A Mechanically Operated Continuous Liquid-Extraction Apparatus d
GEORGE W. PUCHER AND HUBERT BRADFORD VICKERY Connecticut Agricultural Experiment Station, New Haven, Conn.
A modified Widmark extraction apparatus is constructed from two Erlenmeyer flasks connected side by side with a short length of wide-bore tubing sealed into the sloping walls of the flasks. The apparatus is rocked through an angle of t15’ around an axis placed beneath the horizontal connecting tube. A plant extract acidified to pH 1.0 is placed in one flask and 0.5 N sodium bicarbonate in the other; ethyl
acetate is @henadded to the level of the connecting tube. As the solvent flows back and forth during oscillation, the organic acids are gradually collected in the alkali. The apparatus may be used in small sizes for quantitative analytical extractions and in larger sizes for preparation work. It can be applied equally well for the extraction of such basic substances as nicotine.
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pulley mounted on a reduction gear of the ratio 190 to 1which ta in turn driven by a 0.25-horsepower motor that turns a t 1725 r. p. m. The exact speed of rockin is controlled by the size of the pulley on the reduction gear. h i t h the authors’ a paratus, a IO-cm. (4inch) pulley gives about 2 complete c c i s of extraction per minute, which is unnecessarily slow, a n i a 12.5-cm. (5-inch) pulley gives about 2.7, which is a little too fast. The most satisfactory adjustment can easily be made by building up the diameter of a 10-cm. (4inch) ulley with rubber bands cut from the inner tube of an automobiye tire. The platform for the large extractors carries two of these side by side and is furnished with a deep-sided pan fitted with a drain that discharges through rubber tubing into a bottle to provide against accidental breakage. The flasks fit into spring clips soldered to this pan, so that they are held securely in position. The platform for the small extractors carries four or more, which do not need to be mounted exactly over the axis of rotation.
OR the quantitative removal of such substances as organic acids or nicotine from extracts of tobacco leaf tissues, a simple modification of the Widmark extraction apparatus (8) has proved t o be exceedingly efficient and doubtless may have many other applications. The device possesses the advantage of offering no fire hazard and can be constructed in sizes suitable for the extraction of aqueous volumes of from 10 ml. to several liters at one time. The apparatus consists of two equal Erlenmeyer flasks joined closely side by side with a short straight wide-bore tube sealed horizontally into the sloping walls of the flasks somewhat more than one third of the distance up from the bottom. The pair of flasks is mounted on a platform that can be rocked through an angle of about * 15’ from the horizontal around an axis of rotation placed vertically beneath the connecting tube and a t right angles to it. One of the flasks is charged with a volume of the acidified aqueous solution to be extracted such that, when the platform is tilted to the maximum angle, there is no danger that any of it will run through the connecting tube into the second flask. The second flask is charged with a similar volume of sodium bicarbonate solution, and organic solvent is then poured in, with the platform level, until it reaches the connecting tube. The flasks are lightly stoppered and the motor that drives the oscillating platform is started; solvent flows alternately back and forth, each time carrying a small amount of organic acid extracted from the acidified solution and giving it up to the aqueous alkali, The gentle agitation, as the solvent pours from side to side, gives sufficient mixing with the aqueous fluid with little or no danger of froth formation, and ultimately transfers all of the extractable acid to the alkaline solution. The apparatus can be allowed to run without attention save for an occasional check to see if water is migrating f r ~ m one side to the other, as may happen unless the two aqueous solutions are approximately isotonic. At the end of the extraction period, the two aqueous solutions are separately withdrawn from beneath the solvent by suction through a suitable pipet into a receiving flask, a minimal amount of wash water is placed in the flasks, agitated a few times, and withdrawn, and the apparatus is ready for the extraction of a further charge without removal of the solvent.
Choice of Solvent Tests of the apparatus were made with a solution of citric acid, which has been found the most difficult t o extract of any of the common plant acids. Observations on extracts from tobacco leaf tissue showed that 10 days’ continuous operation with ether as solvent removed only 90 per cent of this acid from 3-liter samples of extract in the largest extractors, and a search was therefore made for a more efficient solvent. Data in Table I1 shorn that ethyl acetate OF EXTRACTION APPARATUS TABLE I. DIMEKGIONS
Charge of Aqueous Solution Liters 0 . 0 1 to 0 . 0 5 0 . 5 to 1 . 0 2.5 t o 3 . 0
Table I shows the dimensions of three sets of flasks that have been used successfully in this laboratory for several years. The smallest, constructed from 500-ml. widemouthed Erlenmeyer flasks, is employed for the quantitative extractions required in certain analytical methods; the larger sizes, made from ordinary Erlenmeyer flasks, are used for preparations.
Volume Diameter of Erlenof Conmeyer necting Flask Tube Liters Cm. 0.5 2 3 3.5 6
6
Vertical Distanoe from Bottom of Connecting Tube to Bottom of Flask Cm.
