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THE PHYSICAL
PROPERTIES OF SOE^

A LABORATORY GUIDE

By
ARTHUR G. McCALL

Professor of Agronomy in the College of Agriculture of the

Ohio State University

ILLUSTRA TED

J ' 1 J 1 ) )

NEW YORK

ORANGE JUDD COMPANY

LONDON
KEGAN PAUL, TRENCH, TRUBNER &C0., Limited

1909

ORANGE JUDD COMPANY

[Entered at Stationers' Hall, London, England]

GIFT OF

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PREFACE

The experiments described on the following pages
are designed especially for the use of the students in
the four-year course in agriculture in colleges and
universities.

These exercises will give sufficient work to cover
two or three terms, depending upon the number of
hours devoted to laboratory practice each week. An
effort has been made to outline the experiments as
clearly and concisely as possible, in order that the
student may take up each exercise without delay.

While these practices are the outcome of several
years' experience in teaching Soil Physics at the
Ohio State University, they are not all original with
the author. Material has been drawn from various
sources, and so arranged that it may be adapted to
instruction in soils under a wide range of conditions.

Acknowledgment is due my assistant, Mr. G. R.
Hyslop, for valuable suggestions and aid in working
out these practices, and to the following for material
and suggestions. Prof. M. F. IMiller, University of
Missouri, Prof. E. O. Pippin, Cornell University, Dr.
L. J. Briggs, U. S. Dept. of Agriculture, Professors
Stevenson and Schaub of Iowa State College, and
others.

A. G. McCall.

Soil Physics Laboratory

Ohio State University

Columbus, Ohio.

August, 1908, ivil999e6

CONTENTS

PAGE

General Information i

Soils Laboratory Desk Outfit 3

Stock Soils 5

-^ Determination of Hygroscopic Moisture ... 10

-^Determination of Moisture in Field Soils . . . 12

>: Determination of the Specific Gravity of Soils . 18

-k Determination of Volume Weight and Pore Space 22

Determination of Pore Space in Field Soils . . 26

-i-Percolation of Water Through Soils .... 32

-I- Water-holding Capacity of Soils 38

The Distribution of Capillary Water in Soil

Columns 40

f Flow of Air Through Soils 42

Flow of Air Through Field Soils 44

-j" Capillary Rise of Moisture 46"

4- Interruption of the Capillary Rise of Moisture . 46-

Continuous Rise of Capillary Moisture . . . 50 -

Lateral Movement of Capillary Moisture . . . 54 ■

Co-efficient of Evaporation ....... ^(^

->r Effect of Mulches upon Rate of Evaporation . 60

The Absorptive Power of Soils 64

.^The Flocculating Effect of Lime 6^

Vll

• » •

Viii CONTENTS

PAGE

Power of Soils to Retain Fertilizers in Solution . 70

The Specific Heat of Soils 74

^Mechanical Analysis of Soils 80

Chromic Acid Method of Determining Organic

Matter 92

Directions for Taking Soil Samples .... 96

Standardization of the Eye-piece Alicrometer . 99

Table of Data 100

Index loi

» ' > 111 ^ ^ 1 1 ' 1 > 1 , ' ,

' ' V ' ' \ ,' 1 ' 1 1 :. :. 1 > 1

'I'lii 11 >) 111 .,

The Physical Properties of Soils

GENERAL INFORMATION AND
DIRECTIONS

The laboratory instruction in soils is confined al-
most exclusively to a study of the physical properties
of soils and the relation of these properties to rational
methods of soil management.

The relation of the soil to moisture being of first
importance, a great many of these experiments are
designed to show the influence of physical conditions
upon the movement and retention of moisture in the
soil.

There are various ways of expressing the amount
of water present in a soil : ( i ) as per cent of dry
weight of the soil, (2) as per cent of wet weight,
(3) as pounds per cubic foot, and (4) as surface
inches.

The water content is usually expressed either as per
cent of dry weight or as pounds per cubic foot.

The degree of compactness of soils has a great in-
fluence upon their behavior, hence for all comparative
tests it is very necessary that all the soils be compacted
uniformly. For this purpose specially designed com-
pacting machines are used.

Before beginning an experiment read carefully the
entire exercise and see that all the necessary apparatus
is at hand.

2 THE PHYSICAL PROPERTIES OF SOILS

The character (T) following' the name of a piece
of apparatus means that it must be obtained from the
instructor.

At the close of each experiment all apparatus must
be cleaned thoroughly and returned to its proper place
before credit is given for the work. Full notes on
each exercise must be made at the time the experi-
ment is performed. The final report must be made on
the blank pages in this book, and should contain (i)
a description of the experiment and apparatus used,
(2) the results in a neat tabulated form, so that their
story can be quickly read, and (3) a short discussion
along the lines indicated on the direction sheet.

The references given at the close of the exercises
are to be read before the experiment is written up.
All books to which reference is made will be kept on
a table in the laboratory or adjoining room, where they
will be accessible to the students during laboratory
hours.

Write your name and the hours during which you
are due in the laboratory on the card attached to your
desk.

This book is not to be taken from the laboratory
except by special permission, but must be left in the
place designated by the instructor.

THE PHYSICAL PROPERTIES OF SOILS

SOILS LABORATORY DESK OUTFIT

THE FOLLOWING ARTICLES ARE LOANED TO THE STUDENT

O 6 Aluminum Dishes, 3 in.

Bunsen Burner

Ring Stand with 3 Rings

Tongs, Crucible

Tripod

•y

Porcelain Cups

Spatula

•^

Test Tube Rack

Sets Beakers, i to 5

Dishes, Porcelain No. 0

Desiccator, 8 in.

■J fir

,,-D

Cylinders, Graduated 250 cc. _

Test Tubes

Percolators, Oldberg's Cylin

idrical, 500

cc.

THE FOLLOWING ARTICLES ARE CHARGED TO EACH STUDENT AND

CAN NOT BE RETURNED

I Clay Triangle $ .05

I Wire Gauze

.05

I Glass Rod

.05

3 Ft. Rubber Tubing

.15

I Sponge

.10

I Towel

.10

I Test Tube Brush

.05

I Box Safety Matches

.01

THE PHYSICAL PROPERTIES OF SOILS

STOCK SOILS

Unless otherwise stated, the soils called for in
these exercises will be found in the bins in the soil-
handling room opening off from the main laboratory.
The soils used consist of (i) sand, (2) sandy loam,
(3) loam, or silt, (4) muck, and (5) clay.

1. Sand — clean lake or river sand.

2. Sandy Loam — a loam with sufficient sand to

make open mellow soil.

3. Loam or Silt — heavier type than No. 2, con-

taining more silt and less sand.

4. Muck — well-drained swamp soil containing a

large quantity of organic matter.

5. Clay — a heavy, sticky soil containing a large

amount of clay.

The soils are prepared by drying and pulverizing
until they pass through a 2 mm. sieve. The different
grades of sand are prepared by passing the lake sand
through a series of sieves.

