Sorption by porous solids

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A b str a c t o f P h .D . T h e s is by M a rjo rie J . Brown on "S o r p tio n by P oroua S o l i d s ** A number o f i s o th erm a ls have b e e n d e ter m in e d f o r th e s o r p t io n o f th e vap ou rs o f amino compounds on s i l i c a and f e r r i c o x id e g e l s .

The s o r b a t e s s t u d i e d

in c lu d e th e norm al a l i p h a t i c a m in e s, from e th y la m in e to n -h e p ty la m in e ,

t - b u t y la m in e , e t h y le n e d ia m in e ,

c y c lo h e x y la m in e and p y r i d i n e .

D ata f o r e t h y l a l c o h o l

and w ater i s a l s o in c lu d e d , f o r com p arative p u r p o s e s , A sta n d a rd 'g r a v im e tr ic *

te c h n iq u e h a s b een u sed i n

e v e r y c a s e , e x c e p t t h a t o f e th y la m in e , f o r w hich a new te c h n iq u e h a s b een d e v e lo p e d . The f e r r i c o x id e is o t h e r m a ls a l l c o n ta in a la r g e h y s t e r e s i s l o o p , th e s i z e o f w hich d o e s n o t vary w ith in c r e a s i n g m o le c u la r d ia m e te r , d i l l c a g e l Bg is o t h e r m a ls show a la r g e lo o p w ith w a te r , and s m a ll l o o p s w it h e t h y l a l c o h o l , n -p ro p y la m in e and e th y le n e d ia m in e . r e v e r s i b l e is o t h e r m a ls .

L arger m o le c u le s g i v e c o m p le te ly T h is d a ta c o n fir m s th e m ost

im p o rta n t p r e d i c t i o n o f th e 'o p en -p o re* c a p i l l a r y c o n d e n s a tio n .

th e o ry o f

R e fe r e n c e i s made to d a ta in

the l i t e r a t u r e w hich p r o v id e s f u r t h e r c o n fir m a tio n o f t h is p r e d ic tio n . S ilica gel C and s ilic a gel D systems both contain

la r g e h y s t e r e s is lo o p s .

Only a few r e s n l t s a r e

q u o ted f o r th e form er s y s te m , a s th e is o t h e r m a ls o b t a in e d w ere n o t r e p r o d u c ib le . «h ere p o s s i b l e ,

th e K e lv in e q u a t io n h a s b een

u se d to e s t i m a t e th e m ost f r e q u e n t o c c u r r in g p o r e sp a c e a v a i l a b l e f o r c a p i l l a r y c o n d e n s a t io n .

In some

c a s e s an e s t i m a t e o f th e tr u e p o re r a d iu s h a s b e e n made, by c o r r e c t in g f o r th e t h i c k n e s s o f t h e a d so rb ed la y e r . E v id e n c e i s p r e s e n te d f o r o r i e n t a t i o n o f s o r b a te m o le c u le s i n th e f i r s t la y e r on f e r r i c o x id e g e l , and, to some e x t e n t , on s i l i c a g e l D. The v o lu m es a d so rb ed a t s a t u r a t i o n o b ey G u r w itsc h ’ s R u le i n e v e r y c a s e . E th y le n e d iam in e h a s b e e n shown to h ave a lo w e r f r e e z i n g p o i n t i n th e a d so rb ed s t a t e th a n i n th e b u lk sta te , The vapou r p r e s s u r e s and s u r f a c e t e n s i o n s o f some o f tliB s o r b a t e s h ave b een d e te r m in e d , u s in g m eth od s s u i t a b l e f o r h y g r o s c o p ic l i q u i d s .

#►> • f

SORPTION

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BY POROUS ri

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SOLIDS

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By Ï -

M a r jo r ie J o W Brown,’'B . 3 c . ’

. â j.,

- I ■■> # - A i:. -

Li»* > A TJfieais s u b m itte d to*» th e U n i v e r s i ty o f London f o r tiie D egree o f D o c to r o f ’ H iilo s o îiiy . •»*

r

R oyal H ollow ay C o lle g e ( U n iv e r s ity o f London) h h g l e f i e l d G reen S u rre y

N*

J u n e , 195a - '■-; '

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At P-

ProQuest Number: 10096554

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GOUT [(NTS

Acknowledgpients S e c tio n I .

I n tr o d u c tio n

I . I -2 5

S e c tio n I I . E x p erim en tal A. M a te r ia ls 1 . Thie S o rb e n ts

II. 1

2 . The S o rb a te s

I I .4

B. E x p érim en tal Tedhnlque 1 . G eneral

I I «9

2 . D e s c r ip tio n o f th e Main A p p aratu s

1 1 .1 0

3 .- D e te rm in a tio n o f th e Is o th e rm a l ( a j A c tiv a tio n o f th e S o r b o it

1 1 .1 2

(by F i n a l - p u r i f i c a t i o n o f th e S o rb a te

1 1 .1 4

( 0 ) S a tu r a tio n o f th e S o rb en t

I I . 1$

(d ) The D eso rp tio n Is o th e rm a l

I I .1 6

( e ) "Rie A d so rp tio n Is o th e rm a l

1 1 .1 8

4 . The Low P re s s u re Manometer

1 1 .1 9

3. A i^ a ra tu s f o r D e te rm in a tio n o f sth^km ine Is o th e rm a ls (ay D e s c rip tio n

1 1 .2 2

(b j P r e p a r a tio n o f S e a le d Tubes o f filthylaiaine

I I . 23

(oy D e te rm in a tio n of Dead

1 1 .2 4

Space

(dy Hie D e so rp tio n Is o th e rm a l

1 1 .2 6

C. Vapour P r e s s u r e M easurem ents

1 1 .2 9

D. S u rfa c e T en sio n M easurem ents

I I . 3I

s , S x p erim an ts w ith M ethylam ine

I I «34

P. S p é c if ie G ra v ity M easurem ents

I I «31

G. 1%te r m in a tio n o f S u rfac e A reas 1 . The A p p aratu s

I I » 39

2 . D e te rm in a tio n of Dead Space

1 1 .4 0

3» The Is o th e rm a l

1 1 .4 3

S e c tio n I I I . R e s u lts A. G eneral

I I 1 .1

B. P e r r i c O xide Gel Systems

I I I .2

C. S i l i c a Gel 82 System s

I I I . 13

D.

S i l i c a Gel G % [email protected]

I I I . 3I

E.

S i l i c a Gel D System s

1 1 1.41

F . F re e z in g P o in t of A dsorbed E th y le n e DiamJjie

I I I . 3I

G. Vapour P r e s s u r e M easurements

I I I . 33

H. Surface Tension Measurements

I I I . 55

I . S p e c if ic G ra v ity M easurem ents

I I I . 56

J . S u rfa c e A rea M easurem ents

I I I . 57

S e c tio n IV. D is c u s s io n A. G eneral

I V .1

B. F e r r i c O xide Is o th e rm a ls

IV .2

0.

S i l i c a Gel B2 Is o th e rm a ls

I V .I 9

D.

S i l i c a Gel C I s o th e n a a ls

IV. 30

B.

S i l i c a Gel D Is o th e rm a ls

IV*33

F , F re e z in g P o in t o f A dsorbed E th y le n e Diamine Appendix I .

T ab le o f P h y s ic a l C o n s ta n ts

Appendix I I . B ib lio g ra p h y

IV .41

x ii-v

The a u th o r \idshes t o e x p re s s h e r s in c e r e th a n k s t o D r. A. G. P o s te r f o r th e i n t e r e s t he h a s shown i n t h i s ■work, and f o r h i s c o n s ta n t a d v ic e and encouragem ent th ro u ÿ ^ o u t i t s e n t i r e c o u rs e .

