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A re-consideration of the vapour pressure of cis-decalin Hammersley, Robert Cameron 1947

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liSRftRY CORY A/O / ORIGINAL iW( A RE-CONSIDERATION OF THE VAPOUR PRESSURE OF CIS-DECALIN by ROBERT CAMERON HAMMERSLEY A Thesis submitted, i n P a r t i a l F u l f i l m e n t of The Requirements f o r the Degree of MASTER OF APPLIED SCIENCE i n the Department o f CHEMICAL ENGINEERING THE UNIVERSITY OF BRITISH COLUMBIA APRIL, 1947. ACOOWLEDGMEHTS Hy s i n c e r e a p p r e c i a t i o n t o Dr. Seyer f o r M s guidance i n t h i s r e s e a r c h and t o Canadian I n d u s t r i e s L i m i t e d f o r the GIL Research F e l l o w s h i p f o r 1946-47. ' TABLE OF COIsi'JiialTS Page I# I n t r o d u c t i o n . . . . . . . 1 I I . D i s c u s s i o n of Previous Work.......... 3 Graph showing vapour pressure v a l u e s of flametz, P i l k i n g t o n ; and Mann. • 4 I I I * Treatment of Data of P i l k i n g t o n and of Mann... 9 IV. Attempts t o c a l c u l a t e Vapour Pressure from other Data...... • 15 V. Dl sous s i on of Methods of Determining Vapour Pressure. 22 VI . D e s c r i p t i o n and D i s c u s s i o n of Method Used..... 26 Diagram of Apparatus 29 Photographs of A p p a r a t u s 3 0 Diagram of E l e c t r i c C i r c u i t s . . . . . . . . . . . . . 31 V I I . Data, C a l c u l a t i o n s , and R e s u l t s . • 35 Graph o f Result s. • • 41 Graph comparing r e s u l t s t o values obtained by e x t r a p o l a t i o n of Hemst and Antolne equations.................... 42 V I I I * Conclusions and Recommendations. • 43 (1) A RE-CONSIDERATIQN OF THE VAPOUR PRESSURE  OF CIS-DECALIN I . INTRODUCTION In an attempt to learn more about the structure ©f the isomers of decalinj considerable work has been done at this university on the physical properties of c i s - and trans-decalin. Densityi v iscosi ty , and surface tension were measured by Davenport-*-; refractive index and optical d is -persion by Mizuhara 2; Raman effect by Z©tov3; specific heat by Davie s4", Robinson-^, and Cavers and Howie**, dl e lec tr ic constant by Dunnell;^ heat conductivity by Robinson and Younger8; and vapour pressure by Nemetz?, P i lk ington 1 0 ^ and Mann 1 ! . Veri f icat ion of the work of Robinson and Younger. -Bunnell, and Cavers and Howie i s being carried out at.the present time. 1 Davenport, G . H . , M.A.Sc. Thesisj 1939. f Mizuhara, S.J., M.A. Thesis, 1941 3 Zotov, &., M.A. Thesis, 1940, J Davies, G . F . , M.A.Sc. Thesis* 1939 £ Robinson, M . , M.A. Thesis, 1945. 0 Cavers, S.D. and Howie, H.J., M.A.Sc. Thesis, 1946. 7 Dunell, B . H . , M.A.Sc. Thesis, 1946. ® Robinson, D. and Younger, A . , M.A.Sc. Thesis, 194$. ? Nemetz, H . , M.A.Sc. Thesis, 1938. •J Pilkington, T . , M.A.Sc. Thesis, 1941. 1 Mann, C.W., M.A.Sc. Thesis, 1944. (2)' I t was p o i n t e d out by Giauque 1 t h a t the vapour pressure data p u b l i s h e d by Seyer and Mann 2 d i d not agree w i t h the graph accompanying i t , t h a t the e m p i r i c a l equations g i v e n d i d not represent the data adequately* and t h a t from the view-p o i n t of thermodynamics the vapour pressure values below about 45°C* must be considered i n e r r o r * A c r i t i c a l examination of t h i s paper soon shows t h a t these s e r i o u s f a u l t s do e x i s t * Hence f u r t h e r work on the vapour pressure of d e c a l i n was considered w e l l worthwhile* Though the known vapour pressure values f o r both isomers are apparently u n r e l i a b l e below 45°C*, those of c i s - d e c a l i n are of g r e a t e r i n t e r e s t because o f the p o s s i b i l i t y of i r r e g u l a r i t i e s i n other p r o p e r t i e s a t or near the same temperature^* Consequently t h i s r e s e a r c h was eon-f i n e d to c i s - d e c a l i n * The main purposes o f t h i s r esearch were three i n number: the f i r s t , to go over c a r e f u l l y the r e s u l t s o f Nemetz, P i l k l n g t e n , and Mann; the second, to i n v e s t i g a t e the p o s s i b i l i t y of c a l c u l a t i n g the vapour pressure from some other known p h y s i c a l q u a n t i t y ; and the t h i r d , t o re-determine the vapour pressure below 45°G*, i f p o s s i b l e down t o -40°C* 1 Giauque, : W*F., U n i v e r s i t y of C a l i f o r n i a j Berkeley* P r i v a t e l e t t e r to Dr* Seyer i n June* 1945. • 2 Seyer* W.F. and'Mann, C*W.,, J * Am* Chem* S o c * 67, 528(1945)." 3 See References 5* 6, and.7 on preceding page* ft (3) I I . DISCUSSION OF PREVIOUS WORK As we have mentioned p r e v i o u s l y , the e a r l i e r work done here on the vapour pressure of c i s - d e c a l i n was per-formed by NemetZj P i l k i n g t o n , and Mann* A l l three of these determinations were made u s i n g a standard s t a t i e method* When these three s e t s of r e s u l t s are p l o t t e d on a very l a r g e soale graph as Log P vs* l / T ( f o r a reduced v e r s i o n see F i g * 1), i t i s immediately evident t h a t the values of Hemetz are c o n s i s t e n t l y above those of P i l k i n g t o n and of Mann i n d i c a t i n g the presence.of considerable i m p u r i t y i n the sample used by Hemetz. A l s o , i n the l a t e r determinations of P i l k i n g t o n and Mann, g r e a t e r oare was taken to degas the m a t e r i a l and t h i s added p r e c a u t i o n may aocount i n p a r t f o r the lower v a l u e s which must t h e r e f o r e be considered more r e l i a b l e * The values of P i l k i n g t o n and o f Mann do not co-i n c i d e p r e c i s e l y (see F i g * 1) but they do agree f a i r l y w e l l above 45°C* Below 45°C. however, the values o f both observers must be looked upon w i t h great s u s p i c i o n f o r then not only are the two s e t s of values w i d e l y divergent from eaoh other but a l s o they are oohtrary to aooepted thermo-dynamic theory* I n F i g * 1 i t i s e a s i l y seen t h a t the vapour pressure values below 45°C* become i n c r e a s i n g l y too h i g h w i t h descending temperature* I f a l i q u i d i s c l o s e to being an i d e a l one, i t s Log p vs* l/T graph i s a s t r a i g h t l i n e as i n d i c a t e d by the dotted l i n e i n F i g . 2. This f o l l o w s d i r e c t l y from the u s u a l cs) I n t e g r a t e d form of the Clausius-Clapeyron equation, Log P a • B . For an i d e a l l i q u i d , the assumptions necessary to d e r i v e the above equation from the exaet thermodynamic equation h o l d p r e c i s e l y . However, normal or r e a l l i q u i d s i n v a r i a b l y e x h i b i t a curved l i n e r e l a t i o n s h i p i n d i c a t e d by the unbroken l i n o i n F i g . 