Mar., 1956
325
CHEMISORPTION OF CALCIUM HYDROXIDE BY SILICA
THE CHEMISORPTION OF CALCIUM HYDROXIDE BY SILICA BY SIDNEY A. GREEN BERG^ Johna-Manville Research Center, ManviEle, New Jersey Rsedvad A u g w t 16, IS66
The chemisorption of calcium hydroxide from solution by silica waa studied by measuring the immediate decrease in electrical conductance of calcium hydroxide solutions on the addition of silica. I n this study the chemisorption properties of six varieties of silica were examined. The surface are@ of the silicas ranged from less than one to 750 sq. m./g. Si02 and the water contents varied from almost zero (quartz) to 19.2%. The results indicate that the initial reaction of calcium hydroxide is with the surface SiOH grou s on the silicas. This conclusion is substantiated by the data which show that the amount of calcium hydroxide removdP from solution is proportional to the surface area and to the chemically-combined water in the silica.
The sorption of calcium hydroxide in solution by silica has been studied many times.a However, the nature of the process was described first as chemisorption by Maffei and his co-worker~.~I n many of the earlier studies the times allowed for equilibrium to be established were quite long and no allowance was made for the chemical reaction which can take place a t room temperature between the matrix of the silica particle and the calcium hydroxide.4 I n the present study only the sorption occurring immediately on the mixing of the calcium hydroxide and silica waa measured. It is now generally agreed5-9 that the surfaces of silica gels and quartz are covered with acidic SiOH groups which dissociate in this way
I
I
I
I
S i - O H J _S i - 0 -
+H+
(1)
I n addition, a small amount of monomeric silicic acid and its ions and colloidal silica are found in solution.10-12 The interactions of the polysilicic acid surfaces with bases and neutral salts have been examined extensive1y.l' According to recent theory the reaction of calcium hydroxide and the SiOH surface would be expected to be that of a weak acid ( K I = 10-9.8)14 and a strong base 2AiOH
I
+ Ca(OHk 7(-diO)&a + 2H20 I
(2)
2-430I
(-\i*)2ca
+ ca++
I
AI
2-
io-
+ 2H20 J_ 2--$iOH + 20HI
(3 1 (4)
The hydrolysis of surface SiO- would proceed because of the low ionization constant of silicic acid. Also when silica is allowed to react with neutral salts a decrease in pH results, which is explainedI3 by this reaction -kiOH
I
+ MX salt
-AiOM
I
+ H+ + X-
(5)
insoluhle
In the present study the interaction of silica surfaces with calcium hydroxide and nitrate solutions was studied by measuring the decrease in conductance or pH of solutions of calcium hydroxide or nitrate on the addition of silica. Five varieties of amorphous silica and a-quartz were examined. Adsorption isotherms a t 30 and 82" were obtained on silicas with surface areas varying from less than one to 750 sq.m./g. SiOz and water contents ranging from almost zero (quartz) to 19.2%. In addition, a comparison was made between the interactions of silica with sodium and with calcium hydroxide in solution. Experimental
Equipment.-The pH determinations were made with a Beckman model H-2 meter. A constant temperature bath (=t0.03")regulated by a Thermocap relay (Niagara Electron Laboratories, Andover, N. Y.) was used for all experiments carried out at 30" and above. Electrical conductivity meas(1) Laboratory for Phyma1 and Inorganic Chemistry, Leiden Uoiurements were taken with an Industrial Instruments RClB versity. Holland. bridge and dip conductivity cells with constants of approxi(2) For review see H. H. Steinour. Chsm. Reus., 40, 391 (1947). mately one cm.-'. Calcium hydroxide solutions were (3) (8) A. Maffei and A. Batteglii. Ann. Cham. Applicata, 25, passed through Millipore HA filters (Millipore Filter Co., 309 (1935); (b) A. Mafh, f3w.chim. itd., 66, 197 (1936). Watertown, Mass.) to clarify them. The dehydration (4) H. F. W. Taylor, J . Chsm. Sm., 3682 (1950); L. Heller and curves of the silicas were obtained with a Chevenard thermoH. F. W. Taylor, *%id., 2397 (1951). at a constant heating rate of S"/min. In a prebalan~e'~J7 (5) M.W. Tam& in "Chemid h b i t e c t u r e , Frontiers of Chemisvious aper" the nitrogen adsorption measurements by the try," Vol. V, Interscienee Publ. 1110.. New York, N. Y.. 1948. B . E . 2 method were described. (6) I. Shapiro and H. G . Weias. Tms JOWN~L,57, 219 (1953). Materials.-Mallinckrodt standard luminescent (S.L.), (7) W. A. Weyl. Rascarch, 8, 230 (1950); J . Am. Car. Suc., Jp, 367 special bulky (Sp.B.), and aerogel (Santocel A) silicas were (1949). ellamined. (An excellent review of the properties of silica (8) P. L. deBruyn.
