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1948

The determination of the surface tension of benzyl ether The determination of the surface tension of benzyl ether

Sze-Kwei Min

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THE DETEmrrNATION OF THE SURFACE TENSION

OF BENZYL ETHER

By

SZE - KVY'EI Iv1IN

A

THESIS

submitted to the faculty o~ the

SCHOOL OF MINES AND ~JlETALLURGY OF THE UNIVERSITY OF MISSOURI

in partial fulfillment of the work required for the

Degree of

MASTER OIP SCIENCE, CHEMISTRY MAJOR

Rolla, Missouri

1948

~...~~~~Approved by --,{;-/"""':: ---------------------------------­

Ass i e Proressor of Physical Chemistry

i

ACKNOvVLEDGMENT

The author vlishes to express his sincere apprecia­

tion to Dr. C. J'. Monroe, Associate Professor of

Physical Chemistry, and Dr. W. T. Schrenk, Chairman

of. the Department of Chemistry and Chemical Engineering,

Missouri School of Mines and Metallurgy, for their

invaluable suggestions and guidance in the preparation

of' "this thesis.

ii

CONTENTS

List of Tables •.••.••••.••••••••.•••••••••••

Introduotion •••••••••••• ~ •••••••••••••••••••

Acknowledgment ••••••••••••••••••••••••••••••

Review of Literature ••••••••••••••••••••••••

Traube's Stalagmometer ••••••••••••••••••••••

Calibration of Stalagmometer ••••••••••••••••

Preparation or Substances •••••••••••••••••••

~ag~

i·

iii

1v

1

2

10

13

16

.......................List of Illustrations

Dete~ination of the Density or Benzyl Ether

By the Pycnometer Method ••••••••••••••••••

Procedure or Sur:face Tension Determination

Determination of the Interfacial Tension

Between Benzyl Ether and Water .

Conclusion ••••••••••••••••••••••••••••••••••

f3\lDIDlC1~jr •••••••••••••••••••••••••••••••••••••

Bibliography ••••••••••••••••••••••••••••••••

Vita ••••••••••••••••••••••••••••••••••••••••

18

26

36

38

39

40

41

iii

LIST OF ILLUSTRATION

Drop-Weight Corrections ••••••••••••••••1

2 Diagram of Traubefs Stalagmometer ••••••

7

12

3 Apparatus for the Distillation of

Benzyl Ether ••••••••••••••••••••••••• 17

4 Relation between Density and Temperatura

of Benzyl Ether •••••••••••••••••••••• 25

5 Relation between Temperature and Surface

Tension of Benzyl Ether •••••••••••••• 34

Relation between Temperature and-2/3r(d) for Benzyl Ether ••••••••••• 35

iv

LIST OF TABLES

Tables

1.

3.

4.

5.

Drop-Weight Surface Tension Corrections

Data from Calibration of Stalagmometer

Calculations or Density Measured at 25°C.

Calculations of Density Measured at 300 e.Calculations of Density Measured at 35°C.

5

14

20

22

24

6. Data rrom Surface Tension Determination

of Benzene at 25°0.................... 287. Data rrom Determination of the Surface

Tension of Benzyl Ether at 20°C....... 29

8. Data from Determination of the Surface

Tension of Benzyl Ether at 25°0....... 30

9. Data from Determination of the Surface

Tension of Benzyl Ether at 300 e....... 31

10. Data rrom Detenmination of the SUrface

Tensioa of Benzyl Ether at 35°0....... 32

11. Determination of the Interfacial" -Tension

Between Benzyl Ether and Water at 20°C. 36

1

INTRODUCTION

The accurate determination of surface tension is of

importance in the investigation or theories or surface

structure, the struoture of liquids, molecular cohesion,

in the study of colloids, especially in physiological

work, and in various lines of technical chemistry. The

two methods most commonly used for dete~ining surface

tension are the capillary rise method and the drop

weight method. The theory of the fo rmer is simple, but

its technique is difficult. Its use in some cases is

the cause o~ errors as high as 30%, due to its inapplic­

ability to certain classes of substance, and is much more

sensi~ive to the action of ~puritias. The drop weight

method is applicable to a wide range of liquids and the

experimental work is notdif'ficult. As a result of the

development of this method by Harkins and Brown, the

accuracy of this method is more reliable.

2

REVIIDV OF LI'TERATURE

The theory o:f the drop weight method has been worked

out in a preliminary way be LOhnstein,(l} but, unfortunate­

ly, the surface tension of a liquid oalculated by the aid

or his theoretical curve can diverge 4 per cent to

30 plus per cent. Rayleigh(2} in 1896, determined the

weight or water drops falling from tubes ot various

diameters. His data could be used to standardize the

method, if he had used perforated discs instead of open,

thin walled tUbes, for all his measurements. It is es­

sential that more than one liquid should be used in the

standardization.

