Abdulagatov_2004_Fluid-Phase-Equilibria

Fluid Phase Equilibria 216(2004)189–199Experimental vapor pressures and derived thermodynamic propertiesof aqueous solutions of lithium sulfate from 423to 573KI.M.Abdulagatov a ,∗,1,N.D.Azizov baInstitute for Geothermal Problems of the Dagestan Scientific Center of the Russian Academy of Sciences,Shamilya Street 39-A,367003Makhachkala,Dagestan,Russia b Azerbaijan State Oil Academy,Baku 370601,AzerbaijanAccepted 30January 2003AbstractVapor pressures of four aqueous lithium sulfate solutions (0.279,0.886,1.322,and 1.600mol kg −1)have been measured in the temperature range from 423.15to 573.15K with a constant-volume piezometer immersed in a precision liquid thermostat.The static method was used to measure of vapor pressure.The total uncertainty of temperature,pressure,and composition measurements were estimated to be less than 10mK,0.2,and 0.014%,respectively.The vapor pressures of pure water were measure to confirm the accuracy of the method for aqueous lithium sulfate solutions taken from the apparatus and procedure of measurements.The results for pure water were compared with high-accuracy P S –T S measurements by other authors and with values calculated from IAPWS eful thermodynamic functions (water activities,excess relative partial molar entropy,and relative partial molar enthalpy values of solvent)were derived using measured values of vapor pressure for the solution and pure water.The measured and derived thermodynamic properties for solution were compared with data reported in the literature.Present results are consistent with most of the previous thermodynamic data for the pure water and H 2O +Li 2SO 4solutions.©2003Elsevier B.V .All rights reserved.Keywords:Excess partial molar entropy;Lithium sulfate;Partial molar enthalpy;Partial molar volume;Vapor-pressure;Water activity;Water1.IntroductionVapor pressures as a function of temperature are known for most aqueous salt solutions,but the available literature data sets contain discrepancies or are restricted to a narrow temperature and concentration ranges.Vapor pressures are important in processes related to the storage and handling of hygroscopic salts,are needed for testing and calibration of hygrometers,and in the control of atmospheric humidity in closed spaces [1–3].Vapor pressure data are important also to calculate water activities,excess relative partial molar entropy,and relative partial molar enthalpy values of water [4–7].∗Corresponding author.Present address:Physical and Chemical Prop-erties Division,National Institute of Standards and Technology,325Broad-way,Boulder,CO 80303,USA.Tel:+1-303-497-4027;fax:+1-303-497-5224.E-mail addresses:ilmutdin@,mangur@datacom.ru (I.M.Abdulagatov),nazim azizov@ (N.D.Azizov).1Tel:+7-8722-62-66-23;fax:+7-8722-67-20-67(Russia).Vapor pressures over saturated aqueous solutions of lithium sulfate were previously measured by Rockland [1]and Labuza et al.[2]within a restricted temperature range (5–40◦C)and (20–25◦C),respectively.Seven methods of water activity measurement were tested by Labuza et al.[2]for the saturated salt solutions including H 2O +Li 2SO 4system at 20and 25◦C.Best results was found for the vapor pressure manometric technique.Apelblat and Korin [6]used electronic hygrometer with an electrolyte sensor to measure vapor pressures of saturated aqueous solutions of Li 2SO 4at temperatures 278–323K.The results for saturated H 2O +Li 2SO 4solutions were ex-pressed by the equationln P S =145.239− 11271.6T −18.688ln T,(1)where P s is the vapor pressure in kPa,T the temperature in K.The vapor pressure of aqueous electrolyte solutions are often calculated from other physical properties,for example0378-3812/$–see front matter ©2003Elsevier B.V .All rights reserved.doi:10.1016/j.fluid.2003.01.004190I.M.Abdulagatov,N.D.Azizov/Fluid Phase Equilibria216(2004)189–199 from activity of water a w,osmotic coefficient(φ),and ionicactivity coefficient(γ±)[7].The osmotic coefficient data ofaqueous lithium sulfate solutions previously were