INDUSTRIAL
AND
ENGINEERING CHEMISTRY
A N A L Y T I C A L E D I T 10 N PL’BLISHED
BY T H E
AMERICAN
CHEMICAL
SOCIETY
HARRISON
E.
HOWE,
EDITOR
Photoelectric Color Description and Mensuration of the Color of Petroleum Products I. RI. DILLERl, R. J. DE GRAY, AND J. W . WILSON, JR. Socony-Vacuum Oil Company, Inc., General Laboratories, Technical Service Division, Brooklyn, N. Y. Photoelectric color is a new system for the measurement of the color of lubricating oils. The color is measured directly in technologically significant terms. Only two readings are required: brilliance and characterization of the hue. The system uses a photoelectric colorimeter, designed for accuracy and easy standardization for the measurement of oil colors. The colorimeter has a continuous scale from 1 to 100 for the definition of the intensity of such colors. Deviation of hue of petroleum color from normal is given directly in magnitude and direction. The color definition is independent of the visual response of the operator and of the particular instrument. I. C. I. data can be calculated from photoelectric color, if desired. However, this is rarely desirable in petroleum technology. Photoelectric color can be correlated with the Union system. The system is easily learned and its standardization is based on colored solutions which are reproducible, easily prepared, and sensitive.
called abnormal Wmples, when the brilliance or hue of the oil differs from that of the disk. These methods lack any relation to accepted systems of color definition (3, 8, 9, 10, l d , 19, 16, 17, 20), a brief description of which is given by Gardner (79. Another method ~isesthe Tag-Robinson colorimeter (88). This is a combination of the Union and Saybolt methods and involves similar difficulties. The Lovibond system (11) has a theoretical advantage in that it attempts to overcome differences in hue by virtue of aeries in several hues of standard glasses, more closely spaced. In a limited sense the Lovibond system supplies the equivalent of a spectral curve. However, it suffers from the remaining difficulties of the other systems and, indeed, its added complexity results in an aggravation of the instrumental disadvantages to the point where the actual results obtained are far removed from the theoretical possibilities. A more novel method which has been used occasionally in the petroleum industry is known as “true color” (16). Here, an oil or solution of an oil is chosen as standard either arbitrarily or in accordance with its match to a given Lovibond glass. Oils or their solutions are compared with the standard by variation of the thickness of the unknown. Other investigators have pointed out that the standard oil must be similar in color to that being measured, that the diluent introduces anomalies, and that Beer’s law holds for some samples but not for others. Consequently, a general correlation of true color with Union or Lovibond color is almost impossible, and widely varying values have been published (14, 18, 23, 24). An attempt to correct some of the faults of true color was made in the “optical density” method (6),which uses a neutral filter as standard and a green light source. The improvement is not substantial and the technique is further complicated.
T
HE petroleum industry has employed a number of
systems for the measurement and specifications of the color of petroleum products, each of which depends upon a visual matching of the color of the sample with that of a standard. Those systems commonly in use involve arbitrary standardization and cannot be correlated with each other by fundamental means. Furthermore, they afford no practical means for matching both brilliance and hue and, in lighter colors, purity as well-essential factors for a visual match. Two methods in particular use are specified by the American Society for Testing Materials. The Union colorimeter (1) is used for determining the color of lubricating oils, while lightcolored products are measured with the Saybolt chromometer (Z), which bears no relation to the Union colorimeter except that both depend upon a series of yellow disks and in addition the Saybolt color involves variation in depth of sample. These methods have several disadvantages. The instruments themselves are not entirely uniform. The glass standards are difficult of duplication and are subject to temperature changes, and their optical systems are not completely standardized. The disks correspond only to certain selected points in the range of possible oil colors. Anomalous results have been noted on so1
All these systems are subjective and dependent on the observer and to a greater or lesser extent on the spectral selectivity of his eye a t the time of observation. The instruments are difficult t o standardize, different instruments giving different readings to the same observer. Differences in spectral distribution between standard and sample particularly aggravate the difficulties of the subjective observer. Where a thickness is varied as in the Saybolt, Tag-Robinson, true color, and optical density methods, dependence is placed on the applicability of Lambert’s law. Occasionally petroleum products follow Lambert’s law; often, probably because of fluorescence, they do not. The use of a photoelectric colorimeter has the potentiality of eliminating the effects of the subjective color response of individual observers or their equivalents. A step in this direction was proposed by Story and Kalichevsky @I). Their proposal is limited to a single reading, which cannot express fully the color of an oil. Multiple-reading photoelectric colorimeters have been proposed which by the use
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607
608
INDUSTRIAL AND ENGINEERING CHEMISTRY
of either three or four filters yield values that may be related to the various International Commission on Illumination quantities (19). These systems yield the basic color information but in terms which lack immediate significance in petroleum technology. For oil colors they are unnecessarily complex and fail to take advantage of the fortunate fact that the colors of petroleum oils vary only over a limited range. The spectrophotometric curves of petroleum products are substantially smooth, have the same general shape, and invariably show higher transmission as the wave length increases. For any given brilliance, oils of various origins and methods of refining may be represented by a family of curves intersecting in the general region of 545 mp. Some of these curves will show a higher red transmission than others, and a correspondingly lower blue transmission-that is, all oils of a given brilliance have the same transmission at the point of intersection, but some of the curves passing through this point are steeper than others. Thus for any oil, complete characterization can be obtained by measurements of brilliance and of one other transmission at a wave length remote from that of the intersection. This may be at either the red or blue end of the spectrum but for reasons described below, it is made at a certain point in the red region. This paper presents a new system for the mensuration and description of the color of petroleum oils b y means of a specially developed photoelectric colorimeter, so that it is objective, avoids any unnecessary complexity, and is descriptive of the oil color in terms of direct physical significance. The method is simple to handle and permits rapid determination. Provision is made for checking the instrument’s standardization by means of suitable aqueous solutions which may be easily prepared by any chemist. The results are convertible to the standard I. C. I. terminology (10). The system has been correlated with the Union method. A correlation with the Saybolt method is expected to be furnished shortly. Within the limits of experimental error, the system also lends itself readily to being “additive”. The general method here proposed should have broad application in color mensuration, particularly for classes of materials which have smooth, substantially unidirectional spectrophotometric curves of the same general shape. However, the present study concerned itself only with petroleum products. This system has also been applied to fatty products, with a view to Lovibond correlation (5).
