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Low pressure adsorption of oxygen or charcoal Swain, Lyle Alloway 1933

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LOW PRESSURE ADSORPT: of OXYGEN on CHARCOAL U . B . C , LIBRARYI CAT. r ^ . h B J ^ ^ m M ^ i J j J ' by L y l e Alioway Swain A t h e s i s submitted i n part requirement f o r the degree of MASTER .01. ARTS i n the Department of CHEMISTRY THE UNIVERSITY-OF BRITISH COLUMBIA A p r i l , 1923. PLATE I TABLE OF CONTENTS Page. P l a t e I (Photograph of Apparatus} F r o n t i s p i e c e . I n t r o d u c t i o n 1. Object of I n v e s t i g a t i o n 5. Apparatus 5. Fi g u r e I (Diagram of Apparatus ( t o face) 6. Experimental 8. Tabulation of R e s u l t s 10. R e s u l t s 18. Fi g u r e I I (to face}16. Hypothesis ' . 19. Summary £0. B i b l i o g r a p h y 22. LOW ;|EBS§BRis;- ALSOKPTTOi: of OXYGEN on CHARCOAL I n t r o d u c t i o n . She property of charcoal of absorbing l a r g e quan-t i t i e s of gas was f i r s t noted by de Saussure^in 1814. More d e t a i l e d work by Smith and by Hunter^followed. Lewar's a p p l i c a t i o n of t h i s property to the production of high vacua; and h i s d i s c o v e r y t h a t c o o l i n g to low temperatures increased t h i s s o r p t i v e pov/er , introduced the modern era of t h i s study. Blythswood and A l l a n found the rate of adsorption of a i r at l i q u i d a i r temperature was independent of the pre-ssure and f o l l o w e d the equation 4^= Ai^-x), where X i s volume adsorbed a t time t , i s volume adsorbed when e q u i l i -brium i s a t t a i n e d , and A i s a constant, i'ravers^measured the pressure of 002 and Hg over charcoal at various tempera-8 t u r e s . MeBain found that at l i q u i d a i r temperature, H c u r • 2 was almost completely adsorbed immediately, the process being f o l l o w e d by a slower adsorption extending over a p e r i o d of hours. He concluded t h a t surface condensation and a slow d i f f u s i o n i n t o the i n t e r i o r of the carbon took place.- J . B. F i r t h 9 v e r i f i e d these conclusions. Miss I . F. Homfray 1 0, working w i t h various gases over a v a r i a t i o n of temperature and up to 70 cm* pressure, concluded that her r e s u l t s were best e x p l a i n e d by a s o l u t i o n hypothesis. T i t o f f 1 1 f o u n d that hydrogen was absorbed according to Henry's Law, and that n i t r o g e n , carbon dioxide,ammonia followed the equation a^ .=a p". IB Rhead and Wheeler "assumed the formation of a CxOy complex when oxygen was used* This broke up on heating i n t o COg and GO, the pro p o r t i o n o f the l a t t e r i n c r e a s i n g w i t h i n c r e a s e i n the temperature of r e l e a s e . Langmuir^suggested, an a l t e r n a t e method o f combination of the oxygen, and found th a t at 2300°K part combines d i r e c t l y to form CO, and the r e s t adsorbs. L. B. Elchardson^^ gained no evidence of t h i s compound formation i n an attempt to reverse the r e a c t i o n , u s i n g carbon dioxide' and ch a r c o a l a t high temperatures. Lowry and H u l e t t confirmed the observations of 1 £ de Saussure , Smith , and ot h e r s , that the adsorption of ox-ygen was not complete over a long p e r i o d of time. (H.Berg-strom" reported that adsorption was not complete w i t h i n two years I] They found that both time adsorption and a'"fixation" of oxygen t o form a physico-chemical complex, took p l a c e , and b e l i e v e the slow decrease i n pressure to be due to the slow i n c r e a s e of " f i x e d " oxygen. The true adsorption pro-cess i s as r a p i d as f o r other gases• Benton introduced the terms - primary a d s o r p t i o n , s i m i l a r t o the oxygen " f i x -a t i o n " of Lowry and H u l e t t , and secondary, r e f e r r i n g to the n o n - s p e c i f i c adsorptions observed with i n a c t i v e adsorbents ( c h a r c o a l , mica, g l a s s ) . Blench and Garner- i n 1924 reported a r a p i d increase o f the heat o f adsorption of oxygen on charcoal with the temp-erature of the c h a r c o a l , and at constant temperature, a drop-ping o f f of the heat, w i t h increase i n the concentration of oxygen, They a t t r i b u t e the high i n i t i a l heat to r e a c t i o n w i t h the most a c t i v e and exposed carbon atoms which would be acted upon by the oxygen f i r s t a d m i t t e d 1 9 . Keyes and M a r s h a l l 2 0 found the heat of adsorption of various vapors, i n c l u d i n g oxygen, t o be gre a t e s t at zero concentration* Garner and McKie 2 1 * 2 2 confirmed the e a r l i e r r e s u l t s o f Garner 1 8. 