[email protected] , 291 (1955). is given by Iler in a recent book.9) The du Pont Ludox (9) For an excellent diicnsaion sea R. K. Iler. "The Colloid Chemis(30% Si02) was diluted to 15% and small portions of this try of Silica and Silicates." Comell Univ. Press, Ithaca, N. Y., 1955. concentration were used in the sorption studies. A calcu(IO) 0. B. Alexander, W. M. Heaton and R. E(. Iler. Tars JOUBNAL, lation of the amount of sulfate and hydroxyl ions present in 68, 453 (1954). the 60 ml. of calcium hydroxide solutions used, on the addi(11) F. G . Straub, Univ. Ill. Bull.. 43. No. 59, Eng. Exp. Station, tion of small amounts of 15% Ludox sols, indicated a negBulletin Series No. 364, 1946. ligible concentration of these ions. Eimer and Amend Ca(12) G . C. Kennedy, &con. Cad.. 46, 629 (1950). (N0&4&0 of tested urity was used. Well character(13) For review see J. N. Mukherjee and B. Chatterjee. Natura, 155, ized mineral samples or a-quartz and opaline silica were
Although calcium silicates are relatively insoluble,13J5a certain amount of hydrolysis (reverse reaction of eq. 2)will take place in two steps
85 (1945). (14) P. 8. Roller and G. Erwin,J . Am. Chsn. Soc., 62, 461 (1940). (15) I. M. Eolthoff and V. A. Stenger, TEIE JOUBNAL. 88, 475 (1934).
(16) C. Duval. "Inorganic Thermogravimetric Analysis," Elsevier Publ. Co., New York, N. Y., 1953. (17) 8. A. Greenberg, Tme JOURNAL, 68, 362 (1954),
SIDNEY A. GREENBERG
32(i
available for this study. The ignited opaline silica contained Y5Y0 Si02 and 5% impurities. Baker A.R. calcium hydroxide was found to be superior for the preparation of the solutions. Saturated solutions were made by shaking calcium hydroxide with distilled water at 26" and passing the solutions through a Millipore filter. Non-turbid solutions were prepared by this procedure. The concentration of the solutions was found to be 1.12 g. CaO/l. at 26" which compares very well with previously reported The concentrations a t 30 and 82" are 1.11 g. and 0.65 g. CaO/l., respectively, according to these authors, and solutions of such concentrations were made from the 1.12 g. CaO/l. solution. Experimental Procedures and Theory .-The procedure rived to determine the amount of calcium hydroxide in solution wm employed previously by Cummins and Miller,S1 Beitlich,ll and Budnikov28 for similar purposes. I n this procedure the changes in concentration of electrolytes in solution are determined by conductivity measurements. I t was first established in this study that the conductivities L of the calcium hydroxide solutions were directly pro-
m/
.04
-
v
-
-
a
I
I
I
I
8
IO
12
14
*
LUDOX I
I
16 18 EQUILIBRIUM CONCENTRATION. MOLESIL. X IO'
2
4
6
Fig. 1.-Sorption isotherms (30') of calcium hydroxide by S L , Sp.B. and Ludox silicas. The curves fit the Langmuir adsorption isotherm equation.
