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'^"V^^,
H0¥ CROPS FEED.
HOW CROPS FEED.
A TREATISE ON THE
ATMOSPHERE AND THE SOU
AS RELATED TO THE
Nutrition of Agricultural Plant?
WITH ILLUSTRATIONS.
SAMUEL W! JOHNSON, M.A.,
PKOFESSOB OP ANALYTICAL AND AGRICULTURAL CHKMISTRY IN THK SHBPFIELD
80IKNTIFI0 SCHOOL OF YALB COLLEGE ; CHEMIST TO THE CONNEC-
TICUT STATE AGKICULTITRAL SOCIETY; MEMBER OF THE
NATIONAL ACADEMY OF SCIENCES.
NEW YORK:
OKANGE JUDD COMPANY,
1910
(p^^^
'I^
Entered according to Act of Congress, in the year 1870, by
OI^ANGE JITDD & CO.,
Id th« Clerk's Office of the Dis^trict Court of the United States for the Soathem
District ol New York
,575/
Printed in U. S. %
PREFACE.
The work entitled " How Crops Grow " has been re-
ceived with favor beyond its merits, not only in America,
but in Europe. It has been republished in England under
the joint Editorsliip of Professors Church and Dyer, of
the Royal Agricultural College, at Cirencester, and a
translation into German is soon to appear, at the instiga-
tion of Professor von Liebig.
The Author, therefore, puts forth this volume — the com-
panion and complement to the formei* — with the hope that
it also will be welcomed by those who appreciate the sci-
entific aspects of Agriculture, and are persuaded that a
true Theory is the surest guide to a successful Practice.
I The writer does not flatter himself that he has produced
a popular book. He has not sought to excite the imagi-
nation with high-wrought pictures of overflowing fertility
as the immediate result of scientific discussion or experi-
ment, nor has he attempted to make a show of revolution-
izing liis subject by bold or striking speculations. His
ofiice has been to digest the cumbrous mass of evidence,
in which the truths of Vegetable Nutrition lie buried out
5
075/ ***'"<»llfGfUB»^»y.
VI PUEFACE.
of tlic roacli of the ordinary iu<iuirer, and to set them
forth in 2)roper order and in })lain dress for their legiti-
mate and sober uses.
It has cost the Investigator severe study and labor to
discover tlie laws and many of the facts which are laid
down in the following pages. It has cost the Author no
little work to collect and arrange the facts, and develop
their mutual bearings, and the Reader must pay a similar
price if he would apprehend them in their true signifi-
cance.
In this, as in the preceding volume, the Author's method
has been to bring forth all accessible facts, to present their
evidence on the topics under discussion, and dispassion-
ately to record their verdict. If this procedure be some-
times tedious, it is always safe, and there is no other mode
of treating a subject which can satisfy the earnest inquirer.
It is, then, to the Students of Agriculture, whether on the
Farm or in the School, that the Author commends his
book, in confidence of receiving full sympathy for its
spirit, whatever may be the defects in its execution.
, CONTENTS.
Introduction ..17
DIVISION I.
THE ATMOSPHERE AS RELATED TO VEGETATION.
CHAPTER I .
Atmospheric Air as the Food of Plants.
§ 1. Chemical Composition of the Atmosphere 21
§ 2. Relation of Oxygen Gas to Vegetable Nutrition 22
§3. " " Nitrogen Gas to " " 26
§ 4. " " Atmospheric Water to Vegetable Nutrition 34
§ 5. " " Carbonic Acid Gas " " " 38
§6. » " Atmospheric Ammonia to " " 49
§ 7. Ozone 63
§ 8. Compounds of Nitrogen and Oxygen in the Atmosphere 70
§ 9. Other Ingredients of the Atmosphere 91
§ 10. Recapitulation of the Atmospheric Supplies of Food to Crops 94
§ 11. Assimilation of Atmospheric Food 97
S 12. Tabular View of the Relations of the Atmospheric Ingredients to the
Lifeof Plants 98
CHAPTER II.
The Atmosphere as Physically Related to Vegetation.
S 1. Manner of Absorption of Gaseous Food by Plants »»
DIVISION II.
THE SOIL AS RELATED TO VEGETABLE PRODUCTION.
CHAPTER I.
Introductory 104
7
Vlit HOW CHOPS FKED.
CHAPTEli II.
Origin and Formation op Soils 10(j
§ 1. Chemical Elements of Rocks 107
§ 2. Mineralogical Elements of Rocks 108
§ .3. Rocks, their Kinds and Characters 117
§ 4. Conversion of Rocks into Soil 12*
§ 5. Incorporation of Organic Matter with the Soil, and its Effects 135
CHAPTER III,
Kinds op Soils, their Definition and Classipication.
§ 1. Distinctions of Soils based upon the Mode of their Formation or Deposi-
tion 142
S 2. Distinctions of Soils based upon Obvious or External Characters 146
CHAPTER IV.
Phtsioal Characters of the Soil 167
S 1. Weight of Soils 158
y S. State of Division 159
§ 3. Absorption of Vapor of Water 161
§ 4. Condensation of Gases 165
§ 5. Power of Removing Solid Matters from Solution 171
I 6. Permeability to Liquid Water. Imbibition. Capillary Power 176
§ 7. Changes of Bulk by Drying and Frost 183
§ 8. Adhesiveness 184
§ 9. Relations to Heat 186
CHAPTER V.
The Soil as a Source op Food to Crops : Ingredients whose Elements
ARE OP Atmospheric Origin.
S 1. The Free Water of the Soil in its Relations to Vegetable Nutrition 199
§ 2. The Air of the Soil 217
S 3. Non-nitrogenous Organic Matters. Humus 222
§ 4. The Ammonia of the Soil 238
§ 5. Nitric Acid (Nitrates) of the Soil 251
§ 6. Nitrogenous Organic Matters of the Soil. Available Nitrogen 274
§ 7. Decay of Organic Matters 289
§ 8. Nitrogenous Principles of Urine 293
I 9. Comparative Nutritive Value of Ammonia-Salts and Nitrates 300
CONTENTS. IX
CUAPTER VI.
The Soil as a Source op Food to Ckops : Ingredients whose Elements
ARE Derived from Kocks.
§ 1. General View of the Constitution of the Soil as Related to Vegetable
Nutrition 305
i|§ 2. Aqueous Solution of the Soil 309
§ 3. Solution of the Soil in Strong Acids 329
§ 4. Portion of Soil Insoluble in Acids 330
§ 5. Reactions by which the Solubility of the Elements of the Soil Is al-
tered. Solvent Effects of Various Substances. Absorptive and
Fixing Power of Soils 331
S 6. Review and Conclusion 361
INDEX.
Absorption and displacement, law
of 336
Absorptive power of soils 333
" " cause of.343, 354
" " " significance
of 3-4
Acids in soil 223
" absorbed by soils 353
Adhesion 165
Adhesiveness of soils 184
Air, atmospheric, composition of. . 21
" within the plant, composition
of 45
Alkali-salts, solvent effect of 130
AUotropism 06
Alluvium 145
Aluminum, alumina. 107
Amides 276
Amide-like bodies 277, 300
Ammonia 49, 54
absorbed by clay.... 243, 267
" " " peat 300
" " " plants... .56, 98
" condensed in soils 240
" conversion of into nitric
acid 85
" evolved from flesh, decay-
ing under charcoal 169
" fixed by gypsum 244
" in atmosphere 54
" " " how formed. 77, 85
" of rain, etc 60
" of the soil, formation of.239
" " " chemically
combined. 243
" " " physically
condensed. 240
" " " quantity of.. 248
" " " aolnbility of. 246
" ♦' " volatility of.. 244
11
Ammonia-salts and nitrates, nutri-
tive value of 300
Amphibole 113
Analysis of soils, chemical indica-
tions of 368
" mechanical 147
Apatite .. 116
Apocrenates 231
Apocrenic acid 237, 229
Argillite 119
Ash-ingredients, quantity needful
for crops 363
Atmosphere, chemical composi-
tion 21, 22
" physical constitution.. 99
Atmospheric food, absorbed 99
" " assimilated — 97
Barley crop, ash ingredients of. 364
Basalt 120
Bases, absorbed by soils 335, 359
Bisulphide of iron 115
Burning of clay 185
Calcite 115
Capillarity 175, 199, 201
Carbohydrates in soil 222
Carbon, fixed by plants 43, 48
" in decay 291
" supply of 93
Carbonate of lime 113, 162
" " magnesia 115,162
Carbonic acid 38
" " absorbed by soil 221
" plants.41,
45, 98
" " exhaled by plants.. 43, 99
" " in the soil 218
" " " water of soil.. 220
" " quantity in the air.40,
47, 94
" " solubility in water.4U,13(J
XII
HOW CROPS FEED.
Carbonic acid, solvent action of. . . .128
Carbouic oxide 93
Chabasite 115
" action on saline com-
pounds 345
" formed in Roman mason-
ry a51
Chalk soils 192
Charcoal, absorbs gases 1C5
" defecating action of. 174
Chili saltpeter 253
Chlorite . 113
Chrysolite 114
Clay 132,134, 154
" absorptive power 174
" effect of, on urine 293
Clay-Blate 119
Coffee, condenses gases 168
Color of soil .. . 190
Conglomerates.. 121
Crenates , 231
Crenic acid 227, 229
Decay 289
Deliquescence 103
Deserts 197
Dew : . . 189, 195
Diffusion of gases 100
Diorite 120
Doleri te 120
Dolomite 115, 121
Draining 185
Drain water, composition of 312
Drift 144
Dye stuffs, fixing of 174
Earth-closet 171
Eremacausis 289
Evaporation, produces cold 188
" amount of, from soil. 197
Exhalation 202, 206
Exposure of soil 195
Feldspar 108
" growth of barley in 160
Fermentation 290
Fixtation of bases in the soil 339
Frost, effects of, on rocks 124
" " " on soils 184,185
Fumic acid 258
Gases, absorbed by the plant 103
" " " porous bo.lies.. 167
" " " soils 16.5, 166
" diffusion of 100
" osmose of ^.102
Glaciers 12.i
Glycine 29(1
GlycocoU 296
Gneiss 119
Granite 118, 120
Gravel 152
" warmth of 195
Guanin 296
Gypsum 115
" does not directly absorb
water 163
" fixes ammonia 344
Hardpan 150
neat, absorption and radiation of. .
188, 193
" developed in flowering 24
" of soil 187
Hippuricacid 395, 277
Hornblende 112
Hydration of minerals 127
Hydraulic cement 122
Hydrochloric acid gas ; 93
Hydrogen, supply of, to plants 95
" In decay 291
Hydrous silicates, formation of 352
Hygroscopic quality 164
Humates 230
Humicacid 226, 229
Humin 230, 229
Humus 136, 224, 276
" absorbent power for water.. 162
" absorbs salts from solutions. 172
" action on minerals 138
" chemical nature of 138
" does it feed the plant? 232
" not essential to crops 238
" value of 182
Iodine in sea-water 322
Isomorphism Ill
Kreatin 196
Kaolinite 113,132
Latent heat 188
Lawes' and Gilbert's wheat experi-
ment? .372
Leucite 113
Lime, effects of 184, 185
Limestone 121, 123
Loam 154
Lysimeter 314
Magnesite 115
Marble .. 121
Marl 155
^larsh gas. 91, 99
Mica...' 109
xut
Mica slate 119
Minerals 106, 108
" hydratiouof. 127
" solution of 197
" variable composition of. ...110
Moisture, effect of, on temperature
of soil 193
Mold 156
Moor-bedpan 157
Muck 155
Nitrate of ammonia 71, 73
" " " in atmosphere. 89
Nitrates 253
" as food for plants. 271
" formed in soil 171, 179
" in water 270
" loss of. 270
" reduction of 73, 82, 85
" " "in soil 268
" tests for 75
Nitric acid 70
" " as plant-food 90,98
" " deportment towards the
soil ,357
" " in atmosphere 86
" " " rain-water .. 86
" " " soil... 251, 254
" " " " sources of 256
Nitric oxide 72
Nitric peroxide 72
Nitrification 252, 286
" conditions of 265, 292
Kitrogen, atmospheric supply to
plants 95
" combined, in decay. 291, 293
" " of the soil... 275
" combined, of the soil,
available 283
" combined, of the soil,
inert 278
" combined, of the soil,
quantity needed for crops. 288
" free, absorbed by soil. . .167
" " assimilated by the
soil 259
** " in soil 218
" " not absorbed by
vegetati on 26, 99
" " not emitted by liv-
ing plants 23
Nitrogen-compounds, formation of,
in atmosphere. 75, 77, 83
Nitrogenous fertilizers, effect on
cereals... fi3
Nitrogenous organic matters of soil.274
Nitrous acid 73
Nitrous oxide 71, 93
Ocher 156
Oxidation, aided by porous bodies.
169, 170
Oxide of iron, a carrier of oxj'gen . . 257
" " hydrated, in the soil.SoO
Oxj'gen, absorbed by plants 98
" essential to growth 23
" exhaled by foliage 25,99
" function of, in growth fU
" in soil 218
" supply 94
" weathering action of 131
Ozone 63
" concerned in oxidation of ni-
trogen 82
" formed by chemical action. 66, 67
" produced by vegetation. 67, 84, 99
" relations of, to vegetable nu-
trition 70
Pan, composition of 352
Parasitic plants, nourishment of. . .235
Peat 155,224
" nitrogen of 274
Phosphate of lime 116
Phosphoric acid fixed by the soil . . ..357
" " presence in soil
water 315
Phosphorite 116
Plant-food, concentration of. 320
" maintenance of supply. 371
Platinized charcoal 170
Platinum sponge, condenses oxygenl70
Porphyry 120
Potash, quantity in barley crop 363
Provence, drouths of 198
Pyrites 115
Pyroxene 112
Pumice 120
Putrefaction 290
Quartz ... 108,123
Rain-water, ammonia in 60, 88
'• nitric acid in 86
" phosphoric acid in 94
Ree Ree bottom, soil of 160
Respiration of the plant 43
Rocks 106. 117
" attacked by pjiute 140
now CROrS FEED,
Rocks, conversion into soils 122
Roots, direct action on soil 320
Saline incrustations 179
Saltpeter 252
Salts decomposed or alisorbod by
the soil 330
Sand 153, 102
Sand filter 172
Sandstone 121
Serpentine 114, 121
Schist, micnceou? 110
" talcose 121
chlorite 121
Shales 122
Sherry wine re2;i()n 192
Shrinking of soils laS
Silica 108
" function in the soil 353
" of soil, liberated by strong
acids 330
Silicates 109
" zeolitic, presence in soils.. 349
Silicic acid, fixed in the soil 358
Silk, hygroscopic 165
Soapstone 121
Sod, temperature of 109
Soil 104
" absorptive power of 333
" aid to oxidation 170
" aqueous solution of 309, 323, 328
" condenses gases 105, 166
" capacity for heat 194
" chemical action in 331
" composition of. 302, 369
" exhaustion of. .373
" inert basis 305
" natural strength of. . ., 373
" origin and formation.. 100, 122, 135
" physical characters 157
" porosity of. 170
" portion insoluble in acids 330
" relative value of ingredients... .367
" reversion to rock 332
" solubility in acids 329
" " water 309
" source of food to crops 305
" state of division 159
Soils, sedentary 143
" transported 143
" weight of 158
Solubility, standards of 308
Solution of soil in acids .,370
" " " water 310
Steatite 121
Swamp muck 155
Suli>hatcs, agents of oxidation 258
Sulphate of lime 115
Sulphin-, in decay ..293
Sulphurous acid 94
Sulphydric acid 94
Syenite 120
Talc lis
Temperature of soil 1S6, 187, 194
Transpiration 202, 208
Trap rock 120
Ulmates 230
Ulmic acid 224, 226, 229
Ulmin 224,226, 229
Urea 294, 277
Uric acid 295, 277
Urine 293
" preserved fresh by clay 293
" its nitrogenous principles as-
similated by plants 296
Vegetation, antiquity of 1.38
" decay of. 137
" action on soil 140
Volcanic rocks, conversion to soil.. 135
Wall fruits 199
Water absorbed by roots 202, 210
" functions of, in nutrition of
plant 216
" imbibed by soil 180
" movements in soil 177
" proportion of in plant, influ-
enced by soil 213
" of soil 315, 317
" " bottom water 200
" capillary 200
" hydrostatic 199
" hygroscopic 201
" quantity favorable to crops. .214
Water-currents 124
Water-vapor, absorbed by soil. 101, 164
" exhaled by plants.... 99
" not absorbed by
plants 35, 99
" of the atmosphere 34
Weathering 131-134
Wilting 203
Wool, hygroscopic 164
Zeolites 114,349
HOW CROPS FEED.
INTRODUCTION.
In his treatise entitled " How Crops Grow," the author
has described in detail the Chemical Composition of Agri-
cultural Plants, and has stated what substances are indis-
pensable to their growth. In the same book is given an
account of the apparatus and processes by which the plant
takes up its food. The sources of the food of crops are,
however, noticed there in but the briefest manner. The
present work is exclusively occupied with the important
and extended subject of Vegetable Nutrition, and is thua
the complement of the first-mentioned treatise. "Whatever
infoimation may be needed as preliminary to an under,
standing of this book, the reader may find hi "How Crops
Grow." *
That crops grow by g;ithering and assimilating food ia
a conception with which all are familiar, but it is only by
following the subject into its details that we cm gain hints
that shall apply usefully in Agricultural Practice.
* It has been at least the author's aim to make the first of this series of book*
prepare tlie way for tlie second, as both the fir!«t and the second are written tu
make possible an iiitelli<;ible aceonnt of tlie mode of action of Tillage and of
Fertilizers, which will be the subject of a Mrd work.
XT
18 HOW CROPS FKED.
When a seed germinates in a medium that is totally
destitute of one or all the essential elements of the plant,
the embryo attains a cei'tain development from the mate-
rials of the seed itself (cotyledons or endosperm,) hut
shortly after these are consumed, the plantlet ceases to in-
crease in dry weight,* and dies, or only grows at its own
expense.
A similar seed deposited in ordinary soil, Avatered with
rain or spring water and freely exposed to the atmosphere,
evolves a seedling which survives the exhaustion of the
cotyledons, and continues without cessation to grow,
forming cellulose, oil, starch, and albumin, increases many
times — a hundred or two hundred fold— in weight, nms
normally through all the stages of vegetation, blossoms,
and yields a dozen or a hundred new seeds, each as perfect
as the original.
It is thus obvious that Air, Water, and Soil, are cai)a-
ble of feeding plants, and, under purely natural conditions,
do exclusively nourisli all vegetation.
In the soil, atmosphere, and water, can be found no
trace of the peculiar organic principles of plants. We
look there in vain for celhilose, starch, dextrin, oil, or al-
bumin. The natural sources of the food of crops consist
of various salts and gases which contain the ultimate ele-
ments of vegetation, but which require to be collected and
worked over by the plant.
The embryo of the germinating seed, like the bud of a
tree when aroused by the spring warmth from a dormant
state, or like the sprout of a potato tuber, enlarges at the
expense of previously organized matters, supplied to it
by the contiguous parts.
As soon as the plantlet is weaned from the stores of the
• Since vegetable matter may contain a variable amount of water, either that
which belongs to the sap of the fresh plant, or that which is hygroscopically n-
lained in the pores, all comparisons must be made on the dry, i. e., water-fret
iubstaqce. See "How Crops Grow," pp. 53-5.
IXTktOl^IrCTION. 19
mother seed, the materials, as well as the mode of its nu-
trition, are for the most part completely changed. Hence-
forth the tissues of the plant and the cell-contents must
"be principally, and may be entirely, built up from purely
inorganic or mhieral matters.
In studying the nutrition of the plant in those stages^
of its growth that are subsequent to the exliaustioii of the
cotyledons, it is needful to investigate separately the nu-
tritive functions of the Atmosphere and of the Soil, for
the important reason that the atmosphere is nearly con-
stant in its composition, and is beyond the reach of human
influence, while the soil is infinitely Aariable and may be
exhausted to the verge of unproductiveness or raised to
the extreme of fertility by the arts of the cultivator.
In regard to the Atmosphere, we have to notice minutely
the influence of each of its ingredients, including Water
in the gaseous form, upon vegetable production.
The evidence has been given in " How Crops Grow," which
establishes what fixed earthy and saline matters are essential
ingredients of plants. The Soil is i)lainly the exclusive
source of all those elements of vegetation which cannot as-
sume the gaseous condition, and which therefore cannot ex-
ist in the atmosphere. The study of tlie soil involves a con-
sideration of its origin and of its manner of formation. The
productive soil commonly contains atmosjiheric elements,
which are important to its fertility; the mode and extent
of their incorporation with it are topics of extreme prac*
tical importance. We have then to examine the signif-
icance of its water, of its ammonia, and esjiecially of its
nitrates. These subjects have been recently submitted to
extended investigations, and our treatise contains a large
amount of infoiTnation pertaining to them, which has never
before appeared in any publication in the English tongue.
Those characters of the soil that indirectly affect the
growth of plants are of the utmost moment to the fann-
er. It is through the soil that a supply of solar heat, with'
20 now CROPS FEED.
out which no life is possible, is largely influenced. "Water,
whose excess or deficiency is as pernicious as its proper
quantity is beneficial to crops, enters the plant almost
exclusively through its roots, and hence those qualities
of the soil which are most favorable to a due supply of
this liquid demand careful attention. The absorbent pow-
er of soils for the elements of fertilizers is a subject which
is treated of with considerable fullness, as it deserves.
Our book naturally falls into two divisions, the first of
which is devoted to a discussion of the Relations of the
Atmosphere to Vegetation, the second being a treatise on
the Soil.
DIVISION I.
THE ATMOSPHERE AS RELATED TO
VEGETATION.
CHAPTER I.
ATMOSPHERIC AIR AS THE FOOD OF PLANTS.
§ 1-
CHEMICAL COMPOSITION OF THE ATMOSPHERE.
A multitude of observations has demonstrated that
from ninety-five to ninety-nine per cent of the entire mass
(weight) of agricultural plants is derived directly or indi-
rectly from the atmosj^here.
The general composition of the Atmosphei-e is familiar
to all. It is chiefly made up of the two elementary gases,
Oxygen and Nitrogen, which have been described in " How
Crops Grow," pp. 33-39.* These two bodies are present
in the atmosphere in very nearly, though not altogether,
invariable proportions. Disregarding its other ingredients,
the atmosphere contains in 100 parts
By 7veight. By volume.
Oxygen 23. 17 20. 95
Nitrogen 76.83 79.05
100.00 100.00
Besides the above elements, several other substances oc-
* In our frequent references to this book we shall employ the abbreviatioa
H. C. G.
21
22 now CROPS FEED.
cur or may occur in tlie air in minute and variable quanti-
ties, viz. :
Water, as vapor. . .average proportion by weight, ' l,oo
Carbonic acid gas " " " " •|io-ooo
Ammonia " " " " ' Iso- ooo- ooo ?
' Ozone " " " «' minute traces.
Nitric acid " " '< " " "
Nitrons acid " " " " *' «'
Marsh gas " " »' " " "
In air of (^'^'■'^""''^''^i^^' " " " "
-< Siili>liurous acid, " " " " *' "
towns. ( g„ij,i,^^.(i,.j(. acid " " " " " "
Miller gives for the air of England the following aver-
age proportions by volume of the four most abundant in-
gredients.— {Elements of Chemistry^ part II., p. 30, 3d Ed.)
Oxygen 20.61
Nitrogen 77.95
Carbonic acid 04
Water- vapor 1.40
100.00
We may now appropriately proceed to notice in order
each of the ingredients of the atmosphere in reference to
the question of vegetable nutrition. This is a subject re-
garding which unaided observation can teach us little or
nothing. The atmosphere is so intangible to the senses
that, without some finer instruments of investigation, we
should forever be in ignorance, even of the separate exist-
ence of its two principal elements. Chemistry lias, how-
ever, set forth in a clear light many remarkable relations
of the Atmosphere to the Plant, whose study forms one
of the most instructive chapters of science.
RELATIONS OF OXYGEN GAS TO VEGETABLE NUTRITION.
Absorption of Oxygen Essential to Growtli,— The ele-
ment Oxygen is endowed with great chemical activity.
This activity we find exhibited in the first act of vegetar
A^TMOSPIlEnK' AIR AS THE FOOD OP PLANTS.
23
tlon, viz.: in germination. We know that the presence of
oxygen is an indispensable requisite to the sprouting seed,
and is possibly the means of provoking to action the dor-
mant life of the germ. The ingenious experiments of Traube
(H. C. G., i\ 326.) demonstrate conclusively that free
oxygen is an essential condition of the growth of the
seedling plant, and must have access to the plumule, and
especially to the parts that are in the act of elongation.
De Saussure long ago showed that oxygen is needful to
the development of the buds of maturer plants. He ex-
perimented in the following mamier : Several woody twigs
(of willow, oak, apple, etc.) cut
in spring-time just before the
buds should unfold were placed
under a bell-glass containing
common air, as in fig. 1. Their
cut extremities stood in water
held in a small vessel, while the
air of the bell was separated
from the external atmosphere by
the mercury contained in the
large basin. Thus situated, the
buds opened as in the free air,
and oxygen gas was found to be
consumed in considerable quan- Fig. 1.
tity. When, however, the twigs were confined in an
atmosphere of nitrogen or hydrogen, they decayed, with-
out giving any signs of vegetation. {Reeherches sur la
Yegetatioii, \). 115.)
The same acute investigator found tliat oxj'^gen is ab-
sorbed by the roots of plants. Fig. 2 shows the arrange-
ment by which he examined the effect of difierent gases
on these organs. A young horse-chestnut plant, carefully
lifted from the soil so as not to injure its roots, had the
latter passed through the neck of a bell-glass, and the stem
was then cemented air-tight into the opening. The bell
24
now CHOPS PEED.
was placed in a basin ot'uiereury, C, D, to shut off its con-
tents from the external air. So much water was intro-
duced as to reach the ends of the j^-iucipal roots, and the
space above was occupied by com-
mon or some other kind of air. lu
one experiment carbonic acid, in a
second nitrogen, in a third hydro-
gen, and in three others common
air, was employed. In the first the
roots died in seven or eight days,
in the SL'Cond an^l thii-d they perish-
ed in thirteen or fourteen days,
wliile in the three others they re-
mained healthy to the end of three
weeks, Avhen the experiments were
concludeil. {Recherehes, p. 104.)
Flowers require oxygen for their
development. Aquatic plants send
their flower-buds above the water
to blossom. De Saussure found
that flowers consume, in 24 hours,
several or many times their bulk of oxygen gas. This
absorption proceeds most energetically in the pistils and
stamens. Flowers of very rapid growth expeiience in
this process, a considerable rise of temperature. Garreau,
observing the spadix of Arum itaUcum, which absorbed
28|^ times its bulk of oxygen in one hour, found it 15° F.
wai'mer than the surroiuiding air. In the ripening of
fruits, oxygen is also absorbed in small quantity.
The Function of Free Oxyg^en. — AH those processes
of growth to which free oxygen gas is a requisite appear
to depend upon the transfer to the growing organ of mat-
ters previously organized in some other part of the plant,
and probably are not cases in which external inorgani(?
bodies are built iip into ingredients of the vegetable struc-
ture. Young seedlings, buds, flowers, and ripening fruits^
Fig. 2.
ATMOSPHEllIC AlK As TlUi FoOD OF PLANTS. 2f»
have no power to increase in mass at the expense of the
atmosphere and soil ; tliey liave no provision for the ab-
sorption of the nutritive elements that surround them ex-
ternally, but grow at the expense of other parts of the plant
(or seed) to which they belong. The function of free
gaseous oxygen in vegetable nutrition, so far as c;m be
judged from our existing knowledge, consists in effecting
or aiding to effect the conversion of the materials which
the leaves organize or which the roots absorb, into the
proper tissues of the growing parts. Free oxygen is thus
probably an agent of assimilation. Certain it is that the
free oxygen which is absorbed by the j^lant, or, at least, a
corresponding quantity, is evolved again, either in the un-
combined state or in union witli carbon as carbonic acid.
Exhalation of Oxygen from Foliai^e.— The relation of
the leai^es and green parts of plants to oxygen gas has
thus far been purposely left unnoticed. These organs like-
wise absorb oxygen, and require its presence in the atmos-
phere, or, if aquatic, in the water which surrounds them ;
but they also, during their exposure to lights exhale oxygen.
This interesting fact is illustrated
by a simple experiment. Fill a
glass funnel with any kind of fresh
leaves, and place it, inverted, in a
wide glass containing Mater, fig.
3, so that it shall be completely
immersed, and displace all air from
its interior by agitation. Close the
neck of the funnel air-tight by
a cork, and pour off a portion
of the water from the outer vessel. Expose now the
leaves to strong sunlight. Observe that very soon minute
bubbles of air will gather on the leaves. These will
gradually increase in size and detach themselves, and
after an hour or two, enough gas will accmnulate in
the neck of the funnel to enable tlie experimenter to
2
96 rroAv <nor^ vv.v.r).
prove that it consists of oxygen. For this purpose bring
tlie water outside the neck to u level M'ith that inside;
have ready a splinter of pine, the end of which is glow^
ing hot, but not in flame, remove the cork, and insert the
ignited stick into the gas. It will inflame and burn much
more brightly than in the extei-nal air. (See H, C. G., p.
35, Exp. 5.) To this phenomenon, one of the most ini«
portant connected with our subject, we shall recur under
the head of carbonic acid, the compound which is the
chief source of this exhaled oxygen.
RELATIONS OF NITROGEN GAS TO VEGETABLE NUTRITION.
Nitrogen Gas not a Food to the Plant. — Nitrog n in
the free state appears to be indifferent to vegetation.
Priestley, to wliom we are much indebted for our knowl-
edge of the atmosphere, was led to believe in 1779 that
free nitrogen is absorbed by and feeds the plant. But
this philosopher had no adequate means of investigating
the subject. De Saussure, twenty yeais later, having
command of better methods of analyzing gaseous mix-
tiires, concluded from his experiments that free nitrogen
does not at all j^articipate in vegetable nutrition.
BouSSingault's Experiments. — The question rested un-
til 1837, when Boussingault made some trials, which, how-
ever, were not decisive. In 1851-1855 this ingenious
chemist resumed the study of the subject and conducted
a large number of experiments with the greatest care,
all of which lead to the conclusion that no appreciable
amount of free nitrogen is assimilated by plants.
His plan of experiment was simply to cause plants to
grow in circumstances where, every other condition of de-
velopment being supplied, the only source of nitrogen at
ATMOSPIlEllIO Alli AS TIIK P<)01» OF PLANTS.
their command, besides that contained in the seed itself,
should be the free nitrogen of the atmosphere. For tliis
purpose he prepared a soil consisting of pumice-stone and
the ashes of stable-manure, which was perfectly freed from
all Compounds of nitrogen by treatment with acids and in-
tense heat. In nine of his earlier experiments the soil thus
prepared was placed at the bottom of a large glass globe,
j5, fig. 4, of 15 to 20 gallons' capacity. Seeds of cress,
dwarf beans, or lupins, were deposited in the soil, and a
proper supply of water, purified for the purpose, was add-
ed. After germination of the seeds, a glass globe, D, of
about one-tenth the capacity of the larger vessel, was filled
with carbonic acid (to supply carbon), and was secured air-
tight to the mouth
of the latter, com-
munication being
had between them
by the open neck at
C. The apparatus
was then disposed in
a suitably lighted
place in a garden,
and left to itself for
a period which va-
ried in the diiferent
experiments from 1^
to 5 months. At
the conclusion of the
trial the plants were
lifted out, and, to-
gether with the soil
from Avhich their roots could not be entirely separated,
were subjected to chemical analysis, to determine the
anfiount of nitrogen which they had assimilated during
growth.
The details of these trials are contained in the subjoined
38 aOW CROPS FEED.
Table. The weights are expressed iu the gram and its
fractions.
Kind of Plant.
Duration
of
Erpenrmnt.
m
.so
II If t«
HI
Dwarf bean.
Oat
Bean
Oat . . .
Lupin.
i months
2
3
3 "
2
7 weeks
6 "
. 2 months
•■ ^'/* ':
. 31/2 "
•• as manure
Lupin 5 mouths
" 'as manure
Dwarf bean.
Cress
0.780
0.377
0.5.30
0.618
0.139
2!a02
0.600
0.:343
0.686
0.792
0.665
0.008
0.026
0.627
2.512 f
111.T20 130.11 0
1.87
0.54
0.89
1.13
0.44
1.82
6.73
1.95
1.05
1.53
2.35
2.80
0.65
0.0.349 0.
0078 0.
0.0210 0.
0.0245 0.
0.0031 0.
0.048010.
0.1282 0.
0.03490.
0.02000.
0.0399;0.
0.0354 0.
0.0298|0.
0.00130.0013
0340-0.000!)
0067 -0.0011
0189—0.0021
02261-0.0019
00:M —0.0001
+0.0003
—0.0036
—0.0010
+0.0004
—0.0002
+0.0006
-0.0021
0.0000
—0.0130
While it must be admitted that the unavoidable errors of
experiment are relatively large in Avorkhig Avitb such small
quantities of material as Boussingault here employed, Ave
cannot deny that the aggregate result of these trials is de-
cisive against the assimilation of free niti'ogen, since there
was a loss of nitrogen in the 14 experiments, amounting
to 4 per cent of the total contained in the seeds ; Avhile a
gain was indicated in but 3 trials, and was but 0.13 per
cent of the nitrogen concerned in them. — (Boussingault's
Agro/wmie, Chimie Ar/ricole, et Physlologie, Tome I,
pp. 1-64.)
The Opposite Conclusions of Ville.— In the years 1849,
'50, 'ol, and '52, Georges Ville, at Grenelle, near Paris,
experimented u})on the question of the assimilability of free
nitrogen. His method w\is similar to that first employed
by Boussingault. The plants subjected to his trials were
cress, lupins, colza, wheat, rye, maize, sun-flowers, and to-
bacco. They were situated in a large octagonal cage
made of iron sashes, set with glass-plates. The air was
ATMOSPHERIC AIR AS THE FOOD OF PLANTS.
2d
constantly renewed, and carbonic acid was introduced ia
proper quantity. The experiments were conducted on a
larger scale than those of Boussingault, and their result
was uniformly the reverse. Ville indeed thought to have
established that vegetation feeds on the free nitrogen of
the air. To the conclusions to which Boussingault drew
from the trials made in the manner already described, Ville
objected that the limited amount of air contained in the
glass globes was insufficient for the needs of vegetation ;
that plants, in f ict, could not attain a normal development
under the conditions of Boussingault's experiments. —
(Ville, Recherches sur la Vegetation , pp. 29-58, and 53-98.)
Boussingault's Later Experiments. — The latter there-
upon instituted a new^ series of trials in 1854, in which
he proved that the plants he had previously experimented
upon attain their full development in a confined atmosphere
under the circumstances of his first experiments, provided
they are supplied with some assimilable compound of ni-
trogen. He also conducted seven new experiments in an
ajjparatus which allowed the air to be constantly renewed,
and in every instance confirmed his former results. —
{Agronomic^ Chimie Agrhole et Physiologie^ Tome I,
pp. 65-114.)
The details of these experiments are given in the follow-
ing Table. The weights are expressed in grams.
Kind of Plant.
Duration
of
Expenment.
Lupin
Bean .
Bean .
Bean .
Bean.
Lupin
Cress.
10 weeks
10 "
12 "
14 "
13 "
i 9 "
I as manure
1 10 weeks
I as manure
0.337
0.720
0.718
0.755
1.510
0.310
Q.m)
0.100
2.140 0.0190 0.011S7 —0.0009
2 . 000 0 . 0322 0 . 0325 +0 . 0003
2.^7 0.0;»5 0.0:M1:+0 0006
2.240,0.0339 0.0329 -0.0010
5.150 0.0676 0.0606 —0.0010
1.730 0.0355 0.0324'— 0 0021
I I I
0.533 0.0046 0.0052 4-0.0006
^Mf» .4.780
16.6410. 2269 O.JJ340I-0.0035
30 HOW CROPS FEED.
Inaccuracy of Ville's Results. — In comparing the in-
vestigations of Boussingault an<l Yille as detailed in their
own words, the critical reader cannot fail to be struck
with the greater simplicity of the apparatus used by the
former, and his more exhaustive study of the possible
sources of error incidental to the investigation — facts which
are greatly in favor of the conclusions of this skillful and
experienced philosoi^her. Furthermore Cloez, who was
employed by a Commission of the French Academy to
oversee the repetition of Ville's experiments, found that a
considerable quantity of ammonia was either generated
within or introduced into the apparatus of Ville during
the period of the trials, which of course vitiated all his
results.
Any further doubts with regard to this important sub-
ject have been effectually disposed of by another most
elaborate investigation.
Research of Lawes, Gilbert, and Pugh.— In 1857 and
'58, the late Dr. Pugh, afterward President of the Penn-
sylvania Agricultural College, associated himself with
Messrs. Lawes and Gilbert, of Rothamstead, England,
for the purpose of investigating all those points con-
nected with the subject, which the spirited discussion of
the researches of Boussingault and Ville had suggested as
possibly accounting for the diversity of their results.
Lawes, Gilbert, and Pugh, conducted 27 experiments on
graminaceous and leguminous plants, and on buckwheat.
The plants vegetated witliin large glass bells. They were
cut off from the external air by the bells dipping into
mercury. They were supplied with renewed portions of
purified air mixed Avith carbonic acid, which, being forced
into the bells instead of being drawn through them, e^
fectually prevented any ordinary air from getting access
to the plants.
To li'iw. ail idea of the mode in which these delicate investigations are
c(*nducted, we give here a figure and concise description of the ajipara-
ATMOSPHEl
ilC AIR AS THE FOOD OF PLANTS. 31
32 now CROPS feed.
tus employed by Lawes, Gilbert, and Pugh, in their experiments made in
the year 1858.
^4, tig. 5, represents a stone-ware bottle 18 inches in diameter and 24
inches high.
B, 0, and U, are glass 3-necked bottles of about 1 quart capacity.
F is a large glass shade 9 inches in diameter and 40 inches high.
a represents the cross-section of a leaden pipe, which, passing over all
the vessels A of the scries of 16, supplied them with water, from a reser-
voir not shown, throu;;h tlie tube with stop-cocli a b.
c d eisa leaden exit-tube for air. At c it widens, until it enters the
Vessel A, and another bent tube, q r s, passes through it and reaches to
the bottom of A, as indicated by the dotted lines. The latter opens at
q, and serves as a safety tube to prevent water passing into d c.
Tiie bottles B Care partlj' filled with strong sulphuric acid.
The tube D D,\ inch wide and 3 feet long, is filled with fragments of
pumice-stone saturated with sulphuric acid. At// indentations are made
to prevent the acid from draining against the corks with which the tube
is stopped.
The bottle E contains a saturated solution of pure carbonate of soda.
(7 7t is a bent and caoutchouc-jointed glass tube connecting the interior
of the bottle ^with that of the glass shade F.
i k, better indicated in 2, is the exit-tube for air, connecting the
interior of the shade F with an eight-bulbed apparatus, M, containing
sulphuric acid.
w w is a vessel of glazed stone-ware, containing mercury in a circular
groove, into which the lower edge of the shade F is dipped. These
glass tubes, g h, u v, and i k, 2, pass under the edge of the shade and
communicate with its interior, the mercury cutting off all access of ex-
terior air, except through the tubes. Another tube, n o, passes air-tight
tlirough the bottom of the stone-ware vessel, and thus communicates
•with its interior.
The tubes u v and i k are seen best in 2, which is taken at right
angles to 1.
The plants were sprouted and grew in pots, v, within the shades. The
•tube ?<■> was to supply them with water.
The water which exhaled from the foliage and gathered on the inside
of the shade ran off through 7i o into the bottle 0. This water was re-
turned to the pots through u v.
The renewed supply of pure air was kept up through the bottles and
tube A, B, C\ B, E. On opening the cock a b, A, water enters A, and
Its pressure forces air through the bottles and tube into the shade Fy
whence it finds its exit through the tube i k, and the bulb-apparatus Jf.
In its passage through the strong sulphuric acid of B, C, and B, the air
is completely freed from ammonia, while the carbonate of soda of £ re-
moves any traces of nitric acid. The sulphuric acid of the bulh M puri-
fies the small amount of air that might sometimes enter the shade
through the tube i h, owing to cooling of the air in F-, when the curreut
Al-aiOSPIIERlC AIU AS THE FOOD OF PLANTS. 06
was not passing. The outer ends of the tubes t and u were closed with
caoutchouc tubes and glass plugs.
In these experiments it was considered advisable to furnish to the
plants lUDre carbonic acid than the air contains. This was accomplished
by pouring hj-drochloric acid from time to time into the bottle T, which
contained fragments of marble. The carbonic acid gas thus liberated
joined, and was swept on by the current of air in C. E.Kperiments taught
how much hydrochloric acid to add and how often. Tlie proportion of
this gas was kept within tlie limits which previous experimenters had
found permissible, and was not allowed to exceed 4.0 per cent, nor to
fall below 0.^ per cent.
In these experiments the seeds were deposited in a soil [uirilied from
nitrogen-compounds, by calcination in a current of air and subsequent
washing with pure water. To this soil was added about 0.5 per cent of
the ash of the plant wliieh was to grow in it. Tlie water used for wa-
tering the plants was specially purified from ammonia and nitric acid.
The experiments of Lawes, Gilbert, and Pngh, fully
confirmed those of Boussmgaiilt. For the numerous de-
tails and the full discussion of collateral points bearing on
the study of this question, we must refer to their elaborate
memoir, " On the Sources of the Xitrogen of Vegetation."
. — {Philosophical Transactions, 1831, II, pp. 431-579.)
I\'iti-ogeiL Oils is not I^iiiitte«l l>y I.iiving' I'liiiits. — It
was long supposed by vegetable physiologists that wlien the foliage of
plants is exposed to the sun, free nitrogen is evolved by them in small
quantitj'. In fact, when plants are placed in the circumstances which
admit of coll-^cting the gases tliat exhale fi'om them under the action of
light, it is found tliat besides oxj-gen a quantity of gas appears, which,
unless special precautions arc observed, consists chieily of nitrogen,
which was a iiart of tlie air that fills the intercellular spaces of the plant,
or was dissolved in the water, in which, for the purposes of experiment,
the plant is immersed.
If, as Boussingault has recently (1863) done, this air be removed fpQm
the plant and water, or rather if its quantity be'accurately determined
and deducted from that obtained in the experiment, the result is tliat no
nitrogen gas remains. A small quantity of gas besides oxygen was indeed
usually evolved from the plant when submerged in water. The gas on
examination proved to be marsh gas.
Cloez was unaljle to find marsh gas in tlie air exhaled from either
aquatic or hind plants submerged in water, and in his most recent
researches (186.5) Boussingault found none in the gases given tiflf from
the foliaire of a living tree examined without submergence.
The ancient conclusion of Saussure, Daubeuy, Draper, and others,
that nitrogen is emitted from tlie substance of the plant, is thus showo
to have been based on an inaccurate method of investigation.
2*
I,
IIOAV CROPS FEED.
RELATIONS OF ATMOSPHERIC WATER TO VEGETABLE
NUTRITION.
Occurrence of Water in the Atmosphere.— If w ator be
exposed to the uir in a sliallow, open vessel for some time,
it is seen to decrease in quantity, and finally disapi)ears en-
tirely ; it evaporates, vaporizes, or volatilizes. It is con-
verted into vapor. It assmnes the form of air, and becomes
a part of the atmosphere.
The rapidity of evaporation is gi'eater the more eleva-
ted the temperature of the water, and the drier the atmos-
phere that is over it. Even snow and ice slowly suiFer
loss of weight in a dry day though it be frosty.
In this manner evaporation is almost constantly going
on from the surface of the ocean and all other bodies of
water, so that the air always carries a portion of aqueous
vapor.
On the other hand, a body or mixture whose tempera-
ture is far lower thnn that of the atmosphere, condenses
vapor from the air and makes it manifest in the form of
water. Thus a glass of ice- water in a warm summer's day
becomes externally bedewed with moisture. In a similar
manner, dew deposits in clear and calm summer nights
upon the surface of the ground, upon grass, and upon all
exposed objects, whose temperature rapidly falls when
they cease to be warmed by the sun. Again, when the
invisible vapor which fills a hot tea-kettle or steam-boiler
issues into cold air, a visible cloud is immediately formed,
which consists of mhiute droplets of water. In like man-
ner, fogs and the clouds of the sky are produced by the
cooling of air charged with vapor. When the cooling is
sufficiently great and sudden, the droplets acquire such
size as to fall directly to the ground ; the water assumes
the form of rain.
ATJIO.SPUKKIC AIU AS TIIK FOOD OF I LANTS. oO
Water then exists in the atmosphere during the periods
of vegetable activity as gas or vapor,* and as liquid. In
the former state it is almost perpe'tually rising into the air,
while in the latter form it frequently falls again to the
ground. It is thus in a continual transition, back and
forth, from the earth to the sky, and from the sky to the
earth.
We have given the average quantity of water-vapor in
the air at one per cent ; but the amount is very variable,
and is almost constantly fluctuating. It may range from
less than one-hnlf to two and a half or three per cent, ac-
cording to temperature and othei- circumstances.
When the air is damp, it is saturated with moisture, so
that water is readily deposited upon cool objects. On the
other hand, when dry, it is capable of taking up additional
moisture, and thus ficilitates evaporation.
Is Atmospheric Water Absorbed by Plants 1— It has
long been supposed that growing vegetation has the power
to absorb vapor of water from the atmosphere by its
foliage, as well as to imbibe the liquid water which in the
form of rain and dew may come in contact with its leaves.
Experiments which have been instituted for the purpose
of ascertaining the exact state of this question have, how-
ever, demonstrated that agricultural plants gather little or
no water from these sources.
The wilting of a plant results from the fact that the
leaves suffer water to evaporate from them more rapidly
than the roots can take it up. The speedy reviving of a
wilted plant on the falling of a sudden rain or on the depo-
sition of dew depends, not so much on the absorption by
the foliasie, of the water that gathers on it, as it does
* While there is properly no essential dift'orence between a gas and a vapor,
the former term is commonly applied more especially to aeriform bodies which
are not readily brought to the liquid state, and the latter to those which are easily
condensed to liquids or solids.
36 HOW CROPS FEED.
on the suppression of evaporation, whidi is a consequence
of the saturation of the surrounding air with water.
linger, and more recently Duchartre, have found, 1st,
that plants lose weiglit (from loss of water) in air that is
as nearly as possible saturated with vapor, when their
roots are not in contact with soil or liquid water. Du-
chartre has shown, 2d, that plants do not gain, but some-
times lose weight when their foliage only is exposed to
dew or even to rain continued through eighteen hours, al-
though they increase in weight strikingly (from absorption
of water through their roots,) when the rain is allowed to
fall upon the soil in which they are planted.
Knop has shown, on the otlier hand, that leaves, either
separate or attached to twigs, gain weight by continued
imynersion in water, and not only recover what they may
have lost by exposure, but absorb more tlian they orig-
inally contained. ( Versuchs-Statlonen^ VI, 252.)
The water of dews and rains, it must be remembered,
however, does not often thoroughly wet the absorbent sur-
face of the leaves of most plants ; its contact being pre-
vented, to a grent degree, by the hairs or wax of the
epidermis.
Finally, 3d, Sachs has found that even the roots of
plants appear incapable of taking up watery vapor.
To convey an idea of the method employed in such
investigations, we may quote Sachs' account of one
of his experiments. ( V. St., II, 7.) A young camellia,
having several fresh leaves, was taken from the loose
soil of the pot in which it had been growing ; from
its long roots all particles of earth were carefully remov-
ed, and its weight was ascertained. The bottom of a
glass cylinder was covered with water to a little depth,
and the roots of the camellia were introduced, but not in
contact with the water. The stem was supported at its
ATMOSPHEnlC Ain AS THE POOD OP PLANTS. S?
lower part in a hole in a glass cover,* that was cemented
air-tight upon the vessel. The stem itself was cemented
by soft wax into the liole, so that the interior of the ves-
sel was completely cut off ffom direct communication with
the external atmosphere. The plant thus situated had its
roots in an atmospliere as neaily as possible saturated with
vapor of water, while its leaves were exposed to the ex-
ternal air. After four days had expired, the entire appa-
ratus, plant included, had lost 1.823 grm. Thereupon the
plant was removed from the vessel and weighed by itself;
it had lost 2.188 grm. The loss of the entire apparatus
was due to vapor of water, which had escaped through
the leaves. The diiference between this loss and the los?
which the plant had experienced could be attributed only
to an exhalation of water through the roots, and amount
ed to (2.188 — 1.823=) 0.365 grm.
This exhalation of water into the confined and moist at-
mosphere of the glass vessel is explained, according to
Sachs, by the fact that the chemical changes proceeding
within the plant elevate its temperature above that of the
surrounding atmosphere.
Knop, in experiments on the transpiration of plants,
{Y. St., VI, 25.5,) obtained similar results. He found,
however, that a moist piece of paper or wood also lost
weight wlien kept for some time in a confined space over
water. He therefore concludes that it is nearly impossible in
the conditions of such experiments to maintain the air sat-
urated with vapor, and that the loss of weight by the roots
is due, not to the heat arising from internal chemical
changes, but to simple evaporation from their surface. In
one instance he found that a portulacca standing over
night in a bell-glass with moistened sides, did not lose, but
gained weight, some dew having gathered on its foliage.
* The cover consisted of two semicircular pieces of ground glass, each of
which had a small semicircular notch, so that the twoconld be brought togethei
by their straight edges around the stem.
38 IIOAV CROPS FEEI>.
The result of tliese investigations is, tliat while, perhaps,
wilted foliage in a heavy rain may take u]) a small (juan-
tity of water, and while foliage and roots may absoib
some vajjor, yet in general and for the most part the at-
mospheric water is not directly taken up to any great ex-
tent by plants, and does not therefore contribute immedi-
ately to their nourishment.
itmospheric VFater Enters Crops through the Soil.—
Jt is only after the water of the atmosphere has become in-
corporated with tlie soil, that it enters freely into agricul-
tiiial plants. The relations of this substance to proper
ve'jetable nutrition may then be most appropriately dis-
cussed in detail when we come to consider the soil. (See
p. 199.)
It is probable that certain air-plants (epiphytes) native to the tropics,
■which liave no connection with the soil, and are not rooted in a medium
capable of yielding water, condense vapor from the air iu considerable
quantity. So also it is pi'oved that the mosses and lichens absorb wafer
)an;ely from moist air, and it is well known that they become dry and
brittle in hot weather, recovering their freshness and flexibility when the
air is damp.
§5.
RELATIONS OF CARBONIC ACID GAS TO VEGETABLE
NUTRITION.
Composition and Properties of Carbonic Acid, ~
When 12 grains of pure carbon are heated to redness
in 32 grains of pure oxygen gas, the two boiiies unite to-
gether, themselves completely disappearing, and 44 grains
of a gas are pj-oduced which lias the same bulk as the
oxygen had at the beginning of the experiment. The new
gas is nearly one-half heavier than oxygen, and differs in
most of its properties from both of its ingredients. It is
carbonic acid. This substance is the jiroduct of the burn-
ing of charcoal in oxygen gas, (H. C. G., p. 35, Exp. 6.)
It is, in fact, produced whenever any organic body is
ATMOSlniERIC AIR AS THE I^OOIl OF PLANTS. ,39
binned or decays in contact with the air. It is like oxy-
gen, colorless, but it has a peculiar pungent odor and
pleasant acid taste.
The composition of carbonic acid is evident from what
has been said as to its production from carbon and oxygen.
It consists of two atoms, or 3:2 parts by weight, of oxygen,
united to one atom, or 12 parts, of carbon. Its symbol is
COjj. In the subjoined scheme are given its symbolic,
atomic, and percentage composition.
At. wt. Per cent.
C = 13 27.27
Oo = 32 73.73
CO2 = 44 100.00
In a state of combination carbonic acid exists in nature
in. immense quantities. Limestone, marble, and chalk,
contain, when pure, 44 per cent of this acid united to lime.
These minerals are in chemical language carbonate of lime.
Common salteratus is a carbonate of potash, and soda-
salasratus is a carbonate of soda.
From either of these carbonates it is easy to separate
this gas by tiie addition of another and stronger acid.
For this purpose we may employ the Rochelle or Seidlitz powders so
commonly used in medicine. If we mingle together in the dry state the
contents of a blue paper, which contains carbonate of soda, with those of
a white paper, which consist of tartaric acid, nothing is observed. If,
however, the mixture be placed at the bottom of a tall bottle, and a little
water be poured upon it, at once a vigorous bubbling sets in, which is
caused by the liberated carbonic acid.*
Some important properties of the gas thus set free may be raadily
made manifest by the following experiments.
a. If a burning taper or match be immersed in the gas, the flame is
immediately extinguished. This happens because of the absence of free
oxygen.
6. If the mouth of the bottle from which carbonic acid is escaping be
held to that of another bottle, the gas can be poured into the second ves-
sel, ou account of its density being one-half greater than that of the air.
Proof that the invisible gas has thus been transferred is had by placing
* Chalk, marble, or salaeratus, and chlorhydric (muriatic) acid, or strong vine-
gar (acetic acid) can be equally well employed.
40 ttOtV CEOPS li-KEi).
a burning; toper in the second bottle, when, if the exjieriment was rij^^ht-
]y conducted, the flume will be extinguished.
c. Into a bottle filled as in the last experiment with carbonic acid,
some lime-water is poured and agitated. The previously clear lime-wa-
ter immediately becomes turbid and railliv from the formation oicarbcm-
ate of lime, which is iieaily insoluble in water.
Carbonic Acid iu the Atmospliere.— To show the pres-
ence of carl)oi)ic acid in the atmosphere, it is only neces-
sary to expose lime-water in an open vessel. But a little
time elapses before the liqtiid is covered with a white film
of carbonate. As already stated, the average proportion
of carbonic acid in the atmosphere is 6-lOOOOths
(l-16()0th nearly) by weight, or 4-lOOOOths (l-2500th)
by bulk. Its quantity varies somewhat, however. Among
over 300 analyses made by De Saussure in Switzerland,
Verver in Holland, Lewy in New Granada, and Gilm in
Austria, the extreme range was from 47 to 86 parts by
weight in 100,000.
Deportment of Carbonic Acid towards Water. — Water
dissolves carljonic acid to a greater or less extent, accord-
ing to the temperature and pressure. Under the best or-
dinary conditions it takes up about its own volume of the
gas. At the freezing point it may absorb nearly twice as
much. This gas is therefore usually found in spring, well,
and river waters, as well as in dew and rain. The consid-
erable amount held in solution in cold springs and wells
is a principal reason of the refreshing quality of their wa-
ter. Under pressure the proportion of carbonic acid ab-
sorbed by water is much larger, and when the pressure is
removed, a portion of the gas escapes, resuming its gase-
ous form and causing effervescence. The liquid that flows
from a soda-fountain is an aqueous solution of carbonic
acid, made under pressure. Bottled cider, ale, champagne,
and all effervescent beverages, owe their sparkle and much
of their refreshing qualities to the carbonic acid they con-
tain.
ATMOSl'UKUK
FOOD OV PLANTS. 41
The Absorption of ( arbonic Acid by Plants. — In 1771
Priestley, in Eiigluud, found th;it tlie leaves of plants im-
mersed in water, sometimes disengaged carbonic acid,
sometimes oxygen, and sometimes no gas at all. A few
years later Ingenbouss proved that the exhalation of car-
bonic acid takes place in the absence, and that of oxygen
in the presence, of solar light. Several years more elapsed
before Sennebier first demonstrated that the oxygen which
is exhaled by foliage in the sunlight comes from the car-
bonic acid contained in the water in whicli the plants are
immersed for the purpose of these experiments. It had
been already noticed, by Ingenhouss, that in spring water
plants evolve more oxygen than in river water. We now
know that the former contains more carbonic acid than the
latter. Where the water is by accident or purposely free
from carbonic acid, no gas is evolved by foliage in the
sunlight.
The attention of scientific men was greatly attracted
by these interesting discoveries ; and shortly Percival, in
England, found that a |)lant of mint whose roots were
stationed in water, flourished better when the air bathing
its foliage was artificially enriched in carbonic acid than in
the ordinary atmosphere.
In 1840 Boussingault furnished direct proof, of what
indeed was hardly to be doubted, viz.: the absorption of
the carbonic acid of the atmosphere by foliage.
Into one of the oiiflces iu a tbree-necked glass globe he introduced
and fixed air-tight the brunch of a living vine bearing twenty leaves ;
with another opening he connected a tube through which a slow current
of air, containing, in one experiment, four-lOOOOths of carbonic acid,
could be passed into the globe. This air after streaming over the vine
leaves, at the rate of about 15 gallons per hour, escaped bj' the third
neck into an arrangement for collecting and weighing the carbonic acid
that remained in it. The experiment being set in process in the sun-
light, it was found that the enclosed foliage removed from the current
of air three-fourths of the carbonic acid it at first contained.
Influence of the Relative Quantity of Carbonic Acid. —
De Saussure investigated the influence of various propor-
42 now .Rops PKKD.
tions of carbonic acid mixed with atmospheric air on the
development of ^ egetation. lie found that young peas (4
inches high) when exposed to direct sunlight, endured for
some days an atmosphere consisting to one-half of carbonic
acid. When the proportion of tliis gas was increased to
two-thirds or more, they speedily Avithered. In air con-
taining one-twelfth of carbonic acid the peas flourished
much better than in ordinary atmospheric air. The aver-
age increase of each of the plants exposed to the latter
for five or six hours daily during ten days was eight
grains ; while in the former it amounted in the same time to
eleven gi-aiiis. In the shade, however, Saussure found that
increase of the proportion of carbonic acid to one-twelfth
was detrimental to the plants. Their growth under these
circumstances was but three-fifths of that experienced by
similar plants exposed to the same light for tlie same time,
but in common air. He also proved that foliage cannot long
exist in the total absence of carbonic acid, w'hen exposed
to direct sunlight. This result was obtained by enclosing
young plants whose roots were immersed in water, or the
branches of trees stationed in the soil, in a vessel which
contained moistened quicklime. This substance rapidly
absorbs and fixes carbonic acid, forming carbonate of lime.
Thus situated, the leaves began in a few days to turn yel-
low, and in two to three weeks they dropped ofi".
In darkness the presence of lime not only did not de-
stroy the plants, but they prospered the better for its
presence, i. e., for the absence or constant removal of car-
bonic acid.
Boussingault has lately shown that pure carbonic acid
is decomposed by leaves exposed to sunlight with extreme
slowness, or not at all. It must be mixed with some other
gas, and when diluted with either oxygen, nitrogen, or hy-
drogen, or even when rarefied by the air-pum]) to a certain
extent, the absorption and decomposition proceed as usual.
Conclusioilt — It thus is proved list, that vegetatioa
PHOPERTY OF
1' 1. u rni t Pnr \ \vxtktN!\
aTmospiikkk; aiu as tiii: food <ik i'lants. 4vi
can floiirish only when its foliage is bathed by an atmos-
phere which contains a certain small amount of carbonic
acid ; 2d, that this gas is absorbed by the leaves, and, un-
der the influence of sunlight, is decomposed within the
plant, its carbon being retained, and in an unknown man-
ner becoming a part of the })lant itself, wriile the oxygen
is exhaled into the atmo-^phere in the free state.
Relative volumes of absorbed (arbouic Acid and ex-
baled Oxygen. — From the numeri)us experiments of De
Saussure, and from similar ones made recently with greatly
improved means of research by Unger and Knop, it is es-
tablished that in sunlight the volume of oxygen exhaled
is nearly equal to the volume of cai'bonic acid absorbed.
Since free oxygen occupies the same bulk as the carbonic
acid produced Ly uniting it with carbon, it is evident that
carbon mainly and not oxygen to much extent, is retained
by the plant from this source.
Respiration and Fixation of Carbon by Plants. — In
1851 Garreau, and in 1858 Corenwinder, reviewed experi-
mentally the whole subject of the relations of plants to
carbonic acid. Their researches fully confirm the conclu-
sions derived from older investigations, and furnish some
additional facts.
We have already seen (p. 22) that the jilant requires
free oxygen, and that this gas is absorbed by tliose parts
of vegetation which are in the act of growth. As a con-
sequence of this entrance of oxygen into the plant, a cor-
resj)onding amount of carbonic acid is produced within
and exhales from it. There go on accordingly, in the ex-
panding plant, tAvo opposite processes, viz., the absorption
of oxygen and exhalation of carbonic acid, and the ab-
sorption of carbonic aciil and evolution of oxygen. The
first process is chemically analogous with the breathing
of animals, and may hence be designated as respiration.
We may speak of the other process as the fixation of
carbon.
44
HOW cnoi'S FRED.
These opposite clianges obviously cannot take place at
the same points, but must proceetl in different organs or
cells, or in different parts of the same cells. They further-
more tend to counterbalance each otlier in their effects on
the atmospliere surrounding the plant. The processes to
"which the absorption of oxygen and evolution of carbonic
acid are necessary, appear to go on at all hours of the day
and night, and to be independent of tlie solar liglit. The
production of carbonic acid is then continually occurring ;
but, under the influence of the sun's direct rays, the oppo-
site absorption of carbonic acid and evolution of oxygen
proceed so much more rapidly, that when we experiment
with the entire plant the first result is completely masked.
In our experiments we can, in fact, only measure the pre«
ponderance of the latter process over the former. In sun-
light it may easily happen that the carbonic acid which
exhales from one cell is instantly absorbed by another, and
likewise the oxygen, which escapes from the latter, may
be in part imbibed by the former.
In total darkness it is believed that carbonic acid is not
absoi-bed and decomposed by the plant, but only produced
in, and exhaled from it. In no case has any evolution of
oxygen been observed in the absence of light.
When, instead of being exposed to the direct rays of
the sun, only the diffused light of cloudy days or the soft-
ened light of a dense forest acts upon them, plants may, ac-
cording to circumstances, exhale either oxygen or carbonic
acid in preponderating quantity. In his earlier investiga-
tions, Corenwinder observed an exhalation of carbonic acid
in diffused light in the cases of tobacco, sunflower, lupine,
cabbage, and nettle. On the contrary, he found that let-
tuce, the pea, violet, fuchsia, periwinkle, and others, evolv-
ed oxygen under similar conditions. In one instance a
bean exhaled neither gas. These differences are not pe-
culiar to the plants just specified, but depend upon the in-
tensity of the light and the stage of development in which
ATMOSPHKIMC AIll AS THU FOOD OF PLANTS. 45
the plant exists. Corenwinder noticed that the evolution
of carbonic acid in diffused light was best exhibited by
very young plants, and mostly ceased as they grew older.
Corenwinder has confirmed and extended these observa-
tions in more recent investigations. {Ann. d. Sci. N'at.^
1864, I, 297.)
He finds that buds and young leaves exhale carbonic
acid (and absorb oxygen) l)y day, even in bright sunshine.
He also finds that all leaves exhale carbonic acid not alone
at night, but likewise by day, when placed in the diffused
light of a room, illuminated from only one side. A plant,
which in full light yields no carbonic acid to a slow stream
of air passing its foli:ige, immediately gives off the gas
when carried into such an apartment, and vice versa.
Amount of Tarbonic Acid absorbed. — The quantity of
oarbonic acid absorbed by day in direct light is vastly
greater than that exhaled during the night. According
to Coren winder's experiments, 15 to 20 minutes of direct
sunlight enable colza, the pea, the raspberry, the bean,
and sunflower, to absorb as much carbonic acid as they
exhale during a whole night.
As to the amount of carbonic acid whose carbon is re-
tained, Corenwinder found that a single colza plant took
up in one day of strong sunshine more than two quarts of
the gas.
Boussingault {Comptes Rend., Oct. 23d, 1865) found as
the average of a number of experiments, that a square me-
ter of oleander leaves decomposed ill sunlight 1.108 liters
of carbonic acid per hour. In the dark, the same surface
of leaf exhaled but 0.07 liter of this g.is.
Composition of tlie Air within the Plant. — Full con
tirmation of the statements above made is furnished by
tracing tlie changes which take place within the vegeta-
ble tissues. Lawes, Gilbert, and Pugh, {Phil Trans.^
1861, II, p, 486,) have examined the composition of the
46
HO-\V CUOrS FEED.
air contained in plants, as well when the latter are remov-
ed from, as wlien they are subjected to, the action of light.
To collect the gas from the plants, the latter M'ere placed
in a glass vessel filled with water, from which all air had
been expelled by long boiling ami subsequent cooling in
full and tiglitly closed bottles. The vessel was then con-
nected with a simple apparatus in Avhich a vacuum was
produced by the fall of mercury, down a tube of 30 inches
height. The air contained within the cells of the plant
was thus drawn over into the vacuum and collected fot
examination. We give some of the results of the 6th
series of their examinations. " The Table shows the
Amount and Compositicm of the Gas evolve-l into a Tor-
ricellian vacuum by duplicate portions of oat-jilant, both
kept in the dark for some time, and then one exposed to
sunlight for about twenty minutes, when both were sub-
mitted to exhaustiou."
] Per cent.
Date,
1858.
July 31.1
Aug. 2.
Aug. 2.
Conditiom
Cubic centirneiers
durinq
of
Nitrogen.
Oxygen.
Carbonic Add.
Exhaudion.
Gas collected.
1 III dark.
24.0
77.08
3.75
10.17
■| In sunlight.
?A.o
68.60
24.03
6.38
I In dark.
10. (i
68.28
10.21
21.51
1 In sunlisht.
30.2
67.86
25.05
6.80
) In dark.
\ In sunlight.
30.7
76.87
8.14
14.00
20.5
60.43
27.17
3.40
These analyses show jilainly what it is that happens in
the cells of the plant. The atmosphei-ic air freely pene-
trates the vegetable tissues, (H. C. G., p. 288.) In dark-
ness, the oxygen that is thus contained within the plant
takes carbon from the vegetable matter and forms with it
carbonic acid. This process goes on witli comparative
rapidity, and the projiortion of oxygen may be diminish-
ed from 21, the normal percentage, to 4, or even, as in
some other experiments, to less than 1 per cent of the
volume of the air. Upon bringing the vegetable tissue
into sunlight, the carbonic acid previously formed within
the cells undergoes decomposition, with separation of its
ATMOSPHERIC AIR AS TUB FOOD OF PLANTS. 47
oxygen in the free gaseous coiulition, while its carbon re-
mains in the solid state as a constituent of the plant. Re-
ferring to the table above, we see that twenty minutes'
exposure to the solar rays was sufficient in the second ex-
periment (where the projjortion of nitrogen remained
nearly unaltered) to decompose 14 per cent of carbonic acid
and liberate its oxygen. The total volume of air collected
was 2.4 cubic inches, and the volume of decomposed car-
bonic acid was ^ of a cubic inch, that of the liberated
oxygen being the same.
Supply of ( arboiiic Acid iu the Atmosphere. — Although
tills body forms but toooo of the weight of the atmosphere,
yet such is the immense volume of the latter that it is cal-
culated to contain, when taken to its entire height, no less
than 3,400,000,000,000 tons of carbonic acid. This
amounts to about 28 tons over every acre of the earth's
surface.
According to Chevandier, an acre of beech-forest annu-
ally assimilates about one ton (1950 lbs.) of carbon, an
amount equivalent to 3^ tons of this gas. AV^eie the whole
earth covered with this kind of forest, and did it depend
solely upon the atmosphere for carbon, eight years must
elapse before the existing supply would be exhausted, in
ease no means had been provided for restoring to the air
what vegetation constantly removes.
When we consider that but one-fourth of the earth's
surface is land, ami that on this the annual vegetable pro-
duction is very far below (not one-third) the amount stat-
ed above for thrifty forest, we are warranted in assuming
the atmospheric content of carbonic acitl sufficient, with-
out renewal, for a hundred years of growth. This ingredi-
ent of the atmosphere is maintained in undiminished
quantity by the oxidation of carbon in the slow decay of
organic matters, in tlie combustion of fuel, and in animal
respiration.
That the carbonic acid of the atmosphere may fully suf-
48 HOW CROPS FEED
fice to provide a rapidly growing vegetation with carbon
is demonstrated by numerous facts. Here w^e need only
mention that in a soil totally destitute of all carbon, be-
sides that contained in the seeds sown in it, Boussingault
brought sunflowers to a normal development. The writer
has done the same with buckwheat ; and Sachs, Knop,
Stohmann, Nobbe and Siegert, and others, have produced
perfect plants of maize, oats, etc., whose roots, throughout
the whole period of growth, were immersed in a weak,
saline solution, destitute of carbon. (See 11. C. G., Water
Culture, p. 167 )
Hellriegel's recent experiments give the result that the
atmospheric supply of carbonic acid is probably sufficient
for the production of a maximum crop under all circum-
stances ; at least artificial supply, w^hether of the gas, of
its aqueous solution, or of a carbonate, to the soil, had no
effect to increase the crop. {Chem. Ackersmann, 1868,
p. 18.)
Liebig considers carbonic acid to be, under all circum-
stances, the exclusive source of the carbon of agricultural
vegetation. To this point we shall recur in our study of
the soil.
Carbon fixed by Chlorophyll.— The fixation of carbon
from the carbonic acid of the air is accomplished in, or has
an intimate relation with, the chlorophyll grains of the
leaf or green stem. This is not only evident from the
microscopic study of the development of the carbohy-
drates, especially starch, Avhose organization proceeds from
the chlorophyll, but is an inference from the experiments
of Gris on the effects of withholding iron from plants. In
absence of iron, the leaf may unfold and attain a certain
development ; but chlorophyll is not formed, and the plant
soon dies, without any real growth by assimilation of food
from without. (IT. C. G., p. fiOO.) Filially, experiment
shows that oxygen is given off (and carbonic acid decom-
posed with fixation of carbon) only from those parts of
ATMOSPHERIC AIK AS THE FOOD OF PLANTS. 49
plants ill wliich the microscope reveals chlorophyll, altliough
the prevailing color may be other than green.
Influence of Lij?ht on Fixation of f arbon. — As men-
tioned, Iiigenhouss (in 1779) discovere'l that oxygen gas
is given olF from foliage, and carbon fixed in the i)lant
only under the influence of light. Experiments show that
when a seed germinates in exclusion of light it not only
does not gain, but steadily loses weight from the consump-
tion of carbon (and hydrogen) in slow oxidation (respira-
tion).
Thus Boussingault {Comptes Rendus, 1864, p. 883)
caused two beans to germinate and vegetate, one in the
ordinary light and one in darkness, during 26 days. The
gain in light and loss in darkness in entire (dry) weight,
and of carbon, etc., are seen from the statement below.
In L'ujht. Ill Darkness.
Weight of seed 0.933 gnim ... .0.936 gram.
Weight of plant 1.293 " 0.566 "
Gain = 0.371 gram. Loss 0.360 gram.
Carbon, Gain = 0 1926 " Loss. . .0.1598 "
Hydrogen, " = 0.0200 " " ...0.0232 "
Oxygen, " = 0.1591 " " ...0.1766 "
§6.
THE AMMONL\ OF THE ATMOSPHERE AND ITS RELATIONS
TO VEGETABLE NUTRITION.
Ammonia is a gas, colorless and invisible, but having a
peculiar pungency of odor and an acrid taste.
PiH'parsitioii. — It may be obtained in a state of purity by licat-
ing a mixture of chloride of ammonium (sal ammoniac) and (luielvlime.
Equal qu;intities of tlie two substances just named (50 grams of each)
are separately pulverized, introduced into a flask, and well mixed by
shaking. A straight tube 8 inches long is now secured in the neck of
the flask by means of a perforated cork, and heat applied. The ammonia
gas which soon escapes in abundance is collected in dry bottles, which
are inverted over the tube. The gas, rapidly entering the bottle, in a
few moments displaces the twice heavier atmospheric air. As soou as »
3
50 HOW CROPS FEED.
feather wet with vinegar or dilute chlorlijdric acid becomes surrounded
with a dense smolce when approached to the mouth of the bottle, the
latter may be removed, corlced, and another put in its place. Three or
four pint bottles of gas thus collected will serve to illustrate its proper-
ties, as shortly to be noticed.
Solubility in Water. — This character of ammonia is ex-
hibited by removing, under cold water, the stopper of o
bottle filled with tlie gas. The water rushes witli great
violence into the bottle as into a vacuum, and entirely fills
it, provided all atmospheric air had been displaced.
The aqita ammotihi, or spirits of hartshorn of the drug-
gist, is a strong solution of ammonia, prepared by passing
a stream of ammonia gas into cold water. At the freez-
ing point, water absorbs 1,150 times its bulk of ammonia.
When such a solution is warmed, the gas escapes abund-
antly, sc that, at ordinary summer temperatures, only one-
half the ammonia is retained. If the solution be heated
to boiling, all tlie ammonia is expelled before the water has
nearly boiled away. Th« gas escapes even from very di-
lute solutions wlien they are exposed to the air, as is at
once recognized by the sense of smell.
Composition. — When ammonia gas is heated to redness
by being made to pass through an ignited tube, it is de-
composed, loses its characteristic odor and other proper-
ties, and is resolved into a mixture of nitrogen and hydro-
gen gases. These elements exist in ammonia in the pro-
portion of one part by bulk of nitrogen, to three parts of
hydrogen, or by weight fourteen parts or one atom of
nitrogen and three parts, or three atoms of hydrogeiK
The subjoined scheme exhibits the composition of ammo
nia, as expressed in symbols, atoms, and percentages.
Symbol. At. vj't. Per cent.
N = 14 .. 83.39
H3 = 3 .. 17.61
NH3 = 17 .. 100.00
Formation of Ammonia.— 1. When hydrogen and ni-
trogen gases are mingled together in the proportions to
ATISrOSPHEItlC AIU AS THE FOOD OF PLANTS. 51
form ammonia, they do not combine either spontaneously or
by aid of any means yet devised, but remain for an indef-
inite period as a mere mixture. The oft repeated assertion
that nascent hydro2;en, i. e., hydrogen at the moment of
libei'ation from some combination, may unite with free
nitrogen to form ammonia, has been completely refuted by
the experiments of Will, {Ann. Ch. u. PA., XLV, 110.)
The ammonia observed by older experimenters existed,
ready formed, in the materials they operated with.
2. It appears from recent researches (of Boettgor,
Schonbein, and Zabeliu) that ammonia is formed in minute
quantity from atmospheric nitrogen in many cases of cona-
bustion, and is also generated when vapor of water and
the air act upon each other in contact with certain organic
matters, at a temperature of 120° to 160° F. To this sub-
ject we shall again recur, p. 77.
3. Ammonia may result from the reduction of nitrous
and nitric acids, and from the action of alkalies and lime
upon the albuminoids, gelatine, and other similar organic
matters. To these modes of its formation we shall recur
on subsequent pages.
4. Ammonia is most readily and abundantly formed from
organic nitrogenous bodies; e. g., the albuminoids and
similar substances, by decay or by dry distillation. It is
supposed *to have been called ammonia because one of its
most common compounds (sal ammoniac) was first prepared
by burning camels' dung near the temple of Jupiter Amiu' m
in Libya, Asia Minor. The name hartshorn, or spirits of
hartshorn, by which it is more commonly known, was
adopted from the circumstance of its preparation by dis-
tilling the horns of the stag or hart.
The ammonia and ammoniacal salts of commerce (car-
bonate of ammonia, sal ammoniac, and sulpliate of ammo-
nia) are exclusively obtained from these sources.
When urine is allowed to become stale, it shortly smelly
52 IIOAV CROPS FEED.
of ammonia, which copiously escapes in the form of car-
bonate, and may be separated by distillation.
When bones are heated in close vessels, as in the manu-
facture of bone-black or bone-char for sugar refining, the
liquid product of the distillation is strongly charged with
carbonate of ammonia.
Commercial ammonia is mostly derived, at present, from
the distillation of bituminous coal, and is a bye-product of
the manufacture of illuminating gas. The gases and va-
pors that issue from the gas-retort in which the coal is heat-
ed to redness, are washed by }>assing tlirough water. Tliis
wash water is always found to contain a small quantity of
ammonia, which may be cheaply utilized
The exhalations of volcanoes and fumeroles likewise
contain ammonia, which is probably formed in a similar
manner.
In the processes of combustion and decay the elements
of the organic matters are thrown into new groupings,
which are mostly simpler in composition than the original
substances. A portion of nitrogen and a corresponding
portion of hydrogen then associate themselves to form am-
monia.
Ammonia is a Stroni? Alkaline Base.— Those bases
which have in general the strongest affinity for acids, are
potash, soda, and ammonia. These bodies are very similar
in many of their most obvious char.icters, and are collec-
tively denominated the alkalies. They are alike freely
soluble in water, have a bitter, burning taste, alike corrode
the skin and blister the tongue ; and, united with acids,
form the most permanent saline compounds, or salts.
Carbonate of Ammonia. — If a bottle be filled with car.
bonie acid, (by holding it inverted over a candle until the
latter becomes extinguished when passed a little way into
the bottle,) and its mouth be applied to that of a vessel
containing ammonia gas, the two invisible airs at once
ATMOSPHERIC Ain AS THE FOOD OF PLANTS. !)6
combine to a solid salt, llie carbonate of ammonia, which
appears as a white cloud where its ingredients come in
contact.
Carbonate of ammonia occurs in commerce under the
name "salts of hartshorn," and with the addition of some
perfume forms the contents of the so-called smelling-bot-
tles. It rapidly vaporizes, exhaling the odor of ammonia
very strongly, and is hence sometimes termed sal volatile.
Like camphoi-, this salt passes from the solid state into
that of invisible vapor, at ordinary temperatures, without
assuming intermediately the liquid form.
In the atmosphere the quantity of carbonic acid greatly
preponderates over that of the ammonia; hence it is im-
possible that the latter should exist in the free state, and
we must assume that it occurs there chiefly in combination
with carbonic acid. The carbonate of ammonia, whether
solid or gaseous, is readily soluble in water, and like free
ammonia it evaporates from its solution with the first
portions of aqueous vapor, leaving the residual water rel-
atively free from it.
In the guano-beds of Peru and Bolivia, carbonate of
ammonia is sometimes found In the form of large trans-
parent crystals, which, like the artificially-prepared salt,
rapidly exhale away in vapor, if exposed to the air.
This salt, commonly called bicarbonate of ammonia, con-
tains in addition to carbonic acid and ammonia, a portion
of water, which is indispensable to its existence. Its com-
position is as follows :
Symbol. At. wH. Pbr cent.
NH3 17 21.5
H2O 18 23.8
CO2 44 55.7
NH3. H2O. CO2. 79 100.0
Tests for Amiuoiiia. — «. If salts of ammonia are rubbed to-
gether with slaked lime, ^)e^^t witli the addition of a few drops of water,
tht: ammouia is liberated in the gaseous st:-.te, and betrays itself (1) by
its charaeteristic odor ; (2) by its reaction on moistened test-papers; and
54 now cnopt4 pkEd,
(3) b J giving rise to the funnivfion oi white famea, wllcri nny object (c. ^.^
a glass rod) moistened witli hydrochloric iicid, is brouglit in contact with
it. These fumes arise Irom the formation of solid ammoniucAl salts pro-
duced by the contact of the gases.
6. Xensler's Text.—Yov the detection of e.vceedin-ly minute liuccs of
ammonia, a reaction first pointed out by Nessler may be employed. Di-
gest at a gentle heat 2 grammes of iodide of potassium, and 3 grammes
of iodide of mercury, in 5 cub. cent, of water; add 20 cub. cent, of wa-
ter, let tlie mixture stand lor some time, then filter; add to the filtrate
30 cub. cent, of pure concentrated solution of i)otassa(l : 4); and, should
a precipitate form, filter again. If to this solution is added, in smnll
quantity, a liquid containing ammonia or an ammonia-salt, a reddisli brown
precipitate, or with exceedingly small quantities of ammonia, a yellow
coloration is produced from the formation of dimercurammouic iodide,
NHg2 I.OHj.
c. Bohliff's Test. — According to Bohlig, chh^ride of mercury (corrosive
sublimate) is the most sensitive reagent for ammonia, when in the free
6t;ite or as carbonate. It gives a white precipitate, or in very dilute so-
lutions (even when containing but '|aoo,ooo of ammonia) a white turbidity,
due to the separation of niercurammonie chloride, NH^ Ilg.Cl. In solu-
tions of the salts of ammonia with other acids than carbonic, a clear
solution of mixed carbonate of potassa and chloride of mercury must be
employed, which is prcpaied by adding 10 drops of a solution of the
purest carbonate of potassa, (1 of salt to 50 of water,) and 5 drops of a
Bulution of chloride of mercury to 80 c. c. of water exempt from am-
monia (such is the water of many springs, but ordinary distilled water
rarely). This reagent may be kept in closed vessels for a time without
change. It much more concentrated, oxide of mercury separates from it.
Bj' its use the ammonia salt is first converted into carbonate by double
decomposition with the carbonate of potassa, and the further reaction
proceeds as before mentioned.
Occurrence of Ainnionia in the Atmosphere. — The e.\-
istence of ammonia in the atmosphere was first noticed by
De Saussure, and has been proved repeatedly by direct
experiment. That the quantity is exceedingly minute has
been equally well established.
