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Full text of "The physical properties of soils; a laboratory guide"

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THE PHYSICAL 
PROPERTIES OF SOE^ 



A LABORATORY GUIDE 



By 
ARTHUR G. McCALL 

Professor of Agronomy in the College of Agriculture of the 

Ohio State University 



ILLUSTRA TED 









J ' 1 J 1 ) ) 



NEW YORK 

ORANGE JUDD COMPANY 

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

1909 






Copyright, 1909 



BY 



ORANGE JUDD COMPANY 

All Rights Reserved 

[Entered at Stationers' Hall, London, England] 



GIFT OF 







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PREFACE 

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

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

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

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

A. G. McCall. 

Soil Physics Laboratory 

Ohio State University 

Columbus, Ohio. 

August, 1908, ivil999e6 



CONTENTS 



PAGE 



General Information i 

Soils Laboratory Desk Outfit 3 

Stock Soils 5 

-^ Determination of Hygroscopic Moisture ... 10 

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

>: Determination of the Specific Gravity of Soils . 18 

-k Determination of Volume Weight and Pore Space 22 

Determination of Pore Space in Field Soils . . 26 

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

-I- Water-holding Capacity of Soils 38 

The Distribution of Capillary Water in Soil 

Columns 40 

f Flow of Air Through Soils 42 

Flow of Air Through Field Soils 44 

-j" Capillary Rise of Moisture 46" 

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

Continuous Rise of Capillary Moisture . . . 50 - 

Lateral Movement of Capillary Moisture . . . 54  

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

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

The Absorptive Power of Soils 64 

.^The Flocculating Effect of Lime 6^ 



Vll 



• » • 



Viii CONTENTS 

PAGE 

Power of Soils to Retain Fertilizers in Solution . 70 

The Specific Heat of Soils 74 

^Mechanical Analysis of Soils 80 

Chromic Acid Method of Determining Organic 

Matter 92 

Directions for Taking Soil Samples .... 96 

Standardization of the Eye-piece Alicrometer . 99 

Table of Data 100 

Index loi 



» ' > 111 ^ ^ 1 1 ' 1 > 1 , ' , 

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

'I'lii 11 >) 111 ., 



The Physical Properties of Soils 



GENERAL INFORMATION AND 
DIRECTIONS 

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

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

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

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

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

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



2 THE PHYSICAL PROPERTIES OF SOILS 

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

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

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

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

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



THE PHYSICAL PROPERTIES OF SOILS 

SOILS LABORATORY DESK OUTFIT 

THE FOLLOWING ARTICLES ARE LOANED TO THE STUDENT 

O 6 Aluminum Dishes, 3 in. 





I 


Bunsen Burner 






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I 


Ring Stand with 3 Rings 










I 


Tongs, Crucible 






V 




I 

2 


Tripod 






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Porcelain Cups 










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Spatula 






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Test Tube Rack 










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Sets Beakers, i to 5 










6 


Dishes, Porcelain No. 






V 


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Desiccator, 8 in. 




■J fir 


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X 


2 


Cylinders, Graduated 250 cc. _ 











6 


Test Tubes 






V 




4 


Percolators, Oldberg's Cylin 


idrical, 500 


cc. 





THE FOLLOWING ARTICLES ARE CHARGED TO EACH STUDENT AND 

CAN NOT BE RETURNED 

I Clay Triangle $ .05 



I Wire Gauze 


.05 


I Glass Rod 


.05 


3 Ft. Rubber Tubing 


.15 


I Sponge 


.10 


I Towel 


.10 


I Test Tube Brush 


.05 


I Box Safety Matches 


.01 



THE PHYSICAL PROPERTIES OF SOILS 




THE PHYSICAL PROPERTIES OF SOILS 



STOCK SOILS 

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

1. Sand — clean lake or river sand. 

2. Sandy Loam — a loam with sufficient sand to 

make open mellow soil. 

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

taining more silt and less sand. 

