
92

occurrence of, 18
Physical properties of air, 24
Pialyn, 160

" Pickled " butter, 205
Pigeon dung, 102
Plant poisons, 233
Plants, 76

action of, in soil formation, 41
Plasmolysis, 78
Plums, 139
Plumule, 76
Pop corn, 126

Potash, loss of, by drainage, 59
Potash manures, 113
Potassium, function of, in plants,
93

nitrate, 109

occurrence of, 19
Potatoes, 144

Bweet, 146
Poultry dung, 102
Preservation of foods, 216

of milk, 194
Prickly comfrey, 149
" Process " butter, 205
Proteids, 93
Protein in foods, 166
Ptyalin, 159
Pumpkins, 150
Putrefaction, 9
Pyrethrum, 229

Quartz, 34

Quicklime, as insecticide, 230

Rabbits, action of, in soil forma-
tion, 40
Radicle of seedlings, 76
Rain water, 30
Rape, as fodder, 150

INDEX

249

Rape cake as manure, 103

Rape seed, 135

Reaumur thermometer scale, 237

Recknagel's phenomenon, 187

Reduction, 9

Rennet, in the dairy, 207

in digestion, 159
Rennin, 185
Renovated butter, 205
Resin soap as insecticide, 232
Resins, 91

Respiration of animals, 156
Rice, 124

bran, 125

polish, 125
Rise of sap in plants, 79
River water, 67

muddiness of, 68
Rocks, classification of, 33
Root crops, 142

hairs, 77

pressure, 79
Roots of plant?, 77
Rotation of crops, 153a
Rye. 123
Rye straw, 124»

Salicylic acid, 216

Saliva, 159

Sand, properties of, 42, 43

Sandstones, 36

Sarcine, 157

S ircolactic acid, 158

Schecle's green, 225

Schweinfurth green, i'2i

Sea water, 70

Seaweed, as manure, 102

Sedimentary rocks, 33, 36

Seed, formation of, 82

Semipermeable membranes, 78

Serradella, 149

Sewage as manure, 104

Shales, 86

Shoddy manure, 102
Silage, maize, 128

sour, 153

sweet, 153
Silicon, functions in plants, 92

occurrence of, 22
Skatole, 161
Skimmed milk, 203
Soap, action on hard water, 64

nature of, 90
Sodium, occurrence of, 20
Soft corn, 126
Softening of hard water, 65
Soils, analysis of, 59

composition of, 42

definition of, 33

fixation of nitrogen in, 56

formation of, 38

gases in, 56

retention by, 47

sedentary and transported, 37

water in, 57

why cold, if wet, 75
Soot as manure, 103
Sorghum, 129
Specific heat, 71
Spontaneous combustion, H
Starch, 84
Steapsiu, 160
Stems of plants, 79
Stomata of leaves, 80
Subsoil, 83
Sugars, 87
Sugar-beets, 143

leaves of, 150
Sugar cane, 150
Sugar mealies, 127
Sulphate of ammonia, 108

of potash, 113
Sulphur, functions in plants, 92

occurrence of, 17
Sulphur and lime dips, 227

dioxide, 32, 213, 231

250

INDEX

Sulphuric acid as plant poison, 234

Sunflower seed, 136

Sunrise rays, 83

Sunshine, effect of, on plants, 83

Superphosphates, 112

Surface pressure, 49

Swedes, 143

Sweet corn, 127

potatoes, 146
Symbols, chemical, 3

Tares, 149

Taurocholic acid, 160

Temperature, absolute zero of, 26
effect of, on gases, 26
effect of, on plants, 82
of maximum density of water,
73

Tendons, 158

Thermal value of foods, 173

Thermometric scales, 237

Tobacco as insecticide, 231

Transpiration from leaves, 81

Trefoil, 149

Trypsin, 160

Turnips, 143

Twaddle's hydrometer, 237

Urea, 162

Uric acid, 162
Urine, 162

Valency, lO

Valuation of foods, 178
of manures, 115

Values *'per unit" of manure^

117
Vetches, 149

Voet-gangers (hopping locusts),223
Volatile, 10

Warp soils, 69

Water, action of, on lead, 65

action of, on rocks, 38

hard, 64

mineral, 63

motion of, in soil, 49

natural, 62

organic matter in, 66

physical properties of, 71

rain, 62

required by animals, 178

river, 67

soft, 65

soil-, 57

spring, 63

typical good and bad, 66
Waxes, 90
Weather-glass, 26
Weevils, destruction of, 231
Wheat, 120 *

Whey, 210

White ants, destruction of, 222
Wind, action of, on rocks, 38
Wolff's feeding standards, 175
Woollen waste, 104
Worms, in soil formation, 40

Xanthine, 157

Xenon, in the air, 28

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