H I D E SUBSTANCE WITH HYDROGEN CHLORIDE AND AMMONIA L. R. PARKS AND A. D. MELAVEN The Pond Chemical Laboratories, The Pennsylvania State College, State College, Pennsylvania Received October 10, 1956 INTRODUCTION
In a study of the two-component system hide substance-hydrogen chloride, using the method of Bancroft and Barnett (l), Beek (2) reports that a compound is formed in which the combining weight of hide protein for hydrogen chloride is 332. The complete phase diagram was not obtained, but the compound was reported to have a dissociation pressure equivalent to 30 mm. of mercury at room temperature. Using the same method, Tsai and Hsiao (3) found that a t 35OC.,hydrogen chloride combines with hide protein to the extent of 26.4 mg. of HC1 per gram of hide substance, to give the latter a combining weight of 1380. The dissociation pressure of this compound they reported as being equivalent to 1.41 mm. of mercury at 35°C. In the present work, complete phase rule data, obtained by the method of Bancroft and Barnett, are given for the twocomponent systems hide substance-hydrogen chloride and hide substanceammonia. In neither case is there found to be any evidence of compound formation. MATERIALS
The hide substance used was American Standard Hide Powder, obtained from the Standard Manufacturing Company of Ridgway, Pa., and was used without further treatment other than drying. The hydrogen chloride was generated by the action of C.P. sulfuric acid on crystalline ammonium chloride. It was dried by passing through two 4-in. columns of sulfuric acid before being added to the system. The ammonia gas was taken directly from a cylinder of anhydrous ammonia, obtained from the Matheson Company, North Bergen, N. J. The gas was passed through a 12-in. column of soda lime before being admitted to the reaction flask. The mercury was vacuum distilled before using. METHOD
A weighed amount of hide powder was placed in a calibrated flask, which communicated with the gas supply through one arm of a mercury ma471
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L. R. PARKS AND A. D. MELAVEN
nometer connected directly to the reaction flask. After evacuation of the system, gas was added to the flask a few cubic centimeters a t a time, TABLE 1 Adsorption of hydrogen chloride by hide powder at low pressures ap/av = 0.96 HCl
PRESENT AT 25°C. A N D 760 M M . Hg
1
EQUILIRRIUM PREs8URE
mm. Hg
cc.
9.6 29.9 60.8 76.7 98.5 124.4 165.0 203.5
0.012 0.04 0.10 0.15 0.36 0.48 1.20 2.20
1
HC1 ADSORBED
BY
5.0 G
OF HIDE POWDER
1
-
xlm I N Y O . HCI PER GRAM OF A I D E POWDER
cc.
m0.
9.6 29.9 60.7 76.6 98.1 123.9 163.7 201.2
2.86 8.90 18.1 22.8 29.2 36.9 48.8 60.0
TABLE 2 Adsorption of hydrogen chloride by hide powder d p / d v = 1.24 HCl PRESENT AND
AT 26'c. 760 M M . Hg
cc.
177.2 295 3 312.7 349 I3 374.6 400.7 459 554 709 819 942 1302 1371 1461 1298 1200 1074 934 793 693 573 401
PREBBURE
HC1 ADSORBZD
z / m IN XG. HC1 PER GRAM OF A I D E POWDER
B Y 5.0 C . OF H I D E POWDER
.
mm. Hg
cc
1.5 7 8 9 5 11.5 15.6 19.5 34.8 68.2 150 208 300 586 649 725 555 463 343 224 122 70 32 9
176 289 305 340 362 385 43 1 499 588 651 700 829 848 877 850 826 798 754 695 637 547 394
0
mg.
I
52 86 91 102 108 115 128 149 175 194 209 247 253 26 1 253 246 238 225 207 190 163 117
waiting until the pressure reached a constant value before making further additions. The free gas remaining in the system a t equilibrium was
H I D E SUBSTANCE WITH HYDROGEN CHLORIDE AND AMMONIA
473
calculated from the existing pressure and the previous calibration. Subtraction of this calculated value from the total amount of gas added gave the volume of gas taken up by the sample. By plotting the equilibrium pressure against the corresponding amounts of gas taken up by the sample, the phase diagram for the system gas-hide substance may be obtained. All pressure readings were made at 25°C. Table 1 contains the data obtained for the system hydrogen chloridehide substance, at low pressures. Table 2 contains the data for the same system over a greater range of pressure. Table 3 summarizes the data for the system ammonia-hide substance. The dp/dv values given in the
TABLE 3 Adsorption of ammonia by hide powder d p l d v = 1.82 ~
"3
PRESENT AT 26°C. AND 760 MY. Hg
EQUILIBRIUM PRESSURn
cc.
