V O L U M E 27, NO. 12, D E C E M B E R
1955
1869 (3) Handbook of Chemistry and Physics (C. D . Hodgman, editor),
data given on hydrocarbons represent the start toward the analysis of a limited group of metals as they occur in distillate fuels.
30th ed., Chemical Rubber Publ.. Cleveland, Ohio, 194$. (4) Harrison, G. R., ”IIassachusetts Institute of Technolozy Wavelength Tables,” Wiley, Kew York, 1939. ( 5 ) King, W. H., and Priestly, William, Symposium on Flame Photometry, ASTM Spec. Tech. Publ. 116, 97 (1951). (6) Pearse, R. W. B., and Gaydon, A. G., “Identification of Molecular Spectra,” Chapman &- Hall, London, 1950.
LITERATURE CITED (1)
Beckman Instruments, Inc., South Pasadena, Calif., “Detection Limits for Beckman Flame Spectrophotometer,” Data sheet 2 ,
(2)
Gamble, L. IT., and Jones, W. H., Division of Petroleum Chemistry, General Papers. KO.32, p. 5, 126th Afeeting, ACS, New York, N.Y., September 1954.
1952.
RECEIVED for review &lay 26, 1955.
Accepted August 2 0 , 195;.
Spectrographic Determination of Nickel and Vanadium in Petroleum Products by Catalytic Ashing JAMES E. MCEVOY, THOMAS
H. MILLIKEN,
and ANDRE L. JULIARD
Houdry Process Corp., Marcus Hook, Pa.
.4mounts of nickel and vanadium at the level of 0.1 to 1000 p.p.m. can be rapidly determined in petroleum products by cracking the materials in the liquid phase on ground active silica-alumina catalyst. Nickel and vanadium sorbed on the catalyst by this procedure have the same spectro-emission characi eristics as artificial standards prepared by the impregnation of the same support with dilute nickel nitrate and ammonium vanadate solutions. The spectrographic determination is made by blending the ignited support with a chromium oxide-graphite mixture, pelleting the blend, and sparking under controlled conditions. The repeatability of duplicated results is generally better than 2~5944, and the average deviation between catalytic and conventional photometric results, determined on eight different kinds of oils, is within 2Z15%. For concentrations in the range of 10 p.p.m. only 2 to 5 grams of sample are necessary; the ashing process requires approximately 3 hours, and the spectrographic determination of the two elements an additional 1.25 hours.
T
HERE is still a need in the petroleum industry for rapid and reliable methods for the determination of traces of nickel and vanadium in petroleum products. Accurate methods require, as a first step, the concentration of metallic compounds, and their transformation into inorganic products. This is done either by slow combustion (1, 3, 4, 7) or by sulfuric acid charring (5, 6) of the oil, followed by careful ignition of the coke. More reliable results are obtained by the sulfuric acid procedure. However, this concentration process is a slow operation, which can require many days when the sample has a low metal and a high paraffinic content. The ashing process can be accelerated Jvithout the danger of losing metal by volatilization or mechanical entrainment, if the oil is heated with a cracking catalyst of the silica-alumina type m-hich manifests a poiverful adsorbing affinity for nickel and vanadium. Another advantage of this type of ashing is that such a catalyst can also act as an ash collector and a spectrographic buffer for subsequent analysis. Murray and Plagge (7) have already advocated the addition of a small amount of inert material to the oil as an ash collector and as a spectrographic aid in the determination of nickel and vanadium in petroleum products. These authors obtained semiquantitative results by ashing the oil by dry oxidation after the addition of 0.02 weight % of silica or silica-alumina and by analyzing the ash by the rotating sector method. This paper shows that trace amounts of nickel and vanadium in different types of oil can be rapidly determined with reasonable accuracy by ashing the oil with 7 to 50 weight % of silica-
alumina which decomposes the sample catalytically, and by analyzing the ignited product spectrographically. This conclusion is obtained from a comparison of the nickel and vanadium content of a series of petroleum products determined simultaneously by spectrographic analysis after catalytic ashing and by photometric analysis after sulfuric acid ashing of the sample. EQUIPnl E S T