reportedby Holmes and Mesmer[8,9]in the temperature range from383to498K using isopiestic technique.The results were an-alyzed in term of the Pitzer’s ion interaction model.Pearceand Eckstrom[10]reported vapor pressure data for aque-ous lithium sulfate solutions at temperature of298.15K andat concentrations from0to saturation3.09444mol kg−1.Goldberg[11]critically evaluated of the mean activity andosmotic coefficients in aqueous lithium sulfate solutions at298.15K.The recommended values of the mean activity andosmotic coefficient of lithium sulfate in water are reportedby Goldberg[11].Zarembo and Puchkov[12]and Zaremboet al.[13]reported water activities for H2O+Li2SO4so-lutions at temperatures from423to573K for compositionbetween0.25and2.5m.The following vapor pressure equation for the aqueouslithium sulfate solutions have been developed by Aseyev[14]P S=P0expmP0.434295,(2)with P=W0+W1t+W2m+W3t2+W4mt+W5mt2,P0=P C expT CT(A0+A1τ+A2τ1.5+A3τ3+A4τ3.5+A5τ4),(3)whereτ=1−(T/T C),T is the temperature in K,t the temperature in◦C,P S the vapor pressure of the solution in Pa,P0the vapor-pressure of pure water in Pa,m the con-centration in mol kg−1,W i(i=0–5)thefitting coefficients, P C=2.2064×107Pa the critical pressure of pure water, and T C=647.14K is the critical temperature of pure wa-ter.Eq.(2)is valid in the temperature range from273to 573K and at concentrations between1and25mol%.The adjusting parameters(W i)of Eq.(2)for H2O+Li2SO4so-lutions was determined using experimental and derived val-ues of vapor pressure reported by Holmes and Mesmer[8], Goldberg[11],Zarembo and Puchkov[12],and Zarembo et al.[13].The deviation between measured and calculated with Eq.(2)values of vapor-pressures for H2O+Li2SO4is about0.09%at temperatures up to373K and0.22%at high temperatures(between393and573K).The present paper reports the results of new vapor pressure measurements for H2O+Li2SO4solutions.The data cover the temperature range from423to573K and concentration range between0and1.6mol kg−1.This range extended the temperature range of the previous investigations.There are no direct experimental vapor-pressure results at temperatures greater than498K for the H2O+Li2SO4solutions.2.ExperimentalThe vapor pressures of aqueous Li2SO4solutions were measured by a constant-volume method.The static method was used to measure vapor pressure.The apparatus details were described in our previous publications[15–17].The apparatus used in the present measurements is schematically shown in Fig.1.The main part of the apparatus consisted of a piezometer(1),separating U-shape capillary tube with mercury(5),a liquid thermostat(7),heaters(10)and(11), temperature regulator(12),and platinum resistance ther-mometer(PRT)(13).The cylindrical piezometer withi.d. Fig.1.Schematic diagram of the experimental apparatus for vapor pres-sure and density measurements at high temperatures and high pressures.(1)Piezometer;(2)upper capillary;(3)lower capillary;(4)viewing win-dow;(5)separating U-shape capillary tube with mercury;(6)valve;(7) liquid-filled thermostat;(8)pump with mixer;(9)tube;(10)side heater;(11)bottom heater;(12)temperature regulator;(13)PRT.I.M.Abdulagatov,N.D.Azizov/Fluid Phase Equilibria216(2004)189–199191of45mm and o.d.of75mm was made from stainless steel (1X18H9T,1chrome–18nickel–9titanium).The volume of the piezometer at temperature of298K and at atmospheric pressure(0.1MPa)is95.545±0.02cm3.Two capillaries(upper(2)and lower(3),see Fig.1)are soldered to the ends of the piezometer.The mass of the sample in the piezometer was corrected for the noxious vol-umes(volumes of the capillaries in the room temperature and transitional zones)and evaporating of the sample dur-ing extraction.Capillaries with small i.d.