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INDUSTRIAL AND ENGINEERIKG CHEMISTRY
Healdton asphalt-i. e., 70 as compared with 73, respectively-although the subnormal temperature susceptibility for the latter is considerably higher than for the former asphalt. In other words, while the Healdton asphalt is not as susceptible a t normal temperatures as the Colombian grade, the latter does not harden as rapidly as the temperature is lowered. A similar example can be shown with respect to the fluidity index. West Texas asphalt with 50 penetration a t 25" C. has the same softening point-penetration index as a Midcontinent asphalt of the same consistency, although at elevated temperatures, as measured by the fluidity index, the Midcontinent asphalt has a higher index than the former. In this case also, the low temperature susceptibility is lower for the Midcontinent than for the West Texas product.
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employing apparatus and tests which are commonly used and hence familiar to those in asphalt work. The correlation between service behavior and the susceptibility as determined by the suggested methods should then serve as a guide for future decisions on the suitability of an asphalt for a given purpose. At the present time, the lack of reliable actual service data prevents the authors from giving any specific examples of this correlation in any one field. I n addition, it is hoped that the present contribution will serve as a basis for further thought and experimentation on the subject of susceptibility, which will undoubtedly result in a still greater appreciation of this characteristic of asphalt s.
Conclusions TABLEIV. CHANGES IN SUSCEPTIBILITY CHARACTERISTICS No single factor has thus far been evolved which will adeBETWEEN Low AND ELEVATED TEMPERATURES quately express the temperature susceptibility of an asphalt Softeninn Poink- Buscaptiover the wide range of temperatures encountered in the comPenetration bilityo Fluidity mercial application of asphalts. Source and Grade Index Factor Index Present methods are not entirely suitable, because they are Colombian 53 penetration at 25' C. 70 3.83 81 Healdton b5 penetration at 25' C. 73 6.11 too limited in the range of consistencies over which they can be Midcontihent, 50 penetrFtion at 25' C. 63 3.92 85 West Texas, 50 penetration at 25' C. 63 5.88 70 determined or require the use of apparatus and testing methPenetration at 25' C . ods not commonly used or recognized as standards. a Penetration at 00 C. A combination of factors or indexes is suggested by which a definite measure of the temperature susceptibility characterThus, any theoretical consideration or comparison of asistics of a wide range of asphalts can be determined. The phalts must take into account these differences in behavior. softening point-penetration index indicates this characterisI n practice, certain uses demand a highly susceptible asphalt tic over a narrow range of normal atmospheric temperatures, at elevated temperatures while, in other cases, the low-temthe ratio of penetration a t 25" C. to penetration at 0" C. at perature characteristics are more important, subnormal and the fluidity index a t elevated temperatures. In applying the proposed methods of measuring susceptiThese methods are equally applicable to straight reduced bility as an aid in choosing the proper asphalt for a given servand oxidized asphalts and are easily determined by means of ice, the fact should be borne in mind that susceptibility is tests which are in common use. by no means the sole criterion upon which the quality of an asphalt is based. Other properties, such as resistance to Literature Cited weathering, water absorption, or resistance to acid and alkali, Abraham, H., "Asphalts and Allied Substances," 3rd ed., p. 671, for example, are usually just as important as susceptibility. New York, D. Van Nostrand Co., 1929. In the presentation of the results of this study, no attempts Dean, E. W., and Davis, G. H. B., Chem. & Met. Eng., 35, 618 have been made to establish definite limits to any of the in(1929). Hoepfner, K. A , , Wasser u. Wegebau-Z., 28, Nos. 12, 13, and 14 dexes or factors for the purpose of defining quality or suita(June 20, July 5 and 20, 1930). bility of an asphalt for any particular use. More practicable Zapata, J., paper presented before Association of Asphalt Paving methods than those now in use are suggested, by which the Technologists, January 30, 1935. consumer will be able more accurately to correlate his data on service behavior in so far as susceptibility is concerned. These RECEIVED May 11, 1935. Presented before the Division of Petroleum methods have the advantages of covering a wider range of Chemistry, Symposium on Asphalt, at the 89th Meeting of the American Chemical Society, New York, N. Y.,April 22 to 26, 1935. asphalts and conditions than was heretofore possible, and
Control of High Lights in Reading Microbalance Swings PAUL H. M,-P. BRINTON, University of Southern California, Los Angeles, Calif.
T
HE magnifying lens used in the balance case for observing the pointer of a microbalance, which is not provided with a telescope, is necessarily of high power and therefore gathers light from a large area. In cases where special arrangement for the illumination of the balance is limited, owing to the use of the room for other apparatus, it frequently happens that disturbing highlights from distant light sources are reflected by the lens into the eye of the observer. A very simple device has proved to be a great assistance in overcoming trouble from ill-arranged light sources. It con&ts of a 10- or 12-inch square of dark cardboard (preferably,
but not necessarily, dull black), with a 1-inch circular hole in the center. By holding this card in the hand between the balance case and the observer the highlights are almost totally eliminated, the necessity of closing one eye is removed, and the balance is, in a measure, protected from the hot breath of the observer. The device serves equally well in correcting faulty lighting conditions for ordinary analytical or assay balances which are provided with a magnifying lens in the balance case. RECEIVED December 13, 1935.
