RELATION as shame: AREA 0? LIMING
MATERIALS re REACTION RATE

Thesis {or flu Degrfl 6f M. S.
MICHIGAN STATE UNIVERSITY

Gordon Stanley Miner
1964

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ABSTRACT

RELATION OF SURFACE AREA OF LIMING
MATERIALS T0 REACTION RATE

by Gordon Stanley Miner

Four methods of estimating the surface area of
calciclimestone. dolomitic limestone. basic oxygen processed
slag and open hearth slag were studied. Determination of
surface area of liming materials by isotopic exchange did
not prove satisfactory. The oxalate titration method was
satisfactory for calcic limestone and the nitrogen gas
adsorption method was satisfactory for all materials studied.
Estimation of surface area by calculation. assuming spherical
particles. agreed closely with surface area determined by
oxalate titration suggesting that the titration gives a
measure of external surface area only. Nitrogen gas adsorption.
on the other hand. appears to measure both internal and
external surface area.

An acid Warsaw loam surface soil was used in incu—
bation studies to determine the effect of surface area on
rate of reaction of liming materials. Treatments for one

study consisted of liming materials of different particle
size added individually to samples of soil at a calcium

carbonate equivalent rate of 5.75 tons per acre of pure

Gordon Stanley Miner

calcium carbonate. This produced different surface areas

of liming material for each treatment. The second incu-
bation experiment consisted of treatments of liming

materials added to the soil at constant surface area as
determined by nitrogen gas adsorption. All treatments in
incubation studies were replicated three times and incubations
carried out at the moisture equivalent and at 20 degrees
centigrade.

From an application of experimental data to a
proposed theoretical function it appears that the rate of
reaction of the dolomite studied is controlled by surface
area; however, the reaction of limestone did not appear to
be controlled by surface area except during the later
stages of incubation.

Microscopic examination indicated that the dolomite
studied was uniform and crystalline in nature; whereas. the
calcic limestone studied was hetrogeneous containing a
portion of slow reacting crystalline material and a faster
reacting. porous appearing material.

In general the reaction rate of limestone materials
appeared to be more closely related to the external surface
area as measured by oxalate titration or estimated by cal-
culation than to total surface area as measured by nitrogen

gas adsorption.

RELATION OF SURFACE AREA OF LIMING

MATERIALS TO REACTION RATE

BY

Gordon Stanley Miner

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Soil Science

1964

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ACKNOWLEDGEMENTS

Sincere gratitude and appreciation are expressed
to Dr. B. G. Ellis for his guidance. moral support. and
unfailing interest throughout the course of this work.

Appreciation is extended to R. Pennock for taking
pictures and to Professor Fripiat for furnishing standard
clay samples for comparison of surface area determinations.
The author also wishes to express his sincere appreciation
to the Edward C. Levy Company for financial support of this

study.

ii

TABLE OF CONTENTS

INTRODUCTION 0 O C O C 0 O O O O O C O O O O
REVIEW OF LITERATURE . . . . . . . . . . . .

Effects and Practices of Liming
Methods of Area Determination

Area by Calculation
Area by Radioactive Isotopic Exchange
Area by Oxalate Titration
Area by Gas Adsorption
EXPERIMENTAL PROCEDURES . . . . . . . . . .

Liming Materials
Incubation at Constant Calcium Carbonate
Equivalent
Constant Surface Area Incubation
METHODS OF ANALYSIS . . . . . . . . . . . .

Soils
Liming Materials

RESULTS AND DISCUSSION . . . . . . . . . . .

Determination of Surface Area of Liming
Materials

Calcuhition and Oxalate Titration
Isotopic Tracer Exchange
Gas Adsorption

Incubation Studies

Constant Calcium Carbonate Equivalent
Constant Surface Area

SUMMARY AND CONCLUSIONS . . . . . . . . . .

LIST OF REFERENCES . . . . . . . . . . . . .

iii

10
10
12
l4
l9
19

20
20

22

22
22

25

25
25
26
29
33

33
44

47

49

LIST OF TABLES
Page

Calcium carbonate equivalent of liming
materials studied . . . . . . . . . . . . . 19

Quantity of material added to 900 gm. of soil
to produce constant calcium carbonate
equivalent of liming materials . . . . . . 20

Quantity of calcic limestone added to 850911.
of soil to produce constant surface area
of liming material . . . . . . . . . . . . 21

Surface area of calcic limestone as determined
by oxalate titration and calculation . . . 26

Calibration of sorptometer with standard
clay materials of known surface area . . . 30

Surface area of liming materials as determined
by gas adsorption . . . . . . . . . . . . . 31

Surface areas of liming materials applied to
the soil as determined by three methods . . 34

Soil pH as a function of time after addition
of liming materials at constant neutrali—
zation equivalence . . . . . . . . . . . . 35

Soil pH as a function of time after addition
of different particle size calcic lime-
stone at quantities to give constant total
surface area . . . . . . . . . . . . . . . 44

iv

LIST OF FIGURE S
Figure Page
1. Relationship between particle diameter and

quantity of 0.1 N'KMnO4 used for titration
of oxalate on calcic limestone . . . . . . 27

2. Loss of Ca45 from solution as a function
time . . . . . . . . . . . . . . . . . . . 28
3. Relationship between cube root of hydrogen ion

concentration in a Warsaw loam surface soil
and time after addition of calcic lime-
Stone . O O O O O O O . O C O O O O O O O O 38

4. Relationship between cube root of hydrogen ion
concentration in a Warsaw loam surface
soil and time after addition of dolomitic
limestone . . . . . . . . . . . . . . . . . 39

5. Relationship between cube root of hydrogen ion
concentration in a Warsaw loam surface
soil and time after addition of basic oxygen
processed slag . . . . . . . . . . . . . . 40

6. Relationship between cube root of hydrogen
ion concentration in a Warsaw loam
surface soil and time after addition
of open hearth slag . . . . . . . . . . . . 41

7. Calcic limestone, 40-60 mesh particles
(100 X) . . . . . . . . . . . . . . . . . . 42

8. Dolomitic limestone, 40-60 mesh particles
(100 X) . . . . . . . . . . . . . . . . . . 42

9. Relationship between calculated surface area
of calcic limestone and pH of a Warsaw
loam surface soil eight weeks after
lime application . . . . . . . . . . . . . 45

INTRODUCTION

Particle size distribution as determined by sieve
analysis has been used extensively for predicting the
reaction rate of liming materials applied to acid soils.

The finer the composition of the material the greater should
be the rate of change of pH and the sooner equilibrium
should be reached.