The m easurem ents o f s u r f a c e a r e a were c a r r i e d o u t a t th e W ashington S in g er L a b o r a t o r i e s , E x e te r , by k in d p e rm is s io n o f th e a u t h o r i t i e s o f th e U n iv e r s ity C o lle g e o f th e South W est, and th e a d v ic e o f D r. S. J . Gregg d u rin g t h i s p e r io d i s g r a t e f u l l y acknow ledged.

Thanl Po I s th e s a tu i’a ti o n v a p o u r p re s s u r e and c i s a c o n s ta n t r e l a t e d to th e h e a t o f a d s o rp tio n , g iv e n by c = e wheru

E L za. liT

i s th e h e a t of a d s o rp tio n i n th e f i r s t l a y e r ,

i s t h e l a t e n t h e a t of c c n d e n sa tio n and HP has i t s u su al s ig n ifio a n o e . When th e number of a d so rb e d la y e r s form ed was fin ite

- i . e . i n a porous s o l i d , th e e q u a tio n V

= v„cP r ;

. 1 - (n + l ) p ” ( o '- i ) p “

where P = P /

+ n l^ ^ ^

/p )

-

was s a id t o g iv e good ag reem en t. Po t h i s re d u c e s to ( 1 ) .

When n =

A s t i l l more complex e q u a tio n was p u t fo rw a rd by B.D.D.T. (2 1 ) to acco u n t f o r th e shapes o f Type IV and V is o th e rm a l8 a t h ig h r e l a t i v e p r e s s u r e s , by ta k in g i n t o acco u n t th e in c r e a s e d h e a t of s o r p tio n of th e 3 a s t m o lecu le to e n te r th e c r o s s - s e c tio n of Uie p o r e , as i t i s a t t r a c t e d on two s id e s in s t e a d of only one. In p r a c t i c e a l l e q u a tio n s red u ce to (1 ) f o r th e i n i t i a l p a r t of th e is o th e r m a l, and t h i s i s n o rm ally u se d

1 .1 7 .

f o r t e s t i n g th e th e o ry because of th e l a r g e number of c o n s ta n ts in th e o th e r e q u a tio n s . The e q u a tio n i s t e s t e d by p l o t t i n g ^ / v ( pq - p j a g a in s t

which sh o u ld ^ v e a s t r a i g h t l i n e (se e

e q u a tio n ( 1 ) ) .

. and c can be o b ta in e d from th e s lo p e

and th e i n t e r c e p t .

In p r a c tic e th e s t r a i g h t l i n e o n ly

e x ten d s over th e re g io n Ü.Ü5 ^

0#35*

Both th e claim s and th e fundam ental a ssu m p tio n s o f tlie B .S .T . th e o ry liave been th e s u b je c t of much d i s c u s s io n . F o r exam ple, a s F o s te r has p o in te d o u t (2 6 J ,t h e assu n ip tio n t h a t th e n e t h e a t o f a d s o rp tio n f a l l s to z e ro a f t e r th e com plet,!on o f th e f i r s t ad so rb ed l a y e r i s c o n tra ry to e x p e rim e n ta l e v id e n c e .

Greg-; and Ja c o b s ( 6 2) have p o in te d

o u t t h a t w h ile th e h e a t of a a s o r p tio n of th e f i r s t la y e r c a lc u la te d from th e v a lu e o f c o b ta in e d from th e e x p e rim e n ta l p l o t , i s c o m p a tib le w ith therm odynam ic re q u ire m e n ts a s e x |)re sse a by th e C ia u siu s-C la p e y ro n e q u a tio n , i t i s e q u a lly co m p atib le w ith E, i

- h:

li

« OTInc - RTInC

where C i s any o o n s ta n t.

By th e ex am in atio n of p u b lis h e d

d a t a , Gregg and Ja c o b s have a l s o fo u n d t h a t v a lu e s o f S]^ and o a lo r im e tr io o r I s o s t e r i c h e a ts o f a d s o rp tio n do n o t a g re e i n many c a s e s . S e v e ra l m o d ific a tio n s of th e B .S .T . th e o ry have been s u g g e s te d b u t they g e n e r a lly s e rv e o n ly t o in tro d u c e an a d d i t i o n a l c o n s ta n t, w hich e n a b le s th e e q u a tio n to f i t th e is o th e rm a l over a s l i g h t l y w ider

1.18.

ran g e of p r e s s u r e , e . g . Anderson ( 8 1 ) . One o f th e m ost im p o rta n t a p p lic a tio n s o f th e B .R .T . e q u a tio n i s t o th e d e te rm in a tio n o f th e s u r f a c e a r e a o f th e s o r b e n t.

The d e te rm in a tio n o f v^j has a lre a d y been

d e s c rib e d , an d , i f th e a re a p e r m o lecu le i s knoim , th e s u r f a c e a r e a can be c a lc u la te d f r a a th e e q u a tio n .

where A i s th e c r o s s - s e c t io n a l a r e a of a s i n g l e m o le c u le in th e p la n e of th e s o rb e n t s u r f a c e , S i s th e " s p e c if ic * s u r f a c e , or su rface a r e a p e r gram, and N and M have t h e i r usual s ig n ific a n c e . I t i s im p o rta n t th a t th e ad so rb ed m o lecu le u sed f o r t h i s d e te r m in a tio n should b e as sm all a s p o s s i b l e .

F or

exam ple, s u r f a c e ax*ea v a lu e s d e te rm in e d by b u ta n e a d s o r p tio n a r e n o rm ally c o n s id e ra b ly lower th a n th o se d e te rm in e d by n itr o g e n a d s o r p tio n .

T his i s p ro b a b ly due to th e f a c t t h a t

th e l a r g e r b u ta n e m olecule i s n o t a b le to p e n e tr a te th e f i n e r p o re s o f th e s o l i d .

There s h o u ld also be a d e q u a te

d a ta f o r th e a r e a of th e m o le c u le .

The s o rb a tc s i n g e n e ra l

u se a re n itr o g e n ( a t - 1 8 ) % . o r - 1 9 ) % . ) , oxygen ( a t - 1 8 ) % ) ; argon ( a t - 19) % . ) and k ry p to n ( a t -195% *} &re a l s o u s e d . On th e b a s is th a t th e a d so rb e d phase i s more l i k e th e l i q u i d th a n th e s o l i d s t a t e , th e c r o s s - s o o tio n a l a r e a i s d e riv e d fro m ;= 4

X

o .b 6 6 I

U 4j2N^L

^

1.19.

w hich i s not» u n l i k e s c - = 1 . 3 3 X 10“^

^ b ic h was uœd by F e s te r f o r c a l c u l a ti n g m o le c u la r d ia m e te r s (53 B runauer and Ë to e tt (2 7 ) f i r s t p u b lis h e d s u r f a c e ai'ea d a ta i n 1 935» b e fo re th e e x p o s itio n of th e m ain th eo ry # Tliqy examined a la r g e number o f is o th e r m a ls on th e same c a t a l y s t and c o n s id e re d th e r e l a t i v e m e rits o f v a r io u s p o in ts on th e cu rv es f o r th e co m p letio n o f th e m onolayer. The is o th e rm a ls were a l l S -sh ap ed , w ith a lo n g l i n e a r p o r tio n - i . e . Type I I ( F i g . I . l ) .

They found t h a t th e b e s t

agreem ent was o b ta in e d from v a lu e s ta k e n a t P o in t B, and th e y s u p p o rte d t h i s c o n c lu sio n by d a ta o b ta in e d froffi h e a ts of a d s o r p tio n , w hich showed a s h a rp d ro p i n th e v i c i n i t y of P o in t B. F o s te r has shown t h a t , whien s u f f i c i e n t low p re s s u re d a t a i s a v a ila b l e , th e P o in t A v a lu e s a g ree w e ll w ith th o se o b ta in e d by a p p lic a tio n o f th e Langm uir e q u a tio n , and t h a t t h e r e i s some t h e o r e t i c a l b a s is f o r th e P o in t A, b u t n o t th e P o in t B, method (2 8 J .