Morgan later determined values for drop weights

which are seemingly experimentally accurate, but he paid

no attention to the theory of drop formation. His cal-

culations were carried 'out by a method 'Which insures

that many or his sur~ace tension values must be incorrect.

The Morgan method of calculation does not give the rela­

tive values correctly, and the errors are such that it

glass tips or convenient size were to be chosen for the

determination ·of interfacial tension the error might be

quite large. Even with single liquids the results devi­

ate as muoh as 3 or 4 per cent trom the correct. values.

Thus, almost all of the' surface ten~ion values fO,r organic

--------------------------------------------------------(1) Ann. Physik (4) 20, 237-68 (1906); 21, 1030 (1907)(2) Phil. Mag. , (53) 48, 32],-3"

3

liquids are much too low, while those for water are very

good.

Around 191.2, Harkins and Humphery( 3) carried out

a preliminary standardization of the drop weight method

for the determination of surface tension over a limited

range. In 1918) William D. Harkin and F. E. Brown used

about 30 new extremely accurate dropping tips, to extend

their investigations to such an extent as to make the data

a basis for a method or calculating accurate values of

'surface tension from drop weight data.

While the law of Tate (W=Mg=2~r¥) considers that the

weight of a drop is proportional to the radius r of the

tip, and to the surface tension r, it rails to recognize

the fact that it is also a function of the shape s of

the drop. The shape depends on the rat.io between some

linear dimension of the tip, such as r, and a linear

dimension of the drop 1 or

W = Mg = 21l"rrf( r/1.l

As the cube root of the volume of the drop VJ./3 varies

as a linear d~ension of the drop,

W = Mg = 2Trrr If (r/V) = 2-rrr <p

In p1.ace of VJ/3, any other quantity which varies as a

linear dimension of the drop, such as a, the square root

of the capillary constant a 2 , may be used. Here a should

be expressed in centimeters,

--------------------------------------------------------(3) . J Am. Chem. Soc. 38, 246 (1916)

4

W = Mg = 27Trrf(r/a)

This has the form of Lohnstein's equation, but it

may be deduced without the use of the objectionable hypo­

thesis introduced by Lohnstein, that the angle of contact

of the hanging drop with the tip, is the same immediately

before and after the detachment of the talling drop.

Indeed, this assumption seems to havana real meaning,

since atter the fall of the drop the remaining liquid

changes its form with extreme rapidity, and it seems

dif~icult to detenmine at just what instant to determine

the angle or contact.

For any special drop the values of r/yl/3 and ria

are in general different, but 'f (r/yl/3) and f( ria) are the

same. Harkins and Brown had deteIEined the value of the

function, in terms of r/yl/3 and of ria. Of these two

sets of variables, r/yl/3 is the more convenient, since

both r and V are determined in the experimental procedure,

but a is not, and hence must be oal-culated by methods of

approximation, Which, however, does not reduce the accuraoy

with which it may be calculated.

Table 1 and Figure 1 are Har~ins and Brown's re­

suIts. (4)

--------------------------------------------------------(4) J. Am. ·Chem. Soc. Vol. 41, pp. 515, 519 (1919)

5

factors for multipli-

<f(r/v1/} p

(1.0000) (1.0000)

0.?256 1.3780

0.?011 1.4263

0.6828 1.4645

0.6669 1.4994

0.6515 1.5349

0.6362 1.5718

0.6250 1.6000

0.61?1 1.6205

0.6093 1.6412

0.6032 1.6578

0.6000 1.6667

0.5992 1.6688

0.5998 1.6672

0.6034 1.6572

0.6098 1.6398

0.6179 .1.6183

0.6280. 1.5923

0.6407 1.5508

0.6535 1.5302

(0.6555) (1.5255)

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

••••••••••••••••••••••••

·.......................

••••••••••••••••••••••••

• • • • • • • • • • • • • • • • • • • • • • • •

• • • • • • • • • • • • • • • • • • • • • • • •

••••••••••••••••••••••••

·.......................

1.20

1.225 •••••••••••••••••••••••

0.30

0.00

0.35

1.05

1.15

0.40

0.45

0.50

1.00

0.55

0.65

0.90

0.50

0.70

0.75

0.95

0.85

0.80

TABLE 1 Drop-Weight Surface Tension Corrections

Whioh May be Used Directly Without The Necessity of Em­

ploying Approximation Methods.