Particle size distribution may give an indication
of the expected reaction rate of liming materials: however.
it is at best an approximation and not sufficient for
quantitative estimation of soil pH changes produced by
liming. It reflects no property other than size composition.
To accurately predict the reaction rate of liming materials,
properties other than particle size and factors within the
soil that affect the reaction rate must be taken into
consideration.

Many chemical methods using rate of reaction as a
standard of comparison have also been used to predict the
amount of material needed to rectify undesirable soil
conditions and determine the efficiency with which this
is accomplished. Limestone activities have been measured
by the rate of reaction with ammonium chloride. acetic
acid, an oxalate buffer. and disodium ethylenediaminetetra-

acetate (24, 9). They have been measured by change in pH

of an acid soil colloid. liberation of CO2 from acid soils,
and reactions as predicted by an "a" value conceived by
Schollenberger (23).

No one method of evaluating the efficiency of liming
materials has proven to be totally reliable. Schollenberger
and Whittaker made a comparison of methods and found that
where the mineral composition varied from pure calcite to
pure dolomite the different methods failed to reproduce
actual activities of the liming material (24). High cor-
relations were obtained for some of the methods for a few
materials that were all calcic or dolomitic but other
materials were not so highly correlated.

The efficiency value is defined as the percentage
of the limestone applied that should be expected to react
with the soil in 3 to 12 months as conditions vary from
optimum to average (25). It is difficult to determine in
a few minutes with a chemical reaction how much of the total
material applied to the soil will react in a definite period
of time. The reaction rate may be limited by diffusion of
the reaction products away from the lime particles in the
soil. In a chemical test the agitated media provides for
quick removal of the products from the particles at a more
or less constant rate. Amount and movement of water,
temperature, and placement of the materials also affect
reaction rate. These variables tend to remain constant in

chemical tests and thus the measured rate of reaction

reflects chemical composition, surface area. degree of

crystallinity, and other properties of the liming material.
Since a reliable method for predicting the effective-
ness of a liming material has not been developed, additional
work is needed to study individual rate determining factors.
Reaction rates may be affected by surface area; consequently,
the object of this study was to:
1. Determine surface area of some liming materials
by different methods.
2. Determine how change in pH is related to surface

area.

REVIEW OF LI TE RATURE
Effects and Practices of Liming

The liming of tillable soils was practiced by the
Celts and the Europeans before the time of Christ (8).
Despite early use of lime and benefits obtained in the form
of increased yield, little was known about the specific
effects of lime on soil until modern times.

In our modern era. liming materials have been
defined as materials applied to the soil to improve soil
conditions by substituting metallic cations for hydrogen
ions on the cation exchange complex (8). Many materials
such as marl, chalk, pulverized calcic or dolomitic lime-
stone, burnt or hydrated lime. slag. etc., have been used
as liming agents (8). They have been applied to counter-
act the direct and residual acidic effects on soils of
fertilizers such as some commonly used nitrogen carriers
(31). Most materials are mined but some are by-products of
other industries (8).

Electric furnace slag is obtained from the smelting
of aluminum ores and from rook phosphate reduction furnaces
(8, 28). It has a solubility similar to limestone of the
same fineness. The slag is primarily calcium silicate and

contains from 0.9 to 2.3 per cent P205 (28). The neutralizing

value is from 65 to 80 per cent.

Basic slag is a by-product of the basic open hearth
method of making steel from pig iron (28). It contains 8 to
10 per cent P205 and has a neutralizing value of 65 to 80
per cent. Basic slag is generally used for its phosphorus
content rather than its neutralizing effect.

Blast furnace slag is obtained during the manufacture
of pig iron (28). Calcium oxide combines with the molten
silica to give a slag that reacts similar to calcium
silicate. The neutralizing value is 75 to 90 per cent
and field tests indicate that the material is as effective
as ground limestones when applied on the basis of equivalent
amounts of calcium and magnesium.

A basic oxygenated slag produced as a by—product of
a new method of manufacturing steel has shown very definite
promises of being a good liming material. It has been
demonstrated in a greenhouse experiment that barley responds
to basic oxygen processed slag better than to limestone or
open hearth slag.l

Determining the amount of liming material to apply
to a soil has been the subject of considerable research.
While liming and increasing the pH will make some cations
more available. others such as manganese, iron. zinc. and
boron are precipitated into unavailable forms (8, ll).

Liming some soils low in potassium may cause potassium

 

1Personal communication. B. G. Ellis and E. C.
Doll.

deficiencies in plants (17, 28). Potassium cannot be
adsorbed at a rapid enough rate in the presence of high
concentrations of calcium. Phosphorus is made more avail—
able by liming to pH 6.5 while aluminum tends to precipitate
out with increasing pH (15. 17). In acid soils containing
toxic amounts of aluminum this is very beneficial.

Moderate applications of limestone stimulates the
process of nitrification (8). This results in the
production of nitric acid which causes other plant nutrients
to become more available and reduces the need for fertilizers.

Meyer and Volk found that increasing the rate of
limestone application, gave a trend toward higher exchang—
able calcium for soils (16). The trend was higher with
calcic limestone than it was with dolomitic limestone.

At three tons per acre :1 4-8 mesh material gave 4.1
milliequivalents of exchangable calcium as compared to 3.4
for a check while a.) 100 mesh material gave 8.6 milli-
equivalents. The 4-8 mesh material at ten tons per acre

gave only 6.1 milliequivalents of exchangable calcium.

This would indicate that exchangable calcium is greatly
affected by the size composition of the limestone as compared
to rate of application.

Work by Bishop demonstrated that crop response to
liming depends on the nature of the clay minerals in the
soil (4). Two to one type clay colloids need a higher
degree of calcium saturation than one to one type colloids

to get comparable adsorption of calcium by plants. Below

70 per cent saturation montmorillonite clays have a high
energy of adsorption for calcium ions while kaolinite
releases calcium with equal ease regardless of the degree
of saturation. Soils with a high clay content are conditioned
by lime so that they are more tillable (11).

The root systems of some plants respond greatly to
zones of liming in the soil. Using Crimson Clover. Long-
necker and Merkle demonstrated that fibrous roots developed
very extensively in the limed zones of the soil while they
were few in number and very small in the unlimed zones (15).
Primary roots appeared able to extend through the unlimed
zones. The lack of a fibrous root system in unlimed zones
would indicate that there is little horizontal movement of
the products of lime dissolution. It has been shown that
neutralization of soil acidity occurs only near the reacting
particle.

Lime moves most rapidly during the first year after
its application (22). This movement is in a downward
direction and is the result of the leaching effect of
infiltrating water. The dissolution products of lime are
retained by the subsoil to a great extent. Ririe. gt al.,
found that calcium from Ca(0H)2. CaO. and Ca(OH)2 + MgO
moves more rapidly than calcium from carbonates (22).

