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Diffusion coefficients of aqueous cesium fluoride at 40°C
DIFFUSION
COEFFICIENTS OF AQUEOUS FLUORIDE AT 40°C M.L.
Department
CESIUM
SCXIDand MADHU BALA
of Chemistry, Punjab Agricultural
(Receioed 12 November
1981; in revised
University, form
Ludhiana,
India
8 Mnrch 1982)
Abstract-Diaphragm cell technique has ken employed to determine diffusion coefficient for cesium fluoride at 40°C in the conantration range varying from 0.01 to 0.1 M. The data were analysed in the light of the theory of Onsager and Fuoss (O-F), J. them. Phys. 2.599 (1932)[20]. The results indicate that the O-F theorv is inadeauate to exDlainthe behaviour of this salt at 45°C. The results are also discussed with other 1: 1 type &Its of c&m.
Analysis of the solutions
INTRODUCTION
The initial and final concentrations of the solution From a diffusion experiment were determined conductometrically. From the final conductance readings of the solutions in the two compartments when the steady state has been attained, the concentrations were read from the standard curve which were initially prepared by plotting conductance us concentration at 40 *O.l”C. The conductometer used was of U.S.A. make (Yellow Spring Inst. Co., Ohio, Model 31) and was calibrated before use. The volume of the liquid in the pores of diaphragm were determined as suggested carlier[ 161.
The diffusion coefficients of aqueous c&urn chloride have been studied previously by conductometric[l] and Gouy[2] methods. These methods have their own limitations.[3] The diaphragm cell technique, on the other hand, is universally accepted for finding diffusion coefficients[4]. Further this technique can be successfully employed to determine the diffusion coefficients at elevated temperatures[5]. Keeping in view these facts the present investigations were carried out to find diffusion coefficients of cesium fluoride at 40°C.
EXPERIMENTAL
Calibration
The diaphragm cell technique has been universally accepted for finding diffusion coefficients above 0.05 M[6]. This method of determining diffusion coefficient was first introduced by Northrup and Anson[7] and later on underwent modifications by Hartley and Runnicles[S], McBain and Dawson[9], Mouguin and Cathcart[lO], Stokes[ 1 l] and Sanni and Hutchinson[ 121. The present work was carried out by the modified diaphragm cell in which a new drive system was introduced in this laboratory[ 131. Cesium fluoride and mercury used were of BDH and Analar quality. The pre-diffusion time rI, required to establish steady state in the porous disc, was estimated from the equation[ 141 1.2 12
tg=------, b
of d@usion cell
The calibration of the diaphragm cell was done by using 0.5 M potassium chloride solutions diffusing into water. Previously 0.1 M KC1 was used in our laboratory for calibrating the cell but the present change to 0.5 M KC1 is due to the recommendation given in[4]_ The cell constant /3 was calculated from the diaphragm cell equation[l’-/l.
t is the duration of the diffusion experiment in
in which
seconds, AC’ = C;-C;
(1)
where Dis the integral diffusion coefficient and 1is the effective length of the diaphragm. It has been recently shown that Gordon’s equation gives a ts value which is considerably longer than that necessary to attain steady state[ 151. Experimental procedures for calibration and diffusion runs were the same as described in[12]. The air theromostat was set at 40°C and controlled to &O.l”C by using toluene regulator and electronic relay. The complete experimental set up is discussed elsewhere[13].
and
AC’ = Cl,-Ct,,
where Ci, Cz and Cl, and C: are the initial and final concentrations respectively of the bottom compartment B and upper compartment A. Dis an averaged (integral) diffusion coefficient given by the equation
D= where
1239
cmG3B)- G/G)ll(l
- ~*/G),
(3)
1240
M. L. SOOD AND MADHU BALA
and
is represented
by
TA = (C”A+ C’,)/Z.
(6) The values of D’(zrg) and Do@?” in (3) were obtained by constructing plots of P USC from the literature diffusion data[ 1S].
(
I +Calny* X
>
_- l_ 1~1514SJC (1+A’JC)2 + 2303 BC - C$(d).
(12)
In these equations,
Dl@usion runs with cesiumfluoride solutions From the known time t and the initial and final concentrations, the integral (averaged) diffusion coefficients Bwere c&&ted by means of (2). The integral values were next converted into differential diffusion coefficients D by means of a short series of approximations[l9] for solving (3) and the equation D =WJ+(~)(~).
