T H E COMBIXATION OF GELATIS WITH ACIDS AND BASES'** LEO FRIEDMAN, KARL KLEMM, A N D FRANK K. THOMPSOX Department of Chemzstry, Oregon State College, Coruallis, Oregon Recezved August 7, 1950
The literature on the acid- and base-binding capacity of gelatin contains many values reported by different investigators. Most of these values have been obtained by a study of the combination of gelatin with hydrochloric acid and sodium hydroxide, and they have been accepted by many workers as general values applicable to any acid or base. It was, therefore, thought desirable by the authors that a study of the combination of gelatin with other acids and bases be made in order to determine whether one can correctly accept the combining weights of gelatin with hydrochloric acid and with sodium hydroxide as its equivalent weights as a base and an acid, respectively. Several values for the combining capacity of gelatin with acids and bases as obtained by different investigators have been listed in table 1. I t is to be noted that all work was done with sodium hydroxide and hydrochloric acid except in two cases: namely, the value obtained by Hitchcock (11) for the combination of gelatin with su1fu;:c acid from conductivity studies, and the value obtained by Chapman, Greenberg, and Schmidt ( 5 ) for the combination of gelatin with dyes, I t should be further mentioned that much of the difference found in the values listed results from differences in methods of calculation. THE ACID-BIh'DING
CAPACITY O F GELATIN FROM VISCOSITY STUDIES
In 1929, Bacon (2) reported a value of 1090 for the combining weight of gelatin with hydrochloric acid. This was obtained by studying the viscosity of gelatin-hydrochloric acid solutions to determine the weight ratio of acid to gelatin a t the maximum viscosity. The value is in excellent agreement with those obtained by electrometric methods. Bacon used three different concentrations of gelatin with the same result in each case. 1 Presented a t the Sixteenth Colloid Symposium, held a t Stanford University, California, July 6-8, 1939. 2 Published with the approval of the Monographs Publications Committee, Oregon State College, as Research Paper No. 28, School of Science, Department of Chemistry. 1133
1134
L. FRIEDMAN, K. KLEMM: AND F. K. THOMPSON
COMBININ0 WEIGHT
TABLE 1 Acid- and base-binding capacity of gelatin
I
1 1
-OD
DATn
INVgTIQATOB
Acid-binding capacity
150 130 70 119 300 113 92 89 84 lo4
665 770 1430 840 333 885 1090 1120 1160 1160 1180 960
Electrometric titration Electrometric titration Indicator titration pH from catalysis Electrometric titration Electrometric titration Electrometric titration Electrometric titration Conductivity Conductivity (Hos04) Electrometric titration Combination with dyes
92
1090
92
300
1090 1470 332
96 96
1040 1040
Diffusion potential Electrometric titration Conductivity Viscosity Electrometric titration Adaorption of dry hydrogen chloride by dry gelatin Electrometric titration Electrometric titration
:(
E5 68
Manabe and Matula (16) Procter and Wilson (18) Bracewell (4) Wintgen and Kruger (21) Lloyd and Mays (15) Wintgen and Vogel (22) Hitchcock (9) Hitchcock (10)
1913 1916 1919 1921 1922 1922 1922 1923
1923 Hitchcock (11) 1924 Atkin and Douglas (1) 1927 Chapman, Greenberg, and Sohmidt (5) 1927 Ferguaon and Bacon (7) 1929 Hitchcock (12) 1929 Bacon (2) 1931 Prideaux (17) 1931 Belden (3) 1931 Hitchcock (13) 1932 Hitchcock (14)
Base-binding capacity
130 57 61 90 73
770 1750 1840 1110 1370
Electrometric Electrometric Electrometric Electrometric Electrometric
titration titration titration titration titration
Procter and Wilson (18) Cohn (6) Prideaux (17) Hitchcock (13) Ferguson and Schluchter (8)
1916 1925 1931 1931 1932
Acid-binding capacity of gelatin jrom viscosity studies
I
I HCl.. ...... . . . . . . . HCIO4.. . . . . . . . . . . . H&O4. . , . . . . . . . . . . HiP04. . . . . . . . . . . . . HCSH~OI. ...... ...
3.25 3.13 2.25 3.25 3.19
WEIQHTBATlO
0.0360 0.1010 0.0630 0.1400 4.588
I
ACID-BINDINGCAPAcrTT
99 100.5 10s 143 7700
1010 995 926 700 13
1135
COMBINATION OF GELATIN WITH ACIDS AND BASES
It was reasoned that the viscosity change was largely an electroviscous effect and, therefore, the maximum viscosity should coincide with the maximum salt formation or the maximum amount of acid bound. Since, in the case of gelatin treated with hydrochloric acid, the viscosity maximum yields a value for the combining weight of gelatin which is in good agreement with those obtained by electrometric methods, similar viscosity studies of the combination of gelatin with perchloric, sulfuric, phosphoric, and acetic acids, as well as with hydrochloric acid, have been carried out. Solutions were made up to contain 0.60oO g. of airdry (0.5241 g. of bonedry) Eastman electrodialyzed gelatin and varying amounts of the acids per 100 ml. The viscosities of these solutions were determined at 4OoC., using an Ostwald type viscometer. In each case the combining capacity for the particular acid has been calculated from the viscosity maximum. The results are given in table 2. TABLE 3 Bose-binding capacity of gelatin from viscosity studies I
I
1
NaOH.. . . . . . . . . . . . KOH . . . . . . . . . . . . . . "'OH ...........