(0.5mm)were used to reduce the noxious(ballast)volume to0.15%of the piezometer volume.A correction for this volume was introduced by a calculation using the density of the solu-tion at room temperature.These capillaries led to the room-temperature zone and were connected with the pressure gauge through a U-shaped capillary tubefilled with mercury and oil and with valve(6)located outside the thermostat. The valve was used to extract the sample through the upper capillary.The lower capillary is connected with a viewing window(4)and separating U-shaped capillary tube which is connected to the pressure gauge(piston manometer MP-600or MP-60).Three heaters were used to regulate the ther-mostat temperature.Two heaters were mounted outside the thermostat(on the bottom and side of the thermostat,see Fig.1)and other one inside the thermostat near the piezome-ter.The temperature inside the thermostat was maintained uniform within0.02K with the aid of high-precision temper-ature regulator(P363(3),see Fig.1)which is was connected with heaters and PRT.The piezometer is located vertically in the liquid thermostat(see Fig.1).The cylindrical thermostat with inside volume of0.02m3was made from stainless steel. Pure water was used in the thermostat at temperatures to 350K,glycerin from350to448K,and a molten salt mixture (45%KNO3and55%NaNO3,the melting point of this mix-ture is410K)at temperatures above448K.The liquid in the thermostat was vigorously circulated by a motor-driven stir-rer.The temperature of the thermostat liquid was measured with a10 platinum resistance thermometer(PRT-10,R= 1.39245and resistance at0◦C is9.9980 ).The sensitive elements of the PRT are located in the thermostat very close to the piezometer.The thermometer has been calibrated at the All Russian Scientific Research Institute for Physical and Technical Measurements(Moscow).The sample tempera-ture(IPTS-68)was detected with a precision of±0.015K. The pressure of the sample(solution)was measured with a dead-weight pressure gauge MP-600and MP-60.The maxi-mum uncertainty in vapor pressure measurements was0.2%. The sample in the piezometer was heated in the thermostat until its temperature reached the prescribed value(40MPa) using adjusting heaters inside the thermostat.After thermal equilibration,vapor-pressure measurements were continued by extracting a small amount of sample from the piezome-ter through the upper capillary and valve until two-phase range will reach.After each extraction the piezometer main-tained some time to reach equilibrium state.After reached two-phase state in the piezometer the extraction of the next amount of the sample is not changed the pressure of the so-lution in the piezometer.This is mean that the pressure of the solution in the piezometer is correspond to the vapor pressure at given temperature.This value of the vapor pres-sure almost constant and do not change after changing of the mass of solution in the piezometer.The temperature dependence of the piezometer volume at fixed pressure was calculated asV T=V T[1+3α(T−T0)],(4)where V Tis the volume of piezometer at initial reference temperature T0=293K,α=1.3×10−5K−1is the thermal expansion coefficient of the piezometer material(stainless steel1X18H9T).The pressure dependence of the piezometer volume V P was calculated from the Lave formula[18]for the cylinder.Thefinal equation for the piezometer volume is V PT=V293+ V T+ V P,(5) where V293=94.545±0.02cm3at temperature of293K and at pressure0.1MPa.The value of V293was previously calibrated from the known density of a standardfluid(pure water)with well-known PVT values(IAPWS formulation [19]).The uncertainty in the piezometer volume calculation ␦V PT is less than0.038%.The uncertainty of the mass m of the solution can be estimated to be0.007%.The exper-imental uncertainty in the concentration is estimated to be 0.014%.To prepare of the solution we used Li2SO4with molecular weight of94.946.The additional uncertainty in solution concentration preparing is possible due to purity of the commercial sample of lithium sulfate.The possi-ble additional absolute uncertainty of the concentration of solutions is less than0.1%.This apparatus have been also used(see Refs.