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Title: Principles and practice of agricultural analysis. Volume 1 (of 3),
Soils

Author: Harvey Washington Wiley

Release date: March 31, 2024 [eBook #73302]

Language: English

Original publication: Easton: Chemical Publishing Co., 1894

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*** START OF THE PROJECT GUTENBERG EBOOK PRINCIPLES
AND PRACTICE OF AGRICULTURAL ANALYSIS. VOLUME 1 (OF 3),
SOILS ***

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New original cover art included with this eBook is
granted to the public domain.

PRINCIPLES AND PRACTICE

—OF—

AGRICULTURAL ANALYSIS.

A MANUAL FOR THE ESTIMATION OF SOILS, FERTILIZERS, AND AGRICULTURAL

PRODUCTS.

FOR THE USE OF ANALYSTS, TEACHERS, AND STUDENTS OF AGRICULTURAL

CHEMISTRY.

VOLUME I.

SOILS.

BY HARVEY W. WILEY,
Chemist of the U. S. Department of Agriculture.

EASTON, PA.,
Chemical Publishing Co.,
1894.

COPYRIGHT, 1895,
By Harvey W. Wiley.

PREFACE TO VOLUME FIRST.

In this volume I have endeavored to place in the hands of teachers and
students of Agricultural Analysis, and of analysts generally, the principles
which underlie the science and art of the analysis of soils and the best
approved methods of conducting it.
In the prosecution of the work I have drawn freely on the results of
experience in all countries, but especially in the matter of the physical
examinations of soils, of this country. Science is not delimited by
geographic lines, but an author is not to be blamed in first considering
favorably the work of the country in which he lives. It is only when he can
see nothing of good outside of its own boundaries that he should be judged
culpable. It has been my wish to give full credit to those from whose work
the subject-matter of this volume has been largely taken. If, in any case,
there has been neglect in this matter, it has not been due to any desire on my
part to bear the honors which rightfully belong to another. With no wish to
discriminate, where so many favors have been extended, especial
acknowledgments should be made to Messrs. Hilgard, Osborne, Whitney,
and Merrill, for assistance in reading the manuscript of chapters relating to
the origin of soils, their physical properties, and mechanical analysis. With
the wish that this volume may prove of benefit to the workers for whom it
was written I offer it for their consideration.
H. W. Wiley.

Washington, D. C.,
Beginning of January, 1895.

TABLE OF CONTENTS OF VOLUME FIRST.

PART FIRST.

Introduction, pp. 1–27.—Definitions; Origin of soil; Chemical elements
in the soil; Atomic masses; Properties of the elements; Relative abundance
of the elements; Minerals occurring in rocks; Classification of minerals.
Rocks and Rock Decay, pp. 28–43.—Types of rocks; Microscopical
Structure of Rocks; Composition of rocks; Color of rocks; Kinds of rocks;
Eruptive rocks.
Origin of Soils, pp. 43–63.—Decay of rocks; Effect of latitude on decay;
Action of water; Action of vegetable life; Action of worms and bacteria;
Action of air; Classification of soils; Qualities and kinds of soils; Humus;
Soil and subsoil; Authorities cited in part first.

PART SECOND.

Taking Samples for Analysis, pp. 65–86.—General principles; General
directions for sampling; Method of Hilgard; Official French method;
Caldwell’s, Wahnschaffe’s, Peligot’s, and Whitney’s methods; Samples for
moisture; Samples for permeability; Samples for staple crops; Method of
the Royal Agricultural Society; Method of Grandeau; Method of Official
Agricultural Chemists; Method of Lawes; Instruments for taking samples;
Principles of success in sampling.
Treatment of Sample in the Laboratory, pp. 87–93.—Preliminary
examination; Treatment of loose soils; Treatment of compact soils;
Miscellaneous methods; Authorities cited in part second.

PART THIRD.

Physical Properties of Soils, pp. 95–101.—The soil as a mass; Color of
soils; Odoriferous matters in soils; Specific gravity; Apparent specific
gravity.
Relation of Soil to Heat, pp. 102–103.—Sources of soil heat; Specific
heat; Absorption of solar heat.
Determination of Specific Heat, pp. 104–110.—General principles;
Method of Pfaundler; Variation of specific heat.
Soil Thermometry, pp. 111–115.—General principles; Frear’s method of
stating results; Method of Whitney and Marvin.
Applications of Soil Thermometry, pp. 115–116.—Absorption of heat;
Conductivity of soils for heat.
Cohesion and Adhesion of Soils, pp. 116–117.—Behavior of soil after
wetting; Methods of determining cohesion and adhesion; Adhesion of soil
to wood and iron.
Absorption by Soils, pp. 117–130.—General principles; Summary of
data; Cause of absorption; Deductions of Warington, Way, and Armsby;
Selective absorption of potash; Influence of surface area; Effect of removal
of organic matters; Importance of soil absorption; Methods of determining
absorption; Statement of results; Preparation of salts for absorption.
Relations of Porosity to Soil Moisture, pp. 131–150.—Definition of
porosity; Influence of drainage; Capacity of soil for moisture;
Determination of porosity; Whitney’s method; Relation of fine soil to
moisture; Wolff’s and Wahnschaffe’s method; Petermann’s method;
Mayer’s method; Volumetric determination; Wollny’s method; Heinrich’s
method; Effect of pressure on water capacity; Coefficient of evaporation;
Determination of capillary attraction; Inverse capillarity; Determination of
coefficient of evaporation; Wolff’s method; Water given off in a water-free
atmosphere; Porosity of soil for gases; Determination of permeability in the
field.
Movement of Water Through Soils: Lysimetry, pp. 151–170.—Porosity in
relation to water movement; Methods of water movement; Capillary

movement of water; Causes of water movement; Surface tension of
fertilizers; Methods of estimating surface tension; Preparation of soil
extracts; Lysimetry; Relative rate of flow of water through soils;
Measurement of rate of percolation; Authorities cited in part third.

PART FOURTH.

MECHANICAL ANALYSIS.
The Flocculation of Soil Particles, pp. 171–185.—Relation of
flocculation to mechanical analysis; Effect of potential of surface particles;
Destruction of floccules; Suspension of clay in water; effect of chemical
action; Theory of Barus; Physical explanation of subsidence; Separation of
soil into particles of standard size; Mechanical separation; Sifting with
water.
Separation of Soil Particles by a Liquid, pp. 185–207.—Classification of
methods of silt analysis; Methods depending on subsidence of soil particles;
Methods of Kühn, Knop, Wolff, Moore, Bennigsen, and Gasparin; Method
of Osborne; Schloesing’s method.
Separation of Soil Particles by a Liquid in Motion, pp. 207–247.—
General principles; Nöbel’s Apparatus; Method of Dietrich; Method of
Masure; Method of Schöne; Mayer’s method; Osborne-Schöne method;
Statement of results; Berlin-Schöne method; Hilgard’s method; Colloidal
clay; Properties of pure clay; Separation of fine sediments; Weighing
sediments; Classification of results; Comparison of methods.
Miscellaneous Determinations, pp. 247–281.—Mechanical determination
of clay; Effect of boiling on clay; General conclusions; Distribution of soil
ingredients; Percentage of silt by classes; Interpretation of silt analysis;
Number of soil particles; Surface area of soil particles; Logarithmic
constants; Mineralogical examination of silt; Microscopical examination;
Petrographic microscope; Forms and dimensions of particles; Silt classes;
Crystal angles; Refractive index; Polarized light; Staining silt particles;
Cleavage of soil particles; Microchemical examination of silt particles;
Petrographic examination of silt particles; Separation of silt particles by
specific gravity; Separation with a magnet; Color and transparency; Value
of silt analyses; Authorities cited in part fourth.

PART FIFTH.

Estimation of Gases in Soils, pp. 282–300.—Carbon dioxid; Aqueous
vapor; Maximum hygroscopic coefficient; Absorption of aqueous vapors;
Oxygen and air; General method of determining absorption; Special
methods; Diffusion of carbon dioxid; General conclusions; Authorities cited
in part fifth.

PART SIXTH.

Chemical Analysis of Soils, pp. 301–342.—Preliminary considerations;
Order of examination; Determination of water in soils; General conclusions;
Estimation of organic matter in soils; Estimation of humus; Estimation of
carbonates in arable soils.
Digestion of Soils with Solvents, pp. 342–352.—Treatment with water;
With water saturated with carbon dioxid; With water containing ammonium
chlorid; With water containing acetic acid; Treatment with citric acid; With
hydrochloric acid; With nitric acid; With hydrofluoric and sulphuric acids.
Determination of the Dissolved Matter, pp. 352–367.—Methods of the
Official Agricultural Chemists; Hilgard’s methods; Belgian methods; Bulk
analysis.
Special Methods of Soil Analysis, pp. 367–428.—Determination of
potash; Potash soluble in concentrated acids; Soluble in dilute acids;
Estimation as platinochlorid; German Station methods; Raulin’s method;
Russian method; Italian method; Smith’s method; International method;
Dyer’s method; Estimation of total alkalies and alkaline earths; French
method for lime; Estimation of actual calcium carbonate; Estimation of
active calcareous matter; Russian method for lime; Assimilable lime;
German lime method; Estimation of magnesia; Estimation of manganese;
Estimation of iron; Estimation of phosphoric acid; Estimation of sulfuric
acid; Estimation of chlorin; Estimation of silica; Simultaneous estimation of
different elements; Estimation of kaolin in soils.
Estimation of Nitrogen in Soils, pp. 428–458.—Nature of nitrogenous
principles; Method of Official Agricultural Chemists; Hilgard’s method;
Moist combustion method of Müller; Soda-lime method; Treatment of soil
containing nitrates; Volumetric method with copper oxid; Estimation of
ammonia; Amid nitrogen; Volatile nitrogenous compounds; Late methods of
the Official Agricultural Chemists; Authorities cited in part sixth.

PART SEVENTH.

Oxidized Nitrogen in Soils, pp. 459–496.—Organic nitrogen; Nitric and
nitrous acids; Conditions of nitrification; Production of nitric and nitrous
acids; Production of ammonia; Order of oxidation; Occurrence of nitrifying
organisms; Nitrifying power of soils; Culture of nitrifying organisms;
Isolation of nitrous and nitric ferments; Classification of nitrifying
organisms; Sterilization; Thermostats for cultures; Conclusions.
Determination of Nitric and Nitrous Acids in Soils, pp. 496–531.—
Classification of methods; Extraction of nitric acid; The nitric oxid process;
Schloesing’s method; Warington’s method; Spiegel’s method; Schulze-
Tiemann method; DeKoninck’s method; Schmitt’s process; Merits of the
ferrous salt method; Mercury and sulfuric acid method; Lunge’s nitrometer;
Utility of the method; The indigo method.
Determination of Nitric Nitrogen by Reduction to Ammonia, pp. 531–
542.—Classification of methods; Method of the Official Agricultural
Chemists; German method; Devarda’s method; Stoklassa’s process;
Sievert’s variation; Variation of the sodium-amalgam process; Schmitt’s
method; Process of Ulsch; Reduction by the electric current; Copper-zinc
and aluminum-mercury couples.
Iodometric Estimation of Nitric Acid, pp. 543–548.—Method of
DeKoninck and Nihoul; Method of Gooch and Gruener.
Estimation of Nitric and Nitrous Acids by Colorimetric Comparison, pp.
548–570.—Delicacy of the process; Hooker’s carbazol method;
Phenylsulfuric acid method; Estimation of nitric in presence of nitrous acid;
Metaphenylenediamin method for nitrous acid. Sulfanilic acid test;
Naphthylamin process; Use of starch as indicator; Method of Chabrier;
Ferrous salt method; Potassium ferrocyanid method; Collecting samples of
rain water.
Determination of Free and Albuminoid Ammonia, pp. 570–575.—Nessler
process; Ilosvay’s reagent; Authorities cited in part seventh.

PART EIGHTH.

Special Examination of Waters, pp. 576–583.—Total solid matter;
Estimation of chlorin; Estimation of carbon dioxid; Boric acid.
Special Treatment of Muck Soils, pp. 583–591.—Sampling; Water
content; Organic carbon and hydrogen; Total volatile matter; Estimation of
sulfur; Estimation of phosphoric acid; Estimation of humus; Special study
of soluble matters in muck.
Unusual Constituents of Soil, pp. 580–593.—Estimation of copper;
Estimation of lead; Estimation of zinc; Estimation of boron; Authorities
cited in part eighth. Index, pp. 594–607.

CORRECTIONS.—Page 112, second line from bottom, read “Fig. 14”
instead of “13.”
Page 158, insert “and determining soluble matters therein” after “flow” in
paragraph 172, third line.
Page 468, paragraph 423, read “calcium carbonate about 200
milligrams,” instead of “calcium carbonate, or gypsum fifty milligrams.”
Page 557, read “red-yellow” instead of “blue” in seventh line from
bottom.

ILLUSTRATIONS TO VOLUME FIRST.

Page.
Plate, figures 1–6. To face 29
Figure 7. Microscopic structure of sandstone 36
„ 8. Microstructure of crystalline limestone 39
„ 9. Microstructure of Gneiss 40
Plate, figure 10. View on the broad branch of Rock Creek, Washington, D. C., to
48
face
Figure 11. 82
„ 12. 84
„ 13. Regnault’s apparatus for determining the specific heat of soils 105
„ 14. Soil thermometer 113
„ 15. Zalomanoff’s apparatus for determining absorption of salts by soils 126
„ 16. Müller’s apparatus to show absorption of salts by soils 127
Plate, figure 17. Capacity of the fine soil for holding moisture. Method of Wolff
136
modified by Wahnschaffe, to face
Figure 18. Fuelling’s apparatus 140
„ 19. Apparatus to show capillary attraction of soils for water 145
Plate, figure 20. Apparatus for determining coefficient of evaporation, to face 148
Figure 21. Method of Heinrich 150
„ 22. Method of Welitschowsky 162
„ 23. Ground plan and vertical section of lysimeters and vaults showing
166
position of the apparatus
Plate, figure 24. Deherain’s apparatus for collecting drainage water, to face 168
Figure 25. Knop’s silt cylinder 190
„ 26. Siphon cylinder for silt analysis 191
„ 27. Bennigsen’s silt flasks 195
„ 28. Nöbel’s elutriator 208
„ 29. Dietrich’s elutriator 209
„ 30. Masure’s silt apparatus 211
„ 31. Schöne’s elutriator 212
„ 32. Schöne’s elutriator outflow tube 213
„ 33. Schöne’s elutriator, arrangement of apparatus 214
„ 34. Schöne’s apparatus for silt analysis, modified by Mayer 221
„ 35. Hilgard’s churn elutriator 226
„ 36. Improved Schöne’s apparatus with relay 228
„ 37. 257
Plate, figure 38.
„ figures 39–44. To face
„ figures 45–50. 264
„ figures 51–56.

Figure 57. Machine for making mineral sections 267
„ 58. Thoulet’s separating apparatus 272
„ 59. Harada’s apparatus 275
„ 60. Brögger’s apparatus 276
„ 61. Apparatus of Wülfing 277
„ 62. Schloesing’s soil-tube for collecting gases 291
„ 63. Schloesing’s apparatus for collecting gases from soil 292
„ 64. Schloesing’s apparatus for determination of carbon dioxid 293
„ 65. Knorr’s apparatus for the determination of carbon dioxid 338
„ 66. Bernard’s calcimeter 339
„ 67. Smith’s muffle for decomposition of silicates 381
„ 68. Apparatus by Sachsse and Becker 401
Plate, figures 69 and 70. To face 480
Figure 71. Sterilizing oven 491
„ 72. Autoclave sterilizer 492
„ 73. Arnold’s sterilizer 493
„ 74. Lautenschläger’s thermostat 494
„ 75. Schloesing’s apparatus for nitric acid 501
„ 76. Warington’s apparatus for nitric acid 505
„ 77. Spiegel’s apparatus for nitric acid 509
„ 78. Schulze-Tiemann’s nitric acid apparatus 511
„ 79. DeKoninck’s apparatus 514
„ 80. End of delivery-tube 514
„ 81. Schmidt’s apparatus 516
„ 82. Lunge’s nitrometer 519
„ 83. Lunge’s improved apparatus 521
„ 84. Lunge’s analytic apparatus 523
„ 85. Stoklassa’s nitric acid apparatus 535
„ 86. Variation of the sodium amalgam process 537
„ 87. McGowan’s apparatus for the iodometric estimation of nitric acid 544
„ 88. Apparatus of Gooch and Gruener 547
„ 89. Method of Chabrier 566
„ 90. Schaeffer’s nitrous acid method 568
„ 91. Retort for distilling ammonia 572
„ 92. Gooch’s apparatus for boric acid 581
„ 93. Apparatus for determining sulfur 587

PART FIRST.

INTRODUCTION.

1. Definitions.—The term soil, in its broadest sense, is used to designate
that portion of the surface of the earth which has resulted from the
disintegration of rocks and the decay of plants and animals, and which is
suited, under proper conditions of moisture and temperature, to the growth
of plants. It consists, therefore, chiefly of mineral substances, together with
some products of organic life, and of certain living organisms whose
activity may influence vegetable growth either favorably or otherwise. The
soil also holds varying quantities of gaseous matter and of water, which are
important factors in its functions.
2. Origin Of Soil.—Agriculturally considered, the soil proper is the older
and more thoroughly disintegrated superficial layer of the earth, which has
been longest exposed to weathering and the influences of organic life. It is
usually from six to twelve inches, but occasionally several feet in depth.
The subsoil, which lies directly under this, is not as a rule so thoroughly
disintegrated, since it is protected in a measure by the overlying soil. It
usually contains less organic matter than the soil. There is a freer circulation
of air in the soil than in the subsoil, and the metallic elements usually exist
therein as higher oxids. There is usually a notable difference in color
between the soil and subsoil, and frequently a very sharp color line
separating the two.
Geologically considered, the soil is that portion of the earth’s crust which
has been more or less thoroughly disintegrated by weathering and other
forces from the original rock formations, or from the sedimentary rocks, or
from the unconsolidated sedimentary material. The soil has, therefore, the

same essential constitution as the general mass of the earth, except that this
débris has been subjected to the solvent action of water and the influence of
vegetable growth.
Preliminary to the proper understanding of the methods of the analysis of
soils, there should be some definite knowledge concerning the composition
of the earth’s crust, so that the analyst may understand more thoroughly the
origin and nature of the material he has to deal with, and thereby be better
equipped for his work.
3. The Chemical Elements Present in the Soil.—The chemical
elements present in the soil are naturally some or all of those which were
present in the original rocks. For analytical purposes relating to agriculture,
it is not necessary to take into account the rare elements which may occur in
the soil, but only those need be considered which are present in some
quantity and which enter as an important factor into plant growth. Of the
whole number of chemical elements less than twenty are of any importance
in soil analysis. These elements may be grouped into two classes, the non-
metals, and the metals as follows:

Non-metals. Metals.
Oxygen, Aluminum,
Silicon, Calcium,
Carbon, Magnesium,
Sulfur, Potassium,
Hydrogen, Sodium,
Chlorin, Iron,
Phosphorus, Manganese,
Nitrogen, Barium.
Fluorin,
Boron.

4. Atomic Masses.—For the purpose of facilitating the calculation of
results the latest revised table of atomic masses is given below. All the
known elements are included in this table for the convenience of analysts
who may have to study some of the rarer elements in the course of their
work.

This table represents the latest and most trustworthy results reduced to a uniform basis of
comparison with oxygen = 16 as starting point of the system. No decimal places representing large

uncertainties are used. When values vary, with equal probability on both sides, so far as our present
knowledge goes, as in the case of cadmium (111.8 and 112.2), the mean value is given in the table.

Table of Atomic Masses of the Elements.
Revised by F. W. Clarke, Chief Chemist of the United States Geological Survey, to January 1st,
1894.
Name. Symbol. Atomic mass.
Aluminum Al 27
Antimony Sb 120
Arsenic As 75
Barium Ba 137.43
Bismuth Bi 208.9
Boron B 11
Bromin Br 79.95
Cadmium Cd 112
Cesium Cs 132.9
Calcium Ca 40
Carbon C 12
Cerium Ce 140.2
Chlorin Cl 35.45
Chromium Cr 52.1
Cobalt Co 59
Columbium[A] Cb[Nb] 94
Copper Cu 63.6
Erbium Er 166.3
Fluorin F 19
Gadolinium Gd 156.1
Gallium Ga 69
Germanium Ge 72.3
Glucinum[B] Gl[Be] 9
Gold Au 197.3
Hydrogen H 1.008
Indium In 113.7
Iodin I 126.85
Iridium Ir 193.1
Iron Fe 56
Lanthanum La 138.2
Lead Pb 206.95
Lithium Li 7.02
Magnesium Mg 24.3
Manganese Mn 55
Mercury Hg 200
Molybdenum Mo 96
Neodymium Nd 140.5
Nickel Ni 58.7
Nitrogen N 14.03
Osmium Os 190.8
Oxygen[C] O 16

Palladium Pd 106.6
Phosphorus P 31
Platinum Pt 195
Potassium K 39.11
Praseodymium Pr 143.5
Rhodium Rh 103
Rubidium Rb 85.5
Ruthenium Ru 101.6
Samarium Sm 150
Scandium Sc 44
Selenium Se 79
Silicon Si 28.4
Silver Ag 107.92
Sodium Na 23.05
Strontium Sr 87.6
Sulfur S 32.06
Tantalum Ta 182.6
Tellurium Te 125
Terbium Tb 160.0
Thallium Tl 204.18
Thorium Th 232.6
Thulium Tu 170.7
Tin Sn 119
Titanium Ti 48
Tungsten W 184
Uranium U 239.6
Vanadium V 51.4
Ytterbium Yb 173
Yttrium Yt 89.1
Zinc Zn 65.3
Zirconium Zr 90.6

A. Has priority over niobium.

B. Has priority over beryllium.

C. Standard or basis of the system.

PROPERTIES OF THE ELEMENTS.

Following is a brief description of the most important elements occurring
in the earth’s crust in respect of their relations to agriculture.
5. Oxygen exists in the free gaseous state in the atmosphere of which it
constitutes about one-fifth by bulk, whilst in combination with other
elements it forms nearly half the weight of the solid earth, and eight-ninths
by weight of water. It enters into combination with all the other elements,
except fluorin, forming what are known as oxids, and with many of the
elements it unites in several proportions, forming oxids of different
composition. Combined with silicon, carbon, sulfur, and phosphorus, it
forms an essential part of the silicates, carbonates, sulfates, and phosphates,
most of which are very abundant and all of which are very widely
distributed in the earth’s crust. In this form it is exceedingly stable and is
rarely set free. With the exception of the oxids of silicon these oxids seldom
occur uncombined with the metals as constituents of rocks or soils. The
oxids of iron very commonly occur as such in rocks and soils, and play a
very important part in organic life. The several oxids of iron very frequently
determine the color of soils; as the iron in a soil is more or less oxidized, or
as it is exposed more or less to access of air, the color of the soil changes.
These oxids of iron also play an important part in the absorption capacities
of soils for moisture and other physical conditions of soils, and also in the
oxidation of organic matters in the soil. Many organic substances, and even
the roots of growing plants when deprived of free access of air, can readily
secure oxygen from the iron oxid, thus reducing the iron to a lower form of
oxidation, the oxygen being used for the oxidation of the organic matter or
for the needs of the growing plant; while the lower oxid of iron can more
readily take up oxygen of the air and again be converted into a higher oxid,
ready again to give up a part of its oxygen and thus serve as a carrier.
6. Silicon never occurs in the free state, but combined with oxygen it
forms silica, which constitutes more than one-half of the earth’s crust. The
oxid of silicon occurs in the very common form of quartz, and likewise, as
silicate of alumina, lime or magnesia. Silicon forms an essential part of
many minerals, such as the feldspars, amphiboles, pyroxenes, and the
micas, besides being an essential ingredient of many other minerals. Silica

is relatively very slightly affected by the ordinary forces concerned in the
decay of rocks, and even after the crystals of feldspars, micas, and other
common minerals occurring in rocks have been disintegrated the silica
remains as hard grains of sand, forming the bulk of most soils. By far the
larger part of silicon in soils is in the form of grains of quartz or silica. This
form, however, is probably chemically inert in regard to plant growth, but it
plays a very important part in the physical structure of soils and in the
physical relation of soils to plant growth.
7. Carbon as an elementary substance occurs as diamond and graphite
and in an impure form as anthracite and bituminous coals. In peats and
mucks carbon is the chief constituent. This substance is also contained in
the organic matters of the soil known as humus, and the relation of the
carbon to nitrogen often throws important light upon the amount and
character of the nitrogenous matters. In composition with oxygen it forms
the chief food of growing plants, the carbon of the carbon dioxid of the air
being elaborated into the tissue of the plants and the oxygen returned to the
atmosphere. The content of carbon dioxid in the air is from three to five
parts per thousand by volume. As carbonates this element helps to form
some of the most important ingredients of the earth’s crust, namely,
limestones, marbles, dolomites, etc., and in an organic form it is found in
the shells of the crustaceans. The calcareous matter of the soil, that is, the
carbonates of the earths therein found, are of the highest importance from
an agricultural point of view. The carbonates in the soil not only favor the
process of converting nitrogenous bodies into forms suitable for plant food,
but also exert a most potent influence on the physical state of the soil and its
capacity for holding water and permitting its flow to and from the rootlets
of the plant.
8. Sulfur occurs in nature in both the free and combined state. In the free
state it is found in volcanic regions such as Sicily, Iceland, and the western
United States. Its usual form of occurrence is in combination with the
metals to form sulfids, or with oxygen and a metal to form sulfates. Sulfur
and iron combine to form iron pyrites or iron disulfid (FeS₂), while sulfur,
oxygen, and calcium are found in gypsum, an important fertilizing
compound.
Sulfur plays an important part in the nourishment of plants, being found
in them both as sulfuric acid and in organic compounds. Methods for

estimating the sulfur in both forms will be found in another part of this
manual.
9. Hydrogen is a colorless, invisible gas, without taste or smell. It occurs
free in small proportions in certain volcanic gases, and in natural gas, but its
most common form is in combination with oxygen as water (H₂O), of
which it forms 11.13 per cent by weight. It also occurs in combination with
carbon to form the hydrocarbons, such as the mineral oils (petroleum, etc.)
and gases. Hydrogen is of no importance to agriculture in a free state, but
water is the most important of all plant foods.
10. Chlorin occurs free in nature only in limited amounts and in volcanic
vents. Its most common form is in combination with hydrogen, forming
hydrochloric acid, or with the metals to form chlorids. It combines with
sodium to form sodium chlorid or common salt (NaCl), which is the most
abundant mineral ingredient in sea water and which can usually be detected
in rain and ordinary terrestrial waters. In this form, also, it exists as
extensive beds of rock salt, which is mined for commercial purposes.
Chlorin is found uniformly in plants and must be regarded as an essential
constituent thereof. Common salt applied to a soil modifies its power of
attracting and holding water.
11. Phosphorus never occurs in nature in a free state but exists in
combination in greater or less quantities in all soils. Its combinations are
also found in large deposits of minerals known as phosphorite and apatite
and as so-called pebble deposit and phosphate rock. Phosphorus in some
sort of combination is one of the most essential elements in animal and
plant food. In animals its compounds form almost all of the mineral matter
of the bones, and in plants they are the chief constituents of the ash of
seeds.
The mineral deposits of phosphorus, as well as bones, are chiefly tri-
calcium phosphate, while the slag compound resulting from the basic
treatment of iron ores rich in phosphorus is a tetra-calcium salt.
The pebble deposits and some rock phosphates are supposed to be of
organic origin, derived from the remains of marine, terrestrial, and aerial
animals.
Cereal crops remove about twenty pounds of phosphoric acid per acre
from the soil annually and grass crops about twelve pounds. The total

phosphoric acid removed annually by the cereal and grass crops in the
United States is nearly four billion pounds.
Gautier[1] calls attention to the fact that the oldest phosphates are met
with in the igneous rocks such as basalt, trachyte, etc., and even in granite
and gneiss. It is from these inorganic sources, therefore, that all phosphatic
plant food must have been drawn. In the second order in age Gautier places
the phosphates of hydro-mineral origin. This class not only embraces the
crystalline apatites but also those phosphates of later formation formed
from hot mineral waters in the jurassic, cretaceous, and tertiary deposits.
These deposits are not directly suited to nourish plants.
The third group of phosphates in order of age and assimilability embraces
the true phosphorites containing generally some organic matter. They are all
of organic origin. In caves where animal remains are deposited there is an
accumulation of nitrates and phosphates.
Not only do the bones of animals furnish phosphates but they are also
formed in considerable quantities by the decomposition of substituted
glycerids such as lecithin. The ammonia produced by the nitrification of the
albuminoid bodies combines with the free phosphoric acid thus produced,
forming ammonium or diammonium phosphates. The presence of
ammonium phosphates in guanos was first noticed by Chevreul more than
half a century ago.
If such deposits overlay a pervious stratum of calcium carbonate, such as
chalk, and are subject to leaching a double decomposition takes place as the
lye percolates through the chalk. Acid calcium phosphate and ammonium
carbonate are produced. By further nitrification the latter becomes finally
converted into calcium nitrate. In like manner aluminum phosphates are
formed by the action of decomposing organic matter on clay.
Davidson,[2] explains the origin of the Florida phosphates by suggesting
that they arose chiefly through the influx of animals driven southward
during the glacial period. According to his supposition the waters of the
ocean, during the cenozoic period contained more phosphorus than at the
present time. The waters of the ocean over Florida were shallow and the
shell fish existing therein may have secreted phosphate as well as carbonate
of lime. This supposition is supported by an analysis of a shell of lingula
ovalis, quoted by Dana, in which there were 85.79 per cent of lime
phosphate. In these waters were also many fishes of all kinds and their

débris served to increase the amount of phosphatic material. As the land
emerged from the sea came the great glacial epoch driving all terrestrial
animals southward. There was, therefore, a great mammal horde in the
swamps and estuaries of Florida. The bones of these animals contributed
largely to the phosphatic deposits. In addition to this, the shallow sea
contained innumerable sharks, manatees, whales, and other inhabitants of
tropical waters, and the remains of these animals added to the phosphatic
store.
While these changes were taking place in the quaternary period, the
Florida Peninsula was gradually rising, and as soon as it reached a
considerable height the process of denudation by the action of water
commenced. Then there was a subsidence and the peninsula again passed
under the sea and was covered with successive layers of sand. The
limestones during this process had been leached by rain water containing an
excess of carbon dioxid. In this way the limestones were gradually
dissolved while the insoluble phosphate of lime was left in suspension.
During this time the bones of the animals before mentioned by their
decomposition added to the phosphate of lime present in the underlying
strata, while some were transformed into fossils of phosphate of lime just as
they are found to-day in vast quantities.
Wyatt,[3] explains the phosphate deposits somewhat differently.
According to him, during the miocene submergence there was deposited
upon the upper eocene limestones, more especially in the cracks and
fissures resulting from their drying up, a soft, finely disintegrated
calcareous sediment or mud. The estuaries formed during this period were
swarming with animal and vegetable life, and from this organic life the
phosphates were formed by decomposition and metamorphism due to the
gases and acids with which the waters were charged.
After the disappearance of the miocene sea there were great disturbances
of the strata. Then followed the pliocene and tertiary periods and quaternary
seas with their deposits and drifts of shells, sands, clays, marls, bowlders,
and other transported materials supervening in an era when there were great
fluctuations of cold and heat.
By reason of these disturbances the masses of the phosphate deposits
which had not been infiltrated in the limestones became broken up and
mingled with the other débris and were thus deposited in various mounds or

depressions. The general result of the forces which have been briefly
outlined, was the formation of bowlders, phosphatic débris, etc. Wyatt
therefore classifies the deposits as follows:
1. Original pockets or cavities in the limestone filled with hard and soft
rock phosphates and débris.
2. Mounds or beaches, rolled up on the elevated points, and chiefly
consisting of huge bowlders of phosphate rock.
3. Drift or disintegrated rock, covering immense areas, chiefly in Polk
and Hillsboro counties, and underlying Peace River and its tributaries.
Darton,[4] ascribes the phosphate beds of Florida to the transformation of
guano. According to this author two processes of decomposition have taken
place. One of these is the more or less complete replacement of the
carbonate by the phosphate of lime. The other is a general stalactitic coating
of phosphatic material. Darton further calls attention to the relation of the
distribution of the phosphate deposits as affecting the theory of their origin,
but does not find any peculiar significance in the restriction of these
deposits to the western ridge of the Florida peninsula.
As this region evidently constituted a long narrow peninsula during early
miocene time it is a reasonably tentative hypothesis that during this period
guanos were deposited from which was derived the material for the
phosphatization of the limestone either at the same time or soon after.
Darton closes his paper by saying that the phosphate deposits in Florida
will require careful, detailed geologic exploration before their relations and
history will be fully understood.
According to Dr. N. A. Pratt the rock or bowlder phosphate had its
immediate origin in animal life and to his view the phosphate bowlder is a
true fossil. He supposes the existence of some species in former times in
which the shell excreted was chiefly phosphate of lime. The fossil bowlder,
therefore, becomes the remains of a huge foraminifer which had identical
composition in its skeleton with true bone deposits or of organic matter.
Perhaps the most complete exposition of the theory of the recovery of
waste phosphates, with especial reference to their deposit in Florida, has
been given by Eldridge.[5] He calls attention to the universal presence of
phosphates in sea water and to the probability that in earlier times, as during
the miocene and eocene geologic periods, the waters of the ocean contained

a great deal more phosphate in solution than at the present time. He cites the
observations of Bischof, which show the solubility of different phosphates
in waters saturated with carbon dioxid. According to these observations
apatite is the most insoluble form of lime phosphate, while artificial basic
phosphate is the most soluble. Among the very soluble phosphates,
however, are the bones of animals, both fresh and old. Burnt bones,
however, are more soluble than bones still containing organic matter. Not
only are the organic phosphates extremely soluble in water saturated with
carbon dioxid, but also in water which contains common salt or chlorid of
ammonium. The presence of large quantities of common salt in sea water
would, therefore, tend to increase its power of absorbing lime phosphates of
organic origin. It is not at all incredible, therefore, to suppose that at some
remote period the waters of the ocean, as indicated by these theories, were
much more highly charged with phosphates in solution than at the present
time.
According to Eldridge, the formation of the hard-rock and soft
phosphates may be ascribed to three periods: First, that in which the
primary rock was formed; second, that of secondary deposition in the
cavities of the primary rock; third, that in which the deposits thus formed
were broken up and the resulting fragments and comminuted material were
redeposited as they now occur.
“The first of these stages began probably not later than the close of the
older miocene, and within the eocene area it may have begun much earlier.
Whether the primary phosphate resulted from a superficial and heavy
deposit of soluble guanos, covering the limestones, or from the
concentration of phosphate of lime already widely and uniformly
distributed throughout the mass of the original rock, or from both, is a
difficult question. In any event, the evidence indicates the effect of the
percolation of surface waters, highly charged with carbonic and earth acids,
and thus enabled to carry down into the mass of the limestone dissolved
phosphate of lime, to be redeposited under conditions favorable to its
separation. Such conditions might have been brought about by the simple
interchange of bases between the phosphate and carbonate of lime thus
brought together, or by the lowering of the solvent power of the waters
through loss of carbonic acid. The latter would happen whenever the acid
was required for the solution of additional carbonate of lime, or when,
through aeration, it should escape from the water. The zone of phosphate

deposition was evidently one of double concentration, resulting from the
removal of the soluble carbonate thus raising the percentage of the less
soluble phosphate, and from the acquirement of additional phosphate of
lime from the overlying portions of the deposits.”
“The thickness of the zone of phosphatization in the eocene area is
unknown, but it is doubtful if it was over twenty feet. In the miocene area
the depth has been proved from the phosphates in situ to have been between
six and twelve feet.”
The deposits of secondary origin, according to Eldridge, are due chiefly
to sedimentation, although some of them may have been due to
precipitation from water. This secondary deposition was kept up for a long
period, until stopped by some climatic or geologic change. The deposits of
phosphates thus formed in the Florida peninsula are remarkably free from
iron and aluminum, in comparison with many of the phosphates of the West
Indies.
The third period in the genesis of the hard rock deposits embraces the
time of formation of the original deposits and their transportation and
storage as they are found at the present time. The geologic time at which
this occurred is somewhat uncertain but it was probably during the last
submergence of the peninsula.
In all cases the peculiar formation of the Florida limestone must be
considered. This limestone is extremely porous and therefore easily
penetrated by the waters of percolation. A good illustration of this is seen on
the southwestern and southern edges of Lake Okeechobee. In following
down the drainage canal which has been cut into the southwest shore of the
lake the edge of the basin, which is composed of this porous material may
be seen. The appearance of the limestone would indicate that large portions
of it have already given way to the process of solution. The remaining
portions are extremely friable, easily crushed, and much of it can be
removed by the ordinary dredging machines. Such a limestone as this is
peculiarly suited to the accumulation of phosphatic materials, due to the
percolation of the water containing them. The solution of the limestone and
consequent deposit of the phosphate of lime is easily understood when the
character of this limestone is considered.
Shaler, as quoted by Eldridge in the work already referred to, refers to
this characteristic of the limestone and says that the best conditions for the

accumulation of valuable deposits of lime phosphate in residual débris
appear to occur where the phosphatic lime marls are of a rather soft
character; the separate beds having no such solidity as will resist the
percolation of water through innumerable incipient joints such as
commonly pervade stratified materials, even when they are of a very soft
nature.
Eldridge is also of the opinion that the remains of birds are not sufficient
to account for the whole of the phosphatic deposits in Florida. He ascribes
them to the joint action of the remains of birds, of land and marine animals
and to the deposition of the phosphatic materials in the waters in the
successive subsidences of the surface below the water line.
12. Nitrogen as a mineral constituent of soils, is found chiefly in the
form of nitrates, but, owing to their solubility, they can not accumulate in
soils exposed to heavy rain-falls. The gaseous nitrogen in the soil is also of
some importance, since it is in this material that the anaerobic organisms
which accumulate on the rootlets of some plants probably act in the process
of the fixation of atmospheric nitrogen in a form accessible to plants.
Nitrogen in the free state, it is believed, is not directly absorbed into the
tissues of plants. It is necessary that it be oxidized in some way to nitric
acid before it can be assimilated. The importance of nitrogen as a plant food
can not be too highly estimated. It is as necessary to plant growth and
development as water, phosphoric acid, lime, and potash, and far more
costly. While a large quantity of nitrogen exists in the air in an uncombined
state, it is, nevertheless, one of the least abundant of the elements of high
importance in plant nutrition.
The conservation and increase of the stores of available nitrogen in the
soil is one of the chief problems occupying the attention of agricultural
chemistry. Nitrogen, which is not immediately available for the growth of
plants, is conserved and restored by natural processes in various ways.
The waste nitrogen finds its way sooner or later to the sea, and is restored
therefrom in many forms. Sea-weeds of all kinds are rich in recovered
nitrogen. Many years ago Forchhammer[6] pointed out the agricultural value
of certain fucoids. Many other chemists have contributed important data in
regard to the composition of these bodies.
Jenkins[7] has shown from the analyses of several varieties of sea-weeds
that in the green state they are quite equal in fertilizing value to stall

manure, and are sold at the rate of five cents per bushel. These data are fully
corroborated by Goessmann.[8]
Wheeler and Hartwell[9] give the fullest and most systematic discussion
which has been published of the agricultural value of sea-weeds. Sea-weed
was used as a fertilizer as early as the fourth century, and its importance for
this purpose has been recognized more and more in modern days, especially
since chemical investigations have shown the great value of the food
materials contained therein.
To show the commercial importance of sea-weed, it is only necessary to
call attention to the fact that in 1885 its value as a fertilizer in the State of
Rhode Island was $65,044, while the value of all other commercial
fertilizers was $164,133. While sea-weed, in a sense, can only be
successfully applied to littoral agriculture, yet the extent of agricultural
lands bordering on the sea is so great as to render its commercial
importance of the highest degree of interest.
A large amount of nitrogen is also recovered from the sea in fishes. It is
shown by Atwater[10] that the edible part of fishes has an unusually high
percentage of protein. In round numbers, about seventy-five per cent of the
water free edible parts of fish are composed of albuminoids. Some kinds of
fish are taken chiefly for their oil and fertilizing value, as the menhaden.
Squanto,[11] an American Indian, first taught the early New England settlers
the manurial value of fish.
Immense quantities of waste nitrogen are further secured, both from sea
and land, by the various genera of birds. The well-known habit of birds in
congregating in rookeries during the night and at certain seasons of the year
tends to bring into a common receptacle the nitrogenous matters which they
have gathered and which are deposited in their excrement and in the decay
of their bodies. The feathers of birds are particularly rich in nitrogen, and
the nitrogenous content of the flesh of fowls is also high. The decay of
remains of birds, especially if it take place largely excluded from the
leaching of water, tends to accumulate vast deposits of nitrogenous matter.
If the conditions in such deposits be favorable to the processes of
nitrification, the whole of the nitrogen, or at least the larger part of it, which
has been collected in this débris, becomes finally converted into nitric acid
and is found combined with appropriate bases as deposits of nitrates. The
nitrates of the guano deposits and of the deposits in caves arise in this way.

If these deposits be subject to moderate leaching the nitrate may become
infiltered into the surrounding soil, making it very rich in this form of
nitrogen. The bottoms and surrounding soils of caves are often found highly
impregnated with nitrates.
While for our purpose, deposits of nitrates only are to be considered
which are of sufficient value to bear transportation, yet much interest
attaches to the formation of nitrates in the soil even when they are not of
commercial importance.
In many of the soils of tropical regions not subject to heavy rain-falls, the
accumulation of these nitrates is very great. Müntz and Marcano[12] have
investigated many of these soils to which attention was called first by
Humboldt and Boussingault. They state that these soils are incomparably
more rich in nitrates than the most fertile soils of Europe. The samples
which they examined were collected from different parts of Venezuela and
from the valleys of the Orinoco as well as on the shore of the Sea of
Antilles. The nitrated soils are very abundant in this region of South
America where they cover large surfaces. Their composition is variable, but
in all of them carbonate and phosphate of lime are met with and organic
nitrogenous material. The nitric acid is found always combined with lime.
In some of the soils as high as thirty per cent of nitrate of lime have been
found. Nitrification of organic material takes place very rapidly the year
round in this tropical region. These nitrated soils are everywhere abundant
around caves, as described by Humboldt, caves which serve as the refuge of
birds and bats. The nitrogenous matters, which come from the decay of the
remains of these animals, form true deposits of guano which is gradually
spread around, and which, in contact with the limestone and with access of
air, suffers complete nitrification with the fixation of the nitric acid by the
lime.
Large quantities of this guano are also due to the débris of insects,
fragments of elytra, scales of the wings of butterflies, etc., which are
brought together in those places by the millions of cubic meters. The
nitrification, which takes place in these deposits, has been found to extend
its products to a distance of several kilometers through the soil. In some
places the quantity of the nitrate of lime is so great in the soils that they are
converted into a plastic paste by this deliquescent salt.