I
I
-O-
2.89
4.28' 2.777
* 0.987 g. of gelatin per 100 ml. t 0.473 g. of gelatin per 100 ml.
I
A:
-
0.0500 0.0520 0.1621
I
I
of.;
125
1
800 216 1080
It is to be observed that the value obtained for the combination of gelatin with hydrochloric acid is in fair agreement with those determined electrometrically, but the values obtained for the other acids show definitely that this combining capacity is specific for hydrochloric acid. Although the values obtained with the other strong acids are quite close to that for hydrochloric, those obtained for phosphoric and acetic acids are so far m e r e n t that the mechanism in these cases must be different from the mere binding of the hydrogen ion, as has been assumed to be the case for hydrochloric acid. THE BASE-BINDING CAPACITY OF GELATIN FROM VISCOSITY STUDIEIS
Viscosity studies, similar to those carried out with the acids, have been made on gelatin solutions containing sodium, potassium, and ammonium hydroxides. The results are given in table 3. Although the value obtained for the combination of gelatin with sodium hydroxide is not in good
1136
L. FRIEDMAN, K . KLEMM AND F . K . THOMPSON
agreement with the values listed in table 1, if the weight ratio a t maximum viscosity is any memure of the base-binding capacity of gelatin it is quite e-Tident that gelatin binds distinctly different amounts of the three bases studied. As was the case with the acids studied, much larger amounts of the weak base were bound. THE ACID-BINDING CAPACITY OF GELATIN FROM ELECTROMETRIC TITRATION STUDIES
As a further check on the possible variance of the acid-binding capacity of gelatin for different acids, electrometric titrations have been run on solutions of gelatin with hydrochloric, perchloric, sulfuric, and phosphoric acids. A glass electrode, calibrated against standard phthalate buffer solutions, was used to determine the pH values of the solutions. In each TABLE 4 Acid-binding capacity of gelatin f r o m electrometric studies
1
1
ACID
HC1
EXPERIMENT NO.
EQUIVALENTS PER GRAM OF Q E U T I N
x
COMBIMNQ WEIQEC
1 2
94
104
960
96 95 100
1000
137
730
::i](iiv.
= 1030)
case the pH was carried to values between 1.5 and 2. All determinations were made at 35OC.,and the solutions were weighed at the time of measurement so that correction could be made for changes in concentration due to evaporation of water. Eastman electrodialyzed gelatin was used in all the experiments. The concentration of gelatin was kept at approximately 5 per cent in order to minimize the error at lo^ pH values. Calculations of acid bound were made following the procedure outlined by Hitchcock (14). Table 4 gives the results obtained in these experiments. Activity coefficients used in making the calculations were obtained as follows: for hydrochloric acid, from the data of Scatchard (20); for perchloric acid, the same values used for hydrochloric acid ; for sulfuric acid, values from Randall and Scott (19); for phosphoric acid, values obtained b$ the authors by determining the pH of phosphoric acid solutions with the same apparatus used in the gelatin work.
COMBINATION O F GELATIN WITH ACIDS AND BASES
1137
A comparison of the combining weight values given in tables 2 and 4 shows about as good an agreement as can be expected between such different methods of determination. I t is, however, evident that the combination of gelatin witli acids and bases is not simply a combination of the gelatin with the hydrogen or hydroxyl ions. Until more is known concerning the effect of gelatin upon the activity coefficients of the hydrogen and hydroxyl ions, the possible hydrolysis of the gelatin in strongly acid and alkaline solution, and about the changes in aggregation produced by high and low pH values, it does not seem possible to interpret these results further. REFERENCES (1) ATKINAND DOUGLAS: J. Am. Leather Chem. Assoc. 19, 528 (1924).
BACON:J. Phys. Chem. 33, 1843 (1929). BELDEN:J. Phys. Chem. 35, 2164 (1931). BRACEWELL: J. Am. Chem. SOC.41, 1511 (1919). CHAPMAN, GREENBERG, A N D SCHMIDT: J. Biol. Chem. 73, 707 (1927). COHN:Physiol. Rev. 5, 349 (1925). FERQUSON AND BACON: J. Am. Chem. SOC.49, 1921 (1927). (8) FERGUSON AND SCHLUCHTER: J. Gen. Physiol. 15, 463 (1932). J. Gen. Physiol. 4, 733 (1922). (9) HITCHCOCK: (10) HITCHCOCK: J. Gen. Physiol. 6, 95 (1923). (11) HITCHCOCK: J. Gen. Physiol. 6, 201 (1923). J. Gen. Physiol. 12, 495 (1929). (12) HITCHCOCK: J. Gen. Physiol. 15, 125 (1931). (13) HITCHCOCK: (11) HITCHCOCK: J. Gen. Physiol. 16, 357 (1932). A N D MAYS:Proc. Roy. SOC.(London) B93, 69 (1922). (15) LLOYD (16) MANABEAND MATULA:Biochem. Z. 52, 369 (1913). Proc. Roy. SOC. (London) B108, 224 (1931). (17) PRIDEAUX: (18) PROCTER AND WILSON:Trans. Chem. SOC.109, 307 (1916). AND SCOTT:J. Am. Chem. SOC.49, 647 (1927). (19) RANDALL J. Am. Chem. SOC. 47, 696 (1925). (20) SCATCHARD: (21) WINTGENA N D KRUGER:Kolloid-Z. 28, 81 (1921). (22) WINTGENA N D VOGEL:Kolloid-Z. 30, 45 (1922). (2) (3) (4) (5) (6) (7)
