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

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LIT3 >U 1  /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  ft  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 British. Columbia under the d i r e c t i o n of ©r* f* F . Seyer* In p a r t i c u l a r , i t was to note whether the c i s form gave any unusual values* I t was decided to use the maximum bubble pressure method, as worked out by Hutchinson , wherein a bubble of less dense 1  hydrocarbon i s forced up through the more dense water* His method i s a r e l a t i v e one, i . e . , i t depends upon c a l i b r a t i o n of the apparatus 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 c a p i l l a r y tips of different r a d i i are used and the i n t e r f a e i a l tension calculated from a modified form of the Sugden equation. Tbe apparatus consists of two pyrex bubbling t i p s of different r a d i i mounted r i g i d l y i n 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 o f the other* Side anas,, attached to the sides of the tubes, are p a r t i a l l y 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* o f «&» c o l o n * o f M s p M i a ttte s£tl».fcafewim?m®pmt%m  to ttte preastMr* 4 i f  « fe&feift »t m%h- t l f * fl» © « 1 1 i s lsnec««6 t o a t&*t  #r  « f itttavlfefti*!  efet»Uw6 eongytt** fnw#&Mf  #»4e4«te«l « « r » mi?g#  aty  **&m&t  wMnfa^nf. *  t * * IMMH* «Mte  »- mwwmtim fee  « f ®Itaii«f  ta«f&  f a s t e r to «eeciaBtfori $ * 4 * e « * o f  ' igy$ma*b&& m Urn m$€m® mf u& &ss&i  t#Jjtfcta~  to «*eea&t iSwr tfee i l i f f  i t t d i at0& »t te€ ea tg&s «gb#ee& i m for  JUUM*#  th&»« in i&* litt«*Bt» *»psy%«&.  _ Inftlep*fe*tn©iwicis sod t m a t dwetXis. O R  is* tfe»  »  5® * 0 W'C «»& £®r &4teesoe-*«fttvr f r e » 8» to K ? e *  •fefttt»i '«$iif$$*Hw tare*  An  M l *  »t & r c*.  fe^tM*******  @tsr# mm®  teste  t© f&ga  Sftstrndp .to@&%l§atto  m$m m. mmm «f 4 i f f « « « i t #f«e€  -~5  ACKMOWLEDGEMENT I t i s a pleasure to acknowledge the many h e l p f u l suggestions o f Dr. V/. F. Seyer, under •whose d i r e c t i o n the work was c a r r i e d out. I am also very g r a t e f u l to E. Hutchinson f o r the preliminary work on the apparatus and method u t i l i z e d i n t h i s investigation.  TABLE OF CONTENTS OBJECT OF RESEARCH  1  THEORY  1  Concept of Interfacial Tension . . Theory of Bubble Method  1 2  METHOD AND APPARATUS  5  Methods of Determining Interfacial Tension . . . General Description of Apparatus . . . . . . . . Heating and Temperature Control . . . . . . . . Constant Temperature Bath ...... Bubbling Tubes Pressure Regulating System . . . . . . . . . . .  $ 7 8 8 9 10  MATERIALS .  11  EXPERIMENTAL PROCEDURE  12  Calibration of Apparatus . . . . . . . . . . . . 12 Cleaning of Apparatus . . . . . . 13 Description of Run  13 1$  RESULTS TREATMENT OF RESULTS Empirical Equations Interpretation of Data Accuracy of Method CONCLUSIONS  .16 16 ...18 19 20  LIST OF DIAGRAMS Details of Bubbling Tubes  .7  Details of Pressure System  7  Details of Water Bath Graph of Interfacial Tension vs. Temperature  ... 7 . . . . 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 obtained about cis- and trans-decahydronaphthalene that the present investigation into the interfacial tension of the compounds against 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 molecules from the interior to the surface. This tendency of a surface to contract leads to the concept of surface tension. It is defined as the force in dynes acting 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 molecules are attracted by the molecules of the other surface which tends to reduce the effect of the attractive forces of the interior 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) (2) (3) (U)  Simon, M., Ann. Chim. Phys., 3, $> 1851 Jaeger, G., Sitzb. Akad. Wiss. Wein., 100, 215, 1891 Cantor, M., Weid. Ann. Phys., hi, 399 1892 Jaeger, F. M., Z. Anorg. Allgem. Chem., 100, 1, 1917 3  tube adjustable to a known depth, and although he arrived at i n 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 maximum 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* in 1918.  .  