A STUDY OF SEVERAL PHYSICAL PROPERTIES OF ELECTROLYTES OVER T H E TEMPERATURE RANGE OF 25°C. TO -73°C.’ A. B. GARRETT AND SAMUEL A. WOODRUFF Department of Chemzstry, The Ohio Stale University, Columbus, Ohio Received .+fay 4, 1943
INTRODUCTIOK The purpose of this paper is to present data on the density, viscosity, electrical conductivity, and freezing point of several solvent-electrolyte systems over the temperature range of 25OC. to -73°C. Such data are of intrinsic interest; they are of specific interest in a study of electrolytes (8) and especially in the study of the dissolution process of metals over this temperature range (4,5 , 6, 7). EXPERIMEKTAL 4 . PROCEDURE
1. The cryostat The constant-temperature cryostat used for the density and viscosity measurements consisted of a 4-1. clear-glass Dewar flask into which was placed a 4-in. Pyrex tube which contained two copper “window” frames; the remainder of the flask was packed with pulverized dry ice. The copper “window” frames allowed visibility to the pycnometer or viscometer, which was inserted inside of the tube. This inner tube was suspended in the Dewar flask with an insulating stopper; in the inner tube was also inserted a stopper which was designed to hold a calibrated lom-temperature thermometer, a bimetallic C e n c d e Khotinsky thermoregulator using a mechanical-latch relay, a heating unit consisting of a resistance wire wrapped on a porcelain core and connected in series with a Variac, a stirrer, and the pycnometer or viscometer as required. A temperature control of f0.2”C. could be maintained throughout the entire temperature range of 25’C. to -73°C. 3. Density The pycnometer used for this work mas calibrated to hold 30.142 ml. of water at 20°C. A similar pycnometer was constructed and used as tare weight. All weights were corrected to vacuum weight; the volume of the pycnometer was corrected for the temperature change over the range studied. The density determinations are accurate t o f0.0002 g. The procedure was as follows: The pycnometer was filled with excess of the desired electrolyte and placed in the constant-temperature cryostat. The meniscus of the liquid was adjusted, after equilibrium had been attained, to the cali-
This work was initiated and is supported by the Battery Branch of the Signal Corps Engineering Laboratories a t Fort Monmouth, New Jersey. 477
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A. B. GARRETT AND S. A. WOODRUFF
brated mark on the capillary by withdrawing or adding liquid with the aid of a glass tube drawn into a fine capillary. When the level of the meniscus remained unchanged for 30 min., the system was considered to be at equilibrium. The pycnometer was removed from the cryostat, dried, and weighed after it had reached room temperature. The density was then calculated by dividing the vacuum weight (in grams) of the liquid by the volume (in milliliters) of the pycnometer. 5. Viscosity The viscometer used for these determinations was of the Ostwald type, with a capacity of 50 ml. It was calibrated to have an outflow time of 7.50 sec. at 25°C. with triple-distilled water. The results obtained in the use of the viscometer were also compared at low temperatures against known values of perchloric acid solutions as reported by the National Bureau of Standards (1,2). The average of ten readings (or six consecutive check readings) was taken as the outflow time. The relative viscosity, q , was calculated over the entire temperature range by the use of the formula: ? =
density of liquid X outflow time in seconds density of water x 7.50
which gave the viscosity of the solution at any temperature relative to the viscosity of water a t 25°C. The temperature of the liquid for each viscosity determination wm controlled to *0.2"C.
