INDUSTRIAL A N D ENGINEERING CHEMIXTRY
July, 1923
positions of propeller and heating coils are such that the heated oil is thoroughly mixed with the cooler portions. This arrangement insures uniformity of temperature through‘out the bath. I n this figure the conveyor type of stirrer in the oil tube is also shown. The thermometer is held in a hollow rotating shaft by means of a perforated cork stopper resting on the upper end of the shaft. This makes it possible to read the thermometer by merely grasping its upper end. Figs. 8 to 11, inclusive, show the general views of the bath and of the controlling mechanism.
CONCLUSION As a result of this investigation the authors conclude that it is possible to hold the temperatures quite within the limits specified by the A. S. T. M., but that properly designed apparatus is required to do so. They believe that the requirement of holding the bath constant “at such a temperature as will maintain the desired temperature in the standard oil tube” is a weak point in the specifications. On account of
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the great time lag between a change in bath temperature and the effect of such a change upon the oil-tube thermometer, combined with the desire of the operator to lose no time in making the test, it seems likely that in the ordinary procedure there would be considerable lack of agreement between different laboratories running Saybolt viscosity tests on samples of oil from the same barrel. Furthermore, unless the oil in the tube is adequately stirred, the oil-tube thermometer might indicate almost any value within limits wider apart than the A. 5.T. M. tolerance. With an apparatus of the kind described, assuming the oil in the tube to be well stirred, the bath temperature can be adjusted until the thermometer in the oil tube shows the desired temperature, and held a t this point indefinitely because of the effective control. Although improvement may be possible in the procedure of testing beyond this point, the writers have confined themselves in this work to devise means for meeting the existing requirements.4 4 Patent application has been filed covering the apparatus herein described and its possible applications.
T h e Electrical Charge of Vegetable Tannin Particles‘ .
By Arthur W. Thomas and Stuart B. Foster COLUMBIA UNIVERSITY, New YORK,N.Y.
N A PREVIOUS publication2 the relation between electrical charge and astringency of vegetable tanning materials was demonstrated, and it was shown that the negative charge of astringent quebracho could be reduced to zero by the addition of hydrochloric acid. The experiments herein described were undertaken to determine whether the charge could be reversed in signi. e., whether vegetable tannins are amphoteric, and, if so, a t what hydrogen-ion concentration the reversal in sign of charge takes place. Such data are also needed since Ricevuto3 has made the quite incredible statement that vegetable tannins are cathodic in migration in alkaline solutions and anodic in acid solutions. He was probably led astray by the fact that his electrodes dipped directly into the tanning solutions and the direction of migration of tannin was interpreted through bulk of precipitate a t each electrode upon addition of gelatin, Since Thomas and Frieden4have found that gelatintannin precipitation depends upon the hydrogen-ion concentration, this may account for Ricevuto’s strange findings. Furthermore, a series of papers by Grasser5 on electroosmosis of tan liquors reports variable and somewhat confusing results. Grasser did not determine or control the CH+of his solutions, and as an unfortunate consequence his data are .of very slight practical or theoretical value. APPARATUS The U-tube electrophoresis method was used to determine the direction of migration of the tannin particles a t different hydrogen-ion concentrations.
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The U-tube had limbs about 30 cm. long. The bend of the tube was set off from the limbs by stopcocks so placed t h a t the two 1 Presented before t h e Division of Leather Chemistry a t t h e 64th Meeti n g of t h e American Chemical Society, Pittsburgh, Pa., September 4 t o 8. 1922. Contribution No. 410 from the Chemical Laboratories of Columbia University. 2
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THISJOURNAL, 14 (1922), 191. Kolloid-2.. 3 (19081, 114. Unpublished. Collegium, 1920, 17,49,277, 332.
limbs above them were of equal length The diametk’r of the limbs was 1.3 cm. and the bore in the stopcocks was nearly the same width. The electrodes were supported in 30-cc. distilling flasks, t h e delivery tubes of which had been bent down a t right angles and passed through rubber stoppers into the limbs of the U-tube. Small tubes had been blown into the horizontal arms of the two right-angle bends, and were connected by means of rubber tubing and a small stopcock, thus making a salt bridge across the two electrodes.6 The cathode was a copper wire immersed in a saturated copper sulfate solution, and the anode was a platinum wire in saturated sodium chloride. The source of current was the 120-volt house line, with an electric lamp in series. METHOD
The extract solution, .previously adjusted to the desired hydrogen-ion concentration by means of the hydrogen electrode, was poured into the U-tube, filling the bend and the bores of the stopcocks. Air bubbles were dislodged, the stopcocks closed, and the limbs, after being rinsed with distilled water, were filled to the brim with a citrate buffer mixture of the same CH+as the extract in the bend. The flasks containing the electrodes were attached to the U-tube, forcing sufficient of the buffer solution up the delivery tubes and into the flask to complete the conducting circuit. Levels were adjusted through the salt bridge, which was then closed by means of the stopcock. The stopcocks in the limbs were opened carefully and the current was passed until a definite movement of the boundaries was noted. Considerable experimentation was necessary before a technic was devised which would give consistent results. The first method involved making water solutions of the extracts of such concentration that 100 cc. contained 4 g. of dry solids. It was hoped, of course, that such solutions would really electrophorese-i. e., that the whole column would move toward either the anode or the cathode, according t o the C E + of the extract. But of the six extracts so treated, only one, wattle bark, behaved according to the expectations. Formic acid was then used instead of hydro6
Similar to apparatus described by Michaelis, B i o c h e a . Z.,16 (1909),81.