The theory of Müntz and Marcano in regard to the nitrates of soils,
especially in the neighborhood of caves, is probably a correct one, but there
are many objections to accepting it to explain the great deposits of nitrate of
soda which occur in many parts of Chile. Another point, which must be
considered also, is this: That the processes of nitrification can not now be
considered as going on with the same vigor as formerly. Some moisture is
necessary to nitrification, inasmuch as the nitrifying ferment does not act in
perfectly dry soil, and in many localities in Chile where the nitrates are
found it is too dry to suppose that any active nitrification could now take
place.
The existence of these nitrate deposits has long been known.[13] The old
Indian laws originally prohibited the collection of the salt, but nevertheless
it was secretly collected and sold. Up to the year 1821, soda saltpeter was
not known in Europe except as a laboratory product. About this time the
naturalist, Mariano de Rivero, found on the Pacific coast, in the Province of
Tarapacá, immense new deposits of the salt. Later the salt was found in
equal abundance in the Territory of Antofogasta and further to the south in
the desert of Atacama, which forms the Department of Taltal.
At the present time the collection and export of saltpeter from Chile is a
business of great importance. The largest export which has ever taken place
in one year was in 1890, when the amount exported was 927,290,430
kilograms; of this quantity 642,506,985 kilograms were sent to England and
86,124,870 kilograms to the United States. Since that time the imports of
this salt into the United States have largely increased.
According to Pissis[14] these deposits are of very ancient origin. This
geologist is of the opinion that the nitrate deposits are the result of the
decomposition of feldspathic rocks; the bases thus produced gradually
becoming united with the nitric acid provided from the air.
According to the theory of Nöllner[15] the deposits are of more modern
origin and due to the decomposition of marine vegetation. Continuous
solution of soils, gives rise to the formation of great lakes of saturated
water, in which occurs the development of much marine vegetation. On the
evaporation of this water, due to geologic isolation, the decomposition of
nitrogenous organic matter causes generation of nitric acid, which, coming
in contact with the calcareous rocks, attacks them, forming nitrate of

calcium, which, in presence of sulfate of sodium, gives rise to a double
decomposition into nitrate of sodium and sulfate of calcium.
The fact that iodin is found in greater or less quantity in Chile saltpeter is
one of the chief supports of this hypothesis of marine origin, inasmuch as
iodin is always found in sea and not in terrestrial plants. Further than this, it
must be taken into consideration that these deposits of nitrate of soda
contain neither shells nor fossils, nor do they contain any phosphate of lime.
The theory, therefore, that they were due to animal origin is scarcely
tenable.
13. Boron occurs chiefly in volcanic regions, but is much more widely
distributed in the soil than formerly believed. It is a regular constituent of
the ash of many plants,[16] and is, therefore, thought to be a true plant food.
It is one of the least abundant of the elements, not occurring in sufficient
quantity to find a place in the table showing their relative abundance, which
is to follow. Boracic acid is used to some extent as a preservative.
14. Fluorin does not occur free in nature, but it exists chiefly in
combination with calcium, forming fluorspar, and traces of it are found in
sea water. It occurs in bone, teeth, blood, and the milk of mammals. It is the
only element that does not combine with oxygen, and it can be isolated only
with the greatest difficulty. Only very small traces of it are found ordinarily
and it is usually not considered in the chemical analysis of soils. Fluorin is
found, however, in considerable quantities in certain phosphate deposits.
15. Aluminum is, probably, next to oxygen and silicon, the most
abundant element of the earth’s crust, of which it is estimated to form about
one-twelfth. It has never been found, in nature, in the free state, but
commonly occurs in combination with silicon and oxygen, in which form it
is an abundant constituent of feldspar, mica, kaolin, clay, slate, and many
other rocks and minerals.
By the weathering of feldspar, mica, and other minerals containing
aluminum, kaolin or true clay is formed, which is of the greatest importance
in the constitution of the soil. The compounds of aluminum are not so
important as plant food as they are as the constituents of the soil, forming a
large part of its bulk, and modifying in the most profound degree its
physical properties. It is the custom of some authors to use the word clay to
designate the fine particles of soil which have in general the same relations
to moisture and tilth as the particles of weathered feldspar, etc. In a strict

chemical sense, however, the term clay is applied only to the hydrated
silicate of alumina formed as indicated above. The fertility of a soil is
largely dependent on the quantity of clay which it contains, its relations to
moisture and amenability to culture being chiefly conditioned by its clay
content. The determination of the percentage of clay in soils is an operation
of the highest utility in forming an opinion of the value of a soil on
analytical data alone.
16. Calcium is one of the commonest and most important elements of the
earth’s crust, of which it has been estimated to compose about one-
sixteenth. It does not occur free in nature, but its most common form is in
combination with carbon dioxid, forming the mineral calcite, marble, and
the very abundant limestone rocks. In this form it is slightly soluble in
water containing carbon dioxid, and hence lime has become a universal
component of all soils and is very generally found in natural waters, in
which it furnishes the chief ingredient necessary for the formation of the
shells and skeletons of the various tribes of mollusca and corals. In
combination with sulfuric acid calcium forms the rock gypsum. Lime is not
only a necessary plant food, but influences in a marked degree the physical
condition of the soil and the progress of nitrification. Many stiff clay soils
are rendered porous and pulverulent by an application of lime, and thus
made far more productive. On account of its great abundance and low price,
it has not commanded the degree of attention from farmers and agricultural
chemists which its merits deserve. It forms an essential ingredient of plants
and animals, in the latter being collected chiefly in the bones, while in
plants it is rather uniformly distributed throughout all the tissues.
17. Magnesium occurs chiefly in combination with carbon dioxid or
with lime and carbon dioxid in the mineral dolomite. It is intimately
associated with calcium and a trace of it is nearly always found where lime
occurs in any considerable quantity. The bitter taste of sea water and some
mineral waters is due to the presence of salts of magnesia. In combination
with silica it forms an essential part of such rocks as serpentine, soapstone,
and talc. Magnesia is not of much importance as a plant food nor as a
fertilizing material.
18. Potassium combined with silica is an important element in many
mineral silicates as, for instance, orthoclase. Granitic rocks usually contain
considerable quantities of potassium, and on their decomposition this

becomes available for plant food. In the form of chlorid, potassium is found
in small quantities in sea water, and as a nitrate it forms the valuable salt
known as niter or saltpeter. Potassium, as is the case with phosphorus, is
universally distributed in soils, and forms one of the great essential
elements of plant food. Under the form of kainite and other minerals large
quantities of potassium are used for fertilizing and for the manufacture of
pure salts for commercial and pharmaceutical purposes. The ordinary
potassium salts are very soluble and for this reason they can not accumulate
in large quantities in soils exposed to heavy rain-fall. In the form of
carbonate, potassium forms one of the chief ingredients of hard wood ashes,
and in this form of combination is especially valuable for fertilizing
purposes. Potash salts, being extremely soluble, are likely to be held longest
in solution. Some of them, are recovered in animal and vegetable life, but
the great mass of potash carried into the sea still remains unaccounted for.
The recovery of the waste of potash is chiefly secured by the isolation of
sea waters containing large quantities of this salt and their subsequent
evaporation. Such isolation of sea waters takes place by means of geologic
changes in the level of the land and sea. In the raising of an area above the
water level there is almost certain to be an enclosure, of greater or less
extent, of the sea water in the form of a lake. This enclosure may be
complete or only partial, the enclosed water area being still in
communication with the main body of the sea by means of small estuaries.
If this body of water be exposed to rapid evaporation, as was doubtless the
case in past geologic ages, there will be a continual influx of additional sea
water through these estuaries to take the place of that evaporated. The
waters may thus become more and more charged with saline constituents.
Finally a point is reached in the evaporation when the less soluble of the
saline constituents begin to be deposited. In this way the various formations
of mineral matter, produced by the drying up of enclosed waters, take place.
The most extensive potash deposits known are those in the neighborhood
of Stassfurt, in Germany. The following description probably represents the
method of formation of these deposits:[17]
“The Stassfurt salt and potash deposits had their origin, thousands of
years ago, in a sea or ocean, the waters of which gradually receded, leaving
near the coast, lakes which still retained communication with the great
ocean by means of small channels. In that part of Europe the climate was
then tropical, and the waters of these lakes rapidly evaporated but were

constantly replenished through these small channels connecting them with
the main body. Decade after decade this continued, until by evaporation and
crystallization, the various salts present in the sea water were deposited in
solid form. The less soluble material, such as sulfate of lime or ‘anhydrite,’
solidified first and formed the lowest stratum. Then came common rock salt
with a slowly thickening layer which ultimately reached 3000 feet, and is
estimated to have been 13,000 years in formation. This rock salt deposit is
interspersed with lamellar deposits of ‘anhydrite,’ which gradually diminish
towards the top and are finally replaced by the mineral ‘polyhalite,’ which
is composed of sulfate of lime, sulfate of potash, and sulfate of magnesia.
The situation in which this polyhalite predominates is called the ‘polyhalite
region’ and after it comes the ‘kieserite region,’ in which, between the rock
salt strata, kieserite (sulfate of magnesia) is imbedded. Above the kieserite
lies the ‘potash region,’ consisting mainly of deposits of carnallite, a
mineral compound of muriate of potash and chlorid of magnesia. The
carnallite deposit is from 50 to 130 feet thick and yields the most important
of the crude potash salts and that from which are manufactured most of the
concentrated articles, including muriate of potash.”
“Overlying this region is a layer of impervious clay which acts as a
water-tight roof to protect and preserve the very soluble potash and
magnesia salts, which, had it not been for the very protection of this
overlying stratum, would have been long ages ago washed away and lost by
the action of the water percolating from above. Above this clay roof is a
stratum, of varying thickness of anhydrite, and still above this a second salt
deposit, probably formed under more recent climatic and atmospheric
influences or possibly by chemical changes in dissolving and subsequent
precipitation. This salt deposit contains ninety-eight per cent (often more)
of pure salt, a degree of purity rarely elsewhere found. Finally, above this
are strata of gypsum, tenacious clay, sand, and limestone, which crop out at
the surface.”
“The perpendicular distance from the lowest to the upper surface of the
Stassfurt salt deposits is about 5000 feet (a little less than a mile), while the
horizontal extent of the bed is from the Harz Mountains to the Elbe River in
one direction, and from the city of Madgeburg to the town of Bernburg in
the other.”

According to Fuchs and DeLauny[18] the saline formation near Stassfurt is
situated at the bottom of a vast triassic deposit surrounding Madgeburg. The
quantity of sea water which was evaporated to produce saline deposits of
more than 500 meters in thickness must have been enormous and the rate of
evaporation great. It appears that a temperature of 100° would have been
quite necessary, acting for a long time, to produce this result.
These authors therefore admit that all the theories so far advanced to
explain the magnitude of these deposits are attended with certain
difficulties. What, for instance, could have caused a temperature of 100°?
The most reasonable source of this high temperature must be sought for in
the violent chemical action produced by the double decompositions of such
vast quantities of salts of different kinds. There may also have been at the
bottom of this basin some subterranean heat such as is found in certain
localities where boric acid is deposited.
Whatever be the explanation of the source of the heat it will be admitted
that at the end of the permian period there was thrown up to the northeast of
the present saline deposits a ridge extending from Helgoland to Westphalia.
This dam established throughout the whole of North Germany saline
lagoons in which evaporation was at once established, and these lagoons
were constantly fed from the sea.
There was then deposited by evaporation, first of all a layer of gypsum
and afterwards rock salt, covering with few exceptions the whole of the area
of North Germany.
But around Stassfurt there occurred at this time geologic displacements,
the saline basin was permanently closed and then by continued evaporation
the more deliquescent salts, such as polyhalite, kieserite, and carnallite,
were deposited.
These theories account with sufficient ease for the deposition of the
saline masses, but do not explain why in those days the sea water was so
rich in potash and why potash is not found in other localities where vast
quantities of gypsum and common salt have been deposited. It may be that
the rocks composing the shores of these lagoons were exceptionally rich in
potash and that this salt was, therefore, in a certain degree, a local
contribution to the products of concentration.
19. Sodium is never found free in nature, but its most common form is in
combination with chlorin as common salt, an important ingredient of sea

water. Combined with silica sodium is an important element in many
silicates. Sodium, although closely related to potassium chemically, cannot
in any case be substituted therefor in plant nutrition. In combination with
nitrogen it forms soda or Chile saltpeter which is a valuable fertilizer on
account of its content of nitric acid.
20. Iron is the most abundant of the heavy metals, and occurs in nature
both free and combined with other elements. In the free state it is found
only to a limited extent in basaltic rocks and meteorites, but in combination
with oxygen it is one of the most widely diffused of metals, and forms the
coloring matter of a large number of rocks and minerals. In this form, too, it
exists as the valuable ores of iron known as magnetite and hematite. In
combination with sulfur it forms the mineral pyrite, FeS₂. The yellow and
red colors of soils are due chiefly to iron oxids. It is an important plant
food, although not taken up in any great quantity by the tissues of plants.
21. Manganese, next to iron, is the most abundant of the heavy metals. It
occurs in nature only in combination with oxygen, in which form it is
associated in minute quantities with iron in igneous rocks or in the forms
known mineralogically as pyrolusite, psilomelane and wad. As the peroxid
of manganese it occurs in concretionary forms scattered abundantly over
the bottom of the deep sea. It is found in the ash of some plants but is not
believed to be an essential to plant growth.
22. Barium occurs in nature combined with sulfuric acid, forming the
mineral barite, or heavy spar, or with carbon dioxid forming the mineral
witherite. It is of small importance from an agricultural standpoint.
23. Relative Abundance of the More Important Chemical Elements.
—It will be of interest to the agricultural analyst to know as nearly as
possible the relative abundance of the more important chemical elements.
This subject has been carefully studied by Prof. F. W. Clarke in a paper read
before the Philosophical Society of Washington.[19] The materials
considered in these calculations are the atmosphere, the water, and the solid
crust of the earth to the depth of ten miles below the sea level. Of these
materials the relative quantities of the three constituents named are as
follows:

Per cent.
Atmosphere 0.03
Water 7.08
Solid crust of the earth to the depth of ten miles 92.89

According to these calculations the relative abundance of the important
elements composing the atmosphere, the water of the ocean and the solid
crust of the earth to the depth given is as follows:

Solid crust, ninety-three per Ocean, seven per Mean, including
cent. cent. air.
Oxygen 47.29 per cent. 85.79 per cent. 49.98 per cent.
Silicon 27.21 „„ „„ 25.30 „„
Aluminum 7.81 „„ „„ 7.26 „„
Iron 5.46 „„ „„ 5.08 „„
Calcium 3.77 „„ 0.05 „„ 3.51 „„
Magnesium 2.68 „„ 0.14 „„ 2.50 „„
Sodium 2.36 „„ 1.14 „„ 2.28 „„
Potassium 2.40 „„ 0.04 „„ 2.23 „„
Hydrogen 0.21 „„ 10.67 „„ 0.94 „„
Titanium 0.33 „„ „„ 0.30 „„
Carbon 0.22 „„ 0.002 „„ 0.21 „„
Chlorin 0.01 „„ 2.07 } „„
0.15 „„
Bromin „„ 0.008} „„
Phosphorus 0.10 „„ „„ 0.09 „„
Manganese 0.08 „„ „„ 0.07 „„
Sulfur 0.03+ „„ 0.09 „„ 0.04+ „„
Barium 0.03 „„ „„ 0.03 „„
Nitrogen „„ „„ 0.02 „„
Chromium 0.01 „„ „„ 0.01 „„

100.00 „„ 100.000 „„ 100.00 „„

24. Fluorin is not mentioned in this table but it is stated that its probable
percentage is 0.02 to 0.03 making it thus slightly more abundant than
nitrogen.
One of the chief points of interest in connection with this table is that the
nitrogen which is regarded by most persons as one of the most abundant of

the elements is almost the least abundant of those mentioned.

THE MINERALS OCCURRING IN ROCKS.

25. The Soil, as before stated, being comprised almost exclusively of
decayed rocks, its characteristics would naturally be determined by the
character of the minerals contained in the rocks.
A rock may be composed of a single mineral or an aggregation of several
minerals.
According to the authority of the National Museum[20] it may occur, either
in the form of stratified beds, eruptive masses, sheets or dikes, or as veins
and other chemical deposits of comparatively little importance as regards
size and extent. The mineral composition of rocks is greatly simplified by
the wide range of conditions under which the commonest minerals can be
formed. Thus quartz, feldspar, mica, the minerals of the hornblende, or
pyroxene group, can be formed from a mass cooling from a state of fusion;
they may be crystallized from solution, or be formed from volatilized
products. They are therefore the commonest of minerals and are rarely
excluded from rocks of any class, since there is no process of rock
formation which determines their absence.
Most of the common minerals, like the feldspars, micas, hornblendes,
pyroxenes, and the alkaline carbonates possess the capacity of adapting
themselves to a very considerable range of compositions. In the feldspars,
for example, lime, soda, or potash may replace one another almost
indefinitely, and it is now commonly assumed that true species do not exist,
but all are but isomorphous admixtures passing into one another by all
gradations, and the names albite, oligoclase, anorthite, etc., are to be used
only as indicating convenient stopping and starting points in the series.
Hornblende or pyroxene, further, may be pure silicate of lime and
magnesia, or iron and manganese may partially replace these substances.
Lime carbonate may be pure, or magnesia may replace the lime in any
proportion.
These illustrations are sufficient to show the reason for the great
simplicity of rock masses as regards their chief mineral constituents.
Whatever may be the conditions of the origin of a rock mass, the
probabilities are that it will be formed essentially of one or more of a half a

dozen minerals in some of their varieties.
But however great the adaptability of these few minerals may be they are,
nevertheless, subject to very definite laws of chemical equivalence. There
are elements which they cannot take into their composition, and there are
circumstances which retard their formation while other minerals may be
crystallizing. In a mass of rock of more or less accidental composition
formed under these widely varying conditions it may, therefore, be expected
that other minerals will form, in considerable numbers, but minute
quantities. It is customary to speak of those minerals which form the chief
ingredients of any rock, and which may be regarded as characteristic of any
particular variety, as the essential constituents, while those which occur in
but small quantities, and whose presence or absence does not fundamentally
affect its character, are called accessory constituents. The accessory mineral
which predominates, and which is, as a rule, present in such quantities as to
be recognizable by the unaided eye, is the characterizing accessory. Thus a
biotite granite is a stone composed of the essential minerals quartz and
potash feldspar, but in which the accessory mineral biotite occurs in such
quantities as to give a definite character to the rock.
26. Classification Of Minerals.—The minerals of rocks may also be
conveniently divided into two groups, according as they are products of the
first consolidation of the mass or of subsequent changes. This is the system
here adopted. We thus have:
(1) The original or primary constituents, those which formed upon its
first consolidation. All the essential constituents are original, but on the
other hand all the original constituents are not essential. Thus, in granite,
quartz and orthoclase are both original and essential, while beryl and zircon
or apatite, though original, are not essential.
(2) The secondary constituents are those which result from changes in a
rock subsequent to its first consolidation, changes which are due in great
part to the chemical action of percolating water. Such are the calcite,
chalcedony, quartz, and zeolite deposits which form in the druses and
amygdaloidal cavities, of traps and other rocks.
Below is given a list of the more common, original and secondary
minerals occurring in rocks. It will be observed that the same mineral may,
in certain cases, occur in both original and secondary forms. The tables
following were prepared by Dr. George P. Merrill.

Original Minerals.

1. Quartz, SiO₂.
2. The Feldspars:

2a. Orthoclase. Anhydrous silicate of alumina with varying amounts of lime,
2b. Microcline. potash, or soda and rarely barium.
2c. Albite.
2d. Oligoclase.
2e. Andesite.
2f. Labradorite.
2g. Bytownite.
2h. Anorthite.

3. The Amphiboles:

3a. Hornblende. Anhydrous silicates of lime and magnesia with iron and
3b. Tremolite. alumina in the dark varieties.
3c. Actinolite.
3d. Arfvedsonite.
3e. Glaucophane.
3f. Smaragdite.

4. The Monoclinic Pyroxenes:

4a. Malacolite. Anhydrous silicates of magnesia and lime with alumina and
4b. Diallage. iron in the dark varieties.
4c. Augite.
4d. Acmite.
4c. Aegerite.

5. The Rhombic Pyroxenes:

5a. Enstatite (bronzite). Silicates of magnesia and iron.
5b. Hypersthene.

6. The Micas:

6a. Muscovite. Anhydrous silicates of alumina with potash, soda, and iron.
6b. Biotite.
6c. Phlogopite.

7. Calcite,
8. Dolomite.
9. Gypsum.
10. Olivine.
11. Beryl.
12. Tourmaline.
13. Garnet, variable common form.
14. Vesuvianite.
15. Epidote.
16. Zoisite.
17. Allanite.
18. Andalusite.
19. Staurolite.
20. Fibrolite.
21. Cyanite.
22. Scapolite.
23. Apatite.
24. Elaeolite and Nepheline.
25. Leucite.
26. Cancrinite.
27. The Sodalite Group:

27a. Sodalite.

27b. Haüyn (noseau).
28. Zircon.
29. Chondrodite.
30. Cordierite.
31. Topaz.
32. Corundum.
33. Titanite (sphene).
34. Rutile.
35. Menaccanite.
36. Magnetite.
37. Hematite.
38. Chromite.
39. The Spinels:

39a. Pleonast.
39b. Picotite.

40. Pyrolusite.
41. Halite (common salt).
42. Fluorite.
43. The Elements:

43a. Graphite.
43b. Carbon.
43c. Iron.
43d. Copper.

44. The Metallic Sulfids:

44a. Galena.
44b. Sphalerite.
44c. Pyrrhotite.
44d. Marcasite.
44e. Pyrite.
44f. Chalcopyrite.
44g. Arsenopyrite.
Secondary Minerals.

1. Quartz:

1a. Chalcedony.
1b. Opal.
1c. Tridymite.

2. Albite.
3. The Amphibole Group:

3a. Hornblende.
3b. Tremolite.
3c. Actinolite.
3d. Uralite.

4. Muscovite (sericite).
5. The Chlorites:

5a. Jefferisite.
5b. Ripidolite.
5c. Penninite.
5d. Prochlorite.

6. Calcite (and aragonite).
7. Wollastonite.
8. Scapolite.
9. Garnet.
10. Epidote.
11. Zoisite.
12. Serpentine.
13. Talc.
14. Kaolin.
15. The Zeolites:

15a. Pectolite.
15b. Laumontite.
15c. Prehnite.
15d. Thomsonite.
15e. Natrolite.
15f. Analcite.
15g. Datolite.
15h. Chabazite.
15i. Stilbite,
15k. Heulandite.
15l. Harmotome.

16. Magnetite.
17. Hematite.
18. Limonite.
19. Siderite.

20. Pyrite.
21. Pyrrhotite.

ROCKS AND ROCK DECAY.

27. Types Of Rocks.—Rocks may be divided in reference to their
structure into four types: First, crystalline; second, vitreous; third, colloidal;
fourth, fragmental.
Of these classes there may be selected, as types of the first order, granite
and crystalline limestone.
The second class is typically represented by obsidian. Rocks of this kind
are confined to a volcanic origin.
The third class of rocks is completely amorphous in its structure and is
less common than the others. It is found only in rocks of chemical origin.
Types of this class are the siliceous sinters, opals, flint nodules, and many
serpentines.
Of the fourth class of rocks, sandstone is typical, being comprised wholly
of fragments of rocks pre-existing. The particles may be held together either
by cohesion or by a cement composed of silica, iron oxids, carbonate of
lime or clayey matter.
28. The Microscopical Structure of Rocks.—A great deal more light is
thrown upon the nature of rock materials by microscopical study than by
their study in bulk. The requisites for a microscopical study of rock are that
the material should be cut into extremely thin laminae with parallel sides
and polished so as to transmit the light freely. The study of the crystalline
structure of the material is then conducted by means of a microscope
furnished with polarizing and analyzing appliances. The light before
passing through the mineral film is polarized by a Nicol prism. After
passing through the film it is analyzed by a second Nicol prism. In this way
the crystalline structure of the rock as affecting polarized light is distinctly
brought out. The thickness of the films examined should be from ¹⁄₅₀₀ to ¹⁄₆₀₀
of an inch.

Fig. 1. Microstructure of granite.
Fig. 2. Microstructure of micropegmatite.
Fig. 3. Microstructure of quartz porphyry.
Fig. 4. Microstructure of porphyritic obsidian.
Fig. 5. Microstructure of trachyte.
Fig. 6. Microstructure of serpentine.

The method of rock study by thin microscopic sections is one of
comparatively recent origin. It is scarcely more than a dozen years since the
process was fairly adopted by mineralogists. The value of the method is
based upon the fact that every crystalline mineral has certain definite optical
properties. Therefore, when a crystalline mineral is distorted or misshapen
so as to be incapable of identification by the ordinary method, it can be at
once identified by its optical examination in the manner just described. In
this way not only can one mineral be distinguished from another, but the
crystalline system to which it belongs can be accurately pointed out. The
value of the method is well summed up by Merrill,[21] who says that it is not
merely an aid in determining the mineralogical composition of a rock, but
also, which is often much more important, its structure and the various
changes which have taken place in it since its first consolidation. Rocks are
not the definite and unchangeable mineral compounds they were once
considered, but are rather ever varying aggregates of minerals which even
in themselves undergo structural and chemical changes almost without
number.
Another valuable result of such a study is illustrated by the discovery that
the structural features of a rock are not dependent upon its chemical
composition or geologic age, but upon the conditions under which it cooled
from the molten magma. Portions of the same rock may vary all the way
from a wholly crystalline to a pure vitreous form.
Some typical microstructures of crystalline rocks are shown in the
accompanying figures 1–6.[22]
Although this method of study has thus far been confined mainly to
crystalline rocks, its efficiency is by no means limited to them. The
fragmental rocks and their decomposed débris to which the name soil is
given are equally worthy of study by this method. Indeed, the full value of a
chemical analysis of any rock or soil can not be ascertained unless such an
analysis is accompanied by a microscopic examination. It is desirable to
know not merely what there is in any soil, but in what form these

compounds exist. To this latter question the chemical analysis as ordinarily
made will give no clew. In Germany a beginning has been made in this line
of work, and American scientists are beginning to realize its importance. An
outline of this method of analysis will be given in the proper place.
29. Specific Gravity.—Much information in regard to the properties of a
rock, or mineral constituent thereof, may be derived from its specific
gravity.
The internal structure of a rock may have much to do with its apparent
specific gravity. As an instance of this, it may be stated that an obsidian
pumice will float upon water, buoyed up by the air contained in its vesicles,
while a compact obsidian of the same composition will sink immediately. A
careful discrimination must, therefore, be made between apparent and true
specific gravity. In general it may be said that crystalline rocks have a
higher specific gravity than those of a vitreous nature. The specific gravity
is, therefore, largely dependent upon chemical and crystallographic
properties; for instance, among siliceous rocks those which contain the
largest amount of silica are the lightest, while those with a comparatively
small amount, but rich in iron, lime, and magnesia, are heaviest.
30. Chemical Composition of Rocks.—Rocks are often classified with
respect to the chief mineral constituent which they contain. Rocks which
are composed largely of lime are termed calcareous; of silica, siliceous; of
iron, ferruginous; and of clay, argillaceous. In respect of eruptive rocks, it is
customary to speak of those which show above sixty per cent of silica as
acidic, while those containing less than fifty per cent of silica and a
correspondingly larger amount of iron, lime, and magnesia, are spoken of as
basic. Illustrations of the classification of rocks on the above principles are
given below.[23]

Stratified Rocks.
Kind. Specific Gravity. Composition.
Calcareous:
Compact limestone
2.6 to 2.8 Carbonate of lime.
Crystalline limestone

Compact dolomite
2.8 to 2.95 Carbonate of lime and magnesia.
Crystalline dolomite

Siliceous:
Gneiss 2.6 to 2.7 Same as granite.
Siliceous sandstone 2.6 Mainly silica.
Schist 2.6 to 2.8 60 to 80 per cent silica.

Argillaceous:
Clay slate (argillite) 2.5 Mainly silicate of alumina.

Eruptive Rocks.
Specific Gravity. Per cent silica.
Acidic Group:
Granite 2.58 to 2.73 77.65 to 62.90
Liparite 2.53 to 2.70 76.06 to 67.61
Obsidian 2.26 to 2.41 82.80 to 71.19
Obsidian pumice Floats on water. 82.80 to 71.19

Intermediate Group:
Syenite 2.73 to 2.86 72.20 to 54.65
Trachyte 2.70 to 2.80 64.00 to 60.00
Hyalotrachyte 2.4 to 2.5 64.00 to 60.00
Andesite 2.54 to 2.79 66.75 to 54.73

Basic Group:
Diabase 2.66 to 2.88 50.00 to 48.00
Basalt 2.90 to 3.10 50.59 to 40.74
Peridotite 3.22 to 3.29 42.65 to 33.73
Peridotite (iron rich) 3.86 23.00
Peridotite (meteorite) 3.51 37.70
31. Color Of Rocks.—The color of rocks is determined chiefly by the
oxids of metals which they contain and the degree of oxidation of the
mineral in each particular case. There are, however, many colors of rocks
which seem to depend not upon any particular mineral ingredient which
they contain, but upon some particular crystalline structure or physical
condition.

The chief coloring matters in minerals are those which form colored
bases such as iron, manganese, chromium, etc. The yellow, brown, and red
colors, common to fragmental rocks, are due almost wholly to free oxids of
iron. The gray, green, dull brown, and even black colors of crystalline rocks
are due to the presence of free iron oxids or to the prevalence of silicate
mineral rich in iron, as augite, hornblende, or black mica. Rarely copper
and other metallic oxids than those of iron are present in sufficient
abundance to impart their characteristic hues. As a rule, a white or light-
gray color denotes an absence of an appreciable amount of iron in any of its
forms. The bluish and black colors of many rocks, particularly the
limestones and slates, are due to the presence of carbonaceous matter.
In still other cases, and particularly the feldspar-bearing rocks, the color
may be due in part to the physical condition of the feldspar.
Inasmuch as the color of rocks is due so largely to metallic oxids, it is
easy to see that they may undergo changes when exposed to weathering, or
the degree of oxidation may change, and either, together with changes in the
physical structure of the rock, may cause a distinct change in color. Luster
is often considered in connection with color, and is due almost exclusively
to physical conditions.
32. Kinds of Rocks.—The rocks which form any essential part of the
earth’s crust are grouped under four main heads, the distinction being based
upon their origin and structure.[24] Each of the main divisions may be
subdivided into groups or families, the distinction being based mainly upon
chemical composition, structure, and mode of occurrence. The four chief
families are:
First, aqueous rocks, formed mainly through the agency of water as
chemical precipitates or as sedimentary beds.
Second, aeolian rocks formed from wind-drifted materials.
Third, metamorphic rocks, changed from their original condition through
dynamic or chemical agencies, and which may have been partly of aqueous
and partly of igneous origin.
Fourth, igneous or eruptive rocks, which have been brought up from
below in a molten condition, and which owe their present structural
peculiarities to variations in composition and conditions of solidification.

33. Aqueous Rocks.—Aqueous rocks may be divided into the following
general classes:
First, rocks formed as chemical precipitates.
Second, rocks formed as sedimentary deposits and fragmental in
structure. The second class may again be subdivided into rocks formed by
mechanical agencies and mainly of inorganic materials; and second, rocks
composed mainly of the débris of plant and animal life.
In regard to the first form of aqueous rocks, namely, those formed as
chemical precipitates, it may be said that while their quantity is not large
they are yet of considerable importance from an agricultural point of view.
They embrace those substances which, having once been in a condition of
vapor or aqueous solution, have been deposited or precipitated, either by
cooling or by the evaporation of the liquor holding them in solution, or by
coming in contact with chemical substances capable of precipitating them.
The influence of water as a solvent is perhaps not fully appreciated. Its
solvent influence will be noted particularly under the head of weathering or
decay of rocks. Its importance, however, in producing stratified rocks has
been very great. Water, especially when under great pressure and at a high
temperature, has the power of dissolving many minerals. This power is
often greatly increased by the mineral matter previously in solution in the
water or by the gases which it may contain. As an illustration of the latter
property, the solvent action of water charged with carbon dioxid on
limestone may be cited.
When mineral matters have been dissolved by the water in the ways
mentioned and carried with the water beyond the condition where the
solution has taken place, new conditions are found favorable to the
precipitation of the dissolved matters. The water, which before may have
been very hot, may reach a place where it cools, and being a supersaturated
solution, the excess of the material is thrown down as the water cools.
On the other hand, if the solution be due to the presence of carbon dioxid
and the water reach a place where it is exposed to the air or where the
pressure under which the abundance of the gas has been due is diminished,
the carbon dioxid will escape and the mineral matters which have been
dissolved thereby will be precipitated.
The incrustations which often appear round the mouth of springs and the
occurrence of stalagmites and stalactites in caves are illustrations of this

action.
In respect of the formation of rocks as precipitates from a state of vapor
we have scarcely any illustrations excepting in volcanic regions. Rocky
materials with which we are generally acquainted are practically non-
volatile at the highest temperature which can be secured on the earth’s
surface, but it is possible that in the interior of the earth the temperature
may be so high as to maintain many substances in a state of vapor.
They may, in this case, become disassociated so that the compounds or
elements exist distinctly in a vaporous condition. Such a vapor transported
to regions of diminished temperature would first of all on cooling permit a
union of the chemical elements forming new compounds less volatile,
which, of course, would be at once precipitated.
The rocks and minerals formed in this way which are of some
agricultural importance may be classified as follows:
Oxids, carbonates, silicates, sulfur, sulfids, sulfates, phosphates, chlorids,
and hydrocarbon compounds, the most important from an agricultural point
of view being the phosphates.
The second group of rocks, namely those formed as sedimentary
deposits, differ from those just described in that they are comprised mainly
of fragmental materials derived from the breaking down of pre-existing
rocks. The formation of fragmental rocks includes, therefore, the same
processes as are active in the formation of arable soil. They are deposited
from water, and are as a rule distinctly stratified.
Through the action of pressure and the heat thereby generated, or simply
through the chemical action of percolating solutions, such rocks pass over
into the crystalline sedimentary forms known as metamorphic. All
metamorphic rocks, however, are not of a sedimentary origin. For instance,
by pressure, heat, and the chemical changes thereby induced, granite may
be changed into gneiss and the latter would then be a metamorphic rock.
This group of sedimentary rocks and of sedimentary material, either
unchanged or metamorphosed, is of vast extent and includes materials of
widely varying chemical and mineralogical nature. They form by far the
greater portion of the present surface of the earth, even the mountain ranges
being composed mainly of this sedimentary material. Indeed, in the whole
of this country there is only a comparatively very small extent of igneous or
irruptive rocks. They are of great importance from a purely scientific, as

well as agricultural standpoint, since they contain the fossil records of past
geologic ages. From them it is possible to study the variations in climate,
the meteorological conditions in circumstances and periods far remote, and
thus form some idea of the process by which the crust of the earth has been
modified by natural forces from its original form to the present time.
The sedimentary rocks may be divided, with sufficient accuracy for our
purposes, into two great classes: First, rocks formed by mechanical
agencies and mainly of inorganic materials. These are subdivided again as
follows:
(a) The arenaceous group.
(b) The argillaceous group.
(c) The volcanic group.
The second class of sedimentary rocks is formed largely, or in part at
least, by mechanical agencies, but is comprised chiefly of the débris of
plant and animal life. It may be subdivided as follows:
(a) The siliceous group, such as infusorial earth.
(b) The calcareous group, fossiliferous formations, limestone, etc.
(c) The carbonaceous group, such as peat, lignite, coals, etc. The different
classes of rock described above are distinguished by special qualities
represented largely by the name. The first division, the arenaceous group, is
composed mainly of the siliceous or coarsely granular materials derived
from the disintegration of older crystalline rocks, which have been
rearranged in beds of varying thickness through the mechanical agency of
water. They are, in short, consolidated or unconsolidated beds of sand and
gravel. In composition and texture they vary almost indefinitely. Many of
them having suffered little during the process of disintegration and
transportation are composed essentially of the same materials as the rocks
from which they were derived.
The sandstones, which are the type of these rocks, vary greatly in
structure as well as in composition, in some the grains being rounded while
in others they are sharply angular.
The microscopic structure of sandstone is shown in figure 7.[24]
The material by which the individual grains of a sandstone are bound
together is usually the material of some of the other classes. The calcareous,
ferruginous, and siliceous cements being the chief ones. This cementing

substance is deposited among the granules forming the sandstone by
percolating water.
The colors of sandstone are dependent usually upon iron oxids.
Especially is this true of the red, brown, and yellow colors. In some of the
light grey varieties, the color is that of the minerals comprising the stone.
Some of the darker colored sandstones contain organic matter.

Fig. 7.

Microscopic Structure of Sandstone.

The rocks of the argillaceous group are composed essentially of a
hydrous silicate of alumina, which is the basis of common clay, and varying
amounts of free silica, oxids of iron and manganese, carbonates of lime and
magnesia, and small quantities of organic matter. They may have originated
in situ from the decomposition of feldspars or as deposits of fine mud or silt
at the bottom of large bodies of water. The older formations of these rocks
are known as shales, argillites, and slates and the fissile structure which
enables this to be split into thin sheets is probably due to the conditions
under which they have been formed and not to any properties of the clays
themselves.
One of the purest forms of this rock is kaolin, which is almost a pure
hydrous silicate of alumina formed from the decomposition of feldspathic

rocks from which the alkalies, iron oxids and other soluble constituents
have been removed by water.
Under the volcanic group are included the materials ejected from
volcanic vents in a more or less finely comminuted condition and which
through the drifting power of atmospheric currents may be scattered over
many miles of territory. Various names are applied to such products, names
dependent in large part upon their state of subdivision. Volcanic dust and
sand, or ashes, includes the finer dust-like or sand-like materials, and lapilli,
or rapilli the coarser. The general name tuff includes the more or less
compacted and stratified beds of this material, while trass, peperino, and
pozzuolano are local varietal names given to similar materials occurring in
European volcanic regions.
The second division, namely sedimentary rocks composed of the débris
of plant and animal life includes many forms of great agricultural
importance.
The first subdivision of this group is the infusorial or diatomaceous earth.
It forms a fine white or yellowish pulverulent rock composed mainly of
minute shells, or tests of diatoms, and is often so soft and pliable as to
crumble readily between the thumb and fingers. According to Whitney the
beds are of comparatively limited extent and for this reason are of little
agricultural value, although the weathering of this diatomaceous material
gives rise to a light yellow clay forming very fertile agricultural lands.
The second subdivision of this group includes the rocks of a calcareous
nature derived from animal life; that is to say, what are properly called
limestones. They vary in color, structure, and texture almost indefinitely,
and include all possible grades of materials from those which can be used
only as a flux, or for lime burning, through ordinary building materials to
the finest marbles. These rocks are world-wide in their distribution and
limited to no one particular geologic horizon, but are found in stratified
beds among rocks of all ages from the most ancient to the most recent.
Owing to the fact that their chief constituent, carbonate of lime, is soluble
in ordinary meteoric waters, the rocks have undergone extensive
decomposition, their lime being removed, while their less soluble
constituents or impurities remain to form soil. A single ton of residual soil
represents not infrequently a loss of 100 tons of original rock matter. As this
mass of lime carbonate is removed by solution the residual soil settles, and

as the limestone rocks are more soluble than the adjacent rock formations
limestone formations usually form valley lands with ridges on either side.
Caves are frequently found in such formations. Furthermore, as the lime is
almost all in the form of the easily soluble lime carbonate it can be very
completely removed and the fertile “limestone soils” are often very
deficient in lime and respond readily to an application of burnt lime, which,
not infrequently, is quarried from the same field. From an agricultural
standpoint this group is of very great interest and importance.
The third subdivision of this group, namely, that of vegetable origin,
includes peat, lignite, coals, etc. Rocks of this group are made up of more or
less fragmental remains of plants. In many of them, as the peats and
lignites, the traces of plant structure are still apparent. In others, as the
anthracite coals, these structures have been wholly obliterated by
metamorphisms.
Plants when decomposing on the surface of the ground give off their
carbon to the atmosphere in the shape of carbon dioxid gas leaving only the
strictly inorganic or mineral matter behind. When, however, they are
protected from the oxidizing influence of the air, by water or by other plant
growth, decomposition is greatly retarded, and a large portion of the
carbonaceous and volatile matters is retained, and by this means together
with pressure from the overlying mass, the material becomes slowly
converted into coal. When this process goes on near the surface of the earth,
and without much pressure, peat or muck is the product.
The fourth subdivision of this group, the phosphatic, forms a class of
rocks limited in extent but of the greatest economic importance. Guano,
coprolites, and phosphatic rocks (the phosphorites) come under this head.
34. Aeolian Rocks.—This class of rocks is of less importance than the
others, either geologically or agriculturally. It is formed from materials
drifted by the winds and this material has various degrees of compactness.
Usually the components of these drifts form rocks or deposits of a friable
texture and of a fragmental nature. The very extensive deposits of loess in
China, forming their most fertile lands, are admitted now to have been
formed in this way, but it is now generally admitted that similar deposits in
this country are of subaqueous origin.
Chief among these rocks, are the volcanic ashes which are often carried
to a long distance by the wind before they are deposited and consolidated

into rock masses. Many loose soils may be carried to great distances by the
wind, the deposits forming new aggregates. This is particularly the case in
arid regions.
35. Metamorphic Rocks.—This class of rocks includes all sedimentary
or eruptive rocks, which, after their deposition and agglomeration, have
been changed in their nature through the action of heat, pressure, or by
chemical means. Sometimes these changes are so complete that no
indication of the character of the original rocks remains. At other times the
changes may be found in all the stages of progress, so that they can be
traced from the original fragmental or irruptive to the completely
metamorphosed deposit. This is especially true of rocks containing large
quantities of lime. In those containing silica, the changes are less readily
traced.

Fig. 8.

Microstructure of Crystalline Limestone.

(West Rutland, Vermont.)

The metamorphic rocks may be divided into two subclasses, namely,
stratified or bedded, and foliated or schistose.
The rocks of the first class are represented by the crystalline limestones
and dolomites. The microstructure of a crystalline limestone is shown in

Fig. 8.[25] When lime and magnesia occur together in combination with
carbon dioxid, the substance is known as dolomite. The chemical nature of
these rocks and their soil-forming properties are the same as those of the
ordinary, non-metamorphosed limestones and dolomites to which reference
has already been made. The subject need not, therefore, be further dwelt
upon here.

Fig. 9.

Microstructure of Gneiss.

(West Andover, Massachusetts.)

At a a are shown plagioclase crystals broken and
rounded by the sheering force producing the
foliation.

The second variety of metamorphic rocks is represented by the gneisses
and crystalline schists. Gneiss has essentially the same composition as
granite and can frequently hardly be distinguished from it, except by a
microscopic study of its sections, and even thus it is sometimes difficult to
determine. Frequently a number of new minerals is formed in the
metamorphic changes. The microstructure of a gneiss is shown in Fig. 9.[26]

The schists include an extremely variable class of rocks, of which quartz is
the prevailing constituent, and which, as a rule, are deficient in potash and
other important ingredients.
36. Rocks Formed Through Igneous Agencies, or Eruptive Rocks.—
This group includes all those rocks, which, having been at some time in a
state of igneous fusion, have been solidified into their present form by a
process of cooling. It may be stated, as a general principle, that the greater
the pressure under which a rock solidifies and the slower and more gradual
the cooling the more perfect will be found the crystalline structure. Hence,
it follows that the older and more deep-seated rocks which are forced up in
the form of dikes, bosses, or intrusive sheets, into the overlying masses, and
which have become exposed only through erosion and removal of the
overlying rocks, are the more highly crystalline.
The eruptive rocks are divided into two main groups, viz.:
(a) Intrusive or plutonic rocks, and
(b) Effusive or volcanic rocks.
Among the more important of the first division of the plutonic form, from
an agricultural point of view, are the granites. The essential constituents of
granite are quartz, potash feldspar, and plagioclase. One or more minerals
of the mica, amphibole or pyroxene groups are also commonly present, and
in microscopic proportions apatite and particles of magnetic iron. The more
valuable constituents, from an agricultural standpoint, are the minerals
potash feldspar, and apatite, which furnish by their decomposition the
essential potash and phosphoric acid.
In addition to the granites, which have already been mentioned, the group
includes the syenites, the nepheline syenites, the diorites, the gabbros, the
diabases, the theralites, the peridotites, and the pyroxenites.
The second group, the effusive or volcanic rocks, includes those igneous
rocks, which, like the first group, have been forced up through the overlying
rocks, but which were brought to the surface, flowing out as lavas. These,
therefore, represent, in many cases, only the upper or surface portions of the
first group, differing from them structurally, because they have cooled
under little pressure more rapidly, and hence are not so distinctly
crystalline. These comprise the following groups:

(a) Quartz porphyries. (b) Liparites. (c) Quartz-free porphyries. (d)
Trachytes. (e) Phonolites. (f) Porphyrites. (g) Andesites. (h)
Melaphyrs and augite porphyrites. (i) Basalts. (j) Tephrites and
Basanites. (k) Picrite porphyrites. (l) Limburgites and augitites.
(m) Leucite rocks. (n) Nepheline rocks. (o) Melilite rocks.
It is, in most cases, impossible to state which of the above classes is of
most importance from an agricultural standpoint, since, in the process of
soil formation, both chemical and physical processes are involved, whereby
the character of the resultant soil is so modified as to but remotely resemble
its parent rock. In most soils, the prevailing constituent is but the least
soluble one of the rock mass from which it was derived. Thus a limestone
soil may contain upwards of ninety per cent of silica and alumina, while the
original limestone itself may not have carried more than one or two per cent
of these substances. Of course, if a rock mass contains none of the
constituents essential to plant growth, its resultant soil must by itself alone
be quite barren. It does not absolutely follow, however, that those rocks
containing the highest percentages of valuable constituents will yield the
most fertile soils, since much depends on the manner in which they have
been formed, the amount of leaching, etc., they may have undergone.
Nevertheless, the study of the composition of the rocks in their relation to
soils, is an extremely interesting and by no means unimportant one.
A comparative table of rock compositions is here given. It will be
observed that there is a considerable range of variation even among rocks of
the same class, a fact due to the varying abundance of their mineral
constituents. The figures given are not those of actual analyses on any one
particular rock, but are selected from a number of comparatively typical
cases; and, it is thought, fairly well represent the composition of the class of
rocks indicated.

Composition of Rocks.—The Figures Indicate Parts per Hundred.
Fe₂O₃.
SiO₂. Al₂O₃. MgO. CaO. Na₂O. K₂O. P₂O₅.
FeO.
Granite
63– 0.05–
Quartz poryhyries} 10–15 2–3 0.3–0.5 1–2 2–3 4–5
78 0.15
Liparite

Syenite
Orthoclase 55–
12–16 5–7 2–6 3–5 2–6 4–7 trace.
porphyries} 73
Trachyte

Nepheline syenites} 54– 0.4–
16–22 4–6 2–4 3–7 4–6 0.15
Phonolites 56 0.88

Diorites
52–
Porphyrites} 16–20 7–10 5–7 5–7 2–4 1–2 0.1–0.3
65
Andesites

Gabbros
48– 0.5–
Norites} 12–20 8–15 2–7 6–10 2–4 0.1–0.33
55 2
Melaphyrs

Theralites
43–
Tephrites} 15–23 9–18 1–6 6–10 5–7 2–4 trace.
47
Basanites

Peridotites
23–
Picrite porphyrites} 1–10 10–15 15–45 1–4 0–4 trace. 0.0
43
Limburgites

Pyroxenites} 50–
0.5–4 4–10 20–25 8–15
Augitites 55

Leucite rocks 48–
15–20 7–10 1–2 5–10 3–5 5–7 0.5–2
50

Nepheline rocks 40–
8–20 10–20 1–13 4–10 4–8 1–3 0.2
45
37. Origin of Soils.—The soils in which crops grow and which form the
subject of the analytical processes to be hereinafter described have been
formed under the combined influences of rock decay and plant and organic
growth. The mineral matters of soils have had their origin in the decay of
rocks, while the humic and other organic constituents have been derived
from living bodies. It is not the object of this treatise to discuss in detail the

processes of soil formation, but only to give such general outlines as may
bear particularly on the proper conceptions of the principles of soil
investigation.
38. The Decay of Rocks.—The origin and composition of rocks are fully
set forth in works on geology and mineralogy. Only a brief summary of
those points of interest to agriculture has been given in the preceding pages.
The soil analyst should be acquainted with these principles, but for practical
purposes he has only to understand the chief factors active in securing the
decay of rocks and in preparing the débris for plant growth.
The following outline is based on the generally accepted theories
respecting the formation of soils.[7]
The forces ordinarily concerned in the decay of rocks are:

1. Changes of temperature, including the ordinary daily and monthly
changes, and the conditions of freezing and thawing.
2. Moving water or ice.
3. Chemical action of water and air.
4. Influence of vegetable and animal life:

(a) Shades the rock or soil surface.
(b) Penetrates the rock or soil material with its roots, thus
admitting air.
(c) Solvent action of roots.
(d) Chemical action of decaying organic matter.