4. Specific conductivity The resistance (reciprocal of conductance) of the electrolyte was measured by obtaining the null point of a 1000-cycleA.C. hummer in a Wheatstone bridge circuit containing the conductivity cell which held the electrolyte. Two conductivity cells were used for this research. The cell constant of cell No. 1 was determined aa 6.68 ohm-' cm.-l by measuring the conductivity of 1 N , 0.1 N , and 0.01 N potassium chloride at 25", @",and 0°C. This cell was used for solutions which have a high conductivity, such as hydrochloric acid. Cell No. 2 was similarly calibrated to have a cell constant of 0.028 ohm-' cm.-' and was used for solutions with low conductivity, like pure methyl alcohol. The cells were placed in the constant-temperature cryostat and measurements were taken after equilibrium had been reached, as shown by constancy of resistance readings. The temperature readings were obtained by a platinum resistance thermometer which had been calibrated against a thermometer calibrated by the Xational Bureau of Standards. A constant-temperature cryostat was designed for the measurements of specific conductivity. In the lid of the cryostat were mounted a fan, a heating unit, and a thermoregulator. A bimetallic Cenco-de Khotinsky thermoregulator (110 v.) connected
PHYSIC.4L PROPERTIES OF ELECTROLYTES
479
with a mechanical-latch relay was found to work well over the entire temperature range. The heating unit consisted of a resistance wire on a porcelain core and connected in series with a Variac and to a 110-v. source. Dry ice alone served as the cooling agent. A temperature control of h0.2"C. was easily maintained. B . MATERIALS
Methyl alcohol: Pure methanol was prepared from synthetic methanol by removal of the water by reaction with magnesium turnings, followed by distillation of the dry methanol. The methanol was found to have a refractive index of 1.3287 at 20°C. and a freezing point of -97.8"C. Methylamine hydrochloride: An Eastman Kodak Company grade of methylamine hydrochloride was recrystallized repeatedly from methyl alcohol and dried in air. This product melted at 226°C. Ethanolamine hydrochloride: Since ethanolamine hydrochloride was not commercially available, it was prepared from Eastman ethanolamine by reaction with concentrated hydrochloric acid and recrystallization of the salt formed. This salt was repeatedly recrystallized from ethyl alcohol and dried in air. The ethanolamine hydrochloride had a melting point of 81-82°C. Lithium chloride, lithium bromide, other salts: All salts were of reagent quality. The salt solutions were standardized against standard silver nitrate with dichlorofluorescein as the indicator, according to Fajans' method (3). All volumes were corrected to 20°C. Whenever possible, the densities of the electrolyte solutions were checked against the densities of solutions of known percentage composition as reported in the Inlernational Critical Tables (9). Fluoboric acid (HBF,): The fluoboric acid contained 43.5 per cent fluoboric acid, stabilized with 2.2 per cent boric acid. The freezing point was determined to be about - 73°C. This acid was obtained from the General Chemical Company. Perchloric acid (HClO,) : Perchloric acid of analytical reagent grade and containing 60 per cent perchloric acid was purchased from the Mallinckrodt Chemical Works. All solutions were accurately standardized against standard sodium hydroxide with phenolphthalein indicator.
DISCUSSION A . ACID SYSTEMS
The density data are graphically compared in figures 1 and 2, the viscosity data in figures 3 and 4, and the conductivity data in figures 5 and 6. The data for the densities, relative viscosities, and specific conductivities of the acid systems studied over the temperature range of 25°C. to -73°C. are available in table form in microfilm (Microfilm,2 Table 1). 1. Hydrochlurk acidwater The density data for eutectic hydrochloric acid are the average of three separate determinations and are reproducible to f0.0002.It will be noted in figures * Microfilm Library, The Ohio State University Library, The Ohio State University,
Columbus, Ohio.
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A. B. QARRETT AND 6. A. WOODRUFF
1 and 2 that a linear relationship between density and temperature is not obtained. The relative viscosities of all three mixtures of hydrochloric acid (Microfilm: Table 1) are very similar; there is a slight increase in viscosity with an increase in percentage of hydrochloric acid at the lowest temperatures and there is about a thirtyfold increase in viscosity over the temperature range of 25°C. to -73°C.
1.560 1.540
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TEMPERATURE:C.
FIG.1. Density as a function of temperature. Curve 1, 23.3 per cent hydrochloric acid; curve 2, 24.8 per cent hydrochloric acid; curve 3,27.6 per cent hydrochloric acid; curve 4, 36.0 percent sulfuric acid; curve 5,40.45 per cent perchloric acid; curve6,43.5 percent fluoboric acid; curve 7, 60.5 per cent perchloric acid.
I n the conductance data it is to be noted that the least percentage of hydrochloric acid has the best conductivity at 25"C., but the eutectic hydrochloric acid has the best conductivity at the lowest temperatures. The conductivity is about nineteen times greater at 25°C. than it is at -73°C. However, eutectic hydrochloric acid at -60°C. has as good a conductivity aa 1N potassium chloride at 18'C. A plot of the log of the reciprocal of the conductivity versus the log of the viscosity shows that a linear relationship exists between these two properties over the temperature range studied.