1 5 , showing a s l i g h t maximum i n the curve, and suggest methods of li n k a g e of the CxOy complex. Ward and Hi deal*' found a high i n i t i a l heat of a d s o r p t i o n , i n which they b e l i e v e the drop corresponds to s a t u r a t i o n of the " a c t i v e patches". Their isotherm was almost l i n e a r at pressures l e s s than 20 cm. M a r s h a l l and Bramston-Cook" confirmed the work of Keyes and M a r s h a l l , showing the heat of adsorption of oxy-gen to be a maximum at zero c o n c e n t r a t i o n . This was denied by B u l l and Garner 2 5who showed a maximum at a concentration of .025 c c . per gram of carbon, whereas the i n i t i a l concentration of M a r s h a l l and Bramston-Cook was .05 c c . per gram. L a t e r 26 B u l l , H a l l , and Garner obtained r e s u l t s concordant w i t h those of M a r s h a l l and Bramston-Cook by a d i f f e r e n t arrangement of the thermocouples used t o measure the temperature o f the c a r -bon. They suggest that the slow decrease i n pressure i s due e i t h e r to d i f f u s i o n of the adsorbed, oxygen i n t o the i n t e r i o r of the g r a i n s , or t o a slow r e a c t i o n a c c u r r i n g between the gas f i l m and, the s u r f a c e . . 27 Kruyt and Modderman, reviewing the r e l a t i o n s h i p s between oxygen ads o r p t i o n and i t s accompanying e-volution of heat, conclude that p o s s i b i l i t i e s of chemical combination e x i s t o n l y I n the i n i t i a l stages, and f u r t h e r that no one theory or equation has as yet covered a l l the data adequately. 28 Shah , working w i t h oxygen, n i t r i c oxide, and n i t r o u s oxide, on c h a r c o a l , p r e f e r s Keyes and Marshall's*' 0 suggestion of a " s p e c i a l s t a t e " of the adsorbed molecules wherein sev e r a l l a y e r s are 'built up, r a t h e r than the formation of Ehead and 12 Wheeler's C x 0 y complex . 29 Ward, from h i s work on the s o r p t i o n of hydrogen by copper, concludes the slow secondary process to be due to d i f f -u s i o n of the gas i n t o the copper along g r a i n boundaries. The r a t e of d i f f u s i o n v a r i e s w i t h the amount of gas adsorbed on the s u r f a c e . In 1931, Taylor published a wide v a r i e t y of e x p e r i -mental work i n v o l v i n g adsorption of gases on various surfaces. A l l were explained on the assumption that adsorption i s a pro-cess i n v o l v i n g an energy of a c t i v a t i o n . He deprecated the 31 importance of d i f f u s i o n and s o l u b i l i t y processes . 32' This view has been v i g o r o u s l y attacked by Steaeie , who claims that Taylor's data i s i n some places i n c o r r e c t , and 5 that the remainder can be simply explained on the basis o f s o l u b i l i t y o f the gas i n the s o l i d . A wealth of v a l u a b l e and r e l e v a n t m a t e r i a l and ideas i s t o be found i n a Symposium on Adsorption h e l d by the Fara-day S o c i e t y 3 3 i n 1932. Object o f I n v e s t i g a t i o n . The present research was undertaken to measure more c a r e f u l l y the v a r i a t i o n i n pressure of oxygen i n 'equilibrium" w i t h c h a r c o a l at very low pressures at both room and l i q u i d a i r temperatures9 i n the hope th a t i n f o r m a t i o n confirming some one of these many t h e o r i e s might be forthcoming. An a n a l y s i s of the gas i n ' e q u i l i b r i u m " w i t h the charcoal was pro-j e c t e d , but was not accomplished. An attempt to measure the heat of adsorption at l i q u i d a i r temperatures was prevented by l a c k of s u f f i c i e n t l i q u i d a i r . The apparatus, a photograph of