Description of Method The method, in its bare essentials, consists in focusing a stable beam of light into the sample which is held in a standard container. The light is modified by a n optical filter and falls on a photoelectric cell. Readings are taken directly from the apparatus scale. One reading is required and a second is optionaL The former is taken with the aid of a filter designated as “North Sky” or, in the case of very light oils, with a filter designated as “Violet”. The second reading is taken with a filter designated as “Red”. These readings can be converted directly, if desired, into I. C. I. values or Union color numbers. The present system measures (1) the brilliance and (2) the steepness of the spectral curve. The first factor expresses the appearance of oil of a given thickness to a standard I. C. I. observer looking at C illuminant; and the second factor is best expressed in terms of the deviation of the steepness of the spectral curve from that of the average or normal at the given intensity. I n this manner a deviation in one direction would show that the oil is greenish and in the other direction t h a t it is reddish, with the magnitude of the figure giving the extent of deviation.
Y
FIGURE 1.
Vol. 14, No. 8
- TRISTIYULUS V A W E
COXVERSION CHART OF NORTH SKY IXGS TO BRILLIANCE
READ-
It is expected that as a result of a future accumulation of data involving this second reading, it will become possible to use it as a refining guide as well as for the evaluation of finished oils. The first of these factors is taken with the North Sky filter This filter was so chosen that the instrument (not the filter) would respond as an average observer looking through the oil at the north sky, but was later modified, as the N. P. A. 8 oil gave too low a reading for practical use. By changing the filter to make the instrument correspond to a standard observer and C illuminant, the entire range of the Union system was best accommodated on the scale without reducing the length of light path through the sample. This intensity or brilliance factor is read on a scale 1 to 100 and the reading is reported in lLphotoelectric units”. The North Sky filter is a broad-band filter, but should n o t be confused with daylight glass. (The North Sky reading would otherwise have differed from the combination of C illuminant and standard observer, in that the former rovided for some near ultraviolet. This is ordinarily regaried as invisible and is therefore discounted. Such disregard is erroneous when it is considered that the eye is not “totally” blind to near ultraviolet light. Some fraction, indeed, a very small fraction, does affect the visual response. On the other hand, the absorption of near ultraviolet by a yellow substance such as oil is great as compared with the absorption of the more visible region, so that while the visual res onse in this region is small, such effect is disproportionately felt5 The second factor is determined with a narrow-band filter on either end of the spectrum. For convenience, the red end is preferred. A t the extreme red end, slight anomalies, otherwise unimportant, may arise, and for this reason the filter was so chosen that the instrument would respond to an average wave length of 610 mp. While “color response” appears to be based primarily on brilliance, the eye is also influenced by the hue or dominant wave length of the oil. For this reason, difficulty is encountered in measuring many oils by the Union colorimeter whose comparison disks are fixed in hue which may differ markedly from that of the sample. In order to express this property, two other parameters such as the X and 2 tristimulus values appear to he necessary. A third filter is provided, designated as V , which causes the instrument to respond to an average wave length of 390 mfi. This filter is suitable for “magnifying” the North Sky reading on the very light oils of the Saybolt range, so that the thickness of the sample does not need to be increased. The spectral range of this filter was particularly chosen so that it could be converted to the equivalent of North Sky reading by the simple equation given below. in position.
The correlation of violet with Saybolt and the handling of petroleum colors in the lighter ranges will be taken up in detail in a future paper, but for the present the authors wish to point out that in the very light range, though not in the darker ranges, readings with one filter are equivalent except
August 15, 1942
609
ANALYTICAL EDITION
for magnitude t o readings on oil with any other filter, narrow or broad. By this method, a continuous color scale has been provided covering the entire range from the equivalent of Union No. 8 to Saybolt +30+.
