Photoelectric Colorimeter for Measuring Color Intensities of Liquid Petroleum Products B. W. STORYAND V. A. KALICHEVSKY Research and Development Laboratories, Socony-Vacuum Corporation, Paulsboro, N. J.
I
Commercial colorimeters for measuring the adopted in the petroleum induscolor of petroleum products depend on visually try. However, a photoelectric it is necessary to measure cell has recently been put on the what matching the unknown with some standard market (photronic cell, model L‘color” of is various oils, both the for purposes of controlling refinery scale Of As the standards match 594, m a n u f a c t u r e d by t h e operations and for the final prothe unknown with respect to all the attributes Weston E l e c t r i c I n s t r u m e n t duction of oils sold under a color of color-hue, saturation, and bri1liance-a Co.), which combines to a respecification. Many m e t h o d s large personal equation is introduced, which markable degree the characterishave been proposed for color tics required to evaluate color leads lo erratic results. A simple photoelectric sensation or, accurately measurement and several are used for this purpose. Most of colorimeter been constructed which Cornspeakhg, brilliance. The most them are based on visual sensapletely removes the human equation and still important consideration here is grades the colors closely in accordance with northat the relative sensitivity for tion wherein the attempt is made mal visual sensation. petroleum re$ning operahue should beapproximatelythe to m a t c h the color of the oil same as the human eye. Figure with possibly tions involving the measurement of color may illustrates the r e m a r k a b l e with aLI. s o l u t iglass, o n of oriodine or other colored substance. The now be studied more Precisely because of the similarity for this cell and the oil is then given a color v a l u e greater accuracy of this method. normal eye. This means that, regardless of the spectral disin terms of the scale of colored glasses or solution strength which seems most closely to match tribution of the light transmitted by two substances, if the it. These values are arbitrary, depending on the method. eye perceives one to be darker than the other, the cell will In use, such methods are simple and rapid but generally in- grade them in the same ordez. The somewhat higher senaccurate, because the oil rarely matches the colored glass or sitivity in the region of 4500 A. will, of course, cause the cell solution with respect to the three recognized factors in color to grade certain light-colored oils slightly different from the sensation-hue, saturation, and brilliance. Hence the re- eye, but for practical purposes this is not serious with pesult reported depends to a considerable extent on which troleum oils. Darker oils have little or no transmittance in of the three components of color sensation has the greatest this region, so that what appears to be a substantial difference in response is in reality of small consequence with most appeal to the operator. Petroleum products vary from water-white to black, pass- of the petroleum products. ing through various shades of yellow, orange, and red. No This photoelectric cell possesses other characteristics which definite absorption bands appear in the visible spectrum. I n greatly simplify its adoption to color measurement. It passing from water-white, the first loss of transmittance ap- generates its own current in amounts sufficient to be measured pears in the violet, which, as the color increases, moves pro- directly, the output being about 1.4 microamperes per footgressively toward the red. When the per cent transmittance candle. Its response is quick and it stabilizes rapidly without is plotted against the wave length of the light, the slope of fatigue. It is small, rugged, and inexpensive. the curve is not very steep as compared to similar curves for One of the essential features in a colorimeter is the repromany of the dyes. An oil may or may not approach 100 ducibility of the results obtained. Not only should a single per cent transmittance a t the longer wave lengths, depending instrument reproduce itself, but for its wide applicability it on its source and refinement, and the slope may vary for the must give concordant results with all others of the same type. same reasons. It is evident, then, that for equal brilliance, According to the claims of the manufacturers of the above oils may vary considerably in hue and saturation. For