He h a s p o in te d o i t t h a t

th e lo c a tio n o f P o in t B depends on th e m agnitude of 0 , and th e l a r g e r i t s v a lu e , th e c l o s e r w i l l P o in t B ap p ro ach P o in t A.

T here i s , how ever, l i t t l e doubt th a t b o th P o in ts

A and B l i e f a i r l y c lo s e t o th e t r u e s a t u r a tio n v a lu e f o r u n im o le o u la r a d s o r p tio n . Some modem th e o r ie s of a d s o rp tio n s u g g e s t t h a t th e ad so rb ed la y e r sh o u ld be m o b ile , and sh o u ld e x e r t a s p re a d in g p r e s s u r e s im ila r t o t h a t o f f ilm s on l i q u i d

1.20.

a u rfa c e s.

The aoB o nstiration of p h ase o h a n ^ s in tw o -

d im en sio n al f ilm s on w ater has been ex ten d ed to th e ad8ori)ed l a y e r by Baujdiam (82) and H arkins (83) and t h e i r c o l la b o r ­ a to rs . Gregg (42) h a s p u t fo rw a rd th e view t h a t th e r e i s a c o n s id e r a b le degree o f resem b lan ce betw een in s o lu b le f ilm s on w a te r and a d so rb e d f ilm s on s o l i d s . Gregg and llaggs ( 8 4 ) , have d e riv e d an e q u a tio n r e l a t i n g th e e q u ilib riu m p r e s s u r e

th e tw o -d im en sio n al com press­

i b i l i t y (/3) anu th ey claim t h a t a p l o t o f/3 a,?:aln8t lo g ^g P r e v e a ls ptiase changes i n th e a d so rb e d l a y e r .

They c l a s s i f y

s e v e ra l ty p e s o f t i a n s f o r u a tl o n s and su g g e st t h a t a l l o c c u r "b e fo re Wie m onolayer i s co m pleted. f a l l s t o a minimum

The c o m p r e s s ib ility

a t th e ap p ro x im ate v a lu e f o r th e

m onolayer co m p letio n and th en b e g in s to in c r e a s e a g a in , b u t does n o t su b s e q u e n tly f a l l . H ark in s and J u r a have a l s o compared th e ad so rb ed l a y e r on s o lid s w ith i n s o l u b le f ilm s In v o lv e s m easurem ent o f th e h e a t o f im m ersion o f a s o l i d , p re v io u s ly s a t u r a t e d by e x p o su re t o v a p o u r, i n an ex trem ely s e n s i t i v e c a lo r im e te r . " r e l a t i v e " m ethod r e l i e s on th e u se o f a g e n e ra l

Tiie

1 .2 1 .

e q u a tio n t o i n t e r p r e t a d s o rp tio n d a ta (8 6 ). The g e n e ra l e q u a tio n may be e x p r e s s e d :^ /p o

“ ®

^

Y/here v i s th e volume of vapour ad so rb e d a t p r e s s u r e p ,

Vq i s th e s a t u r a t i o n vapour p r e s s u r e , S i s th e s u r f a c e a r e a and B and k a r e c o n s ta n ts . o n ly , a p l o t of log^o

As lo n g as th e r e i s one phase

^/p q af^&lnst

s t r a i g h t l i n e , h av in g slo p e

-k S ^ .

sh o u ld g iv e a «bien t h i s e q u a tio n

can be a p p lie d , a s t r a i g h t l i n e i s g e n e r a lly o b ta in e d over th e range 0 .0 $

o .} $ .

b e d eterm in ed i f k i s known.

The v a lu e of S can t h e r e f o r e H arkins and J u r a assume k

t o be in d e p e n d e n t o f th e s o l i d f o r a g iv e n s or b a t e , and d eterm in e i t by m easurem ents on a s o l i d of known s u r f a c e a r e a - d e te rm in e d by th e “absolute** m ethod.

Very few

k v a lu e s have been d eterm in ed and th e method i s of l i m i t e d u se. L iv in g s to n (87) has q u e s tio n e d th e c o n stan c y of k .

H ark in s has based th e assu m p tio n on th e f a c t t h a t

th e e q u a tio n o f s t a t e of condensed film s on an aqueous s u b s t r a t a i s n o t a p p re c ia b ly a l t e r e d by changes i n pH o f th e s u b s t r a t e , and he assumed t h a t th e e q u a tio n of s t a t e o f a condensed ad so rb ed film i s in d ep en d e n t o f th e s o l i d . L iv in g s to n b e lie v e s t h a t th e e f f e c t o f change of s o l i d would be f a r g r e a t e r th an th e change i n pH. L iv in g s to n (87) and Emmett (88) have b o th compared th e H a rk in s -J u ra and B .S .T . methods f o r d e te rm in ­ in g s u rfa c e a r e a , and have shown t h a t th e B .E .T .

1.2 2.

oonstant o must be at l e a s t ^

fo r th e H arkins-Jura method

to g iv e a lin e a r p lo t , provided th a t the data follovfS th e B .S.T . eq u a tio n . Harkins and Jura (86) c a lc u la te d th e areas o f n itro g en m o lec u les, u sin g th e ”absolute" method f o r the d eterm in ation o f su rface a re a , and th e B .S.T . method fo r the d eterm in ation of monolayer a d sorp tion .

They quote

s ix te e n d if f e r e n t v a lu e s , grouped mainly round th ree p eak s, the sm a lle st ly in g c lo s e to th at c a lc u la te d from the d e n sity of s o l i d n itrogen ( l ) . 6 R?) and th e la r g e s t c lo s e to th a t c a lc u la te d u sin g th e d e n s ity of th e bulk liq u id (1 6 ,8 s ? ) In th e fo r eg o in g pages an attem pt has been made to p resen t a b r ie f survey o f the variou s th e o r ie s of a d so rp tio n , and to p o in t out t h e ir m erits and li m i t a t i o n s . The p resen t work was undertaken in an attem pt to obtain evidence fo r the v a l id it y or otherw ise of the c a p illa r y condensation theory and th e ' open pore* th eory o f h y s t e r e s is . F o ster has ca rried out a d e ta ile d in v e s t ig a t io n o f the ad sorp tion of the a lip h a t ic a lc o h o ls from nethyl to n -b u tyl on s i l i c a and f e r r ic oxide g e ls ( ) , 8 9 , 4 0 ) .

He

found th a t th er e was no ap p reciab le ohw ^c in the s i z e o f th e h y s te r e s is lo o p as the s iz e o f the m olecule in c r e a se d , although w a ter, w ith a sm aller m o lec u le, showed a much la r g e r lo o p .

He was a b le to obtain c o n s is te n t v a lu es of the

pore ra d iu s, ca lcu la ited by means of th e V elvln eq u a tio n .

1 . 23 ,

Examination o f th e amounts of so rb a te h eld in th e m onolayer, determined by what i s now known as the P oin t A method, gave d if f e r e n t r e s u lt s fo r the two g e l s .

In the ca se o f

f e r r ic o x id e ,th e amounts adsorbed corresponded to a co n sta n t number o f m o lec u les.

F o ste r r e je c te d the theory of a

constant number of a c tiv e c e n tr e s , and assumed in s te a d th a t the m olecules were o rien ted p erp en d icu la rly to the su r fa c e o f th e sorb en t; group.

o r ie n ta tio n b ein g due t o th e a c t iv e -OH

In view of the con stan t rad iu s of th e hydrocarbon

ch ain , t h is assumption does n ot c o n f l i c t w ith th e e x is te n c e o f a co n sta n t su rfa ce area f o r th e so rb en t.