The mechanical analysis of each soil is given on the
card attached to the bin. These analyses should be
recorded on the following page and referred to fre-
quently in interpreting the results obtained in the
laboratory. Use the co-ordinate paper to make a
graphic representation of the mechanical composition
of the soils.

THE PHYSICAL PROPERTIES OF SOILS

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THE PHYSICAL PROPERTIES OF SOILS

FIRST EXERCISE

I. DETERMINATION OF HYGROSCOPIC
MOISTURE IN STOCK SOILS

Determine the hygroscopic moisture of the soil
samples in the bins by proceeding as follows :

Carefully weigh a small dish on the chemical balance,
then place in the dish a lo-gram representative sample

DRYING OVEN HEATED BY GAS

The gas supply is automatically regulated by a relay operated on a

battery circuit

of soil. Dry in the oven at iio° C. for twenty-four
hours. The loss in weight is the hygroscopic moisture.
The loss in weight divided by the weight of the oven-
dry soil will give the per cent of hygroscopic moisture.
Although the hygroscopic moisture varies from day
to day with the humidity of the atmosphere, these re-
sults may be used in subsequent experiments whenever

THE PHYSICAL PROPERTIES OF SOILS II

STUDENT'S NOTES AND REPORT

THE PHYSICAL TROPERTIES OF SOILS

DOUBLE- WALLED DRYING OVEN HEATED BY TWO ELECTRIC-LIGHT

BULBS

it is necessary to know the per cent of hygroscopic
moisture.

What is the effect of soil texture and the temperature
and humidity of the atmosphere upon the hygroscopic
moisture?

II. DETERMINATION OF THE MOISTURE

IN FIELD SOILS

Collect samples in the field from the first, second and
third foot of soil under different crop conditions, such
as sod land, plowed field and fallow. The samples
should come from as small an area as possible in order
to have a uniform soil type.

Drive the sampler (T) to the proper depth for each
foot, lift from the hole and transfer the soil at once to

THE PHYSICAL PROPERTIES OF SOILS 1 3

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

a tight box. Take the samples to the laboratory, weigh
each box separately, remove the lid and expose the
contents to the air. Weigh at the end of three days

"Vi UCvW-^ C\RCUIT

TO "BKTTt.H^ OR
^WUNT CIRCUIT

DIAGRAM SHOWING THE CONNECTIONS FOR THE AUTOMATIC
CONTROL USED ON ELECTRICAL DRYING OVENS

The Tube A is filled with alcohol or a calcium chloride solution and
placed inside the oven. D, the source of heat, is a series of lamps
or a coil of fine wire, also located inside the oven. As the temper-
ature increases the liquid in the tube expands. This expansion forces
the mercury up in the tube E until contact is made with the adjust-
able electrode V. This closes the circuit through the relay, and tiie
armature B is lifted. The heating circuit is broken in the mercury
cup at C, and the source of heat at U is shut off. As the oven cools
the mercury at E drops back and the relay circuit is broken, allowing
the armature B to fall and close the heating circuit.

and at twenty-four hour intervals thereafter until
approximately constant weight is obtained. The loss
in weight is the capillary moisture. Note should be
made of the rainfall of the previous week and of the
weather conditions at the time the sanij^les were taken.

THE PHYSICAL PROPERTIES OF SOILS I5

STUDENT'S NOTES AND REPORT

l6 THE PHYSICAL PROPERTIES OF SOILS

Determine the hygroscopic moisture remaining in
the air-dry samples, and calculate the moisture auitent
of the field samples as follows :

( 1 ) As per cent of the dry weight of the soil.

(2) As pounds per cubic foot.

(3) As surface inches, the total amount to the depth
of three feet.

Tabulate the results and compare the moisture con-
tent of the soils under the different crop conditions.
Discuss the reasons for the observed differences.

References :

Burkett, "Soils," Chapter IV.
Hall, "The Soil," p. 132.
Bulletin No. 4, Bureau of Soils, pp. 22-24.
Stevenson & Schaub, "Soil Physics Laboratory
Guide," pp. 1-7.

THE PHYSICAL PROPERTIES OF SOILS I7

STUDENT'S NOTES AND REPORT

l8 THE PHYSICAL PROPERTIES OF SOILS

SECOND EXERCISE

DETERMINATION OF THE SPECIFIC
GRAVITY OF SOILS

The specific gravity of soil varies from about 2
up to 2.90, the average being about 2.65, which is the
specific gravity of quartz crystal. That is, the soil
calculated free of air spaces weighs about 2.65 times
as much as an equal volume of water. The density
will vary with the mineral constituents of the soil and
with the amount of organic matter present, the specific
gravity decreasing as the organic matter increases.

METHOD OF DETERMINATION

With specific gravity fiasks or pycnometers (T)
of 50 cc. capacity make duplicate determinations of the
specific gravity of soils No. i, No. 4, and No. 5.

Fill the fiask with distilled water and boil for a few
minutes in a salt bath to expel the air. Cool the flask
to 30° C, insert the stopper, wipe dry, and when
it has cooled to room temperature, weigh. Pour out
about half of the water in the flask and introduce into
it about ten grams of soil. Again place the flask in
the salt bath and boil for a few minutes. Fill the flask
with boiled water, cool to 30° C, stopper and weigh
again at room temperature. Transfer the soil to a
porcelain dish, evaporate, and dry in the oven to
determine accurately the amount of soil used.

CALCITLATION

The weight of the soil used divided by the weight of
the water displaced will give the s])ccific gravity of
the soil.

THE PHYSICAL PROPERTIES OF SOILS IQ

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

Tabulate the results and use them in connection
with the next exercise.

Reference :

Wiley, "Agricultural Analysis," Vol. I., pp.

95-98.

SOIL SAMPLE BOXES WITH
CARRYING CASE

THE PHYSICAL PROPERTIES OF SOILS 21

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

THIRD EXERCISE

I. DETERMINATION OF VOLUME WEIGHT
AND PORE SPACE OF STOCK SOILS

The volume weight of a soil is the weight of a given
vokime. The weight of the soil in grams divided by
the volume in cubic centimeters is the density or the
apparent specific gravity.

APPARATUS FOR THE DETERMINATION OF VOLUME WEIGHT AND

PORE SPACE

METHOD OF DETERMINATION

Secure a brass cylinder (T), weigh empty, and fill
with soil No. I, compacting it on the iron compactor
by dropping the weight four times from the 6-inch
mark after each measure of soil. Weigh the tube when
level full and empty the soil back into the bin. Secure
the weight of the cylinder full of each of the soils in this

THE PHYSICAL PROPERTIES OF SOILS 23

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

THE PHYSICAL PROPERTIES OF SOILS 2^

STUDENT'S NOTES AND REPORT

26 THE PHYSICAL PROPERTIES OF SOILS

manner. With a graduated glass cylinder measure the
amount of water required to fill the brass cylinder level
full.

