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perceptible interaction between methylcellulose and gelatin is a dehydration of the former by the latter. Dispersion of the two phases in each other, by shaking, leads to systems which show a gel-sol-gel transformation with rising temperature; a t low temperatures, a gelatin gel structure can include up to 85 per cent by volume of methylcellulose sol without depriving the mixed system of its gel character; a t high temperatures, a methylcellulose gel structure can include, in a similar manner, up t o 30 per cent by volume of gelatin sol. The gel-sol-gel transformation is largely independent of the pH, that is, the phenomenon remains the same whether or not the charges of the gelatin and of the methylcellulose particles have the same or an opposite sign. REFERENCES
(1) BURGENBERG DE JONG, J. : Actualit& scientifipues et industrielles: Volume 397, GinCTalitCs et coacervats complexes; Volume 398, Coacervats autocomplezes. Hermanii e t Cie., Paris (1936). (2) BUNGENBERG DE JONG, J.: Kolloid-2. 80, 359 (1937). (3) HELLER,W.:Compt. rend. 202, 61 (1936). (4) HELLER,W.: Compt. rend. 202, 1507 (1936);207, 991 (1938). (5) HELLER,W.,AND QUIMFE,G.: Compt. rend. 206, 857 (1937). (6) HELLER,W.,AND VASSY,E.: Compt.. rend. 207, 157 (1938). (7) HELLER,W.,AND VASSY,E.: Compt. rend. 208, 812 (1939). (8)HEYMARN, E.:Trans. Faraday SOC. 31, 846 (1935). (9) LANGMUIR, I.: J. Chern. Phys. 6, 873 (1938). (10) MCBAIN,J . M., HARVEY, C. E., AND SMITH, L. E . : J. Phys. Chem. SO, 347 (1926). (11) SZEGVARI, D.:Kolloid-2. 34, 34 (1923). (12) ZOCHER,H.,AND JAKOBSOHN, K . : Kolloid-Beihefte 28, 1 (1929). (13) ZSIGMONDY, R., A N D BACHMANN, W.: Kolloid-2. 11, 150 (1912).
T H E SURFACE TENSION OF AQUEOCS PERCHLORIC ACID AT 15') 2 5 O , A S D 50°C.' C. A. NEROS
AND
W. G. EVERSOLE
Department of Chemistry, The State University of Iowa, Iowa City, Iowa Recieved June 80, 1940
The surface tensions of solutionb of the inorganic acids have been studied by Abonnenc (l),who measured the relative surface tensions by comparing the weights of drops formed a t the end of a cylindrical tube. He found that the surface tensions of the monobasic acids decreased with increasing concentration, but he gave no data. Quantitative data on the 1 Submitted by C. A. Keros to the Graduate College of the State University of Iowa in partial fulfillment of the requirements for the degree of Doctor of Philosophy, August, 1938.
SURFACE TENSION OF AQUEOUS PERCHLORIC ACID
389
surface tension of perchloric acid solutions could not be found in the literature. The present study was made in order to obtain such data over a wide concentration range at different temperatures. The differential capillary-rise method described by Richards, Speyers, and Carver (10) was chosen for the present work. The smaller capillary tube was carefully selected for uniformity of bore by determining the length of short mercury columns in various parts of the tube, while short lengths of tubing of each size were examined a t both ends by means of a microscope until one was found which was nearly circular in cross section.
FIG.1. The apparatus. A, small capillary tube; B, large capillary tube; C, reservoir; D, solid glass rod; E, 'srrew adjustment; F, ground-glass joint.
The radii of the capillaries were determined, according to the method described by Richards (lo), after the capillarimeter had been assembled. Using water as a standard (71.97 dynes per centimeter at 25OC.), the radii of the capillaries were found to be 0.03091 and 0.1923 cm. The apparatus is shown in figure 1. The portions of the two capillary tubes that were used in the measurements were on a common vertical axis and the vertical distance between the menisci was measured by a measuring microscope which could be read to f0.0001 cm. Errors due to the deviation of the capillary tube from a true right circular cylinder were minimized by allowing the meniscus to come to equilibrium in the same position in the smaller capillary tube for all determinations.