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chloric acid in adjusting the CH+,and slightly better results were obtained. The final technic, and that upon which the published reports are based, was to dissolve the extracts in citrate buffer mixture a t -log CH+= 2.0, and then adjust the solutions by means of the hydrogen electrode to the exact hydrogen-ion concentration desired. Using the buffer instead of water as the solvent exerted what was apparently a stabilizing effect, and eliminated or delayed the secondary actions, such as diffusion of the boundaries and change of reaction of the extracts due to electrolysis, which behavior had nullified previous experiments. RESULTS The table below gives the extracts examined, a t the critical hydrogen-ion concentrations, with the corresponding direction of migration of the particles. The extracts mere electrophoresed a t other CH+, but only the important data are submitted. MATERIAL Oak Oak Hemlock Hemlock Hemlock Sumac Sumac Sumac Quebracho Quebracho Quebracho Gambier Gambier Wattle Wattle
-LOG CH+ 2.0 2.5 2.0 2.5 3.0 2.0 2.5 3.0 2.p 2.5 3.0 2.0 2.5 2.0 2.5
DIRECTION OF MIGRATION Cathodic Anodic Cathodic Anodic Anodic Cathodic Anodic Anodk Cathodic (?) No movement No movement Cathodic Anodic Cathodic Anodic
Quebracho was precipitated by the buffer, hence only the clear supernqtant liquid could be used. This fact may account for the inability to obtain positive results. In all cases the upward movement was slight and frequently was not apparent until the current had been passing from 2 to 3 hrs., but since, with the exceptions noted, there was a corresponding downward movement in the opposite side, the results were taken as conclusive. The method was not susceptible of manipulation sufficiently delicate to permit a determination of the isoelectric points-that is, those hydrogen-ion concentrations where there was movement neither to the anode nor the cathode. However, each of the seven extracts examined (with the possible exception of quebracho) contained positively charged particles a t and below -log CEI+= 2.0, and negatively charged particles a t and above -log CH+= 2.5, the isoelectric point or region being between C H += 10-2.0and 10-2.5. It is stated above that formic acid instead of hydrochloric was employed in certain instances to avoid precipitation of the tannins a t high acidities. This is based upon experience of the authors previously published.2 Since in the earlier work they made no measurements of CE+, and since they are firmly convinced that no data on the properties o i vegetable tannin solutions are of complete ultility unless so controlled, data are submitted herewith relative to the degree of precipitation as a function of the Ck+ of acid solutions, and also showing that the nature of the anion of the acid likewise plays a very important role. TECHNIC Aqueous dispersions or solutions of the extracts were prepared in the manner described elsewhere.2 Fifty cubic centimeters of each stock solution were diluted to 100 cc. This dilution was divided into two 50-cc. portions, whose C H + was then determined with the hydrogen electrode attached to a n automatic recorder. The two solutions were adjusted to different CH+on both the acid and alkaline side of the original CH+,and the number of cubic centimetels of standard hydrochloric acid or sodium hydroxide solutions required for each point was recorded.
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All the extracts did not precipitate with each acid, and three, sumac, hemlock, and wattle bark, did not give a precipitate with either of the three acids up to -log CE+= 1. When a precipitate was obtained, the amount invariably increased with increasing hydrogen-ion concentration, where hydrochloric acid or sulfuric acid was used. On the other hand, increasing concentrations of formic acid dissolved the precipitate, or the suspended particles when no precipitate had appeared previously. With decreasing hydrogen-ion concentration there was increasing solution. I n every case clear liquids were obtained a t C E + = 8.0. The hydrochloric acid precipitates were found to be soluble in strong alcohol and in 9 M lactic acid. On shaking up with water these precipitates dispersed but gradually, and settled out more or less completely in 24 hrs. I n the case of oak bark and quebracho i t was found that approximately two-thirds of the original solids present had been precipitated a t CH+= 10-l. ACKNOWLEDGVENT The authors are indebted to A. F. Gallun & Sons Co., of Milwaukee, Wis., for grants in aid of this investigation.