(7)
The integral and differential given in Table 1.
diffusion coefficients
are
Table 1. Diffusion coefficients of aqueous cesium fluoride solutions at 313.16 K
D is the diffusion coefficient in cmzsel, T is the absolute temperature, C is the concentration in mol I-l, y+ is the activity coefficient on the molar concentration scale, E is the dielectric constant of the water and q0 its viscosity. The ionic conductance of the cation and anion are J.(: and 1: and A0 is the equivalent conductance of the electrolyte. S,,, is the limiting slope of the Debye and Hiickel theory. A’/C = A,/5 = in which 7 is the ional concentration, k the reciprocal radius, a the mean distance of closest approach of the ions and A = 35.56 x a (ET)-~“. The quantity d(ku) is the exponential integral function of the theory which may be obtained from tables given by Harned and Owen[Zl]. B is an empirical constant, C+(d), the term required to convert the expression from rational to molar activity coefficient and is given by ((Itd)
Cont.
0.01 0.02
0.03 0.04
0.05 0.06 0.08 0.09
0.10
1.0899
1.0328 1.2414 1.1482 1.1487 1.9356 2.1630 2.3744 2.4017
The theory of Onsager and Fuoss[20] equation 1 +C-
Do = 8-936 x lo- ‘*
leads to the
a Iny* 3C
-M,)]
’
(13)
where d is the density, M, is the molar mass of the solvent and M, that of the solute. The limiting value of the diffusion coefficient was obtained from the equation[22]
2.2526 2.2260 2.2094 2.1970 2.1885 2.1812 2.1715 2.1677 2.1593
THEORY
,
(8)
where V, and vz are the number of ions that dissociate in the solution and ii is a function given by
and
W/W +@oolCu W, - MAI d + 0401C[u(M,
(x KS)
D, = 2.3563 x 10m5cmZsm’ Cont. C in mol I- I, Diffusion coefficient D in cm’s_‘.
where
=
DObS.
.
(14)
In Tables 2 and 3 the data employed for the calculations are recorded. The values of diffusion coefficients obtained from the above equation given by Onsager and Fuoss[20] are, however, recorded in Table 1. Inspection of the results recorded in Table 1 indicate that the observed values increase from 1.0899 x 10e5 to 2.4017 x 10F5 cm2sm1 (except at 0.02 and 0.04M concentration) as the electrolytic concentration increases from 0.01 to 0.10 M. The values of diffusion coefficients obtained from 0-F[20] theory, however, decreasefrom2.2526 x 10m5 to2.1593 x 10-5cm2s~’ as the concentration of the salt is raised from 0.01 to 0.1 M. The departure of the experimental results from those of the theory at 40°C may be attributed to factors such as changing dielectric constant, viscosity of the medium, hydration erc. A somewhat similar type of departure has been observed by Stokes[23] for KCI, KBr, NaCl, NaBr etc. where the diffusion coefficients fall increasingly below the prediction of the O-F[20] Table 2. Specific data employed for theoretical calculations*
n; = .A; = E= T=
99.91 72.76 73.151 313.16
0, = ut = z, = Z,(=
I 1 1 1
go S,/, MI M,
= = = =
6.531 x lo’-’ 0.52616 18.0512 151.90
Mean distance of closest approach of the ions in 8, = 3.05. * For definitions and units see the text.
Diffusion
coefficients
Table 3. Data employed
0.02 0.03 0.04 0.05 0.06 0.08 0.09 0.10
ku
&(ko)
-C+(d)
0.1012 0.1431 0.1753 0.2024 0.2263 0.2479 0.2863 0.3036 0.3201
1.2266 0.9669 0.8248 0.7210 0.6555 0.5963 0.5175 0.4843 0.4590
(;)
also
observed
in this
(I..?)