photoelectric cells, the spectral response curve of the cells this reason it has been practically impossible to measure can be reproduced within 1 per cent of the average, which is color visually as a single value representing sensation with more than sufficient for practical color measurements. The any accuracy, because different operators do not react the results obtained in the authors’ laboratories with different same to variations in hue and saturation, nor does a good photoelectric cells of the kind described are in substantial solution of the problem seem probable as long as there is a agreement with these claims. personal equation in the determination. Therefore, the If a light source of suitable and uniform intensity is placed measurement of color of petroleum oils in the past has in reality a t a short distance from a photoelectric cell, the cell will been an attempt to measure brilliance, which was then ar- generate some current. If the intensity of the light falling bitrarily converted to a so-called “color” scale. on the cell is changed by increasing or decreasing the distance between the cell and the lamp, the current will be respectively PHOTOELECTRIC CELL less or greater. If the light remains stationary but a glass The photoelectric cell has often been proposed as a means cell containing oil or some other transparent colored subof eliminating the personal equation, but for various reasons stance is introduced between the photoelectric cell and the no practical method based on use of such a cell has been light, the current will decrease because some light will be N THE petroleum industry
*
214
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 15,1933
reflected and absorbed by the glass cell and its contents. If now the lamp is brought nearer to the photoelectric cell, the current generated can again be brought to its original value and the quantity of light absorbed by the glass cell and its contents can then be evaluated in terms of the distance it was necessary to move the light to attain the desired effect. I00
1;
60
E2 Jo30 40
I n setting up the colorimeter, the photoelectric cell was made stationary and attached to the frame of the instrument. The oil cell was fastened directly in front of the photoelectric cell, also in a fixed position. The lamp was made movable, in order to vary a t will the intensity of light falling on the oil cell. A special shield was provided in front of the photoelectric and oil cells, to eliminate the possibility of errors due to the reflection of light from the walls of the room or from the nearby objects. In later designs, it was found preferable to make the lamp stationary and the cells movable and to enclose the whole instrument in a light-proof cover.
OPERATIONOF COLORIMETER
;a
In operating the instrument, the oil cell is first filled with a medicinal or similar oil of 30+ Saybolt color. The lamp WAVE LENGTH (6ffiSTRbMJ) is placed at its maximum distance from the photoelectric cell, which was originally 100 cm. but shortened to 50 cm. in FIGURE1. SPECTRAL RESPONSEOF WESTON PHOTRONIC PHOTOELECTRIC CELL later designs. By properly adjusting the depth of the oil cell, this shortening was accomplished without decreasing the The discussion above shows that the color of the oil, as working range of the colorimeter. The reading of the measured by the photoelectric cell, might be expressed either microammeter connected to the photoelectric cell is then as a function of the current with a stationary source of light, taken and is used as the standard reading. This reading or as a function of the distance, if the light is movable. The includes compensations for variations in sensitivity of diflatter arrangement was preferred in constructing the colorime- ferent photoelectric cells, lamps, or ammeters and also for ter, as it does not require a calibrated microammeter, and as reflections at the glass-air and glass-oil interfaces. Theoit permits compensations for slight changes in the sensitivity retically, this last compensation is altered somewhat by the of different photoelectric cells, lamps, or ammeters. intensity of the light falling on the cell and therefore varies with the position of the lamp. However, in practice this is SET-UPOF COLORIMETER of no importance. The amount is small and it cancels out The colorimeter, which has been successfully used in the in the final results because they are comparative and not abauthors’ laboratories for a number of months, is shown