[15–17])to measure of the density of solution.The density of the sample at a given temperature and pressure is calculated from the simple relationρi=M iV PT,(6) withM i=m tot−m coll,(7) where M i is the current mass of sample in the piezometer, m coll is the mass of the sample extracted from the piezome-ter and stored in the collector during the runs,i=1–N(N is the number of extractions),V PT is the temperature and pressure-dependent volume of the piezometer(see Eq.(5)), m tot is the initial total mass before extractions.The total ex-perimental uncertainty in density determination was0.06%. This technique was used to measure of PVTx properties of aqueous Li2SO4solutions in the temperature range from298 to573K and pressures up to40MPa[17].Chemically pure Li2SO4(Merck GR,>99.95wt.%, molecular weight94.946)and distillate water were used192I.M.Abdulagatov,N.D.Azizov /Fluid Phase Equilibria 216(2004)189–199to prepare the solutions.The solutions of desired concen-tration were prepared by the gravimetric method,and the concentration was checked by density at 20◦C and 0.1MPa by means of pycnometers using the reference data.Before preparing of the solution the Li 2SO 4was dried in vacuum oven to constant weight.Solutions of the desired molality were made by adding the necessary weight of water to a known weight of anhydrous salt.3.Results and discussionMeasurements of the vapor pressures of the aque-ous Li 2SO 4solutions were carried out at four composi-tions (0.279,0.886,1.322,and 1.600mol kg −1)for seven isotherms between 423.15and 573.15K.The pressure ranged from 0.47to 8.60MPa.The experimental tempera-tures,pressures,and compositions for the H 2O +Li 2SO 4solutions are presented in Table 1.This table also includes the values of the vapor-pressure for pure water (first col-umn,m =0)measured using same experimental apparatus.Some selected experimental results are shown in Figs.2and 3as projections in the P S –T and P S /P 0–m planes,together with values calculated from IAPWS [19]for the pure water.The temperature dependence of measured vapor pressures is shown in Fig.2for various selected compo-sitions together with values for pure water calculated with IAPWS formulation [19].The composition dependence of measured related pressures (P S /P 0)is shown in Fig.3for selected isotherms between 423.15and 573.15K.Devi-ations between present vapor pressure measurementsforFig.2.Experimental vapor pressures as a function of temperature for H 2O +Li 2SO 4solutions along various fixed compositions.Table 1Experimental values of vapor pressure (MPa)of aqueous lithium sulfate solutions T (K)m (mol kg −1)00.2790.886 1.322 1.600423.150.47660.47190.45860.44910.4438448.150.89360.88470.86150.84540.8356473.15 1.5556 1.5428 1.5055 1.4791 1.4636498.15 2.5530 2.5301 2.4791 2.4383 2.4154523.15 3.9781 3.9496 3.8781 3.8265 3.7940548.15 5.9486 5.9070 5.8240 5.752 5.711573.158.58838.54008.43708.3518.308pure water and values calculated with IAPWS fundamental equation of state [19]are given in Fig.4.As one can see from Fig.4most data shows the deviations within ±0.2%(AAD =0.06%)which is lower than their experimental uncertainty (0.2%).The AAD between present data for pure water and the data by Osborne et al.[20]which have been reported under the same conditions are 0.03%.Slightly systematic shape of the deviations was found for all of the data sets.The average absolute deviation for all of the data is 0.09%,while only for two experimental data points by Kell et al.[21](at temperatures 498.15and 523.15K)the deviations rise to 0.24and 1.03%,respectively.The AAD is about 0.14%found between present measurements and the data reported by Kell et al.[21].Wisniewska et al.[22]reported vapor pressure data for pure water which deviate from present results within 0.15%.Niesen et al.[23]re-ported data deviate from the present results within 0.064%,I.M.Abdulagatov,N.D.Azizov/Fluid Phase Equilibria216(2004)189–199193Fig.3.Experimental related vapor pressures(P S/P0)as a function of concentration for H2O+Li2SO4solutions along various isotherms.Fig.4.Percentage vapor pressure deviations,δP S=100(1−(P Scal/P Sexp)),of the experimental vapor pressures for pure water from the values calculated with IAPWS[19]equation of state and the data reported by other authors.