OXYGEN ABSORPTION INTO SODIUM DITHIONITE SOLUTION
Susumu FUKUSHIMA, Atsuo UYAMA, Yoshiro YAMAGUCHI,Em TSUJI and Seiichi MEZAKI Department of Chemical Engineering, Kansai University, Suita 564
Absorption rates of pure oxygen gas into sodium dithionite solution with sodium hydroxide were measured at 20 and 30°C in a laminar jet. Absorption rates were also measured under 0.315 to 4.0 atm of oxygen pressure in a continuous stirred tank. From analysis of the data on the basis of chemical absorption theory, the rate equation of chemi- cal reaction for molecular oxygen A was obtained, where the molar ratio of sodium dithionite B to sodium hydroxide is lower than 1/2, as where *Of i.9=(3.7±0.7)xl010 exp (-1.20xWfRT) [(//g-mole)° 9 sec 1] The absorption for the bubble stirred tank showed that the reaction orders for respective chemical species are reasonable. Furthermore, the homogeneous reaction assay in the continuous stirred tank established that this rate equation of chemical reaction is reasonable.
where the pH was approximately 13. Introduction There are few reports of kinetic data on the basis To obtain the inter facial area and liquid-phase mass of chemical absorption theory. Jhaveri and Sharma3) transfer coefficient without chemical reaction on the discussed, from an analysis of pure oxygenabsorption basis of chemical absorption theory it is desirable to into dithionite solution in a laminarjet, oxygen absorp- perform absorption experiments in a reaction system tion through free surface into solution in a continuous in which the real rate equation of chemical reaction stirred tank and oxygen absorption into solution in a is already known in a wide concentration range of packed column at 33°C. They reported the first chemical species. order for CBand the zero order for CAwhere the CBis Sharma and co-workers3"5'7>8>15) have reported data smaller than 8xlO~2M, and the second order for of inter facial areas and gas- and liquid-phase mass CBand the zero order for CAwhere the CBis larger transfer coefficients in various gas-liquid contactors than 8xlO"2M. for oxygen absorption with dithionite solution at 33°C. The present work was attempted to find the real rate Since the study of reaction between dithionite and equation of chemical reaction between dithionite and molecular oxygen in aqueous solution was conducted molecular oxygen from an analysis of absorption data by Meyer10) in 1903, various kinetic data have been for a laminar jet and two types of stirred tanks at 20 reported. Rinker et al.12) have shown that the chemi- and 30°C on the basis of chemical absorption theory. cal reaction is a half order for dithionite concentra- Further, this rate equation was established by oxygen tion CBand the first order for molecular oxygen CA monitored assay for a homogeneoussystem in a con- from oxygenabsorption experiments in a batch stirred tinuous stirred tank. tank. The initial CB was varied from 5xlO~3 to 1. Theory 2xlO~2M in 0.1N alkaline solution. Morello et al.U) have also reported the first order of CBand the The following reactions take place in excess sodium zero order of CAin stopped-flow experiments at 37°C. hydroxide solution. The feed concentrations were varied from 8 x 10~5 to Na2S2O4+O2+H2O >NaHSO3+NaHSO4 (1) 4.8X10~4M for CB and 10"4 to 4.8x10"4M for CA9 NaHSO3+NaOH >Na2SO3+ H2O (2) Received December 12, 1977. Correspondence concerning this article should be addressed to S. Fukushima. NaHSO4+NaOH --*Na2SO4+H2O (3)