dia- solute. grammatically in Figure 2. It consists essentially of a photoAfter obtaining the standard microammeter reading, the electric cell connected with a microammeter, an oil cell, and oil cell is filled with oil of unknown color. The lamp is a uniform source of light. The photoelectric cell has already then moved towards the cell until the microammeter gives been discussed, and does not require further description. a reading equal to the standard. The distance between The oil cell is 5.2 mm. in depth and 50 mm. in diameter. the photoelectric cell and the lamp is determined and taken as The diameter is immaterial, providing it completely covers the measure of the color intensity of the unknown oil. the face of the photronic cell. While the depth may be varied It is evident that the “color” indicated by the photoelectric also, a standard depth must be established eventually in order colorimeter is in reality not the measure of the color or hue to provide complete agreement with different instruments on of the oil but the measure of its brilliance. Brilliance is deall oils. fined as that attribute of color in respect to which it may be The light source is a 100-watt, 115-volt Mazda projection classed as equivalent to some number of a series of grays lamp, manufactured by the General Electric Company. ranging between black and white, and, therefore, the photoDeviations from the above specifications are allowable with- electric colorimeter is capable of grading the oils only into out greatly changing the results, provided the spectral energy darker and lighter ones as they appear to the eye. This candistribution of the light source remains about the same. not be accomplished successfully by the present methods Theoretically, the spectral energy distribution of daylight is of measuring the color of oils. An oil which appears darker d e s i r a b l e in a light to the eye-will also be MICROAMHETEA source for color work. graded darker b y t h e CELL However, it was found p h o t o e l e c t r i c color0 1 ~ CELL tjOLDLR experimentally that the i m e t e r but not necesabove-named lamp sarily so by the other answers the p r a c t i c a1 t y p e s of colorimeters requirements. It does now in use. not show any appreciT h e i n t e n s i t y of able loss in i n t e n s i t y illumination is inversely when operated at 105 p r o p o r t i o n a l to the volts, even after several square of the distance months of service, and from the point source different lamps of the of light. In order to same type give color verify how closely the readings which closely photoelectric colorimeagree a m o n g t h e m ter follows this law, selves. It is essential, a flicker-wheel was inhowever, to o p e r a t e troduced between the the lamp a t a constant lamp and t h e p h o t o v o l t a g e (105-volt electric cell. The oil current is employed) to cell was filled in these insure uniform results. e x p e r i m e n t s with a FIGURE2. PROTOELECTRIC COLORIMETER IO 0 tooo
.
215
XXD
4w0
sow
6000
moo
Born
-
ANALYTICAL EDITION
216
medicinal clear oil, although it was found that the readings which were obtained in presence or absence of the oil cell were identical, provided the standard ammeter readings were properly adjusted. Table I shows a very good agreement between the calculated and experimental values. The agreement is believed to be within the limits of the experimental error involved in these measurements and more 5
IO
COLOR
INTfNWY
SO
IW
Vol. 5, No. 3
ciprocal brilliance. I n practice this is easily accomplished by reversing the scale of the colorimeter and placing the one hundred and not the zero point a t the photoelectric cell. The resulting scale, which is designated as the color intensity scale, is shown on Figure 3. It is evident that it bears the same simple relationship to the distance as the brilliance scale and is also plotted as a straight line on double logarithmic paper, because the only difference introduced in the above formula is the substitution of (100 - D ) z for D2. In order t o express the color intensities in some convenient units, the color intensity corresponding to the theoretical position of the lamp in direct contact with the photoelectr?~cell was assigned a value of 1000. TABLE11. COLORINTENSITIES OF IODIXE-POTASSIUM IODIDE SOLUTIONS"
u
E 210
(Solutions contain potassium iodide double by weight of iodine) DISTANCE FROM LAMPTO PHOTRONIC IODINE CONCENTRATION CELL
w
Mg./lO cc.
1.60 3.20 3.40 4.48 6.50 10.05 13.0
Cm.
