Vol. 15, No. 12
INDUSTRIAL A N D ENGINEERING CHEMIXTRY
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Unger and Jiger, “ u b e r Pentosanbestimmung,” Be?., 86, 1222 (1903). Van gkenstein and Blanksma, “ u b e r das w-Oxymethylfurfurol als Ursache einiger Farbreaktionen der Hexosen,” Ber., 43, 2355 (1910). Van Haarst and Olivier, “Determination of Pentosans,” Chem. Weekblad, 11, 918 (1914);abstracted in C. A . , 10, 28 (1916). Vignon, “Osazones Oxycellulosiques,” Bull. SOC. chim., 21, 600 (1899). Volckel, “Fortgestzte Untersuchungen fiber die Producte der trockenen Destillation organischer Rorper,” Ann., 86, 59 (1853). Votocek, “Condensation des Methylfurols mit Phloroglucin,” Ber., 80, 1195 (1897).
Votocek and Potmesil, “Uber die Quantitative Bestimmung des Phloroglucins und des Resorcins mittels Furfurol,” Ber., 49,1185 (1916). Walton, “The Preparation of Rhamnose,” J . A m . Chem. Soc., 43, 127
(1921).
Wedekind, “Heterocyklische Verbindungen,” 1901, p 26. Veit und Comp., Leipzig. Welbel and Zeisel, “Uber die Condensation von Furfurol mit Phloroglucin und eine auf diese gegrtindete Methode der quantitativen Bestimmung des Furfurols aus Pentosen und Pentosanen,” Monatsch., 16, 283 (1895). Wenzel and Lazar, ‘‘uber die Phloroglucinreaktion der Pentosen,” Monatsch., 84, 1942 (1913). Wheeler and Tollens, “Uber die Xylose oder den Holzzucker, eine zweite Pentaglycose,” Ann., 264, 304 (1889). Wheeler and Tollens, “Untersuchungen tiber das Holzgummi,” Ann., 264, 320 (1889).
Wichter and Tollens, “Pentosans of Certain Wood Fungi,” J . Landzu., 68, 238 (1911); abstracted in Analyst, 86, 162 (1911).
Widtsoe and Tollens, “ u b e r die Reactionen des Methylfurfurols und der Methylpentosane,” Ber., 33, 143 (1900).
T h e Influence of Neutral Salts upon t h e Fixation of Tannin by Hide Substance1’* By Arthur W. Thomas and Margaret W. Kelly COLUMBIAUNIVERSITY,NEWYORK,N. Y.
A
NY agent which will decrease the swelling of collagen, or decrease its potential difference against the so’ lution in contact with it, should inhibit the rate of
fixation of tannin. Neutral salts should accomplish both effects, as predicted by the Donnan equilibrium,s shown by Procter and WilsonJ4and recently definitely settled by Loeb.6 On the acid side of the isoelectric point of the protein the anion only of the salt is concerned in this depressing effect, divalent anions being more effective than monovalent anions a t identical hydrogen-ion concentrations. On the alkaline side of the isoelectric point cations only are of significance, again those of higher valency showing the greater depressing effect a t the same concentrations of hydrogen ion. This “salt effect” on the protein is complicated, in the case of vegetable tanning, by additional action of the salt upon the tannin solution. It has been shown by Wilson and Gallune and by Thomas and Foster? that neutral salts decrease or retard the fixation of chrome by hide substance, while Herzog and Adler8 claim that neutral salts either slightly promote the adsorption of phenol by hide substance or have no effect a t all. I n view of reported differences in behavior in the adsorption of these various tanning agents by collagen in the presence of neutral salts, it was decided to extend the study of tannin fixation by collagen to include the effect of added neutral salts in the tanning liquors. EXPERIMENTAL Sodium chloride and sodium sulfate, furnishing examples of monovalent and divalent anions, were selected for these experiments, and their effects a t p H values of 2.0, 5.0, and 8.0 were studied in both hemlock bark and in gambier solutions. The tannin solutions were prepared and clarified as described in a previous paper.e It was also desired to include a study 1 Presented before t h e Division of Leather Chemistry a t the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4 t o
8, 1922. 2 Contribution No. 419 from the Chemical Laboratories, Columbia University. Taken from a part of t h e dissertation submitted b y Miss Kelly in partial fulfilment of t h e requirements for the degree of doctor of philosophy, Faculty of Pure Science, Columbia University, 1923. SZ. Elektrochern., 17, 572 (1911). 4 J . Chem. SOG.(London), 109, 307, 1327 (1916). 6 “Proteins and the Theory of Colloidal Behavior,” McGraw-Hill Co , New York, 1922. J . Gen. Physiol., 1918-22 (about 50 papers published). 8 J . A m . Leather Chem. Assoc., 16, 273 (1920). THIS JOURNAL,14, 132 (1922). 8 K o l l o i d - Z . , 2, Suppl. Heft 2, I11 (1919). 9 Thomas and Kelly, THISJOURNAL, 16, 1148 (1923).