Experimental THE COLORIMETER.The photoelectric colorimeter developed in the course of this work is based on Diller's (4). One of the features of the optical system of the instrument is that it enables the use of test-tube sample containers Tvithout substantial error resulting from variations in the refractive index of the samples. The filters are arranged so that the effects of oil fluorescence are minimized. The light path is fixed. The lamp is of the prefocused type with a bar-shaped filament, and it is operated from a compensating transformer which supplies a constant voltage. In this manner, changes in spectral distribution of the filament emission are avoided. Such changes cannot be overcome by an attempted balancing of photocells. A single cell of the barrier-layer type is used. The sample container is gripped in a wedge by a scratchproof roller, to maintain further the immobility of the optical system. The calibration has been found to be constant over a period of six years. It is not subject to atmospheric variations or fatigue. The instrument is heavily constructed and its galvanometer is both rapid and damped. The filters are mounted in a roulette with additional provision for miscellaneous filters, so that the instrument can also be used for chemical analysis. The optical path through the sample is approximately 18 mm. The instrument containing the photometric color filters is adjusted and standardized as a complete unit, so that readings are the same on any of the instruments within the tolerance described below. Approximat,ely 1000 samples of oil have been used, representing a wide variety of crude source, and of method of refinement. Many of these samples were carefully chosen t o illustrate extremes of viscosity index and of treating, but the majority were merely chosen at random from the samples passing through the laboratory for routine testing. The preliminary work consisted of measuring fifty oils, using ten narrowband glass filters, with dominant wave length ranging from 390 to 660 mp. REFERENCE STANDARD.For such measurements, the colorimeter must be set to some standard reading. This necessitates the use of a standard reference liquid, preferably as light or lighter in color than any of the samples. Since the range of measurement was to include that covered by the Saybolt chromometer, a generally available water-white liquid of reproducible color was sought. For closest similarity to the samples to be measured, a hydrocarbon solvent was indicated. Xylene, toluene, and mineral spirits of various distillation ranges were studied. The colors were found t o vary appreciably with redistillation, distillation over caustic, acid treatment, clay treatment, etc., and after such treatments, the colors changed on storage. Consequently, a hydrocarbon standard would require carefully specified preparation, a t short time intervals. Distilled water, however, is easily prepared, and is stable and reproducible and was, therefore, chosen as the standard. The colorimeter was set to a scale reading of 100.0 per cent transmission with water in the cell, with any filter in the light path.
NORTHSKYFILTER.Twenty-two oils, of widely varying origins and methods of refinement, were submitted to the Electrical Testing Laboratories for measurement on a Hardy spectrophotometer. The North Sky filter also was measured. The spectrophotometric data were handled by the methods described by Hardy ( 8 ) , using the 30 selected ordinates. The North Sky filter was found t o have the following characteristics: Trichromatic Tristimulus Coefficients Values z = 0.2766 X = 0.3768 Y 0.4502 y = 0.3305 I = 0.3929 2 = 0.5351 Dominant wave length 496 mp 45 .O% Relqtive brightness Excitation purity 11.5%
-
The filter described by these data is for use with a 15-c. p., tungsten bar filament bulb, operating at 3100" K. behind a heat filter. The photocell is of the barrier-layer type and the optical path is shown by Diller (4). It cannot be overemphasized that the instrument must be standardized as a complete unit rather than through standardization of the filter. The procedure for checking the standardization is described below. The tristimulus values calculated from the spectrophotometric curves of the 22 oils are given in Table I, which also indicates the nature of each oil sample, and gives the photoelectric color or Korth Sky reading. Columns R and V are readings obtained n-ith other filters, described below.
TABLE Oil NO.
1 2 3 4
5 6 7 8 9 10 11 12 13 14 15
Xatnre Naphthenic Heavy clay Compounded Pennsylvania Acid,mid-continent Pennsylvania No. 14 +,black oil Naphthenic Solvent-Pennsylvania Acid-naphthenic Solvent, clay Compounded Acid, mid-continent Acid, mid-continent Solvent, mid-conti-
I.
Spectrophotometer E a c h Value X 100 X Y 2 1.7 0.74 0.0 2.3 0.0 1.0 2.4 0.0 1.0 8.3 3.8 0.0 7.4 3.9 0.0 11.6 5.8 0.0 8.4 6.2 0.2 11.1 6.7 0.0 19.3 10.9 0.6
Photoelectric Color R LV.S . V 10.0 1.1 0 13.0 1.9 0 ?.? 0 12.0 33.0 0.3 0.8 27.0 5.0 0.3 42.0 8.0 0.8 26.0 10.0 0.6 34.0 8.5 0.3 14.0 1.1 56.5
34.7 42.9 44.8 52.8 50.7 50.6
30.4 36.2 40.7 47.9 50.0 54.9
0.6 0.4 1.2 1.9 3.8 8.7
70.0 81.0 84.0 89.5 84.0 88.5
35.0 40.0 45.0 52.0 54.0 62.0
0.8 0.9 1.0 2.0 2.0 3.9
65.4 66.3 71.4
72.6 75.0 77.5
10.6 18.8 40.4
97.0 99.0 97.0
76.0 80.0 81.0
3.0 6.5 20.0
78.1
83.8
71.0
100.0
95.0
44.0
75.0
83.9
46.3
100.0
90.0
23.0
88.2 88.4
90.3 90.4
105.5 106.2
101.0 101.0
102.0 102.0
100.0 100.0
nent
16 N i i h i h e n i c 17 Naphthenic 18 Solvent. mid-continent 19 Naphthenic-heavy acid 20 h'a hthenic-heavy CLY
21 22
Kerosene White oil
The I. tristimulus value is identical with relative brightness, or visual efficiency, commonly referred to as brilliance. The spectrophotometric response of the instrument with the North Sky filter in position is similar in shape to the Y stimulus. The Xorth Sky readings mere plotted against the Y values as shown in Figure 1. Photoelectric color is seen to be directly related to Y : Brilliance
