Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The interfacial tension of several hydrocarbons against water Rose, William E. 1949

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata


831-UBC_1949_A7 R6 I5.pdf [ 1.98MB ]
JSON: 831-1.0059069.json
JSON-LD: 831-1.0059069-ld.json
RDF/XML (Pretty): 831-1.0059069-rdf.xml
RDF/JSON: 831-1.0059069-rdf.json
Turtle: 831-1.0059069-turtle.txt
N-Triples: 831-1.0059069-rdf-ntriples.txt
Original Record: 831-1.0059069-source.json
Full Text

Full Text

LIT 3 >U 1 ft /UI<f Cry-/ THE INTERFACIAL TENSION OF SEVERAL HYDROCARBONS AGAINST WATER by William E. Rose, B. A. Sc. A Thesis Submitted in Partial Fulfilment of the Requirements for the Degree of MASTER OF APPLIED SCIENCE in the Department of CHEMICAL ENGINEERING The University of British Columbia August, 19h9 MTBBFAGIAL TENSION OF S&7EBAL HY1EOCARB0NS AGAINST WATER ABSTRACT The present research has been carried out t© add t© the knowledge concerning the isomers of decalin already obtained at the University of Bri t ish. Columbia under the direction of ©r* f* F. Seyer* In part icular , i t was to note whether the c is form gave any unusual values* I t was decided to use the maximum bubble pressure method, as worked out by Hutchinson 1, wherein a bubble of less dense hydrocarbon i s forced up through the more dense water* His method i s a relat ive one, i . e . , i t depends upon calibrat ion of the app-aratus against a known interface to obtain an arbitrary constant and than using the same constant to calculate the im-terfseial tensions of other systems. Two capi l la ry t ips of different r ad i i are used and the in ter fae ia l tension calculated from a modified form of the Sugden equation. Tbe apparatus consists of two pyrex bubbling t ips of different r a d i i mounted r i g i d l y in a glass c e l l and isimersed to the same depth i n water* The hydrocarbons are placed In the bubbling tubes ami the water, which i n a l l cases constitutes the other phase, Is placed i a the c e l l . The tubes are attached to a pressure system s© that the pressure can be increased i n ©ne tube independently of the other* Side anas,, attached to the sides of the tubes, are pa r t i a l ly f i l l e d with the hydrocarbon and serve as manometers* Hutchinson's formula involves a knowledge of the arbitrary constant for the apparatus, the density of the hydro-©as-lssn sa& til®. Httvnme* i n teigtet* of «&» co lon* of MspM i a ttte s£tl». fcafewi m?m®pmt%m to ttte preastMr* 4 i f t© f&ga « fe&feift »t m%h- t l f * fl» ©«11 i s lsnec««6 t o a M l * » t&*t « f itttavlfefti*! teste aty #»4e4«te«l ««r » mi?g# #r fe^tM******* »t & r c*. @tsr# mm® 5® *0 W'C «»& £®r &4teesoe-*«fttvr f r e » 8» to K?e* •fefttt»i '«$iif$$*Hw tare* wMnfa^nf. * J U U M*# t#Jjtfcta~ efet»Uw6 eongytt** fnw#&Mf th&»« in i&* l itt«*Bt» *»psy%«&. An **&m&t t * * I M M H * «Mte to «*eea&t iSwr tfee i l i f f _ In ftlep* fe*tn©iwi cis sod tmat dwetXis. O R « f ®Itaii«f i t td i at0& »t te€ ea tg&s «gb#ee& i m ta«f& is* tfe» for »- mwwmtim faster to «eeciaBt for i $ * 4 * e « * of ' igy$ma*b&& m Urn m$€m® mf u& Sftstrndp .to@&%l§atto &ss&i fee m$m m. mmm «f 4iff«««it #f«e€ -~5 ACKMOWLEDGEMENT It i s a pleasure to acknowledge the many helpful suggestions of Dr. V/. F. Seyer, under •whose direction the work was carried out. I am also very grateful to E. Hutchinson for the preliminary work on the apparatus and method u t i l i z e d i n this investigation. TABLE OF CONTENTS OBJECT OF RESEARCH 1 THEORY 1 Concept of Interfacial Tension . . 1 Theory of Bubble Method 2 METHOD AND APPARATUS 5 Methods of Determining Interfacial Tension . . . $ General Description of Apparatus . . . . . . . . 7 Heating and Temperature Control . . . . . . . . 8 Constant Temperature Bath . . . . . . 8 Bubbling Tubes 9 Pressure Regulating System . . . . . . . . . . . 10 MATERIALS . 11 EXPERIMENTAL PROCEDURE 12 Calibration of Apparatus . . . . . . . . . . . . 12 Cleaning of Apparatus . . . . . . 13 Description of Run 13 RESULTS 1$ TREATMENT OF RESULTS .16 Empirical Equations 16 Interpretation of Data ...18 Accuracy of Method 19 CONCLUSIONS 20 LIST OF DIAGRAMS Details of Bubbling Tubes .7 Details of Pressure System 7 Details of Water Bath . . . 7 Graph of Interfacial Tension vs. Temperature . . . . 