Vol. 60
portional to the concentrations C at 30 and 82". In addition, a plot was made of equivalent conductance versus the square root of concentration according to the Onsager equations4 A = A0 - k l / C (6) where C is the concentration in equivalents/l. The equivalent conductance a t infinite dilution A0 was obtained from this plot. The value found was 259 ohms-' (25") as compared to the 246 ohms-' (25') reported by Lea and Bessey.18 These authors point out that the value for A. derived from ionic mobility data a t 25" is 256 ohms-'. Because of the linear relationship of specific conductance and concentration, it is possible to measure changes in concentration by resistance measurements. In this study, silica was added to calcium hydroxide solutions of known initial concentration Gin. By measuring the initial and final conductances Li, and Lr, respectively, Cr was found from the relationship L n - i=
Cin
(7) Lr Cr With a knowledge of Cin and Cr, the amount of CaO sorbed in g r a m x by m grams of SiOzwas calculated. Two types of isotherms were obtained. I n one case silica Sam les containing 0.075 g. of Si02 were added to 60 ml. of sofutions of calcium hydroxide ranging from saturated a t 30" (1.11 g. CaO/l.) and at 82" (0.65 g. CaO/l.) to very dilute solutions. The quantities x and m were calculated and x / m values were plotted as a function of the concentration of calcium hydroxide remaining in solution a t equilibrium as is shown in Figs. 1and 2. I n the second kind of isotherm, samples of silica containing SiOa in the quantities shown in Fig. 3 were added to 60 ml. of saturated calcium hydroxide solutions a t 30 and 82". It was found that equilibrium was reached in the reaction between surface SiOH groups and calcium hydroxide in 15 seconds, except in the case of S.L. silica at 30" where one minute was allowed for equilibrium to be established. The x / m values of silica aerogel, opaline silica and a-quartz were measured in a similar manner.
.26t
1
.24
.20 .I6 M
.12 .02
"p 1 .O8
.04
I
2
4
6
I
8
1 1
I
I
.02
.04
I
I
.06 .OS
I
.IO
I
.I2
I
.I4
.I6 .I8
S O , , GRAMS
Fig. 3.-Dependence of x / m values on amount of S.L., Sp.B. and Ludox silicas added t o equal concentrations of calcium hydroxide solutions.
I
1
0
CONCENTRATION, MOLESIL. X IO' Fig. 2.- -Sorption isotherms (82O) of calcium hydroxide by S.L., Sp.B. and Ludox silicas. The curves fit the Langmuir adsorption isotherm equation. (18) F. M. Lea and G. E. Bessey, J . Chem. Soc., 1612 (1937). (19) H.Bassett, ibid., Pt. 11, 1270 (1934). (20) R.B. Peppler and L. S. Wells, J . Research Null. Bur. Slandorda, 62, 75 (1954). (21) A. B. Cummins and L. B. Miller, Ind. Eng. Chem., 26, 688 (1934). (22) A. E. Beitlich, J . A m . Chem. SOC.,60, 1832 (1938). (23) P. P. Budnikov and M. I. Khigerovich, Doklady Akad. Nauk, S.S.S.R., 96, 141 (1954).
To compare the removal by silica of calcium ions from hydroxyl and nitrate solutions, pH measurements were made before and after the addition of silica. The reagents used at 30" were 60 ml. of calcium hydroxide and of nitrate solutions to which were added 0.08 g. of Sp.B. silica. I n the 82" experiments 60-ml. solutions and 0.10-g. samples of silica were used. The concentrations of the solutions are given in Figs. 7 and 8.
Results Sorption Isotherms.-Figures 1 and 2 show the ratios of the grams of calcium oxide sorbed z per m grams of SiOz plotted as a function of the equilib(24) For discussion see 9. Glasstone, "Textbook of Physical Chemistry," D. Van Nostrand Co.,Inc., New York. N. Y., 1946.
