ANALYTICAL CHEMISTRY
1050 Table 111. Analysis of an Antimony Sulfide by Titration with Permanganate, Iodate, and Ceric Sulfate Run 1 2 3 AV.
Sb, %
0.10612N Permanganate, M1. 43.30 43.33 43.30 43.31 27.95
0.10201N Iodate, M1. 45.10 45.12 45.12 45.11 27.96
0.09245N Ceric Sulfate, M1. 49.75 49.76 49.75 49.75 27.97
A private communication stated that the sample had been prepared by mixing a pure grade of "needle antimony" with anhydrous sodium sulfate; and that after being dried a t 100" C. for 1 hour and being analyzed by the method of 8.H. Low, it had been found to contain 27.85$& antimony. Samples of approximately 20 grams of the ore were dried a t 100' C. for 1 to 2 hours, weighed into 300-ml. conical flasks, and warmed slowly with 20 ml. of 6 formal hydrochloric acid until most of the hydrogen sulfide had been evolved. Then 100 ml. of 12 formal acid were added, a test-tube condenser was inserted in the flask, and the volume of the solution was reduced t F o thirds by evaporation. The resulting solutions were transferred to 1-liter volumetric flasks by means of equal volumes of water, then diluted to the calibration mark with 3 formal hydrochloric acid. Then 50-ml. portions of these solutions were titrated with iodate and permanganate to the iodine monochloride end point, and with ceric sul-
fate with methyl orange as indicator, using the titration procedures described previously. The results of these analyses are tabulated in Table 111. ACKNOWLEDGMENT
A considerable amount of the above experimental data was obtained as the result of a cooperative study by a section of honor students in a sophomore analytical chemistry course. The assistance of Norton Wilson in directing the work of this group and in collecting and interpreting the experimental results has been of great value. Preliminary studies were made by Robert Custer, Wyatt Lewis, and George Wald LITERATURE CITED
(1) Andrews, J . Am. Chem. SOC.,25, 756 (1903). Furman, Ibid., 54, 4235 (1932). Jamieson, J . I n d . Eng. Chem., 3, 250 (1911); "Volumetric Iodate
(2) (3)
(4)
Methods," New York, Chemical Catalog Co., 1926. McNabb and Wagner, IND.ENG. CHEM.,. ~ N A L . ED., 2, 251 (1930).
(5)
(6) (7)
(8) (9)
Mutschin, Z . ana2. Chem., 106, 1 (1936). Rathburg, Ber., 61, 1663 (1928). Swift, J . Am. Chem. SOC.,52, 894 (1930). Swift and Gregory, Ibid., 52, 901 (1930). Willard and Young, Ibid., 50, 1376 (1928).
RECEIVED February 24, 1948.
A lamp for Burning High-Boiling Petroleum Fractions Deter mi nut ion of Hydrogen S. G. HINDIN' AND A. V. GROSSE' Houdry Process Corporation, Marcus Hook, Pa. In lamp procedures previously developed for the determination of hydrogen, carbon, and sulfur in gasolines, the sample is burned in a lamp and the combustion products are collected and determined. A modified lamp design, which allows extension of the procedure to higher boiling petroleum fractions is described.
L
AMP procedures have been developed for determination of
hydrogen (9, 4 ) , carbon ( d ) ,and sulfur (1, 3 ) in low-boiling petroleum fractions and have been applied to analysis of other organic liquids. These procedures entail combustion of the sample a t the end of a wick; the oxidation products are recovered by suitable absorbents and determined. Khile eminently suitable for analysis of low-boiling liquids (below 260" C.), these lamp methods have not been applied to the analysis of higher-boiling materials. High-boiling liquids do not diffuse up the wick a t a rate sufficient to ensure an adequate supply of liquid for combustion; performance of the Javes' lamp (3) has not been definitely established for such materials. A modified lamp design is indicated in Figure 1 which, by use of a variable hydraulic head, reduces the long wick path and permits the application of the lamp technique to high-boiling petroleum fractions (250" to 500" C.) and to other organic liquids in this boiling range. The burner is threaded with cotton wicks, three to five in number, which are trimmed flush with the top of the burner. Five to 10 ml. of sample are placed in the upper reservoir, and the lamp is weighed. The sample is then run into the lower reservoir and allowed to diffuseto the top of the wick. This step may take LO minutes or more. The lamp is then lighted with a microburner and inserted in the chimney, after which the determination is 1 Present addreea, American Sugar Refining Company, Research and Development Division, Philadelphia 48, Pa. Preeent address, Temple Univereity Research Institute, Philadelphia, Pa. f
carried on in the usual manner. After combustion, reweighing of the lamp indicates the amount of sample consumed. The dimensions of the lamp are not critical, the only restriction being that the over-all height and weight should be such as to permit weighing the lamp on an analytical balance. ACCURACY AND PRECISION OF DETERMINATION OF HYDROGEN
The accuracy and precision of the hydrogen determination in higher-boiling fractions are comparable to those obtained in gasoline analysis, as shown in Table I. In this table are indicated analyses for highly Durified hexadecane (cetane) and decahydronaphthalene (Decalin) and a130 for two wide fractions, together with the values that were obtained using the standard train procedure. Duplicate determinations on a large number of samples have Table I.