0.9507 0.9359 0.9262 0.9190 0.9135 0.9090 0.9022 0.8996 0.8950
0.007 0.0014 0.0021 0.0027 0.0035 o.ixl42 0.0056 0.0063 0.0070
I- I.
laboratory
for
salts
like KF[24], NaNO, and K2S04[25], Na,S0,[26] etc. For CsCl, Lyons and Riley[l] found that the diffusion coefficient decreases with the increase in concentration (ie from 0.05 to 0.36 M), then increases up to 5.0 M and again decreases. But in the present study with CsF the diffusion coefficient (except at 0.02 and 0.04 M concentrations) increases continuously as the concentration of the salt is raised from 0.01 to 0.1 M whereas the theoretical values decrease continuously. Such negative departure for CsF from the O-F theory may also be held responsible to a certain extent on the hydration of anion ie F - ion in addition to changing dielectric constant, viscosity of the medium and hydration of cation. F- has been found to be associated with four molecules[27] of water whereas cesium[27] has a hydration number of 2.5. If we assume these values of hydration number of F- and Cs+ to be correct, then it leaves no doubt that these hydrated ions will move at a low speed and the values of diffusion coefficients will be less as compared to those predicted by the O-F[20] theory. Acknowledwmenr--One of the authors IM.L.S.1 is thankful to Professor R. Mills, Research School df Physical Sciences, Australian National University,Canberra for sendinga copy
of their invaluablebook
x 10”
455.0259 454.7635 458.1001 459.1071 460.0864 460.8244 462.2167 462.7572 463.3328
as the electrolytic concentration increases. Departure of the experimental results from those of O-F[20] was
1241
at 40°C coefficients
Cont. in mol.
theory
cesium fluoride
for theoretical calculations of the diffusion for cesium fluoride at 313.16 K
COtlC.
0.01
of aqueous
The Diaphragm Cell.
REFERENCES 1. A. L. Phillip and J. F. Riley,J. Am. &em. Sot. 76, 5216 (1954). 2. H. S. Harned, M. Blander and C. L. Hildreth, J. Am. &em. Sot. 76,4219 (1954). 3. R. A. Robinson and R. H. Stokes, Electrolyte Solutions 2nd edn. p. 253. Butterworths, London (1959).
4. R. Mills and L. A. Woolf, The Diaphragm Cd, Research School of Physical Sciences, Australian National University, Canberra (1968). and H. P. Hutchison, I. & EC 5. J. D. F. Christopher Fundomentols, 10, 303 (1971). 6. M. L. Sood, Pakist. J. Scient. Res. (1977). 7. J. H. Northrup and M. L. Anson, J. gen. Physiol. 12, 543 (1929). 8. G. S. Hartley and D. F. Runnicles, Proc. R. Sot. A168,401 (1938). 9. J. W. McBain and C. R. Dawson, Proc. R. Sot. A148, 32 (1935). 10. H. Mouguin and W. H. Cathcart, J. Am. them. Sot. 57, 1791 (1935). 11. R. H. Stokes, J. Am. &em. Sot. 72, 763 (1950). 12. S. A. Sanni and H. P. Hutchinson, J. scienr. Insr. l(ll), 1101 (1968). 13. M. L. Sood and S. L. Chopra, Indian J. Tech. 13, 329 (1975). Ann. N. Y Arad. Sci. 46, 285 (1945). 14. A. R..Gordon, 15. R. Mills.and L. A. Woolf, The Diaphragm Cell, p. 20. Research School of Physical Sciences, Australian National University, Canberra (1968). 16. M. L. Sood and S. L. Chopra, J. Indian them. Sot. LII, 98 (1975). 17. R. A. Robinson and R. H. Stokes, Electrolyte Solutions 2nd edn. pp. 71-86. Butterworths, London (1959). 18. L. A. Woolfand J. F. Tillev. J. nhvs. them. 71.1962 (1967). ’ 19. R. H. Stokes, .I. Am. ch& S&-72, 2243 (i950). \ 20. L. Onsager and R. H. Fuoss, J. them. Phys. 2,599 (1932). 21. H. S. Harned and B. B. Owen. The Physical Chemistry of Electrolyte Solutions 2nd edn. Reinhold, New York (1957). 22. H. S. Harned and B. B. Owen. The Physical Chemistry of Electrolyte Solutions 2nd edn. p. 244. Reinhold, New York (1957). 23. R. H. Stokes, .I. Am. them. Sot. 72, 2243 (1950). 24. M. L. Sood and G. Kaur, 2. phys. &em. 259,585 (1978). 25. M. L. Sood and S. L. Chopra, Pakist. J. scient. Res. 29, 7 (1977). 26. M. L. Sood, G. Kaur and S. L. Chopra, Indian .I. Chem. 18A, 181 (1979). 27. J. O’M. Boekris and P. P. Saluja, J. phys. Chem. 76(15), 2140 (1972).