CALCULATION

Record all of the above weights in tabular form
and calculate the apparent specific gravity and the
weight in pounds per acre foot. Using the real specific
gravity found in the preceding exercise, calculate the
per cent of pore space in each soil by the formula
given by King, ''Physics of Agriculture," pp. 114-116.

Discuss light and heavy soils, and the effect of tex-
ture upon the pore space.

References :

King, "Physics of Agriculture," pp. 114-116.
Snyder, "Soils and Fertilizers," pp. 12, 13.

11. DETERMINATION OF PORE SPACE IN

FIELD SOILS

In order to determine the pore space in soils in place
in the field it is necessary to know the real specific
gravity and the weight of a given volume of the dry
soil.

METHOD OF DETERMINATION

With sampling tube (T) provided with a steel cut-
ting edge, collect samples from the field which will
represent the first and second foot of soil under dif-
ferent conditions, such as sod, cultivated field and stub-
ble land. The surface of the ground is leveled and the
sampling tube driven into the soil until the 12-inch
mark is exactly level with the ground surface. The
entire sampler is then dug out, a broad spatula or a

THE PHYSICAL PROPERTIES OF SOILS 2^

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

KING SOIL - SAM-
PLINC. TUBE WITH
HAMMER.

piece of steel being inserted under
the lower end before the tube is re-
moved. The tube is laid over on its
side and the soil cut off flush with
the cutting edge.

This operation is repeated to ob-
tain a sample of the second foot.

The soil is removed from the sam-
pler, taken to the laboratory, dried and
weighed. The volume of the sample
is calculated from the area of the end
of the tube and the length of the core.

The cutting edge of the sampler is
slightly smaller than the inside diam-
eter of the tube in order to reduce
the friction to a minimum and thus
prevent the soil on the inside being
forced down below the level of the
surrounding ground.

CALCULATION

The real specific gravity of each
sample is determined and the pore
space calculated by the formula
given by King, "Physics of Agricul-
ture," pp. 1 1 4- 1 1 6.

Tabulate the results and discuss
the factors which affect the volume
weight and pore space of soils in the
field.

References :

Burkett, "Soils," p. 37.
Wiley, "Agricultural Analy-
sis," Vol. I., pp. 143-145-

THE PHYSICAL PROPERTIES OF SOILS 29

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

IKON CO Mr ACTOR

THE PHYSICAL PROPERTIES OF SOILS 3I

STUDENT'S NOTES AND REPORT

TPIE PHYSICAL PROPERTIES OF SOILS

FOURTH EXERCISE

f-BRAis Exre/vs/o/v

RUBBFR QAiktT

■CLASS PCRCOLATCR

PERCOLATION OF WATER THROUGH

SOILS

The rate of percolation of water through soils is

largely dependent upon
the texture of the soil and
the amount of organic
matter present.

Prepare four glass per-
colators by placing a piece
of fine copper gauze in the
bottom of each and filling
to within one-half inch of
the top, as follows :

Percolator No. i —

Sand.
Percolator No. 2 —
Mixture, three parts
sand, one part or-
ganic matter.
Percolator No. 3 —
Mixture, one part
sand, one part or-

\jMopprR qAuzc Percolator No.

11 Sandy loam.

Compact each percolator
on the spring-board com-
pactor by dropping the weight four times from the
lo-inch mark. Fill the remaining half inch with sand
to prevent puddling, clamp on the extensions (T) and

PERCOLATOR TUBE
Sectional View

THE PHYSICAL PROPERTIES OF SOILS 33

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

admit the water. Use a siphon flask to keep the water
at a constant level.

Note the time required for the water to reach the
bottom in each ; and the rate of percolation per hour
under a given head of water, kept constant by means
of the siphon flask.

SPRING-BOARD COMPACTOR

Repeat the above, using the. following soils and mix-
tures :

Percolator No. i — Loam or silt.

Percolator No. 2 — Mixture, one part loam

one part organic matter.
Percolator No. 3 — Clay.
Percolator No. 4 — Mixture, one part clay,

one part sand.

Tabulate the results and calculate the rate of perco-
lation in surface inches per hour. Discuss the effect
of texture and the presence of organic matter upon the
rate of percolation.

THE THYSICAL PROPERTIES OF SOILS 35

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

References :

Burkett, "Soils," pp. 38-39.
Hall, "The Soil," p. y2.
King, "The Soil," p. 170.

APPARATUS USED TO COMPARE THE RATE OF PERCOLATION IN

DIFFERENT SOILS

THE rilYSICAL PROrERTIES UE SOILS 2^^

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

FIFTH EXERCISE

I. WATER-HOLDING CAPACITY OF

SOILS

Prepare six perforated bottom brass cylinders (T)
by placing a moist disk of muslin in the bottom of each.
After weighing fill the cylinders to the mark as follows :
Tube No. I — Sand.
Tube No. 2 — Mixture, one part sand, one

part organic matter.
Tube No. 3 — Loam or silt.
Tube No. 4 — Muck.
Tube No. 5 — Clay.

Tube No. 6 — Loam or silt, not compacted.
Compact each tube (except No. 6) on the iron com-
pactor by allowing the weight to fall four times from
the 6-inch mark after each measure of soil. Weigh and
place in a tank in which the water is kept on a level

APPARATUS USED TU DETERMINE THE WATER-HOLDING CAPACITY

OF SOILS

THE PHYSICAL PROPERTIES OF SOILS 39

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

with the soil in the cyhnders and allow to
stand until free moisture appears on the
surface. Remove from the tank, wipe
dry, and weigh immediately. Then place
the cylinders on a draining board, under
a bell jar (T) and weigh every forty-
eight hours for a week.

Tabulate the weighings and calculate
the per cent of water required to saturate
each soil and the per cent of capillary
w^ater retained in each after seven days
of drainage. Discuss the factors effect-
ing the water-holding power of soils.

Reference:

Burkett, ''Soils," pp. 40-42.

II. THE DISTRIBUTION OF CAP-
ILLARY WATER IN SOIL COL-
UMNS.

Prepare two 36-inch brass cylinders
(T) in the manner described above,
using sand in one and loam or silt in the
other. At the end of the drainage period
make moisture determinations at inter-
vals throughout the length of the columns
by means of samples taken through the
side tubes provided for that purpose.

How is the moisture distributed?
Explain the cause of the unequal dis-
tribution.

References :

Hall, "The Soil," p. 64.

I
I

.-iK

BRASS CYLINDER

Provided with side tubes
for studying the distri-
bution of moisture in
vertical columns of soil.

King, 'Thysics of Agriculture," |:j%t^' raUM-ai" mov^:

mcnt of capillary mois-
ture.

p. 114.