Accuracy and Precision Per Cent Hydrogen
Sample NO. 1 2 3
4
Description Cetane Deoalin 404-912O F. straight run cut 390-945O F. straight run cut
Theoretical 15.13 13.12
... ,.,
Lamp method 15.12 * 0 . 0 2 13.13 * 0 . 0 2
12.01 * 0 . 0 4 13.24
* 0.03
Carbonhydrogen train
...... ...... 12.07 * 0 . 0 4 13.20
* 0.08
1051
V O L U M E 20, NO. 11, NOVEMBER 1 9 4 8 shown precision of the order of *0.02 to 0.03% hydrogen. For the usual hydrocarbon sample, of about 10 to 15% hydrogen, this is equivalent to an absolute accuracy of about 2 to 3 parts per thousand. Similar accuracy may be expected in the determination of carbon using Simmons’ addition (4)to the authors’ technique. NOTESONPROCEDURE
The procedure is very similar to that previously described ( 2 ) ,but, because of the modification in lamp design, a few minor
variations in technique are required. The number of wicks used in the burner tube varies inversely with the fluidity of the sample, as does the height of the liquid head in ieservoir B. Thus, for cetane, with the burner dimensions indicated in the drawing, five wicks were used; for a 800” to 900 O F. cut, three wicks were used. The wicks are threaded in through the open top of the burner tube. With “heavy” materials, the reservoir is filled to a level only a few millimeters below the burner tip; with lighter samples, the level usually lies somewhere in the connecting tube. At no time should the liquid level be so high that unburned material spills over into the incoming air tube. Should such spillage occur, the liquid is held in the belly of the air tube. Liquid should be dropped from reservoir A sufficiently slowly t o prevent air locking in the connecting tube to the burner. Extending the wicks down to the horizontal portion of the tube is also of value in minimizing this condition. The mesh size of the absorbent is important; 6-mesh indicating Drierite, nith a very loose plug of glass wool above and below it, serves very well. If an absorbent of smaller mesh is used, back prcwure builds up in the system, and forces liquid back from the aick. Vacuum on the exit end of the system may be used in conjunction with other absorbents; however, based on actual values, the Drierite appears to give quantitative absorption. The ground joint of the lamp is simply for the purpose of making it consistent with the A.S.T.M. chimney. It must be well greased when in use. For most of the authors’ work, however, the chimney was modified by removing the inner tube and the air inlet side arm, as no secondary air is required. The chimney and glass tube leading to the absorber were maintained a t slightly over 100 a C. by a Trapped Nichrome coil. In general, thc) Taniples analyzed were liquid fractions, boiling
lu 7 INLET AIR
14, GROUND( 10 JOINT 4MMID 50MM __
SLOPE
Figure 1.
Lamp for Burning Heavy Stocks
in the range 250“ to 500” C., and containing less than 35% aromatic material. Such samples may be burned for 30 to 40 minutes, consuming 0.5 to 1.0 gram of liquid, with only slight carbonization on the wick. The extent of this deposition is, however, insufficient to affect the accuracy of the hydrogen determination materially. Highly aromatic samples burn with a smoky flame-they have been analyzed by blending with saturated material. Waxy samples are handled in one of two manners. If the pour point is only a few degrees above room temperature, warming the burner tube may keep the liquid fluid all the way to the burner tip. Otherwise, waxy samples are blended with saturate material to give a mixture liquid at room temperature, When calculated back to the original sample, blending decreases the accuracy (directly with the dilution). No fractionation of the sample occurs during burning. The refractive indexes of several fractions, having a spread in boiling range of some 250 O C., were determined before and after a portion had been burned. In every case, the values checked within experimental error ( *0.0002 unit).