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C. A. NEROS AND W. G. EVERSOLE
For the same per cent of deviation in both tubes, that in the smaller capillary will cause the greater error in the measurement of the differences in height. The accurate adjustment of the position of the meniscus in the capillary tube to the desired position was greatly simplified by the device shown in figure 1. A solid glass rod (D) was attached to n screw adjustment (E), and mounted on the ground-glass stopper (F). A fine line was etched on the capillary A a t G above the elbow. When the capillarimeter was filled, sufficient liquid was added so that upon completely wetting the capillaries the meniscus came to equilibrium slightly below the mark (G). Final adjustment was made by either raising or lowering the glass rod which extends below the surface of the liquid in the reservoir, after the capillarimeter and contents had reached the desired temperature ( =k0.005°C.) in a thermostat. In this way the meniscus could be adjusted to within 0.002 cm. of the mark. All solutions which were used in this work were allowed to stand overnight to permit capillary-active materials (8) to rise to the surface. The liquid was then drawn off from the interior of the reagent vessel by means of a siphon. Before making a determination the capillarimeter was cleaned with a hot mixture of sulfuric and chromic acids, followed by treatment with hot concentrated nitric acid, and then thoroughly rinsed with conductivity water and dried. The perchloric acid used was that obtained from the G. Frederick Smith Chemical Company and was further purified according to the method recommended by Willard (14). It was redistilled twice, and only the middle fraction distilling a t 162-163°C. (at 200 mm.) was used for this work. All solutions were prepared from the concentrated acid on a weight concentration basis and the exact concentrations were determined by titration with barium hydroxide solution, using phenolphthalein as an indicator. The barium hydroxide was kept free from carbon dioxide by means of soda lime tubes and was standardized against acid potassium phthalate (Standard Sample No. 84 from the Bureau of Standards). Conductivity water, which had been distilled from an alkaline solution of potassium permanganate in a large copper still and condensed in a block-tin condenser, was used throughout the investigation. The density of each solution was determined at 25°C. by means of 50-cc. Ostwald pycnometers, using a similar pycnometer as a counterpoise. All weighings were made with a set of precision brass weights which had been accurately calibrated. RESULTS
The experimental results are given in tables 1 to 3. In the first column the concentration of acid is expressed in weight per cent, while in the
TABLE 1 The surface tension of aqueous perchloric acid at 16OC. CONCENTRATION OF ACID
D (6)
H
H
(OBSERVED)
(CORRECTED)
0.9991 1,0277 1,0598 1.1307 1.2098 1.3030 1.4565 1.5487 1,5858 1.6410 1,6790 1 ,7034
4.1308 3.9633 3.7988 3.5044 3.2507 3.0149 2.725O 2.5833 2.5218 2.4352 2.3613 2.3246
4.0811 3.9142 3.7502 3.4560 3.2014 2.9671 2.6774 2.5377 2.4742 2.3876 2.3136 2.2770
U
weight per cent
0.00 4.86 10.01 20.38 30.36 40.37 53.74 60.70 63.47 67.59 70.43 72.25 _____
73.51 72.52 71.66 70.46 69.82 69.72 70.33 70.88 70.77 70.67 70.07 69.96
TABLE 2 The surface tension and density of aqueous perchloric acid at H O C . CONCENTRATTON OF ACID
D
H
H
(ORBEWED)
(CORRECTED)
3.9011 3.7429 3.4593 3.2097 2.9842 2.6958 2.5661 2.5018 2.4180 2.3610 2,3047
3.8525 3.6944 3.4109 3.1616 2.9351 2.6480 2.5154 2.4542 2.3708 2.3134 2.2569
wn'gA1 per cenl
0.00 4.86 10.01 20.38 30.36 40.37 53.74 60.70 63.47 67.59 70.43 72.25
