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The interfacial tension of several hydrocarbons against water Rose, William E.

Abstract

The present research has been carried out to add to the knowledge concerning the isomers of decalin already obtained at the University of British. Columbia under the direction of Dr. W. F. Seyer. In particular, it was to note whether the cis form gave any unusual values. It was decided to use the maximum bubble pressure method, as worked out by Hutchinson¹, wherein a bubble of less dense hydrocarbon is forced up through the more dense water. His method is a relative one, i.e., it depends upon calibration of the apparatus against a known interface to obtain an arbitrary constant and then using the same constant to calculate the interfacial tensions of other systems. Two capillary tips of different radii are used and the interfacial tension calculated from a modified form of the Sugden equation. The apparatus consists of two pyrex bubbling tips of different radii mounted rigidly in a glass cell and immersed to the same depth in water. The hydrocarbons are placed in the bubbling tubes and the water, which in all cases constitutes the other phase, is placed in the cell. The tubes are attached to a pressure system so that the pressure can be increased in one tube independently of the other. Side arm, attached to the sides of the tubes, are partially filled with the hydrocarbon and serve as manometers. Hutchinson's formula involves a knowledge of the arbitrary constant for the apparatus, the density of the hydrocarbon and the difference in heights of the columns of liquid in the side tubes corresponding to the pressure difference to form a bubble at each tip. The cell is immersed in a water bath so that calues of interfacial tension may be determined over a range of temperatures. The apparatus was calibrated against the benzene-water interface at 20°C using the value of 35.00 dynes per ce as listed in the International Critical Tables. The calibration constant thus obtained was verified by checking the interfacial tension of n-octane-water at 20°C. The interfacial tensions of cis and trans decalin and cyclohexane against water have been determined over the temperature range 20 to 70°C and for n-decane-water from 20 to 50°C. Empirical equations have been derived assuming a linear relationship between interfacial tension and temperature. The values thus obtained compare favourably with those in the literature reported by other workers. No unusual values are reported for cis decalin. An attempt has been made to account for the difference in slope between cis and trans decalin on the basis of molecular volume and polarisation. Several suggestions as to further work which might be done on this subject have been made. First, there is the need for a correction factor to account for the drops of hydrocarbon on the surface of the water. Second, investigation could be made more complete by using a range of different sized tips. Finally, the solubility of the hydrocarbons in the water should be investigated. (1)Hutchinson, E., Trans. Ferady Soc., 39,229,1943

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