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SOIL PHYSICS a
LABORATORY GUIDE}

J 2. SCHAUB_ a

Copyright N°

COPYRIGHT DEPOSIT:

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~ Soil Physics
Laboratory Guide

By
W. H. STEVENSON, A. B., B. S. A.

Professor of Soils, lowa State College

and

I. O. SCHAUB, B. S.
Assistant Professor of Soils, Iowa State College

SEY
oF
PROFUSELY ILLUSTRATED

NEW YORK
ORANGE FED D- COM PANY

1905

LIBRARY of CONGRESS
fwo Copies decetyou
Shr. 14 1905

GOvyIN ene

j

UOPYRIGHT 1905
BY

ORANGE JUDD COMPANY

—

ALL RIGHTS RESERVED

ILLUSTRATIONS

PLATES

PAGE

Photograph Showing Soil Physics Laboratory of Iowa

Pte Autom se sae oe ea Frontispiece

PuaTte 1—Outfit for Taking Soil Samples..........
PLATE 2—Apparatus for the Determination of Mois-
I ile ahrachy ic Sd bala ata he neva ko ig Sia yea St
PuaTtE 3—Apparatus to Test the Effect of Lime on
Clay Soil . :
PLATE Ear aacting: Meine me Filling Soil Tubes
PuateE 5—Spring Board Compactor...............
PuatE 6—Apparatus Used in Exercise 20..........
PuLatE 7—Box in Which Soils Are Exposed in a Sat-
WIPAUCU AIO SDPRERE + so sce Aes ere8s cls ba o winwens
PuaTE S8—Apparatus for the Percolation of Water
POPU ETIB US OTIR ff sre Ss Siw, hela 2A dws @
PuatE 9—Aspirator and Frame..
PuLatTe 10—Apparatus for the Study of mS Capillary
Peers A tie ass here Ce vate Grats pale tle «a ie
Puate 11—Apparatus for the Study of the Effect a
MRM se skies Shel Js Salo Wenig oe ee Oe
PuatTE 12—Mechanical Shaker Used in ppeperite Soils
for Mechanical Analysis. .

PuLaTE 13—Centrifugal Machine Used in sckacial
Analysis of Soils, and Tank for the Supply
of Distilled Water Under Pressure.......

_Puiate 14—Nest of Sieves Used to Separate Sand Into
hey AUS AGTHGCS 2 okies wee ko oS bwis'e ae

PiatE 15—Students’ Laboratory Desk..... AN Sys

FIGURES

Figure 1—The Chromic-Acid Method of Determining
birpentio- mation 2 de. eek

a

7

EXERCISE
EXERCISE

_~ EXERCISE

EXERCISE
_. EXERCISE

EXERCISE
EXERCISE

EXERCISE

EXERCISE
EXERCISE

EXERCISE
EXERCISE
EXERCISE

EXERCISE
EXERCISE
EXERCISE

. EXERCISE

CONTENTS

: PAGE
1—Microscopie Study of Soil Particles.... 1
De MITA OIL PAMPICGs <6 iho oa o Ge oie ee 1

38—Determination of Total Moisture in

17—Determination of the Apparent Specific

ravaiOl” SOUS ee bos Sie Bale aan Gee eles»

ici: amples: Oh: DONS. ica woes sc s0 oe 5
4— Determination of Capillary Moisture... 8
5—Determination of Hygroscopic Moisture 9
6—Determination of the Variation in the
Hygroscopic Moisture of Soils......... 10
7—Influence of Cultivation on the Temper-
AUCs ERO Rta eer, bt tes arse oie eR ora 1
8—Influence of Evaporation on Soil Tem-
TOLEDO Se Ss Ue a dR Sone NE By
9—FEffect of Rolling upon Soil Temperature 13
10—Influence of Color on Soil Temperature 14
11—Influence of Vegetation on Soil Tem-
“SGT IG 2 <a ep PRS R Bi on) Ai Soe ee ag Cee 45
12—Variation in Soil Temperature at Differ-
eid ergs MRR gee Oran eae ea aera 16
13—Influence of Topography on Soil Tem-
PRPS vo ney Seiad ess Ae tye) alo k Ae owe Ae 8 Sr? a lg
14—The Absorption of Heat by Soils....... 18

15—The Effect of Lime upon Clay Soil.... 19
16—The Flocculation of Clay..............

L-

Vill Contents

PAGE

— Exercise 18—Determination of the Specific Gravity
of. ‘Sous 65. cca ae ot ee 27

ExercisE 19—Determination of the Weight of Soil
Per Nerve: iy ae heee see ERG 28

EXERCISE 20—Determination of the Power of Loose
Soils to Retain Moisture Against Gravity 30

ExXercisE 21—Determination of the Power of Compact
Soils to Retain Moisture Against Gravity 32

EXErcIseE 22—Effect of Humus on the Water-Holding
Capacity of Solas 4435. a eee 33

EXERCISE 23—The Power of Air-Dry Soils to Absorb
Moisture from a Saturated Atmosphere 35

EXERCISE 24—Determination of the Rate of Percolation
of. Water Throiwieh Soils, ..24.4 o34 aee 38

Exercisr 25—Rate of Flow of Air Through Soils.... 40
EXERCISE 26—Rate of Rise of Capillary Water in Soils 42

Exercise 27—The Amount of Capillary Moisture at
Different Hights from the Water Table 45

EXERCISE 28—The Effect of a Layer of Green or Well-
Rotted Vegetable Matter upon the Cap-

ilary: Rise: of Water ie023) shee 46
EXERCISE 29—The Effect of Mulches cn Evaporation of
Water ‘from Soils<¢ 20/0 ..oee e AT

EXERCISE 30—Effect of Wetting the Surface of the
Soil on the Moisture Content of the
Sub-pau). catak caw SUC ye eae ei eee 49

EXercIsE 81—Determination of Loss on Ignition..... 50

EXERCISE 832—The Effect of Organic Matter on Baking
of Clay Soilsy sings Wis poe eee 51

Contents IX

Dy PAGE
Exercise 33—The Granular Structure of Soils........ 52

_. Exercise 34—The Effect of Alternate Wetting and
reine wpe FAN IstOM ed 5 oso 0h wes 53

EXxeErciIsE 35—The Effect of Alternate Freezing and
Thawing upon Granulation............ 54.

Exercise 36—The Effect of Organic Matter on Gran-
Bleue ete. di c-hurkc woe as awk hea wees arte 54

_— Exercise 87—The Chromic-Acid Method of Deter-
mnie -Oreanic Matters... is. 2. 0Ws..-% 56

EXERCISE 88—Standardization of the Eye-Piece Mi-
| PROINCIER hs cre ae el uals ogee sg he oe 60
ExercisE 39—Mechanical Analysis of Soils.......... 62

Exercise 40—Mechanical Analysis of Soils by the
ealrer Wether a, baited cee shed UE cel es 72
MCR ots are ela lca tiM tid nrc vin vb ako a sels eas ir oo Vine 3 76
eta OEY CGC NGINe ooo e acee odaccaty asx uss eeed 's ws Snips oa 76
Precautions to be Observed in Weighing............ 77

Weights and Measures, with Equivalents............ 79

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PREFACE

Commendable progress has been made during the
past decade in teaching Soil Physics in the Agricul-
tural Colleges and High Schools of this country. Up
to the present time, no comprehensive text book has
been prepared on this subject. The instructors in the
various institutions have prepared notes and outlines
as they have found time and opportunity for this work.

Without doubt, there is at the present time’a wide-
spread demand for a text book which covers the various
phases of the subject.

In these pages the aim has been to present to the
instructor and the student a carefully outlined series of
experiments in Soil Physics.

This book is the outgrowth of laboratory instruc-
tion given in the Iowa State College. A portion of
the experiments outlined in this guide have been used
quite generally in recent years. Many of them, we
believe, are now presented for class work for the
first time.

An earnest effort has been made to outline the
exercises briefly and clearly in order that the student
may proceed with the work without loss of time and
without confusion. ‘The exercises are also listed in a
logical order with reference to their relation to each
other and the skill required on the part of the student.

It is deemed advisable to assign the exercises which
eall for work in the field either at the beginning of
the fall semester or toward the close of the spring
semester.

xi Preface

When there are a Jarge number of students in the
soil laboratory, the work is often facilitated by divid-
ing the class into groups and assigning a certain num-
ber of exercises to each group.

Questions are asked in connection with each
experiment for the purpose of leading the student to
a thoughtful study of the data which he has secured.

- The illustrations are original; they are intended
to show the pieces of apparatus which are new or which
are not widely distributed. Descriptions of the appa-
ratus are given for the benefit of instructors who desire
to equip new soil laboratories or add to their supply
of apparatus. }

A larger number of exercises are incorporated in
this guide than can be covered by the student in a term
of average length; therefore, the work should be ex-
tended beyond the limits of one term or a portion of
the exercises should be omitted.

In the preparation of this guide, the authors have
drawn upon the publications of the Colleges of Agricul-
ture and the Experiment Stations of America; upon
F. H. King’s “Physics of Agriculture;’ A. D. Halls
“The Soil;” Robert Warington’s “Physical Properties
of Soil;” George P. Merrill’s “Rocks, Rock-Weathering
and Soils,” and H. W. Wiley’s “Agricultural Analysis.”

Iowa State College, Ames, Iowa,
July, 1905.
. W. H. STEVENSON.

I. O. SCHAUB.

Soil Physics Laboratory Guide 1

EXERCISE 1
Microscopic Stupy oF SOIL PARTICLES

Object: To study the color, shape, size and
character of soil particles in different classes of soils.

Directions :
1—Place a few grains of coarse sand upon a glass
slide and after careful examination with the low power
of the microscope, make drawings of several of the
particles and describe them with reference to the
following points :
(a) Color—White, grey, brown, red or black.
(b) Shape—Angular, rounded or irregular.
(c) Simple or compound.
(d) Size—Coarse, medium, fine or very fine.
2—Study in the same way samples of fine sand,
loam, loess, clay and peat.

Questions :
(a) What factors determine the shape of the
particles ?
(6) How do the soils vary?
1—In regard to the size of the particles?

2—In regard to the simple or complex
character of the particles?

3—In regard to the shape of the particles?
EXERCISE 2
TAKING SOIL SAMPLES

Object: To acquire skill in taking samples of
soul for laboratory study.

2 Soil Physics Laboratory Guide

Directions :

Great care should be exercised when samples of
soil are taken from the field for analysis or study in |
order to secure samples which accurately represent the
type or types of soil to be studied.

When samples of soil are taken for laboratory pur-
poses, the collector must use care in their selection for
the following reasons:

1—“The process of analysis is long, laborious and
expensive ; and the labor entailed would not be justified
except in case of samples taken in such a manner as
to preclude the possibility of a doubt as to their
typifying the peculiar soils under consideration.

2x—“The samples used for analysis are very small
in comparison to the total mass of material to be repre-
sented by the results of the determination, and a smail
variation of the sample from the true type, when
multiplied and expressed in terms of the mass, would
be productive of a great error in results.

3—“The soil under consideration is apt to be
exceedingly variable in composition, making it a most
difficult operation to secure a sample which shall repre-
sent any definite area. This is especially true of the
soils of glacial origin, and the variation may not be
confined to the surface but is often apparent in samples
taken at the same depth in different places.”

The method of taking soil samples adopted by
the Soil Department of the Iowa State College is that
known as the auger method and is essentially the same
as that used by the Bureau of Soils of the United —
States Department of Agriculture.

Samples are sometimes taken with King’s Soil
Tube, but this piece of apparatus is not often used.

The following directions should be carefully fol-
lowed in taking soil samples with an auger:

Soil Physics Laboratory Guide 3

1—Select the spot where the samples are to be
taken and clean the surface of the ground of grass
and other vegetation.