136 214.5 273 398.5 434 469 548 658 805 908 810 756 688 561 429 255.4 85.7 36.2
VHI
ADSORBED BY 6.0 G OB HIDE POWDER
mm. Hg
cc.
40 91 138 263 295 345 423 560 732 856 718 646 657 394 255 102.5 18 5 5.5
114 165 197 254 272 279 315 350 404 437 415 401 382 344 289 199 75.5 33.2
z/m IN YO. NHDPER GRAY OB H I D E POWDER mi.
15.9 22.9 27.4 35.3 37.9 38.8 43.8 48.7 56.4
60.7 57.5 55.6 53.2 47.8 40.2 27.6 10.5 4.6
tables were obtained from the calibrations, and represent the change of pressure in the system, in millimeters of mercury per cubic centimeter of gas, measured at 25°C. and 760 mm. of mercury. DISCUSSION
+
+
The phase rule, P V =C 2, where P represents the number of phases, V the number of degrees of freedom, and C the number of components, tells us that when a system of two components exists in three phases at constant temperature, the number of variables or degrees of freedom is zero. At constant temperature the pressure must remain
474
L. R . PARKS AND A. D. MELAVEN
constant as long as three phases exist. On the phase diagram, the simultaneous existence of three phases is represented by a “flat,” showing constant pressure, parallel to the axis of composition. The length of the flat, as measured on the composition axis, gives the ratio of the two components in the compound. When two components exist in but two phases at constant temperature, the number of degrees of freedom will be one, and the pressure will vary simultaneously with the composition. In this case a plot of the equilibrium data will result in a smooth curve. Phase diagrams constructed from the data of tables 1, 2, and 3 are of this type, showing that an adsorption complex rather than a true compound is formed. An important factor to be considered in the construction of the phase diagram between hide substance and gases is that of equilibrium and the rate of its attainment. The disagreement of results in the present work with the results of Tsai and Hsiao and with the results of Beek is undoubtedly due t o this factor. Tsai and Hsiao report that the equilibrium between hydrogen chloride and hide substance is established in one to two days. In the early course of this investigation it became apparent that a period of time considerably longer than one t o two days was necessary for the system to arrive a t the true equilibrium value. A period of h e n t y to twenty-five days was found in most cases necessary before readings that checked within the experimental error of the method were obtained, What has just been said applies in particular t o the case where one proceeds from a lower to a higher pressure. In the reverse case, the hysteresis curves, obtained by proceeding from a higher to a lower pressure by removal of gas, represent values nearer the true equilibrium values, since check readings were usually obtained in fifteen to eighteen days after extraction. Since the pressure will decrease after addition of gas and increase after removal of gas, the conclusion is reached that the true equilibrium values lie between the two curves and are more nearly represented by the hysteresis or “down” curve than by the “up” curve. The experimental point a t a pressure of 300 mm. and an z / m value of 209 may be used in support of this argument. This point is the value obtained after standing approximately twenty-five days. At this time it became necessary for the system to remain without further addition of gas for an additional period of time extending from July 14, 1933 to September 8, 1933, or approximately eight weelis. At the end of this time the pressure had fallen to a value of 287 mm. and the x / m value increased correspondingly to a value of 216. These values lie between the “up” and “down” curves. The compound reported by Beek, whose vapor pressure was in the region of 30 mm. of mercury, had an equivalent weight of 332. This corresponds to 110 mg. of HCl per gram of hide substance. An examination of the
H I D E SUBSTANCE W I T H HYDROGEN CHLORIDE AND AMMONIA
475
present work shows that the up curve gives an z / m value of 125 at 30 mm. of mercwy, and the down curve, which probably represents a truer equilibrium value, gives an x / m value of 160 at the same pressure. Thus one must conclude that Beek’s system had not reached equilibrium. SUMMARY
Complete phase rule data, obtained by the method of Bancroft and Barnett, are given for the two-component systems hide substance-hydrogen chloride and hide substance-ammonia. An interpretation of these results indicates that adsorption complexes rather than definite chemical compounds are formed. REFERENCES (1) BANCROFT, W. D., AND BARNETT,C. E.: J. Phys. Chem. 34,449 (1930). Phase rule studies on t h e proteins. I. (2) BEEK, J.: Bur. Standards J. Research 8, 549 (1932). A contribution relative t o t h e structure of collagen. (3) TBAI,L. S., AND HSIAO, C. J.: J. Chinese Chem. SOC.2, 87-98 (1934); Chem. Abstracts 28, 6043 (1934); Chem. Zentr. 1, 210 (1935). Adsorption of hydrogen chloride by hide powder.