Owing partly to the variable extent to whicli ammonia
occurs in the atmosphere, but chiefly to the difficulty of
collecting and estimating such small amounts, the state-
ments of those who have experimented upon this subject
are devoid of agreement.
We present here a tabulated view of the most trust-
worthy results hitherto published:
ATMOSPIIEUIC AIR AS THE TOOD OF PLANTS. 55
1,000,000,000 parts of atinosplicric air contain of ammonia, according to
Graeirer, at MiiliUiausen, Germany, averag:e, 333 parts.
Fresenius, " Wiesbaden, " " 133 "
Pierre, " Caen, France, 1851-52, " 3500 "
" " " " 1852-53, " 500 "
Bineau, " Lyons, " 1852-53, " 250 "
" " Caliiire, " " wiuter, 40 "
" " " " " summer, 80 "
Ville, " Paris, " 1819-50, average, 24 "
" Grenelle, " 1851, "" 21 "
Graham lias shown by experhnent (Ville, Recherches
sur la Vegetation, Paris, 1S53, p. 5,) that a quantity of
ammonia like that found by Fresenius is sufficient to be
readily detected by its eifect on a red litmus pai»er, which
is not altered in the air. This demonstrates that the at-
mosphere where Graham experimented (London) contained
less than '"|j^„^^_^^^ths cf ammonia in the state of bicar-
bonate. The experiments of Fresenius and of Grager
were made with com[)aratively small volumes of air, and
those of the latter, as well as those of Pierre, and some of
Bineau's, were made in the vicinity of dwellings, or even
in cities, where the results might easily be influenced by
local emanations. Bineau's results were obtiuned by a
method scarcely ailmitting of much accuracy.
The investigations of Ville {Recherches, Paris, 1853,)
are, perhaps, the most trustwoi'thy, having been made on
a large scale, and apparently with every precaution. We
may accordingly assume that the average quantity of am-
monia in the air is one part in fifty millions, altliough the
amount is subject to considerable fluctuation.
From the circumstance that ammonia and its carbonate
are so readily soluble in water, we should expect that in
rainy weather the atmosphere would be washed of its am-
monia; while after prolonged dry weather it would con-
tain more than usual, since ammonia escapes from its
solutions with the first portions of aqueous vapor.
The Absorption of Amnioiiia by Vej?etation. — The gen-
eral fact that ammonia in its compounds is appropriated
56
now CROPS FEED
by plants as food is most abundantly established. The
salts of ammonia applied as manures in actual farm prac-
tice have produced the most striking effects in thousands
of instances.
By watering potted plants with very dilute solutions of
ammonia, their luxuriance is made to surpass by far that
of similar plants, which grow in precisely the same condi-
tions, save that they are supplied with simple water.
Ville has stated, 1851-2, that vegetation in conserva-
tories may be remarkably ])romoted by impregnating the
air with gaseous carbonate of ammonia. For this purpose
lumps of the solid salt are so disposed on the heating ap-
paratus of the green-house as to gradually vaporize, or
vessels containing a mixture of quicklime and sal ammo-
niac may be employed. Care must be taken that the air does
not contain at any time more than four ten-thousandths
of its weight of the salt ; otherwise the foliage of tender
plants is injured. Like results were obtained by Petzholdt
and Chlebodarow in 1852-3.
Absorption of Ammonia by Foli-
aj^C. — Although such facts indicate
that ammonia is directly absorbed by
foliage, they fail to prove that the
soil is not the medium through which
the absorption really takes place. We
remember tliat according to Unger
and Duchartre Avater enters the
higher plants almost exclusively by
the roots, after it has been absorbed
by the soil. To Peters and Sachs
( Chem. Ackersmann, 6, 158) we owe
an experiment which appears to de-
monstrate that ammonia, like carbonic
acid, is imbibed by the leaves of
I' iy: ^'- plants. Tlie figure represents the ap-
paratus employed. It consisted of a glass bell, resting below,
AtMOSPHEIllC AIU AS TIIK FOOD OF PLANTS. 57
air-tight, upon a glas^s plate, and having two glass tubes
cemented into its neck above, as in fig. 6. Tlirough
an aperture in the centre of the glass ])late the stem of
the plant experinienled on was introduced, so that its fo-
liage should occupy the bell, while the roots were situated
in a pot of earth beneath. Two young bean-plants, grow-
ing in river sand, were arranged, each in a separate appa-
ratus, as in the figure, on June 19th, 1859, their stems be-
ing cemented tightly into the opening below, and through
the tubes tlie foliage of each plant received daily the same
quantities of mois^t atmosj)heric air mixed with 4-5 per
cent of carbonic acid. One plant was supplied in addition
with a quantity of carbonate of ammonia, w^hich Avas in-
troduced by causing the air that was forced into the bell
to stream through a dilute solution of this salt. Both
plants grew well, until the experiment was terminated, on
the 11th of August, when it Avas found that the plant
Avhose foliage was not supplied with carbonate of ammo-
nia weighed, dry, 4.14 gm., while the other, which Avas
supplied Avith the A\apor of this salt, weighed, dry, 6.74
gms. Tlie fir>t plant had 20 full-sized leaves and 2 side
slioots; the second Ixid 40 leaves and 7 shoots, besides a
much larger mass of roots. The first contained 0.106
gm. of nitrogen; the second, double that amount, 0.208
gm. Other trials on various [»lants failed from the diffi-
culty of making them groAV in the needful circumstances.
Th#absorption of ammonia by foliage does not appear,
like that of carbonic acid, to depend upon the action of
sunlight ; but, as Mulder has remarked,* may go on at
all times, especially since the juices of plants are very fre-
quently more or less charged with acids which directly
unite chemically with ammonia.
When absorbed, ammonia is chiefly applied by agricul*
• Cheraie der Ackerkriime, A'ol. 2, p. 211.
3*
5ft now cRopfi PEEn.
tural plants to tlic production of tlie albuniinokls.* We
measure the nutritive efFoct of aminonia salts applied as
fertilizers by tlie amount of nitrogen whicli vegetation as-
similates from them.
Effects of Ammonia on Vegetation. — The remarkable
effect of carbonate of ammonia upon vegetation is well
described by Ville. We know that most plants at a cer-
tain period of growth under ordinary circumstances cease
to produce new branches and foliage, or to expand those
already formed, and begin a new phase of development in
providing for the perpetuation of the species by producing
flowers and fruit. If, however, such plants are exposed
to as much carbonate of ammonia gas as they are capable
of enduring, at the time when flowers are beginning to
form, these are often totally checked, and the activity of
growth is transferred to stems and leaves, Avhich assume
a new vigor and multiply with extraordinary luxuriance.
If flowers are formed, they are sterile, and yield no seed.
Another noticeable effect of ammonia — one, however,
which it shares with other substances — is its power of deep-
ening the color of the foliage of plants. This is an indi-
cation of increased vegetative activity and health, as a
pale or yellow tint belongs to a sickly or ill-fed growth.
A third result is that not only the mass of vegetation
is increased, but the relative proportion of nitrogen in it is
heightened. This result was obtained in the experiment of
Peters and Sachs just described. To adduce a single other
instance, Ville found that grains of wheat, grown in pure
air, contained 2.09 per cent of nitrogen, while those which
were produced under the influence of ammonia contained
3.40 per cent.
* In tobacco, to th3 prodaction of nicotine ; in coffee, of caffeine ; and in many
other plants to analogous eubstances. Plants appear oflentiraes to contain
small quantities of ammonia salts and nitrates, as well as of asparagin, (C4 Hs
N2 03,)a substance first found in asjjaragus, and which is formed in manj
plants when they vegetate in exclusion of light.
ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 59
Do Healtliy Plants Exhale Ammonia ?— The idea having
been advanced that in tlie act of vegetation a loss of ni-
trogen may occur, possibly in the form of ammonia, Knop
made an cxjieriment with a water-plant, the Typha latl-
folia., a species of Cnt-tail, to determine this point. The
plant, growing imdisturbed in a pond, was enclosed in a
glass tube one and a half inches in diameter, and six feet
long. The tube was tied to a stake driven for the purpose ;
its lower end reached a short distance below the surface
of the water, while the uppiT end was covered air-tight
with a cap of India rubber. This cap was penetrated by
a narrow glass tube, which communicated with a vessel
filled with splinters of glass, moistened with pure hydro-
chloric acid. As tlie large tube was placed over the plant,
a narrow U-shaped tube was immersed in the water to
half its length, so that one of its arms came within,
and the other without, the former. To the outer extremity
of the U-tube was attached an apparatus, for the perfect
absorption of ammonia. By aspirating at the upper end
of the long tube, a current of ammonia-free air was thus
made to enter the bottom of the apparatus, stream upward
along the plant, and pass through the tube of glass-splint-
ers wet with hydrochloric acid. Were any ammonia
evolved within the long tube, it would be collected by the
acid last named. To guard against any amuionia that
possibly might arise from decaying matters in the water,
a thin stratum of oil was made to float on the water with-
in the tube. Through this arrangement a slow stream of
air was passed for fifty hours. At the expiration of that
time the hydrochloric acid was examined for ammonia ;
but none was discovered. Our tests for ammonia are so
delicate, that we may Avell assume that this gas is not ex-
haled by the Typha lati folia.
The statements to be foi;nd in early authors (Sprengel,
Schiibler, Johnston), to the effect tliat ammonia is exhaled
by some plants, deserve further examination.
66 now crops PKED.
The Chenopodium vuharla exhales from its foliage a
body chemically related to ammonia, and that has been
mistaken for it. This substance, known to the chemist as
triinethylamine, is also contained in the flowers of Cra-
ppgus oxycanthd^ and is the cause of the detestable odor
of these plants, which is that of putrid salt fish.* (Wicke,
Liehig's A/m., 124, p. 338.)
Certain fungi (toad-stools) emit trimeth ylamine, or some
analogous compound. (Lehmann, Sachs^ Experimental
Plcyslolojie der I^anzen, p. 273, note.)
It is not impossible that ammonia, also, may be exhaled
from these plants, but we have as yet no proof that such
is the case.
Ammonia of the Atmospheric Waters. — The ammonia
proper to the atmosphere has little effect upon plants
through their foliage when they are sheltered from dew
and rain. Such, at least, is the result of certain experi-
ments.
Boussingault (Agronomie, Chinile Agricole, et Physi-.
ologie, T. I, p. 141) made ten distinct trials on lupins,
beans, oats, wheat, and cress. The seeds were sown in a
soil, and the plants were w.itered with water both exempt
from nitrogen. The plants were shielded by glazed cases
from rain and dew, but had full access of air. The result
of the ten experiments taken together was as follows:
Weiglit of seeds 4.965 grin's.
" dry harvest 18.730 "
Nitrogea in harvest and soil.. .2499 "
" " seeds 2307 "
Gain of nitrogen 0192 grm's = 7.6 per cent of the
total quantity.
When rains fall, or dews deposit upon the surface of the
* Triinethylamine CsHuN = N (01X3)3 may be viewed as ammonia NH3, in
which the three atoms of liydro',aui are replaced by three atoms of methyl
CH3. It is a jras like anmionia, and has its i)nn';ency, but accompanied with the
odor of stale fish. It is prepared from herring pickle, and used iu medicine un-
der the name ijropylamine.
ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 61
soil, or upon the foliage of a cultivated field, they bring
down to the reach of vegetation in a given time a quantity
of ammonia, far greater tlum what is diifiised throughout
the limited volume of air which contributes to the nour-
ishment of plants. Tlie solubility of carbonate of ammo-
nia in water has already been mentioned. In a rain-fall
Ave have the atmosphere actually washed to a great de-
gree of its ammonia, so tliat nearly the entire quantity of
this substance which exists between the clouds and the
earth, or in that mass of atmosphere through Avhich the
rain passes, is gathered by the latter and accumulated
within a small space.
Proportion of Ammonia in Rain-water, etc. — The pro-
portion of ammonia * which the atmospheric waters thus
collect and bring down upon the surface of the soil, or
upon the foliage of plants, has been the subject of inves-
tigations by Boussingault, Bineau, Way, Knop, Bobiere,
and Bretschneider. The general i-esiilt of their accordant
investigations is as follows : In rain-water the quantity of
ammonia in the entiiic fall is very variable, ranging in the
country from 1 to 33 parts in 10 million. In cities the
amount is larger, tenfold the above quantities having been
observed.
The first portions of rain that fall usually contain much
more ammonia than the latter portions, for the reason that
a certain amount of water suffices to wash the air, and
what rain subsequently falls only dilutes the solution at
first formed. In a long-continued rain, the water that
finally falls is almost devoid of ammonia. In rains of
short duration, as well as in dews and fogs, which occasion-
ally are so heavy as to admit of collecting to a sufficient
extent for analysis, the proportion of ammonia is greatest,
and is the greater the longer the time that has elapsed
since a previous precipitation of water.
* III all (luaiilitative statemonis roj^'ardiui,' ammonia, NH3 is to be miderstoodi
ftnauotNH^O.
62 HOW CROPS FEED.
Boussingault found in the first tenth of a slow-falling
rain (24th Sept., 1853) 66 parts of ammonia, in the last
three-tenths but 13 parts, to 10 million of water. In dew
he found 40 to 62; in fog, 25 to 72 ; and in one extraordi-
nary instance 497 parts in ten million.
Boussingault found that the average proportion of am-
monia in the atmosplieric waters (dew and fogs included)
which he was able to collect at Liebfrauenborg (near Stras-
burg, PVance) from the 26th of May to the 8th of Nov.
1853, was 6 parts in 10 million {Agyonomie, etc., T. II,
238). Knop found in the rains, snow, and hail, that fell at
Moeckern, near Leipzig, from April 18th to Jan. 15th,
1860, an average of 14 parts in 10 million. ( Versuchs-
Statlonen, Vol. 3, p. 120.)
Pincus and Rollig obtained from the atmospheric wa-
ters collected at Insterburg, North Prussia, during the 12
months ending with March, 1865, in 26 analyses, an average
of 7 parts of ammonia in 10 million of water. The average
for the next following 12 months was 9 parts in 10 million.
Bretschneider found in the atmospheric waters collected
by him at Ida-Marienhiitte, in Silesia, from April, 1865, to
April, 1866, as the average of 9 estimations, 30 parts of
ammonia in 10 million of water. In the next year the
quantity was 23 parts in 10 million.
In 10 million parts of rain-water, etc., collected at the
following places in Prussia, were contained of ammonia —
at Regenwalde, in 1865, 24; in 1867, 28; at Dahme, in
1865,17; at Kuschen, in 1865,5^; and in 1866, 7^ parts.
{Preus. Ann. d. Layidwirthschaft, 1867.) The monthly
averages fluctuated without regularity, but mostly within
narrow limits. Occasionally they fell to 2 or 3 parts, once
to nothing, and rose to 35 or 40, and once to 144 parts in
10 million.
Quantity of Ammonia per Acre Brought Down by Rain,
etc. — In 1855 and '56, Messrs. Lawes & Gilbert, at Roth-
amstead, England, collected on a large rain-gauge having
ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 63
a surface of ,o'oo of an acre, the entire raiu-fall (dews, etc.,
included) for those years. Prof. Way, at that time chem-
ist to the Royal Ag. Soc. of England, analyzed the waters,
and found that the total amount of ammonia contained in
them was equal to 7 lbs. in 1855, and 9^ lbs. in 1856, for
an acre of surface. These amounts were yielded by
663,000 and 616,000 gallons of rain-water respectively.
In the waters gathered at Insterburg during the twelve-
month ending March, 1865, Pincus and Rollig obtained
6.38 lbs. of ammonia per acre.
Bretschneider found in the waters collected at Ida-Ma-
rienhiitte from April, 1865, to April, 1866, 12 lbs. of am-
monia per acre of surface.
The significance of these quantities may be most appro-
priately discussed after we have noticed the nitric acid of
the atmosphere, a substance whose functions towards vege-
tation are closely related to those of ammonia.
§7.
When lightning strikes the earth or an object near
its surface, a person in the vicinity at once perceives a
peculiar, ; >called " sulphureous " odor, which must belono-
to something developed in the atmosphere by electricity.
The same smell may be noticed in a room in which an
electrical machine has been for some time in vigorous
action.
The substance which is thus pioduced is termed ozone^
from a Greek word signifying to smell. It is a colorless
gas, possessing most remarkable properties, and is of the
highest importance in agricultural science, although our
knowledge of it is still exceedingly imperfect.
Ozone is not known in a pure state free from other
bodies ; but hitherto has only been obtained mixed with
64 HO-\V CROPS FEED.
several times its weight of air or oxygen.* It is entirely
insoluble in water. It has, when breathed, an irritating
action on the lungs, and excites coughing like chlorine gas.
Small animals are shortly destroyed in an atmosphere
charged with it. It is itself instantly destroyed by a heat
considerably below that of redness.
The special character of ozone that is of interest in
connection with questions of agriculture is its oxidizing
power. Silver is a metal which totally refuses to combine
^^itii oxygen under ordinary circumstances, as shown by
its maintaining its brilliancy without symptom of rust or
tarnisli when exposed to piire air at common or at greatly
elevated temperatures. When a slip of moistened silver
is placed in a vessel the air of which is charged with
ozone, the metal after no long time becomes coated with a
black crust, and at the same time the ozone disappears.
By the application of a gentle heat to the blackened
silver, ordinary oxygen gas., having the properties already
mentioned as belonging to this element, escapes, and the
slip recovers its original silvery color. The black crust is
in fact an oxide of silver (AgO,) which readily suffers de-
composition by heat. In a similar manner iron, copper,
lead, and other metals, are rapidly oxidized.
A variety of vegetable pi<2;meuts, such as iiidiijo, litmus, etc., are
speedily hleaclied by ozone. This action, also, is simply one of oxidation.
Gorup-Besanez {Ann. Ch. u. /%., 110,86; also, rhysiologische Vfiemie)
has examined the deportment of a number of orsxanic bodies towards
ozone. He finds that egg-albumin and casein of milk are rapidly altered
by it, while flesh fibrin is unaffected.
Starch, the sugars, the organic acids, and fats, are, when ]nirc, unaf-
fected by ozone. In presence of (dissolved in) alkalies, however, they
are oxidized with more or less rapidity. It is remarkable that oxidation
by ozone takes place only in the presence of water. Dvy substances are
unaffected by it.
The peculiar deportment towards ozone of certain volatile oils will be
presently noticed.
* Babo and Claus (Ann. Ch. v. Ph.. 2d Sup., p. 304) prepared a mixture of oxy-
gen and ozone coutaining nearly G per cent of the latter.
ATMOSPIiHUIC AIU AS THE FOOD OF PLANTS. 65
Tests for Ozone.— Certain phenomena of oxidation tliat are
attended with changes of color serve for the recognition of ozone.
We liave alreiuly seen (II. C. G., p. 64) that starch, when brought in
contact with iodine, at once assumes a dci-];- blue or purple color. When
the compound of iodine with potassium, known as iodide of potas-
sium, is acted on by ozone, its potassium is at once oxidized (to pot-
ash,) and the iodine is set free. If now paper be impregnated with i\
mi.xture of starch-paste and solution of iodide of potassium,* we have i^
test of the pi'esence of ozone, at once most chaiaeteristie and delicate.
Sucli ]>apcr, moi.-tcned and placed in ozonoust air, is spcidi^j turnei\
blue by tiie action of the liberated iodine upon the starch. By the usq
of this test the presence and abundance of oz<.>nte in tiiti atmosphere h;i^
been measured.
Ozone is Active Oxygen. — That ozone is nothino; jnore
or less than o.vygen in a peculiar, active condition, is shown
by the following experiment. When perfectly pure and
dry oxygen is enclosed in a glass tube containing moist
metallic sih'er in a state of fine division, it is possible by
long-continued transmissicn of electrical discharges to
cause the gaseous oxj^gen entirely to disappear. On heat-
ing the silver, which has boconie blackened (oxidized) by
the process, the original quantity of oxygen is recovered
in its ordinary state. The oxygen is thus converted under
the influence of electricity into ozone, which unites with
the silver and disappears in the solid combination.
The independent e.^perimonts of Andrews, Babo, and
Soret, demonstrate that ozone has a greater density than
oxygen, since the latter diminislies in volume when elec-
trized. Ozone is therefore condensed oxygen,\ i. e., its
molecule contains more atoms than the molecule of ordi-
nary oxygen gas.
* Mis 10 parts of starch with 200 parts of cold water and 1 part of recently
fused iodide of potassiiuu, by nibbing them together in a mortar; then heat to
boiling, and strain through linen. Smear pure filter paper with this paste, and dry
The paper should be perfectly white, and must be preserved in a well-stoppered
bottle.
t I. c., charged with ozone.
t Recent observations by Babo and Glaus, and by Soret, show that the density
tf ozone is one and a half times greater than that of oxygen.
DO now CnOPS FEED.
Allotropism.— This occurrence of nn element in two or even
.oore forms is not witliout otlier illustrations, and is termed Allotropism.
Pliosphorus occurs in two conditions, viz., red pliosphorus, which crys-
tallizes in rhonibohedrons, and like ordinary oxyjjen is coiniiaratively
inactive in its affinities; and colorless phosphorus, which crystallizes in
octahedrons, and, like ozone, has vigorous tendencies to unite with ottier
bodies. Carbon is also found in three allotropic foims, viz., diamond,
plumbago, and charcoal, which diflfer exceediugly in their chemical and
physical characters.
Ozone Formed by Chemical Action. — Not only is ozone
produced by electrical disturbance, but it has likewise
been sliown to originate from chemical action ; and, in
fact, from the very kind of action which it itself so vig-
orously manifests, viz., oxidation.
When a clean stick of colorless phosphorus is placed at
the bottom of a large glass vessel, and is half covered
with tepid water, there immediately appear white vapors,
which shortly fill the apparatus. In a little time the pe-
culiar odor of ozone is evident, and the air of the vessel
gives, with iodide-of-potassium-starch paper, the blue color
which indicates ozone. In this experiment ordinary oxy-
gen, in the act of uniting with phosphorus, is partially
converted into its active modification ; and although the
larger share of the ozone formed is probably destroyed by
uniting with phosphorus, a ])ortion escapes combination
and is recognizable in the surrounding air.
The ozone thus developed is mingled with other bodies,
(phosphorous acid, etc.,) which cause the white cloud.
The quantity of ozone that appears in this experiment,
though very small, — under the most favorable circum-
stances but ' |j3„„ of the weight of the air, — is still sufficient
to exhibit all the reactions that have been described.
Schuiibein has shown tliat various organic bodies which
are susceptible of oxidation, viz., citric and tartaric acids,
when dissolved in water and agitated with air in the sun-
light for half an hour, acquire the reactions of ozone.
Ether and alcohol, kept in partially filled bottles, also be-
come capable of producing oxidizing efiects. Many of the
ATMOSPUEllIC AIU AS THE FOOD OF PLANTS. 67
Tegetal)le oils, as oil of turpentine, oil of lemon, oil of
cinnamon, linseed oil, etc., possess the property of ozoniz-
ing oxygen, or at least acquire oxidizing properties when
exposed to the air. Hence the bleaching and corrosion
of the cork of a partially filled turpentine bottle.
It is a highly probable liypothesis that ozone may b i
formed in many or even all cases of slow oxidation, and
that although the chief part of the ozone thus developed
must unite at once with the oxi<lable substance, a portion
of it may diffuse into the atmosphere and escape immediate
combination.
Ozone is likewise produced m a variety of chemical re-
actions, whereby oxygen is liberated from combination at
ordinary temperatures. When water is evolved by gal-
vanic electricity into free oxygen and free hydrogen, the
former is accompanied with a small proportion of ozone.
The same is true in the electrolysis of carbonic acid. So,
too, when permanganate of potash, binoxide of barium,
or chromic acid, is mixed with "strong sulphuric acid, ox-
ygen gas is disengaged which ccmtains an admixture of
ozone.*
Is Ozone Produced by Vej^etation ? — It is an interesting
question whether the oxygen so freely exhaled from the
foliage of }tlants under the influence of sunlight is accom-
panied by ozone. Various experimenters have occupied
* It appears probable that ozone is developed in all cases of rapid oxidation at
high temperatures. This has been long suspected, and Meissiier obtained strong
indirect evidence of the fact. Since the above was written, Pincus has announ-
ced that ozone is produced when hydrogen burns in the air, or in pure oxygen
pas. The quantity of ozone thus developed is sufficient to be recognized by the
odor. To observe this fact, a jet of hydrogen should issue from a fine orifice and
burn with a small flame, not exceeding pg-inch in length. A clean, dry, and cold
beaker glass is held over the flame for a few seconds, when its contents will smell
as decidedly of ozone as the interior of a Leyden jar that has just been discharg-
ed. (Vs. St., IX, p. 47.3.) Pincus has also noticed the ozone odor in similar '.i-
periments with alcohol and oil (Ararand) lamps, and with stearine candles.
Doubtless, therefore, we are justified in making the generalization that I, mI
casus of oxidation ozone is formed, and in many instances a portion of it dififuse*
into the atmosphere and escapes immediato combiuation.
68 HOW CROPS FEED.
themselves with this subject. Tlie most recent investiga'
tions of Daubeny, {Journal Ghem. 8oc., 1867, pp. 1-28,)
lead to the conclusion that ozone is exhaled by plants, a
conclusion previously adopted by Scoutetten, Poey, De
Luca, and Kosraann, from less satisfactory data. Dau-
beny found that nir deprived of ozone by streaming
th.-ough a solution of iodide of potassium, then made to
pa-^s the foliage of a plant confined in a glass bell ami e^-
poseil to sunliglit, actjuired the power of blueing iodide
of-potassium-starch-paper, even when the latter was shield-
ed from the liglit.* Cloez, however, obtained the contrary
results in a series of experiments made by him in 1855,
{Ann. de Chimie et de Fhys., L, 3:26,) in which the oxy-
gen, exhaled both from aquatic aiul land plants, contained
in a large glass vessel, came into contact with iodide-of-
potassium-starch-paper, situated in a narrow and blackened
glass tube. Lawes, Gilbert, and Pugh, in their researches
on the sources of the nitrogen of vegetation, {Phil. Trans.,
1861) examined the oxygen evolved from vegetable matter
under the influence of strong light, without finding evidence
of ozone. It is not impossible that ozone was really pro-
duced in the circumstances of Cloez's experiments, but
spent itself in some oxidizing action before it reached the
test-paper. In Daulieny's experiments, however, the more
rapid stream of air might have carried along over the test-
]iaper enough ozone to give evidence of its presence. Al-
though the question can hardly be considered settled, the
evidence leads to the belief that vegetation itself is a
source of ozone, and that this substance is exhaled, to-
gether with ordinary oxygen, from the foliage, when acted
on by sunlight.
Ozone in the Atmosphere. — Atinospheric electricity,
slow oxidation, and combustion, are obvious means of im-
pregnating the atmosjihere more or less with ozone. If
* Li^lit alone blues this paper after a lime in absence of ozone.
ATMOSPHERIC AIR AS THE POOD OF PLANTS. 69
the oxygen exhaled by plants contams ozone, this sub-
stance must be perpetually formed in the atmosphere over
a large share of the earth's surface.
The quantity present in the atmosphere at any one time
must be very small, since, from its strong tendency to unite
with and oxidize other substances, it shoitly disappears,
and under most circumstances cannot manifest its peculiar
properties, except as it is continually reproduced. The
ozone present in any part of tlie atmosphere at any given
moment is then, not what has been formed, but what re-
mains after oxidable matters have been oxidized. We find,
accordingly, that atmosplieric ozone is most abundant in
winter; since then there not only occurs the greatest
amount of electrical excitement * in the atmosphere, which
produces ozone, but the earth is covered with snow, and
thus the oxidable matters of its surface are prevented
from consuming the active oxygen.
In the atmospliere of crowded cities, in the vicinity of
manure heaps, and wherever considerable quantities of or-
ganic matters pervade the air, as revealed by their odor,
there we find little or no ozone. There, however, it may
actually be produced in the largest quantity, though from
the excess of matters which at once combine with it, it
cannot become manifest.
That the atmospliere ordinarily cannot contain more
than the minutest quantities of ozone, is evident, if we
accept the statement (of Schonbein ?) tliat it conmiunicates
its odor distinctly to a million times its weight of air.
The attempts to estimate the ozone of the atmosphere give
varying results, but indicate a proportion fir less than
sufficient to be recognized by the odor, viz., not more than
1 part of ozone in 13 to 65 million of air. (Zwenger,
Pless, and Pierre.)
These figures convey no just idea of the quantities of
* The amount of electi-ical disturbance is not measured by the number and
Tiolence of thunder-storms : these only indicate its intensity.
70 now CROPS FEED.
ozone actually produced iu tlie atraos2)herc and consumed
in it, or at tiie surface of the soil. We have as yet indeed
no satisfactory means of information on this point, but
may safely conclude from the foregoing considerations that
ozone performs an important part in the economy of
nature.
Relations of Ozone to Vegetable lAutrition. — Of the
direct influence of atmospheric ozone on plants, nothing
is certainly known. Theoretically it should be consumed
by them in various processes of oxidation, and would have
ultimately the same eiFects that are produced by ordinary
oxygen.
Indirectly, ozone is of great significance in our theory
of vegetable iiutiition, inasmuch as it is the cause of chem-
ical changes which are of the highest importance in main-
taining tlie life of ])lants. This fact will appear in the
section on Nitric Acid, which follows.
§ 8-
COMPOUNDS OF NITROGEN AND OXYGEN IN THE ATMOS-
PHERE.
Nitric Acid, NO3H. — Under the more common name
Aqua fortls (strong water) this highly important sub-
stance is to be found in every apothecary shop. It is,
when pure, a coloi-less, usually a yellow liquid, whose
most obvious properties are its sour, burning taste, and
power of dissolving, or acting upon, many metals and other
bodies.
When pure, it is a half heavier than its own bulk of
water, and emits pungent, suffocating vapors or fumes ; in
this state it is rarely seen, being -in general mixed or di-
luted with more or less Avater ; when very dilute, it evolves
no fumes, and is even pleasant to the taste.
It has the properties of an acid in the most eminent de-
gree; vegetable blue colors are reddened by it, and it
ATMOSPHEllIC ATH AS THE FOOD OP PLANTS. 71
unites with great avidity to all basic bodies, forming a
long list of nitrates.
It is volatile, and evaporates on exposure to air, though
not so rapidly as water.
Nitric acid has a strong affinity for water; hence its
vapors, when they escape into moist air, condense the
moisture, making therewith a visible cloud or fume. For
the same reason the commercial acid is always more or less
dilute, it being difficult or costly to remove the water en-
tirely.
Nitric acid, as it occurs in commerce, is made by heat-
ing together sulphuric acid and jiitrate of soda, when
nitric acid distils off, and sulphate of soda remains behind.
Nitrate of Sti^yhuric Bisulphate of Nitric
soda. acid. soda. acid.
NO3 Na + H,S O, = HNa SO, + NO3 H
Nitrate of soda is formed in nature, and exists in im-
mense accumulations in the southern part of Peru, (see
p. 252.)
AnIiydrouM I\itric Acid, NoOs, is what is commonly under-
stood as existing in conibiuation witli bases in the nitrates. It is a
crystallized body, but is not an acid until it unites with the elements of
water.
Nitrate of Ammonia, NH3 NO^H, or NH, NO3, may
be easily })repared by adding to nitric acid, ammonia in
slight excess, and evaporating the solution. The salt read-
ily crystallizes in long, flexible needles, or as a fibrous
mass. It gathers moisture from the air, and dissolves in
about half its weight of water.
If nitrate of ammonia be mixed with potash, soda, or
lime, or with the carbonates of these bases, an exchange
of acids and bases takes place, the result of which is ni-
trate of potash, soda, or lime, on the one hand, and free
ammonia or carbonate of ammonia on the other.
,^'itrou!« Oxide, N^O.— When nitrate of ammonia is heated, it
72 now . rtrtps PKt:r>.
nu'lts, and gTi.lir.ni.v decoiniiosc.s into wiitcr and nitrous oxide, Ji
"langliiiiij s^is," as represented by the equation : —
NH4 NO3 = 3 HoO + N,0
Xitric acid and the nitrates act as powerful oxidizing
agents, i. e., tkey readily yield nj) a portion or all their
oxygen to substances having strong affinities for tliis ele-
ment. If, for example, charcoal he warmed with strong
nitric acid, it is rapidly acted upon and converted into
carbonic acid. If thrown into melted nitrate of soda oi
saltpeter, it takes fire, and is violently burned to carbonid
acid. Similarly, sulphur, phosphorus, and most of tlio
metals, may be oxidized by this acid.
When nitric acid oxidizes other substances, it itself loses
oxygen and suffers reduction to compounds of nitrogen,
containing less oxygen. Some of these compounds require
notice.
Nitric Oxide, NO. — ^When nitric acid somewhat diluted
with water acts upon metallic copper, a gas is evolved,
which, after washing Avith water, is colorless and permanent.
It is nitric oxide. By exposure to air it tmites with oxy-
gen, and forms red, suff.icating fumes of nitric peroxide,
or, if the oxygen be not in excess, nitrous acid is formed.
]Vitric Peroxide, (hyponitric acid,) N0„, appears as a
dark yellowish-red gas when strong nitric acid is ])Oured
npon copper or tin exposed to the air. It is procured in
a state of purity by strongly heating nitrate of lead : by
a cold apjiroaching zero of Fahrenheit's thei'mometer, it
may be condensed to a yelloAV liquid or even solid.
Nitrous Acid, (anhydrous,) ^„0^, is produced when
nitric peroxide is mixed with water at a low temperature,
nitric acid being formed at the same time.
mtric peroxide. Water. Nitric acid. ^'^T'i ''"''^'
-' anhydrous.
4 NO, + H^ = 2 NHO3 + N, O,
It may be procured as a blue liquid, which boils at the
freezing point of water.
ATMOSPnEi:i(; air a>; tiie food op plants. 73
When nitric peroxiJe is ])ut in cont:icL with solutions
of an alkali, there lesults a mixture of nitrate and nitrite
of the alkali.
JVitric Hydnde of Nitrate of Nitrite of -rp-^^g^
peroxide. potash. potash. i)otash.
2 NO, + 2 IIKO = NKO3 + NKO, + II, O
Nitrite of Ammonia, NH^ NO., is known to the chem-
ist as a white crystalline solid, very soluble in water.
When its concentrated aqueous solution is gently heated,
the salt is gradually resolved into water and nitrogen gas.
This decomposition is represented by the following equa-
tion:
NH, NO, = 2 H,0 + 2 N
This decomposition is, however, not complete, A por-
tion of ammonia escapes in the vapors, ami nitrous acid
accumulates in the residual liquid. (Pettenkofer.) Addi-
tion of a strong acid facilitates decomposition; an alkali
retards it. When a dilute solution, 1 : 500, is boiled, but
a small portion of the salt is decomposed, and a part of it
is found in the distillate. Very dilute solutions, 1 : 100,000,
may be boiled without suifering any alteration whatever.
(Schuyen.)
Schonbein and others have (erroneously?) supposed that
nitrite of ammonia is generated by the direct union of
nitrogen and water. Nitrite of ammonia may exist in the
atmosphere in minute quantity.
Nitrites of pot i'<h and soda may be procured by strongly
heating the corresponding nitrates, Avhereby oxygen gas is
expelled.
The Hutuai Convertibility of Nitrates and Nitrites is
illustrated by various statements a'jvady made. There
are, in fact, numerous substances which reduce nitrates to
nitrites. According to Schonbein, {Jour. Prakt. Ch., 84,
207,) this reducing effect is exercised by the albuminoids,
by starch, glucose, and milk-sugar, but not by cane-sugar,
4
74 ilOW <^ROPS FEED.
It is also nianifcst,ed by many miitals, as zinc, iron, and
lead, and by any mixture evolving hydrogen, as, for ex-
ample, putrefying org.inic matter. On the other hand,
ozone instantly oxidizes nitrites to nitrates.
Reduction of Nitrates and Nitrites to Ammonia. —
Some of the substances wliicli convert nitrates into nitrites
may also by their prolonged action transform the latter
into ammonia. When smiU fragments of zinc and iron
mixed together are drenclied with warm solution of caustic
potash, hydrogen is copiously disengaged. If a nitrate be
addecj. to tlie mixture, it is at once reduced, and ammonia
escapes. If to a mixture of zinc or iron and dilute chlor-
hydric acid, sucli as is em;>loyed in preparing hydrogen
gas, nitric acid, or any nitrate or nitrite be added, the
evolution of iiydrogen ceases, or is checked, and ammonia
is formed in the solution, whence it can be expelled by
lime or potash.
Nitric acid. Hydrogen. Ammonia, 'Water.
NO3H + 8H = NPI3 + 3Hp
The appearance of nitrous acid in this process is an in-
termediate step of the reduction.
Further Reduction of Nitric and Nitrous Acids. — Tin-
der certain conditions nit ric acid nnd nitrous acid are still
further deoxidized. Nesbit, who first employed the reduc-
tion of nitric acid to ammonia by means of zinc and dilute
chlorhydric acid as a means of detL-rmining the cpiantity
of the former, mentions {Quart. Jour. Ghem. Soc, 1847,
p. 283,) that when the temperature of the liquid is allowed
to rise somewhat, nitric oxide gas, NO, escapes.
From weak nitric acid, zinc causes the evolution of ni-
trous oxide gas, N'„0.
As already mentioned, nitrate of ammonia, when heated
to fusion, evolves nitrous oxide, N^O. Emmet showed
that by immersing a strip of zinc in the melted salt, nearly
pure nitrogen. gas is set free.
AtMOSPIlKRir AIR AS TIIK FOOD OF PLANTS. 7")
When nitric acid is heated with lean flesh (fibrin), nitric
oxide and nitrogen g.ises botli appear. It is thus seen
that by successive steps of deoxidation nitric acid may
be gradually reduced to nitrous acid, ammonia, nitric oxide,
nitrous oxide, and finally to nitrogen.
Tests for I\iti'ic and Citrous Acids. — The fact that
these substances (iften occur in extremely minute quantities renders it
needful to employ very delicate tests for their recognition.
Price's Test. — Free nitrous acid decomposes iodide of potassium in the
Bame manner as ozone, and hence gives a blue color, witli a mixture of
tliis salt and starch-piiste. Any niti'ite produces the same effect if to
tlie mixture dilute sulphuric acid be added to liberate the nitrous acid.
Pure nitric acid, if moderately dilute, and dilute solutions of nitrates
mixed with dilute sulphuric acid, are without immediate efiFect upon
iodide-of-pota-sium-starch-paste. If the solution of a nitrate be min-
gled with dilute sulphuric acid, and ai^itated for some time witli zinc
filiui^s, reduction to nitrite occurs, and then addition of the starch-paste,
etc., gives the blue coloration. Accorditig to Seh6nl)ein, this test, first
proposed by Price, will detect nitrous acid when mixed with one-hund-
red-tliousand times its Aveight of water. It is of course only applicable
in the absence of other oxidizing agents.
07-een Vitriol Test. — A very characteristic test for nitric and nitrous
acids, and a delicate one, though less sensitive than that just describ-
ed, is furnished by common gieen vitriol, or protosulpliate of iron.
Nitric oxide, the red gas which is evolved from nitric acid or nitrates by
mixing them with excess of strong sulphuric acid, and from nitrous acid
or nitrites by addition of dilute sulj^hiiric acid, gives with green vitriol a
peculiar blackish-brown coloration. To test for minute quantities of
nitrous acid, mix the solution with dilute sulphuric acid and cautiously
pour this liquid upon an equal bulk of cold saturated solution of green
vitriol, so that the former liquid floats upon the latter without mingling
much with it. On standing, the coloration will be perceived where the
two liquids are in contact.
Nitric acid is tested as follows: Mix the solution of nitrate with an
equal volume of concentrated sulphuric acid ; let the mixture cool, and
pour upon it the solution of green vitriol. The coloration will appear
between the two liquids.
Formation of IVitrogen Compounds in the Atmosphere.
— a. From free nitrogen, by electrical ozone. Schonbein
and Meissner have demonstrated that a discharge of elec-
tricity through air in its ordinary state of dryness causes
oxygen and nitrogen to unite, with the formation of nitric
peroxide, NO^. Meissner has proved that not the elec*
H now CROPS PEEf).
tricity directly, but the ozone developed by it, accom-
plishes this oxidation. It has long been known that nitric
peroxide decomposes with water, yielding nitric and ni-
trous acids thus :
2 NO, + HP = NO^H + NO^H.
It is further known that nitrous acid, both in the free
state and in combination, is instantly oxidized to nitric
acid by contact with ozone.
Tims is explained the ancient observation, first made by
Cavendish in 1784, that when electrical sparks are trans-
mitted through moist air, confined over solution of potash,
nitrate of potash is formed. (For information regarding
this salt, see p. 252.)
Until recently, it has been supposed that nitric acid is
present in only those rains which accompany thunder-
storms.
It appears, however, from the analyses of both Way and
Boussiugault, tliat visible or audible electric discharges
do not perceptibly influence the proportion of nitric acid
in the air; the rains accompanying thunder-storms not
being always nor usually richer in this substance than
others.
Von Babo and Meissner have demonstrated that silent
electrical discharges develop more ozone than flashes of
lightning. Meissner has shown that the electric spark
causes the copious formation of nitric peroxide in its im-
mediate path by virtue of the heat it excites, Avhich in-
creases the energy of the ozone simultaneously produced,
and causes it to expend itself at once in the oxidation of
nitrogen. Boussiugault informs us that in some of the
tropical regions of South America audible electrical dis-
charges are continually taking place throughout the whole
year. In our latitudes electrical disturbance is perpetu-
ally occurring, but equalizes itself mostly by silent dis-
charge. The ozone thus noiselessly developed, though
operating at a lower temperature, and therefore more
ATMOSPIIKUIC AlU AS THE FOOD OF PLANTS. 77
slowly than that wlilch is produced by lightning, must
really oxidize much more nitrogen to nitric acid than the
latter, because its action never ceases.
Formation of \itro^CD Compounds in the Atmosphere.
— h. From tree nitrogen (by ozone ?) in the processes of
combustion and slow oxidation.
At high temperatures. — Saussure first observed {Ann.
de Chimie., Ixxi, 'IS'l), that in the burning of a mixture of
oxygen and hydrogen gases in the air, the resulting water
contains .-immonia. He hud previously noticed that nitric
acid and nitrous acid are formed in the same process.
Kolbe {Ann. CJiem. u. Pharm., cxix, 176) found that
when a jet of burning hydrogen was passed into the neck
of an open bottle containing oxygen, reddish-yellow va-
pors of nitrous acid or nitric peroxide were copiously pro-
duced on atmospheric air becoming mingled with the
burning gases.
Bence Jones {Phil, Trans.., 1851, ii, 399) discovered ni-
tric (nitrous?) acid in the water resulting from the burn-
ing of alcohol, hydrogen, coal, wax, and purified coal-gas.
By the use of ttie iodide-of potassium-starch test (Price's
test), Boettger {Jour, far Prakt. Chem., Ixxxv, 396) and
Schonbein (ibid., Ixxxiv, 21.5) have more recently confirm-
ed the result of Jones, but because they could detect
neitlier free acid nor free alkali by the ordinary test-pa-
pers, they concluded that nitrous acid and ammonia are
simultaneously formed, that, in fact, nitrite of aw.monia
is generated in all cases of rapid combustion.
Meissner ( Untersuchumjen Tiber den Sauerstoff^ 1863, p.
283) was unable to satisfy himself that either nitrous acid
or ammonia is generated in combustion.
Finally, Zabelin {Ann. Chem. x. Ph., cxxx, 54) in a
series of careful experiments, found that when alcohol, il-
luminating gas, and hydrogen, burn in the air, nitrous acid
and ammonia are very frequently, but not always, formed.
to HOW CROPS FEED.
When the combustion is so perfect that the resulting wa-
ter is colorless and pure, only nitrous acid is formed ;
when, on the other hand, a trace of organic matters es-
capes oxidation, less or no nitrous acid, but in its place
ammonia, appears in the water, and this under circum-
stances that preclude its absorption from the atmosphere.
Zabelin gives no proof that the combustibles he etn<>
ployed were absolutely free from compounds of nitrogen,
but otherwise, his experiments are not open to criticism.
Meissner's observations were indeed made under some-
what different conditions ; but his negative results were
not improbably arrived at simply because he employed a
much less delicate test for nitrous acid than was used by
Schonbein, Boettger, Jones, and Zabelin.*
We must conclude, then, that nitrous acid and ammonia
are usually formed from atmospheric nitrogen during rap-
id combustion of hydrogen and compounds of hydrogen
and carbon. The quantity of these bodies thus generated
is, however, in general so extremely small as to require the
most sensitive reagents for their detection.
At low te?nperat((res. — Schonbein was the first to observe
that nitric acid may be formed at moderately elevated or
even ordinary temperatures. He obtained several grams
of nitrate of potash by adding carbonate of potash to the
liquid resulting from the slow oxidation of phosphorus in
the preparation of ozone.
More recently he believed to have discovered that ni-
trogen compounds are formed by the simple evaporation
of water. He heated a vessel (which was indifferently of
* Meissner rejected Price's test in the belief that it cannot serve todistinjuish
nitrous acid from peroxide of hydrogen, H2 O2. He therefore made the liquid
to be examined alkaline with a slight excess of potash, concentrated to small
bulk and tested with dilute sulphuric acid and protosulphate of iron. {Uniers.
u. d. Swiers'off, p. 233). Scliiinboin had found that iodide of potassium is decom-
posed after a little time by concentrated sohitions of peroxides of hydrogen, but in
unaff.'Ctcd by this body when dilute. {Jour, fur prakt. Chum., Ixsxvi, p. !)()).
Zabelin agrees with Schonbein that Price's test is decisive between peroxide ol
hydrogen and nitrous acid. {Ann. CItcin. u. Ph., cxsx, p. 5S.)
ATMOSPHERIC AIU AS THE FOOii Of PLANl'S. 79
glass, porcelain, silver, etc.,) so that water would evapo-
rate rapidly from its surface. The purest water was then
dropped into the warm dish in small quantities at a time,
each portion being allowed to evaporate away before the
next was added. Over the vapor thus generated was held
the mouth of a cold bottle until a portion of the vapor
was condensed in the latter.
The water thus ■^'oUccted gave the reactions for nitrous
acid and ammonia, sometimes quite intensely, again faint-
ly, and sometimes not at all.
By simply exposing a piece of filter-paper for a suffi-
cient time to the vapors arising from pure water heated
to boiling, and pouring a few drops of acidified iodide-of-
potassium-ytarch-paste upon it, the reaction of nitrous acid
Avas obtained. When paper which had been impregnated
with dilute solution of pure potash was hung in the va-
pors that arose from water heated in an open dish to 100°
F., it shortly acquired so much nitrite of potash as to re-
act WMth the above named test.
Lastly, nitrons acid and ammonia appeared when a
sheet of filter-paper, or a piece of linen cloth, which had
been moistened with the purest water, was allowed to dry
at ordinary temperatures, in the open air or in a closed
vessel. (Jour, fiir Prakt. Chem., Ixvi, 131.) These ex-
periments of Schonbein arc open to criticism, and do not
furnish perfectly satisfactory eviilence that nitrous acid
and ammonia are generated under the circumstances men-
tioned. Bohlig has objected that these bodies might be
gathered from the atmosphere, where they certainly exist,
though in extremely minute quantity.
Zabelin, in the paper before referred to {Ann. Ch. Ph.
cxxx, p. 76), communicates some experimental results
which, in the writer's opinion, serve to clear up the mat-
ter satisfactorily.
Zabelin ascertained in the first place that the atmos-
pheric air contained too little ammonia to influence Xess-
80 HOM' CROr.3 FEED.
ler's test,* which is of cxtveino delicacy, and -wliich he con«
stantly employed in his invostigntions.
Zabelia operated in closed vessels. The apparatus he
used consisted of two glass flasks, a larger and a smaller
one, which were closed by corks and fitted with glass
tubes, so that a stream of air entering the larger vessel
should bubble through water covering its bottom, and
thence passing into the smaller flask should stream through
Nessler's test. Next, he found that no ammonia and
(by Price's test) but doubtful traces of nitrous acid could
be detected in the purest water when distilled alone in
this apparatus.
Zabelin likewise showed that cellulose (clippings of filter,
paper or shreds of linen) yielded no ammonia to Nessler's
test when heated in a current of air at temperatures of
120° to 160° F.
Lastly, he found that when cellulose and pure water to-
gether were exposed to a current of air at the tempera-
tures just named, ammonia was at once indicated by
Nessler's test. Nitrous acid, however, could be detected,
if at :dl, in the minutest traces only.
Views of SchOnbeiv. — Tiie reader should observe that
Boettger and Schonbein, finding in the first instance by
the exceedingly sensitive test with iodide of potassium
and starch-paste, that nitrous acid was formed, when hy-
drogen burned in the air, while the water thus generated
was neutral in its reaction with the vastly less st iisitive
litmus test-paper, concluded that the nitrous acid was
united with some base in the form of a neutral salt. Af-
terward, the detection of ammonia appeared to denion-
Btrate the formation of nitrite of ammonia.
We have already seen that nitrite of ammonia, by ex-
posure to a moderate heat, is resolved into nitrogen and
water. Schonbein assumed that under the conditions of
* See p. &4
I
ATMOSPIIEUIC Allt AS THE FOOD OF PLANTS. 81
his experiments nitrogen and water combine to form ni-
trite of ammonia.
2 N + 2 H,0 - Nil,, NO^H
This theory, supported by the authority of so distin-
guished a philosopher, has been ahnost universally credit-
ed.* It has, however, little to warrant it, even in the way
of probability. If traces of nitrite of ammonia can be
produced by the immediate combination of these excep-
tionally abundant and universally diffused bodies at com-
mon temperatures, or at the boiling point of Avater, or
lastly in close proximity to the flames of burning gases,
then it is simply inconceivable that a good share of the
atmosphere should not speedily dissolve in the ocean, for
the conditions of Schonbein's experiments preyail at all
times and at all places, so far as these sul)stances are con-
cerned.
The discovery of Zabeliu that ammonia and nitrous acid
do not always appear in equivalent quantities or even
simultaneously, while difiicult to reconcile with Schon-
bein's theory, in no wise conflicts with any of his facts.
A quantity of free nitrous acid that admits of recognition
by help of Price's test would not necessarily have any
effect on litmus or other test for free acids. There re-
mains, then, no necessity of assuming the generation of ni-
trite of ammonia, and the fact of the separate appearance
of the elements of this salt demands another explanation.
The Author's Opinion. — The writer is not able, perhaps,
to offer a fully satisfactory explanation of the facts above
adduced. He submits, however, some speculations which
appear to him entirely warranted by the present aspects
of the case, in the hope that some one with the time at
* Zabelin was inclined to believe that his failure to detect nitrous acid in some
of his experiments where organic matters intervened, was due to a power pos-
sessed by these organic matters to mask or impair the delicacy of Price's test,
as first noticed by Pettenkofer and since demonstrated by Sch<>nbeiu in case of
urine.
4*
82 UOW CROPS FEED.
command for experimental study, will estaldish or disprove
them by suitable investigations.
lie believes, from the exi^tino; evidence, that free nitro-
gen can, in no case, unite directly with water, but in the
conditions of all the foregoing experiments, it enters com-
bination by tlie action of ozone^ as Schonbein formerly
maintain.ed and was the first to suggest.
We have already recounted the evidence that goes to
show tlie formation of ozone in all cases of oxidation, both
at high and low temperatures, p. 67.
In Zabelin's experiments we may suppose that ozone
was formed by the oxidation of the cellulose (linen and
paper) he emiiloyed. In Schimbein's experiments, where
paper or linen was not employed, tlie dust of the air may
have supplied the organic matters.
The first result of the oxidation of nitrogen is nitrous
acid alone (at least Schonbein and Bohlig detected no ni-
tric acid), when the combustion is complete, as in case of
hydrogen, or when organic matters are excluded from the
experiment. Nitric acid is a product of the subsequent
oxidation of nitrous acid. When organic matters exist in
the product of combustion, as when alcohol burns in a
heated apparatus yielding water having a yellowish color,
it is probable that niti'ous acid is formed, but is afterward
reduced to ammonia, as has been already explained, p. 74.
Zabelin, in the article before cited, refers to Schonbein
as authority for the fact that various organic bodies, viz.,
all the vegetable and animal albuminoids, gelatine, and
most of the carbohydrates, especially starch, glucose, and
milk-sugar, reduce nitrites to ammonia., and ultimately to
nitrogen ; and although we have not been able to find such
a statement in those of Schonbein's papers to which we
have had access, it is entirely credible and in accordan«e
with numerous analogies.
If, as thus appears extremely probable, ozone is devel-
oped in all cases of oxidavion, both rapid and slow, then
^TMOSPHEUIC AIU AS THE FOOD OF PLANTS. 83
every flame and fire, every dcicaying plant and animal,
the organic matters that exhale from the; skin and Inngs
of living animals, or from the foliage and flowers of plants,
especially, i)erhaps, the volatile oils of cone-bearing trees,
are, indirectly, means of converting a jiortion of free ni-
trogen into nitrous and nitric acids, or ammonia.
These topics will be recurred to in our discussion of
Nitrification in the Soil, p. 254.
Formation of Nitroi^en ('orapouii<ls in the Atmospliere.
— c. From free nitrogen by ozone accompanying the oxy-
gen exhaled from green foliage in sunlight.
The evidence xipon the question of the emission of ozone
by plants, or of its formation in the vicinity of foliage, has
been briefly presented on page 68. The present state of
investigation does not permit us to pronounce definitely
upon this point. There are, however, some ficts of agri-
culture which, perhaps, find their best explanation by as-
suming this evolution of ozone.
It has long been known that certain crops are especially
aided in their growth by nitrogenous fLTtilizers, while oth-
ers are comparatively indifierent to them. Thus the cereal
grains and grasses are most frequently benefited by appli-
cations of nitrate of soda, Peruvian guano, dung of ani-
mals, fish, flesh and blood manures, or other matters rich
in nitrogen. On the other hand, clover and turnij^s flour-
ish best, as a rule, when treated with phos])hates and alka-
line sxxbstances, and are not manured with animal fertiliz-
ers so economically as the cereals. It has, in fact, become
a rule of practice in some of the best farming districts of
England, where systematic rotation of crops is followed,
to apply nitrogenous manures to the cereals and phos-
phates to turnips. Again, it is a fact, that whereas nitro-
genous manures are often necessary to ]ii-oduce a good
wheat crop, in which, at 30 bu. of grain and 2,000 lbs. of
straw, there is contained 45 lbs. of nitrogen ; a crop of
clover may be produccl without nitrogenous manure, in
84 HOW CROPS FEED.
wliich would be taken from the field twice or thrice the
above amount of nitrogen, although the period of growth
of the two crops is about the s.ime. Ulbricht found in
his investigation of the clover plant ( Vs. St., IV., p. 27)
that the soil appears to have but little influence on the
content of nitrogen of clover, or of its individual organs.
These facts admit of another expression, viz. : Clover,
though containing two or three times more nitrogen, and
requiring correspondingly larger supplies of nitrates and
ammonia than Avheat, is able to supply itself much more
easily than the latter crop. In parts of the Genesee wheat
region, it is the custom to alternate clover with wheat, be-
cause the decay of the clover stubble and roots admirably
prepares the ground for the ]a<t-nanied crop. The same
preparation might be had by the more expensive process
of dressing with a higlily nitrogenous manure, and it is
scarcely to be doubted that it is the nitrogen gathered by
the clover which insures tlie wheat crop that follows. It
thus appears that the plant itself causes the formation in
its neigliborhood of assimilable compounds of nitrogen,
and that some plants excel others in their power of accom-
l)lishing this important result.
On the supposition that ozone is emitted by plants, it is
plain that those crops which produce the largest mass of
foliage develop it most abundantly. By the action of
this ozone, the nitrogen that bathes the leaves is convert-
ed into nitric acid, which, in its turn, is absorbed by the
plant. The foliage of clover, cut green, and of root crops,
maintains its activity until the time the crop is gathered;
the supply of nitrates thus keeps pace with the wants of
the plant. In case of grain crops, the functions of the fo-
liage decline as the seed begins to develop, and the plant's
means of providing itself with assimilable nitrogen fail,
although the need for it still exists. Furthermore, the
clover cut for hay, leaves behind much more roots and
sLubble per acre than grain crops, and the clover stubblu
ATMOSPHEltlC AIU AS THE FOOD OF PLANTS. 85
is twice as rich iu nitrogen as the stubble of ripened grain.
This is a result of the fact that tlie clover is cut when in
active growth, while the grain is harvested after tlie roots,
stems, and leaves, have been exhausted of their own juices
to meet the demands of the seed.
Whatever may be the value of our explanations, the
fact is not to be denied that the soil is enriched in nitrogen
by the culture of large-leaved plants, whicli are harvested
while in active growth, and leave a considerable propor-
tion of roots, leaves, or stubble, on the field. On the other
hand, the field is impoverished in nitrogen Avhen grain
crops are raised upon it.
Formation of IVUric Acid from Ammonia. — Ammonia
(carbonate of ammonia) under tlie influence of ozone is
converted into nitrate of ammonia, (Bauraert, Ilouzeau).
The reaction is such tluxt one-half of the ammonia is oxid-
ized to nitric acid, which unites with the residue and with
water, as illustrated by the equation :
2NH3 + 40 = NH,, NO3 + H,0
In this manner, niti'ate of ammonia may originate in the
atmosphere, since, as already shown, ammonia and ozone
are both present there.
Oxidation and Reduction in the Atmosphere,— The
fact that ammonia and organic matters on the one hand,
and ozone, nitrous and nitric acids on the other, are pres-
ent, and, perhaps, constantly present in the air, involves at
first thought a contradiction, for these two classes of sub-
stances are in a sense incompatible with each other.
Organic matters, ammonia, and nitrous acid, are converted
by ozone into nitric acid. On the contrary, certain or-
ganic matters reduce ozone to ordinary oxygen, or destroy
it altogether, and reduce nitric and nitrous acids to am-
monia, or, peihaps, to free nitrogen. The truth is that
the substances named are being perpetually composed and
decomposed in the atmosphere, and at the surface of the
86 HOW CROPS FEED.
soil. Here, or at one moment, oxidation prevails; there,
or at another moment, reduction preponderates. It is
only as one or another of the results of this incessant ac-
tion is withdrawn from the spliere of change, that we can
give it permanence and identify it. The quantities we
measure are hut resultants of forces that oppose each oth-
er. The idea of rest or permanence is as foreign to the
chemistry of the atmospliere as to its visible phenomena.
Nitric Acid in tlie Atmospliere. — The occurrence of ni-
tric acid or nitrate of aunnunia in the atmosphere has been
abundantly demonstrated in late years (1854-6) by Cloez,
Boussingault, De Luca, and Kletzinsky, who found that
when lai-ge volumes of air are made to bubble through
solutions of potash, or to stream over fragments of brick
or pumice which have been soaked in potash or carbonate
of potash, these absorbents gradually acquire a small
amount of nitric acid. In the experiments of Cloez and
De Luca, the air was first Avashed of its ammonia by con-
tact with sulphuric acid. Their results prove, therefore,
that the nitric acid was formed independently of ammonia,
though it doubtless exists in the air in combination with
this base.
Proportion of Nitric Acid in Rain-water, etc.— In at-
mospheric waters, nitric acid is found much more abund-
antly than in the air itself, for the reason that a small bulk
of rain, etc., washes an immense volume of air.
Many observers, among the first, Liebig, have found ni-
trates in rain-water, especially in the rain of thunder-
storms. The investigations of Boussingault, made in
18.56-8, have amply confirmed Barral's observation that
nitric acid (in combination) is almost invariably present in
rain, dew, fog, hail, and snow. Boussingault, {Agrotiomie,
etc., 11, 325) determined the quantity of nitric acid in 134
rains, 31 snows, 8 dews, and 7 fogs. In only 16 instances
out of these 180 was the amount of nitric acid too small
ATMOSPIIKlilC Ain AS THE FOOD OF PLANTS. 87
to detect. The greatest proportion of nitric acid found in
rain occurred in a slow-fiilling morning shower, (9th Octo-
ber, 1857, at Liehfrauenberg), viz., 62 parts* in 10 million
of water. In fog, on one occasion, (at Paris, 19th Dec,
1857,) 101 parts to 10 million of water were observed.
Knop found in rain-water, collected near Leipzig, in
Jidy, 1862, 5G parts; in rain that fell during a thunder-
storm, 98 parts in 10 million of water.
Boussingault found in rain an average of 2 parts, in
snow of 4 parts, of nitric acid to 10 million of water.
Mr. Way, whose determinations of ammonia in the at-
mospheric waters collected by Lawes and Gilbert, at
Rothamstead, during the whole of the years 1855-6, have
already been noticed, (p. 63,) likewise estimated the nitric
acid in the same waters. He found the proportion of ni-
tric acid to be, in 1855, 4 parts, in 1856 4^ parts, to 10
million of water.
Bretsehneider found at Ida-Marienhiitte, Prussia, for the
year 1865-6 an average of 8^ parts, for 1866-7 an average
of 4^ parts, of nitric acid in 10 million of water. At Regen-
walde, Prussia, the average in 1865-6 was 25 parts, in
1866-7, 22 parts. At Proskau, the average in 1864-5 was
31 parts. At Kuschen, the average for 1864-5 was 6
parts; in 1865-6,7; in 1866-7, 8 parts. At Dahme, in
1865-6, the average was 12 parts. At Insterburg, Pincus
and RoUig obtained in 1864-5, an average of 12 parts; in
1865-6, an average of 16 jtarts of nitric acid in 10 million
of water. The highest monthly average Avas 280 parts,
at Lauersf )rt, July, 1S64 ; and the lowest was nothing,
April, 1865, at Ida-Marienhiitte.
Quantity of IVitric Acid in Atmospheric Water, — The
total quantity of nitric acid that could be collected in the
rains, etc., at Rothamstead, amounted in 1855 to 2.98 lbs.,
and in 1856 to 2.80 lbs. per acre.
* In all the quaiititative statements here and elsewhere, anhydrous nitric add,
Ny Oj, (O— 10, formerly NOj, 0—8) is to be understood.
88
now CROPS FEED.
This quantity was very irregularly distributeil among the
months. In 1855 the smallest amount was collected in
January, the largest in October, the latter being nearly
20 times as much as the former. In 185G the largest
quantity occurred in May, and the smallest in February,
the former not quite six times as much as the latter.
The following table gives the results of Mr. Way entire.
{Jour. Roy. Ag. Soc. of Eng., XVII, pp. 144 and 620.)
Amounts of Rain and of Ammonia, Nitric Acid, and totai. Nitrogen
therein, collected at Rothamstead, Eng., iu the years lSo5-6— calculated per
acre, according to Messrs. Lawes. Gilbert, and Way.
Qvantity of Rain
in Imperud Gal-
lons, (1 gal. = 10
lbs. water.)
1855
1856
Ammonia
in
grains.
Nitric
acid in
grains.
1855| 1856 1855 1856
Toial M-
trogen in
grains.
1855:1856
January. . . .
February . .
March
April
May
June
July
August
September.
October...
November .
December. .
1244
2337
.'.W 32.181,3021
.0751 50.870:2438
Total.
2bciy
4214
5072
3921
2591
4070
3352
i m:i.-3Si\ 616.05ll7.11 9.53 2.98 2.806.
i gall's. I gall's, i lbs. lbs. lbs. lbs. libs. lbs.
230 1561 1084! 4526
944i 544'2169| 3579
1102 8(Hi 39951 1945
32.-) lot;:', 10241 7369
lMo:;i)-,'l ;i9.39:l5863
:i:m •J04(i .^j447| 4540
20*0 1191,8615
:i>77'212.-> 4870
7321756,2917
4480 2075 7414
1(M7 137112749
664 203512180
2670
4021
5373
3767
According to Pincus and Rollig, the atmospheric water
brought down at Insterburg, in the year ending with
March, 1865, 7.225 lbs. av. of nitric acid per English acre
of surface. j
The quantity of nitrogen that fell ns ammonia was^
3.628 lbs.; that collected in the form of nitric acid was
1.876 lbs. The total nitrogen of the atmospheric waters
per acre, for the year, was 5.5 lbs. The rain-fall was
392,707 imperial gallons.
Bretschneider found in the atmospheric waters gathered
at Ida-Marienhiitte, in Silesia, during 12 months ending
April 15th, 1866, 3|- lbs. of nitric acid per acre of surface.
In Bretschneider's investigation, the amount of nitrogen
ATMOSPHEiaO Aia aS THE T<OOI> OP PLANTS. 80
brouglit down per acre in {ho form of ammonia was 9.93G
lbs.; that in the ibrm of nitric acid Mas 0.9T4 lbs. The
total nitrogen contained in the rain, etc., was accordingly
10.91, or, in round numbers, 11 lbs. avoirdupois. The rain-,
fall amounted to 488.309 imperial gallons, (Wilda's Cen-
tmlhlatt, August, 1866.)
Relation of Nitric Acid to Ammonia in the Atmos-
pliere. — The foregoing results demonstrate that there i8
in the aggregate an excess of ammonia over the amount
required to form nitiate with the nitric acid. (In nitrate
of ammonia (XH^ XO3)? ^^'^ acid and base contain the
same quantity of nitrogen.) We are hence justified in
assuming that the acid in question commonly occurs as ni-
trate of ammonia * in the atmosphere.
At times, however, the nitric acid may preponderate.
One instance is on record (Journal de Pharmacie^ Apr.,
1845) of the presence of free nitric acid in hail, which fell
at Nismes, in June, 1842. This hail is said to have been
perceptibly sour to the taste.
Cloez ( Conipt. Mendus, lii, 527) found traces of free
nitric acid in air taken 3 feet above the ground, especially
at the beginning and end of winter.
The same must have been true in the cases already giv-
en, in which exception;dly large quantities of nitric acid
were found, in the examinations made by Boussingault and
the Prussian chemists.
The nitrate of ammonia which exists in the atmosphere
- d'Hibtless held there in a state of mechanical suspension.
it is dissolved in the falling rains, and when once brought
to the surface of the soil, cannot again find its way into
the air by volatilization, as carbonate of ammonia does,
but is permanently removed from the atmospheie, and
* In evaporating large quantifies of rain-water to dryness, there are often found
In the residue nitrates of lime and 6oda. In these cases the lime and soda come
from dust suspended in the air.
00 now CROPS FEED.
until in some way chemically decomposeil, belongs to the
soil or to the rivers and seas,
Mtrous Acid in the Atmospheric Waters. — In most of the researches up-
on the quantity of nitric acid in tlie atmosphere and meteoric waters,
tdtruus acid has not been specially i-egarded. The tests which serve to
detect nitric acid nearly all apply equally well to nitrous acid, and n»
di.-criiuiuatiun has been made until recently. According to Schonbein
:md Bublig, nitrates are sometimes absent from rain-water, but nitrites
never. They occur, however, in but minute proportion. Pincus and
Rollig observed but traces of nitrous acid in the waters gathered at
Iiistcrburg. Reichardt found no weii^hable quantity of nitrous acid in
a samjile of hail, the water from which contained in 10 million parts, 33
parts ammonia and 5}4 parts of nitric acid. It is evident, then, that
nitrous acid, if produced to any extent in the atmosphere, does not re-
main as such, but is chiefly oxidized to nitric acid.
In any case our data are probably not incorrect in respect to the
quantity of nitrogen existing in both the forms of nitrous and nitric
acids, although the former compound has not been separately estimated.
Tlie methods employed for the estimation of nitric acid would, in gen-
eral, include the nitrous acid, with the single error of bringing the latter
into the reckoning as a part of the former.
IVitric Acid as Food of Plants. — A multitude of obser-
vations, both in the field and laboratory, demonstrate that
nitrates greatly promote vegetable growth. The extensive
use of nitrate of soda as a fertilizer, and the extraordinary
fertility of the tropical regions of India, whose soil until
lately furnished a large share of the nitrate of potash of
commerce, attest the fact. Furthermore, in many cases,
nitrates have been found abundantly in fertile soils of tem-
perate climates.
Experiments in artificial soil and in water-culture show
not only that nitrates supply nitrogen to plants, but dem-
onstrate beyond doubt that f/te^ alone are a sufficient
source of this element, and that no other compound is so
well adapted as nitric acid to furnish crops with nitrogen.
Like ammonia-salts, the nitrates intensify the color, and
increase, both absolutely and relatively, the quantity of
nitrogen of the plant to which they are supplied. Their
effect, when in excess, is also to favor the development of
foliage at the expense of fruit.
ATMOSPIIEIMC AIU as Till-: FOOD OF PLANTS. 91
The uiirates do not appear to be absorbed by the plant
to any great extent, except through the medium of tlie
soil, sinre they cannot exist in the state of vapor and are
brought down to the earth's surface by atmospheric waters.
The full discussion of their nutritive effects must there-
fore be deferred until the soil comes under notice. See
Division II, p. 371.
In § 10, p. 96, "Recapitulation of the Atmospheric
Supplies of Food to Crops," the inadequacy of the at-
mospheric nitrates will be noticed.
OTHER INGREDIENTS OF THE ATMOSPHERE; viz., 3farsh Gas,
Carbonic Oxide, Mtroiis Oxide, Hijdrochloric Acid, Sulphurous Acid,
Sulph'jdric Acid, Organic Vapors, Suspended Solid Matters.
There are several other gaseous bodies, some or all of which may oc-
cur in tlie atmosphere in very minute quantities, but whose relations to
vegetation, in the present state of our knowledge, appear to be of no
practical moment. Since, however, they have been the subjects of in-
vestigations or disquisition by agricultural chemists, they require to be
briefly noticed.
IVInrsli «as,* C H4.— This substance is a coloiless and nearly
odorless gas, whicli is formed almost invarialily when organic matters
suffer decomposition in ab.-ence of oxygen. Wlien a lump of coal or a
bilU't of wood is strongly heated, poi-tions of carbon and hydrogen
unite to Conn this among several other substances. It is accordingly
one of the ingredients of the gases whose combustion forms the flame
of all fii-es and lamps. It is also produced in the decay of vegetal)le mat-
ferrf, especially when they arc immer-ed iu water, as happens in swamps
and stagnant ponds, and it often bubbles in large quantities from the
bottom of ditches, when the mud is stirred.
Pettenkofer and Voit have lately found that marsh gas is one of the
f^aseous products of the respiration or nutrition of animals.
It is combustible at high temperatures, and burns with a yellowish,
faintly luminous flame, to water and carbonic acid. It causes no ill ef-
fects when breathed by animals if it be mixed with much air, though of
itself it cannot support respiration.
* Known also to chemists under the names of Light Carburetted Hydrogen,
Hydride of Methyl and Methauc.
02 now CROPS FEED.
The mode or its Arisxin at once fu'^<j;ests its presence in the atmos-
phere. Saussure observed that common air contains some gaseous com-
pound or compounds of carbon, besides carbonic acid; and Boussin-
giiult lonnd in 1834 that the air at Paris contained a very small quantity
(from two to eight-milliontbs) of liydro^^en in some form of combina-
tion besides water. These facti agree witli the supposition that marsh
gas is a normal though minute and variable in-redient of tii(; atmosphere.
Relation!!! oi" 3Ia,i-!^li CSas to Tegelsilioii.— Whether
this gas is absorbed and assimilated by plants is a point on wliich we
have at present no information. It might serve as a source both of car-
bon and hydrogen ; but as these bodies are amply furnished by carbonic
acid and water, and as it is by no means improbable that marsh gas it-
self is actually converted into these substances by ozone, the question
of its assimilation is one of little importance, and remains to be inves-
tigated.
Schultz (Johnston's Lectures on Ag. C/iem., 2d Ed., 147) found on sev-
eral occasions that the gas evolved from jdants when exposed to the sun-
light, instead of being pure oxygen, contained a combustible admixture,
BO that it exploded violently on contact Avith a lighted taper.
This observation shows either that the healthy plants evolved a large
amount ot marsh gas, which forms with oxygen an explosive mixture
(the fire-damp of coal-mines), or, as is most probable, that the vegetable
matter entered into decomposition from too long continuance of the
experiment.
Boussingault has, however, recently found a minute proportion of
marsh gas in the air exhaled from the leaves of plants that are exposed
to sunlight whe7i submerged in water. It does not appear when the leaves
are surrounded by air, as the latest experiments of Boussingault, Cloez,
and Corenwinder, agree in demonstrating.
Carbonic Oxide, CO, is a gas destitute of color and odor. It
burns in contact with aii', with a flame that has a fine blue color. The
result of its combustion is cnrbonic acid, CO + O = COj.
This gas is extremely poisonous to animals. Air containing a few
per cent of it is unfit for respiration, and produces headache, insensi-
bility, and death.
Carbonic oxide may be obtained artificially by a variety of processes.
If carbonic acid gas be made to stream slowly through a tube containing
ignited charcoal, it is converted into carbonic oxide, CO2 -t- C = 3 CO.
Carbonic oxide is largely produced in all ordinary fires. The air which
draws through agrafe heaped with well-ignited coals, as it enters the
bottom of the mass of fuel, loses a large portion of its oxygen, which
there unites w ith carbon, forming carbonic acid. This gas is carried up
into the heated coal, and there, where carbon is in excess, it takes up an-
other proportion of this element, being converted into carbonic oxide.
At the summit of the fire, where oxygen is abundant, the carbonic oxide
burns again with its peculiar blue color, to carbonic acid, provided the
beat be intense enough to inflame the gas, as is the case when the mas»
ATMOSPHKFaC AlB AS TIIK FOOD OF PLANTS. 93
of fuel is tlioroui;l)ly ignited. When, on tlic other liaiid, tlic fire is cov-
ered witli cold fuel, carbonic oxide escapes copiously into the atmos-
phere.
When crystallized oxalic acid is heated with oil of vitriol, it yields
water to the latter, and falls into a mi.Kturc of carbonic acid and carbonic
oxide.
0.112 04, 2HsO = CO.i + CO + 3H,0.
Carbonic oxide may, perhaps, be formed in small quantity in the de-
cay of ori,^anic matters; though Coren winder {Coinpt. Semi., LX, 103)
failed to detect it in the rotting of manure.
ISel:iti«n<« of <'arl»«iiic Oviclo lo Ves^etation. — Ac-
cording to Saussure, while pea-[ilant< languish and die when immersed
in carbonic oxide, certain marsh plants {Kpilobium Mrsutum, Lythrum
salicaria, and Fbhjgonum peisi carlo) flourish as well in this gas as in com-
mon air. Saussure's exi^eriments with these plants lasted six weeks.
There occurred an absorption of the gas and an evolution of oxygen.
It is thus to be inferred that carbonic oxide may be a source of carbon
to aquatic plants.
Boussinuault (Compt. Rend., LXI, 493) was unable to detect any action
of the foliage of land plants upon carbonic oxide, either when the gas
■was pure or mixed with air.
The carbonic oxide which Boussingault found in 18G3 in air exhaled
from submei-ged leaves, proves to have been produced in the analyses,
(from pyroii-allate of potash.) and was not emitted by the leaves them-
selves, as at first supposed, as both Cim-z and Boussingault have shown.
j^'itroux Oxide, NoO.— This substance, the so-called laiig/ivig
gas, is i)repared from nitrate of ammonia by exposing that salt to a heut
somewhat higher than is necessary to fuse it. The salt decomposes into
nitrous oxide and water.
NH4, NO3 = N.^O + 2 H2O.
The gas is readily soluble in water, and lias a sweetish odor and taste.
When breathed, it at first produces a peculiar exhilarating effect, which
is followed by stupor and insensibility.
This gas has never been demonstrated to exist in the atmosphere. In
fact, our methods of analysis are incompetent to detect it, wiien it is
present in very minute quantity in a gaseous mixture. Knop is of the
opinion that nitrous oxide may occur in the atmosi>here, and has pub-
lished an account of exiieriraents {Journal fiir Prakt. Chein., Vol. 59,
p. 114) which, according to him, prove tliat it is absorbed by vegetation.
Until nitrous oxide i< shown to be accessible to plmts, any fuither no-
tice of it is unnecessary in a treatise of this kind.
llydrocliloric Acid C«a<<», IICI, whose properties have been
described in How Crops Grow, p. 118, i- found in minute quantity in the
air over salt marshes. It doubtless proceeds from the decomposition of
the chloride of magnesium of sea-water. Sprengel h:is surmised its ex-
94 HOW CROPS FEED.
h;>Lation hy sea-shore pLints. It is found in the air near soda-works, be-
ing a firoduct of the manufacture, and is destructive to vegetation.
Niilpliiirou!i» Acid, SOo, and Siilpliydric Acid, HS, (see
H. C. G., p. 115,) may exist in the atmosphere as local emanations. In
lars^e quantities, as wlien escaping from smelting worlis, roasting lioaps,
or manufactories, they often prove destructive to vegetation. In contact
witli air tlicy qniclvly suffer oxid.ation to sulpiiurie acid, wliich, dissolv-
ing in the water of rains, etc., becomes incorporated with the soil.
Oi'g^iiiiic Iflattei-s of whatever sort that escape as vapor into the
atmosphere and are tliere recognized I)y their odor, are rapidly oxidized
and have no direct influenee upon vegetation, so far as is now Icnown.
Suspended Solid IWLiitters iit tlie Alinowpliei'e. —
The solid matters which are raised into the air by winds in the form of
dust, and are often transported to great heights and distances, do not
properly belong to the atmosphere, but to the soil. Their presence in
the air explains the growth of certain plants {air-planU) when entirely
disconnected from the soil, or of such as are found in pure sand or on
the surface of rocks, incapable of performing the functions of the soil,
except as dust accumulates upon them.
Barral announced in 1863 {Jour. cTAg. pratique, p. 150) the discovery
of phosphoric acid in rain-water. Robinet and Luca obtained the same
result with water gathered near the surface of the earth. The latter
found, however, that rain, collected at a height of 60 or more feet above
the ground, was free from it.
10.
RECAPITULATION OF THE ATMOSPHERIC SUPPLIES OF
. FOOD TO CROPS.
Oxyfi^en, whether required \n the free state to effect
chemical changes in the processes of organization, or in
combination (in carbonic acid) to become an ingredient
of the plant, is superabundantly supplied by the atmos-
phere.
Carbon. — The carbonic acid of the atmosphere is a
source of this element sufficient for the most rapid growth,
ns is abundantly demonstrated by the experiments in wa-
ter culture, made by Nobbe and Siegert, and by Wolff,
(II. C. G., p. 170), in which oat and buckwheat plants
were brought to more than the best agricultural develop)-
ATMOSPHEKIC AIR AS THE FOOD OF PLANTS.
95
ment, Avith no other than tlic atmospheric sup2:>ly of
carbon.
HydrOfi^cn is adequately supplied to crops by water,
which e(pially belongs to the Attnos|)here and the Soil,
although it enters the plant chiefly fioui the latter.
Nitrogen exists in immense quantities in tlie atmosphere,
and we may regard the latter as the primal source of this
element to the organic world. In the at i no -sphere, how-
ever, nitrogen exists for the mjst part in the free state, and
is, as such, so we must believe from existing evidence, un-
assimilable by crops. Its assimilable compounds, ammo-
iila and nitric acid, occur in the atmosphere, but in pro-
portions so minute, as to have no influence on vegetable
growth directly appreciable by the methods of investiga-
tion hitherto employed, unless they are collected and con-
centrated by rain and dew.
The subjoined Table gives a summary of the amount
of nitrogen annually brought down in rain, snow, etc.,
upon an acre of surface, a -cording to the determinations
hitherto made in England and Prussia.
Amount of Assimilable Nitrogen annually brought down by
THE Atmospheric Waters.
Locality.
Tear.
mtroqen
per Acre.
Wat^ '
per Acre.
Rothamatead, Southern England
18.55*
1856*
1864-5t
1865-6t
1864-5t
1865-6t
lS64-5t
1865-6t
1865*
1864-5+
1865*
6.63 lbs.
8.31 '•
1.86 "
2.50 "
5.49 "
6.81 "
15.09 "
10.38 "
11.83 "
■i0.91 -
6.66 "
6.633,220 lbs.
6.160 510 '•
Kuschen, Province Posen, Prussia
lusterburg, near Koni^sberg, "
Regenwalde, near Stettin, "
Ida-Marienliiittc, near Brcslau, Silesia, " '.'.'.'.
Proskau, Silesia. ■'
Dahme, Province Brandenburg, "
2,680.086 "
4.008.491 "
6,2'22,461 "
5.383,4'r8 "
5,313,562 "
4,-358,053 "
4,877.545 "
4.(131, 7S2 "
3,868,646 "
Averaqe
8.76 lbs.
4.867.075 lbs.
* From Jan. to Jan. t From Apr. to Apr. % From May to May.
Direct Atmospheric Supply of Nitrogen Insufficient
for C^rops. — To estimate the ailequacy of tliese atmos-
pheric supplies of assimilable nitrogen, Ave may compare
their amount with the quantity of nitrogen required in the
96 llUAV CROPS FEED.
eompositiou of standard crop;^, and with the (][uantity con-
tained in appropriate applications of nitrogenous fertil-
izers.