2—Place the auger over the spot where the sample
_is to be taken; give the auger two or three turns to
drive it into the soil, but take care not to force it into
the soil so far that it cannot be readily withdrawn.
The auger can be withdrawn with greater ease if it
is given a slight backward furn before an effort is
made to withdraw it. |.

3—When the auger has been withdrawn, hold it
over a piece of oilcloth which is about eighteen inches
square and release the soil.

4—Repeat this operation until the soil is secured
to about the depth of the plow line, viz.: five to seven
inches. Pour the soil from the oilcloth into a canvas
bag (or air-tight glass jar, if the sample is to be used
for a moisture determination) and plainly mark each
receptacle with a label which gives the location where
the boring was made, character of soil, depth, date and
any other data which are essential for identification in
the laboratory.

5—Place the auger in the hole thus made, and
move it up and down the sides several times, without
turning it, for the purpose of clearing the walls of
the opening to such an extent that the sub-surface soil
may be withdrawn without being brought in contact
with the surface soil.

6—Carefully clean out the enlarged hole by sink-
ing the auger to just the depth reached in taking the
surface soil; reject the soil which is withdrawn in
this operation.

?—Secure a sample of the sub-surface soil, viz. :
the soil between the surface soil and the sub-soil, in
the manner just described for the surface soil; in this

4 Soil Physics Laboratory Guide

work, care is required to detect and remove any surface
soil which may adhere to the outside of the core of
soil as it is removed.

8—Repeat the operation of enlarging and cleaning
the hole; reject about two inches of the soil between
the sub-surface and true sub-soil and then secure sam-
ples of the sub-soil to any desired depth. The sub-soil
can usually be detected by a marked difference in
texture and color.

Plate 1
OUTFIT FOR TAKING SOIL SAMPLES

The auger is an ordinary wood auger one and one-half
inches in diameter to which a three-eighth-inch iron gas

Soil Physics Laboratory Guide 5

pipe shank has been welded, giving the auger a total
length of forty inches. This auger can be provided with
as many additional three-foot lengths of gas pipe as are
desired. The auger is fitted with a short piece of one-
half-inch gas pipe for a handle. The attachment is made
with a T as shown in the illustration.

A convenient auger for extended trips is one made
as described above, except that a joint is placed about
the middle of the shank; this device enables the operator
to unscrew the auger with a wrench and pack it in a
suit case.

The oileloth is eighteen inches square; it has been
found to be a very simple and convenient device for
transferring the soil from the auger to the jars.

The “King” soil tube is made of brass with steel
cutting edge and collar and is provided with an eight-
pound hammer which is shown in the illustration. The
tube is five feet long; the inside diameter of the cutting
edge is fourteen-sixteenths of an inch and that of the
tube one inch.

EXERCISE 3

DETERMINATION OF ToTAL MOISTURE IN FIELD
SAMPLES OF SOILS

Object : To compare the total amount of mois-
ture in soils under the following conditions:

1—Sod ground.
2—Tilled field.
3—Summer fallow.
4—Fall plowed.
5—Stubble.

Directions:

1—Collect quart samples of surface, sub-surface
and sub-soil to a depth of forty inches; follow the direc-
tions outlined in the previous exercise. Secure samples
representing the above mentioned conditions, within as

6 Soil Physics Laboratory Guide

small an area as possible, in order to insure uniformity
in other soil conditions.

2—Determine the total moisture in duplicate for
the surface, sub-surface and sub-soil, using the corre-
sponding depth of soil from each area. As soon as
the soil is removed from the auger, it should be placed
in a-self-sealing glass jar or screw-topped brass box
and properly labeled. Before the vessels are opened
to take samples for the moisture determinations, the
‘contents should be thoroughly mixed by shaking.

3—Number and weigh a small sized drying pan
or evaporating dish and place in it 100 grams of the —
sample to be studied.

4—Place immediately in the drying oven and
keep at 100 to 110 degrees C. for four hours.

5—Allow to cool to nearly room temperature and
weigh. Repeat the drying and weighing until a con-
stant weight is obtained. The loss of weight repre-
sents the total water content of the soil.

6—Determine the percentage of moisture com-
puted on the dry weight of the soil.

%7—Tabulate the work as follows:

TOTAL MOISTURE DETERMINATION

Kind of | Pan | Wt. | Wt. Soil | Wt. Ist | Wt. 2nd | Wt. 3rd | Dry Wt.| Percent
Soil No. | Pan| & Pan Drying | Drying | Drying Soil Moisture

Questions:
(a) Does the surface soil or sub-soil hold the
larger amount of water?
(6) Give a list of the soils studied in the order
of their water holding capacity.

Soil Physics Laboratory Guide 7

‘-(c) Discuss the reasons for this difference in
the water-holding capacity of the various
soils.

Plate 2
APPARATUS FOR THE DETERMINATION OF MOISTURE

The drying oven is of copper set om a strong iron
frame. It is ten inches high, ten inches deep and twelve
inches wide. The oven is provided with a centigrade
thermometer and has a vent for the escape of moisture.
Its cost is approximately eight dollars.

The soil pans are made of tin and are water tight.
They are 4144x3', inches and 11% inches deep. This size
has been found convenient when the pans are used in the
oven described above. These pans can be made by any
tinsmith.

The seale is known as the “Harvard Trip.” It
weighs accurately to a tenth of a gram and costs
about eight dollars.

The jars are quart Mason jars, fitted with good
rubbers to prevent evaporation.

8 Soil Physics Laboratory Guide

EXERCISE 4
_ DETERMINATION OF CAPILLARY MOISTURE

Object : To compare the amount of capillary
moisture in the soils used in the previous exercise.

Directions :

1—Make determinations in duplicate for the vari-
ous depths of the soils to be studied.

2—Carefully weigh the required number of small
pans or evaporating dishes and place in each 100
grams of soil.

3—Break up all lumps with a glass rod and spread
out the soil in a thin layer over the bottoms of the
vessels. Leave the soil exposed to the air at the room
temperature for twenty-four hours and weigh.

4—-Expose the soil as above and re-weigh until an
approximately constant weight is obtained. The loss
in weight represents the amount of capillary moisture
in the sample.

Notre—Keep all the samples used in this exercise
for the determination of hygroscopic moisture.

5—Compute the percentage of capillary moisture
on the basis of water-free soil and tabulate the work
as follows:

CAPILLARY MOISTURE

Let of | No. |} Wt. | Wt. Soil | Wt. Ist eit mee Wt. 8rd ast Wes % Capillary
Soil | Pan) Pan |_& Pan | Day Day _|_ Soil _|_ Moisture
Questions:

(a) What is capillary moisture?

(6) What is the difference between a water-
free soil and a soil containing capillary
moisture ?

Soil Physics Laboratory Guide 9

EXERCISE 5
DETERMINATION OF HyGroscoPpic MOISTURE

Object: To compare the amount of hygroscopic
moisture in the soils used in the two previous exercises.

Directions :
1—Use ten-gram samples of the air-dried soils
used in the previous exercise.

2—Heat the required number of clean porcelain
crucibles with covers in the flame for a short time;
cool in the desiccator and weigh accurately.

3—Place each ten-gram sample of soil in a weighed
crucible and heat in an air bath at 105 degrees C. for
two hours.

4—Cool in a desiccator, place cover on crucible
and weigh as quickly as possible.

5—Heat again for an hour, cool and weigh;
repeat this operation until the weight becomes constant.

The loss of weight from the air-dried sample
equals the amount of hygroscopic moisture.

6—Determine the percentage of hygroscopic mois-
ture on the basis of water-free soil and tabulate the
work as in the previous exercises.

Questions:
(a) What is hygroscopic moisture ?
(b) What is the difference between hygroscopic
and capillary moisture ?

(c). Under certain conditions, what water, in
addition to the two classes referred to
above, may be included in the total mois-
ture content of a soil?

10 Soil Physics Laboratory Guide

EXERCISE 6

DETERMINATION OF THE VARIATION IN THE HyGRo-
scopic MOISTURE OF SOILS

Object: ‘To compare the amount of hygroscopic
moisture in sand, loam, silt, clay and peat.

Directions:

1—Determine the hygroscopic moisture in ten
grams of air-dried samples of sand, loam, silt, clay
and peat.

2—Use duplicate samples and follow the method
given for the estimation of hygroscopic moisture in the
preceding exercise.

3—lHxercise care to weigh out all of the samples
at the same time to avoid any change in the amount
of hygroscopic moisture after a portion of the samples
have been selected, otherwise the comparison will not
be exact. The amount of heating given the different
samples should be approximately the same.

4—-Determine the percentage of hygroscopic mois-
ture on the basis of water-free soil and tabulate the
work as in the previous exercise.

Questions:
(a) What factors determine in a large measure
the amount of hygroscopic water held by
each soil?

(b) Does the organic matter in the soil hold the
moisture in the same way that it is held by
the soil particles?

Soil Physics Laboratory Guide 11

EXERCISE 7

INFLUENCE OF CULTIVATION ON THE TEMPERATURE OF
THE SOIL

Object: To show that loose soil is a poor con-
ductor of heat; that when the soil is stirred deeply, the
lower soil receives less heat, and under certain condi-
tions remains at a lower temperature than when the
surface receives shallow cultivation; that the cultivated
surface soil is warmer than the uncultivated soil.

Directions :

1—For this experiment, prepare three plots as
follows:

(a) Compact, uncultivated soil which is free
from vegetation.

(b) An adjoining plot cultivated to a. depth of
one and one-half inches.

(c) Another plot cultivated to a depth of three
or four inches.

2—Take the temperature of the air at four feet
above the surface of the ground.

3—Take the temperature of the soil in each
plot at a depth of one and one-half, three, six and
twelve inches below the surface.

Note—If an unmounted glass thermometer is’
used, open the soil to the desired depth with a small
pointed iron rod and place the bulb of the thermometer
at the depth at which the temperature is to be taken.
Leave the thermometer in position about two minutes
before taking the reading.

4—Record the temperature for four or more
different days. The temperature recorded for each
depth should be the average of at least four readings
taken a few inches apart.

12 Soil Physics Laboratory Guide

5—Tabulate the data as follows:

Date

Hour -
Condition
of Weather

Temperature of Soil

Plot A Plot B Plot C

15.1 8°16 119 4 Us| BS) e+ | Te) Teel eee ees
in. | in. | ine | ins | in.) in. ins | in. 1) iene ae. eae

Mean Temperature

Questions :

(2)
(5)

What are the sources from which the soil
receives heat?

What effect does the loose texture of the
soil have on absorption of heat? On radia-
tion? On conduction? On evaporation?
On capillarity? Give the reasons why in
each case.

(c) What would be the final effect of all these

(d)
(e)

influences on the soil temperature both of
the surface and the sub-surface, while the
soil is warming up in the spring? What
effect in the fall? What do you find?
What influence has the temperature of the
soil upon the germination of seeds?

What can the farmer do in the spring to
warm up the soil?

EXERCISE 8

INFLUENCE OF EVAPORATION ON SOIL TEMPERATURE

Object : To determine the influence of rapid
evaporation upon the temperature of the soil.

Soil Physics Laboratory Guide 13

Directions :
1—Prepare two plots as follows:
(a) A cultivated plot free from vegetation.
(b) An adjoining plot cultivated and free from
vegetation to which sufficient water has
been applied to bring the soil near the satu-
ration point. The water should be applied
several hours before the readings are taken.
2—Take the temperature of the air at four feet
above the surface of the ground, and also of the soil in
each plot at a depth of one and one-half, three and six |
inches below the surface.
3—Record the temperature for four or more
different days and tabulate the data as in Exercise 7.
Questions:
(a) Why does evaporation lower the temper-
ature of the soil?
(b) Why is an undrained soil colder than one
which is well drained?
(c) What is the specific heat of water compared
with soil?