which i s shown i n P l a t e X and a diagram i n F i g * I , i s s i m i l a r to that used by 34 G. Waddington w i t h the d i f f e r e n c e that a l l stopcocks i n contact w i t h the charcoal have been replaced with mercury s h u t - o f f s , S]_ to Sg. The c h a r c o a l i s contained i n the quartz tube A, which i s fused to the Pyrex apparatus by means of a graded s e a l , a wide tube leads through a s h u t - o f f S, d i r e c t l y to a mercury d i f f u s i o n pump, backed by a Genco Hyvac pump, thereby (to face) 6 a l l o w i n g more r a p i d , and complete exhaustion o f the c h a r c o a l . A l a r g e McLeod Gauge, G, of 518 cc. c a p a c i t y , and s e n s i t i v e to 0.1 x 10 cm. mercury i s connected to the c h a r c o a l through the s h u t - o f f , Sg 1'he oxygen was measured by the gas p i p e t t e , p, the d i f f e r e n c e i n l e v e l s o f mercury i n the two arms being measure by a cathetometer• The volume of the p i p e t t e was 7.141 cc. d u r i n g the f i r s t s e r i e s of measurements, and 7221 c c . during the second. The oxygen could be prepared e i t h e r from pot-assium c h l o r a t e c o n t a i n i n g a trace of manganese d i o x i d e , or from potassium permanganate. Both were heated and exhausted to remove other gases and water vapor. The oxygen was s t o r e d over Pg05 before use. Shut-offs are s i t u a t e d as shown i n F i g . I , so t h a t any p a r t of the system could be evacuated e x c l u s i v e of any o t h e r . At no time was the charcoal i n . c o n t a c t w i t h stopcock grease vapor excepting f o r a p e r i o d of 15-20 minutes a f t e r a f r e s h sample of oxygen had been introduced. The charcoal used was a sample of eocoanut charcoal obtained from the N a t i o n a l Carbon Company. I t had been wash-ed i n a Soxhlet e x t r a c t o r w i t h h y d r o c h l o r i c a c i d ana a f t e r -wards t r e a t e d w i t h h y d r o f l u o r i c a c i d , the f i n a l ash content being .2'67$>. Before use i t . was outgassed at 1020°c«» The weight a f t e r t h i s treatment was 30.115 gm. Before the .series at l i q u i d a i r temperature was begun, i t was necessary to r e -move some mercury from the c h a r c o a l . This was done by heat-7 i n g and evacuating the charcoal i n a l a r g e f l a s k , Fresh c h a r c o a l was added and the outgassing repeated before use. The weight o f ch a r c o a l i n t h i s s e r i e s was 31.146 gm. The apparatus was f i r s t evacuated w i t h no charcoal i n i t to ensure the absence of l e a k s . The volume of the system, determined by expansion of a measured volume of a i r i n t o i t , was found to be 733 c c . a l l o w i n g f o r the volume of the c h a r c o a l . The volume o f the Mcleod Gauge and connecting t u b i n g a f t e r i s o l a t i o n of the charcoal tube by r a i s i n g Sg, $g, and S 4 , was approximately 550 cc. A f t e r f i f t y hours pumping over a p e r i o d of four days, a pressure of 1.8 x 10""5cm. developed i n 70 hours, showing the absence of l e a k s . The charcoal was then i n t r o d u c -ed, by breaking o f f and r e s e a l i n g the tube 0. The system was pumped f o r s e v e r a l days w i t h the char c o a l heated to 1000°C• I t v/ss then f l u s h e d out w i t h oxygen, accompanied by reheating and pumping. A s l i g h t pressure developed i n the system on standings, The h i g h temperature f o r outgassing was obtained w i t h a platinum wound r e s i s t a n c e furnace, the temperature being determined i n the l a t t e r part of the work, by a chromel-alumel thermocouple. The low temperatures were obtained w i t h l i q u i d a i r , contained i n Dewar f l a s k . A t e s t on one sample showed the escaping gas. to be almost completely oxygen. Hence a temperature of -183°C may be assumed f o r t h i s s e r i e s . 