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UNIVERSITY OF CALIFORNIA

LOS ANGELES




GIFT OF

U. C. Library



THE



CHEMISTRY OF AGRICULTURE



FOR STUDENTS AND FARMERS



BY



CHARLES W. STODDART, PH.D.

DEAN, SCHOOL OF THE LIBERAL ARTS, PENNSYLVANIA STATE COLLEGE

SECOND EDITION, THOROUGHLY REVISED
ILLUSTRATED WITH 83 ENGRAVINGS AND 1 PLATE




LEA & FEBIGER

PHILADELPHIA AND NEW YORK
1921



COPYRIGHT

LEA & FEBIGER

1921



38 b

.



PREFACE TO THE SECOND EDITION



IN preparing the second edition some changes have been
made, notably the omission of the summary at the end of
each chapter and the addition of a list of suggestive exercises
designed to make the student think. The subject-matter
presented in the text can, in this way, be brought more
forcefully to the attention of the reader and the facts applied
to practical conditions. There have also been added sections
on new fertilizer materials, showing the development of
our own potash resources as a result of the Great War, and
also of synthetic nitrogenous fertilizers.

More material has been inserted where it seemed desirable;
parts have been rewritten to make the subject clearer; and
an attempt has been made to eliminate errors that crept into
the first edition. The order of the first three chapters has
been changed to facilitate the teaching of the subject-
matter.

The questions at the end of the chapters, many criticisms,
and some of the additional material have been the work of
Professor M. W. Lisse. To him the author wishes to express
his gratitude and esteem.

C. W. S.
STATE COLLEGE, PA.



(v)



480546



PREFACE TO THE FIRST EDITION



THERE is at present need for a text on general agricultural
chemistry which will cover the field briefly, in a logical
manner, giving only the facts, and not consisting of a dis-
connected series of quotations and tables from the very
extended literature of the subject. The need for such a
text has been particularly marked in teaching large classes
of students at The Pennsylvania State College. As a con-
sequence the present book has been written. While it is
intended primarily for students who have had previous
training in Botany, Chemistry, Geology and Physics, it is
sufficiently elementary to make it of value to any intelligent
person.

Concerning some of the statements made in the text it
is well known that a difference of opinion exists among
authorities, but it is deemed better to present them as facts
rather than to give the various arguments or to omit them
altogether.

Since the raising of crop plants is the fundamental business
of agriculture, and since on them depend the life and growth
of animals, there is discussed first the plant, its germination,
growth, and products. Then are taken up the various
conditions necessary for plant growth, such as the atmos-
phere, soil, fertilizers, and spray materials. A short chapter
on the gas engine is inserted at this point, since the increasing
use of power on the farm in the raising and marketing of

(vii)



Vlll PREFACE TO THE FIRST EDITION

crops makes some knowledge of the chemistry of gasoline
and carburetion important. Finally the animal is considered,
together with its food, digestion, and products.

The references at the end of each chapter give the principal
sources of information used in the preparation of this text.
While the lists are by no means complete, they will be of
help for any who desire to pursue the subject further.

The thanks of the author are due to the German Kali
Works, "La Hacienda," Great Western Sugar Co., Economy
Silo and Manufacturing Co., Chilean Nitrate Propaganda,
American Coal Products Co., C. Tennant Sons & Co.,
American Cyanamid Co., and the Avery Co., for many
of the illustrations. Particularly is the author indebted
to Dr. M. B. MacDonald, Mr. F. P. Weaver, and Mr.
R. U. Blasingame for helpful suggestions, and to Messrs.
C. A. Smith and E. DeTurk for some of the drawings*

