I N D UXTRIAL A N D ENGINEERING CHEMISTRY
July 15, 1929
STAXNOUS CHLORIDE SoLuTIox-Dissolve 25 grams of SnC12.2Hz0 in 1000 cc. of dilute (10 per cent by volume) hydrochloric acid solution. Filter if necessary. Store in a bottle with a siphon or side opening near the bottom, arranged with a glass stopcock for delivering the solution in drops. The solution should be protected from the air by floating a layer of white mineral oil about 5 mm. thick over the surface. STANDARD PHOSPHATE SoLuTIoN-Dissohe 0.2195 gram of (recrystallized) potassium-dihydrogen-phosphateand dilute to 1000 cc. This solution contains 50 p. p. m. of phosphorus and is too concentrated to use directly. A second stock solution is made by taking 50 cc. of the first stock solution and diluting to 500 cc. This second stock solution contains 5 p. p. m. and is used for making the standard solution for comparison. To make this standard solution take 5 cc. of the stock solution, dilute to 95 cc. with distilled water, add 4 cc. of the ammonium molybdate-sulfuric acid solution, and mix thoroughly by shaking in an Erlenmeyer flask. Add 6 drops of stannous chloride and shake. Dilute to exactly 100 cc., shake, and the solution is ready for use. It contains 0.25 p. p. m. of phosphorus. For very dilute solutions use 2 cc. of the stock solution, but the same amount of reagents, giving a standard which contains 0.1 p. p. m. of phosphorus. After standing 10 to 12 minutes, the standard starts to fade, and a drop more of stannous chloride should then be added to bring the full color back which will again be permanent for 10 to 12 minutes. ANALYTICAL PROCEDURE-In the analysis of water, water extracts of soils, minerals, fertilizers, etc., it is permissible to add the reagents directly to these unless they are colored, turbid, or decidedly acid or alkaline. Turbidity and color should be removed by appropriate means. A decided acid or alkaline reaction should be neutralized before adding the reagents. Organic materials may be ignited with magnesium nitrate. I n this case i t is best to keep the 10 N sulfuric acid and 2.5 per cent ammonium molybdate as separate solutions in order that the ignited residue may be dissolved with the sulfuric acid and the ammonium molybdate added after proper dilution, I n all cases the reagents should be present after final dilution in the proportion of 4 cc. of 10 N sulfuric acid, 4 cc. of 2.5 per cent ammonium molybdate, and 6 drops of
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stannous chloride per 100 cc. The reagents should be thoroughly mixed with the test solution before the stannous chloride is added, after which thorough mixing should again be accomplished. Comparison with the standard should be made within 10 minutes after adding the stannous chloride. PaECAuTIoNS-Reagents, filter paper, water, and glassware often contain appreciable quantities of phosphorus and arsenic. Blank tests should be made frequently in which all of the reagents and glassware come into play, and there should not be produced more than a very faint blue color if everything is satisfactory. New glassware should be thoroughly weathered by treatment with warm sulfuric acid dichromate solution for 24 hours. Filter paper may be tested by tearing up a sheet of it and throwing the shreds into a blank test and shaking. It is absolutely essential that every new lot of reagents be rigidly tested. Summary of Improvements
1-A stock solution of stannous chloride is prepared by dissolving the pure salt in acidified water and is preserved by covering with a layer of white mineral oil. This is far superior to the old method of preparing it each day as needed by dissolving mossy tin in hydrochloric acid. 2-In comparison to the old method the amount of ammonium molybdate is doubled and the acidity is increased. With these amounts and proportions of reagents the method is made considerably more sensitive, especially to small amounts, because the full effect of all the phosphate is probably brought into play. Evidence that this is the case is furnished by the fact that the full color development takes place immediately on adding the stannous chloride. In this respect there is a lag of 5 to 10 minutes in the old method due to the slowness of the reactions in coming to equilibrium on account of the less favorable conditions. 3-Effects from even high amounts of silica are entirely eliminated with the concentration of reagents recommended. Literature Cited (1) Denig&, Com9t. rend., 171, 802 (1920); Corn#;. rend. 875 (1921). (2) Parker and Fudge, SoiE Science, 34, 109 (1927).
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A Large Metal Soxhlet Extractor' 1,. R. Bryant ONTAEIO
AGRICULTURAL COLLEGE, GUELPA,
N T H E course of some work on poultry nutrition it was found necessary to prepare about 6.8 kg. per day of fatfree material for feeding experiments. To meet this need a relatively inexpensive extractor was required. A large metal extractor of standard make2 was thought to be almost suitable and a drawing was made, modifying this extractor somewhat, and submitted to a local metal worker, who made it up in copper. The modified apparatus has been giving satisfactory service a t this institution for the past year and it is thought that the details of its construction would be of value to other workers in the field, as any good coppersmith should be able to make it up fairly cheaply. The apparatus is constructed in three sections. The lower section is a boiling vessel for the solvent and has a draining faucet a t the bottom. The center section comprises the extraction chamber with a tube for carrying up the solvent
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Received February 14, 1929.
