An
Extractor for Use with Reduced Pressure W. F. BARTHEL
United Stater Department of Agriculture, Bureau of Entomology and Plant Quarantine, Beltsville,
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ing flask may tend to contaminate the extract; however, i t is a small joint, and if only enough grease is used to prevent leakage of air the contamination will be slight. Specially made ground joints sold under the name of “No Lub”, which require no 1,ibrication, could be used where all contamination with rease must be excluded. The manufacturer’s directions must \e followed for proper use of these special joints, or the finely ground face will become marred to the point where they have no advantage over ordinary joints. Solvent can be added through side tube 4. A ca illary tube For the is placed in 4 through a well-rolled tight-fitting cor!. extraction of pyrethrins it is best to run carbon dioxide or nitrogen through the capillary tube. Water enters the condenser at 5 and leaves a t 6. The vacuum line is attached a t 7. It is desirable to trap the vacuum line with ice to-prevent loss of solvent. To prevent vibration of the inner water tube, 8, in the condenser, projections, 9, were blown in the condenser. These projections do not touch the inner tube. I t was found that the time for extraction depended on the kind of,solvent, which passes through the thimble a t about 2 ml. per minute.
T H E course of work on the preparation of purified pyrethrin concentrates ( 1 ) it was desirable to know whether any of the newer commercial solventv could be used in place of petroleum ether and ethylene dichloride for the extraction of pyrethrum dowers. As many of these newer solvents have too high a boiling point to be distilled on a steam bath a t atmospheric pressure, an extractor was designed to permit their use a t reduced pressum. When heated a t temperatures above 100’ C. for any length of time, the structure of the pyrethrins is altered and their toxicity to insects greatly reduced. Soxhlet extraction apparatus has several disadvantages when used with vacuum. The spiral condensers often furnished with B Soxhlet apparatus cannot be used under reduced pressure bea w e they flood. The usual Allihn condensers are too short and also flood when the pressure fluctuates. The siphon of the Soxhlet does not function properly, owing to the difference in pressure between the top part of the apparatus and the bottom. The large joints of the Soxhlet require grease to hold a vacuum and to prevent sticking. Some of this grease is removed on prolonged refluxing, thus contaminating the extract.
For his purpose the author used a water bath tp.heat the boiling flask, but it would work just BS well on a steam’bath. As the pyrethrins tend to decompose a t elevated temperatures, he has
Wasitzky ( 6 ) designed an apparatus for microextractiona under reduced pressure, but it was too small for use with samples as large as were required in this project. A simple enlargement of his apparatus would produce an unwieldy piece of equipment from which the extract would be di5cult to remove and weigh quantitatively. Macheboeuf and Fethke have designed two pieces of apparatus for extractions a t reduced pressure. One (4) was similar to Wasitzky’s in principle and for the same reason was not satisfackory for the author’s work. The other ( 5 ) ,besides bein bulky and fragile, had the disadvantage of having flat g r o u n j joints which permit too much air to leak into the apparatus. When a solvent with a high vapor pressure is used, this air leakage will tend to carry out much of the solvent from the apparatus. The apparatus of Hambleton (3)is constructed with flat ground joints. The statement is made that with this apparatus the leakage amounts to 20 or 30 ml. per minute when the pressure inside is 100 to 200 mm. absolute. In the extractor described below the capillary used to effect smooth ebullition does not permit near this volume of gas to enter. h l l the designs referred to apparently depend upon boiling tubes for smooth ebullition and unless extreme precautions are taken to maintain constant pressure the boiling tube will cease to function properly.
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The apparatus pictured in Figure 1 w&s made for use a t reduced pressures, but it may be used satisfactorily under atmospheric conditions when desirable. I t was made as simple as possible without interfering with good extraction. .is may be seen from Figure 1, it is a modified Butt extractor
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( 2 ) . In order t o keep the material to be extracted continuously
covered with fresh solvent, a glass thimble, D, with overflow tube, 1, was made. A condenser, A , has a cooling-surface extension below the ground joint to prevent contamination of the extract with grease from this joint. This extension aids in holding a good vacuum. There is no trouble with flooding of the finger condenser. In proper use little solvent is lost from the apparatus, owing to the large surface of the condenser. To set up the apparatus a wad of cotton is placed in the closed bottom of the thimble, B, care being taken to get it evenly distributed so t h a t the solid materials will not get into overflow tube 1. The sample (20 to 30 grams) of plant material to be extrticted is next put in place, then another wad of cotton, and tinally a circle of wire screeningto prevent the material from blowing out with variations in pressure. Projections, 2 , keep the wire in place. A small piece of wire may be fastened to the screening to aid in its removal when refilling the thimbie. The thimble is placed in the body of the extractor, B , resting OD projections 3, which permit free flow of vapor and liquid. Condenser A and the boiling flask, C, are put in place, the ground joints being greased. The Krease on the joint of the boil-
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Figure 1.