(Factor for division = t(r/~/3)

cation = /J.)r/v1/ 3

6

1.25 • • • • • • • • • • • • • • • • • • • • • • • (0.6521) (1.5335)

1.30 • • • • • • • • • • • • • • • •• • • • • • • (0.6401) {1.5622}'

1.35 • • • • • • • • • • • • • • • • • • • • • • • (O.6230) (1.6051)

1.40 ••••••••••••••••••••••• (0.6033) (1.6575)

1.45 ••......•.•.•......... ~ (0.5847) (1.7102)

1.50 ••••••••••••••••••••••• (0.5673) (1.7627)

1.55 • • • • • • e • • • • • • • • • • • • • • • • (0.5511) (1.8145)

1.60 ••••••••••••••••••••• e .• (0.5352) (1.8684)

7.

1-I-..1··;-!·+··1·...·+

+·1

·;··1·+

·/+-··1

···...,--/-'1-:-;··1

+-,-,....:"·'··.·I·I~.~.J"'

..I....:;·''"ri

~ji

I..;··,·j·/I

....·f·.....·..r··+·{·····,,,···'..-t·..I-'

......",:

ftl

+"'..~···.''A··.:.o'''F''·,·..·....~....··11

,...J·1.....·..'

.,......j\

..,:._"

:.i

;.'1

--..i··

"!

.....

:,...

I.•.;.!-:.

II

1-1j,

'"...,

'r'

....

...:.;~'Q

,1,,','

.;1/...

,..:I

·r·H'r\

I.U

i"

.,!

.loj

~

~~

~~

~~

~~

~()

r-,.··t·"

,··++

····!-I·!J!I.I

..•..•..,..,.J

.,.

J+

-I-·I-f--f··'·1·+-t··I'+

-·'-'...t'-

y+

'r........-f..·:..,....,.

-I..,

...._or'

I--+-'-+-I-"+"~···;·-+-·f.~t:t-·1

,-..f!.

i.

~~

,........:.....

....Fi

H·i

..........L.

iri')

'l+-~:"

,.++

J._...

~.....

.-t-l-"!r['!

--,--I

~~

\':)~

~~

~'>-

~'a

QQ

~~

~~

8

If a gram-mol of a liquid were suspended under con­

ditions such that it were removed from the influence of

gravity, it '\tvo-uld assume the geometrical form involving

the least surface, namely, the sphere. The surface thus

presented is the molal surrace. The product. of this sur­

face and the surface tension has the dimensions of energy

and represents the energy involved in the formation of

the molal surface against the surface tension of the liquid.

constant

K=or

From these considerations, the following mathematical re­

lations are derived.(5) I~ 80

is the molal surface, we get,

8 Ot:)V2/ 3 = k(M/d)2/3o

and r 8 = k({M/d)2/3oDifferentiating with respect to the temperature,

-d(rS ) kd( nM/d)2/3)____2__ = _ ---------~~--- =

dT dT

d<r(M/d)2/3)

dT

~nen integrated over an appreciable temperature range,

we obtain,

and, finally, we obtain the Eotvos-Ramsay-Shields equation:

r1 (M/d l ) 2/3 . - r 2 (M/d2 )2/3

-------------------------- = KgT2 -T1

where,

9

y 1 and r 2 = surface tensions of the liquid at the

respective temperatures Tl and Tsd1 and d2 = densities of the liquid at the above

temperatures

M = molecular weight of the pure liquid

Though the value or Kg is said to be the same for

all pure non-associated liquids having a value of 2.12 ergs

per degree when the surface tension is expressed in dynes.

Walden and swinne(5) have shown that it varies with the

size of the molecul'~. They developed a simple expression

for calculating the value of Kg from the sum or the square

roots o~ the atomic weights A.

--------------------------------------------------------(5) E. W. Washburn, Principles of Physical Chemistry

2nd.. ad. 1921

10

TRAUBE'S STALAGMOIvJETER(6)

-----------------------------------------~------------ --

(6) Traube, Bar., 1887, 20, 2544, 2824

11

polished, when necessary by means of a piece of fine, soft

linen or clean cotton cloth. Even slight traces of grease

on the dropping surface will markedly alter the size of

the drops formed. Care should also be taken to preserve

the apparatus from being shaken while an experiment is

being carried out, as thereby the drops of liquid may be

caused to raIl before they have attained their maximum

size. For the same reason the velooity of flow of the

liquid must be regulated so that the drops are not fonmed

too rapidly; and although the rate of dropping may be varied

up to a certain point,. without affecting the size of the

drop, it should not be allowed to increase above a maxi-

mum of 2 drops per minute. If the natural rate of drop­

ping is greater, it must be retarded either by placing the

finger lightly on the upper end of the tube, or better,

by attaching to the latter a piece of fine thermometer

capillary tUbing of greater or shorter length according

to the rate of dropping.

