WAPD-TM-204 AEC RESEARCH AND

DEVELOPMENT REPORT

THE BEHAVIOR OF ELECTROLYTIC SOLUTIONS AT ELEVATED TEMPERATURES AS DERIVED FROM CONDUCTANCE MEASUREMENTS

JUNE 1961

CONTRACT AT-1 1-1 -GEN-14

BETTIS ATOMIC POWER LABORATORY, PITTSBURGH, PA., OPERATED FOR THE U. S. ATOMIC ENERGY COMMISSION B Y WESTINGHOUSE ELECTRIC CORPORATION

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

UC-4 Chemistry TID-4500 ( 1 6th Ed.)

THE BEHAVIOR OF ELECTROLYTIC SOLUTIONS AT

ELEVATED TEMPERATURE AS DERIVED

FROM CONDUCTANCE MEASUREMENTS

J. M. Wright, W . T. Lindsay, Jr., and T. R. Druga

June 1961

Contract AT-1 1-1 -GEN-14

Price $ .75 Available from the Office of Technical Services,

Department of Commerce,

Washington 25, D. .C.

NOTE This document is an interim memorandum prepared primarily for internal reference anc does not represent a final expression of the opinion of Westinghouse. When this memorandum i s distributed externally, i t i s with the express understanding that Westinghouse maker no representation as to completeness, accuracy, or usability of informa- tion contained therein.

BETTIS ATOMIC POWER LABORATORY, PITTSBURGH, PA., OPERATED FOR THE U. S. ATOMIC ElNERGY COM.MISSION B Y WESTINGHOUSE ELECTRIC CORPOIRATION

STANDARD: EXTERNAL DISTRIBUTION

UC-4: Chemistry, TID-4500 (16th Edition)

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Manager, Piksburgh Naval R e a c b r a Operations Office, AEC Direztor, Development Division: PIJROO Westbghouse, Plant Apparatus B p a r t r n e ~ t , J. D. Batey

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-

CONTENTS

I. . INTRODUCTION

Page No.

1

11. REVIEW AND INTERPRETATION OF THE NOYES CONDUCTANCE DATA

A. Empirical Method for Determining Complete Ionization of Uni- univalent Electrolytes

B. Equations Describing the Conductance Behavior of Strong 1-1 Electrolytes

C. Determination of A' and the Dissociation Constant, K , for Electrolytes Which Associate

D. Use of the Bjerrum Theory to Determine if Ion-Pair Forma- tion Explains the Decrease in Ionization of Electrolytes at Ele- vated Temperatures

111. MEASUREMENT OF THE CONDUCTANCES OFLiOH AND lu?I OH SOLUTIONS OVER THE TEMPERATURE RANGE OF 100 to 528 F

A. Description of the Apparatus

B. Operational Procedure

C. Specific Conductance of the Water

D. Equivalent Conductances of NH40H Solutions over the Tempera- ture Range of 100 to 560 F

E. Equivalent Conductances of LiOH Solutions over the Tempera- ture Range of 100 to 520 F

F . Best Values for the Equivalent Conductances of NH40B and LiOH at Temperature Intervals of 40 F

G. The Behavior of LiOH Solutions at Elevated Temperatures

H. Behavior of NH40H Solutions at Elevated Temperatures

IV. THE ION-PRODUCT OF WATER AT ELEVATED TEMPERATURES

V. CHANGE IN THE pH OF H20, LiOH,AND NH40H SOLUTIONS WITH TEMPERATURE

VI. SUMMARY AND CONCLUSIONS

APPENDIX I. Data Compiled by Noyes on Various Electrolytes at Elevated Temperatures

REFERENCES

iii

, .- TH1.S PAGE,:; . . '., . . . . . ' - . .

'i .

WAS INTENTIONALLY LEFT BLANK

This project was initialed a ) the Bettis Alomic Power Laboratory to devise methods and technique; for measuring the conductances of reac t~ r solutions at elevated temperatures and to interpret the results with electr~lytic solution theories. This conductance information leads to a better underslanding of the behavior of reactor solutions at elevated te.nperatures and permits recnsonable speculation to be mode regarding behavior of proposed reactor coolant additives.

THE BEHAVIOR OF ELECTROLYTIC SOLUTIONS AT ELEVATED TEMPERATURES AS DERIVED FROM COhDUCTANCE

MEASURE ME NTS

J. M. Wright, W. T. Lindsay, J r . , and T. R. ~ r u g a

I. INTRODUCTION NH40H solutions were measured at 100 to 560F.

This conductance information leads to an under- & the '' "- standing of the brhnvior of reactor solutions at

lutions is of fund~mental importance in under- elevated temperatures and permits rezsonable standing the behavior of electrolytic solutions, and speculation to be made oI1 the behavic.r of proposed provides the simplest and most direct measure of reactor additives.

the ionization of substances upon which their

chemical behavior depends. In spite of its impor-

tance, only A. A. Noyes and associates (Reference 11. REVIEW AND INTERPRETATI12N OF THE NOYESCONDUCTANCE DATA*

1) have successfully measured this property with

reasonable precision for several substances at A. En,pirical Method for Determinin elevated temperatures. From their efforts, a plete Ionization of Uni-univalent

' nucleus has been made available for building gen- Electrolytes

eral principles governing the behavior of electro- Onsager (Reference 2) derived from theoretical lytes at elevated temperatures. considerations the f~llowing limiting equztion de-

A Bettis Project was initiated to devise methods scribing the equivalent conductance of a 1-1

and techniques for measuring the conductances of electrolyte:

reactor solutions at temperatures to 540F (289C)

and to interpret the results with electrolytic solu-

tion theories. As a first step, the conductance data

of Noyes were reviewed and interpreted, and gen- -- eral principles were set forth on the expected *Only 1-1 electroljtes will be discussed, since this

type of electrolyk is the only kind on which suf- behavior of various solutions at reactor tempera- ficient data are ~vailable for application of con- tures. In addition, the conductances of LiOH and ductance theories..

in which

5 (Y* = 8.20411 x 10 . p, = 82.4262

(DT) j2 9

7 (DT) '

A ' i s the equb~alent conductance at t.he ~ l e c t r d y t e

concentration C (equiv~liter); hO is the aquivalent

conductance at infinite dilution; D is the dielectric

constant 0;' the solve&; and 7 is the absolbte

viscosity of the sdvent.