VOL ll NO. 4 1978 283 Thus tion, and then 30 cm3 methyl alcohol was added to the Na2S2O4+O2+2NaOH >Na2SO3+Na2SO4+H2O flask to avoid solidification of leuco-compound. (4) The ampoule was broken by a glass rod under bubbling 1. 1 Chemical absorption nitrogen gas at about 12 cm3/min through glass tubing closed by the bottom of the flask. Whenthe solution The theoretical reaction coefficient of gas absorption is still blue, the dithionite content is less than that of in the (m+#)-th order irreversible reaction, /3, is given methylene blue because the methylene blue is quantita- by Hikita and Asai2) as follows: tively reduced with dithionite on an equimolecular basis from an intense blue color to an almost colorless leuco-form. Thus the content of dithionite in the where sample was 93.4 to 94.0% as determined from the weight of sample at which the solution just became 7 ktl(m+i)m-nAAtJ L(^--i) J colorless. (6) 2) Iodimetric titration12) A glass ampoule was put and in a flask containing 30 cm3 of excess 0.05 N iodine CBoDB\ \DA solution with acetic acid. A nitrogen gas cylinder n /i I ^Bo-^B \ -L^A (H\ was connected with glass tubing that reached close to the flask bottom. This first flask was connected with When the value of j' is larger than 6, Eq. (5) becomes a second flask containing 0.05 N thiosulfate solution and with two other, flasks containing water in the same or fashion. Under bubbling nitrogen gas at about 12 cm3/min, 20 cm3 of 37%formalin was added into the VDA-VDA~~l(m+lfm-nCAi j LT/3--1) SeJ solution in the first flask and then the glass ampoule was broken by a glass rod. All the solutions were (9) mixed and the total content of dithionite and thio- Thus, the reaction orders of m and n are determined sulfate in the sample was determined by back- from the analysis of absorption data by Eq. (9), titration with 0.01 N thiosulfate solution. The total where y'>6. content of dithionite, sulfite and thiosulfate was also 1. 2 Homogeneousreaction identified by the same procedure without formalin. The oxygensolution wasfed into a continuous stir- Thus the total content of dithionite and thiosulfate and red tank filled with aqueous solution. Whenthe tracer the content of sulfite in the sample were found to be of dithionite solution is instantaneously added into the 93.0 to 94.0 wt% and 6.0 to 8.0wt%, respectively. stirred tank, the material balance of oxygen and The former values agree well with the aforementioned dithionite are given as follows : data on dithionite content. For oxygen balance 2. 2 Oxidation products of dithionite sample in chemi- l -A=km,nC?TlCS ,tAmBnrl+(dAldd) (10) cal absorption For dithionite balance In a flask, 0.05 to 0.1 g of dithionite sample was -B=km,nC7inC^Aá"BnTl+(dBldd) (1 1) added into 5 cm3 of 5 N NaOHsolution and oxidized The boundary conditions are written as under bubbling pure oxygen gas at 30°C until no reduc- tion of methylene blue was identified. Apart of this #=0, A=\ and £=1 (12) solution was acidified with acetic acid and titrated The time dependences of A and B are obtained from with indirect iodimetry to determine the total content these equations. of sulfite and thiosulfate. The sulfite was thus the 2. Experimental sum of the impurity in dithionite sample and oxida- tion products. The major part of the solution was 2. 1 Purity of dithionite sample further oxidized in the presence of 10"4M CoCl2 The sodium dithionite (Wako Pure Chemical In- catalyst at pH 8 and 30°C. In this step, the thiosulfate dustries) in this work was used without purification. was stable. Thus sulfite was identified as one of the Sample purity was checked by two different titration oxidation products. The total content of sulfate in methods, as follows, in order to be strictly accurate. the final oxidation products was determined by titra- The sample was sealed in a glass ampoule under dry tion of 10"2 N BaCl2 solution with THQX)as an indi- nitrogen gas. cator. 1) Methylene blue titration12) A glass ampoule It was thus found that the sample contained no containing the sample was put into a flask containing thiosulfate or sulfate and that the dithionite in the 30 cm3 of 10"3 N oxygen-free methylene blue solu- sample was oxidized at excess NaOH according to
284 JOURNAL OF CHEMICAL ENGINEERING OF JAPAN Table 1 Physical properties of dithionite solutions Series p cAi
[°C] [105 Dacm2/sec]DB [g/cm3] [102g/cm[105 cm2/sec] - sec] [104 g-mole//] 1 A 1.0M NaOH-0.5 M Na2S2O4 20 1.10 60 .61 0.806 5.61 1 30 1.10 27 .09 1.05 1 5.12 B 0.5 M NaOH-0.5 M Na2S2O4 30 1.08 ll .31 1.16 6.21 C 0.5 M NaOH-0.3 M Na2S2O4 20 1.06 1.26 92 0.960 8.42 30 1.06 1.01 .48 1.24 7.40 D 0.5 M NaOH-0.25 M Na2S2O4 20 1.05 1.26 .92 0.964 8.81 30 1.05 0.987 ,52 1.26