8 E x p e r i m e n t a l . To make a r u n , a sample o f oxygen was drawn i n t o the gas p i p e t t e and i t s p r e s s u r e n o t e d . A l l mercury s h u t - o f f s were c l o s e d except Sg and S 2 . The oxygen was then a l l o w e d t o expand i n t o ' t h e system, t h e time b e i n g n o t e d . D u r i n g t h e se c o n d s e r i e s o n l y p a r t of t h e oxygen was a l l o w e d t o escape f r o m t h e p i p e t t e . The p r e s s u r e of the r e s i d u a l gas was then measured^ t h e r e b y a v o i d i n g any e r r o r due t o change i n the me r c u r y meniscus a t too w i d e l y v a r i a n t p r e s s u r e s . P r e s s u r e measurements were 'taken a t v a r i o u s i n t e r v a l s o f time u n t i l t h e y became f a i r l y c o n s t a n t . Because of the ti m e consumed i n making a r e a d i n g w i t h the Mcleod gauge (about t h r e e m i n u t e s ) , the r a t e of the p r e s s u r e change may be i n f l u -enced c o n s i d e r a b l y a t the b e g i n n i n g owing to the l a r g e volume o f t h e M c l e o d compared t o the r e s t o f the system. The p r e s s u r e r e a d i n g s t a b u l a t e d below a r e the mean o f s e v e r a l taken i n the f o l l o w i n g manner. A f t e r t a k i n g a r e a d i n g -5 a t t h e 10 r a t i o mark, the c a p i l l a r y volume was compressed one o r more m i l l i m e t r e s and a p r e s s u r e r e a d i n g was taken a t t h i s l e v e l . T h i s was r e p e a t e d over n e a r l y a l l the volume range (7 millfmetres) e M u l t i p l y i n g each by the s u i t a b l e f a c t o r c o n v e r t e d i t t o cm. x 10~ 5. T h e i r average was-assumed to be the p r e s s -u r e ; the second' f i g u r e i s not s i g n i f i c a n t . A t t h e end o f f i f t e e n m inutes s h u t - o f f Sg was c l o s e d , t h e amount o f oxygen i n the t u b i n g c o n n e c t i n g w i t h the p i p e t t e then b e i n g so s m a l l t h a t i t c o u l d be n e g l e c t e d . T h i s i s t h e o n l y p e r i o d at which there i s any opportunity of contamination of the charcoal by p o s s i b l e adsorption of stop-cock grease vapor. When an apparent e q u i l i b r i u m was reached, Sg was c l o s e d , S 4 opened, and the McLeod was exhausted to zero press-ure. On r e s t o r i n g the system to i t s previous c o n d i t i o n , the pressure was found to be lower, and i t rose to a point w e l l beneath the e q u i l i b r i u m p r e v i o u s l y reached. This i s i n accord w i t h the f i n d i n g s of Lowry and H u l e t t 1 5 , and others, that the attainment of a true e q u i l i b r i u m i s a v e r y slow process. The i s o l a t i o n o f the charcoal and evacuation of the gauge were repeated s e v e r a l times. The q u a n t i t y of oxygen thus removed from the system was c a l c u l a t e d and found to be n e g l i g i b l e . The r e s u l t s of t h i s s e r i e s are shown i n Table I . A f t e r t h i s s e r i e s , the system was dismantled to clean out the McLeod Gauge, the mercury showing some tendency to s t i c k i n the c a p i l l a r y . Considerable e t c h i n g , g i v i n g a w h i t i s h opaque appearance to the quartz i n contact with char-c o a l , showed the p o s s i b i l i t y of r e a c t i o n at the higher temper-atures between the two, with e v o l u t i o n of carbon monoxide or d i o x i d e . Greenwood s t a t e s that s i l i c a i s not reduced by charcoal i n a vacuum of one m i l l i m e t r e u n t i l a temperature of 1460°C i s reached, when r a p i d e v o l u t i o n o f carbon monoxide 15 begins, and a s l i g h t sublimation occurs. Lowry and Hulett , however, noted e t c h i n g of the s i l i c a at 1050°C, accompanied by continuous e v o l u t i o n of oxides of carbon. This would ex-10 p l a i n why i t was impossible to pump the charcoal to zero press-ure w h i l e i n the furnace. With the s e r i e s at l i q u i d a i r temperature a s i m i l a r procedure was c a r r i e d out, the r e s u l t s being shown i n Table I I . The c h a r c o a l was outgassed a f t e r the conclusion of the second s e r i e s . Table I I I shows the v a r i a t i o n i n pressure w i t h temp-erature during t h i s treatment, pumping being continuous. A f t e r c o o l i n g s l i g h t l y , the charcoal was i s o l a t e d by c l o s i n g S i and Sg, and the furnace was removed. A f t e r pumping the r e -mainder of the