Shedlovsky !pe€erenl:e 3) tested the applica-

bility of this equstion over various concentration

ranges by substituting measured A values in the

equation, computi~g the A" values, and noting their

constancy. The equation is applicable if the com-

puted h0 values remain constant with cx-~ceritra-

tion and is not app:icabls iftae computed .b" values

deviate from constancy. It was found by using the

most accurate datz meuured at room tempe-ahre,

that the comp~tec A" values were not constant

over any appreciable concentration range. Eow-

ever, observation v a s made that the computed A"

values (designaled by f-' ) plotted against the first

power of the concsntration, usually gave straight

lines up to conzerrtrati~ns of about 0.1 IT. On this

basis, the corract A" -zalu~ for each e1ec:rclyte

is the intercept of the .I: v. l r sus C line at C = 0.

Thus, Shedlovslry found empirically that com?letely

ionized 1-1 electrolytes obey the equation

over a concentrathn range of 0 to 0.1 N and tem-

peratures of 18 and 25 C. Furthermore, it was

observed that the slope, B, usually h d values

greater than, but within 15 percent of the Onsager

limiting slope, [cr*&+p). For those salts gen-

erally considered not lo be completely ionized

(nitrates, chlorates, and iodates), the B valueawere

either much less than Ele Cnsager limiting slope

or no linear relationship existed between A: and

C. Thus, from conductance data, the Shedlovsky

method can be used to determine if' a particular

uni-univalent electrolyte i s completely ionized in

solution at room temperature. The method is also

useful in determining the limiting conductance,

A", for strong electrolytes.

To determine the kinds of curves obtained by

the, Shedlovsky test for different electrolytes at

elevated temperature, A: versus E: plots were

made using the conductance data of Noyes

(Reference 1) for NaC1, KC1, HC1, NaOH, AgN03,

and H3P04 over the temperature rmge of 18 C

(64.4 F) to 306 C (593 F). The first four substances,

NaC1, KC1, HC1, and NaOH, are strong electro-

lytes at room temperature, AgNO is slightly as- 3 sociated, and H3P04 is a weak electrolyte. A: versus C plots for these substances are'shown in

Figures 1 through 6. Appendix I presents the con-

ductance data developed by Noyes, and Tzble Ilists

the dielectric constants and viscosities of water

and the (Y * and P * values at various temperatures.

These data in Table I, along withthe dxta of Noyes,

are required to compute the A values. Values

for the dielectric constant of water from 18 to

100 C were computed by the Wyman and Ingall

(Reference 4) equation,

and from 100 through 306C by the Akerlof and

Oshry (Reference 5) equation,

Values for the viscosity of water from 18 through

306 C were interpolated from smooth curves of the

viscosity data given by Dorsey (Reference 6).

9 0 0 - TEMPERATURE 424 ~ ( 2 1 8 c1

875 - ,8' 1173 -

TEMPERATURE 583 F ( 3 0 6 C) / 8 5 0 - /

/ /

/ /

620 - /

/ TEMRRATURE 313 F (156 C)

6 0 0 -

575 -

4 3 0 - v 1050- TEMPERATURE 538 F (281 C)

415 -

C x lo3 [Equiv/Literl C x 1'03 (Equiv/ Liter)

figure 2. Shedlovrky Test on KC1 Solutions at Various lemperdures

I / TEMPERATURE 4 2 4 F (218 C)

260 C 1 PLOT HAS NEGATIVE SLOPE

306 c ]PLOT WS NEGATIVE SLOPE

TEMPERATURE 212 F ( I 0 0 Cl

8 6 0

8 4 0

410 - TEMPERATURE ' 6 4 4 F (18 Cl

TEMPERATURE M O F (260 C l 390 -

370 I I I I I 0 10 20 40 60 80 100 4 0 60

C x lo3 (Equiv/~iter) Cx lo3 (Equiv/Liter)

Figure 3. Shedlovsky Test on HCI Solutions ot Various Temperatures

TEMPERATURE 424 F @I8 CI

TEMPERATURE 64.4 F (18 C)

Figore 4. Shedlovsky Tesl o r NaOH Solutions at Various Temperrrtures

lmr TEMPERATURE 583 F (m CI

7 TEMPEFATURE 212 F (100 C1

I m r TEMPERATURE 64.4 F (8 C )

Figure 5 . Shedlovsky Test on AgNO, Solutions at Various Temperatures

I . TEMPERATURE 644 F (I8 C:

2. TEMPERATURE 77 F :25 C )

3. TEMPERATURE 122 F 30 2)

4. TEMPERLITURE 212 F i l m 9

111 - a <

0 E 40 60 40 . 6 0 80

C x 10' (Equiv/Liter) C x lo3 (Equiv/Liter)

Fisure 6. Shedlovsky Test on H,PO, Solutions at Various Tempera:ures

TPBLE I

PHYSICAL CONSTANTS AT VARIOUS TEMPERATUJiES

Temperature (C) [F)

Viscosity (millipoise)

10.60 8.949 5.49 3.81 2.839 2.215 2.008 1.793 1.265 1.093 1.008 0.910

Examination of the A: versus C plots shows the

Shedlovsky criterion of a linear relationship was

not obeyed by H3P04 but it was obeyed by NaOH

up to 156 C, by AgN03, NaC1, and HC1 up to 218 C,

and by KC1 up to 281 C. Application of the second

criterion, a B value 0 to 15 percent greater than

the Onsager slope, was not obeyed by AgN03 where

the slope was between 44 and 54 percent less than

the Onsager slope, or NaOH where the slope ex-

ceeded the Onsager slope by 21 to 35 percent.

Thus, if the assumption is made that the Shed-

lovsky criteria are applicable at any temperature,

aqueous solutions of NaC1, HC1, and KC1 are

strong electrolytes up through temperatures of

218, 218, and 281 C ,respectively. Somewhat above

each of these temperatures, the electrolytes begin

to associate. Using this same rule, H3P04 is a

weak electrolyte throughout the measured tem-

perature range. NaOH is peculiar in that the slope

is greater than expected; however, NaOH is probably

a strong electrolyte up to 156 C. The data on AgN03

cannot be properly interpreted because hydrolysis

occurs throughout the temperature range.