5. Earth worms.
6. Bacteria.
39. The Action of Freezing and Thawing.—In those parts of a rock
stratum exposed near the surface of the earth the processes of freezing and
thawing have perhaps had considerable influence in rock decay. The
expansive force of freezing water is well known. Ice occupies a larger
volume than the water from which it was formed. The force with which this
expansion takes place is almost irresistible. The phenomenon of bursted

water pipes which have been exposed to a freezing temperature is not an
uncommon one. While the increase in volume is not large, yet it is entirely
sufficient to produce serious results. The way in which freezing affects
exposed rock is easily understood. The effect is unnoticeable if the rock be
dry. If, on the other hand, it be saturated with water, the disintegrating effect
of a freeze must be of considerable magnitude. This effect becomes more
pronounced if the intervals of freezing and thawing be of short duration.
The whole affected portion of the rock may thus become thoroughly
decayed. But even in the most favorable conditions this form of
disintegration must be confined to a thin superficial area. Even in very cold
climates the frost only penetrates a few feet below the surface, and therefore
the action of ice cannot in any way be connected with those changes at
great depths, to which attention has already been called. Nevertheless,
certain building stones seem very sensitive to this sort of weathering, and
the crumbling of the stone in the Houses of Parliament is due chiefly to this
cause.
On the whole it appears that the action of ice in producing rock decay has
been somewhat overrated, although its power must not by any means be
denied. But on the other hand a freeze extending over a long time tends to
preserve the rocks, and it therefore appears that the entire absence of frost
would promote the process of rock decay.
At best it must be admitted that frost has affected the earth’s crust only to
an insignificant depth, but its influence in modifying the arable part of the
soil is of the utmost importance to agriculture.
40. The Action of Glaciers.—The action of ice in soil formation is not
confined alone to the processes just described. At a period not very remote
geologically, a great part of our Northern States was covered with a vast
field of moving ice. These seas of ice crept down upon us from more
northern latitudes and swept before them every vestige of animal and
vegetable life. In their movement they leveled and destroyed the crests of
hills and filled the valleys with the débris. They crushed and comminuted
the strata of rocks which opposed their flow and carried huge boulders of
granite hundreds of miles from their homes. On melting they left vast
moraines of rocks and pebbles which will mark for all time the termini of
these empires of ice. When the ice of these vast glaciers finally melted the
surface which they had leveled presented the appearance of an extended

plain. No estimate can be made of the enormous quantities of rock material
which were ground to finest powder by these glaciers. This rock powder
forms to-day no inconsiderable part of those fertile soils which are
composed of glacial drift. The rich materials of these soils probably bear a
more intimate relation to the rocks from which they were formed than of
any other kinds of soil in the world. The rocks were literally ground into a
fine powder, and this powder was intimately mixed with the soils which had
already been formed in situ. The melting ice also left exposed to
disintegrating forces large surfaces of unprotected rocks in which decay
would go on much more rapidly than when covered with the débris which
protected them before the advent of the ice. The area of glacial action
extended over nearly all of New England and over the whole area of the
northern tier of States. It extended southward almost to the Ohio river, and
in some places crossed it. The effect of the ice age in producing and
modifying our soil must never be forgotten in a study of soil genesis. It is
not a part of our purpose here to study the causes which produced the age of
ice. Even a brief reference to some of the more probable ones might be
entirely out of place. Before the glacial period it is certain that a tropical
climate extended almost, if not quite, to the North Pole. The fossil remains
of tropical plants and animals which have been found in high northern
latitudes are abundant proofs of this fact.
In the opinion of Sterry Hunt,[27] rock decay has taken place largely in
preglacial and pretertiary times. The decay of crystalline rocks is a process
of great antiquity. It is also a universal phenomenon. The fact that the rocks
of the southern part of this country seem to be covered with a deeper débris
than those further north is probably due to the mechanical translation of the
eroded particles towards the south. The decay and softening of the material
were processes necessarily preceding the erosion by aqueous and glacial
action.
It is possible that a climate may have existed in the earlier geologic ages
more favorable to the decay of rocks than that of the present time.
41. Progress of Decay as Affected by Latitude.—Extensive
investigations carried on along the Atlantic side of the country show wide
differences in the rate of decay in the same kind of rocks in different
latitudes. In general, the progress of decay is more marked toward the
south. The same fact is observed in the great interior valleys of the country;

at least, everywhere except in the arid and semi-arid regions. Wherever
there is a deficiency of water the processes of decay have been arrested.
Where the rock strata have been displaced from a horizontal position the
progress of decay has been more rapid. This is easily understood. The
percolation of water is more easy as the displacement approaches a vertical
position.
A most remarkable example of this is seen in the rocks of North Carolina.
[28]
A kind of rock known as trap is found in layers called dikes in the
Newark system of rocks in that State. These dikes have been so completely
displaced from the horizontal position they at first occupied as to have an
almost vertical dip. The edges thus exposed vary from a few feet to nearly
100 feet in thickness. The trap rock in those localities is composed almost
exclusively of the mineral dolerite, which is so hard and elastic in a fresh
state as to ring like a piece of metal when struck with a hammer. In building
a railroad through this region these dikes were in some places uncovered to
a depth of forty feet and more. At this depth they were found completely
decomposed and with no indications of having reached the lower limit of
disintegration. The original hard bluish dolerite has been transformed into a
yellowish clay-like mass that can be molded in the fingers and cut like
putty. Similar geologic formations in New Jersey and further North do not
exhibit anything like so great a degree of decomposition, thus illustrating in
a marked degree the fact that freezing weather for a part of the year is a
protection against rock decay. The ice of winter at least protects the rocks
from surface infiltration, although it can not stop the subterranean solution
which must go on continuously.
Other things being equal, therefore, it appears that as the region of winter
frost is passed the decay of the rocks has been more rapid than in the North,
because the chief disintegrating forces act more constantly.
42. The Solvent Action of Water.—The water of springs and wells is not
pure. It contains in solution mineral matters and often a trace of organic
matter. The organic matter comes from contact with vegetable matter and
other organic materials near the surface of the earth. The mineral matter is
derived from the solvent action of the water and its contents on the soil and
rocks.
The expressions “hard” and “soft” applied to water indicate that it has
much or little mineral matter in suspension, as the case may be. When

surface and spring waters are collected into streams and rivers they still
contain in solution the greater part of the mineral matters which they at first
carried.
When well or spring waters have more than forty grains of mineral
matter per gallon they are not suitable for drinking waters. Mineral waters,
so called, are those which carry large quantities of mineral matter, or which
contain certain comparatively rare mineral substances which are valued for
their medicinal effects.
The analysis of spring, well, or river waters will always give some
indication of the character of the rocks over which they have passed.[29] The
vast quantities of mineral matters carried into oceans and seas are gradually
deposited as the water is evaporated. If, however, these matters be very
soluble, such as common salt, sulfate of magnesia, etc., they become
concentrated, as is seen with common salt in sea waters. In small bodies of
waters, such as inland seas, which have no outlet, this concentration may
proceed to a much greater extent than in the ocean. As an instance of this, it
may be noted that the waters of the Dead Sea and Great Salt Lake are
impregnated to a far greater degree with soluble salts than the water of the
ocean. The solvent action of water on rocks is greatly increased by the
traces of organic or carbonic acids which it may contain. When surface
water comes in contact with vegetable matter it may become partially
charged with the organic acids which the growing vegetable may contain or
decaying vegetable matter produce. Such acids coming in contact with
limestone under pressure will set free carbon dioxid. Water charged with
carbon dioxid acts vigorously on limestone and other mineral aggregates. If
such solutions penetrate deeply below the surface of the earth their activity
as solvents may be greatly increased by the higher temperature to which
they are subjected. Hence, all these forces combine to disintegrate the
rocks, and through such agencies vast deposits of original and secondary
rocks have been completely decomposed.
The gradual passing of the firm rock into an arable soil is beautifully
shown in Fig. 10, a print from a negative taken by Mr. Geo. P. Merrill, near
Washington, D. C.

Figure 10.

View on the Broad Branch of Rock Creek, Washington, D. C.

The fresh but badly decomposed granitic rock is shown passing upward into material more
and more decomposed until it becomes sufficiently pulverulent and soluble to support plant
life. The roots showing in the upper part of the picture formerly penetrated the decomposed
rock, but have been exposed through quarrying operations. Photograph by George P. Merrill,
1891.

43. Action Of Vegetable Life.—The preliminary condition to vegetation
is the formation of soil, but once started, vegetation aids greatly in the
decomposition of rocks. Some forms of vegetation, as the lichens, have
apparently the faculty of growing on the bare surface of rocks, but the
higher order requires at least a little soil. The vegetation acts by shading the
surface and thus rendering the action of water more effective, by

mechanically separating the rock particles by means of its penetrating roots
and by the positive solvent action of the root juices. The rootlets of plants in
contact with limestone or marble dissolve large portions of these
substances, and while their action on more refractory rocks is slower, it
must be of considerable importance. The organic matter introduced into the
soil by vegetation also promotes decay still further both directly and by the
formation of acids of the humic series. This matter also furnishes a
considerable portion of carbon dioxid which is carried by the water to assist
in its solvent action.
44. Action of Earth-Worms.—Of animal organisms those most active in
the formation of soil are earth-worms. The work of earth-worms has been
exhaustively studied by Darwin.[30] The worms not only modify the soil by
bringing to the surface portions of the subsoil, but also influence its
physical state by making it more porous and pulverulent. According to
Darwin the intestinal content of worms has an acid reaction, and this has an
effect on those portions of the soil passing through their alimentary canal.
The acids, which are formed in the upper part of the digestive canal are
neutralized by the carbonate of lime secreted by the calciferous glands of
the worms thus neutralizing the free acid and changing the reaction to
alkaline in the lower part of the canal. There is a fair presumption that the
acids of the worm are of a humic nature.
The worms further modify the composition of the soil by drawing leaves
and other organic matter into their holes, and leaving therein a portion of
such matter which is gradually converted into humus. Stockbridge[31] gives
a striking illustration of this process due to an experiment by von Hensen.
Darwin estimates that about eleven tons of organic matter per acre are
annually added to the soil in regions where worms abound. A considerable
portion of the ammonia in the soil at any given time may also be due to the
action of worms, as much as 0.18 per cent of this substance having been
found in their excrement. It is probable that nearly the whole of the
vegetable matter in the soil passes sooner or later through the alimentary
canals of these ceaseless soil builders, and is converted into the form of
humus.
45. Action of Bacteria.—The intimate relations which have been found
to subsist between certain minute organisms and the chemical reactions

which take place in the soil is a sufficient excuse for noting the effect of
other similar organisms in the formation of soils.
In addition to the usual forces active in decomposing rocks Müntz[32] has
described the effects of a nitrifying bacillus contributing to the same
purpose.
According to him the bare rock usually furnishes a purely mineral
environment where organisms cannot be developed unless they are able to
draw their nourishment directly from the air. Some nitrifying organisms
belong to this class. It has been shown that these bodies can be developed
by absorbing from the ambient atmosphere carbonate of ammonia and
vapors of alcohol, the presence of which has been determined in the air.
According to the observations of Winogradsky, they assimilate even the
carbon of the carbon dioxid just as vegetables do which contain chlorophyl.
Thus even in the denuded rocks of high mountains the conditions for the
development of all these inferior organisms exist. In examining the particles
produced by attrition, it is easily established that they are uniformly covered
by a layer of organic matter evidently formed by microscopic vegetations.
Thus we see, in the very first products of attrition, appearing upon the rocky
particles the characteristic element of vegetable soil, viz., humus, the
proportion of which increases rapidly with the products of disaggregation
collected at the foot of declivities until finally they become covered with
chlorophyliferous plants.
In a similar manner the presence of nitrifying organisms has been noted
upon rocky particles received in sterilized tubes, and cultivated in an
appropriate environment where they soon produce nitrification. The naked
rocks of the Alps, the Pyrenees, the Auvergnes and the Vosges, comprise
mineralogical types of the most varied nature, viz., granite, porphyry,
gneiss, micaschist volcanic rocks and limestones and all these have shown
themselves to be covered with the nitrifying ferment. It is known that below
a certain temperature these organisms are not active; their action upon the
rock is, therefore, limited to the summer period. During the cold season
their life is suspended but they do not perish, inasmuch as they have been
found living and ready to resume all their activity after an indefinite sleep
on the ice of the glaciers where the temperature is never elevated above
zero.

The nitrifying ferment is exercised on a much larger scale in the normal
conditions of the lower levels where the rock is covered with earth. This
activity is not limited to the mass of rock but is continued upon the
fragments of the most diverse size scattered through the soil and it
gradually reduces them to a state of fine particles. It is therefore a
phenomenon of the widest extension.
The action of these micro-organisms according to Müntz is not confined
to the surface but extends to the most interior particles of the rocky mass.
Where, however, there is nothing of a nitrogenous nature, to nitrify such an
organism must live in a state of suspended animation.
When the extreme minuteness of these phenomena is considered there
may be a tendency to despise their importance, but their continuity and their
generality in the opinion of Müntz place them among the geologic causes to
which the crust of the earth owes a part of its actual physiognomy and
which particularly have contributed to the formation of the deposits of the
comminuted elements constituting arable soil.
The general action of nitrifying organisms in the soil, the nature of these
bodies, and the method of isolating and identifying them will be fully
discussed in another part of this work.
46. Action of the Air.—The air itself takes an active part in rock decay.
Wherever rocks are exposed to decay, there air is found or, at least, the
active principle of air, viz., oxygen. The air not only penetrates to a great
depth in the earth, but is also carried to much greater depths by water which
always holds a greater or less quantity of air in solution. The oxygen of the
air is thus brought into intimate contact with the disintegrating materials
and in a condition to assist wherever possible in the decomposing
processes.
The oxygen acts vigorously on the lower oxids of iron, converting them
into peroxids, and thus tends to produce decay.
There are other constituents of rocks which oxygen affects injuriously
and thus helps to their final breaking up. It is true that, as a rule, the
constituents of rocks are already oxidized to nearly as high a degree as
possible, and on these constituents of course the air would have no effect.
But on others, especially when helped by water with the other substances it
carries in solution, the air may greatly help in the work of destruction.

In a general view, the action of the air in soil formation may be regarded
as of secondary importance, and to depend chiefly on the oxidation of the
lower to the higher basic forms. These processes, while they seem of little
value, have, nevertheless, been of considerable importance in the
production of that residue of rock disintegration which constitutes the soil.
47. Classification of Soils According to Deposition.—In regard to their
deposition soils are divided into five classes:
1. Those which are formed from the decomposition of crystalline or
sedimentary rocks or of unconsolidated sedimentary material in situ.
2. Those which have been moved by water from the place of their
original formation and deposited by subsidence (bottom lands, alluvial
soils, lacustrine deposits, etc.).
3. Those which have been deposited as débris from moving masses of ice
(glacial drift).
4. Soils formed from volcanic ashes or from materials moved by the wind
and deposited in low places or in hills or ridges.
5. Those formed chiefly from the decay of vegetable matter, (tule, peat,
muck).
48. Qualities of Soils.—In respect of quality, soils have been arbitrarily
divided into many kinds. Some of the more important of these divisions are
as follows:
1. Sand. Soils consisting almost exclusively of sand.
2. Sandy Loams. Soils containing some humus and clay but an excess of
sand.
3. Loams. Soils inclining neither to sand nor clay and containing some
considerable portions of vegetable mold, being very pulverulent and easily
broken up into loose and porous masses.
4. Clays. Stiff soils in which the silicate of alumina and other fine
mineral particles are present in large quantity.
5. Marls. Deposits containing an unusual proportion of carbonate of lime,
with often some potash or phosphoric acid resulting from the remains of
sea-animals and plants.
6. Alkaline. Soils containing carbonate and sulfate of soda, or an excess
of these alkaline and other soluble mineral substances.

7. Adobe. A fine grained porous earth of peculiar properties hereinafter
described.
8. Vegetable. Soils containing much vegetable débris in an advanced state
of decomposition. When such matter predominates or exists in large
proportion in a soil the term tule, peat or muck is applied to it.
With the exception of numbers six, seven and eight these types of soil are
so well-known as to require no further description for analytical purposes.
The alkaline, adobe and vegetable soils on the contrary demand further
study.
49. Alkaline Soils.—The importance of a more extended notice of this
class of soils for analytical purposes is emphasized by their large extent in
the United States.
Chiefly through the researches of Hilgard attention has been called to the
true character of these soils which are found throughout a large part of the
Western United States and which are known by the common name of alkali.
The following description of the origin of these soils is compiled chiefly
from Hilgard’s papers on this subject. Wherever the rain-fall is scanty, and
especially where the rains do not come at any one time with sufficient force
to thoroughly saturate the soil and carry down through the subsoil and off
through the drainage waters the alkali contained therein, favorable
conditions exist for the production of the alkaline soil mentioned above.
The peculiar characteristic of this soil is the efflorescence which occurs
upon its surface and which is due to the raising of soluble salts in the soil by
the water rising through capillary attraction and evaporating from the
surface, leaving the salts as an efflorescence.
Soils which contain a large amount of alkali are usually very rich in
mineral plant food, and if the excess of soluble salt could be removed, these
lands under favorable conditions of moisture would produce large crops.
The formation of the alkali may be briefly described as follows: By the
decomposition of the native rocks, certain salts soluble in water are formed.
These salts in the present matter are chiefly sodium and potassium sulfates,
chlorids and carbonates. The salts of potash together with those of lime are
more tenaciously held by the soil than the soluble salts of soda, and the
result of this natural affinity of the soil for soluble potash, lime and
magnesian salts is seen in the formation at the surface of the earth, by the
process of evaporation above described, of a crust of alkaline material

which is chiefly composed of the soluble salts of soda. In countries which
have a sufficient amount of rain-fall, these soluble salts are carried away
either by the surface drainage or by the percolation of water through the
soil, and the sodium chlorid is accumulated in this way in the waters of the
ocean. But where a sufficient amount of rain-fall does not occur, these
soluble salts carried down by each shower only to a certain depth rise again
on the evaporation of the water, reinforced by any additional soluble
material which may be found in the soil itself. The three most important
ingredients of the alkali of the lands referred to are sodium chlorid, sulfate,
and carbonate. When the latter salt, namely, sodium carbonate, is present in
predominant quantity, it gives rise to what is popularly known as black
alkali. This black color is due to the dark colored solution which sodium
carbonate makes with the organic matters or humus of the soil. The black
alkali is far more injurious to growing vegetation than the white alkali
composed chiefly of sodium sulfate and chlorid.
This black alkali has been very successfully treated by Hilgard[33] by the
application of gypsum which reacting with the sodium carbonate produces
calcium carbonate and sodium sulfate, thus converting the black into the
white alkali and adding an ingredient in the shape of lime carbonate to stiff
soils which tends to make them more pulverulent and easy of tillage.
This method of treatment, however, as can be easily seen, is only
palliative, the whole amount of the alkaline substances being still left in the
soil, only in a less injurious form.
The only perfect remedy for alkaline soils, as has been pointed out by
Hilgard, is in the introduction of underdrainage in connection with
irrigation. The partial irrigation of alkaline soils, affording enough moisture
to carry the alkali down to and perhaps partially through the subsoil, can
produce only a temporary alleviation of the difficulties produced by the
alkali. Subsequent evaporation may thus increase the amount of surface
incrustation. For this reason in many cases the practice of irrigation without
underdrainage may completely ruin an otherwise fertile soil by slowly
increasing the amount of alkali in the soil by the total amount of the
alkaline material added in the waters of irrigation.
As Hilgard has pointed out, if a soil can be practically freed from alkali
by underdrainage connected with a thorough saturation by irrigation, it may
be centuries before the alkali will accumulate in that soil again when

ordinary irrigation only is practiced. It may thus become possible to reclaim
large extents of alkaline soil little by little by treating them with an excess
of irrigation water in connection with thorough underdrainage. The
composition of the alkali on the surface of the soil due to the causes above
set forth is thoroughly illustrated by the analyses of Hilgard and Weber,
which follow:

Table Showing Composition of Alkali Salts in San Joaquin Valley.
FRESNO COUNTY.
Sections 13 and 24 T. 14 S. R. 19 E., 4 miles S. W. from Fresno. Miss Austin’s Ranch, N.W. Cor. N ½ Sec. 20 T. Easton. Emigr’nt
Central Colony. 14 S. R. 21 E. Ditch.
Alkali soil, Alkali Spot, 1889. Surface Surface Surface Surface
1888. 1 inch 18 inches 26 inches 42 inches soil, No. 1. soil, No. 2. soil. soil.
surface. bel. surface. bel. surface. hardpan.
Soluble salts in 0.76 0.20 0.18 0.16 3.54 1.90 1.20 2.69
100 parts soil
Potassium sulfate small moderate
[D]Potassium small
nitrate
Potassium
carbonate
(Saleratus)
Sodium sulfate large small small very slight very slight large large much moderate large
(Glauber’s salt)
Sodium carbonate very slight large small large large small chiefly small small chiefly
(Sal-soda)
Sodium chlorid chiefly moderate chiefly moderate moderate chiefly large chiefly chiefly large little
(Common salt)
[D]Sodium
phosphate
Calcium sulfate moderate small very slight very slight very slight small moderate small small much
(Gypsum)
Magnesium sulfate small much
(Epsom salt)
Organic matter

D. Very generally present, but not always in quantities sufficient for determination.

TULARE COUNTY.
Goshen Peopl’s Ditch Near Lake Tulare Visalia Lemoore Tulare Exp’t Station
Surf’ce soil Alkali crust Surf’ce soil Surf’ce soil Alkali crust Alkali crust
Soluble salts in 100 parts soil 1.40 0.83 1.26
Potassium sulfate small
[E]Potassium nitrate small
Potassium carbonate (Saleratus) 18.80
Sodium sulfate (Glauber’s salt) 44.24 1.22 31.30[F] 13.4 chiefly 32.8
Sodium carbonate (Sal-soda) 32.98 88.09 18.2 45.3 36.16
Sodium chlorid (Common salt) 16.74 1.00 4.4 little 31.16
[E]Sodium phosphate 1.97 0.22 10.4
Calcium sulfate (Gypsum) little
Magnesium sulfate (Epsom salt) 8.1 moderate
Organic matter 1.59 9.21 7.5 5.37
KERN COUNTY.
Alkali crusts from the Smyrna artesian belt. Townships 25 and 26 R. 23 E. W. S. W. from Delano, S. P. R. R. Summer. Kern Island
No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 No. 8 Alkali crust Alkali crust
Soluble salts in 100 parts soil
Potassium sulfate 4.72
[E]Potassium nitrate
Potassium carbonate (Saleratus)
Sodium sulfate (Glauber’s salt) small moderate moderate moderate large small small small 19.20 70.61
Sodium carbonate (Sal-soda) 14.82
Sodium chlorid (Common salt) large moderate large large small large small large 37.14 4.13
[E]Sodium phosphate
Calcium sulfate (Gypsum) small small small small small small small small 0.96 0.08
Magnesium sulfate (Epsom salt) small small small small small small small small 18.31
Organic matter 20.87

F. Common and Glauber’s salts.
50. Adobe Soils.—In many parts of the arid regions of this country
which can be recovered for agricultural purposes by irrigation the soil has
peculiar characteristics.
The name adobe as commonly used applies to both the sundried bricks of
the arid regions of the West and Southwest, and to the materials of which
they are composed. The material is described by Russell[34] as a fine grained
porous earth, varying in color through many shades of gray and yellow,
which crumbles between the fingers, but separates most readily in a vertical
direction. The coherency of the material is so great that vertical scarps will
stand for many years without forming a noticeable talus slope.
Distribution.—The area over which adobe forms a large part of the
surface has not been accurately mapped, but enough is known to indicate
that it is essentially co-extensive with the more arid portions of this country.
In a very general way it may be considered as being limited to the region in
which the mean annual rain-fall is less than twenty inches. It forms the
surface over large portions of Colorado, New Mexico, Western Texas,
Arizona, Southern California, Nevada, Utah, Southern Oregon, Southern
Idaho, and Wyoming. Adobe occurs also in Mexico and may there reach a
greater development than in the United States, but observations concerning
it south of the Rio Grande are wanting.

In the United States it occurs from near the sea-level in Arizona, and
even below the sea-level in Southern California, up to an elevation of at
least six or eight thousand feet, along the eastern border of the Rocky
Mountains, and in the elevated valleys of New Mexico, Colorado, and
Wyoming. It occupies depressions of all sizes up to valleys having an area
of hundreds of square miles. Although occurring throughout the arid region,
it can be studied to best advantage in the drainless and lakeless basins in
Nevada, Utah, and Arizona.
Composition.—When examined under the microscope, the adobe is seen
to be composed of irregular, unassorted flakes and grains, principally
quartz, but fragments of other minerals are also present. An exhaustive
microscopic study has not been made, but the samples examined from
widely-separated localities were very similar. The principal characteristics
observed were the extreme angularity of the particles composing the deposit
and the undecomposed condition of the various minerals entering into its
composition. It is to be inferred from this that the material was not exposed
even to a very moderate degree of friction, and had not undergone subaerial
decay before being deposited. Adobe collected, at typical localities is so
fine in texture that no grit can be felt when it is rubbed between the fingers;
in other instances it contains angular rock fragments of appreciable size.
The composition of the material is illustrated by the following analyses:

Analyses of Adobe.

By L. G. Eakins.

Constituents. No. 1. No. 2. No. 3. No. 4.
Sante Fe, New Fort Wingate, New Humboldt, Salt Lake City,
Mexico. Mexico. Nevada. Utah.
SiO₂ 66.69 26.67 44.64 19.24
Al₂O₃ 14.16 0.91 13.19 3.26
Fe₂O₃ 4.38 0.64 5.12 1.09
MnO 0.09 trace 0.13 trace
CaO 2.49 36.40 13.91 38.94
MgO 1.28 0.51 2.96 2.75
K₂O 1.21 trace 1.71 trace
Na₂O 0.67 trace 0.59 trace
CO₂ 0.77 25.84 8.55 29.57
P₂O₅ 0.29 0.75 0.94 0.23
SO₃ 0.41 0.82 0.64 0.53
Cl 0.34 0.07 0.14 0.11
H₂O 4.94 2.26 3.84 1.67
Organic 2.00 5.10 3.43 2.96
matter

99.72 99.97 99.84 100.35

51. Vegetable Soils.—The heavy soils whose origin has been described
are essentially of a mineral nature. The quantity of organic matter in such
soils may vary from a mere trace to a few per cent, but they never lose their
mineral predominance. When a soil on the other hand is composed almost
exclusively of vegetable mold it belongs to quite another type. Such soils
are called tule, peat or muck. In this country there are thousands of acres of
peat or muck soils; the largest contiguous deposits being found in Southern
Florida. The origin of these soils is easily understood. Whenever rank
vegetation grows in such a location as to secure for the organic matter
formed a slow decay there is a tendency to the accumulation of vegetable
mold in shallow water or on marshy ground and where conditions are
favorable to such accumulations. In Florida the muck soils have been
accumulated about the margins of lakes. During the rainy season the
marshes bordering these are partly covered with water, but the vegetation is

very luxuriant. The water protects the vegetable matter from being
destroyed by fire. It therefore accumulates from year to year and is
gradually compacted into quite a uniform mass of vegetable mold.
The composition of the muck is illustrated in the following table which
shows the character of the layers at one, two and three feet in depth:[35]

Carbon. Hydrogen. Nitrogen. Volatile matter.
1 foot 57.67 per cent 4.48 per cent 2.24 per cent 90.60 per cent
2 feet 47.07 „ 5.15 „ 1.40 „ 72.00 „
3 feet 8.52 „ 0.53 „ 0.31 „ 15.00 „

In this sample, No. 3, the muck was only three feet deep, resting on pure
sand. As the bottom of the deposit is approached the admixture of sand
becomes greater and the percentage of organic matter less.
No reliable estimate of the time which has been required to form these
deposits can be given, but in the Okeechobee region in Florida the deposit
of vegetable mold in some places exceeds ten feet in depth.
The purest muck or peat soils contain only small quantities of potash and
phosphoric acid, and especially is this true of the Florida mucks which have
been formed of vegetable growth containing very little mineral matter.
It is not at all probable that the flora now growing on any particular area
of virgin peat contains all the plants that have contributed to its formation.
The principal vegetable growths now going to make up the muck soils of
Florida are the following:

Common names. Botanical names.
Saw grass Cladium effusum
Yellow pond lily Nymphea flava
Maiden cane grass Panicum Curtisii
Alligator Wampee Pontederia cordata
Sedge Cyperus species
Fern brake Osmunda „
Mallow Malva „
Broom sedge Andropogon „
Arrow weed Sagittaria „

The above are only the plants growing in the greatest profusion and do
not include all which are now contributing to increase the store of vegetable
débris.
52. Humus.—The active principle of vegetable mold is called humus, a
term used to designate in general the products of the decomposition of
vegetable matter as they are found in soils. In peat and muck are found a
mixture of humus with undecomposed or partially decomposed vegetation.
According to Kostytchoff[36] vegetable matter decays under the influence
of molds and bacteria. Molds alone produce the dark colored matters which
give soils rich in vegetable matter, their color. One chief characteristic of
humus is its richness in nitrogen. Black Russian soil contains from 4 to 6.65
per cent of nitrogen. This soil is estimated to contain sixty million
organisms per gram and much of the nitrogen which it holds must be in the
form of proteids. The first development in decaying vegetable matter is of
bacteria and there is a tendency of the decaying matter to become acid. This
causes a decay of the bacteria and the ammonia produced by this neutralizes
the acid. The various kinds of mold grow when the reaction becomes
neutral. Afterwards the bacteria and the molds develop together. This
statement of Kostytchoff is not a very satisfactory explanation of even our
limited knowledge of the decomposition of organic matters in the soil.
Ammonia and ammonia salts are formed not by the decay of some forms of
bacteria but by the activities of other forms. Warington found that in
nitrification there were three distinct forms of bacteria concerned in the
final products of ammonia, nitrites, and nitrates. Humus always contains
easily decomposable matter and consequently the rate of decay at any
observed periods is nearly the same. In humus which is produced above the
water-level Kostytchoff states that all trace of the vegetable structure is
destroyed by the leaves being gnawed and passed through the bodies of
caterpillars and wire-worms. Under the water-level the vegetable structure
is preserved and peat results. The decay of humus is most rapid in drained
and open soils. For this reason the presence of clay in a soil promotes the
accumulation of humus. Inferior organisms are the means of diffusing
organic matter through the soil. The mycelia of fungi grow on a dead root
for instance, ramify laterally and thus carry organic matter outward and
succeeding organisms extend this action and the soil becomes darkened in
proportion. Humic acid in black soil is almost exclusively in combination
with lime.

A more common view of the difference between the formation of humus
above and below the water-level is that above the water-level there is a very
free access of air and even the harder parts of the leaf skeleton can be
oxidized through the agency of bacteria, while under the water-level there is
a very limited supply of air and this oxidation cannot proceed as rapidly.
The harder parts of the leaf skeleton are preserved, and from the freer
access of air humus is oxidized more readily in drained and open soils, and
accumulates in clay soils where there is less circulation of air.
The real composition of humus is a matter which has never been
definitely determined. Composed of many different but closely related
substances it has been difficult to isolate and determine them.
Stockbridge[37] gives the following composition of the bodies which form
the larger part of humus:

Ulmin and Ulmic Acid.
Carbon 67.1 per cent Corresponding to C₄₀H₂₈O₁₂ + H₂O.
Hydrogen 4.2 „
Oxygen 8.7 „

Humin and Humic Acid.

Carbon 64.4 per cent Corresponding to C₂₁H₂₄_O₁₂ + 3H₂O
Hydrogen 4.3 „
Oxygen 31.3 „

Crenic Acid.

Carbon 44.0 per cent Corresponding to C₁₂H₁₂O₈?
Hydrogen 5.5 „
Nitrogen 3.9 „
Oxygen 46.6 „

Apocrenic Acid.

Carbon 34.4 per cent Corresponding to C₂₄H₂₄O₁₂?
Hydrogen 3.5 „
Nitrogen 3.0 „
Oxygen 39.1 „

He further states that there are, aside from these humus compounds,
others still less known and the action of which is not yet understood; among
them xylic acid, C₂₄H₃₀O₁₇, saccharic acid, C₁₄H₁₈O₁₁, glucinic acid,
C₁₂H₂₂O₁₂, besides a brown humus acid containing carbon, 65.8 per cent,
and hydrogen, 6.25 per cent, and a black humus acid yielding carbon, 71.5
per cent, and hydrogen, 5.8 per cent.
According to Mulder humic acid has the following composition,
C₆₀H₅₄O₂₇, while Thenard[38] ascribes to it the formula, C₂₄H₁₀O₁₀.
At the present time we can only regard the various forms of humus
bodies as mixtures of many substances mostly of an acid nature and
resulting from a gradual decomposition of organic matter under conditions
which partially exclude free access of oxygen.
For analytical purposes it is only necessary to separate these bodies by
the best approved processes. A further knowledge of their composition can
then be derived by determining the percentages of carbon dioxid and water
which they yield on combustion.
53. Soil and Subsoil.—Many subdivisions have been made of the above
varieties of soil, but they have little value for analytical purposes. For
convenience in description for agricultural purposes, the soil, however, is
further divided into soil and subsoil. In this sense the soil comprises that
portion of the surface of the ground, usually from four to nine inches deep,
containing most of the organic remains of plants and animals and in which
air circulates more or less freely for the proper humification of the organic
matter, which usually gives a darker color to the soil than to the subsoil.
The subsoil proper lies below this, and has usually more characteristic
properties, especially in respect of color and texture, as it has been less
influenced by artificial conditions of cultivation and the remains of
vegetation.
The subsoil extends to an indefinite depth and is limited usually by
deposits of undecomposed or partly decomposed rock matter, or by layers
of clay, sand or gravel.
Inasmuch, however, as the influence of the subsoil on growing crops is of
little importance below the depth of eighteen inches the analysis of samples
from a greater depth has more of a geologic than agricultural value.
Hilgard regards as subsoil whatever lies beneath the line of change, or
below the minimum depth of six inches. But should the change of color

occur at a greater depth than twelve inches, the soil specimen should
nevertheless be taken to the depth of twelve inches only, which is the limit
of ordinary tillage; then another specimen from that depth down to the line
of change, and then the subsoil specimens beneath that line. The depth to
which the last should be taken will depend upon circumstances. It is always
desirable to know what constitutes the foundation of a soil to the depth of
three feet at least, since the question of drainage, resistance to drought, etc.,
will depend essentially upon the nature of the substratum. But in ordinary
cases ten or twelve inches of subsoil will be sufficient. The sample should
be taken in other respects precisely like that of the surface soil, while that of
the material underlying this subsoil may be taken with less exactness,
perhaps at some ditch or other easily accessible point, and should not be
broken up like the other specimens.
In the method of soil sampling adopted by the Royal Agricultural College
of England, the soil is regarded as that portion of the surface of the ground
which is reached by ordinary tillage operations, generally being from six to
nine inches deep; the subsoil is that portion which is ordinarily not touched
in plowing.

AUTHORITIES CITED IN PART FIRST.
1. Comptes rendus, Tome 110, p. 1271.

2. Wyatt, Phosphates of America, p. 66.

3. Engineering and Mining Journal, August 23, 1890.

4. American Journal of Science, Vol. 41, February, 1891.

5. Preliminary Sketch of Florida Phosphates, Author’s edition, pp. 18, et seq.

6. Journal für praktische Chemie, 1st series, Band 38, S. 388.

7. Annual Report Connecticut Experiment Station, 1890, p. 72.

8. Annual Report Massachusetts Experiment Station, 1887, p. 233.

9. Bulletin 21, Rhode Island Experiment Station, 1893.

10. Chemical Composition of Food-Fishes. Report of U. S. Commissioner of Fish and Fisheries,
1888, pp. 679 et seq.

11. G. Brown Goode, American Naturalist, Vol. 14, July, 1890.

12. Comptes rendus, Tome 101, 1885, pp. 65, et seq.

13. Royal Agricultural Society Journal, Vol. 13, 1852, pp. 349 et seq.

14. Gîtes Mineraux, par Fuchs et DeLauny, Tome 1, p. 425.

15. El Salitre de Chile; René F. LeFeuvre y Artūro Dagnino, 1893, p. 12.

16. Crampton, American Chemical Journal, Vol. II, 1890, p. 227.

17. Potash, pamphlet of German Kali Works, pp. 3, 4.

18. Gîtes Mineraux, p. 429.

19. Bulletin of the Philosophical Society of Washington, Vol. II, p. 142.

20. Handbook for the Department of Geology of the U. S. National Museum, by Geo. P. Merrill.

21. Vid. supra, p. 506.

22. Vid. supra, Plate 120.

23. Merrill, op. cit. p. 521.

24. Merrill, op. cit. p. 536.

25. Merrill, op. cit. p. 545.

26. Merrill, op. cit. p. 547.

27. Mineral Physiology and Physiography, p. 251.

28. Bulletin No. 52, United States Geological Survey, p. 16.

29. bis (p. 48), Vid. supra, p. 38.

30. The Formation of Vegetable Mold through the Action of Worms.

31. Rocks and Soils, pp. 131–2.

32. Comptes rendus, Tome 110, p. 1370.

33. Bulletin No. 83, California Experiment Station.

34. Geological Magazine, Vol. 7, No. 6, pp. 291–92.

35. Wiley, Agricultural Science, 1893, pp. 106 et seq.

36. Travaux de la Société des Naturalistes St. Petersburg, Tome 20, 1889.

37. Rocks and Soils, p. 134.

38. Beilstein’s Handbuch der Organischen Chemie, Band I, Ss. 891–2.

PART SECOND.

TAKING SAMPLES OF SOIL FOR ANALYSIS.

54. General Principles.—It would be unwise to attempt to give any
single method of taking soil samples as the only one to be practiced in all
circumstances. In the methods which follow it is believed will be found
directions for every probable case. The particular method to be followed
will in each case have to be determined by circumstances.
The sole object in taking a sample of soil should be to have it
representative of the type of soils to which it belongs. Every precaution
should be observed to have each sample measure up to that standard.
The physical and chemical analyses of soils are long and tedious
processes and are entirely too costly to be applied to samples which
represent nothing but themselves.
The particular place selected for taking the samples as well as the method
employed are also largely determined by the point of view of the
investigations. The collection of samples to illustrate the geologic or
mineralogical relations of soils is quite a different matter from gathering
portions to represent their agricultural possibilities. In a given area the sum
of plant food in the soil would only be determined by the analyses of
samples from that particular field, while samples illustrating geologic
relations could or should be taken at widely distant points. Again the
chemist is content with a sample of a few grams in weight while the
physicist would require a much larger quantity. Much popular ignorance
exists respecting the importance of the collection of soil samples. As an
illustration of this may be cited a recent instance in which a sample of soil
was received by the author with a request for a complete analysis and a

statement of the kinds of crops it was suited to grow. No data relating to the
locality in which the sample was taken accompanied this request. The
sample itself, which weighed a little less than 3.6 grams, was not a soil at
all in an agricultural sense but a highly ferruginous sand.
The collector of samples who understands the purpose for which he is
working will find among the approved methods which follow some one or
some combination of methods, by means of which his work can be made
successful. In these cases it is the collector rather than the method on which
reliance must be placed to secure properly representative samples.
55. General Directions for Sampling.—The locality having been
selected which presents as nearly as possible the mean composition of the
field a square hole is dug with a sharp spade to the depth of eighteen inches.
The walls of this hole should be smooth and perpendicular. The soil to the
depth of six to nine inches is then removed from the sides of the hole in a
slice about four inches thick; or the sample of soil may be taken to the depth
indicated by a change of color. Any particles which fall into the bottom of
the hole are carefully collected and added to the parts adhering to the spade.
The whole is thrown into a suitable vessel for removal to the laboratory.
The sample of soil having been thus secured, the subsoil is taken in the
same way. To insure uniformity in the samples, it is well to take several of
them from the same field. Where more than one sample is taken it is
advisable to mix all the sub-samples in the field, remove large sticks,
stones, roots, etc., and take a general sample of from three to five
kilograms. The character of the débris, etc., removed should be carefully
noted.
It is sometimes desirable to take samples of the subsoil to a greater depth
than eighteen inches. A post-hole auger or large wood auger will be found
very useful for this purpose. It is rarely necessary to take samples of subsoil
to a greater depth than six feet. In taking samples the geologic formation
and the general topography of the field should be noted, also the character
of the previous crops, kind and amount of fertilizers employed, character of
drainage and any other data of a nature to give a more accurate idea of the
forces which have determined the physical and chemical properties of the
sample.
56. Method Of Hilgard.—Hilgard[39] recommends that samples should
not be taken indiscriminately from any locality you may chance to be

interested in, but that you should consider what are the two or three chief
varieties of soil which, with their intermixtures, make up the cultivable area
of your region, and carefully sample these first of all.
As a rule, and whenever possible, samples should be taken only from
spots that have not been cultivated, or are otherwise likely to have been
changed from their original condition of virgin soils and not from ground
frequently trodden over such as roadsides, cattle paths, or small pastures,
squirrel holes, stumps, or even the foot of trees, or spots that have been
washed by rains or streams, so as to have experienced a noticeable change,
and not be a fair representative of their kind. He further suggests that the
normal vegetation, trees, herbs, grass, etc., should be carefully observed and
recorded, and spots showing unusual growth be avoided whether in kind or
quality, as such are likely to have received some animal manure or other
outside addition.
Specimens should be taken from more than one spot judged to be a fair
representative of the soil intended to be examined as an additional
guarantee of a fair average.
After selecting a proper spot pull up the plants growing on it, and scrape
off the surface lightly with a sharp tool to remove half-decayed vegetable
matter not forming part of the soil. Dig a vertical hole, like a post-hole, at
least 20 inches deep. Scrape the sides clean so as to see at what depth the
change of tint occurs which marks the downward limit of the surface soil,
and record it. Take at least half a bushel of the earth above this limit, and on
a cloth (jute bagging should not be used for this purpose, as its fibers, etc.,
become intermixed with the soil) or paper break it up and mix thoroughly,
and put up at least a pint of it in a sack or package for examination. This
specimen will, ordinarily, constitute the soil. Should the change of color
occur at a less depth than six inches the fact should be noted, but the
specimen taken to that depth nevertheless, since it is the least to which
rational cultures can be supposed to reach.
In case the difference in the character of a shallow surface soil and its
subsoil should be unusually great, as may be the case in tule or other
alluvial lands or in rocky districts, a separate example of that surface soil
should be taken, besides the one to the depth of six inches.
Specimens of salty or alkali soils should, as a rule, be taken only toward
the end of the dry season, when they will contain the maximum amount of

the injurious ingredients which it may be necessary to neutralize.
Whatever lies beneath the line of change, or below the minimum depth of
six inches, will constitute the subsoil. Should the change of color occur at a
greater depth than twelve inches the soil specimen should nevertheless be
taken to the depth of twelve inches only, which is the limit of ordinary
tillage; then another specimen from that depth down to the line of change,
and then the subsoil specimen beneath that line.
Hilgard justly calls attention to the fact that all peculiarities of the soil
and subsoil, their behavior in wet and dry seasons, their location, position
and every circumstance in fact, which can throw any light on their
agricultural qualities or peculiarities should be carefully noted and the notes
sent with the samples. Unless accompanied by such information, samples
can not ordinarily be considered as justifying the amount of labor involved
in their examination.
57. Whitney[40] suggests that a geologic map of the region to be sampled
should always be at hand and that all samples should be rejected from spots
showing local discrepancies, washings or other disturbances.
The kind of analyses to which a sample is to be subjected also largely
determines the method to be pursued in selecting it: For instance, a sample
to be used for determining the size of the particles therein, may be taken in
quite a different manner from that designed only for the determination of
moisture.
58. In the directions collated by Richards[41] and which have been largely
followed by the correspondents of the Department of Agriculture, it is
recommended to select in a field, four or five places, at least, per acre,
taking care that these places have an homogeneous aspect, and represent as
far as possible the general character of the whole ground. If the field,
however, present notable differences, either in regard to its aspect or its
fertility, the samples gathered from the different parts must be kept separate.
The sampling of arable soil should be made only after the raising of the
crop and before it has received any new manure. In other soils the sample
should be taken only from spots that have not been cultivated.
59. In the method of soil sampling adopted by the German Experiment
Stations[42] it is directed that the samples of soil should be taken according
to the extent of the surface to be sampled, in three, five, nine, twelve or
more places at equal distances from each other. They should be taken in

perpendicular sections to the depth turned by the plow; and for some studies
of the subsoil to a depth of sixty to ninety centimeters. The single samples
can be either examined separately or carefully mixed and an average
portion of the mixture taken.
60. Method of the Official French Commission.—The official French
commission[43] emphasizes the fact that the sample of soil taken for analysis,
should represent a layer of equal thickness through the total depth of its
arable part. An analysis of the subsoil taken in the same way, will often be
useful to complete the data of the soil study.
First of all, according to this authority, it is necessary to determine the
point of view from which the sample is to be taken. If the object is a general
study, having for its aim the determination of the general composition of the
soils of a definite geologic formation, the sample should be taken in such a
way that the different characteristics of the soil alone should enter into
consideration without paying any attention to its accidental components,
which have been determined by local causes, such as are produced by
continued high cultivation, the application of abundant fertilizers, or the
practice of a particular line of agriculture. The samples of soil therefore,
with such an object in view, should be taken on parts of the earth which are
beyond the reach of the causes mentioned above and which tend to modify
the nature of the primitive soil. In such a case it is the soil which has not
been modified, or better still, virgin soil, such as is found in the woodlands
and prairies, which should be taken for a sample, choosing those places in
which the geologic formation is most perfectly characterized. In such a case
a soil taken in one spot corresponding to the conditions before mentioned,
would be the best for the purposes in view. The sample would thus
represent a true type to be studied, not one of a mean composition got by
taking samples from different localities and mixing them into a
homogeneous parcel. This last method of proceeding could introduce into
the sample earth modified by culture or by influences purely accidental.
However, it would be wise, in a region characterized by the same geologic
formation, to take a certain number of samples in different localities, and
examine singly each one of them in order to be assured that there is a
uniformity of composition in the whole of the soils.
If, on the contrary, it is the purpose of the investigation to furnish
information to the cultivator concerning the fields which are worked, it is

necessary to approach the problem from a different point of view. In this
case the earth which is under cultivation should be first of all considered
with all the modifications which nature causes or practical culture has
caused, in it. But it often happens that upon the same farm the natural soil is
variable, caused either by the washings from the adjacent soils, by the
accumulation at certain points of deposits formed from standing water, or
from other reasons. In such a case it would be necessary to take samples
from every part of the field which exhibited any variation from the general
type, in order to get a complete mean sample of the whole. It is necessary to
be on guard against making a mixture of these different lots which would
neither represent the different soils constituting the farm nor their mean
composition. It would be better to examine each of these samples alone and
then from those parts which appear to have a similar composition, to take a
general sample for the mean analysis.
Most often it is necessary to confine our studies to the really important
part of the farm the composition of which would have a practical interest.
The aspect of the spontaneous vegetation in such a case, will often serve as
a guide to determine the parts of the farms which are similar in nature. The
sample should represent the arable layer, properly so-called, that is, that part
of it which is stirred by the agricultural implements in use and in which the
root system of the plant takes its greatest development and which is the true
reservoir of the fertilizing materials.
When a trench is dug in the soil it is easy to distinguish the arable layer
from the subsoil. In the first place, its color is different, generally being
modified by vegetable débris which forms the supply of humus. The depth
of the arable layer is variable, but it is most frequently between 200 and 300
millimeters. In the analysis the depth and layers should be indicated since
the chemical composition of the earth varies according as the sample is
taken to a greater or less depth. As an example of this it may be said that the
quantity of nitrogen decreases in general in proportion as the depth of the
layer is increased. The sample, therefore, should be limited exactly to the
arable layer of soil.
61. Caldwell[44] advises that according to the purpose of the analysis
samples be taken:
a, from one or from several spots in the field, in order to subject each
sample to a separate analysis; or

b, for an average representation of the soil of the whole field; in this case,
several portions of earth are taken from points distributed in a regular
manner over the field, all of which are most carefully mixed together, and
4–6 kilograms of the mixture, free from any large stones, are preserved as
the average sample.
An excavation in the soil 30–50 centimeters deep, or through to the
subsoil, and 30–50 centimeters square, with one side as nearly vertical as
possible is made and a slice taken from this side of uniform thickness
throughout, weighing 4–5 kilograms. If the subsoil is to be examined, a
sample of it should be taken out in the same manner as directed for the
upper soil, to the depth of about 60 centimeters.
If the character of the soil varies materially in different parts of the field,
samples from several spots should be analyzed separately.
A small portion of the sample should be put at once in a well-stoppered
bottle; the remainder may be allowed to become air-dried, by exposing it in
a thin layer, in summer, to the common temperature in the shade, or, in
winter, to that of a warm room, or a moderately warm drying-chamber,
heated to 30°–40°; in either case it should be carefully protected from dust.
At the time of taking the sample of the soil, observations should be made
in regard to the following points:
a. The geognostic origin of the soil.
b. The nature of the underlying strata, to the depth of 1–2 meters, if
practicable.
c. The meteorology of the locality, by consulting meteorological records,
if possible; otherwise, by the general opinion of the neighborhood; in this
connection, the height of the locality above the level of the sea should be
noted also.
d. The management and rotation of crops in previous years.
e. The character of the customary manuring.
f. The amount of the crops removed in the preceding year, and, if
possible, the average amount of each of the more important crops yielded
by the field.
g. The practical judgment of neighboring farmers in regard to the field.