EXERCISE 9
EFFECT OF ROLLING UPoN Soin TEMPERATURE

Object: To determine the changes in the tem-
perature of the soil due to rolling.
Directions :
1—For this experiment prepare plots as follows:
(a) Plot plowed five or six inches deep with
the surface left loose and open.
(6) An adjoining plot plowed five or six inches
deep with the surface rolled.

14 Soil Physics Laboratory Guide

2—Take the temperature of the air at four feet
above the surface of the ground and also of the soil
in each plot at a depth of one and one-half, three and
six-inches below the surface.

3—Record the temperatures for four or more dif-
ferent days and tabulate the data as in the preceding
exercise.

Questions:

(a) What is the first effect. of rolling a. soil
which is naturally cold?

(6) To what is this result due?

(c) What influence has rolling upon the evap-
oration of water from the rolled surface?

(d) What influence has evaporation upon the
temperature of the soil?

EXERCISE 10
INFLUENCE OF CoLoR ON SOIL TEMPERATURE

Object: To determine the difference in the
temperature of dark and light colored soils.
Directions :
1—Prepare three plots as follows:
(a) Cultivated plot, free from vegetation.

(>) An adjoining cultivated plot, the surface
of which has been blackened with a dressing
of soot or other black material.

(c) A third plot, the surface of which has been
whitened with a dressing of lime.

2—Take the temperature of the air at four feet
above the surface of the ground and also of the soil

Soil Physics Laboratory Guide 15

in each plot at a depth of one and one-half, three and
six inches below the surface.
3—Record the temperatures every three hours for
twelve consecutive hours on a clear day and also on a
cloudy day, and tabulate the data as in Exercise 7.

Questions :
(a) Why are dark colored soils higher in tem-
perature than light colored soils?
(6) What influence has organic matter upon
the temperature of the soil?

EXERCISE 11

INFLUENCE OF VEGETATION ON SOIL TEMPERATURE

Object: To determine the difference in the
temperature between a soil covered with vegetation
and-a bare soil freely exposed to the sky.

Directions :
1—Prepare two plots as follows:
(a) Plot from which all vegetation has been
removed.
(6) An adjoining plot which is covered with a
heavy grass sod.

~2—Take the temperature of the air at four feet ©

above the surface of the ground and also of the soil

in each plot at a depth of one and one-half, three and
six inches below the surface.

3—Record the temperatures every three hours from

6 o'clock a. m. to 9 o’clock p. m., on a day when the

sun is shining and tabulate the data as in Exercise 7.

Questions:

(a) Why is the range of temperature of a soil

16 Soil Physics Laboratory Guide

shaded by vegetation less than that of a
bare soil?

(6) Why is the temperature of the shaded soil
higher in the early morning than: the
temperature of the bare soil?

EXERCISE 12

VARIATION IN Sort TEMPERATURE AT DIFFERENT
DEPTHS

Object: To study the daily, weekly and monthly
variations in soil temperatures to a depth of three feet.

Directions:

1—Place four soil thermometers within a few feet
of each other, at a depth of six, twelve, twenty-four
and thirty-six inches respectively, in the soil which is
to be studied.

2—Take the temperature of the air at four feet
above the surface of the ground, and the reading of
each thermometer at a given time once each day for a.
period of at least two or three months.

3—Tabulate the data as in Exercise 7 and at
the end of the period of observation plot curves show-
ing the daily temperature of the air and of the soil
at the depths mentioned above.

Questions:
(a) Is there a point below the surface of the
soil where the temperature is nearly con-
stant from day to day?

(6) Why do the variations in temperature
diminish with increased depth?

Soil Physics Laboratory Guide 17

EXERCISE 13
INFLUENCE OF TOPOGRAPHY ON SoIL TEMPERATURE

Object: To determine the influence of the
degree of inclination of the land surface and the direc-
tion of the slope upon the temperature of the soil.

Directions :

1—For this experiment, select an area where the
soil of the same type is found upon an approximately
level table and upon a slope.

2—Take the temperature of the soil on the level
table and on the slope at a depth of six, twelve and
twenty-four inches, at a given time once each day for
a period of at least a week.

3—Tabulate the data as follows:

iti f Soil at
Topography | ate | Hour | (opdition, |_Temperature of Sit
6 inches| 12inches | 24 inches

Questions :

(a) When the sun is shining, why is the tem-
perature of the soil on a south slope
higher than the temperature of a level
surface ?

(b) Why is a southeast aspect generally pre-
ferred by gardeners ?

(c) Why is it preferable to plant corn in rows
running north and south rather than in
rows running east and west?

(d) Why does not vegetation growing upon a
slope receive increased radiation from the
sun as does the surface of the ground?

18 Soil Physics Laboratory Guide

EXERCISE 14
Tuer ABSORPTION OF HEAT BY SOILS

Object: To compare the temperature of sand,
loam, clay and peat at different depths, when these soils
are exposed to the direct rays of the sun.

Directions :

1—Provide four zine or tin boxes about four
inches wide and eight inches deep, encased in wooden
covers, except on the top. This cover serves to protect
the box against all heat except the direct sunlight on
the open surface of the soil.

2—Fill each of the boxes respectively with sifted
air-dried sand, loam, clay. and peat.

3—Take the temperature of the soil in each box
at a depth of one and one-half, three and six inches
and then expose the boxes to the direct rays of the
sun for two hours.

4—At the end of this time, take the temperature
of the air directly above the boxes and also of the soil
at the depths named above.

Notr—lIt is a good plan to provide the boxes with
thermometers set at the different depths. The tem-
perature of the soils can thus be read off directly.

5—Tabulate the data as follows:

Temperature of Soil

Temperature of Soil Increase of Soil
at Beginning :

After Exposure Temperature

Kind | Temp.
f °o

ae ee 1.5in.| 8in. | Gin. |1.5in.|-3in. | Gin. |1.8in.| 3in. | 6in.

Soil Physics Laboratory Guide 19

6—Moisten the soil in each box with a given
amount of water and repeat the experiment as above
_in order to determine the action of moist soil under
similar conditions.

Questions:

(a) What are the factors which influence the
difference in the absorption of heat by the
different soils? .

(b) What effect has wetting on the absorptive
power of the soils? Did it affect the
various soils differently ?

EXERCISE 15
Tue Errect or Lime Upon Cray Sorn

Object: To determine the effect of different
amounts of slacked lime upon the tenacity of clay soil.

Directions :
1—Weigh out five 100-gram samples of clay soil.
2—Add to each sample the amount by weight of
calcium hydrate (slacked lime) given below:

No. 1—None.

No. 2— _ .5 percent.

No. 3— 1.0 percent.

No. 4— 5.0 percent.

No. 5—10.0 percent.

3—Mix each sample thoroughly on a “mixing
board” and add just enough distilled water to make
the soil plastic.

4—Mold each sample into the form of a stick by
compressing the moist clay into a zine mold which
is one inch wide and four inches long. First line the

20 Soil Physics Laboratory Guide

mold with cheesecloth and compress all of the samples
to the same degree and then bake in the oven at 110
degrees C. for four hours.

-5—Remove the sticks of baked clay from the
molds and determine the weight required to fracture
each.

Note—This determination may be made by
resting the ends of the stick of clay upon supports
and suspending from the center a bucket into which
shot or sand is slowly poured.

6—Tabulate the data as follows:

Sample No. Weight Required to Fracture Stick

Questions :

(a) How did the lime affect the tenacity of
the clay?

(b) What effect does a liberal application of

| lime have upon the physical condition of
clay soil in the field?

Soil Physics Laboratory Guide 21

Plate 3
APPARATUS TO TEST THE EFFECT OF LIME ON CLAY SOIL

The molds in which the clay is baked are made of
heavy galvanized iron. They are four and one-quarter
inches long, one inch wide and three-quarters inch deep.

As shown in the illustration, retort stands provided
with iron rings are used for supports and the breaking
weight is a galvanized iron bucket into which shot or
sand is poured.

Care must be exercised in this experiment to mount
the sticks of clay in such a way that all of them are
subjected to a uniform strain.

EXERCISE 16
THE FLOCCULATION OF CLAY

Object : To show the effect of calcium hydrate,
calcium sulphate and sodium chloride in producing
flocculation of clay.

22 Soil Physics Laboratory Guide

Directions :

1—Weigh out accurately .2 of a gram of each
salt; place each sample in a_ well-cleaned beaker
and-add 200 c. c. of distilled water.

2—Place 200 ¢. c. of water in another beaker for
a control. Add to each of the four beakers, one gram
of clay soil.

38—Stir the contents of each beaker thoroughly
and then put a sample of each in a centrifuge tube
and whirl in the centrifuge at lowest speed and note
the time required to completely precipitate each solu-
tion, that is, to produce a clear solution.

4—Thoroughly mix the contents of each centrifuge
tube and set aside; note the time required for complete
sedimentation in each case.

5—Tabulate the data as follows:

A Time to Precipitate Time for
Solution with Centrifuge Sedimentation

Questions :

(a) Explain the action of the salts in clarifying
the water.

(b) Why is a flocculated condition of clay soils
desirable ?

(c) What physical effect results from the lim-
ing of clay soils?

Soil Physics Laboratory Guide 23

EXERCISE 17

DETERMINATION OF THE APPARENT SPECIFIC GRAVITY
OF SOILS

Object: ‘To determine the ratio of unit weight
to unit volume of different soils.

Directions :
1—Number and weigh carefully eight clean soil
tubes.

2—Fill four of the tubes level full with air-
dried loess, clay, loam and sand, respectively, by pour-
ing the soils in loosely. Fill the other four tubes with
the same soils, using the compacting machine and
allowing the weight to fall three times from the twelve-
inch mark upon each measure of soil.

3—Weigh the filled tubes carefully.

4—Measure the diameter and hight of the tubes
and compute the number of cubic centimeters of soil
contained in each.

5—Determine the amount of hygroscopic water
in a sample of each of the soils taken when the tubes
are filled.

6—Calculate the apparent specific gravity of the
different soils. (Apparent Specific Gravity equals
weight of 1c. ec. of soil divided by weight of 1 ec. e.
of water.)

”—Tabulate the data as follows and calculate the
weight of an acre of the different soils to a depth of
one foot.

24 Soil Physics Laboratory Guide

Kind | No. | Wt. | Wt. of Amt. | Net |Wt. of| App. he e
0 of of { Tube |Vol. of] Hy. |Wt. of/1¢.c.| Sp. Gr. Soil ig
Soil Tube | Tube| & Soil) Tube | Water| Soil | Soil | of Soil Tons
1
Questions:

(a) Which is heavier, a coarse or fine grained
soil? Why?

(0) What influence has the presence of stones
upon the apparent specific gravity of a soil?

(c) What influence has plowing upon the ap-
parent specific gravity of a soil?

Soil Physics Laboratory Guide 25

COMPACTING MACHINE FOR FILLING SOIL TUBES

The compacting machine shown in the illustration
was designed to pack the soil into the tubes more
uniformly than can be done by hand. The latter
method, even when great care is exercised, gives very
unsatisfactory results.

The illustration shows the construction of the com-
pactor; the table is two feet wide, three feet long and
three feet high; the wooden posts in front are six inches
square. The iron shaft which carries the plunger and
weight is one inch in diameter; the plunger is two inches
in diameter; the weight is four inches long and two
inches in diameter; the weight strikes upon a support
which is attached to the shaft by a set screw.

26 Soil Physics Laboratory Guide

The adjustment of the tube, plunger and weignt .1s
shown. The weight may be dropped any number of times
from a given hight. The soil tubes which are shown on
the compactor and which are used in Exercise 17, are
made of galvanized iron with solid bottoms. These tubes
‘are twelve inches long and two inches inside diameter.