system f o r a day, a sample of oxygen was passed i n . At the end of an hour the pressure was 200 x 10 cm. -5 i n s t e a d of .3 x 10 'cm, (See Table ±V). A d d i t i o n of another sample gave a pressure too great to measure (more than 340 x «5 • • • 10 cm,], A f t e r baking and pumping out, the procedure was r e -peated, and the same r e s u l t was obtained. The c h a r c o a l was baked and pumped f o r two days, and then cooled by removing the hot furnace. F r e s h l y prepared oxygen (from potassium c h l o r a t e ) was added and the v a r i a t i o n of pressure w i t h temperature was noted. T a b u l a t i o n of R e s u l t s : In Tables I and I I , are t a b u l a t e d the concentrations of oxygen i n mols, x 10 per gram of c h a r c o a l , under each of -5 which i s l i s t e d the pressure of oxygen i n cm. x 10 w i t h the corresponding time i n minutes, "Pump" means that the McLeod 11 Gauge was pumped out, the c h a r c o a l being shut;:: o f f . Subsequent times are measured from the time the c h a r c o a l i s again opened to the gauge, "x" means, g e n e r a l l y , t h a t the corresponding p r e s s u r e r e a d i n g was made the f o l l o w i n g morning. SABLE I P r e s s u r e Measurements at Room Temperature, 20~22°C. Conj ^130 PxlO' :;;cm, 295 1 122 7 21 15 :>" 4 27 1.1 39 .9 55 ,9 76 .9 95 .9 111 Pump • .«51v .46 20 Time ,0253 .0388 PxlO" Time PxlO lime 295 1 299 1 41 10 90 7 2 20 XI ©•£ 14 .68 33 .32 29 .58 45 .24 47 e 61 55 ,26 64 .62 106 .25 LOl Pump PUIJTD .33 6 .18 f ;2L-.38 " ..^ S•; ;-6SV.. •36 43 Pump Pump'. : V 1 6 V 29 *23-' : ;L4 . v >19; 2 , .25 ; •' ;X/~' days Pump *20 : 21 . .20 ^ LOl Pump •"..'iB-'vV :15:: : LOO Pump .14 23 . 16 x ,0542 PxlO 331 52 1 .27 .30 ® 28 .. ©2V Pump .17 *20 .19 Pump .13 ©X2 .17 1 8 18 -36 47 60 ' 103 31 83 [141 ;• 20 41 2 Idays ,0670 PxlO 276 144 77 8 1., .91 .as «2 5 • 2 7 .27 Pump .17 .17 Pump .14 .13 ,16 Time 1 7 12 20 33 41 50 72 95 |L20 45 96 2 2 x 1°12 Oon\ xlO' IPxlO1 em± ,0726 [Cime 190 58 9.2 1.7 .49 .22 .20 pump 15 .14 .15 |Pump 09 .14 5 11 17 25 35 46 123 2 25 81 24 x PxlO' >101 Time 184 17.9 3.3 .60 .21 .18 .18 Pump . 13 . 13 Pump .10 e X 2 2 10 18 25 35 77 HlO 65 99 23 x PxlO' ,126 Time 260 65 8.6 X«2| .20 • X 7 .19 Pump © X3 .11 Pump .07 -.09 .18 Pump .11 .14 2 8 15 22 35 65 P. 44 38 :95 23 40 4 days 16 62 .177 PxlO 4 tOime 134 97 15.8 4.1 .80 .30 .31 Pump .21 .21 .20 .24 .13 .13 4 9 14 22 32 42 58 H42 26 68 1183 x 18 93 PxlO ,212 Time 174 63 16.< 3.( .88 © 2o .20 .21 Pump .14 .16 Pump .11 .12 3 8 13 20 26 37 58 IL43 12 41 38 I Corij ixlO" . .270 320 .403 .497 .640 PxlO" Time P x l O 5 S ime : P x l O 5 I ime 5 PxlO lime P x l O 5 lime cm. 243 i'- 214 287 3 303 3 15.6 10 61 -12 ; '40 10 :59: 10 51 ;. 10 X © 2 20 16.8 17 ; 8.1 -17^ : 9.4 ^16- 11..2 17 .46 30 5«tc 24 r ...\r63.--56 .79 :25 5:.o 26 V .59 40 .78 31 •; :. ;i.2l,"' ; : 92 *40 35:": ; .68 40 .28 60 o 2-o 149 - v :• ••-*£! • L87 58 ; r ,24 228 26.; 90 .21 iPump '.29";: 90 Pump .26 132 a 22 ',.:12..v- •23: © 2$ 116 . .14 : 34 Pump © 2X X 2X 85 Pump' ; Y .14 57 .16 26 Pump .13 159 .18 34. .16 97 .16 81 .14 :;44- iPump •" o X 8 89 Pump • 16 151 .15 140 r }^.14:^ ;! X -•" .17 157 e X 2 X Pump Pump Pump .11 52 .09 ; 62 « o X X : 74 •> o X X X i l 3 .13 X Cone x!0« 797 PxlO 21 .64 .48 .39 .34 .32 .32 Pump .19 .18 .17 Pump .13 Time 10 20 30 40< 60 90 120 150 32 52 232 x. .958 PxlO" Time 213 4 35 10 1.7 20 .82 30 .60 : 42 .47 ' 60 .42 > m * 3 O 120 «34 y; 150 180 Pump .19 30 .19 60 .195 90 .18 127 Pump .14 X PxlO' 1.109 Time 233 35 2 6 3 1.01 . 81 .58 ,47 .42 .39 .35 ..34 Pump 920 .20 .21 .20 4 10 20 30 40 60 90 120 150 180 210 27 57 87 117 PxlO 1.266 Time .41 Ptimp .20 .20 41 Hrs:< 16 50 13 1.427 PxlO 1 Time 9.1 £0 2.4 40 •1.0 100 .56 230 .50 330 .76 x. Pump .32 120 Mi 320 .40 X ' Pump .20 75 • 2*w 160 Pump .14 50 Pump .13 -90 .14 190 Pump .14;, 130 TABLE,. 11 Pressure Measurements at L i q u i d A i r Temperature, -183°0, x l O l . .145 ; ..'440 [: .590 PxlO" Time/,; : ^BxlO^ Time . : PxlO? E fine.'..'. P x l O 5 lime cm. 1.4 , , r i g . . . ; 60 30 .41 30 .58 30 ©22 90 ^  .28 L20 © 2 9 70 .29 : 60 ;.!\*14. 