Caldwel’s method is practically identical with that of Wolff[45] which was
one of the earliest of the systematic schemes for taking soil samples.
62. Wahnschaffe[46] insists on rather a fuller preliminary statement to
accompany soil samples but gives essentially the method of Wolff with
some unimportant variations which add little to the value of the process.
63. Method Of Peligot.—According to Peligot[47] the taking of samples
of soil of which the physical and chemical properties are to be determined is
a delicate operation.
These samples should represent as nearly as possible both the good and
bad qualities of a soil.
In the field selected are chosen a certain number of places at least four or
five per hectare. The spots selected should have a homogeneous appearance
—resembling as nearly as possible the general aspect of the field.
By means of a spade a few kilograms of earth are removed to the depth
of the subsoil being careful to include in the sample no accidental detritus
which the upper part of the soil especially may contain.
The samples should be taken immediately after the crop is harvested and
before any fresh fertilizer is applied. The samples are carefully mixed and
placed in a glass bottle or flask.
The sample of subsoil is obtained in the same manner. If the field
presents notable differences in surface or fertility all the samples taken
should be examined separately.
64. Method of Whitney.[48]—An ordinary wood auger, 2½ inches in
diameter is so arranged as to admit of additions to the stem to enable the
operator to take samples at different depths. It may be fitted with a short
piece of gas pipe for a handle and the several pieces of which it is
composed may be taken apart and carried in a knapsack.
In taking a soil sample the boring is continued until a change in color
shows that the subsoil has been reached. The auger cuts a very clean sample
save in excessively sandy soil. After the soil sample is secured the hole is
cleaned out and the sample of subsoil taken by the same instrument. The
soil is conveniently preserved in heavy cloth bags of which the usual size is
6 by 8½ inches. Where larger samples are required the size of the bag is
correspondingly increased. Each bag is to be tagged or labeled to
correspond with the entry in the note book.

Samples to determine the amount of empty space in a soil are taken as
follows: The sampler is a piece of brass cylinder about nine inches long and
about 1½ inches in diameter. A piece of clock spring is soldered in one end
and sharpened to give a good cutting edge. This arrangement permits the
sample to pass into the cylinder without much friction. The area enclosed
by the clock spring is accurately determined and a mark is placed in the
cylinder six inches from the cutting edge. The cylinder is driven into the
soil to a depth of six inches, a steel cap being used to prevent the hammer
from injuring the cylinder. The earth is next removed from about the
cylinder with a trowel, and the separated cylinder of earth is cut smoothly
off by a sharp knife and removed together with its brass envelope. The
sample is taken to the laboratory in a cloth bag, dried and weighed.
65. Taking Samples for Moisture Determination.—A number of brass
tubes is provided nine inches long and ¾ inch in diameter and with a mark
six inches from the bottom.
The tube is pushed down into the soil to the mark and the sample of soil
removed with the tube. There is but little danger of the sample dropping out
of the tube even in sandy soils. When the tube is withdrawn each end is
capped with a rubber finger tip making a perfectly air tight joint. The tubes
containing the samples can be kept several days with no fear of losing
moisture. This method is especially useful in having samples taken by
observers in different localities who can enclose the tubes in a cloth sack
and send them to the laboratory by mail daily or at stated intervals. A tube
of the size given holds about fifty grams of soil.
66. Taking Samples to Determine the Permeability of Soil to Water or
Air.—Whitney[49] determines the permeability of soil or subsoil to water or
air in the following manner:
An excavation two feet square and eighteen inches deep is made in the
soil. On one side of this hole the sample of soil or subsoil is taken by means
of a narrow saw blade and a sharp carving knife. The sample of soil taken
should be two inches square and 3½ to 4 inches long.
It is placed in a brass cylinder three inches long and 3¼ inches in
diameter. The open space in the cylinder is filled with paraffin heated just to
its melting point. As the paraffin cools the upper surface should be kept
stirred to prevent the mass when set from receding from the square column
of soil. Care must be taken to keep the paraffin from the ends of the soil

columns and these should be left, as far as possible in their natural
condition.
The rate of percolation of the water may be determined at the time the
sample is taken. For this purpose an additional section of brass tube two
inches deep is secured to the one holding the sample by a rubber band. An
iron rod is driven into the earth carrying a retort stand ring supporting a
funnel filled with fine gravel. The lower end of the soil column in the brass
cylinder is placed on this gravel. Water is next carefully poured upon the
top of the sample of soil being careful not to disturb the surface. The
surface of the sample may be protected with a little fine sand. The water
should be poured on the paraffin thus affording an additional protection to
the soil surface. When the water begins to drop from the funnel a graduated
glass is set under it and the time required for a given volume to pass
through under an initial pressure of two inches is noted. The volume
required represents one inch in depth over the four square inches of soil
surface, viz.: four cubic inches.
67. Sampling of Soil for Staple Crops.—Some variations from the usual
methods are recommended by Whitney when the samples are taken from
fields growing staple crops.
The immediate object of the work, for which these samples are desired, is
to make a thorough study of the physical and chemical properties of a
number of typical soils adapted to the different staple crops, such as grass,
wheat, truck, and the different types of tobacco. They should be taken for a
careful study of the texture of the soils, the relative amount and
arrangement of sand and clay, the relation of the soils to moisture and heat,
and the ease with which they can maintain a proper water supply for the
different staple crops under existing climatic and cultural conditions. The
ultimate object of such a study is to see how these conditions can be
changed so as to make the soils more productive, and make them yield a
better quality of crop, or to change the conditions in other soils, which
differ from these, so that the culture of the different staple crops can be
extended over wider areas by improved methods of cultivation and
manuring.
The soil selected for sampling for these investigations should be typical,
should represent fairly well a considerable area of land. It should represent
either the very best type of land for the staple crop or crops of the locality,

or the very poorest lands for these same crops. Both of these extremes are
desired for contrast. For example, if the staple crop of the locality is wheat
or a certain type of tobacco, select the soil best adapted to this staple crop,
and another soil, if possible, in the same locality, representing considerable
area of land upon which this staple crop cannot be successfully grown on
account of the inferior yield, quality, or the time of ripening of the crop. The
soil sampled should be, or should recently have been, under actual
cultivation in the crop or crops best adapted to it, so that the real
agricultural value of the land can be accurately known.
The samples should be taken inside the field, some distance away from
fences, roads, or trees. If there are plants growing in the field, the sample
should be taken about midway between two plants. The samples should be
taken where they will typify fairly well the average soil of the field and of
the large area of land which they are to represent.
The samples are taken in some one of the ways described herein. Each
sample should be carefully labelled at the time of taking. The following
blank form will be found convenient for this purpose:
Locality:
LABORATORY No.:
No. of sack:

Date: Description: (virgin or cultivated).
(a) Natural herbage:
(b) Crops best adapted to land (grass, wheat, tobacco, truck, barren).

Collector:

Depth of sample:
(Soil or Subsoil?) Geologic formation:
... in. to ... inches.
68. Method of the Royal Agricultural Society.[50]—Have a wooden box
made, six inches long and wide, and from nine to twelve inches deep,
according to the depth of soil and subsoil in the field. At one of the selected
places mark out a space of twelve inches square; dig around it in a slanting
direction a trench, so as to leave undisturbed a block of soil, with its
subsoil, from nine to twelve inches deep; trim this block to make it fit into
the wooden box, invert the open box over it, press down firmly, then pass a
spade under the box and lift it up and gently turn it over.

In the case of very light, sandy, and porous soils, the wooden box may be
at once inverted over the soil and forced down by pressure, and then dug
out.
Proceed in the same way for collecting the samples from all the selected
places in the field, taking care that the subsoil is not mixed with the surface
soil. The former should be sampled separately.
In preparing the plot for the gathering of the sample, take care to have it
lightly scraped so as to remove any débris which may be accidentally found
there.
The different samples thus procured are emptied on a clean, boarded
surface, and thoroughly mixed, so as to incorporate the different samples of
the same field together. The heap is then divided into four divisions, and the
opposite quarters are put aside, taking care to leave the two remaining ones
undisturbed; these are thoroughly mixed together, the heap divided into
quarters, and the opposite ones taken away as before. This operation of
mixing, dividing into quarters and taking away the opposite quarter is
continued until a sample is left weighing about ten or twelve pounds.
Thus is obtained the average sample of the soil. Of course where only a
single sample is taken from the field this method of quartering is not
resorted to, but the bottom of the box is nailed directly on and sent to the
laboratory, where the soil is to be analyzed.
69. Grandeau[51] suggests that in taking soil samples there are two cases
to be considered; first a homogeneous soil and second, a soil variable in its
appearance and composition. First, if the soil is homogeneous, being of the
same geologic formation it will be sufficient to take a mean sample in
accordance with the following directions:
The field is first divided by diagonals or by transverse lines the direction
of which need not be fixed in advance but as inspection of the form and
configuration of the field may indicate. In the ordinary conditions, of
homogeniety (marly, granite, argillaceous or silicious soils) it will be
sufficient to select about five points per hectare from which the samples are
to be taken. These points having been determined the surface is cleaned in
such a way as to remove from it the detritus which may accidentally cover
it; such as dry leaves, fragments of wood, foreign bodies, etc. The surface
having been prepared, (five to six square meters) a hole is dug four-tenths
of a meter long and as wide as the spade employed. The sides should be as

nearly vertical as possible. As to depth it varies with the usage of the
country in regard to tillage. The layer of arable earth is what in effect
properly constitutes the soil. It ought not to be mixed with any fragments of
the subsoil. When the hole is properly cleaned the samples are secured with
a spade from the sides of the excavations. About five kilograms are taken.
The soil is placed in a proper receptacle as it is removed from the hole.
This operation is repeated on as many points as may be necessary to
obtain a mean sample of the soil of the whole field.
All the samples are now collected on a table sufficiently large, and
intimately mixed together. Two samples, each of about five kilograms, are
then taken from the mixed material. One sample is immediately placed in
bottles and carefully stoppered and sealed; the other is dried in the sun or on
the hearth of a furnace. When sufficiently dry the second sample is also
placed in bottles and well stoppered. While mixing the samples, pebbles,
etc., of the size of a nut and larger are removed, the weight of the rejected
matter being determined. The nature of the pebbles should also be noted;
whether silicates, limestone, etc.
The sample of subsoil is taken in exactly the same manner, using the
same holes from which the samples of soil were taken. The nature, the
arrangement and the appearance of the strata will indicate the depth to
which the subsoil should be taken. In general, a depth equal to that of the
sample of soil will be sufficient. The depth to which the roots of cultivated
plants reach is also a good indication in taking a sample of the subsoil. In
forests the sample of subsoil should be taken from four to five-tenths of a
meter below the surface.
If the soil in respect of its geologic formation, its fertility or its physical
aspect presents great differences, special samples should be taken in each
part in accordance with the directions given above.
70. Method of the Official Agricultural Chemists.—In the directions
given by the Association of Official Agricultural Chemists[52] it is stated that
the soil selected should be as far as possible in its natural condition, not
modified by recent applications of manure, or changed by the transporting
action of water or wind. Surface accumulations of decaying leaves, etc.,
should be removed before taking the sample.
To eliminate accidental variations in the soil, select specimens from five
or six places in the field which seem to be fair averages of the soil, remove

two or three pounds of the soil, taking it down to the depth of nine or ten
inches[53] so as to include the whole depth. Mix these soils intimately,
remove any stones, shake out all roots and foreign matter, and dry the soil
until it-becomes friable.[54] Break down any lumps in a mortar with a
wooden pestle, but avoid pulverizing any mineral fragments; pass eight to
ten pounds of the soil through a sieve, having circular perforations one
twenty-fifth of an inch in diameter, rejecting all pebbles and materials too
coarse to pass through the sieve. Once more mix intimately the sifted soil.
Expose in thin layers in a warm room till thoroughly air dry (or dry it in an
air-bath at a temperature of 40°), place six to eight pounds in a clean bottle,
with label of locality and date, and cork the bottle containing the soil, for
analysis.
The soil is rapidly dried to arrest nitrification; it is not heated above 40°
lest there should be dissipation of ammonia compounds, or a change in
solubility. The normal limit to which the soil may be heated in place by the
sun’s rays should not be exceeded in preparing a sample for an agricultural
chemical analysis.
The relative amount of fragments too coarse to pass through the sieve
should be made a matter of record. They are soil material, but not yet soil,
so far as agricultural purposes are concerned.
71. Method of Lawes.—In a late method of sampling proposed by Sir J.
B. Lawes[55] a steel frame ten by twelve inches, and nine inches deep open
at top and bottom is driven into the earth until its upper edge is level with
the surface of the soil. All above-ground vegetation is then cut off as closely
as possible with scissors. The soil within the frame is then removed exactly
to the depth of the frame, and immediately weighed. It is then partially
dried, and mechanically separated by a series of sieves, all visible vegetable
matter being at the same time picked out. The stones and roots and the
remaining soil are thus separated, and the determinations of dry matter,
nitrogen, etc., are made in the separated soil after being finely powdered.
The loss of water at each stage of preparation and on drying the samples as
analyzed is also carefully determined. This method, which requires the soil
to be taken to an arbitrary depth of nine inches, could not be used when
samples of strictly arable soil are to be taken.
72. In taking a sample by the French commission[56] method it is
necessary to remove from the surface, the living and dead vegetation which

covers the soil. With a spade a square hole is then dug to the depth of about
500 millimeters; in other words, to a depth considerably exceeding that of
the arable layer. Afterwards on each of the four sides of the hole there is
removed by the spade, a prismatic layer of the arable portion of a thickness
equal to its depth. The samples thus obtained are united together and
carefully mixed for the purpose of forming a sample for analysis. If there
are large stones they are removed by hand and their proportion by weight
determined.
In all cases it would prove useful to take a sample of the subsoil which is
far from playing a secondary rôle. The rootlets bury themselves deeply in it
and seek there a part of their nourishment. The subsoil, therefore, furnishes
an important addition to the alimentation of the plants. For taking a sample
of the subsoil a ditch is dug of sufficient depth, say one meter, and the
arable soil carefully removed from the top portion. Afterwards pieces are
taken from the four sides of the hole at variable depths, which should
always be indicated, and which should extend in general, from six to eight-
tenths of a meter below the arable soil since it is demonstrated that the roots
of nearly all plants go at least to this depth. The analysis of the subsoil,
however, is less important than that of the soil, properly so-called, because
the agronomist does not act directly upon it and takes no thought of
modifying it and enriching it as he does the layer of arable soil. But the
composition of the subsoil is a source of information capable of explaining
certain cultural results and capable sometimes, of leading to the correct way
of improving the soil, as in cases where the subsoil can be advantageously
mixed with the superficial layer.
73. Wolff[57] suggests that a hole thirty centimeters square be dug
perpendicularly and a section from one of the sides taken for the sample. To
the depth of thirty centimeters the sample shall be taken as soil and to the
additional depth of thirty centimeters as subsoil. The thickness of the
section taken may vary according to the quantity of the sample desired. For
analytical purposes, five kilograms will usually be sufficient. When culture
experiments are also contemplated a larger quantity will be required.
74. Method of Wahnschaffe.—The method of sampling advised by
Wahnschaffe[58] is but little different from that of Wolff already mentioned.
A square sample hole is dug with a spade having its sides perpendicular
to the horizon. The soil which is removed is thrown on a cloth and carefully

mixed. From the whole mass a convenient amount is next removed care
being taken not to include any roots. In a similar manner it is directed to
proceed for the sample of subsoil. At first the subsoil should be removed to
a depth of two to three decimeters. The number and depth of subsequent
samples will depend chiefly upon the character of the soil. Where samples
are taken to the depth of two meters the use of a post-hole auger is
recommended.
The samples taken should not be too small. In general from two to three
kilograms should remain after all preliminary sampling is finished.
75. Method of König.—The directions given by König[59] for taking soil
samples are almost identical with those prescribed by Wahnschaffe and do
not require any further illustration.
76. Special Instruments Employed in Taking Samples.—In general a
sharp spade or post-hole auger is quite sufficient for all ordinary sampling
but for certain special purposes other apparatus may be used.
The instrument which is used by King[60] consists of a thin metal tube of a
size and length suited to the special object in view, provided with a point
which enables it to cut a core of soil smaller than the internal bore of the
tube and at the same time make a hole in the ground larger than its outside
diameter. Its construction is shown in figure 11, in which A B represent a
soil tube intended to take samples down to a depth of four feet. A′ is a
cross-section of the cutting end of the tube, which is made by soldering a
heavy tin collar, about three inches wide, to the outside of a large tube
allowing its lower end to project about one-half an inch. Into this collar a
second one is soldered with one edge projecting about one-quarter of an
inch and the other abutting directly against the end of the soil tube. Still
inside of this collar is a third about one-half an inch wide which projects
beyond the second and forms the cutting edge of the instrument.

Figure 11.

The construction of the head of the tube is shown at B′. It is formed by
turning a flange on the upper end of the tube and then wrapping it closely
with thick wire for a distance of about three inches, the wire being securely
fixed by soldering. The soil tube should be of as light weight as possible not
to buckle when being forced into the ground, and the cutting edge thin. The
brass tubing used by gas fitters in covering their pipes has been found very
satisfactory for ordinary sampling. With a one inch soil tube four feet long
it is possible to get a clear continuous sample of soil to that depth by simply
forcing the tube into the ground with the hand and withdrawing it, or the
sample may be taken in sections of any intermediate length. Later in the
season when the soil becomes dryer it is necessary to use a heavy wooden
mallet to force the tube, and this should be done with light blows.
The closeness with which it is possible to duplicate the samples in weight
by this method will be seen below, where from each of four localities three
samples were taken from the surface to a depth of four feet.
Showing Variations in the Dry Weight of Triplicate Samples of Soil.
A. B. C.
I. Surface to four feet 716.6 gms. 715.5 gms. 710.3 gms.
II. Surface to four feet 715.4 gms. 687.1 gms. 731.2 gms.
III. Surface to four feet 654.0 gms. 688.3 gms. 709.0 gms.
IV. Surface to four feet 714.0 gms. 687.8 gms. 719.3 gms.
These four series of samples were taken at the four corners of a square
twelve feet on a side and serve to show how much samples may vary in that
distance. The large difference shown in III, A is due to the fact that the soil
tube penetrated a hole left by the decay of a rather large root as shown by
the bark in the sample.
77. Auger for Taking Samples.—It has already been said that the
ordinary auger used for boring fence post-holes may be used to advantage
in taking soil samples. Large wood augers can also be used to advantage for
the same purpose. For special purposes, however, other forms of augers
may be used.
Norwacki and Borchardt[61] have described a new auger for taking
samples of soil for analytical purposes.
In figure 12, A, B and C show the general exterior and interior form of
the instrument. The handle is hollow and made of iron gas pipe covered
with leather. On the inside of this, in the middle, is fixed a wooden plug a,

which leaves two compartments,
one in each end for holding the
brass plug bb,’ and the wicker
lubricating wad cc.’ The stem of
the auger a, is heavy and made of
eight-sided steel and the under
end is strengthened with a heavy
casting fitting into the auger guide
g g. The end of the auger I I′ is
triangular and hardened. The
auger guide g g, is made out of a
single piece of drawn steel tubing.
Above it is strengthened by a ring-
Figure 12. shaped piece of iron or copper and
its lower end is furnished with
saw teeth as shown in K and is
hardened. The fixing key e, is bent in the form of a hook and can be passed
through the two holes o o, of the auger stem and through the one hole o′ in
the strengthened part of the auger guide. It permits the auger guide to be
fixed upon the auger stem in two different positions, higher and lower. On
one end it is cut squarely across and on the other provided with a conical
hole drilled into it. It fits on the one hand exactly in the auger guide and on
the other loosely plays in the cavity of the handle at b, designed to hold it
when not in use. The cap d′ is made of heavy sheet brass and is fastened
upon the end of the handle at c c′ after the manner of a bayonet. The wicker
cartridge is made of rolled and sewed wicker-work. At the upper end it is
provided with a metallic button and before use it is saturated with paraffin
oil. It fits on the one side firmly in the auger guide and on the other in the
cavity, of the handle c where it is kept when not in use. The union h is made
of a brass tube which below is closed with a piece of solid brass upon the
inside of which a hole is bored. In this hole rests the end of the auger stem
when the union is placed firmly upon the auger guide.
The auger is placed together as is shown in A B, the union h is taken off
and it is driven with gentle blows, turning it back and forth, to the proper
depth into the soil. After the key is loosened the auger is lifted high enough
so that the second hole appears and then it is fixed in position by the key.
Then the boring is continued, turning the auger to the right, by which the

auger, eating its way with its saw teeth, presses deeper into the ground and
withdraws the material for analysis. After the auger guide has been filled
through any desired length, say five to ten centimeters with the sample of
soil, the whole auger is drawn out of the soil, the key removed, the auger
stem withdrawn from the auger guide, the apparatus opened by turning the
bayonet fastening of the stopper on the handle, the brass plug placed in the
end and then with the smooth part forward, from above, it is allowed to fall
into the auger guide until it reaches the soil. The auger stem is then put
back, the point of it fitting into the hole of the plug and the sample of soil
shoved out of the auger guide. The auger guide is again fixed on the auger
stem by the key and then the apparatus is ready for a second operation.
When the borings cease the wicker cartridge is drawn out of the handle and
shoved, the soft end forward, from above, into the auger guide and the brass
plug after it and pushed through with the auger stem. By this process the
wicker cartridge gives up a sufficient amount of paraffin oil to completely
grease the inside of the auger guide and to protect it from rust. After use the
instrument should be cleaned on the outside by means of a cloth, the plug
and wicker wad replaced in their proper positions, the cap fixed on the
handle and the union on the point of the instrument.
The length of the whole apparatus may reach one meter or more; the
internal diameter sixteen millimeters. The apparatus weighs with a length of
one meter, together with all its belongings, about two kilograms. For the
investigation of peat and muck soils as well as sand, instead of the steel
auger guide one of brass or copper can be used. For this purpose the length
of the apparatus may reach three to four meters.
In comparison with other apparatus which are used for taking samples, it
appears without doubt that with the one just described a better and less
mixed portion of the soil can be obtained at great depths. The apparatus is
said to have many advantages over a similar one known as Fraenkel’s, and
is much more easy to clean. The advantages of the apparatus are said to be
the following: The farmer with this piece of apparatus in a short time can go
over his whole farm taking samples to the depth of ninety centimeters since
a single boring does not take more than one minute. Geologists and others
interested in the soil at greater depths can use an apparatus three to four
meters in length and obtain unmixed samples from these lower depths.
These are also interesting from a bacteriologic point of view. The entire
apparatus is especially valuable for the investigation of the lower parts of

peat and muck soils. The apparatus has been tried in the collection of
samples for the laboratory of the Department of Agriculture and is too
complicated to be recommended for ordinary use. When however samples
are to be taken at great depths as in peat soils it is highly satisfactory.
78. Soil Sampling depends for its success more on the judgment and
knowledge of the collector than on the method employed and the apparatus
used. One skilled in the art and having correct knowledge of the purpose of
the work will be able to get a fair sample with a splinter or a jack-knife
while another with the most elaborate outfit might fail entirely in collecting
anything of representative value.
There are some special kinds of soil sampling, however, which cannot be
left to the method of the individual and it is believed that with the
descriptions given above nearly all purposes for which samples are desired
may be served.
For the study of nitrifying organisms, however, special precautions are
required and these will be noted in a more appropriate place.
In taking samples for moisture determinations the method of Whitney is
recommended as the best. For the general physical and chemical analytical
work the standard methods are all essentially the same. The principles laid
down by Hilgard will be found a sufficient guide in most cases.

TREATMENT OF SAMPLE IN THE LABORATORY.

79. The Sample, or mixed sample, taken by one of the methods above
described, is placed on a hard smooth board, broken up by gentle pressure
into as fine particles as possible and all pieces of stone and gravel carefully
removed and weighed; all roots, particles of vegetable matter, worms, etc.,
are also to be weighed and thrown out. This can be done very well by using
a sieve of from one to two millimeter mesh. Care should be taken that the
soil be made to pass through, which can be accomplished by subjecting the
lumps to renewed pressure with a rubber-tipped pestle. In the above
operation the soil should be dry enough to prevent sticking. The relative
weights of the pebbles, roots, etc., and the soil should be determined.
80. Order of Preliminary Examination.—Hilgard[62] commences the
examination of a soil sample by washing about ten grams of it into a beaker
with a water current of definite velocity, stirring meanwhile actively the part
carried into the vessel. The residue not carried by the current is examined
macro- and microscopically to determine the minerals which may be
present, and the condition in which the fragments exist—whether sharp or
rounded edges, etc.
This examination will give some general idea of the parent rocks from
which the sample has been derived and of the distance the particles have
been transported. Next follows the hand test, viz., rubbing the soil between
the thumb and fingers first in the dry state and afterwards kneading it with
water and observing its plasticity. Following this should come a test of the
relations of the sample to water, viz., its capacity for absorbing and retaining
moisture. Finally the separation of the soil into particles of definite
hydraulic value and a chemical examination of the different classes of soil
concludes the analytical work.
81. Air Drying.—The sifted soil should be thoroughly mixed and about
one kilogram spread on paper and left for several days exposed in a room
with free circulation of air and without artificial heat. The part of the sample
to be used for the determination of nitrates should be dried more quickly as

described in another place. The sample is then placed in a clean, dry glass
bottle, corked, sealed, and labeled. The label or note book should indicate
the locality where the sample was taken, the kind of soil, the number of
places sampled, and other information necessary to proper description and
identification.
82. Caldwell[63] directs that having taken the sample to the laboratory, the
stones and larger pebbles should be separated from the finer parts by the
hand, or by sifting with a very coarse sieve, and examined with reference to
their mineralogical character, weight and size, making note, in this last
respect, of the number that are as large as the fist or larger, the number as
large as an egg, a walnut, hazel-nut, and pea, or give the percentage of each
by weight.
Pulverize the air-dried soil in a mortar with a wooden pestle, and separate
the fine earth by a sieve with meshes three millimeters wide; this sieve
should have a tightly fitting cover of sheepskin stretched over a loop, and it
should be covered in the same manner underneath, so that no dust can
escape during the process of sifting.
Wash the pebbles and vegetable fibers remaining on the sieve with water,
dry and weigh the residue; the water with which this gravel was washed
should be evaporated to dryness at a temperature not exceeding 50° towards
the close of the evaporation, and the residue mixed with what passed
through the dry sieve.
The sifted fine earth is reserved for all the processes hereinafter
described, and is kept in well-stoppered bottles, marked air-dried fine earth.
The sieve mentioned above is too coarse for the more modern methods of
analysis.
83. Wolff[64] directs that the air-dried earth (in summer dried in thin layers
at room temperature, in winter in ovens at 30° to 50°) be freed from all
stones, the latter washed, dried, and weighed. The soil is next passed
through a three millimeter mesh sieve, the residual pebbles and fiber
washed, dried and weighed. The fine earth passing the sieve is used for all
subsequent examinations. It is air-dried at moderate temperatures and
preserved in stoppered glass vessels.
84. The French[65] commission calls especial attention to the method of
subsampling, and prescribes that the sample of earth which has been taken
in the manner indicated, and of which the weight should be greater as the

material is less homogeneous should not be analyzed as a whole. It should
be divided into two parts. The first includes the finer particles constituting
the earth, properly so-called, with the elements which alone enter into play
in vegetable nutrition and on which it is necessary to carry out the analysis.
The second embraces the coarser particles to which only a superficial
examination should be given and which may have a certain importance
from a physical point of view but which cannot take any part from a
chemical point of view, in the nutrition of plants. It is, however, useful to
examine its mineralogical constitution and to look for the useful elements
such as lime, potash, etc., which it may be able to furnish to the earth, and
in proportion as it is decomposed, finer particles which may be useful in
plant nutrition.
How are we to distinguish between the fine and coarse elements? All
grades of fineness are observed in the soil, from the particles of hydrated
silica so small that with the largest magnifying power of the microscope it
is scarcely possible to distinguish them, up to grains of sand which are of
palpable size and visible to the naked eye, and extending to pebbles of
varying sizes. All intermediate stages are found between these and if it
should be asked what is the precise limit at which it is necessary to stop in
distinguishing the fine from the coarse elements of the soil, the answer is
that this can only be determined by a common understanding among
analysts. In general, it may be said, that the mark of distinction should be
the separation which can be secured with a sieve having ten meshes per
centimeter.
85. Loose Soils.—Having agreed upon a sieve of the above size, the
process of separation in loose soils is as follows: The earth is exposed to the
air and when the touch shows that it is sufficiently dry the conglomerated
particles should be simply divided without breaking the rocky material
which exists in a state of undivided fragments. There are some special
precautions to be taken. Rubbing in a mortar must be forbidden since it
reduces the earth to particles which are unnatural in size, by securing the
breaking up of the fragments consisting of the débris of rocks. When it is
possible the earth should be rubbed simply in the hand and after having
separated that which passes the sieve, the large particles which have not
passed should be again rubbed with the hand, until all the particles which
can be loosened by this simple treatment have passed the sieve. The
separation should be as complete as possible in order that a sample of the

particles passing the sieve should represent as nearly as possible, a correct
sample of the fine particles of the soil.
In regard to the pebbles, they should be washed with water upon the
sieve in order to carry through the last of the particles of earth adhering to
them. They are then dried and their weight taken. The fine part of the earth
is also weighed. On an aliquot part, say 100 grams, the moisture is
determined and then by simple calculation the whole sample of the air-dry
soil can be calculated to the dry state. The sample is then placed in a glass
flask.
The pebbles are examined with a view of determining their mineralogical
constitution; as for instance, on being touched with a little hydrochloric acid
it can be determined whether or not they are carbonate of lime. The nature
of the rock from which they have been derived is often to be determined by
a simple inspection.
86. Compact Soils.—If the soils are not sufficiently loose to be treated as
before described, it is necessary to have recourse to other means of division,
which should not, however, be sufficiently energetic to reduce the rocky
elements to fine particles. For this purpose the earth may be broken by
means of a wooden mallet, striking it lightly and separating the fine
elements from time to time by sifting. A wooden roller may also be used
with a little pressure, for breaking up the particles or a roller made out of a
large glass bottle. These methods will permit of a sufficiently fine division
of the soil without breaking up any of the pebbles. Sometimes, however, a
soil can not be broken up by such treatment. It is then necessary to have
recourse to the following process: The soil is thoroughly moistened and
afterwards rubbed up with water. The paste which is thus formed, is poured
upon the sieve and washed with a stream of water until all the fine particles
are removed. The wash water and the fine particles are left standing until
the silt is thoroughly deposited when the supernatant water is poured off
and the deposited moist earth is transferred into a large dish and dried on a
sand or water-bath. In this way a firm paste is formed which can be worked
up with the hand until rendered homogeneous and afterwards an aliquot
portion be taken to determine moisture.
87. Method of Peligot.—The method recommended by Peligot[66] for the
preparatory treatment of the sample is essentially that already described.
The sample is at first dried in the air and then in an oven at 120°. When dry

and friable 100 grams are placed in a mortar and rubbed with a wooden
pestle. It is then passed through a sieve of ten meshes per centimeter. The
largest particles which remain in the sieve should have about the
dimensions of a pin’s head. The stones are separated by hand. They should
be shaken with water in order to detach any pulverulent particles adhering
thereto. The turbid water resulting from this treatment is added to that
which is used in separating the sand from the impalpable part of the soil.
88. Wahnschaffe prescribes[67] in the further preparation of the sample
for analysis that the coarse pieces up to the size of a walnut be separated in
the field where the sample is taken and their relative weight and
mineralogical character determined. The soil sample is then to be placed in
linen or strong paper bags and carefully labelled. In order to avoid any
danger of loss of label the description or number of the sample should be
put on the cloth or paper directly.
The sample when brought to the laboratory should be spread out to dry,
in a room free of dust. In the winter the room should be heated to the usual
temperature. The air drying should continue until there is no sensible loss of
weight. The samples then are to be placed in dry, glass-stoppered glass
bottles where they are kept until ready for examination. This method of
keeping the samples avoids contact with ammonia or acid fumes with which
a laboratory is often contaminated.
89. The Swedish chemists[68] direct that samples which are to be used for
chemical examination in the manner described below, are most
conveniently brought to such a condition of looseness and humidity that the
soil feels moist when pressed between the fingers without, however,
sticking to the skin. To prepare the sample in this manner, spread it in a
large porcelain dish or on a glass plate in a place where it is not reached by
the laboratory atmosphere; stir it frequently till it assumes the mentioned
humidity (if the sample when sent is too dry, moisten it with distilled water
till its condition is as indicated); then pulverize carefully between the
fingers and finally sift through a sieve with five millimeter holes. In this
way free the sample from stones, undecayed roots and similar parts of
plants, pieces of wood, and other matter strange to the soil, which remain
on the sieve; mix the sample carefully and put it into a glass bottle provided
with a stopper well ground in; keep it in a cool place. Samples prepared in

this way will usually contain 20–30 per cent moisture; boggy soils 60–80
per cent and peat soils 50 per cent.
90. Petermann[69] follows the method below in preparing samples of soil
for analysis.
The soil is gently broken up by a soft pestle and all débris if of organic
nature, cut fine with scissors. About 2500 grams of this soil are passed
through a one millimeter mesh sieve. The organic débris is removed by
forceps, washed free of adhering earth dried at 120° and weighed. The
nature of the organic débris should be noted as carefully as possible.
The pebbles and mineral débris not passing the sieve are worked in a
large quantity of water by decantation. They are also dried at 120° and
weighed. This débris is examined mineralogically and thus some idea of the
origin of the soil obtained.
91. The various methods for the preliminary treatment as practiced by the
best authorities have been somewhat fully set forth in the foregoing résumé.
The common object of all these procedures is to get the soil into a proper
shape for further physical and chemical examination and to determine the
comparative weights of foreign bodies contained therein.
The essential conditions to be observed are the proper sifting of the
material and avoidance of mechanical communition of the solid particles
too large to pass the meshes of the sieve. If possible the material should be
passed through a sieve of one millimeter mesh. In cases where this is
impracticable a larger mesh may be used, but as small as will secure the
necessary separation. Before final chemical analysis a half millimeter mesh
sieve should be employed if the soil be of a nature which will permit its use.
Over-heating of the sample should be avoided. Rapid drying is advisable
when the samples are to be examined for nitrates.
The method recommended by the French commissions seems well
adapted to the general treatment of samples, but the analyst must be guided
by circumstances in any particular soil.

AUTHORITIES CITED IN PART SECOND.
39. Bulletin 38, pp. 61–2.

40. Ms. communication to author.

41. Bulletin No. 10.

42. Landwirtschaftliche Versuchs-Stationen, Band 38, Ss. 309 et seq.

43. Annales de la Science Agronomique, Tome 1, Part 2, p. 240.

44. Agricultural Chemical Analysis, p. 166.

45. Zeitschrift für analytische Chemie, Band 3, S. 87.

46. Anleitung zur Wissenschaftlichen Bodenuntersuchung, S. 17.

47. Traité de Chimie Analytique, p. 149.

48. Bulletin 35, p. 108.

49. Op. cit.

50. Bulletin 10, p. 33.

51. Analyse des Matières Agricoles, p. 131.

52. Bulletin 38, p. 200.

53. This in some instances would include a part of the subsoil.

54. All soils do not become friable on drying.

55. Journal of the Royal Agricultural Society, (2), Vol. 25, p. 12.

56. Annales de la Science Agronomique, Tome 1, Part Second, pp. 240 et seq. The personnel of
the commission is as follows: MM. Risler, Grandeau, Joulie, Schloesing, and Müntz.

57. Vid. 7.

58. Anleitung zur Wissenschaftlichen Bodenuntersuchung, S. 17.

59. Untersuchung Landwirtschaftlich und Gewerblich Wichtiger Stoffe, S. 5.

60. Seventh Annual Report of the Wisconsin Agricultural Experiment Station, p. 161.

61. Deutsche Landwirtschaftliche Presse, Band 19, No. 35, Ss. 383–4.

62. Journal American Chemical Society, Vol. 16, p. 36.

63. Agricultural Chemical Analysis, p. 168.

64. Vid. 7.

65. Vid. 16.

66. Vid. 9.

67. Vid. 8, p. 19.

68. Methods of Analysis of Soils, Fertilizers, etc., adopted by the Swedish Agricultural
Chemists, translated for the author by F. W. Woll.

69. L’Analyse du Sol, p. 14.

PART THIRD.

PHYSICAL PROPERTIES OF SOILS.

92. The Soil as a Mass.—The soil constituted as indicated in the
preceding pages, is now brought to the analyst for investigation. The
properties with which he first becomes acquainted are those which impress
his senses as mass characteristics. There is a perception of color,
consistence, weight and other features which the soil possesses as a whole.
The several constituents of the soil must first be considered as molecular
and mole aggregates. In other words, the soil in its natural state is a
mechanical mixture of particles which must first be considered as a whole.
The physical properties of the soil, therefore, should engage the attention of
the analyst before he proceeds to the investigation of the properties of its
several constituents as classified by the relative size or hydraulic value of
the particles of which they are composed, or to a chemical determination of
the compounds or elements therein contained.

DETERMINATION OF PHYSICAL PROPERTIES.

93. Color.—The color of a soil depends chiefly upon the proportion of
organic matter and iron compounds which it contains and the state of
subdivision of its particles. When a soil contains a large amount of organic
matter, especially when this organic matter is in an advanced state of decay,
it assumes more or less a black color when moist. This black color is to be
distinguished from the black alkali tint which is produced by the action of
carbonate of soda on organic matter. The naturally black color of a soil
containing a large amount of organic matter depends, however, either upon
the action of mineral matters upon this organic matter, as in the case of the
black alkali mentioned, or upon the blackish color of carbon resulting from
the slow combustion of the organic matter during the period of decay.
The presence of a large amount of ferric oxid in soil gives the well-
known red color so well-marked in the soils of southwestern Kentucky and
other portions of the United States. The preponderance of sand in a soil
tends to produce a light yellow or whitish tint, while certain kinds of clay
have a bluish tint probably due to the presence of ferrous salts. The
influence of the color of the soil upon the color of the vegetation is also
well-marked, the black soils as a rule producing a much deeper green tint of
foliage than the light colored soils. This effect should not be attributed to
color alone for as a matter of fact highly colored soils are usually very close
and very retentive of moisture, which is one reason, probably, for their not
being more highly oxidized. Such soils will produce a more vigorous and
ranker growth of vegetation, but it is the texture of the soil and the more
moist condition which it maintains, rather than the color, which produce the
deeper green tint of foliage.
The color of a soil is also used as an index of its fertility, the black and
red soils being usually the most fertile.
It may be well to add here the probable reason as given by Whitney for
this, viz., that the deeper color shows that the oxids of iron and the organic
compounds have less oxygen and indicate that the soils are quite retentive
of moisture and rather tend to the exclusion of air, so that part of the oxygen
of the iron compounds and of the organic matters has been used up in the

oxidation processes within the soil. It is known, for example, that wood
oxidizes much more rapidly around a rusty nail than where it is simply
exposed to the air, the iron oxid acting as a carrier between the oxygen of
the air and the organic matter. In a sandy soil, on the contrary, where there
is usually less moisture and much freer circulation of air, the iron
compounds have more oxygen and usually have a light yellow color. If this
sand is heated, however, with the exclusion of air, and especially in the
presence of organic matters, part of this oxygen will be given off and there
will be the same red color as in the heavier clay soils. It is frequently
noticed, also, in compact clays that where air gains access through cracks or
root-holes, the color is altogether modified.
94. Determination of Color.—There is no process which will give
experimentally and accurately the color of a soil sample. The changes
which the color of a soil undergoes in passing from a saturated to an
anhydrous state are well-marked. The analyst will have to be content with
giving as nearly as possible a description of the color of the sample when
taken and the changes which it undergoes in air drying or on heating in a
bath to 100°–110°, or in heating to redness with or without exclusion of the
air. These changes in color will give some indication of the character of the
organic and mineral matters present.
95. Odoriferous Matters in Soil.—It is known that the soil emits a
peculiar odor which is not disagreeable except when it has been recently
wet, for instance, after a short rain. Several attempts have been made to
discover the nature of this odor. These researches have established the fact
that the essential principle of this odor resides in an organic compound of a
neutral nature of the aromatic family and which is carried by the vapor of
water after the manner of a body possessing a feeble tension. The odor is
penetrating, almost piquant, and analogous to that of camphorated and quite
distinct from other known substances. In regard to the quantity of this
substance, it is extremely minute and can be regarded as being only a few
millionths of a per cent.
According to Berthelot and André[70] this new principle is neither an acid
nor an alkali nor even a normal aldehyd. It is, in a concentrated aqueous
solution, precipitable by potassium carbonate with the production of a
resinous substance. Heated with potash it develops a sharp odor similar to
the aldehyde resin. It does not reduce the ammoniacal nitrate of silver.