CHEMISORPTION OF CALCIUM HYDROXIDE BY SILICA
Mar., 1956
327
TABLE I x / m VALUESA N D SURFACEAREASOF SILICAS
sol,
(x/m)-= 30'
(z/m)m 30
80.8 84.8 93.5 94.0 87.8 99.7
0.20 .13 .095 .OS0 .015
0.20 .ll
%
Silica
S.L. Sp. B. Aerogel Ludox Opaline Quartz
iO)&a groups and the increase in I
I hydrolysis of 4 0 - ions a t the lower concentrations
of calcium and Lydroxyl ions (eq. 3 and 4). It may be seen in Fig. 3 that the x / m values a t 30 and 82" of S.L., Sp.B. and Ludox silicas do not change markedly with an increase in SiOzadditions. A small decrease may, however, be noted for the larger additions of silica. Higher values were obtained at 82" than those observed a t 30" for the reason given previously. I n Table I are listed the maximum z / m values at 30" shown in Fig. 3. These values were considered maximum because the highest equilibrium concentrations of calcium hydroxide were obtained in these experiments by reducing the amount of silica added to the saturated calcium hydroxide solutions. In the experiments performed with equal Si02 additions (Figs. 1 and 2), a fairly large amount of SiOz (0.075 8.) was added in order to obtain a reasonable change in conductance on the addition of silica. Therefore, by using the saturated solutions and decreasing the amounts of silica added as shown in Fig. 3, i t was possible to extrapolate back to almost saturation concentrations. The maximum x/wa values for aerogel, opaline and quartz silicas are listed in Table I. The (x/m) value for quartz is approximate because of the small changes in the resistances of the calcium hydroxide solutions on the addition of quartz. At the suggestion of Dr. Stephen Brunauer the maximum x / m values ((x/m),) were also calculated from the equation2s C --- 1 C x/m
-
(x/m),b
+-( x / m ) ,
Surface area,
sq. m./g. Si02 (x/m
750 383 247 147 (dried) 23 1159,
“Bound”
(115O),
19.2
11.9 9.2
7.3
0.0
6.6 5.5
2.0
3.0 2.3 3.3
2.1 3.1
15.2 5.0 6.8 0.5 0.1
%
%
4.5 3.2 0.03
“Bound“
100 g.
loo g.
HzO(z/m)/ loo g.
8.3 6.6
7.9 4.9
.. ..
(T.B.)/ Si01
Si01 9.0 7.1 3.2 2.5 3.8
%
0.07
Hers predicts the first arrangement of hydroxyls if the surface of amorphous silica is like that of @-cristobalite and the second if it resembles that of 8tridymite. It seems reasonable to assume that all the hydroxyl groups can be made to react with calcium hydroxide if the concentration of the latter is sufficiently high and the silica surface is available to the ions. Therefore, assuming that each molecule of calcium hydroxide reacts with two hydroxyl groups, eight of which occupy one sq. mp (calculated by ller from the arrangement on the surface of @cristobalite) then the surface area in sq.m./g. Si02 can be calculated and the values are listed in the last column of Table I. These values, it may be seen, are reasonably close to those obtained by nitrogen adsorption except in the case of Ludox. Water Contents.-The nature of the water in the silica samples was examined by direct ignition, thermobalance and sorption techniques. In this study it is assumed that the total water in hydrated silica consists of “free,” physically sorbed water and of i‘ bound,” chemically-combined water. The results are summarized in Table 11. 1. The total water in the samples was determined by direct ignition at temperatures higher than 1000” and the results are given in column 1 of Table 11. Similarly the “free”9 water content was determined by measuring the weight loss on samples at 115”. Columns 2 and 3 list the “free” water and bound” (total minus free) water for the samples. In Fig. 5 the relationship of the “bound” water contents and the (x/m),,,ax values is shown graphically.
“Bound“ (>1159/
(T.B.).
Total. %
Si02
..