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PHYSICAL PROPERTIES OF ELECTROLYTES
2. Perchloric acid-wafer
The physical properties of perchloric acid solutions are reported in Microfilm Table I* and shown in figure 1. The physical properties of perchloric acid have been measured and reported by the Xational Bureau of Standards (1, 2). These data were used as a check on the calibration of our apparatus. 7
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6 5
O.94OL
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FIG.2. Density as a function of temperature. Curve 1, 100 per cent methanol; curve 2, 90 per cent methanol 10 per cent of 0.1 N hydrochloric acid; curve 3,14 per cent methylammonium chloride in 60 per cent methanol; curve 4 , 3 3 per cent methylammonium chloride 11 per cent lithium chloride in water; curve 5 , 24.85 per cent lithium chloride; curve 6, 18.6 per cent methylammonium chloride 19.6 per cent lithium chloride in water; curve 7 , 39.4 per cent lithium bromide.
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A plot of the densities gave a linear relationship, as shown in figure 1 . The 60.5 per cent and 40.45 per cent perchloric acid solutions have freezing points of -46°C. and -5g0C., respectively. The relative viscosities of 40.45 and 60.50 per cent solutions were determined and are shown graphically in figure 3. The data on relative viscosity were converted into kinematic and absolute viscosity and compared with the values obtained by the National Bureau of Standards. The kinematic viscosity is equal
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A. B. GARRETT AND S. A. WOODRUFF
to the absolute viscosity dividedby the density. The unit is in stokes, which is the viscosity in poises divided by the density in grams per milliliter. The absolute viscosity was calculated by multiplying the relative viscosity by 1.002, which is the absolute viscosity of water at 20°C. The results are in excellent agreement with the data of the Xational Bureau of Standards at the higher temperatures and in good agreement at the low temperatures.
T E M P E R A T U R E,'C
FIQ.3. Relative viscosity as a function of temperature. Curve 1, 24.8 per cent hydrochloric acid; curve 2, 40.45 per cent perchloric acid; curve 3, 43.5 per cent fluoboric acid; curve 4, 36.0per cent sulfuric acid; curve 5, 60.5 per cent perchloric acid.
The relative viscosity of the 40.45 per cent solution is about half as great as that of the 60.50 per cent solution over the same temperature range; both of them show about a %-fold increase in viscosity from 25°C. t o -60°C. The specific conductivities of the perchloric acid solutions are shown in figure 5 (Microfilm; Table 1). The conductance of the 40.45 per cent perchloric acid was about 25 per cent greater at 20°C. and 300 per cent greater at -50°C. than that of the 60.50 per cent solution. A similar difference between the viscosity data of these two solutions is observed. 8. Sulfuric acid-water
The eutectic mixture of 38.5 per cent sulfuric acid has a freezing point of -72°C. and the 36.0 per cent solution studied has a freezing point of -64°C.
PHYSICAL PROPERTIES O F ELECTROLYTES
483
The densities, relative viscosities, and specific conductivities for the 36.0 per cent solution are shown in figures 1, 3, and 5 (Microfilm: Table 1). Sulfuric acid has the greatest viscosity, at the lowest temperatures, of any of the acids studied and compared in magnitude, a t the higher temperatures, with the viscosity of 60 per cent perchloric acid. Its specific conductivity at room temperatures is the best of the acids studied, but at -73°C. its conductivity is
TEMPER AT U R E,'C.
FIG.4 Relative viscosity as a function of temperature. Curve 1,100 per cent methanol; 10 per cent 0.1 N hydrochloric acid; curve 3, 14 per cent curve 2, 90 per cent methanol
+
methylammonium chloride in 60 per cent methanol; curve 4 , 3 9 . 4 per cent lithium bromide; 11 per cent lithium chloride in water, curve 5 , 33 per cent methylammonium chloride curve 6, 2435 per cent lithium chloride; curve 7, 18.6 per cent methylammonium chloride 19.6 per cent lithium chloride in water.
+
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about 40 per cent of that of eutectic hydrochloric acid. There is a 55-fold decrease in its specific conductivity from 25°C. to -73°C.
4. Fluoboric acidwater The densities, viscosities, and conductivities of 43.5 per cent fluoboric acid stabilized with 2.2 per cent boric acid were measured over the temperature range 25°C. to 73°C. They are shown in figures 1,3, and 5 (Microfilm: Table 1 ) . There is a ninefold increase in viscosity and a 25-fold decrease in specific conductivity over this temperature range. The data indicate that fluoboric acid has
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A . E. GARRETT AND S. A. WOODRUFF
good electrolyte properties at low temperatures and ranks second only to hydrochloric acid in this respect. B. SALT SYSTEMS AND METHANOL
The data for the densities, relative viscosities, and specific conductivities over the temperature range of 25°C. to -73°C. for several salt systems and for
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T E M PE R AT U R E, 'C. FIG.5. Specific conductivity as a function of temperature. Curve 1,14 per cent methylammonium chloride in 60 per cent methanol; curve 2, 1 N potassium chloride; curve 3,
24.85 per cent lithium chloride; curve 4, 33 per cent methylammonium chloride
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11 per cent lithium chloride in water; curve5,60.5 per cent perchloric acid; curve6,40.45 per cent perchloric acid; curve 7,43 per cent fluoboric acid; curve 8,24.8 per cent hydrochloric acid; curve 9, 36.0 per cent sulfuric acid.