16 THE INTERFACIAL TENSION OF SEVERAL HYDROCARBONS AGAINST WATER OBJECT OF RESEARCH Many of the physical and chemical properties of the sterioisomers of decalin have been determined at the University of British Columbia during the past few years under the direction of Dr. W. F. Seyer. It was to add to the knowledge already ob-tained about cis- and trans-decahydronaphthalene that the present investigation into the interfacial tension of the compounds a-gainst water was undertaken. In particular, i t was to determine whether the cis isomer gave any unusual values. THEORY Concept of Interfacial Tension The region in which two phases meet is designated as an interface, and an interface between a gaseous phase and another can be considered a surface. A molecule at a liquid surface is attracted toward the centre of the liquid by the attractive forces of the interior molecules. This resultant force causes the (1) surface to assume the smallest possible area. To increase the area of the surface i t is therefore necessary to do work to bring mol-ecules from the interior to the surface. This tendency of a surface to contract leads to the con-cept of surface tension. It is defined as the force in dynes act-ing at right angles to a line 1 cm long in the surface. The work required to extend the area of a surface 1 sq cm is equal to the surface tension. The work required to enlarge the surface separating two immiscible liquids is called interfacial tension. It is generally less than the larger of the two surface tensions, since the mol-ecules are attracted by the molecules of the other surface which tends to reduce the effect of the attractive forces of the inter-ior molecules. Theory of Bubble Method The idea of obtaining some knowledge of surface tension from the pressure required to liberate bubbles from a capillary tube immersed in a liquid was one of the first suggested. Simon^ ", in 1851, suggested the method and G. Jaeger first used i t in 1891 for the comparison of surface tensions. His work was followed in 1892 by Cantor's^ publication of the first correct theory of bubble formation. F. M. Jaeger** used the absolute method in 1917, with a (1) Simon, M., Ann. Chim. Phys., 3, $> 1851 (2) Jaeger, G., Sitzb. Akad. Wiss. Wein., 100, 215, 1891 (3) Cantor, M., Weid. Ann. Phys., hi, 399 3 1892 (U) Jaeger, F. M., Z. Anorg. Allgem. Chem., 100, 1, 1917 tube adjustable to a known depth, and although he arrived at in-correct values of the surface tension, he did much to establish the method. Many equations were derived to express the surface tension in terms of the dimensions of the capillary and the maxi-mum pressure required to liberate bubbles from the tip. Ferguson^ " and Feustel^ arrived at incorrect equations but Schroedinger^  in 1915 put forth the first correct equation which was approved by Verschaffelt*1 in 1918. . r--r/>- &)'--] T- surface tension p "the maximum pressure difference between the inside and outside of the bubble at the face of the tip r - radius of the tip _ P . h - £j or ^ e a ^ h e i S J l ' t a s read on a manometer d -density of denser phase d'-density of less dense phase In addition, meniscus corrections have to be applied to the ideal height which depend on the diameter of the reservoir. Although the absolute method has been completely worked out in theory, the results obtained with i t in practice are not of sufficient accuracy. It is believed by modern investigators that the inconsistency of results with theory is due to the fact that the theory is based on infinitely slow formation of the bubbles, whereas a l l experimenters have used a dynamic method with the rap-(1) Ferguson, A., Phil. Mag., 28, 128, 19lli (2) Feustel, Drud. Annalen, 16, 6, 1905 (3) Schroedinger, E., Ann. Physik, U6, IjlO, 1915 (U) Verschaffelt, J. E., Commun. Leiden, Suppl. No. U2d, 1918 (U) i d production of bubbles. In 1922, Sugden1 employed two tubes of d i f fe ren t r a d i i immersed to the same depth i n the l i q u i d . He found a r e l a t i o n be-tween the pressure and the r a d i i o f the tubes, such that ; T—surface tension P—pressure difference fo r two tubes X l ' X 2 ^ e c o r r e c t e d r a d i i o f the small and large t i p s respec t ive ly . (These corrected values are ob-tained from Bashforth and Adams Tables . ) A more convenient way of using t h i s r e l a t i v e method i s to ca l ib ra te the apparatus against a known interface and obtain the value of the denominator i n (2) . For tubes o f small radius , Sugden's approximate equation, (3), can be used to give re su l t s accurate