A better grade of tubes are made of brass, but very
satisfactory results are secured with the cheaper galvan-
ized iron tubes.

Plate 5

SPRING BOARD COMPACTOR

The spring board compactor is a cheap but a very
satisfactory compacting machine. It may be used in-
stead of the larger and more expensive compactor shown
in. Plate™ 4:

This piece of apparatus is made of one-inch pine
boards, four feet long and eight inches wide. A two by
four-inch block is placed between the boards, six inches
from the right end. The boards are securely nailed to
this block and are also fastened together by two half-inch
bolts. Another block about an inch and a half in thick-

Soil Physics Laboratory Guide 27

ness is nailed to the lower board ten or twelve inches
from the left end.

The wooden upright in the center is securely
fastened to the lower board and passes loosely through
an opening in the upper board. An iron weight of two
and one-half kilos is dropped upon the board from a
hight of twelve or eighteen inches. The tube which con-
tains the soil which is to be compacted is supported by
rings as shown in the illustration. The tube is filled
with soil and the entire depth compacted at one operation.

EXERCISE 18
DETERMINATION OF THE SPECIFIC GRAVITY OF SOILS

Object: To compare the weights of different
soils with the weights of equal volumes of distilled
water.

Directions :

1—Fill a.specifie gravity flask carefully with dis-
tilled water which has been previously boiled for a few
minutes and allowed to cool to the room temperature,
which is recorded. Have the capillary stopper just
filled with water. Wipe the flask perfectly dry and
weigh.

2—Pour out about one-third of the water and
place in the flask about ten grams of accurately weighed
sand which has been dried to a constant weight at
110 degrees C.

3—Heat the flask for a few minutes on the water
bath, until the air is expelled. Remove the flask and
cool to the first temperature, and fill with previously
boiled and cooled water; dry and weigh at the original
temperature.

_ 4—With the same method determine the specific
gravity of loam, loess, clay and peat.

28 Soil Physics Laboratory Guide

5—Calculate the specific gravity (weight of soil
divided by weight of water displaced by soil), and
tabulate the results as follows:

SPECIFIC GRAVITY OF SOILS

Kind of
Soil

Wie k Fi ‘ c ) ‘ :
: pe ee pale Wt. of Soil Wits oF _ Specific Gravity

$$ $$$ —$—— ->

:
et a
6—From the data in Exercises 17% and 18,
determine the percent of porosity, i. e., the space which
in the dry soil is occupied by the air, of the different
soils which were used.

Questions :

(a) Why is it necessary to use water-free soil?

(b) Why does the sand have a higher specific
gravity than the clay, loam and peat?

(c) How does the amount of humus in the soil
influence its specific gravity?

(d) Why is it necessary to weigh the flask each
time at the same temperature?

EXERCISE 19
DETERMINATION OF THE WEIGHT OF Soin PER ACRE
Object: To determine the weight of dry soil to

a given depth per acre.

Directions :
1—Drive into the soil a brass tube (eight inches
long and about three inches in diameter, sharpened

Soil Physics Laboratory Guide 29

at its lower edge) until the top is level with the
surface.

2—Dig away the soil around the tube; empty the
tube upon a piece of oilcloth and transfer the soil to
a Mason jar; carefully drive the tube down again and
thus obtain a sample of the succeeding eight inches.
Repeat this operation until eight-inch samples of the
soil have been secured to any desired depth.

3—Carefully weigh each sample.

4—Determine the total moisture in 100 grams
of soil from each depth and from these data determine
the dry weight.

5—Calculate in cubic inches the contents of the
tube.

6—Calculate the weight of an acre of soil to the
depth at which each sample was taken and tabulate the
results as follows:

Kind of spa of |CubicInches| Weight of | Percent of | Dry ie are Wt. of Dry
Soil Sample of Soil Soil Moisture of Soil _|Soil per Acre

Question :

(a2) Why does a soil gradually increase in
weight as we go into the sub-soil?

30 Soil Physics Laboratory Guide

EXERCISE 20

DETERMINATION OF THE PowerR OF Loose Sorts To
RETAIN MomsturE AGAINST GRAVITY

Object: To compare the power of various types
of loose soil to hold water against gravity.

. Directions:

1—Place a disc of cheesecloth in the bottom of
a perforated tube, moisten the cloth and weigh care-
fully.

2—Fill the tube with loose sand, exercising care
not to compact the soil, and weigh the filled tube.

3—Stand the tube in a vessel containing water
to a hight nearly equal to that of the surface of the
soil. Leave the tube standing in this position until
the surface of the soil becomes thoroughly moistened.

4—Remove the tube from the water, wipe dry,
place in a small pan and weigh. -

5—Cover the tube with a glass plate and set it
where the water will drain away. Weigh the tube at
the end of the first hour, second hour, and daily there-
after for five days.

6—Determine the hygroscopic moisture in a sep- |
arate sample at the time of filling the tube.

%—Calculate on a water-free basis, the percent
of water held by the sand.

8—In the same way determine the percent of
water held by loam, clay, loess and peat.

Soil Physics Laboratory Guide 31

9—Tabulate the data as follows:

Kind of Weight of Weight of Weight of Percent of Weight.of
Soil Tube Tube and Soil Soil ; H aaa Dry Soil
|

eee,

Weight of Tube and Soil at

Weight of Tube
and Saturated Soil’
lhr. 2 hrs. 26 hrs. 50 hrs. 74 hrs. 98 hrs.
Weight of Water Retained Percent of Water Retained

Hours Hours

Saturated | 1 | 2 | 26 74 | 98 || Saturated | 1 | 2 | 26 | 50 | 74 | 98

Questions:

(a) What is a saturated soil ?

(b) Which type of soil loses water most rapidly
at first? Which percolates for the longest
time ?

(c) Calculate the total number of pounds of
water retained per cubic foot of dry soil
and also the number of inches of rainfall
which it represents ?

32 Soil Physics Laboratory Guide

Plate 6

APPARATUS USED IN EXERCISE 20

A four-gallon jar is a convenient vessel to use in
this exercise.

The soil tubes which are used to determine the power
of soils to retain water are made of galvanized iron.
They are twelve inches long and two inches inside diame-
ter. The bottoms are set up one inch from the lower
end and are perforated as shown in the illustration.

These tubes can be made of brass if tubes of a better
quality are desired.

EXERCISE 21

DETERMINATION OF THE PowrrR OF Compact SoILs TO
RETAIN MorsturE AGAINST GRAVITY

Object: ‘To compare the power of various types
of compact soils to hold water against gravity.

Soil Physics Laboratory Guide 33

Directions :

1—Proceed with this experiment as in the previous
exercise, except that the tubes are to be filled as follows:

Use the soil compacting machine, allowing the
weight to fall three times from the twelve-inch mark
upon each measure of soil.

2—Calculate on a water-free basis, the percent
of water held by the compact soils and tabulate the
data as in the preceding exercise.

Questions:

(a)What conclusions do you draw from these
data, regarding the effect of rolling upon
the water-holding capacity of the soil?

(6) What effect has cultivation upon the
water-holding capacity of the soil?

(c) What type of soil has its water-holding
capacity changed to the greatest extent by
compacting.

EXERCISE 22

EFFECT OF HUMUS ON THE WATER-HOLDING CAPACITY
OF SOILS

Pablent: To determine the effect of different
amounts of humus upon the water-holding ‘eapaeity of
various types of soil. —

Directions:

1—Place a disc of cheesecloth in the bottom of the
required number of perforated soil tubes.
2—Prepare the following samples:
No. 1—600 grams of sand.
No. 2—570 grams of sand and 30 grams of peat.

34 Soil Physics Laboratory Guide

No. 8—540 grams of sand and 60 grams of peat.
No. 4—480 grams of sand and 120 grams of peat.
No. 5—Number of grams of peat required to fill
the tube to the same hight as the other
tubes.
Thoroughly mix each of these samples on a “mix-
ing board” and fill the tubes, which have been num-
bered to correspond with the samples, by using the soil
compacting machine, allowing the weight to fall three
times from the twelve-inch mark upon each measure
of soil.
3—Stand the tubes in a vessel containing about
four inches of water and allow them to remain in the
water until the weight becomes approximately constant.
4—Remove the tubes from the water, place each
in a small pan to catch the possible drainage and weigh.
5—Repeat the experiment with clay and _ loess.
6—Determine the percentage of water retained by
each sample and tabulate the data as follows:

Weight of Tube Weight of Tube, Soil Percent of Water
and Soil Held

Sample No. and Water Held

Questions :

(a) Compare the amount of water held by the
mixtures with the amount held by equal
weights of the sand and peat when tested
separately.

(6) Basing your calculations on the data ob-
tained, determine the additional amount of

Soil Physics Laboratory Guide 35

water which an application of eight tons of
peat will enable an acre of soil to hold to
a depth of five inches.

(c) Why does humus increase the water-holding
capacity of a soil?

EXERCISE 23

THe Power or Artr-Dry Sorts To Apsors MOISTURE
FROM A SATURATED ATMOSPHERE

Object: To determine the total amount of
moisture absorbed from a saturated atmosphere by
different types of air-dry soil.

Directions :

1—Place 400 grams of air-dry loam in an accu-
rately weighed soil pan; weigh also one empty soil pan
to serve as a check.

2—Place the pans on a shelf in a tightly covered
vessel which contains a saturated atmosphere. Record
the temperature of the air in the vessel at each weighing.

3—After twenty-four hours, weigh each pan and
deduct the increase in weight of the empty pan from
the increase in weight of the pan containing the sample.

4—Repeat the weighings every twenty-four hours
until, with the same conditions of temperature, an
approximately constant weight is obtained. Weigh the
pans as rapidly as possible to prevent loss of moisture
by evaporation.

5—Determine the hygroscopic moisture of the loam
with a special sample at the time of placing the soil
in the pan.

6—Calculate the amount of water absorbed by
100 grams of the air-dry loam and the total amount

36 Soil Physics Laboratery Guide

of water taken from the air by 100 grams of water-

free soil.

7—Determine in the same way the amount of water
absorbed from the air by sand, clay and peat and
tabulate the data as follows: :

Wt. of ‘
Kind of |Wt. of Pan| Hygroscopic
Soil and Soil Moisture

Weight of Pan
and Soil

48 hrs.

Total Per-
cent of
Moisture in
Soil

Questions:

(a) Which class of
amount of moisture from the air?

soils absorbs the largest

Why?

(6) How does the amount of water which a
soil is capable of absorbing from the air
compare with the moisture content of the
soil when growing corn plants wilt?

Soil Physics Laboratory Guide 37

Plate 7
BOX IN WHICH SOILS ARE EXPOSED IN A SATURATED
ATMOSPHERE

This box is made of zine. It is twenty-six inches
long, fourteen inches wide and six inches deep and is
provided with a closely fitting cover.

There are two tiers of strips the full length of the
vessel on which rest the soil pans. Openings are cut in
these strips in which pieces of blotting paper are fitted.
The ends of the paper extend into the water, which is
kept not less than an inch deep in the bottom of the
vessel.

The soil pans used in this exercise are made of tin
and are six and one-half by six and one-half inenes and
one and five-eighths inches in depth.

38 Soil Physics Laboratory Guide

EXERCISE 24

DETERMINATION OF THE RATE OF PERCOLATION OF
WATER THROUGH SOILS

Object: To compare the rate of percolation of
water through soils of different texture.

Directions :

1—Use in this experiment sand, clay and loam.

2—Fill, without compacting, within an inch of the
overflow pipes, each of the soil tubes provided for this
experiment, with one of the soils named above, and
place a half-inch layer of gravel on the surface to
prevent disturbance of the soil by the flowing water.