The average atmosplieric supply of nutritive nitrogen
in rain, etc., for 12 months, as above given, is much less
tlian is necessary for ordinary crops. According to Dr.
Anderson, the nitrogen in a crop of 28 bushels of wheat
and 1 (long) ton 3 cwt. of straw, is 45^^ lbs.; that in 2^
tons of meadow hay is 50 lbs. The nitrogen in a crop of
clover hay of 2^ (long) tons is no less than 108 lbs. Ob-
viously, therefore, the atmospheric waters alone are in-
capable of furnishing crops with the quantity of nitrogen
they require.
On the other hand, the atmospheric supply of nitrogen
hy rain, etc., is not inconsiderable, compared with the
amount of nitrogen, which often forms an effective manur-
ing. Peruvian guano and nitrate of soda (Chili saltpeter)
each contain about 15 percent of nitrogen. The nitrogen
of rain, estimated by the average above given, viz., 8f lbs.,
corresponds to 58 lbs. of these fertilizers. 200 lbs. of gua-
no is for most field purposes a sufficient application, and
400 lbs. is a large manuring. In Great Britain, where ni-
trate of soda is largely employed as a fertilizer, 112 lbs.
of this substance is au ordinary dressing, which has been
known to double the grass crop.
We notice, however, that the amount of nitrogen sup-
plied in the atmospheric waters is quite variable, as well
for ditferent localities as for different years, and for differ-
ent periods of the year. At Kuschen, but 2-2^ lbs. were
brought down against 21 lbs. at Proskau. At Regenwalde
the quantity was 15 lbs. in 1864-5, but the next year it
was nearly 30 per cent less. In 1855, at Rothamstead,
the greatest rain supply of nitrogen was in July, amount-
ing to 1^ lbs., and in October nearly as much more was
brought down; the least fell in January. In 1856 the
largest amount, 2^ lbs., fell in May; the next, 1 lb., ia
ATMOSPIIEIIIC AIU AS THE FOOD OF PLANTS. 97
April; and the least in March. At Td.i-^Maiienliiitte,
Kiischen, and Regenwaldc, in 1865-6, nearly half the
year's atmosplieric nitrogen came down in summer ; but
at Insterburg only 30 per cent fell in summer, while 40
•per cent came doAvn in winter.
The nitrogen that is brought down in winter, or in
spring and autumn, when the fields are fallow, can be
counted upon as of use to summer crops only so far as it
remains in the soil in an assimilable form. It is well
known that, in general, much more water evaporates from
cultivated fields during the s'.mmer than falls upon them
in the same period ; while v.) Avinter, the water that falls
is in excess of that which evaporates. But how much of
the winter's fall comes to supply the summer's evaporation,
is an element of the calculation likely to be very variable,
and not as yet determined in any instance.
We conclude, then, th:;t tlie direct atmospheric supply
of assimilable nitrogen, though not miimportant, is insuf-
ficient for crops.
We must, therefore, look to the soil to supjdy a large
share of this element, as well as to be the medium through
which the assimilable .atmospheric nitrogen chiefly enters
the plant.
The Other Injfiedieiits of the Atmosphere, so far as
we now know, are of no direct significance in the nutri-
tion of agricultural i)lants. Indirectly, atmos])iieric ozone
has an influence on the supplies of nitric acid, a point we
shall recur to in a full discussion of the question of the
Supplies of Nitrogen to Vegetation, in a subsequent
chapter.
§ 11-
ASSIMILATION OF ATMOSPIIEPvIC FOOD.
Boussingault lias suggested the very probable view^ that
the first process of assimilation in the chlorophyll cells of
the leaf, — where, under the solar influence, carbonic acid
5
98 IIO-\V CROPS FEED.
is absorbed and decomposed, and a nearly equal volume
of oxygen is set free, — consists in the simultaneous deox-
idation of c:irl)onic acid and of water, wliereby the former
is reduced to carbonic oxide with loss of half its oxygen,
and the latter to hydrogen with loss of all its oxygen, viz.:
Gin-honh ^ Wate - —^ '"Thou I' Hydro- Oxy-
acld ' oxide yen. yen.
CO, + l\f> = CO + H, + O,
In this reaction the oxygen set free is identical in bulk
with the carbonic ncid involved, and the residue retained
in the plant, COH^, multiplied by 12, would give 12
molecules of carbonic oxide and 24 atoms of hydrogen,
Avhich, chemically united, might constitute either glucosj
or levulose, C,^ 11^^ Oj„, from which by elimination of
HjO would result cane sugar and Arabic acid, while sepa-
ration of 211^0 would give cellulose and the other mem-
bers of its group.
Whether the real chemical jiroce^^s be this or a different
and more complicated one is at present a matter of vague
probability. It is, notwithstanding, evident that this re-
action expresses one of the principal results of the assim-
ilation of Carbon and Hydrogen in the foliage of plants.
§ 12.
The following Tabular View may usefully serve the
reader as a recapitulation of the chapter now finisheil.
TABULAR VIEW OF THE RELATIONS OF THE ATMOSPHERIC
INGREDIENTS TO THE LIFE OF PLANTS.
[■ Oxygen, by roots, flowers, ripeiiiuj^ fruit, and by ;ili
f^rowiirj.- jiarts.
Carbonic Acid, by foliaire and rrreeu parts, but only in
j the light.
Absorbed J Ammonia, us carbonate, by folia<;e, probably at all times.
by Pliints. 1 Watek, ax liquid, through the roots.
Nitrous Aoid (^ united to ammonia, and dissolved in wa'
Nitric Aciu ) ter through the roots.
Ozone )
THK ATMOSrUEKE AS KKLATBD TO VEGETATION. 99
Not absorbed ( Nitrogen.
by Plants. ( Water in state of vapor.
(Oxygen, [ by folia;;e and green parts, but only in the
Ozone? ) light. .. , _
M.\RSH Gas in traces by aquatic plants ?
j Water, «.s- vapor, from surface of plant at all times.
(.Carbonic Acid, from the growing parts at all times.
CHAPTER II.
THE ATMOSPHERE AS PHYSICALLY RELATED TO
VEGETATION.
§ 1-
MANNER OF ABSORPTION OF GASEOUS FOOD BY THE PLANT.
Closing here our study of the atmosphere considered as
a source of the food of plants, we still need to remark
somewhat upon the physical properties of gases in rela-
tion to vegetable life ; so far, at least, as may give some
idea of the means by which tliey gain access into the
phmt.
Physical Constitution of the Atmosphere.— That the
atmosi)here is a mixture and not a chemical combination
of its elements is a fact so evident as scarcely to require
discussion. As we have seen, the proportions whicli sub-
sist among its ingredients are not uniform, although they
are ordinarily maintained within very narrow limits of va-=
riation. This is a sufficient proof that it is a mixture^
Th« remarkable fact that very nearly the same relative
quantities of Oxygen, Nitrogen, and Carbonic Acid,
steadily exist in the atmosphere is due to tlie even balance
which obtains between growth and decay, between life
and death. The equally remarkable fact that .the gases
100 HOM' CROPS FEED.
wliich compose the atmosphere are uiiiforinly mixed to*
gether without regard to their specific gravity, is but one
result of a law of nature which we shall immediately
notice.
Diffusion of Gases, — Whenever two or more gases are
brought into contact in a confined space, they instantly
begin to intermingle, and continue so to do until, in a
longer or shorter time, they are both equally diffused
throughout the room they occuj^y. If two bottles, one
filled with carbonic acid, the other with hydrogen, be con-
nected by a tube no wider than a straw, and be placed so
that the heavy carbonic acid is below the fifteen times
lighter hydrogen, we sliall find, after the lapse of a few
hours, that the two gases have mingled somewhat, and in
a few days they will be in a state of uniform mixture. On
closer study of this phenomenon it has been discovered
that gases diffuse with a rapidity proportioned to their
lightness, the relative diffusibility being nearly in the in-
verse ratio of the square roots of their specific gravities.
By interposing a poious diaphragm between two gases of
different densities, we may visibly exhibit the fact of their
ready and unequal diffusion. For this purpose the dia-
phragm must offer a partial resistance to the movement
of the gases. Since the lighter gas passes more rapidly
into the denser than flie reverse, the space on one side of
the membrane will be overfilled, while that on the other
side will be partially emptied of gas.
In the accompanying figure is represented a long glass
tube, b, widened above into a funnel, and having cemented
upon this an inverted cylindrical cup of imglazed porce-
lain, a. The funnel rests in a round aperture inade in the
horizontal arm of the support, wliile the tube below dips
beneath the surface of some water contained in the wine-
glass. The porous cup, funnel, and tube, being occujiied
with common air, a glass bell, c, is filled with hydrogen
gas and placed over the cap, as shown in the figure. In-
THE ATMOSPITEKE AS RELATED rO VEGETATION. 101
stnntly, bubbles begin to escape rap:;lly from the bottom
of the tube throiauh the water of the wine-glass, thus
demonstiMiiiig that hydrogen ])asses into the cup faster
ihan air can escMpe outwards
ihrongli it-: porc-<. If tin- btll be
removed, ihc cuj) is at once butlied
Mgain externally in common air, the
light hydrogen floating instantly
uj)wards, and now the water begins
to rise in the tube in consequence of
the return to the outer atmosphere
of the hydrogen which before had
diffused into the cup.
It is the i)erpetual action of tliis
diffusive tendency which maintains
the atniosplierc in a state of such
uniform mixture that accurate ana-
lyses of it give for oxygen and
nitrogen almost identical figures, at
all tnios of the day, at all seasons,
all altitudes, and all situations, ex-
cept near the central surface of
large bodies of still water. Here,
the fact that oxygen is more largely
absorbed by water than nitrogen,
diminishes by a minute amoimt the
usual proportion of the former gas.
If in a limited volume of a mixture of several gases a
solid or liquid body be placed, which is capable of chemic-
ally uniting witli, or otherwise destroying the aeriform
condition of one of the gases, it will at once absorb those
particles of this gas which lie in its immediate vicinity,
and thus disturb the uniformity of the remaining mixture.
Uniformity at once tends to be restored by diffusion of a
portion of the unabsorbed gas into the space that has been
deprived of it, and thus the absorption and the diffusion
103 now CROPS FKED.
keep pace with each otLer until all the absorhable air is
removed from the gaseous mixture, and condensed or fixed
in tlie al)Sorbent.
In tliis manner, a portion of the atmosphere enclosed in
a large glass vessel may be perfectly freed from watery
vapor and carbonic acid by a small fragment of caustic
potash. By standing over sulphuric acid, ammonia is
taken from it ; a piece of phosphorus will in a few hours
absorb all its oxygen, and an ignited mass of the rare
met.il titanium will remove its nitrogen.
Osmose of Gases. — By this expression is understood the
passage of gaseous bodies through membranes whose
pores are too small to be discoverable by optical rneanSy
such as the imperforate wall of the vegetable cell, the
green cuticle of the plant whore not interrupted by stomata^
vegetable parchment, India rubber, and animal membranes,
like bladder and similar visceral integuments.
If a bottle filled with air have a thin sheet of India
rubber, or a })iece of moist bladder tied over its mouth
and then be placed within a bell of hydrogen, evidence is
at once had that gases penetrate the membrane, for it
swells outwards, and may even burst by the pressure of
the hydrogen that rapidly accumulates in the bottle.
Gaseous Osmose is DiiTusion llodified by the Influence
of the Membrane. — The rapidity of osmose * is of coursa
influenced by the thickness of tlie membrane, and the
character of its pores. An adhesion between the mem-
brane and the gases would necessarily increase their rate
of penetration. In case the membrane should attract or
haA e adhesion for one gas and not for another, complete
separation of the two might be accomplished, and in pro-
portion to the difference existing between two gases as re-
gards adhesion for a given membrane, would be the de-
gree to which such gases would be separated from each
' The osmose of liquids is discussed in detail in "How Crops Grow," p. 854.
THE ATMOSPHKKE AS TIELaTED TO VEGETATION. lOfi
other in penetrating it. In case a meniLrane is moistened
with water or other liquid, or by a solution of solid mat-
ters, this would still further modify tlie I'csult.
Absorption of (Jases by the Plant.— A few words will
now suffice to ."ippiy tliese ficts to the abs()r[)tion of the
nutritive gases by vegetation. The foliage of plants is
freely permeable to gases, as has been set forth in " How
Crops Grow,'' p. 289. The eells, or some portions of their
contents, absorb or condense carbonic acid and ammonia
in a similar way, or at least with tlie same effect, as potash
absorbs carbonic acid. As rapidly as tliese bodies are
removed from the atmosphere surrounding or occupying
the cells, they are re-supplied by diifusion from without ;
so that although the quantities of gaseous plant-food con-
tained in the air nre, relatively considered, very small,
they are by this grand natural law made to flow in con-
tinuous streams toward every growing vegetable cell.
DIVISION 11.
THE SOIL AS RELATED TO VEGETABLE
PRODUCTION.
CHAPTER L
INTRODUCTORY.
For the Husbandman the Soil has this paramount im-
portance, that it is the home of the roots of his crops and
the exclusive theater of his labors in promoting their
growth. Through it alone can he influence the amount
of vegetable production, for the atmosphere, and the light
and heat of the sun, are altogether beyond his control.
Agriculture is the culture of the field. The value of the
field lies in the quality of its soil. No study can have a
grander material significance than the one which gives us
a knowledge of the causes of fertility and barrenness, a
knowledge of the means of economizing the one and over-
coming the other, a knowledge of those natural laws
which enable the farmer so to modify and manage his soil
that all the deficiencies of the atmosphere or the vicissi-
tudes of climate cannot deprive him of a suitable reward
for his exertions.
The atmosphere and all extra-terrestrial influences that
afiect the growth of plants are indeed in themselves
beyond our control. We cannot modify them in kind or
amount ; but we can influence their subserviency to our
purposes through the medium of the soil by a proper un-
derstanding of the characters of the latter.
104
INTUOUrCTORY.
105
The Cencral Fiiuctious of the Soil are of three kinds :
1. The ashes of the plant whose nature and variations
have been the subject of study in a former volume (H.
C. G., pp. 111-201,) are exclusively derived from the soil.
The latter is then concerned in tlie most direct manner
with tlie nutrition of the plant. The substances which
the plant acquires from the soil, so far as they are nutri-
tive, may be collectively termed soil-food.
2. Tlie soil is a mechanical support to vegetation. The
roots of the plant penetrate the pores of the soil in all
directions sidewise and downward from the point of their
junction with the stem, and thus the latter is firmly
braced to its upright position if that be natural to it, and
in all cases is fixed to the source of its supplies of ash-in-
gredients.
3. By virtue of certain special (physical) qualities to be
hereafter enumerated, the soil otherwise contributes to
the well-being of the plant, tempering and storing the
heat of the sun which is essential to the vital processes ;
regulating the supplies of food, which, coming from itself
or fi-om external sources, form at any one time but a mi-
nute fraction of its mass, and in various modes ensuring the
co-operation of the conditions which must unite to produce
the perfect plant.
Variety of Soils. — In nature we observe a vast variety
of soils, which difier as much in their agricultural valuf
as they do in their external appearance. "We find large
tracts of country covered with barren, drifting sands, on
whose arid bosom only a few stunted pines or sliriveled
grasses find nourishment. Again there occur in the high-
lands of Scotland and Bavaria, as well as in Prussia, and
other tem))erate countries, enormous stretches of moor'
land, bearing a nearly useless growth of heath or moss.
In Southern Russia occurs a vast tract, two hundred mil-
lions of acres in extent^ of the tsrhornosem, or black earth,
5*
100 1T(,\V C:nOPS FEED.
which is remarkable for its extraordinary and persistent
fertility. The prairies of our own West, the bottom lands
of the Scioto and other rivers of Ohio, arc other examples
of peculiar soils; while on every farm, almost, may bii
found numerous gradations fi-om clay to sand, from ve<^e-
table mould to gravel — gradations in color, consistence,
composition, and productiveness.
CHAPTER II.
ORIGIN AND FORMATION OF SOILS.
Some consideration of the origin of soils is adapted to
assist in understanding the reasons of their fertility.
Geological studies give us reasons to believe that what is
now soil was once, in chief part, solid rock. We find in
nearly all soils fragments of rock, recognizable as such by
the eye, and by help of the microscope it is often easy to
perceive that those portions of the soil which are impal-
TDable to the feel are only minuter grains of the same rock.
Rocks are aggregates or mixtures of certain minerals.
Minerals, again, are chemical compounds of various ele-
ments.
We have therefore to consider :
I. The Chemical Elements of Rocks.
II. The Mineralogical Elements o.f Rocks.
III. The Rocks themselves — their Kinds and Special
Characters.
IV. The Conversion of Rocks into Soils ; to wliich we
may add :
V. The Incorporation of Organic Matter with Soils.
ORIGIN AND FORMATION' OF SOILS. 107
THE CHEMICAL ELEMENTS OF ROCKS.
The chemical elements of rocks, i. e., ths constituents
of the minerals which go to form rocks, include all the
simple bodies known to science. Those, which, fiom their
universal distribution and uses in agriculture, concern us
immediately, are with one exception the same th:it have
been noticed in a former volume as composing the ash of
agricultural i)lants, viz., Chlorine, Sulphur, Carbon, Silicon,
Potassium, Sodium, Calcium, Magnesium, lion, and Man-
ganese. The description given of these elements and
of their most important compounds in " IIow Crops Grow "
Avill suffice. It is only needful to notice further a single
element.
Allliuinuin, Symbol Al., At. wt. 27.4, is a bluish silver-
white metal, ciiaracterized by its remarkable lightness,
having about the specific gravity of glass. It is now
manufactured on a somewhat large scale in Paris and New-
castle, and is employed in jewelry and ornamental work.
It is prepared by a costly and complex process invented
by Prof. Deville, of Paris, in 1854, which consists essen-
tially in decomposing chlorido of aluminum by metallic
sodium, at a high heat, chloride of sodium (common
salt) and metallic aluminum being produced, as shown by
the equation, Al„ Cl^ + 6 Na = 6 Na CI + 2 Al.
By combining with oxygen, this metal yields but one
oxide, which, like the highest oxide of iron, is a sesqui-
oxide, viz.:
Alumina, Al^ O^, Eq. 102.8. — ^Vhen alum (double sul-
phate of alumina and i)otash) is dissolved in water and
ammonia added to the solution, a white gelatinous body
separates, which is alumina combined with water, Al^ O3,
3 H^O. By drying and strongly heating this hydrated
alumina, a white powder remains, which is pure alumina.
108 ilOW (HOPS FEEt).
In nature alumina is found in tlie form of emery. The
sappliire and ruby are tinely colored crystallized varieties
of aluuiin:i, highly j^rized as gems.
Hydrated alumina dissolves in acids, yielding a numer-
ous class of salts, of which the sulj^hate and acetate are
largely employed in dyeing and calico-printing. The sul-
phate of alumina and potash is familiarly known under
the name of alum, with which all are ac^quainted. Other
compounds of alumina will be noticed presently.
§2.
MINERALOGICAL ELEMENTS OF ROCKS.
The mineralogical elements or minerals * which compose
rocks are very numerous.
But little conception can be gained of the appearance
of a mineral from a description alone. Actual inspection
of the different varieties is necessary to enable one to rec-
ognize them. The teacher should be provided with a
collection to illustrate this subject. The true idea of their
composition and use in forming rocks and soils may be
gathered quite well, however, from the written page. For
minute information concerning them, see Dana's Manual
of Mineralogy. We shall notice the most important.
Quartz. — Chemically speaking, this mineral is anhy-
drous silica — silicic acid — a compound of silicon and ox-
ygen, Si O^. It is one of the most abundant substances
met with on the earth's surface. It is found in nature in
six-sided crystals, and in irregular masses. It is usually
colorless, or white, irregular in fracture, glassy in luster.
It is very hard, readily scratching glass. (See H. C. G.,
p. 120.)
Feldspar (field-spar) is, next to quartz, the most abund-
* The word mineral, or mineral "species," here implies a definite chemical
comoouiid of natural occurrence.
OEIGIX ANIJ FOU.MATIOX OF SOILS. 109
ant mineral. It is a cotnpound of silica with alumina^
and with one armor e of the alJcdies, and sometimes vrith
lime. Mineralogists distinguish several species of feld-
spar according to their composition and crystallization.
Feldspar is found i:i crystals or crystalline masses xisually
of a white, yellow, or flesh color, with a somewhat pearly
luster on the smooth and level surfaces which it presents
on fracture. It is scratched by, and docs not scratch
quartz.
In the subjt>ined Table are given the minefalogical names
and analyses of the principal varieties of feldspar. Ac-
companying each analysis is its locality and the name of
the analyst.
Orthoclase.
A1.BITE.
OUGOCLASE.
Labradouite.
Common or imtmh
Soda feldspar.
Soda-lirm feldspar
Lime-soda
feldspar.
feldspar.
NewRochellcN.Y.
Unionville. Pa.
Iladdam, Conn.
Drummond, C. W.
s
. W. Johnson.
M. C Weld.
G. J. Brush.
T. S. Hunt.
Silica,
64.33
(56.86
64.26
54.70
Alumina,
20.42
21.80
21.00
39.80
Potash,
12.47
.
0.50
0.33
Soda,
2.62
8.78
9 99
2.44
Lime,
trace
1.70
2.15
11.43
Magnesia,
0.48
Oxide of iron, trace
0.36
Water,
0.24
0.48
0.29
0.40
Mica is, perhaps, next to feldspar, the most abundant
mineral. There are three principal varieties, viz.: Musco-
vite, Phlogopite, and Biotite. They are silicates of alumi-
na with potash, magnesia, lime, iron, and manganese.
Mica bears the common name " isinglass." It readily
splits into thin, elastic plates or leaves, has a brilliant
luster, and a great variety of colors, — Avhite, yellow, brown,
green, and black. Muscovite, or muscovy glass, is some-
times found in transparent sheets of great size, and is used
in stove-doors and lamp-chimneys. It contains much
alumina, and potash, or soda, and the black varieties oxide
of iron.
Phloyoplte and Biotite contain a large percentage of
magnesia, and often of oxide of iron.
110 HOW CKOl'S FKED.
The following analyses represent these varieties.
Muscovite. Phlogopite. Biotite.
Litchfield, Mt.Leiiistor, Edwards, N. Burgess, Putnam Co.,
Conn. Ireland. N. Y. Canada. N. Y. Siberia.
Smith & Brush. IlaiiirP.ton. W.J.Craw. T.S.TIunt. Smith & Brush. H. Rosii.
Silica.
44.f)0
44.64
40.. 36
40.97
39.62
40.00
Alumina,
36.23
30.18
16.45
18.56
17.35
13.67
Oxide of iron
1,1.34
6.35
trace.
5.40
19.03
Oxide of
manganese
—
—
—
—
—
0.63
Magnesia.
' 0.37
0.72
29.55
25.80
23.85
15.70
Lime,
0.50 -
Potash,
6.20
12.40
7.23
8.26
8.95
5.61
Soda,
4.10
4.94
1.08
1.01
Water,
5.26
5.32
0.95
1.00
1.41
Variable Composition of Minerals. — We notice in the
micas that two analyses of the same species differ very
considerably in the proportion, and to some extent in the
kind, of their ingredients. Of the two muscovites the
first contains 6°|„ more of alumina than the second, while
the second contains 5° |„ more of oxide of iron than the
first. Again, the second contains 12. 4" |^ of potash, but no
soda and no lime, while the first reveals on analysis 4°|^ of
soda and 0.5° 1,^ of lime, and contains correspondingly less
potash. Similar differences are remarked in the other anal-
yses, especially in those of Biotite.
In fact, of the analyst's of more than 50 micas which are
given in mineralogical treatises, scarcely any two per-
fectly agree. The same is true of many other minerals,
especially of the ainphiboles and pyi'oxenes presently to be
noticed. In accordance with this variation in composition
we notice extraordinary diversities in the color and ap-
pearance of different specimens of the same mineral.
This fact may appear to stand in contradiction to the
statement above made that these minerals are definite
combinations. In the infancy of mineralogy great per-
plexity arose from the numerous varieties of minerals that
were found — varieties th.it agreed togeilier in certain char-
acteristics, but widely differed in others.
ORIGIN AND FORMATION OF SOILS. Ill
Isomorphism. — In 1830, Mitscherlich, a Prussian phi-
losopher, discovered tliat a number of the elementary
bodies are capable o^ replacing each other in, combination^
from the fact of their natur.d crystalline form being identic-
al ; they being, as he termed it, isomorphous^ or of like
shape. Thus, magnesia, lime, protoxide of iron, protoxide
of manganese, whicli are all protovide-hases^ form one
group, each of whose members may take the place of the
other. Alumina (Al.^ OJ and oxide of iron (Fe, O3) be-
long to another group of sesqui oxide-bases, one of which
may replace the other; while in certain combinations
silica and alumina replace each other as acids.
These replacements, which may take place indefinitely
within certain limits, thus may greatly affect the composi-
tion without altering the constitution of a mineral. Of
the mineral amphibole, for example, there are known a
great number of varieties ; some pure Avhite in color, con-
taining, in addition to silica, magnesia and lime ; otliers
pale green, a small portion of magnesia being replaced by
protoxide of iron ; others black, containing alumina in
place of a portion of silica, and with oxides of iron and
m inganese in large jiroportion. All these varieties of
amphibole, however, admit of one expression of their
constitution, for the amount of oxygen in the bases, no
matter what they are, or what their proportions, bears a
constant relation to the oxygen of the silica (and alumina)
they contain, the ratio being 1 : 2.
If the protoxides be grouped together under the gen
eral symbol MO (metallic i>rotoxide,) the composition of
the amphiboles may be expressed by the formula MO SiO,.
In pyroxene the same r(>placements of j^rotoxide-bases
on the one hand, and of silica and alumina on the other,
occur in extreme range. (See analyses, p. 112.) The gen-
eral formula which includes all the varieties of pyroxene
is the same as that of ami)hibole. The distinction of am-
phibole from pyroxene is one of crystallization.
112
HOW CROPS FEED.
We might give in the same style formulpe for all the
minerals noticed in these pages, but for our purposes tJiis
is unnecessary,
Amphibole is an abundant mineral often met with in
distinct crystals or crystalline and fibrous masses, varying
in color from pure white or gray {tretnoHte, asbestifs), light
green {actinolite), grayish or brownish green {anthophyl-
lite), to dark green and black {hornblende), according as
it contains more or less oxides of iron and manganese.
It is a silicate of magnesia and lime, or of magnesia and
protoxide of iron, with more or less alkal'ies.
White. Gray. Ash-gray. Black.
Gouverneur, Lanark, Cuminington, Brevig,
N. Y. Canada. Mass. Norway.
Rammelsberg. T. S. Hunt. Smith & Brash. Plantamour.
57.40
a4.69
13.89
0.40
55.30
22.50
13.36
6.30
trace
0.40
0.80
0.25
0.30
50.74
10.31
trace
as. 14
1.77
0.54
trace
3.04
46.57
5.88
5.91
24.38
2.07
3.41
7.79
2.96
Leekgreen.
Waldheim,
Saxony.
Kuop.
58.71
10.01
11.53
Silica,
Magnesia,
Lime,
Protoxide of
iron,
Protoxide of
manganese,
Alumina,
Soda,
Potash,
Water,
Pyroxene is of very common occurrence, and consider-
ably resembles hornblende in colors and in composition.
Green. Black. Black.
Lake Orange Co., Wetterau,
Cliamplain. N. Y.
Seybert. Smith & Brush. Gmelin.
1.52
12.38
0.50
White. Gray- White.
Ottawa, Batliurst,
Canada. Canada.
T. S. Hunt. T. S. Hunt.
Silica,
54.50
51.50
50.38
39.. 30
56.80
Magnesia,
18.14
17.69
6.83
2.98
5.05
Lime,
25.87
23.80
19. a3
10.39
4.85
Protoxide
1.98
20.40
30.40
12.06
of iron.
Sesquioxide
0.35
of iron.
Protoxide of
trace
0.67
3.72
manganese.
Alumina,
6.15
1.83
9.78
15.32
Soda,
1.66
3.14
Potash,
2.48
0.34
Water,
0.40
1.10
1.95
ORIGIN AND FORMATION OF SOILS. 113
Chlorite is a common mineral occurring in small scales
or plates which are brittle. It is soft, usually exists in
masses, rarely crystallized, and is very variable in color
and composition, though in general it has a grayish or
brownisli-grcen color, and contains magnesia, alumina, and
iron, united with silica. See analysis below.
LeilCite is an anhydrous silicate of akimina found
chiefly in volcanic rocks. It exists in white, hard, 24-sid-
ed crystals. It is interesting as being formed at a high
heat in melted lava, and as being the first mineral in which
potash was discovered (by Klaproth, in 1797). See anal-
ysis below.
Kaolinite is a hydrous silicate of alumina, which is
produced by the slow decomposition of feldspar under the
action of air and water at the usu.il temperature. Form-
ed in this way, in a more or less impure state, it consti-
tutes the mass of white porcelain clay or kaolin, which is
largely used in making the finer kinds of pottery. It ap-
pears in white or yellowish crystalline scales of a pearly
luster, or as an amorphous translucent powder of extreme
fineness. Ordinary clay is a still more impure kaolinite.
Steele Mine, N. C. Vesuvius, Summit Ilill, Chaudie'-e
Eruption of 1857. Pa, Falls. Canada.
Genth. Rammelsberg. S. W. Johnson. T. S. Hunt.
Silica, 24.90 .57.24 45.9.3 46.05
Alumina, 21.77 22.9(5 ,■59.81 38.37
Sesquioxidc of iron, 4.()0
Protoxide of iron, 24.21
Protoxide of manj,'ane8e, 1.15
Magnesia, 12.78 0.63
Lime, 0.91 0.61
Soda, 0.93
Potash, 18.61
Water, 10. .59 14.02 14.00
Talc is often found in pale-green, flexil)le, inelastic scales
or leaves, but much more commonly in compact gray
masses, and is then known as soapstone. It is very soft,
114 now CROPS FEED.
has a greasy feel, and in composition is a hydrous silicate
of magnesia. See analysis.
Serpentine is a tough but soft massive mineral, in color
usually of some shade of green. It forms immense beds
in New England, New York, Pennsylvania, etc. It is also
a hydrous silicate of magnesia. See analysis.
Chrysolite is a silicate of magnesia and iron, Avhich
is found abundantly in lavas and basaltic rocks. It is a
hard, glassy mineral, usually of an olive or brown-green
color. See analysis below.
Talc.
Seupentine.
Chrysolite.
Bristol, Conn.
New Haven, Conn.
Bolton, Mass.
Dr. Lummis.
G. J. Brush.
G. J. Brush.
Silica,
64.00
44.05
40.94
Alumina,
0.27
Protoxide of iron,
4.75
2.53
4.37
Magnesia,
27.47
39.24
50.84
Lime,
1.20
Water,
4.30
13.49
3.28
ZeoliteSi — Under this general name mineralogists are
in the habit of including a number of minerals wliich have
recently acquired considerable agricultural interest, since
they represent certain compounds which we have strong
reasons to believe are formed in and greatly influence the
properties of soils. They are hydrous silicates of alum-
ina or lime, and alkali, and are remarkable for the ease
with which they undergo decomposition imder the influ-
ence of weak acids. We give here the names and compo
sition of the most common zeolites. Their special signif-
icance will come under notice hereafter. We may add
that while they all occur in white or red crystallizntions,
often of great beauty, they likewise exist in a state of
division so minute that the eye cannot recognize them,
and thus form a large share of certain rocks, Avhich, by
their disintegration, give origin to very fertile soils
OKIGIN AND FOUMATIOX OF SOILS. 115
Analcime. Chabasite. Natrolite. Scoi.ecite. Thomsokite.
Lake Superior. Nova Scotia. Bergen Hill, Ghaut's Tun- Magnet
N. J. nel, India. Cove, Ark.
C. T. Jackson. Rammelsberg. Brush. P. Collier. Smith & Brush,
Silica, 53.40 52.14 47.31 45.80 36.85
Alumina, 22.40 19.14 26.77 25.55 28.42
Potash, 0.98 0.35 0.30
Soda, 8.52 0.71 15.44 0.17 3.91
Lime, 3.00 7.84 0.41 13.97 13.95
Magnesia, ■
Sesquioxide j 52 ^
of iron.
Water, 9.70 19.19 9. at 14.28 13.80
Stilbite. Apophyi.lite. Pectolite. Laumontite. Leonhardite
Nova Scotia. Lake Superior. Bergen Hill. Phippsburgh, Me. Lake Sup'r
S.W. Johnson. J. L.Smith. J. D. Whitney. DuWnoy. Barnes.
Silica, 57.63 52.08 55.60 51.98 55.04
Alumina, 16.17 1.45 21.12 22.34
Potash, 4.93
Soda, 1.55 8.89
Lime, 8.08 25.30 32.80 11.71 10.64
Water, 16.07 15.92 2.96 15.05 11.93
€alcite, or Carbonate of Lime, CaO CO^, exists in na-
ture in immense quantities as a mineral and rock. Mar-
ble, chalk, coral, limestone in numberless varieties, consist
of this substance in a greater or less state of purity.
Magnesite, or CurhonatQ of 31(Agiiesia, MgO C0„, oc-
curs to a limited extent as a white massive or crystallized
mineral, resembling carbonate of lime.
Dolomite, CaO C0„ + MgO C'0„, is a compound of car-
bonate of lime with carbonate of magnesia in Aariable
proportions. It is found as a crystallized mineral, and is
a very common rock, many so-called marbles and lime-
stones consisting of or containing this mineral.
Gypsum, orllydrous Sulphate of Lime, CaO SO^ + Wfi^
is a mineral that is widely distril)uted and quite abundant
in nature. When "boiled" to expel the water it is
Plaster of Paris.
Pyrites, or liisulphide of Iron, Fe S„, a yellow shining
mineral often found in cubic or octahedral crystals, and
frequently mistaken for gold (hence called fool's gold),
116 IIOAV ( ROI'S FKKH.
is of almost universal occurrence in small quantities. Some
forms of it easily oxidize when exposed to air, and furnish
the green-vitriol (sulnliatc of protoxide of iron) of com-
merce.
Apatite aii<l Phosphorite. — These names are applied to
the native i)hosphate of lime, which is usually combine
■with some chlorine and fluorine, and may besides conta .
other ingredients. Apatite exists in considerable quantity
at Hammond and Gouverneur, in St. Lawrence Co., X.
Y., in beautiful, transparent, green crystals ; at South
Burgess, Canada, in green crystals and crystalline masses ;
at Hurdstown, N. J., in yellow crystalline masses ; at
Krageroe, Norway, in opaque flesh-colored crystals. In
minute quantity apatite is of nearly universal distribution.
The following analyses exhibit the composition of the
principal varieties.
Kragei'oe, Hurdstown^
Norway. New Jersey.
Yoelcker. J. D. Wliitney.
Lime, 53.84 53.37
Phosphoric acid, 41.25 42.23
Chlorine, 4.10 1.02
Fluorine,* 1.23 ? ?
Oxide of iron, 0.29 trace
Alumina, 0.38
Potash and soda, 0.17
Water, 0.42
Phos[)horite is the usual designation of the non-crysta
line varieties.
Apatite may be regarded as a mixture in indefinite
l)roiiortions of two isomorphous compounds, cJilornpatite
nud Jlxorapc/tite, neither of which has yet been found jiure
in nature, though they have been produced artificially.
* Flnnriiu" wfi-; not dcterminril in i
luiciit arc'calcul;ilud (by Il:iiu;nrl»!)i't
ORIGIX AXn FOUMATION OF SOILS. Ill*
Tliese substances are again compounds of phosphate of
lime, 3 CaO P^O^, with chloride of calcium, Ca Cl„ or
fluoride of calcium, Ca Fl^, respectively.
§3.
ROCKS-THEIU KINDS AND CHARACTERS.
The Rocks which form the solid (unbroken) mass of
the earth are sometimes formed from a single mineral, but
usually contain several minerals in a state of more or less
intimate mixture.
We shall brielly notice those rocks which have the
greatest agricultural importance, on account of their com-
mon and wide-spread occurrence, and shall regard them
pi'incipally from the point of view of their chemical com,'
position, since tliis is chiefly the clue to their agricultural
significance. Some consideration of the origin of rocks,
as well as of their structure, will also be of service.
Igneous Rocks. — A share of the rocks accessible to
our observation are plainly of igneous origin, i. e., their
existing form is the one they assumed on cooling down
from a state of fusion by heat. Such are the lavas that
flow from volcanic craters.
Sedimentary Rocks. — Another share of the rocks are
of aqueous origin, i. e,, their materials have been deposit-
ed from water in the form of mud, sand, or gravel, the
loose sediment having been afterwards cemented and con-
solidated to rock. The rocks of aqueous origin are also
termed sedimentary rocks.
Metamorphic Rocks. — Still another share of the rocks
have resulted from the alteration of aqueous sediments or
sedimentary rocks by the efiect of heat. Without suffer-
ing fusion, the original materials have been more or less
converted into new combinations or uev forms. Thus
limestone has been converted into sta<"uary marble, and
118 ItOM* CROPS FEED.
clay into granite. These rocks, which are the result of
the united action of heat and water, are termed meta-
morphlc (i. e,, metamorphosed) rocks.
One of the most obvious division of rocks is into Crys-
talline nnd Fragmentdl.
Crystalline Rocks are those whose constituents crystal-
lized at the time the rock was formed. Here belong both
the igneous and metamorphic rocks. These are often
plainly crystalline to the eye, i. e., are composed of re.idily
perceptible crystals or crystalline grains, like statuary
marble or granite; biit they are also frequently made up
of crystals so minute, that the latter are only to be recog-
nized by tracing them into their coarser varieties (basalt
and trap.)
Fra^mental Rocks are the sedimentary rocks, formed
by the cementing of the fragments of other older rocks
existing as mud, sand, etc.
The Crystalline Rocks may be divided into two
great classes, viz., the slUchus and calcareous ; the first
class containing silica, the latter, lime, as the predomina-
ting ingredient.
The silicious rocks fall into three parallel series, which
have close relations to each other. 1. The Granitic series ;
2, The Syenitic series; 3. The Talcose or Magnesian
series. In all the silicious rocks quartz or feldspar is a
prominent ingredient, and in most cases these two minerals
are associated together. To the above are added, in the
granitic series, mica ; in the syenitic scries, amphihole or.
pyroxene ; and in the talcose series, talc^ chlorite^ or ser-
pentine. The proportions of these minerals vary indef-
initely.
The Granitic Series
consisting principally of Quartz^ Feldspar, and Mica.
Granite. — A hard, massive* rock, either finely or
• Rocks are massive when they have no tendency to split ii.to slabs or plates
ORIGIN AND FOKMATIOX OP SOILS. 119
coarsely crystalline, of various shades of color, depending
on the color and proportion of tlie constituent minerals,
usually gray, grayish white, or flesh-red. In common
granite the feldspar is orthodase (potash-feldspar). A
variety contains albite (soda-feldspar). Other kinds (less
common) contain oligoclase and lalyradorite.
Gneiss differs from granite in containing more mica, and
in having a banded appearance and schistose * structure,
due to the distribution of the mica in more or less parallel
layers. It is cleavable along the planes of mica into
coarse slabs.
Mica-slate or 3Ilca-schist contains a still larger pro-
portion of mica than gneiss ; it is perfectly schistose in
structure, splitting easily into thin slabs, has a glistening
appearance, and, in general, a grayish color. The coarse
whetstones used for sharpening scythes, which are quar-
ried in Connecticut and Rhode Island, consist of this min-
eral,
Argillite, €lay-Slate, is a rock of fine texture, often
not visibly crystalline, of dull or but slightly glistening
surface, and having a great variety of colors, in general
black, but not rarely red, green, or light gray. Argillite
has usually a slaty cleavage, i. e., it splits into thin and
smooth plates. It is extensively quarried in various local-
ities for roofing, and writing-slates. Some of the finest
varieties are used for whetstones or hones.
Other Granitic Rocks. — Sometimes m,ica is absent ; in
other cases the rock consists nearly or entirely o? feldspar
alone, or of quartz alone, or of mica and quartz. The
rocks of this series often insensibly gradate into each oth-
er, and by admixture of other minerals run into number-
less varieties.
♦ Schists or schistose rocks arc those which have a tendency to break into
slabs or plates from the arrangement of some of the mineral ingredients in
layers.
120 how crops feed.
The Stexttic Series
consisting chiefly of QiKvtz, Feldspar, and Amphibole.
Syenite is granite, save that aipphibole takes the place
of mica. In appearance it is like gi-ainte; its color is usu-
ally dark giay. Syenite is a very tough and durable rock,
often most valuable for building purposes. The famous
Quincy granite of Massachusetts is a syenite. Syenitic
Gficiss and Ilor/tblende Schi^it correspond to common
Gneiss and Mica Schist, hornblende taking the place of
mica.
The Volcanic Series
consisting of Feldspar, Amphibole or Pyroxene, and
Zeolites.
Diorite is a compact, tough, and heavy rock, common-
ly greenish-black, brownish-black, or grayish-black in
color. It contains amphibole, but no pyroxene, and is
an ancient lava.
Dolerite or Trap in tlie fine-grained vai-ieties is scarcely
to be distinguished from Diorite by the appearance, and is
well exhibited in the Palisades of the Hudson and the
East and West Rocks of New Haven. It contains pyrox-
ene in place of amphibole.
Basalt is like dolerite, but contains grains of chrysolite.
The recent lavas of volcanic regions are commonly basaltic
in composition, though very light and porous in texture.
Porpbyry, — Associated with basalt occur some feld-
spathic lavas, of which porphyry is common. It consists
of a compact base of feldspar, with disseminated crystals
of feldspar usually lighter in color than the mass of the
rock.
Pumice is a vesicular rock, having nearly the composi-
tion of feldspar.
TriE Magnesiax Series
consisting of Quartz, Feldsp>ar and Talc, or Chlorite.
Talcose Granite differs from common granite in the
substitution of talc for mica. Is a fragile and more easily
OmCIN AND Foli.MAHlON (»K SOILS. 1-1
decomposable rock than granite. It passes tlirougli talcose
gneiss into
Tak'OSC Schist, which resembles mica-scliist in colors
and in facility of si>litiing into slabs, but has a less glis-
tening luster and a soapy feel.
C'hloritic Schist resembles talcose schist, but has a less
unctuous feel, and is generally of u dark green color.
Related to the above are Steatite, or soajystone, — nearly
pure, granular talc; and Serpentine rOCk, consisting
chiefly of serpentine.
The above are tlie more common and wide-spread si-
licious rocks. By the blending together of the different
members of each series, and the related members of the
different series, and by the introduction of other minerals
into their composition, an almost endless variety of si-
licious rocks has been produced. Turning now to the
Crystalline Calcareous Rocks, we have
Granular Limestone, consisting of a nearly pure car-
bonate of lime, in more or less coarse grains or crystals,
commonly white or gray in color, and having a glistening
luster on a freshly broken surface. The finer kinds are
employed as mo?niinent(d marble.
Dolomite has all the appearance of granular limestone,
but contains a large (variable) amount of carbonate of
magnesia.
The Fragmental or Sedimentary Rocks are as fol-
lows:
Conj^lomerates have resulted from the consolidation of
rather coarse fragments of any kind of rock. According
to the nature of the materials composing them, they may
be granitic, syenitic, calcareous, basaltic, etc., etc. They
pass into
Sandstones, wliich consist of small fragments (sand),
are generally siliciovs in character, and often are nearly
6
162 iiuAV CROPS FEEb,
pure quartz. The freestone of tlie Connecticut Valley la
a granitic sandstone, containing fragments of feldspar
and spangles of mica.
Other varieties are calcareous, argillaceous {clayey)^
basaltic, etc., etc.
Shales are soft, slaty rocks of various colors, gray, green,
red, blue, and black. They consist of compacted clay.
When crystallized by metamorphic action, they constitute
argillite.
Limestones of the sedimentary kind are soft, compact,
nearly lusterless rocks of various colors, usually gray,
blue, or black. They are sometimes nearly pure carbon-
ate of lime, but usually contain other substances, and are
often higlily impure. When containing much carbonate
of magnesia they are termed raagnesian limestones. They
pass into sandstones through intermediate calciferous
sand rocks, and into sliales through argillaceovs lime-
stones. These impure limestones furnish the hydraulic
cements of commerce.
CONVERSION OF ROCKS INTO SOILS.
Soils are broken and decomposed rocks. We find in
nearly all soils fragments of rock, recognizable as such by
the eye, and by help of the microscope it is often easy to
perceive that those portions of the soil which are impalpa-
ble to the feel chiefly consist of minuter grains of the same
rock.
Geology makes probable that the globe was once in a
melted condition, and came to its present state through a
process of cooling. By loss of heat its exterior surface
solidified to a crust of solid rock, totally incapable of sup-
porting the life of agricultural plants, being impenetrable
to their roots, and destitute of all the other external char-
acteristics of a soil.
OKlGm AND r'or.^rAtioN^ oi;" soils. 123
The first step towards tlie formation of a soil must have
been the pulverization of tlie rock. This has been accom-
plished by a variety of agencies acting through long pe-
riods of time. The causes which could produce such re-
sults are indeed stupendous when contrasted with the
narrow experience of a single human life, but are really
trifling compared Avith the magnitude of the earth itself,
for the soil forms upon the surface of our globe, whose di-
ameter is nearly 8,000 miles, a thin coating of dust, meas-
ured in its greatest accumulations not by miles, nor
scarcely by rods, but by feet.
The conversion of rocks to soils has been performed,
1st, by Changes of Temperature ; 2d, by 3Ioving Water
or Ice J 3d, by the Chemical Action of Water and Air j
4th, by the Influence of Vegetable and An imal life.
1. — Changes of Tempekature.
The continued cooling of tlie globe after it had become
enveloped in a solid rock-crust must have been accom-
panied by a contraction of its volume. One effect of this
shrinkage would have been a subsidence of portions of
the crust, and a wrinkling of other portions, thus produc-
ing on the one hand sea- basins and valleys, and on the
other mountain ranges. Another effect would have been
the cracking of the crust itself as the result of its own
contraction.
The pressure caused by contraction or by mere weight
of superincumbent matter doubtless led to the production
of the laminated structure of slaty rocks, which may be
readily imitated in wax and clay by aid of an hydraulic
press. Basaltic and trap rocks in cooling from fusion often
acquire a tendency to separate into vertical columns,
somewhat as moist starch splits into five or six-sided frag-
ments, when dried. These columns are again transversely
jointed. The Giant's Causeway of Ireland is an illustra-
tion. These fractures and joints are, perhaps, tlie first oc-
casion of the breaking down of the rocks. The fact that
124 HOW mors feed.
many rocks consist of crystalline grains of tlistinct niin
erals more or less intLmately blended, is a point of weak-
ness in their structure. The grains of quartz, feldspar,
and mica, of a granite, m lien exposed to changes of tem-
perature, must tend to separate from each other; because
the extent to which they expand and contiact by alterna-
tions of heat and cold are not absolutely equal, and be-
cause, as Senarmont has provdl, the same crystal expands
or contracts unequally in its different diameters.
Action of Freezing Water. — It is, however, when wa-
ter insinuates itself into the slight or even imperceptible
rifts thus opened, and then freezes, that the process of dis-
integration becomes more rapid and more vigorous. Wa-
ter in the act of conversion into ice expands j\ of its bulk,
and the force thus exerted is sufficient to burst vessels of
the strongest materials. In cold latitudes or altitudes this
agency working through many years accomplishes stupen-
dous residts.
The adventurous explorer in the higher Swiss Alps fre-
quently sees or hears the fall of fragments of i-ock thus
loosened from the peaks.
Along the base of the vertical trap cliffs of New Haven
and the Hudson River, lie immense masses of broken rock
reaching to more than half the height of the bluffs them-
selves, rent off by this means. The same cause operates
in a less conspicuous but not less important way on the
surface of the stone, loosening the minute grains, as in
the above instances it rends off enormous blocks. A
smooth, clean pebble of the very compact Jura limestone,
of such kind, for example, as abound in the rivers of
South Bavaria, if moistened with water and exposed over
night to sharp frost, on thawing, is muddy with the de-
tached particles.
2. — Moving Water or Ice.
Changes of temperature not only have created differ-
ences of level in the earth's surface, but they cause a con-
ORIGIX AND I'ORMATION OF SOILS. 1 '25
tinu.'il transf>-r of water froin lowrr to liiglier levels. The
elevates! hinds are cooler than the valleys. In their re-
gion occurs a continual condensation of vapor from the
atmosphere, which is as continually supplied from the
heated vrvlleys. In the mountains, thus beo:in, as rills, the
streams of water, which, gathering volume in their descent,
unite below to vast rivers that flow unceasingly into the
ocean.
These streams score their channels into the firmest rocks.
Each grain of loosened material, as carried downward by
the current, cuts the rock along which it is di'agged so
long as it is in motion.
Tho sides of the channel being undermined and loosen-
ed by exposure to the frosts, fall into the strejtm. In time
of floods, and always, when the j^ath of the river has a
rapid descent, the mere momentum of the water acts pow-
erfully upon any inequalities: of surface that oppose its
course, tearing away the rocky walls of its channel The
blocks and grains of stono, thus set in motion, grind each
other to smaller fragments, and when the turbid waters
clear themselves in a lake or estuary, there results a bed
of gravel, sand, or soil. Two hundred and sixty years
ago, the bed of the Sicilian river Simeto was obstructed by
the flow across it of a stream of lava from Etna. Since
that time the i iver, with but slight descent, has cut a chan-
nel through this hard basalt from fifty to several hundred
feet wide, and in some parts forty to fifty deep.
But the action of water in ]»ulverizing rock is not com-
pleted when it reaches the sea. The oceans are in i)erpet-
xial agitation from tides, wind-waves, and currents like
the Gulf-stream, and work continual changes on their
shores.
Glaciers. — What liappens from the rapid flow of water
down the sides of mountain slopes below the frost-line is
also true of the streams of ice which more slowly descend
from the frozen summits. The glaciers a])pear like motion-
126 uo^y CROPS feed.
less ice-fields, but they are frozen rivers, rising in pei'pct^
ual snows and melting into water, after having reached
half a mile or a mile below the limits of frost. The snow
that accumulates on the frozen peaks of high mountains,
which are bathed by moist winds, descends the slopes by
its own weight. The rate of descent is slow, — a few
inches, or, at the most, a few feet, daily. The motion i:-
self is not continuous, but intermittent by a succession of
pushes. In the gorges, where many smaller glaciers unite,
the mass has often a depth of a mile or more. Under the
pressure of accumulation the snow is compacted to ice.
Mingled with the snows are masses of rock broken off
the higher pinnacles by the weight of adhering ioe, or
loosened by-alternate freezing and thawing, below the line
of perpetual frost. The rocks thus falling on the edge of
a glacier become a part of the latter, and partake its mo-
tion. When the moving mass bends over a convex sur-
face, it cracks vertically to a great depth. Into the cre-
vasses thus formed blocks of stone fall to the bottom, and
water melted from the surface in hot days flows down and
finds a channel beneath the ice. The middle of the glacier
moves most rapidly, the sides and bottom being retarded
by fiiction. The ice is thus rubbed and rolled upon itself,
and the stones imbedded in it crush and grind each other
to smaller fragments and to dust. The rocky bed of the
glacier is broken, and ploughed by the stones frozen into
its sides and bottom. The glacier thus moves until it
descends so low that ice cannot exist, and gradually dis-
solves into a torrent whose waters are always thick with
mud, and whose course is strewn with worn blocks of
stone (boulders) for many miles.
The Rhone, which is chiefly fed from the glaciers of the
Alps, transports such a volume of rock-dust that its muddy
waters may be traced for six or seven miles after they
have poured themselves into the Mediterranean.
3, — Chemical Action of Water axd Aib,
ORIGIN' AND FOKSIATIOX OF SOILS. 127
Water acts chemically upon rocks, or rather upon their
constituent minerals, in two ways, viz., hy Combination
and Solution.
Hydration.— By chemically uniting itself to the mineral
or to some ingredient of the mineral, there is formed in
many instances a new compound, which, by being softer
and more bulky than the original substance, is the first
step towards further change. Mica, feldspar, amphibole,
and pyioxene, are minerals whicli have been artificially
produced in the slags or linings of smelting furnaces, and
thus formed they have been fotuid totally destitute of wa-
ter, as might be expected from the high temperature in
wliich they originated. Yet these minerals as occurrino-
in nature, even when broken out of blocks of apparently
unaltered rock, and especially when they have been di-
rectly exposed to the weather, often, if not always, con-
tain a small amount of water, in chemical combination
(water of hydration).
Solution. — As a solvent, water exercises the most im-
portant influence in disintegrating minerals. Apatite,
when containing much chlorine, is gradually decomposed
by treatment Math water, chloride of calcium, Avhich is
very soluble, being separated from the nearly insoluble
phosphate of lime. The minerals Avhich compose silicious
rocks are all acted on j^erceptibly by pure water. This is
readily observed when the minerals are employed in the
state of fine powder. If pulverized feldspar, amphibole,
etc., are simply moistened with pure water, the latter at
once dissolves a trace of alkali, as shown by its turning
red litmus-paper blue. This solvent action is so slight
upon a smooth mass of the mineral as hardly to be per-
ceptible, because the action, is limited by the extent of
surface. Pulverization, which increases the surface enor-
mously, increases the solvent effect in a similar proportion.
A glass vessel may have water boiled in it for hours with-
out its luster being dimmed or its surface materially acted
128 HOW CROPS FEED.
upon, whereas the same glass * finely pulverized is attack-
ed by "water so readily as to give at once a solution alka-
line to the taste. Messrs. W. B. and R. E. Rogers {Am.
Jour. Sci.,Y, 4:0-1, 1848) found that by continued digestion
of pure water for a week, with powdered feldspar, horn-
blende, chlorite, serpentine, and natrolite,t these minerals
yielded to the solvent fiora 0.4 to 1 per cent of their
weiglit.
In nature we never deal witli pure water, but witli wa-
ter holding in solution various matters, either derived
from the air or from the soil. These substances modify,
and in most cases enhance, the solvent power of water.
Action of Carbonic Acid. — This gaseous substance is
absorbed by or dissolved in all natural waters to a greater
or less extent. At common temperatures and pressure
water is capable of taking up its own bulk of the gas.
At lower temperatures, and under increased pressure, the
quantity dissolved is much greater. Carbonated water,
as we may designate this solution, has a high solvent
power on the carbonates of lime, magnesia, pi'otoxide of
iron, and protoxide of manganese. The salts just named
are as good as insoluble in pure water, but they exist in
considerable quantities in most natural waters. The
spring and well waters of limestone regions are hard on
account of their content of carbonate of lime. Chalyb-
eate waters are those which hold carbonate of iron in
solution. When carbonated water comes in contact with
silicious minerals, these are decomposed much more rapidly
than by pure water. The lime, magnesia, and iron they
contain, are partially removed in the form of carbonates.
Struve exposed powdered phonolite (a rock composed
of feldspar and zeolites) to water saturated with carbonic
* Glass is a silicate of potash or soda,
t Musotj'pe.
ORIGIN AND FORMATION OF SOILS^ 120
acid under a pressure of 0 atmospheres, and obtained a
solution of -winch a pound* contained:
Carbonate of soda, 22.0 grains.
Cliloride of sodium, 3.0 "
Sulphate i.f potash, 1.7 "
" " soda, 4.8 "
Carbonate of lime, 4.5 "
" " magnesia, 1.1 "
Silica, 0.5 "
Phosohoric acid and manjranese, traces
Total, oT.l gi'ains.
In various natural springs, water comes to the surface
so charged with carbonic acid that the latter escapes
copiously in bubbles. Such waters dissolve laige quantities
of mineral matters from the rocks through which they
emerge. Examples are seen in the springs at Saratoga,
N. Y. According to Prof Chandler, the '' Saratoga
Spring," whose waters issue directly from the rock, con-
tains in one sjallon of 231 cubic inches :
Chloride of Sodium (common salt)
308. 3G1
" " Potassium,
9.098
Bromide of Sodium,
0.571
Iodide of Sodium,
0.126
Sulphate of Potash,
5.400
Carbonate of Lime,
86.483
" " Magnesia,
41.050
" " Soda,
8.948
" " Protoxide of i
ron,
.879
Silica,
1.28a
Phospliatc of lime.
trace
Solid matters, 552.799 "
Carbonic acid gas, (407.647 cubic inches at 52° Fah.)
Water, 58,317.110
The waters of ordinary springs and rivers, as Avell as
those tliat fall upon the earth's surface as rain, are, indeed,
I'he Saxon pound contains 7,080 Saxc
6*
130 IIOM^ CROPS FEED.
by no means fully charged with carbonic acid, and their
solvent effect is much less than that exerted by water sat-
urated with this gas.
The quantity (by volume) of carbonic acid in 10,000
parts of rain-water has been observed as follows: Accord-
ing to
Locality.
Lampadius, 8 Country near Freiberg, Saxony.
Mulder, 20 City of Utrecht, Holland.
Von Buumbauer, 40 to 90 " " " "
Peligot, 5 ?
The quantities found are variable, as might be expected,
and we notice that the largest proportion above cited does
not even amount to one per cent.
In river and spring water the quantities are somewhat
larger, but the carbonic acid exists chiefly in chemical com-
bination as bicarbonates of lime, magnesia, etc.
In the capillary water of soils containing much organic
matters, more carbonic acid is dissolved. According to a
single observation of De Saussure's, such water contains
2"! „ of the gas. In a subsequent paragraph, p. 221, is
given the reason of the small content of carbonic acid in
these waters.
The weaker action of these dilute solutions, when con-
tinued through long periods of time and extending over
an immense surface, nevertheless accomplishes results of
vast significance.
Solutions of Alkali-Salts. — Rain-water, as we have
already seen, contains a minute quantity of salts of am-
monia (nitrate and bicarbonate). The water of springs
and rivers acquires from the rocks and soil, salts of soda
and potash, of lime and magnesia. These solutions, dilute
though they are, greatly surpass pure water, or even car-
bonated water, in their solvent and disintegrating action.
Phosphate of lime, the earth of bones, is dissolved by
pure water to an extent that is hardly appreciable ; in
ORIGIN AND FORMATION OF SOILS. 131
salts of ammoTiia and of soda, however, it is taken up in
considerable quantity. Solution of nitrate of aiiimonia
dissolves lime and magnesia and their carbonates with
great ease. In general, up to a certain limit, a saline so-
lution acquires increased solvent power by increase in the
amount and number of dissolved matters. This import-
ant fact is one to which we shall recur at another time.
Action of Oxygen. — This element, the great mover of
chemical changes, which is present so largely in the at-
mosphere, has a strong tendency to unite with certain
bodies which are almost universally distributed in the
rocks. On turning to the analyses of minerals, p. 110, we
notice in nearly every instance a quantity of protoxide of
iron, or protoxide of manganese. The green, dark gray,
or black minerals, as the micas, amphibole, pyroxene,
chlorite, talc, and serpentine, invariably contain these prot-
oxides in notable proportion. In the feldspars they exist,
indeed, in very minute quantity, but are almost never en-
tirely wanting. Sulphide of iron (iron pyrites), in many
of its forms, is also disposed to oxidize its sulphur to sul-
phuric acid, its iron to sesquioxide, and this mineral is
widely distributed as an admixture in many rocks. In
trap or basaltic rocks, as at Bergen Hill, tnetalHe iron is
said to occur in minute proportion,* and in a state of fine
division. The oxidation of these substances materially
hastens the disintegration of the rocks containing them,
since the higher oxides of iron and of manganese occupy
more space than the metals or lower oxides. This fact is
well illustrated by the sulphate of protoxide of iron (cop-
jieras, or green-vitriol), which, on long keeping, exposed to
the air, is converted from transparent, glassy, green crys-
tals to a bulky, brown, opaque powder of sulphate of
sesquioxide of iron.
WeatherinjHf. — The conjoined influence of water, car-
This statement rests on the authority of Professor Henry Wurtz, of New York.
132
HOW CROPS FEED.
bonic acid, oxygen, and the salts held in solution by the
atmospheric waters, is expressed by the word veathering.
Tliis term may likewise include the action of frost.
When rocks weather, they are decomposed or dissolved,
and new compounds, or new forms of tlie original mat-
ter, result. The soil is a mixture of broken or pulverized
rocks, with the products of their alteration by weathering.
a. Weathering? of Quartz Rock.— Quartz (silicic acid),
as occurring nearly pure in quartzite, and in many sand-
stones, or as a cliief ingredient of all the granitic, horn-
blendic, and many other rocks, is so exceedingly hard and
insoluble, that the lifetime of a man is not sufficient for
the direct observation of any change in it, when it is ex-
posed to ordinary weathering. It is, in fact, the least
destructible of the mineral elements of the globe. Never-
theless, quartz, even when pure, is not absolutely insoluble,
particularly in water containing alkali carbonates or sili-
cates. In its less pure yarieti«s, and especially when as-
sociated with readily decomposable minerals, it is acted
on more rapidly. The quartz of granitic rocks is usually
roughened on the surface when it has long been exposed
to the weather.
h. The Feldspars weather much more easily than
quartz, though there are great differences among them.
The soda and lime feldspars decompose most readily,
while the potash feldspars are often exceeding!}^ durable.
The decomposition results in completely breaking up the
liard, glassy mineral. In its place there remains a white
or yellowish mass, which is so soft as to admit of crush-
ing between the fingers, and which, though usually, to the
naked eye, opaque, and non-crystalline, is often seen, under
a powerful magnifier, to contain numerous transparent crys-
talline plates. The mass consists principally of the crys-
talline mineral, ^Y/o/m/^e, ahydrated silicate of a]umina,(the
analysis of which has been given already, p. 113,) mixed
Or.ir.IN AND FOi:.Nf.\Tl<>\ ol' S(>ILS, lii'fi
with liydrated silica, and often with grains of nndecomi>os-
ed mineral. If we compare the composition of pure pot-
ash feldspar with that of kaolinite, assuming, what is
probably true, that all the alumina of the former remains
in the latter, we find what portions of the feldspar have
been removed and washed away by the water, which, to-
gether with carbonic acid, is the agent of this change.
Feldspar. Kaolinite. Liberated. Added.
Alumina 18.3 18 3 0
Silica 64.8 23.0 41.8
Putasb 16.9 16.9
Water 6.4 6.4
100 47.7 58.7 6.4
It thus appears that, in the complete conversion of 100
parts of potash felds])ar into kaolinite, there result 47.7
parts of the hitter, while 58.7" |„ of the feldspar, viz:
41.8° |„ of silica and 16.9° |^ of potasli, are dissolved out.
The potash, and, in case of other feldspars, soda, lime,
and magnesia, are dissolved as carbonates. If much water
has access during the decomposition, all the liberated silica
is carried away.* It usually happens, however, that a por-
tion of the silica is retained in the kaolin (perhaps in a
manner similar to that in which bone charcoal retains the
coloring matters of crude sugar). The same is true of a
portion of the alkali, lime, and oxide of iron, which may
have existed in the original feldspar.
The formation of kaolin may be often observed in na-
ture. In mines, excavated in feldspathic rocks, the fis-
sures and cavities through which surface water finds its
way downwards are often coated or filled with this sub-
stance.
c. Other Silicious Minerals, as Lencite, (Topaz, Scapo-
lite,) etc., yield kaolin by decomposition. It is pi-obable
that the micas, which decompose with difficulty, (phlogo-
♦ We have seen (H C. G., p. 121) that silica, when newly set free from combi-
natiou, is, at tirst, freely soluble in water.
134 ilOAV CROPS PEED.
pite, perhaps, excepted,) and the ampliiboles and pyrox-
enes, which are often easily disintegrated, also yield
kaolin ; but in the case of these latter minerals, the result-
ing kaolinite is largely mixed with oxides and silicates of
iron and manganese, so that its properties are modified,
and identification is difficult. Other hydrated silicates of
alumina, closely allied to kaolinite, appear to be formed in
the decomposition of compound silicates.
Ordinary (lays, as pipe-clay, blue-clay, brick-clay, etc.,
are mixtures of kaolinite, or of a similar hydrated silicate
of alumina, with a variety of other substances, as free
silica, oxides, and silicates of iron and manganese, carbon-
ate of lime, and fragments or fine powder of undecom-
posed mii'.erals. Fresenius deduces from his analyses of
several Xassau clays the existence in them of a compound
having the symbol Al„ O^ 3 SiO,+H,0, and the follow-
ing composition joer cent.
Silica, 57.14
Alumina, 31.72 '
Water, 11.14
100.00
Other chemists have assumed the existence of hydrated
silicates of alumina of still different composition in clays,
but kaolinite is the onh'^ one which occurs in a pure state,
as indicated by its crystallization, and the existence of
the others is not perfectly established. (S. W. Johnson
and J. M. Blake on Kaolinite^ etc.. Am. Jour. Sci., May^
1867, pp. 351-362.)
d. The Zeolites readily suffer change by weathering ;
little is known, however, as to the details of their disinte-
gration. Instead of yielding kaolinite, they appear to be
transformed into other zeolites, or retain something of their
original chemical ccmstitution, although mechanically dis-
integrated or dissolved. We shall see hereafter that there
OKIGIN AXD FOUMaTION OF SOILS. 13S
is strong reason to assume tlie existence of compounds
analogous to zeolites in every soil.
e. Serpentine and Maja^ncsian Silicates are generally
slow of decomposition, and yield a meager soil,
/. The Limestones, when pure and compact, are very
durable : as they become broken, or when impure, they
often yield rapidly to the weather, and impregnate the
streams which How over them with carbonate of lime.
g. Argillite and Argillaceous Limestones, which have
resulted from the solidification of clays, readily yield clay
again, either by simple pulverization or by pulverization
and weathering, according as they have suffered more or
less change by metamorphism.
§5.
JNCORPORATION OF ORGANIC MATTER WITH THE SOIL AND
ITS EFFECTS.
Antiquity of Vegetation. — Geological observations lead
to the conclusion that but small portions of the earth's
surface-rocks were formed previous to the existence of
vegetation. The enormous tracts of coal found in every
quarter of the globe are but the residues of preadaraite
forests, while in the oldest stratified rocks the remains of
plants (marine) are either most distinctly traced, or the
abundance, of animal forms warrants us in assuming the
existence of vegetation previous to their deposition.
The Development of Vegetation on a purely Mineral
Soil. — The mode in which the original inorganic soil be-
came more or less impregnated with organic matter may
be illustrated by what has happened in recent years upon
the streams of lava that have issued from volcanoes. The
lava flows from the crater as red-hot molten rock, often in
masses of such depth and extent as to require months to
cool down to the ordinary temperature. For many years
13(5 HOW CR0Pt5 FEED.
the lava is incapable of bearing atiy vegetation save some
almost microscopic forms. During these years the surface
of the rock suttVrs gradual disintegration by tlie agencies
of air and water, and so in time acquires the power to
support some lichens that appear at first as mere stains
upon its surface. These, by their decay, increase the
film of soil from which they sprung. The growth of
new generations of these p-lants is more and more vigor-
ous, and other superior kinds take root among them.
After another period of years, there has accumulated a
tangible soil, supporting herbaceous plants and dwarf
shrubs. Henceforward the increase proceeds more rapid-
ly ; shrubs gradually give place to trees, and in a century,
more or less, the once hard, barren rock has M'eathered to
a soil fit for vineyards and gardens.
Those lowest orders of plants, the lichens and mosses,
which pi-epare the way for forests and for agricultural
vegetation, are able to extract nourishment from the most
various and the most insoluble rocks. They occur abund-
antly on all our granitic and schistose rocks. Even on
quartz they do not refuse to grow. The white quartz
hills of Berkshire, Massachusetts, are covered on their
moister northern slopes with large patches of a leathery
lichen, which adheres so firmly to the rock that, on being
forced off", ])articles of the stone itself are detached. Many
of the old marbles of Greece are incrusted with oxalate
of lime left by the decay of lichens Avhich have grown
upon their surface.
Humus. — By the decay of successive generations of
plants the soil gradually acquires a certain content of dead
organic matter. The falling leaves, seeds and stems of
vegetation do not in general waste from the surface aa
rapidly as they fwe renewed. In forests, pastures, prai-
ries, and marshes, there accumulates on the surface a brown
or black mass, termed humus, of which leaf mold, swamp-
muck, and peat are varieties, differing in appearance as in
ORIGIN AND F<>li.\[ATi():>l OF SOILS. 1^7
the circumstances of their oriL,Mn. Tii the depths of tlie
soil sitiiilar inattars are formed by the decay of roots and
other subterranean parts of plants, or by the inversion of
sod and stubble, as well as by manuring.
Decay of VcifCtation. — When a plant or any part of a
plant dies, and remains exposed to air and moisture at the
common temi'.eratures, it undergoes a series of chemical
and physical clianges, which are lai-gely due to an oxida-
tion of portions of it)6 carbon and hydrogen, and the
formation of new organic compounds. Vegetable matter
is considerably variable in composition, but in all cases
chiefly consists of cellulose and starch, or bodies of simi-
lar character, mixed with a small proportion of albuminous
and mineral substances. By decay, the white or light-
colored and tough tissues of plants become conveited into
brown or black friable substances, in which less or none
of the organized structure of the fresh plant can be
traced. The bulk and weight of the decaying matter
constantly decreases as the process continues. With full
access of air and at suitable temperatures, the decay,
which, from the first, is characterized by the production
and escape of carbonic aeid and water, proceeds without
interruption, though more and more slowly, until nearlj''
all the carbon and hydrogen of the vegetable matters are
oxidized to the above-named products, and little more
than the ashes of the plant remains. With limited access
of air the process rapidly runs through a first stage of
oxidation, when it becomes checked by the formation of
substances which are themselves able, to a good degree,
to resist further oxidation, especially under the circum-
stances of their formation, and hence they accumulate in
considerable quantities. This happens in the lower layers
of fallen leaves in a dense forest, in compost and manure
heaps, in the sod of a meadow or pasture, and especially
in swamps and peat-bogs.
The more delicate, porous and watery the vegetable
138 now onops FEEti.
matter, and the more soluble substances and albuminoids
it contains, the more rapidly does it decay or humify.
It has been shown by a chemical examination of what
escapes in the form of gas, as well as of what remains as
humus, that the carbon of wood oxidizes more slowly
than its hydrogen, so that humus is relatively richer in
carbon than the vegetable matters from which it origin-
ates. With imperfect access of air, carbon and hydrogen
are to some extent disengaged in union with each other,
as marsh gas (CHJ. Carbonic oxide gas (CO) is proba-
bly also produced in minute quantity. The nitrogen of
the vegetable matter is to a considerable extent liberated
in the free gaseous state ; a portion of it unites to hydro-
gen, forming ammonia (NHJ, which remains in the de-
caying mass ; still another portion remains in the humus
in combination, not as ammonia, but as an ingredient of
the ill-defined acid bodies which constitute the bulk of
humus ; finally, some of the nitrogen may be oxidized to
nitric acid.
Chemical Nature of Humus. — In a subsequent chapter,
(p. 224,) the composition of humus will be explained at
length. Here we may simply mention that, under the in-
fluence of alkalies and ammonia, it yields one or more
bodies having acid characters, called humic and ulmic
(also geic) acids. Further, by oxidation it gives rise to
crenic and apocrenic acids. The former are faintly acid
in their properties ; the latter are more distinctly char-
acterized acids.
Influence of Humus on the Minerals of the Soil.^
a. Disintegration of the mineral matters of soils is aided
by the presence of organic substances in a decaying state, in
so far as the latter, from their hygroscopic quality, main-
tain the surface of the soil in a constant state oi tnoisture.
h. Organic matters furnish copious supplies of carbonic
acid, the action of which has already been considered
ORIGIN AND POUMATION OP SOILS. 139
(p. 128). Boussingault and Lewy {Memoires de CJiimie
Agrk'ole, etc.^p. 369,) liave analyzed the air contained in
the pores of the soil, and, as was to be anticipated, found
it vastly riclier in carbonic acid than the ordinary atmos-
phere.
The following table exhibits the composition of the air
in the soil compared with that of the air above the soil,
as observed in their investigations.
Carbonic acid in 10,000
parts of air (by weight).
Ordinary atinospbeie 6
Air from sandy subsoil of forest 38
" " loamy " " " 134
" " surface-soil " " 130
" " " " vineyard 146
" " " " old asparagus bed 123
" " " " " " newly manured. 333
" " " " pasture 370
*' " *' rich in humus 543
" •' " newly manured sandy field,
durinir dry weather 333
" " " newly manured sandy field,
during wet weather 1413
That this carbonic acid originates in large part by oxi-
dation of organic matters is strikingly demonstrated by
the increase in its quantity, resulting from the application
of manure, and the supervention of warm, wet weather.
It is obvious that the carbonic acid contained in the air
of the soil, being from twenty to one hundred or more
times more abundant, relatively, than in the common at-
mosphere, must act in a correspondingly more rapid and
energetic manner in accomplishing the solution and disin-
tegration of mineral matters.
c. The organic acids of the humus group probably aid
in the disintegration of soil by direct action, though our
knowledge is too imperfect to warrant a positive conclu-
sion. The ulmic and humic acids themselves, indeed, do
not, according to Mulder, exist in the free state in the
soil, but their soluble salts of ammonia, potash or soda,
have acid characters, in so far that they unite energetical-
140 now CROPS FEKD.
]y with other Lases, as lime, oxide of iron, etc. These
alkali-salts, then, should attack the minerals of the soil in
a manner similar to carbonic acid. The same is probably
true of crenic and npoorenic acids.
d. It scarcely requires mention that the ammonia salts
and nitrates yielded by the decay of plants, as well as the
organic acids, oxalic, tartaric, etc., or acid-salts, and the
chlorides, sulphates, and phosphates they contain, act upon
the surface soil where they accumulate in the manner al-
ready described, and that vegetable (and animal) remains
thus indirectly hasten the solution of mineral matters.
Action of Living Plants on the Minerals of the Soil.—
1. Moisture and Carbonic Acid. — The living vegetation
of a forest or prairie is the means of perpetually bringing
the most vigorous disintegrating agencies to bear upon
the soil that sustains it. The shelter of the growing
plants, not less than the hygroscopic humus left by their
decay, maintains the surface in a state of saturation by
moisture. The carbonic acid produced iu living roots,
and to some extent, at least, it is certain, excreted from
them, adds its effect to that derived from other sources.
2. Organic Acids 'within the Plant. — According to
ZuUcr, ( Vs. St. \. 45) the young roots of living plants
(what plants, is not mentioned) contain an acid or acid-
salt which so impregnates the tissues as to manifest a
strong acid reaction with (give a red color to) blue litmus-
paper, which is permanent, and therefore not due to car-
bonic acid. This acidity, Zuller informs us, is most in-
tense in the finest fibrils, and is exhibited when the roots
are simply wrapped in the litmus-paper, without being at
all (?) crushed or broken. The acid, whatever it may be,
thus existing within the roots is absorbed by porous paper
placed externally to them.
Previous to these observations of ZuUer, Salm Horst-
mar {Jour. far. Prakt.Chem. XL. 304,) liaving found in the
ashes of ground pine {Lycopodium, com^planatum), 38° j^, of
ORIGIN AND FORMATION' OF SOILS. 141
alumina, while in the ashes of juniper, growing beside
the Lycopodium, this substance was absent, examined
the rootlets of both plants, and found that tlie former had
an acid reaction, while the latter did not affect litmus-
paper. Salm Ilorstniar supposed that the alumina of
the soil finds its way into the Lycopodium by means of
this acid. Ritthansen has shown that the Lycopodium
contahis malic acid, and since all the alumina of the plant
may be extracted by water, it is probable that the acid
reaction of the rootlets is due, in part at least, to the
presence of acid raalate of alumina. {Joxr. fnr. Prakt.
Chem. LIIL 420.)
At Liebig's suggestion, Zoller made the following ex-
periments. A number of glass tubes were filled with
water made slightly acid by some drops of hydrochloric
acid, vinegar, citric acid, bitartrato of potash, etc. ; the
open end of each tube was then closed by a piece of
moistened bladder tied tightly over, and various salts, in-
soluble in water, as phosphate of lime, phosphate of am-
monia and magnesia, etc., were strewn on the bladder.
A^ter a short time it was found that the ingredients of
these salts were contained in the liquid in contact with
the under surface of the bladder, having been dissolved
by tlie dilute acid present in the pores of the membrane,
and absorbed through it. This is an ingenious illustra-
tion of the mode in which the organic aciils existing in
the root-cells of plants may act directly upon the rock or
soil external to tliem. By such action is doubtless to be
explained the fact mentioned by Liebig hi the following
words :
" We frequently find in meadows smooth limestones
with their surfaces covered with a network of small fur-
rows. "When these stones are newly taken out of the
ground, we find that each furrow corresponds to a rootlet,
which appears as if it had eaten its way into the stone."
{31odern Ag p. 43.)
142 UOW CROPS FEED.
This direct action of the living plant h probably ex-
erted by the lichens, which, as has been already stated,
grow upon the smooth surface of the rock itself Many
of the lichens are known to contahi oxalate of lime to the
extent of half their weight (Braconnot).
According to Goeppert, the hard, fine-grained rock of the
Zobtenberg, a mountain of Silesia, is in all cases softened at
its surface Avhere covered with lichens {Acarospora smar-
agdula, Imhricaria oHvacea, etc.), while the bare rock,
closely adjacent, is so hard as to resist the knife. On the
Schwalbenstein, near Glatz, in Silesia, at a height of 4,500
feet, the granite is disintegrated under a covei-ing of li-
chens, the feldspar being converted into kaolin or washed
away, only the grains of quartz and mica remaining unal-
tered.*
CHAPTER III.
KINDS OF SOILS— THEIR DEFINITION AND CLASSIFI-
CATION.
DISTINCTION OF SOILS BASED UPON THE MODE OF THEIR
FORMATION OR DEPOSITION.
The foregoing considerations of the origin of soils intro-
duce us appropriately to the study of soils themselves.
In the next place we may profitably recount those defini-
tions and distinctions that servo to give a certahi degree
of precision to language, and enable us to discriminate in
some measure the different kinds of soils, which offer
great diversity in origin, comjiosition, external characteis,
♦ See, also, p. 136,
KINDS OF SOILS. 143
and fertility. Unfortunately, while there are almost num-
berless varieties of soil having numberless grades of pro-
ductive power, we are very deficient in terms by which to
express concisely even the fact of their differences, not to
mention our inability to define these differences with ac-
curacy, or our ignorance of the precise nature of their
peculiarities.
As regards mode of formation or deposition, soils are
distinguished into Sedentary and Transported. The lat-
ter are subdivided into Drift., Alluvial., and Colluvial
soils.
Sedentary Soils* or Soils in place, are those which have
not been transported by geological agencies, but which
remain where they were formed, covering or contiguous
to the rock from whose disintegration they originated.
Sedentary soils have usually little depth. An inspection
of the rock underlying such soils often furnishes most
valuable information regarding their composition and
})robable agricultural value; because the still un weathered
rock reveals to the practised eye the nature of the min-
erals, and thus of the elements, composing it, while in the
soil these may be indistinguishable.
In New England and the region lying north of the Ohio
and east of the Missouri rivets, soils in place are not
abundant as compared with the entire area. Nevertheless
they do occur in many small patches. Thus the red-sand-
stone of the Connecticut Valley often crops out in that
part of New England, and, being, in many localities, of a
friable nature, has crumbled to soil, which now lies undis-
turbed in its original position. So, too, at the base of trap-
bluffs may be found trap-soils, still full of sharp-angled
fragments of the rock.
Transported Soils, (subdivided into drift, alluvial, and
colluvial), are those which have been removed to a dis-
tance from the rock-beds whence they originated, by th«
144: HOW ( ROPS FEKD.
action of moving ice (glaciers) or water (rivers), and de-
posited as sediment in their present positions.
Drift Soils (sometimes called diluvial) are characterized
by the following iiarticulars. They consist of fragments
whose edges at least have been rounded by friction, if the
fragments themselves are not altogether destitute of
angles. They are usually deposited without any stratifi-
cation or separation of parts. The materials consist of
soil proper, mingled with stones of all sizes, fiom sand-
granis up to iinmL-nse rock-masses of many tons in weight.
This kind of soil is usually disdnguished from all others
by the rounded rocks or boulders ("hard heads") it con-
tains, which are jiromiscuously scattered through it.
The "Drift" h:is undoubtedly been formed by moving
ice in that period of the earth's history known to geolo-
gists as the Glacial Epoch, a perioil when the present sur-
face of the country was covered to a great depth by fields
of ice.
In regions like Gi-eenland and the Swiss Alps, which
reach above the line of i)erpeLual snow, drift is now ac-
cumulating, perfectly similar in character to that of New
England, or has been obviously produced by the melting
of glaciers, which, in former geological ages and under
a colder climate, were continuations on an immense scale
of those now in existence.
A large share of the northern portion of the country
from the Arctic regions southward as far as latitude 39°,
or nearly to the southern boundaries of Pennsylvania and
to the Ohio River, including Canada, New^ England, Long
Island, and the States west as far as Iowa, is more or less
covered with drift. Comparison of the boulders with the
undisturbed rocks of the regions about show that the
materials cf the drift have been moved southwards or
southeastwards to a distance generally of twenty to forty
miles, but sometimes also of sixty or one hundred miles,
from where they were detached from their original beds.
