V O L U M E 23, NO. 1 1 , NOVEMBER 1 9 5 1 dithizone will be required for greater quantities of zinc. Do is 0.42 at 620 mp for 0.7 mg. dithkone with a 7-mm. light path. The magnitude of the photometric error for different transmittance values can be seen in Figure 9. The photometric reading error with the instrument employed was found to be 1%. Thus, above 54% transmittance ( 5 my of zinc), the analysis error due to photometry is less than 5%. LITERATURE CITED
Glick, David, J . Natl. C a n c e r l n s t . , 10,321 (1949). Holter, H., and Lpivtrup, S., Compf. rend. trao. lab. Carlsberg,
1703 (7) LinderstrBni-Lang, K., and Holter, H., “Die enaymatische
Histoohemie,” in Bamann, E., and hfyrback, K., “Die Methoden der Fermentforschung,” Leipaig, Thieme, 1940. (8) Malmstrom, B. G., and Glick, D., Ezptl. Cell Research, in press. (9) Ringbom, A., 2.anal. Chem., 115, 332 (1939). (10) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” pp. 72-93, Xew York, 1nt.erscience Publishers, 1944. (11) Schmidt-Sielsen, K., C‘onipt. re7zd. traz. lab. Carlsherg, Skr. chim.,24, 233 (1942). (12) Vallee, B. L., and Gibson, J . G., 11, J . H i d . Chem.. 176, 435 ( 1948). (13) Ihid., p. 445
Sir. chz?n., 27, 27 (1949).
Keilin, D., and Mann, T., Biochem. J . , 34, 1163 (1940). Krugelis, E. J., Compt. rend. Zap. traa. C a d s t e r g , S6r. chim., 27, 273 (1950).
Latta, H., and Hartmann, J. F.,Pvoc. SOC.Ezptl. B i d . M e d . , 74, 436 (1950).
Linderstr@m-Lang,K., and Holter, H., Conipf. r e n d . trar. lab. Ciirlsberg, S b . chin?.,19, 1 (1931).
R E C E I V EApril D 16, 1961. S o . S X I in the series, Studies in Histochemistry. KO.XX appeared in ( 1 ) . Work aldrd by grants from the National Cancer Institute, U. S. Public Health Ser\-ice, and the Research F u n d of the Gradua t e School, University of Minnesota. D a t a in this paper were presented in a thesis submitted by B. 0.Malmstroni t o the Graduate Faculty of t h e Cnirersity of hlinnesota in partial fulfillinent of the requirements lor the degree of doctor of philosophy.
Simplified Semimicro Aniline Point Test JENNIE &I. CHENET Humble Oil and Re$ning Co., Baytown, Tex. aniline point method (6)of test can be of great value in the characterization of hydrocarbon mixtures. This “property” is defined as the minimum equilibrium solut,ion temperature for equal volumes of aniline and sample ( 1 ) . Use of this test on narrow cuts from laboratory superfractionations and on other liquid products from bench scale units has been limited, however, by the rather large amounf of sample (10 ml.) required by the standard ASTM procedure (1). Elimination of the UP? of this inforniat,ive trst on many samples is not desirable and in ansn-rr to this problem a “scaled-doivn” version of an ASTM procedure (2) requiring only 0.2 ml. of sample has been developed. A 20-gage B & S copper-constantan thermocouple with clay separators is substituted for the usual ASTN aniline point’ thermometer; it also serves as a stirrer. The modified technique may be used on any hydrocarbon product for which an aniline point determination is desired, provided that t,he sample is light enough in color t o allow the chance from condition of niiscihilit#yto turbidity to be observed satisfactorily through the test. tube. Observation of the aniline point of slightly darker samples is facilitated h y placing n ~nia11light behind the apparatus, APPARATUS
The apparatus for the modified test is easily constructed and inexpensive (Figure 1).
It consists of a test tube, B , 9 to 10 mm. in outside diameter and 8 to 9 cm. in length, fitted by means of a slit cork, E, into a larger tube, A , about 13 111111. in outside diameter and 10 cm. in length. The ends of the thermocouple wires, which also serve as a manual stirrer, form a ring, I),which is slightly smaller than the inside diameter of the inner test tube. Immediately above the ring the wires form a right-angle bend and are held firmly by means of the clay insulation pipes, C. In the present work, niillivolts of thermocouple output measured on a Leeds & Northrup potentiometer (Catalog No. 8662) were converted to degrees centigrade by use of the Leeds & Northrup table (4). -4reference junction a t 0’ C. waa med. PROCEDURE
Before each series of determinations, the aniline point value is obtained on pure n-heptane by both the standard .46TM procedure (1) and the modified method, using aniline from the same container. Although the difference betxeen results on n-heptane Kith the two methods is usually small, applying this difference as a blank correction to the values from the modified test results in more accurate determinations..