Treated with potash and iodin it gives an abundant formation of iodoform,
which, however, is a property common to a great number of substances. For
the qualitative and quantitative estimation of the odoriferous matter the
following process is employed:
About three kilograms of the soil are mixed with sand containing a small
amount of carbonate of lime and some humic substance; after having freed
it from all organic débris which is visible, it is placed in a glass alembic.
The soil should contain from ten to twelve per cent of water at least. The
alembic is placed in a sand bath and is kept at 60° for several hours. The
water evaporated is condensed until about seventy-five cubic centimeters
are distilled over. This distilled water is again rectified so as to obtain in all
about twenty cubic centimeters. The odoriferous matter appears to be nearly
all contained in this twenty cubic centimeters. The liquid thus obtained
shows an alkaline reaction; it contains some ammonia and reduces
ammoniacal silver nitrate. This last reaction is due to some pyridic alkali or
analogue thereof, and is cause for it to be distilled anew with a trace of
sulfuric acid which gives a neutral liquor deprived of all reducing action but
which preserves the odor peculiar to the soil. The twenty cubic centimeters
obtained as before are subjected to two additional distillations and in the
final one only one cubic centimeter of liquid is distilled over.
The peculiar odor is intensified proportionately as the volume of the
liquid is decreased. To this one cubic centimeter, is added some pure
crystallized potassium carbonate. The liquor is immediately troubled and
some hours are required for it to become clear again. Meanwhile there is
formed upon its surface a resinous ring almost invisible, amounting at most
to from ten to twenty milligrams of a matter which has not been identified
with any known principle. The reactions described above, however, permit
of its general character being known. This resinous matter contains the
odoriferous principle, the composition of which is not yet definitely known.
96. Specific Gravity.—The density of a soil depends on its composition,
the fineness of its particles and upon the packing which it has received. It
has in other words an apparent and a real specific gravity. It is easy to see
that a soil in good tilth would weigh less per cubic foot than one which had
been pressed closely together, as in a road or well-pastured field. Ordinary
soils in good tilth have an apparent specific gravity of about 1.2, and when
entirely free from air, a real specific gravity of about 2.5. If the apparent

specific gravity of a soil sample were 1.2 and the air were removed, leaving
a vacuum in the interstices of the soil, the apparent specific gravity would
not be sensibly increased. The figure 1.2 is the apparent specific gravity of a
mixture of soil material which is about 2½ times heavier than water, and of
an extremely small proportion by weight of air which is about 1000 times
lighter than water. The figure 2.5 is about the true specific gravity of the
real soil material, and shows that this material is about 2½ times heavier
than an equal volume of water.
The weights of a cubic foot of different kinds of soil as given by
Schübler[71] are as follows;

Pounds.
Sand 110
Sand and clay 96
Common arable soil 80 to 90
Heavy clay 75
Vegetable mold 78
Peat 30 to 50

In general the specific gravity of soil decreases inversely as its content of
humus.
97. Determination of Specific Gravity.—The ordinary method of
proceeding to determine the true specific gravity is by means of a
pyknometer. The pyknometer should have a capacity of from twenty-five to
fifty cubic centimeters.
From ten to fifteen grams of earth dried to constant weight at 100° are
taken, boiled for a time with a few cubic centimeters of water to remove air
and poured into the pyknometer. All soil particles are washed out of the
vessel in which the boiling took place into the pyknometer with freshly
boiled distilled water and after cooling to the temperature at which the
calibration took place, the pyknometer is filled with distilled water at the
given temperature and weighed. If the soil contain materials soluble in
water, alcohol of definitely known specific gravity may be employed and
the number thus obtained calculated to a water basis.
The calculations when water is used are made as follows:

Grams.
Weight of pyknometer 13.4789
„„ pyknometer full of distilled water at 20° 62.8934
„„ water in pyknometer 49.4145
„„ dry soil taken 10.0000
„„ pyknometer + dry soil + filled with water at 20° 67.9834
„„ soil and water 54.5045
„„ water 44.5045
„„ water displaced by ten grams soil 4.9100

Then specific gravity = 10.000 ÷ 4.9100 = 2.04.
98. Specific Gravity of Undried Soils.—It is often desirable to
determine the specific gravity of an undried portion of the soil. For this
purpose a portion of the sample is dried at 100° to determine its percentage
of moisture. The specific gravity is then determined on a ten gram sample
of the undried soil as just given. The actual weight of soil taken is
calculated from the percentage of moisture obtained in the first instance. In
the case given if the percentage of moisture at 100° be ten then the actual
weight of dry soil taken is nine grams. This number is therefore used in
making the calculations. In all statements of specific gravity taken in the
manner described the temperature at which the pyknometer is calibrated
should be stated and all weighings where water is involved made at that
degree.
99. Volume of Soil.—If it be desired to calculate the volume occupied by
a soil it is easily done by dividing the weight of water displaced by the
weight of one cubic centimeter of water of the temperature at which the
determination took place.
In the case given one cubic centimeter of water at 20° weighs 0.998259.
Then 4.9100 ÷ 0.998259 = 4.9186 cubic centimeters = volume occupied by
ten grams of dry soil excluding interstitial spaces between particles.
100. Volumetric Methods.—The water displaced by a given weight of
soil may also be measured volumetrically by the method of Knop.[72]
Place 200 grams of the soil in a flask of from three to five hundred cubic
centimeters capacity. Add a measured quantity of water, and shake
thoroughly to eliminate air, and fill up to the mark from a burette. The
quantity of water required to complete the volume subtracted from the

number expressing the volume of the flask will give the volume of water
displaced by the earth.
Another method consists in thoroughly shaking about thirty grams of the
soil in a graduated cylinder with fifty cubic centimeters of water containing
a little ammonium chlorid and after twenty-four hours recording the volume
occupied by the whole. The increase in volume over fifty cubic centimeters
shows the quantity of water displaced. This method may also be used to
determine the volume occupied by a soil when saturated with water. The
above methods are only to be used when approximately correct results are
all that are desired.
101. Apparent Specific Gravity.—The apparent specific gravity of a
soil is obtained by dividing its volume, interstitial spaces included, by the
weight of an equal volume of water.
The real and apparent specific gravities of six samples of soil are given
below.[73]

Real specific gravity 2.5445, 2.6315, 2.6508, 2.6400, 2.7325, 2.6603
Apparent specific gravity of air-
dried soil 1.0940, 1.1710, 1.3570, 1.2810, 1.4060, 1.2730
Apparent specific gravity of soil
dried at 125° 1.0990, 1.1770, 1.3750, 1.2910, 1.4640, 1.2850

It is to be noted that in computing the apparent specific gravity of a soil
dried at 125° the volume occupied by the water is assumed to occupy the
same space as if it existed in a free state. The volume of this water is
therefore to be subtracted from the contents of the flask before proceeding
with the computations.
102. Determination of Apparent Specific Gravity.—Place in small
quantity portions of the air-dried sample properly prepared, into an open
glass cylinder, holding one liter, and about 170 millimeters high (if the
height is exactly the mentioned one, the diameter of the cylinder will be
86.6 millimeters); pack the sample by striking the bottom of the cylinder
hard against the palm of the hand after each new filling; close the cylinder
thus filled by a glass plate and weigh on a balance sensitive to 0.1 gram;
deduct the weight of the cylinder and glass plate, and the weight of one liter
of soil in approximately similar conditions as it is found on the dry land
prepared for cultivation, is thus ascertained. The weight of one liter of the

soil in grams multiplied by 2000 will give in kilograms the weight of the
surface soil from a hectare (2.47 acres) of the field from which the sample
is taken when the depth of this is calculated at twenty centimeters.[74]

RELATION OF THE SOIL TO HEAT.

103. Sources of Soil Heat.—The heat of the soil comes from three
sources, viz.: solar heat, as the sun’s rays, heat of chemical and vital action
within the soil, and the original heat of the earth’s interior. The latter is
sensibly a constant quantity, and of great value to plants. The heat of
chemical and vital action is not great in amount except in a few special
cases but is often, as in germination, of the greatest importance to plant
growth. The sun, therefore, remains the greatest source of heat of practical
importance in relation to the production of crops. Dark-colored soils,
absorbing most and radiating the fewest rays, must attain the highest
temperature. Schübler’s classical researches on soil temperatures, show that
there is at times a difference of over 7° in temperature between white and
black soils, all other conditions being alike. Schübler’s researches, being
made on dry soils in the laboratory, do not, however, apply wholly to
conditions in the field.
104. Influence of Specific Heat.—The heat which a soil receives and
retains is largely due to the specific heat of the soil. The specific heat of a
body is expressed by a number which shows the amount of heat necessary
to raise a given weight of the body 1° of temperature, as compared with the
amount necessary to raise the same weight of water 1°. The specific heat of
the soil is usually between 0.20 and 0.25, while that of water taken as the
standard is unity.
105. Influence of Moisture.—The moisture of the soil possesses great
influence on the soil temperature, so much so that a dry, light-colored soil
may attain a greater degree of warmth than a moist, dark-colored one. The
action of water in reducing soil temperature is easily explained. In our
latitude, we see the water in all its forms, solid, liquid, and gaseous, and we
know that these forms are the direct result of temperature. The changing of
water from the solid to the liquid or gaseous form is performed at the
expense of heat; the more water evaporated from the soil the more heat
must be used for the evaporation. Therefore, the more water contained in

the soil at any given time the lower must be its temperature during
subsequent exposure to sun heat because of the greater evaporation. The
experiments of Liebenberg, Pattner, Schübler and Dickenson have
practically settled all the questions of soil temperatures. The radiation of
heat from the soil, and the consequent cooling propensity of the latter, are
directly proportional to the absorptive power of the soil. Two soils of like
absorptive power towards heat possess, as a rule, equal radiating power.
In a general way, it can be said the greater the heating capacity and
conductivity of a soil the more readily and rapidly does it give off its heat
and become cooled.
106. Absorption of Solar Heat.—The quantity of heat absorbed from the
sun by the earth is an important factor in the growth of vegetation. As has
been established in the physics of heat, a black surface, other things being
equal, will absorb a larger amount of heat than one of any other color; so,
other things being equal in the physical and chemical composition of a soil,
variations in the amount of organic matter producing greater or less black
coloration will affect the heat absorption. Thus, black soils, in the
conditions above mentioned, will absorb more heat than lighter colored
soils. As a result, the vegetation in such soils gets an earlier start in the
Spring and matures more rapidly. As an illustration of this it may be noted
that the black prairie soils of Iowa produce uniformly crops of maize which
are matured before the early frosts, while crops grown on lighter soils much
farther South often suffer injury from that source.

DETERMINATION OF SPECIFIC HEAT.

107. General Principles.—The quantity of heat stored in any given
weight of soil is capable of being measured and compared with the quantity
stored in an equal weight of water at the same temperature. The ease,
however, with which disturbing influences operate during the determination
makes the manipulation somewhat difficult. The specific heat of the
containing vessels must be carefully determined. Fortunately this has been
done for most materials and the data thus obtained are recorded in standard
works on physics. The material operated on must be protected from thermal
influences from sources not controlled by the experiment and even the heat
of the operator’s body may often disturb the conduct of the work. The
general conditions which should control the experiment as well as the
details thereof are given in the following method which, however, the
ingenious analyst may profitably simplify.
108. Method of Pfaundler.—The process of estimating the specific heat
of soils by the method of mixture, is essentially that of Regnault and is
described as follows by Pfaundler[75].
The apparatus used is illustrated in Fig. 13.
A and A′ show the heating apparatus. It consists of a vessel of sheet iron
in which a test tube E is fixed by means of a cork. The test tube holds the
soil whose specific heat is to be determined. The apparatus contains water,
which is brought to the boiling point by means of a lamp, and the excess of
steam is conducted away, as indicated in the figure, through one of the axes
of the apparatus; the opposite axis is, of course, closed. It requires about
thirty-five minutes boiling to bring the contents of the test tube to the
temperature of the aqueous vapor. The exact temperature at which the water
boils is determined by observing the barometer at the time and consulting a
table of the boiling temperature of water at different barometric pressures.
The calorimeter is shown in the figures B and B′. It consists of a wooden
box closed on one side by a glass plate G and on the other to the heighth F

by a small board on which a calorimeter of ordinary construction is placed.
The cylinder of the calorimeter is seventy millimeters high and forty-seven
millimeters in diameter.

Figure 13.

Regnault’s Apparatus for Determining the Specific Heat of Soils.

This part of the apparatus is supported by triangular pieces of cork. A
delicate thermometer is fastened to the top of the box of the calorimeter and
the value of the degrees is so arranged that about twelve of them correspond
to about one degree C. The scale of the instrument can be arbitrarily fixed
and the temperature of any part of it determined by comparison with a
delicately graduated thermometer.
Near the thermometer in the calorimeter is a stirrer made of a very thin
copper disk with a bent rim. This stirrer is operated by means of a silk cord
moved by appropriate machinery.
The reading of the thermometer is made through a glass plate and this
should be protected from the heat of the body of the observer by a paper
screen.
The test tube E is first filled with the substance, whose specific heat is to
be determined, and weighed. It is then placed in the water bath until

constant weight is reached. After constant weight has been obtained the
apparatus is again dried and the exact weight of the moisture lost thus
determined. The test tube is then placed in the apparatus A closed with a
well-fitted cork, the top covered with cotton and heated in the aqueous
vapor for about one hour. The heating apparatus should be far removed
from the calorimeter so that the temperature of the latter cannot be
influenced thereby. Meanwhile the calorimeter is filled with water which
has stood in the room for a long time until it has acquired, as nearly as
possible, the room temperature.
The quantity of water is such that the water value of the whole of the
calorimeter together with the immersed portions of the thermometer and
stirrer shall amount to exactly 100 grams. A few minutes before bringing
the substance into the calorimeter, the stirring apparatus is put in motion
and the temperature observations are commenced. These should be at
intervals of twenty seconds and should be continued until ten observations
have been made. Meanwhile the height of the barometer is also read. A few
seconds before the tenth interval the apparatus A is brought quickly to the
calorimeter and its contents emptied into it at the moment of the tenth
interval. The apparatus A should be removed as quickly as possible after its
contents are emptied.
After the introduction of the substance and its thorough incorporation
with the water of the calorimeter by the stirring apparatus, the thermometer
is again read, at intervals of twenty seconds, until its maximum has been
reached and as much longer thereafter as may be necessary to show that an
appreciable fall of temperature has taken place. The test tube, in which the
substance was heated is weighed and the exact quantity of the added
substance thus determined.
In order that the sample of soil may be easily removed from the test tube
in which it is heated, it is best to have it molded into appropriate forms
before being placed in the heating tube. This is easily accomplished by
pressing it into molds of convenient shape and of a size so that six or eight
pieces (best of cylindrical shape) will be necessary to give the quantity
sufficient for the experiment. Since some soils will not retain their shape
after molding, the molds may be made of zinc foil whose water values in
the calorimeter are previously determined and they can be placed with their
contents in the calorimeter thus securing the total immersion of all the

particles of soil in the water. With very dusty materials, it is necessary that
these little cylinders should be closed with pieces of foil at the ends in order
to prevent the particles of dust from escaping and rising to the surface of the
water.
Another source of error consists in the solution of the soluble salts which
the soil may contain. This is avoided by the use of turpentine instead of
water. If the cylinder containing the soil be made water-tight, this danger
from the solubility of the salts in water is avoided. Another method of
correcting these errors is in making a blank experiment in which a quantity
of the earth taken is kept at the temperature of the water in the calorimeter
until both are of the same temperature. The earth is then mixed with the
water and the change of temperature produced noted. In this way the
corrections made necessary by the solution of the salts in water and other
causes are determined.
109. Method of Calculating Results.—Let t represent the mean
temperature of the beginning period of the experiment, and v equal the loss
in heat per interval. Let t′ and v′ represent the same values for the end
period. Let θ₁, θ₂, θ₃, etc., represent the temperature at the end of the first,
second and third intervals of the middle period and θ₀ the temperature at the
beginning of the middle period and θₙ the end temperature of of the middle
period. Let τ₁, τ₂, τ₃, ... τₙ, represent the mean temperature of the single
intervals; then τ₁ = Θ₀ +2 Θ₁; τ₂ = Θ₁ +2 Θ₂, and τₙ = Θn–12+ Θₙ. The constant C
represents the correction which must be applied in order to determine the
true increase of temperature in the calorimetric system. The expression θₙ −
θ₀ + C represents the true temperature increase of the calorimetric system
which we may represent by Δθ and θₙ + C represents the true maximum,
that is, the end temperature, which by exclusion of external influences is
reached. The correction C, as already indicated, is to be added to θₙ − θ₀
when it is positive and is to be subtracted therefrom when it is negative. The
numerical value of C is usually very small, and, in the experiments
indicated, varied between zero and one division of the thermometer
employed, that is it seldom exceeded one degree.
110. Illustration.—The method of determining value of specific heat is
best illustrated by an example:

In one determination the water value of the calorimetric system,
including stirrer and thermometer was 2.50 grams, the weight of water
added was 97.50 grams and the total water value of the system 100 grams.
The substance was dried at 100° and weighed in five envelopes:

Total weight 31.423 grams.
The envelopes alone weighed 10.654 „
Weight of the soil taken 20.769 „

The envelopes holding the soil were made of brass with zinc ends, the
specific heat of which is 0.0939 and the water value of the whole of the
envelopes was 1.0004 grams. Since, however, the ends were soldered on
with zinc the true water value was somewhat smaller being equal to 0.8692
gram. The data of the observations were as follows:

Corrected height of barometer 699.6 millimeters.
Intervals between the observations 20 seconds.

No. of Temperature on the arbitrary scale
Observations. of the thermometer.
{0 162°.6
First Period {10 162°.9 = θ₀ (Moment of
immersion.)

{11 185°.0
{12 200°.0
{13 206°.1
{14 209°.5
{15 210°.7
Second {16 211°.3
Period {17 211°.5 Differences.
{18 211°.5 0
{19 211°.5 0
{20 211°.5 0
{21 211°.5 0
{22 211°.4 –0°.1
= θₙ
–0°.1
–0°.1
{23 211°.3
{24 211°.2 –0°.1
{25 211°.1 –0°.1
Third {26 211°.0 –0°.1
Period {27 210°.9 –0°.1
{28 210°.8 –0°.1
{29 210°.6 –0°.2
{30 210°.5 –0°.1

From the twenty-second interval, the regular fall of temperature begins
and 211°.4 is therefore taken as θₙ. The mean temperature of the beginning
period is therefore 162°.6 +2 162°.9 = 162°.75 = t. The value of v is 162°.610− 162°.9 = –
0°.03. For the end period the value of t′ is 211°.4 +2 210°.5 = 210°.95 and the value
of v′ is 211.4 −8 210.5 = + 0.11. Then the sum of the observations from eleven to
twenty-one inclusive = Σ′n–1θ = 2280.1

θ₀ + θₙ = 187.15
2
The sum = 2467.25
nt = 1953.00
Difference 514.25
This difference multiplied by v − v′ = 0.14
gives a product equal to 71.995
This product divided by t′ − t = 48.20
gives a quotient equal to 1.49
nv = –0.36
The sum = 1.13 =C

Then Δθ = θₙ − θ₀ + C = 211°.4 − 162°.9 + 1°.13 = 49°.63. The true end
temperature = θₙ + C = 212°.53. The zero point of the thermometer =
24°.70, and the actual rise of temperature = 187°.83. The rise of
temperature due to the proximity of the warming apparatus at the beginning
was found by experiment to be equal to 0°.1 of the division of the scale. On
comparing the thermometer used with a standard centigrade scale it was
found that one division of the calorimetric thermometer was equal to
0°.0858. Converting these numbers into expressions of the centigrade scale
we have the following summary:

The true rise of temperature, Δθ = 4°.25
The true end temperature, θₙ + C = 16°.10
The temperature of the steam, as determined by the height of the barometer, was equal
to 97°.70

From these data the specific heat is calculated according to the following
formula:
1 100 × 4.25
Σ = 20.769 × (97.70 − 16.10 − 0.8692) = 0.2089.

From this formula the following rule for calculating specific heat is
deduced:
Multiply the water value of the calorimetric system by the true rise in
temperature in degrees Celsius and divide the product by the difference
between the temperature of boiling water under the conditions of the
experiment and the true end temperature. From the quotient subtract the

water value of the envelopes holding the soil sample. Divide the remainder
by the weight of soil taken.
111. Variations in Specific Heat.—Different soils deport themselves
very differently in respect of specific heat. In a large number of soils
examined by Pfaundler, the specific heats were found to vary from 0.19 to
0.51. The highest specific heat was observed in the case of a peaty soil.
Next to peaty soils came those soils which were highest in humus, and in
general it was found that the specific heat varied directly with the humus
content.

SOIL THERMOMETRY.

112. General Principles.—The measurement of the temperature of the
soil at stated depths is often of use in analytical processes connected with
agricultural chemistry and physics. The general principles on which the
process rests, depend on bringing the bulb of the thermometer into as
intimate contact as possible with the particles of soil at the depth required,
disturbing as little as possible the normal state of the soil particles.
In the thermometer chiefly used for this purpose in this country, the stem
is strong and carries the degrees figured on the glass. The whole is inclosed
in a wooden case which is cut away to expose the face of the scale. The
scale is about eleven inches long. The part which enters the soil is of
varying lengths, according to the depth at which the temperature is desired.
113. Method of Procedure.—An excellent method of determining soil
temperatures and of recording results is well illustrated by Frear.[76]
The thermometers are set in niches cut in a trench, the earth being
afterwards carefully tamped about the bulbs to secure a good contact, the
trench being filled at the same time. The surface of the soil is freed from
vegetation and kept in good tilth.
The depths at which observations are made are at the surface and one,
three, six, twelve, and twenty-four inches. The soil tested was moderately
dark and loamy to a depth of seven inches and below that a stiff clay. Solid
rock existed at from five to seven feet below the surface. Readings were
made three times a day.
114. Method of Stating Results.—The individual readings of the
thermometers should be entered at the time they are made. At the end of
each month the mean of the readings should be determined, together with
the maxima and minima, and a comparison made between the mean
readings of the temperature of the air and maxima and minima. As a sample
of the method of stating these mean results the data are given for the month

of May, 1891, for the atmosphere, surface, and for the depths mentioned
above:

MAY.
T° Fahrenheit.
Atmosphere.
Monthly mean 57.1
Maximum 85.0
Minimum 31.0
Mean daily range 22.5
Greatest daily range 32.0
Least daily range 8.0
Surface.
Monthly mean 56.7
Extremes.
Maximum (10th of month) 77.0
Minimum (5th) 36.0
Mean maximum 65.2
Mean minimum 49.9
Range.
Monthly 41.0
Mean daily 14.9
Greatest daily (19th) 25.0
Least daily (21st) 4.0
One Inch.
Monthly mean 56.8
Extremes.
Maximum (10th) 74.5
Minimum (5th) 36.5
Mean maximum 62.9
Mean minimum 49.5
Range.
Monthly 38.0
Mean daily 11.9
Greatest daily (10 and 19) 20.0
Least daily (23rd) 1.0
Three Inches.
Monthly mean 56.7
Extremes.
Maximum (31st) 71.0
Minimum (6th) 40.0
Mean maximum 60.9

Mean minimum 49.7
Range.
Monthly 31.0
Mean daily 9.3
Greatest daily (19th) 15.5
Least daily (23rd) 1.5
Six Inches.
Monthly mean 56.3
Extremes.
Maximum (31st) 66.0
Minimum (6th and 7th) 43.0
Mean maximum 56.7
Mean minimum 53.2
Range.
Monthly 23.0
Mean daily 4.65
Greatest daily (8 and 19) 8.5
Least Daily (5th) 1.0
Twelve Inches.
Monthly mean 55.6
Extremes.
Maximum (31st) 64.0
Minimum (6th and 7th) 46.0
Mean maximum 56.6
Mean minimum 54.4
Range.
Monthly 18.0
Mean daily 2.18
Greatest daily (8th) 4.5
Least daily (3rd and 20th) 0.0
Twenty-Four Inches.
Monthly mean 53.1
Extremes.
Maximum (31st) 58.0
Minimum (6th and 8th) 48.0
Mean maximum 53.4
Mean minimum 52.8
Range.
Monthly 10.0
Mean daily 0.48
Greatest daily (23rd) 2.0

Least daily (on 12 days) 0.0

115. Method of Whitney and Marvin.[77]—The thermometer devised by
Whitney and Marvin is shown in Fig. 14. The principle on which this
modification depends is as follows:
A mercurial thermometer of the ordinary construction is liable to give
wrong indications of the temperature because it is difficult to determine the
temperature of the column of mercury from the bulb to the surface of the
ground. To avoid this source of error the thermometer figured was
constructed.
The bulb of the thermometer is made quite small and a slender portion of
the stem extends into its spherical portion. The top portion of the
thermometer stem does not differ in any essential respect from the stem of
an ordinary thermometer.
The bulb is almost wholly filled with alcohol, which acts as the principal
thermometric fluid and has the advantages of a high coefficient of
expansion. The thermometer bulb and the stem of the thermometer up to a
point convenient for graduation, are filled with mercury. In the drawing the
mercury is represented by the heavy black marking in and just above the
small bulb. The peculiar construction at this point is for the purpose of
retaining the mercury about the point of the slender capillary stem inside
the bulb and preventing the entrance of alcohol into the stem when the
thermometer is horizontal.
In order to register the maximum and minimum temperatures a short
column of alcohol is placed in the upper portion of the stem, above the
mercury, and within this are arranged two small steel indexes, so
constructed that they will not slide in the tube of their own weight, but are
easily pushed upward by the mercury column or pulled downward by the
top meniscus of the alcohol column. The indexes are set by means of a
small magnet, the one being drawn down upon the top of the mercurial
column and the other raised up against the meniscus of the alcohol column.
The rise of the mercury carries its index upward, leaving it to register the
highest point reached, while the alcohol meniscus withdraws the other
index and leaves it at a point representing the minimum temperature. It
remains only to mention that the graduations are fixed in the usual way,
having reference only to the positions of the mercurial column. Beyond the

highest point supposed to be reached by the
mercury, say about 120°, the graduations are
extended in an arbitrary manner. The scale
numbers represent temperatures by the mercurial
column and are continued in regular sequence
beyond the 120°. On this plan the readings for
minimum temperatures are on a purely arbitrary
scale and are converted into true degrees of
temperature by use of a table prepared for each
thermometer, which table embodies as well all
the corrections for instrumental error.
The arrangement of the alcohol columns above
the mercurial column and the indexes are shown
enlarged at one side of the illustration. The
readings of the maximum temperature are made
from the bottom end of the index next to the
mercurial column. The minimum temperature is
the reading of the top of the uppermost index.
Thus in the figure the maximum temperature
indicated is 76.5°, and the minimum 125.7°,
which, by reference to the table of correction for
this thermometer, No. 10, is found to be 53.3°.
The use of mercury in the stem of the
thermometer not only admits of the use of the
index for registering the maximum temperature,
but possesses the additional advantage of
reducing the error due to uncertain temperature of
the stem to about one-sixth what it would be if
alcohol were used. Moreover, if necessary, as in
the case with thermometers for greater depths
than that figured, the ungraduated portion of the
stem can be made of very much finer bore than
the graduated portion, the effect of which is to
diminish the objectionable error to a
comparatively unimportant quantity.

The chief objection to thermometers of this Fig. 14. Soil Thermometer—
Whitney and Marvin.
construction is the liability of alcohol getting
from the bulb into the stem during the processes
of construction, graduation and subsequent handling, and the difficulty of
safely shipping them.
When once set up, however, there seems to be little or no possibility of
derangement and the error common to mercurial thermometers due to rise
of the freezing point with age does not apply owing to the high coefficient
of expansion of the alcohol used in the bulb.

APPLICATIONS OF SOIL THERMOMETRY.

116. Estimation of the Absorption of Heat by Soils.—A cubical zinc
box, six centimeters square, is filled with the sifted air dried soil. The box,
one side of which is left open, is encased snugly in a wooden cover,
exposing only the open end, and placed for a few hours in the direct rays of
the sun. The temperature is then taken at a given depth. The box may be
provided with thermometers at different depths, the bulbs thereof extending
to the center. In this case the box should be covered with thick felt instead
of wood. The temperature of the layers of soils of different depths can thus
be read off directly. The air temperature directly above the box should be
accurately noted while the experiment continues.
Any other kind of box well protected against all heat save the direct
sunlight on the open surface of the soil will answer as well as the one
described.
To determine the action of moist earth in similar conditions the soil may
be previously moistened; the per cent of moisture being determined in a
separate portion of the soil or the amount of water added to the air-dried soil
being noted.
117. Estimation of the Conductivity of Soils for Heat.—The bulb of a
thermometer is placed in the middle of a mass of fine earth which is then
exposed, best in a metallic box painted with lamp black, in a warm place.
The time required for the thermometer to reach a certain degree is noted. By
reversing the experiment and placing the mass of earth heated to a given
degree in a cool place the conductivity can be determined by the time
required for the mercury in the thermometer to fall to any given point.
The experiment may also be made by packing the soil by gently jolting it
in a glass tube six to eight centimeters in diameter. One end of the tube is
closed with a piece of metal or fine wire gauze painted with lamp black and
is exposed to the source of heat. The bulb of a thermometer is placed at a

given distance from the end of the tube and the time for the mercury to be
affected observed.

COHESION AND ADHESION OF SOILS.

118. Behavior of Soil After Wetting.—The deportment of a soil when
thoroughly wet in respect of its physical state on drying out is a matter of
great practical concern to the agronomist. Some soils on becoming dry fall
into a pulverulent state and are easily brought into proper tilth; others
become hard and tenacious, breaking into clods and resisting ordinary
methods of pulverization. The physical laws which determine these
conditions depend largely on the principles of flocculation soon to be
described. The present task is to describe briefly some of the methods of
estimating the force of cohesion and adhesion.
119. General Method.—The fine earth, air-dried, is mixed with enough
water to make a paste and molded into forms suitable for trial in a machine
for testing strength of cement, etc. The forms most used are cakes three to
five centimeters in length and one to two centimeters thick. These are used
for determining crushing power. For longitudinal adhesion the paste may be
molded in prismatic or cylindrical shape.[78] The prisms should show one to
two centimeters in cross section or the cylinder be one to two centimeters in
diameter. Before use they are to be exposed for several days until
thoroughly air-dried. The force required to separate or crush these prepared
pieces will measure the adhesive or cohesive property of the sample. A
great number of trials should be made and the mean taken.
120. Method of Heinrich.[79]—This process consists in mixing the air-
dried earth with water until its aqueous content is fifty per cent of the
highest water capacity determined by experiment. The sample is next
placed between two pieces of sheet iron of ten centimeters square, each of
which in its middle point is provided with a hook. The thickness of the layer
between the two pieces of iron should be about five to ten centimeters. The
exuding particles of soil are cut off with a knife. The upper piece of sheet
iron is next suspended by a cord in such a way that the iron piece occupies a
horizontal position. A small basket is attached to the lower surface and sand
added thereto, little by little, until the column of earth is separated. The sand

basket and iron plate are weighed, and the total weight gives the power
necessary to separate a column of soil ten centimeters square in cross
section. The iron plates may be roughened so that the adhesion thereto of
the soil is greater than its cohesive force.
121. Adhesion of Soil to Wood, Iron, Etc.—The adhesive power of
moist soil for wood, iron, etc., is measured by Heinrich[80] in the following
way: The soil is mixed with water, as above, until it contains just fifty per
cent of its total water-holding content. It is then placed in a large vessel and
the upper surface made as smooth as possible. A plate of wood, iron, etc., of
ten centimeters square is then pressed on the surface until a complete
contact is secured. This plate, by means of a hook and cord passing over a
pulley, is then subjected to stress by weighting the cord which carries a
basket for that purpose. The basket should be of the same weight as the
plate in contact with the soil. The weight added to the basket necessary to
separate the plate from the soil is taken to represent the cohesive force. The
author of the method appears to take no account of the pressure of the air on
the plate caused by the exclusion of the air from its under surface.

THE ABSORPTIVE POWER OF SOILS FOR SALTS IN
SOLUTION.

122. General Principles.[81]—It is a fact of every-day observation that
soils have a particular property of absorbing certain materials with which
they come in contact. If it were not for this property all our wells would
soon become unwholesome from the reception of decayed animal and
vegetable matter carried to them in the drainage water from the surface. It is
also a well-known fact that burying dead bodies prevents the gaseous
products of decomposition from reaching and vitiating the atmosphere.
Besides this well-known power of soils to absorb the decomposition
products of animal and vegetable matter, they also possess a property which
is of far greater importance in plant economy; that is, the power of
withdrawing and retaining certain mineral constituents from their solutions.
As far back as the sixteenth century mention is made by Lord Bacon of a
process for obtaining pure water on the seashore by simply digging a hole
in the sand and allowing it to fill with filtered sea water, which by this
means is deprived of its salt. Although certain facts were observed by some
of the earlier writers in regard to soil absorption, no systematic researches
were conducted with a view of demonstrating the extent and cause of this
power until within a comparatively few years.
In 1850 Prof. Way published in the Journal of the Royal Agricultural
Society of England, the results of a thorough and most excellent
investigation of the subject. Since then many distinguished chemists, such
as Henneberg, Stohmann, Peters, Heiden, Knop, Ullik, Pillitz, Biedermann,
Tuxen, and others have given their attention to this matter.
123. Summary of Data.—If a solution of a soluble sulfate, chloride or
nitrate of an alkali or an alkaline-earth metal be placed in contact with a
soil, the result is that the soil takes up a part of the base but none of the
acid. This absorption of base is attended with the liberation of some other
base from the soil which combines with the acid of the solution. Any alkali

or alkaline earth base has the power of replacing any other such base.
However, if soluble phosphates and silicates of these bases be placed in
contact with the soil both the base and the acid are removed from the
solution.
Peters[82] has shown that the amount of absorption depends upon the
concentration of the solution, the relation between the quantity of solution
and the soil and the kind of salt used. He treated 100 grams of earth with
250 cubic centimeters of solutions of different potash salts with the
following results:

Strength of solution. ⅒ Normal. ¹⁄₂₀ Normal.
Grams Grams
Salt Used K₂O absorbed. K₂O absorbed.
KCl 0.3124 0.1990
K₂SO₄ 0.3362 0.2098
K₂CO₃ 0.5747 0.3154

Biedermann[83] proves that, for phosphoric acid at least, the absorption
increases with the temperature.
It has also been found that the amount of absorption depends upon the
time of contact between the soil and solution. Way found that the absorption
of ammonia was complete in half an hour, while Henneberg and
Stohmann[84] noticed that the phosphoric acid continued to be fixed after the
expiration of twenty-four hours.
It is a very important fact that the absorption of a base is never complete;
no matter how dilute the solution it will still carry a small portion of the
base with it. Peters states that it requires about 28,000 parts of water to
remove one part of absorbed potash and Stohmann found that it required
about 10,000 parts of water to remove one part of absorbed ammonia. With
phosphoric acid, the resulting compound seems to be much more insoluble.
According to Tuxen[85] the presence of salts of soda and potash in solution
decreases the power of a soil to absorb ammonia compounds and the
presence of sodium salts decreases the power of a soil to absorb potash. On
the other hand the presence of potassium compounds considerably increases
the absorption of phosphoric acid. He further affirms that the compounds of
potash, phosphoric acid, etc., formed in the soil, are decidedly more soluble
in sodium salts than in pure water.

124. Cause of Absorption.—The withdrawing and fixing of phosphoric
acid from solutions by the soil is not very difficult to understand as this acid
forms insoluble compounds of iron, lime, and magnesium, some or all of
which are present in all soils. As to the absorption of the alkalies, the
explanation is far more difficult as nearly all of their ordinary compounds
are readily soluble in water.
As lime is usually found combined with the acid part of an alkali salt,
from which the base has been absorbed by the soil, it might naturally be
supposed that the absorptive power of the soil would depend upon the
amount of lime present. Way found, however, that the addition of chalk in
no way influenced the absorption of ammonia by a soil which contained but
a small amount of lime. This fact was also confirmed by Knop[86] who found
that chalk exerted no influence on the absorption of ammonia salts. These
facts would seem to point to the conclusion that lime was present in
sufficient quantity in these experiments, or that it is not essential to the
phenomena of absorption. However, as any alkali or alkaline-earth base can
replace any other such base, the presence of lime in the filtrate is probably
more of an accidental occurrence, owing to the comparatively large amount
of that substance in most soils, than a necessary condition, as any other base
would doubtless answer in the absence of lime.
125. Warington[87] has shown that hydrated oxides of iron and
aluminum, and especially the former, are capable of absorbing potash and
ammonia, and as more or less of these hydrates exist in nearly all soils, a
part, at least, of absorptive phenomena is to be ascribed to them.
126. Way tried to determine which of the constituents of a soil exercised
chiefly the absorptive power. He passed a solution of ammonia through
tubes containing pure sand and found that it came through apparently
unaltered from the first, while a soil treated in the same way removed the
ammonia for a considerable time. He concluded from this that the
absorptive power does not exist in the sand. He next oxidized the organic
matter in a soil with nitric acid and then treated it with ammonia in the same
way. The first portions of the filtrate showed no ammonia in any form,
hence he concluded that organic matter is not essential to the act of
absorption. He further showed that clay alone is capable of causing
absorption phenomena, by treating powdered clay tobacco pipes with
ammonia.

Having shown that clay was the main constituent in a soil which caused
the absorption of alkalies, he tried next to trace out the particular compound
which caused the absorption. Having tried various natural silicates he at last
succeeded in producing a hydrated silicate of aluminum and soda which
exhibited displacement and absorptive properties very similar to those
shown by the soil.
As Way had succeeded in producing an artificial hydrated silicate
possessing absorptive properties, Eichorn[88] thought of trying natural
hydrated silicates or zeolites and found that they exhibited the same power
as Way’s artificial preparation. It has also been shown by Biedermann,[89]
Rautlenberg,[90] and Heiden[91] that the absorptive power bears a close
relation to the amount of soluble silicates present.
In view of these facts it is now generally accepted that the absorption of
salts of the alkalies, accompanied by the change of base, is due chiefly to
the presence of decomposed zeolite minerals in the soil.
Besides the purely chemical absorption of salts by the soil, we have a
physical absorption of various substances similar to the action of charcoal
when used as a filter.
127. Conclusions of Armsby.—The data connected with the absorption
of bases by a soil have also been reviewed by Armsby.[92] He shows that the
absorption is accompanied by a chemical reaction between the salt whose
base is absorbed and some constituent of the soil, and this change seems to
be due particularly to certain zeolitic silicates, although Liebig and others
were disposed to credit this absorption largely to physical causes.
Knop advances the idea that the soil has the power of disintegrating salts
in the presence of some substances like calcium carbonate which can unite
with the acid. In experiments made with hydrous silicates it was shown that
the absorption resembled in all cases like phenomena in the soil; hence the
supposition already advanced in regard to the influence of such silicates is
doubtless true.
In respect of absorption in general, the following conclusions were
reached:
1. The absorption of combined bases by the soil consists in an exchange
of bases between the salt and the hydrous silicates of the soil.

2. This exchange, which is primarily chemical, is only partial, its extent
varying
(a) with the concentration of the solution, and
(b) with the ratio between the volume of the solution and the quality of
soil used.
3. The cause of these variations is probably the action of mass or the
tendency of resulting compounds to re-form the original bodies, the
absorption actually found in any case marking the point where the two
forces are in equilibrium.
128. Selective Absorption of Potash.—As a rule more potash is
absorbed from the sulfate than from the chlorid. This fact would seem to
point to the advisability of using sulfate as a fertilizer in preference to
chlorid. However, as with the exception of nitrates, the absorptive power of
a soil, for the salts used as fertilizers, is many times greater than it is ever
called upon to exert in fixing applied fertilizers, we need not trouble
ourselves in regard to the absorption of phosphoric acid, potash or
ammonia, in so far as the practical side of the matter is concerned. For
example, an acre of soil to the depth of nine inches weighs about 900 tons.
Now it has been found by Huston,[93] that 100 parts of a soil experimented
upon absorbed over 0.25 part of P₂O₅, hence 900 parts would absorb over
2.25 parts of P₂O₅; or an acre of this soil to the depth of nine inches would
absorb over two and one-fourth tons of phosphoric acid. 500 pounds per
acre is a large dressing of a phosphatic fertilizer for field crops and 500
pounds of a high grade fertilizer would contain about 100 pounds of P₂O₅;
hence the power of such a soil to absorb phosphoric acid is more than forty-
five times as great as it is ever likely to be called upon to exert in fixing the
phosphoric acid added to it as a fertilizer.
Huston has further shown that an acre of soil nine inches deep will
absorb more than 2.7 tons of potash (K₂O) from potassium chlorid from
which salt less potash is absorbed than from the sulfate. Now one-tenth ton
of potassium chlorid per acre would be a large dressing of potash, hence
this soil possesses the power of absorbing more than twenty-seven times as
much potash as is ever likely to be applied as a fertilizer.
In like manner it may be shown that the power of an acre of soil nine
inches deep to absorb ammonia from ammonium sulfate is more than thirty-

two times as great as it would be called upon to exert in fixing the ammonia
from a dressing of one-quarter ton of ammonium sulfate per acre.
With sodium nitrate, however, there is no absorption; hence great care is
necessary in the application of nitrogen as a nitrate, for, if it be put on in
large quantities, at a season when the plant is not prepared to assimilate it,
or during a period of heavy rains, there must unavoidably result loss from
drainage. The best time to apply a nitrate is evidently during the active
growing season.
129. Whitney[94] places great emphasis on the surface area of soil
particles in respect to their power to absorb solutions of salts. The
approximate surface area of a cubic foot of each of the different typical
soils of Maryland is as follows:

Pine barrens 23,940 square feet.
Truck lands 74,130 „ „
Tobacco lands 84,850 „ „
Wheat lands 94,540 „ „
River terrace 106,260 „ „
Limestone subsoil 202,600 „ „

It will be seen that there are about 24,000 square feet of surface area in a
cubic foot of the subsoil of the pine barrens, no less then 100,000 square
feet or two and three-tenths acres of surface area in a cubic foot of the
subsoil of the river terrace, and 200,000 square feet of surface area in a
cubic foot of the limestone subsoil.
These figures seem vast, but they are probably below rather than above
the true values, on account of the wide range of the diameters of the clay
group. This great extent of surface and of surface attraction, which has been
described as potential, gives the soil great power to absorb moisture from
the air, and to absorb and hold back mineral matters from solution. A
smooth surface of glass will attract and hold, by this surface attraction, an
appreciable amount of moisture from the surrounding air. A cubic foot of
soil, having 100,000 square feet of surface, should be able to attract and
hold a considerably larger amount of moisture.
It might have been added that if the potential of the surface, separating
the solution from the soil, be greater than the potential in the interior of the
liquid mass, there will be a tendency to concentrate the liquid on this

surface of separation. It has been shown that certain fluids have greater
density on a surface separating the fluid from a solid. On the other hand, if
the potential were low there might be no tendency for this concentration,
and even the reverse conditions would prevail and the soluble substance
could be readily washed out of the soil.
130. Removal of Organic Matters.—It is probably largely due to this
straining power that organic matters are removed from solutions in
percolating through the soil. Whitney[95] has observed that the organic
matter may be coagulated and precipitated from solution by the soil
constituents, and held in the soil in loose flocculent masses, while the liquid
passes through nearly free of organic matter.
131. Importance of Soil Absorption.—The importance of the absorptive
power of the soil can hardly be overestimated. By means of this power
those mineral ingredients of plant food, of which most soils contain but
little, are held too closely to allow of rapid loss by drainage, and still
sufficiently available to answer the needs of vegetation, provided the store
is large enough. The only important plant food liable to be deficient in the
soil which does not come under the influence of absorption is nitrogen in
the form of salts of nitric acid, and nature has made a wide provision for
this element by binding it in the form of organic bodies which nitrify but
slowly, and by supplying each year a small quantity from the atmosphere.
By means of the absorptive power of soils the farmer, if he puts on an
excess of potash or phosphoric acid as a fertilizer, does not lose it but is
able to reap some benefits from it in the next and even in succeeding crops.
If it were not for this power the best method for applying fertilizers would
be a much more complicated problem than it is at present; and it would be
necessary to apply them at just the proper season and in nicely regulated
amounts to insure against loss.
132. Method of Determining Absorption of Chemical Salts.—The soil
which is to be used for this experiment should be treated as has been
indicated and passed through a sieve the meshes of which do not exceed
half a millimeter in size. From twenty-five to fifty grams of the fine earth
may be used for each experiment.
The fine earth should be placed in a flask with 100 to 200 cubic
centimeters of the one-tenth to one-hundredth normal solution of the
substance to be absorbed. The flask should be well shaken and allowed to

stand with frequent shaking twenty-four to forty-eight hours at ordinary
temperatures. The whole is then to be thrown upon a folded filter and an
aliquot part of the filtrate taken for the estimation. The methods of
determining the quantities of the substances used will be found in other
parts of this manual. It is recommended to conduct a blank experiment with
water under the same conditions in order to determine the amount of the
material under consideration abstracted from the soil by the water alone.
The difference in the strength of the solution as filtered from the soil,
corrected by the amount indicated by the blank experiment, and the original
solution will give the absorptive power of the soil for the particular
substance under consideration.
If it should be desired to determine the absorptive power of the soil for
all the ordinary chemical fertilizing materials at the same time, a larger
quantity of the sample should be taken corresponding to the increased
amount of the standard solutions used. About 500 cubic centimeters of the
mixed salt solution should be shaken with 125 grams of the earth and the
process carried on in general as indicated above. The absorption coefficient
of an earth for any given salt according to Fesca,[96] is the quantity of the
absorbed material expressed in milligrams calculated to a unit of 100 grams
of the soil.
133. Method of Pillitz and Zalomanoff.—It is recommended by Pillitz
and Zalomanoff[25] to reject the old method, viz., shaking the soil with the
solution in a flask, and substitute the filtration method both because it gives
a more natural process and because the results are more constant. The
apparatus is shown in Fig. 15.
Two cylinders are placed vertically, one over the other. The lower
cylinder is graduated in cubic centimeters, the upper cylinder is closed at
each end by perforated rubber stoppers A and B through the openings of
which the glass tubes c and d pass. Within the cylinder A the opening of the
small tube d is closed with a disk of Swedish filter paper. The lower part of
the small tube is d connected by means of a rubber tube carrying a pinch-
cock C, with another small tube e which passes through the stopper f. In
carrying out the process the weighed quantity of soil is placed in the upper
cylinder and afterwards the measured quantity of the solution, the whole
thoroughly mixed and the cylinder closed. The valve C is then opened, a
given quantity of the solution, but not all, is made to drop into the lower

cylinder and the valve C is then closed. The liquid which
has passed into the lower cylinder as well as that which
remains in the upper cylinder, is thoroughly stirred and the
quantity of the material remaining in both liquids
determined and the absorbing power of the soil estimated
from their difference. It does not appear that this method of
estimation of the absorption power possesses any special
advantages over the old and far simpler method of shaking
in a flask.
134. Method of Müller.—The
method of Müller[97] for
illustrating absorption is carried
out by means of the apparatus
shown in Fig. 16. A glass
cylinder A about 750 centimeters
long and four to five centimeters
wide is closed at each end with
rubber stoppers with a single
Figure 15. perforation. The cylinder A is for
Zalomanoff’s
the reception of the soil with
Apparatus for which the experiment is to be
Determining made. Before using, the lower
Absorption of
Salts by Soils.
part of it is filled with glass
pearls or broken glass and above
this a layer of glass wool is
placed about one centimeter thick. The object of
this is to prevent the soil from passing into the
small tube below. As soon as the soil has all been
placed in the cylinder A the upper part of the
tube is also filled with glass wool. The cylinder
A is connected with the pressure bottle B by
Figure 16.
means of a rubber tube and the small glass bulb
tube shown in the figure. The bottle B should Müller’s Apparatus to Show
have a content of about two liters. It is filled Absorption of Salts by Soils.
with the standard solution of the material of
which the absorption coefficient is to be determined. At c the rubber tube is
connected with a glass T one arm of which is provided with a piece of

rubber tubing which can be closed by means of a pinch-cock. At c a screw
pinch-cock is placed which can be used to regulate the flow of the solution
from B to A. By opening the pinch-cock at e on the short arm of the T
piece, a sample of the original liquid can be taken and this can be compared
with the part which runs to b. If it is desired for instance, to show that
potassium carbonate has been absorbed by the soil the two bulbs shown on
the small glass tubes connecting with A can be filled with red litmus paper.
This paper will at once be turned blue in the lower bulb while in the upper
one it will retain its original color because the liquid in passing through the
soil will have lost its alkaline reaction. The solutions used should be very
dilute. The apparatus is designed for lecture experiments and not for
quantitative determinations.
135. Method of Knop.—For rapid determination of the absorption
coefficient of the soil Knop’s method may be used.[98]
The fine earth which is employed is that which passes a sieve with
meshes of half a millimeter. From 50 to 100 grams of this soil are mixed
with from five to ten grams of powdered chalk and with about twice the
weight of ammonium chlorid solution of known strength, viz., from 100 to
200 cubic centimeters. The ammonia solution should be of such a
concentration that the ammonia by its decomposition for each cubic
centimeter of the liquid evolves exactly one cubic centimeter of nitrogen.
This solution is prepared by dissolving in 208 cubic centimeters of water
one gram of ammonium chlorid. With frequent shaking the solution is
allowed to stand in contact with the soil for forty-eight hours. The whole is
now allowed to settle and the supernatant clear liquid is poured through a
dry filter. From the filtrate twenty to forty cubic centimeters are removed by
a pipette, and evaporated to dryness in a small porcelain dish, with the
addition of a drop of pure hydrochloric acid. The ammonium chlorid
remaining in the porcelain dish is washed with ten cubic centimeters of
water into one of the compartments of the evolution flask of the Knop-
Wagner azotometer. It is decomposed with fifty cubic centimeters of bromin
lye and the nitrogen estimated volumetrically. The difference between the
amount of nitrogen in this material and that of the original material will
give the amount of absorption exercised by the fine earth. This number,
without any further calculation, can be taken as the coefficient of
absorption.