E 0.1 M NaOH-0.5 M Na2S2O4 30 1.08 1.10 2.36 1.18 7.24
Eq. (4). without chemical reaction, kf, were also estimated 2. 3 Chemical absorption from the following equation on the basis of penetration 1) Laminarjet The nozzle was 0.18 cm in diameter theory. and the Scriven14)-type receiver for the laminar jet was 0.2 cm in diameter. The liquid jet length was varied ki~V"ir~i^rv f; J (13) from 7.07 to 12.3 cm by adjusting nozzle position and Continuous stirred tank The 18Ni-8Cr-stainless the liquid flow rate was varied from 3.6 to 5.2 cm3/sec. steel tank with coil was 8.5 cm in diameter and 13.8 cm To measurethe laminar jet diameter accurately, in height, mounted with 4 baffles, 0.8 cm in width. two lights were placed on both sides of the jet in The stirred shaft was supported at top and bottom of a triangle with Nikon S-3M cameras, and frosted the tank. The agitators were a 3-blade propeller paper was placed 20 cm behind the liquidjet. Photo- impeller mounted 1 1.5 cmfrom the tank bottom for gas graphs were taken at the top, middle and end of the phase and a 6-blade turbine impeller mounted 2.3 cm jet. Thus, the difference among these diameters was from the tank bottom for liquid phase. Both impellers within:±:5% and the diameter was varied from 1.63 to were 4.3cm in diameter. The liquid volume was 480 cm3. To control the liquid temperature within The apparatus was placed in double thermostatic air ztO.2°C, the tank was provided the two turns of chambers1.81to maintain the oxygenmm.gas temperature 6cm diameter coil made of 0.85cm diameter coil within=j=0.2°C. The liquid temperature was also tubing. The stirred speed was 200rpm. controlled withindzO.2°C. The absorption rate of Oxygen-free dithionite solution of type C was fed pure oxygen saturated with water vapor into dithionite into the lower part of the stirred tank and the reacted solution was measured at atmospheric pressure by a solution was withdrawn from the bottom of the tank soap-film flowmeter at 20 and 30°C. through a constant liquid-level device to atmosphere. Five types of aqueous dithionite solutions were made Pure oxygengas was also fed through a water saturator as follows: A. 1.0M NaOH-0.5M Na2S2O4, B. and a flowmeter into the upper part of the tank at 32 0.5 M NaOH-0.5 M Na2S2O4, C. 0.5 M NaOH-0.3 M cm3/sec and absorbed through the free surface into the Na2S2O4, D. 0.5M NaOH-0.25M Na2S2O4 and E. dithionite solution under 1 to 4 atm at 20 and 30°C. 0.1 M NaOH-0.5M Na2S2O4. By preoxidation of Then unabsorbed oxygen gas was led to atmosphere. these solutions with molecular oxygen before feed to Oxygen absorption from nitrogen-oxygen gas into the absorber, the molar ratio of Na2S2O4to NaOH, dithionite solution was also performed, at a total o), and the value of pHwere varied from 0.182 to 1.05 pressure of 1 atm. The absorption rates were meas- and 12.0 to 13.8, respectively. Thus, the feed solu- ured from the difference of dithionite content be- tions included sulfate. The physical properties of the tween inlet and outlet of the tank. The dithionite solutions were only varied within 2% by reaction in content was determined by the iodimetric titration this experimental condition. Table 1 shows the method mentioned above. No molecular oxygen in physical properties at the initial state. The solubilities the bulk of liquid in the tank was identified with the of oxygen in solutions are estimated by the van Kreve- oxygen analyser. The experimental conditions were len method16} on referring to that for pure water in the as follows: oxygen pressure PA 0.315 to 4 atm, CBoat literature6}. The salt effect of dithionite is assumed to outlet of tank 0.058 to 0.208 M, co at outlet of tank be equal to that of sulfate. The diffusivity of oxygen 0.124 to 0.478, residence time of liquid rz 8.86x 102 to in pure water is given by Wise and Houghton18). The 1.08xlO3sec at 30°C, and PA 0.32 to 4atm, CBo at values for solutions are evaluated by the Stokes- outlet of tank 0.046 to 0.216M, co at outlet of tank Einstein equation and the value for dithionite is as- 0.098 to0.478, zt 9.11X102 to 3.1x103 secat20°C. sumed to be equal to that for sulfate17K Pure oxygen absorption into spdium sulfite solution The values of liquid-phase mass transfer coefficient with CoCl2 catalyst at pH 8 and 30°C was performed to