This is probably due to the higher solubility of these
materials. Where M90 alone was added to the soil the
loss of calcium almost equaled the loss where CaCO3 was

used. This would mean that magneSium replaced exchangable

calcium. In coarse sands CaCO3 leached away faster than
CaC03~MgCO3 and magnesium was lost at a faster rate than
calcium where CaCO3-MgCO3 was used. The solubility rate of
dolomite is about 50 per cent that of limestone (8). The
decrease in diameter of like particles of calcite to dolomite
is about 3 to 1. For comparable effectiveness dolomitic
limestone should be 60-80 mesh compared to 40-50 mesh for
calcic limestone (16).

The degree of fineness of a limestone also deter-
mines the rate of solution in a particular soil. The finer
the material the greater the rate of solution and conse-
quently the greater the rise in pH (16). Meyer and Volk
found that material of 4-8 mesh size had little value cor-
recting soil acidity regardless of rate of application or
time after application. It todk 18 months at a 10 ton
rate for 20-30 mesh limestone material to reach equilibrium.
Twenty mesh material gave an initial rise in pH but after
2 weeks the pH decreased. This was thought to be caused
by the presence of dust on the coarser particles that gave
the initial rise in pH. Fifty to sixty mesh material took
12 months to reach equilibrium and finer than 60 mesh
material took 6 months. At the same rate of application
and particle size, calcic limestone gave higher pH values
than dolomitic limestone during the first 6 to 9 months
after application (16). After 9 months, however. dolomitic
limestone produced higher pH's than calcic materials. The

yield of alfalfa was increased with 3 ton calcic limestone

applications where the degree of fineness was increased up
to 60 mesh. Finer grades than 60 mesh did not give further
increase in yield at this rate.

Meyer and Volk used increase in exchangable calcium
as a measure of the amount of material reacted with the
soil at any given time (16). They determined that 18 months
after applying limestone at a 3 ton per acre rate, 13.4 per
cent of the 4-8 mesh material, 72.5 per cent of the 40-50
mesh material, and 94.5 per cent of the finer than 100
mesh material had reacted.

It is generally agreed that a large portion of the
limestone should pass a 40 mesh sieve to be effective (16).
Particles finer than 40 mesh are approximately equal in
their ability to change pH. Unless maximum effects are
desired within one year there is little advantage in having
limestone ground finer than 100 mesh due to the increased
cost of grinding. Since these particles are effective only
in their immediate vicinity liming materials must be mixed
well with the soil or their efficiency in correcting soil

acidity may be very low.

Methods of Area Determination

There are three general methods of determining
surface area of solids (3). These are calculation from
particle size, determination of adsorption isotherms, and

the relation of some special property which depends in some

known manner on available area.

10

Area by Calculation

 

Area can be calculated arithmetically if the general
shape and density of the particles is known. Determining
shape is the greatest source of error due to geometrical
irregularities of the particles (29). Motto and White
examined calcic limestone particles microscopically and
suggested that spheres would give a close approximation to
the shape (18). The diameter was obtained as the average
of the openings of the larger and smaller screens for each
size class. Areas determined by particle size would be the
lowest possible because internal area in porous materials
would not be considered (3). Small particles also tend to
aggregate into larger particles so that they appear as a

single particle.

_Area by Radioactive Isotopic Exchange

As cited by Brunauer (6) and Wang (29) the radio-
active tracer method of determining surface area was first
applied by Paneth and Vorwerk. They determined the surface
area of lead sulfate using a lead isotope. Thorium B. as
the tracer. This method is based on the assumption that a
constant kinetic exchange occurs between ions in solution
and ions on the surface of the solid. After exchange at
the surface. the tracer is transported within the solid by
recrystallization and self-diffusion. If the rates of
self-diffusion and recrystallization are small in comparison

to surface exchange. a pseudo-equilibrium state is reached.

11

The following formula gives the relationship between the
tracer and the other ions (29):

N' N‘l
fig = N— (l)

(D
[—1

where
N; = number of tracer atoms on the surface.

N = total number of this species of atoms on the
surface.

N1 = number of tracer atoms in the bulk of solution.
and

N1 = total number of this species of atoms in the
bulk of solution.

The total number of atoms on the surface can be calculated
by measuring the other three unknowns and the area can be
determined if the cross-sectional area of one of the atoms
is known.

Paneth and Vorwerk suggested three minutes as the
length of time needed for the Thorium B-lead sulfate exchange
reaction to reach equilibrium. The tracer was absorbed
on the solid surface at a rapid rate up to this time and
then absorption occurred at a slower rate. Kolthoff and
Rosenblum concluded that the absorption of Thorium B at the
lower rate was from penetration of the ion into the lattice
due to recrystallization of the lead sulfate (14).

Kolthoff and Eggertsen studied the kinetics of the.
reaction for a period of several hours and extrapolated the
time-adsorption curve back to zero time (13). This value

was used as the quantity of ions absorbed on the surface

of the solid.

12

There are many difficulties with the surface exchange
method. Adsorption of the tracer without exchange sometimes
occurs which would necessitate using a correction factor (13).
One lattice ion may exchange at a faster rate than others.

The time for equilibrium to be reached may be different in
each case and consequently a point of uncertainty (29). In
new precipitates the rate of diffusion and recrystallization

is rapid and not constant (6. 29).

.Area by Oxalate Titration

Barnes proposed a method of determining surface
area by liming materials by reacting them with saturated
oxalic acid (1). The calcium oxalate formed on the surface
of the particles is dissolved with sulfuric acid and the
oxalate titrated with 0.1 N potassium permanganate. Barnes'
data showed the volume of permanganate used to be directly
proportional to the particle size. Motto and White disputed
this on the grounds that the volume of oxalate used should
be related to surface area which is a function of diameter
squared (l8). Particle size is a function of the first power
of the diameter.

Thomas and Gross proposed using 0.1 N oxalic acid
instead of a saturated solution because magnesia limestone
continued to react on the steam bath with the saturated
oxalic acid as long as free acid or lime particles were
present (27). They found that the concentration of Mg

ions in solution increased while the oxalate gradually

13

dissolved from the surface of the particle exposing more
calcium ions to react with the excess oxalate ions.

Motto and White were unable to express area as
square meters per gram because the area they determined
using the number of Ca ions from a unit cell of calcite
was much higher than the area reported for a ball milled
calcite (18). They suggested that the reaction affected
the subsurface layers as well as the calcium ions on the
surface because the solubility of the carbonate (8.7 x 10-9
at 25°C) is about three times greater than that of the

oxalate (2.57 x 10-9

at 25°C). In determining surface area
all the calcium that reacted would be designated as surface
calcium.