KINDS OF SOILS. 145
The surface of tlie country when covered with drift is
often or usually irregular and hilly, the hills themselves
being conical heaps or long lidges of mingled sand, gravel,
and boulders, the transported mass having often a great
depth. These hills or ridges are parts of the vast trains
of material left by the melting of preadamite glaciers or
icebergs, and have their precise counterpart in the moralneA
of the Swiss Alps. Drift is accordingly not confined to the
valleys, but the northern slopes of mountains or hills, whose
basis is unbroken rock, are strewn to the summit with it,
and immense blocks of transported stone are seen upon
the very tops of the Catskills and of the "White and
Green Mountains.
Drift soils are for these reasons often made Tip of the
most diverse materials, including all the kinds of rock and
rock-dust that are to be found, or have existed for one or
several scores of miles to the northward. Of these often
only the harder granitic or silicious rocks remain in con-
siderable fragments, the softer rocks having been com-
pletely ground to powder.
Towards the southern limit of the Drift Region the
drift itself consists of fine materials which were carried
on by the Avaters from the melting glaciers, while the
heavier boulders were left further north. Here, too, may
often be observed a partial stratification of the transported
materials as the result of their deposition from moving
water. The great belts of yellow and red sand that
stretch across New Jersey on its southeastern face, and
the sands of Long Island, are these finer portions of the
drift. Farther to the north, many large areas of sand
may, perhaps, prove on careful examination to mark the
southern limit of some ancient local glacier.
Alluvial Soils consist of worn and rounded materials
which have been transported by the agency of rumiing
water (rivers and tides). Since small and light particles
are more readily sustained in a current of water thaa
146 HOW CROPS FEED.
heavy masses, alluvium is always more or less sti'atijied
or arranged in distinct layers: stones or gravel at the
bottom and nearest the soiirce of movement, finer stones
or finer gravel above and furtlier down in the path of
flow, sand and impalpable matters at the surface and at
the point where the stream, before turbid from suspended
rock-dust, finally clears itself by a broad level course and
slow progress.
Alluvial deposits have been formed in all periods of the
earth's history. Water trickling gently down a granite
slope carries forward the kaolinite arising from decompo-
sition of feldspar, and the first hollow gradually fills up
with a bed of clay. In valleys are thus deposited the
gravel, sand, and rock-dust detached from the slopes of
neighboring mountains. Lakes and gulfs become filled
with silt brought into them by streams. Alluvium is
found below as well as above the drift, and recent alluvium
in the drift region is very often composed of drift mate-
rials rearranged by water-currents. Alluvium often con-
tains rounded fragments or disks of soft rocks, as lime-
stones and slates, which are more rarely found in drift.
ColIUTial Soils, lastly, are those which, while consisting
in part of drift or alluvium, also contain sharp, angular
fragments of the rock from wliich they mainly originated,
thus demonstrating that they have not b('en transported
to any great distance, or are made u]) of soils in place,
more or less mingled with drift or alluvium.
§2.
DISTINCTIONS OF SOILS BASED UPON OBVIOUS OR EXTER-
NAL CHARACTERS.
The classification and nomenclature of soils customarily
employed by agriculturists have chiefly arisen from con-
sideration of the relative proportions of the principal
KINDS OF SOILS. 147
mechanical ingredients, or from other liighly obvious
qualities.
The distinctions thus established, tliough very vague
scientifically considered, are extremely useful for practical
purposes, and the grounds upon which they rest deserve
to be carefully reviewed for tlie purpose of api)reciating
their deficiencies and giving greater jirecision to the terms
employed to define them.
The farmer, speaking of soils, defines them as gravelly^
sandy^ doyey^ loamy, calcareous, peaty, oehreous, etc.
Mechanical Analysis of the Soil. — Befoie noticing
these various distinctions in detail, we may appro] >riately
Btudy the methods which are employed fi)r separating the
mechanical ingredients of a soil. It is evident that the
epithet sandy, for example, should not be applied to a soil
unless sand be the predominating ingredient ; and in or-
der to apply the term with strict correctness, as well as to
know how a soil is constituted as regards its mechanical
elements, it is necessary to isolate its parts and determine
their relative quantity.
Boulders, stones, and pebbles, are of little present or
immediate value in the soil by way of feeding the plant.
This function is performed by the finvr and especially by
the finest particles. JMechanical analysis serves therefore
to compare together difierent soils, and to give useful in-
dications of fertility. Simple inspection aided by the feel
enables one to judge, perhaps, with sufficient accuracy for
all ordinary jjractical purposes ; but in any serious attempt
to define a soil precisely, for the purposes of science, its
mechanical analysis must be made with care.
Mechanical separation is effected by sifting and wash-
ing. Sifting serves only to remove the stones and coarse
sand. By placing the soil i:i a glass cylinder, adding wa-
ter, and vigorously agitating for a few moments, then
letting the whole come to rest, there remains suspended
in the water a greater or less quantity of matter iu a stJ»*<i
148 ^ao^y crops feed.
of extreme division. This fine matter is in many cases
clay (kaolinite), or at least consists of substances resulting
from the weathering of the rocks, and is not, or not chiefly,
rock-dust. Between this impalpably fine matter and the
grains of sand retained by a sieve, there exist numberless
gradations of fineness in the particles.
By conducting a slow stream of water through a tube
to the bottom of a vessel, the fine particles of soil are
carried otf and may be received in a pan placed beneath.
Increasing the rapidity of the current enables it to remove
larger particles, and thus it is easy to separate the soil in-
to a number of portions, each of which contains soil of a
diflferent fineness.
Various attempts have been made to devise precise
means of sepaiating the materials of soils mechanically
into a definite number of grades of fineness.
This may be accomplished in good measure by washing,
but constant and accurate results are of course only at-
tained when the circumstances of the washing are uniform
throughout. The method adopted by the Society of
Agricultural Chemists of Germany is essentially the fol-
lowing ( Versuchs Stationen, VI, 144) :
The air-dry soil is gently rubbed on a tin-plate sieve
with round holes three millimeters in diameter; what passes
is weighed as fine-earth. What remains on the sieve is
washed with water, dried, weighed, and designated as
gravel, pebbles, stones, as the case may be, the size of the
stones, etc., being indicated by comparison with the fist,
with an Q^g., a walnut, a hazelnut, a pea, etc. Of the^/?;/e-
earth a portion (30 grams) is riow boiled for an hour or more
in water, so as to completely break down any lumps and
separate adhering particles, and is then left at rest for
some minutes, when it is transferred into the vessel 1 of
the apparatus, fig. 8., after ha\ ing j)oured off" the turbid
water with which it was boiled, into 2. This washing ap-
paratus (invented by Nobel) consists of a reservoir, A^
KINDS OP SOILS.
149
made of sheet metal, capable of holding something more
than 9 liters of water, and furnished at h with a stop-cock.
By means of a tube of rubber it is joined to the series of
vessels, 1, 2, 3, and 4, which are connected to each ether,
as shown in the figure, the recurved neck of 2 fitting
^water-tight into the nozzle of 1 at a, etc.
These vessels are made of ghiss, and together hold 4
liters of water; their relative volume is nearly
1 :.8: 27: 64, or = 1= : 2=* : 3= : 4\
5 is a glass vessel of somewhat more than 5 liters,
capacity.
The distance between h and r is 2 feet. The cock, 5, is
opened, so that in 20 minutes exactly 9 liters of water
150 HOW CROPS PEED.
pass it. The apparatus being joined together, and the
cock opened, the soil in 1 is agitated by tlie stream of wa-
ter flowing through, aud the finer portions are carried ovef
into 2, 3) 4; and 5. As a given amount of water requires
eight times hunger to pass through 2 than 1, its velocity
of motion and buoyant power in the neck of 3 are corre-
spondingly less. After the requisite amount of water has
run from A, the cock is closed, the whole left to rest sev-
eral hours, when the contents of the vessels are separately
rinsed out into porcelain dishes, dried and weighed.*
The contents of the several vessels are designated as
follows :f
1. Gravel, fragments of rock.
2. Coarse sand.
3. Fine sand.
4. Finest or dust sand.
5. Clayey substance or impalpable matter.
In most inferior soils the gravel, the coarse sand, and
the Jine sand, are angular fragments of quartz, feldspar,
amphibole, pyroxene, and mica, or of rocks consisting of
these minerals. It is only these harder and less easily
decomposable minerals that can resist the pulverizing
agencies through which a large share of our soils have '
passed. In the more fertile soils, formed from sedimen-
tary limestones and slates, the fragments of these strati-
fied rocks occur as flat pebbles and rounded grains.
The finest or dust-sand, when viewed under the micro-
scope, is found to be the same rocks in a higher state of
pulverization.
* See, also, Wolff's " Ardeitung zur Untermchung landiDirtlischaftlich-wichtiger
Stofe," 1867, p. 5.
t These names, applied by Wolff to the results of washin;; 'he sedentary soils
of Wijrtemberg, do not always well apply to other soils. Thus Grouveu, {3ter Salz-
munder Berkht, p. 32), operating on the alluvial soils of North Gennany, desig-
nated the contents of the 4tli funnel as "clay and loam," and those of the 5th
vessel as " light clay and humus." Again, Schiine found {Bulletin, etc., de Moscou,
p. 402) by treatment of a certain soil in Nobel's apparatus. 45 per cent of "coarse
sand " remaining in the 2d funnel. The particles of this were for the most part
emalkr tliau 1-lOtk millimeter (l-350ih inch), which certainly is not coarse sand i
KINDS OP sorrA 151
What is designated as clayey substance^ or impalpable
matter^ is oftentimes largely made up of rock-dust, so fine
that it is supported hy water, when the latter is in the
gentlest motion. In what are properly termed clay-soils,
the finest parts consist, however, chiefly of the hydrous
silicate of alumina, aln-ady described, p. 113, under the
mineralogical name of haol'mlte^ or of analogous com-
pounds, mixed with gelatinous silica, oxides of iron, and
carbonate of lime, as well as with finely divided quartz
and other granitic miner.ils. 80 gradual is the transition
from true kaolinite clay through its impurer sorts to mere
impalpable lock-dust, in all that relates to sensible char-
acters, as color, feel, adhesiveness, and plasticity, that the
term clay is employed rather loosely in agriculture, being
not infrequently given to soils that contain very little
kaolinite or true clay, and thus implies the general physi-
cal qualities that are usually typified by clay rather than
the presence of any definite chemical compound, like
kaolinite, in the soil.
Many soils contain much carbonate of lime in an im-
palpable form, this substance having been derived from
lime rocks, as marble and chalk, from the shells of mollusks,
or from coral ; or from clays that have oiiginated by the
chemical decomposition of feldspathic rocks containing
much lime.
Organic matter, especially the debris of former vegeta-
tion, is almost never absent from the impalpable portion
of the soil, existing there in some of the various forms as-
sumed by hunnis.
As Schone has shown, {Bulletin de la Societe des JVcttura-
listes de Moscoa, 1867, p. 363), the results obtained by
Nobel's apparatus are far from answering the purposes of
science. The separation is not carried far enough, and no
simple relations subsist between the separated portions, as
regards the dimensions of their particles. If the soil were
composed of spherical particles of one kind of matter, or
152 HOW CROPS PEED.
having all tlie same specific gravity, it would be possible
by tlie use of a properly constructed washing apparatus
to separate a sample into fifty or one hundred parts, and
to define the dimensions of the particles of each of these
parts. Since, however, the soil is very heterogeneous, and
since its particles are unlike in shape, consisting partly of
nearly spherical grains and partly of plates or scales upon
which moving water exerts an unequal floating effect, it is
difficult, if not impossible, to realize so perfect a mechanic-
al analysis. It is, however, easy to make a separation of a
soil into a large number of jjarts, each of which shall ad-
mit of precise definition in terms of the rapidity of flow
of a current of water capable of sustaining the particles
which compose it. Instruments for mechanical analysis,
which provide for producing and maintaining at will any-
desired rate of flow in a stream of water, have been very
recently devised, independently of each other, by E. Schone
{loc. cit., pp. 331-405) and A. Muller ( Vs. St., X, 25-51).
The employment of such apparatus promises valuable re-
sults, although as yet no extended investigations made
with its help have been published.
Gravelly Soils are so named from the abundance of
small stones or pebbles in them. This name alone gives
but little idea of the really important characters of the
soil. Simple gravel is nearly valueless for agricultural
purposes ; many highly gravelly soils are, however, very '
fertile. The fine portion of the soil gives them their crop-
feeding power. The coarse parts ensure drainage and
store the solar heat. The mineralogical chaiacters of the
pebbles in a soil, as determined by a j)ractised eye, may
often give useful indications of its composition, since it
is generally true that the finer parts of the soil agree in
this respect with the coarser, or, if d fferent, are not in-
ferior. Thus if the gravel of a soil contains many pebbles
of feldspar, the soil itself may be concluded to be well
supplied with alkalies; if the gravel consists of limestone,
KINDS OF SOILS. 153
WO may infer tliat lime is abundant in tlie soil. On the
other hand, if a soil contains a large pioportion of quartz
pebbles, the leuitimate inference is that it is of compara-
tively poor quality. The term gravelly admits of various
qualification. We may have a very gravelly or a mod-
erately gravelly soil, and the coarse material may be char-
acterized as a fine or coarse gravel, a slaty gravel, a
granitic gravel, or a diorite gravel, according to its state
of division or the character of the rock from which it was
formed.
But the closest description that can thus be given of a
gravelly soil cannot convey a very precise notion of even
its external qualities, much less of those pro})erties upon
which its fertility depends.
Sandy Soils are those which visibly consist to a large
degree, 9U° |^ or more, of sand, i. e., of small granular
fragments of rock, no matter of what kind. Sand usually
signifies grains of quartz', this mineral, from its hardness,
withstanding the action of disintegrating agencies beyond
any other. Considerable tracts of nearly pure and white
quartz sand are not uncommon, and are characterized by
obdurate barrenness. But in general, sandy soils are by no
means free from other silicious minerals, especially feldspar
and mica. When the sand is yellow or red in color, this fact
is due to admixture of oxide or silicates of iron, and pohits
with certainty to the presence of ferruginous minerals or
their decomposition-products, which often give considera-
ble fertility to the soil.
Other varieties of sand are not uncommon. In New
Jersey occur extensive deposits of so-called green sand,
containing grains of a mineral, glauconlte, to be hereafter
noticed as a fertilizer. Lime sand, consisting of grains
of carbonate of lime, is of frequent occurrence on the
shores of coral islands or reefs. The term sandy-soil is
obviously very indefinite, including nearly the extremes
1^*
154 ItOW CROPS FEED.
of feitility and barrenness, and covering a wide range of
variety as regards composition. It is therefore qualitied
by various epithets, as coarse, fine, etc. Coarse, sandy
soils are usually unprofitable, while fine, sandy soils are
often valuable.
('layey Soils are those in wliicli clay or impalpable mat-
ters predominate. Tliey are commonly characterized by
extreme fineness of texture, and by great retentive power
for water ; this liquid finding passage through their pores
with extreme slowness. When dried, they become crack-
ed and rifted in every direction from the shi-inking that
takes place in this process.
It should be distinctly understood that a soil may be
clayey without being clay, i. e., it may have the external,
physical properties of ndhesiveness and impertneability to
water which usually characterize clay, without containing
those compounds (kaolinite ami the like) which constitute
clay in the true chemical sense.
On the other hand it were possible to have a soil consist-
ing chemically of clay, which should have the physical
properties of sand; for kaolinite has been found in crys-
tals jo'oo of an inch in breadth, and destitute of all cohesive-
ness or plasticity. Kaolinite in such a coarse form is, how-
ever, extremely rare, and not likely to exist in the soil.
Loamy Soils are those intermediate in character between
sandy and clayey, and consist of mixtures of sand with
clay, or of coarse with impal{)able matters. They are free
from the excessive tenacit}' of clay, as well as from the too
great porosity of sand.
The gradations between sandy and clayey soils are
roughly expressed by such terms and distinctions as the
following :
KINDS Ol'' SOILS. }t):
Clay w impaltmble matters. Sand.
Heavy clay contains
T.v-yooio
10- 25»|,
Clay loam "
60-75
25- 40
Loam "
40—60
40— 60
Sandy loain "
25-40
60- 75
Light mjidy loam contains
10-35
75- 90
Satul " 0—10 90—100
The percent:vge composition above given applies to
the dri/ soil, and must be received with great allowance,
since the transition from fine sand to impalj^able matter
not physically distinguishable from clay, is an iinporcep-
tible one, and therefore not well admitting of nice discrim-
ination.
It is furthermore not to be doubted that the difference
between a clayey soil and a loamy soil depends more on
the form and intimacy of admixture of the ingredients,
than upon their relative proportions, so that a loam may
exist Avliicli contains less sand than some clayey soils.
Calcareous or Lime Soils are those in which carbonate
of lime is a predominating or characteristic ingredient.
They are recognizable by effervescing vigorously when
drenched with an acid. Strong vinegar answers for test-
ing them. They are not uncommon in Europe, but in this
country are comparatively rare. In the Northern and
Middle States, calcareous soils scarcely occur to an extent
worthy uf mention.
While lime soils exist containing 75° |„ and more of car-
bonate of limo, this ingredient is in general subordinate
to sand and clay, and we have therefore calcareous sands^
calcareous clays, or calcareous loams.
!>Iarls are mixtures of clay or clayey matters, with finely-
divided carbonate of lime, in something like equal propor-
tions.*
Peat or Swamp Muck is humus resulting from decayed
* In Nuw .Tursey, green sand marl, or marl gimply, 13 tlie name applied to the
green sand emi)l<)yed as a fertilizer. Shell marl is a uame desijjnatiug nearly
pure carbonate of lime found in swamps.
15G How CHOPS FKED,
vegetable matter in bogs and marshes. A soil is peaty or
mucky wlien containing vegetable remains that have suf-
fered partial decay under water.
Vegetable Mold is a soil containing much organic mat-
ter that has decayed without submergence in water, either
resulting from the leaves, etc., of forest trees, from the
roots of grasses, or from the frequent application of large
doses of strawy manures.
Ochcry or Ferruginous Soils are those containing much
oxide or silicates of iron ; they have a yellow, red, or
brown color.
Other divisions are current among practical men, as,
for example, surface and subsoil, active and inert soil,
tilth, and hard pan. These terms mostly explain them-
selves. When, at the depth of four inches to one foot or
more, the soil assumes a different color and texture, these
distinctions have meaning.
The surface soil, active soil, or tilth, is the portion that
is wrought by the instruments of tillage — that which is
moistened by the rains, warmed by the sun, permeated by
the atmosphere, in which the plant extends its roots, gath-
ers its soil-food, and which, by the decay of the subter-
ranean organs of vegetation, acquires a content of humus.
Subsoil. — Where the soil originally had the same char-
acters to a great depth, it often becomes modified down
to a certain point, by the agencies just enumerated, in
such a manner that the eye at once makes the distinction
into surface soil and subsoil. In many cases, however,
such distinctions are entirely arbitrary, the earth changing
its appearance gradually or even remaining uniform to a
considerable depth. Again, the surface soil may have a
greater downward extent than the active soil, or the tilth
may extend into the subsoil.
Hard pan is the appropriate name of a dense, almost
impenetrable, crust or stratum of ochery clay or com-
PHYSICAL. CUAKAOTEKS OF THE SOIL. 157
pactt'd gravel, often underlying a fairly fruitful soil. It
is the soil reverting to rock. The particles once disjointed
are being cemented together again by the solutions of
lime, iron, or alkali-silicates and humates that descend from
the surface soil. Such a stratum often separates the sur-
face soil from a deep gravel bed, and peat swamps thus
exist in basins formed on the most porous soils by a thin
layer of moor-bed-pan.
With these general notions regarding the origin and
characters of soils, Ave may proceed to a somewhat extend-
ed notice of the properties of the soil as influencing fertil-
ity. These divide themselves into physicnl characters —
those which externally affect the growth of llie plant ;
and chemical characters — those which provide it with food.
CHAPTER IV.
PHYSICAL CHARACTERS OF THE SOIL.
The physical characters of the soil are those which con-
cern the form and arrangement of its visible or palpable
particles, and likewise include the relations of these parti-
cles to each other, and to air and water, as well as to the
forces of heat and gravitation. Of these physical char-
acters we have to notice :
1. The Weight of Soils.
2. State of Division.
3. Absorbent Power for Vapor of Water, or Hygro»
scopic Capacity.
4. Property of Condensing Gases.
5. Power of fixing Solid JMatters from their Solutions.
6. Permeability to Liquid Water. Capillary Power.
7. Changes of Bulk by Drying, etc.
8. Adhesiveness.
9. Relations to Heat,
158 HOW CROPS FEED.
In treating of the physical characters of the soil, the
Writer employs an essay on this subject, contributed by
him to Vol. XVI of the Transactions of the N. Y. State
Axricultural Society, and reproduced in altered form in a
Lecture given at the Smithsonian Institution, Dec, 1859,
§ 1-
THE WEIGHT OF SOILS.
The Absolute Weight of Soils varies directly with their
porosity, and is greater the more gravel and sand they
contain. In the following Table is given the weight per
cubic foot of various soils according to Schiibler, and like-
wise (in round numbers) the weight per acre taken to the
depth of one foot (=43,560 cubic feet).
Weight op Soils
per cubic foot per acre to depth
of one foot.
Dry silicious or calcareous sand about 110 lbs. 4,792,000
Half sand and half clay " 96" 4,182,000
Common arable land * " SO to 90 " 3,485,000 to 3,920,000
Heavy clay " 75 " 3,207,000
Garden mold, rich in vegetable matter. . . " 70 " 3,049,000
Peat soil " 30 to 50 " 1,307,000 to 2,178,000
From the above figures we see that sandy soils, which
are usually termed " light," because they are worked most
easily by the plow, are, in fact, the heaviest of all ; while
clayey land, which is called " heavy," weighs less, bulk
for bulk, than any other soils, save those in which vegeta-
ble matter predominates. The resistance offered by soils
in tillage is more the result of adhesiveness than of gravity.
Sandy soils, though they contain in general a less percent-
age of nutritive matters than clays, may really offer as good
* The author is indebted to Prof. Seely, of Middlebury, Vt., for a sample of
one-fourth of a cubic foot of Wheat Soil from South Onondaga, New York. The
cubic foot of this soil, when dry, weighs 86'/^ lbs. The acre to depth of one foot
weighs 3,708,000 lbs. This soil contains a large proportion of slaty gravel. A
rich garden soil of silicious sand that had been heavily dunged, time out of
jnind. Boussingault found to weigh 81 lbs. av. per cubic foot (1.3 kilos per liter).
This would be per acre, cue foot deep, 3,528,000 lbs.
PHYSICAL CIIAUACTEKS OF THE SOIL. 159
nourisliment to crops as the latter, since they j)rcsent one-
half more absolute weight in a given space.
Peat soils are light in both senses in Avhich this word
is used by agriculturists.
The Specific Cravity of Soils is the weight of a given
bulk compared with the same bidk of water. A cubic
foot of water weighs 62^ lbs., but comparison of this num-
ber with the numbers stated in the last table expressing
the weights of a cubic foot of v.u'ious soils does not give
us the true specific gravity of the latter, for the reason
that these weights are those of the matters of the soil
contained in a cubic foot, but not of a cubic foot of these
matters themselves exclusive of the air, occupying their
innumerable interspaces. When we exclude the air and
take account only of the soil, we find that all soils, except
those containing very much humus, have nearly the same
density. Schone has recently determined with care the
specific gravity of 14 soils, and the figures range from
2.53 to 2.71. The former density is that of a soil rich in
humus, from Orcnbcrg, Tiussia ; the latter of a lime soil
from Jena. The density of sandy and clayey soils free from
humus is 2.65 to 2.G9. {Bulletin de la Soc. Imp. des
JVatitrolistes de Moscou, 1807, p. 404.) This agrees with
the density of those minerals which constitute the bulk
of most soils, as seen from tlie following statement of their
specific gravity, which is, for quartz, 2.65; feldspar, 2.62;
mica, 2.75-3.10 ; kaolinite, 2.60. Calcite has a sp. gr. of
2.72 ; hence the greater density of calcareous soils.
§2.
STATE or DIVISION OF THE SOIL AND ITS INFLUENCE ON
FERTILITY.
On the surface of a block of granite only a few lichens
and mosses can exist; crush the block to a coarse powder
and a more abundant vegetation can be supported on itj
160 UOW CKOl'S FEED.
if it is reduced to a very fine dust and duly watered, even
the cereal gfains will grow and perfect fruit on it.
Magnus {Jour, far prakt. Chem., L, 70) caused barley
to germinate in pure feldspar, Avhich was in one experi-
ment coarsely, in another finely, pulverized. In the coarse
feldspar the i)lants grew to a height of 15 inches, formed
ears, and one of them ripened two perfectly formed seeds.
In the fine feldspar the plants were very decidedly strong-
er. One of them attained a height of 20 i:iclics, and
produced four seeds.
It is true, as a general rule, that all fertile soils contain
a large proportion of fine or impalpable matter. The soil
of the " rJee Ree Bottom," on the Scioto River, Ohio, re-
markable for its extraordinary fertility, which has remained
nearly undiminished for GO years, though yielding heavy
crops of wheat and maize without interruption, is char-
acterized by the fineness of its particles. (D. A. Wells,
Am. Jour. ScL, XIV, 11.) In what way the extreme di-
vision of the particles of the soil is connected with its fer-
tility is not difficult to understand. The food of the plant
as existing in the soil must pass into solution either in the
moisture of the soil, or in the acid juices of the roots of
plants. In either case the rapidity of its solution is in
direct ratio to the extent of surface wdiich it exposes.
The finer the particles, the more abundantly will the plant
be supplied with its necessary nourishment. In the Scioto
valley soils, the water which surrounds the roots of the
crops and the root-fibrils themselves come in contai-t wdth
such an extent of surface that they are able to dissolve
the soil-ingredients in as large quantity and as rapidly as
the crop requires. In coarse-grained soils this is not so
likely to be the case. Soluble matters (manures) must be
applied to them by the farmer, or his crops refuse to yield
handsomely.
It is furthermore obvious, that, other things being equal,
the finer the, articles of the soil the more space the grow
PIIY£,:CAL CHARACTEUS OF THE SOIL. IGl
ing roots have in whicli to expand themselves, and the
more abundantly are they able to present their absorbent
Burfaces to the supplies which the soil contains. The fine-
ness of the particles may, however, be excessive. They
may fit each otlier so closely as to interfere with the
growth of the roots, or at least with the sprouting of the
seed. The soil may be too compact.
It will presently a})pear that other very important prop-
erties of the soil are more or less related to its state of
mechanical division.
§ 3.
ABSORPTION OF VAPOR OF WATER BY THE SOIL.
The soil has a power of withdrawing vapor of water
from the air and condensing the same in its pores. It is.
in other words, hygroscopic.
This i^roperty of a soil i-; of the utmost agricultural im-
portance, because, 1st, it is connected with the permanent
moisture which is necessary to vegetable existence ; and,
2d, since the absorption of water-vapor to some degree
determines the absorption of other vapors and gases.
In the following table we have the results of a series
of expeiiments carried out by Schablor, for the purpose
of determining the absorptive power of different kinds of
earths and soils for vapor of water.
The column of figures gives in thousandths the (quantity
of hygroscopic moisture absorbed in twenty-four liours by
the previously dried soil from air confined over water,
and hence nearly saturated with vaj)or.
Quartz suud, course 0
Gypsum 1
Lime sand 8
Ploii.^h laud 2:^
Claj' soil, (60 per cent clay) 28
Slaty marl ;?3
Loam , 35
1C2 lIO-\V CKOPS FEED.
Fine carbonate of lime 35
Heavy clay soil, (80 per cent clay) 41
Garden mold, (7 per cent liuraus) 53
Pure clay 49
Carbonate of mai::ncsi;i (fine jiowder) 83
Humus 130
Davy found that one tliousnnd parts of the soils named
below, after having been dried at 212°, absorbed during
one hour of exposure to the air, quantities of moisture as
follows :
Sterile soil of Bagshot h^ath 3
Coarse sand 8
Fine sand 11
Soil from Mersey, E.-sex 13
Very fertile alluvium, Somersetshire 16
Extremely fertile soil of Ormiston, East Lothian 18
An obvious practical result follows from the ficts ex-
pressed in the above tables, viz.: that sandy soils which
have little attractive force for watery vapor, and are there-
fore dry and arid, may bo meliorated in this respect by
admixture with clay, or better with humus, as is done by
dressing with vegetable composts and by green manuring.
The first table gives us proof that gypsum docs not exert
any beneficial action in consequence of directly attracting
moisture. Humus, or decaying vegetable matter, it will
be seen, surpasses every other ingredient of the soil in
absorbing vapor of water. This is doubtless in some de-
gree connected with its extraordinary porosity or amount
of surface. How the extent of surface alone may act is
made evident by comparing the absorbent power of car-
bonate of lime in the two states of sand and of an im-
palpable powder. The latter, it is seen, absorbed twelve
times as much vapor of water as the former. Carbonate
of magnesia stands next to humus, and it is worthy of
note that it is a very light and fine powder.
Finally, it is a matter of observation that " silica and
lime in the form of coarse sand make the soil in which
they predominate so dry and hot that vegetation perishes
PHYSICAL (JUAllACTEliS OP THE .SOIL. 10.')
from want of moisture; when, however, they occur afijfue
dust, they form too wet a soil, in which plants sufter from
the opposite cause." — [Tlamni's Lindiclrthschaft.)
Every body has a definite power of condensing moist-
ure upon its surface or in its pores. Even glass, though
presenting to the eye a jjerfectly clean and dry surface, is
coated witli a film of moisture. If a piece of glass be
weighed on :i very delicate balance, and then be wiped
with a clean cloth, it will be found to weigh perceptibl}'
less than before. Exposed to the air for an hour or more,
it recovers the weight which it had lost by wiping; this
loss was water. (Stas. Magnus.) The surface of the
glass is thus proved to exert towards vapor of Avater an
adhesive attraction.
Certain compounds familiar to the chemist attract water
with great avidity and to a lai'ge extent. Oil of vitriol,
phosphoric acid, and chloride of calcium, gain weight rap-
idly when exposed to moist air, or when placed contiguous
to other substances which are impregnated with moisture.
For this reason these compounds are employed for pur-
poses of drying. Air, for exaniple, is perfectly freed from
va})or of water by slowly traversing a tube containing
lumps of dried chloride of calcium, or phosphoric acid, or
by bubbling repeatedly througli oil of vitriol contained
in a suitable apparatus.
Solid substances, which, like chloride of calcium, carbon-
ate of potash, etc., gather water from the air to such an
extent as to become liquid, are said to deliquesce or to be
dellques'ent. Certain compounds, such as urea, the char-
acteristic ingredient of human urine, deliquesce in moist
air and dry away again in a warm atmosphei'c.
Allusion has been made in " How Crops Grow," p. 5.5,
to the hygroscopic water of vegetation, which furnishes
another striking illustration of the condensation of water
in porous bodies.
The absorption of vapor of water by solid bodies is not
164 HOW cuops fj:ed.
only dependent on the natin-e of the substance and i'ibT
amount of surface, but is likewise influenced by external
conditions.
The raj)idity of absorption depends upon the amount
of vapor present or accessible, and is greatest in moist
air.
The amount of absorption is determined solely by tem-
perature, as Knop has recently shown, and is unaflected
by the relative abundance of vapor: i. e., at a given tem-
perature a dry soil will absorb the same amount of moist-
ure from the air, no matter whether the latter be slightly
or heavily impregnated with vapor, but will do this the
more speedily the more moist the surrounding atmosphere
happens to be.
In virtue of this hygroscopic character, the soil which
becomes dry superficially during a hot day gathers water
from the atmosphere in the cooler night time, even when
no rain or dew is deposited upon it.
In illustration of the influence of temperature on tha
quantity of water absorbed, as vapor, by the soil, we give
Knop's observations on a sandy soil from Moeckern, Sax-
ony :
1,000 parts of this soil absorbed
At 55° F, 13 parts of hygroscopic water.
" 66° " 11.9 " " " "
" 77° " 10.:2 " " " "
" 88° " 8.7 " "
Knop calculates on the basis of his numerous observa-
tions that hair and wool, which aie more hygroscopic than
most vegetable and mineral substances, if allowed to ah
sorb what moisture they are capable of taking up, contain
the following quantities of water, per cent, at the temper-
atures named :
At 87° Fah., 7.7 per cent.
" 55° " 15.5 " "
" 33° " 19.3 " "
niYSK'AL CHAnAC'TEUS OP THE SOIL. 1 C5
Silk is sold ill Europe by weight with suitable allowance
for hygroscopic moisture, its variable conti-nt of which is
carefully (lelt-rmined by experiment in each important
transaction. It is plain that the circumstances of sale
may affect the weight of wool to 10 or more per cent.
§4.
CONDENSATION OF GASES BY THE SOIL.
Adhesion. — In the fact that soils and porous bodies gen-
erally liave a physical absorbing power for the vapor of
water, we have an illustration of a principle of very wide
application, viz., The surfaces of liquid and solid matter
attract the particles of other kinds of matter.
This force o? adhesion, as it is termed, when it acts up-
on gaseous bodies, overcomes to a greater or less degree
their expansive tendency, and coerces them into a smaller
space — condenses them.
Absorbent Power of Charcoal, etc. — Charcoal serves
to illustrate this tact, and some of its most curious as well
as useful properties depend upon this kind of physical
peculiarity. Charcoal is prepared from wood, itself ex-
tremely porous,* by expelling the volatile constituents,
whereby the porosity is increased to an enormous extent.
When charcoal is kept in a damp cellar, it condenses so
much vapor of water in its pores that it becomes difficult
to set on fire. It may even take up one-fourth its own
weight. When exposed to various gases and volatile
matters, it absorbs them in the same manner, though to
very unequal extent.
De Sanssure was the first to measure the absorbing
power of charcoal for gases. In his experiments, boxwood
chai'coal was heated to redness and plunged under mer-
* Mitscherlich lias calculated that the cells of a cubic inch of boxwood have
no less than 73 square feet of surface.
166 now CROPS feed.
oury to cool. Then introduced into tlie various gases
named below, it absorbed as many times its bulk of them,
as are designated by the subjoined figures:
Ammonia 90 Hydrochloric acid 85
Sulphurous acid G5 Hydrosulphuric acid 55
Protoxide of nitrogen 40 Carbonic acid 85
Oxygen 9}^ Carbonic oxide 9)^
Hydrogen 1% Nitrogen 7)^
According to De Saussure, the absorption was complete
in 24 hours, except in case of oxygen, where it continued for
a long time, though with decreasing energy. The oxygen
thus condensed in the charcoal combined with the carbon
of the latter, forming carbonic acid.
Stenhouse more lately lias experimented, in the same di-
rection. From these researches we learn that the power
in question is exerted towards different gases with very
unequal effect, and that different kinds of charcoal exert
very different condensing power.
Stenhouse found that one gi'amme of dry charcoal ab-
sorbed of several srases the number of cubic centimeters
given below.
Name of Gas.
Ammonia
Hydrochloric acid
Hydrosulphuric acid.
Sulphurous acid
Carbonic acid
Oxygen
A'ind of Charcoal.
Wood.
Peat.
Animal.
98 5
96.0
43.5
45.0
GO.O
30.0
28.5
9 0
32.5
27.5
17.5
14.0
10.0
5.0
0.8
0.6
0.5
The absorption or solution of gases in water, alcohol,
and other liquids, is analogous to this condensation, and
those gases which are most condensed by charcoal are in
general, though not invariably, those which dissolve most
copiously in liquids, (ammonia, hydrochloric acid).
Condensation of (iases by the Soil. — Reichardt and
Blumtritt have recently made a minute study of the kind
and amount of gases that are condensed in the pores of
various solid substances, including soils and some of their
rHOPERTV OF
KftM. COLLEGE LIBRARY.
PHYSICAL fllARACTEnS OP HIE SOIL. 1(57
ingieclieuts. {Jour, filr prakt. Chem., 13d. 98, j). 476.)
Their results relate chietly to these substances as ordinarily
occurring exposed to the atmosphere, and therefore more
or less moist. The following Tahle includes the more im-
portant data obtained by subjecting tlie substances to a
temperature of 284° F., and measuring and analyzing the
gas thus expelled.
100 Gra7m 10 Vols.
100 Vols, of Gas contained:
yielded gus
yielded
,
Substance :
in
mis.
Nitro-
0.ry-
Cartmn-
• Car-
a c.
gas.
gen.
gen.
ic acid.
bonic
Charcoal, airclry.
164
_
100
0
0
0
" moistened and dried i
igain.
, 140
5'J
85
2
9
3
Peat,
162
—
44
5
51
0
Garden soil, moist,
14
20
04
3
24
9
" " air-dry.
38
54
65
2
33
0
Hydrated oxide of iron, air
-dry,
375
309
26
4
70
0
Oxide of iron, ignited.
30
52
83
13
4
0
Hydrated alumina, air-dry,
69
82
41
0
59
—
Alumina, dried at 212'^,
11
14
83
17
0
_
Clay,
33
—
65
21
14
—
" long exposed to air,
26
39
70
5
25
—
" moistened,
29
35
60
6
Zi
_
River silt, air-dry,
40
48
68
0
!■&
14
" moistened,
24
29
67
0
31
2
" " again dried.
26
30
67
9
16
7
Carbonate of lime (whiting
,) 1S64,
43
52
100
0
0
—
18G5,
39
48
74
16
10
_
" " " precipitated,
1864,
65
—
81
19
0
—
" " " "
1865,
51
52
77
15
8
—
Carbonate of magnesia.
729
125
64
7
29
—
Gypsum, pulverized.
17
—
81
19
0
—
From these figures we gather :
1. The gaseous mixture which is contained in the pores
of solid substances rarely has the composition of the at-
mosphere. In but two instances, viz., with gypsum and
precipitated carbonate of lime., were only oxygen and ni-
trogen absorbed in proportions closely apj^roaching those
of the atmos])hei"e.
2. Xitrogeu ajjpears to be nearly always absorbed in
greater proportion than oxygen, and is greatly condensed
in some cases, as by peat, hydrated oxide of iron, and car-
bonate of masrnesia.
168 now CROPS FEED.
3. Oxygen is often nearly or quite wanting, as in char-
coal, oxide of iron, alumina, river silt, and whiting.
4. Carbonic acid, though sometimes wanting entirely,
is usually abundant in the absorbed gases.
5. In the pores of charcoal and of soils containing de-
caying organic matters, carbonic acid is often partially re=
placed by carbonic oxide. The experiments, however, do
not furnish proof that this substance is not formed under
the influence of the high temperature employed (284° F.)
in expelling the gases, rather than by incomplete oxidation
of organic matters at ordinary temperatures.
6. A substance, wlien moist, absorbs less gas than when
dry. In accordance with this observation, De Saussure no-
ticed that dry charcoal saturated Avith various gases evolv-
ed a good share of them when moistened Avith water.
Ground (and burnt ?) coffee, as Babinet has lately stated,
evolves so much gas when drenched with water as to burst
a bottle in which it is confined.
Tiie extremely variable figures obtained by Bluratritt
wlien operating with the same substance (the figures given
in the table are averages of two or three usually discordant
results), result from the general fact that the proportion
in which a number of gases are present in a mixture, in-
iluences the proportion of the individual gases absorbed.
Thus while charcoal or soil will absorb a large amount of
ammonia from the pure gas, it will take up but traces of
this substance from the atmosphere of which ammonia is
but an infinitesimal ingredient.
So, too, charcoal or soil saturated with ammonia by ex-
posure to the unmixed gas, loses nearly all of it by stand-
ing in the air for some time. This is due to the fact that
gases attract each other, and the composition of the gas
condensed in a porous body varies perpetually with the
variations of composition in the surrounding atmosphere.
It is especially the water-gas (vapor of water) which is
a fluctuating ingredient of the atmosphere, and one which
PHYSICAL CIIARACTKUS OF THE SOIL. 160
is iibijorbeil by })orous bodies in the largest quantity.
This not only displaces otlier gases from their adhesion to
solid surfaces, but by its own attractions modifies these
adhesions.
Reichardt and Blumtritt take no account of water-gas,
except in the few experiments where the substances were
purposely moistened. In all their trials, however, moist-
ure was present, and liad its quantity been estimated,
doubtless its influence on the extent and kind of absorp-
tion would have been strikingly evident throughout.
Ammonia and carbonate of ammonia in the gaseous
form are absorbed from the air by the dry soil, to a less
degree than by a soil that is moist, as will be noticed fully
hereafter.
Chemical Action induced by Adhesion. — This physical
property often leads to remarkable chemical effects ; in
other words, adhesion exalts or brings into play the force
of affinity. When charcoal absorbs those emanations
from putrefying animal matters which we scarcely know,
save by their intolerable odor and poisonous influence, it
causes at the same time their rapid and complete oxida-
tion ; and hence a j^iece of tainted meat is sweetened by
covering it with a thin layer of powdered charcoal. As
Stenhouse has shown, the carcass of a small animal may
be kept in a living-room during the hottest weather with-
out giving off any putrid odor, provided it be surrounded
on all sides by a layer of powdered charcoal an inch or
more thick. Thus circumstanced, it simply smells of am-
monia, and its destructible parts are resolved directly in-
to water, carbonic acid, free nitrogen, and ammonia, pre-
cisely as if they were burned in a furnace, and without
the appearance of any of the effluvium that ordinarily
arises from decaying flesh.
The metal platinum exhibits a remarkable condensing
power, which is manifest even with the ])olished surf ice of
foil or wire : but is most striking when the metal is
170 now oitoi'S feed.
brought to the condition of sponge, a form it assumes
when certain of its compounds (e. g. ammonia-chloride of
platinum) are decomposed by lieat, or to the more finely
divided state of platinum black. The latter is capable of
condensing from 100 to 250 times its volume of oxygen,
according to its mode of preparation (its porosity ?) ; and
for this reason it possesses intense oxidizing poAver, so that,
for example, when it is brouglit into a mixture of oxygen
and hydrogen, it causes them to unite explosively. A jet
of hydrogen gas, allowed to play on platinum sponge, is
almost instantly ignited — a fact taken advantage of in
Dobereiner's hydrogen lamp.
The oxidizing powers of platinum are much more vig-
orous than those of charcoal. Stenhouse has proposed
the use of platinized charcoal (charcoal ignited after moist-
ening with solution of chloride of platinum) as an escha-
rotic and disinfectant for foul ulcers, and has shown that
the foul air of sewers and vaults is rendered innocuous
when filtered or breathed through a layer of this material.*
Chemical Action a Result of the Porosity of the Soil,
— From these significant facts it has been inferred that the
soil by virtue of the extreme porosity of some of its ingre-
dients is the theater of chemical changes of the utmost
importance, which could not transpire to any sensible ex-
tent but for this high division of its particles and the vast
surface they present.
The soil absorbs putrid and other disagreeable effluvia,
and undoubtedly oxidizes them like charcoal, though, per-
haps, with less energy than the last named substance, as
would be anticipated from its inferior porosity. Garments
which have been rendered disgusting by the fetid secre-
tions of the skunk, may be " sweetened," i. e. deprived of
* Platinum does not condense hydrogen gas ; but the metal Palladium, which
occurs associated with platinum, has a most astonishing absorptive power for
hydrogen, being able to take up or " occlude " 900 times its volume of the gas,
(.Graham, Proceedings Roy. Hoc., 1868^ p. 432.J
odor, by burying them for a few days in the earth. The
Indians of this country arc said to sweeten the carcass of
the skunk by the same process, when needful, to fit it for
their food. Dogs and foxes bury bones and meat in the
ground, and afterward exhume them in a state of com-
parative freedom fi-om offensive odor.
When human excrements are covered with fine dry
earth, as in the " Earth Closet " system, all odor is at once
suppressed and never reajipears. At the most, besides an
"eartliy" smell, an odor of ammonia appears, resulting
from decomi)osition, which appears to ])roc-eed at once to
its ultimate results without admitting of the formation of
any intermediate offensive compounds.
Dr. Angus Smith, having frequently observed the pres-
ence of nitrates in the water of shallow town wells, sus-
pected that the nitiic acid was derived from animal mat-
ters, and to test this view, made experiments on the action
of filters of sand, and other porous bodies, upon solutions
of different animal and vegetable matters. He found
that in such circumstances oxidation ti)ok place most rap-
idly — the nitrogen of organic matters being converted in'
to nitric acid, the carbon and hydrogen combining with
oxygen at the same time. Thus a solution of yeast, which
contained no nitric acid, after being passed through a
filter of sand, gave abundant evidence of salts of this acid.
Colored solutions were in this way more or less decolor
ized. Water, rendered brown by peaty matter, was found
to be purified by filtration through sand.*
POWER OF SOILS TO REMOVE DISSOLVED SOLIDS FROM
THEIR SOLUTIONS.
Action of Sand upon Saline Solutions. — It has long
been known that simple s<ind is capable of partially re-
* This account of Dr. Smith's experiments is quoted from Prof. Way's paper
"On the Power of Soils to Al)sorb Manure." (Jour. Hoy. Ag. Soc. of England,
XI, p. 317.)
17^ now CROPS FEED.
raoving saline matters from their solutions in water. Lord
Bacon, in his " Syh^i Sylvarura," speaks of a method of
obtaining fresh water, which was practised on the coast
of Barbary. " Digge a hole on the sea-shore somewhat
above high-water mark and as deep as low-water mark,
which, when the tide cometh, will be filled with water
fresh and potable." He also remarks " to have read that
trial hath been made of salt-water passed through earth
through ten vessels, one within anotlier, and yet it hath
not lost its s.'iltiiess as to become potable ; " but when
"drayned througli twenty vessels, hath become fresh."
Dr. Stephen Hales, in a paper read before the Royal
Society in 1739, on '' Some attempts to make sea-Avater
wholesome," mentions on the authority of Mr. Boyle God-
frey that "sea-water, being filtered through stone cisterns,
the first pint that runs thi'ough will be pure water having
no taste of the salt, but the next pint will be salt as usual."
Berzelius found upon filtering solutions of common salt
through sand, that the portions which first passed were
quite free from saline impregnation. Matteucci extended
this observation to other salts, and found that the solu-
tions when filtered through sand were diminished in den-
sity, showing a detention l)y the sand of certain quantities
of the salt operated upon.*
Action of Humus on Saline Solutions. — Heidi n {Hoff-
man)i''s tTalweshericht, 1866, p. 29) found that peat and
various preparations of the humic acids, Mhen brought in-
to solutions of chloride of potassium and chloride of am-
monium, remove a portion of these salts from the liquid,
leaving the solutions perceptibly weaker. The removed
salts were for the most part readily dissolved by a small
quantity of water. W. Schumacher {Hoff. Jahres., 1867,
p. 18) observed tliat humus, artificially prepared by the
* These statements of Bacon, Hales, Berzelius, and Matteucci, are derivec'
from Prof. Way's paper " On the Power of Soils, etc." {Jour. Roy. Ag. Soc. oj
Eng., XI, 316.)
ABSORBKNT P;)\\ KU OF SOILS. 1T3
action of oil of vitriol on sugar, when placed in ten times
its quantity of solutions of various snlts (containing about
■J- per cent of solid matter) absorbed of sulphates of soda
and ammonia, and clilorides of calcium and ammonium,
about 2 per cent ; of sulphate of potash 4 per cent ; and of
phosphate of soda 10 per cent. Schumacher also noticed
tliat sulphate of potasli is able to expel sulphate of ammo-
nia from lumiic acid which has been saturated with the
latter salt, but that the latter cannot displace the former.
In Schumacher's experiments, pure water freely dissolved
the salts absorbed by the humic acitl.
Explanation. — Let us consider wliat occurs in the aci
of solution and i)i this separation of soluble matters from
a liquid. The difference between the solid and the liquid
state, so far as we can define it, lies in the unequal cohe-
sion of the particles. Cohesion prevails in solids, and op-
poses freedom of motion among the particles. In liquids,
cohesion is not altogether overcome but is greatly weak-
ened, and the particles move easily upon each other.
When a lump of salt i'^ put into water, the cohesion that
otherwise maintains its particles in the solid state is over-
come by the attracti(m of adhesion, which is mutually ex-
erted between them and the particles of water, and the
salt dissolves. If now into the solution of salt any in-
soluble solid be placed wliich the liquid can Avet (adhere
to) its particles will exert adhesive attraction for the par-
ticles of salt, and the tendency of the latter will be to
concentrate somewhat upon the surface of the solid.
If the solid, thus introduced into a solution, be exceed-
ingly [Kjrous, or otherwise present a great amount of sur-
face, as in case of sand or humus, this tendency is propor-
tionately heightened, and a separation of the dissolved
substance may become plainly evident on proper examina-
tion. When, on the other hand, the solid surface is rela-
tively small, no weakening of tlie solution may be percep-
tible by ordinary means. Doubtless the glass of a bottle
174 UOW OllOJ'S J'EKL).
containing brine concentrates the latter where the two
are in contact, though the effect may be difficult to dem-
onstrate.
Dcfecatiug Action of Charcoal on Solutions. — Char-
coal manifests a strong surface attraction for various
solid substances, and exhibits this power by overcoming
the adhesion they have to the particles of water when dis-
solved in that fluid. If ink, solution of indigo, red wine,
or bitter ale, be agitated some time with charcoal, the
color, and in the case of ale, the bitter principle, will be
taken up by the charcoal, leaving the liquid colorless and
comparatively tasteless. Water, which is impure from
putrefying organic matters, is sweetened, and brown sugars
are whitened by the use of charc^oal or bone-black. In
case of bone-black, the finely divided bone-earth (phos-
phate of lime) assists the action of the charcoal.
Fixin,^ of Dye-Stutfs. — The familiar process of dyeing
depends upon the adhesion of coloring matteis to the fiber
of textile fabrics. Wool steeped in solution of indigo at-
taches the pigment permanently to its fibers. Silk in the
same way fastens the particles of rosaniline, which consti-
tutes the maizenta dye. Many coloi's, e. g. madder and
logwood, which will not adhere themselves directly to
cloth, nre made to dye by the use of mordants — substances
b'ke alumina, oxide of tin, etc. — which have adhesion both
to the fabric and the pigment.
Absorptive Power of Tlay. — These ejects of charcoal
and of the fibers of cotton, etc., are in great part identical
with those previously noticed in case of sand and humus.
Their action is, however, more intense, and the efi'ects
are more decided. Charcoal, for example, that has ab-
sorbed a pigment or a bitter principle from a liquid, will
usually yield it up again to the same or a stronger solvent.
In some instances, however, as in dyeing with simple col-
ors, matters are fixed in a state of great permanence by
AnsonitENT r(»A\ Eu of soils. 175
the absorbent ; and in others, as where mordants are used,
chemical combinations supervene, which possess extraordi-
nary stability.
Many facts are known which show that soils, or certain
of their ingrcdionts, have a fixing power like that of char-
coal and textile fibers. It is a matter of common expe-
rience that a few feet or yards of soil intervening between
a cess-pool or dung-pit, and a well, preserves tlie latter
against contamination for a longer or shorter period.
J. P. Bronner, of Baden, in a treatise on " Grape Cul-
ture in South Germany," published in 1836, fiist mentions
tliat dung liquor is deodorized, decolorized, and rendered
nearly tasteless by filtration through garden earth, Mr.
Huxtable, of England, made the same observation in 1848,
and Prof Way and olliers have published extended in-
vestigations on this extremely important subject.
Prof Way informs us that he filled a long tube to the
depth of 18 inches Avith Mr. Huxtable's light soil, mixed
with its own bulk of white sand. " Upon this filter-bed
a quantity of highly ofiensive stinking tank water was
])Oured. The liquid did not pass for several hours, but
ultimately more than 1 ounce of it passed quite clear, free
from smell or taste, except a peculiar earthy smell and
taste derived from the soil." Similar results were obtain-
ed by acting upon putrid human urine, upon the stinking
water in which flax hail been steeped, and upon the water
of a London sewer.
Prof. Way found that these elFects were not strikingly
manifested by pure sand, but appeared when cl.iy Avas
used. lie found that solulions of coloring matters, such
as logwood, sandal- wood, cochineal, litmus, etc., Avhen fil-
tered through or shaken up with a portion of clay, are
entirely d(^prived of color. {Jo>n: Hoy. Ag. Soc. of
Eng., XI, p. 364.)
These efibcts of clay or clayey matters, like the fixing
power of cotton ami woolen stulFs upon pigments, must
176 HOW CROPS FEED.
be regarded for the most part as j^urely pliysical. There
are other resuUs of the action of the soil on saline solu-
tions, which, though j)erhaps influenced hy simple physical
action, are prepondcratiugly chemical in their aspect.
These effects, which manifest themselves by chemical de-
compositions and substitutions, will be fully discussed in
a subsequent chapter, p. 333.
PERMEABILITY OF SOILS TO LIQUID WATER. IMBIBITION.
CAPILLARY POWER.
The fertility of the soil is greatly influenced by its de-
portment toward water in the liquid state.
A soil 1?, permeable to water when it allows that liquid
to soak into or run through it. To be permeable is of
course to be porous. On the size of the jjores depends its
degree of permeability. Coarse sands, and soils which
have few but large pores or interspaces, allow water to
run through them readily — water ^:»ercota#es them. When,
instead of runni-ng through, the water is largely absorbed
and held by the soil, the latter is said to possess great
capillary power ; such a soil has many and minute pores.
The cause of capillarity is the same surface attraction
which has been already under notice.
When a narrow vial is partly filled with water, it will
be seen that the liquid adheres to its sides, and if it be not
more than one-half inch in diameter, the surface of the
liquid Avill be curved or concave. In a very narrow tube
the liquid will rise to a considerable heiglit. In these
cases the surface attraction of the glass for the water neu-
tralizes or overcomes the weight of (earth's attraction for)
the latter.
The pores of a sponge raise and hold water in them, in
the same way that these narrow (capillary *) tubes sup-
* From capilli/s, the Latin word fur hair, because as fine as hair; (but a hair la
no tube, as is often supposed.)
PERMEABILITY OF SOILS TO LIQUID WATEK. 177
port it. When a body has pores so fine (surfaces so near
each other) that tlieir surface attraction is greater than
the gravitating tendency of water, then the body will im-
bibe and hohl water — will exhibit capillarity; a lump of
salt or sugar, a lamp-wirk, are familiar examples. When
the pores of a body are so large (the surfaces so distant)
that they cannot fill themselves or keep themselves full,
the body allows the water to run through or to percolate.
Sand is most easily permeable to water, and to a higher
degree the coarser its particles. Clay, on the other hand,
is the least penetrable, and the less so the purer and more
plastic it is.
When a soil is too coarsely porous, it is said to be leachy
or hungry. The rains that fdl upon it quickly soak
through, and it shortly becomes dry. On such a soil, the
manures that may be applied in the spring are to some de-
gree washed down below the reach of vegetation, and in
the droughts of summer, plants siiflfer or perish from want
of moisture.
When the texture of a soil is too fine, — its pores too
small, — as happens in a heavy clay, the rains ]>enetrate it
too slowly ; they flow oif the surface, if the latter be in-
clined, or remain as pools for days and even weeks in the
hollows.
In a soil of proper texture the rains neither soak off into
the under-earth nor stagnate on the surface, but the soil
always (except in excessive 'wet or drought) maintains
the moistness which is salutary to most of our cultivated
plants.
Movements of Hater in the Soil.— If a wick be put
into a lamp containing oil, the oil, by capillary action,
gradually permeates its whole length, that which is above
as well as that below the surface of tlie liquid. Wlien the
lamp is set burning, the oil at the flame is consumed, and
as each particle disappears its place is supplied by a new
one, until the lamp is empty or the flame extinguished,
8*
178 HOW cuors fked.
Sonietliuig quite analogous occurs in the soil, by wliicli
the plant (corresponding to the flame in our illustration) is
fed. The soil is at once lamp and wick, and the water of
the soil represents the oil. Let evaporation of water from
the surface of the soil or of the plant take the place of
the combustion of oil from a Avick, and the matter stands
thus : Let us suppose dew or rain to have saturated the
ground with moisture fur some depth. On recurrence of
a dry atmospliere with sunshine and wind, the surface of
the soil rapidly dries ; but as each particle of Avater es-
capes (by evaporation) into the atmosphei-e, its place is
supplied (by capillarity) from the stores below. The as-
cending water brings along with it the soluble matters of
the soil, and thus the roots of plants are situated in a
stream of their appropriate food, Tiie movement proceeds
in this way so long as the surface is drier than the deeper
soil. When, by rain or otlierwise, the surf^ice is saturated,
it is like letting a thin stream of oil run upon the apex of
the lamp-wick — no more evaporation into the air can oc-
cur, and consequently there is no longer any ascent of
water ; on the contrary, the water, by its own weight,
penetrates the soil, and if the underlying ground be not
saturated with moisture, as can happen where the subter-
ranean fountains yield a meagre supply, then capillarity
will aid gravity in its downward distribution.
It is certain that a portion cf the mineral matters, and,
perhaps, also some organic bodies which feed the plant,
are more or less freely dissolved in the water of the soil.
So long as evaporation goes on from the surface, so long
there is a constant upward flow of these matters. Those
portions wliich do not enter vegetation accumulate on or
near the surface of the ground ; when a rain falls, they are
washed down again to a certain de})th, and thus are kept
constantly changing their place with the Avater, which is
the vehicle of their distribution. In regions Avhere rain
falls periodically or not at all, this upward flow of the soil-
termkability of soils to liquid water. 179
water often causes an accumulation of salts on the surface
of the ground. Thus in Bengal many soils which in the
wet season produce the most luxuriant crops, during the
rainless portion of the year become covered with white
crusts of saltpeter. The beds of nitrate of soda that are
found in Peru, and the carbonate of soda and other salts
which incrust the deserts of Utah, and often fill the air
with alkaline dust, have accumulated in the same manner.
So in our western caves the earth sheltered from rains is
saturated with salts — epsom-salts, Glauber's-salts, and salt-
peter, or mixtures of these. Often the rich soil of gardens
is slightly incrusted in this manner in our summer weather ;
but the saline matters are carried into the soil with the
next rain.
It is easy to see how, in a good soil, capillarity thus
acts in keeping the roots of plants constantly immersed in
a stream of water or moisture that is now ascending, now
descending, but never at rest, and how the food of the
plant is thus made to circulate around the organs fitted
for absorbing it.
The same causes that maintain this perpetual supply of
water and food to the plant are also efficacious in con-
stantly preparing new sup])lies of food. As before ex-
plained, the materials of the soil are always undergoing
decomposition, whereby the silica, lime, phosphoric acid,
potash, etc., of the insoluble fragments of rock, become
soluble in water and accessible to the plant. Water
charged with carbonic acid and oxygen is the chief agent
in these chemical changes. The more extensive and rapi<l
the circulation of water in the soil, the more matters will
be rendered soluble in a given time, and, other things be-
ing equal, tlie less will the soil be dependent on manures
to keep up its fertility.
Capacity of Imbibition. ( apillary Power.— No mat-
ter how favorable the structure of the soil may be to tho
180 HOW CROPS FEED.
circulation of water in it, no continuous upward movement
can take place without tvaporation. The ease and rapid-
ity of evaporation, while mainly depending on the condi-
tion of the atmosphere and on the sun's heat, are to a cer-
tain degree influenced by the soil itself We liave already
seen that the soil possesses a power of absorbing watery
vapor from the atmosphere, a power which is related both
to the kind of material that forms tlie soil and to its state
of division. This absorptive power opposes evaporation.
Again, diffeient soils manifest widely different capacities
for imhib'mg liquid water — capacities mainly connected
with their porosity. Obviously, too, the quantity of liquid
in a given volume of soil affects not only the rapidity,
but also the duration of evaporation.
The following tables by Schiibler illustrate the peculi-
arities of different soils in these respects. The first col-
umn gives the percentages of liquid water absorbed by
the completely dry soil. In these experiments the soils
were thoroughly wet with water, the excess allowed to
drip off, and the increase of weight determined. In the
second column are given the pei-centages of vrater that
evaporated during the space of four hours from the satu-
rated soil spread over a given surface :
Quartz sand 25 88.4
Gypsum 27 71.7
Lime sand 29 75.9
Slaty m:ul 34 68.0
Clay soil, (sixty per cent clay,) 40 52.0
Loam 51 45.7
Plough Luid 53 32.0
Heavy clay, (ehhty per cent clay,) 61 34.9
Pure ^irray clay 70 31.9
Fine carbonate of lime 85 28.0
Garden mould SI) 24.3
Humus 181 25.5
Fine carbonate of ma'.aiesia S^'jO 10.8
It is obvious that these tAVO columns oxitress neai-ly the
same thiniz in different wavs. The am'unt of water re-
PEKMEABILITY OF SOILS TO LIQUID WATER. l8l
taineJ increases from quartz sand to magnesia. The rap-
idity of drying in the air diminishes in the same direction.
Some observations of Zenger ( Wilda's Centralblatt,
1858, 1, 430) indicate the influence of the state of division
of a soil on its power of imbibing water. In the subjoin-
ed table are given in the first column the per cent of wa-
ter imbibed by various soils which had been brought to
nearly the same degree of moderate fineness by sifting off
both the coarse and the fine matter ; and the second col-
umn gives the amounts imbibed by the same soils, reduced
to a high state of division by pulverization.
Coarse.
Fine.
Quartz sand,
26.0
53.5
Marl (used as fertilizer,)
30.3
54.5
Marl, underlying peat,
S9.0
48.5
Brick clay.
66.2
57.5
Moor soil,
104.5
101.0
Aim (lime-sinter,)
108.3
70.4
Aim soil.
178.2
103.5
Peat dust.
377.0
368.5
The effects of pulverization on soils whose particles are
compact is to increase the surface, and increase to a cor-
responding degree the imbibing power. On soils consist-
ing of porous particles, li e lime-sinter and peat, pulver-
ization destroys the porosity to some extent and diminishes
the amount of absorption. The first class of soils are
probably increased in bulk, the latter reduced, by grinding.
Wilhelm, {Wilda's Centralblatt, 1866, 1, 118), in a
series of experiments on various soils, confirms the above
results of Zenger. He found, e. g., that a garden mould
imbibed 114 per cent, but when pulverized absorbed but
62 per cent.
To illustrate the different properties of various soils for
which the farmer has but one name, the fact may be ad-
duced that while Schiibler, Zenger, and Wilhelm found
the imbibing power of "clay" to range between 40 and
TO per cent, Stoeckhardt examined a " clay " from Saxony
182 now cuors feed
that, hold 150 per cent of water. So the humixs of Schul)«
ler imhibed 181 per cent ; the peat of Zenger, 377 per cent ;
while Wilhehn examined a very porous peat that took up
519 per cent. These difFei-ences are dependent mainly on
the mechanical texture or porosity of the material.
The want of capillary retentive power for Avater in the
case of coarse sand is undeniably one of the chief reasons
of its unfruitfulness. The best soils possess a medium re-
tentive power. In tliem, therefore, are best united the
conditions for the regu.ar distribution of the soil- water
under all circumstances. In them this process is not hin-
dered too much either by wet or dry weather. The re-
taining power of humus is seen to be more than double
that of clay. This result might appear at first sight to
be in contradiction to ordinary observations, for we are
accustomed to see water standing on the surface of clay
but not on humus. It must be borne in mind that clay,
from its iraperviousness, holds water like a vessel, the wa-
ter remaining apparent ; but humus retains it invisibly,
its action being nearly like tliat of a sponge.
One chief cause of the value of a layer of humus on
the surface of the soil doubtless consists in this great re-
taining power for water, and the success that has attended
the practice of green manuring, as a means of renovating
almost wortliless shifting sands, is in a great degree to be
attributed to this cause. The advantages of mulching are
explained in the same way.
Soils which are over-rich in humus, especially those of
reclaimed peat-bogs, have some detrimental peculiarities
deserving notice. Stoeckhardt ( WiJdci's Centralblatt^
1858, 2, 2:2) examined the soil of a cultivated moor in
Saxony, which, when moist, had an imbibing power of
60-69° 1„. After being thoroughly dried, however, it lost
its adhesiveness, and the imbibing power fell to 26-30° j„.
It is observed in accordance with these data that such
joils retain water late in spring ; and when they become
CUANGES OF TllK BUI.K OF TIIK SOIL. 183
very dry in summer lliey are slow to take up water again,
so tliat rain-water stands on the surface for a considerable
time without penetrating, and when, after some days, it
is soaked up, it remains injuriously long. Light rains
after drought do little immediate good to such soils,
while heavy rains always render them too wet and cold,
unless they are suitably ameliorated. The same is true to
a less degree of heavy, compact clays.
CHANGES OF THE BULK OF THE SOIL BY DRYING AND
FROST.
The Shrinkin^^ of Soils on Drying is a matter of no
little practical importance. Tliis shrinking is of course
offset by an increase of bulk when the soil becomes wet.
In variable weather we have therefore constant changes
of volume occurring.
Soils rich in humus experience these changes to the
greatest degree. Tiie surfaces of moors often rise and
fall with tlie wet or dry season, through a space of sev-
eral inches. In ordinary light soils, containing but little
humus, no change of bulk is evident. Otherwise, it is in
clay soils that shrinking is most perceptible ; since these
soils only dry superficially, they do not appear to settle
much, but become full of cracks and rifts. Heavy clays
may lose one-tenth or more of their volume on drying,
and since at the same time they harden about the rootlets
which are imbedded in them, it is plain that these indis-
pensable organs of the plant must thereby be ruptured
during the protracted dry Aveather. Sand, on the other
hand, does not change its bulk by wetting or drying, and
when present to a considerable extent in the soil, its par-
ticles, being interposed between those of the clay, prevent
the adhesion of the latter, so that, although a sandy lonni
shrinks not inconsiderably on diyiiig, yet the lines of sepa-
184 uow cEors fked.
ration are vastly more numerous and less wide than In
purer clays. Such a soil does not " cake," but remains
friable aiul powdery.
Marly soils (containing carbonate of lime) are especially
prone to fall to a fine powder during drying, since the
carbonate of lime, which, like sand, shrinks very little, is
itself in a state of exti'eme division, and therefore moi-e
effectually separates the clayey particles. The unequal
shrinking of these two intimately mixed ingredients ac-
complishes a perfect pulverization of such soils. On the
cold, heavy soils of Upper Lusatia, in Germany, the appli-
cation of lime has been attended Avith excellent results,
and the larger share of the benefit is to be accounted for
by the improvement in the textui-e of those soils which
follows liming. Tlie carbonate of lime is considerably
soluble in water charged with carbonic acid, as is the wa-
ter of a soil containing vegetable matter, and this agency
of distribution, in connection with the mechanical opera-
tions of tillage, must in a short time effect an intimate
mixture of the lime with the whole soil. A tenacious clay
is thus by a heavy liming made to approach the condition
of a friable marl.
Heaviu^ by Frost. — Soils which imbibe much water,
especially clay and peat soils, have likewise the disagree-
able ])roperty of being heaved by frost. The expansion,
by freezing, of the liquid water they contain, separates the
particles of soil from each other, raises, in fact, the surface
for a considerable height, and thus ruptures the roots of
grass and especially of fall-sowed grain. The lifting of
fence posts is due to the same cause.
ADHESIVENESS OF THE SOIL.
In the language of the farm a soil is said to be heavy
or light, not as it weighs more or less, but as it is easy or
ADII12S1VKNKSS Oi'' TllK SOIL. 185
difficult to work. The state of dryness Las greut iufluence
oa this quality. Sand, lime, and humus have very little
adhesion when dry, but considerable when wet. Soils in
which they predominate are usually easy to work. But
clay or impalpable matter h;is entirely different characters,
upon which the tenacity of a soil almost exclusively de-
pends. Dry "clay," when powdered, has hardly more
consistence than sand, but when thoroughly moistened its
particles adhere together to a soft and plastic, but tena-
cious mass ; and in dryhig away, at a certain point it be-
comes very hard, and requires a good deal of force to
penetrate it. In this condition it offers great resistance to
the instruments used in tillage, and when thrown up by
the plow it forms lumps which require repeated harrow-
ings to break them down. Since the adhesiveness of the
soil depends so greatly upon the quantity of water con-
tained in it, it follows that thorough draining, combined
with deep tillage, whereby sooner or later the stiffest clays
become readily per meal "le to water, must have the best
effects in making such soils easy to work.
The English piactice of burning clays speedily accom^
plishes the same purpose. When clay is burned and then
crushed, the particles no longer adhere tenaciously to-
gether on moistening, and the mass docs not acquire again
the unctuous plasticity peculiar to unburned clay.
Mixing sand with clay, or incorporating vegetable mat-
ter with it, or liming, serves to separate the particles
from each other, and thus remedies too great adhesiveness.
The considerable expansion of water in the act of solid-
ifying (one-fifteenth of its volume) has already been no-
ticed as an agency in reducing rocks to powder. In the
same way the alternate freezing and thawing of the Avater
which impregnates the soil during the colder part of the
year plays an important part in overcoming its adhesion.
The effect is apparent in the spring, immediately after
" the frost leaves the ground," and is very considerable,
180 now CHOPS FiiED.
fully one-third of the I'esi-'tancc of a clay or loam to the
plow thus disappearing, according to Schiibler's experi-
ments.
Tillage, when carried on with the soil in a wet condi-
tion, to some extent neutralizes the effects of frost, espe-
cially in tenacious soils.
Fall-plowing of stiff soils has been recommended, in
order to expose them to the disintegrating effects of frost.
RELATIONS OF THE SOIL TO HEAT.
The relations of the soil to heat are of tlie utmost im-
portance in affecting its fertility. The distribution of
plants is, hi general, determined by differences of mean
temperature. In the same climate and locality, however,
Ave find the farmer distinguishing between cold and warm
soils.
The Temperature of the Soil varies to a certain depth
with that of the air ; yet its changes occur more slowly,
are confined to a considerably nairower range, and dimin-
ish downward in rapidity and amount, until at a certain
depth a point is reached where the temperature is invari-
able.
In summer the temperature of the soil is higher in day-
time than that of the air; at night the temperature of the
surface rapidly fills, especially when the sky is clear.
In temperate climates, at a depth of three feet, the tem-
perature remains unchanged from day to night ; at a depth
of 20 feet the annual temperature varies but a degree or
two ; at 75 feet below the surface, the thermometer re-
mains perfectly stationary. In the vaults of the Paris
Observatory, 80 feet deep, the tem})erature is 50° Fahren-
heit. In tropical regions the point of nearly unvarying
temperature is reached at a depth of one foot.
DELATIONS OP* THE SOIL TO HEAT. 187
The mean annual temperature of tlie soil is the same as,
or in higher latitudes a degree above, that of the air. The
nature and position of the soil must considerably influence
its temperature
Sources of the Heat of the Soil. — The sources of that
heat v/liieh is found in tlie soil are three, viz.: First, the
original heat of the earth ; second, the chemical process
of oxidation or decay going on within it ; and third, an
external one, the rays of the sun
The earth has Avithin itself a source of heat, which
maintains its interior at a high temperature ; hut which
escapes so rapidly from the surface that the soil would be
constantly frozen but for the external supply of heat from
the sun.
The heat evolved by the decay of organic matters is
not inconsiderable in porous soils containing much vegeta-
ble remains; but decay cannot proceed rapidly until the
external t<?mperature has reached a point favorable to
vegetation, and therefore this source of heat [trobably has
no appr?,"iable effect, one way or the other, on the welfare
of the p'ant. The warmth of the soil, so far as it favors
vegetable growth, njipears then to depend exclusively on
the heat of the sun.
The direct rays of the sun are the immediate cause of
the warmth of the earth's surface. The temperature of
the soil near the surface changes progressively with the
seasons ; but at a certain depth the loss from the interior
and the gain from the sun compensate each other, and, as
has been previously mentioned, the temperature remains
unchangi'd throughout the year.
Daily (hanj?es of Temperature. — During the day the
sun's heat reaches the earth directly, and is absorbed by
the soil and the solid objects on its surface, and also by
the air and water. But these different bodies, and also
the different kinds of soil, have very different ability to
absorb or become warmed by the sun's heat. Air and
lft>! HOVr CROPS FEEP.
■water are almost incapable of being warmed by heat ap-
plied above them. Through the air, heat radiates without
being absorbed. Solid bodies whicli have dull and porous
surfaces absorb heat most rapidly and abundantly. The
soil and solid bodies become warmed according to their
individual capacity, and from them the air receives the
heat which warms it. From the moist surface of the soil
goes on a rapid evaporation of water, which consumes * a
large amount of heat, so that the temperature of the soil
is not rapidly but gradually elevated. The ascent of wa-
ter from the subsoil to supply the plnce of that evaj^orat-
ed, goes on as before described. When the sun declines,
the process diminishes in intensity, and w^hen it sets, the
reverse takes place. The heat that had accumulated on
* When a piece of ice is placed in a vessel whose temperature is increasing,
by means of a lamp, at tlie rate of one desree of the thermometer every minute,
it will be found that the temperature of the ice rises until it attains 32°. When
this point is reached, it begins to melt, but doos not suddenly become fluid : the
melting goes on very gradually. A thermometer placed in the water remains
constantly at 32° so long as a fragment of ice is present. The moment the ice
disappears, the temperature begins to rise again, at the rate of one degree per
minute. The time during which the temperature of the ice and water remains
at 33° is 140 minutes. During each of these minutes one degree of heat enters
the mixture, but is not indicated by the thermometer — the mercury remains sta-
tionary ; 140° of heat have thus passed into the ice and become hidden, latent ;
at the same time the solid ice has become liquid water. The dift'erence, then,
between ice and water consists in the heat that is latent in the latter. If we now
proceed with the above experiment, allowing the heat to increase with the same
rapidity, we find that the temperature of the water rises constantly for ISO min-
utes. The thermometer then indicates a temperature of 212°, (32+180,) and the
water boils. Proceeding with the experiment, the water evaporartes away, but
the thermometer continues stationary so long as any liquid remains. After the
lapse of 972 minutes, it is completely evaporated. Water in becoming steam
renders, therefore, still another portion, 972°, of heat latent. The heat latent in
steam is indispensable to the existence of the latter. If this heat be removed
by bringing the steam into a cold space, water is reproduced. If, by means ol
pressure or cold, steam be condensed, the heat originally latent in it becomes
sensible,/?-«A and capable of affecting the thermometer. If, also, water be con-
verted into ice, as much heat is evolved and made sensible as was absorbed and
made latent. It is seen thus that the processes of liquefaction and vaporization
are cooling processes ; for the heat rendered latent by them must be derived from
surrounding objects, and thus these become cooled. On the contrary, solidifica-
tion, freezing, and vapor-condensation, are tvarminff processes, since in them
large quantities of heat ce-ise to be latent and are made sensible, thus warming
purroundiug bodies.
KELATIONS OF TIIK SOIL TO HEAT. 1*^9
the surface of the earth radiates into the cooler atmos-
phere aiid planetary sj^acc; the temperature of the surface
rapidly diminishes, and the air itself becomes cooler by
convection.* As the cooling goes on, the vapor suspend-
ed in the atmosphere begins to condense upon cool objects,
while its latent heat becoming free hinders the too sudden
reduction of temperature. The condensed water collects
ill drops — it is dew ; or hi the colder seasons it crystallizes
as hoar-frost.
The deposition of liquid water takes place not on the
surface of the soil merely, but within it, and to that depth
in which the temperature falls during the night, viz., 12
to 18 inches. (Krutzsch observed the temperature of a
garden soil at the depth of one foot, to rise 3° F. on a
May day, from 9 A. M. to 7 P. M.)
Since the air contained in the interstices of the soil is at
a little di'pth saturated with aqueous vapor, it results that
the slightest reduction of temper;iture must at once occa-
sion a deposition of water, so that the soil is thus supplied
with moisture independently of its hygroscopic power.
Conditions tliat Affect the Temperature of the Soil.—
The special nature of the soil is closely connected with
the maintenance of a uniform temperature, with the pre-
vention of too great heat by day and cold by night, and
with the watering of vegetation by means of dew. It is,
however, in many cases only for a little space after seed-
time that the soil is greatly concerned in these jjrocesses.
So soon as it becomes covered with vegetation, the char-
* Thoagh liquids and gases are almost perfect non-coiuliictors of heat, yet it can
(Bffuse through them rapidly, if advantage be taken of the fact that by lieatiiig they'
expand and therefore become specifically lighter. If heat be applied to the upper
surface of liquids or gases, they remain for a long time nearly unaflected ; if
it be applied beneath them, the lower layers of jjarticles become heated and rise,
tlieir place is supplied by others, and so currents upward and downward are
established, whereby the heat is rapidly and uniformly distributed. This process
of convection can rarely have any influence in tlie soil. What we have stated
concerning ft shows, however, in what way the atmosphere may coustantly act
in removin'j heat from the surface of the soil.
190 HOAV CROPS FEED.
acter of the latter determines to a certain degi-ee the na«
tnre of the atmospheric changes. In case of many crops,
the soil is but partially covered, and its peculiarities are
then of direct influence on its temperature.
Relation of Temperature to Color and Texture.— It
is usually stated tliat black or dark-colored soils are sooner
"warmed by the sun's rays than those of lighter color, and
remain constantly of a higher temperature so long as the
sun acts on them. An elevation of several degrees in the
temperature of a light-colored soil may be caused by
strewing its surface with peat, charcoal powder, or vege-
table mould. To this influence may be partly ascribed
the following facts. Lampadius was able to ripen melons,
even in the coolest summers, in Freiberg, Saxony, by
strewing a coating of coal dust an inch deep over the sur-
face of the soil. In Belgium and on the Rhine, it is found
tliat the grape matures best, when the soil is covered with
fragments of black clay slate.
According to Creuze-Latouche, the vineyards along the
river Loire grow either upon a light-colored calcareous
soil, or upon a dark red earth. These two kinds of soil
often alternate with each other within a little distance,
and the character of the wine produced on them is remark-
ably connected with the color of the earth. On the light-
colored soils only a weak, white wine can be raised to ad-
vantage, while on contiguous dark soils a strong claret of
fine quality is made. (Gasparin, Gours cT AgricultKre, 1,
103.)
Girardin found in a scries of experiments ou the cultiva-
tion of potatoes, that the time of their ripening varied
eight to fourteen days, according to the color of the soil.
He found on August 25th, in a very dark humus soil,
twenty-six varieties ripe; in sandy soil, twenty; in clay,
nineteen; and in white lime soil, only sixteen. It is not
difticult, however, to indicate other causes that will at^
count in part for the results of Girardin,
EELATIONS OF THE SOIL TO HEAT. 191
Schiibter made observations ou the temperatures at-
tained by various dry soils exposed to the sun's raySj
according as their surfaces were blackened by a thin
sprinkling of latnp-black or whitened by magnesia. Ilis
results are given in columns 1 and 2 of the following table
{ride p. 196,) from which it is seen that the dark surf\ce
was warmed 13° to 14° more than the white. We like-
wise notice that the character of the very surface deter-
mines the degree of warmth, for, under a sprinkling of
lamp-black or magnesia, all the soils experimented with
became as good as identical in their absorbing power for
the sun's hent.
The observations of Mnlaguti and Durocher prove that
the peculiar temperature of the soil is not always so
closely I'elated to color as to other qualities. They studied
the thermometric characters of the following soils, viz. :
Gai-den earth of dark gray color, — a mixture of sand and
gravel with about five per cent of humus ; a grayish-
white quartz sand ; a grayish-brown granite sand ; a fine
light-gray clay (pipe clay) ; a yellow sandy clay ; and,
finally, four lime soils of different physical qualities.
It was found that Avhen the exposure was alike, the
dark-gray granite sand became the warmest, and next to
this th'' grayish-white quartz sand. The latter, notwith-
standing its lighter color, often acquired a higher temper-
ature at a depth of four inches than the former, a fact to
be ascribed to its better conducting poAver. The black
soils never became so warm as the two just mentioned.
After the black soils, the others came in the following oi--
der : garden soil ; yellow sandy clay ; pipe clay ; lime
soils having crystalline grains ; and, lastly, a pulverulent
chalk soil.
To show what different degrees of warmth soils may
acquire, under the same circumstances, the following max-
imum temperatures may be adduced : At noon of a July
day, when the temperature of the air Mas 90°, a thermoni'
192 HOW CROPS FEED.
eter placed at a depth of a little more than one inch, gave
these results:
In quartz sand 126*
In crystalliue lime soil 115°
In j!farflen soil 114°
In yellow sandy cluy 100°
In pipe clay 94°
In chalk soil 87*
Here we observe a difference of nearly 40° in the noon-
day temperature of the coarse quartz and the chalk soil.
Malaguti and Durochcr found that the temperature of the
garden soil, just below the surface, was, on the average
of day and night together, 6° Fahrenheit higher than that
of the air, but that this higher temperature diminished at
a greater depth. A thermometer buried four inches indi-
cated a mean temperature only 3° above that of the at-
mosphere.
The experimenters do not mention the influence of wa-
ter in affecting these results ; they do not state the degree
of dryness of these soils. It will be seen, however, that
the warmest soils are those that retain least water, and
doubtless something of the slowness with which the fine
soils increase in warmth is connected with the fact that
they retain much water, which, in evaporating, appropri-
ates and renders latent a large quantity of heat.