B. Equations Describing the Conductance Behavior of Strong 1-1 Electrolytes

Many equations have been used to describe the

conductance behavior of strong 1-1 electrolytes at

room temperature (Reference 7), a few of which

were considered in seeking to describe the con-

ductance behavior of electrolytes at elevated

temperatures.

The Onsager limiting equation does not de-

scribe the conductance of electrolytes over any

appreciable concentration range. However, the

Shedlovsky linear relationship, Equation f2), has

been shown to describe adequately the conductance

behavior of NaC1, KC1, NaOH, and HC1 to tem-

peratures above 200 C and concentrations up to

0.1. N. Equation (2) can be rewritten as: -

In this form, it is seen to be merely an extension

of the Onsager Equation (1) with the added terms,

B C - ~ * B C ~ / ~ . This equation has the disadvantage

of containing the empirical parameter B.

Shedlovsky (Reference 8) proposed, another em-

p i ~ i c a l modification of the Onsager eguation which

quite accurately represents room-temperature

conductances of strong electrolytes up to con-

centrations of about 0.01 N. This equation is:

which may be rea~ranged as the series,

This equation contains only one undetermined

parameter and is readily applied to the calcula-

t ims required later in Section II-C.

The recently developed Fuoss-Onssger equations

(Reference 17) a re derived entirely from theoretical

gouncs and contain an ion-.size parameter in ad-

dltion to A". It has been shownthat these equations

accurately represent the conductance data for

s;rong electrolytes. However, the complex calcula-

tions required to a p l y the Fuoss-Onsager equations

to the Noyes reslllts have not been carried out,

since a high degree of precision is required of the

data to determine accurately the ion-size

parameter.

To determine if Equation (6) describes the con-

dbctance behavior of electrolytes at elevated tem-

peratures, the Noyes conductance data for NaCl,

KC1, HC1, NaOH, AgN03, and H 3 PO 4 were sub-

stituted into Equation (6); the h" values were

computed and their constancy noted. The results

cf these calculations show that Equation (6) ac-

c-urately represents the data for NaC1, KC1, HC1,

and NaOH to within about 0.1 percent fo- concen- Substituting this expression c-f he, into Equa-

trations up to 0.01 - N (and to about 0.5 p r c e n t up tion (8) and solving fear gives

to 0.1 NJ at temperat=-es which show fhe Shed-

lovsky linear rslationstip behveen A: and C. At

temperatures where the A' versus C plots are in which

not linear, the computed h" values a re not..constant,

but decrease with increasing concentratiozl. There-

fore, the eqcation is not applicable at these and

temperatures. = (.*h"+B*) UTE

Equation (6) describes the AgN03 data to within ( c ) ~ ' ~

about 0.1 percent up to 156 C. The equation does

not describe ee data for H3P04 at any of the 3) Combine the definition of a dissociation

measured temparatures, constant,

Thus, if the Shedlovsk:,r criteria for strong elec-

trolytes is used, then Equation (6) will adequztely with Equation (lo), gisri~ig describe the conductance behavior of these types

of concentrations up to 0.01 N. 2 - As(z) = h" - u C Y=' (h" /K) . (14)

C. Determination of n" and the Dissociation Con- stant, K, for Electrolytes Which Associate The mean molar activity coefficient values,

y f , are calculated! from the Debye-Huckel .The usual method (Rderences 8 and 9) of deter- limiting law (Reference 10) :

mining h" and K value^ for associated electro-

lytes is:

1) Define the degree ccf dissociation, 4 as:

in which f, is the measured equivalent con-

ductance e;' the ele2trolyte at the cmcentra-

tion C, anci. A is the equivalent conductance e that the e l e c t r o l ~ would have if a l y cr C

equiv/liter of the completely dissociated

electrolyte were in solution.

log y z t =

4) Assume a value for h" in Equation (14) and 2 determine AS (Z) and (Y C y = -1sing con-

ductance data at v a r i . 3 ~ ~ concentrations. Plot

the AS (Z) values versus the a2c y -+ values.

If the correct A" value was chosen, the

intercept at C = 0 is n" and the slope is no -- . This trial and error process i s repeated KO

until the assumed he and the A" at C = 0

2) Substitute into Equ&ion (8) an expression for coincide.

Ae which describes the conductance behavior.

H3P04 at those temperatures where the Shed- - (9) lovsky test indicated the; electrolytes were as-

sociating. Table I1 lists the values obtained.

TABLE 11

EQUIVALENT CONDUCTANCES AT INFINITE DILUTION AND DISSOCIATION CONSTANTS FOR SEVERAL ELECTROLYTES AT ELEVATED TEMPERATURES

Electroljte Temperature (C)

NaCl

HCl

NaOH A m 0 3

D. Use of the Bjerrum Theory to Determine if a medium of a fixed macroscopic dielectric con- Ion-Pair Formation Explains the Decrease in stant. With this Bjerrum cllculEted the Ionization of Electrolytes at Elevated Temperatures probability of finding two oppositely charged ions

Table I1 shows k e ionization of all electrolytes

decreases ~ i t h ' i n c r e a s i n ~ temperature. To deter-

mine if this decrease could be caused by ion-pair

formation, recourse was had to the Bjerrum

(Reference 11). While this theory has recently been

superseded by more elegant variations which do

not require certain of the arbitrary assumptions

which are necessary in the Bjerrum treatment

(Reference 17), it has been used extensively in the

' past and is still usea to explain the low-conductance

behavior of strong electrolytes in media of low-

dielectric constant (such as water-alcohol mix-

tures). In such media, the conductance of a strong

electrolyte decreases as the dielectric constant of

the solvent decreases. Since the dielectric constant

for water decreases as temperature increases, the

decrease in ionization constant for the electrolytes

shown in Table I1 could be produced by ion-pair

formation as opposed to covalent bond formation.

Bjerrum assumed an electrolytic solution com-

posed of rigid, nonpolarizable spherical ions in

a distance, r, from each other and noted that the

probability possessed a minimum at a distance, q.