2. Log P i l / T F i g u r e 2 I n the oase of c i s - d e c a l i n , two p o s s i b i l i t i e s e x i s t . E i t h e r the vapour pressure i s c o r r e c t l y shown by the lowest va l u e s ; t h a t i s , those of P i l k i n g t o n o r the experimental values of both observers are i n c r e a s i n g l y i n e r r o r the f a r t h e r one goes below 45°G. The l a t t e r p o s s i b i l i t y i s f a r more l i k e l y c o n s i d e r i n g the f a c t t h a t the vapour pressures of many types o f l i q u i d s have been determined and g i v e Log P v s . l / T graphs of the general shape of the s o l i d l i n e i n F i g . 2. Now comparison of the vapour pressure curve t o be expeoted w i t h t h a t obtained from the experimental r e s u l t s (6) shows t h a t the experimental r e s u l t s are most l i k e l y i n c o r r e c t below 45°C. A very p l a u s i b l e e x p l a n a t i o n of t h i s i n c r e a s i n g e r r o r i n the vapour pressure at low values i s o f f e r e d by Griauque 1. He has found t h a t when the vapour pressure o f an organ!e l i q u i d i s much below 5 mm, of mercury* the s t a t i c methods are extremely u n r e l i a b l e owing to the great d i f f i -c u l t y i n removing a l l d i s s o l v e d gases. Above 5 mm.* the e r r o r i n t r o d u c e d i s n e g l i g i b l e compared t o the vapour pressure i t s e l f but below t h i s amount i t becomes i n c r e a s i n g l y important. Now e i s - d e e a l i n i s capable o f d i s s o l v i n g l a r g e amounts of oxygen q u i t e r e a d i l y 2 so t h a t i t i s p o s s i b l e t h a t d i s s o l v e d gas might account f o r the apparent e r r o r a t the lower temperatures. C e r t a i n l y the present v a l u e s below A5°G must be considered erroneous u n t i l they have been checked by some dynamic method. Unf o r t u n a t e l y * though suoh a check i s d e s i r a b l e , the l i k e l i h o o d o f o b t a i n i n g two s e t s o f v a l u e s which agree e x a c t l y i s s m a l l f o r Thomson^ l i s t s no l e s s than f o u r -teen d i f f e r e n t values obtained by r e p u t a b l e observers f o r benzene a t 80°C. I n the event t h a t the present v a l u e s were proven c o r r e c t , an extremely u n l i k e l y occurrence c o n s i d e r i n g the thermodynamic p r i n c i p l e s i n v o l v e d * the t h e o r e t i c a l r a m i f i -c a t i o n s would be very i n t e r e s t i n g . Suppose the vapour 1 Griauque, W.F., U n i v e r s i t y of C a l i f o r a l a ^ B e r k e l e y . P r i v a t e l e t t e r t o Dr. Seyer, June, 1945. 2 Balsbaugh, Assaf, and Pendleton, Ind. Eng. Chem., 33, 1321-30(1941) 3 Thomson, G.W., Chemical Reviews, 38, 24(1946) (7) ; pressure curve t o be of the general shape shown i n F i g , 3. Log P l/T F i g u r e 3 To produce the abrupt change of slope at A, the l a t e n t heat of vapour!zation would have t o undergo a sudden change i n v a l u e . The d i f f e r e n c e between the two v a l u e s of the l a t e n t heat would have t o be thought of as a heat of t r a n s i t i o n and t h i s would imply a change from one s t a t e to another. F u r t h e r -more, as the slope a t the lower temperatures i s l e s s , the heat of t r a n s i t i o n would have t o be n e g a t i v e . To v i s u a l i z e some so r t of change t o account f o r t h i s behaviour i s not easy. One might account f o r the e f f e c t u s i n g the eybo t a o t i o group theory of Stewart^ provided c e r t a i n assumptions are made. I f one assumes these eybotaetio groups e x i s t * have a g r e a t e r tendency to form at lower temperatures, and exert somehow a vapour pressure g r e a t e r than t h a t exerted by an equal number of un-grouped molecules at the same temperature* an e x p l a n a t i o n Stewart, G.W., Phys. Rev., 30, .232(1927) (8) i s p o s s i b l e * One would expect the e f f e c t of the grouped molecules t o come about g r a d u a l l y as the temperature decreased r e s u l t i n g i n a smooth curve* However* even a sharp t r a n s i t i o n oould be expl a i n e d by assuming the molecules t o be r e l u c t a n t t o form groups u n t i l a c e r t a i n t h r e s h o l d temperature was reached. The existence of oybot a c t i o groups i s extremely d o u b t f u l f o r Stewart advanced t h i s theory as being at best a t e n t a t i v e e x p l a n a t i o n of the f a c t s * I n the case o f c i s -d e c a l i n * an ex p l a n a t i o n of the vapour pressure curve on t h i s b a s i s i s pure s u p p o s i t i o n f o r there i s not confirmatory evidence t o support the values below 45°C* However the p o s s i b i l i t y o f a vapour pressure curve o f the shape shown i n F i g * 3 should not be f o r g o t t e n e n t i r e l y f o r we have as an example the ease of Helium I and Helium I I * The vapour pressures of Helium I and Helium I I were determined by Weber and Horgaard 1, W.H. Keesom 2, and 0. Schmidt? and they are p l o t t e d i n the u s u a l manner i n the book "Phenomena at the Temperature of L i q u i d Helium*"* The vapour pressure curve changes slope a b r u p t l y from Helium I to Helium I I i n a d i r e c t i o n not n o r m a l l y expected from thermodynamic theory* 1 Weber, S* and Norgaard, Gf., Leiden Comm* Supp*, 202b (192?) 2 Keesom, W.H., Leiden Comm*- Supp* 7Ie(1932)* 3 Schmidt, 0., P h y s i c a , 4* 963(1938). 4 Phenomena at the Temperature-of L i q u i d Helium by Burton, Grayson-Smith; and Wilkelm, Rheinhold P u b l i s h i n g Company, 1940. (9) However* i t must be here stated that the most probable explanation to account for the values of the vapour pressure of cis-decalin below 4£ GC. i s experimental error. Only i f the present results obtained by the static method were substantiated by several dynamic determinations, could much fa i t h be placed i n the foregoing assumptions. i III. THEATMEHT OF DATA OF PIIKINGTON AND OF MANN. In the published data of Seyer and Mann1* the following empirical equation i s given as representing the values for cis-decalin, Ln P • 1702.2 • 6*8l39Ln T - 34.52 . T Converting this equation from natural to common logarithms* we have* ' * Log'P - - 739.25 • 6.8l39Log T - 14.905 • T Table I on the following page gives the values for ois-deoalin observed by Mann and those calculated from his equation by the author* It i s obvious that the equation does not even approximate the data* A brief calculus operation with the equation shows that i t i s impossible for suoh an equation to f i t the vapour pressure values obtained experi-mentally* Using the natural logarithm form and A, B, and C 1 Seyer* W.F. and Mann, C.W., J* Am. Chem* Soc, 67, 328(1945). (10) TABLE I Temp. °0. Tap* P r e s s , of Cis-deealin(mm) Temp. ° C Vapour P r e s s , of C i s - d e o a l i n (mm) 0bs*d. 0 a l c fd. 0bs»d. Cal c ' d . -29 .5 0.38 0.22 60.0 8,24 11.64 -1?