The chalk soil is seen to be the coolest of all, its tem-
perature in these observations being three degrees lower
than that of the atmosphere at noonday. In hot climates
this coolness is sometimes of gfeat advantage, as appears
to happen in Spain, near Cadiz, where the Sherry vine-
yards flourish. " The Don said the Sherry wine district
was very small, not more than twelve miles square. The
Sherry grape grew only on certain low, chalky hills, where
the earth being light-colored, is not so much burnt ; did
not chap and split so much by the sun as darker and
heavier soils do. A mile beyond these hills the grape de-
teriorates."— (Dickens' Household Words Nov. 13, 1858.)
REJ.ATION.S OF THE SOIL Tu HEAT. 193
in Explanation of tliose ob.sci-vutions we must recall to
TAmd the fact that all bodies are capable of absorbing and
radiating as well as reflecting heat. These properties, al-
though never dissoci;ited fi'oni color, are not necessarily
dependent upon it. They chiefly depend upon the char-
acter of the surface of bo lies. Smooth, polished surfaces
absorb and radiate lieat least readily; they reflect it most
perfectly. Ivadiation and absorption aie opposed to each
other, and the power of any body to radiate, is precisely
equal to its faculty of absorbing heat.
It must be understood, however, that bodies may differ
in their power of absorbing or radiating heat of different
degrees of intensity. Lamp-blaclc absorbs and ra<liatcs
heat of all intensities in the same degree. White-lead
absorbs heat of low intensity (such as radiates from a ves-
sel filled with boiling Avater) as fully as lamp-black, but
of the intense heat of a lamp it absorbs only about one-
half as much. Snow seem-; to resemble white-lead in this
respect. If a bluck cloth or black paper be spread on the
surflice of snow, iipon whicli the sun is shining, it will
inelt much faster iinder the cloth than elsewhere, and this,
too, if the cloth be not in contact with, but suspended
above, the snow. In our latitude every one has had op-
jiortunity to observe that snow thaws most rapidly when
covered by or lying oa black earth. The people of Cham-
ouni, in the Swiss Alps, strew the surface of their fields
Avith black-slate poAvder to hasten the melting of the suoav.
The reason is that snow absorbs heat of low intensity
Avith greatest facility. Tiie heat of the sun is con\'erted
from a higli to a Ioav intensity by being absoi'bed and then
radiated by the black naaterial. But it is not color that
determines this difference of absorjjtive power, for indigo
and Prussian blue, though of nearly the same color, have
very different absorptive powers. So fir, however, ns oi;r
observations extend, it appears that, usually, dark-coloi"ed
soils absorb heat most rapidly, and that the sun's rays
9
134 now CROPS FEED.
have least effect on lipfht-colored soils. (See the table on
p. 196.)
The Rapidity of Change of Temperature independently
of color or moisture has been determined on a number of
soils by Schiibler. A given volume of dry soil was heat-
ed to 145°, a thermometer was placed in it, and the tim3
•Avas observed whicli it required to cool down to 70°, the
temperature of the atmosphere being 61°. The subjoined
table gives his results. In one column are stated the
times of cooling, in another the relative j^ower of retaining
heat or capacity for heat, that of lime sand being assumed
as 100.
Lime sand 3 hours 30 min
Quartz suud 3
Potter's clny 2
Gypsum 3
Clay loam 2
Cliy plow land 2
Heavy clay 2
Pure iiniy clay .' 2
Garden earth 2
Fine carb. lime 2
Humus 1
Magnesia 1
It is seen that the sandy soils cool most slowly, then
follow clays and hea^-y soils, and lastly comes humus.
The order of cooling above given is in all respects
identical with that of Avarming, provided the circumstances
are alike. In other Avords these soils, containing no moist-
ure, or but little, and exposed to heat of low intensity,
Avould be raised through a given range of temperature i:i
the same relative times that they fall tli rough a given
number of degrees.
It is to be particularly noticed that dark humus and white
magnesia are very closely alike in their rate of cooling,
and cool rapidly ; Avhile Avhite Ihne sand stands at the op-
posite extreme, requiring twice as long to cool to the same
extent. These facts strikingly illustrate the great differv
30 min . . .
...100
27 "....
....95.6
41 "....
....76.9
S-t "....
....73.8
30 "....
71.8
27 "
70.1
24 "....
....68.4
19 "....
....66.7
16 "....
....64.8
10 "....
....61.3
43 "....
....49.0
20 "....
....38.0
RELATIONS OF THE SOIL TO HEAT. 195
ence between the absorption of radiant heat of low inten-
sity or its comumnication by conduction on one hand, and
that of high intensity like tlie Iieat of tlic sun on the other.
Retention of Heat. — Other circumstances being equal,
the power of retaining heat (slowness of cooling) is th«
greater, the greater the weight of a given bulk of soil,
i. e., the larger and denser its particles.
A soil covered with gravel cools much more slowly
than a sandy surface, and the lieat which it collects durhig a
sunny day it carries farther into the night ; hence gravelly
soils are adapted for such crops as are liable to fail of rip-
ening in cool situations, especially grapes, as has been
abundantly observed in practice.
Color is without influence'on the loss of heat from the
soil by radiation, because the heat is of low intensity.
The porosity or rougliness of the surface (extent of sur-
face) determines cooling from this cause. Dew, which is
deposited as tlie result of cooling by radiation of lieat into
the sky, forms abundantly on grass and growing vege-
tation, and on vegetable mould, but is more rarely met with
on coarse sand or gravt'l.
Influence of Moisture on the Temperature of the Soil.
— All soils, when thoroughly wet, seem to be nearly alike
in their power of absorbing and retaining Avarmth. This
is due to the fact that the capacity of water for heat is
much greater than that of the soil. We have seen that
lime sand and quartz sand are the sloAvest of all tlie in-
gredients of soils to suffer changes of temperature when
exposed to a given source of heat. (See table, p. 194.)
Now, water is nine times slower than quartz in being
affected by changes of temperature, and as the entire sur-
face of the wet soil is water, whicli is, besides, a nearly
perfect non-conductor of heat, we can understand that ex-
ternal warmth must affect it slowly.
Again, the immense co)tsum,ption of heat In. the forma-
tioiiof i^apor (see note, p. 188) must prevent the wet soil
196
HOW CKOPS FEED.
from ever acqiiiriiig the temirjiature it sliortly attains
Avhen dry.
From this c:iusc tlij difil-rcnce in temperature between
dry and Avet soil miy often amount to from 10° to 18°.
On this p!)int, again, Schiibler furnishes us witli the re-
sults of his experiments. Columns 4 and 5 in the table
below i;ive tlie temperatures whieli the thermometer at-
tained when its bulb was immersed in A-arious soils, both
wet and dry, eaeh having its natural eolor. (Columns 1
and 2 are referred to on i>. 191.)
Whi t-! Black- Differ-
ened.l cned. | ence.
4 5
Surface.
Wet.
i 121. 3' I 12.G° I 95.2
13.7= 96.1
■■rl 14.0" 97.3
...0': 14.4° 97.7
^■n.rrl 13.3' 9S.2
ir,.t) n.r I 9:).i
1-^1. ri 13.3° I 99.1'
100.2^! 122.9
11(1.3 j 124.3
1(17
99.3°
99.3°
Dry.
Differ-
ence.
108. 7°| 13.5°
109.4°' 13.3°
110.5° 13.2°
111.7° 14.0°
111.4° 13.2'
112.6° 13.5°
112.1° 13.0°
112.1° 12.8°
112. 3°i 13.0°
113.0° 13.5°
113.5°! 14.0°
115.3') 13.5°
117. 3°| 13.7°
Magnesia, pure white |133
Fine carbonate of lime, wiiitc.
Gvpsiiri), liiiirlit \vhiti---rav
I'!(.w l:ni(l. ^rav '.. .
Sandv cl.iv.' vcilowisli
(Quartz s^aud, bri-ht yellowi.-li-..,:-.;.,-. . . lO'i.!)
Loam, yclliiwi.'^h .;..". 1(17. s'
Lime saml, wliitish-trray Kiit.'.i
Heavvclav soil. vi'll(nvisli-;,M-av 107.1
Piireclav.blnisb'-urav ' Kii; :;
Oard.'H mould. blnrki'-li-Lrrav UN.:;
81nly mai-l, bniwiiisli-ivd. . .' los,;:
Hiimiis. bnr.viiish-black Ids. .5
"We note that the difference in fovor of the dry earth is
almost nniform.ly 13° to 14°. This difference is the same
as obserA'ed between the whitened and blackened speci-
mens of the ^ame soils. (Column 3.)
We observe, liowever, that the wet soil in no case be-
comes as warm as tlie same soil Avliitened. AVe notice
further that of the wet soils, the dark-colored ones, humus
and marl, are most highly he.ated. Further it is seen that
coarse lime sand (carbonate of lime) acquires 3° higher
temperature than fine carbonate of lime, both Avet, prob-
ably because evaporation pi-oceeded more slowly from the
coarse than from the fine materials. Again it is plain on
com])aring columns 1, 2, and 5, that the gray to yellowish
brown and black colors of all the soils, save the first three,
assist the elevation of temperature, which rises nearly
RELATIONS OP THE SOIL TO HEAT. 197
with the deepening of the color, until in case of humus it
lacks but a few degrees of reaching the warmth of a sur-
face of lamp-black.
According to the observations of Dickinson, made at
Abbot's Hill, Ilertfonlshire, England, and continued
through eight years, 90 per cent of the Avater falling be-
tween April 1st and October 1st evaporates from the sur-
face of tlie soil, only 10 per cent finding its way into
drains laid three and four feet deep. The total quantity
of water ^hat fell during this time amounted to about
2,900,000 lbs. per acre; of this more than 2,000,000 evap-
orated from the surface. It has been calculated that to
evaporate artificially this enormous mass of water, more
than seventy-five tons of coal must be consiimed.
Thorough draining, by loosening the soil and causing a
rapid removal from below of the surplus water, has a most
decided influence, especially in spring time, in warming
the soil and bringing it into a suitable condition for the
support of vegetation.
It is plain, then, that even if we knew with accuracy
■what are the physical characters of a surface soil, and if
we were able to estimate correctly the influence of these
characters on its fertility, still we must investigate those
circumstances which afiect its wetness or dryness, whether
they be an impervious subsoil, or springs coming to the
surface, or the amount and frequency of rain-falls, taken
in connection with other meteorological causes. We can-
not decide that a clay is too wet or a sand too dry, until
we know its situation and the climate it is subjected to.
The gre'at deserts of the globe do not owe their barren-
ness to necessary poverty of soil, but to meteorological
influences — to the continued prevalence of parching winds,
and the absence of mountains, to condense the atmospheric
water and establish a system of rivers and streams. This
is not the place to enter into a discussion of the causes
that may determine or modify climate ; but to illustrate
198 HOW CROPS FEEi).
the effect that may be iiroduced by means within human
control, it may be stated that previous to the year 1821,
the Frencli district Provence was a fertile and well-water-
ed region. In 1822, the olive trees which were largely
cultivated there were injured l)y frost, and the inhabitants
began to cut them up root and branch. This amounted
to clearing off a forest, and, in consequence, the streams
dried up, and the productiveness of the country was seri-
ously diminished.
The Angle at which the Sun's Rays Strike a Soil is
of great influence on its temperature. The more this ap-
proaches a right angle the greater the heating effect. In
the latitude of England the sun's heat acts most power-
fully on surfaces having a southern exposure, and which
are inclined at an angle of 25° and 30°. The best vine-
yards of the Ehine and Neckar are also on hill-sides, so
situated. In Lapland and Spitzbergen the southern
side of hills may be seen covered with vegetation, while
lasting or even perpetual snow lies on their northern in-
clinations.
The Influence of a Wall or other Reflecting Surface
upon the warmth of a soil lying to the south of it was
observed in the case of garden soil by Malaguti and
Durocher. The highest temperature indicated by a ther-
mometer placed in this soil at a distance of six inches from
the wall, (iui-ing a series of observations lasting seven days
(April, 1852), Avas 32° Fahrenheit higher at the surface,
and 18° higher at a depth of four inches than in the same
soil on the north side of the wall. The average temper-
ature of the former during this time was 8° higher than
that of the latter. In another trial in March the difference
in average temperature between the southern and north-
ern exposures was nearly double this amount in favor of
the former.
As is well known, fruits which refuse to ripen in cold
climates under ordinary conditions of exposure may attaia
The free water of the soil. 199
perfection when trained against the sunny side of a «all.
It is tlius that in the nortli of England pears and pkims
are raised in the most unfavorable seasons, and that the
vineyards of Fontainehleau produce such delicious Chas-
selas grapes fur the Paris market, the vines being trained
against walls on the Tliomery system.
In the Rhine district grape vines are kept low and as
near the soil as possible, so that the heat of the sun may be
reflected back upon them from the ground, and the ripen-
ing is then carried through the nights by the heat radiated
from the earth. — {Journal Highland and Agricidtural
Society, July, I808, p. 347.)
Vegetation. — Malaguti and Durocher also studied the
effect of a sod on the temperature of the soil. They ob-
served that it hindered the warming of the soil, and in-
deed to about the same extent as a layer of earth of three
inches depth. Thus a thermometer four inches deep in
green-sward acquires the same temperature as one seven
inches deep in the same soil not grassed.
CHAPTER V.
THE SOIL AS A SOURCE OF FOOD TO CROPS.—
INGREDIENTS WHOSE ELEMENTS ARE OF
ATMOSPHERIC ORIGIN.
I
§ 1.
THE FREE WATER OF THE SOIL IN ITS RELATIONS TO
VEGETABLE NUTRITION.
Water may exist free in the soil in three conditions,
which we designate i-cspectively hydrostatic, capillary,
and hygroscopic.
Hydrostatic or Flowing* Water is water visible as
I. e., capable of flowing.
300 now CROPS FEED.
such to the eye, and free to obey the laws of gravity and
motion. T\Tien the soil is saturated by rains, melting
snows, or by overflow of streams, its pores contain liy-
drost;itic water, whicli sooner or later sinks away into the
subsoil or escapes into drains, streams, or lower situations.
Bottom Water is permanent hydrostatic water ^ reached
nearly always in excavating deep soils. The surface of
water in a well corresponds with, or is somewhat below, the
upper limit of bottom water. It usually fluctuates in
level, rising nearer tlie surface of the soil in wet seasons,
and receding during drought. In general, agricultural
plants are injured if their roots be immersed for any length
of time in hydrostatic water; and soils in which bottom
water is found at a little depth during the season of
growth are unprofitable for culture.
If this depth be but a few inches, we have a bog,
swamp, or sw\ale. If it is one and a half to three feet,
and the surface soil be light, gravelly, or open, so as to
admit of rapid evaporation, some plants, especially grasses,
may flourish. If at a constant depth of four to eight feet
under a gravelly or light loamy soil, it is favorable to
crops as an abundant source of water.
Heavy clays, which retain hydrostatic water for a long
time, being but little permeable, are for the same reasons
unfavorable to most crops, unless artificial provision be
made for removing the excess.
Rice, as we have seen, (H. C. G., p. 252), is a plant
which grows well with its roots situated in water. Hen-
rici's experiment with the raspberry (H. C. G., p. 254),
and the frequent finding of roots of clover, turnips, etc.,
in cisterns or drain pipes, indicate that many or all
agricultural plants may send down roots into the bottom
water for the purpose of gathering a sufficient supply of
this necessary liquid.
Capillary Water is that which is held in the fine pores
of the soil by the surface attraction of its particles, as oil
TDK FUKK WATlCn OF T;iE SOIL. f20l
is held in tlie Avick of ;i lamp. The adliesion of the water
to the particles of eurLli suspends the flow of the liquid,
and it is no longer subject to the laws of hydrostatics.
Capillary water is usually designated as moisture, though
a soil saturated with capillary water would be, in most
cases, wet. The cai)illary power of various soils has al-
ready been noticed, and is for coarse sands 25° |„ ; for
loams and clays, 40 to 70° |„ ; for garden mould and humus,
much higher, 90 to 300 °|„. (See p. 180.)
I'^or a certain distance above bottom Avater, the soil is
saturated with capillary water, and this distance is the
greater, the greater the cajiillary power of the soil, i. e.,
the finer its pores.
Capillary water is not visible as a distinct liquid layer
on or between the particles of soil, but is still recogniza-
ble by the eye. Even in the driest weather and in the
driest sand (that is, when not shut off" from bottom water
by too great distance or an intervening gravelly subsoil) it
may b'3 found one or a few inches below the surface where
the soil Jool:s moist — has a darker shade of color.
Hygroscopic Water is that which is not perceptible to
the senses, but is appreciated by loss or gain of weight in
the boily which acquires or is deprived of it. (11. C. G.,
p. 54.) The loss experienced by an air-dry soil when kept
for some hours at, or slightly above, the boiling point
(212° F.,) expresses its content of hygroscopic water.
This quantity is variable according to the character of the
soil, and is constantly varying with the temperature; in-
creasing during the night when it is collected from the at-
mosphere, and diminishing during the day when it returns
in part to the air. (See p. 104.) The amount of hygros-
copic water ranges from 0.5 to 10 or more per cent.
Value of these Distinctions. — These distinctions be-
tween hydrostatic, capillary, and hygroscopic water, are
nothing absolute, but rather those of degree. Hygroscopic
water is capillary in all respects, save that its quantity is
202 ilow (R^ps pfiER.
small, and its adhesion to the particles of soil more firm
for that reason. Again, no precise boundary can always
he drawn between capillary and hydrostatic water, espe-
cially in soil having fine i)ores. The terms are neverthe-
less useful in conveying an idea of the degrees of wet-
ness or moisture in the soil.
Roots Absorb Capillary or Hygroscopic Water,— It is
from capillary or hygroscopic water that the roots of most
agricultural plants chiefly draw a supply of this liquid,
though not infrequently they send roots into wells and
drains. The physical characters of soils that have been
already considered suffice to explain how the earth acquires
this water ; it here I'emains to notice how the plant is re-
lated to it.
As we have seen (pp. 35-38), the aerial organs appear
incapable of taking up either vapor or liquid water from
the air to much extent, and even roots continually exhale
vapor without absorbing any, or at least without being able
to make up the loss which they continually suffer.
Transpiration of Water through Plants. — It is a most
familiar fact that water constantly exhales from the surface
of the ])lant. The amount of this exhalation is often very
great. Hales, the earliest observer of this yjhenomenon,
found that a sunflower whose foliage had 39 square feet
of surface, gave off in 24 hours 3 lbs. of water. A cab-
bage, whose surface of leaves equaled 19 square feet, ex-
haled in the same time very nearly as much. Schleiden
found the loss of water from a square foot of grass-sod to
be more than 1^ lbs. in 24 hours. Schiibler states that in
the same time 1 square foot of pasture-grass exhaled
nearly 5^ lbs. of water. In one of Knop's more recent
experiments, {Vs. St., VI, 239), a dwarf bean exhaled
during 23 days, in September and October, 13 times its
weight of water. In another trial a maize-plant transpir-
ed 36 times its weight of water, from May 22d to Sept.
4th. According to Knop, a grass-plant will exhale its own
TliE FREE WATEU OP THE SOIT.. 203
weight of water in 24 liours of hot and dry summer
weather.
Tlie water exhaled from tlie leaves must be constantly
supplied by absorption at the roots, else the foliage soon
becomes flabby or wilts, and finally dies. Except so far
as water is actually formed or fixed within the plant, its
absorption at the roots, its passage through the tissues,
and its exhalation from the foliage, ai-e nearly equal in
quantity and niutually dependent during the healthy ex-
istence of vegetation.
Circumstances that Influence Transpiration.— ^ Tlie
structure of the leaf, including the character of the epi-
dermis, and the number of stomata as they aflfect exhala-
tion, has been considered in " How Crops Grow," (pp.
286-8).
h. The physical conditions which facilitate evapora-
tion increase the amount of water that passes through
the plant. Exhalation of water-vapor proceeds most
rapidly in a hot, dry, windy summer day. It is nearly
checked when the air is saturated Avith moisture, and va-
ries through a wide range according to the conditions just
named.
0. The oxidations that are constantly going on, within
the plant may, under certain conditions, acquire suflicient
intensity to develop a jierceptible amount of heat and
cause the vaporization of water. It has been repeatedly
noticed that the process of flowering is accompanied by
considerable elevation of temperature, (p. 24). In general,
however, the opposite process of deoxidation preponder-
ates with the plant, and this must occasion a reduction of
tem.perature. These interior changes can have no apprecia-
ble influence upon transpiration as compared Avith those
that depend upon external causes. Sachs found in some
of his experiments (p. 3G) that exhalation took place from
plants confined in a limited space over water, Sachs be-
204- now <jRops FBEa
lieved that tlie air surrounding tlie plants in these experi-
ments was saturated Avith vapor of Avater, and concluded
that heat was developed within the plant, which caused
vaporization. More recently, Boelun [Sltzungsherichte
der Wiener Akad., XLVITI, 15) has made probable that
the air was not fully or constantly saturated Avitli moist-
ure in these experiments, and by taking greater precau-
tions has arrived at the conclusion that transpiration abso-
lutely ceases in air saturated with acpieous A\apor.
d. The condition of the tissues of the x)lant^ as depend-
ent upon their age and vegetative activity, likewise has a
marked effect on transpiration, Lawes* and Knop both
found that young plants lose more water than older ones.
This is due to the diminished power of mature foliage to
imbibe and contain Avater, its cells becoming choked up
with growth and inactive.
e. The character of the tnedium in xohich the roots are
situated also remarkably influences the late of transpira-
tion. This fact, first observed by Mr. Lawes, in 1S50, loc.
cit., was more distinctly brought out by Dr. Sachs at a
later period. ( Vs. jSt., I, p. 203.)
Sachs experimented on A'arious i)lants, amz. : beans,
squashes, tobacco, and maize, and observed their transpi-
ration in weak solutions (mostly containing one per cent)
of nitre, common salt, gypsum, (one-fifth per cent solu-
tion) and sulphate of ammonia. He also experimented
with maize in a mixed solution of jihosphate and silicate
of potash, sulphates of lime and magnesia, and common
salt, and likewise observed tlie effect of free nitric acid
and free j^otash on the squash ])lant. The young plants
were either germinated in the soil, then removed from it
and set Avith tlieir rootlets in the solution, or else Avere
kept in the soil and Avatered with the solution. The glass
* Experirnental Investigation into the Amount of Water given ojf by Plant$
flaring tlieir Growtfi, by J. B. Lawes, of Rothauistead, London, 1S50.
THE FKEE WATEll OF THE SOIL. 205
vessel containini^ the plant and solution was closed above,
around the stem of the jilant, by glass plates and cement,
so that no loss of Mater could occux* except through the
l^lant itself, and tliis loss Avas ascertained by daily weigh-
ings. The result was that all the solutions mentioned,
excejit that of free nitric acid, quite imiformly retarded
transpiration to a degree varying from 10 to 90 i)er cent,
"Nvhile the free acid accelerated the transpiration in a cor-
responding manner,
Sachs experimented also with four tobacco plnnts, two
situated in coarse sand and two in yellow loam. The
plants stood side by side exposed to the same temperature,
etc., and daily weigliings were made during a week or
more, to learn tlie amount of exI)alation. The result was
that the total loss, as Avell as the daily loss in the majority
of weighings, was greater from the plant growing in loam,
altliough through certain short 2>eriods the opposite was
noticed.
f. Il^e temperature of the soil considerably affects the
rate of transpiration by influencing the amount of absorp-
tion at the roots. Sachs made a number of Aveighings up-
on tAvo tobacco plants of equal size, potted in portions of
the same soil and liaving their foliage exposed to the same
atmosphere. After observing their relative transpiration
when their roots Avere at the same temperature, one pot
Avas Avarmed a number of degrees, and the result Avas in-
variably observed that elevating the temjserature of the
soil increased the transpiration.
The same observer subsequently noticed the entire sup-
pression of absorption by a reduction of temperature tc
41° to 43° F. A number of healthy tobacco and squash
plants, rooted in a soil kept nearly saturated Avith Avater,
were gioAving late in November in a room, the tempera-
ture of which fell at night to the point just named. In
the morning the leaves of these plants Avere so wilted
that they hung doAvn like Avet cloths, as if the soil Avere
206 HOW CROPS FEED.
completely dry, or tliey had been for a long time acted
upon by a i)Owerful sun. Since, however, the soil was
moist, the wilting could only arise from the inability of
the roots to absorb water as rapidly as it exhaled from
the leaves, owing to the low temperature. Further ex-
periments showed that warming the soil in which thj
wilted plants stood, restored the foliage to its [jroper tur-
gidity in a short time, and by surrounding the soil of a
fresh plant with snow, the leaves wilted in three or four
hours.
Cabbages, winter colza, and beans, similarly circum-
stanced, did not wilt, showing that diiferent plants are un-
equally affected. The general rule nevertheless appears to
be established that within certain limits the root absorbs
mere vigorously at high than at low temperatures.
The Amount of Loss of Water of Vea^etation in Wilt-
ing has been determined by Ilesse ( Vs. St., I, 248) in
case of sugai'-beet leaves. Of two similar leaves, one,
gathered at evening after several days of dryness and sun-
shine, contained 85.74°!^ of water; the other, gathered
the next morning, two hours after a rain storm, yielded
89.57° |„. The difference was accordingly 3.8° |„. Other
observations corroborated this result.
Is Exhalation Indispensable to Plants] — It was for
a long time supposed that transpiration is indispensable
to the life of plants. It was taught that the water which
the i^lant imbibes from the soil to replace that lost by ex-
halation, is the means of bringing into its roots the min-
eral and other soluble substances that serve for its nutri-
ment.
There are, however, sti'ong grounds for believing that
the current of water Avhich ascends through a plant moves
independently of the matters that may be in solution,
either without or within it ; and, moreover, the motion of
soluble matters from the soil into the plant may go on,
TUB FKEE WATEK OF THE SOIL. 207
although there be no ascending .-Kiueous curi-ent. (H. C.
G., ijp. 288 and 340.)
In accordance Avith these views, vegetation grows as Avell
in the confined atniosplierc of green-houses or of Wardian
Cases, Avhere tlie air is for tlie most part or entirely satu-
rated with vapor, so that transpiration is reduced to a mini-
mum, as in the free air, where it may attain a maximum.
As is well known, the growth of field crops and garden
'Tegetables is often most rapid during damp and showery
weather, when the transpiration must proceed with com-
parative slowness.
While the above considerations, together with the asser-
tion of Knop,that leaves lose for the first half hour nearly
the same quantities of water under similar exposure,
whether they are attached to the stem or removed from
it, whether entire or i:i fragments, would lead to the con-
clusion that transpiration, which is so extreinely variable
in its amount, is, so to speak, an accident to the plant and
not a process essential to its existence or welfare, there
are, on the other hand, facts which appear I > indicate the
contrary.
In certain experiments of Sachs, in which the roots of
a bean were situated in an atmosphere nearly saturated
with aqueous vapor, the foliage being exposed to the air,
although the plant continued for two months fresh and
healthy to ajjpearance, it remained entirely stationary in
its development. ( Vs. St., I, 237.)
Knop also mentions incidentally {Vs. St., I, 192) that
beans, lupines, and maize, die when the whole pU^it is
kept confined in a vessel over water.
It is not, however, improbable that the cessfition of
growth in the one case and the death of the plants in the
other were due not so much to the checking of transpii-a-
tion, which, as Ave have seen, is never entirely suppressed
under these circumstances, as to the exhaustion of oxygen
or the undue accumulation of carbonic acid in the narrow
208 HO"\v CKors feed.
and confined atmosphere in wliich these results were
noticed.
On the whole, then, "\ve conclude from the evidence be-
fore us that transpiration is not necessary to vegetation,
or at least fulfills no very important oflices in the nutrition
of plants.
The entra'.K-e of water into the plant and the steady
maintenance of its proper content of this substance, under
all circumstances is of the utmost moment, and leads us
to notice in the next place the
Direct Proof that Crops can Absorb from the Soil
enough Hygroscopic Water to Maintain their Life.— Sachs
sufiercd a young bean-plant standing in a pot of very reten-
tive (clay) soil to remain without watering until the leaves
began to wilt. A high and spacious glass cylinder, having
a layer of water at its bottom, Avas then provided, and the
pot containing the Avilting plant was supported in it, near
its top, while the cylinder was capped by two semicircular
plates of glass which closed snugly about the stem of the
bean. Tlie jiot of soil and the roots of the plant were
thus enclosed in an atmosphere Avhich was constantly sat.
urated, or nearly so, with w^atery vapor, while the leaves
were fully exposed to the free air. It Avas now to be ob-
served Avhether tlie water that exhaled from the leaves
could be supplied by the hygroscopic moisture Avhich the
soil should gather from the damp air enveloping it. This
proved to be the case. The leaves, previously Avilted, re-
covered their proper turgidity, and remained Iresh during^
the two months of June and July.
Sachs, having shown in other experiments that plants
situated precisely like this bean, save that the roots are not
in contact with soil, lose Avater continuously and have no
jiower to recover it from damp air (p. 3G) thus giA'cs us
demonstration that the clay soil Avhich condenses vapor in
its pores and holds it as hygroscopic water, yields it again
to the plant, and thus becomes the medium through Avhich
THE FKEK WATEK OF THE SOIL. 209
water Is continually carriccl from the atmosphere into
vegetation.
In a similar experiment, a tobacco plant was employed
■which stood in a soil of humus. This material was also
capable of supplying the plant with water by virtue of
its hygroscopic power, but less satisfactorily than tlie clay
As already mentioned, these plants, while remaining fresh,,
exhibited no signs of growth. This may be due to the
consumption of oxygen by the roots and soil, or possibly
the roots of plants may I'equire an occasional drenching
with liquid water. Further investigations in this direc-
tion are reqiiired and promise most interesting results.
What Proportion of the Capillary and Hygroscopic
Water of the Soil may Plants Absorb, is a question that
Dr. Sachs has made the only attempts to answer. When
a ])lant, whose leaves are in a very moist atmosphere, wilts
or begins to wilt in the night time, when therefore trans-
piration is reduced to a minimum, it is because the soil no
longer yields it water. The quantity of water still con-
tained in a soil at that juncture is that which the plant
cannot remove from it, — is that which is unavailable to
vegetation, or at least to the kind of vegetation experi-
mented with. Sachs made trials on this principle with
tobacco plants in three different soils.
The plant began to wilt in a mixture of hlack huniKS
(from beech-wood) and sand^ when the soil contained
12.3" |„ of water.* This soil, however, was capable of
holding 46° |„ of capillary water. It results therefore that
of its highest content of absorbed water 33.7" |„ (=46-12.3)
was available to the tol>acco jjlant.
Another plant began to wilt on a rainy night, while the
loam it stood in contained 8°| „ of water. This soil was
able to absorb 52.1°! ^ of water, so that it might after
Ascertained liy diyiiija'at 31
210 HOW CROPS FEED.
saturation, furnish the tobacco }>lant with 44.1"!^ of its
weiglit of water.
A coarse sand that could hohl 20.8° ]„ of water was
found to yield all but 1.5° ]„ to a tobacco plant.
From these trials we gather with at least approximate
accuracy the power of the plant to extract water fro:'
these several soils, and by difference, the quantity of w;>
ter in them that was unavailable to the tobacco plant.
How do the Roots take Hyi^roscopic Water from the
Soil ? — The entire plant, when living, is itself extremely
hygroscopic. Even the dead plant letains a certain pro-
portion of water with great obstinacy. Thus wheat,
maize, starch, straw, and most air-dry vegetable substances,
contain 12 to 15" |^ of water ; and when these matters are
exposed to damp air, they can take up much more. Ac-
cording to Trommer {Bodenkwide., p. 270), 100 parts of
the following matters, when dry, absorb from moist air iu
12 24 4S 72
hours.
Fine cut barley straw,
15
24 34
45 parts of water.
" u rye
12
20 27
29 " " "
" " white unsized paper,
8
12 17
19 " " "
As already explained, a body is hygroscopic because
there is attraction between its particles and the particles
of water. The form of attraction exerted tlius among
different kinds of matter is termed adhesive attraction, or
simply adhesion.
Adhesion acts only through a small distance, but its in-
tensity varies greatly within this distance. If we attempt
to remove hygroscopic water from starch or any similar
body by drying at 212°, we shall find that the greater
part of the moisture is easily expelled in a short time,
but we shall also notice that it requires a relatively much
longer time to expel the last portions. A general law of
attraction is that its force diminishes as the distance bo-
tweeu the attracting bodies increases. This has been ex-
THE FltEK ■WATJiU OK THE SOIL. 211
actly tlemonstrated in case of the force of gravity and
electrical attraction, which act through great intervals of
space.
We must therefore suppose that -when a mass of hygro-
scopic matter is allowed to coat itself with water by the
exeicise of its adhesive attraction, the Liver of aqueous
particles which is in nearest contact is more strongly held
to it than the next outer layer, and the adhesion diminish-
es with the distance, itntil, at a certain point, still too
small * for us to perceive, the attraction is nothing, or is
neutralized by other opposing forces, and further adhesion
ceases.
Suppose, no\v, we bring in contact at a single point two
masses of the same kind of matter, one of Avhich is satu-
rated with hygroscopic water ;ind the other is perfectly dry.
It is plain tliat the outer layers of water-particles adhering
to the moist body come at once Avithin the range of a
more powerful attraction exerted by the very surface of
the dry body. The external particles of water attached
to the first must then pass to the second, and they must
also distribute themselves equally over the surface of the
latter; and this motion must go on until the attraction
of the two surfaces is equally satisfied, and the water is
equally distributed according to the surface, i. e., is uni-
form o\'er the whole surface.
If of two diff"erent bodies put in contact (one dry and
one moist) the surfaces be equal, but the attractive force
of one for water be twice that of the other, then motion
must go on until the one has appiopriated two-thirds, and
the other is left with one-third the total amount of water.
When bodies in contact have thus equalized the water
at their disposal, they may be said to be in a condition of
hygroscopic equWhv'ivm. Any cause which disturbs this
equilibrium at once sets up motion of the hygroscopic
water, which always j^roceeds from the more dry to thy
less dry body.
212 HOAV CHOI'S FEED.
The application of these principles to the question be-
fore us is apparent. The young, active roots tliat are in
contact with the soil are eminently hygroscopic, as is de-
monstrated by the fact that they supply the plant with
large quantities of water when the soil is so dry that it
has no visible moisture. They therefore share with the
soil the moisture which the latter contains. As water
evaporates from the surface of the foliage, its place is
supplied by the adjacent portions, and thus motion is es-
tablished within the plant which j^ropagates itself to the
•roots and through these to the soil.
Each particle of water that flies ofl" in vapor from the
leaf makes room for the entrance of a particle at the root.
If the soil and air have a surplus of water, the plant will
contain more ; if the soil and air be dry, it will contain
less. Within certain narrow limits the supply and waste
may vary without detriment to the plant, but Avlien the
loss goes on more rapidly than the supply can be kept up,
or when the absolute content of water in the soil is re-
duced to a certain point, the plant shortly Avilts. Even
then its content of water is many times greater than that
of the soil. The living tobacco plant cannot contain less
than 80°!^ of water, while the soils in Sachs' experiments
contained but 12.3" |„ and 1.5° |„ respectively. When fully
air-dry, vegetable matter retains IS'l^to 15° j^, of water,
while the soil similarly dry rarely contains more thaq
The plant therefore, especially when living, is much
more hygroscopic than the soil.
If roots are so hygroscopic, why, it may be asked, do
they not directly absorb vapor of Avater from the air of
the soil ? It cannot be denied that both tlie roots and fo-
liage of plants are capable of ti)is kind of absorption,
and that it is taking place constantly in case of the roots.
The experiments before described prove, liowcver, tlat
the higher oi'ders of plants absorb very little ia this W~^y«
THE FREE WATEU OF THE SOn,. 213
too little, in fact, to l)o estimated by tlic methods hitherto
employed. Sachs explains this as follows : Assuming that
the roots have at a given temperature as strong an attrac-
tion for Avater in the state of vapor as for liquid water, the
amount of each taken up in a given time under the same
circumstances would be in pioportion to the weight of
each contained in a given space. A cubic inch of water
yields at 21'2° nearly a cubic foot (accurately, 1,696 times
its volume, the barometer standing at 29.92 inches) of
vapor. We may then a><sumc that the absorption of liq-
uid or hygroscopic water proceeds at least one thousand
times more rapidly than that of vapor, a diffei-ence in
rate that enables us to comprehend why a plant may gain
water by its roots from the soil, when it would lose water
by its roots were they simply stationed in air saturated
with vapor.
Again, the soil need not be more hygroscopic than roots,
to supply the latter with water. It is important only that
it present a sufficient surface. As is well known, a plant
requires a great volume of earth to nourish it properly,
and the root-surface is trifling, compared to the surface
of the particles which compose the soil.
Boussingault found by actual measurement that, accord-
ing to the rules of garden cultuie as practiced near Stras-
burg, a dwarf bean had at its disposition 57 pounds of
soil; a jiotato plant, 190 pounds; a tobacco plant, 470
pounds ; and a hop plant, 2,900 pounds. These weights
correspond to about 1, 3, 7, and 50 cubic feet respectively.
The Quantity of Water in Vegetation is influenced by
that of the Soil. — De Sanssure observed that plants grow-
ing in a diy lime soil contained less water than those from
a loam. It is well known that the grass of a wet summer
is taller and more succulent, and the green crop is heavier
than that fi-om the same field in a dry summer. It does
not, however, make much more hay, its greater weight
consisting to a large degree of water, which is lost in dry
S14 HOW CROPS FEED.
ing. Kitthauscn gives some data concerning two clover
crops of the year 1854, from a loamy sand, portions of
which were manured, one with ashes, others with gypsum.
The following statement gives the produce of the nearly*
fresh and of the air-dry crops.
Weight in pounds per acre.
Fresh.
Air-dry.
Water
lost in drying.
Crop I, manured with ashes,
14,903
5,182
9,721
" '• unmaiiured.
12,380
5,418
6,962
Crop II. manured with gypsum,
22,256
4,800
17,456
" " unmanured.
18,815
5,190
13,625
It is seen that while in both cases the fresh manured
crop greatly outweighed the unmanured, the excess of
weight consisted of water. In fact, the unmanured plots
yielded inore hay than the manured. The manured clover
was darker in color than the other, and the stems were
large and hollow, i. e., Ly rapid growth the pith cells were
broken away from each other and formed only a lining
to the stalk, while in the unmanured clover the pith re-
mained undisturbed, the stems being more compact in
structure. (H. C. G., p. 369.)
The Quantity of Soil-water most favorable to Crops
has been studied by Ilienkoff and Ilellricgel. The former
{Ann. der. Chem. k. Ph. 136, p. 160,) experimented with
buckwheat jjlants stationed in pots filled with garden
eartli. The pots were of the same size and had the same
exposure at the south side of an apartment. The plants
received at each waterinsc in
:*ot
No.
1,
'1.
liter of
water
((
<(
2,
'L
((
((
(C
u
3,
'I
a
u
((
(C
4,
•L
((
u
((
((
5,
'L
u
«
* The clover was collected from the surface of a Saxon square ell, and was
somewhat wilted before coming into Ritthauseu's hands. The quantities above
given arc calculated to Euglith acres and pounds.
THE FREE AVATER OF* THE SOIL.
21.1
The waterings were made simultaneously at tbemonient
when all the Avater previously given to No. 1 was Ab-
sorbed by the soil. During the 67 days of the experi-
ment the plants were watered 17 times. The subjoined
table gives the results :
Weight of
Weight of
fresh Cj'ops in
dry Crops in
Number of
Liters of
No. of pot.
grams.
grams.
Seeds.
water used.
STRAW. 1 SEEDS.
1
27 99
4.52
1.68
Ill
25.0
2
65.05
8.47
5.47
2&3
12.5
3
24.95
4.55
1.73
93
6.25
4
9.98
1.41
0.52
37
3.12
5
2.30
0.30
0.09
12
1.56
The experiment demonstrates that the quantity of
Water supplied to a plant has a decided effect upon the
yield. Pot No. 2 was most favorably situated in this re-
spect. No. 1 had a sni-plus of Avater and the other pots
received too little. The experiment does not teach what
proportion of water in the soil was most advantageous,
for neither the weight of tlie soil nor the size of the pot
is mentioned.
Hellriegel {Chem. Acker smann, 1868, p. 15) experiment-
ed with wheat, rye, and oats, in a pure sand mixed with a
sufficiency of plant-food. The sand when saturated with
water contained 25° l„ of the liquid. The following table
gives further particulars of his experiments and the re-
sults. The weights are grams.
WATER IN THE SOIL.
YIELD OP WHEAT.
YIELD OF RYE.
YIELD OP OATS.
In jier cent
of Soil.
III per cent
of retentive
imver.
Straw
and
Chaff.
Grain.
Straio
and
Chaff.
Grain.
Straw
and
Chaff.
Grain.
2K2-5
5 -10
10 -15
15 -20
10-20
20-40
40-60
60-80
7.0
15.1
21.4
23.3
2.8
8.4
10.3
11.4
8.3
11.8
15.1
16.4
3.9
8.1
10.3
10.3
4.2
11.8
13.9
15.8
1.8
7.8
10.9
11.8
In each case the proportion of water in the soil was
preserved Avithin the limits given in the first column of
the table, throughout the entire period of growth. It is
seen that in this sandy soil 10-15 per cent of water ena-
216 now CROPS feed.
bled rye to yield a maximum of grain and brought wheat
ana oats very closely to a maximum crop. Hcllriegel no*
ticed tliat the plants exhibited no visible symptoms of
deficiency of water, except through stunted growth, in
any of these experiments. Wilting never took place ex-
3ept wlien the supply of water was less than 2' \,^ per cent.
Grouven {Ueber den Zuscwimenhcmc/ zwischen Wit-
teriou/, JBoden und Daitgung in ihrem Einjlusse auf die
Quant itiit und Qualitut der Erndten., Glogali, 186s) gives
the results of an extensive series of field trials, in which,
among other circumstances, the influence of water upon
the crops was observed. His discussion of the subject is
too detailed to reproduce in this treatise, but the great
influence of the supply of water (by rain, etc.,) is most
strikingly brought out. The experimental fields were
situated in various parts of Germany and Austria, and
were cultivated with sugar beets in 186:2, under the same
fertilizing applications, as regards both kind and quantity
Of 14 trials in which records of the rain-fall were kept,
the 8 best crops received from the time of sowing. May
1st, to that of harvesting, Oct. 15th, an average quantity
of rain equal to 140 Paris lines in depth. The 6 poorest
crops received in the f^ame time on the average but 115
lines. During the most critical period of growth, viz.,
between the 20th of June and the 10th of September, the
8 best crops enjoyed an average rain-fall of 90.7 lines,
while the 6 poorest received but 57.7 lines.
It is a well recognized fact that next to temperature,
the water supply is the most influential factor in the prod-
uct of a crop. Poor soils give good crops in seasons ot|
plentiful and well-distributed rain or when skillfully irri-^
gated, but insufficient moisture in the soil is an evil that'
no supplies of plant-food can neutralize.
The Functions of Water in the Nourishment of
Vegetation) so far as we know them, are of two kmd&
THE FIIEE AVATKIi OP THE SOIL. 217
111 the first iilaoe it is an unfailing and sufficient source of
its elements, — hydrogen and oxygen, — and undoubtedly
enters directly or indirectly into chemical combination
with the carbon taken up from cnrbonic acid, to form sug-
ar, starch, cellulose, and other carhohydi-ates. In the
second place it performs important physical offices ; is the
vehicle or medium of all tlie circulation of matters in the
plant ; is directly concerned, it would appear, in imbibing
gaseous food in the foliage and solid nutriment through
the roots ; and by the force with which it is absorbed, di-
rectly influences the enlargement of the cells, and, per-
haps, also the direction of their expansion, — an effect shown
by the facts just adduced relative to the clover crops ex-
amined by Ritthauseii.
Indirectly, also, Avater performs the most important ser-
vice of continually solving an<l making accessible to crops
the solid matters in the vicinity of their roots, as has
been indicated in tlie chapter on the Origin of Soils.
Combined Water of the Soil. — As already stated, there
may exist in tlie soil compounds of which water is a chemi'
cal component. True clay (kaolinite) and the zeolites, as
well as the oxides of iron that result from weathering, con-
tain chemically combined water. Hence a soil which has
been totally deprived of its hygroscopic Avater by drying
at 212°, may, and, unless consisting of pure sand, does,
yield a further small amount of water by exposure to a
higher heat. This combined water has no direct influence
on the life of the plant or on the character of the soil, ex^
cept so far as it is related to the properties of the com
pounds of which it is an ingredient.
§2.
THE AIR OF THE SOIL.
As to the free Oxygen and Nitrogen which exist in the
interstices or adhere to the particles of the soil, there ia
10
218 HOW CROPS FEED.
little to !id(l here to wliat lius been rcinarkt'd in previous
paragrajths.
Free Oxygen, as De Saussure and Traube have shown,
is indispensable to growth, and must tlierefore be access-
ible to the roots of plants.
The soil, being eminently i)orous, condenses oxygen,
Blumtritt and KeicJiardt indeed found no considei-able
amount of condensed oxygen in most of the soils and sub-
stances they examined (p. 167) ; but the experiments of
Stenhouse (p. 169) and the well-known deodorizing effects
of the soil upon fecal matters, leave no doubt as to the
fact. The condensed oxygen must usually spend itself in
chemical action. Its proportion would appear not to be
large ; but, being replaced as rapidly as it enters into com-
bination, the total quantity absorbed may be considera-
ble. Organic matters and lower oxides are thereby ox-
idized. Carbon is converted into carbonic acid, hydrogen
into water, protoxide of iron into peroxide. The upper
portions of the soil are constantly suffering change by the
action of free oxygen, so long as any oxidable matters
exist in them. These oxidations act to solve the soil and
\ender its elements available to vegetation. (See p. 131.)
Free Nitrogen in the air of tiie soil is doubtless indiffer-
ent to vegetation. The question of its conversion into
nitric acid or ammonia will be noticed presently. (See p.
259.)
Carbonic Acid. — The air of the soil is usually richer in
carbonic acid, and poorer in oxygen, than the normal at-
mosphere, while the proportion (by volume) of nitrogen
is the same or very nearly so. The proportions of car-
bonic acid by weight in the air included in a variety of
Boils have alrea'ly been stated. Here follow the totaJ
quantities of this gas and of air, as well as tlie composi-
tion of the latter in 100 parts by volume, as determined by
flTE All; OI' IITE SOIL.
210
Boussingault and Lewy. {Memoires de Chlmie Ayricole^
etc., p. 3G9.)
Cmnposilion of the
air ill tibe soil in 100
imris by volume.
£«";.- Ox- Nitro-
aJid. y^'"- sen.
Sandy subsoil of lorost 4410
Loamy '• " "
Surface soil " "
Clayey " of artichoke field
Soil o"f asparagus bed not manured lor one yeari 11182
newly manured \ 11182
Sandy soil, six days after manuring [of rain
" " ten " " " three days
Vegetable mold-compost
11783
11783
21049
172
257
1144
772
0.24
0.79
0.87
O.fifl
0.74
1.54
2.21
9.74
3.64
79.55
79.52
79.35
19.02} 80.24
18.80J 79.66
10.35 79.91
16.45 79.91
air
above the soil in 100
■parts.
Car-
bonic
acid.
Ox-
ygen.
0.025
20.945
Nitro-
gen.
The percentage, as well as the absolute quantity of car-
bonic acid, is seen to stand in close relation with the or-
ganic matters of the soil. The influence of the recent
apjjlication of manure rich in organic substances is strik-
ingly shown in case of tite asparagus bed and the sandy
soil. The lowest percentage of carbonic acid is 10 times
that of the atmosphere a few feet al)ove the surface of the
earth, as determined at the same time, while the highest
percentage is 390 times that propoi'tion.
Even in the sanily subsoil tlie quantity of free carbonic
acid is as great as in aji equal bulk of the atmosphere ;
and in the cultivated soils it is present in from 6 to 95
^20 now cuors feki;.
times greater amount. In olhor words, in llie cultivated
soils taken to the depth of 14 inches, there was found as
much carbonic acid gas as existed in the same hoiizontal
area of the atmosphere through a height of 7 to 110 feet.
The accumulation of such a percentage of carbonic acid
gas in the interstices of the soil demonstrates the rapid
formation of this substance, which must as rapidly diffuse
off into the air. The roots, and, what is of more signifi-
cance, the leaves of crops, are thus far more copiously fed
with this substance than were they simply bathed by the
free atmosjihere so long as the latter is unagitated.
When the wind blows, the carbonic acid of the soil is
of less account in feeding vegetation compared with that
of the atmosphere. When the air moves at the rate of
two feet per second, the current is just plainly perceptible.
A mass of foliage 2 feet high and 200 feet * long, situated
in such a current, Avould be swept by a volume of atmos-
phere, amounting in one minute to 48,000 cubic feet, and
containing 12 cubic feet of carbonic acid. In one hour it
would amount to 2,280,000 cubic feet of air, equal to 7:20
cubic feet of carbonic acid, and in one day to 69,120,000
cubic feet of air, containing no less than 17,280 cubic feet
of carbonic acid.
In a brisk wind, ten times the above quantities of air
and carbonic acid would pass by or through the foliage.
It is plain, then, that the atmosphere, wliich is rarely at
rest, can supply carbonic acid abundantly to foliage with-
out the concourse of the soil. At the same time it should
not be forgotten that the carbonic acid of the atmosphere
is largely derived from the soil.
Carbonic Acid in the Water of the Soil.— Notwith-
standing the presence of so much carbonic acid in the air
of the soil, it appears that the capillary soil-water, or so
* A sciuare field coutaiuins oue acre is 203 feet and a few inches on each side.
THE AIR OF THE SOIL. 221
much of it as may be expressed by pressure, is not nearly
saturated with this gas.
De Siiussure {Recherches Chimiques sur la VegetatioUy
p. 168) filled large vessels with soils rich in organic mat-
ters, poured on as much water as the earth could imbibe,
allowing the excess to drain off and the vessels to stand
five days. Then the soils were subjected to powerful
pressure, and the water thus extracted was examined for
carbonic acid. It contained but 2"|„ of its volume of the
gas.
Since at a medium temperature (60° F.) water is capa-
ble of dissolving 100" |„ (its own balk) of carbonic acid, it
would appear on first thought inexplicable that the soil-
water should hold but 2 per cent. Henry and Dalton long
ago demonstrated that the relative proportion in which
the ingredients of a gaseous mixture are absorbed by wa-
ter depends not only on the relative solubility of each gas
by itself, but also on the i)roportions in which they exist
in the mixture. The large quantities of oxygen, and
especially of nitrogen, associated with carbonic acid in the
pores of the soil, thus act to prevent the last-named gas
being taken up in greater amount ; for, while carbonic
acid is about fifty times more soluble than the atmos-
pheric mixture of oxygen and nitrogen, the latter is pres-
ent in fifty times (more or less) the quantity of the former.
Absorption of Carbonic Acid by the Soil. — ^According to
Van den Broek, {An>u derChemie n. Ph., 115, p. 87) certain
wells in the vicinity of Utrecht, Holland, which are exca-
vated only a few feet deep in the soil of gardens, contain
water which is destitute of carbonic acid (gives no precipi-
tate with lime-water), while those which penetrate into the
Underlying sand contain large quantities of carbonate of
lime in solution in carbonic acid.
Van den Broek ina<le tlie Ibllowing experiments with
garden-soil newly manured, and containing free carbonic
acid in its interstices, -wiiich could be displaced by a cur*
222 HOW CROPS FEED.
rent of air. Through a mass of this earth 20 inches deep
and 3 inches in diameter, pure distilled water (free
from carbonic acid) was allowed to filter. It ran through
•tcithout taking np any of the gas. Again, Avater contain-
in<T its own volume of carbonic acid was filtered through
a similar body of the same earth. This v-ater gave xip all
its carhonic acid xohlle in contact with the soil. After a
certain amount had run off, however, the subsequent por-
tions contained it. In other words, the soils experiment-
ed with were able to absorb carbonic acid from its aqueous
solution, even when their interstices contained the gas in
the free state. These extraordinary phenomena deserve
further study.
§ 3.
NON-NITROGENOUS ORGANIC MATTERS OF THE SOIL.—
CARBOHYDRATES. VEGETABLE ACIDS. VOLATILE
ORGANIC ACIDS. HUMUS.
Carbohydrates, or Bodies of the Cellulose Group.—
The steps by which organic matters become incorporated
with the soil have been recounted on p. 135. When plants
])erish, their proximate principles become mixed with the
soil. These organic matters shortly begin to decay or to
pass into humus. In most circumstances, however, the
soil must contain, temporarily or i^eriodically, unalter-
ed carboliydrates. Cellulose, especially, may be often
found in an unaltered state in the form of fragments of
straw, etc,
De Saussure {Eecherches, p. 174) found that water dis-
solved from a rich garden soil that had been highly ma-
nured for a long time, several thousandths of organic
matter, giving an extract, which, when concentrated, had
an almost syrupy consistence and a sweet taste, was
ncather acid nor alkaline in reaction, and comported itself
not unlike an impure mixture of glucose and dextriiu
ORGANIC MAITEKS OF THR SOIL. 223
Verdeil and Risler hare made similar observations on ten
soils from the farm of tlie Institut Agronomiqne^ at Ver-
sailles. Thoy found that the water-extract of these soils
contained, on tlie average, 50" j^, of organic matter, which,
wlien strongly heated, gave an odor like burning paper or
sugar. These observers make no mention of crenatcs or
apocrenates, and it, perhaps, remains somewhat doubtful,
therefore, wliether their researches really demonstrate the
presence in tlie soil of a neutral body identical with, or
allied to, dextrin or sugar.
Cellulose, starch, and dextrin, pass by fermentation into
sugar (glucose) ; this may be resolved into lactic acid (the
acid of sour milk and sour-krout), butyric acid (one of the
acids of rancid butter), and acetic acid (the acid of vine-
gar). It must often happen that the bodies of the cellu-
lose group ferment in the soil, the same as in the souring
of milk or of dough, though they suffer for the most part
conversion into humus, as will be shortly noticed.
Vegetable Acids, viz., oxalic, malic, tartaric, and citric
acids, become ingredients of the soil when vegetable mat-
ters are buried in it. When the leaves of beets, tobacco,
and other large-leaved plants fall upon the soil, oxalic and
malic acids may pass into it in considerable quantity.
J'alling fruits may give it citric, m.alic, and tartaric acids.
These acids, however, speedily suffer chemical change
when in contact with decaying albuminoids. Buchner has
shown {Ann. Ch. u. Ph., 78, 207) that the solutions of
salts of the above-named vegetable acids are rapidly con-
verted into carbonates Avhen mixed with vegetable ler-
ments. In this j^rocess tartaric and citric acids ai'e first
partially converted into acetic acid, and this subsequently
jjasses into carbonic acid.
Volatile OrJ^anic Acids. — Formic, propionic, acetic, and
butyric acids, or rather tlieir salts, have been detected by
Jongbloed and others in garden earth. They are comjuoa
224 iiOAv cKO:-s feed. '
products of fermentation, a process that goes on in the
juices of plants that have become a part of the soil or of
a compost.
These acids can scarcely exist in the soil, except tempo-
rarily, as results of fermentation or decay, and tlien in but
very minute quantity. They consist of carbon, hydrogen,
and oxygen. Their salts are all freely soluble in water.
Their relations to agricultural plants have not been studied.
HlinniS (in jiart). — The gen«?ral nature and origin of
humus has been already considered. It is the debris of
vegetation (or of animal matters) in certain stages of de-
composition. Humus is considerably complex in its
chemical character, and our knowledge of it is confessedly
incomplete. In the paragraphs that immediately follow,
we shall give from the best sources an account of its non-
nitrogenous ingredients, so far they are understood, reserv-
ing to a later chapter an account of its nitrogenized con-
stituents.
The Non-nitrofifenoiis (ompoiients of Hiiiuiis. — The
appearance and composition of humus is diiFerent, accord-
ing to the circumstances of its forrnati^m. It has already
been mentioned that humus is brown or black in color.
It appears that the first stage of decom[iositiou yields the
brown humus. It is seen in the dead leaves hanging to a
tree in autumn, in the upper layers of fallen leaves, in the
outer bark of trees, in the smut of Avheat, and in the u}>-
per, dryer portions of peat.
When brown liumus remains wet and with imperfect
access of air, it decomposes further, and in time is convert-
ed into black humus. Black humus is invariably foimd
in the soil beyond a little depth especially if it be com-
pact, in the deeper layers of peat, in the interior of com-
post heaps, in the lower portions of the leaf-mould of
forests, and in the mud or muck of swamps and ponds.
lllmic Acid aild lliuiiu, — The browu humus contains
ORGANIC MATl'ERS OK TlIK SOIL. :i:iO
(besules, perhaps, unaltered vegetable matters) ttvo char-
acteristic ingredients, which have been designated tihnie
add and ulmin, (so named from liaving been found in a
brown mass that exuded from an ehn tree, vlmus being
the Latin for ebu). These two bodies (lem:in<l particular
notice.
"When brown peat is boiled with water, it gives a yel-
lowish or pale-brown liquid, being but little soluble in
jiure water. If, however, it be boiled with dilute solution
of carbonate of soda (sal-soda), a dark-brown liquid is
obtained, which OAves its color to ulmate of soda. The
alkali dissolves the insoluble ulmic acid by combining
with it to form a soluble compound. By repeatedly heat-
ing the same portion of peat Avith new quantities of sal-
soda solution, and pouring off the liquids each time, there
arrives a moment when the peat no longer yields any color
to the solution. The broAvn peat is thus separated into
one portion soluble, and anotlier insoluble, in earl)onate of
soda. ZTlmle acid has passed into the solution, and iflmi/i*
remains undissolved (mixed, it may be, with unaltered
vegetable matters, recognizable by their form and struc-
ture, and with sand and mineral substances).
By adding hydrochloric acid to the brown solution as
long as it foams or effervesces, the ulmic acid separates in
brown, bulky flocks, and is insoluble in dilute hydrochloric
acid, but is a little soluble in pure water. When moist, it
has an acid reaction, and dissolves readily in alkalies or
alkali-carbonates. On drying, the ulmic acid si. rinks
greatly and remains as a brown, coherent mass.
The u/miii* Avhich remains af'ier treatment of brown
peat with carbonate of soda is an indifferent, neutral (i. e.,
not acid) body, which has the same composition as the
* The abovu statoincnt is iii;ukM)ii tlie niithority ol' Miildei-. Tlu- wi-iter has,
however, found, in several cases, that, continued treaimenl with carbonate uf
soda alone completely dissolves the humus, leavinj; a residue of cellulose which
yields nothing to caiistic alkali. He is, therefore, inclined to disbelieve in the
existence of ulmin and humin as distinct from ulmic and hiimic acida.
226 now cKors feed,
ulmic acid. By boiling it with caustic soda or potash-lye.
it is converted without change of composition into ulmic
acid.
On gently heating sugar with dilute hydrochloric acid,
:i brown substance is produced, which appears to be iden-
tical witli the ulmic acid obtained from peat.
Humic Acid and Hiimiii. — By treating black humus
with carbonate of soda as above described, it is separated
into hum^k' acid and humhr^', which closely resemble ulmic
acid and ulmin in all their properties — possess, however, a
black color, and, as it appears, a somewhat different com-
])Osition.
Humic acid and humin may be obtained also by the
action of hot and strong hydiochloric acid, of sulphuric
acid, and of alicalies, upon sugar and the other members
of the cellulose group.
(ompositiou of Ulmin, Ulmic Acid, Humin, and Humic
Acid. — The results of tlie analyses of these bodies, as ob-
tained by different experimenters and from different
sources, are not in all cases accordant. Either several dis-
tinct substances have been confounded under each of the
above names, or the true xdmin and luimin, and ulmic and
liumic acids, are liable to occur mixed with other matters,
from which they cannot be or have' not been perfectly
separated.
Mulder {Chemie der Ackerhrume^ 1, p. 322), who has
chiefly investigated these substances, believes there is a
group of bodies having in general the characters of ulmin
and ulmic acid, whose composition differs only by the ele^
ments of water,f and is exhibited by the general formula
C,„ H,« O,, + nH^O,
in which nll.,0 siucnifies one, two, three, or more of water
• See note ou page 225.
t lu a way analogous to what is known of the sugars. (li. C. G., p.
OK(iAMO MATTERS OF THE SOIL. :^Z4
Ul.iiiL' ucilI from sugar has the following composition in
100 parts :
Carbon, 67.1
Hydrogen, 4.2
Oxygen, 28.7
100.0
which corresponds to C,„ H^, O,^ H^O.
Mulder considers that in the same manner there exist
various kinds of huinic acids and humin, differing from
each other by the elements of water, all of which may
be represented by the general for;iuila C^„ H„^ 0,„ nH^O.
Humic acid and humin from sugar, corresponding to
C40 H„^ 0,„ + 3H„0, have, according to Mulder, the fol-
lowing composition per cent :
Carbon, 64
Hydrogen, 4
Oxygen, 32
100
Apocrenic and €renlc Acids. — In the acid liquid from
which ulmic or himiic acid has been separated, exist two
other acids which were first discovered by Berzelius in
the Porla spring in^ Sweden, and which bear the names
apocrenic acid and crenic acid respectively. By adiling
soda to the acid liquid until the hydrochloric acid is neu-
tralized, then acetic acid in slight excess, and lastly solu-
tion of acetate of copper (crystallized verdigris) as long
as a dirty-gray precipitate is formed, the apocrenic acid is
procured in combination with copper and ammonia. From
this salt the acid itself may be separated* as a brown,
gummy mass, which is easily soluble in water. Accord-
ing to Mulder it has the formula C^^ H,^ 0,^ + H^O, or,
in 100 parts,
By i)recii)itatiuK the copper with sulphm-etted hydrogen.
228 UOAV CKOPS FEED.
Carbon, 56.47
Hydrogen, 2.75
Oxygen, 40.78
100.00
Crenate of copper is lastly [irecipitated as a grass-groe-
substance by adding acetate of copper to the liquid fron
which the apocrenate of copper was separated, and tlien
neutralizing the free acid with ammonia. From tliis com-
pound crenic acid may be prepared as a white, solid body
of sour taste, to which Mulder ascribes th(i formula C^^
■^24 ^16 "•" ^HjO, and in 100 parts the following compo-
sition •
Carbon, 45.70
Hydrogen, 4.80
Oxygen, 49.50
100.00
Mutual Conversion of Apocrcnic and frenic Acids,
— When, on the one hand, apocrenic acid is placed in
contact with zinc and dilute sulphuric acid, the hydrogen
evolved from the latter converts the brown apocrenic acid
(by uniting with a portion of its oxygen) into colorless
crenic acid. On the other hand, the solution of crenic
acid exposed to the air shortly becomes brown by absorp-
tion of oxygen and formation of apocrenic acid. These
changes may be lepeated many times with the same por-
tion of these substances.
Mulder remarks ( Chemie der Ackerkrume, p. 350) :
" In every fertile soil these acids always occur together in
not inconsiderable quantities. When the earth is turned
over by the plow, two essentially different processes fol-
low eacli other: oxidation, where the air has free access;
reduction, where its access is more or less limited by the
adhesion of the particles and especially by moisture. In
the loose, dry earth apocrenic acid is formed j in the firm,
ORGANIC MATlEns OP THE SOIL. 229
moist soil, and in every soil after rain, crenic acid is pro-
dueed, so that tlie action or effects of these substances are
alternately manifested."
The Iliiinjis Bodies Artificially Produced. — When
sugar, cellulose, starch, or uuiu, is boileil with stronu; hy-
drochloric acid or a s rong solution of potash, brown or
bhick bodies result wliich have the greatest similarity with
the ulmin and humin, the ulmic and humic acids of peat
and of soils.
By heating humus with nitric acid (a vigoi'ous oxidizing
agent), crenic and apocrenic acids are formed. The pro-
duction of tliese bodies by such artificial means gives in-
teresting confirmation of the reality of tlieir existence,
and demonstrates the correctness of the views which have
been advanced as to their origin.
While the precise composition of all these substances
may well be a matter of doubt, and from the difficulties
of obtaining them in the pure state is likely to remain so,
their existence in the soil and their importance in agricul-
tural science are beyond question, as we shall shortly have
oj)portunity to understand.
The Coiiditloii of these Humus Bodies in the Soil
requires some comment. The organic substances thus
noticed as existing in the soil are for the most part acids,
but they do not exist to much extent in the free state, ex-
cept in bogs and morasses. A soil that is fit for agricul-
tuial purposes contains little or no free acid, except car-
bonic acid, and oftentimes gives an alkaline reaction with
test-papers.
Regarding ulmic and humic acids, which, as we have
stated, are extracted by solution of carbonate of soda
from humus, it appears that they do not exhibit acid char-
acters before treatment with the alkali. They appear to
be altered by the alkali and converted through its influ-
ence into acids. Only those portions of these bodies
2;>0 now ( nop,; fkkd.
which are acted upon Ly the carbonates of potash, soda,
and lime, that become ini^redients of the soil by tlie
solution of rocks, or by carbonate of ammonia brought
down from the at<nosphere or produced by decay of ni-
trogenous matters, acquire solubility, an<l are, in fact,
acids ; and these portions ai-e acids in combination (salts),
and not in the free state.
The Salts of the Humus Acids that may exist in the
soil, \\z., the ulmates, liumates, apocrenates, and crenatos
of potash, soda, ammonia, lime, magnesia, iron, manga-
nese, and alumina, require notice.
The ulmates and humates agree closely in their charac-
ters so far as is known.
The lUmates and humates of the alkalies (potash, soda,
and ammonia) Vive freely soluble in water. They are foimed
when the alkalies or their carbonates come in contact 1st,
with the ulmic and humic acids themselves ; 2d, with the
ulmates and humates of lime, magnesia, iron, and manga-
nese; and 3d, by the action of the alkalies and their car-
bonates on humin and ulmin. Their solutions are yellow
or brown.
The ulmates and hiimates of lime, magnesia, iron, man-
ganese, and alumina, are insoluble, or bid very slightly
■soluble in water.
From ordinary soils where these earths and oxides pre-
dominate, water removes but traces of humates and
ulmates.
From peat, garden earth, and Icafmould, Avhich contain
excess of the humic and ulmic acids, and carbonate of
ammonia resulting from the decay of nitrogenous matters,
water extracts a perceptible amount of these acids render-
ed soluble by the alkali.
There appear to exist double salts of humic acid and of
ulmic acid, i. e., salts containing the acid combined with two
or more bases. By adding solutions of compounds (e.g.,
.sulphates) of lime, magnesia, iron, manganese, and alumina
ORGANIC Matters op the soit,. 231
(o solutions of liumatcs or ulinates of the alkalies, precipi-
tates are formed in -which the acid is combined Loth with
an alkali anl an earth or oxide. These double salts are
insoluble or nearly so in vater.
Solutions of alkalies and alkali carbonates decompose
them into soluble alkali humates or ulmates, and the
earths or oxides are at least partially held in solution by
the resulting compounds.
Mulder describes the fuUowing experiments, which justifj' the above
conclusions. "Garden-soil was extracted with dilute solution of car-
bonate of soda, the soil being in excess. The solution was filtered and
preeiintateil bj- addition of w:Uer, and the precipitate was washeil and dis-
solved in a little ammonia. Thus was olMained a dark -brown solution
of neutral humate of ammonia. The solution was rendered perfectly
colorless by addition of caustic lime — basic humate of lime is therefore
perfectly insoluble in water.
"Chloride of calcium i-endcred the ?olntion verj' nearly colorless^
neutral humate of lime is almost entirely insoluble.
"Calcined mai^nesia decolorized the solution perfectly. Chloride of
magnesium made the solution very nearly colorless.
"The sulphates of protoxide and peroxide of iron, and sulphate of
manganese, decolorized the solution perfectly.
"These decolorized liquids were made bi-own again by agitating them
and the ju-ecipiiated humates with carbonate of ammonia."
Apocrenatcs and Crenates. — According to Mulder, the
crenates and apocrenates of the soil nearly always contain
ammonia — are, in fact, double salts of this alkali with lime,
i.on, etc.
The (ipocrenotes of the alkalies are freely soluble;
those of the oxides of iron and manganese are moderately
soluble ; those of lime, magnesia, and alumina, are in-
soluble.
The crenates of the alkalies, of lime, magnesia, and
protoxide of iron, are soluble ; those of protoxide of iron
and manganese are less soluble ; crenate of alumina is
insoluble.
All the salts of these acids that are insoluble of them-
selves are decomposed by, and soluble in, excess of tlie
alkali-salts.
2BS tiow cnops T'EBr*.
Do the Orj?anic illatters of the Soil Directly Nourish
Vegetation? — This is a question wliifh, so far as liumns is
concerned, has been discussed witli g-vcat earnestness by
the most prominent writers on Agricultural Science.
De Saussure, Derzelius, a:id Mulder, have argued in the
affirmative ; while Liebig and his numerous adherents to-
tally deny to humus the possession of any nutritive value.
It is probable that luimus may be directly absorbed by,
and feed, plants. It is certain, also, that it docs not con-
tribute largely to the sustenance of agricultural crops.
To ascertain the real extent to which humus is taken up
by plants, or even to demonstrate that it is taken up by
them, is, perhaps, impossible from the data now in our
possession. AYe shnll consider the probabilities.
There have not been wanting attempts to ascertain ex-
perimentallv whether hunuis is capable of feeding vegeta-
tion. Hartig, De Saussure, Wiegmann aiid Polstorf, and
Soubeiran, l;avc observed the growth of plants whose
roots were immersed in solutions of humus. The experi-
ments of Hartig led this observer to conclude that humate
of potash and water-extract of peat do not enter the roets
of plants. Kot having had access to the original account
of this investigation, the writer cannot, perhaps, judge
properly of its merits. It appears, however, that tlie
roots of the plants operated with were not kept constantly
moist, and their extremities were decomposed by too great
concentration of the liquid in wiiich they were immersed.
Under such conditions accurate results were out of the
question.
De Saussure {A/ui. Ch. n. Fh., 42, 275) made two ex-
periments, one with a bean, the other with Polygonum
Persicarid, in whicli these ]ilants were made to vegetetc
with their roots immersed in a solution of humate of pot-
ash (prepared by boiHng humus with bicarbonate of pot-
ash). In the first case tlie bean plant, originally M'eigliing
11 grams, gained during 14 days 6 grms., while the
ORGANIC mattkus of TIIK SOIt. S33
weight of tlie humus decreased 9 rnilligrams. The
Polygonum during 10 days gained 3,5 gims., and the
solution lost 43 milligrams of humus. These experi-
ments Liebig considers undecisive, because an alkali-
humate loses weight by oxidation (to carbonic acid and
Avater) when exposed in solution to the air. Mulder, how-
ever, denies that any appreciable loss could occur in such
a solution during the time of experiment, and considers
the trials conclusive.
In a third experiment, De Saussure placed the roots of
Polygonum Persicaria in the water-extract of turf con-
taining no humic acid but crenic and apocrenic acids,
where they remained nine days in a very flourishing state,
jDUtting forth new roots of a healthy white color. An
equal quantity of the same extract was placed in a simi-
lar vessel for purposes of comparison. It was found that
the solution in which the plants were stationed became
paler in color and remained perfectly clear, while the other
solution retained its original dark tint and became turbid.
The former left after evaporation 33 mgrms.,the latter 39
mgrms. of solid residue. The difference of 6 mgrms., De
Saussure believes to have been absorbed by the plant,
Wiegmann and Polstorf ( Ueher die unorganisclien Be^
standthe'de der Pflanzen) experimented in a similar man-
ner with Mentha und^data^ a kind of mint, and Polygonum
Persicaria, using two plants of 8 inches height, whose
roots were well developed and perfectly healthy. The
plants grew for 30 days in a wine-yellow water-extract
of leaf compost (containing 148 mgrms. of solid sub-
stance— organic matter, carbonate of lime, etc., — in 100
grams of extract), the roots being shielded from light,
and during the same time an equal quantity of the same
solution stood near by in a vessel of the same dimensions.
The plants grew well, increasing Q>\ inches in length, and
put forth long roots of a healthy white color. On the
18th of July the plants were removed from the solution,
234 now CROPS PKEt>.
and 100 grams of the solution left on evajjoration 13S
mgrnis. of residue. The same amount of humus extract,
that had been kept in a contiguous vessel containing no
plant, left a residue of 136 mgrms. The disappearance of
humus from the solution is thus mostly accounted for by-
its oxidation.
De Saussure considers that his experiments demonstrate
that humic acid and (in his third exp,) tlie matters ex-
tracted from peat by water (crenic and apocrenic acids)
are absorbed by plants. Wiegmann and Polstorf attrib-
ute any apparent absorption in their trials to the una-
voidable errors of experiment. Tlie quantities that may
have been absorbed were indeed small, but in our judg-
ment not smaller than ought to be estimated with certainty.
Other experiments by Soubeiran, Malaguti, and Mulder,
are on record, mostly agreeing in this, viz., that agricul-
tural plants (beans, oats, cresses, peas, barley) grow well
when their roots are immersed in, or watered by, solutions
of humates, ulmates, crenates, and apocrenates of ammo-
nia and potash. These experiments are, however, all un-
adapted to demonstrate that humus is absorbed by plants,
and the trials of De Saussure and of Wiegmann, and Pol-
storf, are the only ones that have been made under condi-
tions at all satisfactory to a just criticism. These do not,
perhaps, conclusively demonstrate the nutritive function
of liumus. It is to be observed, however, that w^hat evi-
dence they do furnish is in its favor. They prove eifec-
tually that humus is not injurious to plants, though Liebig
and Wolff have strenuously insisted that it is poisonous*
Let us now turn to the probabilities bearing on the
question.
In the first place there are plants — those living in bogs
and flourishing in dung-heap liquor — which throughout
the whole period of tiieir growth must tolerate^ if not ab-
Borb, somewhat strong solutions of humus.
Again, the cultivated soil invariably yields some humus
ORGAN IC AtAlTKltS OP Til K SOIU S35
(we use this word ns a general collective term) to rain-
water, and tlie richer the soil, as made so by manures and
judged of by its productiveness, the larger ihe quantity,
up to certain limits, of humus it contains. If, as we have
seen, plants always contain silica, though this element be
not essential to their development (II. C. G., p. 186), is it
probable that they are able to reject humus so constantly
presented to them under such a variety of forms?
Liebig opposes the view that humus contributes directly
to the nouiishment of plants because it and its compounds
are insoluble; in the same book, however, {Die Chemle
in Hirer Anwendung auf Agricultur und Physiol ogie^
7th Ed., 18G2) he teaclies the doctrine that all the food
of the agricultural plant exists in the soil in an insoluble
form. This old objection, still m.iintained, tallies poorly
with his new doctrine. The old objection, furthermore, is
baseless, for the humates are as soluble as phosphates,
which are gathered by every plant and from all soils.
It has been the habit of Liehig and his adherents to
teach that the plant is nourished exclusively by the last
l^roducts of the destruction of organic matter, viz., by car-
bonic acid, ammonia, nitric acid, and water, togetlier with
the ingredients of ashes. While no one denies or doubts
that these substances chiefly nourish agricultural plants,
no one can deny that other bodies may and do take part
in the process. It is well established that various organic
substances of animal origin, viz., urea, uric acid, and gly-
cocoll, are absorbed by, and nourish, agricultural plants ;
while it is universally known that the principal food of
multitudes of the lower orders of plants, the fungi, includ-
ing yeast, mould, rust, brand, mushrooms, are fed entirely,
so far as regards their carbon, on organic matters. Thus,
yeast lives upon sugar, the vinegar plant on acetic acid,
tlie Peronospora infestans on the juices of the potato,
etc. There are many parasitic plants of a higher order
common in our forests whose roots are fastened upon and
236 tlOW CROPS FEED.
absorb the juices of the roots of trees ; such are the beech
drops {Epiphegus), pine drops (I-^erosporu), Indian pipe
{3fo/io(rop(()/ the last-named also grows upon decayed
vegL'table matter.
The dodder ( Ct/scitti() is parasitic upon living plants,
especially upon flax, whose juices it appropriates often to
the destruction of the crop.
It is indeed true that there is a wide distinction between
most of these parasites and agricultural plants. The
former are mostly destitute of chlorophyll, and appear to
be totally incapable of assimilating carbon from carbonic
acid.* The latter acquire certainly the most of their food
from carbonic acid, but in their root-organs they contain
no chlorophyll; there they cannot assimilate carbon from
carbonic acid. They do assimilate nitrogen from the or-
ganic principles of urine ; what is to hinder their obtain-
ing carbon from the soluble portions of humus, from the
organic acids, or even from unaltered carbohydrates?
De Saussure, in his investigation just quoted from, says
further: "After having thus demonstrated f the absor-p-
ti(m of humus by the roots, it remains to speak of its as-
similation by the jdant. One of the indications of this
assimilation is derived from the absence of the peculiar
color of humus in the interior of the ])lant, which has ab-
sorbed a strongly colored solution of humate of potash, as
compared to the different deportment of coloring matters
* Dr. Luck (.Inn. C'hem. n. Pharm., 78, 85) has indeed ghown that the mistle-
jw ( Visciim album) decomposes carbonic acid in the sunlight, but this plant has
greenish-yellow leaves containing ddoroplnjll.
t We take occasion here to say explicilly that the only valid criticism of De
Saussure's experiment on the Polygonum supplied with humate of potash, is
Liebig's, to the effect that the solution lost humic acid to the amount of 43 milli-
grams not as a result of absorption by the plant, but by direct oxidation.
Mulder and Soubeiran both agree that such a solution could not lose perceptibly
in this way. That De Saussure was satisfied that such a loss could not occur,
would appear from the fact that he did not attempt to estimate it, as he did in
the subsequent experiment with water-extract of peat. If, now, Liebig be wrong
in his ol)jection (and he has furnished no proof that his statement is true), then
De Saussure lim demonstrated that humic acid is absorbed by plants.
ORGANJC MATIKKS OF THE SOIL. 237
(such as Ink) which cannot nourish tlie plant. The latter
(ink, etc.) leave evidences of their entrance into the plant,
while the former are changed and partly assimilated.
"A bean 15 inches high, whose roots were placed in a
decoction of Brazil-wood (to whicli a little alum had been
added and which was filtered), was able to absorb no more
than the fifth part of its weight of this solution without
wilting and dying. In this process four-fifths of its stem
was colored red.
'•'•Polygomcm Persicaria (on occasion an aquatic or bog
plant) grew very well in the same solution and absorbed
its coloring matter, but the color never reached the stem.
The red principle of Brazil-wood being partially assimilat-
ed by the Polygonum, ixnderwent a chemical change;
while in the bean, which it was unable to nourish, it suf-
fered no change. The Polygonum itself became colored,
and withered when its roots were immersed in diluted
ink."
Blot {Comptes Rendns, 1837, 1, 12) observed that the
re<l juice of Phytolacca decandra (poke-weed), when
poured upon tlie soil in which a wliite hyacinth was blos-
soming, was absorbed by the plant, and in one to two
hours dyed the flowcis of its own color. After two or
three days, however, the red color disappeared, the fiow-
ers becoming white again.
From the facts just detailed, we conclude that some
kinds of organic matters may be absorbed and chemically
changed (certain of them assimilated) by agricultural
plants.
We must therefore liold it to be extremely probable
that various forms of humus, viz., soluble humates, ulmates,
crenates, and apocrenates, together with the other soluble
organic matters of the soil, ai-e taken i;p by plants, and
decomposed or transformed, nay, we may say, assimilated
by them.
S38 Ho^^■ cuors feed.
A few experiments might easily be devised which would
completely SL'ttlo this point beyond all controversy.
Orj?anic blatters as Indirect Sources of Carbon to
Plants. — The decay of organic matters in the soil supplies
to vegetation considerably more carbonic acid in a given
time than would be otherwise at the command of crops.
The quantities of cai'bonic acid found in various soils have
already been given (p. 219). The beneficial eifects of such
a source of carbonic acid in the soil arc sufficiently obvious
(p. 1:>8).
Orjfanic Matters not Essential to the Growth of
Crops. — Although, on the ianii, crops are rarely raised
without the concurrence of humus or at least without its
presence in the soil, it is by no meims indispensable to
their life or full development. Carbonic acid gas is of it-
self able to supply the rankest vegetation with carbon, as
has been demonstrated by numerous experiments, in which
all other compounds of this element have been excluded
(p. 48).
THE AMMONIA OV THE SOIL.
In the chapter on the Atmosphere as the food of plants
we have been led t) conclude that the element nitrogen.,
so indispensable to vegetation as an ingredient of albumin,
etc., is supplied to p'ants exclusively by its compounds,
and mainly by am,monia and nitric acid, or by substances
which yield these bodies readily on oxidation or decay.
We have seen further that both ammonia and nitric acid
exist in very minute quantities in the atmosphere, are dis-
solved in the atmospheric waters, and by them brought
into the soil.
It is pretty fairly demonstrated, too, that these bodies,
as occurring in tlie atmosphere, become of appreciable use
THE AMMONIA OF THE SOIL. 239
to agricultural vegetation only after tlieir incorporation
Avith the soil.