(᭹),IAPWS[19];(᭺),Kell et al.[21];(×),Osborne et al.[20];( ), Wisniewska et al.[22];(+),Keenan et al.[24].Fig.5.Percentage vapor pressure deviations,δP S=100(1−(P Scal/P Sexp)),of the experimental vapor pressure for H2O+Li2SO4solutions from the values calculated with correlation equation(2)by Aseyev[14].(᭹),1.322mol kg−1;(᭺),0.279mol kg−1;(×),0.886mol kg−1;( ),1.600mol kg−1.194I.M.Abdulagatov,N.D.Azizov /Fluid Phase Equilibria 216(2004)189–199Table 2Partial molar volumes (cm 3mol −1)of Li 2SO 4in water m (mol kg −1)423.15(K)473.15(K)523.15(K)573.15(K)P =10MPa 0.0944 6.30−10.1−41.3−105.10.27988.30−6.20−33.2−87.20.611512.8 2.00−16.3−51.00.885017.510.2−0.30−22.01.320025.018.513.5 2.001.600030.025.020.010.0P =20MPa 0.09447.60−7.8−34.3−82.60.27989.60−4.0−27.2−68.90.611514.1 4.0−12.3−41.20.885018.812.0 1.90−15.01.320022.016.09.007.001.600028.024.018.015.0only one data point at temperature of 523.15K observed deviation of 0.16%.Excellent agreement within 0.029%is observed between present vapor pressure data for pure water and the data reported by Keenan et al.[24].This excellent agreement between the present measurements and the data reported by other authors in the literature and the IAPWS standard [19]confirms the reliability and accuracy of the present data for H 2O +Li 2SO 4solutions and correct operation of the instrument.The present vapor pressure measurements for H 2O +Li 2SO 4solutions were compared with the values calcu-lated from correlation (2).The deviation plot is given in Fig.5.The AAD between the present measurements and values calculated with the correlation (2)for eachmeasuredFig.6.Water activities as a function of temperature along various fixed compositions.Table 3Water activities as a function of temperature for various concentrationsT (K)m (mol kg −1)0.2790.886 1.322 1.600423.150.9930.9660.9490.938448.150.9930.9690.9530.943473.150.9940.9730.9580.949498.150.9950.9780.9640.956523.150.9950.9800.9690.963548.150.9960.9850.9760.970573.150.9970.9890.9820.978concentrations are:1.600mol kg −1—1.38%(systematically negative shape); 1.322mol kg −1—0.96%(systematically negative shape);0.886mol kg −1—0.32%(systematically negative shape);0.279mol kg −1—0.12%(systematically positive shape).As one can see from Fig.5good agree-ment is found between the measured and calculated val-ues of vapor pressure for the compositions of 0.279and 0.886mol kg −1.Water activity is an important property in the manufacture of food systems and formulations [1–3].Most chemical re-actions and microbiological activity are controlled directly by the water activity of the food system [3].The water ac-tivities a w were calculated from measured solution vapor pressures P S and pure water vapor pressures P 0by the fol-lowing relationshipln a w =lnP S 0+1RT P 0P S RT −V d P + P 0P S¯V 1d P ,(8)I.M.Abdulagatov,N.D.Azizov/Fluid Phase Equilibria216(2004)189–199195Fig.7.Water activities as a function of concentration along variousfixed temperatures.Table4Coefficients A,B,and C for Eq.(10)Coefficients m(mol kg−1)0.2790.886 1.322 1.600A9.913739×10−19.461626×10−19.307702×10−19.146525×10−1 B(K−1) 1.273273×10−6 1.193814×10−4 6.871502×10−59.683289×10−5 C(K−2) 5.748481×10−87.75439×10−8 3.425411×10−7 3.816350×10−7parison present results for the water activities extrapolated to low temperatures(up to298.15K)with values reported in the literature.196I.M.Abdulagatov,N.D.Azizov /Fluid Phase Equilibria 216(2004)189–199where P 0and P S are the vapor pressures over pure water and solutions,respectively,V the molar volume of pure water vapor,1RTP 0P SRTP−V dPFigs.9and parison of present results for water activity with values of reported by other authors at various isotherms.The solid curves are guidesfor the eye.is the correction on nonideality behavior of the water vapor,1RT P 0P S¯V1d P is the correction on compression of solution from pressureP S to P 0,¯V1is the partial molar volume of water at givenI.M.Abdulagatov,N.D.Azizov/Fluid Phase Equilibria216(2004)189–199197 T,P,and m.The values of partial molar volume¯V1weredetermined as¯V1=M1ρ+mM1(1000+mM2)1000ρ2∂ρ∂m,(9)where M1and M2are the molecular mass of pure water andLi2SO4,respectively;ρthe density of the solution and mis the concentration(molality).Some derived values fromEq.