COEFFICIENTS OF AQUEOUS FLUORIDE AT 40°C M.L.
Department
CESIUM
SCXIDand MADHU BALA
of Chemistry, Punjab Agricultural
(Receioed 12 November
1981; in revised
University, form
Ludhiana,
India
8 Mnrch 1982)
Abstract-Diaphragm cell technique has ken employed to determine diffusion coefficient for cesium fluoride at 40°C in the conantration range varying from 0.01 to 0.1 M. The data were analysed in the light of the theory of Onsager and Fuoss (O-F), J. them. Phys. 2.599 (1932)[20]. The results indicate that the O-F theorv is inadeauate to exDlainthe behaviour of this salt at 45°C. The results are also discussed with other 1: 1 type &Its of c&m.
Analysis of the solutions
INTRODUCTION
The initial and final concentrations of the solution From a diffusion experiment were determined conductometrically. From the final conductance readings of the solutions in the two compartments when the steady state has been attained, the concentrations were read from the standard curve which were initially prepared by plotting conductance us concentration at 40 *O.l”C. The conductometer used was of U.S.A. make (Yellow Spring Inst. Co., Ohio, Model 31) and was calibrated before use. The volume of the liquid in the pores of diaphragm were determined as suggested carlier[ 161.
The diffusion coefficients of aqueous c&urn chloride have been studied previously by conductometric[l] and Gouy[2] methods. These methods have their own limitations.[3] The diaphragm cell technique, on the other hand, is universally accepted for finding diffusion coefficients[4]. Further this technique can be successfully employed to determine the diffusion coefficients at elevated temperatures[5]. Keeping in view these facts the present investigations were carried out to find diffusion coefficients of cesium fluoride at 40°C.
EXPERIMENTAL
Calibration
The diaphragm cell technique has been universally accepted for finding diffusion coefficients above 0.05 M[6]. This method of determining diffusion coefficient was first introduced by Northrup and Anson[7] and later on underwent modifications by Hartley and Runnicles[S], McBain and Dawson[9], Mouguin and Cathcart[lO], Stokes[ 1 l] and Sanni and Hutchinson[ 121. The present work was carried out by the modified diaphragm cell in which a new drive system was introduced in this laboratory[ 131. Cesium fluoride and mercury used were of BDH and Analar quality. The pre-diffusion time rI, required to establish steady state in the porous disc, was estimated from the equation[ 141 1.2 12
tg=------, b
of d@usion cell
The calibration of the diaphragm cell was done by using 0.5 M potassium chloride solutions diffusing into water. Previously 0.1 M KC1 was used in our laboratory for calibrating the cell but the present change to 0.5 M KC1 is due to the recommendation given in[4]_ The cell constant /3 was calculated from the diaphragm cell equation[l’-/l.
t is the duration of the diffusion experiment in
in which
seconds, AC’ = C;-C;
(1)
where Dis the integral diffusion coefficient and 1is the effective length of the diaphragm. It has been recently shown that Gordon’s equation gives a ts value which is considerably longer than that necessary to attain steady state[ 151. Experimental procedures for calibration and diffusion runs were the same as described in[12]. The air theromostat was set at 40°C and controlled to &O.l”C by using toluene regulator and electronic relay. The complete experimental set up is discussed elsewhere[13].
and
AC’ = Cl,-Ct,,
where Ci, Cz and Cl, and C: are the initial and final concentrations respectively of the bottom compartment B and upper compartment A. Dis an averaged (integral) diffusion coefficient given by the equation
D= where
1239
cmG3B)- G/G)ll(l
- ~*/G),
(3)
1240
M. L. SOOD AND MADHU BALA
and
is represented
by
TA = (C”A+ C’,)/Z.
(6) The values of D’(zrg) and Do@?” in (3) were obtained by constructing plots of P USC from the literature diffusion data[ 1S].
(
I +Calny* X
>
_- l_ 1~1514SJC (1+A’JC)2 + 2303 BC - C$(d).
(12)
In these equations,
Dl@usion runs with cesiumfluoride solutions From the known time t and the initial and final concentrations, the integral (averaged) diffusion coefficients Bwere c&&ted by means of (2). The integral values were next converted into differential diffusion coefficients D by means of a short series of approximations[l9] for solving (3) and the equation D =WJ+(~)(~).