C. W. S.
STATE COLLEGE, PA.



CONTENTS



PART I
THE PLANT



CHAPTER I
PLANT COMPOUNDS 17

CHAPTER II
GERMINATION OF THE SEED 72

CHAPTER III
GROWTH OF THE PLANT 80

CHAPTER IV
CROPS 102



PART II
FACTORS IN PLANT GROWTH



CHAPTER V
THE AIR 125

CHAPTER VI
THE SOIL: ORGANIC MATTER 132

CHAPTER VII
THE SOIL: INORGANIC MATTER 153

CHAPTER VIII

FERTILIZERS 186

(ix)



x CONTENTS

CHAPTER IX
NITROGENOUS FERTILIZERS 192

CHAPTER X
PHOSPHATE FERTILIZERS 206

CHAPTER XI
POTASH FERTILIZERS 216

CHAPTER XII
LIME 224

CHAPTER XIII
FARM MANURE 241

CHAPTER XIV

SOIL AND FERTILIZER ANALYSIS 256

CHAPTER XV
INSECTICIDES AND FUNGICIDES 264

CHAPTER XVI

THE GAS ENGINE . 279



PART III
THE ANIMAL



CHAPTER XVII
THE CHEMISTRY OF ANIMAL PHYSIOLOGY 287

CHAPTER XVIII
FOOD AND DIGESTION 304

CHAPTER XIX
MILK AND DAIRY PRODUCTS , 318



THE CHEMISTRY OF AGRICULTURE



PART I

THE PLANT



CHAPTER I
PLANT COMPOUNDS

THERE are a very large number of organic compounds
produced during the growth of plants. Some plants form
one kind, some another. Many of the compounds have no
value commercially, and no known value physiologically.
Some are evidently merely by-products, whereas others
undoubtedly serve some useful purpose to the plant. Since
many of these compounds are of great importance to the
human race, it is necessary to know something of their proper-
ties and uses outside of the plant. In the following discussion
only those plant compounds which are of known physiological
importance to the plant, and particularly those which are of
economic importance to mankind, will be considered. For
convenience the various compounds will be grouped as
follows :

I. Carbohydrates
II. Fixed Oils and Waxes

III. Volatile Oils and Resins

IV. Nitrogenous Compounds

V. Organic Acids and their Salts
2 (17)



18 PLANT COMPOUNDS



I. CARBOHYDRATES

1. General Definition. The most abundant group of
organic compounds is that of the carbohydrates or sac-
charides, comprising about 75 per cent, of the dry matter
of plants. Popularly, a carbohydrate is defined as a com-
pound containing carbon, hydrogen, and oxygen, with the
hydrogen and oxygen in the same proportion as in water;
or, a compound of carbon and water, thus: Dextrose =
6C+6H 2 O. This definition, while not exactly correct, will
hold in a majority of cases and serves very well to dis-
tinguish the group. The exceptions to this statement are
principally acetic acid, whose empirical formula is C2H 4 O2,
but whose graphic formula is CH 3 COOH, showing the acid
or carboxyl group; and lactic acid, C 3 H 6 3 , but otherwise
written CH 3 .CHOH.COOH.

A carbohydrate may be defined more accurately as a
compound containing always one or more hydroxyl (OH)
groups, and usually either an aldehyde

H o

II , I II I

( c c=O) orketone ( c c C ) group.

I I I

The presence of the aldehyde group indicates that the
carbohydrate is easily oxidized, whereas the presence of the
ketone group usually, though not always, indicates that the
carbohydrate is not easily oxidized. The principal carbo-
hydrates contain carbon atoms to the number of six or a
multiple of six. The carbohydrates are divided into two
general classes, the Sugars including the monosaccharides
and disaccharides; and the Non-Sugars or Polysaccharides.

2. Sugars. As a class the sugars are colorless, odor-
less, crystalline compounds, soluble in water, and, ordinarily,
sweet in taste. Their most characteristic property is that
of optical activity, that is, they rotate the plane of polarized



CARBOHYDRATES 19

light either to the right or to the left. 1 The simple sugars,
or monosaccharides, contain from two to nine carbon atoms,
and are named according to the number of carbon atoms in
the molecule: Dioses, trioses, tetroses, etc. Each molecule
consists of a single "sugar" group of atoms. The only
important monosaccharides are the hexoses, or sugars con-
taining six carbon atoms, CeH^Oe. Dextrose and levulose
are the best examples of hexoses. The disacckarides are
formed by the condensation of two molecules of a monosac-
charide with the elimination of one molecule of water. Each
molecule of a disaccharide, then, consists of two single
"sugar" groups of atoms. Sucrose and maltose are the
principle disaccharides found in plants.