For determinations with liquids of great~y different

viscosities and conseQuently, dirferent rate of dropping,

one may also use stalagmometers ·with capillary tubes of

different bores.

In order that the determinations may be carried out

at constant temperature, the end of the stalagmometer is

passed through a rubber stopper which fi ts into the neck

or a small tube or bottle B (Figure 2). The apparatus

may then be placed in:.8. thermostat.

A

B

12.

A. Stalagmometer B. Weighing Bottle

Fig. 2 Diagram of Traube's Stalagmometer.

13

CALIBRATION OF STALAGlIl0n_[ETER

A. Calibration of volume

The object of this experiment was to calibrate the

Stalagmometer so that the exact volume contained between

the upper and lower marks on the tube would be known, and

also to find the exact volume of each of the &aaller

division.

The apparatus was set up as shown in Figure 2 and

during the determination it was kept in the thermostat

at 18°C.

Mercury was placed .in the tuqe and held there by

means of a stopcock to which a capillary tube had been

attached. This stopcock also provided a means for con­

trolling the rate of flow of the liqUid. The mercury was

allowed to fall very slowly until it reached the upper

mark on the surface tension tube. The apparatus was then

placed in the thermostat and the mercury was allowed to

fall from the upper mark to the lower mark into a weighing

bottle which had been attached to the apparatus by means

of a rubber stopper. The mercury in the weighing bottle

was then weighed and from this the volume of the tube was

calculated.

To determine the exact volQme of each of the smaller

divisions, mercury was allowed to fall until it dropped

several divisions, say 10 or more. The mercury in the

weighing bottle was then weighed and from this the weight

corresponding toone scale unit was obtained.

14

TABLE 2 DATi~ FI~Ort CALIBRATION 0]' STALAGI.ICI}/LETER

(1 ) (2 ) (3 ) Average

Vit. of bottleand Hg. ( g. ) 84.7545 84.8372 84.8095

\fit. of bottle(g.) 30.4805 30.4822 30.4822

VIt. of Hg.(g.) 54.2740 . 54.3553 54.3273

Sp. Vol. of Hg.at 18°C.(CC./g.) 0.0738 0.0738 0.0738

Vol. of' Hg. (cc .. )(Vol. of bulb :fromzero to zero at18° C. ) 4.0074 4.0088 4.0090 4.0084

Cubic coefficientof glass per C 0.000025 0.000025 0.000025 0.000025

Vol. or bulb at20°C. (cc.) 4.0076 4.0090 4.0092 4 .0089

Vol. o-r bulb at25°C. (co.) 4.0081 4.0095 4.0097 4.0091

Vol. of bulb at30°C. ( cc. ) 4.0086 4.0100 4.0102 4.0096

Vol. of bulb at35°C. (co. ) 4.0091 4.0105 4.01C)? 4.0101

\Tol. of a smalldivision of lowerscale at ISoe.(co.) O. ('045 0.0046 0.0045 0.0045

Vol. of a smalldivision of upperscale at lSoC.(co.) 0.0051 0.0051 0.0051 0.0051

15

E. Measurement of diameter of tip

The diarIleter of the tip was measured vd tIl a screw

micrometer carrying a microscope which gave a magnifi­

cation of 10 diameters. One division of the screw head

corresponded to O. 0005 em. 8,nd the micrometer reading vvas

cOl'lrected by cOTIlparison wi th an invar scale VJhicll had

been calibrated by the Bureau of Standards. Five read­

ings were made on each five different diameters for the

tip.

Diameter

Radius

(1 )

0.862

0.431

(2 )

0.853

O.42?

(3)

0.858

0.429

(4)

0.856

0.428

(5) Average

0.860 0.858

0.430 0.429'

16

PREPARATION OF SUBSTAl~CES

The benzene was treated by shaking several tlines with

concentrated sulruric acid, then permitted to stand in ,

contact with sulfuric acid :for two days. The acid was

neutralized with sodium hydroxide, and the benzene re­

peatedly washed with conductivity water. After drying

over calcium chloride, it was distilled twice. The

portion coming over between 78°0. was collected for use.

The benzyl ether is a colorless, oily liquid. Its

boiling point is 295°-8°C. (7) As it decomposes at

290 0 -300°0., reduced pressure distillation was used for

purification of this compound. The apparatus was set up

as shown in Figure 3. To prevent bumping the dis­

tilling flask was one-third filled with glass wool. The

portion coming over between 1520 -154°0. , when the baromet­

ric pressure was 7 rom., was collected. After drying over

calcium carbide, it was redist,illed and only the middle

portion was collected and was used for this research.