to one part i n 1000 which i s more accurate than the r e -su l t s obtainable wi th the apparatus. AP ['+ 0-63 ^ £*C^ C3) A—an a rb i t r a ry constant P—pressure difference between the two tubes r - r a d i u s o f l a rge r t i p d —density of denser phase Hutchinson^ modified Sugden's apparatus for i n t e r f a c i a l tension determinations and used the equation: (1) Sugden, S . , J . Am. Chem. S o c , 121, 858, 1922 (2) Bashforth, F . , and Adams, J . C , An Attempt to Test the Theories o f C a p i l l a r y Ac t ion . Camb. U . Press. London, 1883 (3) Hutchinson, E . , Trans. Faraday S o c , 39, 229, 19h3 h" —height of meniscus in tube with smaller t i p h 1 1 — height of meniscus i n tube with larger t i p d — density of phase inside tubes r — radius of larger, t i p h - ( h « - h " ) A - arbitrary constant for apparatus METHOD AND APPARATUS Methods of Determining Interfacial Tension The most accurate values of interfacial tension reported in the literature are accredited to the drop-weight method as orig-i n a l l y employed by Harkins and Humphrey1-. The values l i s t e d In the International C r i t i c a l Tables have almost a l l been obtained i n this manner. However, the method i s not the most applicable i n a l l cases, and a number of special methods have been devised. In the drop-weight method, the t i p must be very accurate-l y made, the drops allowed to form very slowly, and i f this rate i s not controlled with extreme care, results are not reproducible. A modification of this method involving weights rattier than v o l -umes, as worked out by Ward- and Tordai , i s reported to give ex-tremely good results without the tediousness of Harkin's method. •a The use of capillary r i s e methods by Reynolds-^ and other investigators has yielded consistent results which compare favor-ably with the drop-weight values. The trouble with the method, (1) Harkins, W., and Humphrey, E., J. Am. Chem. Soc, 38, 228, 1916 (2) Ward, A., and Tordai, L., J. Sci. Instruments, 21, lU3, 19UU (si) Reynolds, J. Chem. Soc, 119, U66, 1921 however, is that the capillaries must be of uniform bore and i t sometimes takes a great deal of time to select suitable capillaries for the purpose* Modifications of the method have been used by Speakman1 with good results* In his apparatus the interfacial ten-sion can be calculated by noting the difference in pressure re-quired to force liquid to an arbritary level in two tubes of dif-ferent radii. This eliminates having to measure the capillaries at a l l points by merely measuring the radii at the arbitrarily chosen points. The Du Nuoy tensiometer can be used to measure interfa-cial tension. Harkins and Jordan'- established experimental proof of the accuracy of the ring method for surface tension measurements. The apparatus is very delicate, however, and is not readily adapt-able to temperature variation measurements. Several unique methods have been developed; namely, Meyer stein and Morgan ;>s^  centrifugal method, Addison's*1 vibrating jet method, and Vonnegut's • horizontal rotating bubble method. A l l these methods yield values which compare fairly well with the best values in the literature but they require extremely good technique; and in the case of the vibrating jet, elaborate photographic equip-ment. In a l l cases the theory has been worked out by the experi-menters, but not enough determinations have been made to fully en-(1) Speakman, J . , J . Chem. Soc, lU.9, 1933 (2) Harkins, W. D., and Jordan, H. F*, J* Am. Chem. Soc, 52, 1751, 1930 (3) Meyerstein, W., and Morgan, J. D., Phil. Mag., 35, 335, 19hk (U) Addison, C. C , Phil. Mag., 36, 73, 19U5 (5) Vonnegut, B., Rev. Sci. Instruments, 13, 6, 19U2 dorse use of the author's equations. The chief advantage of these methods is that only a small, amount of liquid is needed and this is important when dealing with expensive compounds. The method finally decided upon was one suggested by Hut-chinson1 for measuring the interfacial tension between molten white phosphorous and water. It is a relative method* i .e . , i t depends upon calibration with some interface of known value. The apparatus is readily constructed from laboratory glassware and is suited to temperature variation measurements* An important feature of the apparatus is that only a small amount of material is needed for a determination. General Description of Apparatus The apparatus used is similar