Then it was assumed that ion-pair formation took

plece if two oppositely charged ions were closer

to each other than the distance q and that ion-pair

formation did not take place if the ions. were farther

from each other than the distance q. Bjerrum de-

rived relationships between the constant for dis-

so~iation of an ion-pair, K , the dielectric constant

of the medium D and the temperature of the solu-

tion T and the mean distance approach - a, between

the centers of the two ions forming the pair.

These relationships are:

and Iz+z- I€ 2

b = a D k T

These equations were applied to the K values

shown in Table I1 to determine how the 2alculated

mean distance of approach, a, varied with tem- - perature and dielectric constant. Values for K and

DT were substituted into Equation (16. and Q@)

determined. The value of b was determined from a

plot of Q(B) versus b. The mean distar-ce of ap-

proach, 5, was determined using Equatior (18).

Table I11 shows the variation of a with temper9ture. - Also included in this table are the disfanc=s, q,

at which the probability function possessss a mini-

mKm and ionic radii values obtained from X-ray

diffraction dat&.

According to the B jerrum theory, ion-pair forma-

tian takes place when the mean distance of Aosest

approach for b ions lies between the qmlues and

the. sum of the ionic rac.ii. This condition i s satis-

fied by NaC1, KC1, NaOH, and perhaps 3C1 at the

operative which is different than the coulomb at-

tractive force used in the Bjerrum derivation.

Presumably, H3P03 does not form ion-pairs but

associates by covalent-.2%nd formation. Extensive

hydrolysis must als3 be considered to effect the

behavior of AgN03 so1ut:ons.

IlI. MEASUREMENT 03 THE CONDUCTANCES OF LiOH AND NH4CN SOLUTIONS OVER THE TEMPERATURE RANGE OF 100 TO 520 F.

A. Description of the Apparatus

Figure 7 shows the arrangement of the apparatus.

The solution was pumped from the 50-liter,

polyethylene bottle so'xce tank successively

through a mixed-bed, ion-exchange resin*; a low-

temperature, high-presLcure conductivity cell; a

*The mixed bed resin v a s of the same form as the solution which was passed throuzh it. For the water runs, as-receivd H-OH. for; mixed-bed higher temperatures. Therefore, these elrct?olytes resin was used For the LiOH or runs,

are considered to show ion-pair formation How- the H-OH form resin was converted to the Li +

ever, the Bjerrum theory is not applliczkle to OH- or NH4 + OH- form by passing strong solu- tions of these bases ttrough the rssin column.

AgN03 and H3P04 soldions since their a values Each column was washed with 30 b 40 liters of demineralized water before being used in order are less than :he sum of the ionic ra&i iexcept to remove any soluble amines which might be

for AgN03 at 218 C). This indicates r force is present.

CHANGE IN VALUES; q VALUES AND THE DIELECTRIC CONSTANT OF WATER WITH TEMPERATURE

Temperature E:lectrolyte (c)!

NaCl 281. 30C

KC1 28 1 308

HC1 260 306

NaOH 218 AgN03 2 18

28 1

Sum of Ionic Radii ( ~ 9 ( 1 3 )

not b o r n

2.35 (Na 0 = ) 4.00 from (Ag ~5 (N-0) o=)

3.30 from (P (P-0) O=)

Figure 7. Schematic Arrangement of Apparatus

heated, gold-@abd autoclave; a high-temperature,

high-pressure conductivity cell; a coo-ier; a low-

temperature, high-pressure conductivity cell; a

Bow regulator vdve; a flow meter; and finally to cfrain. A reg-lla;or set the system pessure at

2000 psi. The entire assembly was made as compact

as practical t13 lessen heat losses and t.13 minimiae

contamination from tke surfaces contasted by the

hot solution.

The interior of the autoclave a d high-

temperature conductixity cell were plated with 2

mils of g ~ l d to rrsinimiae contaminaticpn 0fv.e solu-

tion. The aubclave, the high-temperature con-

ductivity cell, aad tke in-stream thermocouples

were insulated. The critical componen: in the as-

sembly was the high-temperature conductivity cell.

Tbe cell design (Figure 8) developed for this

investigation, cansiated of a spark plug attached to the gold-clad steel housing by a threaded con-

nection. The homing ~ a r v e d as one elechode. The

other eleatrode i ~ a s r rod of pure gold attached

to a steel rod which eztended from the bottom of

the spark plug through the top of the plug

allawed electrical contact with the solution in id e

cell. The two electrodes were insulated from ea h

ferent high-temperature cells -8ere used in

P other by the alumina part of &e plug. Two d f-

work; one cell was used in the determinations t f the specific conductances of water and NHq H,

the other was used with the Lin3H solutions.

cell constants for the cells were determined y

measuring the room-temperature resistance

KC1 solutions at five concentrations. i

The used with water and NH40H so!utions had a c 11

constant of 0.0566 cm-1; the cell used with

LiOH solutions had a cell constant of 0.219

The low-temperature conductivity cells were identical to the high-tempera- cells except

the interiors of the housings and the spark pl P g

electrodes were made of steel rather than gold.

Figure B. Component Parfa d FCigh-Temperature, High-Pressere Conductivity CeP

The leads from the conductivity cell electrodes were usually terminated at this point. Low-tem-

were connected to a Type No. 650A Impedance perrture conductance readings were taken to de-

Bridge manufactured by the General Radio Co. termine if contamination of the solutions occurred

This instrument is accurate to 1.0 percent and in the heated portion .3f the system.

operates at a frequency of 1000 cps. A Dumont Dining a run, samples of the solution were taken cathode-ray oscilloscope was used as the detector. tile taps upstream .=f the autoclave and down-

B. Operational Procedure

stream of the cooler. Each sample ms analyzed

for the most conductive specie in the solution.

Fifty liters of distilled water were placed in the

source tank and nitrogen gas was bubbled through

the water for about 30 minutes to remove C02 and

02. A known quantity of the electrolyte solution

was poured into the source tank and nitrogen gas

was bubbled through the solution for about 30

minutes to assure complete mixing. The top of the

source tank was capped and two polyethylene tubing

leads were inserted through the cap. One lead was . . connected to the pump; the other lead was connected

. .* to a C02 absorption bottle, which was partially

filled with a LiOH solution.

