Rapid Determination of Phosphorus in Linseed Oil by Oxygen Bomb GEORGE T. PIERCY,’ EDWIN K. PLANT, AhD 3X. C. ROGERS University of Minnesota, Minneapolis, RXinn.
D
URISG experimental work being coiiducted t o ascertain
removed after its contents are washed into the beaker with the aid of a policeman. At this point there should be about 150 cc. of solution. Evaporate this solution just to dryness, add 2 cc. of concentrated nitric acid, and dilute to about 30 cc. Place the beaker containing this solution and some standard molybdate solution ( 2 ) in a bath kept a t 50” C. After constant temperature has been attained, pour 25 cc. of the molybdate solution into the beaker at such a rat,e that, it requires 30 seconds for the addition. After a short period of stirring pour the solution into the centrifuge tubes and m s h the beaker into the tubes. Then put the tubes into the centrifuge and turn at 1300 r. p. m. for 15 minutes. Remove the tubes from the centrifuge and read the volume of the precipitate in the tube. Pour off the supernatant liquid, which is decidedly acidic, and add 15 cc. of concentrated ammonium hydroxide. Agitate the precipitate with a Nichrome wire until all the yellow color has disappeared. leaving only the FIGURE1. CENTRIblack ashniaterial. Then fill the tubes FUGE TUBE with water and again centrifuge for 15 Dimensions in o m . minutes. Remove aeain and read the volume of the undiisolved material. The initial reading minus the reading of undissolved materials gives the true volume of the ammonium phosphcimolybdate.
the practicabilit’y of a solvent refining process for linseed oil it became necessary to determine the phosphorus content of the oil a t various stages of the refining process. As is vel1 knon-n, the “break” or mucilaginous material which separates o u t on heating linseed nil consists t o a large extent of the phospholipids or sulxtitiitetl fats containing pliosplioric acid and nitrogen. Although the pliospliolipicl content of the oil can be estimated qualitat,ively by t,he simple mechanical means of lieating tlie oil and observing the break, this procedure is very difficult t’o make quantit,ative and therefore i t is difficult t o determine Ti-lietlier the oil has heen improved by treatment. Also, this method is not app1ical)le to the determination of phosphorus in extracts fi,om solvent treating, such as are being obtained in the current investigation. Therefore, some quick satisfactory method had t o lie devised. Among the available nietliods for tlie deterinination of pliosphorus is the Fiske-Siibbarow method ( I ) . Most of the methods are colorimetric and entail a long period of ashing of the oil sample, in order to prevent loss during ignition. Since tlie number of samples for analysis in this investigation was very large and the asliing time would be prohibitive, recourse was had t o the oxygen honih as a means of oxidizing the sample rapidly.
Apparatus The oxygen bomb used was of 400-ml. capacity, made of illium (9). The centrifuge tubes were of the modified Goetz type shown in Figure 1. The tube proper had a volume of 16 ml. and the bottom section was graduated u p to a volume of 0.25 ml. in 0.01-ml. graduations.
Calculation Each 0.01 cc. of ammonium pliosphomolybdate represents 0.00033 gram of phosphorus.
Method
%P=
Weigh 2 grams of oil into a 15-ml. fused silica crucible. (Silica crucibles are preferred to illium because they vivi11 not tarnish on ignition.) Attach 10 to 12 cm. of pure iron fuse wire KO.30 t o the electrical terminals of a standard Parr oxygen bomb, bending the wire so that it hangs in a U-shape in t,he crucible, which is placed in the loop of the terminal. Add 30 to 40 cc. of distilled water to the bomb, wet the gasket and rim with water, and assemble the bomb. Admit ox>-genslowly until the pressure is 30 atmospheres, then remove the filling tube and tighten the thumb nut in place. Place the bomb in a bucket of water that is slightly below room temperature to absorb the heat liberated by the burning oil, and ignite the oil by touching the electrical terminals to a direct current potential of 20 volts. Alloir the bomb to remain in the water for 15 minutes, then remove it from the water and don-ly release the pressure in t,he bomb, taking 4 to 5 minutes for the release. -4slow-release valve may be used, but has not been found necessary. After the pressure is released, loosen and raise the cover on the bomb, and wash the valve with dist,illed n-ater, allowing the drippings to fall into the bomb. Remove the cover and place it over a 250-cc. beaker, taking care to keep it in a vertical position. Then by the use of a stirring rod spill the crucible and its contents into the beaker. Return the cover to its position over the bomb and nash the electrodes so that the water falls into the bomb. Wash the cover of the bomb thoroughly with distilled n-ater, adding the washings to those already in the bomb. Add 10 cc. of concentrated nitric acid (specific gravity 1.42) to the bomb, mix, and then pour the acid solution into the beaker. Then completely wash the bomb into the beaker with distilled water. rldd 20 cc. more of tlie acid and stir. The crucible may be 1
(0.00033 X volume read in 0.01 cc.) X 100 weight of sample
Accuracy of Tests T h e results of running sereral check samples on several oils give the range of values t h a t can he expected on each oil.
TABLE I. CHECKRUNS Sample Oil A Oil B Oil C
50% A, 50% B
1 0.000 0.044 0.040 0.021
2 0.000 0.042 0.041 0.022
3
Av.
0.000 0.043 0,039 0.019
0.000
0.043 0,040 0.020
Examination of Table I iiidicates t h a t the percentage of error is greater for a lower phosphorus content. T h e values run on the break and phosphorus-free oil were used to determine whether the results obtained were all due t o the phosphorus in the oil.
Summary T h e P a r r oxygen bomb is satisfactory for tlie deterniination of phosphorus in linseed oil, and provides a faster means of phosphorus determination than present Inethods. The accuracy compares favorably n-ith other availehle methods.
Literature Cited (1) Fiske and Subbarow, J . B i d . Chem., 66, 375 (192.5). (2) Koithoff and Sandell, “Textbook of Quanti1ative Inorganic Analysis”, p. 373, New York, Macmiilan Co., 1936. (3) Parr, “Analysis of Fuel, Gas, Water and Lubricants”, p. 222, Yen- I’ork, McGraw-Hill Book Co., 1932.
Present address, Standard 011Company of Louisinna, Baton Rouge. La.
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