to that described by Hut-chinson1, see F ig . l . The essential part consists of two pyrex bub-bling tips of different radii for producing bubbles of one liquid inside the other* These tips are joined to a reservoir having side-tubes in which the heights of the liquid can be read with a cathe-tometer. The side tubes are identical so that no capillary correc-tions need be applied. The tubes are rigidly mounted in a rubber stopper and connected to a pressure system (Fig. 2 ) . With the ap-paratus assembled, the faces of the tips are in a horizontal plane with respect to the side tubes. The whole of this apparatus is enclosed in a pyrex cell 5 cm in diameter and about 8 cm long. The cell is placed in a water bath and held firm by a brass collar (Fig. 3). The entire apparatus (1) Hutchinson, E«, op. c i t . , pU DETAILS Or WATER BATH is so arranged that the bubbling tips are as free from vibration as possible. Heating and Temperature Control Water was chosen as the bath liquid since i t provides better visibil i ty than o i l . Agitation is supplied by a 1 in. pro-pellor driven by a variable speed motor. A copper cooling coil through which water at l£°C is circulated is inserted in the bath to provide suitable opposition to the heaters. The heaters are two 125 watt blade heaters which are connected with a thermoregulator at a l l times. A 200 watt heater is used to take the bath from one temperature range to another. A mercury thermometer was used to measure the temperature of the bath. This thermometer was calibrated against a standard resistance thermometer over the range 20 to 70 degrees centigrade. In calibrating the thermometer the mercury and resistance thermo-meters were placed side by side in the bath arid held at each 10° temperature interval for at least twenty minutes to allow for the difference in construction of the two thermometers. The mercury thermometer was placed in such a position that the temperature of the bath should be that inside the cel l . A Cenco De Khotinsky thermoregulator and a Cenco Super-sensitive relay kept the bath temperature constant to within one two hundredth of a degree. This was determined by using the resis-tance thermometer and noting the deflection en the galvanometer scale. \ Constant Temperature Bath The bath was a pyrex cylinder, h£ cm high and 23cm in diameter. The water bath was lagged with 1/U in . of asbestos and covered with a lagged wooden l i d . Since i t was necessary to sight into the cell , the cell was tested for its optical properties and windows were cut in the lagging at the selected spots. The method chosen was to place a brass meter stick inside the cell and measure the distance between two points with a cathetometer, and then meas-ure the same distance with the meter stick outside the cel l . No difference in distance was observable and the apparatus was con-sidered good enough to sight through. Bubbling Tubes Since the heights of the liquids in the side tubes were a l l that one observed for a determination; i t was necessary to make the cell of sufficient diameter that the addition of one drop of liquid inside the tubes to the liquid in the cell would not sub-stantially increase the pressure needed to produce a bubble. The tips were drawn from h mm pyrex tubing, marked with a diamond, then broken off. The tips thus made were found to break off very sharply and were not jagged as expected. The tips were ex-amined with a low power travelling microscope and i t was found that practically a l l of the tips were circular in cross section. Two tips were selected from a large number and these were carefully ground with fine emery until perfectly plane in cross section. The diameter of the larger tip was measured with the same microscope at 3 0 ° intervals of rotation. The position of the side tubes proved somewhat critical and after some experimenting i t was found that the tube should be joined to the reservoir about 1 cm below the level of the tips. This allowed the hydrocarbon to go up the side tubes and yet pre-vented water from backing up in the side tubes. The side tube and tip were placed at right angles to one another to facilitate read-ing the height of liquid and to check the level of the tips. Pressure Regulating System The method of producing the bubbles proved to be a prob-lem in itself. Hutchinson1 had a side tube on his cell and decreased the pressure above the cell liquid with an