A Modified Soxhlet Extractor
The SoxhIet extractor, in its present commercial form, presents a number of difficulties which are frequently met. These are enumerated below:
(1) inefficient extraction due to the fact that the liquid coming in contact with the solids has been cooled almost to room temperature by the reflux condenser;
(2) clogging of the liquid return tube due to crystallization therein or due to entrainment of sollds from poorly fitting thimbles;
(3) the need for the use of makeshift thimbles arising out of the unavailability or high cost thereof.
The modified apparatus consists of an outer jacket A, and a glass thimble, B, which contains the solids supported by a perforated glass plate, C, covered by a filter paper. The jacket is fitted with a ground joint at the bottom, D, which is received by the flask and with another at the top, F, which accommodates a reflux condenser of the usual type. Just below this upper joint three droplets of glass, F, are affixed to the inside of the jacket; these support the inner thimble.
The thirnble itself is flared at the top so that it rests on the supports, and near the bottom it has a perforated glass partition, C, much like that in a Büchner funnel. The liquid return tube, G, is of the conventional form, as shown in the diagram; however, it is suggested that it be fixed to the thimble near the top and bottom, H. In use, a filter paper is placed over the partition and the solids are loaded into the thimble. The thimble is then placed in the jacket and the whole attached to the condenser and flask. Vapors from the boiling liquid pass through the annular space, warming the contents of the thimble and preventing crystallization in the downtake. (The size of the apparatus may be varied; however, the annular space should be as small as possible so that the vapor velocity is a maximum, giving most efficient heating.) The vapors rise and are condensed, whence they return to the thimble which "cycles" in the usual manner. It will be noted that the extracting liquor will be warm and that, although no paper thimble is required, mechanical carry over is eliminated. Other advantages include ease of cleaning and lessened vulnerability of the downtake to breakage.
Prevention of Losses in Soxhlet Extraction. lf some commercial Soxhlet extractors are not mounted in exactly vertical position, the extract instead of falling into the flask may fall onto the joint area. With solvents that creep, the extract may rise into the joint and thus permit loss of extracted material. This difficulty can be obviated readily by inserting into the flask a capillary tube of sufficient length to extend into the end of the siphon tube. This expedient has proved of particular value in extractions with petroleum ether.
Prevention of Air Locks in SoxhIet Extraction. Often an air lock develops in the siphon tube of a Soxhlet apparatus during extractions with water. This results in premature siphoning and lowered efficiency in the extraction. This difficulty can be remedied by surrounding the entire assembly with a shell of asbestos paper. The heat of the burner or hot plate is conducted upward through the chirnney. The siphon tube is thereby kept hot and air locks prevented.
Breaking of Emulsions in Solvent Extractions. In solvent extractions, emulsion of water with the solvent layer is often a problern. Even a haze may interfere in photometric determinations. One method of breaking such emulsions is to pass the solvent through a porous medium, held in a filter. A glass wool plug is effective for this purpose. In the case of a mere haze, the solvent emerging from the plug or disc is clear and the water is retained on the glass fiber.