Rain and dew are means of collecting tliem from the
atmosphere, and, as Ave shall shortly see, the soil is a
storehouse for them and the medium of their entrance into
vegetation.
This is therefore the ])roper place to consider in detail
ilie origin and f )rmation of ammonia and nitric acid, so
far as these points have not been noticed when discussing
their relations to the atmosphere.
Ammonia is formed iu tlic Soil either in the decay of
organic bodies containing nitrogen, as the albuminoids,
etc., or by the reduction of nitrates (p. 74). The former
process is of universal occurrence since both vegetable
and animal remains are constantly present in the soil ; the
latter transformation goes on only under certain condi-
tions, which will be considered in the next section (p.
269).
The statement that ammonia is generated from the free
nitrogen of the air and the nascent hydrogen of decom-
posing carbohydrates, as cellulose, starch, etc., or that set
free from water in the oxidation of certain metals, as iron
and zinc, has been completely disproved by Will. (Ann.
d. Ch. n. Ph., 4.5, pp. lOG-112.)
Tlie ammonia eiicountei-ed in sucli experiments maj' liave been, 1st,
tliat pi-e-existini^ in the pores of tlic substances, or dissolved in the wa-
ter ()i)erated witli. Faraday {Researches in Chemistry and Physics, p. 143)
has shown by a series of exact experiments tliat numerous, we may say
all, porous bodies exposed to the air have a minute amount of ammonia
adheriu;^ to them ; 2d, that which is generated in the process of testiu;^
or experimenting (as when iron is heated with potash), and formed by
the action of an alkali on some compound oF nitrojien occurring in the
materials of the experiment; or, 3d. that which results from tlie reduc-
tion of a nitrite formed from free nitrogen by the action of ozone (pp.
77-83).
Tlic Ammonia of the Soil. — a. Gaseous Ammonia as
Garhonate. — Doussiugault and LcAvy, in their examination
of the air contained la the interstices of the soil, p. 219,
24:0 HOW CPvOPS FEED. ' '
tested it for ammonia. In but two instances did tliey find
sufficient to weigh. In all cases, however, they were able
to detect it, though it was present in very minute quanti-
ty. The two experiments in which they were able to
weigh the ammonia were made in a light, sandy soil from
which potatoes had been lately harvested. On the 2d of'
September the field was manured with stable dung ; oni
the 4th the first experiment was made, the air being taken,
it must be inferred from the account given, at a depth of
14 inches. In a million parts of air by weight were found
32 parts of ammonia. Five days subsequently, after rainy
weather, the air collected at the same place contained but
13 parts in a million.
b. Ammonia phi/slcall^ condensed in the Soil. — Many
porous bodies condense a large quantity of ammonia gas.
Charcoal, which has an extreme porosity, serves to illus-
trate this fact. De Saussure found that box-wood char-
coal, freshly ignited, absorbed 98 times its volume of
ammonia gas. Similar results have been obtained by St en-
house, Angus Smith, and others (p. 1G6). The soil cannot,
however, ordinarily contain more than a minute quantity
of physically absorbed ammonia. The reasons are, first, a
porous body saturated with ammonia loses the greater share
of this substance when other gases come in contact with
it. It is only possible to condense in charcoal 98 times its
volume of ammonia, by c(Joling the hot charcoal in mer-
cury which does not penetrate it, or in a vacuum, and then
bringing it directly into tlie ^:)r<>'e ammonia gas. The
charcoal thus saturated with ammonia loses the latter rap-
idly on exposure to the air, and Stenhouse has foimd by
actual trial that charcoal exposed to ammonia and after-
wards to air retains but minute traces of the former.
Secondly, the soil when adapted for vegetable groAvth is
moist or wet. The Avater of t!; > soil which covers the
particles of carlh, ra'lur tliaii (lie particles themselves,
must contai.i any absorbed auuuonia. Thirdly, there are
THE AMMONIA OF THE SOIL. 241
in fertile soils substances which combiue chemically Avith
ammonia.
Tliat the soil does contain a certain quantity of ammo-
nia adhering to the sjuiface of its particles, or, more prob-
ably, dissolved in the hygroscopic water, is demonstrated
by the experiments of Doussingault and Lewy just alluded
to, in all of which ammonia was detected in the air in-
cluded in the cavities of the soih In case ammonia Avere
physically condensed or absorbed, a portion of it would
be carried off in a current of air in the conditions of
Boussingault and Lewy's experiments, — nay, all of it
would be removed by such treatment sufficiently prolonged.
Brustlein (Boussingault's Agronomie^ et ■., 1, p. 152)
records that 100 parts of moist eartli i:)laced ia a vessel of
about 2.]- quarts capacity containing 0.9 parts of (free)
ammonia, absorbed during 3 hours a little more than 0.4
parts of the latter. In another trial 100 parts of the same
earth dried, placed under the same circumstances, absorb-
ed 0.28 parts of ammonia and 2.6 parts of water.
Brustlein found th:it soil placed in a confined atmos-
phere containing very limited quantities of ammonia can-
not condense the latter completely. In an experiment
similar to those jvist described, 100 parts of earth (tena-
cious calcareous clay) and 0.019 parts of ammonia were
left together 5 days. At the conclusion of this period
O.OIG parts of the latter had been taken up by the earth.
Tiie remainder was found to be dissolved in the Avater
that had evaporated from the soil, and that formed a dew
on the interior of the glass vessel
Brustlein proved fui-ther that while air may be almost
entirely deprived of its ammonia by traversing a long
column of soil, so the soil that has absorbed ammonia,
readily gives up a large sliare of it to a stream of pure air.
He caused air, charged with ammonia gas by being made
to bubble through water of ammonia, to traverse a tube 1
ft. long tilled with small fragments of moist soil. The
11
942 HOW CROPS FEED.
ammonia was completely absorbed in the first part of the
experiment. After about 7 cubic feet of air had streamed
tlirough the soil, ammonia began to escape unabsorbed.
The earth thus saturated contained 0.192" |„ of ammonia.
A current of j^ure air was now passed through the soil as
long as ammonia was removeii by it in notable quantity,
about 38 cubic feet being required. By this means more
than one-half the ammonia was displaced and carried oif,
the earth retaining but 0.084" |^.
Brustlein ascei'tained further that ammonia which has
been absorbed by a soil from aqueous solution escapes
easily when the earth is exposed to the air, especially
when it is repeatedly moistened and allowed to dry.
100 parts of the same kind of soil as was employed in
the experiments already described were agitated witli 187
l^arts of water containing 0.889 parts of ammonia. The
earth absoibed O.loT parts of ;immonia. It was now
drained from tlie liquid :md allowed to dry at a low tem-
perature, which operation required eight days. It was
then moistened and allowed to dry again, and this was re-
peated four times. The progressive loss of ammonia is
shown by the following figures.
100 parts of soil absorbed 0.157 parts of ammonia,
" " " '• contained after the first dryini,' 0.083 " " "
" " " " " " " second " 0.066 " " "
" " " " " " " third " 0.054 " " "
" " " " " " " fourth " 0.041 " " "
" " " " " " " fifth " 0.039 " " "
In this instance the loss of ammonia amounted to three-
fourths the quantity at first absorbed.
The extent to wliich absorbed ammonia escapes from
the soil is greatly increased by the evaporation of water.
Bru.stlein found that a soil containing 0.067° |„ of ammo-
nia suffered only a trifling loss by keeping 43 days in a
dry place, whereas the same earth lost half its aTumonia
in a sliorter time by being thrice moistened and dried.
According to Knop ( Vs. /St., Ill, p. 222), the single
THE AMMONIA OF THE SOIL. 243
proximate ingredient of soils that under ordinary cir-
cunistances exerts a considerable surface attraction for
ammonia gas is clay. Knop examined the deportment of
ammonia in this respect towards sand, soluble silica, pure
alumina, carbonate of lime, carbonate of magnesia, hy-
drated sesquioxide of iron, sulphate of lime, and humus.
To recapitulate, the soil contains carbonate of ammonia
physically absorbed in its pores, i. e., adhering to the sur-
faces of its particles, — as Knop believes, to the particles
of clay. The quantity of ammonia is variable and con-
stantly varying, being increased by rain and dew, or ma-
nuring, and diminished by evaporation of water. The
actual quantity of physically absorbed ammonia is, in
general, very small, and an accurate estimation of it is,
perhaps, impracticable, save in a few exceptional cases.
c. Chemically combined Ammonia. — The reader will
have noticed that in the experiments of Brustlein just
quoted, a greater quantity of ammonia was absorbed by
the soil than afterwards escaped, either when the soil was
subjected to a current of air or allowed to dry after moist'
ening with water. This ammonia, it is therefore to be be-
lieved, was in great part retained in the soil in chemical
combination in the form of compounds that not only do
not permit it readily to escape as gas, but also are not
easily washed out by water. The bodies that may unite
with ammonia to comparatively insoluble compounds are,
1st, the organic acids of the humus group* — the humus
acids, as we may designate them collectively. The salts
of these acids have been already noticed. Their com-
* Mulder asserts that the affinity of iihiiic, luimic, and apocrenic acids for
ammonia is so strong tliat they can only be freed from it liy evaporation of their
solutions to dryness with caustic potash. Boiling with carbonate of potash or
carbonate of soda will not suffice to decompose their ammonia-salts. We hold
it more likely that the ammonia which requires an alkali for its expulsion is
generated by ihe decomposition of the organic acid itself, or, if that be desti-
hite of nitrogen, of some nitrogenous substance admixed. According to Bous-
eingault, ammonia is completely removed from humus by boiling vn.iu water au4
caustic magnesia,
244 IIOAV^ CROPS FEED.
pounds with ammonia are freely soluble in water; hence
strong solution of ammonia dissolves them from the soil.
But when ammonia salts of these acids are put in contact
with lime, magnesia, oxide of iron, oxiile of manganese,
and alumina, the latter being in prej^onderating quantity,
there are formed double compounds which are insoluble
or slightly soluble. Since the humic, idmic, crenic, am,
apocrenic acids always exist in soils which contain organic
remains, there can be no question that these double salts are
a chemical cause of the retention of ammonia in the soil.
2d. Certain phosphates and silicates hereafter to be no-
ticed have the power of forming difficultly soluble com-
pounds with ammonia.
Reserving for a subsequent cliapter a further discussion
of the causes of the chemical retention of ammonia in the
soil, we may now appropriately recoimt the observations
that have been made regarding the condition of the am-
monia of the soil as regards its volatility, solubility, etc.
Volatility of the Ammonia of the Soil. — We have
seen that ammonia may esca])e from the soil as gaseous
carbonate. The fact is not only true of this substance as
physically absorbed, but also under certain conditicms of
that chemically combined. When we mingle together
equal bulks of suli)hale of lime (gypsum) and carbonate
of ammonia, both in the state of fine powder, the mixture
begins and continues to smell strongly of ammonia, owing
to the volatility of the carbonate. If now the mixtuie be
drenched with water, the odor of ammonia at once ceases
to be perceptible, and if, after some time, the mixtuie be
thrown on a filter and washed with water, we shall find
that what remains undissolved contains a large proportion
of carbonate of lime, as may be shown by its dissolving
in an acid with effervescence; Avhile the liquid that has
pnssed the filter contains sulphate of ammonia, as may be
learned by the appropriate chemical tests or by evaporat-
ing to dryness, when it will remain as a colorless, oiloi less.
TTtK AMMONIA OF 'tU\t SOtt, ^45
crystalline solid. Double decomposition lias taken place
between the two salts under the influence of water. If,
again, the carbonate of lime on the filter be reunited to
the liquid filtrate and the whole be evaporated, it will be
found that when the water has so far passed off" that a
moist, pasty mass remains, the odor of ammonia becomes
evident again — carbonate of ammonia, in fact, escaping by
volatilization, while sulphate of lime is reproduced. It is
a general law in chemistry that wlien a number of acids
and bases are together, those which under the circum-
stances can produce by their union a volatile body will
ixnite, and those which under the circumstances can form a
solid body will unite. When carbonic and sulphuric acids,
lime and ammonia, are in mixture, it is the circu instances
which determine in what mode tliese bodies combine. In
presence of nmch water carbonate of lime is formed be-
cause of its insolubility, water not being able to destroy
its solidity, and sulphate of ammonia necessarily results
by the union of the other two substances. When the wa-
ter is removed by evaporation, all the possible compounds
between carbonic and sulphuric acids, lime and am-
monia, become solid ; the compound of ammonia and car-
bonic acid being then vohitile, this fact determines its
formation, and, as it escapes, the lime and sulphuric acid
can but remain in combination.
To apply these principles : When carbonate of ammo-
nia is brought into the soil by rain, or otherwise, it tends
in presence of much water to enter into insoluble combi-
nations so far as is possible. When the soil becomes dry,
these compounds begin to undergo decomposition, provid-
ed carbonates of lime, magnesia, potash, and soda, are
present to transpose with them ; these bases taking the
place of the ammonia, while the carbonic acid they were
united with, forms with the latter a volatile compound.
In this way, then, all soils, for it is probable that no soil
exists which is destitute of carbonates, may give ofi'at th©
246 now CROPS fEEI).
surface in dry weatlier a portion of the ammonia Avhich
before was cliemically retained within it.
Solubility of the Ammoiiia of the Soil.— The distinc-
tions between physically adliering and cliemically combin-
ed ammonia are difficult, if not impossible, to draw with
acciuaey. In what follows, therefore, we shall not attempt
to consider them separately.
When ammonia, carbonate of ammonia, or any of tlie
following ammoniacal salts, viz., chloride, sulphate, ni-
trate, and phosphate, are dissolved in water, and the solu-
tions are filtered through or agitated with a soil, we find
that a portion of ammonia is invariably removed from so-
lution and absorbed by the soil. An instance of this ab-
sorbent action has been already given in recounting
Brustlein's experiments, and further examples will be here-
after adduced when we come to speak of the silicates of
the soil. The points to which we now should direct at-
tention are these, viz., 1st, the soil cannot absorb ammo-
nia completely from its solittions ; and, 2d, the ammonia
which it does absorb may be to a great degree dissolved
out again by water. In other words, the compounds of
ammonia that are formed in the soil, though comparatively
insoluble, are not absolutely so.
Henneberg and Stohmann found that a light, calcareous,
sandy garden soil, when placed in twice its weight of pure
water for 24 hours, yielded to the latter joVo of its weight
of ammonia (=0.0002" |J.
100 parts of the same soil left for 24 hours in 200 parts i
of a solution of chloride of ammonium (containing 2.182'
of sal-ammoniac =0.693 part of ammonia), absorbed 0.112 j
part of ammonia. Half of the liquid was poured off
and its place supplied with pure water, and the whole
left for 24 hours, Avhen half of this liquid was taken, and
the process of dilution was thus repeated to the fifth time.
In the portions of water each time removed, ammonia was
estimated, and the result Avas that the water added dis-
THE AMMONIA OF THE SOIL. 247
'olved out nearly one-half tlie ammonia whieli tlie earth
at first absorbed.
The 1st dilution removed from the soil 0.010
"2d " " " " " ...0.009
" 3d " " " " " 0.014
" 4tli " " " " " 0.011
" 5th " " " " " 0.009
Total 0.053
Deducting 0.053 from the quantity first absorbed, viz.,
0.112, there remains 0.059 part retained by tlie soil after
five dilutions. Knop, in 11 decantations, in which the
soil was treated with 8 time* its weight of water, removed
93° !„ of the ammonia wliich the soil had previously ab-
sorbed. We cannot doubt that by repeating the washing
sufficiently long, all the ammonia would be dissolved,
though a very large volume of water would certainly be
needful.
Causes which ordinarily prevent the Accumulation of
Ammonia in the Soil. — The ammonia of the soil is con-
stantly in motion or suffering change, and does not ac-
cumulate to any great extent. In summer, the soil daily
absorbs auimonia from the air, receives it by rains and
dews, or acquires it by the decay of vegetable and animal
matters.
Daily, too, ammonia wastes from the soil — by volatili-
zation— accompanying the vapor of water which almost
unceasingly escapes into the atmosphere.
When the soil is moist and the temperature not too low,
its ammonia is also the subject of remarkable chemical
transformations. Two distinct chemical changes are be-
lieved to affect it ; one is its oxidation to nitric acid. This
process we shall consider in detail in the next section. As
a result of it, we never find ammonia in the water of or-
dinary wells or deep drains, but inste-nd always encounter
nitric acid united to lime, and, perhaps, to magnesia and
alkalies. The other chemical change appears to be the
alteration of the compounds of ammonia with the humus
248 nq\y chops pked.
acids, wlicrel)}' hoJies result which arc no h)nger soluble
in Avator, and which, as such, arc probably innutritions to
plants. These substances are quite slowly decomposed
when put in contact, especially when heated with alkalies
or caustic lime in the presence of water. In this decom-
jjosition ammonia is reproduced. These indifferent nitrog-
enous matters appear to be analogous to a class of sub-
stances known to chemists as amides, of Avhich asparagin,
a crystallizable body obtained from asparagus, young peas,
etc., and urea and \iric acid, the characteristic ingredients
of urine, are examples. Further account of these matters
will be given subsequently, p. 376.
Quantity of Ammonia in Soils. — Formerly the amount
of ammonia in soils Avas greatly overestimated, as the re-
sult of imperfect methods of analysis. In 1846, Krocker,
at Liebig's instigatiim, estimated the nitrogen of 22 soils,
and Liebig published some ingenious speciilations in which
all this nitrogen was incorrectly assumed to be in the form
of ammonia. Later, various experimenters have attempt-
ed to estimate the ammonia of soils. In 18."35, the writer
examined several soils in Liebig's laboratory. The soils
were boiled for some hours Avith water and caustic lime,
or caustic potash. The ammonia that Avas set free, distill-
ed off, and its amount Avas determined by alkalimetry.
It Avas found that however long the distillation was kept
up, ammonia continued to come over in minute quantity,
and it Avas probable that this substance Avas not simply
expelled from the soil, but Avas slowly formed by the ac-
tion of lime on organic matters, it being Avell known to
chemists that many nitrogenous bodies are thus decom-
posed. The results Avere as follows :
White sandy loam distilled with caustic lime gav«
Yellow clav " •' " ' " " -'00047
iciiowciay (0.0051
" " " " " potash " " one " 0.0075
Black garden soil " " " lime " " ♦wo *' \ o 0951
THIO AMMONIA OK I'M K SOIL.
249
The fact that caustic potasli, a more energetic decom-
posing agent than lime, disengaged more ammonia than
the latter from the yellow clay, strengthens the view that
ammonia is produced and not merely driven oif under the
conditions of these experiments, and that accordingly the
figures^ are too high. Other chemists employing the same
method have obtained similar results.
Boussingault {A(/ronomie, T. Ill, p. 206) was the first
to substitute magnesia for potash and lime in the estima-
tion of ammonia, having first demonstrated that this sub-
stance, so feebly alkaline, does not perceptibly decompose
gelatine, albumin, or asparagine, all of which bodies, espe-
cially the latter, give anmionia when boiled with milk of
lime or solutions of potash. The results of Boussingault
here follow.
Localities. Quantity of Ammonia per cent.
Liebfrauenberg, Alsatia 0.0022
Bischwillor, " 0.0020
Merckwiller, " 0.0011
Bechelbronn, " 0.0009
Mittelhausbei-gen, " 0.0007
He Napoleon, Mulhouse, 0.0006
Argentan, Onie, 0.0060
Quesnoy-snr-Deule, Nord, 0.0012
Eio Madeira, America, 0.0090
Eio Trombetto, " 0.0030
RioNegro, " 0.0038
Santarem, " 0.0083
He du Salut, " 0.0080
Martinique, " 0.0085
Rio Cupari, (leaf mold,) " 0.0525
Peat, Paris, 0.0180
The above results on French soils correspond with those
obtained more recently on soils of Saxony by Knop and
Wolif, who have devised an ingenious method of estimat-
ing ammonia, Avhich is founded on altogether a different
l)rinciple. Knop and "Wolff measure the nitrogen gas
which is set free by the action of chloride of soda (Ja-
velle water*) in a specially constructed apparatus, the
* More properly hypochlorite of soda, which is used in mixture with broimina
Kud caustic soda.
11*
26(i now cuors feicix
Azotometer. {Chemisc/ies Centralhlatt, 1860, pp. 243 and
534.)
By this method, which gives accurate results when ap-
phed to known quantities of ammonia-salts, Knop and
Wolff obtained the following results :
Ammonia in dry soil.
Verj' li<,^ht sandy soil from birch forest 0. 00077" jo
Rich lime soil from beech forest 0.00087
Sandy loam, forest soil 0.00012
Forest soil 0.00080
Meadow soil, red sandy loam .0.00027
Average 0.00056
The rich alluvial soils from tropical America are ten or
more times richer in ready-formed ammonia than those of
Saxony. These figures show then that the substance in
question is very variable as a constituent of the soil, and
that in the ordinary or poorer classes of unmanured soils
its percentage is scarcely greater than in the atmospheric
waters.
The Quantity of Ammonia fluctuates, — Boussingault
has further demonstrated by analysis what we have insist-
ed upon already in this chapter, viz., that the quantity of
ammonia is liable to fluctuations. He estimated ammonia
in garden soil on the 4th of March, 1860, and then, moist-
ening two samples of the same soil with pure water, ex-
amined them at the termination of one and two months
respectively. He found,
March 4th, 0.009" |„ of ammonia.
April " 0.014" "
May " 0.019 " "
The simple standing of the moistened soil for two
months sufficed in this case to double the content of am-
monia.
The quantitative fliuctuations of this constituent of the
soil has been studied further both by Boussingault and
by Knop and Wolff. The latter in seeking to answer the
THE NITKK' ACID OF TIIK SOIt. 251
question — " IIow groat is the ammonia-content of good
manured soil lying fallow ?" — made repeated determina-
tions of ammonia (17 in all) in the same soil (well-ma-
nured, sandy, calcar(>ous loam exposed to all rains and
dews but not washed) during five months. The moist
soil varied in its proportion of ammonia with the greatest
irregularity between the extremes of 0.0008 and 0.0003" |^.
Similar observations were made the same summer on the
loamy soil of a field, at first bare of vegetation, then cov-
ered with a vigorous potato crop. In this case the fluctu-
ations ranged from 0.0009 to 0.0003" |„ as iiregularly as in
the other instance.
Knop and WollF examined the soil last mentioned at
various depths. At 3 ft. the proportion of ammonia was
scarcely less than at the surface. At 6 ft. this loam, and
at a somewhat greater depth an underlying bed of sand,
contained no trace of ammonia. This observation ac-
cords with the established fact tliat deep well and drain-
waters are destitute of ammonia.
Boussingault has discovered [Agrononiie, 3, 195) that
the addition of caustic lime to the soil largely increases its
content of ammonia — an effect due to the decomposing ac-
tion of lime on the amide-like substances already noticed.
NITRIC ACID (NITRATES, NITROUS ACID, AND NITRITES) OF
THE SOIL.
Nitric acid is formed in the atmospliere by the action
of ozone, and is brought down to the soil occasionally in
the free state, but almost invarial)ly in combination with
ammonia, by rain and dew, as has been already described
(p. 86). It is also produced in the soil itself by processes
whose nature — considerably obscure and little understood
■ — will be discussed presently.
^53
now mors fked.
In the soil, nitric acid is always combined ■\vitli an
alkali or alkali-earth, and never exists in the free state in
apjireciable quantity. We speak of nitric acid instead of
nitrates, because the former is the active ingredient com-
mon to all the latter. Before considering its formation
and nutritive relations to vegetation, we shall describe
those of its compounds which may exist in the soil, viz.,
the vitrates of potash, coda, lime, magnesia, andiron.
Nitrate of Potash (K NOJ is the substance com-
mercially known as niter or saltpeter. When pure (refin-
ed saltpeter), it occurs in colorless prismatic crystals. It
is freely soluble in water, and lias a peculiar sharp, cooling
taste. Crude saltpeter contains common salt and other
impurities. Nitrate of potash is largely procured for in-
dustrial uses from certain districts of India (Bengal) and
from various caves in tropicil and tempei'ate climates, by^
simply leaching tlie earth with Avater and evaporating the
solution thus obtained. It is also made in artificial niter-
beds or jDlantations in many European countries. It is
likewise prepared artificially from nitrate of sotia and
caustic potash, or chloride of potassium. The chief use
of the commercial salt is in the manufacture of gunpowder
and fireworks.
Sulphur, charcoal, (which are ingredients of gunpow-
der), and other combustible matteis, when heated in con-
tact with a nitrate, burn with great intensity at the ex-
pense of the oxygen which the nitrate contains in large
proportion and readily parts with.
Nitrate of Soda (Na NO3) occurs in immense quantities
in the southern extremity of Peru, province of Tarapaca,
as an incrustation or a compact stratum several feet thick,
on the ]iampa of Tamarugel, an arid plain situated in a
region where rain never falls. The salt is dissolved in hot
water, the solution poured off from sand and evaporated to
the crystallizing point. The crude salt has in general a
TIIK NITUIO ACID OK THE SOIL, 253
yellow or reddish color. When pure, it is white or color-
less. From the shape of the crystals it has been called
cubic* niter; il is also known as Chili saltpeter, having
been formerly exported from Chilian ports, and is some-
times termed soda-saltpeter. In 1854, about 40,000 tons
were shipped from the port of Iquique.
Nitrate of soda is hygroscopic, and ni damp air be-
comes quite moist, or even deliquesces, and hence is not
suited for making gunpowder. It is easily procured arti-
ficially by dissolving carbonate of soda in nitric acid.
This salt is largely employed as a fertilizer, and for pre-
paring nitrate of potash and nitric acid.
Nitrate of Lime (Ca^NO^) may be obtained as a white
mass or as six-sided crystals by dissolving lime in nitric
acid and evaporating the solution. It absorbs water from
the air and runs to a liquid. Its taste is bitter and sharp.
Nitrate of lime exists in well-waters and accompanies
nitrate of i)otash in artificial niter-beds,
IVitrate of Maj^nesia (Mg2N0J closely resembles ni-
trate of lime in external chaiacters and occurrence. It
may be prepared by dissolving magnesia in nitric acid and
evaporating t.he sohition.
Nitrates of Iron. — Various compounds of nitric acid
and iron, both soluble and insoluble, are known. In the
soil it is probable that only insoluble basic nitrates of
sesquioxide can occur, Knop observed ( F! St., V, 151)
that certain soils when left in contact with solution of ni-
trate of potash for some time, failed to yield the latter en-
tirely to water again. The soils that manifested this
anomalous deportment were rich in humus, and at the
same time contained much sesquioxide of iron that could
be dissolved out by acids. It is possible that nitric acid
entered into insoluble combinations here, though this
hypothesis as yet awaits proof
♦ The crystals arc, in fact, rhomboiUal,
254 HOW CROPS FEED.
Nitrates of alumina are known to the chemist, but have
not been proved to exist in soils. Nitrate of ammonia
has already been noticed, p. 71.
Nitric Acid not usually fixed by the Soil.— In its deport-
ment towards the soil, nitric acid (either free or in its salts)
differs in most cases from ammonia in one important par-
ticular. The nitrates are usually not fixed by the soii, but
remain freely soluble in water, so that washing readily and
completely removes them. The nitrates of ammonia and
potash are decomposed in the soil, the alkali being retain-
ed, while the nitric acid may be removed by washing with
water, mostly in the form of nitrate of hme. Nitrate of
soda is partially decomposed in the same manner. Free
nitric acid unites with lime, or at least is found in the
washings of the soil in combination with that base.
As just remarked, Knop has observed that certain soils
containing much organic matters and sesquioxide of iron,
appeared to retain or decompose a small portion of nitric
acid (put in contact with them in the form of nitrate of
potash). Knop leaves it uncertain whether this result is
simply the fault of the method of estimation, caused by
the formation of basic nitrate of iron, which is insoluble in
water, or, as is perhaps more i:)robable, due to the de-
composing (reducing) action of organic matters.
Nitrification is the formation of nitrates. When vege-
table and animal matters containing nitrogen decay in the
soil, nitrates of these bases presently apj)ear. In Bengal,
during the dry season, when for several months rain sel-
dom or never falls, an incrustation of saline matters,
chiefly nitrate of potash, accumulates on the surface of
those soils, which are most fertile, and which, though culti-
vated in the wet season only, yield two and sometimes
tliree crops of grain, etc., yearly. The formation of ni-
trates, which probably takes place during the entire year,
appears to go on most rapidly in the hottest weather.
THE NiTiiic Aciij oy t:ik soil. 255
The nitrates accumulate near the surface when no rain
falls to dissolve and wash them down — when evaporation
causes a current of capillary water to ascend continually
in the soil, carrying with it dissolved matters which must
remain at the surface as the water escapes into the atmos-
phere. In regions where rain frequently falls, nitrates are
largely formed in ricli soils, but do not accumulate to any
extent, unless in caves or positions artificially sheltered
from the rain.
Boussingault's examination of garden earth fiom Lieb-
frauenberg [Agvonomie, etc., T. II, p. 10) conveys an idea
of the progress which nitrification may make in a soil un-
der cultivation, and highly charged with nitrogenous ma-
nures. About 2.3 lbs. of sifted and -well-mixed soil were
placed in a heap on a slab of stone under a glazed roof.
From time to time, as was needful, the earth was moist-
ened with water exempt from ammonia. The proportion
of nitric acid was determined in a sample of it on the day
the experiment began, and the analysis Mas repeated four
times at various intervals. The subjoined statement gives
the per cent of nitiatcs expressed as nitrate of potash in
the dry soil, and also the quantity of this salt contained
in an acre taken to the depth of one foot.*
Per cent.
Lbs
. per acre.
1857— 5th August,
0.01
34
" — irth
0.0(5
222
" — 2d September,
0.18
631
" -17th
0.22
760
" — 2d October,
0.21
728
The formation of nitrates proceeded rapidly during the
h' at of summer, but ceased by the middle of September.
T^hether this cessation was due to the lower temperature
or to the complete nitrification of all the matter existing
in the soil ca))able of this change, or to decomposition
of nitric acid by the reducing action of organic matters,
• The fi^rures jrivpn above arc abhrpvitited fn^iu the originals, or reduced tO
Kuglisb dcnominatiouij witU a trifling loss of exactu^sij.
256 HOW CROPS FEED.
further researches must decide. The quantities that ac-
cumulated in this experiment are seen to be very consider-
able, when we remember that experience has shown thaf
200 lbs. per acre of the nitrates of potash or soda is a
large dressing upon grain or grass. Had tlie earth been
exposed to occasional rain, its analysis Avould have indi-
cated a much less percentage of nitrates, because the salt
woidd have been Avashcd down far into, and, perhaps,
out of, the soil but no less, probably even somewhat
more, would have been actually formed. In August, 1856,
Boussingault examined earth from the same garden after 14
days of hot, dry weather. He found the nitrates equal to
911 lbs, of nitrate of potash per acre taken to the depth of
one foot. From the 9th to the 29th of August it rained
daily at Liebfrauenberg, more than two inches of water
falling duiing this time. When the rain ceased, the soil
contained but 38 lbs. per acre. In September, rain fell 15
times, and to the amount of four inches. On the 10th of
October, after a fortnight of hot, windy weather, the gar-
den had become so dry as to need watering. On being
then analyzed, the soil was found to contain nitrates equiv-
alent to no less than 1,290 lbs. of nitrate of potash per
acre to the depth of one foot. This soil, be it remembered,
was porous and sandy, and had been very heavily manur-
ed with well-rotted compost for several centuries.
Boussingault has examined more tiian sixty soils of ev-
ery variety, and in every case but one found an apprecia-
ble quantity of nitrates. Knop has also estimated nitric
acid in several soils ( Versuchs jSt., V, 143). Nitrates are
almost invariably found in all well and river waters, and
in quantities larger thaii exist in rain. "We may hence as-
sume that nitrification is a process universal to all soils,
and that nitrates are normal, thougli, for the reasons stat-
ed, very variable ingredients of cultivated earth.
The Sources of the IVitric Acid which is formed within
the Soilf — Nitric acid is produced — a, from ammonia^
THE NITIM
oi'^ TU.: sui:.. '257
either that absorbed by the sol from the atmospliere, or
tliat originating in the soil itself by the decay of nitrog-
enous organic matters. Knoj) made an experiment with
a sandy loam, as follows : The earth was exposed in a box
to the vapor of ammonia for three days, was then mixed
thoroughly, spread out thinly, moistened with pure water,
and kept sheltered from rnin until it became dry again.
At the beginning of the experiment, 1,000,000 parts of
the earth contained 52 parts of nitric acid. During its
exposure to the air, Avhile moist, the content of nitric acid
in this earth increased to 591 parts in 1,000,000, or more
than eleven times ; and, as Knop asserts, this increase took
place at the expense of the ammonia which the earth had
absorbed. The conversion of ammonia into nitric acid is
an oxidation expi*essed by the statement
2 NH3 + 40 = NH, NO3 + 11,0. *
The oxygen may be either ozone, as already explained,
or it may be furnished by a substance which exists in all
soils and often to a considerable extent, viz., sesquioxide
of iron. This compound (Fe,^ O3) readily yields a portion
of its oxygen to bodies which are inclined to oxidize, be-
ing itself reduced thereby to pi-otoxide (FeO) thus : —
Fe, O3 = 2 FeO + O. The protoxide in contact with the
air quickly absorbs common oxygen, passing into sesqui-
oxide again, and in this way iron operates as a carrier of
atmospheric oxygen to bodies whicli cannot directly com-
bine with the latter. The oxidizing action of sesquioxide
of iron is proved to take place in many instances ; for ex-
ample, a rope tied around a rusty iron bolt becomes " rot-
ten," cotton and linen f ibrics are destroyed by iron-stains,
the head of an iron nail corrodes away the wood sur-
rounding it, when exposed to the weather, and after suf-
* The above equation represents l)iit one-half of the ammonia as converted
into nitric acid. In the soil the carbonates of lime, etc., would separate the
nitric acid from the remaining ammonia and leave the latter in u condition to
be oxidized.
258 HOW CROPS FEED.
ficient time this oxidation extends so far as to leave the
board loose upon the nail, as may often be seen on old,
unpainted wooden buildings. Direct experiments by Knop
( Yersuchs St., Ill, 228) strongly indicate that ammonia is
oxidized by the agency of iron in the soil.
b. The organic matters of the soil, either of vegetable
or animal origin, which contain nitrogen, suffer oxidation
by directly combining with ordinary oxygen.
As we shall presently see, nitrates cannot be formed in
the rapid or putrefactive stages of decay, but only later,
when the process proceeds so slowly that oxygen is in large
excess. When the organic matters are so largely dilut-
ed or divided by the earthy parts of the soil that oxygen
greatly preponderates, it is probable that the nitrogen of
the organic bodies is directlj^ oxidized to nitric acid.
Otherwise ammonia is first formed, which is converted in-
to nitrates at a subsequent slower stage of decay.
Nitrogenous organic matters may perhaps likewise yield
nitric acid when oxidized by the intervention of hydrated
sesquioxide of iron, or other reducible mineral compounds.
Thenard mentions {Comptes Mendus, XLIX, 289) that a
nitrogenous substance obtained by him from rotten dung
and called fumic acid* when mixed with carbonate of
lime, sesquioxide of iron and water, and kept hot for 15
days in a closed vessel, was oxidized with formation of
carbonic acid and noticeable quantities of nitric acid, the
sesquioxide being at the same time reduced to protoxide.
The various sulphates that occur in soils, especially sul-
phate of lime (gypsum, plaster), and sulphate of iron
(copperas), may not unlikely act in the same manner to
convey oxygen to oxidable substances. These sulphates,
in exclusion of air, become reduced by organic matters to
sulphides. This often happens in deep fissures in the
earth, and causes many natural waters to come to the sur-
According to Mulder, impure liumate of ammoaia.
TUB 2<ITKIC AOIL) OF TUE SOIL. 259
face charged with sulpliidcs (sulphur-springs). Water
contahiiiig sulpliiites in sohitiou often acquires an odor of
sulphuretted hydrogen by being kept bottled, the cork or
other organic matters deoxidizing the sulphates. The
earth just belo^v the {)aving-stones in Paris contains con-
siderable quantities of sulphides of iron and calcium, the
gypsum in the soil being reduced l)y organic matters.
(Chevreul.) These sulphides, when exposed to air, speed-
ily oxidize to sulphates, to suffer reduction again in con-
tact with the appropriate substances, and under certain
conditions, operate continuously, to gather and impart
oxygen. One of the causes of the often remarkable and
inexplicable effects of plaster of Paris when used as a fer-
tilizer may, perhaps, be traced to this power of oxidation,
resulting in the formation of nitrates. This j^oint requires
and is aa'cII worthy of special investigation.
c. Lastly, the free nitrogen of the atmosphere appears
to be in some way involved in the act of nitrification — is
itself to a certain extent oxidized in the soil, as has been
maintained by Saussure, Gaultier de Claubry, and others
{Cynellii's Hand-book of Chemhtry^ II, 388).
The truth of this view is sustained by some of Bous-
singault's researches on the garden soil of Liebfrauenberg.
{Aijrouomle, et<:, T., 1, SIH)!" On the 29th of July, 1858,
he spread out thinly 120 grammes of this soil in a shallow
glass dish, and for three months moistened it daily with
water exempt from compounds of nitrogen. At the end
of this time analysis of the soil showed that while a small
proportion of carbon (0.825° IJ had wasted by oxidation,
the quantity of nitrogen had slightly increased. The
gain of nitrogen was but 0.009 grm. = 0.008"| ^.
In five other experiments where plants grew for several
months in small quantities of the same garden soil, either
in the free air but sheltered from rain and dew, or in a
confined space and watered with pure water, analyses
: of Crop,
taken as 1.
Quantity of Soil.
Gain of Nitrogen
by plant. by soil.
3!i
130 frrras.
0.0042 grms. 0.0672 grms.
4
130 '•
0.0047 " 0.0081 "
5
40 "
0.0039 " 0.0000 "
5
50 "
0.0226 " 0.0000 "
3
130 "
0.0217 " 0.O154 '•
260 uoAv OKors feed.
were mado of the soil and seed before tlie trial, and of the
soil and crop afterwards.
The analyses show that while in all cases the plants
gained some nitrogen beyond what was originally contain-
ed in the seed, there wns in no instance any loss of nitro-
gen by the soil, and in three cases the soil contained more
of this element after than before the trial. Here follow
the results.
No. of Mip.
1. Lupin,*
2. Lupin,
3. Hemp,
4. Bean,
B. Lupin,*
That the gain of nitrogen by the soil was not due to
direct absorption of nitric acid or ammonia from the at-
mosphere is demonstrated by the fact that it was largest
in the two cases (Exps. 1 and 5) where the experiment was
conducted in a closed vessel, containing throughout the
Avhole time the same small volume, about 20 gallons, of
air.
In Exp. 4, where the soil at the conclusion contained no
more nitrogen than at the commencement of the trial, it
is scarcely to be doubted that the considerable gain of ni-
trogen experienced by the plant came through the soil,
and would have been found in the latter had it borne no
crop.
The experiments show that the quantity of nitrogen
assimilated from the atmosphere by a given soil is very
variable, or may even amount to nothing (Exp. 3); but
they give us no clue to the circumstances or conditions
which quantit.itively influence the result. It must be ob-
served that this fixation of nitrogen took place here in a
soil very rich in organic matters, existing in the condition
of humus, and capable of oxidation, so that the soil itself
Experiments made in confined air.
THE NITRIC ACID OF THE SOIL. S61
lost during three summer months eight-tenths of one per
cent of carbon. In the numerous similar experiments
made by Bonssingault with soils destitute of organic m<(t-
ter, no accumulation of nitrogen occurred beyond the
merest traces coming from condensation of atmospheric
ammonia.
Certain experiments executed by Mulder more than 20
years ago ( Chemistry of Animal and Yegetahle Physi'
ology, p. 673) confirm the view we have taken. Two of
these were "made Avith beans which had germinated in
an atmosphere void of ammonin, and grown, in one case,
in ulmic acid prepared from sugar, and also free from am-
monia; and, in the other case, in charcoal, both being
moistened with distilled water free from ammonia. The
ulmic acid and the charcoal were severally mixed up with
1 per cent of wood ashes, to supply the plants with ash-
ingredients. I determined the proportion of nitrogen in
three beans, and also in the plants that were produced by
three other beans. The results are as follows: —
White beans in nlmic acid. Brown beans in charcoal.
Weight. Nitrogen. Weight. Xitrogen.
Beans, 1.465 grm. 50 cub. cent. 1.277 27 cub. cent.
Plants, 4.167 " 160 " " 1.773 54 "
The white beans, therefore, whilst growing into plants
in substances and an atmosphere, both of which were free
of ammonia, had obtained more than thrice the quantity
of nitrogen that originally existed in the beans ; in the
brown beans the original quantity was doubled," Mulder
believed this experiment to furnish evidence that ammonia
is produced by the union of atmospheric nitrogen with
hydrogen set free in the decay of organic matters. To
this notion allusion has been already made, and the con-
viction expressed that no proof can be adduced in its
favor (p. 239). The results of the experiments are fully
explained by assuming that nitrogen was oxidized in nitri-
fication, and no other explanation yet proposed accords
with existins: facts.
^62 HOW CROPS FEED.
As to the mode in which the soil thus assimilates free
nitrogen, several hypotheses have been offered. One is
that of SchiJnbein, to the effect that in the act of evapora-
tion free nitrogen and water combine, with formation of
nitrite of ammonia. In a former paragraph, p. 79, Ave
have given the results of Zabelin, which appear to render
this theory inadmissible.
A second and adequate explanation is, that free nitrogen
existing in the cavities of the soil is directly oxidized to
nitric acid by ozone, which is generated in the action of
ordinary oxygen on organic matters, (in the same way as
happens when ordinary oxygen acts on phosphorus,) or is,
perhaps, the result of electrical disturbance.
Experiments by Lawes, Gilbert, and Pugh {Phil.
Trans. ^ 1861, II, 495), show indeed that organic matters
in certain conditions of decay do not yield nitric acid
under the influence of ozone.
They caused air highly impregnated with ozone to pass
daily for six months through moist mixtures of burned
soil with relatively large quantities of saw-dust, starch,
and bean meal, with and without lime — in all 10 mixtures
— but in no case was any nitric acid produced.
It would thus appear that ozone can form nitrates in
the soil only when organic matters have passed into the
comparatively stable condition of humus.
That nitrogen is oxidized in the soil by ozone is highly
probable, and in perfect analogy with what must happen
in the atmosphere, and is demonstrated to occur in Schon-
bein's experiments with moistened phosphorus (p. 66,
also Ann. der Chem. v. Pharm., 89, 287), as well as in
.Zabelin's investigations that have been already recounted.
(See pp. 75-83.)
he fact, established by Reichardt and Blumtritt, that
humus condenses atmospheric nitrogen in its pores (p.
167), doubtless aids the oxidation of this element.
The third mode of accounting for the oxidation of
THE NITRIC ACm OP THE SOIL. 263
free nitrogen is based upon the effects of a reducible
body, like sesquioxide of iron or sulphate of lime, to
•which attention has been already directed.
In a very carefully conducted experiment, Cloez * trans-
mitted atmospheric air purified from suspended dust, and
from nitric acid and ammonia, through a series of 10 large
glass vessels filled Avith various porous materials. Vessel
No. 1 contained fragments of unglazed porcelain ; No. 2,
calcined pumice-stone ; No. 3, bits of well-Avashcd brick.
Each of these three vessels also contained 10 grms. of car-
bonate of potash dissolved in water. The next three vessels,
Nos. 4, 5, and G, included the above-named porous materials
in the same order ; but instead of carbonate of potash, they
were impregnated with carbonate of lime by soaking in
water, holding this compound in suspension. The vessel
No. 7 was occupied with Meudon chalk, washed and
dried. No. 8 contained a clayey soil thoroughly washed
with water and ignited so as to carbonize the organic
matters without baking the clay. No. 9 held the same
earth washed and dried, but not calcined. Lastly, in No.
10, was placed moist pumice-stone mixed with pure car-
bonate of lime and 10 grms. of urea, the nitrogenous princi-
ple of urine. Through these vessels a slow stream of puri-
fied air, amounting to 160,000 liters, was jjassed, night and
day, for 8 months. At the conclusion of the experiment,
vessel No. 1 contained a minute quantity of nitric acid,
which, undoubtedly, came from the atmosphere, having
escaped the purifying apparatus. The contents of Nos.
2, 4, and 5, were free from nitrates. Nos. 3 and 6, con-
taining fragments of washed brick, gave notable evidences
of nitric acid. Traces Avere also found in the Avashed
chalk. No. 7, and in the calcined soil. No. 8. In No. 9,
filled Avith washed soil, niter was abundant. No. 10,
* Rcoheiclies sur la Nitrification— Legons de Chimie professtee en 1861 4 I4
Soci6t6 Chimique de Paris, pp. 145-150.
264 noAv CROPS feed.
containing pumice, carbonate of lime, and urea, was desti-
tute of nitrates.
Exj^eriments 2, 4, and 5, demonstrate that the concourse
of nitrogen gas, a porous hody, and an alkali-carbonate,
is insufficient to jjroduce nitrates. Experiment No. 10
shows that the highly nitrogenous substance, urea,* dif-
fused throughout an extremely porous medium and expos-
ed to the action of the air in moist contact Avitli carbonate
of lime, does not suffer nitrification. In the brick (ves-
sels Nos. 3 and 6), something was obviously present,
which determined the oxidation of free atmospheric ni-
trogen. Cloez took the brick fresh fi-om the kiln where
it was burned, and assured himself that it included at
the beginning of the experiment, no nitrogen in organic
combination and no nitrates of any kind. Cloez believes
the brick to have contained some oxidable mineral sub-
stance, probably sulphide of iron. The Gentilly clay,
used in making the brick, as well as some iron-cinder,
added to it in the manufacture, furnished the elements of
this compound.
The slight nitrification that occurred in the vessels
Nos. 7 and 8, containing washed chalk and burned soil,
likewise points to the oxidizing action of some mineral
matter. In vessel Xo. 9, the simply Avashed soil, which
was thus freed from nitrates before the trial began, un-
derwent a decided nitrification in remarkable contrast to
the same soil calcined (No. 8). The infliience of humus
is thus brought out in a striking manner.
It may be that apocrenic acid, which readdy yields
oxygen to oxidable matters, is an important agent in
Urea (COH4 Na) contains in 100 parts :
Carbon, 20.00
Hydrogen, 6.67
Nitrogen, 46.67
Oxygen, 26.68
iiwiot
TIIK Xll'Urc ACID OF TUK SOIL. 205
nitrification. As Ave have seen, this acid, according to
Mukler, passes into crenic acid by loss of oxygen, to be
reproduced from tlie latter by absorption of free oxygen.
The apocrenate of sesquioxide of iron, in wliicli both acid
and base are susceptible of this transfer of oxygen,
should thus exert great oxidizing power. (See p. 228.)
The Conditions Influencing IVitrification have been
for the most part already mentioned incidentally. We
may, however, advantageously recapitulate them.
a. The formation of nitrates appears to require or to be
facilitated by an elevated temperature, and goes on most
rapidly in hot weatlier and in hot climates.
h. Accordhig to Knop, ammonia that has been absorbed
by a soil suffers no change so long as the soil is dry ; but
when the soil is moistened, nitrification quickly ensues.
Water thus appears to be indispensable in this process.
c. An alkali base or carbonate appears to be essential
for the nitric acid to combine with. It has been thought
that the mere presence of potash, soda, and lime, favors
nitrification, " disposes," as is said, nitrogen to unite with
oxygen. Boussingault found, however [Chimie Agri-
cole, III, 198), that caustic lime develo2:)ed ammonia from
the oi'ganic matters of his garden soil Avithout favoring
nitrification as much as mere sand. The caustic lime by
its chemical action, in fact, opposed nitrification ; while
pure sand, probably by dividing the particles of eartli and
thus perfecting their exposure to the air, facilitated this
process. Boussingault's experiments on this point were
made by incloshig an earth of known composition (from his
garden) with sand, etc., in a large glass vessel, and, after
three to seven months, analyzing the mixtures, \\ Inch were
made suitably moist at the outset. Below are the results
of five experiments.
I. 1000 grms. of soil and 850 grms. sand acquired 0.012 grms. amiuouia and
0.482 grms. nitric acid.
n. 1000 grms. of soil and 5500 grms. sand acquired 0.035 grms. ammonia and
0.545 gnus, nitric acid.
12
Ji66 tiow cuors yEtin.
HI. 1000 grm?. of soil and 500 grms. marl acquired 0.002 grms. ammonia and
0.360 grms. nitric acid.
IV. 1000 grms. of soil and 2 grms. carbonate of potash acquired 0.015 grms.
ammonia and 0.290 grms. nitric acid.
V. 1000 grms. of soil and 200 grms. quiclilime acquired 0.303 grms. ammonia
and 0.099 grms. nitric acid.
The unfavorable effect of caustic lime is well pronounc-
ed and is confirmed by other similar experiments. Car-
bonate of potash, which is strongly alkaline, but was used
in small quantity, and marl (carbonate of lime), which is
but very feebly alkaline, are plainly inferior to sand in
their influence on the development of nitric acid.
The effect of lime or carbonate of potash in these ex-
periments of Boussingault may, perhaps, be thus explain-
ed. Many organic bodies which are comparatively stable
of themselves, absorb oxygen with great avidity in j^res-
ence of, or rather when combined with, a caustic alkali.
Crenic acid is of this kind ; also gallic acid (derived from
nut-galls), and especially pyrogallic acid (a result of the
dry distillation of gallic acid). The last-named body,
when dissolved in potash, almost instantly removes the
oxygen from a limited volume of air, and is hence used
for analysis of the atmosphere.*
We reason, then, that certain organic matters in the
soil of Boussingault's garden, became so altered by treat-
ment Avith lime or carbonate of potash as to be susceptible
of a rapid oxidation, in a manner analogous to ^\•hat hap-
pens with pyrogallic acid. Dr. H. Angus Smith has shown
{Jour. Boy. Ag. /Soc, XVII, 436) that if a soil rich in or-
ganic matter be made alkaline, moist, and warm, putre-
factive decomposition may shortly set in. This is what
happens in every well-managed compost of lime and j^eat.
By this rapid alteration of organic matters, as we shall see
(p. 268), not only is nitric acid not formed, but nitrates
added are reduced to ammonia. It is not improbable that
• Not all organic bodies, by any means, are thus affected. Li:
nlteration of urine, flesh, and the albuminoids.
THE NITRIO XC\U OP THE SOIL. S67
emallcr doses of lime or alkali than those employed by
Boussingault Avould have been found promotive of nitri-
fication, especially after the lapse of time sufficient to
allow the first rapid decomposition to subside, for then
we should expect that its presence would favor slow oxida=
tion. This view is in accordance with the idea, universally
received, that lime, or alkali of some sort, is an indispensa-
ble ingredient of artificial niter-beds. The point is one
upon which further investigations are needed.
d. Free oxygen^ i. e., atmospheric air, and the porosity
of soil which ensures its contact with the jiarticles of the
latter, are indispensable to nitrification, which is in all
cases a process of oxidation. When sesquioxide of iron
oxidizes organic matters, its action would cease as soon as
its reduction to protoxide is complete, but for the atmos-
pheric oxygen, which at once combines with the protoxide,
constantly reproducing the sesquioxide.
In the saltpeter plantations it is a matter of experience
that light, porous soils yield the largest product. The
operations of tillage, which promote access of air to the
deeper portions of earth and counteract the tendency of
many soils to " cake " to a comparatively impervious mass,
must also favor the formation of nitrates.
Many authors, especially Mulder, insist upon the physic-
al influence of porosity in determining nitrification by
condensed oxygen. The probability that porosity may
assist this process where compounds of nitrogen are con-
cerned, is indeed great ; but there is no evidence that any
porous body can determine the union of free nitrogen and
oxygen. Knop found that of all the proximate ingredi-
ents of the soil, clay alone can be shown to be capable of
physically condensing gaseous ammonia (humus combines
with it chemically, and if it previously effects physical
condensation, the fact cannot be demonstrated).
The observations by Reichardt and Blumtritt on the
condensing effect of the soil for the gases of the atmos-
S68 HOW CROPS FKEB.
jjhere (p. 107) indicate aLsorption Loth of oxygen and
nitrogen, as well as of carbonic acid. The fact that cliar^
cx)al acts as an energetic oxidizer of organic matters lias
been alluded to (p. 1G9). Tliis action is something very
remarkable, altliough charcoal condenses oxygen but to a
slight extent. The soil exercises a similar but less vigorous
oxidizing effect, as the author is convinced from experi-
ments made under his direction (by J, J. Mattliias, Esq.),
and as is to be inferred from the Avell-known fact that the
odor of putrefying flesh, etc., cannot pa^s a certain thickness
of soil. But charcoal is unable to accomplish the union
of oxygen and nitrogen at common temperatures, or at
212° F., either di-y, moistened with pure water, or with
solution of caustic soda. (Experiments in Sheflield labo-
ratory, by Dr. L. H. Wood.)
Putrefying flesh, covered w^ith charcoal as in Stenhouse's
experiment (p. 169) gives off ammonia, but no nitric acid is
formed. Dumas has indeed stated ( Comptes Rend.^ XXIIT)
that ammonia mixed with air is converted into nitric
acid by a porous body — chalk — that has been drenched
■with caustic potash and is heated to 21r2° F. But this is
an error, as Dr. Wood has demonstrated. It is true that
platinum at a liigh temperature causes ammonia and oxy-
gen to unite. Even a platinum wire when heated to red-
ness exerts this effect in a striking manner (Kraut, Ann.
Gh. V. Ph., loG, 69) ; but spongy platinum is without ef-
fect on a mixture of air and ammonia gas at 212° or lower
temperatures. (Wood.)
e. Presence of organic matters prone to oxidation. Me-
duction of 'nitrates to ammonia, etc., in. the soil. — As we
have seen, the organic matters (humus) of the soil are a
source of nitric acid. But it appears that this is not al-
ways or universally true. In compact soils, at a certain
depth, organic matters (their hydrogen and carbon) may
oxidize at the expense of nitric acid itself, converting the
latter into ammonia. Pelouze {Comptes Bendus, XLIY,
TUB NITKIO ACID OF TlIK SOIL. 2fi{i
118) has proved that putrefying animal substances, as al-
bumhi, thus reduce nitric acid with formation of ammonia.
For this reason, he adds, tlie liquor of dung heaps and
putrid urine contains little or no nitrates. Boussingault
{A(/ro}iomie, II, 17) examined a remarkably rich alluvial
soil from the junction of the Amazon with the Rio Cupari,
made up of alternate layers of sand and partially decayed
leaves, containing 40" |„ of the latter. This natural leaf-
compost contained no trace of nitrates, but an exception-
ally high quantity of ammonia, viz., .05"]^.
Kuhlmann [Ann. de Chim. et de Phys., 3 Ser., XX)
was the first to draw attention to the probability that ni-
tric acid may thus be deoxidized i:i the lower strata of
the soil, and his arguments, drawn from, facts observed
in the laboratory, appear to apply in cases where there
exist much organic matters and imperfect access of air.
In a soil so porous as i^ demanded for the culture of most
crops these conditions cannot usually occur, as Grouven
has taken the trouble to demonstrate [Zeitschnft fur
Deutsche Landwirthe, 1855^ p. 341). In rice swamps and
peat bogs, as well as in wet compost heaps, this reduction
must proceed to a considerable extent.
In some, if not all cases, the addition of much lime or
other alkaline substance to a soil rich in organic matters
sets up rapid putrefactive decomposition, whereby nitrates
are at once reduced to ammonia (p. 266).
In one and the same soil the conditions may exist at
different times that favor nitrification on the one hand,
and reduction of nitrates to ammonia on the other. A
surplus of moisture might so exclude air from a porous
Boil as to cause reduction to take place, to be succeeded
by rapid nitrification as the soil becomes more dry.
It is possible that nitrates may undergo further chemi-
cal alteration in the i)resence of excess of organic matters.
That nitrites may often exist in the soil is evident from
what has been written with regard to the mutual convert-
2T0 HOW CROPS FEED.
ibility of nitrates and nitrites (p. 73). According to
Goppelsroder {Blngler's Polytech. Jour.^ 164, 388), certain
soils rich in liumus possess in a high degree the power to
reduce nitrates to nitrites. It is not unlikely that further
reduction may occur — that, iu fact, the deoxidation may
be complete and free nitrogen be disengaged. This is a
question eminently worthy of study.
Loss of Nitrates may occur when the soil is saturated
with Avater, so that the latter actually flows through and
away from it, as happens during heavy rains, the nitrates
(those of sesquioxide of iron, perhaps, excepted) being
freely soluble and not retained by the soil. Boussingault
made 40 analyses of lake and river Avater, 25 of spring
Water, and 35 of well water, and found nitric acid in ev-
ery case, though the quantity varied greatly, being largest
in cities and fertile regions. Thus the water of the upper
Rhine contains one millionth, that of the Seine, in Paris,
six millionths, and that of the Nile four millionths of ni-
tric acid. The Rhine daily removes from the countiy
supplying its waters an amount of nitric acid equivalent
to 220 tons of saltpeter. The Seine carries daily into the
Atlantic 270 tons, and the Nile pours 1,100 tons into the
Mediterranean every twenty-four hours.
In the wells of crowded cities the proportion of nitrates
is much higher. In the older parts of Paris the well wa-
ters contain as much as one part of niter (or its equiva-
lent of other nitrates) in 500 of water.
The soil may experience a loss of nitrates by the com-
plete reduction of nitric acid to gaseous nitrogen, or by
the formation of inert compounds with humus, as Avill be
noticed in the next section.
Loss of assimilable nitrogen by the washing of nitrates
from the soil may be hindered to some extent in compact
soils by the fact just noticed that nitric acid is li;d)le to be
converted into ammonia, which is at once rendered com-
paratively insoluble.
THE NITRIC A^;ID OF THE SOIL.
271
Mtric Acid as Food to Plants. — Experiments demon-
strating thaf nitric acid is capable of perfectly supplying
vegetation with
nitrogen were
first made by
Bouss i n g a u 1 1
( Agroiiomie ^
Chimie A(jri-
cole, etc., 1,210).
We give an ac-
count of some
of tliese.
Two seeds of
a dwarf Sunflow-
er {Ilellanthus
argophyllxis),
Avere planted in
each of three
pots, the soil of
which, consist-
ing of a mixture
of brick - dust
and sand, as well
as the pots them-
selves, liad been
thoroughly
freed from all ni-
trogenous com-
pounds by igni-
tion and wash-
ing with dis tili-
ng. 0. ed Avater. To
the soil of the pot A, fig. 9, nothing was added save the
two seeds, and distilled water, Avith which all the plants
were watered from time to time. With the soil of pot
C, w^ere incorporated small quantities of phosphate of lime,
272
UOW OROPo FEED.
of ashes of clover, and bicarbonate of potas^i, h orJertTiat
the phmts growing in it miglit have an abundant supply
of all the ash-ingredients they needeil. Finally^ the soil
of pot D received the same mineral matters as pot C, and,
in addition, a small quantity (1.4 gram) of nitrate of pot-
ash. The seeds were sown on the 5th of July, and on the
30th of September, the plants had the relative size and
appearance seen in the figure, whei"e they are represented
in one-eiglith of the natural dimensions.
For the sake of comparison, the size of one of the
largest leaves of the same kind of Sunflower that grew
in the garden is represented at D, in one-eighth of its
natural dimensions.
Nothing can be more striking than the influence of the
nitrate on the growth of this plant, as exhibited in this
experiment. The plants A and C are mere dwarfs, al-
thougli both carry small and imperfectly developed flow-
ers. The plant D, on the contrary, is scarcely smaller
than the same kind of plant growing under the best con-
ditions of garden culture. Here follows a Table of the
results obtained by the examination of the plants.
II
!,§ Acqvired by the
"fe"-^'
II
g,§ plants in '^t days
^S *
g^ of regelatioH.
t^l
1%
<i"~ 1 Xitro-
E^SS
f^5
Cg Carbon.] gen.
cubic 1 1
frrni.
cunt. 1 srm. i grm.
A— nothing added to tlie soil
3.6
0.285
2.45 i 0.114 0.0023
C— aslius, phosphate of lime, and hi-'
carbonate of potash, added to thej
D — ashes, phosphate of lime, and ni-'
irate of potash, added to tlio soil..| 198.3
3.42 I 0.15G ' 0.0027
21.111 I 182.00 I 8.444 I 0.1666
We gather from the above data :
1. That without some compound of nitrogen in the soil
vegetation cannot attain any considerable development,
notwithstanding all requisite ash-ingredients are present
THE NITRIC ACID OF THE SOIL.
273
in abundance. Observe that in exps. A and C the crop
attained but 4 to 5 times greater weight than the seed,
and gathered from the atmospliere during 86 days but 2^
milligrams of nitrogen. The crop, supplied with nitrate
of potasli, weighed 200 times as much as the seed, and
assimilated 6G times as much nitrogen as was acq;iired by
A and C from external sources.
2. That nitric acid of itself may furnish all the nitrogen
requisite to a normal vegetation.
In another series of experiments (Ar/ronomie, etc., I, pp.
227-233) Boussingault prepared four pots, each containing
145 grams (about 5 oz. avoirdupois) of calcined sand
with a little pliosphate of lime and ashes of stable-dung,
and planted in each two Sunflower seeds. To three of
the pots he added weighed quantities of nitrate of soda — ■
to No. 3 twice as much as to No. 2, and to No. 4 three
times as much as to No. 3 ; No. 1 received no nitrate.
The seeds germinated duly, and the plants, sheltered from
rain and dew, but fully exposed to air, and watered with
water exempt from ammonia, grew for 50 days. In the
subjoined Table is a summary of the results.
i
J
1
ji-i
Relative tveights of
matter organized,
that of first Exp.
taken as vnity.
grms.
grms.
grms.
gnus.
grms.
grms.
grms.
grms.
1 . . 0 0033
2.. 0.00.33
8.. 0.0033
4.. 0.0033
0.0000
0.0033
O.OOOf!
0.0264
0.0033
O.OOfifi
0.009!)
0.0297
0.00.53 1 0.002Ut
0.00()3 O.OOO-^t
0.0097 0.0002;
0.0251 0.004f4
0.307
0.720
1.130
1
1.8
2.S
8.5
2
3
9
N=Nitrogen.
In the first Exp. a trifling quantity of nitrogen Avas
gathered (as air.monia?) from the air. In the others, and
especially in the last, nitrate of soda remained in the soil,
12*
2T4 HOW CROPS FEED.
not having been absorbed entirely by the plants. Observe,
however, what a remarkable coincidence exists between
the ratios of supply of nitrogen in form of a nitrate and
those of growth of tlie several crops, as exhibited in the
last two columns of the Table, Nothing could demon-
strate more strikingly the nutritive function of nitric acid
than these admirable investigations.
Of the multitude of experiments on vegetable nutrition
which have been i*ecently made by the process of water-
culture {H. C. G., p. 167), nearly all have depended upon
nitric acid as the exclusive source of nitrogen, and it has
proved in all cases not only adequate to this purpose, but
far more certain in its effects than ammonia or any other
nitrogenous compound.
§6.
NITROGENOUS ORGANIC MATTERS OF THE SOIL.
AVAILABLE NITROGEN.— QUANTITY OF NITROGEN
REQUIRED FOR CROPS.
In the minerals and rocks of the earth's surface nitrogen
is a very small, scarcely ajjpreciable ingredient. So far as
we now know, ammonia-salts and nitrates (nitrites) are
the only mineral compounds of nitrogen found in soils.
When, however, organic matters are altered to humus,
and become a part of the soil, its content of nitrogen ac-
quires significance. In peat, which is humus compara-
tively free from earthy matters, the proportion of nitrogen
is often very considerable. In 32 specimens of peat ex-
amined by the author {Peat and its Uses as Fertilizer and
Fuel, p. 90), the nitrogen, calculated on the organic mat-
ters, ranged from 1.12 to 4.31 per cent, the average being
2.6 per cent. The average amount of nitrogen in the aii--
dry and in some cases highly impure jieat, was 1.4 ]ier
tent. This nitrogen belongs to the (>rL,'a-)ir ni;ittcrs in
KITROGBNOUS ORGANIC MAITEIIS OF THE SOIL. 275
great part, but a small proportion of it being in the form
of ammonia-salts or nitrates.
In 1846, Krocker, in Liebig's laboratory, first estimated
the nitrogen in a number of soils and marls {An?i. Ch. ic.
PA., 58, 387). Ten soils, which were of a clayey or loamy
character, yielded from 0.11 to 0.14 per cent; three sands
gave from 0.025 to 0.074 per cent; seven marls contained
0.004 to 0.083 per cent.
Numerous examinations have since been made by An-
derson, Liebig, Kitthausen, Wolff, and others, with simi-
lar results.
In all but his latest writings, Liebig has regarded thi\
nitrogen as available to vegetation, and in fact designated
it as ammonia. Way, Wolff, and others, have made evi-
dent that a large portion of it exists in organic combina-
tion. Boussingault [Agronomie, T. I) has investigated
the subject most fully, and has shown that in rich and
highly manured soils nitrogen accumulates in considerable
quantity, but exists for the most part in an insoluble and
inert form. In the garden of Liebfrauenberg, which had
been heavily manured for centuries, but 4°!^, of the total
nitrogen existed as ammonia-salts and nitrates. The soil
itself contained —
Total nitrogen, 0.2G1 per cent.
Ammonia, 0.0022 " "
Nitric acid, 0.00034 " "
The subjoined Table includes the results of Boussin-
gault's examinations of a number of soils from France and
South America, in which are given the quantities of am-
monia, of nitric acid, expressed as nitrate of potash, and
of nitrogen in organic combination. These quantities are
stated both in 2)er cent of the air-dry soil, and in lbs. av.
per acre, taken to the depth of 17 inches. In another
column is also given the ratio of nitrogen to carbon in the
organic matters. [Agfrononiie, T IT, pp. 14-21.)
27Q
IIOAV CROPS FEED.
Ammonia, Nitbates, ^yn Organic Nitkogen of various Boils.
Ammonia.
Nitrate of i
potash.
j\itroyen. in
org. combfn.
Soils.
libs.
lbs.
lbs
per per
per
per
per
per
111
cent, jacre
cent
acre
cent.
acre
^ fLicbfrauenbercr. lii:ht ?ard. soil 0.(i()i-J 100
0.0175*
8-5|
0.259
12970
1:9 3
" I Bischwillcr, li;,'lit j,'ardoa soil... .O.OOCdi 100
5 1 Bcchelbronn. wheal field clay, 'o.oood' 45
0.1,520
7(!30
0.295
14755 1:9.7
0.0015
75
0.139
69S5 1:8.2
^ Armenian, rich T)asturc
0.(IO',:(F -150
O.0046
0.0004
230
20 '
0.513
0.143
25050 1:8
«• fRio Madeira, sugar field, clay
7i;o! 1:0.3
^ RioTromhctto.forestheavydo. o.oii-io, Is:!
0.0001
5
0.119
5955, 1:4.9
« 1 Rio Negro, prairie V. fine sand. (l.OO;;Si I'.io
0.0001
5
O.OOS
3440 1:5 «
£ J Santarem, cocoa plantation.. O.00S3
•< j Saracca, near Amazon, loam.. lO.OO^'i
415
0.0011
55,
0.649
32450, 1:11
2io;
none 1
0.102
9U;0 1:8.2
J3 RioCupari, rich leaf mould.... (). 0505
"
0.CS5
34250; 1:18.8
c lies du Salut, French Guiana... l).0:):^0
400
0.0043 13215
0.M3
27170, ]:11.T
,2 1 Martinique, suirar field |l).0055
275
O.OlKfi 1 900
0.112
5590' 1:8
* The same soil whose partial analysis has just been given, but examined for
nitrates at another time.
It is seen that in all cases the nitrogen in the forms of
ammonia f and nitrates J is much less than that in organic
combination, and in most cases, as in the Liebfrauenberg
garden, the disparity is very great.
Nature of the Nitrogenous Org.anic Matters. Amides.
— Hitherto we have followed Mulder in assuming that the
humic, ulmie, crenie, and apocrenic acids, are destitute of
nitrogen. Certain it is, however, that natural humus is
never destitute of nitrogen, and, as we have remarked in
case of peat, contains this element in considerable quanti-
ty, often 3 per cent or more. Mulder teaches that the
acids of humus, themselves free from nitrogen, are nat-
urally combined to ammonia, but that this ammonia is
with difficulty expelled from them, or is indeed impossible to
separate completely by the action of solutions of the fixed
alkalies. In all chemistry, beside, there is no example
of such a deportment, and we may well doubt whether
the ammonia that is slowly evolved when natural humus
is boiled with potash is thus expelled from a humate of
ammonia. It is more accordant with general analogies to
+ .\mmonia contains 82.4 per cent of iiilroQ-on.
^ Nitrate ot ootash contains Ti.b pjr cent of nitrogea.
NJTnOOKXOrfl OnCAXIC Jr.VTTET^S OP THE ROIL. 277
suppose that it is (joierated by the action of the alkali,
In fact, there are a large number of bodies whicli manifest
a similar dep<irtmcnt. Many substances which are pro-
duced from ammonia-compounds by heat and otherwise,
and called (onide^^ to whicli allusion has been already
made, p. 276, are of this kind. Oxalate of ammonia, when
heated to decomposition, yields oxamide, which contains
the elements of the oxalate minus the elements of two
molecules of water, viz.,
Oxalate of ammonia. Oxam,ide. Water.
2 {N HJ C, 0, = 2 (IS" HJ C, O^ + 2 H,0
On boiling oxamide with solution of potash, ammonia
is reproduced by the taking up of two molecules of water,
and passes off as a gas, while oxalate of potash remains in
the liquid.
Nearly every organic add known has one or several
amides, bearing to it a relation similar to that thus sub-
sisting between oxalic acid and oxamide.
Asparagine, a crystallizable body found in asparagus
and many other plants, already mentioned as an amide, is
thought to be an nmide of malic acid.
TJrea, the principal solid ingredient of human urine, is
an amide of carbonic acid. Uric acid, hippuric acid, gua-
nine, found also in urine; kreatin and kreatinine, occurring
in the juice of flesh ; thein, the active principle of tea and
coffee ; and theobromin, that of chocolate, are all regard-
ed as amides.
Amide-like boaies are gelatine (glue), the organic sub-
stance of the tendons and of bones, that of skin, hair,
wool, and horn. The albuminoids themselves are amide-
like, in so far that they yield ammonia on heating with
solutions of caustic alkalies.
Albuminoids a Source of the Nitrogen of Ilumus.^
The organic nitrogen of humus may come from the albu-
minoids of the vegetation that has decayed upon or in the
278 HOW CROPS FEED.
soil. In their alteration by decay, a portion of nitrogen
assumes the gaseous form, but a portion remains in an in-
soluble and comparatively unalterable condition, though
in what particular compounds we are unable to say. The
loss of carbon and hydrogen from decaying organic mat-
ters, it is believed, usually proceeds more rapidly than the
waste of nitrogen, so that in humus, which is the residue
of the change, the relative proportion of nitrogen to car-
bon is greater thnn in the original vegetation.
Reyersion of IVitric Acid and Ammonia to inert Forms.
— It is probable that the nitrogen of ammonia, and of ni-
trates, which are reducible to ammonia under certain con-
ditions, may pass into organic combination in the soil.
Knop ( VersucJis St., Ill, 228) found that when peat or
soils containing humus were kept for several months in
contact with ammonia in closed, vessels, at the usual tem-
perature of summer, the ammonia, according to its quan-
tity, completely or in part disappeared. There having been
no such amount of oxygen present as would be necessary to
convert it into nitric acid, the only explanation is that the
ammonia combined with some organic substance in the
humus, forming an amide-like body, not decomposable by
the hypochlorite of soda used in Knop's azometrical anal-
ysis.
Facts supporting the above view by analogy are not
wanting. When gelatine (a body of animal origin closely
related, to the albuminoids, but containing 18 instead of
15° Id of nitrogen) is boiled with dilute acids for some
time, it yields, among other products, sugar, as Gerhardt
has demonstrated. Prof. T. Sterry Hunt was the first to
suggest {Am. Jour. Sci. d Arts, 1848, Vol. 5, p. 76) that
gelatine has nearly the composition of an amide of dextrin
or other body of the cellulose group, and might be regard-
ed as derived chemically from dextrin (or starch) by the
union of the latter with ammonia, water being eliminated.
viz.:
NITROGENOUS ORGANIC MATTERS OF THE SOIL. 279
Carbohydrate. Ammonia. Water, Gelatine.
C.. H,„ 0,„ + 4 NH3 - 6 11,0 + 2 (C, H,„ N, OJ.
Afterwards Dusart, Schiitzenberger, and P. Thenard, in-
dependently of each otlier, obtained by exposing dextrin,
starcli, and glucose, to a somewhat elevated temperature
(300-360°F.), in contact with ammonia-water, substances
containing from 11 to 19° |„ of nitrogen, some soluble in
water and havhig properties not unlike those of gelatine,
others insoluble. It was observed, also, that analogous
compounds, containing less nitrogen, were formed at lower
temperatures, as at 212° F. Payen had previously observed
that cane sugar underwent entire alteration by prolonged
action of ammonia at common temperatures.
These facts scarcely leave room to doubt that ammonia,
as cai-bonate, by prolonged contact with the humic acids
or with cellulose, and bodies of like composition, may
form combinations with them, from which, by the action
of alkalies or lime, ammonia may be regenerated.
It has already been mentioned that when soils are boil-
ed with solutions of potash, they yield ammonia continu-
ously for a long time.
Boussingault observed, as has been previously remarked,
that lime, when incorporated with the soil at the ordinary
temperature, causes its content of ammonia to increase.
Soil from the Liebfrauenberg garden, mixed with 'j^
its weight of lime and nearly ^ its weight of water, was
placed in a confined atmosphere for 8 months. On open-
ing the vessel, a distinct odor of ammonia was perceptible,
and the earth, which originally contained per kilogram,
11 milligrams of this substance, yielded by analysis 303
mgr. (See p. 265, for otlier similar results.)
Alteration of Albuminoids in the Soil.— Albuminoids
are carried into the soil when fresh vegetable matter is in-
corporated with it. They are so susceptible to alteration,
however, that under ordinary conditions they must speed-
280 now CROPS feed.
ily decomjiose, and cannot therefore themselves be consid<
ered as ingredients of the soil.
Among- the proximate products of their decomposition
are organic acids (butyric, valeric, propionic) destitute of
nitrogen, and the amides leucin (C^ n,^ N0„) and tyrosin
(Cg H,, NO.,). These latter bodies, by further decompo-
sition, yield ammonia. As has been remarked, it is proba-
ble that the albuminoids, when associated as they are in
decay with cellulose and other carbohydrates, may at
once give rise to insoluble amide-like bodies, such as those
whose existence in humus is evident from the consider-
ations already advanced.
Can these Organic Bodies Yield Nitrogen Directly to
Plants ? — Tliose nitrogenous organic compounds that exist
in the soil associated with humus, which possess something
of the nature of amides, though unknown to us in a pure
state, appear to be nearly or entirely incapable of feeding
vegetation directly. Our information on this point is de-
rived from the researches of Boussingault, whose papers
on this subject {De la Terre vegetale consideree dans ses
effets sur la Vegetation) are to be found in his Agronomie,
etc., Vols. I and II.
Boussingault experimented with the extremely fertile
soil of his garden, which was rich in all the elements
needful to support vegetation, as was demonstrated by the
results of actual garden culture. This soil was especially
rich in nitrogen, containing of this element 0.26° |^, which,
were it in the form of ammonia, wonld be equivalent to
more than 7 tons per acre taken to the depth of 13 inches ;
or, if existing as nitric acid, would correspond to more*
than 43 tons of saltpeter to the acre taken to the depth
just mentioned.
This soil, however, when employed in quantities of 40
to 130 grams (1^ to 4^ oz. av.) and shielded from rain
and dew, was scarcely more capable of carrying lupins,
beans, maize, or hemp, to any considerable development,
AVAII.ABr.K XITKOc^.EX OF TTIK SOIL. 281
than the most barren sand. Tri eiglit distinct trials the
crops "weighed (dry) but 3 to 5 times, in one case 8 times
(average 4 times), as much as the seed; while in sand,
pumice, or burned soil, containing no nitrogen, Boussin-
gault several times realized a crop weighing 6 times as
much as the seed, though the average crop of 38 experi-
ments was but 3 times, and tlie lowest result l{r times the
weight of the seed.
The fact that the nitrogen of this garden soil was for
the most part inert is strikingly shown on a comparison
of the crops yielded by it to those obtained in barren
soil with aid of known quantities of nitrates.
In a series of experiments with the Sunflower, Boussin-
gault {Ar/ronomie, etc., I, -p. 233) obtained in a soil desti-
tute of nitrogen a crop weighing (dry) 4.6 times as much
as the seeds, the latter furnisliing the plants 0.0033 grm, of
nitrogen. In a second pot, with same weight of seeds, in
which the nitrogen was doubled by adding 0.0033 grm. in
form of nitrate of soda, the weight of crop was nearly-
doubled — was 7.6 times that of seeds. In a third pot the
nitrogen was trebled by adding 0,0066 grm. in form of ni-
trate, and the crop was nearly trebled also — was 11.3
times the weight of the seeds.
In another experiment (p. 271) the addition of 0.194
grm. of nitrogen as nitrate of potash to barren sand with
needful mineral matters, gave a crop weighing 198 times
as much as the seeds. But in the garden soil, which con^
tained, when 40 grms. were employed 0.104 grm., and when
130 grms. were used 0.338 grm. of nitrogen, the result of
growth was often not greater than in a soil that contained
no nitrogen, and only in a single instance surpassed that
of a soil to which was added but 0.0033 gim. The fact
is thus demonstrated that but a very small proportion of
the nitrogen of this soil was assimilable to A^'getation.
I'rom these beautiful investigations Boussingault deems
it highly probable that in this garden soil, and in soils
,iS,i now CROPS FF.Kn.
generally which have not been recently manured, ammonia
and nitric acid are the exclusive feeders of vegetation with
nitrogen. Such a view is not indeed absohitely demon-
strated, but the experiments alluded to render it in the
highest degree probable, and justify us in designating the
organic nitrogen for the most part as inert, so far as vege-
table nutrition is concerned, until altered to nitrates or
ammonia-salts by chemical change.
To comprehend the favorable results of garden-culture
in such a soil, it must be considered what a large quantity
of earth is at the disposal of the crop, viz., as Boussingault
ascertained, 57 lbs. for each hill of dwarf beans, 190 lbs.
for each hill of potatoes, 470 lbs. for each tobacco plant,
and 2,900 lbs. for every three hop-plants.
The quantity and condition of the nitrogen of Boussin-
gault's garden soil are stated in tlie subjoined scheme.
Available \ Ammonia 0.00220 per cent = Nitrogen 0.00181 per cent I „ nmn „ f
nitrogen "(Nitric acid 0.00034 " '• = " 0.00009" " )' U-UUi.i per ct.
Inert nitrogen— of organic compounds 0.2591 " "
Total nitrogen 0.2610 per ct.
Calculation shows that in garden culture the plants
above named would have at their disposal in this soil quan-
tities of inert and available nitrosren as follows :
Weight of soil. Inert
nitrogen.
Available
nitrogen.
Bean (dwarf) hill
57 lbs. 75 gi
rams.*
1 gram.
Potato, "
190 " 242
"
3 grams.
Tobacco, single plant,
470 " 555
"
7 "
Hop, three plants.
2900 " ^m
ns avoirdupois nearly.
44 "
* 1 gram = 15 grai
17 gramas 1 oz.
283 " = lib.
.; u
Indirect Feeding of Crops by the Organic Nitrogen
of tlie Soil. — In what has been said of the oxidation of
the organic matters of the soil, (whereby it is probable
that their nitrogen is partially converted into nitric acid,)
and of the effect of alkalies aud lime upon them, (whereby
ammonia is generated,) is given a clue to the understand-
AVAILABLE NITROGEN OF THE SOIf.. S8.^
ing of their indirect nutritive influence upon vegetation.
By these chemical transformations the organic nitrogen
may pass into the two compounds wliich, in the present
state of knowledge, we must regard as practically the ex-
clusive feeders of the plant with nitrogen. The rapidity
and completeness of the transformation depend upon
circumstances or conditions which we vinderstand but im-
perfectly, and which are extremely important subjects for
furtlier investigation.
Difliciilty of estimating ttic Available Nitrogen of any
Soil. — The value of a soil as to its j^ower of supplying
plants with nitrogen is a problem by no means easy to
solve. The calculations tliat have just been made from
the analytical data of Boussingault regarding the soil of
his garden are necessarily based on the assumption that
no alteration in the condition of the nitrogen could take
place during the period of growth. In reality, however,
there is no constancy either in the absolute quantity of
nitrogen in the soil or in its state of availability. Por-
tions of nitrogen, both from the air and from fertilizers,
may continually enter the soil and assume temporarily the
form of insoluble and inert organic combinations. Other
portions, again, at the same time and as continually, may
escape from this condition and be washed out or gathered
by vegetation in the form of soluble nitrates, as has al-
ready been set forth. It is then manifestly impossible to
learn more from analysis, than how much nitrogen is avail-
able to vegetation at the moment the sample is examined.