While the solution was being mixed, the auto-

clave was drained, isolated by the flow control

valve and the valve immediately before the auto-

clave, and evacuated. The valve before the auto-

clave was opened and the solution was allowed to

fill the system. The flow control valve was set at

50 cc/min. When the solutionhas shown to be of

constant composition throughout the system (as

indicated by the conductivity measurements on the

three cells), the autoclave heaters were turned on

and the temperature of the solution, measured at

the autoclave outlet, was raised to 580 F. When

this temperature was reached, the autoclave heaters

were turned off and the solution flow rate was

increased from 50 to 200 cc/min. This increase

in rate essentially eliminated any temperature

drop across the high-temperature conductivity cell.

Conductance and temperature readings were made

simultaneously every 3 to 10 F as the temperature

decreased from 580 F to about 100 F. The runs

C. The Specific Conductance of the Water

Specific conductance measurements of the water

used in preparing solutions were made over the

terqerature range cf 100 to 570 F several times

during the course of this work. These measurements

ser-~ed as a check 3n the cleanliness of the ap-

paratus and are subtracted from the total measured

conductivity of the solution in calculating the spe-

c i fk conductance of the electrolyte. It shculd be

pointed out that these measurements do not yield

the correct conductance values of pure water at

the elevated temperatures since: (1) the initial

water contained some impurities, and (2) pickup of

additional impurities occurred in the system.

The conductivity data obtained in each of the

wajer r m s are shown in Figure 9. The first three

rum were made prior to the NH OH determications. 4 The fourth run was made bebeen the NHqOH and

LiOH determinations. The conductivity of the cooled

water leaving the system is also shown.

D. Equivalent Conductances of NH40H Solutions

over the Temperature Range of 100 to 560 F

The resistances of the NH40H sclutions were

measured over the room-temperature concentra-

tian range of 0.00473 to 0.0933 Nanda temperature

r-ge of 100 to 560 F. The equivalent conductances

of the solutions were calculated using the standard

definition of an equivalent conductance.

Figure 10 shows a plot of the data from each

determination. The room-temperature concentra-

tions of the NH40R solutions were obtained by

SYWOL RUN NO.

0 I

TEMPERATURE ( F )

L

- SYMBOL RUN NO. -

I - 0 0 0 0 o o

2 0 0

7 5 - - A 3 \ 0 - v 4 z

v - O 4 v

f igure 9. Specific Conriuctance o f W a t e r Used in the Experiments

w 0 z 2 0 3 0

mm 6m'%mm moo

0 O SIM~OL CON,:. AT ROOM

OQm m TEMP.

m m 0 009333

u + 009308

m mm A 0 04747 o 0009607

0 0 @ 0 0 0 4 7 3 0

m m 0

4- 00 v -

B - O A

- P oft= - HIGH TEMPERPTURE

Figure 10. /ar iat ion of the Equivolect C o n d ~ r t a n c e s of NH,OH Solutions wi th Temperuturs

CONDUCTIYGTY v A

0 - Y - B ti

- 0 vc 'a

- 7 0

2 - v o a

o 4 - P 0 % CONDUCTIVITY OF WATER 0 *O+

A 0 v & - AFTER COOLING TO OnA~ava a & - ROOM TEMP ,, o " * #A

0 A - v A

I - v t vouO

100 150 200 250 300 350 400 450 500 550 600

titration against standardized 0.1 N H2S04 or

standardized 0.01 N HC1 using methyl red as the

indicator. The W40H concentrations remained es-

sentially constant throughout all determinations.

Baker and Adamson CP grade ammonium hydroxide

was used in preparing the initial solutions.

E. Equivalent Conductances of LiOH Solutions Over the Temperature Range of 100 to 520 F

The resistances of LiOH solutions were measured

over the room-temperature concentration range of

0.00073 N to 0.0015 N and a solution temperature

range of 100 to 520 F. Since LiOH is a strong

electrolyte, it was necessary to use very dilute

solutions to maintain the conductance within reason-

able limits.

The use of very dilute solutions introduced two

difficulties: (1) Initially, titration of the so1,ution

to determine OH- concentration yielded erratic

results. It was determined that the solutions were

being contaminated by C02 from the air during

sampling and analysis. To prevent contamination,

plastic hoods were placed around the sample taps

and titration vessels to permit N2 blanketing ofthe

samples at all times. Thereafter, titration results

were reproducible to better than 1 percent. (2) The

OH- concentration was not constant during a run.

The changes were followed as a functionof solution

temperature by titrating samples takenperiodically

from the system. Plots were made of the room-

temperature concentrations as a function of solution

temperature and the concentrations for any tem-

perature were estimated by interpolation. It was

difficult to decide whether the inlet concentration,

the outlet concentrations, or an average of these

should be used to calculate the equivalent con-

ductances. The impurity (or impurities) which

entered the solutions and tended to neutralize the

OH- could have come from the thermal decomposi-

tion of nonionized, slightly soluble materials in the

ion-exchange resins; or from surfaces of the heated

autoclave, the high-temperature conductivity cell,

or the steel tubing located between the high-

temperature conductivity cell and the .=oole-.. The

interference by impwities was not appreciably

decreased by increasing the flow rate of solution

through the system. This indicated the concentra-

tion change occurred in the autoclave, which could

not be adequately Eushed because of its large

volume. If this is true, the resistance readings of

the high-temperature cell were affected by the

change. Therefore, the outlet concer~tration was

chosen as the true concentration of the solution.

The conductance data are shown in Figure 11.

F. Best Values for ihs Equivalent Cor-ductances of m4OH and LiOH At Temperature Intervals of L F

The best values of the equivalent conductances

for the W40H solutions and the LiOH 'solutions

at various concentr~tions and at temperature in-

tervals of 40 F were obtained from smooth plots

of :he data shown in Figures 1 0 and 11. The values

obtained: are shown in Tables IV and V.

G. The Behavior of LiOH Solutions at Elevated Temperatures

Darken and Meier (Reference 13) measured the

equivalent conductances of LiOH, NaOH, and KOH

solutions at 25 C as a function of concentration

and conlpared their ionization characteristics using

the Shedlovsky test described in Section 11-A. They

found the A', versus C plot for LiOH had a slight

dip in it and concluded that LiOH behaves as a

weak electrolyte. An ionization constant of 1.2 was

cdculated. NaOH showed very nearly complete

ionization and the KOH showed complete ionization.