Spectrograph, 1.5-meter ARL grating spectrograph. Excitation source, ARL Multisource unit with a spark-ignited direct current discharge. Densitometer, ARL projection microphotometer. Developing, ARL thermostatic developing machine, and ARL film dryer. Calculator, Dunn-Lowry calculation board. Spectrophotometer, Beckman, Model DU. REAGENTS AND STANDARDS
Reagents are all of analytical grade, conforming to the specifications of the Committee on Analytical Reagents of the AMERICAN CHEMICAL SOCIETY. References to n-ater concerns distilled water, demineralized by ion exchange, to a residual salt content of less than 0.2 p,p.m. Silica-Alumina, very pure synthetic silica-alumina catalyst containing approximately 8770 of silica and 137, of alumina, having an internal surface of approximately 200 square meters per gram. This material is ground in an agate mortar to a fineness comparable to talc. No quantitative amounts of nickel or vanadium were detectable by spectrographic or chemical analysis in this material. Chromic Oxide, prepared by thermal decomposition of chromium nitrate. The nitrate is first fused and dehydrated in a borosilicate glass beaker by slow heating on hot plate. The dry product is then ignited with a blast burner in a porcelain dish for approximately 3 hours. The oxide is cooled in a desiccator and kept in a dry bottle. Graphite Powder, spectrographically pure, suitable for briqueting. Can be prepared by finely grinding spectrographic graphite electrodes with a pencil sharpener reserved for that purpose. Graphite-Internal Standard Mixture. A mixture of 5.000 grams of chromic oxide and 1.000 gram of spectrographic graphite powder is milled in a ball mill with hard ceramic balls for a t least 48 hours. Standard Stock Solutions. KICKELSOLUTION, 0.4055 gram of nickel sesquihydrated nitrate dissolved in 1000 ml of water. The nickel concentration of this solution is theoretically 100.0 mg. per liter. This concentration, checked photometrically by the dimethyl glyoxime method, was found equal to the theoretical value, within the limit of precision of the determination. VANADIU~I SOLUTIOS,0.2296 gram of ammonium vanadate dissolved in 1000 ml. of water. The vanadium concentration of this solution is theoretically 100.0 mg. per liter. This concentration, checked photometrically by the phosphotungstic method, was found equal to the theoretical value, within the limit of precision of t h i s determination. Standard Working Solutions. These solutions are prepared by diluting the standard stock solution with water, just before preparation of the catalyst standards.
ANALYTICAL CHEMISTRY 5 01
0 +
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E
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50
100
MICROGRAMS OF NI/PER GRAM
500
1000
MICROGRAM OF V PER GRAM OF CATALYST
OF CATALYST
Figure 2.
Figure 1. Analytical c u r v e s for nickel
Catalyst Standards. The spectrographic standards are prepared by adding to 10.00 grams of active silica-alumina a known amount of nickel and vanadium from a dilute nickel nitrate and ammonium vanadate solution. The working solutions ale adjusted so that 5 to 10 ml. of solution are added a t one time. The slurry is stirred gently, and evaporated to dryness on a steam bath. Standards of higher concentration are prepared by repeating the impregnation process. After the appropriate amount of metal has been added, the material adhering to the wall of the dish is washed with a small amount of water, and the slurry is stirred and again evaporated to dryness. This wmhin procedure is repeated three times, to ensure even distribution of the elements throughout the standard. After drying the standard is thoroughly ground in an agate mortar and redried a t 105' C. for 2 hours. Pellets for Arcing. The ignited, metal-impregnated catalyst and the mixture of graphite-internal standard are weighed into a I-ounce wide-mouthed screw-cap bottle in the proportions of 1 to 2. Eight '/*-inch stainless steel ball bearings are added to the mixture and the bottle is shaken for 1 minute to obtain a uniform distribution. The mix is pelleted in a small press. The die is 8/16 inch in diameter, and 7/8 inch deep. It is filled with the mix, and pelleted a t a pressure of 3000 pounds er square inch gage. The pellet is inserted in the crater of the Ewer electrode. It is cut flat a t the rim of the crater with a steel razor blade. SPECTROGRAPHIC TECHNIQUE