2.6
2.2
2.7 0.55 0.71
3.6
..
0.07
the total water content of the samples. I n addition the assumption was made that a sample heated under these conditions ( 8 O / m h . ) begins to show the loss of “bound” water at the sharp change in the slope a t approximately 225”. The weight losa above 225” of each silica watj calculated and the results are listed in the column labeled “bound” (T.B.).
LUDOX
SPB
I
I
eo0
I
I 400
I
TEMPERATURE:
Fig. 6.-Dehy&ation
curvy of
I
600
I
800
I
c
S.L., Sp.B. and Ludox
sdcas.
In the following two columna the “bound” water contents are converted to the amounts per 100 g. SiOz. It may be noted that the values for “bound” water found by the ignition and thermobalance techniques are approximately the same. 3. In the last method for estimating the water contents, the (x/m), values were used. Equations 8 and 9 show that the reaction of one molecule 0.24 of calcium hydroxide with two hydroxyl groups 0.20 corresponds to the liberation of one molecule of water. Hence, if the (zlm), values correspond to a completely reacted SiOH surface then the amount of “bound” water in SiOH groups can be calculated. In the last column of Table I the results are listed. It may be noted that the water contents (last three columns of Table 11) found by the three methods show differences, but are of the same order 2 4 6 8 1 0 of magnitude. An exception may be observed in Bound water/100 g. SiOt. the difference between the water content of opaline Fig. 5.-The relationship of ( ~ / r n ) , , , ~ values = and “bound silica obtained from the (z/m),= value and the wawater” (1115’) contents of: 1, S.L.: 2, Sp.B.; 3, aerogel; ter content determined by weight loss measure4, Ludox; 5, opaline silica; 6, quartz silica. ments. I n general, the “bound” water contents 2. Dehydration curves were made with a Chev- measured by ignition methods are higher than those enard thermobalance and three may be seen in Fig. calculated from sorption experiments. These higher 6. From these curves it was possible to calculate values may be attributable to the difficulty in removing strongly-sorbed water at 115”. Therefore, (27) I. ShaDiro and I. M. Kdthoff, J . Am. Cham. SOC.,18, 776 the “bound” water determined by ignition meth(1850).
} 1
I
Mar., 1956
CHEMISORPTION OF CALCIUM HYDROXIDE BY SILICA
ods may include a certain amount of sorbed water
in addition to the water in SiOH groups. Interaction of Silica with Calcium Nitrate.-The reaction would be expected to proceed according to this equation 2biOH
I
+ Ca(NO&
I (-SiO)2Ca + 2HNOs I
sorbed is listed. It may be seen that the magnitude of the sorption of both ions is quite different. TABLE I11 CHEMISORPTION OF SODIUM AND CALCIUM HYDROXIDES Silica type
(11)
Because both the reactants and products contribute to the conductance of solutions, the amount of reaction was determined by p H measurements. It may readily be seen in Figs. 7 and 8 that the decreases in p H on addition of Sp.B. silica to calcium hydroxide solutions were small and may be attributed to the decrease in hydroxyl ion concentration. Equation 11 serves to explain the larger drop in p H found in the calcium nitrate solutions. It should be pointed out that the change in concentration of the saturated solution of calcium hydroxide at 30” on the addition of silica is from 0.020 to 0.016 mole/ 1. according to the conductivity measurements and corresponds to a hydrogen ion change of 7.2 X lou3 equivalent/l. However, the pH change on addition of silica to the calcium nitrate solution corresponds to a change of hydrogen ion concentration of only 3.7 X lo4 equivalent/l. This could be expected because of the larger degree of hydrolysis of
S.L. Sp.B. Ludox
0,0074
.00053
.0053 .0018
I
I
groups. The order in which the silicas remove sodium ions is the same as for the removal of calcium ions.
I
t
I
8-
0.0048 .0033
I
solution than at the pH of 12.5 found in the saturated calcium hydroxide solutions.