1  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  ^  hei  S 't Jl  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) (2) (3) (U)  Ferguson, A., Phil. Mag., 28, 128, 19lli Feustel, Drud. Annalen, 16, 6, 1905 Schroedinger, E., Ann. Physik, U6, IjlO, 1915 Verschaffelt, J. E., Commun. Leiden, Suppl. No. U2d, 1918  (U)  i d production o f bubbles. In 1922, Sugden employed two tubes o f d i f f e r e n t r a d i i 1  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 between the pressure and the r a d i i o f the tubes, such t h a t ;  T—surface tension P—pressure difference f o r two tubes X  l'  X  2 ^ d r a d i i o f the small and l a r g e t i p s r e s p e c t i v e l y . (These corrected values are obt a i n e d from Bashforth and Adams Tables . ) e  c  o  r  r  e  c  t  e  A more convenient way o f using t h i s r e l a t i v e method i s to c a l i b r a t e the apparatus against a known i n t e r f a c e and o b t a i n the value o f the denominator i n ( 2 ) . For tubes o f small r a d i u s , Sugden's approximate equation, ( 3 ) , can be used to give r e s u l t s accurate to one p a r t i n 1000 which i s more accurate than the r e s u l t s obtainable w i t h the apparatus.  AP  ['+  0-63 ^£*C^  C3)  A—an a r b i t r a r y constant P—pressure difference between the two tubes r - r a d i u s of larger t i p d —density o f denser phase Hutchinson^ modified Sugden's apparatus f o r 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 A c t i o n . Camb. U . Press. London, 1883 (3) Hutchinson, E . , Trans. Faraday S o c , 39, 229, 19h3  h" — h e i g h t of meniscus i n tube with smaller t i p h  1 1  — height of meniscus i n tube with l a r g e r t i p  d — density of phase inside tubes r — radius of larger, t i p h-(h«-h") A - a r b i t r a r y constant f o r apparatus METHOD AND APPARATUS Methods of Determining I n t e r f a c i a l Tension The most accurate values o f i n t e r f a c i a l tension reported i n the l i t e r a t u r e are accredited to the drop-weight method as o r i g i n a l l y employed by Harkins and Humphrey -. The values l i s t e d In the 1  International C r i t i c a l Tables have almost a l l been obtained i n t h i s manner. However, the method i s not the most applicable i n a l l cases, and a number of s p e c i a l methods have been devised. In the drop-weight method, the t i p must be very accuratel y made, the drops allowed to form very slowly, and i f t h i s rate i s not controlled with extreme care, r e s u l t s are not reproducible. A modification of t h i s method involving weights rattier than v o l umes, as worked out by Ward- and Tordai , i s reported to give extremely good r e s u l t s without the tediousness of Harkin's method. •a  The use of c a p i l l a r y r i s e methods by Reynolds ^ and other -  investigators has y i e l d e d consistent r e s u l t s which compare favorably with the drop-weight values. The trouble with the method, (1)  Harkins, W.,  228, (2) (si)  and Humphrey, E., J . Am.  Chem. S o c ,  38,  1916  Ward, A., and Tordai, L., J . S c i . Instruments, 21, Reynolds, J . Chem. S o c , 119, U66, 1921  lU3,  19UU  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 Speakman with good results* In his apparatus the interfacial ten1  sion can be calculated by noting the difference in pressure required to force liquid to an arbritary level in two tubes of different 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 interfacial 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 adaptable to temperature variation measurements. Several unique methods have been developed; namely, Meyer stein and Morgan ;>s^ centrifugal method, Addison's* vibrating 1  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 equipment. In a l l cases the theory has been worked out by the experimenters, 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 Hutchinson for measuring the interfacial tension between molten white 1  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 Hutchinson , see F i g . l . The essential part consists of two pyrex bub1  bling tips of different radii for producing bubbles of one liquid inside the other* These tips are joined to a reservoir having sidetubes in which the heights of the liquid can be read with a cathetometer. The side tubes are identical so that no capillary corrections need be applied. The tubes are rigidly mounted in a rubber stopper and connected to a pressure system (Fig. 2 ) . With the apparatus 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 visibility than o i l . Agitation is supplied by a 1 i n . propellor 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 thermometers 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 cell. A Cenco De Khotinsky thermoregulator and a Cenco Supersensitive relay kept the bath temperature constant to within one two hundredth of a degree. This was determined by using the resistance 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 i n . 