150 .20 L80 .28 120 .17 90 :-;,;.L'8' ;• 175 9 23 150 e 14: 120 •• i2-2 175 .11 • 145 Cone . .740 .892 1.162 1.482 tc\ O 5 PxlO 5 Dime P x l O 5 Oime P x l O 5 ?ime P x l O 5 Dime .-.dm'.. .75 15 9 3 2 315 1.1 18 .61 45 .40v: 60 .£6 240 .57 45 .47 80 .£8 L05 370 .56 215 Pump »28 L25 Pump . £8 240 .40 SO © 23 90 .28 270 .38 60 O A L25 Pump & 25 17 .24' : £9 . Cone £.103 2.5 33 5.002 x l O 5 P x l O 5 Time " B X I Q 5 l i m e - P x l O 5 JOime P x l O 5 Time cm. .75 50 .83 55 69£ 85 .96 150 .57 90 ; «70 90 .83 L£0 : .91 2 £5 Pump ; Pump Pump .45 . ISO .66 30 .66 -90-; .76. 15 .63 57 .63 , 135 : .74 : 30 Cone . 3.474 5.949 4.4£7 5.559 6.2 45 x l O 5 PxXG^ Time PxlO- Time ; Pxl05 Time PxlO £ Time P x l 0 D Time cm, £i © 7 15 ; £.1 •30 : 87.0 .5 16.6 10 11.5 10 1 © 3 *5 60 1.59 60 3 .6 15 // 4.. e 20 5.4 £0 X.»2 90 1,41 90 2,5 25 3 © o 30 4.3 30 1£0 Pump /v'.2,0:  .-45 , 3.0 40 • 3.7 40 Puinp; X © 2X 45 , 1.8 •55 .. £.8 50 3.4 50 1*1. - 30 1.14 : 75 1.7 65 £.4 70 3.1 60 1.0';; 60 1.07/ 95 1.5 85 2 © X o 90 2,6 100 1.03 120 1.48 95 -1,97 110 2.5 130 1 .99 150 1.28 XX 5 1,90 130 2.40 160 X«3 136.;.; 1,83 150 :• 2.32 190 Pump : 1,77 170 Pump •1-ifr' - 2 1,69 190 l.£6 1 1,21 10 1.45 250 21» 2 7 10 1.24 £0 Pump £.£4 3£ t X 0 01 110 X © X 2 £ e £ £ 60 1.45 10 . 1.42 30 The high values recorded i n the l a s t run may be due to s l i g h t warming, as there was l e s s l i q u i d a i r than i n any previous run» On removal of the l i q u i d a i r the pressure rose i n 10 minutes to 1.25 cm. and dropped i n 10 minutes more to 1.15 cm., which i t h e l d f o r at l e a s t 25 minutes. During t h i s l a s t h a l f -hour p e r i o d the charcoal was i n a water-bath at 19°C. 27 hours l a t e r the pressure had dropped to something o f the order of .1 mm. The q u a n t i t y of oxygen present, 194.6 x 10" 5mols., would by i t s e l f , exert a pressure of about 4,8 cm. i n the system. TABLE I I I Time : Temp.,°0. Pressure cm.xlO 5 9:00 a.m. 9:50 10:30 11:20 12:00 : 1 :,45 p.m. Eurnac e an • 454 702 942 1028 1046 1054 1 pump s t a r t e d >300 210 9.7 7,3 The f o l l o w i n g Table shows the l o s s i n adsorptive power of the c h a r c o a l . The pressure value at zero time i s c a l c u l a t e d . TABLE IV Odhc. >06 & X 2 2 x l o 5 P x l O 5 lime i i x i o - Time cm. 3930 0 285 >340 20 224 10 >340. 230 201 31 >340 24 200 60 h r s . 199 70 In Table Y are l i s t e d a l l the concentrations of oxygen used, i n both s e r i e s . The second column shows the p FI&URE U 25! L Equilibrium Pressure Omen on Charcoal i. Room Temp-KEUFFEL & ESSER CO. ure a t t a i n e d a f t e r standing, and the t h i r d shows the pressure a f t e r the f i n a l pumping out. The comparison i s very rough be-cause of v a r i a t i o n i n the time allowed f o r e q u i l i b r i u m to be a t t a i n e d , and because d i f f e r e n t runs were pumped out a d i f f -erent number of times. The concentrations measured at l i q u i d a i r temperature are u n d e r l i n e d . These r e s u l t s are al s o graph-i c a l l y shown i n f i g u r e I I . • ' 'TABLE V Gone. 10 D Pi em. xIO 5 Ppcm. xl05 .013 ,9 .51 .025 ,62 . 16 o059 «2 «5 .19 ,054 .27 .17 .067 o 27 ,16 .073 ,20 .14 .101 .18 .'••;>^.»'12': .126 :f ^ .14 .145 e l l .177 .30 '••! : '• -.13 e 21 2 ,*.2p..v.; .12 .270 • 21, .13 .296 .18 .320 .21 .14 .403 .29 • & 13. ' .440 & 2 0 <tM» .497 .24 ,12 ,590 .22 .640 o 26 • 11 Cone. P-i cm. Pgcm. xIO 5 2105 xIO 5 .740 0 28 7797 eO 2 .15 .892 .23 .24 .958 .33 .14 1,109 .34 e 20 1.«"L 6.2 .28 .24 1.266 .41 *20 -1.427:.: .50 .14 1,482 .47 .- .57 .: :.- .38": T779T: .45 ^2^103: .70 e 63 2 & .63 9 '91 . 7 4 : 3^:474: • • 1.2 1.0 3.949 1.41 ,99 4 . 4 2 7 1 ©3 1.01 15.339° 1,45 1.42 6.245 2.32 2.22 In the f o l l o w i n g t a b l e i s shown the v a r i a t i o n of pressure w i t h temperature, with a concentration of .130 x 10* mols. per gram c h a r c o a l , the charcoal having l o s t i t s high a d s o r p t i v e power. 17 vTABJJE VI Time Deo. Sept, 16 10:30 a.m. 10:40 a.m. Sept. 17 2:20 p.m. 2:30 2:50 3 :03 3 :£0 3 :35 3^43 '.