of tannin fixation in the presence of barium and magnesium chlorides in order to compare the effects of these divalent cations with that produced by the monovalent sodium cation. However, difficulties arose on the alkaline side of p H = 5 owing to the formation of the insoluble alkaline earth tannates, and consequently the study of the comparative effect of cations of differentvalence on the alkaline side of the isoelectric point of collagen was abandoned. The results obtained with these salts on the acid side of the isoelectric point were very similar to those obtained with sodium chloride, as was to be expected. In the case of sodium chloride and sodium sulfate 100-cc. portions of the tanning solution (concentration of 40 grams total solids per liter, and previously adjusted to the desired p H by addition of 0.5 M hydrochloric acid or 0.5 M sodium hydroxide) were added to bottles containing 2.000-gram portions (absolutely dry basis) of hide powder, previously defatted by chloroform, and the required weight of dry salt. The bottles were rotated a t room temperature for 24 hours; the samples were then filtered in Wilson and Kern extractors, washed with water until a negative test was shown by the washings for the salt used as well as for tannins and non-tans, dried, and the increase in weight was computed as tannin fixed. Since a t certain concentration of hydrogen ion the salts precipitate “insolubles” which would count as tannin fixed, blanks were always run in the absence of hide powder to determine the extent of the formation of such “insolubles” and, where found, the amount of tannin fixed was corrected accordingly. RESULTS The results are shown in the tabulation and figure. INFLUENCE OF SODIUM CHLORIDEAND SODIUM SULFATE UPON TANNIN FIXATION^ p H of Molar ConcenOriginal tration of Added Y G a m b i e r b - Liquor Salt Present NaCl NaaSOi 21 0 0.5 47 loss 56 loss 2.0 1.0 62 loss 82 loss 2.0 1.5 90 loss 2.0 2.0 94 loss
. ...
5.0 5.0 5.0 5.0
0.5 1.0 1.5 2.0
8.0
0.5 1.0 1.5 2.0
8.0 8.0
. . ..
b
... .
68 loss
4 gain 5 gain
17 loss 50 loss 75 loss
27 gain
32 loss 63 loss
58 loss 79 loss 92 loss
9 loss 25 loss
.. . . 4 loss .. ..
.... . . ..
8.0 86 loss Compared with fixation in absence of salt. Figures are in per cent.
a
-Hemlock NaCl 58 loss 66 loss
Barkbi‘?a&o4 70 loss 86 loss
.... .. . ,
8 loss .. .. .. .. 23 loss 54 loss No change . . . .
.... 66 loss
14 loss 44 loss 70 loss
... .