fnr -3 _"vanadium
Analytical c u r v e s for v a n a d i u m
silica-alumina standards containing known amounts of these metals. Analytical Curves. The analytical curves, represented by Figures 1 and 2, give the relation between the intensity ratios of the nickel or the vanadium line to the reference chromium line, and the amount of metal added to the catalyst, for the two types of excitation conditions. Each experimental point of the curve is the average value of 10 arcings. The repeatability of the intensity ratio of the analytical line t o the chromium-reference line is approximately the same with the standard catalysts and with the oil ash impregnated catalyst. The spread of successive ratio determinations of the same sample can be evaluated from Table I, which gives the average deviation of six arcings. The wave length of the analytical and reference line, and the arcing conditions are given with the analytical curves. These curves cover a range of concentrations from 3 to 700 y of metal per gram of catalyst, and intensity ratios from 0.3 to 1.3. The intensity of the vanadium line 3184.0 A. of Figure 2, marked F , is compared to the chromium line 3445.6 A. by adding a 50 t o 100% split-field filter. PROCEDURE
Excitation and E x p o s u r e High amperage, T y p e A Type of sparking Cauacitance. microfarads 60 Inductance, ' microhenries 480 Discharge a s charge 9: Discharge point control Initiator Low power Resistance, ohms 18 OutDut current, amperes 11 5 Voltaae. volts 330 Off Voltage control 150 cone Upper electrode, 0.242 inch Lower electrode, 0.242 inch 2/16 x 8/16 inch crater 8 G a p mm. Slit b i d t h , microns 30 n Prespark, seconds 20 Exposure, seconds 2 for nickel Filter, transmittance
0.f
L o w amperage, T y p e B
60 480
9: Low power 300 2 2 940 On 15' cone 8/16 X 8/18 inch crater 4 40 0 60 12 for nickel
___ vanadium
A- fnr
Photo raphy. Emulsion, Eastman Spectrum A4nalysisNo. 1, 35-mm. Blm. Development. Kodak D-19, rocked for 3 minutes. Short stop, 57" acetic acid for 10 seconds. Fixing, Eastman rapid x-ray fixer with hardener for 3 minutes. Washing, running water in large reservoir, for 5 minutes. Drying, blower and lamp heater, 1.5 minutes. Calibration. With pure iron spectrum, photographed through a split field, using the two-line method of Churchill ( 8 ) . Densitometry. Transmittance measurements for analytical line pairs are converted into intensity ratios using the calculating board. These ratios are then converted into percentages of nickel or vanadium using analytical curves established from
Sampling. The sample is kept in a glass bottle not more than two thirds filled. I n handling heavy oils, a representative sample is obtained by raising the temDerature of the oil to 70" C.. bv shaking the bottle vigor&sly, and by transferring to a 400-mi. 6eaker anamount of oil large enough for performing a series of catalytic ashing determinations. Duplicate samples are prepared by warming the beaker and stirring the oil thoroughly with a glass rod before the oil is added to the catalyst. Spectrographic Determination. Two procedures are used to coke the oil on the catalyst, the choice being determined by the metallic content and the volatility of the sample. Samples with a nickel or vanadium content greater than 1 p.p.m., or nonvolatile samples with a metal content less than 1 p.p.m,, are directlv blended with the ground catalyst and a small amount of concentrated nitric acid (Blend Procedure). Volatile samples with a nickel or vanadium content below 1 p.p.m. are added dropwise to the hot catalyst (Drop Procedure). Two to 30 grams of oil are blended, by BLENDPROCEDURE. means of a glass stirring rod, with 2 grams of catalyst in a No. 4to 6 porcelain dish, and a volume of concentrated nitric acid equivalent to 0.1 the volume of the oil is added to the blend. The mixture is carefully heated, with stirring, on an air bath, until foaming ceases. If any liquid remains after this treatment, successive 1-ml, portions of concentrated nitric acid are added (not to exceed one fourth of the volume of the sample), while the temperature is progressively raised until all the oil is charred. The temperature is further increased until fuming is completed.