• 3-:4S 4:00 4:15 4:£5 • 4:40 5:05 5:30 5:40 5:53 5:59 6:10 6:30 6:56 7:15 7:31 7:52 8:10 8:25 8:40 8:55 9:08 9:20 9:35 9:45 10:00 10:00 10:13 10:20 6 (D. H< LePage) Pressure xlO bcm. 0 240 211 259 262 265 266 278 292 295 312 320 322 332 332 333 338 336 340 344 347 554 355 378 382 375 369 367 378 398 400 352 326 209 Temperature 50 (Water bath) 75 98.5 154 (Furnace & 14£ Thermocouple 182 201 201 201 £04 250 £50 301 305 400 400 400 400 400 4£5 450 450 Furnace removed. £0 18 R e s u l t s o The f i r s t S e r i e s (Table I ) shows evidence of the two types of ad s o r p t i o n as reported by many i n v e s t i g a t o r s . The i n i t i a l pressure i n the f i r s t run was c a l c u l a t e d to be 984 x 10 cm., becoming 295 x 10 cm, i n one minute. Accurate measurements of t h i s rate are impossible w i t h a McLeod Gauge because of the lon g p e r i o d of time (three minutes) during wh-i c h the bulk of the unadsorbed oxygen i s i s o l a t e d from the charcoal» A continuous reading gauge of some type i s nec-es s a r y f o r t h i s . That the second part of the adsorption i s much slower i s evidenced i n the second to l a s t run. A f t e r standing f o r 41 hours, the E q u i l i b r i u m " pressure was s t i l l t wice that a t t a i n e d a f t e r evacuation of the Gauge. The r e g u l a r i t y o f the f i n a l pressure a f t e r several evacuations of the Gauge, i s con s i s t e n t throughout the s e r i e s , -5 averaging about .15 x 10 cm. In the second s e r i e s (Table I I ) , comparison of the same concentration at the same time shows that adsorption i s more r a p i d , the pressure being much l e s s i n the second case. A l s o the pressure reached a f t e r s e v e r a l hours i s only s l i g h t -l y h i g h e r than that r e s u l t i n g a f t e r evacuation of the gauge. The values are therefore c l o s e r to the r e a l e q u i l i b r i u m v a l u e . The high e q u i l i b r i u m values noted w i t h the i n i t i a l c o ncentrations present i n t e r e s t i n g p o s s i b i l i t i e s . They may 19 be due to gas being d i s p l a c e d from the charcoal s u r f a c e , or may be connected i n some way w i t h high i n i t i a l heats of ad-s o r p t i o n mentioned above. Shis p o i n t of e q u i l i b r i u m i s apparently undisturbed by the decrease,in temperature s i n c e the l i m i t s defined by the pressures i n Sable I i n c l u d e those defined by the press-ures i n i'able I I , as shown i n Table V and f i g u r e II„ Jpurther data, i n Tallies IV and VI, i n d i c a t e that i n some way, the adsorptive power of the charcoal was g r e a t l y decreasede The reason f o r t h i s i s at present unknown, but f u r t h e r work i s being c a r r i e d out. In Table V I , showing the v a r i a t i o n of pressure of oxygen i n e q u i l i b r i u m w i t h the charcoal i n t h i s c o n d i t i o n , i t i s i n t e r e s t i n g to note t h a t the pressure u l t i m a t e l y r e -turned to i t s o r i g i n a l v a l u e , i n d i c a t i n g i t to be a d e f i n i t e e q u i l i b r i u m pressure. (The l a s t pressure reading was obtained through the courtesy of D. H. LePage„). Hypothesis. Suppose almost a l l the oxygen be adsorbed and chem-i c a l l y combined, i n some manner such as Ehead & Wheeler's C xOy complex, and that there be a very small amount moleeular-l y adsorbed (van der Waal 1s a t t r a c t i o n ) , which i s changing over s l o w l y to the combined form. Suppose i t to be i n d i r e c t and simple e q u i l i b r i u m with the gas phase. On pumping o f f the l a t t e r , the m o l e e u l a r l y adsorbed oxygen goes i n t o the gas phase to r e s t o r e e q u i l i b r i u m . T h i s 20 w i l l be at a lower pressure because the concentration of mole-c u l a r l y adsorbed oxygen i s markedly decreased. C o i n c i d e n t w i t h t h i s the combined oxygen would r e v e r t s l o w l y to m o l e c u l a r l y adsorbed oxygen, maintaining a d e f i n i t e e q u i l i b r i u m . There would be no f u r t h e r drop of t h i s e q u i l i -brium pressure because of the ve r y l a r g e concentration of c h e m i c a l l y adsorbed oxygen as compared to p h y s i c a l l y adsorbed oxygen. This e x p l a i n s the drop i n the e q u i l i b r i u