(7)
The integral and differential given in Table 1.
diffusion coefficients
are
Table 1. Diffusion coefficients of aqueous cesium fluoride solutions at 313.16 K
D is the diffusion coefficient in cmzsel, T is the absolute temperature, C is the concentration in mol I-l, y+ is the activity coefficient on the molar concentration scale, E is the dielectric constant of the water and q0 its viscosity. The ionic conductance of the cation and anion are J.(: and 1: and A0 is the equivalent conductance of the electrolyte. S,,, is the limiting slope of the Debye and Hiickel theory. A’/C = A,/5 = in which 7 is the ional concentration, k the reciprocal radius, a the mean distance of closest approach of the ions and A = 35.56 x a (ET)-~“. The quantity d(ku) is the exponential integral function of the theory which may be obtained from tables given by Harned and Owen[Zl]. B is an empirical constant, C+(d), the term required to convert the expression from rational to molar activity coefficient and is given by ((Itd)
Cont.
0.01 0.02
0.03 0.04
0.05 0.06 0.08 0.09
0.10
1.0899
1.0328 1.2414 1.1482 1.1487 1.9356 2.1630 2.3744 2.4017
The theory of Onsager and Fuoss[20] equation 1 +C-
Do = 8-936 x lo- ‘*
leads to the
a Iny* 3C
-M,)]
’
(13)
where d is the density, M, is the molar mass of the solvent and M, that of the solute. The limiting value of the diffusion coefficient was obtained from the equation[22]
2.2526 2.2260 2.2094 2.1970 2.1885 2.1812 2.1715 2.1677 2.1593
THEORY
,
(8)
where V, and vz are the number of ions that dissociate in the solution and ii is a function given by
and
W/W +@oolCu W, - MAI d + 0401C[u(M,
(x KS)
D, = 2.3563 x 10m5cmZsm’ Cont. C in mol I- I, Diffusion coefficient D in cm’s_‘.
where
=
DObS.
.
(14)
In Tables 2 and 3 the data employed for the calculations are recorded. The values of diffusion coefficients obtained from the above equation given by Onsager and Fuoss[20] are, however, recorded in Table 1. Inspection of the results recorded in Table 1 indicate that the observed values increase from 1.0899 x 10e5 to 2.4017 x 10F5 cm2sm1 (except at 0.02 and 0.04M concentration) as the electrolytic concentration increases from 0.01 to 0.10 M. The values of diffusion coefficients obtained from 0-F[20] theory, however, decreasefrom2.2526 x 10m5 to2.1593 x 10-5cm2s~’ as the concentration of the salt is raised from 0.01 to 0.1 M. The departure of the experimental results from those of the theory at 40°C may be attributed to factors such as changing dielectric constant, viscosity of the medium, hydration erc. A somewhat similar type of departure has been observed by Stokes[23] for KCI, KBr, NaCl, NaBr etc. where the diffusion coefficients fall increasingly below the prediction of the O-F[20] Table 2. Specific data employed for theoretical calculations*
n; = .A; = E= T=
99.91 72.76 73.151 313.16
0, = ut = z, = Z,(=
I 1 1 1
go S,/, MI M,
= = = =
6.531 x lo’-’ 0.52616 18.0512 151.90
Mean distance of closest approach of the ions in 8, = 3.05. * For definitions and units see the text.
Diffusion
coefficients
Table 3. Data employed
0.02 0.03 0.04 0.05 0.06 0.08 0.09 0.10
ku
&(ko)
-C+(d)
0.1012 0.1431 0.1753 0.2024 0.2263 0.2479 0.2863 0.3036 0.3201
1.2266 0.9669 0.8248 0.7210 0.6555 0.5963 0.5175 0.4843 0.4590
(;)
also
observed
in this
(I..?)