Table 11. Determination of Sulfur Sample 420-750° F. cut 150-800’ F. cut 400-900O F. cut
Per Cent Sulfur Bomb procedure Lamp method 0.115 0.120 * 0.0ot 0.432 0.438 A 0.008 3.54 3.33 A 0.04
The presence of nitrogen in the samples (up to several tenths of 1%) has no effect on the accuracy of the analysis. Thus sample 3 in Table I contained approximately 0.2% nitrogen, while sample 4 contained approximately 0.7% nitrogen. This is also true of sulfur in amounts up to 3.5%. The sulfur dioxide formed in burning may be simultaneously or separately determined. Table I1 shows results obtained in the analysis of three samples when this lamp was used in conjunction with the A.S.T.M. system (I). As Simmons has shown in his excellent paper (4j, carbon may be determined with great accuracy by the lamp method in light petroleum fractions. Similarly, the present lamp may be used for the simultaneous determination of carbon, hydrogen, and sulfur. The “lamp train” would require t’he following parts, in series: lamp and chimney, absorber for water, bubbler (neutral hydrogen peroxide) for sulfur dioxide, absorber (for water evaporated from the bubbler), hot copper oxide bed, and absorber for carbon dioxide. With this system, a secondary air supply to the chimney and application of vacuum a t the exit end are required. The major difficulty in burning high-boiling materials liet in keeping the burner warm to the tip to prevent solidification of sample material. Though no quantitative determinations have been made. the authors have qualitatively studied the following methods for maint,aining the sample fluid and all appear to be satisfactory: wrapping a Sichrome coil around the tube from the reservoir to the tip (with tungsten seals through the glass); suspending a Nichrome coil from the chimney into which the burner would fit; making the burner tube of metal (for heat conduction) and warming the horizontal portion; and warming the incoming air. Thus, it should be a simple matter to extend the lamp technique to materials boiling above 1000 O F. By merely elongating the vertical portions of the lamp so that the reservoir tube and burner are more than 100 to 150 mm. long, it may also be used for the analysis of gasolines and other light fractions. Still another slikht variation in design allows the use of this lamp for burning highly aromatic materials. By inserting a secondary air supply directly into the burner tube (a 1-mm. metal tube coming up into the burner tube and concentric with
ANALYTICAL CHEMISTRY
1052 it) and wrapping the wick around this metal tube, the authors have been able to burn methylnaphthalene without smoking. Attempts have been made to burn bottoms samples in this lamp. So far they have been unsuccessful, and the results have indicated that more radical lamp modifications would be needed.
ACKNOWLEDGMENT
The assistance of J. Grider with most of the experimental work is gratefully acknowledged. W. T. Harvey of the Sun Oil Company, Marcus Hook, Pa., very kindly contributed the results of the carbon-hydrogen train analyses.
SUMMARY
A modified lamp design is presented, allowing analysis of highboiling organic liquids Accuracy of the determination of hydrogen is of the order of *0.02 to 0.037, hydrogen, absolute. Variations in this design are suggested, which should permit the use of only one lamp for the determination of the hydrogen and carbon contents of all organic liquids from those volatile at room temperature to those of boiling point greater than 500" C.
LITERATURE CITED
(1) Am. SOC. Testing Materials, D90-46T. (2) Hindin, S.G., and Grosse, A . V., IND. ENG:CHEM.,ANAL.ED., 17, 767-9 (1945). (3) Javes, A. R., J. Inst. Petroleum Tech., 31, 129-53 (1945). (4) Simmons, M. C., ANAL.CHEM.,19, 385-9 (1947).
RECEIVED March 16. 1948.