=
0.9 X photoelectric color
Distilled water is used as the standard for photoelectric color, whereas brilliance is based on a pure, theoretical white. The brilliance of distilled water is approximately 90 per cent, accounting for the factor 0.9 in the above equation. RED FILTER.Petroleum oils have the peculiar property of varying in the relation between brilliance, hue, and saturation in a substantially fixed manner and only one other parameter-to determine the steepness of the transmission curveis required. The parameter could be similar to either X or Z. The 2 values, as shown in Table I, remain very small until the brilliance exceeds 50 per cent (Union No. Z1/*) while t h e X values are of conveniently measurable magnitude over the entire range with the same liquid stratum used for the North Sky measurement. Consequently, red or orange glasses were preferred. Dyes of various colors were also added to the oils to give products whose colors differed intentionally from those of normal petroleum products. One of the filters of this series was found to be most satisfactory in distinguishing between all of these samples. Oils which were measured had viscosity indices approximating 0 and 100. The spectral absorption of water is reasonably uniform
INDUSTRIAL AND ENGINEERING CHEMISTRY
610
Vol. 14, No. 8
insufficient spread and must be “magnified”. This may be done by a substantial increase in sample depth. However, this would involve other factors such as slight turbidity and fluorescence, which mould lead to error. Another means of magnification of the spread lies in the use of a violet filter which in this range of light colors results in readings parallel to North Sky readings but of greater spread. The latter means is preferable. The filter was prepared so that for kerosenes in t’he Saybolt range the instrument gave exactly 10 times the sensitivity as with the S o r t h Sky filter. This filter is designated as t.he violet filter. The violet filter used has the folloving characteristics : Tristimulus Trichromatic Values Coefficients X = 0.0622 z = 0.1593 Y = 0.0048 y = 0.1023 Z = 0.3226 z = 0.8280 Dominant wave length 446 mp 0 . 48V0 Relative brightness Excitation purity 100%
X- TRISTIMULUS VALUE
FIGURE 2 . COSVERSION CHART OF REDREADINGS TO X
The spectrophotometric curve of the violet filter corresponds roughly to the 2 stimulus, as is shown in Figure 4,
throughout the visible region escept at the extreme red end (greater than 700 mp) where the absorption increases. Thus, in this region of the spectrum, the use of water as the standard results in readings which are higher than the corresponding readings a t 610 mp by too great a difference. The oils theniselves also sometimes exhibit slight absorption peculiarities in this region, so that anonislous results may be obtained. A consideration of these and the other factors led t o a choice of 610 mp as the average response equivalent of the instrument uith the R filter. The characteristics of the particular filter used in order to have an instrument response equivalent to 610 mp is: Tristimulus Values
Trichromatic Coefficients z = 0.6992 ff = 0.3008 = 0.0000 e = 0.0000 Dominant wave length 624 mp Relative brlghtness 4.470 Excitation purity 100%
X 0,1039 Y = 0.0447
z
Readings taken with the instrument when using this filter are shown in Table I under R where the correspondence to X stimulus mag be observed. The red filter readings of Table I were plotted against the respective X values. The resultant curve (Figure 2) shows the relationship of R readings to X values. RELATIOK BETWEEX NORTHSKYASD R READIKGS. Approximately 300 oils have been measured with both the North Sky and red filters, in order to establish the relation between the two readings. Since oils containing blooming or deblooming agents must be excluded from this work, only oils of known origin and treatment were used. This limited the choice of samples. Figure 3 shows this variation, the two lines denoting the widest variation found. It is possible that oils from unusual sources or methods of treatment will be encountered which lie outside this lens; but, it is not to be expected that such samples mill change the essential narrowness of the lens. An average line is drawn through the lens, so that the R readings can be reported as plus or minus deviations from normal. I n general, oils of low viscosity index lie near the lower line. However, the method of refinement also affects the position, acid treatment tending to move the color toward the upper line, and clay treatment toward the lower. VIOLET FILTER.The Saybolt range (-16 to +30+) corresponds t o S o r t h Sky readings of 96 to 100. This is an
I
0 0
IO
[
20
30 40 50 60 70 80 X NORTH SKY TRANSMISSION
!
/
90
100
OF R FIGURE 3. A-ORXILDEVII.IIOS
‘ 0
IO
20
30
40
50
60
70
80
90
100
2- TRlSTlMULUS VALUE
FIGURE 4. COXVERSIOS CHART OF VIOLET RE~DINGS TO Z
August 15, 1942
ANALYTICAL EDITION
T4BLE 11. TRI~TIUULUS VALUES 7-x x 100-7 7-Y x 100--Z
x 10'1PhotoPhotoPhot >Spectral electlrc Spectral electrlc Sample Spectrala electricb 1 1.7 2.1 0.74 0.0 0 0 2 2 3 3.0 1 0 0.0 0.0 3 2.4 z., 1 .I) 1.2 0 0 0 .0 4 8.8 3 8 4.9 0.0 0.0 5 7.8 3 9 4.5 0.0 n.o g 11.6 12.0 5.8 7.2 0 .(I 0.0 8.4 6.2 6 2 9.0 0 2 0.0 11.1 9.0 6.7 7.6 0.0 0.0 12.6 0.6 0.0 10.9 9 19.3 19.5 30.4 31.5 10 34.7 30.0 0. 6 0.0 36.0 0 4 0.0 11 42.9 41.0 36 0 12 44.8 44.5 40.7 40.5 1.31 0 0 47.9 46.8 1.9 0.0 13 52.8 52.5 14 50.7 44.5 50.0 48.6 3,s 0 0 10 0 15 50.6 51.0 54.9 55.8 S., 0 I) 72.6 68.4 16 65.4 67.0 10.6 75.0 16 3 72.0 18.8 17 66.3 65.5 40 4 $.!I 72.9 18 11.4 72.0 77.5 83.8 85.5 71 0 il.0 19 ~ s . 1 79.0 20 13.0 73.0 83.0 46 3 4ij 3 81 0 90.3 21 88.2 88.2 91.8 105 J 103 3 90.4 22 88.4 88.2 91.8 106 2 103.5 .\lean deviation of photoelectric irom spectral + 1.0 a Computed irom H a r d y spectrophotometric curves. b Converted irom readings on photaelectric colorimeter.