The determination of the aniline point on a given sample calli: first for pipetting precisely equal volumes of dry aniline and sample (about 0.2 in]. each) into the clean dry apparatus, which is clamped on a ring stand. The thermocouple ring is then centered in the apparatus and the outer test tube is slowly heated by use of an open flame. Throughout the operation, the thermocouple ring is lifted and loir-ered by means of the clay pipes, causing a gentle stirring action. Care is taken that the thermocouple is not lifted above the surface of the liquid. The heating and stirring action is continued until complete miscibility is obtained, and then the mixture is allowed to cool dowly but with continued stirring. The potentiometer reading at which the mixture becomes cloudy t’hroughout with complete separation of aniline and sample phases is recorded. This heating and cooling procedure and record of temperature of complete cloudiness are repeated until a constant value is D - Thermocovple LOOP obtained. Not more than 5 cycles are usually required. Figure 1. hpparatue for Semimicrodeterminations of Aniline Point
ACCURACY AND PREClSlON
The accuracy and reproducibility of the small scale method were tested by a series of determinations on compounds of a nominal purity of 95 to 99%, as well ae on a refinew sample. Results on the pure compounds are compared with those given in t,he literature (3) anti those obtained on the same samples by the APT11 method ( 2 )in Table I. Deviations from theoretical Bureau of 1Iines values average about 0.4’ C. high, and deviations from the ASTU procedure average about 0.4” C. high. A maximum deviation from theoretical of 0.9” C. was observed for methylcyclohexanr. Results on t’he pure compounds, on the averagr, check the theoretical and A4STMmethod values ( 1 ) with about the same order of reproducibility ae the other ASTM method (Wj,which has a “reproducibility (different operator and different apparatus)” of ~ k 0 . 4 C.~
,
ANALYTICAL CHEMISTRY
1704 Table I. Aniline Point Results with Small Scale Test for Pure Compounds Results on Substances Literature Used in Study Compound Value (9), ’ C. ASTM 1012-49T Small scale test n-Decanea 77.5 76.4 77.9 n-Heptaneb 69.7 69.4 69.5 Methylcyclohexane b 39.5 40.0 40.4 hlethylcyclopentaneb 33 .O 33.8 33.7 l-octene’l 32.5 32.6 32.7 -4verage deviatjon from theoretical i0.48 Average deviation from ASTh‘f method zk0 44 a Humphrey-Wilkinson, Inc.: minimum purity. 95%. b Phillips Petroleum Co.; minimum purity, 99%.
Table 11. Reproducibility of Aniline Point Results with Small Scale Test Using Methylcyclohexane and a Refinery Sample Determination No: 1 2 3 4 Methylcyclohexane 40.3 40.0 40.4 Refinery sample 2410 76 9 7 7 . 5 7 7 . 1 7 6 : 9
Aiv.,A”, ~
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40.2 77.1
0
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\V.C. Jones for advice and assistance with the experimental arrangement. LITERATURE CITED
Table I1 illustrates the repeatability of the test (same opwatoi and apparatus) for aniline point determinations on methylcyclohexane and on a refinery sample. These results indicate a repeatability similar t o that of the ASTLI method (I)-namely, A 0 . 2 ”c. ACKNOWLEDGMENT
The author wishes t o express her appreciation t o the Humble Oil and Refining Co. for permission to publish this paper and to
( 1 ) .lm. Soc. Testing Materials, “ASTM Standards on Petroleum
Products and Lubricants,” Methods D 611 and D 1012, 235-40, 43i-9 (1950). ( 2 ) Ibtd.. Method D 101249T. ( 3 ) Ball, J. S., U.9. Bur. Mines, Rept. Invest. 3721, 3147 (1943). (4) Leeds & Korthrup, Philadelphia, “Standard Conversion Table 21031 for Thermocouples.” (5) Tiaard, H. T., and Marshall, A. G., J . Soc. Chen. Ind., 40, 20-5T (1921). R L C E ~ EMarch D 31, 1951.