IhTDUXTRIRL A N D ENGINEERING CHEMISTRY
December, 1923
It is to be noted from the tabulation that a t pH of 2 and 8 both salts inhibit the fixation of tannin, this effect increasing with increasing concentration of the salt, and for. the same molar concentration of salt the inhibition by sodium sulfate is always more pronounced than that caused by sodium chloride, just as Thomas and Fosterlo found in the case of chrome tanning. At p H = 5 , the isoelectric point of collagen, the effect of the added salts is much less pronounced, and for the lower concentrations sodium chloride appears to increase the fixation of tannins. 018,
I
1
I
I
I
I
I
I
I*
0.7
.k
0. /
A ; Mo/arify ,L ; o f
% / Added Salt 0
I
/ M 2
FIG.1
c
Sirice Thomas and Baldwinll hare found that sodium chloride increases the concentration of hydrogen ion (hydrogen-ion activity) of acid solutions, while sodium sulfate lowers it, measurements of the pH of the tanning liquors, after addition of the salts, were attempted in order to determine whether changes in hydrogen-ion concentration had been a determining factor in effecting the changes observed in tannin fixation. The results showed that at p H values of 2 and 5 sodium chloride was without appreciable effect upon the p H of the tanning solution, while sodium sulfate caused a slight decrease in acidity. At pH = 8 the measuremeni s mere most unsatisfactory, owing to “poisoning” of the electrode, Apparently, therefore, the effect of these salts in changing the hydrogen-ion concentration of the tanning liquors was not of any considerable importance, and the explanation for the observed changes in tannin fixation must be sought in the effects, pointed out above, of salts upon collagen and tanning solution. EI‘FECT UPON CoLLAGEN-It would be expected that on the acid side of the isoelectric point sulfates would have a greater depressing effect than chlorides upon swelling and potential difference of collagen, and consequently fixation should be inhibited more by the sulfate than by the chloride, which is actually the case as will be seen upon examination of the figures a t pH = 2. At p H = 8 the differences between THISJ O U R N A G , 14, 132 (1922). 1 1 J . A m . Chem. Soc., 41, 1981 (1919). 10
1263
sodium chloride and sodium sulfate are not so marked. On this, the alkaline side of the isoelectric point, the anions of the salt exert the same influence regardless of valence. Here the cations only are of significance and the greater inhibitory effect shown by sodium sulfate is due to ,the fact that equimolar solutions of the two salts are being compared. Since there are twice as many available sodium ions in a molar solution of the sulfate as in the chloride, compared on the molar basis, sodium sulfate will lower the swelling and the potential difference of collagen to a greater extent than sodium chloride, as the data show. In the table it is seen that 0.5 M-sodium sulfate shows about the same inhibition as 1.0 M sodium chloride. Such agreement is not expected to be rigid and general throughout, since the effects of the salts upon the tannins must be considered. Furthermore, ionization of the salts is by no means complete a t such concentrations, nor are the salts ionized to the same extent. At the isoelectric point the effects of the salts upon collagen should not be marked, according to the Donnan theory, since a t this point collagen is already in the condition of minimum swelling and minimum potential difference. INFLL-ENCE ON THE TAE\“IP\’G SOLUTIONS-(~) Aggregation of the tannin particles, which will result in a lower diffusibility thereof, thus inhibiting fixation, but which may proceed to the point at which the tannins are precipitated (“salted out”) from solution, whereby the concentration of tannin in solution is decreased; ( 2 ) hydration of the added salts, by which a virtual increase in tannin concentration is effected. The net effect of these two factors upon tannin fixation will depend upon the original concentration of tanning solution as well as upon the amount by which this concentration is increased or decreased. At a concentration of 40 grams of total solids per liter, which was used in these experiments, reference to the concentration curves in a separate paper9 for the extracts in question shows that any increase in concentration of the extract a t pH = 5 will effect a decrease of fixationof tannin, while decrease in concentration from 40 to approximately 20 grams of total solids per liter will cause an increase in tannin fixed, below which concentration the amount of tannin fixed will decrease regularly toward zero. As will be seen by reference to the tables, this decrease in concentration of tannin by sodium chloride a t p H = 5 is slight enough a t the lower concentrations of the salt to effect the increase in fixation which would be expected, while for the higher concentrations of the salt the salting out effect has lowered the concentration of tannin sufficiently to effect a decrease in tannin fixation. Hydration of the salt and lowered diffusibility resulting from aggregation of the tannin particles will augment this latter factor. On the other hand, the experimental results a t p H = 5 show that sodium sulfate produces a decrease in fixation a t all concentrations, thus differing from sodium chloride. Experiments upon the comparative effects of these two salts in salting out the tannins from tan liquors showed that the sulfate is more effective than t h e chloride. Consequently, it may be concluded that sodium sulfate decreases the degree of dispersion of tannin particles and effects subsequent reduction of concentration of tannins in solution more powerfully than sodium chloride, and only the later effect of this decreased Concentration, augmented by increased aggregation of the particles and by the hydration factor, is shown in the experimental results obtained. ACKNOWLEDGMENT The writers wish to express their indebtedness to A. F. Gallun & Sons Co., Milwaukee, Wis.. for grants in aid of this investigation.