1 Optical Activity : An ordinary ray of light is supposed to consist of
particles vibrating in every direction at right angles to the direction of the
ray. When such a ray is passed through a properly cut crystal of Iceland
spar called a Nicol prism, it is separated into two rays, one of which is
reflected out to one side of the prism, and the other passes through, its
particles now vibrating in only one plane. This ray is said to be polarized,
and substances which have the power of rotating this plane of polarized
light in one direction or the other are said to be optically active, either
dextrorotatory ( +) or levorotatory ( ) as they turn the plane of polarized
light to the right or to the left. The amount of rotation depends on the
specific property of the substance and the number of molecules through
which the light passes. The amount of rotation can be measured, and by
calculation the percentage composition of sugar or other substance can be
determined in a solution. The instrument for measuring the amount of
rotation is called a polariscope, or, since it is used mostly for the determina-
tion of sugar, a saccharimeter. It consists essentially of a tube containing
at one end a polarizing prism which polarizes a ray of light from some source,
and an analyzing prism at the other end mounted on a revolving disk gradu-
ated into degrees. Between the two prisms is a trough in which may be
placed a tube, closed at both ends with glass, containing the solution to be
examined. The polarized light if undisturbed passes through the analyzer
and illuminates the field of vision through an eye-piece. If the ray is rotated
by an optically active substance, the light does not pass through the analyzer
and the field of vision is darkened. If the analyzer is now rotated to the right
or left, as the case may be, just as much as the substance rotates the polarized
ray, the field of vision, will again be brightly illuminated. There are many
modifications of this polariscope tending to increase the accuracy of obser-
vation, but the principle is the same in all of the instruments. For com-
paring the rotatory power of different substances, there is used the term
specific rotation which is the amount of dextro- or levorotation of plane
polarized sodium light caused by a solution 10 cm. long, each cubic centi-
meter of which contains one gram of substance, at a temperature of 20 C.



20



3. Dextrose, Glucose, Grape Sugar. CeH^Oe, graphically:

H

H C O H




This constitutes what may be termed a single "sugar"
group of atoms, hence, monosaccharide. It is found free in
nature in all parts of the plant, but for the most part it occurs
associated with an equal quantity of levulose in such sweet
fruits as grapes, cherries, and pears. It is also found in
onions. Dextrose occurs in glucosides 1 in combination with
different kinds of compounds such as alcohols, acids, and
aldehydes, which hydrolyze naturally under the action of
enzymes to form glucose and the other compounds. It is
formed in nature (Section 62) by the condensation of for-
maldehyde in the leaf, and by hydrolytic enzyme (Section
46) action on such storage forms of carbohydrates as starch
and sucrose (Section 63).

1 The formation of a glucoside can best be seen from a graphic formula:
H H

H C O H H C O H

I I

H C O H H C O H



H C O H + H
H C O H
H C O H



H C



=




O R = H C 1 + H 2 O



O R



R represents the alkyl group of an alcohol, acid, aldehyde, or ketone.



CARBOHYDRATES 21

Physiologically dextrose is the usual transport form of
carbohydrates, but occasionally it is the storage form, as in
the onion. Dextrose is a nearly white solid, easily soluble
in water and in hot alcohol, insoluble in ether, crystallizes
as a hydrate, CeH^Oe.I^O, from water, and in the dehydrated
form from alcohol (Fig. 1). It is not as sweet as ordinary
sugar. It is dextrorotatory, from which fact it gets the name




Fro. 1. Crystals of anhydrous dextrose. Magnified. Drawing l>y
C. A. Smith.



dextrose, "right sugar." The specif c rotation of ordinary
dextrose is +52.5. Since it contains the aldehyde group
it is easily oxidized to various compounds. This oxidation is
measured by the equivalent reduction of what is called
Fehling's solution 1 and this reduction of Fehling's solution
is a characteristic reaction for dextrose. Dextrose also