To estimate with accuracy what is assimilable during the
whole season of growth is simply out of the question.
The nearest approach that can be made to this result is to
ascertain how much a crop can gather from a limited vol-
ume of the soil.
Brctschneidcr's ExperinicntSt — We may introduce here
a notice of some recent researches made by Bretschneider
in Silesia, a brief account of Avhich has appeared since the
284
ttOAV CROPS FKEO.
foregoing paragraplis were Avritten. {JaJireshericht il.
Ag. Chem., 18G5, 29.)
Bretschneider's experiments were made for the purpose
of estimating how much ammonia, nitric acid, and nitro-
gen, exist or are formed in the soil, either fallow or occu-
pied Avith various crops during the period of growth.
For this purpose he measured olf in the field four plots of
ground, each one square rod (Prussian) in area, and sepa-
rated from the others by paths a yard wide. The soil of
one plot was dug out to the depth of 12 inches, sifted,
and after a board frame 12 inches deep had been fitted to
the sides of the excavation, the sifted earth was filled in
again. This and another — not sifted — plot were planted
to sugar beets, another was sown to vetches, and the
fourth to oats.
At the end of April, six accurate and concordant anal-
yses were made of the soil. Afterwards, at five difterent
periods, a cubic foot of soil was taken from each plot, and
from the spaces between that bore no vegetation, for de-
termining the amounts of nitric acid, ammonia, and total
nitrogen. The results of this analytical work are given
in the following Tables, being calculated in pounds for the
area of an acre, and to the depth of 12 inches (English
measures*) :
AMOUNT OP AMMONIA.
Beet plot,
sifted soil.
Beet plot.
Vetch plot.
Oatplot.
Vacant plot.
Elul of April,
59
59
59
59
59
l-2th June,
15
48
41
32
28
30th June,
12
41
24
40
32
22(1 July,
9
29
39
22
29
13th August,
8
15
16
11
43
9th September,
0
16
16
7
23
* It is plain that when the i-esults of analj'«os made on a small amount of soil
are calculated upon the 3,500,000 lbs. of soil (more or less) contained in an acre
to llie depth of one foot (see p. 158), the errors of the analyses, which cannot be
absolutely exact, are enormously multiplied. Wlmt allowance ou;rht to be made
in this case we cannot say, but should suppose that 5 per cent would not be too
jHHch. On this basis differences of 200-300 lbs. in Table IV should be overlooked
AVAILABLE NITROGEN OP' THE SOIL.
285
TABLE
II.
Amount op nitric
ACID.
Beet plot,
sifted sou.
Beet jM.
Vetch plot.
Oat plot.
Vacant j.
End of April,
56
56
56
56
56
12th June,
281
270
102
28
106
30th June,
328
442
15
93
318
22d July,
116
89
58
0
43
13th August,
53
6
71
14
81
«th September.
0
0
12
0
0
TABLE m.
TOTAJ- ASSIMILABLE NITROGEN (OF AMMONIA AND NITRIC ACID).
Beet iM,
sifted soil.
Beet plot.
Vetch ijlot.
Oat plot.
Vacant plot.
End of April,
63
63
63
63
63
12th June,
84
109
60
33
50
30th June,
95
148
23
57
108
22d July,
37
47
31
18
35
13th Au'TUPt,
21
14
31
13
56
Bth September,
0
13
TABLE
16
IV.
6
19
TOTAL
NITROGEN
OF THE SOIL.
BeetjM,
sifted sou.
Beet })lof.
Vetch jM.
Oat plot.
Vacant jilot.
End of April,
4052
4652
4652
4652
4652
12th June,
4861
5209
5606
6140
4720
30th June,
4667
5744
5688
5514
4482
22d July,
5398
5485
4724
49:24
13th August.
5467
6316
6316
6266
4412
9th September,
5164
4656
6522
5004
4294
From the first Table we gather that the quantity of
ammonia, which was considerable in the spring, dimin-
ished, especially in a porous (sifted) soil until September.
In the compnct earth of tlie uncultivated path, its diminu-
tion was less rapid and less complete. The amount of
nitric acid (nitrates), on the other hand, increased, though
not alike in any two cr.ses. It attained its maximum in
the hot weather of June, and thence fell off until, at the
close of the experiments, it was completely wanting save
in a single instance.
The figures in the second Table do not represent the
absolute quantities of nitric acid that existed in the soil
286 HOW CROPS FEED.
throughout the period of expermient, but only those
amounts that remained at the time of taking the samples.
What the vegetation took up from the planted plots, what
was washed out of the surface soil by rains, or otherwise
removed by chemical change, does not come into the
reckoning.
Those plots, the surface soil of which was most occupied
by active roots, would naturally lose the most nitrates by
the agency of vegetation; hence, not i;nlikely, the vetch
and oat plots contained so little in June. The results up-
on the beet, and vacant ground ])lots demonstrate that in
that month a rapid formation of nitrates took place. It
is not, perhaps, impossible that nitrification also proceeded
vigorously in the loose soils in July and August, but was
not revealed by the analysis, either because the vegetation
took it up or heavy rains washed it out from the surface
soil. ■ In the brief account of these experiments at hand,
no information is furnished on these j)oints. Since m.oist-
ure is essential to nitrification, it is possible that a period
of dry weather coming on shortly before the soil was
analyzed in July, August, and September, had an influence
on the results. It is certainly remarkable that with the ex-
ception of the vetch plot, the soil was destitute of nitrates
on the 9th of September. This j^lot, at that time, was
thickly covered with fallen leaves.
We observe further that the nature of the crops influ-
enced the accumulation of nitrates, whether simply bo-
cause of the different amount of absorbent rootlets pro-
duced by them and unequally developed at the given
period, or for other reasons, we cannot decide.*
From the third Table may be gatliered some idea of the
total quantity of nitrogen that was present in the soil in
* It is remarkable that the large-leaved beet plant had a great surplus of ni-
trates, while the oat plot was comparatively deficient in them. Has this fact any
connection with what has been stated (p. 84) regarding the unequal power of
plants to provide themselves with nitrogenous food ?
AVAILABLE NITIIOGEK OF THE SOIL. 287
a form available to crops. Assuming' that ammonia and
nitric acid chiefly, if not exclusively, supply vegetation
with nitrogen, it is seen that the greatest quantity of
available nitrogen ascertained to be present at any time in
the soil was 148 lbs. per acre, taken to the depth uf one
foot. This, as regards nitrogen, corresponds to the follow-
ing dressings: —
lbs. per acre.
Saltpeter (nitrate of potash) - - 1068
Chili saltpeter (nitrate of soda) - 898
Sulpliate of ammonia ... - 909
Peruvian guano (14 per cent of nitrogen) 1057
The experience of Britisli farmers, among whom all
the substances above mentioned have been employed,
being that 2 to 3 cwt. of any one of them make a large,
and 5 cwt. a very large, application per acre, it is plain
that in the surface soil of Bretschneidei-'s trials there was
formed during the growing season, a large manuring of
nitrates in addition to rohat was actually consumed by the
crops.
The assimilable nitrogen increased in the beet plots iip
to the 30th of June, thence rapidly diminished as it did
in the soil of the paths. In the oat and vetch plots the
soil contained, at none of the times of analysis, so much
assimilable nitrogen as at the beginning of the experi-
ments. In September, all the plots were much poorer in
available nitrogen than in the spring.
Table IV confirms what Boussingault haa taught as to
the vast stores of nitrogen which may exist in the soil.
The amount heie is more than two tons per acre. We ob-
serve further that in none of the cultivated plots did this
amount at any time fall below this figure ; on the other
hand, in most cases it was considerably increased during the
period of experiment. In the uncultivated plot, perhaps,
the total nitrogen fell off somewhat. This difference may
have been duo to the root fibrils that, in spite of the ut-
288
UOAV CKOPS FEED.
most care, unavoidably remain in a soil from which gro\v«
ing vegetation is removed. The regular and great increase
of total nitrogen in the vetch plot was certainly due in
part to the abundance of leaves that fell from the
plants, and covered the surface of the soil. But this ni-
trogen, as well as that of the standing crops, must have
come from the atmosphere, since the soil exhibited no
diminution in its content of this element.
We have here confirmation of the view that atnmonia^
as naturally supplied^ is of very trifling importance to
vegetation, and that, consequently, nitrates are the chief
natural means of providing nitrogen for crops. The fact
that atmospheric nitrogen becomes a part of the soil and
enters speedily into organic and inert combinations, also
appears to be sustained by these researches.
Quantity of Nitrogen needful for illaximum Grain
Crops. — Hellriegel has made experiments on the eftects
of various quantities of nitrogew (in the form of nitrates)
on the yield of cereals. The plants grew in an artificial
soil consisting of pure quartz sand, with an admixtni-e of
ash-ingredients in such proportions as trial had demon-
strated to be appropriate. All tlie conditions of the ex-
periments were made as nearly alike as possible, except as
regards the amount of nitrogen, which, in a series of eight
trials, ranged from nothing to 84 parts per 1,000,000 of soil.
The subjoined Table contains his results.
EFFECTS OF VARIOUS PROPORTIONS OF ASSIMILABLE NITROGEN
IN THE SOIL.
Nilroqen in
1,000,000
Yield of Grain, in lbs.
lbs. of soil.
Wheal.
Hue.
Oats.
Found
Calculated
Found
Calculated
Found
Calculated
0
0.002
Increase
0.218
Increase
0.330
Increase
7
0.553
0.926
0.832
0.966
0.929
1.168
14
1.708
i.a5i
1.944
1.933
2.605
2 336
21
2.767
2.777
2.669
2.899
3.845
3.503
28
3. 703
3.703
4.172
3.866
6.211
4.671
42
6.005
5.554
5.162
5.798
7.030
7.007
56
7.10S
7.406
7.163
7.732
9.0.52
9.342
84
9.257
9.257
8.698
8.698
9.ai2
9.342
DECAY OF NITUU(JE^'UUS liODIES, '-^9
From numerous other experiments, not })ublislied at
this writing, Ilellriegel believes himself justified in assum-
ing that the highest yield thus observed, with 84 lbs. of
nitrogen in 1,000,000 of soil, might have been got with
70 lbs. of nitrogen in case of wheat, Avith G3 lbs. in case
of rye, and with 56 lbs. in case of oats. On this assump-
tion he has calculated tlie yield of each of these crops,
and the figures obtained (see Table) present on the whole
a remarkable coincidence with those directly observed.
DECAY OF NITROGENOUS BODIES.
We have incidentally noticed some of the products of
the decay of nitrogenous bodies, viz., those which remain
in the soil. We may iiov/, with advantage, review the
subject connectedly, atid make our account of this ])rocess
more complete.
It will be needful in the first place to give some ex-
planations concerning the nature of the familiar trans-
formations to which animal and vegetable matters are
subject.
By the word decay, as popularly employed, is under-
stood a series of chemical changes which are very differ-
ent in their manifestations and results, according to the
circumstances under which they take place or the kinds
of matter they attack. Under one set of conditions we
have slow decay, or, as Liebig has fitly designated it,
even <iusis j* wnoieY oi\\Qvs fermentation; and under still
others putrefaction.
Eremecausis* is a slow oxidation, and lequires the
constant presence of an excess of free oxygen. It pro-
ceeds upon vegetable matters which are comparatively
'From the Greek, sisnifying slow comhitstion.
13
290 HOW CROPS FEED,
difficult of alteration, such as stems and leaves, consist-
ing chiefly of cellulose, with but little albuminoids, and
both in insoluble forms.
What is said in a former j)aragraph on the " Decay of
Vegetation," p. I.'IT, applies in general to eremecausis.
Fermentation is a term commonly applied to any
seemingly spontaneous change taking place Avith vegeta-
ble or animal matters, Avherein their sensible qualities
suffer alteration, and lieat becomes perceptible, or gas is
rapidly evolved. Chemically speaking, fermentation is
the breaking up of an organic body by chemical decom^
position, A\ hich may go on in absence of oxygen, and is
excited by a substance or an organism called a ferment.
There are a variety of fernaentations, viz., the vinous, acetic, lactic, etc.
In vinous fermentation, the yeast-fungus, Tonnda cerevisice, vegetates
in an impure solution of sugar, and causes the latter to breaic up into
alcohol and carbonic acid with small quantities of other jiroducts. In
the acetic fermentation, the vinegar-plant, Jlycodeiina viiii, is believed
to facilitate the conversion of alcohol into acetic acitl, but this change
is also accomplished by platiniim sponge, which acts as a ferment. In
the lactic fermentation, a fungus, Penicilium glaucum, is thought to de-
termine the conversion of sugar into lactic acid, as in the souring of milk.
The transformation of starch into sugar has been termed the saccha-
rous fermentation, diastase being the ferment.
Putrefaction, or putrid fermentation, is a raydd internal
change which j^roceeds in comparative absence of oxygen.
It most readily attacks animal matters which are rich in
albuminoids and other nitrogenous and sulphurized prin-
ciples, as flesh, blood, and urine, or the highly nitrogenous
parts of plants, as seeds, when they are fully saturated
with water. Putrefying matters commonly disengage
stinking gases. According to Pasteur putrefaction is oc-
casioned by the growth of animalcules ( Vibrios).
Fermentation is usually and putrefaction is always a
reducing (deoxidizing) process, for either the ferment it-
self or the decomposing substances, or some of the prod-
ucts of decomposition, are highly prone to oxidation, and
DECAY OF NITROGEMOUS BODIES, 291
in absence of free oxygen may remove this element fruin
reducible bodies (Traiibe, Fermentwirkungen, pp. G3-78).
In a mixture of cellulose, sugar, and albuminoids, ere-
mecausis, fermentation, and putrefaction, may all proceed
simultaneously.
When the albuminoids decay in the soil associated with
carbohydrates and humus, the final results of their altera-
tion may be summed up as folloMs :
1. Carbon unites mainly with oxygen, forming carbonic
acid gas, Avhich escapes into the atmosphere. With im-
perfect supplies of oxygen, as Avhen submerged in water,
carbonic oxide (CO) and marsh gas (CIIJ are formed. A
portion of carbon remains as humus.
2. Hydrogen, for the most part, combines with oxygen,
yielding water. In deficiency of oxygen, some hydrogen
escapes as a carbon compound (marsh-gas), or in the free
state. If humus remains, hydrogen is one of its con-
stituents.
3. a. Nitrogen always unites to a large extent with
hydrogen, giving ammonia, which escapes as gaseous car-
bonate in considerable quantity, unless from presence of
carbohydrates much humus is formed, in which case it
may be nearly or entirely retained by the latter. Lawes,
Gilbert, and Pugh, {Phil. Trans. 1861, II., p. 501) made
observations on the decay of wheat, barley, and bean
seeds, either entire or in form of meal, mixed with a large
quantity of soil or powdered pumice, and exposed in vari-
ous conditions of moisture to a current of air for six
mouths. They found in nine experiments that from 11 to
58" |„ of the nitrogen was convei'ted into ammonia, al-
though but a trifling proportion of this (on the average
but 0.4"! J escaj^ed in the gaseous form.
b. In presence of excess of oxygen, a portion of nitro-
gen usually escapes in the free state. Reiset proved the
escape of free nitrogen from fermenting dung. Boussm-
292 HOW CROPS FEED.
gault, In his investigations on the assimilability of free
nitrogen, found in various vegetation-experiments, in
which crushed seeds were nsed as fertilizers, that nitrogen
was lost "by assuming some gaseous f )rm. This loss prob-
ably took place to some slight extent as ammonia, but
chiefly as free nitrogen. Lawes, Gilbert, and Pugh, found
in thirteen out of fifteen trials, including the exj^eriments
just referred to, that a loss of free nitrogen took place,
ranging from 2 to 40 per cent of the total quantity con-
tained originally in the vegetable matters submitted to
decomposition. In six: experiments the loss was 12 to 13
per cent. In the two cases where no loss of nitrogen oc-
curred, nothing in the circumstances of decay was discov-
erable to which such exceptional results could be at-
tributed. Other experiments (Phil. Trans. 1861, II., p.
509) demonstrated that in absence of oxygen no nitrogen
was evolved in tlie free state.
c. Nitric acid is not formed from the nitrogen of or-
ganic bodies in rapid or putrefactive deca}', but only in
slow oxidation or eremecausis of humified matters.
Pelouze found no nitrates in the liquor of dung heaps.
Lawes, Gilbert, and Pugh, {loc. c«Y.). found no nitric acid
when the seed-grains decayed in ordinary air, nor Avas it
produced when ozonized air was passed over moist bean-
meal, either alone or mixed with burned soil or with
slaked lime, the exjjeriments lasting several months. It
thus appears that the carbon and hydrogen of organic
matters have such an affinity for oxygen as to prevent the
nitrogen from acquiring it in the quicker stages of decay.
More than this, as Pelouze has shown [Comptes Rendus,
XLIV., p. 118), putrefying matters rob nitric acid of its
oxygen and convert it into ammonia. "We have already
remarked that putrefaction and fermentation are reducing
processes, and until they have run their course and the
organic matters have passed into the comparatively stable
forms of humus, their nitrogen appears to be incapable of
THE NITROGENOUS PRINCIPLES OF URINE. 293
oxidation. So soon as compounds of carbon and hydrogen
are formed, which miite but slowly with free oxygen, so
that the latter easily maintains itself in excess, then and
not before, the nitrogen begins to combine witli oxygen.
4. Finally, the sulphur of the albuminoids may be at
first partially dissipated as sulphuretted hydrogen gas,
while in the slower stages of decay, it is oxidized to suK
phuric acid, which remains as sulphates in the soil.
§8.
THE NITROGENOUS PRINCIPLES OF URINE.
The question " How C'rops Feed " is not fully answered
as regards the element Nitrogen, without a consideration
of certain substances — ingredients of urine — which may
become incorporated with the soil in the use of animal
manures.
Professor Way, in his investigation on the " Power of
Soils to Absorb Maiuire," describes the following remark-
able experiment : " Three quantities of fresh urine, of
2,000 grains each, were measured out into similar glasses.
With one portion its own weight of sand was mixed ;
with another, its own weight of white c^ay/ the tliird
being left without admixture of any kind. When smelt
immediately after mixture, the sand appeared to have
had no effect, whilst the clay mixture had entirely lost
the smell of urine. The three glasses Avere covered light-
ly Avith paper and put in a Avarm place, l)eing examined
from time to time. In a few honrs it was found that the
urine containing sand had become slightly putrid ; then
followed the natural urine ; but the quantity with which
clay had been mixed did not heeome putrid at all, and
at the end of seven or eight Aveeks it had only the pecu-
liar smell of fresh urine, without the slightest putridity.
The surface of the clay, however, became afterwards coa'-
294 now (;Rors teeI).
ered with a luxuriant growth of confervae, which did not
happen in the other glasses." {Jour. Boy. Ag. Soc. of
Eng., XL, 366.)
Professor Way likewise found that filtering urine
through clay or simply shaking the two together, allow-
ing the liquid to clear itself, and pouring it off, sufficed to
prevent putrefaction, and keep the urine as if fresh for a
month or more. Cloez found, as stated on p. 264, that in
a mixture of moistened pumice-stone, carbonate of lime,
and urea (the nitrogenous principle of urine), no nitrates
were formed during eight months' exposure to a slow
current of air.
These facts make it necessary to consider in what state
the nitrogen of xirine is absorbed and assimilated by
vegetation.
Urine contains a number of compounds rich in nitro-
gen, being derived from the waste of the food and tissues
of the animal, which require a brief notice.
Urea (CO N^HJ* may be obtuii.ed from the urine of
man as a white crystalline mass or in distinct transparent
rhombic crystals, which remain indefinitely unaltered in
dry air, and have a cooling, bitterish taste like saltpeter.
It is a weak base, and chemists have prepared its nitrate,
oxalate, phosphate, etc.
Urea constitutes 2 to 3 per cent of healthy human
urine, and a full-grown and robust man excretes of it
about 40 grams, or 1' I3 oz. av. daily.
When urine is left to itself, it shortly emits a putrid
odor ; after a few days or hours the urea it contained en-
tirely disappears, and the liquid smells powerfully of am-
monia. Urea, when in contact with the animal matters
Carbon 20.00
Hydrogen 6.6T
Nitrogen 46.67
Oxygen 26.66
100.00
THE -XlTROGENOtTS PllIXCIPLES OP URINE. 295
of mine, suffers decomposition, and its elements, combin-
ing with the elements of water, are completely transformed
into carbonate of ammonia.
Urea. Water. Carbonate of Ammonia.
CO NJI, + 2H,0 = 2(NHJ, H,0,CO,.
As we have learned from Way's experiments, clay is
able to i-emovefrom urine the "ferment" which occasions
its putrefaction.
Urea is abundant in the urine of all carnivorous and
herbivorous mammals, and exists in small quantity in the
urine of carnivorous birds, but has not been detected in
that of herbivorous birds.
Uric acid (CJI^N^Og)* is always present in healthy
human urine, but in very minute quantity. It is the chief
solid ingredient of the urine of birds and reptiles. Here
it exists mainly as urate of ammonia.** The urine of
birds and serpents is expelled from tiie intestine as a white,
thickish liquid, which dries to a chalk-like mass. From
this, uric acid may be obtained in the form of a white
powder, which, when magnified, is seen to consist of mi-
nute crystals. By powerful oxidizing agents uric acid is
converted into oxalate and carbonate of ammonia, and
urea. Peruvian guano, when of good quality, contains
some 10 per cent of urate of ammonia.
Hippuric acid (C^H^NOJf is commonly abundant in
the urine of the ox, horse, and other herbivorous animals.
By boiling down fresh urine of the pastured or hay-fed
cow to ' 1^ its bulk, and adding hydrochloric acid, hippuric
acid crystallizes out on cooling in four-sided prisms, of-
ten two or three inches in lensrth.
• Carbon 35.72 •♦ Carbon 32.43 t Carbon 60.74
Hydrogen 2.38 Hydrogen 3.78 Hydrogen 4.96
Nitrogen 33.33 Nitrogen 37.84 Nitrogen 7.88
Oxygen 28.57 Oxygen 25.95 Oxygen ....26.48
100.00 100.00 100.00
296
now CROPS FEED.
iilycOCOll or CilycilIC^'= is a sweet substance that re*
suits from the decomposition of hippuric acid under the
influence of various agents. It is also a product of the
action of acids on gelatine and horn.
Guanine (CJI^N^O) f occurs to the extent of about
' |j per cent in Peruvian guano, and is an ingredient of
the liver and pancreas of animals, whence it passes into
the excrement in case of birds and spiders. By oxidation
it yields among other products urea and oxalic acid.
kreatin (CJl^N^Oj I is an organic base existing in
very minute quantity in the flesh of animals, and occa-
sionally found in urine.
Cameron was the first, in 1857, to investigate the assimi-
lability of urinary products by vegetation. His experi-
ments {Chejnistnj of Agriculture, pp. 139-144) were
made with barley, which was sown in an artificial soil,
destitute of nitrogen. Of four pots one remained without
a supply of nitrogen, another was manured with sulphate
of ammonia, and two received a solution of urea. The
pot without nitrogen gave plants 8 inches high, but thes«
developed no seeds. The pot with sulphate of ammonia
gave plants 22 inches high, and 300 seeds. Those with
urea gave respectively stalls s of 26 and 29 inches height,
and 252 and 270 seeds. The soil in neither case contained
ammonia, the usual decomposition-product of urea. Dr.
Cameron justly concluded that nrea enters plants un-
changed, is assimilated by them, and equals ammonia-salts
as a means of supplying nitrogen to vegetation.
The next studies in this direction were made by the au-
thor in 1861 {Am. Jour. Science, XLI., 27). Experiments
were conducted with uric acid, hippuric acid, and guanine.
'Carbon 39.73 t Carbon 32.00 J Carbon 36.64
Hydrogen 3.31 Hydrogen 6.67 Hydrogen 6.87
Nitrogen 46.36 Nitrogen 18.67 Nitrogen 32.06
Oxygen 10.60 Oxygen 42.66 Oxygen 24.43
100.00 100.00 100.00
THE XITUOr.ENOUS nUNt'irM.EH OF URINE. 297
Washed and ignited flower-pots were employed, to con-
tain, for eacli trki!, a soil consisting of 700 grms. of
ignited and -washed granitic sand, mixed with 0.25 grni.
sulphate of lime, 2 grms. ashes of hay, prepared in a muffle,
and 2.75 grms. bone-ashes. This soil was placed upon
100 grms. of clean gravel to serve as drainage.
In each of four pots containing the above soil was de-
posited, July 6th, a weighed kernel of maize. The pots
were watered with equal quantities of distilled water con-
taining a scarcely appreciable trace of ammonia. The
seeds germinated in a healthy manner, the plants devel-
oped slowly an<l alike until July 28th, M'hen the addition
of nitrogenous matters was begun.
To No. 1, no solid addition was made.
To No. 2 was added, July 28th, 0.420 grm. uric acid.
To No. 3 was added 1.790 grm. hipjjuric acid, at four
different times, viz: July 28,0.358 g!5m.,Aug. 26th, 0.358
grm., Sept. 16th, 0.716 grm., Oct. 3d, 0.358 grm.
To No. 4 was added 0.4110 gim. hydrochlorate of gua-
nine, viz: July 28th, 0.0822^ grm., Aug. 26th, 0.0822
grm., Sept. 16th, 0.1644 grm., Oct. 3d, 0.0822 grm.
The nitrogenous additions contained in each case, 0.140
grm. of nitrogen, and were strewn, as fine powder, over
the surface of the soil
The ^ilants continued to grow or to remain healthy (the
lower leaves withering more or less) until they were re-
moved from the soil, Nov. 8th.
The plants exhibited striking diffei'ences in their devel-
opment. No. 1 (no added nitrogen) produced in all seven
slender leaves, and attained a height of 7 inches. At the
close of the experiment, only the two newest leaves were
perfectly fresh ; the next was withered and dead through-
out one-third of its length. The newer portions of this
plant grew chiefly at the expense of the older parts. No
sign of floral organs appeared.
13*
998 BOW CROPS PEED.
j^o. 2, fed with uric acid, was the best developed plant
of the series. At the conclusion of the experiment, it
bore ten vigorous leaves, six of which were fresh, and two
but partly withered. It was 14 inches high, and carried
two rudimentary ears (pistillate flowers), from the upper
one of which hung tassels 6 inches long.
No. 3, supplied with hippuric acid, bore eight leaves,
four of which were withered, and two rudimentary ears,
one of which tasseled. Height, 12 inches.
No. 4, with hydrochlorate of guanine, had six leaves,
one withered, and two ears, one of which was tasseled.
Height, 12 inches. The weight of the crops (dried at
212° F.), exclusive of the fine rootlets that could not be
removed from the soil, was ascertained, with the subjoined
results.
12 3 4
WithoTit Hippuric
Nitrogen. Uric Acid. Acid. Guanine.
Weightof dried crop, 0.1925 grm. 1.9470 grm. 1.0149 grm. 0.9820 grm.
«» " seed, 0.1644 " .1725 " 0.1752 " 0.1698 "
gain,
0.0291 " 1.7745 " 0.8397 " 0.8132
We thus have proof that all the substances employed
contributed nitrogen to the growing plant. This is con-
clusively shown by the fact that the development of pis-
tillate organs, which are especially rich in nitrogen,
occurred in the three plants fed with nitrogenous com-
pounds, but was totally wanting in the other. The rela-
tion of matter, new-organized by growtli, to that derived
from the seed, is strikingly seen from a comparison of the
ratios of the weight of the seed to the increase of organ-
ized matter, the former being taken as unity.
The ratio is approximatively
for No.
1,
1
0.2
2
1
10.2
3,'
1
4.8
4,
1
4.8
THE NlTKOGfiXOUS rRINOIPLES OF UKlNK 290
The relative gain by growth, that o^ Xo. 1 assumed as
unity, is for No. 1 , — 1
" " 2, — 61
" " 3^ _ 29
" " 4, — 28
The crops were small, principally because the supply
ofunitrogen was very limited.
These experiments demonstrate that the substances
added, in every case, aided growth by supplying nitro-
gen. They do not, indeed, prove that the organic fertil-
izers entered as such into the crop without decomposition,
but if urea escapes decomposition in a soil, as Cameron
and Cloez have shown is true, it is not to be anticipated
that the bodies employed in these trials should suffer al-
teration to ammonia-salts or nitrates.
Hampe afterwards experimented with urea and uric
acid by the method of Water-Culture ( Vs. St., VII., 308 ;
VIII., 225 ; IX., 49 ; and X., 175). He succeeded in pro-
ducing, by help of urea, maize plants as large as those
growing in garden soil, and fully confirmed Cameron's
conclusion regarding the assimilability of this substance.
Hampe demonstrated that urea entered as such into the
plant. In fact, he separated it, in the pure state, from
the stems and leaves of the maize which had been pro-
duced with its aid.
Hampe's experiments with uric acid in solution showed
that this body supplied nitrogen without first assuming
the form of ammonia-salts, but it suffered partially if not
entirely a decomposition, the nature of which was not
determined. Uric acid itself could not be found in the
crop.
Hampe's results with hippuric acid were to the effect
that this substance furnishes nitrogen without reversion
to ammonia, but is resolved into' other bodies, probably
benzoic acid and glycocoll, which are formed when hip-
SOO now CROPS FEED.
puric acid is subjected to the action of strong acids or
ferments.
Hampe, therefore, experimented with glycocoll, and
from his trials formed tlie opinion that this body is di-
rectly nutritive. In fact, he obtained with it a crop equal
to that yielded by ammonia-salts.
Knop, who made, in 1857, an unsuccessful experiment
with hippuric acid, found, in 186G, that glycocoll is as-
similated {Chem. Centndblatt, 1866, p. 774).
In 1868, Wagner ex])erimented anew with hippuric
acid and glycocoll. His results confirm those of Hampe.
Wagner, however, deems it probable that hippuric acid
enters the plant as such, and is decomposed within it into
benzoic acid and glycocoll ( Vs. St., XI., p. 294).
Wagner found, also, that kreatin is assimilated by
vegetation.
The grand result of these researches is, that the nitrog-
enous (amide-like) acids and bases which are thrown off
in the urinary excretions of animals need not revei't, by
decay or putrefaction, to inorganic bodies (ammonia or
nitric acid), in order to nourish vegetation, but are either
immediately, or after undergoing a slight and easy altera-
tion, taken up and assimilated by growing plants.
As a practical result, these facts show that it is not
necessary that urine should be fermented before using it
as a fertilizer.
COMPARATIVE NUTRITIVE VALUE OF AMMONIA-SALTS AND
NITRATES.
The evidence that both ammonia and nitric acid are ca-
pable of supplying nitrogen to plants has beeii set forth.
It has been sliown further that nitric acid alone can per-
fectly satisfy the wants of vegetation as regards the ele-
ment nitrogen. In respect to ammonia, the case has not
VALUE OF AMMONIA AM) NITKIC ACID,
301
been similarly made out. Wo have learned that ammonia
occurs, naturally, in too small proportion, either in the
atmosphere or the soil, to supply much nitrogen to crops.
In exceptional cases, however, as in the leaf-mold of Rio
Cupari, examined by Boussiiigault, p. 276, as well as in
lands manured with fermenting dung, or with sulphate or
muriate of ammonia, this substance acquires importance
from its quantity.
On the assumption that it is the nitrogen of these sub-
stances, and not their hydrogen or oxygen, which is of
value to the plant, we should anticipate that 17 parts of
ammonia would equal 54 j^arts of nitric acid in nutritive
effect, since each of these quantities represents the same
amount (14 parts) of nitrogen. The ease with which
ammonia and nitric acid are mutually transformed favors
this view, but the facts of experience in the actual feed-
ing of vegetation do not, as yet, admit of its acceptance.
In earlier vegetation-experiments, wherein the nitro-
genous part of an artificial soil (wit) i out humus or clay)
consisted of ammonia-salts, it was found tliat these were
decidedly inferior to nitrates in their producing power.
This was observed by Yille in trials made Avith wheat
planted in calcined sand, to which was added a given
quantity of nitrogen in the several forms of nitrate of
potash, sal-ammoniac (chk)ride of ammonium), nitrate of
ammonia, and j^hosphate of ammonia.
Ville's results are detailed in the following table. The
quantity of nitrogen added was 0.110 grm. in each case.
Source of Nitrogen.
Nitrate of Potas
Sal-aminouiae. ..
Nitrate of amnio
Straw and
Roots. JGraiii.
( I. 20.70 6.20)
) II. l'J.22, 7.30 \
i 1. 15.10 4.93)
I II. 1'
III. 14. S7
Phosphate of ammonia ■ ,j" ir 'i-.i
Average
crop.
...26.71
...18.83
...18.32
:i;g[... 18.40
3.54 f
Nitrogen
in average
crop.
0.231
0.148
0.133
0.133
30a HOW CROPS FEED.
It is seen that the ammonia-salts gave about one-fourth
less crop than the nitrate of potash. The potash doubt-
less contributed somewhat to this difference.
The author began some exj^eriraents on this jjoint in
1861, which turned out unsatisfactorily on account of the
want of liglit in tlie apartment. In a number of these,
buckwheat, sown in a weathered feldspatliic sand, was ma-
nured with equal quantities of nitrogen, potash, lime,
phosjihoric acid, sulphuric acid, and chlorine, the nitrogen
being j^resented in one instance in form of nitrate of potash,
in the others as an ammonia-salt — sulphate, muriate, phos-
phate, or oxalate.
Although the plants failed to mature, from the cause
above mentioned, the experiments plainly indicated the
inferiority of ammonia as compared with nitric acid.
Explanations of this fact are not difficult to suggest.
The most reasonable one is, perhaps, to be found in the
circumstance that clayey matters (which existed in the
soil under consideration) " fix " ammonia, /. e., convert it
into a comparatively insoluble compound, so that the
plant may not be able to appropriate it all.
On the other hand, Hellriegel {A)m. d. Landw., VII.,
53, n. VIII., 119) got a better yield of clover in artificial
soil with sulphate of ammonia aiid phosphate of ammonia
t*ian with nitrate of ammonia or nitrate of soda, the quan-
tity of nitrogen being in all cases the same.
As Sachs and Knop developed the method of Water-
Culture, it was found by the latter that ammonia-saJts did
not effectively replace nitrates. The same conclusion was
arrived at by Stohmann, in 1861 and 1863 {Henneherg' s
Journ., 1862, 1, and 1864, 65), and by Rautenberg and
Kuhn, in 1863 (Hermeherg' s Journ., 1864, 107), who ex-
perimented with sal-ammoniac, as well as by Birner and
Lucanus, in 1864 {Vs. St., VIII., 152), who employed
sulphate and phosphate of ammonia.
The cause of failure lay doubtless in the fiict, first noticed
VALUE OF AMMONIA AND NITRIC ACID. 303
by Kiilin, that so soon as ammonia was taken up by the
plant, the acid with which it was combined, becoming free,
acted as a poison.
In 1866, Ilampe ( Vs. St., IX., 165), using i^hosphate
of ammonia as the single source of nitrogen, and taking
care to keep the solution but fjxiutly acid, obtained a
maize-plant which had a dry Aveight of 18 grams, includ-
ing 36 perfect seeds ; no nitrates were formed in the
solution.
The same summer Kiihn ( Vs. St., IX,, 167) produced
two small maize-plants, one with phosphate, the other
with sulphate of ammonia as the source of nitrogen, but
his experiments were interrupted by excessive heat in the
glass-house.
In 1866, Beyer ( T^. St., IX., 480) also made trials on
the growth of the oat-plant in a solution containing bi-
carbonate of ammonia. The j^lants vegetated, though
poorly, and several blossomed and even produced a few
seeds. Quite at the close of tlie experiments the plants
suddenly began to grow, with formation of new shoots.
Examination of the liquid showed that the ammonia had
been almost completely converted into nitric acid, and the
increased growth was obviously connected with this nitrifi-
cation.
In 1867, Hampe ( Vs. St., X., 176) made new experi-
ments with ammonia-salts, and obtained one maize-plant
2' I, ft. high, bearing 40 handsome seeds, and weighing,
dry, 25' \^ grams. In these trials the seedlings, at the
time of unfolding the sixth or seventh leaf, after consum-
ing the nutriment of the seeds, manifested remarkable
symptoms of disturbed nutrition, growth being sup-
pressed, and the foliage becoming yellow. After a week
or two the plants recovered their green color, began to
grow again, and preserved a healthy appearance until
mature. Experiment demonstrated that this diseased
state was not affected by the concentration of the nour-
804 now CEOPS FEED.
ishing solution, by the amount of free acid or of iron
present, nor by the illumination. Hamj)e observed that
from these trials it seemed that the j^lants^ while young^
were unable to asshnilate ammonia or did so with diffi-
culty^ but acquired the 2>ovjer with a certain age.
In 1868, Wagner {Vs. >S?., XL, 288) obtained exactly'
the same results as Ilampe. He found also that a maize-
seedling, allowed to vegetate for two weeks in an artificial
soil, and then placed in the nutritive solution, with phos-
phate of ammonia as a source of nitrogen, grew nor-
mally, without any symptoms of disease, Wagner ob-
tained one plant weighing, dry, 26' |^ grams, and carrying
48 ripe seeds. In experiments with carbonate of ammonia,
Wagner obtained the same negative result as Beyer had
experienced in 1866.
Beyer reports {Vs. St., XI., 267) that his attempts to
nourish the oat-plant in solutions containing ammonia-
salts as the single source of nitrogen invariably failed,
although repeated through three summers, and varied in
several ways. Even with solutions identical to those in
which maize grew successfully for Ilampe, the oat seed-
lings refused to increase notably in weight, every precau-
tion that could be thought of being taken to provide
favorable conditions. It is not imiDossible that all these
failures to supply plants with nitrogen by the use of am-
monia-salts depend not upon the incapacity of vegetation
to assimilate ammonia, but upon other conditions, unfa-
vorable to growth, which are inseparable from the meth-
ods of experiment. A plant gro\ving in a solution or in
pure quartz sand is in abnormal circumstances, in so for
that neither of these media can exert absorbent power
sufficient to remove from solution and make innocuous any
substance which may be set free by the selective agency
of the plant.
Further investigations must be awaited befoi-e this
point can be definitely settled. It is, however, a matter
CONSTITUTIOX OK THE SOIL. 805
of little practical importance, since ammonia is so sparse-
ly supplied by nature, and the ammonia of fertilizers is
almost invariably subjected to the conditions of speedy
nitrification.
CHAPTER VI.
THE SOIL AS A SOURCE OF FOOD TO CROPS.— INGRE.
DIENTS WHOSE ELEMENTS ARE DERIVED FROM
ROCKS.
§ 1.
GENERAL VIEW OF THE CONSTITUTION OF THE SOIL AS
RELATED TO VEGETABLE NUTRITION.
Inert, Active, aaid Reserve Matters. — In all cases the
soil consists in gre.at ])art of matters thnt are of no direct
or present use iu feeding the plant. The cliemical nature
of this inert portion may vary gre.atly Avithout coi-respond-
ingly influencing the fertility of tho soil. Sand, either
quartzose, calcareous, micaceous, fi'ldspatliic, hoi-nblendic,
or augitic ; clay in its many varieties ; chalk, ocher (oxide
of iron), humus ; iu short, any porous or granular material
that is insoluble and little alterable by ^veather, may con-
stitute the mass of the soil. The physical and mechanical
characters of the soil are chielly influenced by those ingre-
dients which preponderate in quantity. Hence Ville has
quite appropriately desi^'nated them the "mechanical
agents of the soil." They aifect fei'tility principally as
they relate the plant to moisture and to temperature.
They also have an influence on croj)S by gradually assum-
ing moie active forms, and yielding nourishment as the
result of chemical changes. In generalj it is probable
306 HOAV CROPS FEED.
that 99 per cent and more of the soil, exclusive of water,
does not in the slightest degree contribute directly to the
support of the present vegetation of our ordinary field
products.
The hay crop is one that takes up and removes from
the soil the largest quantity of mineral matters (ash-
ingredients), but even a cutting of 2^ tons of hay car-
ries off no more than 400 lbs. per acre. From the
data given on page 158, we may assume the weight of
the soil upon an acre, taken to the depth of one foot,
to be 4,000,000 lbs. The ash-ingredients of a heavy
hay crop amount therefore to but one ten-thousandth of
the soil, admitting the crop to be fed exclusively by the
12 inches next the surface. Accordingly no less than 100
full crops of hay would require to be taken off to consume
one per cent of the Aveight of the soil to this depth. "We
confine our calculation to the ash-ingredients because we
have learned that the atmosphere furnishes the main sup-
ply of the food from which the combustible part of the
crop is organized. Should we spread out over the surface
of an acre of rock 4,000,000 lbs. of the purest quartz
sand, and sow the usual amount of seed upon it, maintain-
ing it in the 2:)roper state of moisture, etc., we could not
produce a crop ; we could not even recover the seed. Such
a soil would be sterile in the most emphatic sense. But
should we incorporate with such a soil a few thousand
lbs. of the mineral ingredients of agricultural plants, to-
gether with some nitrates in the appropriate combinations
and proportions, we should bestow fertility upon it by this
addition and be able to realize a crop. Sliould we add to
our acre of pure quartz the ashes of a hay crop, 400 lbs.,
and a j^roper quantity of nitrate of potash, we might also
realize a good crop, could we but ensure contact of the
roots of the plants with all the added matters. But in
this case the soil would he fertile for one crop only, and
after the removal of the latter it would be as sterile aa
CONSTITUTION^ OF THE SOIL. 3O7
fcefore. We gather, then, that there are three items to be
regarded in the simplest view of the chemical compo-
sition of the soil, viz., the inert mechanical basis, the
presently available nutritive ingredients, and the reserve
matters from which the available ingredients are supplied
as needed.
In a previons chapter we have traced the formation of
the soil from rocks by the conjoint agencies of mechanical
and chemical disintegration. It is the i>erpetual operation
of these agencies, especially those of the chemical kind,
which serves to maintain fertility. The /ragments of rock,
and the insoluble matters generally that exist in the soil,
are constantly suffering decomposition, whereby the ele-
ments that feed vegetation become available. What,
therefore, we have designated as the inert basis of the soil,
is inert for the moment only. From it, by perpetual
change, is preparing the available food of crops. Various
attempts have been made to distinguish in fact between
these three classes or conditions of soil-ingredients ; but
the distinction is to us one of idea only. We cannot realize
their separation, nor can we even define their peculiar con-
ditions. We are ignorant in great degree of the power
of the roots of plants to imbibe their food; we are equally
ignorant of the mode in which the elements of the soil are
associated and combined ; we have, too, a very imperfect
knowledge of the chemical transformations and decomposi-
tions th?.t occur within it. We cannot, therefore, dissect
the soil and decide what and how much is immediately
available, and what is not. Furthermore, tlie soil is chem-
ically so complex, and its relations to the plant are so com-
plicated by physical and physiological conditions, that we
may, perhaps, never arrive at a clear and unconfused idea
of the mode by which it nourishes a crop. ISTevertheless,
what we have attained of knowledge and insight in this
direction is full of value and encoui-agemcnt.
Deportment of the Soil towards Solvents,— When wo
308 HOW CROPS FEED.
put a soil in contact with water, certain matters are dis-
solved in this liqui'l. It has been thought that the sub-
stances taken up by water at any moment are those which
at that time represent the available plant-food. This no-
tion was based upon the supposition that the plant cannot
feed itself at the I'oots save by matters in solution. Since
Liebig has brought into prominence the doctrine that roots
are able to attack and dissolve the insoluble ingredients
of the soil, this idea is generally regarded as no longer
tenable,
Agam, it has been taught that the reserve plant-food of
the soil is represented by the matters whicli acids (hydro-
chloric or nitric acid) arc c;ipable of bringing into solu-
tion. This is true in a certain rough sense oidy. The
action of hydrochloric or nitric acid is indeed analogous
to that of carbonic acid, Avhich is the natural solvent ; but
between the two there are great diiferences, independent
of those of degree.
Although we have no means of learning with positive
accuracy what is the condition of the insoluble ingredients
of the soil as to present or remote availability, the deport-
ment of the soil towards water and acids is highly in-
structive, and by its study -we make some approach to the
solution of this question.
Standards of Solubility. — Before proceeding to details,
some words upon the limits of solubility and upon what
is meant by soluble in water or in acids will be appropri-
ate. The terms soluble and insoluble are to a great de-
gree relative as applied to the ingredients of the soil.
When it is affirmed that salt is soluble in water, and that
glass is insoluble in that liquid, the meaning of the state-
ment is plain ; it is simply that salt is readily recognized
to be soluble and that glass is not ordinarily perceived to
dissolve. The statement that glass is insoluble is, however,
only true Avhen the ordinary standards of solubility arc re-
ferred to. The glass bottle vrhich mav contain water f^r
AQUEOUS SOKUTIOX OF THE SOIL. 309
years without perceptibly yielding aught of its mass to the
liquid, does, nevertheless, slowly dissolve. We may make
its solubility perceptible by a simple expedient. Pulver-
ize the bottle to the fiiiest dust, and thus extend the sur-
face of glass many thousand or million times; weigh the
glass-powder accurately, then agitate it for a few minutes
with water, remove the liquid, dry and weigh the glass
again. We shall thus find that the glass has lost several
per cent of its original weight (Pelouze), and by evapo-
rating the water, it will leave a solid residue equal in
weight to the loss experienced by the glass.
AQUEOUS SOLUTION OF THE SOIL.
The soil and the rocks from which it is formed would
commonly be spoken of as insoluble in water. They are,
however, soluble to a slight extent, or rather, we should
say, they contain soluble matters.
The quantity that water dissolves from a soil depends
upon the amount of the liquid and the duration of its
contact ; it is therefore necessary, in order to estimate
properly any statements respecting the solubility of the
soil, to know the method and conditions of the experi-
ment upon which such statements are based.
We subjoin the results of various investigations that
exhibit the general nature and amount of matters soluble
in water.
In 1852 Verdeil and Risler examined 10 soils from the
grounds of the Instltut Agronomlque, at Versailles. In
each case about 22 lbs. of the fine earth were mixed with
pure lukewarm water to the consistence of a thin pap,
and after standing several hours with frequent agitation
the water vras poured ofi"; this process was repeated to
the third time. The clear, faintly yellow solutions thus
obtained were evaporated to dryness, and the residues
were analyzed with results as folloAvs, per cent •
310
now CKOPS FEED,
NameqfMdd,
etc.
Mall .-..[Walk
Pheasant
Turf
Queen's Ave..
Kitchen Gard.
S_''.tory..[Galy
Clay soil of
Lime soil, do.
Peat boir
Sand pit
43.00
70.50
3.5.00
44.00
37.00
33.00
57.00
29.90
65.00
5().00
03.00
67.00
48.00;52.U0
47.00 53.00
46.00 54.00
47.04153.06
Per cent of Ash.
■^^•
48.9:2
31.49'
4S.45|
43.75!
30.60
18.70
18.75
17.21
34.43
32.31
25.60
35.29
6.08
6.08
12.35
24.25
45.61
48.50
30.61
34.. 59
4.27
2.16
2.75
6.32
11.20
18.50
3
9.00
0.92
8.10
81
1..55i 0.62
0.474race
I.21I -
2. 00, trace
trace [trace
3.721 0.50
0.95
trace
5.15
1.02
1.55
^■^.°s
Here we notice that in almost every instance all the
mineral ingi-edients of the plant were extracted from
these soils by water. Only magnesia and chlorine are in
any case missing. We are not informed, unfortunately,
what amount of soluble matters was obtained in these
experiments.
We next adduce a number of statements of the jo>-o-
portio7i of matters which water is capable of extracting
from earth, statements derived from the analyses of soils
of widely differing character and origin.
I. Very rich soil (excellent for clover) from St. Martin's,
Upper Austria, treated with six times its quantity of cold
water (Jarriges).
II. Excellent beet soil (but clover sick) from Schlan-
staedt, Silesia, treated with 5 times its quantity of cold
water (Jarriges).
III. Fair wheat soil, Seltendorf, Silesia, treated with 5
times its weight of cold water (Peters).
IV. Inferior wheat soil from Lampersdorf, Silesia —
5-fold quantity of water (Peters).
V. Good wheat soil, Warwickshire, Scotland — 10-fold
quantity of hot water (Anderson).
VI. Garden soil, Cologne — 3-fold amount of cold water
(Grouven).
AQUEOUS SOLUTIOT^ OF THE SOIL.
Sll
"Vn. Garden soil, Heidelberg — 3-fold amount of cold
Water (Grouven).
VIII. Poor, sandy soil, Bickendorf— 3-fold amount of
cold water (Grouven).
IX. Clay soil, beet field, Liebesnitz, Bohemia, extract-
ed with 9.6 times its weight of water (R. Hoffmann).
X. Peat, Meronitz, Bohemia, extracted with 16 times
its weight of water (R. Hoffmann).
XI. Peaty soil of meadow, extracted with 8 times its
•weight of water (R. Hoffmann).
XII. Sandy soil, JMoldau Valley, Bohemia, treated with
twice its weight of water (R. Hoffmann).
XIII. Salt meadow, Stollhammer, Oldenburg (Hai-ms).
XIV. Excellent beet soil, Magdeburg (Hellriegel).
XV. Poor beet soil, but good grain soil, Magdeburg
(Hellriegel).
XVI. Experimental soil, Ida-Marienhiitte, Silesia, treat-
ed with 2^ times its weight of cold water (Kiillenberg).
XVII. Soil from farm of Dr. Geo. B. Loring, Salem,
Mass., treated with twice its weight of water (W. G.
Mixter).
MATTERS DISSOLVED BY WATER FROM 100,000 P.^RTS OF
VARIOUS SOILS.
I
s.-
«•
•e
i
«^
1
1
e
^•S
i
tg-^
1
<fe:§
1
I
18
2
13
8
2
1
5
11
5
m\ 134
II
6
6
2 '4
1
3
4
5./.
trace
trace
trace
trace
1
41/2
6.4
24! 51
III
23
43
IV
10
trace
1
2
__
trace
1
11
3
18
46
V
34
7
S
13
—
7
9
22
—
36
136
VI
17
3
9
7'/,
5
2>/„
6'/,
13'/2
1
22
87
VII........
2.3
l'/2
7
4'/2
l'/2
IH
1
38
2
30
110
VIII
8
%
V„
3'/,
trace
1
l'/2
20
—
10
45
IX
33'/,
164
:;..
i'-
9
12
5
trace
i"
18
302
trace
trace
—
70
147
X
449 i 1095
XI
92
1
44
2V„
21
2
24
1
trace
trace
trace
trace
trace
1
trace
2
2:30) 425
XII
33| 39>/,
XIII
79
43
16
476
—
407
144
58
—
170 1393
XIV
19
8
3
5
1
4
4
20
3
88 150
XV
26
5
3
4
1
5
15
2
S3 147
XVI
6'/i
2
1
3
Vi
.5>/,
3>/2
12
7
12 53
XVII
8
2
6!4
1
'1,0
7'/2
l'/2
17
12! 55'/$
312 HOW CROPS TEED.
Tlie foregoing analyses (all the author has access to
that are sufficiently detailed for the purj^ose) indicate
1. That the quantity of soluble matters is greatest— 400
to 1,400 in 100,000— in wet, peaty soils (X, XI, XIII),
though their aqueous solutions are not rich in some of the
most important kinds of plant-food, as, for example, phos«
phoric acid.
2. That poor, sandy soils (VIII, XII) yield to water the
least amount of soluble matters,— 40 to 45 in 100,000,
3. That very rich soils, and rich soils especially when
recently and heavily manured as for the hop and beet
crops (I, II, V, VI, VII, IX, XIV, XV, XVI), yield, in
general, to water, a larger proportion of soluble matters
than poor soils, the quantity ranging in the instances be-
fore us from 50 to 150 parts in 100,000.
4. It is seen that in most cases phosphoric acid is not
present in the aqueous extract in quantity sufficient to be
estimated; in some instances other substances, as mag-
nesia, chlorine, and sulphuric acid, occur in traces only.
5. In a num.ber of cases essential elements of ])lant-
food, viz., phosphoric acid and sulphuric acid, are wanting,
or their j^resence was overlooked by the analyst.
Composition of Drain-Water.— Before further discus-
sion of the above data, additional evidence as to the kind
and extent of aqueous action on the soil will be adduced.
The water of rains, falling on the soil and slowly sinking
through it, forms solutions on the grand scale, the study
of which must be instructive. Such solutions are easily
gathered in their full strength from the tiles of thorough-
drained fields, when, after a period of dry weather, a rain-
fall occuis, sufficient to saturate the ground.
Dr. E. Wolff, at Moeckern. Saxony, made two analyses
of the A\ater collected in the middle of May from newly
\aid tiles, when, after a period of no flow, the tiles had
AQtrEOUS SOLUTION OF THE SOIL.
nis
been running full for several hours in consequence of a
heavy rain. The soil was of good quality. He found :
IN 100,000 PARTS OF DRAIN-WATER.
Rye field.
Meadow.
Organic matters,
2.6
3.3
Carbouate of lime,
21.9
4.4
" " magnesia,
3.1
1.4
" " potash,
0.3
0.5
" " soda,
1.9
1.4
Chloride of sodium,
2.3
trace
Sulphate of potash,
1.2
trace
Alumina, )
Oxide of iron, )
0.8
0.6
Silica,
0.7
0.4
Phosphoric acid.
trace
1.9
34.8 13.8
Prof. Way has made a series of elaborate examinations
on drain-waters furnished by Mr. Paine, of Farnham,
Surrey. The wateis were collected from the pipes (4-5
ft. deep) of thorough-di-ained fields in December, 1855,
and in most cases were the Jjrst flow of the ditches after
the autumn rains. The soils, with exception of 7 and 8,
were but a few years before in an impoverished condition,
but had been brought up to a high state of fertility by ma-
nuring and deep tillage. {Jour. Hoy. Ag. jSoc, XVII, 133.)
IN 100,000 PAHTS OP DRAIN-WATER.
W/wat
field.
Hop
Hop
field.
4
Wheat
field.
5
W/t^ai
field.
6 1
Hop Hop
field, field.
Potash
Soda
Lime
Maj^iiesia
Oxide or iron and ahimina
Silica
Chlorine
Sulphuric acid
Phosphoric acid
Nitric acid
Ammonia
Soluble organic matter
Total
^ 14
trace
1.4.3
6.93
0.97
0.59
1.35
1.00
2.35
trace
10. ai
0.025
10. OU
trace
3.10
10.24
3.. 31
O.OT
0.G4
1.57
7.35
0.17
21. ('5
0.025
10.57
158.1
0.03
3.23
8.64
3.54
0.14
0.78
1.84
6.23
trace
18.17
0.02c
17.85
0.(17
1.24
0!58
none
1.71
1.16
2.44
trace
2.78
0.017
8.00
trace
2.03
3.60
0..30
1.85
2.57
1.80
1.84
0.11
4.93
0.025
8.14
0.01 h-ace
2.00 4.57
8 31 18.50
1.33 I 3.57
0.50
0.93
1.73
4.45
0.09
11.50
0.025
O.T
1.21
3.74
13.58
0.17'
16.35
0.009
10.57
.5251 21.227 I 27.195 39.455172.979
814 TTO\r rnoPS TEKt).
Krocker has also published analyses of drain- waters
collected in summer from poorer soils. He obtained
IN 100,000 PARTS :
a
b
c
d
e
/
Organic matters,
2.5
2.4
1.6
0.6
6.3
5.6
Carbonate of lime,
8.4
8.4
12.7
7.9
7.1
8.4
Sulphate of lime.
20.8
21.0
11.4
1.7
7.7
7.2
Nitrate of lime,
0.2
0.2
0.1
0.2
0.2
0.2
Carbonate of magnesia.
7.0
6.9
4.7
2.7
2.7
1.6
Carbonate of iron,
0.4
0.4
0.4
0.2
0.2
0.1
Potash,
0.2
0.2
0.2
9.2
0.4
0.6
Soda,
1.1
1.5
1.3
1.0
0.5
0.4
Chloride of sodium.
0.8
0.8
0.7
0.3
0.1
0.1
Silica,
0.7
0.7
0.6
0.5
0.6
0.5
Total, 42.1 42.5 aS.t 15.3 25.8 24.7
Krocker remarks {Joiir.far Praht. Chem., 60-466) that
phosphoric acid could be detected in all these waters,
though its quantity was too small for estimation.
a and b are analyses of Avater from the same drains — a
gatliered April 1st, and h May 1st, 1853 ; c is from an ad-
joining field ; d, from a field whei-e the drains run con-
stantly, where, accordingly, the drain-water is mixed with
spring water ; e and f are of water running from the sur-
face of a field and gathered in the furroAvs.
Lysimeter-Water, — Entirely similar results Avere ob-
tained by Zoller in the analysis of Avater AA^hich was col-
lected in the Lysimeter of Fraas. The lysimeter * con-
sists of a Aessel Avith A^ertical sides and open above, the
upper part of AA'hich contains a layer of soil (in these ex-
periments 6 inches deep) supported by a perforated shelf,
while below is a reservoir for the reception of AVater.
The vessel is imbedded in the ground to Avithin an inch of
its upper edge, and is then filled from the diaphragm up
with soil. In this condition it remains, the soil in it being
exposed to the same influences as that of the field, Avhile
the water AA^hich percolates tiie soil gathers in the reservoir
• Measurer of solution.
AQtTTilOUS SOLUTION OP THK SOIL. 315
below. Dr. Zijller analyzed the water that was tbus col-
lected fi'om a number of soils at Munich, in the half year,
April 7th to Oct. 7th, 1857. He found
IN 100,000 OF LYSIMETER- WATER:
Potash,
0.65
0.24
0.20
0.55
0.38
Soda,
0.71
0.5G
0.74
2.37
0.60
Lime,
14.58
5.7G
7.08
6.84
9.23
Magnesia,
2.05
0.89
0.13
0.29
0.51
Oxiiie of iron.
0.01
0.G3
0.83
0.57
0.43
Chlorine,
5.75
0.95
2.08
3.94
3.53
Phosphoric acid,
0.22
—
—
—
—
Sulphuric acid,
1.75
2.71
2.78
2.93
3.35
Silica,
1.04
1.13
1.75
0.95
0.93
Organic matter, with some
1 20.47
12.59
13.67
12.08
10.19
nitric and carbonic acids.
Total, 47.23 2,5.40 29.20 30.52 29.15
The foregoing analyses of drain and lysimeter-water
exhibit a certain general agreement iu their results.
They agree, namely, iu demonstrating the presence in the
soil- water of all the mineral food of the plant, and while
the figures for the total quantities of dissolved matters
vary considerably, their average, 36|- parts to 100,000 of
water, is probably about equally removed from the ex-
tremes met Avith on the one hand in the drainage from a
very highly manured soil, and on the other hand in that
where the soil-solution is diluted wdth rain or spring water.
It must not be forgotten that in the analyses of drain-
age water the figures refer to 100,000 parts of water ;
whereas in the analyses on p. 311, they refer to 100,000
parts ot soil, and hence the two series of data cannot be
directly compared and are not necessarily discrepant.
Is Soil-Water destitute of certain Nutritive Matters I
— We notice that in the natural solutions which flow off
from the soil, phosphoric acid in nearly every case exists
in quantity too minute for estimation ; and when estimat-
ed, as has been done in a number of instances, its propor-
tion does not reach 2 parts in 100,000. This fact, together
with the non-appearance of the same substance and of oth«
SI 6 iTO-\V CROPS T'EED.
er nutritive elements, viz., clilorine and sulphuric ncld, In
the Table, ii,311 , leads to the question. May not the aqueous
sohxtion of the soil be altogether lacking in some es-
sential kinds of mineral plant-food in certain instances ?
May it not happen in case of a rather poor soil that it will
support a moderate crop, and yet refuse to give up to
water all the ingredients of that crop that are derived
from the soil ?
The weight of evidence supports the conclusion that
■water is caj^able of dissolving from the soil all the sub-
stances that it contains which serve as the food of plants.
The absence of one or several substances in the analytical
statement would seem to be no proof of their actual ab-
sence in the solution, but indicates simply that the sub-
stance was overlooked or Avas too small for estimation by
the common methods of analysis in the quantity of solu-
tion which the experimenter had in hand. It would ap-
pear probable that by employing enough of the soil and
enough water in extracting it, solutions would be easily
obtained admitting of the detection and estimation of ev-
ery ingredient. Knop, however, asserts ( Chem. Central-
hlatt, 1864, 168) that he has repeatedly tested aqueous
solutions of fruitful soils for phosphoric acid, emj^loying
the soils in quantities ranging from 2 to 22 lbs., and water
in similar amounts, without in any case finding any traces
of it. On the other hand Schulze mentions having inva-
riably detected it in numerous trials ; and Yon Babo, in
the examination of seven soils, found phosphoric acid in
every instance but one, which, singularly enough, was
■that of a recently manured clay soil. In no case did he
fail to detect lime, potash, soda, sulphuric acid, chlorine,
and nitric acid ; magnesia he did not look for. {Hoff-
mann's Jahresberirht der Ag. Chem., I. 17.)
So Ileiden, in answer to Knop's statement, found and
estimated phosphoric acid in four instances in proportions
AQUEOUS SOLUTIOX OF THE SOIL. 31 7
ranging from 2 to 6 parts in 100,000 of soil. {Jahreshe-
richt der Ag. Chem., 18G"), p. ?A.)
It should be remnrkod that Knop's failure to find phos-
phoric acid may depend on the (uranium) method he euj-
ployed, a method different from that commonly used.
Can the Soil-water supply Crops with Food I — As-
suming, then, that all the soil-food for plants exists in solu-
tion in the water of the soil, the question arises, Does the
water of the soil contain enough of these substances to
nourish crops ? In case of very fertile or highly manured
fields, this question without doubt should be answered af-
firmatively. In respect of poor or ordinary soils, how-
ever, the answer has been for the most part of late years
in the negative. While to decide such a question is, per-
haps, impossible, a closer discussion of it may prove ad-
vantageous.
Russell [Journal IIi</hlai>d and ^ig. iSoc., New Series,
Vol. 8, p. 534) and Liebig {^Inn. d. Chem. ti. Pharm.., CV,
138) were the first to bring prominently forward the idea
that crops are not fed simply from aqueous solutions. Dr.
Anderson, of Glasgow, presents the argument as follows
(his Ag. Chemistry., p. 113):
" In order to obtain an estimate of the quantity of the
substances actually dissolved, we shall select the results
obtained * by Way. The average rain-fall in Kent, where
the waters he examined were obtained, is 25 inches. Now,
it appears that about two-fifths of all the rain which fiills
escapes through the drains, and the rest is got rid of by
evaporation. f An inch of rain falling on an English acre
weighs rather more than a hundred tons ; hence in the
course of a year, there must pass off by the drains about
1,000 tons of drainage watoi*, carrying with it, out of the
reach of plants, such substances as it has dissolved, and
* On (liaiii-water*, see p "13.
t From Parke's measurcaicnts, Jour. Roy. Ag. Soc., Eny., Vol. X^'II, p. 137
318 HOW CROPS FEED.
1,500 tons must remain to give to the plant all that it liolds
in solution. These 1,500 tons of water must, if they have
the same composition as that which escapes, contain only-
two and a lialf pounds of potash and less than a pound
of ammonia. It may be alleged that the water which re-
mains lying longer in contact with the soil may contain a
larger quantity of matters in solution ; but even admit-
ting this to be the case, it cannot for a moment be sup-
posed that they can ever amount to more than a very
small fraction of what is required for a single crop."
The objection to this conclusion which Anderson al-
ludes to above, but which he considers to be of little mo-
ment, is, perhaps, a serious one. The soil is saturated
with water sufficiently to cause a flow from drains at a
depth of 4 to 5 ft., for but a small part of the grow-
ing season. The Indian corn crop, for example, is planted
in New England in the early part of June, and is harvest-
ed the first of October. During the four months of its
growth, the average rain-fall is not enough to make a flow
from drains for more, perliaps, than one day in seven.
During six-sevenths of the time, then, there is a current of
water ascending in the soil to supply the loss by evapora-
tion at the surface. In this way the solution at the sur-
face is concentrated by the carrying upward of dissolved
matters. A heavy rain dilutes this solution, not having
time to saturate itself before reaching the drains. Ac-
cordingly we find that the quantity of matters dissolved
by water acting thoroughly on the surface soil is greater
than that washed out by an equal .amount of drain-water ;
at least such is the conclusion to be gathered from the
experiments of Eichhorn and Wunder.
These chemists have examined the solution obtained by
leaving soil in contact with Just sufficient water to saturate
it for a number of days or weeks. ( Vs. St., II, pp. 107-
111.)
The soil examined by Eichhorn was from a garden near
AQUEOUS SOLUTION OF THE SOIL. 319
Bonn, Prussia, not freshly manured, and was treated with
about one-third its weiglit (36.5 per cent) of cold water
for ten days.
Wunder employed soil from a field of the Experiment
Station, Chemnitz, Saxony. This soil had not been re-
cently manured, and was of .rather inferior quality (yield-
ed rS bushels wheat per acre, English). It was also
treated with about one-third its weight (34.5 per cent) of
water for four weeks.
The solutions thus procured contained in 100,000 parts,
Bonn. Chemnitz.
Silica,
4.80
3.57
Sulphuric acid,
10.02
Phosphoric acid,
3.10
traces
Oxide of iron and alumina.
trace
1.17
Chloride of sodium,
5.86
4.76
Lime,
13.80
8.36
Magnesia,
3.84
3.74
Potash,
11.54
0.75
Soda,
1.10
3.04
if we assume with Anderson that 1,500 tons (= 3,360,000
lbs.) of water remain in these soils to feed a crop, and that
this quantity makes solutions like those whose composition
is given above, we have dissolved (in pounds per English
acre) from the soil of
Bonn.
Chemnitz.
Silica,
161
86
Sulphuric acid,
343
—
Phosphoric acid,
104
?
Oxide of iron and alumina,
89
Chloride of sodium,
197
160
Lime,
430
381
Magnesia,
139
126
Potash,
387
35
Soda,
37
103
These results differ widely from those based on the com-
position of drain-water. Eichhorn, by a similar calcula-
tion, was led to the conclusion that the soil he operated
with was capable of nourishing the heaviest crops with
320 HOW CROPS FEED.
its aqueous solution. Wunder, on the contrary, calculat-
ed that the Chemnitz soil yields insufficient matters for
the ordinary amount of vegetation ; and we see that as
respects potash, the wants of grass and root crops could
not be satiified with the quantities in our computation,
while sulphuric acid and phosphoric acid are nearly or en-
tirely wanting. We do not, however, regard such calcu-
lations as decisive, either one way or the other. The
quantity of water whicli may stand at the actual service
of a crop is beyond our power to estimate witli anything
like certainty. Doubtless the amount assumed by Ander-
son is too large, and hence the calculations relative to the
Bonn and Chemnitz soils as ahove interpreted, convey an
exaggerated notion of the extent of solution.
Proper Concentration of Plant-Food. — Let us next
inquire what streiKjth of solution is necessary for the sup-
port of plants.
As has been shown by Nobbe ( Vs. St., VIII, p. 337),
Birner & Lucanus {Vs. St., VIII, p. 134), and Wolff ( Fs.
St., VIII, p. 102), various agricultural plants flourish to
extraordinary perfection when their roots are immersed in
a solution containing about one part of ash-ingredients
(together with nitrates) to 1,000 of water.
The solutions they employed contained the following
substances in the proportions stated (apjiroximately) be-
low:
In 100,000 parts of Water.
Nobbe.
Birner & Lucanus.
Wolff.
Lime,
16
19
19
Magnesia,
3
QH
^'{
Potash,
31
16
16
Phosphoric acid,
7
24
14
Chlorine,
21
none
2
Sulpluiric acid,
6
13
4
Oxide of iron,
M
J-f
X
Nitric acid,
31X
36
51
Nobbe found further that the vigror of vesfetation in his
AQUEOUS SOLUTION OF TH-E SOU,, 321
solution was diminished either by reducing the proportion
of soHd matters below 0.5, or increasing it to 2 parts in
1,000 of water. The proper dilution of the food of plants
for most vigorous growth and most perfect development
is thus approximately indicated.
We notice, however, considerable latitude as regards
the 2^roportions of some of the most important ingredients
Vhich are usually present in least quantity in the aqueous
solution of the soil. Thus, phosphoric acid in one case is
thrice as abundant as in the other. We infer, therefore,
that the minimum limit of the individual ingredients is
not fixed by the above experiments, especially not for or-
dinary growth.
Birner and Lucanus communicate other results ( Vs. St.,
VIII., J). 154), which throw much light on the question un-
der discussion. They compared the growth of the oat plant,
when nourished respectively by a rich garden soil, by
ordinary cultivated land, by a solution the composition
of Avhich is given above, and lastly by a natural aqueous
solution of soil, viz., a well-water. Below is a statement
of the weight in grams of an average plant, produced iia
these various media, as well as that of the grain yielded
by it.
Dry crops compared
Weight of aver- Weiirht of with seed, the hitter
age plant, dry. dry Grain. taken as unity.
Garden 5.27 1.23 193
Field 1.75 0.63 &i
Solution 3.75 1.53 137
Well-water 2.91 1.25 lOG
We gather from the above figures that well-water, in
quantities of one quart for each plant, renewed weekly,
gave a considerably heavier plant, straw, and grain, than
a field under ordinary culture ; the yield in grain being
dovble that of the latter, and equal to that obtained in a
rich garden soil.
14*
322 HOW CROPS FEED.
The analysis of the Avell-water sliows that the nutritive
solution need not contain the food of plants in greater
proportion than occurs in the aqueous extract of ordinary
soils.
The well-water contained, in 100,000 parts,
Lime, 15.14
Magnesia, 1.53
Potash, 2.13
Phosphoric acid, - - - - 0.16
Sulphuric acid, .... 7.45
Nitric acid, 6.03
We thus have demonstration that a solution containing
but one-and-a-hiilf jjarts of jjhosphoric acid to ten million
of water is competent, so far as this substance is concern-
ed, to support a crop bearing twice as much grain as an
ordinary soil could produce under the same circumstances
of Aveather. Do we thus reach the limit of dilution ?
We cannot answer for agricultural plants, but in case of
some other forms of vegetation, the reply is obvious and
striking.
Various species of Fucus, Lam'niarla^ and other ma-
rine plants, contain iodine in notable quantities. This
element, so much used in photography and medicine, is
made exclusively from the ashes of these sea-Aveeds, one
establishment in Glasgow producing 35 tons of it annu-
ally. The iodine must be gathered from the water of tlie
ocean in which these plants Aegetate, and yet, although
the starch-test is so delicate thnt one part of iodine can
be detected when dissolved in 300,000 parts of water, it
is not possible to recognize iodine in the " bitterns" Avhirh
remain when sea-water is concentrated to the one-hund-
reth of its original bulk, so that its proportion must be
less than one part in thirty millions of water! [Otto''s
Lehrhich, der Cheni'e^ Ate, A>'Jf., \i\^. 743-4.)
AQUEOL'S SOLUTIOJf OF TIIK SOIL. 323
Mode whereby dilute solutions may nourish Crops.—
There are other considerations Mliicli niay en:il)lc us to
reconcile extreme dilution of the nutritive liquid of the
soil, with the conveyance by it into the plant of the req-
uisite quantity of its appropriate food. It is certain
that the amount of matters found in solution at any
given moment in the water of the soil by no means repre-
sents its power of supplying nourishment to vegetation.
If the water which has saturated itself with the solu-
ble matters of the soil be deprived of a portion or all of
these matters, as it might be by the absorptive action of
the roots of a plant, the water would immediately act
anew upon the soil, and in time would dissolve another
similar quantity of the same substance or substances, and
these being taken up by plants, it would again dissolve
more, and so on as long and to such an extent as the soil
itself would admit. In other words, the same water may
act over and over again in the soil, to transfer from it to
the crop the needful soluble matters. It has been shown
that the substances dissolved in water may diffuse through
animal and vegetable tissues independently of each other,
and independently of the water itself. (11. C. G., p. 340.)
Deportment of the Soil to renewed portions of Water.
— ^It remains to satisfy ourselves tliat the soil is capa1)le
of yielding soluble matters continuously to renewed por-
tions of water. The only observations on this point that
the writer is acquainted Avith are those made by Schulze
and Ulbricht. Schulze ex[)erimented on a rich soil from
Goldberg, in Mecklenburg ( Vs. St., YI., 411). This soil,
in a quantity of 1,000 grams (= 2.3 11)S.) Avas slowly
leached Avith pure water, so that one liter (— 1.056 quart)
of liquid passed it in 24 hours. The extraction was con-
tinued during six successive days, and each portion was
separately examined for total matters dissolved, and for
phosphoric acid, which is, in general, the least soluble of
the soil-ingredients.
824
HOW CROPS FEED.
The results were as follows, for 1,000 j^arts of extract,
Portion of
aqueous
extract.
Total
matters
dissolved.
Organic
and
Tolatile.
Inorganic.
Phosphoric
acid.
1
0.535
0.340
0.195
0.0056
2
0.120
0.057
0.063
0.0082
3
0.261
0.101
0.160
0.0088
4
0.203
0.083
0.120
0.0075
5
0.260
0.082
0.178
0.0009
6
0.200
0.077
0.123
0.0044
1.579
"We see that each successive extraction removed from
the soil a scarcely diminished quantity of mineral mat-
ters, including phosphoric acid. In case of a poor soil,
we should not expect results so striking, as regards quan-
tity of dissolved matters, but doubtless tliey would be
similar in kind.
This is shown by the investigations that follow.
Ulbricht gives ( Vs. St.^ V., 207) the results of the simi-
lar treatment of four soils. 1,000 grams of each were
put in contact with four times as much pure water for
three days, then two-thirds of the solution was poured off
for analysis, and replaced by as much pure water; this
was repeated ten times. Partial analyses were made of
some of the extracts thus obtained ; we subjoin the pub-
lished results :
Dissolved by 40,000,000 parts of water from 1,000,000 parts of—
Loamy Sand from Heinsdorf.
1st
Extract.
2d
Extract.
3d
Extract.
4th
Extract.
7th
Extract.
10th
Extract.
Potnsh
80K
95
30 1^
trace.
15
14
39
12
IK
15
21
38
10
3
8
18
39
10
3
4
Soda
11
Lime...
Pliosphoiie acid...
Total
190
sn4 1 87 1 78 '
AQUEOUS SOLUTIOX OP THE SOIL.
225
Loamy Sand from Wahleclorf.
Potash
23
36
lie
12
16
43
15
3
13
20
;;',)
14
4
6
16
42
12
4
48
14
4
Soda
Lime.. .
phosphoric acid..
Total
2081^
89
90
80
1
Loamy ferruirinous Sand from Dahme, containing 4J^
of humus.
Potash
Soda
Lime
Magnesia
Phosphoric acid..
Total.
7
6
7
7
1
41
11
26
17
96
70
55
48
62
14
10
9
8
trace.
tnice.
T
158
99
97
80
Fine Sandy Loam from Fallvcnberg.
Potash
15
47
47
17
3
11
12
27
8
9
12
19
5
trace.
9
8
18
6
trace.
Soda
Lime
Phosphoric acid..
Total
129
60
45
41 1
As Schulze remarks, it is practically impossible to ex-
haust a soil completely by water. This liquid will still
dissolve something after the most prolonged or frequently
renewed action, as not one of the components of the soil
is possessed of absolute insolubility, although in a sterile
soil the amount of matters taken up would presently be-
come what the chemist terms " traces," or might be sueli
at the outset.
The two analyses by Krocker, a and i, p. 314, made
on water from the same drain, gatliered at an interval of
one month, further show that water, rapidly percolating
the soil, continuously finds and takes up new portions of
all its ingredients.
In addition to the simple solution of matters, the soil
suffers constantly the chemical changes which have been
already noticed, and are expressed by the term weather-
326 TiOW CROPS FEED.
ing. Matters insoluLle in water to-day become soluble
to-morrow, and substances that to-morrow icsist the action
of water are taken up the day after. In this way tliere
is no limit to the solution of the soil, and we cannot there-
fore infer from what the soil yields to Avater at any given
moment nor from what is taken out of it by any given
amount of water, the real extent to which aqueous action
operates, during the long period of vegetable growth, to
present to tlie roots of a croj) the indispensable ingredi^
ents of its food.
The discussion of the question as to the capacity of
water to dissolve from the soil enough of the various in*
gredients to feed crops, while satisfactorily establishing
this capacity in case of rich soils, and making evident
that in poor soils most of the inorganic matters are pre-
isented to vegetation by water in sufficient quantity, does
not entirely satisfy us in reference to some of the needful
elements of the ]ilant, especially phosphoric acid.
It is therefore appropriate, in this place, to pursue fur-
ther inquiries into the mode by which vegetation acquires
food from the soil, although to do so will somewhat inter-
rupt the general plan of our chapter.
Direct action of Roots upon the Soil. — In noticing
the means by whicli rocks are converted into soils, the
action of the organic acids of the living plant has been
mentioned. Since that chapter was written, fuitlier evi-
dence has been obtained concerning the influence of the
plant on the soil, whicli we now proceed to adduce,
Sachs [Experimental Physlologie^ 189) gives an ac-
count of observations made by him on the action of roots
on marble, dolomite (carbonate of lime and magnesia),
magnesite (carbonate of magnesia), osteolite (phosphate
of lime), gypsum, and glass. Polished plates of these
substances were placed at the bottom of suitable vessels
and covered several inches in dept'.i with fine quartz sand.
Seeds of various plants were planted in the sand and kepi
DIRECT ACTION* OF HOOTS UPON TIIE SOIL. 3^27
moist. The roots jienetrated the sand and came in con-
tact with the plates below, and branched horizontally on
their surfaces. After several days or weeks the plates
were removed and examined. The plants employed were
the bean, maize, squash, and wheat. The carbonates of
lime and magnesia and the phosphate of lime were plain-
ly corroded Avhere they had been in contact with the
roots, so that tlie course of the latter could be traced with-
out difficulty. Even the action of the root-hairs was mani-
fest as a faint roughening of the surface of the stone
either side of tlie path of the root. Gypsum and glass
were not perceptibly acted on.
Dietiich has m:ide a series of experiments {SoffmanrCs
tTahreshericlit^ VI, 3) on the amount of matters made solu-
ble from basalt and sandstone, both coarsely powdered,
and kept watered with equal quantities of distilled water,
when supporting and when free from vegetation. The
crushed rocks were employed in quantities of 9 and 11
lbs. ; they were well washed before the trials with dis-
tilled water, and access of dust was prevented by a layer
of cotton batting upon the surface. After removing the
plants, at the termination of the experiments, each sam-
ple of rock-soil was washed with the same quantity of
Nvater, to which a hundredtli of nitric acid had been
added. It was found that the plants employed, especially
lupins, peas, vetches, spurry, and buckwheat, assisted in
the decomposition and solution of the basalt and sand-
stone. Not only did these plants take up mineral mat-
ters from the rock, but the latter contained besides, a
larger amount of soluble matters than was found in the
experiments where no plants were made to grow. The
cereal grains had the same effect, but in less degree. In
the subjoined table we give the total quantities of sub-
stances dissolved under the influence of the growing
vegetation. These figures were obtained by adding to
what was found in the washin<j:s of the rock-soils the ash
328 HOW CROPS FEED.
of the crops, and subtracting from that sum the ash of
the seeds, together Avith the matters made soUible in the
same soils, which had sustained no pLints, but which had
been treated otherwise in a similar manner.
MATTERS DISSOLVED BY ACTION OF ROOTS.
On 9 lbs. of On 11 lbs. of
sandstone. basalt.
Of 3 lupin plants 0. COS grams. 0.749 grams.
3 pea " 0.481 " 0.713 "
20spurry " 0.268 " 0.365 "
lObuckwh't" 0.332 " 0.327 "
4 vetch " 0.221 " 0.251 "
8 wheat " 0.027 " 0.196 "
8 rye " 0.014 " 0.132 "
These trials appear to show conclusively that plants
exert a decided effect on the soil. We are not informed,
however, what particular substances are rendered soluble
under this influence.
We conclude, tiien, that the direct action of the roots
of a crop may in all cases contribute toward supplying it
with food, and in many instances may be absolutely
essential to its satisfactory growth.
Further Notice of Matters Soluble in Water.— The
analyses we have quoted sliow that every chemical ele-
ment of the soil may pass into aqueous solution. They
also show that some substances are dissolved more easily
and in greater quantity than others.
In general, chlorine, nitric acid, and sulphuric acid,
are most readily and completely taken up by water, and,
for the most part, in combination with lime, soda, and,
magnesia. In some cases, sulphuric acid appears to exist
in a difficultly soluble condition ( Fan Bemmelen, Ys.
St., VIII., 263).
Potash, ammonia, oaride of iron, (/lamina, silica, and
phosphoric acid, are tlie substances which are usually
soluble in but small proportion. These, together with
ACID SOLUTION OF THE SOIL. 329
lime, magnesia, and soda, it is difficult or impossible to
wash out completely from a soil of good c|.uality.
