AN WVESTIGA'E’EON OF SOME MEWODS
OF Clv'iEAMCAL PRECWI'E'ATSON IN THE
MUS ECIAL GRG‘NTH OF CALCWE

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This is to certify that the
thesis entitled

"An Investigation of Some Methods of
Chemical Precipitation in the Artificial
Growth of Calcite"

presented by

Robert F. Curran

has been accepted towards fulfillment

of the requirements for

__M_'S'__ degree in M

mlw

 

 

Major professor

Date May 201 1953

 

AN INVESTIGATION OF SOME METHODS
OF CHEMICAL PRECIPITATION IN
THE ARTIFICIAL GROWTH

OF CALC ITE

BY
Robert F . Curren

A THEIS

Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
' in partial fulfillment of the requirements
' for the degree of

MASTER OF SCIENCE

Department of Geology and Geography
1953 x.

“1‘ 9/) 2

ACKNOWLEDGEMENTS

The writer wishes to express his appreciation to the staff members
of the Department of Geology and Geography at Michigan State College
for their helpful suggestions and assistance. Dr. Justin Zinn, under
whose direction the report was prepared, is thanked both for his
initial encouragement which made this investigation possible and for
his inyaluable guidance as the work progressed. He is also greatly
indebted to Dr. S. G. Bergquist for his critical review of the manu-
script and gracious assistance in obtaining the necessary apparatus

and facilities.

9’1
%5;
h“-
2::
p.

Tables . . . . . . . . . . .
Illustrations . . . . . . .
Abstract . . . . . . . . . .
Introduction . . . . . . . .
Apparatus and Methodology .
Results . . . . . . . . . .
Conclusions . . . . . . . .
Suggestions for Future Study
Appendix .|. . . . . . . . .

References . . . . . . . . .

CONTENTS

iii

Page

iv

vi

16

23

25

27

TABLES

Table Page

I' Results of Precipitation by Carbon Dioxide Method . . . . . 24
II Results of Precipitation by'Mixing of Solutions . . . . . . 25

III' Growth of Seed Crystal in Erlenmeyer Flask . . . . . . . . 26

iv

ILLUSTRATIONS

Plate Page

I Diagram of apparatus for precipitation by carbon
diOfide O O O O O O O O O O O O O O O O O O O O O O O O 8

II Diagram.of apparatus for precipitation by mixing
of solutions . . . . . . . . . . . . . . . . . . . . . 13

III Curve showing variation in rate of growth with rate
of solution flow in precipitation by carbon
diOXide O O O O O O O O O O O O O O O O 0 I O O O O 0 0 17

IV Curve showing variation in rate of growth with time
in precipitation by mixing of solutions . . . . . . . . 19

V Curve showing variation in rate of growth.with time
(Erlenmeyer flask) in precipitation by mixing of
S o lutions . O . O C . O O O O O O C O O O O O O O O O C 19

AN INVESTIGATION OF SOME METHODS
OF CHEMICAL PRECIPITATION IN
THE ARTIFICIAL GROWTH

OF CALCITE

By

Robert F. Curren

INTRODUCTION ’

Many diverse forms of apparatus have been designed for the artificial
growth of crystals, and a variety of chemical and physical principles
are employed to this end. The underlying principle, common to all
methods of growing crystals from solution, is that of producing a super-
saturated solution (one containing an amount of the solute in excess of
its normal solubility) from which ions may be deposited to build up the
crystal lattice of a nucleus or seed crystal. In instances where seed
crystals are introduced into such a solution it is desirable to keep the
number of crystal nuclei which will form spontaneously at a minimum so
that the growth will occur primarily upon the seed crystals. It is also
desirable to keep the number of nuclei formed as small as possible when
crystals are to be grown without seeding the solution so that the crystals
thus formed will reach the maximum possible size.

The number of crystal nuclei which will form depends upon the degree

of supersaturation of the solution as expressed by the Von Weimarn ratio

-L
Degree of supersaturation : 9..

L
where Q is the total concentration of the salt in solution and L is the
equilibrium solubility of the salt. It is apparent from the above
relationship that the most favorable conditions for crystal growth are ‘
obtained when a state of continuous but slight supersaturation exists in
the solution from which the crystals are to be grown.