3 . 5 to 3 . 8 11 14
Horiiontal Distance between Flasks at Bottom Cm. 3 to 3 . 5 5 to 8 10 to 12
OF CITRICACIDWITH VARIOUS SOLVENTS TABLE 11. EXTRACTION
(Apparatus osoillated t o give 144 extractions per hour) Citric Volume of Acid Aqueous Extraction Solvent Taken Solution Time Recovery Uram M1. Hours % 40 29 34.0 0.032 Ether 40 23 33.0 0.032 Methyl amyl ketone 40 48 81.0 0.032 Amyl acetate Isopropyl acetate 0.032 40 24 90.0 Ethyl acetate 0.032 40 17 to 24 95.0toQS.O
The oscillating platform is bolted with suitable brackets on the beam of a discarded two-cylinder Geryk vacuum ump from which the pump mechanism had been removed. T i e flywheel (44.5 om., 17.8 inches in diameter) is driven by a belt from 8 656
DECEMBER 15, 1939
ANALYTICAL EDITION
is the most advantageous of those tried and may be relied upon to bring about nearly quantitative extraction in about 24 hours. Malic and oxalic acids, as well as the small proportion of unknown acids in tobacco leaf extracts, are somewhat more readily extracted. I n preparation for extraction, the aqueous solution is brought to pH 1.0 by the addition of sufficient sulfuric acid. The alkali solution usually employed is 0.5 N sodium bicarbonate. Ethyl acetate possesses the disadvantage of undergoing slight hydrolysis with a corresponding accumulation of acetate in the alkaline extract. Accordingly extracts prepared in this way cannot be used for organic acid titrations (1). The acidity to which the solution on the acid side is adjusted must be carefully controlled. Oxalic acid is incompletely extracted unless the reaction is close to pH 1.0, but a high acidity is to be avoided because of the danger of hydrolyzing excessive amounts of ethyl acetate. Nitric acid, if present in the tissue extract, is likewise quantitatively extracted along with the organic acids, when the reaction is adjusted to pR 1.0, but extraction is incom-
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plete a t pH 1.5 in 22 hours on samples in the small apparatus. Extraction by this technique therefore provides a convenient method for removing nitric acid from a plant extract if subsequent investigation of organic nitrogenous substances is contemplated. The large extractors have also been of service in the isolation of nicotine. Benzene or ether may be used as solvent, the tissue extract is made strongly alkaline to phenolphthalein, and the nicotine is absorbed in 0.5 N sulfuric acid. In one preparation, 5 liters of extract were treated simultaneously in two large extractors. Of the 200 grams of nicotine present, 95 per cent had been .removed in 24 hours at the usual oscillation rate of 144 extractions per hour. The application of the small extractors to the quantitative removal of pyrrolidone carboxylic acid forms one step in a new method to determine glutamine, to be described in another paper.
Literature Cited (1) Pucher, G . W., Vickery, H. B., and Wakeman, A. J., IND. ENQ. CHEM., Anal. Ed., 6,140 (1934). (2) Widmark, E. M. P., Skand. Arch. Physiol., 48,61 (1926).
Lead-Sodium Alloy as a Drying Agent HAROLD SOROOS Ethyl Gasoline Corporation, Detroit, Mich.
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EAD-sodium alloy has been used in this laboratory for several years in place of metallic sodium for drying inflammable liquids such as ether because it is less hazardous to handle. Fires occasionally occur in the handling of fresh
metallic sodium and in the disposal of incompletely reacted metal in contact with inflammable liquids or vapors. Leadsodium alloy reacts only slowly with air or water, yet dries ether as completely as sodium wire. Furthermore, the residues of ether or other liquids still containing some active alloy can safely be destroyed by the addition of water, as the reaction never reaches the violence observed in the case of the metal itself. The alloy is very brittle and can, therefore, be prepared in any desired state of subdivision much more conveniently than in the case of sodium wire. The reactivity of sodium in this form also suggests that the alloy might well be considered as a substitute for pure sodium in chemical reactions wherever the presence of lead is not objectionable and where the extreme state of subdivision which can readily be obtained with the alloy is of material interest.
Preparation of Alloy An iron crucible is fitted with a lid through which is passed a stout iron wire which should be used as a stirrer a# shown in the diagram. The crucible is filled with 90 parts of lead and 10.5 parts of sodium and the lid is inserted. These proportions are selected to give NaPb as the product, because this sodium @oncentration is the lowest and safest which still provides an active, brittle material. The crucible is heated on a flame or in an electric furnace until the mass is liquid, a t which time the stirrer is operated for a few minutes. The crucible is then tipped at an angle of approximately 45" and allowed to cool, after which its contents are readily removed by inverting and hammering lightly on the side and bottom. The alloy falls out in brittle lumps which can be transferred at once to an air-tight container for storage. Whenever alloy is needed for use, an appropriate amount is removed from the container, broken into small lum s in a mortar, and quickly poured into the liquid t o be dried. If more rapid reaction is desired, the alloy may be ground to a fine owder; in this case it is advisable to effect the grinding under t t e liquid to be dried in order to minimize the absorption of moisture from the air. Finely ground powder, if not protected by the liquid, may react