VOL. ll NO. 4 1978 285 7.73 mole/atm-cm2-sec. It was found that the mass- transfer resistance was ruled by liquid side in oxygen absorption from nitrogen-oxygen gas with dithionite solution. 3) Batch bubble stirred tank The bubble stirred tank used was made of stainless steel, 16 cm in diam- eter, mounted with 4 baffles, 1.6cm in width. The agitator was a 4-blade turbine impeller, 6.4cm in diameter. The liquid height was equal to tank diam- eter and liquid volume was 3.3 /. The gas distribu- tor mounted at the tank bottom consisted of 72 holes, 1 mmin diameter, in a triangular arrangement, 4 mm in pitch. The air flow rate was 8.65//min and the stirred speed was 350 rpm. The oxygen absorption Fig. 1 Observed fi versus CBofor the laminar jet rate was measured from the time dependence of CBo and the continuous stirred tank in the stirred tank at 30°C. The solution concentra- tion at initial state consisted of 1.5 MNaOH, 0.2 M Na2S2O4 and 0.1 M Na2SO4. The liquid-phase volu- metric coefficient of mass transfer, kfa, was obtained from oxygen absorption at low CBo. 2. 4 Oxygen monitored homogeneous reaction The first-stage stirred reactor used was made of polyvinyl chloride, 10cm in diameter and 7cm in height, mounted with 4 baffles, 1 cm in width. The agitator was 4-blade turbine impeller, 5 cm in diameter, mounted on a shaft at the center of the tank. The sensor of the BeckmanField-lab oxygen analyser was located at mid-height in the tank. The liquid volume was 530 cm3. The stirred speed was 380rpm. The solutions, consisting of 0.1 M Na2SO4and Fig. 2 Determination of reaction order on sodium 7.5xlO~2M NaOH at pH 13.4, contained 64.0 and dithionite for the laminar jet 65.0% saturated oxygen in the bubble stirred tank. These were fed to the stirred reactor at 21.1 cm3/min determine the area of free surface, wheresulfate was by a micro tubing pump. These solutions were added to the solution so as to attain the same dynamic withdrawn from the reactor bottom through a constant viscosity as that of dithionite solution. The rate con- liquid-level device to atmosphere. For both feed stant of chemical reaction was 8.7x 106 //g-mol-sec solutions, 0.5 and 0.9 cm3 of the oxygen-free solutions given from data analysis of oxygen absorption with containing 0.46M Na2S2O4 and 1 M NaOH were sulfite solution in the aforementioned laminar jet on instantaneously injected by a syringe into the stirred the assumption that the chemical reaction rate is first reactor. Thus the initial concentrations of dithionite order for oxygen concentration and first order for in the reactor were 3.9xl0~4 and 7.0xl0~4M. CoCl2. Thus the free surface area was 52.8 cm2 in The dimensionless concentrations of oxygen in the the continuous stirred tank. This value is equal to reactor, A, were measured according to time by an the geometrical surface area. Hence, the inter facial oxygenanalyser. area a was 0.ll cm"1. Physical oxygen absorption was also performed to 3. Result and Discussion obtain the kfa. The values ofkf were 3.0X 10"3 cm/ 3. 1 Determination of rate equation of chemical sec at 20°C and 3.3x10"3cm/sec at 30°C, given by reaction from absorption data dividing kfa by a. The values of w in the bulk of the liquid were small- Furthermore, methanol desorption from sulfate er than 1/2 for the data mentioned below. Figure 1 solution to nitrogen gas was performed to obtain the shows plots of the observed /3 versus bulk concentra- gas-phase mass-transfer coefficient kg. The desorp- tion CBo for the laminarjet at 20 and 30°C and for the tion rate was measuredfromthe difference of refrac- stirred tank where PA=\.5 atm at 20°C. The rear- tive index in liquid between inlet and outlet of tank. rangement of these data according to Eq. (9) is shown Thus, the value of kg for oxygen was 3.3xl0"5g- inFig. 2. The slopes of the lines are 0.95. Thus the