This condition may be readily obtained when the material to be grown
has a reasonably high solubility by evaporating at a slow rate a portion
of the solvent from a saturated solution of the salt. When provision is
made to prevent the formation of additional crystals at the surface of
the solution and to provide for adequate circulation of the solution
around the suspended seed crystal, this method produces excellent results
and has been used successfully to produce crystals of a considerable
number of substances.

Advantage is taken of the appreciable difference in solubility with
temperature which is a property common to a number of substances. By
changing the temperature of a saturated solution slowly in the direction
of decreasing solubility, a condition of supersaturation is obtained in
the solution and growth upon the crystal occurs. The actual apparatus
employed generally provides some means whereby the solution is heated at
one point in the presence of an excess of the salt and conducted to the
point at which the crystal is suspended, where it is cooled to decrease
the solubility of the salt. Naturally, in substances whose solubility
decreases with increasing temperature the heating and cooling processes

are interchanged.

-3-

Frequently less direct methods must be devised to obtain the
necessary condition of supersaturation in the solution. In substances of
limited solubility use may be made of the common ion effect in which a
soluble salt containing one of the ions of the salt to be crystallized
is added to a saturated solution of that salt causing precipitation. A
familiar example is the addition of hydrogen chloride to a saturated
solution of sodium chloride, causing the sodium chloride to crystallize
out of solution, the chloride ion, of course, acting as the common ion.
This method is not applicable to the preparation of crystals of salts of
very low solubility.

A limited number of substances virtually insoluble in water are
appreciably soluble in mixtures of water and various organic solvents.

A solution of these salts in water and the organic liquid may be pre-
pared and crystallization of the salt accomplished by the controlled
removal of the organic liquid.

Other methods include the controlled decomposition in solution of a
soluble salt. This method is applicable when the salt to be crystallized
is one of the decomposition products of and has an appreciably lower
solubility than the salt originally placed in solution. Simple chemical
precipitation may be accomplished by combining solutions of soluble salts,
each of which contains one of the ions of the insoluble salt whose
crystals are to be prepared. Although simple in theory, this last
method is difficult to adapt to crystal growth and no record was found
of the development of a technique which was even moderately successful.

It may be readily appreciated that most of the above methods may

not be used in growing crystals of calcite simply because calcite does

-4-

not possess the properties of which these methods were designed to take
advantage. The solubility of calcite is 1.45 x 10"3 grams in a hundred
grams of solution at 17° C. The carefully controlled evaporation of
almost seventy liters of solution would thus be required to deposit one
gram of the material. The insignificant change in solubility with tempera-
ture makes this method, too, impractical for the growth of calcite.
Because of the low solubility of calcite the common ion effect may not

be used to advantage nor is there any known organic solvent which, when
combined with water, might dissolve a sufficient quantity of the material
that slow extraction of the organic solvent might facilitate precipita-
tion. 0f the methods previously described only the decomposition
reaction and the chemical precipitation appear to offer the possibility
of adaptation to the growth of calcite and these are the only methods
which are mentioned in the literature concerning crystal growth.

Although investigations concerning the artificial preparation of
crystals have been conducted at an ever-increasing rate during the past
hundred or more years, very little record exists of the development of
methods by which crystals of calcite may be grown in the laboratory.

Buckley'makes reference to the work of H. Vater in 1899 in preparing
calcite crystals from solution by the slow conversion of calcium bicarbon-
ate to calcium.carbonate by heating the solution. The reaction is given

by the following equation:

Ca(HCb3)2 -EEEEQ—9 ’CaCO3 + H20 + CO2

The growth was controlled by regulating the rate at which the carbon
dioxide was permitted to escape from the system. The solubility of
calcium bicarbonate at 100° C is 0.1660 grams in 100 grams of water,
while that of calcium carbonate is 1.45 x 10'”3 grams. Thus, the conversion
of one liter of a saturated bicarbonate solution would yield nearly
1.22 grams of calcium.carbonate.

Crystals of many minerals, including calcite, have been prepared
through chemical precipitation by separating with a membrane solutions of
soluble salts, each of which contains one of the ions of the mineral to
be grown. As the solutions diffuse slowly through the membrane chemical
reaction proceeds to produce cryStals of the desired mineral. The mem-
brane, however, soon becomes clogged with the insoluble precipitate and
the resulting crystals do not attain more than microscopic size.

Since so little investigation has been conducted on methods of
chemical precipitation in the artificial growth of calcite crystals and
inasmuch as this method appears to offer one of the very few possibilities
of application to the problem of growing calcite, it has been selected
for further investigation insofar as it may be adapted to the growth of
calcite. The methods employed and the reSults obtained will be dis-

cussed in subsequent sections of this thesis.