* Baird and Tatlock, Ltd., London, England.
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vapor, a siphon for returning the solvent and extract to t h e lower vessel, and a glass level gage to indicate the height of liquid in the extraction chamber. A faucet is provided for draining the extraction chamber. The cover of the lower chamber with the tubes attached forms a part of the center section. The top section is a reflux condenser consisting of a copper coil inside a copper tank. The center section fits into a groove in the top of the lower boiling chamber. An asbestos gasket has been placed in the bottom of t h e groove and the center section is provided with lugs so that the two sections may be fitted together and tightened by means of wing nuts, making an air-tight joint. The reflux condenser is fastened to the top of the extraction chamber in the same way. The material to be extracted is put into a linen bag, which is placed in a copper frame, shown a t right of diagram. An extra copper ring holds the bag firmly in place. The bag holder containing the material is then placed in the extrac-
ANALYTICAL EDITION
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Vol. 1, No. 3
tion chamber and rests upon a perforated copper plate. The bottom of the siphon tube emerges from the space directly underneath this plate. The total height of the extractor as sketched is 134.5 cm. The tube which carries the solvent vapor up into the extraction chamber is of 2.54 cm. external diameter and 2.22 cm. internal diameter, and that of the siphon tube of 4.77 mm. internal diameter. These dimensions were found to be very important in constructing a successful extractor, as with this ratio between the diameters of the two tubes premature siphoning never occurs. The solvent in the extraction chamber always rises to the level of the top of the siphon tube before it is returned to the boiling chamber. The apparatus is set upon an ordinary domestic hot plate of 800 watts, 110 volts, with “low, medium, and high” switch. Among other materials, the writer has extracted a considerable quantity of cod-liver meal containing a large proportion (about 40 per cent) of fat. Very satisfactory results have been obtained with solvent naphtha. The solvent naphtha is put into the extractor, distilled into the extraction chamber, allowing only the fraction which distils a t 100’ C. or below to pass up into the upper chamber. This fraction is usually about 40 per cent by volume of the solvent naphtha as purchased, and the residue is used as tractor fuel. The linen bag is filled with cod-liver meal (about 7 kg.) and loaded into the extractor. At the end of 40 hours the codliver meal has been found to be fat-free, using the ordinary Soxhlet extractor with ether, as a check. There is practically no loss of solvent except what remains absorbed in the extracted material, which is spread out on flat trays until all this solvent has evaporated. Both the solvent and extract can be recovered by running the apparatus for an hour or two after the bag of extracted material has been removed.
Modification of the Kjeldahl Trap’ Geo. H.W. Lucas DBPARTMENT OP PHARMACOLOGY, UNIVERSITYOF TORONTO, TORONTO, CANADA
A research which involved the determination of a few I Nmilligrams of bromine in the presence of a large amount of chlorine, the bromine was steam-distilled into a solution of potassium iodide. It was found in the earlier experiments that some of the oxidizG ing agent was carried over into the potassium iodide with the steam and the analysis rendered useless; several types of Kjeldahl traps were tried but none proved trustworthy. The accompanying diagram illustrates a trap that was designed and proved to be very efficient. A is a 500-cc. Pyrex Kjeldahl flask; B i s a wide glass tube about 1 cm. bore fused into it; the end C is directly over the opening D and is about 3 cm. long. From the opening D a small tube 3 mm. bore runs a t an angle of about 45 degrees to join E. At F the sides of the tube are pushed in and a small funnel is thereby SUSpended; the funnel is filled with glass wool. The tube G leads to a con1
Received February 11, 1929.
denser. TheItop of the trap is not sealed off, but is closed with a rubber stopper in order to allow replacement of the glass funnel and glass wool if necessary. During violent ebullition the froth passes up the stem E very easily and is directed down. As the tube leading from D is small, the gaseous pressure in the flask H does not force the liquid back. There is a continual drop of fluid from the flask through D back into H. This trap is large and is not intended for the ordinary KjeIdahl distillation, but when one is faced with the problem of distilling a very frothy substance in a Kjeldahl or with steam distillation where the ordinary trap is useless, it is invaluable. Table I shows the quantitative recovery of small quantities of bromine by use of this trap. Table I-Bromine Recovery with Modified Kjeldahl Trap DISTILLATION FLASKCONTAINED BESIDES BROMINE HzSO4, KzCrzO?, AND HzO RECOVERED DATE 1926 Mg. December 20 Nothing 0.0 1927 101.4 3000 mg. NaCI, 100 mg. bromine as KBP January 17 January 17 100 mg. bromine as KBr 99.2 104.6 2000 mg. NaCl, 100 mg. bromine as KBr January 17 January 17 100 mg. bromine as KBr 98.7 February 2 Sodium sulfide 0.0 February 3 Nothing 0.0 Halides from 250 cc. normal rabbit urine plus March 7 94.6 100 mg. bromine as KBr March 7 Halides from 250 cc. normal rabbit urine Trace Halides from 100 cc. normal rabbit urine plus March 7 37.4 40 mg. bromine as KBr