The Shedlovsky test was applied to the Bettis

LjOH data using ths equivalent conductance values

shown in Table V. The A', versm C plots are

stown in Figure 12. These' plots show that the

slopes of the lines became more negative as the

temperature of the solution increased, indicating

LiOH becomes less ionized as the solution tem-

perature is increased.

- @v v V -

@ @ 0: - 4 v \ - 4@, +- - - SYMBOL CONCENTRATOV ( WUIv/L TIF;) *v To

-0- o0 - o 0 001502 -OWIS5 - + OW1136 -OW1160 %"

- v OOW9BC3

+@:& - 0 v

0 0000736-0000 8 3 e - C - 4 v + 0 - t S + O

- - $8

- %! 0

- *,a - Oo+O

- .gf!O0 - - &* - @& - &%@ - - b - - d*

C 0 - - F - ,& - - ,,&- - P - - - b." - - - 5.J - woo - d - v 8 - v @ - - @

1 0s-

- 8 :@O

4 1 1 I I I I I I I I I I I I ~ I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

Figure 1 7 . Variation of Equiralent Conduc'ances of LiOH Solutions with Temperature

320 100 150 200 25.3 300 350 400 450 50C 550 600

TEMPERATURE (F l

OTPEOO '0 6'01 PZ6900 '0 96'L EZPEO '0 PL 'E 11L90 '0 P9'Z

619E00'0 P '91 8PELOO'O Z .I1 EE9EO '0 L1 '9 ZZILO'O . 69'E

06LE00'0 Z 'OZ 969LOO '0 9 'PI P08E0 '0 9'9 8P9LO.O 89'P

8E6E00 '0 8 'PZ L66LOO.O L 'L1 E96EO '0 0 '8 OSLLO'O 9L '9

P90P00 '0 9'62 792800 '0 8 '02 GLWO '0 P'6 L66LO '0 RL'9

Z81POO '0 L 'EE Z6P800'0 9 'EZ 861PO'O 9'01 OEZ80 '0 9S'L

88ZPOO '0 9 '9E LOL800'0 P,'% SOEPO '0 9 '11 6EP80 '0 9t '8 ZWCIU'U L~'L

P8EPOO '0 9'8s 106800 '0 6-97. OOPPO '0 00 '21 LZ980 '0 8P.8 6P980'0 6E '8

1LWOO '0 9 '8E 8L0600'0 8 '92 88WO '0 00 '21 86L80 '0 1E '8 02880'0 1E '8

L~SPOO '0 9 '9s 292600 '0 Z 'SZ PL9PO '0 Z .11 L9680'0 08'L 06680 '0 E6'L

PZWOO '0 9 'ZE 886600 '0 Z 'ZZ 1PWO '0 0'01 66060 '0 10'L ZZ160'0 PO'L

099

029

08P

OPP

om . 09E

OZE

08 2

OPZ

002

091

021

08

BEST VALUES FOR TIIE EQUIVALENT CONDUCTANCES OF LiOH SOLUTIONS AT VARIOUS TEMPERATURES AND CONCENTRATIONS

Run 1 Run 2 Run 3 Run 4 -- --

Equivalent Conc. at Equivalent Conc. at Equivalent Conc. at Equivalent Conc. at Temperature Conductance Temperature Conductance Temperature Conductance Temperature Conductance Temperature

(F) (mho-cm2/eq) ( ed l i t e r ) (mho-cm2/eq) (eq/liter) (mho/cm2/eq) ( e d l i t e r ) (mho/cm2/eq) ( e d l i t e r )

120 350 O.OQifi24 347 0.001143 359 0.0009668 352 0.0007535

TEMPERATURE = 520 F

TEMPERATURE = 4EO F

TEMPERANRL XO F

TEMPERATUFe : YO F

8 5 0 1

' ' 50

TEMPERATURE 9 200 F 0 0

5 5 0

- TEMPERATURE = 440 F

- 0 -

TEMPERATIRE = 160 F 0

4 5 0 0 I - - -

TEMPERANRE = IM F - I . . . . I . . . . I . , , P I . . ,

3 5 0 l " l " " " " " l t ' r ~ " " '

0 2 4 6 8 I) 12 14 16

CONCENTRATION AT TEMPERATUE X lo4 (EOUIV/ LITER)

Figure 12. Shedlovsky Test for the Ionization of LiOH ~olut ions

The equivalent conductances a t infinite dilution

and the ionization constants were computed using

the method outlined in Section 11-C. The final re-

sults a r e shown in Table VI. The A S(Z) versus

(r2c Y *2 plots and the change in the ionization

constants with temperature a r e shown in Figures

13 znd 14, respectively.

It i s clear from the K versus temperature plot

(Figure 14) that the number of ~ i + and OH- ions

in solution decreases a s the temperature of the

solution increases. The theory of Bjerrum pre-

sented in Section II-D was used to determine whether

TABLE VI

EQUIVALENT CONDUCTANCES AT INFINITE DILUTION AND THE IONIZATION

CONST-4NTS FOR LiOH AT TEMPERATURES FROM 120 F ID 580 F

Temperature (F) 120 160 200 240 28 0 3 20 360 400 440 480 520

(K molar scale)

0.128 0.0685 0.0742 0.0456 0.0310 0.0435 0.0396 0.0414 0.0255 0.0234 0.0172

- TEMPERATURE.BO F

- - TEMPERATURE ~ 4 ~ 3 F - - - 0 n

1- TEMPERATURE .4+3 F

- 0 -

- TEMPERATURE -3- F

950 - - - .- , TEMPERATURE -3a3 F

TEMPERATLIRE - 2 Q F

TEMPERATURE = 2 0 3 F

550 3 450 r - - TEMPERATURE.IOC F

Figure 13. Determinotior ol .Ls and Y by ,\SfZ) Versus a ly' f C Plot

this decrease couldbe c a ~ s e d by ion-pair fmmakion, this relationship as o shown in Figure16. The equation

The - a values and the distances, q, at \;-hich the relating the A' for LiOH and the viscosity of

probability function possesses a minimum are water is:

shown in Table VII. This tabls shows the c d c W e d A"= 7.4 -0.75 'I 0 (20)

a vrlues r r e l e ~ s than the sum of the ior.ic r.ldii, - indicating that some force in addition to s i r - p l ~ ion- H. Behavior of -NH40H Solutions at Elzvated

