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VOL. 9, NO. 8
INDUSTRIAL AND ENGINEERING CHEMISTRY
large quantities these gases impart a yellow color to the wash solution which interferes with the matching of the blue color. This interference may be avoided by using, for comparison, a yellow blank obtained by passing the gas over the copper in the cell after the removal of oxygen. If the copper in the cell becomes blackened by it may be ,,leaned by drawing into the cell a dilute solution of nitric acid.
Determination of Dissolved Oxygen For the determination of dissolved oxygen a sample of liquid containing about 0.1 ml. of oxygen is drawn directly into the sampling tube on top of the mercury. The analysis cell is filled with wash solution up to stopcock 10, which is then closed, 6 is opened, and the sample is passed through the flooded cell at a rate of 10 ml. per minute. The mixture of water and wash solution is caught in a Nessler tube at 5, and made up t o 100 ml. with wash solution
which is used t o rinse the cell after the sample has been passed.
Bx,m:i;e“”c”,Ra~~B
s&&,’$t~~~$~~ with fresh wash solution. The blank solution used for comparison should contain a volume of water equal to that of the sample, in order t o keep the concentration of the solutions nearly the same, In calculating results, the same conversion factor is used as for the gaseous samples. The method is obviously not applicable t o strongly acid liquid samples.
Literature Cited (1) Badger, W.L.,J. IND.EEQ.CHEM.,12, 161 (1920). (2) Haehnel and Mugdan, 2. angew. Chem., 33,35 (1920). (3) Hempel, “Gasanalytisohe Methoden,” p. 142,1900. (4)Van Brunt,J. Am. Chem. Soc., 36, 144 (1914). RBCEIVED May 15, 1937. Part of the work of a research fellowship supported by the Consumers’ G ~ Company S of Toronto.
Graphic Analysis of Hydrocarbon Oils Volume-Physical Constants Relationship Resulting from Successive Extractions with Sulfuric Acid C. H. FISHER ANDABNER EISNER, Pittsburgh Experiment Station, U. S. Bureau of Mines, Pittsburgh, Pa.
S
ULFURIC acid of various concentrations has long been used as a reagent in determining the composition of hydrocarbon oils, such as gasoline, kerosene, and neutral oils from coal-tar distillates. Although differing in details, most of these procedures (4, 9) employ two concentrations of sulfuric acid and follow the outline given below. Extraction of the oil with the acid of lower concentration (usually 80 to 92 per cent), followed by distillation to remove olefin polymers, is recommended for the estimation of unsaturated hydrocarbons. The distillate obtained in this manner is taken as olefin-free oil and used in the second stage of the analysis. Aromatic hydrocarbons usually are determined in the olefinfree oil by sulfuric acid of higher concentration (96 to 100 per cent and fuming acid are recommended), the oil not removed as water-soluble sulfonic acids being considered as saturated hydrocarbons. Although this procedure for analyzing hydrocarbon oils has been studied and used extensively, it is generally agreed that methods of this kind are not very satisfactory. Since attempts to devise improved modifications of the analytical procedure described above have been disappointing, it appeared that a study directed to methods of another type might be profitable. The graphic method of characterizing hydrocarbon oils described in the present paper, developed during a recent investigation (2) of sulfuric acid extraction methods of determining olefins and aromatics, is a departure from the usual type of sulfuric acid method and has several interesting advantages. The new method is based on the changes in physical constants that accompany the stepwise removal of olefins and aromatics, as effected by successive extractions with several sulfuric acid solutions. As is shown below, a hydrogenated-coal distillate and two synthetic solutions were analyzed more accurately and characterized more completely by this method than by several methods of the older type.
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the preparation of synthetic solutions were purified by washing with sulfuric acid and distillation. Hydrocarbons available in good grades were used as purchased. Diamylene (commercial grade) was purified by distillation through a sixball Snyder column, only the middle fraction being retained. This left in the diamylene an impurity which could be removed by washing with 80 per cent sulfuric acid. Bromine number determinations, as carried out by Francis (S),were made to ascertain the purity of most of the olefins. Details of the Morrell-Levine (IO), Towne ( l a ) ,and KesterPohle (6) methods used to analyze the synthetic solutions of Table I1 may be obtained from the original articles. Procedures not previously reported are described in appropriate places in the text.
Materials and Procedure I n most cases the concentrated sulfuric acid solutions were analyzed by titration, the more dilute acid solutions by the specific gravity method. Some of the hydrocarbons used in
Volume of residual oil, cubic centimeters
FIGURE 1. PHYSICAL CONSTANTS AND VOLUMEOF RESIDUAL. OIL (HYDROGENATED COALDISTILLATE)
AUGUST 15, 1937
ANALYTICAL EDITION
361
Characterization of Oils by the Volume-Physical Constants Relationship The method developed in the present work consists in washing the oil successively with sulfuric acid solutions of increasing concentration and determining each time the volume, specific gravity, and refractive index of the unsulfonated oil. The olefin and aromatic contents are then ascertained by plotting volumes of residual oil against the corresponding physical constants. The behavior of the oil and the changes in physical constants during these washings with sulfuric acid are as follows: Treatment initially with dilute sulfuric acid and later with acid of higher concentration removes olefins and aromatics progressively, the olefins being first extracted. As the olefins are removed the concentration of aromatics in the residual oil is increased and, as a result, the physical constants (specific gravity and refractive index) observed are higher. The maximum values are reached a t the stage of compbh removal of olefins (some unreactive olefins may be present) and incipient extraction of aromatics. The volume loss occurring to the point of maximum physical constants Is taken as the olefin content. CONSTANTS OF RESIDUAL OIL FROM SULTABLE I, PHYSICAL FONATION OF HYDROGENATED-COAL DISTILLATE Concentration of Yolume Residualof
H1S04 %
Oil
Bp, Gr. a t
15.5' C.
Refractive Index a t 15.5' C.
Refractivitv SDecific Intercept,- Refraction,
, - -d2
c
l
d
FIGURE2. VOLUME,SPECIFICREFRACTION, AND REFRACINTERCEPT OF RESIDUAL OIL (HYDROGENATED COAL DISTILLATE)
TIVITY
Cc.
(Original oil) 100 75 95 5 77 94 5 80 93 5 92 0 82 91 0 84 5 87 89 0 83 5 90 93 67 0 19 0 96 9a 17 Q
Volume of residual oil cubic centimeters
0 941 0 938
0 0 0 0 0 0 0 0 0
936 938 938 938 939 940 937 $34
827
1 1 1 1 1 1 1 1 1 1 1
5335 5340 5325 5340 5330 5340 5333 5309 5248 4624 4555
1.063 1.065 1.065 1.065 1.064 1.065 1.064 1.061 1.056 1.045 1.042
0.567 0.569 0.569 0.569 0.569 0.569 0.568 0.565 0.560 0.554 0.551
I n the second stage of the analysis the sulfuric acid of higher concentration removes the aromatics, causing the physical constants to fall until the removal of aromatics is complete, when the constants observed are those of the residual naphthenes and paraffins. Treatment with strong sulfuric acid beyond this point has not been studied extensively, but it is known that the volume of oil and physical constants are little changed by further treatment unless the reagent is fuming sulfuric acid. The aromatic content of the