In th e ca se

o f s i l i c a g e l , evidence was in favour of random o r ie n ta t io n . This work was extended by Broad and P o ste r (2 ,3 2 ) who in v e s t ig a te d the e f f e c t of th e nature end s i z e of the swisorbed m olecule on th ese so r b e n ts.

They were

ab le to fin d eviaen oe fo r th e o r ie n ta tio n of a c e t ic a c id and n -octan e on f e r r i c oxide g e l (th e former was a ls o ohemisorbed) but other r e s u lt s on t h i s g e l , and on two s i l i c a g e l s , gave no evidence f o r o r ie n ta tio n . S i l i c a g e l A, which had f in e p o res, gave a h y s te r e s is lo o p w ith water only; b ein g com pletely r e v e r s ib le .

th e other iso th erm a ls

This g e l was unusual i n th a t

the volumes adsorbed at sa tu r a tio n d id n ot obey G urw itsch's Rule (2 5 ) »

Broad and P oster p o in ted out th a t t h is

phenomenon, Icnown as 'p e r so r p tlo n ', could be exp lain ed by th e assumption of ta p erin g c a p i l l a r i e s , open at t h e ir wider ends (2 6 ) .

1.24.

Only a few measurements were ctirried out on S i l i c a g e l B, and i t has already been mentioned th a t th e h y s te r e s is lo o p , which was p resen t in every c a se , had shrunk to alm ost n e g lig ib le dim ensions in th e Si02Btrietliy la m ln e system . Pore r a d ii were c a lc u la te d by means of the K elvin eq u ation , and good agreement was obtained a fte r allow ance had been made fo r th e th ic k n e ss of the adsorbed la y e r . As an ex ten sio n to t h i s work, i t was d ecid ed to in v e s tig a te th e adsorption of another homologous s e r ie s on f e r r i c oxide and s i l i c a g e l s , as the data obtained would be valu able fo r fu rth er in v e s t ig a t io n s in to th e problem o f o r ie n ta tio n and the e f f e c t o f th e s i z e of the m olecule on the h y s t e r e s is lo o p . Ttie ch o ice o f the a c tu a l s e r ie s was governed m ainly by s u ita b le vapour p ressu res, although chemical natu re had a ls o to be con sid ered . In th e f i r s t c a se , the ad sorp tion o f the s t r a ig h t chain a lip h a tic amines was s tu d ie d , u sin g a standard g ravim etric technique in every case except th at o fe th y lamine.

The in v e s t ig a tio n was th m extended to in clu d e

m olecules of a d iffe r e n t str u c tu r a l ty p e , although s t i l l co n ta in in g th e

group.

I t was hoped to obtaiiyevidenoe

fo r o r ie n ta tio n by in clu d in g eth y len e diam ine, c y c lo h e x y lamine and t e r t ia r y butylam ine.

ly r id in e was a ls o s tu d ie d ,

to see in what way the shape o f the isoth erm al d iffe r e d

! rÿl,

1 .2 3 :

when a rin g compound was adsorbed. F in a lly th e su rfa ce areas of th e sorb en ts were measured, u sin g the B.E.T. gas ad sorp tion te ch n iq u e , as i t was hoped th a t th ese v a lu es would serve to confirm v a lu es o f th e su rfa ce areas c a lc u la te d from other r e la tio n s .'

m & . ^

i

à 1^'^^

i

,

I i

r .

^4

I l.l.

SECTION I I . aXPtiSXMaKTAL A. M a terials (1 ) The Sorbents (a ) F errio Oxjhe G el.

Samples o f a b atch of

g e l prepared by Broad ana F o s te r , according to the in s tr u c tio n s o f Lambert and Clark ( l ) , and used by them fo r th e ir in v e s tig a tio n s ( 2 ) , were used throughout t h i s work. Isotherm als of w ater and e th y l a lc o h o l were determ ined, p a r tly to s e t a standard fo r ocraparison w ith l a t e r r e s u l t s , and p a r tly to s e e t o what e x te n t the stru ctu re o f the g e l had a lte r e d by 'agein g' (as no in v e s t ig a tio n s had been carried out on t h is g e l s in c e 1939)» (b; S i li c a G els.

S up p lies o f the g e ls used

by F o ster i n previous I n v e s tig a tio n s ( 3 ) , d esig n a ted A and B by him, were low and i t was n ecessary to lo o k fo r new g e l s . S i l i c a g e l G was obtained from a M in istry o f Supply drying co n ta in er, and was s l i g h t l y brown in co lo u r, p o s s ib ly due to the presence of ir o n or organ ic im p u r itie s . unusual ty p e .

The g el gave a w ater isoth erm al of ra th er The e th y l alco h o l isotherm al in d ic a te d th a t

th e g e l was of type B in th a t a h y s t e r e s is lo o p was ob tain ed , but tho shape of the curve showed th a t th e g e l d if f e r e d co n sid era b ly from s i l i c a g e l B used by F o ste r .

S everal

iso th erm a ls were determined on t h i s g e l and are d escr ib ed l a t e r , but i t became obvious th a t c o n s is te n t r e s u lt s could

II.2

not,

be obtained unless high a ctiv a tio n ta-Dperatures,

involving th e use of a quartz co n ta in e r , could be employed. A ccord in gly, in vestigation s were d isco n tin u ed . S i l i c a g e l Bg was ob tain ed from a S i l i c a Gel Company b alan ce

dryer and was a v a ila b le in a sm all

q u a n tity o n ly .

I t was of i n t e r e s t as i t gave an e t h y l

a lco h o l isoth erm al comparing w e ll with th at obtained by F oster on th e g e l d esign ated SiOgB ())« S i l i c a g el D was obtained from the S i l i c a Gel Company.

The e th y l a lco h o l isotherm al showed a la r g e r

h y s t e r e s is lo o p than that ob tained w ith s i l i c a g e l Bg» Water Content of S i li c a The g e ls were sto r e d in b o t t le s w ith w e ll f i t t i n g s to p p e r s.

The removal of samples fo r ex p erim en ts,

however, n e c e s s it a t e d exposure to th e atmosphere and some adsorption of m o istu re.

In consequence the t o t a l w ater

co n ten t, and the water content a f t e r a c tiv a tio n by th e standard co n d itio n s employed in th e se experim taits, were determined on two samples removed a t the same tim e. The t o t a l water con ten t was determined by h ea tin g a weighed sample to con stan t w eight in a platinum c r u c ib le , u sin g a Maker burner.

During t h is p ro ce ss the

g e l s , which were i n i t i a l l y tr a n slu c e n t and c r y s t a llin e in form, became opaque and ' d i a l k y .' The second sample was heated in a vacuum f o r s ix te e n hours a t th e standard a c t iv a t io n tmspsr a tu r e , which d iffe r e d fo r each g e l .

The lo s s o f water was

determ ined and hence, by d iff e r e n c e , the r e sid u a l water

I

II.3

content of the g e ls during the d e te i^ ln a tio n of the isoth erœ als* The fig u r e s ob tain ed , vfhlch are quoted in Table I l . l , are n e c e s sa r ily appro.xi:f.ate, as no allov/ance was made fo r the vacuum co n d itio n s of one d eterm in ation , but they serv e t o ooæpare the w ater con ten ts of the th ree g e ls under the co n d itio n s of the experim ents. Table 11.1

Percenta5?e Water Uont ont of S i l i c a Gels A c tiv a tio n te m p e ra tu re

Sorbent

1 %%

200%

310282

1*1

^1020

3 .8

3 .0

SiO^D *2^

-

2 .3

960% **■ 1 .2

The brown colour of s i l i c a g e l 0 has alreadybeen mentioned.