Temperatures ion attraction is ?rubably operative between the ~ i +

The conductances of NH OH solutions were meas- and OH- ions. 4

ured by A. A. Noyes (Reference 1) at 212, 313,

Johnston (Refere~ce 15) showed from tts PJoyes

conductance data that a log-log plot of the eq;~ivalent

conductances at infinite dilution for salts versus

viscosities of water at various demperatures yie!ded

straight lines, and furtker noted that bases and

acids did not follow this relationship. Fiigure 15

illustrates this plot. The Betils LiOH data f o l l ~ ~ s

424, and 583 F. The method consisted of: (1) placing

an ammonium hydroxide solution of known concen-

tration in a platinum lined autoclave and measilring

the room temperature ,(18 C) conductance of the

solution; (2) heating the solution to some pre-

determined temperature and measuring the conduc-

tance, and (3) cooling the solution to.room tempera-

ture and remeasuring the conductance. The best

TEMPERATURE (F)

Figure 14. Variat ion of Ionization Consfunt ol LiOH wi th Temperature

TABLE VII

CALCULATED MEAN DISTANCES OF CLOSEST APPROACH FOR LiOH

Temperature (F) 7 7 120 160 200 240 280 3 20 360 400 440 480 520

Dielectric Constant

78.5 70.1 63.3 57.1 51.5 46.4 41.8 37.6 33.8 30.2 26.8 23.6

a Sum of Ionic Radar

(Aq (Li+ + o =) A0 - 2.41

1.28 0.77 0.84 0.81 0.80 0.95 1.02 1.16 1.16 1.27 1.37

value data of Noyes a re compared against the Bettis room-temperature conductances of his solutions

best value data in Table VIII. The percentage dif- ware less than the initial conductances znd attri-

ference between the two sets of data was seen to buted this change to a catalytic oxidation 'f NH40H

increase with increasing temperature. This in- bp the platinum lining of the autoclave:

' dicated impurities were leaching into the Bettis

solutions or decomposition was taking place in the

Noyes solutions. Noyes observed that the final

O N a C L .

KC1

1.3 - @ NaOH

C> AaNo3 :.2 - -()- N H ~ A c

?I - A HCL

0 NaAc z9 -

28 -

Figure 15. Log it, Versus Log qo for Several Elecfrolytes

TABLE VIII

BEET 'ALUES FOR THE EQUnrALENT CONDUCTANCES OF NHSCH SOLUTIONS

03TAINED BY A. A , YOYES AND BETTIS

Concentration Temperacure a t Temperature .Equivalent Conductance YO Difference

(F) (equisr/liter) Bettis Data Noyes Data (Bebtis-Noyes)

O BETTIS DATA

DARKEN AND MElER DATA

I 1.5 , 2 3 4 5 6 7 8 9 0

(VISCOSITY X I O ~ ) ( P ~ ~ S E )

Figure 16. Variat ion of the Equivalent Conductances of

LiOH a t Infinite Dilution with the Viscosity of the Solvent

The conductance decrease amounted to about 1 per-

cent for the solutions heated to 212 F and to about

2 percent for the solutions heated to 424 F. The

Bettis analyses showed no apparent change in

NH40H concentration on passage through the gold-

lined system.

The h0 and K values for NH40H cannot be

determined by the method described for LiOH since

the equivalent conductance ,values for NH40H are

about two orders of magnitude less than the limiting

conductances, A' , and extrapolation of the data

to C = 0 is very inaccurate. The A' values were

determined using the Noyes do values for NaOH,

NH Ac, and NaAc at various temperatures and the 4 Kohlrausch limiting conductance law. The dissocia-

tion constants were determined by substituting the

N H 4 0 H best value data (Table IV) into Equations

(8) and (9) and solving for CY ; tien, solving for

y,* using Equation (15) and substituting the CY and

Y * valugs into Equation (13). The final A' and

K values at various temperatures are shown in

Tattle E.

IV. THE ION-PRODUCT OF WATER -4T ELEVATED TEMPERATURES

Beretofore, all reactor coolant data have been

related to the room-temperature pH of reactor

coolants. One of the main purposes cf this report

is to determine the truespH of reactor cooiants at

reactor temperaturts. The ion-product of water

must be known before these values can be

deermined.

Noyes, Kato, and Sosman (Reference 13) have

determined the ion-product of water at ~ levated

temperatures by a series of experiments which

consisted of: (1) measuring the conductances of

sohtions containing a hydrolyzable salt at different

initial salt concentrations, and (2) measuring the

conductances of solutions of the hydrolyzable salt

mixed with added amounts of one of the hydrolysis

products. The addition of the hydrolysis product

represses the hydrolysis of the salt, and the con-

ductance measured is essentially that conductance

which the salt would have if it did not hydrolyze.

The difference in conductances found in steps (1)

and (2) is a measure of the hydrolysis of the salt.

,TABLE IX

A0 AND K VALUES FOR NH40H

AT VARIOUS TEMPERATURES

Temperature, (F)

120 160 200 240 280 320 360 400 440 480 5 20 560

K (molar units)

2.08 x 101; 1.79 x 1.49 x 1.13 x 9.05 x 6.41 x 4.39 x 2.52 x 1. .75 x 9.38 x 6.16 x 2.40 x 10

The ion-produ2t of water i s calculated using the

hydrolysis coristant of the salt and the iolization

cc-nstants of the hydro1::sis products. Ta.3le X lists

the Noyes Kw vzlues for water at five diffment

temperatures. Tk~ese Kw values in Table X may

nct be accurate since a close examina:ioil of the

data shows that in some cases insufficie3t &mounts

of the hydrolysis produ.;ts were added foz complete

suppression of the salt hydrolysis. S e v e r ~ l different

approaches were taken in an attempt to wcalculate

the ion products from the data; however, none of

the methods appeared to be improvements over

the empirical method of Noyes and until more

eqerimental data are available to obtain a more

acnurate expression to represent c h a n e s in con-

du2tance of mixtures: the values for the icn-?roduct

for water, listed in T a l e X, will have t~ be used.

