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I N D U S T R I A L A N D ENGINEERING CHEMISTRY
Vol. 23, KO.6
Freezing and Boiling Points of the Ternary System Ethanol-Methanol-Water' Elizabeth W. Aldrich and Dale W. Querfeld BUREAUOF STANDARDS, WASHINGTON, D.
c.
In connection with an investigation of antifreeze expressed in volume per cent T HAS been known for liquids, freezing-point data were obtained on aqueous of total alcohol presentsome time that smaller solutions of methanol, of ethanol, and of binary mixnamely, the s u m m a t i o n of quantities of m e t h a n o l tures of the two alcohols containing 12.5, 25.0, 33.3, the original volumes of the than of ethanol in aqueous 50.0, 66.7, 75.0, and 87.5 volume per cent of methanol. t w o alcohols a t 15.6" C. solution are required for the Boiling-point data were obtained on these same soluwhich when diluted with the same protection against freeztions excluding the methanol-water solutions. The appropriate amount of water ing when used as antifreeze boiling-point measurements covered the complete gave a total volume of 100 ml. liquids (3). It is probably range of total alcohol content from 0 to 100 volume a t 15.6' C. In the case of not so well known, however, per cent, while the range covered by the freezing-point the binary alcohol solutions t h a t u p t o compositions of determinations was from 0 to as high as 50 to 70 per the c o m p o s i t i o n was ex40 per cent by volume the cent. It was found that aqueous solutions of the two pressed in volume per cent of boiling points of methanol soalcohols possessed no advantages over those of the one of the alcohols-namely, lutions are not very different individual alcohols for antifreeze purposes. the volume of this alcohol a t from those of ethanol. On a 15.6' C. which when added to mol Der cent basis the methano1 Galues are even higher than those for ethanol up to 15 the appropriate volume of the other alcohol a t 15.6" C. gave a summation of volumes equal to 100 mi. mol per cent (3). The possibility therefore existed that ternary systems of Determination of Freezing Points ethanol-methanol-water might have advantages when used as antifreeze liquids, over either of the binary mixtures from Several slightly different types of simple freezing-point the combined standpoint of freezing point apparatus were tried and the one shown in Figure 1 was and boiling point. Accordingly, an in- chosen. An apparatus capable of greater precision but of vestigation was made of the boiling points more complex design was used by Kanolt ( 5 ) . It was found, over the entire ternary field a t atmos- however, that the simpler apparatus permitted sufficiently pheric pressure and of the freezing points precise measurements for the present purpose. of these solutions containing as high as In making a determination, the alcohol solution was cooled 50 to 70 per cent total alcohol. to approximately 5" C. above the freezing point by immersion of the freezing-point tube in liquid air. The tube was then Preparation of Solutions
I
The ethanol used was a high grade of c. P. absolute alcohol containing 0.15 per cent water as deduced from its measured specific gravity (15.6"/15.6" C.) of 0.7947. The methanol was a c. P. product containing 0.10 per cent of water. Its boiling point was 64.60" C. and its specific gravity (15.6"/15.6" C.) svas0.7962. Freshly distilled water was used in tJhe preparation of all aqueous solutions. The aqueous binary solutions were prepared by measuring out appropriate volumes of either alcohol in one of several small volumetric flasks and making up to the desired concentration by the addition V of water in a large volumetric flask. In Figure 1-Freezingthe preparation of the ternary solutions a Point Apparatus series of alcoholic binary solutions was first prepared by mixing measured volumes of the two alcohols. These solutions were then made up t o the desired total alcohol content by the addition of water in a large volumetric flask. All the volumetric flasks were calibrated and all solutions were made up a t 15.6" C. In the case of the binary aqueous solutions, compositions were expressed in volume per cent-namely, the volume of alcohol a t 15.6" C. which when added to the appropriate amount of water gave a total volume of 100 ml. a t 15.6" C. The composition in the case of the ternary solutions was 1 Received March 13, 1931. Publication approved by the Director of the Bureau of Standards of the U. S. Department of Commerce.
Percent M e f h n o / i nA/cahd Blend Figure 2-Freezing
Points of Aqueous Alcohol Solutions
placed in the Dewar cylinder shown in Figure 1 so that additional cooling was effected by means of vapors from liquid air. The alcohol solution was stirred vigorously during this process. The cooling was maintained a t a convenient rate by evacuating the annular space around the freezing-point tube to
June, 1931
INDUSTRIAL A N D ENGINEERING CHEMISTRY
approximately 0.01 mm. of mercury and by adjusting the depth of liquid air in the flask. The temperature a t which crystals f i r s t appeared was observed. Cooling was continued until the temperature dropped another 2" or 3" C. The f r e e z i n g - p o i n t tube was then raised sufficiently to permit the temperature to rise slowly and the reading of the thermometer was noted when crystals disappeared completely. This procedure was repeated four or five times for each solution and an average of the freezing points and melting points thus obtained was taken as the freezing point. Difficulty was experienced in determining the exact time a t which crystals appeared or disappeared in the case of the more concentrated solutions, thereby limiting the accuracy of the values. Successive determinations normally agreed within 0.5" C., although occasional differences of as much as 3" C. were obtained a t the lower temperatures. The average difference between the observed freezing points and melting points was 1' C. A mercury-in-glass thermometer graduated in 0.2' C. was used for temperatures down t o -36" C. For lower temperaFigure 3-Boiling-Point t u r e s a toluene thermometer Apparatus similarly graduated, and with a range from -66' to f30" C. was employed. Both thermometers were carefully calibrated as partial immersion instruments.
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ing points. The average deviation between observed and smooth values as found by this procedure was 0.5' C. Table I-Smoothed METHANOL IS ALCOHOL BLEXD
Freezing-Point Data
TOTAL ALCOHOLI N AQUEOUSSOLUTION
"n 0
10%
20%
30%
O C .
OC.
O C .
40%
=c.
50%
60%
oc.
o c
12.5 25.0 33.3 50.0 66.7 75.0 87.5
100
Table 11-Smoothed
1
~
BLEND
~
1
Boiling-Point Data
TOTAL .4LCOHOL IX AQUEOCSS O L U T I O N
&