THE PHYSICAL PROPERTIES OF SOILS 4I

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OP SOILS

SIXTH EXERCISE

I. FLOW OF AIR THROUGH LABORATORY

STOCK SOILS

Fill six aspirator tubes (T) with soils from the
bins as follows :

Tube No. I — Sand.

Tube No. 2 — Mixture, three parts sand, one

part organic matter.
Tube No. 3 — Loam or silt.
Tube No. 4— Muck.
Tube No. 5 — Clay.
Tube No. 6 — Mixture, three parts clay, one

part organic matter.

BOTTLE ASPIRATOR
Used in comparing the rate of flow of air through diflferent soils

Compact each tube on the iron compactor by drop-
ping the weight four times from the 6-inch mark after
each measure of soil. Connect tube No. i to the as-

THE PHYSICAL PROrERTIES OF SOILS 43

STUDENT'S NOTES AND REPORT

44 THE PHYSICAL PROPERTIES OF SOILS

pirator bottle, open the stop-cock, and note the time
necessary for one hter of water to escape. Repeat with
each of the soils, and tabulate the results in liters per
hour. Make at least two determinations on each soil.
What effect has the texture of the soil and the pres-
ence of organic matter upon the rate of aeration?

II. FLOW OF AIR THROUGH FIELD
SOILS IN PLACE

The permeability of undisturbed field soils may be
determined with this apparatus in the manner described
by King, ''Physics of Agriculture," p. 127.

The movement of air in field soils in place may be
determined also by the Heinrich method, as described
by Wiley, ''Agricultural Analysis," Vol. I., pp.
163, 164.

References :

Burkett, "Soils," pp. 95-96.
King, "The Soil," p. 239.
Hilgard, "Soils," p. 279.

THE PHYSICAL PROPERTIES OF SOILS 45

STUDENT'S NOTES AND REPORT

46 THE PHYSICAL PROPERTIES OF SOILS

SEVENTH EXERCISE

I. CAPILLARY RISE OF MOISTURE IN

SOILS

Prepare five brass capillary tubes (T) and fill them
as follows :

Tube No. I — Sand.

Tube No. 2 — Mixture, three parts sand, one

part organic matter.
Tube No. 3 — Loam or silt.
Tube No, 4 — Clay.
Tube No. 5 — Mixture, three parts clay, one

part organic matter.

Compact each tube on the spring-board compactor
by dropping the weight four times from the lo-inch
mark, and weigh. Place the tubes in a rack with the
lower ends dipping into a tray of water, the depth of
the water being kept at a constant level by means of
a siphon flask. Record the height of the rise of water
after thirty minutes, one hour, and every twenty-four
hours thereafter for seven days.

Express the results in tabular form and by means of
curves. Discuss the efifect of texture and the presence
of organic matter upon the capillary rise of moisture.

References :

Hall, "The Soil," pp. 68 and 94.
Hilgard, "Soils," pp. 202-208.

II. INTERRUPTION OF THE CAPILLARY
RISE OF MOISTURE

Fill three brass tubes (T) to the depth of one foot
with sandy loam soil, and place them in a rack with

THE PHYSICAL PROPERTIES OF SOILS

APPARATUS USED TO COMPARE THE CAPILLARY RISE OF MOISTURE

IN DIFFERENT SOILS

The brass tubes are lined with thin celluloid and have a slit the length
of one side. The inverted flask keeps the water in the tray at a con-
stant level.

48 THE PHYSICAL PROPERTIES OF SOILS

the lower ends dipping into a tray containing one inch
of water. After the water has risen to the top of the
soil, add to the first about one inch of moist cut straw,
and to the second the same quantity of well-rotted
organic matter, and to the third nothing. Then add
to each tube about six inches of dry soil to represent
the furrow slice.

Observe the effect of the organic matter upon the
capillary rise of moisture, and draw conclusions as to
the effect of plowing under heavy top-dressings of
manure just before seeding.

Reference :

Vivian, *Tirst Principles of Soil Fertility," pp.
102 and 168.

THE PHYSICAL PROPERTIES OF SOILS

STUDENT'S NOTES AND REPORT

PLAIN CO-ORDINATE PAPER

50 THE PHYSICAL PROPERTIES OF SOILS

EIGHTH EXERCISE

CONTINUOUS RISE OF CAPILLARY

MOISTURE

At the beginning of the term the instructor will
fill twelve long capillary tubes with the following
materials :

Tube No. I — Clay.

Tube No. 2 — Loam or silt. '

Tube No. 3 — Sandy loam.

Tube No. 4 — Sand.

Tube No. 5— Muck.

Tube No. 6 — Sand, lOO to 120 mesh.

Tube No. 7 — Sand, 60 to 80 mesh.

Tube No. 8 — Sand, 20 to 40 mesh.

Tube No. 9 — Mixture, one part clay, one

part muck.
Tube No. 10 — Mixture, one part sand, one

part muck.
Tube No. II — Mixture, one part clay, one

part sand.
Tube No. 12 — Mixture, one part loam, one

part sand.

After filling, these tubes are placed in a rack with
their lower ends resting in a tray into which water is
admitted to the depth of one inch. The experiment is
now ready for observation, and each student in the
class is required to make measurements and to record
the height of the rise of moisture at stated intervals
during the term. Observations should be made every
hour during the first day and at daily intervals for the

THE PHYSICAL PROPERTIES OF SOILS 5 1

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

first week. After the first week the intervals may be
lengthened to three days.

A short time before the end of the term make a close
comparison of the different tubes. Plot a curve show-
ing the height of the water at each observation. Dis-
cuss the effect of texture and the presence of organic
matter upon the capillary rise of moisture as shown
by the behavior of the soils in these tubes.

How do these results compare with those obtained
in the preceding exercises ?

References :

Hilgard, "Soils," pp. 202-207.

King, "Physics of Agriculture," pp. 161-165.

?f '

^mmgmmmgt

'''^''^^HMnnfflnnn

^V^WI^WwIB^^^^^^^^^WIIb^wJEI

TORSION BALANCR

Used for all rough weighings. A chemical balance is used where

greater accuracy is required

THE PHYSICAL PROPERTIES OF SOILS 53

STUDENT'S NOTES AND REPORT

54 THE PHYSICAL PROPERTIES OF SOILS

NINTH EXERCISE

THE LATERAL MOVEMENT OF CAP-
ILLARY MOISTURE

The forces which produce capillary movement of
moisture in soils in the field may act in direct opposi-
tion to, or at any angle with the force of gravity.
During periods of drought, growing plants may be
supplied with water by a vertical movement from the
moist sub-soil or by a lateral movement from the ad-
jacent surface soil.

Prepare the two brass cylinders used in the Fifth
Exercise, Part 11. , by filling one with loam or silt and
the other with clay. Make the soils up to 15
or 20 per cent of moisture and pack the cylinders level
full by means of a wooden rammer. Cap the lower
end, and tie a piece of moist cheese-cloth over the top
of each cylinder and place them in a horizontal posi-
tion. Weigh at the beginning of the experiment and
at twenty-four hour intervals for one week.