3—Connect the filled tubes with short pieces of
rubber tubing, by means of the lateral inlets, and close
with corks the openings at the extreme ends of the
series.

4—Pour in water gently in quantities sufficient to
keep the tubes almost level full and maintain the same
water level in each tube.

5—Note the time until percolation begins from
the drainage tubes, then place an Erlenmeyer flask
beneath each. When the flow becomes constant, collect
the water which percolates through the soil in thirty
minutes and measure carefully.

6—Determine in the same way the amount of
water which percolates in thirty minutes through
compacted sand, clay and loam.

Soil Physics Laboratory Guide 39

¥Y—Tabulate the results as follows:

Loose Compact
Kind of Soil | a J ae ive a Ars
Time for c.c. Water Perco- Time for ce. c. Water Perco-
Percolation lated in 30 Min Percolation lated in 30 Min.

Questions :

(a) Why does the water percolate most rapidly
through the soil which has the least total
pore space? |

(6) What factors, other than texture, facilitate

‘ the percolation of water through loam and
clay soils under natural field conditions?

Plate 8
APPARATUS FOR THE PERCOLATION OF WATER THROUGH SOILS

The soil tubes used in this exercise are made of
galvanized iron. They are eighteen inches long and two

40 Soil Physics Laboratory Guide

inches in diameter, with solid bottoms. The lateral inlets
are three-eighth-inch tubes, one inch long; they are
placed one and one-half inches below the top of the soil
tubes. The drain pipe is one-quarter inch in diameter,
two and one-half inches long, and is three-quarters of an
inch above the bottom of the tube.

The block which is used to support the tubes is three
by three inches. The holes are two and one-quarter
inches in diameter, two inches deep, and are five inches
from center to center.

-Notches are cut in the side of the block to accom-
modate the drain pipes. This block can be used also in
other exercises.

EXERCISE 25
Rate oF FLtow or Atr THrovucHu Soirs

Object: To compare the rate of the flow of air
through soils of different texture. |

Directions :

1—For this experiment use sand, loam, clay and
loess.

2—Fill the required number of soil tubes pro-
vided for this experiment with the above named soils.
Use the compacting machine as directed in previous
exercises.

3—Connect the soil tubes successively to the cock
on the aspirator with rubber tubing and note the num-
ber of degrees passed by the pointer in a given time.

4—Determine the rate of flow per hour for the
different soils and tabulate the data as follows:

Kind of Soil Si est ea a Rate of Flow per Hour

Soil Physics Laboratory Guide 4]

Questions :
(a) What relation does the aeration of the soil
sustain to the action of bacteria in the soil?
(b) Do the different soils sustain the same rela-
tion to each other in regard to the rate of
the flow of air that is sustained in the
percolation of water?

Plate $

ASPIRATOR AND FRAME

The base of the frame is four feet long, twelve
inches wide and two inches thick. The uprights and
eross-bar are made of two by two-inch material. The
total hight is three feet ten inches.

A2 Soil Physics Laboratory Guide

The outside can, which holds the water, is eightcen
inches high and nine and one-quarter inches in diameter.
The inside can is eighteen inches high and eight and one-
half inches in diameter. It is fitted with a ring and cock
as shown in the illustration.

' The larger can is nearly filled with water; the smaller
can is pushed down into the water with the cock open
to permit the air to escape. The cock is then closed and
the tube containing the soil is attached to the cock of
the aspirator by means of a piece of rubber tubing which
is long enough to extend to the top of the frame.

The weight is about twice as heavy as the can to
which it is attached with window cord. The cord passes
through a pulley near the end of the frame which is
similar to the one shown in the illustration, except that
the axle passes through the dial and carries a pointer.
To operate the aspirator, open the cock and start the
weight from the same point each time.

The soil tubes are made of galvanized iron. They
are eighteen inches long and two inches in diameter.
The tube near the bottom is one-fourth of an inecli in
diameter, two inches long and is curved upward as shown.
The block in which the tubes are supported is similar to
the one used in the previous exercise.

s

EXERCISE 26
RATE OF Rist ofr CAPILLARY WATER IN SOILS

Object: To compare the rate of the rise of
capillary water in soils of different texture.

Directions :

1—For this experiment use coarse sand, fine sand,
loam, clay, loess and peat.

2—Select twelve glass tubes, one inch in diameter,
of uniform bore, and close one end of each by means of
a piece of cheesecloth, firmly tied on.

3—Fill six of the tubes with the finely pulverized

Soil Physics Laboratory Guide 43

air-dried soils, pouring the soil in loosely, care being
taken not to compact it. Fill the remaining six tubes
by .compacting the soil by gently tapping the tubes
during the time of filling.

4—-Place the tubes in a wooden frame in such a
manner that the lower ends are immersed in about an
inch of water.

5—Make readings at the following intervals:
1 hour, 2 hours, 3 hours, 6 hours, 9 hours, 12 hours,
18 hours, 24 hours, 36 hours, 48 hours, and daily there-
after until no further rise is noted. Note the total
hight to which the water has risen and the rise in the
water column since the previous reading.

6—Tabulate the data as follows:

Hight of Water in Inches

7
Kind of Soil 1 2 3! S 9 12 18 24 | 36 | 48 | 72 Hours
Loose
Compact

Questions:

(a) What factors influence the capillary rise of
water in soils?

(b) Does the water rise to the greatest hight in
the soil in which the rise is most rapid at
first ?

44 Soil Physics Laboratory Guide

samen

Plate 10
APPARATUS FOR THE STUDY OF THE CAPILLARY RISE OF WATER

The frame in which the glass tubes are supported is
two and one-half feet wide and four feet high. It is
made of material one inch thick and four inches wide.
The frame rests upon two blocks, sixteen inches long.
The holes in the upper cross-bar, which receive the glass
tubes, are flush with the edge and the tubes are held in
position by wooden buttons as shown.

Soil Physics Laboratory Guide 45

EXERCISE 27

THe AMOUNT OF CAPILLARY MOISTURE AT DIFFERENT
HIGHTS FROM THE WATER TABLE

Object : To determine the amount of capillary
_ moisture held at different hights from the water table
by soils of different texture.

Directions:
1—Use the same soils which were used in the
preceding exercise.

2—Fill six sectional brass soil tubes, five feet in
length, over the lower ends of which pieces of cheese-
cloth have been firmly tied, with the finely pulverized
air-dried soils, pouring the soil in loosely, care being
taken not to compact it. Fill six other tubes by com-
pacting the soil by tapping the tubes gently.

3—Place the tubes in a frame with the lower ends
standing in about one inch of water.

4—-At the end of thirty days, separate the one-foot
sections from each other and determine the percent of
moisture held in each successive foot above the water
table. For the moisture determination use about a 100-
gram sample of the soil taken from the top of each
section.

5—Tabulate the data as follows:

Percent of Moisture

et Po ie PR ee
Kind of Soil

5 ft. | 1ft. | 2 ft.

2ft.| 3ft. | 4 ft.

3 ft. | 4ft. | Sit.

|
es

46 Soil Physics Laboratory Guide

Question :
(a) Why is there a difference in the percent of
water held at the different hights from the
water table? 7

EXERCISE 28

THE EFrect oF A LAYER OF GREEN OR WELL-ROTTED
VEGETABLE MATTER UPoN THE CAPILLARY RISE
OF WATER

Object : To determine the extent to which a
layer of vegetable matter breaks the capillary rise of
water in soils.

Directions :

1—Select three glass tubes about two feet long
and two inches in diameter, of uniform bore, and close
one end of each by means of a piece of cheesecloth
firmly tied on.

2—Fill one tube with finely pulverized air-dried
loam, pouring the soil in loosely. Fill a second tube
with the same soil to a depth of one foot; then place
in the tube a two-inch layer of coarsely cut green
material and complete the filling of the tube-with the
loam. Fill the third tube in the same way except that
well-rotted manure is to be substituted for the green
material.

3—Place the tubes in a frame with the lower ends
standing in about one inch of water.

4—Observe the rise of the capillary water in each
tube and report in narrative form your observations,
which should extend over one week.

Question :

(a) What is the practical lesson taught by this
experiment ?

Soil Physics Laboratory Guide 47

EXERCISE 29

THE-HFFECT OF MULCHES ON EVAPORATION OF WATER
FROM SOILS

Object: To determine the amount of evapora-
tion which takes place from soils when they are culti-
vated at different depths and when they are mulched
with various materials.

Directions :

1—Fill the required number of soil cylinders
provided for this experiment with fine air-dried loam,
compacting the soil uniformly and filling the cylinders
to the same level.

2—Treat the soils in the different cylinders as
follows:

No. 1—No treatment.

No. 2—Cultivated one inch deep.

No. 3—Cultivated three inches deep.

No. 4—Cultivated five inches deep.

No. 5—Mulched with two inches of leaves.
No. 6—Mulched with two inches of cut straw.

3—Cultivate the soil each day by thoroughly
stirring the surface to the required depth.

4—Fill the water supply tubes on the cylinders
with water to the same level every day, and after evap-
oration begins, keep a careful record for one week of
the amount of water given off every twenty-four hours.
Cover the supply tubes with corks or glass plates in
order to prevent evaporation from the water surface.

5—Determine the surface area of the cylinders
and compute the number of tons of water evaporated
per acre during a period of. one week.

6—Repeat this experiment with a sandy soil.

48 Soil Physics Laboratory Guide

%—Tabulate the data as follows:

l Lie
Number of c. c. Water Evaporated |

; Ist day 2d day|3d Sele othday Ptah Fee Total No. Tons per
| | | | c.c. Water S« Acre

|
|

Questions :
(a) What is the effect of a mulch?
(0) Which method of cultivation conserves the
greatest amount of moisture?
(c) Is the amount of water evaporated from
day to day the same? If not, why?

Plate 11

APPARATUS YOR THE STUDY OF THE EFFECT OF MULCHES

The cylinders are made of galvanized iron. They
are eleven inches in diameter and thirteen inches high.

Soil Physics Laboratory Guide 49

The water supply tubes are one inch in diameter. Cylin-
ders of this style permit evaporation to take place from
quite a large area.

EXERCISE 30

EFFECT OF WETTING THE SURFACE OF THE SOIL ON
THE MOISTURE CONTENT OF THE SuB-SOIL

Object: To study the translocation of water
occasioned by wetting the surface of the soil.

Directions :

1—Select a plot of fallow ground eight feet
square and make moisture determinations with samples
taken in six-inch sections down to a depth of three feet.
Each sample should be made up of soil from several
borings.

2—Add to the plot slowly with a sprinkler, 128
pounds of water.

3—Twenty-four hours after applying the water,
take composite samples near the points at which the
first samples were taken and determine the amount of
water in each. Also take samples a few feet from the
wet area and determine the moisture content.

4—Make moisture determinations in the same way
forty-eight hours after applying the water.

5—Tabulate the data as follows:

Wet Area Area Not Wet

Depth Percent of Water Percent of Water
Samples

Before 24 hrs. After | 48 hrs. After 8
Wetting Wetting Wetting aes | om
|
|

50 Soil Physics Laboratory Guide

Questions :
(2) What effect may a light rain in summer
have upon the water content in some of the
lower strata?

(b) In dry weather is it advisable to simply
wet the surface around a recently planted
tree? If not, why ? |

(c) Why is it advisable to practice shallow
cultivation as soon after a considerable rain-
fall as the implements will work satis-
factorily ? i

EXERCISE 31
DETERMINATION OF Loss ON IGNITION

Object: To determine the loss on ignition due
to the removal of water in combination with certain
materials, all organic acids and ammoniacal com-
pounds, all organic matter and the carbon dioxide in
carbonates.

Directions :
(Method of the Official Agricultural Chemists.)