93.0 90.5 90.8 88.5 85.0
83.0 80.2 79.5 78.5 FIGURE 3. CALIBRATION OF PHOTOELECTRIC COLORIMETER 50.0 61.7 WITH FLICKER WHEELS 60.0 59.2 2 10 41.5 281 37.0 than sufficient for practical purposes. It has also been found 282 38.2 305 36.7 that the variation of the correction factor for the reflection of 581 29.4. 663 28.4 light from the oil-glass and glass-air interfaces a t various dis1270 23.0 tances of the lamp from the photoelectric cell is too small to be a Specific gravity of these solutions is fairly closely represented by the formula: S = 0.997 0.00023121, where S = sp. gr. at 25' C . and I = of importance and can, therefore, be neglected. iodine concentration in milligrams per 10 cc. of solution. I
COLOR I N T E N l l N
13.8 15.0
+
TABLEI. THEORETICAL AND EXPERIMENTALLY DETERMINED An attempt was made to calibrate the photoelectric DISTANCES OF THE PHOTOELECTRIC COLORIMETER CORRE- colorimeter in terms of iodine solutions of known concentraSPONDING TO EQUAL TRANSMITTANCES OF LIGHT tions. Solutions containing iodine and double its amount by LIQATTRANSMITTED DISTANCE (Measured by flicker-wheel) Calculated Observed weight of potassium iodide were used. Iodine was se% Cm. Cm. lected, as the iodine colors are more or less familiar to pe100.0 100.0 troleum chemists and as this substance is easily obtained in 93.6 94.8 '
89.4 83.7 77.5 70.7 67.1 63.2 59.2 54.8 50.0 44.7 38.7 31.6 24.5 20.0 14.1
87.7 81.8 75.7 69.0 65.2 61.0 57.2 53.0 47.8 43.5 37.0 30.3 24.0 19.5 14.0
On the basis of these findings it is simple to calibrate the instrument in terms of visual brilliance, by taking the square of the distance between the photoelectric cell and the position of the lamp a t the point a t which the reading is taken. For this purpose, however, the distance should be expressed as a per cent of the maximum distance of the lamp from the photoelectric cell. It is therefore preferable to divide this maximum distance into one hundred equal parts instead of measuring it in generally accepted units of length, such as centimeters, inches, etc. The resulting equation connecting the distance D and brilliance B B = AD4 (where A is a constant depending on the units chosen for expressing brilliance or distance) can be easily expressed graphically as a straight line on double logarithmic paper. The calibration of the instrument on the basis of the above scale, which might be designated as the brilliance scale, is not suitable for industrial use, as refinery men are generally accustomed to speak of the color of the oil and not its re-
MITbWE FROM PdDTOfLfCTRIL CELL TO L l ( m l YXRCL
CM.
II I 1 l l l l l l l l l l l I I I I I I I o IO zo w 40 M m m 8o 9o Nal Di5TANlrE FROM PHOTOLLLLTRI~E L L TO LlbHT S O W
CM.
CALIBRATION OF PHOTOELECTRIC COLORIMETER WITH IODINESOLUTIONS
FIGURE%'%.
(2:l ratio of KI t o 12 in solution)
pure state. The strength of diluted solutions was ascertained by titration with sodium thiosulfate, according to the standard analytical method, The calibration curve for the colorimeter is shown in Figure 4. From the shape of this calibration curve, it is apparent that the color intensities of iodine solutions cannot be proportional to iodine concentrations throughout the whole experimental
May 15, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
range (1, 6,3, 6). It is of interest, however, that for the major portion of the curve the logarithms of iodine concentrations are a straight-line function of distances to which the lamp must be moved to obtain the standard ammeter readings. Because of the questionable value of the iodine colors as indicators of the color intensities of petroleum oils, no further work along these lines has been done. The change in the color intensity of oils on diluting them with benzene was investigated in order to determine the additive character of the proposed scale. The experimental data presented in Table I11 include also the Lovibond colors and the “true” colors (4) of the same diluted samples. The Lovibond colors were taken by several experienced operators and are given as average readings in order to obtain their best possible approximation. It is believed that the color intensities of diluted solutions obtained by means of the photoelectric colorimeter are as additive as might be expected theoretically, being superior in this respect to many other color scales now in use, but still unsatisfactory. TABLE111. COLORS OF LUBRICATING OIL SOLUTIONS IN BENZENE LOVIBOND COLOR 500 IODINECOLORAMBER SERIES TRUE INTENSITY 0.25-IN. CELL COLOR
VOLUMX OF STOCK IN BENZENE SOLUTION
%
COLOR INTENSITY
Mg./10 cc. 1.
