ANALYTICAL EDITIOhT
280
1'01. 3, No. 3
Application of Oxalic Acid-Uranyl Acetate Actinometer to Measurement of Sunlight Intensity in Connection with Photochemical Changes in Gasoline' . L. C. Beard, Jr., and 0. M. Reiff2 GENERAL LABORATORIES, STANDARD OIL COMPANY OF NEWYORK, 230 PARK AYE.,NEW YORK, N. Y.
A method for determining the stability of gasoline in progresses, a bottle is reof sunlight of varying intensity and at various temperamoved a t intervals and its visible pump bowls has tures is described. This method permits a comparison contents titrated. When the made thelight stability to be made on the stability of gasoline under different titration indicates t h a t t h e of gasoline a matter of conclimatic conditions and at different times of the year, Dump bowl has had the desiderable imDortance. In ad;ired exposure, the color is. dition some iefiners have used the formation of color in gasoline, exposed to sunlight for a defi- taken on the gasoline contained therein. The temperature of nite period of time, as a measure of its color stability under the gasoline is noted at the beginning and end of the test. The titration with permanganate is carried out in the usual ordinary storage conditions in the dark. It is obvious, of course, that the developmeiit of color in manner. The contents of the actinometer bottle are transgasoline during exposure to sunlight is dependent on three ferred t o a beaker together with washings. Twenty-five cubic factors: first, the length of the time of exposure; second, the centimeters of 2 N sulfuric acid are then added and the volintensity of the sunlight; and third, the temperature of the ume brought to 200 cc. with distilled water, heated to 170" F. gasoline during exposure, In the past, little attention has (76.67' C.) and titrated to the usual pink end point. As has been mentioned, it is suggested that a 0.0005 M been paid to the last two factors, and the usual procedure for measuring the sunlight stability of gasoline has been to uranyl acetate solution be used for exposures of 3 to 6 hours expose the gasoline for a definite period of time to bright sun- and a 0.001 M solution for exposures of 3 hours or less. I n light and note the development of color which occurred during no case should the decomposition be carried beyond 100 mg. such exposure, with little regard to the sunlight intensity or of oxalic acid per 25 cc. In Table I is given a comparison between these two solutions. the temperature of the gasoline. I n this paper is described an adaptation of the oxalic acidTable I-Comparison of Uranyl Acetate Solutions of Different Molarity uranyl acetate actinometer (2) suitable for the measurement OXALICACIDDECOMPOSED RATIO: of sunlight intensity in connection with the evaluation of the DURATION OF 0.0005 M 0.001 M 0001 M sunlight stability of gasoline. EXPOSURE soh. soln. 0.0005 JM Hours Mg. Mg. Procedure 11/1 13.86 23.94 1.727
HE i n c r e a s i n g
3
An oxalic acid-uranyl acetate solution is used which has the following composition: 6.30 grams of c. P. oxalic acid (HzCz04.2H20)per liter of solution and 0.2121 gram of c. P. uranyl acetate, UOz.(C2H302)2.2H20,per liter of solution. This solution is 0.0005 M with respect t.;, uranyl acetate, and is generally satisfactory for exposure in bright sunlight up to 6 hours. For exposure of 3 hours or less, the use of a solution 0,001 A4 with respect to uranyl acetate is recommended. The uranyl acetate serves as a sensitizer, causing the decomposition of the oxalic acid in the sunlight. The amount of decomposition is followed by titrating with a standard 0.1 N solution of potassium permanganate. The permanganate solution is standardized by titrating the standard oxalic acid-uranyl acetate solution before exposure to sunlight. Exposure of the test solution is carried out in 4 fluid-ounce soft glass oil-sample bottles containing 25 cc. of the solution and stoppered with cotton plugs. The bottles must be carefully cleaned with chromic acid, rinsed with distilled water, and dried. The titrations are made in duplicate. The uranyl acetate used in the standard solution does not affect the titration with permanganate, nor does it cause decomposition of the oxalic acid when stored in the dark without previous exposure to sunlight. In measuring the sunlight stability of gasoline, a number of bottles containing 25 cc. of the oxalic acid-uranyl acetate solution are placed near the glass pump bowl in such a manner that their exposure t o the sunlight is complete. As the test 'March 17, 1931. Presented before the Division of Petroleum Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind , March 30 t o April 3, 1931. 2 Present address, 412 Greenpoint Ave.. Brooklyn, N. Y. 1 Received
35 28 57.96 74.97
41/2
6
60.48 100.17 134.19
1.714 1.714 1.790
Table I shows that exposures made with one concentration are readily convertible to those made with another concentration. Results
I n Table I1 are given the results of two experiments made a t 77" F. (25" C.) on two samples of gasoline of quite different character, in strong and weak sunlight. Table 11-Discoloration Time of exposure Hours
Saybolt color
0
2 6 12 18
28 261/2 26 22 21
0
25 1@/2
-----
of Gasoline in Sunlight of Different Intensity WEAKLIGHT----Saybolt Oxalic acid color decomposed
_____ STRONOLIGHT--
7
Oxalic acid Time of decomposed exposure Mg. Hours
Mg.