At the end of the period take samples through the
side tubes and determine the per cent of moisture in
each.

Discuss the results with respect to the total loss of
moisture and to its distribution, at the close of the
experiment.

References :

Bureau of Soils, Bulletin No. 10.
Bureau of Soils, Bulletin No. 38.

THE PHYSICAL PROrERTIES OF SOILS

STUDENT'S NOTES AND REPORT

PLAIN CO-ORDINATE PAPER

THE PHYSICAL PROPERTIES OF SOILS

TENTH EXERCISE

CO-EFFICIENT OF EVAPORATION

Prepare four evaporimeters (T) and fill level full
with the following soils:

PCRF««ATf<|

EVAPORIMETER
Sectional View

Evaporimeter No. i — Sand.

Evaporimeter No. 2 — Loam or silt.

Evaporimeter No. 3 — Muck.

Evaporimeter No. 4 — Clay.

Fill the water-jackets, and after the water has ap-
peared at the surface weigh the entire system. A
crystallizing dish having the same amount of exposed
surface should be filled with water and weighed at the
same time. Expose the surfaces to the air for twenty-
four hours, weigh and calculate the rate of evaporation
in pounds per acre.

Empty the water from the jackets and determine the
loss from each surface by evaporation by forty-eight-
hour periods for one week.

THE PHYSICAL PROPERTIES OF SOILS 57

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

EVAPORI METERS
Apparatus used for comparing the loss of moisture from different

soils by evaporation

Tabulate the results and compare the rate of evapora-
tion from the different soils with each other and with
that from the water-free surface.

Discuss the effect of texture upon the rate of
evaporation, and plot curves to represent the rate of
evaporation from each soil.

References :

Burkett, ''Soils," p. i66.
Fletcher, "Soils," pp. 88, 89.
Wiley, "Agricultural Analysis," Vol. I., pp.
160, 161.

THE PHYSICAL PROPERTIES OF SOILS

STUDENT'S NOTES AND REPORT

■ .

PLAIN CO-ORDINATE PAPER

THE PHYSICAL PROPERTIES OF SOILS

ELEVENTH EXERCISE

EFFECT OF MULCHES UPON THE RATE

OF EVAPORATION

Mulching the soil either by earth mulches (tillage)
or by artificial mulches (straw or
manure) is the most effective means
of conserving soil moisture.

Fill five galvanized iron cylinders
(T) to within one-half inch of the
top with the same soil, compacting
uniformly. Fill the water-jackets
and apply pressure until the mois-
ture appears on the surface of each
soil. Remove the water from the
jackets and treat the surfaces of the
cylinders as follows:

MULCH CYLINDER
Sectional View

No. I — No treatment.

No. 2 — Cultivate one inch deep each day.

No. 3 — Compact the surface.

No. 4 — Remove the surface inch of soil and
replace with sand.

No. 5 — Remove the surface inch of soil and
replace with cut straw.

Care must be taken to have the finished surface of
the soil in all of the cylinders at exactly the same dis-
tance below the rim, and to expose all of the cylinders
to the same atmospheric conditions.

THE PHYSICAL PROPERTIES OF SOILS 6l

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

I-

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>

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^s ^mT^^V ^wL 'W ^ '* W^'m

m""r-"'^

BBunsj^sa^^n^MK

"-s*^--r«s-;^~. "^ -«&.

GALVANIZED IRON CYLINDERS
Used in studying the eflfectiveness of different mulches in conserving

soil moisture

Weigh and record the loss in weight at forty-eight-
hoiir intervals for one week. Calculate the loss in tons
per acre for each treatment, and discuss the relative
effectiveness of the different mulches.

References :

Burkett, "Soils," Chapter XXL
King, "The Soil" p. 194.
Hall, "The Soil," p. 97.

THE PHYSICAL PROPERTIES OF SOILS 63

STUDENT'S NOTES AND REPORT

64 THE PHYSICAL PROPERTIES OF SOILS

TWELFTH EXERCISE

THE ABSORPTIVE POWER OF SOILS

In common with other finely divided substances,
soils have the power of absorbing water vapor and
other gases from the atmosphere. The hygroscopic
capacity of different soils may be compared by exposing
them to a saturated atmosphere for a given length of
time under standard temperature conditions, and ob-
serving the increase in weight.

METHOD OF DETERMINATION

Weigh out carefully into shallow aluminum trays
or pans, 25-gram samples of each of the following
soils :

Tray No. i — Sand.

Tray No. 2 — Loam or silt.

Tray No. 3 — Clay.

Tray No. 4 — Mixture, one part sand, one

part organic matter.
Tray No. 5 — Mixture, one part loam, one

part organic matter.

Spread thin in the trays, dry to constant weight,
either in a drying oven or over sulphuric acid,
cool in a desiccator, and place the trays, with lids off,
into a constant temperature chamber in which the air
is kept saturated with water vapor. Allow the samples
to remain in contact with the saturated atmosphere
until a constant weight is obtained. An empty tray
should be kept with those containing the soil, and its

THE PHYSICAL PROPERTIES OF SOILS 65

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

increase in weight deducted from the total increase
in the soil trays.

■'■■^.:..->-.-y:^.$i:^:''iMf'-i.:.:^ '■''-'- -'"^"'ff^^^^'y^^'^'^v^^^"''-^^

;
i

■^S|: ^^:ili-y-^ ■.■.■.^■:■:■ ■ ■■ ' ; ^ ^^^^^Sjt M^. .^ "'

1 ' 9

#W«w^^

■^^^^^^SSSj^ ^v

^■■1

CONSTANT TEMPERATURE CHAMBER
Used in determining the hygroscopic capacity of soil. Heat is sup-
plied by means of a coil of fine wire attached to the lighting circuit
and coiled around the inner chamber. An air thermometer regulates
the temperature automatically.

Tabulate the results and express the absorptive
capacity of each soil in per cent and as pounds per
acre-foot.

How is the absorptive capacity effected by the tex-
ture of the soil and by the presence of organic matter?

References :

Hall, "The Soil," p. 8i.
King, ''The Soil," p. 252.

THE rilYSICAL PROPERTIES OF SOILS 6/

STUDENT'S NOTES AND REPORT

68 THE PHYSICAL PROPERTIES OF SOILS

THIRTEENTH EXERCISE

THE FLOCCULATING EFFECT OF LIME
UPON CLAY SOILS

The addition of lime to a clay soil produces floccula-
tion, or a grouping together of the fine soil grains into
granules, which act physically very much as single
soil grains. The effect is equivalent to increasing the
size of the soil grains and giving to the soil the prop-
erties of a much coarser textured material. Fine
grained, stiff, clay soils tend to become loose and
friable when flocculation is induced.