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Apparatus
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
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had no occasion to use this apparatus a t temperatures higher than 100" C. If a solvent that does hot boil a t reduced pressure on a steam bath is to be used, a heating mantle with a transformer for temperature control might be desirable. The a p paratus may be set up in banks, in which case one ice trap would do for several extractors, provided, of course, that the capillary tubes are small enough to prevent too much gas from entering. When the apparatus is used at atmospheric pressure, no capillary tube is required; side tube 4 is then closed with a tightfitting cork. Smooth boiling in this case is brought about by boiling chips.
Vol. 17, No. 1
The apparatus as described has been used a t reduced preesuree with many solvents that boil a t temperatures between 90" and 125' C. (760 mm.). LITERATURE CITED
(1)Barthel, Haller, and LaForge, Soap S a d . Chem., 20, No.7 121 (1944). (2) Butt, J. IND.ENG.CHEM.,7, 130 (1915). (3) Hainbleton, J. BioE. Chem., 99, 259 (1932). (4) Macheboeuf and Fethke, Bull. SOC. chim. bid., 15, 796 (1933). (5) Ibid., 16, 229 (1934). (6) Wasitsky, Mikrochemie, 11, 1 (1932).
Flowmeter for Gaseous Anhydrous Hydrogen Fluoride WARREN S. PETERSON Process Metallurgy Division, Aluminum Research Laboratories, N e w Kensington, Pa.
A
NEIYDROUS hydrogen fluoride has become a common laboratory reagent available commercially in cylinders. Because of the reaction between hydrogen fluoride and glass and the marked dependence of viscosity and molecular weight of gaseous hydrogen fluoride on temperature (1) the usual type of laboratory flow gage cannot be used. 'The flowmeter (Figure 1) described here was of great value in determining approximately the amounts of anhydrous hydrogen fluoride used in operations where a relatively small, continuous flow of gas was employed. The parts of the apparatus exposed t o hydrogen fluoride were constructed of copper; kerosene served as the confining liquid. Copper-glass construction of the two open-end manometers allowed readings of pressure differentials caused by the passage of gas through the capillary in the copper rod; Monel metal or magnesium might be used t o advantage for this capillary. Copper tubing 1.1 cm. inch) in inside diameter was used, with 9-mm. Pyrex tubing in the manometers. The capillary was a 0.07-cm. (0.02Sinch) diameter hole in a 3.1-cm. (1.25-
inch) length of copper rod. To ensure constant molecular weight and viscosity, the hydrogen fluoride immediately before entering the flowmeter waa led through a copper tube in a condenfier maintained a t 100' C. by the condensation of steam. The connection between the meter and the copper tube in the condenser was made with neoprene tubing; this 'connection could be improved by making a permanent brazed joint or introducing an automobile-oil-line type of connection. The flowmeter was calibrated by absorbing the hydrogen fluoride in solid sodium fluoride in aluminum tubes. A flowmeter of this type was recalibrated after almost continuous use for over a month and found to check very closely with the original calibration. This gage had a range up to 0.78 gram of hydrogen fluoride per minute for a change in pressure up to 100 mm. in the glass arm of the manometer. The meter should be purged with dry air immediately after the hydrogen fluoride flow is discontinued, to prevent corrosion that might occur if residual hydrogen fluoride picked up moisture while the meter was not in use. LITERATURE CITED
(1) Simons and Hildebrand, J. Am. Chcm. SOC.,46, 2183 (1924).
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3 - S H R I N K FIT, T U B I N G T O R O D 4- COPPER R ~ W DI T H O R I F I C E 5 - K E ROSENE-CONFINING LIQUID 6- NEOPRENE T U B I N G ?-GLASS TUBING
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9- ENTRANCE TUBE F R O M S T E A M G E N E R A T O R IO-EXIT TUBE FOR CONDERSED S T E A M 11-COPPER TUBE C O N N E C T E D TO HF TANK 12-GLASS TUBE CONDENSER FOR M A I N T A I N I N G H F AT
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T E M P . AND M O L E C U L A R WT.
Figure 1