1871
V O L U M E 2 7 , NO, 12, D E C E M B E R 1 9 5 5
sulfuric acid in a large porcelain dish, the coke is reduced to a small volume by slow burning in a Vycor dish, and the reduced product is ignited to (Mid-continent 15% bottom) ash in a platinum dish. Five hundred grams of oil are blended with Nickel Vanadium Intensity Intensity 100 ml. of concentrated sulfuric acid in a 1,5-liter Hh'Oa, Weight ratio, ratio, porcelain dish, covered with another dish of the Date and Ml./Gram Ratio, Ni 3646.31' V3184.0/ same size. The mixture is slowly heated with inOperator Cat. Cat./Oil Cr 3 4 4 5 . W P.p.m. Cr2967.6' P.p.m. termittent stirring to a temperature a t which 0.153 0.85 10.04 12.3 0 . 8 5 i0 . 0 6 9 . 1 5/24/55 A 0.0 heavy white fumes are evolved. This heating 0 . 7 7 k 0.04 1 2 . 1 0 . 8 5 i0 . 0 6 9 . 4 0.171 5/24/55 a 0.0 process requires 4 to 5 hours. Two hundred and 0.189 1.14 k 0 . 0 7 14.1 0 . 3 8 10.05 5 . 1 0.0 2/7/55 B 0.247 0 . 9 0 10 . 0 5 1 3 . 1 0.37 1 0 . 0 4 6.2 1/4/55 C 1.0 fifty milliliters of concentrated sulfuric acid are 0,303 0.75 1 0 . 0 5 12.1 0 . 3 9 i0 . 0 2 8 . 2 1.0 1/17/55 C added in 50-ml. portions, at 1-hour intervals. 1.54 k 0.05 13.6 0.69 1 0 . 0 5 7 . 3 0.119 2.0 1/4/55 C The mixture is kept at the same temperature as 0.154 1.20 k 0.06 12.5 0..58 1 0 . 0 4 7 . 7 1/17/55 C 2.0 0 . 2 3 2 0 . 9 5 0 . 3 8 =+ 0 . 0 6 1 3 . 5 f 0 . 0 2 6 . 0 12/20/54 C 2.5 long as the oil is not completely charred. If com0.244 1 . 0 0 10 . 0 6 1 4 . 9 0.41 f0.02 7 . 2 12/20/54 C 2.5 plete coking is not achieved after 24 hours, 50 ml. 1 3 . 1 zt 1 . 0 7 . 3 zt 1 . 4 Average value of spectrographic determinations b more of concentrated sulfuric are added. When 1 1 . 7 zt 0 . 5 6 . 0 f0.6 Average value of photometric determinations the oil is completely coked, the temperature is Deviations of ratios are average deviatittn. ii1i.n~:ir.d from six arcinzq. gradually raised to get rid of the excess sulfuric b Deviations oi avtrnge values are calculated fron. ?in+ deteriiiinations. acid. The dry coke is transferred to a 350-ml. Vycor dish, and reduced to a small volume by slow burning on an electric heater a t about 500" C. Table 11. Accelerated Blend Procedure The remaining ash is finally transferred to a 100-ml. platinum (Mid-continent 157, bottom. Weight ratio catalyst/oil = 0.10) dish and ignited for 2 hours at 600' C. After cooling, 2 ml. of Acid Added, hydrofluoric acid and 1 ml. of concentrated sulfuric acid are RII./Gram Catalyst Xi, P.P.hI. V, P.P.11. added to the ash. The liquid is evaporated on a hot plate, to ( 2 7 . 4 ) 6 3 "01, 3 0 get rid of the silica. 12 2 7 1 HUOr 3 . 0 The residual product is fused with sodium carbonate. The Hk01: 3 . 0 + HzSOd,0.3 11.1 6.0 vanadium is leached out of the insoluble carbonates with boiling 12 8 6.6 HISO,, 3 0 12 5 7 . 0 HzSOi, 1 0 . 0 0 water, and the extract is reduced to 50 ml. after being acidified 6 . 6 i0 , s with diluted hydrochloric acid. The leached carbonates are disAverage value, accelerated procedure 12.1 + 0 . 8 7.3 & 1.4 Average value, regular procedure 1 3 . 1 i 1.0 solved in hydrochloric acid. Traces of remaining nickel are ex(from Table I) tracted from the platinum dish by a pyrosulfate fusion, and added to the nickel solution. The nickel solution is also adjusted to 50 ml. Table 111. Yickel and Vanadium Determination by Blend Convenient aliquots of the vanadium and the nickel solution and Drop Procedures are treated according to conventional procedures given by Sandell (8),the nickel being determined as nickelic dimethylglyoxime, and Weight Ni, P.P.M. V , P.P.M. Ratio, Nature of the vanadium as phosphotungstic complex. -4bsorbances are Sample Oil/Cat. Blend Drop Blend Drop measured with the spectrophotometer, using a 1-cm. cell. Table I.
Repeatability and Accuracy of Blend Procedure
Wyoming tar 10 0.71 0.67iO.12 aeparator 0 . 6 7 i0 . 0 4 overhead San Ordo gas 15 0.47 0.63 oil 0 . 4 3 f0.04° a Without acid added to slurry.