Flocculation is best shown in a soil suspended in
water. Work up in a mortar two lo-gram samples of
clay soil and place one in each of two glass cylinders.
Fill two-thirds full of distilled water. Leave one
cylinder untreated, and to the other add 20 cc. of a
saturated solution of lime-water. Shake both for sev-
eral minutes and note the formation of floccules in the
tube containing lime. Examine some of the suspended
material from both cylinders under the microscope.

How does lime aid in clearing the solution? What
other materials are effective in producing flocculation?

Set the cylinders aside and note the time required
for each to become clear by settling. Discuss the effect
of lime upon the physical character of the soil in the
field.

References:

Burkett, "Soils," Chapter XL
King, ''The Soil," p. 30.
Hall, 'The Soil," pp. 38-40.

THE PHYSICAL PROPERTIES OF SOILS 69

STUDENT'S NOTES AND REPORT

70 THE PHYSICAL PROPERTIES OF SOILS

FOURTEENTH EXERCISE

THE POWER OF SOILS TO RETAIN FER-
TILIZERS APPLIED IN SOLUTION

All soils have the power of removing from sohition
certain salts which may be dissolved in percolating
waters. This is accomplished by direct absorption in
some cases, while in others it involves a preliminary
chemical change. The extent to which different fer-
tilizer constituents are retained has a direct bearing
upon the theory and practice of manuring.

Prepare two glass percolator tubes and place a piece
of fine copper gauze in the bottom of each. Make up
to about 15 per cent of moisture a sufficient quantity
of sandy loam to fill both tubes. Carefully fill both
percolators to the same depth, compacting the soil
gently and uniformly by means of a wooden rammer.

Suspend both percolators, and pour into one a solu-
tion of n-ioo sodium phosphate and into the other a
solution of n-ioo sodium nitrate, and keep adding the
solution until it begins to percolate from the bottom.

Collect the filtrates separately and test each for the
salts applied and compare with the original solutions.

A very rough quantitative test for phosphorus and
nitrogen will serve a useful purpose, but if the appara-
tus is available exact quantitative determinations
should be made on both the original solution and the
filtrates.

What practical bearing has the experiment upon the
time and manner of applying commercial fertilizers to
soils in the field?

THE PHYSICAL PROPERTIES OF SOILS 7I

STUDENT'S NOTES AND REPORT

72 the physical properties of soils

References :

Hall, "The Soil," Chap. VIII.

Vivian, 'Tirst Principles of Soil Fertility," p.

193.
Bureau of Soils, Bulletin No. 32.

THE PHYSICAL PROPERTIES OF SOILS 73

STUDENT'S NOTES AND REPORT

74 THE PHYSICAL PROPERTIES OF SOILS

FIFTEENTH EXERCISE

THE SPECIFIC HEAT OF SOILS

The specific heat of a body is the ratio between the
amount of heat necessary to raise a given weight of
the substance one degree, and the amount necessary
to raise the temperature of the same weight of water
one degree. The specific heat of dry soil is usually be-
tween 0.20 and 0.30, but this is greatly modified by
the presence of moisture, the wetter the soil the larger
the quantity of heat required to raise the temperature
a given number of degrees.

APPARATUS FOR THE DETERMINATION OF THE
SPECIFIC HEAT OF SOILS

The apparatus consists of a double-walled cylin-
drical heater (AJ made of heavy copper, and connected
to a steam-system. Extending through the heater
is a hollow core (C), open at both ends, but provided
with movable covering at either end. The calori-
meter consists of a polished brass cup (E) of about
500CC. capacity, supported on corks and insulated from
outside influences by means of an air space (F) and
an outer jacket (G) of wood and felt. The lid to the
outer jacket is also covered with heavy felt and carries
a thermometer graduated to tenths of degrees.

The calorimeter is mounted on a sliding base, which
permits it to be brought under the heater at the proper
moment to receive the heated sample.

METHOD OF DETERMINATION

Determine the specific heat of a sand and of a
clay soil, first in the dry state and then in a moist

THE PHYSICAL rROPERTIES OF SOILS

g» >

JSET

i'j

HEATER

SOIL

SECTIONAL VIEW OF THE APPARATUS USED IN THE DETERMINATION
OF THE SPECIFIC HEAT OF SOILS

76 THE PHYSICAL PROPERTIES OF SOILS

condition. If time will permit study also the effect of
organic matter upon the specific heat.

The soils are heated in the oven to drive off the
hygroscopic moisture, and two 25-gram samples from
each are weighed out, one to be used for the deter-
mination of the specific heat of dry soil and the other
made up to 15 per cent of moisture for the determina-
tion on the moist sample.

The sample under consideration is enclosed in a
bag of thin oiled paper and suspended, by a fine thread,
in the heater near a delicate thermometer. The steam
is turned into the jacket, and the soil is left in the
heater until a uniform temperature is reached. This
will require from one-half to one hour. Meanwhile
the calorimeter (E) is partly filled with water which
has stood in the room for a long time and has acquired,
as nearly as possible, th€ room temperature. The
quantity of water should be such that the water value
of the entire system shall amount to exactly 100 or 150
grams of pure water.

A few minutes before the soil is brought into the
calorimeter the stirrer should be started, and the ther-
mometer read at frequent intervals. If the ther-
mometer shows a constant reading the calorimeter
is quickly brought under the heater, the sample
lowered into it, and the thread cut. The calorimeter
is removed as promptly as possible, the lid replaced,
and the soil thoroughly incorporated with the water
by the stirring apparatus. The thermometer is again
read at frequent intervals until the maximum is
reached, as indicated by a gradual fall in temperature.

The specific heat is calculated by the following
formula, in which the loss in heat by the soil is

THE PHYSICAL PROPERTIES OF SOILS 'J'J

STUDENT'S NOTES AND REPORT

78 THE PHYSICAL PROPERTIES OF SOILS

equated against the gain in heat by the water in the
calorimeter.

mC(h—T)=M(T—To)
or

M ( T—To)

Specific heat C^=

in (tn — T)

where in^mass of soil taken.

to^the temperature of the mass.
M=mass of water including water

value of the calorimeter.
Tn=: the temperature of the mass.

calorimeter.
T=final temperature of water in the

calorimeter.
C= specific heat.

References :

King, 'Thysics of Agriculture," p. 29 and pp.

215, 216.
Wiley, ''Agricultural Analysis," Vol. L, pp.
100- 1 10.

THE PHYSICAL PROPERTIES OF SOILS 79

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

SIXTEENTH EXERCISE

MECHANICAL ANALYSIS OF SOILS-
BOTTLE METHOD

By this method an approximate analysis can be
made without the use of a centrifugal machine. The

silt and clay groups are
estimated together.

Duplicate analyses
should be made upon
prepared stock samples,
in order to give the stu-
dent practice. As soon
as he is familiar with
the details of the sepa-
ration, field samples
should be used. For the
method of preparing field
samples see the instruc-
tions given on page 96.