Motto and White plotted change in pH for one week
against surface area of the particles determined by assuming
particles to be spheres (18). The plot was a curve with an
increasing slope from which the surface of the finer
particles appear to be more reactive than the surface of
the coarser particles. They made an analogy comparing
small drops of liquid having higher vapor pressures than
big drops to fine material having higher vapor pressure.
greater solubility. and a lower melting point than coarse
crystals. Greater reactivity was suggested to be the
result of an increase in the surface energy of a crystal
with a decrease in particle size.

Motto and White also proposed that the presence of

a "Beilby" layer on particles gives a surface of greater

14

reactivity and solubility (18). This is an amorphous

layer produced by grinding. They cited where Beilby had
found this layer up to 50 A thick on calcite crystals. with
effects to a depth of 5.000 to 10.000 3 produced by grinding
action. Finer particles would have this layer to a

greater degree than coarser particles because of the in—

creased grinding required to reduce the particle size.

Area bngas Adsorption

The physical adsorptive properties of solids have
led to other methods of determining Surface area. Brunauer.
Emmett. and Teller derived the relationship between the
volume of polymolecular layers of gas adsorbed on the
surface of a solid and the relative pressure of the gas (7).
This relationship produces a curve called an adsorption
isotherm that is concave to the abscissa at lower relative
pressures and convex to the “abscissa at.higher relative
pressures with a linear portion between (3. 6. 7). The
beginning of the linear portion corresponds to the first
layer of gas adsorbed. Brunauer found there was a sharp
decrease in the net heat of adsorption at this point when
using nitrogen as the adsorbate (6). It was assumed the
higher values were due to the interaction between the
gas molecules of a monolayer and the solid surface while
the lower values were due to the interaction between gas
molecules as more layers were adsorbed. He also obtained
better agreement in calculating surface area from this point

than from other points on the adsorption isotherm.

15

The relationship derived by Brunauer. Emmett. and

Teller is known as the BET equation and is expressed by (20):

_l__

 

 

P C-l P
——-- —— + (2)
Vads (PO P) VmC PO VmC
where
V = total volume of adsorbed gas on surface of
ads
adsorbent.

Ym = volume of adsorbed gas covering entire
adsorbent surface with a complete mono-
molecular layer.

P0 = saturation pressure of the adsorption gas
at the temperature of the coolant.

P = partial pressure of the adsorption gas.

C = constant expressing net adsorption energy.
and

P/PO = relative pressure of the adsorbate.

P P . .
A plot of versus-—- gives a curve that 13
V (P --P) P
ads 0 0

linear in the range of relative pressure values from 0.05 -
0.30 (3. 7. 10. 19. 20).

Adsorption occurs upon cooling the sample to low
temperatures (6. 7. 19. 20. 30). Where nitrogen gas is
used as the adsorbate. liquid nitrogen is usually used as
the coolant (6). Brunauer suggested that perhaps adsorption
is closely related to condensation if condensation can
occur at pressure far below the vapor pressure of the liquid
in capillaries of molecular dimensions (7). He stated that
the convex portion of isotherms at higher pressures may be

due to condensation.

16

Nelsen and Eggertsen developed the continuous flow
method to determine the variables of the BET equation (19).
This method is faster and does not require the skill or
fragile high vacuum apparatus needed to measure pressure—
volume relationships by the volumetric method. The adsor-
bate mixed with an inert gas carrier moves by the sample
in a continuous flow. Cooling the sample causes adsorption
of nitrogen and the change in flow rate of nitrogen is indi-
cated by an output signal from thermal conductivity cells
monitoring the gas stream. This output signal is proportional
to the change in flow rate of the adsorbate gas and is
recorded as a curve by a potentiometric recorder. Warming
the sample causes desorption which is recorded in the same
manner. A known volume cf adsorbate is introduced into the
gas stream and the output signal is recorded. The area
from the known volume of adsorbate is compared with the
area produced by desortpion to determine the volume of
adsorbate adsorbed. The desorption peak area is used in
calculations because most of the effects of tailing are
eliminated (19. 20). This procedure is repeated at different
flow rates of adsorbate to determine the adsorption isotherm.

Molecules are held to the surface of solids either
by chemical binding known as chemisorption or by physical
forces known as Van der waals forces (3. 6. 10. 19. 20. 30).
The theory of the BET equation is based on physical adsorp-

tion; therefore. the adsorbate and sample must not react

in any way other than with Van der waals forces (7). Berl

17

lists the characteristics an adsorbate must have as follows
(3):
1. Must not react with the sample. This changes
the surface and other products may be formed
either on the surface or by complete reaction.
2. Must not dissolve with the solid. The gas

moves into the solid and may or may not form

interstitial compounds. This gas would not

desorb.

3. Chemical nature of the gas must not be changed
by the solid acting as a catalyst.
4. Gas should be pure.

Chemisorbed air and molecules held by Van der waals
forces must be removed from the surface of the solid before
areas are determined (3. 6. 19. 20. 30). Wise and Lee
removed impurities by outgassing in a helium stream at 250°C
to 300°C for one hour (30). Nelsen and Eggertsen outgassed
at 500°C with helium at a 20 ml per min flow rate for one
hour (19).

The boiling points of pure compounds are best for
cooling temperatures to be used (3). These temperatures
remain quite constant so that the equilibrium pressure of
the adsorbed gas will also remain constant.

Most workers agree that the area covered by one
nitrogen molecule is about 16.2 32 (3. 6. 19). This area
is determined by assuming the packing to be the same as

for liquid nitrogen (3). The area varies with the temperature

18

as does the saturation pressure; therefore. the temperature
of the liquid nitrogen must be measured (19).

The thermal conductivity of a nitrogen—helium
mixture is not linear for different concentrations of the
gases (20). The volume of nitrogen used for calibration
should be about the same as the amount adsorbed on the
sample (19. 20). Errors in determining volume adsorbed
result otherwise but they should be small (20).

Small surface areas require the use of a calibration
gas made up of 10 to 20 per cent nitrogen in helium (20).
The effective volume of nitrogen introduced gives an area
comparable to the desorption area. Samples with large
areas require smaller samples to be used (20). Care must
be taken so that variability of sample does not enter the
calculation.

The continuous flow method has been found to give
results comparable to the volumetric method (19. 20. 30).
Wise and Lee compared the two methods and found the

following areas (30):

 

 

Material Adsorp. Method Vol. Method
activated charcoal 1372.0 m2/g 1360.0 mZ/g
activated alumina 218.0 195.0

red chromosorb 4.6 4.8

EXPERIMENTAL PROCEDURES

Liming Materials

Bellevue calcic limestone. dolomite obtained from
the L. Hill Co.. open hearth slag. and basic oxygen processed
slag obtained from Levy & Co.. were dry sieved to produce
five particle size fractions. 20-40. 40-60. 60-80. 80-100
and > 100 mesh material. All materials were placed in
Erlenmeyer flasks and repeatedly washed with distilled
water to remove fine material adhering to the surface.