4. Muck — well-drained swamp soil containing a 

large quantity of organic matter. 

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

amount of clay. 

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

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



THE PHYSICAL PROPERTIES OF SOILS 



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THE PHYSICAL PROPERTIES OF SOILS 



FIRST EXERCISE 

I. DETERMINATION OF HYGROSCOPIC 
MOISTURE IN STOCK SOILS 

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

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






DRYING OVEN HEATED BY GAS 

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

battery circuit 

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



THE PHYSICAL PROPERTIES OF SOILS II 

STUDENT'S NOTES AND REPORT 



12 



THE PHYSICAL TROPERTIES OF SOILS 




DOUBLE- WALLED DRYING OVEN HEATED BY TWO ELECTRIC-LIGHT 

BULBS 

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

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



II. DETERMINATION OF THE MOISTURE 

IN FIELD SOILS 

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

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



THE PHYSICAL PROPERTIES OF SOILS 1 3 

STUDENT'S NOTES AND REPORT 



14 



THE PHYSICAL PROPERTIES OF SOILS 



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



"Vi UCvW-^ C\RCUIT 




TO "BKTTt.H^ OR 
^WUNT CIRCUIT 



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

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



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



THE PHYSICAL PROPERTIES OF SOILS I5 

STUDENT'S NOTES AND REPORT 



l6 THE PHYSICAL PROPERTIES OF SOILS 

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

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

(2) As pounds per cubic foot. 

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

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

References : 

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



THE PHYSICAL PROPERTIES OF SOILS I7 

STUDENT'S NOTES AND REPORT 



l8 THE PHYSICAL PROPERTIES OF SOILS 

SECOND EXERCISE 

DETERMINATION OF THE SPECIFIC 
GRAVITY OF SOILS 

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

METHOD OF DETERMINATION 

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

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

CALCITLATION 

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



THE PHYSICAL PROPERTIES OF SOILS IQ 

STUDENT'S NOTES AND REPORT 



20 



THE PHYSICAL PROPERTIES OF SOILS 



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

Reference : 

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

95-98. 




SOIL SAMPLE BOXES WITH 
CARRYING CASE 



THE PHYSICAL PROPERTIES OF SOILS 21 

STUDENT'S NOTES AND REPORT 



22 



THE PHYSICAL PROPERTIES OF SOILS 



THIRD EXERCISE 

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

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




APPARATUS FOR THE DETERMINATION OF VOLUME WEIGHT AND 

PORE SPACE 



METHOD OF DETERMINATION 

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



THE PHYSICAL PROPERTIES OF SOILS 23 

STUDENT'S NOTES AND REPORT 



24 



THE PHYSICAL PROPERTIES OF SOILS 




THE PHYSICAL PROPERTIES OF SOILS 2^ 

STUDENT'S NOTES AND REPORT 



26 THE PHYSICAL PROPERTIES OF SOILS 

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

CALCULATION 

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

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

References : 

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



11. DETERMINATION OF PORE SPACE IN 

FIELD SOILS 

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

METHOD OF DETERMINATION 

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



THE PHYSICAL PROPERTIES OF SOILS 2^ 

STUDENT'S NOTES AND REPORT 



28 



THE PHYSICAL PROPERTIES OF SOILS 



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KING SOIL - SAM- 
PLINC. TUBE WITH 
HAMMER. 



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

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

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

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

CALCULATION 

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

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

References : 

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



THE PHYSICAL PROPERTIES OF SOILS 29 

STUDENT'S NOTES AND REPORT 



30 



THE PHYSICAL PROPERTIES OF SOILS 




IKON CO Mr ACTOR 



THE PHYSICAL PROPERTIES OF SOILS 3I 

STUDENT'S NOTES AND REPORT 



3^ 



TPIE PHYSICAL PROPERTIES OF SOILS 



FOURTH EXERCISE 



f-BRAis Exre/vs/o/v 



RUBBFR QAiktT 



■CLASS PCRCOLATCR 



PERCOLATION OF WATER THROUGH 

SOILS 

The rate of percolation of water through soils is 

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

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

Percolator No. i — 

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

\jMopprR qAuzc Percolator No. 