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 measure the same distance with the meter stick outside the cell. No difference in distance was observable and the apparatus was considered 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 substantially 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 examined 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 prevented water from backing up in the side tubes. The side tube and tip were placed at right angles to one another to facilitate reading 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 problem in itself. Hutchinson had a side tube on his cell and decreased 1  the pressure above the cell liquid with an aspirator. This method was tried without success. It was found that the bubbles were produced too rapidly and could not be properly controlled. Since the meniscus could not be closely followed, the method was finally abandoned 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 produced very slowly. After some practice i t was found that the pressure 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 filled with mercury, 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 vessel. 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 temperature 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 crystallization 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 darkness. It was noted that the trans tended to discolour in the presence 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 benzenewater 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  dif-  ference f o r the two t i p s was observed s e v e r a l times and the mean constant c a l c u l a t e d . Cleaning o f Apparatus Before each determination* the bubbling t i p s and tubes were cleaned w i t h hot s u l f u r i c a c i d and bichromate s o l u t i o n , washed w i t h a l c o h o l and r i n s e d w i t h d i s t i l l e d water. The tubes,were then d r i e d f o r 20 min a t 110°C. A f t e r making a determination, .with c i s d e c a l i n i t was found necessary to heat the cleaning s o l u t i o n to about 120°C before any s a t i s f a c t o r y cleaning was observed. The c r i t e r i o n f o r c l e a n l i n e s s was t h a t 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 c l e a n i n g the c e l l . D e s c r i p t i o n o f Run The c e l l was f i l l e d w i t h d i s t i l l e d water to such a height t h a t 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 o f the t i p s . The c e l l was placed i n the constant temperature bath to allow 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 f o l l o w i n g manner* D i s t i l l e d water was poured i n t o the s i d e tubes u n t i l the t i p s were j u 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 i n t o 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 equilibrium, the hydrocarbons were shaken with distilled water and left overnight. The organic phase was then used in place of the anhydrous 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 certain 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 unt 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 meniscus 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 temperature 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 temperature at the upper end* RESULTS The calibration constant used in Equation (U), as determined using a benzene-water interface was found to be value of the interfacial tension was taken as o  35.00  0*01813.  The  dynes per cm  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 Davenport , this corresponds to 1  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 Interfacial Tension  20  30  UO  50  60  70  51.U0' 50.99 50.55 50.09 U9.69 U9.U0  Cis-decalin '.Temperature  20  30  Interfacial Tension  51.7U  51.U5  20  30  hO  50  51.12 50.89  60  70  50.5U  50.U0  60  70  Cyclohexane Temperature  UO  50  Interfacial 51.01 50.67 50.15 U9.72 U9.U0 U9.09 Tension N-decane Temperature  20  30  hO  Interfacial 51.2U 50.71 50.U2 Tension  50 U9.86  Table 2. The densities of benzene, n-octane, cyclohexane and ndecane 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 relationship 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 = $2.20 - o.oiaot  Cis-decalin  y = 52.26 - 0.0275t  Cyclohexane  y - 51.79 - 0.0395t  N-decane .  y = 52.11 Table 3.  where:y  interfacial tension in dynes per cm  t  temperature in °C  Although only temperature has been considered in the above equations, i t must be realized that other factors influence the values of interfacial tension. The change of solubility of the hydrocarbons in water with temperature will cause density changes and these should be included in the equations to make them completely correct. However, since the solubility of hydrocarbons in water is very slight, i t was considered negligible in the present case. Comparison of values obtained using the bubble pressure method with values listed in the literature obtained using the drop-weight method are given below. Trans-decalin-water at 25°C Guest and Lewis"'"  50.98 dynes per cm  Bubble pressure method  5l»18  Percent deviation  "  0.39$ 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  0.3556 too high  Percent deviation Cyclohexane-water at 25°C Matthews"'"  50.28 dynes per cm  Bubble pressure method  50.80  11  1.03% too high  Percent deviation Table k.  