*2 0,65 ' 0.37 70.0 12.57 16.52 -10.0 0*86 0.60 80.1 19.50 23.20 0.0 1.09 0.98 92*4 32.81 34.46 12.0 1.48 1.71 105.1 54*50 50.83 20.0 1,82 2.43 109.8 63.15 58,45 38.0 3.44 5.09 112.4 68*66 63.06 43.4 4.00 6.28 124 .6 IO5.2I 89i27 49.9 5.30 8.04 148 .7 225*82 171.10 50.4 5.41 > 8.20 172*7 434*28 308.ZQ 52.9 6.06 8,95 194.7 761*02 512.20 56*9 7.31 10.17 f o r the constants, we may w r i t e , Ln P 5 - A / l • B k ! - C D i f f e r e n t i a t i n g twioe w i t h respect t o l / T , we get f i r s t d(Ln P) « -A - B (1) and then d2(Ln P) s B (2) d2(l/T) ( l / T ) 2 Equation ( l ) g i v e s the slope of the curve on a Ln P v s . l / T p l o t . The slope i s always negative f o r l / T i s always p o s i t i v e but equation (2) g i v e s the r a t e o f change of slope and i t i s (11) always p o s i t i v e f o r p o s i t i v e l / T . Hence the graph o f such an equation must be of the same.general shape as shown i n F i g . 4 and oan not be as shown i n F i g . 5. 1/T Next, the r e s u l t s of F i l i n g t o n and of Mann were examined w i t h the object of f i n d i n g f a i r l y r e l i a b l e v alues i n the temperature r e g i o n above 45®C. and f i t t i n g e m p i r i c a l equations to t h i s data f o r e x t r a p o l a t i o n down to lower temperatures. Mundell found that the Nernst' vapour pressure equation gave s a t i s f a c t o r y r e s u l t s when used i n t h i s way and Mundel, C i F . , Z e i t . p h y s i k i ohemie, 83* 435(1913) (12) Thomson-1- shows th a t the Antoine equation f i t s the g i v e n data f o r a l a r g e number of l i q u i d s extremely w e l l . The two equations are Hernst: Log P » - k/T • I.75Log T - BT • C Antoine: Log P a A - B . In eaoh equation A, B, and C are e m p i r i c a l constants, T i n the Hernst equation i s absolute temperature, and t i n the Antoine equation i s temperature on the normal s c a l e . From the l a r g e s c a l e p l o t of the data o f P i l k i n g t o n and o f Mann, those values which f e l l w i t h i n a narrow band were taken f o r t h i s curve f i t t i n g work. The constants f o r the ffernst equation were determined by the method of l e a s t squares; those of the Antoine equation by the method of Thomson 2. The values of the constants are l i s t e d i n Table I I below. Table I I Constant Nernst Equation Antoine Equation A 2590.9 7.2237 B 0.003483 1844 C 5.3786 230 The vapour pressure values used i n f i n d i n g the above constants are t a b u l a t e d i n Table I I I . Inoluded f o r comparison are the values c a l c u l a t e d from the two vapour pressure equations and the d i f f e r e n c e s from the experimental v a l u e s . The f i g u r e s i n 1 Thomson; G.W., Chemical Reviews, 38, 23-37(1946). 2 I b i d , pp 12-14. - -Table I I I Temp. °c. Obs«cL V.P. mm Hg ' TT.P. Calc* a from ISTemst Equation Qbs'i minus Cale'd V.P. Calc*a. from Antoine Equation Obs'a 1 minus Gale'd--40 .0 (0.05) 0.004 0.003 -35.0 (0.07) 0.007 0.006 -25*0 (0.14) 0.018 ^ » «M ^ » 0.017 * • w -15 .0 (0.23) 0.046 0.044 - 5.0 (0,38) 0.108 0.106 5*0 (0.62) 0.237 0.237 15.0 (0.99) 0.481 0*496 25.0 (1.50) 0.959 • 0.979 — 35*0 £2.20) 1*794 1*842 — 46.0 3.34 3.44 -0.10 3.49 -0.15 52*0 4.33 4.73 -0.40 4.83 -0.50 59,0 6*44 6.83 -0.39 6.97 -0.53 68.0 11.00 10.70 0*30 10 ,86 0*14 70.0 12.57 12.57 0.00 11.94 0*63 80.0 18.86 18*70 0.16 18.85 0.01 80.1 19.50 I8.78 0.72 18.94 0.56 92 .4 32.81 31*85 0.96 31.92 0.89 102.0 48.57 46.91 1.66 46.72 I . 8 5 105.1 54.50 52.99 1.51 52.59 1.91 109.0 62.56 61.29 1.27 60.84 1.72 109.8 63.15 63.15 0.00 62.66 0.49 112*4 68.66 69.51 -O.85 68.90 -Q.24 124 .6 105 .21 107.02 -1.81 105*60 -0.39 148 .7 225.82 230.20 -4.38 226.50 -0*68 (14) Table I I I (Gont) Temp, °cf Obs*4 V.P. mm Eg V.P. Cale»d from Hernst Equation Obs'd minus Calo»4 V.P. Calo»d from Antoine Equation Obs'4 minus Calo»d 172.7 434.28 447.63 -13.35 441.20 -6 .92 194.6 760.00 760.90 - 0*90 76O.OO 0.00 194.7 7 6 l i 0 2 763.23 - 2.23 761.70 -0.68 b r a c k e t s are v a l u e s taken from the l a r g e - s c a l e p l o t o f P i l k i n g -ton's r e s u l t s . Ho d i f f e r e n c e s are t a b u l a t e d because o f the great discrepancy between the c a l c u l a t e d and observed values i n t h i s temperature r e g i o n . I n f i n d i n g these equations, the author had two purposes i n mind one t o see how w e l l the experimental data between 45°C. and 195°C. could be represented by a recognized vapour pressure equation the other to have a means of c a l -c u l a t i n g values below 45°C. The f i t of the e m p i r i c a l equations i s only f a i r t h a t of the Hernst equation being s l i g h t l y b e t t e r than t h a t of the Antoine equation. The maximum percent d e v i a t i o n of the c a l c u l a t e d from the observed value f o r the Hernst equation i s 9.23 but the average percent d e v i a t i o n i s only 2.50. The corresponding d e v i a t i o n s f o r the Antoine equation are 11.52% and 2.75% r e s p e c t i v e l y . The values g i v e n by both equations below 45°G agree q u i t e w e l l and t h e r e f o r e a f f o r d an e x c e l l e n t i n d i c a t i o n of the vapour pressure values to be expected a t the lower temperatures. (15) IV. ATTEMPTS TO CALCULATE VAPOUR PRESSURE  FROM OTHER DATA. I n the previous s e c t i o n , values of the vapour pressure of c i s - d e c a l i n were c a l c u l a t e d f o r temperatures below 45°G. by e x t r a p o l a t i o n o f val u e s above 45°C u s i n g the Nernst and Antoine equations. I t was f e l t t h a t another means of e s t i m a t i n g the vapour pressure would be an i n t e r e s t i n g check on t h a t a l r e a d y used. Othmer 1.has shown th a t v i s c o s i t y and vapour pressure can be c o - r e l a t e d and as the v i s c o s i t y of c i s - d e c a l i n i s known over s u b s t a n t i a l l y the whole l i q u i d range, two p o s s i b i l i t i e s i n v o l v i n g v i s c o s i t y were i n v e s t i g a t e d . Othmer shows t h a t L o g r i s * E Log P» • C where X» i s the v i s c o s i t y of the l i q u i d under c o n s i d e r a t i o n , E i s r e l a t e d t o the a c t i v a t i o n energy o f v i s c o s i t y * P» i s the vapour pressure of the reference l i q u i d , and L * i s the l a t e n t heat of v a p o u r i z a t i o n o f the reference l i q u i d . Because the quotient E/L 1 i s very n e a r l y constant, Othmer found t h a t p l o t s of L o g i \ v s . Log P* were s t r a i g h t l i n e s f o r a l a r g e number of l i q u i d s . Now i t i s a simple matter t o r e -arrange /the equation g i v i n g , Log P m * L Log-n' * C where H* Othmer, D.F., Ind. Eng. Chem*, 57• 1112(1945). (16) the symbols hare the same meanings as before but the primed q u a n t i t i e s are now a s s o c i a t e d w i t h v i s c o s i t y r a t h e r than vapour pressure. This r e l a t i o n i s a l s o l i n e a r and i f r e l i a b l e values of the v i s c o s i t y and vapour pressure are known a t only two d i f f e r e n t temperatures, the c o e f f i c i e n t s oan be determined. To be r e a l l y e f f e c t i v e , the method r e q u i r e s t h a t the two temperatures a t which the v i s c o s i t y and