INDUSTRIAL AND ENGINEERING CHEMISTRY
396
Vol. 13, No. 6
Mixtures were found in a few cases, such as those described by van Wijk and Boelhouwer, wherein the aniline-oil mixture was more opaque above the solution temperature than after separation of the phases took place. The temperaturemeter deflection curves for these mixtures break sharply upward a t the aniline point in a direction opposite to that shown in Figures 4 and 6. The aniline point of an oil whose solution temperature with aniline is below room temperature is determined by blending the oil with a hydrocarbon diluent of higher aniline point. One such method (3) involves the use of a standard diluent such as a narrow boiling petroleum fraction of 60" C. (140" F.) aniline point and approximately 130 average molecular weight. A 50/50 per cent by volume mixture is made of the sample and the diluent. The aniline point of this blend is then determined. The aniline point of the sample is read from a reference curve showing the relation between the aniline points of oils and blends of these with the diluent. The reference curve is established by the visual method on a series of transparent oils covering a wide range of solution temperatures.
7511i3kYw 7035
45
40
50
60
55
65
TEMPERATURE OF MIXTURE- "C.
FIGURE6. ANILINEPOINT
OF CRACKED TAR DETERMINED BY IXFRARED RADIATION
Acknowledgment an exponential law. The rate a t which the temperature of the liquid is falling is as follows:
Thanks are due to R. A. Krause for his valuable assistance in developing the electrical system.
de deg.
Temperature,
zlix
C.
4.8
90 75 60 45
2.8 1.3 0.6
0 = temperature i = time
Literature Cited (1) 4 m . SOC.Testing Materials, "Standards on Petroieum Products
and Lubricants", Appendix 11, p. 14, September, 1940. (2) Donn, Leon, IND.ESG. CHEW., -4nal. Ed., 9, 202 (1937). (3) du Pont de Nemours & Co., E . I., Inc., Wilmington, Del., private
communication.
Results The apparatus and procedure described here have given satisfactory results on a wide variety of stocks, including straight-run residue, cracked tars, extracts from solventrefining operations, and black fuel oils. Figure 4 is the temperature-meter deflection curve for a transparent mixture of aniline and a blend of a highly paraffinic lubricating oil and a low aniline point extract. The point at which phase separation took place, as indicated by the meter, was 55.6" C. From Figure 5 the value for the temperature correction, AT2 is 1.1" C.; and the aniline point by the infrared method is 54.5" C. The value obtained by the visual method was 54.4" C. Comparison of the results obtained with transparent oils tested by both the visual and infrared methods indicates that when the correction froin Figure 5 is applied, the two methods check within 1O C. Application of the correction for cooling obtained from Figure 5 increases the accuracy of the present infrared method over that of van Wijk and Boelhouwer, who obtain agreement within 2" C. on tests of duplicate samples. The curve shown in Figure 6 was obtained on a black cracked tar. The aniline point after applying the correction, AT, is 51.7" C. In general, the form of the curves is erratic after phase separation has begun. The left side of Figures 4 and 6 clearly shows this. The erratic behavior is due to variations in the state of the dispersion of the separated aniline and to their effect on the amount of transmitted radiation. Secondary effects enter as other solubility phenomena appear. For example, in the case of the cracked tar--aniline solution, a point is reached where the transmission of radiation is greater than it was when the solution was above its separating temperature. This is probably due to the formation of large globules of aniline which transmit a wide band of radiation extending into the visible region.
(4) Van Wijk, W. R., and Boelhouwer, J. Tech., 24, 598 (1938).
IT.XI., J. Znst. PetroZeum
Thermoelectric Effects in Photometry J
J. K. BERRY Messrs. Courtnulds, Ltd., Coventry, England
A
PHOTOMETER employing the barrier-layer type of cells for measuring light intensity can find many applications both in industry and other fields, particularly as ail aid to routine testing. Since most light sources have a variable intensity it is necessary to compensate for this, and it is usually done by a second photocell connected in opposition to the first across a suitable galvanometer. As pointed out by Lluller (3) the compensating device can be either optical or some form of resistance bridge. If the latter device is used it may be subject to considerable errors unless certain precautions are taken. Consider the circuit auggeatcd by Wilcos (4); a balance is obtained by varying resistors R1 and Rz (Figure 1). I n practically every case the metal of the sliding contact and that of the resistance wire will be different and will therefore be a potential source of a thermoelectric e. in. f. On varying the resistance, the friction of the contact arm on the wire causes a rise in temperature and the Seebeck effect a t once becomes considerable, the magnitude depending upon the metals of the resistance and speed of variation. For certain types of photometry this effect will probably be negligible, but for
ANALYTICAL EDITION
June 15, 1941
TABLEI.
THERMOELECTRIC
EFFECTS
Sample .I R; - P R: - P Mean
310 500 503
510 500 50:
510 300
510 500
510 500
505
505
505
436
430 435
430 435
432
432
432
Sample Li
KI
-
p p
435 435
430 435
>lean
43j
432
K: -
430
Sample C KI
-
RJ’ -
p p
Slean
:323
:if33 320
370 320
365 325
365 325
:342
342
345
345
346
B60
more accurate work where small differences in intensity are to be measured it becomes important and must be eliminated. Gall (2) in a comprehensive survey of potentiometers discusses the effects of thermoelectric e. m. f.’s when measuring fractions of a pv and states “the galvanometer itself may have dissimilar metal junctions and must therefore be kept free from temperature changes. Brass terminals are not advisable and copper should be used throughout.” It is not always easy or practicable to make a circuit of one metal only, but in the case of the photometer resistance bridge i t has been found possible to eliminate thermoelectric e. m. f.’s. The thermoelectric effects caused by friction can be eliminated by using a resistance made of copper throughout. If the resistor is to be small and compact its resistance must be low (. El
The author is indebted to the directon of Messrs. Courtaulds, Ltd., for permission to publish this paper.
Adding (1) and (2)
Literature Cited
(3)
(1) Berry, J. K., J. Sci. Instruments, 18, 6 (1941). (2) Gall, D. C., J . Inst. Elec. Engrs. (London), 85 (October, 1939) (3) Muller, R. H., 1x0. ENQ.CHEM.,Anal. Ed., 11, 1-17 (1939). (4) Wilcos, L.V., Ihid., 6,167-9 (1934).