(?) Huntress and Mulliken, "Identification of Pure Or­ganic Compoundsu , Order I, P. 551,1:7640 (1941)

17.

~

'"t~~~~~

'"~

~~~~

~~~~

t~

.~

~~

~

~

0

.\

~~

r

~~~

.,~

~"'"

~"

.~~

~

~.

...

~'-lj

~

~

~"\.

~

~~

~.,

~~

II(

.~

""~

~~

~'~

~

l~

~~

~~

~~

.")~

,~

"~""

~

'"~

~~

'"t

-~

,~

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~~ ,~

~\J

~

~

DETEffi\lIINATION OF THE DENSITY OF BENZYL ETHER

BY TI-IE PYCNO:METER IJ1ETHOD

18

19

and escape of any liquid while the bottle is being trans­

ferred to the balance room and weighing made there at a

temperature which may be higher than that of the thermo­

stat. Repeat this determination, cooling the pycnometer

with liquid below 25°0. and adding-some -more of the liquid,

returning the pycnometer to the thermostat for the requi­

site t~e and reweighing. Repeat the detenmination until

the weighings check within 2 or 3 mgs. (An error of one

IDlll. in the adjustmerlt of the liquid in the pycnometer

with capillary tube of diameter 0.7 mm. and volume 25 CC.

corresponds to a weight change of about 0.3 mg. or tem­

perature change or 0.01 degree e.).

Record the barometric pressure, the temperature of

the air in the balance room, and the density of the air

at the temperature and pressure in the balance room, which

may be obtained from tables.

The calculations were indicated in the following

tables 3, 4 and 5.

Figure 4 shows the relation between the density and

temperature. It appears that the relation between the

temperature and density can be represented by an equation.

d = do +rJ.(t - to) + f3 (t - t '2oJ ..:·

where d = density at 25°C.0

~ = -0.00015

(3 = -0.000034

20

TABLE 3 Ci-iLCULJ\.TION OF lJEI~SITY IvIE.A.SURED AT 25°0.

( 1) ( 2) (3 ) Aver.

1. Wt. of dry pyc. P + A 26.5074 26.5072 26.5074 26.5074

2. Vit. of pyc. + 'Vvater P + v: 50.6615 50.6625 50.6618 50.6617

3. Wt. of pyc. + li~uid P + L 51.7320 51.7325 51.7318 51.7323

4. Density of water at 25°C. dw (from table) 0.99707

732.00

28.4

5. Barometric pressure (rum.)o

6. Temperature of balance room ( C.)

7. Density of air at Bar. p. and Bal. Room Temp.

(from table)

8. (2)-(1) = Vi - A ( approx. Vvt. of water in pyc. )

9. (3)-(1) = L - A (approx. V!'t. of liquid in pyc. )

10. {W-A)/dw = V ( approx. volume of pyc. )

0.001129

24.1543

25.2249

24.2255

11. A = Vda (approx. m. of air in pyc.) 0.0273

12. (W-A) + A = W (Wt. of water corrected for

buyancy of pyc.) 24.1816

13. Density of wts = dwts (density of brass) 8.40

.14. Diff. in vol. of weights {W-A)/8.4 2.871

15. Buoyancy correction for weights {W-A)da/8.4 = a 0.00324

16. Wt. of water corrected for buoyancy of wts = W -a 24.17826

17. (3)-(1) = L - A !5.2249

18. (~A) + A 25.2521

19. (L-A)da/8.4 = at (buoyancy correction for weights) 0.0034

20. Wt. of liquid corrected for baoyancy of pyc. and

wts. = (L-A) + A-a'

21 d25 = density' of li~. at 25°C. relative to that• 25' '1

of water at 25°0. = t1~t-··

25.248'1

1.0443

22.

(l) (2) (3)

21

Aver.

1.0412

22

TABLE 4 CALCULATION OF DENSITY MEASURED AT 30°0.

(1) (2 ) (3) Aver.

1. Wt. of dry pyc. P + A 26.5074 26.5072 26.5074 26.5074

2. Wt. of pyc. + water P + W 50.6090 50.6090 50.6084 50.6088

3. Wt. of pyc. + liquid P +"L 51. 6333 51. 6333 51.6334 51. 6333

4. Density of water at 300 dw (from table)

5. Barometric pressure (mill.)

6. Temperature of balanoe room (OC~

7. Density of air at Bar. p. and Bal Room Temp

(:from table)

8. (2)-(1)=W-A= approx. wt. of water in pyc.

9. (3)-(1)=L-A approx. wt. of liquid in pya.

10. 'B=A. = V = approx. volume of PYP.dw

11. A=V da = approx. wt. of air in pyc.

12. (W-A) + A = W = Wt. of water corrected for

buyancy of pyc.

13. Density of wts. = dwts = density of brass