METHOD OF MAKING THE
SEPARATIONS

Take twenty or thirty
grams of dry, pulver-
ized, sifted soil ; mix
thoroughly, and dry in
the oven and cool in a
desiccator. Weigh out
two 5-gram portions.
Ignite one of these samples and calculate the loss on
ignition. Transfer the other sample to an 8-ounce

APPARATUS USED IN THE BOTTLE
METHOD OF MECHANICAL

ANALYSIS {after M osier).

THE PHYSICAL PROPERTIES OF SOILS 8l

STUDENT'S NOTES AND REPORT

82 THE PHYSICAL PROPERTIES OF SOILS

Sterilizing bottle (T), add about 150 cc. of distilled
water and ten drops of ammonium hydrate to break
up flocculation. Place the bottle in the mechan-
ical shaker and agitate until, when viewed under the
microscope, the soil particles are free from each other
and present a clear-cut appearance.

Transfer from the shaker-bottle to the apparatus
shown on page 80 (T). Adjust this bottle so that
the opening into the long tube will be i^ inches from
the bottom. Fill to the 3-inch mark by means of a
small jet of sufficient force to thoroughly stir up the
contents.

Allow the apparatus to stand until a microscopic
examination shows that all of the sand grades have
settled below the opening of the tube. Blow off into
a beaker all of the liquid above the end of the tube,
and continue the operation of filling, settling and
blowing off until the grades that settle contain no silt
or clay. The liquid blown off contains the silt and
clay, the amount of which is determined by evaporating
to dryness and weighing. No attempt is made at this
time to separate the silt from the clay.

The decanting process may be continued for the sep-
aration of the finest sand grades, or the material may
be dried and the separation made by means of a nest
of sieves. After the removal of the sands the bottle
is used to accomplish the separation of the clay from
the silt.

Tabulate the results of the analyses.

Reference :

Bulletin No. 24, Bureau of Soils.

THE niYSlCAL PROPERTIES OF SOILS 83

STUDENT'S NOTES AND REPORT

84 THE PHYSICAL PROPERTIES OF SOILS

SEVENTEENTH EXERCISE

MECHANICAL ANALYSIS OF SOILS— CEN-
TRIFUGAL METHOD

Make duplicate analyses of sandy loam and of clay
soil from the bins. Then, if time will permit, make
analyses of samples from the home farm.

The method by which the separation is accomplished
is as follows:

Take twenty to thirty grams of dry, pulverized soil,
mix thoroughly and dry in the oven. Cool in a des-
iccator, weigh out two 5-gram portions, transfer
one to an 8-ounce sterilizing bottle and the other to
a porcelain dish for ignition.

Add to the sample in the sterilizing bottle about
150CC. of distilled water and ten drops of ammonium
hydrate to break up flocculation. (For the method of
preparing field samples see page 96.) Place the
bottle in a mechanical shaker and agitate until, when
viewed under the microscope, the soil particles are all
free from each other and present a clear-cut appear-
ance. Transfer the contents to the centrifugal test-
tube by means of a jet of distilled water.

The separates to be determined are as follows :

Fine gravel 2.0 — i.o mm

Coarse sand i .0 — 0.5

Medium sand 0.5 — 0.25

Fine sand 0.25 — o. i

Very fine sand o. i — 0.05

Silt 0.05 — 0.005 "

Clay 0.005

THE PHYSICAL PROPERTIES OF SOILS

„- *

THE PHYSICAL PROPERTIES OF SOILS

CLAY SEPARATION

Whirl the tubes in the centrifuge about one minute,
or until all of the particles larger than clay (0.005

SHAKER USED IN THE PREPARATION OF SOIL SAMPLES FOR

MECHANICAL ANALYSIS

mm.) have settled. Decant the liquid into a granite
saucepan, stir up the soil remaining in the tube by
means of a jet of distilled water, and again whirl for

THE PHYSICAL PROPERTIES OF SOILS 8/

STUDENT'S NOTES AND REPORT

88 THE rilYSlCAL PROPERTIES OF SOILS

the same length of time. Again decant, and continue
the process until the water becomes clear. Evaporate
the liquid in the saucepan almost to dryness on a hot
plate, and transfer the residue to a weighed porcelain
dish. Complete the evaporation on a steam bath and
dry in the oven, cool in a desiccator and weigh. This
weight, less the weight of the dish, gives the amount
of clay which should be expressed as per cent of the
dry weight of the soil.

SILT SEPARATIONS

Stir up the soil remaining in the centrifugal tube
and allow to stand for about one minute, or until all
particles larger than silt (0.05) have settled. Decant
the liquid into a saucepan, stir the remaining soil in
the tube, and decant as before. Continue decanting
at the proper time until the water is again clear.
Evaporate the liquid in the saucepan as before, trans-
fer the residue to a porcelain dish, dry, weigh, and
calculate as in case of the clay.

SAND SEPARATIONS

Wash the sand remaining in the centrifugal tube into
a porcelain dish, evaporate on the steam bath, dry in
the oven, and weigh. This weight, less the weight of
the dish, represents the total sands. Sift this sand
through a nest of sieves provided for the purpose.
The material remaining in the first sieve is the fine
gravel ; in the second, coarse sand ; in tlic third, medium
sand; in the fourth, fine sand; and in the fifth, very
fine sand. Carefully transfer each grade of sand sep-
arately from the sieve to a dish and weigh.

Calculate the i)cr cent of each grade, and tabulate

THE PHYSICAL PROPERTIES OF SOILS 89

STUDENT'S NOTES AND REPORT

90 THE PHYSICAL PROPERTIES OF SOILS

the results. Discuss the value of mechanical analysis
as an indicator of the adaptability of soils to crops.

DETERMINATION OF THE LOSS ON IGNITION

Heat the dishes containing the oven-dry samples to
dull redness, over a bunsen burner, until all of the
organic matter is burned away. Allow to cool, and
then moisten the mass with a few drops of ammonium
carbonate. Heat slowly to about 150° C, to drive off
the excess of ammonia, cool in a desiccator and weigh.

The loss in weight of the sample represents the or-
ganic matter, volatile salts, and water of combination.

References :

Burkett, "Soils," pp. 30-33.
Bureau of Soils, Bulletin No. 5.
Bureau of Soils, Bulletin No. 24.

THE PHYSICAL PROPERTIES OF SOILS

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92 THE PHYSICAL PROPERTIES OF SOILS

EIGHTEENTH EXERCISE

CHROMIC ACID METHOD OF DETER-
MINING ORGANIC MATTER

Many of the physical properties of soils are in-
fluenced by the amount of organic matter present. An
accurate method for its determination is important,
therefore, in the study of the physical properties of
soils.

The determination of organic matter by dry combus-
tion usually gives results that are too high, owing to
the fact that combined water is driven off at the high
temperature necessary for the complete combustion of
the organic matter. The chromic acid, or wet com-
bustion, method does not drive off this combined water,
hence it is free from this objection.