The supernatant liquid was decanted until it was clear.
The materials were then dried in an oven at 105°C. The
calcium carbonate equivalent of each size range was deter-
mined for each material and is given in Table 1.

Table 1. Calcium carbonate equivalent of liming materials
studied.l

Particle Size

 

 

 

Materials
20-40 40-60 60-80 80-100 > 100

Calcic
Limestone 91.1 77.7 65.7 67.4 80.6
Dolomitic
Limestone 105.9 107.1 106.6 106.6 99.5
Open Hearth
Slag 59.9 56.4 57.2 57.9 60.4
Basic Oxygen
Processed Slag 73.0 79.5 81.1 80.7 80.1

1

Determined by titration method as described by
Jackson (12).

19

20

Incubation at Constant Calcium Carbonate Equivalent

Soil from the surface layer of a Warsaw loam was
air—dried and screened through a one—fourth inch screen.
Each treatment in the incubation consisted of one particle
size of a particular liming material added in sufficient
quantity to be equal to 5.75 tons of pure CaCO3 per acre.
The material was thoroughly mixed with 900 grams of soil
and the moisture content was brought to the moisture equi-
valent with distilled water. Each size fraction and a
check with no lime added were replicated three times. The
rates added to the soil are as shown in Table 2. The soils
were incubated in a constant temperature room at 20°C. Soil
samples were Obtained at l. 2. 4. 6. and 8 weeks.

Table 2. Quantity of material added to 900 gm of soil

to produce constant calcium carbonate equivalent
of liming materials.

 

 

Materials (gms)

 

 

PSEE:CI6 Calcic Dolomitic Basic Oxygen Basic

Limestone Limestone Processed Slag Slag
20-40 6.00 5.16 7.39 9.20
40-60 7.03 5.10 6.87 9.68
60-80 8.32 5.13 6.73 9.55
80-100 8.11 5.13 6.77 9.43
> 100 6.78 5.49 6.82 9.05

 

Constant Surface Area Incubation

previous study.

This incubation study was conducted similar to the

Eight hundred fifty grams of soil and five

21

size fractions of calcic limestone were used. The amount of
> 100 mesh material required was determined on a CaCO3
basis as in the previous incubation study. Other size
fractions were added in sufficient quantities to give
surface areas equal to the surface area of the > 100 mesh
material. Rates added to the soil are shown in Table 3.
Table 3. Quantity of calcic limestone added to 850 gm of

soil to produce constantsnrface area of liming
material.

 

 

 

Particle Size Grams Added
20 - 40 15.87
40 - 60 14.25
60 - 80 16.48
80 - 100 16.75

> 100 6.40

 

METHODS OF ANALYSIS

Soils

Soil pH was measured immediately after sampling of
moist soils with a Beckman (Model G) potentiometer using
a 4:5 soil to water ratio.

Lime requirement of the soil as determined by the
buffer method of Shoemaker. et_al. (26) was 6 tons per acre.

Moisture equivalent of the soil as determined by

the method of Briggs and McLane (5) was 25 per cent.

LiminggMaterials

Calcium carbonate equivalence of the liming materials
was determined by the official A.O.A.C. method as described
by Jackson (12).

Limestone density as determined by water displace-
ment in a pycnometer was 2.75.

Surface areas were determined by four methods:

1. Arithmetically calculated.
2. Oxalate method as described by Barnes (1).
3. Dynamic physical adsorption method as described

by Nelsen and Eggertsen (19). The volume of gas

adsorbed as a monomolecular layer can be determined

from the slope and intercept of the BET equation

as follows:

22

23

m = 91.1.
VmC (l)
_ _l_
b " v c (2)
m

From (2) substitute the value of C into equation (1) to

obtain:

- b (3)

and solve for Vm.

where

_ l
Vm - m + b (4)

 

m = slope.

b = intercept.

Vfi = volume occupied by monomolecular layer. and
C = constant expressing net adsorption energy.

The specific surface is obtained by multiplying Vh
by the area covered by one unit of this volume and
dividing by the sample weight.

Areas were determined using a Perkin-Elmer
Shell Model 212B sorptometer. Four point adsorption
isotherms were determined on materials outgassed
at 160°C for 10-12 hours with helium. The areas of
calcic limestone are the average of 3 different
samples while 2 different samples were averaged for
all other materials. Liquid nitrogen temperatures
were measured with an oxygen thermometer.
Radioactive isotopic exchange method. Samples of

material from 1 to 8 gm were placed in 100 ml of

24

water until saturation equilibrium was reached.

One ml of a Ca45 solution giving approximately 4.000
counts per minute in 100 ml of water was added to
the sample. Ten m1 aliquots were taken at 2. 5.

10. 15. 20. and 25 minutes. These were centrifuged
immediately and a 2 m1 portion placed on counting
plates. Water was evaporated and counts taken to

45 from solution. Amount

determine the loss of Ca
absorbed versus time was plotted and the curve
extrapolated back to 0 time to determine amount
absorbed on the surface of the material.
Radioactive measurements were made on a Nuclear
Measurements Corp. Model DS-l scalar with a Geiger-
Mueller tube having a mica window of 1.4 mg per cm2
density.
Ca45 was obtained from the Oak Ridge National
Laboratory as CaCl2 in HCl. The concentration was

4.30 i 10 per cent mc per ml. The specific activity

of the solid CaCl2 was 14.144 mc per gm.

RESULTS AND DI SCUS SION

.Qetermination of Surface Area of Liming Materials

Four methods were studied to determine their appli—
cability in determining the surface area of liming materials.
Each of the methods will be discussed individually in the

following paragraphs.

Calculation and Oxalate Titration

Table 4 shows the comparison of calculated area to
area determined by oxalate titration. The area determined
increases with decreasing particle size for both methods
but the calculated area increases at a faster rate than
the area determined by titration. The 20-40 or 40-60
mesh titrated area is greater than the corresponding calcu-
lated area for spheres while the reverse is true for the
60-80 and 80-100 mesh material. The calculated area and
the area determined by titration.are about the same
magnitude which would indicate that only external surface
area is measured by the titration method.

Figure 1 supports Motto and Whitefs proposal that
the volume of permanganate used is not directly proportional
to the diameter of the particle for the calcic limestone

studied (18).

25

26

Table 4. Surface area of calcic limestone as determined by
oxalate titration and calculation.