évacuation a t '}6o ^ 0 caused an i n t e n s i f i ­

ca tio n of t^iis co lo u r, some pai‘tlG le s becoming alm ost b lack . As t h is c o lo r a tio n disappeared com pletely when the g e l was heated s tr o n g ly , i t was obvious th at some organic im purity was p r e se n t.

The w ater coi&mt e stim a tio n s are

th er efo re too h ig h , as the fig u r e fo r t o t a l water co n ten t (8J^) i s r e a lly an estim a te of t o t a l w ater and organic im purity co n te n t. As th ese d eterm inations were not c a jr ie d out u n t il work on s i l i c a g e l C had been d isco n tin u ed , no attem pt was made to p u r ify the g e l .

However, the rather ir r e g u la r

r e s u lt s obtained when some of the h igh er amines were adsorbed on t h i s g e l oan probably be exp lain ed by th e h ig h er

II.4

water oontent o f SlOgC as eoujpara'l w ith 3IO2B and SlOgD, as w ell as by th e presence o f th e organic im p u rity. I t i s p o s s ib le th a t Uie re sid u a l water con ten t p la y s no sm all p art in view o f the w e ll )mo\m hygroscopic n atu re o f the am ines(2 ) I n i t i a l pur if ic a t io n o f th e sorba tes (a > )• Water,#

Laboratory ^ d is t i .l ie d water was used.

(b ) a tliy l a lc o h o l.

A b s o lu te ly d ry alo câio l

was p re p a re d by d i s t i l l i n g 99^ e th y l a lc o h o l w ith magnesium and f r a c t i o n a t i n g th e d i s t i l l a t e .

Ih e f r a c t i o n b o i l i n g

at J8 .2 - 79 »3 °G-waa c o lle c t e d . Ethylene diam ine.

( 0)

The amine was p u

by the method o f Putnem and Kobe (4 ) in order to f r e e i t from eth y len e diamine h yd rate, which has n ea rly id e n t ic a l p h y sica l p r o p e r tie s . 100 gm. eth y len e diamine {su p p lied by L . L if^ t and Go. L td .) was h eated f o r ten hours w ith 47 gm. o f sodium hydroxide and 3 gm. of water in an o i l b ath .

The s o lu tio n separated i n t o two la y e r s above 60*0.

The top la y e r was decanted and l e f t overnigh t on 25 gm. of s o lid sodium hydroxide.

ïîie liq u id was decanted, r e flu x e d

fo r fou r hours w ith sodium, d i s t i l l e d in to a f la s k co n ta in in g f r e s h ly out sodium and re flu x e d fo r a fu r th e r p eriod o f fo u r hours.

The e th y le n e diamine was then

fr a c tio n s illy d i s t i l l e d , and th e p o rtio n b o ilin g a t 116.1 116. 4 *0 . was c o lle c t e d over sodium. (d) t-B u tylam in e.

t-B u ty lu rea was prepared

by the method o f Harvey and Gaplan ( 5 ) .

1

I I .)

107 mi# of concenirat.ed su lp iiu ric aoid (>94^) was add&d, 'with s t i r r in g , to 60 gn# of urea in a l i t r e I beaker# Trie temperature was kept below 7^ G. during the addition#

The m ixture was l e f t to stand a t about oO^G-

u n t il a l l th e s o lid had d isso lv ed #

140 ga# o f r e d i s t i l l e d

t-b u ty l a lc o h o l was then added, 'with s t ir r in g ;

the

temperature s t i l l being kept below 70^0# The mixtiii's nas l e f t t o stand a t room tem perature fo r twenty' hours and was t^ien d ilu te d 'with 1200 ml# of water*

C r y sta ls of mono-*tcrtiary b u tyiu roa were thrown

out and f i l t e r e d o f f .

The f i l t r a t e was n e u tr a lis e d w ith

d ila t e sodium hydroxide s o lu tio n and the fu rth er crop of c r y s ta ls f i l t e r e d off#

15ie crude product was r e c r y s t a ll i s e d

from e tiiy l alcoh ol#

'

X ield o f r e a r y stg d iise d product = 43#5 gm. M elting p o in t = 179«5^C. t-B u tylu i'ca was oonvertea to v-^butylphthalimide by th e me thou o f ü a ith ana iflaerson ( 6 )#

35 EP*# o f t - b u t y l‘

urea was thoroughly mixea wxth 100 gm# of p h th a lic antiydride and p laced in a l i t r e f l a s k , wiiich was plunged in to an o i l bath at 200^0.

iif t e r ton m inutes Uxe i n i t i a l

vigorous e ffe r v e sc e n c e su b siaed , anu the temperature o f the bath was r a is e d to 24^ 0. and. m aintained fo r f i v e minutes# 100 m l. o f etiiy l a lco h o l was added to d is s o lv e p art of the cooled product, and th e mixtux’e was maue a lk a lin e to litm u s w ith sodium cai'bonavo s o lu tio n .

$00

m l. of water was then

added, and the s o lid f i l t e r e d a t th e pump and p ressed as dry as p o s s ib le .

II.6

The crude t-b u ty lj^ th a lim id e was warmed w ith 500 tal. of petroleum eth er (B » p t.6ü~8ü®C*J and the h o t m ixture f i l t e r e d .

The f i l t r a t e was allow ed to co o l wid

was f i l t e r e d from a muall amount o f s o lid m a te r ia l, which sepai'ated a t room tem perature. The petroleum ether s o lu tio n was con centrated to about o n e-th ird of i t s o r ig in a l volume, end was l e f t in a r e fr ig e r a to r .

The t-butyl%d)thalimlde which sep arated

was f i l t e r e d a t th e pump and p ressed ix y . Y ield » 4 0 .2 gjD.

M.pt. = 59- 6®C.

A fu rth ie r 3 gm. was o b ta in e d by c o n c e n tra tio n of Wie filtra te . The t - b u t y l^ t h a l im ide was converted to t-lxitylam in e hydrochloride by the a c tio n o f Ijyoraaine hydrate {'})• y} gm. o f t-b u ty lï^ th a lim id e and 10 @n. o f 92^ hyarazine hydrate wore warmed in 7 $ m l. o f eth y l a lc o h o l. A

w hite g e la tin o u s p r e c ip ita te was soon formed, and t h i s

was decomposed by worming w ith 75 tnl* o f 20X h y d ro ch lo ric a o id .

Tho In so lu b le #[email protected] lylhydraslde which was formed

was fUtorod o f f and washed w ith o l l u t e h yd roch loric a c id , and the

aqueous so lu tio n o f t-b u tylam in e h yd roch lorid e

was evaporated to dryn ess. The oruua product was r e c r y s t a llis e d from e th y l a lco h o l and, a f t e r d ryin g, was tr e a te d w ith e x c e ss potassium hydroxide s o lu tio n anu d i s t i l l e d .

t-B utylam ine

was c o lle c t e d over sodium in a r e c e iv e r , cooled w ith l e e and s a l t .

I t was allow ed to s ta n d over sodium u n t i l

n.7. I I

e ffe r v e sc e n c e ceased and was then f r a c t io n a lly d i s t i l l e d on to fr e s h sodium.