methanol are summarized in table form in microfilm (Microfilm,2Table 2). The density data are shown in figure 2, the viscosity data in figure 4, and some of the specific conductivity data in figure 6. 1. P V Tmethanol ~ Pure methanol had the lowest density, the lowest viscosity, and the lowest specific conductivity of any solvent studied. It has a linear relationship between density and temperature. Its viscosity at -73°C. is about six times greater than at 25"C., but at this temperature its viscosity is only 9 per cent of that of eutectic
485
PHYSICAL PROPERTIES OF ELECTROLYTES
hydrochloric acid. The conductivity of pure methanol is of the same order of magnitude as that of distilled water. There is only a 25 per cent decrease in specific conductivity over the temperature range.
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TEMPE R AT URE, * C.
FIQ.6. Specific conductivity as
a function of temperature. Curve 1, eutectic
24.85 per cent lithium chloride; curve 2, 33 per cent ethanolamine hydrochloride; curve 3, eutectic 18.6 per cent methylammonium chloride 19.6 per cent lithium chloride in water; curve 4,18.5per cent methylammonium chloride 18.5per cent lithium chloride in water; curve 5,eutectic 39.4 per cent lithium bromide; curve 6,24.4per cent methylammonium chloride 11.8 per cent lithium chloride in water; curve 7,31.5per cent methylammonium chloride.
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Methanol (90 per cent) and 0.1 N hydrochloric acid (10 per cent) This solvent system was prepared for the purpose of increasing the conductivity of methanol without sacrificing too much of its other desirable properties. The density curve shows a nearly linear relationship with temperature. The viscosity curve increases steadily with a decrease in temperature. At -73°C. the viscosity is three times as great as the viscosity of pure methanol. The specific conductivity is greatly improved over that of pure methanol but still does not compare favorably with eutectic hydrochloric acid. There is a tenfold decrease in conductivity from room temperature to - 73°C. 8.
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A. B. GARREZT AND S. A. WOODRUFF
8. Methyhamine hydrochloride (14 per cent) in methanol (60 per cent) The addition of methanol to a solution of methylamine hydrochloride in water lowers the freezing point but also lowers both the solubility of the salt and the conductivity of the solution. Thirty per cent methanol in water remained fluid and conductive at -60°C. Fourteen per cent (by weight) of methylamine hydrochloride in a mixture of 60 per cent methanol in water was studied as an
%SALT
IN W A T E R
FIG.7. Crystal melting point as a function of the percentage composition of the salt in water. Curve 1, lithium chloride; curve 2, zinc chloride; curve 3, methylammonium chloride;
+
curve 4,lO per cent ammonium chloride methylammonium chloride; curve 5, ammonium chloride; curve 6,lO per cent ammonium chloride lithium chloride; curve 7, 10 per cent 5 per cent zinc chloride lithium chloride. ammonium chloride
+
+ +
electrolyte system; here the viscosity was greatly increased, with a fiftyfold increase over the temperature range of 25°C. to -70°C. The conductivity was also increased but not enough to make the system compare to other salt systems investigated.
4. Lithium chloride-zuater system The eutectic mixture of 24.85 per cent lithium chloride in water was found to have a freezing point of about -73°C. These data are shown in figure 7 (Microfilm: Table 5 ) . The physical properties of this solution are shown in figures 2, 4, and 5 (Microfilm: Table 2). The conductivities of two other lithium chloride
PHYSICAL PROPERTIES OF ELECTROLYTES
487
solutions with concentrations above and below the eutectic mixture are compared in microfilm (Microfilm,? Table 3). In spite of the 150-fold increase in viscosity for the eutectic lithium chloride from 25°C. to -7O”C., this salt solution has a fair specific conductivity over the entire temperature range. 6. Lithium bromide-water system The eutectic mixture of lithium bromide was found to contain 39.4 per cent lithium bromide and have a freezing point of -73°C. The data on physical properties are shown in figures 2, 4, and 6 (Microfilm: Table 2). This solution has a better conductivity than eutectic lithium chloride but requires about 60 per cent more salt to give the eutectic composition.
