INDUSTRIAL A N D ENGINEERING CHEMISTRY
928
There are many places where the mill can be used in the chemical industry provided the cost-of driving it is not excessive for the product. It has two main disadvantages a t present-first, the power required to operateit, and, second, its small capacity. It is quite possible that its capacity and efficiency may be increased to the point where the cost per unit of material obtained will put the mill on a plane
Vol. 15, No. 9
where it can be used commercially. There is a great deal of development work to be done, but this will probably be done best by the different industries themselves, as they are better acquainted with their own problems than any outside firm could possibly be. It is up to the individual firm to decide whether or not it will pay to develop it to meet the conditions under which it will have to operate,
Concentration Factor in t h e Combination of Tannin with Hide Substance' By Arthur W. Thomas and Margaret W. Kelly COLUMBIA UNIVERSITY, NEWYORK, N. Y .
T
HE effect of time of reaction and concentration of the vegetable tannins gambier and quebracho upon the combination of tannin with hide substance was shown in an earlier paper.2 The results given herein continue this investigation, including extracts of barks of hemlock, larch, oak, and wattle. The method used was identical with that described in the earlier paper2 except that portions of defatted hide powder (sifted to remove all particles finer than 100 mesh) equal to 5 grams of anhydrous substance were used, and the time of contact was set at 24 hours. The hydrogen-ion concentrations of all solutions were adjusted electrometrically to pH = 5 , using sodium hydroxide. For economy of space all data incidental to the analyses by the original Wilson and Kern method3 are omitted. The fixation of tannin has been calculated to grams tannin combined per 100 grams hide protein, and plotted against concentration of the vegetable tanning extracts in terms of grams total solids per liter of solution, as shown in the curves. The tannin content of each extract was determined by the modified Wilson and Kern method,4 and for the purpose of studying the fixation as a function of the concentration of tannin, the following data are submitted: EXTRACT Oak Larch Hemlock Wattle
Tannin in Total Solids Per cent 20.6 20.6 27.2 30.4
The sharp maximum previously shown by quebracho2 is found here with each extract studied. The decrease in fixation following increased concentration of tanning solution was tentatively explained in the earlier paper as due to heavy surface tannage, thus impeding the diffusion of uncombined tannin into the interior of the hide-powder particles. I n addition to this it should be noted that decreased rate of fixation with increasing concentration of tanning solution is predicted by the Procter-Wilson theory. The rate of fixation is at a maximum where the positive charge of the collagen and the negative charge of the tannin particles are at their maximum. Now increase of electrolyte concentration resulting from increased concentration of the tanning extract will reduce the potential of the collagen. Likewise, the negative potential difference of the tannin particles decreases with increase in concentration, as experimentally 1 Presented before the Division of Leather Chemistry at the 64th Meeting of the American Chemical Society, Pittsburgh, Pa., September 4i;to 8, 1922. Contribution No. 414 from the Chemical Laboratories, Columbia University. 2 THISJOURNAL, 14, 292 (1922). 8 I b i d . , 12, 465 (1920). 4 I b t d . , 13, 772 (1921).
demonstrated by Thomas and Foster5 in the case of quebracho. Furthermore, the decreasing degree of dispersion of the tannin particles causes a decrease in the rate of diffusion of the same. Since in all cases the reaction of the solutions was adjusted to pH = 5 , the charge of the collagen would be a t its minimum, and consequently the downward slope of the curves could be ascribed almost entirely to the changes in potential difference and degree of dispersion of the tannin particles.
25
50
75
lW
,
125
I
I50
175
200
225
23
Grams Total Solids per Lifero f Orgtnal Tantr?gSoJuhor?
The "gelatin-salt" test for detection of tannin was applied to all filtrates in the fixation experiments plotted above, and showed complete removal of tannin by the hide substance up to the maximum points in all curves, and where more tannin was present than could be fixed by the hide, the curves rapidly sloped downward. In other words, the maximum points were obtained with amounts of tannin ia the solutions which corresponded to the saturation point of the hide substance for the particular tannin, and this was in the range of 10 to 17 grams of tannin per liter of solution. The order of magnitude of the maxima is in the order of the astringency of the tannins. It will be seen from inspection of the percentages of tannin in the extracts used that the order of relative proportion of tannin to non-tan is wattle>hemlock>larch = oak, while the order of the magnitudes of maximum fixation is wattle >hemlock>larch >oak. The upward trend of the curves beginning at the concentration of 140 grams total solids per liter seems to be due to the accumulation of insolubles in these very concentrated solutions, which are not removed completely by the washing of the tanned samples with cold water. The authors express their indebtedness t o A. F. Gallun & Sons Co., for grants in aid of this investigation. THIS J O U R N 4 L . 14, 191 (1922).
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