1 Fehling's solution is made by mixing equal parts of a solution of copper
sulphate with a solution of sodium potassium (artrate (Rochelle salts)
in sodium hydroxide. The sodium hydroxide forms copper hydroxide which
dissolves to a deep blue color in the sodium potassium tartrate. The copper
hydroxide in solution is the reacting compound. It is reduced according
to the following equation:

4 Cu(OH)a = 4 CuOH + 2 H 2 O + Oj.

On boiling the solution the yellow cuprous hydroxide, 4 CuOH, changes
to the brick red cuprous oxide and water, CmO+HaO. The amount of
red precipitate is a measure of the amount of dextrose in solution.



22 PLANT COMPOUNDS

unites with calcium hydroxide and barium hydroxide to
form compounds which might be called "dextrates" or
"dextroxides," C 6 HiiO 6 .CaOH and CeHnOe.BaOH. 1 They
are soluble in water but insoluble in alcohol. Dextrose
is easily changed, or fermented, by fungi and bacteria to
alcohol and carbon dioxide, as follows: CeH^Oe = 2C 2 H 5 OH
+ 2CO 2 ; to lactic acid, as follows: C 6 H 12 O 6 = 2CH 3 .CHOH.-
COOH; and to butyric acid, carbon dioxide, and hydrogen,
as follows: C 6 H 12 O 6 = CH 3 .CH 2 .CH 2 .COOH + 2CO 2 + 2H 2 .
Pure dextrose can be made by the hydrolysis of starch or
sucrose with dilute hydrochloric acid, and recrystallization
from hot alcohol. Commercial glucose is made in this country
by boiling cornstarch under pressure with hydrochloric acid,
neutralizing the acid with sodium carbonate, and clarifying
the liquid with bone charcoal. The product is sold as a thick,
amber-colored liquid containing 30 to 40 per cent, of dextrose,
the rest being dextrins and other impurities. By boiling the
mass longer more dextrins are converted to dextrose and a
crystallizable product containing 70 to 80 per cent, dextrose
is obtained. Glucose is used largely in making candy,
jellies, preserves, table syrup, etc.

1 Their formation can be best illustrated graphically. The exact location
of the hydroxyl group which combines with the base is not known, but the
one chosen will at least illustrate the reaction :

H H

I I

H C O H H C O H

H C O H H C O H + H.O

H C O H = H C O H

I I

H C O H H C O H



H C O+H + H O v H C O Ca O H

I \/



I I >Ca



H C=O H O/ H C=O



CARBOHYDRATES 23

4. Levulose, Fructose, Fruit Sugar. CeH^Oj, graphically:




This constitutes another single "sugar" group of atoms.
Levulose is found in plants, particularly the sweet fruits,
and nearly always with dextrose. Honey is almost wholly
a mixture of levulose and dextrose. Levulose is formed
naturally by the enzyme hydrolysis of sucrose, or arti-
ficially by hydrolysis of sucrose with dilute hydrochloric
acid. In either case there are produced equal quantities
of dextrose and levulose. Physiologically it probably plays
the same role as dextrose. Levulose is a white solid, crystal-
lizable with considerable difficulty, very soluble in water
and in hot alcohol. It is much more strongly levorotatory
than dextrose is dextrorotatory, the specific rotation being
92.5. Hence it is called levulose, "left sugar." It is
sweeter than dextrose. Although it does not contain an
aldehyde group it is easily oxidized, that is, it reduces
Fehling's solution. Levulose forms compounds with calcium
hydroxide and barium hydroxide "levulates" insoluble in
water and in alcohol. It is fermented by fungi and bacteria
like dextrose. One way to make it is to boil sucrose with
hydrochloric acid and thereby change the sucrose to dextrose
and levulose. On treating the cold solution with an excess
of calcium hydroxide, the crystals of calcium levulate
are precipitated and can be filtered. On decomposing the
precipitate with oxalic acid, and concentrating the filtered
solution, levulose will crystallize out. Aside from its use



24 PLANT COMPOUNDS

as a food in fruit and honey, where it occurs naturally,
levulose has no economic importance.