:.Y
P.:
k
the spectral curves and from the photoelectric readings. Finally, from z and y, the hue and purity of the oil color may be obtained (Table IV). Table V gives data on the reproducibility of the readings for one of the oils, using spectrophotometric curves and p!mtoelectric readings obtained on the two dates given. The photoelectric colorimeter used in this work is a t least as stable as is the recording spectrophotometer. The above may be summarized as indicating that photoelectric color readings, in conjunction with Figures 1, 2 , and 4 d l yield tristimulus values agreeing with spectrophotometric data to *0.01. trichromatic coefficients t o h0.02,
TABLEIV. BRILLI-~ITCE, HUE,AND PURITY Simple
+ 1
8
8 9 10
11
12 13 14 15
PhotoPhotoPhotoSpectral electric Spectral electric Soectral electric 0.697 0.0 o n 0 .0 0.696 0 0 0.0 0 0 0.706 0 . !I 0 .0 0,686 0.655 0 0 0.0 0.667 0 u 0 . I1 0.569 0.0 0.011 0 624 0 IJ 0.0 0.019 0 627 0 0 0.528 0.009 0.0 0.340 0.005 0 0 0,517 0.0 0.014 0.515 0.018 0.0 0.037 0.0 0.485 0.443 0,076 0.085 0.440 0.0331 0.071 0.414 0.107 0.118 0.377 0.225 0,214 0 305 0 301 0.335 0.226 0.234 0.365 0 371 0.369 0.311 0 369 0.373 0.310 1Iean deviation of photoelectric irom spectral 10.020
9
10
11 14
13 14 13 16 17 1s 19 "0 21 22
= 90
0.74
1 .0 1.7 1.2 4 8 2.7 ,.a 9.0 7.6 12.6 31.5 36 0 40.3 46.8 48.6 55.8 68 4 72.0 72.9 85.5 81 0 92.0 92.0
1 .0
1.0 3.8 3.9 3 8 6.2 6.7 10.9 30.4 36.2 40.7 47.9 50.0 54.9 72.6 75.0 77 5 83 8 83.Y 90.3 90 4
Purity Photoelectric
Spectral 100 100 100 100 100 100 97 100 95 0 96.0 99 0 96.0 96.0 90.0 80.0 82.0 69.0 43.0 18.0 49.0
100 100 100 100 100 100 100 10') 100 100 10'1 100 1011 100 78 84 71.5 40.0 19 0 37.5
1
1
1
TABLEV. COMPARATIVE REPRODCCIBILITY April 30 PhotoSpectral electric Red reading 1..S . reading Vi ,let reading
Y
N . S.
Hue, mp Photoelectric
Spectral
Mean deviation of photoelectric iram spectral 5 nip, 2L'o
s
where the violet filter readings of Table I, column I-, i v x e plotted against the corresponding Z values. RELATIOXSHIP O F I.' BND XORTH SKY READINGS. Khen the S o r t h Sky reading is 96 or higher, the violet filter is used, its reading converted to S o r t h Sky, and the equivalent reading reported as photoelectric color. The violet filter readings on petroleum products are related to the Xorth Sky readings by the following equation:
Brilliance Photoelectric
Spectral
1
2 3
TABLE111. TRICHROMATIC COEFFICIEST~ Sample
61 1
Z z
Y Hue Purity
... ,
..
iii
78 9 40.0 0.378 0.412 573 44
June 20 PhotoSpectral electric
97.0 82.0 20.0 72.0 73.8 42.0 0.383 0.393 577 40
...
97.0 81.0 20 0 72.0 72.9 42.0 0.385 0.390 578 40
... ...
71.4
77.5 40.4 0.377 0.409 573 43
Difference Phot iiSpectral electric
... ... ...