0.9507 0.9359 0.9262 0.9190 0.9135 0.9090 0.9022 0.8996 0.8950
0.007 0.0014 0.0021 0.0027 0.0035 o.ixl42 0.0056 0.0063 0.0070
I- I.
laboratory
for
salts
like KF[24], NaNO, and K2S04[25], Na,S0,[26] etc. For CsCl, Lyons and Riley[l] found that the diffusion coefficient decreases with the increase in concentration (ie from 0.05 to 0.36 M), then increases up to 5.0 M and again decreases. But in the present study with CsF the diffusion coefficient (except at 0.02 and 0.04 M concentrations) increases continuously as the concentration of the salt is raised from 0.01 to 0.1 M whereas the theoretical values decrease continuously. Such negative departure for CsF from the O-F theory may also be held responsible to a certain extent on the hydration of anion ie F - ion in addition to changing dielectric constant, viscosity of the medium and hydration of cation. F- has been found to be associated with four molecules[27] of water whereas cesium[27] has a hydration number of 2.5. If we assume these values of hydration number of F- and Cs+ to be correct, then it leaves no doubt that these hydrated ions will move at a low speed and the values of diffusion coefficients will be less as compared to those predicted by the O-F[20] theory. Acknowledwmenr--One of the authors IM.L.S.1 is thankful to Professor R. Mills, Research School df Physical Sciences, Australian National University,Canberra for sendinga copy
of their invaluablebook
x 10”
455.0259 454.7635 458.1001 459.1071 460.0864 460.8244 462.2167 462.7572 463.3328
as the electrolytic concentration increases. Departure of the experimental results from those of O-F[20] was
1241
at 40°C coefficients
Cont. in mol.
theory
cesium fluoride
for theoretical calculations of the diffusion for cesium fluoride at 313.16 K
COtlC.
0.01
of aqueous
The Diaphragm Cell.
REFERENCES 1. A. L. Phillip and J. F. Riley,J. Am. &em. Sot. 76, 5216 (1954). 2. H. S. Harned, M. Blander and C. L. Hildreth, J. Am. &em. Sot. 76,4219 (1954). 3. R. A. Robinson and R. H. Stokes, Electrolyte Solutions 2nd edn. p. 253. Butterworths, London (1959).
4. R. Mills and L. A. Woolf, The Diaphragm Cd, Research School of Physical Sciences, Australian National University, Canberra (1968). and H. P. Hutchison, I. & EC 5. J. D. F. Christopher Fundomentols, 10, 303 (1971). 6. M. L. Sood, Pakist. J. Scient. Res. (1977). 7. J. H. Northrup and M. L. Anson, J. gen. Physiol. 12, 543 (1929). 8. G. S. Hartley and D. F. Runnicles, Proc. R. Sot. A168,401 (1938). 9. J. W. McBain and C. R. Dawson, Proc. R. Sot. A148, 32 (1935). 10. H. Mouguin and W. H. Cathcart, J. Am. them. Sot. 57, 1791 (1935). 11. R. H. Stokes, J. Am. &em. Sot. 72, 763 (1950). 12. S. A. Sanni and H. P. Hutchinson, J. scienr. Insr. l(ll), 1101 (1968). 13. M. L. Sood and S. L. Chopra, Indian J. Tech. 13, 329 (1975). Ann. N. Y Arad. Sci. 46, 285 (1945). 14. A. R..Gordon, 15. R. Mills.and L. A. Woolf, The Diaphragm Cell, p. 20. Research School of Physical Sciences, Australian National University, Canberra (1968). 16. M. L. Sood and S. L. Chopra, J. Indian them. Sot. LII, 98 (1975). 17. R. A. Robinson and R. H. Stokes, Electrolyte Solutions 2nd edn. pp. 71-86. Butterworths, London (1959). 18. L. A. Woolfand J. F. Tillev. J. nhvs. them. 71.1962 (1967). ’ 19. R. H. Stokes, .I. Am. ch& S&-72, 2243 (i950). \ 20. L. Onsager and R. H. Fuoss, J. them. Phys. 2,599 (1932). 21. H. S. Harned and B. B. Owen. The Physical Chemistry of Electrolyte Solutions 2nd edn. Reinhold, New York (1957). 22. H. S. Harned and B. B. Owen. The Physical Chemistry of Electrolyte Solutions 2nd edn. p. 244. Reinhold, New York (1957). 23. R. H. Stokes, .I. Am. them. Sot. 72, 2243 (1950). 24. M. L. Sood and G. Kaur, 2. phys. &em. 259,585 (1978). 25. M. L. Sood and S. L. Chopra, Pakist. J. scient. Res. 29, 7 (1977). 26. M. L. Sood, G. Kaur and S. L. Chopra, Indian .I. Chem. 18A, 181 (1979). 27. J. O’M. Boekris and P. P. Saluja, J. phys. Chem. 76(15), 2140 (1972).