286 JOURNAL OF CHEMICAL ENGINEERING OF JAPAN reaction order n is 1.9 in the CBo range of4x10~2 to 3.5xlO-1M. Figure 3 indicates the rearranged data of various PA according to Eq. (9). The slopes of the lines for 20 and 30°C are -0.5. Hence, the reaction order m is zero. In the bubble stirred tank, the rearranged data according to Eq. (9) are shown in Fig. 4. The slope of the line is 0.93. This result also indicates that the values of m and n are 0 and 1.9, respectively, even though the CBo is lower than 8x 10"2 M. The dependence of rate constant of chemical reac- tion on temperature is obtained from the Arrhenius Fig. 3 Determination of reaction order on molec- plots. Thus, the rate equation of chemical reaction ular oxygenfor the laminar jet and the continuous between dithionite and molecular oxygen in aqueous stirred tank solution is given as follows: AC1 rA=k0, 1.9C° whereB-» (14) fco,i.9=(3.7±O.7)x 1010 exp (-1.20X lO'/RT) (15) It suggests a radical reaction where the activation energy is appreciably low. This rate equation is approximately written as follows : r^=[4.6 x 1010 exp (-1.20X W/RT)]CB (16) 3. 2 Dependence of molar ratio of dithionite to alkali on reaction rate Figure 5 indicates the dependence of V^o.i.q on w, Fig. 4 (NA/VCAi) versus CBo for the bubble on the assumption that even though a>> 1/2 the values stirred tank (30°C) ofm and n are the same as aforementioned. The solid lines indicate the predicted values given by Eq. (15) at 20 and 30°C. In the case when w=4A, which belongs to the type E solution for pH 12.0 at 30°C for the laminar jet, the value of V^o,i.9 is much larger than that where o><1/2, and the exhaust gas had on offen- sive odor. This result suggested that the solution near the interface is much more acidic than the ob- served value of pH, because it is known9) that dithio- nite in acidic solution decomposes very rapidly. Hence, the reaction where
VOL. ll NO.4 1978 287 order of 1O~5M. Conclusions The conclusions drawn from this investigation are : 1. Analysis of the data for oxygen absorption with aqueous dithionite solution in the laminar jet and the stirred tank on the basis of chemical absorption theory resulted in a rate equation of chemical reaction, that is the 1.9-th order of dithionite concentration and the zero order of molecular oxygenconcentration, where the molar ratio of dithionite to alkali in the bulk of liquid is approximately smaller than 1/2. 2. This absorption for bubble stirred tank indicated that the reaction orders for respective chemical species presented are reasonable. 3. The homogeneous reaction assay established that the rate equation of chemical reaction presented is reasonable, even though the dithionite concentra- tion is on the order of 10"5 M. Fig. 6 Comparison of the data and predicted values ofA according to reaction time for the homo- Nomenclature geneous reaction in the continuous stirred tank A = dimensionless concentration of oxygen, CJCA ln [-] a = inter facial area per unit liquid volume [cm"1] -<(iV£-££) B = dimensionless concentration of sodium dithionite, CB/CB it [-] The diffusivity of electrolyte is given13} as follows : C = concentration in liquid phase [g-mole//] n_RT n++n_ X+X__ /* /., m?