aspirator. This method was tried without success. It was found that the bubbles were pro-duced too rapidly and could not be properly controlled. Since the meniscus could not be closely followed, the method was finally a-bandoned and another tried. The tubes were connected to a two-way stopcock so that the pressure could be raised in one tube without influencing the other. This was in turn connected to a pressure system consisting of a piece of pressure tubing which was placed in a vise so that i t could be compressed allowing the bubble of liquid to be pro-duced very slowly. After some practice i t was found that the pres-sure could be controlled very nicely and the height of the liquids in the side tubes could be reproduced without any great difficulty. An alternate form of pressure device was used in which a burette dripped liquid slowly into a flask, displacing the air in the system and producing bubbles of liquid. This was found to be the best form of pressure device since the investigator does not control any vise or in anyway cause sudden increases in pressure. (1) Hutchinson, E., op. c i t . , pU The operator merely sets the burette, which may be fi l led with mer-cury, sulfuric acid or the liquid under investigation, so that the pressure is slowly increased. He then follows the rise of liquid in the side tube until the maximum height is reached. The meniscus •can be followed easily with a cathetometer. The apparatus is i l l u -minated so that the meniscus can be read. MATERIALS Distilled Water In a l l the measurements conductivity water was used. This was doubly distilled; first from a 2-litre florence flask, secondly from alkaline permanganate solution in a large copper ves-sel. The water was stored in a pyrex florence flask equipped with a siphon to prevent contamination with the atmosphere. Benzene The benzene used to calibrate the apparatus was Merck's thiophene-free technical grade. This was purified by fractional crystallization until the freezing point remained constant. The purified benzene thus obtained was dried over sodium and stored in a glass stoppered bottle. The freezing point of the benzene used was 5.38°C. H-Octane The n-octane was obtained from the Certified Chemical Company and was of high purity. The freezing point was -£6.2°C. Cis- and Trans-decalin The two isomers were separated from technical grade decalin obtained from the Eastman Kodak Company. This separation was carried out in a Stedman column operating at 9 mm Hg. The run was controlled by allowing slop to come over until a steady temp-erature was obtained and then taking off trans. The overhead was switched back to slop while the temperature varied until i t became constant once more at which point cis was taken off. Both isomers were further purified by fractional crystal-lization until a constant freezing point was recorded. The freezing point of trans was -30.60°C and that of the cis was -U3.U°C. The hydrocarbons were dried over sodium and kept in dark-ness. It was noted that the trans tended to discolour in the pres-ence of light, becoming somewhat yellowish. This did not seem to affect the freezing point however. N-Decane This was obtained from the Certified Chemical Company and was of high purity. The freezing point was -29.8°C, Cyclohexane The purity of the cyclohexane was doubtful as i t had been standing for some time and had become slightly discoloured. The freezing point obtained was 6.1°C. EXPERIMENTAL PROCEDURE Calibration of Apparatus Before taking any readings i t was necessary to calibrate the apparatus against a known interface and get the value of the arbitrary constant indicated in Equation (li). The system benzene-water was selected because the value of the interfacial tension o has been accurately determined at 20 C and agreed upon by invest!