Area (cmZ/gm)

 

 

 

Particle . . l 2
Size Oxalate Titration Calculated (spheres)

20 - 40 51.3 34.9

40 - 60 71.0 65.6

60 - 80 91.2 102.6

80 - 100 106.4 135.9

> 100 422.4 --

1

Area determined by method of Barnes (8 cmz/ml of
.1 N KMnO4).

2 0 0 0
Diameter based on the average of two Sieve Sizes
for each range.

Isotopic Tracer Exchange

Data from the isotopic tracer exchange method of
determining surface area was inconsistent and did not
permit determination of surface areas. Figure 2 is an
illustration of data obtained for Ca45 lost from solution
as a function of time of exchange. The curves for the 20-40
and 40-60 mesh range show a decrease in loss of Ca45 from
solution after an initial increase. The same characteristic
can be detected slightly for the 60—80 mesh material. This
is in contrast to what should be expected. An initially

45

fast removal of Ca with a distinct slower rate of removal

should occur which would correspond to surface exchange and
incorporation of Ca45 within the internal structure

respectively.

 

27

 

 

 

60 IF
db
50 T
g 40 -
v
E
m
z
30 ‘
H
o
LH
o
E
5 20 t
H
o
>
10 '
A
V
O 41 l 1 l l l
100 200 300 400 500 600
Diameter of Particles (u)
Figure 1. Relationship between particle diameter and

quantity of 0.1 N KMnO4 used for titration
of oxalate on calcic limestone.

28

 

 

 

 

 

Sir
A = 20-40 mesh
[:1 = 40—60 mesh
0 = 60—80 mesh .3
[A G
4 — "
H
“P
o
r...
x A
c: 3 '
O .‘I
-a
4.)
5 A
H L.
o
m
E
o
1..
R4
5 2 -
o
r-l
m
.LJ
c
5
o x
U u
l b
4] l l l 1 l
0 4 8 12 16 20 24

Time in Minutes

Figure 2. Loss of Ca45 from solution as a function of time.

29

Different limestone samples varying from 1 to 8
grams in weight were run without a significant change in
amount of Ca45 exchanged. This would suggest that the loss
of Ca45 was by a mechanism other than surface exchange.

It is difficult to explain why this method gave
variable results. The equilibrium of the system may have
been disrupted by addition of the tracer and co-precipitation

45

may have taken place. Ions of Ca would have been removed

from solution as part of the precipitated material. The

subsequent increase in Ca45

ions found in solution may be
the result of exchange of newly precipitated Ca45 ions with
calcium ions in solution. This would cause an increase in
the Ca45 count at a later time. The reason for a fast
initial uptake of Ca45 ions not occurring was perhaps

caused by impurities on the surface of the limestone
particles. These impurities may have masked the exchange
and caused exchange at a slower rate. As cited by Wang (29).
Paneth obtained initial uptake in about one minute for

lead chromate and lead sulfate. These materials were pure

salts. however. The time of initial uptake on the lime-

stone samples was in the range of 5 to 15 minutes.

_§as Adsorption

Materials were obtained from Professor Fripiat of
the University of Louvain. Belgium. that have had surface

areas determined by several laboratories. Table 5 compares

30

the accepted areas1 with areas determined by gas adsorption

on samples of two different weights.

Table 5. Calibration of sorptometer with standard clay
materials of known surface area.

 

 

 

. Sample Accepted Area by
Materials Weight (gms) Area (Mg/gm)1 Sorptometer (Mg/gm)
Kaolinite .0396 45.5
(yangambi) .5530 42.0 50.2
Kaolinite .2212 20.7
(zettlitz) .3032 20.2 20.4
Gel .0314 282.9

.1455 —- 344.0
Gibbsite -- <1 <1

 

lSurface areas by Professor Fripiat. Louvain.
Belgium.

Gibbsite had such a low surface area that adsorption
was hardly detectable. The area found agreed at least
qualitatively with the accepted area. The areas for Zettlitz
kaolinite compared very well with the accepted area. The
area of Yangambi kaolinite deviated from the accepted area
but the deviation was not large. The differences may have
been due to experimental error or to variability between
samples. All of these samples gave good adsorption isotherms.

The areas of the liming materials determined by gas
adsorption are given in Table 6. Preliminary work was done

to determine the best procedure on the sorptometer to obtain

 

l I I I I
Personal communication from Professor Fripiat.
Louvain. Belgium.

31

reproducibility. Warming the sample with room air gave
slow desorption. The slow desorption did not appear to be
reproducible and areas under the curves were inconsistent.
The sample holder was immersed in water at room temperature
immediately after cooling to produce more rapid desorption.
Although this improved the appearance of the desorption
curves. areas determined on the same samples were not

very consistent.

Table 6. Surface area of liming materials as determined
by gas adsorption.l

 

 

Particle Size

 

 

Materials 20-40 40-60 60-80 80-100 > 100
Calcic

Limestone 3.24 3.43 3.13 3.08 8.06
Dolomitic

Limestone .25 .22 .22 .23 .77

Open Hearth
Slag 3.10 4.41 4.83 4.65 4.08

Basic Oxygen
Processed Slag .41 .47 .69 .68 .62

 

Expressed in square meters per gram of material.

The final method tested and the one found to give
most reproducible results was to immerse the sample holder
in water heated to 60°C to produce a rapid desorption.
Repeated determinations on the same sample using this method
gave very reproducible results.

All liming materials studied except dolomite gave

smooth. rapid desorption curves. Curves produced by

32

desorption of nitrogen from dolomite were quite different
from those of other liming materials. For dolomite the
desorption curve would drop below the base line indicating
that adsorption was occurring. The curve would remain below
the base line for approximately two minutes and then return
to the base line. No logical explanation could be
conceived for this behavior. Areas were determined for
dolomite using the point where the desorption curve crossed
the base line and neglecting the portion that fell below
the base line. Consequently. the areas reported for
dolomite are subject to large experimental errors.

Calcic limestone was found to have a surface area
of 10 to 15 times the corresponding size fraction of dolomitic
limestone. Except for the > 100 mesh size there was little
difference in surface area for different particle sizes
of the same material. The finer than 100 mesh fraction has
from 2.5 to 3 times larger area than fractions larger than
100 mesh.

Comparing the external area of the four coarser
fractions of calcic limestone by the titration and calcu-
lation method with the total area suggests that the ratio
of external area to internal area increases with decreasing
particle size while the total area remains constant. This
would be expected if the material in these size fractions
had the same composition and porosity. The higher area
of the > 100 mesh material suggests that the smaller particles

of this class may be primary particles with little internal

33

surface area. Larger particles may be aggregates of these
primary particles.