P“ 9 -
Ca(0H z meq. sorbedp. si02
degree of dissociation of (4iO)Na than (-SiO)&a
I
IO -
22%%a;
More calcium ions than sodium ions are removed from solution. This is consistent with the results of Mukherjee and Chatterjeela who found that the hydroxyl ion concentrations of solutions of calcium hydroxide containing silica sol were lower than those with equivalent concentrations of sodium hydroxide. This may, perhaps, be attributed to the greater
(-SiO)&a at the lower p H in the calcium nitrate
II
329
L
Ca(NO,),
7
6
0
.002 .004 ,006 .008 .OlO .012 INITIAL CONCENTRATION, MOLESIL.
Fig. %-The p H of solutions (82’) of calcium hydroxide and of nitrate before ( 1 ) and after (2) the addition of 0.10-g. samples of Sp.B. silica.
Discussion On the basis of the results, several conclusions can be drawn concerning the initial interaction between calcium ions and silica, and the nature of silica. 1. The results confirm the hypothesis that chemisorption of calcium ions by acidic SiOH groups is the initial step in the reaction of these two substances. The correlation between the amount of INIT1AL CONCENTRAT1ON, MOLES/ L. sorption and the surface areas and the “bound” Fig. 7.--The H of solutions ( 3 0 O ) of calcium hydroxide and nitrate begre ( 1 ) and after (2) the addition of water contents is strong evidence. In addition, the presence of limiting x / m values shows that 0.08-g. turnplea of Sp.B. silica. only a monolayer forms. Sorption of Sodium Hydroxide.-A comparison 2. The presence of SiOH groups on the surface was made of the milliequivalents of sodium hy- and in the pores of the amorphous silicas provides droxide and calcium hydroxide sorbed by S.L., evidence that silica is a condensation polymer of Sp.B. and Ludox silicas at room temperature. To silicic acid. 60 ml. of 0.04 N solutions, 0.075 g. of Ludox silica, 3. The effect of p H on the hydrolysis of the SiOand 0.10-g. samples of S.L. and Sp.B. silicas were Ca bond is clearly indicated by the results of this added. In Table 111 the amount of each species study. Additional evidence also is offered that 7-
330
THOMAS A. GOVERA N D PAULG. SEARS
the hydrogen ion in SiOH groups can be replaced by calcium ions in solutions of p H greater than five and less than thirteen (Fig. 7). 4. The similarity between the surface areas determined by nitrogen adsorption and those found by sorption measurements assuming a P-cristobalite structure indicates that the local order of amorphous silicas is that of P-cristobalite. The lack of correlation between the surface areas of dried Ludox (measured by nitrogen adsorption) and the sol (determined by the sorption method) may be due to the change in orientation of the silica structure on dehydration. Additional study is necessary to establish the cause of the difference between the "bound" water content of opaline silica found in the sorption experiment and the content measured by the ignition methods (Table 11). It might be suggested as an alternate mechanism that the calcium hydroxide in solution reacts with soluble monomeric Si(0H)r (silicic acid), which goes into solution at a rate proportional to the sur-
Vol. 60
face areas and water contents. Two pieces of evidence refute this mechanism. First, the similarity of (x/rn),,, values at 30 and 82" is inconsistent with the difference in the solubility of silica at the two temperatures. Second, it frequently has been reported that silicic acid goes into solution slowly.10J2 Alexander, et a1.,'0 found that it was necessary to wait 20 days to reach the equilibrium concentration at room temperature. Acknowledgments.-The author wishes to acknowledge the assistance of Mr. J. Pellicane of this Laboratory in making the measurements reported in this study. Thanks are due to Dr. F. Pundsack for the well-characterized opaline silica .and the stimulating discussions on the nature of the surface of silica. The nitrogen adsorption measurements were made by Mr. G. Reimschussel and Miss M. Cronin of this Laboratory. The author also wishes to thank Dr. Stephen Brunauer (Portland Cement Association, Skokie, Ill.) for his helpful comments on the manuscript.