The product seemed very pure and th e

la r g e fr a c tio n b o ilin g at 4 3 .8 - 4 3 .9°G.was c o lle c t e d . Y ield = approxim ately 12 m l. ( s ) Normal a liiA ia tic am ines.

n-Propylam ine,

n -butylam ine, n-amylamine, n-hexylam ine and n-heptylam ine were su p p lied by L . Ligjit and Co. L td ., and were p u r if ie d by r e flu x in g w ith sodium fo r fou r to s i x h ou rs, fo llo w ed by two fr a c t io n a l d i s t i l l a t i o n s ;

th e d i s t i l l a t e b ein g c o lle c te *

over f r e s h ly cu t sodium each tim e . Sthylamine was allow ed to stand over f r e s h ly out sodium in a f la s k , f i t t e d w ith a drying tu b e, which was immersed in m eltin g i c e , u n t il e ffe r v e sc e n c e cea sed . Three to fo u r days was s u f f i c i e n t .

I t was then fr a c tio n a te d .

The b o ilin g p o in ts of th e r e ta in e d fr a c tio n s of th e amines are given in Table I I . 2 . Table I I . 2 .

B oiling' P oin ts of M iines

Ethyl amine

l 6.^ C .

n-Propylamine

4 8 .6 - 4 8 . 7° G.

n-Eutylam ine

7 7 .6 - 7 7 . 8°C.

n-Amylamine

104. 2 °C.

n-ïîexylam ine

1 3 2 .5 - 1 3 2 .7 °C.

n-H eptyl amine

156.0°C.

Cyolohaxylamine

134.0 - 134. 2°C.

( f ) Cyolohexylam ine.

_

The emine was p u r if ie d

in th e same way and th e b o ilin g p o in t of the c o lle c t e d fr a c tio n i s recorded in Table I I . 2 .

II.8 ‘ 1 -I (g ) P y r id in e .

T sohn ical p y rid in e was p o r if ie d

by th e method of Heap, Jones and Speakman ( 8 ) .

A fte r

d ^ in g w ith s o l i d sodium h yd roxid e, i t was d i s t i l l e d through an e f f i c i e n t fr a c tio n a tin g column and th e f r a c t io n b o ilin g a t 115~117®C. was c o lle c t e d .

100 m l. o f r e d i s t i l l e d

p yrid in e was added to a reagen t prej)ared by d is s o lv in g 85 gn. o f mine c h lo rid e in 75 m l. o f W ater, 35 ml» of con centrated h y d ro ch loric aoid and 69 m l. of r e c t i f i e d s p i r i t , The c r y s t a llin e a d d itio n compound formed was f i l t e r e d o f f and r e o r y s t a llls e d tw ice from dry a lc o h o l.

The b ase was

lib e r a te d by a d d itio n o f a con cen trated s o lu t io n o f 2 6 .7 gn . o f sodiijm hydroxide to 100 g a . o f r e c r y s t a ll is e d compound, f i l t e r i n g from the p r e c ip it a t e and d ryin g over sodium hydroxide p e l l e t s .

The p y rid in e was fr a c tio n a te d

and the p o r tio n which b o ile d a t 115*5®C- was c o lle c t e d . The f i n a l p u r i f i c a t i o n o f th e s o rb e t es i s d e s c rib e d d u rin g th e account of th e e x p e rim e n ta l te c h n iq u e .

j

II.9

B. SxTierlmeHt.al technique ( l ) General remarks The whole o f t h is work was c a r ried out under h ig h vacuum c o n d itio n s . In order to ob tain ad sorp tion or d e so r p tio n iso th erm a ls two q u a n titie s were re q u ired : t (a ) th e q u a n tity of so rb a te a ss o c ia te d w ith a standard q u a n tity of sorbent; (b ) the p ressu re e x e r te d by th e sorb ate

over

the so rb en t. The former was ob tain ed by d ir e c t w eig h in g , u sin g a d eta ch a b le co n ta in er, ex c ep t in th e ca se o f eth ylam in e, fo r which a new tech niq ue was d evelop ed . (T his w i l l be d escrib ed a t a l a t e r

sta g e ).

At h i ^

p ressu res th e number o f d ir e c t w e i^ in g s could be reduced, to some e x t e n t , by th e anployment o f th e 'p ressu re change' tech n iq u e, b u t, in view of the r a th e r sm all 'd ea d -sp a ce' in th e ap paratu s, the use of t h i s method was lim it e d . P ressures were measured u sin g a \sid e-b ore mercury manometer;

the d iffe r e n c e in h e i ^ t b ein g

measured by a oath etom eter.

For so rb a tes having a

s a tu r a tio n vapour p ressu re low er than I 5 mm. a t th e experim ental tem perature a s p e c ia l low p ressu re manometer was u sed .

T his w i l l be d escrib ed a t a l a t e r s ta g e . B efore the c o n str u c tio n of the apparatus a l l

th e g la s s tu b in g , ta p s, ground j o in t s and p ie c e s o f apparatus were soaked in chromic a o id o v e m i ^ t , washed

11.10

w ith d i s t i l l e d w ater, mid d ried in a steam oven. At the com pletion of th e s e t o f experim ents w ith eadi so r b a te , the c o n ta in e r , manometer and o th e r d etachab le p a r ts o f the apparatus were removed and clea n ed in the same manner.

The taps were clean ed and r e -g r e a se d

(as some amine always became d is s o lv e d in the ta p -g r e a se ) and th e apparatus was evacuated fo r s i x h ou rs, t o remove a l l tr a c e s o f vapour, before th e in tr o d u c tio n of th e n ex t so rb a te. ( 2 ) D esc rip tio n o f th e apparatus For a diagrammatic s k e td i o f the apparatus see P i g . I I . l .

The major part was co n stru cted in soda g la s s . D was a pyrex c o n ta in e r fo r the sorb en t f i t t e d

w ith an a c c u r a te ly ground tap le a d in g to a sid e-arm .

The

side-arm ended w ith a ground g la s s cone (B .1 4 ) which f i t t e d in t o corresp on d irg so ck ets: (a) on th e manometer M to form th e j o in t Jj (b) a t th e fa r end of th e apparatus to form th e j o i n t J2 (fo r th e I n i t i a l a c t iv a t io n ) . The tap s T^^ and T2 served f o r th e evacu ation o f the 'open' and 'c lo s e d ' lim b s o f the manometer. A cone and sock et j o i n t

a tta d ie d th e mano­

meter to th e r e s t of th e apparatus. The co n ta in er tap and tap s T^, Tg» were a l l o f th e mercury s e a l type and th e co n ta in er and manometer were inmersed in a therm ostat up to the le v e l of th e cu p s. The therm ostat was e l e c t r i c a l l y c o n tr o lle d , th e tem perature

11.11

b ein g m aintained a t is o th e n a a ls .

2

^ . 0 Q°C. ± 0 . 0 $°C. f o r most of th é

For th e iso th erm a ls which were determ ined

a t 0 ®G-, the co n ta in er was icKuersod up to the l e v e l o f th e side-arm in a la r g e Dewar v e s s e l co n ta in in g m e ltin g i c e . The manometer was illu m i.ia te d from behind by a 40 w att e le c t r ic - b u lb , which was p a r tly Ism ersed in th e w ater, and a f i a t motal p la t e c o n tr o lle d by a lo n g w ire liandle was arranged b efo re e a d i read in g so th a t th e top o f the m eniscus was ju st illu m in a te d .