vapour pressure are simultaneously known be reasonably f a r apart and t h a t the values themselves be of h i g h accuracy. The accuracy of the. vapour pressure values a v a i l a b l e i s questionable and though the method could be used, the values so obtained would be no b e t t e r c e r t a i n l y than those obtained by e x t r a p o l a t i o n of the Hernst and Antoine equations. Glasstone, L a i d l e r , and E y r i n g have a p p l i e d t h e i r theory o f r a t e processes t o v i s c o s i t y and d i f f u s i o n 1 . They d e r i v e an equation f o r A F w + , the f r e e energy of a c t i v a t i o n f o r visoous f l o w « where R i s the gas constant, v* i s the m o l a l volume* h i s Planck's constant, and T\ i s the v i s c o s i t y . E y r i n g et a l a l s o s t a t e t h a t *Bv*p = 2.45 Glasstone, L a i d l e r , and E y r i n g , Theory of Rate Processes, McGraw-Hill, 1941, pp 477r551. (17) This r e l a t i o n was found by p l o t t i n g ^ E v ^ P t the energy of v a p o u r i z a t i o n , against A . F v i s * f o r over one hundred d i f f e r e n t substances and drawing the best s t r a i g h t l i n e through a l l the p o i n t s . Thus they a r r i v e a t the f o l l o w i n g expression f o r v i s c o s i t y . ^ - M e 2 A S R T From t h i s equation, the v i s c o s i t y of a substance can be estimated provided the m o l a l volume a n d ^ E V A , P a r e known. The reverse o p e r a t i o n seems a l o g i c a l one; t h a t i s , i f the mo l a l volume and the v i s c o s i t y are known, then A E v a p can be c a l c u -l a t e d . ETow^Ev^p i s r e l a t e d t o ^ H V A R the u s u a l l a t e n t heat o f v a p o u r i z a t i o n i n t h i s way A . E v a p a * RE and hence i f the normal b o i l i n g p o i n t were a l s o known, the vapour pressure c o u l d be c a l c u l a t e d u s i n g the Clausius-Clapeyron equation i n the form d(Ln P) a -AHVA. P I n the case of c i s - d e c a l i n , the d e n s i t y and v i s c o s i t y are known a c c u r a t e l y from l80°G. t o -?0 oC., the normal b o i l i n g p o i n t i s 194.6°C.l, and the m o l a l volume can e a s i l y be com-puted from the d e n s i t y so t h a t we are i n a p o s i t i o n to c a l c u -l a t e the vapour pressure I n t h i s way. The f i r s t step was determining the values of *F V, S*. At f i r s t , t h i s was done only f o r c i s - d e c a l i n as shown i n 1 Seyer, W.F. and Walker, R.D., J . Am. Chem. Soc. 60, 2127 ( W 8 ) . (18) Table IT the two values i n brackets being e x t r a p o l a t e d * gable IV. Temp* Temp. ©C. C a l o r i e s °C. C a l o r i e s -30 4175 90 4385 *20 4150 100 4415 -10 4150 110 4450 0 4150 120 4490 10 4155 130 4535 20 4170 140 4575 30 4190 150 4625 40 4215 160 4665 50 4240 170 4715 60 4265 180 4760 70 4300 190 (4805) 80 4345 194.6 (4825; I I A glance a t the above t a b l e shows th a t A P v , s i n c r e a s e s s t e a d i l y w i t h temperature. Now i f the r a t i o o f * E V A P to A F V 1 5 * i s to be 2 .45 a t a l l temperatures, flEVAP must i n c r e a s e i n the same p r o p o r t i o n a s ^ F v l s * . On the other hand, A E v a p s A H v / x p « RT and f o r a l l known l i q u i d s , A I V A P decreases as the temperature i n c r e a s e s . Since the ••RT11 term i n c r e a s e s w i t h temperature, then * E V A P must decrease w i t h r i s i n g temperature. This would seem to i n d i c a t e t h a t e i t h e r t h e A F v , s * f u n c t i o n f o r e i s - d e e a l i n i s abnormal o r (1?) t h a t the r a t i o AEV«P S 2.45 does not h o l d a t a l l temperatures. However, c a l c u l a t i o n s o f the A F V i & * f u n c t i o n f o r t r a n s - d e c a l i n showed t h a t i t i n c r e a s e d i n the same manner as t h a t f o r c i s - d e e a l i n (see Table 7 ) . Table 7. Temp. A ' v i a * Temp. ° C C a l o r i e s °C. C a l o r i e s -30 3830 90 4190 -20 3835 100 4230 -10 3850 110 4275 0 3870 120 4315 10 3895 130 4375 20 3930 140 4415 30 3960 150 4475 40 3995 160 4525 50 4025 170 4565 60 4060 180 4610 70 4080 185,3 (4635) 80 4145 As the two substances so f a r i n v e s t i g a t e d are isomers, i t i s p o s s i b l e t h a t both might be abnormal i n t h i s r e s p e c t . Consequently, AF v i s*- was c a l c u l a t e d f o r a number o f wi d e l y d i f f e r e n t l i q u i d s . F or these compounds, v i s c o s i t i e s were taken from I.C.T. and the Handbook o f Chemistry and (20) Physies(1945); d e n s i t i e s from the same sources o r computed from equations i n I.C.T. The AF v»s* v a l u e s f o r the l i q u i d s i n v e s t i g a t e d are t a b u l a t e d i n Tables V I , V I I , and V I I I . Table V I . Methyl A l o o h o l E t h y l A l o o h o l Formic A c i d A c e t i c A c i d Temp. * F V I S * Temp. A F V I S * Temp. Temp. AFVIS* °C. C a l . °C. C a l . ° C C a l . ° C C a l . 0 2395 0 3005 20 3000 18 3020 20 2390 20 3005 40 2975 41 3115 40 2400 40 3000 70 2973 59 3070 50 2405 60 2985 100 3000 70 3075 100 3125 Table V I I . Water G l y c e r i n B u t y l A l c o h o l Temp. A F V ( S * Temp. AF V, 5* Temp. °0. C a l . °C. C a l . 0C. C a l . 0 2390 2.8 7430 6 3830 25 2270 8.1 7290 20 3790 50 2070 14.3 7110 40 3770 75 1990 20.3 696O 50 3725 100 1925 26.5 6800 70 3685 (For Table V I I I see f o l l o w i n g page) For benzene, toluene, meta-xylene, c i s - and t r a n s -d e c a l i n , n-heptane, n-ootane, and mercury, A J v i s + i n c r e a s e s w i t h temperature; f o r methyl a n l e t h y l a l c o h o l , a c e t i c and (21) Table T i l l , Mercury n-Heptane Toluene Benzene Temp. Temp. Temp. *FV,«* Temp. ©C, C a l . 00, C a l . °C. C a l . ®C. C a l . 50 2535 0 2840 0 2880 10 2885 100 2825 20 2930 20 2950 20 2905 150 3125 40 3020 40 3025 40 2950 200 3415 70 3160 70 3160 50 2975 250 3760 n-octane Meta-zylene 70 3035 300 4080 Temp. * F V , & * Temp. — 350 4425 °0i C a l . °C. C a l . — — - — 0 3055 0 2985 — — ** 20 3145 20 3055 — mm 40 3240 40 3145 — — f o r m i c a c i d , i t shows no d e f i n i t e t r e n d ; and f o r water, g l y c e r i n , and b u t y l a l c o h o l , i t decreases w i t h i n c r e a s i n g temperature. C e r t a i n l y i t i s now safe to say t h a t A p w t f o r e i s - d e o a l i n i s not abnormal and, t h e r e f o r e , the other p o s s i b i l i t y must be considered; namely, t h a t the r a t i o t AEVAP s 2.45 does not h o l d f o r a l l temperatures. The graph from which t h i s r e l a t i o n i s d e r i v e d shows much s c a t t e r i n g of p o i n t s about the s t r a i g h t l i n e i n d i c a t i n g t h a t the f i g u r e *2f45" i s a very mean v a l u e . I t would seem t h a t E y r i n g et a l have p i c k e d temperatures d i f f e r e n t f o r each l i q u i d to get as good agreement as they d i d . The j u s t i f i c a t i o n f o r doing t h i s does not concern us (22) -- -here* What does concern us however, i s the f a c t