11 Sandy loam. 

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



PERCOLATOR TUBE 
Sectional View 



THE PHYSICAL PROPERTIES OF SOILS 33 

STUDENT'S NOTES AND REPORT 



34 



THE PHYSICAL PROPERTIES OF SOILS 



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

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




SPRING-BOARD COMPACTOR 

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

Percolator No. i — Loam or silt. 

Percolator No. 2 — Mixture, one part loam 

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

one part sand. 

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



THE THYSICAL PROPERTIES OF SOILS 35 

STUDENT'S NOTES AND REPORT 



36 



THE PHYSICAL PROPERTIES OF SOILS 



References : 

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




APPARATUS USED TO COMPARE THE RATE OF PERCOLATION IN 

DIFFERENT SOILS 



THE rilYSICAL PROrERTIES UE SOILS 2^^ 

STUDENT'S NOTES AND REPORT 



3S 



THE PHYSICAL PROPERTIES OF SOILS 



FIFTH EXERCISE 

I. WATER-HOLDING CAPACITY OF 

SOILS 

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

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

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




APPARATUS USED TU DETERMINE THE WATER-HOLDING CAPACITY 

OF SOILS 



THE PHYSICAL PROPERTIES OF SOILS 39 

STUDENT'S NOTES AND REPORT 



40 



THE PHYSICAL PROPERTIES OF SOILS 



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

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

Reference: 

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

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

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

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

References : 

Hall, "The Soil," p. 64. 



m 



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I 



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i 



CM 




.-iK 



BRASS CYLINDER 

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

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

mcnt of capillary mois- 
ture. 



p. 114. 



THE PHYSICAL PROPERTIES OF SOILS 4I 

STUDENT'S NOTES AND REPORT 



42 



THE PHYSICAL PROPERTIES OP SOILS 



SIXTH EXERCISE 

I. FLOW OF AIR THROUGH LABORATORY 

STOCK SOILS 

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

Tube No. I — Sand. 

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

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

part organic matter. 




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

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



THE PHYSICAL PROrERTIES OF SOILS 43 

STUDENT'S NOTES AND REPORT 



44 THE PHYSICAL PROPERTIES OF SOILS 

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

II. FLOW OF AIR THROUGH FIELD 
SOILS IN PLACE 

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

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

References : 

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



THE PHYSICAL PROPERTIES OF SOILS 45 

STUDENT'S NOTES AND REPORT 



46 THE PHYSICAL PROPERTIES OF SOILS 

SEVENTH EXERCISE 

I. CAPILLARY RISE OF MOISTURE IN 

SOILS 

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

Tube No. I — Sand. 

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

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

part organic matter. 

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

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

References : 

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

II. INTERRUPTION OF THE CAPILLARY 
RISE OF MOISTURE 

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



THE PHYSICAL PROPERTIES OF SOILS 



47 




APPARATUS USED TO COMPARE THE CAPILLARY RISE OF MOISTURE 

IN DIFFERENT SOILS 

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



48 THE PHYSICAL PROPERTIES OF SOILS 

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

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

Reference : 

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



THE PHYSICAL PROPERTIES OF SOILS 



49 



STUDENT'S NOTES AND REPORT 






PLAIN CO-ORDINATE PAPER 



50 THE PHYSICAL PROPERTIES OF SOILS 



EIGHTH EXERCISE 

CONTINUOUS RISE OF CAPILLARY 

MOISTURE 

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

Tube No. I — Clay. 

Tube No. 2 — Loam or silt. ' 

Tube No. 3 — Sandy loam. 

Tube No. 4 — Sand. 

Tube No. 5— Muck. 

Tube No. 6 — Sand, lOO to 120 mesh. 