By t h i s means

r e f le c t io n e f f e c t s were e lim in a te d , thus p rev en tin g er ro rs in th e apparent p o s it io n o f th e m eniscus. The cathetom etar was f ix e d r ig id ly on a metal p la te in fr o n t of the manometer a n i was s e n s i t i v e to 0 .0 2 mm. F l , ? 2 , P3 were sm all bulbs of about 2 m l. ca p a city a tta ch ed to th e apparatus by ground j o in t s (B .IO ). V was a detac^iable tra p which was immersed in liq u id a i r , and served to condense vapours b efo r e th ey reached th e pumping system . T-j was a three-w ay tap con n ectin g th e apx>aratus to th e pimps or to an a i r le a k L. The evacuatin g

system c o n s is te d of an

Edwards "Speed!vac** u n it - com prising a tw o-stage mercury d iffu s io n pump and a rotary oil-pum p. Hie furnace H was u sed f o r th e p relim in a ry a c tiv a tio n o f th e sc ib e n t and was a tu b ular e l e c t r i c furnace made by embedding a h e a tin g c o i l of nlohrcme w ire

11.12 I

i n a hollow o f asb'jstos ( 9 ) .

j

B was ths ' sto ra g e ' b ulb f o r th e h y g ro sco p ic sorb a tes and K m.s a narrow-borc mercury manoaetsr» of g r e a te r than barom etric h e ig h t, f i t t e d w ith a wooden s c a l e ,, w ith which i t was o r ig in a lly hoped to measure s a tu r a tio n vapour p r e s s u r e s ,

'this proved im p r a c tic a b le , how ever,

owing to th e s o lv e n t a c tio n of the sa tu ra te d vapours on th e ta p -g re a se when l e f t f o r lo n g p erio d s,a n d H was l e f t i n th e apparatus to d e te c t sudden le a k s due to t h is s o lv e n t a c tio n on ta p s Tg, Tg, T^q, and on the waxed j o in t s in th e system . The co n ta in er tap and tap s greased w ith Edwards'

and Tg ware

Vacuum Orease (hard g r a d e ),

w h ile the o th er tap s in th e system and th e ground j o in t on th e liq u id a ir trap were lu b r ic a te d w ith Apiezon Grease K.

The j o in t a t G was lu b r ic a te d w ith S ilic o n e

^

H t ^ Vacuum Grease (Dow C orn in g), b u t, a lth o u ^ t h i s r e s is t e d the s o lv e n t a c tio n o f th e am ines, i t was n ot used f o r the other tap s in th e apparatus.

A fter a sh ort tr i& i t was

found th a t th e g rea se d id not h o ld s.s hard a vacuum as the Apiezon g rea se over a lhe tap v?as c lo s e d , the calcium c h lo r id e tube s e a le d o f f , and the f la s k and adaptor tr a n sfe r r e d to a ground j o i n t on the main apparatus (A, C, P i g . I I . l ) .

By t h is d ev ice th e

en try o f m oistu re was prevented. The liq u id was then fr o zen out in liq u id a i r and th e g a se s evolved were pumped o f f .

A f i r s t f r a c t io n

was then pumped o f f , and th e amine d i s t i l l e d on to sodium in th e bulb B, which was inmersed in liq u id a i r .

The

adaptor and f l a s k were se a le d o f f by means of the c a p illa r y a t C. P y rid in e could not be d i s t i l l e d from sodium because of th e form ation o f d ip y r id y ls .

I t was d i s t i l l e d

from sodium h yd roxid e, tr a n sfe rre d in the same manner, and sto re d w ith ou t a drying agen t. %hm th e sorb ate was req u ired , i t was d i s t i l l e d in to ?2

fr o zen out s e v e r a l tim e s.

Any rem aining

in th e sm all b u lb , a fte r the g e l had been sa tu r a te d , was returned to th e sto rage bulb B, to ensure th a t i t was kept dry. (d ) S atu ration o f Sorbent.

The a c tiv a te d sorb en t

was c o o led , by surrounding the co n ta in er by co tto n wool m oistened w ith a l i t t l e e th e r , and opened t o the pure liq u id so r b a te .

%hen s u f f i c i e n t l iq u i d had d i s t i l l e d on

to the sorbent ( i t became m oist and adhered to the w a ll of the c o n ta in e r ), the tap was c lo s e d , and the c o n ta in e r tr a n sfe r r e d to th e manometer. In the ca se o f w ater and e th y l a lc o h o l

II.l6 . ü

th e sa tu ra te d sorbent was l e f t o v e m i ^ t t o s e t t l e , but t h is was not p o s s ib le w ith the low er am ines, owing to s o lv e n t a c tio n a t h i ^ vapour p r e ss u r e s, and d e so r p tio n was begun im m ediately a f t e r the p erio d o f evacuation (one hour) n ece ssa r y to remove a l l adsorbed a ir from th e w a lls of th e apparatus. The h igh er amines, h avin g lower vapour p r e s s u r e s , did not a tta c k the tap grease so r e a d ily , and in some o a s e s , n o ta b ly w ith 810282» i t was n ecessa ry to le a v e th e sa tu ra ted g e l fo r a day or two b efo r e eq u ilib riu m was e s ta b lis h e d . In most c a s e s , however, i t was apparent th a t eq u ilib riu m had been reached b e fo r e th e d eterm in ation of th e isoth erm al began. (d) The d eso rp tion is o th e r m a l.

A fter ev a c u a tio n ,

th e manometric system was c lo s e d from th e pumps, and the co n ta in er opened up.

As th e g e l was norm ally sa tu ra te d

th e p ressu re was th e sa tu ra tio n p ressu re of the pure so rb a te.

T h is was checked b efo r e each isoth erm al was

determ ined.

By c lo s in g the co n ta in er tap and opening T^,

le a v in g Tg and T^ c lo s e d , T^]^ open and liq u id a ir surround­ in g P^, th e presence o f any permanent gas could be d e te c te d .

In th e absence o f a McLeod gauge, t h is d e v ic e

was employed in th e eeirly sta g e s o f the work.

The "open"

limb o f th e manometer was then pumped out f o r a sh o rt w tiile and th e c o n ta in e r tap opened a g a in , the p ressu re b ein g n o ted .

T his was repeated u n t il th e p ressu re f e l l ju s t

n .i7

below th e s a tu r a tio n vapour p ressu re v a lu e , when th e co n ta in er was c lo s e d , removed and w e i r e d . S u c c e ssiv e p ressu re read in gs were then ta k en , and the amount of vapour con tain ed in th e dead space was pumped o f f in between each. change' te ch n iq u e .

T liis i s loiovai as the 'p r e ssu r e

This p rocess cou ld only be c a r r ie d out

fo r f i v e or s i x readings owing to th e f a i r l y sm all volume o f tl% 'dead s p a c e '.

The q u a n tity of vapour removed

each tiDoe than became in c o n v e n ie n tly sm a ll.

The co n ta in er

was w e ld e d again and the a c tu a l w e i ^ t of vapour removed each time was c a lc u la te d as fo llo w s : If

Aq mg. o f vapour per gram o f sorbent i s removed

between two we in n in g s and

i s the summation of th e

p ressu re rea d in g s between th ese two p o in ts , then Aq X p mg. vapour i s ranoved per read in g, where p i s th e p ressu re recorded by the manometer b efo re pumping o f f . The s l i f ^ t m r l a t i o n of th e volume of th e 'dead sp a ce' w ith the p ressu re in tro d u c es only a n e g li g ib l e erro r. The rem aining p o in ts were obtained by opening the co n ta in er d ir e c t to the pamps, f o r a few seconds a t f i r s t , then fo r in c r e a s in g ly lo n g e r in t e r v a ls , and the amount of adsorbed vapour d eteim in ed by d ir e c t w e i r i n g . The r e s u lt s obtained by th e ' p ressu re chauige' technique were n o t e n t ir e ly tru stw o rth y , and were u s u a lly checked by a w e i r e d p oin t when th e isotherm al was re p ea ted . I t was n o tic e d on se v e r a l o cc a sio n s th a t , when the n e a r ly

1 1 .1 8

satu ra ted g e l was opened to a vacuum, th e p ressu re r o se to a maximum v a lu e and then f e l l g ra d u a lly .

:"'t / ^

This was

a ttr ib u te d to th e so lu tio n of a sm all amount of amine in the fr esh g rea se of the manometer ta p .