t h a t the i n v a l i d a t i o n of the r a t i o precludes the p o s s i b i l i t y of u s i n g i t i n e s t i m a t i n g vapour pressure values from density.and v i s c o s i t y data and the normal b o i l i n g p o i n t except perhaps f o r the most approximate of values* Any values so obtained would c e r t a i n l y not be as good as those a l r e a d y obtained from the e x t r a p o l a t i o n of the Hernst and Antoine equations* V. DISCUSSION OF METHODS OF DETERMINING VAPOUR PRESSURE. . . The methods used f o r determining vapour pressure can be d i v i d e d i n to two main c l a s s e s s t a t i c and dynamic* A l l the ' s t a t i c methods are based e s s e n t i a l l y on one p r i n c i p l e the measuring ©f the vapour pressure d i r e c t l y or i n d i r e c t l y w i t h some s o r t of manometer* However* there are a number of q u i t e d i f f e r e n t dynamic methods* There i s the constant pressure method used e x t e n s i v e l y by Ramsay and Young 1 i n which the vapour pressure i s determined by measuring the b o i l i n g p o i n t s at a s e r i e s ©f.known, f i x e d pressures; the e f f u s i o n method f i r s t employed by Khudsen 2 and l a t e r by Egerton? and Rodebush 4 i n which i t . i s determined by measuring the r a t e of e f f u s i o n through a s m a l l hole; the evaporation method used by 1 Ramsay and Young, P h i l . Trans. Roy* S o c , 175, 37(1884). 2 Khudsen, Ann. der physik, 28, 999(1909). 3 Egerton, A.C., P h i l . Mag., 53, 33*48(1917). 4 Rodebush and Devries, J . Am. Chem. Soc., 47, 2488(1925). (23) Marshall' 1' and E y r l n g c i n which i t i s determined by measuring the r a t e o f evaporation from a surface o f known area; and the s a t u r a t i o n o r t r a n s p i r a t i o n method of Regnault? i n which i t i s determined by f i r s t s a t u r a t i n g an i n e r t gas w i t h vapour of the l i q u i d and then weighing t h i s amount necessary t o s a t u r a t e by some s u i t a b l e a d s o r p t i o n arrangement. As we have mentioned p r e v i o u s l y , i f the necessary precau t ions are taken, the s t r a i g h t - f o r w a r d s t a t i c method i s qu i t e s a t i s f a c t o r y f o r measuring the vapour pressure of even organic l i q u i d s a t values above say 5mm o f mercury and perhaps a l i t t l e below 5mm i n some eases but i t has proven inadequate i n the case of c i s - d e c a l i n because the vapour pressure i s l e s s than 5mm below about 55°C. or roughly 37% o f the l i q u i d range. Let us now consider the dynamic methods. I n p a r t i c u l a r , the constant pressure method was used by Young 4 t o evaluate the vapour pressures of a l a r g e number of l i q u i d s but the lowest value r e p o r t e d i s 1.63 mm. The values e x t r a p o l a t e d from the Hernst and Antoine equations i n d i c a t e t h a t the vapour pressure of c i s - d e c a l i n w i l l be l e s s than t h i s below approximately 34°G. so t h a t t h i s method would not s u f f i c e . The e f f u s i o n method has a l r e a d y been used to measure the vapour pressure o f both o i s - and t r a n s - d e c a l i n ^ but the valu e s so obtained f o r c i s -1 M a r s h a l l , A.L., J . Am. Chem. S o c , 59, 1161(1937). 2 E y r i n g ; H., I b i d , 50, 2398(1928). 3 H.Y. Regnault (1845). 4 Young, S c i . Proc; Roy. D u b l i n S o c , 12, 3 7 4 - 4 4 3 ( 1 9 U ) . 3 Zil»berman-Crranovskaya, -A.A., J . Phys. Chem. (USSR), 14, ~ - 759nb7(19 4 0). . , . (24) . . . d e c a l i n are not a t a l l compatible w i t h the e x t r a p o l a t e d v a l u e s . (See Table IX) Table IX. Temp. Vapour Pressure i n Mm. OG. Zil»berman-Granovskaya Cale'd* u s i n g Hernst Equation 23.2 . 0.01807 0.86-32.7 0 .03?8l 1.56 47*0 0*15610 3*60 The great d i f f e r e n c e oan not be a t t r i b u t e d t o a l a r g e amount of i m p u r i t y because the d e n s i t y and b o i l i n g : p o i n t s of Zil'berman-Granovskaya 1s samples compare f a v o u r a b l y w i t h the values used i n t h i s l a b o r a t o r y . (See Table X.) Table X. Observed by Density @ 20°G.- gm./co. B o i l i n g P o i n t °C. Davenport .. Walker (B.P.) Zil'berman-Graaovskaya , 0.8967 0.895 194 .6 193*0 The r a t e of evaporation method used by M a r s h a l l and E y r i n g i s s u i t a b l e .for substances having n e g l i g i b l e vapour pressures a t room temperature. The s a t u r a t i o n methods have been used s u c c e s s f u l l y i n the determination of f a i r l y h i g h vapour pressures such as those of water* o f water i n s a l t e (25) hydrates, and of c e r t a i n s o l u t i o n s . I t has a l s o been employed by von Wartenberg 1 t o measure the vapour pressure of metals such as l e a d and s i l v e r . As i t i s extremely d i f f i c u l t t o a s c e r t a i n t h a t the gas is saturated, he determined the weight , l o s s at v a r i o u s r a t e s o f f l o w and e x t r a p o l a t e d t o zero r a t e of f l o w . However, f o r t h i s method i t i s again necessary t h a t the substance have a n e g l i g i b l e vapour pressure a t room temperature otherwise accurate weighing would be p r a c t i c a l l y i m p o s s i b l e . The t r a n s p i r a t i o n method i s i n h e r e n t l y v e r y simple the u s u a l procedure being to pass an i n e r t gas through a s e r i e s of s a t u r a t o r s . I f a l l the s a t u r a t o r s are kept at the same temperature, the number r e q u i r e d to ensure s a t u r a t i o n i s r e l a t i v e l y h i g h but by the use of p r e - s a t u r a t o r s a t a somewhat high e r temperature, the t o t a l number of s a t u r a t o r s oan be reduced c o n s i d e r a b l y . The number of s a t u r a t o r s must be made as s m a l l as p o s s i b l e to keep the back pressure down t o a reasonable amount. A h i g h back pressure i n c r e a s e s the l i k e l i -hood of l e a k s and according to some observers, causes f l u c t u -a t i o n s whioh e f f e c t the vapour pressure v a l u e s obtained. Another considerable source of e r r o r i n the t r a n s p i r a t i o n method i s the measurement of the l a r g e volume of gas used. Pearce and Snow 2 surmounted t h i s d i f f i c u l t y by u s i n g a mixture of hydrogen and oxygen produced e l e c t r o l y t i e a l l y the volume being c a l c u l a t e d from the e l e c t r o - c h e m i c a l e q u i v a l e n t by means of a s i l v e r ooulometer. However, the use of a hydrogen-oxygen 1 H. von Wartenberg, Z e i t . f u r Electrochemie, 19, 482(1913) and 20 * 443(1914)* , 2 Pearce and Snow, J . Phys* Chem., 31, 231(1927). -(26) mixture i s not p o s s i b l e with, cis- c L e e a l i n owing t o i t s great oxygen a b s o r p t i o n 1 and the p o s s i b i l i t y of peroxide f o r m a t i o n 2 even a t room temperature. I'he main reason f o r d e c i d i n g t o use the t r a n s p i r a t i o n method was the r e s u l