-gators* Furthermore benzene can be obtained i n reagent grade and r e a d i l y p u r i f i e d by f r a c t i o n a l c r y s t a l l i z a t i o n . The pressure d i f -ference for the two t i p s was observed several times and the mean constant ca lcu la ted . Cleaning of Apparatus Before each determination* the bubbling t i p s and tubes were cleaned wi th hot su l fu r i c ac id and bichromate so lu t ion , washed with a lcohol and r insed with d i s t i l l e d water. The tubes,were then dr ied for 20 min at 110°C. Af te r making a determination, .with c i s -decal in i t was found necessary to heat the cleaning so lu t ion to about 120°C before any sa t i s fac tory cleaning was observed. The c r i t e r i o n fo r c leanl iness was that the l i q u i d should not adhere to the glassware i n droplets but rather form a smooth continuous f i l m . over the glass surface. The same procedure was followed i n cleaning the c e l l . Descr ipt ion of Run The c e l l was f i l l e d wi th d i s t i l l e d water to such a height that when the tubes were placed i n the c e l l , the l i q u i d would be about 1 cm above the l e v e l of the t i p s . The c e l l was placed i n the constant temperature bath to al low the d i s t i l l e d water to come to the bath temperature. The tubes were f i l l e d i n the fo l lowing manner* D i s t i l l e d water was poured in to the side tubes u n t i l the t i p s were ju s t f i l l e d and no more. This was to prevent the hydrocarbon from forming drops i n the d i s t i l l e d water when the tubes.were placed i n the c e l l . The hydrocarbons were then poured in to the side tubes u n t i l the l i q u i d was 2 or 3 cm above the face o f the t i p . The tubes were now placed i n the c e l l and the cell was firmly bolted into position by tightening the brass collar. The cell and bubbling tubes were kept in the bath for 20 min before any readings were taken. This was not only to ensure thermal equilibrium but also to make i t possible to neglect any aging effects at the interface. To check for interfacial equilib-rium, the hydrocarbons were shaken with distilled water and left overnight. The organic phase was then used in place of the anhy-drous hydrocarbon. No differences in the values of the interfacial tension were observed, however, and i t was not deemed necessary to repeat this in subsequent determinations. The tips were checked with the cathetometer to make cer-tain that they were in the same horizontal plane and adjusted i f necessary. At the end of the 20 min period, the pressure in the tube having the smaller tip was raised with the levelling bulb un-t i l the hydrocarbon was almost ready to leave the tip. The vise was now used to very slowly raise the pressure in the tube. The menis-cus was followed with the telescope until the bubble had formed and the meniscus in the side tube suddenly f e l l . The maximum height of the meniscus was recorded and the pressure in the system reduced by means of the capillary stopcock. The two-way stopcock was now turned and the maximum height of the meniscus for the tube with the larger tip was recorded. This procedure was repeated at 10° intervals throughout the temperature range. Several readings were taken at each temper-ature interval and the mean used in the calculations. While no difficulty was encountered in holding the temperature constant at. OS) the lower end of the range* i t was harder to control the tempera-ture at the upper end* RESULTS The calibration constant used in Equation (U), as deter-mined using a benzene-water interface was found to be 0*01813. The value of the interfacial tension was taken as 35.00 dynes per cm o at 20 C as listed in the International Critical Tables. As a check on the calibration constant* the interfacial tension of the system n-octane-water was determined at 20°C and found to be 50.98 dynes per cm as compared with the International Critical Tables value of 50.8 dynes per cm. To give some idea of the pressure differences that are encountered, the values for trans at 20°C are listed in cm of trans-decalin. Trial 1 2 3 U Mean AH 3.295 3.260 3.285 3.280 3.280 Table 1. Taking the density of Trans-decalin as 0.8700 gm per cc at 20°C, as reported by Seyer and Davenport1, this corresponds to a mean difference in height of 2.85 cm of water. The mean values of the interfacial tension at the various temperatures are listed in Table 2 and plotted in Fig. U assuming a linear relationship. (1) Seyer, W. F., and Davenport, C. H*, J . Am. Chem. Soc, 63, 2U25, 19l|l Trans-decalin Temperature 20 30 UO 50 60 70 Interfacial 51.U0' 50.99 50.55 50.09 U9.69 U9.U0 Tension Cis-decalin '.Temperature 20 30 hO 50 60 70 Interfacial 5 1 . 7 U 51.U5 51.12 50.89 50.5U 50.U0 Tension Cyclohexane Temperature 20 30 UO 50 60 70 Interfacial 51.01 50.67 50.15 U9.72 U9.U0 U9.09 Tension N-decane Temperature 20 30 hO 50 Interfacial 51.2U 50.71 50.U2 U 9 . 