1.0 1.4
0,4 0.001 0.033 0 1
+ 3V
CORRELATION WITH I. C. I. VALCES. To test the accuracy of the smoothed curves shown in Figures 1, 2 , and 4,and of the authors' instrument, the values of X , Y , and 2 corresponding t o the red, S o r t h Sky, and violet readings of Table I were read from them. Table I1 gives a comparison of results from the present colorimeter, and from the spectrophotometer readings. The three photoelectric readings made with the colorimeter used in this work require less than 2 minutes, and X , l-, and 2 are obtained directly from the curves. The spectrophotometric curve using a Hardy spectrophotometer requires about 10 minutes, and the required subsequent calculation of X, I-, and 2 from that curve occupies a minimum of another 30 minutes. For red readings above 97, where Figure 2 flattens, a more accurate graph than Figure 3 was used to find S. From the tristimulus values, the trichromatic coefficients may be calculated. Table I11 shows the results, again from
0
1
2
3 UNION
4
5
6
7
8
COLOR
FIGURE 5 . CONV~RSION CHARTOF NORTH SKYTO UNION
0.0 1.0 0.0 0.0 0.9 0.0 0.002 0.003
1 0
612
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLEVI. COLORS OF UNIONDISKS
National Bureau of Standards representative disks, corrected t o 18-mm. sample depth h-0. Brilliance Hue Purity % mfi 70 1 75.1 57 1 28 65.4 573 59 11 / 1 44.3 2 578 86 582 88 36.5 21/r 585 3 91 28.7 589 94 21.1 31/1 594 98 4 9.6 599 99 6.5 4‘/2 606 3.6 5 100 613 1.7 6 100 617 0.66 7 100 634 0.20 100 8
hue to i.5 mp, purity to *l per cent, and brilliance to *1 per cent. These results are obtained in less than 5 minutes, in contrast to the half hour or more required for spectrophotometric measurement and calculation. I n addition, the former method requires considerably less operative skill and is substantially less expensive. This correlation has been based only on petroleum oils, whose spect’ral curves are substantially smooth and of the same generic shape. CORRELATION WITH UNIONCOLOR. The smooth curve of Figure 5 shows the correlation of photoelectric color with Union color, obtained by measurement on over 1000 samples, using one Union colorimeter. Other laboratories which examined the photoelectric colorimeter found that this curve did not apply a t all points to their Union color readings. This cannot be avoided, in view of the inherent limitations of the Union method. However, a correlation may be made between Union color and photoelectric color through the medium of the I. C. I. system and the National Bureau of Standards representative disks. Spectrophotometric data obtained by the bureau on a set of Union disks believed t o be representative (19) were converted t o brilliance, hue, and purity (Table VI). North Sky readings were then converted to Union readings through the brilliance relationship after due correction for difference in sample depth. The hue and purity of the Union disks are fixed, but a t a given brilliance the hue and purity of oils vary over a considerable range. While the photoelectric colorimeter, through the h’orth Sky reading, is capable of measuring the brilliance factor alone in complete disregard of the other factors, the eye normally cannot make such a separation. Visual matching of color, such as is demanded by the Union colorimeter, involves matching the hue, the brilliance, and purity, or any combination of these three properties. The human eye has difficulty in estimating the relative brilliances of two colors if the hues also are dissimilar. Differences in purity cause an additional complication. I n Figure 6, the brilliances of the twenty-two oils and of the representative disks are plotted against their respective hues. Sample 6 has a hue and brilliance corresponding to a Union No. 6 disk, Sample 7 has the brilliance of a Union No. 6 disk and the hue of a KO.3l/2 disk. Five operators with normal visual response and one who was totally color blind in the red region of the spectrum compared these oils visually and took Union colors on them. The five normal operators said Sample 6 was darker than KO.7 but all gave a reading of 5 l / 2 or light 6 to Sample 7 and a reading of 6 on Sample 6. The color-blind observer rated both samples as Union KO.6 and could barely distinguish between them. This and other observations of a similar nature indicate that in the region of Union No. 1 t o Union KO.6 the brilliance is used, consciously or unconsciously, as the basis for “color” matching. Hue influences the designation t o a small extent. However, in the region corresponding to Union S o . 6 t o Union KO,8, it appears that hue is of increasing importance and the designation is made on the basis of the redness of the oil. Brilliance is not ignored entirely but is of decreasing importance in this range.
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Figure 6 compares the brilliance with the respective hues, both for the representative disks and some typical oils. As will be seen a t a glance, the brilliance does not fix the hue and the range of possible hues for a given brilliance is extensive. Indeed, hue and brilliance do not vary uniformly or smoothly among the representative disks themselves (Figure 7). On the other hand, photoelectric color (North Sky) is actual transmittance and does, therefore, vary uniformly with brilliance.
640
6wA
’
1
IO
1
~
I
I
2’0
50
i
I
l
1
40 50 60 BRILLIANCE
1.8CY. DEPTH
7b
I
1
80
90
‘
I
li
FIGURE6. COMBINATIONS OF BRILLIAKCE AND HUE OF OILS AND DISKS I n view of the above considerations, a really smooth correlation curve between North Sky and Union cannot be expected. However, the deviations from the authors’ smooth curve of Figure 5 are not greater than the customary differences between various sets of Union glasses. The deviation of the Bureau of Standards disks from the smooth curve is shown by the circles in Figure 5 . Since the variations among Union colorimeters usually exceed this deviation, the correlation curve for photoelectric color us. Union color might as well be drawn smoothly as in Figure 5. The disparity between the data of Table VI1 may be attributed t o the difference between the authors’ Union instrument and that of the bureau. TABLEVII. CORREL.4TIOS O F UNION SORTH SKY Union Color 1 1’/1 2 2’11 3 3’/1 4 411’1 5 6 7 8
Photoelectric Color-N. S. from FI ures 1 6 86 79 63 54 46 38 23 18 12.5 7.7 4.0 0.8
mf
WITH PKOTOELECTRIC-
Smoothed Correlation Curve From Figure 5 89 77 65 54 44 34 26 19 13 6 2.5 1
STANDARDIZATION OF COLORIMETER.The reading obtained on any oil depends upon the lamp used, the voltage a t which it is operated, the filter used, the light path, the spectral response of the photocell, and its circuit. Many of these variables can be changed by limited amounts and other variables changed to compensate, so that the same oil
ANALYTICAL EDITION
August 15, 1942
613
tions, therefore, should be filtered through clean, dry asbestos before measurement. This filtration does not noticeably affect the content of the colored ion (see below). To standardize the instrument, the above solutions are handled by exactly the same technique as is used for the measurement of the color of a sample. Under these conditions, the scale readings obtained on the standard solutions, with the appropriate filters, should agree with the following values to * 1 unit: Standard Solution 4a 5a 5b 6a
Scale Reading
(% Transmission) North Sky Filter
6 1
650
Red Filter
4a 4b 5a 6a
64
0
1
2
3 4 5 6 UNION COLOR DISCS
7
48 32
49 94
44
80 99
100
8
FIGURE7. HUEAND BRILLIAKCE OF REPRESENTATIVE DISKS readings can be obtained under differing conditions. For this reason, it is necessary to specify the entire combination of parts, not each part. The I. C. I. data given above for the three filters need not be adhered to strictly, provided compensating adjustments are made. Readings taken on oils by different operators on six different instruments of the same type agreed within one unit. The Union colorimeter uses a specified source of illumination, and disks of specified Y , z, and y. However, the user of one of these instruments is rarely equipped to determine how closely his colorimeter conforms to the standards or what changes, if any, have taken place. The standardization of the colorimeter used in this work may be readily checked by using standard, reproducible, and easily prepared colored solutions in the same cell as that used for the sample. To accomplish this with the Korth Sky, red, and violet filters in position, the solutions described below have been chosen.