Tube No. 7 — Sand, 60 to 80 mesh. 

Tube No. 8 — Sand, 20 to 40 mesh. 

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

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

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

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

part sand. 

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



THE PHYSICAL PROPERTIES OF SOILS 5 1 

STUDENT'S NOTES AND REPORT 



52 



THE PHYSICAL PROPERTIES OF SOILS 



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

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

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

References : 

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

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







l. 


1^ 


J. 






?f ' 








1 











^mmgmmmgt 






'''^''^^HMnnfflnnn 










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



TORSION BALANCR 

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

greater accuracy is required 



THE PHYSICAL PROPERTIES OF SOILS 53 

STUDENT'S NOTES AND REPORT 



54 THE PHYSICAL PROPERTIES OF SOILS 



NINTH EXERCISE 

THE LATERAL MOVEMENT OF CAP- 
ILLARY MOISTURE 

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

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

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

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

References : 

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



THE PHYSICAL PROrERTIES OF SOILS 



55 



STUDENT'S NOTES AND REPORT 







PLAIN CO-ORDINATE PAPER 



56 



THE PHYSICAL PROPERTIES OF SOILS 



TENTH EXERCISE 



CO-EFFICIENT OF EVAPORATION 

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




PCRF««ATf<| 



EVAPORIMETER 
Sectional View 

Evaporimeter No. i — Sand. 

Evaporimeter No. 2 — Loam or silt. 

Evaporimeter No. 3 — Muck. 

Evaporimeter No. 4 — Clay. 

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

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



THE PHYSICAL PROPERTIES OF SOILS 57 

STUDENT'S NOTES AND REPORT 



S8 



THE PHYSICAL PROPERTIES OF SOILS 




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

soils by evaporation 

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

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

References : 

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



THE PHYSICAL PROPERTIES OF SOILS 



59 



STUDENT'S NOTES AND REPORT 



 . 


1 



PLAIN CO-ORDINATE PAPER 



6o 



THE PHYSICAL PROPERTIES OF SOILS 



ELEVENTH EXERCISE 



EFFECT OF MULCHES UPON THE RATE 

OF EVAPORATION 

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

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



/ 



i 



MULCH CYLINDER 
Sectional View 



No. I — No treatment. 

No. 2 — Cultivate one inch deep each day. 

No. 3 — Compact the surface. 

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

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

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



THE PHYSICAL PROPERTIES OF SOILS 6l 

STUDENT'S NOTES AND REPORT 



62 



THE PHYSICAL PROPERTIES OF SOILS 











I- 




i^^^ 


\ ^' 1 






 


K < ' 


. 


s 






t'* \ 


f' i 






1- i 


$ i 


r-- i 


' 




^ 4 

A 


< 
> 


'■ t . 






I 


% 


r'' » 


'• 




 




r^ ; 


It 


^^'\ M^ PwA i 


h 


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






m""r-"'^ 




BBunsj^sa^^n^MK 


"-s*^--r«s-;^~. "^ -«&. 





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

soil moisture 



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

References : 

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



THE PHYSICAL PROPERTIES OF SOILS 63 

STUDENT'S NOTES AND REPORT 



64 THE PHYSICAL PROPERTIES OF SOILS 



TWELFTH EXERCISE 

THE ABSORPTIVE POWER OF SOILS 

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

METHOD OF DETERMINATION 

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

Tray No. i — Sand. 

Tray No. 2 — Loam or silt. 

Tray No. 3 — Clay. 

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

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

part organic matter. 