0.99707 1 ,02476 1.05597 1.12534 1,20272 1.29396 1.44528 1.53579 1.57515 1.63016 1.66637 1.69495
71.97(7) 71.18 70.34 69.21 68.57 68.49 69.02 69.69 69.73 69.71 69.54 69.01
TABLE 3 The surface tension of aqueous perchloric acid at 60°C. CONCENTRATION O F ACID
H
H
(OBSERVED)
(CORRECTED)
U
3.8746 3.7458 3.6076 2.3529 3.1268 2.9151 2.6544 2.5315 2.4728 2.3888 2.3340 2.2809
3.8259 3.6973 3.5592 3.3048 3.0788 2.8673 2.6068 2.4838 2.4252 2.3412 2.2815 2.2333
68.16 67.60 66.97 66.12 65.66 65.74 66.60 67.40 67.44 67.41 67.26 66.85
weight per cenl
0.00 4.86 10.01 20.38 30.36 40.37 53.74 60.70 63.47 67.59 70.43 72.25
0.9881 1.0140 1.0436 1.1096 1.1827 1.2714 1.4166 1.5045 1.5416 1.5964 1.6344 1.6595
391
392
C. A. NEROS AND
W. G. EVERSOLE
fourth column values of the surface tension, u, are given in dynes per centimeter. The surface tensions were calculated by means of the following expression (10) : u = KH(D
- d)
where
K
__
rlg
2(1
- G)
is the radius of the small capillary; r2 is the radius of the large capillary; G is the ratio of the two radii (rl/rz); D is the density of the liquid; d is the density of air; g is the gravitational constant (980.311); and K is a constant for any apparatus a t any given temperature. At 25°C. K was found to be 18.05. This value was also used at 15' and 50"C., since Richards has shown that the temperature coefficient of K is less than 1 part in 1000 over a temperature interval of 60°C., which is within the experimental error of the results. H = hl - hz, where hl is the corrected rise in the smallcapillary and hz is the corrected rise in the large capillary. If h - h' is the observed difference in height of the two capillaries, then TI
H
=
hl
- hp
= (h
- h') +
[ry] [$- $1 0.1288
+ 0.1312 [$-
$1
where the correction terms are those of Poisson and Lord Rayleigh. DISCUSSION
The relation between the surface tension and the concentration of aqueous perchloric acid is shown graphically in figure 2 for three different temperatures. The surface tension of the solutions gradually decreases with increasing concentration of acid up to approximately 40 per cent. As the concentration is increased still further, the surface tension rises to a maximum at a concentration of approximately 65 per cent. Acid concentrations higher than 72 per cent were not used, since anhydrous perchloric acid (5, 13), from which the solutions must be prepared, is unstable overa period of time. At 15°C. the minimum is reached at a concentration of 40 per cent, while the maximum is observed at approximately 63 per cent. The surface tension-concentration curve at 25°C. is very nearly parallel to the curve at 15'C., except that the maximum has shifted slightly towards the higher concentrations of acid. It will be observed that the isotherm for 50°C. has the minimum a t about 30 per cent, whereas the maximum is essentially
SURFACE TENSION OF AQUEOUS PERCHLORIC ACID
393
the same as was found for the isotherms at 15" and 25'C. The graph also shows that the effect of perchloric acid on the surface tension of water is much less at higher temperatures for all concentrations than at the lower temperatures. A similar situation arises for sulfuric acid, where the same sort of behavior has been observed by Morgan (9). Using the drop-weight method, he determined the surface tension of sulfuric acid a t 0", 30°, and 50°C. Both a minimum and a maximum were found at OOC., while only a maximum was found at the higher temperatures. He also calculated the values of surface tension at 18OC. and found that this, too, contained both a
c *
x by
WYt.
nao,
FIG.2. Relation between the surface tension and concentration of aqueous perchloric acid a t three different temperatures. The curve a t 50°C. is slightly low (see table 3).