5. Sucrose, Saccharose, Cane Sugar. C^H^On, graphi-
cally:

H



H (
H (
Hf


3 H H

: o H H c o H

1

- f) TT n r\


H (


3 O H


H C O H


H C O H
TT C" C


H C O H
> r.



H C O H



This constitutes a double "sugar" group of atoms or the
union of two single groups. Hence it is a disaccharide. It
is very widely distributed in plants, being found particularly
in sweet fruits, stalks of corn and sugar cane, in seeds, roots,
bulbs, and the sap of maple, birch, and other trees. Sugar
cane and sugar beets are the principal sources of sucrose,
the former containing about 20 per cent., the latter, 15
per cent. Fig. 2 illustrates the harvesting of a crop of
sugar cane, and Fig. 2 a growing crop of sugar beets.
From the physiological point of view, sucrose is a storage
form of carbohydrates, particularly in roots and tubers such
as beets and sweet potatoes, it being formed in all proba-
bility by a condensation of dextrose and the elimination of
water.

Sucrose is a colorless solid, crystallizing in large, clear crys-
tals (Fig. 3). As it is usually purchased, it consists of very
small crystals, the mass of which appears white because
of reflected light. It is easily soluble in water, slightly
soluble in hot absolute alcohol, more easily soluble in dilute
alcohol, insoluble in ether and in cold absolute alcohol. It
is dextrorotatory, the specific rotation being +66.5. Its
sweetness is too well known to need description.



CARBOHYDRATES



25




=



26 PLANT COMPOUNDS

Sucrose does not reduce Fehling's solution, that is, it is
not easily oxidized. It melts at about 160 C. From 170
up to 190 C. it decomposes, by losing water, to a mixture
of unknown condensation products, the mass turning brown
in color and having a peculiar, agreeable flavor. Caramel
is the name given to the material. Caramel is soluble in
water, reduces Fehling's solution, and is used to a large
extent as flavoring for candy and ice-cream.



FIG. 3. Crystal of sucrose. Natural size. Drawing by C. A. Smith.

Under the action of an enzyme (Section 46) called inver-
tase, sucrose hydrolyzes to equal parts of dextrose and levu-
lose. 1 This is the way it changes naturally in plants. Arti-

1 The hydrolytic change of sucrose into equal parts of levulose and dex-
trose is shown best by the graphic formula, and illustrates very well the
glucoside-like character of the sucrose molecule. (See footnote on p"age 20.)
In fact it may be considered a " levulo-glucoside, " or "levulin. "
H H

I I

H H C O H H

H O C H H C O H H O C H
O C H H C O H H O C H




H O C H = H C O H + H O C H
H O C H H C O H H O C H
C H C=O O=C



H O C H H O C H

I I

H H

Sucrose. Dextrose. Levulose.
The hydrogen and oxygen of water enter the sucrose molecule as indi-
cated by the heavy letters, and the molecules of dextrose and levulose
result.



CARBOHYDRATES 27

ficially, sucrose can be hydrolyzed by boiling with a dilute
mineral acid like hydrochloric, the products of this acid
hydrolysis being the same as with invertase. The mixture of
levulose and dextrose thus produced is known as invert sugar,
because the levorotatory power of levulose is greater than the
dextrorotatory power of dextrose, the net result being levo-
rotation. The specific rotation of invert sugar is 20 V
Fungi and bacteria containing invertase change sucrose to
dextrose and levulose, and can then ferment to the usual
products of alcohol, carbon dioxide, etc. It is not directly
fermentable in most cases.

With alkalies and alkaline earths sucrose forms saccha-
rates, or "sucroxides," those of calcium being the most im-
portant. There are three compounds with calcium : Mono-
calcium saccharate, Ci 2 H 2 iOu.CaOH; dicalcium saccharate,
Ci2H 2 oOn.2CaOH; tricalcium saccharate, C^HigOu.SCaOH.
The monocalcium compound is readily soluble in water, the
tricalcium compound difficultly soluble. The latter is used
commerically in the separation of sucrose from beet molasses.
The molasses is treated with freshly burned lime. The
resulting precipitate of tricalcium saccharate is filtered,
washed with cold water and decomposed by carbon dioxide
in aqueous suspension. The reaction is as follows:

C^HnOn.SCaOH + 3COj = ciiHaOu + 3CaCO 3 .