14. Ditf. in vol. of: wts. = Y:!:~8.4

0.99567

732.00

28.4

0.001129

24.1014

25.1259

24.2063

O.02?3

24.1288

8.40

2.8693

0.003215. Buoyancy correction for wts. = ~=! da = a8.4

16. Wt. of water corrected for buoyancy of wts. = W-a 24.1256

25.1259

25.1533

0.0033

25.1500

(1) (2) (3 )

23

Aver.

21 d 30 =• 30

density of liq. at 30°0 relative to that

of water at 30°C ~ i~Ql_(16)

1.0424

1.0379

24

TABLE 5 ; CALCULATION OF ,DENSI~ MEASURED AT 35°0

(1 ) (2 ) (3) Aver.

28.4

732.00

0.99406

1. Wt. of dry pya. P + A 26.5074 26.50?2 26.5074 26.5074

'2. Wt. of pyc. + water P + W 50.5755 50.5755 50.5750 50.5754

3. Wt. or pyc. + liquid P + L 51.5371 51.5376 51.5374 51.5374

4. Density or water at 35°C dw (from table)

5. Barometric pressure (mm.)

6. Temperature of balance room (°0.)

7. Density of air at Bar. p. and Bal. Room Temp.

(from table) O.OOl12S

8. (2)-(1) = W-A (approx. wt. of water in pyc.) 24.0680

9. (3)-(1) = L-A (approx. wt. of liquid in pyc.) 25.0300

10. (W-A)/dw = V (approx. volume of pyc.) 24.2118

11. A = Vda (approx. wt. ,of air in pyc.) 0.0273

12. (W-A) + A = W (Wt. of water corrected for buyancy

of pyo~) 24.0953

13. Density of wts. = dwts(density of brass) 8.40

14. Diff. in vol. of wt.s. = (W-A)/S.4 2.8842

15. Buoyancy correction for weights = (W-A)da!S.4 0.0030

16. Vlt., of water corrected for., buoyancy of wts. = W-a 24.0923

17. (3)-(1) = L-A 25.0300

18. (L-A) + A 25.0573

19. (L-A)da/S.4 = a' (buoyancy correction for wts.) 0.0033

20. Vit. of li<luid correoted for buoyancy of pyc. and

wts. = (L-A) + A-a' 25.0540

21. dg~= d~sity Df liq. at 25°G relative to that of

water at 25°C = fi~1 1.0399

22. d25 = dg~dw 1.0337

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26

PROCEDURE OF SURFACE TENSIOI~ DETEillvlINATION

Certain precautions should be emphasiz8cl, since

careful attention to experimental details is requisite

to successful results. Though the drop may be formed on

the tip as rapidly as desired, it is imperative that it

be growing extremely slowly just before detaclllnellt.

Since the surface tension varies with the temperature

care should be taken that the temperature stays constant

within O.loC. range during the experiment. The capillary

tube must be perfectly clean and remain undisturbed

during the last stage of the drop formation.

The assembled apparatus is shown in Figure 2. The

capillary pipette is filled with warm ohromic acid solu­

tion and allowed to stand for several hours. The clean­

ing fluid is then removed and the pipette rinsed several

times with distilled water and finally with pure alcohol.

It is then carefully dried by drawing clean, dry air

through the capillary by suction. The liquid whose sur­

face teIlsion is to be determined is drawn through the

tip, filling the pipette to the upper mark O. The tip

is inspected, Inaking sure that the whole or the plane

surface is wetted by the liquid and that the vertical

surface adjacent to the edge of the tip is dry. The

apparatus is clamped rigidly in position in the water

bath, taking care that the plane surface of the tip is

horizontal and tubes protrude from the surfaee of the

27

water bath. The temperature of the water in the thermo-o

stat must be constant to 0.1 C. The liquid in tile pipette

is allovved to reacll therIllal equilibri urn Vvi ttl the thermo-'I

stat bath. This should take about fifteen minutes.

By allowin~; a dl~OP to fall, the drop e-luivalent per

scale division can be determined. The pipette is re-

filled/to the upper mark, then allowed to drop until the

liquid surface drops down to the lower mark. The total

nmuber of drops were counted and the surface tension of

this liquid can be Qetermine~ by the following calcula-

tions:

ris the surface tension in dynes