No data could be found in the literature for the interfacial 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 equation 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- configuration 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 transconfiguration accounts for the difference in slope of the cis- and trans-decalin. Accuracy of Method The accuracy of the method depends chiefly on the accuracy 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. Therefore there are other factors which must play a more important part than the accuracy of the cathetometer. Some measurements were made with the apparatus improperly cleaned and results 10 to 1$% higher than the reported values were obtained. It was noted that unless the tips were very thoroughly cleaned before each determination; the readings became progressively higher. The importance of clean apparatus cannot be stressed to greatly in interfacial tension measurements. Comparing the difference between reported values and those listed in the literature, the greatest deviation is 1.03$ 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, Hutchinson makes no mention of how he corrects 1  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 will 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 f e r e n t s i z e d t i p s and t e s t i n g the l i m i t s o f the equation. The l i q u i d s could be interchanged allowing the denser water to be bubbled through the l e s s dense hydrocarbon and noting whether any d i f f e r e n t values of the i n t e r f a c i a l tension were obtained. This was not attempted because o f the l i m i t e d quant i t y o f pure hydrocarbons a v a i l a b l e . T h i r d , there i s the need o f knowing the s o l u b i l i t y o f 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 y e t the d e n s i t y of the organic phase has to be accurately known to c a l c u l a t e the i n t e r f a c i a l tension from Equat i o n (U). The method seems to give c o n s i s t e n t r e s u l t s and the apparatus i s simple to b u i l d and operate. The method i s one t h a t could be a p p l i e d to i n d u s t r y w i t h great advantage. Once the apparatus has been c a l i b r a t e d against a known i n t e r f a c e o n l y the heights o f the l i q u i d s i n the side tubes need to be read f o r a determination.  SUMMARY  i  — — — —  1. The bubble pressure method has been s u c c e s s f u l l y used to determine the i n t e r f a c i a l tension o f severa l hydrocarbons against water over the temperature range 20 t o 70°C. The hydrocarbons used were c i s and t r a n s - d e c a l i n , n-decane and cyclohexane. 2. E m p i r i c a l equations have been determined f o r 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 i o n s h i p has been assumed* 3* A d i s t i n c t difference i n slope between c i s - and t r a n s - d e c a l i n was noted and an attempt made to a c count f o r i t on the b a s i s of molecular volume and polarization. U* An attempt has been made to give some i d e a o f the accuracy o f the method and the e r r o r s i n v o l v e d . 5.. Several suggestions have been made whereby the method might be improved.  BIBLIOGRAPHY Addison, C. C., P h i l . Mag., 36, 73, 19U5 Bashforth, F., and Adams, J . C , An Attempt to Test the Theor i e s o f C a p i l l a r y Action, Camb. U. Press, London, 1883 Cantor, M., Weid. Ann. Phys., hi,  399, 1892  Ferguson, A., P h i l . Mag., 28, 128, 191a Feustel, Drud, Annalen, 16, 6, 1905 Guest, W., and Lewis, W., Proc. Roy. S o c , 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. S o c , $2, 1751, 1930 Hutchinson, E., Trans. Far. S o c , 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. S o c , 35, 1113,  1939  Meyerstein, W., and Morgan, J . D., P h i l . Mag., 35, 335, 19hh Reynolds, J . Chem. S o c , lltU9,  1933  Schroedinger, E., Ann. Physik, 1*6, 1*10, 1915 Seyer, W. F., and Barrow, G. M», J . Am. Chem. S o c ,  70, 802, 19a8  Seyer, W. F., and Davenport, C. H., J . Am. Chem. S o c ,  63, 2U25, 19U1  Simon, M., Ann. Chim., Phys., 3, 5, 1851 Speakman, J . C , J . Chem.sSoc, lhh9, 1933 Sugden, S., J . Am. Chem. S o c , 121, 858, 1922 Verschaffelt, J . E.,.Commun. Leiden, Suppl. No. U2d, 1918 Vonnegut, B., Rev. S c i . Instruments, 13, 6, 19^2 Ward, A., and Tordai, L., J . S c i . Instruments, 21, lU3, 19UU  

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