6. Ammonium chloride-water system The eutectic mixture of ammonium chloride-xater (18.6 per cent salt) has a eutectic temperature of - 15.8”C. (Microfilm,* Table 5). 7. Zinc chloride-water system The eutectic mixture of 51 per cent zinc chloride has a eutectic temperature of -62°C. (Microfilm,*Table 5).
8. Methylamine hydrochloridewater system The eutectic temperature of methylamine hydrochloride in water was found to be -43°C. (figure 7) (Microfilm,2Table 5), the eutectic comprising 44.6 per cent of the salt. This salt has good conductivity but alone does not have a w r y low freezing point. 9. Methylamine hydrochloride-lithium chloridewater system The eutectic mixture was found to be composed of 18.6 per cent methylamine hydrochloride and 19.6 per cent lithium chloride in water. This eutectic mixture froze into a noncrystalline solid at - 100°C. It was found that a mixture of 18.5 per cent of each salt in water has a crystal melting point of -73°C. and a better conductivity than the true eutectic mixture. These two solutions were studied further by adding to them such salts as ammonium chloride and lithium chloride. In these measurements, in order to speed up the experimental time necessary to find the eutectic points and to avoid the troublesome problem of supercooling, a “crystal melting” method was used. In this method the solution was cooled, with stirring, until a copious amount of crystals formed. The temperature of the solution was then slowly raised, and the vigorous stirring was continued until the last crystals in the solution disappeared; this temperature was called the “crystal melting point” and was found to be very sharp and experimentally reproducible. I n most cases, the crystal melting point was found to be very close to the freezing point of the salt mixture as determined from cooling curves. In order to find the above eutectic mixture, each of the four exactly known mixtures of methylamine hydrochloride plus lithium chloride (each of which had
488
A . B. GARRETT AXD S. A . W’OODRUFF
a different ratio of the salts) was studied separately to find the minimum crystal melting point (see Microfilm: Table 3, for the conductivities of these solutions). The percentages of the salts were varied either by evaporating water or by adding water (in known weighed amounts) and determining the individual crystal melting point of each composition. The lowest freezing point of each ratio was plotted as temperature against the composition ratio and the intersection of the curves should theoretically give the eutectic point at a known ratio of the salts. (These data are summarized in Microfilm,2 Table 4.) The physical properties data of the eutectic methylamine hydrochloridelithium chloride electrolyte systems are compared with other electrolytes in microfilm (Microfilm: Table 2 ) and graphically shown in figures 2 , 4, and 6. Generally these data were comparable with eutectic lithium chloride but, of course, are extended to a much lower temperature. However, this eutectic solution had the greatest viscosity of any electrolyte studied. The 33 per cent methylamine hydrochloride plus 11 per cent lithium chloride in water solution has a much better conductivity and less viscosity but has a crystal melting point of only -55OC., as shown in figure 5. 10. Methylamine hydrochloride-lithium chloride-ammonium
chloride-zinc chloridewater system A preliminary investigation was made on this five-component system to obtain an indication of the greatest number and amounts of salts which might be used as an electrolyte. The data are compared graphically in figure 7 (Microfilm: Table 5). The eutectic points of the individual salts are given, as well as the effect of holding one or two components constant and varying the other components. Ammonium chloride seemed to be the most limiting salt and was the first to separate out of mixtures. Zinc chloride raised the freezing points rapidly. In microfilm (Microfilm,2 Table 3) data are shown for the specific conductivities of ( 1 ) several methylamine hydrochloride-lithium chloride mixtures, ( 2 ) the m e mixtures with 1 per cent and 3.5 per cent ammonium chloride, (3) these m e solutions with 1 per cent and 3.5 per cent zinc chloride, and ( 4 ) again with a 0.5 per cent of each salt. Generally speaking these two salts did not affect the conductivities very much, with ammonium chloride slightly increasing and zinc chloride slightly decreasing the conductivity. I n conclusion, the data indicate that not much ammonium chloride or zinc chloride could be added to a eutectic mixture of methylamine hydrochloride and lithium chloride without raising the crystal melting points of the electrolytes appreciably. 11. Ethanolamine hydrochloridewater systems Since ammonium chloride was found to be the first salt to be thrown out of salt mixtures studied above, as the temperature waa lowered it was hoped to find a salt which had ionization or hydrolysis constants similar t o those of ammonium chloride but which would remain in solution at low temperatures. For this reason the ethanolamine hydrochloride (CH20HCHSNHt.HC1)-water
489
PHYSICAL PROPERTIES OF ELECTROLYTES
system was investigated. A eutectic mixture, composed of 45 per cent salt, had a eutectic temperature of -30.5"C., as shown in figure 8 (Microfilm,*Table 6). Furthermore, the specific conductivity of ethanolamine hydrochloride was found to be about half as good as that of methylamine hydrochloride (Microfilm,* Table 3).