M" is the weight of one drop

r is the dia. of tip

g is the gravity constant

~ (r/v1/ 3 ) is obtained from Figure L

28

OF BE1~ENE AT 25°C

Ko. of small divisions per drop

No. of drops from 4.0091 co.

Vol. of one drop (cc.)

D - f \T1/ 3

~m. 0 v

Ratio of r/v1/ 3

tf(r/v1/ 3 )

Yo-eight of one drop (€~~.)

Surface tension (dyne/em)

(1 ) (2 ) ( 3) (4 )

13 13 13 13

71.50 71.21 71. J.1 70.82

0.0561 0.0564 0.0564 0.0;566

0.3812 0.3820 0.3820 0.3821

1.112 1.121 1.121 1.121

0.632 0.632 0.632 0.632

0.0489 0.0494 0.0494 0.0493

28.02 28.40 28.40 28.39

Value for benzene at 25°C. is 28.36±O.05dynes/cm. (as

recorded in the International Critical Tables). The experi­

mental value in the above table checks this closely. The

experiment on benzene was performed to verify the condition of

the glass tip as good.

TABLE 7 Di\.TA TI10IJl DETEIUviINATION 01'1 THE ·SURJ?ACE

TE]~TSIOI'J 0]1 BEI~rzYL ETHER AT" 20° C

29

(1 ) (2) (3) (4)

110. of small divisions per drop 14 14 14 14

1':0 _ of drops frODl 4. 0089 CC. 60.00 60.91 60.89 60. t)4

Vol. of one dI-OP (cc.) 0.0668 0.0660 0.0659 0.0659

DiTa. of V1/ 3 0.406 0.4045 0.404 0.404

Ratio of r/v1/ 3 1.058 1.060 1.060 1.060

'/( r/v1/ 3 ) 0.61'79 0.6179 0.6179 0.6179

Vleight of one drop (g- ) 0.0697 0.0688 0.0687 0.0687

Surface tension (dyne/em) 41.00 40.49 40.42 40.42

30

TABLE 8 DATA FROM DETER1iINATION 0F THE SuRFACE

TENSION OF BENZYL E~{ER-AT 25°C

(1 )

No. of small divi'sions per drop 14

(2 )

14

(3)

14

(4)

14

No. o~ drops from 4.0091 CC.

Vol. of one drop (co.)

Dim. of v1/ 3

Ratio of r/v1/ 3

\f( r/v1/

3)

Weight of one drop (g.)

Surface tension (dyne/em)

61.65 61.48 61.52 61.65

O.Oq50 0.0651 0.0652 0.0650

0.402 0.402 0.402 0.402

1.067 1.067 1.06? 1.067

0.6179 0.6179 0.6179 0.6179

0.0677 0.0678 0.0678 0.0677

39.94 40.01 40.01 39.94

TABLE 9 DATA FROM DETEIUUNATION OF THE SURFACE

31

32

TABLE 10 DATA FR011 DETERMINATION OF THE SURFACE

TEI\jSION OFt BENZYL ETHER AT 35°0

No. of small divisions per drop

No. of drops from 4.0101. co.

Vol. of one drop (co.)

Dim. o:f yl/3

Ratio o:f r/v1/ 3

'f{r/yl/3)

V{eight or one drop (g.)

Surface tension (dyne/em)

(1) (2) (3 ) (4: )

14 14 14 14

62.74 62.80 62.78 62.80

0.06392 0.06386 0.06388 0.06386

0.400 0.399 0.399 0.399

1.070 1.070 1.070 1.070

0.6179. 0.6179 0.6179 -0.6179

0.06607 0.06601 0.06603 0.06601

38.9879 38.9525 38.9643 38.9525

From the preceding four tables, the relation between

the temperature and surface ·tension of benzyl ether can

be determined by plotting a curve (Figure 5). It shows

that it is a straight line. The data were rearranged as

:follows:

Temperature (G.)<l

20

Surface Tension (dyne/em)

40.44

39.97

39.48

38.97

As the plot o:f

33

-2/3 .(d) against temperature gives a

straight line, (Figure 6), the Eotvos~Ramsay-Sheilds

equation:

d(t - t - 6)cfits the experL~ental facts.

The molecular weight of non-polar substance of lOW'

Dlolecular weight IvI may be cal cula ted from the equation

and assumption that k = 2.12. This value of k leads to

a low val ue of' M f'or benzyl ether. The val ue of k is

known to increase as the number of carbon atoms increase.

For benzyl ether, ass~ling a molecular weight equal to

the formula weight 198.25, k is equal to 2.96, approxi­

mately the same as the tabular val ue 2.90 for benzQ-

phenone; the number of carbon atoms is 14 for ether and

13 :for the phenone, the molecular volume and electro­

static force is approximately the s~e, therefore, the

value of k should agree to the extent indicated, and

greater to the extent found.

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35.

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DETE~IINATION OF THE INTERFACIAL TENSION

BETVYEEN BENZYL ETHER AND VIATER AT 20° C