STEAM-REFINED MIDCONTINENT GASOLINE
0.0
10 7 27.1 64 2 83 1
0 2 6 12 18
28 27l/z 26% 26 23
0.0 4 4 15 1 29.6 50 4
VAPOR-PHASE REFINED CRACKED GASOLINE
5
0.0
37.0
0
15
25
181/a
0.0
31.5
From these tests it is seen that in one case three times the exposure was required to get the same discoloration in the gasoline in weak as in strong sunlight, and that the oxalic acid decomposed was approximately the same for the same change in gasoline color. Effect of Temperature
In order to investigate the effect of temperature on the discoloration of gasoline in the sunlight, experiments were made in a special apparatus such that the temperature could be
July 15, 1931
INDUSTRIAL AND ENGINEERING CHEMIXTRY
controlled. This apparatus consisted of a condenser of soft glass having a spiral inner tube through which water of any desired temperature could be circulated. The gasoline was contained in the outer jacket' into which was sealed a thermometer. The gasoline quickly attained and held the temperature of the circulating water. The results of tests on a sample of vapor-phase refined cracked gasoline a t three temperatures are given in Table 111. of T e m p e r a t u r e on Discoloration of Gasoline i n Sunlight COLORAFTER 15 HRS. EXP. TO SUNLIGHTGUM. COLORAFTER AND 24 HRS. STEAMOXALICACID IN 15 HRS. EXP. STORAGE OVEN DECOMPOSED~ TEMP. TO SUN LIGHT^ DARK TEST 0.001 M 0.0005 M
Table 111-Effect
53 77 96 Q
b
2.3 37 21 1gL/2 37 20 18'1'2 3,6 191/2 181/2 37 The gasoline prior to exposure had a color of 25. 15 hours.
20.7 20 7 20.7
From these results it will be observed that for this particular gasoline the effect of temperature on discoloration in the sunlight was not of any great importance. It cannot be assumed, however, that such will be the case for all gasolines. For strictly comparable results, therefore, information relative to the effect of temperature on any gasoline should be obtained before attempting a comparison of sunlight colorstability tests made a t different temperatures. The importance of this in comparing tests made in visible pump bowls in the winter and summer is obvious. Effect of Storage o n Gasoline Exposed to Sunlight Another point of interest in connection with the discoloration of gasoline in the sunlight is that such discoloration when once started continues to get worse during subsequent storage in the dark. I n Table 111 some results indicative of this fact are given, and in Table IV will be found additional
281
data illustrating this point. The three tests were made in sunlight of different intensities. T a b l e IV-Effect of Exposure t o S u n l i g h t Followed by Storage i n Dark on Color of Vapor-Phase Refined Gasoline of 25 Colors COLORAFTER COLOR E X P . AND OXALICACID IMMEDIATELY 24 HRS. STORAGE TEST DURATION DECOMPOSEDAFTER E X P . I N D.4RK 1 2 3
Hours
Mg.
6 .5 5
25.2 17.6 11.3
21 22 24
l8V2 19 20
It is iecogniaed that the distribution of spectral energy of sunlight is highly variable, and that for strictly comparable results filters should be used such that only that portion of the light which is completely absorbed by both the actinometer and gasoline is utilized (1). The accuracy of reading the color on the Saybolt chromometer, however, is not sufficient to justify such a refinement. The following precautions should be observed: The containers for the actinometer solution and for the gasoline should be of the same general character of glass, The actinometer solution should be titrated immediately after exposure, as the decomposition of the oxalic acid progresses to a slight extent in the dark after having been exposed to the sunlight. The color should be taken on the gasoline immediately following exposure or at some specified and constant time thereafter, since the discoloration started in the light continues to occur to some degree in the dark. Tests on the stability of gasoline to sunlight should, when possible, be completed in a single day. When this is not possible or desirable, fresh actinometric solution should be used on the second day and the total exposure be determined by the sum of the amounts of oxalic acid decomposed on the first and second days. ; Literature Cited (1) Leighton and Forbes, J . Am. Chem. Soc., 62, 3139 (1930). (2) Mathews and Dewey, J . Phys. Chem., 17,216 (1913).
All-Glass Steam Distillation Apparatus for Analytical Purposes' Victor E. Wellman THEB. F. GOODRICH COMPANY, AKRON,OHIO
H E necessity of determining precisely small amounts T of aniline present in mixtures of various compositions whose other constituents were non-volatile with steam, led to the development of the one-piece all-Pyrex glass apparatus shown in the accompanying diagram. The steam-distillation flask, B , has a steam inlet, A , sealed into it a little to one side of the true bottom. Flask B is tilted to prevent any froth which may form (as often happens with alkaline solutions) from climbing easily into the Hopkins distillation head, C. The delivery tube from C is sealed to a safety bulb, D , which is placed at the top of the condenser tube, E. The sample is introduced into B by means of a small-stemmed funnel placed in A. I n case the material is a solid, it may be dissolved in some low-boiling solvent, such as alcohol, and introduced in solution form, or may be powdered and flushed into B with water. Steam is then admitted through A , and if necessary the distillation is furnished additional heat from a burner, G. The distillate is collected in any suitable receptacle, such as beaker F , which may be cooled if necessary. In the particular work mentioned above the mixture containing aniline was introduced into the flask, after which an excess of sodium hydroxide solution was admitted through A . The steam-distilled aniline was collected in a beaker of dilute hydrochloric acid. The entire apparatus was 1
Received March 13, 1831.
clamped to one ringstand, making it possible to remove the residue quantitatively from the distillation flask by tilting the stand so that the liquid flowed from A.
A
Diagram of A p p a r a t u s
The apparatus will be found useful in quantitative work particularly, and generally whenever the distillate is of such nature as to prevent the use of corks, metal foil-covered corks, or rubber stoppers in the neck of the distilling flask.