The surface area of all dolomite particles studied
was less than one square meter per gram. Relative differences
between size fractions probably mean very little because
of the large error in determination of surface areas less
than one square meter per gram. The areas are approaching
that calculated assuming solid spheres which suggest that
the dolomite studied contained very little internal pore
space and may be more crystalline than the calcic limestone
studied.

The two slags appeared to have a large difference
in surface area. Open hearth slag was similar to calcic
limestone while the basic oxygen processed slag compares
with dolomite. Washing the basic oxygen processed slag with
distilled water dissolved a considerable portion of the slag.
This may have altered its surface area as well as its
composition. Except for the 20-40 mesh fraction the
areas are approximately the same for all size fractions.
Most of the open hearth slag less than the 100 mesh size
is just slightly less than 100 mesh consequently the area

is about the same as for coarser fractions.
Incubation Studies

Constant Calcium Carbonate Equivalent

The surface areas of the liming materials added to

produce a constant calcium carbonate equivalent as estimated

34

by three methods for calcic limestone and two methods for
other liming materials are given in Table 7. The change in
pH resulting from liming with each of the materials for

l. 2. 4. 6. and 8 week periods is given in Table 8. Even
though the same calcium carbonate equivalent was added for

each treatment. it is obvious that another factor is

controlling the rate of reaction.

 

 

 

 

Table 7. Surface areas of liming materials applied to the
soil as determined by three methods.
Particle Weight Methods of Determining Area
Materials Size ?dd:? Ca . Adsorp. Titration
gm (cm ) (M2) (cmz)
Calcic 20-40 6.00 210 19.4 308
Limestone 40-60 7.03 461 24.1 499
60—80 8.32 691 26.0 758
80—100 8.11 1094 25.0 863
> 100 6.78 -- 54.7 2864
Dolomitic 20—40 5.16 180 1.3
Limestone 40—60 5.10 335 1.1
60-80 5.13 526 1.1
80-100 5.13 691 1.2
> 100 5.49 -- 4.2
Basic 20-40 7.39 257 3.0
Oxygen 40-60 6.87 451 3.2
Processed 60-80 6.73 691 4.7
Slag 80-100 6.77 913 4.6
> 100 6.82 -- 4.2
Open 20-40 9.20 321 28.5
Hearth 40-60 9.68 635 42.7
Slag 60-80 9.55 980 46.1
80-100 9.43 1272 43.9
> 100 9.05 -- 36.9

 

If surface area controls the rate of reaction of

liming materials.

the rate of disappearance of liming

material as a function of surface area may be expressed

35

 

 

 

 

Table 8. Soil pH as a function of time after addition of
liming materials at constant neutralization
equivalence.

Time of Incubation
Particle

Materials Size 1 week 2 week 4 week 6 week 8 week

Calcic 20-40 5.85 5.87 6.03 6.08 6.16

Limestone 40—60 6.10 6.25 6.45 6.55 6.66

60-80 6.39 6.64 6.90 6.99 7.08
80-100 6.61 6.83 7.15 7.21 7.30
> 100 7.21 7.32 7.49 7.45 7.50
Dolomitic 20-40 5.63 5.66 5.75 5.70 5.79
Limestone 40—60 5.73 5.74 5.90 5.95 5.99
60-80 5.79 5.86 6.05 6.10 6.20
80-100 5.85 5.93 6.19 6.25 6.42
> 100 6.68 6.79 6.95 6.98 7.04

Basic 20-40 5.83 5.94 6.08 6.14 6.20

Oxygen 40-60 6.15 6.33 6.57 6.61 6.65

Processed 60-80 6.51 6.59 6.85 6.89 6.94

Slag 80-100 6.57 6.86 7.04 6.99 7.03

> 100 7.04 7.11 7.15 7.08 7.09

Open 20-40 5.81 5.86 5.95 5.91 5.94

Hearth 40-60 6.02 6.07 6.22 6.24 6.26

Slag 60-80 6.27 6.27 6.45 6.45 6.50

80-100 6.32 6.40 6.58 6.69 6.62
> 100 6.92 6.83 6.92 6.89 6.88
No Lime 5.55 5.59 5.58 5.52 5.46

 

36

by the following differential equation:

dP _ _
dt — kS (1)
where
P = quantity of liming materials present.
t = time;

k = proportionality constant. and
S = surface area.
The quantity of lime material will be proportional to
volume:
P = AV (2)

where

5-
ll

proportionality constant. and

V = volume.
The volume of a sphere as a function of diameter is as
follows:

V =--— (3)
where

d = diameter of particles.
The surface area of a sphere is given by the following
equation:

8 = 1rd2 (4)

Combining equations (2). (3). and (4) yields:

 

 

2/3 1/3
S = 6 w P2/3 = BP2/3 (5)
2/3
A
where
B _ 62/3 F1/3
A2/3

Combining equation (5) and (1) gives the quantity of liming

37

material as a function of time:

dP

Integrating this equation

1/3

P = - 1/3 Bkt + c (7)
At t = to. P = P0; therefore C = P0. The final equation is:
Pl/3 = - K't + P0 (8)
where
l
I =_
K 3 Bk

If it is assumed that the change in the hydrogen
ion concentration in the soil system is proportional to the
rate of disappearance of liming material P. then a plot
of cube root of hydrogen ion concentration against time
should produce a straight line. Figures 3. 4. 5. and 6
givethe plot of the cube root of hydrogen ion concentration
versus time for calcic limestone. dolomite. basic oxygen
processed slag. and open hearth slag respectively. The
curve for the 20—40 mesh calcic limestone approaches
linearity; however. the other size fractions give a linear
curve only in the last 4 weeks of incubation. With dolomite
the curves appear to be linear for all size fractions.

Materials of both calcic limestone and dolomite were
examined under a petrographic microscope to attempt to
explain the differences between materials. Pictures taken
through the microscope of 40-60 mesh calcic limestone and
40—60 mesh dolomite are shown in Figures 7 and 8 respectively.

The calcic limestone consisted of a heterogeneous mixture

38

 

 

12 -
10-
8&—

m

O

H

X

Q 6'

I—i

+f_'

E
4..
2-
O i 1 l l J

 

2 4 6 8 10
Time in weeks

Figure 3. Relationship between cube root of hydrogen ion
concentration in a Warsaw loam surface soil and
time after addition of calcic limestone.

12

10

8
m
c:
H
N

Q 6
H
+f—Q
E

4

2

0

Figure 4.

 

 

0 > 100

2 4 6

Time in weeks

1‘0

(I).-

Relationship between cube root of hydrogen ion
concentration in a Warsaw loam surface Soil and
time after addition of dolomitic limestone.

12

10

8
m
o
H
N
m
\
H

t“ 6
E.

4

2

0

Figure 5.