-6-

APPARATUS AND I~ETIDDOLOGY

Two separate methods of effecting the precipitation of calcium
carbonate from solution were employed and apparatus was assembled to
adapt these methods to the growth of calcite crystals. The first method
involved the precipitation of calcium carbonate from a solution of calcium
hydroxide by the reaction of the solution with carbon dioxide. In the
second method the carbonate was precipitated by the controlled mixing of
solutions of calcium chloride and sodium carbonate. These two methods
will subsequently receive detailed description and will be discussed

separately, for the most part, throughout the remainder of this paper.

Precipitation with Carbon Dioxide

At 25° C the solubility of carbon dioxide is about 0.15 grams in
one hundred milliliters of water, which is equivalent to a concentration
of 0.034 moles per liter. The carbon dioxide and water unite chemically
to form.a dilute solution of carbonic acid (H2003) which ionizes in two
steps as represented by the equations:

. H2003 —---) H" 4- H003“
(3*) 01003“)
(H2003)

= 305 X 10-7

 

and

Hco3 ———> H" +003

(H") (CO "')
3 = 7.0 x 10'11

 

(3003-)

In calculating the carbonate ion concentration from the latter equation,
the hydrogen ion and bicarbonate ion concentrations are found to be very
nearly equal and will cancel in this expression. The carbonate ion
concentration is, therefore, equal in value to the second ionization
constant, namely, 7 x 10'"11 mole per liter. Since the solubility product
constant for calcium.carbonate at 25° C is 8.7 x 10""9 mole per liter it
is apparent that precipitation.of calcium carbonate from a solution of a
soluble calcium salt by the direct addition of carbon dioxide may not be
accomplished unless the equilibrium can be shifted so as to produce a
greater concentration of the carbonate ion.

The increase in concentration of the carbonate ion may be accomplished
by lowering the hydrogen ion concentration through the addition of a
base. Calcium hydroxide is the only compound which will fulfill the
requirements of providing a source of calcium ions as well as furnishing
the basic ions to lower the hydrogen ion concentration and is, therefore,
the only calcium.salt which, in solution, will combine with carbon
dioxide to produce a precipitate of calcium carbonate.

The apparatus designed to adapt the above reaction to growing crystals
of calcite (see Fig. I) consisted of a two hundred millimeter test tube
with a sidearm.opening near the top of the tube, this opening being

connected by rubber tubing to a carbon dioxide generator constructed to

Tip of Separatory
Funnel

 

 

 

 

 

 

 

 

 

 

 

\\ K N
A») '
II/r/P
Seed Crystal
l
I
l
l
05.]. Film —A Raf. L
Siphon

 

 

 

 

Fig. I. Apparatus for precipitation by carbon dionde

-9-

maintain a constant pressure of the gas very slightly in excess of
atmoSpheric pressure. The top of the test tube was closed by a two-hole
rubber stopper through which the tip of a 125 milliliter separatory
funnel extended into the tube about one inch. One end of a U-shaped
section of small diameter glass tubing reached to the bottom of the test
tube through the stopper, and was used to withdraw the used solution
which collected in the test tube. The seed crystal was suspended by a
piece of Chromel wire about one centimeter below the tip of the separa-
tory funnel. The entire apparatus was clamped to a ring stand for
support. ‘

The seed crystals used in this investigation were small cleavage
rhombohedrons of clear calcite. In activating the apparatus the air was
swept from.the test tube with carbon dioxide, the rubber stopper from
which the seed crystal was suspended was fitted into place, and the stop-
cock of the separatory funnel which contained the calcium.hydroxide
solution was opened slightly to permit the solution to drop»at a slow
rate upon the seed crystal. Thus, the surface of the seed crystal was
continuously'coated with a film of the calcium hydroxide solution which
reacted with the surrounding athSphere of carbon dioxide to precipitate
calcium.carbonate. One distinct advantage of this method was that the
chemical reaction occurred only in the thin film of solution at the
surface of the seed crystal. It was anticipated that by keeping at a
minimum.the amount of solution reacting at a given time, the tendency
for crystal nuclei to form.could be kept at a low value and the greatest
peasible proportion of the precipitated calcium.carbonate could be trans-

lated into growth upon the seed crystal.