maximum and a minimum. Sabinina (11) has studied the same system by means of the capillary-rise method at temperatures ranging from 10' to 50°C. His data show that only a maximum is obtained for each isotherm within this range. A possible explanation for this phenomenon has been postulated by Ariyama (2). He presupposes the structure for water as presented by Bernal and Fowler (3), that is, the oxygen atom is situated in the center of a tetrahedron. Then two of the corners of the tetrahedron are occupied by two protons, while two negative charges are distributed a t the two heads as yet unoccupied. The protons or other molecules having a structure similar to that of water will then be attracted by negative charges situated at two corners of the tetrahedron. If the molecules of water are
394
C. A. NEROS AND W. G. EVERSOLE
distributed a t random both a t the surface and a t the interior of the liquid, negative adsorption of protons should result, since the ions forming the hydrogen bond between molecules of water will be distributed uniformly throughout the liquid and the effect due to the hydrogen bond can be neglected. It is therefore apparent that the hydrogen bond cannot by itself give rise to the positive adsorption of protons at the surface of water. I n order that positive adsorption of protons may occur at the surface, the distribution of the hydrogen bond must be different a t the surface than in the interior of the liquid. Ariyama assumes that most of the water molecules a t the surface have their hydrogen heads facing upward, and therefore one might expect positive adsorption of protons. If the molecules of water are oriented a t the surface in this may, a decrease in the surface tension of perchloric acid would be expected. The maximum obtained for sulfuric acid has been explained by Morgan as due to the formation of a compound in solution. Assuming Denison’s (4)theory to be correct, that “the deviation of a property from the mixture law, plotted against the composition, shows at the point of maximum deviation the presence of a compound identical in composition with that of the solution leading to that maximum deviation,” he found that the property of surface tension indicated the existence of the compound, HzS04.3Hz0. Sabinina (11) concluded that a substance, HzS04.2Hz0, was present, since the minimum found for the temperature coefficient and also the maximum obtained from the deviations of the surface tension from the mixture law both occurred for a solution of this composition. The above-mentioned authors used the same criteria in the interpretation of their results, although the outcome in each case was not the same. If Denison’s method of interpretation is to be applied, the deviations of the surface tensions from the additive values should be plotted against the concentration. This cannot be done, however, since the surface tension of the anhydrous acid is not known. But, if it is assumed that the maximum can be interpreted directly as being due to the formation of a new substance, the maximum composition a t approximately 63 to 65 per cent is found to correspond to the hydrate, HC104.3HzO (12), which is known to exist in the solid state. SUMMARY
By means of a simple device, errors due to variation in the radii of the capillaries could be reduced to a minimum in the differential capillary-rise method. Both a maximum and a minimum were observed when the surface tension of perchloric acid was plotted against the percentage composition. The initial lowering of surface tension was explained as being due to the formation of a hydrogen bond at the interface, as postulated by Ariyama.
ADSORPTION AT CRYSTAL-SOLUTION
INTERFACES
395
The maximum in the u-c curve was found to correspond to the composition of the hydrate, H C l O ~ . 3 H ~ 0 . REFERENCES ABONNENC:Compt. rend. 186, 948-50 (1927). ARIYAMA:Bull. Chem. Soc. Japan 12, 109-13 (1937). BERNAL A N D FOWLER: J . Chem. Phys. 1, 515 (1933). DENISON:Trans. Faraday SOC.8, 20 (1912). GOEALERAND SMITH:Ind. Eng. Chem., Anal. Ed. 3, 55 (1931). International Critical Tables, Vol. 111, p. 54. McGraw-Hill Book Company, Inc., iTew York (1928). International Critical Tables, Vol. IV, p. 447. ,McGraw-Hill Book Company, Inc., New York (1928). JONES AND RAY: J. Am. Chem. SOC. 69, 187 (1937). MORGAN AND DAVIS:J. Am. Chem. SOC.38, 555 (1916). RICHARDS, SPEYERSAND CARVER:J . Am. Chem. SOC. 46, 1196 (1924). SABININAAND TERPUGOW: Z. physik. Chem. A173, 237 (1935). VANWYK: 2.anorg. Chem. 48, 1 (1906). VORLANDER A N D SCHILLING: Ann. 310, 369 (1900). WILLARD:J. Am. Chem. SOC. 34, 1480 (1912).
ADSORPTIOK AT CRYSTAL-SOLUTION INTERFACES. XI
A STUDYOF THE ADSORPTIONOF ISOMERIC MONOAZO DYESBY CRYSTALS OF SODIUMSITRATE, SODIUMBROMATE, AND SODIUM CHLORATE DURING THEIR GROWTH FROM SOLUTION' WESLEY G. F R A F C E
AND
K A T H R Y F M. WOLFE
Department of Chemistry, T h e Ohio State University, Columbus, Ohio Received J u n e 14, 1940
In the preceding paper (12) of this series (1,3, 5, 6, 8, 9, 10, 11, 12, 13, 14) of investigations on adsorption a t crystal-solution interfaces, attention was centered particularly upon the effect of certain polar groups, in the foreign molecules, on the adsorption and subsequent habit modification of potassium sulfate crystals. A series of acid and basic isomeric monoazo dyes was used as foreign materials, and it was found that those dyes containing sterically hindered polar groups were in general not adsorbed by the growing crystal. In order to obtain further information on this steric and other effects, the present investigation of the adsorption of these dyes by crystals of sodium nitrate, sodium bromate, and sodium chlorate was Presented before the Division of Colloid Chemistry a t the Ninety-ninth Meeting of the American Chemical Society, held in Cincinnati, Ohio, April, 1940.