1.4
1.6zk0.7 1.6 1 0 . 1
EXPERIMENTAL RESULTS 0.45 0.35"
0.35
The blend procedure can be accelerated by combining the acidcatalyst ashing with a dry oxidation, the blend of the sample with catalyst and concentrated acid is cautiously heated in aVycor dish, while stirring, until foaming ceases and the sludge begins to thicken. It is then rapidly heatedon a hot plate to a temperatureat which the hydrocarbon vapors can be ignited. The temperature is slowly increased to maintain slow combustion. The dry coke is finally oxidized a t 600" C. as in the regular procedure. The accelerated procedure can be successfully performed with concentrated nitric acid, sulfuric acid, or a 1 to 10 mixture of sulfuric and nitric acid. The time devoted to the coking can be reduced with the accelerated procedure from 1.5 hours to 25 minutes. DROPPROCEDURE. Two grams of catalyst, moistened with a few drops of concentrated nitric acid, are heated to approximately 250" C. in a S o . 2 porcelain dish. A volume of 30 to 100 ml. of oil is then added dropwise, a t the rate of approximately 2 drops per second, to the hot catalyst. The temperature is then adjusted, low enough to allow sorption of the oil on the catalyst, and high enough to crack and vaporize it within half a second. Intermittent stirring is an aid to uniform cracking. After coking, the ratalyst is placed in an oven a t 600" C. for about 2 hours to oxidize the carbonaceous residue and to convert the nickel and the vanadium to their oxides. The catalyst is then finely ground in an agate mortar, blended n-ith the graphitechromic oxide mixture as quickly as possible to avoid water absorption, pelleted, and finally arced under the conditions given in the spectrographic section. The weight ratio of oil to catalyst is not too critical. However, this ratio should not be below 1 and above 15 in the blend procedure, nor below 10 and above 50 in the drop procedure. With samples of very low metal content, accurate results can be obtained by repeated additions of oil, after ignition of the coke products a t 600' C. Photometric Determination. The sample is charred with concentrated sulfuric acid according to a procedure similar to that recommended by Milner and others (6). Briefly, the ashing proceeds in three steps: The oil is charred with concentrated
Table I gives the results of repeated analysis of a mid-continent 15% bottom obtained from three operators over a period of 6 months, by using the catalytic ashing method. The experiments were performed n-ith different ratios of catalyst to oil, from 0.1 to 0.3, and with different amounts of nitric acid, from 0 to 2.5 ml. per gram of catalyst. Each intensity ratio is the average value of six arcings. The ratios and the average values of the nickel and vanadium determination are given with their standard deviations. Table I1 gives the nickel and vanadium content of the same sample determined by the accelerated blend procedure, In this table each value corresponds to a single determination. The average values of the nickel and the vanadium are given with their standard deviations. Table I11 gives the nickel and vanadium concentration of two kinds of oil with a low metal content, determined by the blend and the drop procedure. Figures mentioned with a deviation value are the average value of duplicate determinations run simultaneously. Table IV gives the nickel and vanadium content of different types of petroleum products determined spectrographically after catalytic ashing, and photometrically after sulfuric acid ashing. The samples are classified according to their decreasing nickel content. Each result represents the average value of duplicate analyses run simultaneously. DISCUSSION
The reliability of the catalytic clacking method for determining the nickel and vanadium content of petroleum products cannot be directly evaluated from the analysis of synthetic samples, as knowledge of the organometallic components of petroleum products is limited. The reliability can be indirectly evaluated by checking the reproducibility of the results obtained with different types of
1872
ANALYTICAL CHEMISTRY