1—Place five grams of the water-free soil in a
weighed crucible and heat to low redness. |
2—Stir the soil occasionally and continue the heat-
ing until all organic material is burned away, but below
the temperature at which alkaline chlorides volatilize.

3—Moisten the cold mass with a few drops of a
saturated solution of ammonium carbonate, dry and
heat to 150 degrees C. to expel excess of ammonia.
The loss in weight of the sample represents organic
matter, water of combination, salts of ammonia, ete.

Soil Physics Laboratory Guide 51

4—Determine by this method the loss on ignition,
of the following soils: sand, loam, clay, loess and peat.

Tabulate the data as follows:

| Wt. Crucible | Wt. Crucible
Kind of Soil | Qvo.of i

and Soil Be- and Soil bes on Percent
| fore Heating aime Heating) Jguition of Loss
Questions:
(a) Does the soil change color on ignition?
Why?

(b) Why is there a greater loss on ignition with
loam than with sand?

EXERCISE 32

THE EFFECT OF ORGANIC MATTER ON BAKING OF
CLAY SOILS

Object: To show the degree to which organic
matter prevents the baking of clay soils.

Directions :

1—Secure four one-gallon jars provided with drain-
age outlets and fill them to within one inch of the top
as follows:

No. 1—Clay.

No. 2—Clay thoroughly mixed with five per-
cent of peat by weight.

No. 3—Clay thoroughly mixed with ten per-
cent of peat by weight.

52 Soil Physics Laboratory Guide

No. 4—Clay thoroughly mixed with twenty per-
cent of peat by weight.
2—Apply enough water to saturate the soil, using
the same amount of water in each case, and expose the
jars to the direct rays of the sun until the soil is baked.
3—Examine the soils and determine the ease with
which the baked surface can be pulverized with the
fingers.
4—Record your observations in narrative form in
your note book.

Questions :

(a) What causes a clay soil to bake?

(b) In what way does the crust formed by the
baking injure the growing plant?

(c) How does organic matter tend to prevent
the “running together” or baking of soils?

(dq) What can the farmer do to prevent the
baking of the soil?

EXERCISE 33
THE GRANULAR STRUCTURE OF SOILS

Object: To compare the granular structure of
surface, sub-surface and sub-soils.

Directions:

1—Secure samples of the surface, sub-surface and
sub-soil of loam without destroying the granular
structure.

2—Examine a small portion of each sample with
the microscope; make drawing showing the granular
structure and note the shape and size of the granules.

Soil Physics Laboratory Guide 53

38—Place about ten grams of each sample in a
shaker bottle with 75 c. c. of distilled water and shake
for fifteen hours.

4—-Again examine each sample with the micro-
scope and note the difference in the size and structure
of the particles.

Questions:

(a) What factors cause a difference in the
granular structure of a soil at different
depths ?

(6) Why is granulation a desirable property
of soils?

EXERCISE 34

THe Errect of ALTERNATE WETTING AND DRYING
Uron GRANULATION

Object: To study the effect of alternate wetting
and drying upon the granulation of a loam soil rich in
organic matter and a clay soil deficient in organic
matter.

Directions :

1—Mix 400 grams of each of the soils with water
and completely puddle by working on the “mixing
board.”

2—Mold each sample into a large ball; place the
balls on a board or cloth and thoroughly dry by expos-
ing to the rays of the sun or heating in the oven at
about forty degrees C.

3—Again moisten the mass and dry as before.
Repeat the operation two additional times.

4—-Examine the soils after each period of drying
and describe in narrative form what has taken place.

5A Soil Physics Laboratory Guide

EXERCISE 35 7

Tor Errect oF ALTERNATE FREEZING AND THAWING
Upon GRANULATION

Object: To study the effect of alternate freezing
and thawing upon the granulation of a loam soil rich
in organic matter and a clay soil deficient in organic
matter.

Directions :

1—Mix 400 grams of each of the soils with water
and completely puddle by working on the “mixing
board.”

2—Mold each sample into a large ball; place the
balls on a board or cloth and expose in a freezing
temperature until the soil is frozen solid.

Notrre—In freezing weather the balls may be ex-
posed out of doors; at other times, if a cold storage
room is not at hand the balls may be placed in a
covered can and packed in ice and salt after the manner
of an ice cream freezer.

3—Next thaw out the soils by exposing the balls
at the temperature of the laboratory.

4—Repeat this alternate freezing ae thawing
three additional times.

5—Examine the soils after each period of thawing
and describe in narrative form what has taken place.

EXERCISE 36
THE EFFECT oF ORGANIC MATTER ON GRANULATION

Object: To study the effect of organic matter
upon the granulation of a soil rich in that material.

Soil Physics Laboratory Guide 55

Directions :

1—Secure a loam soil which is rich in organic
matter.

2—Wet about 300 grams of the soil and thor-
oughly puddle by working on the “mixing board.”
Then mold the soil into a large ball.

3—Place another 300-gram sample in a percolator
and leach out the soluble salts with a one percent
solution of hydrochloric acid. Wash the soil free of
acid, puddle and mold into a ball.

_ 4—Extract the soluble salts from another 300-
gram sample of soil; wash free from acid and transfer
the soil to a four-liter bottle. Nearly fill the bottle
with a four percent solution of ammonia and shake
occasionally for twenty-four hours in order to extract
a portion of the humus. Decant the ammonia solution
into a vessel and set aside. Wash the soil free from
ammonia and mold into a ball.

5—Freeze and thaw the three balls four times in
the manner described in the preceding exercise.

6—Note the appearance of the balls after each
period of thawing.

7—Evaporate the ammonia solution which was
used in extracting the humus from ball No, 3 nearly
to dryness on the water bath.

8—Mix the residue left after the evaporation, with
the soil from which it was removed. Mold the mass
into a ball and freeze and thaw four times.

9—Compare the condition of this ball after each
thawing with the condition of the other balls.

Questions:

(a) Why is the soil in better condition for
cultivation after a cold winter?

(6) What influence has organic matter on
granulation ?

56 Soil Physics Laboratory Guide

EXERCISE 37

THe CyHromic-Acip MreTHOD or DETERMINING
ORGANIC MATTER

“Se D

Fig. 1
THE DESCRIPTION OF THIS “METHOD IS TAKEN FROM
BULLETIN NO. 24, BUREAU OF SOILS

The combustion is effected in a round-bottomed
flask F, Fig. 1, of about 400 c. ¢. capacity, fitted with
a three-hole rubber stopper. The stopper is fitted with
a dropping funnel, a tube for the introduction of air
previously freed from carbon dioxide by bubbling
through a solution of potassium hydrate in the flask G,
and a tube leading through a condenser to a train of
absorption bulbs. This train contains first, a Peligot:
tube A, containing a saturated and slightly acidified
solution of silver sulphate to absorb both hydrochloric
acid and sulphur trioxide or dioxide should they be
generated; then a guard tube B, containing concen-
trated sulphuric acid, followed by a potash bulb C,
and an acid bulb D, to be weighed with the potash
bulb. An acid guard bulb E, completes the train.
The whole apparatus is attached to an aspirator so that

Soil Physics Laboratory Guide 57

air free from carbon dioxide can be drawn through the
combustion flask and train. The procedure is as
follows:

“A sample of the soil, usually about ten grams,
is carefully weighed and brought into the combustion
flask. If the sample be rich in organic matter, it has
been found advisable to introduce also some sand,
previously ignited before the blast, and in an amount
dependent roughly upon the apparent quantity of
organic matter in the soil. From five to ten grams of
pulverized potassium bichromate are then added and
the whole mixed thoroughly by shaking, care being
taken to prevent any of the mixture adhering to the
sides of the flask above the level of the mixture. The
flask is closed securely by the stopper, and a gentle
stream of air drawn through the whole apparatus by
means of the aspirator. When this stream of air has
been passing for about ten minutes, concentrated sul-
phurie acid (sp. gr. about 1.83) is slowly and cau-
tiously run in by means of the dropping funnel until
the tip of the glass tube for the introduction of air is
covered. When this point has been reached, and if no
very vigorous action is taking place, the combustion
flask is slowly heated until the sulphuric acid com-
mences to give off fumes. It is held at this temper-
ature for from five to ten minutes, and then allowed
to cool slowly, unless there is reason to believe com-
bustion has not been complete, in which case the tem-
perature is again raised. Care must be exercised to see
that a steady current of air be kept passing through
the apparatus, and that the mixture in the flask be not
forced back toward the wash bottles. If necessary,
quite a rapid stream can be drawn through the absorp-
tion bulbs without much risk of losing the determina-
tion. It is advisable to have the bulb of the dropping

58 Soil Physics Laboratory Guide

funnel empty before commencing the heating, so that
the tube can be quickly opened. In over 400 exper-
iments with this method, the flask broke but once, and
then the dropping funnel could not be opened because
it eontained a quantity of sulphuric acid. A sudden
large increase of pressure was generated in the flask,
owing to faulty manipulation. The dangerous char-
acter of such an accident is sufficiently obvious, but
with ordinary care, liability of its occurrence is
extremely small.”

MODIFICATIONS FOR SOILS CONTAINING CHLORIDES AND
CARBONATES

In many soils from arid, semi-arid or marshy
areas there is a considerable content of chlorides. By
following the procedure just described with these soils,
chlorine gas may be generated, which would be collected
in the potash bulbs, forming a mixture of the chloride
and hypochlorite in proportions difficult to estimate
accurately, and vitiating any attempt to determine the
amounts of carbon dioxide absorbed.. We have made
a number of attempts to get around this difficulty and
have found that it can be met quite simply. If the
bichromate of potash be not mixed with the sample
before running in the concentrated sulphuric acid, but
be dissolved in the acid itself and the solution be
slowly and cautiously run in upon the soil, with no
attempt to heat the mixture until the reaction in the
flask has proceeded for some time, no hydrochloric
acid, chlorine nor chromyl chloride gas is generated,
or in but very small amounts. The procedure thus
modified has been used a large number of times with
artificial mixtures and natural soils, and has proven
satisfactory, although no explanation is obvious why

Soil Physics Laboratory Guide 59

hydrochloric acid should not be formed and oxidized
under these conditions. We can only say that, although
we discovered the fact empirically, we have thoroughly
tested it with the most gratifying results for the
method.

When the amount of chlorides is relatively large,
it has sometimes been found desirable to treat the
sample with a small volume of dilute sulphuric agjid,
adding more acid in small quantities from time to
time, if necessary, to digest on the steam bath until
the major part of the hydrochloric acid has been
removed, and to evaporate as much of the water remain-
ing as can be done without permitting a noticeable
action of the solution upon the organic matter. The
combustion is then carried out as above described.

With soils which contain carbonates of the alkalies
or alkaline earths, it would probably be found satis-
factory first to treat with sulphurous acid to decompose
the carbonates and drive out the carbon dioxide with-
out oxidizing the organic matter, and then try to get
rid of the water and sulphurous acid by evaporating
to dryness before proceeding with combustion.

This method presents, however, a number of dif-
ficult manipulations and requires a great deal of time.
It has been found, in the experience of this laboratory,
much more convenient to make a separate determina-
tion of the carbon dioxide liberated from the carbon-
ates, by treating a separate sample of the soil with
dilute sulphuric acid (1:6 by volume), and subtracting
the amount thus found from the total obtained in the
combustion. While this method is not entirely free
from objections for very accurate work, it does unques-
tionably lead to values with all the accuracy necessary
for most purposes to which the determination of the
organic matter in a soil is applicable.

60 Soil Physics Laboratory Guide

In determining the percentage of organic matter
in the soil from the percentage of carbon dioxide found,
it is of course necessary to use a conversion factor
which, multiplied by the weight of CO, gives the
weight of organic matter. The factor generally used
for this purpose is 0.471, based upon Wollny’s investi-
gation of the percentage of carbon in the humus of
the soil.