_ $r\ nn\ D = diffusivity in liquid phase [cm2/sec] D~T^' n+n_ 'Vf^'TTV T "dm'") ( j d = diameter of laminar jet [cm] F = volumetric flow rate of laminar jet [cm3/sec] The values of limiting equivalent conductivities, X±, F° = Faraday [(A/cm2)(V/cm)(g-eqiv/cm2)] for NaOHand activity coefficient j for 0.1-1 M h = height of laminar jet [cm] NaOHat 25°C are given in the literature13>. Thus kg = gas-phase mass-trasnfer coefficient V'D^/DB=1.3 at 20°C and 1.1-1.2 at 30°C and the [g-mole/atm à" cm2 à" sec] ki - liquid-phase mass-transfer coefficient [cm2/sec] second term in Eq. (19) is negligible in this absorption kf = liquid-phase mass-transfer coefficient condition. Hence, co<0.65 at 20°C and o><0.60 at without chemical reaction [cm2/sec] 30°C. These results agree fairly well with the experi- km>n = rate constant of (m+«)-th order mental data mentioned above. Therefore, oxygen chemical reaction [(//g-mole)(m+n~ 1} à" sec" *] m = reaction order of molecular oxygen [-] absorption with dithionite solution according to m' = molality of solute per solvent [g-mole//] Eqs. (1), (2) and (3) has to be performed at the operat- NA = mass transfer rate of oxygen ing condition according to Eq. (19). at interface [g-mole/sec] 3. 3 Homogeneous reaction A^oo = maximummass-transfer rate of oxygen at interface [g-mole/sec] Figure 6 shows plots of the observed A versus di- ND = masstransfer rate of sodium mensionless time 6 in the oxygen monitored homogene- hydroxide from bulk of liquid ous reaction for pH 13.4 at 30°C, where the initial to interface [g-mole/sec] values of CB were 3.9x10~4 and 7.0x10"4M. The n = reaction order of sodium dithionite [-] thick solid lines and thin solid lines are predicted values «+, /i_ = valences of cation and anion, respecti vely [-] ofA and CB given by Eqs. (10), (ll), (12), (14) and (15), P = pressure [atm] where m=0, n=l.9. The broken lines and dotted R = gas constant [cal/g-moleà"°K] or [J/g-moleà"°K] lines indicate predicted values of A where m=0, n= r = chemical reaction rate [g-mole// - sec] 1.8 and m=0, n=2.0, respectively. The thick solid T = temperature [°K] lines are in excellent agreement with the experimental / = time [sec] data in comparison of broken lines and dotted lines for both initial values of CB. /3 = reaction coefficient [-] /3oo = maximumvalue of reaction coefficient Hence, this result established that the rate equation defined by Eq. (7) [-] of chemical reaction given by Eqs. (14) and (15) is T = activity coefficient [-] reasonable at low o>, even though the CBvalue is the 7' = dimensionless factor defined by Eq. (6) [-]
283 JOURNAL OF CHEMICAL ENGINEERING OF JAPAN 0
X =dimensionless time [-] 5) Juvekar, V. A. and M. M. Sharma: ibid., 28, 976 (1973). = limiting equivalent conductivity [cm2/£2 à"equiv] 6) Linke, W. F. and A. Seidell: "Solubilities: Inorganic and II viscosity [g/cm à"sec] Metal-Organic Compounds", 4th edn., Vol. 2, p. 1228, D. 9 density [g/cm3] van Nostrand, New York, U. S. A. (1965). T residence time [sec] 7) Mehta, K. C. and M. M. Sharma: Brit. Chem. Eng., 15, 0) molar ratio of sodium dithionite to 1440 (1970). a sodium hydroxide [-] 8) Mehta, V.D. and M. M. Sharma: Chem. Eng. Sci., 26, 461 (1971).
9 sodium hydroxide 10) Meyer, J.: Z. anorg. Chem., 34, 43 (1903).
i gas-phase ll) Morello, J. A., M. R. Craw, H. P. Constantine and R. E. i nterface Forster: /. Appl. Physiol, 19, 522 (1964). in inlet of tank it initial state in tank 12) Rinker, R. G., T. P. Gordon, D. M. Mason, R. R. Sakaida / liquid-phase and W. H. Corocoran: /. Phy. Chem., 64, 573 (1960). bulk of liquid 13) Robinson, R. A. and R. H. Stokes: "Electrolyte Solutions", o 2nd edn., Butterworths, London, England (1970). w water + cation 14) Scriven, L. E. and R. L. Pig ford: AIChEJ., 5, 397 (1959), 15) Shende, B. W. and M. M. Sharma: Chem. Eng. Sci., 29, anion 1763 (1974). Literature Cited 16) van Krevelen, D. W. and P. J. Hoftijzer: Chem. Ind. XXIeme Congr. Int. Chim. Ind., p. 168 (1948). 1) Fritz, J. S. and M.Q. Freeland: Analy. Chem., 26, 1593 (1954). 17) Washburn, E. W.: "International Critical Tables of Numerical Data, Physics, Chemistry and Technology", 2) Hikita, H. and S. Asai: Kagaku Kogaku, 27, 823 (1963). Vol. 5, p. 67, McGraw-Hill, New York, U. S. A. (1926). 3) Jhaveri, A. S. and M. M. Sharma: Chem. Eng. Set, 23, 1 (1968). 18) Wise, D. L. and G. H. Houghton: Chem. Eng. Sci., 21, 999 (1966). 4) Jhaveri, A. S. and M. M. Sharma: ibid., 23, 669 (1968).
VOL. ll NO. 4 1978 289