t obtained by P i l k i n g t o n ^ as a supple-ment t o h i s main work. As a rough check on h i s s t a t i c method values* P i l k i n g t o n made one determination of the vapour pressure of c i s - d e c a l i n a t 37°0. by the t r a n s p i r a t i o n method. The value so obtained; 1.93 mm. was c o n s i d e r a b l y below t h a t obtained by the s t a t i c method, a r e s u l t a t t r i b u t e d by P i l k i n g * ton at the time to incomplete s a t u r a t i o n of the gas. However* i f t h i s value of 1.93 mm. i s compared w i t h the value of 2.02 mm. c a l c u l a t e d from the Hernst equation or 2.08 mm. c a l c u l a t e d from the Antoine equation, i t i s then seen t h a t the t r a n s -p i r a t i o n v a l u e though perhaps a l i t t l e low i s much c l o s e r t o the e x t r a p o l a t e d values than P i l k i n g t o n * s s t a t i c value of 2.52 mm. a t 3 7 ° ° . T I . DESCRIPTION AND DISCUSSION OF METHOD USED. The one t r a n s p i r a t i o n determination made by P i l k i n g -t o n was done w i t h a simple apparatus.. The apparatus used by the author i s e s s e n t i a l l y the same but c e r t a i n improvements have been made. The important p a r t of the apparatus i s th a t used t o saturate the i n e r t gas. The s a t u r a t o r t r a i n f i r s t 1 Balsbaugh, Assaf, and Pendleton, Ind. Eng. Chem., 33, 0 : 1321-30(1941). 2 Criegee, R., Ber, 77B, 22-4(1944). 2 P i l k i n g t o n , T., M.A.Sc. Thesis; 1941. (27) used c o n s i s t e d of up t o s i x simple bubblers(see F i g . 6) i n s e r i e s . However, the back pressure of s i x suoh bubblers was too great and t h i s number was s t i l l not s u f f i c i e n t t o s a t u r a t e the gas. In the next t r a i n used, the number of bubblers was reduced to th r e e and these were used I n c o n j u n c t i o n w i t h and S-tube (see F i g . 7) f i l l e d w i t h a m a t e r i a l having a f a i r l y l a r g e surface area. I t was hoped t h a t a l a r g e surface area wetted w i t h c i s - d e c a l i n would favour v a p o r i z a t i o n and thereby f u l l y s a t u r a t e the i n e r t gas* The m a t e r i a l s used i n t h i s S-tube were small g l a s s c y l i n d e r s , small p o r c e l a i n b u r l saddles, and g l a s s fragments s i z e d by screening. S t i l l the back pressure was h i g h and the percent s a t u r a t i o n low. The 1 F i g . 6 c r i t e r i o n of s a t u r a t i o n used was the average of the vapour pressure v a l u e s e x t r a p o l a t e d from the ETernst and Antoine equations. Furthermore, the r e s u l t s were very i n c o n s i s t e n t probably because of e n t r a i n -ment. The t h i r d and f i n a l s a t u r a t i o n t r a i n used was composed of f o u r s a t u r a t o r s 0 & D F i g . 7 (28) designed originally by Bichowsky and Storeh 1 and modified by Pearce and Snow . This modified saturator i s shown in Fig. 8, F i g . 8 Gas enters at A and passes up the slightly inclined tube B producing a succession of gas bubbles i n contact with the li q u i d . The gas then passes back over the surface of the liqu i d to the outlet tube C. The inlet tube D i s for f i l l i n g purposes. The complete apparatus i s represented diagram-matioally in Figure 9(see also photographs on the following page). Each constant temperature bath accommodated two saturators only one being shown to simplify the drawing. The heating, temperature control; and bath st i r r i n g motor circuits are shown in Fig. 10. The experimental procedure was as follows. Commercial, water-pumped nitrogen was dried and f i l t e r e d by passing i t through drying towers f i l l e d with sodium hydroxide pellets and tubes f i l l e d with glass wool. The purified 1 Biohowsky and Storch, J. Am. Chem. Soc, 37, 2696(1915). 2 Pearce and Snow, J. Phys. Chem., 31, 231(1927). © © © FIGURE 9 D I A G R A M OF A P P A R A T U S 0 © © V///////////////////, 1/ 4> 3 \ f W////// / / / / /A U —To SINK L E G E N D ® NITROGEN TANK ®CAS SCRUBBERS-FILLED & CD WITH GLASS WOOL @ BUBBLE COUNTER © CONSTANT TEMPERATURE BATH A (?) CONSTANTTEMPERATURE BATH B ® ADSORB TION TUBE ® PRYING TUBE ®GAS SCRUBBER-NAQH PELLETS ® GAS VOLUME MEASURING IOWER (30) ( 3 1 ) FIGURE 10 L E G E N D A - AMMETER H - H E A T E R L - LIGHT-INDICATING M - M O T O R M/B - M A K E - B R E A K S - S W I T C H U2) n i t r o g e n was then passed through the f o u r s a t u r a t o r s , The c i s - d e e a l i n absorbed by the gas was adsorbed on a c t i v a t e d c h a r c o a l i n sm a l l U-tubes, The volume of gas passed through was measured i n a long* g l a s s c y l i n d e r of 4360 cc. t o t a l c a p a c i t y . A d r y i n g tube f i l l e d w i t h calcium c h l o r i d e was pl a c e d between the gas measuring tower and the IX-tubes t o prevent water vapour from reaching the c h a r c o a l . The f l o w of n i t r o g e n was c o n t r o l l e d by an o r d i n a r y diaphragm type r e g u l a t o r . Temperature c o n t r o l was maintained t o w i t h i n 0.05°C. by a s e n s i t i v e l i q u i d - m e r c u r y c i r c u i t breaker and a Cenco r e l a y m o d i f i e d t o s u i t the purpose. The temperatures i n the two baths and the gas measuring tower were measured by thermometers which were c a l i b r a t e d a g a i n s t a platinum r e s i s t a n c e thermometer. The bath l i q u i d used was water covered w i t h an i n c h of Stanolax t o cut down evaporation. The connecting tube between the two s a t u r a t o r s i n Bath A and the two i n Bath B and tha t between the l a s t s a t u r a t o r and the f i r s t IT-tube were heated t o prevent premature condensation. The three q u a n t i t i e s which had t o be determined t o c a l c u l a t e the vapour pressure were the weight o f the c i s -d e c a l i n adsorbed on the c h a r c o a l , the volume of the n i t r o g e n passed through the system, and the pressure o f the system. The l a s t mentioned was e a s i l y done. The gas volume was measured i n a column composed of a f o u r f o o t l e n g t h of 75 mm. g l a s s t u b i n g f i t t e d a p p r o p r i a t e l y . The volume of t h i s tube was c a l i b r a t e d i n 500 co. d i v i s i o n s by t a k i n g the average of f o u r determinations u s i n g water. Any s m a l l e r r o r s i n measuring (33) the gas volume are not a p p r e c i a b l e i n the vapour pressure but such i s not the case i n the weighing of the e i s - d e e a l i n adsorbed,* Undoubtedly, t h i s p a r t of the work i s the g r e a t e s t source of e r r o r . She weight i n c r e a s e f o r 4000 co. of n i t r o g e n was never g r e a t e r than 50 mg. and a great d e a l of d i f f i c u l t y was encountered i n weighing such s m a l l q u a n t i t i e s a c c u r a t e l y * The procedure f i n a l l y adopted gave f a i r l y c o n s i s t e n t r e s u l t s but o c c a s i o n a l l y something would go wrong f o r no apparent reason* The s m a l l XT-tubes were made from 10 mm. pyrex g l a s s t u b i n g and f i l l e d w i t h a c t i v a t e d cocoanut c h a r c o a l screened to a s i z e range of 0.05-0.10 lnch(see F i g . 