Note—Another method for the determination of
organic carbon in soils is now used by the Illinois
Experiment Station. This method, which has been
found to be quite satisfactory, is described in detail in
the Journal of the American Chemical Society, Vol.
26, page 294, and Vol. 26, page 1640.

EXERCISE 38

STANDARDIZATION OF THE EYE-PIECE MICROMETER*

Object : To determine the number of spaces on
an eye-piece micrometer which the soil particles must
cover to belong to a given grade.

Directions : In order to separate the particles cf
a given sainple of soil into different grades according
to size, it becomes necessary to measure them with
sufficient accuracy to determine the grade within which
limits they fall. As the greater mass of the soil par-
ticles are microscopic objects or bodies of such small
dimensions that we cannot measure them accurately
without first enlarging them sufficiently to permit of
exact measurements, the compound microscope is used
for this purpose.

*From laboratory notes used at the Illinois College of Agriculture.

Soil Physics Laboratory Guide 61

To be able to measure accurately bodies of such
small proportions, it is essential that we possess a
standard or measure whose value is known with each
different degree of magnification resulting from differ-
ent optical combinations. The stage micrometer 1s
well adapted to this purpose and affords a fixed standard
of comparison where it can be used. There are certain
conditions, however,. which make its use unadvisable
for general miscroscopic work. One of these is its cost
and its liability to be broken when it is used for the
purpose of direct comparison with the object to be
measured. Another is the mechanical difficulty con-
nected with the ruling of a stage micrometer which
shall be accurate and sufficiently close to permit satis-
factory measurements when used under a high power.
To avoid these objections as well as to facilitate rapid
measurements with the microscope and to obviate the
annoyance of using a stage micrometer in connection
with the object to be measured, we employ for our
purpose the eye-piece micrometer, which possesses the
advantage of being more accurately ruled where high
powers are desired.

When using the eye-piece micrometer it is placed
within the ocular of the microscope and above the
lenses so that it is not enlarged as is the object to
which it is to be compared. The value of the rulings
upon the eye-piece micrometer is .1 mm., but as the
value of the object changes with each combination of
the microscope, it becomes necessary for us to know
the magnifying power of each combination of lenses in
order to determine the size of our object, or to first
standardize the eye-piece micrometer for each com-
bination which we are to use by comparing it with a
standard of known value which is magnified to the
desired degree. This is done by comparing the eye-piece

62 Soil Physics Laboratory Guide

with the stage micrometer and computing the value of
one space of the eye-piece micrometer for each combi-
nation of the microscope. When this is known the num-
ber of the spaces which the soil particles must cover to.
belong to a given grade is determined by dividing the
value of one space into the size of the particle. This
operation is performed for each of the grades and the
results are arranged in a tabular form together with
the actual size of the particles and the combinations
of the microscope used in measuring them for conven-
lence in saving computation during analysis.

) Each student will make the standardizations and
compute the value of the eye-piece micrometer with the
different combinations of the microscope needed to
measure the particles and tabulate the results as follows:

Div. Name | Size of Particles i nchepe es Obiestivems
1 | Fine gravel 2tolmm. |
2 Coarse sand lto.5 mm.
3 Medium sand .6 to .25 mm.
4 Fine sand .25 to .l mm.
5 Very fine sand -lto .05 mm. |
6 Silt -05 to .005 mm.
7 Clay | -005 to .0001 mm.
|
EXERCISE 39
\
MECHANICAL ANALYSIS OF SOILS
Object : To determine the percentage of gravel,

fine gravel, coarse, medium, fine and very fine sand,
silt and clay in a sample of “fine earth.”

Directions :

1—Thoroughly mix, upon a heavy paper or oil-
cloth, the sample of air-dried soil to be analyzed; take
from the well-mixed mass about 100 grams of soil and

Soil Physics Laboratory Guide 63

weigh accurately ; roll the sample with a wooden rolling
pin and sift it with a 2 mm. sieve. Weigh all small
stones and pebbles which do not pass the sieve and
determine the percentage of this material.

2—Place about ten grams of the sifted soil which
is designated as “fine earth” in a crucible and dry to a
- constant weight in an oven maintained at 110 degrees C.

3—Place five grams of the water-free soil in a
shaker bottle and add about 75 c. ec. of distilled water
and ten drops of.ammonia. Exercise care in weighing
the sample of soil and in transferring it to the bottle.

4—Place the bottle in the shaking apparatus and
agitate it until a microscopic examination of the
contents shows that the soil particles are completely
separated and no compound particles exist. “When
this condition is reached the individual particles will
appear clear and semi-transparent in the field of the
misroscope, while any remaining compound particles
will be darker and variously colored from reflected
light. This may require from twelve to twenty-four
hours, or even longer, depending very much upon the
nature of the soil. As the determination is quantita-.
tive but a small amount of the liquid is taken from the
bottle with a capillary pipette, and mounted on a slide
for examination. When the examination is complete,
the slide and cover glass are carefully rinsed with dis-
tilled water back into the shaker bottle to recover the
small portion of soil taken. Great care is necessary
throughout the analysis to prevent the loss of any part
of the sample and for the purpose of comparison and
greater accuracy in results, duplicate samples are used
of each soil analyzed.” 3

5—When no compound particles are found in the
samples, transfer the contents of the shaker bottles into
centrifuge tubes.

64 Soil Physics Laboratory Guide

6—Place the tubes in the centrifuge, care being
taken to have the weight evenly distributed so that the
apparatus will run steadily. Rotate the tubes in the
centrifuge for two or three minutes at a _ speed
sufficiently high to throw down all particles except those
which belong to the grade listed as clay. To determine
the speed and time required for this operation, examine
the suspended material with the microscope, taking
the sample and mounting it as described above.

?—When it is found that no particles larger than
005 mm. are left in suspension, carefully decant the
liquid in each tube into a weighed 400 ec. c. beaker,
which is numbered to correspond with the number of
the tube. :

8—Nearly fill the tubes with distilled water which
is delivered with sufficient pressure to thoroughly stir
up the contents of the tubes.

9—Continue to rotate the centrifuge and decant
until the contents of each tube are free from particles
which belong to the grade designated as clay. Care
must be taken to determine quite accurately just the
time required for the particles larger than .005 mm.
to settle, for if the centrifuge is rotated too long, a
portion of the clay also goes down and the time
required to complete the separation is thus greatly
lengthened.

10—Evaporate the contents of the beakers to dry-
ness on the water bath; then dry the residual matter
in the beakers to a constant weight in the oven at 110
degrees C. and determine the percent of clay in the
sample of soil.

11—After the clay particles have been separated
as described above, place the tubes in a rack and thor-
oughly stir the contents by filling the tubes with dis-
tilled water which is delivered under pressure.

Soil Physics Laboratory Guide 65

12—Examine the suspended material with the
microscope and in this way determine the length of
time required for all the particles to settle which are
larger than .05 mm. Decant into large beakers which
are numbered to correspond to the number of the tubes.
Repeat the operation of stirring the contents of the
- tubes and decanting until all of the silt particles are
removed.

13—Set aside the beakers containing the silt for
twelve hours or more, or until all of the silt has settled.
Then decant nearly all of the water from each beaker ;
carefully transfer the silt to a weighed and numbered
porcelain or nickel dish and evaporate to dryness on
the water bath. Dry the silt in the oven at 110 degrees
C. to a constant weight and determine the percent of
silt in the sample of soil.

14—Wash the sand which is left in the tubes after
the clay and silt are removed, into weighed and num-
bered crucibles; evaporate to dryness on the water bath
and dry to a constant weight in the oven at 110 degrees
C. Weigh and record as total sand.

15—Separate the sand into the various grades by
the use of a series of sieves fitted with bolting cloth
and determine the percent of each grade in the sample
of soil.

66 Soil Physics Laboratory Guide

16—Make a mechanical analysis of the soils
furnished by the instructor and tabulate the data
as follows:

MECHANICAL ANALYSIS
Sample No. 22m Date

Gravel > 2 mm. Percent

Analysis of 5 grams of soil << 2mm.

No. Dish Sands 1-5 No. Dish Silt 6__. No. Dish Clay 7.___
Wt. Dish & Soil paths DEO aaa Le eee
Weight of Dish Sabra VAP et paramere as Ra 4

Weight of Soil soot Ee tt SR,

Diameter ‘ : Weight
mm. grams Percent
1 et ERS
2 5 RA
3 = Seb
4 25 - 1 |
5 1 - .05 |
6 05 — .005
e < .005
Total ay

Soil Physics Laboratory Guide 67

Plate 12
MECHANICAL SHAKER USED IN PREPARING SOILS FOR
MECHANICAL ANALYSIS

The shaker consists of a platform which carries the
trays resting upon four three-quarter-inch iron supports
which are thirty inches high.

The trays are divided into individual compartments,
each tray holding eight bottles which correspond to the
number of samples usually analyzed at a time. The
trays are made of half-inch material. They are sixteen

68 Soil Physics Laboratory Guide

inches long, nine and one-quarter inches wide and three
inches deep outside measurement.

Each tray has a pin placed at either end, which fits
into holes in the tray above it, so that four or more trays
may be placed upon the shaker at one time.

The shaker is driven by a 110-volt, one-sixteenth-
horse power motor which is belted to a fiber worm reduc-
ing gear provided with a crank to which the shaker is
connected as shown in the illustration. The motor is
provided with a regulating rheostat to adjust the speed
when the shaker is not fully loaded.

The 110-volt motor with shaker attachment costs
about twenty-five dollars.

The bottles for use in the shaker may be purchased
from Whitall Tatum Company, Philadelphia. They are
known as eight-ounce sterilizing bottles, flint glass,
graduated. They require E & A rubber stoppers No. 1.
They cost about four dollars per gross.

Soil Physics Laboratory Guide 69

Plate 13
CENTRIFUGAL MACHINE USED IN MECHANICAL ANALYSIS OF
SOILS AND TANK FOR THE SUPPLY OF DISTILLED
WATER UNDER PRESSURE

The following description of the centrifugal appa-
ratus which is shown in the illustration is taken from
Bulletin No. 24, Bureau of Soils:

“The centrifugal apparatus consists of a 110-volt,
sixteen-inch fan motor mounted with its shaft in a ver-
tical position, to which is attached a spider carrying eight
trunnioned frames. The distance from the center of the
motor shaft to the center of the trunnion screws is
10 em., and the depth of the trunnioned racks is
15 em. The centrifugal tubes consist of large, heavy
glass test tubes, 18x3 cm., which are supported in the
trunnioned racks. The aperture in the upper ring of
the support is made large enough to admit the test
tube readily, while the opening in the lower ring is
smaller than the tube and is faced with a felt cushion
on which the tube rests. It is important that the tubes
should be thoroughly annealed; otherwise breakage is
apt to occur under the strain to which they are subjected

70 Soil Physics Laboratory Guide

during rotation. To protect the operator from such
accidents a guard surrounds the movable portion of the
machine.

“The motor is provided with a rheostat in its base,
giving four different speeds, which enables one to start
the motor slowly and bring it gradually up to full speed.
The machine, when loaded and running at full speed,
requires about one minute to stop after the circuit is
opened. To avoid this delay, the motor is provided with
a reversing switch, by means of which the direction of
the current through the armature may be reversed and
the motor brought quickly to rest. Before stopping the
machine in this way, the rheostat should be set at the
first speed, then slowly moved to the second or third in
order that the motor may not be subjected to too great
mechanical and electrical strain in the reversing process.”