8 6 Tension Table 2. The densities of benzene, n-octane, cyclohexane and n-decane used to calculate the interfacial tensions listed above, were obtained from the International Critical Tables. TREATMENT OF RESULTS Empirical Equations Equations have been developed assuming a linear relation-ship between interfacial tension and temperature. These have been derived in the usual method of least squares using the values l i s t -ed in Table 2. The equations thus derived are listed in Table 3. Trans-decalin y = $2.20 - o.oiaot Cis-decalin y = 52.26 - 0.0275t Cyclohexane y - 51.79 - 0.0395t N-decane . y = 52.11 -Table 3. where:-y interfacial tension in dynes per cm t temperature in °C Although only temperature has been considered in the above equations, i t must be realized that other factors influence the values of interfacial tension. The change of solubility of the hydrocarbons in water with temperature wi l l cause density changes and these should be included in the equations to make them com-pletely correct. However, since the solubility of hydrocarbons in water is very slight, i t was considered negligible in the present case. Comparison of values obtained using the bubble pressure method with values listed in the literature obtained using the drop-weight method are given below. Trans-decalin-water at 25°C Guest and Lewis"'" 50.98 dynes per cm Bubble pressure method 5l»18 " Percent deviation 0.39$ too high (1) Guest, W. and Lewis, W., Proc. Roy. Soc, A170, 501, 1939 N-octane-water at 20°C International Critical Tables 50.8 dynes per cm Bubble pressure method 50.98 11 Percent deviation 0.3556 too high Cyclohexane-water at 25°C Matthews"'" 50.28 dynes per cm Bubble pressure method 50.80 11 Percent deviation 1.03% too high Table k. No data could be found in the literature for the inter-facial tensions of cis-decalin-water and n-decane-water to compare with experimental values. Interpretation of Data From Figure h i t can be seen that the slope of the equa-tion for cis-decalin differs considerably from that of the other three compounds. This may be due to the difference between the cis- and trans- configurations of the molecules. It has been found' that cyclohexane exists almost entirely in the trans- configura-tion in the equilibrium state at ordinary temperatures. In general the cis- molecule occupies a smaller space than the trans-. This would cause greater attractive forces between the cis- molecules and the water molecules thus decreasing the interfacial tension somewhat. It has also been found that cis-decalin has a slightly (1) Matthews, J. B., Trans. Far. Soc, 35, 1113, 1939 (2) Seyer, ¥. F., and Barrow, G. M., J . Am. Chem. Soc, 70, 802, 19U8 higher polarization than trans-decalin. The polarization would add to the attractive forces between the cis- and water molecules and would play an important role at increasing temperatures. It is suggested that some combination of the differences in molecular shape and polarization between the cis- and trans-configuration accounts for the difference in slope of the cis- and trans-decalin. Accuracy of Method The accuracy of the method depends chiefly on the accur-acy with which the difference in height for the two tips can be read. In the present investigation, the cathetometer was accurate to the nearest 0.005 cm. Consider the readings for trans-decalin in Table 1 where the difference in height was 3.28 cm. If the error was cumulative, the maximum error would be 1 part in 328. However, from Table 1, the maximum deviation from the mean value is 2 parts in 328. There-fore there are other factors which must play a more important part than the accuracy of the cathetometer. Some measurements were made with the apparatus improper-ly cleaned and results 10 to 1$% higher than the reported values were obtained. It was noted that unless the tips were very thor-oughly cleaned before each determination; the readings became pro-gressively higher. The importance of clean apparatus cannot be stressed to greatly in interfacial tension measurements. Comparing the difference between reported values and those listed in the literature, the greatest deviation is 1.03$ as obtained with cyclohexane. It is believed that the other compounds give a truer picture of the accuracy which can be obtained with the apparatus since, as previously stated, the cyclohexane was of doubtful purity. That the readings are higher than those listed in the literature is probably due to a concentration of impurities at the interface. CONCLUSIONS The bubble pressure