CONDUCTANCES OF SOME ELECTROLYTES I N I-PROPANOL AT 25" BY T H O M 4 S A. GOVERAND
PAUL
G.
SEARS
Contribution f r o mthe Department of Chemistry, University of Kentucky, Lm*n@on,Kentwky Received Auguat f6,1966
Conductances of sodium and potassium iodides and thiocyanates and of tetraethylammonium and tetra-n-propylammonium bromides and iodides in 1-pro anol have been determined a t 25" for concentrations in the range 8-300 X lo-( N. Limiting equivalent conductances and fisociation constants have been determined by the Shedlovsky extrapolation method. The results indicate that limivng ionic conductances are additive in I-propanol. 2. Salts.-The salts were purified as described preIntroduction v i o ~ s l y and ~ * ~were dried to constant weight in a vacuum Although many studies2 have been made con- oven a t 70" prior to using. 3. Apparatus and Procedure.-Resistances of the sohcerning the properties of solutions of electrolytes in tions were measured a t 500, 1000 and 2000 cycles with an methanol and in ethanol, very few data have been assembly consisting of the followin parts having the reported regarding the behavior of electrolytes in designated numbers according to the keeds and Northrup 1-propanol. Hovorka and Simmsa have reported Catalog EN-95: Jones conductivity bFidge (4666), tuned the most systematic previous study regarding 1- audio frequency amphfier (9847), audio frequency oscl(9842) and telephone receiver (9874). propanol solutions; however, their results indicate lator The conductance cells, the constant temperature bath that the Kohlrausch law of independent ion migra- and the experimental procedure have been described adetion does not apply to electrolytic solutions in this quately in previous paper^.^^^ In converting concentrations from a weight to a volume solvent. Inasmuch as this law has been found to basis, it was assumed that the densities of the solutions be applicable to solutions of electrolytes in metha- were equal t o that of the solvent. AU weights were cornol, ethanol and most other solvents, their results rected to vacuum. The conductivity of a salt was obappear questionable. The purpose of this study, tained by subtracting the conductivity of the solvent from therefore, has been to re-examine the additivity of that of the solution. The following data for 1-propanol at 25' were deterionic mobilities in 1-propanol. mined by using several samples of the solvent: density, 0.8008 /ml.; viscosity, 0.0193 poise; dielectric constant, Experimental 20.4. &he values for the density compare favorably with 1. Purification of Solvent.-1-Propanol (Eastman Kodak Co. White Label) was fractionated a t atmospheric pressure through a 120-cm. vacuum-jacketed column acked e t h glass helices. Traces of water were removerfas a minimum-boiling ternary azeotrope using benzene as the third component. The retained nuddle fractions had conductivities of 2 X 10" ohm-' cm.+ or less. (I) Based in part upon a report submitted by Thomas A. Gover in an undergraduate independent work courae in chemistry. (2) D. A. MacInnes, "The Principles of Electrochemistry," Reinhold Publ. Corp., New York, N. Y., p. 356. (3) F. Hovorks and J. C. Simma, J . Am. Chem. SOC.,60, 92 (1937).
those which have been resorted by Dunstan and Tholef The value for the dielectric constant agrees m t h the data reported by Maryott and Smith.' The values of the fundamental constants which were used in the calculation of the Onsager constants were taken from the latest report of the Subcommittee on Fundamental Constants.'
(4) D. P. Amea and P. G. Sears, TRIBJOURNAL, 59, 18 (1955). ( 5 ) p. a. Sears, E. D. Wilhoit and L. R. Dawson. ibid., 59,373 (1955). (6) A. E. Dustan and F. B. Thole, J . Chem. Soc., 96, 1556 (1909). (7) A. A. Maryott and E. R. Smith. NBS Ciroular 514, August 10,
1951. ( 8 ) F. D. Rossini, F. T. Ducker. Jr.. H. L. Johnston, L. Pauling and ( I w. . Vinal,,J. Am. Chem. Sac.. 74, 2699 (1962).