A series of nine trial runs of this apparatus were made with growth
periods ranging from 24 hours to two weeks. During this period the
apparatus was adjusted and modified as needed so as to provide a‘system
whereby the process might continue over extended periods of time with.a
minimum.of attention.

A bank of six of these units was set up using five hundred milliliter
distilling flasks in place of the test tube. Carbon dioxide was provided
by a single generator which was connected to the sidearm of the flasks
by means of rubber tubing. Solution was supplied to the flasks from.a
350 milliliter separatory funnel, and the rate of flow of the solution
to each individual flask was controlled by adjusting a screw clamp
placed upon the rubber tubing connecting the flask with the separatory
funnel.

The seed crystals were carefully weighed and suspended in the flasks
and the flow of solution to each flask was adjusted at a different rate.
The process continued without interruption for a period of 18 days. At
the end of this period the crystals were removed from the flasks and
reweighed. The concentration of the calcium hydroxide solution was
determined analytically and samples of the solution which collected in
the bottom.of each flask, having been protected by a thin layer of light
oil from further reaction with the carbon dioxide, were analyzed to
determine the amount of unreacted calcium hydroxide remaining in the

solution.

-11..

Precipitation by the Mixing of Solutions

This method involves the precipitation of calcium.carbonate by the
addition of calcium chloride to a solution of sodium carbonate, accord-
ing to the reaction

—

By controlling the rate at which the solutions were combined, any degree
of supersaturation relative to calcium carbonate could be obtained.
Theoretically, at a low degree of supersaturation few, if any,
crystal nuclei.should ferm. In practice, however, the initial mixing of
the two solutions could not be accomplished with sufficient thoroughness
to avoid local concentrations great enough to initiate crystal formation.
Once crystallization has begun, it proceeds rapidly until all calcium
carbonate present in the solution in excess of its normal solubility is
precipitated as fine crystals. While it would appear that a state of
supersaturation could not be maintained in the solution under these
conditions, this is not true if the dimensions of the crystals thus
formed lie within certain low size limits. These crystals are more
soluble (supersoluble) than are the larger crystals and a conditidn of
supersaturation is maintained until the small crystals are completely
dissolved and the solution reaches a state of equilibrium with the
precipitated material. The concept of the larger crystals growing at
the expense of smaller ones in the same solution is a familiar one to
most chemists, and frequent use is made of this principle in causing a

precipitate to become coarser, thereby increasing the ease of handling.

-12—

It was noted that the time required for the settling of calcium
carbonate crystals (prepared by the mixing of solutions of calcium
chloride and sodium.carbonate) decreased rapidly for several hours
following the initial preparation, and continued to decrease noticeably
for several days. The growth of these crystals, as indicated by the
increased settling velocity, provided evidence that crystals sufficiently
small to be supersoluble were formed in the mixing of these solutions.
Thus, it would appear that the necessary state of supersaturation could
be maintained.

In constructing the apparatus with which to adapt these principles
to the artificial growth of calcite, it was recognized that, while the
multitude of tiny crystals formed by the reaction were necessary in
maintaining the supersaturation of the solution, their presence in the
crystallizing vessel would cause considerable difficulty. For the
purpose of carrying off these tiny crystals and preventing them, insofar
as was possible, from settling on the seed crystals, it was considered
desirable to have a constant flow of water through the vessel.

A A two hundred millimeter test tube (see Fig. II) with sidearm.open-
ing near the top served as the crystallizing cell. Through a two-hole
rubber stopper were inserted short lengths of small diameter glass
tubing, each of which had the lower end drawn out to a reduced diameter
and bent upward in the form.of a hook. The longer of these tubes
reached to the bottom of the test tube, while the lowest portion of the
other reached a point about one inch above the bottom of the test tube.

The shorter tube was connected by rubber tubing to a glass siphon

 

 

 

 

 

 

 

 

l/ Ai Bl ed '
r e ‘ To Container of
To Container \q Calcium Chloride
of Sodium Carbonate > “ - Solution
Solution \
f
Overflow

 

 

 

(in

 

 

 

 

 

 

 

A 3 g:

I
Connected /
to Water Tap NJ

 

 

 

 

Seed Crystals

 

 

 

 

 

Fig. II. Apparatus for precipitation by mixing of solutions

-14...

placed in a two liter bottle of the calcium chloride solution. The
longer tube was connected through two glass "Y" tubes to the water tap
by means of rubber tubing. The “Y“ tube nearest the tap provided the
inlet fer the sodium carbonate solution, which was automatically with-
drawn from a four liter beaker by means of a siphon connected to the "Y".
The second "I" tube served as an air bleed, the bubbles of air thus
released at the bottom.of the test tube aiding materially in mixing the
solutions. The sidearm of the test tube served as an overflow and was
equipped with a piece of rubber tubing to carry off the surplus solution.
Flow of the solutions was controlled with screw clamps. The seed crystals
were suspended on short lengths of Chromel wire within the test tube.