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Fro. 8 . Crystal melting point as a function of the percentage composition of the salt in ethanolamine hydrochloride; curve 2, 20 water. Curve 1, 20 per cent lithium chloride per cent ethanolamine hydrochloride lithium chloride; curve 3, 10 per cent ammonium ethanolamine hydrochloride; curve 4, ethanolamine hydrochloride. chloride
+
+
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1% Ethanolamine hydrochloride-lithium chloridewater system The data for these systems are reported in Microfilm; Table 6, and graphically compared in figure 8. Twenty per cent of ethanolamine plus 25 per cent lithium chloride gave a low crystal melting point of -75°C.
CONCLUSIONS The eutectic mixtures, freezing points, electrical conductivities, viscosities, and densities of many of the more promising solvent-electrolyte systems that are liquid over the temperature range 25°C. to - 7 3 ° C . have been investigated. Especially significant among these data are ( 1 ) the rapid increase in viscosities at low temperatures, (2) the comparison of the electrical conductivities of the acid and salt systems (over the entire temperature range) with that of potas-
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W. 0 . MILLIQAN AND HARRY E. W W E R
mum chloride at room temperature, and (3) the large decreese in electrid conductivities as the temperature was dropped to -73°C. Our findings indicate the following solvent-electrolyte systems as the more promising to be used at -73OC.: ( 1 ) eutectic hydrochloric acid, (8) 43 per cent fluoboric acid, (3) methylamine hydrochloride in methanol, (4) eutectic lithium chloride and eutectic lithium bromide in water, and ( 6 ) methylamine hydrochloride and lithium chloride in water. REFERENCES (1) BRICKWEDDE, L. H., AND PARDO, B. G.: Unpublished data in National Bureau of Standards report entitled “Densities of Perchloric Acid Solutions from +50° t o -SO’C.,” January, 1944. (2) BRICKWEDDE,L. H., A N D PARDO, B. G.: Unpublished data in National Bureau of Standards report entitled “Viscosity of Perchloric Acid Solutions from +Meto -boDC.,” August, 1944. (3) FAUNS, K., AND HASSEL,0.: 2. Elektrochem. Is, 495 (1923). (4) GARRETT,A. B.,AND COOPER,R.: J. Phys. & Colloid Chem. 64,4374 (1960). (5) GABBETT,A. B., A N D HEIKS, J.: To be submitted for publication. (6) GAB~ETT, A. B., AND WELSH,J.: To be submitted for publication. (7) G,AB~ETT, A. B., A N D WELSH,J.: To be submitted for publication. (8) GABBETT,A. B., WELSH,J., WOODRUFF, 8.A., COOPER,R., AND HEIKS, J.:J. Phys. & Colloid Chem. 69, 505 (1949). (9) Intenational Critical Tables, Vol. 111, pp. 60,64, 77. McGraw-Hill Book Company, Inc., New York (1928).
ORIENTATION EFFECTS I N TRANSPARENT ALUMINA FILMS* W. 0. MILLIGAN AND HARRY B. WEISER Deparfment of Chemistry, The Rice Institute, Houston, Tezas
Received January IS, 1060
The hydrous particles in alumina sols prepared by the peptization of precipitated alumina consist of minute crystals of -/-AlnOs.H20or y-Al00H (for a survey of the literature we reference 14). X-ray Mraction examination of (a) airdried precipitated gels, (b) moist gels, (c) the alumina particles in the sol d t e , and electron diflraction examination of thin films from evaporated sols show that the dispersed phase has a crystal structure identical withthat of relatively large crystals of y A l 0 0 H (boehmite). The structure of y A l 0 0 H haa not been determined by single-crystal methods, but de Lapparent (2) obmrved that the crystals are orthorhombic. Comthe x-ray powder photographs of r-Al00H and the corresponding r-FeOOH, Hocard and de Lappsrent (7) and Goldstaub (6)concluded, from the close similarity of the powder 1 P m n t e d before the Division of Colloid Chemistry at the 104th Meeting of the Ameriian Chemioal &&ty, which WIW held in Bu5810, New York, September 7-11, 1942.