136. Method of Huston.—The salt solutions recommended by Huston[99]
are sodium phosphate (Na₂HPO₄), potassium chlorid, potassium sulfate,
ammonium sulfate and sodium nitrate.
The solutions should be approximately tenth normal, the actual strength
in each case being determined by analysis. The phosphorus is determined as
magnesium pyrophosphate in the usual way, the potash as potassium
platinochlorid, the ammonia by collecting the distillate from soda in half
normal hydrochloric acid and titrating with standard alkali, and the nitrate
by Warington’s modification of Schlösing’s method for gas analysis. The
details of these methods of determination will be given later. One hundred
grams of the sifted, air-dried soil are placed in a rubber stopped bottle and
treated with 250 cubic centimeters of the solution to be tested. The
digestion is continued for forty-eight hours in each case, the bottles being
thoroughly shaken at the end of twenty-four hours. At the end of the
treatment the solutions are filtered and the salts determined in aliquot
portions. The details of this method are essentially those already described.
137. Statement of Results.—Duplicate analyses should be made and the
tabulation of the data is illustrated in the following analyses by Huston:

Na₂HPO₄ cubic Weight of Mg₂P₂O₇ in Weight of P₂O₅ Salt
centimeters twenty-five cubic Mg₂P₂O₇ in absorbed by removed
filtrate taken. centimeters of the solution. filtrate. 100 grams per cent.
soil.
(a) 25 0.1368 gram 0.0962 gram
(b) 25 0.0963 „ 0.2589 gram 29.6

Mean 0.0963 „

KCl cubic Weight of K₂PtCl₆ in Weight of K₂O Salt
centimeters twenty-five cubic K₂PtCl₆. absorbed by removed
filtrate taken. centimeters of solution. 100 grams per cent.
soil.
(a) 25 0.6154 gram 0.4505 gram
(b) 25 0.4540 „ 0.3161 gram 26.5

Mean 0.4523 „

K₂SO₄ cubic Weight of K₂PtCl₆ in Weight of K₂O Salt
centimeters twenty-five cubic K₂PtCl₆. absorbed by removed
filtrate taken. centimeters of solution. 100 grams per cent.
soil.
(a) 25 0.6113 gram 0.4426 gram
(b) 25 0.4371 „ 0.3324 gram 28.0

Mean 0.4399 „

(NH₄)₂SO₄ Number cubic centimeters Half normal acid N absorbed Salt
cubic one-half normal acid neutralized. by 100 absorbed
centimeters neutralized by fifty cubic grams soil. per cent.
filtrate taken. centimeters of solution.
(a) 50 10.00 7.25 grams
(b) 50 7.25 „ 0.0964 gram 27.5

Mean 7.25 „

NaNO₃ cubic Number cubic centimeters Cubic centimeter N absorbed Salt
centimeters N₂O₂ afforded by ten cubic N₂O₂ at 0° and by 100 absorbed
filtrate taken. centimeters of solution at 1000 millimeters. grams soil. per cent.
0° and 1000 millimeters
pressure.
(a) 10 16.63 16.77 grams

(b) 10 16.70 „ none 00.00

Mean 16.73 „

Upon comparing the figures it will be found that the absorption, passing
from the greatest to the least, is as follows: phosphoric acid (P₂O₆),
potassium sulfate, ammonium sulfate, potassium chlorid and sodium nitrate.
It will be seen that there was no absorption in the case of the nitrate,
while with each of the other salts there was quite a marked absorption. It
will also be noticed that the percentages of absorption are not very different,
and especially is this true of the potassium and ammonium salts, the P₂O₅
being somewhat higher. Whether this fact is merely an accidental
occurrence or is due to the law of combination by equivalents could hardly
be predicted from the single soil experimented upon; but taking into
consideration the possibility of difference in solubility of the resulting
compounds in the saline solutions used, and of other varying conditions, the
percentages are evidently not far enough apart to exclude the possibility of
the bases uniting in equivalent proportions.
138. Preparation of Salts for Absorption.—The salts employed in the
foregoing determinations are conveniently prepared, in fractional normal
strength.
In grams per liter the following quantities in grams are recommended,
viz., 5.35 g NH₄Cl; 10.11 g KNO₃; 16.40 g Ca(NO₃)₂; 24.60 g MgSO₄ +
7H₂O; 23.4 g CaH₄(PO₄)₂, etc.
The ammonium chlorid, potassium nitrate and magnesium sulfate can be
weighed as chemically pure salts and the standard solution be directly made
up. Calcium nitrate is so hygroscopic that a stronger solution must be made
up, the calcium determined and the proper volume taken and diluted to one
liter.
Monocalcium phosphate is prepared as follows:
A solution of sodium phosphate is treated with glacial acetic acid and
precipitated with a solution of calcium chlorid. It is then washed with water
until all chlorin is removed. The fresh precipitate is saturated with pure,
cold phosphoric acid of known strength. After filtering the solution is
placed in a warm room and left for two or three weeks until crystallization
takes place.

The crystals are pressed between blotting papers and finally dried over
sulfuric acid and washed with water-free ether, and again dried. Since this
salt is decomposed in strong solutions it should be used only in one
hundredth normal strength, viz., 2.34 grams per liter.

POROSITY AND ITS RELATIONS TO MOISTURE.

139. Porosity.—The porosity of a soil depends upon the state of
divisibility and arrangement of its particles, and upon the amount of
interstitial space within the soil. If a soil be cemented together into a
homogeneous mass, its porosity sinks to a minimum; if it be composed,
however, of numerous fine particles, each preserving its own physical
condition, the porosity of the soil will rise to a maximum. The porosity of a
soil may be judged very closely by the percentage of fine particles it yields
by the process of silt analysis to be described further on. In general, the
more finely divided the particles of a soil, the greater its fertility. This arises
from various causes; in the first place, such a soil has a high capacity for
absorbing moisture and holding it; thus the dangers of excessive rain-falls
are diminished, and the evil effects of prolonged drought mitigated. In the
second place, a porous soil permits a freer circulation of the gases found in
the soil. The influence of lime in securing the proper degree of porosity of a
soil is very great, especially in alluvial deposits and other stiff soils. It
prevents the impaction which will necessarily follow in a soil which is too
finely divided. In general, the porosity of the soil may be said to depend on
three factors, viz.: 1. Upon the state of divisibility or the number of particles
per unit volume; 2. Upon the nature and arrangement of these particles; 3.
Upon how much interstitial space there is in the soil.
140. Influence of Drainage.—Good underdrainage increases the
porosity of a soil by removing the excess of water during wet seasons and
rendering the soil more suitable to capillary attraction which will supply
moisture during dry seasons. The influence of tile drainage on the
production of floods has been carefully studied by Kedzie,[100] who shows
that surface ditching in conjunction with deforesting may increase floods
and contribute to droughts, and that tile-draining may increase flood at the
break-up in spring, when the water accumulated in the surface soil by the
joint action of frost and soil capillarity during the winter, and the surface
accumulations in the form of snow are suddenly set free by a rapid thaw.

He also points out that during the warm months tile-draining tends to
prevent flood by enabling the soil to take up the excessive rain-fall and hold
it in capillary form, keeping back the sudden flow that would pass over the
surface of the soil if not absorbed by it, and it mitigates summer drought by
increased capacity of the soil to hold water in capillary form and to draw
upon the subsoil water supply.
141. Soil Moisture.—The capacity of a soil to absorb moisture and retain
it depends on its porosity and is an important characteristic in relation to its
agricultural value.
The following general principles relating to soil moisture are adapted
from Stockbridge:[101]
During dry weather plants require a soil which is absorptive and retentive
of atmospheric moisture. The amount of this retention is generally in direct
ratio to two factors, viz., the amount of organic matter and its state of
division. The capillary water of the soil is very closely related to its
percolating power, since all waters in the soil are governed in their
movements by what is known as capillary force. Liebenberg has shown that
this movement may be either upwards or downwards, according as the
atmosphere is dry or supplies soil-saturating rain. The water absorbed by
the roots passes into the plant circulation, and the greater part is evaporated
from the leaves. Where the supply of water is insufficient, the plant wilts,
and if the evaporation long continue in excess of the supply obtained from
the soil, the plant must die. The experiments of Hellriegel have shown that
any soil can supply plants with all the water they need, and as fast as they
need it, so long as the moisture within the soil is not reduced below one-
third of the whole amount that it can hold. The quantity of water required
and evaporated by different agricultural plants during the period of growth
has been found to be as follows:

One acre of wheat exhales 409,832 pounds of water.
„ „ „ clover „ 1,096,234 „ „ „
„ „ „ sunflowers „ 12,585,994 „ „ „
„ „ „ cabbage „ 5,049,194 „ „ „
„ „ „ grape-vines „ 730,733 „ „ „
„ „ „ hops „ 4,445,021 „ „ „

Dietrich estimates the amount of water exhaled by the foliage of plants to
be from 250 to 400 times the weight of dry organic matter formed during
the same time. Cultivation conserves soil moisture. It must be remembered
that this water contains soil ingredients in solution. Hoffmann has estimated
that the quantity of matter dissolved from the soil by water varies from
0.242 to 0.0205 per cent of the dried earth. The experiments of Humphrey
and Abbott have shown that about one-sixth of the total sediment of the
Mississippi river is soluble in water.
142. Determination of the Porosity of the Soil.—The porosity of the
soil is fixed by the relative volume of the solid particles as compared with
the interstitial space. It is most easily determined by dividing the apparent
by the real specific gravity.
Let the real specific gravity of a soil be 2.5445 and the apparent specific
gravity of the same soil be 1.0990.
The porosity is then calculated according to the following ratios, viz.:
2.5445 : 1.099 = 100 : X
Whence X = 43.2 = per cent volume occupied by the solid particles of the
soil.
The per cent volume occupied by the interstitial space is therefore 56.8.
143. Method of Whitney.—The total volume of interstitial space within
the soil, in which water and air can enter, is best determined by calculation
from the specific gravity and the weight of a known volume of soil. To
determine this in the soil in its natural position in the field, a sample is
taken in the following way: A brass tube, about two inches in diameter and
nine inches long, has a clock spring securely soldered into one end, and this
end turned off in a lathe to give a good cutting edge of steel. The area
enclosed by this steel edge is accurately determined, and a mark is placed
on the side of the tube exactly six inches from the cutting edge. A steel cap
fits on top of the brass cylinder to receive the blows of a heavy hammer or
wooden mallet. The cylinder is driven into the ground until the six-inch
mark is just level with the surface. The whole is then dug out, care being
taken to slip a broad piece of steel under the cylinder before it is removed,
so as to prevent the soil which it contains from falling out. The cylinder is
then carefully laid over on its side, and the soil is cut off flush with the
cutting edge of steel. The soil is then removed from the cylinder, carried to

the laboratory and properly dried and weighed. The object of the steel
inserted in one end of the cylinder is to reduce the friction on the inside of
the tube to a minimum, and thus prevent the soil inside the cylinder being
forced down below the level of the surrounding earth. The volume of the
soil removed with this sampler can readily be determined by calculation, as
the area of the end of the tube is known and the sample is six inches deep.
In a sampler, such as described here, this volume is about 300 cubic
centimeters. From the weight of soil and the volume of the sample, the
volume of interstitial space may be found by the following formula:

S is the per cent by volume of interstitial space, V is the volume of the
tube in cubic centimeters, W is the weight of soil in grams, and ω is the
specific gravity of the soil. The specific gravity can be determined for each
soil, or the factor 2.65 can be used, which is sufficiently accurate for most
work.
The per cent by volume of interstitial space in the undisturbed subsoil is
found to range from about thirty-five for sandy land, to sixty-five or seventy
for stiff clay lands.
For the determination of the amount of water an air-dried soil will hold, if
all the space within it is completely filled with water, an eight-inch straight
argand lamp chimney, with a diameter of about two inches, can be
conveniently used. A mark is placed on the side of the tube, six inches from
one end, and the volume of the tube up to this mark is found by covering
the end with a piece of thin rubber cloth, or by pressing the chimney down
firmly on a glass plate, and making a water-tight joint with paraffin or wax.
Water is then poured into the tube up to the six-inch mark, and the weight or
volume of water determined. The tube can then be dried, a piece of muslin
tied tightly over the top and the whole then weighed. Soil is carefully
poured in and the tube gently tapped on a soft support until the soil is six
inches deep in the tube, and has the desired degree of compactness. The
weight and volume of the soil can thus be determined, and the volume of
the interstitial space from the formula already given. This can also be
determined directly by introducing water from above, or by immersing the

cylinder of soil up to the six-inch mark in water, and allowing the water to
enter the soil from below. With such a short depth of soil, very little water
will flow out when the cylinder is suspended in the air. The amount which
will flow out when the cylinder is thus suspended, will depend both upon
the texture and the depth of soil. It is impossible, however, by this method,
to completely remove the air or to completely fill the space within the soil
with water; for as the water enters the soil, a considerable amount of air
becomes entangled in the capillary spaces, and this could not be removed
except by boiling and vigorous stirring, which would altogether change the
texture of the soil. The amount of water held by the soil, or the amount of
space within the soil into which water and air can enter, will evidently
depend upon the compactness of the soil, and this is best expressed in per
cent by volume of space.
144. Capacity of the Fine Soil for Holding Moisture.—The soil, as it is
taken from the field, may have quite a different water coefficient from the
same soil after it has been passed through a fine sieve or been dried at air
temperatures or at 100° or 110°. The method of determination which
depends upon adding excess of water to a given weight of fine earth, and
afterwards eliminating the excess by percolation or filtration, is apt to give
misleading results. If, however, the results are obtained by working on the
same weight of soil, and in the same conditions, they may have value in a
comparative way. The comparison between soils must be made with equal
weights, in like apparatus and with the same manipulation, to have any
value. These determinations, however, cannot have the same practical value
as those made in the samples in a natural condition as has just been
described.
145. Method of Wolff Modified by Wahnschaffe.[102]—A cylindrical
zinc tube (Fig. 17), sixteen centimeters long and four centimeters internal
diameter, is used, the cubical capacity of which is 200 cubic centimeters.
The cylinder is graduated by placing the moist linen disk on the gauze
and tying a piece of rubber cloth over the bottom. Water is now poured in
until the level is even with the gauze bottom. Add then exactly 200 cubic
centimeters of water, mark its surface on the zinc, throw out the water, and
file the zinc down to the mark.
The bottom of the tube is closed with a fine nickel-wire gauze. Below
this a piece of zinc tubing, of the size of the main tube, is soldered; pierced

laterally with a number of holes.
Before using, the gauze bottom of the cylinder is covered with a moist,
close fitting linen disk, and the whole apparatus weighed. It is then filled
with the fine earth, little by little, jolting the cylinder on a soft substance
after each addition of soil to secure an even filling. When filled even full
the whole is weighed, the increase in weight giving the weight of soil taken.

Figure 17.

Capacity of the Fine Soil for Holding Moisture. Method of Wolff Modified
by Wahnschaffe.

A large number of cylinders can be filled at once and placed in a large
glass crystallizing dish containing water and covered with a bell jar (Fig.
17). The water should cover the gauze bottoms of the cylinders to the depth
of five to ten millimeters. More water should be added from time to time as
absorption takes place. The cylinders should be left in the water until when

weighed at intervals of an hour no appreciable increase in weight takes
place. The temperature and barometer reading should be noted in
connection with each determination. With increasing temperature the water
coefficient is diminished.
The method of Wolff, as practiced in the laboratory of the Chemical
Division of the U. S. Department of Agriculture, has given very concordant
results. Five determinations were made on a sample of vegetable soil with
the Wolff cylinders, which were weighed at intervals of ten, twenty, and
thirty days, with the following results:

No. 1. Water absorbed after ten days 106.25 per cent
„ 2. „ „ „ „ „ 105.68 „ „
„ 3. „ „ „ „ „ 105.86 „ „
„ 4. „ „ „ „ „ 106.11 „ „
„ 5. „ „ „ „ „ 105.83 „ „

Mean 105.95 „ „

No. 1. Water absorbed after twenty days 106.44 per cent
„ 2. „ „ „ „ „ 105.98 „ „
„ 3. „ „ „ „ „ 106.56 „ „
„ 4. „ „ „ „ „ 106.52 „ „
„ 5. „ „ „ „ „ 106.38 „ „

Mean 106.38 „ „

No. 1. Water absorbed after thirty days 108.35 per cent
„ 2. „ „ „ „ „ 107.60 „ „
„ 3. „ „ „ „ „ 108.32 „ „
„ 4. „ „ „ „ „ 107.86 „ „
„ 5. „ „ „ „ „ 107.87 „ „

Mean 108.00 „ „

The data obtained show that there was a very slight increase in the
amount of moisture absorbed after the tenth day.
As will be seen, however, from the following data, the soil within the
cylinder does not contain in all parts the same percentage of moisture, the

lower portions of the cylinder containing notably larger proportions than the
upper parts. The cylindrical soil column was divided into four equal parts
and the moisture determined in each part. Beginning with the top quarter
the percentages of moisture were as follows:

First quarter 97.52 per cent
Second „ 105.91 „ „
Third „ 112.83 „ „
Fourth „ 116.48 „ „

146. Method of Petermann.[103]—The method of Wolff as practiced by
the Belgian Experiment Station, at Gembloux, is essentially the same as
described above.
Petermann recommends the use of tared cylinders twenty to twenty-five
centimeters long and six to eight centimeters in diameter. The cylinder is to
be filled with the fine earth, little by little, with gentle tapping after each
addition. The bottom of the cylinder is closed with a perforated rubber
stopper on which is spread a moistened disk of linen. The cylinder, thus
prepared and filled, is weighed and afterwards placed in a vessel containing
distilled water, to such a depth as to secure a water level about two
centimeters above the lower surface of the soil in the cylinder. The level of
the water is kept constant as the contents of the cylinder are moistened by
capillarity. When the earth appears to be thoroughly moistened, as can be
told by the appearance of the upper surface, maintain the contact with water
for about five or six hours.
The cylinder is then removed, the upper surface covered to avoid
evaporation, allowed to drain for a few hours, wiped and weighed. The
cylinder is again placed in water to see if any increase in weight takes place.
The weight of the fine earth and of the absorbed water being known, the
percentage of absorption is easily calculated.
147. Method of A. Mayer.[104]—A glass tube, one and seven-tenths
centimeters in diameter, composed of two pieces, seventy-five centimeters
and twenty-five centimeters in length, is united by a piece of rubber tubing.
The lower free end of the seventy-five centimeter piece is closed with a
piece of linen. The tube is filled, with gentle jolting, to the depth of one
meter with fine earth, the earth column thus extending twenty-five

centimeters above the point of union of the two pieces. Thus prepared, a
quantity of water is poured into the upper tube sufficient to temporarily
saturate the whole of the soil.
During the sinking of the water in the tube there is thus effected a
moistening of the material before it is wholly filled with water. After
waiting until the water poured on top has disappeared the tube is separated
at the rubber tube connection and a sample of the moist soil taken at that
point. This is at once weighed and then dried at 100°. The loss in weight
gives the water absorbed.
The number thus obtained is calculated to the standard by volume, by use
of the number representing the apparent specific gravity of the fine earth.
For sand of different degrees of fineness the following numbers were
found:

Degree of fineness 2 3 4
Per cent water absorbed 7.0 13.7 44.6

The numbers thus obtained are taken to represent the absolute water
capacity of a mineral substance in powder.
The full water capacity, i. e., the power of holding water when the
powder is immersed in water, the excess of which is then allowed to flow
away is much greater than the absolute number.
This difference is shown in the following data:

Quartz, size three. Clay, size three.
Full water capacity 49.0 per cent 46.8 per cent
Absolute water capacity 13.7 „„ 24.5 „„

In general the absolute is markedly inferior to the full water capacity.
Only in the finest dust do the two numbers approach each other.
148. Volumetric Determination.—A convenient apparatus for this
determination has been devised by Mr. J. L. Fuelling, of the Chemical
Division, Department of Agriculture. It is shown in Fig. 18.
It consists of an ordinary percolator the diameter of which decreases
slightly towards the lower end, a thick-wall rubber tube and an ordinary
burette, divided in tenths. A rubber stopper is fitted to the mouth of the

percolator and perforated twice—in the middle and at the side, the former
for a small tube provided with pinch-cock and the latter for the neck of a
small funnel. The whole is supported on a convenient stand, the clamp
holding the percolator being placed above that supporting the burette, both
clamps arranged to slide on the stand-rod.
The method is as follows:
A mark is placed upon the projecting tube
at the lower end of the percolator, and the
tube at this point may be drawn out
sufficiently to decrease the width of
meniscus to one-eighth inch. Into the
percolator is first introduced a small disk of
wire gauze or perforated porcelain, with
heavy wire pendant in the tube. Through the
rubber stopper a small glass tube is passed
and its lower end pressed firmly upon the
wire or porcelain disk, its upper end being
curved and supplied with a pinch-cock. Into
the percolator is now poured one inch of fine
shot (No. 20) and then one inch of fine sand
which has been previously digested with
hydrochloric acid and well cleaned of dust
by washing.
The zero.—After the shot and sand have
been shaken even, the burette is filled with
water and raised above the level of the sand,
wetting the percolator for four inches of its
length. The burette is lowered and the shot
and sand bed allowed to drain by opening the
pinch-cock of the inner tube. The burette is
raised and the shot-sand flooded repeatedly
Figure 18. until, by lowering the burette until the zero
mark of the percolator tube is reached, a
Fuelling’s Apparatus.
uniform reading on the burette is secured.
Thus the shot-sand bed is completely
charged with water. The water level is now made zero on the percolator

stem, the burette filled to its zero mark and the apparatus is prepared for
introduction of the soil.
The Determination.—From 100 to 200 grams of soil, previously dried
free of moisture, are weighed, the burette raised until the water level is three
inches above the sand, and the soil gently dropped through a funnel into the
water. When the soil has been introduced and wetted completely the water
level is raised above the soil and allowed to remain thus two hours. The
burette is then lowered and the water allowed to drain from the wetted soil.
Four to six hours are usually given the draining, the reading taken on the
burette after establishing the zero on the percolator stem, the volume of
absorbed water thus ascertained and divided by the weight of soil multiplied
by 100; the result expresses the water absorbed per hundred of soil.
Example:

Water required to saturate disk, etc. 0.50 cubic centimeter.
Weight of air-dried soil taken 20.00 grams.
Moisture at 105° therein 14.25 per cent.
Weight water in soil 2.85 grams.
Reading of burette after saturation 10.75 cubic centimeters.
Less water required for disk, etc 9.25 „„
Temperature 20°.00
Weight of 9.25 cubic centimeters H₂O at 20° 9.22 grams.
Total weight of water retained by soil 12.07 „
Per cent water retained by soil 60.35 per cent.

For general analytical work the correction for variations in the weight of
water for different temperatures is of no practical importance.
149. Accuracy of Results.—A sample of soil from the beet sugar station,
in Nebraska, gave the following duplicate results:

First trial 45.75 per cent water.
Second trial 44.85 „ „ „

Muck soils from Florida, containing varying proportions of sand, gave
the following numbers:

Soil number one, 144.85 per cent, and 145.43 per cent; soil number two, 109.13 per cent, and
107.93 per cent; soil number three (very sandy), 46.86 per cent, and 46.51 per cent.

150. Method of Wollny.[105]—A zinc tube, ninety centimeters long and
four centimeters internal diameter, carries at each end, at right angles to the
axis, a flattened rim 1.5 centimeters broad. The lower end of the tube is
closed with a strong piece of coarse linen. The soil to be examined is then
filled in little by little, with gentle tamping.
On the upper end two glass tubes are placed, each ten centimeters long
and four centimeters internal diameter. These tubes are furnished at each
end with cemented brass cylinders which are expanded to a circular, evenly
ground rim, 1.5 centimeters wide, also at right angles to the axis of the main
tube. These rims are greased and placed together, one on the other, and held
together by wooden clamps.
The glass tube in immediate connection with the zinc tube is also firmly
filled with the soil sample, while the second tube is only partly filled, so
that any settling which may take place in the soil on the addition of water
may still find the first glass tube full of the sample.
The empty part of the upper glass tube is now filled with water and
additional quantities of water are added from time to time until the soil is
saturated. In order to be able to observe when this takes place there is a slit
at the lower end of the zinc tube which is closed with a piece of glass. This
slit should be about two centimeters broad and ten centimeters long. The
lower end of the zinc tube is set on a glass plate to prevent evaporation.
As soon as the water shows itself at the lower end of the zinc tube, the
excess of water in the upper glass tube is at once removed by a pipette and a
stopper inserted through which a glass tube passes drawn out into a fine
point above. The object of this is to avoid evaporation on the upper surface.
The apparatus is then left at rest for thirty-six hours.
At the end of this time the clamps are removed and the column of moist
earth cut with a piece of platinum foil, and the two ends of the glass tube,
next to the zinc tube, covered with glass plates. It is then weighed and the
weight of moist earth determined by deducting the weight of the tube and
its glass covers. The moist earth is carefully removed to a large porcelain
dish and dried at 100°. Before weighing it is allowed to stand twenty-four

hours in the air. The data obtained are used to calculate the water content to
volume per cent.
The volume of the glass tubes should be determined by careful
calibration.
151. Method of Heinrich.[106]—The soil to the depth turned by the plow
is dug out and in the hole a lead vessel without bottom, twenty centimeters
in diameter and forty centimeters high, is placed. The soil is then thrown
back around and outside the lead vessel until the latter appears buried in the
fragments.
The rest of the soil is passed into the lead vessel, through a sieve having
four meshes to the centimeter, using for this purpose enough water to
thoroughly moisten it. Care should be taken not to use enough water to
cause any separation of the fine from the coarse particles.
By this process all coarse stones, sticks, etc., are separated. In sandy soils
the flask is left for a few hours while in clay soils a much longer time is
necessary. When the excess of water has disappeared the lead cylinder is
removed, and a piece cut out of the center of it placed in a weighed drying
flask and dried at 100°.
152. Effect of Pressure on Water Capacity.[107]—The increasing
capacity of soil to hold water developed by shaking or pressure, is
determined by Henrici in the following way:
Into a glass cylinder of twenty millimeters internal diameter are poured
twenty cubic centimeters of water. A given quantity of soil is next added,
and after standing until thoroughly saturated, the residual water is measured
by pouring off, or better, by graduations on the side of the tube. The
increase in the volume of the clear water is also measured, after shaking, in
the same way. The data of a determination made as above described follow:

Water in cylinder 30 cubic centimeters.
Water and saturated soil 40 „ „
Volume of unsaturated soil = e = 10 „ „
Volume of saturated soil = e + w = 20.5 „ „
Water contained therein = w = 10.5 „ „

By repeated shaking the volume of e + w, the content of w therein, and
the relative values of we were found to be as follows:

Cubic Cubic Cubic Cubic
centimeters. centimeters. centimeters. centimeters.
e+w 20.5 16.0 15.7 15.0
w 10.5 6.0 5.7 5.0
w 1.05 0.60 0.57 0.50
e

If e′ represent the volume of the saturated soil then e′ = e + w, and this
gives the relation to the volume of dry earth represented by the equation e′e =
1 + we. This indicates that the relative volume of the saturated soil is equal to
unity increased by the relative content of water.
153. Coefficient of Evaporation.—At an ordinary room temperature in
the shade, samples of soil, if they are subjected to experiment in tolerably
thin layers have nearly an equal coefficient of evaporation. That is, the
absolute quantity of water evaporated in a given time is almost entirely
conditioned upon the magnitude of the surface exposed and the temperature
of the surrounding air. Only when exposed in conditions as nearly as
possible natural in thin layers to the action of the sunlight and shade do the
soils show their peculiarities in respect of the evaporation of moisture. In
order to see these peculiarities, samples of soil which have been previously
examined must be subjected to examination at the same time with the soil
whose properties are to be determined.
The zinc box, before described, should be protected with a well fitting
cover of thick paper, and the different samples of soil which are to be tested
placed therein. This should now be placed in a wooden box, the top of
which is exactly even with the top of the zinc vessel. This box containing
the vessel should be exposed to the sunlight. After twenty-four hours the
zinc boxes can be taken away from position and their loss in moisture
determined, and these weighings, according to the condition of the
atmosphere, can be continued from fourteen days to three weeks, the
temperature of the air of course being carefully determined at each time. At
first, all the different soils being saturated with moisture, it will be observed
that the loss of moisture is proportionately the same for all. Soon, however,
the rapidity of the evaporation in the samples of soil rich in humus and clay
will be decreased as compared with the sandy soils, and in general, those
which possess a high capillary power capable of bringing the moisture

rapidly from the deeper layers to the surface. There soon comes a point
when the difference in evaporation is at its greatest; and then there will be a
gradual diminution until the samples lose no further moisture. This point,
for the different soils, can be determined by frequent weighings of the
vessel.
154. Determination of Capillary Attraction.—Long glass tubes
graduated in centimeters may be used for this determination, or plain tubes
so arranged as to admit of easy measurements with a rule. The tubes may be
from one to two centimeters internal diameter and about one meter long.
The fine earth should be evenly filled in little by little, with gentle jolting.
The lower end of each tube, before filling, is closed with a piece of linen.
The tubes, after filling, are supported in an upright position by a frame
AE, Fig. 19, in a vessel B containing water in which the linen covered ends
D dip to the depth of two centimeters. The height of the water in the several
tubes should be read or measured at stated intervals. The water contained in
the supply vessel should be kept at a constant height by a Mariotte bottle.

The observations may be
discontinued after one
hundred and twenty hours, but
even then the water will not
have reached its maximum
height.
It is recommended by some
experimenters to cut the tubes,
after the above determination
is completed, into pieces ten
centimeters in length, and to
determine the per cent of
water in each portion.
155. Statement of Results.
—The following table Figure 19.
illustrates a convenient
method of tabulating the Apparatus to show Capillary Attraction of Soils for
Water.
observed data as given by
König.[108]

Number of sample 1 2 3 4 5 6
24 hours. 27.3 38.0 16.7 36.4 8.0 28.8 centimeters.
48 „ 35.9 50.8 24.5 49.2 11.9 40.5 „
Height of moisture
72 „ 41.5 59.5 30.0 57.9 15.2 49.1 „
column after:
96 „ 44.4 66.2 33.5 63.8 17.5 55.2 „
120 „ 46.7 70.0 36.3 68.5 19.2 60.5 „

156. Inverse Capillarity.—In tubes filled with fine earth, as described in
paragraph 154, water is quickly poured, the same quantity into each tube of
the same diameter, or such quantities in tubes of different diameters as
would form a water column of the same depth over the surface of the
sample. The rate at which the water column descends in each tube, the time
of the disappearance of the water at the surface and the final depth to which
it reaches, are the data to be entered.
157. Statement of Results.—The points to be observed in the
determination of inverse capillarity are the number of hours required for the
total absorption of a column of water of a given height, the depth of the

moisture column at that moment, and the total depth to which the moisture
column finally reaches. The data of observations with six samples with a
water column four centimeters high are given by König[109] as follows:

Number of sample 1 2 3 4 5 6
Number of hours required for water to
disappear 4.3 1.8 10.3 3.0 21.0 4.3
Depth of moisture at time of
disappearance of water 11.0 12.0 11.4 13.3 11.7 12.0 centimeters.
Total depth of moisture 13.0 18.1 13.0 19.0 12.0 16.5 „

158. Determination of the Coefficient of Evaporation.—The
coefficient of evaporation is the number of milligrams of water evaporated
from a square centimeter of soil surface in a given unit of time. It is evident
that this number will vary with the physical state of the soil, the velocity of
the wind, the saturation of the air with aqueous vapor and the temperature.
In all statements of analyses these factors should appear.
The process may be carried on first (a) with soil samples kept continually
saturated with water and (b) with samples in which the water is allowed to
gradually dry out.
Method a.—The determination may be made in the shade or sunlight.
In the Shade.—A zinc cylinder (Z Fig. 20), fifteen centimeters in
diameter and 7.5 centimeters high, with a rim one centimeter wide and one
centimeter from top, is covered at one end with linen or cotton cloth and
filled with fine earth, with gentle jolting, until even with the top. It is then
placed in a zinc holder H, into the circular opening of which it snugly fits as
in A. This holder is twenty centimeters in diameter and 7.5 centimeters
deep. It has an opening at O through which water can be added until it is
filled so as to wet the bottom of Z when in place. As the water is absorbed
by the soil more is added and, the top being covered, the apparatus is
allowed to stand for twenty-four hours. At the end of this time the soil in the
zinc cylinder is saturated with water to the fullest capillary extent.
The whole apparatus, after putting a stopper in O, is now weighed on a
large analytical balance and placed in an open room, with free-air
circulation, for twenty-four hours. At the end of this time it is again
weighed and the loss of weight calculated to milligrams per square
centimeter. Where large and delicate balances can not be had, the apparatus

can be constructed on a smaller scale suitable for use with a balance of the
ordinary size.
In the Sunlight.—The apparatus described above is enclosed in a wooden
box having a circular opening the size of the soil-zinc cylinder. In the
determination of the rate of evaporation, the apparatus, charged and
weighed as above described, is exposed to the sun for a given period of
time, say one hour. On the second weighing the loss represents the water
evaporated. The time of year, time of day, velocity of wind and temperature,
and degree of saturation of the air with aqueous vapor, should be noted. The
data obtained can then be calculated to milligrams of water per square
centimeter of surface for the unit of time.
Method b.—As in method a the determination may be made in the shade
or in the sunlight. The rate of evaporation is, in this method, a diminishing
one and depends largely on the reserve store of water in the sample at any
given moment.
The same piece of apparatus may be used as in the determinations just
described. After charging the sample with moisture all excess of water in
the outer zinc vessel is removed and the rate of evaporation determined by
exposure in an open room or in the sunlight, as is done in the operations
already described.
Alternate Method.—The zinc cylinders used in determining saturation
coefficient, paragraph 145, may also be employed in determining the rate of
evaporation. Each cylinder should be wrapped with heavy paper or placed
in a thick cardboard receptacle, and all placed in a wooden box, the cover of
which is provided with circular perforations, just admitting the tops of the
cylinders, which should be flush with the upper surface of the cover.
Arranged in this way the cylinders previously weighed are exposed in the
shade or to direct sunlight and reweighed after a stated interval. On account
of the small surface here exposed in comparison with the total quantity of
soil and moisture it is recommended to weigh the cylinders once only in
twenty-four hours. The weighings may be continued for a fortnight or even
a month.
In soils fully saturated with water the rate of evaporation is at first nearly
the same on account of the surface being practically that of water alone. As
the evaporation continues, however, the rate changes markedly with the
character of the soil.

159. Rapid Method of Wolff.—In order to expose a larger surface to
evaporation and to secure the results in a shorter period of time, Wolff[110]
fills square boxes, having wire-gauze bottoms, with fine earth, and after
saturating with moisture weighs and suspends them in the open air. The
wire-gauze bottoms are previously covered with filter paper to prevent loss
of soil.

Figure 20.

Apparatus for Determining Coefficient of Evaporation.

160. Estimation of Water Given up in a Water-Free Atmosphere.—
The air-dried sample, in quantities of from five to ten grams in a thin layer
on glass, is placed over a vessel containing strong sulfuric acid. It is then
placed on a ground glass plate and covered with a bell jar. The sample is
weighed at intervals of five days until the weight is practically constant.
This method is valuable in giving the actual hygroscopic power of a soil
depending on its structure alone.
161. Estimation of the Porosity of the Soil for the Passage of Gases.—
Some further notion of the physical state of the soil known as porosity, may
also be derived by a study of the rate at which it will admit of the
transmission of gases. A method for estimating this has been devised by
Ammon.[111]
Air is compressed in two gas holders by means of a column of water of
proper height to give the pressure required.
The tubes through which the air passes out of the gas holders are each
furnished with a stop-cock and united with a glass tube having a side tube
set in at right angles for carrying off the air.
The use of two holders makes it possible to carry on the experiment as
long as may be desired, one holder being filled with air while the other is
emptying.
The common conducting tube is joined with a meter which is capable of
measuring, to 0.01, the volume of air passing through it. The pressure is
regulated by means of the stop-cocks. The air passing from the meter is
received in a drying tube filled with calcium chlorid.
From the drying tube the air enters a drying flask filled below with
concentrated sulfuric acid and above with pumice stone saturated therewith.
Next the dried air passes through a worm, eight meters long, surrounded
with water at a given temperature. The dried air of known temperature next
enters the experimental tube. This tube is made of sheet zinc 125
centimeters in length and five centimeters in internal diameter. It is placed
in an upright position, and about six centimeters from its upper end carries a
small tube at right angles to the main one for connection with a water-filled
manometer.
The upper and lower ends of the tube are closed with perforated rubber
stoppers carrying tubes for the entrance and exit of the air.

In the inside of the zinc tube are found two close-fitting but movable
disks, of the finest brass wire gauze, between which the material to be
experimented upon is held.
The layer of fine soil is held between these disks and may be of such a
depth as is required for the proper progress of the experiment. With soils of
firm texture opposing a great resistance to the passage of the air the column
of earth tested should be shorter than with light and very permeable soils.
The experimental tube is surrounded with a water jacket, which may also be
made of sheet zinc, carrying small tubes directed upwards for holding
thermometers. The water jacket should be kept at the same temperature as
the air which is used in the experiment.
The process of filling the tube, the amount of pressure to be used and the
air and soil temperature, will naturally vary in different determinations.
The volume of air at a given pressure and temperature which passes a
column of soil of a given length in a unit of time will give the coefficient of
permeability.
162. Determination of Permeability in the Open Field.—A method for
determining the rate of transmission of a gas through the soil in the field has
been devised by Heinrich.[112]
A box C (Fig. 21) is made of strong sheet iron and has an opening below,
ten centimeters square, and a height of about twenty centimeters. At exactly
ten centimeters from the bottom, the box has a rim at right angles to its
length so that it can be placed only ten centimeters deep in the soil. The box
holds a volume of earth equal to 1,000 cubic centimeters.
The part of the box above ground is connected with the bottle B by a
glass tube as indicated in the figure. The bottle B should have a capacity of
about ten liters. The air in B is forced out through C by water running in
from the supply A and the pressure in B is recorded by the manometer D.
The experiment should be tried on a soil thoroughly moist.
In measuring the pressure in B the water pressure should be cut off by the
pinch-cock between A and B, and the pressure on the manometer observed
after the lapse of one to two minutes.

MOVEMENT OF WATER
THROUGH SOILS:
LYSIMETRY.

163. Porosity in Relation to Water
Movement.—The intimate relation which
water movement in a soil bears to fertility
makes highly important the analytical
study of this feature of porosity. A soil
Figure 21. deficient in plant food, in so far as
chemical analysis is concerned, will
Method of Heinrich.
produce far better crops when the flow of
moisture is favorable than a highly fertile
soil in which the water may be in deficiency or excess.
Aside from the actual rain-fall the texture of the soil, in other words its
porosity, is the most important factor in determining the proper supply of
moisture to the rootlets of plants. Even where the rain-fall is little, a
properly porous soil in contact with a moist subsoil will furnish the
moisture necessary to plant growth. This fact is well illustrated by the beet
fields in Chino Valley, California. In this locality most excellent crops of
sugar beets are produced without irrigation and almost without rain.
164. Methods of Water Movement—The translocation of soil water is
occasioned in at least two ways; namely,
1. By changing the porosity of a given stratum of soil.
2. By changing the amount of water a given stratum contains.
The following experiment by King[113] illustrates a convenient method of
studying this movement of water:
On a rich fallow ground of light clay soil, underlaid at a depth of eighteen
inches by a medium-grained sand, water, to the amount of two pounds per
square foot on an area of eight by eight feet, was slowly added with a
sprinkler, samples of soil having been previously taken in six-inch sections

down to a depth of three feet. The samples were taken along a diagonal of
the square under experiment and one foot apart. The middle sample of the
line being from the center of the area. The sampling and wetting occurred
between one and three P. M., on July 22, and on the evening of the 23 a
corresponding series of samples was taken along a line parallel to the first
but eight inches distant. The changes in the percentages of water in the soil
are given in the following table, showing the translocation of water in soil
due to wetting the surface:

PER CENT OF WATER. DIFFERENCE.
Inches. Before wetting. After wetting. In per cent. In pounds per cu. ft.
0–6 14.00 22.23 +8.23 +2.873
6–12 15.14 15.71 +0.57 +0.199
12–18 16.23 15.75 –0.48 –0.213
18–24 17.70 16.92 –0.78 –0.347
24–30 16.76 14.41 –2.35 –1.032
30–36 15.51 15.21 –0.30 –0.132

The figures given in the last column of the table are computed from the
absolute dry weights of the upper three feet of soil as determined in a
locality some rods from the place of experiment, and are therefore only
approximations, but the error due to this cause is certainly small. It will be
seen that while only two pounds of water to the square foot were added to
the surface, the upper six inches contained 2.87 pounds per square foot
more than before the water was added, and the second six inches contained
0.199 pound more, and this too in the face of the fact that the evaporation
per square foot from a tray sitting on a pair of scales close by, was 0.428
pound during the interval under consideration. Similar experiments were
made by taking the samples of soil at 5.30 P. M. in one-foot sections down to
four feet, at four equally distant places along the diagonal of a square, six
by six feet, and having the ground sprinkled. At the same time four similar
sets of samples were taken on lines vertical to each of the sides of the
square but four feet distant from them. The amount of water the soil
contained was then determined, and at 11.30 A. M., nineteen hours later,
another series of samples was taken at points about four inches distant from
the last and the amount of water determined with the result given below.