Checking of Standardization SOLUTION 1, 300 grams of concentrated sulfuric acid (sp. gr. about 1.84) in 1 liter of solution. SOLUTION 2, 250 ml. of concentrated ammonium hydroxide (sp. gr. about 0.90) diluted to 1 liter with distilled water. SOLUTION 3, 10 grams of borax (NazBaO7.10Hz0)and 30 grams of potassium hydroxide dissolved in water and diluted t o 1 liter with water. SOLUTION 4a. Weigh approximately 2.5 grams of nickel sulfate (NiSOd.GH10) and dissolve in Solution 2, making up t o approximately 100 ml. with Solution 2. Analyze by accepted analytical procedure. Dilute with Solution 2 t o give 0.500 gram of nickel per 100.0 ml. of solution. Restandardize, and readjust if necessary. SOLUTION 4b. Dilute 25.0 nil. of Solution 4a to 100.0 ml. with Solution 2. SOLUTION 5a. Weigh exactly 10,000 grams of dry, c. P. potassium dichromate. Dissolve in Solution 1, making up to exactly 100.0 ml. with Solution 1. SOLUTION 5b. Dilute 10.0 ml. of Solution 5a t o 100.0 ml. with Solution 1. SOLUTION 623. Weigh 0.0200 gram of pure, dry potassium dichromate. Dissolve in Solution 3, and make up t o 100.0 ml. with Solution 3. SOLCTION 6b. Dilute 10.0 ml. of Solution 6a t o 100.0 ml. with Solution 3.
If these solutions are to be kept, they should be stored in glass-stoppered, alkali-resistant glass bottles. Even with this precaution, the solutions may develop a very fine precipitate. The photoelectric color reading is affected by turbidity too slight to be visible to the eye. All these solu-
These particular solutions were chosen because the potassium dichromate solutions are sensitive to variations in the blue and green regions of the spectrum, the potassium chromate solutions to variations in the violet, and the nickel ammino sulfate solutions to variations in the red and blue. I n this way variations are covered throughout the entire visible spectrum. These solutions mere chosen to be readily reproducible, sensitive to variations in the colorimeter, but relatively insensitive to slight errors in their preparation. The concentration of the colored ion must, of course, be rigidly fixed but variations in the other components of these solutions have little effect. This is illustrated in the following table: Solution
Variation
4a
10% change in KH4OH concentration 80% increase i n %SO4 concentration 20% change in borax concentration and 1 6 . 7 % change in KOH concentration
Sa
6a
Change in Filter Reading Xorth Sky Red Violet 0.7
1.5
1.0
1.3
1.8
0.0
1.0
0.5
0.3
Changes in the more dilute solutions would be even smaller. I n order to check the reproducibiLity of the potassium dichromate, solutions 5a, 5b, 6a, and 6b were made up using potassium dichromate from four sources: Merck, Baker, Eimer and Amend, and Mallinckrodt. The variation was less than 0.5 scale division in all cases. Nickel sulfate from the same four sources was used in making up solutions 4a and 4b and the variation was again less than 0.5 scale division in all cases. Readings on six different instruments of the same type were reproducible to * 1.0 scale division. Sets of solutions were prepared by three different operators and agreed to *l.O scale division. Thus, these solutions give an accurate, easily prepared, and reproducible set of standards for the whole system.
Conclusion This paper has defined a system, designated as photoelectric color, for the measurement of the color of petroleum oils. Photoelectric color rates petroleum oils in the same order as visual inspection and enables a further characterization by one parameter in terms of relative reddishness or greenishness. The color definition is independent of the visual response of the operator. The system can be learned eisily and requires no previous experience in dealing with oil colors, and the standardization can be checked with aqueous inorganic solu-
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
tions which are reproducible and easily prepared. From photoelectric color, I. C. I. data can be calculated if desired. Photoelectric color can be correlated with the Union system on a statistical basis.
Acknowledgment The authors’wish to acknowledge the invaluable cooperation of Hellige, Inc., in preparing the experimental equipment required during the course of this work. The instrument developed for the present purpose is known as the Hellige-Diller photoelectric colorimeter, Model 405.4. They also wish to acknowledge the assistance obtained by frequent reference to a private report by 1‘. -4.Kalichevsky and B. IT. Story.