During preliminary runs with the apparatus it was noted that a hard
coating of calcium carbonate formed upon objects with which the overflow
solution came in contact, indicating that the solution was still super-
saturated at this point. A second crystallizing cell in the form of a
two hundred milliliter Erlenmeyer flask was, therefore, connected to the
lower end of the overflow tube. The solution was carried to the bottom.
of the flask by a short piece of glass tubing extending through the two-
hole rubber stopper closing the neck of the flask. Escape for the
solution was provided at the top of the flask by a second length of
glass tubing which curved downward on the outside of the flask in the
form of a siphon. The seed crystals were suspended in the solution on
silk threads attached to the stopper.

Actual control of the degree of supersaturation was accomplished by

regulating the rate of flow of the calcium chloride solution into the

-15-

test tube. The concentration of the calcium chloride solution was
determined analytically and the extent to which it was subsequently
diluted was determined by measuring the total flow through the outlet
during a given time interval. The flow of the sodium carbonate solution
was not actually measured, but was maintained at a rate slightly in excess
of that necessary to react with the amount of calcium chloride present in
the solution at any time. Frequent checks were made on the solution
escaping through the overflow tube to assure that the necessary level of
carbonate ion concentration was being maintained. A number of separate
runs were made with this apparatus at a variety of different degrees of
supersaturation. The seed crystals were weighed prior to and at the end
of each run to determine the amount of growth, and frequent microscopic
examinations of the growing crystals were made to determine the nature

of the growth.

-15-

RESULTS

Precipitation with Carbon Dioxide

An initial run of 18 days duration was made with the bank of six
units previously described at rates of solution flow ranging from 2.1 to
8.3:milliliters per hour. The seed crystals were removed from the flasks
at the end of this period and were reweighed after being cleansed to
remove the coating of small crystals (fermed by the chemical reaction)
which adhered to the surface. Results of this run indicated that
solution of the seed crystals had occurred, the loss of weight varying
inversely with the rate of flow of the solution over the crystal.
Although all of the crystals were somewhat reduced in weight, the results
suggested that growth might be expected to occur at rates of flow higher
than those which were used. Accordingly; a second series of runs was
made at rates varying from.5.9 to 47.6 milliliters per hour. Because of
the large volume of solution required to maintain a flow at these rates
a two liter bottle with a siphon was substituted for the separatory
funnel and the period of time over which the run was made was reduced to
twelve days.

The crystals were cleansed and weighed as previously described and
it was found that growth occurred at rates of flow greater than twenty
milliliters per hour. The results of the two runs were combined and
are presented in Table I. The variation in change of weight of the

crystal with rate of solution flow is shown graphically in Figure III.

-17-

 

 

 

 

2
0
(.0
G
A 0
‘ H
-3 0
.- +5
+3 0 --
'5.
0H
0
3
0
50 2.1L.
0 a
H 63
° 2
49 0
§ 8
4 __
O
E
O‘
U)
éj l f l

2 ' 5 10 20 50
Rate of Flow ( ml./ hr.)

Fig. III. Variation in rate of growth with rate of solution~flow

It was found that the relationship most closely approached linearity
when the square root of the change in weight in milligrams was plotted
against the log of the rate of flow in milliliters per hour, and

Figure III has been prepared in this manner.

-18-
Precipitation by the Mixing of Solutions

Preliminary runs with this apparatus indicated an appreciable
variation in the rate of growth with time and a series of determina-
tions was planned by which this variation might be measured. The
calcium chloride solution was standardized and found to be 0.1560 molar.
The total flow of solution through the overflow tube was measured
(150 milliliters per minute) and the amount of calcium chloride
solution which must enter the crystallization tube to maintain one
degree of supersaturation of calcium carbonate in the solution was
calculated as sixteen milliliters per hour.