Determination of Phosphorus Pentoxide in Phosphate Rock JAMES L. KASSNER, HOWARD P. CRAMMER, AND 3IARY ALICE OZIER School of C h e m i s t r y , Metallurgy, a n d Ceramics, University, Ala. Perchloric acid may be used for the dehydration of silica in phosphate rock, prior to the determination of phosphorus pentoxide. A new mixed indicator comprised of phenol red and bromothymol blue gives a sharp color change at pH 7.5. When this mixed indicator is used, the phosphorus pent-
I
N THE determination of phosphorus pentoxide in phosphate
rock, it is customary to separate the phosphate from the interfering substances by precipitating it as ammonium molybdiphosphate (9). The most common procedures for the treatment of the ammonium molybdiphosphate are the alkalimetric method, in which the nitric acid-free precipitate is dissolved in an excess of a standard solution of sodium hydroxide and the excess caustic is titrated Kith standard nitric acid in the presence of phenolphthalein; and the gravimetric method, in which the ammonium molybdiphosphate is dissolved in dilute ammonium hydroxide, citric acid is added, the phosphate is doubly precipitated with magnesia mixture, and the resulting magnesium ammonium phosphate hexahydrate is ignited to the pyrophosphate. Hillebrand and Lundell (3) have shown through the cooperation of representative analysts that the results obtained by the alkalimetric method when phenolphthalein is used as the indicator are approximately 0.3% higher than those obtained by the double precipitation as magnesium ammonium phosphate. In order to avoid this error, it is common practice among commercial laboratories to determine the titer of the alkali empirically by analyzing a Bureau of Standards phosphate rock rather than by using its stoichiometrical measurement. An improved procedure developed in this laboratory eliminates the empirical nature of the present alkalimetric method. A mixed indicator has been developed which gives a sharp color change a t the stoichiometric end point; the molybdate solution has been stabilized; and the conditions for precipitation have been established which give an ammonium molybdiphosphate precipitate of uniform composition. Data are presented which show that the precision and accuracy of the improved procedure are both very good. The maximum deviation in thirty consecutive samples mas 0.1 mg., and the average deviation 0.05 mg. of phosphorus pentoxide. REAGENTS AND STANDARD SOLUTIONS
Indicator. Prepare the phenol red and bromothymol blue solutions by triturating 0.1000 gram of each of the indicators in an agate mortar with an excess of sodium hydroxide. When the
oxide titer of the alkali may be determined with potassium acid phthalate. Free molybdic acid does not separate at the boiling point when molybdate solutions containing citric and nitric acids of prescribed composition are used. At the boiling point, the yellow precipitate separates almost immediately.
indicator has dissolved completely, adjust the pH with nitric acid to 7.5 and dilute the solution to 250 ml. in a volumetric flask. Prepare the mixed indicator by mixing 40.0 ml. of the bromothymol blue solution with 25.0 ml. of the phenol red solution. Use 0.5 ml. of this indicator for each 100 ml. of solution a t the end point. Citromolybdate Solution. SOLUTION A. Dissolve the following reagents in 1360 ml. of water, without heating: 54 grams of ammonium nitrate, 52.6 grams of citric acid, and 68 grams of ammonium molybdate, (r\rH,)&10&.4H20. SOLUTIONB. Dilute 253 ml. of concentrated nitric acid (specific gravity 1.42) with 310 ml. of water. Prepare the citromolybdate solution by pouring solution A into solution B. Clear it as follows: Bdd filter paper pulp or a few drops of diammonium hydrogen phosphate solution, boil for about 5 to 10 minutes, allow to stand overnight; then siphon off the clear solution. (Such a solution remained clear 7 years and is still clear.) Sodium Hydroxide Solution. Prepare a carbonate-free sodium hydroxide solution (approximately 0.3 N ) by diluting a saturated solution of sodium hydroxide with carbon dioxide-free distilled water. Standardize the solution with a Bureau of Standards sample of potassium acid phthalate (4) using_ phenol_ phthalein indicator. Nitric Acid Solution. Standardize the nitric acid solution (approximately 0.1 N ) with the sodium hydroxide solution, using phenolphthalein or the mixed indicator. PROCEDURE
Wet a 1-gram sample of phosphate rock with 15 ml. of water; add 5 ml. of concentrated nitric acid and 10 to 20 ml. of 60 to 70y0 perchloric acid and heat to copious fumes of perchloric acid. Cover the container and boil gently for 20 minutes to dehydrate the silica. Cool somewhat, add 75 ml. of water, heat to boiling, and filter into a 250-ml. volumetric flask. Wash filter with hot dilute nitric acid solution and then with hot water. Add any phosphate remaining in the silica to the original solution after treating it with hvdrofluoric and nitric acids and fusing- it with sodium-carbonate.. To a 25-ml. aliquot of the sample add 80 ml. of the citromolybdate solution. Heat the resultant solution to boiling, keep a t this temperature for 2 or 3 minutes, and filter either hot or cold. By decantation wash the precipitate four or five times with neutral 1% potassium nitrate or cold water, using 20 to 25 ml. for each wash. Transfer the precipitate to the crucible and wash ten
