B e r n a r d J. Bulkin' and P a u l T e r g i s Polytechnic Institute of New York Brooklyn. New York 11201 and Hunter College--CUNY New York, New York 10021
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A Simplified Apparatus
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for Ebullioscopic Measurements of AirIMoisture Sensitive Compounds
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Ehullioscopic m e a s u r e m e n t is o f t e n t h e most, n h v i o ~ w ~ sa y
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to d e t e r m i n e molecular weieht 01' s m a l l m o l e ~ u l e in s snl~~tioti.
m e n i s a r e p;~rt.icularlypertinent for org;tnomelz~llicchemistry. w h e r e associntion o f t e n i n l ' l ~ t m r e sspectroscopic s t r u c t u r a l d e t e r m i n a t i o n s heing carried o u t . I n m a n y cases t h e s d u t i o n s a r e a i r a n d / o r m o i s t u r e sensitive. W a l k e r a n d Ashby:' have attacked this problem successfully. I n t h e i r a p p a r a t u s , hoiling point. i s m e a s u r e d dirertlv. A s t h e boiling p o i n t h a s a substantial d e p e n d e n r e o n pressrlre. t h e p r e s s u r e m u s t b e r n m s u r e d w r v a r c n r a t e l y , lest t h i s h e c o m e a limiting factor in t h e molecu1:rr weight determination. T h i s i m p o s e d n e e d f o r a highly a c c u r a t e p r e s s u r e g a u g e g r e a t l y i n c r e a s e d t h e cost of t h e \Valker a n d A s h h v a p p a r a t u s , l i n it.ing it? application in instructional lahorntnries o r in research w h e r e u s e i s o n l y occasional. In this paper. we dwwihe an ehulli~wopicapparatus in which cmlv the difference hrlween the hcding ~rointd t h p solution and that of the p w e SOIVCII~ is measwed. HP(.R,ISPthe iolulitm imd s d v m t huilittg points have almost identical pressure d ~ p e n d ~ n c i ethis s , difference has a negligible d e p e n d ~ n r on e ~ ~ ~ R E I IKt,. I P . the m d a l hoiling point elevation constant, has a small d ~ p c n d m r eo n pressure (e.g. lur diethylelher 0.0'24''/torrl. Thi-. cnlrilimti;rlly reduces the cost of lhc apparatos and simplifies the- oppr:ition, while maintaining prerisirm. T ~ aP p p u a t o s is s h m w schrwxttin~llyin t h r figure. Twu hoiling chamhers, A and R in the figure. iw? used. one ( A ) with pure s d w n t . the other with solntim. TI, insure uniform heating of thp chamhers, both are heatpd in the same rlil hath. The r o n d ~ n s r r silttarhrd , t o the h d i n g rhamhrrs. should he rc,oled with ire water if a lkrw hoiling solvent such as diethvlether is wed. In manv areas tan water %.illIIQ ~
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cortrell pump