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



THE PHYSICAL PROPERTIES OF SOILS 65 

STUDENT'S NOTES AND REPORT 



66 



THE PHYSICAL PROPERTIES OF SOILS 



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



n 


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


; 
i 


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


1 ' 9 


#W«w^^ 


r 


Pi 


■^^^^^^SSSj^ ^v 




^■■1 



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



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

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

References : 

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



THE rilYSICAL PROPERTIES OF SOILS 6/ 

STUDENT'S NOTES AND REPORT 



68 THE PHYSICAL PROPERTIES OF SOILS 



THIRTEENTH EXERCISE 

THE FLOCCULATING EFFECT OF LIME 
UPON CLAY SOILS 

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

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

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

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

References: 

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



THE PHYSICAL PROPERTIES OF SOILS 69 

STUDENT'S NOTES AND REPORT 



70 THE PHYSICAL PROPERTIES OF SOILS 



FOURTEENTH EXERCISE 

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

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

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

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

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

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

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



THE PHYSICAL PROPERTIES OF SOILS 7I 

STUDENT'S NOTES AND REPORT 



72 the physical properties of soils 

References : 

Hall, "The Soil," Chap. VIII. 

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

193. 
Bureau of Soils, Bulletin No. 32. 



THE PHYSICAL PROPERTIES OF SOILS 73 

STUDENT'S NOTES AND REPORT 



74 THE PHYSICAL PROPERTIES OF SOILS 

FIFTEENTH EXERCISE 

THE SPECIFIC HEAT OF SOILS 

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

APPARATUS FOR THE DETERMINATION OF THE 
SPECIFIC HEAT OF SOILS 

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

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

METHOD OF DETERMINATION 

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



THE PHYSICAL rROPERTIES OF SOILS 



75 



g» > 



JSET 



i'j 



HEATER 



^ 



m 



® 



^ 



SOIL 




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



76 THE PHYSICAL PROPERTIES OF SOILS 

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

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

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

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

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



THE PHYSICAL PROPERTIES OF SOILS 'J'J 

STUDENT'S NOTES AND REPORT 



78 THE PHYSICAL PROPERTIES OF SOILS 

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

mC(h—T)=M(T—To) 
or 

M ( T—To) 

Specific heat C^= 

in (tn — T) 

where in^mass of soil taken. 

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

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

calorimeter. 
T=final temperature of water in the 

calorimeter. 
C= specific heat. 

References : 

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

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



THE PHYSICAL PROPERTIES OF SOILS 79 

STUDENT'S NOTES AND REPORT 



8o 



THE PHYSICAL PROPERTIES OF SOILS 



SIXTEENTH EXERCISE 



MECHANICAL ANALYSIS OF SOILS- 
BOTTLE METHOD 

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

silt and clay groups are 
estimated together. 

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

METHOD OF MAKING THE 
SEPARATIONS 

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




APPARATUS USED IN THE BOTTLE 
METHOD OF MECHANICAL 

ANALYSIS {after M osier). 



THE PHYSICAL PROPERTIES OF SOILS 8l 

STUDENT'S NOTES AND REPORT 



82 THE PHYSICAL PROPERTIES OF SOILS 

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

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

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

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

Tabulate the results of the analyses. 

Reference : 

Bulletin No. 24, Bureau of Soils. 



THE niYSlCAL PROPERTIES OF SOILS 83 

STUDENT'S NOTES AND REPORT 



84 THE PHYSICAL PROPERTIES OF SOILS 



SEVENTEENTH EXERCISE 

MECHANICAL ANALYSIS OF SOILS— CEN- 
TRIFUGAL METHOD 

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

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

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

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

The separates to be determined are as follows : 

Fine gravel 2.0 — i.o mm 

Coarse sand i .0 — 0.5 

Medium sand 0.5 — 0.25 

Fine sand 0.25 — o. i 

Very fine sand o. i — 0.05 

Silt 0.05 — 0.005 " 