Translation of Water Occasioned by Wetting the Surface.
Depth of WET AREA. AREA NOT WET.
samples. Before wetting. After wetting. First samples. Second samples.
Pounds Pounds Pounds Pounds
of water of water of water of water
Per per Per per Per per Per per
cent of cubic cent of cubic cent of cubic cent of cubic
water. foot. water. foot. water. foot. water. foot.
0–12
inches 16.86 11.78 20.15 14.06 17.72 12.38 18.27 12.75
12–24 „ 17.76 15.79 19.71 17.52 19.18 17.05 19.94 17.72
24–36 „ 16.76 14.73 17.72 15.58 16.97 14.92 17.52 15.40
36–48 „ 15.01 14.03 16.47 15.40 15.49 14.48 15.16 14.17
Averages 16.59 14.08 18.51 15.64 17.34 14.71 17.71 15.01

Total
amount
of water 56.33 62.56 58.83 60.04
Amount
of change +6.23 +1.21
The above data show sufficiently well the method of investigation to be
pursued in studies of this kind.
165. Capillary Movement of Water.—The method of investigation
proposed by King[114] consists in taking samples of soil at intervals of one,
two, three, or four feet in depth, and determining the amount of moisture in
each in connection with the amount of rain-fall during the period. The
quantity of water contained in a given soil, at various depths and on
different dates, is shown in the following table:

Depth in Date. Per cent Pounds per cubic Increase or decrease.
feet. water. foot. Pounds per cubic
foot.
1 March 24.33 16.98
8th
1 April 22.37 15.61 –1.37
18th
2 March 15.80 14.05
8th
2 April 21.64 19.24 +5.19
18th
3 March 11.16 9.81
8th
3 April 16.24 14.27 +4.46
18th
4 March 7.87 7.36
8th
4 April 11.19 10.46 +3.10
18th

The rain-fall during the interval was 4.18 inches, equal to 21.77 pounds
per square foot.
166. Lateral Capillary Flow.—To determine the lateral capillary flow of
water in a soil the following method, used by King[115] may be employed:
A zinc lined tray, six by six feet in area and eight inches deep, is filled
with a soil well packed. In one corner of this tray a section of five inches of
unglazed drainage tile, having its lower end broken and jagged, is set and
the dirt well filled in round it. By means of a Mariotte bottle water is
constantly maintained in the bottom of this tile, three-quarters of an inch
deep, so that it will flow laterally by capillary action into the adjacent soil,
the object being to determine the extent and rate of capillary flow laterally.
The water content of the soil is determined at the time of starting the
experiment, on the circumferences of circles described with the tile as a
center, the distance between the circles being one foot. At stated periods,
usually at intervals of one day, the content of moisture is again determined
at the same points. The investigations show that the lateral movement of
water in the soil is not rapid enough to extend much beyond three feet in
thirty-one days, for beyond that distance the soil was found to be drier than
at the beginning of the experiment. A record is to be kept of the amount of

water delivered to the soil by weighing the supply bottle at intervals, and
the rates given at which the soil takes up the water in grams per hour and
pounds per day. Also the amount of flow per square foot of soil section
together with the mean daily evaporation should be noted. The mean flow
per foot of soil section is computed on the assumption that the outer face of
the zone of completely saturated soil is the delivering surface. In King’s
work this point, as nearly as could be determined, was twelve inches from
the corner of the tray and hence the figures at best can only be regarded as
approximations. The method of stating results is shown in the following
table:

Showing the Rate of Lateral Capillary Flow of Water in Clay Loam.

Date. No. of Total mean, Total mean, Mean daily flow Mean daily
days. hourly flow, daily flow, per square foot, evaporation,
grams. pounds. pounds. pounds.
Jan. 28 to 5 70.70 3.73 2.38
Feb. 2
Feb. 2–7 5 85.98 4.54 2.91
Feb. 7–12 5 79.33 4.19 2.64
Feb. 12–17 5 79.41 4.19 2.64 0.598
Feb. 17–22 5 70.79 3.74 2.38 0.534
Feb. 22–28 6 59.89 3.16 2.01 0.451
Feb. 28 to 6 60.74 3.21 2.04 0.458
March 6
Mar. 6–13 7 60.37 3.14 2.00 0.448
Means 2.38 0.498

From this table it will be seen that the flow of water in the soil varied in
rate, being slower during the first five days than in the succeeding fifteen
days. After twenty days the flow dropped again to the beginning rate and
then fell below, but remained quite constant during the following nineteen
days. For the sake of uniformity in units of measure the daily quantity of
flow should be given in kilograms when the hourly flow is given in grams.
167. Causes of Water Movement in the Soil.—The movement of water
in a soil as explained by Whitney[116] is due to two forces, viz., gravitation
and surface tension.
The force of gravitation in a given locality is always uniform, both in
direction and magnitude per unit volume of water.

Surface tension is the tendency of any exposed water surface to pull itself
together. It may act in any direction, according to circumstances, and may
thus sometimes help and sometimes antagonize the force of gravitation.
According to the law of surface tension any particle of moisture tends to
assume the smallest possible area. This tendency is a constant definite force
per unit of surface at a given temperature. In the soil this constant strain on
the free surface of water particles serves, in a high degree, to move them
from place to place, in harmony with the requirements of the different
portions of the field.
When a soil is only slightly moist the water clings to its grains in the
form of a thin film. When these soil particles are brought together the films
of water surrounding them unite, one surface being in contact with the soil
particles and the other exposed to the air. If more water enter the soil the
film thickens until finally, when the point of saturation is reached, all the
space between the soil particles becomes filled with water, and surface
tension within the soil is thus reduced to zero. Gravity then alone acts on
the water and with a maximum force.
In a cubic foot of ordinary soil the total surface of the soil particles will
be at least 50,000 square feet. It follows that when the soil is only slightly
moist the exposed water surface of the films surrounding the soil particles
approximates that of the particles themselves. If such a mass of slightly
moist soil be brought in contact with a like mass saturated with water, the
films of water at the point of contact will begin to thicken in the nearly dry
soil at the expense of the water content of the saturated mass. The water
will thus be moved in any direction.
During evaporation the surface tension near the surface of the soil is
increased, and water is thus drawn from below. In like manner, when rain
falls on a somewhat dry soil, the surface tension is diminished and the
greater surface tension below pulls the moisture down even when
gravitation would not be sufficient for that purpose.
Certain fertilizers have the faculty of modifying surface tension and thus
change the power of the soil in its attraction for moisture. In this way such
fertilizers act favorably on plant growth, both by providing plant food and
by supplying needed moisture.
168. Surface Tension of Fertilizers.—Whitney gives the following data
in respect of the surface tension of aqueous solutions of some of the more

common fertilizing materials. It is expressed in gram meters per square
meter, i. e., on a square meter of liquid surface there is sufficient energy to
lift the given number of grams to the height of one meter.

Surface Tension of Various Fertilizing Solutions.

Solution of— Specific gravity. Gram meters per square meter.
Salt 1.070 7.975
Kainite 1.053 7.900
Lime 1.002 7.696
Water 1.000 7.668
Acid phosphate 1.005 7.656
Plaster 1.000 7.638
Ammonia 0.960 6.869
Urine 1.026 6.615
Magnesium chlorid 1.1000 7.964
Basic slag 1.0012 7.890
Marl 1.0013 7.855
Potassium chlorid 1.1000 7.853
Ammonium sulfate 1.1000 7.834
Dried blood 1.0001 7.764
Ground bone 1.0007 7.749
Sodium nitrate 1.1000 7.730
Sodium sulfate 1.1000 7.730
Wood ashes 1.0038 7.674
Potassium nitrate 1.1000 7.661
Potassium sulfate 1.0830 7.658
Ammonium nitrate 1.1000 7.656
Dried fish 1.0026 7.594
Stable manure 1.0013 7.464
Cotton-seed meal 1.0054 6.534
Tankage 1.0169 4.844
Cotton seed 1.0070 4.788

Surface Tension of Soil Extracts.

Kind of Soil. Specific gravity. Surface tension.
Kentucky blue grass 1.000 7.244
Triassic red sandstone 1.000 7.244
Wheat soil 1.000 7.098
Garden soil 1.000 7.089

169. Method of Estimating Surface Tension.—The determination of
surface tension is made by measuring the rise of the liquid in a capillary
tube. A short piece of thermometer tubing is used, the diameter of the bore
being determined by careful microscopic measurements with a micrometer
eyepiece. The diameter of the tube should be about 0.5578 millimeter. The
tube is very thoroughly cleaned after each observation, or set of
observations, with a strong caustic potash solution, and, after washing, is
allowed to stand for some time in a saturated solution of potassium
bichromate in strong sulfuric acid. The height of the rise in the capillary
tube is measured with a cathetometer.
The following formula is used for the calculation of the results:
T = 4hcos.
dω
a

Where T is the surface tension, d is the diameter of the tube in
centimeters; h the height to which the liquid rises in the capillary tube in
centimeters; ω is the specific gravity of the solution; and 4 cos. a refers to
the angle of the liquid with the sides of the glass tube. For a tube of the size
given above, 5° 24′ is the value of this edge angle. In regard to saline
solutions, Quincke[117] says, that the edge angle appears to increase a little
with augmenting concentration of the saline solution, but otherwise to differ
only inconsiderably from the edge angle of pure water.
170. Effect of the Solutions on Surface Tension.—The mineral
fertilizers, as a rule, increase the surface tension of water, while organic
matters in solution decrease it. But it must not be forgotten in this
connection that but little of the organic matter in the fertilizers employed for
the experiment passes into solution. Moreover, with these substances, the
accuracy of the work is impaired somewhat by the increased viscosity. In
general, the results of the experiment are in harmony with the well-known
effect of magnesium, sodium, and potassium chlorids, and sodium nitrate,

to make the soil more moist in dry weather, and the opposite effect
produced by the application of organic matter.
171. Method of Preparing Soil Extracts.—The soil extracts used in
determining the surface tension, as given in the above table, are prepared as
follows:
Ten grams of the soil are rubbed up with fifteen to twenty cubic
centimeters of distilled water and allowed to stand for twenty-four hours
with frequent stirring. Any fine particles not removable by a filter are
neglected, although they may give a turbid appearance to the solution.
172. Lysimetry.—The process of measuring the capacity of a soil to
permit the passage of water and of collecting and determining the amount
of flow and determining soluble matters therein is known as lysimetry. In
general, the rate at which water will pass through a soil depends on the
fineness and approximation of its particles. Water will pass through coarse
sand almost as rapidly as through a tube, while a fine clay may be almost
impervious. The study of the phenomena of filtration through soil, and the
methods of quantitatively estimating them, are therefore closely related to
porosity.
Two cases are to be considered, viz.: First, percolation through samples of
soil prepared for analysis, and second, the passage of the water through soil
in situ, whether it be virgin or cultivated.
The determination of the rate of flow through a soil in laboratory
samples, gives valuable information in respect of its physical properties,
while the same determination made on the soil in situ, has practical
relations to the supply of moisture, to growing plants, and the waste of
valuable plant food in the drainage waters. The determination of the rate of
flow of water through a small sample, disturbed as little as possible in its
natural condition, is classed with the first divisions of the work, inasmuch
as the removal of a sample of soil from a field, and its transfer to the
laboratory, subjects it to artificial conditions, even if its texture be but little
disturbed by the removal.
173. Calculation of the Relative Rate of Flow of Water Through Soils.
—There will evidently be one space, or opening, into the soil for every
surface grain, as pointed out by Whitney,[118] and the approximate number of
grains, or of openings, on a unit area of surface may be found by the
following formula:

N = (√(M V× W)⅔
where N is the number of grains, or openings, on one square centimeter of
surface, M is the approximate number of grains in one gram of soil, W is
the weight of soil, V is the total volume of the soil grains and the empty
space.
If the grains are assumed to be symmetrically arranged and the spaces
between them cylindrical in form, the radii of the spaces can be found by
the following formula:
r = √πNL
V₁

where r is the radius of a single space, V is the total volume of the empty
space, N is the number of grains or spaces on one square centimeter of
surface, and L is the depth of the soil.
If the space within the soil is completely filled with water the relative rate
of flow of water through the soil will be according to the fourth power of
the radius of a single space multiplied by the number of spaces on the unit
area of surface, as shown by the following formula:
N(r)⁴T
T₁ = N₁(r₁)⁴
where N-N₁ are the numbers of spaces, and r-r₁ are the radii of single
spaces in the respective soils, and T-T₁ the times required for a unit volume
of water to flow through the soils under the same head or pressure.
The space within the soil is rarely filled with water in agricultural lands,
and the most favorable amount of water for the soil to hold, as Hellriegel
and others have shown, is from thirty to fifty per cent of the total amount of
water the soil can hold if all the space within it were filled.
If the space within the soil be only partly filled with water, as in most
arable lands, the water will move in a thin film surrounding the soil grains
and according to the fourth power of the thickness of the film. The mean
thickness of the film surrounding the soil grains may be theoretically
determined by the following formula, which is based on the conception that
the film is cylindrical and of uniform size throughout:
t = r(1 − √s +s p)
where s is the per cent by weight of water which the soil will hold when the
empty space is filled with water, p the per cent of water actually contained

in the soil, r the radius of a single space, and t the mean thickness of the
film surrounding the soil grains.
The relative rate of flow of water through the soils will then be according
to the following formula:
N(t)⁴T
T₁ = N₁(t)₁⁴ )
It must be remembered that these formulæ give only approximate and
comparative values for comparing one soil with another. The structure of
the soil is altogether too intricate to expect ever to obtain absolute values.
If the observed rate of flow varies widely from the relative rate calculated
from the mechanical analysis, it will indicate a difference in the
arrangement of the soil grains, or in the amount or condition of the organic
matter in the soils. In the older agricultural regions of the United States,
south of the influence of the glacial action, the great soil areas appear to
have sensibly similar arrangements of the soil grains, and sensibly uniform
conditions of organic matter, save where these have been modified by local
conditions.
174. Measurement of Rate of Percolation in a Soil Sample.—In order
to measure the power of the soil for permitting the passage of water, a box,
about twenty-five centimeters high and having a cross section of about three
centimeters square, is used. Below, this box has a funnel-shaped end with a
narrow outlet tube, which at its lower end is closed with cotton, in such a
way that a portion of the cotton extends through the stem of the funnel. A
little coarse quartz sand is scattered over the cotton and afterwards the
funnel part of the apparatus filled with it. The sand and the cotton are
saturated with water and the apparatus weighed. The box is then filled with
the fine sample of earth, with light tapping, until the depth of earth has
reached about sixteen centimeters. The apparatus, after the addition of the
air-dried earth, is again weighed to determine the amount of earth added,
and the soil is then saturated by the careful addition of water. After the
excess of water has run down the funnel, the total quantity of absorbed
water is determined by reweighing the apparatus and the total water-holding
power of the soil is determined. There is carefully added, without stirring up
the surface of the soil, a column of water eight centimeters high, making in
all from sixty to seventy grams. The time is observed until the water ceases
to drip from the funnel. The dripping begins immediately after the water is
poured on and ceases as soon as the liquid on the surface of the soil has

completely disappeared. On the repetition of this operation a longer time for
the passage of the water is almost always required than at the first time. The
experiment, therefore, must be tried three or four times and the mean taken.
175. Method of Welitschowsky.[119]—The soil is placed in the vessel a,
Fig. 22, which is cylindrical in shape and five centimeters in diameter. The
lower end of the cylinder is closed with a fine wire-gauze disk and the
upper end is provided with an enlargement for the reception of the tube b,
which is connected to a with a wide rubber band. The lower end of the tube
b is also closed with a wire-gauze disk. These tubes may be conveniently
made of sheet zinc. The tube b carries on the side, at distances of ten
centimeters, small tubes of fifteen millimeters diameter. On the opposite
side it is provided with a glass tube set into a side tube near the bottom for
the purpose of showing the height of the water. The side tube carrying the
water meter is provided with a stop-cock as shown in the figure.
In conducting the experiment, after the apparatus has been arranged as
described, the small lateral tubes are, with one exception, closed with
stoppers. On the open one, d, a rubber tube is fixed for the purpose of
removing the water. The required water pressure is secured by taking the
lateral opening corresponding to the pressure required. Water is introduced
into the apparatus slowly through the glass tube f.
The water rises to d and then any excess flows off through e. By a proper
regulation of the water supply the pressure is kept constant at d. The water
flowing off through a is collected by the funnel and delivered to graduated
flasks where its quantity can be measured for any given unit of time. Since
the rate of flow at first shows variations, the measurement should not be
commenced until after the flow becomes constant.
In general, the experiments should last ten hours, and, beginning with a
water pressure of 100 centimeters, be repeated successively with pressures
of eighty, sixty, forty, and twenty, centimeters, etc. In coarse soils, or with
sand, one hour is long enough for the experiment.
176. Statement Of Results.—In the following tables the results for
ninety centimeters, seventy centimeters, etc., are calculated from the
analytical data obtained for 100 centimeters, eighty centimeters, etc.

Figure 22.

Method of
Welitschowsky.

Material—Quartz Sand.

Liters of Water Passing in Ten
Hours.
No. of Diameter of sand Water pressure
Exp. particles in in Thickness of Soil Layer.
mm. cm. 10 cm. 20 cm. 30 cm.
10 0.244 0.187 0.151
20 0.282 0.198 0.154
30 0.320 0.209 0.158
40 0.358 0.220 0.161
50 0.396 0.231 0.165
1. 0.01–0.71
60 0.434 0.242 0.168
70 0.472 0.253 0.172
80 0.510 0.264 0.175
90 0.548 0.275 0.179
100 0.586 0.286 0.182

10 2.194 1.724 1.425
20 2.898 2.012 1.578
30 3.602 2.300 1.731
40 4.306 2.588 1.884
50 5.010 2.876 2.037
2. 0.071–0.114
60 5.714 3.164 2.190
70 6.418 3.452 2.343
80 7.122 3.740 2.496
90 7.826 4.028 2.649
100 8.530 4.316 2.802
Similar sets of data have been collected with powdered limestone, clay
and humus.
The general conclusions from the experiments are as follows:
1. Clay (kaolin) and humus (peat) are almost impermeable for water, and
fine quartz and limestone dust are also very impermeable.
2. The permeability of a soil for water increases as the particles of the
soil increase in size, and when particles of different sizes are mixed together
the permeability approaches that of the finer particles.
3. The quantity of water passing through a given thickness of soil
increases with the water pressure but is not proportional thereto, increasing
less rapidly than the pressure.
4. The quantity of water passing under a given pressure is inversely
proportional to the thickness of the soil layer when the particles are very

fine and the pressure high.
177. Method of Whitney.—To determine the permeability of the soil or
subsoil to water or air, in its natural position in the field, the following
method, due to Whitney, can be recommended:
A hole should be dug, and the soil and subsoil on one side removed to the
depth at which the observation is to be made. A column of the soil or
subsoil, two inches or more square, and four or five inches deep, is then to
be carved out with a broad bladed knife, or a small saw can be conveniently
used for cutting this out. A glass or metal frame, a little larger than the
sample and three or four inches deep, is slipped over the column of soil, and
melted paraffin is run in slowly to fill up the space between the soil and the
frame. The soil is then struck off even with the top and bottom of the frame,
preferably with a saw, or at any rate taking care not to smooth it over with a
knife, which would disturb the surface and affect the rate of flow. The frame
is then placed upon some coarse sand or gravel, contained in a funnel, to
prevent the soil from falling out and to provide good drainage for the water
to pass through. Another similar frame can then be placed on top and
secured by a wide rubber band. A little coarse sand, which has been
thoroughly washed and dried, is then placed on the soil, and water carefully
poured on until it is level with the top of the frame. When the water begins
to drop from the funnel more water must be added to the top, so as to have
the initial depth of water over the soil the same in all the experiments. A
graduated glass is then pushed under the funnel, and the time noted which is
required for a quantity of water to pass through the soil. The quantity
usually taken for measurement is equivalent to one inch in depth over the
soil surface. In taking the sample, root and worm-holes are to be avoided,
and these are particularly troublesome in clay lands.
178. Measurement of Percolation through the Soil in Situ.—If lateral
translocation could be prevented, the measurement of the quantity of water
descending in the soil through a given area would be a matter of simplicity.
But to secure accurate results all lateral communication of a given body of
soil with adjacent portions must be cut off. Various devices have been
adopted to secure this result. An elaborate system of lysimetric
measurements is illustrated by the apparatus erected by the Agricultural
Experiment Station, of Indiana.
The plan and section of the apparatus are shown in Fig. 23.

Each lysimeter box, when finished, resembles somewhat a hogshead with
one head out. The sides, however, are perfectly straight inside, having a
slight thickening in the center, on the outside, for making them stronger.
The sides and bottom of the apparatus are constructed of oak and lined with
sheet copper carefully soldered so as to be water-tight. Six inches above,
and parallel to the bottom of each of the boxes, is a perforated copper tube,
which extends entirely across the lysimeter, and passing through one of the
sides connects the box with an underground vault in which the observations
are taken. These tubes give an outlet to the drainage water, as described
further on. The lysimeters are made of any required depth, the two which
are shown in section being three and two-thirds and six and two-thirds feet
deep, respectively.
The following method is employed for filling them with soil: There are
first placed in the bottom of each lysimeter six inches of fine sand, sifted
and washed, which fills them up to the level of the drainage tubes. The
lysimeters are then filled with fine, sifted surface soil, to the depth of three
and six feet, respectively, making a complete pair of lysimeters, and leaving
two inches of the lysimeter boxes projecting above the surface of the soil so
that each one will receive exactly its proper share of the rain-fall.
The lysimeters of the other pair, which are the same size as the first, are
filled in a different way. The lysimeters are first constructed and placed over
vertical columns of soil in situ, which are obtained by digging away all the
surrounding soil and leaving the columns standing. The shorter lysimeter is
sunk in this way to within two inches of its entire length. It is then tipped
over carrying the column of soil with it. Six inches of the subsoil are then
removed, when the drainage tube and sand are put in, as in the first pair, and
the bottom of the tube soldered in place. The lysimeter is thus filled with
the natural soil in place. The longer box is in the same way filled, as far as
possible, with the soil in place, but a gravelly nature of the soil may render
it impossible to do the filling with a single column unbroken, so the gravel
and sand from the lower portion of the soil are to be filled in separately. The
drainage tube and bottom of sand are placed in the longer lysimeter in the
same way as in the shorter.

Figure 23.

Ground Plan and Vertical Section of Lysimeters and Vaults Showing Position of
the Apparatus.

1, 1, 1, 1, Lysimeters.
2, 2, 2, 2, Receiving bottles.

3, 3, Supplying apparatus.
4, 4, Skylights.
5, 5, 5, 5, Wall of vault.
6, 6, Brick walls.
7, Entrance Steps.
8, Vault.

The purpose of placing sand at the bottom of each lysimeter is to offer a
porous stratum in which free water may collect and rise to the level of the
perforated copper tube, which would prevent any further rise by conveying
the surplus above into the vault as drainage water. The soil above the tube
will therefore be constantly drained and the sand below constantly
saturated, unless the water be drawn up by the capillary action of the soil as
the result of evaporation from the surface.
By means of a proper arrangement within the vault, of a kind of
Mariotte’s bottle, the water may be caused to flow back through the
drainage tube into the lysimeter to take the place of that lost by evaporation,
and thus maintain the level of free water just below the drainage tube. The
water flowing back to the lysimeter, and the amount of drainage water, are
carefully measured by a system of graduated tubes.
The lysimeters thus constructed represent tile-drained land; in one case
the tile being three feet below the surface and in the other six feet below.
The drainage waters collected in the receiving bottles can be measured and
analyzed from time to time, as occasion may require, to determine the
amount of plant food which is removed.
179. Improved Method of Deherain.[120]—Deherain’s earlier
experiments were made in pots containing about sixty kilos of soil. These
vases serve very well for some kinds of plants, but there are other kinds
which do not grow at all normally when their roots are imprisoned. For
instance, in pots, even of the largest size, wheat is always poor, beets
irregular, maize never acquires its full development, and the conclusions
which can be drawn from the experiments can not be predicated of the
action of the plant under conditions entirely normal.
It is necessary therefore to carry on the work in an entirely different way,
and to construct boxes so large as to make the conditions of growth entirely
normal. The arrangement of these boxes is shown in Fig. 24.

They are placed in a large trench, two meters wide, one meter deep, and
forty meters long. There are twenty boxes in this trench, the upper surface
of each containing four square meters area. The boxes are one meter deep,
and therefore can contain four cubic meters of soil. The sides and bottoms
of the boxes are made of iron lattice work, covered with a cement which
renders them impervious to water.
The bottom inclines from the sides towards the middle, and from the
back to the front, thus forming a gutter which permits of the easy collection
of the drainage. The drainage water is conveyed, by means of a pipe and a
funnel, into a demijohn placed in the ditch in front of the apparatus, as
shown in the figure. These receptacles stand in niches under the front of the
cases, and are separated by the brick foundations. Access to them is gained
by means of the inclined plane shown in the figure, and this plane permits
the demijohns in which the drainage water is collected, to be removed with
a wheelbarrow for the purpose of weighing. This apparatus is especially
suitable for a study of the distribution of the nitrogen to the crop, the soil
and the drainage waters. The loss in drainage waters of potash and
phosphoric acid is insignificant in comparison with the loss in nitrogen.
The cases having been placed in position they are filled with the natural
soil, which is taken to the depth of one meter, in such a way that the relative
positions of the soil and subsoil are not changed.
While the soil is transferring to the cases it is carefully sampled in order
to have a portion representing accurately the composition of both the soil
and subsoil. These samples are subjected to analysis and the quantities of
nitrogen, phosphoric acid, and potash contained therein carefully noted.
One or two cases should be left without crop or fertilizer to determine the
relations of the soil and subsoil to the rain-fall. Three or four cases should
be kept free of vegetation and receive treatment with different fertilizer, in
order to determine the influences of these on the deportment of the soil to
rain-fall. The rest of the cases should be seeded with plants representing the
predominant field culture of the locality, and some of them should be
fertilized with the usual manures used in farm culture.

Figure 24.

Deherain’s Apparatus for Collecting Drainage Water.

AUTHORITIES CITED IN PART THIRD.
70. Comptes rendus, Tome 112, p. 598.

71. Stockbridge, Rocks and Soils, p. 153.

72. Die Landwirtschaftlichen Versuchs-Stationen, Band 8, S. 40.

73. König, Untersuchung Landwirtschaftlich und Gewerblich Wichtiger Stoffe, S. 48.

74. Methods of Swedish Agricultural Chemists, translated for author by F. W. Woll.

75. Poggendorff’s Annalen, Fifth Series, Band 9, Ss. 102, et seq.

76. Pennsylvania Agricultural Experiment Station Report, for 1891, pp. 194, et seq.

77. Agricultural Science, Vol. 8, pp. 28, et seq. (Correction. For Fig. 13, second line from
bottom of page 112, read Fig. 14.)

78. Haberland. Forschungen auf der Gebiete der Agricultur-Physik, 1878, S. 148.

79. Grundlagen zur Beurteilung der Ackerkrume, Weimar, 1882.

80. Vid. supra, 10.

81. These general principles are taken chiefly from a résumé of the subject by Prof. H. A.
Huston. Indiana Agricultural Experiment Station, Bulletin 33, pp. 46, et seq.

82. Knop’s Agricultur Chemie, Abteil II.

83. Beiträge zur Frage der Bodenabsorption.

84. Henneberg’s Journal, 1859, S. 35.

85. Die Landwirtschaftlichen Versuchs-Stationen, Band 27, S. 107.

86. Die Bonitirung der Ackererde, S. 49.

87. Journal Chemical Society of London, 1868.

88. Landw. Central-Blatt, Band 11, S. 169.

89. bis Die Landwirtschaftlichen Versuchs-Stationen, Band 12, Ss. 21–50.

90. Jour. f. Landw., 1862, Band 3, Ss. 49–67.

91. Ann. d. Landw., Band 34, S. 319.

92. American Journal of Science, Vol. 14, p. 25.

93. bis (p. 122). Ms. communication to author.

94. Maryland Agricultural Experiment Station, Fourth Annual Report, p. 282.

95. Bulletin No. 4, U. S. Weather Bureau, p. 80.

96. bis (p. 125), Beiträge zur Agronomische Bodenuntersuchung, S. 31.

97. Zeitschrift für angewandte Chemie, 1889, S. 501.

98. Die Landwirtschaftlichen Versuchs-Stationen, Band 17, S. 85.

99. Ms. communication to author.

100. Proceedings of the Ninth Meeting of the Society for the Promotion of Agricultural Science,
p. 51.

101. Rocks and Soils, pp. 155 et. seq.

102. Anleitung zur Wissenschaftlichen Bodenuntersuchung, S. 137.

103. Analyse du Sol, p. 13.

104. Landwirtschaftliche Jahrbücher, Band 3, Ss. 771.

105. Forschungen auf dem Gebiete der Agricultur-Physik, 1885, Ss. 177, et seq.

106. Vid. supra, S. 259.

107. Poggendorf, Annalen, Band 129, Ss. 437, et seq.

108. König, Untersuchung Landwirtschaftlich und Gewerblich Wichtiger Stoffe, S. 59.

109. Vid. 37, S. 60.

110. Landwirtschaftliche Jahrbücher, Band 2, S. 383.

111. Forschungen auf dem Gebiete der Agricultur-Physik, 1880, S. 218.

112. Beurteilung der Ackerkrume, S. 222.

113. Wisconsin Agricultural Experiment Station, Seventh Annual Report, pp. 134, et seq.

114. Vid. supra, pp. 139, et seq.

115. Wisconsin Agricultural Experiment Station, Seventh Annual Report, p. 145.

116. Bulletin No. 4, Weather Bureau, pp. 13, et seq.

117. Philosophical Magazine, 1878.

118. Weather Bureau, Bulletin No. 4.

119. Forschungen auf dem Gebiete der Agricultur-Physik, 1891, S. 11.

120. Annales Agronomiques, Tome 16, p. 337; Tome 17, p. 49; Tome 18, p. 237; Tome 19, p. 69.

PART FOURTH.

MECHANICAL ANALYSIS OF SOILS.

THE FLOCCULATION OF SOIL PARTICLES.

180. Relation of Flocculation to Mechanical Analysis.—The tendency
of the fine particles of silt to form aggregates, which act as distinct particles
of matter, is the chief difficulty connected with the separation of the soil
into portions of equal hydraulic value by the silt method of analysis. This
tendency has been discussed fully by Johnson[121] and Hilgard.[122]
181. Illustration of Flocculation.—A sediment, consisting of particles
of a hydraulic value, equal to one millimeter per second, is introduced into
an ordinary conical elutriating tube placed vertically, in which the current of
water entering below performs all the stirring which the particles receive.
A current of water corresponding to a velocity below one millimeter per
second will, of course, not carry any of the particles out at the top of the
cylindrical tube, but will keep them moving through the conical portion of
the tube. If now the current be increased until its velocity is greater than one
millimeter per second after having run at the slower velocity for fifteen or
twenty minutes, very little of the sediment will pass over, although
theoretically the whole of it should. Even at a velocity of five millimeters
per second, much of the sediment will remain in the tube. This, of course, is
due to the coagulation of the particles into molecular aggregates having a
higher hydraulic value even than five millimeters per second. These

aggregates can be broken up by violent stirring or moderate boiling, and the
sediment reduced again to its proper value. The conclusions which Hilgard
derives from a study of the above phenomena are as follows:
1. The tendency to coagulation is, roughly, in an inverse ratio to the size
of the particles. With quartz grains it practically ceases when their diameter
exceeds about two-tenths of a millimeter having a hydraulic value of eight
millimeters per second. The size of the aggregates formed follows
practically the same law as above. Sediment of 0.25 millimeter hydraulic
value will sometimes form large masses like snow-flakes on the sides of the
elutriator tube.
2. The degree of agitation which will resolve the aggregates into single
grains is inversely as the size of the particles; or, more properly perhaps,
inversely as their hydraulic value.
3. The tendency to flocculation varies inversely as the temperature. So
much so is this the case that Hilgard at one time contemplated the use of
water at the boiling point in the mechanical analysis of soils, in place of
mechanical stirring.
4. The presence of alcohol, ether, and of caustic or carbonated alkalies,
diminishes the tendency to flocculation, while the presence of acids and
neutral salts increases it.
5. As between sediments of equal hydraulic value, but different densities,
the tendency to flocculation seems to be greater with the less dense
particles.
In regard to the mechanical actions which take place between the
particles, Hilgard considers them as irregular spheroids, each of which can
at best come in contact at three points with any other particle. The cause of
aggregation cannot therefore be mere surface adhesion independent of the
liquid, and the particles being submerged there is no meniscus to create an
adhesive tension.
Since experiment shows that the flocculative tendency is measurably
increased by the cohesion coefficient of the liquid, it seems necessary to
assume that capillary films of the latter interposed between the surfaces of
solids create a considerable adhesive tension even in the absence of a
meniscus.

182. Effect of Potential of Surface Particles.—Whitney suggests that
this is due to the potential of the surface particles of solids and liquids.[123]
The potential of a single water particle is the work which would be required
to pull it away from the surrounding water particles and remove it beyond
their sphere of attraction. For simplicity, it may be described as the total
force of attraction between a single particle and all other particles which
surround it. With this definition, it will be seen that the potential of a
particle on an exposed surface of water is only one-half of the potential in
the interior of the mass, as half of the particles which formerly surrounded
and attracted it were removed when the other exposed surface of water was
separated from it. A particle on an exposed surface of water, being under a
low potential, will therefore tend to move toward the center of the mass
where the potential, i. e., the total attraction, is greater, and the surface will
tend to contract so as to leave the fewest possible number of particles on the
surface. This is surface tension.
If, instead of air, there is a solid substance in contact with the water, the
potential will be greater than on an exposed surface of the liquid, for the
much greater number of solid particles will have a greater attraction for the
water particles than the air particles had. They may have so great an
attraction that the water particle on this surface, separating the solid and
liquid, may be under greater potential than prevails in the interior of the
liquid mass. Then the surface will tend to expand as much as possible, for
the particles in the interior of the mass of liquid will try to get out on the
surface. This is the reverse of surface tension. It is surface pressure, which
may exist on a surface separating a solid and liquid.
Muddy water may remain turbid for an indefinite time, but if a trace of
lime or salt be added to the water the grains of clay flocculate, that is, they
come together in loose, light flocks, like curdled milk, and settle quickly to
the bottom, leaving the liquid above them clear. Ammonia and some other
substances tend to prevent this and to keep the grains apart if flocculation
has already taken place.
If two small grains of clay, suspended in water, come close together they
may be attracted to each other or not, according to the potential of the water
particles on the surface of the clay. If the potential of the surface particle of
water is less than that of the particle in the interior of the mass of liquid,
there will be surface tension, and the two grains will come together and be

held with some force, as their close contact will diminish the number of
surface particles in the liquid. If, on the other hand, the potential of the
particle on the surface of the liquid is greater than of the particle in the
interior of the mass, the water surface around the grains will tend to enlarge,
as there will be greater attraction for the water particles there than in the
interior of the mass of liquid, and the grains of clay will not come close
together and will even be held apart, as their close contact would diminish
the number of surface particles in the liquid around them.
183. Influence of Surface Tension.—Hilgard supposes that the surface
tension which is assumed to exist between two liquid surfaces must exert a
corresponding influence between the surfaces of solids and liquids, apart
from any meniscal action.
It is then to be expected that the adhesion of the particles constituting one
of these floccules will be very materially increased whenever the formation
of menisci between them becomes possible by the removal of the general
liquid mass. Suppose one of the floccules to be stranded, it will, in the first
place, remain immersed in a sensibly spherical drop of liquid. As this liquid
evaporates, the spherical surface will become pitted with menisci forming
between the single projecting particles, and as these menisci diminish their
radius by still further evaporation, the force with which they hold the
particles together will increase until it reaches a maximum. As the
evaporation progresses beyond this point of maximum, the adhesion of the
constituent particles must diminish by reason of the disappearance of the
smaller menisci, and when finally the point is reached when liquid water
ceases to exist between the surfaces, the slightest touch, or sometimes even
the weight of the particles themselves, will cause a complete dissolution of
the floccule, which then flattens down into a pile of single granules.
In regard to natural deposits from water, Hilgard supposes that they are
always precipitated in a flocculated state. The particles of less than two-
tenths millimeter diameter are carried down with those of a larger diameter
having much higher hydraulic value. Thus the deposition of a pure clay can
take place under only very exceptionable circumstances.
Whitney, on the other hand, suggests that grains of sand and clay carry
down mechanically the particles of fine silt and clay as they settle in a
turbid liquid in a beaker; and it is often difficult to wash out a trace of fine

material from a large amount of coarse particles, for this reason, although
there may be no trace whatever of flocculation.
184. Destruction of Floccules.—The destruction of the natural floccules
is seen in the ordinary process of puddling earth or clay. It is also the result
of violent agitation of water or of kneading or boiling, or, finally, to a
certain extent, of freezing. All these agencies are employed by the workers
in clay for the purpose of increasing the plasticity which depends essentially
upon the finest possible condition of the material to be worked. As an
illustration of this, Hilgard cites the fact that any clay or soil which is
worked into a plastic paste with water, and dried, will form a mass of
almost stony hardness. If, however, to such a substance one-half per cent of
caustic lime be added, a substance which possesses in an eminent degree
the property of coagulating clay, the diminution of plasticity will be obvious
at once, even when in a wet condition. If now the mass be dried, as in the
previous case, it is easily pulverized. This is an illustration of the effect of
lime upon stiff lands, rendering them more readily pulverulent and tillable.
The conversion of the lime into a carbonate in the above experiment by
passing bubbles of carbonic acid through the mass while still suspended in
water does not restore the original plasticity, thus illustrating experimentally
the fact known to all farmers that the effect of lime on stiff soil lasts for
many years, although the whole of the lime in that time has been converted
into carbonate.
185. Practical Applications.—The practical application of this is,
according to Hilgard, that the loosely flocculated aggregation of the soil
particles is what constitutes good tilth. For this reason the perfect rest of a
soil, if it is protected from the tamping influence of rains and the tramping
of cattle, may produce a condition of tilth which cannot be secured by any
mechanical cultivation. As an illustration of this, the pulverulent condition
of virgin soils protected in a forest by the heavy coating of leaves may be
cited. On the contrary, as pointed out by Hilgard, there are some kinds of
soil in which a condition of rest may produce the same effect as tamping.
These are soils which consist of siliceous silt without enough clay to
maintain them in position after drying. In such a case, the masses of
floccules collapse by their own weight or by the least shaking, and fall
closely together, producing an impaction of the soil. This takes place in
some river sediment soils in which the curious phenomenon is presented of
injurious effects produced by plowing when too dry, which is the direct

opposite of soils containing a sufficient amount of clay and which are
injured by plowing too wet.
It is further observed that the longer a soil has been maintained in good
tilth, the less it is injured by wet plowing. This is doubtless, according to
Hilgard, due to the gradual cementation of the floccules by the soil water
which fixes them more or less permanently.
Whitney believes that the arrangement of the grains, or the condition of
flocculation in the soil, or the distance apart of the soil grains, is
determined, to a large extent, by the potential on the surface of the grains;
and he suggests that by changing this the exceedingly fine grains of silt and
clay can be pulled together or can be pushed further apart, and so alter the
whole texture of the land.
The action of alkaline carbonates in preventing flocculation, and thus
rendering tillage difficult or impossible, is pointed out by Hilgard in the
case of certain alkali soils of California. The soils which are impregnated
with alkaline carbonates are recognized by their extreme compactness. The
suggestion of Hilgard to use gypsum on such soils has been followed by the
happiest results. This gypsum renders any phosphates present insoluble, and
thus prevents loss by drainage, and yet leaves the plant food in a sufficiently
fine state as to be perfectly available for vegetation.
186. Suspension of Clay in Water.—The suspension of clay in water
and the methods of producing or retarding flocculation and precipitation
have also been studied by Durham.[124] His experiment is made as follows:
In a number of tall glass jars fine clay is stirred with water, and the
results of precipitation watched. In all cases it will be noticed that the clay
rapidly separates into two portions, the greater part quickly settling down to
the bottom of the jars, and the smaller part remaining suspended for a
greater or less length of time.
The power which water possesses of sustaining clay is gradually
destroyed by the addition of an acid or salt; a very small quantity, for
instance, of sulfuric acid, is sufficient to precipitate the clay with great
rapidity. In solutions of sulfuric acid and sodium chlorid of varying
strengths, suspended clay is precipitated in the order of the specific gravity
of the solutions, the densest solutions being the last to clear up. This may be
due to the greater viscosity of the denser liquids.

The power which water possesses of sustaining clay is gradually
decreased by the addition of small quantities of certain salts and of lime.
187. Effect of Chemical Action—Brewer[125] emphasizes the importance
of chemical action in the flocculation of clays. As expressed by him the
chemical aspects of the phenomena of sedimentation have either been
lightly considered or entirely ignored. Brewer is led to believe that the
action of clay thus suspended is analogous to that of a colloidal body. Like a
colloid, when diffused in water, the bulk of the mass is very great, shrinking
enormously on drying. He therefore concludes that clays probably exist in
suspension as a series of hydrous silicates feebly holding different
proportions of water in combination and having different properties so far
as their behavior to water is concerned.
Some of them he supposes swell up in water much as boiled starch does,
and are diffusible in it with different degrees of facility, and that the strata
observed on long standing of jars of suspended clay represent different
members of this series of chemical compounds which hold their different
proportions of combined water very feebly and are stable under a very
limited range of conditions.
These compounds are probably destroyed or changed in the presence of
acids, salts and various other substances, and are stable only under certain
conditions of temperature, those which exist at one temperature being
destroyed or changed to other compounds at a different temperature.
188. Theory of Barus.—Brewer’s hypothesis, however, is not in
harmony with the demonstration of Barus, who proves that a given particle
of clay has the same density in ether as in water.
The physical and mathematical aspects of sedimentation have also been
carefully studied by Barus.[126] The mathematical conditions of a fine
particle suspended in a liquid and free from the influences of flocculation
are described by Barus in the following equations.
If P be the resistance encountered by a solid spherule of radius r, moving
through a viscous liquid at the rate x, and if k be the frictional coefficient,
then P = 6πkrx. Again, the effective part of the weight of the particle is P´ =
⁴⁄₃πr³ (ρ-ρ´)g, where g is the acceleration of gravity and ρ and ρ´ the density
of solid particle and liquid, respectively. In case of uniform motion P = P´.
Hence x = 9k2 r² (ρ-ρ´)g ... (1).