A fter the f i r s t

p o in t had been determ ined, t h is e f f e c t was no lo n g er observed, and i t was assumed that the grease had become sa tu r a te d . A good vacuum could always be obtained a f t e r evacuation l a s t i n g fo r a period of one hour, and t h i s p e r s is te d when th e system was cu t o f f from the liq u id a ir tr a p .

As the g rea se sm elt str o n g ly o f amine, when th e tap

was removed, i t was assumed th a t th e l a t t e r was f a i r l y stro n g ly h e ld , and, a f t e r the i n i t i a l amine take-up was allow ed f o r , would n ot co n trib u te a la r g e error to th e r e s u lts .

A ccord in gly, the p r a c tic e was adopted o f a llo w in g

the con tain er holdin g th e sa tu ra ted g e l to remain open fo r a w h ile , so th a t the grease on th e manometer tap became sa tu ra te d , b e fo r e the p ressu re was reduced below th e sa tu ra tio n v a lu e . In a l l ca ses when *p ressu re change* read in gs were begun from sa tu ra tio n p r e ssu r e , w ltl out a llo w in g fo r t h is e f f e c t , erroneous r e s u lts were obtained. In view of t h is d i f f i c u l t y , the shape of th e isotherm al as the g e l approached sa tu r a tio n was n ot stu d ie d c lo s e ly , and isoth erm als are p lo tte d as though the p ressu re f a i l s sharply from the satiu*ation v a lu e . (0 ) The Adsorption I s o th e rm al.

The open lim b

o f the manometer was f i l l e d w ith vapour from the f r e e z in g

11.19

bulb

anû th e con tain er tap opened.

The sorbent was

l e f t in co n ta ct w ith the vapour from the fr e e z in g bulb u n t il the req u ired amenant of vapour had been adsorbed (in d ic a te d by th e p r e ssu r e ), when th e manometer was sh u t o f f from th e fr e e z in g bulb and th e system l e f t to s e t t l e down.

E quilibrium was g e n e r a lly a tta in e d a fte r two h ou rs,

but a lon ger tim e was n ecessary fo r saae r e s u lt s fo r SiÜ2B2* (4 ) The low p ressu re manometer. (a ) D esign .

A diagram i s shown in P i g . I I . 2 .

The manometer was made of pyrex g l a s s .

% e bore o f th e wide

p art of the lim bs was 2 . ) cm. and th a t o f the narrow p a rt 1 cm. C lean, fr e s h ly d i s t i l l e d mercury was put in to the manometer u n t il the l e v e l was h alf-w ay up the wide part of each lim b , and dry, fr e s h ly d i s t i l l e d d ib u ty l p h th a la te was introduced on the vacuum s id e o f the manometer, u n t il the wide p o rtio n was ju s t f i l l e d . By tliis arrangonent movement of th e mercury in the l e f t hand limb o f the manometer was m agnified th ree­ f o ld by movement of the d ib u ty l p h th a la te in the r ig h t hand lim b. Even though the d ib u ty l p h th a la te was dry and fr e s h ly d i s t i l l e d , when t h is lim b o f the manometer was shut o f f th ere was seme tendency fo r a s l i g h t pressure to d ev elo p , over a p erio d of a few hours.

In consequence, th is lim b

was kept open to the pumps w h ile read in gs were taken, and the zero was checked a f t e r each read in g.

11.20.

(b; C a lib r a tio n .

I t was n ecessary to àeterm ine

the h eig h t o f th e d ib u ty l p h th a la te column fo r se v e r a l d e f in it e p r e s s u r e s . The manometer was waxed, in to p o s itio n in th e vacuum l i n e and a con tain er h o ld in g a l i t t l e d i s t i l l e d water was waxed on to the sock et in p la ce of the co n ta in er holding th e g e l . The system was evacuated fo r s i x hours;

th e

water in the co n ta in er b ein g frozen out se v e r a l tiroes during t h is p erio d . A s e r ie s of organic so lv en ts» w ith m e ltin g p o in ts ranging from - ) 0^C. to 11 ^G., was c a r e fu lly p u r if ie d . A Dewar f la s k was f i l l e d h a lf f u l l w ith each s o lv e n t, and liq u id a ir was poured i n , th e so lv e n t b ein g w ell s t ir r e d , u n t il the fr e e z in g p o in t was reached.

The

temperature was noted by means o f a mercury Uiermometer reading from -

to

The con tain er was immersed

in t h is fr e e z in g m ixture, and s e v e r a l readings of the p ressu re fo llo w ed by zero rea d in g s, were determ ined.

when stea d y

v a lu es were obtained the fr e e z in g m ixture was changed. A specimen r e s u l t , , which i s shown in Table I I . ) , -

in d ic a te s th e agreement that was ob tain ed . Table determined

j ‘

11. 4 . g iv e s th e v a lu es th a t wei*e

fo r th e s e r ie s of

s o lv e n ts , andth e

■ ■

c a lib r a tio n

curve i s p lo tte d in P i g . I I . 3 .

à

1 1 .2 1 . 1-4 TABLE I I . 3 . Solv e n t t Methyl Benzoate.

M.Pt. = - 12.

.

Vapour p ressu re o f Ic e a t - 12. 5°C. = l . $ 6 mm. (2 )

(I)

Observed h e l ^ t

12.42 mm.

12.31 m .

(3) 1 2 .3 6

COS.

Zero reading

7.6o mn._______ 7.51 mm.

7 .5 5 mm.

Aotual h eig h t

4 .8 2 mm.

4 .8 0 mm.

4 .8 1 mm.

Water Vapour pressure.mmi

H eight of column.mm.

Mean v a lu e ;- 4 .8 1 am. TABLE I I . 4 . Solvent

U Pt.O c.

Brcmbenzene

- 3 0 .6

( lo e )

0 .2 5

0 .8 0

Methyl benzoate

- 1 2 .5

(Ic e )

1 .5 6

4 .8 1

A n ilin e

- 6 .2

(-water)

2 .8 9

9 .0 4

Metïij/l s a l i c y l a t e

— 1 . 2 (—8 .6 ) ( " ,)

4 .2 0

1 3 .3 8

4 .5 8

1 4 .4 0

6 ,6 4

2 0 .6 0

1 0 .2 4

3 1 .8 6

M elting i c e

0 .0

Benzene

3 2 3 3

Bioxan.

. (. )

1 1 .6

Where the observed m eltin g p o in t d lf f e i- s from th at quoted in th e l i t e r a t u r e , the l a t t e r i s given in b r a c k e ts.

1 1 .2 2 . 1

(5 ) A pparatus f o r detei*miningr Is o th e rm a ls of E th y lao iin e (a j Ik^aoriptlQ il e f th e A p p aratu s The e n tir e apparatus which i s shown in F i g . I I . 4a* was b u i l t o f Pyrex g l a s s .

'

Ax 5 A2» A^* A4 were mercury c u t - o f f s w ith s in te r e d g la s s f i l t e r s .

A fter some time i t was d isc o v e r e d

th a t the s in te r e d g la s s would allow th e p assage o f mercury when the ex cess p ressu re on one s id e was g rea ter than 'about h a lf an atm osphere.

The mercury blocked th e passage

of vapours through th e s in t e r s and sometimes was fo rced in to the main p art o f the apparatus. To remedy t h is two

sumps” , B, were b u i l t

on A^ and A4, and # ien the mercury c o lle c t e d In th e tu b in g above the s i n t e r s , i t then ran back to the sump, and, by turning th e ta p , could be retu rn ed to the storage b o t t l e . A small con stan t amount of mercury was kept above th e tap to prevent the a tta c k o f the tap g r e a se . The in tro d u ctio n o f th e s in te r e d