Very poor soils may be deficient in soluble forms of
any or several of the aoovc ingredients, and therefore
readily admit of nearly complete extraction by a small
amount of water.
Certain soils contain soluble salts of iron and alumina
(sulphates and humates) in considerable quantity, and
are for that reason unproductive. Such are many marsh
lands, as well as upland soils containing bisulphide of iron
(iron pyrites), of the kind that readily oxidizes to sulphate
of protoxide of iron (copperas).
SOLUTION OF THE SOIL IN STRONG ACIDS.
The strong acids, hydrochloric (muriatic), nitric, and
sulphui-ic, by virtue of their vigorous affinities, readily
remove from the soil a considerable quantity of all its
mineral ingredients. The quantity thus taken up is
greatly more than can be dissolved in water, and is, in
general, the gieater, the more fertile the soil. Exceptions
are soils consisting largely of carbonate of lime (chalk
soils), or compounds of iron (ochreous soils). The differ-
ent acids above named exercise very imlike solvent effects
according to their concentration, the time of their action,
the temperature at which they are applied, and the chemi-
cal nature and state of division of the soil.
The deportment of the minerals which chiefly constitute
the soil towards these acids will enable us to under-
stand their action ujDon the soil itself Of these minerals
quartz, feldspar, mica, hornblende, augite, talc, steatite,
kaolinite, chrysolite, and chlorite, when not altered by
weathering, nearly or altogether resist the action of even
hot and moderately strong hydrochloric and nitric acids.
.130 itOW CROPS FEEf>.
On the other hand, all carbonates, sulphates, and phos-
phates, are completely dissolved, while the zeolites and
serpentine are decomposed, their alkalies, lime, etc., enter-
ing into solution, and the silica they contain separating, for
the most part, as gelatinous hydrate.
According to the nature of the soil, and the concentra-
tion of the reagent, hydrochloric acid, the solvent usually
employed, takes up from two to fifteen or more per cent.
Very dilute acids remove from the soil the bases, lime,
magnesia, potash, and soda, in scarcely greater quantity
than they are united with chlorine, and with sulphuric,
phosphoric, carbonic, and nitric acids. Treatment with
stronger acids takes up the bases above mentioned, par-
ticularly lime and magnesia, in greater proportion than
the acids specified. We find that, by the stronger acids,
silica is displaced from combination (and may be taken
up by boiling the soil with solution of soda after treat-
ment with the acid). It hence follows that silicates, such
as are decomposable by acids, (zeolites) exist in the soil,
although we cannot recognize them directly by inspec-
tion even with the help of the microscope. To this point
we shall subsequently recur.
§4.
PORTION OF SOIL INSOLUBLE IN ACIDS.
When a soil has been boiled with concentrated hydro-
chloric acid for some time, or until this solvent exerts no,
further action, there may remain quartz, feldspar, mica,
hornblende, augite, and kaolinite (clay)^ together with
other similar silicates, which, in many cases, are ingredients
of the soil. Treatment with concentrated sulphuric acid
at very high temperatures (Mitscherlich), or syrupy phos-
phoric acid (A. Mailer), decomposes all these minerals,
quartz alone excepted. By making, therefore, in the first
cnEMirAT, ACTION- IN THE SOIT.. Jj5t
place, a mechanical analysis, as described on page 147, and
subjecting the fine portion, which consists entirely or in
great part of clay, to the action of tliese acids, the quan-
tity of clay may be approximately estimated. Or, by
melting the portion insoluble in acids with carbonate of
soda, or acting upon it with hydrofluoric acid, the whole
may be decomposed, and its elementary composition be
ascertained by further analysis.
Notwithstanding an immense amount of labor has been
expended in studying the composition of soils, and chiefly
in ascertaining what and how much, acids dissolve from
them, we have, unfortunately, very few results in the way
of general principles that are of application, either to a
scientific or a practical purpose. In a number of special
cases, however, these investigations have proved exceed-
ingly instructive and useful.
§5.
REACTIONS BY WHICH THE SOLUBILITY OF THE ELEMENTS
OF THE SOIL IS ALTERED. SOLVENT EFFECT OF
VARIOUS SUBSTANCES THAT ARE COMMONLY
BROUGHT TO ACT UPON SOILS. THE AB-
SORPTIVE AND FIXING POWER OF SOILS.
Chemical Action in the Soil. — Chemistry has proved
that the soil is by no means the inert thing it appears to
be. It is not a passive jumble of rock-dust, out of which
air and water extract the food of vegetation. It is not
simply a stage on which the plant performs the drama of
growth. It is, on the contrary, in itself, the theater of
ceaseless activities; the seat of perpetual and complicated
changes.
A large share of the rocks now accessible to our study
at the earth's surface have once been soil, or in the condi-
tion of soil. Not only the immense masses of stratified
limestones, sandstones, slates, and shales, that cover so
332 tiOW CROPS FEED.
large a part of the Middle State?, bxxt most of the rocks
of New England have been soil, and have supported vege-
table and animal life, as is proved by the fossil relics that
have been disinterred from them.
We have explained the agencies, mechanical and chemi-
cal, by which our soils have been formed and are forming
from the rocks. By a reverse metamorphosis, involving
also the cooperation of mechanical and chemical and even
of vital influences, the soils of earlier ages have been so-
lidified and cemented to our rocks. Xor, indeed, is this
process of rock-making brought to a conclusion. It is
going on at the present day on a stupendous scale in vari-
ous parts of the world, as the observations of geologists
abundantly demonstrate. If we moisten sand with a so-
lution of silicate of soda or silicate of potash, and then
drench it Avith chloride of calcium, it shortly hardens to
a rock-like mass, possessing enough firmness to answer
many building purposes (Ransome's artificial stone). A
mixture of lime, sand, and water, slowly acquires a simi-
lar hardness. Many clay-limestones yield, on calcination,
a material (water-lime cement) which hardens speedily,
even under water, and becomes, to all intents, a rock.
Analogous changes proceed in the soil itself Hard pan,
which forms at the plow-sole in cultivated fields, and
moor-bed pan, which makes a peat basin impervious to
water in beds of sand and gravel, are of the same nature.
The bonds which hold together the elements of feldspar,
of mica, of a zeolite, or of slate, may be indeed loosened
and overcome by a superior foi-ce, but they are not de-
stroyed, and reassert their power when the proper cir-
cumstances concur. The disintegration of rock into soil
is, for the most part, a slow and unnoticed change. So,
too, is the reversion of soil to rock, but it nevertheless
goes on. The cultivable surface of the earth is, however,
on the whole, far more favoi-able to disintegration than
to petrifaction. Nevertheless, the chemical affinities and
ABSORPTIVE POWEK OF THE SOIL. 333
physical qualities that oppose disintegration are inherent
in the soil, and constantly manifest themselves in the
kind, if not in the degree, involved in the making of rocks.
The fourteen elementary siihstances that exist in all soils
are capable of forming and tend to form a multitude of
combinations. In our enumeration of tlie minerals from
which soils originate, we have instanced but a few, the
more common of the many which may, in fact, contribute
to its formation. The mineralogist counts by hundreds
the natural compounds of these verj^ elements, com-
pounds which, from their capability of crystallization,
occur in a visibly distinguishable shape. The chemist is
able, by putting together these elements in different pro-
portions, and under various circumstances, to identify a
further number of their compounds, and both mineralogy
and chemistry daily attest tlie discovery of new combi-
nations of these same elements of the soil.
We cannot examine the soil directly for many of the
substances which most certainly exist in it, on account of
their being indistinguishable to the eye or other senses,
even when assisted by the best instruments of vision.
We have learned to infer their existence either from analo-
gies with what is visibly revealed in other spheres of ob-
servation, or from the changes we are able to bring about
and measure by the art of chemical analysis.
Absorptive Power of the Soil. — We have already
drawn attention to the fact that various substances, when
put in contact with the soil, in a stale of solution in water,
are withdrawn from the liquid and held by the soil. As
has been mentioned on p. 175, the first appreciative rec-
ord of this fact appears to have been published by
Bronner, in 1836. In his work on Grape Culture occur
the following passages : " Fill a bottle which has a small
hole in its bottom with fine river sand or half-dry sifted
garden earth. Po;ir gradually into the bottle thick and
putrefied dung-liquor until its contents are saturated. The
S34 HOW CKOPS FEED.
liquid that flows out at the lower opening appears almost
odorless and colorless, and has entirely lost its original
properties," After instancing the facts that wells situ-
ated near dung-pits are not spoiled by the latter, and that
tlie foul water of the Seine at Paris becomes potable af-
ter filtering through porous sandstone, Bronner contin-
ues: "These examples sufficiently prove that the soil,
even sand, possesses the property of attracting and fully
absorbing the extractive matters so that the water which
subsequently passes is not able to remove them ; even the
soluble salts are absorbed, and are only washed out to a
small extent by nev) quantities of waterP
It was subsequently observed in the laboratory of
Liebig, at Giessen, that water holding ammonia in solu-
tion, when poured upon clay, lan through deprived of
this substance. Afterward, Messrs. Thompson and IIux-
table, of England, repeated and extended the observa-
tions of Bronner, and in 1850, Professor Way, then
chemist to the Roy. Ag. Soc. of Eng., published in the
Journal of that Society, Vol. XL, pp. 313-379 an account
of a most laborious and fruitful investigation of the sub-
ject. Since that time many chemists have studied the
phenomena of absorption, and the results of these labors
will be briefly stated in the paragraphs that follow.
There are two kinds of absorptive power exhibited by
soils. One is purely physical, and is the consequence of
adhesion or surface-attraction, exerted by the particles of
certain ingredients of the soil. The other is a chemical
action, and results from a i)lay of affinities among certain
of its components.
I The physical absorptive power of various bodies, in-
cluding the soil, has been already noticed in some detail
(pp. lGl-176). In experiments like those of Bronner,
just alluded to, the absorption of the coloring and odor-
ons ingredients of dung-liquor is doubtless a physical
process. These substances are separated from solution by
ABSOIIPTIVK POWEU OF THE SOIL. . 335
the soil just as a mass of clean wool separates indigo from
the liquor of a dye-vat, or as bone-charcoal removes the
brown color from syrup.
Chemical absorptions depend upon tlie formation of
new compounds, and in many cases occasion chemical
decompositions and displacements in such a manner that
while one ingredient is absorbed, and becomes in a sense
fixed, another is released from combination and becomes
soluble. Brief notice has already been made of the
chemical absorption of ammonia by the soil (p. 243).
We shall now enter upon a fuller discussion of this and
allied phenomena.
When solutions of the various soluble acids and bases
existing in the soil, or of their salts, are put in contact
with any ordinary earth for a short time, suitable exami-
nation proves that in most cases a chemical change takes
place, — a reaction occurs between the soil and the
substance.
If we provide a number of tall, narrow lamp-chimneys
or similar tubes of glass, place on the flanged end of each
a disk of cotton-batting, tying over it a piece of muslin,
then support them vertically in clamps or by strings, and
fill each of them compactly, two-thirds full of ordinary
loamy soil, which should be free from lumps, we have an
arrangement suitable for the study of* the absorptive
power in question.
Let now solutions, containing various soluble salts
of the acids and bases existing in the soil, be pre-
pared. These sohations should be quite dilute, but
still admit of ready identification by their taste or by
simple tests. We may emploj^ for example, any or all of
the following compounds, viz., saltpeter, common salt, sul-
phate of magnesia, phosphate of soda, and silicate of soda.
If we pour solution of saltpeter on the soil, which
should admit of its ready but not too rapid percolation,
we shall find that the first portions of li(piid which pasa
336 HOAV CR0P6 FEED.
are no longer a solution of nitrate of potash, but one of
nitrates of lime, magnesia, and soda. The potash has
disappeared from sohition* and become a constituent of
the soil, while other bases, chiefly lime, have been dis-
placed from the soil, and now exist in the solution with
the nitric acid.
If we operate in a similar manner on a fresh tube
of soil with solution of salt (chloride of sodium), we
shall find by chemical examination that the soda of the
salt is absorbed by the soil, while the chlorine passes
through in combination with lime, magnesia, and potash.
In case of sulphate of magnesia, magnesia is retained, and
sul])hates of lime, etc., pass through. With jihospliatcs
and silicates we find that not only the ba'^e, but also these
acids are retained.
Law of Absorption and Displacement. — From a great
number of experiments made by AYay, Liebig, Brustlein,
Henneberg andStohmann, Rautenberg, Pcteis, Weinhold,
Ktillenberg, Ileiden, Knop, and others, it is established
as a general fact that all cultivable soils are able to de-
compose salts of the alkalies and alkali earths in a state
of solution, in such a manner as to retain the base together
with phosj^horic and silicic acids, while chlorine, nitric
acid, and sulphuric acid, remained dissolved, in union with
some other base or bases besides the one with which they
were originally combined. The absorptive power of the
soil is, however, limited. After it has removed a certain
quantity of potash, etc., from solution its action ceases, it
has become saturated, and can take up no more. If,
therefore, a large bulk of solution be filtered through a
small volume of earth, the liquid, after a time, passes
through unaltered.
* The absence of pofasli may be s^hown by aid of strong, cold solution of
tartaric acid, which will precipitate bitartrate of jxitasli (cream of tartar) from
the ori^'inal solution, if not too dilute, but not from that which lias filtered
through the soil. Tlie prcs.ence of lime in tlie liquid that passes the soil may ba
shown by adding to it either carbonate or oxalate of ammonia.
ABSORrXIVE POWER OF THE SOIL. 337
Experiments to ascertain how much of a substance the soil Is able to
absorb are made by putting a known amount of tbc drij soil (e. g. 100
grms.) in a bottle with a given volume (e. g. 500 cubic cent.) of solution
whose content of substance has been accurately determined. The solu-
tions are most conveniently prepared so as to contain as many grms. of
the salt to the liter of water as corresponds to the atomic weight or
equivalent of the former, or one-half, one tenth, etc., of that amount.
The soil and solution are kept in contact with occasional agitation for
some hours or days, and then a measured portion of the liquid is
filtered off and subjected to chemical analysis.
The absorptive power of tlio soil is exerted unequally
towards individual substances. Thus, in Peters' experi-
ments ( Vs. St., II., 140), the soil he operated with absorb-
ed the bases in quantities diminishing in the following
order :
Potash, Ammonia, Soda, Magnesia, Lime.
Another soil, experimented upon by Ktillenberg
{Jahresbericht ilber Agricidtur. Chemie, 1865, p. 15), ab-
sorbed in a different order of quantity, as follows :
Ammonia, Potash, Magnesia, Lime, Soda.
As might be expected, different soils evert ahsorptive
•power toioards the same substance to an u)iequal extent.
Kautenberg {Henneberg' s Jour, far Landicirthsrhaft,
18G2, p, 62), operated with nine soils, 10,000 parts of which,
under precisely similar circumstances, absorbed quantities
of ammonia ranging from 7 to 25 parts.
The time required for absorjytion is usually short.
Way found that in most cases the absorption of ammonia
was complete in half an hour. Peters, however, observed
that 48 hours were requisite for the saturation of the soil
he employed with potash, and in the ex2:)eriinents of Hen-
neberg and Stohmann {Uenneberf s Jourmd.^ 1859, p. 35),
phosplioric acid continued to be fixed after the cxpiiation
of 24 hours.
The strength of the solution influences the extent of
absorjition. The stronger the solution., the more subsia)tce
is taken up from it by the soil. Thus, in Peters' experi-
15
338 HOW CKOPS FEED.
ments, 100 grms. of soil absorbed from 250 cubic centi-
meters of solutions of chloride of potassium of various
degrees of concentration, as follows:
strength of Solution. Pota-ih absorbed by
Designa- Quantity of potash in ^0 c.c. 100 parts By lO.OOO parts in ProjMrtion
tion. of solution. of soil, round numbers. absorber/
|g„ equiv. = 0.1472 gram. 0.9S88 gram. 10 ^i^
\ta " — 0.2944 " O.iaSl '• 14 Mo
a, " = 0.5888 " 0.1990 " 20 ' I3
1,0 " - 1.17-7 " 0..3124 " 31 'U
U " = 2.3555 " 0.4503 " 45 ' U
A glance at the right-hand column shows that although
absolutely less potash is absorbed from a weak solution
than from a strong one, yet the weak solutions yield
relatively more than those wiiich are concentrated.
The quantity of base absorbed in a given time, also de-
pends upon the relative mass of the solution and soil. In
these experiments Peters treated a soil with various bulks
of ' |„ solution of chloride of potassium. The results are
subjoined : —
From 250 c.c. of solution 10,000 parts of soil absorbud 20 parts.
500 " " " " " " " " 25 "
" 1,000 " " " " " " " " 29 "
The quantity of a substance absorbed by the soil de-
pends somewhat on the state of combination it is in, i, e.,
on tlie substances with which it is associated. Peters
found, for example, that 10,000 parts of soil absorbed from
solutions of a number of potash-salts, each containing
'1 ,3 of an equivalent of that base expressed in grams, to
the liter, the following quantities of potash : —
From phosphate, 49 parts.
« hydrate, 40 «
" carbonate, 32 "
" bicarbonate, 28 "
« nitrate, 25 «
« sulphate, 21 «
" chloride* and carbonate, 21 "
« chloride, 20 «
• ChloriUe of Potassium, KG!.
ABSORPTIVE POWER OF THE SOIL 339
We observe that potash was absorbed m this case in
largest proportion from the phosphate, and in least from
the chloride. Ilenneberg and Stohmann, operating on a
garden soil, observed a somewhat different deportment of
it towards ammonia-salts. 10,000 parts of soil absorbed
as follows: —
From phosphate, 21 parts.
((
hydrate, 13 "
" sulphate, 12 "
" hydrateand chloride,* ir I, "
« chloride, 11
" nitrate, U "
Fixation neither complete nor permanent. — A point
of the utmost importance is that none of the bases are
ever completely absorbed even from the most dilute solu-
tions. Liebig indeed, formerly believed that potash is en-
tirely removed from its solutions. We find, in lixct, that
when a dilute solution of potash is slowly filtered through
a large body of soil, the first portions contain so little of
this substance as to give no indication to the usual tests.
These portions are similar in composition to drain-waters,
and like the latter they contain potash in very minute
though appreciable quantity.
In accordance with the above fact, it is found that icater
will dissolve and remove a portion of the potash, etc.,
which a soil has absorbed.
Peters placed in 250 c.c. of a solution of chloride of
potassium 100 grams of soil, which absorbed 0.2114 gram
of potash. At the expiration of two days, one-half of the
solittion was removed, and its place was supplied with
pure water. After two days more, one-h:ilf of the liquid
was again removed, and an equal volume of water added j
♦ Chloride of Ammonium, NH^Cl,
340
now CROPS FEED.
and this process was repeated ten times,
thus in the several washin<?s as follows :
The soil lost
In 2d,
0.0075
3d,
0.0096
4th,
0.0082
In 8th,
0.0112
5th.
0.00G9
nth,
0.0201
6th, 7th extract.
0.0075 0.0082 grams.
10th extract.
0.083 irrams.
Removed in all, 0.0875 gram of i)otash.
Remained in soil, 0.1239 gram.
In these experiments one part of absorbed potash re-
quired 28,100 parts of water for solution.
Similnr results were obtained by Ilenneberg and Stoh-
mann with a soil wliich had absorbed ammonia; one part
of this base required 10,000 parts of water for re-solution.
It has been already stated, that the ahsorption of one
base is accompanied In/ the liberation of a corresponding
quantity of other bases, while the acid element, if it be
sulphinic or nitrii acid, or cJdorine, is found in its
original quantity in the solnt'on. As an illustration of
this rule, the following data obtained by Weinhold in the
treatment of a soil witli sulphate of ammonia are ad-
duced. The quantities are expressed in grnms, except
where otherwise stated.
Content of Sohition
before i
"ontact with the soil.
after
contact w'ith the soil.
II
ll
t
ll
■^s
ll
k
1
e
^
^
1
1
300
200
0.303
0.455
0.129
0.193
0;48S
0.056
0.120
0.012
0.011
0.121
0.034
0.110
0.105
0.049
0.0.30
We observe that the soil not only retained no sulphuric
acid, but gave up a small quantity to the solution. Of
the ammonia a little more than one-half in one case, and
three-eighths in the other, was absorbed, and in the solu-
tion its place was supplied chiefly by lime, but to some
extent also by potash, soda, and magnesi.i, which were
dissolved from the soil. It is also to be noticed that in
the two cases — unlike quantities of the same soil aud
ABSORPTIVK POWER OP TTTE SOIL.
341
solution liaving been employed — the bases were displaced
in quantities that bear to each other no obvious relation.
Another fact wliich follows from the rule just illustra-
ted, is the following : Any base that has been absorbed by
the soil, may be released from combination partly or en-
tirely by any other.
Peters subjected a soil which had been saturated with
potash and subsequently washed coi)iously with water to
the action of various solutions. The results, which exhib-
it the principle just stated, are subjoined. The soil was
employed in portions of 100 grams, each of which con-
tained 0.204 gram of absorbed potash. These were di-
gested for three days with 250 c.c. of solutions (of ni-
trates) of the content below indicated.
For sake of comparison the amount of matters taken up
by distilled water is added.
Dissolved by tlie solution.
Content of
soluiion:
Lime.
Magne-
sia.
Potash.
Soda.
Ammo-
nia.
Abs(yrl>ed
by the soil.
gram.
0.2808 soda.
0.2165 ammonia.
0.2996 lime.
0 2317 magnesia.
Dist. water.
0.0671(?)
0.0322
0.2380
0.0542
trace
0.0006
0.0020
0.1726
0.0983
0.1455
0.1252
0.1224
0.0434
0.2197
0.0024
0.0252
0.0245
0.0004
0.1590
0.0611 goda.
0.0569 ammonia.
I0.O6I6 lime.
1O.O59I magnesia.
"We notice that while distilled water dissolved about ' j
of the absorbed potash, the saline solutions took up two,
three, or more times that quantity. We observe further
that soda liberated lime and magnesia, ammonia liberated
lime and soda, lime brought into solution magnesia and
soda, and magnesia set free lime and soda from the soil
itself.
Again, Way, Brustlein, and Peters, have shown in case
of various soils they experimented with, that the satura-
ting of them, with one ha'^e (potasii and ' lime wore tried)
increases the absorbent power for other bases, and on the
other hand, treatment with a-ids, ichl-h remores absorbed
^ases, diminishes their absorptive power.
342
now r-Rors fkkb.
This f:ict is made evident hy the following data furnish-
ed by PctiTS. The soils employed were
No. 1. Unaltered Soil.
No. 2. Soil heated with hydrochloric acid for some
time, then thorouglily washed with water.
No. 3. No. 2, boiled with 10 grams of sulphate of lime
and water, and washed.
No. 4. No. 2, boiled with solution of 10 grams of chlo-
ride of calcium, and well washed with water.
No. 5. No. 2, boiled with water and 10 grams of car-
bonate of lime.
No. 6. No. 2, boiled with solutiou of bicarbonate of
lime, and washed.
Portions of 100 grams of each of the above were placed
in contact with 250 c.c. of ' \^^ solution of chloride of po-
tassium for tlirce days. Tlie results are subjoined:
Number
Dissolved by the solution.
Potash absorbed
of soil.
Lime.
Magnesia.
Soda.
Chlmine.
by the sou.
1
0.0940
0.0084
0.0261
0.4482 1
0.1841
2
0.0136
0.0004
0.4444 !
0.0227
3
0.0784
0.00-24
0.0019
0.4452
0.0883
4
0.05H0
0.0004
0.0024
0.4453
0.1343
5
O.llTtt
0.00i)4
0.0019
0.4425 1
0.1378
6
0.1456
0.0074
0.4404 '
0.2011
It is seen that the soil which had been waslied with
acid, absorbed but one-ninth as much as tlie unaltered
earth. The treatment with the various lime-salts increas-
ed the absorbent power, in the order of the Table, until
in the last instance it surpassed that of the original soil.
Here, too, we observe that the absorption of potash ac-
companies and is made possible by the displacement of
other bases, (in this case almost entirely lime, since the
treatment with acid liad nearly removed the others). We
observe further that the quantity of chlorine remained
the same throughout (within the limits of experimental
error,) not being absorbed in any instance.
Way first showed that the absorptive power of the soil
ABSOIIPTIVK POWER OP THE SOIL. 343
is diminished or even destroyed by burning o)' calcination.
Peters, experimenting on this point, obtained the follow-
ing results :
Potash absorbed from solution of chloride of potassium by
unburned burned
Vegetable mould, 0.2515 0.0303
Loam, 0.1S41 0.1200
The Cause of the Absorptive Power of Soils for
Bases when combined with chlorine, sul])huric, and nitric
acids, has been the subject of several extensive investiga-
tions. Way, in his papers already referred to, was led to
conclude that the quality in question belongs to some pe-
culiar compound or compounds that are associated with
the clayey or impalpable portion of the soil. That these
bodies were compounds of the bases of the soil with
silica, was a most probable and legitimate hypothesis,
which he at once sought to test by experiment.
Various natural silicates, feldspars, and others, and some
artificial preparations, were examined, but found to be
destitute of action. Finally, a silicate of alumina and
Boda containing water was prepared, which possessed ab-
soi'ptive properties.
To produce this compound, pure alumina was dissolved
in solution of caustic soda on the one hand, and pure silica
in the same solution on the other. On mingling the two
liquids, a white precipitate separated, which, when washed
from soluble matters and dried at 212°, had the following
composition * :
Silica, .46.1
Alumina, 26.1
Soda, 15.8
Water, 12.0
100.0
* Way gives the composition of the anhydrous salt, and says it contained,
dried at 212% about 12 per cent of water. In the above statement this water is in-
cluded, since it is obviously an essc'ntial ingredient.
344 sow CROPS FEED.
This compound is analogous in constitution to tte
zeolites, in so far as it is a highly basic silicate containing
water, and is easy of decomposition. It is, in fact, de-
composed by water alone, which removes from it silicate
of soda, leaving insoluble silicate of ahimina.
On digesting this soda-silicate of alumina witli a solu-
tion of any salt of lime, Way found that it was decom-
posed, its soda Avas eliminated, and a lime-silicate of
alumina was produced. In several instances he succeeded
in replacing nearly all the soda by lime. Potash-silicate
of alumina was procured by acting on either the soda or
lime silicate with solution of a potash-salt ; and, in a simi-
lar mannei*, am,monia and m^agnesia-silicates were gener-
ated. In case of the ammonia-compouml, however. Way
succeeded in replacing only about one-third of soda or
other base by ammonia. All of these compounds, when
acted upon by pure water, yielded small proportions of
alkali to the latter, viz. :
The soda- silicate gave 3.36 parts of soda to 10,000 of water.
The potash- '" " 2.27 " " potasli " " " "
The ammonia- '• " 1,06 " " ammonia" " " "
Way found furthermore that exposure to a strong heat
destroyed the capacity of these substances to undergo the
displacements we have mentioned.
From these facts Way, concluded that there exist in all
cultivable soils, compounds similar to those he thus pro-
cured artificiall}^ and that it is their presence which oc-
casions the absorptions and displacements that have been .
noticed.
Way gives as characteristic of this class of double sili-
cates, that there is a regular order in which the common
bases i-eplace each other. He arranges them in the fol-
lowing series :
Soda — Potash — Lime — Magnesia — Ammonia:
and according to him, potash can replace soda but not the
Other bases; while ammonia replaces them all : or each base
ABSOUPTIVE POWKU OF THE SOIL. 345
replaces those ranged to its left in the above series, but
none of tliose on its right. Way remarks, that " of course
the reverse of this action cannot occur." Liebig {A)in. der
Chem. u. Pharm., xciv, 380) drew attention to the fact
that Way himself in the preparation of the potash-alumi-
na-silicate, demonstrated that there is no invariable order
of decomposition. For, as he asserts, this compound may
be obtained by digesting cither the lime-alumina-silicate, or
soda-alumina-silicate in nitrate or sulphate of potash, when
the soda or lime is dissolved out and replaced by potash.
Way was doubtless led into the mistake of assuming a
fixed order of replacements by considering the?;e exchanges
of bases as regulated after the ordinary manifestations of
chemical affinity. His own experiments show that among
these silicates there is not only no inflexible order of de-
composition, but also no complete replacements.
The researclics of Eichhorn, " Ueber die Einwirkung ver-
dtinnter Salzlusungen auf Ackererde," {Landwirthschaft-
liches Gentralblatt, 1858, ii, 169, and Potyg. Ann., No. 9,
1858), served to clear up the discrepancies of Way's in-
vestigation, and to conflrm and explain his facts.
As Way's artificial silicates contanicd about 12 per cent
of water, the happy thought occurred to Eichhorn to test
the action of saline solutions on the hydrous silicates
(zeolites) whii-h occur in nature. He accordingly insti-
tuted some trials on chabazite, an abstract of which is
here given.
On digesting finely pulverized chabazite (hydrous sili-
cate of alumina and lime) with dilute solutions of chlo-
rides of potassium, sodium, ammonium, lithium, barium,
strontium, calcium, magnesium, and zinc, sulphate of
magnesia, carbonates of soda and ammonia, and nitrate
of cadmium, he found in every case that the basic ele-
ment of these salts became a part of the silicate, while
lime passed into the solution. The rapidity of the re-
placement varied exceedingly. The alkali-chlorides re*
15*
546
no"\v cRors peed.
acted evidently in two or tliree days. Chloride of barium
and nitrate of cadtnium were slower in their effect. Chlo-
rides of zinc and strontium at first, appeared not to react ;
but after twelve days, lime was found in the solution.
Chloride of magnesium was still tardier in replacing lime.
Four grams of powdered chabazite were digested with
4 grams of chloride of sodium and 400 cubic centimeters
of water for 10 days. The composition of the original
mineral (i,) and of the same after the action of chloride of
sodium (ii,) were as follows :
Silica,
47.44
48.31
Alumina,
30.69
21.04
Lime,
10.37
6.65
Potash,
0.65
0.64
Soda,
0.42
5.40
Water,
20.18
18.33
Total, 99.75 • 100.37
Nearly one-half the lime of the original minei'al was
thus substituted by soda. A loss of water also occurred.
The sokition separated from the mineral, contained nothing
but soda, lime, and chlorine, and the latter in precisely its
original quantity.
By acting on chabazite with dilute chloride of ammo-
nium (10 grams to 500 c.c. of water) for 10 days, the
mineral was altered, and contained 3.33 per cent of am-
monia. Digested 21 days, tlie mineral yielded 6.94 per
cent of ammonia, and also lost water.
These ammonia-chabazites lost no ammonia at 212°, it
escaped only when the heat was raised so high that water
began to be expelled ; treated with warm solution of pot-
ash it was immediately evolved. The ammonia-silicate
was slightly soluble in water.
As in the instances above cited, there occurred but a
partial displacement of lime. Eichhorn made correspond-
ing trials with solutions of carbonates of soda and am*
At^soTiPTivK ro^v^:t^ of titk snTT,. fiAt
monia, in order to asceitain whether tlie formation of a
Bohible salt of the (lis[)laccd base limited the reaction;
but the results were substantially the same as before, as
shown by analyzing the residue after removing carbonate
of lime by digestion in dilute acetic acid.
Eichliorn found that the artificial soda-chabazite re-ex-
changed soda for lune when digested in a solution of
chloride of calcium ; in solution of chloride of potassium,
both soda and lime were separated fiom it and replaced
by pot:i8h. So, the ammonia-chabazito in solution of chlo-
ride of calcium, exchanged ammonia for lime, and in so-
lutions of chloi-ides of potassium and sodium, both am-
monia and lime passed into the liquid. The ammonia-
chabnzite in solution of sulphate of magnesia, lost ammo-
nia but not lime, thougli doubtless the latter base would
have been found in the liquid had the digestion been con-
tinued longer.
It thus appears that in the case of chabazite all the
protoxide bases may mutually re})lace each other, time
being the only element of difference in tlie reactions.
Similar observations were made with natrolite (hydrous
silicate of alumina and soda,) as well as with chlorite and
labradorite, although in case of the latter difficultly de-
composable silicates, the action of saline solutions was
very slow and incomplete.
Mulder has obtained similar displacements with the
ZL'olitic minerals stilbite, thomsonite, and prehnite. {C/te-
mie der Ackerkrume, T, 396). He has also artificially
prepared hydrous silicates, having properties like those
of Way, and has noticed tl:at sesquloxide of iron readily
participates in the displacements. Mulder also found that
the gelatinous zeolitic precipitate obtained by dissolving
hydraulic cement in hydrochloric acid, precipitating by
ammonia and long washing with water, underwent the
same substitutions when acted upon by saline solutions.
348 Mow cuors feed.
The precipitate he operated with, contained (water-free)
in 100 parts:
Silica 49.0
Alumina 11.1
Oxide of iron 21.9
Lime 6.9
Matrnesia 1.1
Insoluble matters -with traces of alkalies, etc 10.0
100.0
On digesting portions of this substance witli sohitions
of sulphates of soda, potash, magnesia, ammonia, for a
single hour, all tlie lime was displaced and replaced by-
potash — two-thirds of it by soda and nearly four-fifths of
it by magnesia and ammonia.
Further investigations by Rautenberg {Henneherg^s
Jour, fur Landiotrthschaft, 1862, pp. 405-454), and
Knop ( Vs. St., VII, 57), which we have not space to re-
count fully, have demonstrated that of the bodies possible
to exist in the soil, those in the following list do not pos-
sess the power of decomposing sulphates and nitrates of
lime, potash, ammonia, etc., viz.:
tlj f Quartz sand. "j
S I Kaoliuite (purified kaolin.') i
•S J Carbonate of lime (chalk.) I These liodies have no absorptive effect, either
^ 1 Iluinus (decayed wood.) f separately or together.
g I Hydrated oxide of iron. 1
p5 (Hydrated alumina. I
Hamate of lime, magnesia, and alumina. [Knop.
Phosphate of alumina.
Gelatinous silica.
" dried in the air.
These observers, together with Heiden [Jahresbericht
lUber Agricultvrchemie, 1864, p. 17), made experiments on '
soils to which hydrated silicates of alumina, and soda, or
of lime, etc., were added, and found their absorptive
power thereby increased.
Rautenberg and Ileiden also found an obvious relation
to subsist between the absorptive powers of a soil and cer-
tain of its ingredients. Rautenberg observed that the ab-
sorptive power of the nine soils he operated with was
closely connected with the quantity of alumina and oX'
ABSORPTIVK POWER OF TUE SOIL. 349
ide of iron which llie soils yielded to hydrochloric acid.
Heiden traced a similar relation between the silica set free
by the action of acids on cluven soils and their absorptive
power. Rautenberg and Heiden further confinued what
Way and Peters Imd previously shown, viz., that treat-
ment of soil with acids diminished their absorbent power.
These facts admit of interpretation as follows : Since
neither silica, hydrated alumina, nor hydrated oxide of
iron, as such, have any absorptive or decomposing power
on suljihates, nitrates, etc., and since these bodies do not
ordinarily exist as sncli to much extent in soils, therefore
the connection found in twenty cases to subsist between
their amount (soluble in acids) in the soil, and the ab-
sorptive power of the latter points to a compound of
these (and other) substances (silicate of alumina, iron,
lime, etc.), as tlie absorptive agent.
That the absorbing compound is not necessarily hydra-
ted, is indicated by the fact that calcination, wliich must
Temove water, though it diminishes, does not always alto-
gether destroy the absorptive quality of a soil. (See p.
343.) Eiciihorn, as already stated, found that the anhy-
drous silicates, chlorite and labradorite, Avere acted upon
by saline solutions, though but slowly.
Do Zeolitic Silicates, hydrated or otherwise, exist
in the Soil? — When a soil which is free from carbonates
and salts readily soluble in water, is treated with
acetic, hydrochloric, or nitric acid, there is taken up a
quantit-y (several per cent.), of matter Avhich, while con-
taining all the elements of the soil, consists chiefly of
alumina and oxide of iron. Silica is not dissolved to much
extent in the acid, but the soil which before treatment
with acid contains but a minute amount of uncoinbined.
silica, afterwards yields to the ))roper solvent (hot solution
of carbonate of soda) a considerable quantity. This is our
best evidence of the presence in the soil of easily decora*
850
HOW CROPS FEED.
posable silicates. A number of analyses which illustratfl
these facts are subjoined :
Water
Orsranic matter
Siiiui and insoluble silicates.
(Clay, kaoliiiite)
f Silica
(jD , Oxide of iron
£. Alumina
g. ' Lime
5- I Magnesia
Potash
Soda
Phosiphoric acid
Sulphuric acid
Carbonic acid, clilorine,
^ and loss
Sandy Loam.
Heiden.
1.613
2.387
89.754
(10.344)
2.630*
1.8-2
1.152
o.ini
0.201
0.242
0.034
0.083
0.007
White
Clay.
5.
Porce-
lain
Vlay.
Rautenbekg.
Bed
Clay.
6.15
none
58.03
18.73
2.11
12.15
0,27
0.29
0.86
1.41
none
.095 I
.(XW 1
6.80
0.90
4.35
89.46
0.04t
0.12
0.08
6.
White
Pottery
Clay.
Wat.
6.18
none
58.72
13.41
5.38
13.90
0.61
0.43
100.00 I100.20 lioo.oo
• This soil yielded to solution of carbonate of soda before treatment with
acid, 0.340 "u silica.
+ The eilica in this case is the small portion held in the acid solution.
The first three analyses especially, show that the soils
to which they refer, contained a silicate or silicates in
which iron, alumina, lime, magnesia and the alkalies ex-
isted as bases. How much of such silicates may occur in
any given soil is impossible to decide in the present state
of our knowledge. In the soil, free silica, is usually, if not
always present, as may be shovvn by treatment with solu-
tion of carbonate of soda, but it appears difficult, if not
impossible, to ascertain its quantity. Again, hydratcd
oxide of iron (according to A. Miiller and Knop) and hy-
li'ated alumina* (Knop) may also exist, as can be made
evident by digesthig the soil in solution of tartrate of
.■^oda and potash (Mtillcr, Ys. St , IV, p. 277), or in a mi.x-
ture of tartrate and oxalate of ammonia (Knop, Vs. St.
VIII, p. 41). Finally, organic acids occur to some ex-
tent in insoluble combinations with iron, alumina, lime,
• Jl'ire probably, highly basic carbonates, or mixtures of hydrates and car
bunates.
ABSORPTIVE POWER OF THE SOIL. 351
&c. This complexity of the mW effectually ])revents au
accurate analysis of its zeolitic silicates.
If further evidence of the existence of zeolitic com-
pounds in the soil were needful, it is to be found in con-
sidering the analogy of the conditions whiirh there obtain
with those under which these compounds are positively
known to be formed.
At Plombieres, in France, the water of a hot spring
(temperature, 140" F.) has flowed over and penetrated
throuo-h a mass of concrete, composed of bricks and sand-
stone laid in lime, which was constructed centuries ago by
the Romans. The water contains about nine ten-thou-
sandths of solid matter in solution, a quantity so small as
not to affect its taste perceptibly. As Daubree has shown
{Ann. des Mifies, 5me., Serie, T. XIII, p. 242), the cavi-
ties in the masonry frequently exhibit minute but well-
defined crystals of various zeolitic minerals, viz, : chaba-
site, apophyllite, scolezite, hnrraotome, together with hy-
drated silicate of lime. These minerals have been pro-
duced by the action of the water upon the bricks and lime
of the concrete, and while a high temperature prevails
there, which probably has facilitated the crystallization of
the minerals, as it certainly has done the chemical altera-
tion of the bricks and sandstone, the conditions otherwise
are just those of the soil.
In the soil, we should not expect to find zeolitic com
binations crystallized or recognizable to the eye, because the
small qu intities of these substances that could be formed
there must be distrilmted throughout twenty, fifty, or
more times their Aveight of bulky matter, which would
mechanically prevent their crystallization or segregation
in any form, more especially as the access of water is very
abundant ; and the carbonic acid of the surface soil, which
powerfully decomposes silicates, would operate antago-
nistically to their accumulation.
352 HOW CROPS FEED.
The water of the soil holds silica, lime, magnesia, alka»
lies, and oxide of iron, often alumina, in solution. In-
stances are numerous in Avhich the evaporation of water
containing dissolved salts lias left a solid residue of sili-
cates. Thus, Kersten has described {Jour, fur praki.
Chem., 22, 1) a hydrous silvate of iron and manganese
that occurred as a hard incrustation upon the rock, in one
of the Freiberg mines, and was deposited where the water
leaked from the pum2)s. Kersten and Berzelius have lio-
ticed in the evaporation of mineral waters which contain
carbonates of lime and magnesia, together with silica, that
carbonates of these bases are first deposited, and finally
silicates separate. {B's:hof^s Chem. Geolo^/y^ Car. Ed.^
Vol. 1, p. 5). Bischof (loc. cit., p, 6) has found that silica,
even in its most inactive form of quartz, slowly decom-
poses carbonate of soda and potash, forming silicate when
boiled with their aqueous solutions. Undoubtedly, simple
contact at ordinary temperature has the same effect,
though more slowly and to a slight extent.
Such facts make evident that silica, lime, the alkalies,
oxide of iron and alumina, when dissolved in water, if they
do not already exist in combination in the water, easily
combhie when adverse affinities do not jirevent, and may
react upon the ingredients of the soil, or upon rock dust,
with the formation of zeolites.
The " pan," which often forms an impervious stratum
under peat bogs, though consisting largely of oxide of iron
combined with organic acids, likewise contains consider-
able quantities of hydrated silicates, as shown by the
analyses of Warnas and Michielsen {Mulder'' s Chem. d.
Ackerkrume, Bd. 1, p. 566.)
Mulder found that when Portland cement (silicate of
lime, alumina, iron, cte.) was treated with strong hydro-
chloric, acid, whereby it was decomposed and in part dis-
solved, and then with ammonia, (which neutralized and re*
ABSOEPTIVE POWER OF THE SOIL. 353
moved the acid,) tlie gelatinous precipitate, consisting
chiefly of free silica, free oxide of iron, free alumina, with
smaller quantities of lime and magnesia, contained never-
theless a portion of silica, and of these bases in combina-
tion, because it exhibited absorbent power for bases, like
Way's artificial silicates and like orilhiary soil. Mere
contact of soluble silica or silicates, with finely divided
bases, for a short time, is thus proved to be sufficient for
chemical union to take place between them.
Recently precipitated silicic acid being added to lime-
Avater, unites with and almost completely removes the lime
from solution. The small portion of lime that remains
in the liquid is combined with silica, the silicate not being
entirely insoluble. (Gadolin, cited in Storer's Diet, of
Solubilities, p. 5.51.)
The fict that free bases, as ammonia, potash and lime,
are absorbed by and fixed in soils or clays that contain no
organic adds, and to a degree different, usually greater th.in,
when presented in combination, would indicate that they
directly nnite either with free silica or with simple sili-
cates. The hydrated oxide of iron and alumina are in-
deed, under certain conditions, capable of retaining free
alkalies, but only in minute quantities. (See p. 359.)
The fact that an admixture of cai'b onate of lime, or of
other lime-salts with the soil, usually enhances its absorbent
])Ower, is not improbably due, as liautenberg first suggest-
ed, to the formation of silicates.
A multitude of additional considerations from the his-
tory of silicates, especially from the chemistry of hydraulic
cements and fiom geological metamorphism, might be
adduced, were it needful to fortify our position.
Enough has been written, however, to make evident
that silica, which is, so to speak, ;m accident in the plant,
being unessential (we will not affirm useless) as one of its
ingredients, is on account of its extraordinary capacity for
chemical union with other bodies in a great variety of
354 now CKOPS feed.
proportions, extremely important to the soil, and espe«
cially 50 when existing in combinations admitting of the
remaikable changes whicli liave come under our notice.
That we cannot decide us to tlie precise composition of
the zeohtic compounds which may exist in tlie soil, is plain
from what lias been, stated. We have the certainty of
their anah)gy with the well-defined sihcates of the miner-
alogist, which have been termed zeolites, an analogy of
chemical composition and of chemical properties ; we know
further that they .ire likely to be numerous and to be in
perpetual alteration, ac, they are subjected to the influence
of one and another of the salts and substances that are
brought into contact with them ; but more than this, at
present, we cannot be certain of
Physical agencies in the phenomena of absorption.—
While the absorption by the soil of ])otash or other base
is accompanied by a chemical decomposition, which Way,
Rautenberg, Heiden, and Knop's researches conclusively
connect Avith certain hydrous silicates whose j^resence in
the soil cannot be doubted, it has been the opinion of
Liebig, Brustlein, Henneberg, Stohmann and Peters,
that the real cause of the absorption is physical, and is
due to simple surface attraction (adhesion) of the jjorous
soil to the absorbed substance. Brustlein and Peters have
shown that bone and wood-charcoal, washed with acids,
absorb ammonia and potash from their salts to some ex-
tent, and after impregnation with carbonate of lime to as
great an extent as ordinary soil. While the reasons al-
ready given appear to show satisfactorily that the ab-
sorbent power of the soil, /or bases hi combination^ re-
sides in the chemical action of zeolitic silicates, the facts
just mentioned indicate that the pliysical properties of the
soil may also exert an influence. Indeed, the fixation of
free bases by the soil may be in all cases pai'tially due to
this cause, as Brustlein has made evident in case of am-
monia {BoyssingaulCs Agronomie, etc., T., II, p. 153).
ABSUKPTIVJi: roWKU OF THE SVlL. 355
Peters concludes the account of his valuable investiga-
tion with the following words : " Absorption is caused by
the surface attraction vhich the j)< articles of eurth esrert.
In the absorption of bases from salts^ a chemical trans-
position uith the ingredients of the soil is necessary,
which is m.ade possible through cooperation of the surface
attraction of the soil for the base:' (Ys. St., IT, p. 151.)
If "we admit the soundness of tliis conclusion, Ave must
also admit that in the soil the physical action is exerted
in sufficient intensity to decompose salts, by the hydrated
silicates alone. We must also allow that the displace-
ments observed by Way and Eichhorn in silicates, are
primarily due to mere physical action, thoiigh they have
imdeniably a chiefly cliemical aspect.
That the phenomena are modified and limited in certain
respects by physical conditions, is to be expected. The
facts that the quantity of solution compared with the
amount of soil, the strengtli of the solution, and up to
a certain point the time of contact, influence the degree
of absorption, point unmistakably to purely physical in-
fluences, analogous to those with whose action the chem-
ist is familiar in his daily experience.
Absorption of Acids. — It has been mentioned
already that phosphoric and silicic acids are absorbed
by soils. Absorption of phosphoric acid has been
invariably observed. In case of silicic acid, excep-
tions to the rule have baen noticed. In very few in-
stances has the absorption of sulphuric and nitric acids
or chlorine, from their compounds, been remarked
hitherto by those who have investigated the ab-
sorbent power of the soil. The nearly universal con-
clusion has been that these substances are not subject in
any way, chemical or physical, to the attraction of tlie
soil. Yoelcker was the first to notice an absorption of
sulphuric acid and chlorine. In his papers on " Farm
Yard Manure," etc., (Jour. Roy. Ag. Soc.,XYIII,,p. 140,)
35ft HOW CROPS FEED.
and on the "Changes which Liquid Manure undergoes in
contact with different Soils of Known Composition" {idem
XX., 134-57), he found, in seven experiments, that dung
liquor, after contact with various soils, lost or gained acid
ingredients, as exhibited l)y the following figures, in grains
per gallon : (loss is indicated by — , gain by +) :
1 2 34567 A. B.
Chloride of Potassium — S.Sl +9.17 —2.74 +2.14 —2.74 +2.55 —1.10
Chloride of Sodium. . .—3.05 —2.43 —7.04 —1.12 —1.10 —1.24 +3.CG -1.89 +19.05
Sulphuric Acid +3.32 —4.21 —1.06 —1.21 —0.27 +1.24 +3.44 +2.26 —0.42
Silicic Acid +1.63 +10.33 —1.64 +0.72 +2.76 —0.11 —0.07 undet. —1.57
Phosphoric Acid — — —4.23 —3.09 —2.91 —3.38 —0.13 —8.76 —7.71
We notice that chlorine was perceptibly retained in
three instances, while in the other four it was, on the
whole, dissolved from the soil. Sulphuric acid was re-
moved from the solution in four instances, and taken up
by it in three others. In four cases silica was absorbed,
and in three was dissolved. In his first paper. Professor
Way recorded similar experiments, one with flax-steep
liquor and a second with sewage. The results, as regards
acid ingredients, are included in the above table, A and B,
where we see that in one case a slight absorption of chlo-.
rine, and in the other of sulphuric acid, occurred. Way,
however, regards these diiferences as due to the unavoid-
able errors of experiment, and it is certain that in Vcelck-
er's results similar allowance must be made. Neverthe-
less, these errors can hardly account for the large loss of
chlorine observed i:i 1 and 3, or of sulphuric acid in 2.
Liebig found in his experiments "that a clay or lime-
soil, poor in organic matter, withdrew from solution of
silicate of potash, both silicic acid and potash, whereas
one rich in humus extracted the potash, but left the silicic
acid in solution." (Compare pp. 171-5.)
As regards nitric acid , Knop observed in a single in-
stance that this body could not be wholly removed by
water from a soil to which it had been added in known
quantity. He regards it probable that it was actually
ABSORPnVE POWER OF THE SOIL. 357
retained rather than altered to ammonia or some other
compound.
The fixation of acids in tlie soil is unquestionably, for
the most part, a chemical process, and is due to the for-
mation of comparatively insoluble compounds.
Hydrated oxide of iron and hydrated alumina are
capable of forming highly insoluble compounds with all
the mineral acids of the soil. The chemist has long been
familiar with basic clilorides, nitrates, sulphates, silicates,
phosphates and carbonates of these oxides. Whether such
compounds can be actually jjroduced in the soil is, how-
ever, to some extent, an open question, especially as re-
gards chlorine, nitric and sulphuric acids. Their forma-
tion must also greatly depend upon what other substances
are present. Thus, a soil rich in these hydrated oxides,
and containing lime and the other bases in minuter quan-
tity (except as firmly combined in form of silicates,) would
not unlikely fix free nitric acid or iree sulphuric acid as
well as the chlorine of free hydrochloric acid. When the
acids are presented in the form of salts, however, as is
usually the case, the oxides in question have no power to
displace them from these combinations. The acids, can-
not, therefore, be converted into basic aluminous or iron
salts unless they are first set free — unless the bases to
which they were previously combined are first mastered
by some separate agent. In the instance before referred
to where nitric acid disappeaied from a soil, Knop sup-
poses that a basic nitrate of iron may have been formed,
the soil employed being, in fact, highly ferruginous.
The hydrated oxides of iron and alumina do, however,
form insoluble compounds with phosphoric acid^ and may
even remove this acid from its soluble combinations with
lime, as Thenard has shown, or even, perhaps, from its
compounds with alkalies.
Phosphoric acid is fixed by the soil in various ways.
When a phosphate of potash, for example, is put in
358 IK^W CROPS FKEU.
contact with tlie soil, the base may be withdrawn by tlie
absorbent silicate, and the acid may iniite to lime or mag-
nesia. The phosphates of lime and magnesia thus formed
arc, however, insoluble, and hence the acid as well as the
base remains fixed. Again, if the alkali-phosphate be
present in quantity so great that its base cannot all be
taken up by the absorbent silicate, then the hydrated
oxide of iron or alumina may react on the phosphate, chemi-
cally combining with the phosphoric acid, while the alkali
gradually saturates itself with carbonic acid from the air.
It is, however, more likely that organic salts of iron (cre-
nates and apocrenates) transpose with the phosphate. So,
too, carbonate of lime may decompose with phosphate of
potash, producing carbonate of potash and pliosphate of
lime (J. Lawrence Smith). Vadeker, in a number of ex-
periments on the deportment of the sohible superphosphate
of lime toward various soils, found that the absorption of
phosphoric acid was more rapid and complete with soils
containing much carbonate of lime tlian with clays or
sands.
All observers agree that phosphoric acid is but slowly
fix;ed by the soil. Vcelcker found the process was not
completed in 26 days. Its absorption is, therefore, mani-
festly due to a different cause from that which completes
the fixation of ammonia and potash in 48 hours.
As to silicic ac'id^ it may also, as solid hydrate, unite
slowly with the oxides of iron and with alumina (see Kers-
ten's observations, p. 352). When occurring in solution, as
silicate of an alkali, as happens in dung liquor, it Avould
be fixed by contact with solid carbonate of lime, silicate
of lime being formed (Fuchs, Kuhlmann), or by encoun-
tering an excess of solutions of any salt of lime, magnesia,
iron or ammonia. In presence of free carbonic acid in
excess, a carbonate of the alkali would be formed, and the
silicic acid would be separated as such in a nearly insoluble
ABSORPTIVE fOWEll OF THE SOIL. 350
form. Dung liquor, rich in carbonate of potash, on the
other hand, would dissolve silica from the soil.
Sulphuric acid, existing in considerable quantities in
dung liquor as a readily soluble salt of ammonia or potash,
would be partially retained by a soil rich in carbonate of
lime by conversion into sulphate of lime, which is com-
paratively insoluble.
Absorption of Bases, from their Hydrates, Carbonates
and SilicateSi — 1. Incidentally it has been remarked that
free bases, among which ammonia, potash, soda and lime
are specially implied, may be retained by combining with
undissolved silica. Potash, soda (and ammonia?) may
at once form insoluble compounds if the silica be in large
proportion ; otherwise they may produce soluble silicates,
wliich, however, in contract with lime, magnesia, alumina
or iron salts, will yield insoluble combinations. As is
well proved, gelatinous silica and lime at once form a
nearly insoluble compound. It is probable that gelatinous
silica may remove magnesia from sobxtion of its bicarbon-
ate, forming a nearly insoluble silicate of magnesia.
2. It has long been known that hydrated oxide of iron
and hydrated alumina may unite with and retain free
ammonia, j^otash, etc. Rautenberg experimented with
both these substances as freshly prepared by artificial
means, and found that, under similar conditions,
10 j,'rm9. ofbytlrated 10 grms. of hydrated
oxide of iron. alumina.
Absorbed of free ammonia 0.046 grm. 0.066 grm.
" " free potash - 0.U7 " not det.
Long continued washing with water removes the alkali
from these combinations. That oxide of iron and alumina
commonly occur in the soil in quantity suflicient to have
appreciable effect in absorbing free alkalies is extremely
improbable.
Liebig has shown {Ann. Ch. u. Fh. 105, p. 122,) that
hydrated alumina unites with silicate of potash with great
360 HOW CROPS PEEi).
avidity (an insoluble double silicate being formed just as
in the experiments of Way, p. 343). According to Liebig,
a quantity of hydrated alumina equivalent to 2.696 gnns.
of anhydrous alumina, absorbed from a liter of solution
of silicate of potash containing 1.185 grra. of potash and
3.000 grm. of silica, fifteen per cent of the silicate. Doubt-
less hydrated oxide of iron would behave in a similar
manner.
3. The organic acids of humus are usually the most
effective agents in retaining the bases when the latter are
in the free state, or exist as soluble carbonates or silic-
ates. The properties of the humates have been detailed
on page 230. It may be repeated here that they form
with the alkalies* when the latter preponderate, soluble
salts, but th.nt tliese cumjjounds unite readily to other
eartliy* and metallic* humates, forming insoluble com-
pounds. Lime at once forms an insoluble humate, as
do the metallic oxides. When, as naturally happens, the
organic acids are in excess, ttieir effect is in all cases to
render the soluble free bases or their carbonates nearly
insoluble.
In some cases, ammonia, potash and soda are absorbed
more largely from their carbonates than from their hy-
drates. Thus, in some experiments male by the author,
a sample of Peat from the New Haven Beaver Meadow
Avas digested with diluted solution of ammonia for 48
hours, and then the excess of ammonia was distilled off
at a boiling heat. The peat retained 0.95° |^ of this alkali.
Another portion of the same peat was moistened with
diluted solution of carbonate of ammonia and then dried
at 212° until no ammoniacal smell was perceptible. This
sample was found to have retained 1.30" |„ of ammonia.
This difference was doubtless due to the fact that the
* In the customary language of Chemistry, potash, soda, and ammonim ara
alkalies or alkali-bases. Lime, magnesia, and alumina are earths or earthy bases,
and oxide of iron and oxide of maaganese are metallic bases.
KEVIKW AND CONCLUSION. S61
peat contained hamate o/'^/me, which was not affected by
tlio pure ainuionia, but in contact witli carbonate of am-
monia yielded carbonate of lime and huniate of ammonia.
In these cases the ammonia was la excess^ and the chemical
changes were therefore, in some particulars, unbke those
which occur when the humus preponderates.
Brustlein, Liebig and others have observed that soils
ricli in organic matter (forest mold, decayed wood,) have
their absorptive power much enhanced by mixture with
carbonate of lime.
Although Rautenberg has shown {Henneherg''s Journal
186, p. 439,) that silicate of lime is probably formed when
ordiaiary soils are mixed with carbonate of lime, it may
easily happen, in the case of soils containing humus, that
humate of lime is produced, which subsequently reacts
upon the alkali-hydrates or salts with which absorption
experiments are usually made.
§ 6.
REVIEW AND CONCLUSION.
The limits assigned to this work having been nearly
reached, and the more important facts belonging to the
present chapter brought under notice, with considerable
fulness, it remains to sum up and also to adduce a few
considerations which may appro2:>riately close the volume.
There ai-e indeed a number of topics connected with the
feeding of crops which have not been treated upon, such,
especially as come up in agricultural practice ; but these
find their place most naturally and properly in a discussion
of the improvement of the soil by tillage and fertilizers,
to which it is proposed to devote a third volume.
What the Soil mast contain.— In order to feed crops,
16
362 BOW CROPS FEED.
the soil must contaiu the ash-ingredieuts of plants, together
with assimilable nitrogen-com[iounds in proper quantity
and proportion. The composition of a very fertile soil is
well exhibited by Baumhauer's analysis of an alluvial de-
posit from the waters of the Rhine, near the Zuider Zee,
in Holland. This soil, which produces large crops, con«
tained —
Surface.
15 inches deep.
.30 itiches deep.
Insoluble eillca, quartz,
57.646
51.706
55.372
Soluble silica,
2.340
2.496
2.286
Alumina,
1.&30
2.900
2.888
Peroxide of iron,
9.039
10.305
11.864
Protoxide of iron,
0.350
0.563
0.200
Oxide of manganese,
0.288
0.354
0.284
Lime,
4.092
5.096
2.480
Magnesia,
0.130
0.140
0.1-28
Potash,
1.026
1.430
1.521
Soda,
1.972
2.069
1.937
Ammonia,*
0.060
0.078
0.075
Phosphoric acid,
0.466
0..324
0.478
Sulphuric acid,
0.896
1.104
0.576
Carbonic acid,
6.085
6.940
4.775
Chlorine,
1.240
1.302
1.418
Humic acid,
2.798
3.991
3.428
Crenic acid,
0.771
0.731
0.037
Apocrenic acid,
0.107
0.100
0.152
Other organic matters, and com-
bined water (nitrates ?),
8.324
7.700
9.348
Lobs in analysis,
0.540
0.611
0.753
A glance at the above analyses shows the unusual rich-
ness of this soil in all the elements of plant-food, witli ex-
ception of nitrates, which were not separately determined.
The alkalies, phosphoric acid, and sulphuric acid, were
present in large proportion. The absolute quantities of
the most important substances existing in an acre of this
soil taken to the depth of one foot, and assuming thia
* The figures are probably too high for ammonia, because, at the time the analy-
ses wore made, the methods of estimating this substance in the soil had not been
Btudied sufficiently, and the ammonia obtained was doubtless derived in great
part from the dfcomposition of humus under the action of au alkali.
REVIEW A>fD CONCLUSION. 36^
quantity to weigh 3,500.000 lbs., (p. 158,) are as follows;
Soluble silica
81.900
Lime,
143.2:20
Potasli,
35.910
Soda,
68,920
Ammonia,
2.100
Phosphoric acid
16.310
Sulpliuric acid,
31.360
Nitric acid,
?
Quantity of Available Ash-ingredients necessary for
a Maximum Crop. — We have already given some of the
results of Hellriegel's experiments, made for the purpose
of determining how much of the various elements of nu-
trition are required to produce a maximum yield of cereals
(pp. 215 and 288). This experimenter found that 74 lbs.
of nitrogen (in form of nitrates) to 1,000.000 of soil was
sufficient to feed the heaviest growth of wheat. Of his
experiments on the ash-ingredients of crops, only those
relating to potash have been published. Tiiey are here
reproduced.
EFFECTS OF VARIOUS PROPORTIONS OF AVAILABLE POTASH • IN
THE SOIL ON THE BARLEY CROP.
Yi£ld
Potai^h in
1,000.000 »s.o/«ot;.
Of straw and Chaff.
Of Grain.
Total.
0
0.798
6
3.809
2.993
6.802
12
5.740
4.695
10.435
24
6.859
7.851
14.710
47
8.195
9.578
17.773
71
9.. 327
10.097
19.424
94
8.693
9.083
17.776
141
8.764
8.529
17.293
282
8.916
8.962
17.878
It is seen that the greatest crop was obtained when 71
parts of potash were present in 1,000.000 lbs. of soil. A
♦ Other conditions were in all respects as nearly alike as possible.
S64 HOW CROPS PEED.
larger quantity depressed the yield. It is iirobable that less
than 71 lbs. would have ])roduced an equal effect, since 47
lbs. gave so nearly the same result. The ash composition
of barley, grain, and straw, in 100 parts, is as follows,
according to Zoeller, (H. C. G., pp. 150 to 151) :
Orain.
Straio.
Potash,
18.5
12.0
Soda,
3.9
4.6
Magnesia,
7.0
3 0
Lime,
2.7
7.3
Oxide of iron,
0.7
1.9
Phosphoric acid.
33.4
6.0
Sulphuric acid,
2.8
2.8
Silica,
31.1
59 7
Chlorine,
1.1
2.6
Tlie proportion of ash in the air-dry grain is 2^ per
cent, that in the straw is 5 per cent, {Ann. Ch. u. Ph.
CXII, p. 40). Assuming the average barley crop to be
33 bushels of grain at 53 lbs. per bushel = 1,750 lbs., and
one ton of straw,* we have in the barley crop of an acre
the following quantities of ash-ingredients :
il
1
"fe^
1
•£
S
s|
1
1
1
^1
!i
i
Grain,
43.75
8.1
1.7
3.1
1.3
0.3
14.2
1.2
0.5
Straw,
100.00
13.0
4.G
3.0
7.3
1.9
0.0
2.8
2.G
_ .
.
—
. —
—
.
—
—
In the account of Ilellriegel's experiments, it is stated
that the maximum barley crop in some other of his trials,
corresponds to 8,160 lbs. of grain, or 154 bushels of 53
lbs. each per acre. This is more than 4^ times the yield
above assumed.
The above figures show th:it no essential ash-ingredi-
ent of the oat crop is present in larger quantity than
potash. Phosphoric acid is quite the same in amount,
* These figuree are employed by Anderson, and are based on Scotch statistics
REVIEW AND CO^'CLUSION, 365
while lime is but one-luilf as much, and the other acids
and bases are still less abundant. It follows then that if
71 lbs. of available potash in 1,000.000 of soil are enough
for a barley croj) 4.]- times greater than can ordinarily be
produced under agricultural conditions, the same quantity
of phosphoric acid, and less than half that amount of litne,
.etc., must be ample. Calculating on this basis, we give
in the following statement the quantities required per
acre, taken to the depth of one foot, to produce the max-
imum crop of Ilellriigel (1), and the quantities needed
for the average crop of 33 l)ushels ('2). The amounts of
nitrogen are those which liellriegel found adequate to the
wheat crop. See p. 289.
1 s
Potash,
248
55
Soda,
78
17
Magnesia,
76
17
Lime,
105
23
Pliospboric acid,
250
55
Sulplmric
acid.
49
11
Clilorine,
38
8
Nitrogen,
245
54
If now we divide the total quantities of potash, etc.,
found in an acre, or 3,500.000 lbs. of the soil analyzed by
Baumhauer, by the number of pounds thus estimated to
be necessarily present in order to produce a maxinmra
or an average yield, we have the following quotients, which
give the number of maximum barley crops and the number
of average crops, for which the soil can furnish the re-
spective materials.
The Zuider Zee soil contains enough
Lime for 1364 maximum and 6138 average barlej- crops.
Potash " 144 " " 648 "
Phosphoric acid " 65 " " 292 " " "
Sulphuric " " 64 " " 288 "
Nitrogen in ammonia " 7 " " 31 " " "
We give next the composition of one of the excellent
366 HOW CROl'S FEED.
wheat soils of Mid Lothian, analyzed by Dr. Anderson.
The air-dry surface-soil contained in 100 parts :
Silica 71.553
Alumina 6.935
Peroxide of iron 5.173
Lime 1.229
Magnesia 1.082
Potash 0.354
Soda 0.433
Sulphuric acid 0.044
Phosphoric acid 0.430
Chlorine traces
Organic matter 10.198
Water 2.684
100.116
"We observe that lime, potash, and sulphuric acid, are
much less abundant than in the soil from the Zuider Zee.
The quantity of ])hos2:)horic acid is about the same. The
amount of sulphuric acid is but one-twentieth that in the
Holland soil, and is accordingly enough for 15 good bar-
ley crops.
Lastly may be instanced the author's analysis of a soil
from the Upper Palatinate, which was characterized by
Dr. Sendtner, who collected it, as " the most sterile soil in
Bavaria."
Water .0.535
Organic matter 1.850
Silica ; 0.016
Oxide of iron and alumina 1.640
Lime 0.096
Magnesia trace
Carbonic acid trace
Phosphoric acid trace
Chlorine trace
Alkalies none
Quartz and insoluble silicates 95.863
100.000
Here we note the absence in weighable quantity of
magnesia and phos})horic acid, while potash could not even
REVIEW AND ( ONOIX'SIOX. 367
be detefted by the tests employed. This soil was mostly
naked and destitute of vegetation, and ils composition
shows tlie absence of any crop-producing 2>o\ver.
Relative Importance of the In^^redients of the Soil.
— From the general point of view of vegetable nutrition,
all those ingredients of tlie soil which act as food to the
plant, are equally important as they are equally indispens-
able. Absence of any one of the substances which water-
culture demonstrates must be presented to the roots of a
plant so that it shall grow, is fatal to the productiveness
of a soil.
Thus regardeil, oxide of iron is as important as phos-
phoric acid, and chlorine (for the crops which require it)
is no less valuable than potash. Practically, however,
the relative importance of the nutritive elements is meas-
ured by their comparative ahundance. Those which, like
oxide of irou, are rarely deficient, are for that reason less
])rominent among the factors of a crop. If any single
substance, be it phosphoric acid, or sulphuric acid, or pot-
ash, or magnesia, is lacking in a given soil at a certain
time, that substance is then and for that soil the most im-
portant ingredient. From the point of view of natural
abundance, we miy safely state that, on the whole, availa-
ble nitrogen and phosphoric acid are the most imj^ortant
ingredients of the soil, and potash, perhaps, takes the next
rank. These are, most coaimoidy, the substances whose
absence or deficiency impairs fertility, and are those
which, when added as fertilizers, j^roduce the most frequent
and remarkable increase of productiveness. In a multi-
tuile of special cases, however, sulphuric acid or lime, or
magnesia, assumes the chief prominence, Avhile in many in-
stances it is scarcely possible to make out a greater crop-
producing value for one of these substances over several
others. Again, those ingredients of the soil which could
be spared for all that they immediately contribute to the
368 HOW CROPS FEED.
nourishment of crops, are often the chief factors of fer<
tility on account of their indirect action, or because they
supply some necessary physical conditions. Thus humus
is not in any way essential to the growth of agricultural
plants, for plants have been raised to full perfection with-
out it ; yet in the soil it has immense value practically,
since among other reasons it stores and supplies water and
assimilable nitrogen. Again, gravel may not be in any
sense nutritious, yet because it acts as a reservoir of heat
and promotes drainage it may be one of the most import-
ant components of a soil.
What the Soil must Supply, — It is not sufficient that
the soil contain an adequate amount of the several ash-in-
gredients of the plant and of nitrogen, but it must be able
to give these over to the plant in due quantity and pro-
portion. The chemist could without diffi'culty compound
an artificial soil that should include every element of
plant-food in abundance, and yet be perfectly sterile. The
potash of feldspar, the pl)osphoric acid of massive apatite,
the nitrogen of peat, are nearly innutritions for crops on
account of their immobility — because they are locked up
in insoluble combinations.
Indications of Chemical Analysis. — The analyses by
Baumhauer of soils from the Ziuder Zee, p. 362, give in a
single statement their ultimate composition. We are in-
formed how much phosphoric aci<l, potash, magnesia, etc.,
exist in the soil, but get from the analysis no clue to the
amount of any of these substances which is at the dispo-
sition of the present crop. Experience demonstrates the
productiveness of the soil, and experien(>e also shows that
a soil of such composition is fertile ; but the analj^sis does
not necessarily give proof of the f ict. A nearer approach
to providing the data for estimat ing what a soil may sup-
ply to crops, is made by ascertaining what it will yield to
acids.
Chlorine,
Sulphuric acid,
Carbonic acid,
Potash and Soda,
Lime,
Magnesia,
Scsquioxide of iron,
REVIEW AND CONCLUSION. 369
Boussingault liua analyzed in this manner a soil from
Calvario, near Tacunga, in Equador, South America, which
possesses extraordinary fertility.
He found its composition to be as follows:
Nitrogen in organic combination, 0.343
Nitric acid, 0.975
Ammonia, O.OIQ.^-
Phosphoric acid, "j 0.460 *
0.395
0.023
traces
- Soluble in acids. ^ q„q
1.256
0.875
2.450
Sand, fragments of pumice, and clay insolul)le in acids, 83.195
Moisture, 3.150
Organic miitters (less nit rogen), undetermined substances,
and loss, 5.938
100.000
This analysis is much more complete in reference to ni.
trogen and its compounds, than those by Baumhauer al'
ready given (p, 36:2), and therefore has a peculiar value.
As regards the other ingredients, we observe that phos-
phoric acid is present in about the same proportion ; lime,
alkalies, sulphuric acid, and chlorine, are less abundant,
while magnesia is more abundant than in tlie soils from
Zuider Zee.
The method of analysis is a guarantee that the one per
cent of potash and soda does not exist in the insoluble
form of feldspar. Boussingault found fragments of pumice
by a microscopic examination. This rock is vesicsular feld-
spar, or lias at least a composition similar to feldspar, and
the same insolubility in acids.
The inert nitrogen of the humus is discriminated from
that which in the state of nitric acid is doubtless all assim-
ilable, and that which, as ammonia, is probably so for the
most part. The comparative solubility of the two per
cent of lime and magnesia is also indicated by the analysis,
10*
370 HOW CROPS PEED.
Boussingault does not state the kind or concentration,
or temperature of the acid employed to extract the soil
for the above analysis. These are by no means points of
indifference. Grouven {Iter db 3ter Salzm under Herichte)
has extracted the same earth with hydrochloric acid, con-
centrated and dilute, hot and cold, with greatly different
results as was to be anticipated. In 1862, a sample from
an experimental field at Salzmiinde was treated, after be-
ing heated to redness, with boiling concentrated acid for
3 hours. In 1867 a sample was taken from a field 1,000
paces distant from the former, one portion of it was treat-
ed with boiling dilute acid (1 of concentrated acid to 20
of water) for 3 hours. Another portion was digested for
three days with the same dilute acid, but without applica-
tion of heat. In each case the same substances were ex-
tracted, but the quantities taken up were less, as the acid
was weaker, or acted at a lower temperature. The follow-
ing statement shows the composition of each extract, cal-
culated on 100 parts of the soil.
EXTRACT OF SOIL OP SALZMtJNDE.
not
strong acid.
IM dilute acid.
Cold dilute acid.
Potash,
.635
.116
.029
Soda,
.127
.067
.020
Lime,
1.677
1.046
1.098
Magnesia,
.687
.539
.2.37
Oxide of iron and alumina
, 7.931
3.180
.650
Oxide of manganese,
.030
.086
.071
Sulpliui'ic acid,
.059
.039
.020
Phosphoric acid,
.059
.091
.057
Silica,
1.785
.234
.175
The most interesting fact brought out by the above fig-
ures, is that strong and weak acids do not act on all the
ingredients with the same relative power. Comparing the
quantities found in the extract by cold dilute acid with
those which the hot dilute acid took up, we find that the
latter dissolved 5 times as much of oxide of iron and
j^lumiua, 4 times as much potasli, 3 times as much soda,
REVIEW AND CONCLUSION. 371
twice the amount of magnesia, sulphuric acid, and phos-
phoric acid, and the same quantity of lime. These facts
show liow very far chemical analysis in its present state
is from being able to say definitely what any given soil
can supply to crops, although we owe nearly all our pre-
cise knowledge of vegetable nutrition directly or indi-
rectly to this art.
The solvent effect of water on the soil, and the direct
action of roots, have been already discussed (pp. 309 to
328). It is unquestionably the fact tliat acids, like pure
water in Ulbricht's experiments (p. 324), dissolve the
more the longer they are in contact with a soil, and it is
evident that the question : How much a pai'ticular soil is
able to give to crops ? is one for which we not only have
no chemical answer at the present, but one that for many
years, and, perhaps, always can be answered only by the
method of experience — by appealing to the crop and not
to the soil. Chemical analysis is competent to inform us very
accurately as to the ultimate composition of the soil, but as
regards its proximate composition or its cliemical consti-
tution, there remains a vast and difficult Unknown, which
will yield only to very long and laborious investigation.
Maintenance of a Supply of Plant-food. — By the recip-
rocal action of the atmosphei-e and the soil, the latter
keeps up its store of available nutritive matters. The
difficultly soluble silicates slowly yield alkalies, lime, and
magnesia, in soluble forms ; the sulphides are converted
into sulphates, and, generally, the minerals of the soil are
disintegrated and fluxed under the influence of the oxy-
gen, the water, the carbonic acid, and the nitric acid of
tlie air, (pp. 122-135). Again, the atmospheric nitrogen
is assimilated by the soil in tlie sliape of ammonia, ni-
trates, and the amide-like matters of humus, (pp. 254-265).
Tlie rate of disintegration as well as that of nitrifica-
tion depends in part upon the chemical and physical char-
acters of the soil, and partly upon temperature and mete*
372 UOW CROPS FEED.
orological conditions. In tte tropics, both ttese processes
go on more vigorously than in cold climates.
Every soil has a certain inherent capacity of production
in general, which is chiefly governed by its power of sup-
plying plant-food, and is designated its " natural strength."
The rocky hill ranges of the Housatonic yield once in
30 years a crop of wood, the value of which, for a given
locality and area, is nearly uniform from century to cen-
tury. Under cultivation, the same uniformity of crop is
seen when the conditions remain unchanged. Messrs.
Lawes and Gilbert, in their valuable experiments, have
obtained from " a soil of not more than average wheat-
producing quality," without the application of any ma-
nure, 20 successive crops of wheat, the first of Avhich was
15 bushels per acre, the last 17^ bushels, and the average
of all 161 bushels. {Jovr. Roy. Ag. Soc. of Enrj., XX Y,
490.) The same investigators also raised barley on the
same field for 16 years, each year applying the same quan-
tity and kinds of manui-e, and obtaining in the first 8
years (1852-59) an average of 44|^ bushels of grain and
28 cwt. of straw ; for the second 8 years an average of 51§
bushels of grain and 29 cwt. of straw ; and for the 16
years an average of 48j^ bushels of grain and 28^ cwt. of
straw. {Jour, of Bath and West ofEnr/.Ag.Soc, XYI,214.)
The wheat experiments show the natural capacity of
the Rothamstead soil for producing that cereal, and de-
monstrate that those matters which are annually removed
by a crop of 16^ bushels, are here restored to availability
by weathering and nitrification. The crop is thus a
measure of one or both of these processes.* It is probable
♦ In the experiments of Lawes and Gilbert it was found that phosphates, sul-
phates, and carbonates of lime, potash, magnesia, and soda, raised the produce
of wheat but 2 to 3 bushels per acre above the yield of the unmanured soil, while
sulphate and muriate of ammonia increased the crop 6 to 10 bushels. This re-
sult, obtained on three soils, viz., at Rothamstead in Herts, Ilolklmm in Nor-
folk, and Rodmersham in Kent, the experiments extending over periods of S. 3,
and 4 years, respectivelj;. shows tliat tliese soils were, for the wheat croj). rela-
tively deficient in assimilable nitroircn. The crop on tlie nnmanured soil was
therefore a measure of nitrification rather tlian of mineral disintegration.
REVIEW AND CONCLUSION.
^n
tliat this native power of producing wheat will last unim-
paired for years, or, perhaps, centuries, provided the depth
of the soil is sufficient. In time, however, the silicates
atid other compounds whose disintegration supplies alka-
lies, phosphates, etc., must become relatively less in quan-
tity compared with the quite inert quartz and alumina-
silicates which cannot in any way feed plants. Then the
crop will fall off, and ultimately, if sufficient time be al-
lowed, the soil will be reduced to sterility.
Other things being equal, this natural and durable pro-
ductive power is of course greatest in those soils whioh
contain and annually supply the largest proportions of
plant-food from their entire mass, those which to the great-
est extent originated from good soil-making materials.
Soils formed from nearly [)ure quartz, from mere chalk,
or from serpentine (silicate of magnesia), are among those
least capable of maintaining a supply of food to crops.
These poor soils are often indeed fairly productive for a
few years when first cleared from the forests or marshes;
but this temporary fertility is due to a natural manuring,
the accumulation of vegetable remains on the surface,
M'hich contains but enough nutriment for a few crops and
wastes rapidly under tillage.
Exhaustion of the Soil in the language of Practice has
a relative meaning, and signifies a reduction of producing
power below the point of remuneration. A soil is said to
be exhausted when the cost of cropping it is more than
the crops are worth. In this sense the idea is very indef-
inite since a soil may refuse to grow one crop and yet may
give good returns of another, and because a crop that re-
munerates in the vicinity of active demand for it, may be
worthless at a little distance, on account of difficulties of
transportation. The speedy and absolute exhaustion of a
soil once fertile, that has been so much discussed by spec-
ulative writers, is found in their writings only, and does
not exist in agriculture. A soil may be cropped below the
374 now CROPS peed.
point of remuneration, but the sterility thu5 induced is of
a kind that easily yields to rest or other meliorating agen-
cies, and is far from resembling in its permanence that
which depends upon original poverty of constitution.
Significance of the Absorptive Quality.— Disintegration
and nitrificntion would lead to a waste of the resources
of fertility, were it not for the conserving effect of those
physical absorptions and chemical combinations and re-
placements which have been described. The two least
abundant ash-ingredients, viz., potash and phosphoric acid,
if liberated by the weathering of the soil in the form of
phosphate of potash, Avould suffer speedy removal did not
the soil itself fix them both in combinations, which are at
once so soluble that, while tliey best serve as plant-food,
they cannot ordinarily accumulate in quantities destruct-
ive to vegetation, and so insoluble that the rain-fall cannot
wash them off into the ocean.
The salts that are abundant in springs, rivers, and seas,
are naturally enough those for which the soil has the least
retention, viz., nitrates, carbonates, sulphates, and hydro-
chlorates of lime and soda.
The constituents of these salts are either required by
vegetation in but small quantities as is the case with chlo-
rine and soda, or they are generally speaking, abundant
or abundantly formed in the soil, so that their removal
does not immediately threaten the loss of productiveness.
In fact, these more abundant matters aid in putting into
circulation the scarcer and less soluble ingredients of
crops, in accordance with the general law established by
the researches of Way, Eichhorn, and others, to the effect
that any base brought into the soil in form of a freely sol-
uble salt, enters somewhat into nearly insoluble combina-
tion and liberates a corresponding quantity of other bases.
" The great beneficent law regulating these absorptions
appears to admit of the following expression : those bodies
which are most rare and ^vecious to the (proving plant art
HEVIBW AN1> CONCLUSION. 375
hythe soil converted into, and retained In, a condition not
of absolute, bxt <>f relative insolubility, and are kept avail-
able to the plant by the continual circulation in the soil
of the more abundunt saline matters.
" Tlie soil (spt'uking in the widest sense) is then not only
tlie ultimate exhaustless source of mineral (fixed) food,
to vegetation, hut it is the storehouse and conservatory
of this food, protecting its own resources from waste and
from too rapid use, and converting the highly soluble
matters of animal exuviae as well as of artificial refuse
(manures) into permanent supplies."*
By absorption as well as by nitrification the soil acts
therefore to prepare the food of the plant, and to present
it in due kind and quantity.
* The author quotes here the concluding paragraphs of an article by him " On
Some points of Agricultural Science," from the A?nerican Journal of Science and
Arts, May. IRj-:). (p. 85). which have historic interest in being, so far as he is
aware, the earliest, broad and accurate generalization on record, of the facts of
soil-absorption.
NOTICE TO TEACHERS.
At the Author's request, Mr. Louis Stadtmuller, of New Haven,
Conn., will undertake to furnish collections of the minerals and rocks
which chiefly compose soils (see pp. 108-122), suitable for study and
illustration, as also the apparatus and materials needful for the chemieal
experiments described iu "How Crops Grow.^'
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