METHOD OF DETERMINATION

The apparatus (T) consists of a round-bottomed
flask of about 400 cc. capacity in which the combustion
is effected. Connected to this flask is a train of ab-
sorption bulbs, so arranged that the CO:; produced by
the breaking down of the organic matter is absorbed,
and may be weighed at the close of the experiment.

A carefully weighed sample of soil of about ten
grams is brought into the combustion flask, from five
to ten grams of pulverized potassium bichromate is
added, and the whole thoroughly mixed. The flask is
closed, and a gentle stream of air is drawn through
the entire system by means of an aspirator. After
about ten minutes, concentrated suli)huric acid (sp. gr.
about 1.83) is added by means of a dropping funnel.

The combustion flask is slowly heated until the acid
begins to give off fumes. It is held at this temperature

THE PHYSICAL PROPERTIES OF SOILS 93

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

for about ten minutes or until the combustion of the
organic matter is complete, and then allowed to cool.
Care must be taken that a steady stream of air is kept
passing through the system.

The amount of CO2 given off is determined by
weighing the potash absorption bulb, and its acid guard
bulb, at the beginning, and again at the close of the
experiment. In calculating the per cent of organic

APPARATUS USED FOR THE DETERMINATION OF THE ORGANIC

MATTER IN SOILS BY THE WET-COMBUSTION METHOD

(Bulletin No. 24, Bureau of Soils)

matter in the soil from the weight of CO^ found, it is
necessary to use a conversion factor which, multiplied
by the weight of the CO2, gives the weight of the or-
ganic matter from which the gas was derived. The
factor generally accepted for this purpose is 0.471,
based upon the investigations of Wollny and his study
of the carbon content of the humus of soils.

Certain modifications of the above method are neces-
sary when large quantities of chlorides and carbonates
are present in the soil.

For a full description of the apparatus, and complete
details of the method, the student is referred to Bul-
letin No. 24, Bureau of Soils.

THE PHYSICAL PROPERTIES OF SOILS 95

STUDENT'S NOTES AND REPORT

THE PHYSICAL PROPERTIES OF SOILS

APPENDIX

DIRECTIONS FOR TAKING SOIL SAMPLES

In securing samples of soil from the field for
analysis or for the determination of moisture content
or pore space, great care must be taken to have the

SAMPLING APPARATUS

Used for taking samples when a large quantity of soil is desired.

The sampling tube is 4 inches in diameter and 15 inches long

samples represent, as nearly as possible, average field
conditions. When taken for laboratory use the sample
should be representative of the soil type, or of the field
conditions which are under consideration.

Soils of glacial origin arc (juite variable in composi-
tion, making it extremely difficult to secure a sample
that will accurately represent any definite area or a
particular soil type. wSoils of residual origin are much
less variable in composition.

THE PHYSICAL PROPERTIES OF SOILS

STUDENT'S NOTES AND REPORT

L»— -. «——____ — -..__—..-. — —

—

_ ——__—__ — — — — — —

1 1 1

JXLLLL-- ; : ^j_ ; ^_ ij-i._

PLAIN CO-ORDINATE PAPER

98 THE PHYSICAL PROPERTIES OF SOILS

In order to secure a sample that will be representa-
tive of a given field or plot it is necessary to drive
down a sampling tube in a number of places and com-
bine the cores into a composite sample. A moisture
determination made in duplicate on this composite
sample may be taken to represent the average moisture
of the soil over the field under observation.

Samples taken for mechanical analysis should be

METHOD OF SUB-SAMPLING SOIL BY SUCCESSIVE DIVISIONS
OF THE MAIN SAMPLE

dried, thoroughly mixed, and the lumps broken with
a rolling-pin. They should then be passed through a
2 mm. sieve to remove the gravel and sticks. The
portion of the sample passing through the sieve is
spread out on a piece of heavy paper and thoroughly
mixed with a large spatula. The sample is then
divided into four parts and one portion is again
thoroughly mixed. A twenty or thirty gram sample
is taken from this fine material, dried in the oven and
used for the analysis.

The method of taking the sample and its subsequent
treatment will vary with the purpose for which the
sample is taken.

THE PHYSICAL PROPERTIES OF SOILS 99

References

Stevenson & Schaub, "Soil Physics Laboratory
Guide."

Bulletin No. i6, Bureau of Soils, pp. 13-15.

Bulletin No. 24, Bureau of Soils, p. 9.

STANDARDIZATION OF THE EYE-PIECE

MICROMETER

The microscope used in the mechanical analysis of
soils must be provided with an eye-piece micrometer
for measuring the diameter of the soil grains com-
posing the different separates. The value of the di-
visions on this eye-piece micrometer will vary with the
different magnifying powers of the microscope. It
becomes necessary, therefore, to determine the value
of the divisions in the eye-piece by comparison with
a standard of known value placed on the stage of the
microscope. This is done by comparing the eye-piece
with a stage micrometer of known value, and com-
puting the value of one division on the eye-piece mi-
crometer for each optical combination. When this is
known, the number of spaces which the soil particles
must cover to belong to a given grade is determined
by dividing the diameter of the particles by the value
of one space.

Each student is required to make a standardization
and compute the value of the divisions of the eye-piece
for all of the combinations of the microscope used in
the laboratory. The results must be tabulated and
kept in this book for reference.

100 THE PHYSICAL PROPERTIES OF SOILS

TABLE OF DATA

I cc. of water := i gram.

I cu. ft. of water = 62.25 ^bs. avoirdupois.

I gram = 0.0022 lbs. avoirdupois.

I cc. = 0.061 cu. in.

I gal. = 231 cu. in.

I oz. avoirdupois = 28.35 grams.

I kilogram = 2.20 lbs. avoirdupois.

I inch = 25.4 mm.

IN DEX

PAGE

Air in field soils 44

Analysis of soils 80

Capillary water, its distribution 40

rise of moisture 46

rise of moisture interrupted 46

moisture, continuous rise 50

moisture, lateral movement 54

Clay separation 86

Fertilizers retained in soils 70

Flow of air in soils 42

Hygroscopic moisture 10

in the field 12

Laboratory desk outfit 3

Lime flocculates soils 68

Lime and clay soils 68

Mechanical analysis of soils 6

bottle method 80

centrifugal method 84

Mulches, effect of, on evaporation 60

Evaporation controlled by 60

Absorptive power of 64

Organic matter 90

Report on 91

Determination of 9^

Percolation of water 32

Pore space, determination of 26

Calculation of 28

Physical properties of soils 1

Sand 88

Silt 88

Soil samples 9°

Directions for taking 96

Apparatus for sampling 9°

Eye-piece micrometer 99

lOI

I02 INDEX

PAGE

Specific gravity i8

Calculation of i8

Method of determination i8

Specific heat 74

in soils 74

Determination of 74

Stock soils 5

Volume weight 22

Calculation of 26

Method to determine 22

Water-holding capacity 38

Apparatus to determine 38

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