Clay 0.005 






THE PHYSICAL PROPERTIES OF SOILS 



8s 





„- * 



86 



THE PHYSICAL PROPERTIES OF SOILS 



CLAY SEPARATION 



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




SHAKER USED IN THE PREPARATION OF SOIL SAMPLES FOR 

MECHANICAL ANALYSIS 



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



THE PHYSICAL PROPERTIES OF SOILS 8/ 

STUDENT'S NOTES AND REPORT 



88 THE rilYSlCAL PROPERTIES OF SOILS 

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

SILT SEPARATIONS 

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

SAND SEPARATIONS 

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

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



THE PHYSICAL PROPERTIES OF SOILS 89 

STUDENT'S NOTES AND REPORT 



kP 



90 THE PHYSICAL PROPERTIES OF SOILS 

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

DETERMINATION OF THE LOSS ON IGNITION 

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

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

References : 

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



THE PHYSICAL PROPERTIES OF SOILS 



91 



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92 THE PHYSICAL PROPERTIES OF SOILS 

EIGHTEENTH EXERCISE 

CHROMIC ACID METHOD OF DETER- 
MINING ORGANIC MATTER 

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

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

METHOD OF DETERMINATION 

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

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

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



THE PHYSICAL PROPERTIES OF SOILS 93 

STUDENT'S NOTES AND REPORT 



94 



THE PHYSICAL PROPERTIES OF SOILS 



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

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




APPARATUS USED FOR THE DETERMINATION OF THE ORGANIC 

MATTER IN SOILS BY THE WET-COMBUSTION METHOD 

(Bulletin No. 24, Bureau of Soils) 

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

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

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



THE PHYSICAL PROPERTIES OF SOILS 95 

STUDENT'S NOTES AND REPORT 



96 



THE PHYSICAL PROPERTIES OF SOILS 



APPENDIX 

DIRECTIONS FOR TAKING SOIL SAMPLES 

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




WM 



SAMPLING APPARATUS 

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

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

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

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



THE PHYSICAL PROPERTIES OF SOILS 



97 



STUDENT'S NOTES AND REPORT 



1 



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PLAIN CO-ORDINATE PAPER 



98 THE PHYSICAL PROPERTIES OF SOILS 

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

Samples taken for mechanical analysis should be 




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



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

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



THE PHYSICAL PROPERTIES OF SOILS 99 



References 



Stevenson & Schaub, "Soil Physics Laboratory 
Guide." 

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

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



STANDARDIZATION OF THE EYE-PIECE 

MICROMETER 

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

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



100 THE PHYSICAL PROPERTIES OF SOILS 

TABLE OF DATA 

I cc. of water := i gram. 

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

I gram = 0.0022 lbs. avoirdupois. 

I cc. = 0.061 cu. in. 

I gal. = 231 cu. in. 

I oz. avoirdupois = 28.35 grams. 

I kilogram = 2.20 lbs. avoirdupois. 

I inch = 25.4 mm. 



IN DEX 

PAGE 

Air in field soils 44 

Analysis of soils 80 

Capillary water, its distribution 40 

rise of moisture 46 

rise of moisture interrupted 46 

moisture, continuous rise 50 

moisture, lateral movement 54 

Clay separation 86 

Fertilizers retained in soils 70 

Flow of air in soils 42 

Hygroscopic moisture 10 

in the field 12 

Laboratory desk outfit 3 

Lime flocculates soils 68 

Lime and clay soils 68 

Mechanical analysis of soils 6 

bottle method 80 

centrifugal method 84 

Mulches, effect of, on evaporation 60 

Evaporation controlled by 60 

Absorptive power of 64 

Organic matter 90 

Report on 91 

Determination of 9^ 

Percolation of water 32 

Pore space, determination of 26 

Calculation of 28 

Physical properties of soils 1 

Sand 88 

Silt 88 

Soil samples 9° 

Directions for taking 96 

Apparatus for sampling 9° 

Eye-piece micrometer 99 

lOI 



I02 INDEX 

PAGE 

Specific gravity i8 

Calculation of i8 

Method of determination i8 

Specific heat 74 

in soils 74 

Determination of 74 

Stock soils 5 

Volume weight 22 

Calculation of 26 

Method to determine 22 

Water-holding capacity 38 

Apparatus to determine 38 



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