11). Before being used, each tube was heated i n an oven f o r a t l e a s t 24 hours; removed, t e m p o r a r i l y s e a l e d w i t h short l e n g t h s of rubber t u b i n g plugged w i t h g l a s s beads, pl a c e d i n a d e s i c c a t o r , and kept there f o r a minimum of three days. During the f i r s t few runs, the tr-tubes were cooled w i t h dry i c e but t h i s p r a c t i s e was d i s c o n t i n u e d as i t caused the weights t o be e r r a t i c . Also,' i n the beginning, f o u r adsorbtlon tubes were used but t h i s number was cut i n h a l f because i t was found t h a t only the f i r s t two gained i n weight at l e a s t 98% of the g a i n being i n the f i r s t one. Glass Wool Charcoal O v e r a l l l e n g t h 10 cm. F i g . 11. (34.; After use* eaoh U-tube was again dealed with the rubber tubing devices and desiccated fer three days pr ier te re-weighing. Preliminary experiments in which puri f ied nitrogen was passed d irect ly through two U-tubes, showed that the scrubbing tra in removed any detectable amount of impurity that might have been i n the nitrogen. The baths A and B were kept at the desired temper-ature for at least twelve hours before a run with a slow stream of nitrogen passing through and flushing to atmosphere. The pressure in the saturators was measured by a simple mano-meter using cis-decalin i t s e l f as the manometer f l u i d . To prevent any of this c is -decal in from reaching the gas stream, the tube connecting the manometer to the apparatus proper was made quite long. The pressure of the nitrogen collected i n the measuring tower at the conclusion of a run was measured i n inches of water above or below atmospheric. Several times during each-run* the atmospheric pressure was read from a standard mercury column barometer corrections for temperature and menicus height being applied. The average value was used as the basis for calculating the actual pressure i n the saturators and the last value read for calculating the volume of the.nitrogen at S . T . P . Two thermometers were suspended i n the gas measuring tower one to measure the temperature of the gas, the other that of the water. Seldom did the two thermo-meters d i f fer by more than 0 . 2 ° C . A great deal of time was spent i n experimenting with the previously described saturation trains consisting of f i r s t II I (33) six bubblers and then three bubblers plus the S-tube. Because of their great inconsistency* the results of these experiments were qualitative only. The f i r s t few runs using the inclined tube saturators, showed that.with both baths at the same temperature, four saturators were insufficient to saturate the nitrogen. Rather than waste more time constructing the larger baths necessary to accommodate a greater number of saturators, subsequent experiments were conducted with the temperature i n bath A considerably above that i n bath B. For a given temperature in bath B, several runs were made with that i n bath A 10°C. higher, then several more were made with .that i n bath A 2 0 ° higher* and f i n a l l y several more with that in bath A JO 0 higher. Although the maximum vapour pressure values obtained i n this way were s t i l l lower than expected* the last 1 0 ° rise i n temperature produced no increase i n the weight of ois-deoalin absorbed by the nitrogen. A certain minimum rate of flow of nitrogen was necessary to make the saturators work properly and i t may be that at this rate of flow* the limit of saturating power of four suoh devices had been reached. V I I . DATA, CAI.CULATI0NS, AND RESULTS. During an actual run, the quantities recorded were temperature, of bath A, bath B, upper and lower measuring tower; pressure, average atmospheric during run and atmos-pheric at end of run, i n saturator, i n measuring column; volume of nitrogen in measuring column; and weight of eis-deoalin adsorbed on the charcoal. For the sake of brevity, (36) o n l y the r e l e v a n t temperatures, the volume of n i t r o g e n a t S.T.P, passed through the apparatus, the weight of c i s r d e c a l i n adsorbed, and the t o t a l pressure i n the s a t u r a t o r are recorded f o r each run i n ' Table XI• Table XI. Temperature V o l . U 2 Wt, of C i s -d e c a l i n T o t a l P r e s s , i n s a t u r a t o r Bath A Bath B @ S.T.P. • c.c. adsorbed mg. mm. of Eg* 35 35 35!0 26.2 748.5 35 . 35 3935 28.6 758.9 35 35 3565 26.8 750.4 45 . 35 3650 34.8 758.3 45 35 3520 35.3 751.2 55 33 3495 40.0 - 739.3 55 35 3575 -38*5 744.6 65 35 3565 39.6 755*0 65 35 3570 . 38.1 758.3 65 35 3870 42.5 754.7 25 25 3535 14.6 757.2 25 25 • 3565 . 17*6 748,8 35 25 3610 18.8 745.6 35 25 3485 20*1 " 739.9 45 .25 3665 21*2 755.0 45 25 3130 19*4 755.3 55 25 3585 20.? 762.1 55 25 2690 16.0 758.5 (37) Table X l ( C o n t ) . Temperature °C. V o l . ^2 @ S.T.P. o.e. Wt, of C i s -d e c a l i n adsorbed, mg. T o t a l P r e s s , i n s a t u r a t o r mm. of Hg. Bath A Bath B 25 15 - 3565 10,8 755-6 25 15 3605 14*1 757.3 35 15 3635 12.2 756.8 35 15 3095 11.1 753*9 45 15 3915 15.9 757*6 45 15 3590 16.0 760.5 33 15 3630 12.7 739.8 55 3605 13*8 758*4 The b a s i c equation of the t r a n s p i r a t i o n method of determining vapour pressure f o l l o w s from Dalton's law of p a r t i a l pressures. The equation i s Vapour pressure s Volume o f vapour • T o t a l pressure T o t a l volume Now l e t V.P. 3 vapour pressure of c i s - d e c a l i n i n mm. Of Hg., P-t s t o t a l pressure i n s a t u r a t o r i n mm, of Hg., V c - volume of c i s - d e c a l i n i n o.e, at S.T.P., V 0 - volume of n i t r o g e n i n o.c. at S.T.P., w s weight of c i s - d e c a l i n adsorbed on char c o a l i n grams, P a - average barometric pressure i n mm. of Hg, du r i n g run, p s reading o f s a t u r a t o r manometer i n mm. of c i s -d e c a l i n , 08) % r volume of n i t r o g e n as measured i n tower i n c . c , Pt -s pressure of n i t r o g e n i n tower above atmospheric i n mm, of water, p s vapour pressure of water at temperature o f measuring tower, F r barometric pressure a t end of run i n mm. of Hg., P n s a c t u a l pressure of n i t r o g e n i n tower i n mm. of Hg., and t e • temperature of n i t r o g e n i n tower i n °C. Expr e s s i n g the b a s i c equation i n symbols and r e a r r a n g i n g , we have, V.P. = ?t (V — T T — -o F i r s t , c a l c u l a t e P-fc. P t a P a • Ps(Q» 8 9) s P a + 0.066 p s . 15.56" Second, c a l c u l a t e V 0. v"e a 22.400 w - 162.1 w . 