oil under different ashing conditions, and by comparing the spectrographic Table IV. Nickel and Vanadium Determination by Spectrographic and Photometric Procedures results with the photometric determiWeight nation after sulfuric acid ashing. The Ratio, Oil/Cat. latter analysis is generally accepted as in SpectroKi, P.P.M. v, P.P.hI. graphic reliable (4,6). Piature of Sample Procedure Spectrographlo Photometric Spectrographic Photometric Tables I and I1 show that the nickel Boscan full crude 1 123 i 10 107 k2 1120 1 45 1160 1 3 and vanadium concentration determined South California residuum 1 66.5 1 0 . 4 66 i i 7 28 32.2 10 . 3 by catalytic ashing is not appreciably Tia Juana residuum 2.5 16.0 1 0 . 4 28 =J 71.0 1 1.5 78 I0 Kuwait 65% botaffected by the ratio of catalyst to oil, or 2 toms 17 1 1 12 5 1 0 . 5 35 1 2 30 11 by the amount or the nature of the illid-continmt 14% bottoms (from ” acid added to the slurry. Table I11 blend) 4 9 . 5 1 0.0 12 io 6 7 1 0.0 7.0 k 0 . 3 9.0 1 1.0 shows furthermore that approximately .\lid-continent 15% the same results are obtained by the bott0n.s 2.5 12.2 1 0.4 11.5 rtO.5 4 . 5 =k 0 . 6 5.4 i 0 . 3 011.8 ‘6.0 f 0 . 3 blend and the drop procedures. TTest Texas heavv 6 3.3 i 0.1 4.2 k O . 1 0.80i 0.06 1 . 1 i0 . 1 Table I shows, that with the mid-continent 15% bottom there is an excellent 5 1 . 7 0 1 0.05 1.6 z t O . 1 2.2 i 0 . 2 1.8 1 0.2 agreement between the results obtained 10 0 . 4 0 i 0.05 0 . 3 0 ?c 0 . 0 5 0.85k 0.03 1.1 1 0 . 1 by the spectrographic-catalytic ashing a Dry oxidation ashing. procedure and the conventional photometric-sulfuric ashing procedure. The difference between the results obtained by the two methods, equal to 1.4 p.p.m. for nickel and 1.3 p.p.m. mination of vanadium can easily be affected by the slightest turbidity of the solution. for vanadium, is just a t the maximum limit that can be expected The agreement between the spectrographic and the photofrom the fluctuation of individual determinations. Because of the great retentive capacity of the catalyst for metallic compounds, metric procedures appears even more clearly in Figure 3, which slightly higher results obtained by the catalytic ashing method gives the relationship between the experimental points corresponding to these two procedures for the eight petroleum samples may be a more accurate value of the metal content of the oil. of Table IV. The straight line indicates the position that the points should occupy in a perfect agreement of the two pi ocedures. Statistical computations show that the ratios of the variance of the results obtained by the spectrographic and the photometric methods fluctuate between larger limits than the theoretical expected value, when the variance is calculated from the range between duplicate determinations of the same sample obtained simultaneously with the same method (9). This discrepancy can be due to some random error depending on the nature of the oil, or perhaps to the choice of working curve. Further investigations are being conducted to clarify this point. ACKNOWLEDGMENT
It is a pleasure to acknowledge the contribution of S. Gerald Hindin to the establishment of the technique for determining trace amounts of nickel and vanadium in silica-alumina using chromic oxide as an internal standard; Charles R. MacTntyre in the establishment of the dropping procedure and for the spectrographic work; James A. Crielly and Walter J. Savournin in the chemical analyses, and Jack Grider in the coordination of the analytical work and the review of this paper. The authors also express their thanks to the Houdry Process Corp. for release for publication of the present paper. Figure 3. Relation betweera nickel and vanadium determinations by spectrographic and photometric procedures
LITERATURE CITED (1)
Table IV shows ‘that the agreement between the spectrographic and photometric determination appears also with other kinds of samples, from full crude to tar separator overhead. The results for nickel determined by both methods are in fairly good agreement, with the exception of the Tia Juana Residuum sample. The repeatability of the sulfuric acid ashing analysis of this sample is rather poor. This fact would cast some doubt on the homogeneity of that sample. The vanadium results, obtained by both methods, are also in good agreement. At a low concentration level, below 5 p.p.m., there is a tendency to get slightly lower results with the catalytic ashing procedure. It is possible that the results obtained by sulfuric acid ashing procedure are slightly too high, became a t low concentrations the photometric deter-
Anderson, J. R7.,and Hughes, H. K , ANAL. CHEM.,23, 1 3 5 8
(1951). (2) Churchill, J. R., IND. ENG.CHEM.,AXAL.ED., 16, 653 (1944). (3) Gunn, E. L., and Power, J. M., ANAL.CHEY.,24, 742 (1952). (4) Karchmer, J. H., and Gunn, E. L., Ibid., 24, 1733 (1952). (5) h!Iill~,G. A,, Ind. Eng. Chem., 42, 182 (1950). ( 6 ) hIilner, 0. I., Glass, J. R., Kirchner, J. P., and Yuriok, A. N., ANAL.CHEM., 24, 1728 (1952). (7) Murray, 11. J., and Plagge, H. A., Proc. Am. Petroleum Inst.. 29 M (111), 8 4 (1949).
( 8 ) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” Interscience, New York, 1950. (9) Youden, W. J., “Statistical Methods for Chemists,” Wiley, New
York, 1951. RECZIVED for review J u n e 15, 1955. Accepted September 12, 1955. Division of Refining, American Petroleum Institute, St. Louis, Mo., 1956.