V. CHANGE IN THE pH OF H20, LlOB, AND

NH40H SOLUTIONS WITH TEMPERATURE

The pH of pure water at various tem?erat '~res

was calculated -1sing the equation,

in which @I+) represenx the molar hy&ogen ion

concentration. The K ralues at various tempera- W

tul-es are s h o w in Table X.

The procedu~e used t3 calculate the pH of LiOH

anc NH40H solutions at various temperat-~res was:

1) Assume an ammonium hydroxide or lithium

hydroxide solution to have a certzin pH at

room temperature.

,TABLE X

THE ION-PRODTJCT OF WATER AT VARIOUS TEMPERATURES

Temperakre Ion-Product of Water -

2) From the assumed pH and the equation

pH = - log @I+) (22)

calculate the (H+) concentr~tion.

3) From the relationships

(MOH) = C(l - a! j (27)

in which the molar concentration of the base

is C and a! is the degree of ionization of the

base, it can be s h o w that:

of+) and

Substitute the room-temper3ture values for

%ase, Kw, and (H') into Equation (28) an3

solve for . Substitute a! ixto Equation (2%

and solve for C.

4) Determine the concentration of the solutiox

at various temperatures by divirling the spe-

cific volume of the solution at the various

temperatures in,b the rocjm temperature

concentration, C.

5) From the relationships listed in step (3), it

can be shown that

Use the values for .FCBase, C, and Kw at the

temperature in question, and cdculate @I+).

6) Substitute (Ht) into Equation (22) and calculate on NaC1, HCl, KCl, NaOH, AgN03, and H3P04

the p~ of the solution. solutions. It was found that the first four elec-

trolytes behave as strong electrolytes up through and Figure l7 the pH of temperatures of 218, 218, 281, and C, re-

neutral water at various temperatures, the pH spectively. Application of the Bjerrum theory show-

values for NH40H solutions having a room tempera- ed that, somewhat above each of these temperatures,

ture pH of 8'0 and 9'5, and the pH of LiOH these electrolytes begin to associate by ion-pair solutions having room temperature pH values of formation, PO solutions associate room

9.0 and 10.5. 3 4 temperature and above. AgNO solutions appear 3

. It i s clear from this table that, for the NH40H

concentrations specified for reactor coolants, the

coolant at reactor temperatures is more basic

than neutral water (pH = 5.75) by only 0.5 pH unit,

whereas, a reactor coolant containing LiOH is 1.5

to 2 pH units more basic than neutral water. Dif-

ferences in concentrations of insoluble corrosion

products found in the two coolants may well be

attributed to this difference in basicity of the

solutions. Suspensoids are very sensitive to changes

to associate at all temperatures, but no condlusions

can be drawn because of complications caused by

hydrolysis. The equivalent conductances at in-

finite dilution and the dissociation constants for each

of the aforementioned .electrolytes were calculated

over their measured! temperature ranges by the

Shedlovsky method. The dissociation constants

decrease with increasing temperature.

B. An apparatus was constructed and measure-

ments were made ,on the conductances of LiOH

in environment and additions of electrolytes can and NH40H solutions over the temperature range

easily cause flocculation or agglomeration and of 100 F (38 C) to ,520 F (271 C). The equivalent

settling. The corrosion mechanism may alsobe di- conductmces at infinite dilution and the dissociation

rectly affected by the pH of the solution. The added constants were calculated for these solutions by the

basicity in LiOH coolants may be the direct cause Shedlovsky method. Application of the Bjerrum

for the lower levels of suspended corrosion products theory indicated LiOH that some attractive force,

observed in plants using this coolant as opposed to in addition to ion-ion attraction, was actingbetween

plants using coolant containing NH40H. the ~ i + and OH- ions.

C. The pH of reactor coolants using LiOH or

VI. SUMMARY AND CONCLUSIONS NH40H was calculslted from the dissociatim con-

stants for water, LiOH, and NH40H at elevated

A. Criteria applied to room-temperature con- temperatures. Reactor coolants containing NH OH 4 ductances for determining complete ionization are only 0.5 of a pH unit more basic than water

of 1-1 electrolytes were applied to the A. A. at reactor temperature whereas a reactor coolant

Noyes high-temperature conductance data obtained containing LiOH is 1.5 to 2 pH units more basic

TABLE M

CHANGE IN THE pH OF WATER, NH40H, AND LiOH SOLUTIONS AS A FUNCTION OF TEMPERATURE

Temperature pH pH (F) Water NH40H Solutions LiOH Solutions 77 7.00 8.00 9.30 9.00 10.50

212 6.16 6.41 7.77 7.30 8.80 3 13 5.83 5.96 6.96 6.62 8.12 4 24 5.67 5.71 6.41 6.29 7.76 583 5.89 5:: 90 6. 28 , 6.64 8.12

than water. The differences in concentrations

of suspended corrosion products found in the differ-

ent reactor coolants may well be explained by this

difference in basicity.

APPENDDZ I. DATA COMPILED BY NOYES ON

VARIOUS ELECTROLYTES AT

ELEVATED TEMPERATURES

(TABLE 1-1)

TABLE 1-1

DATA COMPILED BY NOYES ON VARIOUS ELECTROLYTESATELEVATED

TEMPERATURES

c 103 Temperature (C) 52 (equiv/liter)

A. NaCl

TABLE 1-1

DATA COMPILED BY NOTES ON VARIOUS ELECTROLYTES AT ELEVATED

TEMPERATURES (Cont)

C x 103 Temperature (C) 52 (equ iv/liter)

TABLE 1-1 TABLE 1-1

DATA COMPILED BY NOYES ON VARIOUS ELECTROLYTESATELEVATED

TSMPERATURES (Cont)

DATA COMPILED BY NOYES 3~ VARIOUS ELECTROLYTES AT ELEVATED

TEMPERATURES (Cc~nt) .

"v 103 Temperature (C) A (equiv/liter)

306 1337 2.010 306 1162 10.010

D. NaOH

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3. T. Shedlovsky, "An Equation for Electrolytic

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N.A. Lange and G.M. Forker, "Handbook of

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13.. L.S. Darken and H.F. Meier, "Conductances of

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15.5. Johnston, "The Change of the Equivalent

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, ', A, . ..

P. . , _ - _ _ _ TH r:S' PAGE . . :, : . . , : . . . . : .. . '.: .:

WAS ;INTENTIOaN,ALLY LEFT BLANK