138.14 F i n a l l y , c a l c u l a t e V 0. v*e s 273 ( P n ) (ym) waere 760U73 • t 0 ) P n s P + 0,074P e - p. The values so obtained are t a b u l a t e d i n Table X I I . The temperature corresponding to a vapour pressure d e t e r -mination i s t h a t i n bath B. (.39') Table X I I . Temperature °o. Vapour Pressure Temperature Vapour Pressure Bath A Bath B i n mm. Bath A Bath B i n mm. 35 35 0.91 35 25 0*69 35 35 0.89 45 25 0.71 35 35 0.92 45 25 0*76 45 35 1.17 55 25 0.72 45 35 1.22 55 25 0.73 55 35 1.37 25 15 0.37 55 35 1.30 25 15 0.48 65 35 1.36 35 15 0.41 65 35 1.31 35 15 0.44 65 35 1.34 45 15 0.50 25 25 0*51 45 15 0.55 25 25 0.60 55 15 0.43 . 35 25 0*63 55 15 0.47 The data i s shown g r a p h i c a l l y i n F i g * 12. The braoketted f i g u r e beside each curve i s the temperature i n bath B. The maximum value on each curve was taken as the e x p e r i -mental value of the vapour pressure at each of the three temperatures. For ease of comparison, these three values are p l o t t e d i n the u s u a l way along w i t h values e x t r a p o l a t e d from the Kernst and Antoine equations, (see F i g . 13) ( 4 0 ) INDICATED VAPOUR P R E S S U R E IN M M o.z 0.4- 0.6 o.& l.O 1.2 1.4 1.6 1.6 FIG 13 GRAPH SHOWING DELATION OF EX PER MENTAL RESULTS TO VALUES EXTRAPOLATED FROM NERNST AND AWTO/A/f EQUATIONS o EXPERIMENTAL. aNERNST AN TGINlEL \ \ — X / o T 37 38 39 o (42) T i l l . .CONCLUSIONS AMD REOOMMENDATIONS Regarding the c e r t a i n t y of the three experimental values p l o t t e d as vapour pressure i n F i g . 13, grave doubts e x i s t i n the mind of the author. Though the n i t r o g e n was run through as s l o w l y as p o s s i b l e f o r smooth f l o w (4000 c c . i n 6 hours i n most runs) and the curves i n F i g . 12 reaoh a maximum, there i s no way of t e l l i n g w i t h absolute c e r t a i n t y t h a t the gas was saturated. The only way of a s c e r t a i n i n g the s a t u r -a t i o n has been obtained i s to inc r e a s e the number of s a t u r a t o r s one at a time u n t i l no f u r t h e r increase i n weight of absorbed m a t e r i a l occurs. On the other hand i n the t r a n s p i r a t i o n method, there i s always the p o s s i b i l i t y of entrainment. An enlarged s e c t i o n of the o u t l e t tube from the l a s t s a t u r a t o r was f i l l e d w i t h a p l u g of g l a s s wool t o prevent t h i s and, c o n s i d e r i n g t h a t the r e s u l t s appear t o be low, i t seems l i k e l y t h at t h i s p r o v i s i o n was e f f e c t i v e . The p o s s i b i l i t y of pre-mature condensation on t h i s p l u g was avoided by p l a c i n g i t below the surface of the bath l i q u i d . I t i s safe to say t h a t the three values obtained are q u a l i t a t i v e only and the work which has been done serves t o i n d i c a t e the d i f f i c u l t i e s i n v o l v e d i n u s i n g the t r a n s p i r a t i o n method f o r low vapour pres s u r e s . I f i n the f u t u r e a d d i t i o n a l work i s done on the vapour pressure of c i s - d e c a l i n u s i n g t h i s method, the f o l l o w i n g p o i n t s should be kept i n mind. A s i n g l e , constant temperature bath l a r g e enough to accommodate up t o twenty s a t u r a t o r s should be used. I f p r e - s a t u r a t i o n i s thought (43) d e s i r a b l e , a smaller a u x i l i a r y bath could be used f o r t h a t purpose* The determination of the sm a l l weight i n c r e a s e of the T T -tubes i s open to s i g n i f i c a n t e r r o r s ; e.g., an e r r o r o f one m i l l i g r a m - i n f o r t y i s 2*5%* I f the weight i n c r e a s e were 200 mg., a s i m i l a r e r r o r would be only Q»51»» Therefore* the volume o f n i t r o g e n run through should be i n c r e a s e d f i v e f o l d f o r temperatures above 15°C* and g r a d u a l l y up to a hundred-f o l d f o r temperatures c l o s e t o the m e l t i n g p o i n t * This e n t a i l s f i n d i n g some way of making the procedure continuous without much s u p e r v i s i o n f o r p e r i o d of up t o three weeks* One of the g r e a t e s t problems would then be the measurement of the l a r g e volume of n i t r o g e n passed through the apparatus. I f a f l o w meter capable of measuring small r a t e s of flow; i . e * , about 700 o.c./hr. could be obtained and the r a t e of flow kept constant, i t would not be necessary t o c o l l e c t the n i t r o g e n at a l l . I n the o p i n i o n of the author u n l e s s such arrange-ments are made, the t r a n s p i r a t i o n method i s not s u i t a b l e f o r the determination of low vapour pressures* BIBLIOGRAPHY 1. Balsbaugh, Assaf, and. Pendleton, Ind. Eng. Chem., 33, 1321-30(1941). 2 . Biehowsky and Storeh, J. Am. Chem. Sod.* 37* 2696(1913). 3. Cayera and Howie, M.A.Sc. Thesis, University of B.C.(1946). 4 . Griegee; R., Ber. 77B, 22-4(1944). 5. Bavenport, C.H., M.A.Sc. Thesis, University of B,C .(1939). 6. Bavies, G.F., M.A.Sc. Thesis, University of B.C . (193?). 7. Dunell, B.H., M.A.Sc. Thesis, University of B.C.(1946;. 8. Egerton, A.C.G., P h i l . Mag., 33, 33-48(1917). 9. Eyring, H,, J. Am. Chem. Soc., 5 0 , 2398(1928). 1 0 . Giauquej W.F.* Private l e t t e r to W.F.Seyer from University of California* Berkeley, California in.June, 1945. 11 . Glasstone, Laidler* and Eyring* Theory of Rate Processes, McGraw-Hill, 1?41* pp 477-351. 1 2 . Handbook of Chemistry and Physics, Chemical Rubber Pub-lishing Company(1945). 1 3 . International C r i t i c a l Tables. 14. Keesbm, W.H., Leiden Comm. Supp. 71e(1932). 1 5 . Khudsen, Ann. der physik, 28* 999(1909). 16 . Mann., C.W., M.A.Sc. Thesis, University of B.C.(1944). 17. Marshall* A.L., J. Am. Chem. Soc, 59* 1161(1937)• 1 8 . Mizuhara* S.J., M.A. Thesis* University of B.C.(1941). 19 . Mundel* CP., Zeit. fur physik. ehemie, 8 5 , 435(1913). 2 0 . Hemetz, H,, M.A.Sc. Thesis, University of B.C.(1938)• 21 . Othmer. B.F.* Ind. Eng. Chem., 37» 1112(1945). 2 2 . Pearce and Snow, J. Phys. Chem., 31 . 231(1927). Bibliography(Cont) 23. Phenomena at the Temperature of Liquid. Helium, Burton, Grayson-Smith, and Wilkelm, Hheinhold P u b l i s h i n g Company, 1940• 24. P i l k i n g t o n , T., M.A.Sc. Th e s i s , U n i v e r s i t y of B.C. (1941), 25. Ramsay and Young, P h i l . Trans. Roy. Soo. 175, 37(1884), 26* H.V,Regnault(l845). * • • 27. Robinson, M,, M,A.Thesis, U n i v e r s i t y of B.C.(1945). 28. Robinson and Younger, M.A.Sc* Thesis* U n i v e r s i t y of B.C. (1946). 29. Rodebush and Devries, J . Am. Chem. Soo. 47 , 2488(1925)* 30. Sohmidt, G*, P h y s i c a , 4, 963(1938). 31. Seyer and Mann, J . Am. Chem. Soo., 67* 328(1945). 32. Seyer and Walker, J . Am* Chem. Soc* 60, 2127(1938). 33. Stewart, G.W., Phys. Rev., 30» 232(1927). 34. Thomson, G.W., Chemical Reviews, 38, 1-40(1946). 35. von Wartenberg, H., Z e i t * f u r electrochemie, 19, 482(1913). 36. Weber and Bforgaard, Leiden Comm. Supp. 202b(1929). 37. Young, C,, S o i * Proo. Roy* D u b l i n S o c , 12, 374-443(1911)* 38. Zil'beraan-Granovskaya, J . Phys. Chem* (USSR), 14, 759-67(1940)* 39. Zoto0v, G., M.A. Thesis* U n i v e r s i t y of B.C.(1940). 

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