Control of Throughput, Temperature, and Purity of Solvent in Soxhlet Extraction KAROL J. RIYSELS', HAROLD H. POMEROY, AND GEROULD H. SMITH2, Stunford University, Culq. tubing, b, high enough to stand above the level of liquid. The total reflux is led into the thimble by means of a glass fiber, c. The solvent passes through the soap column, flowing out from the bottom of the tube, and then rises up on its outside until the level is high enough to start the siphon. Thus the total reflux passes through the soap once and once only.
HE value of the conventional Soxhlet extractor lies mainly in T the small volume of solvent used, together with automatic functioning at the boiling point of the solvent. In addition, the extract may be easily recovered or the solvent treated continuously by a nonvolatile agent placed in the reboiler flask. In the purification and study of aluminum soaps ( 1 ) it became important to combine the advantages of the conventional unit with complete protection from moisture causing hydrolysis, with better throughput control for small samples, with frequent extraction at temperatures other than the boiling point, with occasional recovery of extract, and with continuous drying of the solvent. For these purposes the units shown in Figures 1 to 3 were designed and proved very useful.
If a small thimble and a large Soxhlet extractor are used, most of the solvent is available for siphoning when the siphon starts instead of being in the thimble and having to filter through before siphoning. The use of the confining tube assures constant renewal of the extracting liquid in the immediate vicinity of the soap, as the holdup of the soap column is of the order of 5 ml. only. The rate of reflux may be held constant by adjusting the heating rate of the boiler flask; the total time of extraction then determines the extracting volume. Temperature Control. In the conventional Soxhlet extractor the actual temperature of extraction is within 2 ' C. of the boiling point of the pure solvent. It is even closer to it in the above modification.
TO DRYIWG TUBE
FRIEDRICHS CONDENSER
To control this temperature in the range below the boiling point it was necessary to introduce a cooler (d, Figure 2) between the reflux condenser, e , and the extractor, and to surround the GLASS
FIBER
(C;
PAPER THIMBLE ( a ) SOXHLET EXTRACTOR
GLASS TUBING (b) SAMPLE
FLASK
[--~-z--k SOLVENT DRYING AGENT
Figure 1. Conventional Soxhlet Apparatus with Special Sample Container
Control of Throughput. In the conventional Soxhlet apparatus, especially when small samples are used, the time of contact between sample and solvent may be easily determined, but the composition and volume of this solvent are variable and indefinite. To reduce these uncertainties small samples of soap are placed in a filter paper thimble (a, Figure 1) enclosed in a section of glass
Figure 2. Modified Soxhlet Apparatus for Operation, at Controlled Temperatures
Present address, Department of Chemistry, University of Southern California, Los AngIes 7, Calif. 2 Present address, Union Oil Company of California, Oleum, Calif. 1
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Figure 3. Modified Soxhlet Apparatus For operation at controlled temperatures and for independent ,recovery and treatment of solvent
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trap, h. was providedhetween the extractor snd-th; bol'linp flask.
room 'temperature or a t bo C. with solvents such as acctone or iso-octane boiling at much higher temperatures, and the effect of varying temperatures oi extraction for a given solvent wBs studied. Assembly is facilitated when ball and socket joints, or two ground joints at right angles, are inserted in the vertical tube above the boiling flask, Independent Recovery and Treatment. In both above modifications as well as in the conventional model, the extract may be recovered in the boiling flask or a treating went far the solvent, such BS a drying agent-for example, Drierite, calcium sulfate-may be placed therein. To accomplish both these abjectives simultaneously and still retain the temperature con1rol and automatic operation, the unit of Figure 3 was designed.
It is a modification of the unit of Figure 2 in which the previously dried solvent is freed of extract in a 500-ml. boiler flask, k, its vapor is condensed and led into a 500-ml. treating flask, 1, where it, meets the drying agent, and pure solvent, is finally
distilled therefrom through tube m into the oondenser, cooler, and extractor. Any amount of solvent between 250 and 500 ml. may be used. Automatic o eration requires that distilling rates from the two flasks, k and l,%e the same so that neither can lack liquid. This is accomplished by heating 2 a t a definitely faster rate than k, which ensures an adequate supply of hquid in k. The level in 1 is prevented from falling low by oondenser n which refluxes most of the vapor as soon as the level ofliquid fall! helow the end of the tube, 0, and is inactive when o dips~inthe liquid. Gooseneck traps (h, p , and q) direct the stream of vapor in the proper direction. This apparatus performed very siEtisiaotorily. At the time of building these units, hall and socket joints were not availitble, but it is presumed that their use would greatly simplify both the assembly and the operation. LITERATURE CITED
(1) Mysels, K. J.. Pomeroy, H.H., H , and Smith, G.H., J . Am. A, Chem. Soc., 70, 1053 (1948).
RECEIVED R ~ c ~ i v rJuly n 12, 1946.
Study condueled under contract OEMsr-IO57 OE !between .m+.mnn ."A the ih. Office OR*n of "f Emergency Pma*ann*., Mrr Stanford TT"..,*-i+., University and Management, recommended by Division 11.3 of the National Defense Research Counoil. and supervised by I . W. MoBain.
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HE description covered this month, 0-pyridinesulionio acid, mas completed from data obtained during work on an
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industrial research project a t the Armour Research Foundation. Samples ai the pure compound mere obtained through the courtesy of Edmond T. Tisza ai the Pyridium Corporation.
10. Beta-Pyridinesulfonic Acid Crystals of 0-pyridinesulfonic acid are readily obtained from water either on a microscope slide or macroscopieally. There is no ovidence of polymorphism during crystallization from solution or the melt. CRYSTALMORPHOLOQY (determined and checked by W. C. McCrone, V. Gilpin, and P. T. Cheng). CrvstalSvstem. Orthorhombic. Form a