Many other saccharates are also formed, such as those of
iron, aluminium, nickel, and copper. Those of iron are used
medicinally.

Pure sucrose is prepared by precipitating it from a solu-
tion of commercial sucrose with cold, absolute alcohol, and

1 The specific rotation of levulose is 92.5 and of dextrose is + 52.5, but
that of invert sugar is not 40, but 20, since specific rotation is the
angular rotation of a column 10 centimeters long which contains 1 gram of
substance in 1 cubic centimeter (footnote p. 19), and 1 gram of invert
sugar consists of i gram of dextrose and J gram of levulose, thus giving
only $ the angular difference between the specific rotations of levulose and
dextrose.



28



PLANT COMPOUNDS



washing the fine crystals with absolute alcohol. Commercial
sucrose is made from sugar cane by squeezing out the juice
in mills, clarifying with lime to remove impurities, evapo-
rating the filtrate, and finally crystallizing out the sucrose.
Fig. 4 shows the interior of a sugar factory where the cane
juice is being evaporated. Further solution, treatment
with lime and bone black, and recrystallization yields the
pure granular sugar (sucrose) of commerce. Brown sugar




FIG. 4. Boiling cane juice in a sugar factory at Guadaloupe.



is obtained by evaporating to dryness the mother liquor
from which no sucrose will crystallize. Brown sugar origin-
ally contained some caramel because the evaporation of the
syrup was carried on in vats heated by a free flame, and part
of the material, being overheated, caramelized. Modern
evaporators are steam-heated vacuum pans, and thus
caramelization is avoided.

From the sugar beet, sucrose is made by slicing the beets
and soaking them in water, thus allowing the sucrose to



CARBOHYDRATES 29

diffuse gradually out of the beet cells. The concentrated
juice is clarified and purified much as in the case of sugar
cane juice. Beet sugar is exactly the same as cane sugar,
although when first made methods of purification were not
perfect, and the admixed impurities made its quality poorer
than that of cane sugar.

The various uses of cane sugar are too well known to
need description.

6. Maltose, Maltobiose, Malt Sugar. Ci^H^On, graphi-
cally :




This constitutes another double "sugar" group. It is
one of the most widely distributed sugars in plants, but
since it is never a storage form of carbohydrates it is not
found in any quantity, as are the other sugars. It is one
of the transition forms from starch to dextrose, and is
formed to a large extent in the germinating seed (Section 47).
Of itself, however, it may serve as a transport form of
carbohydrate without undergoing a change to dextrose.
It is a white, crystalline solid, readily soluble in water;
slightly soluble in cold alcohol; not as sweet as sucrose.
It is dextrorotatory, the specific rotation being +138.
Maltose reduces Fehling's solution, since it belongs to the
aldehyde group. Under the action of an enzyme called mal-
tase, it is hydrolyzed to dextrose, one molecule of maltose



30 PLANT COMPOUNDS

breaking up into two molecules of dextrose. 1 It is also
hydrolyzed to dextrose on boiling with a dilute mineral acid
like hydrochloric. Maltose ferments only as it is hydro-
lyzed to dextrose by enzymes (Section 46) in the fungi and
bacteria. It forms compounds with alkalies and alkaline
earths, but they are of no importance.

Maltose is prepared by treating starch paste with malt
extract (Section 47) at 60 C., and extracting the maltose thus
formed with successive portions of hot 87 per cent, alcohol,
finally evaporating and allowing it to crystallize. It is
recrystallized from hot methyl alcohol, after purifying with
bone black.

Commercially it occurs in malt and malt products which
are made from germinating barley (Section 96, a). It also



Online LibraryCharles William StoddartThe chemistry of agriculture : for students and farmers → online text (page 1 of 24)