MTD-CONTIXENT CYLINDER STOCK (TREATED)
405 245 130 62
28 12 2.
122 41 16.6 7.8 3.3
100
50 25 12.5 6.25 a.
4.
220 120 59 29 15
325 145 61 29 15
250 125 52 22 10
P E N N S Y L V A N I A CYLINDER STOCK (PERCOLATED)
357 113 41 18.3 9.0 3.7
100 50 25 12.5 6.25 3.125 100 50 25 12.5
COABTAL CYLINDER STOCK (TREATED)
350 210 120 61 34
13
660 305 145 63 34 13
425 245 125 59 26 11
PENNSYLVANIA CYLINDER STOCK (PERCOLATED)
22.8 12.9 6.5 3.4
112 64 40 22
125 68 40 22
74 38 19 10
In making dilutions it has been found that the same color intensities of diluted samples are obtained, irrespective of whether benzene or a “colorless” medicinal oil was used as diluent . The proposed method for evaluating colors of lubricating oils is a means of measuring only the color intensity and does not take into consideration other attributes of color-i. e., hue and saturation. The determination of these attributes, particularly the hue of the oil, might be possible by means of the same photoelectric colorimeter but equipped with color filters. The information now available on this subject is not sufficient, however, to warrant its further discussion. The 5.2-mm. oil cell has been used almost entirely in the development work with this colorimeter. For all oils which are darker than a bright yellow (2 NPA), a cell of this thickness is very satisfactory. As the trend is now toward lighter colored oils, the use of a thicker oil cell is desirable in order to obtain greater precision in these oils. Therefore, the use of one-inch cell and a shorter working distance (50 cm.) has been adopted for the new design. These changes do not affect the principles or operation of the instrument except that dilution of very dark oils may be required. This is considered to be justified in view of the greater precision throughout most of the scale and especially with pale yellow oils below 2 NPA.
217
ACKXOWLEDGMENT The authors wish to thank W. V. Betts of this laboratory for malting some of the measurements included in this paper. LITERATURE CITED (1) Dossios and Weith, 2. Chem., 1869,379. (2) Jakovkin, 2. p h y s i k . Chem., 13,539 (1894); 20, 19 (1896). (3) Koyes and Seidensticker, I b i d . , 27, 357 (1898). (4) Parsons and Wilson, J. IND. ENG.CHEM.,14,269, 1169 (1922). (5) Roloff, 2.physik. Chem., 13,327 (1894).
RECEIVED February 1, 1933. Presented before the Division of Petroleum C h e m i s t r y at the 85th Meeting of the A m e r i c a n Chemical Society, Washington, D. C . , March 26 t o 31, 1933.
Device for Removing Frozen Glass Stoppers from Reagent Bottles CHARLESWIRTH,I11 Research and Development Laboratories, Universal Oil Products Company, Riverside, Ill.
A
N EFFICIEKT stopcock key remover (1) has recently
been described which possesses many novel and desirable features. With a small and readily available addition to this device, it may be made to serve as an excellent means for the removal of “frozen” glass stoppers from reagent bottles. The necessity for such an instrument is apparent. ‘Its value is emphasized in the handling of bottles containing such chemicals as bromine, fuming sulfuric acid, etc. The addition is shown in Figures 1 and 2 and consists of a U-shaped bar, A , which fits under the jack screw, C, and rests upon the outer edges of the bottle o p e n i n g . The jaws (B-R) fit a r o u n d the head of the stopper and are adjusted by the k n u r l e d nut, D, to accommodate stoppers of various sizes. P r e s s u r e is a p p l i e d u p w a r d u p o n the head of the stopper by the downward force of the
FIGURE2
FIGURE1
jack screw upon the bar, A . The stopper is then lifted from the bottle. LITERATURE CITED (1) Bailey,
H. W., IND.EXG.CHEM.,Anal. Ed., 4, 324 (1932)
KICEIVEDMarch 20, 1933.