(9),of partial molar volumes¯V1using our previous PVTx measurements[17]for aqueous Li2SO4solutions for twoisobars,are given in Table2.Derived from Eq.(8)valuesof water activities are given in Table3and are shown inFigs.6and7as a function of temperature and concentration,respectively.Derived values of water activities arefitted tosecond-order polynomial equationa w=A+B T+C T2,(10) where T=T−273.15.Maximum absolute deviation be-tween calculated with Eq.(10)and values of water activi-ties presented in Table3is about0.001.The values of A, B,and C are given in Table4for each measured concentra-tions.As Fig.6shows,the water activity monotonically in-creases with temperature in the temperature range from423 to573K while a w decrease with increasing concentration of the solution(see Fig.7).As one can see from Fig.6at low concentrations the temperature behavior of water activity is close to the linear.The deviation of the curve of a w–T de-pendency from linearity more markedly pronounced at high concentrations and high temperatures.At low concentrations (m<0.886mol kg−1)a w is little affected by temperature. The concentration dependency of the water activity(a w–m dependency,see Fig.7)is almost linear in the range up to 1.6mol kg−1for the all measured isotherms between423 and573K.Figs.8-10compare the present results for wa-ter activities a w with the data reported by various authors in the literature.Good agreement within±0.25%is found be-tween the present data and values reported by Zarembo et al.[13]at temperatures of473and498K.The agreement be-tween present water activity data and the data derived fromosmotic coefficients by Holmes and Mesmer[8,9]is about ±0.5%.Excellent agreement within±0.23%is observed be-tween the present data and values derived by Holmes and Mesmer[8,9]at low concentration(up to1.2mol kg−1).To compare present data with the values recommended by Gold-berg[11]our results were extrapolated to low temperatures (up to298.15K)using Eq.(10)for each measured compo-sitions.The agreement between our extrapolated values of water activity and the data recommended by Goldberg[11] is excellent(deviation is about0.12%)at low concentra-tions while at higher concentration the extrapolated values of water activities show deviations within0.9%.The values of the vapor pressures calculated using water activities from Zarembo et al.[13]and Holmes and Mesmer[8,9]are de-viate from present direct measured results within0.5–0.7%. Maximum deviation is0.9%was found at concentration of 0.279mol kg−1.Table5Relative partial molar enthalpies- ¯H1(J mol−1)of water as a function of temperature for various concentrationsT(K)m(mol kg−1)0.886 1.322 1.600 423.152******** 448.152******** 473.152******** 498.153******** 523.153******** 548.15412658789 573.15458762909The relative partial molar enthalpies ¯H1of solvent(wa-ter)were calculated from derived values of water activity by using the thermodynamic relation[7]¯H1=−RT2∂ln a wm,P,(11)where the values of derivative(∂ln a w/∂T)m,P were calcu-lated using Eq.(10).The results are presented in Table5and are shown in Fig.11.As Fig.11shows,the relative partial molar enthalpies ¯H1of water are negative in the temper-ature range from423to573K and increasing with concen-tration of solution.The concentration dependence of ¯H1 at low temperatures(T<450K)is small,while at high tem-peratures the concentration has a significant effect on ¯H1. The excess partial molar entropy ¯S1exc of solvent(water) were also calculated from derived values of water activity by using the thermodynamic relation[7]¯S1exc=R ln N1−RT∂ln a w∂Tm,P−R ln a w,(12)where R ln N1is the ideal part of the ¯S1exc.The derived results are given in Table6and are shown in Fig.12.All derived