Mineral Analysis with the Flame Photometer SAMUEL B. KNIGHT, W. C. MATHIS, AND J. R. GRAHAM Venable Chemical Laboratory, Cniversity of .\-orth Carolina, Chapel Hill,4. C . E C E S T L Y Biffen ( 1 ) reported the determination of sodium and potassium in refractory materials by means of the flame photometer. The samples were rendered soluble by a calcium carbonate fusion. Blanks were run to correct for the large amount of calcium introduced, and excellent results were obtained. The Bureau of Standards samples reported in this paper were dissolved by fuming down with hydrofluoric and perchloric acids and then diluting to the desired volume, using a modified version of the method of Marvin and Woolaver (6). This method should be faster than the fusion method, and has the advantage of not introducing large amounts of calcium. However, certain silicates are difficult to dissolve in hydrofluoric-perchloric mixtures and the fusion method ( 1 ) is probably of more general application. Of the five samples reported in this paper, only one (opal glass) is r? duplicate of those reported by BifYen (1 ). FLAME PHOTOMETER MEASUREMENTS
ness using overhead heat and a stream of air directed over the surface of the platinum dish. The overhead heating greatly reduced spattering and the air stream saved time. Some samples re uired two or three evaporations for complete solution, and, if Righ in calcium, a final evaporation with perchloric acid only to ensure complete removal of fluoride. Finally, the sample was transferred to a 100-ml. volumetric flask and diluted to the mark. Aliquots of this same 100-ml. portion were diluted to volumes, so that the final sodium or potassium concentrations were about 15 p.p,m., and the calcium concentration was about 30 p.p.m. Dilution to these optimum concentrations often requires a preliminary dilution and rough reading on the flame photometer. In order to prepare the known solution necessary for reading the instrument according to methods 3 and 4 above, it is necessary to make first a reading of the unknown by method 1 or 2. This gives the ap rovimate percentages of sodium, potassium, and calcium, Otger analytical data are necessary in order t o add the proper amount of aluminum, magnesium, and other metals that might be present. All reasonable precautions were taken to ensure contaminationfree samples. Reagents were tested for contamination and appropriate corrections made when necessary. Borosilicate glass volumetric flasks were used, and standard solutions were made up frequently. Calibration curves were checked before each set of readings. Calibration curves were made using the best reagent grade obtainable of potassium chloride, sodium chloride, lithium nitrate, and calcium carbonate. I n addition, the synthetic knowns
The flame photometer used in this work was a Perkin-Elmer, Model 52A, which can be read by using the internal standard principle or the direct (or absolute) method. Readings were made on most samples by (1) direct reading; (2) the internal standard method after lithium had been introduced uhtil its concentration in the finaldilutedsamplewas100p.p.m.; (3) direct reading after the instrument had been “zeroed” with a synthetic Table 1. Determination of Sodium known of approximately the same com% Kat0 Found and Percentage Error, Flame Photometer position as that of the unknown, except Data Direct Internal that the substance to be determined was Bureau of Standards Data with standard with omitted; and (4) the internal standard XaD, Direct Internal synthetic synthetic method after the instrument had been Sample R Reading standard knoan known set with a synt>heticknown. 1. Soda feldspar 99 10 73 1 0 . 2 7 i 0 . 1 2 1 0 . 7 1 z t 0 . 1 3 10.57 & 0 . 0 3 1 0 . 8 6 z t 0 . 0 4 2.
Soda-lime glass 128
3.
.4rgillaceous limestone 1-a
EXPERIMENTAL PROCEDURE
One-gram samples were placed in flat bottomed platinum dishes and treated with 15 ml. of 700/, perchloric acid and 10 ml. of 47% hydrofluoric acid. The samples were evaporated t o near dry-
Opal glass 91
(-4.3%) (-0.2%) (-1.5%) (+1.2%) 1 6 . 8 3 15.37 z t O . 3 1 1 6 . 4 9 z t O . 1 3 1 5 . 4 3 3z 0 . 3 6 16.67 i: 0 . 0 8 (-8.7%) (-2.0%) (-8.3%) (-1.5%) 0 . 3 9 0 . 3 8 i 0 . 0 1 0 . 4 1 i: 0 . 0 1 0 . 3 8 i: 0 . 0 1 0 . 3 9 3z 0 . 0 1 (3%) (5%) (3%) (0%) 8 . 4 8 7 . 6 9 z k 0 . 1 0 8 . 3 O i O . 0 5 8.70=kOo.03 8 . 7 6 z k 0 . 0 4 (-9.3%) (-2.1%) (+2.6%) (+3.3%)
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