Literature Cited (1) Am. Soc. Testing Materials, Standards on Petroleum Products
and Lubricants, Designation Dl55-39T. Ibid., Designation D156-38. Chevreul, M. E., “Color Chart” (publisher unknown). Diller, I. M., J. Biol. Chem., 115,315-22 (1936). Diller, I. M., paper presented before the rlmerican 011 Chemists’ Society, fall meeting, 1941. (6) Ferris, F. W., and McIlvain, J. M.,IND.ENG.CHEM., ANAL. ED.,6,23-9 (1934). (7) Gardner, H. A., “Physical and Chemical Examination of Paints, Varnishes, Lacquers and Colors”, 9th ed., Washington, D. C., Institute of Paint and Varnish Research, 1939. (2) (3) (4) (5)
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Hardy, -4. C., “Handbook of Colorimetry”, Cambridge, Mass., Technology Press, 1936. Harris, Moses, ”Prismatic Chart” and “Compound Chart”, 1811. Judd, D. B., J . Opticd Soc. Am., 23,369-74 (1933). Lovibond, J. W., “Light and Color Theories and their Relation to Light and Color Standardization”, London, E. and F. X , Spon, 1916. Maerz, A. and Paul, M .P., “Dictionary of Color”, New York, McGraw-Hill Book Co., 1930. Munsell, A. H., “A Color Notation” and “A Color AtlaJ”, Baltimore, Md., Munsell Color Company, 1933. Kelson. 15’. L., Oil Gas J . , 37, No. 3, 74 (June 2, 1938). Ostwald, W., Chem.-Ztg., 43, 681-2 (1919). Parsons, L. W., and Wilson, R . E., J. IND.EX. CHEM.,1 4 , 269-78 (1922). Ridgway, R., “Color Standards and Somenclature”, London, Weslev. 1912. Rogers, T . H., Grimm, F. V.,and Lemmon, S . E., IND.ENG. CHEM.,18, 164-9 (1926). Scofield, F., Judd, D. B., and Hunter, R . S., A . S.T. .If. Bull., 110,19-24 (May 1941). Societe Franpaise des Chrysanthemistes, “Repertoire de Couleurs”, designed by Dauthenay and others. Story, B. W., and Kalichevsky, V. 9 . , IND.ENG.CHEX,A N LL. ED., 5,214-17 (1933). C. J. Tagliabue Mfg. Co., Brooklyn, N . Y., “New and Revised Tag Manual for Inspectors of Petroleum”, page 57, 25th ed., 1939. Vinoch, H., Refiner Natural Gasoline M f r . , 16,601 (1937). Weir, H. M.,Houghton. W. F., and Majewski, F . SI., P r o c rlm. Petroleum Inst., XI, No. 75, 60-72 (1930).
Determining the Deterioration of Cellulose Caused by Fungi Improvements in Methods GLENN A. GREATHOUSE, DOROTHEA. E. KLERIME, AND H. D. BARKER Bureau of Plant Industry and Bureau of Home Economics, Department of Agriculture, Washington, D. C.
A
CCURATE practical methods of determining the factors
involved in the deterioration of fabrics and other fiber products are widely needed a t the present time. Numerous investigations have shown that cellulose deterioration may be a result of the action of fungi, bacteria, ultraviolet radiation, chemicals, or a combination of these factors. Nost of the effort has been directed toward a comparison and appraisal of preventive treatments rather than toward a better understanding of the causes and mechanism of deterioration. Methods of evaluating deterioration have varied so greatly that it is extremely difficult to make accurate comparisons. The present paper deals largely with (1) experiments on the refinement of technique for testing the amount and rate of cellulosic decomposition that might be caused by various types of microorganisms, and (2) suggestions for the establishment, within certain limitations, of a standardized quantitative technique for testing the effectiveness of mildew-resisting treatments. For the latter purpose certain modifications of the preparatory treatments for the fabric would probably be required.
Literature Review Several excellent reviews (6,6,7, I d , 13) on the microflora associated with fabrics and raw fibers composed principally
of cellulose have been published. They show that most of the reports on the microbiology of cotton and its manufactured products give only the identification of microorganisms found on these materials. Only a few investigators have attempted to secure quantitative data that may represent the ability of these organisms to destroy cellulose. For example, Searle (10) determined the wet breaking strength
of mildewed fabrics t o estimate deterioration. He developed a method in which 37.5 x 3.75 cm. (15 X l . 5 inch) strips of cotton fabric were wound on filter candles which had been coated previously with a soil suspension. These strips were then incubated for 3 or 6 weeks by placing each candle in a test tube containing a small quantity of \rater. A loss of 55 t o 93 per cent in stren t h occurred during 6 weeks’ incubation. Searle’s method k e quently failed t o give close agreement between replicates under apparently identical conditions. Thom. Humfeld, and Holman (18) determined the breaking strength of mildewed duck after conditioning in a standard temperature and humidity room for 2 or more days. They abandoned mixed cultures because of the difficulty in obtaining comparable results, and after testing pure cultures of many organisms, selected Chaetomium globoszlm Kunze. A mineral agar was used t o support the cellulose sample which was incubated 14 dags at 28” t o 30” C. Rogers, Wheeler, and Humfeld (9) made quantitative chemical and physical analyses of mildewed duck. They measured the activity of Ch. globosum and Spirochaeta cytophaga Hutchison