In any given case of thoroughly triturated material the particles vary in
size from a very small to a relatively large value; but by far the greater
number approach a certain mean figure and dimension. An example of this
condition of things may be formulated. To avoid mathematical
entanglement let y = Ax³⁄₂e-x² ... (2) where y is the probable occurrence of the
rate of subsidence x. If now the turbidity of the liquid (avoiding optical
considerations) be defined as proportional to the mass of solid material
particles suspended in unit of volume of liquid, then the degree of turbidity
which the given ydx particles add to the liquid is, caeteris paribus,
proportional to r³ydx, where r is the mean radius. Hence the turbidity, T, at
the outset of the experiment (immediately after shaking), is T = T₀∫₀∞r³ydx =
T₀, where equations (1) and (2) have been incorporated.
If the plane at a depth d below the surface of the liquid be regarded, then
at a time after shaking the residual turbidity is

The equation describes the observed occurrences fairly well.
The phenomena of stratification observed by Brewer are explained by
Barus from the above formula: In proportion as the time of subsidence is
greater, the tube shows opacity at the bottom, shading off gradually upward,
through translucency, into clearness at the top. If, instead of equation (2),
there be introduced the condition of a more abrupt maximum, if, in other
words, the particles be very nearly of the same size, then subsidence must
take place in unbroken column capped by a plane surface which at the time
zero coincided with the free surface of the liquid. Again, suppose one-half
of the particles of this column differ in some way uniformly from the other
half. Then at the outset there are two continuous columns coinciding, or, as
it were, interpenetrating throughout their extent. But the rate of subsidence
of these two columns is necessarily different, since the particles, each for
each, differ in density, radius and frictional qualities, by given fixed
amounts. Hence the two surfaces of demarcation at the time zero coincided
with the free surface. In general, if there be n groups of particles uniformly
distributed, then at the time zero n continuous columns interpenetrate and
coincide throughout their extent. At the time t, the free surface will be

represented by n consecutive surfaces of demarcation below it, each of
which caps a column, the particles of which form a distinct group.
From a further discussion of the mathematical condition under which the
subsidence of the particles takes place, Barus is of the opinion that
Durham’s theory of suspension being only a lower limit of solution is
rapidly gaining ground, yet without being attended with concise
experimental evidence which will account for the differences in the rate of
subsidence. On the contrary, Brewer’s hypothesis of colloidal hydrates is
more easily subjected to experimental proof. The test shows that the
particles retain their normal density, no matter how they are suspended or
circumstanced.
Further, in the explanation of the phenomenon of sedimentation, the
following principle may be regarded as determined; namely, if particles of a
comminuted solid are shaken up in a liquid, the distribution of parts after
shaking will tend to take place in such a way that the potential energy of the
system of solid particles and liquid, at every stage of subsidence, is the
minimum compatible with the given conditions.
According to Barus it is necessary, in order to pass judgment on the
validity of any of the given hypotheses, to have in hand better statistics of
the size of the particles relatively to the water molecule, than are now
available. Inasmuch as the particles in pure water are individualized and
granular, it is apparently at once permissible to infer the size of the particles
from the observed rates of subsidence. His observations show that the said
rate decreases in marked degree with the turbidity of the mixture. Hence the
known formulæ for single particles are not rigorously applicable, though it
cannot be asserted whether the cause of discrepancy is physical or
mathematical in kind. It follows that special deductions must be made for
the subsidence of stated groups of particles before an estimate of their mean
size can fairly be obtained.
Rowland[127] reaches a closer approximation for the fall of a single
particle by showing that the liquid, even at a large distance from the
particle, is not at rest.
In the case of water, however, it is noticed that despite the large surface
energy of the liquid, subsidence takes place in such a way that for a given
mass of suspended sediment the surfaces of separation are a maximum. On
the other hand, in case of subsidence in ether or in salt solutions, the solid

particles behave much like the capillary spherules of a heavy liquid shaken
up in a lighter liquid with which it does not mix. In other words, the
tendency here is to reduce surfaces of separation to the least possible value,
large particles growing in mass and bulk mechanically at the expense of
smaller particles; in other words, exhibiting the phenomenon of
flocculation.
189. Physical Explanation of Subsidence.—Whitney[128] thinks that the
phenomena of the suspension of clay in water may be explained on purely
physical principles, and that neither the partial solution nor hydration
hypotheses are necessary, or will explain the suspension of clay in water,
for the solution, or hydrated substance, would still have a higher specific
gravity than the surrounding liquid. He calls attention in the first place to
the fact, that in a turbid liquid, which has been standing for weeks and
which is only faintly opalescent, the grains in suspension are still of
measurable size, if properly stained as in bacteriological examinations and
viewed through an oil emersion objective. He gives a value of 0.0001
millimeter, as the lower limit of the diameters of these particles of “clay,”
which are usually met with in agricultural soils. He refers to the fact that
fine dust and ashes, and even filings of metals, may remain in suspension in
the air for days and even months in very apparent clouds, or haze, although
they may be a thousand times heavier than the surrounding air. Particles of
clay, no smaller than the limits which have been assigned, should remain in
suspension in the much heavier fluid, water, for an indefinite time, for the
volume or weight of the particles (⁴⁄₃)(πr³) decreases so much more rapidly
in proportion than the surface (4πr²), that there is, relatively, a larger amount
of surface area in these fine clay particles, and a great deal of surface
friction in their movement through a medium, and they would settle very
slowly. Under ordinary conditions, however, the mean daily range of
temperature is about twenty degrees, the mean monthly range is fifty
degrees, and the yearly range 100° F., and the ordinary convection currents,
induced by the normal change of temperature, would be sufficient of itself
to keep these fine particles in suspension in the liquid for an indefinite time,
as it is known that currents of air keep fine particles of dust and ashes in
suspension. If the volume or weight of a fine gravel, having a diameter of
one and five-tenth millimeters, be taken as unity, then for a particle, having
a diameter of 0.00255 millimeter, which is the mean diameter for Whitney’s

clay group, the volume decreases in the ratio 1:0.000000004853, and the
surface decreases only in the ratio 1:0.000286.
190. Practical Applications.—The action of mineral substances in
promoting flocculence has been taken advantage of in later times in the
construction of filters for purifying waters holding silt in solution. In these
filters the introduction of a small quantity of alum, or some similar
substance, into the water usually precedes the mechanical separation of the
flocculent material. In the same way the action of iron and other salts on
sewage waters has been made use of in their purification and in the
collection of the sewage material for fertilizing purposes.
191. Separation of the Soil Into Particles of Standard Size.—The
agronomic value of a soil depends largely on the relative size of the
particles composing it. The finer the particles, within a certain limit, the
better the soil. The size of the particles may be estimated in three ways: (1)
by passing through sieves of different degrees of fineness; (2) by allowing
them to subside for a given time in water at rest; (3) by separating them in
water moving at a given rate of speed. The first method is a crude one and
is used to prepare in a rough way, the material for the second and third
processes.
192. Separation in a Sieve.—The soil should be dry enough to avoid
sticking to the fingers or to prevent agglutination into masses when
subjected to pressure. It should not, however, be too dry to prevent the easy
separation of any agglutinated particles under the pressure of the thumb or
of a rubber pestle.
The sieve should have circular holes punched in a sheet of metal of
convenient thickness to give it the requisite degree of strength. Sieves made
of wire gauze are not so desirable but it is difficult to get the finer meshes as
circular perforations. Such sieves cannot give a uniform product on account
of the greater diagonal diameter of the meshes and the ease with which the
separating wires can be displaced. It is convenient to have the sieves
arranged en batterie; say in sets of three. Such a set should have the holes in
the three sieves of the following dimensions; viz.,

1st sieve 2 millimeters diameter.
2nd „ 1 millimeter „
3rd „ 0.5 „ „

Coarser single sieves may be used to separate the fragments above two
millimeters diameter if such a further classification be desired. Each sieve
fits into the next finer one and the separation of a sample into three classes
of particles may be effected by a single operation. In most cases, however,
it is better to conduct each operation separately in order to promote the
passage of agglutinated particles by gentle pressure with the thumb or with
a rubber pestle. In no case should a hard pestle be used and the pressure
should never be violent enough to disintegrate mineral particles.
There is much difference of opinion concerning the smallest size of
particles which should be obtained by the sieve.
Most analytical processes prescribe particles passing a sieve of one
millimeter mesh (¹⁄₂₅ inch). There is little doubt, however, of the fact that a
finer particle would be better fitted for subsequent analysis by the hydraulic
method.
For this purpose a sieve of 0.5 millimeter circular mesh is preferred.
193. Sifting with Water.—In soils where the particles adhere firmly the
sifting should be done with the help of water. In such cases the soil is gently
rubbed with a soft steple or the finger in water. It is then transferred to the
sieve or battery of sieves which are held in the water, and rubbed through
each of the sieves successively until the separation is complete. After the
filtrate has stood for a few minutes the supernatant muddy liquor is poured
off, the part remaining on the sieve is added to it and the process repeated
until only clean particles larger than 0.5 millimeter are left on the sieve.
These particles can be dried and weighed and entered on the note book as
sand. The filtrate should be evaporated to dryness at a gentle temperature
and when sufficiently dry be rubbed up into a homogeneous mass by a
rubber pestle.
The sieve recommended by the Association of Official Agricultural
Chemists[129] for the preparation of fine earth for chemical analysis has
circular openings ¹⁄₂₅ inch (one millimeter) in diameter.
Wahnschaffe[130] directs that a sieve of two millimeters mesh be used in
preparing the sample for silt analysis and that the residue after the silt
analysis is finished, which has not been carried over by a velocity of
twenty-five millimeters per second, be separated in sieves of one millimeter
and 0.5 millimeter meshes respectively.

Hilgard objects to leaving this coarse material in the sample during the
process of churn elutriation on account of the attrition which it exerts and
therefore directs that it be separated by sieve analysis before the elutriation
begins.
194. Method of the German Experiment Stations.[131]—In the method
recommended for the German Agricultural Stations an attempt is made to
secure even a finer sieve separation than that already mentioned.
Sieves having the following dimensions are employed; sieve No. 1,
square meshes 0.09 millimeter in size, diagonal measure 0.11 millimeter;
sieve No. 2, square meshes 0.14 to 0.17 millimeter in diameter, diagonal
measure 0.22 to 0.24 millimeter; sieve No. 3, square meshes 0.35 to 0.39
millimeter in diameter, diagonal measure 0.45 to 0.50 millimeter; finally a
series of sieves one, two and three millimeters circular perforations.
Five hundred grams of the soil (in the Halle Station only 250) are placed
in a porcelain dish with about one liter of water and allowed to stand for
some time with frequent stirring, on a water bath. After about two hours,
when the soil is sufficiently softened so that with the help of a pestle it can
be washed through the sieves, the process of sifting is undertaken in the
following manner: Sieve No. 3 is placed over a dish containing water, the
moistened soil placed therein and the sieve depressed a few centimeters
under the water and the soil stirred by means of a pestle until particles no
longer pass through. After the operation is ended the residue in the sieve is
washed with pure water and dried. The part passing the sieve is thoroughly
stirred and then washed with water into sieve No. 2 and treated as before.
The product obtained in this way is brought into sieve No. 1 and carefully
washed. All the products remaining on each of the sieves are dried at 100°
and weighed. The portion passing sieve No. 1 is either dried with its wash
water or estimated by loss by deducting from the total weight taken, the
sum of the other weights obtained. If a more perfect separation of the first
sieve residue be desired it can be obtained by passing it through sieves of
the last series which may have meshes varying in size, viz.: one, two, or
three millimeters in diameter. Each sieve of the same class should have
holes uniformly of the same size.
The sieve products are characterized as follows: The part passing a three
millimeter sieve is called fine earth, while the part remaining is called
gravel. The fine earth is separated into the following products: The part that

passes through the three millimeters opening and is left by the two
millimeters opening is called steinkies. The product from the two
millimeters opening and the residue from the one millimeter opening is
called grobkies. The product from the one millimeter opening and the
residue on the sieve No. 3 is called feinkies. The product from the sieve No.
3 and the residue from the sieve No. 2 is called coarse sand. The product
from sieve No. 2 and the residue from sieve No. 1 is called fine sand. The
product from sieve No. 1 is called dust. The dust can be further separated
into sand, dust, and clay. For the examination of the clay the Kühn silt
cylinder as modified by Wagner, is recommended. The cylinder has a
diameter of eight centimeters and a height of thirty centimeters, and is
furnished with a movable exit tube reaching to its bottom.
195. General Classification of the Soil by Sieve Analysis.—The
classification recommended by the German chemists is satisfactory but the
following one is more simple. All pebbles, pieces of rock, etc., should first
be separated by a two millimeters circular mesh sieve, dried at 105° and
weighed. The result should be entered as pebbles and coarse sand.
The finer sand may be separated with a sieve of one millimeter circular
openings.
The still finer sand is next separated with the sieve of 0.5 millimeter
circular openings as indicated above.
The sample may now be classified as follows:

1. Coarse pebbles, sticks, roots, etc., separated by hand.
2. Pebbles and coarse sand not passing a two millimeters sieve.
3. Sand not passing a one millimeter sieve.
4. Fine sand not passing a 0.5 millimeter sieve.
5. Fine earth passing a 0.5 millimeter sieve.
196. Classification of Orth.[132]—As fine silt are reckoned those particles
which range from 0.02 to 0.05 millimeter; as fine sand the groups from 0.05
to 0.2 millimeter; as medium sized sand those ranging from 0.2 to 0.5
millimeter and for large grained sand those particles ranging from 0.5 to 2
millimeters in diameter. Particles over two millimeters form the last
classification.

SEPARATION OF THE EARTH PARTICLES BY A LIQUID.

197. Methods of Silt Analysis.—The further classification of the
particles of a soil passing a fine sieve can best be effected by separation in
water. The velocity with which the current moves or with which the
particles subside will cause a separation of the particles into varying sizes.
The slower the velocity the smaller the particles which are separated. There
is, however, a large and important constituent of a soil which remains
suspended in water, or in a state of seeming solution. This suspended matter
would still be carried over by a current of water moving at a rate so slow as
to make a subclassification of it impossible. This suspended matter passing
off at a given velocity may be classed as clay, and it consists in fact chiefly
of the hydrated silicate of alumina, or other particles of equal fineness. The
laws which govern its deposit have already been discussed.
The apparatus which have been used for silt analysis may be grouped
into four classes.
(1) Apparatus depending on the rate of descent of the particles of a soil
through water at rest. The apparatus for decanting from a cylinder or a
beaker belong to this class.
(2) Apparatus which determine the rate of flow by passing the liquid
through a vessel of conical shape. The system of Nöbel is a good illustration
of this kind of apparatus.
(3) Apparatus in which the elutriating vessel is cylindrical and the rate of
flow determined by a stop-cock or pressure feed apparatus. The system of
Schöne represents this type.
(4) Apparatus in which the above system is combined with a device for
mechanically separating the particles and bringing them in a free state into
the elutriating current. The system of Hilgard is the type of this kind of
apparatus.
In practice the use of cylindrical apparatus with or without mechanical
stirring and the method by decantation have proved to be the most reliable
and satisfactory procedures. Between the beaker and churn methods, of
separation there is little choice in regard to accuracy. Which is the superior
method, is a question on which the opinions of experienced analysts are

divided. The various processes will be described in the order already
mentioned.
198. Methods Depending on Subsidence of Soil Particles.—The
simplest method of effecting the further separation of the soil particles is
without doubt that process which permits them to fall freely in a liquid
sensibly at rest. The practical difficulties of this method consist in the
trouble of securing a perfect separation of the particles, in preventing
flocculation after division and in avoiding currents in the liquid of
separation.
For the separation of the soil particles for this method boiling and wet
pestling are the only means employed. The flocculation of the separated
particles may be partially prevented by adding a little ammonia to the water
employed. The author has also tried dilute alcohol as the separating liquid
but the results of this method are not yet sufficiently definite to find a place
in this manual. Evidently the practical impossibility of avoiding convection
currents prevents the use of water at a high temperature for this separation,
although the tendency to flocculation almost disappears as the temperature
approaches 100°. The general method of avoiding the errors due to
flocculation in the subsidence method consists in repestling the deposited
particles and thus subjecting them as often as may be necessary to
resedimentation. These principles are well set forth by Osborne,[133] who
states that when a soil is completely suspended in water by vigorous
agitation, particles of all the sizes present are to be found throughout the
entire mass of liquid. When subsidence takes place, the larger particles will
go down more rapidly than the smaller ones, but some of the small particles
that are near the bottom will be deposited sooner than some of the larger
ones which have a much greater distance to travel. Thus, independently of
the fact that the larger particles in their descent are somewhat impeded by
the smaller, the smaller being at the same time somewhat hastened by the
larger, the sediment that reaches the bottom at any moment is a more or less
complex mixture of all the mechanical elements of the soil. The liquid,
however, above this sediment at the same moment will have completely
deposited all particles exceeding certain dimensions of hydraulic value,
determined mainly by the time of subsidence.
If now the aforesaid first sediment be suspended in pure water, and
allowed to subside for the same time as before, the larger part of it will be

again deposited, but some will remain in suspension, consisting of a
considerable part of the finer matter of the first sediment. By pouring off
these suspended particles with the water and agitating the sediment again
with clear water as before, another portion of fine particles will be
suspended and may be decanted from it. On continuing this process of
repeated decantations it will soon be found that the soil has been separated
into two grades.
It is evident that in this way a separation can be made, but it is perhaps
not so clear that such a separation would be sharp enough for the purposes
of a mechanical soil analysis. If, for instance, the separation is to be made at
0.05 millimeter diameter, it is evident that by repeated decantations all
below 0.01 millimeter can be washed out of that above 0.05 millimeter, but
it may not appear so probable that all below 0.045 millimeter can be
removed without removing some above 0.055 millimeter.
Such a result may be easily attained, however, if the following principle
be adhered to:
Make the duration of the subsidence such that the liquid decanted the
first few times shall contain nothing larger than the desired diameter. Then
decant into another vessel, timing the subsidence so that the sediment shall
contain nothing smaller than the chosen diameter. This can not be done
without decanting much that is larger than the chosen diameter, but the
greater part of the particles greater and less than the chosen diameter can be
removed and an intermediate product obtained, the diameters of whose
particles are not very far from that desired.
If this intermediate portion be again subjected to the same process, two
fractions may be separated from it, one containing particles larger than the
chosen diameter and another containing particles smaller than this diameter,
while a new intermediate product will remain which is less in amount than
that resulting from the first operation. By frequent repetitions of this
process this intermediate product can be reduced to a very small amount of
substance the particles of which have diameters lying close to the chosen
limit and may then be divided between the two fractions.
The principles of the separation described by Osborne set forth with
sufficient clearness the purposes to be achieved by the analysis. The chief
methods of manipulation practiced will be found below.

199. Kühn’s Silt Cylinder.—A simple form of apparatus for the
determination of silt by the sedimentation process is the one described by
Kühn.[134]
The cylinder should be about twenty-eight centimeters high with a
diameter of 8.5 centimeters. At the lower end of the cylinder five
centimeters from the bottom it carries a tube 1.5 centimeter in diameter
furnished with a pinch-cock and held in position by a rubber stopper.
In carrying out the process thirty grams of sifted soil (two millimeters
mesh sieve) are boiled with water for an hour and after cooling the soil and
water are washed into the separating cylinder. The cylinder is then filled
with water with constant shaking.
After standing for ten minutes the stop-cock is opened and the water with
its suspended matter allowed to flow into a porcelain dish.
The cylinder is then again filled with water and the process is continued
until the water drawn off is practically clear.
The fine particles having been separated in this way the next coarser
grade of particles is separated by repeating the process at intervals of five
minutes.
By these two operations it is considered that the clay is entirely removed.
The residue remaining in the cylinder is dried and weighed. The relative
proportions of clay and residue in the sample are thus determined.
The residue is then separated into two portions by sieves of one
millimeter and 0.5 millimeter mesh.
The soil is thus separated into the following parts:

1. By the first sifting coarse quartz larger than two millimeters diameter.
2. Fine quartz two millimeters, to one millimeter diameter.
3. Coarse sand one millimeter, to 0.5 millimeter diameter.
4. Fine sand finer than 0.5 millimeter diameter.
5. Silt, clay, humus, etc., separated by the water.
200. Knop’s Silt Cylinder.—The cylinder recommended by Knop[135] is
essentially that of Kühn being furnished with four lateral tubes instead of
one (Fig. 25).

The sample of soil, twenty-five to thirty grams,
after passing a two millimeters mesh sieve, and
long boiling, is washed through a series of sieves
of the following diameters of mesh respectively;
viz., one millimeter, 0.5 millimeter, 0.25
millimeter, and 0.1 millimeter. The part which
passes the finest sieve is placed in a Knop’s
cylinder, the cylinder filled with water one
decimeter above upper tube and well shaken. The
cylinder is allowed to rest for five minutes when
the upper cock is opened and the water drawn off.
After five minutes more the next tube is opened
and so on with equal intervals for the three upper
tubes. The operation is repeated with fresh water
until the water drawn off is clear. Finally the
lowest tube is opened and all the water poured off
of the sandy residue. The space between each tube
Figure 25. is one decimeter. The dust remaining is dried and
Knop’s Silt Cylinder. weighed and the weight of material carried over as
silt determined by difference.
201. Siphon Silt Cylinder.—Instead of the tubulated cylinder one
furnished with a siphon can be employed[136] (Fig. 26).
It should be about forty centimeters high and six centimeters internal
diameter. The cylinder first receives twenty-five to thirty grams of the well
boiled fine earth and then water until there is but a small space between it
and the stopper when the latter is inserted.
The cylinder is marked exactly 200 millimeters below the surface of the
water with a narrow strip of paper at a, stoppered, inverted and well shaken.
The cylinder being again placed in normal position the soil particles under
the influence of gravity tend to sink with greater or less rapidity according
to their size. The siphon a b c is filled with water, the cock at c closed and
the opened end a placed in the cylinder A just at the mark 200 millimeters
below the surface of the water, and the water thus transferred to B when
desired. If the suspended matter is allowed to stand for 100 seconds the
particles of more than two millimeters hydraulic value will have fallen
below the open end of the siphon. If allowed to stand 1,000 seconds the silt

value of the particles will be 0.2 millimeter per second. Whatever the
number of seconds may be, the operation is continued until the water
removed is practically clear. The open end of the siphon a should be bent
upwards so that no disturbing current may bring the particles below the line
into the liquid discharged into B.

Figure 26.

Siphon Cylinder for Silt Analysis.

While the results obtained by this method are satisfactory as compared
with other similar processes it cannot be highly recommended because of
the time and trouble required to get a complete separation and by reason of
the difficulty of collecting the separated silt.
202. Wolff’s Method.[137]—As modified by Wolff the Knop process is
conducted as follows: Fifty grams of fine earth are boiled with water and
then the entire mixture is passed through three sieves with openings of one

millimeter, 0.5 millimeter, and 0.25 millimeter in diameter, respectively.
The finest part is mixed with water to a height of eighteen centimeters in a
bottle twenty centimeters high and having a capacity of one liter and
thoroughly agitated, after which it is left to rest, and finally the turbid liquid
is drawn off with a siphon, the bottle refilled with water, agitated, and left to
rest, and the process repeated as long as the water carries any suspended
matter after a definite time.
Wolff proposes for the first three periods of rest one hour, for the second
three, a half an hour, for the third three, a quarter of an hour, and for the
fourth three, five minutes.
203. Moore’s Modification of Knop’s Method.[138]—The sample of soil
is first passed through a sieve having round perforations three millimeters in
diameter. The weight of the particles remaining on the sieve is then
determined, and likewise that of the portion passing through, which is
known as fine earth. The last named portion constitutes the material for all
subsequent operations of mechanical and chemical analysis.
Thirty grams of the fine earth are boiled rapidly with water until the
lumps are disintegrated and clayey portions separated from the sand. The
material is then successively washed through perforated metal sieves, the
holes of which are respectively 1, 0.5, and 0.25 millimeter in diameter. The
portions retained on the sieves are severally dried, ignited and weighed, and
the finest portion, or that passing through the 0.25 millimeter sieve, is then
submitted to the following process of separation:
The sediment and water passing through the 0.25 millimeter sieve are
placed in a glass cylinder fifty centimeters long and thirty-seven millimeters
in internal diameter. The cylinder is closed at the bottom and is provided
with a lateral tube inserted six centimeters above the bottom. Three other
lateral tubes are inserted at intervals of ten centimeters above the first tube,
and a ring is etched into the cylinder ten centimeters above the uppermost
tube. The lateral tubes are closed with rubber tubes compressed by spring
clips. The sediment being placed in the cylinder, water is added to the mark
or ring, the cylinder closed with a rubber stopper, and vigorously shaken
until the contents are thoroughly mixed. It is then placed upright, the
stopper removed, and after standing undisturbed for five minutes the clip on
the uppermost tube is opened and the water allowed to flow into a beaker.
After five minutes further standing, the second clip is opened and the water

drawn off into the same beaker; in the same manner the water is drawn off
from the other tubes at intervals of five minutes until the level of the lowest
tube is reached. The cylinder is then refilled with water to the mark,
thoroughly shaken after inserting the stopper and the water again drawn off
at intervals of five minutes, as before; the operation being repeated until the
water drawn off is almost free from turbidity. The sediment remaining in the
cylinder from this process of washing by subsidence is termed by Knop,
fine sand, the material flowing off in suspension in the wash waters, dust,
and the process of separation by Knop’s original method ends here.
In order to remedy the imperfect separation into definite particles secured
by the above method, Moore proposes the following device:
The fine sand from the first series of subsidences is placed in a separate
vessel, the washings are allowed to remain undisturbed for twelve hours,
the turbid liquid decanted and the sediment returned to the cylinder. Water
is then added to the mark, the whole shaken, and the liquid drawn off at
intervals of five minutes, as in the first series. The sediment from this
operation is placed in a separate beaker, the washings returned to the
cylinder, and again allowed to subside as before; the sediment from this
second subsidence is added to that from the preceding operation, and the
washings again returned to the cylinder, the operation being repeated as
long as any sediment can be obtained from renewed treatment of the
washings; the final washings are then placed in a separate vessel for
subsequent microscopic measurements.
The collective sediments from the last series of operations are then
returned to the cylinder and allowed to subside with fresh additions of
water, as in the case of the first series; the fine sand thus obtained being
added to that from the first series, and the washings being collected in a
large beaker. The latter are left at rest for twelve hours, and the sediment
returned to the cylinder and treated as before until no further separation can
be effected. The fine sand resulting from all of these operations is then
dried, ignited and weighed; the weight of the portion removed by the
washing being determined by difference, as it is, owing to its excessively
slow rate of subsidence, found impracticable to collect it for direct
weighing. The size of the particles of fine sand is then determined by
micrometric measurement. Similar measurements are made on the material
obtained by long subsidence from the washings from the foregoing

operations. The average diameter of the largest particles should not exceed
0.01 millimeter.
204. Statement of Results.—The results of the analyses on three soils
from the localities indicated in the table, and the method of stating them, are
given in the following table:

New Milford, Clarksville, Tenn., Granville, N. C.,
Conn., per cent. per cent. per cent.
Particles larger in diameter than 8.55 0.32 0.23
3.0 millimeters
Particles of diameter from 3.0 4.96 0.45 15.04
millimeters to 1.0 millimeter
Particles of diameter from 1.0 4.43 0.96 33.43
millimeter to 0.5 millimeter
Particles of diameter from 0.5 11.86 1.25 18.82
millimeter to 0.25 millimeter
Particles of diameter from 0.25 60.54 61.58 23.59
millimeter to 0.01 millimeter
Particles smaller in diameter than 9.66 35.44 8.89
0.01 millimeter
Total 100.00 100.00 100.00

205. Method of Bennigsen.—The silt flasks recommended by
Bennigsen[139] are shown in Fig. 27.
The glass flask b carries a long cylindrical neck a the upper part of which
is graduated in cubic centimeters. Ten grams of the fine soil are shaken with
water in the flask, the neck of which is closed with a rubber stopper. The
flask is then inverted bringing the soil and water into the neck. The flask is
hung up and sedimentation is assisted by imparting a pendulous motion to
the neck for ten minutes. After an hour the soil particles have separated into
a coarse layer below and a fine layer above. The relative volumes of the two
layers are then read off in cubic centimeters. While this method may be
useful in helping to form a speedy judgment concerning the character of a
soil it can lay no claim to being an accurate method of silt separation.
206. Method of Gasparin.—The method of Gasparin only gives a very
primitive separation of the various components of the earth according to
their fineness. It is conducted as follows:
Ten grams of sifted earth are put into a beaker, water is added and
strongly agitated; after five minutes the water is decanted into another

vessel, the first vessel is filled anew
with water, agitated, decanted, and this
process is repeated until the liquid
remains perfectly clear. Only two
portions are weighed, i. e., the pebbles
which remain in the sieve and the
coarse sand which remains in the
beaker; while the argillaceous portion
drawn off with the water is determined
by the difference.
207. The Italian Method.—The
following modification of Gasparin’s
process is practiced by the Italian
chemists:[140]
Twenty grams of earth are passed
through a sieve having openings of one
millimeter in diameter, then the sifted
part is mixed with 100 cubic
Figure 27. centimeters of water in a 200 cubic
centimeters beaker and left to rest for
Bennigsen’s Silt Flasks.
some hours, then strongly agitated and
after ten seconds the turbid liquid is
poured into another vessel of half a liter capacity. This manipulation is
repeated until the liquid is clear.
The decanted liquid is thoroughly agitated, then left to stand until the
movement shall be completely arrested, after which the supernatant liquid is
poured into another vessel holding two liters. To the residuum is added
more water; it is agitated, decanted, and this process is repeated until the
water is no longer turbid.
208. Method of Osborne.—In the foregoing paragraphs the methods of
silt separation by subsidence as practiced in different countries have been
outlined. The good points of the various methods are combined in the
process as carried out by Osborne.[141] The details of this method will be
given with sufficient minuteness to make its practice possible by all
analysts.

Selecting the Sample.—Several pounds of air-dried, fine earth are
secured by passing the soil through a sieve, the holes of which are three
millimeters in diameter.
Sifting.—Thirty grams of the above fine earth are stirred with 300 to 400
cubic centimeters of water and then thrown successively upon sieves with
circular holes of 1, 0.5, and 0.25 millimeter diameter respectively. By
means of successive additions of water and the use of a camel’s hair brush,
all the fine material is made to pass through the sieves and these at the last
are agitated under water in a shallow dish in such a way that the soil is
immersed. The finest sieve should be well wet with water on its lower
surface just before using. The finest particles which render the water turbid
are easily washed through. The turbid water is kept separated from the clear
water which comes off with the last portions that pass the sieves. The turbid
water usually does not amount to more than one liter.
Elutriation.—The elutriation should be carried on so as to secure three
grades of silt; the diameters of the particles ranging in the first grades from
0.25 to 0.05 millimeter, in the second grade from 0.05 to 0.01 millimeter,
and in the third grade from 0.01 millimeter to the impalpable powder. The
term sand is applied to the first grade, silt to the second, and dust to the
third. After the turbid liquid from the sifting has stood a short time it is
decanted from the sediment and after standing until a slight deposit is
formed, is again decanted and the sediment examined with a microscope. If
sand be present, the subsidence of the turbid liquid is continued until no
more sand is deposited. As the sand subsides rapidly there is no difficulty in
altogether freeing the liquid first decanted from this grade of particles. The
sediment thus obtained contains all the sand, a part of the dust and much
silt. As only dust and the finest silt render the water turbid the sediment is
stirred a few times with a fresh quantity of water and decanted after
standing long enough to let all the sand settle. When the water decanted is
free from turbidity, the last portions of the soil passing through the sieve
with clear water are added to the sediment and the decantations continued
so as to remove most of the silt. When no more silt can be easily removed
from the sediment without decanting sand, the decantations are made into a
different vessel and the subsidences so timed as to remove as much of the
silt as possible. By using a little care, at least three-quarters of the sand are
thus obtained free from silt. The rest of the sand is mixed with the greater
part of the silt which has been decanted into the second vessel. The size of

the smallest particles in this vessel is determined with the microscope, to
make sure that its contents are free from dust as they usually will be if, after
settling for a few moments, they leave the water free from turbidity.
The soil is thus separated into three portions, one containing sand, one
sand and silt, and the other silt, dust, and clay. The sand and silt are
separated from each other by repeating the subsidences and decantations in
the manner just described.
In this way there is removed from the sediment, on the one hand, a
portion of silt free from sand and dust, and on the other hand a portion of
sand free from silt. Thus is obtained a second intermediate portion
consisting of sand and silt, but less in amount than the first and containing
particles of diameters much more nearly approaching 0.05 millimeter. By
repeating this process a few times, this intermediate portion will be reduced
to particles whose diameters are very near 0.05 millimeter and which may
be divided between sand and silt, according to judgment. The amount of
this is usually very small. As soon as portions are separated, which the
microscope shows to be pure sand or pure silt, they are added to the chief
portions of these grades already obtained.
The same process is applied to the separation of silt from dust. When all
the silt has been removed from the dust and clay, the turbid water
containing the dust and clay is set aside and allowed to settle in a
cylindrical vessel for twenty-four hours. The vessel is filled to a height of
200 millimeters. According to Hilgard, the separation of the dust from clay
during a subsidence of twenty-four hours, will give results of sufficient
accuracy, although the clay then remaining suspended will not be entirely
free from measurable fine particles up to 0.001 or 0.002 millimeter
diameter.
Small beakers and small quantities of distilled water are used at first for
the decantations, as thus the duration of subsidence is less and more
decantations can be made in a given time than when larger quantities of
water are employed. Beakers of about 100 cubic centimeters capacity are
convenient for the coarser grades, but it is necessary to use larger vessels
for the fine sediments from which turbid water accumulates that cannot be
thrown away, as may be done with the clear water, from which the coarse
sediments settle out completely in a short time.

It is best to keep the amount of water as small as possible in working out
the dust since loss is incurred in using too large quantities.
It is also necessary in most cases to subject the various fractions obtained
during elutriation, to careful kneading with a soft rubber pestle so that the
fine lumps of clay may be broken up and caused to remain suspended in the
water. This treatment with the pestle should be done in such a way as to
avoid as far as possible all grinding of the particles, the object being merely
to pulverize the minute aggregations of clay and extremely fine particles
which always form on drying a sample of soil after removing it from the
ground.
Measurement of the Particles.—To determine the size of particles in
suspension, a small glass tube is applied to the surface of the liquid in such
a way as to take up a single drop which is transferred to a glass slide. This
drop will contain the smallest particles in the liquid.
To obtain a sample of the coarsest particles the liquid is allowed to stand
long enough to form a very slight sediment and a portion of this sediment is
collected with a glass tube.
To determine the diameter of the particles in a sediment it is stirred
vigorously with a little water and the pipette at once applied to the surface
of the water. On decanting the greater part of the sediment, the large
particles remain at the bottom of the beaker and may be easily examined.
Time.—The time required to make the separations, above described, is
about two hours for each, so that an analysis including the sittings, is made
in five or six hours, exclusive of the time necessary for collecting the dust
and separating the clay, for which a subsidence of twenty-four hours is
allowed.
Weighing the Sediments.—The sediments are prepared for weighing by
allowing them to subside completely, decanting the clear water as far as
possible, rinsing them into a weighed platinum dish and igniting. The dish
is cooled in a desiccator.
Effect of Boiling.—The analyses show a very decided increase in the
particles smaller than 0.01 millimeter diameter at the expense of coarser
particles as the result of boiling. The surfaces of the coarser particles are
seen to be polished and of a lighter color than those not boiled. The surfaces
of the unboiled particles are coated with a film of fine material probably
cemented to them by clay. When these coarse particles which have not been

boiled, are violently stirred with water for a short time, no fine particles are
detached from them; and a careful examination under the microscope fails
to reveal in any of the sediments more than an occasional grain exceeding
the 0.05 millimeter limit by so much as 0.01 millimeter, or the 0.01 limit by
as much as 0.005 millimeter. It would, therefore, appear that these small
particles thus set free by long boiling are really a part of the larger ones and
should be treated as such in a mechanical analysis of these soils.
209. The French Method.—The Schloesing method[142] as practiced by
the French agricultural chemists[143] differs essentially from those already
described in attempting to first free the silt from carbonates and organic
matter. It is conducted as follows:
One kilogram of the soil previously dried in the air, is taken and passed
through a sieve of which the meshes are five millimeters. The agglomerated
particles of earth are broken up by the hand. The pebbles are also taken out
and weighed. The pebbles are then treated with hydrochloric acid until all
effervescence is over. The insoluble part is dried and again weighed. The
difference in weight gives the quantity of calcium carbonate contained on
the external surface of the pebbles. The earth which passes the sieve of five
millimeters mesh is next passed through a sieve having ten meshes to the
centimeter. The masses on the sieve are broken up with the hand or with a
pestle, in such a manner as to separate the fine agglomerated particles. The
material which remains upon the sieve after being dried at 100°, is weighed.
This gives the coarse sand. This is treated with hydrochloric acid as were
the pebbles before, washed and the residue dried and weighed. The
difference in weight gives the quantity of calcium carbonate adhering to the
surface of the coarse sand.
The mechanical analysis is continued with the matter which has passed
the sieve with ten meshes to the centimeter and which consists of the soil,
properly so-called. Ten grams of this are taken, dried at 100° until no
further loss takes place and the moisture thus determined. Another ten
grams are taken and placed in a capsule with a flat bottom, and from nine to
ten centimeters in diameter. This is moistened with a small quantity of
water in such a way as to make a paste. This paste is rubbed with the finger
in fifteen cubic centimeters of water. Ten seconds after the stirring is
completed the supernatant liquid is poured into a precipitating jar of about
250 cubic centimeters capacity, taking great care not to allow any particles

to pass over which have been deposited during that time. This operation is
repeated in the same way waiting about ten seconds each time before
decanting, until the decanted liquor is almost perfectly clear. In this way the
particles of different fineness are separated. The decanted portions contain
the fine sand and clay. The remaining portion contains the sand and
particles of medium fineness. This last part is dried, being kept at 100° until
it has a constant weight. It is afterwards treated with dilute nitric acid to
dissolve the calcium carbonate. When the carbonate is abundant, it is
sufficient to determine it by difference which is done by washing the
material, drying and weighing. But when the proportion of carbonate is very
small and in consequence when its exact determination acquires a greater
importance, it is better to determine the lime directly. For this purpose the
part soluble in dilute nitric acid is collected, treated with ammonia and
acetic acid and precipitated with ammonium oxalate. Details of this
operation will be given in another part of this manual.
In regard to the matter which is insoluble in nitric acid, it is composed
chiefly of silica or silicates, and sometimes also of vegetable débris. The
vegetable matter is determined by the incineration of the material which has
been previously dried. The loss of weight gives the proportion of vegetable
or organic débris contained in the soil and of combined water.
The portion which has been decanted, the volume of which should not
exceed 500 cubic centimeters, is treated with nitric acid until effervescence
ceases. It is then left to digest for some time, in order to permit the whole of
the carbonate to dissolve. It is next thrown upon a smooth filter about one
decimeter in diameter. After filtration it is washed to secure the complete
elimination of the soluble lime salts. The lime is determined in the filtered
liquid.
The insoluble portion contains the fine sand, the clay and humus bodies.
In order to separate the three elements the precipitate which was received
upon the filter, is rubbed with water, the filter is broken and all its contents
washed through. The volume of wash water is made up to 200 cubic
centimeters; two or three cubic centimeters of ammonia are added and the
whole left to digest for two or three hours. The volume of the liquid is then
made up to one liter with distilled water, vigorously shaking in such a way
as to put all the matter in suspension. It is then left to settle for twenty-four
hours. At the end of this time the supernatant liquid is decanted by the aid

of a siphon. To the residue are added two cubic centimeters of ammonia and
one liter of water. The matter is again brought into suspension and allowed
to settle for twenty-four hours. The supernatant liquid is again decanted
with a siphon, and added to the liquid previously removed. For ordinary
soils two decantations are generally sufficient but when the soils contain a
large quantity of clay it is convenient to decant three or four times. By an
examination of the supernatant liquid it is easy to tell if the washings have
been sufficiently prolonged. The decanted liquors contain the organic
matter and that which it is convenient to call clay, which is constituted of
very fine particles of sand and colloidal clay which play, in arable soil, a
rôle somewhat like that of cement.
These matters are estimated in the following manner: The liquor is first
treated with nitric acid and the clay and the humic matters are precipitated
together. They are collected upon a smooth filter one decimeter in diameter
and washed with water. By means of a washing bottle all the solid matters
which have stuck to the sides of the filter are finally collected in the bottom
of it. Since the last washings pass the filter very slowly, they can be
removed after the complete deposition of the matter they contain, by means
of a pipette. When all the liquid is removed the filter is placed upon blotting
paper, great care being taken to avoid desiccation, having in view only the
elimination of the excess of humidity. The folds in the filter are then
carefully smoothed out with the finger. The matter which has collected upon
the filter is then removed completely with a washing bottle, placed in a dish
and dried at 100° and weighed. After weighing, the mass is incinerated in a
muffle in order to destroy the humic bodies. The difference in weight before
and after incineration, gives the total weight of the humic bodies and since
the diminution in weight comprises not only the weight of the humic
bodies, but also the weight of the combined water which is lost during the
process of incineration, there should be subtracted from the total loss of
weight ten per cent of the weight of the residual mineral matter, which
represents the water of composition of the hydrated silicate.
210. Statement of the Analysis.—Schloesing in his original paper[144]
recommends that the analysis be commenced with 1,000 grams of soil. The
data of the analysis and the method of arrangement are illustrated by the
following example.

The physical examination of the earth having been completed as above,
the results can be tabulated as follows: taken, 1,000 grams of dry earth,
digested in water, thoroughly worked by hand, sifted, and passed through
the meshes of the sieve by a stream of water, the meshes having a diameter
of one millimeter.
Pebbles 21 grams.
Dry residue, fifty-five grams, contains Gravel 33 „
Organic débris 1 „

Sifted earth by difference, 1000 − 55 = 945 „

1000 grams.
Humidity of the homogeneous paste, twenty-seven per cent. Then 945
grams of the dry sifted earth correspond to 1.00945− .27 = 1294.5 of paste.
The analysis, therefore, should be carried on upon this weight or some
aliquot part say 0.01 thereof; viz., 12.945 grams.
Noncalcareous 3.05 grams.
1st.—Coarse sand dry sand
12.945 grams of the paste after giving by treatment with
Calcareous sand 1.19 „
successive kneadings and acid and ignition.
Organic débris 0.08 „
decantations furnish dry:
2nd.—Fine elements decanted with the water, their weight
calculated by difference, 9.45 − 4.32 = 5.13 grams.
Treatment of the Fine Elements.—Treated by nitric acid until a complete
decomposition of the calcareous matter is secured, filtered, washed, the
residual matter collected upon a filter, and the liquid received in a two-liter
flask, a little ammonia added, allowed to digest, the flask filled with
distilled water, left for twenty-four hours at repose, and decanted:
The decantation furnishes 1st.—A deposit of fine calcareous sand weighing dry 3.14 grams.
2nd.—Clayey liquid giving after coagulation by acid, filtration and
drying 0.85 grams of clay.

Then: Total fine elements 5.13 grams.
Fine elements determined Fine calcareous sand 3.14 3.99 „
directly. Clay 0.85

Fine calcareous sand by difference 1.14 „
Calculating these results to the original quantity of 1,000 grams the
following data are obtained:
RÉSUMÉ.

One thousand grams of dry earth contain:

Pebbles 21 grams.
Gravel 33 „
Organic débris 1 gram.
Fine earth 945 grams.

Total 1000 „

945 grams of fine earth Coarse sand 432 gms. Noncalcareous sand 305 gms.
contain: Calcareous sand 119 „
Organic débris 8 „

Fine elements 513 Fine, noncalcareous 314 gms.
gms. sand
Clay 85 „
Fine calcareous sand 114 „

Total 1000 „
There are counted as clay all the elements which have remained in
suspension in the water after a period of repose of twenty-four hours. In
fact, these elements comprise a notable proportion of very fine sand which
is not deposited during that time. In order that the liquid should become
entirely freed from this sand it would be necessary to wait several weeks
and even several months. Such a prolongation of the analysis is evidently
inadmissible. The period of twenty-four hours of repose therefore has been
adopted. This is merely conventional, in the same way that the period of ten
seconds adopted for the precipitation of the gravel is conventional. But this
convention is justified by the fact that the substance which is called clay
presents, when it has a proper degree of humidity and cohesion, a plasticity
entirely analogous to that property of natural clay. Moreover, as has already
been said, that which is chiefly important in these analyses is the
employment of processes always comparable among themselves in their
results and generally followed.
211. The Belgian Method.—The method of estimating the percentage of
sand and clay practiced at the Gembloux Station[145] is essentially that
recommended by Schloesing with a few minor modifications.
With the ball of the thumb or with the finger, 100 grams of fine earth are
rubbed with water in a porcelain capsule or mortar with a capacity of about

250 cubic centimeters. The suspended particles are poured off with the
wash water and the process repeated five or six times, using in all about 200
cubic centimeters of water.
The water containing the sediment is rendered slightly acid (hydrochloric
acid) adding the acid in minute particles with constant stirring for about an
hour in order to dissolve all the carbonate and to separate the organic acids
from the bases with which they are combined.
The liquid is allowed to remain at rest for five or six hours and a part of
the liquor decanted to remove any supernatant particles of organic matter
which may have passed the sieve in the original preparations of the sample.
Filter through a smooth filter about twelve centimeters in diameter, wash
until the chlorin has disappeared, and throw the filtrate away.
Break the filter paper over the vessel in which the soil was treated with
hydrochloric acid and wash all the contents of the filter into this vessel with
as little water as possible (about 100 cubic centimeters), add five cubic
centimeters of strong ammonia water, allow to stand for three hours,
shaking from time to time and with distilled water make the volume up to
250 cubic centimeters. Stir vigorously with a glass rod or spatula, take this
out and wash any adhering particles back, leave at rest for twenty-four
hours, siphon the turbid liquid into a two-liter vessel. Make the volume up
again to 250 cubic centimeters and treat as above described and repeat the
operation until the water becomes clear after standing for twenty-four
hours. Usually eight or ten washings are necessary. Wash the residual sand
into a weighed dish, evaporate to dryness, ignite and weigh. The weight
obtained divided by the weight of the original sample gives the per cent of
sand. The sand is separated by sieves of varying fineness into coarse, fine,
and pulverulent sand.
Add to the ammoniacal liquor collected in the two-liter flask some
powdered potassium chlorid (five grams per liter) to hasten the coagulation
and rapid deposit of the clay.
After twenty-four hours siphon the clear liquor, collect the deposited clay
in a smaller vessel, allow to remain at rest and decant as much of the clear
liquor as possible. Pass through a plain tared filter about nine centimeters in
diameter, dry at 150° and weigh the clay.
212. The Italian Method.—Schloesing’s method as carried out by the
Italian chemists[146] is as follows:

A kilo of earth dried in the air is passed through a sieve the threads of
which are separated a distance of five millimeters; and with this the small
pebbles are separated.
With another sieve having spaces of one millimeter, the coarse sand is
separated. The pebbles and sand are dried, weighed, treated with
hydrochloric acid and again weighed in order to find the quantity of
calcareous matter contained in them. In ten grams of this fine earth the
humidity is determined by drying at 100°.
Ten grams are mixed in a capsule with fifteen to twenty cubic centimeters
of water and after eight to ten seconds the supernatant liquid is poured into
a beaker having a capacity of 250 cubic centimeters. The same operation is
repeated until there are contained in the beaker the fine sand and the clay,
while the coarser sand remains in the capsule.
This last is then dried and weighed and the quantity of calcium carbonate
determined by treating it with diluted nitric acid. By means of calcination
the organic matter is determined. The liquid decanted in the beaker, the
volume of which must not surpass 200 to 250 cubic centimeters, is treated
with nitric acid, filtered after some time, washed and the calcium is directly
determined by precipitating the solution with ammonium oxalate.
The part in the filter which contains the fine sand, the clay, and the
humus material is mixed with water to a volume of about 200 cubic
centimeters; there are then added to it two to three cubic centimeters of
ammonia and after two or three hours it is diluted to a liter and strongly
agitated.
After twenty-four hours of rest it is decanted and the residuum is treated
a second time with diluted ammonia, decanting after twenty-four hours.
Ordinarily these two treatments suffice, if, however, the earth is very
argillaceous, this operation should be repeated three and even four times.
The clay which is found in the liquid suspended in colloidal form
coagulates and is precipitated by adding thirty to forty cubic centimeters of
a saturated solution of potassium chlorid, while the humus substance, under
the influence of the ammonia remains dissolved.
Sestini found that the method of Schloesing was the only one which
indicated exactly the quantity of clay in the soil. He modified this method
by reducing the time of rest from twenty-four hours, as proposed by