 

4O

 

 

 

p-

l l

2 4 6 8 10

Time in weeks

4.-
L

Relationship between cube root of hydrogen ion
concentration in a warsaw loam surface soil and
time after addition of basic oxygen processed
slag.

41

 

 

 

 

 

 

12-
10'
8..
m
O
H
X
m
\
s—4 6*-
+I_'I
E
4-
2P
0 I 1 I l J
2 4 6 8 10

Time in weeks

Figure 6. Relationship between cube root of hydrogen ion
concentration in a Warsaw loam surface soil and
time after addition of open hearth slag.

42

 

Figure 7. Calcic limestone. 40—60 mesh particles (100 X).

 

Figure 8. Dolomitic limestone. 40—60 mesh particles (100 X).

43

of clear crystalline particles and darker. porous appearing
particles. Ten particles were obtained of each type and the
time necessary for complete reaction with 5 N HCl determined.
The crystalline material took approximately 50 seconds per
particle to completely react while the porous appearing
material took approximately 35 seconds. The different
reacting rates of the material may mean that the observed
plots were the result of these two types of material. The
faster reacting particles may give a linear relationship
with a large negative slope during early incubation while
the slower reacting particles may give a linear relationship
with less negative slope during the latter part of incuba-
tion. The change in soil pH produced would be a function
of the two types of particles. Although experimental
data are not sufficient during the first four weeks of
incubation to determine the exact nature of the curve. the
experimental points may be the resultant of two linear
curves. The curve for 20-40 mesh material of calcic
limestone was more linear than other fractions. From
microscopic observation it appeared that this fraction
contained very few crystalline particles as compared to
other fractions. thus giving a more homogeneous material.
Dolomite was found to be very uniform in composition
as shown in Figure 8 and appeared to be rather crystalline.
Although the analysis just presented would indicate
that the rate of reaction of liming material is a function

of surface area. it does not distinguish between external or

44

the combination of external and internal surface area.

If soil pH at any sampling time is plotted against
surface area estimated by calculations based on particle
size. a relationship is obtained that is nearly linear at
least for the smaller size fractions. As an example. the
eight week sampling for calcic limestone is shown in
Figure 9. On the other hand. there appears to be no
correlation between total surface area and change produced
in soil pH (see Table 8). This would indicate that external
surface area is much more important than internal surface

area in controlling reaction rate.

Constant Surface Area

Table 9 shows the pH change that occurred when
calcic limestone was applied at constant total surface
area as determined by nitrogen gas adsorption.

Table 9. Soil pH as a function of time after addition of

different particle size calcic limestone at
quantities to give constant total surface area.

 

Time of Incubation

 

 

Particle
Size 1/2 week 1 week 2 weeks 4 weeks

20-40 6.36 6.38 6.38 6.55
40-60 6.69 6.73 6.90 7.09
60-80 6.95 7.06 7.20 7.43
80—100 7.19 7.33 7.49 7.67
> 100 7.35 7.46 7.49 7.62
No lime 5.70 5.62 5.57 5.59

 

45

 

 

7.5 r
7.0 L
I]:
O.
l
H
‘8
m 6.5 L
6.0 P
505 ‘ 1 1 1 1 1 1 l 1 1 1 1 ’1
O 200 400 600 800 1000 1200

Calculated Surface Area (cm2)

Figure 9. Relationship between calculated surface area of calcic
limestone and pH of a Warsaw loam surface soil eight
weeks after lime application.

46

The 80—100 and > 100 mesh material gave similar
rates of reaction in the soil even though about three times
as much material had been applied for the 80-100 mesh
material. The coarser fractions. however. did not react
as fast even though they were applied to give the same
total surface area. This lends evidence to the theory that
internal surface area is not as important as external sur-
face area in controlling reaction rate. particularly in

the coarser fractions.

SUMMARY AND CONCLUSIONS

Methods of determining surface area of liming
materials were studied. Two laboratory studies were con-
ducted by incubating liming materials with an acid Warsaw
loam surface soil to determine the effect of surface area
on rate of reaction of liming materials. The first incuba-
tion study consisted of various size fractions of liming
materials added to the soil at a calcium carbonate equivalence
rate equal to 5.75 tons per acre of pure calcium carbonate
to give different surface areas. The second incubation
experiment consisted of treatments of liming materials
added to the soil at constant surface area as determined
by nitrogen gas adsorption.

The results of these studies are summarized as
follows:

1. Determination of surface area of liming materials
by isotopic exchange is not satisfactory.

2. Determination of surface area by the oxalate
titration method suggested by Barnes (1) agrees

at least qualitatively with surface areas

estimated by calculations assuming spherical

particles. This would indicate that both methods
give an indication of external surface area only.

Surface area determined by nitrogen gas adsorption

47

48

appear to measure both internal and external surface
area.

Total area of calcic limestone studies appeared to
be constant for particle sizes coarser than 100
mesh while the ratio of external area to internal
area increases with decreasing particle size.

A plot of diameter of particle versus volume of
KMnO4 used for titration of oxalate is not a

linear function as suggested by Barnes (1).

Rate of reaction of liming materials studied appears
to be largely dependent upon the external surface
area of the material. However. internal surface
area may also influence reaction rate to some
extent.

A function was derived which indicated that the

cube root of the hydrogen ion remaining in the soil
system would be a linear function of time if surface
area of the liming material is controlling the rate
of reaction. Reaction of dolomite appeared to
follow this function; however. the reaction of
limestone followed this function only during the
latter stages of incubation.

Microscopic examination indicated that the dolomite
studied was uniform and crystalline in nature:
whereas. the calcic limestone studied was hetrogeneous
containing a portion of slow reaction crystalline
material and a faster reacting. porous appearing

material.

10.

11.

12.

LIST OF REFERENCES

Barnes. E. E. A.new method for estimating the surface
of liming materials and other insoluble calcium
compounds. Soil Sci. 63:285-289. 1947.

Bear. F. E.. and Allen. L. Relation between fineness
of limestone particles and their rate of solution.
Indus. and Engin. Chem. 24:998-1001. 1932.

Berl. Walter G. Physical Methods in Chemical Analysis.
Academic Press. New York. 1951.

Bishop. R. F. The effect of lime on the chemical com-
position of a Charlottetown fine sandy loam and the
effect of several amendments on its content of
water-soluble boron as shown by soil and plant
analysis. Ph.D. Dissertation. Michigan State
University. 1953.

Briggs. L. J.. and McLane. J. W. The moisture
equivalent of soils. U.S.D.A. Tech. Bul. 45. 1907.

Brunauer. S. The Adsorption of Gases and Vapors.
Princeton University Press. Princeton. 1945.

Brunauer. S.. Emmett. P. H.. and Teller. E.
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