values of ¯S1exc are negative.This is means that at high temperatures the structure of solution more ordered than pure water at same T and P.With increasing of temperature and concentration the values of ¯S1exc are becomes more negative.Table6Excess relative partial molar entropy values− ¯S1exc(J mol−1)of water as a function of temperature for various concentrationsT(K)m(mol kg−1)0.886 1.322 1.600 423.150.620.770.95 448.150.690.91 1.11 473.150.77 1.06 1.29 498.150.85 1.22 1.48 523.150.93 1.39 1.67 548.15 1.01 1.57 1.88 573.15 1.09 1.75 2.09198I.M.Abdulagatov,N.D.Azizov /Fluid Phase Equilibria 216(2004)189–199Fig.11.Relative partial molar enthalpies − ¯H1of water as a function of temperature for various fixedconcentrations.Fig.12.Excess relative partial molar entropy values − ¯S1exc of water as a function of temperature for various concentrations.4.ConclusionsVapor pressures of four aqueous Li 2SO 4solutions weremeasured with a constant-volume piezometer immersed in a precision liquid thermostat.Measurements were made at seven temperatures between 423and 573K.The total un-certainty in temperature,pressure,and concentration mea-surements were estimated to be less than 10mK,0.2,and 0.014%,respectively.The accuracy of the method was con-firmed by vapor-pressure measurements for pure water.Wa-ter activities,relative partial molar enthalpies ¯H1of sol-vent (water),and excess partial molar entropy ¯S1exc of solvent (water)were derived using measured values of va-por pressures for solutions and pure water.The temperature,pressure,and concentration dependence of measured and de-rived properties were studied.The values of measured vapor pressures and derived values of water activities were com-pared with data reported in the literature.I.M.Abdulagatov,N.D.Azizov/Fluid Phase Equilibria216(2004)189–199199AcknowledgementsI.M.Abdulagatov thanks the Physical and Chemical Prop-erties Division of the National Institute of Standards and Technology for the opportunity to work as a Guest Re-searcher during the course of this research.References[1]L.B.Rockland,Anal.Chem.32(1960)1375–1376.[2]buza,K.Acott,S.R.Tatini,R.Y.Lee,J.Flink,W.J.McCall,J.Food Sci.41(1976)910–917.[3]buza,Theory,Determination and Control of Physical Proper-ties of Food Materials,D.Riedel Publishing Co.,Dordrecht,Holland, 1974,p.119(Chapter10).[4]A.T.Williamson,Trans.Faraday Soc.40(1944)421–436.[5]M.Modell,R.C.Reid,Thermodynamics and its Applications,Prentice-Hall,Englewood Cliffs,NJ,1974,pp.338–339.[6]A.Apelblat,E.Korin,J.Chem.Thermodyn.30(1998)459–471.[7]A.L.Horvath,Handbook of Aqueous Electrolyte Solutions:Physi-cal Properties,Estimation Methods and Correlation Methods,Ellis Horwood,West Sussex,England,1985.[8]H.F.Holmes,R.E.Mesmer,J.Chem.Thermodyn.18(1986)263–275.[9]H.F.Holmes,R.E.Mesmer,J.Sol.Chem.15(1986)495–517.[10]J.N.Pearce,H.C.Eckstrom,J.Am.Chem.Soc.59(1937)2689–2691.[11]R.N.Goldberg,J.Phys.Chem.Ref.Data10(1981)671–764.[12]V.I.Zarembo,L.V.Puchkov,Russian Review on ThermophysicalProperties of Substances,USSR Academy of Sciences,Moscow, 1981.[13]V.I.Zarembo,M.Yu.Maturenko,V.Yu.Egorov,Russ.J.Inorg.Chem.54(1981)920–981.[14]G.G.Aseyev,Methods for calculation of multicomponent systemsand experimental data on thermal conductivity and surface tension, Electrolytes Properties of Solutions,Begell-House Inc.,New York, 1998.[15]N.D.Azizov,T.S.Akhundov,L.A.Azizova,Russ.J.High Temp.34(1996)973–977.[16]N.D.Azizov,T.S.Akhundov,Russ.J.Appl.Chem.12(1997)1955–1959.[17]I.M.Abdulagatov,N.D.Azizov,J.Chem.Thermodyn.,2003,inpress.[18]F.G.Keyes,L.B.Smith,Proc.Am.Acad.Arts Sci.68(1933)505–519.[19]W.Wagner,A.Pruß,J.Phys.Chem.Ref.Data31(2002)387–535.[20]N.S.Osborne,H.F.Stimson,E.F.Fiock,D.C.Ginnings,J.Res.NBS10(1933)155–188.[21]G.S.Kell,G.E.McLaurin,E.Whalley,Phil.Trans.R.Soc.LondonA315(1985)235–246.[22]B.Wisniewska,J.Gregorewicz,S.Malanowski,Fluid Phase Equilib.86(1993)173–186.[23]V.Niesen,A.M.F.Palavre,A.J.Kidney,V.F.Yesavage,Fluid PhaseEquilib.31(1986)283–298.[24]J.H.Keenan,F.G.Keyes,P.G.Hill,J.G.Moore,Steam Tables,Wiley,New York,1969.。