m pressures w i t h each pumping u n t i l a constant value of about .12 to 20 -5 x 10 cm. i s reached throughout the f i r s t s e r i e s . The d i f f e r e n c e between e q u i l i b r i u m pressures before and a f t e r pumping i n the l i q u i d - a i r s e r i e s i s very much l e s s . Here the oxygen i s p r a c t i c a l l y a l l m o l e c u l a r l y adsorbed and e q u i l i b r i u m i s more r a p i d l y a t t a i n e d . Oxygen adsorbed a t l i -q uid a i r temperature i s recoverable completely (Dewar ), whereas oxygen adsorbed at room temperature i s only p a r t l y 15 recoverable as such (Lowry & H u l e t t ), and at higher temper-atures only oxides o f carbon are relea s e d (Ehead and "Wheeler^),, This means tha t chemical combination does not take place at low temperatures. f u r t h e r t h e o r e t i c a l c a l c u l a t i o n s are being conducted to f i n d what c o r r e l a t i o n , i f any, e x i s t s between t h i s data and the current t h e o r i e s of a d s o r p t i o n , Summary. The 'equilibrium pressure" of oxygen over charcoal has ' ' 21 been measured between the l i m i t s o f .015 and 1.427 x 1 0 " 5 mols. per gram charcoal at room temperature, and between -5 the l i m i t s of ,145 and 6.245 x 10 mo I s . per gram charcoal at l i q u i d a i r temperature*, I t s value i s apparently unchanged at the d i f f e r e n t temperatures, and i s a l i n e a r f u n c t i o n of the concentration of oxygen. By some p e c u l i a r i t y i n treatment, as yet undiscovered, the e f f i c a c y of the char c o a l as an adsorbent was g r e a t l y r e -duced, In conclusion I wish -to express my thanks to Dr. M. J . M a r s h a l l f o r h i s guidance and cooperation during t h i s i n v e s t i g a t i o n . 22 BIBLIOGRAPHY 1. de Saussure, G i l b e r t ' s Ann, der Physik, 47, 112, (1814) Thomson's Anhals of Philosophy, 6_, 241, (1815) 2. E. A. Smith, Proc. Roy. Soc., (London), 12, 424, (1863) 112fi, 296, (1926) 3* J . Hunter, P h i l . Mag., ( 4 ) , 25, 364, (1863) 29, 116, (1865) 4,. J . Lewar and T a i t , Roy. soc., Edinburgh, Mar., 1874. &.. J . Lewar, Proc. Roy. Soc. (London), 74, 122, (1905) Ghem, ITews, 94, 173, 185, (1906) 6. Blythswood and A l l a n , P h i l . Mag,, 10, 497, (1905) 7o M. W, T r a v e r s , P r o c . Roy. Soc. , 78, 9, (1906) 8. J . W. McBain, P h i l . Mag., ( 6), 18, 916, (1909) 9. J . B, F i r t h , Z e i t . p h y s i k a l . Chem,, 86, 294, (1913) 10. I . E. Homfray, Z e i t , p h y s i k a l , Chem., 74, 129, (1910) 11. A, T i t o f f , S e i t , p h y s i k a l . Chem., 74, 641, (1910) 12. Rhead and Wheeler, J . Chem Soc., 103, 461, (1913) 13. I . Langmuir, J . Am. Chem. Soc., 37, 1154, (1915) 14. L. 3. Richardson, J . Am. Chem. S o c , 39, 1828, (1917) 15. Lowry and H u l e t t , J . Am. Chem, S o c , 42, 1408, (1920) 16. II. Bergstrom, . Jernkontorets Ann., 82_, 21, (1927) 17. A. P. Benton, J . Am. Chem. S o c , 45, 887, 900, (1923) 18. Blench and Garner, J • Chem. S o c . 125, 1288, (1924) 19. W. E. Garner, Nature, 114, 932, (1924) 20. Keyes and M a r s h a l l , J . Am. Chem, S o c , 49 ,• 156, (1927) 23 21. Garner and McKie, J . Chem. Soe. , 150, 2451, (1927) 22. D. McKie, J . Chem. Soc., (1928), 2870. 23. Ward and R i d e a l , J . Chem. S o c , 130, 3117, (1927) 24. M a r s h a l l and Bramston-Cook, J , Am. Chem, S o c , 51, 2019, (1929) ™~ 25. B u l l and Garner, Nature, 124, 409, (1929) 26. B u l l , H a l l , and Garner, J . Chem. S o c , (1931), 837 27. H. R. Kruyt and J . G. lodderman, Chem. Rev., 7_, 259,(1930) 28. M. S. Shah, J , Chem. S o c , (1929), 2661, 2676 29. A. P. H. Ward, P r o c Roy. S o c , 135A, 506, .522, (1931) 30. Greenwood, J . Chem. S o c , 93, 1483, (1908) -31. H. S, Ta y l o r , J . Am. Chem. S o c , 53, 578, (1931) '.V.- Chemical Reviews , 9_, 1, (1931) 32. B, W. R, S t e a c i e , J , Phys. Chem, 55, 2112, (1951) Proc. Roy. S o c , Canada, (May, 1932) Trans. Faraday S o c , 28., 617, (1952) 33. , Transactions o f the Paraday S o c i e t y , 28, 151, (1932) 54. G. Waddington, Thesis, U n i v e r s i t y of B r i t i s h Columbia. 

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