method has been successfully used to determine the interfacial tension of several hydrocarbons against water. However, there are several suggestions for further work with this type of apparatus. First, Hutchinson1 makes no mention of how he corrects for drops of the liquid in the tubes forming on the surface of the liquid in the cell . In the present investigation, the height of meniscus in the tube with the smaller tip was recorded before reading the height of meniscus for the larger tip. This is not strictly correct and yet there seems no immediate way around the difficulty. From the theory of bubble formation, i t is seen that bubbles formed from the same sized tip wi l l not a l l be of the same volume, so that a standard correction for any one tip cannot be calculated. The measurements were a l l made in the same respective order to minimize the error. Some work to show the magnitude of error involved would be very helpful. Second, the results could be made more conclusive by (1) Hutchinson, E«, op. c i t . , pU using a number o f d i f ferent s ized t i p s and tes t ing the l i m i t s o f the equation. The l i q u i d s could be interchanged al lowing the dens-er water to be bubbled through the l e ss dense hydrocarbon and noting whether any d i f fe ren t values of the i n t e r f a c i a l tension were obtained. This was not attempted because of the l i m i t e d quan-t i t y o f pure hydrocarbons ava i l ab l e . Th i rd , there i s the need of knowing the s o l u b i l i t y of hydrocarbons i n water. No data was found i n the l i t e r a t u r e on t h i s subject and ye t the densi ty of the organic phase has to be accurately known to ca lcula te the i n t e r f a c i a l tension from Equa-t i o n (U). The method seems to give consistent r e su l t s and the ap-paratus i s simple to b u i l d and operate. The method i s one that could be applied to industry wi th great advantage. Once the appa-ratus has been ca l ib ra ted against a known interface only the heights of the l i q u i d s i n the side tubes need to be read fo r a determination. SUMMARY i — — — — 1. The bubble pressure method has been successful ly used to determine the i n t e r f a c i a l tension of sever-a l hydrocarbons against water over the temperature range 20 to 70°C. The hydrocarbons used were c i s -and t rans-decal in , n-decane and cyclohexane. 2. Empir ica l equations have been determined for the hydrocarbons over the temperature range r e l a t i n g i n t e r f a c i a l tension and temperature* A l i n e a r r e -l a t ionsh ip has been assumed* 3* A d i s t i n c t difference i n slope between c i s - and t rans-decal in was noted and an attempt made to ac-count fo r i t on the bas is of molecular volume and p o l a r i z a t i o n . U* An attempt has been made to give some idea of the accuracy o f the method and the errors involved. 5.. Several suggestions have been made whereby the method might be improved. BIBLIOGRAPHY Addison, C. C., Phil. Mag., 36, 73, 19U5 Bashforth, F., and Adams, J. C , An Attempt to Test the Theo- ries of Capillary Action, Camb. U. Press, London, 1883 Cantor, M., Weid. Ann. Phys., hi, 399, 1892 Ferguson, A., Phil. Mag., 28, 128, 191a Feustel, Drud, Annalen, 16, 6, 1905 Guest, W., and Lewis, W., Proc. Roy. Soc, A170, $01, 1939 Harkins, W, D., and Humphrey, E, C , J. Am. Chem. Soc,, 38, 228, 1916 Harkins, W, D., and Jordan, H. F., J. Am. Chem. Soc, $2, 1751, 1930 Hutchinson, E., Trans. Far. Soc, 39, 229, 19U3 Jaeger, F. M., Z. Anorg. Allgem. Chem., 100, 1, 1917 Jaeger, G., Sitzb. Akad. Wiss. Wein., 100, 2u5, 1891 Matthews, J. B., Trans. Far. Soc, 35, 1113, 1939 Meyerstein, W., and Morgan, J. D., Phil. Mag., 35, 335, 19hh Reynolds, J. Chem. Soc, lltU9, 1933 Schroedinger, E., Ann. Physik, 1*6, 1*10, 1915 Seyer, W. F., and Barrow, G. M», J. Am. Chem. Soc, 70, 802, 19a8 Seyer, W. F., and Davenport, C. H., J. Am. Chem. Soc, 63, 2U25, 19U1 Simon, M., Ann. Chim., Phys., 3, 5, 1851 Speakman, J. C , J. Chem.sSoc, lhh9, 1933 Sugden, S., J. Am. Chem. Soc, 121, 858, 1922 Verschaffelt, J. E.,.Commun. Leiden, Suppl. No. U2d, 1918 Vonnegut, B., Rev. Sci. Instruments, 13, 6, 19^2 Ward, A., and Tordai, L., J. Sci. Instruments, 21, lU3, 19UU 


Citation Scheme:


Citations by CSL (citeproc-js)

Usage Statistics



Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            async >
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:


Related Items