A series of runs was made at one degree of supersaturation over
periods of twelve, twentyhfour, and sixty hours. At the end of each
period the crystals were removed, cleansed and reweighed, and the
interior of the apparatus was rinsed with dilute hydrochloric acid to
remove all traces of calcium carbonate. The series of runs was repeated
,at two and five degrees of supersaturation and the average increase in
weight of the three seed crystals used in each run is shown graphically
in Figure IV.

The crystals in the Erlenmeyer flask continued to grow over a
somewhat longer period of time and did not show a significant change
in rate of growth with change in supersaturation. The amount of growth
occurring on these crystals under varying conditions is given in
Table III and the average of these results has been used in preparing

Figure Ve

3

Increase in Weight (mg.)

Increase in Weight (mg.)

 

 

 

 

 

 

 

 

 

 

 

6 -
Five Degrees of Supersaturation
5 a!
Two Degrees of Supersaturation
4 .
One Degree of Supersaturation

3 -1

2 «4

1 .J

O 7‘ T I 1 “IT‘ ““““ T

0 10 20 30 40 50 60
Time (hrs.)
Fig. IV. Variation in rate of growth with time

8:

7e

6-

5i

4-1

3..

2%}

Growth in Erlenmeyer Flask
1+
0 r l r l f II I
0 20 40 60 80 100 120 11.0
Time (hrs.)

Fig. V. Variation in rate of growth with time

 

-20-

CONCLUSION

Precipitation with Carbon Dioxide

While growth upon the seed crystals occurred at rates ranging up—
ward from approximately 20 milliliters per hour, this method obviously
does not offer a practical solution to the problem of growing crystals
of calcite. The results indicate that roughly'AOO liters of saturated

calcium hydroxide solution (containing 660 grams of Ca(0H)2) flowing at

a rate of 40 milliliters per hour for 400 days would be required to
increase the weight of the seed crystal by one hundred milligrams.

Probably the major weakness in this method is a result of the low
solubility of the calcium hydroxide. The reaction between the carbon
dioxide and calcium hydroxide is virtually instantaneous and the forma-
tion of tiny crystals of calcium carbonate is apparent in the clouding
of the solution as it drops into the atmosphere of carbon dioxide.

While the hydroxide ion is present in the solution, the reaction

proceeds. When the hydroxide ion is depleted by this reaction the
concentration of carbonic acid in the film of solution surrounding the
crystal increases and the following reaction occurs between the

solution and the crystal:

CaCOB + H2903 --9’Ca(HCO3)2

-21-

At 20° C the solubility of calcium bicarbonate is 0.1840 grams in

100 grams of water while that of calcium hydroxide is 0.165 grams in

100 grams of water. If a drop of the solution remained on the surface

of the crystal sufficiently long for the second reaction to reach

completion, a net loss of as much as 190 milligrams of calcium carbonate

from the seed crystal per liter of solution might be expected to occur.
The greater part of the calcium.hydroxide in solution appears to

be precipitated in the form of crystals which are not sufficiently

small to be supersoluble. It must be concluded that an appreciable

degree of supersaturation cannot be maintained in the solution surround-

ing the seed crystal and that growth at any but an exceedingly slow

rate is not possible under these conditions.

Precipitation by the Mixing of Solutions

Although a high initial rate of growth was obtained, certain
limiting conditions must be overcome before this method may be con-
sidered successful for growing crystals of calcite. A deposit of small
crystals of calcium carbonate accumulated rather rapidly on the inside
of the crystallization tube. This deposit on the interior of the tube
presented a surface upon which growth might occur that was many times
greater than the surface area of the seed crystal, and tended to absorb
most of the growth potential of the solution. In addition, a soft
crust of the small crystals formed in the solution tended to collect on
the surface of the seed crystal, effectively insulating it against

further growth.

—22_

In the Erlenmeyer flask connected to the overflow tube these
conditions developed less rapidly and as a result the growth continued
over a somewhat longer period. Due largely to previous settling of the
suspended particles, the solution flowing through the flask remained
essentially clear at all degrees of supersaturation. Although the forma-
tion of a carbonate coating on the sides of the flask was slower to
develop and the growth period was correspondingly increased, no method
was feund to completely eliminate this difficulty and a period of growth

of more than a few days duration could not be attained.