To determine the interfacial tension between benzyl

ether and water, the procedure is the same as the detenmi­

nation of the surface tension of benzyl ether between the

ether and air, except the weighing bottle was filled two

thirds f~l with distilled water and the tip of the

Stalagmometer was dip~edbelow the surface of the water.

The data and calo.U1ations are shown in table 11.

TABLE II DATA FROM DETERMINATION OF TEE

INTERFACIAL TENSION BET\\~EN BENZYL ETHER

AND WATER AT 20°0

(1 ) (2) (3)

No. of small divisions per dxop 16 16 16

No. of drops from 4.0089 c,c. 42.19 42.52 42.81

Vol. of one drop (co.) 0.0950 0.0943 0.0936

Dim. or VJ./3 0.457 0.456 0.455

Ratio or r/vJ./3 O. 939 O. 940 0.941

t(r/vl / 3 } 0.6034 0.6034 0.6034

Weight of one drop (g.) 0.0991 0.0983 0.0976

Interfacial tension (dynes/em.) ~2~~2 ~2!.!! -~~.!.Z~-

Mean 59.12 dynes per em.

Work or cohesion of benzyl ether equals to 2 times its

surface tension.

2 x 40.44 = 80.88 dynes/em.

Work o:fadhesion between the benzyl ether and water equals

to the sum of surface tensions of these two liquids minus

the interfacial tension between them.

40.44 + 72.75 - 59.12 = 54.07 dynes/em.

Spreading coefficient of benzyl .ether on water

equals to the work of adhesion between the benzyl and

wat~r minus the work of cohesion of benzyl ether.

54.07 - 80.88 = -26.81 dynes/em.

38

From the preceding experiments and discussion,

it can be concluded that:

1. The density of benzyl ether varies vdth the

temperature according to the rollowing equation

( 2d = do -j- J.. t - to) + (J (t - to)

and

and

odo - density at to = 20 c.

-0.00015

-0.000034

and water is larger than the surface tension of ben-

zyl ether, but it is smaller than that of water.

4. The work of cohesion of benzyl ether is larger

than the work of adhesion bet"veen be.nzyl etller and water,

therefore the ether will be little soluble in water.

5. As the spreading coefficient is negative, the

ether '\\Till llot spread orl water.

1. A stalagrnolueter Vlas calibrated, vlith respect

to volume, using pure mercury.

2. Benzene and benzyl ether were purified.

3. The surface tension of benzene was deterrrO_ned,

a value agreeirlg closely vii th the accepted Valtle be-

ing obtained.

4. r.phe densi,ties of benzyl ether at different

teXl1peratures vvere deternlined. ttl\. curve represented by

the equation

was obtaihed.

5. The surface tensions of' benzyl etller at differ­

ent temperatures were measured by the drop-weight

method. A straight line was obtained by p+otting sur­

face tension against temperature.

6. The i11terfacial tension betvleen benzyl ether

and ,vater \~laS 1~OUlld to be 59.12 dynes per em. at 20° C•.

7. The spreading coerficient of ether on water

is -26.81 dynes per em••

o

BIBLIOGlRAPHY

Books

1. Hand Books of Chemistry and Physics. (1945)

2. Heilbron: UDictionary of Organic Compound." (1934)

3. Jasper: r'Laboratory Methods of Physical Chemistry."(1938)

4. Mulliken: "Identification of Pure Organic Com­pound. tr (1941)

5. Sprague: "Basic Laborat.ory Practice. 1t (1941)

6. Taylor: "Treaties on Physical Chemistry." (1931)

Periodicals

1. Harkin and Brown: J • .Am. Chern. Soc. -(1919')

3.

Harkin and Hilln~hrey: J. ~ Chern. Soc. Vol. 38,p. 246 (1916)

Lohustein: Ann. Physik. (4) Vol. 20, pp. 237-268(1906); Vol. 21, p. 1030 (1907)

4. Morgan, F.~ An~r. Chem~ Soc. Vol. 33, p. 349 (1911)

5. Rayleigh: Phil. Mag., .( 53), Vol. 48, :PP. 321.-37

41

VITA

Sze-I~v{ei ltlin 1;\1(18 borri in Peipillg, China on Sept­

era.ber 28, 1 918 • Elera.entary and Sacondal"~r Schooling

was rec~ived in Peiping, a!ld a Bachelor of Science in

Chemistry vvas ob1jained ill July, 1942 frorn the IJational

Southwest J4..ssociated University of China at }~ttnm.ing,

Chilla.