lugh (Hive Bee)
08-08-01 01:31
No 202327
      Simply Constructed Soxhlet  Bookmark   

Long ago, F Shultz devised and constructed metal soxhlet extraction equipment, as he was dissatisfied with glass breakage in his department at Jena. From Biochemische Zeitschrift 247, 474 (1933):

The shown apparatus worked in the best way for the extraction of larger quantities. A cylinder, manufactured from tinplate, serves as an extraction  thimble, which is lined with canvas, fine gauze or raw silk. The apparatus is manufactured from tinplate,  a slightly conical bulge is pressed onto the base quicklly, the extraction thimble aligned with the base. The apparatus is provided with curved brass tubes, which allows the ether vapor to reach the condenser, and the U -- pipe is intended for the liquid outlet. The glass u-tube's legnth can be varied depending upon the height, depending on how fast you wish the solvent to flow. The condenser  is attached to a cover made from tinplate, which just like the extraction equipment is provided with a broad, flat edge. The two edges (flanges) use a canning jar ring for a gasket, and are attached by a set of bolts or screws with nuts inserted into holes drilled into the flanges. Apparatus for 300 cm it is pressed that the apparatus becomes close. The apparatus (with extraction cylinder of 300 and 600 cm we have apparatus in use; when isolation, by lining also with filter paper, felt, asbestos, etc. are usable probably for larger apparatus for extractions with ether, chloroform, benzene, alcohol worked. When using chloroform the rubber seals must be replaced after several extractions. The advantage of this apparatus over the extraction apparatus of glass is that the apparatus is not  so fragile. The apparatus can be manufactured by a skillful plumber for approximately 8 to 10 Reich Marks. Naturally also copper or nickel sheet etc. could be used

Obviously, silver solder would be the best method of joining the metal pieces, though other types would also work. One modification of this apparatus not available to Mr. Schulz would be the use of tygon tubing for the drain U-tube, this would allow for adjustment of the speed of extraction. Solubility of desired product dictates the speed, a more selective solvent should drain more slowly, to maximize the amount extracted. This apparratus should be usable for all types of extraction, except those requiring an acidic solvent. The picture doesn't show the condenser, it was made from copper tubing.
(Master Searcher)
08-08-01 02:25
No 202336
      Re: Simply Constructed Soxhlet  Bookmark   

They use 95:5 tin/antimony solder in plumbing in the US now.  I think the code doesn't allow the use of 60:40 tin/lead (or is it lead/tin) because of the lead content.
(Hive Addict)
08-08-01 08:07
No 202446
      Re: Simply Constructed Soxhlet  Bookmark   

It would be easy to make if you had some stainless steel threaded pipe and some taps/dies. 

Actually you could use one of the round stainless steel pots made to go in restaurant steam tables(probably $50 or so), anyone who has worked in a restaurant knows the containers I am talking about.  They approx. 6in wide by 10 inches deep, and other assorted sizes.
Affix the tubeing as above and rig a condensor/coldfinger on top.  A bead of automotive silicone gasket maker and some C-clamps could seal the top if spilling was a concern.  If you wanted to go all out you would have a welder put a 24/40 joint in the top.  They have plactic inserts for joining metal to ground glass joints.

Do Your Part To Win The War
(Stoni's sexual toy)
08-08-01 15:06
No 202495
      Re: Simply Constructed Soxhlet  Bookmark   

Metal parts with the exact dimensions of ground glass joints are available. I had a rotovap steam tube made from steel which provided a perfect seal with glassware, and there are also metal joint parts to be used in vacuum applications.
(Hive Bee)
08-08-01 16:24
No 202511
      Re: Simply Constructed Soxhlet  Bookmark   

As far as that goes, a skilled machinist can fabricate such fittings, that's how they were first made. There are many good methods to connect things, but  undoubtedly, the simplest expedient for making a vacuum tight connection between any type of "close but not close enough" tubular fitting and hole is to simply wrap the male fitting with PTFE tape until it's big enough, converting the joint/tube into a teflon stopper, and press fitting it into the hole. 
(Master Searcher)
08-10-01 03:17
No 202982
      Re: Simply Constructed Soxhlet  Bookmark   

These pictures don't seem to be too reliable.  Here's some glass soxhlets.
(Hive Bee)
08-27-01 00:07
No 207596
      More Soxhlet tips  Bookmark   

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.