A jet of distilled water under considerable pressure
is needed to wash the samples from the shaker bottles
and in bringing the soil into suspension after it has been
packed into the bottom of the tubes by centrifugal action.
For this purpose, a thirty-gallon tank is located near the
centrifugal machine. The tank is filled about half full
of distilled water and air is admitted from the pressure
cock. The water is drawn from the tank through a pipe
and rubber tubing as shown. If the laboratory is not
provided with compressed air a large bicycle pump may
be used. The tank and fixtures are not expensive and
have been found very satisfactory.

Soil Physics Laboratory Guide 71

Plate 14

NEST OF SIEVES USED TO SEPARATE SAND INTO THE
VARIOUS GRADES

The large brass sieve shown in the illustration is
six inches in diameter with 2 mm. meshes.

The nest of sieves is made of brass and is four
inches in diameter. The two upper sieves have circular
perforations 1 mm. and .5 mm. respectively. The two
lower sieves are made of silk bolting cloth stretched over
brass frames and held in position by slip rings.

The sieves shown in the illustration are fitted with
suk bolting cloth.

The bolting cloth may be purchased from B. F. Starr
& Co., Baltimore, Md.

72 Soil Physics Laboratory Guide
EXERCISE 40

MECHANICAL ANALYSIS OF SOILS BY THE BEAKER
METHOD

Directions :

1—Thoroughly mix upon a heavy paper or oil-
cloth, the sample of air-dried soil to be analyzed; take
from the well-mixed mass about 100 grams of soil and
weigh accurately.

Roll the 100-gram sample with a wooden rolling-—
pin and sift it with a 2 mm. sieve. Weigh all small
stones and pebbles which do not pass through the sieve
and determine the percentage of this material.

2—Place about thirty grams of the sifted soil
which is designated as “fine earth” in a porcelain dish
and dry to a constant weight at 110 degrees C.

3—Place twenty grams of the water-free soil in a
shaker bottle and add about 75 c. c. of distilled water
and fifteen drops of ammonia. Exercise care in —
weighing the sample of soil and in transferring it to
the bottle.

4—Place the bottle in the shaking apparatus and
agitate it until a microscopic examination of the con-
tents shows that the soil particles are completely
separated. (See the preceding exercise for the method
of making this examination.)

5—When no compound particles are found in the
samples, transfer the contents of the shaker bottle into
a 400 ec. ec. beaker; add about 200 ec. ec. of distilled water
and stir thoroughly with a glass rod.

6—Allow the contents of the beaker to settle until
all particles larger than .05 mm. have subsided. ‘This
is determined by examining a drop of the turbid liquid

Soil Physics Laboratory Guide 73

which is drawn from near the bottom of the beaker
with a capillary pipette, under a microscope fitted
with an eye-piece micrometer.

%7—When all of the particles larger than .05 mm.
have subsided, decant the turbid liquid containing the
silt and clay into a larger beaker. Repeat this oper-
ation until all particles smaller than .05 mm. have
been removed. |

8—Transfer the sediment to a weighed evapor-
ating dish, dry to a constant weight in the oven at 110
degrees C. and weigh as total sand.

9—Further separate the sand into the various
grades by: passing it through a series of brass sieves
four inches in diameter which fit into each other. The
first sieve has circular openings 1 mm. in diameter
and the second .5 mm. ‘The particles passing through
the lower sieves are sifted through screens of No. 5 and
No. 13 bolting cloth. ©

10—Allow the turbid liquid in the beaker contain-
ing the silt and clay to settle until the microscope
shows that all particles larger than .005 mm. have
settled.

11—Decant the liquid containing the clay into a
third beaker of about 2000 c. ¢. capacity. Stir the
sediment in the bottom of the beaker with more water,
allow to settle and decant. Repeat this operation until
all particles smaller than .005 mm. are removed.

12—Wash the silt into a small weighed porcelain
dish. Evaporate to dryness on the water bath. Dry
to a constant weight in the oven at 110 degrees C.
and weigh.

13—Accurately measure the clay water in the
third beaker and, after thoroughly stirring, take an

74 Soil Physics Laboratory Guide

aliquot portion, evaporate to dryness on the water bath,
dry to a constant weight in the oven and weigh.

14—Make a mechanical analysis of the soils fur-
nished by the instructor and tabulate the data as in
the preceding exercise.

Plate 15

STUDENTS’ LABORATORY DESK

The illustration shows one end of a desk used in the
Soil Physics Laboratory at the Iowa State College. The
desks are thirty-three inches high, sixty inches long from
the end to the center of the sink, and have a total width
of fifty-six inches. Students work on both sides of
these desks.

The space from the end of the desk to the center of
the sink is provided with two sets of drawers and lockers.
This arrangement enables the class to work in two sec-
tions; the student in each section has a drawer and locker
in which to store and lock up his apparatus and has five
feet of desk room during his laboratory period.

Soil Physics Laboratory Guide 75

The desks are supplied with sinks, gas cocks and
water cocks as shown. All of the plumbing is exposed
and thus is easily kept in repair. The lower shelf is five
inches wide and is five inches above the desk. The upper
shelf is six inches wide and is fifteen and one-half inches
above the desk.

APPENDIX
LABORATORY NOTES

Each student should keep a careful record of his
laboratory work in a well-bound notebook. This book
should always be at hand during the progress of an
experiment and all data should be recorded promptly.
It is never safe to record weights or data of any kind on
loose sheets of paper. They are too often lost.

The outlines for the tabulation of data which are
printed in the guide are for the direction of the student.
No figures should be entered in the guide but the data
should be recorded in the notebook as indicated in the
outlines.

The student should study each exercise carefully, |
before beginning work, in order to obtain a clear under-
standing of the nature of the exercise, the directions
to be followed and the data to be secured. All of the
experiments should be done in duplicate.

The laboratory directions should not be copied into
the notebook but all of the data should be recorded
in tabular form and a brief, concise statement should
be made covering the following points:

1—The object of the experiment.

2—The materials used.

3—The apparatus employed.

4—The manner of conducting the experiment.

5—The facts noted during the progress of the
experiment.

6—The conclusions which are drawn, and
finally suggestions regarding any changes
in the experiment.

Soil Physics Laboratory Guide 77

With nearly every experiment, questions are asked ;
the answers to these questions should be given in full
in the notebook. The student should refer to author-
ities on Soil Physics as an aid in answering some of the
questions and his statements should embody a com-
plete, comprehensive answer.

Each experiment should be written up at the time
it is performed. Confusion and loss of time inevitably
follow an effort to write up several experiments which
have been worked out but only the weights or measure-
ments recorded.

The notebook should be kept in a neat and orderly
way and should always be ready for examination by the
instructor. The student should never fail to correct
the errors which are marked by the instructor, and it
is far better to perform a limited number of experi-
ments correctly than to pass over a large number in a
slip-shod manner.

PRECAUTIONS TO Br USED IN WEIGHING

The following directions for weighing are taken
from the laboratory notes used in Johns Hopkins
University : |

1—Sit directly in front of the center of the
balance so as to avoid parallax while observing the
movements of the pointer.

2—See that the balance is level.

3—Release and arrest the beam with a slow and
steady movement of the hand. Jerky movements are
sure to injure the knife edges. The beam should be
arrested only when it is in a horizontal position.

a nes
Sans 4) Ive

78 Soil Physics Laboratory Guide

4—Avoid giving to the pans any rotary motion
in a horizontal direction and all other movements
which would cause a knife edge to scrape on its
bearing.

5—Release the pans before releasing the beam.

6—Arrest the beam and pans before placing any-
thing upon or removing anything from the latter.

_ %—Place the object to be weighed and the larger

weights in the middle of the pans.

8—See that the rider is not so near the beam as
to be hit by it while swinging.

9—AlIl weighings should be made with the balance
case closed.

10—If the beam does not begin to swing as soon
as it is released, set it in.motion by wafting the air
over one of the pans with the hand or by raising and
releasing it again.

11—Hot objects cannot be correctly weighed,
owing to the upward draughts which they create about
the pans on which they rest. They may also, through
their heating effects upon the beam, produce a change
in the relative lengths of the arms.

12—Hyeroscopic and volatile substances, also those
which absorb carbon dioxide from the air, must be
weighed in closed vessels. If the vessels have been
tightly closed while hot, there may be diminished
pressure within, in which case they must be opened
for a moment before weighing.

13—All substances which are exposed to the air
condense moisture on their surface to an extent which
sensibly affects their weight. The amount of moisture
thus condensed varies with the humidity of the atmos-
phere; hence a substance which is transferred from a

Soil Physics Laboratory Guide 79

desiccator to the balance pan will gain weight for a
time, while one which is brought from a damper
atmosphere than that within the balance case will
lose weight. By keeping drying reagents in the case,
it is endeavored to maintain a fairly uniform condition
of humidity, and thus to reduce the errors from this
source to a minimum. Powdered substances which
have been dried in a hot bath, or in a desiccator, should
be weighed in closed vessels; since, owing to the great
surface which they present to the air, they condense
large amounts of moisture. In all cases, it is neces-
sary to be sure that the object which is being weighed
has ceased to gain or lose weight before taking the
final reading.

14—An object which, like glass, is likely to become
electrified by friction, should not be wiped or brushed
immediately before weighing. Glass and quartz weights
often become strongly electrified when lifted out of
their places in the box in which they are kept.

15—Long tubes and other objects .not easily
centered on the pans should be suspended from the
hooks above the pans.

WEIGHTS AND MEASURES, WITH EQUIVALENTS

METRIC
Meter (Unit of Length) Millimeter (mm. = 0.001 meter
Centimeter (cm. = 0.01 meter
Kilometer — 1000 meters
Micron = 0.001 millimeter
Gram (Unit of Weight) Milligram (mg.) — 0.001 gram
Kilogram (kilo) — 1000 grams
Liter (Unit of Capacity) Cubic Centimeter = 0.001 liter

0.03937 (or 1-25 approx.) inch
1000 microns

0.3937 (or 2-5 approx.) inch
0.0328 foot

39.37 inches

1 millimeter = {
1 meter = Pe 3.28 feet

1 centimeter =

1-25000 inch

1 micron 0.001 millimeter

80

Soil Physics Laboratory Guide

_ § 0.035 ounce .
1 gram = ane pound \ avoir.

x

35.27 ounces on
{33 pounds i se Nhe

{i (or 1 approx.) quart

1 kilogram =

61.02 cu. inches
1000 cu. centimeters

1 liter =

0.00155

0.1550 Sq. inches
1550

10.76 sq. ft.

OCEm } eu. inch

0.001 liter

1 Bie cu. feet
61025.4 cu. inches

sq. millimeter
sq. centimeter
sq. meter
sq. meter

Hue tal

. millimeter
cu. centimeter
cu. centimeter

cu. meter

Hell

a re ere rer
°
[=|

I

1 inch = 25.399 millimeters

1 sq. inch = 6.451 sq. centimeters
1 cu. inch = 16.387 cu. centimeters
1 foot = 30.48 centimeters

1 sq. foot = 0.093 sq. meter

1 cu. foot = 0.028 cu. meter

AVOIRDUPOIS WEIGHT

1 pound = 16 ounces ©
1 ounce = 28.35 (or approx. 30) }

1 pound = 453.59 (approx. 500) | ects as

FORMULAE, ETC.
A cubic foot of water weighs 62.42 pounds

TEMPERATURE: Centigrade degree= 0.555 (Fahr.—32°);
95° F. = 0.555 (95°-32) = 34-97° C.
Fahrenheit degree — 1.8 x Cent. + 32°

$0°.C,.22 1.8 x 801492 == 17

Area of circle = mr?, where r = radius. «= 3.1416

Circumference of circle = 27r

{ Circumference
Radius=
27 .
Area of cylinder = 2mrh; wherer = radius of cross

section, and h= hight or length
Volume of cylinder = zr*h

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