Flow line. MeBr storage. bulb Vac Vac. line. line. Needle Manometer Valve %uL"Water V ✓ I Toluene FIG. 3, re s e rv o ir, DIAPHRAGM VALVE.. Operating grip. K ftN \\N V C s\N N N N V sX Diaphragm PIG.4.
S
w 3 lO rH «H CM 00 CM lO40
c o n tro l being obtained by a needle valve between th e re s e rv o ir and in je c tio n c a p illa ry (see f i g . 5)«
The argon was sto red in th re e 3 l i t r e bulbs and reproducible q u a n titie s could be adm itted to th e flow system by means of a m anostat.
?o r mass spectrom eter c a lib ra tio n s , adm ission of methane
and hydrogen to th e flow system could be gahed from a gas b u r e tte . For such c a lib ra tio n s ca lc u la b le amounts of hydrogen or methane
could be g r i t t e d to th e flovf system in to a knov/n p ressu re of argon. The whole v/as allow ed to c irc u la te f o r some tim e, u n til a
homogeneous gas m ixture was obtaned, before readings were ta k en . The gas b u re tte was emptied by means of a T oepler pump in je c tin g
s tr a ig h t in to th e flow system . The p ressu res on th e flct? McLeods gave the argon p ressu re since th e d ilu tio n of methane or hydrogen was high. Such a c a lib ra tio n i s shown in fig u re $, th e readings being based on a measured argon s e n s itiv ity as i s u su a l. The flow system argon was used as th e re fe re n c e . Reading of any
subsequently measured peak h eig h ts was always done w ith an immediate referen ce to th e argon s e n s itiv ity since th is could vary from day to day and during th e day.
3* P u rific a tio n of r e a c ta n ts .
Methyl Bromide supplied by B.L.H. in 100 ml. ampoules was d i s t i l l e d tw ice from -80°C to a liq u id a i r tra p (-180°0), I t was
th e in je c tio n system . I t s p u rity was checked on th e mass spectrom eter*
Toluene. I t i s known th a t p u r ific a tio n of to lu en e by
shaking w ith su lp h u ric a c id , d i s t i l l a t i o n and c r y s ta llis a tio n s t i l l leàlsto irre p ro d u c ib le gas k in e tic d ata (Sawarc (2))*
P a r tia l p y ro ly sis tw ice a t 850^0 follow ed by f r a c tio n a l
d i s t i l l a t i o n from sodium y ie ld s to lu en e which gives r e lia b le k in e tic d a ta . Toluene p u rifie d in t h i s way was used - th e d e ta ils are
described f u lly by B arraclough ( l ) .
Argon. The c a r r ie r gas obtained from a c y lin d e r Y/as p u rifie d by slow passage through a -80°G tra p to remove w ater and then through two successive sodium tra p s h eated to 300^0 to remove tra c e s of
oxygen. A mass spectrum of th e p u rifie d argon v/as taken to check th e f in a l p u rity .
Hydrogen Bromide was prepared by dropping concentrded aqueous hydrobromic a c id onto P^O^, drawing tho re s u ltin g vapour through a tra p a t -20^0 to remove w ater and then c o lle c tin g th e HBr in a
liq u id a i r cooled tr a p . The HBr vfas d i s t ille d * from a «80°0 b ath to a -180^0 b ath on th e vacuum system and sto red in a blackened b u lb .
Methane. A sample of pure methane v-ras a v a ila b le from N .G .L., Teddington. This Y/as sto red ad jacen t to a gas b u re tte f o r in je c tio n in to the flov/ system as re q u ire d .
TOLUENE INJECTION CALIBRATION