SUGGESTIONS FOR FUTURE STUDY

Calcite is a mineral of considerable geologic importance, and the
study of the conditions under which it will crystallize from solution
may be applied directly to the formation of limestone by chemical
precipitation and to the cementation of various sediments.‘

The calcium carbonate-carbon dioxide equilibrium is significant in
both the solution and deposition of calcite under conditions found near
the surface of the earth. A successful study of this equilibrium.would
represent an important contribution to the knowledge concerning the
actual mechanics involved in these processes.

In the opinion of the writer the most fruitful avenues for further
investigation are:

(1) Continued study of the method of growth involving the

mixing of solutions with the aim.of reducing or
eliminating the factors which limit the length of
the growth period. The use of substances which

would serve as mineralizers may be an appreciable
aid toward achieving this end.

(2) The rate of increase in the permeability of limestones
caused by the migration through them.of water carryb
ing dissolved carbon dioxide at various pressures.
This might be related to the redeposition of
calcium carbonate in unconsolidated sediments upon
release of pressure.

APPENDIX

TABLE I

RESULTS OF PRECIPITATION BY CARBON DIOXIDE METHOD

 

 

Time Total Soln.

(Dara) (ml.)
18 9MB
18 1,030
18 1,300
18 1,860
18 3,010
18 3,540
12 1,700
12 3,600 ‘
12 5,320
12 7,370
12 11,210
12 13,700

 

 

 

Flow Per
Hr. (ml.)

1.. u“

-e" ‘1; :‘1’ '

2.1
2.4
3.0
4.3
7.2‘
8.3
5.9
12.5
18.5
25.6
38.9
47.6

Change in Wt. (mg.)

 

 

1?

i
I

 

 

-- --'.-a --‘. s'w-‘a-M

Total

-93.0
-72.0 1
-53.0
-30.0
-l2.0

-9.0.

-11.5
- 1.5

1.0 '

1.5
5.0

I

P

I

D

 

Far 6 Days
run-vi.- -

- -.-.-~ “wuss-Is.- ,

—31
-24

-17.7
- 9.3
- 4.0
- 3.0
- 5.8
- .7

Not Measurable

.5
.7
2.5

.y.-

I
1
l
J
l

 

—_.- ,4... .“~._A_- -

 

5.57
4.9
4.20
3.05
2.0
1.65
2.39
.84

.7
.84
1.6

Sq. Root of
Change Per 6 Days

- ..0 *em- r'rr m-mn'v-w-c—

 

 

—_

Av. Increase
in Wt. (mg.)

3.1
4.1
3.7
4.3
4.4
5.7
6.2
6.1

4.1

trill-'1‘ 4'

 

‘L—u “A“.

Increase '

in Wt. (mg.)

340. “ma/wow 824 40.6. 848 6.6.0. Qua/Mow 236. Owen?“
233 443 341m 343 443 444 655 6.56. 656

 

TABLE II
Time

(Hrs.)

 

 

 

RESUIES OF PRECIPITATION BY MIXING OF SOLUTIONS

Degrees of Supersaturation

 

 

 

u u ,w m u w n u w
l 2 5

~ II a _.I.—-_mr.m

 

'IZ’I"\.,.

 

TABIE III

GHJWTH OF SEED CRYSTAL IN ERIHVWR FLASK

—26—

 

 

Time (Hrs.)
12 121+ w w60 96 156
1.8 4.2 6.6 7.2 7.4
2.0 4.2 6.2 7.0 7.4
2.0 4.4 7.0 7.4 7.7
W' ”W 44.2"“ " " W W W
2.0 4.3 6.6 7.2 7.5

 

 

 

 

 

~-.---—-~- ‘P'VP '- vtv-c-u

 

v

..- «run-0* ~ *P—v—

 

 

 

-27-

REFERENCES
1.

Buckley, H. E. (1951) CEYStal Growth, New York, John Wiley & Sons,
Inc . , passim.

2. Hogness, T. R. and Warren Johnson (1947) Mlitativflnalysis and,
Chemical E‘gnilibrimn, 2d. ed. New York, Henry Holt 8c 00.,
pp. 163-165.

3.

Pierce, W. C. and E. L. Haenisch (1948) anntitative Analysis,
3d. ed. New York, John Wiley & Sons, Inc., Ch. 18 & 19.

yM

MM

'2‘ .

 

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T548 30:1?1

C97: Curran

T548 304191
0976 Curren
.An investigation of
some methois of chemical
precipitation in the
artificial growth of
calcite.

2 h
/4 C31?" /' '4...

 

 

 

 

 

 

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1293 02446 8666